Acidic deep eutectic solvents for pretreatment of corn stalk biomass: Effects on cellulose and lignin structure and...

Modern achievements of science allow lignocellulosic biomass to be processed into multifunctional products to meet a variety of needs. The further development of chemical technologies in the field of plant polymer processing should take into account the principles of green chemistry, sustainable development, and circular economy. The use of acidic deep eutectic solvents (DES) as promising and environmentally friendly solvents is attracting particular attention. In this study, acidic eutectic solvents were prepared using acetic acid as a hydrogen bond donor and choline chloride or 1,2 propanediol as hydrogen bond acceptors to pretreat corn stalk and obtain cellulose-rich solid residue. FTIR and ¹H NMR spectra confirmed the formation of new hydrogen bonds between the two DES components and the success of their synthesis. The studied DES are electrically conductive solvents, have an acidic pH value (2.65-2.62), and have a sufficiently low surface tension value (35-38 × 10^-3 J/m²). The influence of the cо-solvents (water and 1,4-butanediol) on the electrical conductivity and surface tension are discussed. The results showed that under the pretreatment condition of 100 °C for 1 h, DES with a molar ratio of 1:2 had a lignin removal rate less than 5%. The changes in nanopore structure and surface roughness of biomass, after DES-based pretreatment were investigated using SEM. Thus, it has been established that the studied DES act to a greater extent as extractants of organic substances for efficient pretreatment process from raw materials, rather than delignifiers, and will be more useful as a pre-treatment of raw materials before the delignification procedure of corn stalk.