Study On The Zeolite Catalysts For Dehydration Of Lactic Acid To Acrylic Acid

Acrylic acid is an important monomer of organic polymer.At present,acrylic acid in the industry are produced from two step oxidation method by propylene,and propylene mainly comes from non-renewable resources.As the global oil resources decrease,the cost of two-step oxidation increased.To reduce its dependence on oil resources,the dehydration of lactic acid to acrylic acid arouses widely attention,a lot of literatures have reported the study of the method.This paper took lactic acid as raw material and molecular sieve as catalyst to catalyze dehydration of lactic acid to acrylic acid.In the thesis,we adjusted the type of molecular sieve,Si/Al₂ ratio,catalyst preparation conditions and reaction process conditions to improve lactic acid conversion,acrylic acid yield and catalytic stability.First,the catalytic results of different zeolites?NaY,H?,MCM-41,ZSM-5?have been analyzed and compared in the paper,concluding that NaY and ZSM-5 zeolites can better catalyze dehydration of lactic acid.In contrast with the catalytic activity,selectivity and stability of NaY and ZSM-5,we found that ZSM-5 zeolite has the better catalytic performance and stability.Second,ZSM-5 zeolite were modified by alkaline earth,rare earth and alkali metals.The catalysts were characterized by XRD,TG,CO₂-TPD,NH₃-TPD and Py-IR.The results showed that ZSM-5 catalysts modified by alkali metals?Na,K,Rb,Cs?had the better catalytic performance,and could effectively improve the selectivity of lactic acid into acrylic acid,especially introduction of K⁺,which significantly changed the surface acid-base property and achieved the high acrylic acid selectivity.Combining with the characterization results,it was found that the surface acid-base strength of ZSM-5 modified by alkali metal decreased,the amount of weak acid and weak base site increased,and the nature of acid-base mainly showed as Lewis acid-base.The corporation between weak acid and weak base makes lactic acid convert into acrylic acid with high selectivity.On this basis,ion-exchange concentration,temperature,time,calcination temperature of catalyst,and reaction process conditions including reaction temperature,LHSV and flow rate of carried gas were investigated in the process of the ZSM-5 catalyst modified by K⁺to gain influence on lactic acid dehydration reaction.It is concluded that the best catalyst preparation conditions:1 mol/L of KNO₃ solution,exchange temperature 80,exchange time 6h,calcination temperature 550.Optimum reaction conditions:reaction temperature 365,LHSV=0.94h^-1,carrier gas flow rate 50 ml/min?P=0.15 MPa?,under the optimal conditions,the lactic acid conversion 95.21%,the acrylic acid selectivity76.47%.Finally,KZSM-5 catalyst,which was prepared under the optimal conditions,has been investigated with the stability and regeneration performance,it is concluded that the KZSM-5 catalyst has good stability and regeneration performance,which has the good prospects for industrial application.