# Distil Col

1. May 6, 2007

### scott_for_the_game

If you were to design a distil col and didn't know the feed conditions how would you go about starting. You know xd, xb, xf, R, Eq data.

Theres 5 potential q's.

Also how would u make enthpy diagram for PS.

Thanks.

2. May 11, 2007

### siddharth

Can you elaborate on what your notation stands for? What I'd guess is that xd and xb are the mole fractions of the more volatile component in the liquid phase in the distillate and residue, while xf is the mole fraction in the feed. To start solving for this (ie, find the number of stages or trays), you need the H-x-y diagram.

q as in q-line?

Usually one constructs the enthalpy diagram as follows from the VLE data, Heat capacities of liquid, Latent heat of vapourization and Heat of solution. The VLE data for most systems can be easily found (for ex, Perry's handbook)

If you set the reference temperature or base temperature corresponding to the heat of solution, you can find the enthalpy of saturated liquids as
$$H_L=C(T_{sat} - T_{base})M_{av} + (\Delta H_s)x$$
where H_L is the enthalpy of sat liquid, C is the heat capacity, M_av is the average molecular weight H_s is the heat of solution and x is the mol frac of volatile compound in liq phase.

Similarly, one can calculate the enthalpy of the saturated vapor from the VLE data, and then plot the H-x-y diagram needed for the PS method.

You might want to look up the relevant chapters in either "Mass-Transfer Operations" by Treybal, or "Separation Process Principles" by Seader and Henley. It's very well explained there with worked out examples.

Last edited: May 11, 2007
3. May 13, 2007

### scott_for_the_game

Cheers for the feedback.

Yeh q-line.

So with the calculation of H and h.. with those equations you'd get what a function of x and y of the most volatile component to plot..