Hydro-solvothermal synthesis
Our activity exploits the specific properties of sub- and supercritical fluids to synthesize emerging nanostructured materials to meet today’s societal challenges. All types of solvents (water, alcohols, carbon dioxide, ammonia, etc. or mixtures) can be used depending on the materials to be produced: oxides, metals, nitrides, sulphides, phosphides, etc. Materials are mainly developed from continuous processes at different scales of production, from the milligram scale in microfluidic reactors for a deep understanding of the involved mechanisms to the kilogram scale for industry transfer, through the gram scale for materials science studies. This sustainable technology, based on a coupling between chemistry and process, allows synthesizing materials with novel properties or materials that cannot be obtained with conventional synthesis methods.
Material’s recycling
We are also interested in the end-of-life of materials through their recycling. With an approach similar to the one followed for the synthesis of materials, the implementation of different types of solvent systems in sub- and supercritical conditions allows the deconstruction of materials through physico-chemical processes, ranging from delamination to chemical transformation. Once the mechanism is mastered, a process is designed. The developments range from laboratory to pilot scale. The studies focus on the recycling of food packaging, thermoplastics, organic matrix composites, photovoltaic cells and permanent magnets. The environmental impact of all the developed technologies is assessed through life cycle assessment.
Management of anthropogenic CO2
We are strongly involved in the mitigation of environmental issues, through studies concerning in particular the carbon cycle and the energy transition. One of our main research activities concerns the aspects of CO2 capture and storage. Using high-pressure and high-temperature millifluidic and microfluidic approaches (Geological Laboratory on Chip – GLoCs), we are developing original high-throughput approaches for the optimization of CO2 capture processes, but also for understanding CO2 storage in deep geological environments (saline aquifers), whose conditions can be reproduced on a chip. In this context, the ERC (European Research Council) project “BIG MAC” (Microfluidic Approaches mimicking BIoGeological conditions to investigate subsurface CO2 recycling) aims at studying the biovalorisation of CO2 in subsurface conditions by methanogenesis (formation of reusable methane) thanks to the extremophilic micro-organisms populating these environments.
Deep environments and biogeochemical cycles
Our research is also interested in the interaction between the deep biosphere and the global chemical cycles, including the carbon cycle, and the reciprocal interactions between anthropogenic pollution (e.g. CO2, microplastics, etc.) and deep environments. To this end, we are developing innovative high-pressure methodologies for the study and the understanding of deep ecosystems in real subsurface conditions, taking into account the interactions between the microbiological, geochemical and reactive transport mechanisms that manage biogeochemical cycles. This aims at studying microbial diversity, metabolic strategies and adaptive mechanisms developed by these piezophilic microorganisms, as well as their interactions with anthropogenic pollution, in order to better understand the biodegradation mechanisms and to propose new alternatives to current bioremediation strategies.
In parallel, the skills and tools developed enable us to study hydrothermal fluids ranging from geochemical systems linked to deep hydrothermal sources (complexification of matter, prebiotic chemistry, origins of life) to degradation reactions of organic compounds via the hydrothermal oxidation process (SuperCritical Water Oxidation – SCWO), both on ground and in microgravity environments.
SKILLS
The Supercritical Fluids group has cross-disciplinary skills allowing taking into account all the Thermo-Hydro-Bio-Chemical (THBC) mechanisms occurring within processes using reactive fluids under pressure and temperature.
Thermodynamics and hydrodynamics of critical and supercritical fluids
Physics . Phenomena occurring in the vicinity of the critical point are of particular interest for studying the universality properties of critical phenomena observed in many systems displaying extremely different organizations at the molecular scale. The group has a strong experimental activity in microgravity environments (International Space Station – ISS), very close to the gas-liquid critical point in weightlessness, dedicated to the understanding of the behavior of dense, hyperdilatable and hypercompressible systems belonging to the universality class of uniaxial three-dimensional Ising systems. Based on this fundamental knowledge, experimental approaches are now oriented towards new scientific objectives, ranging from understanding the boiling crisis, to the study of the behavior of water-salt mixtures in supercritical, reactive or non-reactive conditions.
Thermodynamics. The group has an extensive expertise in modeling and acquiring thermodynamic data for complex fluid mixtures under pressure and temperature (density, pressure, phase envelope, in the range 20 < T(°C) < 500 and 0.1 < p (MPa) < 40). We use, in particular, innovative high-throughput approaches based on supercritical microfluidic tools (for the determination of phase diagrams or the development of microdistillation tools, for example).
Hydrodynamics. Mastering hydrodynamics in fluidic reactors is a critical parameter in process engineering. In order to improve the understanding and control of multi-scale flows (from micrometer to meter scale), we use coupled experiment / numerical simulation strategies. In particular, our skills enable us to study mixing conditions for applications in continuous supercritical processes in a wide range of sizes (microfluidic and millifluidic) and flow regimes (laminar and turbulent).
Chemical reactivity in supercritical fluid environment
Beyond physico-chemical systems, we are also interested in high-pressure microbiology for the study and the use of microorganisms from the deep biosphere. The contribution of rapid screening approaches brought by high-pressure microfluidics already allows us to reproduce in the laboratory the conditions encountered on the ocean floor or in deep geological environments. These tools are used to monitor the growth and to determine the metabolisms of extremophilic strains in situ and in real time. We are developing bio-assisted processes, in particular, for the bioconversion of CO2.
High pressure microbiology
Beyond physico-chemical systems, we are also interested in high-pressure microbiology for the study and the use of microorganisms from the deep biosphere. The contribution of rapid screening approaches brought by high-pressure microfluidics already allows us to reproduce in the laboratory the conditions encountered on the ocean floor or in deep geological environments. These tools are used to monitor the growth and to determine the metabolisms of extremophilic strains in situ and in real time. We are developing bio-assisted processes, in particular, for the bioconversion of CO2.
Germination – growth
The understanding of nucleation-growth phenomena is essential for the mastering of material synthesis. The methodology is based on the coupling of experimental and numerical approaches. In situ tools have been developed to understand material pre-nucleation, nucleation and growth stages. It is important to stress that supercritical conditions favor nucleation over growth.
TOOLS
The understanding of the THBC processes requires coupled experiment / numerical simulation approaches, through the development of reactors allowing in situ characterization and simulation tools.
In situ instrumentation and characterization
The Supercritical Fluids group has been developing for 25 years an original multi-scale instrumentation to study and implement fluids under pressure and temperature. Most of the reactors are designed and built in-house. The processes and tools developed enable the group to work in batch, semi-continuous or continuous mode. The technologies used in the group cover a wide range of processes, from microscales (microfluidics, 1 – 500 µl.min-1) through intermediate scales (millifluidics, 0.5 – 10 ml.min-1) to industrial pilot reactors (liter up to 100 l.h-1). In addition, we have the ability to access microgravity conditions (experiments in the “Zero G” airbus or in the ISS) in order to study transport phenomena close to the critical point (heat and matter). These phenomena are difficult to characterize on the ground because of the gravitational effects leading to a stratification in density of supercritical environments.
A wide range of in situ characterization techniques can be implemented within these reactors, in order to experimentally capture the mechanisms involved when using supercritical fluids, allowing process optimization to be carried out in real time. Several in situ and non-invasive characterization techniques are used, such as UV-visible, Raman or infrared spectroscopy, but also confocal microscopy, X-ray laminography and total X-ray scattering. The latter is of particular interest as it allows Pair Distribution Function analysis (PDF), giving information on the atomic organization of nanomaterials before crystallization.
CFD modelling and simulation
The large number of parameters that can influence supercritical processes for material synthesis makes it difficult to understand them solely by experimental means. Numerical simulation, taking into account all the physico-chemical phenomena (Thermo-Hydro-Nucleation-Growth), appears therefore as a complementary tool to better understand and, ultimately, to determine the experimental conditions, which are likely to significantly influence the nucleation and growth process of particles. The choice of using High Performance Computing (“High Performance Computing” – Notus code developed at the I2M laboratory https://notus-cfd.org/) makes it possible to propose simulations at a very fine description scale (down to the Kolmogorov scale for direct numerical simulations) for reactor sizes ranging from microliters (typically the microfluidic chip) to liters (typically the conventional laboratory reactor). The simulations, which require significant computing resources, are carried out in parallel on national supercomputers (GENCI, regional mesocentres) in order to reach acceptable computing times. The use of this type of tool is particularly original within the national and international “supercritical processes” community.
