An innovative approach for storing low-grade thermal energy using liquid phase thermoreversible reaction

Highlights: • The potential of $\mathrm{methanol}+\mathrm{acetaldehyde}\leftrightarrow \mathrm{hemiacetal}$, as a thermoreversible reaction, is studied for long-term energy storage. • A full description of forward and backward reactions is provided. • The technical issues associated with both forward and backward reactions are discussed. • The presented approach has a great potential for storing low-grade thermal energy in regional areas of cold weather. This study investigates the potential of "$\mathrm{methanol}+\mathrm{acetaldehyde}\leftrightarrow \mathrm{hemiacetal}$" as a liquid phase thermoreversible reaction for long-term storing of low-grade thermal energy to overcome the mismatch between energy supply and demand. Both forward and backward reactions are studied experimentally and the technical issues associated with employing such a system are discussed. Methanol and acetaldehyde would react via an exothermic reaction ($-\Delta H_r=31.8\frac{\text{kJ}}{\text{mole}}\mathrm{or}104.7\frac{\text{kWh}}{{\text{m}}^3}$) at low temperature range ($k=26.26\times {10}^2\exp \left(-\frac{4099}{T}\right)$). The regeneration of parent reactants with high purity occurs at 48 °C which can easily be delivered using low-grade heat. The low operating temperature required for forward reaction and the reduction in backward reaction rate caused by methanol accumulated are the main engineering challenges. These technical problems need to be solved before this reaction could be utilised commercially.