Pretreatment and fractionation of lignocellulosic biomass for production of biofuel and value-added products

Biorefineries are sustainable biomass conversion processes to make bio-based fuels and chemical products. In this thesis, several different lignocellulosic biomass pretreatment and fractionation processes are developed and described with possible biorefinery applications. Fractionation using aqueous ammonia and hot-water, hybrid fractionation using zinc chloride (ZnCl2) and simultaneous saccharification and fermentation (SSF), low-moisture anhydrous ammonia pretreatment, and photocatalyst-assisted ammonia pretreatment are investigated to improve the utilization of lignocellulosic biomass. The two-stage fractionation process using aqueous ammonia and hot-water separated three main components with relatively high purity of each component. Ammonia treatment selectively removed lignin from biomass, while hot-water treatment separately hydrolyzed hemicellulose in the following stage. Under the optimal reaction conditions using RSM, relatively high purity of hemicellulose and lignin were recovered. High enzymatic digestibility and fermentability were also resulted with cellulose fraction. A hybrid fractionation process using ZnCl2 and SSF was also investigated to improve the utilization of lignocellulosic biomass. The ZnCl2 showed high swelling effect and selectivity for hemicellulose; hence most of the hemicellulose was released into the liquid hydrolysate by ZnCl2 treatment. The fractionated hemicellulose in the liquid hydrolysates was converted into furfural by thermal reaction, while the residual solids which have high cellulose and lignin contents were converted into ethanol by SSF. Up to 98% of theoretical maximum ethanol yield was obtained; therefore, the residual solids could be high purity lignin. Low-moisture anhydrous ammonia pretreatment was studied in an effort to minimize ammonia and water input and to obtain high enzymatic digestibilities and ethanol yield. Gaseous ammonia treatment significantly reduced ammonia input (0.1 g ammonia/g biomass) and water input (1.0 g water/g biomass). In addition, there was no washing step which required significant washing water. Even though water and ammonia inputs were significantly reduced compared to previous ammonia pretreatment methods, the maximum theoretical ethanol yield (based on glucan and xylan in the biomass) reached 90% by simultaneous saccharification and cofermentation (SSCF). A photocatalyst-assisted ammonia pretreatment method was developed to enhance the effects of liquid ammonia pretreatment by oxidation reaction with photocatalysts. Higher delignification and enzymatic hydrolysis yield of treated solids resulted from photocatalyst-assisted ammonia pretreatment compared to ammonia pretreatment itself. Moreover, photocatalysts shortened the pretreatment time. Improving the pretreatment effects and shortening the pretreatment time by UV treatment using photocatalysts show a potential of photocatalytic treatment as a useful technology for lignocellulosic biomass utilization. These studies show that the development of biomass conversion process can contribute to the utilization of lignocellulosic biomass. Each approach has its own particular solution to the problems of biomass conversion processes. Fractionation processes propose ways to produce valuable building blocks, and pretreatment processes suggest efficient methods by enhancing conversion yields and reducing production costs. Although there are still many obstacles to overcome, these studies are believed to help commercialize lignocellulosic biomass products