JPH05154303A - Method for separating ethylbenzene or mixture of ethylbenzene and paraxylene from mixture of xylene isomers - Google Patents

Abstract

PURPOSE: To provide an adsorptive separation method of a xylene isomer mixture by using carbon dioxide as a carrier and a desorbent. CONSTITUTION: By introducing a certain amount of a xylene isomer mixture with a carrier of high pressure phase carbon dioxide into a bed of high silicon zeolite adsorbent, adsorption is performed and the first product flow including large amounts of metaxylene and orthoxylene is obtained after passing through the adsorbent bed. After a mixture of ethylbenzen and paraxylene appears in the flow, supercritical carbon dioxide under higher pressure is introduced to sorb the absorbent bed thereby obtaining the second product flow including large amounts of ethylbenzen and paraxylene. It is preferable to introduce each of the first product flow and the second product flow to different absorbent beds of active carbons, to adsorb those xylene isomers products under isothermal and isobaric conditions and to reuse while circulating substantially pure carbon dioxide passing through those adsorbent beds of active carbons.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for separating a mixture of xylene isomers, more specifically, carbon dioxide as a carrier and a desorbent, a high silicon zeolite as an adsorbent, and ethylbenzene or ethylbenzene and parabenzene from a mixture of xylene isomers. Method for separating a xylene mixture relates to a method for separating ethylbenzene or a mixture of ethylbenzene and para-xylene from a xylene isomer mixture.

[0002]

BACKGROUND OF THE INVENTION Xylene isomer mixtures occur in general naphtha cracking plants and reforming plants.
-Includes four important petrochemical raw materials such as xylene (OX), m-xylene (MX), p-xylene (PX) and ethylbenzene (EB), OX is a source of phthalic anhydride and MX is isophthalic acid. It is a raw material of acid and is isomerized into p
It can also be xylene, PX being the raw material for polyester fibers and EB being the raw material for styrene. The boiling points of the components in the xylene isomer mixture are very close (E
B, 136.2 ° C; PX, 138.1 ° C; MX, 139.1
(° C; OX, 144.4 ° C), so it is difficult to separate by the distillation method. In order to separate the xylene isomer mixture by the freezing crystallization method from the conventional method, this mixture is frozen, p-xylene is first crystallized, and other components are left in the liquid phase, but there are many drawbacks to this frozen crystallization method. However, for example, it requires a considerable amount of energy, and the yield of p-xylene reaches only 73% at most due to the limitation of the liquid-solid phase equilibrium.

At present, it is recognized in the industry that the selective adsorption method in which a zeolite is used as an adsorbent in a liquid phase or a gas phase is most economical in a separation process of xylene isomers. 3rd, 558,732; 3,943,183; 4,05
1,192; 4,326,091; 4,439,535 and the like. These methods usually require a desorbent. The most commonly used deattaching agents include isopropylbenzene, para-diethylbenzene, toluene and the like. DM Ru for details
thven's Principles of Adsorption and Adsorption
Processes ", John Wiley & Sons New York (1984). Sautacesaria, E. et al. "Separaation
of Xylenes on Y Zeolites, in the Vapor Phase. 1.
Determination of the Adsorption Equilibrium Param
eters and of the Kenetic Regime '', Ind. Eng. che
m. Process Dev. 24, 78-83 (1985) disclosed the separation of xylene isomers in a gas phase state with Y zeolite, and the separation in the gas phase was superior to the separation in the liquid phase and the desorption was performed. It was found that the amount of adsorbent used was also small.

All of the above separation methods require a considerable amount of energy because the desorbent has to be recovered by distillation.

[0005] One of the inventors of the present invention, Sunko Tan and Cai Masaru, "Separation of Xylene Isomers on Silicalite in S
upercritical and Gaseous Carbon Dioxide '', Ind. En
g.chem. Res., Vol. 29, 502-504 (1990), high silicon zeolite (silicalite) adsorbent, gas state and supercritical
(Supercritical) carbon dioxide is used as a carrier to separate equal weight para-xylene and meta-xylene isomer mixture, and it is disclosed that gaseous carbon dioxide exhibits a separation effect superior to that of supercritical carbon dioxide. influence on the separation effect of the flow rate also studied, volume of 1 cm ³ Purus feed (a
Pulse of 1.0cm ³ of Xylene Isomers Feed) and 3
With 9.5 g of high silicon zeolite adsorbent, the most suitable operating conditions are a temperature of about 358 ° K and a pressure of about 47.6 atm.
And the flow rate is about 15.0 cm ³ / min.

The main object of the present invention is to provide a method for carrying out adsorption separation for a xylene isomer mixture using carbon dioxide as a carrier and a desorbent. Preferably, the carbon dioxide is recovered in the isothermal and isobaric adsorption step and recycled. Therefore, the desorbent used in the conventional adsorption / separation method is not used, and the distillation separation step of the desorbent, which consumes a large amount of energy, can be omitted.

[0007]

SUMMARY OF THE INVENTION To achieve the above object, the present invention provides a method for separating a mixture of ethylbenzene and para-xylene from a mixture of xylene isomers, using high-pressure gaseous carbon dioxide as a carrier, the mixture of xylene isomers being a high-silicon zeolite. Sent to the adsorbent bed for adsorption, to obtain a first product stream containing a large amount of metaxylene and orthoxylene that has passed through the adsorbent bed, and the mixture of ethylbenzene and para-xylene in the mixture begins to appear in the product stream. From the above, a second product stream containing a large amount of ethylbenzene and para-xylene is obtained by introducing high-pressure supercritical carbon dioxide and desorbing the adsorbent bed. Preferably, the first product stream and the second product stream are respectively sent to different activated carbon adsorbent beds, and these xylene isomer products are adsorbed under isothermal and isobaric pressures so as to be substantially pure through the activated carbon adsorbent beds. Recycled fresh carbon dioxide. Further, the adsorption of the high-pressure gaseous carbon dioxide is optionally carried out until all the meta-xylene, ortho-xylene and para-xylene in the mixture are almost deposited, and then the supercritical carbon dioxide is introduced to remove the adsorbent bed. It is also possible to adsorb and obtain a second product stream rich in ethylbenzene.

In the above method of the present invention, the adsorption force of the adsorbent is changed by changing the pressure of carbon dioxide, and the deadsorbent is not used. Therefore, the problem of distillation recovery of the adsorbent is avoided. Further, since the carbon dioxide can be preferably separated from the xylene isomer product at isothermal and isobaric pressure, it can be directly recovered and recycled without applying temperature and pressure. Therefore, it is possible to avoid the disadvantage that the carbon dioxide carrier cannot be reused unless a pressure-increasing step that consumes more energy is added during gas-liquid separation of the product and the carrier by depressurization as in the conventional method. ..

[0009]

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for separating an ethylbenzene and paraxylene mixture from a xylene isomer mixture, which mixture additionally contains metaxylene and orthoxylene. (a) using a high-pressure gaseous carbon dioxide stream as a carrier, sending a certain amount of the xylene isomer mixture to a high-silicon zeolite adsorbent bed for adsorption, and containing a large amount of meta-xylene and ortho-xylene that have passed through the adsorbent bed. A first product stream is obtained, (b) after most of the meta-xylene and ortho-xylene in the mixture feed have precipitated, a higher pressure supercritical carbon dioxide stream is introduced to desorb the adsorbent bed, A second product stream rich in para-xylene and ethylbenzene is obtained, and (c) the second product stream is first
It is sent to the bed of activated carbon adsorbent, and paraxylene and ethylbenzene in it are adsorbed and collected at about isothermal and isobaric pressure, and the high-purity carbon dioxide flow through these beds of activated carbon adsorbent is supercritical carbon dioxide of (b). Recycled to the carbon stream, (d) desorbing the first activated carbon adsorbent bed to obtain a product mixture of paraxylene and ethylbenzene, and (e) sending the first product stream to a second activated carbon adsorbent bed. , At about isothermal and isobaric pressure, the meta-xylene and ortho-xylene therein are adsorbed and collected, and the high-purity carbon dioxide stream that has passed through the second activated carbon adsorbent bed is recycled by The second activated carbon adsorbent bed is desorbed to obtain a mixture product of meta-xylene and ortho-xylene.

The present invention also provides a method for separating ethylbenzene from a mixture of xylene isomers, which mixture additionally contains meta-xylene, ortho-xylene and para-xylene, the method comprising: (a) ' A high-pressure gaseous carbon dioxide stream is used as a carrier, and a certain amount of the xylene isomer mixture is sent to a bed of high-silicon zeolite adsorbent to adsorb ethylbenzene, and the first mixture containing substantially no ethylbenzenelen which has passed through the bed of adsorbent is adsorbed. After obtaining a product stream, (b) 'most of the other isomers of ethylbenzene in the mixture feed have been deposited and then a higher pressure supercritical carbon dioxide stream is introduced to desorb the adsorbent bed, The second containing a lot of ethylbenzene
After obtaining the product stream, (c) 'sending the second product stream to the first activated carbon adsorbent bed, adsorbing and collecting ethylbenzene in it at about isothermal and isobaric pressure, and passing it through the first activated carbon adsorbent bed. Recycle the pure carbon dioxide stream to the (b) 'supercritical carbon dioxide stream,
(d) 'The first activated carbon adsorbent bed is desorbed to obtain a product of ethylbenzene, (e)' The first product stream is sent to the second activated carbon adsorbent bed, and the product is fed at about isothermal and isobaric pressure. Adsorbing and collecting the xylene isomers of, and recirculating the high-purity carbon dioxide stream passing through the second activated carbon adsorbent bed to desorb the second activated carbon adsorbent bed. , Their xylene isomers are obtained.

The xylene isomer mixture used in the method of the present invention is preferably a xylene isomer mixture obtained in a large amount in the petrochemical industry. For example, o-, m-, p- generated in a naphtha cracking plant or reforming plant. It contains four components, xylene and ethylbenzene, and generally has a composition of 5-75% by weight of ethylbenzene and 10-4 of meta-xylene.
5% by weight, 5-45% by weight ortho-xylene and 5-25% by weight para-xylene. In a preferred embodiment of the present invention, the weight composition is ethylbenzene 54.55%, metaxylene 2
6.43%, paraxylene 10.10%, orthoxylene 8.
The raw material is a mixture of 92%. However, a mixture of three or two components of the above four xylene isomer components is also applicable to the method of the present invention.

The high silicon zeolite used in the present invention has a Si / Al ratio of 500 or more, and the larger the ratio, the better the separation effect. The Si / Al value used in the examples of the present invention was 10
40 has a better separation effect than 540. Basically, there are no particular restrictions on the shape and size of the adsorbent, but we prefer 24-32 mesh powdery high-silicon zeolite to a cylindrical high-silicon zeolite with a diameter of 1.55 mm and a length of 6.2 mm. We found that the separation effect was good. Speaking from the object of the present invention, any zeolite having the ability to separate xylene isomers in gaseous carbon dioxide and capable of desorbing by washing supercritical carbon dioxide is effective or operated with the high silicon zeolite of the present invention. Should be regarded as the equivalent.

In the above steps (a) and (a) ', when adsorption separation is carried out using high-pressure gaseous carbon dioxide, the operating temperature is 323-
393 ° K, preferably about 340-360 ° K, operating pressure is 500-800 psia, preferably about 600-70
It is 0 psia.

In the steps (b) and (b) 'above, when desorbing with supercritical carbon dioxide at a higher pressure, the operating pressure is 1
Should be above 070 psia. As a general rule, the higher the pressure, the faster the desorption, but increasing the pressure also increases equipment and operating costs. Therefore, a pressure of about 1200-1500 psia is preferable.

Basically, the amount of activated carbon used in the first activated carbon adsorbent bed used in the above-mentioned steps (c) and (c) 'is in the second product stream generated in the steps (b) and (b)'. It should be sufficient to fully adsorb the xylene isomer product. Similarly, the
The amount of activated carbon used in the second activated carbon adsorbent bed used in steps (e) and (e) 'is the complete adsorption of xylene isomer products in the first product stream generated in steps (a) and (a)'. Should be sufficient to collect.

In order to desorb the activated carbon adsorbent bed in the above steps (d) and (d) ', (e) and (e)', any known activated carbon regeneration technique in the prior art, such as steam washing, can be used. , Supercritical carbon dioxide cleaning, and similar techniques. When cleaning with supercritical carbon dioxide, the first step in (c) above
The high purity carbon dioxide stream through the activated carbon adsorbent bed can optionally be used to regenerate the second activated carbon adsorbent bed in step (e).

Example 1 Separation of Ethylbenzene and Metaxylene Mixture In this example, the separation system shown in FIG. 1 is used to separate a mixture containing equal weight of ethylbenzene and metaxylene. The adsorbent used in this example is a high silicon zeolite, obtained from Union Carbide Co., USA, its structure is similar to ZSM-5, the pore size is about 6Å, Si
/ Al value is 1040. The main difference between ZSM-5 and high silicon zeolite is that the content of aluminum in the crystal of high silicon zeolite is low. The high silicon zeolite is a pellet having a diameter of about 1.55 mm and a length of about 6.2 mm, and its physical properties are shown in Table 1.

[0018]

[Table 1] The surface area in Table 1 was measured by the BET (Brunaauer-Emmett-Teller) method, and the pore volume was measured by the nitrogen adsorption method and the mercury method, respectively. Pore larger than this data (> 600Å)
Indicates that the proportionality of is not small.

Before using the above-mentioned high silicon zeolite, it is first dried in a high temperature oven at 120 ° C. for 4 hours, further heated to 600 ° C. for 24 hours to be activated by firing, and then lowered to 120 ° C. , Weigh and quickly place on the adsorption packed bed 11.

The packed bed 11 has an inner diameter of 2.12 cm and a length of 25 c.
It is a 316 stainless steel cylinder of m.
Approximately 14 cm in height of 9.5 g of treated high silicon zeolite
To fill. In order to obtain a uniform distribution in the flow through the packed bed, glass beads having a diameter of 0.1 cm were filled at 6.3 cm and 5.3 cm, respectively, above and below the high silicon zeolite packing section.

An equal weight of reagent grade ethylbenzene and meta-xylene were mixed to prepare a feed mixture to be separated. As shown in FIG. 1, this mixture is sent by a pump 9 to a 6-point sampling valve 7 (Rheodyne), in which the sampling loop has a feed mixture volume of 1.0 ml. Carbon dioxide having a purity of at least 99% or more in the cylinder 1 is first passed through a bed of zeolite 4A to remove all the above-mentioned carbohydrates, compressed by a diaphragm compressor 4 and sent to a surge tank 5. The pressure was adjusted within ± 5 psi of the desired value by the controller 2 at each measurement, and the temperature was adjusted to the oil bath 13
Adjust to the desired value ± 0.5 ° C with the preheating coil inside.

Before injecting the feed mixture of the sampling loop into the adsorbent packed bed 11, the six-point sampling valve 7 is turned so that carbon dioxide bypasses the sampling loop and is introduced into the packed bed first. After adjusting the metering valve 14 so that the flow rate of carbon dioxide reaches a stable operation flow rate, the six-point sampling valve 7 is turned to allow carbon dioxide to carry the mixture in the sampling loop into the packed bed 11. The fluid flowing out from the packed bed 11 has a metering valve 14
And then flow into the cooling collection bottle 15 at about -20 ° C. Ethylbenzene and meta-xylene are used in the cooling collection bottle 15
The cold collection bottle 15 contains 1.0 L of 95% ethyl alcohol and is placed in an ice bath. A sample (6.0 μl) is taken from the cooling collection bottle 15 every 20 minutes, and the GC (Varian
3700) and analyze its composition. The flow velocity in the packed bed 11 was obtained by measuring the gas volume with a wet gas flow meter 17.

The total amount of EB and MX collected in the cold collection bottle 15 was obtained by measuring the final concentration in the cold collection bottle 15. This total amount is in good agreement with the one obtained by the integral calculation from the concentration-time curve, and this total amount is also very close to the initial injection amount (the error is within 5%). The obtained results are shown in Table 2, and the reaction curves of the partial test are shown in FIGS. 3 and 5.

[0024]

[Table 2]

[Equation 1] The definition of the average retention time t in Table 2 is

[Equation 2] In the formula, C represents concentration and t represents time.

In Table 2, the MX recovery rate refers to the% of the amount collected when the purity of metaxylene flowing out from the packed column is greater than 98%, divided by the feed amount. The definition of EB recovery rate is also the same.

Considering both factors of average retention time and recovery rate,
The data in Table 2 show that a pressure of 600 psia, a temperature of 80 ° C. and a flow rate of 15 cm 3 / min are preferred operating conditions.

In order to further shorten the cycle time for completing the separation, the system pressure is increased to 120 after the metaxylene has flowed out.
Raise to 0 psia to increase the solvency of carbon dioxide for ethylbenzene, allowing ethylbenzene to completely flow out within a shorter time, see FIG. According to the same principle, when the system pressure is further increased when ethylbenzene in the latter stage flows out, the separation cycle can be further shortened.

Example 2 Separation of Paraxylene and Ethylbenzene As Example 1 except that a mixture of paraxylene and ethylbenzene of equal weight was used as the feed mixture and the amount of the feed mixture in the sampling loop was 0.5 ml. Repeat again. The results are shown in Table 3.

From Table 3, the temperature is 120 ° C. and the pressure is 70
0 psia indicates a preferred operating condition. Under these operating conditions, the recoveries of para-xylene and ethylbenzene are 68.4% and 77.5%, respectively.

[0030]

[Table 3] The description of a and b is the same as in Table 2.

[Example 3]: Separation of four-component mixture Composition: meta-xylene 26.0 wt%, ortho-xylene 8.8
% By weight, paraxylene 10.3% by weight, ethylbenzene 5
Separation was carried out in place of the binary isomer mixture of Example 1 with 4.9 wt. 1200ps pressure when time is 120 minutes
Raise to ia. The result of the experiment is shown in FIG. 7.

From FIG. 7, the separation was completed within the operation time of 350 minutes, and the product flowing out from the previous stage was a mixture of metaxylene and orthoxylene, and next was a mixture of paraxylene and ethylbenzene. It is a pure ethylbenzene product. Exclusively this pure ethylbenzene product is 34% by weight of the original ethylbenzene feed
Is. If the mixture of para-xylene and ethylbenzene coming out of the middle stage is subjected to the separation of Example 2 above, a higher yield of ethylbenzene can be obtained.

Further, referring to FIG. 7, the quaternary xylene isomer mixture can be first separated into both parts. The first part contains meta-xylene and ortho-xylene and the second part contains para-xylene and ethylbenzene. The mixture of the second part containing para-xylene and ethylbenzene was further prepared in Example 2.
Separation gives pure ethylbenzene and pure para-xylene products.

[Example 4]: Ethylbenzene was directly separated from the four-component mixture. The composition was 26.43% by weight of meta-xylene and 8.
The same procedure as in Example 1 is repeated except that a mixed quaternary mixture of 92% by weight, 10.10% by weight of paraxylene and 54.55% by weight of ethylbenzene is used as a feed material and the adsorbent amount is 37.63 g.

In this example, operating variables such as temperature, pressure, pressurization and pressurization time are changed to determine the operating conditions that give a better yield of ethylbenzene. The results are shown in Table 4.

[0036]

[Table 4] * Operation time required for separation ** Start time to recover ethylbenzene In Table 4, the high silicon zeolite used in Test 1-7 was a pellet with a diameter of about 1.55 mm and a length of about 6.2 mm. The high silicon zeolite used in 8-10 is particles of mesh 24-32 (0.707-0.5 mm). From the data in Table 4, the latter clearly shows a better separation effect.

Further, in Table 4, the yield of ethylbenzene in Test 8 is the highest (97.1%), but the operating time (380 minutes) is obviously longer than 280 minutes in Test 9. Therefore, in consideration of both factors of yield and recovery cycle, test 9 is superior. FIG. 8 shows the separation result of test 8.

Example 5: Adsorption of xylene isomer product at isothermal and isobaric pressure on activated carbon In this example, a high-pressure carbon dioxide stream containing a xylene isomer product is subjected to isothermal isobaric adsorption of activated carbon on which xylene isomers are adsorbed. The pure carbon dioxide collected from the product and passed through the activated carbon adsorbent bed is immediately recirculated without heating and pressurization to obtain a high-pressure gaseous carbon dioxide carrier or supercritical carbon dioxide in a method of adsorbing and separating a mixture of xylene isomers. It can be a carbon adsorbent.

When 6 g of 8-10 mesh activated carbon granules were used and adsorption collection was carried out at 100 ° C. and 650 psia with different concentrations of meta-xylene (flow rate of carbon dioxide carrier was 15 cm 3 / min), the breakthrough curve was As in 9. From this, the concentration of meta-xylene was 221.9 × 10 ^-6 g / m 2.
In the case of 1, the meta-xylene starts not being adsorbed and collected on the activated carbon after 150 minutes.

FIG. 10 shows one of ethylbenzene with different concentrations.
It is a breakthrough curve at 00 ° C and 1500 psia.
When the concentration of ethylbenzene is 7.84 × 10 ⁻⁴ g / ml, ethylbenzene starts not to be adsorbed and collected on the activated carbon after about 15 minutes.

From FIG. 8 of Example 4, the maximum concentration of precipitated meta-xylene is about 2.0 × 10 ⁻⁴ g / ml, and the separation and deposition time is about 250 minutes. As seen from the breakthrough curve in FIG. 9, when the amount of activated carbon is increased to 10 g, metaxylene and orthoxylene can be completely adsorbed and collected within 250 minutes of the precipitation time.

According to FIG. 8 of Example 4, when the separation / precipitation time of ethylbenzene is about 130 minutes, the breakthrough curve of FIG. 10 indicates that ethylbenzene is completely adsorbed and collected unless the amount of activated carbon is about 54 g or more. I can't.

[Example 6]: Separation operation of xylene isomer mixture From the data of Examples 4 and 5, the mixture is separated in the system shown in Fig. 2, of which carbon dioxide is recycled.

As shown in FIG. 2, first, carbon dioxide is raised to 2500 psia and 100 ° C. by the compressor 4 and the heat exchanger 50, stored in the surge tank 5, and adjusted to a desired operating pressure by the pressure control valves R2 and R3. Then, the circulation pump 22 controls so that the flow rate of carbon dioxide in the system is stabilized at 15 ml / min.
The method of feeding is to introduce carbon dioxide through the sampling valve 7 and a xylene mixed solution. Prior to the feed, first the fixed bed (IV) inlet valve 60 is turned to a 650 psia pressure tube and the outlet valve 61 is turned to the activated carbon bed 20 adsorbing meta-xylene, ortho-xylene and para-xylene. During operation, one fixed bed was fed every 50 minutes, and when the operation time of a single fixed bed reached 200 minutes, the inlet valve 60 was immediately turned to a pressure pipe of 1500 psia and the outlet valve 61.
Is passed through an activated carbon bed 21 for adsorbing ethylbenzene, and 650 psia carbon dioxide originally contained in the bed (that is, refluxed carbon dioxide) is sent to another fixed bed as a feed fluid, and the operation sequence is as shown in Table 5. At 5, the V-bed feed carbon dioxide is the raw I-bed feed carbon dioxide.

[0045]

[Table 5]

The system of FIG. 2 has a total of four activated carbon beds,
When divided into two groups, one group of activated carbon beds 21 absorbs and collects ethylbenzene, and the other group 20 absorbs and collects meta-xylene, ortho-xylene, and para-xylene.
Products are collected using only one activated carbon bed for each group, and when adsorption is near saturation, regeneration is performed.
Replace individual activated carbon beds to collect product and enable continuous operation. For example, if an activated carbon bed that adsorbs and collects ethylbenzene and an activated carbon bed that collects meta-xylene, ortho-xylene and para-xylene are packed with activated carbon that can completely collect a product separated from 10 fixed beds, respectively, It is only necessary to regenerate the activated carbon once for every 10 operation sequences.

[Brief description of drawings]

1 is a flow chart of a more preferred embodiment of the method of the present invention.

FIG. 2 is a flowchart of another preferred embodiment of the method of the present invention.

FIG. 3: Reaction curves for EB and MX mixtures at different operating pressures.

FIG. 4. Reaction curves for EB and MX mixtures at different operating temperatures.

FIG. 5: Reaction curves for EB and MX mixtures at different carbon dioxide flow rates.

FIG. 6 is a reaction curve of the EB and MX mixture when the operating pressure was increased from 650 psia to 1200 psia at 120 minutes.

FIG. 7: Reaction curve of a quaternary xylene isomer mixture.

FIG. 8 is a reaction curve when the operating pressure of the quaternary xylene isomer mixture was raised from 650 psia to 1500 psia at 325 minutes, and the high silicon zeolite used was particles of mesh 24-32.

FIG. 9: Breakthrough curves of activated carbon beds at different concentrations of meta-xylene at 100 ° C. and 650 psia.

FIG. 10: Breakthrough curve of activated carbon bed in different concentrations of ethylbenzene at 100 ° C. and 1500 psia.

[Explanation of symbols]

1 Carbon dioxide cylinder 2 Regulator 3 Zeolite 4A 4 Compressor 5 Surge tank 6 Pressure gauge 7 Sampling valve 8 Needle valve 9 Piping pump 10 Xylene isomer feed 11 Adsorbent packed bed 12 Thermocouple 13 Oil bath 14 Metering valve 15 Cooling trap 16 Electromagnetic Stirrer 17 Wet Gas Flow Meter 20 Activated Carbon Bed 21 Activated Carbon Bed 22 Circulation Pump 50 Heat Exchanger 60 Three-way Valve 61 Three-way Valve IV Adsorbent Packed Bed R1, R2, R3 Pressure Controller

Claims (18)

[Claims] 1. A method for separating ethylbenzene from a xylene isomer mixture containing at least one selected from the group consisting of metaxylene, orthoxylene, and paraxylene in addition to ethylbenzene, wherein (a) a high-pressure gaseous carbon dioxide stream is used as a carrier. And sending a certain amount of the xylene isomer mixture to the high-silicon zeolite adsorbent bed to adsorb ethylbenzene to obtain a first product stream passing through the adsorbent bed, and (b) in the first product stream. When the contained ethylbenzene component of the xylene isomer reaches the expected proportion, a higher pressure supercritical carbon dioxide stream is introduced to desorb the adsorbent bed and produce a second product stream containing substantially pure ethylbenzene. A method of obtaining. 2. The method of claim 1 wherein the expected proportion of ethylbenzene in step (b) is 98% by weight. 3. The method of claim 1 wherein the xylene isomer mixture comprises metaxylene, orthoxylene, paraxylene and ethylbenzene. 4. The weight composition of the xylene isomer mixture is ethylbenzene: paraxylene: metaxylene: orthoxylene = 5-75% by weight: 10-45% by weight: 5-45.
%, 5-25% by weight. 5. The method of claim 1, wherein the xylene isomer mixture comprises paraxylene and ethylbenzene. 6. A method for separating ethylbenzene from a xylene isomer mixture containing at least one selected from the group consisting of metaxylene, orthoxylene and paraxylene in addition to ethylbenzene, wherein (a) a high-pressure gaseous carbon dioxide stream is used as a carrier. And sending a certain amount of the xylene isomer mixture to the high-silicon zeolite adsorbent bed to adsorb ethylbenzene to obtain a first product stream passing through the adsorbent bed, and (b) in the first product stream. When the contained ethylbenzene component of the xylene isomer reaches the expected proportion, a higher pressure supercritical carbon dioxide stream is introduced to desorb the adsorbent bed and produce a second product stream containing substantially pure ethylbenzene. Then, (c) the second product stream is sent to the first activated carbon adsorbent bed, and substantially pure ethylbenzene therein is adsorbed and collected at an isothermal and isobaric pressure to obtain the first activated carbon. The high-purity carbon dioxide stream through the adsorbent bed is recirculated to the (b) stage supercritical carbon dioxide stream, and (d) the first product stream is sent to the second activated carbon adsorbent bed for isothermal and isobaric pressure. The other xylene isomers therein are adsorbed and collected, and a high-purity carbon dioxide stream is passed through the second activated carbon adsorbent bed (a).
A step of recirculating the gaseous carbon dioxide flow of the step to desorb the second activated carbon adsorbent bed. 7. The method of claim 6 wherein the expected proportion of ethylbenzene in step (b) is 98% by weight. 8. The method of claim 6 wherein said xylene isomer mixture comprises metaxylene, orthoxylene, paraxylene and ethylbenzene. 9. The weight composition of the xylene isomer mixture is ethylbenzene: paraxylene: metaxylene: orthoxylene = 5-75% by weight: 10-45% by weight: 5-45.
Weight%: 5-25% by weight. 10. The method of claim 6 wherein said xylene isomer mixture comprises paraxylene and ethylbenzene. 11. A method for separating ethylbenzene and paraxylene from a xylene isomer mixture containing at least one selected from the group consisting of metaxylene and orthoxylene in addition to ethylbenzene and paraxylene, comprising: (a) high-pressure gaseous carbon dioxide. Using the stream as a carrier, a certain amount of the xylene isomer mixture is sent to the high-silicon zeolite adsorbent bed to adsorb ethylbenzene and para-xylene to obtain a first product stream that has passed through the adsorbent bed, and (b) When both the ethylbenzene and para-xylene components of the xylene isomers contained in the first product stream have reached their expected proportions, a higher pressure supercritical carbon dioxide stream is introduced to desorb the adsorbent bed to remove ethylbenzene and paraxylene. A method comprising obtaining a second product stream containing xylene. 12. The method of claim 11 wherein the expected proportion of both ethylbenzene and paraxylene components in step (b) is 98% by weight. 13. The method of claim 11 wherein said xylene isomer mixture comprises metaxylene, orthoxylene, paraxylene and ethylbenzene. 14. The weight composition of the xylene isomer mixture is ethylbenzene: paraxylene: metaxylene: orthoxylene = 5-75% by weight: 10-45% by weight: 5-4.
The method of claim 13, wherein 5% by weight: 5-25% by weight. 15. A method for separating ethylbenzene and paraxylene from a xylene isomer mixture containing at least one selected from the group consisting of metaxylene and orthoxylene in addition to ethylbenzene and paraxylene, wherein (a) high-pressure gaseous carbon dioxide Using the stream as a carrier, a certain amount of the xylene isomer mixture is sent to the high-silicon zeolite adsorbent bed to adsorb ethylbenzene and para-xylene to obtain a first product stream that has passed through the adsorbent bed, and (b) When both the ethylbenzene and para-xylene components of the xylene isomers contained in the first product stream have reached their expected proportions, a higher pressure supercritical carbon dioxide stream is introduced to desorb the adsorbent bed to remove ethylbenzene and paraxylene. A second product stream containing xylene is obtained (c) the second product stream is sent to the first activated carbon adsorbent bed and isotherm isothermally By adsorbing and collecting ethylbenzene and para-xylene, and recirculating the high-purity carbon dioxide stream passing through the first activated carbon adsorbent bed to the (b) stage supercritical carbon dioxide stream; (d) the first product. The stream is sent to a bed of the second activated carbon adsorbent, and the other xylene isomers among them are adsorbed and collected under isothermal and isobaric pressure,
A method characterized in that a high-purity carbon dioxide stream that has passed through an activated carbon adsorbent bed is recirculated in the gaseous carbon dioxide stream of step (a). 16. The method of claim 15 wherein the expected proportion of both ethylbenzene and paraxylene components in step (b) is 98% by weight. 17. The method of claim 15 wherein said xylene isomer mixture comprises metaxylene, orthoxylene, paraxylene and ethylbenzene. 18. The weight composition of the xylene isomer mixture is ethylbenzene: paraxylene: metaxylene: orthoxylene = 5-75% by weight: 10-45% by weight: 5-4.
The method of claim 17, wherein 5% by weight: 5-25% by weight.