New renewable raw materials for thermal energy storage

The thermal behavior of materials based on the renewable raw resource, beeswax, was studied to evaluate their potential as phase-change materials, PCMs, for latent heat thermal energy storage, LHTES. Beeswax, transesterified beeswax methyl esters and mixtures of beeswax with paraffin were studied. Additionally, waste vegetable cooking oil, a widely available and underused renewable raw material, was fully hydrogenated and the product, and its mixtures with beeswax, were investigated as candidates to PCMs. Transesterified beeswax shows an increase of about 15% in melting/crystallization enthalpies relative to the already suitable beeswax. In addition, the phase transitions take place at a 10 °C higher temperature range. These characteristics, and the minimal undercooling for crystallization, make both samples good PCM candidates. The addition of beeswax to hydrogenated waste cooking oil was found to be efficient in promoting the formation of the most stable triacylglycerides polymorph, making mixtures of these two renewable raw materials promising candidates for LHTES. Beeswax + paraffin mixtures, with 40% beeswax content, show near ideal thermal behavior for a PCM, while decreasing the amount of the crude derivative. Additionally, the volume change upon melting, one of the major problems of paraffins as PCMs, is considerably less for this mixture (about 50%).