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 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).

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.

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.