Aldose-Ketose Transformation for Separation and/or Chemical Conversion of C6 and C5 Sugars from Biomass Materials

Abstract

Systems for converting aldose sugars to ketose sugars and separating and/or concentrating these sugars using differences in the sugars' abilities to bind to specific affinity ligands are described.

What is claimed is: 
     
         1 . A system for converting an aldose sugar to its ketose sugar, comprising:
 a) contacting a C5 and/or C6 aldose sugar present in a saccharified hydrolysate with a catalyst to form a ketose isomer of the C5 and/or C6 sugar;   b) contacting isomerized ketose C5 and/or C6 sugar with a complexing agent (CA) to form a ketose-CA conjugate; the CA have a much higher binding affinity to the ketose sugar compared to the aldose sugar;   c) optionally, repeating steps a) and b) to provide a hydrolysate having more ketose-CA conjugate than aldose sugar; and   d) isolating ketose sugar from the ketose-CA conjugate; and   e) recovering the ketose sugar.   
     
     
         2 . The system of  claim 1 , including removing free ketose from hydrolysate to overcome an unfavorable equilibrium ratio of xylose:xylulose. 
     
     
         3 . The system of  claim 1 , wherein the ketose sugars are isolated by:
 lowering pH of the concentrated hydrolysate to effect the release of the ketose from the ketose-CA conjugate; and   converting the CA to a lipophilic conjugate acid form.   
     
     
         4 . The system of  claim 1 , wherein the saccharified hydrolysate has a pH between about 7.5 to about 11 when the catalyst comprises a solid acid/base catalyst. 
     
     
         5 . The system of  claim 1 , wherein the CA is present in an organic phase, the xylulose extracting the complexing agent (CA) from the organic phase via ester formation with a conjugate base form of the CA. 
     
     
         6 . The system of  claim 5 , including extracting the CA from the organic phase and allowing the ester formation until nearly all of the xylose is isomerized. 
     
     
         7 . The system of  claim 5 , including:
 acidifying the isomerized hydrolysate containing the ketose-CA conjugate to a pH that favors the conjugate acid form of the CA, such that the conjugate acid form of the CA dissociates from the ketose, and the dissociation of the ketose increases the hydrophobicity of the CA in the isomerized hydrolysate, and   driving the conjugate acid form of the CA back into the organic phase, thereby forming a CA-depleted/ketose-rich hydrolysate.   
     
     
         8 . The system of  claim 7 , including: adjusting the pH of the CA-depleted/ketose-rich hydrolysate to a pH at which the ketose sugar can be fermented to ethanol by  S. cerevisiae.    
     
     
         9 . The system of  claim 7 , including driving the hydrophobic CA back into the organic phase to form a CA-enriched organic phase, and contacting the CA-enriched organic phase with a fresh batch of saccharified hydrolysate. 
     
     
         10 . The system of  claim 1 , including: immobilizing the complexing agent (CA) to a support material. 
     
     
         11 . The system of  claim 1 , including circulating the hydrolysate through at least a first column comprised of a packed bed of immobilized xylose isomerase (XI) or solid acid/base catalyst particles, and through a second column comprised of a packed bed of a complexing agent (CA) immobilized on a support material. 
     
     
         12 . The system of  claim 11 , wherein as the hydrolysate passes through the XI column, xylose and a portion of glucose present in the hydrolysate are converted to corresponding keto-isomers (xylulose and fructose, respectively). 
     
     
         13 . The system of  claim 11 , wherein as the hydrolysate mixture is routed through the immobilized CA column, mainly the ketose will complex with bound CA sites, thereby lowering free ketose concentration in the hydrolysate. 
     
     
         14 . The system of  claim 11 , including circulating the hydrolysate through two-columns connected in series. 
     
     
         15 . The system of  claim 11 , including isolating the immobilized CA column and flushing the immobilized CA column with a carrier solution of low pH sufficient for bound ketose to be released from the CA and to accumulate in the low pH carrier solution. 
     
     
         16 . The system of  claim 11 , including regenerating the immobilized CA column and reusing with a fresh batch of hydrolysate. 
     
     
         17 . The system of  claim 16 , wherein the pH is about 4.0 to about 4.5. 
     
     
         18 . The system of  claim 1 , further including a lipophilic salt with the complexing agent (CA) in the organic phase, and extracting the ketose out of the aqueous phase. 
     
     
         19 . The system of  claim 1 , wherein the complexing agent (CA) comprises a complexing agent soluble in organic solvents and/or capable of being covalently-bound to a solid substrate. 
     
     
         20 . The system of  claim 1 , wherein the complexing agent (CA) comprises one or more of aryl boronic acids (ABAs), including, but not limited to PBA, 3aPBA, 4cPBA, and 4-biphenylboronic acid 
       
         
           
           
               
               
           
         
       
     
     
         21 . The system of  claim 1 , wherein the complexing agent (CA) comprises one or more aryl boronic acids (ABA), Ar—B(OH) 2 , where Ar represents unsubstituted or substituted “aryl” group. 
     
     
         22 . The system of  claim 21 , wherein the aryl boronic acids (ABA), comprise one or more of the aryl groups: 4-PhC 6 H 4 —; 4-MeC 6 H 4 —, where Me is methyl; 2-iPrC 6 H 4 —, where iPr is isopropyl; 2-naphthyl,3-BnOC 6 H 4 —, where Bn is benzyl; 4-MeO 2 CC 6 H 4 —, where Me is methyl; and 4-pyridinyl. 
     
     
         23 . The system of  claim 19 , wherein one or more functional groups such as NH 2  or COOH are incorporated into the aryl group to enable covalent bonding of the aryl boronic acids to a functionalized support. 
     
     
         24 . The system of  claim 23 , wherein functionalization of the support includes one or more of: oxirane, amine, aldehyde, carboxyl, or other complementary groups that covalently attaches to the functional group on the aryl boronic acid. 
     
     
         25 . The system of  claim 1 , wherein the CA is contained in a holding vessel that includes a contacting device that physically separates the hydrolysate from the organic phase while allowing movement of the CA into the hydrolysate. 
     
     
         26 . The system of  claim 25 , wherein the contacting device comprises a CA permeable membrane. 
     
     
         27 . The system of  claim 25 , wherein the contacting device comprises a microporous hollow fiber contactor. 
     
     
         28 . The system of  claim 1 , having a configuration as shown in  FIG. 2  for separating xylose (in the form of its keto-isomer, xylulose) from a biomass hydrolysate containing a mixture of glucose and xylose. 
     
     
         29 . A system for converting an aldose in a biomass hydrolysate to its ketose isomer and for making the ketose available for fermentation reactions at an appropriate pH, comprising:
 1a) adjusting a pH of a saccharified biomass hydrolysate containing one or more aldose sugars to a value between about 7.5 and about 11;   1b) contacting the pH-adjusted-hydrolysate of step 1a) with a catalyst where at least a portion of the aldose sugar in the pH-adjusted-hydrolysate is converted to its ketose isomer;   2a) contacting the ketose isomer in the isomerized-hydrolysate of step 1b) with a complexing agent (CA) to form a ketose-conjugate base form of the CA;   2b) optionally, repeating steps 1a+b)-2a) as needed, until a desired concentration of the aldose in the isomerized-hydrolysate is converted into an esterified ketose-CA conjugate;   3) ceasing the isomerization cycle of steps 1a)-2b);   4) acidifying the isomerized-hydrolysate, containing the esterified ketose-CA conjugate, to a pH (optionally, between about pH 2 to about 4.5) that favors formation of a conjugate acid form of the CA, causing the CA to dissociate from the ketose; and,   5) ontacting the ketose-rich hydrolysate of step 4) with CA-depleted organic material, causing the dissociated CA to be separated from the ketose-rich hydrolysate; and optionally,   6) recovering the dissociated CA material and returning to the organic material of step 2a).   
     
     
         30 . The system of  claim 29 , wherein the ketose present in the isomerized hydrolysate extracts the CA from the organic material via ester formation with a conjugate base form of the CA, thereby shifting the aldose/ketose equilibrium in favor of more ketose formation in the isomerized hydrolysate. 
     
     
         31 . The system of  claim 1 , having a configuration as shown in  FIG. 3  for separating xylose (in the form of its ketoisomer, xylulose) from a biomass hydrolysate containing a mixture of glucose and xylose. 
     
     
         32 . A system for converting an aldose in a biomass hydrolysate to its ketose isomer and for making the ketose available for fermentation reactions at an appropriate pH, comprising:
 incorporating an immobilized xylose isomerase XI (or solid acid/base catalyst) column in an extraction step;   converting xylose to xylulose at high yield and high selectivity over glucose to fructose; and,   separating xylulose from glucose by binding xylulose to an aryl boronic acid.   
     
     
         33 . The system of  claim 1 , having a configuration as shown in  FIG. 4  for separating xylose (in the form of its keto-isomer, xylulose) from a biomass hydrolysate containing a mixture of glucose and xylose. 
     
     
         34 . The system of  claim 1 , including immobilizing the complexing agent CA to a solid support material, such that the immobilized CA acts as a solid-phase extraction medium for the sugar. 
     
     
         35 . The system of  claim 34 , including removing the bound sugar from the hydrolysate medium by contacting the support material with a lower pH solution to achieve separation from the hydrolysate. 
     
     
         36 . The system of  claim 1 , having a configuration as shown in  FIG. 5  for separating xylose (in the form of its keto-isomer, xylulose) from a biomass hydrolysate containing a mixture of glucose and xylose. 
     
     
         37 . A system of separating xylose (in the form of its keto-isomer, xylulose) from a biomass hydrolysate containing a mixture of glucose and xylose; comprising:
 circulating the biomass hydrolysate through a first column comprised of a packed bed of immobilized xylose isomerase (XI) or solid acid/base catalyst particles; and a second column comprised of a packed bed of a complexing agent (CA) immobilized on a support material; the CA and its binding chemistry to the support material being chosen so that the CA substantially binds to xylulose, and not in any appreciable amounts to glucose, xylose, or fructose;   passing the hydrolysate through the first (XI) column such that, xylose and a portion of glucose are converted to their corresponding keto-isomers (xylulose and fructose, respectively);   passing the isomerized hydrolysate through the immobilized CA second column,   wherein the xylulose complexes with bound CA sites, thereby lowering the xylulose concentration in the hydrolysate, and the reduction in concentration of non-bound xylulose in the isomerized hydrolysate drives the isomerization reaction in the direction of more xylulose formation;   optionally, isolating the second immobilized CA column and contacting the second (CA) column with a low pH carrier medium, so the bound xylulose is released from the CA sites and accumulates in the low pH carrier medium; and,   controlling the volume of the low pH aqueous solution such that xylulose concentration in the recovered stream is higher than the xylose concentration in the original hydrolysate.   
     
     
         38 . A fuel formed by a system of  claim 1 . 
     
     
         39 . The system of  claim 30 , including an immobilized CA column to recover both glucose and xylose from the hydrolysate by binding glucose and xylose to appropriately chosen CA, and recovering glucose and xylose from the hydrolysate, while leaving behind other inhibitory compounds in the biomass hydrolysate. 
     
     
         40 . A fuel formed by a system of  claim 39 . 
     
     
         41 . The system of  claim 32 , including an immobilized CA column to recover both glucose and xylose from the hydrolysate by binding glucose and xylose to appropriately chosen CA, and recovering glucose and xylose from the hydrolysate, while leaving behind other inhibitory compounds in the biomass hydrolysate. 
     
     
         42 . A fuel formed by a system of  claim 41 . 
     
     
         43 . The system of  claim 37 , including an immobilized CA column to recover both glucose and xylose from the hydrolysate by binding glucose and xylose to appropriately chosen CA, and recovering glucose and xylose from the hydrolysate, while leaving behind other inhibitory compounds in the biomass hydrolysate. 
     
     
         44 . A fuel formed by a system of  claim 43 .