The Laboratory of Advanced Separations (LAS) has been engaged in multidisciplinary research focused on material chemistry and engineering at the Å length scale to develop high-performance inorganic and hybrid membranes for energy-efficient molecular separation (see figure below). We focus on engineering ultrathin films, down to the thickness of a single atom, from chemically, thermally, and mechanically robust nanoporous materials using scale-up-conducive chemistries with high precision in pore size and functionality.
Summary of research direction at the Laboratory of Advanced Separations
Our approach is motivated by the fact that nanoporous two-dimensional membranes can enable large gas permeance which reduces the needed membrane area for handling a certain volume of a gas mixture, and therefore, reduces the module cost for a given gas flow rate, the membrane footprint, and the process CAPEX. Our recent techno-economic analysis has shown that large permeance also favors the use of vacuum pumps in the permeate stream of membrane processes without pressurizing the feed which improves the energy-efficiency for handling gases in low concentration in a feed mixture, e.g., removing CO2 from flue gas. Our approach is also motivated by the fact that nanoporous inorganic and hybrid materials such as nanoporous graphene, zeolites, graphitic carbon nitride, and metal-organic framework possess thermal (high-temperature applications, e.g., zeolites for pre-combustion capture), mechanical and structural robustness making them superior to the polymeric materials in these aspects. We are aware of the fact that concentration polarization for high-permeance membrane elements could be a bottleneck in realizing the high gas permeance at the module scale especially when high permeance is combined with high selectivity. To address this, we are developing membrane modules, in collaboration with our industrial partners (Shell), where the feed-side mass transfer coefficient from the bulk phase to membrane interface is improved without creating a significant pressure drop.
Our efforts in the chemistry of two-dimensional materials have enabled us to realize carbon capture membranes with performances (a combination of high permeance and pair selectivity) that significantly exceed that of the state-of-the-art membrane technologies. We have started scale-up activities to push the technology readiness level (TRL) of the technologies developed at LAS by projects funded by industry and the Swiss Federal Office of Energy, geared toward pilot plant demonstration. These membranes are ideally suited to address the energy transition challenges in the fields of hydrogen purification, precombustion and postcombustion carbon capture.
On the fundamental science front, we have established a multidisciplinary program in chemical engineering, chemistry, and material science, focusing on the crystal, interface, morphology, and defect engineering of nanoporous two-dimensional materials (perforated single-layer graphene, exfoliated nanosheets of crystalline g-C3N4, and zeolitic materials). In parallel, we have developed rapid-processing routes to synthesize sub-0.5-µm-thick polycrystalline metal-organic frameworks (MOF) films, while at the same time, have developed routes which reduce their lattice flexibility to apply them as molecular sieving films. More recently, we have developed two-dimensional polycrystalline MOF films, with a thickness of just one unit-cell, compatible with our overall efforts to develop nanometer-thick selective layers (manuscript under preparation).
Our crystal and morphology engineering routes involve the development of chemical vapor deposition, solvothermal, solid-state, and interfacial crystallization. Our defect engineering toolkit, based on the highly scalable ozone-based graphene gasification chemistry has allowed us to carry out high-precision nucleation and growth of vacancy defects in graphene, resulting in achieving sub-1-Å resolution in molecular differentiation (based on the difference between the kinetic diameter of gas pair). These results have been aided by the state-of-the-art instrumentations available at LAS as well as the excellent characterization facilities, infrastructure, and collaboration opportunities within EPFL. The following is a summary of our efforts since the launch of our laboratory on July 1, 2016. The summary is categorized as per several material platforms being developed in our laboratory. We work on both scientific as well as engineering challenges to resolve fundamental bottlenecks as well as issues related to film fabrication and scale-up.