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 one or more reducing monosaccharide sugars and/or corresponding sugar alcohols thereof, comprising subjecting said solution to one or more purification steps selected from nanofiltration and optionally hydrolysis and chromatography, whereby said reducing monosaccharide sugar and/or corresponding sugar alcohol thereof is recovered in the nanofiltration permeate and said crystallization inhibitors are recovered in the nanofiltration retentate.  
     
     
         2 . A process as claimed in  claim 1 , wherein said reducing sugar is xylose.  
     
     
         3 . A process as claimed in  claim 1 , wherein said reducing sugar is fructose.  
     
     
         4 . A process as claimed in claims  1 , wherein said crystallization inhibitor is selected from compounds which have a larger molar mass than said reducing sugar or the corresponding sugar alcohol thereof.  
     
     
         5 . A process as claimed in  claim 4 , wherein said crystallization inhibitor is selected from compounds which in their molecule include at least one monosaccharide or corresponding unit more than said reducing sugar or the corresponding sugar alcohol thereof.  
     
     
         6 . A process as claimed in  claim 4  wherein said crystallization inhibitor is selected from dimeric and/or oligomeric compounds.  
     
     
         7 . A process as claimed in  claim 6 , wherein said dimeric and/or oligomeric compounds are selected from dimeric and/or oligomeric forms of said reducing sugar and/or the corresponding sugar alcohol thereof.  
     
     
         8 . A process as claimed in  claim 2 , wherein said crystallization inhibitor is selected from xylobiose, xylotriose and xylooligosaccharides.  
     
     
         9 . A process as claimed in  claim 3 , wherein said crystallization inhibitor is selected from difructose anhydrides, fructose dianhydrides, diheterolevosanes and diheterolevulosans.  
     
     
         10 . A process as claimed in claims  1 , wherein the nanofiltration is carried out at a pressure of 10 to 50 bar.  
     
     
         11 . A process as claimed in claims  1 , wherein the nanofiltration is carried out at a temperature of 5 to 95° C.  
     
     
         12 . A process as claimed in claims  1 , wherein the nanofiltration is carried out with a flux of 5 to 100 liters/m 2 h.  
     
     
         13 . A process as claimed in claims  1 , wherein the nanofiltration is carried out using a nanofiltration membrane selected from polymeric and inorganic membranes having a cut-off size of 100 to 2500 g/mol.  
     
     
         14 . A process as claimed in  claim 13 , wherein the cut-off size of the nanofiltration membrane is 150 to 1000 g/mol.  
     
     
         15 . A process as claimed in  claim 14 , wherein the cut-off size of the nanofiltration membrane is 150 to 500 g/mol.  
     
     
         16 . A process as claimed in claims  13 , wherein the nanofiltration membrane is selected from ionic membranes.  
     
     
         17 . A process as claimed in claims  13 , wherein the nanofiltration membrane is selected from hydrophobic and hydrophilic membranes.  
     
     
         18 . A process as claimed in claims  13 , wherein the nanofiltration membrane is selected from cellulose acetate membranes, polyethersulfone membranes, sulfonated polyether sulphone membranes, polyester membranes, polysulfone membranes, aromatic polyamide membranes, polyvinyl alcohol membranes and polypiperazine membranes and combinations thereof.  
     
     
         19 . A process as claimed in  claim 18 , wherein the nanofiltration membrane is selected from sulfonated polyether sulfone membranes and polypiperazine membranes.  
     
     
         20 . A process as claimed in  claim 18 , wherein the nanofiltration membrane is selected from NF-200, Desal-5 DL, Desal-5 DK, Desal G10 and NTR 7450 membranes.  
     
     
         21 . A process as claimed in claims  13 , wherein the form of the nanofiltration membrane is selected from sheets, tubes, spiral membranes and hollow fibers.  
     
     
         22 . A process as claimed in claims  13 , wherein the nanofiltration membrane is selected from high shear type membranes.  
     
     
         23 . A process as claimed in claims  1 , wherein the nanofiltration process is repeated at least once.  
     
     
         24 . A process as claimed in  claim 1 , wherein said purification steps further comprise hydrolysis.  
     
     
         25 . A process as claimed in  claim 24 , wherein said hydrolysis comprises enzymatic hydrolysis.  
     
     
         26 . A process as claimed in  claim 24 , wherein said hydrolysis comprises acid hydrolysis.  
     
     
         27 . A process as claimed in  claim 1 , wherein said purification steps further comprise chromatographic separation.  
     
     
         28 . A process as claimed in  claim 27 , wherein said chromatographic separation is carried out using a column packing material selected from cation exchange resins and anion exchange resins.  
     
     
         29 . A process as claimed in  claim 28 , wherein said cation exchange resins are selected from strongly acid cation exchange resins and weakly acid cation exchange resins.  
     
     
         30 . A process as claimed in  claim 28 , wherein said resin is in a monovalent metal form or a divalent metal form.  
     
     
         31 . A process as claimed in claims  28 , wherein the resin has a styrene skeleton or acrylic skeleton.  
     
     
         32 . A process as claimed in claims  1 , wherein said solution comprising one or more reducing sugars and/or corresponding sugar alcohols thereof is a biomass hydrolysate.  
     
     
         33 . A process as claimed in  1 , wherein said solution comprising one or more reducing sugars and/or corresponding sugar alcohols thereof is a fraction enriched in said reducing sugar and/or sugar alcohol and obtained from the separation of said reducing sugar and/or sugar alcohol.  
     
     
         34 . A process as claimed in  claim 33 , wherein said solution comprising one or more reducing sugars and/or sugar alcohols thereof is obtained from the chromatographic separation of said reducing sugar and/or sugar alcohol.  
     
     
         35 . A process as claimed in claims  1 , wherein said solution comprising one or more reducing sugars and/or corresponding sugar alcohols thereof is a mother liquor obtained from the crystallization of said reducing sugar and/or sugar alcohol.  
     
     
         36 . A process as claimed in  claim 2 , wherein said solution comprising xylose is a spent liquor obtained from a pulping process.  
     
     
         37 . A process as claimed in  claim 2 , 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.  
     
     
         38 . A process as claimed in  claim 2 , wherein said solution comprising xylose is a mother liquor obtained from the crystallization of xylose.  
     
     
         39 . A process as claimed in  claim 3 , wherein said solution comprising fructose is a fructose solution obtained from the hydrolysis of starch.  
     
     
         40 . A process as claimed in  claim 3 , wherein said solution comprising fructose is a fructose solution obtained from hydrolyzed and isomerized saccharose.  
     
     
         41 . A process as claimed in  claim 3 , wherein said solution comprising fructose is a fructose fraction obtained from the separation of fructose from a fructose solution obtained from the hydrolysis of starch and/or isomerisation of saccharose.  
     
     
         42 . A process as claimed in  claim 41 , wherein said solution comprising fructose is a fructose fraction obtained from the chromatographic separation of fructose from a solution obtained from the hydrolysis of starch and/or isomerisation of saccharose.  
     
     
         43 . A process as claimed in  claim 3 , wherein said solution comprising fructose is a mother liquor obtained from the crystallization of fructose.  
     
     
         44 . A process as claimed in  claim 10 , wherein the nanofiltation is carried out at a pressure of 15 to 40 bar.  
     
     
         45 . A process as claimed in  claim 11 , wherein the nanofiltration is carried out at a temperature of 30 to 60° C.