The data presented in the previous paper have shown that titanium had excellent corrosion resistance under the experimental conditions of the acetic acid synthesis from methanol and carbon monoxide. The object of this paper is to find out the materials of construction for purification of the crude acetic acid.
As test solution, 50-70wt% acetic acid solutions, acetic acid solutions containing a small amount of catalysts (cobalt acetate and potassium iodide) and aqueous solution of the catalysts were used under several gas atmospheres at temperatures below the boiling points. 31 kinds of metals and alloys including titanium were tested in these solutions.
The catalysts in acetic acid solutions accelerated corrosion rate in the greater parts of the samples (except titanium and high-silicon iron) and induced pitting corrosion in austenitic stainless steels. In catalyst-free acetic acid solutions, titanium, high-silicon iron, monel metal, high nickel stainless steels and yellow brass showed satisfactory corrosion resistance. While yellow brass showed layer-type dezincification, the rate of which was considerably slow as compared with the previous data.

View full abstract

Mercaptan-film on the surface of either copper catalyst or test coupons can be made by dipping it in mercaptan solution. Whatever sort of the solution it may be, the temperature of solution, at which we immersed the metal in it, is one of most important factors to get more resistible film to hydrogenation, or corrosion reactions.
As the temperature increased to 100°C, stronger film which can interfere hydrogenation or corrosion is obtainable. Over 100°C, contrarily, the persistency of the film becomes poorer. The persistency of the film, prepared either in a non-polar solvent as xylene or n-cetane, or in a polar solvent as butanol, was examined in 5% HCl aqueous solution by using filmed test coupons or by using filmed catalyst in hydrogenation of methyl oleate. The best films were those prepared at 100°C in non-polar solvents, as they showed better inhibition in the reactions. And the film prepared over 100°C showed lower inhibition. The persistency of the film to hydrogenation was not so good. And moreover, xylene which was used as a solvent in mercaptan-filming treatment over 100°C was distilled with water which cannot be detected before the metal-filming treatment. But the film prepared over 100°C in butanol can give better persistency than those films prepared at lower temperatures.
From those results, we suppose that the adsorbed water on metal surface acts the leading part as follow: Mercaptan film can only be formed when mercaptan replace the water which xylene removes from the metal surface. But over 100°C, water is mostly removed by xylene over the extent as mercaptan can follow to fill the place where the water has been desorbed. Butanol can act in similar manner to water such as adsorbing the metal instead of water and being replaced by mercaptan.
Catalyst becomes less active as it loses more adsorbed water.

View full abstract