Experimental Study On Supercritical Fluid Liquefaction Of Lignin Under Cu - Based Catalyst

Transforming biomass resources into high quality fuel and chemical raw materials is one of the most feasible ways under the existing industrial system to solve the problem of energy shortage and environmental pollution. Lignin is the second most abundant organic matter in the world, and it is the only natural renewable resources which can directly provide aromatic ring structure. Liquefaction is the key step of using lignin to developing high quality liquid fuels and chemicals. This paper studies the catalytic liquefaction of lignin and typical biomass——walnut shell in the supercritical fluid.A series of Cu/Mn/Al/La and Cu/Zn/Al/La hydrotalcites were prepared through parallel flow co-precipitating method. Copper-based oxide catalysts were obtained from hydrotalcites which were calcinated at 500 ℃ in air atmosphere. Physical and chemical properties and phase structures of catalysts and their precursors were studied by TG, XRD, H2-TPR, BET and SEM analysis.Cu/Mn/Al/La-O catalysts were used for catalytic liquefaction of lignin in supercritical methanol. The effects of the La content in catalysts, reaction time and reaction temperature on the lignin liquefaction were discussed. The results shown that La can improve the catalytic activity and stability effectively; But La can inhibit methanol reforming at the same time, and too much La in catalysts can not improve the lignin conversion under low temperature.Cu/Zn/Al/La-O catalysts were used for catalytic liquefaction of lignin in supercritical methanol. Single factor experiments found that:Z0.1 catalyst which has 1% mole percent La has the best catalytic effect on lignin liquefaction; Lignin conversion first rise after falling with the increase of catalyst mass, and the lignin conversion was the highest of 70.52% at the catalyst mass of 30 mg; Lignin conversion decreased with the increase of S/L ratio; Lignin conversion risen with the increase of reaction time, and the rising speed first was fast and then slow, gradually leveling off; Lignin conversion increased with the rising of temperature, and the conversion rate can be up to 97.52% at 360 ℃; Lignin conversion increased with the increase of water content in methanol, and it was 98.45% at the water content of 30%.Z0.1 catalyst was used for the walnut shell liquefaction in supercritical methanol/water mixture. The conversion of walnut shell increased with the increase of water content, reaction time and reaction temperature.23 full factorial design and analysis found that contribution of each factor to the walnut shell conversion was as follows: reaction temperature (67.99%)> reaction time (11.12%)> water content (7.17%)> interaction of water content and reaction temperature (4.39%)> interaction of reaction time and reaction temperature (3.47%)> interaction of water content and reaction time (0.071%).The main compositions of walnut shell liquefaction products are esters, alcohols, ketones, ethers, hydrocarbons, furans, phenols and arylethers. Esters, alcohols, ketones and ethers were produced by cellulose and hemicellulose of walnut shell. The aromatic substances including hydrocarbons, phenols and arylethers were produced by the lignin in walnut shell. The increase of water content, reaction time and reaction temperature were reduced in favour of methyl acetate in the product of walnut shell liquefaction.