Biogas, natural gas and other fuel gasses may contain corrosive components such as H2S, which has detrimental effects on the environment when combusted. Consequently, it is required to remove H2S from gas before it can be used. Hence, a biotechnological desulfurization process was developed at Wageningen University, which uses natron-alkaline sulfide oxidizing bacteria to convert the H2S to harmless and re-usable elemental sulfur (Fig. 1).
The biological process is an alternative to chemophysical processes which are commonly applied in industry. Advantages of the biological process are (i) no consumption of chelating chemicals, (ii) operation at atmospheric pressure and ambient temperature, (iii) high removal efficiency with a sulfide-free waste stream and (iv) beneficial use of the biologically produced sulfur. The elemental sulfur can be re-used in various industries as raw material or as fertilizer or fungicide in agriculture.
In the process, H2S is absorbed into a mild alkaline liquid and dissociated (Eq.1). Subsequently, the dissolved HS- is oxidized to elemental sulfur in a bioreactor (Eq.2). The produced OH- regenerates the buffer by the production of CO32- (Eq.3).
H2S (l) + CO32- ⇄ HS- + HCO3- (1)
HS- +½O2 → ⅛S80 + OH- (2)
HCO3- + OH- ⇄ H2O + CO32- (3)
Knowledge on how to control the properties (like size and morphology) of the produced sulfur particles is crucial for stable process operation and the future of this technology.
The optimization of sulfur particle growth and recovery is studied by operating biological lab-scale reactors (Fig. 2) and performing batch crystallization experiments. The technological challenges are to:
- Develop a crystallization model that describes elemental sulfur particle formation and growth under the mentioned process conditions.
- Translate the crystallization model to practical control strategies for the properties of sulfur particles formed in biological desulfurization.
Mol AR, van der Weijden RD, Klok J, Buisman CJ. Properties of sulfur particles formed in biodesulfurization of biogas. Minerals. 2020 May;10(5):433.