Study On The Catalytic Performance Of Composite ZSM-5/MCM-41 Catalyst For Ethanol Dehydration

Compared to the conventional zeolite catalysts, the ZSM-5/MCM-41 composite catalyst with meso-microporous structure exhibit greatly catalytic performance. The ZSM-5/MCM-41 composite catalysts were made by mechanical kneading method and the hydrothermal method, and the catalytic performance of the catalysts was evaluated in a continuous flow fixed-bed reactor, using the ethanol dehydration reaction as the probe reaction. The influences of the preparation conditions, impregnation modification and the ion exchange modification on the performance of catalyst were investigated.The evaluate results of catalysts prepared by the mechanical kneading method and the hydrothermal method showed that the suitable mass ratio of ZSM-5: MCM-41 is 8:2 for the desired catalyst; using ZSM-5 as silica source, the appropriate preparation conditions of ZSM-5/MCM-41 composite with the mass ratio 8:2,prepared by the hydrothermal method were as follows, crystallization temperature110?, crystallization time 48 h, crystallization pH 9.5, n(CTAB): n(SiO2) =0.3.The evaluate results of modified composite ZSM-5/MCM-41 catalyst showed that the modifications of Zn?Ni?Co impregnation were no any improvement to the catalytic performance of the catalyst, but the modification of phosphorus(P)impregnation(P mass/catalyst mass = 0.3%), effectively improved the catalytic ethanol dehydration performance of ZSM-5/MCM-41, and the suitable P ion exchange modification conditions were follows, exchange concentration 0.5 P mol/l,exchange time 3h and exchange temperature 80?. The modification function of P ion exchange is better than that of P impregnated method. The characterization results obtained by XRD?NH3-TPD?Py-IR of the catalysts with and without medication showed that the phosphorus modication had no effect on the crystalline phase of the catalyst, but greatly increased the amount of L acid sites,and slightly reduced the amount of B acid sites. Compared with unmodified composite ZSM-5/MCM-41 catalyst, the catalytic activity and the stability of the ZSM-5/MCM-41 catalyst modification with P ion exchange were considerably improved. Under the conditions of standard atmosphere, 295 ?, LHSV 2h-1, the ethanol conversion and ethylene selectivity were both above 98%, and the declining trend of the catalytic activity of the catalyst was not found after running 100 h.The characterization results obtained by TG show that the main reasons of catalyst deactivation are that the deposited coke might block the pores or cover active centers the catalyst. Under the conditions of the speeding deactivation, the carbon amount of the deactivation catalyst is about 8.2% of the catalyst mass. Regeneration of in-situ coke combustion under the conditions of temperature 450?, air flow 50mL/min could effectively recover the activity of deactivated catalyst. After three time regenerations by coke combustion, no difference between the performances of the fresh catalyst and the regenerated catalyst was found.