Studies in dehydrochlorination of 1,1, 2, 2 Tetrachloroethane

Abstract

Dehydrochlorination of tetrachloroethane is studied both in homogeneous as well as in heterogeneous phases. The feasibility of the reaction has been evaluated from thermodynamic considerations. The reaction is found to be highly feasible. The experimental setup is fabricated out of Pyrex glass. The setup consists of (a) feeding arrangement, (b) preheater, (c) reactor and product collection system. In homogeneous vapour?phase dehydrochlorination the parameters studied are: (1) time factor, 83 to 470 (c.c.)(hr.)/ g?mole, (2) temperature, 220, 240, 260 and 280°C, and (3) chlorine concentration 0.75, 1.25, 2.00 and 2.75 weight%. The data has been analysed by both integral and differential methods. The following correlation between W/FW/FW/F, chlorine concentration, temperature and conversion is developed and tested: WF=(30.6913?3.0940c(RT/Pf))[?1000e(3.3704?0.1734c)?1x2ln?(1?x)?x]\frac{W}{F} = \left( \frac{30.6913 - 3.0940c}{(RT/P_f)} \right) \left[ -1000 e^{(3.3704 - 0.1734c)} - \frac{1}{x^2} \ln(1 - x) - x \right]FW?=((RT/Pf?)30.6913?3.0940c?)[?1000e(3.3704?0.1734c)?x21?ln(1?x)?x] The above equation is found to predict entire experimental data with an overall average error of ±15%. A radical chain mechanism for the reaction is postulated and tested. In heterogeneous dehydrochlorination of tetrachloroethane, detailed kinetic studies are carried out with two catalysts: (a) barium chloride on silica gel, and (b) active carbon catalyst. The ranges of various parameters studied are: (a) Temperature [220–300°C] (b) W/FW/FW/F [8 to 50 g catalyst·hr./g?mole] (c) Bed height [1.85 and 3.70 cm] (d) Particle size [?35 +43, ?48 +65, ?65 +100 and ?100 +150 Tyler mesh size] (e) Effect of trichloroethylene in feed [12.95, 17.20, 24.4 and 54.09 mole%] (f) Effect of hydrogen chloride in feed [10 mole%]. The reaction is found to be of first order. The equation developed on the basis of first?order kinetics predicted experimental data with the following deviations: (a) Barium chloride on silica gel catalyst … ±9.3% (b) Active carbon catalyst … ±8.4%. Rate equations have also been developed for both catalysts on the basis of Hougen–Watson type approach. Adsorption of tetrachloroethane — single site (trichloroethylene adsorbed) — is found to be the rate?controlling step in the case of barium chloride on silica gel catalyst, and desorption of hydrogen chloride — single site — is found to be the rate?controlling step in the case of active carbon catalyst. These rate equations predicted experimental data with the following deviations: (a) Barium chloride on silica gel catalyst … ±15.2% (b) Active carbon catalyst … ±10.2%. The Hougen–Watson models are re?examined by non?linear estimation of parameters. A considerable decrease in residual sum of squares of rate?controlling mechanisms is achieved. Optimization studies are carried out in the case of active carbon and chlorine catalysts. The following optimum conditions are obtained with active carbon catalyst: Temperature … 289.76°C W/FW/FW/F … 32.67 g catalyst·(hr.)/g?mole Conversion … 96.86%. However, with chlorine catalyst a saddle point is observed and hence optimum conditions could not be evaluated. Results with BaCl? on silica gel catalyst are not considered for optimization because of low conversions when compared with the results of active carbon catalyst.