Thermochimica Acta 547 (2012) 6–12 Contents lists available at SciVerse ScienceDirect Thermochimica Acta jo u r n al hom ep age: www.elsevier.com/locate/tca Vapor pressure data for fatty acids obtained using an adaptation of the DSC technique Rafael M. Matricarde Falleiro a , Luciana Y. Akisawa Silva b , Antonio J.A. Meirelles c , Maria A. Krähenbühl a,∗ a LPT, Departamento de Processos Químicos (DPQ), Faculdade de Engenharia Química, Universidade de Campinas (UNICAMP), 13083-852 Campinas – SP, Brazil b Departamento de Ciências Exatas e da Terra, Universidade Federal de São Paulo (UNIFESP), 09972-270 Diadema – SP, Brazil c EXTRAE, Departamento de Engenharia de Alimentos (DEA), Faculdade de Engenharia de Alimentos, Universidade de Campinas (UNICAMP), 13083-862 Campinas – SP, Brazil a r t i c l e i n f o Article history: Received 29 May 2012 Received in revised form 24 July 2012 Accepted 25 July 2012 Available online xxx Keywords: Fatty acids Vapor pressure Differential Scanning Calorimetry (DSC) a b s t r a c t The vapor pressure data for lauric (C 12:0 ), myristic (C 14:0 ), palmitic (C 16:0 ), stearic (C 18:0 ) and oleic (C 18:1 ) acids were obtained using Differential Scanning Calorimetry (DSC). The adjustments made in the exper- imental procedure included the use of a small sphere (tungsten carbide) placed over the pinhole of the crucible (diameter of 0.8 mm), making it possible to use a faster heating rate than that of the standard method and reducing the experimental time. The measurements were made in the pressure range from 1333 to 9333 Pa, using small sample quantities of fatty acids (3–5 mg) at a heating rate of 25 K min -1 . The results showed the effectiveness of the technique under study, as evidenced by the low temperature deviations in relation to the data reported in the literature. The Antoine constants were fitted to the experimental data whose values are shown in Table 5. © 2012 Published by Elsevier B.V. 1. Introduction Nowadays vegetable oils occupy a prominent position on the world stage especially as raw materials in the production of alter- native fuels (biodiesel), and also because fatty acids are of great interest to the chemical, pharmaceutical and food industries. On the other hand, vapor pressure data for some fatty compounds, e.g. oleic acid, are scarce in the literature, as indicated in the DIPPR database [1], or the purity of the chemicals used in the measure- ments are not available, since the cost of just a few grams of fatty acids is very high (very pure compounds), which can make it impractical to determine this thermodynamic property by con- ventional techniques such as ebulliometry. However, using the DSC technique it is possible to obtain such data with very small quantities of these fatty compounds and in a short period of time, avoiding the risk of thermal degradation due to the high heating rate. Some authors, such as Pool and Ralston [2] and Stull [3], reported vapor pressure data obtained, respectively, using ebulliometry and a summary of data found in the literature, in the pressure range from 133 to 101325 Pa for fatty acids with both long and short chains. Other research groups [4–10] reported the vapor pressure data for organic compounds in different pressure ranges, obtained ∗ Corresponding author. Tel.: +55 19 3521 3964; fax: +55 19 3521 3965. E-mail address: mak@feq.unicamp.br (M.A. Krähenbühl). by Differential Scanning Calorimetry (DSC). In this technique, the boiling temperature is measured as a function of a previously estab- lished pressure, within a dynamically heated environment [8]. For this method to work properly, one important procedure is to make a small hole in the lids of the DSC crucibles, called a pinhole. This pinhole is capable of providing greater sharpness of the differential thermal curves, avoiding a significant pre-vaporization, provided that the heating rate is fast enough to reduce the loss of sample [10]. The authors cited previously worked with different sizes of pinhole, obtaining satisfactory results in their studies. In the present study, the main aim was to obtain vapor pres- sure data for selected fatty acids between 1333 and 9333 Pa by modifications of the DSC methodology. For this purpose, amounts between 3 and 5 mg of the fatty acids were used in experimental trials with a controlled heating rate of 25 K min -1 , since this rate had already been established and shown to be effective in deter- mining the vapor pressure data in a previous study [7] by the same authors. With respect to the diameter of the hole, there is significant difficulty in making it with the appropriate size (0.05–0.075 mm) as recommended by Method E 1782-03, Standard Test Method for Determining Vapor Pressure by Thermal Analysis [11]. Another possibility would be to purchase laser drilled pinhole lids, but these are very expensive, which would have prevented carrying out the present study. In an attempt to overcome these impediments, a practical alternative suggested by Farritor and Tao [12] was applied, in which a small ball (in this case made of tungsten carbide with a diameter of 1.0 mm) was placed over a larger pinhole made with a 0040-6031/$ – see front matter © 2012 Published by Elsevier B.V. http://dx.doi.org/10.1016/j.tca.2012.07.034