ComBioTES: bio-based PCM selection process

One of the goals of ComBioTES is to select a Bio-based Phase Change Material (PCM) for heating and hot tap water, which is biodegradable, chemically stable and with as less safety issues as possible.

In the first place, Roquette and CEA has developed a grid of selection of the bio-based PCM, with relevant parameters on performance, safety, supply, cost etc. It led to a first screening PCM suitable for ComBioTES, with the selection of Octadecanol, RT70HC, Crodatherm 74 and Isosorbide (more specifically, POLYSORB® PA developed by ROQUETTE, which contains an additive to improve stability and reduce the risk of thermal degradation).

Octadecanol, RT70HC and Crodatherm 74 were already known and have already been characterized by partners from ComBioTES in previous projects. Since Isosorbide experiences supercooling, preliminary characterization and tests were performed to assess (or not) its use as PCM.
Thus, Roquette characterized the thermo-physical properties of the Isosorbide in lab conditions with measurements at small scale of the properties relevant for TES applications. Roquette supplied 150 Kgs of Isosorbide to CEA to test it in actual TES conditions.

Eventually CEA performed some melting/solidification tests with the 500 mL dedicated installation in photo. CEA also completed tests without and with systems to help the solidification. Those systems were “seeding” (i.e., addition of solid particles of Isosorbide to initiate the solidification) and “bubbling” (i.e., nitrogen bubbling inside the vessel). The test results show that Isosorbide is experiencing supercooling at small-scale reactor, with primary nucleation and that seeding, and bubbling are efficient to initiate the crystallization.

In the end, Isosorbide is kept as potential PCM in ComBioTES. Its performances and its supercooling behaviour will be evaluated at reactor-scale (prototype of PCM thermal storage) in task T2.1 to conclude on its suitability (or not) in the project.