Highly Efficient Oxidation Of Lactate To Pyruvate Catalyzed By High Stable TS-1

As an important organic carbon resource,biomass reserve is abundant and the regeneration cycle is short.Replacing fossil resources with biomass can alleviate the environmental pressures caused by the depletion of fossil resources.The catalytic conversion of biomass to produce high value-added chemicals is one of the important strategies for the efficient use of biomass resources.Pyruvate is an important chemical raw material and intermediate,and has a wide range of uses in the food,cosmetics,spices,pharmaceuticals and other industries.Lactate is important biomass-based platform compounds which are abundant in origin and can be easily prepared from raw materials such as cellulose,starch,and sugar.Pyruvate and lactate have structural similarities.It is of great scientific significance and application prospect to design and develop a highly efficient catalytic system for the conversion of lactate to pyruvate.In this paper,by using H₂O₂?30 wt%?as an oxidant,highly efficient oxidation of ethyl lactate?ELA?to ethyl pyruvate?EP?was realized under low-temperature over MFI titanium silicalite?TS-1?catalyst without adding other solvents.After reaction at50^oC for 9 h,the conversion of ELA and EP yield reached 100%and 97.8%respectively.The conversion rate of ELA is sensitive to the reaction temperature.At70 ^oC,100%ELA conversion and 97.9%EP yield were obtained after only 1.5 h.However,high reaction temperature?70^oC?increases the rate of EP decomposition while increasing the rate of ELA conversion.Continued prolonged reaction time led to a dramatic decrease in EP yield.The results showed that the decomposition of the product mainly comprised the hydrolysis and decarboxylation side reactions of EP.The main by-products were acetic acid and CO₂.In addition,based on the characterization results?pyridine-FTIR and UV-vis?and the compare reaction results,it was confirmed that the catalytically active species was Ti?OOH?in the catalytic system.Meanwhile,this paper also proposes the catalytic mechanism of this process.First,the active species Ti?OOH?is fromed by H₂O₂ on Ti?OSi?₄ in TS-1.Then,the hydroxyl group of ELA reacts with Ti?OOH?leading to dehydration.After that,desorption of EP from TS-1 occurs,and Ti?OH?species form.Finally,dehydration occurs between Ti?OH?and Si?OH?,and Ti?OSi?₄ species are reformed.The catalytic cycle is completed.Furthermore,through the kinetic analysis of the reaction results,it was determined that the rate-determining step was the formation step of the Ti?OOH?species,and the activation energy of the reaction was measured to be 103.4 kJ mol^-1.This paper also studied the stability of the catalyst and the separation of the product.In terms of catalyst stability,without any treatment,it was used for the next reaction directly.After ten times runs,the conversion rate of ELA and the yield of EP hardly decreased compared with the first time.It indicates that TS-1 is very stable in this reaction.The structures of the catalysts before and after the reaction were characterized by XRD,N₂ physisorption,pyridine-FTIR and ICP.After ten times runs,it was found that the structure of TS-1 remained basically unchanged.The high performance stability and high structural stability exhibited by TS-1 facilitate the industrialization of this process.In terms of product separation,using methylene chloride as extracting agent,a 91.3%extraction rate of EP and 97.9%purity were obtained after five parallel extraction.