Study On The Effects Of Dilute Acid Pretreatment Combined With Mechanical Refining On The Poplar Wood Substrate's Characteristics

With the decrease of petroleum resources and the emergence of environmental issues,it has become a trend that using the biofuels,which are produced by lignocellulosic biomass and other renewable resources,partly or totally substitute for fossil fuel.In the process of biofuel producting,there are many limiting factors for enzymatic hydrolysis to gain fermentable sugar.The characteristics of biomass and enzyme hydrolysis conditions are two major limiting factors.In this study,poplar chips were used as the raw material.In order to obtain the chemi-mechanical pulp(substrate of enzymatic hydrolysis),the raw material was subjected to dilute acid pretreatment with different intensities(the combination of temperature,time and pH)combined with mechanical refining.The substrate characteristics were analyzed and then the substrate was subjected to enzymatic hydrolysis.The effects of different substrate characteristics on the enzymatic hydrolysis efficiency were envaluated through the linear relationship that was established between them.The effect of different dilute acid pretreatment on the compositions of wood chips was investigated.The yield of wood chips was decreased as the increase of pretreatment intensity.In the process of dilute acid pretreatment,the component dissolved mainly was xylan and its dissolving-out amount was increased with the increase of the pretreatment intensity.The lignin on the surface of wood chips was increased due to the formation of the pesudo-lignin and re-deposited ligrun which was detected and analyzed by the X-ray energy spectrum(XPS)and scanning electron microscope(SEM).The lignin's concentration in the fiber cell wall was reduced after the pretreatment which was comfirmed by scanning electron microscope combine with energy dispersive X-ray analysis(SEM-EDXA).The enzymatic dosage and substrate concentration conditions in the enzymatic hydrolysis processing were optimized.After that the optimal enzymatic hydrolysis condition(20 FPU/g substrate and 4%of substrate concentration)was obatained and then the substrates with different pretreatment intensities were hydrolyzed under this optimal condition.The enzymatic hydrolysis efficiency was enhanced after the optimizing and the dilute acid pretreatment.The subatrate with pretreatment intensity factor of 1.38 had a highest glucose conversion was 93.32%while the subatrate without dilute acid pretreatment was 45.3 1%.In addition,different characteristics of substrate were measured and analyzed.The results showed that surface area and the eontent of fines eomponents were increased first and then decresed as the increasing of pretreatment intensity while the content of surface lignin was decresed first and then increased.The degree of crystallinity and mean fiber length had a decrease trend after the dilute acid pretreatment.It was found that the surface area,fines content and surface lignin concentration had a significant influence on enzymatic hydrolysis efficiency while other characteristics had an insignificant influence on it.