(641d) Synergism of Subcritical H2O and Supercritical CO2 for Glucose Conversion to 5-Hydroxymethylfufural

The declining amount of petroleum resources has prompted researchers worldwide to explore various alternatives including biomass as alternative feedstocks. In this context, 5-hydroxymethylfurfural (5-HMF) has attracted growing interest because it can be produced from biomass-derived sugars, and has the potential to be further converted into fuels and fine chemicals. Acid-catalyzed conversion of fructose to 5-HMF has been widely investigated. However, glucose is more cost-effective and readily available. This research focuses on the conversion of glucose into 5-HMF employing the synergy of subcritical H₂O and supercritical CO₂. Carbonic acid, resulting from mixing supercritical CO₂ and subcritical H₂O, could act as an acid catalyst. The operating conditions were optimized, and addition of alcohol such as isopropanol and low transition temperature mixtures was also investigated. Furthermore, combined reactive separation technique was also employed to enhance yield of the target products by simply passing scCO₂ through the reacting mixture in the aqueous phase. In this approach, since 5-HMF has low polarity, scCO₂ can dissolve 5-HMF. Thus, continuous CO₂ flow enables simultaneous reaction and separation, and could also suppress the formation of by-products or degradation products.

The highest yield (30.4%) and selectivity (62.8%) were obtained under the condition of 200 °C, 20 MPa, 1.5 h. Higher scCO₂ pressures favor the yield of 5-HMF due to its increased solubility. Addition of isopropanol also had positive effect on the yield of 5-HMF.

The results suggest the applicability of adding isopropanol and the use of reactive separation approach employing the synergy of subcritical H₂O and supercritical CO₂ to the conversion of glucose to 5-HMF. The reaction using a microreactor system was also investigated, and the mechanism was then elucidated using Raman spectroscopy.