Process optimization and thermal hazard analysis of the preparation of diphenyl sulfoxide using hydrogen peroxide as oxidant

In this study, diphenyl sulfoxide was prepared by oxidizing diphenyl sulfide with hydrogen peroxide using phosphotungstic acid as catalyst in semi-batch mode. In order to optimize the synthesis process, a four-factor three-level Box-Behnken design was adopted. The result showed that under the optimal condition, namely catalyst concentration 0.19 mmol/mol, oxygen-sulfur ratio 1.08, reaction temperature 30 ºC, and dosing time 15 min, the yield of diphenyl sulfoxide could reach up to 79.05%. In addition, the thermal behavior of synthesis process was systematically investigated using a reaction calorimeter (EasyMax 102) equipped with a situ FTIR monitoring. The receivable mechanism is that H₂O₂ is activated by the catalyst and subsequently reacts with diphenyl sulfide to produce oxidized product. H₂O₂ was relatively stable when PTA was used as catalyst. Thermal risk index was used to assess the thermal hazard of H₂O₂ & PTA. Furthermore, risk matrix method as well as Stoessel criticality diagram was used to assess the thermal risk of the process and an unacceptable risk was obtained. One of the main hidden dangers was the potential chemical splatter caused by decomposition of H₂O₂. It should be equipped with a pre-set quench or sufficient emergency discharge to avoid further loss. The results of this work proposed a solid foundation for the safe operation of this process and can be further used for scale-up.