Study On Isomerization Of N-Butane Over Pt Modified Sulfated Zirconia Catalyst

C₄ resource is an important petrochemical raw material,which mainly originates from the catalytic cracking unit and the steam cracking for ethylene unit.With the development of alkylation,isobutane is in short supply and the utilization of n-butane is low.Therefore,n-butane isomerization can not only make use of n-butane,but also meet the domestic demand for isobutane and improve the economic benefits of C₄ resources.The effects of alumina and sulfated medium on the catalyst are investigated in this paper.When the content of aluminum is 4 wt.%,the reaction effect of sulfated zirconia catalyst?SZA?is the best.Using sulfuric acid as vulcanizing agent is the best for n-butane isomerization.The impregnation method has little effect on the n-butane isomerization performance.Hydrogen plays a major role in the interaction with the sulfated catalyst in the reaction.A better reaction result can be obtained at the reaction temperature of 200 ?,the feed velocity of 0.60 h^-1 and the ratio of hydrogen hydrocarbon of 0.31.The loading amount of Pt has an influence on the n-butane isomerization reaction.The best performance can be obtained at the mass loading of 0.05 wt.%,indicating that there is an optimal ratio between the metal active site and the acid site.In the process of catalyst preparation,the impregnation order of sulfuric acid and chloroplatinic acid can affect the performance of n-butane isomerization.The catalyst impregnated sulfuric acid has the best performance,followed by co-impregnation and the worst is to impregnate the chloroplatinic acid firstly.The sulfuric acid impregnated catalyst can be used to anchor Pt atoms and prevent the loss of S and Pt.The influence of pre-reduction process on the performance of the catalyst is investigated.The best performance can be obtained at the catalyst calcination temperature of400 ?,reduction temperature of 300 ? and reduction time of 2 h.The stability of platinum modified catalyst is obviously better than that of unmodified catalyst when the olefins are contained in the raw material.The Pt in the catalyst is very sensitive to sulfur and arsenic compounds in the raw materials.The introduction of Pt into the sulfated zirconia catalyst by mechanical mixing can also improve the activity and slow down the deactivation of the catalyst.Pt/Al₂O₃ and SZA can have a synergistic effect and this synergy does not require the formation of a certain kind of chemical bond,but requires a good contact between the two catalysts.The space between the two kinds of active sites determines the diffusion rate of butene intermediate species.The metal Pt in the Pt/SZA catalyst obtained by direct impregnation also acts as a catalyst for the hydrogenation of n-butane dehydrogenation to isobutylene and promotes hydrogen spillover reaction.In the mechanical mixing isomerization catalyst,metal active components have an effect on n-butane dehydrogenation and isobutene hydrogenation,but it plays a major role in promoting hydrogen spillover reaction.The adsorption and dissociation of H₂ at the Pt active sites exhibit a high hydrogenation activity of hydrogen proton?H⁺?and hydrogen anion?H^-?.The heterogeneous intermediates generated during the reaction can be rapidly hydrogenated and saturated to obtain isobutane,which can reduce the secondary reaction of unsaturation species,such as agglomeration and coke generation,and improve the selectivity of isobutane.