Research On The Conversion Of Lignin And Its Derivatives During Production Of Liquid Bio-fuel From Biomass

Biomass energy is the only renewable energy that can be directly converted into carbon-based liquid fuel.The efficient conversion of lignocellulosic biomass into high-grade liquid fuel is of great significance for diversifying the national energy structure and reducing energy and environmental issues.Based on the scientific problems in the research,the experimental study of lignin pyrolysis,bio-oil catalytic upgrading and lignin catalytic depolymerization was carried out,and the process integration of biomass liquid fuel as well as their comparison was done in this paper.Aiming at the cross-cutting problem of the influence of biomass microstructure on enzymatic properties and pyrolysis characteristics,five poplars were used as raw materials to analyze the differences in composition and microstructure.The enzymatic hydrolysis results indicated significant difference on the release of enzymatic sugars from five plants.The main factor affecting its enzymatic properties was not its three component content,whereas the microstructure had a more important influence.The tube furnace was used to pyrolyze poplar powder,and the yield of pyrolysis oil was about 55%.There was no significant difference in the pyrolysis yield of the five poplar samples and the molecular weight of the oil.GC-MS was used to detect the product distribution of pyrolysis oil,which indicated a negative correlation between the content of G-type lignin monomer derivative in biomass pyrolysis oil and the amount of enzymatic glucose release.The ratio of S-type monomer and G-type monomer derivative(S/G)is positively correlated to that.The hydroxyl content of the whole component of bio-oil was further tested by ³¹P NMR.It was confirmed that there was a negative correlation between the content of G-type monomeric hydroxyl in pyrolysis oil and the amount of glucose released from biomass.The above results indicate that the composition and structure of lignin monomer in biomass are important factors affecting the enzymatic and pyrolysis characteristics of biomass.Catalytic hydrogenation of pyrolysis oil was carried out in supercritical methanol by copper-magnesium-aluminum hydrotalcite catalyst.The pyrolysis oil was analyzed by ¹H NMR spectrum and ³¹P NMR spectrum,and the aliphatic hydroxyl and monocyclic phenolic hydroxyl content was significantly reduced in the upgraded oil.Further studies found that under a small amount of catalyst,it could also catalyze the decomposition of aliphatic alcohols and the hydrodeoxygenation and dehydration reaction of alcoholic hydroxyl groups.The higher catalyst usage ccould promote the hydroconversion of monocyclic phenols,but there was no obvious catalytic effect on the hydrogenation of condensed phenol.Higher reaction temperature and longer reaction time ccould further promote the hydrogenation reaction of monocyclic phenolic compounds,so that the content of monocyclic phenols was greatly reduced or even disappeared,but the hydrogenation of carboxyl groups was more difficult.On the other hand,the hydroxyl group content of condensed phenols in the oil was increased,as further condensation of the phenolic compound occurred and resulted in more condensed phenols which were difficult to hydrogenate.The catalytic depolymerization of alkali lignin,enzymatic lignin and pyrolytic lignin was studied in a supercritical methanol under nitrogen atmosphere.The temperature of240-260°C and the reaction time of 4 h were optimum experimental conditions.The conversion rate and monophenol yield of the three lignin treatments were:alkali lignin64.0%,9.52%;enzymatic lignin 87.3%,19.32%;pyrolytic lignin 46%,4.67%.Increasing the reaction time does not increase the conversion rate of lignin,but instead causes the secondary condensation of the depolymerized product to cause a decrease in oil yield and monophenol yield.The product distribution was analyzed by quantitative GC-MS and 2-D HSQC NMR analysis.The alkali lignin catalyzed depolymerization product was mainly G-type monomer derivative.The side chain of the benzene ring was highly oxidized,and the para-functional group was mainly acid,aldehyde,ketone and ester.The enzymatic lignin contained three lignin monomers of H,G and S type,with more propyl branches and higher hydroxyl groups on the branches,and some?-O-4 ether linkages between the monomers.The reaction of the catalytic depolymerization process mainly included ether bond disconnection,hydroxyl group removal and double bond hydrogenation.The pyrolytic lignin structure was mainly composed of G-type and H-type monomers,the proportion of S-type monomers was low,and the para-branches contained less oxygenated functional groups,mainly methyl and ethyl groups.Its catalytic depolymerization indicateed that the hydrogenation reaction of branched double bonds increased at higher temperatures,and the condensation reaction between monomers formed a?-?linkage structure,which was the basis of ring formation and coking.The catalytic depolymerization characteristics of lignins indicated that different pore size,specific surface area and supported metals of catalysts had significant effects on lignin depolymerization.The microstructure of the raw materials was the main factor affecting the depolymerization product.The catalytic depolymerization process had limited effect on the removal of the phenolic methoxyl and phenolic hydroxyl groups,but was very effective on the removal of hydroxyl group in side-chain and the hydrogenation of the double bond.Aspen Plus was used to simulate the different process routes of biomass conversion to liquid fuel,the energy efficiency of several process routes was calculated.The results show that the energy efficiency of biomass hydrolysis and ethanol production system is significantly improved by the use of enzymatic lignin in cross-coupling pathway BE-ELUP.The utilization of pyrolytic lignin is the key constraint point and potential of biomass rapid pyrolysis and upgrading system PY-DPL-OUP.