Experimental evaluation of the partial thermal energy compensation of hydrate crystallization from cyclopentane-loaded porous activated carbon particles immersed in brine

Hydrate-based desalination (HBD) is a potential water desalination technology that has been studied over the past decades. Recently, an HBD process based on hydrate formation from cyclopentane (CP) loaded on porous activated carbon particles (PACP) was patented (“Method for crystallizing clathrate hydrates, and method for purifying an aqueous liquid using the clathrate hydrates thus crystallized”, EP3153606, 2017). It is thought that the crystallization of CP hydrates from CP adsorbed on PACP might cause partial thermal energy compensation. Actually, the heat released by the exothermic hydrate crystallization should be partially balanced by the endothermic desorption of CP from the PACP. In order to investigate this phenomenon, calorimetric and optical studies (heat flow and refractive index measurements respectively) of hydrate formation in systems consisting of CP-saturated PACP immersed in brines (3.5 wt% NaCl and 8 wt% NaCl) were performed. Comparison of the thermal energy measured directly (through the calorimetric study) - i.e. the energy produced by both hydrate crystallization and CP desorption - and the thermal energy measured indirectly (deduced from the optical study) - i.e. the energy generated by hydrate crystallization only - revealed a balanced energy ranging from 9 to 47 kJ/mol of CP. Comparison of the latter with the differential enthalpy of CP desorption from PACP suggests that the CP converted to hydrates was contained in the large pores of the PACP. It is interesting to note that salinity had no significant impact on the degree of thermal energy compensation obtained. •Hydrates crystallize from cyclopentane (CP) desorbed from activated carbon.•CP-desorption enthalpy partially compensates hydrate crystallization enthalpy.•Salinity seems not to impact the degree of thermal energy compensation.•CP involved in hydrate crystallization is mainly contained in the large pores.