Catalytic hydrodechlorination of chlorinated hydrocarbons in a medium of sodium hydroxide solutions. I: Conversion of carbon tetrachloride

Abstract

Carbon tetrachloride, classified as an ozone-depleting substance in the Montreal Protocol, is formed as a byproduct in the production of chlorinated hydrocarbons (chloromethanes, perchloroethylene, etc.). To develop a rational method of CCl4 utilization (an alternative to burning), in this work we study the liquid-phase catalytic hydrodechlorination of CCl4 with the formation of useful products such as sodium formiate, hexachloroethane, and perchloroethylene in the presence of aqueous sodium hydroxide solutions. Experiments are performed in a 300-mL autoclave at pressures of up to 1.5 MPa within a temperature range of 80–120°C on a Pd catalyst on sibunite (5 fractions, 0.1 to 1.6 mm). The dependences of the CCl4 conversion and the selectivities with respect to the principal reaction products on the initial concentrations of CCl4 and NaOH, the temperature, the partial pressure of hydrogen, the size of catalyst particles, and the palladium content in a catalyst are studied. Using the obtained data as a basis, we propose a process flowsheet, make some recommendations on the process conditions (depending on the specified composition of products), and determine the optimum catalyst characteristics: 1.5 wt % Pd on sibunite with a grain size of 0.315–0.63 mm. The proposed process allows us not only to solve the problem of recycling CCl4-containing wastes, but also to provide the production of three marketable products.