Sulfonic Acid-Functionalized, Hyper-Cross-Linked Porous Polyphenols as Recyclable Solid Acid Catalysts for Esterification and Transesterification Reactions

Easy, safe, and cost-effective hydroxyl-containing microporous hyper-cross-linked polymers based on phenol (pPhOH) and 4,4′-(propane-2,2-diyl)diphenol (or bisphenol A; BPA) were prepared by the Friedel–Crafts alkylation reaction of phenol and bisphenol A using dimethoxymethane as an external cross-linker. The pPhOH and pBPA were functionalized by chlorosulfonic acid to yield corresponding sulfonic acid-functionalized polymers, pPh-SO3H and pBPA-SO3H, respectively, with their surface areas of 210 m2/g and 324 m2/g, respectively. The physicochemical properties of pPh-SO3H and pBPA-SO3H were analyzed by Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, Brunauer–Emmett–Teller analysis, and X-ray photoelectron spectroscopy. The pPh-SO3H and pBPA-SO3H polymers show excellent catalytic activity for the esterification of free fatty acids and transesterification of vegetable oils at room temperature, as well as excellent recyclability, signifying ...