Microbial desulfurization coals

Kargi, F., and Robinson, J. M., Microbial desulfurization of coal by thermophilic microorganism Sulfolobus acidocaldarius. Biotechnol. Bioeng., 1982. 24(9) pp. 2115-2121. 

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. 

Dibenzothiophenes. Because of its commercial availability, dibenzothiophene is the most extensively used compound in studies of organosulfur metabolism. It has been used as a model compound in the studies of petroleum and coal biodesulfurization. These topics have been reviewed by Foght, J.M. Fedorak, P.M. Gray, M.R. Westlake, D.W.S. (Microbial desulfurization of liquid fossil fuels. In Microbial Mineral Recovery, in press) and Monticello and Finnertv (501. 

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. 

Dugan, P.R. and Apel, W.A. 1978. f,Microbial Desulfurization of Coal." In Metallurgical Application of Bacterial Leaching and Related Microbial Phenomenon." Editors, L.E. Murr Torma, A.E. Brieley, J.A. Academic Press, N.Y.pp. 223-250. 

Rai, C., Microbial Desulfurization of Coal and Texas Lignites. Presented at the AIChE Spring National Meeting, Houston, TX,... 

Rai, C. Microbial Desulfurization of Coals in a Slurry Pipeline Reactor Using Thiobacillus ferrooxidans. Biotechnology Progress 1, pp. 200-204, 1985. 

Kargi F, Weissman JG (1987) Kinetic parameter estimation in microbial desulfurization of coal. Biotechnol Bioeng 30 1063-1066... 

The second patent describes the use of a microbial mixed culture (Hansenula sydowiorum, Hansenula ciferrii, Hansenula lynferdii, and/or Cryptococcus albidus) in coal desulfurization [160], In this process, the raw mined coal is ground to a particle size smaller than 200 mesh forming a slurry with water, at a solids concentration of less than 40wt%. The bacterial cultures are then inoculated into the feedstock slurry. An incubation step is carried out at a temperature near 25°C and at a pH close to neutral. The highest removal achieved was in the range of 46% S removal. 

Kargi, F. 1982. Microbial Coal Desulfurization. Microbial Enzyme Technol. 4( 1) 13.20. 

Extraction with an organic solvent, such as molten anthracene or a sequential series of solvents, after conventional coal cleaning is also used [20, 21]. Microbial methods of coal desulfurization have also been tested. Precombustion cleaning measures such as these dramatically improve the emission characteristics of coal-burning installations. Coal conversion to a liquid or gaseous fuel permits much greater improvement in the residual precombustion impurities present, but also at greater cost. 

Also, as precombustion sulfur removal becomes an attractive alternative to flue gas scrubbers, scientists have explored several methods of removing inorganic sulfur from coal and coal chars. Oxidation, microbial oxidation/desulfurization, and halogenation are avenues that are now, and have been, under investigation for some time (Thomas, 1995). 

The chemical methods are not effective in removing major amounts of organic sulfur. Thus, removal of total sulfur to produce a clean-burning fuel is very difficult. It is envisioned that the optimum desulfurization of coal will include physical, chemical, and microbial treatment. The raw coal will be ground fine to liberate most of the pyritic sulfur and then processed by using the column... 

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