Preparation And Evaluation Of Micro-mesoporous ZSM-5/γ-Al₂O₃ Composite Catalyst

With the development of the world economy, research on coal tar hydrogenation technology is increasingly important. For the particularity of coal tar, developing dedicated hydrogenation catalyst. Traditional coal tar hydrodesulfurization catalyst mostly used γ-Al2O3 as the carrier, the microporous ZSM-5 is a microporous molecular sieve have high acid resistance, thermal stability and acid. While combines two materials, that can complement each other and interact to meet the purposes of multifunctional catalysis.In this paper, firstly pretreated to γ-Al2O3, then used one step crystallization method to prepare micro- mesoporous ZSM-5/γ-Al2O3 composite materials, and used the materials as hydrodesulfurization catalysts’ carriers of coal tar, supported Pd as the active component, studied its effect on DBT hydrodesulfurization.Firstly, selected pretreatment conditions to prepare micro- mesoporous ZSM-5/γ-Al2O3 composite materials. The effects of pretreatment methods, pretreatment agents and pretreatment time on the performance of composite material were investigated. The products were characterized by XRD, N2 adsorption/desorption, SEM and FT-IR. The results indicate that, TPAOH as the pretreatment agent, and mixed with the γ-Al2O3, heated under reflux condensation for 4h, filtered and immersed in absolute ethanol for 24 h, finally washed and dried. The micro- mesoporous ZSM-5/γ-Al2O3 composite materials under this condition can meet the requirements, that has the best crystalline structure of ZSM-5, the specific surface area is 203.6m2·g-1, holes concentrate around 1nm and 4nm, the grain morphology present ellipsoidal.Secondly, optimized preparation conditions to prepare micro- mesoporous ZSM-5/γ-Al2O3 composite materials, to obtain better crystal structure and pore structure of composite materials. Specific studied the influences of Si O2/Al2O3 and Na2O/Si O2 to the degree of crystallinity. Researched the effects of templates, mass ratio of ZSM-5 to γ-Al2O3, mixing methods, crystallization methods and crystallization time on the pore structure of materials. And their thermal stabilities, hydrothermal stabilities were tested. The results indicate that, the crystallinity of samples are better when Si O2/Al2O3 is 100~150 and Na2O/Si O2 is 0.08~0.09 of ZSM-5 precursor solution, the pore structure of materials are better when template is TPAOH, the mass ratio of ZSM-5 to γ-Al2O3 is 1:1.5~1:3, mixing method is stirred and mixed, crystallization method is two-stage heating and crystallization time is 16h~24h. And thermal stability and hydrothermal stability of the composite materials are excellent.Finally, with DBT as model compounds of sulfur component in coal tar, contrasted hydrodesulfurization effects of four different catalysts: ZSM-5/γ-Al2O3 composite catalyst, ZSM-5, γ-Al2O3 and mechanical mixture of γ-Al2O3 and ZSM-5. The results conclude that the best effect of the hydrodesulfurization is the catalyst that used micro-mesoporous ZSM-5/γ-Al2O3 composite material as the carrier, the hydrodesulfurization rate as high as 97.28%. Contrasted hydrodesulfurization effect of composite catalysts by different conditions. The results indicate that, the preparation conditions of catalyst composite as best hydrodesulfurization effect are: Si O2/Al2O3=150, Na2O/ Si O2=0.09, template is TPAOH, the mass ratio of ZSM-5 to γ-Al2O3 is 1:3, mixing method is stirred and mixed, crystallization method is two-stage heating and crystallization time is 24 h. The GC-MS results show that, the hydrogenation products of tetralin are: naphthalene, cis/trans- decahydronaphthalene and butylbenzene, and the hydrogenation products of DBT are: phenyl cyclohexane and biphenyl.