Catalytic Liquefaction Of Lignin In Cu / Zn / Al Composite Oxide In Supercritical Methanol

Among the numerous renewable energy, biomass for its universality, renewable, clean characteristics is favored by governments and scientists to become the most potential energy of the energy supply in the21st century. Lignin which account for as high as40%o f the dry biomass weight is formed by an amorphous and highly branched polymer of benzene propane units. Lignin macromolecule structure makes little lignin can effective use. Supercritical fluid due to good diffusivity, solubility, liquidity has caused great attention of scholars both domestic and overseas in the biomass conversion. Hydrogenation or hydrogenolysis reaction may be the most efficient way of lignin liquefaction. Under supercritical conditions, methanol could provide hydrogen by reforming for lignin hydrogenation and hydrogenolysis reaction. The use of catalyst can reduce the condensation reaction of lignin liquefaction intermediate and the generation of carbon. One-pot catalytic liquefaction of lignin in supercritical methanol could realize the combination of the above two kinds of advantage and efficient liquefaction of lignin.This article selects the Cu/Zn/Al composite oxide as catalyst(abbreviation: Cu/Zn/Al catalyst), the lignin liquefied rate as an index, to explore one-pot catalytic transfer hydrogen from supercritical methanol for liquefaction of lignin The main research content is as follows:1. A series of Cu/Zn/Al based catalysts were prepared by calcination of the Cu/Zn/Al hydrotalcite which was synthesized by the coprecipitation method at different temperatures. The catalysts were analysed by XRD, TG/DTG, BET, H2-TPR and activity evaluation to study the effect of calcination temperature on the catalyst liquefaction activity and stability of lignin in supercritical methanol. The results indicated that hydrotalcite was almost exactly decomposed at500℃, the CuO nanoparticles was segregated and stabilized by precipitation of ZnO and ZnAl2O4spinel phase. The catalyst calcined at500℃showed good activity and stability for the repeatability test at the conditions of340℃, lignin80mg, catalyst30mg,4mL methanol and holding time3h. 2. Direct liquefaction of lignin under the condition of supercritical methanol using Cu/Zn/Al oxides as catalysts was carried out in a pressurized batch reactor. The effects of liquefaction temperature, liquefaction time, ratio of lignin to methanol, and dosage of catalyst on the lignin conversion were investigated. The experimental results from orthogonal matrix showed that the optimum liquefaction conditions were reaction temperature of340℃, holding time3h,and lignin methanol ratio of20:1mg/mL, the catalyst dosage of37.5%, which results in an overall conversion of94.26%for lignin.3. The kinetic analysis of lignin catalytic liquefaction was studied by using a model method. The kinetics calculation of lignin catalytic liquefaction in supercritical methanol indicated that the apparent activation energy is55.217kJ/mol, and frequency factor is50513.7, and kinetics equation is4. Direct liquefaction and catalytic liquefaction of lgnin test results show that the catalyst increase lignin conversion rate from60.5%to94.26%; Catalyst has promoted addition and substitution of the lignin pyrolysis product with H2. The product of alcohols, ethers, esters has improved dramatically, and ketones, aldehydes, benzene has reduced.