Integrated continuous process for anhydro sugar alcohol manufacture

A process for the preparation, recovery and purification of dianhydro sugar alcohol, comprising:

• a) continuously feeding an aqueous solution of a sugar alcohol to a reaction vessel maintained at an elevated reaction temperature and a reduced pressure;
• b) contacting the sugar alcohol with a dehydration catalyst;
• c) evaporating most of the water from the aqueous solution;
• d) continuously dehydrating the sugar alcohol, with the evolution of water vapor, to form a reaction mass comprising dianhydro sugar alcohol, monoanhydro sugar alcohols, dimers and polymers;
• e) separating from the reaction mass most of the dianhydro sugar alcohol formed, by volatilizing it with the water vapor evolved to form a vapor stream and a byproduct stream;
• f) introducing the vapor stream into a condensation-crystallization vessel maintained at a controlled pressure and a controlled temperature;
• g) partially condensing the vapor stream, under controlled pressure and temperature, to recover most of the dianhydro sugar alcohol as a slurry of high purity crystals in a supersaturated solution;
• h) removing the uncondensed vapors, comprising mostly water, from the crystallization vessel;
• i) withdrawing the dianhydro sugar alcohol slurry from the crystallization vessel;
• j) separating the dianhydro sugar alcohol crystals from the mother liquor in the slurry;
• k) withdrawing from the reaction vessel the byproduct stream, comprising monoanhydro sugar alcohol isomers, dimers, polymers, and the dianhydro sugar alcohols not volatilized from the reaction mass in (b);
• l) diluting the byproduct stream with water and allowing most of the polymers to precipitate;
• m) separating the precipitated polymers to form a solution of soluble sugar alcohol species;
• and
• n) recycling the solution of soluble species to the reaction vessel;
• wherein steps (a) through (n) are conducted substantially continuously.

An integrated process for continuous production of high purity, polymer grade dianhydro sugar alcohols comprising the steps of

• a. continuously dehydrating, with evolution of water vapor, an aqueous solution of a sugar alcohol, in the presence of a dehydration catalyst, in a reaction vessel maintained at an elevated reaction temperature and under reduced pressure, and simultaneously separating from the reaction mass most of the dianhydro sugar alcohol formed, by volatilizing it with the water vapor evolved to form a vapor stream and a high boiling byproduct stream;
• b. withdrawing the vapor stream of (a), comprising mostly the dianhydro sugar alcohol product and water vapor, from the reaction vessel and partially condensing the stream by contacting it under controlled temperature and pressure with a glycol used in polyester production to recover most of the dianhydro sugar alcohol as a slurry of higher purity crystals in a glycol mother liquor;
• c. separating the dianhydro sugar alcohol crystals formed in (b) from the mother liquor;
• d. withdrawing the high boiling byproduct stream, comprising mostly monoanhydro sugar alcohol isomers, dimers, and polymers produced from the species present in the reaction mass, and dianhydro sugar alcohol not volatilized from the reaction mass in (a);
• e. diluting the byproducts stream from (d) with water in amount sufficient to precipitate the polymers;
• and
• f. separating the polymers precipitated in (e) and recycling the remaining byproduct solution to the reaction vessel,
• wherein the flows in and out of steps (a)-(f) are maintained at substantially steady rates and coordinated to maintain substantially steady processing conditions.