One-pot Base-free Conversion Of Glycerol To Alkyl Lactate Using Heterogeneous Catalysts

As renewable resources,biomass can be used as an alternative to fossil resources.This can relieve the economical and environmental stress from excessive consumption of fossil resources.Conversion of biomass to fuel and high-value chemicals has attracted much attention.As a platform compound,Lactic acid(ester)has wide uses.As the main by-product of biodiesel industry,glycerol has a huge annual output.Researching on catalytic conversion of glycerol to lactic acid(ester)has great scientific significance and application value.Here,a bifunctional Au/Sn-USY catalyst was designed and prepared for the reaction of base-free one-pot synthesis of alkyl lactate from glycerol.The effects of preparation conditions of catalysts and reaction conditions on the structure and catalytic performance were studied in detail.(1)Influence of the pH of Au solution: lower(pH = 1)or higher(pH = 7)pH value would lead to the formation of large Au nano particles(Au NPs)(> 10 nm).This caused the decrease of catalytic activity.When the pH value was 3 or 5,the size of Au NPs were smaller(< 10 nm).(2)Effect of the mass ratio of Au to PVA: when the mass ratio was 1,Au NPs with average particles diameter of 6.2 nm were obtained.However,decreasing or increasing the mass ratio resulted in an increase of average particles diameter of Au NPs.(3)Effect of the Sn content: when the content of Sn was 0 wt% to 2 wt%,the Sn species were inserted into the framework via the reaction with the silanols in the hydroxyl nests that were created by dealumination.When the content of Sn was more than 2 wt%(such as 3 wt% or 4 wt%),the excess Sn could react with the silanols groups around the mesopores.This part of Sn became extra-framework species and the interaction between Au and Sn made Au nanoparticles tend to locate at the Sn sites around the mesopores.As a result,Au nanoparticles were smaller and dispersed well.After modification of the synthesis conditions of the catalysts,reaction conditions including reaction time,reaction temperature and catalyst amount were also modified.79% yield of methyl lactate with 90% selectivity was achieved at 160 oC for 10 h.Subsequently,the conversion of glycerol to alkyl lactate at low temperature was investigated.Our group has realized the conversion of 1,3-dihydroxyacetone(DHA)to alkyl lactate at room temperature.Thus,this work focuses on the synthesis of DHA from glycerol at low temperature.Au/CuO catalysts were prepared with different source of CuO and used for synthesis of DHA from glycerol in methanol at low temperature.The physical and chemical properties of CuO supports prepared with different precursor are different dramatically.The catalyst prepared through the decomposition of copper acetate has the best performance.Yield of DHA and conversion of glycerol were 33% and 55%,respectively(50 oC,4 h).Thus,conversion of glycerol to intermediate product DHA in methanol at low temperature was realized.