Catalyst comprising oxides of silicon, zinc and aluminium used for the preparation of LPG and high octane aromatics and a process for preparing the same

This invention relates to a novel porous crystalline synthetic catalyst having the general formula expressed in the form of oxides: M 2/n o. x Al.sub.2 O.sub.3 Y SiO.sub.2, Z ZnO wherein, M represents a proton and/or a metallic cation, n is the valence of the said cation, Y/x is a number ranging from 5 to 1000 (SiO.sub.2 /Al.sub.2 O.sub.S molar ratio), and a process for preparing such catalyst by (a) forming a reaction medium comprising water, a silicon source, an aluminium source, a zinc source and a source of structure directing agent capable of providing organic cations, (b) heating the said reaction mixture to a temperature ranging from 80.degree. C. to 230.degree. C. at autogeneous phase, and (c) heating the solid content obtained at the end of step (b) to a temperature greater than 400.degree. C., so as to eliminate the organic species present due to the use of the structuring agent.

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We claim:

1. A process for the preparation of a porous crystalline synthetic material comprising silicon, zinc and aluminum oxides designated as Zn--ZSM-5 in which Zn forms part of a crystallineframework of the material, the material being useful as a catalyst for the preparation of high octane gasoline blending feed stock, BTX aromatics and LPG from a feed stock that is non-reformable by conventional means, the feed stock being selected fromthe group of: natural gas condensate, aromatic extraction raffinate and light naphtha, the process comprising:

(a) forming a reaction medium comprising water, a silicon source, an aluminum source, a water-soluble zinc source and a source of structure directing agent capable of providing organic cations,wherein the source of zinc used is selected from zincsalts which are capable of being converted into zinc oxide upon calcination, and wherein the zinc salt is Zn(NO.sub.3).sub.2 ;

(b) heating the reaction mixture to a temperature ranging from 80.degree. C. to 230.degree. C. at autogeneous phase; and

(c) heating solid content obtained at the end of step (b) to a temperature greater than 400.degree. C., so as to eliminate the organic species present due to the use of the structuring agent.

2. A process as claimed in claim 1 wherein the catalyst obtained is incorporated into a matrix of synthetic or naturally occurring substances.

3. A process as claimed in claim 2, wherein the matrix is selected from the group consisting of clays, silica, alumina and metal oxides.

4. A process as claimed in claim 2 wherein the relative proportion of the catalyst and the matrix on anhydrous basis vary between 10-90% by weight.

5. A process as claimed in claim 1 wherein said catalyst has a MF1 structure and exhibits the following X-ray diffraction spectrum:

TBL dhk 1 (A.degree.) dhk 1 (A.degree.) (10-.sup.10 m) I/Io (10-.sup.10 m) I/Io 11.08-11.26 Strong 3.83-3.89 Very strong 9.94-10.20 Medium to strong 3.80-3.86 Very strong 9.68-9.90 Weak 3.74-3.78 Medium to strong 7.40-7.52 Very weak 3.70-3.74Strong 6.30-6.42 Weak 3.63-3.68 Medium to strong 5.95-6.08 Very weak 3.46-3.50 Weak 5.54-5.61 Weak 3.33-3.37 Weak 4.59-4.64 Very weak 3.29-3.33 Very weak 4.34-4.40 Weak 3.03-3.07 Weak 4.23-4.29 Weak 2.97-2.99 Weak.

6. A process as claimed in claim 1 wherein the heating of the reaction mixture at step (b) is performed between 140.degree. C. to 210.degree. C.

7. A process as claimed in claim 1 wherein the source of silica used is selected from silica in the form of hydrogels, aerogels, colloidal suspensions or solutions of soluble silicates.

8. A process as claimed in claim 1 wherein the source of alumina used in selected from aluminum salts aluminum hydroxide and oxide aluminates, and esters of monorthoaluminic acid.

9. A process as claimed in claim 1, wherein oxides of alumina and silica selected from the group consisting of amorphous alumina, silicagel, crystalline aluuminosilicate, including clays and zeolites, are combined and used.

10. A process as claimed in claim 1 wherein the structuring agent used to provide organic cation is selected from tetrahydral lower alkyl ammonium cations.

11. A process as claimed in claim 1 wherein the pH is adjusted by the use of hydrochloric acid, nitric acid, sulphuric acid, acetic acid, or acid salts.

12. A process as claimed in claim 1 wherein a metal selected from the group consisting of sodium, potassium, gallium, platinum, tin, iron and rhenium is incorporated into the catalyst to enhance the catalyst activity.

13. A process as claimed in claim 1 wherein the total amount of such metals added ranges from 0.1 to 0.5% by weight.