The Functionalization Of MCM-48Mesoporous Molecular Sieve And The Preparation Of Its Membrane

In the recent years, with the development of industry, the emission of greenhouse gases, especially carbon dioxide, is increasing, which has already done harm to our living environment. It is extremely urgent to reduce the emission of CO2and develop the low carbon economy. Using methanol and carbon dioxide as raw material to synthesize dimethyl carbonate (DMC) not only solves the emission problem of carbon dioxide, but also makes full use of carbon dioxide to produce a green chemical DMC, which is a new foundation of the current organic synthesis. However, because of some factors from thermodynamics and kinetics, the conversion of the whole reaction isn’t high, which limites the industrial application of this method. Therefore, the main research fields in the future are as follow: seeking a highly efficient catalyst, developing a new type of process and improving the balance limit. Ordered mesoporous materials have highly ordered porous, uniform pore diameter, high surface area and relatively good thermal stability. MCM-48, one member of these new materials, contains two independent three-dimensional pore systems to decrease the plugging hole conditions, which makes it better than any other mesoporous materials in macromolecular adsorption, separation and catalytic applications. But the pure silicon MCM-48does not have catalytic activity center and cannot be directly used in catalytic reaction. We can add the active component of the above reaction into MCM-48to prepare the doping M-MCM-48mesoporous molecular sieve. In order to make full use of the role of the membrane separation, it can be made into molecular sieve membrane and further be assembled the membrane reactor, which can make the capture of CO2and catalytic conversion integrate.In this paper, by hydrothermal synthesis method, the high quality MCM-48mesoporous molecular sieves was successfully prepared in short time at high temperature through the optimized synthesis conditions in the base of the original preparation of mesoporous molecular sieves MCM-48. The influences of the CTAB surfactant amount, crystallization temperature, crystallization time, the order of adding CTAB and NaF and fluoride ions on the formation of MCM-48were systematically studied here. The products were characterized by powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that with CTAB/Si=0.1, F-/Si=0.1, the high quality MCM-48mesoporous molecular sieve with fluorine was synthesized at423K for12h. However, with CTAB/Si=0.12, the high quality MCM-48mesoporous molecular sieve was also synthesized at423K for12h without fluorine. But its hydrothermal stability was worse than MCM-48with fluorine, which preserved its framework structure even after being boiled in water for12h.Through the direct hydrothermal method and impregnation method, the active components Cu and Ni was added into MCM-48one by one. The products were characterized by powder XRD, SEM, energy dispersive X-ray detector (EDX) and infrared radiation (IR). The results showed that the molar ratio of M/Si had an important effect on the preparation of doping MCM-48mesoporous molecular sieve. There was an optimal value whether the preparation of MCM-48with single metal or double metal. Continuing to increase the amount of metal mixed, the structural of original hole would suffer from damage to different degree. Compared with impregnation method, the doping MCM-48mesoporous molecular sieves not only contained more metal mixed, but also were characteristic of higher hydrothermal stability.The mesoporous MCM-48membrane was synthesized on α-Al2O3support with pore size of2-4μm through in-situ hydrothermal synthesis method. The effects of the carrier surface pretreatment, preparation method and synthetic times were systematically studied here. The pretreated supports and the membranes were characterized by XRD, SEM and single gas permeation test. The results showed that the higher quality membrane was prepared three times by in-situ hydrothermal synthesis method on the support which was diped in tetraethyl orthosilicate (TEOS). However, after calcination, the surface of membrane appeared some fissures, which had an effect on the quality of the membrane. These fissures were largely attributed to the contraction of the lattice of MCM-48mesoporous molecular sieves in the process of calcination.