Studies on catalytic of technical importance carbon monoxide at high pressures

Abstract

A comprehensive study has been made on the pressure-vapour phase synthesis of (i) Acetic acid by the reaction of methyl alcohol and carbon monoxide, and (ii) Propionic acid by the reaction of ethyl alcohol and carbon monoxide, using the static method and volatile types of nickel, cobalt, and iron catalysts. These studies indicate that the halides of the above-mentioned metals were superior to the metals themselves, and among the halides, the iodides were superior to the bromides and chlorides as catalysts for the synthesis. Further, mica gel was found to be superior to either kieselguhr, pumice, or kaolin as the catalyst support. Nickel iodide deposited on a mica gel exhibited the maximum catalytic activity for the synthesis. Products of the reaction included acetic acid, methyl acetate, carbon monoxide, carbon dioxide, hydrogen, and methane, together with unreacted alcohol and carbon monoxide. No ether or oily products were detected. The optimum conditions for the synthesis of acetic acid were:

Catalyst containing metal iodide deposited on silica gel (composition: Metal:Silica = 50:50) Temperature: 180°C Pressure: about 460 atm Methyl alcohol concentration: 95% (5% water)

Under these conditions, using nickel iodide-silica gel catalyst, a total conversion of 89.2% of methanol was obtained in 2 hours, corresponding to:

Acetic acid: 45.9% Methyl acetate: 3.7% Gaseous decomposition products: 9.6%

Decomposition studies of (i) carbon monoxide, (ii) methyl alcohol, and (iii) acetic acid individually in the presence of the nickel iodide-silica gel catalyst explained the course of reactions leading to the formation of various gaseous products obtained during the synthesis. Studies on the synthesis of propionic acid by the reaction of ethyl alcohol and carbon monoxide gave results very similar to those obtained during the reaction of methyl alcohol and carbon monoxide. Products included propionic acid, ethyl propionate, carbon dioxide, and a mixture of gaseous saturated hydrocarbons and hydrogen, along with unreacted carbon monoxide and ethyl alcohol. Neither ethylene nor liquid hydrocarbons were obtained. The formation of acid was, however, less while water and gaseous decomposition products were more than those observed in the case of acetic acid synthesis. It was found that the iodides were superior to the metals or their bromides or chlorides, and that nickel iodide was superior to cobalt iodide or ferrous iodide as the catalyst for the synthesis. The optimum conditions for the best yields of propionic acid were:

Catalyst containing metal iodide deposited on silica gel (composition: Metal:Silica = 50:50) Temperature: 230°C Pressure: about 520 atm Ethyl alcohol concentration: 95% (5% water)

Under these conditions, using the nickel iodide-silica gel catalyst, a total conversion of 69.6% of ethyl alcohol was obtained in 2 hours, of which:

Free propionic acid: 37.5% Ethyl propionate: 11.4% Gaseous decomposition products: 20.9%

Decomposition studies of (i) ethyl alcohol and (ii) propionic acid in the presence of the nickel iodide-silica gel catalyst indicated the course of the reactions leading to the formation of the various gaseous products obtained during the above syntheses. In all the above experiments, the behaviour of the catalysts was rather peculiar. When the products of the reaction were released from the bomb at the high temperature of the reaction, the reduced metal catalysts and the chloride catalysts retained their maximum activity (though their activity for the synthesis was very low) indefinitely. However, the bromide and iodide catalysts exhibited their maximum activity only in the first experiment, and their activity decreased considerably in the second and subsequent experiments. But the “spent” bromide and iodide catalysts could be reactivated completely by the addition of a few drops of cold water on the surface of the spent catalyst. Further, in the case of the above catalysts, the problem of catalyst deactivation did not arise at all if the reaction products were released from the bomb at a sufficiently low temperature (60-80°C), under which conditions they appeared to retain their maximum activity indefinitely. Certain physico-chemical studies on the nickel iodide-silica gel catalyst were also made, and these included: (i) Carbon monoxide adsorption (ii) Magnetic susceptibility measurements (iii) Differential thermal analysis The above studies indicated both the thermal sensitivity of the catalyst and the significance of the presence of traces of water in the catalyst.