An attempt to achieve the direct hydrogenolysis of tetrahydrofurfuryl alcohol in supercritical carbon dioxide

Abstract

The use of supercritical carbon dioxide (scCO₂) in the hydrogenolysis of tetrahydrofurfuryl alcohol was investigated over a Rh supported MCM-41 catalyst (metal loading ≈ 1%). Without any additive, tetrahydrofurfuryl alcohol was converted to 1,5-pentanediol with high conversion (80.2%) and selectivity (91.2%) under mild reaction conditions (temperature = 80 °C and H₂ pressure = 4 MPa). The effects of different variables like CO₂ and H₂ pressure, temperature and the reaction time were also optimized. A strong influence of CO₂ pressure on the conversion was observed. The conversion was increased with pressure due to the enhanced solubility of tetrahydrofurfuryl alcohol in CO₂ and reached the maximum at 14 MPa, as the single phase (CO₂–H₂–substrate) was formed, but the selectivity of 1,5-pentanediol remained unaltered. On the other hand, H₂ pressure also changed the conversion as well as the selectivity. Temperature was found to play an important role in enhancing the catalytic efficiency; conversion of the substrate was increased along with the temperature, but the selectivity of 1,5-pentanediol dropped after reaching 120 °C. The Rh catalyst exhibited strikingly different product distribution under the solvent-less conditions compared to scCO₂. In addition, instead of CO₂, when the reaction was carried out in H₂O, the conversion and the selectivity of 1,5-pentanediol decreased substantially. However, addition of only 7 MPa of CO₂ modified the conversion and the product selectivity. Under similar reaction conditions, hydrogenolysis of THFA over a Pd catalyst provides a maximum of 50% conversion and the product distribution was different in comparison with Rh catalysts.