Abstract:
Production of spinnable polyhexamethylene adipamide of high molecular weight from adiponitrile, hexamethylene diamine, water and additives, preferably continuously in a reaction cascade and in a finisher as the final stage, catalytically accelerated by catalysts as disclosed. 
     The polyamides can be produced from dinitriles, diamines and excess water in the presence of catalysts selected from the group consisting of: alkyl, aryl and alkyl/aryl esters of phosphoric, phosphorous, phosphonic and phosphinic acids. The catalyst is present in the amount of 0.001 to 1.0% based upon the total weight of the reactants.

Description:
REFERENCE TO RELATED APPLICATION 
     This is a continuation-in-part of co-pending application Ser. No. 375,971, filed May 10, 1982, now U.S. Pat. No. 4,436,898 issued Mar. 13, 1984 which is a continuation-in-part of Ser. No. 370,271 filed Apr. 20, 1982, now abandoned, which is a continuation-in-part of Ser. No. 264,982, filed May 18, 1981, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a method for producing spinnable polyamides of the so-called nylon type by a conversion and polycondensation of dinitriles with aliphatic α,ω-diamines and excess water in the presence of catalysts of an inorganic or organic nature in catalytic quantities. 
     The method disclosed herein is utilized for the continuous production of polyhexamethylene adipamide, Nylon-6.6, from adiponitrile and hexamethylene diamine in the presence of ammonia-containing water and small quantities of catalysts, preferably oxygen-containing compounds of phosphorus which exert an accelerating influence on the total kinetics of the process, thereby facilitating a higher degree of polymerization and/or reduction in the time required for said polymerization. 
     Up to now, adipic acid, that could be produced only from aromatics, has been used to produce polyamides. A separate saponification of adiponitrile into adipic acid is bothersome, does not proceed well quantitatively, and is therefore not considered practical. At present, adiponitrile can be produced considerably more economically electrochemically from propylene or acrylonitrile, as well as catalytically by the conversion of butadiene and hydrogen cyanide on a large scale and with high purity. 
     At the present time, adipic acid is shipped by costly transport means in solid form, and hexamethylene diamine in a liquified state with a small amount of water in separate containers; or a neutralized solution of adipic acid and hexamethylene diamine, each approximately in a 60% concentration, is shipped in heated tank cars. Aside from the difficulties in connection with longer distances, the co-shipping of approximately 40% water is costly. 
     The shipping of solid salt comprising equimolar quantities of adipic acid and hexamethylene diamine, the so-called AH-salt, does not eliminate the above difficulties. This is due to the fact that the AH-salt must be obtained in a costly manner with respect to energy by evaporation or precipitation from water or methanol. For further processing, again, a 60% AH-salt solution, increased by the water from the reaction, must be evaporated during the polycondensation. 
     Literature on the reaction between adiponitrile, hexamethylene diamine and water in excess does not mention an efficient technical process for the reaction. Thus, in Greenewalt, U.S. Pat. No. 2,245,129, a total reaction time of more than 20 hours is required for a conversion as in example II therein. Also, in Onsager, U.S. Pat. No. 3,847,876, all disadvantages, which would be alleviated by an economical, continuous working method, are not eliminated, especially because Onsager calls for a minimum content of 1% of free ammonia in the reaction product. Thus, in examples 1-10 therein, which led to spinnable products, total reaction times of more than 8 hours were required. By a recycling, as in example 3 therein, a residence time spectrum was brought about and reached, which was unfavorable and undesirable for polyhexamethylene adipamide. 
     From experience it has been known that, based on the thermal instability of polyhexamethylene adipamide, short residence time and good residence time spectra are desirable, in all phases of the method, and which become more critical with an increasing degree of polycondensation and with increasing temperatures. It is with this background that the present invention was developed. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a method for the production of spinnable polyamides, specifically spinnable polyhexamethylene adipamide of high molecular weight from adiponitrile, hexamethylene diamine, water and additives, preferably continuously in a reaction cascade and in a finisher as the final stage, accelerated by catalysts, and under conditions of reaction, which will produce less than 1% of free ammonia in the reaction product at a temperature of more than 225° C. 
     It is a further object of the present invention to provide an economical method for the production of spinnable polyhexamethylene adipamide which avoids the use of adipic acid and uses, instead, adiponitrile that is economically produced from reasonably priced raw materials, such as propylene and butadiene. 
     Another object of the present invention is to provide a method for the production of spinnable polyhexamethylene adipamide which utilizes equimolar mixtures of adiponitrile and hexamethylene diamine which are in a liquid state at room temperatures with the addition of a small amount of water and which can be shipped conveniently over long distances with minimal ballast. 
     It is yet another object of the present invention to provide a method for the production of spinnable polyhexamethylene adipamide which is more economical than previous methods with respect to energy requirements and reactant requirements. This fact becomes apparent in light of the following comparisons and examples: 
     (a) Per ton of polyhexamethylene adipamide, approximately 1,160 kg AH-salt is required but only 992 kg of an equimolar mixture of adiponitrile and hexamethylene diamine is required. 
     (b) Per ton of polyhexamethylene adipamide, there are formed according to the method as defined in the present invention, approximately 150 kg of ammonia, gaseous or in watery solution, which, as a salable by-product, helps to lower the production costs (use, for instance, for fertilizers). 
     (c) Per ton polyhexamethylene adipamide, there must be evaporated, according to the conventional manner (starting from 60% AH-salt solution), about 930 kg of water during the polycondensation. According to the method as defined in the present invention, only approximately 130 kg water and 150 kg ammonia have to be evaporated for the same quantity of polyamide. 
     Still another object of the present invention is to provide a method for the production of spinnable polyhexamethylene adipamide, which utilizes ammonia-containing water and the addition of varying amounts of catalysts preferably oxygen-containing compounds of phosphorus, in the form of esters, to exert an accelerating and stabilizing influence on the total reaction. Typical of such compounds of phosphorus so utilized are the alkyl, aryl and alkylaryl esters of hypophosphorous acid, phosphorous acid, phosphoric acids phosphinic and substituted phosphinic acids and phosphonic and substituted phosphonic acids, which are advantageously added in water solutions. Catalyst quantities, which are effectively added, range from 0.005 to 4.0, preferably 0.1 to 1.0, weight percent of an equimolar mixture of adiponitrile and hexamethylene diamine. 
     Yet another object of the present invention is to provide a method for the production of spinnable polyhexamethylene adipamide in which chain controllers in the form of monocarboxylic acids of monamines, in quantities of 2-30 mmol per kg of an equimolar mixture of adiponitrile and hexamethylene diamine, are added at the start of the reaction of the stabilization of the polymer melt so that there is a constant melt viscosity during the later processing operations. As monocarboxylic acids, for example, acetic acid, propionic acid or benzoic acid can be used. Of the monoamines, butylamine, n-hexylamine, n-octylamine and cyclohexylamine are recommended. 
     An object supplementary to the present invention is the stabilization of the spinnable polyhexamethylene adipamide against light and heat attack depending on the application desired. In particular its use for technical yarns and tire cord requires good stabilization of the polymeric mass and formed fibers against heat and oxygen by adding well-known heat stabilizers such as diarylamines, N-substituted p-phenylenediamines, mercaptobenzimidazoles, copper salts and iodine compounds either alone or in the form of mixtures. Addition may take place prior, during, or on completion of the reaction. 
     In a principal aspect, the present invention relates to the multi-stage conversion of adiponitrile and hexamethylene diamine in the presence of excess water which takes place according to the following summzation reaction: ##STR1## 
     Intermediate products of a low molecular weight are formed from the addition and conversion of nitrile groups with water into different acid amides, for instance, δ-cyanovaleric acid amide and adipic acid diamide. When the reaction conditions, as defined in the present invention and described further hereinafter, are observed, pure adiponitrile is completely converted and disappears after a short reaction period without noteworthy development of ammonia. The acid amides and nitrile amides which formed then react in the form of a transamidation with the amino groups of hexamethylene diamine, forming ammonia, and then reacting further to aminoalkylated acid amides and to the initial polyamide products. A certain part of the saponifications of the nitrile groups or the resulting acid amides into the corresponding acids or ammonium salts are also feasible. As the thermally most unstable compound in this process, the adiponitrile can easily react, intramolecularly, to 2-cyanocyclopentanoneimine which leads to gels and discolorations by further undesirable reactions. 
     Surprisingly it has been further found, in contrast to the teachings of Onsager, that utilizing the conditions according to the present invention, i.e., using an autogenous pressure of 22-24 bar and the preferred temperatures of more than 225° C., always less than 1% free ammonia is present in the reaction product. Because of the physical conditions according to the present invention, a maximum ammonia content of 0.30 to 0.45% is present during the pressure phase in the reaction product. Higher ammonia contents as expressly required by Onsager, necessitate higher pressure, i.e., 30 bar as a minimum, and temperatures lower than 225° C. at the beginning of the reaction. 
     The economic advantages of the present invention are quite obvious, since a maximum pressure up to 25 bar utilizes less expensive equipment, shorter reaction times, less waste water, and produces better product qualities. 
     These and other objects, advantages and features of the invention will be set forth in the detailed description which follows. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     As detailed, hexamethylene diamine and adiponitrile are fed continuously in equimolar quantities into a heatable preparation boiler. At the same time, a catalyzer solution, approximately 10% in water, and demineralized water, or ammonia-containing water, are stirred in. The homogeneous mixture is continuously heated by means of a controllable piston pump, by way of a heat exchanger, to approximately 220° C., and is led to the first stage of the reaction cascade. At a controlled reaction temperature of approximately 245° C. and a reaction pressure of 24 bar, gaseous ammonia and water, which are carried along according to partial pressure, escape through the relief valve by way of the dephlegmator. The water is condensed to a great extent by the dephlegmator and returned to the reactor. The dephlegmator is operated at a temperature of approximately 45° C. 
     If necessary, pigments, preferably as titanium dioxide, may be added as prepared suspensions in adiponitrile or mixtures of adiponitrile and water as 10-40% suspension concentrates. The pigments are led to the first stage of the reaction cascade by way of line along the dispersion agents, which may be polymetasilicates, polyphosphates or polyvinyl alcohols. The pigment concentrations are preferably 0.1-3 mass %. 
     Because of the difference in the levels of the reaction cascade, the partially converted reaction product enters continuously into the second stage of the reaction cascade with equal pressure. Further heating of the reaction mass to 270° to 280° C. takes place in the second stage. 
     Released ammonia and water flow from the second stage to the common relief valve also by way of a dephlegmator. The water is condensed for the greatest part by the dephlegmator and then travels again to the reactor. The working temperature of the dephlegmator is at approximately 55° C. Released ammonia and also water, in small quantities, flow by way of a condensing receiver, with an attached cooler, at a temperature of approximately 35° C., to a separate ammonia recovery. 
     The polyamide precondensate from the second stage of the reaction cascade flows by way of a controlled relief valve into a stirred polycondensation reactor, which has a working pressure of between 1.5 and 3 bar, to which unsaturated H 2  O vapor or inert gases can be added. Ammonia is released from the reactor and flows jointly with excess water to the descending cooler by way of the relief valve and subsequently flows into the condensating receiver. The ammonia, which is not dissolved under normal pressure in the process, escapes together with the ammonia from the reaction cascade to the ammonia recovery by way of the rising cooler. 
     In a finisher, the reaction mass, which has nearly been converted in the polycondensation reactor at 285° C., is subsequently put into the desired final state, which is chosen depending on the degree of polymerization desired. For this purpose, the polyamide mass present in the polycondensation reactor is continuously discharged by means of a gear pump and, by means of the heat exchanger, is brought to temperatures between 290° and 300° C. and led to a finisher system which consists of an expansion vessel attached for final relief of the rest of the volatile compounds, connected to a screw reactor. In the expansion vessel, heated inert gases, in the form of pure nitrogen or unsaturated water vapor, can be added in order to accelerate the rest of the polycondensation, and further additives can be added by the line. 
     In the present invention, a double screw reactor with an additional degassing zone is used. Depending on the intended use, the polyamide product has adjustable relative solution viscosities between n rel . 2.3-3.2. (The relative solution viscosity is measured here in a concentration of 1 g/100 ml, 96% sulfuric acid at 25° C.) The spinnable polyamide melt produced in the finisher can be led to the usual granulate production as well as to a direct spinning process. 
     For the following applications, the following relative solution viscosities are common for polyhexamethylene adipamide: 
     
         ______________________________________            rel. visc.______________________________________(a)     textile filaments                  2.4-2.6(b)     carpet yarn    2.7-2.8(c)     technical filaments and                  2.8-3.2   tire cord______________________________________ 
    
     In addition to its use as a fiber, these polyamides can be used in any other application calling for the use of a nylon-type polymer. For example, these polyamides can be used as plastics, films and molding compounds. 
     The diamines suitable for use in this reaction are the diamines containing from 1 through 20 carbon atoms. The diamines may be aliphatic, straight chain or branched, or aromatic or they may contain a hetero-atom. Also useful are substituted diamines, provided the substituents are inert under the reaction conditions. Preferably the diamines are the aliphatic or aromatic diamines which contain from 4 through 12 carbon atoms such as hexamethylene diamine, 1,4-diaminobutane, 1,5-diaminopentane, 1,8-diaminoctane, 1,10-diaminodecane, 1,12-diaminododecane, 2,5-dimethylhexane-2,5-diamine, 4,4&#39;-diaminodicyclohexylsulfur, p-diaminodicyclohexylmethane, 4,4&#39;-diaminodicyclohexylether, octamethylenediamine, tetramethylenediamine and the like, i.e., diamines of the formula: 
     
         R&#39;HN--R&#34;--NHR&#39; 
    
     wherein R&#34; is an alkylene or arylene group containing 4 to 12 carbon atoms and each R&#39; is independently hydrogen or a univalent organic radical. The most preferred diamine is an α,ω-aliphatic diamine. 
     The dinitriles which can be used in accordance with the inventive reaction are dinitriles containing from 2 through 20 carbon atoms. These dinitriles may be aliphatic, straight chain or branched, or aromatic or they may contain a heteroatom. Also useful are substituted dinitriles so long as the substituents are inert under the reaction conditions. Most preferably, however, the dinitriles are the aliphatic or aromatic dinitriles which contain from 4 through 12 carbon atoms, such as adiponitrile, succinonitrile, glutaronitrile, suberonitrile, sebaconitrile, 1,10-decanedinitrile, isophthalonitrile, terephthalonitrile and the like, i.e., dinitriles of the formula: 
     
         NC--R--CN 
    
     wherein R is an alkylene or arylene group of 2 to 10 carbon atoms. 
     The phosphorus ester catalysts suitable for use in the invention include esters of phosphorous, phosphonic, alkyl, aryl and alkyl/aryl substituted phosphonic, hypophosphorous, alkyl, aryl and alkyl/aryl substituted phosphinic, and phosphoric acids. In the substituted acids, the alkyl, aryl or alkyl/aryl group replaces the hydrogen connected directly to the phosphorus atom. The esters are formed conventionally with the alkyl, aryl, alkyl/aryl group replacing the hydrogen of an --OH group comprising the acid. To clarify the nomenclature, the names of the acids are identified with the structural formulas as follows: ##STR2## 
     One or more of the --OH groups may be substituted to form the esters useful in the invention as set forth in the specific examples below. 
     As discussed above, it is preferred commercially to run this process continuously, in a reaction cascade under the disclosed reaction conditions. However, the reaction can also be performed with very simple equipment under a broad range of process conditions. 
     This reaction is normally carried out in a pressure vessel in the absence of air. The reaction is also normally initially carried out a superatmospheric pressure with a later reduction to atmospheric pressure. It is preferable to then remove the excess water and ammonia from the reaction system by either reducing the pressure to subatmospheric pressure or by adding an inert gas. During this polymerization it is preferable to release the ammonia while at least initially maintaining some or all of the water in the reaction system. This can be accomplished, for example, by the use of return flow coolers. 
     The method as defined in the present invention is better understood with reference to the following examples: 
     EXAMPLES 1-30 
     Equimolar quantities of adiponitrile and hexamethylene diamine, partly varying quantities of water, and catalytic quantities of inorganic or organic compounds, as detailed in TABLE 1, with 100 ppm silicon-antifoam additive, were put into a stirring autoclave of stainless steel having a volume of 2 liters and were mixed. The autoclave was provided with a dephlegmator and, after a pressure relief valve, with a descending cooler and was steplessly heated continuously and controllably with a heat transfer oil. Before the start of each test, the filled autoclave was rinsed with nitrogen several times and subsequently put into a pressureless state. 
     With continuous stirring the reaction mixture in the autoclave was heated in such a way that a product temperature of 225° C. was reached within 45 minutes. The autogenous pressure was then between 22-24 bar. During a pressure period of 50 minutes, further heating was done, the developed ammonia being continuously released via the dephlegmator. Simultaneously, evaporated water was returned as dephlegmate into the autoclave. 
     After a further 135 minutes, a product temperature of 275° to 285° C. was reached. After that, a pressure relief period followed during which the pressure was lowered from 22-24 bar to 1 bar within 60 minutes. Thereupon, an equalization period of 45 minutes followed with the subsequent emptying of the autoclave contents being accomplished by passing out with excess nitrogen pressure. 
     As far as possible, the obtained polyamides were granulated, dried and analyzed. The obtained degree of polymerization was calculated by the determination of the relative viscosity of the solution. (Polyamide concentration: 1 g polyamide was dissolved in 100 ml 96% sulfuric acid and the viscosity measurement was carried out at 25° C. in an Ubbelohde viscosimeter). The results of the examples are found in TABLE 1 below. 
     
                                           TABLE I__________________________________________________________________________  Parts  Hexa-                       Pres-  Rel. Vis-   Parts  methyl-                     sure                                 Rel.                                     cosityTest   Adipo-  ene  Parts           Dephleg-                Catalyzer                         Parts                              in Vis-                                     accordingNo.   nitrile  diamine       Water           mator                type     Catalyzer                              bar                                 cosity                                     to ASTM                                           Spinnable__________________________________________________________________________1  216 232.4       366 -    --       --   22 2.15                                     24.5  conditional2  216 232.4       366 -    phosphoric                         0.15 22 2.50                                     41.5  good                acid3  216 232.4       366 -    phosphoric                         0.15 22 2.53                                     42.7  good                acid4  216 232.4       366 -    phosphoric                         0.15 22 2.52                                     42.0  good                acid5  216 232.4       120 -    --       --   22 1.25                                     --    no6  216 232.4       120 +    --       --   22 2.20                                     28.0  conditional7  216 232.4       120 +    phenyl-  0.25 22 2.60                                     46.5  good                phosphonic                acid8  216 232.4       180 +    di-ammonium                         0.15 22 2.75                                     55.0  good                phosphate9  216 232.4       180 +    triphenyl-                         0.45 22 2.65                                     49.5  good                phosphate10 216 232.4       125 +    without  --   22 1.95                                     &lt;20   no11 216 232.4       125 +    4-toluene-                         0.72 24 2.50                                     41.5  good                sulfonic acid12 216 232.4       125 +    2-naphthalene-                         0.81 24 2.51                                     42.0  good                sulfonic acid13 216 232.4       125 +    boric acid                         0.47 24 2.25                                     30.2  good14 216 232.4       125 +    oxalic acid                         0.70 24 2.22                                     29.0  conditional15 216 232.4       125 +    hydrogen 0.49 24 2.45                                     39.1  good                iodide16 216 232.4       125 +    ammonium 0.65 24 2.42                                     37.7  good                sulfamate17 216 232.4       125 +    ammonium 0.55 24 2.48                                     40.6  good                iodide18 216 232.4       125 +    benzene  0.58 24 2.51                                     42.1  good                phosphinic                acid19 216 232.4       125 +    Tris-nonylphenyl-                         1.53 24 2.54                                     43.5  good                phosphite20 216 232.4       125 +    Diphenylisooctyl-                         0.74 24 2.55                                     44.2  good                phosphite21 216 232.4       125 +    Tri-isooctyl-                         0.90 24 2.51                                     42.0  good                phosphite22 216 232.4       125 +    Di-lauryl-                         0.90 24 2.54                                     43.5  good                phosphite23 216 232.4       125 +    2-Ethylhexyl-                         0.81 24 2.52                                     42.0  good                diphenyl-                phosphate24 216 232.4       125 +    Tris-nonylphenyl-                         3.83 24 2.55                                     44.2  very good                phosphite25 216 232.4       125 +    Dimethyl-methyl-                         0.08 24 2.47                                     40.3  good                phosphonate26 216 232.4       125 +    Phenyl-diisooctyl-                         1.00 24 2.50                                     41.5  good                phosphite27 216 232.4       125 +    Diisodecyl-                         0.90 24 2.52                                     42.7  good                pentaerythrol-                diphosphite28 216 232.4       125 +    Tris-n-butyl-                         0.50 24 2.42                                     40.3  good                phosphate29 216 232.4       125 +    Di-2-Ethylhexyl-                         0.60 24 2.45                                     39.0  good                phosphate30 216 232.4       125 +    Tris-phenyl-                         0.50 24 2.55                                     44.2  good                phosphite__________________________________________________________________________ 
    
     EXAMPLE 31 
     From a preparation vessel blanketed with purified nitrogen, a homogenous mixture of 
     38.0%: adiponitrile 
     40.8%: hexamethylenediamine 
     21.1%: water 
     0.1%: phosphorous acid 
     is, at a rate of 1 kg/h, continuously fed to a reaction cascade using a metering pump. The reaction cascade consists of two 2-1 mixing reactors whose respective filling level amounts to 75%. Both mixing reactors are equipped with partial condensers and a joint gas system. They may be operated at different temperatures, their filling levels being, however, identical. 
     During continuous operation, the following parameters are required to be observed: 
     
         ______________________________________Reactor I    Pressure       24 bar        Temperature    242° C.        Dephlegmator   55° C.        TemperatureReactor II   Pressure       24 bar        Temperature    265°-270° C.        Dephlegmator   90° C.        Temperature______________________________________ 
    
     After cooling to 30° C., the ammonium gas stream from Reactor I and II amounts to approximately 173 l/h. 
     The reaction product obtained from Reactor II is continuously fed to mixing vessel heated to 280° C. releasing the pressure to 5-6 bar, while the water vapours forming are condensed with the aid of a descending cooler. 
     From the mixing vessel, a clear, colorless prepolycondensate is periodically withdrawn, which then solidifies to a white mass of n rel . approximately 1.8. 
     As is well-known, this prepolycondensate may be further polymerized, either continuously or discontinuously, to form spinnable highly molecular polhexamethylene adipamide. 
     Moreover, it is also well possible to polymerize it by way of solid-state polycondensation. 
     It should be understood that the foregoing disclosure emphasizes certain specific embodiments of the invention and that all modifications of alternatives equivalent thereto are within the spirit or scope of the invention as set forth in the appended claims.