JP2008094685A - Crystalline metallosilicate, production method therefor and use of the same as catalyst - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a metallosilicate catalyst on which coke hardly sticks and which is easily regenerated and effective for a dehydration reaction. <P>SOLUTION: A crystalline metallosilicate is synthesized which is characterized in that the outer surface of a silicate crystal substantially constituted of only silicon and oxygen is covered with a metallosilicate layer having the same crystal structure, wherein silicon atoms are substituted with divalent and/or trivalent metal elements. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  In the present invention, the outer surface of a silicate crystal composed substantially only of silicon and oxygen is coated with a metallosilicate layer having the same crystal structure in which silicon atoms are replaced with divalent and / or trivalent metal elements. The present invention relates to a crystalline metallosilicate, a method for producing the same, and a method for converting an organic compound using the crystalline metallosilicate as a catalyst.

  In particular, it is useful for a conversion method for dehydrating an organic compound having an alcoholic hydroxyl group. Specific examples of the substance that can be generated by the dehydration reaction include unsaturated ethers, unsaturated alcohols, unsaturated aldehydes, cyclic ethers, and cyclic amines. These unsaturated compounds and cyclic compounds are useful as intermediates for various organic chemicals and as raw materials for polymers.

  Crystalline metallosilicate is a substance in which a part of silicon of crystalline silicate composed of silicon and oxygen having micropores of 1 nm or less is substituted with another metal element (T atom), and a crystal in which T atom is aluminum. Aluminosilicates are known as zeolites.

  Methods for synthesizing crystalline metallosilicates have been known for a long time, and so-called hydrothermal synthesis methods are often used. Generally, silicon sources (colloidal silica, water glass, silicate esters, etc.) and metal element sources that substitute part of silicon atoms (aluminum sulfate, sodium aluminate, boric acid, gallium chloride, etc.), alkali metal sources A method in which a structure directing agent (tetrapropylammonium hydroxide, tetraethylammonium bromide, etc.) is thoroughly mixed and charged in an autoclave and hydrothermal synthesis is performed under conditions of high temperature and pressure is often used.

For example, a method for producing ZSM-5 zeolite is known (see Patent Document 1). Also, a dry gel conversion method is disclosed in which a gel (dry gel) obtained by evaporating and drying these solutions and aqueous slurry is brought into contact with high-temperature and high-pressure steam in an autoclave for crystallization (see Patent Document 2). The crystalline metallosilicate thus obtained is widely used as a catalyst for chemically converting organic substances.

US Pat. No. 3,702,886 JP 2000-344515 A specification

  In many cases where crystalline metallosilicate is used as a catalyst, the deterioration of the activity of the catalyst becomes a problem. It is often observed that the organic material as a reaction raw material or product becomes a precipitate on carbon (so-called coke), causing a phenomenon called coking that covers the active site, and the activity deteriorates.

  In the crystalline metallosilicate, micropores having a diameter of 1 nm or less are present, and when coking occurs, it is often observed that coke closes the micropores. Compared to the outer surface of the crystalline metallosilicate crystal, the surface area inside the crystal where the micropores are present is large, and when the active sites are inside the micropores, most of the coke will be inside the micropores.

  The catalyst deteriorated by coking can usually be regenerated by circulating and removing oxygen-containing gas at a high temperature. However, coke deposited inside the micropores has a large oxygen diffusion resistance and a large amount of coke, which makes it difficult to remove by combustion, and the conditions become harsh and difficult to implement.

  The active sites inside the micropores are liable to be deteriorated by coking, and the amount of coke is simply increased to make regeneration difficult. When active sites near the metallosilicate crystal outer surface or the micropore opening are effective sites, the active sites inside the micropores are not necessary. The active site of the metallosilicate is a portion in which the silicon forming the crystal and the silicon of the oxygen framework are replaced with a divalent or trivalent metal element (T atom) such as aluminum or boron.

  When active sites near the metallosilicate crystal outer surface or the micropore opening are effective sites, if the layer substituted with this metal can be formed only on the surface layer, coking to the active sites inside is suppressed and regenerated. It becomes easy to do.

  If active sites exist only on the very surface layer of the catalyst as in the present invention, reaction activity is not impaired, and no active sites are present inside the micropores, so coking does not occur in the micropores and the amount of coke is small. Therefore, it is expected that the reproduction becomes easy.

  First, a metallosilicate crystal containing substantially no metal element other than silicon is synthesized, and then a metal element (Al, Ga, In, B, Ni, Co, Zn, etc., particularly Al is preferred) is added to the metal element. If the crystal substituted by is continuously formed on the surface layer, the active point structure described above can be realized.

Specifically: Hydrothermal synthesis: Prepared in an autoclave as an aqueous slurry in which a silicon source (colloidal silica, water glass, silicate ester, etc.), an alkali metal source, and a structure indicator (tetrapropylammonium hydroxide, tetraethylammonium bromide, etc.) are mixed well. Hydrothermal synthesis is performed under high-pressure conditions to synthesize a silicate slurry that contains substantially no metal other than silicon, such as silicalite-1, in the framework. A metal element source (aluminum sulfate, sodium aluminate, boric acid, gallium chloride, etc.) that replaces a part of silicon atoms is added here (in this case, silicon source and other raw materials may be added), and further hydrothermal By synthesizing, a metallosilicate crystal having an active site can be epitaxially grown on the crystalline metallosilicate crystal synthesized earlier.

  2. Dry gel conversion method: Evaporate and dry a solution or aqueous slurry in which a silicon source (colloidal silica, water glass, silicate ester, etc.), an alkali metal source, and a structure indicator (tetrapropylammonium hydroxide, tetraethylammonium bromide, etc.) are mixed well. A dry gel is obtained which becomes a solidified silicate crystal precursor. This is transferred into an autoclave and treated with high-temperature and high-pressure steam to synthesize a crystalline metallosilicate crystal solid A that does not contain a metal other than silicon, such as silicalite-1, substantially in the framework. This solid A was impregnated with an aqueous solution of a metal element source (aluminum sulfate, sodium aluminate, boric acid, gallium chloride, etc.) for substituting a part of silicon atoms, dried and transferred again into an autoclave. Treat with steam. At this time, an additional silicon source, alkali metal source, and structure indicator may be added. Alternatively, the metal element source (aluminum sulfate, sodium aluminate, boric acid, gallium chloride, etc.) that disperses the solid A obtained earlier in water and replaces part of silicon atoms, and an additional silicon source, alkali metal source, structure By adding an indicator and hydrothermal synthesis in an autoclave, a metallosilicate layer can be formed on the surface layer.

  The surface layer here means 2 nm or more and 20 nm or less of the outer surface of the crystal. This layer is preferably 10 nm or less, and more preferably 5 nm or less. By making it within this range, coating is performed sufficiently and efficiently, so that coking is suppressed and reproduction is facilitated, which is preferable.

  In the surface layer portion, the atomic ratio of silicon and T atoms varies depending on the crystal system, but is usually in the range of T / Si = 5 to 1000. Preferably it is 10-500, More preferably, it is 10-200.

  The covering degree of the silicate crystal outer surface is preferably 50% or more, more preferably 70% or more, still more preferably 90% or more, and most preferably 100% with respect to the silicate crystal outer surface area.

  Main examples of metallosilicate crystal systems that can be synthesized include MFI, MEL, BEA, MWW, and the like. These crystal systems can be separately formed by properly using the cation species of the structure directing agent to be used. Examples include MFI: tetrapropylammonium cation, MEL: tetrabutylammonium cation, BEA: tetraethylammonium cation, MWW: hexamethyleneimine, and the like.

  The synthesized metallosilicate contains a structure indicator and an alkali metal. When used as a catalyst, it is desirable to decompose and remove the structure indicator by heat treatment at a high temperature. When used as an acid catalyst, it is desirable to remove the alkali metal by ion exchange with ammonium ions or the like, and to make it proton type by heat treatment at high temperature.

  The crystalline metallosilicate synthesized in this way becomes a catalyst with good chemical conversion of organic compounds. Applicable reactions include dehydration reaction, cyclization reaction, isomerization reaction, alkylation reaction, transalkylation reaction, cracking reaction and the like.

  In particular, it is useful for a conversion method for dehydrating an organic compound having an alcoholic hydroxyl group. Examples of substances that can be generated by dehydration include unsaturated ethers, unsaturated alcohols, unsaturated aldehydes, cyclic ethers, and cyclic amines.

  Specific examples include glycol ethers to vinyl ethers (methyl cellosolve to methyl vinyl ether, ethyl cellosolve to ethyl vinyl ether, etc.), ethanolamine to ethyleneimine, glycerin to acrolein, N-hydroxypyrrolidone to N-vinylpyrrolidone, and the like. . In particular, MFI-type metallosilicates are effective for reactions that produce acrolein from glycerin.

Such a dehydration reaction is mainly carried out in the gas phase, preferably under conditions of a raw material partial pressure of 100 Pa to 100 kPa, a reaction temperature of 200 ° C. to 500 ° C., and an SV of about 10 to 10,000 hr ⁻¹ . The raw material gas may be accompanied by a gas inert to the reaction, such as water vapor, nitrogen, argon, or the like.

EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, the scope of the present invention is not limited only to these Examples. Unless otherwise specified, “%” indicates “mass%” and “part” indicates “mass part”.

(Catalyst preparation comparative example 1)
Ammonium type ZSM-5 (CBV5524G) manufactured by Zeolis was calcined in the air at 550 ° C. for 5 hours to obtain catalyst A as H type ZSM-5. The Si / Al atomic ratio contained was 50, and the Na ₂ O content was 0.5%.

(Catalyst preparation comparative example 2)
Synthesis of silicalite-1 having MFI structure: Precursor: 1.4 g of sodium hydroxide is dissolved in 10 g of ion-exchanged water, and 44 g of colloidal silica slurry containing 30% by mass of silicon dioxide is added thereto. Next, a solution in which 2.34 grams of tetrapropylammonium bromide (TPABr) was dissolved in 15 g of ion-exchanged water was added to prepare a precursor slurry. The composition of this liquid is 2 mol of Na ₂ O, 25 mol of SiO _{2 and} 345 mol of H ₂ O with respect to 1 mol of tetrapropylammonium hydroxide.

  The precursor slurry was transferred to a polytetrafluoroethylene-coated autoclave and heated at 200 ° C. for 72 hours for hydrothermal synthesis. The obtained reaction product was dried at 110 ° C. in air after filtration and washing with water.

It was confirmed by powder X-ray diffraction analysis that the structure was MFI. From compositional analysis, it was 0.016 mol of tetrapropylammonium ions (as (TPA) ₂ O) and 0.011 mol of Na ₂ O with respect to 1 mol of SiO ₂ . About 400 ppm of alumina was contained as an impurity.
This was baked in air at 550 ° C. for 5 hours to decompose and remove organic substances, washed three times with a 20% aqueous ammonium nitrate solution, and then heat treated at 550 ° C. for 5 hours. This is referred to as catalyst B.

(Catalyst Preparation Example 1)
Until the hydrothermal synthesis, the same operation as in Catalyst Preparation Comparative Example 2 was performed to obtain a slurry of silicalite-1. 0.1 g of sodium aluminate is dissolved in 5 g of ion-exchanged water, and 6.5 g of a colloidal silica slurry containing 30% silicon dioxide is added thereto. Next, a solution of 0.21 grams of tetrapropylammonium bromide (TPABr) dissolved in 2 g of ion-exchanged water was added to prepare an additional precursor solution. This was added to the previously synthesized silicalite slurry and heated at 200 ° C. for 24 hours to grow a ZSM-5 layer on the silicalite surface. The obtained reaction product was dried at 110 ° C. in air after filtration and washing with water.

It was confirmed from the powder X-ray diffraction analysis that the MFI structure was the same as that of the catalyst A. From compositional analysis, it was 0.016 mol as (TPA) ₂ O, 0.0004 mol as Al ₂ O ₃ , and 0.012 mol Na ₂ O with respect to 1 mol of SiO ₂ . This was baked in air at 550 ° C. for 5 hours to decompose and remove organic substances, and after ion exchange three times with a 20% aqueous ammonium nitrate solution, heat treatment was performed at 550 ° C. for 5 hours. This is referred to as catalyst C.

(Example of organic conversion reaction)
Using the catalysts A, B, and C, glycerin was dehydrated by the following method using a fixed bed reactor to produce acrolein.

A stainless steel reaction tube (inner diameter 10 mm, length 200 mm) filled with 5 ml of catalyst was prepared as a fixed bed reactor, and this reactor was immersed in a salt bath at 360 ° C. Thereafter, nitrogen was circulated in the reactor at a flow rate of 20 ml / min for 30 minutes, and then a reaction gas composed of a vaporized gas of 80% glycerol aqueous solution and nitrogen (reaction gas composition: glycerin 27 mol%, water 34 mol%, nitrogen 39 mol%). ) At a flow rate of 500 hr ⁻¹ . The effluent gas was liquefied and collected for 30 minutes between 0.5 to 1 hour and 2.5 to 3 hours after the reaction gas was circulated in the reactor (hereinafter referred to as “the collected effluent gas "Cooled liquefaction" is referred to as "effluent").

  Then, qualitative and quantitative analysis of the effluent was performed by gas chromatography (GC). As a result of qualitative analysis by GC, by-products such as 1-hydroxyacetone were detected together with glycerin and acrolein. Further, the conversion rate, acrolein yield, and acrolein yield were calculated from the quantitative analysis results. Here, the conversion is a value calculated by (1 ((number of moles of glycerin in the collected effluent) / (number of moles of glycerin introduced into the reactor in 30 minutes))) × 100. . The yield of acrolein is a value calculated by ((molar number of acrolein) / (molar number of glycerin introduced into the reactor in 30 minutes)) × 100.

After reacting for 3 hours, nitrogen was passed through the reactor at a flow rate of 20 ml / min for 30 minutes, and then the catalyst was extracted, and coke adhered to the catalyst was measured by thermogravimetric-differential thermal analysis (TG-DTA). Thermal analysis was performed by the following two methods.
1: Temperature rise from room temperature to 600 ° C. at 10 ° C./min under air flow and hold for 20 minutes 2: Temperature rise from room temperature to 400 ° C. under air flow at 10 ° C./min, then hold for 1 hour, then 10 ° C./min Held for 20 minutes after raising the temperature to 600 ° C.

(Reaction result)
Table 1 summarizes the reaction results and the analysis results of coke.

  In the catalyst B having no Al as an active point, the reaction hardly proceeds and coke hardly adheres. Catalyst A, which also has active sites inside the micropores, has a large amount of coke deposition, and DTA analysis shows two exothermic peaks, 380 ° C and 530 ° C, which is considerably higher than the reaction temperature. I know that there is. Even after holding at 400 ° C. for 1 hour from thermal analysis, 5.5% of coke remains and it is difficult to remove coke at the reaction temperature.

  In the catalyst C according to the present invention, since there are no active sites inside the micropores, the amount of deposited coke is small, and no exothermic peak on the high temperature side is observed. In addition, most of the coke is burned and removed by holding at 400 ° C. for 1 hour.

  In a chemical reaction in which coking proceeds inside the pores when a crystalline metallosilicate having active sites only in the surface layer portion of the crystal of the present invention and having no active sites inside the micropores is used as a catalyst. A large amount of coke is avoided in the pores. Therefore, the regeneration of the catalyst becomes easy and it is very valuable in practical use. In particular, it can be effectively used as a catalyst for a reaction for producing acrolein from glycerin.

Claims (7)

The outer surface of a silicate crystal composed substantially only of silicon and oxygen is covered with a metallosilicate layer having the same crystal structure in which silicon atoms are substituted with divalent and / or trivalent metal elements. Crystalline metallosilicate. 2. The crystalline metallosilicate according to claim 1, wherein the metal element substituting silicon in the metallosilicate layer is at least one element selected from Al, Ga, In, B, Ni, Co and Zn. . 3. The crystalline metallosilicate according to claim 1, wherein the crystalline metallosilicate has a crystal structure of any one of MFI, MEL, BEA, and MWW. Silicate crystal particles containing substantially no metal element other than silicon are synthesized from a raw material containing a silicon source, an alkali source and a structure directing agent, and then a raw material containing a divalent and / or trivalent metal element is added. The crystalline metallosilicate according to any one of claims 1 to 3, wherein a crystalline silicate layer containing a divalent and / or trivalent metal element having the same crystal structure is grown on the surface layer of the silicate crystal previously synthesized. Production method. 5. A method for converting an organic compound, wherein the crystalline metallosilicate according to claim 1 is used. 6. The method according to claim 5, wherein the conversion of the organic compound is a dehydration reaction from an organic compound having an alcoholic hydroxyl group. The method for producing acrolein using the method according to claim 7, wherein the conversion of the organic compound is a dehydration reaction in which acrolein is produced from glycerin.