Abstract
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.