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Abstract
In the presented work, five bio-based and bio-degradable cyclic esters, i.e. lactones, have been investigated as possible phase change materials for applications in latent heat storage systems. Commercial natural lactones such as ε-caprolactone and γ-valerolactone were easily purchased through chemical suppliers, while 1,2-campholide, oxa-adamantanone and dibenzochromen-6-one were synthesized through Baeyer-Villiger oxidation. The compounds were characterized with respect to attenuated total reflectance spectroscopy and gas chromatography coupled with mass spectroscopy, in order to confirm their chemical structures and identity. Subsequently, thermogravimetric analysis and differential scanning calorimetry were used to measure the phase change temperatures, enthalpies of fusion, degradation temperatures, as well to estimate the degree of supercooling. The lactones showed a wide range of phase change temperatures from −40 °C to 290 °C, making them a high interest for both low and high temperature latent heat storage applications, given the lack of organic phase change materials covering phase change temperature ranges below 0 °C and above 80 °C. However, low enthalpies of fusion, high degrees of supercooling and thermal degradations at low temperatures were registered for all samples, rendering them unsuitable as phase change materials.
Highlights
Due to the increasing global energy consumption in addition to concerns related to the growing scarcity of fossil fuels and environmental degradation, energy efficiency and the integration of renewable energies in our energy systems are of utmost importance
Such temperatures are nowadays being covered in Latent HeatStorage (LHS) applications mainly by salt hydrates or other inorganic PCM, and no mention of organic PCMs at such high or low temperatures has been reported in the literature
Of all the lactones shown hereby, only oxa-adamantanone is characterized by supercooling ≤5 ◦ C, while for the others supercooling between 10 ◦ C and 30 ◦ C is observed
Summary
Due to the increasing global energy consumption in addition to concerns related to the growing scarcity of fossil fuels and environmental degradation, energy efficiency and the integration of renewable energies in our energy systems are of utmost importance. Storage (LHS) systems are increasingly gaining attention in the scientific community as a result of several advantages in comparison to current Sensible Heat Storage (SHS) systems, such as water or stone tanks [1,2,3,4]. They offer more compact systems and a high energy density, which is of crucial importance in urban environments due to space scarcity. To be classified as an attractive PCM, a material needs to primarily exhibit qualities including a congruent phase change over narrow temperature ranges, thermal stability over repeated cycles, high latent energy of phase transition (in the case of solid-liquid transition it is latent energy of fusion), Molecules 2019, 24, 1300; doi:10.3390/molecules24071300 www.mdpi.com/journal/molecules
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