Study On The Effects Of Acid Pretreatment On The Lignin Distribution And Subsequent The Enzymatic Hydrolysis Of Poplar

With the development of global economy,energy supply and environmental protection have become more and more important.The petroleum and fossil energy resources in nature are limited and nonrenewable.Therefore,it is very necessary to develop biorefinery to produce biofuels and biomaterials from biomass.Utilizing enzymatic hydrolysis to gain fermentable sugar is a critical process for biofuel production.The accessibility of cellulose by enzymes is greatly hindered by the natural complexity of plant cell walls.At present,it is very limited for people to know about the understanding?chemical composition distribution of plant tissue after ptrtreatment and the enzymatic hydrolysis.As a consequence,it is significance that acid pretreatment effect on the lignin distribution of the poplar and the enzymatic hydrolysis.Poplar chips were studied in this article as the raw material.After sulfuric acid pretreatment,poplar chips with different severity(in term of intensity factor log R0)were processed into a substrate.Bio-enzymes were used to hydrolyze the substrate and the effects of enzymatic hydrolysis were studied in this paper.The research contents are as follows:(1)Changes of chemical composition of hydrolysate and wood that after dilute acid pretreatment;(2)Dilute acid pretreatment of poplar chips result in the changes of lignin distribution in the chips;(3)The effects of enzyme hydrolysis conversion rate of the substrate due to dilute acid pretreatment of poplar chips.The main conclusions of the studies were as follows:The yield of poplar chips was decreased with the increase of the intensity of pretreatment,while the insolubles and volatile matter content in pretreatment liquid were increased.There was a same tendency of sugar content(glucose,glucan,xylose,xylan and arabinose)in the pretreatment liquid with the changing of pretreatment intensity.In this experiment,hydrolysis liquid glucose and xylose mainly exists in the form of oligosaccharides.The main chemical components including carbohydrate and lignin of wood after dilute acid pretreatment were decreased due to the increase of the intensity of pretreatment.Especially,it is obviously decreased for the content of xylan.The relative content of acid soluble lignin and acid insoluble lignin decreased with the increase of the intensity factor.The downtrend of acid insoluble lignin was more evident and this has a very nice interpretation about why acid insoluble lignin increased in the hydrolysate.The lignin distribution of poplar chips acid-pretreated was studied by confocal laser scanning microscopy(CLSM)and the result showed:after acid pretreatment,content and distribution of lignin in poplar chips were changed.Compared with the blank,acid pretreatment could improve the lignin solubility.With the increase of pretreation severity,the area of this region that containing lignin in secondary cell wall reduced.Most lignin between the secondary cell wall and middle lamella were lost,and the lignin in secondary cell wall started to move to the surface and deposit on it,which can be received by SEM(Scanning Electron Microscope)and XPS(X-ray Photoelectron Spectroscopy).The pretreatment increased the effect of enzymatic hydrolysis.The conversion of glucose was increased with the development of pretreat intensity.In a relatively short period of time,the acid pretreated substrate has high conversion rate.At the enzyme hydrolysis time of 48 h,the glucose conversion rate increased by 68%under the intensity factor 3.38 compared with the blank sampl.