WO1999017876A1

WO1999017876A1 - Treatment to improve the durability of a hydrodechlorination catalyst and catalyst

Info

Publication number: WO1999017876A1
Application number: PCT/EP1998/006348
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
Also published as: WO1999017876B1

Abstract

The durability of a supported nobel metal hydrodechlorination catalyst can be improved by treating the supported catalyst, which comprises support and catalytic noble metal, with hydrogen, in the presence of water, at elevated temperature. The temperature of the treatment can be at least about 400 °C and the time of treatment can be at least one half hour. The amount of water that is used can range from about 0.1 to 99.9 molar % based on the total moles of water and hydrogen that are utilized.

Description

TREATMENT TO IMPROVE THE DURABILITY 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 nobei 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 hydrogen in the presence of water at elevated temperature.

Description of Detailed Embodiments

The present invention is directed to a process for enhancing the durability, also known as stability, of a supported nobel metal hydrodechlorination catalyst. By the term "durability" is meant that there is a substantial retention of activity, over time, 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 80% conversion for at least about twenty-four hours. The type of catalyst to which the present invention relates is a supported catalyst which comprises both support and a nobel metal. It is well within the skill of persons of ordinary skill in the art and familiar with prior art hydrodechlorination catalysts, to select appropriate support materials and appropriate catalytic nobel metals for use in the fabrication of appropriate supported catalysts which can be treated with the present invention. The type of support which 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 preferably to use a shaped, such as pelletized or extruded support. The type of catalytic 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 is treated with hydrogen gas in the presence of water at elevated temperature. In general, according to preferred embodiments of the present invention, the temperature of the treatment is at least about 400°C and the time of treatment is at least one half hour. The amount of water that is used can range from about 0.1% to about 99.9%, on a molar basis based on the total amount of moles of hydrogen and water that are utilized. Preferably, 5 to 95%, more preferably 10 to 90% of water is used on a molar basis based on the moles of hydrogen and water that are utilized (molar% = moles per 100 moles). Longer treatment times will allow the use of lower water to hydrogen ratios whereas shorter treatment times will typically require higher water to hydrogen ratios. It is within the contemplation of the present invention to have either additional reducing or inert gases also present. Examples of additional reducing gases include hydrazine and primary and secondary amines, whereas inert gases may be exemplified by helium, argon and nitrogen. The primary and secondary amines may be any conventional amine but they are preferably volatile at the process conditions.

In order to achieve the most effective durability 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

A Johnson Matthey 0.3% Pt/AI₂O₃ catalyst (Type 73, 1.0 gram) was activated in a dry hydrogen gas flow of 20 ml/min at 500^°C 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 initial CCI₄ conversion was 70%. The conversion dropped to less than 5% during the two subsequent hours of reaction, which was indicative of rapid catalyst deactivation.

Example 1

Moist hydrogen, made from 20 ml/min hydrogen gas flow and 5 gram/hour distilled water was used to treat a Johnson Matthey 0.3% Pt/AI₂O₃ catalyst (Type 73, 1.0 gram) at 500°C 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 performance was stable at a CCI₄ conversion of 90% with CHCI₃ selectivity of 70%. For an additional evaluation period of twenty-four hours, no deactivation of the catalyst was observed.

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, which follow.

Claims

1. A process for enhancing the durability 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 hydrogen, in the presence of water, at elevated temperature.

2. A process as claimed in Claim 1 wherein the temperature is at least 400^┬░C.

3. A process as claimed in Claim 1 or 2 wherein the temperature is at least about 400^┬░C and the amount of water ranges from 0.1% to 99.9%, on a molar basis, based on the total amount of moles of hydrogen and water that are utilized.

4. A process according to Claim 3 wherein from 5 to 95 molar%, more preferably 10 to 90 molar%, of water is used, based on the total amount of moles of hydrogen and water.

5. A process as claimed in Claim 1 wherein an additional reducing gas is used.

6. A process as claimed in Claim 5 wherein the reducing gas is selected from the group consisting of hydrazine and primary and secondary amines.

7. A process as claimed in Claim 1 wherein an inert gas is also used.

8. A process as claimed in Claim 7 wherein the inert gas is selected from the group consisting of helium, argon, and nitrogen.

9. A process according to any one of the preceding claims, wherein the catalyst is treated prior to being used as a catalyst.

10. An improved hydrodechlorination catalyst formed by any one of the processes of claims 1-9.