Survey of renewable chemicals produced from lignocellulosic biomass during ionic liquid pretreatment

Abstract

BackgroundLignin is often overlooked in the valorization of lignocellulosic biomass, but lignin-based materials and chemicals represent potential value-added products for biorefineries that could significantly improve the economics of a biorefinery. Fluctuating crude oil prices and changing fuel specifications are some of the driving factors to develop new technologies that could be used to convert polymeric lignin into low molecular weight lignin and or monomeric aromatic feedstocks to assist in the displacement of the current products associated with the conversion of a whole barrel of oil. We present an approach to produce these chemicals based on the selective breakdown of lignin during ionic liquid pretreatment.ResultsThe lignin breakdown products generated are found to be dependent on the starting biomass, and significant levels were generated on dissolution at 160°C for 6 hrs. Guaiacol was produced on dissolution of biomass and technical lignins. Vanillin was produced on dissolution of kraft lignin and eucalytpus. Syringol and allyl guaiacol were the major products observed on dissolution of switchgrass and pine, respectively, whereas syringol and allyl syringol were obtained by dissolution of eucalyptus. Furthermore, it was observed that different lignin-derived products could be generated by tuning the process conditions.ConclusionsWe have developed an ionic liquid based process that depolymerizes lignin and converts the low molecular weight lignin fractions into a variety of renewable chemicals from biomass. The generated chemicals (phenols, guaiacols, syringols, eugenol, catechols), their oxidized products (vanillin, vanillic acid, syringaldehyde) and their easily derivatized hydrocarbons (benzene, toluene, xylene, styrene, biphenyls and cyclohexane) already have relatively high market value as commodity and specialty chemicals, green building materials, nylons, and resins.

Catalytic Oxidation and Depolymerization of Lignin in Aqueous Ionic Liquid

“…The fact that products obtained from oxidation reactions were mainly G-lignin derived compounds corroborates the G-lignin rich source. Similar profile of compounds were reported in a previous study using [C2C1Im][OAc] IL for the pretreatment of switchgrass, eucalyptus, and Kraft lignin (Varanasi et al, 2013). In another study, Stärk et al (2010) reported similar product profiles from the catalytic oxidation of organosolv beech wood lignin with guaiacol as the main product probably due to the cleavage of β-aryl ether bond.…”

The Effect of Plant Source on the Properties of Lignin-Based Polyurethanes

“…Due to the highly aromatic structure of lignin, different processes have been developed that break down lignin molecules to produce other valuable aromatic chemicals, such as benzene, toluene, xylene, styrene, phenols, cyclohexane, aromatic aldehydes, vanillin, and vanillic acid (da Silva et al, 2009;Varanasi et al, 2013;Yamaguchi et al, 2017). Since lignin is a polyol, different synthesis techniques have also been used to study the effect of lignin incorporation on the properties of biodegradable polymer materials.…”

Alkaline Partial Wet Oxidation of Lignin for the Production of Carboxylic Acids

“…Lignin is also the largest renewable source of biopolymers [9]. However, unlike cellulose and hemicellulose, lignin has received limited attention and its potential has been underutilized with regard to valorization [6,10]. The main reason for the limited interest is that, unlike cellulose and hemicellulose which are easily convertible fractions of wood, the heterogeneous and cross-linked structure of the lignin molecule complicates its controlled depolymerization into single chemicals [3,9].…”

“…The main reason for the limited interest is that, unlike cellulose and hemicellulose which are easily convertible fractions of wood, the heterogeneous and cross-linked structure of the lignin molecule complicates its controlled depolymerization into single chemicals [3,9]. Nevertheless, it is clear that lignin holds promise as a significant resource for the production of a wide range of renewable chemicals, due to its high energy content, its aromatic structure, the presence of highly reactive groups, and the fact that it will be generated in large quantities as second-generation biorefineries are deployed [10].…”