NO763320L - - Google Patents

Description

The present invention relates to a method

for the production of zeolites with a SiC^/Al-pO^ ratio above 15, e.g. the zeolite family ZSM 5 which includes zeolites ZSM 5,

8, 11, 12 and 21 and zeolites Zeta 1 and 3, from reaction mixtures. which would normally give the sodium zeolites Y, mordenite, analcite, gismondite, gmelinite or natrolite or the potassium/sodium zeolites L, chabazite or erionite.

Crystalline zeolites, which are commonly known as molecular sieve materials, are characterized by a highly ordered structure comprising a network of SiO^ and AlO^ tetrahedra which are connected by sharing O atoms, so that O/Al + Si = 2.

The negative charge is offset by cations, usually Na or K or H. Until recently, it was not possible to synthesize zeolites with SiC^/A^O^ ratios above 11, and naturally occurring zeolites never have such a ratio above 11. However, this problem has been overcome in recent times, and this has resulted in a number of zeolites with a high SiC^/A^O-^ ratio, high stability and a very high degree of acidity, as well as the ability to catalyze the conversion of methanol and other simple compounds into aromatic hydrocarbons. This was achieved by using large nitrogen-containing cations such as tetraalkylammonium, e.g. in the synthesis of ZSM 5 (US Patent No. 3,702,886) and Zeta 3 (applicant's UK Patent Application No. 46968/74 and New Zealand Application No.

179 072, as well as Dutch patent application no. 7 512 645). By using such large cations, zeolites with a SiO 2 /Al 2 O 4 ratio of at least 65 can be produced. It is assumed that the large cations act as a template for the new structures that are formed. Without such cations, the product would be mordenite with a SiO2/Al20.2 ratio of 10.

However, the compounds that give the large cations are very expensive and are destroyed or lost during the zeolite synthesis. It was now surprisingly found that zeolite-^synthesizing reactions give highly silicon-containing zeolites (SiC^/A^O^ ratio, for example above 15 and up to 200) if one or more alcohols are present. It is assumed that the alcohol can form a complex with the aluminum oxide that is formed in the early stages of the reaction, so that aluminum oxide becomes too little available after a zeolite network is built up. This would result in a very silicon-rich network being built up. The present method is believed to be fundamentally different from a previously described zeolite synthesis in the presence of an alcohol (British patent no. 1 365 318), as the alcohol's function in this

synthesis is to quaternize a non-quaternary amine present in the reaction mixture.

The method according to the invention for producing zeolites is characterized by reacting an aqueous mixture comprising at least one silicon oxide source, at least one aluminum oxide source, at least one alkali as defined below, and at least one alcohol.

The term "alkali" as used herein means free alkali, i.e. a hydroxide or a salt of an acid such as aluminum or silicic acid which is not stronger than carbonic acid of lithium, sodium or potassium or of quaternary ammonium or quaternary phosphonium, which is present at the beginning of the zeolite synthesis. This definition thus excludes non-quaternary ammonium and non-quaternary phosphonium compounds, except insofar as these are completely quaternized in the aqueous mixture before the beginning of the zeolite synthesis.

The alkali present in the mixture need not include - and preferably does not include - any quaternary ammonium or quaternary phosphonium compounds. If such a quaternary compound is present, however, it preferably contains 4-20 carbon atoms per quaternary nitrogen or phosphorus atom and is singly charged; examples are tetramethyl, tetraethyl, tetrapropyl, tetrabutyl and trimethylcetyl ammonium compounds. The alkali metal preferably includes sodium, especially in an amount of at least 90% of the alkali, calculated as equivalents, and the zeolite product can then be of the ZSM 5 type.

The source of the silicon dioxide can be any of the materials that are usually considered usable in the synthesis of zeolites, e.g. powdered solid silica, silicic acid, colloidal silica or dissolved silica. Among the powdered silicon dioxides that can be used are precipitated silicon dioxide, especially those obtained by precipitation from a solution of alkali metal silicate, e.g. of the "KS 300" type manufactured by AKZO, and similar products, aerosil silicas, silica fumes and silica gels, suitably in grades suitable for use as reinforcing pigments for rubber or silicone rubber. Colloidal silicon dioxides of different particle sizes can be used, e.g. 10-15 or 40-50 µm, as marketed under the trademarks "LUDOX", "NALCOAG" and "SYTON". The usable dissolved silicas include commercially available water glass silicates of sodium and/or potassium containing 0.5-6.0 and especially 2.0-4.0 mol SiO 2 per. mol Na 2 O or K 2 O, "active" alkali metal silicates as stated in British Patent No. 1,193,254, and silicates prepared by dissolving silicon dioxide in alkali metal hydroxide or quaternary ammonium hydroxide as a preliminary step in the preparation of the synthesis mixture. The water glass silicates are preferred both because the price and the technological properties.

A mixture of silicate materials can be used. If desired, an aluminosilicate such as clay or a non-crystalline synthetic aluminosilicate or a zeolite other than that to be produced by the process can be used as a source of silicon dioxide, but usually an additional silicon dioxide material will then be necessary due to the relatively low ratio between silicon dioxide and aluminum oxide in readily available alumino-silicates.

The alumina source is most conveniently sodium aluminate, but may be or include an aluminum salt, e.g. the chloride, nitrate or sulfate, or alumina, which is preferably used in a hydrated or hydratable form, such as colloidal alumina, pseudoboehmite, boehmite, gamma alumina or the alpha or beta trihydrate. The aluminum oxide can be wholly or partly provided from an alumino-silicate compound, as mentioned in connection with the source of silicon dioxide.

If a clay is a component of the reaction mixture, this can for example be kaolin (especially in the form of metakaolin which is obtained by calcining kaolin at 500-950°C, especially 530-600°C), or one or more of the materials attapulgite, dickite , halloysite, illite and montmorillonite. Other possible aluminosilicate compounds include naturally occurring zeolites and substances such as nepheline and calcilite. A de-aluminized aluminosilicate can be used if desired. When composing the reaction mixture, reactants such as water and alkali metal compounds which are added as part of the aluminosilicate compound are included in the calculation.

The molar ratio between silicon dioxide and aluminum oxide in the mixture is preferably at least 20, e.g. 20-200, preferably 40-120.

The reaction mixture may also contain a mineralizing agent, which is a lithium, sodium or potassium salt of a strong acid, e.g. halides, nitrates or sulfates.

Such an agent can be added as such or it can be formed

in situ, in particular by reaction between an aluminum salt or a quaternary salt (if this is used) and a hydroxide or lithium, sodium or potassium salt of a weak acid or by neutralizing such a hydroxide or salt of a weak acid with a strong acid. The proportion of mineralizing agent is appropriate within the range 5-100, calculated as moles of monovalent ion or equivalent monovalent ion per moles of A^O^. The cation of the mineralizing agent should be chosen taking into account the nature of the alkali cation.

The alcohol may be monovalent, divalent or polyvalent and may be a primary, secondary or tertiary alcohol. It can preferably have 1-20, especially 1-4 carbon atoms per hydroxy group. Preferably, it contains at most 3 hydroxy groups in the molecule.

The proportion of alcohol is appropriate within the range 1-100, especially 20-100 OH groups per moles of Al2O3>

The molar composition of the reaction mixture is appropriate as follows when aiming to produce a zeolite of the ZSM 5 family:

where M is or includes sodium as indicated above and/or (less preferred) a singly charged ion of a quaternary ammonium and/or quaternary phosphonium compound;

M 20 denotes free alkali, as indicated above; and OH(R) is a hydroxy group present as an alcohol.

The reaction temperature can be within the range 80-300°C and is appropriate within the range 150-200°C. The time required for the reaction depends, among other things, on a. of the temperature and of the zeolite to be produced. When the above-mentioned mixture is used, the product is a zeolite of the ZSM 5 family where a temperature of 180°C is maintained for 6 days, between 0.5 and 12 days being considered a representative time for temperatures within the range of 150-200° C. The mixture may be supplemented with seeds of the intended product, but this does not seem to be necessary.

When the temperature is above the boiling point, the synthesis is carried out under pressure, which may be autogenous or may be in the presence of non-reactive gas under pressure, especially if boiling is desired to be avoided; however, the reaction is generally carried out under agitation. The reaction container is conveniently made of or lined with stainless steel or glass, for example "Pyrex" (registered trademark).

After sufficient formation of the zeolite product, the reaction mixture is allowed to cool, and the solid phase is collected on a filter and washed, after which it is usually dried unless the material is to be subjected to further wet process steps. The subsequent treatment of the product with a view to dehydrated or ion-exchanged forms, such as the ammonium and/or hydrogen form and/or other (metal-containing) forms, can be carried out by known methods.

The product obtained when the synthesis is carried out under conditions which lead to the formation of a zeolite with a silicon dioxide/alumina ratio above 10 (e.g. of the type ZSM 5)

and in the absence of quaternary compounds, typically has the general formula

and an X-ray diffraction pattern that is characteristic of the ZSM 5 type and is - due to absence a<y>quaternary compounds - a new one

product. Such a product could probably not previously be produced without a calcination step.

EXAMPLE 1

The reaction mixture had the following molar composition:

where OH(R) represents isopropanol, and X represents a half sulfate ion formed by reaction between aluminum sulfate, sulfuric acid and the sodium oxide of the water glass.

112.5 g of water glass (Na 2 O; 3.4 SiO 2 ; 24 H 2 O) was dissolved in a mixture of 141 g of water and 12.7 g of isopropyl alcohol, which gave solution A. Then 3.9 g of aluminum sulfate

(A^O^; 3 SO^; 16 H2O) dissolved in a mixture of 192 g of water and

9.4 g of sulfuric acid, which gave solution B. The acid brings the composition of the reaction mixture into the desired M20/SiC>2 range by neutralizing the excess alkali. Finally, solution B was stirred into solution A (10 minutes) and then reacted with vigorous stirring for 24 hours at 180°C in a 1 liter stainless steel autoclave. The solid phase was collected on a filter, washed with water and dried at 120°C for 20 hours. The product was a highly crystalline sample of zeolite Zeta 3, with principal X-ray diffraction lines as follows:

The product had a crystallite size of OjOl^um, a composition corresponding to 0.10 Na20 • Al203 • 75 Si02 • 24 H20 and the following adsorption capacities, calculated in % by weight, at 25°C, P/Po = 0.5: for water 9; for n-hexane 11; for p-xylene 9.0; for M-xylene under 1.

EXAMPLE 2

Example 1 was repeated except that the following alcohols were used instead of 12.7 g of isopropyl alcohol:

Each of the products had approximately the same composition as the product in Example 1 and was identified as Zeolite Zeta 3 by X-ray diffraction analysis. Products b, c and d were the most crystalline. Products a and e were like the product in example 1 and had a smaller crystallite size than products b, c and d. Product f contained more amorphous material than products a-e. The crystallite sizes of products b-d were in the range 1-5 µm, while products a and e and the product in example 1 had crystallite sizes of 0.01-0.5 µm.

EXAMPLE 3

(a) A reaction mixture with the molar composition

A1203• 59 Si02• 12.65 Na20 • 30 OH(R)"3330 H20

where OH(R) represents methanol, was prepared by suspending 36 g of silicon dioxide KS 300 (98.9% SiO 2 , 1.1% Na 2 O) in 300 g of water, after which the suspension was stirred into a solution of 1.8 g sodium aluminate (1.25 Na 2 O Al 2 O 3 ) and 8.6 g sodium hydroxide in a mixture of 300 g water and 9.6 g methanol. The mixture was then reacted at 180°C for 6 days in a 1 liter stainless steel autoclave with stirring. The solid phase was collected on a filter, washed with water and dried at 120°C for 24 hours. The product had the composition

and had an X-ray diffraction pattern showing that it was an excellent sample of zeolite Zeta 3, with crystallite size of approx. lyum. (b) Example 3(a) was repeated, but without methanol. The product had the composition

and an X-ray diffraction pattern characteristic of mordenite.

Claims (13)

1. Process for the production of a zeolite, characterized by reacting an aqueous mixture containing at least one source of silicon dioxide, at least one source of aluminum oxide, at least one alkali as stated above, and at least one alcohol. 2. Method according to claim 1, characterized in that the silicon dioxide/alumina ratio in the mixture is at least 20. 3. Method according to claim 1 or 2, characterized in that the alkali does not include any quaternary ammonium or phosphonium compounds. 4. Method according to one of the preceding claims, characterized in that the alkali includes sodium. 5. Method according to one of the preceding claims, characterized in that the mixture includes a mineralizing agent in a proportion of 5-100 mol monovalent ion or equivalent per moles of A^O^ . 6.. Method according to one of the preceding claims, characterized in that the alcohol contains 1-4 carbon atoms per hydroxy group. 7. Method according to one of the preceding claims, characterized in that the alcohol contains no more than 3 hydroxy groups. 8. Method according to one of the preceding claims, characterized in that a zeolite of the ZSM 5 family is produced by reacting a mixture with the composition where M is an alkali metal including sodium and/or a singly charged ion of a quaternary ammonium and/or quaternary phosphonium compound, M2 0 denotes free alkali as indicated above, OH(R) is a hydroxy group that exists as an alcohol. 9.. Method according to one of the preceding claims, characterized in that the silicon dioxide/alumina ratio lies within the range 40-120. 10. Method according to one of the preceding claims, characterized in that the mixture contains the alcohol in an amount corresponding to 20-100 OH groups per moles of A^O^. 11. Process for producing a zeolite mainly as described in examples 1, 2 and 3(a). 12. Zeolite produced by a method according to one • of the preceding claims. 13. New material composition consisting of a freshly synthesized zeolite with a silicon dioxide/alumina ratio above 10, which does not contain a quaternary ammonium or quaternary phosphonium compound.