PROCESS FOR SEPARATING DICHLOROCUMENE ISOMER

Abstract: A specific isomer of dichlorocumene is separated from a mixure containing dichlorocumene isomers by adsorptive separation, wherein the zeolite having at least 2 of silica/alumina molar ratio and 0.6 to 1.0 nm of pore size is used as the adsorbent and halogenated benzene or halogenated alkyl benzene is used as desorbent.

Description: This invention relates a process for separating a specific isomer of dichlorocumene from a mixture containing of dichlorocumene isomers. Dichlorocumene, in particular, 3,5-dichlorocumene (hereinafter referred to as "3,5-DCC") is important as intermediate substances for agricultural chemicals, medicines and dies. Dichlorocumene is obtained by reacting dichlorobenzene with propylene or isopropyl halide in the presence of the catalyst. In particular, 3,5-DCC is obtained by isomerization of 2,4-dichlorocumene (hereinafter referred to as "2,4-DCC") in the presence of the catalyst. 2,4-DCC is obtained by alkylation of m-dichlorobenzene (hereinafter referred to as "m-DCB"). The resulting isomer mixture of dichlorocumene is contains mainly 2,4-DCC and 3,5-DCC at thermal equilibrium and further contains unreacting material of m-DCB, by-product of 2,5-dichlorocumene (hereinafter referred to as "2,5-DCC"), by product of dichlorodiisopropylbenzene hereinafter referred to as "DCDIPB"), and the catalyst. From the reaction mixture containing dichlorocumene isomers, the catalyst is removed by filtered off, and unreacting m-DCB and DCDIPB having high boiling point are removed off by distillation. However, considerable difficulties are encountered in separation of dichlorocumene isomer from the mixture of dichlorocumene isomers by distillation because their boiling points are very close one another. Therefore, in the prior, the mixture of dichlorocumene isomer is alkylated, whereby 2,4-DCC is selectively converted to DCDIPB, and thereafter, 3,5-DCC is separated by having advantage of distillation (USP 4,104,315). However, since thus obtained 3,5-DCC contains still small amount of unreacing 2,4-DCC and by-producing 2,5-DCC, 3,5-DCC is brominated, whereby 3,5-DCC is selectively brominated and be able to separated and purified by distillation (USP 4,087,473). According to FR-A-2,538,379 a faujasite zeolite in the Cu or Ag form is used for separation of a desired isomer from a feed containing a meta-substituted benzine or a 1,3,5-substituted benzine in which the substituents are methyl, ethyl, hydroxyl or halogen. Recovered unreacting m-DCB and by-producing DGDIPB are feed to the prior alkylation process, whereby m-DCB and DCDIPB are converted to 2,4-DCC by transalkylation and reused (USP 4,329,524). However, the prior separation purification process which repeats reactions and distillation such as alkylation (first)---isomerization---removal of catalyst---distillation---alkylation(second)---distillation---bromination---distillation is disadvantageous for energistic economical and industrial use. Moreover, the repetition of the reaction give rise to the increase of the undesirable by-product. In the prior art, the problem is remained in both economical disadvantage and low quality of the product. One object of the present invention is to provide a process for separating selectively a specific dichlorocumene isomer (namely 3,5-DCC) from a mixture containing dichlorocumene isomers at a high efficiency. Another object of the present invention is to provide a process for separating 3,5-dichlorocumene isomer using an adsorbent having high ability of adsorbing said specific dichlorocumene isomer. The other object of the present invention is to provide a process for separating 3,5-dichlorocumene isomer using an desorbent having desirable ability of expelling the isomer adsorbed in the adsorbent. Further object of the present invention is to provide a process for separating 3,5-DCC from the mixture containing dichlorocumene isomers at a high efficiency. Other and further objects, features, and advantages of the invention will appear more fully from the following description. These objects are attained by a process for separating 3,5-dichlorocumene from a mixture containing dichlorocumene isomers, comprising contacting the isomer mixture with a zeolite adsorbent having at least 2 silica/alumina molar ratio and 0.6 to 1.0 nm pore size and desorbing that isomer from the zeolite by use of a halogenated benzine of halogenated alkyl benzine as desorbent. FIG. 1 is a flow sheet illustrating continuous adsorptive separation of dichlorocumene isomer using a simulated moving bed. The present invention will be explained in detail. The mixture containing dichlorocumene isomers in the present invention usually contains mainly 2,4-DCC, 2,5-DCC and 3,5-DCC and further contains by-product of DCDIPB. Zeolites are crystalline three dimensional structures wherein regular tetrahedra of SiO₄ and AlO₄ are cross-linked by sharing of oxygen atoms. Different zeolites have different shapes of voids and pore paths. Their pores have uniformal significant diameter (hereinafter referred to as "pore size"). This pore size can vary a little according to crystal structure of zeolite and kinds of cation. Zeolites used in the present invention need to have 0.6 to 1.0 nm pore size. If the pore size is less than 0.6 nm or more than 1.0 nm, 3,5-dichlorocumene isomer can not be separated by the adsorption separation. Moreover, zeolite used in the present invention need to have a silica/alumina molar ratio of at least 2, preferably 2 to 30. If silica/alumina molar ratio is less than 2,3,5-dichlorocumene isomer can not be separated by the adsorption separation. Preferred zeolites used in the present invention are faujasite type zeolite, L type zeolite, beta type zeolite, mordenite type zeolite, pentasil type zeolite, omega type zeolite, and offretite type zeolite. Most preferably, faujasite type zeolite, L type zeolite or beta type zeolite is used in the present invention. The faujasite type zeolite used in the present invention is a crystalline aluminosilicate represented by the following formula: (0.9±0.2)M 2/n O:Al₂O₃:xSiO₂:yH₂O wherein M stands for a cation selected from proton, ammonium ion, univalent metal cation, divalent metal cation, and trivalent cation; n indicates the valency of the cation M; and the value of y differs according to the degree of hydration. The faujasite type zeolite represented by the above formula is classified into a type X in which x in the above formula is in the range of 2.5±0.5 and a type Y in which x in the above formula is from 3 to 6. That is, type X zeolites have 2.5±0.5 silica/alumina molar ratio and type Y zeolites have 3 to 6 silica/alumina molar ratio. Both type X zeolite and type Y zeolite typically have about 0.74 nm pore size, but may have 0.6 to 0.9 nm pore size by changing the cation of the zeolite. The L type Zeolite used in the present invention is a crystalline aluminosilicate represented by the following formula: (1.0±0.1)M 2/n O:Al₂O₃:(5 to 8)SiO₂:yH₂O wherein M stands for a cation selected from proton, ammonium ion, univalent metal cation, divalent metal cation, and trivalent cation; n indicates the valency of the cation M; and the value of y is optional number of 0 to 7. That is, L type zeolites have 5 to 8 silica/alumina molar ratio and typically have about 0.71 nm pore size, but may have 0.6 to 0.9 nm pore size by changing the cation of the zeolite. The beta type Zeolite used in the present invention is a crystalline aluminosilicate in use condition represented by the following formula: M 2/n O:Al₂O₃:(5 to 100)SiO₂:yH₂O wherein M stands for a cation selected from proton, ammonium ion, univalent metal cation, divalent metal cation, and trivalent cation; n indicates the valency of the cation M; and the value of y differs according to the degree of hydration. That is, beta type zeolites have 5 to 100 silica/alumina molar ratio and can have 0.6 to 0.9 nm pore size according to the cation which is present. It is also preferred that the cation M be at least one member selected from metals of the groups IA, IB and IIA of the Periodic Table, proton and ammonium ion, and it is especially preferred cation be at least one member selected from lithium, sodium, potassium, magnesium, calcium, strontium, barium, copper, silver, gold, proton, and ammonium. These cations can be introduced by ion exchange according to known ion exchange processes. Ordinarily, the ion exchange is effected with an aqueous solution containing a water-soluble salt of a required cation or an aqueous solution containing an ammonium salt. Proton is introduced as a cation by calcining the ammonium-exchanged zeolite. Zeolite used in the present invention is obtained by optional methods, for example, obtained by methods described in Japanese Unexamined Patent Publication No. 28126/1978, Japanese Examined Patent Publication No. 3675/1961, or USP 3,308,069. The adsorptive separation according to the present invention may be accomplished by any ordinary method, for example, a chromatographic separation method or a continuous adsorptive method using a simulated moving bed. In the continuous adsorptive separation technique according to the present invention, a simulated moving bed having a plurality of adsorption chambers filled with an adsorbent is used. This adsorptive separation technique comprises as the basic operations, an adsorption operation, a concentration operation, a desorption operation and a desorbent recovery operation, which are continuously repeated. These basic operations are as follows. (1) Adsorption Operation A starting mixture containing dichlorocumene isomers is brought into contact with a bed of an adsorbent and the 3,5-isomer is selectively adsorbed. The remaining weakly adsorbable component is withdrawn from the adsorbent bed together with a desorbent in the form of a raffinate flow. (2) Concentration Operation The adsorbent having the 3,5-isomer selectively adsorbed therein is brought into contact with a part of an extract described hereinafter to expel the weakly adsorbable component left on the adsorbent and increase the purity of the strongly adsorbable component. (3) Desorption Operation The adsorbent bed containing the 3,5-isomer having an increased purity is brought into contact with the desorbent, and the isomer is withdrawn from the adsorbent bed together with the desorbent in the form of an extract flow. (4) Recovery Operation The adsorbent bed containing the desorbent is brought into contact with a part of the raffinate flow and the desorbent is withdrawn from the adsorbent bed. Typical examples of the simulated moving bed operation will be described hereinafter in the working examples with reference to the accompanying drawings. The simulated moving bed used will now be described with reference to FIG. 1. Four adsorption chambers 1 through 4 are connected with series, and reference numerals 5 , 6 , 7 , 8 and 9 represents a desorbent feed line, an extract withdrawal line, a feed supply line, a raffinate withdrawal line and a desorbent recovery line, respectively. The desorption operation is carried out in the adsorption chambers 1 , the concentration operation is carried out in the adsorption chambers 2 , the adsorption operation is carried out in the adsorption chamber 3 , and the recovery operation is carried out in the adsorption chamber 4 . The liquid flows downward in the drawings. The line between the adsorption chamber 1 to 4 is closed by a valve 10 . The extract and raffinate flows are separated into dichlorocumene isomer components and desorbent component by rectifier columns. At predetermined time intervals (hereinafter referred to as "changeover time"), the lines 5 thorough 9 and valve 10 are transferred counter clockwise by one adsorption chamber. If it is assumed that the above-mentioned lines and valve are kept stationary in FIG. 1, it may be considered that the adsorption chambers 1 to 4 are apparently transferred clockwise by one extract flow was withdrawn from line 6. The above-mentioned dichlorocumene isomer mixture was supplied from the line 7 and a raffinate flow was withdrawn from the line 8 . The remaining liquid was withdrawn from the line 9 . The desorbent used in the present adsorptive separation method is one or more compounds selected from the group consisting of halogenated alkyl benzene and halogenated benzene, for example, chlorotoluene, dichlorobenzene and dichlorotoluene. Such compounds may be used individually or as mixtures of two or more compounds. A single isomer or a mixture of isomers of such compounds may be used as desorbent. The adsorptive separation is carried out at a temperature of from room temperature to 350 °C, preferably from 50° to 250 °C, under a pressure of from atmospheric pressure to 50 bar (Kg/cm²G), preferably from atmospheric pressure to 40 bar (Kg/cm²G). In the present invention, the adsorptive separation may be carried out either in the vapour phase or in the liquid phase. However, in order to prevent occurrence of an undesirable side reaction in the starting mixture or desorbent, it is preferred that the operation be carried out at a low temperature in the liquid phase. The process of the present invention will now be described in detail with reference to the following Examples. In the examples, the adsorbing characteristic of the adsorbent is expressed by the following adsorptive selectivity α A/B : In the above formula, A and B designate dichlorocumene isomers respectively, S designated the adsorbed phase, and L designates the liquid phase equilibrated with the adsorbed phase. If the value α A/B larger than unity, the component A is selectively adsorbed and if the value α A/B is smaller than unity, the component B is selectively adsorbed. If the value α A/B is more larger than unity (or is smaller than unity and closer to zero) in the adsorbent, the adsorptive separation of components A and B becomes easier. In the examples, the desorbing characteristic of the desorbent is expressed by the following adsorptive selectivity α DES/DCC : In the above formula, DES designates desorbent, and DCC designate dichlorocumene isomer being adsorbed most strongly by the adsorbent, S designated the adsorbed phase, and L designates the liquid phase equilibrated with the adsorbed phase. The value α DES/DCC , most preferably, closes unity. If the valued α DES/DCC larger than unity, the desorption is strongly carried and the next adsorption becomes to be difficult. If the value α DES/DCC is smaller than unity and closer to zero, adsorbed dichlorocumene isomer can not be fully desorbed. EXAMPLE 1 Granular zeolite of the Na-Y type having 5.5 silica/alumina molar ratio and about 0.74 nm pore size was subjected to the ion-exchange treatment with an aqueous solution of cation-equivalent potassium nitrate at a solid/liquid ratio of 5 ml/g at 90 °C for 2 hours. This treatment was repeated ten times to replace more than 98 mol% of the sodium ion with the potassium ion and thereby prepare the K-Y zeolite. After the ion-exchange, the resulting K-Y zeolite was washed with pure water at solid/liquid ratio of 5 ml/g at 90 °C ten times, then dried at 120 °C overnight. Immediately before use it was calcined at 500 °C for 2 hours. In order to determine the adsorptive selectivity of this adsorbent of K-Y zeolite for adsorption of dichlorocumene isomers containing DCDIPB, about 2 g of the K-Y zeolite and 2.5 ml of the mixture containing dichlorocumene isomers [Mixture A] were charged into an autoclave having an inner capacity of 5 ml and heated at 150 °C for 0.5 hour while conducting stirring now and then. The mixture containing dichlorocumene isomers [Mixture A] charged comprises as follows; [Mixture A] 2,4-DCC 36(weight parts) 2,5-DCC 1 3,5-DCC 56 DCDIPB 7 n-Nonane was added as the internal standard substance for the gas-chromatographical analysis, and it was substantially inactive relatively to the adsorption under the experimental conditions. The composition of the liquid-phase mixture after the contact with the adsorbent was analyzed by the gas chromatography, and the adsorptive selectivities for the dichlorocumene isomers were calculated according to the above-mentioned formula. The obtained results are shown in Table 1. EXAMPLE 2 TO 6 Instead of the zeolite of the Na-Y type, Na-beta zeolite having 20.0 silica/alumina molar ratio was subjected to ion-exchange treatment in the same manner as described in Example 1 to give K-beta zeolite. Na-Y zeolite having 4.8 silica/alumina molar ratio and about 0.74 nm pore size was subjected to ion-exchange treatment with an aqueous solution of barium nitrate in the same manner as described in Example 1 to give Ba-Y zeolite. Na-Y zeolite having 4.8 silica/alumina molar ratio and about 0.74 nm pore size was subjected to ion-exchange treatment with each an aqueous solution containing 0.15 cation-equivalent ammonium nitrate and 0.85 cation-equivalent of potassium nitrate and an aqueous solution containing 0.3 cation-equivalent ammonium nitrate and 0.7 cation-equivalent of potassium nitrate in the same manner as described in Example 1 to give 0.15H-K-Y zeolite and 0.3H-K-Y zeolite, respectively. The resulting 0.15H-K-Y zeolite and 0.3H-K-Y zeolite were calcined, whereby ammonium ion is converted to proton. A K-L zeolite having 6.1 silica/alumina molar ratio and about 0.71 nm pore size, the K-beta zeolite resulting 0.15H-K-Y zeolite and the 0.3H-K-Y zeolite were tested in the same manner as described in Example 1, and the adsorptive selectivities for the dichlorocumene isomers were determined. The obtained results are shown in Table 1. EXAMPLE 7 TO 13 Na-X zeolite having 2.5 silica/alumina molar ratio and about 0.74 nm pore size and Na-Y zeolite having 4.8 silica/alumina molar ratio and about 0.74 nm pore size were subjected to the ion-exchange treatment in the same manner as described in Example 1 to provide the various zeolite adsorbents shown in Table 2. The resulting zeolite adsorbents shown in Table 1 were tested using the following mixture containing dichlorocumene isomers [Mixture B] in the same manner as described in Example 1, and the adsorptive selectivities for the dichlorocumene isomers were determined. The obtained results are shown in Table 2. [Mixture B] 2,4-DCC 40(weight parts) 3,5-DCC 60 COMPARATIVE EXAMPLE 1 Na-A type zeolite having 2.0 silica/alumina molar ratio and about 0.42 nm pore size was tested in the same manner as described in Example 1. However neither dichlorocumene isomer nor DCDIPB was adsorbed. It was impossible to separate any dichlorocumene isomer from the mixture containing dichlorocumene isomers. EXAMPLE 14 TO 23 The 0.15H-K-Y zeolite obtained by Example 5 was tested using the following mixture containing dichlorocumene isomers and each desorbent shown in Table 3 [Mixture C] in the same manner as described in Example 1, and the adsorptive selectivities for the dichlorocumene isomers and the adsorptive selectivities for the dichlorocumene isomer and the desorbent were determined. The obtained results are shown in Table 3. [Mixture C] Desorbent shown in Table 3 50(weight parts) 2,4-DCC 15 2,5-DCC 15 3,5-DCC 20 COMPARATIVE EXAMPLE 2 to 14 The 0.15H-K-Y zeolite obtained by Example 5 was tested using the following mixture containing dichlorocumene isomers and each desorbent shown in Table 4 [Mixture D] in the same manner as described in Example 1, and the adsorptive selectivities for the dichlorocumene isomers and the adsorptive selectivities for the dichlorocumene isomer and the desorbent were determined. The obtained results are shown in Table 4. [Mixture C] Desorbent shown in Table 4 50(weight parts) 2,4-DCC 15 2,5-DCC 15 3,5-DCC 20 EXAMPLE 24 3,5 DCC isomer was separated from the mixture containing dichlorocumene isomer and DCDIPB comprising the following composition, using the simulated moving bed as shown in FIG. 1. 3,5-DCC 63.3% 2,4-DCC 35.6% 2,5-DCC 0.7% DCDIPB 0.4% K-Y zeolite obtained in Example 1 was charged into four adsorption chamber 1 , 2 , 3 , and 4 , all of them having an inner capacity of about 40 ml respectively. The above-mentioned mixture containing dichlorocumene isomers was supplied at a rate of 12.6 ml/hr form the line 7 , and the dichlorotoluene mixture having the following composition as desorbent was supplied at a rate of 422 ml/hr from the line 5 . 2,4-dichlorotoluene 34% 2,5-dichlorotoluene 63% 2,6-dichlorotoluene 2% 2,3-dichlorotoluene 1% The extract flow was withdrawn at a rate of 61.7 ml/hr from the line 6 , and the raffinate flow was withdrawn at a rate of 66.9 ml/hr from the line 8 . The remaining liquid was withdrawn from the line 9 . The line between adsorption chamber 1 and 4 was closed by a valve 10 . At every changeover time of 150 seconds, the adsorption chamber 1 was transferred to the adsorption chamber 4 , the adsorption chamber 4 was transferred to the adsorption chamber 3 , the adsorption chamber 3 was transferred to the adsorption chamber 2 , and the adsorption chamber 2 was transferred to the adsorption chamber 1 , simultaneously. The adsorption temperature was 170 °C and the adsorption pressure was 20 (bar) (kg/cm²). The purity of 3,5-DCC in the DCC component in the extract flow was 99.8 % and the recovery ratio of 3,5-DCC was 91.7 %.

Claims: A process for separating 3,5-dichlorocumene isomer from a mixture containing dichlorocumene isomers comprising contacting the isomer mixture with a zeolite adsorbent having a silica/alumina molar ratio of at least 2 and a pore size of 0.6 to 1.0 nm and removing the adsorbed isomer by contacting the zeolite adsorbent with a desorbent selected from halogenated benzene and halogenated alkyl benzene. A process according to claim 1 wherein said zeolite is selected from the group consisting of faujasite type zeolite, L type zeolite and beta type zeolite. A process according to claim 1 wherein said zeolite is substituted by a cation selected from the group consisting of proton, ammonium, and metal cation of the groups IA, IB and IIA of the Periodic Table. A process according to claim 3 wherein the metal cation is selected from the group consisting of lithium, sodium, potassium, magnesium, calcium, strontium, barium, copper, silver and gold. A process according to any preceding claim wherein said desorbent is selected from the group consisting of chlorotoluene, dichlorobenzene and dichlorotoluene.

Inventors: KIMURA, MICHIO, NOGUCHI, YOSHIO, YAMADA, BUNSHI
Applicants: TORAY INDUSTRIES, INC.
Application year: 1988
Main classification: C07C25
IPC codes: C07C17