Abstract:
A process for the preparation of hexamethylene imine from hexamethylene diamine by the vapor phase reaction in the presence of water, hydrogen, and a palladium catalyst.

Description:
FIELD OF THE INVENTION 
     This invention relates to the preparation of hexamethyleneimine, also known as perhydroazepine, from hexamethylene diamine at high conversion and at high yield. 
     BACKGROUND OF THE INVENTION 
     The preparation of hexamethyleneimine by the catalytic reaction of hexamethylene diamine and hydrogen in the vapor phase is described in U.S. Pat. No. 4,001,213. The preferred catalysts disclosed are nickel, copper, cobalt and iron, but novel metals of Group 8 are also disclosed; i.e. rhodium, palladium and platinum catalyst. Example 6 of this patent shows a catalyst of palladium and cobalt. The example concludes with the statement: &#34;While palladium increased the activity of the catalyst system it drastically reduces the selectivity to the desired imine product&#34;. 
     SUMMARY OF THE INVENTION 
     The present invention is a process for the preparation of hexamethyleneimine by contacting a gaseous mixture containing 1,6-hexamethylene diamine, water and hydrogen with a solid palladium catalyst at a temperature of 160° to 260° C. at a pressure of 0 to 100 psig. 
     If desired, the gaseous mixture may also contain methane, ammonia, nitrogen, or other inert gases. The methane or ammonia, apparently pass through the reactor without directly participating in reaction, but increase the activity of the catalyst, especially at higher pressures of operations. 
     The palladium catalyst comprises an inert substrate, on which is dispersed palladium metal. Normally the amount of palladium in the catalyst is about 0.1 to 10% by weight palladium. 
     The amount of water in the gaseous mixture may vary widely. Normally the gaseous mixture will be made by vaporizing an aqueous mixture of water and hexamethylene diamine. The amount of water in this aqueous mixture may vary from 1 to 40% by weight. 
     The amount of hydrogen in the gaseous mixture may also vary widely but is usually present in an amount, on a molar basis, about 5 to 15 times the amount of hexamethylene diamine. The amount of hydrogen employed may be lowered if methane, ammonia, nitrogen or other inert gas is also present in the gaseous mixture. Ammonia is a product of reaction; but, added NH 3  or methane or nitrogen may be used in high pressure operations to reduce the partial pressure of H 2 . 
    
    
     DETAILED DESCRIPTION 
     The process of the invention may be carried out by passing a gaseous mixture of 1,6-hexamethylene diamine, water and hydrogen through a reactor filled with loosely packed palladium metal catalyst. A suitable laboratory reactor is a metal tube having an internal diameter of 0.5 to 1 inch. The tube may be mounted vertically, or horizontally. If it is mounted vertically it is preferred to pass the gaseous mixture downwardly through the reactor. 
     The palladium metal catalyst comprises an inert substrate having dispersed palladium metal on its surface. The inert substrate can be aluminum oxide, glass, silica, etc. Aluminum oxide in the form of spheres having a diameter of about 1/20 to 1/8 inch is a preferred substrate. 
     The palladium metal content of the catalyst should be in the range of 0.1 to 10% by weight of the catalyst, preferably 0.5 to 2% by weight. The palladium need not completely coat the substrate; finely dispersed particles of palladium metal on the substrate are satisfactory. 
     After the gaseous mixture passes through the reactor, the mixture is cooled to condense a hexamethylene imine containing liquid, the hydrogen removed and recycled to the feed, and the liquid separated into its components by conventional techniques. 
     EXAMPLE 
     A five foot long thin walled stainless steel tube having an external diameter of 0.5 inch and an internal diameter of 0.42 inch was loaded with 110 grams of palladium metal on Al 2  O 3  spheres having a diameter of 1/16 inch. The palladium content was 0.5% by weight. The palladium was in the form of a thin coating on the surface of the Al 2  O 3  spheres. The reactor was heated to 220° C. by oil in an external jacket, and a vapor of 70% 1,6-hexamethylene diamine and 30% water was fed to the top of the reactor along with hydrogen, and in some runs ammonia, and in some runs methane. The reaction is isothermal. The conditions and results are shown in the table below. 
     
         ______________________________________FLOWRATES         70%      H.sub.2 PRES.   HMD      CC/  NH.sub.3                              % HMD  % HMIRUN   PSIG    ML/HR    MIN  CC/MIN CONV.  YIELD______________________________________ 1    20      61       2000  0     99.8   92.6 2    20      61       2000  0     99.8   92.3 3    20      50       2000  0     99.9   91.9 4    60      50       2000  0     83.0   96.0 5    80      50       2000  0     69.9   95.2 6    60      50       1700 295    97.6   93.9 7    60      50       1500 490    99.1   94.6 8    60      50       1250 735    99.7   88.5 9    60      50        500 1470   99.7   76.710    80      50       1700 295    78.2   94.711    80      50       1500 490    87.4   94.312    80      50       1250 735    97.3   94.513    60      75        500 1470   99.6   83.314    80      50       2000 0000   63.5   83.315    80      50       2000 0000   51.6   90.616    80      50       1700 300    56.4   92.617    80      50       1500 500    67     9118    80      50       1250 750    85.3   91.619    80      50       1000 1000   95.8   91.820    80      50       1000 1000   97.8   91.6______________________________________