JP3111519B2 - Adsorbent for purifying exhaust gas containing high-boiling components and purification method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a process for producing a material having a boiling point of 120 at atmospheric pressure.
The present invention relates to an adsorbent for exhaust gas containing an organic component having a high boiling point of not less than ° C. and a method for purifying the exhaust gas by using the adsorbent.

[0002]

2. Description of the Related Art Conventionally, activated carbon has been widely used as an adsorbent for purifying exhaust gas containing organic components such as solvents. However, the boiling point of the organic component is 120 ° C. or more,
When the temperature was as high as 50 ° C. or higher, the carbon was not easily desorbed from the activated carbon layer, and accumulated on the activated carbon, causing an adsorption failure. When the reactivity of the high-boiling organic components accumulated on the activated carbon in this manner is high, an oxidation reaction is caused by the catalytic action of the activated carbon, and the oxidation reaction proceeds in a chain by the reaction heat generated when oxygen is supplied, Eventually, the activated carbon layer itself may ignite. The ignition temperature of fresh activated carbon is
The temperature is about 400 to 500 ° C., but may be 200 ° C. or less when a large amount of high-boiling organic components are accumulated. Further, even if the exhaust gas containing a high boiling point component is treated with activated carbon, it is difficult to regenerate as described above. Therefore, the used activated carbon must be discarded or regenerated by a specialist. As described above, purification of exhaust gas containing high-boiling organic components using activated carbon is often economically or safety disadvantageous.

In recent years, zeolite with enhanced hydrophobicity has been used as an adsorbent for organic compounds instead of activated carbon (Japanese Patent Publication No. 60-501495 and Japanese Unexamined Patent Publication No. Sho 64-64).
-85113).

[0004]

However, in the case of using hydrophobic zeolite as an adsorbent for purifying exhaust gas containing organic compounds having a high boiling point, the regeneration method and the behavior of the high boiling point component on the adsorbent, particularly its catalytic action No consideration has been given to caulking or decomposition by the method. We have a boiling point of 12
When purifying exhaust gas containing high-boiling organic components of 0 ° C or higher, it is possible to purify exhaust gas containing high-boiling components safely without special operation, paying particular attention to the method of regenerating the adsorbent and the catalytic properties of the adsorbent. We have been diligently studying how to develop a method.

The basic structure of a zeolite crystal is a tetrahedral structure of SiO ₄ and its substituted AlO ₄ , which share the oxygen atom at the apex of 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. The entrance diameter of these pores depends on the zeolite, but is usually 3 to 9 Å, and various molecules can be trapped inside the pores. In addition, a cation exists inside the crystal to supplement the negative charge of AlO ₄ . Polar molecules are selectively adsorbed under the influence of the electrostatic field formed by the cations. The SiO ₂ / Al ₂ O ₃ molar ratio of A-type zeolite, X-type zeolite, Y-type zeolite and the like generally used as general-purpose adsorbents is as low as 2 to 5, and these zeolites are more water-soluble than organic compounds. Is selectively adsorbed. 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, a part of the adsorbed high-boiling organic component is carbonized during the heating and regeneration process. If the exhaust gas contains a highly reactive organic compound, it is oxidized by the catalytic action of the hydrophobic zeolite during the heating and regeneration process. The catalytic nature of such hydrophobic zeolites is a negative factor for the life of the adsorbent or the safety of the device.

[0007] It is considered that the catalytic cause of the hydrophobic zeolite is mainly due to the acid sites in the crystals. Therefore, SiO ₂ / A
A zeolite having an infinity of 1 ₂ O ₃ molar ratio is considered to have no acid point or base point and has no catalytic action. However,
Zeolite SiO ₂ / A which is actually available or tunable
The limit of the l ₂ O ₃ molar ratio is about 500. This is because the silicon source used as a raw material for preparing zeolite contains a small amount of aluminum oxide. For example, in the case of the direct synthesis method, a trace amount of aluminum oxide in the silicon source is 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 aluminum oxide in zeolite.

For these reasons, hydrophobic zeolites exhibit catalytic properties that cause carbonization and oxidation of the adsorbed organic solvent. In particular, it has been difficult to use exhaust gas containing an organic component having a high boiling point as an adsorbent. However, the crystal skeleton of zeolite is formed of an inorganic oxide such as SiO ₄ or AlO ₄ and is nonflammable. For this reason, the adsorbent itself does not ignite for purification of exhaust gas containing high boiling components, and high-temperature regeneration at 180 ° C. or higher is possible, which is extremely attractive.

The present inventors have prepared various zeolites by a direct synthesis method or a method of modifying the synthetic zeolites, and prepared a zeolite-based adsorbent that does not exhibit catalytic properties in the regeneration process for exhaust gas containing high boiling components. We worked diligently to obtain.

[0010]

As a result, the hydrophobic zeolite has a SiO ₂ / Al ₂ O ₃ molar ratio of 50 or more,
And a hydrophobic zeolite having a solid acid amount of pyridine by a temperature-programmed desorption method (hereinafter, "solid acid amount" means a value measured by this method unless otherwise specified) is 0.1 mmol / g or less. Is an excellent adsorbent that does not exhibit catalytic properties and has no danger of reduced adsorption performance or ignition due to carbonization for high-boiling organic components having a boiling point under atmospheric pressure (hereinafter referred to as boiling point) of 120 ° C or higher. I found something.

The hydrophobic zeolite has a solid acid content of 0.1 mm
Hydrothermal treatment is effective as a method for controlling the amount to ol / g or less. However, the hydrophobic zeolites of the present invention are based on SiO ₂
/ Al ₂ O ₃ molar ratio must be 50 or more. SiO ₂ / Al ₂ O ₃ molar ratio of hydrophobic zeolite 5
If it is less than 0, it is difficult to reduce the amount of solid acid to 0.1 mmol / g or less even when the hydrothermal calcination treatment is performed. Therefore, the conditions of the hydrothermal calcination treatment vary depending on the structure of the hydrophobic zeolite or the molar ratio of SiO ₂ / Al ₂ O ₃ . It is possible to obtain no adsorbent.

As a method for preparing a hydrophobic zeolite, a natural zeolite or a synthetic zeolite is used as a starting material to prepare by a dealumination treatment using a mineral acid or the like, or a silica source, an alumina source, an alkali source, and an organic mineral. 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 (Japanese Patent Application Laid-Open No. 54-122700, Stu)
dies in Surface Sciencean
d Catalysis, Volume 5, 203-2
10 (1980)), hydrophobic L-type zeolite (JP-A-6
No. 3-50312).

The hydrophobic zeolite prepared by the direct synthesis method includes ZSM-5 (JP-B-46-10064).
ZSM-11 (JP-B No. 53-23280), ZSM-12 (JP-B No. 52-16079), ZSM-22 (JP-A-59-111912), ZSM-23 (JP-A-59-112912). 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 for producing the adsorbent 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 recovering the organic solvent from the exhaust gas, it is sufficient that the pore entrance diameter of the zeolite is larger than the adsorbed molecular diameter. Normally, it is sufficient that the pore inlet is a zeolite having an oxygen-containing 8, 10 or 12-membered ring. Chabazite, offretite, mordenite, faujasite, L, Ω, ZSM
Crystal structures such as -5 and ZSM-11 are suitable.

The water vapor concentration of the hydrothermal calcination treatment on the hydrophobic zeolite needs to be at least 2 vol% or more,
Desirably, a water vapor concentration of 5 vol% or more is a practical implementation condition. 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, even if hydrothermal calcination is performed at a temperature of 500 ° C. or less, it is difficult to reduce the solid acid amount of the adsorbent to 0.1 mmol / g or less. Further, when calcined at a temperature of 1200 ° C. or more, the crystal structure of the hydrophobic zeolite itself collapses, and the adsorbent of the present invention cannot be obtained. Therefore, the preferred temperature range for performing hydrothermal firing is 500 ° C.
~ 1200 ° C, preferably 600 ° C ~ 1000 ° C
It is. The time of the hydrothermal calcination depends on the steam concentration and the calcination temperature, but it is necessary to perform the hydrothermal calcination at least 30 minutes in the above temperature range.

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 (usually, thermally stable ammonia or pyridine is used) is adsorbed on a sample, and then desorbed while increasing the temperature at a constant rate. At this time, the adsorption of the basic substance to the acid site is considered to be one-to-one by the acid-base action,
The amount of the eliminated basic substance can be regarded as the amount of acid sites. Further, it is considered that the basic substance adsorbed at the stronger acid point does not desorb 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. The TPD method using pyridine (Py-TPD method) is a flow-type TPD method.
The following operation procedure may be performed using the 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 to the sample, and then the temperature is raised at a constant rate while flowing He as a carrier gas for degassing the gas phase and the physically adsorbed pyridine, and the desorption spectrum is observed.

Sample 0.4 g Pretreatment 500 ° C., 1 hour vacuum evacuation Adsorption Room temperature, 15 minutes, 50-60 Torr Deaeration 100 ° C., 5 minute evacuation Desorption He flow 60 cc / min Heating rate 10 ° C./min When the amount of solid acid in the Py-TPD method is higher than 0.1 mmol / g in the zeolite adsorbent, the organic components having a high boiling point are carbonized when desorbed because the acid sites, which are the main active sites, are large. Gradually decreases the effective adsorption amount. In addition, the high-boiling components and carbides accumulated in the adsorbent are oxidized by oxygen supplied at the time of adsorption, and may form hot spots, which is not preferable in terms of maintenance management of the apparatus. When the amount of the solid acid is 0.1 mmol / g or less, the number of active sites, which are active sites, decreases, and carbonization hardly occurs during desorption. Therefore, the effective adsorption amount does not decrease and the high-boiling components and carbides do not accumulate, which is advantageous in terms of the maintenance of the apparatus.

When a hydrophobic zeolite powder is used as an adsorbent, it must be in a columnar or spherical or honeycomb shape. At that time, since the hydrophobic zeolite crystal itself has no binding property, an inorganic binder component such as silica sol, silica gel or clay mineral is added in order to enhance the binding property between the carrier and the zeolite crystal or the zeolite crystal, and molding and honeycomb formation are performed. And the like. As the binder component, an inactive one is desirable, and one that shows a reaction activity with respect to an 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 firing operation is performed under hydrothermal conditions, it is not necessary to hydrothermally fire the hydrophobic zeolite powder in advance. That is, as a rational method for producing an adsorbent having a solid acid content of 0.1 mmol / g or less, a method of first performing a secondary processing of a hydrophobic zeolite powder and subsequently performing a 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 JP-A-62-70225 and JP-A-62-138320. Like this,
A zeolite molded body containing no binder component is subjected to a dealumination treatment to obtain a hydrophobic zeolite, which is calcined hydrothermally, and has a large adsorption amount, which is more suitable as the adsorbent of the present invention.

The adsorbent of the present invention is effective when the exhaust gas contains an organic solvent having a boiling point of 120 ° C. or more at atmospheric pressure. In particular, for purifying exhaust gas from processes using paints containing additives such as cellosolves or carbitols, exhaust gas from plastic or resin film processing processes or exhaust gas from processes using methylpyrrolidone as a reaction solvent or cleaning agent It is particularly useful as an adsorbent and can be suitably used in any apparatus such as a fixed bed adsorption apparatus, a fluidized bed adsorption apparatus, a moving bed adsorption apparatus, and a honeycomb rotor concentrator.

[0023]

As described above, according to the present invention, even when used for purification of exhaust gas containing a high-boiling organic component having a boiling point of 120 ° C. or more, or even 150 ° C. or more, the adsorbent has no catalytic property. Since it is not shown, the component to be adsorbed can be desorbed without oxidation, carbonization, etc., and therefore, there is no ignition or a decrease in adsorption capacity. This makes it possible to perform an adsorption operation, such as concentration of an organic solvent exhaust gas containing a high-boiling component and recovery of the solvent, which has been difficult in the past, without any special measures for the adsorption device.

[0024]

Embodiments of the present invention will be described below. 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 of to obtain an adsorbent.
The amount of the solid acid of this adsorbent by the Py-TPD method was described later in “Method for measuring the amount of solid acid by the Py-TPD method”, and the adsorbed components were p-xylene (boiling point: 138.4 ° C.) and n-butyl cellosolve (boiling point). : 170.2 ° C.) and the degree of deterioration and the degree of deterioration were measured by the “adsorption / desorption test method”. The results are shown in Tables 1 and 2. The adsorbent after eight adsorption / desorption cycles had a color tone almost equal to that of the new adsorbent (before use in measurement).

Comparative Example 1 The Y-type zeolite used in Example 1 was molded under the same conditions as in Example 1 without being subjected to a dealumination treatment, and calcined to obtain an adsorbent. Further, in the same manner as in Example 1, the amount of solid acid, the effective adsorption capacity, and the degree of deterioration of this adsorbent by the Py-TPD method were measured. The results are shown in Tables 1 and 2. The adsorbent after eight adsorption / desorption cycles had a brown color indicating carbonization. <Measurement Method of Solid Acid Content by Py-TPD Method> An adsorbent was filled in a measuring tube, treated at 500 ° C. for 1 hour in a vacuum to remove water, nitrogen was introduced, and the temperature was maintained at 500 ° C. for 1 hour.
Cooled to ° C. Further, the pyridine gas evaporated by nitrogen was adsorbed on the sample at 300 ° C. for 20 minutes. Next, the sample was heated from 300 ° C. to 950 ° C. at a rate of 10 ° C./min, and 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>
It was pulverized to 0μ to obtain a sample. 1 for adsorption-desorption (hot air desorption)
Cycle, and p-xylene (boiling point:
138.4 ° C.) and n-butyl cellosolve (boiling point: 1
70.2 ° C.). Hereinafter, the adsorption operation, the desorption operation, and the method for evaluating the adsorption ability will be described.

A Adsorption operation The air from the compressor is dehumidified by a silica gel column, a part of the dry air is passed through a steam generating tube of p-xylene or n-butyl cellosolve, mixed with the remaining dry air, and the concentration of the generated steam is adjusted. , 350 ppm of p-xylene,
n-Butyl cellosolve was 150 ppm. The adsorption column used had an inner diameter of 1.55 × 10 ⁻² m and a layer height of 0.07 m, and was placed in a thermostat and kept at 25 ° C. The gas flow rate was 0.2 m / sec, and adsorption was performed for 40 minutes. FIG. 1 shows a schematic diagram of the adsorption device used.

B Desorption operation The adsorbent after the adsorption operation was removed together with the column, and the desorption operation was performed. Air from the compressor was dehumidified by a silica gel column and heated by a heater to obtain hot air for desorption.
The temperature in the layer at the time of desorption was 200 ° C., and desorption was performed for 40 minutes. FIG. 2 shows a schematic diagram of the adsorption device used.

(C) Evaluation of Adsorption Amount of p-xylene adsorbed on the adsorbent after a predetermined adsorption / desorption cycle was measured, and the performance was compared with that of an unused adsorbent. The effective adsorption amount was determined by flowing 400 ppm of p-xylene vapor through the column and measuring the breakthrough curve.

The effective adsorption amount (kg / kg) and the degree of deterioration (%) were determined by the following formulas.

Effective adsorption amount (kg / kg) = p-xylene adsorption amount after several cycles / new adsorbent weight Deterioration degree (%) = ｛(new adsorbent effective adsorption amount-effective adsorption amount)
/ New adsorbent effective adsorption amount x 100

[0032] Table 2 Effective adsorption amount and degree of deteriorationExample 1 Comparative Example 1  Number of cycles Effective adsorption amount Deterioration degree Effective adsorption amount Deterioration degree(Times) (Kg / kg) (%) (Kg / kg) (%)  0 0.1450-0.1298 -2 0.1448 0.14 0.1295 0.23 4 0.1435 1.03 0.1249 3.78 8 0.1438 0.83 0.1197 7.78

[Brief description of the drawings]

FIG. 1 is a view schematically showing an adsorption device in an embodiment.

FIG. 2 is a view schematically showing a desorption device in an embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Compressor 11 Compressor 2 Silica gel column 12 Silica gel column 3 Flow controller 13 Flow controller 4 Flow meter 14 Preheater 5 Constant temperature bath 15 Electric furnace 6 Adsorbed component vapor generation tube 16 Sampling bag 7 Adsorption column 8 Gas chromatography

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) B01J 20/18 B01D 53/04 B01D 53/44 B01D 53/81

Claims (3)

(57) [Claims] 1. The method according to claim 1, wherein the amount of the solid acid is 0.1 mmol / g or less as measured by a pyridine thermal desorption method, and SiO ₂ / Al ₂ O ₃
A ketone-based organic material, comprising a zeolite having a molar ratio of 50 or more and a boiling point of 120 ° C. or more under atmospheric pressure.
Exhaust gas purifying adsorbent containing organic components excluding solvents . Wherein the atmospheric pressure boiling point of 120 ° C. or higher, and, keto
A method for purifying exhaust gas containing high-boiling components, comprising contacting an exhaust gas containing an organic component other than an organic solvent with the adsorbent according to claim 1, and regenerating the adsorbent at 180 ° C or higher. . 3. The exhaust gas has a boiling point of 150 ° C. or more under atmospheric pressure , and
3. The method according to claim 2, further comprising an organic component excluding a ketone-based organic solvent .