Chemo-biochemical Desulphurization of Various Gaseous Streams on Bench Scale

Abstract

The gaseous streams containing hydrogen sulphide (H2S) mixed with nitrogen gas (N2) (H2S, 0.00145 mol L-1), H2S mixed with liquefied petroleum gas (LPG) and refinery fuel gas were evaluated, in batch operation, in a bubbled column reactor for desulphurization using ferric sulphate as an oxidant. Further, the ferrous sulphate produced in the process of oxidation is biologically oxidized to ferric sulphate using biomass enriched with Thiobacillus ferrooxidans-JSPR1 in flask culture experiments. In all the cases, the gases were bubbled into the biologically generated ferric sulphate (from ferrous sulphate solution) for the oxidation of H2S. The results indicate that0.00426 mol L-1 of ferric ions are required for reacting with0.00145 mol L-1 of H2S in a gaseous stream containing mixture of N2 and H2S. A concentration of 0.00447 mol L-1 of ferric ions is needed for oxidation of 0.00145 mol L-1 of H2S mixed with LPG. Similarly, the refinery fuel gas containing 0.0031 mol L-1 of H2S requires 0.00428 mol L-1 of ferric ion for effective desulphurization. The ratio of moles of H2S reacted to moles of Fe2+ produced at optimal condition was 0.533, 0.516, 0.510, respectively, for nitrogen mixed H2S, LPG mixed H2S and refinery fuel gas containing H2S. The removal of H2S from these gaseous streams was more than 98%sulphate produced in the process could be biologically oxidized to ferric sulphate with an efficiency of 98%, using shake flask culture experiments. Based on flask culture experiments for biooxidation of commercial ferrous sulphate to generate ferric sulphate, the biokinetic constants viz. yield coefficient y, maximum specific growth rate constant μmax and half saturation rate constant Ks were evaluated. The yield coefficient was found to be 0.112 while μmax and Ks were observed to be 0.1686 hr-1 and 187.9 mg L-1, respectively. The evaluation of biokinetic constants for bio-oxidation of ferrous sulphate generated during the scrubbing of refinery fuel gas containing H2S indicated the value of μmax and Ks as 0.1426 hr-1 and 205 mg L-1, respectively. The value of yield coefficient in this real system was found to be 0.102.