Study on phase diagram of fatty acids mixtures to determine eutectic temperatures and the corresponding mixing proportions

This study was focused on preparation and characterization of fatty acid eutectic mixtures as phase change materials (PCMs). The four common fatty acids: stearic acid (SA), palmitic acid (PA), myristic acid (MA) and lauric acid (LA) were selected as representative to prepare binary and ternary eutectic mixtures by heating-ultrasonic method. The melting points of LA–MA, LA–SA, SA–MA, SA–PA, MA–PA, LA–MA–SA, MA–SA–PA mixtures with varying combination proportions were determined and then analyzed by drawing the phase diagrams to determine the eutectic points and the corresponding mixing proportions. The results showed that the eutectic temperature of ternary fatty acids was lower than binary fatty acids’; ternary mixture possessed the same thermal properties with pseudo-binary mixture in both melting temperature and latent heat of phase change; the Schröeder-Van Laar equation can be taken as a basis for mixing proportion of pseudo-binary fatty acid and ternary fatty acid systems; the ternary eutectic point on the ternary phase diagram was just in the vicinity of a small triangle which was formed by the connection between the three vertices and the three eutectic points of binary fatty acid in the corresponding across flats. Moreover, ternary and pseudo-binary mixtures had advantage in energy conservation applications such as building heating/cooling and indoor temperature controlling especially when the temperature in need was low.