Study On The Performance Of Catalyst For Ethanol To 1.3-butadiene

As an important basic chemical raw material,1,3-butadiene is mainly produced by C4 fraction extraction and depends on petroleum resources.In order to reduce the dependence on the petroleum route,it is of great significance to study the production of butadiene from ethanol.After removing aluminum from Al-βmolecular sieve to produce silanol nests,the introduction of metals can be used to convert ethanol to butadiene.Since the Si-O-Al bond is relatively stable,it is difficult to generate silanol nests by removing aluminum:concentrated nitric acid is required,and the treatment time is long.The removal of B in the B-βmolecular sieve is relatively simple:no concentrated acid is required,the treatment time is short,and the boron removal efficiency is high.Based on this,B-βmolecular sieves were synthesized by hydrothermal method.After alkali treatment to introduce mesopores,acid elution was performed to remove boron to generate silanol nests.Metal zinc and yttrium are introduced into beta molecular sieve silanol nests,and the obtained catalyst is used for ethanol conversion to produce butadiene.The main research contents and results are as follows:By adjusting the dosage of ammonium fluoride,sodium hydroxide and boric acid in the system,B-βmolecular sieve with a silicon-boron ratio of 10-50 was synthesized hydrothermally.The results show that when the nano-sized B-βmolecular sieve with a silicon-boron ratio of 30 is used as the precursor,the selectivity to butadiene is 49.1%.The skeleton boron was removed by hydrochloric acid and then metal was introduced.The effects of hydrochloric acid concentration and calcination temperature on the physicochemical properties and catalytic activity of the catalyst were investigated,and the appropriate hydrochloric acid treatment concentration（1 mol/L）and calcination temperature（550℃）were screened to prepare the catalyst.The effects of metallic zinc and yttrium on ethanol dehydrogenation and C-C coupling were investigated overβ-HCl-1Zn,β-HCl-4Y andβ-HCl-1Zn4Y catalysts,as well as the synergistic effect of zinc and yttrium on catalysis performance impact.The dehydrogenation of ethanol to acetaldehyde mainly occurs at the Zn-Lewis acid site,which has higher dehydrogenation capacity and lower C-C coupling activity.The single Y-Lewis acid site has low dehydrogenation ability,and it is difficult to generate acetaldehyde,which affects the progress of subsequent reactions.Two Lewis acid sites of Zn and Y were combined inβ-HCl-1Zn4Y,and there was a synergistic effect between Zn and Y,which promoted the conversion of ethanol to butadiene.B-βzeolite was treated with alkali to introduce mesopores,and the effect of alkali treatment on the structure and catalytic activity of the catalyst was explored.The results show that the inner framework of the molecular sieve is destroyed when treated with sodium hydroxide and ammonia water inorganic base,which reduces the catalytic activity.When treated with 0.1mol/L TEAOH at 65℃,mesopores were generated without destroying the framework structure of the molecular sieve,which increased the specific surface area and the volume of micropores and mesopores of the catalyst,and improved the diffusion of carbon precursors in the molecular sieve pores.It is beneficial to the dispersion of zinc-yttrium species and inhibits the polymerization reaction in the micropores of molecular sieves,thereby enhancing the catalytic activity.Under the reaction conditions of 400℃and 6 h^-1,the butadiene selectivity ofβ-AT₁-HCl-1Zn4Y catalyst was 55.6%,and the ethanol conversion rate was 98.5%.The stability of theβ-AT₁-HCl-1Zn4Y catalyst was investigated,and the reason for the deactivation of the catalyst was preliminarily discussed.It was found that the coke compound formed during the conversion of ethanol to butadiene could lead to partial blockage of the pores,covering the active species of zinc and yttrium,making it impossible to further reaction.After24 h of reaction,theβ-AT₁-HCl-1Zn4Y catalyst was calcined in air at 600℃for 6 h,and the catalytic performance could be roughly recovered.Coking was one of the main reasons for the deactivation of the catalyst.