3.1 Mixing performance in the microreactor system
In this work, since a small amount of CB was dissolved in sulfuric acid, the reaction involved a homogeneous liquid system. Because the nitration reaction is rapid, it is necessary to ensure sufficient mixing performance, which is related to the flow rates of the two streams.24,25 The concentration distribution of CB in the mixed solution was simulated by computational fluid dynamics (CFD). The flow rates of the solution 1 and solution 2 were 0.4 mL/min and 0.9 mL/min, respectively, as shown in Figure S3 . The mixing performance of the two fluid streams was significantly enhanced at the intersection of the T-micromixer. The distance at which the substance concentration was homogenized was only 3 mm. By knowing the total flow rate, the mixing time of the two streams can be calculated, and it was found to be much less than the reaction time, indicating that mixing was not the limiting factor in the nitration reaction. In addition, the properties of the two fluids were very similar due to the low solubility of CB in sulfuric acid. To eliminate any mixing limitations, all of the following experiments were operated at the same flow rate.