METHOD FOR THE OXYCHLORINATION OF ETHYLENE

Abstract: 1,2-Dichloroethane is produced by oxychlorination of ethylene wth hydrogen chloride and oxygen-enriched air (about 28-60 volume % oxygen). Ethylene is used in about 110-120%, and oxygen in about 105-115% of stoichiometric, respectively, based on hydrogen chloride.

Description: METHOD FOR THE OXYCHLORINATION OF ETHYLENE Background and Prior Art The invention concerns a method for the oxychlorination of ethylene in a fixed bed system which consists of at least two serially connected reactors, in the pres2nce of a supported cupric chloride cata- lyst. Oxychlorination reactions in the presence of Deacon type cate lysts are appropriately carried out in a temperature range of approximate- ly 200-350 C. stile a temperature of approximately 200 C should be maintained in order to obtain adequate conversion rates, tepperatures of approximately 350 C should not be exceeded since catalyst damage, selec- tivity losses or even explosive operating conditions can occur. Because of the strongly exothermic character of the oxychlorination reaction and the associated tendency for the formation of highly overheated zones (hot spots) in the catalyst bed, considerable problems arise in operating witfr in the cited upper limit of the temperature range. Therefore, a method has been proposed in Federal Republic of Germany Offenlegungsschrift 14 93 213 in which the oxychlorination is carried out in a system of several serially connected reactors and the total quantity of oxygen required for oxychlorination is divided up the corresponding nunber of reactors. Dilution of the Deacon catalyst by the addition of an inert material to avoid overheating in the catalyst bed was also proposed. In accordance with U.S. Patent 3,892,816, oxychlorination is carried out in a multireactor system in the presence of a large ethylene excess. Pure oxygen must be used in this operation; its addition, togeth- er with addition of hydrogen chloride, is distributed over the correspond- ing nunber of reactors. Excess, unreacted ethylene is recycled. However, such a recycling method is extrenely costly and subject to disturbance. Also, the cost efficiency of the method can be questioned since the total oxygen requirement must be used in the form of relatively expensive pure oxygen. The methods in accordance with the prior art have in common the control of the strongly exothermic oxychlorination reaction by dilution either by diluting the reaction mixture with large quantities of inert gases (for example, with nitrogen fran the air) or by using a large excess of one of the reaction components (for example, ethylene) or by adding inert material to the catalyst. Reaction control is therefore carried out at the expense of the space-time performance of a given installation. This represents a conflict of goals, that is, the attainment of as high a production rate as possible in a given installation without having to accept disadvantages such as reductions in selectivity, etc. It is solved by the known methods in a manner Which is not very econanical. Sumnary of the Invention According to this invention, ethylene is converted to 1,2-di chioroethane by oxychlorination with hydrogen chloride and an oxygen containing gas in a multiple reactor fixed bed catalyst bed system containing a cupric chloride catalyst, in which the total amounts of methylene and oxygen, introduced into the process, are respectively fran about 110% to about 120% and fran about 105% to about 115% of stoichianetric, based on hydrogen chloride, and the oxygen-ccntaining gas is air which has been enriched to contain from about 28 to about 60 volune % oxygen. Detailed Description of the Invention surprisingly, it has now been found that in processes of this type it is possible to keep down the combustion rate with an increased oxygen fraction based on the total quantity of reactants. Despite the method-related reduction in contact times, the catalyst-specific hydrogen chloride conversion is increased by use of the method according to the invention. Furthermcre, it was unexpected that, despits a low inert gas fraction and an increased production rate, no impermissibly high hot-spot temperatures appear in the catalyst bed. The oxygen content of the oxygen-enriched air is about 28-60, preferably about 30 to 35 volune %. The oxychlorination is carried out in a fixed bed reactor system consisting of at least two serially connected reactors. Twt or threeand particularly three- reactor installations are preferred. Multitubular reactors of approximately the sane size are used with an appropriate vertical arrangement for flow fran top to bottan. The tubular reactors are equipped with cooling jackets. Water under increased pressure is used in particular as the cooling medium. The tubes contain a supported catalyst with cupric chloride as the active component and alumina, silica gel, aliminosilicate, etc. as supports. The support material may be present in the form of spheres, cones, cubes, hollow strands, etc. The catalyst preferably has an activity profile within each reactor which increases in the direction of flow and which may be prepared by increasing the quantity of active substance, based on the total weight of catalyst, in the direction of flow. For a given active substance concentration at the reactor entrance of 5 to 7 wt. %, the active substance concentration increases continuously or discontinuously up to the reactor exit by up to a factor of 2.5 to 4. In addition to the cupric chloride active substance, the catalyst can also contain promoters such as the chlorides of potassium, magne siam, calcium and silver. The e concentration of promoters is an essentially uniform 1.5 to 3.5 wt. % based on the total weight of the catalyst. The e ethylene, oxygene and hydrogen chloride reaction components are used in quantities such that, based on the stoichianetry of the oxychlorination reaction, there is a total ethylene excess of 10 to 20 mole % and an oxygen excess of 5 to 15 mole %, based in each case on the total quantity of hydrogen chloride used. Approximately equal parts of the oxygen,enriched air (28 to 60 vol. % oxygen) are conducted to the individual reactors. On the other hand, the total cuantity of ethylene is added in the first of the serially connected reactors. In twctreactor installations, the total quantity of hydrogen chloride is also added in the first reaction; the hydrogen chloride is divided into approximately equal parts among the first to serially connected reactors for installations with three or more reactors. The e reaction components in two- and three-reactor systems are preferably supplied according to the followings scheme. The percentage refers in each case to the total auantities of the individual reaction components. Two-Reactor System Reactor 1 . Reactor 2 ethylene total volume hydrogen chloride total volume oxygen 40-45% of total volume 55-60% of total volume Three-Reactor System Reactor 1 Reactor 2 Reactor 3 ethylene total volume hydrogen chloride 70-80% of total 20-30% oxygen 35-45% of total 38-40% 20-27% Small quantities of steam can also be added to the reaction mixtures before the first reactor. This supply takes place, for examle, together with the oxygen-enriched air in quantities of 0.05 to 0.20 mole % steam based on the total quantity of hydrogen chloride. The e reaction components may be supplied individually or in a mixture according to the supply scheme described above after pre-heating to temperatures of 100 to 2000C. The reaction temperatures in the reactor lie at 200 to 350 C and preferably at 200 to 3000C. The e system pressure in the reactors is 3 to 8 bar abs. The reaction mixture exiting the reaction system is worked up in a known manner by cooling, condensing and separation into organic and inorganic phases. According to the method of the invention, it is possible without high investment costs to increase the production capacity of an existing installation up to 50% in comparison to the installation operated with air fran the anbient atmosphere. For custanary commercially used multitubular reactors (with inside tube diameters of 25-30 mm), an HCl throughout of 2.2-2.4 Nm3 per tube per hour is attained in conventional methods; however, an HCl throughput of 3.5-3.7 Nm3 per tube per hour is attained according to the method of the invention. Other advantages occur during the work-up of the reaction mixture leaving the reactor installations, particularly in the condensation stage, because of the snall inert fraction. MAPLE A reaction installation was used which consisted of three serially connected multitubular reactors of the sane size. Each reactor contained 1570 nickel tubes with an inside diameter of 27.5 nrn. The nickel tubes contained catalyst with an activity profile which increased in the direction of flow. Aluminum oxide was used as the support material; it was present in the form of 3-5 mm pellets. An activity profile increasing in the direction of flow was realized by a concentration of cupric chloride of 6.5 wt. % in the entrance third of each reactor; 11 wt. % in the middle third and 19 wt. % in the final third. In addition to the cupric chloride active component, the catalyst also uniformly contained 2 wt. % potassium chloride. The catalyst volume was 10.2 m3. The nickel tubes were surrounded with an external jacket in which water was used as the cooling medium to remake the released reaction heat. The water was under a pressure of 19 bar abs. in the first reactor, 21 bar abs. in the second reactor and 24 bar abs. in the third reactor. Air which had been enriched to an oxygen content of 30 vol. % by the addition of pure oxygen was used as the oxygen source. A mixture of 175 Kmol/h hydrogen chloride, 144 knolXh ethylene and 84 kmol/h air enriched to 30 vol. % oxygen was fed to the first reactor at regulated pressures of 8 bar abs. The oxygen-enriched air was injected with 28 knol/h steam and this mixture was pre-heated to 180 C before mixing with the other reaction components. The e temperature of the reaction mixture before entering the reactor was 130 C. Before entering the second reactor, the reaction mixture exitinq the first reactor was mixed with a mixture of 75 kmol/h hydrogen chloride and 90 hmol/h air enriched to 30 vol. % oxygen (pre-heated to a temperature of 180 C). Fially, another 51 knol/h air enriched to 30 vol. % oxygen was supplied to the reaction mixture between the second and third reactors. The e system pressure before the first reactor was 6.5 bar abs. the pressure drop across the reactors was 0.28 bar in the first reactor, 0.38 bar in the second reactor and 0.41 bar in the third reactor. The hot-spot temperatures were 282 'C in the first reactor, 275*C in the second reactor and 260 C in the third reactor. The e reaction mixture exited the third reactor at a temperature of 220 'C and was cooled and condensed. The e liquid condensate was separated into organic and aqueous phases in a downstream decanter. The e organic phase had the following composition: ethyl chloride 0.29 wt. % 1,1-dichloroethane 0.01 wt. % chloroform 0.04 wt. % carbon tetrachloride 0.09 wt. % dichloroethylene 0.01 wt. % 1,1, 1-trichloroethane 0.40 wt. % chloral 0.26 wt. % 1,2-dichloroethane 98.75 wt. % other 0.10 wt. % An analysis of the condensed aqueous phase produced the following: hydrogen chloride 1.94 wt. % chloral hydrate 0.45 wt. % 1, 2-dichloroethane 0.83 wt. % A hydrogen chloride conversion of 99.4@ is this calculated from the hydrogen chloride content. The analysis of the uncondensable waste gas flow proluced the following (without entrained stean, ethyl chloride and 1,2-dichloroethane): nitrogen 87.10 wt. 8 oxygen 2.10 wt. % ethylene 8.07 wt. % carbcn monoxide 1.53 vol. % carbon dioxide 1.30 vol. % The e waste gas quantity was 4050 Nm3/h. A specific combustion ratio of 9.4 Nm3 CO+CO2/1000 kg of pro duced raw 1 ,2-dichloroethane resulted from the carbon monoxide and carbon dioxide content. The production rate is 12,200 kg 1,2-dichloroethane per hour. The space-time performance was 1196 kg 1,2-dichloroethane per m3 catalyst x hour based cn all three reactors. Comparaison Example An operation according tD the Example was repeated with the modification that, instead of air enriched to 30 vol. % oxygen, air from the ambient atmosphere was used (corresponding to an oxygen content of 20.9 vol. %). It was possible to supply the reactor installation with only 98 kmol/h ethylene, 179 knol/h hydrogen chloride and 88 kmol/h air together with 19 knol/h steam to the first reactor: 51 kmol/h hydrogen chloride and 98 kmol/h air to the second reactor and 45 kmol/l air to the third reactor. Because of the large pressure losses in the reactors, a system pressure of 6.8 bar abs. had to be established in the first reactor. A further throughout increase was not possible because of the small pressure difference with respect to the entry flows. The hydrogen chloride conversion was 98.9%. The specific combustion rate was 9.3 Nm3 CO + CO2/1000 kg of produced raw dichloroethane. The production rate was 8260 kg 1,2-dichloroethane per hour. The space-time performance was 810 bg 1,2-di- chloroethane per m3 catalyst x hour based on all three reactors. The waste gas quantity was 4310 Nn3/h, corresponding to a spe- cific waste gas quntity of 521.8 Nm3 per 1000kg of produced dichloroethane as canpared with only 332 Nm3 in the operation according to the in,enticn.

Claims: WHAT IS CLAIMED IS: 1. A process for the production of 1,2-dichloroethane by cxychlorinaticn of ethylene with hydrogen chloride and an oxygencontaining gas in a multiple-reactor fixed bed catalyst system in which the total amounts of ethylene and oxygen introduced into the process are respectively fran about 110% to about 120% and fran about 105% to about 115% of stoichiometric, with respect to hydrogen chloride and the oxygen containing gas is air which has been enriched to contain from about 28 to about 60 volune % oxygen. 2. A process according to Claim 1 in Which the catalyst con- prises cupric chloride. 3. A process according to Claim 1 in which the reactors are multitubular reactors in which the tubes are packed with the catalyst. 4. A process according to Claim 3 in which the strength of the catalyst in each reactor increases fran the reactor inlet to the outlet. 5. A process according to Claim 1 in which the air is enriched to contain fran about 30 to about 35 volune % oxygen.

Inventors: DUMMER, GERHARD, HASELWARTER, KLAUS, HIRSCHMANN, PETER, SCHMIDHAMMER, LUDWIG, DR., STRASSER, RUDOLF, DR.
Applicants: WACKER-CHEMIE GMBH
Application year: 1984
Main classification: C07C19
IPC codes: B01J27, C07B61, C07C19, C07C17, C07C67