System analysis of a commercial scale acrylonitrile process



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The synthesis of acrylonitrile from hydrogen cyanide and acetylene was studied in a large industrial reactor. Gas chromatographs on the reactor feed and off-gas streams were used to provide material balance data every fifteen minutes. The reaction system is heterogeneous, with the gas phase being contacted with the catalyst phase, an aqueous slurry which contains suspended cuprous chloride, the catalyzing agent. Since the reaction system is heterogeneous, kinetic rate expressions of the Hougen-Watson type were derived for several postulated reaction mechanisms. Mass transfer between the liquid catalyst phase and the acetylene containing gas phase was believed to be important. Therefore, mass transfer effects were considered in formulating the kinetic rate equations. The material-balance data were used for statistically estimating constants in the derived rate expressions. One proposed rate equation was found to be very good from the standpoint of fitting the data and from correctly predicting the signs of the coefficients in the rate expression,. This rate equation was derived for a mechanism which involved the reaction occurring at a single catalyst site, with the desorption of the product acrylonitrile being the rate-determining step. [...]