Study On The Catalysts For Dehydration Of Methyl Lactate

At present,the demand for energy is increasing dramatically,and the dependence on primary energy makes human face the dual crisis of energy depletion and global warming.As the only sustainable carbon energy,biomass is the most important alternative resource of fossil fuel in current energy situation.Efficient conversion of biomass is an important measure to achieve the goal of carbon peak and carbon neutralization.Lactic acid/Lactate is one of the platform molecules with research significance.Acrylic acid/Acrylate prepared by catalytic dehydration of lactic acid/lactate is an important industrial intermediate,which has broad application fields.The dehydration of methyl lactate is an acid catalyzed reaction,the acidity of the catalyst is decisive to the product distribution.Based on the low selectivity of acrylic acid/acrylate and the poor stability of the catalyst in the catalytic dehydration of lactic acid/lactate,a reducible acid supported tungsten catalyst was proposed,including non stoichiometric tungsten oxide and transition metal tungstate.In this paper,the catalytic dehydration of methyl lactate was evaluated in a packed bed reactor.The acidity,crystal and electronic structure of the catalyst were characterized by XRD,H2-TPR,Raman,XPS,NH3-TPD,Py-IR.Firstly,the reduction of methyl lactate was dominated by tungsten oxide support.The conversion of methyl lactate was 70.5%and the selectivity of acrylic acid/acrylate was 13.9%when the catalyst hydrogenated at 200℃.The selectivity of 2Na/WO3 catalyst increased to 38.2%after adding basic metal;The conversion of methyl lactate was 54.7%and the selectivity of acrylic acid/acrylate was 42.8%after 8 h reaction on NiWO4.The selectivity increased to 45.3%after further optimization of reaction conditions.Furthermore,the characterization results of structure and acid sites of tungsten based oxide catalysts were summarized.On the tungsten oxide catalyst,there is a positive correlation between the hydrogenation temperature and oxygen vacancy concentration.Oxygen vacancy is the active site for the reduction of methyl lactate and participates in the catalytic cycle.There is an interaction between WO3 support and metal additives.Strong interaction leads to decarbonylation reaction,and weak interaction leads to reduction reaction.The interaction between W&O with divalent metals of different tungstate catalysts is different.The coordination mode of Ni-O-W is beneficial for the dehydration of methyl lactate.In this study,the acidity of the catalyst is derives from Lewis acid.The reduction reaction tends to occur when the number of acidic sites is large.Numerous acidic sites result in reduction reaction,weak acidity and less acidic sites result in dehydration reaction,a wide range of acidity result in decarbonization reaction.