Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2002-12-23
2003-12-30
Solola, Taofiq (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C568S864000, C502S185000
Reexamination Certificate
active
06670490
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a catalyst with an inert support for hydrogenation in an aqueous solution and a method for using the catalyst in the production of tetrahydrofuran and 1,4-butanediol from a hydrogenatable precursor in an aqueous solution.
2. Description of the Related Art
Various methods and reaction systems have been proposed in the past for manufacturing tetrahydrofuran (THF) and 1,4 butanediol (BDO) by catalytic hydrogenation of gamma butyrolactone (GBL), maleic acid (MAC), maleic anhydride (MAN), succinic acid (SAC) or related hydrogenatable precursors. Also, a variety of hydrogenation catalysts have been historically proposed for this purpose, including various transition metals and their combinations deposited on various inert supports, all as generally known in the art. Many of these catalysts are proposed for use in hydrogenations carried out in an organic solvent or organic reaction media and not in an aqueous solution phase. At least one prior publication suggests that water and succinic acid may be considered as inhibitors to the desired catalysis, see Bulletin of Japan Petroleum Institute, Volume 12, pages 89 to 96 (1970).
A laid-open Japanese patent application (Kokai) 5-246915 for the aqueous phase catalytic hydrogenation of an organic carboxylic acid or ester teaches the use of any Group VIII noble metal, optionally in combination with either tin, rhenium or germanium, on a defined activated carbon support.
U.S. Pat. No. 5,698,749 discloses a process for producing 1,4-butanediol by aqueous hydrogenation of a hydrogenatable precursor using a catalyst comprised of a noble metal of Group VIII and at least one of rhenium, tungsten and molybdenum on a carbon support pretreated with an oxidizing agent.
In U.S. Pat. No. 5,478,952 a highly effective catalyst for aqueous phase hydrogenations is disclosed. This catalyst consists of ruthenium and rhenium wherein both metal components are present in a highly dispersed reduced state on a carbon support which is characterized by a BET surface area of less than 2,000 m
2
/g.
U.S. Pat. No. 6,008,384 discloses a catalyst of highly dispersed, reduced Ru and Re in the presence of Sn on a carbon support used for an improved hydrogenation process for the production of tetrahydrofuran, gamma butyrolactone, 1,4-butanediol and the like from a hydrogenatable precursor such as maleic acid, succinic acid, corresponding esters and their mixtures and the like in an aqueous solution in the presence of hydrogen. This patent is incorporated herein by way of reference.
SUMMARY OF THE INVENTION
This invention is hydrogenation catalyst comprising about 0.5% to 3% platinum, about 1% to 10% rhenium and about 0.1% to about 5% tin supported on carbon, wherein the percentages are by total weight of the supported catalyst.
This invention is also a method for making tetrahydrofuran, 1,4-butanediol or mixtures thereof by hydrogenating a hydrogenatable precursor in a reactor in the presence of a catalyst comprising about 0.5% to 3% platinum, about 1% to 10% rhenium and about 0.1% to 5% tin, supported on carbon, wherein the percentages are by total weight of supported catalyst.
DETAILED DESCRIPTION OF THE INVENTION
This invention is a novel trimetallic platinum-rheniúm-tin catalyst that exhibits certain advantages when employed during hydrogenation of a hydrogenatable precursor in an aqueous solution. The invention is also an improved process or method for making tetrahydrofuran, 1,4-butanediol or mixtures thereof by hydrogenating a hydrogenatable precursor such as gamma butyrolactone, maleic anhydride, maleic acid, succinic acid, or mixtures thereof. As such, the trimetallic catalyst of this invention and the process of using this catalyst may be viewed as an improvement of the bimetallic ruthenium-rhenium carbon-supported catalyst of U.S. Pat. No. 5,478,952 and of the trimetallic ruthenium-rhenium-tin carbon-supported catalyst of U.S. Pat. No. 6,008,384.
This catalyst composition results in the conversion of a hydrogenatable precursor in an aqueous solution at high conversion rates for an extended period of time consistent with large-scale commercial operations and with significantly lower over-hydrogenation. Moreover, it has been discovered that the addition of tin to a platinum and rhenium catalyst leads to an improved control of selectivity among the more useful products, such as tetrahydrofuran and 1,4-butanediol. Concurrently, reduced relative production of undesirable by-products, such as n-butanol, n-propanol and volatile hydrocarbons, such as methane, ethane, propane and butane has been discovered. Although not confining possible explanation for this discovery to any single rationale or theory, it is currently believed that the addition of relatively small amounts of tin moderates the high catalytic activity of the platinum-rhenium catalyst and the overall rate of hydrogenation so as to improve selectivity to the desired products. This results in a superior yield of desired products and control of the ratio of tetrahydrofuran to by-products being produced without significantly promoting over-hydrogenation and production of undesirable by-products.
Consistent with this view, the respective lower limit or minimum loading of platinum and rhenium metals relative to the carbon support is somewhat higher than it would be for the bimetallic catalyst without tin in order to at least partially compensate for the presence of tin. Thus, the trimetallic catalyst comprises at least 0.5% by weight of platinum metal and at least 1% of rhenium metal relative to the combined weight of metals and inert support. The upper limit of the platinum and rhenium metal will be about 3% platinum and about 10% rhenium on the same basis. It should be appreciated that concentrations of platinum and rhenium in excess of these upper limits may be operative and as such should be considered equivalent for purposes of the present invention. However, such concentrations are believed to offer little advantage in terms of convenience and/or cost.
Thus, the present invention provides an improved hydrogenation catalyst of about 0.5% to 3% platinum, about 1% to 10% rhenium, and about 0.1 to 1.0% tin, supported on carbon, wherein the percentages are by total weight of supported catalyst and wherein the carbon support is characterized by a BET surface area of less than 2,000 m
2
/g. Preferably, the catalyst composition is about 0.8% to 2% platinum, about 3% to 8% rhenium, and about 0.1% to 1.5% tin, supported on the aforementioned carbon, wherein the percentages are by total weight of the supported catalyst.
The carbon useful as a catalyst support in the present invention is preferably a porous particulate solid characterized by a size distribution typically ranging from about 5 to 100 micrometers for slurry applications and from about 0.8 to 4 millimeters (mm) for fixed bed applications and a BET surface area typically ranging from a few hundred to nearly 2,000 m
2
/g. Preferably, the carbon support material is a commercially available material having an average particle size of about 20 micrometers for slurry applications and about 3 mm for fixed bed applications and a BET surface area from about 700 to about 1,600 m
2
/g. The catalyst support can be manufactured to have a latent acid, a neutral, or a basic pH. Optionally, the catalyst support can be treated prior to metal deposition by one or more techniques as generally known in the art, such as, impregnation with alkali metal salts and/or calcination or acid wash. Examples of suitable carbon supports are SX-2 and Darco KBB carbons, supplied by Norit Americas Inc., with BET surface areas of 700 and 1,500 m
2
/g, respectively.
The method of preparing the catalyst of the present invention can be generally any such process as known in the art, provided that the desired composition of metals and inert support is achieved. One such method is to prepare a water solution of a soluble platinum compound, a soluble rhenium compound and a soluble tin compound and then add this soluti
Campos Daniel
Sisler Gregg Mason
E. I. du Pont de Nemours and Company
Solola Taofiq
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