FIGURE 2 Effect of temperature and residence time on the conversion of CB. The mass fraction of H2SO4 = 95%, molar ratio of HNO3 to CB = 1.3, Q or = 0.4 mL/min, and Q ac = 0.9 mL/min
It is worth mentioning that DNCB is an undesirable byproduct, and to obtain accurate kinetic data for the nitration of CB, the selectivity of DNCB needs to be controlled to a low level. The selectivity of each CB nitration product was investigated as a function of the reaction temperature, as shown in Figure 3 . As the temperature and residence time increased, NCB was further nitrated to form DNCB, resulting in an increase in the selectivity of DNCB. However, at the low temperature used in this work and with the short residence time, the selectivity of DNCB remained below 1%. In addition, lowering the temperature had a more obvious inhibitory effect than shortening the residence time on the formation of DNCB. Therefore, the formation of DNCB had a negligible effect on the accuracy of the primary CB nitration kinetic data. When substituents are introduced on the benzene ring, the nitration difficulty will change. For example, in the tertiary nitration of CB, because the introduced nitro functional group is an electron-withdrawing group, the electron cloud density of the benzene ring decreases, and a certain steric hindrance is generated, making nitration more difficult. Therefore, no 1-chloro-2,4,6-trinitrobenzene was detected after reaction.