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Study On The Synthesis Of Diphenyl Carbonate From Transesterification Of Dimethyl Oxalate With Phenol

Posted on:2004-11-16Degree:DoctorType:Dissertation
Country:ChinaCandidate:S P WangFull Text:PDF
GTID:1101360092980635Subject:Chemical processes
Abstract/Summary:PDF Full Text Request
Diphenyl carbonate (DPC) is a raw material for non-phosgene production of polycarbonates, which are excellent engineering thermoplastics and substitutes for metals and glass because of their good impact strength and transparency. Several alternative non-phosgene methods for DPC synthesis have also been proposed. Among them, the transesterification of dimethyl oxalate (DMO) with phenol to diphenyl oxalate (DPO) followed by decarbonylation of DPO to DPC is a promising process. It is an environmentally benign process with the mild reaction condition, no azeotrope mixture formed and easy separation of co-products methanol and CO from reaction system. In the thesis, the process of DPC synthesis from the transesterification of DMO with phenol has been studied.Methylphenyl oxalate (MPO),the intermediate product of the transesterification of DMO with phenol to DPO, was qualitatively determined through GC/MS and αcataclasm scheme. This proved that the synthesis of DPO followed a 2-step reaction module consisting of the transesterification of DMO with phenol to MPO and the disproportionation of MPO to DPO. An easy and effective gas chromatographic method for quantitatively analyzing DPC and DPO was set up. DPC and the related compounds, as well as DPO and the related compounds, were well separated through an OV-101 chromatographic column.The synthesis of DPO was carried out over catalysts with Lewis acid and molecular sieves such as TS-1, H-ZSM-5 and Hβ. It was observed that the by-product anisole could be produced via a methylation of phenol with DMO. The acid strength of catalyst had a significant influence on the selectivity of the product. The weak acid sites were in favor of the production of MPO and DPO through the cracking of acyloxy bond, while the strong acid sites took advantage of formation of byproduct anisole through the cracking of alkoxide bond. The selectivity of anisole decreased significantly on KOH modified Hβcatalyst through neutralizing strong acid sites by alkali. On SnO2 modified Hβcatalyst, the synergetic effect of SnO2 active centers with acid sites made the conversion of DMO and the selectivity of DPO improved. The monolayer dispersion of SnO2 on the Hβplayed a key role in the transesterification and the saturated SnO2 monolayer dispersion on Hβ was 0.021g/g. When Sn loading was over 2.1%, SnO2 on the surface of Hβwas transfomed from the monolayer dispersion to the crystal phase, resulting in the decrease of catalytic activity. When the synthesis of DPO was carried out over SnO2 and KOH co-modified Hβ, the selectivity of DPO increased while the selectivity of anisole decreased accompanying with the high DMO conversion. TS-1 catalyst showed high selectivity of MPO and DPO during transesterification of DMO with phenol. The total selectivity of MPO and DPO was up to 99.2% over TS-1. The characterization of catalysts was carried out by FTIR of absorbed pyridine and NH3-TPD. The results showed that the weak Lewis acid sites were the active sites for the transesterification. The conversion of DMO and the selectivity of DPO can be increased by addition SnO2 to TS-1 since SnO2 active centers cooperated with Lewis acid sites of TS-1 to stimulate the transesterification of DMO with phenol over Sn modified TS-1. XRD, XPS, EDS results proved that the high dispersion of SnO2 was favorable for DPO synthesis. However, when Sn loading was over 2%, the existence state of SnO2 on the support was transformed from monolayer dispersion to crystal phase, which resulted in the decrease of DMO conversion. TiO2 /SiO2 catalyst was best for improving the total selectivity of MPO and DPO as well as the conversion of DMO. The large pore size, new acid sites and high specific surface area of TiO2 /SiO2 catalyst were favorable for increasing the catalytic activity. The higher selectivity of MPO and DPO was attributed to the weak acid sites on TiO2 /SiO2. Also, Ti loading was one of the factors affecting its catalytic activity. 10% TiO2 /SiO2 was the optimum catalyst and the DMO conversion, the...
Keywords/Search Tags:Diphenyl carbonate, Diphenyl oxalate, Dimethyl oxalate, transesterification, acid sites, solid acid catalyst, decarbonylation
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