Complementary vapor pressure data for 2-methyl-1-propanol and 3-methyl-1-butanol at a pressure range of (15 to 177) kPa Arturo Bejarano, Nathalie Quezada, Juan C. de la Fuente * Departamento de Ingeniería Química y Ambiental, Universidad Técnica Federico Santa María, Avda. España 1680, Valparaíso, Chile article info Article history: Received 31 December 2008 Received in revised form 4 April 2009 Accepted 16 April 2009 Available online 23 April 2009 Keyword: Dynamic recirculation method 3-Methyl-1-butanol 2-Methyl-1-propanol Vapor pressure abstract The vapor pressure of pure 2-methyl-1-propanol and 3-methyl-1-butanol, components called congeners that are present in aroma of wine, pisco, and other alcoholic beverages, were measured with a dynamic recirculation apparatus at a pressure range of (15 to 177) kPa with an estimated uncertainty <0.2%. The measurements were performed at temperature ranges of (337 to 392) K for 2-methyl-1-propanol and (358 to 422) K for 3-methyl-1-butanol. Data were correlated using a Wagner-type equation with stan- dard deviations of 0.09 kPa for the vapor pressure of 2-methyl-1-propanol and 0.21 kPa for 3-methyl- 1-butanol. The experimental data and correlation were compared with data selected from the literature. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Congeners are polar compounds (different from ethanol and water) that are present in very low concentrations (10 6 to 10 4 ) mg/dm 3 in mixtures obtained from alcoholic distillation, such as the chilean spirit called pisco [1]. Congeners are important constituents of aroma and their concentration is a significant enol- ogy parameter [2]. According to chilean legislation, 2-methyl-1- propanol and 3-methyl-1-butanol, among others, are considered congeners. Faúndez and Valderrama [3] analyzed the phase equi- librium modeling of binary and ternary mixtures including water, ethanol, and congeners, they concluded that the use of prediction models such as Universal Functional Activity Coefficient (UNIFAC) and Predictive Soave-Redlich-Kwong EoS (PSRK) could be used when experimental data are not available. However, these authors recommended testing the validity of the model results by compar- ison with experimental data. Data of vapor pressure of pure cong- eners is a relevant property on which the vapor–liquid calculations have a strong dependence. Moreover, several derived physical– chemical properties can be estimated from the vapor pressure data. The main objective of this work was to contribute with new experimental information of the vapor pressures for two congen- ers, 2-methyl-1-propanol and 3-methyl-1-butanol, in the range of (15 to 177) kPa, by measuring the isobaric (vapor + liquid) equilibrium. 2. Experimental 2.1. Materials Pure nitrogen (N 2 ) was supplied by AGA Chile with no less than 99.999% of N 2 . HPLC-grade n-heptane and pro-analysis 2-methyl- 1-propanol were obtained from Aldrich (St. Louis, MO) with purity greater than 99%. Pro-analysis 3-methyl-1-butanol with purity greater than 99%, were obtained from Merck (Darmstadt, Ger- many). These materials were used without further purification. 2.2. Apparatus and procedures The vapor pressure was measured using a commercial all-glass dynamic recirculation isobaric (vapor + liquid) equilibria (VLE) apparatus (Labodest model 602D, i-Fischer Engineering GmbH, Waldbüttelbrunn, Germany) [4]. Its operation procedure relies on the principle of the recirculation of both liquid and vapor phases at controlled pressure. The operation ranges of equilibrium tem- perature and pressure were (10 to 300) kPa and (293 to 573) K, measured with precisions of ±0.1 K and ±0.1 kPa. The apparatus (figure 1) is equipped with a Cottrell pump (1), where an intensive phase exchange and separation takes place; an electrical immer- sion heater (2), that provides the energy to achieve the evaporation of the compound; a mixing chamber (3), stirred by a magnetic bar, where the separated vapor and liquid phases are recirculated; a Pt-100 temperature probe (4), used to measure the equilibrium temperature. The pressure in the system is controlled by a control device (5), equipped with a precision pressure transmitter, and a 0021-9614/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.jct.2009.04.009 * Corresponding author. Tel.: +56 32 654221; fax: +56 32 654478. E-mail address: juan.delafuente@usm.cl (J.C. de la Fuente). J. Chem. Thermodynamics 41 (2009) 1020–1024 Contents lists available at ScienceDirect J. Chem. Thermodynamics journal homepage: www.elsevier.com/locate/jct