JPH0529604B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing crystalline aluminosilicate zeolite, and more specifically, the present invention relates to a method for producing crystalline aluminosilicate zeolite, which improves the utilization rate of raw materials used in producing crystalline aluminosilicate zeolite, particularly the utilization rate of silica sources and alkali sources. Relates to a method for producing crystalline aluminosilicate zeolite. Crystalline aluminosilicate zeolite can be prepared by preparing SiO ₂ /Al ₂ O ₃ , M ₂ O/Al ₂ O ₃ (M represents an alkali metal) and H ₂ using a suitable silica source, alumina source, alkali source and water. By preparing an aqueous reaction mixture in which the molar ratio of each oxide O/Al ₂ O ₃ is within a specified range and reacting this mixture at a temperature sufficient for a sufficient time to crystallize the zeolite. Manufactured. and the Kayban ratio (means the molar ratio of SiO ₂ /Al ₂ O ₃ ; the same applies hereinafter) of the crystalline aluminosilicate zeolite produced from the aqueous reaction mixture.
is generally influenced by the types of silica, alumina, and alkali sources used in preparing the aqueous reaction mixture, the oxide molar ratio in the aqueous reaction mixture, and the crystallization conditions. By the way, the Cavan ratio of phasiasite-type zeolite is usually in the range of 2 to 6, and in order to produce such a zeolite, it is necessary to prepare an aqueous reaction mixture with a Cavan ratio even higher than the Cavan ratio. It won't happen. However, when the C-ban ratio of the aqueous reaction mixture is increased, crystallization takes a long time, and the yield of zeolite decreases when a reasonable reaction time is used. This means that the utilization rate of the silica source and the alkali source contained in the reaction mixture is low. The utilization rate of the silica source (or alkali source) is expressed as follows. Utilization rate of silica source (or alkali source) = amount of SiO ₂ (or M ₂ O) in the produced zeolite / amount of SiO ₂ (or M ₂ O) in the aqueous reaction mixture x 100 (%) Contained in the reaction mixture In order to avoid economic losses caused by insufficient utilization of silica sources and alkali sources, measures have been taken to recover and reuse unused silica sources and alkali sources. For example, in U.S. Pat. No. 4,164,551, a crystalline aluminosilicate zeolite formed in an aqueous reaction mixture is filtered off, and an aluminum sulfate solution is added to the resulting mother liquor to form a silica-alumina hydrogel. Methods of filtering and washing and reuse as feedstock for aqueous reaction mixtures are taught. However, recovering and reusing unused silica sources and alkali sources is not necessarily practical because recovery is expensive. The present invention relates to the process of producing crystalline aluminosilicate zeolite in an aqueous reaction mixture, more specifically, by adding a second alumina source to the reaction mixture before the crystallization of the zeolite is completed, the produced zeolite is Increasing the utilization of silica and alkali sources in the aqueous reaction mixture without reducing the crystallinity of the crystalline aluminosilicate with high Caiban ratio, even though the Caiban ratio in the mixture decreases. A method for producing zeolite in high yield is provided. That is, in the method of the present invention, the molar ratio of oxides is SiO ₂ /Al ₂ O ₃ = 3 to 20 M ₂ O/Al ₂ O ₃ = 2 to 6 (where M represents an alkali metal) H ₂ O/ A second source of alumina is added to the aqueous reaction mixture in the range of Al ₂ O ₃ =50-300 in the process of heating the mixture at a temperature of at least 50°C to crystallize the aluminosilicate zeolite. addition to complete the crystallization reaction and then recovering the formed crystalline aluminosilicate from the reaction mixture. Roughly speaking, when producing crystalline aluminosilicate zeolite from an aqueous reaction mixture of a certain composition, if an alumina source is added to the reaction mixture, the utilization rate of the silica source and alkali source contained in the reaction mixture can be increased. can be improved. However, in that case, the C-Ban ratio of the crystalline aluminosilicate zeolite produced decreases. However, according to the method of the present invention, by appropriately selecting the composition of the aqueous reaction mixture to which the second alumina source is added, the timing of its addition, and the type and amount of the second alumina source, the production can be improved. It is possible to increase the Ca-Ban ratio of zeolite rather than to decrease it, and therefore to improve the utilization rate of silica sources and alkali sources. In the method of the present invention, an aqueous reaction mixture having an oxide molar ratio in the range shown in (A) below is first prepared. (A) SiO ₂ /Al ₂ O ₃ = 3-20 M ₂ /Al ₂ O ₃ = 2-6 H ₂ O/Al ₂ O ₃ = 50-300 For the preparation of this aqueous reaction mixture, conventionally known silica Sources, alumina sources, and alkaline sources can be used. For example, in the production of faujasite-type zeolite, silica sol, sodium silicate, white carbon, etc. are used as silica sources, sodium aluminate, aluminum sulfate, etc. are used as alumina sources, and caustic soda is used as an alkali source. However, in the present invention, these raw materials can also be used to prepare the above-mentioned aqueous reaction mixture. The aqueous reaction mixture having an oxide molar ratio in the range (A) is optionally aged at room temperature and then heated at a temperature of at least 50°C, preferably at a temperature of 80 to 150°C. It is thought that a crystal precursor of crystalline aluminosilicate zeolite is generated during the aging stage at room temperature, and crystallization (including crystal growth) of the zeolite occurs during the heating stage. According to the method of the invention, a second alumina source is added to the aqueous reaction mixture in which zeolite crystallization is proceeding. As this second alumina source, it is preferable to use one or more of aluminum hydroxide, χ-alumina, and ρ-alumina, and the aluminum hydroxide mentioned here includes gypside, boehmite, bayerite, etc. Crystalline aluminum hydroxide and amorphous aluminum hydroxide such as alumina hydrogel and alumina hydrosol are included. The second alumina source of the present invention needs to be relatively unreactive. By the way, if this alumina source is a highly reactive alumina source such as sodium aluminate or aluminum sulfate, in other words, it is a highly water-soluble alumina source, the utilization rate of the silica source and alkali source can be improved to some extent. However, the C-ban ratio of the zeolite produced is markedly reduced, and sometimes zeolite crystals may not even be produced. Further, when the second alumina source is α-alumina, γ-alumina, η-alumina, etc., which have very low reactivity, it is not possible to improve the utilization rate of the silica source and the alkali source as in the present invention. . The amount of the second alumina source added is 100% or less of the amount of alumina in the aqueous reaction mixture in which the oxide molar ratio is within the range of (A) above. Adding more than this is not preferable because the C-Ban ratio of the produced zeolite will drop significantly. As mentioned above, the second alumina source is
It can be added in one or more portions at any time during the process of crystallization of the zeolite in the aqueous reaction mixture; later additions generally produce zeolites with higher C-Ban ratios. can be done. However, the addition of the second alumina source must be completed before the crystallization of the zeolite is completed, and addition after the crystallization is completed cannot improve the utilization rate of the silica source and the alkali source. The effective timing for adding the second alumina source is preferably in the first half of the heat aging stage. The aqueous reaction mixture is maintained at a temperature of at least 50% during and after the addition of the second alumina source.
℃, preferably between 80°C and 150°C, and this temperature is maintained until the crystallization of the zeolite is completed. After the crystallization is completed, the desired crystalline aluminosilicate zeolite can be obtained by recovering the crystals from the aqueous reaction mixture according to a conventional method. As described above, according to the method of the present invention, in contrast to the conventional practice, crystalline aluminosilicate zeolite with a high Cylban ratio is produced by improving the utilization rate of the silica source and the alkali source contained in the aqueous reaction mixture. The reason for this can be explained as follows. That is, in the method of the present invention, the aqueous reaction mixture before adding the second alumina source is
It has the oxide molar ratio shown in (A). Adding a second alumina source to this aqueous reaction mixture results in
Naturally, the Cayban ratio of the aqueous reaction mixture is reduced, so that in the normal case the zeolite obtained from this aqueous reaction mixture will have a lower zeolite compared to the zeolite obtained from the aqueous reaction mixture before addition of the second alumina source. Cavan ratio decreases. However, in the method of the present invention, crystallization of zeolite is first started in an aqueous reaction mixture having the oxide molar ratio shown in (A) above, and a second alumina source is added while the crystallization is progressing. and because the alumina source is relatively unreactive, the molar ratio of dissolved silica to dissolved alumina in the aqueous reaction mixture in which zeolite crystallization is proceeding is reduced by the addition of a second alumina source. It is assumed that the method of the present invention can improve the utilization of the silica source and the alkali source without reducing the Cavan ratio of the zeolite. Next, the present invention will be explained in more detail with reference to Examples. Example 1 2086 g of sodium aluminate solution (22% Al ₂ O ₃ ) was weighed and mixed with 958 g of 48% caustic soda solution.
To this was added 1548 c.c. of water, and with rapid stirring, 7176 g of silica sol (30% SiO ₂ ) was further added over 60 minutes to prepare an aqueous reaction mixture (silica-alumina hydrogel slurry) with a Cavan ratio of 8.0. Stirring was stopped and the mixture was left at room temperature for 16 hours.
Thereafter, the reaction mixture was heated to 95° C. for 2 hours for crystallization, and then a second source of alumina was added in an amount sufficient to reduce the Cavan ratio of the original aqueous reaction mixture to 6.0. Crystallization was carried out for an additional 46 hours. As the second alumina source, gypsite obtained by the Bayer method was used in the first experiment, and χ-alumina obtained by calcining gypsite in a hot air stream at 600° C. was used in the second experiment. After completion of crystallization in each experiment, the mixture was cooled to 40°C, filtered with water, washed with sufficient water, and dried to obtain zeolite. Regarding this zeolite, the yield, C-Ban ratio, degree of crystallinity, utilization rate of silica source and alkali source were measured. In addition, the crystallinity is determined by comparing the peak areas of CHAT at 2θ = 23.6 and 26.9 with that of commercially available zeolite (SK-40) by X-ray analysis.
In addition, the utilization rates of silica source and alkali source were determined by chemical analysis. The results are shown in Table-1. In addition, for comparison, a sodium aluminate solution (Al ₂
2086 g of 22% O ₃ ) and 958 g of 48% caustic soda solution were mixed, and with rapid stirring, 5399 g of silica sol (30% SiO ₂ ) was added over 60 minutes to form an aqueous reaction mixture (silica-alumina hydrogel) with a Cavan ratio of 6.0. Slurry) was prepared. Stirring was stopped and the mixture was left at room temperature for 16 hours, then warmed to 95°C and incubated at 48°C.
Time crystallization was performed. After crystallization, the mixture is heated to 40
The mixture was cooled to 0.degree. C., dehydrated and filtered, then washed with sufficient water and dried to obtain zeolite (c) for comparison. This zeolite (c) was also measured in the same manner as the previous zeolite. The results are shown in Table-1.

[Table] As is clear from Table 1, zeolite with a Cayban ratio of 4.1 can only be obtained from a reaction mixture whose Cayban ratio is 6.0 from the beginning. The addition of an alumina source of 2 can produce a zeolite with a Cayban ratio of 4.8, even if the amount added makes the Cayban ratio of the starting reaction mixture 6.0. Example 2 An aqueous reaction mixture with a Cavan ratio of 8.0 was prepared in exactly the same manner as in Example 1, and after stirring was stopped, the mixture was left at room temperature for 16 hours to obtain a slurry (X). After heating this slurry (X) to 95°C and proceeding with crystallization for 12 hours,
Enough Bayer gypsite was added to the slurry to reduce the Cavan ratio of the original aqueous reaction mixture to 7.0, and crystallization was carried out for an additional 46 hours. After the crystallization was completed, the product was treated in the same manner as in Example 1 to obtain zeolite (e). Also, the amount of gypsite added to the slurry (X) is adjusted so that the Cavan ratio of the initial aqueous reaction mixture is 5.0 and
Zeolites (f) and (g) were obtained in exactly the same manner as above except that the amount was reduced to 4.0. Furthermore, for comparison, slurry (X) was heated to 95°C without adding gypsite and crystallized for 48 hours to obtain zeolite (d). The zeolites (d) to (g) thus obtained were subjected to the same measurements as in Example 1, and the results shown in Table 2 were obtained.

[Table] From the comparison of zeolites (d) and (e) in the table above, it can be seen that according to the present invention, by adding the second alumina source, the silica source, alkali The yield of zeolite can be increased by improving the resource utilization. Example 3 Water 96 c.c. and water glass (SiO ₂ 24%, Na ₂ O/SiO ₂ =
3.3) 405g and 187g of 48% caustic soda were mixed.
Add 51g of sodium aluminate solution (Al ₂ O ₃ 22%) to this.
and 138 c.c. of water with stirring to prepare a silica-alumina hydrogel slurry, which was heated at 30°C for 20
The mixture was left to stand for a period of time to form a seed slurry. Next, 1323.4 g of metakaolin (Al ₂ O ₃ 2SiO ₂ ) previously calcined at 600°C for 2 hours was dispersed in 600/cc of water, 8607.5 g of the above-mentioned water glass was added while stirring, and 668.8 g of 48% caustic soda was added. g was added.
After that, 876.6g of the seed slurry prepared earlier
were mixed and stirred for 3 hours to obtain a slurry (Y) with a Kayban ratio of 8.0. After heating this slurry (Y) to 95℃,
Beyer method gypsite slurry (Y) in an amount that lowers the Cavan ratio of the slurry (Y) to 6.0.
In addition, heating was continued for an additional 48 hours to complete crystallization of the zeolite. Thereafter, the produced zeolite was treated in the same manner as in Example 1 to obtain zeolite (h). In addition, the timing of adding gypsite to the slurry (Y) was shifted to 2 hours, 4 hours, 6 hours, 8 hours, and 10 hours after the slurry (Y) reached 95°C. Zeolites (i) to (m) were obtained in exactly the same manner as above, except that the crystallization times were changed to 46 hours, 44 hours, 42 hours, 40 hours, and 38 hours, respectively. Furthermore, for comparison, a slurry (Y) with a Cavan ratio of 8.0 without adding gypsite was heated to 95°C and crystallized for 48 hours to obtain zeolite (n). In addition, after 6 hours had elapsed since the slurry (Y) was heated to 95°C, sodium aluminate was added to the slurry in an amount that lowered the Cayban ratio of the slurry to 6.0, and crystallization was continued for 42 hours. In that case, it was not possible to obtain zeolite crystals. Example 1 for each of the above zeolites (h) to (n)
When similar measurements were carried out, the results shown in Table 3 were obtained.

[Table] As is clear from Table 3, when implementing the method of the present invention, as long as the second alumina source is added during the process of crystallization of the zeolite, the later the addition time, the higher the C-ban ratio. zeolite can be produced.

Claims (1)

[Claims] 1 The molar ratio of the oxides is SiO ₂ /Al ₂ O ₃ = 3 to 20 M ₂ O/Al ₂ O ₃ = 2 to 6 (here, M represents an alkali metal) H ₂ O/ A second alumina is added to the mixture in the process of preparing an aqueous reaction mixture in the range of Al ₂ O ₃ =50-300 and heating the mixture at a temperature of at least 50°C to crystallize the crystalline aluminosilicate zeolite. 1. A method for producing crystalline aluminosilicate zeolite, which comprises adding a source to complete the crystallization, and then recovering the formed crystals. 2. The method of claim 1, wherein the amount of the second alumina source added is 100% or less of the amount of alumina contained in the aqueous reaction mixture. 3 The second alumina source is aluminum hydroxide, χ
- The method according to claim 1, wherein one or more types of alumina and ρ-alumina are used. 4. The method according to claim 1, wherein the crystalline aluminosilicate zeolite is a faujasite type zeolite.