NL8603170A - ZSM-5 zeolite prodn. from sources of silica, alumina and alkali metal - ethanol, water and ZSM-5 crystal seed, avoiding organic base - Google Patents

Abstract

A zeolite of the ZSM-5 type is prepd. from a reaction mixt. contg. a source of SiO2, a source of Al2O3, a source of alkali metal ethanol, water, and previously synthesised ZSM-5 zeolite crystals, by (a) dispersing a precise amt. of 0.002-0.03% of ZSM-5 seed, based on the total wt. of SiO2 to be used, in deionised water, and dividing the suspension into two almost equal portions, (b) adding about half of the seed suspension from step (a) to an Al salt, e.g. Al2(SO4)3 or Na aluminate, (c) adding the other half of the seed suspension to a source of SiO2, e.g. Na silicate, (d) combining the suspensions from (b) and (c), (e) adding ethanol and 98%H2SO4, in predetermined amts., to form a gel, (f) homogenising the gel by mechanical stirring for 20 mins., (g) subjecting the gel to hydrothermal conversion in an autoclave, at 135-180 deg. C, under autogenous pressure, for 1-5 days, and (h) recovering the ZSM-5 zeolite.

Description

r * <VO 8501

Title: Process for the preparation of a ZSM-5 type zeolite.

The present invention relates to a process for the preparation of a ZSM-5 type zeolite.

More particularly, the present invention relates to a process for the preparation of a ZSM-5 type zeolite in the presence of extremely small amounts of pre-synthesized ZSM-5 type zeolite inoculum, in the absence of organic bases.

The present application is carried out in the presence of a traditional substance, typically ethyl alcohol, to improve product quality.

As is known to those skilled in the art, the synthesis of ZSM-5 zeolite is described in US Patent 3,702,886, wherein the product is obtained from a mixture of silica and alumina containing, as a conductor to form the ZSM-5 structure, of an organic cation, that is, tetrapropylammonium cation (TPA).

15 This document also provides X-ray diffraction data that defines the zeolite structure.

In addition to the TPA cation, other structure directing agents are known, which are constituted by organics that organize the oxide tetrahedra in a particular geometric topology around them, and thus provide the starting unit for a specific structure type. This structure regulating phenomenon is known as "templating".

D.W. Break provided in "Zeolite Molecular Sieves Structure, Chemistry and Use", Wiley, N.Y. 1974 as well as B.M. Lok et al in 25 Zeolites, 3_, October 1983, p. 282-291, detailed information on this topic. Therefore, it has been found that the use of such ions such as TPA, as well as organic bases such as n-propylamine, choline, pyrrolidine, etc. has made it possible to make zeolites with high silica / alumina ratio (greater than 20), such as those of the 30 ZSM-5, ZSM-8 and ZSM-11 structure types. However, a problem associated with the conventional synthesis using significant amounts of nitrogen-containing bases or cations is the high cost of the nitrogen-containing reactants and their corrosive effect on the equipment, in addition to their losses during the process, 8603170 2 - 2 - making the conventional method uneconomical. For this reason, it is essential to find a more economical synthesis method, with equally good technical results in terms of product purity. In order to achieve this, British Patent 1,567,948 teaches that zeolites 5 of the ZSM-5 family can be defined by a silica / alumina ratio between 5 and 100 and a pore diameter of 6 to 6 Angstroms, corresponding to rings consisting of 10 SiO4. and Al 10 tetrahedra and that the zeolites of this family can be obtained without the need for the TPA ion to be present, but in the presence of a grafting amount of a zeolite having the same pore diameter as the desired zeolite. This publication indicates that it is possible to obtain a ZSM-5 zeolite with grafting of a structure different from that of the ZSM-5 zeolite, by checking the reaction conditions. ZSM-5 zeolites are prepared using 0.2 to 2.0 grams of graft per 100 grams of 15 SiC> 2, with pore diameters ranging from 5.8 to 7.0 Angstroms, by adding the graft material to an alkaline mixture consisting of an alumina source, silica source and alkali metal ions. Also, an alcohol such as isopropyl alcohol may be present as a promoter for the formation of high silica zeolite and to assist in reducing the crystallite size of the ZSM-5 product.

East German Patent 205,674 teaches adding 0.01 to 10% (5% on average) as a weight basis of zeolite graft that has been pre-activated by milling. The graft zeolite can be any partially or fully crystallized product, mixed crystals of low ZSM-5 content, or amorphous precursors of high silica-containing compounds.

In addition, U.S. Patent Nos. 4,175,114, 4,199,556, and 4,341,748 rely on the same approach, that is, the use of a grafting technique with one of. pre-synthesized zeolite, wherein the graft is used in an amount of 1 to 6% by weight based on the silica weight. This technique allows the authors to omit the normally required calcination treatment for conventional ZSM-5 zeolite, if it is desired to obtain ion exchange. These patents describe the use of grafts 35 alone, or in mixture with ammonium hydroxide and / or alcohol, and also 8603170 * - 3 - the alcohol alone or mixed with ammonium hydroxide. However, the results given by these patents are not conclusive, more particularly with regard to the synergistic aspect of the graft-alcohol or alcohol-ammonium hydroxide mixtures- Moreover, although the use of grafts gives an advantage over the state of the technique, relatively large amounts (1 to 6% by weight based on silica) of seed material are still used in the above patents.

It is therefore one object of the present invention to provide a process for the preparation of ZSM-5 type zeolites, based on the synergistic effect of mixing extremely small amounts of seed material, 0.002 to 0.03 wt% with respect to the silica weight, with a 1-300 wt%, based on the weight of the silica, amount of ethanol, corresponding to an ethanol / silica molar ratio of 0-4.0.

Another object of the present invention is to provide the process for preparing a ZSM-5 type zeolite in the absence of an organic base (organic nitrogen), in order to obtain a product of high purity and low cost, while the the need for corrosion protection has been eliminated, as has the loss of 20 expensive reactants.

Of course, the ZSM-5 type zeolite prepared in accordance with the method of the present invention can be used in all areas of application where the prior art ZSM-5 zeolite is generally used, ie, hydrocarbon conversion process, conversion of alcohols into olefins or aromatics, separation processes for organic compounds, as well as for catalyst carriers.

The present invention therefore provides a process for preparing a ZSM-5 type crystalline aluminosilicate, basically with a low organic nitrogen content, comprising zeolite formation in the presence of 0.002-0.03 wt% of pre-formed ZSM-5 zeolite inoculum, based on total silica weight, and ethanol, at an ethanol / silica molar ratio of 0-4.0, the inoculum zeolite having been prepared in accordance with known techniques, such as U.S. Pat. No. 3,702,886.

8303170 ί * - 4 -

The method of the present invention makes it possible to obtain a ZSM-5 zeolite having an X-ray diffraction diagram similar to that of U.S. Patent 3,702,886, the composition of which, in terms of oxide mol ratio, is as follows: 0.9 ± 0 2M 2 / nO: Al 2 sX SiO 4: ZE 2 D, wherein M is an alkali metal, typically sodium, and tetraalkylammonium cations, the silica / alumina ratio being greater than 20.

Preparation of the zeolite of the present invention, as well as the known zeolites, is carried out to provide an alumino-silicate prepared from materials providing the appropriate oxide elements. Such materials include aluminum sulfate, a mineral acid such as sulfuric acid, sodium aluminate, alumina, sodium silicate, silica hydrosol, silica gel, silica and.

Sodium hydroxide, in addition to the reactants of the method of the present invention, is added in specific sequences and amounts.

The method now described and claimed is therefore characterized by the following steps: (a) dispersing an accurate amount of 0.002 to 0.03% by weight of ZSM-5 seed materials, based on the total weight of the silica to be used, in deionized water (e.g. in an ultrasonic device), and dividing said suspension into two substantially equal amounts; (B) adding about half of the graft suspension from step (a) to an aluminum salt, such as aluminum sulfate or sodium aluminate; (c) adding the other half of the graft suspension from step (a) to a source of silica, such as sodium silicate; (D) combining the suspensions of steps (b) and (c) together; (e) adding ethanol and sulfuric acid in predetermined amounts to form a gel; (f) homogenizing the gel by mechanical stirring for about 20 minutes; 8303170 * - 5 - (g) subjecting the gel to hydrothermal transformation, in an autoclave, at 135-180 ° C under autogenous pressure, for 1 to 5 days.

The present process therefore differs from the prior art in the order of mixing and the amounts of the components. For example, U.S. Patent 4,257,885 adds the total amount of the seed material to the aqueous silica, the aluminate to the pre-formed mixture of silica and seed material, followed by heating the gel. In Brazilian Patent Application No. 10 PI 8306419, the total amount of seed material is added to a portion of the silica and the aluminate is added to this silica seed material mixture, with stirring, adding a further portion of silica as a thickener.

It should be noted that the ZSM-5 zeolite inoculum 15 used in step (a) was prepared by a conventional method and calcined in air at high temperature, such as 500eC, for 4 hours to remove organic compounds (tetrapropylammonium hydroxide and derivatives thereof), while the X-ray diffraction diagram indicates zeolite formation with higher purity and crystallinity.

The aluminum salt from step (b) is hydrated aluminum sulfate

Al, (SO.) .. 28 H, 0 or sodium aluminate.

2 4 3 2

The sodium silicate used in step (c) is available from MAMA Company, with a silica (SiCl 2) content of 27.9% by weight, 8.8% sodium oxide (Na 2 O) and 64.3% water.

The gel formed in step (e) (reaction mixture) has the following molar composition: H 2 O / SiO = 20-40 ~ 0H / SiO 2 = 0.2 - 0.4 Al 2 O 3 / SiO 2 = <1/20 C 2 H 50 H / SiO 2 = 0-4.0

Conversion of the gel is effected in a steel reactor or a steel reactor with an internal "Teflon" capsule, with the reactor sealed. After crystallization under autogenous pressure at 135-180 ° C for 1 to 5 days, the product is cooled to room temperature at 8603-170, and washed with deionized water in an amount of about 30 ml of water per gram of product.

The following examples illustrate the present invention without limiting it.

Table A summarizes the results obtained which clearly demonstrate that only the ethanol-graft combination is indeed effective and synergistic. Therefore, Examples IV and V prove that the combination of appropriate amounts of seed material and ethanol yields a particularly pure and crystalline ZSM-5, compared to Examples I-III, which are run with ethanol alone (Example I) or with seed material without ethanol (examples II and III). Examples V and VI (a and b) are better than Example IV, perhaps because of the extremely small amount of structure-oriented agents. Examples V1 and VIb illustrate the reproducibility of the method. Examples VII and VIII demonstrate that, in the presence of seed material alone, without the synergistic aid, increasing amounts of seed material are not sufficient to obtain the highly crystalline ZSM-5 type structure, whereby an impurity, alpha quartz (Example VII) is formed is becoming.

The attached drawings, figures 1, 2, 3 and 4 confirm the superiority of the method according to the present invention.

Figure 1 therefore shows the X-ray diffraction diagram of the ZSM-5 crystal seed material, as synthesized using a known method (U.S. Patent 3,702,886).

Figure 2 shows the X-ray diffraction pattern of the products of Examples 1, 2 and 4, demonstrating the synergistic effect of the use of ethanol graft material in the low amounts of the invention, compared to the use of ethanol alone, or inoculum only.

Figure 3 shows the X-ray diffraction pattern for product 6, compared to the conventional synthesis.

Figure 4 shows the X-ray diffraction pattern of the products of Examples VIb and VII, in which it can be seen that in Example VII a small amount of alpha quartz was formed as an impurity, while the product of Example VIb is particularly pure.

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Claims (4)

A process for the preparation of ZSM-5 type zeolite from a reaction mixture comprising a source of silicon oxide, a source of aluminum oxide, a source of alkali metal / ethanol, water and pre-synthesized ZSM-5 zeolite crystals, characterized by the steps: 5 (a) dispersing an exact amount of 0.002 to 0.03% ZSM-5 inoculum based on the total weight of silica to be used in deionized water and dividing said suspension into two substantially equal portions; (b) adding about half the amount of seed material suspension from step (a) to an aluminum salt, such as aluminum sulfate or sodium aluminate; (c) adding the other half of the seed suspension of step (a) to a source of silica, such as sodium silica; (d) combining the suspensions of steps (b) and (c); (E) adding ethanol and 98% sulfuric acid in predetermined amounts to form a gel; (f) homogenizing the gel by mechanical stirring for about 20 minutes; (g) subjecting the gel to a hydrothermal conversion in an autoclave, at 135-180 ° C, under autogenous pressure, for 1 to 5 days, and recovering the ZSM-5 zeolite product. Process for the preparation of ZSM-5 type zeolite according to claim 1, characterized in that the mixture has the following molar composition: 25 H20 / Si02 = 20-40 0H_ / Si02 = 0.2-0.4 Al2O3 / Si02 = <1/20 C2H50H / Si02 - 0-4.0 3. Process for the preparation of IzSM-5 type zeolite according to claim 1, characterized in that the amount of the graft material, based on the total weight of silica, is about 0.002 to 0.03% by weight, and the molar ratio of ethanol to total silica is between 0 and 4.0. 8603170 - 12 - Process for the preparation of ZSM-5 type zeolite according to claim 1, characterized in that crystallization of the gel is effected for 1 to 5 days at 135-180 ° C under autogenous pressure. 8803170