Experimental Study On Preparation Of Chloroform Via Catalytic Hydrogenation Of Carbon Tetrachloride

Tetrachloride Carbon(CTC) is an ozone depleting substance (ODS). It is mainly used as feedstock of chlorofluorocarbons(CFC), chemical process agent and cleaning solvent. According to the Montreal Protocol and the Country Program for ODS phaseout in China, the consumption of CTC will be reduced to 15% of that in 1999 by January 1 2005. However, the CTC output as a byproduct in the production of chlorinated methane is about 20,000-30,000 tons per year. In contrast, the feedstock use of CTC in producing non-ODS product is not restricted, hence the development of CTC conversion technology is an urgent subject.Chloroform is a commodity chemical with wide applications and large consumptions. Hence converting CTC to chloroform is one of the best options, which can solve the environmental pollution, besides it is of economical advantages.With a new kind of support- active carbon fiber, the effects of such factors as temperature, pressure, loading of Pt, reaction time, catalyst's composition and its manufacturing conditions, on conversion of CTC andselectivity to chloroform were studied experimentally, the reaction was conducted in liquid phase without diluent used, and the optimum conditions were determined. The results show that the performance of carbon fiber supported Pt catalyst is superior to that of Pd/A; The active of catalysts of Fe> Ni and Fe-Ni alloy is much inferior to Pt; In comparison with Pt/ion exchange resin, both conversion and selectivity of Pt/carbon fiber catalyst are high. Pt catalyst can be produced by reducing H2PtCl6 with hydrogen at high temperature, with reducing agent ethanol under ambient temperature or with NaBH4, and the first approach gives the best catalytic performance. Under the optimum conditions of the experiment, i.e. at temperature of 393K, H2 pressure of 4.0MPa, Pt load of 0.8% and reaction time of 22h, both conversion of CTC and selectivity to CHCls can exceed 90%.For the gas phase reduction of CTC to chloroform, the effect of Pt load, the flow rate of H2 and mole ratio of H2/CC14 on CTC conversion and selectivity to chloroform were also studied. The results show that compared to the catalyst Pd/Al2O3, Pt/active carbon fiber is better. In the condition range studied, the following conclusions can be drawn, i.e. the catalyst active and selectivity increase with the load of Pt on the support of carbon fiber, Reducing flow rate of H2 can improve the conversion of CTC, however its effect on selectivity to chloroform is marginal, as H2/CC14 mole ratio increases, higher CTC conversion and lower selectivity to chloroform is found, however, as the ratio exceed a definite level, the effect of H2pressure becomes limited. Under the optimum conditions of the experiment, i.e. using Pt/carbon fiber as the catalyst, Pt load of 0.5%, at temperature of 423K, H2/CC14 mole ratio of 10, and residence time of 9 seconds, both conversion of CTC and selectivity to CHCls can exceed 70%.Triphenylchlorinated methane was prepared by using CTC as a reacting material. The operation condition for this reaction is simple and mild, and hence the reaction is feasible in converting CTC in the future, although the present yield is about 50%.