Research On Modification And Molding Conditions Of The Catalysts For Xylene Isomerization

In this paper, HZSM-5with SiO2/Al2O3ratio120was synthesized by hydrothermal method. The zeolite was modified and formed with a series of steps to improve its catalytic ability.Using salt solution of Me(Me=La, Ce, Ni, Co, Zn,Sn) as modifier, single metal modified catalysts were prepared by impregnation method. Their catalytic performance was evaluated and they were characterizated by XRD、XPS、BET、NH3-TPD and Py-FTIR.Finding out that La/HZSM-5gain high PX yield, while Zn/HZSM-5can improve selectivity of the target product. Zn/HZSM-5with0.5%loadings show better performance in its series. Based on experimental results of single metal modification,La-Zn, Ga-Zn bimetallic catalysts were investigated. The evaluation of bimetallic modified catalyst result shows that1%La-0.5%Zn/HZSM-5and1%Ga-1%Zn/HZSM-5showed a relative better m-xylene isomerization performance. Characterization shows that metal modification doesn’t change the structure of zeolite, it optimizes zeolite’s acid distribution. B/L vaule decreases and so does pore size.During molding process, the effect of additives (extrusion promoter, peptizators, hole-expanding agent etc) to zeolite physical properties in the reaction were investigated by single factor experiments.(1) Extrusion promoter and adhesive have little effect on the catalytic performance. Activity is higher when nitrite used as peptizator, its suitable amount is8%. PEG200showed up better catalytic performance while used as hole-expanding agent. Activity becomes higher with its amount15%.(2) Using8%nitric acid as peptizators the catalyst can have good strength; Increasing SB powder help to improve the forming strength; Increasing PEG200as hole-expanding agent is unfavourable for strength.(3) Hole-expanding agent help to promote pore structure,pore size increases with molecular weight while choosing it. Using inorganic acid as peptizator have more aicd when forming; the total acid content increases with PEG200and nitrate.(4) The suitable molding condition is:water powder rotio=0.5g/ml, sesbania powder2.5%, nitrate8%, SB powder30%,PEG20010%.