A gas mixture at $300$ K and $1$ bar analyzing by volume $20\%$ N and $80\%$ CH$,$ is subjected to liquefaction at a rate of $1500$ kg$/$h$.$ It is found that only $30\%($weight$)$ of the entering gas is liquefied and the concentration of N in the liquid is $60\%$ by weight. The unliquefied gas leaves the unit at $273$ K and $1$ bar. Determine $($a$)$ the volume of unliquefied gas, m$^3/$h $($b$)$ the composition of the gas leaving expressed as volume $\%.$

Answer a$)1373\mathrm{.}93$m$^3$ b$)$ N$2=10\mathrm{.}97\%$ and CH$4=89\mathrm{.}03\%$

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