Study On The Preparation Of Methyl-chloroacetate By Selective Hydrodechlorination Of Mixed Esters Of Mother Liquor Of Chloroacetic Acid

The catalysts, which are used in the hydrDdechlorination of mixed esters of mother liquor of chloroacetic acid, were mainly studied in this paper.The catalysts of Pd supported on active carbon prepared by impregnation were suitable for the hydrodechlorination, after the preliminary intermittent and continuous experiments on the supports and Ihe active constituents of catalysts respectively. The length-of-life tests on the Pd/C catalysts ,which were prepared at different temperatures, were further carried out in a continuous fixed bed reactor withl45 reaction temperature, 140mlAnin volume-velocity of hydrogen and the 10g/(g cat h) space-time yield. And the results show that: All these catalysts prepared at 550 and below 550 bad a stable activity of above 99.9%, and the span-life of the catalysts became shorter, with the increase of the preparative temperature. But in the view of prepared at 650 , not only the activity was very low ,but also the range of change was very broad. So span-life and stability considered ,the and catalysts, which were prepared at 250 and350 respectively, were the most satisfactory catalysts. In the point of , the activity and selectivity were still above 99.9% and in the range of 91-96% respectively, when the treatment capacity of DCME reached 1150g/(g cat), furthermore, activity didnt seem to begin to decrease. As far as considered, the activity and selectivity were still above 99.9% and 92% respectively. And Ihe activity didnt begin to decrease until the treatment capacity of DCME was 2200g/(g cat).In order to study the causes of deactivation, fresh and used catalysts were characterized by X-ray diffraction, X-ray photoelectron spectroscopy and thermogravimery. Characterization results indicate lhat the deactivation is mainly due to the formation of carbonaceous deposits, which causes the active sites of catalysts to be covered and the valence of Pd to increase. With the raise of preparative temperature, the dimensions of active particles become larger, so the speed of carbon depositions on the catalysts can be promoted. Most of carbon depositions are physisorpted in the surface of active sites and support, and they can be removed by sweeping in indifferent gases, so that the catalysts can be regenerated to some extent But 1he carbon depositions combined with Pd by chemical bond and cokes can not be removed by this mean Furthermore, with the increase of reparative temperature, Ihe hydrogenation of supports can also be promoted, which inhibit the hydrodechlorination.the sieving tests on the assistants of La2O3, Se₂O₃ and ThO2 had also been carried out in the continuous fixed bed reactor. Best stability considered, ThO2 will become the mostsatisfactory assistantThe success in the research field will promote the intermittent production of chloroacetic acid without the disposal of wastes. So this paper is realistically important...