Studies On Friedel-Crafts Reation Of Anisole Catalyzed By Zeolites

Friedel-Crafts reaction is one of the most important methods for the production of aromatic compounds. Friedel-Crafts reaction is carried out commercially using Lewis acids, such as AlCl3, or Br?nsted acids, typically H2SO4 or HF. However, these traditional catalysts have limitations such as environmental pollution hazards arising from the disposal of potential toxic wastes, reactor corrosion and difficulty in handling. Furthermore, the catalyst amount to be employed is more than the stoichiometric quantity required. In recent years, zeolite is being more and more regarded as an environmentally friendly catalyst instead of traditional catalysts for Friedel-Crafts reaction.p-Methoxyacetophenone was synthesized by Friedel-Crafts acylation of anisole and acetic anhydride over Cr-doped Hβzeolite in this paper. The conversion of acetic anhydride and selectivity to p-methoxyacetophenone are both over 99.0% under the optimized reaction conditions. This is attributed to the increase of weak and moderately-strong acid sites, caused by the Cr addition. The formation of carbonaceous materials and their coating of the acid sites are believed to be the reasons for the deactivation of the reused Cr-doped Hβzeolite, as indicated by BET, SEM, XPS and NH3-TPD measurement results. The catalyst activity can be recovered effectively by a subsequent calcination. Meanwhile, the effect of phosphoric acid modiffition on catalytic performance of Hβzeolite for acylation of anisole is presented. Effect of phosphoric acid modification was studied based on XRD and NH3-TPD characterization. The influence of the reaction temperature, the catalyst amount and the reaction time on the acetic anhydride conversion were investigated and optimized. The conversion of acetic anhydride and the selectivity to p-methoxyacetophenone are both higher than 99.0% in four runs catalyzed by the recycled catalysts under the optimum reaction conditions, while the reaction temperature is 120℃, the catalyst amount is 2.0 g and the reaction time is 2 h.On the other hand, oxalic acid modified Hβ(OA-Hβ) zeolite is found to have better catalytic performance than Hβzeolite in the Friedel-Crafts hydroxyalkylation of anisole with chloral. This is attributed to the increase of weak and moderately-strong acid sites, caused by oxalic acid modification. Furthermore, it is believed that the carbonaceous deposits on the acid sites and the blockage of the pores, together with poisoning by chlorinated materials, are responsible for the deactivation of OA-Hβzeolite, as indicated by XPS, XRD, NH3-TPD, BET, SEM, Py-IR and TG measurement results. Moreover, partial regeneration of OA-Hβzeolite can be achieved via subsequent calcination.