Preparation of composite microencapsulated phase change material based on phosphogypsum for passive building applications

[Display omitted] •MPCM with graphite/SiO2 coating was successfully prepared.•The thermal conductivity and durability were enhanced due to graphite/SiO2 shell.•The modified Phosphogypsum (PG) has good energy storage capacity with MPCM.•PG-MPCM had good thermal stability after 2000 cycles. High-performance thermal energy storage technology based on phase change material (PCM) plays an important role in reducing the building energy consumption and realizing efficient energy utilization. However, the drawbacks such as liquid phase leakage, poor thermal conductivity, and low cycle stability, significantly reduces its service life and limits its further application. In this paper, a new microencapsulated phase change material (MPCM) containing graphite-SiO2 shell and eicosane-octadecane (E-O) core was prepared by the sol–gel method. A high thermal conductivity shell was successfully constructed inside the MPCM by double-layer encapsulation technology to accommodate the poor thermal conductivity of E-O. The prepared MPCM had core–shell structures and spherical morphologies, with great enhancement in the thermal conductivity. When the mass ratio of E-O/SiO2 is 2:1, the encapsulation ratio reaches 71.2%, and the corresponding phase change enthalpy of the MPCM is 133.2 kJ/kg. The MPCM is further added to phosphogypsum (PG) which is a by-product of the wet-process production of phosphoric acid, to form composite MPCM. The compressive strength of the composite material is still as high as 5.8 MPa with 15% MPCM despite the negative effect on strength by MPCM. The PG-MPCM showed a good thermal storage capacity and compatibility, furthermore, the thermal stability was maintained also after 2000 thermal cycles. Therefore, the composite PG-MPCM developed in this work is capable of energy storage to reduce the building energy consumption and provides great potential in the PG resource utilization for enhanced environmental protection.