United States Patent C Patented Aug
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3,336,412 United States Patent C Patented Aug. 15, 1967 1 2 3,336,412 tion reaction can be eliminated by the addition of a halogen PRODUCTION OF UNSATURATED HYDROCAR gas to the reaction mixture. In one preferred embodiment BGNS BY PYROLYSIS 0F SATURATED HY it has now been discovered that the addition of chlorine DROCARBONS to a mixture of methane and oxygen increases the yield of Richard Kenneth Lyon, Elizabeth, and William Bartok, acetylene and eliminates the need for preheating‘ the West?eld, N.J., assignors to Esso Research and Engi neering Company, a corporation of Delaware methane and oxygen reactants. While not wishing to be No Drawing. Filed June 29, 1964, Ser. No. 379,031 bound by any particular theory, it is believed that the ad_ 8 Claims. (Cl. 260-679) dition of chlorine promotes the formation of acetylene in the reaction 3H2+C2<:>2CH4 by formation of HCl This invention relates ‘to an improved process for the 10 thereby driving the reaction in accordance with familiar pyrolysis of certain saturated hydrocarbons to obtain un principles of equilibrium reaction. Furthermore, the re saturated hydrocarbons. More particularly, this invention action H2+Cl2—>2HCl is exothermic and therefore adds relates to the production of unsaturated hydrocarbons additional heat to the reaction. The utilization of chlorine by partial combustion of saturated hydrocarbons. In a pre gas with the unsaturated hydrocarbon-oxygen mixture ferred embodiment, this invention relates to the produc 15 possesses a further advantage in that the halogen gas will tion of acetylene by partial combustion of hydrocarbons not react with the unsaturated hydrocarbon as will water, such as methane. described above, since carbon-halogen compounds are not Processes for the production of acetylene by incomplete stable at the high reaction temperatures. combustion of hydrocarbons are well known in the prior In one preferred embodiment for producing unsatu art. In all these partial combustion processes the energy 20 rated hydrocarbons by the above-described method, the for the endothermic pyrolysis of the saturated hydrocar unsaturated hydrocarbon, oxygen and halogen gases are bon feed is provided by burning part of that feed with subjected to rapid intimate mixing and passed at a high oxygen in an exothermic reaction. For example, the en linear velocity to a reaction chamber wherein the partial dothermic reaction: 2CH4SC2H2+3H2 is supplied energy combustion takes place with the formation of a ?ame. The by burning part of the feed with oxygen in accordance 25 gases undergoing combustion are passed through the re with the reaction: CH4+11/zO2SCO+2H2O. In the actor at a high linear velocity so that the temperature commercial processes for carrying out the partial combus reached during combustion is only maintained for a very tion of methane to produce acetylene it has been found short period in the range of about 0.001 to 0.1 second, necessary to separately preheat the methane and oxygen preferably 0.001 to 0.1 second. It is an essential feature v reactants to about 600°—700° C. before mixing and ig 30 of such partial combustion reactions that the mixing and niting them to produce the desired acetylene product. feeding of the gaseous reactants take place rapidly in such Such a procedure is dictated by the fact that water formed a manner that the ?ame reaction does not ?ash back and in the combustion reaction will react with acetylene at cause premature combustion in the mixing zone. Further high temperatures in accordance with the reaction: more, the short reaction period is insured by providing 35 2H2O+C2H2S2CO+3H2. Thus, if su?‘icient oxygen were a rapid quench zone for the hot reacted gases existing employed to obtain the amount of heat needed for the from the reaction zone. The mixing, reacting, and quench pyrolysis, signi?cant amounts of water would be formed ing steps of this invention may be carried out by utilizing which, under the conditions of pyrolysis, would react with any of the well known prior art devices which have been employed for the partial combustion of hydrocarbons. acetylene and thereby reduce the yield of desired product. 40 The prior art partial combustion processes therefore have The temperature of the ?ame reaction will vary be employed oxygen-poor reaction feeds and preheated the tween 1000° and 2000° (3., preferably 1400“ and 1600" C. reactants in order to obtain the proper reaction tempera depending upon the nature and composition of the react ture. It is obvious that such a procedure not only sub ants. stantially increases the capital investment necessary for A wide variety of saturated hydrocarbons may be em the production of acetylene but also results in increased 45 ployed in the process of this invention to produce the de processing costs. Furthermore, due to the nature of the sired unsaturated hydrocarbons. Thus any normally above-described competing chemical reactions as well as gaseous or liquid cyclic or acyclic hydrocarbon can be thermodynamic considerations, the yields of the desired converted into C2 unsaturates, predominantly acetylene, unsaturated hydrocarbon product from prior art com by this process. It will, of course, be necessary to pre mercial processes has been severely limited and in most 50 vaporize a liquid hydrocarbon feed prior to the earlier cases has not exceeded 8%, based on the dry gas output. ‘described mixing stage. Preferred saturated hydrocarbon It is an object of this invention to provide an improved feeds are the lighter paraffins including C1 to C6 para?ins process for preparing unsaturated hydrocarbons from sat such as propane, butane and petroleum fractions in the urated hydrocarbons in which a portion of the heat neces light naphtha range. It will be understood that the feed sary for the reaction is supplied by the partial combustion 55 may constitute mixtures of the above mentioned hydro of the hydrocarbon itself. carbons and may also contain minor amounts of other or It is a further object of this invention to provide an im ganics such as unsaturated hydrocarbons and aromatics. proved process for the production of unsaturated hydro A particularly preferred saturated hydrocarbon feed is carbon by partial combustion of a saturated hydrocarbon methane. The methane feed may be derived from natural in which a portion of the heat necessary for the reaction 60 gas which ordinarily contains 95% methane and about is supplied by the partial combustion of the hydrocarbon - 5% ethane and heavier hydrocarbons. In a preferred em itself and the necessity for preheating the reactants is bodiment, the hydrocarbons heavier than methane are re eliminated. moved from the natural gas before mixing the hydrocar Yet a further object of this invention is to provide an bon with the other reactants necessary in the process. The improved process for the production of acetylene, by par 65 halogen promoters which may be employed in this process tial combustion of methane, in higher yields than have are selected from the group consisting of chlorine and heretofore been obtainable. bromine with chlorine being the preferred reactant. It has now been discovered that the yield of unsaturated The molar ratio of the reactants is an important fea hydrocarbon derivable from the partial combustion of ture of the invention. The molar ratio of oxygen to satu— saturated hydrocarbon can be drastically increased and 70 rated hydrocarbon feed will be in the range of 0.05 to that the need for preheating the reactants in the combus 0.6 and the molar ratio of halogen to saturated hydro 3,336,412 3 4 carbon will be in the range of 0.1 to 2.0. In a preferred As can be seen in the table, acetylene concentrations embodiment the halogen/hydrocarbon and oxygen/hy as high as 17-18 mole percent were achieved with rich drocarbon molar ratios are mutually adjusted to provide mixtures of methane and chlorine. the optimum total amount of oxidant. Thus, when the The carbon mass balance was calculated by determin molar ratio of oxygen to hydrocarbon is low, for exam ing the ratio of the C0, C02, CZHZ and CH4 products ple 0.05 to 0.3, the halogen/hydrocarbon range will be to the CH4 input feed. This data indicates that while maintained between 1.5 and 2.0 and when employing a some of the feed was degraded to carbon, the amounts high ratio of oxygen near the upper limit speci?ed above are clearly not large. The mass balance of oxygen was the halogen/hydrocarbon ratio will be maintained be calculated by the ratio of oxygen in the CO2 and CO tween 0.1 to 0.5. Thus, in one typical embodiment, the 10 products to the oxygen input. The calculated ratios indi feed mixture to the reaction will contain 35 to 40% cate that very little water is formed in the product since methane, 5 to 25% oxygen and 40 to 60% chlorine. almost all of the oxygen is consumed to form CO and The invention will be further understood by reference CO2. to the following illustrative examples. Example 2 Example 1 15 Experiments similar to those described in Example 1 A series of partial combustion reactions were carried were carried out with the exception that no chlorine was out in which the ratio of methane, oxygen and chlorine employed in the reaction mixture. Under the same ex in the feed composition was varied in each run. Before perimental conditions the only mixtures which would each experiment, the individual feed components were burn were those for which O2/CH4 was so high that no 20 measured by pressure into a 3-liter mixer flask. Thorough CZHZ was formed.