Vapor pressure and normal boiling point predictions for pure methyl esters and biodiesel fuels W. Yuan * , A.C. Hansen, Q. Zhang Department of Agricultural and Biological Engineering, University of Illinois at Urbana-Champaign, 360 AESB 1304 W. Pennsylvania Avenue, Urbana, IL 61801, USA Received 17 February 2004; received in revised form 14 September 2004; accepted 10 January 2005 Available online 19 January 2005 Abstract Temperature dependent vapor pressures of the methyl esters of fourteen fatty acids that are commonly present in biodiesel fuels were predicted by the Antoine equation and a group contribution method. The predicted boiling points of these esters up to a pressure of 100 mmHg were within G1.0% of reported data for these two methods. Normal boiling points were determined from both the predicted vapor pressure and a correlation equation and the prediction errors were less than 5 K comparing to available published data. The vapor pressure and normal boiling points of 19 real-world biodiesel fuels were predicted and compared with reported data where available. The prediction errors of normal boiling points were less than 1.0%, and the predicted vapor pressures were also observed to closely match the reported data among the methyl esters of soybean oil, rapeseed oil and tallow. The predicted results showed that, except for coconut and butterfat, most of the methyl esters of the vegetable oils and animal fats had a normal boiling point in the range of 620–630 K. A sensitivity analysis indicated that the variation of fatty acid composition and the uncertainty of the normal boiling point of C18:2 were the main factors that affected the predicted normal boiling points of the biodiesel fuels. q 2005 Elsevier Ltd. All rights reserved. Keywords: Biodiesel; Methyl ester; Normal boiling point; Vapor pressure 1. Introduction Animal fat or vegetable oil ester biodiesel fuels have been shown to be a very promising alternative to crude-oil derived diesel fuels because they are renewable, they reduce particulate matter emissions and the net production of CO 2 from combustion sources, and they relieve US dependence on foreign crude oil. Because of these advantages, biodiesel has gained considerable attention and support in the past few years, as demonstrated by its commercial availability in many parts of the US and the provision of state tax incentives to encourage its use. The provision of standards and quality control in the manufacture and distribution of biodiesel is necessary to insure that the quality and properties of this fuel are reliable and consistent when supplied to users. Boiling point, T b , is a key fuel property for biodiesel as is the case for quality control in petroleum based diesel fuel industry. Besides its importance for quality control, boiling point, especially at atmospheric pressure, called normal boiling point T nb , is also the basis for the prediction of the critical properties, and temperature-dependent properties such as vapor pressure, density, latent heat of vaporization, viscosity, and surface tension of biodiesel. These properties are required for biodiesel combustion modeling [1], but the wide range of temperature required for these properties makes it difficult to experimentally measure them. There- fore, the accurate boiling points of the pure fatty acid esters and their biodiesel mixtures will be useful for predicting fuel properties and consequently will be important for combustion modeling. Several equations were reviewed by Reid et al. [2] to estimate or correlate the temperature dependent vapor pressure of pure liquids, of which the following three 0016-2361/$ - see front matter q 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.fuel.2005.01.007 Fuel 84 (2005) 943–950 www.fuelfirst.com * Corresponding author. Tel.: C1 217 333 8595; fax: C1 217 244 0323. E-mail address: wyuan@uiuc.edu (W. Yuan).