Process for the manufacture of ethylenediamine.

Brief Summary of the Invention

Technical Field

This invention relates to a continuous process for the manufacture of ethylenediamine starting from the reaction of ethylene oxide with ammonia to produce a mixture of alkanolamines and the conversion of the alkanolamines by amination to ethylenediamine and other alkyleneamine products.

Background Art

In a private report by the Process Economics Program. Report No. 138, entitled "Alkyl Amines", by Michael Arne, of SRI International, dated March 1981, there is a section which covers the production of "Ethyleneamines from Monoethanolamine" (see pps. 81-107, 116 and 117). The author considered a substantial collection of the prior art relating to the conversion of monoethanolamine to, in particular, ethylenediamine. For example, the author considers: U.S. Patent No. 3,068,290, describing the reaction of ammonia and monoethanolamine over a nickel/magnesium oxide catalyst to give ethylenediamine: U.S. Patent No. 3,270,059, describing the reaction of monoethanolamine and ammonia in the presence of hydrogen over a cobalt/nickel catalyst at 150-300 °C and 200 bar; U.S. Patent No. 3,766,184, describing the reaction of ammonia and monoethanolamine to give ethylenediamine; U.S. Patent No. 3,520,933, describing the reaction between ammonia and monoethanolamine over a cobalt/nickel/copper/silver catalyst in the presence of hydrogen to give ethylenediamine; French Patent No. 2,065,046, describing the production of ethylenediamine from monoethanolamine and ammonia by reaction over a cobalt catalyst containing phosphorus pentoxide and boric oxide; U.S. Patent No. 4,014,933, describing the reaction of ammonia and monoethanolamine over a cobalt/nickel catalyst in the presence of hydrogen; U.S. Patent No. 4,123,462, describing the reaction of ammonia with monoethanolamine or a mixture of alkanolamines such as one which contains 90% by weight of monoethanolamine, 7% by weight of diethanolamine and 3 weight percent of triethanolamine, in the presence of a nickel-rhenium supported catalyst; U.S. Patent No. 4,153,581, describing the reaction of ammonia and monoethanolamine, in a mole ratio of about 7/1, in the presence of a co- balt/copper/zinc oxide catalyst at 1035 bar abs. (1500 psia) to produce ethylenediamine: and U.S. Patent No. 4,209,424, directed to the production of ethylenediamine from monoethanolamine and ammonia over a nickel catalyst utilizing a rhodium promoter.

GB-A-808114 describes a process for an conversion of ethanolamine and ammonia into ethylene diamine, piperazine and diethylenetrieamine under pressure over a hydrogenations catalyst in form of nickel, cobalt etc.

The significance of the aforementioned report by Arne is its evaluation of the prior art and its interpretation, on the basis of his evaluation of the prior art, of a process for the manufacture of ethylenediamine from monoethanolamine and ammonia. According to Arne, ethyleneamines are currently being produced in Europe from monoethanolamine and ammonia and Union Carbide has announced a plant expansion based on the same process. Regardless of the accuracy of this statement, it is to be recognized that ethyleneamines are known to the produced from the reaction of ammonia and monoethyleneamines. According to Arne, this route has the advantage of virtually eliminating the environmental problems associated with the ethylene dichloride process. In characterizing the process, Arne states that: "It has the disadvantage of producing only small quantities of polyethylene polyamines, producing instead substantial amounts of less valuable piperazine and substituted piperazines". What this means is that according to Arne, polyethylene polyamines are regarded to be valuable products and the piperazines are not regarded to be valuable products because the market for the piperazines is not large enough compared to the capacity existing for producing the same.

According to Arne, a desirable process for the manufacture of ethyleneamines would be one which would produce substantially smaller amounts of the piperazines and larger amounts of the various polyethylene polyamines.

In the analysis of the prior art that Arne relied upon, some interesting factors which induce the manufacture of the piperazines are revealed. For example, U.S. Patent 3,766,184 reveals in example 10 that when diethanolamine was reacted with ammonia and water at 225 _°C and 230 bar in the presence of hydrogen gas and 7 grams of the reduced catalyst in tablet form comprising 3 to 4% each of nickel oxide, cobalt oxide and iron oxide, the remainder being aluminum oxide, 26% of the diethanolamine had been converted of which 49% has formed aminoethylethanolamine, 36% formed piperazine, and 8% formed ethylenediamine. After 5 hours of reaction, the example shows that 82% of the diethanolamine had been converted, of which 16% had been aminated to aminoethylethanolamine, 60% to piperazine, and 10% to ethylenediamine. Thus when diethanolamine is reacted with ammonia, considerably more piperazine is formed than ethylenediamine. This should be contrasted with example 17 of the same patent which reacted ammonia with monoethanolamine in the presence of water and obtained ethylenediamine as 60% of the yield of product, piperazine as 12% of the product yield, aminoethylpiperazine as 2% of the product yield and hydroxyethylpiperazine as 2% of the product yield. When diethanolamine is combined with monoethanolamine as a reactant in the process of that patent, we see from example 11 that the conversions to piperazine is intermediate of those conversions obtained in examples 10 and 17, suggesting that the presence of diethanolamine is a major factor for this increased conversion to the unwanted piperazine.

U.S. Patent 4,014,933, in example 5, also demonstrates the reaction ammonia with diethanolamine. In that example, the patentees obtained a product composition comprising 4% ethylenediamine, 22% of piperazine, 17% of aminoethylethanolamine, and 54% of unreacted diethanolamine. Essentially the same results can be seen in example 8 of German application no. 1,950,604.

The aforementioned examples which clearly demonstrate the propensity of diethanolamine to react with ammonia to produce a disproportionate amount of piperazines is further demonstrated in U.S. Patent No. 3,766,184. By comparing examples 11 and 17 of the patent, we find that the presence of diethanolamine and triethanolamine in the reaction feed, as demonstrated in example 11, contribute to the formation of a disproportionate amount of piperazine. It should be noted in the case of example 17 that the feed with ammonia with monoethanolamine and the amount of the piperazines which were formed constituted essentially 1/1 Oth the amount of the ethylenediamines formed. In example 11, the piperazines which were formed constituted about 1/5th the amount of the ethylenediamine which was formed. However, in example 17 the process was operated in such a manner as to favor the formation of piperazine; note that the monoethanolamine conversion in example 17 was 55% which indicates a longer reaction time thus favoring high conversions which "leads to lower selectivity to the desired ethylenediamine and to more of the undesirable piperazine", see Arne, pg. 83, supra.

This would suggest that the presence of diethanolamine and/or triethanolamine in the feed along with monoethanolamine contributes to the formation of an amount of piperazine which exceeds that which would be obtained from monoethanolamine alone. It also suggests that the amount of the piperazines formed exceeds that amount which the amount of diethanolamine and/or triethanolamine, per se, would form under the reaction conditions employed. This being the case, it is logical to assume that diethanolamine and/or triethanolamine are in some manner reacting with monoethanolamine or inducing the unfavorable reaction of monoethanolamine so as to form increased amounts of the unwanted piperazines.

The foregoing analysis also suggests that while the manufacture of alkyleneamines from monoethanolamine reaction with ammonia is sound, if one were to utilize a reaction feed of monoethanolamine combined with diethanolamine and/or triethanolamine, more of the unwanted piperazines would be produced and this would constitute an economic loss.

However, the use of monoethanolamine alone is not without disadvantages. It is known that monoethanolamine is formed by the reaction of ammonia and ethylene oxide and the products of that reaction constitute a mixture of monoethanolamine, diethanolamine and triethanolamine. If monoethanolamine has to be isolated before it is utilized in the manufacture of the alkyleneamines, it means that the monoethanolamine must be distilled from the product mixture in which it is formed and this adds to the cost of the monoethanolamine. Moreover, such monoethanolamine, when recovered, is brought to room temperature and when it is subsequently utilized in the formation of the ethyleneamines, it has to be heated and pressurized to the conditions utilized for the manufacture of the alkyleneamines. Consequently, there is a considerable energy cost involved in the effective utilization of monoethanolamine per se. It should also be appreciated that the ammonia which is utilized in the reaction to produce the monoethanolamine is not directly available for the reaction to produce the alkyleneamines unless it is subjected to the same treatment of heating and pressurization as is the monoethanolamine.

Disclosure of Invention

There is described herein a continuous process for producing ethylenediamine which comprises providing a continuous, homogeneous fluid stream containing ammonia and monoethanolamine wherein the moles of ammonia substantially exceed the moles of alcoholic hydroxyl in said stream, to an amination zone comprising a solid amination catalyst to form an amination product stream and continuously recovering ethylenediamine from said amination product stream, characterized in that (a) the homogeneous fluid stream is the product of the direct reaction of ethylene oxide and ammonia, wherein a single supercritical fluid phase is maintained with a density of at least 240 kg/m³ in the presence of 0.5% to 5% by weight of water based on the weight of the reaction mixture as the only catalyst and in the absence of hydrogen, and contains additionally diethanolamine and triethanolamine, (b) a stream consisting essentially of monoethanolamine is separated from the amination product stream and fed to the homogeneous fluid stream and (c) an amination feed stream is formed in which at least 70 weight percent of the total ethanolamines is monoethanolamine and based on the total ethanolamines the weight percent of monoethanolamine is at least 5 percent greater than in the homogeneous fluid stream.

The process of this invention provides a number of advantageous novel features. For example, one may utilize in the amination reaction a product stream obtained directly from an ethanolamines reactor (which involves the reaction of ethylene oxide with ammonia as aforedescribed) and thereby reduce significantly the raw material and energy cost attendant in the formation of alkyleneamines. As a consequence of doing this, there is provided to the amination reaction a feed stream which contains diethanolamine and triethanolamine. This invention gives recognition to the fact that by maintaining a concentration of monoethanolamine in the feed stream to the amination zone at a level greater than is provided by the reaction of ethylene oxide and ammonia, that one can enhance the capacity in the amination zone to reduce the formation of the piperazines. This is believed to occur by virtue of diluting the product stream from the ethylene oxide and ammonia reactor, i.e., the homo- nogeneous fluid stream, with monoethanolamine whereby to materially reduce the effect that diethanolamine and/or triethanolamine have on enhancing the formation of the piperazines.

Details of the Invention

Reaction Between Ethylene Oxide and Ammonia to form Alkanolamines

The method for making ethanolamines involves the reaction of ethylene oxide with a large excess of ammonia in a single supercritical fluid phase. The process is run continuously under isothermal or adiabatic conditions. The reactor is of a design which provides for the minimization of product recycle and thereby maximizes the production of the desired ethanolamines, minimizing the formation of higher molecular weight ethanolamine products. The preferred process for making the ethanolamines involves reacting a homogeneous stream of a mixture of ethylene oxide and ammonia in a molar ratio of ammonia to ethylene oxide within the range between 15:1 and 50:1. The stream is maintained in a single, homogeneous supercritical fluid phase by maintaining a temperature and pressure which creates such a phase. The temperature for effecting the supercritical fluid is that temperature which constitutes the minimum critical temperature for the fluid composition. The supercritical fluid phase has a density of at least 240 kg/m³ (15 pounds per cubic foot). This supercritical fluid phase is maintained for a period of time sufficient to permit the reaction to proceed to completion and thus to form a product mixture containing predominantly monoethanolamine (frequently at least about 70 weight percent of the composition of the ethanolamines) and small amounts of the di- and triethanolamine.

In practicing the process for making the ethanolamines, the temperatures employed to carry out the reaction between ethylene oxide and ammonia is above the critical temperature of the reaction mixture. When maintained at that temperature, a single supercritical fluid phase is achieved within which the reaction between ethylene oxide and ammonia will occur. The reaction proceeds when the reaction mixture is maintained above its critical temperature to achieve the single supercritical fluid phase. If one increases the pressure of the reaction zone, then there will be a consequent increase in the reaction rate. An increase in pressure is reflected by an increase in the density of the supercritical fluid phase. The degree of increase in the density of the reaction mixture is only important as it relates to the reaction rate, but in terms of practicing the process for making the ethanolamines it is only necessary that the reaction mixture be maintained as a single phase supercritical fluid. The density of the single phase supercritical fluid will be at least 240 kg/m³ (15 pounds per cubic foot).

The reaction may be carried out under isothermal or, preferably adiabatic conditions. The presence of 0.5% to 5% by weight of water based on the weight of the reaction mixture in the reaction mixture has an advantageous catalytic effect. In the most preferred embodiment, it is desirable to effect the reaction in a plug-flow type reactor by feeding a stream comprising ammonia and ethylene oxide to one end of a tubular plug-flow type reactor and withdrawing the effluent containing the desired alkanolamines from the other end thereof. It is also very desirable in the practice of the invention to maximize the plug-flow characteristics of the reactor and for this reason the geometry of the reactor should be such as to minimize any backmixing or recycling that might occur as a consequence of improper reactor design or improper fluid velocities.

In making the ethanolamines, it is preferred that a large excess of ammonia relative to the ethylene oxide be used in the reaction to obtain yields of monoethanolamines of at least 65 weight percent, preferably at least 70 weight percent. In a typical practice of the invention in order to obtain these desirable yields of monoethanolamine, one may employ between 15 to 50 moles, and preferably between 20 to 35 moles, of ammonia for each mole of ethylene oxide.

As indicated above, the temperature at which the reaction between ethylene oxide and ammonia is carried out such that the reaction mixture is maintained in single supercritical fluid phase during the course of the reaction. As pointed out previously, the temperature is above the critical temperature for the reaction mixture in order to achieve the supercritical fluid phase. The temperature should be above 130°C and may be as high as 225 _°C through the upper limit of the reaction temperature is not critical so long as the critical temperature of the reaction mixture is exceeded. In the most preferred embodiment, the reaction temperature is within the range from about the critical temperature of the reaction mixture, generally from 130_°C to 225 °C. Under isothermal conditions, since the reaction is strongly exothermic, it is necessary to withdraw heat from the reaction mixture to keep the temperature approximately constant.

In cases where the reaction is to be carried out under adiabatic or nearly adiabatic conditions, the reactants are preheated to a temperature which is at least sufficient to effect an interreaction between the reactants, such as a temperature as low as 20 _°C and higher. It should be understood that if one attempts to effect the reaction at such low temperatures as 20 _°C that such will not occur with the reaction mixture being in a single supercritical fluid phase and therefore it will be necessary to preheat and/or utilize the exotherm of the reaction to achieve conditions which would bring the reaction mixture under supercritical fluid conditions as aforestated. However, in the practice of this invention the reactant mixture is introduced at a temperature such that they achieve a supercritical fluid condition. Under such conditions, the reaction occurs rapidly with a strong exotherm. In the typical case, the reactant mixture is heated and introduced to the reaction zone at a temperature sufficient to achieve the supercritical fluid conditions. The pressure of the reaction zone, coupled with its temperature must be such as to achieve the supercritical fluid state. The pressure throughout the course of the reaction maintains the single phase supercritical fluid state. The pressures applied in the reaction of ammonia with ethylene oxide is within the range of 138 bar abs. (2000 pounds per square inch absolute) to 345 bar abs. (5000 pounds per square inch absolute). It has been found that the above amount of water has an advantageous catalytic effect on the reaction rate for forming ethanolamines though it does not appear to affect the yield of monoethanolamine in the product mixture.

In this embodiment, before carrying out the reaction of ethylene oxide with ammonia, the process (as pointed out previously) is carried out continuously under isothermal or, preferably adiabatic conditions, in a plug-flow type reactor or a series of reactors which in combination achieve the results of a plug-flow type reaction system. A turbulent single directional flow of the reaction mixture through a plug-flow type reactor, under plug-flow type reaction conditions, results in the flow of the stream through the reactor with a minimum amount of backmixing and thermal stratification. This results in essentially eliminating hot spots in the reactor which will effect the reaction rates and product distribution, i.e., as between monoethanolamine, diethanolamine and triethanolamine, and minimize the reaction of ethylene oxide with already formed ethanolamines.

The Amination Reaction

The amination reaction employed in carrying out the process of this invention is not narrowly limited provided that the objectives of the invention are obtained. To that extent, one may employ the technology of Arne and the above mentioned U.S. Patents to produce ethylenediamine from the product mixture derived from the reaction of ethylene oxide with ammonia, as hereinabove described.

However, in the preferred practice of this invention, the amination process is carried out in such a manner as to favor the selectivity of the reaction towards the production of ethylenediamine. This is accomplished by utilizing the nickel-rhenium catalyst which are described in the aforementioned U.S. patent 4,123,462 and U.S. Patent No. 4,111,840.

Broadly speaking, the objective of the amination reaction is to convert the products of the reaction of ethylene oxide and ammonia, which products contain, monoethanolamine, diethanolamine and triethanolamine, to ethyleneamines. In the typical practice of the invention, the amination reaction serves to convert such products to ethylenediamine. As mentioned above the reaction of ethylene oxide and ammonia produces a stream which contains essentially ammonia, monoethanolamine, diethanolamine and triethanolamine. The amount of ammonia in the product mixture is subject to the amount of ammonia which is utilized in the reaction with ethylene oxide. In the typical case the amount of ammonia which will be used will be vastly in excess of the stoichiometry of the reaction to produce the product mixture and therefore the available ammonia which is used in the reaction between ethylene oxide and ammonia will in large part be adequate for the subsequent amination reaction to produce the ethyleneamines. The aforementioned mixture of ammonia, monoethanolamine, diethanolamine and triethanolamine will comprise the continuous homogeneous fluid stream mentioned previously. The homogeneous fluid stream can be supplied directly to the amination reaction. In practicing the process of this invention there is provided with the homogeneous fluid stream additional monoethanolamine as described above and that additional amount of monoethanolamine with the homogeneous fluid stream when provided to the amination reaction will comprise the amination feed stream.

As mentioned previously, the amination feed stream is supplied to the amination zone at a pressure which is equal to or somewhat lower than the pressure of the homogeneous fluid stream. Consequently, the amination reaction zone is at a pressure which is essentially equivalent to the pressure of the amination feed stream as it exists when introduced to the amination reaction zone.

In the typical case the amination feed stream will be composed of the components of the homogeneous fluid stream, recycled monoethanolamine and, optionally, hydrogen and/or ammonia. In the operation of the process of this invention the amination feed stream is supplied to the amination reaction as a single phase supercritical fluid stream. However, the pressure of that supercritical fluid stream will be less than the pressure of the continuous homogeneous fluid stream which is removed from the reaction between ethylene oxide and ammonia, even though the latter stream is also in the typical case a single phase supercritical fluid stream.

The amination zone comprises as an essential ingredient in order to effect the amination reaction a catalyst material which will convert the aforementioned amination feed stream into a stream containing ethylenediamine. Such material effects the production of the ethyleneamines, as aforedescribed, preferably favoring the formation of ethylenediamine. Though the catalysts which are generally described in the prior art as capable of converting a mixture of ammonia and monoethanolamine in the vapor state to ethylenediamine may be utilized in the practice of this invention, the preferred catalyst is a solid material comprising nickel and rhenium on a support as described in the aforementioned Best patents. Such catalyst is characterized as having high activity and selectivity in amination processes and comprises rhenium and nickel impregnated on a support material such as alpha-alumina, silica, silica- aluminas, kieselguhrs or diatomaceous earths, and silica-titania, in which the mole ratio of nickel to the rhenium is in the range of 2:1 to 30:1 and the total nickel and rhenium metal present is in the range of 3 to 30 percent by weight of the support. Such catalysts are discussed at length in U.S. Patent 4,123,462, and in particular that disclosure set forth in column 4, lines 24-34, that disclosure starting at column 5, line 59, all of columns 6, 7, and 8 to line 23 of column 9, examples 2, 3, 4, 5, 6, 7, 8, 9, 10 and 12. The same disclosure can be found in U.S. Patent 4,111,840.

The amination feed stream contains at least 70 weight percent monoethanolamine based on the total ethanolamines content, not more than 30 weight percent of diethanolamine, same basis, not more than 15 weight percent of triethanolamine determined on the same basis, and the sum of the diethanolamine and triethanolamine does not exceed 30 weight percent of the total ethanolamine content thereof. The amination feed stream also contains ammonia in an amount which is in stoichiometric excess of the alcoholic hydroxyl groups which are present in the amination feed stream. In the preferred case there is contained at least 10 moles of ammonia for each moles of ethanolamine present in the amination feed stream. In the most preferred embodiment there is provided at least 15 moles of ammonia from each mole of ethanolamine provided in the amination feed stream and the utilization of at least 20 moles of ammonia for each mole of monoethanolamine which is present in the amination feed stream being the most highly preferred embodiment. The amination feed stream may also possess a limited amount of water. The water that is present will typically be that which is provided as a result of the ethylene oxide-ammonia reaction. The water content in the amination feed stream may range between 0 weight percent to 10 weight percent, basis the weight of the amination feed stream and preferably the water content is kept between 0-5 weight percent, based on the total weight of the amination feed stream.

In further characterizing the amination feed stream, the preferred monoethanolamine content thereof is at least 90% of the weight of the total ethanolamines contained therein, while the diethanolamine content of the amination feed stream is typically at least 3% of the weight of the aforementioned total ethanolamines content. Usually the triethanolamine content of the amination feed stream is at least 0.5% by weight of the total ethanolamines content.

The reaction which involves the amination feed stream to produce ethyleneamines is accomplished in the amination zone. This zone contains the solid catalyst in the form of a fixed bed and has a temperature and pressure sufficient to cause the amination feed stream to react to form the ethyleneamines, such as ethyleneamine, etc. The amination zone contains the appropriate catalysts for the amination reaction, as described above, the amination feed stream, hydrogen and ammonia. When hydrogen and ammonia are not components of the amination feed stream in the appropriate proportions, optionally, they are added separately.

The hydrogen may be supplied to the reaction zone as a separate feed stream into the amination zone or as a component of the amination feed stream. Hydrogen serves the purpose of a promoter for the catalyst. When hydrogen is not provided in the reaction zone and the catalyst is a nickel-rhenium catalyst as described above, the catalyst life is greatly shortened and the rare of amine production is materially reduced. By providing hydrogen in the amination zone, the catalyst is continuously promoted to effectively cause the amination of the ethanolamines to produce the desired products. It is believed that hydrogen acts in part as a continuously supplied inert to keep available sites at the catalyst surface for the desired reaction between ammonia and the ethanolamines and preclude the stabilization of the catalyst sites by ethyleneamines and/or ammonia. Inerts which can also be supplied to the reaction are inert gases such as nitrogen, helium, methane, and the like. Such inert gases can be utilized to help in the control of the reaction temperature and assist in maintaining the desired pressure conditions during the course of the reaction. Suitable inert solid diluents for the catalyst can be any of the aforementioned support materials utilized in the manufacture of the catalyst and preferably is a material such as alpha-alumina, silicon carbide, silica, glass shot or balls. Such solid inert materials serve the purpose of adequately diluting the bed for the purpose of controlling gas flow characteristics within the catalyst bed as well as assisting in the control of the temperature within the reaction zone.

As mentioned immediately above, the catalyst is provided in the reaction zone in the form of a bed of particles. Typically, such beds are supported upon distribution plates or screens which allow for the passage of gases or fluids through the bed. In this respect, the process is carried out utilizing standard fluid-solid heterogeneous catalytic techniques.

Also supplied to the amination zone is an amount of monoethanolamine in addition to that which is supplied to the amination feed stream from the homogeneous fluid stream. This monoethanolamine is provided to the amination zone in admixture with the amination feed stream, and therefore becomes a part thereof either immediately prior to the feeding of the amination feed stream to the amination zone or at some point further upstream of the amination zone.

As mentioned previously, hydrogen is supplied as a promoter for the catalyst. The amount of hydrogen that should be present in the amination feed stream should be from 1 mole percent to 30 mole percent based on the total moles in the amination feed stream. Preferably the amount of hydrogen which is provided in the amination zone is from 2 to 15 mole percent based on the total moles in the amination feed stream.

The temperature of the amination zone in the usual case is selected based upon the temperature characteristics of the catalyst which is utilized for the amination reaction. When employing the nickel-rhenium catalyst mentioned above, this temperature is 120°C to 225 _°C, preferably in a range of 150 to 215_°C. It should be mentioned that in carrying out the process in its most desirable embodiment, the stream within the amination zone is under supercritical fluid or vapor phase conditions, preferably under supercritical fluid conditions as described above. Therefore, the pressure within the reaction zone should be correlated with the temperature so as to achieve either the supercritical fluid conditions or a vapor phase condition. It is most desirable to avoid the presence of any liquid on the catalyst. That is, the catalyst should be essentially free of any liquid deposition on its surface. If such deposition occurs, it will very rapidly cause the dissolution of the catalyst on the surface of the support used with it and consequently the catalyst will become liquified and be carried away with the effluent from the amination zone. As that occurs, the catalyst within the zone will contain less and less of the desired nickel and rhenium, and consequently its activity will decrease to such an extent that eventually it will no longer activate the amination reaction.

In carrying out this process, in a preferred embodiment utilizing a nickel-rhenium catalyst which also contains boron, as described in the aforementioned U.S. patents 4,123,462 and 4,111,840 the pressure is in the range of 103,5-207 bar abs. (1500-3000 psia), with the preferred pressure being approximately 155,25 bar abs. (2250 psia). When operating at such pressures, the temperature is in the range of 150-215 °C and the fluid velocity through the amination zone is carried out to effect a residence time in the reactor of from 3 to 8 minutes.

The amination reactor which provides the amination zone may be any reactor configuration ranging from a fixed bed tubular reactor to a back- mixed fixed bed reactor. In view of the fact that the amination reaction does not provide a significant exotherm, it is not necessary for one to utilize a fluid bed reactor. However, one may utilize a fluid bed reactor if such is desired. One important feature of a reactor is that it should be designed to provide for a uniform flow distribution of the amination feed stream (and hydrogen, ammonia, and the like gases, to the extent that such are not included with the amination feed stream) to the reaction zone. The better interdispersion of the various components of the amination feed stream (as well as hydrogen, ammonia and other gases supplied to the amination zone) the better will be the overall effectiveness of the amination reaction.

After the fluids are removed from the amination zone, they are subjected to a variety of separation stops for the purpose of removing the various components contained therein. For example, the effluent gas stream from the amination zone will be subjected to distillation to remove water, ammonia ethylenediamine, monoethanolamine (which will be recycled as described above), hydroxyethylpiperazine, aminoethylethanolamine. tetraethylenepentamine, diethylenetriamine, aminoethylpiperazine, piperazine, triethylenetetramine, diethanolamine and triethanolamine. Because of the vast differences between the boiling points of monoethanolamine, diethanolamine and triethanolamine, the separation of monoethanolamine from the composition is very readily obtained and an extremely pure stream of monoethanolamine can be produced by simple distillation. In the normal course, the monoethanolamine which can be obtained by distillation will contain at least 99 weight percent of monoethanolamine with extremely small amounts of piperazine, diethylenetriamine, aminoethylpiperazine, and hydroxyethylpiperazine being present.

High Pressure Separation

In a preferred embodiment of this invention, the homogeneous fluid stream which comprises the effluent from the reaction of ethylene oxide and ammonia is introduced to a high pressure separator which serves the purpose of producing an amination feed stream which is enriched in respect to its monoethanolamine content without creating a significant energy loss resulting from a large pressure reduction. In essence, what occurs is that the homogeneous fluid stream is passed to a simple separation tank in which a modest phase separation occurs resulting in the removal from the tank of a gaseous stream which is richer in monoethanolamine than the homogeneous fluid stream which is provided to the tank. Withdrawn from the bottom of the tank is a stream which contains a smaller content of monoethanolamine. In a preferred embodiment of the invention, this high pressure separation is practiced as follows. The homogeneous fluid stream which is removed from the reaction between ammonia and ethylene oxide is passed as a supercritical fluid to admixture with monoethanolamine recycle introduced at a temperature substantially below that of the homogeneous fluid stream. As a result, the temperature of the homogeneous fluid stream is reduced and the resulting stream that is formed from admixture with the recycled monoethanolamine is no longer in a supercritical fluid condition. That stream is thereafter passed to a heat exchanger and the temperature of the stream is raised to a temperature which allows the enriched amination feed stream which is taken from the high pressure separator tank to be again a supercritical fluid stream. For example, if the effluent from the ethylene oxide-ammonia reaction, which comprises the continuous homogeneous fluid stream, is at 170°C. it will be cooled by recycled monoethanolamine which is at about 45 _°C to form a lower pressure stream having a temperature of about 143°C which is no longer a supercritical fluid. That stream is thereafter heated to form an effluent from the high pressure separator tank having a temperature of 160°C and consequently being further heated to a stream having a temperature of 180_°C, and possessing the conditions of a supercritical fluid. It also follows that by introducing the recycled monoethanolamine into the fluid stream followed by high pressure separation that there is a loss of pressure from that at which the homogeneous fluid stream is at when taken as an effluent from the ethylene oxide-ammonia reaction. As described previously, that reaction is carried out at pressures within the range of 138 bar abs. (2000 pounds per square inch absolute) to 345 bar abs. (5000 pounds per square inch absolute). For example, should the effluent from the ethylene oxide-ammonia reaction be at 207 bar (3000 psi), it typically will be reduced to a pressure of 152 bar (2200 psi) before it is fed to the high pressure separator tank and reheated through a heat exchanger to a temperature which achieves a supercritical fluid condition.

The high pressure separator tank is nothing more than a simple tank containing therein a demister pad at its upper area to remove any liquid components trapped in the volatile components removed from the upper portion of the tank. The liquid body which is created in the tank as a result of the phase separation occurring therein will be removed from the bottom thereof and will be richer in diethanolamine and triethanolamine than is the homogeneous fluid stream minus any amount of ethanolamine which has been added to such stream prior to its addition to the high pressure separator tank.

The monoethanolamine recycle which is provided can be an amount which is equivalent to the amount of monoethanolamine not converted in the amination zone to ethyleneamines. The monoethanolamine recycle can be introduced before or after the aforementioned high pressure separation, but at least, in any case prior to the amination zone in admixture with the amination feed stream. If it is introduced prior to the amination zone to the components of the amination feed stream, then for the purposes of this invention, it is considered a part of the amination feed stream and to the extent that the previous discussion refers to a supply of an amination feed stream to the reaction zone, such additional monoethanolamine is considered a component part thereof. In the preferred practice of this invention, the monoethanolamine is removed from the product stream effluent from the amination zone after the removal of piperazine, and this monoethanolamine recycle is reduced in temperature from 60 °C to 25 °C and has a purity as aforedescribed. The monoethanolamine is recycled back to a point in the reaction chain prior to the high pressure separator to affect admixture with the homogeneous fluid stream as described previously. It is also possible to instead recycle at least a part of the monoethanolamine stream subsequent to the high pressure separation step so that it is not necessary to reduce the temperature of the monoethanolamine prior to its reintroduction as a recycle stream into the ethanolamine feed going to the amination zone. In such a case, where there is effected monoethanolamine enrichment by the utilization of a high pressure separation step, as described above, then the homogeneous fluid stream is cooled by heat exchanger to a temperature low enough to take it from a supercritical fluid stream to a liquid stream which allows separation to occur in the high pressure separation tank.

Coming now to the drawing, the drawing illustrates a schematic flow diagram of an integreated process for carrying out this invention which includes the separation of products from the amination reaction to the extent necessary to allow for the recovery of monoethanolamine for recycle. Excluded from the drawing is the recovery of other components of the amination reaction as well as diethanolamine and triethanolamine. Their individual separation is effected by conventional distillation techniques and the order of their separation is predicated upon the respective volatilities of such components.

As shown in the drawing, ethylene oxide for the reaction is fed through lines 16 into admixture with ammonia recycle fed through line 18. Makeup of ammonia is supplied through line 15 into line 18 on an as needed basis. The admixture of ammonia and ethylene oxide is achieved simply by connecting the respective lines for each and they are pumped (not shown) with a high pressure feed pump to heat exchanger 14.

In order to effectively utilize the energy resources of the process, the reaction mixture stream comprising ethylene oxide and ammonia are fed through a high pressure feed pump (not shown) to a shell and tube heat exchanger 14, with is supplied with heat by passing the effluent from the catalytic reactor 36, that is the effluent fed through line 33 or line 45 for a bottom feed, to the shell side of the heat exchanger 14. As a result, the ethylene oxide-ammonia reaction mixture is heated by passage through the tube side of the heat exchanger 14 to a temperature which is considered desirable for effecting the adiabatic reaction of ethylene oxide with ammonia under supercritical fluid conditions. For example, the feed stream to the reactor is brought to a temperature of about 136°C and 207 bar abs. (3,000 psia). It is then fed into tubular reactor 10 having for example, a length to diameter ratio of 40:1 and which contains in the entry port thereof a swirling device. The continuous homogeneous fluid stream removed from reactor 10 is in the form of a supercritical fluid. The temperature and pressure of the fluid is sufficient to effect the supercritical state, such as a temperature of 170°C and a pressure of 207 bar abs. (3,000 psia). The pressure in the stream is controlled by a pressure reducing valve, not shown, and is fed to interconnect with the fluid from line 19. The fluid from line 19 can contain the monoethanolamine recycle or a mixture of monoethanolamine recycle and ammonia which is also recycled or simply ammonia from recycled ammonia. In the preferred practice of the invention, the monoethanolamine recycle is mixed with some of the ammonia recycle and the combination is fed through line 19 to effect admixture with the effluent from reactor 10, that is the homogeneous fluid stream. The control of ammonia recycle to line 19 is effected by valve 13 located in line 21. The control for monoethanolamine addition to line 21 is effected by valve 23 located in line 20. If it is desired to introduce the monoethanolamine recycle at a later stage, then valve 23 can be closed thereby diverting flow of the monoethanolamine recycle through line 27. In such a case, valve 25 will be opened and allow the flow of the monoethanolamine recycle to a later stage in the process scheme. The admixture of the monoethanolamine recycle and the homogeneous fluid stream is achieved upon contact of line 19 with line 11 through which the homogeneous fluid stream is passed. The admixture is thereafter fed to heat exchanger 12 for the purpose of further reducing the temperature of the mix stream in line 11 to a desired temperature for the gas-liquid phase separation to be effected in the high pressure separator 30. The temperature reduction is effected by both the reduced temperature of the monoethanolamine recycle stream and any ammonia which is also recycled therewith into line 19 and thereafter into line 11. Further reduction in the temperature may be thereafter obtained by heat exchanger 12 to effect the desired temperature for effective gas-liquid separation under the conditions of high pressure which are existing in separator 30. The pressure in line 11 and separator 30 is controlled so as to effect, in coordination with the temperature therein, separation of the homogeneous fluid stream from reactor 10. The effluent vapor taken from the top of separator 30 is fed through line 34 to a heat exchanger (not shown) whereby to increase the temperature of the effluent stream which at this instance is characterized as the amination feed stream. By increasing the temperature, while maintaining a pressure of from 103.5 (1500) to 172.5 bar 2500 psi), and preferably about 152 bar abs. (2200 psia) for the amination food stream, the amination feed stream is converted into a supercritical fluid stream. This supercritical fluid stream is fed through line 34 into the top of amination reactor 36 which contains a fixed bed of rhenium-nickel catalyst containing boron supported upon a diatomaceous earth particulate support.

Alternatively, the amination feed stream may be advantageously fed through line 60 controlled by valve 55 into the bottom of amination reactor 36 so as to effect an upward flow of the amination feed stream through the catalyst bed contained therein during the amination reaction.

In order to provide the necessary hydrogen promoter to the reaction, hydrogen which is within the system is recycled through hydrogen compressor 24 into the upper portion of the high pressure separator 30 through line 22 and is thereafter carried with the amination feed stream through line 34, or alternatively line 60, into reactor 36.

The effluent from reactor 36 is passed into line 33, or alternatively line 45, and thereafter through the shell side of the heat exchanger used for preheating the ammonia-ethylene oxide reaction mixture as described previously, designated in the drawing as heat exchanger 31, for convenience sake. Heat exchanger 31 depicts the shell side of the same heat exchanger previously characterized as heat exchanger 14 which characterizes the tube side thereof. The reaction product effluent from reactor 36 is thereafter passed through line 35 into an ammonia flash tank 38 for the purpose of separating ammonia and hydrogen from the effluent liquid stream. The ammonia and hydrogen are taken off through line 28 and subsequently separated whereby the ammonia is fed through ammonia recycle compressor 26 and then into line 18 for subsequent recycle or it is passed to line 29 for eventual introduction into line 18, also for ammonia recycle, as described previously. The hydrogen is fed into a recycle compressor 24 so that the hydrogen can be recycled to separator 30 as described previously. The bottoms from flash tank 38 are fed through lines 39 into which the bottoms from high pressure separator 30 are also fed by way of line 32 and the admixture is fed into a second flash separator, 37, for additional separation of ammonia to be recycled through line 18 by way of line 43 and ammonia recycle compressor 26. The bottoms from separator 37 is fed to an ammonia stripping still 40 through lines 41 for final removal of ammonia from the amine reaction product mixture. The bottoms from the still 40 is passed through line 42 into distillation column 50 maintained at a temperature sufficient to remove the water contained in the reaction through line 49. The heavies from the reaction are recovered from distillation column 50 through line 44 and passed to still 52 for the recovery of ethylenediamine by way of line 51. The heavies from that distillation are removed through line 54 into piperazine still 56 from which piperazine is recovered through line 57. The bottoms from that separation are removed through line 53 and passed to still 58 for the recovery of monoethanolamine which is recycled by way of line 20 for eventual addition to the homogeneous fluid stream either prior to or after the high pressure separator 30. The bottoms of that separation are passed from line 59 into a series of refining columns for recovering each of the various components of the stream.

Example

The reaction system and apparatus shown in the drawing and discussed above, comprising an adiabatic, tubular ethylene oxide/ammonia reactor, an amination catalytic reactor, and associated equipment, is used in this run. In this run, a liquid ethylene oxide feed of 220 moles per hour is mixed with a liquid ammonia-water mixture (98 percent NH₃, 2 percent water) to give an ammonia to ethylene oxide mole ratio of 30:1). The mixed ammonia/ethylene oxide feed is pumped into the first reactor stage of reactor 10, which is a four stage adiabatic, tubular reactor having a 40:1 length to diameter ratio, after preheating to a temperature of 135°C. The pressures in the reactor stages are controlled to maintain the flowing stream in a single, swirling, supercritical fluid phase having an average reaction mixture density of 344 kg/m³. The pressure at the outlet of the final reactor stage of reactor 10 is 207 bar and the temperature of the product mixture is 170°C after a residence time within the reactor of 20 minutes.

The homogeneous product mixture stream from the ethylene oxide/ammonia reactor 10 contains 95 mole percent ammonia, 1.9 mole percent water, 2.4. mole percent monoethanolamine, 0.4 mole percent diethanolamine and less than 0.1 mole percent triethanolamine. The homogeneous fluid stream in line 11 is depressurized to 152 bar end is mixed with a monoethanolamine recycle stream carried in line 19 from line 20 containing 89 mole percent monoethanolamine and an ammonia recycle stream containing about 98 mole percent ammonia and 2 mole percent water carried in line 19 from lines 18 and 21, and then preheated to a temperature of 155°C before being fed to a 3t foot diameter high pressure separator, 30, which is maintained at a pressure of 152 bar. A recycle stream containing about 80 mole percent hydrogen and 20 mole percent ammonia is also fed to the product mixture in high pressure separator 30 through line 22.

The overhead stream from the high pressure separator is heated to 170°C to form a homogeneous single phase before being fed to the catalytic amination reactor 36. The overhead stream from the separator 30, contains 7.2 mole percent hydrogen, 87.0 mole percent ammonia, 1.4 mole percent water, 4.3 mole percent monoethanolamine, 0.1 mole percent diethanolamine and less than 0.01 mole percent triethanolamine.

Amination reactor 36 is a 2,30 m diameter vertical reactor containing an 31 m³ bed of solid catalyst comprising 7.0% nickel; 1.85% rhenium; 1.44% boron on a silica-alumina support. The feed stream enters the bottom thereof through a line and valve 55 and flows upward through the catalyst bed while being maintained in a single supercritical fluid phase at a temperature of 170 _°C and a pressure of 152 bar.

The effluent taken from the top of the amination reactor 38 through line 45 comprises a single phase fluid stream containing 7.2 mole percent hydrogen, 85 mole percent ammonia, 3.1 mole percent water. 1.3 mole percent ethylenediamine, 0.1 mole percent diethylenediamine (piperazine), 0.1 mole percent diethylenetriamine, 2.6 mole percent monoethanolamine, 0.1 mole percent diethanolamine and less than 0.01 mole percent each of aminoethylpiperazine, aminoethylethanolamine, and triethanolamine. This stream is cooled to 150°C and depressurized to 27.6 bar abs. before being fed through a 1.8 m diameter flash separator 38 where unreacted ammonia is recovered for recycling back to the ethylene oxide-ammonia reactor 10 and recovered hydrogen is recycled back to the high pressure separator 30, respectively. The liquid bottoms from the flash separator 38 contains 70 mole percent ammonia, 12 mole percent water, 5.3 mole percent ethylenediamine, 0.4 mole percent piperazine. 10.5 mole percent monoethanolamine, 0.3 mole percent diethylenetriamine, 0.04 mole percent aminoethylpiperazine, 0.3 mole percent, aminoethylethanolamine, 0.36 mole percent diethanolamine and less than 0.05 mole percent of other amine products. This stream is combined in line 39 with the liquid bottoms product from the high pressure separator, 30, containing 61 mole percent ammonia, 4.3 mole percent water. 24.7 mole percent monoethanolamine, 4.1 mole percent diethanolamine and 0.6 mole percent triethanolamine, depressurized to 15,5 bar abs. and heated to 80 _°C in a flash separator, 37, where 80 percent of the remaining unreacted ammonia is removed and recycled to the ethylene oxide/ammonia reactor 10, through line 18.

The liquid bottoms from the flash separator 37 is fed to ammonia stripping still 40, a standard distillation column operating with a pressure of 3.45 bar abs. to remove the remaining unreacted ammonia and about 40 percent of the water for recycle.

The bottom stream from the distillation column 40, comprising the mixed products contains 24 mole percent water and 18 mole percent ethylenediamine, 1.3 mole percent piperazine, 1.2 mole percent diethylenetriamine, 0.1 mole percent aminoethylpiperazine, 0.1 mole percent hydroxyethylpiperazine in addition to 50 mole percent monoethanolamine, 1.0 mole percent of aminoethylethanolamine, 3.5 mole percent of diethanolamine and less than 0.5 mole percent of triethanolamine. This stream is then separated by standard distillation techniques into component alkanolamines and alkylemamines for recovery or recycle. Monoethanolamine is recycled through line 20 to and mixed with the homogeneous fluid product mixture in line 11. The run produces 115 mole per hour of ethylenediamine, 8 moles per hour of piperazine, 7.6 moles per hour of diethylenetriamine and 7.0 moles per hour of aminoethylethanolamine. 23 moles per hour of diethanolamine is also recovered.