GB2245550A

GB2245550A - A process for accelerating the crystallization of mordenite

Info

Publication number: GB2245550A
Application number: GB9014289A
Authority: GB
Inventors: Johannes Martinus Nanne; Jean-Pierre Gilson
Original assignee: Shell Internationale Research Maatschappij BV
Current assignee: Shell Internationale Research Maatschappij BV
Priority date: 1990-06-27
Filing date: 1990-06-27
Publication date: 1992-01-08
Also published as: GB9014289D0

Abstract

A process for accelerating the crystallization of mordenite comprises forming an aqueous alkaline mixture comprising a source of silica, a source of alumina and/or a source of silica/alumina, heating the obtained mixture to at least 140 DEG C, adding as seeds mordenite crystals to the mixture and crystallizing the mordenite from the mother liquor.

Description

A PROCESS FOR ACCELERATING THE CRYSTALLIZATION OF MORDENITE The invention relates to a process for accelerating the crystallization of mordenite and to mordenite prepared by such process. The typical oxide formula of synthetic mordenite is Na2O.A12O.10SiO2.6H2O with the structural unit cell Na8A18Si40096.24H20, the product also being called sodium-mordenite. In Japanese patent application 54157796 is disclosed a process for the preparation of mordenite with a high purity from an alumina/silica/sodium hydroxide/water system by addition of mordenite seed crystals to the system. The reaction temperature is low, namely 70 "C to 120 OC.

Applicant has now found a process for accelerating the crystallization of mordenite, which comprises forming an aqueous alkaline mixture comprising a source of silica, a source of alumina and/or a source of silica-alumina, heating the obtained mixture to at least 140 "C, adding as seeds mordenite crystals to the mixture and crystallizing the mordenite from the mother liquor.

Preferred temperatures are in the range of from 150 "C to 210 "C, although higher temperatures are not excluded, even a temperature up to 300 "C. Applicant carried out an experiment wherein in the preparation of mordenite no seed was used and found that at 100 "C the reaction took 4 weeks; even at a temperature of 250 "C (no seed) the reaction was slow and took 16 hours.

It is thus surprising that the process for the preparation of mordenite according to the invention can be carried out in a few hours, preferably within 3 hours, more preferably in 2 hours. The molar ratio of silica to alumina may vary within wide ranges, generally from 10 to 500, preferably from 12 to 300, more preferably from 30 to 120.

The molar ratio of silica to alkali oxide may preferably range from 2 to 5. The reaction is generally carried out under autogeneous pressure in an autoclave.

Since the reaction time and crystallization time are rather short, compared with conventional processes for the preparation of mordenite, it is possible to carry out the reaction according to the invention in a semi-continuous or in a continuous manner.

A synthetic mordenite may be prepared by heating a stable sol of silica with an aqueous solution of sodium aluminate. The pH of the solution is preferably between 10 and 13. Any aluminium source can be used, such as various aluminium salts, e.g. the chloride, nitrate or sulphate. As a source of silica, sodium silicate can be used as well. Silica gels are suitable as well. Basic compounds to be used as sources of alkali, silica and alumina are sodium hydroxide, sodium silicate, silica sol and aluminium sulphate.

Seed addition is carried out whereby the weight amount ranges from 0,1 to 3 per cent on the weight of the total mother liquor.

The optimum level is about 2 per cent by weight.

The chemical composition of the basic starting materials may vary considerably.

Example 1 In a teflonlined autoclave provided with a stirrer and having a content of 0,3 litre were introduced 5,2 g of aluminiumsulphate A12(S04)3.18H20 dissolved in 15 g of demineralized water and 91,65 g of waterglass, having the composition 8,8 %wt Na2O.28,7 %wt Six2.62,5 %wt H2O. The overall molar composition of the reactants was 56,1 Six2.1 Awl203. 16,67 Na20.532 H2O. The slurry was thoroughly mixed at 300 r.p.m. Then 2 g of crystalline mordenite was added to the reaction mixture. The autoclave was closed and heated to 180 OC for 1 hour under the same stirring conditions.

The reaction mixture was allowed to cool and the mordenite was separated from the mother liquor. 8,5 g of mordenite was harvested with 100 per cent crystallinity, determined by X-ray diffraction.

Neither another crystalline phase, nor an amorphous phase was observed. The example showed that the reaction time and crystallization time of mordenite was very short.

Comparative example A The same reaction as in example 1 was carried out under the same conditions, except that no seed of crystalline mordenite was introduced into the autoclave. After 4 hours no crystalline mordenite was found, only but amorphous material.

Comparative example B The same reaction as in example 1 was carried out under the same conditions, except that the temperature was 130 C.

Crystalline mordenite together with amorphous material was found.

Examples 2-7 In a teflonlined autoclave with a content of 0,3 litre were introduced aluminiumsulphate dissolved in water and sodiumsilicate in water. The slurry was thoroughly mixed at 300 r.p.m. The overall molar composition of the reactants could vary as indicated in the following Table. 2 g of crystalline mordenite was used in every experiment. After closing the autoclave, the respective compositions were heated to 180 C for 2 hours. The reaction mixture was allowed to cool and the mordenite was separated from the mother liquor. In all the experiments crystalline mordenite was obtained.

TABLE Example Overall composition X-ray diffraction SiO2 Awl 203 2 H2 0 2 30 1 8,9 532 crystalline mordenite 100% 3 40 1 16,67 532 " " 90% 4 51 1 16,67 532 " " 100% 5 56 1 16,67 532 " " 100% 6 75 1 22,25 620 " " 90% 7 100 1 29,67 829 " " 100% Example 8 In a teflonlined autoclave with a content of 0,3 litre were introduced the same amounts of aluminiumsulphate and sodiumsilicate as in the example 1. The slurry was thoroughly mixed at 300 r.p.m.

2 g of crystalline mordenite was added to the reaction mixture. The autoclave was closed and heated to 150 "C for 2 hours. The reaction mixture was then allowed to cool and the mordenite was separated from the mother liquor. 100% crystalline mordenite was obtained according to X-ray diffraction analysis.

Claims

1. A process for accelerating the crystallization of mordenite which comprises forming an aqueous alkaline mixture comprising a source of silica, a source of alumina and/or a source of silica/alumina, heating the obtained mixture to at least 140 OC, adding as seeds mordenite crystals to the mixture and crystallizing the mordenite from the mother liquor.

2. A process as claimed in claim 1, wherein the heating is carried out at a temperature in the range of from 150 "C to 210 "C.

3. A process as claimed in claims 1 or 2, wherein the crystallization time is from 0,5 hour to 3 hours.

4. A process as claimed in one or more of the claims 1-3, wherein the weight amount of seed ranges from 0,1 to 3 per cent on the weight of the total mother liquor.

5. A process as claimed in one or more of the claims 1-4, wherein the molar ratio of SiO2/A1203 ranges from 30 to 120.

6. A process as claimed in one or more of the claims 1-5, wherein the molar ratio of SiO2/Na20 ranges from 2 to 5.

7. A process as claimed in one or more of the claims 1-6, wherein the reaction is carried out in an autoclave.

8. A process as claimed in one or more of the claims 1-7, wherein the process is carried out semi-continuously or continuously.

9. A process as claimed in claim 1 as hereinbefore described with special reference to the examples 1-8.

10. Mordenite prepared by means of a process as claimed in any one of the claims 1-9.