Sustainable recycling of benzoic acid production waste: Green and highly efficient methods to separate and recover high value-added conjugated aromatic compounds from industrial residues

Industrial residues formed in the industrial production of benzoic acid by cobalt-catalyzed oxidation of toluene are traditionally disposed as waste materials and often burnt or buried. It therefore may become a significant source of environmental pollution. In this report, we describe simple techniques to obtain high value conjugated aromatic compounds, including 9-fluorenone, 6H-benzo[c]chromen-6-one, biphenyl-3-carboxylic acid, and biphenyl-4-carboxylic acid, from benzoic acid industrial residue using inexpensive alkalis and acids. The separation methods involve simple and mild procedures with high economic effectiveness and low environmental contamination.