Etherification of 5‐Hydroxymethylfurfural to Biofuel Additive Catalyzed by Aquivion® PFSA Modified Mesoporous Silica

Abstract

Catalytic etherification of 5‐hydroxymethylfurfural (HMF) with isobutene (IB) to a biodiesel additive, that is, 5‐(tert‐butoxymethyl)‐furfural (tBMF), is studied on the Aquivion® perfluorosulfonic acid resin (PFSA) modified mesoporous silica (Aquivion®/m‐SiO2) solid acid. Mesoporous silica, composed of amorphous silica‐particle aggregates, is synthesized by the sol–gel method using the amphiphilic Aquivion® PFSA as both the acidic and the template reagent. The silica surface is then modified by the Aquivion® resin, leading to the hybrid Aquivion®/m‐SiO2 solid acid bearing highly accessible sulfonic acid sites and adequate porous structure. The catalytic properties, including composition, thermal stability, acidity, porosity, and morphology, are characterized by FTIR spectroscopy, Raman spectroscopy, solid‐state NMR spectroscopy, XPS, TGA/DTG, elemental analysis, potentiometric titration, N2 physisorption, SEM, and TEM. The influence of different reaction parameters, such as catalyst dosage, reaction time and temperature, reactants composition, and solvent, is investigated. The optimal Aquivion®/m‐SiO2 catalyst (10 wt.‐%), with an accessible acidity of 45 µmolH+ gcatal.–1 demonstrates 78 % conversion of HMF and 66 % yield of tBMF, in the presence of THF, after 3 h at 90 °C, whereas the yield of byproduct 5,5′‐[oxy‐bis(methylene)]bis‐2‐furfural (OBMF), generated by the oligomerization of HMF, is lowered to 4 %. The developed catalyst demonstrates good stability after regeneration for five consecutive cycles.