Separation of cumene from 3-ethyl toluene by azeotropic distillation

Abstract

Cumene cannot be separated from 3-ethyl toulene by distillation because of the proximity of their boiling points. They are readily separated by azeotropic distillation. Effective agents are methyl salicylate, diethylene glycol butyl ether and 3-nitrotoluene.

Description

FIELD OF THE INVENTION

This invention relates to a method of separating cumene from 3-ethyl toluene using certain organic liquids as the agent in azeotropic distillation.

DESCRIPTION OF PRIOR ART

Azeotropic distillation is the method of separating close boiling compounds or azeotropes from each other by carrying out the distillation in a multiplate rectification column in the presence of an added liquid said liquid forming an azeotrope with one or more of the compounds to be separated. Its presence on each plate of the rectification column alters the relative volatility in a direction to make the separation on each plate greater and thus require either fewer plates to effect the same separation or make possible a grater degree of separation with the same number of plates. The azeotrope forming agent is introduced with the feed to a continuous column. The azeotrope forming agent and the more volatile component are taken off as overhead product an the less volatile component comes off as bottoms product. The usual methods of separating the azeotrope former from the more volatile component are cooling and phase separation or solvent extraction.

The usual method of evaluating the effectiveness of azeotropic distillation agents is the change in relative volatility of the compounds to be separated. Table 1 shows the degree of separation or purity obtainable by theoretical plates at several relative volatilities. Table 1 shows that a relative volatility of at least 1.2 is required to get an effective separation by rectification.

TABLE 1______________________________________Effect of Relative Volatility onTheoretical stage Requirements.Separation Purity, Relative VolatilityBoth Products Theoretical Stages at Total Reflux.(Mole Fraction) 1.02 1.1 1.2 1.3 1.4 1.5 2.0 3.0______________________________________0.999 697 144 75 52 40 33 19 120.995 534 110 57 39 30 25 14 90.990 463 95 49 34 28 22 12 70.98 392 81 42 29 22 18 10 60.95 296 61 31 21 16 14 8 40.90 221 45 23 16 12 10 5 3______________________________________

There are a number of commercial processes which produce complex mixtures in the cumene boiling range. Cumene and 3-ethyl toluene boil only one degree apart and have a relative volatility of 1.1. A process to separate these two would enhance their value as pure compounds. The close relative volatilities make it impossible to separate them by conventional rectification. Azeotropic distillation would be an attractive method of effecting the separation of these two if agents can be found that (1) will create a large apparent relative volatility between cumene and 3-ethyl toluene and (2) are easy to recover from cumene. Table 2 shows the relative volatility required to obtain 99% purity. With an agent giving a relative volatility of 1.5 only 31 actual plates are required.

TABLE 2______________________________________Theoretical and Actual Plates Required vs. RelativeVolatility for Cumene-3-EthylToluene SeparationRelative Theoretical Plates Required Actual Plates RequiredVolatility At Total Reflux, 99% Purity 75% Efficiency______________________________________1.4 28 381.5 22 30______________________________________

OBJECTIVE OF THE INVENTION

The object of this invention is to provide a process or method of azeotropic distillation that will enhance the relative volatility of cumene from 3-ethyl toluene in their separation in a rectification column. It is a further object of this invention to identify organic compounds which in addition to the above constraints, are stable, can be separated from cumene and recycled with little decomposition.

SUMMARY OF THE INVENTION

The objects of this invention are provided by a process for separating cumene from 3-ethyl toluene which entails the use of certain organic compounds as the agent in azeotropic distillation.

DETAILED DESCRIPTION OF THE INVENTION

I have discovered that certain organic compounds will greatly enhance the relative volatility between cumene and 3-ethyl toluene and permit the separation by rectification when employed as the agent in azeotropic distillation. Table 3 lists the compounds that I have found to be effective in separating cumene from 3-ethyl toluene by azeotropic distillation. They are 2,6-diethyl aniline, methyl salicylate, dipropylene glycol, 2-undecanone, polyethylene glycol 400, diethylene glycol butyl ether, 2-pyrrolidinone, 3-nitrotoluene, ethyl salicylate and tetramethylsulfone.

THE USEFULNESS OF THE INVENTION

The usefulness or utility of this invention can be demonstrated by referring to the data presented in Tables 1, 2 and 3. All of the successful agents show that cumene can be separated from 3-ethyl toluene by means of azeotropic distillation in a rectification column and the ease of separation as measured by relative volatility is considerable.

TABLE 3______________________________________Effective Azeotropic Distillation Agents ForSeparating Cumene From 3-Ethyl Toluene RelativeCompounds Volatility______________________________________None 1.12,6-Diethyl aniline 1.33Methyl salicylate 1.5Dipropylene glycol 1.352-Undecanone 1.42Polyethylene glycol 400 1.3Diethylene glycol butyl ether 1.452-Pyrrolidinone 1.33-Nitrotoluene 1.45Ethyl salicylate 1.4Tetramethylsulfone 1.35______________________________________

WORKING EXAMPLE

Example 1

Fifty grams of a cumene--3-ethyl toluene mixture and fifty grams of methyl salicylate were charged to a vapor--liquid equilibrium still and refluxed for two hours. Analysis indicated a vapor composition of 92% cumene and 8% 2-ethyl toluene; a liquid composition of 88.4% cumene and 11.6% 3-ethyl toluene. This is a relative volatility of 1.5

Claims

1. A method for recovering cumene from a mixture of cumene and 3-ethyl toluene which comprises distilling a mixture of cumene and 3-ethyl toluene presence of an azeotrope forming agent, recovering the cumene and the azeotrope forming agent as overhead product and obtaining the 3-ethyl toluene as bottoms priduct, wherein said azeotrope forming agent consists of one material selected from the group consisting of 2,6-diethyl aniline, methyl salicylate, dipropylene glycol, 2-undecanone, polyethylene glycol 400, diethylene glycol butyl ether, 2-pyrrolidinone, 3-nitrotoluene, ethyl salicylate and tetramethysulfone.