| Gaseous hydrogenation of nitrobenzene (NB) over catalyst is an important way to prepare aniline (AN), an important raw material for the synthetic dyes, rubber chemicals, amino resins, and polyurethane. The nitrobenzene is prepared by the nitrification of benzene. However, little amount of di-nitrobenzene (DNB) (0.3%-1%) as byproduct will be synthesized in this process inevitably. At present, raw NB is usually rectificated to concentrate to around 30% before the hydrogenation reaction,which costs much energy. In this paper, the existing craft has been improved and the simultaneous hydrogenation of NB and DNB useing one reactor and one kind of catalyst has been achieved. In the improved process , the DNB can be transferred to Phenylenediamine(PD), which can be romoved in the following step.Gaseous hydrogenation over a Cu/SiO2 catalyst has been studied in a two-stage and a single-stage fluidized bed reactor, at 513-553 K and atmospheric pressure, respectively. Thus the conversion of nitrobenzene and the selectivity of aniline production and the stable life of the catalyst are significantly increased in the two stage fluidized bed reactor, as compared with those in the single stage one.The coke-deposited catalysts from the experimental scale reactor is characterized by thermo-gravimetric analysis (TGA), the x-ray diffraction (XRD), and Raman, respectively. The investigation show that the deactivity of the catalyst is due to the increase of the coke-deposited, which can change to the graphite, to covers the active site. There exists two kinds of coke on the deactivated catalyst, one can be burned at low temperature, and the other is combined coke which is similar with the SiC. These results provide a guidency to the operating of industrial reactor and reactivation of the catalyst.The reaction kinetics of hydrogenation studied in a micro reactor show that The reaction order for DNB is 0.3 when the ratio of hydrogen to NB is more than 5. |
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