Destructive Adsorption of Chlorinated Benzenes on Ultrafine (Nanoscale) Particlesof Magnesium Oxide and Calcium Oxide

摘要

The thermodynamically favored but kinetically inhibited exchange of oxide forchloride in the reaction of MgO/CaO with chlorinated benzenes has been investigated. In order to enhance kinetic parameters, MgO/CaO particles with very large surface areas have been employed. The presence of MgO/CaO allows the destruction of chlorinated benzenes at lower temperatures than simple pyrolysis or combustion processes. The presence of hydrogen as a carrier gas allows still lower temperatures to be employed. Main reaction pathways have been deduced for mono-, di-, and trichlorobenzenes over MgO and CaO of varying surface areas and using helium, air, and hydrogen as flow gases. Significant differences between MgO and CaO have been realized, perhaps due to the fact that MgO can be prepared in higher surface areas. For example, CaO induces more carbon formation. A search for certain trace toxins as products (particularly the dibenzo-p-dioxin backbone with 0-3 chlorine substituents) was carried out. Under our analysis conditions, it was determined that such products were not formed under any circumstances with MgO, and if oxygen in the carrier gas was absent, no dioxins were formed with CaO either. However, with low surface area CaO and air as a flow gas, dihenzo-p-dioxin (no chlorine substituents) and a monochloro derivative were produced in small amounts. p3.