Hydrophobic Mesoporous Polymeric Acid Catalysts for Glycerol Coetherification with Isobutene and tert-Butanol

Etherification with tert-butanol or isobutene converts biodiesel-derived glycerol to fuel additives in demand. Combining the advantages of isolated etherifications with tert-butanol or isobutene, we previously proposed to etherify glycerol with isobutene and tert-butanol simultaneously and proved that the coetherification could enhance the reaction rate, conversion, and yield to the desired ethers. In this work, considering the characteristics of the coetherification, a series of hydrophobic mesoporous acid catalysts PDVB-x-SO3Hs were synthesized via solvothermal polymerization of divinylbenzene and sodium p-styrenesulfonate. Characterizations show that the PDVB-x-SO3Hs have a mesoporous structure, large surface areas (310–1074 m2/g), rich and tunable acid sites (0.40–2.36 mmol/g), good thermal stability, excellent hydrophobicity (139–163°), and strong acid strength. Due to their different affinities with reactants, PDVB-x-SO3Hs are more active than Amberlyst 15 in activating isobutane, while the reverse applies for the activation of TBA. Hydrophobic PDVB-x-SO3Hs demonstrated a significantly higher TOF for isobutene than for tert-butanol. In contrast, the TOFs on the hydrophilic Amberlyst 15 were nearly identical for both reactants. In the coetherifications with varied initial compositions, the synthesized PDVB-x-SO3Hs with suitable hydrophobicity consistently resulted in higher yields to the desired ethers, compared to Amberlyst 15. The introduction of water led to a reduction of the TOF on all of the tested catalysts. However, the decrease observed in superhydrophobic samples is less pronounced compared to that observed in weakly hydrophobic samples and Amberlyst 15. Active groups of PDVB-x-SO3H exhibited good stability, maintaining consistent catalytic activity throughout several cycles.