A Review on the Partial and Complete Dissolution and Fractionation of Wood and Lignocelluloses Using Imidazolium Ionic Liquids

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.

Ionic Liquids as Antifungal Agents for Wood Preservation

“…Due to trace amounts of impurities (<0.1 wt.%), unwanted cellulose hydrolysis could occur, as well as cellulose and lignin thermal and chemical degradation at temperatures higher than 110 °C. Moreover, due to their very high viscosity (typically 100–2000 cP at room temperature), wood additivating with these compounds usually implies ILs dissolution in a carrier (water or ethanol) or high temperatures, the latter which can promote unwanted modifications in wood [ 99 ].…”

“…If in 2010, 1-ethylimidazolium chloride of 95% purity cost about €720 per kg, today the price has dropped to €435 per kg, and it is expected that it will continue to lower, as more large-scale companies will be involved in their mass production. Still, alkylimidazolium chlorides (among the most commonly used ILs) are 1000 times more expensive than traditional solvents employed for wood finishing (ethanol, acetone, dimethylsulfoxide) or preservatives used for wood impregnation [ 99 , 127 ].…”

Present and Future Perspectives for Biocides and Antifouling Products for Stone-Built Cultural Heritage: Ionic Liquids as a Challenging Alternative

“…The results were more efficient than conventional EDTA [75]. ILs have been widely exploited for the pretreatment, processing, and preservation of lignocellulose materials [76,77], displaying, among other characteristics, effective antibacterial and antifungal activities and wettability properties.…”

“…An interesting example is represented by ILs based on the multifunctional polyoxametalated [α-SiW11O39] 8-(POM) polyanion, a multifunctional class of metal cluster oxides never exploited in this frame. The two tetralkylammonium POM-ILs (Figure 7 ILs have been widely exploited for the pretreatment, processing, and preservation of lignocellulose materials [76,77], displaying, among other characteristics, effective antibacterial and antifungal activities and wettability properties.…”

Bio-Based Polymers for Engineered Green Materials

“…With regard to biomass constituents, cellulose is certainly the more investigated subject in bio-polymer science. Despite pulping and paper-making having been used for centuries, there is a strong interest in improving the process and applying it to other biomasses, in an effort to enhance yield and pulp quality [5,6].…”