Organic compounds -- part of the class 532-570 series – Organic compounds – Amino nitrogen containing
Reexamination Certificate
2001-05-31
2002-04-23
Davis, Brian J. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Amino nitrogen containing
C564S491000
Reexamination Certificate
active
06376714
ABSTRACT:
FIELD OF THE INVENTION
The present invention concerns the hydrogenation of aliphatic or alicyclic dinitriles to produce diamines and/or aminonitriles, e.g. adiponitrile to produce hexamethylenediamine and/or 6-aminocapronitrile.
BACKGROUND OF THE INVENTION
Dinitriles are common feedstocks to the chemical, pharmaceutical, and agrochemical industries. Through hydrogenation they can be converted to diamines or aminonitriles, which are used in or as polymer intermediates, surfactants, chelating agents, and chemical synthesis intermediates. As a particular example, adiponitrile can be converted to 6-aminocapronitrile and/or hexamethylenediamine by hydrogenation. Hexamethylenediamine is an intermediate in the production of Nylon 6,6. 6-Aminocapronitrile can be used as an intermediate in the production of Nylon 6.
Traditional methods of producing hexamethylenediamine include hydrogenation of adiponitrile over a reduced iron oxide or cobalt oxide catalyst at very high pressures and temperatures. One disadvantage associated with these high-pressure processes is the high cost of the equipment required to conduct them on a commercial scale. An alternative low pressure process for hexamethylenediamine production uses an active nickel catalyst, such as Raney™ Ni, which is promoted by aqueous caustic (an alkali metal hydroxide such as sodium hydroxide) and operates at about 3.1 MPa (450 psig) and about 75° C. While these conditions are comparatively milder than the high pressure process and offer savings on the capital expense associated with a commercial scale plant, they are deterred by the necessity of using caustic to maintain catalyst activity, which complicates refining and poses waste handling and potential environmental problems. As an example, sodium hydroxide, itself, cannot be disposed by incineration. An alternative method is deep-well disposal, which is environmentally undesirable.
Some commercial processes for hexamethylenediamine production from adiponitrile are conducted using Raney™ Ni catalyst with a solvent. Unlike water, solvents are undesirable from an environmental point of view, because they may result in volatile organic compound emissions (VOCs) to the atmosphere. Solvents are, also, undesirable because they necessitate recycling and the use of additional refining equipment, which increase capital cost.
U.S. Pat. No. 5,900,511 concerns a process where adiponitrile is hydrogenated to hexamethylenediamine and optionally 6-aminocapronitrile in the presence of a sponge cobalt catalyst in a reaction medium that is substantially free of caustic. While this process does operate at relatively low pressure and avoids the use of caustic, it would be desirable to develop a process with an even longer catalyst lifetime and corresponding increased catalyst productivity.
SUMMARY OF THE INVENTION
In its first aspect the present invention is a process for converting aliphatic or alicyclic dinitriles to diamines and optionally aminonitriles e.g. adiponitrile to hexamethylenediamine and optionally 6-aminocapronitrile, comprising forming a reaction mixture that comprises: (1) an aliphatic or alicyclic dinitrile e.g. adiponitrile; (2) hydrogen; (3) a catalyst comprising a Group VIII element; and (4) one or more modifiers selected from the group of compounds consisting of quaternary ammonium hydroxides, quaternary ammonium cyanides, quaternary ammonium fluorides, quaternary phosphonium hydroxides, and quaternary ammonium thiocyanides; said reaction mixture containing less than a 1:1 molar ratio of solvent to dinitrile; wherein the process is performed at a pressure and temperature sufficient to convert at least a portion of the dinitrile to a diamine and optionally an aminonitrile.
In its second aspect, the invention is a process for converting aliphatic or alicyclic dinitriles to diamines and optionally aminonitriles e.g. adiponitrile to hexamethylenediamine and optionally 6-aminocapronitrile, comprising contacting a Group VIII element-containing hydrogenation catalyst with one or more modifiers selected from the group of compounds consisting of quaternary ammonium hydroxides, quaternary ammonium cyanides, quaternary ammonium fluorides, quaternary phosphonium hydroxides, and quaternary ammonium thiocyanides to form a modified catalyst; and forming a reaction mixture comprising: (1) an aliphatic or alicyclic dinitrile e.g. adiponitrile; (2) hydrogen; (3) modified catalyst; and optionally (4) one or more modifiers selected from the group of compounds consisting of quaternary ammonium hydroxides, quaternary ammonium cyanides, quaternary ammonium fluorides, quaternary phosphonium hydroxides, and quaternary ammonium thiocyanides; said reaction mixture containing less than a 1:1 molar ratio of solvent to dinitrile; wherein the process is performed at a pressure and temperature sufficient to convert at least a portion of the dinitrile to a diamine and optionally an aminonitrile.
The use of the modifiers to maintain and/or improve the activity, selectivity and lifetime of the catalyst in the absence of large concentrations of solvent is advantageous over the use of caustic due to environmental and waste disposal concerns.
DETAILED DESCRIPTION OF THE INVENTION
According to the present invention, an aliphatic or alicyclic dinitrile can be hydrogenated to a diamine or a mixture of diamine and aminonitrile (for example adiponitrile can be hydrogenated to hexamethylenediamine or a mixture of hexamethylenediamine and 6-aminocapronitrile using a catalyst) in the absence of caustic. The process employs one or more catalyst modifiers to maintain or improve the activity, selectivity and/or lifetime of the catalyst and to reduce the overall concentration of unwanted byproducts. In the example of adiponitrile hydrogenation, hexamethyleneimine and bis(hexamethylene)triamine are unwanted byproducts. The use of modifiers such as quaternary ammonium hydroxide, cyanide, fluoride or thiocyanide salts, or quaternary phosphonium hydroxide salts is advantageous over the use of caustic due to environmental and waste disposal concerns. The modifiers of the present invention can be used instead of sodium hydroxide even in existing commercial facilities. Because the modifiers decompose to simple organic materials, under refining conditions they do not pose the waste handling and environmental concerns experienced with caustic. Specifically, these salts or the products of their decomposition may be incinerated similarly to any process organic waste stream. Unlike sodium hydroxide, the commonly used caustic, the modifiers of the present invention will not build-up in the incinerator firebricks, nor will they require disposal via deep-wells. While this invention does not exclude the use of caustic, an environmental benefit will be garnered by avoiding its use.
Suitable aliphatic or alicyclic dinitriles, for use herein, have the general formula R(CN)
2
, wherein R is a saturated hydrocarbylene group. A saturated hydrocarbylene group contains carbon and hydrogen atoms in branched or straight chains or rings and does not contain a double or triple bond between any pair of carbon atoms. Preferred hydrocarbylene groups contain from 2 to 25, more preferably 2 to 15, and most preferably 2 to 10 carbon atoms per group. In other words, preferred dinitriles contain from 4 to 27, more preferably 4 to about 17, and most preferably 4 to 12, carbon atoms per dinitrile molecule. The preferred type of hydrocarbylene group is a linear alkylene group.
Examples of suitable dinitriles include, but are not limited to, adiponitrile; methylglutaronitrile; succinonitrile; glutaronitrile; alpha, omega-heptanedinitrile; alpha, omega-octanedinitrile, alpha, omega-decanedinitrile, alpha, omega-dodecanedinitrile; and combinations of two or more thereof. The preferred dinitrile is adiponitrile.
The catalyst in the process is a hydrogenation catalyst suitable for hydrogenating a dinitrile to a diamine or a mixture of diamine and aminonitrile. Preferred are catalysts based on Group VIII elements including iron, cobalt, nickel, rhodium, palladium, ruth
Allgeier Alan M.
Koch Theodore A.
Sengupta Sourav K.
Davis Brian J.
Deitch Gerald E.
E. I. du Pont de Nemours and Company
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