MXPA98004544A - Treatment to improve the durability of a catalyst of dehydrochroration and catalyst - Google Patents

Abstract

The durability of a supported noble metal dehydrochlorination catalyst can be improved by treating the supported catalyst, which comprises a support and a catalytic noble metal, with a non-elemental halide compound which is not a mineral acid (such as a metal halide) alkali, an ammonium halide, an alkaline earth metal halide and / or a halogenated hydrocarbon), then using the catalyst treated in a dehydrochlorination reaction, compounds suitable for the treatment include ammonium chloride, lithium chloride or a chlorinated hydrocarbon The treated catalyst is a novel composition of matter comprising at least one metal of the platinum group, supported by a support oxide in which the metal, which is in the zero-valent state, resides predominantly adjacent to the surface of the metal. support and is predominantly visible under a microscope that has a resolution of approximately

Description

TREATMENT TO MEASURE THE PURABIIIPAP PE A GATA IZAPQR PE PESHIPRQCLQRACIQN AND CATALYST ANTECEPENTES AND THE INVENTION Various techniques are known for the regeneration or treatment of dehydrohalogenation or dehydrochlorination catalysts. The following are some examples of descriptions that are considered relevant to the present invention. The patent of E.U.A. No. 4 »980.324 to C.S. Kellner et al. Describes the regeneration and / or activation of a noble metal catalyst by the use of a luorohalogenocarburo and / or a luorohydrocarbon. The patent of E.U.A. No. 5,057,470 C.S. "Latest Kellner" refers to the contact of a dehydrohalogenation catalyst with an atmosphere comprising chlorine gas at elevated temperature for a time which is sufficient to improve the catalytic activity of the catalyst. The patent of E.U.A. No. 4,374,047 to A. Bozon et al. Would teach preloading a porous catalyst vehicle with an aqueous solution of ammonium chloride before applying a coating containing platinum and / or palladium to the surface of the treated porous catalyst vehicle. The patent of E.U.A. No. 5,105,032 to M.T. Holbrook et al., More recent, indicates that a supported platinum catalyst that has been subjected to pretreatment with chloride can be used in the dehydrochlorination of carbon tetrachloride to produce chloroform and methylene chloride. The types of chloride treatment described in this patent include treatment of the catalyst with hydrochloric acid and chlorine at an elevated temperature. The regeneration of a deactivated catalyst that is useful in the production of aromatic compounds, rather than as a dehydrochlorination catalyst. it is described in European Patent Publication No. 534,619. In this patent. a deactivated catalyst containing a zeolite and a noble metal of group VIII of the periodic table, is treated with a variety of halogens and halogen-containing compounds including species such as hydrogen chloride, ammonium chloride and ammonium fluoride. Certain prior art disclosures relating to dehydrochlorination catalysts comprising metal (s) from the platinum group supported by an oxide support indicate that the metal of the platinum group is homogeneously distributed over and through the support. Examples of such descriptions include: D.J. Sith and others. Journal of Catalysis 81. 107-118 (1983); I. Sushumna and others. Journal of Catalysis 109 »433-462 (1988); R. cCabe and others. Journal of Catalysis 114, 354-367 (1988); A. Bellare and others. Journal of Catalysis 117, 78-90 (1989); and J. Hancsók et al., Hungarian Journal of Industrial Chemistry, Vol. 17. 131-137 (1989). However, commercially available catalysts comprising at least one metal of the platinum group supported by an oxide support can be obtained in which the metal, which is in the +1 valent state, resides predominantly adjacent to the support surface. (to produce a so-called "egg shell" appearance for the distribution of the metal if the support containing it is broken and viewed transversally). The metal component in said catalyst is not predominantly visible under a microscope having a resolution of about 5 & since a predominant portion of this metal species has a particle size well below approximately 5 *.

BRIEF DESCRIPTION OF THE PRESENT INVENTION The present invention relates to a process for improving the durability of a supported noble metal dehydrochlorination catalyst. The process comprises treating the supported catalyst, which comprises a support and a catalytic noble metal, with a non-elemental halide compound, which is not a mineral acid. An example of a suitable compound is ammonium chloride. The treated catalyst is then used in a dehydrochlorination reaction that will demonstrate the increased durability of the catalyst as measured by the retention of the desired performance over a longer period of time compared to an untreated catalyst. The treated catalyst of the present invention is also a novel composition of matter comprising at least one metal of the platinum group supported by an oxide support in which the metal, which is in the zero-value state, resides predominantly adjacent to the surface of the support and is predominantly visible under a microscope having a resolution of approximately 5%.

DESCRIPTION OF THE DRAWINGS The present invention will be better understood by reference to the drawings forming part of the present application, in which: Figure 1 is a schematic, cross-sectional view of the catalyst of the present invention, showing the distribution of "shell of egg "of platinum particles" and of a conventional catalyst showing the homogeneous distribution of platinum particles; and Figure 2 illustrates the results of a durability test of the catalyst of the present invention, as described more fully in Example 11 hereinafter.

DETAILED DESCRIPTION OF THE MODALITIES The present invention is directed to a process for improving the durability of a supported noble metal dehydrochlorination catalyst. By the term "durability" is meant that there is a substantial retention of activity "over time, when the catalyst is used in its desired form in a dehydrochlorination reaction. For example, a conventional catalyst of the type to be described herein, which is not treated in accordance with the present invention, will range from an initial conversion rate of about 90%, initially, to about 2% in about half an hour. In contrast, the present invention, in a highly preferred embodiment, will allow said catalyst to remain at a conversion of approximately 85% for at least about one week. The type of catalyst to which the present invention refers is a supported catalyst comprising both a support and a noble catalyst metal. It is within the abilities of those skilled in the art who are familiar with dehydrochlorination catalysts of the prior art, the selection of suitable support materials and suitable catalytic noble metals to be used in the manufacture of suitable supported catalysts which can be treated with the present invention.

The type of support that is preferred, for the purposes of the present invention, is an oxide support.

Representative supports of this type include silica »alumina» zirconia, titania and the like. A pei-etized support is preferred. The type of catalytic metal that forms the other component of the catalyst, which will be treated according to the present invention, is preferably a noble metal of group VIII such as platinum, palladium or mixtures thereof. It is generally present at levels of about 0.1J4 to about 55% by weight of the support, preferably from about 0.1% to about 1% by weight. If desired, the group VIII noble metal catalyst may contain other metals that are normally used with catalysts of this type. Examples of such metals which may be contained in the catalyst include tin, titanium, gernium, rhenium, silicon, lead, phosphorus, arsenic, antimony, bismuth, copper, silver, cobalt or mixtures thereof. In accordance with the present invention, the above-mentioned type of supported dehydrochlorination catalyst, which is generally known to those skilled in the art, is treated with a non-elemental halide compound that is not a mineral acid. In other words, the present invention excludes the use of chlorine or hydrochloric acid as shown in the patent of E.U.A. No. 5,105,032 to M.T. HolbrooK and others, previously mentioned.

Examples of suitable compounds that may be used in accordance with the present invention include the alkali metal halides, including ammonium halide, alkali metal halides, and halogenated hydrocarbons. In said compounds, it is preferred that the halogen atom is chlorine so that the compounds can be selected from the alkali metal chlorides, including ammonium chloride, the alkali earth metal chlorides and the chlorinated hydrocarbons. 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 example »of about five minutes at about twenty-four hours, preferably from about thirty minutes to about four hours to achieve the desired degree of improvement in the durability of the catalager. The treatment method described above also affects the morphology of the conventional "egg shell" type dehydrochlorination catalyst (which is compared with a conventional homogeneous distribution type catalyst in the scheme of Figure 1) in two main forms. The first is the conversion of the metal from a formal valence state +1 to the zero valence state »determined by X-ray spectroscopy with photoelectrons. The second is a growth in the particle size of the metal species, so that a predominant amount of these particles are visible under a microscope that has a resolution of approximately 5A »since they are predominantly on the size scale particle size from about 10 amp; Approximately 200 &, As demonstrated in some of the examples below "the reagent feed may comprise hydrogen and carbon tetrachloride alone" or these reagents together with one or more gases that are inert to the desired reaction "such as HC1 gaseous »helium» nitrogen and / or methane. To achieve the most desirable performance characteristics for the catalyst treated in the desired dehydrochlorination reaction, it is preferred to avoid overheating the catalyst during the reaction; avoid the use of a ratio of hydrogen to carbon tetrachloride that is very low; and allow the presence of liquid condensation in the reactor. The invention is further illustrated by means of the examples below.

COMPARATIVE EXAMPLE 3.

This example illustrates the performance of an untreated catalyst as a comparison with the results obtained from the use of the present invention. The dehydrochlorination of CCl., Was carried out in the vapor phase using a Johnson Matthey catalyst pelletized from Pt / Ala03 at 0.3% having a Cl content of approximately 0.3% »at 90 ° C» 1200 hr-? »13% of CC1" in Ha and one atmosphere. The catalyst was activated in a hydrogen atmosphere at 350 ° C for two hours before being cooled to 90 ° C, at which time the reaction gas mixture was introduced. It showed an initial conversion of CCl ^ of 85%. The conversion of C l ^ fell to 2% in one hour.

COMPARATIVE EXAMPLE 2 This example also lustrates the performance of an untreated catalyst as a comparison with the results obtained from the use of the present invention. A Degussa catalyst of Pt / AljB03 at 0.3% was used in the same pretreatment and reaction conditions as those specified in comparative example 1. The catalyst had an initial conversion of CCl ^ of 18% and the conversion fell to 2% in one hour.

EXAMPLE 3 The Degussa catalyst of Pt / AlaOa at 0.3% deactivated from Comparative Example 2. after four hours of showing 2% conversion at 90 ° C. was activated at 200 ° C in a mixture of 13% reaction gas of CC1"in hydrogen. The conversion of CCl ^ was more than 95%. After two hours, the temperature was lowered to 90 ° C and the reaction was continued. The conversion of CCl ^ remained above 45% for five hours. Although this catalyst showed deactivation, the deactivation rate was much slower than that of the catalyst used in comparative example 2.

EXAMPLE 4 A Johnson Matthey catalyst pelletized from Pt / AljD, at 0.3% of the same batch as that used in comparative example 1. was activated at 350 ° C in hydrogen for two hours. Then it was cooled to 200 ° C. At that time CCl ^ was introduced to 13% in hydrogen. The conversion of CCl ^ was more than 95%. Two hours later. the temperature was decreased to 90 ° C and the reaction was continued. The conversion remained above 40% for four hours. Although this catalyst showed deactivation, the deactivation rate was also much slower than that of the catalyst used in comparative example 1.

EXAMPLE 9 A Johnson Matthey catalyst pelletized from Pt / Al-gOa at 0.3% of the same batch as that used in comparative example 1 was washed with a saturated NH.sub.1 Cl solution.

It was then dried in air at room temperature followed by activation at 350 ° C in hydrogen for two hours. Subsequently »was cooled to 90 ° C» time at which the reactive gas mixture of example 4 was introduced. This catalyst showed a CCl ^ conversion of 85% for three days without deactivation. The selectivity for CHC1.:, Was 80% and the balance was methane. No heavy byproducts were detected.

EXAMPLE A Degussa catalyst pelletized from Pt / Al ^ 0, al 0. 3% of the same batch as the one used in Example 4 was washed with a saturated NH.sub.1 Cl solution. It was then dried in air at room temperature followed by activation at 350 ° C in hydrogen for two hours. It was then cooled to 90 ° C »at which time the reactive gas mixture of Example 4 was introduced. This catalyst showed a CCl ^ conversion of 85% for seven days without deactivation. The selectivity for CHC13 was 80% and the balance was methane. No heavy byproducts were detected.

EXAMPLE 7 A Johnson Matthey catalyst pelletized from Pt / AlajOj, at 0.3% of the same batch as that used in comparative example 1 was washed with a saturated solution of LiCl.

It was then dried in air at room temperature followed by activation at 350 ° C in hydrogen for one and a half hours. Subsequently "it was cooled to 90 ° C" at which time the reactive gas mixture of example 4 was introduced. This catalyst showed a CCl ^ conversion of 91-95% for seven days without deactivation. The selectivity for CHC1 ... "was 70% and the balance was methane. No heavy byproducts were detected. EXAMPLE 8 A Johnson Matthey catalyst pelletized from Pt / Als-fOj. at 0.3% of the same batch as that used in comparative example 1 was crushed to form smaller pellets. The interior A1303 of the original pellet was exposed. The crushed catalyst was deactivated more rapidly than the non-crushed pellets, indicating that untreated A1303 is not desirable for the reaction. Another batch of crushed pellets was washed with a saturated solution of NH 4 Cl. It was then dried in air at room temperature followed by activation at 350 ° C in hydrogen for two hours. Subsequently, it was cooled to 90 ° C, at which time the reactive gas mixture of Example 4 was introduced. This catalyst showed a CCl ^ conversion of more than 90% for seven days without deactivation, at a selectivity of more than 70% for CHC1 ..-. The selectivity for CHC1 increased as the conversion decreased; the conversion of CCl ^ was decreased by lowering the reaction temperature. The selectivity for CHC13 was more than 80% between a conversion of 20-70%.

EXAMPLE 9 A Johnson Matthey catalyst pelletized from Pt / AljjOa at 0.3% of the same batch as that used in comparative example 1 was washed with a saturated NH.sub.1 Cl solution. It was then dried in air at 80 ° C followed by activation at 320 ° C in hydrogen for three hours. Subsequently »was cooled to 90 ° C. time at which the reactive gas mixture of example 4 was introduced. This catalyst showed a CCl ^ conversion of 85% for three days without deactivation. The selectivity for CHC13 was 80% and the balance was methane.

EXAMPLE 10 An "egg shell" type catalyst from Johnson Matthey of Pt / Al303 at 0.3% "as received from the manufacturer" was reduced in hydrogen for two hours. This catalyst is called here the "untreated catalyst". Analysis of this untreated catalyst by X-ray spectroscopy with photoelectrons (XPS) indicated that the platinum content in this untreated catalyst had a +1 oxidation state. Investigation of this transmission electron microscopy (TEM) catalyst indicated that most platinum particles were invisible "although some visible platinum particles were approximately 2 n in size. The type of catalyst not treated above was treated with a saturated solution of NH.sub.1 Cl. Analysis by XPS indicated that the platinum content of this untreated catalyst had an oxidation state 0 which indicated that the platinum was in the metallic state. Analysis by TEM indicated that most of the platinum particles had a size of approximately 8 nm. The Cl content of this catalyst was about 1.5%.

EXAMPLE U As shown in the figure, the catalyst was subjected to a durability test at a H ^ / CCl ^ ratio of approximately 6, although, as indicated below, it was lower on hot days when an operational problem occurred. The conversion of carbon tetrachloride was 74%, being the selectivity for CHC1 .. ,, of 80% in the final analysis. Despite the various discomforts due to sampling and temperature fluctuation, the durability was judged to be excellent. During the test, an attempt was made to maintain the temperature of the carbon tetrachloride bath at 24 ° C in order to maintain the aforementioned H3 / CC1 ratio. Since the first water bath in the experimental test did not have refrigeration, its temperature rose to 2B ° C, or possibly more, after thirty-two days over current. The H ^ / CCl ^ ratio decreased to approximately 4.5 at this temperature, which caused decreased activity. This problem lasted more than a week before placing a cold circulation bath in the test. Despite this problem, it should be noted that the catalyst still had a stable yield during that period of decreased activity. The activity was recovered to the previous level after the problem was solved. There followed several cold days that caused some fluctuation in the conversion.

A Johnson Matthey catalyst pelletized from Pt / alumina 0.3% of 3.2 mm was treated with a saturated solution of ammonium chloride. Then it was dried in air to 80 ° C. One gram of the treated catalyst was charged in a glass reactor where it was activated at 320 ° C in hydrogen for three hours. The catalyst bed was subsequently cooled to 90 ° C »at which point a reactive mixture of carbon tetrachloride in hydrogen was introduced. The total vapor flow of carbon tetrachloride was 3.5 ml / minute "and the hydrogen flow rate was 22 ml / minute. The reaction was carried out for 75 hours. The carbon tetrachloride conversion was maintained at more than 80% with a selectivity for CHC13 of more than 70%. Gas HCl was then added to the reaction mixture at flow rates of 5, 8, 10, 13 and 15 ml / minute, in steps increments. The conversion decreased to 50% at 15 ml / minute when HCl was added, and the selectivity for CHC13 was increased to 83%. The catalyst yield was stable under the high HCl flow for fifteen hours, when the test was completed.

EXAMPLE 13 This example used the same procedure as that described in example 12, adding HCl at 15 ml / minute in the mixture at a temperature of 120 ° C. The conversion of carbon tetrachloride was 64%, the selectivity for CHCl-1 being 82%. At 130 ° C the conversion of carbon tetrachloride was 74% and the selectivity for CHC13 was 80%.

EXAMPLE 14 The same catalyst used in Example 12 was treated, dried, charged in a reactor, and activated as described in that example, and the catalyst bed was also cooled similarly to 90 ° C. point at which the same reactive mixture of carbon tetrachloride in hydrogen was introduced. However, the reaction was carried out for one hundred and twenty-eight hours. The conversion of carbon tetrachloride was also maintained above 80% with a selectivity for CHC1.:|1 of more than 70%. Helium was then added to the reaction mixture so that the total flow rate of hydrogen and helium was maintained at 22 ml / minute. The helium / hydrogen ratio was increased to 1/1 in the reaction mixture. The catalytic conversion of carbon tetrachloride and the selectivity to CHC13 were not affected during a five hour test period.

COMPARATIVE EXAMPLE 15 This example illustrates the results achieved by duplicating the chloride pretreatment technique taught in the U.S. patent. No. 5,105,032 to M.T. Holbrook and others. A Johnson Matthey catalyst pelletized from Pt / Al30 0.3% 3.2 (1.0 gram) was dried at 200 ° C under nitrogen before cooling to 100 ° C »temperature at which the dry hydrogen gas mixture (20 ml / min) and hydrogen chloride (20 ml / min) was passed through the catalyst bed. The HCl was used as the pretreatment reagent with chloride according to the teaching of the Holbrook et al. Patent. The temperature of the catalyst bed was then slowly lowered to 200 ° C and maintained at that temperature for two hours in the flow of mixed gas. The dehydrochlorination reaction was initiated by cooling to 100 ° C under hydrogen maintaining the ratio of hydrogen to carbon tetrachloride during the reaction at 7: 1. The conversion of CC1. "Decreased from 98% to 32% in less than one hour, and the selectivity for CHC13 increased slightly from 59% to 66%. This procedure was then repeated and it was found that HCl had little effect on the performance of the Johnson Matthey catalyst. The above examples, which are presented for illustrative purposes only, should not be considered in a limiting sense. The scope of protection sought is established in the following claims.

Claims (22)

NOVELTY OF THE INVENTION REIVI.NPICACIQNE5

1. - A method for improving the durability of a supported noble metal dehydrochlorination catalyst, as measured by a subsequent dehydrochlorination reaction, which process comprises treating the supported catalyst, comprising a support and a catalytic noble metal, with a compound selected from halogenides of alkali metal, earth alkali metal halides or ammonium halides.

2. A method according to claim 1, further characterized in that the support is an oxide support.

3. A process according to claim 1, further characterized in that the noble metal is a noble metal of group VIII.

4. A method according to claim 1, further characterized in that the noble metal is selected from platinum or palladium.

5. A method according to claim 1, further characterized in that the support is an oxide support and the noble metal is selected from platinum or palladium.

6. A process according to claim 1, further characterized in that the halide is chloride.

7. A process according to claim 5, further characterized in that the halide is chloride.

8. An improved dehydrochlorination catalyst that is obtained by the process according to claim 1.

9. An improved dehydrochlorination catalyst obtained by the process according to claim 5.

10. A catalyst dehydrochlorination of noble metal supported in which the noble metal particles reside predominantly adjacent to the surface of the support »said particles have a size of about 10 A to about 200 A» determined by a microscope »and said noble metal is in the state of zero valence.

11. A catalyst according to claim 12 »further characterized in that the support is an oxide support. 12. A catalyst according to claim

12. further characterized in that the noble metal is a noble metal of group VIII.

13. A catalyst according to claim 12 »further characterized in that the noble metal is selected from platinum or palladium.

14. A catalyst according to claim 12 »further characterized in that the support is an oxide support and the noble metal is selected from platinum or palladium.

15. A catalyst according to claim 12 »further characterized in that the support is a pelletized oxide support and the noble metal is selected from platinum or palladium.

16. The use of a supported noble metal catalyst for dehydrochlorination, further characterized in that the supported catalyst comprising a support and a catalytic noble metal has been treated with a compound selected from chlorinated hydrocarbons, alkali metal halides, alkali metal halides. earth or ammonium halides.

17. The use of a noble metal catalyst according to claim 16. further characterized in that the support is an oxide support.

18. The use of a noble metal catalyst according to claim 16 »further characterized in that the noble metal is a noble metal of group VIII.

19. The use of a noble metal catalyst according to claim 16, further characterized in that the noble metal is selected from platinum or palladium.

20. The use of a noble metal catalyst according to claim 16, further characterized in that the support is an oxide support and the noble metal is selected from platinum or palladium.

21. The use of a noble metal catalyst according to claim 16, further characterized in that the halide is chloride.

22. The use of a noble metal catalyst according to claim 20, further characterized in that the halide is chloride.