Effect of surface modification of sludge hydropyrolysis residue on the heat storage performance of composite hydrated salt

The use of hydrated salts as thermal storage materials has become a current research focus for its large latent heat, but the problems of phase separation and high supercooling degrees are the main factors in preventing its application. The composite phase change materials (CPCMs) of Sodium Acetate Trihydrate (SAT) loaded on the sludge hydropyrolysis residue (SHR) has been confirmed better performance to solve these two problems in our past work. But the varied surface hydrophobicity of SHR results in significant fluctuations in supercooling degree of the CPCM. In response to this problem, sodium dodecylbenzene sulfonate (SDBS) was used here to modify the SHR surface to compose hydrated salt of SAT. The surface-modified SHR was mixed with the unmodified one in the ratio of 3:1, 1:1, and 1:3, respectively, and all the three carriers loaded the SAT at the ratio of 1:6 to prepare CPCM. Characterization by SEM, BET, and DSC, melting/solidification multi-cycle testing, and thermal conductivity measurement were conducted. The results showed that the best performance was achieved when the modified SHR mixed with the unmodified one in a 1:1 ratio. After the 100-cycle of melting/solidification of CPCM, the latent heat decreased about 6 %, the phase change process of CPCM repeated very well, and the supercooling degree was kept below 3 °C. The surface modification of the SHR carrier is beneficial for the steady heat storage performance during the CPCM melting/solidification cycle. [Display omitted] •SDBS is used to modify the surface of sludge hydropyrolysis residue (SHR).•The hydrophilic group ensured sufficient adsorption of SAT to SHR.•Blending modified and unmodified SHR gets a better performance of CPCM.•The best performance of CPCM is achieved by mixing two SHR with the same quality.