This work proposed and investigated key strategies that contribute to the advancements of low-cost protic ILs (PILs) for use in the future sustainable chemical industry, particularly in the areas of waste valorization and decontamination.
In large, this PhD research contributed to the ongoing development of a lignocellulose fractionation process using PILs. First, the use of contaminated waste wood was investigated as a low-cost alternative feedstock to expensive virgin biomass. Fractionation of post-consumer waste wood collected from construction activities was shown to be highly effective using 1-methylimidazolium chloride [H1Cim]Cl, producing a highly digestible metal-free cellulose pulp, with >70% glucose yield during enzymatic hyrolysis. Evaluation of key process parameters such as solid loading, waste wood composition variation, metal chelation with lignin and IL-clean up were also investigated. The study was expanded to include the valorization of hazardous creosote waste wood using the low-cost PIL N,N,N-dimethylbutylammonium hydrogen sulfate [DMBA][HSO4]. The fractionation produced a highly digestible, PAH-free cellulose pulp stream with 70% glucose release, and a PAH-lignin stream.
Second, to develop a better understanding of the process boundary conditions, water use as co-solvent and anti-solvent was investigated using a variety of promising lignocellulosic biomass. It was shown that the impact of water as a co-solvent on the fractionation ability of [DMBA][HSO4] is feedstock-dependent. A reduced water input for lignin precipitation was found not to compromise the cellulose digestibility, while significantly reducing the process energy. In addition, the impact of ionoSolv pretreatment severity on fractionation performance was evaluated using a modified pretreatment severity factor, incorporating the Hammett acidity of the aqueous IL solution. The modified severity factor can better predict the fractionation outcome compared to the classical pretreatment severity factor, particularly regarding delignification and hemicellulose removal. Attention was then turned to utilization of the cellulose pulp derived from the ionoSolv process to produce functionalized nanocellulose crystals (CNCs). Alkaline-H2O2 oxidation was used as a simple and more environmentally friendly method for facile extraction of carboxylated CNCs. The impact of pretreatment severity and cellulose composition on the properties of extracted CNCs was evaluated. The produced CNCs had the ability to form self-standing nanofilms and exhibited similar thermal and colloidal stability to CNCs produced by TEMPO-mediated oxidation.
Lastly, a novel approach for textile waste decontamination and synthetic dye reuse using PILs was developed. The PIL [DMBA][HSO4] was used to selectively extract dyes from polyester-based synthetic textiles, leaving the dye-free polyester fiber behind for upcycling. Subsequent dyeing using the dye-rich [DMBA][HSO4] solutions was shown to be possible, achieving a similar color strength to commercially dyed products. The process provides key and novel advantages that can provide a new circular dimension to the textile recycling sector by eliminating virgin dye use, applying a closed-loop solvent-based dyeing process, and creating dye-free polyester fibers.