Biomass-derived acid catalysts for the sustainable production of diphenolic acid

Diphenolic acid (DPA) is an important building block for the synthesis of various polymers and resins, today proposed as a short-term, bio-based alternative to the currently marketed bisphenol A. DPA is traditionally prepared by the condensation between levulinic acid and phenol, under acidic conditions, generally in the presence of hydrochloric or sulfuric acids. In recent years, significant efforts have been made to develop more sustainable and efficient methods for the DPA production. However, up to now, non-suitable heterogeneous systems have been reported in the literature for the DPA production due to scarce yields, low stability and difficult recyclability. On this basis, we propose the sustainable synthesis of carbon-based sulfonated acid catalysts from microcrystalline cellulose and real biomasses, to be used in the production of DPA. In particular, hydrothermal carbonization technique was adopted to obtain hydrochars which were tested as heterogeneous acid catalysts in the DPA synthesis starting from levulinic acid and phenol. Yields of about 15-20 mol% were achieved, confirming the potential of these acid catalysts for DPA production.