About 100 trillion cubic feet of proven and futurenatural gas reserves are expected to have high hydrogen sulfide(H2S) concentrations, requiring treatment and removal. Currenttreatment processes are expensive, emit large quantities ofsulfur gases to the environment, and can be applied only to verylarge reserves. Technology that can be economically applied tosmall, as well as large, gas reserves is needed to ensure cheapand abundant natural gas in the future. This project willinvestigate a simple biological process for the conversion of H2Sinto elemental sulfur. Certain anaerobic photosynthetic bacteriametabolize H2S and carbon dioxide (C02) to produce sulfur andcell mass. Prior research has concentrated on the use ofChlorobium species, which deposit sulfur outside the cellmembrane where it is easily recovered by density difference. Themicroorganisms can use gas with a wide range of H2Sconcentrations, and other gases, such as nitrogen, have no effectupon the reaction. C02 is used in the reaction, reducing theemission of greenhouse gases. A single cell protein by-productis also produced which has a large market as an animal feed. Thepurpose of this three-phase study is to demonstrate the conceptand perform bench-scale experiments to define scale-up parametersfor commercial design. In Phase I, bacteria for producingextracellular sulfur from H2S will be screened, and the bestselected for optimization of sulfur yield and rates. Reactorstudies will be performed to define reaction rates and retentiontimes for design and economic projections. Phase II of theproject will investigate advanced bioreactor concepts to minimizereactor volume. Methods for sulfur and single cell proteinrecovery will be developed. A bench-scale unit utilizing thebest bacteria and bioreactor system will be operated for aprolonged period to confirm the viability of the culture. Scale-up parameters will be defined and a large commercial designand economic analysis conducted. Phase III will involve afield demonstration of this process.Anticipated Results/Potential Commercial Applications as described by the awardee:The development of this technology will result ina simple economical process for sulfur production, involving onlya bioreactor and product separator. Gases passed through thebioreactor would have the H2S removed, with effluent gasesintroduced into the pipeline. This simple process should find wideapplication in natural gas processing.
