The Study On Preparation Of Paraxylene Precursor Chemical From Lignocellulose Biomass

With the yearning for a better life and the demand for the quality of life,the chemical paraxylene(PX)is closely related to people’s life.It is one of the main raw materials for textile and chemical fiber,and the domestic demand is up to 25 million tons.Due to the severe environmental pollution caused by the former industrial chain of pxylene,which is mainly based on the exploitation of crude oil,researchers have been forced to find a new energy to replace the fossil energy.Lignocellulose biomass has become a hot topic in recent years due to its advantages of wide source,low cost and renewable energy.Therefore,based on the development of petroleum-based PX industry,it is transforming to bio-based PX process route.In this paper,several common biomass raw materials in nature(corn straw,rice bran,rubber wood,sweet potato residue)were selected for pretreatment and enzymatic hydrolysis saccharization to obtain high valueadded product-glucose.Finally,the process pathway of glucose to fructose and 5-HMF,the precursor chemicals of paraxylene(PX)was explored.The main research content of this paper:(1)Corn stalk was pretreated with low concentration ethylenediamine(EDA)system.Under the conditions of 10%EDA,160℃ and 130 min,the glucose yield reached the highest,which was 308.12 g/kg corn stalk.Under these conditions,the content of acid insoluble lignin is 7.70%,indicating that the removal effect of lignin is significant.At the same time,after 72 h enzymatic hydrolysis,the efficiency of glucan was 97.38%and the yield of glucose was 69.19%.The rubber wood and the rubber bark were pretreated by 50%ethanol+1%H2SO4 mixed solvent and 10%ethylenediamine(EDA)+ 4%polyethylene glycol(PEG)(8000)mixed solvent.At 160℃,10%EDA+4%PEG(8000)and 60min,the glucose yield of rubber wood reached the highest 350.83 g/kg,while the glucose yield per kg of rubber bark was only 228.13 g.Under these conditions,the glucose yield per kg of rubber wood was 122.70 g higher than that of rubber bark.This is because the rubber bark tissue contains cell walls and other structures that hinder the enzymatic hydrolysis and saccharification process of cellulose.The lowest recovery was 49.90%,which was lower than that of corn stalk.At the same time,after 72 h enzymatic hydrolysis,the concentration of glucose was 42.18 g/L,the enzymatic hydrolysis efficiency of glucan was 91.95%and the yield of glucose was 61.08%.These indexes are all higher than that of rubber bark,indicating that the utilization value of rubber wood is higher than that of rubber bark.Compared with corn stalk,the yield of rubber-wood glucose per kg was increased by 42.71 g.Rice bran was pretreated with diluted H2SO4.The maximum glucose yield of rice bran was 261.41 g/kg at 160℃ for 60 min and 2%H2SO4.Sugar yield loss is severe,much lower than corn stalk and rubber wood.(2)A kind of low cost biomass raw material-sweet potato residue was determined through the research.The first pretreatment process of sweet potato residue is to make sugar by amylase hydrolysis and the pretreatment of the remaining residue,and then carry out the enzymatic hydrolysis saccharification process.523.82 g of glucose was obtained per kg of sweet potato residue,and the yield of glucose was 91.90%.The second pretreatment process of sweet potato residue is "mechanical ball milling+two-step acid process" to make sugar.The optimal hydrolysis temperature of sweet potato residue in the first step by starch acid method was 130℃,5%H2SO4,60 min.In the second step,H2SO4/ethanol was 1.5%(w/v),and the amount of ethanol was 1:10(w/v).The mixed beads(small:medium:large=5:3:2)were used for ball milling for 3h.531.75 g glucose was obtained per kg of sweet potato residue,and the yield of glucose was 93.04%.Comparing of the above two kinds of sugar technology,it was found that the glucose yield and yield of the new sugar production process of "mechanical ball milling and two-step acid process" of sweet potato residue increased by 7.96 g and 1.03%,respectively.Moreover,this process not only reduced the use of enzyme,reduced the expensive cost of enzyme,but also solved the problem of industrial wastewater.After five industrial cycles,the concentration of glucose reached 105 g/L,the yield of glucose was 86.71%,and the waste water could be reduced by 80%.Therefore,this technology is more conducive to industrialization and brings greater economic benefits to enterprises.(3)Based on the above situation,a coupling process system of enzymatic isomerization of glucose and separation of fructose was constructed.It can be divided into three stages:isomerization of glucose,organic phase extraction of fructose and back-extraction of fructose.The optimum technological conditions of three raw materials(commercial glucose,enzymatic hydrolysate of corn stalk and enzymatic hydrolysate of cassava)were investigated.Under the optimal technological conditions,The fructose selectivity reached 89.21%after three cycles of commercial glucose process.When the enzymatic hydrolysate of corn stalk was used as substrate,the selectivity of fructose reached 83.30%after three cycles.When cassava hydrolysate was used as substrate,the fructose selectivity could reach 83.40%after five cycles.Meanwhile,the yield of 5-HMF prepared by one-pot method with different substrates was studied.The results showed that the yield of 5-HMF from high to low was commercial glucose>sweet potato residue enzymatic hydrolysate>corn stalk enzymatic hydrolysate>The enzymatic hydrolysates of cassava residue.were 70%,64.29%,53.31%and 34.26%.