Modeling of <i>m</i> -Xylene Oxidation to <i>m</i> -Toluic Acid without Solvent: Catalyst Concentration and Mass Transfer Effect Quantification

3-Methylbenzoic acid (m-TA) serves as an excellent material additive and finds extensive application in the field of plastics. Limited in-depth research has been performed to establish a kinetic model for the oxidation of m-xylene (MX) to m-TA under solvent-free conditions. In this work, a novel MX oxidation process without acetic acid as solvent was developed, which occurs at mild conditions (403 K; 0.3 MPa) and achieves a high selectivity of m-TA (83.63 mol %). A kinetic model incorporating the catalyst and oxygen concentration was established to describe the MX oxidation behaviors under various catalyst concentrations and mass transfer conditions accurately. The parameters of the kinetic model are statistically meaningful (R2 being 0.998, F-value is 1.47 × 107). Moreover, the model exhibits strong predictive performance even under continuous industrial operation conditions (pilot-scale testing, ARD < 10%). This work provides valuable insights into the kinetic modeling of aromatic bulk oxidation processes and their industrial-scale upscaling.