| The process of CO coupling reaction to form dimethyl oxalate (DMO) is the first step of the process of producting ethylene glycol (EG) by using syngas. The process of CO coupling reaction to form DMO is composed of two processes, the catalytic coupling reaction between CO and methyl nitrite (MN) to form DMO and NO, and the reaction between NO,O2, and methanol to regenerate MN. In this dissertation, it was invetstgated the mechanism of CO coupling reaction to form DMO, the intrinsic kinetics of the CO coupling reaction, the egg-shell Pd/α-Al2O3 catalysts applied in CO coupling reaction, and the process of MN regeneration.The main conclusions of this dissertation are as follows:1. The influence of operating conditions on CO coupling reaction was investigated. It was discovered that the reaction temperature had large influence on the reaction. When the reaction temperature was increased from 100℃to 140℃, the conversion of MN increased from 60% to 95% under the operating conditions of CO/MN=2,3000h-1.But the raising of reaction temperature also resulted in MN decomposition to form methanol and formaldehyde. So, the CO coupling reaction should be carried out below the decomposition temperatue of MN,135℃.There was an optimal value of CO/MN with the aim of the maximum value of DMO yield. The optimal value of CO/MN could vary with changing space velocity. Generally, the optimal value of CO/MN is between 1 and 2 generally. The MN catalytic decomposition to form methanol and methyl formate (MF) would be raised if the value of CO/MN was below 1; and if the value of CO/MN was above the optimal value, the rate of DMO formation would be slow, because excess CO could occupy active centers over catalysts.Space velocity has great influence on the side reaction, the selectivties of products, and the optimal value of CO/MN. When the CO coupling reaction occurred under the low space velocity, by-prodcuts of MF and methanol, which were resulted from MN catalytic decomposition, could be detected. But when the reaction occurred under the high space velocity, few MF and methanol can be detected. Moverover, it was discovered that with the increasing of space velocity, the optimal value of CO/MN could decrease to 1.2. The mechanism of CO coupling reaction to form DMO was investigated by using in situ FTIR. It was identified three intermediates, CH3O-Pd-NO, CH3OCO-Pd-NO, and Pd(COOCH3)2 during the reaction. And the third intermediate could generate DMO. Moverover, the by-product DMC is generated from the reaction between CH3O-Pd-NO and CH3OCO-Pd-NO.Futhermover, the role of adsorbed CO in the reaction was investigated in this dissertation. It was discovered that only bridge bonded CO rather than linearly bonded CO participated in the reaction. With the increasing of CO partial pressure, the ratio of linearly bonded CO to bridge bonded CO increased over catalysts. It means the more linearly bonded CO the more active centers were occupied, which resulted in the slow reaction rate. The detailed mechanism is decribed as follow figure.3. H2 and NO could resulte in inactivation of Pd/α-Al2O3 catalysts. However, the inactivation resulted from H2 and NO is reversible; the catalysts could be reactivated by outgasing with N2.Furethermore, H2 could give rise to different influence on CO coupling reaction under different space velocity. When the coupling reaction occurred under the low space velocity, the addition of H2 resulted in the increasing of the selectivity of methanol, and no MF was detected. However, when the CO coupling reaction occurred under the high space velocity, the main byproduct was MF, and no methanol was detected, which is very different from the one under low space velocity. The particular phenomenon can be explained as the difference of diffusion rates from gaseous buck to catalysts surface between H2 and CO. The reaction between CH3O-Pd-NO and H2 to form methanol occurs under low space velocity. With the increasing of space velocity, the diffusion rate of CO was increased, which resulted in the increasing of adsorbed CO over catalysts. With the inceasing of adsorbed CO, CH3O-Pd-NO reacted more easily with adsorbed CO to form CH3OOC-Pd-NO than with H2 to form methanol. The reaction between CH3OOC-Pd-NO and H2 resulted in the formation of MF.4. There are three factors, the pore structure, Pd dispersion over catalysts, and the Pd distribution in egg-shell Pd/α-Al2O3 catalysts, affecting catalytic performance of egg-shell Pd/α-Al2O3 catalysts. It was discovered:(1) The specific surface area and pore volume of the support are not as much important as the pore distribution for the activity of Pd/α-Al2O3, and the double pore structure of the support is necessary for preparing catalysts with high activity. Especially, increasing the proportion of the pore with diameter ranging from 1 nm to 10 nm is positive for high catalytic activity. (2) The CO coupling reaction is a so-called structure sensitive reaction. (3) The shell thickness of the egg-shell Pd/α-Al2O3 catalyst with the best catalytic activity was 50μm. (4) The shell thickness of egg-shell catalysts has the greatest influence on catalytic activity in the three factors above-mentioned.5. The reaction between CO and MN to form DMO was investigated in a continuous flow integral-type fixed-bed reactor with the aim of kinetic modeling studies. Based on the latest work on reaction mechanism, a new kinetic model was proposed. It was discovered that the rate-determining step is the surface reaction over catalysts surface. The kinetic expression is described as follows.6. In present paper, The MN regeneration was composed of two reactions, the NO oxidation to N2O3 and the reaction between N2O3 and methanol to form MN. It was found that the reaction between N2O3 and methanol occurred in gaseouse phase. And the reaction was investigated in a double-stirring reactor with the aim of kinetic modeling studies. A power law rate model was used to represent the formation of MN. The expression is described as follows. PNO is used to represent PN2O3, because the mixture of NO and NO2 (NO:NO2=1:1) is considered as N2O3.
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