USE OF GRAPHITE PARTICLES AS DILUENT IN A FIXED BED EXOTHERMIC REACTION AND PROCESS FOR THE CATALYTIC OXYCHLORINATION OF ETHYLENE

Abstract: Disclosed is a catalyst diluent which is made up of a graphite in a columnar shape having a diameter of between 3 and 6 mm and a height of between 3 and 6 mm. The cayalyst diluent produces the desired product in a high yield while preventing local overheating portion in a catalyst bed.

Description: A CATALYST DILUENT BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel diluent suitable for a solid catalyst in use for a fixed bed reactor. More specifically, it relates to an improved catalyst diluent which produces the desired product in a high yield while preventing overheating portion from taking place locally in a catalyst bed in a reaction accompanying huge heat generation. 2. Description of the Prior Art In practicing a reaction such as an oxychlorination reaction of ethylene, accompanying h;uge heat generation, one of the problems to be given care to is control of the reaction temperature. Stated generally, the thermal conductivity of a catalyst per se is low and thus inviting local formation of overheating portion in a catalyst bed. The local formatianof overheating portion inevitably brings about a danger such as runaway of reaction, explosion and the like, and even when such a danger is prevented, it increases undesired side reactionssuchasidecomposition to thereby lower selectivity of the desired product. Still worse, the formation of local overheating portion promotes disadvantageously corrosion of the reactor as well as reduction in catalytic performance. In order to eliminate the foregoing defects in effecting exothermic reactions, there is proposed a process for diluting a catalyst with inert substance particles. As the inert substance particles used for this purpose, silica, alumina, glass beads, graphite, silicon carbide and the like are suggested. Notwithstanding, when silica, alumina and glass beads are used, the mixing ratio to the catalyst has to be increased to prevent the generation of local overheating portion since the thermal conductivity of these substances is not so high as compared with that of activated alumina, silica alumina and the like widely used as a catalyst and a carrier. As a result, productivity per unit volume of a reactor is forced to be reduced. Moreover, those normally possess approximately twice the apparent specific gravity of the catalyst particles and hence a heterogeneous mixture tends to result when a catalyst is mingled with those diluents. As far as silicon carbide and graphite are concerned, it is pointed out that they cause chemical reaction and degradation in catalytic activity, while exhibiting superior thermal conductivity (Japanese Patent Examined Publication No. 7948/1966). The present inventors have carried out an oxychlorination reaction of ethylene using those diluents commercially available and ascertained that ethyl chloride was prepared in a grater amount than the case where &alpha;-alumina was employed as a diluent, and that no difference was observed, as compared with a-alumina, in an effect of controlling reaction temperature. Moreover, the diluents used heretofore. have, as a whole, neither substantially the same size nor the same shape, which also causes a heterogeneous mixture. Another process is proposed to solve the foregoing drawbacks in which the reaction temperature and local overheating is controlled y a combination of several kinds of catalysts having different catalytic activities, without using a diluent . The process, however is also disadvantageous in that the thermal conductivity of the catalyst particles is so low that it is rather difficult to control overheating portion as compared with the case where a diluent is used. A series of studies have been made by the present inventors as to a catalyst diluent which not only eliminates the foregoing drawbacks of those known diluents including formation of local overheating portion and-a decrease in selectivity as well as catalytic . performance, but is capable of enhancing the mixing ratio of a catalyst to a diluent, and the inventors have discovered that only graphite particles in a columnar shape having the specified dimensions achieve these objents. SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide à catalyst diluent generating no formation of local overheating portion in the catalytic fixed bed. It is another object of the present invention to provide a catalytic diluent which is capable of increasing the mixing ratio of a catalyst to the diluent and providing a uniform mixture with the catalyst. It is further object of the present invention to provide a catalyst diluent exhibiting a superior selectivity and preventing degradation in catalytic performance. These and other objects of the present invention together with the advantages thereof will become apparent to those skilled in the art from the detailed disclosure of the present invention as set forth hereinbelow. The present invention encompasses a catalyst diluent suitable for a fixed bed exothermic reaction which is made up of a graphite in a columnar shape having a diameter of a circular portion of between 3 and 6 mm and a height of tetween 3 and 6 mm, or having dimensions within the foregoing ranges in a substantially predominant quantity. DETAILED DESCRIPTION OF THE INVENTION The diluent of the present invention may most preferably be in a columnar shape having a diameter of a circular portion of between 4 to 5.5 mm and a height of between 4 to 5.5 mm, or having dimensions within the foregoing ranges in a substantially predominant quantity. In cases where the diameter is more than 6 mm, the thermal conductivity, when mixed with catalyst particles, becomes inferior and uniform and intimate mixing with the catalyst particles is not feasibly provided. Inversely, in cases where the outer diameter is less than 3 mm, there are -brought about problems such as increased pressure loss exerted on the effluent and increased cost in manufacture. The diluent of the present invention is not necessarily required to possess a complete circle or a circle close thereto as a circular portion of a columnar shape, an oval shape is also within the present invention which provides a satisfactory result. Although it has been known to be able to employ graphite particles as a catalyst diluent, the graphite particles of an irregular shape such as a broken shape. or of a great porosity having an apparent specific gravity of less than 1.5 have been used, and thus superior-- - thermal conductivity a graphite per se possesses has not been made the most of. In addition, they exhibit undesired reactivity including an increase in side reactions and hence they are rarely used today. According to experimental results made by the present inventors, they only showed almost the same temperature controlling effect as the other diluents such as a-alumina and even spherical graphite particles also demonstrated similar results. Inversely, the graphite particles having a specified shape of the present invention have been found to produce an outstanding effect of controlling temperature in a catalytic bed as a diluent, thus the present invention being completed. Another prominent advantage of the diluent of the present invention is to increase the mixing ratio of a catalyst to the quantity of the diluent, so that degradation in catalytic activity is not only reduced relatively, but productivity per unit volume of a reactor is raised. A further advantage of the diluent of the present invention is.to prevent the occurrence of local overheating portion owing to the irregularity of mixing, because it possesses an apparent specific gravity close to that of catalyst particles commonly employed to thereby facilitate uniform and intimate mixing. On the other hand, a-alumina, fused silica and silicon carbide possess a fairly large apparent specific gravity as compared with a catalyst supported on activated alumina as a carrier and, i onsequence, uniform and intimate mixing with a catalyst is not so easy. The heterogeneous mixing also leads to a disadvantage that local ovrbeating portion is likely to take place. The material of the diluent of the present invention is a graphite, which is generally produced by mixing tar and pitch with petroleum coke, pitch coke, carbon black and the. like, molding the mixture, heating it at fist at a temperature between 1,000 and 1,300 C and thereafter sintering at a temperature between 2,000 and 3,00OQC A columnar shaped graphite of the present invention may be obtained by molding the mixture by a compression type pelletizer after mixing and prior to wintering or by extruding the mixture into a rod shaped article, then cutting it after heating or sintering to be a desired height. The diluent of the present invention need not be a pure single crystal graphite but may preferably be one having a specific gravity of 2.0. or more and an apparent specific gravity of 1.5 or more to enhance a temperature controlling effect as a diluent. As regards undesired reactivity and degradation in catalytic activity which were deficiencies in the case where the conventional graphite particles were used as a catalyst diluent, the present inventors have dis-. covered after an extensive study that these deficiencies. are caused by iron remained or entered during the ma flu facturing, and that the foregoing deficiences can be eliminated by reducing the amount of iron contained in or deposited to the graphite particles to 0.1 percent by weight, more preferably 0.05 percent by weight. The graphite particles containing of iron in an amount of 0.1 percent by weight or less are obtained by the use of materials with a low content of iron such as petroleum - coke, pitch coke, carbon black, tar pitch and the like and further by preventing iron from mixing into or depositing on the graphite particles from the outside. The graphite particles with a low content of iron may also be prepared by washing out iron contained or deposited with hydrochloric acid and the like. When the diluent of the present invention is employed on an industrial scale, the diameter of catalyst particles should preferably be close to that of the diluent but is not specifically limited thereto. The catalyst may be in any shape such as sphere, column, ring, singly or in conjunction with two or more. Above all, the most preferable as a catalyst is a cylindrical shape the present inventors made a patent application earlier (Japanese Patent Application No. 45925/1980) and when the cylindrical shaped catalyst is used in conjunction with the diluent of the present invention, the characteristics the both possess inherently are markedly enhanced to produce unexpected synergistic effects. Furthermore, the catalyst mixed with the diluent of the present invention is not limited to one sort, but used in combination with one.or more sorts of catalysts which are different in composition, activity and shape. The foregoing applications are also included in the scope of the present invention. As the reaction that marked effects can be expected by effecting a contact reaction in a fixed bed containing the present diluent on an industrial scale, there are included, by example, an oxychlorination reaction, a vapor phase chlorination, a vapor phase hydrogenation and a vapor phase oxidation. Hereinafter the present invention will be explained in more detail relating to an oxychlorination reaction producing ethane dichloride, comparing the examples with the comparative examples, to which the present invention is not construed to be limited EXAMPLES 5 to 6 COMPARATIVE EXAMPLES 1 to 5 A reactor used for reaction was a vertical type reactor of a nickel tube having an interior diameter of 26.3 mm and a length of 1,200 mm to the entirety of which a jacket was welded, through which a heating medium (DOWTHEREI E, trademark of Dow Chemical Japan Co.) was permitted to be recycled in a state of liquid. At an inlet and an outlet of the reactor, were manometers provided to measure the flow resistance through the packed layer of a catalyst and a diluent. A reactant gases were introduced from the upper portion of the reactor. The gases reacted were led from the lower portion of the reactor to the outside of the reactor, cooled at two stages, i.e., first to 50C and second to --350C to condense condensable reaction products, then the resultant condensates and non-condensed gases being subjected to the analysis by a gaschromatography in a normal manner. As a catalyst, a commercially available spherical catalyst made up of a system of CuC12-KCl-yA12Q3 (20 percent of CuC12 and 2.3 percent of KC1 are contained and the diameter is 5 to 6 mm, hereinafter referred to as "Catalyst A") or a ring-shaped catalyst made up of a system of CuC12-KCl-yA1203 (18 percent of CuC12 and 1.5 percent of KC1 are contained and the height is 5 mm, the outer diameter is- 5 mm and the inner diameter is 2.2 mm, hereinafter referred to as "Catalyst B") prepared by the inventors was employed. The foregoing catalysts were respectively mixed adequately with a variety of diluents to prepare dn intimate mixture and 205 ml of the mixture were packed into the upper portion of the reactor and 205¯my of the non-diluted catalyst were packed into the lower portion of the reactor, then the reaction was allowed to take place. The reactant gases were introduced into the reactor, respectively, at a rate of 40 Nl/hr for hydrogen chloride, 21.6 Nl/hr for ethylene and 57 Nl/hr for air. The pressure at the outlet of the reactor was maintained at atmospheric pressure The reaction temperature was controlled by the adjustment of the temperature of a heating medium in the jacket so that conversion of hydrogen chloride introduced might come to 99 percent. The obtained results were given in Table 1. TABLE 1 EMI12.1 <SEP> Ex. <SEP> 1 <SEP> Ex. <SEP> 2 <SEP> Ex. <SEP> 3 <SEP> Ex. <SEP> 4 <SEP> Ex. <SEP> 5 <SEP> Ex. <SEP> 6 <tb> Catalyst <SEP> diluent <tb> <SEP> Short <SEP> Graphite <SEP> Graphite <SEP> Graphite <SEP> Graphite <SEP> Graphite <SEP> Graphite <tb> <SEP> Shape <SEP> Column <SEP> Column <SEP> Column <SEP> Column <SEP> Column <SEP> Column <tb> <SEP> Diameter <SEP> (mm) <SEP> 5 <SEP> 6 <SEP> 4 <SEP> 5 <SEP> 5 <SEP> 5 <tb> <SEP> Height <SEP> (mm) <SEP> 5 <SEP> 6 <SEP> 4 <SEP> 5 <SEP> 5 <SEP> 5 <tb> <SEP> Content <SEP> of <SEP> iron <SEP> (wt%) <SEP> 0.03 <SEP> 0.02 <SEP> 0.03 <SEP> 0.02 <SEP> 0.2 <SEP> 0.04 <tb> <SEP> Apparent <SEP> specific <SEP> gravity <SEP> 1.6 <SEP> 1.6 <SEP> 1.6 <SEP> 1.6 <SEP> 1.6 <SEP> 1.45 <tb> <SEP> Catalyst <SEP> A <SEP> A <SEP> A <SEP> B <SEP> A <SEP> A <tb> <SEP> Heat <SEP> medium <SEP> temp. <SEP> (T1) <SEP> ( C) <SEP> 205 <SEP> 202 <SEP> 207 <SEP> 201 <SEP> 204 <SEP> 200 <tb> <SEP> Highest <SEP> reaction <SEP> temp. <SEP> (T2) <SEP> ( C) <SEP> 285 <SEP> 288 <SEP> 284 <SEP> 270 <SEP> 285 <SEP> 290 <tb> <SEP> T2 <SEP> - <SEP> T1 <SEP> 80 <SEP> 86 <SEP> 77 <SEP> 69 <SEP> 81 <SEP> 90 <tb> Selectivity <SEP> (%) <tb> <SEP> 1,2-Dichloroethane <SEP> 97.4 <SEP> 96.9 <SEP> 97.6 <SEP> 98.7 <SEP> 96.6 <SEP> 96.6 <tb> <SEP> Ethyl <SEP> chloride <SEP> 0.4 <SEP> 0.5 <SEP> 0.4 <SEP> 0.2 <SEP> 0.8 <SEP> 0.5 <tb> <SEP> Other <SEP> halides <SEP> 0.9 <SEP> 1.0 <SEP> 0.8 <SEP> 0.5 <SEP> 1.1 <SEP> 1.2 <tb> Conbustion <SEP> rate <SEP> of <SEP> ethylene <SEP> (%) <SEP> 1.3 <SEP> 1.6 <SEP> 1.2 <SEP> 0.6 <SEP> 1.5 <SEP> 1.7 <tb> Conversion <SEP> of <SEP> HCl <SEP> (%) <tb> <SEP> Initial <SEP> stage <SEP> of <SEP> reaction <SEP> 99.0 <SEP> 99.1 <SEP> 99.1 <SEP> 99.2 <SEP> 98.8 <SEP> 99.0 <tb> <SEP> After <SEP> 500-hour <SEP> reaction <SEP> 98.7 <SEP> 98.7 <SEP> 98.7 <SEP> 98.8 <SEP> 98.3 <SEP> 98.4 <tb> EMI13.1 <SEP> Comp. <SEP> Comp. <SEP> Comp. <SEP> Comp. <SEP> Comp. <tb> <SEP> Ex. <SEP> 1 <SEP> Ex. <SEP> 2 <SEP> Ex. <SEP> 3 <SEP> Ex. <SEP> 4 <SEP> Ex. <SEP> 5 <tb> Catalyst <SEP> diluent <tb> <SEP> Short <SEP> Graphite <SEP> Graphite <SEP> Graphite <SEP> &alpha;alumina <SEP> Silicon <SEP> carbide <tb> <SEP> Shape <SEP> Sphere <SEP> Broken <SEP> shape <SEP> Column <SEP> Sphere <SEP> Sphere <tb> <SEP> Diameter <SEP> (mm) <SEP> 4-6 <SEP> 3-7 <SEP> 7 <SEP> 5-6 <SEP> 4-6 <tb> <SEP> Height <SEP> (mm) <SEP> - <SEP> - <SEP> 7 <SEP> - <SEP> <SEP> Content <SEP> of <SEP> iron <SEP> (wt%) <SEP> 0.03 <SEP> 0.08 <SEP> 0.03 <SEP> 0.02 <SEP> 0.10 <tb> <SEP> Apparent <SEP> specific <SEP> gravity <SEP> 1.6 <SEP> 1.45 <SEP> 1.6 <SEP> 3.4 <SEP> 2.2 <tb> <SEP> Catalyst <SEP> A <SEP> A <SEP> A <SEP> A <SEP> A <tb> <SEP> Heat <SEP> medium <SEP> temp. <SEP> (T1) <SEP> ( C) <SEP> 195 <SEP> 196 <SEP> 198 <SEP> 192 <SEP> 190 <tb> <SEP> Highest <SEP> reaction <SEP> temp. <SEP> (T2) <SEP> ( C) <SEP> 300 <SEP> 298 <SEP> 277 <SEP> 303 <SEP> 305 <tb> <SEP> T2 <SEP> - <SEP> T1 <SEP> 105 <SEP> 102 <SEP> 99 <SEP> 111 <SEP> 115 <tb> Selectivity <SEP> (%) <tb> <SEP> 1,2-Dichloroethane <SEP> 95.7 <SEP> 95.9 <SEP> 96.1 <SEP> 95.1 <SEP> 94.7 <tb> <SEP> Ethyl <SEP> chloride <SEP> 0.7 <SEP> 0.8 <SEP> 0.7 <SEP> 0.8 <SEP> 0.9 <tb> <SEP> Other <SEP> halides <SEP> 1.4 <SEP> 1.3 <SEP> 1.3 <SEP> 1.6 <SEP> 1.8 <tb> Conbustion <SEP> rate <SEP> of <SEP> ethylene <SEP> (%) <SEP> 2.2 <SEP> 2.0 <SEP> 1.9 <SEP> 2.5 <SEP> 2.6 <tb> Conversion <SEP> of <SEP> HCl <SEP> (%) <tb> <SEP> Initial <SEP> stage <SEP> of <SEP> reaction <SEP> 99.2 <SEP> 98.9 <SEP> 99.0 <SEP> 99.1 <SEP> 99.0 <tb> <SEP> After <SEP> 500-hour <SEP> reaction <SEP> 98.1 <SEP> 98.0 <SEP> 98.2 <SEP> 97.8 <SEP> 97.5 <tb> The highest temperature portion (hot spot) was found to be present in the upper portion of the reactor, i.e., in the portion where the diluent was mixed.in every example and comparative example. It is understood from the results of Table 1 that the diluent of the present-invention:is superior in thermal conductivity and reaction results, as compared with graphite particles in other shapes, and alumina and silicon carbide commonly employed.

Claims: WHAT WE CLAIM IS: 1. A catalyst diluent for use in a fixed bed exothermic reaction which comprises a graphite in a columnar shape having a diameter of a circular portion of between 3 and 6 mm and a height of between 3 and 6 mm. 2. The catalyst diluent of Claim 1, wherein the apparent specific gravity of the graphite is or or more. 3. The catalyst diluent of Claim 1, wherein the amount of iron deposited onto or contained in the graphite is 0.1 percent or less. 4. The catalyst diluent of any preceding Claims 1 to 3, wherein the fixed bed exothermic reaction is an oxychlorination reaction of ethylene. 5, The catalyst diluent of Claim 1, wherein a catalyst used is in a cylindrical shape in a substantially predominant quantity. 6. The catalyst diluent for use in a fixed bed exothermic reaction which comprises, in a substantially predominant quantity, a graphite in a columnar shape having a diameter of a circular portion of between 3 and 6 mm and a height of between 3 and 6 mm. 7. The catalyst diluent of Claim 6, wherein the apparent specific gravity of the graphite is 1.5 or more. 8. The catalyst diluent of Claim 6, wherein the amount of iron deposited onto or contained in the graphite is 0.1 percent or less. 9. The catalyst diluent of any preceding Claims 6 to 8, wherein the fixed bed exothermic reaction is an oxychlorination reaction of ethylene. 10. The cayalyst diluent of Claim 6, wherein a catalyst used is in a cylindrical shape in a substantially predominant guantity.

Inventors: OHNISHI, AKIRA, SHIOZAKI, KEN
Applicants: KANEGAFUCHI KAGAKU KOGYO KABUSHIKI KAISHA
Application year: 1981
Main classification: B01J37
IPC codes: C07C19, B01J8, C07C21, C01B31, C07C67, C07C17, B01J35, B01J21, C07B61