Study On The Synthesis Of Catalysts And Its Performance For The Side Chain Alkylation Of Toluene With Methanol

Styrene which is used to produce plastics and rubbers is an important chemical raw material. The main production methods of styrene are catalytic dehydrogenation, ethylbenzene co-oxidation and selective oxidative dehydrogenation. Compared with traditional methods, styrene by side chain alkylation of toluene with methanol has many irreplaceable advantages such as low cost of raw materials, simple process, reducing energy consumption and pollution. Therefore, this reaction is arousing more and more widespread attention in recent years.Catalysts for styrene from toluene with mathanol by side chain alkylation need appropriate acid-base sites. The strength of acid and alkali which is too strong or too weak is unfavorable to the reaction. In an attempt to improve reactivity of the catalysts, different solid catalysts with acid-base sites were prepared. The catalysts were characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM), temperature programmed desorption of CO2(CO2-TPD) and temperature programmed desorption of NH3(NH3-TPD)and the performance of the catalysts was investigated. By associating the characterization with the performance of the catalysts, the conclusions can be drawn as following:1. In order to enhance the resistance to coke formation, the ordered mesoporous carbon supported catalysts were prepared. The ordered mesoporous carbon(OMC) is synthesized by two-step method of soft template using resorcinol and formaldehyde as carbon precursor, triblock copolymer pluronic F127 as a template. When the thermal polymerization time is 24 h and precursor calcination temperature is 700 ℃, the order degree of mesoporous carbon is the highest. The ordered mesoporous carbon supported catalysts were prepared by impregnation of cesium and boron component using OMC as carrier. The performance of the catalysts for the side chain alkylation of toluene with mathanol were investigate and the results show that the catalysts had no reaction activity.2. For the purpose of obtaining catalysts with different acid and alkali characteristic, Mg(CH3COO)2 and H3BO3 modified CsX zeolite catalysts were prepared by impregnation method. Modified CsX with a moderate amount of Mg(CH3COO)2 and H3BO3 created new middle base sites(400-550 ℃), strong base sites(650-750 ℃) and weak acid sites(60-150 ℃) which were key active sites for the side chain alkylation of toluene with mathanol. The yield of ethylbenzene and styrene reached 15.2% and the selectivity of styrene reached71.0% over the catalyst with 5.0 wt% Mg and 1.0 wt% B.3. We had used grinding method and impregnation method to prepare MgO and H3BO3 modified Cs X zeolite catalysts. The catalysts prepared by grinding method had strong base sites and weak acid sites, so its main product was mathane and the selectivity of styrene decreased to 28.7%. The catalysts prepared by impregnation method had a small amount of weak base sites and many weak acid sites, so the main product was methyl ether and the yield of ethylbenzene and styrene was only 0.6%.4. We had designed and prepared alkaline-earth metals and B modified Cs X zeolite catalysts. The performance of the catalysts for the side chain alkylation of toluene with mathanol was 5Ca1B/Cs X > 5Mg1B/CsX >5Ba1B/Cs X > 5Sr1B/CsX. The yield of ethylbenzene and styrene reached19.6% and the selectivity of styrene reached 82.2% over the 5Ca1B/Cs X catalyst. The high reactivity of 5Ca1B/CsX was mainly due to its lower strength of strong base sites and it further validated that middle-strong base sites are beneficial to improve the reactivity.