Introduction to Chemical Engineering Thermodynamics
Introduction to Chemical Engineering Thermodynamics
8th Edition
ISBN: 9781259696527
Author: J.M. Smith Termodinamica en ingenieria quimica, Hendrick C Van Ness, Michael Abbott, Mark Swihart
Publisher: McGraw-Hill Education
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ans Q4 a) x≈0.38; y≈0.73; b) T≈348.5 K 

Note that the x-y diagram was to be used for part (i).
The x-y diagram relates the compositions of vapour and liquid at equilibrium; thus, we know the
methanol mole fractions in the liquid (x) and vapour (y) leaving the flash stage must be represented
by a point on this line (x, y).
A steady-state material balance must also be fulfilled. We can represent the material balance (total
and component combined) as a straight-line on the x-y diagram. The outlet composition is found
where this line crosses the equilibrium line.
Some of you had difficulty plotting the material balance line since the y-intercept was off the scale,
however it was possible to determine another point on the line, such as the x-intercept, and draw
the line extending from there through the point (x₁, xf) and beyond.
Once the exit stream compositions are known, the temperature can be read off the T-xy diagram.
Note that our old friend the "Lever Rule" could also have been used to determine the compositions,
but this is probably more cumbersome and less accurate - have a go and see if you agree.
(please note that the diagonal line y=x is merely there to guide the eye - e.g. when the equilibrium
line crosses this diagonal we can identify an azeotropic point).
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Transcribed Image Text:Note that the x-y diagram was to be used for part (i). The x-y diagram relates the compositions of vapour and liquid at equilibrium; thus, we know the methanol mole fractions in the liquid (x) and vapour (y) leaving the flash stage must be represented by a point on this line (x, y). A steady-state material balance must also be fulfilled. We can represent the material balance (total and component combined) as a straight-line on the x-y diagram. The outlet composition is found where this line crosses the equilibrium line. Some of you had difficulty plotting the material balance line since the y-intercept was off the scale, however it was possible to determine another point on the line, such as the x-intercept, and draw the line extending from there through the point (x₁, xf) and beyond. Once the exit stream compositions are known, the temperature can be read off the T-xy diagram. Note that our old friend the "Lever Rule" could also have been used to determine the compositions, but this is probably more cumbersome and less accurate - have a go and see if you agree. (please note that the diagonal line y=x is merely there to guide the eye - e.g. when the equilibrium line crosses this diagonal we can identify an azeotropic point).
4) A mixture containing equal molar amounts of methanol and water is fed into a vessel which is at
pressure of 1 atm. Thirty-five percent of the feed is flashed off.
i) Using the x-y diagram below find the methanol mole-fraction in the vapour and liquid leaving the
vessel (where the exit streams are in equilibrium).
ii) Use the temperature-composition diagram below to find the temperature of the exit streams.
x-y diagram for methanol/water at 1 atm
Ym (molefraction of methanol in vapour)
Temperature (K)
1
0.8
0.6
0.4
0.2
375
370
365
360
355
350
345
340
335
0
0
0.2
0.6
0.2
0.4
Xm (molefraction of methanol in liquid)
Temperature-composition diagram for methanol/water at 1 atm
0.8
0.4
0.6
molefraction of methanol
0.8
1
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Transcribed Image Text:4) A mixture containing equal molar amounts of methanol and water is fed into a vessel which is at pressure of 1 atm. Thirty-five percent of the feed is flashed off. i) Using the x-y diagram below find the methanol mole-fraction in the vapour and liquid leaving the vessel (where the exit streams are in equilibrium). ii) Use the temperature-composition diagram below to find the temperature of the exit streams. x-y diagram for methanol/water at 1 atm Ym (molefraction of methanol in vapour) Temperature (K) 1 0.8 0.6 0.4 0.2 375 370 365 360 355 350 345 340 335 0 0 0.2 0.6 0.2 0.4 Xm (molefraction of methanol in liquid) Temperature-composition diagram for methanol/water at 1 atm 0.8 0.4 0.6 molefraction of methanol 0.8 1
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