Study On Catalytic Dehydration Of Methyl Lactate To Acrylic Acid(Ester)

At present,facing the rising energy demand and environmental crisis,all countries are committed to adjusting the energy structure and increasing the proportion of renewable energy.Among them,biomass energy has attracted extensive attention.Acrylic acid（ester）is an important raw material for organic synthesis.At present,the production of acrylic acid mainly comes from petrochemical products.Therefore,the development and utilization of biomass resources to synthesize acrylic acid（ester）is one of the important directions.Lactic acid is one of the ten platform molecules of biomass,so the catalytic dehydration of lactic acid（methyl lactate）to prepare acrylic acid（ester）has important research value.In this paper,in view of the problems of difficult adjustment of acidity and poor stability of methyl lactate dehydration catalysts,an attempt was made to use partially reducible WO₃ and its tungstate NiWO₄ as the main catalysts to control the acidity and active sites through reduction;The modification of alkali metal phosphate or alkali metal salt was carried out.Finally,WO₃ was supported on CaSO₄ with better dehydration selectivity to explore the influence of the catalyst stability.The catalyst crystal structure and surface acidity were characterized by XRD,NH₃-TPD,Py-IR and other characterization methods.First,when the reduced WO₃ is used as the catalyst,the dehydration performance of methyl lactate is poor.Therefore,it was modified with alkali metal phosphate,and the dehydration performance on 2K₂HPO₄/WO₃ was the best,and the selectivity and conversion were 30.1%and 70.7%,respectively.Secondly,when NiWO₄ was used as catalyst,the reaction activity and stability were improved compared with WO₃.After alkali metal modification,the stability of 2K/NiWO₄ was significantly improved.The conversion rate was70.1%at the 8th hour,and the average selectivity was 50.6%.Finally,the dehydration reaction of methyl lactate on CaSO₄ was explored.The results showed that its acidic conditions were very suitable for the dehydration reaction,and the selectivity was much higher than that of WO₃ and NiWO₄,which was83.2%.After hydrogenation reduction,the dehydration performance of CaSO₄has increased,but the deactivation was still fast.Therefore,it was modified with W promoter,and the stability of catalyst on 4W/CaSO₄ was greatly increased.In the stability investigation experiment,the conversion rate after 22 hours of reaction is 69.2%,which is more than 3 times longer than that of unmodified CaSO₄.From the characterization results of the catalyst,it can be seen that hydrogenation reduction will increase the concentration of oxygen vacancies on the surface of the catalyst and enhance the activity and acidity of the catalyst.However,too strong acidity is not conducive to dehydration reaction,so different catalysts have different requirements for reduction conditions.The addition of alkali metals and their phosphate promoters can weaken the surface acidity of the catalyst.The interaction force between different promoters and catalysts is different,and the surface acidity and product distribution are also different.When the acidity is too weak,the activity and dehydration selectivity of the catalyst are low,so there is an optimal loading amount of the promoter.All the catalysts in this subject only have Lewis acid centers,and the dehydration reaction of methyl lactate is more likely to occur in weaker acidity and with a suitable amount of acid.