Construction Of A Novel Sulfonic Acid Functionalized Carbon-based Solid Acid And Its Catalytic Biodiesel Synthesi

The decline in conventional fossil fuel reserves worldwide poses an even greater challenge to the energy future.Biofuels are found to be a promising alternative to the dwindling fossil fuels.Biodiesel is a kind of sustainable biofuel developed from renewable resources with low pollutant emission.With the development of green chemistry,the use of ideal biomass-based catalysts for efficient biodiesel production of renewable liquid biomass has been paid more and more attention.The environmental protection and excellent performance of sulfonic acid biochar catalyst make it a research hotspot in biodiesel production.However,the complicated and strict sulfonation process is one of the major defects of traditional carbon-based sulfonic acid catalysts.At the same time,it is worth noting that significant mass transfer obstruction is also an important aspect of heterogeneous biodiesel production catalytic system.In this paper,using biomass as raw material,a series of new high-activity sulfonic acid functionalized carbon-based solid acid catalysts were successfully prepared by a simple one-step hydrothermal carbonization and sulfonation process under relatively mild conditions.The adsorption of the catalysts to the reactants was improved by modification,thus improving the mass transfer barrier in the biodiesel reaction system.The details are as follows:（1）A novel sulfonated cellulose carbon-based solid acid catalyst HTC-SO₃H-1was synthesized by one-step hydrothermal carbonization and sulfonation using cellulose as carbon material,which was used for esterification of oleic acid to produce biodiesel.The catalyst is rich in-COOH,which promotes the adsorption of the catalyst to the reaction substrate,improves the mass transfer barrier in the catalytic system,and improves the reaction efficiency.Under the ideal reaction conditions（2℃,5.3 h,7.3wt%,21.9/1）,the biodiesel yield can reach 97.50%.In addition,the catalyst has good reusability,and the biodiesel yield of 80.31%can be achieved after 5 times of repeated use.According to the mechanism study,there is a synergistic effect between-COOH and-SO₃H in the catalyst,which reduces the difficulty of mass transfer between substances in the reaction system and enhances the reaction rate.（2）A novel chitosan carbo-based solid acid catalyst containing nitrogen was prepared by chitosan as raw material.The N element in the catalyst can improve the mass transfer efficiency of the reaction system and make it show better catalytic activity.This is mainly attributed to the synergistic effect between the basic groups（-NH₂）and-SO₃H contained in NTC-SO₃H,which improves the mass transfer barrier in the catalytic reaction system and improves the reaction efficiency.Under the optimal reaction conditions（82℃,4.3 h,4.4 wt%and 18.7:1）,the biodiesel yield could reach98.28%.At the same time,the catalyst has certain reusability,and the biodiesel yield of 82.26%can be reached after repeated use for 5 times.In conclusion,NTC-SO₃H solid acid catalyst prepared from chitosan biomass showed good catalytic performance for esterification of FFAs.（3）On the basis of chitosan,the effects of different sulfonating agents on the properties and activities of catalysts were investigated.A series of sulfonic acid functionalized carbon-based solid acid catalysts were prepared with different sulfonators for biodiesel production.The results show that the prepared solid acid catalysts have certain catalytic activity for biodiesel production.Among them,NTC-NH₂SO₃H catalyst for sulfamic acid sulfonation showed the best catalytic performance（90.47%）in the process of OA esterification into biodiesel,which was related to its relatively good specific surface area,acidity and nitrogen content.Although NTC-NH₂SO₃H has more abundant basic nitrogen,its catalytic activity is worse than NTC-Ts OH,which may be due to the introduction of excessive basic groups leading to the inhibition of the reaction.