RESUMO
Stable molecular hydrogen isotopes, D2 and T2, are both scarce and essential in several energy, industrial, and large-scale fundamental research applications. Due to the chemical similarity of these isotopes, their extraction and purification from hydrogen has relied for decades on expensive and energy-demanding processes. However, factoring in the phenomenon of quantum sieving could provide a new route for these separations. In this work, we have explored how to separate hydrogen isotopes by adsorption taking these quantum effects into account. To this end, we have conducted adsorption measurements to test our deuterium model and performed a widespread computational screening over 210 pure-silica zeolites for D2/H2 and T2/H2 separations. Based on low-coverage adsorption properties, a reduced set of zeolites have been singled out and their performance in terms of adsorption capacity, selectivity, and dynamic behavior have been assessed. Overall, the BCT-type zeolite clearly stands out for highly selective separations of both D2 and T2 over H2, achieving the highest reported selectivities at cryogenic temperatures. We also identified other interesting zeolites for the separation of hydrogen isotopes that offer an alternative way to tackle similar isotopic separations by an aimed selection or design of porous materials.
RESUMO
Carbon dioxide release has become an important global issue due to the significant and continuous rise in atmospheric CO2 concentrations and the depletion of carbon-based energy resources. Plasmolysis is a very energy-efficient process for reintroducing CO2 into energy and chemical cycles by converting CO2 into CO and O2 utilizing renewable electricity. The bottleneck of the process is that CO remains mixed with O2 and residual CO2. Therefore, efficient gas separation and recuperation are essential for obtaining pure CO, which, via water gas shift and Fischer-Tropsch reactions, can lead to the production of CO2-neutral fuels. The idea behind this work is to provide a separation mechanism based on zeolites to optimize the separation of carbon dioxide, carbon monoxide, and oxygen under mild operational conditions. To achieve this goal, we performed a thorough screening of available zeolites based on topology and adsorptive properties using molecular simulation and ideal adsorption solution theory. FAU, BRE, and MTW are identified as suitable topologies for these separation processes. FAU can be used for the separation of carbon dioxide from carbon monoxide and oxygen and BRE or MTW for the separation of carbon monoxide from oxygen. These results are reinforced by pressure swing adsorption simulations at room temperature combining adsorption columns with pure silica FAU zeolite and zeolite BRE at a Si/Al ratio of 3. These zeolites have the added advantage of being commercially available.
RESUMO
Double-layered zeolitic imidazolate framework (ZIF) membranes were fabricated inside polyimide P84 hollow fibers by a step-synthesis conducted by microfluidic technology and applied to pre-combustion gas separation. Our hypothesis, based on the information provided by a combination of molecular simulation and experiments, is that a CO2 adsorption reduction on the surface of the ZIF-9 would enhance the molecular sieving effect of this ZIF-9 layer and therefore the selectivity in the H2/CO2 mixture separation of the entire membrane. This reduction would be achieved by means of a less-CO2-adsorptive methylimidazolate-based ZIF-67 or ZIF-8 layer coating the ZIF-9. ZIF-8/ZIF-9 and ZIF-67/ZIF-9 double-layered membranes were prepared and characterized by XRD, FTIR, SEM, FIB, TEM and EDS. This unprecedented strategy led to a H2/CO2 separation selectivity of 9.6 together with a 250 GPU H2 permeance at 150 °C, showing a significant improvement with respect to the pure ZIF-9 membrane. Double-layered membranes also showed higher apparent CO2 activation energies than single-layered membranes, attributable to a diminished adsorption.
