JPS6323977B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for adsorptive separation of halogenated toluene isomers, and more specifically, p-halogen The present invention relates to an improvement in a desorbent in a method for adsorbing and separating oxidized toluene isomers. It is known from Japanese Patent Publication No. 37-5155 that halogenated toluene isomers can be adsorbed and separated using a zeolite adsorbent, and chlorobenzene is known as a desorbent in this case. However, conventionally known desorbents do not exhibit sufficient performance. An object of the present invention is to provide a desorbent for adsorbing and separating halogenated toluene isomers using a zeolite-based adsorbent. The object of the present invention is to provide a novel desorbent that is highly effective in separating and recovering p-halogenated toluene isomers from mixtures. The continuous adsorption separation of halogenated toluene isomers according to the present invention basically consists of a combination of the following adsorption and desorption operations. (1) In the adsorption operation, the raw material feed containing the halogenated toluene isomer mixture is brought into contact with the adsorbent that has completed the desorption operation described in (2), and the strongly adsorbed components in the raw material feed are brought into contact with the adsorbent. It is selectively adsorbed while expelling a portion of the desorbent remaining inside. At the same time, the less adsorbable components in the raw material feed are recovered together with the desorbent as a roughinate stream. (2) In a desorption operation, selectively adsorbed components are expelled from the adsorbent by a desorbent and recovered as an extract stream. The following points are important when selecting an adsorbent to be used in the above adsorption separation method. In other words, in order to cycle through and continuously perform the adsorption and desorption operations shown in (1) and (2), the desorbent must be able to drive out the strongly adsorbed components adsorbed onto the adsorbent during the desorption operation. The resulting desorbent remaining on the adsorbent must be driven out by strongly adsorbed components in the feedstock during the adsorption operation, allowing the adsorbent to be recycled and used continuously. It won't happen. In other words, in the desorption operation, it is preferable to use a desorbent that adsorbs more strongly than the strongly adsorbed component.
In adsorption operations, it is better to use desorbents that weakly adsorb components rather than strongly adsorbed components. In order to satisfy these conflicting demands at the same time, it is necessary to select a desorbent whose adsorption power for strongly adsorbed components is similar to that of the adsorbent for the desorbent. In addition, in this adsorption separation method, the adsorbent washed with a desorbent in order to drive out the strongly adsorbed components in the desorption operation (2) is transferred to the adsorption operation (1) while containing the desorbent, and the raw material is supplied. Since selective adsorption of the strongly adsorbed components in the substance is carried out, competitive adsorption between the strongly adsorbed components and the desorbent remaining in the adsorbent occurs in the adsorption operation. Therefore, another important factor required when selecting a desorbent is that since the selective adsorption of halogenated toluene is carried out in the presence of the desorbent, isomers other than the strongly adsorbed components of the adsorbent are The selective adsorption capacity for strongly adsorbed components when compared to the desorbent must not be impaired by the presence of the desorbent. The selective adsorption ability of the adsorbent for the strongly adsorbed component when compared with isomers other than the strongly adsorbed component and the desorbent is the selective adsorption rate of the strongly adsorbed component expressed by equation (a) α (A/B or D) It can be displayed in α(A/B or D) = (weight fraction of A in adsorbed phase/weight fraction of B or D component in adsorbed phase/(weight fraction of A in non-adsorbed phase/weight fraction of A in non-adsorbed phase) (weight fraction of component B or D)...(a) where A is a strongly adsorbed component, B is an isomer other than the strongly adsorbed component, D is a desorbent, and the adsorbed phase and non-adsorbed phase are in equilibrium. In equation (a), the larger the value of α (A/B) compared to 1, the more selectively the strongly adsorbed component is adsorbed compared to other isomers. Low α (A/B) means a decrease in the selective adsorption power of the strongly adsorbed component, and if a highly purified strongly adsorbed component is to be recovered, the concentration of the strongly adsorbed component in the raffinate flow increases, and the strongly adsorbed component recovery rate decreases.
If an attempt is made to improve the recovery rate of the strongly adsorbed components, isomers other than the strongly adsorbed components will increase in the extract stream, and a decrease in the purity of the recovered strongly adsorbed components will be unavoidable. α (A/D) in equation (a) indicates the selective adsorption rate of the strongly adsorbed component compared to the desorbent, but in order for the desorbent and the strongly adsorbed component to be adsorbed almost equally, α
(A/D) is preferably a value close to 1, particularly in the range of 0.5 to 2.0. If α (A/D) is much larger than 1, a large amount of desorbent is required to expel the strongly adsorbed components selectively adsorbed from the adsorbent during the desorption operation, or most of the strongly adsorbed components are removed. It becomes impossible to expel the adsorbed components, which reduces the recovery rate of strongly adsorbed components and becomes uneconomical. On the other hand, if α(A/D) is too small than 1, the adsorbent will be difficult to be expelled by the strongly adsorbed components in the raw material feed during the adsorption operation, and as a result, the adsorption of the strongly adsorbed components will be hindered, resulting in strong adsorption. This results in a substantial reduction in the adsorption capacity of the component, increasing the concentration of the strongly adsorbed component in the roughinate stream and reducing the recovery rate of the strongly adsorbed component, which is also uneconomical. Therefore, when selecting a desorbent to be used in a method for adsorbing and separating a halogenated toluene isomer mixture, it is necessary to select a desorbent that has a higher α (A/B) measured in the presence of the desorber and α (A/D). Selecting a desorbent with a value close to 1 is an extremely important requirement for increasing the economic efficiency of the adsorption separation method of the present invention. From the above points of view, the present inventors conducted extensive research to find a better desorbent, and as a result, they found that a desorbent containing an alkyl aromatic hydrocarbon has extremely high performance compared to conventional ones. The present invention was achieved by discovering that the following is true. That is, the present invention provides a method for adsorbing and separating halogenated toluene isomers including o-, m-, and p-halogenated toluene using a zeolite adsorbent, in which an alkyl aromatic hydrocarbon is used as an essential component as a desorbent. The present invention provides a method for separating p-halogenated toluene isomers, which comprises using a desorbing agent containing p-halogenated toluene isomers. The usefulness of alkyl aromatic hydrocarbons as a desorbent is demonstrated by their high selective adsorption rate (α
(A/B)), and the selectivity α(A/D) of the strongly adsorbed component to the desorbent is close to 1. Therefore, by using the alkyl aromatic hydrocarbon as the desorbent of the present invention, p-halogenated toluene isomers can be separated more economically. In the present invention, an alkyl aromatic hydrocarbon refers to an alkyl group having 1 to 3 carbon atoms attached to a benzene nucleus.
It means a 4-substituted monocyclic alkyl aromatic hydrocarbon, and preferable examples thereof include toluene, ethylbenzene, meta-xylene, ortho-xylene, meta-diethylbenzene, ortho-diethylbenzene, and para-diisopropylbenzene. As the desorbent in the method of the present invention, these alkyl aromatic hydrocarbons may be used alone or in combination, or may be used together with a diluent such as paraffin or cycloparaffinic hydrocarbon. The zeolite adsorbent used in the method of the present invention is not limited to a specific one, but mainly contains one or two cations selected from Group A metals other than sodium, Group A metals, and protons. Faujasite-type zeolite containing zeolite and the like are preferred adsorbents. In particular, Y-type zeolite whose cation is potassium is preferred. Of course, it is also preferably used that additionally contains at least one other cation component such as strontium, barium, zirconium, yttrium, and proton. The operating conditions for the adsorption separation method of the present invention include a temperature of 0 to 350°C, particularly preferably room temperature to 250°C;
Further, the pressure is selected from atmospheric pressure to 40 kg/cm ² , particularly preferably from approximately atmospheric pressure to 30 kg/cm ² . Although the adsorption separation method of the present invention can be carried out in either gas phase or liquid phase,
Liquid phase operation is more preferred in order to lower operating temperatures and reduce undesirable side reactions of the feedstock or desorbent. Next, the method of the present invention will be explained by giving examples. Example 1 The adsorbent was sodium-type zeolite Y, which was ion-exchanged with potassium nitrate for more than 90% of the sodium ions, and dried at 120°C for 5 hours.
A KY type adsorbent was prepared by baking at 500°C for 1 hour. 1.8 of the adsorbent in an autoclave with an internal volume of 5 ml.
g and chlorotoluene (CT) isomer mixture,
2.5 g of a liquid phase mixture consisting of an alkyl aromatic hydrocarbon and n-nonane was charged and left at 130°C for about 1 hour with occasional stirring. The composition of the liquid phase mixture charged here was n-nonane: o-CT: m-CT: p-CT: alkyl aromatic hydrocarbon 1:1:1:1:4 (weight ratio). - Nonane was added as a reference material in gas chromatography analysis, and under the above conditions it is a substance that is substantially inert to the adsorbent. The composition of the liquid phase mixture after contact with the adsorbent was analyzed by gas chromatography, and the selective adsorption rate was calculated from the amount of change in the composition of the liquid phase mixture. The results are shown in Table 1.

[Table] Comparative Example 1 When no desorbent was used in Example 1,
Table 2 shows the selective adsorption rates when chlorobenzene was used as the desorbent.

[Table] Example 2 Table 3 shows the selective adsorption rate when the mixture shown below was used as the raw material in Example 1. n-nonane: o-CT: p-CT: alkyl aromatic hydrocarbon = 1:1:1:3

[Table] Example 3 In Example 1, the selective adsorption rate was calculated using an adsorbent in which some of the potassium ions in the KY type adsorbent were replaced with protons, zirconium, and strontium, and toluene was used as the desorbent. It is shown in Table 4.

[Table] Example 4 Table 5 shows the selective adsorption rate when the mixture shown below in Example 1 was used as a raw material. n-nonane: m-bromotoluene (m-
BT): p-bromotoluene (p-BT): ethylbenzene = 1:1:1:3 Comparative Example 2 In Example 4, when chlorobenzene was used instead of the alkyl aromatic hydrocarbon and no desorbent was used. Table 5 also shows the selective adsorption rate.

[Table] Example 5 o-CT:m-CT:p-CT=51.6:34.9:
A CT isomer mixture consisting of 13.5 wt% was adsorbed and separated using the simulated moving bed apparatus shown in FIG. FIG. 1 will be briefly explained. Adsorption chambers 1 to 16 each having an internal volume of about 13 ml were filled with the adsorbent prepared in Example 1. Toluene, a desorbent, was supplied from line 17 at a rate of 383.8/hr, and the above isomer mixture was supplied from line 19 at a rate of 33.5 ml/hr. Extract flow from line 18
Roughinate flow was withdrawn from line 20 at 63.4 ml/hr, and the remaining fluid was withdrawn from line 21 at 87.9 ml/hr. In addition, adsorption chambers 1 and 1
Fluid flow between the valves 6 and 6 is closed by a valve 22. At this time, change adsorption chamber 1 to 16 at approximately 110 second intervals.
15 was moved to 14, 10 to 9, and 5 to 4 at the same time (the other adsorption chambers were also moved upward by one adsorption chamber at the same time). The adsorption temperature was 110°C. The purity of p-CT in the CT isomer mixture contained in the extract stream obtained in the above experiment was 99.2%.
The recovery rate of p-CT was over 95%.

[Brief explanation of the drawing]

FIG. 1 shows one embodiment of the invention. FIG. 2 is a diagram schematically showing an adsorption separation operation using a simulated moving bed. 1-16...Adsorption chamber, 17...Desorbent supply line, 18...Extract extraction line, 19
...isomer mixture supply line, 20 ... roughinate extraction line, 21 ... desorbent recovery line,
22...Valve.

Claims (1)

[Claims] 1 In a method for adsorbing and separating p-halogenated toluene isomers from a halogenated toluene isomer mixture containing o-, m-, and p-halogenated toluene using a zeolite-based adsorbent, an alkyl aromatic hydrocarbon is used as a desorbent. 1. A method for separating p-halogenated toluene isomers, the method comprising using a desorbent containing p-halogenated toluene isomers as an essential component.