(679d) Catalytic Production and Solvent Properties of Furfural-Derived Tetrahydropyran

This work addresses the growing demand for green biobased solvents for use in paints, adhesives, plastic upcycling, and reaction media. Major industrial solvents in use today, such as tetrahydrofuran (THF) and 1,4-dioxane, are heterocyclic ethers that are produced from petrochemical sources and form explosive peroxides when exposed to air. On the contrary, tetrahydropyran (THP) does not form peroxides even after exposure to air for 30 days and has a higher boiling point than THF. We have developed a 3-step reaction pathway for the production of THP: hydrogenation of furfural to tetrahydrofurfuryl alcohol (THFA) over Ni/SiO₂; dehydration of THFA to dihydropyran (DHP) over γ-Al₂O₃; and hydrogenation of DHP to THP over Ni/SiO₂. Kinetic experiments in a packed bed reactor at 150 °C and 200 psig have demonstrated that DHP hydrogenation has an apparent activation energy of 31.0 ± 0.1 kJ/mol, and the selectivity to THP is nearly 100%. THP formation has a 1^st order rate dependence on DHP partial pressure and 2^nd order rate dependence on H₂ partial pressure. Ni/SiO₂ with 10 wt% Ni loading was synthesized using incipient wetness impregnation and has a low deactivation rate constant of 0.012 mmol/h/g_cat. As seen from thermogravimetric analysis (TGA), most of the catalyst deactivation is from coking and the catalyst can be regenerated by calcination in air. Using Hansen Solubility Parameters and molecular dynamics (MD) simulations, we have predicted the solvent properties of THP. We have experimentally demonstrated that THP can be used to recover polyethylene (PE) from plastic waste containing PE/EVOH (ethylene-vinyl alcohol)/PET (polyethylene terephthalate). We have also shown that unlike THF, THP remains inert at reaction conditions containing Lewis/Brønsted acids and does not undergo ring opening polymerization. Our results establish THP as a renewable solvent with superior oxidative and thermal stability that can be produced from catalytic upgrading of biomass.