A New Process for Synthesis of Dimethyl Carbonate from Ethylene Carbonate and Methanol without any C

Chinese Chemical Letters Vol. 16, No.6, pp 767-770, 2005767http://www.imm.ac.cn/journal/ccl.htmlA New Process for Synthesis of Dimethyl Carbonate from EthyleneCarbonate and Methanol without any Catalyst underSupercritical ConditionsXiu Juan FENG, Xiao Gang LI, Ren HE*, Hui ZHOUState Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116012Abstract: Dimethyl carbonate was synthesized by transesterification reaction between ethylenecarbonate and methanol under supercritical conditions without any catalyst. Experimentalresults showed that the residence time and the molar ratio of methanol to ethylene carbonate allcan affect the conversion of ethylene carbonate. When the molar ratio of methanol to ethylenecarbonate was 8:1, 81.2 % conversion can be achieved at 9.0 MPa and 250C after 8 h.Keywords: Supercritial methanol, dimethyl carbonate, ethylene carbonate, transesterification.Dimethyl carbonate (DMC) has extensive applications as an environmentally benignsolvent, an octane booster in gasoline to meet oxygenate specifications and a precursorfor polycarbonate resins-. Also, it can be used as a substitute reagent of poisonousphosgene and dimethyl sulphate for carbonylation and methylation in organicsynthesis'4. DMC is mainly synthesized by oxidative carbonylation of methanol(non-phosgene route) or phosgenation of methanol (phosgene route). Both routesinvolve the use of poisonous or corrosive phosgene or carbon monoxide. DMC wasalso synthesized by transesterification reaction between ethylene carbonate andmethanol in the presence of a Lewis acid or base catalyst' "(Scheme 1). However, toour best knowledge, there is no report on the transesterification of ethylene carbonateand methanol for the synthesis of dimethyl carbonate in the absence of any catalystunder supercritical conditions. It is of great interest to study a practically possibleprocess without any catalyst.Scheme1H2C-0CH2OH2C- -CH2==0+2CHfOH二:二中国煤化工MHCNMHGE-mail: ho@ maildpt.ln.cn768Xiu Juan FENG et al.Recently, the use of supercritical fluids as substitute solvent has received muchattention because of their tunable solvent properties by variation of pressure andtemperaturel213.Furthermore, supercritical fluid may be a particularly advantageousreaction medium when it serves as both reactant and solvent. The improved rates forcatalytic hydrogenation of carbon dioxide to formic acid in supercritical conditionsprovided support for this approach'4. However, only limited reactions have beenexplored based on this ideal. Herein, we report an efficient synthesis of DMC fromsupercritical methanol/ethylene carbonate mixture without any catalyst. Supercriticalmethanol serves as both reactant and solvent.ExperimentalThe reactions were carried out in a 15 mL stainless steel autoclave reactor which hasinner diameter of 6 mm and length of 480 mm (Figure 1). In a typical procedure,methanol and ethylene carbonate mixture were put into the reactor. The reactorretained at a constant temperature and pressure. The effluent from the reactor wascooled and reduced to atmospheric pressure, then collected in a vessel. The conversionbased on ethylene carbonate was analyzed by gas chromatography method (Agilent6890，DB-FFAP30 mx0.25 mm， injection temp.=250°C， column temp.=200°C,detection temp.-=250"C, N2 flow rate =30 mL/min).Figure 1 Equipment used for the transesterification reaction(⑤)④-(671 [318中国煤化工CNM H G.(1) reactor, (2) oil bath, (3) electrical furnace, (4) te.JMH......._. pressure controlmonitor, (6) product exit valve, (7) condenser, (8) product collecting vessel.Synthesis of Dimethyl Carbonate769Results and DiscussionIn Table 1 shown, the transesterification reaction between ethylene carbonate andmethanol proceeded in a very fast rate and achieved 57.9 % conversion of ethylenecarbonate within 5 minutes. The residence time of the reactants in the reactor has apositive effect on the conversion of ethylene carbonate. The conversion of ethylenecarbonate increases with the enhancement of the residence time. For example, theresidence time increases from 5 minutes to 30 minutes, the conversion of ethylenecarbonate was enhanced from 57.9 % to 58.9 %.It is well-known that transesterification of ethylene carbonates with methanol is anequilibrium reaction. The enhancement of the ratio of methanol to ethylene carbonateis beneficial for this reaction. The result was illustrated in Figure 1.D. Kusdiana and S. Saka reported supercritical methanol as acid catalyst in thetransesterification of rapeseed oilo.It supported our hypothesis of an acidself-catalyzed in the transesterification reaction between methanol and ethylenecarbonate and we proposed a plausible mechanism in this transesterification reaction asfollows.Table1Effect of residence time on the conversion of ethy lene carbonateResidence time(min)48036040120503015105EC Conversion/ %81.276.4 .70.964.460.058.958.0 58.0 57.9Conditions: temperature, 250 C; pressure, 9.0 MPa; methanolethylene carbonate=8/ l(molar ratio)Figure 1 Effect of methano/EC (molar ratio) on the conversion of ethylene carbonate6055下o言4035 t30 F25Methano/EC中国煤化工Conditions: temperature, 250°C; pressul:TYHCNMHG770Xiu Juan FENG et al.Scheme 2CHzOHzocH,品甲H2c=o亡CHzO-C-O-CH2CH2OHCH2i.cH,0+ H+ cH,o-C-0-CH2CH,OH亡CH,O-C-0CH3 + HOCH2CH2OHIn conclusion, we found that DMC could be rapidly, successively synthesized fromsupercritical methanol/ethylene carbonate mixture in the absence of any catalyst. Inparticular, the reaction perfectly eliminates any problem probably caused by the use ofcatalysts, and completely conforms to“environmentally benign concept”.AcknowledgmentGratitude is expressed to the National Natural Science foundation of China (No. 20204002) andthe Natural Science Foundation of Liaoning Province (No.2003 1074) for financial support.References1. Y. Ono, Appl. Catal. A, 1997, 155, 133.M. A. Pacheco, C. L. Marshall, Energy Fuels, 1997, 11,2.S. Fujita, B. M. Bhanage, Y. Ikushima, M. Arai, Green Chem., 2001,3, 87.4. A. A. G. Shaikh, S. Sivaram, Am. Chem. Soc., Div. Fuel Chem, 1995, 40, 119.B. M. Bhanage, S. Fujita, Y. Ikushima, K. Tori, M. Arai, Green Chem., 2003, 5, 71.T. Wei, M. Wang, W. Wei, Y. Sun, B. Zhong, Green Chem., 2003, 5, 343. .7. J. F. Knifton, R. G. Duranleau, J. Mol. Catal, 1991, 67, 389.8. Y. Okada, T. Kondo, S. Asaoka, Prepr. Pap-Am. Chem. Soc. , Div. Fuel Chem, 1994, 39,359.9. Y. Watanabe, T. Tatsumi, Micropor. Mesopor. Mater., 1998, 22, 399.10. T. Tatsumi, Y. Watanabe, K. A. Koyano, Chem. Commun, 1996, 2281.B. M. Bhanage, S. Fujita, Y. Ikushima, M. Arai, Appl. Catal. A., 2001, 219, 259.12. C. A. Eckert, B. L. Kuntson, P. G. Debenedetti, Nature, 1996, 283, 313.13. J. M. Desimone, Z. Guan, C. S. Elbernd, Science, 1992, 257, 945.P. G. Jessop, T. Ikariya, R. Noyori, Nature, 1993, 363, 685.15. X. B. Lu, R. He, C. X. Bai, J. Mol. Catal. A: Chem, 2002, 186, 1.D. Kusdiana and S. Saka, Bioresour. Technol, 2004, 91, 289.Received 15 June, 2004中国煤化工MHCNMHG