The Studies On The Catalysts Used In Selective Nitration Of Toluene

The industrial nitration of toluene to synthesize p-mononitrotoluene (MNT) involving the concentrated mineral acids as the catalysts which is one of the most environmentally harmful processes. The process produces huge amounts of wastes along with a large amount of undesired o-MNT due to the nonselective nitration of toluene. In this thesis, the solid acids catalysts including zeolites and heteropolyacids were examined for the regioselective nitration of toluene with liquid NO2 in the presence of O2. The influences of different structure of the zeolites and the modifications of zeolites with different methods were investigated by using XRD, solid sate NMR, FT-IR, NH3-TPD, etc.It is found that all the solid acid catalysts including zeolites HZSM-5, Hβ, HY and heteropolyacids were active for the nitration of toluene. Among them, zeolite beta is one of the most active catalysts. However, the highest catalytic selectivity for p-MNT formation of the zeolite beta was the mostly noticeable. Moreover, it is found that the cation exchanges, the cation exchange degree of Na+, SiO2/Al2O3 ratios and calcinating temperature had the different effects on their catalytic performances for HZSM-5 and H-beta, respectively.Cation exchanges with Fe3+, Mg2+, Zn2+ and B3+, as well as the dealumination or alumination of the zeolite beta had little effect on the catalytic performance of the catalyst. The catalytic activity and selectivity for the p-MNT were gradually decreased with the increase of the Na+ exchange degree on the zeolite. Calcinations of the catalyst at 550℃ lead to the best catalytic performance for the para-selective nitration of toluene. Increases of the amount of the catalyst and the time for the reaction were of benefit to the increases of catalytic activity for the nitration and selectivity for the p-MNT. At a moderately high reaction temperature, the reaction gave a result with a high conversion of NO2, a reasonable yield of nitration products and a high para-selectivity.On the other hand, cation exchanges with Fe3+, Mg2+, Zn2+, B3+ showed remarkable enhancement on the catalytic activity of HZSM-5. The cation exchanges had little effect on selectivity of the zeolite. Exchange of Na+ had resulted in the decrease of the selectivity of HZSM-5,while it showed little effects on the activity of HZSM-5 . Increase of SiO2/Al2O3 ratios had significant influence on both the activity and the selectivity for HZSM-5. HZSM-5 showed the best results at the calcination temperature of 500℃.