JPH0679171A - Carbon-modified zeolite - Google Patents

Abstract

PURPOSE:To provide a carbon-modified zeolite with improved adsorption characteristics, especially adsorption characteristics when each constitutional gas component is separated from air. CONSTITUTION:Carbon is carried on the surface of fine pores of zeolite and the carbon is formed by pyrolysis of a hydrocarbon species formed by plasma treatment of a hydrocarbon. In general, it is preferable that the amt. of a modified carbon is at most 3% of the weight of dried zeolite and as a zeolite for a raw material, a zeolite with a fine pore diameter of about 5Angstrom or larger is suitable. In addition, the amt. of modified carbon and the adsorption speed are adjustable by changing only plasma treating time and they are usable as adsorbents and catalysts with various surface characteristics. As the amt. of adsorption of nitrogen with a large molecular diameter and Ar with a small molecular diameter are increased and the amt. of adsorption of oxygen with an intermediate molecular diameter between them are little changed by this treatment, oxygen in air can be separated with high selectivity from nitrogen and Ar by utilizing this characteristics.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbon-modified zeolite having a significantly improved adsorption property, particularly when separating each constituent gas component from air.

[0002]

2. Description of the Related Art Heretofore, from air, nitrogen (N ₂ ), oxygen (O ₂ ), and argon (Ar), which are the main constituents, have been used.
Various methods for separating and recovering bromine have been investigated, and in recent years, an adsorption method has come to be used in place of the cryogenic rectification separation method which has been widely used conventionally. The adsorbent used in such an adsorption method is required to have a large adsorption capacity and excellent selectivity, and N ₂ (3.75
Zeolite is the most common adsorbent having a structure suitable for separating O (3.54 Å), Ar (3.3 Å), and O ₂ (3.54 Å) with high accuracy. This zeolite is an adsorbent having a uniform pore size, and synthetic zeolite is known as molecular sieve and is also used for separating hydrocarbons.

The structural characteristics of such zeolites are as follows: (1) Zeolites in a narrow sense generally called A type, X type and Y type are silicon (Si) and aluminum (Al),
Oxygen (O) as a main component, positive tetravalent Si in the crystal structure,
In order to maintain the electrical neutrality of the negatively charged ion locus resulting from the charge imbalance of positive trivalent Al and negative divalent O,
It has a chemical structure that is exchanged with a cationic metal ion such as a, K, or Ca. (2) Since the pores of zeolite are due to the crystal structure of constituent atoms and ions,
Highly regular with a basket type consisting of repeated wide internal cavities connected to a narrow inlet, a channel type that is a cylindrical shape with a constant pore size, or a constant shape in which both types of pores are combined two-dimensionally and three-dimensionally. For example, it has pores.

However, zeolites whose surfaces have not been treated do not have sufficient adsorption and separation characteristics. Therefore, to date, the above-mentioned structural characteristics of zeolites have been utilized to adsorb zeolites. Various techniques have been developed for controlling the characteristics and separation characteristics to improve and improve the characteristics. Already known zeolite reforming technologies are the ion exchange method based on the above (1) "ion exchangeability" and chemical vapor deposition focusing on the "constant shape pore structure" of (2) above. Method (CVD), etc., all of these conventional techniques utilize the “molecular sieving effect” based on the difference in the size and shape of each molecule that enters and adsorbs into the pores, and It is intended to modify adsorption properties by mechanically or physically reducing or limiting the diameter.

For example, a method for enhancing the adsorption characteristics of gas components in the air by utilizing the above-mentioned characteristic (1) of zeolite is described in M. Iwamoto, et al: J. Phys. Chem., 88, 4195.
Page (1984), it is possible to enlarge the pore size in the zeolite used in this method by changing the size of the exchanged ions. However, when the pore size is increased, both large molecules and small molecules are easily diffused and penetrated into the pores, and there is a problem that the selectivity as an adsorbent is lowered. On the contrary, when the pore size of zeolite is reduced by performing the treatment by this method, the component having a large molecular diameter and originally difficult to be adsorbed,
Not only does it become more difficult to adsorb, but also the adsorption of molecular components with low adsorbability is limited, and as a result, the adsorption capacity of each component decreases, which is inevitable.

[0006] Further, as a method for enhancing the adsorptivity of gas constituents of air by utilizing the characteristic of (2), for example, M. Niwa, et al: CHEMISTRY LETTER, p. 411, (19
1989), in which a change in adsorption capacity of N ₂ and O ₂ when a zeolite treated by the Si chemical vapor deposition method is used is reported. However, such a zeolite has a drawback that the pore size on the surface of the zeolite is reduced by the treatment, gas molecules are less likely to enter the pores, and the adsorption capacity is reduced.

Further, when separating N ₂ and O ₂ from air, PSA (Pressu
re Swing Adsorption)
Increasing the _second adsorption capacity, but have been also studied to reduce the adsorption capacity of the O ₂ Conversely, than with zeolite according to conventional physical pore diameter control method, selectively adsorb molecules It was difficult to achieve this, and it was not possible to improve the adsorption characteristics of Ar, which has the smallest molecular size.

[0008] As described above, since the prior art pore-treated zeolite cannot avoid the reduction of the adsorption capacity due to the treatment, when the adsorption separation device is designed using such zeolite, the adsorption In order to compensate for the decrease in capacity, the volume of the adsorption tower is increased, the amount of adsorbent used is increased, and the temperature of the adsorption tower is lowered until the decrease in adsorption capacity is compensated. It was necessary to take such specifications.

[0009]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems in the prior art and to provide a zeolite having significantly improved adsorption characteristics, particularly air separation adsorption characteristics.

[0010]

The carbon-modified zeolite of the present invention is one in which carbon is supported on the surface of the pores of the zeolite, and the carbon heats the hydrocarbon species produced by the hydrocarbon plasma treatment. It is characterized by being generated by decomposing. That is, in the carbon-modified zeolite of the present invention, the zeolite is plasma-treated in a hydrocarbon atmosphere to attach a hydrocarbon species to the pores, and heat is applied to the zeolite to decompose and carbonize it to generate carbon on the pore surface. It is obtained by the above, and the production thereof includes two steps of a hydrocarbon plasma treatment step and a pyrolysis treatment step.

First, in the first treatment step for producing the carbon-modified zeolite of the present invention, the zeolite is treated with hydrocarbon plasma to produce a zeolite in which the hydrophilicity of the pore surface is suppressed. In the treatment step, hydrocarbons are introduced into the reaction chamber whose pressure has been reduced by a vacuum pump, and in this state, plasma is generated by the plasma generator to treat the zeolite surface. In the present invention, the hydrocarbon species generated on the pore surface of the zeolite is not particularly limited, and various hydrocarbons used for general hydrocarbon plasma treatment can be used, for example, n-hexane (n-C ₆ H ₁₄₎ and benzene (C ₆ H _6), cyclohexane (C ₆ H _12), and the like. Then, by such a first hydrocarbon plasma treatment step, the surface of the micropores of the zeolite structurally structured is coated with the hydrocarbon species generated from the plasma state, whereby the chemical surface An effect of changing the interaction force and a physical molecular sieving effect (invasion restriction) of coating the entrance surface of the pores with a hydrocarbon species to reduce the entrance diameter are provided.

Next, in the second thermal decomposition treatment step, the hydrophobic zeolite after the hydrocarbon plasma treatment is heat treated to carbonize the hydrocarbon species generated and adhered to the zeolite surface, and the zeolite pore surface. The carbon is supported on, but the atmosphere conditions for this thermal decomposition are generally in a nitrogen stream or under reduced pressure. In addition, when the temperature is raised, the temperature is raised relatively slowly from room temperature at a constant rate (for example, 1 to 2 ° C./min) so that the crystal structure of zeolite is not destroyed and the pyrolysis of hydrocarbons generated from plasma is performed. It is preferable to heat to a temperature at which effectively occurs (for example, 600 ° C.) and hold at that temperature for a time sufficient to complete the thermal decomposition.

The carbon-modified zeolite of the present invention obtained by performing the above-mentioned plasma treatment and thermal decomposition treatment in combination is chemically modified to control the adsorption interaction on the surface. , A conventional zeolite whose pore inlet diameter is physically controlled, for example, one whose pores are modified with "soot" -like carbon produced by combustion of a hydrocarbon gas such as benzene or butane, or acetone of phenol resin powder The adsorption properties are superior to those obtained by impregnating the solution and then thermally decomposing it to modify the pores.

The reason why the carbon-modified zeolite of the present invention exhibits excellent adsorption characteristics is that the quadrupole moment on the surface of the zeolite is strengthened by supporting a small amount of carbon on the inner and outer surfaces of the zeolite pores, and the nitrogen adsorption force is increased. , And the synergistic effect of reducing the oxygen adsorption power, and the effect of promoting the adsorption of argon on the carbon portion is added to this. However,
In the carbon-modified zeolite of the present invention, if the amount of modified carbon is too large, the physical molecular sieving effect is affected, and the adsorption characteristics for nitrogen, oxygen and argon are reduced. In the present invention, a small amount of modified carbon suitable for adsorptive separation is sufficient, and generally, it is preferably 3% by weight or less of the dry zeolite mass, and particularly preferably in the range of 0.1 to 2.5% by weight. preferable. In the present invention, when adjusting the amount of modified carbon that is carbonized and supported by thermal decomposition, it is only necessary to change the plasma treatment time, so that it is possible to easily obtain carbon-modified zeolite having various surface characteristics. There are advantages.

According to the experiment using the carbon-modified zeolite of the present invention obtained by the above-mentioned treatment, in the present invention, N ₂ having the largest molecular size and Ar having the smallest molecular size in the air component are used.
It was confirmed that the adsorption capacities near room temperature increased 1.5 times and about 2 times, respectively, and the adsorption capacity of O ₂ having a molecular size intermediate between N ₂ and Ar was not significantly affected. Therefore, in the case of the X-type zeolite before the treatment,
The order of adsorption capacities at ° C is CO ₂ > CH ₄ > N ₂ > O ₂
> Is a Ar, with the carbon modified zeolites of the present invention to a plasma treatment and thermal decomposition treatment has been performed, the adsorption capacity of N ₂ and Ar is increased, since the adsorption capacity of the O ₂ does not change significantly, and N ₂ The difference in adsorption capacity with O ₂ expands, and the O
The properties in separating ₂ from N ₂ and Ar are improved.
In this case, the adsorption capacities of CO ₂ and CH ₄ are hardly affected. Further, in the present invention, by modifying the zeolite pores with carbon, the diffusion and penetration rate of each gas into the zeolite pores changes, and the characteristics as an adsorption separator can be improved. The carbon-modified zeolite of the present invention having is very suitable as an adsorbent for a PSA separator.

As the zeolite used for producing the carbon-modified zeolite of the present invention, molecular sieve 5A is nominally Ca-A type zeolite (pore size is about 5).
Zeolite with a larger pore inlet diameter than Å) is preferable,
Type A zeolite having an inlet diameter smaller than that of the molecular sieve 5A is not so preferable because hydrocarbon species due to plasma treatment are not easily supported on the surface.

The carbon-modified zeolite of the present invention obtained by the above-mentioned steps has excellent adsorption characteristics particularly when air is separated into constituent components (gas). Adsorption of air using this carbon-modified zeolite When the separation is carried out, the carbon-modified zeolite is filled in the separation column of the apparatus which has been conventionally used, and the constituent components can be adsorbed and collected according to the conventional adsorption separation method. The carbon-modified zeolite of the present invention can not only easily separate N ₂ and O ₂ which were difficult to be separated by the conventional surface-treated zeolite, but also with high selectivity, and also can remove N ₂ , O ₂ , Ar Besides, C
Gases such as O ₂ and CH ₄ can be adsorbed and separated, and can also be used for separation of various mixed gases.

[0018]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto. Example 1 Commercially available X-type zeolite (MS13
X) is used, and this is a plasma of n-hexane (about 1 To
rr; oscillation frequency 13.56 MHz; output approx. 30 W), and then pyrolyzed for 1 hour at 600 ° C. in N ₂ stream,
A carbon-modified zeolite of the present invention was obtained. The increased mass based on the dry mass of the carrier in this case was 0.8 wt%. Example 2 In the same manner as in Example 1 except that the plasma treatment time was 19 hours, the increase in mass based on the dry mass of the carrier was 2.7 wt.
% Carbon-modified zeolite of the invention was obtained. The adsorbents of Examples 1 and 2 differed in the amount of modified carbon due to the difference in plasma treatment time, but under the above heat treatment conditions, the crystal structure of the carrier zeolite remained without being destroyed.

Comparative Example 1 The X-zeolite described in Example 1 was used without treatment. Comparative Example 2 The same X-type zeolite as in Example 1 was impregnated with an acetone solution of a phenol resin, air-dried at room temperature, and then pyrolyzed at 600 ° C. for 1 hour under reduced pressure. Comparative Example 3 The same X-type zeolite as in Example 1 was used, and this was treated in the same plasma as in Example 1 for 5.5 hours.
No thermal decomposition treatment was performed.

Then, the equilibrium adsorption capacities of the adsorbents of Examples 1 and 2 and Comparative Examples 1 to 3 were evaluated. In this evaluation, the conventionally known capacitance method is used, and N ₂ (dynamic diameter: 3.75Å), O ₂ (3.54Å), Ar (3.3 Å), n− at equilibrium pressure of about 2800 Torr or less.
The gas phase adsorption isotherms (30 ° C.) of butane (4.3 Å) and i-butane (5.0 Å) were measured, and the obtained isotherms were formulated by the Langmuir equation. Table 1 shows N ₂ , O ₂ , Ar at 1200 Torr as typical values of the adsorption capacities of the above adsorbents.
The values of n-butane and i-butane are summarized.

[0021]

[Table 1]

From the experimental results shown in Table 1, the carbon-modified zeolite of the present invention (Examples 1 and 2) has a higher adsorption amount of N ₂ and Ar than the carrier zeolite before the treatment (Comparative Example 1). It is increasing, and the difference in adsorption capacity between N ₂ and O ₂ is increasing. In particular, in the adsorbent of Example 1, the adsorption amounts of N ₂ and O ₂ were increased by about 1.6 times and 1.2 times, respectively, as compared with those of Comparative Example 1, and the capacity difference was also enlarged. And
The adsorption properties are greatly improved. Also, the amount of butanes adsorbed is slightly increased.

On the other hand, in the sample in which a large amount of carbon was supported by the phenol resin carbon supporting treatment (Comparative Example 2), adsorption of N ₂ and O ₂ was higher than that of the carrier zeolite before the treatment (Comparative Example 1). The capacity difference increases, but the adsorption amount decreases. Further, in the adsorbent of Comparative Example 2, n-
Both the adsorption amounts of butane and i-butane were reduced to about 2/3 of those of Comparative Example 1, and the effect of improving the adsorption characteristics was not observed. Further, in the adsorbent of Comparative Example 3 which was subjected to the plasma treatment, the relative ratio of the adsorption amounts of N ₂ and O ₂ was large, but the absolute amount was remarkably lowered, and the separation performance was deteriorated. Thus, the carbon modified zeolites of the present invention (Examples 1 and 2) is greater adsorption amount of the relative ratio of the N ₂ and O ₂ is, moreover since the absolute value of the adsorption amount, the high the N ₂ and O ₂ It was shown to be an adsorbent that can be separated with high accuracy and efficiency.

Further, using the adsorbents of Example 1 and Comparative Examples 1 and 3, the relationship between the adsorption capacity of N ₂ and O ₂ at 30 ° C. and the equilibrium adsorption pressure was investigated. The result is shown in FIG. From the curve shown in FIG. 1, in the adsorbent of Comparative Example 3 which was subjected to the hydrocarbon plasma treatment, both the N ₂ adsorption capacity and the O ₂ adsorption capacity of the adsorbent of Comparative Example 1 were about 1/2. It can be seen that it decreases to below. On the other hand, in the carbon-modified zeolite of the present invention (Example 1) obtained by heat-treating the adsorbent of Comparative Example 3, the N ₂ adsorption capacity was also O _2.
Adsorption capacity of also increased, remarkable improvement is observed in particular N _2.

Next, the above-mentioned Examples 1 and 2 and Comparative Example 1
~ 3 adsorbent, dry air [N ₂ (78.1%)-O ₂ (2
1.0%)-Ar (0.9%)] was used to perform a PSA air separation experiment using both adsorbate-PSA and non-adsorbate-PSA systems, and the separation results were evaluated. For this experiment, the adsorbent volume was 33 cm
The performance in a standard operation cycle was measured using ³ single-column, pressure-reducing PSA devices. The experimental results obtained are also shown in Table 1 above.

From the results of the representative PSA results shown in Table 1, the carbon-modified zeolite of the present invention (Examples 1 and 2)
Shows improved adsorption properties in adsorbate-PSA as compared to the pre-treated support zeolite (Comparative Example 1),
Excellent N ₂ concentration results were observed. In particular, in the present invention,
The separation performance is improved even in the case of the sample in which the amount of supported carbon is increased by prolonging the plasma treatment time (Example 2). On the other hand, both the adsorbent of Comparative Example 2 which was subjected to the treatment of supporting phenolic resin carbon and the adsorbent of Comparative Example 3 which was subjected to the hydrocarbon plasma treatment had lower separation performance than the carrier zeolite (Comparative Example 1). However, no improvement in adsorption characteristics was observed.

Example 3: Relation between modified carbon amount and adsorption capacity By adjusting the plasma treatment time described in Example 1, the modified carbon amount was 0.1 wt% according to the method described in Example 1, 0.8 wt%, 2.3 wt%, 2.7 wt% 4
Different types of adsorbents were prepared. Then, in addition to these four kinds of adsorbents, starting material zeolite (untreated product) was added, and the relationship between the modified carbon amount and the adsorption capacity was investigated for a total of five kinds of adsorbents. In this case, the adsorption capacity was measured by the capacitance method, and the adsorption capacities of N ₂ , O ₂ and Ar at 30 ° C. and an equilibrium adsorption pressure of 1900 Torr were measured. The results obtained from this experiment are shown in Table 2 below.

[0028]

[Table 2]

From the experimental results shown in Table 2, the adsorption capacity of carbon-modified zeolite having a modified carbon content of 0.1 to 2.3 wt% for N ₂ and Ar is about 1.4 times the adsorption capacity of untreated zeolite. Although it was about 2.3 times, it was found that the adsorption capacity of O ₂ did not change significantly, and thereby the adsorption separation characteristics were improved. It is also shown in Table 2 that when the amount of modified carbon exceeds 2.3 wt%, the adsorption capacities for N ₂ , O ₂ and Ar start to decrease sharply.

Regarding the adsorption characteristics of the carbon-modified zeolite of the present invention, the temperature programmed desorption amount of adsorbed ammonia was measured by the usual temperature programmed desorption method (TPD method) to measure the intensity distribution of solid acid points. As a result, a thermal desorption curve as shown in FIG. 2 was obtained. As a result, in the intensity distribution of the solid acid points, there is little quantitative change in the total acid points including the strong acid points and weak acid points, but the strong acid points observed in the high temperature region decrease, and the weak acid points observed in the low temperature region are reduced. It is observed that the points increase.
This suggests that the surface modification with carbon extends inside the pores. From the above, the carbon-modified zeolite of the present invention has a surface having characteristics similar to those of carbon and can be used as an adsorption / separation agent or a catalyst in which the acid strength characteristics of solid acid are controlled.

[0031]

As described above, the carbon-modified zeolite of the present invention has improved surface adsorption characteristics as compared with the zeolite before the carbon-modification treatment. By using this, oxygen in the air is converted to nitrogen. It can be efficiently adsorbed and separated from argon. Therefore, the volume of the adsorption tower can be made smaller than ever, and the amount of adsorbent used can be reduced, which is economical. Further, in the present invention, by adjusting the amount of modified carbon supported on the pore surface of zeolite, an adsorbent having controlled adsorption capacity and adsorption rate for various gas components can be obtained, particularly for PSA processes. Very suitable as an adsorbent.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the adsorption capacity of N ₂ and O ₂ and the equilibrium adsorption pressure.

FIG. 2 is a temperature programmed desorption curve of adsorbed ammonia for a carbon-modified zeolite of the present invention (Examples 1 and 2) and a raw material before treatment (Comparative Example 1).

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ichiro Funada 7-126 Tomokagaoka, Suma-ku, Kobe City, Hyogo Prefecture 163 Kitasuma housing complex 163 (72) Inventor Kenji Yasuoka Tanabe-cho, Tanabe-cho, Tsuzuki-gun, Kyoto 30

Claims (1)

[Claims] 1. A zeolite having carbon supported on the surface of pores, wherein the carbon is produced by thermally decomposing a hydrocarbon species produced by a hydrocarbon plasma treatment. Characterized, carbon-modified zeolite.