(8c) Elucidating Green and Sustainable CO2-H2o Synergy for Biomass Valorization into Platform Chemicals

The “Glasgow Climate Pact” agreed at the UN Climate Change Conference of the Parties (COP26) commits to accelerate global action this decade, by limiting global warming to 1.5°C over pre-industrial levels. To help achieve this goal, CO₂, the main contributor to the climate change, can be turned from a liability to an asset by mixing it with H₂O to produce an acidic condition suitable for many reactions. This opens new opportunities and challenges for researchers, process engineers and technologists. In this regard, we explore the CO₂-H₂O synergy under elevated temperatures and pressures as applied to many reactions involving biomass valorization. Taking for example the conversion of glucose to 5-hydroxymethylfurfural (HMF). While HMF can be derived from biomass, specifically sugars, its synthesis typically requires the use of metal-based catalysts and ionic liquids. In this study, the supercritical CO₂-subcritical H₂O system was proposed as a green reaction medium for the conversion of glucose to HMF. The response surface methodology based on the Box-Behnken design was used to investigate the effect of temperature, pressure, and isopropanol concentration on the yield of HMF. From the quadratic models, the highest HMF yield was predicted to be 38.3% with a corresponding glucose conversion of 87.5% at 200 °C, 16 MPa, and 8 vol% IPA. A mechanistic study using DFT calculations was also performed and the results revealed that isopropanol can facilitate the various hydride shifts that occur in the conversion of glucose to HMF. Some of our unpublished works on the incorporation of the system in a microreactor for millisecond reactions, as well as the elucidation of the mechanism using Raman spectroscopy and quantum calculations will also be introduced. Furthermore, the positive effect of adding CO₂ to deamination to obtained high quality bio-oil by hydrothermal liquefaction of biomass will also be reported.