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New Vapor Phase Process for Synthesis of Ethylenimine by Catalytic Intramolecular Dehydration of Monoethanolamine
Guni, L et ol. (Editors), New Frontiers in Cotolysis Proceedings of the 10th International Congress on Catalysis, 19-24 July, 1992,Budapest, Hungary 0 1993 Elsevier Science Publishers B.V. All rights reserved
NEW VAPOR PHASE PROCESS FOR SYNTHESIS OF ETHYLENIMINE BY CATALYTIC INTRAMOLECULAR DEHYDRATION OF MONOETHANOLAMJNE
M. Ueshima, Y.Shimasaki, K.Ariyoshi H. Yano and H. Tsuneki Nippon Shokubai Co.Ltd., Central Research Laboratory, 5-8 Nishi Otabicho, Suita, Osaka 564, Japan
.1.INTRODUCTION
Ethylenimine (EI) is an important fine chemical in chemical industry, which has been used as a raw material of pharmaceuticals and amino resins. EI generally has been produced from monoethanolamine (MEA) in the liquid phase by using H2S04 and NaOH, but this production process is not attractive from an industrial view-point because of the formation of a large quantity of by-product (Na2SO4) and hence, low productivity. On the other hand, some studies of MEA intramolecular dehydration to EI directly in the vapor phase over various acidic oxides such as SiO2-WO3 and NbsO5-based catalysts,as a new route to EI, were already reported. However, these catalysts did not show any high catalytic performance on selectivity and life, and hence, it was not successful to develop the vapor phase process for this reaction. Recently, Nippon Shokubai has been successful in developing new catalysts for the vapor phase EI production process from MEA and industrialized this process at the end of 1990. This process is more attractive and effective than the conventional liquid phase process. The developed catalysts were solid base oxides having the composition of Si-X,-Y,-0, (X=alkali metal cation, Y is selected within P,Nb,Al,Ti). A characteristic feature of present catalysts was that both acid and base strengths of them were adjusted to be very weak (+4.8
Catalysts were prepared as follows. Si02 (Aerosil OX-50) was kneeded together with aqueous solution of alkali metal hydroxide or nitrate (X element) at room temperature. To the resulting slurry-liked mixture, the oxide of Y elements (P,Nb,Al,Ti)or its salt was added with through stirring at room temperature. The mixture was evaporated and dried at 120'C for 12 hours, pulverized to size of 9 to 15 mesh and calcined at 500-700°C for 2 hours.
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5 ml of the catalyst was filled in a reaction tube (10 mm ID), and a reaction gas mixture of 5 vol% MEA in N2 was passed through the tube at 370-4OO'C with space velocity (SV)in the range of 1000-2500hr-1. The optimum reaction temperature and SV were changed depending on the kinds of catalysts, and the products were analyzed by gas chromatography. TPD experiments of NH3, CO2, and MEA adsorbed on SilXO.lPO.08O2.26 (X=Na,Cs)were carried out by using a quadrupole mass spectrometer with Ar gas as an internal standard. IR spectra of the catalyst after evacuation of adsorbed MEA was obtained by using a FT-IR spectrometer (Shimazu IR-7000).The acid and base strength of catalysts were measured by Hammett indicator method [ll. 3. RESULTS AND DISCUSSION
The catalytic behaviors of various single metal oxides and binary oxides consisting of acidic oxides and alkali metal cations in intramolecuar dehydration of MEA to EI were already reported [21. Acidic metal oxides such as Si02, Al2O3SiO2,TiOn,etc. showed low selectivity t o EI and deactivation in short time, the main reaction being the formation of intermolecular condensation products such as piperazine and its derivatives. Basic oxides such as CaO, MgO, and BaO did not have an ability of EI formation, the main products being acetaldehyde by elimination of NH3 from MEA. Combination catalysts of Si02 with alkali metal cation (Si-X,-O,, X=alkali metal cation) which showed the Ho values of +4.8 to +9.3 (weak acid-base strength) were effective for EI formation. Moreover, these catalysts were improved by addition of Y elements (Si-X,-Y,-0,, Y is selected within P,Nb,Al,Ti). The catalysts of which Ho value was adjusted to +4.8 to +9.3 by control of the amounts of X and Y showed high selectivity [Table 11.
Table 1 No Catalyst Atomic Ratio
Ho
Reaction Acid Base TemD.'C +18.4< 400 1 MgO 2 SiO2 +3.3< 370 3 Si-Cs-0 l10.112.05 +4.8< <+9.3 400 4 Si-Na-P-0 llO.110.0812.25 +4.0< <+8.3 370 (Si-Na-P-0 llO.ll0.0312.125 +6.3< <+9.3 370 5 Si-K-P-0 1/0.ll0.0512.175 +4.8< <+9.3 370 6 Si-Rb-P-0 llO.ll0.0812.25 +6.8< <+8.3 370 7 Si-Cs-P-0 llO.ll0.0812.25 +6.8< <+8.3 370 8 Si-Na-Al-0 llO.310.312.3 +4.8< <+9.3 400 1/0.02/QJ&21 +6.3< <+9.3 400 MEA conc. 5~01% balanced N2
SV MEA y h r v . % 1000 25.8 2500 11.6 1000 72.7 2500 85.1 2500 21.4 2500 51.1 70.7 2500 70.1 2500 37.6 1500 1500 39.4
b
EI &J/& 0 57.4 48.2 33.3 67.8) 70.1 76.4 78.7 60.3 78J
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These weak acid-base bifunctional catalysts provided extremely stable catalytic activity. The results of stability performance ‘in continuous flow reaction for 200 hours over Si02 (solid acid) and Si1Cs0.1Po.osO2.2~ (Table 1 No.”) were shown in Fig.1. Si02 was deactivated in a few hours by deposition of large amount of coke over the catalyst. However SilCso.lPo.o802.2~showed a stable catalytic performance for long term. I
t aon V
I
1
-1
MEA Conv.(SiO2) I
I
0
100 200 Time on Stream (hr) Fig.1. Catalytic performance in continuous flow reaction. Reaction Temp. 370’C. balanced N2 SV=25OOhr1.MEA conc. 5~01% 3.1. TPD study
TPD of N H s was carried out on Si&.lPo.o802.25 (X=Na and Cs).In the case of X=Cs (Table 1N0.7), which showed an excellent selectivity to EI, the adsorption of NHs was not observed. On the other hand, in X=Na (Table 1 No.41, which showed higher activity and lower selectivity, small amount of NHs adsorption was observed. This indicates acidity of former catalyst (XtCs) is extremely weak but that of the latter (X=Na)is moderate. In TPD of C02 experiments of both catalysts, the adsorption of C02 was not observed. This indicates basicity of both catalysts are extremely weak. These results suggest that the selective intramolecular dehydration of MEA is promoted by weak acid-base bifimctional effects. TPD of MEA was carried out on these same catalysts (Fig.2) . The catalyst (X=Cs)had only one desorption peak a t 360’C, however in another one (X=Na), two peaks were observed at 360’C and 520’C. It is considered the desorption peak at 360’C corresponds to very weak acid and base sites, and another one at 520’C corresponds to strong acid sites which cause low selectivity to EI. This supports above weak acid-base bifunctional effects. 3.2.
IR study
IR spectra at room temperature to 200’C of the catalyst (X=Cs) after evacuation of adsorbed MEA are shown in Fig.3. The characteristic absorption
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band of -NH3+, belonging to the intermediate of EI formation, appeared at 2350cm-1(doublet) at room temperature. On raising the temperature to 150°C, the intensities of the bands due to -OH and - N H 2 groups decreased, while those due to -NH3+ increased. However these absorption bands disappeared at 200'C with desorption of EI. The results of TPD and IR measurements of Si-X-P-0 system oxides support that MEA is preferentially adsorbed at the -OH group on the catalyst surface, and -OH is dissociated on acid and base sites simultaneously (-O---H+)and consecutive dehydration to form EI occurs through nucleophilic attack of nitrogen t o &carbon.
0
100200300400500600 Temp. 'c Fig2 TPD of MEA over Sil&.~Po.o802.25
R.'r.
--L 4000
3000 2000 cm-' Fig.3 IR spectra of adsorbed MEA Over SilCsO.lP0.0802.25
4. CONCLUSION The important factors of the catalyst in this intramolecular dehydration are concluded to be as follows. 1. Coexistence of very weak acid and base sites. 2. Optimum distance between acid and base sites for MEA molecule. The authors acknowledge Prof. Hideshi Hattori (Rokkaido University) for his support in experiment of TPD and IR measurement and fruitful discussion.
5. REFERENCES [l] K. Tanabe, Solid Acids and Bases, Kodansha, Tokyo, 6 (1970). [21 M. Ueshima, Y. Shimasaki, Y. Hino, H. Tsuneki. "Acid-BaseCatalysis", Kodansha, Tokyo, VCH, Basel, 41 (1988).
NEW VAPOR PHASE PROCESS FOR SYNTHESIS OF ETHYLENIMINE BY CATALYTIC INTRAMOLECULAR DEHYDRATION OF MONOETHANOLAMJNE
M. Ueshima, Y.Shimasaki, K.Ariyoshi H. Yano and H. Tsuneki Nippon Shokubai Co.Ltd., Central Research Laboratory, 5-8 Nishi Otabicho, Suita, Osaka 564, Japan
.1.INTRODUCTION
Ethylenimine (EI) is an important fine chemical in chemical industry, which has been used as a raw material of pharmaceuticals and amino resins. EI generally has been produced from monoethanolamine (MEA) in the liquid phase by using H2S04 and NaOH, but this production process is not attractive from an industrial view-point because of the formation of a large quantity of by-product (Na2SO4) and hence, low productivity. On the other hand, some studies of MEA intramolecular dehydration to EI directly in the vapor phase over various acidic oxides such as SiO2-WO3 and NbsO5-based catalysts,as a new route to EI, were already reported. However, these catalysts did not show any high catalytic performance on selectivity and life, and hence, it was not successful to develop the vapor phase process for this reaction. Recently, Nippon Shokubai has been successful in developing new catalysts for the vapor phase EI production process from MEA and industrialized this process at the end of 1990. This process is more attractive and effective than the conventional liquid phase process. The developed catalysts were solid base oxides having the composition of Si-X,-Y,-0, (X=alkali metal cation, Y is selected within P,Nb,Al,Ti). A characteristic feature of present catalysts was that both acid and base strengths of them were adjusted to be very weak (+4.8
Catalysts were prepared as follows. Si02 (Aerosil OX-50) was kneeded together with aqueous solution of alkali metal hydroxide or nitrate (X element) at room temperature. To the resulting slurry-liked mixture, the oxide of Y elements (P,Nb,Al,Ti)or its salt was added with through stirring at room temperature. The mixture was evaporated and dried at 120'C for 12 hours, pulverized to size of 9 to 15 mesh and calcined at 500-700°C for 2 hours.
2448
5 ml of the catalyst was filled in a reaction tube (10 mm ID), and a reaction gas mixture of 5 vol% MEA in N2 was passed through the tube at 370-4OO'C with space velocity (SV)in the range of 1000-2500hr-1. The optimum reaction temperature and SV were changed depending on the kinds of catalysts, and the products were analyzed by gas chromatography. TPD experiments of NH3, CO2, and MEA adsorbed on SilXO.lPO.08O2.26 (X=Na,Cs)were carried out by using a quadrupole mass spectrometer with Ar gas as an internal standard. IR spectra of the catalyst after evacuation of adsorbed MEA was obtained by using a FT-IR spectrometer (Shimazu IR-7000).The acid and base strength of catalysts were measured by Hammett indicator method [ll. 3. RESULTS AND DISCUSSION
The catalytic behaviors of various single metal oxides and binary oxides consisting of acidic oxides and alkali metal cations in intramolecuar dehydration of MEA to EI were already reported [21. Acidic metal oxides such as Si02, Al2O3SiO2,TiOn,etc. showed low selectivity t o EI and deactivation in short time, the main reaction being the formation of intermolecular condensation products such as piperazine and its derivatives. Basic oxides such as CaO, MgO, and BaO did not have an ability of EI formation, the main products being acetaldehyde by elimination of NH3 from MEA. Combination catalysts of Si02 with alkali metal cation (Si-X,-O,, X=alkali metal cation) which showed the Ho values of +4.8 to +9.3 (weak acid-base strength) were effective for EI formation. Moreover, these catalysts were improved by addition of Y elements (Si-X,-Y,-0,, Y is selected within P,Nb,Al,Ti). The catalysts of which Ho value was adjusted to +4.8 to +9.3 by control of the amounts of X and Y showed high selectivity [Table 11.
Table 1 No Catalyst Atomic Ratio
Ho
Reaction Acid Base TemD.'C +18.4< 400 1 MgO 2 SiO2 +3.3< 370 3 Si-Cs-0 l10.112.05 +4.8< <+9.3 400 4 Si-Na-P-0 llO.110.0812.25 +4.0< <+8.3 370 (Si-Na-P-0 llO.ll0.0312.125 +6.3< <+9.3 370 5 Si-K-P-0 1/0.ll0.0512.175 +4.8< <+9.3 370 6 Si-Rb-P-0 llO.ll0.0812.25 +6.8< <+8.3 370 7 Si-Cs-P-0 llO.ll0.0812.25 +6.8< <+8.3 370 8 Si-Na-Al-0 llO.310.312.3 +4.8< <+9.3 400 1/0.02/QJ&21 +6.3< <+9.3 400 MEA conc. 5~01% balanced N2
SV MEA y h r v . % 1000 25.8 2500 11.6 1000 72.7 2500 85.1 2500 21.4 2500 51.1 70.7 2500 70.1 2500 37.6 1500 1500 39.4
b
EI &J/& 0 57.4 48.2 33.3 67.8) 70.1 76.4 78.7 60.3 78J
2449
These weak acid-base bifunctional catalysts provided extremely stable catalytic activity. The results of stability performance ‘in continuous flow reaction for 200 hours over Si02 (solid acid) and Si1Cs0.1Po.osO2.2~ (Table 1 No.”) were shown in Fig.1. Si02 was deactivated in a few hours by deposition of large amount of coke over the catalyst. However SilCso.lPo.o802.2~showed a stable catalytic performance for long term. I
t aon V
I
1
-1
MEA Conv.(SiO2) I
I
0
100 200 Time on Stream (hr) Fig.1. Catalytic performance in continuous flow reaction. Reaction Temp. 370’C. balanced N2 SV=25OOhr1.MEA conc. 5~01% 3.1. TPD study
TPD of N H s was carried out on Si&.lPo.o802.25 (X=Na and Cs).In the case of X=Cs (Table 1N0.7), which showed an excellent selectivity to EI, the adsorption of NHs was not observed. On the other hand, in X=Na (Table 1 No.41, which showed higher activity and lower selectivity, small amount of NHs adsorption was observed. This indicates acidity of former catalyst (XtCs) is extremely weak but that of the latter (X=Na)is moderate. In TPD of C02 experiments of both catalysts, the adsorption of C02 was not observed. This indicates basicity of both catalysts are extremely weak. These results suggest that the selective intramolecular dehydration of MEA is promoted by weak acid-base bifimctional effects. TPD of MEA was carried out on these same catalysts (Fig.2) . The catalyst (X=Cs)had only one desorption peak a t 360’C, however in another one (X=Na), two peaks were observed at 360’C and 520’C. It is considered the desorption peak at 360’C corresponds to very weak acid and base sites, and another one at 520’C corresponds to strong acid sites which cause low selectivity to EI. This supports above weak acid-base bifunctional effects. 3.2.
IR study
IR spectra at room temperature to 200’C of the catalyst (X=Cs) after evacuation of adsorbed MEA are shown in Fig.3. The characteristic absorption
2450
band of -NH3+, belonging to the intermediate of EI formation, appeared at 2350cm-1(doublet) at room temperature. On raising the temperature to 150°C, the intensities of the bands due to -OH and - N H 2 groups decreased, while those due to -NH3+ increased. However these absorption bands disappeared at 200'C with desorption of EI. The results of TPD and IR measurements of Si-X-P-0 system oxides support that MEA is preferentially adsorbed at the -OH group on the catalyst surface, and -OH is dissociated on acid and base sites simultaneously (-O---H+)and consecutive dehydration to form EI occurs through nucleophilic attack of nitrogen t o &carbon.
0
100200300400500600 Temp. 'c Fig2 TPD of MEA over Sil&.~Po.o802.25
R.'r.
--L 4000
3000 2000 cm-' Fig.3 IR spectra of adsorbed MEA Over SilCsO.lP0.0802.25
4. CONCLUSION The important factors of the catalyst in this intramolecular dehydration are concluded to be as follows. 1. Coexistence of very weak acid and base sites. 2. Optimum distance between acid and base sites for MEA molecule. The authors acknowledge Prof. Hideshi Hattori (Rokkaido University) for his support in experiment of TPD and IR measurement and fruitful discussion.
5. REFERENCES [l] K. Tanabe, Solid Acids and Bases, Kodansha, Tokyo, 6 (1970). [21 M. Ueshima, Y. Shimasaki, Y. Hino, H. Tsuneki. "Acid-BaseCatalysis", Kodansha, Tokyo, VCH, Basel, 41 (1988).