A natural gas contains $85$ mol$\%$ methane and $15$ mol$\%$ ethane. The gas

must be separated into two product streams, one that is $99$ mol$\%$ methane,

and the other that is $90$ mol$\%$ ethane. Draw and label a block flow diagram.

Choose a basis, and list the stream composition specifications. Calculate

the fraction of methane in the feed that goes to the methane$-$rich product,

and the fraction of ethane going to the ethane$-$rich product.