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Oxidative dimerization of dimethyl ether with solid catalysts
Catalysis, 53 (1989) L5-L9 Elsevier Science Publishers B.V., Amsterdam -
Applied
Printed in The Netherlands
Oxidative Dimerization of Dimethyl Ether with Solid Catalysts HIROSHI YAGITA*, KENJI ASAMI, ATSUSHI MURAMATSU and KAORU FUJIMOTO Department Bunkyo-ky
of Synthetic Chemistry, Tokyo 113 (Japan)
Faculty of Engineering,
The University
of Tokyo, Hongo,
(Received 27 February 1989)
ABSTRACT It was found that the oxidative coupling of dimethyl ether (DME) to dimethoxyethane was catalyzed by SnO,/MgO catalyst at around 200°C and 16 atm. The formation of 1,2-dimethoxyethane was favored for lower reaction temperatures, intermediate operating pressures and higher DME/O? ratios. The reaction mechanism for the supported tin catalyst system was assumed to be based on a redox cycle.
INTRODUCTION
Several attempts have been made to make ethylene glycol by dimerizing methanol. One method proposed is to dimerize methanol directly, either by yray irradiation [l] or by utilizing a rhodium complex and ultra violet irradiation [ 21. By these techniques, methanol is initially converted to a hydroxymethylene radical via C-H bond dissociation followed by coupling to form ethylene glycol. However, the methods have the disadvantage that the selectivity for the desired product is low because of the higher reactivity of the O-H bond. Another method proposed is first to protect the hydroxy group of methanol with a tri-alkyl silanol, dimerize it with an organic peroxide and then recover the silanol and ethylene glycol by hydrolysis [ 31. The oxidative dimerization of organic molecules which have been reported so far are: toluene to diphenyl ethane or stilbene (Sn-Bi mixed oxide catalyst) [ 41, propylene to 1,5-hexadiene (Bi-containing catalyst) [ 561 and methane to ethane and ethylene (catalyzed [ 7-101 and non catalyzed system [ 111). In these cases a hydrogen atom is abstracted from the substrate by either oxide ions, gaseous oxygen or adsorbed oxygen to form free radicals which couple to form dimerized products. The present study utilizes methanol as its own protectant, which means that two molecules of methanol are converted to one dimethyl ether (DME) mol-
L6
eeule and then the DME is oxidatively dimerized to dimethoxyethane. The dimethoxyethane (DMET) is expected to be hydrolyzed to ethylene glycol with a proper acidic catalyst. EXPERIMENTAL
Catalysts were prepared by impregnating commercially available MgO (Kanto, specific surface area, 4.6 m”/g) and a silica gel (Fuji-Davision ID gel, specific surface area, 140 m2/g) with aqueous solutions of metal nitrates, followed by calcining at 450°C. X-ray diffraction (XRD) showed that the supported tin oxide was present as SnOz. Reactions were conducted with a mixed gas composed of only DARE and oxygen and by using a pressurized fixed bed flow-type reaction apparatus. Products were analyzed by gas chromatography. RESULTS AND DISCUSSION
Products were DMET, methanol, formaldehyde, dimetoxymethane (DMM) , hydrocarbons and carbon oxides. The results are shown in Tables 1 and 2. The non-catalyzed reaction, which proceeded at temperatures above 46O”C, gave no dimerized product but methane and CO as the main products even under pressurized conditions. A free MgO catalyst or a PbO/~~ catalyst, which have been known to be highly active for the oxidative coupling of methC,,
TABLE 1 Oxidation of dimethyl ether on supported catalysts GataIyst
non
Loading (wt.-%) Temp. (“C) 510 Press. (atm) 1 W/F (g*h/mol) 0 DME/O, (mol ratio) 6.0 DME conv. (%) 22.1 0, conv. (%} 100 Selectivity (carbon-%) DMET 0 MeOII 2.0 CB, 38.4 c, + G:s 0 DMM 0 co 51.4 co, 8.2
PbOfMgO
Pd/SiO,
Pd/AlzOnn Bi~O~/~gO
A.G.
20 230 16 3.8 5.0 9.9 82.4
4 240 6 3.2 5.8 32.2 100
1 200 16 3.1 5.8 5.0 35.5
5 230 16 3.8 5.0 9.2 72.6
5 280 200 6 16 3.8 3.2 58 5.0 1.3 10.8 82.4 78.1
1.1 3.8 22.6 1.3 13.9 40.1 17.0
0 0 50.1 tr. 0 16.4 33.5
0 30.9 47.5 tr. 0 13.2 0
1.2 4.5 12.8 1.0 13.3 27.7 39.5
“Modified with NaBr, Na/Pd: l/l atom ratio. “t.r.= traces.
0
tr.6 0 0 0 32.0 66.7
SnO,/MgO
34.5 3.5 9.6 0.8 13.5 23.2 14.8
5 250 6 2.9 6.0 24.2 75.6
0 6.8 0 0 0 0 93.2
Loading (wt.-%) Tempt. (“C) Press. (atm ) W/F (g-h/mol) DME/O, (mol ratio) DME con”. (%) O? cony. (W )
Selectivity (carbon-%) DMET MeOH CH, c,+c:, DMM co co.,
0 6.8 0 0 0 46.7 41.7
20 250 11 3.2 5.4 0.6 8.0
SnOl/TiOP
“Modified with NaOH, Na/Sn: l/5 atom ratio. “Modified with NaBr, Na/Sn: l/5 atom ratio.
Sn0,/Si02
Catalyst
1.7 0 0 0 26.6 70.9 0.8
20 250 16 3.2 5.4 0.4 6.1
SnOJCaO
Oxidation of dimethyl ether with supported tin oxide catalysts
TABLE 2
34.5 3.5 9.6 0.8 13.5 23.2 14.8
5 200 16 3.8 5.0 10.8 78.1
SnO,/MgO
26.9 68.5 0.9 1.2 2.3 0.2 0.2
5 200 16 3.8 5.0 0.3 2.1
SnO,/MgO”
0 57.5 2.4 2.9 35.2 0 2.1
5 200 16 1.9 5.0 0.1 0.3
SnOJMgO”
59.9 31.4 0.1 0.1 3.1 0 5.1
20 200 16 1.9 5.0 1.1 3.4
SnO,/MgO
2.7 0.6 10.3 0.9 20.2 30.8 34.4
20 220 31 1.6 7.0 7.9 73.1
SnO,/MgO
2.3 0.9 10.1 0.9 21.5 32.0 32.4
20 250 31 1.6 7.0 8.5 79.3
SnOJMgO
63.5 25.3 1.4 0.1 1.2 0 8.0
20 200 16 1.6 7.0 0.7 3.6
SnWMgO
L8
ane [9,12] and a Bi 203 catalyst showed little catalytic activity for dimethyl ether dimerization but was active for the complete oxidation. A Pd/Si0 2 catalyst, which is an active oxidation catalyst, converted DME to CH 4 , CO and CO 2, A Pd-Br/ Al20 3 catalyst, which was an excellent catalyst for the oxidative dehydrogenation of hydrocarbons, gave no dimerized product and produced CH 4 , CH 30H, CO and HCHO. Only a Sn02/MgO catalyst produced 1,2-dimethoxyethane with high selectivity. Table 2 shows the catalytic performances of a variety of supported Sn03 catalysts. A Sn02/MgO catalyst showed excellent catalytic activities for the oxidative dimerization of DME, while MgO alone exhibited no activity and Sn02 catalysts supported on other carrier materials such as Si0 2, CaO, Ti0 2 showed little or no activities for the reaction. A 5 wt.-% Sn02/MgO catalyst showed a higher activity, a 20 wt.-% Sn02/MgO showed higher selectivity; this catalyst gave methanol as the main by-product. Since methanol is a hydrolyzed product from DME and it is also a precursor of DME, the real by-products are CO, CO 2 and hydrocarbons. Thus the actual selectivity to the disired product is 88%. The added alkali, which has been known to be effective for the oxidative dimerization of propylene [5] or methane [8], was effective in suppressing the hydrolysis of DME to some extent, but promoted the formation of carbon dioxide. The reaction mechanism and the reason why the Sn02/MgO catalyst is effective for this reaction is not yet clear. However, the redox mechanism which has been postulated for the PbO catalyzed dimerization of methane [13] would most probably be Sn02 + 2
CH30CH3~ Sn02_x + CH30-CH2CH2-OCH3+ H 20
Sn02_x+x/2
02~Sn02
(1)
(2 )
The excellent support effect of MgO should be attributed to its basisity.
REFERENCES 1 B.Ya. Ldygin, Kinet. CataI., 18 (1965) 189. 2 H. Arakawa, Y. Sugi, K Takeuchi, K Bando and Y. Takami, Shokubai, 25 (1983) 392. 3 K Schwetlich, W. Geyer and H. Hartman, Angew. Chern., 72 (1960) 779. 4 KH. Liu and Y. Yamazaki, Bull. Jpn. Petrol. lnst., 18 (1976) 45. 5 T. Sakamoto, M. Egashira and T. Seiyama, J. Catal., 16 (1970) 407. 6 M.G. White and J.W. Hightower, J. Catal., 82 (1983) 185. 7 G.E. Keller and M.M. Bashin, J. Catal., 73 (182) 9. 8 W. Hinsen, W. Bytyn and M. Boerns, in Proceedings 8th Congress on Catalysis, Vol. 3, Verlag Chemie, Weinheim, 1984, p. 581. 9 T. Ito, .r.x. Wang, C.H. Lin and J.H. Lunsford, J. Am. Chern. Soc., 107 (1985) 5062. 10 K Otsuka, K Jinno and A. Morikawa, J. Catal., 100 (1986) 353.
L9 11 12 13
K. Asami, K. Omata, K. Fujimoto and H. Tominaga, J. Chem. Sot., Chem. Commun., (1987) 1287. K. Asami, S. Hashimoto, T. Shikada, K. Fujimoto and H. Tominaga, Ind. Eng. Chem. Res., 26 (1987) 1485. K. Asami, S. Hashimoto, T. Shikada, K. Fujimoto and H. Tominaga, Ind. Eng. Chem., 26 (1987) 2348.
Applied
Printed in The Netherlands
Oxidative Dimerization of Dimethyl Ether with Solid Catalysts HIROSHI YAGITA*, KENJI ASAMI, ATSUSHI MURAMATSU and KAORU FUJIMOTO Department Bunkyo-ky
of Synthetic Chemistry, Tokyo 113 (Japan)
Faculty of Engineering,
The University
of Tokyo, Hongo,
(Received 27 February 1989)
ABSTRACT It was found that the oxidative coupling of dimethyl ether (DME) to dimethoxyethane was catalyzed by SnO,/MgO catalyst at around 200°C and 16 atm. The formation of 1,2-dimethoxyethane was favored for lower reaction temperatures, intermediate operating pressures and higher DME/O? ratios. The reaction mechanism for the supported tin catalyst system was assumed to be based on a redox cycle.
INTRODUCTION
Several attempts have been made to make ethylene glycol by dimerizing methanol. One method proposed is to dimerize methanol directly, either by yray irradiation [l] or by utilizing a rhodium complex and ultra violet irradiation [ 21. By these techniques, methanol is initially converted to a hydroxymethylene radical via C-H bond dissociation followed by coupling to form ethylene glycol. However, the methods have the disadvantage that the selectivity for the desired product is low because of the higher reactivity of the O-H bond. Another method proposed is first to protect the hydroxy group of methanol with a tri-alkyl silanol, dimerize it with an organic peroxide and then recover the silanol and ethylene glycol by hydrolysis [ 31. The oxidative dimerization of organic molecules which have been reported so far are: toluene to diphenyl ethane or stilbene (Sn-Bi mixed oxide catalyst) [ 41, propylene to 1,5-hexadiene (Bi-containing catalyst) [ 561 and methane to ethane and ethylene (catalyzed [ 7-101 and non catalyzed system [ 111). In these cases a hydrogen atom is abstracted from the substrate by either oxide ions, gaseous oxygen or adsorbed oxygen to form free radicals which couple to form dimerized products. The present study utilizes methanol as its own protectant, which means that two molecules of methanol are converted to one dimethyl ether (DME) mol-
L6
eeule and then the DME is oxidatively dimerized to dimethoxyethane. The dimethoxyethane (DMET) is expected to be hydrolyzed to ethylene glycol with a proper acidic catalyst. EXPERIMENTAL
Catalysts were prepared by impregnating commercially available MgO (Kanto, specific surface area, 4.6 m”/g) and a silica gel (Fuji-Davision ID gel, specific surface area, 140 m2/g) with aqueous solutions of metal nitrates, followed by calcining at 450°C. X-ray diffraction (XRD) showed that the supported tin oxide was present as SnOz. Reactions were conducted with a mixed gas composed of only DARE and oxygen and by using a pressurized fixed bed flow-type reaction apparatus. Products were analyzed by gas chromatography. RESULTS AND DISCUSSION
Products were DMET, methanol, formaldehyde, dimetoxymethane (DMM) , hydrocarbons and carbon oxides. The results are shown in Tables 1 and 2. The non-catalyzed reaction, which proceeded at temperatures above 46O”C, gave no dimerized product but methane and CO as the main products even under pressurized conditions. A free MgO catalyst or a PbO/~~ catalyst, which have been known to be highly active for the oxidative coupling of methC,,
TABLE 1 Oxidation of dimethyl ether on supported catalysts GataIyst
non
Loading (wt.-%) Temp. (“C) 510 Press. (atm) 1 W/F (g*h/mol) 0 DME/O, (mol ratio) 6.0 DME conv. (%) 22.1 0, conv. (%} 100 Selectivity (carbon-%) DMET 0 MeOII 2.0 CB, 38.4 c, + G:s 0 DMM 0 co 51.4 co, 8.2
PbOfMgO
Pd/SiO,
Pd/AlzOnn Bi~O~/~gO
A.G.
20 230 16 3.8 5.0 9.9 82.4
4 240 6 3.2 5.8 32.2 100
1 200 16 3.1 5.8 5.0 35.5
5 230 16 3.8 5.0 9.2 72.6
5 280 200 6 16 3.8 3.2 58 5.0 1.3 10.8 82.4 78.1
1.1 3.8 22.6 1.3 13.9 40.1 17.0
0 0 50.1 tr. 0 16.4 33.5
0 30.9 47.5 tr. 0 13.2 0
1.2 4.5 12.8 1.0 13.3 27.7 39.5
“Modified with NaBr, Na/Pd: l/l atom ratio. “t.r.= traces.
0
tr.6 0 0 0 32.0 66.7
SnO,/MgO
34.5 3.5 9.6 0.8 13.5 23.2 14.8
5 250 6 2.9 6.0 24.2 75.6
0 6.8 0 0 0 0 93.2
Loading (wt.-%) Tempt. (“C) Press. (atm ) W/F (g-h/mol) DME/O, (mol ratio) DME con”. (%) O? cony. (W )
Selectivity (carbon-%) DMET MeOH CH, c,+c:, DMM co co.,
0 6.8 0 0 0 46.7 41.7
20 250 11 3.2 5.4 0.6 8.0
SnOl/TiOP
“Modified with NaOH, Na/Sn: l/5 atom ratio. “Modified with NaBr, Na/Sn: l/5 atom ratio.
Sn0,/Si02
Catalyst
1.7 0 0 0 26.6 70.9 0.8
20 250 16 3.2 5.4 0.4 6.1
SnOJCaO
Oxidation of dimethyl ether with supported tin oxide catalysts
TABLE 2
34.5 3.5 9.6 0.8 13.5 23.2 14.8
5 200 16 3.8 5.0 10.8 78.1
SnO,/MgO
26.9 68.5 0.9 1.2 2.3 0.2 0.2
5 200 16 3.8 5.0 0.3 2.1
SnO,/MgO”
0 57.5 2.4 2.9 35.2 0 2.1
5 200 16 1.9 5.0 0.1 0.3
SnOJMgO”
59.9 31.4 0.1 0.1 3.1 0 5.1
20 200 16 1.9 5.0 1.1 3.4
SnO,/MgO
2.7 0.6 10.3 0.9 20.2 30.8 34.4
20 220 31 1.6 7.0 7.9 73.1
SnO,/MgO
2.3 0.9 10.1 0.9 21.5 32.0 32.4
20 250 31 1.6 7.0 8.5 79.3
SnOJMgO
63.5 25.3 1.4 0.1 1.2 0 8.0
20 200 16 1.6 7.0 0.7 3.6
SnWMgO
L8
ane [9,12] and a Bi 203 catalyst showed little catalytic activity for dimethyl ether dimerization but was active for the complete oxidation. A Pd/Si0 2 catalyst, which is an active oxidation catalyst, converted DME to CH 4 , CO and CO 2, A Pd-Br/ Al20 3 catalyst, which was an excellent catalyst for the oxidative dehydrogenation of hydrocarbons, gave no dimerized product and produced CH 4 , CH 30H, CO and HCHO. Only a Sn02/MgO catalyst produced 1,2-dimethoxyethane with high selectivity. Table 2 shows the catalytic performances of a variety of supported Sn03 catalysts. A Sn02/MgO catalyst showed excellent catalytic activities for the oxidative dimerization of DME, while MgO alone exhibited no activity and Sn02 catalysts supported on other carrier materials such as Si0 2, CaO, Ti0 2 showed little or no activities for the reaction. A 5 wt.-% Sn02/MgO catalyst showed a higher activity, a 20 wt.-% Sn02/MgO showed higher selectivity; this catalyst gave methanol as the main by-product. Since methanol is a hydrolyzed product from DME and it is also a precursor of DME, the real by-products are CO, CO 2 and hydrocarbons. Thus the actual selectivity to the disired product is 88%. The added alkali, which has been known to be effective for the oxidative dimerization of propylene [5] or methane [8], was effective in suppressing the hydrolysis of DME to some extent, but promoted the formation of carbon dioxide. The reaction mechanism and the reason why the Sn02/MgO catalyst is effective for this reaction is not yet clear. However, the redox mechanism which has been postulated for the PbO catalyzed dimerization of methane [13] would most probably be Sn02 + 2
CH30CH3~ Sn02_x + CH30-CH2CH2-OCH3+ H 20
Sn02_x+x/2
02~Sn02
(1)
(2 )
The excellent support effect of MgO should be attributed to its basisity.
REFERENCES 1 B.Ya. Ldygin, Kinet. CataI., 18 (1965) 189. 2 H. Arakawa, Y. Sugi, K Takeuchi, K Bando and Y. Takami, Shokubai, 25 (1983) 392. 3 K Schwetlich, W. Geyer and H. Hartman, Angew. Chern., 72 (1960) 779. 4 KH. Liu and Y. Yamazaki, Bull. Jpn. Petrol. lnst., 18 (1976) 45. 5 T. Sakamoto, M. Egashira and T. Seiyama, J. Catal., 16 (1970) 407. 6 M.G. White and J.W. Hightower, J. Catal., 82 (1983) 185. 7 G.E. Keller and M.M. Bashin, J. Catal., 73 (182) 9. 8 W. Hinsen, W. Bytyn and M. Boerns, in Proceedings 8th Congress on Catalysis, Vol. 3, Verlag Chemie, Weinheim, 1984, p. 581. 9 T. Ito, .r.x. Wang, C.H. Lin and J.H. Lunsford, J. Am. Chern. Soc., 107 (1985) 5062. 10 K Otsuka, K Jinno and A. Morikawa, J. Catal., 100 (1986) 353.
L9 11 12 13
K. Asami, K. Omata, K. Fujimoto and H. Tominaga, J. Chem. Sot., Chem. Commun., (1987) 1287. K. Asami, S. Hashimoto, T. Shikada, K. Fujimoto and H. Tominaga, Ind. Eng. Chem. Res., 26 (1987) 1485. K. Asami, S. Hashimoto, T. Shikada, K. Fujimoto and H. Tominaga, Ind. Eng. Chem., 26 (1987) 2348.