Dechlorination Stability And Basic Mechanism Of Cs-Based Catayst And Its Application In The Synthesis Of Vinylidene Chloride

Vinylidene chloride (VDC) is an important monomer for polyvinylidene chloride (PVDC), known as "green" packaging materials. With the rapid development of economy and the gradual improvement of the people’s living standard, people pay more attention to the food safety, resulting in the rapid increase of the demand of vinylidene chloride in market. At present, the industrial production of vinylidene chloride is mainly the saponification process, which can produce a large number of highly salty organic wastewater and may encounter enormous pressure of environmental pollution. Vapor phase catalytic dehydrochlorination from 1,1,2-trichloroethane (TCE) to VDC is an environmentallybenign synthetic route. so that it gradually becomes a hotspot research in this field. Catalyst is the key factor in the vapor phase catalytic synthesis of VDC fromTCE.In the study of gas-phase synthesis of VDC from catalytic cracking TCE, the more prominent problem is the poor stability of the catalyst, and the deactivation mechanism is not clear. In addition, the alkaline of catalysts could have a significant impact on the selectivity to VDC, but few relevant literatures were reported. To solve these problems, this paper mainly has done the three aspects.1. CsNO3/SiO2 catalysts were prepared via an impregnation method, and were applied in the vapor phase catalytic synthesis of VDC from TCE. The influence of reaction temperature on the deactivation of CsNO3/SiO2 catalysts was investigated in detail. It was found that low reaction temperature (< 350 ℃) would lead to a rapid deactivation, while high reaction temperature (> 400 ℃) could afford a high and stable catalytic activity. In the process of the dehydrochlorination, CsNO3 species were transformed into CsCl species, and coke was formed and deposited on the catalyst surface. However, the chemical change of Cs species and deposited coke were not the main reason for the deactivation of CsNO3/SiO2 catalyst. Some chlorine-containing species (organic products or HCI) which were formed during the reaction and difficultly desorbed from the catalyst surface should account for the deactivation of CsNO3/SiO2 catalysts at low reaction temperature. High temperature treatment (550℃) in non-oxidizing atmosphere could remove them and regenerate the catalysts completely. The life test of CsNO3/SiO2 catalyst was carried out at 400 ℃ for 100 h. The TCE conversion and the selectivity to VDC remained stable at 98% and 78% respectively, showing a good prospect for industrial applications.2. A series of M/SiO2(M=CsCl、KCI、 NaCl、 ZnCl2) catalysts were prepar ed via an impregnation method. These catalysts were applied in the vapor phas e catalytic synthesis of VDC from TCE,Focus is on the influence of the basici ty of catalyst on the dehydrochlorination of TCE. With characterizations of C O2-TPD and NH3 TPD, tt is found that CsCI/SiO2 is the most alkaline catal yst, while NaCl/SiO2 is the neutral catalyst.. From IR and XPS characterization s, it can be concluded that a new bond of Si-O-Cs was generated in CsCl/S iO2 catalyst,which is the main reason for the strong basicity of CsCl/SiO2 catal yst. As for CsCl/SiO2 catalyst can obtain a high selecitivity to VDC (ca.78%), while NaCl/SiO2 catalyst gets a poor VDC selectivity, it can be concluded that the basicity of catalyst is the key factor for generating VDC in the dechlori nation process of TCE. Increasing basicity of catalyst can promote the selecti ve dehydrochlorination of TCE into VDC.3. A serious of Cs-Mg double composition catalysts supported on SiO2 we re prepared using an impregnation method. The influence of the ratio of cataly st composition and reaction temperature of the dehydrochlorination were studied. It was shown that selectivity to VDC was increased with increase of Cs cont ents, while the selectivity to cis-DCE was increased with increase of Mg conte nts. With increase of reaction temperature, selectivity to trans-DCE could sho w an apparent increase. Herein, it is possible to freely adjust the composition of the product by changing the composition of the catalyst and the reaction te mperature.