High yield byproduct recycle process for anhydro sugar alcohols

A continuous byproducts recycle process for the manufacture of dianhydro sugar alcohols, comprising the steps of:

• a) continuously dehydrating a sugar alcohol in the presence of an acid catalyst to produce a reaction mass comprising monoanhydro sugar alcohols, dianhydro sugar alcohols, dimers, and polymers;
• b) continuously separating a portion of the dianhydro sugar alcohols from the reaction mass to produce a product stream and a byproduct stream;
• c) continuously removing at least a portion of the byproduct stream, said stream comprising mostly monoanhydro sugar alcohol isomers, dimers, polymers and dianhydro sugar alcohol;
• d) diluting the byproducts stream of (c) with water in an amount sufficient to precipitate the polymers;
• e) allowing most of the polymers to precipitate from the diluted mixture of (d);
• f) separating the polymers precipitated in (e) from the dissolved byproducts;
• and
• g) feeding the dissolved byproducts solution from (f) to the dehydration step of (a);
• while maintaining the flows in and out of steps (a)-(g) at substantially steady rates and coordinated to maintain substantially steady process conditions.