Crystallization of Sugars

Abstract

The invention relates to removing crystallization inhibitors from a solution comprising one or more reducing sugars by nanofiltration, hydrolysis and/or chromatography. The reducing sugars are typically selected from fructose and xylose.

1 . A process of removing crystallization inhibitors from a solution comprising at least one reducing monosaccharide sugars selected from xylose and fructose or corresponding sugar alcohols thereof, followed by crystallization of said xylose or fructose or corresponding sugar alcohol thereof, comprising 
 subjecting said solution to chromatography,    whereby said xylose or fructose or corresponding sugar alcohol thereof is recovered in a separate fraction and said crystallization inhibitors are recovered in the separate fraction,    and subjecting said fraction containing said xylose or fructose or corresponding sugar alcohol thereof to a crystallization process selected from boiling crystallization, cooling crystallization, precipitation crystallization and combination thereof,    to produce crystals of said xylose or fructose or corresponding sugar alcohol thereof,    and collecting the crystals by centrifugation and filtering.    
     
     
         2 . A process as claimed in  claim 1 , wherein said crystallization inhibitor is selected from compounds which have a larger molar mass than said xylose or fructose or the corresponding sugar alcohol thereof.  
     
     
         3 . A process as claimed in  claim 2 , wherein said crystallization inhibitor is selected from compounds which in their molecule includes at least one monosaccharide or corresponding unit more than said xylose or fructose or the corresponding sugar alcohol thereof.  
     
     
         4 . A process as claimed in  claim 2 , wherein said crystallization inhibitor is selected from dimeric and/or oligomeric compounds.  
     
     
         5 . A process as claimed in  claim 4 , wherein said dimeric and/or oligomeric compounds are selected from dimeric and/or oligomeric forms of said xylose or fructose or the corresponding sugar alcohol thereof.  
     
     
         6 . A process as claimed in  claim 1 , wherein said crystallization inhibitor is selected from xylobiose, xylotriose and xylo-oligosaccharides.  
     
     
         7 . A process as claimed in  claim 1 , wherein said crystallization inhibitor is selected from difructose anhydrides, fructose dianhydrides, diheterolevosanes and diheterolevulosans.  
     
     
         8 . A process as claimed in  claim 1 , wherein said process additionally comprises hydrolysis.  
     
     
         9 . A process as claimed in  claim 8 , wherein said hydrolysis comprises enzymatic hydrolysis.  
     
     
         10 . A process as claimed in  claim 8 , wherein said hydrolysis comprises acid hydrolysis.  
     
     
         11 . A process as claimed in  claim 1 , wherein the chromatography of said solution is carried out using a column packing material selected from cation exchange resins and anion exchange resins.  
     
     
         12 . A process as claimed in  claim 11 , wherein said cation exchange resins are selected from strongly acid cation exchange resins and weakly acid cation exchange resins.  
     
     
         13 . A process as claimed in  claim 11 , wherein said cation exchange resin is in a monovalent metal form or a divalent metal form.  
     
     
         14 . A process as claimed in  claim 11 , wherein the resin has a styrene skeleton or acrylic skeleton.  
     
     
         15 . A process as claimed in  claim 1 , wherein said solution comprising one or more reducing sugars selected from xylose and fructose or corresponding sugar alcohols thereof is a biomass hydrolysate.  
     
     
         16 . A process as claimed in  claim 1 , wherein said solution comprising one or more reducing sugars selected from xylose and fructose or corresponding sugar alcohols thereof is a fraction enriched in said xylose or fructose or sugar alcohol thereof and obtained from the separation of said xylose or fructose or sugar alcohol.  
     
     
         17 . A process as claimed in  claim 1 , wherein said solution comprising at least one reducing monosaccharide sugar or corresponding sugar alcohols thereof is a mother liquor obtained from the crystallization of said reducing sugar or sugar alcohol.  
     
     
         18 . A process as claimed in  claim 1 , wherein said solution comprising xylose is a spent liquor obtained from a pulping process.  
     
     
         19 . A process as claimed in  claim 1 , wherein said solution comprising xylose is a xylose fraction obtained from the chromatographic separation of xylose from a spent liquor obtained from a pulping process.  
     
     
         20 . A process as claimed in  claim 1 , wherein said solution comprising xylose is a mother liquor obtained from the crystallization of xylose.  
     
     
         21 . A process as claimed in  claim 1 , wherein said solution comprising fructose is a fructose solution obtained from the hydrolysis of starch.  
     
     
         22 . A process as claimed in  claim 1 , wherein said solution comprising fructose is a fructose solution obtained from hydrolyzed and isomerized saccharose.  
     
     
         23 . A process as claimed in  claim 1 , wherein said solution comprising fructose is a fructose fraction obtained from the separation of fructose from a fructose solution, wherein said fructose solution is obtained from the hydrolysis of starch and/or isomerisation of saccharose.  
     
     
         24 . A process as claimed in  claim 23 , wherein said solution comprising fructose is a fructose fraction obtained from the chromatographic separation of fructose from a solution, wherein said fructose solution is obtained from the hydrolysis of starch and/or isomerisation of saccharose.  
     
     
         25 . A process as claimed in  claim 1 , wherein said solution comprising fructose is a mother liquor obtained from the crystallization of fructose.