The preparation of a green shape-stabilized composite phase change material of polyethylene glycol/SiO2 with enhanced thermal performance based on oil shale ash via temperature-assisted sol–gel method

Abstract

A novel polyethylene glycol (PEG)/SiO2 shape-stabilized composite phase change material (ss-CPCM) was prepared with the ‘hazardous waste’ oil shale ash. In this composite, PEG serves as the phase change material for thermal energy storage and SiO2 acts as the carrier matrix to provide structural strength and prevent the leakage of melted PEG. The calcination-alkali leaching method was applied to prepare the sodium silicate solution with the ash. When the calcination temperature, calcination time, sodium hydroxide concentration, reaction time and liquid/solid ratio were 900°C, 60min, 20wt%, 4h, and 4mL/g, respectively, the silica extraction efficiency could reach 60.36%. Then the PEG/SiO2 ss-CPCM was prepared with sodium silicate solution as the precursor via the temperature-assisted sol–gel method without any co-solvent or surfactant. Various characterization techniques were adopted to study the structures and properties of the prepared PEG/SiO2 ss-CPCM. SEM, FT-IR, and XRD results indicated that PEG was well encapsulated and that no chemical change took place during the phase change process. TGA results showed that the composite presented an excellent thermal stability. DSC analysis results indicated that the composite had considerably high phase change enthalpy, encapsulation ratio, encapsulation efficiency and thermal storage capability. Moreover, the supercooling extent, melting and solidifying time of the composite were respectively 22.3%, 26.5% and 22.6% less than those of pristine PEG. Based on the element analysis, there are no safety hazards for the prepared ss-CPCM to be seen as a potential candidate for thermal energy storage applications in building envelopes.