Synthesis Of Dimethyl Carbonate Over Bi-functional Catalyst

Gas-phase oxidative carbonylation synthesis from methanol is a potential synthesis routes fordimethyl carbonate (DMC) at present. The co-product water in this reaction, however, ofteninduces catalyst deactivation and equipment corrosion. If the dimethyl ether (DME) is introducedas a co-feed gas to the methanol carbonylation reaction, the above problems may be diminishedsomewhat via the coupling reaction of DME hydrolysis and methanol carbonylation over abi-functional catalyst. Meanwhile, partial consumption of the produced water via the hydrolysisof DME can also increase the yield of DMC.In this paper, the thermodynamic feasibility of the coupling reaction of methanolcarbonylation and DME hydrolysis was analyzed. And hydrolysis performance of dimethyl etherat low temperature was investigated to develop a catalyst for DME hydrolysis with high activityat low temperature. Furthermore, the catalytic performance in the co-feeding system over thebi-functional catalysts, which were prepared by mixing the hydrolysis catalyst withcarbonization catalyst, was also studied. The results are summarized as follows:1. The results of thermodynamic analysis show that the DME hydrolysis reaction wasendothermic reaction and the methanol carbonylation reaction was exothermic reaction amongselective temperatures. The energy coupling of DME hydrolysis and methanol carbonylation wasachieved. The Gibbs tree energies of the coupling reaction were under zero, which mdicated thatthis synthetic route was advantaged from the thermodynamic point of view.2. ZSM-5 zeolite was synthesized, and the effect of the silicon aluminum mote ratio,modification on the hydrolysis activity of dimethyl ether at low temperatttre over the zeolitecatalysts was investigated. The acidity of the catalysts was characterized by NH₃-TPD and Py-IR.The results show that the performance of the catalysts was dependent on the acidity of thezeolites. Over the SO₄^2-/ZrO₂-ZSM-5 catalyst, the conversion of DME increased markedly, butthe selectivity of methanol decreased. On the contrary, the conversion of DME was decreasedand the selectivity of methanol increased over the MgO/ZSM-5 catalyst. The ZSM-5 catalystsmodified by Cu and Pd exhibited high DME hydrolysis activity and high selectivity towardsmethanol at relative low temperatures. At 150℃, the conversion of DME increased by 5.9% to13.0%, and the selectivity of methanol was increased by 3.8% to 99.1%, and the space time yieldof methanol increased by 148.8 mg·(g-cat·h)^-1 to 312.6 mg·(g-cat·h)^-1, Based on the aboveresults, the problem of reaction temperature matching for the coupling DME hydrolysis withmethanol oxidative carbonylation was resolved effectively.3. The space time yield of DMC over the bi-functional catalysts of Cu-Pd-TBAB/AC and Cu-Pd/MCM-22 can be improved effectively after the dimethyl ether was introduced to thereaction system. At 150℃, when the ratio of Cu-Pd-TBAB/AC to Cu-Pd/ZSM-5 was 5 and theflux of DME was 6mL/min, the conversion of methanol and space time yield of DMC were15.9% and 633.7 mg·(g-cat·h)^-1, respectively. The results indicate that the introduction of DMEin the reaction system of oxidative carbonylation could increase the stability of the catalysts.This is because that the hydrolysis of dimethyl ether can consume some of the water produced inthe oxidative carbonylation of methanol.