7760
Ind. Eng. Chem. Res. 2006, 45, 7760-7766
Gas-Phase Hydrodechlorination of Dichloromethane at Low Concentrations with Palladium/Carbon Catalysts Zahara M. de Pedro, Luisa M. Go´ mez-Sainero,* Eloisa Gonza´ lez-Serrano, and Juan J. Rodrı´guez Ingenierı´a Quı´mica, Facultad de Ciencias, UniVersidad Auto´ noma de Madrid, Cantoblanco, 28049 Madrid, Spain
The behavior of a commercial (CE) and homemade (CH) palladium/carbon catalyst in the gas-phase hydrodechlorination of dichloromethane (DCM) has been investigated, at low concentration, in a fixed-bed microreactor, with a view of application to the treatment of residual gas streams. The influence of space time (1.0-6.6 kg h mol-1), reaction temperature (423-623 K), and H2/DCM molar ratio (50-400) was investigated. The catalysts showed high performance, with DCM conversions up to 97% and selectivities to nonchlorinated products of ∼80%. Modification of the operating conditions highly affects the activity of the catalyst while also showing scarce influence on the selectivity. At equal palladium loadings, the CH catalyst showed higher activity than the CE catalyst; however, the product distribution was fairly similar. This was attributed to a different dispersion and distribution of palladium particles, but a similarity in the nature of the palladium species involved in both types of catalysts. Introduction
Experimental Section
Currently, the emission of organic chlorinated compounds into the atmosphere seems to be a significant concern. Carbon tetrachloride (CTC), chloroform (TCM), and dichloromethane (DCM) are some of the most common chlorinated compounds in residual gas streams.1 Because of their high toxicity,2 carcinogenic character,3 and the potential contribution to the destruction of the ozone layer,4 their emission is progressively restricted by strong legal regulations. This leads to the necessity of developing effective treatment techniques that are compatible with the environment. Catalytic hydrodechlorination becomes, in that way, one of the most promising emerging technologies. It operates at relatively low temperatures and atmospheric pressure, and the reaction products are less hazardous than those resulting from the application of other techniques. While the bibliography is profuse in regard to works related to the hydrodechlorination of CTC,5-9 the other chloromethanes have been scarcely studied.10-14 On the other hand, most of the work that has been reported involves pure compounds or mixtures where chloromethanes are present at high concentrations. To our knowledge, there are very few papers that are focused on the hydrodechlorination of chloromethanes at concentrations of
