Energy conservation during plural stage distillation

In a multistage distillation method for the purification of a methyl tertiary butyl ether reaction product comprising methyl tertiary butyl ether, tertiary butyl alcohol, methanol, isobutylene and water, the improvement which comprises the steps of:

• charging said methyl tertiary butyl ether reaction product to a recovery zone comprising a plurality of distillation columns equipped with reflux condensers and reboilers and including a primary methyl tertiary butyl ether distillation column, a water extraction column, a methyl tertiary butyl ether purification column, a methyl tertiary butyl ether recovery column, a methanol recovery column, and a tertiary butyl alcohol distillation column,
• separating said methyl tertiary butyl ether reaction product in said primary methyl tertiary butyl ether distillation column into a lower boiling methyl tertiary butyl ether, isobutylene and methanol-containing distillation fraction and a higher boiling aqueous tertiary butyl alcohol fraction,
• separating said higher boiling aqueous tertiary butyl alcohol fraction in said tertiary butyl alcohol distillation column into a vaporized overhead tertiary butyl alcohol distillation fraction and a higher boiling water fraction,
• separating said lower boiling methyl tertiary butyl ether, isobutylene and methanol-containing distillation fraction in a water extraction zone into an isobutylene-containing methyl tertiary butyl ether extract and a raffinate comprising methyl tertiary butyl ether alcohol, methanol and water,
• separating said isobutylene-containing methyl tertiary butyl ether extract in said methyl tertiary butyl ether purification column into a lower boiling water-containing isobutylene fraction and a higher boiling purified methyl tertiary butyl ether fraction,
• separating said raffinate in a methyl tertiary butyl ether recovery column into a lower boiling methyl tertiary butyl ether fraction and a higher boiling aqueous methanol fraction,
• separating said aqueous methanol fraction in said methanol recovery column into a lower boiling methanol fraction and a higher boiling water fraction,
• charging cooling water to the reflux condenser for said tertiary butyl alcohol distillation column to liquify the vaporized overhead tertiary butyl alcohol distillation fraction whereby the cooling water is converted to low pressure steam,
• charging a portion of the low pressure steam generated in said reflux condenser for said tertiary butyl alcohol distillation column to the reboiler for said primary methyl tertiary butyl ether distillation column to supply the heat necessary for the distillation to be effected therein, and
• charging another portion of the low pressure steam generated in said reflux condenser for said tertiary butyl alcohol distillation column to the reboiler for said methanol recovery column to supply the heat necessary for the distillation to be effected therein.