Study On HZSM-5 Zeolite Catalysts For Coupling Conversion Of Methanol And Butylene To Propylene

Propylene is one of the most important organic chemical materials. In recent years, with the demand for propylene increasing substantially, the traditional routes for producing propylene cannot keep up with the demand. A promising way of producing propylene is by coupling conversion of methanol and C₄ hydrocarbon. This process has many advantages. On one hand, both methanol and C₄ resources can be used effectively. On the other hand, the coupling reaction can reduce energy consumption and improve the economic benefit. It is highly desirable to develop the effective catalysts and further explore the properties-reactivity relationship. In this thesis, a series of HZSM-5 zeolite and modified HZSM-5 catalysts ?B-modified and Ce-modified? were synthesized. The relationship between the physicochemical properties of catalysts and their catalytic reactivity were investigated systemically. The main contents and results are as follows:?1? The thermodynamic calculation of the coupling conversion of methanol and butylene was performed. The enthalpy changes, gibbs free energy changes and equilibrium constants of the main reactions were obtained. The influences of reaction temperature, pressure, the molar ratio of methanol to butylene and the diluent content on the equilibrium composition of C₂-C₄ olefin products were discussed. Compared with the methanol conversion and butylene cracking, the reaction temperature had a stronger effect on equilibrium composition of C₂-C₄ olefin products in the coupling process. For the coupling conversion of methanol and butylene, the butylene cracking could be promoted by adding the proper amount of methanol. On the basis of thermodynamics, the comparatively higher equilibrium mole fraction of propylene was obtained under the following reaction conditions ?500?550 ?,0.1 MPa, the molar ratio of methanol to butylene:0.6?1.5, dilution component mole fraction ?yd?:0.2?0.6?.?2? The catalytic performance of the HZSM-5 zeolite catalysts with different morphology was investigated in the coupling conversion of methanol and butylene. A series of HZSM-5 catalysts ?NZ-1?NZ-2?NZ-3 and MZ? have been synthesized under different preparation conditions, and their catalytic performance of these catalysts was tested. The results indicated that different preparation conditions led to different morphologies, textural properties and different distribution of acid sites. The nano-sized HZSM-5 zeolite catalysts had many advantages, such as larger surface area, shorter channels, more accessible acid sites, etc. Therefore, the nano-sized HZSM-5 catalysts exhibited better catalytic reactivity and anti-coking ability than the micro-sized MZ catalyst. It was known that NZ-1 ?20?70 nm? and NZ-2 ?30 nm? particles had serious aggregation. This serious aggregation of particles was not conducive to the intermediate products diffusion in the coupling reaction. The NZ-3 ?200 nm? catalyst had smooth particle surface and good dispersion, which was favored to the products diffusion. Therefore, the NZ-3 catalyst showed the best stability among the four catalysts in the coupling conversion of methanol and butylene.?3? The catalytic performance of the Ce-modified HZSM-5 ?Ce/NZ? zeolite catalysts was investigated in the coupling conversion of methanol and butylene. A series of Ce-modified HZSM-5 zeolite catalysts were prepared and their catalytic performance was tested. The influences of reaction conditions ?methanol/butylene molar ratio, reaction temperature and space time? on the reactivity of 2.5Ce/NZ catalyst were studied. The results showed that the Ce content of influenced the structure, texture and acidity of Ce/NZ catalyst, which further influenced its reactivity. The Ce species interacted with hydroxyl groups on the HZSM-5 zeolite catalyst and modified the acid properties of the catalysts. On one hand, the interaction decreased the concentration of B acid sites. On the other hand, it increased the concentration of L acid sites by generating new L acid sites of Ce?OH?²⁺. The highest propylene yield was obtained on the catalyst with 2.5 wt% Ce loading ?2.5% Ce/NZ?, under the optimal reaction conditions of 550 ?,0.1 MPa, space time= 2.3 g_cat·h/mol_CH2, methanol/butylene molar ratio = 0.8, possibly because of the moderate density and distribution of acid sites on the catalyst.?4? The catalytic performance of the B-modified HZSM-5 ?B/NZ and B,Al-NZ? zeolite catalysts was investigated in the coupling conversion of methanol and butylene. A series of B-modified HZSM-5 zeolite catalysts were prepared by impregnation method and hydrothermal method and their catalytic performance was tested. The influences of reaction conditions ?methanol/butylene molar ratio, reaction temperature and space time? on the reactivity of B,Al-NZ-1 catalyst were studied. The results indicated that different preparation conditions led to different morphologies, textural properties and the distribution of acid sites of the catalysts, which further influenced its reactivity. The introduction of boron atoms into the HZSM-5 zeolite catalysts resulted in the increasing of surface area and pore volume of the catalysts. And the introduction of boron atoms changed the acidity of the HZSM-5 zeolite catalyst. On one hand, the hydroxyl groups from Si?OH?Al decreased and the concentration of the strong B acid sites decreased. On the other hand, the hydroxyl groups from Si?OH?B increased and the concentration of the weak and medium B acid sites increased. Compared with aluminosilicate NZ, B,Al-NZ catalyst exhibited higher butylene conversion, propylene yield, catalyst stability and anti-coking ability in the coupling conversion of methanol and butylene. The highest propylene yield of 44.2% was obtained on the catalyst with the B/Al ratio=1 ?B,Al-NZ-1? under the optimal reaction conditions of 550 ?,0.1 MPa, space time= 2.2 g_cat·h/mol_CH2, methanol/butylene molar ratio= 1.2.?5? The deactivation and regeneration of B,Al-NZ-1 catalyst was studied. The influences of the reaction conditions ?methanol/butylene molar ratio, reaction temperature, and space time? on the stability of B,Al-NZ-1 catalyst were investigated. The results showed the higher reaction temperature could accelerate coke deposition of the B,Al-NZ-1 catalyst. The catalyst stability was improved by properly decreasing the methanol/butylene molar ratio and properly increasing the space time. The stability of B,Al-NZ-1 catalyst was improved in the coupling reaction after regeneration.