Octane number of oxygen generating gasoline additives, which is measured by different methods.
The article describes the technology of synthesis of absolute ethyl alcohol, as well as the types, properties and efficiency of water-withdrawing reagents and types, properties and efficiency of reagents (CaO, tetraethoxytitanium), which chemically bind water and dehydrate ethanol. The composition and properties of the absolutized ethanol were studied using the infrared spectroscopy, mass spectroscopy and gas-chromatography. The octane number of gasoline with the addition of absolutized ethanol together with the combustion activator (diethyl ether) was measured as well. It has been shown that the content of even very small amounts (up to 2%) of the combustion activator in absolutized ethanol results in the increase of the octane number and improves running abilities of gasoline.
- absolutized ethanol
- calcium oxide
- diethyl ether
- octane number
Some methods for obtaining absolute alcohol are well known, namely: (1) by binding water to water by subtracting substances; (2) pressure absolutization on many column rectification (distillation) plants; (3) the so-called azeotropic rectification using methods based on the phenomenon of azeotropism of three-component systems; (4) using methods based on the phenomenon of vapor diffusion through porous partitions or molecular sieves [1, 2]. Using as a desiccant, calcined calcium oxide can achieve an ethanol concentration of 99.8%, using magnesium sawdust—89.95%. With the combined use of sodium alcoholate ethanol can be absolutized to 99.5% .
Another way to obtain absolute ethyl alcohol is to separate the mixtures in distillation columns operating at different pressure values. The method is based on the dependence of ethanol content in the mixture on pressure. Typically, the installation consists of two columns. In the first column receive the alcohol strength of 70–95%, which comes in second column under pressure. The pressure in different methods varies from 8 kPa to 7.6 MPa. It is in the second column that absolute alcohol (99.2%) is obtained. The absolute alcohol (99.2%) is obtained in the second column. The disadvantage of these methods is their high energy consumption, because the rectification columns operate under pressure and require of the using of vapor or other high-temperature media to provide the necessary parameters [4, 5, 6, 7, 8, 9, 10]. Many industrial distillation plants that produce absolute ethanol are azeotropic using a third component, which forms an azeotrope with the components of the mixture—alcohol and water. Analysis of the literature shows that substances such as benzene, toluene, isooctane, cyclohexane and hexane can form the third component, which is capable of forming azeotropes with ethanol and water. The concentration of alcohol, obtained by this method, is reached to 99.7% [11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21].
Others are the methods built on the application of the phenomenon of adsorption. For this purpose, the alcohol-water mixture should be converted into a vapor phase in which the water molecules are in dissociated form and can be separated by adsorbents that absorb only water molecules from the vapor mixture and can be regenerated for reuse. Such adsorbents include polymer compositions based on dioxols, silica gel, synthetic zeolites and the like. Technologically, they can be made in the form of membranes, which are ceramic tubes, the inner layer of which is covered with a thin layer of zeolite or in the form of molecular sieves. Different composition of synthetic zeolites is known, but aluminum-potassium and aluminum-sodium zeolites have become the most widely used because they have a high adsorption capacity [22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33]. Due to the high cost of synthetic zeolites, ethanol absolutization methods have been developed, using the so-called natural zeolites—clinoptilolite: (NaK)4CaAl6Si30O72·24H2O and mordenite, which are widespread in the form of ores in certain territories of Ukraine, which is an undeniable advantage of their use .
Due to stabilization production of the volume petroleum and decrease in its price and the ban on the use of the tetraethyl lead gasoline in recent years, many countries of the world tend to increase the usage of oxygen-containing compounds as the additions in commercial high-octane gasoline. Methyl (MA), ethyl (EA) and tert-butyl (TBA) alcohols, methyl tert-butyl ether (MTBE), having high octane numbers and low boiling points are quite widely used among the oxygen-containing compounds. The usage of these additions results in an increase of the octane number and the improvement of the oxygen coefficient and the efficiency of the fuel combustion. All types of the fuel with oxygen-generating additives reduce the release of carbon monoxide (CO) and unburnt fuel parts (C) into the atmosphere. Thus, the addition of 10–15% MTBE reduces CO content in exhaust gases by 20%. The use of alcohol-gasoline mixtures as a motor fuel is also promising. The world ethanol production has recently reached 90 million m3 per year . The main producers are the USA, Brazil and India. It should be noted that more than 80% of produced ethanol is used as a component of motor fuels (fuel ethanol). The rest is used for manufacture of the strong drinks, solvents, the ethyl ethers and esters synthesis and as a raw material for organic synthesis .
In many countries of the world, gasoline with 10–15% of various fuel additives is already used. In particular, a mixture of gasoline and ethanol (10–12%) is successfully used in the USA, Canada and Brazil, where its production is based on a national program. In the United States, 80% of produced ethanol is used as a fuel. In France, fuel containing ethanol (5%) is used too. Ukraine consumes around 200 million tons of fuel and energy resources annually and has a deficit of energy resources because the needs for energy consumption are covered only up to 53% by its own resources. The rest is covered by import: 75% of the required volume of natural gas and 85% of crude oil and petroleum products. Such a structure of the energy economy creates Ukraine’s dependence on oil and gas exporters and is threatening its energy and national security. Motor transport occupies a leading place in the transportation of goods. The prognosis of the development of Ukraine’s motor car park proves the tendency toward a steady increasing of the number of cars and fuel consumption. In 2016, the total motor car park and the park of light commercial vehicles in Ukraine consist of, according to AUTO-Consulting, 9121,000 cars, which consume 32.7 million tons of motor fuel. The alcohol industry of Ukraine fully provides internal needs of alcohol for the manufacture of alcoholic drinks, working only up to 30% of its total capacity .
Recently, ethanol production of Ukraine has decreased almost twice from 310 million liters in 1996 to 140 million liters in 2017. Today, 25% of the 80 distilleries with a total capacity of 480 million liters per year operate. To date, in Ukraine there are more than 40 licensed distilleries that can process 900,000 tons of grain per year and obtain 320 million liters of grain ethanol. The annual need of beet molasses is 1.1 million tons, from which you can get other 300 million liters of ethanol. In the structure of realization of rectified ethanol the largest part is occupied by vodka and ethanol from 81 to 94.5% in 2015. In January 2016, the manufacturer “Ukrspirt” produced more than 860,000 l of ethyl alcohol, 85,000 l of strong drinks and 756,000 l of car washers. At the same time, the company work is provided by 16 factories .
In recent years, the production of bioethanol has been steadily increasing. From 2000 to 2014 the amount of produced ethanol has increased by five times. The market leaders are: USA (corn), Brazil (sugar cane), Germany and France (sugar beet and grain). Governments of these countries intend to increase the bioethanol production by 70%. If 10% of bioethanol is added to gasoline, emissions of aerosol particles are reduced by 50% and carbon monoxide emissions by 30%. Therefore, there is a Directive 2009/28/EC, which requires up to 10% bioethanol in a motor fuel by 2020. Ukraine signed the Association Agreement with the European Union, so it should undertake the similar obligations. While in the EU this index is gradually approaching 5% in Ukraine, it does not exceed 1% .
Macroeconomic analysis has shown that adding 20% of bioethanol to gasoline leads to an annual decrease in gasoline import by $ 400 million, which will result in $ 640 million increase in Ukraine’s gross domestic product (GPD). Replacing 20% of heavy distillates with biodiesel will reduce imports by $ 1 billion, which can increase Ukraine’s GDP by $ 1.4 billion.
In August 2014, there were 13 enterprises operating in Ukraine that produced alcoholic fuels, 10 of which based on the state alcohol distilleries with a capacity of 23,700 tons/month. However, in August 2014 there was introduced 99 EUR tax on alternative gasoline in favor of importers and network monopolists, resulting in the fact that by the beginning of 2015 only two plants (“Haysinsky” and “Ekoeenergy”) with a total capacity of 2700 tons/month worked . The cost of growing rape grain in recent years ranged from 800 to 1200 UAH/t. At the same time, when the seed market price is 3000 UAH/t, the cost of production of biodiesel from the fossil is 11,000–12,000 UAH/t (about 10 UAH/l), which is 2.5 times lower than the existing prices for diesel oil from oil . The dynamics of growth of bioethanol and biodiesel part in the world represented by the author  speaks for itself, so the production of bioethanol has exceeded 100 billion liters, and biodiesel amount reaches 30 billion liters.
It is known that for homogenization of gasoline ethanol mixtures the third component is used. This component is aromatic hydrocarbons , which are added to ordinary gasoline to increase the octane number. In addition, it is not profitable, because the cost of toluene is by many times higher than the cost of absolute ethanol. As for the preparation of perfect mixtures of bioethanol and biodiesel with gasoline and diesel, only absolute ethanol (99.95%) must be used, therefore the research of new methods and reagents of ethanol absolutization is an actual problem and purpose of our work, which has a practical and economic value.
The properties of known oxygen-generating additives which activate the motor fuel combustion are presented in Table 1 . The table shows reagents which do not contain water, including ethyl alcohol and ethers, but in this work it is not described how the ethyl alcohol was absolutized, therefore in different sources it has a different octane number. Consequently, we propose our own method of ethanol absolutization with calcium oxide or tetraethoxytitanium (TET).
|Research octane number (RON)||112–130||120||105–115||111.6||120||106||108|
|Motor octane number (MON)||75–115||102||95–105||98.4||90||95||98|
|Octane number index (RON + MON)/2||110||111||105||105||101||100.5||103|
|Saturated vapor pressure, МPа (at 293 K)||0.06||0.03||0.02||0.03||0.42||0.13||0.07|
Researches of the method of ethanol absolutization by chemically binding water reagents such as calcium oxide and TET are conducted. Alcohols practically do not interact with alkalis, because among the reaction products there is water that decomposes formed alcoholate and a reverse reaction takes place.
Therefore, fresh prepared (1123 K, 2 h) mineral calcium carbonate, which has the following characteristics, presented in Table 2, was used for ethanol absolutization.
|The component content of calcium oxide||Types of CaO obtained from mineral calcium carbonate, CaCO3|
|CaCO3 and MgCO3 carbons||≥3||≥5||≥10|
|Impurities SiO2 and Al2O3||≥1||≥10||≥15|
After calcination, samples of CaO were cooled in a vacuum desiccator, to reduce air access and to re-carbonize calcium oxide. Only 1 grade with minimum content of impurities was taken for work (Table 2).
It was suggested that if you take freshly calcined calcium oxide, then absolutized ethyl alcohol and alcoholates of the corresponding metals can be obtained during an irreversible reaction:
The insoluble calcium hydroxide in the alcohol was filtered off, and the absolute ethyl alcohol by reactions (4) and (3) was discharged through a direct refrigerator, and the calcium hydroxide remained in the flask in the precipitate form.
Tetraethoxytitanium (CH3CH2O)4Ti as a dehydrator acts in different way.
During the hydrolysis of TET the titanium tetrahydroxide, which is insoluble in alcohol, precipitates and can be filtered out; the absolutized alcohol is distilled at a special installation under vacuum, or with air dehydrators under normal conditions.
As can be seen from Table 3 , ethanol has the most similar properties with gasoline according to the main indicators (boiling point and octane number). In addition, it is the cheapest and most affordable as a bioethanol—a product of natural raw materials processing, therefore, it was selected for absolutization. The ethanol concentrations were measured by the weight pycnometer method and determined by theoretical data . The volume concentration of alcohol is determined by the areometers (ASP-1, ASP-2) using tabular data. Chromatography of ethanol and gasoline is carried out on by a gas–liquid chromatography, a method for determining oxygen-containing compounds in gasoline (HPCHEM\SEQUENCE\D161124A. S\METHOD\ D4815N.M) by internal standard (ISTD) based on 15 known calibrated substances, including ethanol (Figures 2–4). Infrared spectroscopy of ethanol samples is carried out by IR spectroscope (IS 50 FT-IR “NICOLET” Slovensko). Mass spectroscopy of the samples is carried by a mass spectroscope (MX-7304A, AO.SELMI, Sumy, Ukraine, 1 to 210 mass range). Determination of the cetane number of diesel fuel L-0.2-40 and the octane number of petrol A-80, as well as the freezing point of diesel fuel was carried out using the laboratory analyzer “Octane meter” of Shatox sx-100 k type . Also, an assessment of the petrol gasoline by a motor method was carried out at the “OKKO” quality control laboratory in Galich, Ivano-Frankivsk region of Ukraine.
|Saturated vap. pres.||kPa, 298 K||16.2||6.5–7.5||0.8||12.7|
|Vapor density||g/l, 298 K||1.3||1.9||2.4||3.2|
|Water solubility||g/100 ml||Unlimited||Unlimited||7.9 g/100 ml||1800 mg/l|
|Viscosity||s·Pа, 298 K||0.544||1.074||–||0.649|
|Henry’s constant||, 298 K||1.087Е−4||2.097Е−4 to 2.571Е−4||–||2.219Е−1|
|Octane number RON||–||156||132||104||82.5–98.0|
|Cetane number MON||–||92||89||78||95|
3. Results and discussion
Table 4 shows the results of the ethanol absolutization using tetraethoxytitanium. As can be seen from the table, absolutized ethanol can be obtained with the ethanol concentration, which increases from 92.5 to 93–96 wt% (or 95.41–99.50 vol%), but does not reach 100 wt%.
|Initial ethanol amount, SSU 4221:200 95 vol%, 92.5 wt %||The amount of ethanol obtained after absolutization||Ethanol yield after absolutization||The amount of Ti(OC2H5)4||Ethanol density after absolutization||Ethanol concentration after absolutization|
Therefore, at the second stage of our research, we used a more reactive dehydrator—calcium oxide which was calcined at 1123 K; its characteristics are presented in Table 2. We selected a sample no. 1 with a minimum content of magnesium oxide (MgO—5%), carbonates (CaCO3 + MgCO3−3%) and other impurities (SiO2 + Al2O3–1%). As can be seen from the results presented in Table 4, the CaO consumption decreases to 17 wt%, compared with 25 wt% of (C2H5O)4Ti, and the concentration of absolutized ethanol increases to 99.5–100.0 wt %, or 99.7–100.0 vol%. In addition, the loss of alcohol decreases. After absolutization with (C2H5O)4Ti these losses reaches 15–25% C2H5OH (Table 3), while for CaO they decrease to 8–13% relative to the initial C2H5OH (Table 4). So we can say that calcium oxide as a chemically binding water reagent is much more effective dehydrator. As can be seen from Figure 1, the ethanol concentration after treatment with calcined calcium oxide (17.5% CaO) reaches 99.95 wt%, while the absolutization with tetraethoxytitanium increases the concentration of ethanol only to 96.5 wt%.
|The initial ethanol amount, 95 vol%, 92.5% mas.||The amount of ethanol obtained after absolutization||Ethanol yield after absolutization||The amount of СаО||Ethanol density after absolutization||Ethanol concentration after absolutization|
At the same time, the non-absolutized 95% ethanol contains an admixture of MTBE (0.09531 wt %). In this case, the low-boiling impurity in the non-absolute ethanol is absent (Figure 2).
According to the chromatogram (Figure 2), the concentration of non-absolutized ethanol reaches 97.8499 vol % against 95.0%, as it was measured by the weight pycnometer method (Tables 4 and 5). At the same time, the concentration of ethanol absolutized with calcium oxide (Figure 3) is 97.5724 vol %. Taking into account 2.3432% of unidentified low-boiling impurity (
Taking into account the chromatogram data in Figure 3 and its interpretation, we determine the qualitative composition of one of the unknown components (X = 2.3432%), which appears in the chromatogram of ethyl alcohol (99.95%), absolutized with CaO for 2.8 min. At the same time, the chromatographic analysis of 99.99% ethyl alcohol absolutized by industrial method  (Figure 4), shows 100.03 vol % of ethanol. The difference of 0.03% might be a mistake of the device or an alcohol supplier analysis method.
Unfortunately, this impurity is not identified by graded chromatograms of alcohols and ethers, therefore, an IR spectral analysis of this alcohol is performed, which is compared with the IR spectra of the original (95%) and pure absolute (100%) ethyl alcohol (Figure 5). As can be seen from Figure 5, the IR spectra of all three samples do not differ significantly from each other. Only in two absorption regions 3320–3330 and 1630–1640 cm−1, there is a noticeable difference in the absorption intensity of the fluctuations of the corresponding groups, which significantly decrease from the maximum in the original non-absolutized 95% C2H5OH (curve 1, Figure 5) to a minimum in absolute 100% C2H5OH (curve 3,
First of all, the amount of water in samples of ethanol decreases from 4–5% in the initial non-absolutized alcohol (
For identification and more proper determination of the composition and structure of the impurity (
As can be seen in the mass spectrogram of non-absolutized 95% ethyl alcohol (Figure 6a), radical composition of the impurity is formed by the electron action of the mass spectrometer, there can be three types of free radicals with molecular weights such as 32.01 m.u.—C2H5• = 29 m.u.; 76.99 m.u.—(CH3)3O• = 73 m.u.; 105.1 m.u.—C(CH3)3OOCH2• = 103 m.u. They may be formed by the action of electrons of the mass spectrometer on ethyl alcohol C2H5OH and methyl
Taking into account that we know the retention time of the impurity (
The analysis of the curves shows that the diethyl ether retention time at the boiling point of 307.6 K (34.6°C) is 2.85 min, which coincides with the chromatogram data (2.845 min). In this way, we confirm the assumption that during the absolutization of 95% ethanol with calcium oxide, ethyl alcohol containing 2.3432% of diethyl ether and 97.5724% C2H5OH can be obtained.
We checked how 2.3432% of diethyl ether influences the ethanol octane number and the gasoline octane number. Previously, the physico-chemical characteristics of some oxygen-generating additives for gasoline, shown in Figure 8, were analyzed. As can be seen from Figure 8, the density and molecular mass of diethyl ether are close to those of gasoline A-95. The boiling point of the diethyl ether 307.6 K is lower than that of gasoline. It is approaching the boiling point of the first fraction of gasoline, which is 307.6 K. These properties are especially useful for accelerated engines of gasoline cars in winter, when ignition is hampered by a lowered ambient temperature (below 263 K). Thus, the diethyl ether presence improves the gasoline combustion efficiency, which we have checked by adding 10–95% absolutized (97.5%) alcohol containing 2.34% of diethyl ether, which is presented in Figure 9 .
Octane numbers of A-80 gasoline with absolute ethanol additives (gasoline-ethanol mixture) are counted according to the authorship formula which is derived from experimental data . These octane numbers are compared with the octane numbers of gasoline, in which ethanol with diethyl ether is added.
where ONGE—octane number of gasoline-ethanol mixture; ON0—octane number of initial gasoline; Ce—ethanol content. ,
Obtained data of the octane number dependence is performed in Figure 9 (
The properties and high ability of calcium oxide and tetraethoxytitanium as dehydrators for chemical binding of water and absolutization of 96% ethyl alcohol to 99.95% have been investigated. The dependence of the properties and composition of the absolute alcohol on the dehydrator nature was shown. Infrared spectroscopy, mass spectroscopy, and gas-liquid chromatography confirmed the presence of 2–2.34% of diethyl ether in ethanol, which is absolutized by freshly prepared calcium oxide. It was determined that the octane number of gasoline A-80 with the addition of 20–90% of the absolutized ethanol containing 2.34% of the combustion activator—diethyl ether—increases gasoline octane number more significantly than with the addition of the same amount of an ordinary absolute 99.95% alcohol without diethyl ether and reaches 95–97 U, whereas the octane number of gasoline with ordinary absolute ethanol reaches only 88–95 U. We confirmed literary data that the content of even very small amounts of ethers, as combustion activators, combined with the absolute ethyl alcohol leads to an improvement in the gasoline running abilities .