Energy & Fuels 2002, 16, 177-181
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Production of Diethyl Carbonate from Ethanol and Carbon Monoxide over a Heterogeneous Catalyst Brian C. Dunn, Catherine Guenneau, Steven A. Hilton, Jorg Pahnke, and Edward M. Eyring* University of Utah, Department of Chemistry, Salt Lake City, Utah 84112
Jacek Dworzanski, Henk L. C. Meuzelaar, J. Z. Hu, Mark S. Solum, and Ronald J. Pugmire University of Utah, Department of Chemical and Fuels Engineering, Salt Lake City, Utah 84112 Received July 20, 2001. Revised Manuscript Received October 12, 2001
Diethyl carbonate (DEC) has been produced by the oxidative carbonylation of ethanol in the gas phase over a heterogeneous CuCl2/PdCl2 catalyst supported on activated carbon. Yields of DEC with this catalyst are approximately 10 wt % with the byproducts diethoxymethane, ethyl formate, and acetaldehyde also formed in significantly lower yields. Treatment of the catalyst immediately after preparation with potassium hydroxide enhances the production of DEC almost 2-fold without increasing the amount of byproducts formed. The reactions that form DEC and the byproducts occur in a parallel, rather than a sequential, manner indicating that it should be possible to identify a catalyst which is more selective for DEC.
Introduction The use of methyl tert-butyl ether (MTBE) as an oxygen-containing fuel additive in the United States has had a negative environmental impact.1 This effect, as well as the possibility of reducing emissions from diesel engines by adding oxygen to the fuel, has led to an increased interest in alternative oxygen-containing additives. While many candidates exist for replacing MTBE, all properties of these candidates, including toxicity and environmental impact, must be considered. One promising candidate is diethyl carbonate (DEC). It has more oxygen than MTBE (40.6% versus 18.2%), engine tests2,3 on similar compounds predict that DEC will reduce emissions from gasoline and diesel engines, gasoline/water distribution coefficients4 are more favorable for DEC than for dimethyl carbonate (DMC) and ethanol, and when released into the environment, DEC should slowly hydrolyze into carbon dioxide and ethanol,5 two reasonably benign products. Little data on its toxicity exist, but in light of DEC’s tendency to hydrolyze, the toxic effects have a reduced importance. * Corresponding author. Fax: 801-581-8433. E-mail: eyring@ chem.utah.edu. (1) Moran, M. J.; Zgorski, J. S.; Squillace, P. J. Water Resour. Conf., Proc. 1999, 91-112. (2) Murayama, T.; Zheng, M.; Chikahisa, T.; Oh, Y.-T.; Fujiwara, Y.; Tosaka. S.; Yamashita, M.; Yoshitake, H. Simultaneous Reductions of Smoke and NOx from a DI Diesel Engine with EGR and Dimethyl Carbonate; SAE Technical Paper 952518; Warrendale, PA, 1995. (3) Miyamoto N.; Ogawa, H.; Obata, K.; Cao, G.-H. JSAE Rev. 1998, 19, 154-156. (4) Pacheco, M. A.; Marshall, C. L. Energy Fuels 1997, 2-29. (5) Crandall, J. W.; Deitzler, J. E.; Kapicak, L. A.; Poppelsdorf, F. Process for the Hydrolysis of Dialkyl Carbonates. U.S. Patent 4,663,477, 1987.
Several routes exist for the possible production of DEC: (1) the phosgene method6 in which COCl2 is reacted with ethanol obviously involving dangerous phosgene gas; (2) the ethyl nitrite route7 in which ethanol is first converted into ethyl nitrite (CH3CH2ONO) and then into DEC via reaction with CO, but while this second scheme is promising it involves the use of two separate reactors with two separate reaction schemes; (3) the oxidative carbonylation of ethanol over a slurry of CuCl8 produces significant amounts of DEC, but only when an extreme excess of CO is employed; (4) the gas-phase oxidative carbonylation of ethanol9 using a heterogeneous supported CuCl2/PdCl2 catalyst. This fourth method produces DEC using stoichiometric amounts of carbon monoxide at reasonably low temperatures (
