Possible Absorbent Regeneration in Biogas Purification and Upgrading: A Review

Abstract

South Africa has the highest emission levels of CO2 equivalent to 315,957.24. CO2 emissions are proportional to fuel consumption in a sense that 1% rise in fuel consumption results in 1% rise in CO2 emissions. Many alternative energy sources to address this issue have been exploited, that is most preferably renewable. Biogas has been proved to reduce over 90% CO2 emissions to the atmosphere. Its application is limited until its upgraded and chemical absorption is one of the techniques used. The following chemicals MEA, NH4OH, CaO, Ca(OH)2, KOH, NaOH, FeCl2, FeCl3, FeSO4, Fe2O3, Fe(OH)3 and ZnO are used for absorption. The alkalis can be regenerated but a penalty of high-temperature requirements has to be paid making their process not desirable. Considering the amines, they can be regenerated using Ca(OH)2 or iron exchange resin with anionic resin. NaOH can be regenerated using electrodialysis and causticization is normally used to convert Na2CO3 to NaOH. Ammonia has proven to be a good absorbent because its purchase price is low and it can be regenerated with ease. Furthermore, it has an added advantage since its by-product can be applied directly as a fertilizer without any further treatment. However, MEA also stands to be a good absorbent because it has a potential of removing both CO2 and H2S.