Delignification of hemp stalk using a low transition temperature mixture composed of choline chloride and lactic acid

Abstract

This work used a literature search to select the most suitable system for the delignification process of annual plants. This process was evaluated in terms of lignin removal from plant biomass. Based on previous experiments, a low transition temperature mixture (LTTM) was used, which was a mixture of choline chloride and lactic acid in a molar ratio of 1:2. Samples of hemp fibers were examined. The delignification of biomass was monitored by changing the content of the main components. After application of the solvent at a temperature of 100, 120, or 140 °C and a delignification time of 2 or 4 h, the lignin content expressed by Kappa number decreased to the level of 22 to 13.7. Yields of hemp fibers sown after LTTM application ranged from 72.5 to 90.6%. The results confirmed that the use of LTTM (choline chloride/lactic acid) is a suitable system for the extraction of lignin from biomass. The findings showed that LTTM was an effective delignifying agent for hemp, as a relatively low Kappa number of 13.7 and a yield of 75.9% were achieved after only 2 h and at 140 °C.

Exploiting Deep Eutectic Solvent-like Mixtures for Fractionation Biomass, and the Mechanism Removal of Lignin: A Review

“…Due to the environmental, health, and negative consequences of some organic solvents, the impetus to replace solvents is growing globally. The challenge arises from the difficulty of obtaining more sustainable and ecological alternatives to toxic volatile organic chemicals with the required chemical and physical properties [5].…”

“…More than 70% of the total biomass consists of polymeric carbohydrates and phenolic lignin. The physicochemical properties of specific biomass are strongly dependent on the concentration and nature of the main components [3][4][5][6]. Lignocellulosic biomass is highly resistant to fractionation by the heterogeneous matrix formed between hemicelluloses, cellulose, and lignin, which are crosslinked through strong covalent and hydrogen bonds.…”

“…The fractionation of biomass before its processing is very important. Although various biomass pretreatment and fractionation technologies have been used, such as alkaline hydrolysis, mechanical milling, and the use of acids and bases, the use of more ecological and efficient pretreatment strategies for lignocellulosic materials is necessary [4][5][6][7]. This has led to the development of green pretreatment solvents that can help solve the problem faced by conventional pretreatment.…”

“…DES-like mixtures are binary or ternary mixtures formed from hydrogen bond acceptors (HBAs) and hydrogen bond donors (HBDs) in different molar ratios by forming hydrogen bonds. DES-like mixtures are formed by mixing an HBA and an HBD in a specific molar ratio, resulting in an eutectic point that leads to a liquid phase at room temperature or slightly above [5][6][7]. Therefore, DES-like mixtures represent a chemical combination of two or more HBAs and HBDs, where there is a large decrease in melting point, and they exist as liquids at room temperature [10].…”

“…Researchers have extensively investigated the breakdown, fractionation, and/or extraction of lignocellulosic biomass, as well as the modification and treatment of cellulose, in recent decades. The primary objective is efficient pretreatment, which can be achieved through the extraction, and dissolution of value-added substances, and the cleavage of lignin structures [5][6][7][8][9][10]. The ultimate goal is to obtain lignin-free fibers or substrates for enzymatic treatment, biofuel production, or the manufacturing of modified cellulose, nanocellulose fibrils, and crystals [11].…”