Chapter 4, Problem 4.68P

Ethane is chlorinated in a continuous reactor:

C₂H6 + Cl₂ - C₂H₅C1 + HC1

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

C₂H₅C1 + Cl₂ - C₂H4C1₂ + HC1

1. Suppose your principal objective is to maximize the selectiv ity 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?
2. Take a basis of I (X) mol CSH5CI 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.
3. The reactor is designed to yield a 15% conversion of ethane and a selectivity of 14 mol CSHsCl/moi C2H4CI2, with a negligible amount of chlorine in the product gas. Calculate the feed ratio (mol CI2/ mol C₂H*) and the fractional yield of monochloroethane.
4. Suppose the reactor is built and started up and the conversion is only 14%. Chromatographic analysis shows that there is no CI2 in the product but another species with a molecular weight higher than that of dichloroethane is present. Offer a likely explanation for these results.