Study On Synthesis And Catalytic Performance Of ZSM-35

As an important organic chemical raw materials, isobutene is mainly used for producing methyl tert-butyl ether (MTBE), butyl rubber, tert-butanol and other fine chemicals. However, in recent years, because of the increasing demand for MTBE, the isobutene from traditional catalytic cracking of petroleum can't meet the market demand. Therefore, finding more efficient ways to produce isobutene has an important practical significance. Among them, the isomoerization of n-butene has many advantages, such as a simple process, mild operation condition, no corrosion to equipment, cheap and abundant raw materials(the C4 fraction coming from steam cracking or catalytic cracking and the surplus resources of n-butene) and so on. Especially combining it with the synthesis technology of MTBE can not only improve the utilization rate of C4 fraction, but also increase the yield of MTBE, which has become the most promising method for the production of isobutene.The ten-memebered ring zeolites show extremely high selectivity in the skeletal isomerization of n-butene. Besides, the stability of these catalysts is superior than the traditional ones. ZSM-35, which has a two-dimensional pore system with eight-membered rings intersected by ten-membered rings, is one with the highest selectivity, the best stability and the greatest industrial application value.In this paper, by using silicon sol as silicon source, sodium aluminate as aluminum source, ZSM-35 with high crystallinity and purity was synthesized under the dynamic hydrothermal condition. The samples under different synthetic conditions were analyzed by X-ray analyzer. The results show that:when the crystallization temperature is 170?, the crystallization time is 40h, the silica alumina ratio is 30, the temple agent is CHA, n(CHA)/n(Al2O3)=6, n(Na20)/n(Al203)=3.3-3.6, n(H2O)/n(Al2O3)=900, we can quickly get a series of ZSM-35 with high relatvie crystallinity. Besides, we successfully synthesized ZSM-35 by adding non-calcined ZSM-35 seeds to the initial gel without the help of organic structure-directing agents. However, it should be noted that the seed-assisted, organic structure-directing agent(OSDA)-free synthesis often leads to lower crystallinity in comparison with the conventional synthesis.Synthesized ZSM-35 zeolites were applied to the skeletal isomerization of 1-butene. We systematically investigated the effects of reaction temperature, WHSV, N2 dilution and other technological conditions on the isomerization performance of the catalyst. Experimental results show that:when the reaction temperature is 380?, the WHSV is 19h-1 and the rate of inactive gas (N2) flow is 100ml/min, the amount of by-product generated in the reaction is relatively small and the catalyst shows good catalytic activity and high selectivity.ZSM-35 molecular sieve was modified in different conditions. The results show that:(1) appropriate degree of ammonium exchange can effectively regulate the acid center distribution and the acid amount of the molecular sieve. When the concentration of the exchange liquid NH4NO3 is 0.6mol/L, the modified catalyst can give the highest yield of isobutene; (2) When the hydro-thermal treatment temperature is 400?, hydrothermal modification can effectively promote the removal of aluminum from the framework of molecular sieve, decrease strong acid amount, improve pore canal structure and increase the selectivity of target product; (3) When the loading amount of phosphorus surpasses 1.0w%, the non selective activity center on the ZSM-35 surface can be effectively deactivated or eliminated. The strong acid amount can be decreased, and the catalytic performance of molecular sieve can be improved.