Acetylation of anisole by acetic anhydride over a HBEA zeolite—Origin of deactivation of the catalyst

Abstract

The liquid phase acetylation over a HBEA zeolite (Si/Al=10) of anisole with acetic anhydride in equimolar amounts was carried out in a batch reactor at 60°C. p-Methoxyacetophenone is selectively and rapidly formed on the fresh catalyst. However, a rapid deactivation occurs which could be attributed to a large extent to the pronounced inhibiting effect that p-methoxyacetophenone has on the acetylation. In a flow reactor and at a higher temperature (90°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. Catalyst samples were recovered after various times on stream and the organic 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 extraction in methylene chloride. Due to its high polarity, this reaction product is strongly retained in the large mesopore volume of the HBEA zeolite. The minor part can only be recovered after dissolution of the zeolite in a hydrofluoric acid solution. It consists mainly of di- and triacetylated anisole entrapped in the zeolite micropores. As shown by nitrogen adsorption, these compounds cause pore blockage. The latter is responsible for part of the catalyst deactivation, the other part being 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 polyacetylated anisoles.