JPH0523586A - Adsorbent and method for decontaminating exhaust gas containing high boiling component - Google Patents

Abstract

PURPOSE:To maintain high adsorption performance for exhaust gas containing a high boiling component without carbonizing and oxidizing an adsorbent by using this adsorbent consisting of zeolite wherein the amount of solid acid measured by a pyridine temperature rise elimination method is specified amount or below and the molar ratio of SiO2/Al2O3 is specified value or more. CONSTITUTION:An adsorbent for decontaminating exhaust gas consists of hydrophobic zeolite wherein the amount of solid acid measured by a pyridine temperature rise elimination method is <=0.1mmol/g and the molar ratio of SiO2/Al2O3 is >=50. Even when this adsorbent is used for decontaminating exhaust gas containing the organic components of high boiling point of >=120 deg.C furthermore >=150 deg.C, it does not thoroughly show catalytic properties. Accordingly the components to be adsorbed are eliminated without oxidizing and carbonizing the adsorbent. Therefore both ingition and deterioration of adsorption capacity are not caused. Thereby adsorption operation difficult heretofore described below is enabled without executing special device for an adsorption device. As this adsorption operation, both concentration of the exhaust gas of an organic solvent containing the components of high boiling point and recovery of the solvent are shown.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention has a boiling point of 120 at atmospheric pressure.
The present invention relates to an exhaust gas adsorbent containing an organic component having a high boiling point of ℃ or higher and a method for purifying the exhaust gas 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 an organic component such as a solvent. However, the boiling point of the organic component is 120 ° C or higher, and
When the temperature was as high as 50 ° C. or higher, it was not easily desorbed from the activated carbon layer, and this accumulated on the activated carbon, which was a cause of adsorption failure. In this way, when the high-boiling organic components accumulated on the activated carbon have high reactivity, the catalytic reaction of the activated carbon causes an oxidation reaction, and the reaction heat generated when oxygen is supplied advances the oxidation reaction in a chain, Finally, 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 lower 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 it as described above. Therefore, the used activated carbon must be discarded or the regeneration must be entrusted to a specialist. Thus, purification of exhaust gas containing high-boiling point organic components by activated carbon is often economically or safety disadvantageous.

In recent years, zeolite having enhanced hydrophobicity has begun to be used as an adsorbent for organic compounds in place of activated carbon (Japanese Patent Laid-Open No. 60-501495 and JP-A-64).
-85113 publication).

[0004]

However, when a hydrophobic zeolite is used as an adsorbent for purification of exhaust gas containing an organic compound 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 was given to coking or disassembling. We have a boiling point of 12
When purifying exhaust gas containing high boiling point organic components above 0 ° C, pay particular attention to the method of regenerating the adsorbent and the catalytic properties of the adsorbent, and safely purify exhaust gas containing high boiling point components without any special operations. We have earnestly studied to develop the method.

The basic structure of a zeolite crystal is SiO ₄ and its substituted AlO ₄ tetrahedrons, which share oxygen atoms at their vertices and form a crystal structure developed in a three-dimensional direction. As a result, zeolite crystals have very large cavities and channels that are not found in other minerals. The entrance diameter of these pores varies depending on the zeolite, but is usually 3 to 9 angstrom and various molecules can be trapped inside the pores. Further, cations are present inside the crystal to supplement the negative charge of AlO ₄ . Polar molecules are selectively adsorbed by 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, etc., which are generally used as a general-purpose adsorbent, is as low as 2 to 5, and these zeolites are more water than organic compounds. Selectively adsorb. 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. Like the activated carbon, the zeolite having hydrophobicity is useful as a hydrophobic adsorbent for purification of exhaust gas containing an organic solvent. However, the hydrophobic zeolite also has a catalytic action. Therefore, part of the adsorbed high-boiling point organic component is carbonized during the process of heating and regeneration. When the exhaust gas contains a highly reactive organic compound, it is oxidized by the catalytic action of the hydrophobic zeolite in the process of heating and regeneration. The catalytic property of such a hydrophobic zeolite is a negative factor for the life of the adsorbent or the safety of the device.

The catalytic properties of the hydrophobic zeolite are considered to be mainly due to the acid sites in the crystals. Therefore, SiO ₂ / A
Zeolites with an infinite l ₂ O ₃ molar ratio have no acid or base points and are considered to have no catalytic action. However,
Actually available or adjustable zeolite SiO ₂ / A
The limit of the l ₂ O ₃ molar ratio is about 500. This is because the silicon raw material 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 aluminium 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, the hydrophobic zeolite has a catalytic property that causes carbonization and oxidation of the adsorbed organic solvent. In particular, it has been difficult to use as an adsorbent for exhaust gas containing an organic component having a high boiling point. However, the crystal skeleton of zeolite is formed of an inorganic oxide such as SiO ₄ or AlO ₄ and is nonflammable. Therefore, the adsorbent itself does not ignite for purification of exhaust gas containing a high boiling point component, 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 subjecting synthetic zeolites to a modification treatment, and a zeolite-based adsorbent that does not show catalytic properties in the regeneration process for exhaust gas containing high-boiling components. Earnestly studied repeatedly.

[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 in which the solid acid amount of pyridine by the temperature programmed desorption method (hereinafter, “solid acid amount” means the value measured by this method unless otherwise specified) is 0.1 mmol / g or less. Is an excellent adsorbent that does not show catalytic properties for adsorbed high-boiling organic components with a boiling point under atmospheric pressure (hereinafter referred to as boiling point) of 120 ° C. or more, and does not have a risk of deterioration of adsorption performance due to carbonization or ignition. I found something.

The solid acid content of the hydrophobic zeolite is 0.1 mm
Hydrothermal calcination is effective as a method for controlling the amount to be not more than ol / g. However, hydrophobic zeolite of the present invention, SiO ₂
/ Al ₂ O ₃ molar ratio must be 50 or more. Hydrophobic zeolite SiO ₂ / Al ₂ O ₃ molar ratio 5
This is because if it is less than 0, it is difficult to set the solid acid amount to 0.1 mmol / g or less even if the hydrothermal calcination treatment is performed. Therefore, the condition of the hydrothermal calcination depends on the structure of the hydrophobic zeolite or the SiO ₂ / Al ₂ O ₃ molar ratio, but by devising the condition of the hydrothermal calcination, the catalytic properties of the high boiling point component adsorbed can be improved. It is possible to obtain no adsorbent.

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

As the hydrophobic zeolite prepared by dealumination treatment, dealumination mordenite (NY Chen, J. Phy. Chem., 8
0, (1), 60-64 (1976)), superhydrophobic Y-type zeolite (Japanese Patent Laid-Open No. 54-122700, Stu)
Dies in Surface Science
dCatalysis, Volume 5, 203-2
10 (1980)), a hydrophobic L-type zeolite (Japanese Patent Laid-open No. Sho 6-66).
3-50312 (public information) etc. are known.

As the hydrophobic zeolite prepared by the direct synthesis method, ZSM-5 (Japanese Patent Publication No. 46-10064) is available.
No. Public Relations), ZSM-11 (Publication No. 53-23280), ZSM-12 (Publication No. 52-16079), ZSM-22 (Publication No. 59-111912), ZSM-23 (JP No. 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.

Further, since zeolite exhibits a molecular sieving effect, the type of molecule that can be adsorbed is determined by the type of zeolite. When recovering the organic solvent from the exhaust gas, the pore inlet diameter of the zeolite may be larger than the adsorbed molecular diameter. Usually, the pore inlet is a zeolite having 8-, 10-, and 12-membered oxygen rings, such as chabazite, offretite, mordenite, faujasite, L, Ω, ZSM.
Those having a crystal structure such as −5 and ZSM-11 type are suitable.

The water vapor concentration of the hydrothermal calcination process for the hydrophobic zeolite must 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, it is possible to obtain the adsorbent of the present invention even under conditions where the calcination temperature is relatively mild. However, even if the hydrothermal calcination is performed at a temperature of 500 ° C. or lower, it is difficult to set the solid acid amount of the adsorbent to 0.1 mmol / g or lower. Further, when calcined at a temperature of 1200 ° C. or higher, the crystal structure itself of the hydrophobic zeolite collapses, and the adsorbent of the present invention cannot be obtained. Therefore, the suitable temperature range for carrying out hydrothermal firing is 500 ° C.
~ 1200 ° C, preferably 600 ° C to 1000 ° C
Is. The hydrothermal calcination time depends on the water vapor concentration and the calcination temperature, but it is necessary to carry out the hydrothermal calcination treatment for at least 30 minutes or more within the above temperature range.

There is a relatively simple thermal desorption method (TPD method) as a method for measuring the acid property of zeolite. In the TPD method, a basic substance (usually thermally stable ammonia, pyridine or the like is used) is adsorbed on a sample and then desorbed while the temperature is raised at a constant rate. At this time, since the adsorption of the basic substance on the acid site is considered to be 1: 1 due to the acid-base action,
The amount of the eliminated basic substance can be regarded as the amount of acid sites. Further, since it is considered that the basic substance adsorbed on the stronger acid point does not desorb up to a higher temperature, the strength of the acid point can be known from the desorbed temperature. Thus, in the TPD method, the amount of acid and the acid strength can be known at the same time. The TPD method using pyridine (Py-TPD method) is a distribution type TPD.
The operation may be carried out in the following manner using the device.
That is, the sample is filled in the adsorption tube under the following conditions, and vacuum exhaust is performed as a pretreatment. Desorption spectrum is observed by adsorbing pyridine on the sample, then heating the gas at a constant rate while flowing He as a carrier gas for degassing the gas phase and the physically adsorbed pyridine.

Sample 0.4 g Pretreatment 500 ° C., 1 hour vacuum exhaust adsorption Room temperature, 15 minutes, 50-60 Torr degassing 100 ° C., 5 minutes vacuum exhaust desorption He flow 60 cc / min Temperature rising rate 10 ° C./min In the zeolite adsorbent, when the solid acid amount of this Py-TPD method is higher than 0.1 mmol / g, since the number of acid points which are the main active points is large, the organic component having a high boiling point is carbonized during desorption, and The effective adsorption amount of is gradually decreased. Further, the high-boiling point component and the carbide accumulated in the adsorbent may be oxidized by oxygen supplied at the time of adsorption to form a hot spot or the like, which is not preferable from the maintenance management of the apparatus. When the amount of solid acid is 0.1 mmol / g or less, the number of acid points that are active points decreases, and carbonization hardly occurs during desorption. Therefore, the effective adsorption amount does not decrease, and high boiling point components and carbides do not accumulate, which is advantageous in maintenance management of the device.

When the hydrophobic zeolite powder is used as an adsorbent, it must be cylindrical, spherical or honeycomb-shaped. At that time, since the hydrophobic zeolite crystal itself does not have a binding property, in order to enhance the binding property between the carrier and the zeolite crystal or the zeolite crystal, an inorganic binder component such as silica sol, silica gel or clay mineral is added to form or honeycomb. Secondary processing such as. As the binder component, an inactive one is desirable, and one showing a reaction activity to an organic solvent such as alumina sol or alumina gel is not suitable. In addition, after forming or forming a honeycomb structure, a firing process 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 hydrocalcinate the hydrophobic zeolite powder in advance. That is, as a rational implementation method for producing an adsorbent having a solid acid content of 0.1 mmol / g or less, a method in which the hydrophobic zeolite powder is first subjected to secondary processing and subsequently subjected to hydrothermal calcination is possible. Of course, the adsorbent of the present invention can also be obtained by subjecting the hydrophobic zeolite powder hydrothermally baked to secondary processing and baking it under mild conditions.

By the way, zeolite moldings produced without using a binder are disclosed in JP-A-62-70225 and JP-A-62-138320. Like this,
Those obtained by subjecting a zeolite molded body containing no binder component to a dealumination treatment and making hydrophobic zeolite hydrothermally baked have a large adsorption amount and are 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 higher under atmospheric pressure. In particular, for exhaust gas purification from processes that use paints containing additives such as cellosolve-based or carbitol-based additives, exhaust gas from processes that process plastic or resin films, or exhaust gas purification processes that use methylpyrrolidone as a reaction solvent or detergent. It is particularly useful as an adsorbent, and can be suitably 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 concentrating device.

[0023]

As described above, according to the present invention, the adsorbent has no catalytic property even when it is used for purifying exhaust gas containing a high boiling point organic component having a boiling point of 120 ° C. or higher, further 150 ° C. or higher. Since it is not shown, the components to be adsorbed can be desorbed without causing oxidation or carbonization, and therefore ignition or reduction in adsorption capacity does not occur. As a result, adsorption operations such as concentration of organic solvent exhaust gas containing a high-boiling point component and solvent recovery, which have been difficult in the past, can be performed without special measures for the adsorption device.

[0024]

EXAMPLES Examples of the present invention will be described below. Example 1 SiO ₂ / Al ₂ O ₃ molar ratio 14 and lattice constant 24.33
Angstrom Y-type zeolite at 50 ℃ 1.5N
The aqueous hydrochloric dealuminated, _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 as a binder was added to 100 parts by weight of this hydrophobic zeolite to obtain a cylindrical molded body having a diameter of 3 mm. This molded product has a water vapor concentration of 20 vol%
Under air circulation, the mixture was calcined at 800 ° C. for 2 hours to obtain an adsorbent.
The solid acid amount of this adsorbent by the Py-TPD method is described later in "Measurement method of the solid acid amount by Py-TPD method" and the components to be adsorbed are p-xylene (boiling point: 138.4 ° C) and n-butyl cellosolve (boiling point). : 170.2 ° C.) and the effective adsorption capacity and the degree of deterioration were measured by the “adsorption / desorption test method”. The results are shown in Tables 1 and 2. The adsorbent that had undergone eight adsorption / desorption cycles had almost the same color tone as that of the new adsorbent (before being used for measurement).

Comparative Example 1 The Y-type zeolite used in Example 1 was molded under the same conditions as in Example 1 without undergoing dealumination treatment and calcined to obtain an adsorbent. Further, as in Example 1, the amount of solid acid, the effective adsorption capacity and the degree of deterioration of this adsorbent were measured by the Py-TPD method. The results are shown in Tables 1 and 2. The adsorbent that had undergone the eight adsorption / desorption cycles was a brownish color indicating carbonization. <Measurement method of solid acid amount by Py-TPD method> A measuring tube is filled with an adsorbent and treated in vacuum at 500 ° C for 1 hour to remove water, and then nitrogen is introduced and kept at 500 ° C for 1 hour to hold 300
Cooled to ° C. Further, 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 heating rate of 10 ° C./min, and the amount of desorbed pyridine was measured by gas chromatography (detector: FID). The solid acid amount of the sample was determined by graphically integrating the amount of desorbed pyridine in the range of 300 ° C to 950 ° C.

<Adsorption / desorption test method> Adsorbents are 710 to 91
It was crushed to 0 μ and used as a sample. Adsorption-desorption (hot air desorption) 1
Cycle and p-xylene (boiling point:
138.4 ° C) and n-butyl cellosolve (boiling point: 1
70.2 ° C) was used. The methods of adsorption operation, desorption operation and evaluation of adsorption ability are shown below.

A The air from the adsorption operation 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, and the remaining dry air is mixed to obtain a concentration of the generated steam. P-xylene is 350 ppm,
The amount of n-butyl cellosolve was 150 ppm. The adsorption column used had an inner diameter of 1.55 × 10 ⁻² m and a bed height of 0.07 m, and was placed in a constant temperature bath 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 view of the adsorption device used.

B Desorption operation The adsorbent, which had completed the adsorption operation, was removed together with the column and desorption operation was carried out. The air from the compressor was dehumidified with a silica gel column and heated with a heater to be hot air for desorption.
The layer temperature during desorption was set to 200 ° C. and desorption was performed for 40 minutes. FIG. 2 shows a schematic view of the adsorption device used.

C Evaluation of adsorptive capacity With respect to the adsorbent that had been subjected to a predetermined adsorption / desorption cycle, the adsorbed amount of p-xylene was measured and the performance was compared with that of an unused product. The effective adsorption amount was determined by passing 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 calculated 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} × 100

[0032]   Table 2 Effective adsorption amount and deterioration degree               Example 1  Comparative Example 1   Number of cycles Effective adsorption amount Degradation degree Effective adsorption amount Degradation 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 drawings]

FIG. 1 is a diagram showing an outline of an adsorption device in an example.

FIG. 2 is a diagram showing an outline of a desorption device in an example.

[Explanation 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 pipe 16 Sampling bag 7 Adsorption column 8 Gas chromatography

Claims (3)

[Claims] 1. A solid acid amount of 0.1 mmol / g or less measured by a pyridine thermal desorption method, and SiO ₂ / Al ₂ O.
Characterized by comprising the ₃ molar ratio of 50 or more zeolites, adsorbent for exhaust gas purification comprising a boiling point 120 ° C. or more organic components of the atmospheric pressure. 2. An exhaust gas containing an organic component having a boiling point of 120 ° C. or higher under atmospheric pressure is contacted with the adsorbent according to claim 1, and then the adsorbent is regenerated at 180 ° C. or higher. A method for purifying exhaust gas containing a boiling point component. 3. The method according to claim 2, wherein the exhaust gas contains an organic component having a boiling point of 150 ° C. or higher under atmospheric pressure.