Straw Steam Explosion Pretreatment Conditions Combined With Chemical Optimization

When straw fiber converts to fuel ethanol, highly effective pretreatment is an essential procedure, because straw fiber in natural state has low efficiency of enzymatic hydrolysis.This thesis studies the optimized parameters of straw stream explosions combined with chemical pretreatment, and corresponding result of enzymatic hydrolysis and saccharification. To be specific, we conducted several process optimizations such as straw fiber chemical impregnation, straw fiber steam explosion, and straw fiber enzymatic hydrolysis and saccharification etc. The conclusion is as follows:(1) Untreated straw after being enzymatic hydrolyzed has reducing sugar concentration of 0.86g/L, and enzymatic hydrolysis and saccharification rate of 1.28%. Steam explosion destroys internal structure of straw, so after the enzymatic hydrolysis, reducing sugar concentration is up to 11.72g/L, and enzymatic hydrolysis and saccharification rate is 17.5%. Steam explosion, combined with chemical impregnation, catalyzes the dissolution of hemicellulose during the pretreatment process and eliminate some of lignin. As a result of it, reducing sugar concentration rate will be up to 24.56g/L and enzymatic hydrolysis and saccharification rate will be 36.67%. Experiment result indicates that different impregnation reagents for pretreatment process generate significantly different results. Among them, ammonia produces the best one.(2) In the experiment of optimizing pretreatment condition, five variables-solid liquid ratio, impregnation concentration, impregnation time, explosion pressure and steaming time-have been studied in single factor experiments. And the three most influential variables have been studied using response surface methodology. Analysis of the experiment result suggests that the most optimized condition for pretreatment is the combination of solid liquid ratio of 1:2.5, impregnation concentration of 3.5%, impregnation time of 2h, explosion pressure of 2.0Mpa and steaming time of 210s.(3) In the experiment of optimizating enzymatic hydrolysis condition, straw under the most optimised pretreatment condition is used as raw material. Five variables-substrate concentration, pH value, enzyme volume, enzymatic hydrolysis time, and enzymatic hydrolysis temperature-have been analyzed in the single factor experiments. The best condition for enzymatic hydrolysis observed from the experiment is the combination of substrate concentration of 10%, pH value of 4.9, enzyme volume of 25 IU/g, enzymatic hydrolysis time of 12h, and enzymatic hydrolysis temperature of 50℃.