The Study Of Catalyst Preparation And Kinetics Of Methanol To Olefins

Methanol to olefins (MTO) is an emerging technology which is the most promising method to replace traditional petroleum cracking olefin route. The research of MTO process focuses on the development of catalysts. Based on the MTO reaction, the experiments of preparation and performance evaluation of SAPO-34catalyst have been carried out. As a result, the optimal catalyst has been selected certainly. The instrinsic kinetic experiments of methanol to olefins over this optimal catalyst have completed, and the intristic kinetic model established here has a good compatibility with the experimental data.SAPO-34molecular sieve was synthesized under the conditions of temperature crystallization200℃and reaction time48h by hydrothermal method. Under a certain formulation of raw materials, we investigated the influence of dual template ratio, Si/Al2O3ratio and P2O5/Al2O3ratio on the performance of SAPO-34molecular sieve, through the method of combining performance evaluation with the characterization of XRD, SEM and TPD. The results showed that, SAPO-34molecular sieves could be synthesized under the investigated range of dual-template ratio in the experiment.when MOR:TEA=1.0:2.0, the synthesized SAPO-34molecular sieve had the relatively best catalytic performance of MTO, the yield of olefins can reached 87.5%. Under dual-template, lower silica-alumina ratio would affect the crystal structure of SAPO-34molecular sieve, leading to the generation of SAPO-5mixed crystal. The relatively appropriate ratio of silica-alumina was0.4. The ratio of P2O5/Al2O3affected the pH of initial gel in the synthesis of the molecular sieve, higher or lower P2O5/Al2O3ratio was not conducive to improve the performance of SAPO-34molecular sieve on MTO reaction, and the relatively suitable P2O5/Al2O3ratio was1.0.The modification effect of rare earth metal ions of La, Ce and Y on SAPO-34by in situ synthesis method was studied. The results showed that:(1) The modification of metal did not affect the crystal structure of molecular sieve, three kinds of metal modified catalysts were pure SAPO-34;(2) Compared with the unmodified SAPO-34, the modification of La, Ce and Y resulted in the slightly decrease of MTO lifespan and olefins yield.Finally, the relatively suitable catalyst formula was:MOR:TEA=1:2, Si/Al2O3=0.4, P2O5/Al2O3=1.0. We have studied the MTO intrinsic kinetics characteristics over SAPO-34molecular sieve which were synthesized with the suitable formulations on a fixed bed reactor under the conditions of temperature400～500℃, WHSV3～6h-1and H2O/CH3OH mass ratio2.0The intristic kinetic model corresponding to the six lumps was established, it has a good compatibility with the experimental datas.