Deactivation Behavior Of ZSM-5 Zeolites Modified By Alkali-metal In Dehydration Of Lactic Acid To Acrylic Acid

In recent years,the dehydration of biomass lactic acid to acrylic acid has received wide attention.At present,the zeolites catalyst used for the reaction of lactic acid dehydration to acrylic acid has good initial activity,but its stability is poor.The deactivation behavior of the catalyst is helpful to further enhance the performance of the catalyst.In this paper,the reason of deactivation of ZSM-5 zeolites with different alkali-metal in this reaction was studied,and the catalytic and anti-carbon deposition properties of the monolithic catalytic were explored.In this paper,The deactivation behavior of fresh and regenerated alkali-metal modified catalyst in the dehydration of lactic acid to acrylic acid was studied by XRD,FT-IR,TG-DSC,XPS.It was found that the deactivation of Li-ZSM-5 is mainly due to the formation of ketones or aldehydes coke precursors from acetaldehyde and acrylic acid at the acid sites,furthermore carbon deposits of low hydrocarbons and high hydrocarbons,which resulted in decrease of active sites.Na-ZSM-5 is mainly the reaction intermediate sodium lactate is decomposed into sodium propionate and sodium acetate.It will be further polymerized with lactic acid to form polycarboxylate.The reaction intermediate sodium lactate is reduced and deactivated.the formation of sodium polycarboxylate,the reaction intermediate sodium lactate reduced result in deactivation.K-ZSM-5 forms a large amount of ester material to cause catalyst agglomeration.the deactivation of Li-ZSM-5 is mainly due to the formation of unsaturated small molecule coke precursors,furthermore carbon deposits of low hydrocarbons and high hydrocarbons,which resulted in decrease of active sites.The catalyst is regenerated by calcining,if incomplete removal of the carbon species deposited in the catalyst surface will lead to an increase in carbon deposition rate during the next cycle,and accelerating the rate of active sites reduction,so the stability of Li-ZSM-5 and Rb-ZSM-5 decrease.After the regeneration of Na-ZSM-5,the rate of sodium polycarboxylate species was decreased and the stability of the catalyst was increased due to the formation of Na₂O as the surface sodium species.The Na-ZSM-5/cordierite monolithic catalyst was prepared by coating method.The catalytic performance and carbon deposition of lactic acid were investigated by different loading and reaction process conditions including liqure space velocity,lactic acid concentration and reaction temperature.It was found that the monolithic catalysts and granular catalyst deactivation mechanism.And the loading of 20.7%when the highest yield of acrylic acid,the minimum amount of carbon deposition is7.62%,the best anti-carbon deposition capacity.Optimum reaction conditions,liqure space velocity 2.43 L·g-1·h-1,reaction temperature 365℃,lactic acid concentration39%.Under the optimal loading and optimal conditions,the stabitity of the catalyst was 128h,and the amount of carbon was 22.34%.