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

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 1)-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) contacting 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).

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;
• 2) 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;
• wherein the contacting comprises
• 3) bringing the isomerized hydrolysate from the packed bed reactor into contact with an immiscible organic phase that dissolves the CA and a lipophilic salt (QX);
• and allowing the ketose in the isomerized hydrolysate to be extracted into the organic phase via ester formation with a conjugate base form of the CA that is coupled via ion pair formation with Q+, thus reducing the concentration of ketose in the hydrolysate, and shifting the aldose/ketose equilibrium in favor of more ketose formation;
• 4) preparing an aqueous medium having a pH in the range of about 2 to about 4.5 that contains an acid HX (where X is the same anion as that of the lipophilic salt) for stripping of the xylulose from the organic phase generated in step 3;
• 5) bringing the low pH aqueous medium from step 4) into contact with the ketose-rich organic phase from step 3);
• wherein, at the low pH, the ketose and hydroxyl ion are released into the aqueous phase and the CA is converted to its non-ionic conjugate acid;
• and, wherein, at the same time, the Q+ ion that formed the ion pair combines with an X− ion from the aqueous medium to reform the lipophilic salt;
• and
• 6) recovering the ketose from the concentrated ketose-rich medium.

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.