JPH059420B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The technical field to which this invention pertains is the solid bed adsorptive separation of isomers of toluene diisocyanate. That is, the present invention relates to a method for separating either 2,6-toluene diisocyanate isomers or 2,4-toluene diisocyanate isomers from toluene diisocyanate isomers using a solid bed adsorption system.

[Background of the invention] 2,4-toluene diisocyanate and 2,6-
Both isomers of toluene diisocyanate are important as starting materials for the production of polyurethanes, which can be used in rigid or flexible form or for example in insulation, soundproofing, clothing and sleeping bag cores, It has a wide range of uses as a fiber for cushions, spandex, etc.

For the production of polyurethanes, isomer mixtures of 2,4- and 2,6-toluene diisocyanate (TDI) derived from 2,4- and 2,6-toluene diisocyanate (TDI), for example 80/20 or 65/
It is industrially customary to manufacture from a mixture of 35. This is because it is difficult and expensive to separate the two using existing technology. Modern methods of separating isomers include crystallization, but this is a time-consuming process. Furthermore, polyurethanes synthesized from pure 2,4- and 2,6-toluene diisocyanates have significantly different properties compared to materials synthesized from mixtures thereof. 2,
A prepolymer made with 6-toluene diisocyanate is less likely than a prepolymer made with an 80/20 mixture of 2,4-toluene diisocyanate.
Reacts with polyols almost 5 to 10 times faster,
It has already been shown that the tensile strength of polyurethanes made from 2,6-toluene diisocyanate and 2,6-toluene diisocyanate is greater than polyurethanes made from 2,6-toluene diisocyanate or any mixture of toluene diisocyanates. In fact, their tensile strength is 2,
The improvement increases as the amount of 4-toluene diisocyanate increases. Additionally, the 2,6-toluene diisocyanate system is known to give a significantly higher modulus than the 2,4-toluene diisocyanate system when the polyol is a polyester, e.g., butanediol adipate. . Tear resistance and tear propagation resistance are both defined when polyester is used as a polyol.
It is considerably high in 2,6- series. Therefore, it would be desirable to separate TDI isomers in an economical manner.

It is known in the field of separation technology that certain aluminosilicates can be used to separate hydrocarbon mixtures. Zeolites X and Y have been used in a variety of ways to separate individual hydrocarbon isomers.

US Pat. No. 3,069,470 teaches the use of type X zeolite to separate the meta isomer of toluidine from other isomers. US Patent No.
No. 4,480,129 teaches that transition metal exchanged X and Y zeolites are paraselective in isomeric mixtures of toluidine.

US Pat. No. 4,061,662 describes that unreacted toluene diisocyanate from polyisocyanate is adsorbed onto Type X zeolite. U.S. Patent No. 4169175 is 0.7% from urethane prepolymer
It is described that the following unreacted toluene diisocyanate is removed using X-type zeolite.

U.S. Pat. No. 4,246,187 teaches a method for separating the 2,4- and 2,6-isomers of toluene diisocyanate, such as by a crystallization step and a centrifugation step.

U.S. Pat. No. 3,575,820 describes that the ortho isomer of toluene diisocyanate can be removed from the mixture by introducing aluminum oxide into the mixture, which polymerizes the ortho isomer, and non-neighboring isomers are removed from the mixture. Can be separated by distillation. chemical abstract
101:116099X (1984) describes an adsorption treatment with activated carbon to remove toluene diisocyanate from exhaust gas.

Japanese Patent Publication No. 54-56905 released on November 20, 1980
It is described in the issue that a solid adsorbent containing titanium oxide selectively adsorbs the para isomer of toluidine.

U.S. Pat. No. 4,270,013 discloses that orthonitrotoluene can be separated from other nitrotoluene isomers using a type X zeolite containing one cation selected from the group including potassium and barium at the exchangeable cationic site. is listed. The desorbent materials shown in this US patent are toluene and 1-hexanol. The separation of isomers of disubstituted benzenes with crystalline aluminosilicates having a silica/alumina molar ratio of at least 12 is described in US Pat. No. 4,467,126.

SUMMARY OF THE INVENTION Briefly summarized, one embodiment of the present invention comprises:
This is a method for separating a raw material mixture containing 2,6-toluene diisocyanate and 2,4-toluene diisocyanate. The method uses an adsorbent containing Y-type zeolite that selectively adsorbs 2,6-toluene diisocyanate due to cation exchange with K;
Or, the above-mentioned adsorbent containing a Y-type zeolite that selectively adsorbs 2,4-toluene diisocyanate isomer by being cation-exchanged with a cation selected from the group of Na, Ca, Li, Mg and mixtures thereof. of the raw material mixture under adsorption conditions. The remainder of the feed mixture is then removed from the adsorbent and the adsorbed isomer is recovered by desorption under desorption conditions with a desorbent material containing toluene.

Other embodiments of the invention relate to details such as feed mixtures, adsorbents, desorbent materials, and operating conditions, which are described in detail below.

DESCRIPTION OF THE INVENTION At the outset, it may be helpful to define the terms used herein to clarify the operation, objects, and advantages of the present invention.

A "raw mixture" is a mixture containing at least one extract component and at least one roughinate component separated by the method of the invention. "Feed stream" refers to the flow of the feed mixture that is passed through the adsorbent being used.

"Extract components" are compounds or types thereof that are adsorbed with higher selectivity by the adsorbent, while "ruffinate components" are compounds or types thereof that are adsorbed with lower selectivity. In one embodiment of the invention, when the adsorbent is a K-exchanged Y-type zeolite, 2,6-toluene diisocyanate is the extract component and 2,4-toluene diisocyanate is the roughinate component.
In other embodiments using Y-type zeolites exchanged with Na, Ca, Li, Mg, and mixtures thereof, 2,4-toluene diisocyanate becomes the extract component and 2,6-toluene diisocyanate becomes the roughinate component. Becomes an ingredient. "Desorbent material" generally refers to a material capable of desorbing extract components. "Desorbent stream" or "desorbent input stream" refers to the flow in which desorbent material is forced through the adsorbent. “Roughinate style” or “Roughinate output style” is
Refers to the flow of roughinate components removed from the adsorbent. The composition of the roughinate stream ranges from essentially 100% desorbent material to essentially 100% roughinate component.
It can vary up to %. “Extract style” or “Extract output style” is
refers to the stream in which the extract material desorbed by the desorbent material is removed from the adsorbent. As above, the composition of the extract stream can vary from essentially 100% desorbent material to essentially 100% extract components. At least a portion of the extract stream, and preferably at least a portion of the raffinate stream, is sent to a separation device, typically a fractionation device, where at least a portion of the desorbent material is separated to produce an extract product. and a roughinate product are obtained. "Extract product" and "ruffinate product" refer to a product that contains extract and roughinate components at higher concentrations than the extract and raffinate streams, respectively. Although it is possible to obtain highly purified products with a high recovery rate in the method of the present invention, the extract components are not completely adsorbed to the adsorbent, and the roughinate components are completely non-adsorbed to the adsorbent. It's not adsorption. Therefore, changes in the amount of roughinate components are observed in the extract stream, and similarly changes in the amount of extract components are observed in the roughinate stream. Extract streams and roughinate streams are therefore distinguished from each other and from the feedstock mixture by the concentration ratios of the extract and roughinate components of the individual streams. That is, the ratio of the concentration of isomers adsorbed with high selectivity to the concentration of isomers adsorbed with low selectivity is lowest in the raffinate stream, next highest in the feed mixture, and highest in the extract stream.

The “selective pore volume” of the adsorbent
volume) is defined as the volume of adsorbent that selectively adsorbs extract components from the feed mixture. The “non-selective spatial volume” of the adsorbent
"selective void volume" is the volume of adsorbent that does not selectively retain extract components from the feed mixture. This volume includes the adsorbent cavities that do not contain adsorption sites and the spatial volume between adsorbent particles. The selective pore volume and non-selective spatial volume are
It is generally expressed in terms of volume and is important in determining the appropriate flow rate of fluid that must be delivered to the operating zone for effective operation at a given amount of adsorbent. When the adsorbent is transferred to the operating zone used in one embodiment of the present invention, its non-selective spatial volume, along with the selective pore volume, carries fluid into the zone. The non-selective space volume is used to determine the amount of fluid that must be passed countercurrently into the same zone as the adsorbent in order to replace the fluid present in this section. If the flow rate of fluid through a zone is less than the amount of non-selective spatial volume of adsorbent material passing through that zone, entrainment of fluid into that zone over the adsorbent will occur. Since this entrainment is the fluid present in the non-selective spatial volume of the adsorbent, it often contains feedstock components that are retained with low selectivity. In other cases, the selective pore volume of the adsorbent is
The adsorbent adsorbs some of the roughinate material from the surrounding fluid. If a large amount of ruffinate material surrounds the adsorbent compared to the extract material,
The more the roughinate material is adsorbed onto the adsorbent, the more competitive it becomes.

It is recognized in the art that certain properties of the adsorbent, although not absolutely necessary, are highly desirable for the successful operation of selective adsorption processes. Such properties are equally important in the method of the invention. These properties include the adsorption capacity of extract components per volume of adsorbent;
These include selective adsorption for extract components relative to ruffinate components and desorbent materials, and sufficiently rapid rates of adsorption and desorption of extract components from the adsorbent. The capacity of the adsorbent to adsorb a particular amount of extract component is of course necessary, and an adsorbent without such capacity is useless for adsorptive separation. The higher the capacity for extract components, the better the adsorbent. Increasing the capacity of the adsorbent can reduce the amount of adsorbent required to separate the extract components contained in a given feed rate of the feed mixture. Reducing the amount of adsorbent required for a particular adsorptive separation reduces the cost of the separation process. It is important that a good initial capacity of the adsorbent is maintained during its practical use with an economically desirable lifetime in the separation process.

The second property required of an adsorbent is the ability of the adsorbent to separate the components of the feedstock, in other words, the adsorbent's adsorption selectivity ( B). Relative selectivity can be expressed for one component in the feed compared to other components, as well as between components of the feed mixture and the desorbent material. Selectivity (B) is defined as the ratio of two components in the adsorbed phase divided by the ratio of the same two components in the non-adsorbed phase at equilibrium. Relative selectivity is expressed as in Equation 1 below.

Equation 1 Selectivity (B) = [Volume % of C / Volume % of D] _A / [Volume % of C / Volume % of D] _U where C and D are two components of the raw material, and the subscript A
and U indicate an adsorbed phase and a non-adsorbed phase, respectively. The equilibrium state is a state in which the feed passed through the adsorbent bed comes into contact with the adsorbent bed and no change in composition is observed. In other words, at equilibrium there is no net mass transfer between the non-adsorbed and adsorbed phases.
When the selectivity of two components approaches 1.0, one component will not be adsorbed onto the adsorbent in preference to the other, and both will be adsorbed to the same extent or not at all. When (B) is smaller than or larger than 1.0, one component is adsorbed onto the adsorbent in preference to the other component. Comparing the selectivity of components C and D, (B)
is larger than 1.0, which indicates that component C is preferentially adsorbed on the adsorbent. The fact that (B) is less than 1.0 indicates that component D is preferentially adsorbed, the non-adsorbed phase is rich in component C, and the adsorbed phase is rich in component D.

The third important characteristic is the rate of exchange of the desorbent to the extract components of the raw mixture, i.e.
Relative desorption rate of extract components.
This property is directly related to the amount of desorbent material that must be used to recover extract components from the adsorbent. A faster exchange rate reduces the amount of desorbent material required to remove extract components, thus reducing the operating costs of the process. The faster the exchange rate, the less desorbent material is pumped into the process and the desorbent separated from the extract stream is reused in the process.

The adsorbent used in the method of the invention contains specific crystalline aluminosilicates. Such crystalline aluminosilicates that can be used in the present invention include crystalline aluminosilicates in which alumina and silica tetrahetra are intimately bonded in a three-dimensional framework structure to form a cage structure with window-like pores of about 8A in diameter. Includes aluminosilicates. The tetrahedra crosslink with each other by sharing oxygen atoms, leaving space between them, and before partial or total dehydration, this space is occupied by water molecules. Dehydration of zeolites yields crystals studded with cells of molecular dimensions. Crystalline aluminosilicates are therefore often referred to as molecular sieves when separation relies solely on molecular size differences of the feeds. One example is the use of certain molecular sieves to separate small normal paraffin molecules from larger isoparaffin molecules.

The hydrated form of crystalline aluminosilicate used in the present invention generally includes a zeolite represented by Chemical Formula 1 below.

Chemical formula 1 M _2/o O: Al ₂ O ₃ : wSiO ₂ : yH ₂ O Here, M is a cation that balances the ion valence of aluminum-centered terohedra and is usually an exchangeable cation site, and n is a cation. , w represents the number of moles of SiO ₂ , and y represents the number of moles of water. The generally indicated cation M can be monovalent, divalent, trivalent or a mixture thereof.

The prior art recognizes that adsorbents including type X and Y type zeolites can be used in certain adsorption separation processes. These zeolites are described in US Pat. No. 2,882,244 and US Pat. No. 3,130,007, respectively, which are incorporated herein by reference. Hydrated or partially hydrated Y-type zeolite can be represented by the following chemical formula 2 in terms of oxide molar ratio.

Chemical formula 2 (0.9±0.2)M _2/o O: Al ₂ O ₃ :wSiO ₂ :yH ₂ O where M is at least one cation with a valence not less than 3, and n is the valence of M. , w has a value of about 3 to about 6, and y has a value of up to about 9 depending on the degree of hydration of the crystal and the type of M. Therefore, the _SiO2 / _Al2O3 molar ratio _of Y-type zeolite is about 3 to about 6. The cation M can be one or more cations such as hydrogen, alkali metals, alkaline earth metals or other selected cations, which are exchangeable cation sites, but the initial Y The cation M of type zeolites is usually predominantly sodium.
Y-type zeolite containing mainly sodium cations at exchangeable cation sites is Na-
It is called Y zeolite.

The cations occupying the exchangeable cation sites of the zeolite can be replaced by other cations by ion exchange methods well known to those skilled in the art of crystalline aluminosilicates. The process generally involves contacting a zeolite or zeolite-containing adsorbent material with an aqueous solution of a soluble salt of the cation desired to be loaded onto the zeolite. Once the desired degree of exchange has occurred, the sieves are removed from the aqueous solution, washed and dried to the desired moisture content. By such a method, sodium and other cations occupying the exchangeable sites of the zeolite as impurities can be partially or essentially completely replaced by other cations. The zeolite used in the method of the present invention contains potassium cations at exchangeable cation sites when the selectivity for the 2,6-TDI isomer is desired. If desired, cations selected from sodium, calcium, lithium, magnesium and mixtures thereof are included at the exchangeable cation sites.

Typically, adsorbents used in separation processes contain zeolite crystals dispersed in an amorphous material or inorganic matrix. Zeolites are typically present in the adsorbent in a range of about 75 to about 98 wt% on a volatile-free composition basis. Volatile-free compositions are formulated to remove all volatiles.
It is usually determined after calcination of the adsorbent at 900°C.
The remainder of the adsorbent is generally an inorganic matrix material such as silica, titania, alumina, mixtures thereof, or clay, which is present in intimate admixture with small particles of zeolite. This matrix material may be an adjunct to the zeolite production (e.g., intentionally incompletely purified during zeolite preparation), or may be added to relatively pure zeolite.
In any case, its use is as a binder for forming zeolites into hard particles. Usually, the adsorbent is in the form of particulates such as extrudates, aggregates, tablets, macrospheres or granules in the desired particle size range. Typical adsorbent particle size is approximately 16-60 mm, corresponding to a nominal aperture of 0.25-1.19 mm.
(standard US mesh) range. An example of a zeolite used in adsorbents known in the art is "SK-40" available from Linde Company, Tonawanda, New York, USA. "SK-40" contains Y-type zeolite.

Ideally, the desorbent material should have a selectivity for all extract components equal to or slightly less than about 1. If so, all the extract components can be totally desorbed with the desorbent material at a reasonable flow rate, and the extract components can be replaced by the desorbent material in the next adsorption step. It is theoretically possible to separate the extract component from the roughinate component if the selectivity of the adsorbent for the extract component in relation to the roughinate component is slightly higher than 1.0, but the selectivity is only moderately higher than 1.0. It is preferable that the temperature is high. As with specific volatility, the higher the selectivity, the easier the separation will be.

The desorbent materials used in various conventional adsorption separation processes vary depending on factors such as the type of operation employed. In swing bed systems, where selectively adsorbed feedstock components are removed from the adsorbent by a purge flow desorbent, the choice of desorbent is not critical, and gaseous hydrocarbons such as methane, ethane, or gaseous hydrocarbons such as nitrogen, hydrogen, etc. A desorbent material containing a gas can be used at elevated temperature or at reduced pressure or at elevated temperature and reduced pressure to effectively purge the adsorbed feedstock components from the adsorbent. however,
In adsorption separation processes, which are usually operated continuously at substantially constant pressure and low temperature to maintain a liquid phase, the desorbent material must be carefully selected to meet a number of criteria. First, the desorbent material must displace the extract components from the adsorbent at a reasonable flow rate without being adsorbed so strongly as to unduly prevent the extract components from displacing the desorbent material in the next adsorption cycle. . In terms of selectivity (more on this later), it is preferred that the adsorbent be selective for all extract components with respect to the ruffinate component, rather than being selective for the desorbent material with respect to the ruffinate component. Second, the desorbent material must be able to coexist stably with the particular adsorbent and the particular raw material mixture. That is, the desorbent material must not reduce or eliminate the selectivity of the adsorbent relative to the extract component with respect to the roughinate component. Furthermore, the desorbent material should be a material that can be easily separated from the feed mixture fed to the process. Because both the roughinate and extract streams are removed from the adsorbent in a mixture with the desorbent material, the purity of the extract and roughinate products is not high unless at least a portion of the desorbent material is separated; Also, the desorbent material cannot be reused. Therefore, the desorbent material used should have an average boiling point that is substantially different from the feed mixture so that at least a portion of the desorbent material can be separated from the feed components of the extract stream and the ruffinate stream by simple fractional distillation. is preferred. If so, the desorbent material can be reused. Here, "substantially different" means that the difference in average boiling point between the desorbent material and the raw material mixture is at least about 5°C.
say that it is. The boiling range of the desorbent material may be higher or lower than that of the raw mixture. Finally, the desorbent material should be a readily available and therefore reasonably priced material. In the preferred isothermal isobaric liquid phase operation of the present invention, toluene is highly selective for both 2,6-toluene diisocyanate isomers and 2,4-toluene diisocyanate isomers as long as the adsorbents described above are used. It is known that

The adsorbent can be used in the form of a dense, compact fixed bed in alternating contact with the feed mixture and the desorbent material. In the simplest embodiment of the invention, the adsorbent is used in the form of a single stationary bed, in which case the process is semi-continuous. In other embodiments, two or more stationary beds are used, connected by suitable baths, with the feed mixture being fed to one or more adsorbent beds while the desorbent material is being fed to the other bed. supplied to one or more bets. The flow of the feed mixture and desorbent material may be upstream or downstream relative to the adsorbent. Any conventional equipment used for fluid-solid contact can be used in the present invention.

However, the simulated moving bed system is preferable because its separation efficiency is much higher than that of the fixed bed system. In a moving bed or simulated moving bed system, the holding and displacement operations occur continuously, so the feed stream and the displacement fluid stream are used continuously to continuously produce an extract stream and a raffinate stream. I can do it. In a preferred embodiment of the present invention, as a simulated moving bed countercurrent system,
Those known in the art are used. The procedure and operating principles of this distribution system are described in US Pat. No. 2,985,589, which is incorporated by reference herein. In this method, a large number of fluid inlets into the molecular sieve chamber sequentially move downward, so that the molecular sieve in the chamber is in the same state as if it were moving upward. Society of Chemical Engineers held in Tokyo on April 2, 1969.
``Continuous Adsorptive Processing - New Separation Techniques'' presented by D.B. Broughton at the 34th Annual Meeting.
-A New Separation Technique), which teaches details of the simulated moving bed countercurrent system, is also incorporated by reference into the present invention.

Another embodiment of a simulated moving bed flow system suitable for use in the process of the present invention is the co-current simulated moving bed system described in U.S. Pat. No. 4,402,832, which is also incorporated by reference in the present invention. Document it as a document.

Whatever flow system is used to carry out the invention, at least a portion of the extract output stream is fed to a separation device where at least a portion of the desorbent material is separated;
An extract product is obtained which has a reduced concentration of desorbent substances. Although not necessarily operationally necessary, preferably at least a portion of the roughinate output stream is fed to a separation device to obtain a ruffinate product with a reduced concentration of desorbent material and a desorbent material that can be reused in the process. At least a portion of the desorbent material is separated. Such separation devices are typically fractionation columns, the design and operation of which are well known in the separation art.

Although liquid phase and gas phase operations can be used in many adsorption separation processes, liquid phase operation is preferred for the present invention. This is because liquid phase operation requires lower temperature conditions and yields a higher extract product than gas phase operation. Therefore, desorption conditions include sufficient pressure to maintain a liquid phase and a temperature of 20-200°C, as described above. Adsorption conditions include the range of temperatures and pressures used for desorption.

Static experimental procedures and equipment can be used to test various adsorbents with particular feed mixtures to determine the relative retention by the adsorbent of each component of the mixture. The procedure involves mixing equal amounts of each component whose relative retention is to be determined with a suitable solvent or desorbent material. The desorbent is chosen to have a boiling point that allows it to be easily separated from the isomer being tested. Pour the mixture into a container containing an appropriate amount of adsorbent and leave it for about 24 hours with occasional stirring. The solution is then analyzed for each component and its relative retention is determined by the ratio of relatively weakly adsorbed components to relatively strongly adsorbed components, R. The higher the relative retention of relatively strongly adsorbed components, the higher the ratio.

Dynamic laboratory equipment is used to test various adsorbents with specific feed mixtures and desorbent materials to determine adsorption properties such as retention capacity and exchange rate. This device consists of a helical adsorbent chamber approximately 70-80 c.c. in volume with an inlet and an outlet at opposite ends of the chamber. The chamber is housed within a temperature regulating device and a pressure regulating device is used to operate the chamber at a predetermined constant pressure. Quantitative and qualitative analytical instruments such as refractometers, polarimeters and chromatographs are also connected to the outlet line of the chamber to qualitatively or quantitatively analyze one or more components contained in the stream exiting the adsorbent chamber. analyse. Pulse tests performed with this equipment and the general procedure described below are used to determine data for various adsorbent systems. Passing a desorbent material through the adsorbent chamber fills and equilibrates the adsorbent with the desorbent material. At appropriate times, a pulse of a feed containing a known concentration of tracer diluted with a desorbent material and a particular extract or ruffinate component, or both, also of known concentration, is injected over a period of several minutes. The supply of desorbent material is resumed and the tracer and extract or raffinate components (or both) are eluted as in a liquid-solid chromatographic operation. The effluent can be analyzed on-stream, or effluent samples can be collected periodically and analyzed separately at a later time to delineate the trajectory of the envelope or the peak of the corresponding component.

From the information obtained in this experiment, the performance of the adsorbent can be measured in terms of spatial volume, retention capacity for extract or raffinate components, and rate of desorption of extract components from the adsorbent. The holding capacity of the extract or roughinate component is
It may be characterized by the distance between the center of the peak envelope of the extract or roughinate component and the center of the peak envelope of the tracer component or other known reference point. It is expressed as the volume of desorbent material pumped in cubic centimeters during the time interval given by the distance between the peak envelopes. The rate of exchange of extract components by a desorbent substance is generally characterized by the half-width of the peak envelope. The narrower this width is, the faster the desorption speed is. The desorption rate also varies from the center of the peak envelope of the tracer component to
It can also be characterized by the distance until the desorbed extract components disappear. This distance corresponds to the volume of desorbent material pumped during the time interval.

The following examples illustrate the method of the invention, but are not intended to limit the scope of the invention.

Example 1 Static experiments were performed to demonstrate that isomers can be separated by an adsorption process. In this case, since there is no method for complete analysis of TDI isomers, adsorption experiments were performed with the analog phenyl isocyanate.
2,6-toluene diisocyanate and 2,4-
Phenyl isocyanate, which can be analyzed from both toluene diisocyanate, was mixed separately with each of the isomers and two sets of experiments were performed for each adsorbent. The static relative selectivity A of isomers was obtained by first calculating the relative selectivity of each isomer and phenyl isocyanate as follows.

A _PI/2,4 = PI(A)/2,4(A)/PI(U)/2,4(U
) A _2,6/PI = 2,6(A)/PI(A)/2,6(U)/PI(U
) Therefore, A _2,6/2,4 = A _PI/2,4 × A _2,6/PI In an inert atmosphere, stock solutions of toluene diisocyanate, phenyl isocyanate, and isooctane were prepared as follows. and conducted separate experiments.

2,4-TDI or 2,6-TDI 5.88vol.% Phenyl Isocyanate 5.88vol.% Isooctane Balance In static experiments, the volume ratio of stock solution to adsorbent is
It was 1.5. The temperature was 25°C. Mix the stock solution and adsorbent in a flask, measure the amount of each isomer released into the ruffinate, and add 2,6-TDI/
The static selectivity A of 2,4-TDI was calculated by the method described above for several adsorbents. The results are as follows.

Adsorbent 2,6-/2,4-A BaK-X Non-adsorbed K-Y 1.63 Na-Y 0.79 Li-Y 0.71 Mg-Y 0.60 These experiments indicate that 2,6-TDI is selective for K-Y. This shows that 2,4-TDI is selectively adsorbed on Na-Y, Li-Y, and Mg-Y. Therefore, these isomers can be separated by the adsorption method of the present invention. Ba-X does not adsorb any isomer.

Example 2 In this example, a potassium-exchanged Y-type zeolite was used in the pulse experimental setup described above to obtain data. The liquid temperature was 150°C, and the liquid flow rate to the column was 1.2 cc/min. The feed stream was a pulse of 2.6 cc of a solution containing 1 c.c. of a 65/35 mixture of 2,4- and 2,6-, and 0.8 cc of n.
-C contained tracer ₁₄ . The column was packed with 30 to 60 meshes of adsorbent hardened with clay. The desorbent is 100% toluene.

The selectivity (B) described above was calculated from the peak locus obtained for each component. FIG. 1 shows the envelope drawn during the pulse experiment. The selectivity B of 2,6/2,4 is 1.48, which means that the 2,6-toluene diisocyanate isomer is preferentially adsorbed on the potassium-exchanged Y-type zeolite over the 2,4-isomer. shows. Since 2,6-toluene diisocyanate is a minor component, separation of the 2,6-isomer from the adsorbed material can be done inexpensively.

Example 3 In this example, sodium-exchanged Y-type zeolite is
Data were obtained using the pulse experimental setup described above.
The liquid temperature was 153°C, and the liquid flow rate to the column was 1.2 cc/min. The feed stream was a pulse of 2.6 cc of a solution containing 1 c.c. of a 65/35 mixture of 2,4- and 2,6-, and 0.8 cc of n.
-C contained tracer ₁₄ . The column was packed with 30 to 60 meshes of adsorbent hardened with clay. The desorbent is 100% toluene.

The selectivity (B) described above was calculated from the peak locus obtained for each component. The experimental results for this example are shown in FIG. The selectivity for 2,4/2,6 was 1.40, indicating that 2,4-TDI was preferentially adsorbed.

Examples 4 and 5 Another pulse experiment was performed using the same conditions as in Example 3, except that the temperature and adsorbent were changed as shown in the table below, and from the peak trajectories in Figures 3 and 4, 2, 4/
The selectivity B of 2,6 was calculated.

Example Adsorbent Liquid temperature Selectivity B Desorbent 4 Ca-Y 150℃ 1.72 Toluene 5 Li-Y 150℃ 1.44 Toluene Example 6 In this example, sodium-exchanged Y-type zeolite is
Data were obtained using the pulse experimental setup described above.
The liquid temperature was 100°C, and the liquid flow rate to the column was 1.26 cc/min. The feed stream contained a pulse of 2.6 cc of a solution containing 2 c.c. of an 80/20 mixture of 2,4- and 2,6-, 0.5 cc of n-C ₁₄ tracer and a balance amount of desorbent. Ta. 30 to 60 hardened with clay in the column
Filled with mesh adsorbent. The desorbent is 100% toluene.

The selectivity (B) described above was calculated from the peak locus obtained for each component. The experimental results of this example are shown in FIG. The selectivity of 2,4/2,6 is 1.90, and at 100°C, the selectivity of 2,4-
It shows that TDI is more preferentially adsorbed (see results of Example 3 at higher temperature).

Generally, the above experimental data are based on Na, Ca, Mg
and Li-exchanged Y-type zeolite is selective for 2,4-toluene diisocyanate, and K-exchanged Y-type zeolite is selective for 2,6-toluene diisocyanate. , indicating that the separation method of the present invention has sufficient selectivity for commercial use.

[Brief explanation of drawings]

FIG. 1 is a plot showing the chromatographic separation of the 2,4- and 2,6-isomers of toluene diisocyanate using a K-Y zeolite adsorbent. FIG. 2 is a plot showing the chromatographic separation of the 2,4- and 2,6-isomers of toluene diisocyanate on a Na-Y zeolite adsorbent at 153°C. FIG. 3 is a plot showing the chromatographic separation of the isomers on a Ca-Y zeolite adsorbent. FIG. 4 is a plot showing the chromatographic separation of the isomers on a Li-Y zeolite adsorbent. FIG. 5 is a plot showing the chromatographic separation of the isomers on a Na-Y zeolite adsorbent at 100°C.

Claims (1)

[Claims] 1 2,6-toluene diisocyanate and 2,4
- An adsorbent containing Y-type zeolite that selectively adsorbs 2,6-toluene diisocyanate isomer by cation-exchanging the raw material mixture containing toluene diisocyanate with K, or an adsorbent containing Na, Ca,
Contacting under adsorption conditions with an adsorbent containing a Y-type zeolite that selectively adsorbs 2,4-toluene diisocyanate isomer due to cation exchange with a cation selected from the group of Li, Mg and mixtures thereof, A method for separating the raw material mixture comprising removing the remainder of the raw material mixture from an adsorbent and then desorbing it under desorption conditions with a desorbent material containing toluene to recover the adsorbed toluene diisocyanate isomer. 2 The above adsorption conditions and desorption conditions are 20℃ to 200℃
2. The method of claim 1, comprising a temperature in the range of and a pressure sufficient to maintain the liquid phase. 3. The method according to claim 1, wherein the separation method is carried out using a simulated moving bed flow method. 4. The method according to claim 1, wherein the separation method is carried out in a static bed method.