Comparison of various chemical pretreatment methods of lignocellulosic biomass

Abstract

Rice straw is one of Thailand’s agricultural biomass feedstocks. An effective way to eliminate rice straw is by changing it to biofuel such as butanol. A chemical pretreatment process is usually used to disrupt the complex structure of rice straw to enhance the yield of sugar by hydrolysis step. In this study, 50% concentration of [EMIM][Ac], an alternative chemical pretreatment, was used to pretreat rice straw. The effects of temperature (140, 150, and 160 ℃) and time in a microwave (25, 40, and 55 min) were considered to obtain an optimum condition which was found by response surface methodology (RSM). From RSM result, the maximum sugar concentration of 21.58 g/L was derived when rice straw was pretreated at 162 ℃ and 48 min. And when compared to NaOH (0.5% conc., 140 ℃ for 15 min) and HNO3 (2% conc., 100 ℃ for 7 min) pretreatment, the highest total sugar yield was obtained via NaOH pretreatment (94%) but [EMIM][Ac] pretreatment gave a comparable yield (82.47%) to NaOH pretreatment indicating [EMIM][Ac] has a potential to use in pretreatment process of rice straw. Moreover, pretreated rice straw from each chemicals exhibited the higher surface area, pore diameter and crystallinity index than untreated rice straw due to the removal of lignin and hemicelluloses could enhance enzymatic accessibility to easily hydrolyze cellulose. When hydrolysate from each chemical pretreatments were fermented by Clostridium beijerinckii TISTRI1461 at 37 ℃ for 72 h. The highest ABE yield was found in sugar solution from [EMIM][Ac] pretreatment whereas sugar product from HNO3 pretreatment could not present the ABE product.