title: Supercritical CO2 and ionic liquids for the pretreatment of lignocellulosic biomass in bioethanol production.
abstract: Owing to high petroleum prices, there has been a major push in recent years to use lignocellulosic biomass as biorefinery feedstocks. Unfortunately, by nature's design, lignocellulosic biomass is notoriously recalcitrant. Cellulose is the most abundant renewable carbon source on the planet and comprises glucan polysaccharides which self-assemble into paracrystalline microfibrils. The extent of cellulose crystallinity largely contributes to biomass recalcitrance. Additionally, cellulose microfibrils are embedded into both hemicellulose and lignin polymeric networks, making cellulose accessibility an additional obstacle. Pretreatment is necessary before enzymatic hydrolysis in order to liberate high yields of glucose and other fermentable sugars from biomass polysaccharides. This work discusses two pretreatment methods, supercritical CO2 and ionic liquids (ILs). Both methods utilize green solvents that do not emit toxic vapours. Mechanisms for destroying or weakening biomass recalcitrance have been explored. Various pretreatment operating parameters such as temperature, pressure, time, dry biomass/solvent ratio, water content, etc. have been investigated for the pretreatment of various biomass types such as corn stover, switchgrass, sugarcane bagasse, soft and hard wood. The two pretreatment methods have their pros and cons. For example, supercritical CO2 explosion pretreatment uses inexpensive CO2, but requires a high pressure. By comparison, while IL pretreatment does not require an elevated pressure, ILs are still too expensive for large-scale uses. Further research and development are needed to make the two green pretreatment methods practical.
authors.affiliation: Department of Chemical and Biomolecular Engineering, Ohio University, Athens, OH 45701, USA. gu@ohio.edu
authors.forename: Tingyue
authors.initials: T
authors.lastname: Gu
authors.affiliation: Department of Chemistry and Biochemistry, Ohio University, Athens, OH 45701, USA.
authors.forename: Michael A
authors.initials: MA
authors.lastname: Held
authors.affiliation: Environmental and Plant Biology Department, Ohio University Athens, OH 45701, USA.
authors.forename: Ahmed
authors.initials: A
authors.lastname: Faik
mesh_terms: D056804:Biofuels; D018533:Biomass; D001709:Biotechnology / Q000379:methods; D002241:Carbohydrates / Q000737:chemistry; D002245:Carbon Dioxide / Q000737:chemistry*; D002473:Cell Wall / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism; D002482:Cellulose / Q000737:chemistry / Q000378:metabolism*; D025924:Chromatography, Supercritical Fluid; D000431:Ethanol / Q000032:analysis / Q000737:chemistry* / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D052578:Ionic Liquids / Q000737:chemistry*; D008031:Lignin / Q000737:chemistry* / Q000378:metabolism; D010944:Plants / Q000737:chemistry* / Q000187:drug effects / Q000378:metabolism; D013696:Temperature
chemical_list: D056804:Biofuels; D002241:Carbohydrates; D052578:Ionic Liquids; C036909:lignocellulose; D002245:Carbon Dioxide; D000431:Ethanol; D002482:Cellulose; D008031:Lignin