GB681805A - Improvements in and relating to the production of methyl acetylene - Google Patents

Abstract

Methyl acetylene and allene are obtained by subjecting a dihalogenated propane or a monohalogenated propylene, or a mixture thereof, to decomposition at a temperature of 920 DEG C. to 1050 DEG C. It is preferred to employ the chloro compounds, particularly alpha- and beta-monochloropropylene. When a dichloro propane is used as starting material it may be converted directly to methyl acetylene or it may be converted to a monochloropropylene, e.g. by treatment with alkali and the monochloropropylene, then decomposed at 920 DEG to 1050 DEG C. The halogenated compound may be mixed with a diluent gas, e.g. nitrogen, methane, or carbon dioxide or preferably with steam which is used in a molar ratio to chlorinated hydrocarbon of 8 : 1 to 20 : 1. It is preferred to use contact times of 0.01 to 0.1 second and to subject the products to rapid cooling. The reaction may be carried out in the presence of an activator selected from oxygen, chlorine or compounds capable of liberating free halogen under the reaction conditions, e.g. thionyl chloride, and the decomposition tube may contain silica chips as packing material. Allene may be recycled to the decomposition zone in which it is largely converted to methyl acetylene. In examples, a mixture containing methyl acetylene and allene is obtained by: (1) passing a mixture of alpha and beta chloropropylenes and water through a silica tube at 920 DEG C., the gas mixture being preheated to 550 DEG C. before entering the decomposition zone and the vapour contact time in the decomposition zone calculated at 20 DEG C. and atmospheric pressure being 0.05 second; (2) passing allyl chloride and steam through a silica tube at 970 DEG C., the vapour contact time being 0.07 second; (3) decomposing as in (1) a preheated mixture of 1 : 2-dichloropropane and steam at 1000 DEG C. with a vapour contact time of 0.07 second; (4) subjecting a mixture of 2 : 2-dichloropropane and steam, preheated to 800 DEG C., to decomposition at 1000 DEG C. with a vapour contact time of 0.05 second; (5) decomposing a preheated mixture of 1 : 3-dichloropropane and steam as in (4); (6) subjecting a preheated mixture of 1 : 1-dichloropropane and steam to decomposition at 950 DEG C. as in (1). The products of examples (3) to (6) also contain alpha and beta chloropropylenes. Specifications 518,325 and 573,532 are referred to. According to the first Provisional Specification the decomposition may be effected at 600 DEG to 1500 DEG C. and in the presence of metals, metal oxides, or metal salts such as metal halides as catalysts whilst the second Provisional Specification gives the decomposition temperature as 850 DEG to 1050 DEG C.