Delignification Kinetics Study on the Tetrahydrofurfuryl Alcohol/HCl Pulping of Rice Straw

Microwave-Assisted Urea-Based-Hydrotropic Pretreatment of Rice Straw: Experimental Data and Mechanistic Kinetic Models

The three major lignocellulose components can be transformed into various biomass-derived platform fuels, chemicals, and materials upon pretreatment and chemical upgrading. Lignocellulose pretreatment is an important step to obtain an eco-friendly, economical, and effective biomass utilization process. The combination of microwave heating and hydrotropic pretreatment is considered as a green method of lignocellulose pretreatment. Experimental data and two mechanistic kinetic models of microwave-assisted pretreatment of rice straw are presented. Here, the use of urea solution as the hydrotropic agent was examined to facilitate the degradation of three major lignocellulose components. The first kinetic model assumes that the soluble lignin does not undergo condensation, while the second one assumes that part of the soluble lignin condenses to a solid product. The mechanistic models were validated with a series of experimental data obtained from microwave-assisted hydrotropic pretreatment of rice straw. The results show that both models could generally describe the experimental data well. However, based on the evaluation of the results of the kinetic models, it turned out that the rate of lignin condensation was relatively slow compared to the rate of lignin degradation to soluble lignin (the value of k c is relatively small compared to the value of k l1). Hence, the kinetic model with exclusion of lignin condensation is suggested more since it is mathematically simpler. The proposed mechanistic model can also predict the cellulose and hemicellulose dissolution and thereby can be used as a process optimization tool. The microwave-assisted urea-based hydrotropic pretreatment conducted at a solid-liquid ratio of 1:35, a urea concentration of 36.8%, a reaction temperature of 90 °C, and a pretreatment duration of 73.6 min is predicted to give a solid residue with low lignin content and high cellulose content which resulted in a cellulose to lignin ratio of 5.53. Cellulosic biomass characterization revealed that microwave-assisted hydrotropic pretreatment was able to produce higher crystallinity and thermally stable cellulosic biomass.

Dissolution reaction kinetics and mass transfer during aqueous choline chloride pre-treatment of oak wood

Lignocellulosic biomass processing employing ionic liquids is of recent research interest for the biorefinery industry. The data on biomass dissolution kinetics in ionic liquids is important for designing scale-up pre-treatment reactor design. In this study, the reaction mechanism and kinetics of oak wood dissolution in aqueous choline chloride was investigated. In an extended effort, a correlation of dimensionless numbers was developed for the estimation the mass transfer coefficient. The analyses suggested that oak wood dissolution in choline chloride occurred in two stages. The diffusion of ionic liquid through the product layer was the dominating rate-controlling step in the first stage of dissolution followed by the surface chemical reaction in the second stage. The diffusivity of choline chloride into the oak wood matrix was ranging between 2.96E-14 and 2.84E-13 m²/s. The activation energy of the diffusion controlled stage and surface chemical reaction controlled stage was approximately 24.2 and 40.3 kJ mol^-1, respectively. The proposed mathematical correlation for mass transfer coefficient fitted well with the experimental mass transfer coefficient values.

Tetrahydro-2-furanmethanol pretreatment of eucalyptus to enhance cellulose enzymatic hydrolysis and to produce high-quality lignin

In this study, an organosolv process based on tetrahydro-2-furanmethanol/acid aqueous solution was developed to release lignin and hemicelluloses from eucalyptus for the enhancement of enzymatic hydrolysis. The pretreatment with 80% THFA aqueous solution containing 1% HCl at a solid to liquid ratio of 1:10 was conducted at 120-180 °C for 30 min. Under the serious conditions, the cellulose-rich residue had a high proportion of cellulose up to 87.31%. The enzymatic hydrolysis rate of the cellulose-rich fraction was 94.18%, which was enhanced by 7.3-fold as compared to that of the raw material without pretreatment. The fractionation process resulted in a high delignification rate of 93.95%. The lignin produced with medium molecular weight (2190 g/mol) and high purity (contaminated sugar content 0.6%) was a good substrate for further application as chemicals.