Eutectic mixtures of sugar alcohols for thermal energy storage in the 50–90 °C temperature range

• Erythritol–xylitol, erythritol–sorbitol and xylitol–sorbitol eutectic mixtures as PCMs.
• Phase diagrams were established experimentally by DSC and XRPD.
• Melting temperatures of the mixtures are suitable for heating and DHW applications.
• Low recrystallization rates limit the use of the mixtures for short term storage.
• Further research is needed to control the crystallization behavior of the materials.

This article studies new binary eutectic mixtures of sugar alcohols for their use as phase change materials (PCMs) in the 50–90 °C temperature range. This range is suitable for domestic solar thermal systems and cogeneration devices. The mixtures studied were composed of erythritol and xylitol, erythritol and sorbitol, and xylitol and sorbitol. Their phase diagrams were experimentally established by differential scanning calorimetry and X-ray powder diffraction. Polarized thermomicroscopy was employed to determine the crystallization rate of the pure materials and eutectic compositions. Additionally, the polymorphic behavior of the pure materials was assessed and compared with data from the literature. The results showed that, with respect to thermal properties and economic aspects, the eutectic compositions found are suitable for the intended purpose. Unfortunately, their crystallization rates are noticeably low, which limits their use as PCMs. A modeling approach based on thermodynamics was used to predict solid–liquid equilibria of the studied mixtures and their melting enthalpies. The simulated results were in good agreement with experimental results. The modeled and experimental results were finally used to highlight a few practical aspects relevant for the development of new eutectic mixture-based PCMs.