You may discuss this problem in pairs or in groups but each individual must gain

Question

You may discuss this problem in pairs or in groups but each individual must gain the ability to succeed on the exam. VLE data for the binary system n-pentane (1) and toluene (2) are shown in the graph below for three different temperatures. Use the inverse lever arm rule (ILAR) to determine the quality of the vapor-liquid mixture at 20 degree C and 200 torr for an overall composition of 37.5% n-pentane. Repeat for 30 degree C and 40 degree C. What is the trend? At what pressure will L/V 1 for a 50/50 mixture at 40 degree C?

Explanation / Answer

1 torr=1 mm hg

a horizantal line is drawn at 200 mm hg and a vertical line is drawn at 37.5% composition .

For a P -x,y at 20 oc, taking the horitantal line drawn at 200 mm hg as tieline cuts the p-x cuvrve ( bubble curve) at 32% and its equillibrium composition in vapor phase is 89% i.e(the composition of n- pentane in liquid phase is 0.32 and its equillibrium composition in vapor phase is 0.89)

For a P -x,y at 30 oc, taking the horitantal line drwan at 200 mm hg as tieline cuts the p-x cuvrve ( bubble curve) at 19% and its equillibrium composition in vapor phase is 85.5% i.e(the composition of n-pentane in liquid phase is 0.19 and its equillibrium composition in vapor phase is 0.855)

For a P -x,y at 40 oc, taking the horitantal line drwan at 200 mm hg as tieline cuts the p-x cuvrve ( bubble curve) at 10% and its equillibrium composition in vapor phase is 73% i.e(the composition of n-pentane in liquid phase is 0.10 and its equillibrium composition in vapor phase is 0.73) .

As temperature is increased the compositions of n-heptane in both the liquid and vapor phases is decreased.

Draw a vertical line at 50% composition. also draw tie lines at different pressures for the p-xy plot at 40 oC. find the presuure at which the width of the tie lines onthe left and right of the verticle line drwan at 50 % are same. ( the width of the tielines indicates amounts of vapor and liquids i.e L/V=1)

This pressure found to be 250 mm hg approximately.

p t x y* 200 mm hg 20 oC .32 0.89 200 mm hg 30 oC .19 0.855 200 mm hg 40 oC .10 .73

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