Question

2. (no calculations required) A mixture of n-butanol and water is being separated using two distillation columns coupled together by a liquid-liquid separator. Both columns have 30 trays and operate at 1 atm with the internal reflux ratio adjusted to four times the minimum Vapor-liquid- liquid equilibrium data for this system at 1 atm is provided below in the form of a T-x-y diagram. If the feed to the distillation towers is a saturated liquid that contains 65 mol% water, estimate the mole fraction of water in all exiting streams (i.e., B1, B2, and the vapor leaving each tower) and estimate the temperature of all exiting streams Feed Specific Gravity water = 1.00 n-butanol = 0.81 Column-1 Column-2 -B2 T-x-y for Water/N-Butanol 0.1 0.2 0.8 0.9 0.3 0.4 0.5 0.8 0.7 x,y (mol, fract, water)

Answer 1

FEED S8 S13 B2 B10 B6 B1 S11 S6 B4 B8 2 WAT BUT

Stream results as per above flowsheet:

	Units	FEED	WAT	BUT	S6	S11
Phase		Liquid Phase	Liquid Phase	Liquid Phase	Vapor Phase	Vapor Phase
Temperature	C	40	90	117	91	92
Pressure	bar	2.0	1.0	1.0	1.0	1.0
Average MW		37.65	22.65	74.12	32.83	31.59
Mole Flows	kmol/hr	100	71	29	43	63
BUTANOL	kmol/hr	35	6	29	11	15
WATER	kmol/hr	65	65	0	32	47
Mole Fractions
BUTANOL		0.35	0.08	1.00	0.26	0.24
WATER		0.65	0.92	0.00	0.74	0.76
Mass Flows	kg/hr	3765	1605	2160	1412	1978
BUTANOL	kg/hr	2594	434	2160	841	1123
WATER	kg/hr	1171	1171	0	570	855
Mass Fractions
BUTANOL		0.69	0.27	1.00	0.60	0.57
WATER		0.31	0.73	0.00	0.40	0.43