Study Number 4 - Separation of Alcohols from the Acetate Alcohol Water Ternary by Extractive Distillation

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STUDIES IN EXTRACTIVE AND AZEOTROPIC DISTILLATION SERIES

Study Number 4 - SEPARATION OF ALCOHOLS FROM THE ACETATE/ALCOHOL/WATER TERNARY BY EXTRACTIVE DISTILLATION

A summary of experimental results (in outline format) from a series of investigations of hard-to-separate acetate/alcohol/water ternary mixtures

Dr. Lloyd Berg,

Chairman and Director of Research, Brix-Berg Company PLLC
Emeritus Department Head and Professor, Chemical Engineering Department, Montana State University
and

A. Terry Brix, President, Brix-Berg Company PLLC

Separations Studied:

Acetate/alcohol/water ternary mixtures are found in the manufacture of acetates, in some waste solvent or process streams, and in laboratory preparations. Specific ternary systems studied by Brix-Berg include:

Ethyl acetate/ethanol/water (Table 1)

n-propyl acetate/n-propanol/water (Table 2)

Isopropyl acetate/isopropanol/water (Tables 3 and 4)

n-butyl acetate/n-butanol/water (Table 5)

2-butyl acetate/2-butanol/water (Table 6)

iso-butyl acetate/iso-butanol/water (Table 7)

n-amyl acetate/n-amyl alcohol/water (Table 8)

n-hexyl acetate/n-hexanol/water (Tables 9 and 10)

Typically, these acetate/alcohol/water ternary systems are complex mixtures in that they often contain combinations of binary and ternary azeotropes. To illustrate this complexity, Table 1. provides boiling point and azeotrope compositional data for the ethyl acetate/ethanol/water system.

Table 1 - Azeotropes in the Ethyl Acetate/Ethanol/Water System

Compound(s)	BP - ^oC	Azeotrope Composition ( %)
		Ethanol	Ethyl Acetate	Water
Ethanol	78.3
Ethyl acetate	77.1
Water	100
Ethanol/water	78.2	95.4		4.6
Ethyl acetate/water	70.4		91.9	8.1 (2 phases)
Ethanol/ethyl acetate	71.8	31	69
Ethanol/ethyl acetate/water	70.2	8.4	82.6	9.0

We have found that many of these acetate/alcohol/water ternary mixtures can be separated by extractive distillation. In general, the acetate/water component goes overhead, but we have found agents that do bring the alcohol overhead for some systems.

Experimental:

For each ternary system studied, typically 100 to 200 different organic solvents were evaluated for potential as agents in extractive distillation. Tests consisted of determination of relative volatility - with and without agent - in an Othmer vapor-liquid equilibrium still.

In a number of cases (but not all), where favorable relative volatility was found in the Othmer still, a batch distillation test was conducted in a 3" diameter - 5.5 theoretical plate glass distillation column. All testing was conducted at atmospheric pressure at Bozeman MT.

Analyses were conducted by the author or his assistants using a Varian Gas Chromatograph.

Results:

Following are a series of Tables summarizing the test series for each organic hydrocarbon separation studied in this work.

Table 1 - Ethyl acetate/ethanol/water Separation

Separation	Ethyl acetate from ethanol/water
Method	Extractive Distillation
Relative Volatility - no agent	1.00 (azeotrope)
Effective Extractive agents found	~50, including combinations
Range of Relative Volatilities found with agents	1.6 to >3
Effective agent classes	Glycols, oxygenated, sulfur-containing or nitrogenous organic compounds, and mixtures thereof