Kinetic Study of Gas–Liquid Heterogeneous Chlorination of Acetic Acid Using Elemental Sulfur as a Catalyst Precursor: Process Optimization for Enhanced Monochloroacetic Acid Selectivity and Productivity

Monochloroacetic acid (MCA) is a pivotal intermediate in agrochemicals and pharmaceuticals, but its industrial synthesis via acetic acid chlorination faces challenges related to selectivity and reaction time. This study investigates the kinetics of gas–liquid heterogeneous acetic acid chlorination using elemental sulfur as a catalyst precursor to establish a scientific basis for process optimization. A consecutive-parallel reaction mechanism was proposed incorporating acetic acid consumption, acetyl chloride conversion, MCA formation, and dichloroacetic acid (DCA) formation. Kinetic parameters were determined at 353, 363, 373, and 383 K in a steel bubble column reactor with fixed initial sulfur concentration (1.92 mol/L) and Cl 2 space velocity (4.028 L L −1 h −1 ). The activation energy for DCA formation (87.55 kJ mol −1 ) was substantially higher than that for MCA accumulation (52.40 kJ mol −1 ). Relative rate analysis revealed that k 3 / k 4 decreases continuously from 1.83 at 353 K to 0.76 at 383 K, confirming that lower temperatures favor MCA selectivity. The proposed kinetic model showed excellent agreement with experimental data ( R 2 > 0.98). Based on the kinetic analysis, three optimization strategies were derived: maintaining high acetic acid concentration, dynamic adjustment of Cl 2 feed rate, and implementation of a decreasing temperature–time profile. This work provides a scientific basis for optimizing industrial MCA synthesis using low-cost sulfur as a catalyst precursor.