| LO-CAT processes use chelated iron in aqueous solution as a redox material for absorption of hydrogen sulfide from sour natural gas streams and convert the dissolved species to elemental sulfur by oxidation. The reduced iron chelate is then re-oxidized by passing air or oxygen through the solution, and then recycled. But this requires equipment for regeneration, chemicals that degrade and energy for air and liquid circulation. The specific objective of this project jointly supported by the U.S. Department of Energy, Gas Research Institute, Texas Higher Education Co-ordinating Board is to advance the technology of the commercial iron-based chelate processes utilizing biologically-enhanced re-oxidation of the redox solutions used in these processes, such as the ARI LO-CAT 310C.;The main goal of this project was to evaluate the effect of the bacteria Thiobacillus ferrooxidans, Thiobacillus denitrificans and the Chilean Cultures, ORE 3, on re-oxidation rate of reduced iron chelate. Gas streams containing hydrogen sulfide in concentrations of 0.5% and 5% were used with a mature solution redox system in a batch reactor with a working volume of one liter.;The mature solution contained 1000 ppm chelated iron catalyst prepared by dilution of an appropriate quantity of the commercial iron chelate concentrate, ARI-310C, together with a buffer, stabilizer and chelon degradation products. An enhancement of 100% or higher in the re-oxidation rate using the bacteria is desired for commercial applications. The laboratory experiments showed that all of the bacterial strains studied enhance the re-oxidation rate significantly as compared to the rate in the absence of bacteria at both H2S concentrations used. However, Thiobacillus denitrificans produced the best results, with rate enhancements of up to 300%. |
