Research On Conversion Of High Concentration Lignin To Cycloalkane

The excessive exploitation of fossil energy leads to energy shortage and environmental damage,which switches the research interest to the renewable resource.Lignin is a renewable lignocellulose biomass comprised by C9 benzene ring structure units.It shows potentials for partly replacing petrochemical resources to produce aromatics and cycloalkanes.However,due to the unfixed C-O linkage unit and the facile polymerization of phenol intermediates,the conversion efficiency of lignin is low,i.e.,low conversion rate and low lignin concentration of raw materials.Herein,this work developed a tandem catalysis approach for converting of high concentrated lignin to stable cyclic alkanes by introducing Pt/HAP into Ni/ASA catalyst.The one-step conversion of high concentration lignin?150 g/mL?to ethyl cyclohexane and polycyclic alkane is realized.The conversion rate is close to 80%and the liquid yield is 41.8 wt%at 300?and 6 MPa H₂.As far as we know,this is the highest solid concentration of lignin liquid phase transformation reported at present.The introduced Pt/HAP changed the simultaneous hydrogenation and hydrogenolysis of lignin on Ni/ASA to a tandem reaction on a physically mixed Pt/HAP+Ni/ASA,involving the initial selective lignin depolymerization over Pt/HAP and following phenols hydrodeoxygenation over Ni/ASA,as evidenced by the kinetic studies.In the tandem approach,the preferred initial lignin depolymerization instead of lignin hydrogenation originates from the strong adsorption and high C-O cleavage selectivity of lignin on the introduced Pt/HAP,as confirmed by UV-Vis,GPC,2D-HSQC NMR,and catalytic tests.Rates of lignin depolymerization and depolymerized phenols hydrodeoxygenation were matched when the mass ratio of Pt/HAP and Ni/ASA was set as 1.0,allowing this approach to be successfully processed with the highest lignin concentrations?150 mg/mL?as reported to cyclic alkanes with 42 wt%yield in dodecane at 300°C in presence of 6MPa H₂.Promisingly,the developed approach may lay a solid foundation for the future industrial application of lignin valorization.