Liquid redox processes use a proprietary chelated redox solution for the oxidation of hydrogen sulfide present in sour natural gas. The chelated ferric ions present in the solution oxidize the H2S to elemental sulfur and are reduced to the ferrous state. The reduced ferrous chelate is then regenerated by passing air through the solution to oxidize the ferrous ions back to the ferric state.; This project investigated the use of an iron-oxidizing bacterium, Thiobacillus ferrooxidans, which is capable of regenerating chelated iron-catalyst at a much faster rate than in a purely chemical system. The objective of the study was to develop a biologically enhanced liquid redox scavenger for natural gas sweetening. The laboratory study showed that Thiobacillus ferrooxidans enhances the re-oxidation rates from 50–130% and increases sulfur removal significantly as compared to the same process in the absence of bacteria. The experiments were conducted in a batch reactor as well as in a fixed-bed continuous system at 25°C and pH of 8.5. By using a fixed-bed reactor containing immobilized bacterial cells, the iron oxidation rate was increased by a factor of five as compared to the rate obtained with suspended cells in a batch reactor.
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