JPH04210235A - Adsorbent and cleaning method for gas containing ketone type organic solvent - Google Patents

Abstract

PURPOSE:To obtain a useful adsorbent for cleaning gas containing keton type organic solvent by using hydrophobic zeolite hydrothermally treated. CONSTITUTION:A natural or synthetic zeolite is dealuminized by treating with an inorganic acid to produce a hydrophobic zeolite having >=50 ratio of SiO2/Al2 O3. A binder, etc., is added to this zeolite and molded. The product is calcined hydrothermally at 0-1200 deg.C for >=30min in the air containing >=2vol.% moisture. The adsorbent thus obtained can adsorb ketone type organic solvents without causing decomposition or polymerization thereto and with a high durable capacity of adsorptivity thereof. Therefore ketone type organic solvent can be recovered stable and in high purity.

Description

[Detailed description of the invention]

[00011

[Industrial Field of Application] The present invention relates to an adsorbent useful for purifying gases containing ketone organic solvents and a method for using the same. [o o O2] [Prior Art] Activated carbon has heretofore been widely used as an adsorbent for purifying gases containing solvents. However, when the gas contains a ketone organic solvent, the production of a small amount of decomposition products is often observed due to the catalytic action of activated carbon. Among these decomposition products, those that are easily desorbed reduce the purity of the recovered solvent, and those that are difficult to desorb contaminate the activated carbon and cause adsorption problems. Furthermore, the decomposition products are often acids, which have adverse effects such as corrosion on equipment materials. [0003] Ketones generate carboxylic acids through enol-type intermediates due to oxidation on the surface of the adsorbent. This reaction is exothermic, so it progresses rapidly, and the generated reaction heat accumulates. If there is a sufficient supply of oxygen, the reaction proceeds in a chain reaction, and the activated carbon layer itself may ignite. . The ignition temperature of fresh activated carbon is 400-50
The temperature is about 0℃, but if high boiling substances have accumulated in Taho, it will be 2℃.
Temperatures may drop below 00°C. [0004] When activated carbon is used to purify gas containing ketone organic solvents, there are various problems. For this reason, efforts have been made to use activated carbon with low catalytic activity and to install a humidifying device upstream of the adsorption layer to prevent the temperature of the layer from rising due to heat of adsorption, heat of reaction, etc. However, as long as activated carbon is used as an adsorbent, some catalytic action on the ketone organic solvent is unavoidable. If a humidifying device is installed, it is possible to suppress the catalytic action, but as the relative humidity increases, the amount of organic solvent adsorbed by activated carbon decreases. For this reason, careful attention was required to manage the operation of the adsorption device. [0005] Also, in recent years, zeolite with increased hydrophobicity has begun to be used as a new adsorbent to replace activated carbon for adsorbing organic compounds (Japanese Patent Publication No. 60-501495 and Japanese Patent Application Laid-Open No. 64-85113). [0006]

[Problems to be Solved by the Invention] However, when the present inventors attempted to adsorb ketone organic solvents using this hydrophobic zeolite, they found that it exhibited catalytic activity similar to that of activated carbon. In other words, it is possible to adsorb ketone-based organic solvents in the purification of exhaust gas containing ketone-based organic solvents using activated carbon or hydrophobic zeolite. Its catalytic action causes decomposition or polymerization reactions. As a result, the purity of the ketone organic solvent in the concentrated or recovered organic solvent was low and could not be reused. In addition, as adsorption and desorption operations are repeated, the adsorption performance of the adsorbent itself deteriorates, and not only is stable exhaust gas purification not possible,
There were also safety and maintenance problems such as ignition and equipment corrosion. [0007] The inventors paid particular attention to the catalytic activity of the adsorbent against ketone organic solvents, and found that it is possible to recover high-purity ketone organic solvents from exhaust gas without performing special operations, and to prevent ignition and deterioration of adsorption performance. We have conducted extensive research to provide a fear-free adsorbent that does not exhibit catalytic properties against ketone organic solvents. [0008]

[Means for Solving the Problems] The present invention provides an adsorbent made of hydrophobic zeolite subjected to hydrothermal calcining, which is suitable for purifying exhaust gas containing a ketone organic solvent, and a method for using the same. [00091 The details of the present invention will be explained below. [-00101 The basic structure of zeolite crystal is a tetrahedron of SiO4 and its substituted product AlO4,
They share oxygen atoms at the apex with each other, forming a three-dimensionally developed crystal structure. As a result, zeolite crystals have extremely large cavities and pores not found in other minerals. Although the entrance diameter of these pores varies depending on the zeolite, it is usually 3 to 9 angstroms, and various molecules can be trapped inside the pores. Furthermore, cations exist inside the crystal to compensate for the negative charge of AlO4. Polar molecules and polarizable molecules are selectively adsorbed under the influence of the electrostatic field formed by these cations. SiO such as A-type zeolite, X-type zeolite, and Y-type zeolite, which are commonly used as general-purpose adsorbents.
The 2/A1203 molar ratio is as low as 2-5, and these zeolites selectively adsorb water over organic compounds. Therefore, it is not suitable as an adsorbent for purifying exhaust gas containing organic solvents. [0011] Zeolite loses its hydrophilicity at a SiO2/Al:+03 molar ratio of 20 or more and gradually becomes hydrophobic. Zeolites exhibiting such hydrophobic properties are useful as hydrophobic adsorbents, similar to activated carbon, for purifying exhaust gases containing organic solvents. However, hydrophobic zeolites also have catalytic activity. Therefore, when brought into contact with a highly reactive organic compound such as a ketone organic solvent, the ketone organic solvent adsorbed during the heating regeneration process decomposes or undergoes a heavy reaction due to the catalytic action of the zeolite. Furthermore, when used as an adsorbent for a long period of time, residual ketone organic solvents become low polymers or decomposed products.
It may cause ignition, decrease in adsorption capacity, equipment corrosion, etc. Such a catalytic reaction occurs particularly vigorously in a desorption operation when regeneration is performed by heating, and also proceeds, albeit slightly, in a PSA operation performed at low temperatures. Furthermore, since the decomposition reaction of the ketone organic solvent is an exothermic reaction, even in the case of the PSA method that does not involve thermal regeneration, the reaction heat may accumulate in the adsorbent layer and the adsorbent temperature may rise rapidly. [0012] The active sites for this catalytic reaction are considered to be acid sites or basic sites in the hydrophobic zeolite crystal. therefore,
A zeolite with an infinite SiO2/A 1203 molar ratio is considered to have no catalytic activity. However, S i 02 / of zeolite that can actually be obtained or adjusted
The limit of the A1203 molar ratio is about 500. This is because a silicon source that can be used as a raw material for zeolite contains a trace amount of metal oxides other than silicon. For example, in the case of a direct synthesis method, trace amounts of metal atoms such as aluminum in the silicon source are selectively incorporated into the zeolite crystal skeleton during the crystallization process. Further, even in the case of acid extraction using mineral acids, etc., it is practically impossible to completely remove trace amounts of metal atoms in zeolite. [0013] For these reasons, it has been difficult to use hydrophobic zeolite as an adsorbent due to its catalytic action on exhaust gas containing highly reactive ketone organic solvents. [0014] Although L, the crystal skeleton of zeolite is S
It is made of inorganic oxides such as iO4 and AlO4, and is nonflammable. For this reason, the adsorbent itself does not ignite when purifying exhaust gas containing flammable substances such as organic solvents.
It is an extremely attractive adsorbent from a safety standpoint. [0015] The present inventors prepared various zeolites by a direct synthesis method or a method of modifying synthetic zeolites, and conducted extensive studies in order to obtain a zeolite-based adsorbent that has no catalytic activity against ketone-based organic solvents. Ta. As a result, it was found that hydrophobic zeolite subjected to hydrothermal calcining shows no catalytic activity against ketone organic solvents and is an excellent adsorbent with no risk of ignition. [0016] S jo2/A12 to hydrophobic zeolite 1
When the 03 molar ratio is less than 50, it is difficult to completely eliminate the active sites for ketone organic solvents even if hydrothermal calcination is performed, and in order to better eliminate the active sites, it is necessary to use hydrophobic zeolite as a hydrophobic zeolite. is S i Oz / A 1
203 molar ratio of 50 or more is preferred. The conditions for the hydrothermal calcination treatment are based on the structure of the hydrophobic zeolite and the S l 02
/A1203 Although it depends on the molar ratio, it is possible to obtain an adsorbent that does not exhibit catalytic activity toward ketone organic solvents by devising the conditions of the hydrothermal calcination treatment. [0017] Hydrophobic zeolite can be prepared by using natural zeolite or synthetic zeolite as a starting material and by dealumination treatment using mineral acids, etc., or by using a silica source, an alumina source, an alkali source, and organic mineralization. There is a direct synthesis method in which the agents are mixed and crystallized. [0018] Hydrophobic zeolites prepared by dealumination treatment etc. include dealumination mordenite ((N, Y, Chen, J, Phy, Chem, 8
0, (1), 60-64 (1976)), superhydrophobic Y-type zeolite (JP-A-54-122700,
5tudies in 5urface 5ci
ence and Catalysis, Volume
5,203-2LO (1980)), hydrophobic zeolite (Japanese Unexamined Patent Publication No. 63-50312), and the like. [0019] As a hydrophobic zeolite prepared by a direct synthesis method, ZSM-5 (Japanese Patent Publication No. 46-10064
ZSM-11 (Japanese Patent Publication No. 53-23280), ZSM-12 (Japanese Patent Publication No. 52-16079)
, ZSM-22 (Japanese Unexamined Patent Publication No. 111912/1983),
ZSM-23 (Japanese Unexamined Patent Publication No. 51-149900), Z
SM-48 (Japanese Unexamined Patent Publication No. 56-22622), Silicalite (Japanese Unexamined Patent Publication No. 54-72795), etc. are known. [00201 Any of these can be suitably used as the hydrophobic zeolite of the present invention. [00211 Furthermore, since zeolite exhibits a molecular sieving effect, the types of molecules that can be adsorbed are determined by the type of zeolide. When recovering a ketone organic solvent from exhaust gas, it is sufficient that the pore entrance diameter of the zeolite is larger than the molecular diameter to be adsorbed. Usually, zeolite with 8,10 or 12-membered oxygen rings at the pore entrance is sufficient, such as chabasite,
offretite, mordenite, faujasite,
Crystal structures such as Ω, ZSM-5, and ZSM-11 types are suitable. [0022] The water vapor concentration in the hydrothermal calcination treatment for hydrophobic zeolite is preferably 2 vol% or more, and 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, in hydrothermal calcination at a temperature of less than 500° C., it is difficult to completely eliminate the catalytic activity of the adsorbent toward ketone organic solvents. Furthermore, when the temperature exceeds 1200°C, the crystal structure of the hydrophobic zeolite itself tends to collapse. That is, the temperature range suitable for carrying out hydrothermal firing is r500 to 1200°C, preferably 600 to 1000°C. The time for the hydrothermal calcination treatment varies depending on the water vapor concentration and the calcination temperature, but it is necessary to perform the hydrothermal calcination treatment for 30 minutes or more in the above temperature range. [0023] The adsorbent is typically used in a cylindrical, spherical or honeycomb form. In order to make zeolite powder into these shapes, since hydrophobic zeolite crystals themselves have no bonding properties, an inorganic binder such as silica sol, silica gel, clay mineral, etc. is used to increase the bonding properties between the carrier and zeolite crystals or between the zeolite crystals. Components are added and secondary processing such as molding and honeycomb formation is performed. As the binder component, it is desirable to use an inert material, and it is unsuitable to use a material that shows reactivity with ketone organic solvents, such as alumina sol or alumina gel. Furthermore, after forming or forming a honeycomb, 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 hydrothermally calcinate the hydrophobic zeolite 1 to powder in advance. That is, as a rational method for producing the adsorbent of the present invention, firstly, two-dimensional hydrophobic zeolite powder is prepared.
It is possible to perform the next processing and then perform hydrothermal firing. Of course, the adsorbent of the present invention can also be obtained by secondary processing hydrophobic zeolite powder subjected to hydrothermal calcination and calcination under mild conditions. [0024] By the way, zeolite molded bodies produced without using a binder are disclosed in publications such as JP-A-62-70225 and JP-A-62-138320. Such a zeolite molded body containing no binder component is dealuminated to form a hydrophobic zeolite, which is then hydrothermally calcined, which has a large adsorption amount and is more suitable as the adsorbent of the present invention. [0025] The adsorbent of the present invention comprises methyl ethyl ketone,
It is particularly useful as an adsorbent for purifying exhaust gas containing ketone organic solvents such as methyl isobutyl ketone and cyclohexanone, and can be used in any equipment such as fixed bed adsorption equipment, fluidized bed adsorption equipment, moving bed adsorption equipment, and honeycomb rotor concentrators. It can be used suitably. Moreover, there are PSA method, PTSA method, TSA method, etc. as a method of adsorption/desorption operation, and any method can be applied. [0026]

As described above, the present invention provides an adsorbent for purifying exhaust gas containing hydrophobic zeolite powder subjected to hydrothermal calcination and an organic solvent. As a result, adsorption operations such as concentration of ketone organic solvent exhaust gas and solvent recovery, which were difficult in the past, have become possible without special modifications to the adsorption device. Furthermore, since the adsorbent of the present invention exhibits no catalytic properties, the dangers of corrosion of the adsorption device and ignition of the adsorbent layer, which were problems in the past, are eliminated. [0027]

EXAMPLES The present invention will be explained in detail below. Example 1. Comparative Example 1 (Example 1) S i02 /A1203 molar ratio 14, lattice constant 24.
33 angstrom Y-type zeolite was heated to 50°C in 1.
Dealuminated with 5N hydrochloric acid aqueous solution and 5iC
A hydrophobic Y-type zeolite with an h/Al2O3 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 with a diameter of 3 mm. This molded body is heated to a water vapor concentration of 20 vol.
% of air circulation at 800° C. for 2 hours to obtain an adsorbent. (0028) (Comparative Example 1) On the other hand, 25 parts by weight of clay was added as a binder to 100 parts by weight of Y-type zeolite with a SiOz /AI203 molar ratio of 14 that had not been subjected to dealumination treatment with an aqueous hydrochloric acid solution, and a 3 mm diameter A cylindrical molded body was obtained.This molded body was heated at 800 °C under air circulation with a water vapor concentration of 20 vol.
The adsorbent was obtained by calcining at ℃ for 2 hours. [0029] An adsorption/desorption test of these adsorbents for methyl ethyl ketone was conducted by the following method. [00301 <Adsorption/desorption test method> The adsorption/desorption test column was made of glass with an inner diameter of 6 cm and a length of 45 cm.
cm was used. Add adsorbent to this column at a bed height of 35
cm, and an adsorption/desorption test was conducted. The adsorption test was conducted at 25°C. Methyl ethyl ketone concentration 3
000 ppm air (moisture concentration 1010000 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 reached 150 ppm was defined as the breakthrough time (minutes). Furthermore, an adsorption test was conducted until the concentration of methyl ethyl ketone at the outlet reached 3000 ppm.
The column weight (Wa) after completion of the adsorption test was measured. [00311 The desorption test was performed by heating the column to 150°C with a ribbon heater while flowing dry air at 0.075 m/sec through the adsorbent layer that had adsorbed methyl ethyl ketone until the outlet concentration of methyl ethyl ketone became 10 ppm or less. The weight of the column after the desorption test (W
d) was measured. In addition, the methyl ethyl ketone concentration in the desorbed gas is integrated graphically, and the amount of methyl ethyl ketone recovered (W r
) was sought. [0032] The recovery rate (%) of methyl methyl ketone was determined by the following formula. The results are shown in Table 1. [0033] Methyl engineered methyl ketone recovery rate (%) = WrX
100/ (Wa - Wd) The methyl ethyl ketone concentration at the inlet and outlet of the adsorption layer is
It was measured by gas chromatography (detector: FID). Example 2. Comparative Example 2 (Example 2) A synthetic mordenite-type zeolite was dealuminated to obtain a hydrophobic mordenite-type zeolite with a Si 02 /A 1203 molar ratio of 200. 25 parts by weight of silica sol as a binder was added to 100 parts by weight of this hydrophobic mordenite type zeolite to obtain a cylindrical molded body with a diameter of 3 mm. This molded body was calcined at 700° C. for 10 hours under air circulation with a water vapor concentration of 20vol% to obtain an adsorbent. (00341 (Comparative Example 2) Adsorbents were obtained in the same manner as in Example 2 except that the calcination was performed in dry air. [0035] These adsorbents were also adsorbed and desorbed in the same manner as in Example 1. A test was conducted to determine the methyl ethyl ketone recovery rate. [0036] Table 1

Claims (4)

[Claims] 1. An adsorbent comprising hydrophobic zeolite subjected to hydrothermal calcination treatment. Claim 2: Hydrophobic zeolite SiO_2/Al_2O
The adsorbent according to claim 1, wherein the _3 molar ratio is 50 or more. 3. The adsorbent according to claim 1, wherein the hydrothermal calcination treatment is performed at a water vapor concentration of 2 vol % or more, a calcination temperature of 500 to 1200° C., and a calcination time of 30 minutes or more. Claim 4: A gas containing a ketone organic solvent as claimed in claim 1.
, 2 or 3. A method for purifying a gas containing a ketone organic solvent, the method comprising bringing the gas into contact with the adsorbent according to any one of paragraphs 2 and 3.