JP3096989B2 - 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 low catalytic activity or installing a dehumidifier upstream of the adsorption device to prevent the temperature of the bed from rising due to heat of adsorption, heat of reaction, or the like. However, as long as activated carbon is used as the adsorbent, for example, 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 hydrothermally calcined hydrophobic zeolite which is suitable for purifying exhaust gas containing a ketone-based organic solvent, and a method of using the same.

Hereinafter, the present invention will be described in detail.

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 it is 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 regeneration causes a decomposition or polymerization reaction by the catalytic action of zeolite. Furthermore, the ketone-based organic solvent remaining during use as an adsorbent for a long time becomes a low polymer or a decomposed product,
It may cause ignition, decrease in adsorption capacity, and corrosion of equipment. Such a catalytic reaction occurs particularly violently in the desorption operation in the case where 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 or a base site in the hydrophobic zeolite crystal. Therefore,
A zeolite having an infinite SiO ₂ / Al ₂ O ₃ molar ratio is considered to have no catalytic action. However, the zeolite SiO ₂ / Al ₂ O ₃ that is actually available or tunable
The limit of the molar ratio is about 500. 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 intensively studied to obtain a zeolite adsorbent having no catalytic activity for a ketone organic solvent. Was. As a result, it has been found that the hydrothermally calcined hydrophobic zeolite does not exhibit catalytic activity with respect to the ketone-based organic solvent and is an excellent adsorbent having no danger of ignition.

The hydrophobic zeolite SiO ₂ / Al ₂ O ₃
When the molar ratio is less than 50, it is difficult to completely extinguish the active sites for the ketone-based organic solvent even when the hydrothermal calcination treatment is performed, and in order to extinguish the active sites better, as a hydrophobic zeolite, SiO ₂ / Al ₂ O ₃ molar ratio 5
Those having 0 or more are preferable. The conditions of the hydrothermal calcination treatment vary depending on the structure of the hydrophobic zeolite and the SiO ₂ / Al ₂ O ₃ molar ratio, but by devising the conditions of the hydrothermal calcination treatment, no catalytic activity is exhibited for the ketone-based organic solvent. It is possible to obtain an adsorbent.

The hydrophobic zeolite may be prepared by a method of preparing a natural zeolite or a synthetic zeolite as a starting material by dealumination using a mineral acid or the like, or a silica source, an alumina source, an alkali source and an organic mineralizer. There is a direct synthesis method in which an agent is mixed and crystallized.

Examples of the hydrophobic zeolite prepared by dealumination or the like include 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 Science a
nd Catalyst, Volume 5,203
-210 (1980), hydrophobic L-type zeolite (JP-A-63-50312) and the like.

The hydrophobic zeolite prepared by the direct synthesis method includes ZSM-5 (JP-B-46-10064).
JP), ZSM-11 (JP-B No. 53-23280), ZSM-12 (JP-B No. 52-16079), ZSM-22 (JP-A No. 59-111912), and ZSM-23 (JP-A No. 59-111912). JP-A-51-149900), ZSM-48 (JP-A-56-22622), silicalite (JP-A-54-72795).
Etc. are known.

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

Since zeolite exhibits a molecular sieving effect, the types of molecules that can be adsorbed are 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. Normally, the pore entrance may be a zeolite having an 8, 10 or 12-membered enzyme ring, such as chabazite,
Offretite, mordenite, faujasite, L,
Crystal structures such as Ω, ZSM-5 and ZSM-11 are suitable.

The water vapor concentration in the hydrothermal calcination treatment on the hydrophobic zeolite is preferably 2 vol% or more, and a water vapor concentration of 5 vol% or more is a practical condition for practical use. When the water vapor concentration is high, the adsorbent of the present invention can be obtained even under the condition that the calcination temperature is relatively mild. However, in the case of hydrothermal calcination at a temperature lower than 500 ° C., it is difficult to completely eliminate the catalytic activity of the adsorbent for the ketone-based organic solvent.
When the temperature exceeds 1200 ° C., the crystal structure itself of the hydrophobic zeolite tends to collapse. That is, the temperature range suitable for performing hydrothermal calcination is 500 to 1200 ° C, preferably 600 to 1000 ° C. The time of hydrothermal firing varies depending on the water vapor concentration and firing temperature,
It is necessary to carry out for 30 minutes or more in the above temperature range.

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, since the hydrophobic zeolite crystal itself has no crystallinity, an inorganic binder such as silica sol, silica gel, clay mineral or the like is used to enhance the binding between the carrier and the zeolite crystal or zeolite crystal. The components are 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. At this time, if the calcination operation is performed under hydrothermal conditions, it is not necessary to previously hydrophobize the hydrophobic zeolite powder. That is, as a rational method for producing the adsorbent of the present invention, a method in which the hydrophobic zeolite powder is firstly subjected to secondary processing and then hydrothermal firing is possible. Needless to say, the adsorbent of the present invention can be obtained by subjecting the hydrophobic zeolite powder subjected to hydrothermal firing to secondary processing and firing under mild conditions.

Incidentally, zeolite molded bodies produced without using a binder are disclosed in Japanese Patent Application Laid-Open Nos. 62-70225 and 62-138320. Such a zeolite molded body that does not contain a binder component is subjected to dealumination treatment to obtain a hydrophobic zeolite, which is then subjected to hydrothermal calcination, which has a large adsorption amount and is more suitable as the adsorbent of the present invention.

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.

[0026]

As described above, the present invention provides a hydrothermally calcined hydrophobic zeolite as an adsorbent for purifying exhaust gas containing a ketone-based organic solvent. As a result, adsorption operations such as concentration of exhaust gas of a ketone-based organic solvent and solvent recovery, which have been difficult in the past, can be performed without special measures for the adsorption device. In addition, since the adsorbent of the present invention does not show any catalytic property, the danger of corrosion of the adsorber and ignition of the adsorbent layer, which have been problems in the related art, are eliminated.

[0027]

Embodiments of the present invention will be described below. Example 1, Comparative Example 1 (Example 1) SiO ₂ / Al ₂ O ₃ molar ratio 14, lattice constant 24.33
Angstrom Y-type zeolite with 1.5N at 50 ° C
Dealumination with a hydrochloric acid aqueous solution of SiO ₂ /
A hydrophobic Y-type zeolite having an Al ₂ O ₃ molar ratio of 500 was obtained. 25 parts by weight of clay was added as a binder to 100 parts by weight of this hydrophobic zeolite to obtain a columnar molded body having a diameter of 3 mm. This molded body is subjected to a water vapor concentration of 20 vol%.
The mixture was calcined at 800 ° C. for 2 hours under an air flow to obtain an adsorbent.

[0028] (Comparative Example 1) On the other hand, 25 parts by weight of the clay added as a binder with respect to Y-type zeolite 100 parts by weight of _SiO 2 / _Al 2 _{O 3} molar ratio 14 not subjected to dealumination by aqueous hydrochloric acid, A cylindrical molded body having a diameter of 3 mm was obtained. The molded body was fired at 800 ° C. for 2 hours under an air flow having a water vapor concentration of 20 vol% to obtain an adsorbent.

The adsorption / desorption test of these adsorbents with respect to methyl ethyl ketone was performed by the following method.

<Adsorption / desorption test method> The adsorption / desorption test column was made of glass and had an inner diameter of 6 cm and a length of 45 cm.
cm. This column is filled with adsorbent at bed height 35.
cm, and an adsorption / desorption test was performed. The adsorption test was performed at 25 ° C. Methyl ethyl ketone concentration 3
000 ppm air (moisture concentration 10,000 ppm) was flowed through the adsorbent layer at a flow rate of 0.2 m / sec, and the time when the methyl ethyl ketone concentration at the outlet became 150 ppm was defined as breakthrough time (minutes). Further, the adsorption test was performed until the methyl ethyl ketone concentration at the outlet became 3000 ppm, and the column weight (Wa) 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. After cooling the column, the column weight (W
d) was measured. In addition, the methyl ethyl ketone concentration in the desorbed gas is integrated, and the recovered methyl ethyl ketone (Wr)
I sought.

The methyl ethyl ketone recovery rate (%) was determined by the following equation. Table 1 shows the results.

Methyl ethyl ketone recovery rate (%) = Wr × 100 / (W
a-Wd) The methyl ethyl ketone concentrations at the inlet and outlet of the adsorption layer are
It was measured by gas chromatography (detector: FID). Example 2, Comparative Example 2 (Example 2) Synthesis mordenite zeolite _{dealuminated,} hydrophobic-mordenite type zeolite of SiO 2 / _Al 2 _{O 3} molar ratio of 200. 100 parts by weight of this hydrophobic mordenite type zeolite is used as a binder as 25
The silica sol in parts by weight was added to obtain a cylindrical molded body having a diameter of 3 mm. This molded body was fired at 700 ° C. for 10 hours under an air flow having a water vapor concentration of 20 vol% to obtain an adsorbent.

Comparative Example 2 An adsorbent was obtained in the same manner as in Example 2 except that calcination was performed in dry air.

For these adsorbents, an adsorption / desorption test was performed in the same manner as in Example 1, and the methyl ethyl ketone recovery rate was determined.

Table 1 Breakthrough time (min) Methyl ethyl ketone recovery rate (%) Example 1 260 99.9 Comparative Example 1 260 94.8 Example 2 151 99.2 Comparative Example 2 155 84.7

Claims (3)

(57) [Claims] 1. A hydrothermal sintering treatment is performed to obtain SiO ₂ / Al ₂ O
_An adsorbent comprising a hydrophobic zeolite for adsorbing a ketone-based organic solvent, wherein the molar ratio is ₃ or more. 2. The adsorbent according to claim 1, wherein the hydrothermal calcination treatment is performed under the conditions of a steam concentration of 2 vol% or more, a calcination temperature of 500 to 1200 ° C., and a calcination time of 30 minutes or more. 3. A method for purifying a gas containing a ketone-based organic solvent, comprising bringing a gas containing a ketone-based organic solvent into contact with the adsorbent according to claim 1 or 2.