Abstract
Ionic liquids have shown great potential in the last two decades as solvents, catalysts, reaction media, additives, lubricants, and in many applications such as electrochemical systems, hydrometallurgy, chromatography, CO2 capture, etc. As solvents, the unlimited combinations of cations and anions have given ionic liquids a remarkably wide range of solvation power covering a variety of organic and inorganic materials. Ionic liquids are also considered “green” solvents due to their negligible vapor pressure, which means no emission of volatile organic compounds. Due to these interesting properties, ionic liquids have been explored as promising solvents for the dissolution and fractionation of wood and cellulose for biofuel production, pulping, extraction of nanocellulose, and for processing all-wood and all-cellulose composites. This review describes, at first, the potential of ionic liquids and the impact of the cation/anion combination on their physiochemical properties and on their solvation power and selectivity to wood polymers. It also elaborates on how the dissolution conditions influence these parameters. It then discusses the different approaches, which are followed for the homogeneous and heterogeneous dissolution and fractionation of wood and cellulose using ionic liquids and categorize them based on the target application. It finally highlights the challenges of using ionic liquids for wood and cellulose dissolution and processing, including side reactions, viscosity, recyclability, and price.
Highlights
The dependency on fossil feedstock and the current consumption style are global challenges that triggered the search for sustainable processes for the efficient utilization of renewable resources such as biomass [1,2]
There are four imidazolium cations that are most commonly used for the dissolution of wood and cellulose: 1-ethyl-3-methylimidazolium ([EMIM]), 1-butyl-3-methylimidazolium ([BMIM]), 1-allyl-3-methylimidazolium ([AMIM]), and 1-benzyl-3-methylimidazolium ([BnMIM])
When an anti-solvent is added to a reaction mixture, the ions of the ionic liquids are extracted phase through hydrogen bonding and coulombic forces shielding them from direct interaction with into the liquid phase through hydrogen bonding and coulombic forces shielding them from direct wood polymers
Summary
The dependency on fossil feedstock and the current consumption style are global challenges that triggered the search for sustainable processes for the efficient utilization of renewable resources such as biomass [1,2]. In the 1990s, ionic liquids were proposed as “green solvents” for wood and cellulose dissolution They are salts that are liquids at temperatures below 100 ◦ C. The low vapor pressure of ionic liquids, which is a result of the strong interaction forces between their constituting ions, made them considered green solvents Polymers in general do not emit potentially hazardous organic compounds during use, 2020, 12, xas FORthey. Ionic liquids production has been industrialized by many companies organic solvents in chemical processes. Other than their potential as solvents, they have shown such as BASF (Germany), Acros. In the last five years (2014–2018), the literature was enriched by around 2000 publications on the use of ionic liquids for liquids for wood and cellulose dissolution and processing. Based on 1-alkyl-3-alkylimidazolium as a cation (Table 1)
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