Microwave Enhanced Hydrothermal Alkali Activation And Degradation Of Lignin And The Synthesis Of Lignin-based Phenolic Resin

Lignin as a natural polymer compound after cellulose content,Its high value utilization has a very positive significance for the development of new energy sources,chemical raw materials and environmental protection.However,due to its large molecular weight and low activity,it has not been fully utilized for a long time,resulting in a great waste of energy.In this paper,the cleavage reaction of ether bond in lignin under different basic catalysts was studied.At the same time,low molecular weight,polyhydroxy functional active degradation products are substituted for phenolic alcohols to prepare lignin-based phenolic resin(LPF).First,corncorb lignin are chosen as raw materials considering grass lignin has a large amount in China.Element composition,functional group structure,the number of phenolic hydroxyl groups and the thermal decomposition properties of the raw material corncob lignin were analyzed by elemental analysis,GPC,FT-IR,UV,1H-NMR and TG.The results showed both molecular weight and molecular weight distribution of the raw material was broad,which is difficult to be directly used in the synthesis of phenolic resin.Due to the relative content of hydrogen and oxygen in lignin,the ether bond,methoxy group and hydroxyl group have higher content.Second,we used NaOH and KOH as catalyst to degrade lignin by microwave assisted.The effects of microwave and conventional heating methods,reaction temperature,reaction time and soaking ratio on the activation of lignin were investigated.The results showed that the alkali activation reaction of lignin mainly occurred in the hydrolysis of ether bond,and the new phenolic hydroxyl derivative was formed.Microwave heating can greatly improve the efficiency and efficiency of the activation degradation reaction.At the same time,the optimum technological conditions of these two different alkali degradation lignin were established:reaction temperature 160 ?,reaction time 45 min,mass ratio of lignin to alkali 1:1.Under these conditions,the weight average molecular weight of lignin decreased to 2100 and 1840 respectively,and the content of phenolic hydroxyl groups increased by 58.4%and 50.8%,respectively.CaO/MgO and KOH/SBA-15 solid base catalysts were prepared by impregnation method.The preparation conditions of solid base catalysts were optimized,and the degradation efficiency of two kinds of solid bases under different experimental conditions was also investigated.It was found that the higher the alkalinity of the solid base,the greater the catalytic efficiency.Under optimum preparation conditions,the basicity of CaO/MgO solid base can reach 29.2,and the basicity of KOH/SBA-15 solid base can reach up to 18.9.The results showed that the phenolic hydroxyl content of degraded lignin was significantly higher than that of corncob lignin,the highest growth rate was 78.2%and 70.2%respectively,at the same time,both molecular weights and molecular weight distribution of lignins were decreased.The lignin molecules were more homogeneous after degradation,and the number of active functional groups of lignin increased,while the lignin reactivity was enhanced.This makes it more suitable for the preparation of lignin-based phenolic resin.Finally,we used modified corncob lignin to replace and partially replace phenol to synthesize lignin-based phenolic resin,and the basic properties of LPF were tested.Experimental results showed that LPF synthesized by lignin with alkali activation and solid alkali activation all had good performance,in line with national standards.When the amount of modified lignin substitute phenol reached 50%,the LPF was prepared with highest industrial value.