A review of biogas purification through chemical absorption

Biogas is an alternative source of energy which is produced by anaerobic digestion (AD) of waste materials. Biogas contains 50 -70% methane and 30-50% carbon dioxide as well as small a amounts of other gases with a calorific value of about 21-24 MJ/m3 . These trace components limit the usage of the biogas as they lower the calorific value of the gas and limit its commercialization. Hence, there is a need for purification and upgrading to meet specified application standards. The purification and upgrading processes can be classified into four major techniques which are absorption, adsorption, membrane separation and cryogenic separation. This review is focused on biogas enrichment through chemical absorption. This process involves amine washing with mono-,di- or tri-ethanolamine solutions, alkali washing with calcium oxide, calcium, potassium and sodium hydroxides, and synthesised ionic solutions of halide imidazolium ionic liquids. The regeneration of the spent chemicals for re-use will also be studied