The Study Of Catalytic Liquefaction For Kraft Lignin In Supercritical Alcohol/water

With the growth of worldwide population and development of economy,the demand for fossil energy is increasing,while the fossil energy is non-renewable with limit storage on the earth.As a result,the exhaustion of fossil energy is inevitable.Meanwhile,the use of it will release a large number of greenhouse gases,which is a threat to global ecology.Biomass energy is considered to be a potential alternative fossil energy because of its high reserves,renewable and no carbon dioxide emissions.The development of biomass energy has become an important development strategy for many countries.Lignin is one of the most important components of biomass energy,which is the second most abundant organic compound in the world.Unfortunately,it is a great waste in the paper industry as a by-product.Therefore,how to convert lignin into available energy has become a difficult problem for scientists.Compared to the traditional treatment of lignin(pyrolysis and gasification),supercritical degradation is an effective and rapid method for lignin conversion.It is because the process of liquefaction not only do not need to pretreat lignin,but also can obtain high quality bio-oil and high value-added chemicals like aromatic hydrocarbons and phenolic compounds.However,there are a lot of researches on the topic of improving the bio-oil yield for the liquefaction of lignin,and only a few researchers put their attention on the fundamental reaction pathway,the selectivity of high-value chemicals,gaseous products distribution and gas-liquid product distribution relationship in present.In my opinion,the later is more significant and meaningful.Based on the above considerations,this paper tried to select different catalysts to degrade kraft lignin in different supercritical systems and discuss how the factors affected the distribution of liquid products.According to the distribution of the liquid products,the formation process of the main components was speculated,and the catalytic degradation path of kraft lignin was put forward in supercritical system.The high efficient catalyst was selected for the supercritical system in order to obtain high value-added chemicals with high yield and high selectivity.Based on the analysis of the variation trend of liquid product composition along with H2 selectivity and yield,the relationship between liquid product distribution and H2 selectivity was investigated.The main work and results were summarized as follows:1.The study of the alcoholysis reaction for kraft lignin in supercritical isopropanol.The alcoholysis reaction of kraft lignin in supercritical isopropanol system was discussed,and the effect of the reaction temperature(270-350 ℃),reaction time(1-5 h)and the mass ratio of kraft lignin to isopropanol(1-3 wt%)on liquefaction process were studied.The optimal reaction conditions(350 ℃ reaction temperature,4 h reaction time,1 wt%lignin concentration)were proposed for the highest bio-oil yield and heating value.By exploring the influence of reaction temperature on liquid products distribution,a conclusion could be drawn that high temperature conditions were conducive to the conversion between guaiacol/catechols(containing two or more oxygen atoms)and alkylphenolic compounds(containing a single oxygen atom),which laid a good experimental foundation for further analysis of catalytic depolymerization of kraft lignin.2.The study of the alcoholysis reaction catalyzed by noble metal catalyst for kraft lignin in supercritical isopropanol.The effect of reaction temperature(270-350℃),reaction time(1-5 h),the mass ratio of kraft lignin to isopropanol(1-3 wt%),noble metal catalysts(Pd/C;Pt/C;Ru/C;Rh/C)and the mass ratio of catalyst to kraft lignin(10-50 wt%)on the liquefaction process of kraft lignin were researched by orthogonal array design(OAD)in supercritical isopropanol.The results showed that the reaction temperature and the kind of catalysts were the main influence factors in the yield and heating value of bio-oil.The degradation process of kraft lignin catalyzed by five kinds of catalysts was further analyzed at 330 and 350 ℃,a conclusion was drawn that Rh/C was the optimal catalyst for obtaining high HHV bio-oil base on the analysis for the stability of isopropanol,the inhibition of the formation of oxygen-containing chain compounds and the effect of the hydrogenation of phenol compounds under the catalysis conditions.By comparisons between bio-oil and liquid products from sole isopropanol depolymerization in high temperature,the formation process of oxygenic-chain compounds and cyclohexanol/ones was deduced presumably.The catalytic degradation pathway of kraft lignin in supercritical isopropanol was proposed.3.The study of the depolymerization catalyzed by multi-functional supported catalyst Rh/La2O3/CeO2-ZrO2 for kraft lignin in supercritical alcohol/water system.The effect of the catalyst Rh/La2O3/CeO2-ZrO2 on liquid products and gaseous products distribution were analyzed during degradation of kraft lignin in supercritical ethanol system.The degradation reaction obtained high selectivity of aromatic alcohols(57%)and H2(82%).The reusability of catalyst was investigated and catalyst deactivation was discovered.By comparison between the fresh and the used catalyst,the carrier aggregation,the loss of precious metals and the increase of carbon deposition rate were observed.The performance of the catalyst was also tested in supercritical water/formic acid,methanol,isopropanol system,and it was found that none hydrogenation of benzene ring saturation appeared in the previous two systems and a large number of cyclic compounds formed from the hydrogenation of benzene ring in supercritical isopropanol system.Compared with the H2 selectivity in supercritical ethanol system,the supercritical water/formic acid and methanol system was lower,and the supercritical isopropanol was the most.Considering the liquid and gaseous products distribution,the supported catalyst showed the highest activity in the supercritical ethanol system.4.The study of the corresponded relationship between the liquid products distribution and the selectivity of gaseous products obtained from kraft lignin depolymerization in supercritical alcohol/water system.Supercritical isopropanol/water system was chosen as the medium for the liquefaction of kraft lignin.By adjusting the volume ratio of isopropanol to water to regulate the selectivity and yield of gaseous products,it was found that the distribution of liquid products changed regularly with H2 selectivity(93%-77%)and yield(48.95-0.44 mmol).In order to further expand the adjustable range of H2 selectivity,formic acid was introduced into supercritical isopropanol/water systems.The selectivity of H2 expand from 35%to 90%,but there was little change in the yield of H2(38.63-0.65 mmol).Based on the analysis of the variation trend of the liquid products distribution with the gaseous product selectivity,the relationship between the liquid product distribution and H2 selectivity was proposed.The corresponded relationship between liquid products distribution and H2 selectivity was checked in the different temperature,solvents and catalysts,and it was found that the relationship was good applicability.