Synthesis And Performance Of Catalysts For Side Chain Alkylation From Toluene With Methanol

Styrene is an important chemical raw material that is used to produce plastics, rubbers and ion exchange resins. With the rapid development of automotive electronics and building materials industry, the global demand for styrene increases year by year. The traditional process for the synthesis of styrene is firstly the Friedel-Crafts reaction of benzene and ethylene to produce ethylbenzene, and then the dehydrogenation of ethylbenzene to styrene. Compared with traditional methods, styrene by side chain alkylation of toluene with methanol has many irreplaceable advantages such as a wide source and low cost of raw materials, simple process, reducing energy consumption and greenhouse gas emissions significantly. Therefore, this reaction is arousing more and more widespread attention in recent years.Currently accepted reaction mechanism about side chain alkylation of toluene with methanol is described as follows, basic sites of catalysts are mainly used for the formation of formaldehyde by dehydrogenation of methanol and the activation of the methyl group of toluene, the acid sites are mainly used for the adsorption of formaldehyde and toluene, the coordination of appropriate acid-base sites promotes the formation of ethylbenzene and styrene. Based on the research, we have designed and prepared different types of catalysts with acid-base sites, which contains aluminum based catalysts, ordered mesoporous carbon supported catalysts and catalysts modified with different carriers. The catalysts were characterized by X-ray diffraction (XRD), nitrogen adsorption-desorption isotherm, transmission electron microscopy (TEM), temperature programmed desorption of CO2 (CO2-TPD) and temperature programmed desorption of NH3 (NH3-TPD). The performance of catalysts was investigated for side chain alkylation of toluene with methanol. Compared and associated with characterization and performance of catalysts, the conclusions are drawn as follows.In order to provide acid sites by Al and provide base sites by alkali metal K, Cs as the active ingredient, the bifunctional acid-base catalysts were prepared by sol-gel method using aluminum isopropoxide and alkali metal hydroxides. Compared with the characterization and performance, the catalysts had strong acid and basic sites, low specific surface area and poor catalyst activity, which illustrates that the strong acid-basic sites and specific surface area are not conducive to side-chain alkylation of toluene and methanol.Using ordered mesoporous carbon as catalyst carrier to improve the catalyst specific surface area. The effects of acid and alkali amount were investigated in synthesis of ordered mesoporous carbon (OMC) support by two-step method of soft template using resorcinol and formaldehyde as carbon precursor, triblock copolymer Pluronic F127 as a template. The results showed that the amount of base and acid both effect the carbon physical phase separation time and the self-assembly crosslink degree of polymerization and template. Appropriate to reduce acid and base consumption and prolong the phase separation time are favorable to improve the orderly degree of OMC. The OMC was synthesized with specific surface area of 752m/g and pore size about 6 nm by the deployment of appropriate proportions amount of acid and base.For the purpose of obtaining catalysts with different acid and alkali characteristic, and investigating their impact law on the catalytic activity, the ordered mesoporous carbon supported catalysts were prepared by impregnation of cesium and boron component using OMC as carrier. The performance and characterization results of catalysts with different loading combination of Cs and B were compared. The yield of ethylbenzene and styrene (YSTY+EB/%) reached 43% and the selectivity of styrene reached 23.8% over the catalyst with 8.0 wt% Cs and 1.3 wt% B. It revealed that the high activity of catalysts was mainly due to the high dispersity of loading components on OMC and the appropriate base-acid active sites. The amount of weak base sites and medium-strong base sites can be increased by increasing the content of Cs appropriately, the amount of medium-strong base site can be enhanced by improving the B content. Both factors are beneficial to improve the selectivity of styrene.Different carriers modified catalysts characterization and performance were investigated to further study the effects of different carriers properties on the reaction. The results showed that catalytic activity of side chain alkylation decreases in the order CsB/OMC>CsB/MCM-41>CsB/AC>CsB/ZSM-5. Compared with the mesoporous and microporous carriers modified catalysts, the catalytic activities of the mesoporous carrier modified catalysts are higher than the microporous carriers modified catalysts. Compared with catalyst CsB/OMC, the pore structure of aluminosilicate zeolite framework of the catalyst CsB/MCM-41 is subjected to a greater extent of damage, and the surface area and pore volume decrease significantly because of the carbon deposition phenomenon. Integrated catalytic performance and characterization, the results validate that the weak acid sites and a medium-strong base sites are conducive to improve the selectivity of styrene.