ACETYLATION OF ANISOLE BY ACETIC-ANHYDRIDE OVER A HBEA ZEOLITE - ORIGIN OF DEACTIVATION OF THE CATALYST

The liquid phase acetylation over a HBEA zeolite (Si/Al = 10) of aniso le with acetic anhydride in equimolar amounts was carried out in a bat ch reactor at 60 degrees C. p-Methoxyacetophenone is selectively and r apidly formed on the fresh catalyst. However, a rapid deactivation occ urs which could be attributed to a large extent to the pronounced inhi biting effect that p-methoxyacetophenone has on the acetylation. In a flow reactor and at a higher temperature (90 degrees C), the catalyst deactivation is much slower particularly when an anisole rich mixture (anisole/acetic anhydride molar ratio of 5) is used as a reactant. Cat alyst samples were recovered after various times on stream and the org anic material which was retained in significant amounts on the zeolite was analysed by GC and GC/MS. The major part of this material, which consists of p-methoxyacetophenone, can be recovered by soxhlet extract ion in methylene chloride. Due to its high polarity, this reaction pro duct is strongly retained in the large mesopore volume of the HBEA zeo lite. The minor part can only be recovered after dissolution of the ze olite in a hydrofluoric acid solution. It consists mainly of di- and t riacetylated anisole entrapped in the zeolite micropores. As shown by nitrogen adsorption, these compounds cause pore blockage. The latter i s responsible for part of the catalyst deactivation, the other part be ing due to-p-methoxyacetophenone located in the mesopores. The use of an excess of anisole enhances catalyst stability as it limits both the retention of p-methoxyacetophenone and the formation of the polyacety lated anisoles. (C) 1998 academic Press.