AU2111395A

AU2111395A - Zeolites and processes employing them

Info

Publication number: AU2111395A
Application number: AU21113/95A
Authority: AU
Inventors: Philip Luc Buskens
Original assignee: Exxon Chemical Patents Inc
Current assignee: ExxonMobil Chemical Patents Inc
Priority date: 1994-03-31
Filing date: 1995-03-31
Publication date: 1995-10-23
Also published as: KR970702213A; CA2183597A1; JPH09512246A; WO1995026928A1; PL316570A1; GB9406434D0; EP0752975A1; CZ274196A3; BR9507209A

Description

"Zeolites and Processes Employing Them"

This invention relates to zeolites, especially those useful as catalysts, their manufacture, and chemical processes using them.

Zeolite Beta is a large pore high silica zeolite first described in 1967, in U.S. Patent No. 3308069. Its large pore size, based on 12-membered rings, makes it useful in catalysing organic reactions involving relatively large molecules. More recently, a related titanium-containing Beta zeolite has been synthesized and proposed for use as a catalyst, especially for the oxidation of organic molecules - see PCT Application WO 94/02245.

Redox zeolites are important because they catalyse the oxidation of hydrocarbons, but their synthesis is still at an embryonic stage.

The present invention provides a Beta zeolite having vanadium in its framework, hereinafter referred to as V-Beta zeolite.

The invention also provides a process for the manufacture of V-Beta zeolite, wherein a synthesis mixture comprising a source of vanadium, a source of silicon, a source of aluminium, a source of tetraethylammonium ions, and water, is subjected to a hydrothermal treatment. The aluminium may be wholly or partly replaced by other cations, especially gallium, boron, or iron.

Advantageously, the synthesis mixture has a molar composition within the range:

Siθ2 : 1 ; VO²⁺ : 0.0001 to 0.2; AI₂O₃ : 0.0005 to 0.1 ; H₂O : 10 to 100; Tetraethylammonium hydroxide (TEAOH) : 0.01 to 1.

V-Beta zeolite according to, and produced according to, the invention is advantageously characterized both by a band at about 960cm^-1 in its IR spectrum and a band at about 47500cm^-1 in its Diffuse Reflectance Spectrum.

Preferably, the molar composition is within the range:

SiO₂ : 1 ; VO²⁺ : 0.02 to 0.08; AI₂O₃ : 0.005 to 0.02; TEAOH 0.1 to 1. The synthesis mixture is advantageously substantially free from alkali metal cations; by substantially free is meant the absence of more alkali metal than is inevitably present in commercial supplies of the essential components. If alkali metal ions, e.g., sodium or potassium ions, are present, they are advantageously present in a molar proportion of SiO₂:M⁺ of 1: at most 0.5.

Preferred sources of the components are: for silicon, colloidal silica, advantageously a colloidal silica substantially free from alkali metal cations, or a tetraalkylammonium orthosilicate; for vanadium, vanadyl sulphate; and for aluminium, aluminium powder. If the aluminium is replaced by other cations, suitable sources are, for example; gallium nitrate or oxide; boric acid or an alkoxide thereof, e.g., B(OC H5; or ferric nitrate. The tetraethyl ammonium cations are advantageously provided by TEAOH.

Advantageously, to assist dissolution of any reactants, hydrogen peroxide is present in the synthesis mixture, although it may decompose before or during hydrothermal treatment. Preferably it is present in aproportion of 10 to 200 moles per mole of vanadium source. When hydrogen peroxide is present the oxidation state of the vanadium in the synthesis mixture subjected to hydrothermal treatment may be changed from that of its original source, and/or the oxidation state in the original source may be different from that given above.

Advantageously, especially if it contains hydrogen peroxide, the synthesis mixture is aged between its formation and the hydrothermal treatment. Ageing may be carried out at room temperature or at elevated temperatures, for example at from 60 to 90°C, advantageously about 70°C, the ageing time being from 2 to 24 hours, depending inversely on the temperature. A preferred ageing treatment comprises initial room temperature ageing for from 12 to 24 hours, followed by elevated temperature ageing, e.g., at 70°C, for from 2 to 6 hours.

Elevated temperature ageing also causes evaporation of water from the synthesis mixture, if desired reducing the initial volume by as much as 65%, thereby producing a synthesis mixture of a concentration advantageous for hydrothermal treatment. If desired, or required, the aged mixture may be diluted before treatment, e.g., with ethanol. If ethanol is added, it is advantageously present in the synthesis mixture subjected to hydro-thermal treatment in a proportion of at most 2 moles per mole of SiO₂. The synthesis mixture, preferably aged, is advantageously subjected to hydrothermal treatment at a temperature within the range of from 120°C to 200°C, preferably from 130°C to 150°C, advantageously for a time in the range of from 1 hour to 30 days, preferably from 6 days to 15 days, until crystals are formed. Hydrothermal treatment is advantageously effected in an autoclave.

If desired, at least a part of the hydrothermal treatment may be carried out under an atmosphere containing substantial proportions of ethene.

Advantageously, ethene is present in the reaction vessel from the commencement of the hydrothermal treatment.

While not wishing to be bound by any theory, it is believed that under the conditions prevailing under the hydrothermal treatment tetraethyl ammonium ions decompose and are unavailable to form a template effective in zeolite formation. By carrying out the treatment in the presence of ethene, a decomposition product, the equilibrium of the decomposition reaction is displaced and more tetraethylammonium ions remain available to act as templates.

If hydrothermal treatment is carried out under ethene, the ethene partial pressure is advantageously at least 5 bar, preferably at least 20 bar, and most preferably at least 30 bar, for at least a part of the period of hydrothermal treatment. Also, advantageously, the total pressure is at least 30 bar, and preferably at least 40 bar. Advantageously, the ethene partial pressure is at least 80%, preferably at least 90%, of the total pressure.

After crystallization has taken place, the synthesis mixture is cooled, and the crystals are separated from the mother liquor, washed and dried.

To eliminate the organic base from the crystals, they are advantageously then heated to from 200 to 600°C, preferably about 500°C, under nitrogen, oxygen, or in air, for from 1 to 72 hours, preferably about 12 hours.

The resulting calcined product may either be used as such or subjected to further treatment e.g., by acid, for example, HCI, or by bases e.g., ammonium or sodium ions. The product may be post-treated, as by steaming. The V-Beta zeolite produced by the process of the invention is highly crystalline.

The accompanying drawings show, in Fig. 1 , the X-ray diffraction spectrum of the uncalcined product, in Fig. 2, the infra-red spectrum of the uncalcined product (trace a) and the calcined product (trace b) and, in Fig. 3, the Diffuse Reflectance Spectrum of the uncalcined product.

The V-Beta zeolite produced according to the invention is useful as a catalyst in all reactions where an acidic catalyst is effective, especially in the production and conversion of organic compounds, for example cracking, hydrocracking, dewaxing, isomerization (including e.g., olefin bond isomerization and skeletal isomerization e.g., of butene), oligomerization, polymerization, alkylation, dealkylation, hydrogenation, dehydrogenation, dehydration, cyclization and aromatization. The present invention therefore provides a process for the production or conversion of an organic compound comprising the use of a zeolite catalyst prepared in accordance with the invention. The zeolite can also be used (either as initially prepared or in a modified form) in a selective adsorption process e.g. a separation or purification.

More especially, the zeolite produced by the process of the invention is an active oxidation catalyst, especially for reactions employing a peroxide as oxidant, including organic peroxides, including hydroperoxides, as well as hydrogen peroxide. The use of organic hydroperoxides avoids the two phase system necessarily associated with aqueous hydrogen peroxide. Compared to titanium- and vanadium-silicalite catalysts, V-Beta zeolite is more effective in the oxidation of larger molecules, e.g., cycloparaffins and cycloolefins.

The present invention accordingly also provides the use of the product of the process of the invention as a catalyst in the oxidation of an organic compound, especially in single phase oxidation by an organic peroxide.

The catalyst of the invention is effective in oxidizing saturated hydrocarbons, e.g., paraffins and cycloparaffins, and the alkyl substituents in alkylaromatic hydrocarbons. In cycloparaffins, ring-opening and acid formation may take place, for example, in the oxidation of cyclohexane by tertiary butyl peroxide or H₂O₂ adipic acid is produced, and in the oxidation of cyclopentane glutaric acid is produced. The catalyst is also effective in the epoxidation of unsaturated hydrocarbons, e.g., olefins and dienes, and the production of ether glycols, diols, the oxidation of alcohols, ketones or aldehydes to acids, and the hydroxylation of aromatic hydrocarbons.

In the oxidation process of the invention the oxidizing agent may be, for example, ozone, oxygen, nitrous oxide, or preferably hydrogen peroxide or an organic peroxide including a hydroperoxide. Examples of suitable organic hydroperoxides include di-isopropyl benzene monohydroperoxide, cumene hydroperoxide, tert.butyl hydroperoxide, cyclohexyl hydroperoxide, ethylbenzene hydroperoxide, tertamyl hydroperoxide, and tetralin hydroperoxide. Advantageously the compound to be oxidized is liquid or in the dense phase under the conditions used for the reaction. Advantageously, the reaction is carried out in the presence of a suitable solvent. The use of a tertiary butyl hydroperoxide is particularly beneficial since the tertiary butyl alcohol produced can readily be converted to the valuable isobutylene molecule.

The oxidation reaction may be carried out under batch conditions or in a fixed bed, and the use of the heterogeneous catalyst facilitates a continuous reaction in a monophase or biphase system. The catalyst is stable under the reaction conditions, and may be totally recovered and reused.

The following Examples illustrate the invention.

Example 1 Catalyst Synthesis

Mixture A was prepared by dissolving 1.00 g of vanadyl sulphate in 63 ml H₂O and cooling the resulting blue solution to 5°C before adding 39 ml H O₂ (35% in H₂O). The resulting orange solution is stirred for 3 hours at 5°C, giving a clear yellow-orange solution.

Mixture B was produced by adding 0.0316 g Al powder to 29.42 g of TEAOH (40% in H O) and dissolving it by heating at 90°C for 2 hours. Then, 32.72 g of distilled H₂O were added. This mixture was cooled to 5°C.

Solutions A and B were mixed and the resulting blue-green solution stirred for 1 hour at 5°C. Subsequently, 12.53 g of colloidal silica (Ludox AS40, 40% in H O, stabilized by NH ⁺) were added. This mixture was stirred at room temperature for 18 hours and afterwards for another 4 hours at 70°C, to evaporate ethanol and transferred to a stainless steel autoclave.

The autoclave was put in an oven and crystallization proceeded without agitation at 140°C for 10 days. After this time the autoclave was cooled and the solids separated from the clear mother liquor by centrifugation at 13,000 rpm. The organic template was then removed from the zeolite pores by calcination in a U-tube, initially under nitrogen for 8 hours at 500°C then, after allowing the tube to cool to 400°C, under oxygen for 2 hours at 500°C. The yield was 50% of theory.

The spectra of the product of this Example are shown in the accompanying drawings. Figure 1 shows that the product is all Beta zeolite phase. In Figure 2, the band around 960cm^-1 shows the vanadium as part of the zeolite framework. The band at 47500^-1 in Figure 3 is absent in vanadium-free Beta zeolite.

Example 2 Oxidation of Cyclohexane

The V-Beta zeolite produced as described in Example 1 was used as a catalyst for the oxidation of cyclohexane using tert.butyl hydroperoxide (TBHP). 8.42 g (100 mmole)of cyclohexane were treated with 28.32 (246 mmole) of TBHP, in the form of an 80% THBP solution in tert.butyl peroxide, in the presence of 0.15 g of V-Beta, for 7 hours at 100°C, the reaction mixture being subsequently stored at 5 to 10°C for 3 weeks. The results are shown in the Table below.

Product Selectivity, % Time Conversion % Cyclohexanol Cyclohexaπone Adipic Acid Other

1 hour 8 48 52 0 0

4 hours 28 23 46 0 31

7hours 35 16 27 9 48

21 days* 35 16 27 25 32*

It appears possible that other products included esters that are cleaved to adipic acid by the zeolite catalyst while standing at low temperatures for 21 days. Alternatively, adipic acid already formed may have diffused slowly out of the zeolite during the standing period.

Claims

CLAIMS:

1. A Zeolite Beta containing vanadium in its framework.

2. A Zeolite Beta containing vanadium in its framework and having an absorption band in its Diffuse Reflectance Spectrum at wavenumber 47500 cm^-1 and a band at about 960cm^-1 in its Infra Red Spectrum.

3. A process for the manufacture of V-Beta zeolite wherein a synthesis mixture comprising water, a source of silicon, a source of aluminium, a source of vanadium, and a source of tetraethylammonium ions is subjected to hydrothermal treatment.

4. A process as claimed in claim 3, wherein the molar composition of the synthesis mixture is within the following ranges:

SiO₂ (1 ); AI₂O₃ (0.0005 to 0.1); VO²⁺ (0.001 to 0.2); H₂O (10 to 100); TEAOH (0.01 to 1 ).

5. A process as claimed in claim 3, wherein the molar composition of the synthesis mixture is within the following ranges:

SiO₂ (1); AI₂O₃ (0.05 to 0.02);

VO²⁺ (0.02 to 0.08); and TEAOH (0.1 to 1).

6. A process as claimed in any one of claims 3 to 5, wherein the synthesis mixture contains colloidal silica.

7. A process as claimed in claim 6, wherein the colloidal silica is substantially alkali metal free.

8. A process as claimed in any one of claims 3 to 7, wherein the synthesis mixture contains vanadyl sulphate.

9. A process as claimed in any one of claims 3 to 8, wherein the synthesis mixture, at least initially, contains hydrogen peroxide.

10. A process as claimed in any one of claims 3 to 9, wherein the synthesis mixture is aged between its formation and the hydrothermal treatment.

11. A process as claimed in claim 10, wherein at least part of the ageing is carried out at room temperature.

12. A process as claimed in claim 10 or claim 11 , wherein at least part of the ageing is carried out at an elevated temperature.

13. A process as claimed in any one of claims 3 to 12, wherein the synthesis mixture subjected to hydrothermal treatment contains ethanol, advantageously in a proportion of at most 2 moles per mole of SiO₂.

14. A process as claimed in any one of claims 3 to 13, wherein hydrothermal treatment is carried out at a temperature within the range of from 120°C to 200°C.

15. A process as claimed in any one of claims 3 to 14, wherein hydrothermal treatment is carried out for from 1 hour to 30 days.

16. A process as claimed in any one of claims 3 to 15, wherein after hydrothermal treatment the resulting crystals are recovered and heated at from 200 to 600^βC, for from 1 to 72 hours.

17. A process as claimed in claim 16, wherein the calcined product is subsequently treated with an acid or a base, or is steamed.

18. A process as claimed in any one of claims 3 to 17, wherein hydrothermal treatment is carried out under ethene pressure.

19. V-Beta zeolite obtainable by the process of any one of claims 3 to 18.

20. The use of the product as claimed in any one of claims 1 , 2 and 19, as a catalyst in the production or conversion of an organic compound.

21. The use as claimed in claim 20, wherein the conversion is oxidation.

22. The use as claimed in claim 21 , wherein the oxidation is carried out using an organic peroxide.

23. The use as claimed in claim 21 or claim 22, wherein the organic compound is a saturated hydrocarbon.

24. Any new feature described herein or any new combination of hereindescribed features.