Preparation Of Monolithic ZSM-5/Cordierite Catalysts On Reaction Process Of Methanol To Olefins

Abstract:Methanol to olefins technology (MTO) is a new process that utilizes coal or natural gas to make ethylene, propylene etc via methanol. It is the most promising route that substitutes the traditional oil route for light olefins. And the research mainly focused on the preparation of catalysts with higher selectivity to olefins.ZSM-5zeolite is one of the effective catalysts. However, zeolites are traditionally used in the forms of powder, which will inevitably increase the path of the product detaching from catalyst and subsequently result in the further reaction. Moreover, the unexpected "hot spot" caused by limited heat transfer area and relatively poor radial heat transfer of catalyst particle packings may also rapidly deactivate the zeolite catalyst as the MTO reaction is strongly exothermic. Therefore, to improve the selectivity of light olefins and the stability of catalyst, monolithic catalysts by loading ZSM-5onto cordierite support were prepared and evaluated in the MTO reaction. The main work and results are as follows.ZSM-5powder and ZSM-5/cordierite were firstly prepared in situ synthesis hydrothermal method. The catalytic performance of the catalysts was evaluated with MTO reaction in a fixed-bed micro-reactor. The effect of silica alumina ratio was investigated on the performance of catalytic activities. Catalysts were characterized by XRD, SEM and NH3-TPD, The result shows that the catalysts prepared by this method have larger crystalline size and a few of strong acid sites. Both ZSM-5powder and ZSM-5/cordierite with SiO2/Al2O3ratio80have the highest selectivity to light olefins, especially ZSM-5/cordierite has a higher selectivity to propylene which increase by18%(from28%to46%), and higher stability compared with ZSM-5powder.ZSM-5powder and ZSM-5/cordierite catalysts were prepared in second synthesis method. The catalysts as-prepared possess smaller particles (100nanometers), higher crystallinity, and barely strong acid sites. The effects of synthesis temperature of the seeding suspension, SiO2/Al2O3ratio, addition of seeds and dip-coating times on the properties of catalysts were studied. The results show that the catalysts possess high catalytic performance when the temperature is80℃. SiO2/Al2O3ratio is80, Addition of seeds on the surface of substrate by the way of dip-coating is more suitable. ZSM-5/cordierite which have the highest selectivity of propylene, which were51%and49.4%, respectively, and higher stability.