Study On The Catalytic Oxidation Of Ethyl Lactate To Ethyl Pyruvate Over VPO

Biomass energy is the only carbon-containing energy among many renewable resources.Converting biomass into high-value chemicals not only has high economic benefits,but also effectively alleviates various environmental problems caused by excessive use of fossil energy.Pyruvic acid is a kind of chemical raw material with high commercial value.At present,the tartaric acid dehydration and decarboxylation method which developed in the last century is still used in industry to produce pyruvic acid.This process not only consumes a large amount of KHSO4,but also releases the same molar amount of CO2 as the product,and the atomic efficiency is very low.The yield of pyruvic acid is only 50-55%.Using biomass-based lactate as a raw material,through catalytic oxidation,the hydroxyl in the lactate molecule is oxidized to carbonyl to generate high value-added pyruvate,which not only has high atomic economic efficiency,but also promotes the effective use of biomass energy.Compared with the preparation of pyruvate by the gas-phase catalytic oxidation of lactate,the liquid-phase method has milder reaction conditions and fewer by-products,which is more in line with the green chemistry concept advocated by the country.In the reported liquid-phase method of lactate with O2 as the oxidant,there are disadvantages such as excessive solvent consumption or complex catalyst synthesis steps,which makes it difficult to realize large-scale application.Therefore,looking for a highly efficient heterogeneous catalyst that is easy to prepare with high yield of pyruvate under mild liquid phase conditions has high economic value.Vanadium phosphate oxide(VPO)catalyst has been widely used in the selective oxidation of low-carbon alkanes,and it has also showed excellent performance in the catalytic oxidation of cyclohexanol to cyclohexanone.For this reason,this work proposes and explores VPO catalyzing the oxidative dehydrogenation of ethyl lactate(ELA)to ethyl pyruvate(EP)under mild conditions by the liquid-phase method with O2 as the oxidant.The specific research contents and conclusions are as follows.(1)A two-step method was used to synthesize the precursor VOHPO4·0.5H2O-1 which was further calcined to prepare the VPO-1 catalyst.Its catalytic oxidation performance of ELA to EP with O2 as the oxidant was explored.After reacting at 130℃for 8 h,the conversion of ELA was 98.2%,and the selectivity of EP was 82.5%.(2)An organic phase method was used to synthesize the precursor VOHPO4·0.5H2O-2 which was further calcined to prepare the VPO-2 catalyst.Its catalytic oxidation performance of ELA to EP with O2 as the oxidant was explored.After reacting at 120℃ for 7 h,the conversion of ELA was 98.3%,and the selectivity of EP was 84.5%.(3)The difference in the catalytic performance of VPO-1 and VPO-2 for ELA to EP was investigated.It was found that the adsorbed oxygen content on the surface of VPO-2 is 10.4%higher than that of VPO-1,and its specific surface area(21.3 m2·g-1)is larger than that of VPO-1(4.7 m2·g-1).VPO-2 not only has stronger redox ability,but also has larger contact area with ELA,which improves the reaction rate.Therefore,VPO-2 can achieve a better catalytic effect than VPO-1 at lower reaction temperature and shorter reaction time.(4)In order to improve the dispersion of VPO-2,a series of VPO-2 supported catalysts were prepared,and it was found that VPO-2 supported on hydrophobic SiO2 can achieve the best catalytic performance.After reacting at 120℃ for 7 h,the conversion of ELA reached 99.2%,and the selectivity of EP reached 87.8%,both of which were better than the unsupported VPO-2 catalyst.Through BET characterization,it was found that the specific surface area of VPO-2/SiO2(hydrophobic)reached 314.2 m2·g-1,which was greatly improved compared to VPO-2.(5)The influence of the surface hydrophobicity of SiO2 on the catalytic performance was studied with VPO-2 being loaded with different hydrophobicities.It was found that as the hydrophobicity of SiO2 increased,the selectivity of EP gradually increased.The hydrophobic surface of SiO2 has the repulsive effect on proton acids,thereby reduces the hydrolysis of ELA and EP on the surface of catalyst and improves the selectivity of EP.