Tetradecyl oxalate and octadecyl oxalate as novel phase change materials for thermal energy storage

摘要

This paper related to synthesis, structural characterization, thermal properties and thermal reliability of novel phase change materials (PCMs) running at different temperatures. Dicarboxylic acid esters were synthesized via the reaction of oxalic acid, 1-tetradecanol and 1-octadecanol without using any catalyst and under vacuum for the first time at high yield. Synthesized ditetradecyl oxalate (DTO) and dioctadecyl oxalate (DOO) were characterized structurally by Fourier transform infrared (FT-IR) spectroscopy with ATR accessory and H-1 Nuclear Magnetic Resonance (H-1 NMR) spectroscopy techniques. Thermophysical properties including melting and freezing temperature, phase change enthalpy, total enthalpy, and specific heat capacity were determined by a differential scanning calorimeter (DSC) as degradation temperatures were determined by a thermogravimetric analyzer (TGA). Phase change temperatures of DTO and DOO were 47 degrees C and 65 degrees C for melting and 44 degrees C and 63 degrees C for solidification respectively. Latent heat capacity of DTO and DOO ranged from 210.6 J/g to 244.9 J/g for heating period and from 208.3 J/g to 241.7 J/g for cooling period. TGA measurements indicated that degradation temperature of DTO and DOO started at 231 degrees C and 238 degrees C respectively, which are sufficiently above their potential working temperatures. Crystalline morphology of PCMs was examined by a polarized optic microscope (POM). Thermal conductivity of DTO and DOO were found slightly lower than the precursors. However it was proven that it could be gradually increased by graphite. DTO and DOO were confirmed in terms of structure and thermal reliability after 1000 times accelerated heating-cooling cycles. All results pointed out that synthesized dicarboxylic acid esters can be validated as solid-liquid PCMs for some solar energy storage applications.