Optimization Of Parameters Of LAT And LATH Pretreatment For Enzymatic Hydrolysis Of Crop Straw

Crop straw is a considerable lignocellulosic resource with7tons/year in China, which will become an important feedstock of cellulosic ethanol. Pretreatment, hydrolysis and fermentation are the three key technologies in the production of cellulosic ethanol. In this study, the pretreatment and enzymatic hydrolysis of crop straw was investigated. In the present work crop straws such as rice straw, alfalfa and sorghum straw were pretreated by liquid ammonia treatment (LAT), H2O2pretreatment (HP) and with hydrogen peroxide presoaked prior to LAT (LATH) to overcome biomass recalcitrance, followed by enzymatic hydrolysis. Pretreatment conditions including temperature, residence time, water loading, ammonia loading, hydrogen peroxide loadings, and cellulase loading were varied to maximize hydrolysis yields. Some experimental results are as following.(1) The optimal LAT and LATH pretreatment conditions of rice straw were90℃(LAT) or130℃(LATH),3.0ammonia loading,10min residence time, and2.0water loading. Approximately90.86%glucan and76.30%xylan conversions of LAT-pretreated rice straw were achieved after72hours enzymatic hydrolysis, and approximately91.16%glucan and73.95%xylan conversions of LATH-pretreated sample were achieved. The yields of monosaccharides of LAT-treated and LATH-treated rice straw were550.83g and537.59g respectively. It is about2.9-fold and2.8-fold increase in sugars yield for LAT-treated and LATH-treated rice straw respectively. The lignin removal of LATH is more efficient than that of LAT.(2) The optimal high-temperature HP pretreatment conditions were120℃,0.75H2O2loading (30%solution), and60min residence time. Approximately61.55%glucan and47.82%xylan conversions were achieved after72hours enzymatic hydrolysis. The sugar yield was334.5g per kg of rice straw (dry basis) after144hours enzymatic hydrolysis, which is lower than that of LAT and LATH.(3) The experimental result from optimization of cellulase loading shows that the effect of cellulase loading in improving enzymatic conversions was far lower than that of LAT. There was little effect on improving enzymatic conversions even if the cellulase loading was greater than FPU/(g of glucan) at1%glucan loading. And the LAT pretreatment can improve the effectiveness of enzyme.(4) The optimal LAT pretreatment conditions of alfalfa and sorghum straw were110℃(LAT),1.0ammonia loading,5min residence time, and0.6water loading. Approximately61.51%glucan and67.32%xylan conversions of LAT-pretreated alfalfa, and82.51%glucan and91.12%xylan conversions of sorghum straw were achieved after72hours enzymatic hydrolysis. The sugar yield was342.53g and559.51g per kg of dry basis after144hours enzymatic hydrolysis. So the LAT pretreatment effectiveness of sorghum straw is better than that of alfalfa.(5) Approximately84.90%glucan and81.02%xylan conversions were achieved after72hours enzymatic hydrolysis using the LAT-treated mixture of rice stra, alfalfa and sorghum straw. The enzymatic hydrolysis effect of the pretreated mixture was more than that of single material. The sugar yield was499.24g per kg of the mixture dry basis after144hours enzymatic hydrolysis. The glucose yield was363.80g using the LATH-treated mixture at the maximum conversion after144hours enzymatic hydrolysis, which is74%of total sugar yield, and which is greater than that of the LAT-treated mixture.