Hydrogenolysis Lignin To Prepare Monophenolic Compounds In Organic Solvent/Water Biphasic System

Lignin is the most abundant renewable biomass resource next to cellulose in nature,and its molecular structure is rich in benzene rings.It is of great significance to catalytic depolymerize lignin into monophenolic compounds for preparing high value-added platform compounds and liquid fuels.The efficient utilization of lignin is favourable for alleviating energy problems and environmental pollution to achieve the sustainable development of human society.It is very difficult to improve the yield of monophenolic compounds due to the repolymerization of degraded products of lignin.In this work,an effective approach for the hydrogenolysis of alkaline lignin?AL?was explored first from the perspective of solvent,in which organic solvent/water biphasic system was used for improving the yield of monophenolics.The results indicated that the MIBK/H₂O biphasic solvent system was the optimum for the hydrogenolysis of AL.Under optimized conditions,the yields of monophenolic compounds and bio-oil were 18.42 wt%and 87.57 wt%,respectively,and the conversion rate of lignin reached 99.77 wt%.The promotion of hydrogenolysis efficiency was attributed to the good extraction ability of MIBK to phenols.The MIBK/H₂O biphasic solvent system could inhibit the repolymerization and promote the depolymerization of lignin and model compounds effectively,and thereby improved the yield of monophenolic compounds compared to the homogeneous solvent system.On this basis,pine organosolv lignin?POSL?and birch organosolv lignin?BOSL?isolated by using organic solvent method were hydrogenolyzed in a biphasic solvent system to explore the effect of lignin structure on the choice of solvent.The results indicated that the yield of monophenolic compounds hydrogenolyzed from POSL reached 25.32 wt%in n-butanol/H₂O,while the yield of monophenolic compounds hydrogenolyzed from BOSL was 35.15 wt%in methyl acetate/H₂O.2D-HSQC NMR was used to characterize the structure of lignin,and the content of?-O-4 linkages in AL,POSL and BOSL was 26.92/100Ar,52.94/100Ar and52.63/100Ar respectively.The extraction capacity of solvent depended on the obtaining and stabilizing of monophenolic compounds for AL with low content of?-O-4 linkages.It was the key to stabilize the degraded products for POSL and BOSL with high content of?-O-4linkages.The n-butanol/H₂O solvent system was more conducive to depolymerizing POSL with relatively difficult degradation,while methyl acetate/H₂O solvent system was favourable for hydrogenolysis of BOSL due to the esterification reaction between acetic acid hydrolyzed by methyl acetate and alcohol hydroxyl group of degraded products to improve the stability of products,and hence improved the yield of monophenolic compounds.