JP3149443B2 - Adsorbent and gas purification method containing ketone organic solvent - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an adsorbent useful for purifying a gas containing a ketone organic solvent and a method for using the same.

[0002]

2. Description of the Related Art Conventionally, activated carbon has been widely used as an adsorbent for purifying gas containing a solvent. However, when a ketone-based organic solvent is contained in the gas, the formation of trace amounts of decomposition products is often confirmed by the catalytic action of activated carbon. Of these decomposition products, those that are easily desorbed will lower the purity of the recovered solvent, and those that are hardly desorbed will contaminate the activated carbon and cause adsorption failure. The decomposition products are often acids, which have an adverse effect such as corrosion of equipment materials.

[0003] Ketones generate a carboxylic acid via an enol-type intermediate by an oxidizing action on the surface of the adsorbent. Since this reaction is exothermic, it progresses rapidly, and the generated reaction heat accumulates.If there is sufficient oxygen supply, the reaction proceeds in a chain, and eventually the activated carbon layer itself may ignite. . The ignition temperature of fresh activated carbon is 400-5
The temperature is about 00 ° C., but it may be 200 ° C. or less when a large amount of high-boiling substances is accumulated.

As described above, there are various problems when using activated carbon for purifying a gas containing a ketone-based organic solvent. For this reason, various measures have been taken such as using activated carbon having a low catalytic activity or installing a dehumidifier upstream of the adsorption layer to prevent the temperature of the layer from rising due to heat of adsorption or reaction. However, as long as activated carbon is used as the adsorbent, some catalytic action on the ketone organic solvent cannot be avoided. When a humidifier is installed, the catalytic action can be suppressed, but when the relative humidity increases, the amount of activated carbon adsorbed on the organic solvent decreases. For this reason, extreme care was required in the operation management of the adsorption device.

Further, in recent years, zeolite having enhanced hydrophobicity as a new adsorbent replacing activated carbon has begun to be used for adsorption of organic compounds (Japanese Patent Publication No. 60-501495 and Japanese Patent Application Laid-Open No. 64-85113).

[0006]

However, when the present inventors tried to adsorb a ketone organic solvent with this hydrophobic zeolite, they found that they exhibited catalytic activity similar to activated carbon. In other words, in the purification of exhaust gas containing a ketone-based organic solvent using activated carbon or hydrophobic zeolite, etc., the adsorption operation of the ketone-based organic solvent is possible, but in the process of heating and regeneration of the adsorbent, the ketone-based organic solvent is deposited on the adsorbent. A decomposition or polymerization reaction is caused by the catalytic action. As a result, the purity of the ketone-based organic solvent in the concentrated or recovered organic solvent was low and could not be reused. In addition, as the adsorption / desorption operation is repeated, the adsorption performance of the adsorbent itself decreases, and not only cannot stable exhaust gas purification be performed,
There were also safety and maintenance issues such as ignition and equipment corrosion.

The inventors have paid particular attention to the catalytic activity of the adsorbent for ketone-based organic solvents, and have been able to recover high-purity ketone-based organics from exhaust gas without performing any special operation. The present inventors have conducted intensive studies to provide an adsorbent that does not show a catalytic property with respect to a ketone organic solvent without fear.

[0008]

SUMMARY OF THE INVENTION The present invention provides an adsorbent comprising a hydrophobic zeolite of an alkali metal type or an alkaline earth metal type suitable for purifying exhaust gas containing a ketone organic solvent, and a method of using the same. Things.

The details of the present invention will be described below.

The basic structure of a zeolite crystal is a tetrahedron of SiO ₄ and its substituted AlO ₄ , which share the apex oxygen atom with each other to form a crystal structure developed in a three-dimensional direction. . As a result, zeolite crystals have very large cavities and pores that are not found in other minerals. Although the entrance diameter of these pores differs depending on the zeolite, it is usually 3 to 9 Å, and various molecules can be trapped inside the pores. Also,
A cation exists inside the crystal to supplement the negative charge of AlO ₄ . Polar molecules and polarizable molecules are selectively adsorbed under the influence of the electrostatic field formed by the cations. SiO such as A-type zeolite, X-type zeolite and Y-type zeolite which are generally used as general-purpose adsorbents
_{The 2} / Al ₂ O ₃ molar ratio is as low as 2 to 5, and these zeolites adsorb water selectively over organic compounds. Therefore, it is not suitable as an adsorbent for purifying exhaust gas containing an organic solvent.

Zeolite loses hydrophilicity at a SiO ₂ / Al ₂ O ₃ molar ratio of 20 or more and gradually becomes hydrophobic. The zeolite exhibiting such hydrophobicity is useful as a hydrophobic adsorbent, similarly to activated carbon, for purifying exhaust gas containing an organic solvent. However, hydrophobic zeolites also have a catalytic effect. Therefore, when brought into contact with a highly reactive organic compound such as a ketone-based organic solvent, the ketone-based organic solvent adsorbed in the process of heating and regenerating causes a decomposition or polymerization reaction by the catalytic action of zeolite. The ketone organic solvent remaining during use as an adsorbent becomes a low polymer or a decomposed product,
Such a catalytic reaction, which causes ignition, a decrease in adsorption capacity, and corrosion of the apparatus, occurs particularly violently in the desorption operation when the regeneration is performed by heating, and progresses to a small extent even in the PSA operation performed at a low temperature. Furthermore, since the decomposition reaction of the ketone-based organic solvent is an exothermic reaction, even in the case of the PSA method without heat regeneration, the heat of reaction accumulates in the adsorbent layer and the adsorbent temperature may rise rapidly.

The active site of this catalytic reaction is considered to be an acid site in the hydrophobic zeolite crystal. Therefore, SiO ₂ / A
Zeolites with an infinite l ₂ O ₃ molar ratio are considered to have no catalytic action. However, the zeolite that can be actually obtained or adjusted has a SiO ₂ / Al ₂ O ₃ molar ratio of 5
About 00 is the limit. This is because a small amount of a metal oxide other than silicon is contained in a silicon source usable as a raw material of zeolite. For example, in the case of the direct synthesis method, a trace amount of metal atoms such as aluminum in a silicon source are selectively incorporated into the zeolite crystal skeleton during the crystallization process. Further, even in the case of an acid extraction method using a mineral acid or the like, it is practically impossible to completely remove a trace amount of metal atoms in zeolite.

For these reasons, zeolite exhibiting hydrophobicity has been conventionally difficult to use as an adsorbent due to its catalytic action on exhaust gas containing highly reactive ketone-based organic solvents. However, the crystal skeleton of zeolite is S
It is made of an inorganic oxide such as iO ₄ or AlO ₄ and is nonflammable. For this reason, the adsorbent itself does not ignite for purification of exhaust gas containing flammable substances such as organic solvents,
It is a very attractive adsorbent for safety.

The present inventors have prepared various zeolites by a direct synthesis method or a method of modifying the synthetic zeolites, and have conducted intensive studies to obtain a zeolite adsorbent having no catalytic activity for a ketone organic solvent. Was. As a result, they have found that hydrophobic zeolite, which is an alkali metal type, does not exhibit catalytic activity with respect to ketone organic solvents and is an excellent adsorbent having no danger of ignition. SiO ₂
In the case of an alkali metal or alkaline earth metal zeolite having a / Al ₂ O ₃ molar ratio of less than 50, the hydrophobicity is reduced,
It is not suitable as the adsorbent of the present invention because it adsorbs a lot of water. Therefore, the alkali metal type hydrophobic zeolite of the present invention preferably has a SiO ₂ / Al ₂ O ₃ molar ratio of 50 or more.

Further, the zeolite to show the molecular sieving effect, the kind of adsorbable molecules is determined by the type of zeolite. When the ketone-based organic solvent is recovered from the exhaust gas, it is sufficient that the pore entrance diameter of the zeolite is larger than the molecular diameter to be adsorbed. Usually, the pore inlet may be a zeolite having an oxygen of 8, 10 or 12 members, and may include chabazite offretite, mordenite, faujasite, L,
Crystal structures such as Ω, ZSM-5 and ZSM-11 are suitable.

As a method for preparing the hydrophobic zeolite, a method in which natural zeolite or synthetic zeolite is used as a starting material by dealumination using a mineral acid or the like, or a silica source, an alumina source, an alkali source and organic mineralization There is a direct synthesis method in which an agent is mixed and crystallized.

As the hydrophobic zeolite prepared by dealumination, etc., dealuminated mordenite ((NY Chen, J. Phy. Chem. 8)
0, (1), 60-64 (1976)), superhydrophobic Y-type zeolite (JP-A-54-122700, Stu)
dies in Surface Sciencean
d Catalysis, Volume 5,203-
210 (1980)) and hydrophobic L-type zeolite (JP-A-63-50312). The hydrophobic zeolites prepared by the direct synthesis method include Z
SM-5 (Japanese Patent Publication No. 46-10064), ZSM-
11 (JP-B-53-23280), ZSM-12
(JP-B-52-16079), ZSM-22 (JP-A-59-111912), ZSM-23 (JP-A-51-149900), and ZSM-48 (JP-A-56-22622). ), Silicalite (JP-A-54
-72795) and the like.

Any of these can be suitably used as the hydrophobic zeolite of the present invention.

Usually, the hydrophobic zeolite obtained by the above method is of the proton type. In order to obtain the alkali metal type hydrophobic zeolite of the present invention, it is necessary to convert these proton type hydrophobic zeolites into an alkali metal type or an alkaline earth metal type by a neutralization method or an ion exchange method.

As the alkali metal or alkaline earth metal suitable for the present invention, Li, Na, K, Cs, Be, M
g, Ca, Sr, Ba and the like. SiO ₂ / Al ₂ O
_In the case of a hydrophobic zeolite having a molar ratio of 200 or less,
Local imbalance of charge in zeolites may occur, indicating solid acidity. That is, the hydrophobic zeolite, which is the adsorbent of the present invention, has a SiO2 / Al2O3 mole of 200.
In the following cases, a monovalent alkali metal type such as Li, Na, K, and Cs is preferable because it has no catalytic property for a ketone-based organic solvent.

As a method for converting a proton type hydrophobic zeolite powder into an alkali metal type or an alkaline earth metal type,
There are a neutralization method, an ion exchange method, and a combination method of both.
In the neutralization method, an aqueous solution of a hydroxide of an alkali metal or an alkaline earth metal is slowly dropped onto a slurry of a proton type hydrophobic zeolite to neutralize the solid acid point of the zeolite, and the alkali metal or alkaline earth metal is neutralized. It is a method to make a type. The ion exchange method is a method in which a proton type hydrophobic zeolite is put into an aqueous solution of a salt of an alkali metal or a metal on an alkali, and ion-exchanged at a temperature of normal to 100 ° C. into an alkali metal type or an alkaline earth metal type. is there. In the case of the ion exchange method, when the exchange equilibrium is reached, the ion exchange does not proceed any more and the single ion exchange does not result in a complete alkali metal or alkaline earth metal type.
Further, it is necessary to repeat ion exchange several times. Also,
As a method of using both of them, there is a method in which a hydrophobic zeolite is slurried with an aqueous solution of an alkali metal or alkaline earth metal salt and neutralized with an aqueous solution of an alkali metal or alkaline earth metal hydroxide.

By this combined method, complete alkali metal type hydrophobic zeolite can be obtained, and the operation is simple and is the most rational method. However, the hydrophobic zeolite can be suitably used as the adsorbent of the present invention if the hydrophobic zeolite is a perfect alkali metal type or alkaline earth metal type regardless of which method is used. The hydrophobic zeolite of the alkali metal type or alkaline earth metal type thus obtained is further thoroughly washed and dried. If the washing operation is insufficient, the adsorption performance may be reduced due to the attached alkali metal salt or the like.

As a method for measuring the acid property of zeolite, there is a relatively simple thermal desorption method (TPD method). In the TPD method, a basic substance (generally, thermally stable ammonia, pyridine or the like is used) is adsorbed on a sample, and then desorbed while heating at a constant rate. At this time, since the adsorption of the basic substance to the acid site is considered to be one-to-one due to the acid-base action, the amount of the eliminated basic substance can be regarded as the amount of the acid site.
Further, it is considered that a basic substance adsorbed at a stronger acid point cannot be desorbed to a higher temperature, so that the strength of the acid point can be known from the desorbed temperature. As described above, in the TPD method, the amount of acid and the acid strength can be simultaneously determined. Py-T
The PD method may be performed according to the following operation procedure using a flow-type TPD device. That is, the sample is filled into the adsorption tube under the following conditions, and the sample is evacuated as a pretreatment. Pyridine is adsorbed on the sample, and then H 2 is used as a carrier gas for degassing the gas phase and physically adsorbed pyridine.
The temperature is raised at a constant rate while flowing e, and the desorption spectrum is observed.

Sample 0.4 g Pretreatment 500 ° C. for 1 hour Vacuum evacuation Adsorption at room temperature, 15 minutes, 50-60 Torr Deaeration 100 ° C. for 5 minutes Vacuum desorption Desorption He flow rate 60 cc / min Heating rate 10 ° C./min In the alkali metal or alkaline earth metal zeolite of the present invention, the Py-TPD has a solid acid content of 0.0
If it is higher than 5 mmol / g, there are many acid sites which are main active sites, so that decomposition occurs at the time of elimination, and the purity of the recovered organic solvent is reduced. In other words, the catalytic activity for the ketone organic solvent is high, which is not preferable. When the content is 0.05 mmol / g or less, the number of acid sites, which are active sites, is reduced, so that decomposition hardly occurs at the time of elimination, and a high-purity organic solvent can be recovered.
In other words, if the amount of solid acid is 0.05 mmol / g or less, the ketone-based organic solvent can be recovered and reused without causing decomposition or polymerization reaction of the ketone-based organic solvent on the adsorbent due to its catalytic action. be able to.

Next, in order to control the amount of the solid acid to 0.05 mmol / g or less, the proton-type hydrophobic zeolite is ion-exchanged, neutralized, or a combination of the two to form an alkali metal or alkali. It is necessary to use an earth metal type hydrophobic zeolite.

The adsorbent is usually used in the form of a column, a sphere or a honeycomb. In order to make the zeolite powder of these shapes, alkali metal type or alkaline earth metal type hydrophobic zeolite crystal itself has no binding, silica sol to enhance the binding between the carrier and zeolite crystal or zeolite crystal, An inorganic binder component such as silica gel or clay mineral is added, and secondary processing such as molding and honeycomb formation is performed. As the binder component, an inactive one is desirable, and one that shows a reaction activity with respect to a ketone-based organic solvent such as alumina sol or alumina gel is inappropriate. Further, after forming or honeycomb formation, a baking treatment is required to maintain the shape of these secondary processed products. It is also possible to form an alkaline metal type or an alkaline earth metal type after molding or honeycombing a proton type hydrophobic zeolite. However, in this case, washing and cleaning of the alkali metal type hydrophobic zeolite
It is necessary to perform drying, and in this process, the secondary processed product collapses, or excessive alkali metal or alkaline earth metal type salt remains attached due to insufficient washing, causing trouble such as deterioration of adsorption performance. . Therefore, as a method for producing the adsorbent of the present invention, first, a proton type hydrophobic zeolite powder is converted into an alkali metal type or an alkaline earth metal type by a neutralization method, an ion exchange method, or a combination thereof, and is subjected to molding or honeycombing. The next processing method is a reasonable method.

Incidentally, zeolite molded articles produced without using a binder are disclosed in Japanese Patent Application Laid-Open Nos. 62-70225 and 62-138320. Such a zeolite molded body containing no binder component is subjected to dealumination treatment to form a hydrophobic zeolite into an alkali metal type or an alkaline earth metal type, which has a large adsorption amount and is more suitable as the adsorbent of the present invention. is there.

The adsorbent of the present invention comprises methyl ethyl ketone,
It is particularly useful as an adsorbent for purifying exhaust gas containing ketone-based organic solvents such as methyl isobutyl ketone and cyclohexanone, and can be used in any device such as a fixed-bed adsorption device, a fluidized-bed adsorption device, a moving-bed adsorption device, and a honeycomb rotor concentration device. It can be suitably used. In addition, there are a PSA method, a PTSA method, a TSA method, and the like as a method of the adsorption / desorption operation, but any method can be applied.

[0029]

As described above, the present invention provides an alkali metal or alkaline earth metal type hydrophobic zeolite as an adsorbent for purifying exhaust gas containing a ketone organic solvent. By this, adsorption operation such as concentration and solvent recovery of exhaust gas of ketone organic solvent, which was difficult in the past,
This is possible without any special measures for the adsorption device. Also, since the adsorbent of the present invention does not show any catalytic properties,
The dangers such as corrosion of the adsorption device and ignition of the adsorbent layer, which have conventionally been problems, are eliminated.

[0030]

Embodiments of the present invention will be described below.

Example 1 A SiO ₂ / Al ₂ O ₃ molar ratio of 200 was obtained by a direct synthesis method.
ZSM-5 was obtained, and calcined in air at 600 ° C. for 4 hours to remove the organic mineralizer in the zeolite.
A 500 ml aqueous Cl solution is added, and the mixture is stirred to form a slurry. The slurry was neutralized by slow addition of 0.1N NaOH. Furthermore, washing was carried out sufficiently with warm water of 60 ° C. and dried at 120 ° C. overnight to obtain sodium-type hydrophobic ZSM-5. Sodium type hydrophobic Z
25 as a binder for 100 parts by weight of SM-5
The silica sol in parts by weight was added to obtain a columnar molded body having a diameter of 1.5 mm, and calcined at 600 ° C. for 2 hours in the atmosphere to obtain an adsorbent.

Comparative Example 1 Proton type ZSM having a SiO ₂ / Al ₂ O ₃ molar ratio of 200
25 parts by weight of a silica sol as a binder was added to 100 parts by weight of a -5 type zeolite to obtain a cylindrical molded body having a diameter of 1.5 mm, which was calcined at 600 ° C. for 2 hours in the atmosphere to obtain an adsorbent.

[0033] performs a dealumination treatment by mineral acids for Examples 2 _SiO 2 / _Al 2 _{O 3} molar ratio of 20 synthetic mordenite zeolite, a proton-type hydrophobic mordenite of _SiO 2 / _Al 2 _{O 3} molar ratio of 200 Was. Thereafter, an adsorbent was obtained in the same manner as in Example 1.

Comparative Example 2 On the other hand, 25 parts by weight of silica sol as a binder was added to 100 parts by weight of a proton-type hydrophobic mordenite having a SiO ₂ / Al ₂ O ₃ molar ratio of 200, and a cylindrical molded article having a diameter of 1.5 mm was added. The molded body was heated at 600 ° C.
After calcination for an hour, an adsorbent was obtained.

The measurement of the water adsorption capacity of the adsorbent obtained in each of the above examples, the measurement of the amount of solid acid by the pyridine TPD method, and the adsorption / desorption test for methyl ethyl ketone were carried out by the following methods. Table 1 shows the results.

<Moisture Adsorption Capacity> The adsorbent is put into a constant weight crucible (W ₁ g),
After heating at 50 ° C. for 2 hours to remove water, the mixture was cooled in a desiccator containing a desiccant and weighed (W ₂ g). The crucible was placed in a desiccator at a relative humidity of 20 %, left at 20 ° C. for 24 hours, and weighed (W ₃
g) was measured. The water adsorption capacity was determined by the following equation.

Water adsorption capacity (wt%) = {(w ₃ −w ₂ ) / (w ₂ −w ₁ )} × 100 <Method for measuring the amount of solid acid by pyridine TPD method> After treating in vacuum at 500 ° C. for 1 hour to remove water, nitrogen was introduced and the temperature was maintained at 500 ° C. for 1 hour.
Cooled to 0 ° C. Further, the pyridine gas evaporated by nitrogen was adsorbed on the sample at 300 ° C. for 20 minutes. Next, the sample is heated at a rate of 10 ° C./min from 300 ° C. to 950 ° C.
The amount of pyridine released was measured by gas chromatography (detector FID). The amount of the solid acid in the sample was determined by integrating the amount of the removed pyridine in the range of 300 ° C to 950 ° C.

<Adsorption / Desorption Test Method for Methyl Ethyl Ketone> The adsorption / desorption test column is made of glass and has an inner diameter of 6 cm and a length of 45 cm.
cm. This column is filled with adsorbent at a bed height of 12
cm, and an adsorption / desorption test was performed. The adsorption test was performed at 25 ° C. Methyl ethyl ketone concentration 300
0 ppm, air having a moisture concentration of 10,000 ppm and a flow rate of 0.1 ppm.
The solution was passed through the adsorbent layer at 2 m / sec, and the time when the methyl ethyl ketone concentration at the outlet became 150 ppm was defined as the breakthrough time (minute). Further, the concentration of methyl ethyl ketone at the outlet is 30.
The adsorption test was performed until the concentration reached 00 ppm, and the column weight (Wag) after the completion of the adsorption test was measured.

In the desorption test, the column was heated to 150 ° C. with a ribbon heater while flowing dry air at 0.075 m / sec through the adsorbent layer adsorbing methyl ethyl ketone until the outlet concentration of methyl ethyl ketone became 10 ppm or less. The column was cooled, and the column weight (W
dg) was measured. In addition, the methyl ethyl ketone concentration in the desorbed gas is integrated, and the recovered methyl ethyl ketone (Wr
g) was determined.

The methyl ethyl ketone recovery rate (%) was determined by the following equation.

Methyl ethyl ketone recovery rate (%) = Wr × 100 / (Wa−Wd) The methyl ethyl ketone concentrations at the inlet and outlet of the adsorption layer are as follows:
It was measured by gas chromatography (detector FID).

Table 1 Water adsorption capacity Breakthrough time Methyl ethyl ketone Solid acid amount wt% (min) Recovery rate (%) (mmol / g) Example 1 2.33 102 99.8 0.026 Comparative Example 1 2.76 90 65.1 0.119 Example 2 2.55 57 99.8 0.007 Comparative Example 2 2.73 60 84.7 0.083

Claims (3)

(57) [Claims] (1) a hydrophobic zeolite of an alkali metal type or an alkaline earth metal type;
An adsorbent having an O ₂ / Al ₂ O ₃ molar ratio of 50 or more;
An adsorbent for recovering the ketone-based organic solvent by absorbing and then desorbing a gas containing a ketone-based organic solvent. 2. The adsorbent according to claim 1, wherein the amount of solid oxygen in the adsorbent measured by a pyridine thermal desorption method is 0.05 mmol / g or less. 3. A gas containing a ketone-based organic solvent as claimed in claim 1.
A method for purifying a gas containing a ketone-based organic solvent, comprising contacting the organic solvent with the adsorbent according to claim 2, adsorbing the organic solvent, desorbing the organic solvent from the adsorbent, and collecting the organic solvent.