Ethane is chlorinated in a continuous reactor: C2H6 Cl2 ! C2H5Cl HCl Some of the product

Chapter 4, Problem 4.68

(choose chapter or problem)

Ethane is chlorinated in a continuous reactor:

\(\mathrm{C}_{2} \mathrm{H}_{6}+\mathrm{Cl}_{2} \rightarrow \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{Cl}+\mathrm{HCl}\)

Some of the product monochloroethane is further chlorinated in an undesired side reaction:

\(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{Cl}+\mathrm{Cl}_{2} \rightarrow \mathrm{C}_{2} \mathrm{H}_{4} \mathrm{Cl}_{2}+\mathrm{HCl}\)

a) Suppose your principal objective is to maximize the selectivity of monochloroethane production relative to dichloroethane production. Would you design the reactor for a high or low conversion of ethane? Explain your answer. (Hint: If the reactor contents remained in the reactor long enough for most of the ethane in the feed to be consumed, what would the main product constituent probably be?) What additional processing steps would almost certainly be carried out to make the process economically sound?

(b) Take a basis of 100 mol \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{Cl}\) produced. Assume that the feed contains only ethane and chlorine and that all of the chlorine is consumed, and carry out a degree-of-freedom analysis based on atomic species balances.

(c) The reactor is designed to yield a 15% conversion of ethane and a selectivity of 14 mol \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{Cl}\)/mol \(\mathrm{C}_{2} \mathrm{H}_{4} \mathrm{Cl}_{2}\), with a negligible amount of chlorine in the product gas. Calculate the feed ratio (mol \(\mathrm{Cl}_{2}\)/ mol \(\mathrm{C}_{2} \mathrm{H}_{6}\)) and the fractional yield of monochloroethane.

(d) Suppose the reactor is built and started up and the conversion is only 14%. Chromatographic analysis shows that there is no \(\mathrm{Cl}_{2}\) in the product but another species with a molecular weight higher than that of dichloroethane is present. Offer a likely explanation for these results.