Modification of Asphaltene Dispersions in Crude Oil

Abstract

The physical structure of asphaltene dispersion in crude oil is important from the point of view of refining technology and can subject to modification, for example, using an aromatic component, such as pyrolysis oil. The lab results were verified in industrial tests in the atmospheric-vacuum distillation (AVD) process of crude oil. Positive test results made it possible to use pyrolysis oil on an industrial scale as the component, favorably changing crude oil’s dispersion structure and properties. The implementation of a new method of distillation of crude oil partially confirmed the expected effects and revealed new aspects of technology modification. In the course of research on this type of petroleum dispersion, carried out for the refining industry, several patented solutions have been developed, some of which have been successfully applied in the industry.

1. Introduction

The crude oil extracted from the field is usually an emulsion with water, containing dissolved mineral salts, mainly sodium, potassium, magnesium, and calcium chlorides. Removal of brine from crude oil hinders demulsification by surfactants in the crude oil, which acts as natural emulsifiers. These include, first of all, naphthenic acids, which, depending on the pH of the aqueous phase, can stabilize water in oil (W/O) or oil in water (O/W) emulsions. Other polar compounds, found in crude oil and concentrated mainly in resin fractions, also have an affinity for water and are adsorbed at the emulsion interface. The higher the surface activity of the surfactant, the stronger the adsorption at the water-oil interface, and the lower the concentration is sufficient to stabilize the emulsion. Another group component that significantly affects emulsion stability is petroleum asphaltenes. Asphaltene molecules contain sulfur, nitrogen, and oxygen heteroatoms and complexes of metals, and, therefore, show high polarity and tendency to aggregate in the environment of liquid petroleum components.

Many data show that aggregates of asphaltenes, solid particles, demonstrate the ability to stabilize petroleum emulsions [1]. Some of the asphaltenes in crude oil are in a molecularly dispersed state in the oil phase, and the rest are included in aggregates, forming the solid phase of the crude oil dispersion. The proportion of dispersed and aggregated asphaltenes depends on chemical factors and physical parameters. The dispersing ability of the liquid phase plays a fundamental role here, as measured by the solubility parameter. The higher the dispersing power of the liquid phase, the smaller proportion of asphaltenes tends to aggregate. The second important factor affecting the degree of aggregation of asphaltenes is the content of petroleum resins in crude oil and the mutual ratio of the content of resins and asphaltenes. Polar resins form solvation layers on the asphaltene particles and thus maintain the dispersion system in a state of kinetic stability. Both of these factors result from the chemical and group composition of crude oil. External factors such as temperature, pressure, and hydrodynamic conditions (shear stresses) also significantly impact the degree of aggregation of asphaltenes [2].

The degree of asphaltene aggregation affects the stability of the brine emulsion in crude oil. On the other hand, the state of their dispersion changes the proportions of the solid and liquid phases of crude oil. Hence, the issue of the dispersion structure of crude oil, particularly the form of asphaltenes, is of significant importance in the refining technology of this raw material.

The problem, discussed in this chapter, concerns the possibility of changing the dispersion structure of crude oil and the impact on the technology of refining processes, and especially on the preliminary purification and the crude oil distillation process. An aromatic fraction of petrochemical origin, specifically oil from the olefin pyrolysis process, was used to modify the structure of asphaltene dispersion in crude oil.

The problem analysis includes the characteristics of crude oil and pyrolysis oil, a description of the phase stability of asphaltene dispersion in crude oil, laboratory test results, two industrial trials, and test implementation of the solution lasting over a year.

1.1 Characteristics of crude oil

In the Polish and Mid-European refineries, the primary crude oil processed and transported via the “Friendship” pipeline has been referred to as REBCO (Russian Export Blend Crude Oil) for many years. In many aspects, REBCO is a medium, sulfuric, and paraffin-naphthenic crude oil with properties resembling those of many other widely produced crude oil grades, often referred to as “conventional crude oil.”

The elemental composition of crude oil varies widely, depending on the origin of the raw material—Table 1.

Element name	Content limits, % m/m	Content in REBCO crude oil, % m/m
Carbon	80.4–87.0	85.1
Hydrogen	9.6–14.6	13.0
Sulfur	0.01–7.4	1.6
Oxygen	0.04–2.0	0.1
Nitrogen	0.03–0.9	0.2

Table 1.

Elemental composition of crude oil [3].

The mutual proportion of carbon and hydrogen results from the nature of the hydrocarbons contained in crude oil and essentially determined its quality as a refinery raw material.

The presented data show that even in crude oil with an average content of the three main heteroelements, the range of their compounds is an essential factor determining the technology of its processing. The compounds of sulfur, oxygen, and nitrogen are present in all crude oil distillates in increasing amounts with the boiling point. The components of the oil with the highest content of these elements are resins and petroleum asphaltenes.

Most of the crude oil extracted and processed in refineries is classified as sulfur and paraffin oil. Due to the highly complex chemical composition, this raw material is characterized by the content of group components. They include hydrocarbons and non-hydrocarbon components, where the group of hydrocarbons includes: n-paraffinic, isoparaffinic, naphthenic, and aromatic. The group of other components includes petroleum resins, asphaltenes, and mineral compounds. The mutual proportions of the mentioned ingredients are very different and depend on the age and origin of the mineral. An example of the composition of distillates and typical crude oil residues depending on the boiling point of the component is shown in Figure 1.

Figure 1.

Crude oil group composition [3].

The content of individual group components depends mainly on the age of the oil, which is illustrated by the data in Table 2.

Group component	Content, % m/m
	Light oil	Heavy oil
n-paraffinic hydrocarbons	23.3	1.0
Isoparaffin hydrocarbons	12.8	3.2
Naphthenic hydrocarbons	41.0	19.2
Aromatic hydrocarbons	6.4	9.1
Aromatic-naphthenic hydrocarbons	8.1	17.9
Resin and asphaltene compounds	8.4	39.6

Table 2.

The content of group components in crude oil.

The basic group of crude oil hydrocarbon components is naphthenes; their content is 40–75% m/m. Gasoline distillates contain cyclopentane, cyclohexane, and their alkyl derivatives. The content of monocyclic naphthenic hydrocarbons decreases with the boiling point of the distillate. Dicyclic naphthenes, decalin derivatives, and bridged hydrocarbons occur mainly in diesel distillates. As the boiling point and molecular weight of this type of linkage increases, chain elongation of one of the ring alkyl substituents is observed. The content of dicyclic naphthenes in crude oil distillates decreases with the increasing boiling point of the fraction. The group of tricyclic naphthenic hydrocarbons includes adamantane (Figure 2), tricyclo [3.3.1.13.7] decane, a compound of spherical symmetry, and unusual properties; the density of adamantane is above 1 g/cm³ and the melting point is above 260°C.

Figure 2.

Adamantane (C₁₀H₁₆).

Tricyclates are present in all crude oil distillates starting at about 200°C. Polycyclic naphthenic hydrocarbons containing four or more rings in the molecule are present in the fractions boiling above 300°C. Their content increases with the increasing boiling point of the fraction. This group includes the hydrocarbons of the adamantane series, steranes, and terpenes. Ten-ring naphthenic hydrocarbons were found in the oil fractions. About 1/3 of the polycyclic naphthenic hydrocarbons contain a six-membered ring and are able to dehydrogenate to aromatic hydrocarbons; 1/3 undergoes dehydrogenation after isomerization, the remaining 1/3 does not dehydrogenate even after isomerization, that is, it contains only bridge connections in molecule.

Paraffinic, straight-chain, and branched hydrocarbons constitute 20 to 60% m/m of crude oil. They exist as gases, liquids, and solids and contain from 1 to more than 50 carbon atoms per molecule. n-paraffinic hydrocarbons are present in all crude oil distillates as well as in the vacuum residue. In general, their content decreases with increasing boiling point of the fraction; in some grades of crude oil, the maximum content of n-paraffins is in the C₁₅– C₂₂ range.

The isoparaffins present in crude oil are usually low-branching; the most common are 2-methyl and 3-methyl alkanes and dimethyl alkanes. The exception are isoprenoids occurring in the fractions distilling between 200 and 450°C. Some of them, such as phytane or pristane, may be present in crude oil in amount of 2.5–3.5% m/m (Figure 3).

Figure 3.

Structural formula of pristane (2,6,10,14-tetramethylpentadecane).

Aromatic hydrocarbons are usually present in crude oil in an amount up to 10% m/m, and, starting from C₈, and their content decreases with the increasing boiling point of the fraction. Aromatics of above C₁₂ contain several substituents in the molecule, including one n-paraffin with an increasingly long chain. Simultaneously with the increase in the number of condensed aromatic rings in the molecule, the number of alkyl substituents, usually methyl, decreases.

A composite structure, alkyl naphthenic hydrocarbons, occurs in diesel distillates and mainly in vacuum distillates. They generally contain one or two aromatic rings and up to six naphthenic rings. As the total number of rings in the molecule increases, the number of alkyl substituents decreases. As the boiling point of the fraction increases, the hydrocarbon content of the mixed structure decreases. Naphthenic-aromatic hydrocarbons are also present in the bottoms—vacuum residue.

The non-hydrocarbon constituents are mainly sulfur compounds, to a lesser extent a combination of oxygen and nitrogen. In most of the crude oils, the sulfur content is between 1 and 3% m/m, but sulfur compounds is 10–12 times more. Sulfur compounds in crude oil are mainly: mercaptans, aliphatic sulfides and disulfides, thiophanes and thiophenes, and combinations with aromatic compounds, such as dibenzothiophene (Figure 4).

Figure 4.

Structure of dibenzothiophene.

Nitrogen compounds are found mainly in a vacuum distillates and bottoms. They can be basic—pyridine and quinoline derivatives, or neutral—pyrrole, indole, carbazole derivatives.

Petroleum porphyrins form complexes with metals and distills under reduced pressure (Figure 5).

Figure 5.

The structure of the petroleum porphyrin-vanadium complex.

Oxygen compounds in crude oil occur mainly as naphthenic acids and phenols.

Petroleum resins and asphaltenes contain up to 90% of the heteroatoms present in crude oil. They are composed of condensed aromatic structures linked by bridges of heteroelements (Figure 6). These compounds also include metals such as iron, nickel, vanadium, cobalt, and others.

Figure 6.

Hypothetical molecular structure of petroleum asphaltenes [3].

The fractional composition of crude oil determines the amount of distillates obtained during AV distillation. REBCO oil produces about 26% m/m of fractions distilling up to 200°C, 39% m/m up to 300°C, and 58% m/m up to 350°C. Compared to REBCO oil, light crude oils are characterized by a higher yield of light products, that is, gasoline distillates, gas oils, and vacuum fractions. The vacuum residue usually contains crude oil components with a boiling point above 530–560°C. Heavy and extra heavy crude oils, on the contrary, yield a small percentage of bright products such as gasoline, kerosene, gas oil, and vacuum oils, but sometimes more than 50% of vacuum residue.

1.2 Crude oil dispersive structure

From the point of view of the physical structure, crude oil is a complex dispersion system in which the continuous liquid phase (saturated and aromatic hydrocarbons, called “oils”) contains two dispersed phases: solid particles composed of petroleum asphaltenes and a second liquid phase comprising droplets of an aqueous solution of mineral salts, known as brine. In addition, petroleum wax agglomerates and solid mineral impurities may be present in the solid phase. The physical structure of crude oil dispersion is of great importance for the refinery processing of crude oil and has been the subject of researchers’ interest for many years [4, 5, 6, 7].

Dehydrated and desalted crude oil can be regarded as a dispersion system in which the asphaltene particles (A) are surrounded by resin molecules (R) as a solid-in-liquid dispersant. The continuous phase is a mixture of the asphaltene solvent (a) and the non-solvent, i.e., the precipitating agent (s) [8]. This system remains in a state of phase equilibrium, from which it can be unbalanced as a result of changes in temperature, pressure, or chemical composition [9]. The measure of the stability of the dispersion system is asphaltene flocculation point, defined as a volume fraction of n-alkane which, when added to the dispersion, initiates the precipitation of asphaltene sediment (Heithaus parameter) [10]. The precipitation of asphaltenes also occurs by mixing different grades of crude oil or petroleum fractions.

The compatibility of different types of oil is based on the assumption that the flocculation parameter of a given asphaltene-resin system is stable.

The model uses the so-called Hildebrand solubility parameter (δ) [11], describing the cohesion energy density of the substance:

$$\delta ={\left[E_v/V\right]}^{0,5}$$E1

where: Ev—enthalpy of evaporation, cal/mol.

V—molar volume, cm³/mol.

The determination of this quantity, based on the measurement of the heat of vaporization and the molar volume, is simple when it comes to the characteristics of a single-component liquid; assuming additivity of components, it is possible to calculate the parameter of the liquid mixture [12]. The solubility parameter of petroleum asphaltenes is about 9.5 (cal/cm³)^1/2 [13]. Therefore, a liquid with a solubility parameter below 9.5 (cal/cm³)^1/2 does not dissolve or precipitate asphaltenes, while a liquid with a solubility parameter greater than 9.5 (cal/cm³)^1/2 completely dissolves asphaltenes.

Stable crude oil asphaltenes are characterized by a low density, a relatively low carbon-to-hydrogen ratio (C/H), and high stability (onset flocculation). The phase stability of dispersion is determined by the group composition of raw material [14] in such a way that it results from the stabilizing ability of resins and maltenes and the stability of the asphaltenes themselves.

The thermodynamically stable colloidal system of crude oil contains some part of the asphaltenes as a molecular solution and the remainder as a solid dispersed in a liquid. The disturbance of the equilibrium state toward phase separation begins with the flocculation of the dispersed asphaltenes.

A number of analytical methods and measuring instruments have been developed to determine the start of flocculation (onset). Optical methods are the most common methods of determining the flocculation point of asphaltenes. These methods use changes in the absorption or scattering of light by a colloidal system with varying dispersion. Turbidimetric titration is used to determine the onset of asphaltene flocculation. A complex method using turbidimetric titration with three organic substances as asphaltene precipitants was used to determine the structural stability of asphalts [15, 16].

By measuring changes in the turbidity of visible radiation, 740 nm, the kinetics of the flocculation process of asphaltenes precipitated with isooctane from the asphalt solution in toluene was investigated [17]. Laboratory research confirmed state of aggregation of asphaltenes in crude oil and crude with pyrolysis oil (PO) component [18, 19]. A significant influence of the shear stresses on the aggregation of asphaltene molecules was found. Such a phenomenon occurs during the flow of crude oil in a pipeline and especially in pumps.

The bimolecular reaction equation described the velocity of process and the rate constant k was calculated; the maximum number of flocculating particles and the process activation energy were determined. An Automated Flocculation Titrimeter (AFT) was used for the tests.

Another type of apparatus for determining the flocculation point of heavy oil asphaltenes and distillation residues, uses the measurement of the intensity of the reflected light. The instrument’s software allows the calculation of parameters characterizing the stability and compatibility of crude oil [20].

Changes in the asphaltene dispersion state in crude oil diluted with n-heptane will enable the recording of an instrument called “Turbiscan” (Figure 7) [21].

Figure 7.

The principle of the Turbiscan apparatus operation [21]. Reprinted with permission from “Formulactions.”

It registers changes in light intensity with a wavelength of 850 nm scattered backward (at an angle of 45°) and passing through the sample at different heights. Depending on the kinetics of changes in colloidal dispersion, scanning can be performed at a different, programmable speed. Based on the automatically registered changes in the radiation intensity, it is possible to determine the flocculation point of asphaltenes and the stabilizing effect of dispersing additives.

The asphaltene flocculation occurs in a narrow range of the refractive index values of crude oil solutions. In turn, the refractive index and the solubility parameter of non-polar substances show a linear correlation, which indicates the possibility of determining the phase stability of crude oil by measuring changes in the refractive index with an increase in the volume of non-solvent in the mixture [22]. It is possible to precisely determine the value of the (extrapolated) refractive index of the solid components of crude oil since the specific refraction shows additivity to the volume of the liquid components of the mixture. By treating asphaltenes as a solute and maltenes, being a solution of resins in oil components, as a solvent, the refractive index of bituminous shale asphaltenes was determined to be 1.708 [23].

Light absorption and fluorescence measurements were used to record the concentration at which asphaltene aggregation begins [24]. The linearly increasing absorbance of light with a selected wavelength (analytical band) is recorded by increasing the concentration of asphaltenes in toluene. The break of the straight line indicates the beginning of solute aggregation. Asphaltenes separated from more stable crude oil begin to aggregate at a higher concentration in the solution; the process starts with a concentration of about 50 mg of asphaltenes per dm³ of solution.

Contrary to optical methods, which are difficult to apply to completely opaque heavy crude oil and residues, the conductometric method does not demonstrate such limitations [25, 26]. This method uses the low electrical conductivity of oil derived from polar asphaltene particles. Changes in the concentration of dispersion particles as a result of dilution cause a linear increase in the conductivity of the solution, according to the formula:

$$\mathrm{\Lambda }=k\left(1+x\right)$$E2

where: Λ— normal conductivity of the solution n, (nS/cm)/(g/cm³);

κ—measured conductivity, nS/cm;

x—the ratio of the solvent volume to the mass of crude oil, cm³/g.

The collapse of the straight line occurs when the asphaltene flocculation in the solution begins.

The measurement of thermal conductivity of the petroleum product also allows the observation of sludge formation. The temperature of the lower asphalt layer to which the non-solvent (n-heptane) was added was measured in a pressure apparatus. Reducing the viscosity of the diluted solution increases the thermal conductivity, and the formation of a precipitate produces the opposite effect. In this way, the course of temperature changes as n-heptane is added to detect the asphaltene flocculation point [27]. The device enables measurements to be carried out in conditions similar to industrial ones or those prevailing in the bed, that is, at a temperature of up to 350°C and a pressure of up to 4 MPa.

Another way to detect a flocculation point is to measure the filtration resistance of a mixture of petroleum and non-solvent. This method uses the difference in the size of the asphaltene particles in colloidal systems and their flocculates, reaching four orders of magnitude. It has many advantages due to the possibility of testing concentrated dispersions, using variable pressure and temperature, introducing solvents and additives [28].

In our works, we applied tensiometer K100 as a sedimentation balance to register mass of sediments which occurred in crude oil (degassed), crude with pyrolysis oil and with asphaltene dispersing additives, all subjected to shear stress (Figure 8).

Figure 8.

Sedimentation tendency of crude oil and sheared crude oil with additives. 1. Stabilized (degassed) crude oil subjected to shear stress; 2. Stabilized crude oil; 3. Stabilized crude oil +20 ppm of asphaltene dispersant, subjected to shear stress; 4. Stabilized crude oil +2% of pyrolysis oil (PO), subjected to shear stress.

The sedimentation test is one of the most accurate and reliable ways to measure the stability of asphaltene dispersion in crude oil. It does not use solvents or thinners, only crude oil. It is only necessary to remove the dissolved gases and stabilize the oil, because the microbubbles released from the raw material during the test settle on the bottom surface of the sedimentation cap, lifting it and falsifying the measurement result.

Long-term experience in optimizing measurement conditions has led to very accurate and repeatable measurements. The tested oil is heated to 40°C for 24 hours, then cooled to room temperature, sheared in the Couette apparatus, and placed in a measuring vessel with a K100 tensiometer sedimentation attachment. The tested degassed crude oil in the amount of 40 ml is subjected to shear stress for 10 minutes at the speed of 108 rpm. A sample of degassed crude oil and crude oil with dispersant and/or pyrolysis oil is prepared and tested in the same way. The use of additives and shearing of samples does not change the total content of asphaltene in the sample, but only changes the degree of dispersion of sediments and thus the phase stability of asphaltene dispersion.

The obtained results indicate that the shearing of crude oil significantly increases the mass of sedimentation deposits in degassed crude oil and at the same time indicates a significant improvement in the stability of asphaltene dispersion in crude oil as a result of the addition of a dispersant and pyrolysis oil as a component.

The state and transformations of dispersion systems, which are by definition characterized by an extensive interface, are determined by the properties of the boundary surfaces. The surface of both solid and liquid particles is characterized by the amount of energy per unit area and the degree of its polarity. On the basis of changes in the interfacial tension between crude oil and water, the beginning of asphaltene precipitation can be ascertained [29]. The addition of n-heptane to crude oil changes the surface tension resulting in a minimum. In contrast, the interfacial tension at the water interface shows a significant change when the asphaltene precipitate begins. Due to their high polarity, the particles migrate to the oil-water interface, forming a boundary film. The adhesion or settlement of particles at the interface is the cause of instability in the interfacial tension.

The electrical properties of dispersion and their changes caused by thermal transformations of asphaltenes can be observed under the conditions of a strong electric field of direct current [30]. Significant amounts of cathode deposits are released from the visbreaking products diluted with n-heptane, while vacuum residue and crude oil deposits are collected at the anode. The paraffinic solvent (n-C₇) influences the structure of electrically balanced asphaltene-resin micelles differently. By partially dissolving the resins in the continuous liquid phase of the system, the peptization degree of the positively charged asphaltene core of the micelles is reduced. The particle acquires a positive charge and, under the influence of the electric field, goes to the cathode. Micelles in crude oil have a slightly negative charge and deposit a small amount of deposits on the anode. Heavy fuel oil, composed of a thermally cracked product and crude oil, releases deposits on the cathode and the anode.

The nature of molecular forces affecting the stability of asphaltene dispersion is determined by the LSER (Linear Solvation Energy Resolution) method. It allows determining the share of dispersion and polar interactions and hydrogen bonds with the division into acidic and basic. The parameter of crude oil solubility and asphaltene dispersion stability is determined by dispersion and acid-base interactions to a lesser extent [31]. The asphaltene solubility parameter, determined by the LSER method, has a value that is determined by measuring the flocculation point.

A new hypothesis involving free radical interactions as an additional significant contributor to the bonding structure and formation of aggregates in asphaltenes was assumed on the base of sophisticated methods of investigation [32]. The hypothesis takes into account structural features of polycyclic aromatic hydrocarbons contributing to this interaction involving a stable free radical.

2. Modification of asphaltene dispersion in crude oil

Additives or components increasing the stability of asphaltene dispersion should act as resins in stable colloidal systems. It seems justified to search for effective asphaltene dispersants in chemical compounds with properties and chemical composition similar to petroleum resins. The resins are rich in nitrogen compounds occurring as derivatives of pyrrole and indole. Sulfur compounds are represented by benzothiophene and oxygen by esters. By analogy to the coking processes in which the flocculation of asphaltenes is an important stage, proton donors, represented by tetralin, may act as inhibitors of the phenomenon.

The effectiveness of additives stabilizing the asphaltene dispersion was compared by measuring the thermal conductivity of sedimenting settlements. The difference in the asphaltene flocculation point of the petroleum product with and without addition was adopted to measure the additive effectiveness. Phenanthrene, representing polycyclic aromatic hydrocarbons, shows the greatest ability to peptize asphaltenes and tetralin to a lesser extent. Nitrogen derivatives are the least effective among the heterocyclic compounds, similar in composition to natural petroleum resins.

Surfactants show much greater stabilizing efficiency compared to aromatic hydrocarbons, proton donors, or heterogenic compounds. The anionic surfactant significantly exceeds the effectiveness of the non-ionic additive, which may be due to the powerful attraction of the anion to the polar surface of asphaltenes with a low positive charge.

The asphaltene stability additives must be individually selected for specific petroleum products. The decisive criterion for choosing the additive seems to be the interaction energy of the surfactant with the particle surface. The comparison of the stabilizing effect of the series of surfactants, used at a concentration of 0.1–1% m/m to the atmospheric residue and the visbreaking product, indicates a significant role of the polar groups: phenol and carboxyl, as well as the chain length of the alkyl substituent in the additive molecule [33].

The ability to solubilize asphaltenes in a toluene solution by alkylbenzene derivatives also depends on the number of hydroxyl groups; alkylresorcinol shows higher efficiency compared to alkylphenol [34]. The minimum number of carbon atoms in the substituent is 6, and the effectiveness of the various additives also depends on the type of solvent.

The explanation of the mechanism of the stabilizing action of the additives is based on the asphaltene micellization model. It confirms that the effectiveness of the resorcinol derivative is over three times greater than that of the identical phenol derivative [35]. Stabilizing additives, in addition to shifting the solution-dispersion equilibrium, determined by the onset of asphaltene flocculation may reduce precipitation’s kinetics (inhibit). Studies on the effect of dodecylbenzene sulfonic acid (DBSA), nonylphenol (NP), and toluene as stabilizing additives to three different crude oil (1000 ppm) have shown that each of these compounds significantly reduces the rate of asphaltene sedimentation [36]. In other studies, DBSA showed a high ability to solubilize asphaltenes, while ethoxylated phenols and alcohols showed a greater ability to stabilize the dispersion by shifting the asphaltene flocculation point [37].

The higher the dispersion stability of crude oil, the more paraffinic the asphaltenes show; the lower molar mass of asphaltenes found in light crude oil makes the process more sensitive to temperature changes. Asphaltenes showing a marked tendency to aggregate through hydrogen bonding react similarly. Asphaltene sediments are characterized by a significant development of the adsorption surface, which is over 100 m²/g, and the greater it is, the more polar the nature of the asphaltenes is.

The measure of effectiveness of surfactant stabilizing activity can be the heat of adsorption on the surface of the asphaltene core of the micelles. In the case of dodecylphenol, the heat of adsorption is about two times higher than that of hydrogen bonding, and in the case of DBSA, it is about five times higher than that of hydrogen bonding [38].

The polymer additive, introduced into crude oil, binds the polar part of the molecule with the asphaltene particle through acid-base interactions and hydrogen bonds [39]. Adsorption of surfactants on the surface of asphaltene particles occurs in two stages: in the first stage, individual surfactant molecules are adsorbed, and when their surface concentration increases sufficiently, a second stage takes place—the formation of surfactant micelles on the particle surface. The created adsorption layer constitutes a steric barrier preventing flocculation and coalescence of particles. The activity of surfactants from the group of alkylphenols and their ethoxylated derivatives increases with a higher concentration of the adsorbed substance on the particle surface [40].

The thermodynamic model of asphaltene micellization in crude oil predicts the stabilizing effect of both surfactants and aromatic hydrocarbons. Representatives of both types of the mentioned additives are partially adsorbed on the surface of the micelle core, causing the desorption of petroleum resins. In this way, the chemical composition of the solvation layer, the interfacial energy, the size, and stability of the micelles in the dispersion undergo changes.

The partition coefficient of the additive between the solvation layer and the liquid phase of the system influences the amount of shift of the flocculation point of crude oil asphaltenes. The partition coefficient is about 4 for dodecylphenol (DP) and about 108 for DBSA. For a few aromatic hydrocarbons, the factor is above 3 and increases in the benzene → toluene → o-xylene series. The influence of various aromatic hydrocarbons, by changing the size of the maltene solubility parameter, varies the stability of asphaltenes dispersion in the same direction.

The concept of crude oil colloidal structure modification with the addition of a mixture of aromatic hydrocarbons was developed based on the knowledge of the physicochemistry of dispersion systems. The leitmotif of the research was the problem of technological use of pyrolysis oil. It was assumed that the waste product of the pyrolysis process, with its properties changing over time, should be used in refining technology. Due to its aromatic nature, it could act as a factor regulating the state of asphaltene dispersion in crude oil [41].

2.1 Characteristics of pyrolysis oil

In the process of olefin pyrolysis, next to the leading products, ethylene, propylene, and butadiene, liquid products arise, rich in aromatic hydrocarbons. As a process residue, pyrolysis oil (PO) is obtained. It is a waste product, the quantity, and properties of which result from the quality of the pyrolyzed raw material and the process conditions (Table 3).

Fraction	Share, % m/m
Fractions of gases	5.8
Liquefied petroleum gases	6.7
Light petrol	12.6
Middle gasoline	39.6
Heavy gasoline	15.0
Diesel fuel fractions	7.6
Residue from Hydrocracking	10.3

Table 3.

Composition of the raw material of the pyrolysis plant [42].

The average efficiency of pyrolysis products obtained from the above-mentioned raw material is presented in Table 4.

Product	Yield, % m/m
Hydrogen + fuel gas	13.6
Ethene	27.8
Propene	13.3
Propane	1.0
Fraction C4	8.1
Pyrolysis gasoline	24.2
Pyrolysis oil	9.3

Table 4.

The yield of pyrolysis products [42].

Pyrolysis oil plays the role of a factor that directly cools (quench) the gaseous products of the process—pyro gas, and the physicochemical properties of pyrolysis oil are determined by its role as a process agent in the pyrolysis installation scheme. One of the basic parameters of oil as a cooling and sealing agent is viscosity and thermal stability.

Pyrolysis oil, in terms of its chemical composition, is not a fully understood petrochemical stream. The scope of motion analysis includes the determination of density, viscosity, pour point, and water content. The extended analysis does not show repeatability due to the variability of the oil quality, which results mainly from the diversity of the raw material of the olefin production plant (Table 5).

Properties	I	II	III
Density, d20, g/cm^3	1.042	1.061	1.058
Relative viscosity at 50°C,°E	5.91	10.24	12.11
Flash point, °C	110	124	113
Freezing point, °C	−12	−12	<−12
Water content, % m/m	0.03	0.03	0.03
Bromine number, g Br/100 g	20.2	19.6	20.7
Fractional composition (normal distillation)
Initial distillation temperature, °C	229	224	211
5% v/v distils to temp., °C	249	248	238
70% v/v distils to temp., °C	405	431	448
End-of-distillation temperature, °C	450	446	470
Distillation yield, % m/m	78.3	74.6	73.4

Table 5.

Selected properties of pyrolysis oil [42].

Pyrolysis oil has a content of unsaturated hydrocarbons as measured by the bromine number and, in general, more than 50% m/m of aromatic hydrocarbons. This stream also contains metal compounds, the source of which may be impurities brought into the process by the liquid pyrolysis raw materials and corrosion of the apparatus (Table 6).

Element	Unit	I	II	III	IV
Iron	mg/dm^3	4.3	—	2.3	—
Arsenic	μg/dm^3	16	50	30	29
Copper	μg/dm^3	67	88	73	68
Lead	μg/dm^3	70	280	163	171

Table 6.

The content of some elements in pyrolysis oil [42].

For the project’s implementation, several PO analyses were performed, applicable from the point of view of using pyrolysis oil as a raw material component for AV distillation.

The fractional composition of PO shows significant variability. The content of light fraction (distilling up to a temperature of 220°C) in oil samples is presented in the diagram (Figure 9).

Figure 9.

The content of light fraction in pyrolysis oil [42].

The presented data show how different amounts of low-boiling hydrocarbons contribute pyrolysis oil to gasoline distillates, from 2 to 20%m/m. The bromine number of the light fraction of pyrolysis oil, which characterizes the content of unsaturated hydrocarbons, shows a similarly significant diversity (Figure 10). These components may cause changes in the properties of the gasoline fraction as a raw material of the catalytic reforming process.

Figure 10.

Bromine number of a light fraction of pyrolysis oil [42].

The chemical composition of two samples of the light fraction of pyrolysis oil was tested by GC-MS. The first sample was the light PO fraction, while the second sample was obtained by distilling the fraction with a boiling range of 110–117°C from a mixture of equal parts by mass of PO and toluene. The toluene fraction, like the light pyrolysis oil fraction, shows a green color. Both samples contained a dozen or so identical hydrocarbons. The comparison of the admixture composition of toluene and the light PO fraction is shown in Figure 11.

Figure 11.

The content of selected hydrocarbons in the light fraction of pyrolysis oil (LFOP) and the toluene fraction from the distillation of the toluene-PO (FT) mixture [42].

Certain hydrocarbons in the light PO fraction and the toluene fraction are unsaturated. Examples include cyclic unsaturated hydrocarbons (Figure 12), hydrocarbons of hybrid structure (Figure 13), or hydrocarbons containing a vinyl substituent on the aromatic ring.

Figure 12.

Cyclooctatetraene C₈H₈ (bp 140–142°C).

Figure 13.

Indene C₉H₈ (bp 175–185°C).

As part of the test implementation of pyrolysis oil as a component of the AV distillation raw material, an attempt was made to analyze the average sample of pyrolysis oil to characterize the stream. During half of the year, 1 liter of PO was taken daily for distillation with crude oil in the AVD plant, mixed every 10 days, and 1 liter of an average decade sample was taken from the mixture. In this way, about 20 liters of oil were collected, which is an average sample for several months. The sample collected in this way should better reflect the properties of the PO flux.

An average sample of PO was subjected to normal distillation, obtaining the following fractions:

• forerun—up to a temperature of 188°C distills <0.5% m/m (2 drops);

• fraction I—in the temperature range 188–270°C distils 50.8% m/m;

• fraction II—distills 37.1% m/m in the temperature range of 270–335°C.

The residue from normal distillation solidifies with visible signs of coking. 11.6% m/m of residue from normal distillation of pyrolysis oil results from standard distillation conditions. The same product distilled under reduced pressure gives no residue greater than diesel distillates, about 0.5% m/m.

The density of the average sample PO is 1.0234 g/cm³, and the densities of the fractions are: I—0.9631 g/cm³ and fraction II—0.9989 g/cm³.

The content of unsaturated compounds is characterized by the bromine number of PO distillates: fraction I—1.89 g Br/100 g and fraction II—0.86 g Br/100 g. Both distillates show a dark green color.

To determine the type of PO components causing the characteristic greenish color of gasoline from crude oil distillation, the light fraction boiling to 250°C in amount c.a. 2 liters was distilled from 4 liters of the average PO.

The light PO fraction obtained in this way was further fractionated, using a rectification column, packed with Fensky rings. As a result, six distillates were obtained with the boiling point and color range given below:

1. up to 150°C—slightly yellow color

2. 150–190°C—slightly yellow color

3. 190–200°C—yellowish-brown color

4. 200–212°C—greenish color

5. 212–225°C—green color

6. 225–230°C—intense blue color.

White crystals, probably naphthalene and/or durene, were separated from fraction 4 and fraction 5 at room temperature. The color of the obtained distillates is shown in the photo (Figure 14).

Figure 14.

Color of light fractions of pyrolysis oil [42].

The fraction from PO, with a distillation range of 225–230°C and an intense blue color, was analyzed by GC-MS method, and it was found, among other, the presence of the following ingredients:

45.8% m/m of indenes (1H-dihydro alkyl and alkenyl).

13.3% m/m azulene.

12.9% m/m of alkyl naphthalenes.

6% m/m of alkenylbenzenes.

4.0% m/m biphenyl.

3.5% m/m of alkylbenzenes.

The performed analysis does not show the content of any hetero compounds in the analyzed pyrolysis oil fraction. Therefore, the cause of the coloration is only hydrocarbons, mainly azulene-bicyclo [5.3.0] decapentane (Figure 15), a hydrocarbon with an intense dark blue color.

Figure 15.

Azulene C₁₀H₈ (bp 242°C, D).

Thus, it was found that the pyrolysis oil contains intensely blue, cyclic unsaturated hydrocarbons, which, when combined with yellow fractions, cause their green color.

It means that greenish fractions arising during distillation of crude oil with addition of pyrolysis oil do not contain any hetero compounds and should be treated in hydrogen processes in the same way as another hydrocarbon containing fractions.

2.2 Laboratory tests of asphaltene dispersion modification in crude oil with pyrolysis oil

The colloidal structure of crude oil affects the results of raw material distillation and determines the amount of energy needed to separate it into fractions [43, 44]. Dehydrated and desalinated crude oil is a colloidal system of a lyophilic character. Polar asphaltene particles (aggregates) are surrounded by a solvation layer formed by resins and polarizable crude oil components (Figure 16).

Figure 16.

Illustration of changes in the dispersion structure of crude oil due to the addition of pyrolysis oil.

To reduce the phase instability of the raw material, crude oil was selected for laboratory-scale tests. The light gasoline fraction was distilled from crude oil in the AVD installation in amount of 4.5% m/m; stabilized heavy product is referred to as degassed crude oil (DCO). As a result, the raw material does not contain dissolved gaseous components and is characterized by higher density and viscosity (Table 7).

	Property	Value
CRUDE	Density, d20, g/cm^3	0.835
	Kinematic viscosity, ν20, mm^2/s	6.14
DCO	Density, d20, g/cm^3	0.872
	Kinematic viscosity, ν20, mm^2/s	27.73

Table 7.

Selected properties of crude oil and degassed crude oil [44].

Changes in the state of asphaltene dispersion in desalinated and degassed crude oil (DCO) due to the addition of various amounts of PO were assessed on the basis of several indicators, such as kinematic viscosity (Table 8), asphaltene content (Table 9), turbidity of the solution (Table 10), and surface tension (Figure 17).

Analyzed product	Viscosity, mm^2/s
DCO	24.73
DCO + 2.37% PO	22.73
DCO + 4.11% PO	25.53

Table 8.

Kinematic viscosity at 40 °C of degassed crude oil and mixtures with the addition of pyrolysis oil [44].

Analyzed product	Content of sediment insoluble in n-heptane, % m/m
DCO	2.25
DCO + 1.38% m/m PO	1.88
DCO + 2.23% m/m PO	1.24

Table 9.

Solid-phase content in degassed crude oil and mixtures with the pyrolysis oil [44].

Sample	Turbidity (NTU) for the wavelength of light, nm
	500	560	610	810	860
0.2% m/m DCO in n-C16	1385	340	139	4.95	3.90
0.2% m/m DCO + PO in n-C16	1440	345	140	5.14	4.11
0.3% m/m DCO in n-C16	2630	530	208	7.80	6.19
0.3% m/m DCO + PO in n-C16	2825	548	217	8.09	6.55

Table 10.

Turbidity of samples of degassed crude oil solutions in n-hexadecane and solutions of crude oil mixture with the addition of 2.2% m/m pyrolysis oil [46].

Figure 17.

Effect of pyrolysis oil addition on the surface tension of degassed crude oil.

The reduction in viscosity is caused by both the dilution of the liquid phase by pyrolysis oil and the change in the state of the asphaltene dispersion. An increase in the concentration of PO above 4% m/m does not decrease but increases the system’s viscosity. This type of viscosity change is probably the influence of aromatic hydrocarbons on the aggregation state of petroleum asphaltenes.

Increasing the aromaticity of the continuous dispersion phase leads to an increase in the surface tension of the liquid phase and the dissolution part of the resins. As a result, there is a reduction in the solvation layers surrounding the colloidal particles and the mass of the solid phase of the dispersion system. In this way, adding the aromatic fraction changes the proportions of the dispersion phases in crude oil (Table 9).

At a particular concentration of pyrolysis oil, the system achieves the maximum degree of dispersion of asphaltene particles, and subsequent portions of the aromatic component reduce the degree of dispersion. In the dynamic equilibrium aggregation-fragmentation, the aggregation processes of asphaltenes predominate, which, by creating spatial flocculants, immobilize part of the liquid phase and the viscosity of the system increases.

A similar dependence of the change in the physicochemical properties of degassed crude oil due to the introduction of pyrolysis oil was also observed in the case of surface tension. It was found that with the content of about 2% m/m of PO in the degassed crude oil, a maximum occurs in this relationship (Figure 17).

These changes can be explained from the point of view of the thermodynamics of dispersion systems. Good dispersibility or wettability of the solid phase requires similar polarity of both phases of the dispersion system. If we denote ${\sigma }_s^D$ as the dispersion component and ${\sigma }_s^P$ as the polar component of the surface energy of the solid phase (σ_s), and likewise denote ${\sigma }_l^D$ i ${\sigma }_l^P$ as the surface tension components of the continuous liquid phase (σ_l), the formula describing the interfacial energy of the system takes the following form [45]:

$${\left[{\sigma }_s^D{\sigma }_l^D\right]}^{0,5}+{\left[{\sigma }_s^P{\sigma }_l^P\right]}^{0,5}={\sigma }_l{\left[\mathit{cos}\Theta +1\right]}^{0,5}$$E3

where: Θ denotes contact angle of the solid by the continuous liquid phase.

The system achieves the minimum energy value and, therefore, maximum wettability or dispersibility when its components are compatible, that is, the continuous phase and the solid dispersed phase show similar polarity. The polarity of asphaltene particles is much higher than that of the liquid phase—maltenes. The addition of an aromatic fraction to crude oil increases the total surface tension of the maltenic phase and, at the same time, increases the polarity of this phase, bringing it closer to that of asphaltenes. In this way, the system becomes more compatible than the original one.

An attempt was made to evaluate the particle size of the dispersed phase through turbidimetric measurements of degassed crude oil and mixtures of it with OP. Due to the dark color of the samples, they were diluted to a concentration of 0.2 and 0.3% m/m with a suitable solvent. To obtain a stable suspension, n-hexadecane was used as a solvent, which has a high viscosity at room temperature.

Turbidity was measured with a HACH 2100 AN turbidimeter using interference filters of different wavelengths—Table 10.

The turbidity of dispersion media depends on the concentration and particle size of the dispersed phase and the refractive indexes of both phases. Based on turbidity measurements, through a series of calculations (spreadsheet), the size of colloidal particles contained in the degassed oil and its mixture with the aromatic component was estimated. In case of the mixture with the addition of pyrolysis oil, the average particle size is about 10% smaller than the starting degassed crude oil. Laboratory tests conducted later confirmed the significant effect of the addition of pyrolysis oil on the degree of asphaltene particle dispersion in the oil.

By influencing the state of the dispersion of the degassed crude oil, pyrolysis oil changes the distillation balance. The yield of light products is increased, and the amount of residues is reduced simultaneously. The yield of the gasoline fraction, boiling up to 180°C, increases in proportion to the concentration of the additive in the range of PO concentration from 0 to 2.2% m/m. In the gasoline fraction, the proportion of C₈-C₁₂ hydrocarbons, particularly naphthenic hydrocarbons, increases, and the density and viscosity of this fraction increase. A higher concentration of pyrolysis oil reduces the yield of the gasoline fraction. The output of the oil fraction, distilling up to 450°C, increases with the concentration of the additive similar to that of the gasoline fraction. The proportion of aromatic hydrocarbons in the oil fraction increases, which increases the density and viscosity of the distillate. The introduction of pyrolysis oil to the degassed crude oil at a concentration greater than 4% m/m causes a reduction in the oil fraction obtained. The total yield of light products reaches the highest value when the pyrolysis oil concentration is 2.26% m/m (Figure 18).

Figure 18.

The effect of the addition of pyrolysis oil to the degassed crude oil on the change in the total yield of light distillation products [46].

The increase in aromaticity of the continuous phase of the petroleum dispersion under the influence of the addition of pyrolysis oil leads to a decrease in the solubility and partial precipitation of high-molecular n-paraffin hydrocarbons. Petroleum wax associations, as colloidal particles, are solvated with low-molecular-weight paraffinic hydrocarbons because the most stable dispersion systems (solid-liquid) are formed by chemical compounds of similar polarity, i.e., by hydrocarbons belonging to the same homologous series. Probably, this mechanism explains the reduction in the content of n-paraffin hydrocarbons in the gasoline and oil distillate due to the addition of pyrolysis oil to the distilled raw material.

The influence of aromatic hydrocarbons on results of crude oil distillation is much more significant than it could result from the amount of the additive used. Even a low concentration of pyrolysis oil causes the release of additional amounts of polar compounds from the solvation layers of the petroleum asphaltene particles. The consequence of this is an increase in the amount (volume) of distilling components from crude oil.

It has been experimentally found that the addition of pyrolysis oil enables the distillation of crude oil at a lower temperature. This is confirmed in the literature [47] and results from reducing the enthalpy of the liquid phase components vaporization with a higher degree of dispersion. This means that using an aromatic component that changes the structure of asphaltenes dispersion in crude oil reduces the amount of energy needed to obtain distillates.

2.3 Industrial tests of using the pyrolysis oil additive to crude oil

The solution, developed on a laboratory scale for the modification of the dispersive structure of crude oil with the addition of pyrolysis oil, was submitted for the patent, and then an offer for the application of the invention in a refinery was presented [48]. The analysis indicated that many problems might hinder or prevent the practical use of the proposed solution.

From an industrial point of view, the most important was the lack of any references and reports on the use of similar solutions in refining technology.

The second difficulty relates to the way the additive is introduced into the feedstock of the distillation process. Two streams with such different chemical composition and physicochemical properties show limited miscibility. This phenomenon is observed in industrial practice, e.g., when composing heavy fuel oils.

The method of crude oil distillation in the conditions of an industrial AV installation, different from the laboratory method, requires a new optimization of the amount of pyrolysis oil added to the raw material.

The initial preparation of the raw material for distillation, i.e., dehydration and desalination of crude oil, is crucial for conducting almost all refining processes. The influence of pyrolysis oil on the course and depth of the removal of mineral impurities from crude oil can be verified only in industrial equipment.

One of the more serious problems related to the developed technology change is the possibility of causing too deep desorption of the solvation layers of asphaltene particles and causing flocculation and sedimentation of asphaltenes.

To explain the problems described above, after analyzing the technical conditions, industrial trial of crude oil distillation was carried out with the addition of about 2% m/m of pyrolysis oil.

The 2 weeks’ test run results confirmed the possibility of using pyrolysis oil as a component, favorably changing the balance of crude oil distillation. During the test, in the total balance of crude oil distillation, the total yield of diesel oil fraction increased by the amount of processed pyrolysis oil.

Concerning the crude oil distillation balance, before the dosing of pyrolysis oil, there were slight changes in the efficiency of individual fractions, like:

medium gasoline fraction—average increase from 14.6 to 14.8% m/m.

naphtha fraction—average increase from 9.4 to 9.6% m/m.

heavy diesel fraction—average increase from 7.3 to 7.6% m/m.

vacuum diesel fraction—average increase from 3.7 to 3.9% m/m.

other fractions did not show any changes in yield.

During the industrial test, no adverse effects of adding PO to the raw material on the operation of the AVD installation were observed. This applies to the operation of the vacuum generation system, the set of heat exchangers for the crude and desalinated crude oil heating system, and the operation of columns and coolers. There were also no changes in heat exchange processes.

The presence of pyrolysis oil in the crude oil did not noticeably change the effectiveness of mineral salt removal in the raw material desalination unit. The exceptionally high chloride level in the raw material in the last four test days is not related to the addition of pyrolysis oil to the crude oil. During this period, the electrodehydration system (EH) showed high work efficiency, reducing the mineral salt content from 60 to 80 mg/kg in the raw material to 3–8 mg/kg in desalinated crude oil (Figure 19).

Figure 19.

Comparison of the content of mineral salts (chlorides) in crude and desalinated oil [48].

Taking into account the results of the analysis performed in accordance with the sample schedule, it was found that the physicochemical properties of the distillates did not change in any way, maintaining their full technological suitability. The above statement is confirmed by the results of analysis of the group composition of the middle gasoline fraction—catalytic reforming raw material (Figure 20).

Figure 20.

Group composition of the middle gasoline fraction [48].

This fraction was analyzed in detail for its slightly greenish color and the quality of the raw material of the Naphtha Hydrotreating (NHT) catalytic reforming (Platforming) installation.

The technological trial confirmed the possibility of processing waste pyrolysis oil and crude oil in the AV distillation process. However, the relatively short test duration, the observed disturbances, and the method of processing the distillates obtained did not ensure that the invented solution could be permanently incorporated into the refinery production scheme.

The concept of waste stream management in the refinery was returned after 2 years when the amount of pyrolysis oil significantly increased. Among the considered methods of refining or processing PO, only this one did not require significant investment outlays and created an opportunity to obtain economic benefits directly at the refinery. The decision to repeat the industrial test to add PO to crude oil was made after some shortcomings of the first test move had been addressed. Various activities were undertaken, including efforts to stabilize the amount of oil for the trial period and assess the impact of possible changes in the quality of distillates on the selected production processes.

During second industrial test, the variability of the physicochemical properties of the PO flux did not noticeably affect the operating parameters of the AVD installation. The addition of PO to crude oil did not deteriorate its desalination efficiency, and the chloride content remained unchanged. There was no deterioration in the quality of the brine discharged from the crude oil desalination unit. The operation of the raw material heating system in heat exchangers and technological furnaces did not show any changes concerning the installation process when supplied with crude oil alone. The vacuum generation systems and all distillation columns worked properly without any changes.

During the test, slight changes in the distillation balance were once again observed with an increase in the total efficiency of the vacuum fractions by 0.3% m/m and, to a lesser extent, the gasoline and diesel fractions, each by 0.1% m/m. This was done at the cost of reducing the yield of the vacuum residue, by 0.5% m/m. There were also some shifts in the yield of vacuum distillates, namely increase in the amount of three fractions at the expense of reducing the amount of the heaviest one.

The quality analysis of the obtained fractions showed that the dosing of the assumed amount of pyrolysis oil did not even deteriorate the color of the vacuum products. While maintaining a stable amount of PO at the level of 1.5% m/m of raw material for the AVD installation, the color of gasoline fractions and diesel fractions showed a slight greenish. This, however, was within the scope of the applicable Technical Conditions (Standard of Production) and was comparable to the color of fractions with the same distillation range obtained from other AVD installations.

In gasoline fractions, an increase in nitrogen and arsenic content was found, which are impurities particularly undesirable from the point of view of the requirements of reforming catalysts.

Typical gasoline fractions from decomposition processes (cracking, pyrolysis) are characterized by a higher nitrogen content than gasoline fractions from crude oil distillation. Nitrogen compounds are transformed in the NHT process that the platformer raw material should contain no more than 0.5 mg/kg nitrogen in fraction.

The contamination of gasoline fractions with copper, lead, and arsenic compounds is temporary. Pyrolysis oil indirectly influences the increase in pollution of naphtha fractions.

The increased content of nitrogen compounds and metal combinations in crude oil distillates appears in the first period of dosing pyrolysis oil to the raw material of the AVD installation. After a few days, the level of contamination with such compounds is reduced. However, due to the short period of the second industrial trial, at this stage, it is not possible to verify the hypothesis of the transient nature of an increased level of metals and nitrogen in gasoline distillates.

The increase in the bromine number of middle (0.42 to 0.82) and heavy naphtha (0.47 to 0.81) distillates results from the unsaturated nature of light components of pyrolysis oil.

In vacuum distillates, obtained during the test run, an increase in the tendency to coke these fractions is observed. This is evidenced by the increase in Conradson Carbon Residue, especially in the heavy fraction, rising from 0.84 to 1.27 and from 2.40 to 2.97 in the heaviest portion.

Pyrolysis oil slightly increases the surface tension of desalinated crude oil and distillates. The increased surface tension of the raw material may have a particular effect on the operation of the plant and the contamination of the distillation products. With the addition of pyrolysis oil, crude oil shows an increased ability to dissolve or disperse coke settlements deposited in all parts of the installation. In this way, impurities deposited in the sediment can get into the products of the process, especially in the initial phase of additive dosing. The slight but noticeable increase in surface tension of virtually all distillation products is due to the rise in the content of aromatic hydrocarbons derived from pyrolysis oil.

The test run showed a reduction in the amount of vacuum residue and significant changes in its properties. The content of asphaltenes, n-heptane-insoluble components, and carbenes, insoluble in toluene, remains unchanged, but the paraffin content increases, and the vacuum residue viscosity decreases. This is due to the higher concentration of aromatic hydrocarbons in the crude oil and the atmospheric residue, reducing the solubility of high-molecular-weight paraffin-solid petroleum waxes.

The results of the verification test run and product stream analysis allowed for the decision to implement the invention in a refinery. After some necessary works, the AVD installation was prepared to receive a controlled amount of pyrolysis oil.

2.4 Industrial implementation of pyrolysis oil additive to crude oil

This was due to the need to verify the current research results and two industrial trials. In this stage of technology development, the implementation conditions are determined by the location of AVD plant in the refinery scheme and consequences of this fact. This relates to the processing directions of crude oil distillation products, the frequency of their analysis, variability of crude oil composition, changes in weather conditions, and events in the operation of apparatuses or devices. It is not a test run but the regular operation of the installation. The main goal is to obtain products that meet the requirements specified by the technical conditions and performance indicators of the production unit.

This chapter describes the changes in the AVD installation operating parameters, product balance, and the quality of distillates, and vacuum residues in the operating conditions of the production plant.

Dosing a similar amount of PO over a more extended period allows for a more reliable assessment of the observed changes. However, not all effects may be perceived to the same extent. For example, the initial increase in metal contamination of the distillates after adding PO to oil was probably due to the increased dissolution of sediment accumulated in some parts of the plant; the return to the previous level of the content of the analyzed elements usually took place after a few days. On the other hand, other effects of introducing PO may appear after a more extended period of use and thus remain unnoticed in the described and analyzed period.

The amount of pyrolysis oil in the raw material destined for distillation increases from about 1% m/m to over 4.5% m/m during the first 5 months of implementation. In the second half of the year, the PO dosage was maintained at level between 1.7% and 2.5% m/m.

The assessment of the functioning of the implemented method of crude oil distillation concerns the balance changes of the process, the yield of fractions and distillation residue, and quality of the key products of the AVD plant.

Since factors such as changes in the composition of the raw material (REBCO and light crude oil) and variations in distillate collection methods may occur concurrently during the operation of the installation, evaluating the impact of pyrolysis oil becomes more difficult. It can be performed with the periods of supplying the AVD installation with the same raw material, REBCO crude oil, and work in a constant regime. However, it should be noted that crude oil in pipeline also changes its physicochemical properties as it is a mixture of West Siberian crude oils, from 863 to 873 kg/m³; changes in the density of REBCO and mixtures with light crude oil are from 850 to 868 kg/m³.

Based on balance data, it can be concluded that the use of PO for the distillation of crude oil increases the efficiency of light products—diesel and gasoline fractions (Figure 21).

Figure 21.

The yield of light products from crude oil distillation depending on the concentration of pyrolysis oil in the raw material [48].

This confirms the results obtained in the test run, but the increase in the yield of the diesel fraction is much more significant. The yield of gasoline fractions is periodically lower compared to the base period efficiency. This is because the changes in the chemical composition of crude oil resulting from the addition of pyrolysis oil are insignificant compared to the changes in the colloidal structure of the raw material intended for distillation. In the 2 months period, when dosing of pyrolysis oil to REBCO crude oil was about 2% m/m, the most significant and differential increase in the yield of the diesel fraction was obtained (Figure 22).

Figure 22.

Changes in the efficiency of the diesel fraction [48].

Increasing the yield of atmospheric distillates causes a corresponding reduction in the amount of vacuum distillates and vacuum residue. The operating conditions of the AVD installation, which supplies the raw material for the production of base oils, require frequent changes in way of collecting vacuum distillates. Consequently, the mutual proportions of the yield of individual oil fractions are very different, although the total output remains almost unchanged. Due to changes in the boiling range and physicochemical properties of distillates and maintaining the parameters of the vacuum residue required for the production of asphalt, the installation does not allow for deep de-oiling of vacuum residue. Probably for the reasons mentioned, the performance of the vacuum residue is not noticeably affected by the presence or the amount of pyrolysis oil added to the raw material.

In summing up the distillation balance analysis, it should be stated that pyrolysis oil can be distilled with crude oil, thereby increasing the yield of atmospheric distillates without affecting the output of vacuum distillates and vacuum residue. This way of managing the waste product of olefin pyrolysis makes it possible to obtain additional amounts of raw material to produce diesel fuels.

Due to the increasingly higher quality of fuels manufactured from crude oil, particularly the shallow permissible sulfur content, practically all distillates are subjected to catalytic hydrogen processes. This places high demands on the quality of distillation products, the fulfillment of which is a prerequisite for effective and long-term operation of catalytic systems in hydrotreating and hydrocracking processes. Particular attention, in a modern refinery, is paid to the content of certain impurities in the raw materials of hydrogen processes. Therefore, in implementing the addition of pyrolysis oil to crude oil, the most attention was paid to the quality of distillates as a raw material for gasoline reforming and diesel hydrodesulfurization processes.

In the first period of supervision over implementing the described technological solution, special attention was paid to the quality of gasoline fractions as catalytic raw materials for isomerization and reforming processes.

The fractions of rectified light gasoline and those obtained from the atmospheric column were analyzed—following the requirements of technical conditions—in terms of arsenic, copper, and lead content. These elements irreversibly deactivate active centers of catalysts containing platinum or platinum group metals. The source of metal contamination of gasoline distillates is crude oil, and when pyrolysis oil is added to the distillation process, metals may also come from pyrolysis oil. The composition of the olefin pyrolysis raw material indicates that pyrolysis oil, the highest boiling product of this process, may contain some amounts of copper, lead, and arsenic compounds, which is confirmed by the results of the analysis.

The total content of metals (Cu, As, and Pb) in individual gasoline fractions is within the range of 5–12 ppb, regardless of the level of pyrolysis oil dosing to crude oil. Therefore, it can be assumed that the addition of PO does not change the concentration of these metals in gasoline fractions.

The presence of pyrolysis oil in the raw material for distillation, at any concentration, causes a slightly greenish color of gasoline distillates (Figure 23).

Figure 23.

Gasoline fractions obtained by distillation of crude oil (colorless) and distillation of crude oil with the addition of pyrolysis oil (greenish) [48].

The discoloration of the distillates takes place only during the addition of PO to oil on an industrial scale and indicates that the low-boiling PO components enter the distillates. Gasoline fractions obtained in the laboratory from raw material with PO addition are colorless, showing significant differences between simple distillation and flash distillation (single evaporation), carried out under industrial conditions. The analysis of the colored fractions by the GC-MS method did not identify substances causing the greenish color. This problem was thoroughly analyzed in the course of further research and described in Section 2.1.

Due to the content of unsaturated components in the light pyrolysis oil fraction, an increase in the bromine number of gasoline fractions can be expected. The bromine number and the metal content are essential indicators of the quality of the feedstock in the hydrotreating process. Experimental data show a significant increase in the concentration of unsaturated hydrocarbons in gasoline distillates due to adding pyrolysis oil to crude oil.

The bromine number of the low-boiling gasoline distillates, rectified, is 0.2 to 0.3 gBr/100 g and remains practically unchanged when pyrolysis oil is added to distilled crude oil.

The heavy gasoline fraction shows an average two-fold increase in the bromine number, from 0.3–0.4 to 0.6–0.8 gBr/100 g, regardless of the concentration of pyrolysis oil added to the crude oil. This can be explained by the fact that the distillation start temperature of pyrolysis oil is close to the distillation end temperature of this fraction.

The addition of PO to crude oil has a much more significant impact on the content of unsaturated hydrocarbons in the kerosene fraction. The value of the bromine number of this fraction, obtained from the distillation of crude oil, is about 0.5 gBr/100 g. By adding pyrolysis oil to distilled crude oil, this parameter increases to the level of 1.5 to 3.0 gBr/100 g. Taking into account the fluctuations in this value, it can be assumed that the content of unsaturated hydrocarbons depends more on the nature of pyrolysis oil than on the level of its dosing to the crude oil.

Generally, the degree of unsaturation of gasoline fractions obtained from distilled crude oil with the addition of pyrolysis oil does not disqualify them as catalytic hydrogen raw materials. Increased content of unsaturated hydrocarbons will increase hydrogen consumption in primary gasoline hydrodesulfurization processes (Naphta Hydrotreating—NHT).

From the point of view of the motor fuels production, it is crucial to maintain a constant level or increase the amount of diesel fuels produced. In Poland and Europe, there has been a deficit of fuels for self-ignition engines for years, and the forecasts provided for a further, steady increase in demand for this type of the fuel.

The introduction of pyrolysis oil to distilled crude oil increases the pool of diesel distillates, which aligns with the refinery’s production goals. There remains the problem of crude oil additive influence on quality of the raw material in the hydrorefining and hydrotreating processes. As a result of the hydrotreating of the light fraction of diesel fuel (LDF) at a temperature of about 300°C and under a hydrogen gas pressure of 3–4 MPa, a component of the finished fuel of appropriate quality is produced. Diesel distillates of a higher end-of-distillation temperature, highest boiling atmospheric fractions, and gas oil vacuum fractions contain higher amounts of sulfur compounds, nitrogen, and aromatic hydrocarbons. To obtain appropriate quality components of the finished fuel from these fractions, they must be subjected to much deeper refining with hydrogen (hydrotreating), which is carried out under higher temperature and pressure (6–7 MPa). Under such conditions, sulfur compounds are removed, the content of nitrogen compounds is significantly reduced, aromatic hydrocarbons are partially hydrogenated, and hydrocracking reactions begin.

The requirements for the quality of the diesel fraction, the raw material for hydrodesulfurization processes, are determined by the type of catalysts used. These requirements relate to such fraction properties as thermal stability, which determines the tendency to coke or form resin deposits and the As, Cu, and Pb content.

Thermal stability is a derivative of the chemical composition, including the content of unsaturated hydrocarbons. Therefore, the first parameter analyzed in detail during the implementation was the bromine number of diesel distillates.

The unsaturated nature of pyrolysis oil influences the value of the bromine number of the diesel fraction differently. The additive increases the bromine number of the mid diesel fraction (MDF) by 1 to 3 gBr/100 g, with a tendency to slightly increase with the share of pyrolysis oil in crude oil. The value of the bromine fraction of heavy diesel fraction (HDF) is generally in the range of 2–3 gBr/100 g and increases very slightly with the increase of PO concentration; the diesel vacuum fraction (DVF) is of biggest bromine number and increases from 4 to about 5 gBr/100 g, regardless of the concentration of the additive. An apparent reduction in the degree of unsaturation of the vacuum fraction is observed during the distillation of the mixture of REBCO crude oil with light crude oil.

In the second period of supervision, the influence of pyrolysis oil on the quality of diesel oil fraction was also analyzed. For this purpose, distillates with a similar boiling point range were compared, obtained from three other AVD plants, one of which was fed with REBCO crude oil with the addition of PO and the other two were fed only with REBCO crude oil.

Four series of samples were taken, and the averaged results of bromine number determinations were presented in the form of a graph in Figure 24.

Figure 24.

Comparison of average values of the diesel distillates bromine number [48].

The distillates from crude oil with PO (A22, A23, A24, and P20) show slightly higher values of bromine number concerning the corresponding two atmospheric fractions and vacuum one. It proves that unsaturated hydrocarbons pass from pyrolysis oil to diesel fuel distillates, but do not change the thermal stability of the fractions.

One of the essential technological problems resulting from the introduction of pyrolysis oil to crude oil is a significant increase in the content of “present resins” observed in the analyses of diesel fuel distillates. Industrial experience may increase the amount of sludge deposited in heat exchangers when the feedstock is heated in the hydrodesulfurization process.

Most analyses of the heavy diesel fraction show the content of “present resins” between 100 and 200 mg/100 ml, the vacuum fraction between 150 and 300 mg/100 ml, regardless of the presence of PO as an additive to crude oil and its concentration in the raw material of the AVD plant.

The content of “present resins” is a practice-accepted measure of the tendency of petroleum streams to form deposits at elevated temperatures. However, it is doubtful whether the method of determining the content of “resins present” reflects the conditions of apparatus and devices in which the distillation stream is subjected to high temperatures. According to the standard PN-EN ISO 6246:2017-2105 Petroleum products - Resin content of fuels - In-stream evaporation method, the analyzed product or raw material is evaporated in a stream of hot air, and the residue after evaporation is determined.

The main difference between the conditions of laboratory determination and the method of heating the raw material in an industrial installation is the presence of oxygen. Oxygen causes the initiation and development of free radical reactions leading to the formation of macromolecular products through condensation and polymerization reactions. These products are insoluble in petroleum fractions, form dispersions of solid particles, and are deposited on the metal surface. Thus, the determination of the resin content from the point of view of assessing the sedimentation tendency of petroleum products under industrial conditions seems unreliable. The decision according to the standard characterizes the thermo-oxidative stability of the gas oil distillates, whereas the thermal stability test would provide more adequate results.

In order to compare the tendency to form sediments by diesel fractions, the thermal stability of distillates obtained from crude oil with the addition of PO and their equivalents from other AVD installations was tested. The investigated fractions were subjected to derivatographic analysis under nitrogen atmosphere, determining the residue at 300, 350, and 400°C. The results of the measurements show that under anaerobic conditions, at elevated temperature, the fractions of diesel fuels obtained from the distillation of crude oil with the addition of PO create smaller amounts of sediment compared to the distillates obtained by distillation of crude oil without the addition of PO—Figure 25.

Figure 25.

Comparison of thermal stability of diesel oil fractions obtained from REBCO crude oil distilled with the addition of OP (blue) and without the addition of OP (red) [48].

The results of the determination of the content of “present resins” and the content of unsaturated hydrocarbons (bromine number) in the diesel fractions do not show a mutual correlation. It seems that the thermal stability characteristics of diesel fuel distillates better reflect the stream behavior in higher temperature in industrial apparatus than the commonly used thermooxidative stability determination of “resins present” content [49].

It should be added that the content of some pyrolysis oil components in the diesel fuel fractions increases the surface tension of these fractions, and thus the ability to dissolve and disperse petroleum sediments. Although no research in this area was carried out, this fact was confirmed based on observations made during the overhaul of the hydrotreating installation. The transport and heat exchange system on the raw material side of the installation was perfectly clean, with no traces of resin or asphaltenic deposits when operated with raw material obtained from crude oil with PO.

In terms of arsenic, copper, and lead content, the distillates obtained from the installation using the PO addition to crude oil show a higher or comparable quality to those obtained from the crude oil distillation unit without the additive. This is evidenced, among other things, by the results of arsenic content determinations carried out in the first period of supervision, in the HDF and VDF fractions, received with PO in REBCO and, respectively, in the HDF and VDF fractions from REBCO crude (Figure 26).

Figure 26.

Comparison of arsenic content in diesel distillates [48].

The presented data show that adding pyrolysis oil to crude oil does not increase the contamination of high-boiling diesel fractions with metal compounds deactivating the catalysts.

During the second period of supervision, a comparison was made regarding the metal content of all diesel distillates obtained from three AVD installations. One of these installations processed crude oil with the addition of PO, while the other two distilled crude oil without it. The results show a lower content of copper and lead in distillates obtained by distillation of crude oil with the addition of PO (fractions MDF, HDF, VDF) than distillates produced by distillation of only REBCO crude oil (fractions MDF, HDF, VDF) (Figure 27).

Figure 27.

Averaged metal contents in diesel fractions [48].

A complete quantitative comparison in terms of the content of selected elements in diesel fractions is obtained after considering the amount of appropriate distillates collected from individual installations. Diesel fractions (HDF and VDF) obtained from the PO additive installation contain 6.2 g/h of arsenic, copper, and lead, i.e., twice more minor than the corresponding fractions from the AVD installation feeding by REBCO crude oil, 11.8 g/h. The presented data show that the addition of pyrolysis oil reduces the content of impurities in the raw materials of the hydrotreating process. The only logical explanation for such changes could be the increased efficiency in the desalination process of removing metal compounds from crude oil.

By summarizing the results of the analyses of diesel fractions, it should be stated that, the addition of PO to crude oil does not deteriorate quality of the raw material for hydrotreating processes of diesel fuel components.

Vacuum distillates were analyzed in the first period of technology implementation. Earlier, as part of the test run, their quality was examined from the point of view of their use as raw materials for the production of base oils and no adverse effect of adding about 2% m/m pyrolysis oil to crude oil was found. Vacuum distillates are primarily the raw material of the hydrocracking process, and several parameters were determined in this respect, which may be influenced by the presence of unsaturated and aromatic pyrolysis oil in the raw material of the AVD installation. The content of aromatic hydrocarbons, including mono-, di-, and polycyclic, does not change due to the addition of PO to crude oil. Vacuum distillates show a slight increase in the bromine number due to the introduction of PO to crude oil, regardless of concentration of the PO additive in the range used during technology implementation. The use of mixed crude oil (REBCO + light crude oil), as the raw material of the AVD installation, does not affect the content of unsaturated hydrocarbons in the distillates.

The tendency of vacuum distillates to create coke, as measured by the residue after coking determined by Conradson’s method, slightly increases as a result of adding PO to crude oil, but concentration of the additive practically does not affect this property of the distillates.

The literature data and laboratory test results show that both the efficiency and properties of vacuum distillates are expected to undergo significant changes when introducing an aromatic additive to crude oil. The results obtained so far, during the technology implementation, do not confirm this thesis. Probably, a different method of raw material distillation in industrial conditions (flash distillation through single evaporation) to a small extent reflects the changes in the dispersion structure of crude oil.

The vacuum residue is also subject to very little change due to the addition of pyrolysis oil to the crude oil. The content of asphaltenes (designated as n-heptane insoluble matter) is slightly decreased. The content of carbenes (defined as toluene insoluble substances) increases in the initial period of PO dosing to crude oil. The lowest range of carbenes in vacuum residue occurs during the distillation of the mixture of REBCO crude oil and light crude oil. The content of mineral compounds, as evidenced by the determined residue after vacuum residue incineration, is significantly reduced when PO is added to crude oil. This serves as further evidence of the beneficial effect of adding pyrolysis oil on the crude oil desalination process (Figure 28).

Figure 28.

The ash and carbene content in vacuum residue [48].

The changes in the colloidal structure of the vacuum residue are, therefore, not as significant as they would appear from the laboratory tests.

The AVD plant operation indicators undergo specific changes during the implementation period, resulting from the influence of pyrolysis oil on the crude oil dispersion structure. One of the essential elements of the AVD plant is the crude oil desalination plant. The main goal and measure of its operational effectiveness are to remove mineral impurities from the raw material.

The desalination process extracts mineral salts, mainly sodium, magnesium, calcium, and potassium chlorides, into the water phase. Specially prepared water in amount 2 to 5% m/m is heated and added to the crude oil about temperature 100°C, whose purpose is to dissolve the maximum amount of mineral salts. To develop the mass exchange surface, the mixture is expanded in a special valve to properly disperse the water in crude oil. The pressure drop in the mixing valve determines the size of the dispersed water droplets. The stream of the W/O emulsion is fed to the electrodehydrators, where the brine droplets coalesce in a strong electric field. The phase separation generally requires the addition of a demulsifier so that a small amount of water remains in the desalinated crude oil and no organic petroleum components are present in the brine phase. The process is usually carried out in two or three desalination stages (Figure 29).

Figure 29.

A simplified diagram of the crude oil desalination unit [48]. 1—Crude oil pump, 2—Heat exchanger, 3—Steam heater, 4—Electrodehydrator, 5—Tank - separator; I—Crude oil, II—Demulsifier, III—Water, IV—Vapor, V—Condensate, VI—Desalinated oil, VII—Brine.

The efficiency of the process is primarily determined by reducing the salt content of the crude oil. Changes in chloride content in crude and desalinated crude oil during the implementation period are shown in Figure 30.

Figure 30.

The chloride content in crude and desalinated oil [48].

In crude oil sent to the desalination unit, the chloride content varies between 20 and 50 mg/kg over more than half a year. Despite significant fluctuations in this parameter value, the desalination system effectively removes mineral salts to the level of 1–2 mg/kg. This means that adding pyrolysis oil to crude oil certainly does not deteriorate the operation of the desalination plant.

The reduction of mineral salts content is not the only indicator of the efficiency of the crude oil desalination and dewatering unit. It was assumed that metal compounds in the crude oil, after the desalination process, mainly accumulated in the distillation residue. In the first period of monitoring, the mineral residue, after vacuum residue ashing, was analyzed to compare desalination. Compared to the base period, a significant decrease in the range of mineral substances in the vacuum residue was observed, which indicated an improvement in the efficiency of the crude oil desalination unit. This fact is also confirmed by the results of measurements of arsenic, copper, and lead content in diesel distillates obtained from REBCO crude oil distillation when are lower the corresponding distillates obtained from REBCO crude oil with the addition of pyrolysis oil.

The heat transfer in the AVD raw material heating system depends, to a large extent, on the amount of sludge deposited in the exchangers on the crude oil side of the tubes. In the initial period of adding pyrolysis oil, an improvement in heat transfer was observed, resulting from the dissolution and dispersion part of the sediments. The aromatic addition to oil increases the surface tension and increases the dissolving capacity of polar resin and asphaltenic deposits. This effect is also transferred to mid-range distillates, causing an increase in surface tension and washing and dispersing capacity. Maintaining the cleanliness of the surface of the heat exchange apparatus is undoubtedly a beneficial effect of the presence of pyrolysis oil in crude oil.

There are extremes in the dependence of the surface tension of crude oil and distillates on the concentration of pyrolysis oil in the raw material. This means the need to maintain the concentration of the additive at an optimal level, mainly from the point of view of the phase stability of asphaltene dispersion in crude oil.

The energy effects that should occur when changing the dispersion structure of crude oil remain difficult to observe on the scale of an industrial installation. This is mainly due to the variable calorific value of energy media, oil, and fuel gas used for combustion in technological furnaces. Nevertheless, a slight decrease in media consumption per unit of processed raw material was observed in the first period of supervision. The reduction of energy expenditure on the distillation of crude oil with the addition of pyrolysis oil is associated with an increase in the yield of light products obtained at the distillation stage under atmospheric pressure. The energy input per unit product of vacuum distillation is at least three times higher than atmospheric distillation.

The solution concerning the possibility of using pyrolysis oil as an additive to crude oil, based on theoretical premises, laboratory tests, industrial trials, and experience from industrial implementation, is gaining recognition among researchers and engineers of the petroleum industry [50].

3. Discussion of results and summary of research

In the field of research on asphaltene dispersion in crude oil, the possibility of changing the dispersion state and aggregation of asphaltene molecules was explored through the application of an aromatic additive to the raw material of the AVD plant process. The problem of crude oil phase stability was solved by introducing a waste petrochemical component—pyrolysis oil (PO). Taking into account, the need for technological management of pyrolysis oil, an in-depth analysis of this stream was performed. Due to its origin as a by-product of the olefin pyrolysis process, pyrolysis oil is characterized by considerable variability in composition and properties. Pyrolysis oil has been tested in terms of its use in refinery production and its potential impact on crude oil distillation. It was found that the average mid-year sample distilled at 88% m/m in the range of diesel fuel under normal distillation conditions. In the PO fraction boiling up to 220°C, no non-hydrocarbon components were found, meaning the additive does not directly add nitrogen or sulfur compounds to gasoline distillates. From the point of view of the quality of the raw material for the NHT process of gasoline reforming and hydrorefining of diesel fractions, an important parameter is the content of unsaturated hydrocarbons, the measure of which is the bromine number of the fraction. Many olefins, dienes, and polyenes have been identified in the low-boiling fraction of pyrolysis oil that can be found in gasoline and diesel distillates. Although they increase the bromine number of the stream, their hydrogenation is much easier than removing sulfur compounds and presents no process difficulties.

Adding the optimal amount of PO to crude oil increases the yield and improves the quality of the diesel distillate. PO increases the surface tension of crude oil and its distillates. This influences the ability to peptize asphaltenes and dissolve sediments previously accumulated in pipelines and apparatuses. Despite the increase in the content of the so-called present resins, diesel distillates do not show changes in thermal stability, which is also crucial from the possibility of sediment deposition on the surface of heat exchangers.

When used in an appropriate concentration, aromatic hydrocarbons increase the stability of asphaltenes dispersion in crude oil and distillation residues—atmospheric and vacuum residue. In practice, the improved phase stability of the dispersion means that asphaltenes are less prone to flocculation, sedimentation, and electrodeposition of sludge in production installations. This is confirmed by the results of crude oil tests performed using scanning turbidimetry (TurbiScan) (Figure 31).

Figure 31.

Dependence of the change in the intensity of backscattering (ΔBS) on the concentration of pyrolysis oil in crude oil [50].

Such studies illustrate the natural transformations of the dispersion system under the influence of pyrolysis oil, as asphaltenes are found in their natural environment—crude oil. Scanning turbidimetry, similar to the measurements of surface tension and kinematic viscosity, confirms the occurrence of the maximum dispersion stability at the concentration of PO in the crude oil of about 2% m/m in the case of REBCO crude. The effect of PO addition on the results of the crude oil dehydration and desalination process is significant. The depth of the extraction of mineral salts in electrodehydrators depends also on the aggregation state of asphaltenes, which stabilize water-in-oil emulsions. The aromatic component, increasing the solubility of the asphaltene molecules, shifts the aggregation-fragmentation balance of asphaltenes. Pyrolysis oil, added to the raw material in the amount of 1.5 to 2.0% m/m, improves the efficiency of crude oil desalination, which is manifested by a reduced content of metal compounds in the petroleum fractions and a significant reduction in the content of mineral compounds, ash residue, in vacuum residue.

The results of research works and technological analyses confirmed the previously obtained results of laboratory measurements. It has been proven that the dispersion structure of crude oil is an essential factor in the technological value of the raw material. Utilizing the additives, or in this case, a component, the physical structure of the crude oil can be intentionally modified. By optimizing the surface properties of the dispersion, the quality of the crude oil as a raw material for the distillation can be advantageously altered.

Changing the dispersion structure of crude oil also means increasing the proportion of the liquid phase and reducing the enthalpy of evaporation of distillates, which reduces the energy expenditure on the distillation of the raw material. An additional factor that favorably changes the energy balance of the process is the higher proportion of light products, especially the atmospheric fractions, obtained during the distillation of the raw material. Industry data show that vacuum distillation consumes about three times more energy per unit distillate mass than atmospheric distillation.

All the effects mentioned above, applying the optimal pyrolysis oil to crude oil, were verified during the over one-year implementation period of the patented method of raw material preparation for the AVD plant in the refinery.

The change in the method of crude oil distillation by introducing the optimal amount of the additive in the form of pyrolysis oil has been patented, is being implemented at the refinery, and the solution has been awarded twice at international exhibitions of inventions.

In the summary of the research, it should be added that the solution to particular problems should be found through the use of the transformation potentials (the first technological principle) of individual phenomena. In the area of asphaltenes dispersion in crude oil (according to the technological principle of the best use of materials), a waste product was used to modify the crude oil advantageously.

Generally, laboratory experiments, industrial trials, and more than 1 year of implementing pyrolysis oil as component of crude oil provided relatively extensive knowledge about the effects of modification of the dispersion structure of the crude oil. There are still questions and doubts, especially one of the less studied refining processes is crude oil desalination. It is necessary to learn more about the mechanisms of water-demulsifying additives in crude oil with a changed asphaltene dispersion state. The dispersion behavior under shear stresses (in the flow) or the influence of periodically appearing crude oil impurities that change should also be studied to understand the form and properties of the dispersion.

In this way, the structure and transformation of petroleum dispersions may be the subject of further research based on the experience to date. This work is a contribution to the understanding and economical use of specific properties of petroleum dispersion systems.

4. Additional information

Some parts of this chapter were originally published in Polish, in the work Physicochemistry of Petroleum Dispersions in Refining Technology Optimizing, dated year 2007. The results of our own research presented in the form of tables and figures in Sections 2.2 and 2.3 come from extensive industrial research reports.

Acknowledgments

The author would like to thank PETROL Invention Enterprise for financial support for the publication of this work. Author wants to thank many co-workers, researchers, technical assistants, and students preparing their diploma in industrial researches. Special thanks to Mr. Romuald Zębrzycki for his help in preparing graphics of this work.