Sulfur microbial desulfurization

Desulfurization using purified enzymes Investigations into enzymatic desulfurization as an alternative to microbial desulfurization has revealed several enzymes capable of the initial oxidation of sulfur. A study reported use of laccase with azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) as a mediator for oxidation of DBT [181]. The rate of this reaction was compared to hydrogen peroxide-based phosphotungstic acid-catalyzed oxidation and the latter was found to be about two orders of magnitude higher. The authors also oxidized diesel oil sulfur to no detectable levels via extraction of the oxidized sulfur compounds from diesel. In Table 9, the enzymes used in oxidation of DBT to DBTO are reported. 

A class of enzymes capable of removing sulfur from alkane sulfonates exists, which may have relevance in microbial desulfurization of alkyl sulfides. A gene cluster ssuEADCB was identified in E. coli. The enzyme SsuD was capable of conversion of pentane sulfonic acid to pentaldehyde and sulfite. It was reported to be capable of conversion of alkyl sulfonates from C2 to CIO, as well as substituted ethanesulfonates and sulfonated buffers. The SsuE was a flavin-reducing enzyme that provided FMNH2 to the SsuD. 

Kohler, M. Genz, I.-L. Schicht, B., and Eckart, V., Microbial Desulfurization of Petroleum and Heavy Petroleum Fractions. 4. Anaerobic Degradation of Organic Sulfur Compounds. Zentralbl. Mikrobiol., 1984. 139 pp. 239-247. 

Lee, M. Senius, J. D., and Grossman, M. J., Sulfur-specific microbial desulfurization of sterically hindered analogs of dibenzothiophene. Applied and Environmental Microbiology, 1995. 61(12) pp. 4362-4366. 

Gallagher, J. R. Olson, E. S., and Stanley, D. C., Microbial Desulfurization of Dibenzoth-iophene A Sulfur Specific Pathway. Ferns Microbiology Letters, 1993. 107 pp. 31-36. 

Grossman, M. J. Lee, M. K. Prince, R. C., et al., Microbial Desulfurization of a Crude Oil Middle-Distillate Fraction Analysis of the Extent of Sulfur Removal and the Effect of Removal on Remaining Sulfur. Applied and Environmental Microbiology, 1999. 65(1) pp. 181-188. 

Nakahara, T. Nakajima, T. Nomura, N., and Nekotsuka, S., Microbial desulfurization of sulfur-containing hetero-cyclic compound Patent No. JP10243791. 1998, Sep. 14. 

Microbial desulfurization of sulfur-containing hetero-cyclic compound [156],... 

Two patents were awarded on microbial desulfurization of sulfur-containing heterocyclic compound [155,156], the first targeting DBT and alkylated DBTs and the other benzothiophenes and alkylated benzothiophenes. In both cases, the selective cleavage of the C—S bonds is reported as the main mechanism. The claimed bacteria strains are Mycobacterium G3 strain (PERM P-16105) and R. erythropolis KA2-5-1 strain (PERM P-16277), respectively. Special emphasis was made to the desulfurization of the recalcitrant 4,6-dimethyl-dibenzothiophene. The main product from DBT... 

Rudimentary investigations of microbial desulfurization have received little attention in the literature at this time (2). One successful example of desulfurization is the removal of pyrite from coal by Thiobacillus sp. and Ferrobaccus sp. (3). While studies of the complex hydrocarbon-sulfur systems are of great value, being closer to in situ reality, investigation of a defined system should form the foundation of these more detailed studies. 

Beyer et al. (49) found that, during microbial desulfurization, pyritic sulfur decreases and elemental sulfur increases with time, whereas the organic sulfur remains unchanged. They suggested that microbial oxidation of pyrite produces ferric sulfate [Fe2(S04)3] and that the simultaneous inorganic reaction of ferric iron with pyrite produces elemental sulfur and ferrous iron, as follows ... 

The full potential for removing pyritic sulfur from various coals by physical coal cleaning is significant but difficult to achieve. However, SO2 control by precombustion removal of pyrite could be an important S02-emissions reduction strategy. The cleaned coal produced could be used in coal-fired utilities, constructed both pre-and post-NSPS, as well as in industrial boilers. To realize the potential for coal cleaning in actual practice, however, new techniques must be demonstrated in the laboratory and then at the "proof-of-concept" scale (approximately one ton of coal per hour). These new coal beneficiation techniques could be advanced physical-coal-cleaning (PCC) processes, or they could employ microbial desulfurization or chemical desulfurization to remove organic sulfur. These latter processes could be used by themselves or in concert with PCC processes. 

Mechanism of Microbial Desulfurization. The microbial dissolution of pyritic sulfur in coal by acidophilic bacteria has been thoroughly investigated (17,18,29). The pyrite is readily oxidized by oxygen or ferric ion, resulting in the ferrous state as follows ... 

Most microbial desulfurization studies have been conducted in the laboratory shake-flask type experiments, and the major drawback cited against such a process has been that the rates of pyritic sulfur removal were not high enough to reduce the reactor size to a reasonable capacity (2,6). In this study an attempt has been made to determine the effectiveness of T. ferrooxidans under simulated pipeline conditions for pyritic sulfur removal. Since the microbial desulfurization process is conducted under acidic environment, an attempt has been made to determine the corrosion rates under dynamic conditions using Illinois //6 and Indiana 3 bituminous coals and to investigate the effectiveness of a commercial corrosion inhibitor for controlling the corrosivity. 

About 80% pyritic sulfur removal has been achieved by microbial desulfurization of Illinois 6 and Indiana 3 coals using T. ferrooxidans in laboratory shake-flask experiments and in a two-inch pipeline loop. The 10 to 25 wt% coal/water slurry was recirculated at 6-7 ft/sec for 7 to 12 days at 70-90°F. Results also show that the rates of bacterial desulfurization are higher in the pipeline loop under turbulent flow conditions for particle sizes, 43 to 200/m as compared to the shake-flask experiments. It is visualized that the proposed coal slurry pipelines could be used as biological plug flow reactors under aerobic conditions. The laboratory corrosion studies show that use of a corrosion inhibitor will limit the pipeline corrosion rates to acceptable levels. 

Ohshiro, T. Izumi, Y. Microbial desulfurization of organic sulfur compounds in petroleum. Biosci. Biotechnol. Biochem. 1999, 62 (1), 1-9. 

The distinction between oxidative and reductive systems is a useful way to divide the world of microbial desulfurization, as it refiects a basic difference in the underlying biochemistry. In this article, the major areas of research in biological desulfurization of inorganic and organic sulfur compounds in waste streams and petroleum-derived fuels are addressed. Both reductive and oxidative approaches are covered. 

Commercialization of the Sulfur-Specific Organic Sulfur Biodesulfurization System, in 1991, IGT granted exclusive license to the patents covering the Rhodococcus strain IGTS8 to EBC, which subsequently pursued the development of a commercial microbial desulfurization process based on this technology. Significant advances have been made in improving catalyst performance and... 

Better understanding of the mechanism of biodesulfurization, as shown in Figure 8, may be gained from some recent studies ° Gallagher et al. reported a sulfur-specific pathway in microbial desulfurization of DBT. Rhodococcus rhodochrous strain IGTS8 metabolizes DBT in a sulflir-specific manner. Two routes of desulfurization have been identified. Under growth conditions, the intermediates are dibenzothiophene sulfoxide, dibenzothiophene sulfone, 2 -hydroxybipheny 1-2-sulfonate, and 2,2 -... 

Lee et al. studied microbial desulfurization of DBTs bearing alkyl substitutions adjacent to the sulfur atom, such as 4,6-diethyldibenzothiophene (4,6-DEDBT), which are referred to as sterically hindered with regard to access to the sulfur moiety. By using enrichment cultures with 4,6-DEDBT as the sole sulfur source, bacterial isolates which selectively remove sulfur from sterically hindered DBTs were obtained. The isolates were tentatively identified as Artiirobacter species, 1,6-DEDBT sulfone was shown to be an... 

Lee, M.K. Senius, ID. Grossman, M. J. Sulfur-Specific Microbial Desulfurization of Sterically Hindered Analogs of Dibenzothiophene. Applied And Environmental Microbiology, 1995,61 (12), 4362-4366. 

Constanti, M. Giralt, J., and Bordens, A., Degradation and Desulfurization of Dibenzothiophene Sulfone and Other Sulfur Compounds by Agrobacterium MC501 and a Mixed Culture. Enzyme and Microbial Technology, 1996. 19 pp. 214-219. 

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