Catalyst – solid sorbent – or support therefor: product or process – Regenerating or rehabilitating catalyst or sorbent – Gas or vapor treating
Reexamination Certificate
2002-03-19
2004-11-09
Silverman, Stanley S. (Department: 1754)
Catalyst, solid sorbent, or support therefor: product or process
Regenerating or rehabilitating catalyst or sorbent
Gas or vapor treating
C502S053000
Reexamination Certificate
active
06815388
ABSTRACT:
The present invention relates to a process for hydrogen activation of passivated iron useful as catalytically active component after said activation at elevated temperature and elevated pressure, which comprises effecting said activation in the presence of a nitrile at from 20 to 180° C.
Catalysts consisting wholly or substantially of elemental iron are very important, for example for the synthesis of ammonia from nitrogen and hydrogen, for producing hydrocarbons from synthesis gas (Fischer-Tropsch synthesis) and for the hydrogenation of nitriles to amines (J.W. Geus, Applied Catalysis 25, 313-333 (1986)).
Such catalysts are usually prepared by reducing iron oxides with hydrogen. To this end, the iron oxide is reduced in a hydrogen stream at high temperatures, the oxide oxygen being converted into water and removed in that form.
DP patent 855,263 describes the reduction of molten and subsequently comminuted iron oxide at 400° C. in a hydrogen stream.
J. Mater. Sci. Lett. 8 (8) (1989), 895-898 reports the experimental finding that the complete reduction of iron oxides to iron in a hydrogen stream can only be achieved at temperatures above 400° C. and that the reduction of doped iron oxides as used in ammonia synthesis can be achieved only at above 500° C.
U.S. Pat. No. 3,758,584 discloses at column 1 lines 47 to 65 reducing iron oxides at 300 to 600° C. in the presence of 0.01 to 10 percent by volume of ammonia. Preference is given to a temperature of 350 to 420° C., in which case the hydrogen contains 0.25-3 percent by volume of ammonia (column 2 lines 12-18). Such iron catalysts are used for example for hydrogenating adiponitrile to hexamethylenediamine.
According to U.S. Pat. No. 4,480,051, the reduction can also be carried out in three stages by reducing the iron oxide with hydrogen or mixtures of hydrogen and ammonia in a first step, then treating the resulting elemental iron with an oxygen-containing gas in a second step and then as third step repeating the reduction similarly to the first step.
The reduced iron catalyst obtained according to the processes mentioned is pyrophoric. If the reduction of the iron oxide was carried out directly in the synthesis reactor contemplated for the later reaction, the catalyst can subsequently be used for the contemplated chemical reaction. However, the reduction in the synthesis reactor has disadvantages: since the reduction together with the heating and cooling takes many hours, the reactor is unavailable for manufacture during this period. In addition, the reduction temperature can be distinctly above the later synthesis temperature. So the reactor has to be overengineered because of the reduction.
It can therefore be advantageous to reduce the iron oxide outside the contemplated synthesis reactor. However, the pyrophoric catalyst has to be passivated by treatment with air in order that it may be transported to the synthesis reactor and installed.
According to WO 98/11059, this passivation may be effected with nitrogen-oxygen mixtures at temperatures from 20 to 80° C., preferably 25 to 60° C. The activation of such catalysts (“reduced/passivated”) is then effected in the synthesis reactor in a hydrogen atmosphere at from 180 to 500° C., preferably from 200 to 400° C.
Activation for the purposes of the present invention is the conversion of reducedly [sic]/passivated iron into a catalytically active form.
The disadvantage is that even the subsequent activation in the reactor necessitates high temperatures in the range from 200 to 400° C. This leads to appreciable extra costs on account of the increased equipment needs (preheater, cycle gas compressor, reactor material, etc.). Also, although the time needed for the activation is less than with the initial reduction of the iron oxide, it is still high. For instance, A. V. Slack, G. R. James: Ammonia, Part II, Marcel Dekker Inc., 1977, 113-114 describes the procedure for activating a passivated iron used in ammonia synthesis. The activation takes place at from 300 to 480° C. and takes about 17 hours, to which has to be added the same time for heating the reactor.
DE-A-3,524,330 describes the activation of passivated iron in the presence of a Redox system, eg ketone/alcohol, at temperatures of about 200° C. The disadvantages here are the high temperature and the appreciable time required for the activation.
It is an object of the present invention to provide a process for a technically simple and economical elevated temperature, elevated pressure hydrogen activation of passivated iron useful as catalytically active component after the activation without the disadvantages mentioned.
We have found that this object is achieved by the process defined at the outset.
The passivated iron which is used in the process of the invention and which is useful as catalytically active component after the activation can be obtained according to processes known per se.
Useful precursors for such an iron accordingly include iron oxides, iron hydroxides, iron oxyhydroxides or mixtures thereof (component a). Examples include iron(III) oxide, iron(II, III) oxide, iron(II) oxide, iron(II) hydroxide, iron(III) hydroxide or iron oxyhydroxide such as FeOOH. Synthetic or naturally occurring iron oxides, iron hydroxides or iron oxyhydroxides can be used, such as magnetite, which has the idealized formula of Fe
3
O
4
, brown ironstone, which has the idealized formula of Fe
2
O
3
×H
2
O, or red ironstone (hematite), which has the idealized formula of Fe
2
O
3
.
Such compounds can be used to produce supported iron catalysts, but are preferably used for producing unsupported iron catalysts.
Useful precursors for such an iron include as component a) readily water-soluble salts of iron, such as nitrates, chlorides, acetates, formates or sulfates, preferably nitrates, or mixtures thereof, and also mixtures of such salts with the aforementioned iron oxides, iron hydroxides or iron oxyhydroxides.
Such compounds can be used to produce unsupported iron catalysts, but are preferably used for producing supported iron catalysts.
The passivated iron which is used in the process of the invention and which is useful as catalytically active component after activation may include further components, such as promoters.
Advantageous promoters are one or more of the following elements or compounds based on the following elements or mixtures thereof (component (b)):
palladium, cobalt, ruthenium, rhodium, platinum, iridium, osmium, copper, silver, gold, chromium, molybdenum, tungsten, manganese, rhenium, zinc, cadmium, lead, aluminum, tin, phosphorus, arsenic, antimony, bismuth and rare earth metals, silicon, zirconium, vanadium, titanium.
Advantageous further components (component (c)) are one or more compounds based on one or more alkali or alkaline earth metals.
To prepare the passivated iron useful as catalytically active component after activation, the precursor of component (a) may already contain component (b) or its precursors partially or completely. Similarly, to prepare the passivated iron useful as catalytically active component after activation the precursor of component (a) may already contain component (c) or its precursors partially or completely.
Preferred precursors for component (b) include readily water-soluble salts or complexes of the elements mentioned, such as nitrates, chlorides, acetates, formates, sulfates, preferably nitrates.
Preferred precursors for component (c) include readily water-soluble salts or complexes of the elements mentioned, such as hydroxides, carbonates, nitrates, chlorides, acetates, formates, sulfates, preferably hydroxides and carbonates.
Catalyst precursors including passivated iron useful as catalytically active component after activation with or without component (b) or (c) or components (b) and (c) are useful as precursors for supported or unsupported catalysts.
Such supported catalysts may include conventional carrier materials, preferably aluminum oxide, silicon oxide, alumosilicates, lanthanum oxide, titanium dioxide, zirconium dioxide, magnesium oxide, zinc oxide, ze
Ansmann Andreas
Bassler Peter
Fischer Rolf
Luyken Hermann
Melder Johann-Peter
BASF - Aktiengesellschaft
Keil & Weinkauf
Silverman Stanley S.
Strickland Jonas N.
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