Separation of 2-Methyl -1-Propanol From 2-Butanol by Azeotropic Distillation

This invention relates to a method for separating 2-methyl-1-propanol from 2-butanol using certain organic compounds as the agent in azeotropic distillation.

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 both 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 greater 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 and 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.

2-Methyl-1-propanol and 2-butanol boil eight degrees apart and ave a relative volatility of 1.35 and are difficult to separate by conventional rectification. Table 2 show that to get 99% ourity, 41 actual plates are required. With an agent giving a relative volatility of 1.95, only 20 actual plates are required.

The object of this invention is to provide a process or method of azeotropic distillation that will enhance the relative volatility of 2-methyl-1-propanol from 2-butanol in their separation in a rectification column. It is a further object of this invention to identify effective azeotropic distillation agents that are stable and can be recycled.

The objects of this invention are provided by a process for the separation of 2-methyl-1-propanol from 2-butanol which entails the use of certain organic compounds when employed as the agent in azeotropic distillation.

I have discovered that certain organic compounds will effectively increase the relative volatility between 2-methyl-1-propanol and 2-butanol during rectification when employed as the agent in azeotropic distillation. Table 3 summarizes the data obtained with these agents. The agents which are effective are tetrahydrofuran, methyl benzoate, methyl propionate, butyl propionate, methyl acetate, di-tert. butyl dicarbonate, ethyl acetate, cyclopentane, acetal, 2,2-dimethoxypropane, triethyl amine,acetonitrile and sulfolane.

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 2-methyl-1-propanol can be separated from 2-butanol by means of azeotropic distillation and that the ease of separation is considerable.

Example 1

Fifty grams of 2-methyl-1-propanol--2-butanol mixture and fifty grams of sulfolane as the azeotrope forming agent were charged to a vapor-liquid equilibrium still and refluxed for two hours. The vapor composition was 17.4% 2-methyl-1-propanol and 82.6% 2-butanol; the liquid composition was 10.5% 2-methyl-1-propanol and 89.5% 2-butanol. This is a relative volatility of 1.8.