Vapor phase carbonylation of methyl acetate to acetic anhydride over Ni-Sn-Cr/AC catalyst

Ni-Sn-Cr/AC catalyst was prepared through impregnation with Ni(NO₃)₂·6H₂O, SnCl₄·5H₂O and Cr(NO₃)₃·9H₂O as precursors and activated carbon as support; it was used in vapor phase carbonylation of methyl acetate to proroduce acetic anhydride in a continuous flow type fixed-bed reactor. The effects of each metal loading on the catalytic activity as well as the influence of reaction temperature, pressure, and time on the reaction behavior were investigated. The results showed that the Ni9%-Sn12%-Cr6%/AC catalyst calcined at 600℃ for 4h exhibits excellent performance in the carbonylation; over it under the optimized reaction conditions of 5.5MPa and 205℃, the conversion of methyl acetate and the selectivity to acetic anhydride reach 38.8% and 81.1%, respectively. The fresh catalyst and spent catalysts after reaction for different times on stream were characterized by means of X-ray diffraction and element analysis; the results suggested that Ni⁰ is main active sites. During the test, the activity of the catalyst is decreased dramatically with the time on stream, which could be ascribed to the loss of active component Ni, carbonaceous deposition and destruction of activated carbon framework.