Abstract:
This invention pertains to an improved process for preparing noncyclic polyalkylene polyamine compounds in high selectivity by reacting an alkanolamine and an alkylene amine in the presence of an inert gas and an acidic catalyst. The improvement resides in effecting the reaction under fixed bed catalytic conditions and maintaining the reaction conditions such that a vapor phase condition exists for the reaction mixture comprising both reactants and products. To accomplish the formation of vapor phase conditions sufficient inert gas is injected into the feedstream along with alkanolamine and alkylene amine so that the dew point temperature of the reaction product mix is below the reaction temperature at reaction pressure.

Description:
BACKGROUND OF THE INVENTION 
     The condensation of a hydroxy-containing compound with an amine to liberate water is well known. In many instances, the condensation has been effected by using an acid catalyst; such as a phosphorus-containing compound. The ability to effect intermolecular condensation of a hydroxy-containing compound with an amine has been of substantial interest in the preparation of polyalkylene polyamines, particularly polyethylene polyamines. 
     A variety of polyalkylene polyamines can be formed by the basic reaction of the hydroxy compound and amine compound. However, one of the objectives in the preparation of polyalkylene polyamines has been to maximize the intermolecular condensation to form the linear or noncyclic polyalkylene polyamine as opposed to effecting an intramolecular condensation of such compounds which convert to the cyclic amine. The former amines are utilized in preparing lubricant formulations, acid gas scrubbing compositions, and the like. Numerous patents have issued since the 1960&#39;s which illustrate various embodiments for preparing linear polyalkylene polyamines in high selectivity by reacting an alkylene amine and an alkanolamine in the presence of an acidic catalyst. Representative patents include: 
     Meuly, U.S. Pat. No. 3,121,115, discloses the reaction of an amine with an alkanolamine in the presence of a phosphorus-containing compound to produce alkylated amines. Reaction conditions used were 200°-350° C. and pressures ranged from atmospheric to super atmospheric. 
     U.S. Pat. No. 4,036,881 discloses the preparation of polyalkylene polyamines, particularly polyethylene polyamines, by the reaction of monoethanolamine and ethylenediamine under liquid phase conditions. An acidic phosphorus-containing compound was utilized to effect catalysis of the reaction. Representative catalyst systems included alkyl and aryl phosphinic acids, phosphoric and phosphorous acid compounds and their anhydrides, and metal phosphates such as iron, aluminum and boron phosphate and so forth. The patentees pointed out that it was important to maintain liquid phase conditions in the reaction zone for achieving high selectivity to linear polyethylene polyamines. If vapor phase conditions were encountered, as shown in Example 12, then selectivity to linear polyethylene polyamines was sacrificed. 
     Other patents which show the preparation of polyethylene polyamines or broadly, polyalkylene polyamines under liquid phase conditions include U.S. Pat. Nos. 4,394,524; 4,399,308; 4,362,886; 4,314,083; and European patent application Nos. 0,093,434 and 0,093,983. 
     The above patents describe various processes for producing polyalkylene polyamines using a variety of acidic catalytic systems such as, for example, Lewis acids, arsenic, antimony or bismuth sals; a variety of phosphorus containing catalyst systems including phosphoric acid, boron phosphate as noted in the Brennan, et al., U.S. Pat. No. 4,036,881, and phosphoramides. Each of the processes involves the reaction of an alkanolamine with an alkylene amine compound at temperatures from about 175°-300° C., and preferably temperatures in excess of 225° C. to produce linear polyalkylene polyamines. Each of the processes employs conditions which maintain the reactants in liquid phase, and thus the reaction pressure is controlled to the extent necessary to maintain such liquid phase conditions at reaction temperature. 
     U.S. Pat. No. 4,394,524 diffes slightly from the processes described above in that ammonia is included as an additional reactant to convert alkanolamine to an alkylene amine in situ. With the utilization of ammonia, higher selectivities to polyethylene polyamines were reported. However, pressures were maintained such that the reaction was carried out in essentially liquid phase. 
     U.S. Pat. No. 4,463,193 discloses the production of noncyclic polyalkylene polyamine from an alkanolamine, an alkyleneamine and ammonia using a Group IIIB metal acid phosphate catalyst. Under some of the conditions disclosed, vapor phase reaction is effected while under other conditions liquid phase reaction is effected. 
     Although the above liquid phase processes result in producing linear polyalkylene polyamines in relatively high selectivity, the processes suffer from a series of processing disadvantages. The processing disadvantages arise because of the solubility of the catalyst systems in the reactants or reaction products. This is particularly true in the case of phosphorus-containing catalytic compounds in that high proportions of phosphorous are recovered in the reaction product and must be removed. This is typically done by distillation. An additional problem associated with these processes is that the catalyst must be continually replaced or replenished. 
     SUMMARY OF THE INVENTION 
     This invention relates to an improvement in a process for producing noncyclic polyalkylene polyamines in high selectivity. The basic process comprises: 
     contacting (a) an alkylene amine compound having two primary amino groups with the general formula: ##STR1## wherein R is hydrogen or a lower alkyl (C 1  -C 4 ) radical; 
     X is a number from 2 to about 6; and 
     Y is a number from 1 to about 4; with 
     (b) an alkanolamine compound having primary or secondary hydroxyl groups of the general formula: ##STR2## wherein R is hydrogen or a lower alkyl (C 1  -C 4 ) radical; 
     R 1  is hydrogen or a lower alkyl (C 1  -C 4 ) radical; 
     X is a number from 2 to about 6; and 
     Y is a number from 0 to about 3. 
     This contacting is carried out in the presence of an effective amount of an acidic catalyst system, and at a temperature sufficient to effect reaction between the alkylene amine compound and alkanolamine compound. The improvement in the basic process and constituting the invention comprises: 
     passing the reactants into a catalytic reactor packed with a solid phase acidic catalyst; 
     effecting the reaction under conditions such that the reactor contents remain essentially in the vapor phase, said reaction being carried out within a temperature range from about 200°-285° C., and within a pressure range from about 75 to 275 psig. Vapor phase conditions are maintained within the temperature and pressure range by adding sufficient inert gas into the reaction zone to lower the dew point temperature of the reactor contents in the reaction zone to a level lower than said reaction temperature. 
     There are numerous advantages associated with the practice of this invention. One of the advantages is that there is no need for catalyst separation from the reaction product in view of the low concentration of catalyst material therein. Another is that the process readily lends itself to continuous operation. A third advantage is that the reaction can be carried out at relatively low pressures, at least lower than those required for many liquid phase conditions thus providing for energy savings. A fourth is that one can achieve very high selectivity to linear polyalkylene polyamines. A fifth is that the process can be carried out using the same catalyst for extended periods of time. A sixth advantage of using an inert volatile gas is that the gas can be recovered without resort to a high pressure distillation column. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention relates to a process for synthesizing noncyclic polyalkylene polyamines and preferably linear and branched polyethylene polyamines, such as diethylene triamine and higher homologues. In the process, an alkylene amine having two primary amino groups and, preferably, an unbranched alkylene moiety, such as ethylenediamine is reacted with ammonia and an alkanolamine having a primary or a secondary hydroxy moiety and a primary amino group. The alkylene amine reactants which typically can be used in practicing the process are represented by the general formula: ##STR3## wherein R is a hydrogen or a lower alkyl; (C 1  -C 4 ) radical; 
     X is a number from 2 to about 6; and 
     Y is a number from 1 to about 4. 
     A preferred R radical is hydrogen, while the x value is 2 and the y value is 1. Examples of alkyleneamine compounds suited for the reaction include 1,3-propylene diamine, 1,2-propylene diamine, diethylene triamine, triethylene tetramine and ethylene diamine. The latter diamine is the preferred alkylene amine compound for preparing linear polyethylene polyamines. 
     The alkanolamines reactants which can be used in the process and represented by the formula: ##STR4## wherein R is hydrogen or a lower alkyl (C 1  -C 4 ) radical; 
     R 1  is hydrogen or a lower alkyl (C 1  -C 4 ) radical; 
     x is a number from 2 to about 6, and 
     y is a number from 0 to 3. 
     A preferred R radical is hydrogen while x is 2 and y is 0. Examples of alkanolamine compounds suited for practicing the process are monoethanolamine, isomeric propanolamines, and N-(2)-aminoethyl(ethanolamine). Monoethanolamine is preferred. 
     Linear and branched polyalkylene polyamines that are produced by the reaction of an alkylene amine and an alkanolamine as described above, are represented by the general formula: ##STR5## wherein R is a hydrogen or a lower alkyl (C 1  -C 4 ) radical, preferably a methyl radical; 
     x is a number from 2 to about 6; 
     y is a number from 2 to about 6 and 
     X may vary for a given value of Y. 
     Examples of linear polyalkylene polyamines that are produced in accordance with the process of this invention include dipropylenetriamine, tributylenetetramine and various polyethylene polyamines such as diethylenetriamine, triethylenetetramine and tetraethylenepentamine. Other types of polyamines include di(2-methylethylene)triamine, tri(2-methylethylene)tetramine and N-(2-aminoethyl)-1,3-propylenediamine. 
     A variety of acidic catalytic systems can be utilized for effecting condensation of the hydroxyl group of the alkanolamine with the alkylene amine compound and numerous catalytic systems have already been described in the Background Portion of this Application and such catalysts are incorporated by reference; i.e., from U.S. Pat. No. 4,036,881; European No. 0 093 434 and U.S. Pat. No. 4,394,524. In view of the fact that the reaction is carried out under vapor phase conditions, the catalyst is material capable of being compounded as a particulate material or capable of being supported by a solid phase carrier. The nonvolatile catalytic systems may be incorporated upon or impregnated into an inert support. Silica, carbon or zeolite are representative of the latter. By utilizing a catalyst system, which is in solid phase form, a fixed bed catalytic reactor can be utilized to effect the condensation of the alkanolamine, alkylene amine and ammonia reactant system. 
     Catalyst systems suited for effecting intermolecular condensation include the phosphorus containing compounds such as boron phosphate, aluminum phosphate, phosphoric acid on silica or carbon, rare earth metal acid phosphates such as lanthanum mono hydrogen and di hydrogen phosphates, yttrium mono or di hydrogen phosphates, gadolinium acid phosphates, thorium acid phosphates, neodymium acid phosphates, praseodymium acid phosphates, samarium acid phosphates or mixtures of lanthanum hydrogen phosphates with other rare earth metal acid phosphates. The rare earth metals suited are scandium, yttrium, lanthanum, and those in the lanthanide series of the periodic table having an atomic number from 59-71 and the rare earth actinides having atomic numbers 89 to 92. Such catalysts are shown in U.S. Pat. No. 4,463,193 and are incorporated by reference. Rare earth and hydrogen exchanged zeolites can be used provided the cage structure is sufficiently large; e.g., greater than about 8 A° to permit formation of the amine. Other catalytic systems include halide salts such as zinc chloride, the sulfur and nitrogen containing acids and salts such as nitric acid, sulfuric acid, beryllum sulfate, ammonium nitrate, etc. These catalysts can be used so long as they are effective as solid phase catalysts under the conditions specified in the reaction zone for effecting condensation. Antimony, bismuth and arsenic salts can also be used. 
     The basic difference between this process and the processes described and utilized heretofore in the preparation of polyalkylene polyamines resides in the injection of sufficient inert gas into the reaction system and the maintainance of an appropriate temperature and pressure commensurate with the level of inert gas in the reaction zone such that the mixture of reactants and reaction products are maintained in the vapor phase. If liquid phase conditions are encountered in the reaction zone, then the concentration of catalyst in the reaction product leaving the reactor may increase substantially, particularly when a phosphate system is used, and catalyst must be replaced in the reactor. In addition the catalyst may agglomerate and plug the reactor. 
     In order to achieve high selectivity to linear or branched polyalkylene polyamines under vapor phase conditions the reaction temperature must be at a temperature above the dew point temperature of the reactor contents but at a temperature less than 285° C. Although the condensation reaction can be effected at temperatures above about 285° C., as indicated in the prior art, selectively to linear polyalkylene polyamines decreases substantially as the temperature is increased above that level when using vapor phase conditions. The lowest temperature suited for practicing invention is that temperature at which the catalyst is catalytically effective for generating polyalkylene polyamines via the intermolecular condensation of the alkanolamine and alkyleneamine. 
     The condensation reaction is carried out at pressure sufficient to effect the reaction of alkanolamine with the alkyleneamine. Typically the pressure will range from about 75 to 275 psig. Higher pressures serve no useful purpose and tend to require increased inert gas levels at a preselected reaction temperature to maintain vapor phase conditions. 
     The term &#34;inert gas&#34; as used herein is intended to refer to compositions which are non-reactive with the alkyleneamine and alkanolamine under reaction conditions, insoluble in the reactants and products, and has a boiling point below about -40° C. at atmospheric pressure. Examples of inert gases include nitrogen, argon, helium; hydrocarbons such as methane, ethane and propane and aliphatic ethers such as dimethyl ether and diethyl ether. 
     The generation of vapor phase conditions in the process, with concomitant high selectivity to linear polyalkylene polyamines is unique. In the prior art, as exemplified by Brennen, et al. in the U.S. Pat. No. 4,036,881, selectivity to linear polyalkylene polyamines was sacrificed when vapor phase conditions were employed in the reaction of monoethanolamine and ethylene diamine. Although not intending to be bound by theory, it is believed there are two primary reasons for high selectivity to cyclics in the Brennen et al example. First the reaction was carried out at too high of a process temperature and second the process pressure was too low. Such conditions were deemed necessary because of the exclusive usage of ethylenediamine and monoethanolamine as feeds. On the other hand in accordance with the invention described here an inert gas is introduced into the reaction zone until the dew point temperature of the components of the reaction zone is below a preselected low reaction temperature at reaction pressure. By increasing the amount of inert gas in the reaction zone one can then lower the dew point temperature of the contents in the reaction zone and thereby establish a condition in which vapor phase conditions exist throughout the process. The selection of pressure, temperature and reactants then permits one to achieve high selectivity typically achieved previously only under liquid phase conditions. 
     Dew point temperatures can be derived from vapor-liquid equilibria for feed and products at various conditions. These vapor-liquid equilibria can be calculated using standard chemical engineering techniques. For example the following articles can be reviewed for producing computer or mathematical models for calculating specific temperature conditions. These articles are: 
     1. Zellner, et al., Industrial Engineering Chemical Fundamentals, Vol. 9, Nov. 9, 549-564 (1970); 
     2. Abrams, et al., AICHE Journal, Vol. 21, No. 116-128 (1975). 
     Both of these articles are incorporated by reference. 
     There are some general principles which apply in aiding the determination of a set of conditions for vapor phase operation. First, the dew point temperature decreases with increasing mole ratios of inert gas to monoethanolamine. Second, the dew point temperature increases as conversion of reactant to product increases. Third, the dew point temperature increases, for a given conversion, as the selectivity of the product increases to higher molecular weight polyamines. By monitoring variables which affect these parameters, one can maintain vapor phase conditions under reaction conditions. These rules are perhaps self-evident but they permit one to develop specific processes embraced within the scope of the invention. 
     If one prefers not to calculate reactor conditions necessary for vapor phase conditions, one can use physical characteristics of the process to make that determination. The latter technique may require some experimentation. One of the easiest methods for determining whether liquid or mixed phase conditions exist in the reactor is to monitor reactor product composition. For example if a phosphorus catalyst is used high levels; e.g., greater than 20 ppm catalyst levels occur, in the reaction product indicate the presence of some liquid phase. This is because of the solubility of the catalyst in the reactants and products. An increasing pressure drop or modification of catalyst structure, e.g. rounded corners of pellets, etc. will also reveal this feature if some liquid phase is present. If such conditions exist the inert gas level or reaction temperature must be increased if below 275° C. or the pressure decreased if above 75 psig. 
     Generally, the level of inert gas used in the reaction at the temperature and pressure specified will be from 2 to 20, and preferably is 4-12 moles per mole of alkanolamine; e.g., monoethanolamine. The molar ratio of alkylenediamine to alkanolamine; e.g., ethylenediamine to monoethanolamine, will be from 1 to 5:1. 
     The following examples are provided to illustrate various embodimens of the invention as well as illustrate some of the differences between the process described herein and other processes utilized in the prior art. 
    
    
     EXAMPLE 1 
     A series of reactions were carried out under various operating conditions. In those instances where vapor phase conditions were utilized or attempted, the reaction was carried out in a stainless steel packed bed reactor filled with solid phase catalyst pellets of 34% phosphoric acid on silica. The feeds were introduced into the top of the reactor and the reactants passed downflow over the catalyst bed. The reaction product was withdrawn from the bottom of the reactor as a vapor. The pressure was maintained in the reactor by a backpressure regulator. 
     Table I provides a description of the reaction conditions for producing polyethylene polyamines and such conditions include the usage of various liquid hourly space velocity (LHSV), and mole ratio of nitrogen or ammonia to monoethanolamine to ethylene diamine. A reaction temperature of 250° C. and reaction pressure of 250 psig was utilized. 
     Table II provides the results in terms of the quantities of conversion and various selectivity of components in the reaction product in weight percent. The analysis was done by the use of gas chromatography. 
     
                       TABLE I______________________________________REACTOR EFFLUENTS OBTAINED WITHAMMONIA AND NITROGENIN VAPOR PHASE POLYAMINES PROCESS.sup.a         Ammonia Nitrogen Ammonia         Run 1   Run 2    Run 3______________________________________Flow Rates:EDA (cc/hr)     21.9      21.9     22.7MELA (cc/hr)    9.6       9.6      10.0Ammonia (cc/hr).sup.b           35.1      0        34.7Nitrogen (sccm).sup.c           0         454      0Weight (%).sup.dEthylenediamine 61.3      60.3     61.5Monoethanolamine           19.7      20.2     22.8Piperazine      0.7       0.6      0.5Diethylenetriamine           7.9       7.4      6.2Aminoethylethanolamine           0.6       0.6      0.7Aminoethyl piperazine           1.1       1.0      0.8Triethylenetetraamine           3.9       3.9      3.2Tetraethylenepentaamine           3.3       3.6      2.8Others          1.5       2.3      1.6______________________________________ .sup.a Feed of ethylenediamine (EDA) and monoethanolamine (MELA) (66.3% and 33.7% by wt) at 250° C., 250 psig. .sup.b Measured as a liquid at 20° C. .sup.c Standard (at ambient conditions) cubic centimeters per minute. .sup.d Ammonia and water free weight percents from GC. 
    
     
                       TABLE II______________________________________CONVERSIONS AND SELECTIVITIES OBTAINED WITHAMMONIA AND NITROGEN IN VAPOR PHASEPOLYAMINES PROCESS.sup.a         Ammonia Nitrogen Ammonia         Run 1   Run 2    Run 3______________________________________Conversion (%).sup.b :MELA            41.5      40.1     32.3EDA             7.5       9.0      7.2Selectivities (wt %).sup.c :Piperazine      3.7       3.2      3.2Diethylenetriamine           41.7      38.1     39.6Aminoethylethanolamine           2.9       3.2      4.2Aminoethyl piperazine           5.7       5.2      5.1Triethylenetetraamine           20.7      19.8     20.1Tetraethylenepentaamine           17.2      18.6     17.6Others          8.0       11.9     10.2______________________________________ .sup.a Feed of EDA and MELA (66.3% and 33.7% by wt) at 250° C., 25 psig. .sup.b Conversion based on inlet concentration obtained from GC. .sup.c Ammonia, water, EDA and MELA free weight percents from GC. The results show that nitrogen was comparable to ammonia under similar conditions for producing polyamines. Conversions and selectivities were similar.