Pretreatment of lignocellulose has received considerable research globally due to its influence on the technical, economic\r\nand environmental sustainability of cellulosic ethanol production. Some of the most promising pretreatment methods require\r\nthe application of chemicals such as acids, alkali, salts, oxidants, and solvents. Thus, advances in research have enabled the\r\ndevelopment and integration of chemical-based pretreatment into proprietary ethanol production technologies in several pilot and\r\ndemonstration plants globally, with potential to scale-up to commercial levels. This paper reviews known and emerging chemical\r\npretreatment methods, highlighting recent findings and process innovations developed to offset inherent challenges via a range\r\nof interventions, notably, the combination of chemical pretreatment with other methods to improve carbohydrate preservation,\r\nreduce formation of degradation products, achieve high sugar yields at mild reaction conditions, reduce solvent loads and enzyme\r\ndose, reduce waste generation, and improve recovery of biomass components in pure forms. The use of chemicals such as ionic\r\nliquids, NMMO, and sulphite are promising once challenges in solvent recovery are overcome. For developing countries, alkalibased\r\nmethods are relatively easy to deploy in decentralized, low-tech systems owing to advantages such as the requirement of\r\nsimple reactors and the ease of operation.
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