WO1999017877A1

WO1999017877A1 - Treatment to improve the durability and selectivity of a hydrodechlorination catalyst and catalyst

Info

Publication number: WO1999017877A1
Application number: PCT/EP1998/006349
Authority: WO
Inventors: Zongchao Zhang
Original assignee: Akzo Nobel N.V.
Priority date: 1997-10-02
Filing date: 1998-10-01
Publication date: 1999-04-15

Abstract

The durability and selectivity of a supported nobel metal hydrodechlorination catalyst can be improved by treating the supported catalyst, which comprises support and catalytic noble metal, with a halide salt (such as a late transition metal halide salt, a post transition metal containing halide salt, or a combination thereof), together with the use of an alkali metal halide, ammonium halide, or a combination thereof. Suitable late transition metal and post transition metal halides for use herein include zinc chloride, tin chloride, and cupric chloride. A suitable alkali metal halide for use herein includes lithium chloride. The novel resulting supported catalyst has its noble metal component, which is in the zero valent state, predominantly residing adjacent, the surface of the support in a form which is predominantly visible under a microscope having a resolution of about 5 Å. The catalyst also comprises the late transition metal, the post transition metal or combination thereof, optionally in the presence of the alkali metal moiety, ammonium moiety, or combination thereof.

Description

TREATMENT TO IMPROVE THE DURABILITY AND SELECTIVITY OF A HYDRODECHLORINATION CATALYST AND CATALYST

Background of the Invention

Various techniques are known for the regeneration or treatment of hydrodehalogenation or hydrodechlorination catalysts. The following are some examples of disclosures deemed to be relevant to the present invention.

U.S. Patent No. 4,980,324 to C.S. Kellner et al. discloses the regeneration and/or activation of a nobel metal catalyst by the use of a fluorohalocarbon and/or a fluorohydrocarbon. In more recent U.S. Patent No. 5,057,470 C.S. Kellner advocates the contacting of a hydrodehalogenation catalyst with an atmosphere comprising chlorine gas at elevated temperature for a time that is sufficient to improve the catalytic activity of the catalyst.

U.S. Patent No. 4,374,047 of A. Bozon et al. teaches the pre-loading of a porous catalyst carrier with an aqueous solution of ammonium chloride prior to applying a coating containing platinum and/or palladium to the surface of the treated porous catalyst carrier.

More recent U.S. Patent No. 5,105,032 to M.T. Holbrook et al. indicates that a supported platinum catalyst that has been subjected to chloride pre-treatment, can be used in the hydrodechlorination of carbon tetrachloride to produce chloroform and methylene chloride. The types of chloride treatment that are disclosed by this patent include treatment of the catalyst with hydrochloric acid and chlorine at an elevated temperature.

The regeneration of a deactivated catalyst which is useful in the production of aromatic compounds, rather than as a hydrodechlorination catalyst, is described in European Patent Publication No. 535,619. In this patent, a deactivated catalyst containing a zeolite and a nobel metal from Group VIII of the Periodic Table is treated with a variety of halogen and halogen-containing compounds including such species as hydrogen chloride, ammonium chloride, and ammonium fluoride.

In U.S. Patent No. 5,721 ,189, a process for enhancing the durability of a supported nobel metal hydrodechlorination catalyst is taught which comprises treating the supported catalyst, which comprises support and catalytic nobel metal, with specific halide compounds, which are not mineral acids. A preferred halide compound for use in that invention is ammonium chloride.

Summary of the Present Invention

The present invention relates to a process for enhancing the durability of a supported nobel metal hydrodechlorination catalyst. The process comprises treating the supported catalyst, which comprises support and catalytic nobel metal, with both a late transition metal halide salt, a post transition metal salt, or combinations thereof and an alkali metal halide salt, ammonium chloride, or combinations thereof. The treated catalyst is then utilized in a hydrodechlorination reaction which will demonstrate the greater selectivity and durability of the catalyst as measured by retention of desired performance for a longer period of time as compared to a catalyst that is treated otherwise.

The treated catalyst of the present invention is also a novel composition of matter. Contrary to conventional catalysts it comprises:

- at least one nobel, preferably platinum group, metal in the zero valent state, - an oxidic support,

- a late transition metal halide salt, a post transition metal salt, or combination thereof, and

- an alkali metal halide salt, ammonium chloride, or combinations thereof. Preferably, at least 10 % by number, based on the total number of particles, of the metal at the surface of the support is present in particles with a size of 10- 200A, as can be determined by microscopic analysis of the surface using a microscope having a resolution of about 5A. More preferably, more than 20 % by number, and most preferably more than 50% by number, of all particles has a size between 10 and 200A.

Description of Detailed Embodiments

The present invention is directed to a process for enhancing the durability and selectivity of a supported nobel metal hydrodechlorination catalyst. By the term "durability" is met that there is a substantial retention of activity, over time, also known as stability, as the catalyst is used in its intended manner in a hydrodechlorination reaction. For example, a conventional catalyst of the type to be described herein, which is not treated in accordance with the present invention, will go from an initial conversion rate of about 90%, initially, to about 2% in about one half hour time. In contrast, the current invention, in a most preferred embodiment, will allow such a catalyst to stay at about 90% conversion for at least about fifty-six hours. Also of significance to the present invention is the superior selectivity of the hydrodechlorination reaction of, for example, tetra to CH₃CI for the catalyst of the present invention (namely, about 80% to 92%), as compared to the ammonium chloride-treated catalyst described and claimed in the above-described, U.S. Patent No. 5,721 ,189 (namely, about 75% to 80%).

The type of catalyst to which the present invention relates is a supported catalyst that comprises both support and catalyst nobel metal. It is well within the skill of persons of ordinary skill in the art familiar with prior art hydrodechlorination catalysts to select appropriate support materials and appropriate catalytic nobel metals, including the late and post transition metals, for use in the fabrication of appropriate supported catalysts which can be treated with the present invention. The type of support that is preferred for purposes of the present invention, is an oxidic support. Representative supports of this type include silica, alumina, zirconia, titania, and the like. It is preferred to use a shaped support, such as a pelletized or extruded support. Zeolitic materials, either the naturally occurring aluminosilicate or aluminophosphate materials or the synthetic zeolites, may be selected as the oxidic support for use in connection with the present invention, if desired. These zeolities may also contain one or more transition metal additives, such as vanadium, molybdenum, titanium, manganese, zirconium, iron, and copper and/or one or more post-transition metals, such as tin.

The nobel metal which forms the other component of the catalyst which is to be treated in accordance with the present invention, comprises preferably a Group VIII nobel metal such as platinum, palladium, or mixtures thereof. It is generally present at from about 0.1% to about 5%, by weight of the support, preferably from about 0.1% to about 1 %, by weight. If desired, the Group VIII nobel metal catalyst can contain other elements which are ordinarily used with catalyst of this type. Examples of other such other elements, which can be contained in such a catalyst include tin, titanium, germanium, rhenium, silicon, lead, phosphorus, arsenic, antimony, bismuth, copper, silver, cobalt, nickel, iron, or mixtures thereof.

In accordance with the present invention, the aforementioned type of supported hydrodechlorination catalyst, which is generally known to persons of ordinary skill in the art, is treated with a late transition metal halide salt, a post transition metal salt, or combinations thereof together, or subsequently (the order not being important), with an alkali metal halide salt, ammonium chloride, or combinations thereof. The late transition metal halide salt preferably is a chloride. The late transition metal is preferably selected from Group IB of the Periodic Table of the Elements while the post transition metals are selected from Groups IIB, IIIA and IVA of the Periodic Table of the Elements (as depicted on page 662 of The Condensed Chemical Dictionary, Ninth Edition, 1977). Examples of especially suitable compounds which can be used in accordance with the present invention include zinc chloride, tin chloride, and cupric chloride. The late and/or post transition metal preferably is used in a quantity of 0.01 to 20 % by weight, based on the weight of the support. More preferably, the late and/or post transition metal is used in a quantity of 1 to 5 % by weight of the support.

For the alkali metal halide salts again chlorides are preferred. Examples of preferred and suitable compounds that can be used in accordance with the present invention include lithium chloride and ammonium chloride. If desired, mixtures of the transition metal halide salt and the non-transition metal halide salt may be used. The alkali metal halide salts and/or ammonium chloride is preferably used in an amount of 0.1 to 10 % by weight, based on the weight of the support.

The catalyst can first be treated with the late transition metal salt and subsequently with the alkali metal halide salt or ammonium chloride. However, the catalyst may also first be treated with the alkali metal halide salt or ammonium chloride and subsequently with the late transition metal salt. In a preferred treatment procedure, the catalyst is treated with late transition metal salt and alkali metal halide salt and/or ammonium chloride in a single treatment step.

Generally speaking, the treatment of the supported catalyst can take place at temperatures ranging from about 100°C to about 500°C, preferably from about 200°C to about 400°C for a sufficient length of time, for instance, from about five minutes to about twenty-four hours, preferably from about thirty minutes to about four hours in order to effect the desired degree of enhancement in the durability of the catalyst.

The previously described treatment procedure also affects the morphology of the conventional "egg-shell"-type hydrodechlorination catalyst in several major ways. The first is the conversion of the metal from a +1 formal valence state to the zero valence state, as determined by X-ray photoelectron spectroscopy. The second is a particle size growth of the metal species so that a predominant amount of such particles become visible under a microscope having a resolution of about 5A since they are predominantly in the particle size range of from about 10A to about 200A. Finally, the composition that is produced will contain the late transition metal and/or post transition metal treatment agent as well as the alkali metal and/or ammonium treatment agent. Hence, the catalysts according to the invention differ from the known hydrodechlorination catalysts as for instance obtained by calcination in an oxidizing environment, which is known to reduce the size of the nobel metal particles.

In order to achieve the most effective durability and selectivity improvement of the catalyst, it is preferably treated according to the invention before it is used as a catalyst. More preferably, it is treated according to the invention before it is contacted with the reactants to be converted. Also, for similar reasons, it is preferred to treat a fresh catalyst, most preferably prior to its first use, rather then a catalyst that has been used as a catalyst prior to the treatment. However, although less preferred, it is possible to treat a catalyst according to the invention after it has been regenerated and before re-use.

The foregoing invention is further illustrated by the Examples, which follow. Comparative Example 1 (LiCI-treated catalyst)

A Johnson Matthey 0.3% Pt/AI₂O₃ catalyst (Type 73) was treated by soaking in an aqueous solution of LiCI (0.4 g/ml) for thirty minutes. The excess LiCI solution was drained afterward. The catalyst was then dried at 100°C for twelve hours in an oven. One gram of the dried catalyst was subsequently loaded into a glass reactor. It was first activated at 350°C under H₂ flow (20 ml/min) for two hours. The catalyst was then cooled to 90°C for CCI₄ hydrodechlorination. The reaction was conducted at a H₂/CCI₄ ratio of 7 with a hydrogen flow rate of 20 ml/min. The catalyst showed stable performance for eighteen hours with the CCI₄ conversion at 80% and the CHCI₃ selectivity at 75%.

Comparative Example 2 (ZnCI₂-treated catalyst)

A Johnson Matthey 0.3% Pt/AI₂O₃ catalyst (Type 73) was treated by soaking in an aqueous solution of ZnCI₂ (0.4 g/ml) for thirty minutes. The excess ZnCI₂ solution was drained afterward. The catalyst was then dried at 100°C for twelve hours in an oven. One gram of the dried catalyst was subsequently loaded into a glass reactor. It was first activated at 350°C under H₂ flow (20 ml/min) for two hours. The catalyst was then cooled to 90°C for CCI₄ hydrodechlorination. The reaction was conducted at a H₂/CCI₄ ratio of 7 with a hydrogen flow rate of 20 ml/min. The CCI₄ conversion was below 20%, and the catalyst was deactivated rapidly. Heavier by-products, such as C₂CI₆, were formed at high selectivity (40%-56%).

Example 1 (ZnCI₂ and LiCI-treated catalyst at lower concentrations)

A Johnson Matthey 0.3% Pt/AI₂O₃ catalyst (Type 73) was treated by soaking in an aqueous solution of ZnCI₂ (0.05 g/ml) and LiCI (0.35 g/ml) for thirty minutes.

The excess solution was drained afterward. The catalyst was then dried at 100°C for twelve hours in an oven. One gram of the dried catalyst was subsequently loaded into a glass reactor. It was first activated at 350°C in a H₂ flow (20 ml/min) for two hours. The catalyst was then cooled to 90°C for CCI₄ hydrodechlorination. The reaction was conducted at a H₂/CCI₄ ratio of 7 with a hydrogen flow rate of 20 ml/min. The catalyst showed stable performance for forty-three hours. A high selectivity to CHCI₃ (80%-90%) was found on this catalyst which had a CCI₄ conversion of 65%-80%. Especially the selectivity of the hydrodechlorination is unexpectedly high.

Example 2 (ZnCI₂ and LiCI treated catalyst at higher concentrations) A Johnson Matthey 0.3% Pt/AI₂O₃ catalyst (Type 73) was treated by soaking in an aqueous solution of ZnCI₂ (0.06 g/ml) and LiCI (0.4 g/ml) for thirty minutes. The excess solution was drained afterward. The catalyst was then dried at 100°C for twelve hours in an oven. One gram of the dried catalyst was subsequently loaded into a glass reactor. It was first activated at 350°C under H₂ flow (20 ml/min) for two hours. The catalyst was then cooled to 90°C for CCI₄ hydrodechlorination. The reaction was conducted at a H₂/CCI₄ ratio of 7 with a hydrogen flow rate of 20 ml/min. The catalyst showed stable performance for forty-nine hours. High selectivity to CHCI₃ (85%-92%) was found for this catalyst together with a CCI₄ conversion of 70%-88%.

The foregoing Examples, which are presented for illustrative purposes only, should not be construed in a limiting sense. The scope of protection sought is set forth in the claims that follow.

Claims

1. A process for enhancing the durability and selectivity of a supported nobel metal hydrodechlorination catalyst, as measured by a later hydrodechlorination reaction, which process comprises treating the supported catalyst, which comprises support and catalytic noble metal, with:

- one or more salts selected from the group consisting of a late transition metal halide salts and post transition metal halide salts, and 0 - one or more salts selected from the group of alkali metal halide salt and ammonium chloride.

2. A process as claimed in claim 1 wherein the support is an oxidic support.

5 3. A process as claimed in claim 1 or 2 wherein the noble metal is a Group VIII noble metal, preferably platinum or palladium.

4. A process as claimed in any one of claims 1-3 wherein a late transition metal halide salt is used selected from salts of Group IB metals of the o Periodic Table, preferably a chloride of copper.

5. A process as claimed in any one of claims 1-3 wherein a post transition metal halide salt is used selected from salts of Group IIB, IIIA or IVA metals of the Periodic Table, preferably zinc or tin. 5

6. A process as claimed in any one of the preceding claims wherein the alkali metal halide salt that is used is LiCI.

7. An improved hydrodechlorination catalyst obtainable by the process of 0 any one of claims 1-6.

8. A supported noble metal hydrodechlorination catalyst wherein the noble metal, which is in the zero valent state, predominantly resides adjacent the surface of the support and is predominantly visible under a microscope having a resolution of about 5A, and which also comprises a late transition metal, a post transition metal, or a combination thereof, as well as an alkali metal moiety, ammonium moiety, or a combination thereof.

9. A catalyst as claimed in claim 8 wherein the support is an oxidic support, which preferably is pelletized.

10. A catalyst as claimed in claim 8 or 9 wherein the noble metal is a Group VIII noble metal, preferably platinum and palladium.

11. A catalyst as claimed in any one of claims 8-10 wherein a late transition metal is used selected from Group IB of the Periodic Table, preferably copper.

12. A catalyst as claimed in any one of claims 8-10 wherein a post transition metal is used selected from Group IIB, IIIA or IVA of the Periodic Table, preferably zinc or tin.