The methanol (1) and isobutyl acetate (2) need to be separated by distillation i
ID: 1062711 • Letter: T
Question
The methanol (1) and isobutyl acetate (2) need to be separated by distillation in a sieve tray column at 150 [kPa]. The feed enters the column at a rate of 25 [mol/s], contains 20 % (by mole) of methanol, and 11.1% of it is vapor. A distillate with a 90 % purity and that recovers 79 % of the methanol is desired. The reflux ratio will be 1.6 times the minimum value. The column is equipped with a total condenser and a partial reboiler. Equilibrium data at 150 [kPa], from Susial et al. (Afinidad, LXIX, 558, 2010), are provided on the next page. Please calculate or estimate: (a) Outgoing molar flow rates, in [mol/s] and bottoms mole fraction. b) Minimum external reflux ratio. (c) Number ideal stages required (including the reboiler). Report an integer number.Explanation / Answer
Let us assume the letter for stream flows in mol/s,
Feed (Methanol + isobutyl acetate), = F = 25 mol/s
Distilate product = D
Bottoms Product = B
In feed we have,
Methanol = 25 * 0.2 = 5 mol/s
isobutyl acetate = 25 * 0.8 = 20 mol/s
In distilate we are recovering Methanol about 79%, Therefore,
Methanol in Distilate = 5 * 0.79 = 3.95 mol/s
We know the fraction of Methanol in Distilate, i.e .0.9,
We know that, Mole % = Individual moles / Total Moles
0.9 = 3.95 / Total Moles (D)
Total moles of Distillate, D = 4.39 mol/s
Now, write down the Over all material balance equation across the distilation column:
F = D + B
25 (mol/s) = 4.39 mol/s) + B .................Eqn (1)
So, Bottoms flow rate, B = 25 - 4.39 = 20.61 mol/s
In first step we have seen that, we are recovering 79% methanol on Top distilate product, therefore remaining 21% on Bottoms, so,
Methanol in Bottoms = 5 * 0.21 = 1.05 mol/s
Isobutyl acetate in bottoms = B - Methanol in Bottoms = 20.61 - 1.05 = 19.56 mol/s
Methanol mole fraction in bottoms = 1.05 / 20.61 = 0.051
Isobutyl acetate mole fraction in bottoms = 19.56 / 20.61 = 0.949.
Hope it helps.
For remaining part of question to answer I require, Equilibrium data.