Zhengqiu Yuan

Investigation on the structural effect of lignin during the hydrogenolysis process

Structure has a significant effect on the lignin degradation, so the investigation of structural effect on the lignin depolymerization is important and imperative. In this study, hydrogenolysis of three typical lignins with different structures, dealkaline lignin, sodium lignosulfonate and organosolv lignin, was intensively compared over the synergistic catalyst of CrCl3 and Pd/C. The effects of reaction temperature, time, hydrogen pressure and catalyst dosage on the catalytic performance of lignin species were investigated. The structure evolution of lignins during the hydrogenolysis process was also compared. The results showed that organosolv lignin was more sensitive for hydrogenolysis than others due to its high unsaturation degree and low molecular weight. Further analysis indicated that the hydrogenolysis, hydrodeoxygenation and repolymerization reactions took place and competed intensely. Wherein, the depolymerization products with unsaturated carbonyl groups were prone to repolymerize. And the methylation was helpful to stabilize the depolymerization products and suppress the further repolymerization.

Efficient and product-controlled depolymerization of lignin oriented by metal chloride cooperated with Pd/C.

An efficient lignin depolymerization process with highly controllable product distribution was presented using metal chloride (MClx) cooperated with Pd/C. The catalytic performances of MClx were investigated. The effect of reaction conditions on the lignin depolymerization and products distribution were also studied. Results showed that more than 35.4% yield of phenolic monomer including 7.8% phenols and 1.1% guaiacols could be obtained under optimized condition. And the product distribution can be efficiently controlled by the modification of the metal cation through different pathway of Lewis acid catalysis and coordination catalysis. Furthermore, the Pd/C catalyst showed an excellent recyclability, where no significant loss of the catalytic activity was exhibited after 3 runs. Moreover, the product control mechanism was proposed.

Effect of the temperature on the dissolution of corn straw in ethanol solution

Lignocellulosic biomass is undissolvable in water and conventional solvents for its complex natural recalcitrance, which significantly hinders its efficient utilization. Herein, we provided an efficient process for the dissolution of corn straw under mild conditions with the solution of ethanol, H2SO4, H2O2 and H2O. The research emphasis is the effect of temperature on the dissolution process. Results showed that the components of cellulose, hemicellulose and lignin can be separated from the corn straw by adjusting the dissolution temperature. Part of the dissolved cellulose and hemicellulose were further converted into sugars and chemicals (such as furfural, 5-hydroymethylfurfural, ethyl levulinate, levulinic acid) during the dissolution process. Released lignin was destroyed into fragments and was recovered as organosolv lignin with lower molecular weight. Furthermore, residues and the recovered lignin obtained at different dissolution temperature were characterized carefully by FTIR, NMR, GPC and elemental analysis and the dissolution mechanism was discussed.

Intensification effect of peroxide hydrogen on the complete dissolution of lignocellulose under mild conditions

Lignocellulose is generally resistant to dissolving in water and conventional organic solvents, which significantly hinders its efficient utilization. In this work, we provide a novel and efficient technology on lignocellulose dissolution under mild conditions for down-stream conversion with heterogeneous catalysts. In a mixture of hydrogen peroxide, sulfuric acid, ethanol and water, corn straw was completely dissolved in the mixture at 170 °C for 120 min without significant volatile chemical production (less than 16%). Cellulose and hemicellulose existed as water-soluble oligosaccharides in the solvent, which were more easily converted than the original polymeric carbohydrate. During the dissolved process, peroxide hydrogen exhibited a significant intensification effect on dissolving the hemicellulose, decrystallization of cellulose and delignification with sulfuric acid. Furthermore, lignin was destroyed into fragments in the course of dissolution, which had a looser structure and lower molecular weight.