| Chlorine has been used extensively as an industrial compound for synthesis of innumerable commercial product, including bleaches, organic diluents, adhesives, dust reducing agents, cutting oils, disinfectants, and monomers for plastics, pharmaceuticals, and pesticides. Despite societal contribution of chlorinated chemicals, there have recent suggestion by some environmental associations and scientists to ban the industrial use of chlorine. After their release into environment, organochlorine pollutants are stable and resistant to chemical and biodegradation and preferentially accumulation in the sequence food chain.; As a detoxification hydrodechlorination (HDC) reactions change neither the thermodynamics of the reaction nor the equilibrium composition. Also, there is no possibility of producing hazard by-product such as polychlorodibenzodioxins and polychlorodibenzofuran.; Liquid phase hydrodechlorination of 4-chlorophenols was studied over the temperature range from room temperature (R.T) to 80 °C using various Nickel catalysts and active hydrogen sources. Raney Nickel system converted 4-chlorophenol to ∼49 mol% of phenol and ∼34 mol% cyclohexanol at R.T. and proved to be more reactive than Ni0 and Ni-Fe. The HDC system with borohydrides as hydrogen source achieved hydrodechlorination at lower temperature than the system with molecular hydrogen. Ni-Al proved to be reactive for hydrogenolysis in the presence of borohydride at R.T. A somewhat surprising temperature dependence of Ni-Al mediated HDC in absence of H2 and borohydride was absented. Optimization with Ni-Al under mild condition was performed using central composite design (CCD). Optimal condition for maximum phenol production was predicted to be 80 °C, for 11 h with 30 mg of catalyst. 98 mol% phenol is produced under this condition.; A continuous stream of pentachlorophenol (PCP, 0.5 mg/min) in mixture of supercritical carbon dioxide (scCO2) and hydrogen was hydrodechlorinated by a heated column of gamma-alumina supported palladium (5 % w/w). Dechlorination efficiencies and time to reach equilibrium were influenced appreciable by the temperature and substrate delivery rate. The product from reaction at 210 °C, 2000 psi accounted for 92 mol% phenol and 2.3 mol% cyclohexanone. The temperature was maintained at 210 °C while the pressure and content of H2 in the gas mixture was changed to 1000 ∼ 2000 psi, 5 % and 16 % (v/v) H2/CO2. The production of phenol and cyclohexanone was greater at higher pressures (2000 psi.) with the formation of methoxy-cyclohexane. The content of H2 in the gas mixture was not appreciable influenced the product distribution. |
