Study On The Pollution-Free Treatment Of Carbon Tetrachloride (CT)

Carbon tetrachloride (CT) is a colorless and easily volatile liquid. It is largely used for metal degreasing, dry-cleaning fluid, fabric spotting fluid, fire extinguisher fluid and reaction medium. As a consequence of its refractory nature and large scale, produce of CT is environmentally ubiquitous. Since the advent of the Montrel Protocol, which has limited further production of CT, there has become a need for environmentally friendly and efficient means to decompose CT. Import of CT has been forbidden in China by 2000. Because CT can not be easily decomposed under ambient conditions, and is a suspected human carcinogen and an Environmental Protection Agency (EPA) priority pollutant, a wide variety of studies on the decomposition of CT has been carried out in aqueous and gas-phases including the use of a liquid-phase, anaerobic activated carbon reactor, UV photolysis, and high pressure and electron-beam plasmas. Since the elimination of CT as proposed in these techniques requires the input of substantial quantities of energy, the development of decomposition methods which produce usable by-products is essential from a practical viewpoint. Several methods of degradation of CT were discussed in this paper, such as catalytic hydrogenation and high temperature combustion and so on. Each methods had a series of disadvantages. Catalytic hydrogenation leads to hydrogen chloride, and can corrupt apparatures. High temperature combustion leads to quantitative conversion to COCl₂ and to secondary pollution. Other methods are not available for industrialized production, such as microbial transformation and photo-decompositon. A new decomposition method was selected in this paper. CT reacting with sulfur has been investigated under atmospheric pressure and high temperature. The productions only include carbon disulfide and sulfur chloride, and no other long-chain compounds and no phosgene . The reaction production was detected for quantitative analysis and qualitative analysis by gas chromatography. Orthogonal designs for experiments in the gas-liquid system and the gas-gas system were introduced respectively. In the process of gas-liquid reaction, the influencing factors on the conversion rate of CT were investigated in detail, such as reaction temperature, the molar ratio of sulfur and CT and the reflux rate of CT and catalysis. In this process, bubbling reactor was designed and the four influencing factors were reviewed. The optimal result is achieved, the reaction temperature is 400℃, the molar ratio of sulfur and CT is 12:1, the reflux of CT is 0.2g/min and catalysis is iron and glass paddings. In the course of gas-gas reaction, three influencing factors on the conversion rate of CT were investigated, such as reaction temperature, the molar ratio of sulfur and CT and the reaction time. The reasonable result is achieved, the reaction temperature is 550℃, the molar ratio of sulfur and CT is 12:1 and the reaction time is 25min. The experiment results were analysed with orthogonal design by STATISTICA math software, and optimal reaction conditions were achieved. The influencing factors include reaction temperature, the molar ratio of CT and sulfur, and the reflux of CT and so on.