| Lignin is the second largest natural organic matter after cellulose.Due to the structure particularity,it has the potential for the conversion of important chemical raw materials such as aromatic hydrocarbons.That is concerned that the global shortage of fossil energy issues.To make full use of renewable reso urces can maximize the benefits at the same time it also can ameliorate environmental pollution issues.Lignin can be used by thermal cracking,liquefaction,biotransformation and other methods.Through these methods lignin could be converted into aromatic,hydrocarbons,esters and ketones and other compounds.In liquefaction technology,supercritical fluid liquefaction technology has high conversion efficiency,high product selectivity and other advantages.At present stage,however,there is little research on the liquefaction of lignin in supercritical organic solvents and the discussion about the type of organic solvents was not found a lot.In this paper,three kind of organic solvents(methanol,ethanol and cyclohexane)were used in liquefaction process of lignin.After the initial experimental rules were obtained,the effect of five solvents on lignin was studied by mixed solvents.This work thus offers an effective guidance to further study the catalytic liquefaction mechanism and establish the liquefaction reaction paths of lignin.In this paper,lignin liquefaction in supercritical methanol(Tc=239.4 ?,Pc=8.092 Mpa)/ethanol(Tc=240.7 ?,Pc=6.137 Mpa)/cyclohexane(Tc=280.4 ?,Pc=4.05 Mpa)were carried out by an autoclave,respectively.The reaction product could be divided into bio-oil and residue,researching the relationship between liquefaction product and the three kinds solvents.The liquid products and solid residues were analyzed by GC-MS and FT-IR to explore influences of the solvents on the reaction of lignin liquefaction and the distribution of main compounds.The main research contents and results are as follows:(1)The paper studied the effects of methanol / ethanol / cyclohexane / mixed solvent in different reaction conditions of lignin in liquefaction reaction.To explore the effects,the reaction temperature,solvent dosage and reaction time were studied.The conversion rate and the yield of bio-oil could have a good result under the higher reaction temperature(340~360?),suitable solvent dosage(120~150mL),shorter reaction time(30~60min).Initially,the result shows the three kinds solvents have a good effect on promoting lignin liquefaction and control the produce of residue.When lignin has a liquefaction in ethanol,the higher reaction temperature(320~340?)can gain the higher lignin conversionrate(71.56%)and bio-oil yield(54.30%),the suitable ethanol dosage(120~150mL)can gain the higher lignin conversion rate(71.56%)and bio-oil yield(54.30%),the shorter reaction time(60min)also can obtain the highest conversion rate(71.56%).Though lignin has a higher conversion rate with the supercritical ethanol but the selectivity of the aromatic compounds still live at a low level,so it is necessary to find a new solvent to gain the more aromatic compounds.And we found that lignin liquefaction at supercritical mixed solvent(methanol : ethanol 1:1)can gain the highest yield(71.82%)of aromatic compounds with the higher reaction temperature(340~360?).(2)Comparing the selectivity of aromatic compounds in five organic solvents,it can be seen that there are three main categories in aromatic compounds: aromatic hydrocarbons,phenols and polycyclic aromatic hydrocarbon.The highest aromatic compounds yield of 71.82% was obtained in the mixed solvent(methanol: ethanol 1: 1).And no matter what solvent,phenols were main products in the aromatic compounds,aromatic hydrocarbons and polycyclic aromatic hydrocarbon accounted for not much.The order of phenols yield in different solvents is as follows: cyclohexane > mixed solvent(methanol: ethanol 1: 4)> ethanol > mixed solvent(methanol: ethanol 1: 1)> methanol.While the more aromatic hydrocarbons were obtained in methanol and mixed solvents(methanol: ethanol 1: 4).(3)The content of benzene ring,hydroxyl and methoxy in raw lignin was high.The liquefied products and residues from supercritical liquefaction of lignin in five organic solvents were analyzed by GC-MS and FT-IR.The results showed that the cleavage of lignin can be effectively promoted by organic solvents,resulting in higher yield of aromatic compounds and comparatively less yield of alkanes,esters,ketones,alcohols and acids and other compounds. |
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