Ethylenediamine-modified pure silicalite molecular sieves applied in preparation of caprolactam via cyclohexanone oxime gas-phase rearrangement
The preparation of caprolactam(CPL)by cyclohexanone oxime(CHO)gas-phase Beckmann rearrangement is a green and environmentally friendly production process,but the performance of gas-phase rearrangement catalysts has always restricted the industrial application of this process.In order to enhance the reaction performance of gas-phase Beckmann rearrangement,ethyleneamine with different molecular sizes were used to modify pure silicalite molecular sieves.Characterization of the modified pure silicalite molecular sieves was carried out by scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray diffraction(XRD)and N2 adsorption/desorption tests,and the catalytic performance of the catalysts for CHO gas-phase Beckmann rearrangement was evaluated.The results indicate that the pure silicalite molecular sieves maintain their original MFI topology after ethyleneamine-modification,and the Brunner-Emmet-Teller(BET)specific surface area decreases to 354.1 m2/g,and the CPL selectivity increases to 97.00%.The effects of reaction temperature,weight hourly space velocity and mass fraction of CHO on gas-phase Beckmann rearrangement were investigated.The optimal reaction processes are as follows:reaction temperature 370℃,weight hourly space velocity of CHO 1.0 h-1 and mass fraction of CHO 30%.Under the optimal reaction processes,the CHO conversion rate of S-1-B catalysts is≥99.90%,and the CPL selectivity of S-1-B catalyst is≥97.00%.The S-1-B catalyst has single-pass life of 1200 hours and stable regeneration performance,which has good industrial application prospect.
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