Technologies used for sulfur reduction in oil and gas industry.
Abstract
Biodesulfurization (BDS) is one of the most promising technologies used together with traditional hydrodesulfurization (HDS) to reduce the sulfur content of fossil fuels. In this research study, a strain of Cunninghamella elegans (UCP 596) was isolated from mangrove sediments to metabolize an organosulfur dibenzothiophene (DBT) compound in the concentrations of 0.5 and 1 mM and transform to DBT sulfone (DBT-5-dioxide), followed by dibenzothiophene 5,5-dioxide and 2-hydroxybiphenyl metabolites, thus suggesting the use of the “4S” metabolic pathway. The fungus also degraded the DBT completely in the first 24 h of growth on a 2.0 mM DBT concentration by angular deoxygenation, which suggests that a new second metabolic pathway was used. The DBT was consumed as the carbon source, and the sulfur was removed in the form of sulfite ion. A new product, benzoic acid, was formed at the end of the catabolism of DBT by C. elegans using an angular route.
Keywords
- Cunninghamella elegans
- biodesulfurization
- dibenzothiophene
- angular deoxygenation
1. Introduction
Environmental pollution, acid rain, and health problems are caused when sulfur dioxide is emitted into the atmosphere as the result of the combustion of petroleum fractions. To solve these problems, regulations are increasingly stringent in order to minimize the levels of sulfur emitted into the atmosphere. Hydrodesulfurization (HDS) is a conventional technology used to remove sulfur from fossil fuels. This is achieved by using metal catalysts and hydrogen gas, but despite the extremely high pressures and temperatures, the process does not eliminate heterocyclic organosulfur compounds, especially those such as dibenzothiophene (DBT) [1, 2, 3]. Hydrodesulfurization is a very effective technique for removing thiols, sulfides, and disulfides, but it is not suitable for removing thiophene compounds. Therefore, petrochemical industries have sought techniques that enable the sulfur to be removed from these heterocyclic compounds [4].
An alternative is biodesulfurization (BDS), a more efficient and low-cost process, which uses microorganisms to desulfurise these compounds, by promoting selective metabolism of the sulfur (attacking C-S) without degrading the carbon skeleton (CC), thus keeping the energy source of the molecule intact. Dibenzothiophene is considered a model compound for studying the biological desulfurization of fossil fuels and persistent compounds such as S-heterocycles in the environment [4, 5].
Several microorganisms have been studied with a view to using them to remove sulfur biochemically from DBT. Prokaryotic organisms that desulfurise organosulfur compounds without metabolizing the carbon skeleton are uncommon and are usually used in ways that seek to oxidize sulfur selectively [5, 6, 7, 8, 9, 10, 11, 12].
Eukaryotic organisms, such as
The fungus
Dibenzothiophene is a heterocycle compound that is regarded as the most potent environmental pollutant. Microbial degradation of this pollutant is attractive, and the bioprocesses for DBT biodegradation are environment friendly. This study focuses on investigating the biotechnological potential of
2. Materials and methods
2.1. Preserving the microorganism
A microorganism was isolated from mangrove sediment of the Rio Formoso, Pernambuco, Brazil. The fungus was identified as
2.2. Chemicals
The DBT was purchased from Aldrich, cat: D3, 220-2 and a stock solution prepared in NN-dimethylformamide at a concentration of 1 M (w/v). The solution was sterilized in a Millipore® filter, as described by Araújo et al. [22]. All other chemicals were of analytical grade. All organic solvents were of HPLC grade (E Merck).
2.3. Inoculum and culture conditions
Inoculum from these actively growing cultures was used.
2.4. Extraction of the metabolite produced
The metabolic liquid was extracted by chromatography, using the method described by Labana et al. [19]. To determine the intermediate compounds in the metabolic pathway used by
2.5. Analysis using gas chromatography-mass spectrometry (GC-MS)
The analysis was conducted by using a Varian Star 3600 CX Gas Chromatograph, coupled to a Varian Saturation 2000 Mass Spectrometer, with a CP-WAX 58 FFAP-CB column, 50 m, 0.32 mm ID, DF = 0.2 mm. The carrier gas used was White Martins helium 5.0, Pressure 8 PSI. The programmed temperature was 50°C for 5 min, which was increased by 10°C min−1, until the temperature reached 250°C for 5 min, with a total time of 30 min. The temperature of the injector and detector was 250°C. Approximately 3.0 μL of each solution extracted with ethyl acetate was injected into the chromatograph. Spectrometry was performed at 70 eV. The scan speed was 1.5 scans s−1 at 40–500 m/z. The samples containing DBT were also analyzed using the GC/MS. DBT was identified by comparing the mass spectro obtained in the MAINLIB library of the GC/MS system and the Spectral Database for Organic Compounds SDBS library.
2.6. Determining the removal of DBT
The level of removal of DBT from a solution of 1–10 mM DBT was determined by using a UV Sensor to visualize a curve with at a wavelength of 250 nm running through the metabolic liquid for different concentrations of DBT (0.5, 1.0, and 2.0 mM) at a constant temperature of 28°C and shaken at 150 rpm for 144 h. Measurements were made every 24 h [20].
3. Results and discussion
3.1. Biodegradation of DBT by C. elegans
The remarkable ability of fungi to survive in different niches is a consequence of the evolution of enzyme systems, which have coexisted for billions of years with an enormous variety of natural substances of different origins. This diversity of substrates, which have the potential for microbial growth in hydrophobic sources, induced the production of enzymes that are suitable for transforming organic molecules with very different structures. Enzyme “arsenals” have even been able to act on synthetic chemical substances that are derived from human activities. When there are hydrophobic sources, there is no doubting that the response of the metabolism of certain microorganisms gives some additional advantages to microbial cells. This includes exploiting new ecological niches as energy sources [14]. Among fungi,
In this study, a strain of
However, the environmental problems with DBT degradation have received much more attention from researchers worldwide. Organic compounds containing sulfur are a small but important fraction of some fuels and due to it being difficult to biodegrade them, they are considered to be recalcitrant compounds. The presence of sulfur is undesirable because it contributes to the corrosion of equipment in the refinery, and also to the emission of sulfur oxides (SOx) into the atmosphere by the combustion of oil, thus causing environmental problems, such as air pollution and being a potential cause of acid rain [17].
The metabolites produced by biodegradation of
However, although these studies detected several products because DBT was biodegraded, desulfurization with the formation of 2-hydroxybiphenyl was not observed. In our results, dibenzothiophene dioxide 5-5, a compound found in the “4S” pathway, was found.
This pathway is one strategy for reducing these emissions, namely to remove sulfur from mineral carbon, petroleum and its derivatives before combustion. Currently, physical and chemical processes deemed to be hydrodesulfurization (HDS) ones are being used in refineries to remove inorganic sulfur ( Table 1 ). These treatments incur very high costs since they involve using chemical catalysts under extreme conditions (200–425°C) and high pressures of from 150 to 205 psi [1]. Inorganic sulfur and organic sulfur can be removed by HDS, but this process is unsuitable for producing fuels with low sulfur content since this process is unable to remove sulfur compounds from complex polycyclical hydrocarbons, containing sulfur, which are present in petroleum and coal. Thus, tiophenic compounds represent a large amount of sulfur after treatment of HDS in fuels. Another strategy to reduce the sulfur content is to expose these subtracts to microorganisms that can specifically break the carbon-sulfur chain, thus releasing sulfur to a water-soluble portion, in an inorganic form. This process of microbial desulfurization or biodesulfurization (BDS) is an effective and low-cost technique [1, 2, 21].
Hydrodesulfurization (HDS) | Most commonly used method in the petroleum industry to reduce the sulfur content of crude oil. In most cases, HDS is performed by co-feeding oil and H2 to a fixed-bed reactor packed with an appropriate HDS catalyst. |
Extractive desulfurization | It is a liquid-liquid extraction process and the two liquid phases must be immiscible. It depends on the solubility of the organosulfur compounds in certain solvents. |
Ionic liquid extraction | It is an interesting alternative to provide ultra clean diesel oils. |
Adsorptive desulfurization | It depends on the ability of a solid sorbent to selectively adsorb organosulfur compounds from the oil. |
Oxidative desulfurization (ODS) | It involves a chemical reaction between an oxidant and sulfur that facilitates desulfurization. ODS is a field of considerable interest at present. |
Autoxidation | Refers to oxidation by atmospheric oxygen, i.e., oxygen in air. |
Chemical oxidation | The use of a peroxide species avoids the initiation period associated with the slow in situ formation of hydroperoxides by autoxidation. The sulfur-containing compounds can directly be oxidized by the hydroperoxide to yield a sulfoxide and then a sulfone. |
Catalytic oxidation | Reduce the energy barrier of oxidation by facilitating the oxidation reaction itself on the catalytically active surface; some materials serve as oxygen carriers and are more active oxidation agents than oxygen; some catalysts facilitate the decomposition of hydroperoxides, thereby accelerating the propagation step in the oxidation reaction. |
Ultrasound oxidation | Provides energy for the oxidation process by ultrasound, but it does not affect the oxidation chemistry. |
Photochemical oxidation | It has a high efficiency and requires mild reaction conditions. The method involves two steps: first, sulfur compounds are transferred from the oil into a polar solvent and then the transfer is followed by photooxidation or photodecomposition under UV irradiation. |
Biodesulfurization (BDS) | Biodesulfurization takes place at low temperatures and pressure in the presence of microorganisms that are capable of metabolizing sulfur compounds. It is possible to desulfurize crude oil directly by selecting appropriate microbial species |
Aerobic biodesulfurization | Aerobic BDS was proposed as an alternative to hydrodesulfurization of crude oil. |
Anaerobic biodesulfurization | The main advantage of anaerobic desulfurization processes over aerobic desulfurization is that oxidation of hydrocarbons to undesired compounds, such as colored and gumforming products, is negligible. |
Alkylation-based desulfurization | It has been tested with thiophenic sulfur compounds at small scale, and it is commercially applied for light oil at large scale as the olefinic alkylation of thiophenic sulfur (OATS) process developed by British Petroleum. |
Chlorinolysis-based desulfurization | Chlorinolysis involves the scission of C–S and S–S bonds through the action of chlorine. |
Supercritical water-based desulfurization | The effect of supercritical water (SCW) on desulfurization of oil is marginal. The purpose of using SCW (critical point of water: 374°C and 22.1 MPa) as reaction medium is to break C–S bonds. |
3.2. Pathways for biodegradation of DBT by C. elegans
On the basis of these findings, the highest DBT biodegradation was observed in
Figure 2
which shows that the fungus
The use of gas chromatography coupled to mass spectrometry identified the possible products obtained from metabolizing DBT by
|
|
|
184 | Dibenzothiophene | 185 (13.37), 184 (100), 139.3 (12.14), 45.1 (10.43) |
200.2 | Dibenzothiophene 5-oxide | 201.2 (19.05), 200.2 (100), 172.5 (43.06), 171.5 (73.15), 139.3 (12.42), 86.3 (5.95), 50.2 (14.25) |
216.1 | Dibenzothiophene 5,5-dioxide | 216.1 (100), 187.2 (21.34), 144.3 (16.12), 104.3 (7.98), 50.2 (13.12) |
170.2 | 2-Hydroxybiphenyl | 227.3 (5.58), 170.2 (100), 140.2 (16.10), 114.2 (53.73), 85.2 (17.38), 41.2 (13.38) |
105.1 | Benzoic acid | 118.0 (22.67), 105.1 (100), 58.2 (15.49), 45.1 (60.30) |
Figure 3
confirmed the four compounds found were: dibenzothiophene 5-oxide (38.7 min, m/z = 200.2); dibenzothiophene 5,5-dioxide (29.1 min. m/z = 216.1) 2-hydroxybiphenyl (22.4 min., m/z = 170.2), and benzoic acid (22.3 min., m/z = 105.1), which were detected in the degradation of DBT (26.7 min, m/z = 184), by
The literature describes three well-known pathways in the process of degrading DBT by microorganisms: Kodama; angular dioxygenation; and the sulfoxide, sulfone, sulfonate, sulfate pathway deemed the “4S” [6, 9, 18, 19, 20, 23]. Figure 4 shows the proposed routes of microbial degradation.
Dahlberg et al. [24] reported that DBT 5,5-dioxide is involved in the process of biodesulfurization by the 4S pathway. Degradation pathways of DBT by bacteria have been widely studied as in: Brevibacterium [7], Arthrobacter [24, 25], Mycobacterium [26, 27, 28, 29].
A similar behavior was also observed with
In addition, benzoic acid was detected after 48 h of cell growth. This is a compound present in the Van Afferden or angular dioxygenation pathway that uses the DBT as a carbon source and removes the sulfur in the form of sulfite ion, the final product of which is benzoic acid. The metabolic pathway known as Van Afferden has no great interest in terms of biodesulfurization processes of fossil fuels, since the complete mineralization of the carbonaceous structure occurs, which will necessarily involve reducing the potential chemical energy of the fuels. However, microorganisms that use this metabolic pathway are potentially useful in formulating a mixed microbial inoculum for bioremediation processes of polyaromatic hydrocarbons containing sulfur released into the environment [7, 38, 39].
The results show that
According to Schlenk et al. [13], the filamentous fungus
The data presented indicate the potential of
4. Conclusion
The activity pattern of DBT degradation by
Acknowledgments
This work was supported by Coordination Unit for Improving the Qualifications of Higher Education staff (CAPES), Foundation for Supporting Science and Technology of the State of Pernambuco (FACEPE), and National Council for Scientific and Technological Development (CNPq). The authors are grateful to the Catholic University of Pernambuco (Recife-PE, Brazil) for the use of its laboratories and the technician Severino Humberto de Almeida for his assistance.
References
- 1.
C-L Y, Zhai X-P, Zhao L-Y, Liu C-G. Mechanism of hydrodesulfurization of dibenzothiophenes on unsupported NiMoW catalyst. Journal of Fuel Chemistry and Technology. 2013; 41 :991-997. 8th ed. DOI: 10.1016/S1872-5813(13)60043-2 - 2.
Izumi Y, Ohshiro T, Ogino H, Hine Y, Shimao M. Selective desulfurization of dibenzothiophene by Rhodococcus erythropolis D-1. Applied and Environmental Microbiology. 1994;60 :223-226. PMID: 16349153 - 3.
Hosseini SA, Yaghmaei S, Mousavi SM. Biodesulfurization of dibenzothiophene by a newly isolated thermophilic bacteria strain. Iranian Journal of Chemistry and Chemical Engineering Research Note. 2006; 25 :65-71. 3rd ed - 4.
Zhang SH, Chen H, Li W. Kinetic analysis of biodesulfurization of model oil containing multiple alkyl dibenzothiophenes. Applied Microbiology and Biotechnology. 2013; 97 :2193-2200. DOI: 10.1007/s00253-012-4048-6 - 5.
Amin GA. Integrated two-stage process for biodesulfurization of model oil by vertical rotating immobilized cell reactor with the bacterium Rhodococcus erythropolis . Journal of Petroleum & Environmental Biotechnology. 2011;2 :1-4. DOI: 10.4172/2157-7463.1000107 - 6.
Bahuguna A, Lily MK, Munjal A, Singh RN, Dangwal K. Desulfurization of dibenzothiophene (DBT) by a novel strain Lysinibacillus sphaericus DMT-7 isolated from diesel contaminated soil. Journal of Environmental Sciences. 2011;23 :975-982. DOI: 10.1016/S1001-0742(10)60504-9 - 7.
Van Afferden M, Schacht S, Klein J, Truper HG. Degradation of dibenzothiophene by Brevibacterium sp. Archives of Microbiology. 1990;153 :324-328. DOI: 10.1007/BF00249000 - 8.
Bhatia S, Sharma DK. Thermophilic desulfurization of dibenzothiophene and different petroleum oils by Klebsiella sp. 13T. Environmental Science and Pollution Research International. 2012;19 (8):3491-3497. 8th ed. DOI: 10.1007/s11356-012-0884-2 - 9.
Rath K, Mishra B, Vuppu S. Biodegrading ability of organo-sulphur compound of a newly isolated microbe Bacillus sp. KS1 from the oil contaminated soil. Archives of Applied Science Research. 2012;4 :465-471. 1st ed - 10.
Kilbane JJ, Jackowski K. Biodesulfurization of water-soluble coal-derived material by Rhodococcus rhodochrous IGT S8. Biotechnology and Bioengineering. 1992;40 :1107-1114. DOI: 10.1002/bit.260400915 - 11.
Boltes K, del Águila AR, García-Calvo E. Effect of mass transfer on biodesulfurization kinetics of alkylated forms of dibenzothiophene by Pseudomonas putida CECT5279. Journal of Chemical Technology and Biotechnology. 2013;88 :422-431. DOI: 10.1002/jctb.3877 - 12.
Nassar HN, El-Gendy NS, Abo-State MA, Moustafa YM, Mahdy HM, El-Temtamy SA. Desulfurization of dibenzothiophene by a novel strain Brevibacillus invocatus C19 isolated from Egyptian coke. Biosciences, Biotechnology Research Asia. 2013;10 :29-46. 1st ed. DOI: 10.13005/bbra/1090 - 13.
Schlenk D, Bevers RJ, Vertino AM, Cerniglia CE. P450 catalysed S-oxidation of dibenzothiophene by Cunninghamella elegans . Xenobiotica. 1994;24 :1077-1083. DOI: 10.3109/00498259409038667 - 14.
Zahra E, Giti E, Sharareh P. Removal of dibenzothiophene, biphenyl and phenol from waste by Trichosporon sp. Scientific Research and Essays 1. 2006;1 :72-76. 3rd ed - 15.
Van Hamme JD, Wong ET, Dettman H, Gray MR, Pickard MA. Dibenzyl sulfide metabolism by white rot fungi. Applied and Environmental Microbiology. 2003; 69 :1320-1324. DOI: 10.1128/AEM.69.2.1320-1324.2003 - 16.
Faison BD, Clark TM, Lewis SN, Ma CY, Sharkey DM, Woodward CA. Degradation of organic sulfur compounds by a coal-solubilizing fungus. Applied Biochemistry and Biotechnology. 1991; 28 :237-250. DOI: 10.1007/BF02922604 - 17.
Kilbane JJ, John J. Sulfur-specific microbial metabolism of organic compounds. Resources, Conservation and Recycling. 1990; 3 :69-79. DOI: 10.1016/0921-3449(90)90046-7 - 18.
Crawford D, Gupta RK. Oxidation of dibenzothiophene by Cunninghamella elegans . Current Microbiology. 1990;21 :229-231. DOI: 10.1007/BF02092161 - 19.
Labana S, Pandey G, Jain RK. Desulphurization of dibenzothiophene and diesel oils by bacteria. Letters in Applied Microbiology. 2005; 40 :159-163. DOI: 10.1111/j.1472-765X.2004.01648.x - 20.
Morais GS, Pesenti EC, Cestari MM, Navarro-Silva MA. Genotoxic effect of phenanthrene on Chironomus sancticaroli (Diptera: Chironomidae). Zoologia. 2014;31 :323-328. 4th ed. DOI: 10.1590/S1984-46702014000400003 - 21.
Liu S, Suflita JM. Ecology and evolution of microbial populations for bioremediation. Trends in Biotechology. 1993; 11 :344-352. DOI: 10.1016/0167-7799(93)90157-5 - 22.
Araújo HWC, Freitas da Silva MC, Lins CM, Elesbão AN, Alves da Silva CA, Campos-Takaki GM. Oxidation of dibenzothiophene (DBT) by Serratia marcescens UCP 1549 formed biphenyl as final product. Biotechnology for Biofuels. 2012;5 :1-9. DOI: 10.1186/1754-6834-5-33 - 23.
Calzada J, Alcon A, Santos VE, García-Ochoa F. Mixtures of Pseudomonas putida CECT 5279 cells of different ages: Optimization as biodesulfurization catalyst. Process Biochemistry. 2011;46 :1323-1328. DOI: 10.1016/j.procbio.2011.02.025 - 24.
Dahlberg MD, Rohrer RL, Fauth DJ, Sprecher R, Olson GJ. Biodesulfurization of dibenzothiophene sulfone by Arthrobacter sp. and studies with oxidized Illinois no. 6 coal. Fuel. 1993;72 :1645-1649. DOI: 10.1016/0016-2361(93)90349-7 - 25.
Seo JS, Keum YS, Cho IK, Li QX. Degradation of dibenzothiophene and carbazole by Arthrobacter sp. P1-1. International Biodeterioration and Biodegradation. 2006;58 :36-43. DOI: 10.1016/j.ibiod.2006.04.005 - 26.
Furuya T, Kirimura T, Kuno K, Usami S. Thermophilic biodesulfurization of dibenzothiophene and its derivates by Mycobacterium phlei WU-F1. FEMS Microbiology Letters. 2001;204 :129-133. DOI: 10.1016/S0378-1097(03)00169-1 - 27.
Okada H, Nomura N, Nakahara T, Maruhashi K. Analysis of dibenzothiophene metabolic pathway in mycobacterium strain G3. Journal of Bioscience and Bioengineering. 2002; 93 :491-497. DOI: 10.1016/S1389-1723(02)80097-4 - 28.
Li W, Zhang Y, Wang MD, Shi Y. Biodesulfurization of dibenzothiophene and other organic sulfur compounds by a newly isolated microbacterium strain ZD-M2. FEMS Microbiology Letters. 2005; 247 :45-50. DOI: 10.1016/j.femsle.2005.04.025 - 29.
Li F, Zhang Z, Feng J, Cai X, Xu P. Biodesulfurization of DBT in tetradecane and crude oil by a facultative thermophilic bacterium Mycobacterium goodii X7B. Journal of Biotechnology. 2007;127 :222-228. DOI: 10.1016/j.jbiotec.2006.07.002 - 30.
Martin AB, Alcon A, Santos VE, García-Ochoa F. Production of a biocatalyst of Pseudomonas putida CECT5279 for DBT biodesulfurization: Influence of the operational conditions. Energy & Fuels. 2005;19 :775-782. DOI: 10.1021/ef0400417 - 31.
Li F, Zhang Z, Feng J, Cai X, Xu P. Biodesulfurization of DBT in tetradecane and crude oil by a facultative thermophilic bacterium Mycobacterium goodii X7B. J. Biotechnol. 2007; 127 :222-228. DOI: 10.1016/j.jbiotec.2006.07.002 - 32.
Lin X, Liu J, Zhu F, Wei X, Li Q, Luo M. Enhancement of biodesulfurization by Pseudomonas delafieldii in a ceramic microsparging aeration system. Biotechnology Letters. 2012;34 :1029-1032. DOI: 10.1007/s10529-012-0872-0 - 33.
Laborde AL, Gibson DT. Metabolism of dibenzothiophene by Beijeninckia species. Applied and Environmental Microbiology. 1977; 34 :783-790. PMID: 596875 - 34.
Setti L, Rossi M, Lanzarini G, Pifferi PG. Barrier and carrier effects of n-dodecane on the anaerobic degradation of benzothiophene by Desulfovibrio desulfuricans . Biotechnology Lettters. 1993;15 :527-530. DOI: 10.1007/BF00129331 - 35.
Omori T, Monna L, Saiki Y, Kodama T. Desulfurization of dibenzothiophene by Corynebacterium sp. strain SY1. Applied and Environmental Microbiology. 1992;58 :11-15. PMID: 1575493 - 36.
Denome SA, Olson ES, Young KD. Identification and cloning of genes involved in specific desulfurization of dibenzothiophene by Rhodococcus sp. strain IGTS8. Applied and Environmental Microbiology. 1993;59 :283-2843. PMID: 16349035 - 37.
Oldfield C, Pogrebinsky O, Simmonds J, Olson E, Kulpa CF. Elucidation of the metabolic pathway for dibenzothiophene desulfurization by Rhodococcus sp. strain IGT S8 (ATCC 53968). Microbiology. 1997;143 :2961-2973. DOI: 10.1099/00221287-143-9-2961 - 38.
Van Afferden M, Schacht S, Beyer M, Klein J. Microbial desulfurization of dibenzothiophene. American Chemicak Society Division of Fuel Chemistry. 1988; 33 :561-572 - 39.
Xiao P, Mori T, Kamei I, Kondo R. A novel metabolic pathway for biodegradation of DDT by the white rot fungi, Phlebia lindtneri andPhlebia brevispora . Biodegradation. 2011;22 :859-867. 5th ed. DOI: 10.1007/s10532-010-9443-z - 40.
Bezalel L, Hadar Y, PP F, Freeman JP, Cerniglia CE. Initial oxidation products in the metabolism of pyrene, anthracene, fluorene, and dibenzothiophene by the white rot fungus Pleurotus ostreatus . Applied and Environmental Microbiology. 1996;62 :2554-2559. PMID: 16535361 - 41.
Nojiri H, Habe H, Omori T. Bacterial degradation of aromatic compounds via angular dioxygenation. The Journal of General and Applied Microbiology. 2001; 47 :279-305. 6th ed. PMID: 12483604 - 42.
Javadli R, Klerk A. Desulfurization of heavy oil. Applied Petrochemical Research. 2012; 1 :3-19. DOI: 10.1007/s13203-012-0006-6