NO173004B - PROCEDURE FOR THE REGENERATION OF A SULFUR AND EVENTS WASTE CARBON POLLATED CATALYST CONTAINING A LARGE PORETZEOLITE - Google Patents

Description

The present invention relates to a method for regenerating a sulfur- and possibly also carbon-contaminated catalyst comprising a large-pore zeolite. More specifically, the invention is directed to the regeneration of sulphur-contaminated, monofunctional, zeolitic reforming catalysts which contain at least one metal from Group VIII.

Over the past few years, monofunctional zeolitic reforming catalysts have become the subject of considerable interest. A monofunctional reforming catalyst exhibits little or no acid catalytic activity, all of its activity for promoting aromatization reactions being provided by a Group VIII metal. The interest in these catalysts is primarily due to their surprisingly high selectivity for the dehydrocyclization of paraffins to aromatics, see US Patent Nos. 4,104,320, 4,517,306. 4,447,316, 4,434,311 and 4,435,283. However, it has also been shown that these catalysts are extremely sensitive to sulphur. They are almost completely deactivated even when contaminated by a small amount of sulphur, see e.g. US Patent No. 4,456,527. During reforming, the sulfur content of the feed material must be kept lower than 100 ppb (parts per billion parts), more preferably lower than 50 ppm to achieve an acceptable operating time. However, sulfur will inevitably build up on the catalyst, either as a result of an unanticipated entry or through slow accumulation, forcing a regeneration of the sulfur-contaminated catalyst. As sulfur is deposited on the catalyst, the reactor temperature must be increased to keep the conversion constant. This can be done until a maximum temperature limit is reached (about 510°C-538°C, determined either by the selectivity of the process or the metallurgical limitations of the reactor). Regeneration is usually necessary when approx. 1 sulfur atom has been accumulated per 10 platinum atoms on the catalyst. Accordingly, there is a need for a method of regenerating sulfur-contaminated, monofunctional, zeolitic reforming catalysts containing a Group VIII metal.

A number of regeneration procedures have been proposed to remove sulfur from sulphur-contaminated, bifunctional reforming catalysts (bifunctional catalysts have an acidic component that provides additional catalytic functions, namely cracking and isomerization), see e.g. US Patent Nos. 2,853,435, 2,892,770 and 3,622,520. More recently, regeneration procedures for sulfur contaminated bimetallic (eg platinum/rhenium) bifunctional catalysts have been disclosed, see e.g. US Patent Nos. 3,617,523 and 4,033,898. However, these sulfur regeneration methods are inefficient with respect to monofunctional zeolitic reforming catalysts.

Since the possibility of sulfur poisoning of the catalyst cannot be completely eliminated, even by strict control of the sulfur content of the feed material, the need for a sulfur regeneration procedure specific to monofunctional zeolitic catalysts is obvious.

Several methods for the regeneration of monofunctional zeolite catalysts have previously been proposed. They are claimed to be effective for the removal of carbon and/or for the redistribution of platinum. However, none of these methods are related to sulfur contamination or sulfur removal. For example, European patent application no. 0,142,352 describes a regeneration procedure for deactivated platinum/L-zeolite catalysts. The deactivation that is remedied by this procedure is caused by coke deposition and platinum agglomeration, not by sulfur contamination. Moreover, this European patent application states that it is preferable to add a certain amount of sulfur to the catalyst to reduce the occurrence of cracking. The application mentions a step for burning off carbonaceous material and an oxychlorination step for redispersing the agglomerated platinum particles.

Another regeneration procedure for a monofunctional reforming catalyst is described in US Patent No. 4,493,901, where it is stated that the regeneration procedure for coke deactivation can be improved by having an oxygen combustion step and an oxychlorination step followed by a hydration step. Pollution with sulfur is not mentioned.

Consequently, a regeneration procedure is needed to restore the activity of monofunctional zeolitic catalysts that have been completely or partially deactivated by contamination with sulfur. This need has now been fulfilled by

by means of the present invention.

The present invention thus provides a method for the regeneration of a sulfur-contaminated catalyst comprising a large-pore zeolite, preferably an L-zeolite, optionally a zeolite with a medium pore size, preferably a silicalite, and a metal from Group VIII chosen from platinum , rhodium, ruthenium, iridium and osmium. The method is characterized by the fact that the metal from Group VIII is agglomerated by keeping the catalyst in contact with an oxygen-containing gas at a temperature between 427°C and 649°C and that sulfur is then removed from the catalyst by keeping it in contact with a halogen acid gas that does not contain sulphur.

A key feature of the process according to the invention is the degree of agglomeration of the metal from Group VIII before the removal of sulfur from the catalyst. For example, it is preferred for a sulphur-contaminated platinum-containing catalyst to form platinum agglomerates with a diameter greater than 50 Å, more preferably greater than 75 Å and most preferably greater than 150 Å. The amount of agglomerated platinum on the catalyst is preferably greater than 50% by weight of the total amount platinum.

Metal agglomeration is preferably carried out in an oxidizing gas by (1) bringing the catalyst into contact with a gas containing between 1 vol% and 50 vol% oxygen, at a temperature between 427°C and 649°C, at a gas velocity GHSV of between 50 and 5000 and a pressure of between 1 and 30 atm for a period of between 1 and 100 hours, and sulfur is preferably removed by (2) bringing the catalyst into contact with a gas comprising more than 0.1% hydrogen chloride in hydrogen in a time longer than 1 hour, at a temperature between 427°C and 649°C, at a pressure between 1 and 30 atm and at a gas velocity GHSV of between 50 and 5000.

The present invention thus provides a method for regenerating a carbon- and sulfur-contaminated catalyst comprising a large-pore zeolite and platinum, characterized in that: (a) the catalyst is brought into contact with a gas containing between 0.1% and 2.0 % oxygen, at a temperature between 260°C and 482°C, at a pressure between 1 and 10 atm, using a gas velocity GHSV of between 150 and 1500, for a time between 1 and 24 hours, to remove carbon from the catalyst, (b) the catalyst from step (a) is contacted with a gas containing between 2% and 21% oxygen, at a temperature between 482°C and 566°C, using a gas velocity GHSV of between 150 and 1500, at a pressure between 1 and 10 atm, for a time between 8 and 50 hours, to agglomerate the platinum, and (c) contacting the catalyst from step (b) with a gas comprising more than 1% hydrogen chloride in hydrogen, in a time between 8 and 50 hours, at a temperature between 427 °C and 538 °C, at a pressure between 1 and 10 at m, and using a gas velocity GHSV of between 150 and 1500, to remove sulphur.

Platinum agglomeration and removal of sulfur can also preferably be carried out by means of one or more steps where the catalyst is brought into contact with a gas containing at least 2 vol% carbon monoxide and more than 0.1 vol% hydrogen chloride, at a temperature between 427°C and 649 °C, for a time longer than 1 hour, at a gas velocity GHSV of between 50 and 5000 and at a pressure of between 1 and 30 atm.

The present invention also provides an alternative method for regenerating a carbon- and sulfur-contaminated catalyst comprising a large-pore zeolite and platinum, characterized in that: (a) the catalyst is brought into contact with a gas containing between 0.1% and 2.0% oxygen, at a temperature between 260 °C and 482 °C, at a pressure between 1 and 10 atm, and using a gas velocity GHSV of between 150 and 1500, for a time between 1 and 24 hours, to remove carbon from the catalyst, and (b) the catalyst from step (a) is contacted with a gas comprising more than 1% hydrogen chloride and between 50 and 99% carbon monoxide, at a temperature between 427°C and 538°C, for more than 3 hours , using a gas velocity GHSV of between 150 and 1500 and a pressure between 1 and 10 atm, to both agglomerate platinum and remove sulphur.

The present invention also provides a method for regenerating a carbon- and sulphur-contaminated, monofunctional, large-pore zeolite reforming catalyst comprising platinum and L-zeolite.

The procedure is characterized by the fact that it includes:

(I) a carbon removal step according to which one: (a) brings the catalyst into contact with a gas containing between 0.1% and 2.0% oxygen, at a temperature between 260°C and 482°C, using a gas velocity GHSV of between 150 and 1500, at a pressure of between 1 and 10 atm, for between 1 and 24 hours, to remove carbon from the catalyst, (II) a stage for agglomeration of platinum and removal of sulphur, in according to which one: (a) brings the catalyst from step (I) (a) into contact with a gas containing between 2% and 21% oxygen, at a temperature between 482°C and 566°C, using a current- ning rate GHSV of between 150 and 1500, and a pressure of between 1 and 10 atm, for a time of between 8 and 50 hours, to agglomerate the platinum, (b) contacting the catalyst from step (II) (a) with a gas comprising between 2% and 5% hydrogen chloride in hydrogen, for a time between 8 and 50 hours, at a temperature between 482°C and 538°C, at a pressure between 1 and 10 atm and using a gas velocity GHS V of between 150 and 1500, to remove sulphur, (III) an oxychlorination procedure to redistribute the platinum, according to which one: (a) brings the catalyst from step (II)(b) into contact with a chloride-containing compound in a gas containing between 1% and 21% oxygen and from 1% to 4% water in an amount sufficient to provide between 5 and 200 chloride atoms per platinum atom, for a time between 1 and 3 hours, at a temperature between 482°C and 538°C and a pressure between 1 and 10 atm, (b) stops the flow of the gas in step (III)(a) and brings the catalyst in contact with dry nitrogen at a temperature between 454°C and 510°C, at a pressure between 1 and 10 atm, and using a gas velocity GHSV of between 150 and 1500, for a time between 0.1 and 2.0 hours , and (c) contacting the catalyst with dry hydrogen at a temperature between 427°C and 510°C and a pressure between 1 and 10 atm, for less than 2 hours, using a gas has-

density GHSV of between 150 and 1500.

A variant of the method according to the invention consists in replacing the above-described step (II) with (II) a step for agglomeration of platinum and removal of sulphur, according to which one: (a) brings the catalyst from step (I) (a) in contact with a gas comprising more than 1% hydrogen chloride in carbon monoxide, at a temperature between 482°C and 538°C, at a pressure between 1 and 10 atm, for more than 24 hours, and using a gas velocity GHSV of between 150 and 1500.

Catalysts which can advantageously be regenerated by the method according to the invention comprise a metal component from Group VIII and a zeolite component. Preferably, the zeolite is a zeolite with large or medium-sized pores.

An example of a zeolite with medium-sized pores is silicalite. It has an apparent pore size of between 5 Å and 6 Å.

The composition for silicalite, expressed in molar ratio between oxides in the anhydrous state, can be represented as follows:

where M is a metal which, however, is not from Group HIA, n is the valence of said metal, R is an alkylammonium radical and x is a number greater than 0 but not exceeding 1.

Silicalite is described in US Patent Nos. 4,309,275, 4,579,831, 4,517,306 and Re. 29,948. Silicalite can also contain metals from Group IA or Group IIA.

Large-pore zeolites are defined as zeolites with an effective pore diameter of between 6 and 15 Å. The method according to the invention can be used on catalysts containing zeolite of type L, zeolite X, zeolite Y and faujasite. All these zeolites have apparent pore sizes of the order of 7-9 Å.

The material of the L-zeolite type, indicated by the molar ratio between oxides, can be represented by the following formula: (0.9-1.3)M2/nO:Al2O3( 5.2-6.9 )Si02:yH20 where M denotes a cation, n denotes the valence of M, and y can have any value from 0 to 9. Zeolite L, its X-ray diffraction pattern and properties, and the method of its preparation are described in detail in US Patent No. 3,216,789. The actual formula may vary, without this changing the crystalline structure. For example, the molar ratio between silicon and aluminum (Si/Al) can vary from 1.5 to 3.5.

The chemical formula for zeolite Y, indicated by the number of moles of oxides, can be written:

where x has a value between 3 and 6, and y has a value up to approx. 9. Zeolite Y has a characteristic X-ray diffraction pattern which can be used for identification, together with the above formula. Zeolite Y is described in more detail in US Patent No. 3,130,007 and is applicable to the present invention.

Zeolite X is a synthetic, crystalline, zeolitic molecular sieve that can be represented by the formula:

where M denotes a metal, especially alkali and alkaline earth metals, n is the valence of M, and y can have any value up to 8, depending on the identity of M and the degree of hydration of the crystalline zeolite. Zeolite X, its X-ray diffraction pattern and properties and the method for its production are described in detail in US Patent No. 2,882,244 and are applicable to the present invention.

The zeolite catalysts that can be regenerated according to invention, preferably contains exchangeable cations. Common cations which are applicable for catalysts according to the invention are cations from Groups IA (alkali metals) and IIA (alkaline earth metals). When alkali metals are used, sodium, potassium, lithium, rubidium or cesium are preferred. When metals from Group IIA, i.e. alkaline earth metals, are used, either barium, calcium or strontium is preferred. However, barium is most preferred. The alkaline earth metal can be incorporated into the zeolite by synthesis, impregnation or ion exchange.

In the present method of regeneration, it is important that the catalyst contains at least one metal from Group VIII. Preferably, the Group VIII metals are ruthenium, rhodium, osmium, iridium or platinum, more preferably platinum or iridium, and most preferably platinum. (When a specific Group VIII metal is referred to herein, this represents the group.) The preferred percentage of the Group VIII metal in the catalyst is between 0.1% and 5%.

Metals from Group VIII are introduced into the large-pore zeolite during synthesis, or after synthesis, by impregnation or ion exchange using an aqueous solution of a suitable salt. If it is desired to introduce two metals from Group VIII into the zeolite, the operations can be carried out simultaneously or one after the other.

For example, platinum can be introduced by impregnating or ion-exchanged the zeolite with an aqueous solution of tetrammine platinum(II) nitrate [Pt (NH3 )4] (N03 )2, tetrammine platinum(II) chloride [Pt(NH3)4]Cl2 or dinitrodiaminoplatinum [Pt (NH 3 ) 2 ( NO 2 ) ] .

An inorganic oxide is preferably used as a matrix to bind the catalyst together. This binder can be a naturally occurring or synthetically produced inorganic oxide or combination of inorganic oxides. Typical inorganic oxide binders that can be used are clay materials, aluminum oxide and silicon dioxide. Acidic sites on the binder are preferably ion-exchanged with cations that do not give strong acidity (such as Na, K, Rb, Cs, Ca, Sr or Ba).

The method of regeneration according to the present invention can be used for catalysts in the form of extrudates, pills, pellets, granules, broken pieces or various other special forms.

During reforming, carbon also accumulates on the catalyst, and this too must be removed at intervals. In a preferred embodiment of the present invention, carbon is removed by burning carbon in an oxygen-containing atmosphere before sulfur is removed. During carbon combustion, the amount of oxygen is in the range between 0.1 vol% and 2.0 vol% (all gas volumes are calculated in vol.). When more than 0.5% oxygen is present in the gas, care must be taken to reduce the catalyst temperature to a minimum , until the carbon content has been significantly reduced. Nitrogen or other inert gas is preferably present in sufficient quantity to make up the rest of the gas. The GHSV (= Gas Hourly Space Velocity = gas space velocity per hour) used in the carbon burning is preferably in the range between approx. 50 and 5000, more preferably between 150 and 1500. The pressure is preferably in the range between 1 and 30 atmospheres, more preferably between 1 and 10 atm. The temperature is preferably in the range between 260°C and 482°C. The duration of this carbon burning step is preferably between 1 and 24 hours.

Regeneration of sulfur-contaminated catalysts is carried out using a method which includes the features of deliberately agglomerating the platinum on the catalyst and removing the sulfur with a halogen acid gas. The regeneration process has at least two basic embodiments. In one embodiment, the platinum is agglomerated in the oxidizing gas at high temperature. Sulfur is then removed with a halogen acid gas. In another embodiment, the platinum is agglomerated and the sulfur removed in one step with a carbon monoxide/halogen acid gas mixture.

Preferably, the platinum on the catalyst is agglomerated into agglomerates with a diameter greater than 50 Å, more preferably greater than 75 Å, most preferably greater than 150 Å. The amount of platinum on the catalyst that is agglomerated is preferably greater than 50% by weight of the platinum, more preferably greater than 75% by weight and most preferably greater than 90% by weight. The platinum agglomerates can have different shapes and their "diameters" can vary. They can be spherical, cube-shaped, pyramidal, cuboid-octahedral or irregular in shape.

Agglomeration in an oxidizing gas abbreviated as AIOG (Agglomeration In an Oxidizing Gas) involves general conditions that are stricter than those used during carbon burning, although some of the conditions at these treatment steps may overlap.

When the platinum is agglomerated in an oxidizing gas, the gas preferably contains between 1 vol% and 50 vol% oxygen, more preferably between 2 vol% and 21 vol% oxygen, in the total gas volume. Preferably, the oxygen is diluted with an inert gas, such as e.g. nitrogen. The AIOG temperature is preferably between 427°C and 649°C, more preferably between 482°C and 566°C. The duration of the oxidation is preferably between 1 hour and 100 hours, more preferably between 8 hours and 50 hours. However, it should be noted that in order to agglomerate the platinum to the desired degree, the time, temperature and oxygen concentration can be varied in relation to each other and that it may be necessary to increase one of the factors to compensate for inadequacy in a second of the factors.

After AIOG is performed, a reducing gas is contacted with the catalyst to transfer the oxidized sulfur into a form in which it can be removed from the catalyst with a halogen acid gas. Hydrogen, carbon monoxide or another reducing gas (e.g. a light hydrocarbon) can make up part of the gas or all of the gas. The concentration of the reducing gas is preferably higher than 10% of the total gas volume and more preferably constitutes between 50% and 99% of this. In this embodiment, hydrogen is preferred as the reducing gas for practical reasons such as availability, purity, lack of toxicity, etc.

In order to remove the reduced sulphur, it has been found appropriate to bring the catalyst into contact with a halogen acid gas, either in a subsequent treatment step or, more preferably, at the same time as the catalyst is brought into contact with the reducing gas (the treatment gases must not contain any sulphur) . Examples of halogen acids are hydrogen chloride, hydrogen bromide and hydrogen iodide. Hydrogen chloride is specifically preferred. Hydrogen fluoride is not preferred. By the term "halogen acid" (or any specific halogen acid) is also meant any precursor which will form the halogen acid gas in situ under the specific conditions under which it is used. Precursor compounds for hydrogen chloride are e.g. phosgene, CH3C1, CH2C12 and CC14, etc.

If the halogen acid gas is brought into contact with the catalyst in a step carried out after the reduction, it may be present in a carrier gas. A preferred carrier gas is either an inert gas, such as e.g. nitrogen, or a reducing gas. The halogen acid gas preferably constitutes more than 0.1% of the total gas volume, more preferably more than 1% and most preferably between 2% and 5%, of this. The reducing gas and the gas containing the halogen acid are preferably brought into contact with the catalyst at a temperature in the range between 427°C and 649°C, more preferably between 427°C and 538°C and most preferably between 482°C and 538°C. The pressure is preferably between 1 and 30 atm, more preferably between 1 and 10 atm. The gas velocity is preferably a GHSV of between 50 and 5000, more preferably between 150 and 1500. The time the catalyst is in contact with the reducing gas and the gas containing the halogen acid is preferably longer than 1 hour, more preferably 8-50 hours.

Agglomeration in a carbon monoxide-halogen acid mixture, abbreviated COSG (carbon monoxide-halogen acid-qass), means that preferably a gaseous mixture of carbon monoxide (CO) and a halogen acid is brought into contact with the catalyst at the same time to both agglomerate the platinum and remove the sulphur. In this embodiment, the CO and the halogen acid (e.g. HC1) must be mixed together. The gas combination is called the COSG mixture.

In the same way as in the previous embodiment, the halogen acid can be formed in situ. Also in this embodiment, HC1 is preferred. The amount of halogen acid (eg HCl) in the COSG mixture is preferably greater than 0.1%, more preferably greater than 1%. Preferably, the CO concentration is higher than 2%, with a more preferred range being 50%-99%. The COSG mixture is contacted with the catalyst at a temperature which is preferably in the range between 427°C and 649°C, more preferably between

427°C and 538°C, most preferably between 482°C and 538°C. The pressure is preferably between 1 and 30 atm, more preferably between 1 and 10 atm. The gas velocity GHSV is preferably between 50 and 5000, more preferably between 150 and 1500. The time during which the catalyst is kept in contact with the COSG mixture is preferably longer than 1 hour, more preferably longer than 3 hours and most preferably longer than 24 hours.

The COSG mixture can be prepared by bringing a stream consisting of 100% CO into intimate contact with an aqueous HCl solution. Water is preferably present in the mixture in an amount of between 0 and 10%.

As a result of the previous steps in the method according to the invention, the metal atoms are from Group

VIII (e.g. platinum) has been strongly agglomerated. The average diameter of the agglomerates is in typical cases between 150 and 300 Å, and each agglomerate contains approximately from 200,000 to 2,000,000 platinum atoms. If the catalyst is to be able to exhibit significant activity for aromatization, the platinum must be redispersed in the zeolite in the form of platinum particles which are preferably smaller than 50 Å, more preferably smaller than 25 Å, most preferably smaller than 10 Å.

Many redispersion procedures are available. However, a preferred method for redispersing metal from Group VIII is an oxychlorination procedure which involves bringing the catalyst into contact at elevated temperature with an oxygen-containing gas and then a chloride-containing gas, with subsequent purification with nitrogen and reduction with hydrogen. The three main steps are outlined below.

In the first step, the catalyst with platinum agglomerates is brought into contact with a gaseous mixture of oxygen, water and chlorine or a chloride. The oxygen is preferably present in a concentration higher than 0.1%, more preferably in an amount between 1% and 21% and most preferably in an amount between 2% and 6%, of the total gas volume. Water is preferably present in an amount of from 0% to 10%, more preferably from 1% to 4% and most preferably from 2% to 3%. The chloride or chlorine is preferably present in an amount which is sufficient to give a quantity ratio between chlorine atoms and platinum atoms that is higher than 4:1, more preferably in the range between 4:1 and 1000:1, even more preferably in the range between 5:1 and 200:1, and further preferred in the range between 10:1 and 50:1. Either a chlorine-containing or a chloride-containing gas can be used, but it is preferred to use a chloride, e.g. hydrogen chloride or an organic chloride, such as carbon tetrachloride, etc. The preferred temperatures in this first step of the oxychlorination process are between 427°C and 593°C, more preferably between 482°C and 538°C, most preferably between 496°C and 524°C. The duration of this first step is preferably from 1 to 24 hours, more preferably from 1 to 3 hours. The gas velocity is preferably a GHSV of between 50 and 5000, more preferably between 150 and 1500. The pressure is preferably between 1 and 30 atm, more preferably between 1 and 10 atm.

In the second step, the catalyst is preferably brought into contact with dry nitrogen (or other inert gas) for a sufficiently long time to clean the catalyst layer of oxygen. (By "dry" is meant that the water content is preferably less than 1000 ppm, more preferably less than 500 ppm and most preferably less than 100 ppm. ) The cleaning time is preferably between 0.1 and 5 hours, more preferably between 0.1 and 2 hours, and most preferably between 0.5 and 1 hour. The temperature is preferably between 316°C and 538°C, more preferably between 454°C and 510°C, and most preferably between 469°C and 407°C. The gas velocities and pressures are preferably in the same ranges as for the first stage.

In the third and final step, the catalyst is brought into contact with dry hydrogen for a sufficient time to reduce practically all of the platinum. The duration of this step is dependent on the flow rate and the reduction temperature. From commercial considerations, a short time is preferred, preferably shorter than 5 hours, more preferably less than 2 hours. The temperature is preferably between 316°C and 538°C, more preferably between 427°C and 510°C and most preferably between 469°C and 496°C. The gas velocities and pressures are preferably in the same ranges as for the first and second stages.

An oxygen post-treatment step can be interleaved between the first step (oxychlorination step) and the second step (nitrogen cleaning step). During the oxygen aftertreatment, the catalyst is preferably kept in contact for up to 3 hours with an oxygen-containing gas which has an oxygen concentration higher than 0.1%, more preferably between 1% and 21%. The temperature is preferably between 427°C and 538°C, more preferably between 482°C and 524°C. Water is preferably present in an amount of between 0 and 10%, more preferably between 1 and 4%, most preferably between 2 and 3%. The gas velocities and pressures are preferably in the same ranges as in the oxychlorination procedure.

EXAMPLES

The following examples are summarized in Table I.

All the consecutive steps in Examples 1-13 were carried out at a pressure of 1 atm and with a gas flow rate GHSV of 150. Examples 1-7 describe the removal of sulfur according to the COSG embodiment. Examples 1-3 show that at least 50% of the sulfur can be removed with a mixture of CO, HC1 and H20 for at least 3 hours, and that 94% of the sulfur can be removed within 102 hours. These examples also show that the larger the platinum agglomerates that are formed, the more sulfur is removed.

Example 1

A catalyst containing 0.8 wt% platinum on a barium-potassium L-zeolite containing 8 wt% barium was sulfided until it had taken up 325 ppm sulfur and had been substantially deactivated for paraffin dehydrocyclization (as measured by an isothermal test where a light naphtha feedstock containing mostly C6-C8 paraffins was reformed at 493°C, a pressure of 689 kPa and an LHSV of 6). This catalyst was designated "Catalyst A", and samples of this were also used in later examples.

Catalyst A was treated according to the COSG embodiment. Catalyst A was contacted with a gas stream consisting of 1% O 2 and 99% N 2 at 482°C for 16 hours. It was then contacted with a CO gas stream that had been bubbled through a 34.5% by weight HCl solution at room temperature. This gave a nominal gas composition of approximately 0.5% H2O, 10% HC1 and the remainder CO. This treatment was carried out during 102 hours at 482°C. The catalyst was then cooled in flowing nitrogen to ambient temperature. The catalyst's sulfur concentration after treatment was 20 ppm. Photographs taken by transmission electron microscopy (TEM) showed that the catalyst contained platinum agglomerates with diameters in the range between 40 Å and 340 Å. The most frequently occurring agglomerate size was 180 Å. 70% of the agglomerate diameters were between 140 Å and 240 Å.

Example 2

Another catalyst, containing 0.8 wt% platinum on a barium-potassium L-zeolite containing 8 wt% barium, was subjected to sulfidation until it had taken up about 400 ppm sulfur and had been substantially deactivated for paraffin dehydrocyclization. This catalyst will be designated "Catalyst B", and samples were also used in other examples.

Catalyst B was also treated according to the COSG embodiment. Catalyst B was contacted with a gaseous stream of 1% O 2 and 99% N 2 , at 482°C and for 19 hours. It was then contacted with a gaseous CO stream which had been bubbled through a 32% by weight aqueous HCl solution at room temperature. This gave a nominal gas composition of 3.5% HC1, 1% H20 and the rest CO. Contact with the reducing gas lasted 24 hours, and the temperature was 482°C. The catalyst was then cooled to ambient temperature in flowing nitrogen. After the treatment, the sulfur concentration was 78 ppm. The platinum agglomerate size was between 30 Å and 80 Å.

Example 3

Another sample of Catalyst A was processed according to the COSG embodiment. Catalyst A was kept in contact with a gas stream consisting of 1% O 2 and 99% N 2 at 482 °C for 24 hours. It was then kept in contact with a gaseous CO stream which had been bubbled through 34.5% by weight HCl solution, so that a nominal gas composition of 10% HCl, 0.5% H2O and the balance CO had been obtained. . It was treated with this gas at 482°C for 3 hours. Finally, the catalyst was cooled to room temperature in flowing nitrogen. After the treatment, the sulfur concentration was 160 ppm.

Example 4

A comparison between examples 4 and 2 shows that sulfur can be removed from the catalyst without a prior oxidation step.

Another sample of Catalyst B was also treated according to the COSG embodiment. Catalyst B was contacted with a gaseous CO stream that had been bubbled through a 32% by weight aqueous HCl solution at room temperature. This gave the nominal gas composition 3.5% HC1, 1% H20 and the rest CO. The catalyst was exposed to this gas for 21 hours at 482°C. The catalyst was then cooled in flowing nitrogen to ambient temperature. After the treatment, the sulfur concentration was 138 ppm.

Example 5

A comparison of example 5 with examples 1-3 shows that sulfur can be removed in a shorter time when the temperature is increased.

Another sample of Catalyst A was also processed according to the COSG embodiment. Catalyst A was oxidized in 1% O 2 in 99% N 2 at 527°C for 3 hours. It was then treated with a gas mixture containing 3.5% HCl and 1% H 2 O, the remainder being CO, at 566°C for 3 hours. The catalyst was then cooled to room temperature in flowing nitrogen. After the treatment, the sulfur concentration was 98 ppm.

Example 6

Example 6 shows that water is not necessary to achieve the removal of sulphur.

Another catalyst containing 0.8 wt% platinum on a barium-potassium L-zeblite containing 8 wt% barium was sulfided until it had taken up 440 ppm sulfur and had been substantially deactivated, as measured by dehydrocyclization of paraffin.

Also the deactivated catalyst was treated according to the COSG embodiment. The catalyst was first contacted with a gaseous stream of 1% O 2 and 99% N 2 at 482 °C for 3 hours. It was then kept in contact with a mixture of 50% HCl and 50% CO at 482°C for 3 hours. After the treatment, the sulfur concentration was 184 ppm.

Example 7

Example 7 shows that a halogen acid precursor can be used to remove sulfur from the catalyst.

A sample of Catalyst B was treated according to the COSG embodiment, with the exception that carbon tetrachloride

(CC14) was used as the source of the halogen acid gas. The catalyst was first treated with 1% O 2 and 99% N 2 for 2 hours at 482°C. Then it was treated with 1% CC14, 2.8% H2O and the rest CO for 4 hours at 482°C. Said CC14 was injected into the CO stream which was saturated with water at room temperature by means of a syringe pump. Using this technique, approx. 10% more total chloride in the gas stream than was present in the gas mixture consisting of 3.5% HC1, 1% H20 and the rest CO. After 4 hours of treatment, this sample was cooled to room temperature in flowing nitrogen. After the treatment, the sulfur concentration was 131 ppm.

Example 8

Example 8 describes sulfur removal using a combination of the COSG and AOIG embodiments.

Another catalyst, comprising 0.8% by weight of platinum on a barium-potassium-L-zeolite containing 8% by weight of barium, was sulphided until it had taken up approx. 317 ppm sulfur and had been substantially deactivated for paraffin dehydrocyclization. This catalyst was designated "Catalyst C" and was used in later examples.

First, Catalyst C was heated with 1% O 2 in 99% N 2

for 16 hours at 649°C. Then it was treated with a mixture consisting of 3.5% HCl, 1% H 2 O and the rest CO at 482°C for 48 hours. This mixture was prepared by bubbling CO through an aqueous solution containing 32% by weight of HC1 at room temperature. After the treatment, the catalyst's sulfur concentration was 26 ppm.

Example 9

Examples 9-13 describe the removal of sulfur according to the AIOG embodiment.

A sample of Catalyst C was first contacted with a gaseous stream of 1% O 2 in 99% N 2 at 649°C for 16 hours. The size of the platinum agglomerates was in the range between 10 and 800 Å. Many particles had a diameter of approx. 60 Å. Then the catalyst was kept in contact with a mixture consisting of 3.5 HCl, 1% H 2 O and the rest H 2 at 482°C for 48 hours. This mixture was prepared by bubbling H2 through an aqueous solution containing 32% by weight of HC1 at room temperature. The catalyst's sulfur concentration after treatment was 19 ppm.

Example 10

Example 10 shows that sulfur can be removed when the catalyst is treated with a mixture of H2, HC1 and H2O at 427°C.

Another catalyst comprising 0.8% by weight of platinum on a barium-potassium-L-zeolite containing 8% by weight of barium was sulphided until the catalyst had taken up approx. 260 ppm sulfur and had been substantially deactivated for paraffin dehydrocyclization.

The deactivated catalyst was treated according to the AIOG embodiment. The catalyst was kept in contact with 1% O 2 in 99% N 2 at 649°C for 16 hours. Then it was kept in contact with a mixture consisting of 3.5% HCl, 1% H 2 O and the rest H 2 at 427°C for 48 hours. This gas was formed by bubbling H2 at room temperature through an aqueous solution containing 32% by weight of HC1. The catalyst's sulfur concentration after treatment was 75 ppm.

Example 11

This example shows that it is advantageous to treat the catalyst simultaneously with the reducing gas and the halogen acid gas.

A sample of Catalyst C was processed according to a modification of the AIOG embodiment. Catalyst C was contacted with 1% O 2 in 99% N 2 at 649°C for 16 hours. It

was then kept in contact with dry hydrogen at 482°C for 24 hours. Finally, the catalyst was treated for 24 hours at 482°C with a gaseous mixture consisting of 3.5% HCl, 1% H 2 O and the balance N 2 . This mixture was formed by bubbling N2 at room temperature through an aqueous solution containing 32% by weight of HC1. After treatment, the catalyst's sulfur concentration was 191 ppm.

Example 12

This example shows that hydrogen bromide (HBr) can be used instead of hydrogen chloride.

Another catalyst comprising 0.8 wt% platinum, 8 wt% barium and L-zeolite was sulfided until it had taken up 191 ppm sulfur and had been substantially deactivated for paraffin dehydrocyclization.

The deactivated catalyst was subjected to the AIOG embodiment. The catalyst was kept in contact with a gaseous stream consisting of 1% O 2 in 99% N 2 at 649°C for 32 hours. Then for 48 hours it was kept in contact at 482 °C with a gaseous stream consisting of 3.0% HBr and 14.4% H 2 O in H 2 . The gaseous stream was formed by injecting 0.1 ml/h of an aqueous HBr solution containing 48% by weight HBr continuously into the hydrogen for the 48 hours. The catalyst's sulfur concentration after treatment was 78 ppm.

Example 13

This example shows that oxidation at 538°C leads to sufficient agglomeration of the platinum to enable the removal of sulphur.

Another catalyst comprising 0.8 wt% platinum on a barium-potassium L-zeolite containing 8 wt% barium was sulfided until it had taken up 313 ppm sulfur and had been substantially deactivated for paraffin dehydrocyclization.

This deactivated catalyst was treated according to the AIOG embodiment. It was first contacted for 16 hours at 538°C with a gaseous stream of 1% O 2 in 99% N 2 . This treatment resulted in the formation of platinum agglomerates of sizes in the range from 10 to 100 Å, the most common size being approx. 60 Å. Then the catalyst was kept in contact for 48 hours at 482°C with a mixture consisting of 3.5 HCl, 1% H 2 O and the rest H 2 . This mixture was formed by bubbling H2 at room temperature through an aqueous solution containing 32% by weight of HC1. The catalyst's sulfur concentration after treatment was 70 ppm.

Example 14

This example shows an oxychlorination procedure.

A catalyst comprising 0.8 wt% platinum on a barium-potassium L-zeolite containing 8 wt% barium was reduced for 1 h at 482 °C in H 2 and then purged with N 2 . Then the catalyst was heated in dry air for 3 hours at 538°C and 1 atm. This reduced the dehydrocyclization activity to 50% of the fresh catalyst's activity. Furthermore, the platinum had been agglomerated by this treatment. TEM showed that approx. 70% of the platinum agglomerates had a diameter between 70 Å and 80 Å.

To redisperse the platinum and restore the catalyst's activity, the catalyst was subjected to an oxychlorination procedure. This procedure was carried out as follows: The catalyst was kept in contact with moist air for 2 hours at a GHSV of 1400, 1 atm and a temperature of 510°C, while chlorine was injected as CC14 in sufficient quantity to expose the catalyst to 20 chlorine atoms per platinum atom. Then the supply of moist air was continued with a GHSV of 1400 at a temperature of 510°C for 1 hour without injection of CC14. Dry nitrogen was then introduced for 1 hour with a GHSV of 1400, at 1 atm and 482°C. After this, the catalyst was kept in contact with dry hydrogen for 1 hour, with a GHSV of 1400, 1 atm and a temperature of 482°C. The catalyst was tested for paraffin dehydrocyclization and the activity was found to be the same as that of the fresh catalyst. Moreover, TEM showed that the platinum had been redispersed as a result of the treatment. All the platinum was present in agglomerates less than 10 Å in diameter.

Example 15

This example shows the combination of the sulfur removal procedure and the platinum redispersion procedure.

The treated catalyst from Example 2 contained 78 ppm sulfur and was inactive even when dehydrogenating cyclohexane. It contained cubic platinum agglomerates with an edge length of 30-80 Å.

To restore the activity and redisperse the platinum, the catalyst was subjected to an oxychlorination step. The catalyst was kept in contact with moist air supplied at a flow rate GHSV of 1400, at 1 atm and at a temperature of 538°C for 1 hour. Then the catalyst was kept in contact for 2 hours with moist air supplied with a GHSV of 1400 at a temperature of 482°C, while chloride was injected in the form of CC14. The total amount of injected CC14 corresponded to 20 chlorine atoms per platinum atom. Then the supply of moist air was continued with a GHSV of 1400 at 482°C for another 1 hour without injection of CC14. Then dry nitrogen was kept in contact with the catalyst for 10 minutes, at a GHSV of 1400 and 482°C. After this, dry hydrogen was kept in contact with the catalyst for 1 hour at a GHSV of 1400 and a temperature of 482°C. The catalyst was then analyzed by TEM, and it was found that the only visible platinum was present in the form of agglomerates of size 10 Å or less. The catalyst was tested for paraffin dehydrocyclization and it was found to exhibit approx. 40% of the activity of the fresh catalyst (both measurements were made after 20 hours in operation).

Claims (27)

1. Method for regenerating a sulfur-contaminated catalyst comprising a large-pore zeolite, preferably an L-zeolite, optionally a zeolite with a medium pore size, preferably a silicalite, and a metal from Group VIII chosen from platinum, rhodium, ruthenium, iridium and osmium, characterized in that the metal from Group VIII is agglomerated by keeping the catalyst in contact with an oxygen-containing gas at a temperature between 427 °C and 649 °C and that sulfur is then removed from the catalyst by keeping it in contact with a halogen acid gas that does not contain sulphur. 2. Method according to claim 1, characterized in that more than 50% of the platinum is agglomerated into agglomerates with a diameter greater than 50 Å. 3. Method according to claim 1, characterized in that more than 50% of the platinum is agglomerated into agglomerates with a diameter greater than 75 Å. 4. Method according to claim 1, characterized in that more than 50% of the platinum is agglomerated into agglomerates with a diameter greater than 150 Å. 5. Method according to claims 1-4, characterized in that the catalyst is kept in contact with an oxygen-containing gas containing between 1 and 50% oxygen, at a gas velocity GHSV of between 50 and 5000 and a pressure of between 1 and 30 atm, for a period of time of between 1 and 100 hours. 6. Method according to claims 1-4, characterized in that the catalyst is kept in contact with a gas containing between 2% and 21% oxygen, at a temperature between 482°C and 566°C and at a gas velocity GHSV of between 150 and 1500, at a pressure of between 1 and 10 atm and for a time between 8 and 50 hours. 7. Process according to claims 1-4, characterized in that hydrogen chloride is used as the halogen acid. 8. Method according to claims 1-4, characterized in that the catalyst is brought into contact with a reducing gas, either before or simultaneously with the halogen acid. 9. Method according to claim 8, characterized in that a reducing gas selected from carbon monoxide and hydrogen is used. 10. Method according to claim 9, characterized in that the catalyst is brought into contact with the reducing gas at the same time as it is brought into contact with the halogen acid. 11. Method according to claim 10, characterized in that the catalyst is brought into contact with a gas comprising more than 0.1% hydrogen chloride in hydrogen, for a time longer than 1 hour, at a temperature between 427°C and 649°C, at a pressure between 1 and 30 atm and at a gas velocity GHSV of between 50 and 5000. 12. Method according to claim 10, characterized in that the catalyst is brought into contact with a gas comprising more than 1% hydrogen chloride in hydrogen, for between 8 and 50 hours, at a temperature between 427°C and 538°C, at a pressure between 1 and 10 atm and using a gas velocity GHSV of between 150 and 1500. 13. Method according to claim 1, characterized in that the catalyst is brought into contact with a gas containing between 0.1% and 2.0% oxygen, at a temperature between 260°C and 482°C, at a pressure between 1 and 30 atm , using a gas velocity GHSV of between 50 and 5000, for a time between 1 and 24 hours, to remove carbon from the catalyst before the platinum agglomerates. 14. Method for regenerating a carbon and sulfur contaminated catalyst comprising a large pore zeolite and platinum, characterized in that: (a) the catalyst is brought into contact with a gas containing between 0.1% and 2.0% oxygen, at a temperature between 260°C and 482°C, at a pressure between 1 and 10 atm, in use of a gas velocity GHSV of between 150 and 1500, for a time between 1 and 24 hours, to remove carbon from the catalyst, (b) the catalyst from step (a) is brought into contact with a gas containing between 2% and 21% oxygen, at a temperature between 482°C and 566°C, using a gas velocity GHSV of between 150 and 1500, at a pressure between 1 and 10 atm, for a time between 8 and 50 hours, to agglomerate the platinum, and (c ) the catalyst from step (b) is contacted with a gas comprising more than 1% hydrogen chloride in hydrogen, for a time between 8 and 50 hours, at a temperature between 427°C and 538<*>C, at a pressure between 1 and 10 atm, and using a gas velocity GHSV of between 150 and 1500, to remove sulphur. 15. Method according to claim 14, characterized in that the catalyst is brought into contact with a chloride or chlorine-containing gas under oxy-chlorination conditions to redisperse the platinum. 16. Method according to claim 14, characterized in that the platinum is agglomerated and the sulfur is removed by bringing the catalyst into contact with a halogen acid at the same time as it is brought into contact with carbon monoxide. 17. Method according to claim 16, characterized in that hydrogen chloride is used as the halogen acid. 18. Method according to claim 16, characterized in that the platinum is agglomerated and the sulfur is removed from the catalyst by bringing the catalyst into contact with a gas containing more than 2% carbon monoxide and more than 0.1% hydrogen chloride, at a pressure between 1 and 30 atm , using a gas velocity GHSV of between 50 and 5000, at a temperature between 427°C and 649°C, for more than 1 hour. 19. Method according to claim 16, characterized in that the platinum is agglomerated and the sulfur is removed from the catalyst by bringing the catalyst into contact with a gas containing between 50 and 99% carbon monoxide and more than 1% hydrogen chloride, at a pressure between 1 and 10 atm, using a gas velocity GHSV of between 150 and 1500 and at a temperature between 427°C and 538°C, for more than 3 hours. 20. Method according to claim 16, characterized in that the catalyst is brought into contact with a gas containing between 0.1% and 2.0% oxygen, at a temperature between 260°C and 482°C, at a pressure between 1 and 30 atm , using a gas velocity GHSV of between 50 and 5000, for a time between 1 and 24 hours, to remove carbon from the catalyst before agglomeration of the platinum. 21. Method for regenerating a carbon and sulfur contaminated catalyst comprising a large pore zeolite and platinum, characterized in that: (a) the catalyst is brought into contact with a gas containing between 0.1% and 2.0% oxygen, at a temperature between 260°C and 482°C, at a pressure between 1 and 10 atm, and at using a gas velocity of between 150 and 1500 GHSV, for a time between 1 and 24 hours, to remove carbon from the catalyst, and (b) contacting the catalyst from step (a) with a gas comprising more than 1% hydrogen chloride and between 50 and 99% carbon monoxide, at a temperature between 427°C and 538°C, for more than 3 hours, using a gas velocity GHSV of between 150 and 1500 and a pressure between 1 and 10 atm, to both agglomerate platinum and remove sulphur. 22. Method according to claim 21, characterized in that the catalyst is brought into contact with a chloride or chlorine-containing gas under oxy-chlorination conditions to redisperse the platinum. 23. Method according to claim 22, characterized in that the oxychlorination conditions include sufficient contact between the catalyst and the chloride or chlorine-containing gas to achieve a ratio corresponding to more than 4 chlorine atoms for each platinum atom. 24. Method according to claim 23, characterized in that the oxychlorination conditions include contact between the catalyst and a sufficient amount of the chloride or chlorine-containing gas to achieve a ratio between chlorine atoms and platinum atoms of between 4:1 and 1000:1. 25. Method according to claim 24, characterized in that the oxychlorination conditions include the features of: (a) bringing the catalyst into contact with a chloride- or chlorine-containing gas in the presence of an oxygen-containing gas containing more than 0.1% 02, in between 1 and 24 hours, (b) purging the catalyst with a dry inert gas at a temperature between 316°C and 538°C for a time between 0.1 and 5 hours, and (c) contacting the catalyst with dry hydrogen at a temperature between 316 °C and 538 °C for a time less than 5 hours. 26. Process for the regeneration of a carbon and sulfur contaminated, monofunctional, large pore zeolite reforming catalyst comprising platinum and L-zeolite, characterized in that it comprises: (I) a step for removing carbon according to which one: (a) brings the catalyst in contact with a gas containing between 0.1% and 2.0% oxygen, at a temperature between 260°C and 482°C, using a gas velocity GHSV of between 150 and 1500, at a pressure between 1 and 10 atm, for between 1 and 24 hours, to remove carbon from the catalyst, (II) a step for agglomeration of platinum and removal of sulfur, according to which one: (a) brings the catalyst from step (I) (a) in contact with a gas containing between 2% and 21% oxygen, at a temperature between 482°C and 566°C, using a flow rate GHSV of between 150 and 1500, and a pressure between 1 and 10 atm, in a time between 8 and 50 hours, to agglomerate the platinum, (b) contacting the catalyst from step (II) (a) with a gas comprising between 2% and 5% hydrogen chloride in hydrogen, for a time between 8 and 50 hours, at a temperature between 482°C and 538°C, at a pressure between 1 and 10 atm and using a gas velocity GHSV of between 150 and 1500, to remove sulphur, (III) an oxychlorination procedure to redistribute the platinum, according to which one: (a) brings the catalyst from step (II)(b) into contact with a chloride-containing compound in a gas containing between 1% and 21% oxygen and from 1% to 4% water in an amount sufficient to provide between 5 and 200 chloride atoms per platinum atom, for a time between 1 and 3 hours, at a temperature between 482°C and 538°C and a pressure between 1 and 10 atm, (b) stops the flow of the gas in step (III)(a) and brings the catalyst in contact with dry nitrogen at a temperature between 454°C and 510°C, at a pressure between 1 and 10 atm, and using a gas velocity GHSV of between 150 and 1500, for a time between 0.1 and 2.0 hours , and (c) contacting the catalyst with dry hydrogen at a temperature between 427°C and 510°C and a pressure between 1 and 10 atm, for less than 2 hours, using a gas velocity GHSV of between 150 and 1500. 27. Process for the regeneration of a carbon and sulfur contaminated, monofunctional, large pore zeolite reforming catalyst comprising platinum and L-zeolite, characterized in that it comprises: (I) a step for removing carbon, according to which one: (a) contacting the catalyst with a gas containing between 0.1% and 2.0% oxygen, at a temperature between 260°C and 482°C, using a gas velocity GHSV of between 150 and 1500, at a pressure between 1 and 10 atm, for a time between 1 and 24 hours, to remove carbon from the catalyst, (II) a stage for agglomeration of platinum and removal of sulphur, according to which one: (a) brings the catalyst from stage (I)( a) in contact with a gas comprising more than 1% hydrogen chloride in carbon monoxide, at a temperature between 482°C and 538°C, at a pressure between 1 and 10 atm, for more than 24 hours, and using a gas velocity GHSV of between 150 and 1500, (III) an oxychlorination procedure to redistribute the platinum, according to which m an: (a) contacting the catalyst from step (II)(b) with a chloride-containing compound in a gas containing between 1% and 21% oxygen and from 1% to 4% water in an amount sufficient to provide between 5 and 200 chloride atoms per platinum atom, for a time between 1 and 3 hours, at a temperature between 482°C and 538°C and a pressure between 1 and 10 atm, (b) stops the flow of the gas in step (III)(a) and brings the catalyst in contact with dry nitrogen at a temperature between 454°C and 510°C, at a pressure between 1 and 10 atm, and using a gas velocity GHSV of between 150 and 1500, for a time between 0.1 and 2.0 hours , and (c) contacting the catalyst with dry hydrogen at a temperature between 427°C and 510°C and a pressure between 1 and 10 atm, for less than 2 hours, using a gas velocity GHSV of between 150 and 1500.