两步酯交换工艺连续合成碳酸二甲酯反应过程的研究

Dimethyl Carbonate (DMC) has been recently given much attention as for use as an environmentally benign substitute for highly toxic phosgene or dimethyl sulfate in organic synthesis. It is considered to be a valuable commercial product finding utility as an organic solvent, a nontoxic carbonating and methylating agent and in the production of other alkyl and aryl carbonates. In addition, DMC has high oxygen content, a good blending octane, low toxicity, and can be effectively used as a fuel additive. The traditional synthesis of DMC has been known by reaction of methanol with phosgene. Recently, A tremendous amount of researth has been pursued to establish environmentally compatible non-phosgene routes for the production of DMC. For example,Methanol, carbon monoxide and oxygen has been industrialized by using a Cu-based catalyst. Although the yields of DMC obtained in these systems were high, they have disadvantages of high cost of the starting materials and the difficulty of catalyst-product separation due to the homogeneous nature of the catalysts. Therefore, it is important to study and find alternative routes for the sysnthesis of DMC with solid catalysts. This work gives a comprehensive study on two-step synthesis of DMC from propylene oxide,carbon dioxide and methanol using solid catalysts. The first step is the cycloaddition of propylene oxide with CO2 to form propylene carbonate, and the second step is the transesterification reaction of propylene carbonate with methanol to DMC and glycols. Among the solid catalysts examined, KI/NaY catalyst is the most active and selective for the cycloaddition of carbon dioxide with propylene oxide under mild conditions.Prepared by heating treatment under flowing nitrogen, KI/NaY catalyst had a 99.1% yield of propylene carbonate based on 99.3% conversion of propylene oxide. The activity of the catalyst reached its maximum at reaction temperature of 423K and pressure of 4.0MPa .Moreover, Na2CO3 /CaO solid base is an effective heterogeneous catalyst for the synthesis of DMC via transesterification reaction between propylene carbonate and methanol. The catalysts containing different amounts of Na2CO3 were characterized by XRD,IR and TPD to elucidate the catalytically active sites,whose performance varies with the pretreatment temperature.It can be concluded that strong basic sites are active for the transesterification reaction of propylene carbonate and methanol.The higher activities of the catalysts would be ascribed to the larger numbers of those basic sites.In conclusion, the highly active and selective catalysts have been developed for the DMC synthesis from methanol and CO2. The catalysts employed are heterogeneous in nature, which allow easy separation of reactants and products .The unconverted reactants can be recycled efficiently. The effect of preparation and reaction conditions on the catalytic reactivities were intensively evaluated in terms of methanol conversion and DMC yield.

对两步法酯交换工艺连续合成碳酸二甲酯反应过程中的催化剂与反应器的匹配、连续工艺参数的优化以及反应器的数学模型化进行研究。过程采用了新型固体催化剂、催化反应蒸馏技术。过程具有反应器体积小、催化剂易分离、可重复使用、碳酸二甲酯生产能力高的优点。过程的研究对加快我国碳酸二甲酯合成工业的发展具有重要的现实意义。