Synthesis and Investigation of Thermal Properties of Highly Pure Carboxylic Fatty Esters to Be Used as PCM

Abstract

Latent heat storage systems are gaining the attention of researchers as possible substitutes to conventional sensible heat storage systems due to their compactness and their ability to absorb and release heat almost isothermally. Among the Phase Change Materials (PCM) for energy storage studied so far, esters are believed to show promising properties. In particular, a broad range of melting temperatures, little to no supercooling, low corrosivity, chemical and thermal stability, and high enthalpies of fusion are reported. Many esters have the advantage of being bio-based and biodegradable, making them more sustainable in comparison to other popular PCM. Still, a clear lack of experimental data exists in regards to this class. In the present study, esters derived from saturated fatty carboxylic acids (myristic, palmitic, stearic, behenic), coupled with primary linear alcohols of different length (methanol, 1-decanol) were synthesized through Fischer esterification and their properties were investigated. Purities higher than 89% were obtained for all cases as proven by gas chromatography coupled with mass spectroscopy and nuclear magnetic resonance analysis. Additionally, the esters' formation and reaction kinetics were characterized by attenuated total reflectance infrared spectroscopy. The esters produced showed to possess relatively high enthalpies of fusion above 190 J/g and thermal stability over three repeated cycles with differential scanning calorimetry. The melting points measured ranged between 20 • C and 50 • C, therefore proving to be interesting candidates for low-medium temperature applications such as heating and cooling in buildings. A correlation could be observed between the chemical structure and melting point of the produced esters. Additionally, thermogravimetric analysis revealed a higher thermal resistance for esters with longer aliphatic chains in comparison to shorter-chained ones.

Investigation of the Thermal Properties of Diesters from Methanol, 1-Pentanol, and 1-Decanol as Sustainable Phase Change Materials

“…All diesters presented were synthesized in house according to the synthesis proposed by Ravotti et al [18,19] for saturated fatty esters. Given that the synthesis procedure had been optimized for fatty esters and not diesters, its success in the case of diesters had to be validated first.…”

“…They observed a high thermal stability with low supercooling rates and enthalpies of fusion of around 150 J/g in a low-mid temperature range between 20 and 32 • C. Sari et al [16] synthesized and studied esters from stearic acid with isopropanol, n-butanol, and glycerol, and obtained similar results. Other studies include those of Stamatiou et al [17], where the authors investigated 11 commercial saturated unbranched esters, and Ravotti et al [18,19], where 15 carboxylic fatty esters were synthesized and their thermal properties were characterized. In general, these authors measured enthalpies of fusion between 150 and 190 J/g in a temperature range of 10-50 • C, which would be suitable for low-mid temperature applications such as space heating.…”

“…In particular, MeOH = methanol, PeOH = 1-Pentanol, DeOH = 1-Decanol, Ox = oxalic acid, Su = succinic acid, Sub = suberic acid, Se = sebacic acid (see chemical structures and IUPAC names in Appendix A Figure A1). The alcohols of provenance have been chosen in order to allow the diesters to be comparable to the fatty esters synthesized by Ravotti et al [18,19]. The dicarboxylic acids of origin were selected based on their natural occurrence with increasing carbon number in order to evaluate the influence of the aliphatic chains' lengths on the thermal properties of the diesters produced.…”

Lipid‐derived monoamide as phase change energy storage materials

“…The amides presented in the literature thus far comprise of long‐chain (C22‐34) monoamide/fatty acid eutectics, pure short‐chain (C16‐26) monoamides, and pure long‐chain fatty acid–derived diamides (C30‐46) . Generally, long‐chain molecules are selected for their higher enthalpies . While structure‐property studies are available for the long‐chain fatty acid–derived diamides, similar fundamental studies have not been established for pure long‐chain monoamides.…”

“…13 Generally, long-chain molecules are selected for their higher enthalpies. 7,19 While structure-property studies are available for the long-chain fatty acid-derived diamides, 13 similar fundamental studies have not been established for pure long-chain monoamides. Other gaps are also evident in the literature.…”