Abstract:
A method of purifying 4,4&#39;-diaminodiphenylmethane comprising partially melting a crystal of crude 4,4&#39;-diaminodiphenylmethane and removing a melt to obtain a high purity 4,4&#39;-diaminodiphenylmethane. By utilizing the method, a high purity 4,4&#39;-diaminodiphenylmethane is obtained efficiently with a low level of energy consumption.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method of purifying 4,4&#39;-diaminodiphenylmethane, which is useful as an intermediate in the preparation of polyurethane or as an additive for rubbers. 
     2. Description of the Related Art 
     4,4&#39;-Diaminodiphenylmethane can be prepared by reacting aniline and formaldehyde. But, in addition to the desired 4,4&#39;-diaminodiphenylmethane, many by-products such as polymeric condensates (e.g. polymethylenepolyphenylamine) and diaminodiphenylmethane isomers (e.g. 4,2&#39;-diaminodiphenylmethane and 2,2&#39;-diaminodiphenylmethane) are produced. Therefore, further purification of 4,4&#39;-diaminodiphenylmethane is necessary to improve its quality. 
     However, using conventional rectification, cause a part of the 4,4&#39;-diaminodiphenylmethane to be lost because of thermal deterioration, or the separation of by-products having close boiling points to that of 4,4&#39;-diaminodiphenylmethane (such as diaminodiphenylmethane isomers) is difficult. Moreover, in an industrial scale production, rectification is not advantageous in view of energy consumption, and facilities and equipment requirements. 
     It has been proposed to purify 4,4&#39;-diaminodiphenylmethane by forming an adduct of 4,4&#39;-diaminodiphenylmethane with an alkali metal halide or cyanide, separating the adduct and decomposing the adduct to recover 4,4&#39;-diaminodiphenylmethane (GB Patent No. 1 169 127), or by condensation reacting aniline and formaldehyde, and diluting, partially neutralizing, crystallizing and neutralizing the product (Canadian Patent No. 745,173). However, these methods are troublesome or insufficient in purification effects, or provide low productivity for the desired product per unit volume. Therefore, these methods are unsatisfactory for the industrial production of 4,4&#39;-diaminodiphenylmethane. 
     SUMMARY OF THE PRESENT INVENTION 
     An object of the present invention is to provide a method for the purification of 4,4&#39;-diaminodiphenylmethane which is less troublesome than the conventional purification methods, and which can be industrially used. 
     According to the present invention, there is provided a method for the purification of 4,4&#39;-diaminodiphenylmethane, the method comprising partially melting a crystal of crude 4,4&#39;-diaminodiphenylmethane and removing a melt to obtain a high purity 4,4&#39;-diaminodiphenylmethane. 
     DETAILED DESCRIPTION OF THE INVENTION 
     In the present invention, crude 4,4&#39;-diaminodiphenylmethane may be obtained by removing unreacted starting materials or high boiling products from a reaction mixture prepared through the reaction of aniline and formaldehyde by, for example, recrystallization or simple distillation under reduced pressure. Preferably, crude 4,4&#39;-diaminodiphenylmethane contains at least 90% by weight of 4,4&#39;-diaminodiphenylmethane and 10% by weight or less of impurities such as diaminodiphenylmethane isomers (e.g. 4,2&#39;-diaminodiphenylmethane or 2,2&#39;-diaminodiphenylmethane), polymethylenepolyphenylamines (e.g. α,α&#39;-di(4-aminophenyl)xylidine). 
     Although polymers such as polymethylenepolyphenylamine are impurities having the boiling points higher than that of 4,4&#39;-diaminodiphenylmethane, they can be removed by the purification method of the present invention. 
     For carrying out the purification method of the present invention, any apparatus that can control its internal temperature and separate a melt from a crystal, for example, a reactor having a valve at its bottom, or a crystallizer may be used. 
     The crystal of crude 4,4&#39;-diaminodiphenylmethane may be of any form, for example, bulk, particle or powder. 
     A temperature at which the crystal of crude 4,4&#39;-diaminodiphenylmethane is partially molten is usually from 70° to 93° C. In general, the crude 4,4&#39;-diaminodiphenylmethane is slowly heated. In particular, in a temperature range higher than 70° C., it is heated at a heating rate of 6° C./hour or less, preferably 2° C./hour or less, more preferably 1° C./hour or less. 
     If necessary, a small amount of a solvent may be added. Examples of the solvent are aniline, benzene, toluene, chlorobenzene and the like. 
     The amount of the melt depends on the purity of crude 4,4&#39;-diaminodiphenylmethane, the required purity of purified 4,4&#39;-diaminodiphenylmethane, purification conditions, and so on. The amount of the melt is usually from 20 to 90% by weight, preferably from 50 to 80% by weight, more preferably from 60 to 80% by weight based on the weight of charged crystals of crude 4,4&#39;-diaminodiphenylmethane. 
     The melt can be removed through the bottom valve of the reactor, or the like. The melt can be removed successively or at one time. Preferably the melt is successively removed. The removed melt can be recycled. 
     The purity of purified 4,4&#39;-diaminodiphenylmethane can vary according to the final use of 4,4&#39;-diaminodiphenylmethane or the purification conditions. Usually, the purity of 4,4&#39;-diaminodiphenylmethane is at least 97%. 
     The purified 4,4&#39;-diaminodiphenylmethane can be recovered by a conventional method, for example, by cooling and removing crystallized 4,4&#39;-diaminodiphenylmethane from the apparatus, or by melting 4,4&#39;-diaminodiphenylmethane once and removing molten 4,4&#39;-diaminodiphenylmethane from the apparatus. 
     In the present invention, when the crude 4,4&#39;-diaminodiphenylmethane crystal is once liquefied by melting and recrystallized by gradual cooling, the purification effect is further increased. If necessary, a small amount of a solvent such as an aromatic amine, aromatic hydrocarbon or aromatic halohydrocarbon (e.g. aniline, benzene, toluene, chlorobenzene, etc.) may be added. 
     The liquefied crude 4,4&#39;-diaminodiphenylmethane is gradually cooled to 60° C., preferably at a cooling rate of 5° C./hour or less, more preferably 1° C./hour or less to crystallize it. 
     The cooling temperature is usually 60° C. or lower, preferably 50° C. or lower, more preferably 40° C. or lower. After the liquefied crude 4,4&#39;-diaminodiphenylmethane is cooled to a desired temperature, it may be kept standing at the same temperature, if desired. 
     If necessary, 4,4&#39;-diaminodiphenylmethane may be added as a seed crystal in the crystallization step. 
     In the crystallization step, a crystallization amount is usually at least 50% by weight, preferably at least 70% by weight, more preferably at least 90% by weight based on the weight of liquefied crude 4,4&#39;-diaminodiphenylmethane. An uncrystallized portion may be removed through the bottom valve of the reactor. 
     The removed uncrystallized liquid of the liquefied 4,4&#39;-diaminodiphenylmethane may be recycled. 
    
    
     PREFERRED EMBODIMENTS OF THE INVENTION 
     The purification method of the present invention will be illustrated by following Examples, which will not limit the scope of the present invention in any way. 
     In the following Examples, &#34;%&#34; is by weight. 
     The crude 4,4&#39;-diaminodiphenylmethane used in the following Examples was prepared by reacting aniline and formaldehyde and adjusting a composition by distillating the reaction product under reduced pressure. 
     EXAMPLE 1 
     (1) In a vessel equipped with a nitrogen inlet tube at its upper part, crude 4,4&#39;-diaminodiphenylmethane [composition: 94.1% of 4,4&#39;-diaminodiphenylmethane; 3.4% of 4,2&#39;-diaminodiphenylmethane; 2.3% of α,α&#39;-di(4-aminophenyl)-3,5-xylidine; 0.3% of N-methyl-4,4&#39;-diaminodiphenylmethane] (147.8 g) was charged and heated to 95° C. While adding seed crystals of 4,4&#39;-diaminodiphenylmethane, the liquefied crude 4,4&#39;-diaminodiphenylmethane was cooled down to 60° C. at a cooling rate of 2° C./hour and further to room temperature, and kept standing at room temperature for 12 hours, whereby all the crude 4,4&#39;-diaminodiphenylmethane was crystallized. 
     (2) The crystal obtained in the above step (1) was heated from 60° to 81° C. at a heating rate of 2° C./hour, from 81° to 88° C. over a period of 3 hours, from 88° to 91° C. over a period of 30 minutes and from 91° to 92° C. over a period of 10 minutes. At 88° C., 91° C. and 92° C., 35.7 g, 37.1 g and 30.4 g of the melts Nos. 1, 2 and 3 (103.2 g in total) were removed, respectively to obtain 44.6 g of purified 4,4&#39;-diaminodiphenylmethane [composition: 98.1% of 4,4&#39;-diaminodiphenylmethane; 1.1% of 4,2&#39;-diaminodiphenylmethane; 0.7% of α,α&#39;-di(4-aminophenyl)-3,5-xylidine; 0.1% of N-methyl-4,4&#39;-diaminodiphenylmethane]. 
     The above results are summarized in Table 1. 
     
                                           TABLE 1__________________________________________________________________________                           Trinuclear*.sup.5)Melting temp.       Weight                   4,4&#39;-*.sup.3)                       4,2&#39;-*.sup.4)                           product                                  N--CH.sub.3 compound*.sup.6)(°C.) Melting time               (g) (%) (%) (%)    (%)__________________________________________________________________________Charged*.sup.1) --     --     147.8                   94.1                       3.4 2.3    0.3Melt No. 1 81 → 88        3  hrs.               35.7                   87.8                       6.4 4.9    0.7Melt No. 2 88 → 91        30 min.               37.1                   93.1                       3.9 2.7    0.3Melt No. 3 91 → 92        10 min.               30.4                   95.9                       2.3 1.6    0.2Purified*.sup.2) --     --     44.6                   98.1                       1.1 0.7    0.1__________________________________________________________________________ Note: *.sup.1) Crude 4,4&#39;-diaminodiphenylmethane. *.sup.2) Purified 4,4&#39;-diaminodiphenylmethane. *.sup.3) 4,4&#39;-Diaminodiphenylmethane. *.sup.4) 4,2&#39;-diaminodiphenylmethane. *.sup.5) α,α&#39;-Di(4-aminophenyl)xylidine. *.sup.6) N-Methyl-4,4&#39;-diaminodiphenylmethane. 
    
     EXAMPLE 2 
     (1) In a vessel equipped with a nitrogen inlet tube at its upper part, crude 4,4&#39;-diaminodiphenylmethane [composition: 98.6% of 4,4&#39;-diaminodiphenylmethane; 1.4% of 4,2&#39;-diaminodiphenylmethane] (144.1 g) was charged and heated to 95° C. While adding seed crystals of 4,4&#39;-diaminodiphenylmethane, the liquefied crude 4,4&#39;-diaminodiphenylmethane was cooled down to 60° C. at a cooling rate of 2° C./hour and further to room temperature, and kept standing at room temperature for 12 hours, whereby all the crude 4,4&#39;-diaminodiphenylmethane was crystallized. 
     (2) The crystal obtained in the above step (1) was heated from 60° to 81° C. at a heating rate of 2° C./hour, from 81° to 91° C. over a period of 11 hours, from 91° to 92° C. over a period of 1 hour and from 92° to 93° C. over a period of 10 minutes. At 91° C., 92° C. and 93° C., 40.7 g, 33.4 g and 22.8 g of the melts Nos. 1, 2 and 3 (96.9 g in total) were removed, respectively to obtain 47.2 g of purified 4,4&#39;-diaminodiphenylmethane [composition: 99.7% of 4,4&#39;-diaminodiphenylmethane; 0.3% of 4,2&#39;-diaminodiphenylmethane]. 
     The above results are summarized in Table 2. 
     
                                           TABLE 2__________________________________________________________________________                           Trinuclear*.sup.5)Melting temp.       Weight                   4,4&#39;-*.sup.3)                       4,2&#39;-*.sup.4)                           product                                  N--CH.sub.3 compound*.sup.6)(°C.) Melting time               (g) (%) (%) (%)    (%)__________________________________________________________________________Charged*.sup.1) --     --     144.1                   98.6                       1.4 N.D    N.DMelt No. 1 81 → 91        11 hrs.               40.7                   97.6                       2.4 N.D.   N.D.Melt No. 2 91 → 92        1  hr. 33.4                   97.9                       2.1 N.D.   N.D.Melt No. 3 92 → 93        10 min.               22.8                   98.9                       1.1 N.D.   N.D.Purified*.sup.2) --     --     47.2                   99.7                       0.3 N.D.   N.D.__________________________________________________________________________ Note: *.sup.1)- *.sup.6) See the Note for Table 1. N.D. Not detected. 
    
     EXAMPLE 3 
     (1) In a vessel equipped with a nitrogen inlet tube at its upper part, crude 4,4&#39;-diaminodiphenylmethane [composition: 90.8% of 4,4&#39;-diaminodiphenylmethane; 7.2% of 4,2&#39;-diaminodiphenylmethane; 1.4% of α,α&#39;-di(4-aminophenyl)-3,5-xylidine; 0.7% of N-methyl-4,4&#39;-diaminodiphenylmethane] (151.4 g) was charged and heated to 95° C. While adding seed crystals of 4,4&#39;-diaminodiphenylmethane, the liquefied crude 4,4&#39;-diaminodiphenylmethane was cooled down to 60° C. at a cooling rate of 1° C./hour and further to room temperature, and kept standing at room temperature for 12 hours, whereby all the crude 4,4&#39;-diaminodiphenylmethane was crystallized. 
     (2) The crystal obtained in the step (1) was heated from 70° to 81° C. over a period of 2 hours, from 81° to 86° C. over a period of 6 hours, from 86° to 89° C. over a period of 2.5 hours, from 89° to 90° C. over a period of 2.5 hours, from 90° to 92° C. over a period of 1.5 hours and kept standing at 92° C. for 30 minutes. At 81° C., 86° C., 89° C., 90° C. and 92° C. (before and after being kept standing), 19.6 g, 21.4 g, 20.5 g, 18.0 g, 20.1 g and 19.5 g of the melts Nos. 1 to 6 (119.1 g in total) were removed, respectively to obtain 32.3 g of purified 4,4&#39;-diaminodiphenylmethane [composition: 98.6% of 4,4&#39;-diaminodiphenylmethane; 0.9% of 4,2&#39;-diaminodiphenylmethane; 0.5% of α,α&#39;-di(4-aminophenyl)-3,5-xylidine; 0.1% of N-methyl-4,4&#39;-diaminodiphenylmethane]. 
     The above results are summarized in Table 3. 
     
                                           TABLE 3__________________________________________________________________________                           Trinuclear*.sup.5)Melting temp.       Weight                   4,4&#39;-*.sup.3)                       4,2&#39;-*.sup.4)                           product                                  N--CH.sub.3 compound*.sup.6)(°C.) Melting time               (g) (%) (%) (%)    (%)__________________________________________________________________________Charged*.sup.1) --     --     151.4                   90.8                       7.2 1.4    0.7Melt No. 1 70 → 81        2  hrs.               19.6                   75.3                       20.3                           2.9    1.4Melt No. 2 81 → 86        6  hrs.               21.4                   83.2                       13.8                           2.0    1.0Melt No. 3 86 → 89        2.5           hrs.               20.5                   89.0                       9.0 1.5    0.5Melt No. 4 89 → 90        2.5           hrs.               18.0                   93.4                       5.2 1.0    0.4Melt No. 5 90 → 92        1.5           hrs.               20.1                   96.1                       2.9 0.8    0.3Melt No. 6 92° C.        30 min.               19.5                   97.4                       1.8 0.6    0.2Purified*.sup.2) --     --     32.3                   98.6                       0.9 0.5    0.1__________________________________________________________________________ Note: *.sup.1)- *.sup.6) See the Note for Table 1. 
    
     EXAMPLE 4 
     (1) In a vessel equipped with a nitrogen inlet tube at its upper part, crude 4,4&#39;-diaminodiphenylmethane [composition: 92.0% of 4,4&#39;-diaminodiphenylmethane; 7.3% of 4,2&#39;-diaminodiphenylmethane; 0.2% of α,α&#39;-di(4-aminophenyl)-3,5-xylidiene; 0.6% of N-methyl-4,4&#39;-diaminodiphenylmethane] (142.8 g) was charged and heated to 95° C. While adding seed crystals of 4,4&#39;-diaminodiphenylmethane, the liquefied crude 4,4&#39;-diaminodiphenylmethane was cooled down to 60° C. at a cooling rate of 1° C./hour and further to room temperature, and kept standing at room temperature for 12 hours, whereby all the crude 4,4&#39;-diaminodiphenylmethane was crystallized. 
     (2) The crystal obtained in the above step (1) was heated from 70° to 87° C. over a period of 16 hours, from 87° to 90° C. over a period of 3.5 hours and from 90° to 91° C. over a period of 2 hours. At 87° C., 90° C. and 91° C., 42.7 g, 20.6 g and 14.8 g of the melts Nos. 1, 2 and 3 (78.1 g in total) were removed, respectively to obtain 64.7 g of purified 4,4&#39;-diaminodiphenylmethane [composition: 98.0% of 4,4&#39;-diaminodiphenylmethane; 1.4% of 4,2&#39;-diaminodiphenylmethane; 0.6% of N-methyl-4,4&#39;-diaminodiphenylmethane]. α,α&#39;-Di(4-aminophenyl)-3,5-xylidine was not detected. 
     The above results are summarized in Table 4. 
     
                                           TABLE 4__________________________________________________________________________                           Trinuclear*.sup.5)Melting temp.       Weight                   4,4&#39;-*.sup.3)                       4,2&#39;-*.sup.4)                           product                                  N--CH.sub.3 compound*.sup.6)(°C.) Melting time               (g) (%) (%) (%)    (%)__________________________________________________________________________Charged*.sup.1) --     --     142.8                   92.0                       7.3 0.2    0.6Melt No. 1 70 → 87        16 hrs.               42.7                   80.4                       17.3                           0.9    1.4Melt No. 2 87 → 90        3.5           hrs.               20.6                   91.3                       7.5 0.3    0.9Melt No. 3 90 → 91        2  hrs.               14.8                   95.3                       3.9 N.D.   0.8Purified*.sup.2) --     --     64.7                   98.0                       1.4 N.D.   0.6__________________________________________________________________________ Note: *.sup.1)-*.sup.6) See the Note for Table 1. N.D. Not detected.