Microwave-Heated Pretreatment of Corncob, Giant Juncao Grass, and Hemp Using Choline Derivatives with Glycerol

Abstract

Lignocellulosic biomass has diverse applications in bioenergy, biochemical, and biomaterial production. Enhancing these processes through pretreatment to obtain cellulose-rich material (CRM) using low transition temperature mixtures (LTTMs) is crucial. This study explores the impact of biomass type, LTTMs type, and heating methods on biomass pretreatment. Choline derivatives combined with glycerol were used for pretreatment of corncob, giant Juncao grass, and inflorescence hemp. Microwave irradiation heating was compared to conventional heating at 90 °C and 150 °C, with residence times of 5 and 10 min. The study demonstrated efficient breakdown of lignocellulosic structures to obtain CRMs. Corncob showed high-efficiency pretreatment with a 153% increase in cellulose content and 27% lignin removal. Pretreatment with LTTMs effectively increased cellulose content and delignification. The impact of different choline derivatives (ChCl, ChOAc, ChOH) was evident, with extraction efficiency influenced by anion type in the order OH⁻ > OAc⁻ > Cl⁻. The ChOH pretreatment increased cellulose content by 157% and lignin removal by 56%. Microwave-assisted heating surpassed conventional heating in lignocellulosic fractionation, achieving higher cellulose content and effective lignin removal. Microwave heating increased cellulose content by 343% and lignin removal by 82% at 150 °C, which was three times more than conventional heating, with a reaction time of 10 min compared to 720 min. Temperature and residence time were critical in lignin removal. The process allowed for the preservation of hemicellulose at lower temperatures or its extraction at higher temperatures.

Graphical Abstract