Ivan Vasilevich Grenev

Technologies of membrane-based gas separation can be integrated into existing industrial processes for low-temperature helium recovery from natural gas at the stages of crude helium separation from the N₂/He mixture and its purification. The effectiveness of these processes is most affected by the properties of the materials from which the membrane is made. Due to their unique properties, metal-organic framework are promising materials for use in gas separation. In the present work, both the Monte Carlo and equilibrium molecular dynamics methods were employed to examine the temperature dependence of membrane selectivity and nitrogen permeability for separation of an equimolar mixture of N₂ and He by a HKUST-1-based membrane at a pressure drop of 0.1, 0.3, and 1 MPa. It was shown that the selection of optimal temperature conditions made it possible to obtain a significant increase in membrane selectivity and permeability for nitrogen compared to corresponding parameters at room temperature.

Низкотемпературное разделение N 2 и He на мембране HKUST-1

In silico screening of 10,143 metal−organic frameworks (MOFs) and 218 all-silica zeolites for adsorption-based and membrane-based He and N₂ separation was performed. As a result of geometry-based prescreening, structures having zero accessible surface area (ASA) and pore limiting diameter (PLD) less than 3.75 Å were eliminated. So, both gases can be adsorbed and pass-through MOF and zeolite pores. The Grand canonical Monte Carlo (GCMC) and equilibrium molecular dynamics (EMD) methods were used to estimate the Henry’s constants and self-diffusion coefficients at infinite dilution conditions, as well as the adsorption capacity of an equimolar mixture of helium and nitrogen at various pressures. Based on the obtained results, adsorption, diffusion and membrane selectivities as well as membrane permeabilities were calculated. The separation potential of zeolites and MOFs was evaluated in the vacuum and pressure swing adsorption processes. In the case of membrane-based separation, we focused on the screening of nitrogen-selective membranes. MOFs were demonstrated to be more efficient than zeolites for both adsorption-based and membrane-based separation. The analysis of structure–performance relationships for using these materials for adsorption-based and membrane-based separation of He and N₂ made it possible to determine the ranges of structural parameters, such as pore-limiting diameter, largest cavity diameter, surface area, porosity, accessible surface area and pore volume corresponding to the most promising MOFs for each separation model discussed in this study. The top 10 most promising MOFs were determined for membrane-based, vacuum swing adsorption and pressure swing adsorption separation methods. The effect of the electrostatic interaction between the quadrupole moment of nitrogen molecules and MOF atoms on the main adsorption and diffusion characteristics was studied. The obtained results can be used as a guide for selection of frameworks for He/N₂ separation.

The effect of structural defects and framework flexibility on the water adsorption in CAU-10-H was explored by a grand canonical Monte Carlo simulation.