GB340587A - Improvements in the manufacture and production of styrenes and their homologues - Google Patents

Abstract

Styrene and its homologues and polymers are produced by passing one or more aromatic hydrocarbons, having at least one aliphatic side chain with at least 2 carbon atoms, in the form of vapour, which may be mixed with diluents, over a dehydrogenating catalyst at high temperature. The catalysts may be metal compounds difficulty reducible by hydrogen, such as the oxides of calcium, lithium, strontium, magnesium, beryllium, zirconium, aluminium, chromium, tungsten, molybdenum, and uranium; sulphides such as molybdenum sulphide, aluminium phosphate, chromium phosphate, calcium aluminate, magnesium chromate, calcium uranate; anthracite or deposits of similar nature occurring in the thermal destruction of gaseous hydrocarbons; Florida earth, active carbon, silica gel, pieces of clay and the like, or mixtures of these substances with each other, phosphates, and phosphoric acid. The addition of small amounts of metal compounds which are reducible under the conditions of working such as copper or iron oxides, frequently increases the activity of the catalysts. The catalysts may be employed on carriers such as active carbon, pumicestone, and silica gel. The catalysts have a long working life when they have been pretreated at elevated temperature with gaseous compounds of carbon such as ethylene, acetylene, and benzine. It is preferable to operate at temperatures between 500 DEG and 800 DEG C., and while adding an inert gas such as nitrogen, methane, and the like or preferably carbon dioxide or steam which does not attack the initial material. It is also preferable to carry out the reaction in apparatus of such material, as for example porcelain or a copper manganese alloy or an enamel-lined substance that the deposition of carbon and the setting up of the water gas equilibrium is prevented as far as possible. When working up the reaction product as by distillation, the styrenes can be obtained pure, but the styrenes may first be obtained in the form of a resinous condensation product which by thermal decomposition, furnishes styrene or its homologues. The unconverted initial material is returned to the process. As the pretreatment of the catalyst with carbon compounds may lead to cracking of the styrene hydrocarbons under treatment, the catalyst may be pretreated by another process, in which gaseous substances free from carbon are passed over it at elevated temperatures such as from 300 DEG C. to 600 DEG C. It is preferable slowly to heat the catalysts to the reaction temperature alone or in the presence of water vapour, nitrogen, hydrogen, ammonia or other gaseous substance of inert nature. With catalysts containing oxides which are capable of forming oxides of a lower degree of oxidation than that in which they are employed, such as tungsten or molybdenum oxides, reducing oxides such as ammonia or hydrogen are preferably employed for given reasons. With this second method of treating the catalyst, the temperature employed is preferably near the lower limit already given, say between 500 DEG and 620 DEG C. No undesirable condensation products are formed, and the gas formed during the reaction usually consists of hydrogen sometimes with traces of methane and ethylene. In the examples, the starting materials mentioned are ethylbenzene, isopropyl benzene, the product of the action of propylene on benzene, ethyl toluene, diethyl benzene, and diethyl toluene. The products of known constitution include styrene and methyl styrene.