Selective chlorination of aromatic hydrocarbons.

摘要

Toluene chlorination is a very important industrial process to manufacture the precursors and the solvents for the pharmaceutical, pesticides, fungicides, and dyes industries. The conventional processes are in the liquid phase and use metal chlorides as the catalysts. The selectivity for the para-isomer is around 40% in these methods.; For environmental reasons, heterogeneously catalyzed aromatics chlorinations have been widely studied in recent years. The selectivity for the para-isomer is improved as well. In these studies, zeolite catalyzed aromatic chlorinations are found to have a higher selectivity for the desired product, para-chlorotoluene, than that in the conventional process. The zeolite L is most commonly used in this category. During the reaction, degradation of the catalyst structure, dealumination of zeolite, and formation of polychlorinated materials as the side product may deactivate the catalysts. The zeolite ZSM-5 is found to be as active as zeolite L, which is reported to be the most active zeolite in the aromatic chlorination. It is also found that the ZSM-5 does not structurally degrade in the reaction environment on repeated use. The activity and the selectivity of the ZSM-5 can be fully recovered by oxidation treatment of the used catalyst at elevated temperature.; Sulfuryl chloride has been used as the chlorinating agent during the aromatic chlorination in the liquid phase in the first part of the studies. In order to have a better understanding of the reactions, both zeolite ZSM-5 and AlCl₃ have been used as catalysts in the studies. A comprehensive kinetic model, using ZSM-5 as the catalyst, has also been proposed.; Dichlorine gas has been used as the chlorinating agent for aromatic chlorination in the vapor phase in the second part of the studies. A reactor system for this study has also been fabricated. Toluene is the aromatic hydrocarbon for the reactions and is carried to the reactor in the vapor phase by using nitrogen as a carrier gas. The pulsed feed reaction, the sequential feed reaction, and the co-feed reaction have been studied. The zeolite ZSM-5 has been used as the catalyst in the vapor phase reaction.; Membrane reactor has been studied since 60'. The studies on this topic are looking for a device, which could have chemical reaction and product separation under one unit, for the real application. With selected removing or adding certain species of the reagent from/to the reagent mixture, the selectivity for desired product of the overall conversion can be enhanced.; The mathematical simulation of the series reaction and series-parallel reaction network in the membrane reactors has been attempted. The membrane reactors with plug flow at the reaction zone or backmixing at the reaction zone have been studied. Backmixing the reaction side of the reactor might have three effects upon yield. First, the concentration of the reactant would be lower and consequently the driving force for losing it through the membrane would be reduced. Second, the concentration of the desired intermediate would be increased thereby increasing the driving force for its removal through the membrane. These two positive effects will be offset by the second consequence of a higher concentration of the desired intermediate, namely that the rate at which it reacted to form the undesired product will also be increased. Based on the basic parameters and the properly selected permeability of the membrane, the yield of the desired product is increased by 42% in the back-mixed model and 34.8% in the plug flow model.; Then, the hydrodechlorination of 1,2-dichloroethane was studied over a Rh/SiO₂ catalyst. The catalyst deactivated with use; only part of the deactivation was reversible. The reversible deactivation could be quantitatively accounted for by assuming quasi-equilibrium between surface chlorine and gas phase HCl. An empirical power-law rate expression was found