JPH08217701A - Method for separating p-xylene - Google Patents

Abstract

PURPOSE: To efficiently separate high-purity p-xylene by bringing a 8C aromatic hydrocarbon mixture containing p-xylene into contact with a specific adsorbent in the presence of a specific desorbing agent having high desorbing performances and carrying out adsorption and separation treatment. CONSTITUTION: (A) An 8C aromatic hydrocarbon mixture containing p-xylene is brought into contact with (C) a Y type zeolite adsorbent containing potassium and having >=5 molecular ratio of silica/alumina in the presence of (B) a desorbing agent of naphthalene or a lower alkylnaphthalene [preferably a lower alkylnaphthalene of the formula (R<1> and R<2> are each H or a lower alkyl with the proviso that at least one of R<1> and R<2> us a lower alkyl)] and p-xylene is selectively adsorbed. p-Xylene is desorbed from the adsorbent by the desorbing agent and separated. The desorption and separation treatment are preferably carried out on a pseudomoving bed. The amount of the component B used is preferably 1-5 pts.wt. based on 1 pt.wt. component A.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to C containing paraxylene.
_The present invention relates to a method for separating para-xylene with high purity by subjecting an aromatic hydrocarbon mixture to adsorption separation treatment.

[0002]

2. Description of the Related Art Conventionally, in order to separate para-xylene contained therein from a C ₈ aromatic hydrocarbon mixture, the raw material mixture is adsorbed by a crystalline aluminosilicate (zeolite) containing a Group IA or Group IIA metal ion. After adsorbing para-xylene by contact with the agent, a desorbent composed of diethyltoluene is contacted with the adsorbent containing para-xylene,
A method for desorbing paraxylene contained in the adsorbent is known (Japanese Patent Laid-Open No. 3-77834). However, according to the research conducted by the present inventors, it was found that the performance of diethyltoluene, which is used as a desorbing agent in this method, is not yet satisfactory as a desorbing agent.

[0003]

[SUMMARY OF THE INVENTION The present invention, in order to selectively separate paraxylene contained from C ₈ aromatic hydrocarbon mixture to, contacting the C ₈ aromatic hydrocarbon mixture with the zeolite adsorbent After adsorbing para-xylene, in the method of desorbing para-xylene by contacting the adsorbent containing the para-xylene with the adsorbent, by using a desorbent having enhanced desorption performance The task is to provide a method of separation.

[0004]

As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that lower alkylnaphthalene has excellent performance as a desorbing agent, and have completed the present invention. I arrived. That is, according to the present invention, in a method for adsorbing and separating para-xylene from a C ₈ aromatic hydrocarbon mixture containing para-xylene, the raw material mixture containing metal potassium in the presence of a desorbing agent, silica / alumina mole The method comprises contacting a Y-type zeolite adsorbent having a ratio of 5 or more to selectively adsorb para-xylene to the adsorbent, and then desorbing para-xylene from the adsorbent with a desorbent. , Naphthalene or lower alkylnaphthalene is used to provide a method for separating para-xylene.

The C ₈ aromatic hydrocarbon mixture used as a raw material in the present invention contains para-xylene. Such a mixture includes a mixture of at least one selected from ortho-xylene (o-xylene), meta-xylene (m-xylene) and ethylbenzene and para-xylene (p-xylene). In this raw material mixture, the content of para-xylene is usually
It is 5% by weight or more, preferably 10 to 40% by weight.

The adsorbent used in the present invention is a Y-type zeolite containing potassium. In this zeolite, the silica / alumina molar ratio is 5 or more, preferably in the range of 5.0 to 6.0. When the silica / alumina molar ratio is smaller than this range, the amount of the adsorbed substance per unit weight of the adsorbent decreases, which is not preferable. The adsorbent used in the present invention has a K ion exchange rate of 80% or more, preferably 90% or more. The particle size of the adsorbent is 10-150 mesh, preferably 20-
It is 80 mesh, and may be appropriately selected depending on the type of adsorption bed. Further, the adsorbent can be adjusted in its water content to improve its adsorption selectivity. The water present in the adsorbent is either partially contained at the K ion or base exchange positions or contained in the voids of the adsorbent. Moisture content measured by weight loss under burning at 1000 ° C is 0-10 wt% based on the weight of adsorbent
It is preferably in the range of%. The water content can be adjusted by adding an appropriate amount of water to the raw material mixture.

The desorbent used in the present invention is naphthalene or lower alkylnaphthalene. The lower alkylnaphthalene is one having 1 or 2 to 4 lower alkyl groups. The lower alkyl group may be an alkyl group having 1 to 4 carbon atoms such as a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group and a t-butyl group. The preferred lower alkylnaphthalene used in the present invention has a boiling point of 240 to 400 ° C., preferably 2
Those having a temperature of 40 to 350 ° C., particularly those represented by the following general formula are preferable.

Embedded image In the above formula, R ¹ and R ² represent hydrogen or a lower alkyl group, at least one of which is a lower alkyl group. The use ratio of the desorbent is not particularly limited, but when the separation is performed by a simulated moving bed system, it is usually used in a ratio of 1 to 5 parts by weight with respect to 1 part by weight of the raw material mixture.

In the present invention, the adsorbent composed of naphthalene or lower alkylnaphthalene as described above is used in combination with the specific zeolite adsorbent, so that the adsorbate (p-xylene and adsorbent per unit weight of the adsorbent is used) It is possible to improve the amount of other C ₈ aromatic hydrocarbons) and to obtain a p-xylene adsorption separation process with high equipment efficiency.
Further, since the desorbent used in the present invention has a boiling point higher than that of the C ₈ aromatic hydrocarbon as described above, the desorbent is separated by distillation from the raffinate or extract in the adsorption separation operation of the raw material mixture. At this time, the desorbent can be separated and recovered as a bottom product of the distillation column. Therefore,
In the case of the present invention, it is not necessary to evaporate the desorbent used in large amounts, so that the consumption of heat energy can be small, and as a result, the operating cost of the apparatus can be reduced.

The adsorption / separation method of the present invention includes an adsorption step and a desorption step. The temperature in the adsorption / desorption step is 150 to 300 ° C., preferably 150 to 250 ° C., and the pressure is liquid phase in the system. It is sufficient if the pressure is sufficient to maintain the state. The adsorptive separation method of the present invention is carried out by a chromatographic method, and can be carried out in any system such as a fixed bed, a fluidized bed and a moving bed, but industrially it is preferably carried out in a simulated moving bed system. . Adsorption separation by the simulated moving bed method is an already established technology.

The adsorption separation by the simulated moving bed system will be described in further detail. This adsorption separation technique is carried out by continuously circulating the following adsorption operation, concentration operation, desorption operation and desorbent recovery operation as basic operations. To be done. (1) Adsorption operation: The raw material to be treated comes into contact with the zeolite adsorbent, the target adsorption component as a strong adsorption component is selectively adsorbed, and the other component, which is a weak adsorption component, is recovered as a raffinate stream together with the desorbent. It (2) Concentration operation: The adsorbent that selectively adsorbs the adsorbed target component is brought into contact with a part of the extract described later, and the non-adsorbed component remaining on the adsorbent is expelled to concentrate the target component. It (3) Desorption operation: The adsorbent containing the concentrated adsorption target component is brought into contact with the desorption agent to expel the adsorption target component from the adsorbent, and is collected as an extract stream together with the desorption agent. (4) Desorbent recovery operation: The adsorbent that has substantially adsorbed only the desorbent contacts a part of the raffinate stream, and a part of the desorbent contained in the adsorbent is recovered as a desorbent recovery stream.

FIG. 1 shows a schematic diagram of an adsorption separation operation using a simulated moving bed. In this figure, 1 to 16 are adsorption chambers containing a zeolite adsorbent, which are connected to each other. 1
7 is a desorbent supply line, 18 is an extract extraction line, 19 is a raw material supply line, 20 is a raffinate extraction line, and 21 is a recycle line. In the arrangement state of the adsorption chambers 1 to 16 and the lines 17 to 20 shown in FIG. 1, the adsorption chambers 1 to 3 are desorbed, the adsorption chambers 4 to 8 are concentrated, the adsorption chambers 9 to 13 are adsorbed, and the adsorption chambers are adsorbed. The desorbent recovery operation is performed in each of 14 to 16. In such a simulated moving bed, each supply and extraction line is moved by one valve in the liquid flow direction by one adsorption chamber at regular time intervals. Therefore, in the next arrangement state of the adsorption chambers, the desorption operation is performed in the adsorption chambers 2 to 4, the concentration operation is performed in the adsorption chambers 5 to 9, the adsorption operation is performed in the adsorption chambers 10 to 14, and the desorbent recovery operation is performed in the adsorption chambers 15 and 16. Will be carried out respectively. By performing such an operation in sequence, the adsorption separation process by the simulated moving bed is achieved. In the drawing, the adsorption chamber is 1
It should be noted that although the number of adsorption chambers is specified to be 6, the number of adsorption chambers is not limited.

FIG. 2 shows an example of a flow sheet for carrying out the adsorption separation method of the present invention. In FIG. 2, A is an adsorption separation column, and B and C are distillation columns. The raw material C ₈ aromatic hydrocarbon mixture is supplied to the adsorption separation column A through the line 25, and the circulating desorbent is introduced into the adsorption separation column A through the line 32. In the adsorption separation column A, para-xylene is selectively adsorbed and separated, and the extract containing this para-xylene as a main component is extracted through a line 26.
On the other hand, the raffinate containing C ₈ aromatic hydrocarbons other than para-xylene is withdrawn through line 27. Line 2
The raffinate withdrawn through 7 is introduced into the distillation column C, where it is subjected to a distillation treatment, and the desorbent contained in the raffinate is withdrawn through the line 31 from the bottom of the distillation column and desorbed. The raffinate after separation of the agent is withdrawn through line 30 as the overhead of the distillation column. This raffinate contains a C ₈ aromatic hydrocarbon other than paraxylene as a main component.

On the other hand, the extract withdrawn from the adsorption / separation column A through a line 26 is introduced into a distillation column B, where it is subjected to a distillation treatment, and the desorbent contained in the extract is the bottom of the distillation column. Is extracted through the line 29.
Paraxylene is recovered from the top of the distillation column B through a line 28. The desorbents extracted from the bottoms of the distillation top column B and the distillation column C through lines 29 and 31, respectively, are circulated to the adsorption separation column 20 through a line 32.

[0014]

EXAMPLES The present invention will now be described in more detail with reference to examples, but the present invention is not limited to these examples. Note that the relative separation coefficient β shown below
The value gives an index of the strength of the relative adsorption force of the mixed components based on P-xylene when the raw material mixture containing P-xylene is subjected to adsorption treatment using a zeolite adsorbent. Indicated by. The larger this β value is, the more difficult it is to be adsorbed by the adsorbent. β [i] = K [PX] / K [i] β [i]: Relative separation coefficient of mixed component i K [i]: Adsorption equilibrium constant of mixed component i K [PX]: Adsorption equilibrium constant of P-xylene K [i] = (wt% of component i in the adsorption phase) / (wt% of component i in the liquid phase) K [PX] = (wt% of P-xylene in the adsorption phase) /
(Wt% of P-xylene in liquid phase)

Example 1 As a raw material of a C ₈ aromatic hydrocarbon mixture having the composition shown in Table 1, an adsorption separation experiment was conducted. The adsorbent used in the experiment was a Y-type zeolite containing K, Li, Pb or Ba and having a silica / alumina ratio of 5.5 and having a particle size of 40-8.
It is 0 mesh.

(Adsorption separation experiment) About 4.0 g of adsorbent, about 3.0 g of feed oil, and about 7.0 g of desorbent β-isopropylnaphthalene were charged in an autoclave having an internal volume of 30 cc,
The temperature was raised to 120 ° C. with stirring and kept for 120 minutes. The adsorbent and the raw material residual liquid were separated by filtration, and the adsorbate in the adsorbent was desorbed by washing the adsorbent with isooctane and then Soxhlet extraction for 2 hours using a toluene solvent. The compositions of the raw material residual liquid (liquid phase) and the substance to be adsorbed (adsorption phase) were analyzed by gas chromatography, and the relative separation coefficient β value was calculated. Table 2 shows the results. As can be seen from the results shown in Table 2, when the adsorbent and desorbent specified in the present invention are used, P-xylene can be selectively adsorbed and separated from other components.

[0017]

[Table 1]

[0018]

[Table 2]

Example 2 The same adsorption separation experiment as in Example 1 was conducted, except that KY type zeolite having various silica / alumina molar ratios was used as the adsorbent. Table 3 shows the results. In addition, Table 3 shows the amount (g) of the adsorbed material per 1 g of the adsorbent. The amount of the adsorbed substance was measured by measuring the amount of the adsorbed substance separated from the adsorbent by Soxhlet extraction in the adsorption separation experiment, and based on the measured value, the amount of the adsorbed substance per 1 g of the adsorbent (g).
Is calculated.

[0020]

[Table 3]

Example 3 The same as Example 1 except that KY type zeolite having a silica / alumina molar ratio of 5.5 was used as the adsorbent and various alkyl aromatic hydrocarbons were used as the desorbent. An adsorption experiment was conducted. The results are shown in Table 4.

[0022]

[Table 4]

Example 4 Using the simulated moving bed type continuous adsorption separation device shown in FIG. 1, the KY type zeolite shown in Example 1 as the adsorbent and β-isopropylnaphthalene as the desorbent were used, and the temperature was 190. A separation test was carried out at a temperature of 8 ° C. and a pressure of 8 kg / cm ² G. The adsorbent was filled in column adsorption chambers 1 to 16 having an internal volume of 70 ml, the raw material was supplied from line 19 at 370 ml / hr, and the desorbent was supplied from line 17 at 806 ml / hr. Extract from line 18 to 538 ml / hr
And raffinate from line 20 with 638 ml
/ Hr. At this time, the supply lines of the raw material and the desorbent and the extraction lines of the extract and raffinate were simultaneously moved in the direction of the liquid flow by 90 minutes at intervals of 90 seconds. P-xylene was obtained from the extract, and its P-xylene concentration was 99.3 wt% on a desorbent-free basis, and the recovery rate was 95 wt%.

[0024]

According to the present invention, due to the excellent desorption performance of the lower alkylnaphthalene used as the desorbent, the relative separation coefficient β of the xylene isomer based on para-xylene is β
Is high, and the para-xylene contained in it can be separated with high purity and efficiency from a C ₈ aromatic hydrocarbon mixture.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an adsorption separation operation by pseudo mobility.

FIG. 2 is an example of a flow sheet for obtaining high-purity para-xylene from a C ₈ aromatic hydrocarbon mixture according to the present invention.

[Explanation of symbols]

 1-16 Adsorption chamber 17 Desorbent supply line 18,26 Extract extraction line 19,25 Raw material supply line 20,27 Raffinate extraction line 21 Recycle line 22 Pump A Adsorption separation column B, C Distillation column

Claims (2)

[Claims] 1. A method for adsorbing and separating paraxylene from a C ₈ aromatic hydrocarbon mixture containing paraxylene, the raw material mixture containing potassium in the presence of a desorbing agent, and having a silica / alumina molar ratio of 5 or more. And adsorbing para-xylene to the adsorbent selectively, and then desorbing the para-xylene from the adsorbent with a desorbent. A method for separating para-xylene, which comprises using alkylnaphthalene. 2. The method according to claim 1, wherein the adsorption separation process is carried out in a simulated moving bed.