GB827438A - Improvements in the cracking of hydrocarbons - Google Patents

Abstract

<PICT:0827438/IV (b)/1> In the production of acetylene and/or olefines by cracking liquid hydrocarbons in a flame burning below the surface of the liquid hydrocarbons while continuously supplying such hydrocarbons, continuously or periodically part of the hydrocarbons is removed from the reaction vessel together with the carbon formed during the reaction. Preferably the withdrawal of the suspension of carbon in hydrocarbon and the introduction of fresh hydrocarbon are correlated so that the hydrocarbon remains capable of forming drops under the reaction conditions. Suitable liquid hydrocarbons are those boiling within the range 50-450 DEG C. or mixtures such as petroleum or tar distillates. Flame temperatures of 1,000-2,800 DEG C. are used while the liquid is maintained at 150-300 DEG C. and pressures of 1-100 atmospheres are used. When using highboiling hydrocarbons, more readily combustible fuels can be added to the flame such as hydrogen, methane, coke oven gas or low-boiling liquid hydrocarbons. The oxygen supply depends on the desired end product; when cracking petroleums to ethylene 0.55 cubic metre of oxygen may be used per kilogram of petroleum whereas 0.65 cubic metre is necessary to produce acetylene. Ignition of the flame may be caused by an electric spark, by heating the oxygen to a temperature to cause spontaneous combustion, e.g. 600 DEG C., or by adding to the hydrocarbon and/or oxygen reactants which react with other compounds present with flame formation, e.g. fluorine and manganese heptoxide, zinc diethyl or aluminium triethyl For safety the oxygen valve may be coupled with the inverse function of an inert gas (e.g. nitrogen) valve; the two valves may be automatically controlled by a photo-electric cell depending on the flame and/or the oxygen content in the space above the hydrocarbon measured continuously, p e.g. by measuring the paramagnetism, so that if the flame is extinguished or the oxygen content above the liquid rises above 2.5% by volume the oxygen valve is closed and the inert gas valve opened and the apparatus thereby purged of explosive mixtures. In a preferred embodiment the reactor 1 contains a burner 2 through which nitrogen from pipe 3 is blown while the reactor is filled by pipe 31. Oxygen is then introduced by pipe 4 and ignited. From the sump of the reactor oil is drawn by pump 6 with or without separation of carbon in filter 5 and admixed with oxygen. The amount of carbon-containing oil so mixed may be 3-50 times the amount which could be completely burnt by the oxygen introduced. At the same time oil is withdrawn by pipe 9 through pump 10, cooled if desired in cooler 11 and reintroduced to the reactor by pipe 14 which surrounds the burner. The whole burner may therefore comprise three tubes arranged one within another, the innermost being fed with oil from pump 6, the middle one with oxygen and the outermost with oil from pipe 14. The flame will therefore be surrounded by cool oil. Vaporous and gaseous products leave by pipe 15, is mixed with a washing oil from pipe 25 and centrifuged in separator 17 from which washing oil containing carbon black is returned to the reactor by pipe 18. The products pass to condenser 20 and gaseous material then passes through coke filter 27 before passing to a recovery plant by pipe 28. Condensed material from pipes 21 and 29 pass to separator 22 from which water is withdrawn by pipe 24 and washing oil by pipe 25. Fresh hydrocarbon is introduced by pipe 31.