Catalytic Conversion Of C₃ Sugars To Lactic Acid And The Reaction Kinetics

Biomass is the unique carbon-containing renewable resource on the Earth.It has many reamrkable advantages,for example,sustainable,carbon neutral,and widely spreaded.Therefore,efficient conversion of lignocellulose to high value-added chemicals has been a hot topic in view of the increasing environmental pollution and energy crisis.Lactic acid,one of multifunctional platform chemicals,is widely used in chemical,food,pharmaceutical and cosmetics industry.Currently,lactic acid is produced by fermentation process.However,there are some disadvantage of this method,such as low yield,high energy consumption,high cost and difficulty purification.Therefore,it is important to prepare lactic acid from inexpensive renewable lignocellulose.Among the process of cellulose to lactic acid,the catalytic conversion of C₃ sugars is the key step and rate-determining step.Hence,the design and study of a novel catalytic system for the efficient conversion of C₃ sugars to lactic acid under mild conditions is of great significance for the production of renewable biomass-based lactic acid.The main purpose of this paper is to screen out suitable metal salts and prepare solid acid catalyst,which can produce lactic acid from C₃ sugars with high selectivity under mild conditions.In addition,we also explore the dynamic behavior and catalytic mechanism of the process.The main study is as follow.?1?A new system of dihydroxyacetone to lactic acid catalyzed by commercial metal salts was constructed.A series of metal salts were screened according to their catalytic activity.It was found that aluminum salts and tin salt had better catalytic activity than other metal salts,especially aluminum salts.Under the optimum conditions,the conversion of dihydroxyacetone was 100%and the yield of lactic acid was 82%catalyzed over Al?NO₃?₃.According to the reaction kinetics study,the conversion of dihydroxyacetone to lactic acid can be divided into two first-order reactions.The activation energy required for hydrolysis of dihydroxyacetone to pyruvaldehyde is 58.48 kJ/mol,and the activation energy for the conversion of pyruvaldehyde to lactic acid is 44.54 kJ/mol.?2?A new type of tin phosphate catalyst was designed and constructed,and its catalytic process and mechanism for the conversion of dihydroxyacetone to lactic acid were studied.A series of tin phosphate catalysts were prepared and used to prepare lactic acid from dihydroxyacetone.The optimum reaction conditions were determined through various experiments.Under the optimum conditions,the conversion of dihydroxyacetone was 100%and the yield of lactic acid was 76%.The reaction of dihydroxyacetone to lactic acid catalyzed over tin phosphate was in accordance with the first-order reaction kinetics.The activation energy of dihydroxyacetone to pyruvaldehyde was 76.42 kJ/mol,and the activation energy of pyruvaldehyde to lactic acid was 97.22 kJ/mol.After 18 times recycle,the catalyst was still active.Analyzed by FT-IR,BET,EA and other methods,it was found that the increase of carbon deposition in the catalyst was the main reason for the decrease of lactic acid yield.