Novel mesoporous silica supported ZnO adsorbents for the desulphurization of biogas at low temperatures

Biogas, a valuable renewable energy carrier, can be used as a fuel or as a raw material for the production of synthesis gas and hydrogen. However, the significant quantities of undesirable contaminants, especially hydrogen sulphide (H₂S), constitute process problems and also generate harmful environmental emissions. The key objective of this work was to develop an adsorbent system for the H₂S desulphurization of biogas at ambient temperature, which would be capable of reducing H₂S to less than 1ppmv in order to achieve high removal efficiency (>99%). The potential of MCM-41, KIT-6, SBA-15-Spherical type (SBA-15-S) and SBA-15-Fibre type (SBA-15-F) supported ZnO adsorbents has been explored at ambient temperature for H₂S desulphurization in order to develop a more effective adsorbent for this important application. ZnO loadings of 10, 15 and 20wt% were impregnated by the incipient wetness method to achieve mesoporous silica supported ZnO adsorbents. The adsorbents were characterized by N₂ adsorption/desorption, using the BET method and the field emission scanning electron microscope (FESEM) technique, to investigate their various characteristics. 15wt% ZnO supported on MCM-41/, KIT-6/, SBA-15-S/or SBA-5-F showed a higher adsorption capacity than 10 or 20wt% ZnO loadings, this might be due to the smaller size of the ZnO particles in dispersed form with improved loading. However, the adsorption capacity decreased, at a higher loading of 20wt% of ZnO, because of the increased particle size which is due to agglomerated dispersed form. The SBA-15-F and SBA-15-S supported ZnO showed better desulphurization performances than MCM-41, KIT-6 or the widely adopted commercial activated carbon material ROZ3 and commercial or synthesized titania supported ZnO adsorbents, due to their retained superior physical properties as well as to the size and dispersion of ZnO on the surface of these materials.