Abstract:
Poly(oxytetramethylene) diamines useful in the preparation of polyamide and polyurea elastomers are prepared by the catalytic reductive amination of a poly(oxytetramethylene) glycol feedstock under reductive amination conditions in the presence of ammonia and hydrogen using a hydrogenation/dehydrogenation catalyst composed of, on an oxide-free basis, about 70 to 75 wt. % of nickel, about 20 to about 25 wt. % of copper, about 0.5 to 5 wt. % of chromium and about 1 to 5 wt. % of molybdenum.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field of the Invention 
     This invention relates to a method for the catalytic reductive amination of a poly(oxytetramethylene) glycol in order to provide the corresponding poly(oxytetramethylene) diamine in high yield and with good selectivity. 
     More particularly, this invention relates to an improvement in the method for the catalytic reductive amination of a poly(oxytetramethylene) glycol in the presence of hydrogen and ammonia under reductive amination conditions wherein the reaction is conducted in the presence of a catalyst composed of nickel, copper, chromium and molybdenum and containing, on an oxide-free basis, about 70 to about 75 wt. % of nickel, about 20 to about 25 wt. % of copper, about 0.5 to 5 wt. % of chromium and about 1 to 5 wt. % of molybdenum. 
     Still more particularly, this invention relates to a process wherein a poly(oxytetramethylene) glycol, excess ammonia and hydrogen are passed through a bed of a pelleted nickel, copper, chromium, molybdenum catalyst on a continuous basis in order to continuously provide a reaction product comprising the poly(oxytetramethylene) diamine corresponding to the poly(oxytetramethylene) glycol feedstock. 
     2. Prior Art 
     Methods for the preparation and use of poly(oxytetramethyl) qlycols are disclosed in Smith et al. U.S. Pat. Nos. 3,824,198, 3,824,219, and 3,824,220, patented July 16, 1974. Other patents disclosing methods for making and using poly(oxytetramethyl) glycols and poly(oxytetramethyl) diamines include Hubin et al. U.S. Pat. No. 3,436,359 patented Apr. 1, 1969 and Leir et al. U.S. Pat. No. 4,833,213, patented May 23, 1989. 
     The catalyst to be used in conducting the process of the present invention is suitably a catalyst of the type disclosed in Moss et al. U.S. Pat. No. 3,151,115 wherein reductive amination catalysts are disclosed containing nickel, cobalt and copper or mixtures thereof and chromium oxide, molybdenum oxide, manganese oxide, thorium oxide and mixtures thereof. 
     The preferred catalyst disclosed by Moss et al. is a nickel, copper, chromia catalyst containing, on an oxide-free basis, from about 70 to 75 wt. % of nickel, about 20 to about 25 wt. % of copper and about 1 to about 5 wt. % of chromium. 
     Renken et al. U.S. Pat. No. 4,618,717, issued Oct. 21, 1986 is directed to a method for reductively aminating ethylene glycol monoalkyl ethers in order to provide the corresponding primary amines using a catalyst composed of about 50 to 90 wt. % of nickel, about 10 to 50  wt. % of copper and about 0.5 to 5 wt. % of an oxide of chromium, iron, titanium, thorium, zirconium, manganese, magnesium or zinc. Larkin et al. U.S. Pat. No. 4,766,245, issued Aug. 23, 1988 discloses a method for reductively aminating polyoxyalkylene diols and triols in the presence of a Raney nickel/aluminum catalyst. 
     The purification of tertiary butyl alcohol by the catalytic decomposition of impurities such as tertiary butyl hydroperoxide is disclosed in a series of patents. The catalyst of Marquis et al. U.S. Pat. No. 4,758,681, issued July 19, 1988, contains about 30 to 60 wt. % of nickel, about 5 to 40 wt. % of copper, about 1 to 30 wt. % of iron and about 0.5 to 10 wt. % of chromium. Sanderson et al. disclose the use of a catalyst containing 20 to 80 wt. % of iron, 5 to 40 wt. % of copper, 0.1 to 10 wt. % of chromium and 0.01 to 5 wt. % of cobalt for this purpose. In Sanderson et al. U.S. Pat. No. 4,742,179, the catalyst that is used for this purpose contains 1 to 20 wt. % of iron and 1 to 6 wt. % of chromium, the balance being composed of a mixture of nickel and copper, while the catalyst of Sanderson et al. U.S. Pat. No. 4,873,380, issued Oct. 10, 1989 is composed of 1 to 20 wt. % of barium, 1 to 6 wt. % of chromium and the balance a mixture of nickel and copper. 
     SUMMARY OF THE INVENTION 
     This invention relates to a method for preparing poly(oxytetramethylene) diamines. Poly(oxytetramethylene) diamines are useful for the preparation of polyamide and polyurea elastomers. The poly(oxytetramethylene) diamines are conveniently prepared from the corresponding poly(oxytetramethylene) glycols, commonly referred to as polytetrahydrofuran glycols. However, when the poly(oxytetramethylene) diamines are prepared by catalytic reductive amination of the corresponding poly(oxytetramethylene) glycols, using hydrogenation/dehydrogenation catalysts, and in particular, nickel hydrogenation/dehydrogenation catalysts, problems are normally encountered in obtaining both a good yield and a good selectivity in converting the poly(oxytetramethylene) glycol to the desired poly(oxytetramethylene) diamine product. 
     These and other problems are overcome in accordance with the present invention by conducting the reductive amination reaction in the presence of a catalyst composed of nickel, copper, chromium and molybdenum and containing, on an oxide-free basis, from about 70 to 75 wt. % of nickel, about 20 to about 25 wt. % of copper, about 0.5 to about 5 wt. % of chromium and about 1 to about 5 wt. % of molybdenum. 
     DETAILED DESCRIPTION 
     The starting materials for the present invention are a nickel, copper, chromia, molybdenum catalyst which may suitably be a powdered catalyst if the reaction is to be conducted in an autoclave on a batch basis or a pelleted catalyst if the reaction is to be conducted on a continuous basis in a continuous reactor. Also used as starting materials are ammonia, hydrogen and a poly(oxytetramethylene) glycol such as a poly(oxytetramethylene) glycol having the following formula: 
     
         HO--CH.sub.2 --CH.sub.2 --CH.sub.2 --CH.sub.2 --[--O--CH.sub.2 --CH.sub.2 --CH.sub.2 --CH.sub.2 --].sub.n --O--CH.sub.2 --CH.sub.2 --CH.sub.2 --CH.sub.2 --OH                                           (I) 
    
     wherein n represents 0 or a positive number having a value of 1 to about 50. 
     In accordance with the present invention, a poly(oxytetramethylene) glycol feedstock is substantially quantitatively converted to the corresponding poly(oxytetramethylene) diamine with excellent yields and selectivities when the reaction is conducted in the presence of a catalyst composed of from about 70 to about 75 wt. % of nickel, about 20 to about 25 wt. % of copper, about 0.5 to about 5 wt. % of chromium and about 1 to about 5 wt. % of molybdenum. 
     More particularly, an especially preferred catalyst composition of the present invention is one containing from about 70 to about 78 wt. % of nickel, about 20 to about 25  wt. % of copper, about 0.5 to about 3 wt. % of chromium, and about 1 to about 3 wt. % of molybdenum. 
     The reductive amination reaction of the present invention is suitably conducted at a temperature within the range of about 150° to about 220° C. and a pressure of about 100 to about 10,000 psig., such as a pressure of about 100 to about 3,000 psig. 
     The reductive amination is conducted in the presence of ammonia. Suitably, from about 1 to about 300 moles of ammonia per mole of poly(oxytetramethylene) glycol are employed, and more preferably, from about 10 to about 150 moles of ammonia are employed per mole of poly(oxytetramethylene) glycol. 
     The reaction is also preferably conducted in the presence of added hydrogen. The amount of added hydrogen used may be about 0.1 to about 10 mole per mole of poly(oxytetramethylene) glycol. Preferably, from about 0.5 to about 80 mole of hydrogen per mole of poly(oxytetramethylene) glycol will be employed. 
     The process of the present invention may be conducted batch-wise using an autoclave containing powdered catalyst, in which case the residence time is suitably from about 0.5 to about 5 hours. 
     More preferably, the reaction is conducted on a continuous basis using a bed of pelleted catalyst through which the hydrogen, ammonia and poly(oxytetramethylene) glycol are passed. When the reaction is conducted on a continuous basis, the poly(oxytetramethylene) glycol is suitably charged to the catalyst bed at the rate of about 0.1 to about 20 grams per hour of said poly(oxytetramethylene) glycol per cc of said catalyst and, more preferably, about 0.2 to about 0.6 grams per hour of poly(oxytetramethylene) glycol per cc of catalyst. 
     The reaction mixture formed as a result of the reductive amination of the poly(oxytetramethylene) glycol may be recovered and fractionated in any suitable manner, such as by fractional distillation, to obtain unreacted feed components, by-products and the desired poly(oxytetramethylene) diamine reaction product. Conversions of 90 wt. % or more and selectivities of 90% or more are obtainable with the process of the present invention, such that only minor quantities of unreacted feedstock and by-products are present in the reaction mixture. 
    
    
     EXAMPLES 
     The present invention will be further illustrated by the following specific examples which are given by way of illustration and which are not intended as limitations on the scope of this invention. 
     The nickel, copper, chromium, molybdenum catalyst used in conducting the batch and continuous experiments reported in the examples was a catalyst composed of about 75 wt. % of nickel, about 21 wt. % of copper, about 2 wt. % of chromium and about 2 wt. % of molybdenum. 
     In Example 1, which was conducted in an autoclave, the catalyst was powdered. In the subsequent examples, which were conducted on a continuous basis in a continuous reactor, a bed of pelleted catalyst was employed. 
     Example 1 
     A one-liter autoclave was charged with 299 g of a 2000 molecular weight poly(oxytetramethylene) glycol, 48 g of catalyst, and 90 g of ammonia. The clave was then pressured to 350 psig with hydrogen and heated over a 46-minute period to 220° C. It was held at that temperature for 3 hours. The reaction was then cooled and vented. The catalyst was removed by filtration and the product stripped at reduced pressure. The product had the following analysis: 
     
         ______________________________________Total Acet.     0.847 meq/gTotal Amine     0.688 meq/gPrimary Amine   0.556 meq/g______________________________________ 
    
     Example 2 
     A. In the following examples a tubular reactor filled with a Ni--Cu--Cr--Mo catalyst was used. Hydrogen, ammonia and the polyol (a 1000 molecular weight poly(oxytetramethylene) glycol) in the proportions of Example 1 were fed to the bottom of the reactor. The crude produced was then stripped under vacuum and analyzed. 
     
                                           TABLE I__________________________________________________________________________       Total            Total                Primary                      Total                          Primary   Temp Polyol       Acet.            Amine                Amine Amine                          AmineEx.   °C.   SV  meq/g            meq/g                meq/g %   %__________________________________________________________________________1  185  0.56       1.908            1.766                1.651 93  932  190  0.56       1.879            1.781                1.618 95  913  195  0.56       1.835            1.740                1.529 95  884  200  0.56       1.705            1.660                1.338 97  815  175  0.43       1.954            1.730                1.630 89  946  180  0.43       1.957            1.779                1.671 91  947  185  0.43       1.848            1.773                1.570 96  898  190  0.43       1.788            1.738                1.477 97  859  150  0.20       1.975            0.989                0.956 50  9710 155  0.20       1.944            1.419                1.347 73  9511 160  0.20       2.000            1.564                1.523 78  9712 165  0.20       2.000            1.773                1.709 89  9613 170  0.20       1.952            1.838                1.729 94  9414 175  0.20       1.830            1.814                1.625 99  9015 180  0.20       1.751            1.767                1.511 101 86__________________________________________________________________________ 
    
     As can be seen in examples 1, 2, 6, 13 and 14, high total amine content as well as high primary amine content can be obtained by the process of the present invention. The examples also show that a variety of space velocities can be used and that for each space velocity there is an optimum temperature. 
     B. This is a comparison example conducted under the conditions of Example 2A, except as noted. In this example, Raney Ni was used as the catalyst and a 1000 molecular weight polyol was used. 
     
                       TABLE II______________________________________ Polyol   Total   Total Primary                               Total PrimaryTemp. Space    Acet.   Amine Amine  Amine Amine°C. Velocity meq/g   meq/q meq/g  %     %______________________________________180   0.28     1.911   1.577 1.286  83    82175   0.28     1.900   1.550 1.260  82    81185   0.28     1.609   1.549 1.172  96    76190   0.20     1.536   1.512 1.104  98    73______________________________________ 
    
     None of the reaction conditions gave high total amine content and high primary amine content. 
     C. In this example conducted under the conditions of Example 1A, except as noted, a 650 molecular weight polyol and the catalyst in example A were used. 
     
                       TABLE III______________________________________ Polyol   Total   Total Primary                               Total PrimaryTemp. Space    Acet.   Amine Amine  Amine Amine°C. Velocity meq/g   meq/g meq/g  %     %______________________________________155   0.20     2.849   2.083 2.028  73    97160   0.20     2.840   2.444 2.334  86    95165   0.20     2.708   2.559 2.363  94    92170   0.20     2.662   2.541 2.223  95    87______________________________________ 
    
     At 165° C. a product high in both total and primary amine was obtained. 
     D. In this example, conducted under the conditions of Example 1A, except as noted, a 2000 molecular weight polyol and the catalyst in example A were used: 
     
                       TABLE IV______________________________________ Polyol   Total   Total Primary                               Total PrimaryTemp. Space    Acet.   Amine Amine  Amine Amine°C. Velocity meq/g   meq/g meq/g  %     %______________________________________160   0.20     0.927   0.818 0.792  88    97165   0.20     0.906   0.845 0.805  93    95170   0.20     0.933   0.846 0.779  91    92155   0.20     0.948   0.753 0.737  79    98______________________________________ 
    
     At 170° C., a product high in both total amine and primary amine was obtained. 
     E. This is a comparison example conducted under the conditions of Example 1A, except as noted. In this example a Ni--Cu--Cr catalyst was used and a 1000 molecular weight polyol was used. 
     
                       TABLE V______________________________________ Polyol   Total   Total Primary                               Total PrimaryTemp. Space    Acet.   Amine Amine  Amine Amine°C. Velocity meq/g   meq/g meq/g  %     %______________________________________160   0.20     1.835   1.314 1.144  72    87165   0.20     1.773   1.358 1.147  77    84170   0.20     1.723   1.411 1.165  82    83175   0.20     1.686   1.458 1.178  86    80180   0.20     1.67    1.461 1.163  87    80______________________________________ 
    
     High amination and high primary amine content were not obtained with this catalyst.