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.