Study on gas–liquid sulfonation reaction under annular flow pattern in micro-reactor: Mechanism, model and process optimization

Micro-sulfonation is a new sulfonation method with great development potential. The gas–liquid micro-sulfonation are safe, efficient and low-cost, however, limited by the research progress and application scope of micro-reactors, the development of gas–liquid micro-sulfonation technique is far from enough. The gas–liquid sulfonation reaction process under annular flow pattern in micro-reactor is experimentally studied in this paper. The maximum MESA (fatty acid methyl ester sulfonic acid) yield under the experimental conditions in this study achieves 89.771 %, which is obviously higher than that (64.1 % for gas–liquid sulfonation and 76.82 % for liquid–liquid sulfonation) in conventional reactors and should be higher if the micro-reactor structure or operating conditions being further optimized. Based on the analyses of experimental results, the effect mechanisms of mass transfer and reaction on the gas–liquid micro-sulfonation efficiency are explored, and the sulfonation efficiency models and pressure drop model of four micro-reactors are established by dimensional analysis method. On account of both the mass transfer characteristics of gas–liquid two-phase flow and the high-viscosity of sulfonation products, enhancing the local disturbance of liquid phase can significantly improve the reaction efficiency. Finally, the operating conditions of two-phase flow rates and reaction time are optimized to ensure the high sulfonation product yield meanwhile reduce the fluid pressure drop or energy consumption of sulfonation process using the improved NSGA-II algorithm.