JPH0568413B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for precisely controlling the entrance diameter of zeolite pores, and more specifically, using a silizing agent in a flowing state to support silica (SiO ₂ ) on zeolite by chemical vapor deposition (CVD). The present invention relates to a method for precisely controlling the entrance diameter of zeolite pores, in which the amount of silica supported is adjusted by pretreating zeolite with ammonia and controlling the amount of acid in the zeolite, thereby controlling the entrance diameter of zeolite pores. [Problems to be solved by the invention] Zeolite is a porous aluminum silicate crystal that (1) adsorbs water and organic substances well; (2)
It has many industrial uses as a solid catalyst and adsorbent because it has the physical and chemical characteristics of being a cation exchanger, (3) having uniform pores, and having molecular sieving properties. . The biggest use as a solid catalyst is as a petroleum cracking catalyst, which utilizes cation exchange properties, and replaces sodium cations with protons, alkaline earth metals such as calcium, or rare earth elements such as lanthanum, giving acidic properties. When done in this way, it exhibits extremely strong solid acid properties. In addition, certain zeolites are used to produce gasoline from methanol, to produce p-xylene from methanol and toluene, and to disproportionate toluene to produce p-xylene; Zeolite is characterized by its shape selectivity, which shows that its reactivity varies depending on the shape of the zeolite. This shape selectivity is characterized by (1) no reaction with molecules that do not enter the pore (reactant molecule shape selectivity), (2) no formation of molecules that cannot exit from the pore (produced molecule shape selectivity), (3)
Products that cannot form a transition state are not produced (transition state shape selectivity), and these shape selectivities are controlled by the pore diameter of the zeolite. Thus, when zeolite is used as a catalyst or adsorbent, the important properties are acidity and pore size.
Therefore, instead of using zeolite as it is,
It has been considered that some kind of treatment can be applied to change the properties of zeolite, and the most commonly used treatments are ion exchange and dealumination, and these treatments have a large effect on the acid properties of zeolite. On the other hand, there is a known method for changing the pore size by utilizing the difference in size between alkali metal cations and alkaline earth metal cations, but this method significantly changes the acid properties. There is a drawback. From this point of view, a method is desired in which the acid properties are maintained as they are and the size of the pores is controlled. For this reason, it has been proposed to support zeolite with an organic compound containing silicon, or to sinter it to form silica after supporting it, but none of these methods allow precise control of the pore entrance diameter. Furthermore, using a specific silanizing agent in a fixed state,
It has also been proposed to control the entrance diameter of zeolite pores by supporting silica on zeolite by chemical vapor deposition under vacuum conditions, but carrying out under vacuum is not suitable on an industrial scale, and When supporting silica on zeolite, variations occurred in the amount of silica supported, making it impossible to precisely and uniformly control the entrance diameter of zeolite pores. The performance of zeolite varies greatly depending on the slight difference in the amount of silica supported, so although various attempts have been made to support silica on zeolite, it has not been possible to uniformly support a predetermined amount of silica on zeolite on an industrial scale. A method for precisely controlling the zeolite pore entrance diameter has not yet been obtained. The present invention was made from this point of view, and it is possible to uniformly support a predetermined amount of silica on zeolite and precisely control the entrance diameter of zeolite pores on an industrial scale. The purpose is to provide a control method. [Means and effects for solving the problem] In accordance with the above purpose, the present inventors have as a result of their studies,
When depositing silica onto zeolite by chemical vapor deposition using a circulating silizing agent, alkali metal ions, alkaline earth metal ions, or ammonium ions are used as a pretreatment to partially remove the acid sites of the zeolite. By poisoning the silica and controlling the amount of acid, the amount of silica supported can be adjusted uniformly.
The present invention was achieved by discovering that the entrance diameter of zeolite pores can be precisely controlled by this method. That is, the present invention uses a flowing silanizing agent to support silica on zeolite by a chemical vapor deposition method, and when controlling the entrance diameter of zeolite pores, it is possible to pre-load silica with alkali metal ions, alkaline earth metal ions, and ammonium ions. This invention provides a method for precisely controlling the entrance diameter of zeolite pores, which is characterized by adjusting the amount of silica supported using treated zeolite. In the present invention, a silanizing agent is deposited on zeolite using a chemical vapor deposition method, and a predetermined amount of silica is uniformly supported on the zeolite surface. The chemical vapor deposition method is a method of producing a solid thin film by applying energy such as heat, plasma, light, etc. to decompose or react gas molecules in the gas phase, and in the present invention, various conditions such as the reaction atmosphere are determined as appropriate. . The characteristics of zeolite prepared by this chemical vapor deposition method are that silica is supported only on the outer surface of the zeolite using a silanizing agent with a molecular size that does not fit into the pores of the zeolite, and that the silica is supported in multiple layers. This allows the pore diameter to be changed continuously.
As a result, zeolites with different pore entrance diameters can be arbitrarily prepared from one zeolite, and can be used appropriately depending on the intended use. Further, in the present invention, chemical vapor deposition is carried out while the silanizing agent is in a flowing state. When chemical vapor deposition is performed on zeolite using a silanizing agent in a flowing state, the silica is supported from the upper part of the silica reaction layer, and the reaction zone sequentially moves downstream. At the initial stage of the reaction, all of the silanizing agent reacts and there is no unreacted material. When unreacted substances start to be detected, the reaction rate becomes 0 in a very short time. This indicates that the reaction between the zeolite and the silanizing agent is extremely fast. It also shows that once a certain amount of silanizing agent is supported, no further reaction occurs.
The amount of silica supported is a function of the chemical vapor deposition reaction temperature, and the amount of silica supported can be adjusted by changing the chemical vapor deposition reaction temperature. Although it is possible to control the amount of silica supported by the chemical vapor deposition reaction temperature in this way, even finer control is required depending on the purpose of use. Therefore, in the present invention, zeolite is pretreated with alkali metal ions such as sodium, alkaline earth metal ions such as calcium, and ammonium ions to poison a part of the melting point of zeolite and adjust the amount of acid. The diameter of the hole entrance is minutely controlled. The alkali metal ions and alkaline earth metal ions used here are not particularly limited, but sodium ions, potassium ions, magnesium ions, calcium ions, barium ions, etc. are preferably used from the viewpoint of economy. In addition, the amount of acid in zeolite can be controlled by ion exchange with H-type zeolite, or by ion exchange with alkali metal ions or alkaline earth metal ions in advance, and then exchanging some of these ions with hydrogen ions or ammonium ions. (However, in the case of exchange with ammonium ions, it is half-baked to leave some ammonium ions, or completely calcined and used as H-type zeolite). The zeolite used in the present invention is not particularly limited, and zeolites such as A type, mordenite type, Since the zeolite has no melting point, it cannot support silica and is therefore undesirable. The silanizing agent used in the present invention may be a gas or a liquid at room temperature. In addition, this silanizing agent needs to be used in a distributed state,
Specifically, Si(R ₁ ) x (R ₂ ) y [R ₁ : alkyl group from C ₁ to C ₅ , R ₂ : alkoxide group from C ₁ to _{C 5} , 0≦x≦3, 1 ≦y≦4, x+y=4]. However, compounds containing halogens such as chlorine or sulfur are not preferable because when zeolite is used as a catalyst, the chlorine or sulfur attached to the zeolite becomes a catalyst poison or changes the properties of the zeolite. In addition, the molecular diameter of the silanizing agent must be larger than the zeolite pore diameter; if it is smaller than the zeolite pore diameter, the silanizing agent will penetrate into the zeolite pores and change the properties inside the zeolite pores. It will change. [Examples] The present invention will be specifically described below based on Examples, Comparative Examples, and Experimental Examples. Examples 1 to 3 A NaNO ₃ aqueous solution was added to NH ₄ type mordenite to convert some of the ammonium ions to sodium ions, and then calcined at 500°C for 3 hours to form NaH
Obtained type mordenite. The exchange rate of sodium ions is expressed in %; for example, when 50% of sodium ions have been exchanged, it is expressed as Na(50)M. By this method, Na(80)M, Na(50)M, and Na(30)M were prepared, respectively. 1g of this zeolite with an inner diameter of 4mm
The mixture was filled into a stainless steel reaction tube and pretreated for 1 hour at 320°C by flowing dry helium. then
Chemical vapor deposition was carried out at 220° C. by flowing a mixed gas of tetramethoxysilane (partial pressure 3 mmHg) and Heilm at SV = 9000 h ^-1 . The reaction amount of tetramethoxysilane was analyzed by gas chromatography, and the reaction was stopped when the reaction amount reached zero. Then, to remove residual organic matter, heat at 500°C.
The product was calcined under air circulation for 3 hours to obtain silica-supported zeolite. The amount of silica supported was analyzed using XPS.
It is expressed as the thickness of supported silica. The thickness of silica was determined using the following formula. Si/Al=t(n+1)/(d-t)+n Si/Al: Atomic ratio of Si and Al based on XPS, t: Thickness of supported silica (Å), n: Si/Al of zeolite Table 1 shows Al (atomic ratio), d: electron escape depth (Å), and thickness of supported silica (Å). _Examples 4-6 K( ₈₀ )M, K(50)M,
Prepare K(30)M and perform chemical vapor deposition,
The amount of silica supported was measured. The thickness of supported silica is shown in Table 1. Examples 7-8 Ammonium ion exchange was performed on H-type mordenite using NH ₄ NO ₃ . Zeolite NH ₄ (50) M, NH ₄ with different ammonium ion exchange rates
(30) M was prepared, chemical vapor deposition was performed in the same manner as in Examples 1 to 3, and the amount of silica supported was measured. The thickness of supported silica is shown in Table 1. Comparative Example 1 Examples 1 to 3 except that H-type mordenite was used
Chemical vapor deposition was performed in the same manner as above, and the amount of silica supported was measured. The thickness of supported silica is shown in Table 1. Comparative Examples 2 and 3 Using NaNO ₃ and KNO ₃ , ion exchange was repeated until there was no more exchange, and Na(100)M, K(100)
M was prepared, chemical vapor deposition was performed in the same manner as in Examples 1 to 3, and the amount of silica supported was measured. The thickness of supported silica is shown in Table 1.

[Table] As shown in Table 1, silica is not supported in the zeolites of Comparative Examples 2 and 3, which were 100% ion-exchanged with sodium ions or potassium ions. In addition, in the zeolites of Examples 1 to 8 that were partially ion-exchanged with sodium ions, potassium ions, or ammonium ions, the smaller the ion exchange rate, the thicker the silica was. It can be seen that the zeolite has the maximum thickness of silica. This shows that sodium ions, potassium ions, and ammonium ions interfere with silica loading, and that the thickness of silica can be precisely controlled by controlling the amount of exchange of sodium ions, potassium ions, and ammonium ions. . Note that there is a difference in the thickness of silica for sodium ions, potassium ions, and ammonium ions even if the exchange rate is the same.
The cause was unknown. [Effects of the Invention] As explained above, in controlling the entrance diameter of zeolite pores by supporting silica on zeolite by chemical vapor deposition using a flowing silanizing agent, alkali metal ions, alkaline earth metal ions, etc. The method of precisely controlling the zeolite pore entrance diameter of the present invention, which uses zeolite pretreated with ammonium ions to adjust the amount of silica supported, precisely controls only the zeolite pore entrance diameter and controls the properties inside the pores. Since the zeolite is not changed, the desired performance can be imparted to the zeolite, and since a silanizing agent in a circulating state is used, it can be carried out on an industrial scale and maintenance etc. are easy. In particular, by combining the method of the present invention with a method of changing the chemical vapor deposition reaction temperature, the supported amount can be changed arbitrarily. Therefore, the zeolite obtained by the present invention has selectivity and can be suitably used for adsorption, catalyst, etc. applications.

Claims (1)

[Claims] 1 Using a flowing silanizing agent, silica is supported on zeolite by chemical vapor deposition, and when controlling the zeolite pore entrance diameter, zeolite pretreated with alkali metal ions, alkaline earth metal ions, and ammonium ions is used. A method for precisely controlling the entrance diameter of zeolite pores, which is characterized by adjusting the amount of silica supported using the method.