Capillary Condensation Measurements in Multimodal Nanoporous Media and Pore Critical Point Determination:...

Area of Science:

• Thermodynamics
• Materials Science
• Chemical Engineering

Background:

• The behavior of confined mixtures in nanoporous media is not well understood.
• Phase transitions in nanoporous materials are crucial for applications like gas storage and separation.

Purpose of the Study:

• To experimentally investigate the phase transition of a methane/propane mixture in multimodal nanoporous media.
• To provide the first measurements of phase transitions in such systems.
• To validate theoretical models for confined mixtures.

Main Methods:

• Utilized isochoric cooling and differential scanning calorimetry (DSC) for accurate measurements.
• Employed multimodal nanoporous media with independent pore domains.
• Applied the three-line approach to determine the pore critical point (PCP).

Main Results:

• Capillary condensation occurred at distinct temperatures and pressures, correlating with pore size and supporting independent domain theory.
• Thermogram peaks for multimodal pores were a linear combination of individual pore size peaks, validating the superimposition principle for mixtures.
• The pore critical pressure was lower than bulk, but the pore critical temperature of the confined mixture was observed to be higher than its bulk counterpart.

Conclusions:

• The superimposition principle is valid for confined gas mixtures in independent domains.
• The pore critical temperature of confined mixtures can exceed bulk values, challenging existing assumptions.
• This research fills a significant knowledge gap in understanding confined mixture phase transitions.