p-Toluic Acid Oxidation to Terephthalic Acid via Bromine-Free Process Using Nano Manganese and Manganese-Copper Mixed Oxides

Abstract

The industrial process of terephthalic acid (TPA) production suffers from many environmental and economical drawbacks. Liquid phase catalytic oxidation of alkylbenzene by oxygen usually is initiated by bromine in a corrosive acetic acid solvent. A recent catalytic system used environmentally benign n-hydroxysuccinimide (NHSI) as a free radical promoter rather than more hazardous bromine molecules. Manganese dioxide and Cu-Mn mixed oxide nanoparticles with different ratios (CuMn11, CuMn12, and CuMn13) were prepared and examined as oxidation catalysts for p-toluic acid (p-TA) to produce TPA in an oxygen atmosphere. These catalyst samples were characterized by HRTEM, XRD, and N2-adsorption-desorption isotherm techniques. The catalytic activity of prepared nanocatalysts for TPA was studied at different conditions (reaction time, catalyst dosages, reaction solvent and varied oxygen pressure and reaction temperature) to maximize the yield (%) and selectivity (%) toward TPA synthesis. Catalyst characterization indicates that CuMn11 sample has a new phase of the spinal structure. Furthermore, it is the most active catalyst that produces 99.5 and 99.6% in acetonitrile and ethylacetate solvents respectively under oxygen pressure 20 atm.