Production of xylitol using biological pathways (fermentation) offers a more environmentally and economically sustainable way to produce the platform molecule, which can be converted into commodity chemicals and high-value products, such as diols and xylonates. One key challenge in the production of xylitol via fermentation is the separation of xylitol from the rest of the fermentation hydrolysate and subsequent crystallization and recovery of high-purity xylitol. This study builds on previous work to explore possible avenues for xylitol crystallization, and purification or conversion into other chemicals. Three parameters were varied to maximize retrieval of xylitol crystals: temperature, addition of ethanol as antisolvent, and addition of a pure xylitol starting seed. The eluents produced from prior fermentation and subsequent ion-exchange experiments were concentrated down to facilitate a saturated xylitol solution. First, temperatures of -16°C and -20°C were tested using standard laboratory freezers. Then, differential scanning calorimetry (DSC) was used to investigate the actual crystallization and melting temperatures of the xylitol crystals in the aqueous solution. In the trials using DSC, three xylitol seeding conditions were used: no seed, 1% by weight, and 10% by weight. For each of these trials, two cycles each of heat removal and addition were run on the same 10 μL sample. During these cycles the temperature changed from 25°C to -30°C at a rate of 3K/minute. Xylitol seeding with 1 wt% facilitated crystallization at relatively higher temperatures than other conditions where the crystallisation occurred between -15°C and -20°C while the melting occurred between -10°C to 8°C. This information was used to run the crystallization experiments at 5 mL working volume to extract the xylitol crystals . The main focus of the macro-scale experiment was achieving high crystal yield and/or purity through one or more of the xylitol retrieval methods, since pure xylitol can then be converted into other high-value chemicals such as propylene glycol, ethylene glycol, xylaric acid, and xylonates. Optimizing crystallization of xylitol advances the sustainable production of the aforementioned chemicals which are widely used in food, pharmaceutical, and polymer synthesis industries.
