Two-stage etherification of tertiary butyl alcohol using second stage zeolite catalysts for the intermediate preparation of isobutylene

A method for the preparation of methyl tertiary butyl ether (MTBE) from tertiary butyl alcohol (TBA) and methanol (MeOH) in three stages which comprises the steps of:

• a) charging a reaction feed mixture comprising methanol and tertiary butyl alcohol to a primary MTBE reaction zone containing a bed of a cationic ion-exchange resin catalyst and reacting the reaction feed mixture therein to form a primary etherification reaction product comprising unreacted methanol, unreacted tertiary butyl alcohol, water, isobutylene and methyl tertiary butyl ether,
• b) charging the primary reaction product to a first methyl tertiary butyl ether distillation zone and separating it therein into a first lighter distillation fraction comprising isobutylene, methanol and methyl tertiary butyl ether and a first heavier distillation fraction comprising methanol, tertiary butyl alcohol and water,
• c) charging the first heavier distillation fraction to a second stage MTBE reaction zone containing a bed of a fluoride-treated Y-zeolite or a fluoride-treated silicoaluminophosphate (SAPO) molecular sieve operated under conversion conditions including a temperature of 160.degree. to 240.degree. C. and a pressure of 50 to 500 psig. selected to convert at least 80 wt. % of the tertiary;
• butyl alcohol so as to form a second stage two-phase etherification reaction product comprising primarily isobutylene and about 6 to about 13 mol % methyl tertiary butyl ether, and also containing unreacted tertiary butyl alcohol, methanol and water,
• d) charging the second stage reaction product to a separation drum and separating it therein into a lighter supernatant fraction comprising tertiary butyl alcohol, isobutylene and methyl tertiary butyl alcohol and a heavier aqueous fraction comprising methanol and water,
• e) charging the first lower boiling (lighter) distillation fraction, an isobutylene conversion product and the heavier aqueous fraction to a methanol solvent extraction zone and countercurrently contacting them therein with water to provide an overhead extract comprising isobutylene, water and methyl tertiary butyl ether and a raffinate comprising methanol, MTBE, isobutylene, dimethyl ether and water;
• f) charging the extract to a third isobutylene distillation zone and separating it therein into a third lower boiling (lighter) distillation fraction comprising water, a third intermediate boiling fraction comprising isobutylene and a third higher boiling (heavier) distillation fraction comprising methyl tertiary butyl ether;
• g). charging the third intermediate isobutylene fraction, the lighter supernatant fraction and added methanol to an isobutylene conversion reaction zone containing a bed of a cationic ion-exchange resin catalyst and reacting the reaction feed mixture therein to thereby convert the charged methanol and isobutylene to methyl tertiary butyl ether and form an isobutylene conversion product comprising methyl tertiary butyl ether, isobutylene, methanol, tertiary butyl alcohol and water;
• and
• h). recycling said isobutylene conversion product to said methanol solvent extraction zone.
• i), the fluoride treated strongly acidic Y-zeolite having a silica/alumina ratio of about 100:1 to about 10:1 and a unit cell size of 24.20 to 24.45 A;
• and
• j). the fluoride-treated silicoaluminaphosphate having a pore size of from 5 to 9 A, and being selected from the group consisting of SAPO-37 and SAPO-5, SAPO-11 and SAPO-31.