United States Patent Office Patented Feb

3,235,600 United States Patent Office Patented Feb. 15, 1966 2 quality and color stability of the polyamide product re 3,235,600 Sulting from the polycondensation of hexamethylenedi REDUCTION OF DAMENOCYCLOHEXANE CON. CENTRATION IN CRUDE HEXAMETYLENED amine with dibasic carboxylic acids. The 1,2-diamino AMNE cyclohexane gives rise to salt solutions of hexamethylene Philip W. Evans, Pensacola, Fla., assignor to Monsanto diamine and dibasic carboxylic acids which have poor Company, a corporation of Delaware and variable color, and the polyamides prepared from No Drawing. Filed Nov. 28, 1962, Ser. No. 240,742 these Salt solutions not only have poor color but also are characterized by irregular tensile strength and nonuniform - 4 Claims. (C. 260-583) dyeing properties. This invention relates to the production of amines and Although one major cause for polyamide product more particularly, it relates to a process for the produc 10 quality, color, and dyeing problems has been ascertained tion of amines in a high degree of purity. and explained, the saisfactory removal on a commercial Hexamethylenediamine is now a well-known com Scale of the Small amounts of 1,2-diaminocyclohexane pound which may be prepared on a commercial scale present in manufactured crude hexamethylenediamine to most conveniently by catalytically hydrogenating adipo eliminate the cause presents a difficult problem. Accord nitrile in the presence of ammonia. A principal use of ing to present commercial practices, the 1,2-diaminocyclo hexamethylenediamine involves condensing it with di hexane is removed from the hexamethylenediamine by basic acids to produce polyamides, and in manufacturing fractional distillation; however, because of the proximity these polyamides, important advantages are obtained by of the boiling points of 1,2-diaminocyclohexane and hexa reacting the diamine in a first step with an equivalent 20 methylenediamine, a fractional distillation process de amount of dibasic carboxylic acid to form a salt using a signed to separate these compounds must of necessity be Solvent Such as water, methanol or ethanol in accord one which is capable of separating constituents whose ance with procedures well known in the art. This salt volatilities are in the same order of magnitude. Distilla thus prepared is subsequently converted in a second step tion processes that meet this requirement are known to to the polyamide condensation product. 25 be not too efficient and to be extremely expensive to Although there are a number of methods for the prepa operate. Moreover, to effect the desired removal of the ration of hexamethylenediamine which are known and 1,2-diaminocyclohexane by fractional distillation, there used in industry, none of these methods result in the pro are attending losses in the prime product, hexamethylene duction of hexamethylenediamine which is free from diamine, and the apparatus to perform the distillations products of side reactions and the like. Consequently, 30 is expensive to install and in most instances, presents a further refinement of the crude hexamethylenediamine major bottleneck to increased output from continuous produced is necessary generally to obtain a product which processes for the production of refined hexamethylenedi exhibits the high degree of purity necessary when the amine. hexamethylenediamine is to be used in industrial proc It is, therefore, an object of this invention to provide esses which culminate in the production of commercially an improved hexamethylenediamine composition and to saleable articles. This is especially true, for example, in provide a process for preparing this composition. the production of polyamides wherein hexamethylenedi Another object of this invention is to provide a process amine is reacted with adipic acid to produce polyhexa for the preparation of highly purified hexamethylenedi methylene adipamide which is used in many end products. amine. Utilization of poorly refined hexamethylenediamine in 40 A further object is to provide a process for the catalytic the production of polyhexamethylene adipamide causes hydrogenation of adiponitrile to hexamethylenediamine a restriction of the molecular weight, results in a polymer wherein the production of the by-product, 1,2-diamino having bad color characteristics and poor dyeability, and cyclohexane, is suppressed. affects various other physical and chemical properties of These and other objects of this invention will be ap the polymer or products made therefrom. For example, 45 parent from the description hereinafter. in the textile field where polyhexamethylene adipamide In accordance with this invention, it has been dis is used widely for the production of filaments and fibers, covered that the above and other objects are accomplished the use of poorly refined hexamethylenediamine results in by catalytically hydrogenating a nitrile under controlled Weak filaments and fibers, as well as ones having poor conditions of temperature and pressure in the presence coller characteristics which do not meet the stringent tex of ammonia and at least one of the group of compounds tile standards. comprising organic and inorganic carbonates, organic and One process currently in wide use throughout industry inorganic carbamates, and carbon dioxide. for the production of hexamethylenediamine is the hydro In a particular preferred embodiment of the invention, genation of adiponitrile in the presence of a catalyst such a mixture of adiponitrile, ammonia, hydrogen, and at as cobalt. This process is generally operated on a con least one of the group of compounds comprising organic tinuous basis by passing hydrogen and adiponitrile over and inorganic carbonates, organic and inorganic carba or through a catalyst under conditions of elevated pres mates, and carbon dioxide is passed over or through a sure and temperature. Liquid ammonia is added to the hydrogenation catalyst under conditions of elevated tem process to absorb exothermic heat of reaction and to perature and pressure, whereby crude hexamethylenedi limit the formation of unwanted by-products. After the 60 amine containing a suppressed quantity of the hydrogena crude product is formed, unwanted by-products may be tion by-product, 1,2-diaminocyclohexane, is produced. removed by passing the crude product through a series of The nitrile which is employed may be derived from any distillation stills or by chemical treatments or combina suitable source and when adiponitrile is used it may be tions of these methods. obtained from the reaction of adipic acid with ammonia, It is well known in the art that the catalytic hydrogena the reaction of dichlorobutane with hydrogen cyanide, the tion of adiponitrile under commercially attractive condi hydrogenation of dicyanobutene, or other known means tions results in the formation of very small amounts of for the preparation thereof and should be of the degree the compound 1,2-diaminocyclohexane along with the de of purity well known in the art. sired product, hexamethylenediamine, and that the pres The hydrogenation of the nitrile to the amine may ence of this cyclic compound, even in very minute quan be effected by using various hydrogenation catalysts such tities, has a drastic and critically adverse effect on the as nickel, cobalt, copper, zinc, platinum, palladium, rubid 3,285,600 3 4. ium, ruthenium, and the like; and these elements, either of depending upon the hydrogenation reactants and the in the form of free metals or in the form of compounds desired conditions of temperature and pressure for the Such as the oxides or salts, may be employed, if desired, hydrogenation. The hydrogenation reactants, the am in conjunction with known promoters and/or supports. monia, and the deleterious by-product suppressant may For the hydrogenation of adiponitrile to hexamethyl be fed separately to the catalyst or catalysts for contact enediamine, cobalt catalysts and in particular catalysts ing or any two or more of the components may be mixed comprising cobalt oxide are preferred. With each other prior to their contacting the catalyst. These above mentioned catalytic materials are used In the example of the hydrogenation of adiponitrile to preferably in a finely divided form and may be deposited hexamethylenediamine, is has been found advantageous on a porous Supporting means such as pumice, kieselguhr, 10 to mix the hexamethylenediamine carbonate or amino alumina gel and silica gel. Catalyst powders are pre capronitrile carbamate or combinations of these with pared conveniently for use in the hydrogenation process the adiponitrile or the ammonia or combinations of these by compressing the catalyst into pellets or brickets of suit prior to the contacting of the resultant mixture with the able size. Stabilized catalysts containing a substantial pro hydrogen and the catalyst or catalysts. Water may be portion of oxide, catalysts comprising the carbonate, ox 5 present in one or more of the components of the hydro ide or hydroxide of the hydrogenating metal deposited genation feed stream to the catalyst or catalysts with on an inert porous support, and catalysts in which the hy Out affecting the beneficial results obtained from the del drogenating metal is combined with a non-reducible oxide eterious by-product suppressant compound. are preferably reduced in a stream of hydrogen-contain The following examples are intended to illustrate the ing gas prior to exposure to the reaction compounds. 20 present invention more fully but are not to be construed The temperature for the

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