Effect Of TS-1Treatment By Tetrapropyl Ammonium Hydroxide On Cyclohexanone Ammoximation

Cyclohexanone oxime, as a key intermediate, is mainly used in the production ofε-Caprolactam. The traditional cyclohexanone-hydroxylamine processes forcyclohexanone oxime synthesis generate large amounts byproducts and haveenvironmental pollution. In the1980’s, Italian Enichem company successfullydeveloped a new technology in which the ammoxidation of cyclohexanone iscatalyzed by titanium silicalite-1. It overcomes the shortages of the traditionalprocesses and meets the requirements of “Green Chemical Engineering” withzero-emission. But there are two problems in this technology: First, the preparation ofcatalysts with high stability; second, the difficulty in separation of the catalyst.In this work, TS-1was hydrothermally synthesized using tetrapropylammoniumhydroxide (TPAOH) as the template, tetraethyl orthosilicate (TEOS) as Si source andtetrabutyl orthotitanate (TBOT) as Ti source. TS-1was treated with TPAOH solutionto improve its stability in the ammoximation of cyclohexanone. The treatmentconditions were investigated, including treatment time, treatment temperature andtreatment times. The optimal TPAOH treatment conditions were obtained.The treated TS-1has been characterized by XRD, nitrogen physical adsorption,FT-IR, UV-Vis and SEM, and studied in cyclohexanone ammoximation. The resultsshow that the MFI structure of TS-1is not destroyed, while mesopores are formed inTS-1crystals and the pore diameters increase with the TPAOH concentrations; theamount of the framework Ti species decreases slightly with the increase of TPAOHconcentrations; the activity and the selectivity of TS-1are not affected by thetreatment, but the catalyst stability first increases, then decreases with increasing thepore diameters after reaching to a certain value. In order to explain the effect on TS-1by TPAOH treatment in depth, the mechanism of the catalyst deactivation and theeffect of TPAOH on the acidity of TS-1also have been investigated.