Many of the commercial processes for isomerization of paraffinic hydrocarbons, e.g., butane, use either of two types of anhydrous liquid catalysts containing aluminum chloride with hydrogen chloride present as catalyst promoter. The type which consists of an aluminum chloride-hydrocarbon complex has been found to be similar to aqueous hydrochloric acid in its corrosiveness to many alloys. For this catalyst complex satisfactory inhibition of corrosion in one process has been obtained by addition of ca. 0.4 percent antimony trichloride. Factors controlling corrosion by this catalyst complex are discussed and mechanism for the corrosive action of this catalyst and for its inhibition are presented.
The other liquid catalyst commonly used, a liquid melt of aluminum chloride and antimony trichloride, while appreciably less corrosive than the hydrocarbon complex type, is sufficiently corrosive to carbon steel under some plant conditions to require use of resistant alloys such as nickel. Plant corrosion experience with processes employing this catalyst is discussed. Data relating to factors influencing the corrosiveness of this catalyst are presented, and a mechanism for the corrosion reaction is proposed.
