Chacterization And Of ZSM-5 Sieve With Small Crystal Size And Its Study On Catalytic Performance

Since it was first reported in 1970s, ZSM-5 zeolite was found to be an important shape-selective catalytic materials due to its unique structure and relative flexible demand for the synthesis system. It was widely used in the petrochemical engineering process, such as hydrocarbon’s selective cracking, alkylation, isomerization, disproportionate, etherification and other areas. For zeolite catalyst, the crystal size of zeolite is an important factor that affects the activity of reaction and the selectivity of product. Compared with micro-size ZSM-5 zeolite, small crystal ZSM-5 zeolite possesses high exterior surface area and shorter pore pathway, so there are lots of apertures and acid sites exposed at the outside surface of the crystal. Thus small crystal ZSM-5 zeolite has strong adsorption ability, excellent diffusion performance and anti-carbon deposition property. Based on the above advantages, small crystal ZSM-5 zeolite aroused people’s great interest.While in this paper, the synthetic method and technology was explored in detail to synthesize small crystal ZSM-5 zeolite with different silicon to aluminum ratio, aiming at paving the way for industrial application. In order to investigate the influence of synthetic condition on the physicochemical properties of samples, such as crystallinity, crystal size, morphology, element composition, BET specific area, pore structure, acidity distribution and so on, the samples were characterized by X-ray diffraction (XRD), fourier transform infrared (FT-IR), scanning electron microscopy (SEM), X-ray fluorescence spectrometry (XRF), N2 adsorption/desorption and temperature-programmed desorption of ammonia (NH3-TPD).In addition, the synthetic zeolite ZSM-5 zeolite was applied to methanol-to-propylene (MTP) process and their catalytic performance was investigated. The results indicated that comparing with micro-size ZSM-5 zeolite, small crystal ZSM-5 zeolite possessed large exterior surface area and pore volume. Thus the diffusion environment of product molecules was improved, which was helpful for inhibiting the secondary reactions. So, small crystal ZSM-5 zeolite exhibited higher propylene selectivity and excellent anti-carbon deposition property in MTP reaction. At the same time, the test results demonstrated that ZSM-5 catalyst with the same crystal size and different silicon to aluminum ratio had similar pore structural parameters, but different acidity distribution. With the silicon to aluminum ratio of HZSM-5 catalyst increasing, the amounts of strong acid reduced significantly, which was also beneficial for controlling the side reaction and raising the propylene selectivity.