Binary sorption of CO2 and H2S over polyamine modified fumed silica pellets in a double stage fixed-bed system

Low cost fumed silica (fSi) modified by polyethyleneimine (MW of 800) at 40 wt.% (fSi-PEI800-40) appears to be a promising sorbent for the binary sorption of CO2 and H2S. This study aimed to pelletize this powder sorbent using an extrusion method with starch, polyvinyl alcohol (PVA) or bentonite clay as a binder. The effect of the amount and type of the binder on the mechanical strength and the CO2 and H2S binary sorption performance of the sorbent were evaluated. The molecular weight of binder appeared to have an important effect on the sorbent's strength, where PVA at 5 wt.% gave the pelletized sorbent the highest mechanical strength (0.892 MPa) but a slightly lower sorption capacity for CO2 and H2S than did bentonite clay. The sorption capacity decreased with increasing levels of binder because strong interactions between the binder and particles resulted in particle aggregation. The pre-treatment conditions and flow rate of the mixed gas (CH4/CO2/H2S/N2) were investigated in an up-scale system. The pelletized sorbents could be regenerated at a mild temperature (90 °C) for at least 18 reuse cycles, and so the fSi-PEI800-40/PVA5% sorbent has a high potential for application in the acid gas treatment process.