Ind. Eng. Chem. Prod. Res. Dev. 1981, 20, 399-407
Acknowledgment The authors wish to thank Dr. Takako Takahashi for the measurements of the gas chromatograph-mass spectrometer. Literature Cited Allen, S. D. Proc. Soc. Photo-Opt. Instrum. Eng. 1980, 198. Ambartzumian, R. V.; Chekalin. N. V.; Letokhov, V. S.; Ryabov, E. A. Chem mys. Lett. 1 ~ 7 5 3, 6 , 301. Dean, A. M.; Kistiikowsky, G. B. J . Chem. Phys. 1970, 5 3 , 830. Draper, C. W. Metall. Trans. 1980, 11A. 349. Hummel, R. W. Discuss. Faraday Soc. 1983, 36, 7 5 . Isenor, N. R.; Richardson, M. C. Appl. Phys. Lett. 1971, 16, 224. Kevorkian, V.; Heath, C. E.; Boudart, M. J. Phys . Chem. 1960, 6q, 964.
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Lln, S. T.; Ronn, A. M. Chem. Phys. Lett. 1978, 5 6 , 414. Met”, B. H.; Mandel, R. J. Chem. phys. 1962, 3 7 , 207. Ralzer, Y. P. “Laser Induced Discharge Phenomena”, Consultants Bureau: New York, 1977. Ronn, A. M. Chem. Phys. Lett. 1978, 42, 202. Ronn, A. M.; Earl, B. L. Chem. Phys. Lett. 1977, 45, 556. Ronn, A. M. Scl. Am. 1979(5), 103. Tardieu de Malelssye, J.; Lempereur, F.; Marsal, C. “Laser In Chemistry”, West, M. A., Ed.; Elsevler Scientific Publishing Co.: New York, 1977, p 271. Taylor, H.; Van Hook, A. J. Phys. Chem. 1935, 39, 811. Yeddanapalll, L. M. J . Chem. Phys. 1942, IO, 249.
Received for review September 29, 1980 Accepted March 11, 1981
Ethylenediamine by Low-Pressure Ammonolysis of Monoethanolamine Charles M. Barnes and Howard F. Rase’ Department of Chemical Engineerlng, The University of Texas, Austin, Texas 78712
A catalytic route to ethylenediamine (EDA) via monoethanoiamine (MEA) and supported nickel catalysts has been studied in detail. A mixed SiOp and A1203 support was found to be preferable to Si02 alone. The effects of
temperature, ammonia and hydrogen pressures, water concentration, and catalyst size were studied. Powdered catalyst was found to give improved EDA yields, as did operation with recycled piperazine. Water was shown to be advantageous in improving EDA selectivity, as was H2 up to an optimum partial pressure. Low water concentrations would not only be economical but were also found to produce less piperazine. Experiments with pure side reaction products enabled establishing major reaction paths for this complex system.
Ethylenediamine, an important chemical intermediate, is primarily produced from ethylene chloride (EDC) by a noncatalytic reaction with ammonia. ClCH2CH2Cl+ 2NH3 NH2CH2CH2NH2.2HC1 (1) ClCH2CHzCl+ NH2CH2CH2NH2.2HC1+ 2NH3 NH4CI + NH&H2CH2NHCH2CH2NH2*3HCl (2) ClCH2CHzCl + NH3 ClCHxCH2 + NHdCl (3) The resulting HC1 salts with ethylenediamine (EDA), diethylenetriamine (DETA), and triethylenetetramine (TETA), are reacted with NaOH to free the amines in an aqueous phase. Byproduct gases such as vinyl chloride are separated. An aqueous slurry of unreacted NaOH, product NaC1, and residual amines is evaporated to concentrate the caustic and remove the NaC1. The caustic can be recycled, but the NaCl cannot be used for electrolysis because of its residual amine content, and disposal of this NaCl can be a problem. A typical product composition may be 40% EDA, 30% H20, 15% DETA, and 10% TETA and higher ethyleneamines as well as 5% piperazine (PP) and aminoethylpiperazine (AEP). Because of the waste disposal problem and the corrosive HC1 environment, there is much merit in possible nonchloride routes. Recently, a catalytic nonchloride process was introduced in the U.S.A. using ethylene glycol as a raw material (Chem.Eng., 1980). Monoethanolamine (MEA) has also been used as a starting material for a nonchloride route catalyzed by hydrogenation catalysts (see Table 11). The apparently simple reaction of NH3 and MEA to yield EDA is deceptive, for several catalytic steps are involved, and a number of side reactions occur. More complete understanding of this reaction system and the op-
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erating variables and catalytic characteristics affecting yield could lead to improved processes that might supplant the traditional chloride process with its several disadvantages. The present study places particular attention on catalyst characteristics and operating conditions for aminating MEA by ammonolysis, and an attempt is made to strengthen the conceptual framework as well as contribute useful empirical observations for an energy-efficient lowpressure process. Background A plausible mechanism for EDA formation from MEA can be deduced from detailed studies on ammonolysis of various alcohols.
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NH2CH2CH2-OH
2 NHzCHzC,
-
4” fNH3 H
NH2CH2CH=NH
OH
I
NH2CH2-C-NHp
- H20
I
k 5 N H z C H ~ C H ~ N H( 4~ )
Ethanol and butanol are known to give their corresponding aldehyde and primary, secondary, and tertiary amines when reacted with ammonia (Pasek et al., 1972). In testing hydrogenation catalysts in the ammonolysis of dodecanol, Baiker and Richarz (1977) isolated the intermediate aldehyde. Langden et al. (1962) presumed the intermediate aminoacetone to explain the synthesis of 2,5-dimethylpiperazine from isopropylamine. Aston et al. (1934) theorized that aminoacetaldehyde is the first step in the synthesis of pyrazine from MEA and deduced that nonisolation was due to further reaction of the aldehyde to resinous products. The most direct evidence is from work 0 1981 American Chemlcal Society
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Ind. Eng. Chem. Prod. Res.
Dev., Vol. 20, No. 2,
1981
-MEA
CH3CHO t--C H ~ C H = N C H Z C H ~ O H +H 2O
HOCH2CH2NHCH2CH20H
4
H°CH CH
CHzCHzOH (CH2CH20H
-NH
HOCH2CH2NHCH2CH2NHCH2CH20H
-H 2O
CH2CH2NH2 :(CH2
I
P
CH2 NH 2
./.-NH,
1 .1-
+MEA -NH3
--
Note Any step adding MEA and eliminating H20 can also be accomplished by adding EDA and eliminating NH3. Figure 1. Sequence of possible reactions in MEA ammonolysis.
done by Bashkirov et al. (19711, who investigated the amination of ethanol with isotopic labeling. Using iron catalysts shown to be active for dehydrogenation of alcohols and aldehydes, they compared conversions of unlabeled ethanol with a-and P-deuterated ethanol, and their data support the dehydrogenation step as opposed to a direct dehydration of the alcohol with ammonia. Details on the role of the components of the catalyst are sparse. Baiker and Richam (19771, using several long-chain alcohols over copper catalysts, showed that dehydrogenation and hydrogenation take place on Cu centers. Catalysts of Cu or Ni were found to be more active than other metals. Karpeiskaya and Gorshkov (1970) concluded that the carrier plays an important role in the dehydration step and proposed a mechanism for Co-catalyzed ammonolysis of MEA. Based on thermodynamic data in the literature or estimates using group contributions, an array of possible overall reactions can be deduced as shown in Figure 1. Table I provides a key to the chemical formulae and abbreviations used in the text. Most of the reported work on MEA ammonolysis is recorded in the patent literature. Table I1 summarizes this literature with emphasis on product distribution and operating conditions. While the results are not strictly comparable because of differences in reactor type, hydrogen partial pressure, and other factors, some general
observations can be made about reaction conditions. The temperature range is 160 to 240 "C, and there seems to be no correlation with EDA selectivity. The pressure is generally 100 to 300 atm, and it also appears to have no relation to conversion or selectivity. Conversion is rarely complete and is reported to be less than 50% as often as greater than 50%. EDA selectivity is generally higher with higher ratios of NH3:MEA,which range from 1:l to 15:l. Higher conversions often correspond to lower EDA selectivities. Clearly, the most effective catalysts thus far studied contain nickel, and emphasis in this research was placed on two commercially available nickel catalysts that differed primarily in the nature of the supports. Although the patent literature reports reactor pressures in the 100-300 atm range, an effort was made to find conditions for satisfactory yields at pressures below 100 atm in order to favor catalysts and operating conditions with potentially lower energy consumption. Experimental Procedures Reactor and Test Procedure. A 300-cm3Autoclave Engineers, Inc. autoclave equipped with furnace and magnetically driven turbine was used for all reactions. Technical grade MEA, the catalyst, and water-if usedwere loaded into the open reaction chamber. One hundred milliliters of liquid and generally 5 g of catalyst were used.
Ind. Eng. Chem. Prod. Res. Dev., Vol. 20, No. 2, 1981 401
Table I. Abbreviations, Names, and Formulas of MEA-Derived Amines MEA = monoethanolamine EDA = ethylenediamine DETA = diethylenetriamine HEEDA = hydroxyethylethylenediamine
PP = piperazine
HOCH,CH,NH, NH,CH,CH,NH, NH,CH,CH,NHCH,CH,NH, HOCB,CH,NHCH,CH,NH, CH,CH, HN< >NH CH.CH. CH,CH, HOCH,CH,N< >NH CH,CH, CH.CH, NH,CH,CH,N< ' '>NH CH,CH, NH,CH,CH,NHCH,CH,NHCH~CH,NH, .
HEP = hydroxyethylpiperazine AEP = aminoethylpiperazine TETA = triethylenetetramine
a
TEDA = triethylenediamine
,CH,CH,\ NCH,CH,N \ I CH,CH,
TAEA = trisaminoethylamine
NH,CH,CH,N
NH CH,CH, the amount of that used for the Ni/A120/Si02 in order to obtain comparable conversions. Although possible differences in dispersion of nickel between the two catalysts couId account for some of the differences observed, evidence by others strongly suggests that A1203may play an important role. As suggested by Karpeiskaya and Gorshkova (1970),the catalytic dehydration characteristics of A1203are apparently important in the reaction sequence that forms EDA. Although the reaction will proceed without A1203in the support, the yield and activity are improved when it is present. The undesired side reaction products, PP and AEP, are formed by dehydration or deammonation, for which either A1203is not required or is not involved in catalyzing the slow steps. Because of the demonstrated superiority of the alumina-based catalyst, it was used in the more detailed studies described in the following sections. Preliminary Survey of Variables. The Ni/A1203/ Si02was subjected to a survey of variables using the batch reactor. Total conversion of 4 to 8% MEA per hour was found to occur at 150 "C and a catalyst ratio of 1:20. A ratio of 1:lO gave complete conversion in less than 10 h, and this ratio was used for most runs. Water was added to the reaction mixture as a means for avoiding higher pressures and minimizing the reaction of MEA with itself. It acted as a solvent for NH3 thus increasing the NH3concentration in the liquid phase. A 50% H20, 50% MEA solution was found to give a dramatic improvement in selectivity to EDA at an initial NH3 pressure of 2.4 atm. Effect of Water. Because of the beneficial effect of water on EDA yield, testa were made with differing initial water compositions. Figure 2 illustrates the result of changing water concentration at contant initial NH, and H2 partial pressures. The yield of EDA increases with a decrease in water concentration except at higher contact times and low water concentrations where ammonia concentration in the batch reactor ultimately declines to the point that EDA is consumed by side reactions. This problem can be overcome by adding additional NH3 as the reaction progresses. Quite logically,the rate of EDA production declines with dilution by water, but, as shown in Table V, EDA selec-
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