JP2915420B2 - Adsorbent - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an adsorbent. More specifically, the present invention relates to a novel adsorbent capable of selectively adsorbing oxygen.

(Conventional technology and its problems) Conventionally, in the chemical industry, gas manufacturing industry, research facilities, etc., an adsorption separation method using a solid adsorbent to separate or remove only a predetermined component from a mixture of chemical substances has been developed. Has been adopted. This adsorption method has been widely used in the field of pollution prevention.

As a method of such adsorption separation, for example, a method of using a zeolite as an adsorbent and adsorbing and separating a specific gaseous compound is already known.

However, although a large number of adsorbents have been known, it is not so easy to selectively adsorb only specific components from a mixture and separate them with high efficiency. The types of solid substances that can be used as adsorbents are limited, and their separation activity varies greatly depending on their adsorption activity and pore size, and specific components can be selectively separated on an industrial scale. Is not easy.

An example of such an example is air component separation. This is a method in which zeolite is used as an adsorbent and nitrogen (N ₂ ) in air is preferentially adsorbed to separate nitrogen and oxygen. This is based on the adsorption characteristics of zeolite.

However, even in this method, the separation efficiency is not satisfactory. This method utilizes, for example, the property that A-type zeolite adsorbs nitrogen more easily than oxygen, but uses a molecular sieve based on pore size corresponding to the difference in molecular diameter characteristic of zeolite. It does not use effects. For this reason, the characteristics of zeolite were not fully utilized, and the separation efficiency was naturally limited.

The present invention has been made in view of the circumstances as described above, and pays attention to the characteristics of zeolite as a solid adsorbent, and can realize a larger separation action corresponding to the size of pore diameter. The purpose is to provide a new adsorbent of great practical value.

(Disclosure of the Invention) The present invention provides an adsorbent obtained by chemically depositing silica on the surface of an A-type zeolite using tetraalkoxysilane, and preferentially adsorbs oxygen over nitrogen. An object of the present invention is to provide an adsorbent characterized by having an adsorption ability.

That is, in the present invention, a tetraalkoxysilane as a silicate compound is deposited on the outer surface of the A-type zeolite by a chemical vapor deposition method, and the pore diameter of the pores of the A-type zeolite is precisely controlled by the generated thin film of silica; This makes it possible to preferentially adsorb this chemical substance according to the size of the molecule of the chemical substance to be adsorbed.

The pore diameter is controlled by vapor deposition. Generally, the control of the pore diameter is determined by the amount of vapor deposition, that is, the state of the silica thin film to be formed. When using tetraalkoxysilane, deposition is performed at room temperature to 500 ° C.
It can be performed at a temperature of the order of magnitude. When the reaction is stopped by saturation, it can be hydrolyzed by steam and reactivated. By alternately performing deposition and hydrolysis, the amount of deposition can be increased.

In the case of the adsorbent of the present invention in which the pore diameter is controlled by such silica deposition, it is possible to selectively adsorb oxygen from the air, which has been conventionally difficult.

That is, only molecular sieve carbon is known as the only adsorbent that selectively adsorbs oxygen over nitrogen so far, and in this case, the adsorption capacity is large because the composition of carbon is not constant. Variations were not practical. However, the present invention also allows preferential adsorption of smaller diameter oxygen from a mixture of oxygen and nitrogen, whose molecular diameters are only 3.46A and 3.64A of nitrogen, and only 0.18A.

Such extremely high-precision adsorption / separation is possible even for various chemical substances other than oxygen and nitrogen. In addition, it is possible to control the adsorption ability of A-type zeolite itself.

For example, when silica is not vapor-deposited, even if the substance is adsorbed at a high rate, the degree of adsorption can be reduced by silica vapor deposition. The case of nitrogen described above corresponds to this.

Hereinafter, the present invention will be described in more detail with reference to examples.

Examples 1-2 A Na-type zeolite was formed into a 28-48 mesh, and this was mounted only on a quartz spring capable of vacuum processing. The zeolite is first degassed in vacuum at a temperature of 400 ° C. to sufficiently remove water.

Then, at the same temperature, a gas of about 2.5 Torr of tetramethoxysilane (Si (OCH ₃ ) ₄ ) is introduced to react with the outer surface of the zeolite, and silica is deposited on the outer surface. At the end of the reaction after about one hour, unreacted alkoxide in the gas phase and gas such as alcohol generated at the time of vapor deposition are removed. Thereafter, steam is introduced to reactivate the surface by hydrolysis.

The above evaporation and introduction of water vapor are repeated a plurality of times to control the amount of silica evaporation.

Thus, a sample was prepared by depositing 0.47% by weight and 0.57% by weight of silica on zeolite.

Using this sample, the difference in the adsorption rate between oxygen and nitrogen at a temperature of -76 ° C was evaluated. FIG. 1 and FIG. 2 show the results.

As is clear from comparison with FIG. 3 showing the results of a comparative example described later, it can be seen that the adsorption of oxygen greatly exceeds that of nitrogen.

Comparative Example For comparison, the adsorption rate of oxygen and nitrogen was evaluated in the same manner as described above, using Na-type zeolite on which silica was not deposited as an adsorbent. FIG. 3 shows the result.

It can be seen that the adsorption rate of nitrogen is much higher than that of oxygen.

Example 3 The effect of silica deposition on CO adsorption was evaluated.

4 (a), 4 (b) and 4 (c) show the results of measuring the adsorption of CO at -78 ° C by gas chromatography.

(A): Blank test (b): Na-type zeolite (without silica deposition), 300 mg (c): Na-type zeolite with 0.29% by weight of silica deposited, 300 mg As can be seen from the results, when silica was not deposited, Although 100% CO adsorption was observed, CO adsorption was reduced to 19% by silica deposition.

 Silica deposition makes it possible to control the CO adsorption capacity.

(Effect of the Invention) According to the present invention, even chemical substances having slightly different molecular sizes can be adsorbed and separated from each other with high selectivity.

Specifically, preferential adsorption of oxygen from the air is also realized. Furthermore, control can also be performed to reduce the ability to adsorb a specific substance.

[Brief description of the drawings]

FIG. 1 and FIG. 2 are measurement diagrams of the adsorption speed showing an example when the adsorbent of the present invention is used. FIG. 3 is a measurement diagram of the adsorption speed showing an example for comparison. FIGS. 4 (a), (b) and (c) are gas chromatographic diagrams showing the adsorption of CO, respectively.

Continuation of front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B01J 20/18

Claims (1)

(57) [Claims] 1. An adsorbent obtained by chemically depositing silica on the surface of an A-type zeolite using tetraalkoxysilane, wherein the adsorbent has an adsorbing ability to preferentially adsorb oxygen over nitrogen.