Method for recovering xylitol
AssigneeSuomen Sokeri Osakeyhtio (Finnish Sugar Company)
InventorsAsko J. Melaja, Jouko J. Virtanen, Heikki O. Heikkila
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Abstract
A method for preparing pharmaceutical grade xylitol from an aqueous solution containing mixtures of polyols including xylitol which comprises subjecting the solution to a crude crystallization and recrystallization of xylitol followed by the recovery of residual xylitol from the mother liquor by fractionating the solution using at least two columns of ion-exchange resin in two different metal forms.
Claims10
A method for obtaining xylitol crystals of pharmaceutical grade from an aqueous solution of a mixture of polyols including xylitol which comprises the steps of
- a. subjecting said solution to a crude xylitol crystallization step to crystallize a major portion of the xylitol therein while leaving a mother liquor,
- b. removing the crude crystals from the mother liquor,
- c. recrystallizing the xylitol by dissolving the crude crystals in water and crystallizing them to provide crystals of high purity, while leaving a mother liquor, and
- d. recovering residual xylitol from the mother liquors from the crystallization and recrystallization steps by subjecting at least a portion of the mother liquors to a chromatographic fractionation using at least two columns containing sulfonated polystyrene cation exchange resins cross-coupled with di-vinyl benzene, one of said columns containing the resin in an alkaline earth form and the other of said columns containing the resin in an Al.sup.+++ or Fe.sup.+++ form.
A method for obtaining xylitol crystals of pharmaceutical grade from an aqueous solution of a mixture of polyols including xylitol which comprises the steps of
- a. subjecting said solution to a crude xylitol crystallization step to crystallize a major portion of the xylitol therein while leaving a mother liquor,
- b. removing the crude crystals from the mother liquor,
- c. purifying the crude crystals by washing the crystals to remove microcrystals of galactitol formed during the xylitol crystallization steps from their surfaces,
- d. recovering microcrystals of galactitol by combining the washing liquid and the crystallization mother liquor and subjecting it to a galactitol removal step whereby the microcrystals of galactitol are recovered from the said combined liquids, and
- e. recovering residual xylitol from the liquids in step (d) by subjecting at least a portion of the liquids to chromatographic fractionation.
A method for obtaining xylitol crystals of pharmaceutical grade having less than about -0.2% by weight of galactitol, which comprises
- a. preparing a pentose-rich hemicellulose hydrolysate,
- b. purifying the hydrolysate by removing suspended solids, inorganic salts, and a major portion of organic impurities and color therefrom,
- c. hydrogenating the purified hydrolysate to form a mixed polyol solution containing from 60-85% xylitol on a dry solids basis,
- d. subjecting said mixed polyol solution to a crude xylitol crystallization step to crystallize a major portion of the xylitol therein while leaving a mother liquor,
- e. removing the crude xylitol crystals from the mother liquor,
- f. recrystallizing the xylitol by dissolving the crude crystals in water and recrystallizing the xylitol to provide crystals of high purity,
- g. separating the crystals from the mother liquor, and
- h. recovering residual xylitol from the mother liquor obtained in step (d) by
- i. removing galactitol crystals from the mother liquor,
- ii. passing the thus treated mother liquor through a chromatographic column containing sulfonated polystyrene cation exchange resins cross-coupled with di-vinyl benzene to provide a mixed polyol by-product fraction, a return fraction, and a xylitol-rich fraction,
- iii. removing the mixed polyol by-product fraction from the system,
- iv. returning the return fraction as a portion of the feed solution to the chromatographic column, and
- v. adding the xylitol-rich fraction to the stream feeding the crude crystallization step (d).
Dependencies are inferred from the claim text.