A FLEXIBLE PROCESS FOR THE PRODUCTION OF DI AND TRIALKYLAMINES

Abstract: This invention relates to a process for the nonequilibrium controlled production of di and trialkylamines containing at least one C₂₋₄ alkyl substituent in high selectivity by the catalytic amination of an alkanol with ammonia under conditions for forming said mono, di and trialkylamines. The improvement in the process for producing di and trialkylamines comprises: initially contacting a C₁₋₄ alkanol with ammonia in the presence of hydrogen, under conditions for forming a mixture of mono, di and trialkylamines; separating the monoalkyl and dialkylamines from the trialkylamine formed in the initial amination of the alkanol; and contacting the dialkylamine with a C₂₋₄ alkanol in a fixed bed reactor under gas phase conditions in the presence of hydrogen and a cobalt or nickel containing hydrogenation catalyst, the mole ratio of alkanol to dialkylamine ranging from 1 to 3:1, the reaction temperature ranging from 275 to 400°F, the pressure ranging from 150 to 350 psig and the gas hourly space velocity ranging from 500 to 2000 hr⁻¹. Monoalkylamine is converted to dialkylamine by reaction with a C₂₋₄ alkanol in a fixed bed reactor under gas phase conditions in the presence of hydrogen and a cobalt or nickel-containing hydrogenation catalyst, the mole ratio of alkanol to monoalkylamine ranging from about 1 to 3:1, the reaction temperature ranging 275 to 400°F, the pressure ranging from 150 to 350 psig a gas hourly space velocity of 500 to 2000 hr⁻¹.

Description: This invention relates to an improved process for producing di and trialkylamines containing at least one C₂₋₄ alkyl substituent in high selectivity. BACKGROUND OF THE INVENTION Alkylamines which usually comprise the reaction product of a C₁₋₄ alkanol with ammonia to produce the resultant alkylamine are widely known and used as intermediates in the manufacture of many commercial products. The current commercial process schemes for producing the alkylamines involve the reaction of an alcohol or their corresponding ethers with ammonia and the subsequent separation and recycling of the mono di, and trialkylamine products to obtain a desired product distribution. Alkylation of ammonia or an amine by contact with an alcohol or its ether resulting in the production of a mixture of mono, di and trialkyl substituted amines is generally thought of as being equilibrium controlled. The product slate falls along an equilibrium line which changes with temperature or amine to alkanol (N/R) mole ratio. In the synthesis of higher alkylamines, typically consisting of C₂₋₄ alkyl-containing amines, there is an additional problem associated with an equilibrium controlled distribution of products and that is minimizing formation of undesired products through the reforming of higher amines with themselves to form lower amines, dehydrogenation to produce the corresponding olefin and dehydrogenation of the amine to produce the nitrile. The following patents are representative of the prior art with respect to the synthesis of alkylamines, including, C₂₋₄ alkylamines, such as ethlyamines, propylamines, and butylamines: U.S. 4,398,041 discloses the nonequilibrium controlled production of C₁₋₄ alkylamines by passing a mixture of a C₁₋₄ alcohol and ammonia into a reaction zone containing a shape-selective crystalline alumino-silicate zeolite catalyst, e.g., an H-mordenite or H-erionite which is capable of catalyzing the synthesis of mono and dialkylamines but which has a pore size too small to permit the passage of a tri-substituted alkylamine therethrough. A fraction of the first product stream containing mono and dialkylamines is removed and the remainder is passed through a second conversion zone containing a catalyst having intracrystalline pores sufficiently large for permitting the production of an equilibrium controlled distribution of mono, di and trialkyl substituted amines. The streams are combined to form a nonequilibrium controlled product slate. An H-Y zeolite, REY zeolite or silica-alumina is used as the catalyst for the second reactor zone. German Application 3,539,266 discloses a process for preparing trialkyl amines by reacting a dialkylamine with a C₂₋₄ alcohol in the presence of a hydrogenation/dehydrogenation catalyst containing essentially only copper as a catalytically hydrogenating/dehydrogenating metal. The reaction is carried out in liquid phase with a mole ratio of dialkylamine e.g., dimethylamine to C₂₋₄ alkanol from 1-10:1 and further carrying out the reaction in the presence of water. The patentees point out that at the synthesis of tertiary amines by alkylation of secondary amines with alcohols had been difficult because of concomitant transalkylation and disproportionation reactions which occur along with the amination of the alcohol. Example 4 shows the production of triethylamine from diethylamine and ethanol (N/R of 0.2:1) under liquid phase conditions. European Patent Application 0 211 552 discloses a process for producing alkylamines by reacting an alcohol with an amine, e.g., ammonia using a nickel or cobalt containing catalyst and a difficulty reducible metal oxide, e.g., alumina plus a rare earth. As the patentees note, conventional hydrogenation catalysts typically have given rise to appreciable quantities of by-products, particularly hydrocarbons and high boiling contaminants, e.g., nitriles and amides. To minimize the formation of such by-products, it had been customary to reduce the reaction temperature. To maximize selectivity to a desired product slate, extensive recycling of undesired alkylamines had been necessary. U.S. 4,014,933 discloses a process for producing alkylamines by the reaction of an alcohol with ammonia or an amine in the presence of hydrogen utilizing a cobalt, nickel, copper or copper-containing aluminum oxide or silicon dioxide supported catalyst optionally including a phosphorus containing cocatalyst and a promoter in the form of an alkali or alkaline earth metal. U.S. 4,314,084 discloses a gas phase process for producing C₂₋₆ alkylamines by the amination of C₂₋₆ alkanols. A hydrogen/dehydrogenation catalyst, e.g., nickel or cobalt is carried on a neutral alumina support promoted with an alkaline material to enhance selectively and minimize olefin production. The product slate however was equilibrium controlled. SUMMARY OF THE INVENTION This invention relates to an improved process for the production of a nonequilibrium controlled product slate of di and trialkylamines by the catalytic amination of a C₁₋₄ alkanol and ammonia where the reaction is carried out in the presence of hydrogen and particularly to a process for producing trialkylamines, e.g., triethylamine. The improvement for producing trialklyamine resides in utilizing a feedstock comprising essentially a dialkylamine and contacting that feedstock with C₂₋₄ alkanol in a fixed bed catalytic reactor containing a hydrogenation/dehydrogenation catalyst containing cobalt or nickel under gas phase conditions wherein the temperature is maintained from about 135 to 204°C (275 to 400°F), the gas hourly space velocity is maintained from 500 to 2000 hr.⁻¹, and the pressure is maintained at about 10.3 to 24.1 bar (150 to 350 psig). A nonequilibrium reaction product rich in trialkylamine is produced in high selectivity without producing substantial by-products in the form of olefins or lower amine by-products through reforming reactions. Conversion of alkanol is maintained at 50 to 70 mole percent. To further enhance the nonequilibrium product slate from an alkanol/ammonia reactant system, the mono and dialkylamine are separated from the reaction product and contacted with C₂₋₄ alkanol under gas phase conditions in a fixed bed reactor. The catalyst utilized is a cobalt or nickel-containing catalyst and the mole ratio of alkanol to amine is from about 1 to 3:1. Conversion of alkanol is maintained at a level from 50 to 70 mole% by controlling the gas hourly space velocity from 500 to 2000 hr⁻¹, and the temperature from 135 to 204°C (275 to 400°F). THE DRAWING The drawing is a process flow diagram of a reaction process for producing di and trialkylamines containing at least one C₂₋₄ alkyl substituent in high selectivity using the process of this invention. DETAILED DESCRIPTION OF THE INVENTION The process of this invention is well suited for the production of C₁₋₄ alkylamines with high selectivity to the di and trialkylamines. In this process, and to facilitate an understanding thereof, reference is made to the drawing. A feedstock of a C₁₋₄ alkanol, such as ethanol, propanol, either isopropanol or n-propanol, and butanol, either isobutanol or n-butanol, is passed through line 2 and combined with recycle alkanol from line 3 and ammonia from line 4 and introduced through line 5 to reactor 6 to produce a reaction product containing a mixture of mono, di and trialkylamine. A high mole ratio of ammonia to alkanol is used in this initial reaction, e.g., from about 0.5 to 20.0 moles ammonia per mole alkanol and preferably between 1.5 to 16 moles ammonia per mole alkanol at pressures ranging from 0 to 48.2 bar (0 to 700 psig) and preferably from 8.9 to 29.6 bar (130 to 430 psig), and temperatures typically ranging from 149 to 422°C (300 to 800°F) and preferably from 176 to 395°C (350 to 750°F). The initial amination reaction may be carried in the presence of a hydrogenation/dehydrogenation catalyst typically, one containing cobalt or nickel carried on a support such as alumina (unneutralized and neutralized), silica, kaolin, zeolites, e.g., H- mordenite, H-Y, rare earth zeolites and silica-alumina. To minimize olefin production, a weakly acidic or neutral support is used to carry the active metal. Silica-alumina may also be used as the catalyst to produce higher quantities of mono alkylamine in the initial amination. In the amination reaction where C₂₋₄ alkanols are used, it is customary to incorporate hydrogen into the reaction zone to maintain activity of the hydrogenation/dehydrogenation catalyst e.g. 0.25 to 4 moles hydrogen/mole alkanol and to minimize olefin production. In addition, it is customary to employ a high ratio of ammonia to alkanol as noted above to act as a heat sink in the reaction zone for maintaining temperature and minimizing reforming reactions between amines and deamination or dehydrogenation resulting in the production of hydrocarbons and nitriles. If in the initial amination, the alkanol is methanol, hydrogen may not be required. Continuing with the process flow scheme, the reaction product obtained from the initial amination reaction is removed from reactor 6 via line 8 and separated in distillation column 10. Mono and dialkylamine in preselected amount are recovered as an overhead and removed as stream 12. A dialkylamine/alkanol bottoms is removed from column 10 through line 14. The level of dialkylamine in the bottoms is regulated via control of the level of dialkylamine removed with the monoalkylamine in the overhead. To overcome many of the difficulties associated with prior art processes, particularly in the synthesis of trialkylamines, the dialkylamine is removed via line 14 and charged to reactor 16 which involves the reaction of a primary C₂₋₄ alkanol with a secondary alkylamine to produce the trialkyl amine. The mole percent secondary alkylamine in the feedstock should be at least 90 percent and preferably about 100 percent of the amine in the feedstock. Although a similar type feedstock may have been used in the past to produce trialkylamines, one of the problems associated with the use of a dialkylamine as a feedstock was that it is capable of reacting with itself or with the amine generated by the reaction, and resulted in substantial by-product formation. This problem was particularly acute when a hydrogenation/dehydrogenation catalyst containing cobalt or nickel was used to effect alkylation of the amine and thus, one of the customary practices has been to utilize different catalysts which are selective to a particular product slate, e.g., a shape-selective zeolite. A further problem associated with the reaction was that the product mix remained an equilibrium mixture and thus, substantial recycle of amines was required to produce a desired product slate. To minimize the rate of a competing reforming reaction that generates equilibrium amounts of unwanted primary and secondary amines, the alcohol is used in excess of the amine in the reaction, with the mole ratio of alkanol to amine ranging from about 1 to 3:1 preferably 1.5 to 2.5:1. The alkyl substituent of the amine feedstock need not be the same as the alkanol used here, but such combination will result in a mixed or unsymmetrical product slate. However, at least one of the alkyl substituents in the di and trialkylamine is a C₂₋₄ substituent, the other substituents may be a C₁ methyl substituent. Therefore, examples of di and trialkylamines include diethylmethylamine, triethylamine, dimethylethylamine, diethylpropylamine, tripropylamine and tributylamine. The temperature preferably is maintained from 163 to 190°C (325-375°F), and the pressure is maintained from 15.5 to 19 bar (225 to 275 psig). The key to producing a kinetically controlled slate, as opposed to equilibrium controlled slate, is in maintaining a gas hourly space velocity of about 1,000 - 2,000 hours⁻¹. This limits conversion of the alkanol to a range from 50 to 70 mole% and thereby enhances selectivity. Longer residence times tend to produce more by-products. The product from the reactor 16 is removed via line 18, and the reaction product separated in distillation column 20 where an overhead stream 22 rich in trialkylamine is generated and a bottoms rich in alkanol is recycled via line 3 to the initial reaction zone. To enhance the yield of dialkylamine in the process, the monoalkylamine/dialkylamine overhead mixture is removed via line 12 from distillation column 10 and charged to distillation column 24 wherein the monoalkylamine is separated from the dialkylamine. The product dialkylamine removed via line 26 may be recycled to reactor 16 or used as product depending upon the level of trialkylamine desired. The overhead consisting essentially of monoalkylamine is removed from column 24 via line 28 and contacted with additional C₂₋₄ alkanol which is introduced through line 30. The reactant mixture is introduced via line 32 to fixed bed catalytic reactor 34. The reactants are converted to a product of essentially dialkylamine and removed via line 36. Conversion of monoalkylamine, particularly monoethylamine, to dialkylamine, e.g., diethylamine, is effected in high selectivity and at high conversion by utilizing a hydrogenation/dehydrogenation catalyst containing nickel or cobalt in the catalytic reactor. The metal content of nickel or cobalt in the catalyst used in the conversion of dialkylamine to trialkylamine, is at conventional levels, e.g., from 30 to 40% by weight as metal. A mole ratio of alkanol to monoalkylamine of from about 0.1 to 3:1 is used. Conversion is limited to a range from 50 to 70% in order to enhance selectivity to avoid reforming, etc., that results in by-product formation. This is accomplished by using a gas hourly space velocity from 500 to 2000 hr⁻¹ and a temperature from 135 to 204°C (275 to 400°F), Pressures are similar to the conversion of dialkylamine to trialkylamine, e.g., 10.3 to 24.1 bar (150 to 350 psig). The following examples are provided to illustrate various embodiments of the invention that are not intended to restrict the scope thereof. All ratios are expressed as mole ratios unless otherwise specified. Example 1 Synthesis of Triethylamine Diethylamine, obtained from a commercial process for the production of ethylamines by the reaction of ethanol and ammonia was used as a feedstock for reaction with ethanol in an effort to synthesize triethylamine in high selectivity. The reaction was carried in a conventional, commercial fixed bed reactor system packed with a cobalt on calcium-alumina hydrogenation catalyst, the concentration of cobalt being approximately 35% as active metal. During the test, the mole ratio of ethanol, to diethylamine (R/N) ranged from 0.5 to 2.3:1, the pressure from 12.4 to 15.8 bar (180 to 230 psig); the gas hourly space velocity ranged from 1,000-1,800 hr⁻¹ and the temperature ranged from 135 to 218°C (275-425°F). Hydrogen was used to maintain the catalyst in an active, reduced state. The mole ratio of hydrogen to ethanol ranged from 1.1 to 2.8. Table 1 below sets forth the reaction conditions and performance. The results show excellent conversion of diethylamine to triethylamine in high selectivity through the process described. Less than 5% by-products were achieved in almost all cases and limited reforming to monoethylamine was noted. Comparing the results from Runs 23 and 28 to the ones of lower temperatures shows that as temperature is increased toward the upper end of the range, there is more by-product formation. Runs 24-29 show that when the R/N mole ratio is below about 1:1, conversion of diethylamine to triethylamine is substantially reduced (compare to Runs 18-22). The ratio of hydrogen to alkanol (H/R) at the higher ratio seemed to have little influence on conversion as compared to the lower ratios (compare Runs 1-4 versus 14-17). The higher mole ratio of ethanol to diethylamine shows an increase in triethylamine production, but at higher temperatures reforming to monoethylamine may increase (note Run 3). A typical product slate obtained from the equilibrium controlled reaction of ammonia and ethanol is MEA/DEA/TEA of 0.48 to 1 to 0.40 (molar) as formed in Runs 10 and 11. Attempts to increase triethylamine levels through higher temperatures and lower N/R mole ratios tends to increase the level of olefins, deamination products and nitriles produced in the process. Thus a nonequilibrium product slate can be achieved by the present process (compare Run 1 slate vs. the one obtained from the equilibrium controlled Run 10).

Claims: A process for the production of trialkylamines in high selectivity by the amination of a C₂₋₄ alkanol with a C₁₋₄ dialkylamine in the presence of a hydrogenation/dehydrogenation catalyst and hydrogen in sufficient amount for maintaining the hydrogenation/dehydrogenation catalyst in an active state, which process comprises: reacting said dialkylamine with said C₂₋₄ alkanol in a fixed bed catalytic reactor utilizing a cobalt or nickel-containing hydrogenation/dehydrogenation catalyst; maintaining gas phase conditions during said reaction; maintaining a reaction temperature of from 135 to 204°C (275 to 400°F), a pressure from 10.3 to 24.1 bar (150 to 350 psig), a gas hourly space velocity of from 500 to 2000 hr⁻¹; and maintaining a mole ratio of C₂₋₄ alkanol to said dialkylamine from 1 to 3:1. The process of Claim 1 wherein ethanol is the C₂₋₄ alkanol and it is reacted with diethylamine as the C₁₋₄ dialkylamine. The process of Claim 2 wherein the operating temperature range is from 163 to 190°C (325 to 375°F). The process of Claim 3 wherein the operating pressure range is from 15.5 to 19 bar (225 to 275 psig). The process of Claim 4 wherein the operating gas hourly space velocity range is from 1000 to 2000 hr⁻¹. The process of Claim 5 wherein the operating mole ratio range for ethanol/diethylamine is from 1.5 to 2.5:1. The process of Claim 6 wherein ethanol conversion to all products is maintained from 50 to 70%. The process of Claim 1 wherein ethanol is the C₂₋₄ alkanol and is reacted with dimethylamine as the C₁₋₄ dialkylamine. The process of Claim 1 wherein ethanol is the C₂₋₄ alkanol reacted with dibutylamine. A process as claimed in claim 1 for producing an alkylamine product slate which process comprises: i) initially contacting a C₁₋₄ alkanol with ammonia in the presence of a catalyst to produce a reaction mixture comprising mono, di and trialkylamines; ii) separating the dialkylamine from the reaction mixture; iii) contacting the dialkylamine with a C₂₋₄ alkanol in a fixed bed catalytic reactor utilizing a cobalt or nickel-containing hydrogenation/ dehydrogenation catalyst under gas phase conditions by maintaining an alkanol to dialkylamine mole ratio of from 1 to 3:1, a gas hourly space velocity of 1000 to 2000 hr⁻¹, a reaction temperature from 163 to 190°C (325 to 375 °F) and a pressure from 15.5 to 19 bar (225 to 275 psig) to generate a trialkylamine-rich reaction mixture; iv) separating the monoalkylamine from the reaction mixture; and then v) contacting at least a portion of the monoalkylamine with a C₂₋₄ alkanol in a fixed bed catalytic reactor utilizing a cobalt or nickel-containing hydrogenation/dehydrogenation catalyst under gas phase conditions by maintaining a reaction temperature of from 135 to 204°C (275 to 400°F), a gas hourly velocity from 500 to 2000 hr⁻¹, a alkanol to monoethylamine mole ratio of from 0.1 to 3:1 and a pressure of from 0.3 to 24.1 bar (150 to 350 psig); and recovering the resultant reaction mixtures comprising dialkylamine. The process of Claim 10 wherein the hydrogenation/dehydrogenation catalyst is a cobalt-containing catalyst and the level of active metal in said catalyst is from 30 to 40% by weight. The process of Claim 11 wherein propanol is the C₂₋₄ alkanol and monopropylamine is the C₁₋₄ monoalkylamine. The process of Claim 11 wherein the C₂₋₄ alkanol is ethanol and the dialkylamine is diethylamine. The process of Claim 11 wherein the C₂₋₄ alkanol is ethanol and the monoalkylamine is monobutylamine. The process of Claim 11 wherein the catalyst used to form the reaction mixture comprising mono, di and trialkylamines is silica-alumina.

Inventors: COOPER, CAWAS ADARJI, FORESTER, JR., LEWIS SAMUEL,, FOWLKES, ROBERT LEE, HEFT, BRIAN KEITH
Applicants: AIR PRODUCTS AND CHEMICALS, INC.
Application year: 1990
Main classification: C07C211
IPC codes: C07B61, C07C211, C07C209, B01J23