Sustainable synthesis of p,p'-diphenolic acid from renewable levulinic acid with heterogeneous acid resins

Diphenolic acid (p,p’-DPA) is a very interesting substitute for bisphenol A. In this work, the optimization of its synthesis from phenol and bio-based levulinic acid was proposed, comparing homogeneous (e.g. mineral acids) and heterogeneous catalysts (commercial acid resins), the latter being preferred due to their greater industrial relevance. Some unresolved bottlenecks still hinder p,p’-DPA industrial development, in particular 1) lack of systematic optimization studies; 2) preference for lab-scale synthesized catalysts, rather than commercial ones, the latter industrially available and well-characterized; 3) sporadic evaluations on catalyst recycling; 4) undeveloped purification of the product from the reaction medium with non-toxic solvents; 5) complete lack of kinetic studies on heterogeneous systems. The present work aims to address these issues, optimizing the p,p’-DPA synthesis with commercial acid resins. Aquivion P87S was identified as the best heterogeneous catalyst, with the highest yield and selectivity to p,p'-DPA (both 91.7%), as well as good stability over time (4 cycles), all remarkable achievements, well beyond those of the state of the art. Ethanol was identified as the most compatible solvent with Aquivion P87S, enabling its effective swelling and mild regeneration. For the intensification development, p,p'-DPA purification was successfully achieved (purity degree of 94%), developing a new sustainable procedure with water as the crystallization solvent. Green metrics and LCA energy analysis demonstrated the potential sustainability of this process. The activation energies of all the tested resins were calculated with the Arrhenius equation and the Weisz Prater criterion was utilized to assess potential internal diffusion limitations within the systems.