JPS5940367B2 - C↓8 aromatic isomer separation method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for selective adsorption and separation of aromatic isomers having 8 carbon atoms (hereinafter referred to as C8 isomers) using synthetic zeolite.

Methods for separating each isomer from a C8 isomer mixture are difficult to separate by distillation because the specific volatilities of each isomer are close to each other. Separation methods that form junction compounds, etc., have been implemented industrially.

Recently, a selective adsorption separation technique has also been developed in which each isomer is separated by adsorption on an adsorbent having selective adsorption ability, such as zeolite. When separating C8 isomers by selective adsorption separation, the important point is first to determine an adsorbent with high selectivity between the isomers, and second, to determine the adsorbent performance and separation method. The key is to select the optimal desorbing agent, developing agent, and displacing agent.

Regarding the separation of C8 isomers, especially xylene isomers, by selective adsorption separation, there are currently effective adsorbents, developing agents,
Combinations of adsorbents and developing agents have already been disclosed (see Japanese Patent Publication No. 49-28181, Japanese Patent Publication No. 51-46093, Japanese Patent Publication No. 49-17246, etc.).

Methods for separating C8 isomers by selective adsorption separation are broadly divided into batch separation methods and continuous separation methods.

In the batch separation method, the C8 isomer is brought into contact with an adsorbent, the adsorbent components are retained, the non-adsorbable components are first recovered, and the retained adsorbent components are then desorbed and recovered thermally or using a desorbent. It's a method. Although this method allows a wide selection of desorbents, it requires repeated batch operations and usually has extremely low efficiency, so there are few examples of industrial implementation. On the other hand, the continuous separation method is a method in which a C8 isomer adsorption zone is formed in a packed bed of adsorbent, and the target C8 isomer component is separated and recovered by moving this adsorption zone with a developing agent. This is a method of separating by chromatography.

The basic requirements for the developing agent necessary to move the C8 isomer adsorption zone in continuous separation methods, that is, separation by chromatography, are: first, it should not deteriorate even after long-term use; and second, it should not deteriorate even after long-term use. The boiling point is different from that of the C8 isomer, making it easy to separate and recover the developing agent by distillation.Thirdly, the C8 isomer has an appropriate elimination power.

Conventionally, aromatic hydrocarbons such as toluene, benzene, diethylbenzene, and cumene, naphthalenes, alcohols, ketones, and the like are known as developing agents used to separate xylene isomers. The present inventors have discovered that when C8 isomers are separated by chromatography, one of the major factors that greatly affects the separation cost is when recovering the developing agent from the product obtained as a mixture of the developing agent and the C8 isomer. It is the distillation cost of Depending on the method, when a developing agent with a specific desorption force and adsorption characteristics is used for a specific adsorbent, C8
The inventors discovered that the higher the concentration, the more effective the separation, leading to the present invention.

That is, the present invention aims at forming and moving a C8 isomer mixture adsorption zone by alternately supplying a plurality of C8 aromatic isomer mixtures and a developing agent to a separation tower packed with an adsorbent. In a method for separating and obtaining isomers, a phasiasite type zeolite substituted with potassium at a molar fraction of 0.60 or more is used as an adsorbent, and the adsorption characteristics of the zeolite to the adsorbent are used as a developing agent.

−
Ratio of relative adsorption power of FRS to paraxylene KPX (developer with 10 to 90% coexistence of developer/C8
Provided is a method for separating C8 aromatic isomers, characterized by using an ether compound having a value of 0.3 to 3 (measured in a mixed isomer system).

The first separation method in chromatography is called displacement chromatography, in which a forward displacement agent (FS) that is less adsorbent than the C8 isomer is placed in front of the C8 isomer adsorption zone.
), and a rear displacement agent (R
This is a method in which C8 isomer adsorption zone and displacing agent zone are kept substantially separated from each other by moving S) adjacent to each other.

In this method, the interface between the C8 isomer adsorption zone and the displacing agent does not diffuse and a product with a high C8 concentration can be obtained, but on the other hand, a regeneration operation is required to replace the backward displacing agent with the forward displacing agent after the C8 adsorption zone is developed. However, since methods such as heating and washing with a large amount of forward displacement agent are usually added, a large amount of energy is required, and it cannot be said to be economically advantageous. On the other hand, the second method called elution type chromatography is a method in which the same developing agent is placed adjacent to the front and rear ends of the adsorption zone and the adsorption zone is moved.

In this method, since the developing agent enters the adsorption zone, B separation progresses while gradually diffusing at the interface as the adsorption zone moves.

Now, the selectivity K between C8 isomers is small (A.B; C8 isomer component). If a considerable distance is required to move to reach the desired degree of separation, the diffusion at the interface is also significant, and the C8 isomers are B. is diluted with a large amount of developer.

On the other hand, in a system where K is relatively large A, separation can be obtained before significant diffusion occurs at the interface, and a product with a high C8 concentration can be obtained.

In this way, the degree of penetration of the developing agent into the C8 adsorption zone is greatly influenced by the B method of chromatography and K;
) The present inventors have found that the adsorption characteristics of a developing agent for a specific adsorbent affect the C8 concentration at the time of obtaining a separated product and the amount of C8 separated product obtained.

In other words, if we consider an elution curve plotted with the vertical axis representing the C8 concentration distribution in the adsorption zone and the horizontal axis representing the amount of liquid required for movement (eluent volume), the front-end interface distribution and the rear-end interface distribution are It has been found that the separation material can be obtained in a better balance and the C8 concentration is higher when the shape is more symmetrical with respect to the center. As a result of testing the adsorption properties of many developing agents and the separation results of C8 isomers, the present inventors found that the elution curve was symmetrical and the separation results were good with the developing agents having the following adsorption characteristics. I found out. In other words, the relative adsorption power of the developing agent (FRS) to paraxylene (PX) is expressed as, but it is desirable that this KFR8 is within a certain range (PX), and that 10 to 90% of the developing agent coexists. It has been found that it is preferable that the values of KFRSPX measured in a mixed system of C8 isomers are all 0.3 to 3.

One possible reason for this is that even for most developing agents that are generally considered suitable for separating C8 isomers, the FRSK value is determined by the concentration of the coexisting developing agent (FR
S%) shows dependence on PX, and F at high FRS%
RS Kpx tends to decrease.

In such an expanded FRS developer, K is suitable for PX in the central part where the C8 concentration is high and has a desorption force, but C
This is because at the rear end of the interface with a low FRS concentration of 8, K decreases and the dissociation force is lost, causing an abnormal tailing in the elution curve at PX, and the C8 concentration tends to decrease significantly.

Further requirements for the developing agent include K (A.B; C8 isomer component) B in the absorption zone mixed with the developing agent.
It is preferable to use FRS, which does not reduce the FRS, but preferably improves it.

The highly adsorbent developer 0PXA with high K tends to lower K, and since a large amount of B is adsorbed on the adsorbent, the adsorption capacity FRS amount of the C8 isomer also decreases, which is not preferable.

On the other hand, a developing agent with low K and weak adsorption of PX does not have enough power to move through the C8 isomer adsorption zone, so the xylene isomer may be left behind, making separation impossible.

FRS In this sense, K is P in a wide range of FRS%.
XO. It is desirable that it is 3-3.

The above developer is particularly effectively used when the average C8 concentration in the adsorption zone at the time of separation is relatively high.
When the front and rear interfaces are sufficiently sharp, it is necessary that the sharpness is at least 20% or more.

A This condition is B under the condition of an adsorbent with relatively high K.
This corresponds to the case where the moving distance is relatively short, that is, the maximum value of the C8 concentration in the adsorption zone is high and the front and rear interfaces are relatively sharp.

The present inventors selected a developing agent that satisfies the above conditions from among many substances, and as a result, they found that very specific ethers satisfy these conditions. That is, specifically, R
Chain ethers consisting of -0-R'(R,.R!; alkyl group having 3 to 5 carbon atoms excluding n-butyl group); Cyclic ethers consisting of furan, 2-methylfuran, hexamethylene oxide, and cineol: from At least one developing agent selected from the group consisting of:

Among these, isopropyl ether is most preferably used because it has the smallest dependence on FRS%, has a boiling point considerably different from that of xylene, and has a high specific volatility.

When the above developing agent was used, each C8 isomer component was separated and recovered from the vicinity of the front end interface and the rear end interface in a well-balanced manner at approximately the same ratio as the raw material composition, and both the amount obtained and the C8 concentration were maximum.

Here, the C8 concentration is the average C8 concentration (mol%) obtained by dividing the total amount of C8 isomers existing in the adsorption zone by the sum of the invading developer and the above C8 isomer amount, and it is the average C8 concentration (mol%) that This is a value that directly affects the value.

In the separation method in which these developing agents are most effectively used, a fixed amount of developing agent is first supplied to an adsorbent-packed column, and then a fixed amount of a C8 isomer mixture is supplied to adsorb the C8 isomer.
Then, when the developing agent is supplied again, the front and rear interfaces gradually become symmetrically diffused. When the predetermined degree of separation is reached, C8
The separated components of isomers are recovered.

As mentioned above, KB is particularly effective in this case when the system is relatively large and the average C8 concentration at the acquisition port is high.

Of course, even when applied to ordinary elution type chromatography, these solvents do not reduce the C8 adsorption capacity and selectivity of zeolite, but rather tend to slightly improve them, and can be used satisfactorily.

The above developer was subjected to one repeated use test over a long period of time, but no phenomena such as decomposition, deterioration, selectivity, or decrease in adsorption amount of the developer itself were observed, and it can be used industrially. I understood.

The separation column used in the present invention is a container that can be filled with zeolite to form a fixed bed, and is usually a cylindrical column equipped with a liquid supply port and a liquid intake port at one or more locations in the container. It will be done. Preferably, a liquid uniform dispersion plate and a liquid uniformity collection plate are provided at the liquid inlet and liquid acquisition ports of the tower, respectively, and the structure is designed to prevent liquid-liquid mixing, vortex, etc. from occurring and remixing the separated substances. . Furthermore, when the diameter of the packed column and the length of the packed bed (column length) are large, separation is performed not only by one column but also by multiple columns. At this time, the liquid outlet of one column is connected with the liquid inlet of the next column by piping, and the liquid is obtained from the last column. In addition, a flow path switching valve (three-way valve, four-way valve, multi-way valve, etc.) for liquid switching between the C8 isomer and the developing agent liquid or for dividing sampling at the time of product acquisition is provided, and furthermore, a pipe through which the liquid flows, C in a part of the separation tower
It is also desirable to provide a concentration detector for the C8 isomer and/or developing agent and use it for detecting the C8 isomer adsorption zone, operating the switching valve, supplying raw materials, and extracting the product.

The setting of the moving distance of the C8 isomer adsorption zone, that is, the length of the column, is determined based on the C8 isomer concentration at the time of product acquisition and the C8 per unit time.
The amount of isomer separation is determined by the yield.

In other words, in general, when the travel distance is increased, the product C8 isomer concentration increases up to a certain distance, and then it remains constant or tends to decrease slightly (the distance at which the C8A isomer concentration is maximum is the smaller K is, the greater B is). On the other hand, the time it takes to obtain the product increases and the yield decreases.

Taking these two conflicting factors into consideration, the final decision is made through economic calculations based on model experiments, but it is generally 2 to 50m.
The travel distance is set to . The amount of C8 isomer liquid adsorbed at one time varies depending on the selectivity of the substance to be separated, the raw material composition, the C8 isomer adsorption capacity for zeolite, the moving distance, the zeolite packing density, the temperature, and other operating conditions, so it is always the optimum C8 It is necessary to consider the isomer feed rate.

If the amount of C8 isomer supplied is too large, a large amount of unseparated portion will remain at the time of product acquisition, and the amount recycled to raw materials will increase. Conversely, if the amount of C8 isomer supplied is too small, there will be a large amount of unseparated portion remaining at the time of product acquisition, and conversely, if the amount of C8 isomer supplied is too small, there will be a large amount of unseparated portion remaining at the time of product acquisition. Since the separation progresses excessively and an excessive amount of zeolite is used, neither method is economical. Examples of very standard operating conditions are PX2O%, EB2O%, MX4O%.
, 0x20% four-component xylene isomer at a temperature of 100℃
, xylene adsorption amount is 0.1 when separating with a moving distance of 10 m.
Assuming 90PXm1/7 zeolite, K = 6.0, packing density MX゜ゝ0.60y/CC column,
The amount of xylene adsorption (Wxml/y-zeolite) per time is selected in the range of 0.10 to 0.35 m1/7-zeolite A per unit weight of the zeolite used (total zeolite to which the C8 adsorption band has been transferred).

If selectivity KB decreases, Wx also decreases, and if it becomes larger than 6, Wx tends to increase slightly. Furthermore, Wx is approximately proportional to the adsorption amount XR (ml/7-zeolite). As mentioned above, there are many factors that change Wx, but W
x (ml/y-zeolite) is generally determined in the range of 0.02 to 2 m1/7 zeolite, and for Y-type zeolite, it is 0.04 to 2 m1/7 zeolite, preferably 0.1 to 1 m1/Y. ．． 0 in X-type zeolite
．． 02~1m1/7 zeolite, preferably 0.05~
It is selected within the range of 0.5m1/7. The developing speed of the C8 isomer adsorption zone or the developing solution flow rate A can be determined arbitrarily, but in a system with a relatively large K, mutual separation of B is achieved faster than the spread of the interface, so the higher the flow rate, the better the separation. The amount increases.

However, the pressure loss in the zeolite layer increases and the A
It is not economical to increase the flow rate, and the optimum flow rate can be considered in system B where K is small.

Usually the superficial velocity is chosen between 0.5 m/hr and 80 m/hr. The operating temperature is preferably as high as possible from the viewpoint of adsorption/desorption rate, and relatively low as it is from the standpoint of adsorption capacity. Generally 20
-200°C, preferably 40-160°C
It is ℃.

When developing a low boiling point developing agent above its boiling point, it is necessary to maintain the entire system of the column at a level higher than the sum of its vapor pressure and xylene vapor pressure, and the inlet pressure of the liquid is further reduced by the pressure loss of the zeolite packed bed. is added. The adsorbent used in the present invention is C8
Zeolites with high selectivity between isomers are used.

Many types of zeolite are known, and their pore size, SiO2
/Al2O3 ratio, manufacturing method, and other composition changes
Many common names are used, such as type, L type, X type, Y type, and H type. Among these, the higher the A selectivity between the C8 isomers, the more desirable it is for the present invention, and it is desirable for K to have B at least 1.2, preferably 1.5 or more.

The specific type of zeolite used is a so-called phosiaside zeolite, which is classified into the fourth group among crystalline aluminosilicates in terms of crystal structure and is called 6W double hexacyclic 71.

The fourth group includes biolites called faujasite, chaabasite, gmelinite, ZK-50, and L, and among these, faujasite is a type of polyhedral cage and is characterized by β 26-hedron (H). In addition to natural faujasite, there are synthetic products such as X-type synthetic zeolite (IJN = 1 ＾ 2 I? ~ Y-type synthetic zeolite L) Do-J? -Mulberry-C Furthermore, the cation composition of this faujasite type zeolite is important, and it is necessary to replace the aluminosilicate, which is usually synthesized in the Na type, with other cations.

As a metal ion type that increases selectivity between C8 isomers, 60% or more (molar ratio) of exchangeable cation sites
is replaced with potassium, and the remainder is replaced with lithium, sodium,
Those substituted with at least one selected from potassium, cesium, barium, lead, cadmium, lanthanum, and thallium are preferred. A In order to further improve the selectivity K, it is preferable to use the Fuge B Jasite type zeolite which has been treated to change the SiO2/Al2O3 ratio, and which has optimized activation conditions.

The most preferred group of adsorbents are zeolites of the faujasite type having an X- or Y-type structure, or modified faujasite zeolites which have been treated with inorganic or organic acids to increase the SiO2/Al2O3 ratio. It is a complex-substituted zeolite whose cation composition has a molar ratio of 60% or more being replaced with potassium, and the remainder being replaced with lithium, barium, potassium, cesium, and thallium.

The particle size of the zeolite is determined by considering separation efficiency and pressure loss, but an average particle size of 20 microns to 1 mm is usually selected.

Any shape such as pellet, amorphous, or spherical can be used, but spherical zeolite, which is close to a true sphere, is preferably used. Reference Example 1 According to the equilibrium experimental method described below, K, , and P-xylene were measured for various developing agents FRS (FRS).

In the equilibrium experiment, an equilibrium solution having the following composition is prepared for each developing agent using n-decane as a diluent.

Next, each equilibrium solution was brought into contact with a zeolite adsorbent in the liquid phase at room temperature, and the selective adsorption rate K was determined from the change in composition before and after. The results are shown in Table 1. In addition, commercially available synthetic faujasite Y type zeolite (Na type, SlO2/Al2O
3 ratio -4.8), 80% of the exchangeable ion sites
The product was ion-exchanged with a KNO3 aqueous solution until the K ions were obtained, and then thoroughly washed with water and calcined at 400° C. for 2 hours to prepare a zeolite adsorbent for equilibrium experiments. Examples 1-3 Inner diameter 8m77! , three stainless steel chromatography columns with an inner diameter of 1 m, each having a jacket with a length of 2,000 mm, a distributor for liquid dispersion at the top and bottom, and a collector for liquid collection.
Prepare chromatographic separation devices interconnected with 1 L stainless steel pipes.

Reference Example 1 was applied to each of the three columns of these chromatographic separation devices.
The zeolite (60 to 100 mesh) used in the above was filled. After filling the column with zeolite, the temperature is 120℃.
First, FRS is supplied to condition the zeolite, and then mixed xylene consisting of 15% by weight of p-xylene, 20% by weight of ethylbenzene, 45% by weight of m-xylene, and 20% by weight of o-xylene is used as the substance to be separated. 5
A mixed xylene adsorption zone is formed by supplying 0 ml with a micrometer pump.

Thereafter, FRS was again supplied to the column at a constant flow rate of 9.5 CC/min to develop a mixed xylene adsorption zone. The eluent flowing out from the bottom of the column is separated into fractions of 1 to 10 CC and collected. p-xylene, ethylbenzene, m-xylene, o-
The weight percentages of xylene and FRS were quantitatively analyzed by gas chromatography. From near the front end interface of the mixed xylene adsorption zone in the traveling direction of the eluent, C other than p-xylene is
A solution rich in the 8-isomer is recovered, and a liquid rich in p-xylene is recovered from the vicinity of the trailing interface. As a guideline for separation efficiency, the xylene weight S99 (grams) contained in a fraction with a purity of 99% or more for the C8 isomer of p-xylene, and the xylene concentration C relative to the entire fraction.
.
Comparative Examples 1-2 The same methods as Examples 1-3 were repeated except that anisole and n-butylbenzene, which are outside the scope of the present invention, were used as developing agents.

The results are also listed in Table 2. Examples 4 to 6 Using the same chromatographic separation apparatus and zeolite as in Examples 1 to 3, the column was kept at a temperature of 120 DEG C. and the zeolite was first conditioned by supplying FRS.

Then, 50% by weight of ethylbenzene, m
- 50 m of a C8 isomer mixture consisting of 50% by weight of xylene
1 is supplied using a micrometer pump to form a C8 isomer adsorption zone. Thereafter, FRS was again supplied to the column at a constant flow rate of 7.5 CC/min to develop a C8 isomer adsorption zone. The eluent flowing out from the bottom of the column is divided into fractions of 1 to 10 CC and collected. The collected sample liquid was used in Example 1~
Quantitative analysis was performed by gas chromatography in the same manner as in 3. A solution rich in m-xylene is recovered from the vicinity of the front end interface of the C8 isomer adsorption zone in the traveling direction of the eluent, and a liquid rich in ethylbenzene is collected from the vicinity of the rear end interface.
As a guideline for separation efficiency, the xylene weight Srn-xS/. L/>. (grams), xylene concentration based on the total, Cm-xylene (wt%), weight of ethylbenzene contained in the fraction with a purity of 99% or higher, S. Bease)/(grams), ethylbenzene concentration relative to the total Cchech)L. (% by weight) and the average concentration within the C8 isomer adsorption zone at the separation port were measured, and the results are shown in Table 3.

Comparative Examples 3-4 The same methods as Examples 4-6 were repeated except that n-hexyl ether and n-butylbenzene, which are outside the scope of the present invention, were used as developing agents.

The results are also listed in Table 3. Comparative Examples 5 to 7 First, in the same manner as in Reference Example 1, commercially available synthetic faujasite Y-type zeolite (Na type, SiO2/Al2O3
=4.8), 55% of the exchangeable ion sites were exchanged with K ions, and after thorough washing with water, it was fired at 400°C for 2 hours.

Claims (1)

[Scope of Claims] 1 A mixture of C8 aromatic isomers and a developing agent are alternately supplied to a separation tower packed with an adsorbent to form and move a C8 isomer mixture adsorption zone to obtain the desired isomer. In the method for separating and acquiring para-xylene, a phosiasite-type zeolite substituted with potassium at a molar fraction of 0.60 or more is used as an adsorbent, and the adsorption characteristics of the developer to the adsorbent are determined by the relative adsorption power for para-xylene. Ratio K^F^R^S_P_X
A method for separating C8 aromatic isomers, characterized in that an ether compound having a value in the range of 0.3 to 3 (measured in a mixed developer/C8 isomer system in which 10 to 90% of the developing agent coexists) is used. 2 Average C in the C8 isomer adsorption zone at the separation acquisition port
The method for separating C8 aromatic isomers according to claim 1, wherein the C8 isomer concentration is 20% by weight or more. 3. A patent claim in which the ether compound is at least one type selected from chain ethers represented by the formula R-O-R' (R, R' are alkyl groups having 3 to 5 carbon atoms excluding n-butyl group) The C8 aromatic isomer separation method according to item 1 or 2. 4. The method for separating C8 aromatic isomers according to claim 3, wherein the ether compound is isopropyl ether. 5. The C8 aromatic isomer according to claim 1 or 2, wherein the ether compound is at least one cyclic ether selected from the group consisting of furan, 2-methylfuran, hexamethylene oxide, and cineole. Separation method.