Solvent Effects on Fructose Dehydration to 5-Hydroxymethylfurfural in Biphasic Systems Saturated with Inorganic Salts

Furan derivatives, such as 5-hydroxymethylfurfural (HMF), obtained from acid-catalyzed dehydration of carbohydrates, can serve as renewable chemical platforms for the production of fuels and chemical intermediates. Addition of an inorganic salt to concentrated aqueous solutions of fructose (30 wt% fructose on salt free basis) in biphasic systems containing an organic extracting phase improves HMF yields by increasing the partitioning of HMF into the extracting phase, as measured by the partition coefficient, R, equal to the concentration of HMF in the organic phase normalized by the concentration in the aqueous phase. We have studied the impact of solvent choice on HMF yield using primary and secondary alcohols, ketones, and cyclic ethers in the C-3-C-6 range as extracting solvents in biphasic systems saturated with NaCl. Biphasic systems containing C-4 solvents generated the highest HMF yields within each solvent class. Tetrahydrofuran demonstrated the best combination of high HMF selectivity (83%) and high extracting power (R = 7.1) at 423 K. The presence of NaCl provided the additional benefit of creating biphasic systems using solvents that are completely miscible with water in the absence of salt. We have also studied the impact of different salts on HMF yield in systems using 1-butanol as the extracting solvent. Na+ and K+ showed the best combination of extracting power and HMF selectivity of the monovalent and divalent chloride salts tested. Changing the anion of the salt from Cl- to Br- resulted in R-values and HMF selectivity values resembling the non-salt system, while changing to the SO4 (2-) divalent species generated a high R-value (8.1), but a low HMF selectivity value (71%).