Water intrusion in mesoporous silicalite-1: An increase of the stored energy

In silicalite-1 (pure silica MFI-type zeolite), the water adsorption is extremely weak when the pressure is lower than the water saturation vapor pressure. The water condensation (intrusion) is obtained by applying a high hydraulic pressure, approximately of 100 MPa. Extrusion of water occurring at the similar pressure, the “water–silicalite-1” system constitutes thus a real molecular spring, which can store and restore mechanical energy. In order to increase the stored energy in this system, the porous volume of this zeolite was increased by the creation of additional micro-, meso- and macropores using carbon black or surfactant [3-(trimethoxysilyl)propyl]hexadecyldimethylammonium chloride, as porogen and templating agents, respectively. The presence of meso- and macropores modifies the water condensation behavior in silicalite-1. Indeed, the water intrusion takes place in two stages. The first one, from 3 to 7 MPa, corresponds to the filling of meso- and macropores but the amount of stored energy is very low. The second one, at 100 MPa, corresponds to the filling of micropores. The increase of the microporous volume leads to an increase of the intruded water volume at high hydraulic pressure. Consequently, the stored energy is greater than for a conventional silicalite-1 zeolite.