Reactivation of Noble Metal-Containing Zeolite Catalyst Materials

1. Field of the Invention

The invention relates to a process of reactivating catalysts. In particular, it relates to the reactivation of nobel metal-containing zeolite catalysts which have been deactivated by coke build-up. Catalysts which may be reactivated by the process of the present invention include those that have become deactivated during hydrocarbon hydroprocesses, such as the reforming or catalytic dewaxing of hydrocarbon feedstocks.

2. Discussion of the Prior Art

Reactivation of platinum catalysts utilized in hydrocarbon hydroprocessing procedures such as reforming is known in the art. Processes which utilize chlorine and oxygen in catalyst reactivation are particularly well-known. For example, U.S. Pat. No. 2,906,702 to Brennan et al discloses a method of restoring an alumina-supported platinum catalyst after deactivation occurring during the reforming of hydrocarbons. This method teaches contacting a deactivated platinum-alumina catalyst with a gaseous chlorine, fluorine, or other halogen or halogen-affording substance at an elevated temperature. U.S. Pat. No. 3,134,732 to Kearby at al teaches a method for reactivating noble metal catalyst supported on alumina by contacting the catalyst with halogen-containing gas, stripping excess halogen therefrom, and subjecting the resulting catalyst to a reduction step with a hydrogen-containing gas. In this disclosure, the agglomerated metal is present on the surface of the alumina as small crystallites. It is also known in the art to regenerate noble metal- and platinum group metal-containing zeolite catalysts. Regeneration of noble metal-loaded zeolite catalysts requires certain procedural modifications to regain the activity of the metal. U.S. Pat. No. 3,986,982 to Crowson et al treats deactivated platinum group metal-loaded zeolites by contacting them with a stream of an inert gas containing from 0.5 to 20 percent volume of free oxygen and from 5 to 500 ppm volume of chlorine as chlorine, HCl, or an organic chlorine-containing material. The resulting catalyst is purged to remove residual oxygen and chlorine and then reduced in a stream of hydrogen at 200.degree. to 600.degree. C.

The treatment of noble metal-containing catalyst material with sulfur compounds is also known in the art. For example, U.S. Pat. No. 3,661,768 to Davis, Jr., et al. describe a method of regenerating a bimetallic reforming catalyst such as platinum-rhenium on alumina which includes contacting the catalyst with hydrogen sulfide to convert platinum to platinum sulfide. Prior to sulfiding, the catalyst is contacted with chlorine and steam in order to effect chlorination.

However, all of the above treatments require certain precautions owing to the corrosive nature of the halogens use. In addition, certain halogen materials employed in these processes add significantly to the cost of catalyst regeneration. In order to avoid the drawbacks associated with halogen use, it would be advantegeous to reactivate catalysts in the absence of halogens. However, when deactivating coke present on a catalyst material is exposed to an oxidizing atmosphere consisting of oxygen and an inert gas, such as nitrogen, substantially all of the nobel metal present on the catalyst becomes catalytically inactive.

U.S. patent application Ser. No. 604,268 filed Apr. 26, 1984, now U.S. Pat. No. 4,555,495, incorporated herein by reference teaches reactivating coke deactivated noble metal-containing zeolites by sulfiding the catalyst prior to subjecting the catalyst to oxidative regeneration by contact with an oxygen and sulfur dioxide-containing gas.

It has now been found that coke-deactivated noble metal-containing zeolite catalyst materials can be reactivated while minimizing noble metal agglomeration without sulfiding the catalyst before coke burn-off and without significant loss of the metal function activity of the zeolite. In accordance with the present invention, a deactivated platinum group or noble metal-containing zeolite catalyst material containing at least 0.5 weight percent coke, e.g., 0.5 to 3 weight percent coke is regenerated by a method which comprises: removing the deactivating coke to provide a catalyst containing less than about 0.3 weight percent coke, e.g., less than about 0.2 weight percent coke while enhancing noble metal dispersion or at least minimizing noble metal agglomeration by contacting the deactivated zeolite catalyst material with oxygen only in the presence of sulfur dioxide, under oxidizing conditions, and thereafter reducing the resulting catalyst material by exposure to a suitable reducing agent such as hydrogen, hydrogen sulfide or a mixture thereof under reducing conditions. The catalyst treated in accordance with the present invention exhibits enhanced activity owing to the burn-off of deactivating coke as well as retention of significant noble metal dispersion.

The present invention relates to a process for regenerating an aged noble metal-contaiing zeolite catalyst material to provide a catalyst material of enhanced activity which retains a substantial portion of its noble metal in a dispersed form. The process consists essentially of oxidizing the coke on the aged catalyst material with oxygen in the presence of sulfur dioxide under suitable oxidizing conditions, and thereafter reducing the catalyst material by contact with hydrogen under suitable reducing conditions.

The aged catalyst material is treated to burn off deactivating coke materials under controlled oxidizing conditions at moderate temperatures and oxygen concentrations. Suitable oxidizing conditions include temperatures ranging from about 100.degree. to 500.degree. C., preferably about 400.degree. to 450.degree. C., pressures ranging from about 100 to 400 psig, preferably about 150 to 250 psig. It is preferred that the oxidizing conditions be mild enough to prevent any alteration in the crystal structure of the zeolite being treated. The aged zeolite catalyst material is contacted with a gas stream containing oxygen as well as sulfur dioxide. Generally, the gas stream may contain about 1 to 10 volume percent oxygen and 100 ppm to 2 volume percent sulfur dioxide, preferably 1 to 3 volume percent oxygen and 0.5 to 1 volume percent sulfur dioxide. The presence of sulfur dioxide prevents or reduces agglomeration of the noble metals dispersed through out the catalyst during the removal of coke from the zeolite catalyst material.

Dispersion of the noble metals can be measured by hydrogen chemisorption, e.g., Temperature Programmed Desorption (TPD) of hydrogen. This technique can indicate the extent of noble metal agglomeration of a catalyst material. Details of this analytical technique may be found in "The Stoichiometry of Hydrogen and CO Chemisorption of Ir/.gamma.-Al.sub.2 O.sub.3 ", Vol. 78, Journal of Catalysis, pp. 319-326, Krishnamurthy et al., (1982).

The reducing procedure which follows removal of the coke from the catalyst material utilizes any suitable reducing agent, preferably hydrogen. Reduction of the catalyst material is achieved by contacting it with the reducing agent under suitable reducing conditions. These include temperatures ranging from about 300.degree. to 500.degree. C., preferably about 350.degree. to 450.degree. C. and contact times ranging from about 0.5 to 10 hours, preferably about 1 to 2 hours. Where the reducing agent is in the gaseous form, e.g., hydrogen, said reduction is carried out at pressures ranging from about 1 to 400 psig, preferably about 150 to 250 psig.

The zeolites which may be rejuvenated by the process of the present invention include large pore zeolites such as Zeolite Y, zeolite beta, ZSM-3, ZSM-4, ZSM-18 and ZSM-20, as well as zeolites having a constraint index of about 1 to 12 and silica to alumina mole ratio greater than about 12. Examples of such materials includes ZSM-5, ZSM-11, ZSM-5/ZSM-11 intermediates, ZSM-12, ZSM-23, ZSM-35, ZSM-38, ZSM-48 and other similar materials.

Zeolite Y is described in greater detail in U.S. Pat. No. 3,130,007. The entire description contained within this patent, particularly the X-ray diffraction pattern of therein disclosed Zeolite Y, is incorporated herein by reference.

Zeolite beta is described in U.S. Pat. No. 3,308,069. That description, including the X-ray diffraction pattern of zeolite beta, is incorporated herein by reference.

ZSM-3 is described in greater detail in U.S. Pat. No. 3,415,736. That description, and in particular the X-ray diffraction pattern of said ZSM-3, is incorporated herein by reference.

ZSM-4 is described in U.S. Pat. No. 4,021,447. That description, and in particular the X-ray diffraction pattern disclosed therein, is incorporated herein by reference.

ZSM-5 is described in greater detail in U.S. Pats. Nos. 3,702,886 and Re 29,948. The entire descriptions contained within those patents, particularly the X-ray diffraction pattern of therein disclosed ZSM-5, are incorporated herein by reference.

ZSM-11 is described in greater detail in U.S. Pat No. 3,709,979. That description, and in particular the X-ray diffraction pattern of said ZSM-11, is incorporated herein by reference.

ZSM-5/ZSM-11 intermediate compositions are described in U.S. Pat. No. 4,229,424. That description, and in particular the X-ray diffraction pattern of said compositions disclosed therein, is incorporated herein by reference.

ZSM-12 is described in U.S. Pat. No. 3,832,449. That description, and in particular the X-ray diffraction pattern disclosed therein, is incorporated herein by reference.

ZSM-18 is described in U.S. Pat. No. 3,950,496. That description, and in particular the X-ray diffraction pattern disclosed therein, is incorporated herein by reference.

ZSM-20 is described in U.S. Pat. No. 3,972,983. The entire content thereof, particularly the specification of the X-ray diffraction pattern of the disclosed zeolite, is incorporated herein by reference.

ZSM-23 is described in U.S. Pat. No. 4,076,842. The entire content thereof, particularly the specification of the X-ray diffraction pattern of the disclosed zeolite, is incorporated herein by reference.

ZSM-35 is described in U.S. Pat. No. 4,016,245. The description of that zeolite, and particularly the X-ray diffraction pattern thereof, is incorporated herein by reference.

ZSM-38 is more particularly described in U.S. Pat. No. 4,046,859. The description of that zeolite, and particularly the specified X-ray diffraction pattern thereof, is incorporated herein by reference.

ZSM-48 is more particularly described in U.S. Pat. No. 4,234,231, the entire contents of which is incorporated hereby by reference.

Particularly preferred zeolites for the purposes of the present invention are those which have high silica-to-alumina mole ratios, e.g. greater than about 20 or even greater than 70 to 100.

The catalyst treated by the process of the present invention contains at least one noble metal such as platinum, palladium, iridium, osmium, rhodium, rhenium and ruthenium in amounts ranging from about 0.1 to 5 weight percent, preferably about 0.3 to 0.9 weight percent. These noble metals are generally associated with and supported on a zeolite catalyst. The process may also be used to regenerate multimetallic catalysts which contain one of the above noble metals and another metal selected from Groups IB, IVB, VIIA, or VIII of the Periodic Table. The zeolite catalyst treated can be binder free or it may contain an inorganic oxide binder such as alumina, silica, silica-alumina, magnesia, titania, zirconia, or thoria.

This invention will be better understood by reference to the following examples.

A catalyst material of zeolite beta comprising 35 wt % alumina and 0.59 wt % platinum was exposed to hydrocarbon conversion conditions resulting in a coke build-up of about 10 weight percent thereon. After deoiling for a half hour in hydrogen, the deactivated catalyst was regenerated by exposure to a gas containing 96.3 wt % N.sub.2, 3 wt % O.sub.2 and 0.7 wt % SO.sub.2 at 400.degree. to 450.degree. C. for about 0.5 to 2 hours at about atmospheric pressure in order to burn off the coke. The resulting catalyst contained less than about 0.005 weight percent coke. The regenerated catalyst was thereafter reduced for one hour at 450.degree. C. in hydrogen. The resulting catalyst was measured by hydrogen chemisorption for platinum dispersion. The regenerated catalyst had a platinum dispersion of 0.2 compared with a dispersion of 0.57 for a fresh catalyst.

A 10 g sample of the coked catalyst of Example 1 was regenerated by contact with a mixture containing 97 volume percent N.sub.2 and 3 volume percent O.sub.2 at 400.degree. to 450.degree. C. to achieve coke burn-off. The resulting catalyst contained less than about 0.005 weight percent coke. The regenerated catalyst was thereafter reduced for one hour at 450.degree. C. in hydrogen. Platinum dispersion as measured by hydrogen chemisorption was 0.

A comparison of Examples 1 and 2 indicates that the addition of sulfur dioxide to the oxygen used in regeneration of the zeolite in the present invention is effective in retaining a significant portion of the initial Pt dispersion of a catalyst which would otherwise be lost by conventional regeneration treatment.