Influence of reaction conditions on hydrothermal carbonization of fructose.

Hydrothermal carbonization is a powerful way to convert cellulosic waste into valuable platform chemicals and carbonaceous materials. In this study, in order to optimize the process, fructose was chosen as the carbon precursor and the influence of reaction time, acid catalysis, feed gas and pressure on the conversion products was evaluated. 5-hydroxymethylfurfural (HMF) is produced in high amounts in relatively short time. Both strong and weak acids accelerate fructose conversion. Levulinic acid (LevA) formation is faster than that of hydrothermal (HT) carbon in acidic conditions. Strong acid catalysts should be considered to target preferentially LevA production, while milder conditions should be preferred for HMF production. Moreover, a slight initial overpressure of the reactor is always beneficial in terms of conversion. FT-IR, 13C ss-NMR and SEM showed that HT carbon evolves through time from a furanic-based structure with alkylic linkers to an increasingly cross-linked condensed structure. MALDI-ToF MS showed the existence of a series of oligomers in a mass range within 650 Da and 1500 Da formed by condensation of repeating units.