Increasing the Selectivity for Sulfur Formation in Biological Gas Desulfurization

Abstract

In the biotechnological desulfurization process under haloalkaline conditions, dihydrogen sulfide (H2S) is removed from sour gas and oxidized to elemental sulfur (S8) by sulfide-oxidizing bacteria. Besides S8, the byproducts sulfate (SO42–) and thiosulfate (S2O32–) are formed, which consume caustic and form a waste stream. The aim of this study was to increase selectivity toward S8 by a new process line-up for biological gas desulfurization, applying two bioreactors with different substrate conditions (i.e., sulfidic and microaerophilic), instead of one (i.e., microaerophilic). A 111-day continuous test, mimicking full scale operation, demonstrated that S8 formation was 96.6% on a molar H2S supply basis; selectivity for SO42– and S2O32– were 1.4 and 2.0% respectively. The selectivity for S8 formation in a control experiment with the conventional 1-bioreactor line-up was 75.6 mol %. At start-up, the new process line-up immediately achieved lower SO42– and S2O32– formations compared to the 1-bioreactor line-up. When the microbial community adapted over time, it was observed that SO42– formation further decreased. In addition, chemical formation of S2O32– was reduced due to biologically mediated removal of sulfide from the process solution in the anaerobic bioreactor. The increased selectivity for S8 formation will result in 90% reduction in caustic consumption and waste stream formation compared to the 1-bioreactor line-up.

Syngas as Electron Donor for Sulfate and Thiosulfate Reducing Haloalkaliphilic Microorganisms in a Gas-Lift Bioreactor

“…The sulfide (H2S) present in the gas is dissolved in an alkaline solution as HS − using a scrubber (1). This HS − rich solution goes to an aerobic bioreactor (2) where it is biologically oxidized under controlled microaerophilic conditions to mostly elemental sulfur (S 0 ) and a minor fraction to sulfate (SO4 2− ) followed by chemical oxidation via polysulfides, to thiosulfate (S2O3 2− ). The S 0 is separated in a settler (3) and most of the liquid is recycled to the scrubber (1).…”

“…Part of the liquid from the settler (3) goes to an anaerobic bioreactor (4) where SO4 2− and S2O3 2− are reduced to HS − using syngas as an electron donor. The HS − produced is recycled back to the aerobic bioreactor (2). With time, this prevents accumulation of SO4 2− and S2O3 2− in the whole system and theoretically reduces the amount of caustic required to increase the pH to almost zero.…”

“…In biodesulfurization systems, sulfide is removed from the gas and elemental sulfur is formed. Biodesulfurization systems that produce elemental sulfur operated under haloalkaline conditions have been studied and applied for more than 25 years [ 1 , 2 ]. The efficiency of converting sulfide to elemental sulfur in laboratory experiments is close to 97% [ 2 ] and models suggest that 98% efficiency is possible [ 3 , 4 ].…”

“…Biodesulfurization systems that produce elemental sulfur operated under haloalkaline conditions have been studied and applied for more than 25 years [ 1 , 2 ]. The efficiency of converting sulfide to elemental sulfur in laboratory experiments is close to 97% [ 2 ] and models suggest that 98% efficiency is possible [ 3 , 4 ]. The remaining part of the sulfide is biologically oxidized to sulfate or chemically to thiosulfate.…”

Development of quantitative PCR for the detection of Alkalilimnicola ehrlichii, Thioalkalivibrio sulfidiphilus and Thioalkalibacter halophilus in gas biodesulfurization processes

“…The addition of these toxic thiols not only affected SOB community composition, but alterations of the biodesulfurization process conditions can also cause a community change. For example, changes in the bioreactor design or addition of an extra bioreactor can also result in SOB community composition shift (De Rink et al 2019).…”