Ionic liquids in the pretreatment of lignocellulosic biomass

Abstract

The pretreatment is a key step in the processing of lignocellulosic biomass for its transformation into chemicals and materials of biorenewable origin. Ionic liquids, with their characteristic set of unique properties, have the potential to be the basis of novel pretreatment processes with higher effectiveness and improved sustainability as compared to the current state-of-the-art processes. In this opinion paper, the author provides a perspective on possible processing strategies for this pretreatment with ionic liquids, identifying different advantages as well as challenges to be overcome.

Imidazole Processing of Wheat Straw and Eucalyptus Residues—Comparison of Pre-Treatment Conditions and Their Influence on Enzymatic Hydrolysis

“…Imidazole, along with ionic liquids [16][17][18][19], high-pressure fluids [20][21][22], and deep eutectic solvents [23,24], belongs to these new pre-treatment options and, up until now, has demonstrated considerable potential in the valorization of biomass, especially in the context of biorefinery [4] focused on value-added products. Imidazole, being an environmentally benign and non-hazardous solvent, turns the process of biomass pre-treatment into an attractive alternative, offering the possibility of delivering a depolymerized lignin and highly hydrolyzable polysaccharide fraction [25,26].…”

Alkylimidazolium Ionic Liquids Absorption and Diffusion in Wood

“…These 1-alkyl-3-methylimidazolium ionic liquids were chosen for their relatively low price compared to other ionic liquids, wide commercial availability, ease of synthesis and good interaction with the wood components [21,22]. At room temperature, negligible dissolution of lignocellulose or wood extractives occurred [23], and several useful properties were imparted to the wood as demonstrated from both the authors' previous work and other independent studies [15,24,25].…”

Liquid Systems Based on Tetra(n-butyl)phosphonium Acetate for the Non-dissolving Pretreatment of a Microcrystalline Cellulose (Avicel PH-101)

“…A good example of such a technology for a large market is the Ioncell-F process for the production of regenerated cellulose fibers, which avoids the use of the very toxic carbon disulfide necessary in the state-of-the-art Viscose process. , Except in the case of direct transformation of cellulose into the desired products in the same ionic liquid dissolving medium, this dissolution strategy requires a complementary stage of regeneration of the dissolved cellulose. Due to the non-volatile character of both ionic liquid and cellulose, an antisolvent strategy (the addition of a substance miscible with the ionic liquid and with no capacity to dissolve cellulose) has been adopted in the scientific literature for such regeneration at a laboratory level. , However, the large amounts of antisolvent needed (with water being by far the most popular antisolvent choice) are likely to lead to a prohibitive energy penalty in the vaporization of this antisolvent for recycling of the ionic liquid to the process at the industrial scale …”

“…Besides pretreatment methods based on the dissolution of cellulose with subsequent regeneration via a precipitation mechanism, a second alternative consists of a non-dissolving approach that typically uses volatile organic solvents or aqueous NaOH solutions (mercerization). ,, Interestingly, the ability of ionic liquids to interact with cellulose is not restricted to those capable of dissolving it in relevant amounts. Some ionic liquids with negligible cellulose dissolution capacity have been proven to establish an effective interaction with the crystalline structure of cellulose .…”

“…Due to the non-volatile character of both ionic liquid and cellulose, an antisolvent strategy (the addition of a substance miscible with the ionic liquid and with no capacity to dissolve cellulose) has been adopted in the scientific literature for such regeneration at a laboratory level. 12,13 However, the large amounts of antisolvent needed (with water being by far the most popular antisolvent choice) are likely to lead to a prohibitive energy penalty in the vaporization of this antisolvent for recycling of the ionic liquid to the process at the industrial scale. 14 Besides pretreatment methods based on the dissolution of cellulose with subsequent regeneration via a precipitation mechanism, a second alternative consists of a non-dissolving approach that typically uses volatile organic solvents or aqueous NaOH solutions (mercerization).…”