Synthesis Of Lactate And Calcium Lactate By Hot Dehydrogenation Of Glycerol On Supported Copper-based Catalysts And Reaction Kinetics

With the increasingly serious environmental pollution caused by plastics,the research and development of biodegradable plastics has attracted the attention of domestic and foreign rescuers.Polylactic acid and its copolymer have good biodegradable properties and can replace traditional biodegradable polyethylene（PE）and polyvinyl chloride（PVC）.The traditional production of lactic acid monomer uses saccharide fermentation technology,which has the disadvantages of low yield and high cost,restricting the development and application of polylactic acid.New lactic acid synthesis technology is worthy of research and exploration.In addition,as an important food and medicinal compound,calcium lactate is generally synthesized by neutralizing reaction between lactic acid and calcium hydroxide.As raw lactic acid comes from saccharide fermentation,the production cost is high.The production of glycerol,the main by-product of biodiesel,accounts for 10%of the total production of biodiesel,with an annual output of more than 3 million tons.The market demand for glycerol is in a state of oversupply.The synthesis of high value-added lactic acid and calcium lactate from low value-added biomass glycerol has attracted the attention of domestic and foreign researchers.It has good theoretical and practical value to study a new,clean and environmentally friendly preparation technology of lactic acid and calcium lactate.The synthesis of lactic acid and calcium lactate from glycerol in alkaline aqueous solution by supported copper-based catalyst was studied.The effects of catalyst carrier,type of alkaline solution and reaction temperature on catalytic activity about the formation of lactic acid and calcium lactate from glycerol in alkaline aqueous solution catalyzed by copper base catalyst were studied.A new technical route of synthesis of lactic acid and calcium lactate from biomass glycerol was formed.The main research content and innovation of this paper are as follows.（1）Cu/HA,Cu/C and Cu/Na₂Ti O₃ catalysts with nanometer copper as active center were prepared by chemical precipitation method with hydrazine hydrate as reducing agent,and were used to catalyze the synthesis of calcium lactate by glycerol in Ca（OH）₂ aqueous solution.The results show that zero-valent copper nanoparticles are the active center for the synthesis of lactic acid by dehydrogenation of glycerol under alkaline conditions.Compared with the low alkaline Cu/C catalysts,the high alkaline HA nanorods and titanate nanocrystalline supported Cu catalysts have higher catalytic activity.Copper and carrier synergistically catalyzed the synthesis of calcium lactate from glycerol and Ca（OH）₂.With Cu（16）/HA catalyst as the catalyst,the conversion rate of glycerol and the selectivity of calcium lactate can reach 92%,91%at the molar ratio of Ca（OH）₂ to glycerol of 0.6:1.0,230 ^oC and 2-4 h,respectively.The activation energy（Ea）of Cu（16）/HA catalyst is 43.85 k J mol^-1.Calcium lactate was separated from the reaction liquid by evaporation crystallization technology.The yield and purity of calcium lactate products were 87.9%and 95.5%,respectively.（2）A series of CuO/CaO and Cu/CaO supported by calcium oxide were prepared by impregnation,calcination and H₂ reduction.The catalytic activity of CuO/CaO and Cu/CaO catalysts for glycerol dehydrogenation to lactic acid in Ca（OH）₂ alkaline aqueous solution was studied.Compared with CuO/CaO catalyst,Cu/CaO catalyst has higher catalytic activity for glycerol dehydrogenation to lactic acid.It is attributed to the high catalytic glycerol dehydrogenation activity of copper nanoactive sites,thus improving the selectivity of lactic acid.Cu（8）/CaO and Cu（16）/CaO catalysts catalyzed the glycerol dehydrogenation at a weight ratio of5:100,a molar ratio of Ca（OH）₂ to glycerol of 0.8:1,230℃,and a reaction time of 4～6 h,the glycerol conversion rate was between 91.4%and 98.8%.And the selectivity of lactic acid ranges from 91.1%to 97.1%.Reaction kinetics simulation results show that the activation energies of dehydrogenation on CuO（16）/CaO and Cu（16）/CaO are 102.8 and 22.2 k J mol^-1,respectively.The active component of Cu can catalyze glycerol dehydrogenation more effectively than the active component of CuO.（3）Cu catalysts supported by HAP nanorods were prepared by impregnation（or deposition）,calcination and reduction.The preparation of Cu/HAP catalysts under different impregnation（or deposition）p H values was studied.The catalytic activity of Cu/HAP catalysts for glycerol dehydrogenation to lactic acid in sodium hydroxide aqueous solution was also studied.It was found that under the conditions of 210℃and the Na OH/glycerol molar ratio of 1.1:1.0,Cu（2）/HAP（p H=5,7,9 and 11）catalysts catalyzed the hydrothermal reaction of glycerol for 2 h,the glycerol conversion rate was between 32.3%and 45.9%.Lactic acid selectivity ranged from50.8%to 84.3%.The Cu/HAP catalyst with high copper content prepared under high alkaline condition has high catalytic activity of glycerol dehydrogenation to lactic acid.The kinetics results show that the activation energies of Cu（2）/HAP（p H=5,7,9 and 11）catalysts for glycerol dehydrogenation are 78.8,66.6,56.4 and 50.8 k J mol^-1,respectively.The preparation of Cu active component in Cu（2）/HAP catalyst can catalyze glycerol dehydrogenation more effectively and reduce the energy barrier.