Isolation of C5-sugars from the hemicellulose-rich hydrolyzate of distillers dried grains

A three-stage process for isolation and separation of C5-sugars in dry form from the hydrolyzate of distillers dried grains (DDG) is described. The salient features include extraction of bis(boronic ester) adducts of xylose and arabinose into toluene on treatment of neutralized hydrolyzate with phenylboronic acid (PBA) and subsequent addition of propylene glycol to the organic phase to induce sugar precipitation for ready collection. The PBA used in the process is largely reclaimed on hydrolysis of the propylene glycol boronic ester formed during the process. A preparative scale example afforded 48% of the xylose content in DDG as a crystalline solid also containing an additional 11% of the arabinose content.