Chemistry of inorganic compounds – Zeolite – Aging to induce zeolite formation from inorganic mixture
Reexamination Certificate
1999-05-26
2001-10-23
Sample, David R (Department: 1755)
Chemistry of inorganic compounds
Zeolite
Aging to induce zeolite formation from inorganic mixture
C423S711000, C423S716000, C423SDIG002, C502S079000
Reexamination Certificate
active
06306363
ABSTRACT:
The present invention relates to a fine low silica faujasite type zeolite of high purity having a SiO
2
/Al
2
O
3
molar ratio of from 1.9 to 2.1, which is excellent in gas adsorption performance, particularly nitrogen adsorption performance and which is used as a zeolite adsorbent separator for separating and concentrating oxygen from a gas mixture of oxygen and nitrogen by an adsorption method, and a process for its production.
With respect to a process for producing a low silica faujasite type zeolite having a SiO
2
/Al
2
O
3
molar ratio of from 1.9 to 2.1 (hereinafter referred to as “LSX”), various processes have been disclosed. For example, GB-1580928 discloses a process which comprises crystallizing a mixture comprising sodium, potassium, an aluminate and a silicate at a temperature of not higher than 50° C., or aging such a mixture at a temperature of not higher than 50° C. for a very long period of time of from 15 hours to 72 hours, followed by crystallization within a temperature range of from 60 to 100° C. but discloses nothing about a process for obtaining fine LSX in high purity.
ZEOLITES, vol 7, September p.451-457 (1987), discloses in detail the influence of the SiO
2
/Al
2
O
3
molar ratio, the K/(Na+K) molar ratio and the alkali concentration in the starting material, the aging conditions and the crystallization conditions over the formation of the low silica faujasite type zeolite, and the aging and the crystallization are carried out in a sealed plastic container. This reference discloses the effects of the molar ratio of K/(Na+K) over the particle size of LSX to be formed. It is disclosed that as the molar ratio of K/(NA+K) decreases, the particle size of LSX to be formed becomes small, and at a molar ratio of 0.20, LSX having a particle size of not larger than 2 &mgr;m will be formed. It is considered possible to prepare finer LSX by further lowering the molar ratio, but if the molar ratio is further lowered, A-type zeolite will be formed as a by-product, whereby it will be difficult to obtain fine LSX in high purity.
Further, U.S. Pat No. 4,859,217 discloses a process which comprises mixing and gelling a mixture containing sodium, potassium and an aluminate and a mixture containing a silicate at a low temperature of from 4 to 12° C., then aging this gel at a temperature of 36° C. for 48 hours and then raising the temperature to 70° C. for crystallization, wherein it is disclosed important to avoid generation of excessive mechanical energy and cooling in the final mixing, but nothing is disclosed about a method for obtaining fine LSX in high purity.
As described in the forgoing, according to the conventional techniques, it is extremely difficult to obtain a fine low silica faujasite type zeolite in high purity.
Further, it has been considered essential for the production of a low silica faujasite type zeolite to mix and gel a solution containing sodium, potassium, an aluminate and a silicate, at a low temperature, then age the gel in a stand still condition for a long period of time, and further raise the temperature to a crystallization temperature in a stand still condition, for crystallization. However, it is industrially disadvantageous to cool the starting material to a low temperature, and further, the gel has very poor heat conductivity, whereby in the production on a large scale, there has been a difficulty such that it takes a very long period of time to bring the temperature uniform in a stand still condition.
Under the above described circumstances, it is an object of the present invention to provide fine LSX in such a high purity that has not been known heretofore and to provide a process for producing fine LSX of high purity in a short period of time, particularly a process for producing fine LSX of high purity on a large scale in a short period of time.
The present inventors have conducted an extensive study on a process for producing fine LSX of high purity on a large scale continuously and constantly and as a result, have made the following discoveries, which have led to the present invention.
SUMMARY OF THE INVENTION
Namely, it has been found that fine LSX of high purity can be prepared by a process which comprises mixing and gelling a solution containing an aluminate and a solution containing a silicate, followed by aging and crystallization, wherein after the gelation and/or at the initial stage of the aging, a solution having a composition of 10-20 Na
2
O.Al
2
O
3
.5-20 SiO
2
.100-250 H
2
O and preliminarily aged at a temperature of from 10 to 60° C. for from 10 minutes to 3 hours, is added in an amount of from 0.03 to 10% as Al
2
O
3
to the low silica faujasite type zeolite to be formed.
Further, it has been surprisingly found that by employing this process, highly pure LSX can be prepared in an extremely short period of aging time. The present invention has been accomplished on the basis of these discoveries.
Further, the SiO
2
/Al
2
O
3
molar ratio of the low silica faujasite type zeolite in the present invention, is theoretically 2.0, but it should be understood that when errors in measurement of the chemical composition, etc., are taken into consideration, a low silica faujasite type zeolite having a SiO
2
/Al
2
O
3
molar ratio of from 1.9 to 2.1 falls within the scope of the present invention.
Now, the present invention will be described in detail with reference to the preferred embodiments.
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Patent Abstracts of Japan vol. 018, No. 625 (C-1279) 06-240082, Aug. 1994.
Funakoshi Hajime
Shirakura Yoshinori
Sample David R
Sughrue Mion Zinn Macpeak & Seas, PLLC
Tosoh Corporation
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