Purification and Concentration of Xylose and Glucose from Neutralized Bagasse Hydrolysates Using 3,5-Dimethylphenylboronic Acid and Modified Aliquat 336 as Coextractants

Experimental trials of the extraction of xylose, glucose, and fructose from aqueous solutions were conducted using 3,5-dimethylphenylboronic acid (DMPBA) and modified Aliquat® 336 (MA) as combined extractants dissolved in Exxal®10 diluent. MA was produced by contacting an Aliquat 336/Exxal 10 solution with a concentrated caustic soda solution so that the quaternary ammonium ions of Aliquat 336 would ion pair with hydroxide ions. The DMPBA/MA/Exxal 10 organic solution containing equimolar amounts of MA and DMPBA was contacted with a neutral aqueous solution containing one of glucose, xylose, or fructose and the extraction isotherms were determined. The molar ratio of DMPBA:sugar in a fully loaded organic solution was 2:1. The use of the MA instead of Aliquat 336 enabled significant proportions of the sugars to be extracted from aqueous solutions over a wide pH range (∼2-11). Loaded organic solutions were stripped using aqueous hydrochloric acid solutions. Complete recovery of the sugar was possible by ensuring sufficient acidity was available in the strip solution. Solutions of MA in Exxal 10 were also found to extract sugar, although to a lesser extent than when DMPBA was included. Extraction of xylose and glucose from solutions derived from the acid hydrolysis of bagasse was performed. By varying the volumetric ratio of strip to organic phases, strip solutions with xylose concentrations up to 4× that of the original hydrolysate were produced while reducing the concentration of the undesirable acid soluble lignin by up to 90%. Hence, this process has the potential to produce high concentration monosaccharide solutions suitable for direct fermentation.