The things given : Distillatio

Answer:

No! you can not take X_B = 0.02

• X_F is the mole/wt fraction of more volatilecomponent in the feed stream.
• X_D is the mole/wt fraction of more volatilecomponetn in the distillate.
• X_B is the mole/wt fraction of more volatilecomponent in the bottom stream.

X_D = 0.98 means 98 % of Distllate contains molevolatile component and rest 2 % other component. (if it is binarydistillation)

Assume basis: per unit time.

For example, if the distllate (D) is 80 mol and X_D =98 mol %. Then the amount of more volatile component in thedistillate will be

• = (X_d x D)
• = 0.98 x 80 mol
• = 78.4 mol

The other component will be 2 mol %. i., the amount of othercomponent in the distillate will be

• = 0.02 x D
• = 0.02 x 80 mol
• = 1.6 mol

Note: This 0.02 mol fraction or 1.6 mol refers to thecomposition in the distillate not in the bottomstream.

X_B refers to composition in bottom stream. Tocalculate the amount of X_B one shoud know the value ofB.

To find unkonwn values. These two material balances veryimportant.

Overallmaterial balance:

Feed = Distillate + Bottoms

F = D + B

Overallcomponent balance:

FX_F = DX_D + BX_B

You can even take material balance over the top of columncontaining Vapor stream (V) , Distillate (D) and some portion ofdistillate fed back to the column in liquid form (L).

V = L + D

Reflex ration R = L/D

Then, the above equation can further be modified to

V = (R+1)D

If you still have any doubt feel free to ask me.