Low-pressure one-step synthesis of methyl isobutyl ketone from acetone and hydrogen over metal modified solid base catalysts

One-step synthesis of methyl isobutyl ketone (MIBK) from acetone and hydrogen over metal modified solid base catalysts has been studied at atmospheric pressure and 175-250 degreesC by using a fixed-bed, integral-flow reactor. Two types of catalysts have been utilized: (1) zeolites modified with palladium (Pd/Kbeta, Pd/KZSM-5); and (2) metal oxides modified with sodium and palladium (Pd/Na/MgO, Pd/Na/NaOH/ gamma-Al2O3). The catalyst properties were characterized by the methods of atomic absorption, temperature-programmed desorption and gas adsorption. Sodium vapor deposition on magnesia, followed by impregnation with tetraamine palladium (11) chloride apparently enhances the catalyst basicity as compared with that of magnesia supported palladium. For catalysts with different supports, the base amount decreases in the order of Pd/Na/MgO > Pd/Na/NaOH/gamma-Al2O3 > Pd/KZSM-5 > Pd/Kbeta, in accordance with the catalytic activities. As the amount of sodium or palladium in Pd/Na/MgO increases, the catalyst base amount, acetone conversion and MIBK selectivity are also enhanced to a maximum and then decline. Better catalytic results were attained at a higher pretreating temperature of hydrogen on the catalyst. The optimum conditions for this reaction are 0.5%Pd/0.47%Na/MgO pretreated with hydrogen at 400 degreesC, reaction temperature 200 degreesC, acetone/hydrogen mol ratio 1, and W/F-a 6g.h/mol. Under these conditions, the acetone conversion and MIBK yield are 47.3% and 30.7%, respectively, at 480 min time-on-stream. The reaction network and reaction mechanism for the formation of MIBK are proposed and discussed.