A Txy diagram for methanol?water mixtures at 1 atm absolute is shown below. The

ID: 914453 • Letter: A

Question

A Txy diagram for methanol?water mixtures at 1 atm absolute is shown below. The feed to the

drum and the liquid and vapor product streams are shown as points B, A, and C, respectively.

The feed contains 40 mol% methanol where a fraction feed (f) is vaporized, and the vaporizer

operates at a pressure of 1 atm absolute and 80 oC. Vapor and liquid leaving the drum are in

equilibrium at the temperature and pressure of the system and have methanol mole fractions of y

and x, respectively.

(a) Prove that f can be estimated from

Use this result to determine f for the given system conditions given above.

(b) Use the Txy diagram to estimate the minimum and maximum temperatures at which the

given feed stream could be separated into vapor and liquid fractions at 1 atm. In each case,

what fractions of the feed would be vaporized?

Pvap = 1 atm
Tvap = 80°C

CH3OH --- 40% mol

vapor ---- f = ?

A solid line (T - x) is a saturated liquid line.

A dashed line (T - y) is a saturated vapour line.

Let’s define

V/F = f : the fraction of the feed that vaporises.

f = V/F = (ZF - x) / (y - x)

analyzing the plot;

f = V/F = (length of chord AC)/(length of chord AB)

If CH3OH is 40% mol (liquid phase) then f (vapor phase) it's 60% mol.

T CH3OH(boiling point) = By / Ay - log (Pvap)
T Vap(boiling point) =Bx / Ax - log (Pvap)

Make these calculations and you will be able to understand the flash destillation.

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