Synthesis Of Dimethyl Carbonate By Gas-phase Oxidative Carbonylation Of Methanol

Dimethyl carbonate(DMC), as an important green chemical intermediate, has considerable potential for green chemicals synthesis, and is known as a new benign building block of organic synthesis in the new century. There are several ways to the synthesis of DMC, in which vapor-phase oxidative carbonylation of methanol has many advantages, such as low erosion, relatively easier separation of products, attainable raw materials etc. However, the major drawback for this reaction is a low methanol conversion together with rapid deactivity of catalysts.In this paper, promoter and support were investigated to study the change of catalyst activity for synthesis of dimethyl carbonate by gas-oxidative carbonylation of methanol. The results are summarized as follows:1. In the reaction of gas-phase oxidative carbonylation of methanol, the activity of PdCl2-CuCl2/AC catalyst was low, the conversion of methanol and the selectivity of DMC to methanol are 2.8% and 88.9%. When the catalyst was modified by glycerol, its catalytic performance was improved significantly: the conversion of methanol and the selectivity of DMC to methanol are 26.1% and 92.1%. The catalysts use polyhydroxy compounds as promoter were characterized by means of XRD, SEM and XPS. The results showed that the addition of promoter can significantly enhance the dispersal of active species. And there would not have leftover after calcinations which will enwrap active component. However, the polyhydroxy compounds promoters would reduce the metal active component, and this situation would induce the deactivation of catalysts.2. Using SBA-15 as hard templates, sucrose as the carbon source, mesoporous carbon materials were prepared. The results of SEM and XRD showed that mesoporous carbon had a rod with loose texture, there were three XRD peaks which could be assigned to (100), (110) and (200) diffractions of the 2-d hexagonal space group, it indicated that carbon materials had highly ordered structure. And the carbon material has uniform mesopores about 4 nm in size. Mesoporous carbon was used as catalyst support in the synthesis of dimethyl carbonate by gas-phase oxidative carbonylation of methanol. At the beginning, the conversion of methanol and the selectivity of DMC to methanol are 30% and7%. While the activity of catalyst remains stable, the conversion of methanol and the selectivity of DMC to methanol are 17% and 90%. Compare with the catalysts support on the AC, it appeared that the change of pore structure and the increase of pore diameter can enhance the catalytic activities. So it can conclude that the key factors is dispersion of metal active species.3. The activated carbon (AC) which treated with different methods were investigated to study the change of PdCl₂-CuCl₂/AC catalysts activity, and found that the AC treated with nitric acid (0.5M) had the best performance. At the beginning, the conversion of methanol was more than 30%; the conversion received 25% and the selectivity of DMC to methanol was more than 90% while catalyst remains stable. The results of characterization showed that the treatment of HNO3 can significantly increase the concentration of oxygen-containing groups on AC, so the dispersal of active species on AC will be enhanced. However, a too-large concentration of HNO3 will destroy the mesopore and micropore structure of AC which will decrease the activity of catalysts.