Tagatose production using simulated moving bed separation

A continuous SMB process for the production of d-tagatose, said process comprising:

• a. passing a lactose hydrolysate stream comprising water, d-galactose, d-glucose, lactose, disaccharides, and salts to an ion exclusion SMB zone containing a plurality of adsorbent beds comprising a strong acid cation calcium exchange resin adsorbent, to provide a first extract stream comprising water, d-galactose and glucose and to reject an ion exclusion raffinate stream or first raffinate stream comprising lactose, disaccharides, water and salts;
• b. passing the first extract stream to a second SMB zone containing a plurality of adsorbent beds comprising a strong acid cation calcium exchange resin adsorbent to provide a second extract stream comprising substantially pure d-galactose, water, and a minor portion of d-glucose, and to provide a second raffinate stream or glucose product stream comprising substantially pure d-glucose, water, and a minor portion of d-galactose ;
• c. passing the second extract stream to an isomerization zone to isomerize at least a portion of the d-galactose to d-tagatose in the presence of calcium oxide and calcium chloride at a pH of between about 12 and 13, an isomerization temperature of between about 9° C. and about 14° C., and in a d-galactose/calcium oxide molar ratio of from 1.1:1 to 1:1.1 to provide an isomerate stream comprising water, d-tagatose, d-galactose, glucose, calcium oxide and salts;
• d. neutralizing the isomerate stream to a pH of between about 6 and about 7 with a dilute hydrochloric acid stream to provide a neutralized isomerate stream comprising water, d-tagatose, d-galactose, glucose, calcium chloride and salts;
• e. passing the isomerate stream to a first concentration zone to remove at least a portion of the water to provide a first concentrated stream;
• f. passing the first concentrated stream to a third SMB zone containing a plurality of adsorbent beds comprising a strong acid cation calcium exchange resin adsorbent to provide a substantially pure d-tagatose product stream comprising d-tagatose, water, and a minor portion of d-galactose and a third raffinate stream comprising water, d-galactose, glucose, and salts;
• g. passing at least a portion of the third raffinate stream to a second concentration zone to provide a second concentrated stream;
• and,
• h. combining the second concentrated stream with the lactose hydrolysate stream prior to passing the lactose hydrolysate stream to the ion exclusion SMB zone.

A process for producing a pure d-tagatose crystal product from a feed stream of fermented lactose hydrolysate comprising lactose, d-galactose, glycerol, other sugars, and salts, said process comprising:

• a. passing the feed stream to an ion exclusion SMB zone comprising a plurality of adsorbent columns containing a strong acid cation stationary phase and operating in a 2-3-2-2 SMB cycle with water as a desorbent to provide a first extract stream comprising water, d-galactose and glycerol, and to reject a first raffinate stream comprising lactose, water, other sugars, and salts;
• b. passing the first extract stream to a second evaporation zone to provide an evaporated first extract stream having a Brix value of between about 15 and about 20 and passing the evaporated first extract stream to an isomerization zone containing calcium oxide or calcium hydroxide to provide an isomerized reactor mixture:
• c. neutralizing the isomerized reactor mixture to provide a neutralized isomerization reactor mixture and passing the neutralized isomerized reactor mixture to a second SMB zone comprising a plurality of adsorbent columns containing a strong acid cation calcium exchange resin stationary phase and operating in a 2-3-2-2 SMB cycle with water as a desorbent to provide a second extract stream comprising substantially pure d-tagatose, water, and glycerol and a second raffinate stream comprising substantially pure d-galactose, water, salts and a minor portion of d-tagatose;
• d. passing the second extract stream to a third evaporization zone to provide a d-tagatose syrup having a Brix value of 60-65 and passing the d-tagatose syrup to a tagatose crystallizer to provide a pure d-tagatose crystal product and a mother liquor comprising d-tagatose and glycerol;
• e. passing the mother liquor to glycerol removal zone to remove glycerol to provide a glycerol free tagatose recycle stream;
• f. returning at least a portion of the glycerol free tagatose recycle stream to be admixed with the isomerized reactor mixture;
• and,
• g. returning at least a portion of the second raffinate to a first concentration zone to provide a concentrated second raffinate stream and admixing the concentrated second raffinate stream with the feed stream prior to passing the feed stream to the first SMB zone.