Repeat the calculation of problem 5.22 with the vapor being recycled to the compressor

Problem 5.22

Isobutane is to be liquefied to make liquid petroleum gas (LPG). The butane is available at 25^◦C and 1 bar, it will be compressed to 15 bar, cooled to 0^◦C in a heat exchanger, and expanded and flashed to 1 bar in an adiabatic valve, and the vapor and liquid separated. Determine the work required per kg of LPG produced if the compressor has an isentropic efficiency of 100%, and none of the vapor is recycled.