Organic compounds -- part of the class 532-570 series – Organic compounds – Amino nitrogen containing
Reexamination Certificate
2001-02-13
2002-03-19
Davis, Brian J. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Amino nitrogen containing
Reexamination Certificate
active
06359178
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a process for catalytic hydrogenation of adiponitrile to hexamethylenediamine at elevated temperature and elevated pressure in the presence of catalysts based on elemental iron as catalytically active component and ammonia as solvent, which comprises
a) hydrogenating adiponitrile at from 70 to 220° C. and from 100 to 400 bar in the presence of catalysts based on elemental iron as catalytically active component and ammonia as solvent to obtain a mixture comprising adiponitrile,
6-aminocapronitrile, hexamethylenediamine and high boilers until the sum total of the 6-aminocapronitrile concentration and the adiponitrile concentration is within the range from 1 to 50% by weight, based on the ammonia-free hydrogenation mixture,
b) removing ammonia from the hydrogenation effluent,
c) removing hexamethylenediamine from the remaining mixture,
d) separating 6-aminocapronitrile and adiponitrile from high boilers individually or together, and
e) returning 6-aminocapronitrile, adiponitrile or mixtures thereof into step a).
DESCRIPTION OF RELATED ART
U.S. Pat. No. 3,696,153 discloses hydrogenating adiponitrile to hexamethylenediamine at temperatures of 100 to 200° C. and pressures of about 340 atm in the presence of granulated catalysts comprising very predominantly iron and small amounts of aluminum oxide and in the presence of ammonia as solvent.
Hexamethylenediamine yields of 98.8%, 98.8%, 97.7% and 97.7% are reached in the examples of Table 1 (run 2) and Table 2 (runs 1 to 3) at pressures of 340 atm. Complete conversion is reported for the first three examples and 99.9% conversion for the fourth example. With regard to the life of the iron catalysts, Tables 1 and 2 merely reveal that catalyst activity is high at the end of the runs (after around 80 to 120 hours).
U.S. Pat. No. 4,064,172 discloses hydrogenating adiponitrile to hexamethylenediamine at pressures of 20 to 500 bar and temperatures of 80 to 200° C. in the presence of iron catalysts synthesized from magnetite and in the presence of ammonia. A hexamethylenediamine yield of 98.2% is reported in Example 1.
U.S. Pat. No. 4,282,381 describes the hydrogenation of adiponitrile to hexamethylenediamine with hydrogen at temperatures of 110 to 220° C. and a pressure of about 340 atm in the presence of ammonia and iron catalysts. The hydrogenation effluent contains 0.04 to 0.09% by weight of adiponitrile and 0.2 to 0.5% by weight of 6-aminocapronitrile.
McKetta, Encyclopedia of Chemical Processing and Design, Marcel Dekker Inc. 1987, volume 26, page 230, Table 3, confirms that a typical hydrogenation product contains 0.01 to 0.11% by weight of adiponitrile and 0.10 to 0.21% by weight of aminocapronitrile. Illustrations 2 and 4 reveal that these small aminocapronitrile quantities can be separated off and returned into the hydrogenation.
These processes suggest that the reaction conditions in the industrial production of hexamethylenediamine have to be directed to achieving complete conversion of the adiponitrile and of the 6-aminocapronitrile intermediate of the hydrogenation.
The disadvantage with this is that this requires a relatively high temperature and a very high reaction pressure. If the adiponitrile and 6-aminocapronitrile conversion decreases markedly in the course of the hydrogenation, it has to be pushed back up again by raising the temperature and optionally the reaction pressure and/or lowering the catalyst loading, or a not inconsiderable loss of product of value will be incurred.
If, to obtain complete conversion, the temperature cannot be further increased because of decreasing hexamethylenediamine selectivity and/or the pressure cannot be further increased for technical reasons, then the catalyst loading has to be reduced. However, this means that catalyst productivity, i.e., the amount of hexamethylenediamine produced per unit time, will decrease. If the productivity drops below a certain level, the hydrogenation plant has to be shut down and the iron catalyst moved and replaced with an unused or regenerated catalyst. The greater the frequency of such shutdowns required per year, the lower the hexamethylenediamine quantity which a given production plant can produce per year.
It is an object of the present invention to provide a process for the catalytic hydrogenation of adiponitrile to hexamethylenediamine in the presence of catalysts comprising very predominantly elemental iron and ammonia as solvent in an economical and technically simple manner while avoiding the disadvantages mentioned.
DETAILED DESCRIPTION OF THE INVENTION
The process of the invention does not require complete adiponitrile and 6-aminocapronitrile conversion. This provides distinctly higher catalysts onstream times at lower pressures, fewer shutdowns for the hydrogenation plant and hence distinctly higher hexamethylenediamine productivities compared with the prior art.
It was unforeseeable and hence it is surprising that recycling 6-aminocapronitrile, adiponitrile or mixtures thereof into the hydrogenation stage does not cause any shortening of the catalyst onstream time. It is also surprising that the entire recycle does not cause any troublesome buildup of by-products in the system.
The adiponitrile used in the process of the invention can generally be prepared by conventional processes, preferably by reaction of butadiene with hydrocyanic acid in the presence of catalysts, especially nickel (0) complexes and phosphorus-containing cocatalysts, via pentenenitrile as intermediate.
The catalysts used can be conventional iron catalysts known for the production of hexamethylenediamine by hydrogenation of adiponitrile. Preferred catalyst precursors are those which comprise from 90 to 100% by weight, preferably from 92 to 99% by weight, based on the total mass of the catalyst precursor, of iron oxides, iron(II, III) oxide, iron(II) oxide, iron(II) hydroxide, iron(III) hydroxide or iron oxyhydroxide such as FeOOH. It is possible to use synthetic or naturally occurring iron oxides, iron hydroxides or iron oxyhydroxides, magnetite, which has the idealized formula of Fe
3
O
4
, brown ironstone, which has the idealized formula of Fe
2
O
3
x H
2
O, or hematite, which has the idealized formula of Fe
2
O
3
.
Preferred catalysts are those which comprise
a) iron or a compound based on iron or mixtures thereof,
b) from 0.001 to 5% by weight based on a) of a promoter based on 2, 3, 4, 5 or 6 elements selected from the group consisting of aluminum, silicon, zirconium, titanium, vanadium and manganese, and
c) from 0 to 5% by weight based on a) of a compound based on an alkali metal or on an alkaline earth metal.
Further preferred catalyst precursors are those in which component b) comprises from 0.001 to 5% by weight, preferably from 0.01 to 4% by weight, especially from 0.1 to 3% by weight, of a promoter based on 2, 3, 4, 5 or 6 elements selected from the group consisting of aluminum, zirconium, silicon, titanium, manganese and vanadium.
Further preferred catalyst precursors are those in which component c) comprises from 0 to 5% by weight, preferably from 0.1 to 3% by weight, of a compound based on an alkali or alkaline earth metal preferably selected from the group consisting of lithium, sodium, potassium, rubidium, cesium, magnesium and calcium.
The catalysts can be supported or unsupported catalysts. Examples of suitable support materials are porous oxides such as aluminum oxide, silicon oxide, alumosilicates, lanthanum oxide, titanium dioxide, zirconium dioxide, magnesium oxide, zinc oxide and zeolites and also activated carbon or mixtures thereof.
Preparation is generally effected by precipitating precursors of component a) if desired together with precursors of the promoter components b) and if desired with precursors of the trace components c) in the presence or absence of support materials (depending on which type of catalyst is desired), if desired processing the resulting catalyst precursor into extrudates or tablets, drying and subsequently calcining. Supported catalysts are generally also obtainable by
Ansmann Andreas
Bassler Peter
Fischer Rolf
Luyken Hermann
Melder Johann-Peter
BASF - Aktiengesellschaft
Davis Brian J.
Keil & Weinkauf
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