Continuous Synthesis Of Vulcanization Accelerator Cbs In Gas-liquid Slug Flow Microreactors

N-cyclohexyl-2-benzothiazole sulfenamide(CBS),as an environmental friendly accelerator,is widely utilized in vulcanization process.It can not only improve the vulcanization rate,but also prolong the scorch period and flat period.Therefore,the safety of the operation process and the properties of the vulcanized rubber can be improved.The sodium hypochlorite is widely used in industry,which will produce a large amount of saline wastewater,making follow-up treatment costly and heavy pollution.In this paper,catalytic oxidation method is used to prepare CBS,avoiding environmental pollution.To solve the problems of low-efficiency and high-risk in oxidation process with high-pressure pure oxygen in batch reactor,microreactor is proposed to optimize this method and realize the continuous operation of accelerator preparation.In this paper,2-mercaptobenzothiazole(MBT)and cyclohexylamine were used as raw materials.Copper acetate monohydrate was used as catalyst,and ammonia was added as an additive.CBS was prepared by catalytic oxidation under high pressure.The uniform and stable gas-liquid segmented flow was formed after passing through the T-junction.The formation of flow pattern realizes high-speed mixing in the divided micro unit and improves the reaction efficiency.The effects of catalyst concentration,mass fraction of ammonia,temperature,pressure,reactant ratio and reactor material on reaction rate and yield were investigated.By exploring the influence of operating conditions on mixing and mass transfer,such as the selection of capillaries,total flow rate and gas-liquid volumetric flow ratio,an appropriate operational zone where mass transfer resistance was eliminated was selected.The kinetics of the oxidation reaction was systematically studied in the kinetic-control region,and a simplified kinetic model was established.The experimental results showed that when the stainless-steel capillaries with an inner-diameter of 0.6 mm was used,the optimal reaction temperature was 50 ℃,the oxygen pressure was 0.4 MPa,the molar ratio of cyclohexylamine to MBT was 10:1,the concentration of copper acetate monohydrate was 31.1 m M,and the ammonia concentration was 8.3 wt%.The reaction time was shortened to 200 seconds and the yield was 87.8%.When the flow rate was 9-18 m L/ min and the gas-liquid volumetric flow ratio was 8-12,the reaction was not controlled by mass transfer resistance.Through data fitting,a simplified kinetic model(0 and 0.56 order with respect to MBT and pure oxygen,respectively)was established and the reaction activation energy is 28.3 ± 1.8 k J/ mol.The accelerator CBS prepared by catalytic oxidation in this paper has met the chemical industry standard of rubber accelerator.Meanwhile,this method is of no production of saline wastewater.It is an economic and environmental process.