Stable highly active supported copper based catalysts

Details Stable highly active supported copper based catalysts Stable highly active supported copper based catalysts

2001-09-28

2002-10-29

Kumar, Shailendra (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Amino nitrogen containing

C564S126000, C564S127000

Reexamination Certificate

active

06472561

ABSTRACT:

TECHNICAL FIELD
This invention relates to highly active supported copper based catalysts. More particularly, this invention is directed to mechanically stable aluminum oxide supported copper based catalysts useful, e.g., for hydration of nitrites to amides, especially for the hydration of acrylonitrile to acrylamide.
BACKGROUND OF THE INVENTION
Acrylamide is considered the most commercially important of the acrylic and methacrylic amides. It is useful, for example, for waste water treatment, soil stabilization, papermaking, manufacture of polymers, and as an additive for textiles, paints, and cement. Industrially, acrylamide is manufactured by acrylonitrile hydration.
Early commercial nitrile hydration was mediated by sulfuric acid. But this environmentally unfriendly process required expensive equipment and presented waste disposal problems. Subsequently, the acid mediated process was abandoned in favor of metal catalyzed hydration. Beginning in 1971, a series of patents issued that described various unsupported elemental copper based nitrile hydration catalysts, some of which have since achieved commercial success; i.e., U.S. Pat. Nos. 3,597,481; 3,631,104; 3,342,894; 3,642,643; 3,642,913; 3,696,152; 3,758,578; and 3,767,706. Since then, hundreds of variations and improvements have been disclosed and the topic has been reviewed (E. Otsuka et al.
Chem. Econ. Eng. Rev.
7(4), 29, (1979)).
Of the unsupported elemental copper catalysts, Raney copper is one of the most popular for commercial scale acrylonitrile hydration (See, e.g., U.S. Pat. Nos. 3,767,706 and 3,985,806) because of its high surface area and activity per unit copper metal relative to other forms of elemental copper. Preparation comprises leaching an alloy of copper and aluminum with a strong base. But an inherent problem with elemental copper is inefficient metal utilization and therefore high loading is required to achieve reasonable reaction rates and conversions. Another significant drawback of elemental copper hydration catalysts is the limited lifetime, that is, over a period of days to weeks of continuous use, a gradual decrease in activity is observed. Yet another disadvantage is low mechanical stability and catalyst fragmentation into increasingly fine articles. This causes variations in catalyst surface area so that, even if other conditions are maintained, the amount of reaction per catalyst unit will vary and, as a consequence, the conversion rate will be erratic and the catalyst lifetime will be reduced.
Some problems with these elemental metal catalysts can be mitigated, in certain applications, by depositing the metal onto a substrate support. As is well known in the art, supported metals generally have higher surface areas—and thus higher activities—per unit metal than their unsupported counterparts. Hence, with supported catalysts, the metal is used much more efficiently and this, of course, is economically advantageous. One reason for the higher surface area is that the metal can be dispersed on the solid substrate support as small crystallites. This favorable trend, however, is undermined because it is difficult to impregnate supports with small metal crystallites (i.e., having a high metal surface area per unit metal) while simultaneously achieving high metal loading.
The art relating to metals and promoters supported on aluminum oxide (Al
2
O
3
or alumina) is mature and the references are numerous. Activated aluminum oxide is available via dehydration of the hydrated form (Al
2
O
(3−x)
(OH)
2x
). Several types of hydrated aluminum oxide are readily available, including Gibbsite and Bayerite (Al(OH)
3
). Loss of a molecule of water leads to the oxyhydroxides (AlO(OH)), boehmite, pseudo boehmite, and diaspore (for reviews see: Augustine R. L., Heterogeneous catalysis for the Synthetic Chemist, Marcel Dekker, Inc. New York, N.Y. (1996) pp. 161-163 and
The Encyclopedia of Chemical Technology,
2 Kirk-Othomer (4
th
ed. at 426)) both of which are incorporated herein by reference.
Significantly, it is known that aluminum oxide's surface area, mechanical stability, and resistance to hydration are highly dependent upon the temperature at which the aluminum oxide is calcined. In general, as hydrous aluminum oxide is calcined, water is driven off, leaving a porous solid structure of activated aluminum oxide. Simple drying of aluminum oxide at temperatures lower than about 500° C. affords aluminum oxide that has relatively low mechanical stability and low water reabsorption resistance. On the other hand, calcination between about 550° C. to 850° C. affords the more mechanically stable and hydration resistant gamma aluminum oxide phase (&ggr;-alumina), which has a surface area of about 150 to 300 m
2
/g. Further heating (875 to 1150° C.) effects further phase shift through delta-alumina (&dgr;-alumina), to theta-alumina (&thgr;-alumina), and finally to the alpha-alumina (&agr;-alumina) phase. This phase change—i.e., &ggr;-,&dgr;-,&thgr;-, to &agr;-alumina—is accompanied by increased mechanical stability and increased hydration resistance. Resistance to rehydration is very important to a catalyst's stability and lifetime under aqueous phase reaction conditions (e.g., in hydration reactions). High resistance to rehydration correlates with improved structural integrity. But on the downside, the phase change through &ggr;-,&dgr;-,&thgr;-, to &agr;-alumina is accompanied by surface area reduction (i.e., to about 5 m
2
/g for &agr;-alumina). Accordingly, for the purposes of the present invention, the phrase: mechanically stable aluminum oxide phase; refers to either &ggr;-,&dgr;-,&thgr;-, or &agr;-alumina or any mixture thereof.
In short, &ggr;-,&dgr;-,&thgr;-, and &agr;-alumina are favorable supports in view of their good hydration resistance and high mechanical stability. But a disadvantage of &ggr;-,&dgr;-,&thgr;-, and &agr;-alumina as catalyst supports is that the derived metal catalysts are expected to have relatively low activity per unit copper metal.
Disclosures of catalyst compositions comprised of elemental copper and copper oxide supported on aluminum oxide and preparation methods are widespread. In general, a copper salt is bonded to the aluminum oxide support and the support-copper salt complex is calcined to convert the copper salt to copper oxide. If desired, the copper oxide crystallites may be converted to elemental copper by chemical reduction.
One popular procedure for preparation of aluminum oxide supported copper oxide based catalysts is the single pore volume impregnation procedure (or PVI, also known as the incipient wetness procedure). One variation of the pore volume impregnation procedure comprises saturating the pores of an aluminum oxide phase with aqueous copper salt solution, drying, then calcining the impregnated aluminum oxide to convert the copper salt to copper oxide. Unfortunately, this single impregnation procedure affords relatively large metal crystallites concentrated at the surface of the support particle. For an example see M. Kotter et al Delmon et al. editors
Preparation of Catalysis II,
Elsevier Scientific Publishing Company, New York (1979) p. 51-62.
As disclosed in the three references discussed below, a second version of the pore volume impregnation procedure involves a double impregnation technique. This procedure is similar to the single PVI procedure above, but in the first impregnation, a metal chelating agent is bound to the catalyst support. In the second impregnation, the pre-doped support is contacted with an aqueous metal salt solution, dried, and calcined as above. But this process, in general, does not yield catalysts characterized by high metal loading simultaneously with small metal crystallite size. Accordingly, high activities per unit metal are not achieved.
In the first reference, Barcicki et al. (
React. Kinet. Catal. Lett.,
Vol 17, No. 1-2, 169-173 (1981))—incorporated herein by reference—discloses nickel catalysts characterized by small metal crystallites in the range of 20 to 30 Å supported on &ggr;-alumina. But in

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