Fixed bed catalysts

Details Fixed bed catalysts Fixed bed catalysts

2001-07-17

2002-12-03

Davis, Brian J. (Department: 1621)

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

Organic compounds

Oxygen containing

C568S885000, C502S301000

Reexamination Certificate

active

06489521

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to fixed bed catalysts and their use for the hydrogenation of saturated and unsaturated esters.
2. Description of the Background
Activated metal catalysts are known in the field of chemical engineering as Raney catalysts. They are used, largely in powder form, for a large number of hydrogenation, dehydrogenation, isomerization reductive alkylation, reductive amination, and hydration reactions of organic compounds. These powdered catalysts are prepared from an alloy of a catalytically active metal, also referred to herein as a catalyst metal, with a further alloying component which is soluble in an alkali. Suitable catalytically active metals include nickel, cobalt, copper and iron. Aluminum is generally used as the alloying component which is soluble in an alkali, but other components may also be used, in particular, zinc or silicon or mixtures of either one of these elements with aluminum.
Powdered catalysts have the disadvantage that they can be used only in a batch process and, after the catalytic reaction, have to be separated from the reaction medium by costly sedimentation and/or filtration techniques. Therefore, a variety of processes for preparing molded forms of the catalysts, which lead to activated metal fixed-bed catalysts after extraction of the aluminum have been disclosed. Thus, for example, coarse particulate Raney alloys, i.e., Raney alloys which have only been coarsely milled, can be prepared and these alloys can be activated by treatment with a caustic soda solution. Extraction and activation then occurs only in a surface layer, the thickness of which can be adjusted by the conditions used during extraction.
A substantial disadvantage of catalysts prepared by these known methods are the poor mechanical stability of the activated outer layer. Since only this outer layer of the catalysts is the catalytically active component, abrasion leads to rapid deactivation and renewed activation of deeper lying layers of alloy using caustic soda solution then leads at best to partial reactivation.
It is known that Re doped Pd (DE 25 19 817 A1)or Re doped Ru (WO 96/27436) supported catalysts are useful for the production of gamma-butyrolactone (GBL), tetrahydrofuran (THF), and 1,4-butanediol (BDO) by either maleic acid or maleic anhydride hydrogenation. These systems work as either powder or fixed bed catalysts at pressures of 138 bar or higher and temperatures of 250° C. or higher. In this respect, a system that performs this reaction at milder conditions would be a strong advantage. Copper-chromite is another catalyst system that has used for ester hydrogenation with some success (DE 39 03 029 A1).
EP 0 648 534 A1 describes shaped, activated Raney metal fixed-bed catalysts (Metalyst®) and their preparation. These catalysts avoid the disadvantages described above, i.e., the poor mechanical stability resulting from activating an outer layer. To prepare these catalysts, a mixture of powders consisting of a catalyst alloy and a binder are used, where the catalyst alloy contains at least one catalytically active catalyst metal and an extractable alloying component. The pure catalyst metals or mixtures thereof, which do not contain an extractable component, are used as the binder. The use of the binder in an amount of 0.5 to 20 weight percent with respect to the catalyst alloy, is essential in order to achieve sufficient mechanical stability after activation. After shaping the catalyst alloy and the binder with conventional shaping aids and pore producers, the freshly prepared items which are obtained are calcined at temperatures below 850° C. As a result of sintering within the finely divided binder, solid compounds are produced between the individual granules of the catalyst alloy. These compounds, in contrast to catalyst alloys, are non-extractable or only extractable to a small extent so that a mechanically stable structure is obtained even after activation without endangering the strength of the shaped item.
SUMMARY OF THE INVENTION
Accordingly, one object of the present invention is to provide fixed bed activated base metal catalysts that hydrogenate saturated and unsaturated esters under milder conditions than existing technologies with better activities and selectivities.
Briefly, this object and other objects of the present invention as hereinafter will become more readily apparent can be attained by a shaped, activated Raney metal fixed-bed catalyst prepared by a method comprising preparing a mixture of powders consisting essentially of at least one catalyst alloy of (1) at least one catalytically active Raney process metal, a leachable alloy component and optionally a promoter, (2) at least one binder containing at least one pure Raney process metal, and (3) a moistening agent, and optionally an additive selected from the group consisting of a shaping aid, lubricant, plasticizer, pore-producer, and mixtures thereof; homogenizing the mixture; shaping the mixture into a molded catalyst precursor which is not activated; calcining the molded catalyst precursor at a temperature below 850° C. to prepare a sintered catalyst precursor, and activating the sintered catalyst precursor by leaching the leachable alloy component with alkali until the leached and thereby activated outer layer has an adjustable thickness corresponding up to 70% or more of the of the molded form being activated, and subsequently washing the final catalyst; doping said catalyst with rhenium as a promoter after said activation and washing by introducing said catalyst into a rhenium solution. The pH of the Re solution may or may not be adjusted, and the temperature of the doping solution may vary from lower than room temperature to substantially higher temperatures. Moreover, the rhenium may be added to the unactivated alloy, the binder, or introduced in any other fashion that allows for its presence in the catalyst. The Re content can range from 0.01% Re to 30% Re, preferably from 0.01% to 15%, more preferably from 0.01% to 10% by weight of the catalyst.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The fixed bed catalysts of the invention have the advantage that Re doped metal catalysts promote the hydrogenation of maleic acid or maleic anhydride to gamma-butyrolactone, tetrahydrofuran or 1,4-butanediol at a temperature of 200° C. and a pressure of 80 bar. Additionally the present catalyst is able to hydrogenate fatty esters to the corresponding fatty alcohols at higher activities and selectivities than the standard copper chromite catalysts.
Preferred Raney process metals include nickel, cobalt, copper, or combination thereof and the leachable alloying components include aluminum, zinc, silicon, or combinations thereof. These metals are generally leached by an alkali such as NaOH. The ratio by weight of Raney process metal to leachable alloying component in the catalyst alloy is in the range from 10:90 to 90:10, as is normally the case with Raney alloys. The Raney process metal used as binder, in a real practical application, does not have to be the same as the catalyst metal present in the catalyst alloy. Rather, it is possible to combine different Raney process metals with each other as well as with promoter metals, in the catalyst alloy and as binder, offering a further important degree of freedom when adjusting the catalytic properties to the particular catalytic process. Thus the binder employed in the present invention can be nickel, cobalt, copper, iron, and optionally promoter metals. Generally any of the metals used for making Raney metal catalysts are suitable. The binder metal is employed in an unreachable and unadulterated form. Catalyst alloy and binder are processed in the form of powders, typically with the addition of moistening agents and optionally with the addition of conventional additives such as shaping aids, lubricants, plasticizers, and optionally pore-producers to give a moldable material. Any materials conventionally used for these purposes may be used as the shaping aid, lubricant, pl

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