Process for the separation of halogenated benzene derivatives

Abstract: By a process for preparing halogenated benzene derivatives comprising distilling or stripping a mixture of the isomers of a halogenated benzene derivative containing a hydrogen halide to remove the hydrogen halide from the isomeric mixture of the halogenated benzene derivative and then contacting with a zeolite adsorbent for selectivity separating the desired isomer of the halogenated benzene derivative it is possible to prevent from degrading the zeolite adsorbent. And it is possible to separate selectively industrially an desired isomer of the halogenated benzene derivative for a long time without reduction of productivity and to separate selectively the desired isomer in high purity.

Description: This invention relates to a process for the adsorptive separation of a specific isomer of a halogenated benzene derivative Halogenated benzene derivatives include typically dichlorobenzene, chlorotoluene, dichlorotoluene and dichlorocumene, and these are important as intermediates for synthesis of agricultural chemicals and medicines. A halogenated benzene derivative is generally obtainable as a mixture of isomers"through halogenation of benzene, alkyl benzene or halogenated alkyl benzene and is provided by isolating the desired isomer from such mixture of isomers. Separation of the isomer is generally made by distillation, crystallization or adsorption. But, as these isomers are not much different in boiling or freezing point, the conventional distillation or crystallization method is hardly applicable. On the other hand, there have recently been developed a method of isomerizing a dialkylbenzene such as xylene in the presence of a catalyst (USP 4,409,413) and a method of adsorptive separation of a mixture of alkylbenzene isomers with a zeolite adsorbent (Japanese Examined Patent Publication No. 15681/1977 and Japanese Examined patent Publication No. 38202/1983). According to these methods, the desired isomer is obtainable'at a considerable purity. Further, by feeding the remaining components after separation to an isomerization process and thus isomerizing them, and then separating the desired isomer in adsorptive separation once more, it is possible to ultimately produce the desired isomer only. However, when said method of isomerization and adsorption separation is applied to production of a halogenated benzene derivatives (see for instance EP 0 125 077 A1), degradation of the zeolite adsorbent occurs gradually, resulting in reduction of productivity. The problem of the invention is to avoid the degradation of zeolite adsorption in the adsorptive sepration of a halogenated benzene derivative. The:problem is solved by the process of claim 1. The inventors looked into the cause of degradation of the zeolite adsorbent and found that a very small amount of hydrogen halide contained in the material and a very small amount water cause degradation of the zeolite adsorbent. Further, the inventors found that the zeolite adsorbent of the type adsorbing water strongly, such as faujasite type zeolite, is degraded to the considerable extent. Moreover, the inventors found that the zeolite adsorbent is deteriorated by the co-presence of the water and hydrogen halide at high concentration in the material to be adsorbed, and degraded the adsorbing capacity. Therefore, the inventors found that it is required to suppress the water content in the material to be adsorbed as far as practicable, and that it is possible to prevent degradation of the zeolite adsorbent. The present invention provides a process of preventing degradation of the zeolite adsorbent selectively separating industrially an desired isomer of the halogenated benzene derivative for a long time without reduction of productivity. Other and further objects, features and advantages of the invention will appear more fully clear form the following description. Detailed Description of the Preferred Embodiments The halogenated benzene derivative used as a starting material according to the method of the invention, is any compound expressed by the following general formula (I): wherein X¹ representing a halogen atom, X² and X³ a halogen or hydrogen atom, and R a lower alkyl group or halogen atom. R may be an alkyl group of 1 to 4 carbon atoms. Specifically, there may be listed a methyl group, ethyl group, n-propyl group, iso-propyl group, n-butyl group, sec-butyl group, and tert-butyl group. When X¹, X², X³ or R represents a halogen atom, the halogen atom may be the same or different. Specifically, the halogen atom includes chlorine atom and bromine atom and iodine atom, preferably chlorine atom and bromine atom. Halogenated benzene derivatives include, for example, dichlorobenzene, chlorotoluene, dichlorotoluene, trichlorobenzene, trichlorotoluene, tetrachlorobenzene, dibromobenzene, bromotoluene, dibromotoluene, dichlorobromobenzene, tribromobenzene, dibromochlorobenzene, chlorocumene, dichlorocumene, trichlorocumene, dibromocumene and bromocumene. Of these, chlorobenzene, chlorotoluene, dichlorotoluene and dichlorocumene are preferably usable. These halogenated benzene derivatives are respectively supplied as a mixture of isomers. The mixture of isomers of a halogenated benzene derivative used as a material according to the method of the invention is provided by isomerization reaction, and contains a very small amount of a hydrogen halide as by-product. The isomer mixture of halogenated benzene derivative usually contains a small amount of the water inherently. The isomerization reaction may be carried out by a conventional method. For example, the isomerization reaction is carried out by contacting a starting material for a mixture of isomers of a halogenated benzene derivative with a catalyst. Here, as a catalyst, aluminium trichloride or zeolite is usable, and as specific examples of zeolite catalyst, a faujasite type zeolite, pentasil type zeolite and mordenite type zeolite may be listed. When a zeolite catalyst is used for isomerization, the isomerization may be effected according to the Unexamined Japanese Patent Publication No. 144330/1983. That is, any system of gas phase reaction, liquid phase reaction, fixed bed, moving bed or fluidized bed is usable under the conditions of a reaction temperature of 200 to 550 °C, preferable 250 to 500 °C, and a weight hourly space velocity (WHSV) of 0.05 to 30 hours⁻¹, preferably 0.1 to 20 hours⁻¹. In the method of the invention, it is important that the mixture of isomers of a halogenated benzene derivative containing a hydrogen halide is subjected to a distillation or stripping treatment for removal of the hydrogen halide. Absorption with an aqueous alkaline solution that is a conventional method for removal of the hydrogen halide is not preferable in that the isomeric mixture of halogenated benzene derivative unavoidably comes into contact with water and thus has a very small amount of water dissolved which in turn causes degradation of the zeolite adsorbent used in the subsequent process. The distillation or stripping treatment enables to remove the hydrogen halide without contact with water. The isomeric mixture of the halogenated benzene derivative to be subjected to the distillation or stripping treatment is not restricted, and may be the isomerization reaction mixture itself or be the halogenated benzene derivative extracted or distilled. In the method of the invention, the stripping treatment refers to blowing an inert gas such ad N₂ into the reaction liquid containing a hydrogen halide to remove hydrogen halide, water and volatile components from the reaction liquid. The distillation treatment refers to the distillation process carried out according to a conventional method. The distillation or stripping treatment is practicable either by a plate tower or by a packed tower. The operation may be under atmospheric, vacuum or increased pressure. The distillation or stripping treatment is carried out until the concentration of the hydrogen halide in the reaction liquid is reduced to 10 ppm or less, preferably 1 ppm or less. In the process of the invention, water present in the material is also simultaneously removed by the distillation or stripping treatment. The distillation or stripping treatment is carried out until the water content in the reaction liquid is reduced to 10 ppm or less, preferably 1 ppm or less. If the isomerization of a halogenated benzene derivative involves side reactions such as transalkylation, dehalogenation and/or demethylation, there are produced demethylated and/or dehalogenated low boiling components as by-products. For example, when chlorotoluene is isomerized, toluene and chlorobenzene are incidentally produced, each in a very small amount. Such low boiling components scarcely degrade the zeolite adsorbent. But, when a high purity product is required, the low boiling components should be removed. Here, by the distillation or stripping treatment, the low boiling components can be simultaneously removed. When the low boiling components are of a small relative volatility, a multi-stage distillation or stripping tower should be used. The isomeric mixture of halogenated benzene derivative having the distillation or stripping treatment rendered is fed to a process of adsorptive separation, and in the adsorptive separation process, the desired isomer of the halogenated benzene derivative is selectively separated. For the adsorbent, a zeolite is used Those zeolite adsorbents which are subject to great degradation by the hydrogen halide provide particularly good results. Specifically, the most preferable result can be obtained, when such zeolites as X type, Y type and other faujasite type zeolites, pentasil type zeolites such as ZSM-5, mordenite type zeolites, L type zeolites and beta type zeolites are used. As a desorbent, toluene, xylene and other aromatic compound are usable. For adsorption and desorption, ordinary methods and conditions may be employed. For example, adsorption and desorption may be made according to the method in Japanese Examined Patent Publication No. 24981/1988. The mixture of isomers after adsorptive separation of the desired isomer may be placed again to isomerization reaction to enhance the concentration of the desired isomer to an equilibrium rate. By such recycling, the desired isomer can be industrially advantageously produced. The invention will be more clearly understood as it is described with reference to the following examples. Example 1 An aqueous mixture comprising 135g of sodium silicate, 8.6g of Al₂(SO₄) 18H₂O, 15g of n-propylamine, 11.2 g of H₂SO₄ and 400 g of water was maintained 155 °C for 72 hours for crystallization, and thus there was produced a powder of Zeolite ZSM-5 of SiO₂/Al₂O₃ molar ratio of 45.5 mol/mol. This ZSM-5 powder has subjected to ion exchange for five times with a 10 % by weight aqueous solution of ammonium chloride used (solid/liquid ratio, 2.0 l/kg at about 90 °C), then thoroughly rinsed. dried at 120 °C for 15 hours and calcined at 600 °C for 2 hours in air, and there was obtained an acid type ZSM-5 catalyst. Using the acid type ZSM-5 catalyst thus obtained, and employing a fixed bed flow reactor, isomerization of o-dichlorobenzene was carried out in a liquid phase, and there was obtained a mixture of isomers of dichlorobenzene containing hydrogen chloride. o-Dichlorobenzene was dehydrated with a molecular sieve. The conditions for isomerization are shown below. WHSV = 4.5 hour⁻¹ Reaction temperature = 300 °C Reaction pressure = 30 bar (30 kg/cm²) After the reaction, the composition of the mixture of isomers was o-dichlorobenzene:m-dichlorobenzene:p-dichlorobenzene=58:27:15, and the concentration of hydrogen chloride was 120 ppm, and water was 10 ppm. The concentration of the by-product chlorobenzene was 0.09 % by weight. The obtained reaction mixture was distilled at 267mbar (200mmHg) for about 30 minutes to remove hydrogen chloride and water from the reaction mixture. After distillation, the hydrogen chloride in the reaction mixture was 1 ppm, water 6 ppm and low boiling components 0.01 % by weight. This isomeric mixture was subjected to adsorptive separation by a simulated moving bed system which will now be briefly described. To twelve adsorption chambers No. 1 to 12 each of an inner capacity of about 13 ml, an X type zeolite adsorbent represented by 0.75 LiO₂·O.25Na₂O·Al₂O₃·2.5SiO₂ (hereinafter referred to as "Li-X type zeolite") was charged. The desorbent, toluene, was charged at 300 ml/hr, and a mixture of isomers was fed at 17 ml/hr. The extract flow was discharged at 74 ml/hr, and the raffinate flow was discharged at 29 ml/hr. The remaining liquid was discharged. Flow of the liquid between the adsorption chambers No. 1 and No. 12 is closed by a valve. Then, the adsorption chamber No. 1 was shifted to the position of the adsorption chamber No. 12, the chamber No 11 to No 10, No 8 to No 7 and No 5 to No 4 respectively at an interval of about 150 seconds (the other chambers being also shifted upward by one chamber simulataneously). The adsorption temperature was 130 °C. At two hours after start of adsorptive separation, the purity of m-dichlorobenzene in the mixture of isomers of dichlorobenzene contained in the raffinate flow was 99.5 %, and the recovery rate of m-dichlorobenzene was 70 %. Further, preserving the raffinate flow and extract flow, the composition after 100 hours was examined, and the purity of the product, m-dichlorobenzene in the dichlorobenzene mixture in the raffinate flow was 99.5 %, and recovery rate was 68 %. Example 2 Isomerization and adsorptive separation were carried out as in Example 1, except that instead of distillating the reaction mixture, N₂ gas was bubbled in the reaction mixture at about 1 l/min for about 1 hour under room temperature and atmospheric pressure to strip hydrogen chloride and water and thus remove them. After the stripping, the concentrations of hydrogen chloride, water and low bioling components in the reaction mixture were 8 ppm, 7 ppm and 0.08 % by weight, respectively. The purity of the product, m-dichlorobenzene in the raffinate flow at 2 hours after start of the adsorptive separation was 99.6 %, and the recovery rate of the product, m-dichlorobenzene was 68 %. After 100 hours, the purity of the product, m-dichlorobenzene in the raffinate flow was 99.6 %, and recovery rate was 67 %. Comparative Example 1 Isomerization and adsorptive separation were carried out as in Example 1 except that the reaction mixture was not distilled but was directly fed to the process of adsorptive separation. In the reaction mixture, the hydrogen chloride was 120 ppm, water 10 ppm and low boiling components were 0.09 % by weight. The product, m-dichlorobenzene in the raffinate flow at 2 hours after start of the adsorptive separation was of a purity 99.5 % and of a recovery rate 68 %. After 48 hours, the purity of the product, m-dichlorobenzene in the raffinate flow was 91.3 % and the recovery rate was 60 %. Example 3 With 2,5-dichlorotoluene used in place of o-dichlorobenzene and with X type zeolite substituted by Ag used in place of Li-X type zeolite in Example 1, isomerization, distillation and adsorptive separation were carried out as in Example 1. The product, 2,6-dichlorotoluene was obtained. The results are shown in Table 1. Isomerization and adsorptive separation were carried out as in Example 3 except that the reaction mixture was not distilled but was directly fed to the process of adsorptive separation. The results are shown in Table 1 as Comparative Example 2. Example 4 With 2,4-dichlorocumene used in place of o-dichlorobenzene and with Y type zeolite substituted by K used in place of Li-X type zeolite in Example 1, isomerization, distillation and adsorptive separation were carried out as in Example 1. The product, 3,5-dichlorocumene was obtained. The results are shown in Table 1. Isomerization and adsorptive separation were carried out as in Example 4 except that the reaction mixture was not distilled but was directly fed to the process of adsorptive separation. The results are shown in Table 1 as Comparative Example 3.

Claims: A process for the adsorptive separation of a specific isomer of a halogenated benzene derivative having the following general formula (I): wherein X¹ represents a halogen atom, X² and X³ a halogen or hydrogen atom, and R a lower alkyl group or halogen atom, from an isomer-mixture obtained through isomerization using a zeolite as adsorbent, characterized by the process step of removal of hydrogen halide and water contained in the isomeric mixture by distilling or stripping the isomer-mixture before the adsorptive separation step. A process according to claim 1, wherein the zeolite adsorbent is chosen from the group consisting of mordenite type zeolites, pentasil type zeolites, faujasite type zeolites, L type zeolites and beta type zeolites.

Inventors: KANAI TAKASHI, KIMURA MICHIO, NOGUCHI YOSHIO, KANAI, TAKASHI, KIMURA, MICHIO, NOGUCHI, YOSHIO
Applicants: TORAY INDUSTRIES, TORAY INDUSTRIES, INC.
Application year: 1989
Main classification: C07C25
IPC codes: C07C17, C07C25