One hundred pound-moles per hour of a mixture of 60 mol% methanol in water at 30oC and 1 atm is to be separated by distillation at the same pressure into a liquid distillate containing 98 mol% methanol and a bottoms liquid product containing 96 mol% water. Enthalpy and equilibrium data for the mixture at 1 atm are given in Table 7.8. The enthalpy of the feed mixture is 765 Btu/Ibmol.

(a) Using the given data, plot an enthalpy'concentration diagram.

(b) Devise a procedure to determine, from the diagram of part (a), the minimum number of equilibrium stages for the condition of total reflux and the required separation.

(c) From the procedure developed in part (b), determine N. Why is the value independent of the feed condition?

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Methanol–Water Vapor-Liquid Equilibrium and Enthalpy Data for 1 atm (MeOH= Methyl Alcohol) Table 7.8 Enthalpy above 0°C, Btu/lbmol Solution Vapor Liquid Equilibrium Data Mol% Saturated Mol% Saturated Vapor МеОН in Liquid Temperature, °C МеОн Liquid T, °C T, °C Vapor hy hi y or x 100 100 20,720 100 3,240 96.4 13.4 2.0 20,520 92.8 3,070 5 98.9 23.0 93.5 20,340 87.7 4.0 10 97.7 2,950 91.2 6.0 30.4 96.2 20,160 84.4 2,850 15 36.5 89.3 94.8 20,000 81.7 2,760 8.0 20 87.7 10.0 41.8 19,640 78.0 2,620 30 91.6 75.3 51.7 84.4 88.2 19,310 2,540 15.0 40 57.9 81.7 18,970 73.1 20.0 50 84.9 2,470 66.5 18,650 30.0 78.0 60 80.9 71.2 2,410 2,370 2,330 72.9 75.3 76.6 18,310 69.3 40.0 70 50.0 77.9 73.1 72.2 17,980 67.6 80 71.2 68.1 17,680 66.0 60.0 82.5 90 2,290 70.0 87.0 69.3 100 64.5 17,390 64.5 2,250 91.5 80.0 67.6 90.0 95.8 66.0 65.0 97.9 95.0 64.5 100.0 100.0