Porous liquids – Future for CO2 capture and separation?

Abstract Porous liquids form a new class of materials, which are liquid at room temperature and possess permanent porosity. The latter is a characteristic generally associated with solid-state only. Since the idea of porous liquid was exploited over a decade ago, the researchers see an opportunity of solving the solid material's limitation in gas capture and separation. In this discussion, we present the most recent developments on porous liquids and, in our perspectives, how they can tackle energy and environmental issues by their coupling with membrane technology. In a broader context, the need to reduce greenhouse gas, chlorofluorocarbons and other gaseous emissions is essential for tackling climate change and to achieve the 2015 Paris Agreement goals. In addition, the energy used for chemical separations in industrial processes accounts for 10–15% of the world's energy consumption. Thus, improved separation technologies will reduce energy consumption and the spreading of negative-emission technologies such as carbon capture sequestration and utilization (CCSU). Despite the imperative necessity of CCSU, many candidates are still considered the key technology due to the complex balancing between economic, technical and ecological advantages and drawbacks. Porous materials, which are usually solids, are of great interest for absorption due to the presence of permanent cavities, but liquids are easier to handle at the industrial scale. Porous liquids are a good compromise between these two traditional classes of materials

Computational and experimental studies on membrane-solute interactions in desalination systems using ion-exchange membranes

Des études antérieures ont mis en évidence que le transfert de solutés neutres à travers des membranes est influencé par la présence d'ions en solution. Ainsi, la connaissance des interactions multiples à l'échelle nanométrique, entre le polymère, l'eau et les solutés (ions, espèces organiques) constituent un verrou pour l'amélioration des performances des procédés membranaires. Dans cette étude une approche multi-échelle fondamentale est proposée, combinant des outils théoriques et expérimentaux, afin d'obtenir les paramètres microscopiques et macroscopiques caractérisant les interactions étudiées pour différentes compositions ioniques. Plus précisément, il s'agit de comprendre comment les ions affectent le transfert d'un soluté organique. Dans un premier temps, certaines propriétés caractérisant l'hydratation des ions sont calculées et comparées aux flux de diffusions de sucres à travers des membranes de Nanofiltration et échangeuses d'ions obtenus pour différentes compositions ioniques. Dans un deuxième temps, des systèmes constitués d'une membrane échangeuse de cations (CMX) équilibrée avec différents cations ainsi que le glucose hydraté sont modélisés en utilisant une approche combinée Mécanique Quantique/ Mécanique Moléculaire. Cette approche a permis d'étudier la solubilité du sucre dans la matrice polymère ainsi que les interactions polymère-polymère comme l'énergie de cohésion. Enfin, l'influence des ions sur les caractéristiques physiques de la membrane CMX est étudiée en utilisant diverses méthodes expérimentales comme la détermination des angles de contacts et des spectres IR ou la mesure de la température de solidification par DSC. Les propriétés vibrationnelles sont également calculées dans le cadre de la théorie de la fonctionnelle de la densité (DFT). L'ensemble de ces données sont comparées avec les grandeurs de transport afin de valider les mécanismes moléculaires proposés. Ce travail montre que la nature des contre-ions de la membrane modifie l'énergie de cohésion entre les fragments de la membrane. Ainsi, l'énergie de cohésion influe sur la diffusion des composés organiques neutres à travers les membranes.Previous works have shown that the transfer of neutral solutes through membranes is influenced by the presence of ions in solution. In the framework of process intensification, the knowledge of the molecular mechanisms involved is of fundamental importance to increase and predict the process performances. The aim of this Thesis is to use a combined quantum/molecular computational approach and experimental methodologies to better understand how ions can affect the solute flux. In the first part of the work, some properties of ions in solution are computed and compared with sugar fluxes through membranes for nanofiltration and electrodialysis. In the following, systems composed of Cation-exchange membrane equilibrated by different counter-ion and hydrated glucose are examined by Quantum Mechanics/Molecular Mechanics. This is done mainly to investigate the sugar solubility in the polymer matrix and diffusion related interactions like polymer chain-chain cohesion energy. In the last part, contact angle, differential scanning calorimetry and Infra-Red spectra are measured to characterize the physical properties of the membrane and possible influence of the counter-ion on cation exchange membrane. This work shows that the nature of the counter-ions modifies the cohesion energy between the membrane polymer fragments. In its turn, the cohesion energy affects the diffusion of neutral organic compounds through the membranes

Correlation between macroscopic sugar transfer and nanoscale interactions in cation exchange membranes

Previous experimental work has shown that the transfer of organic solutes through ion-exchange membranes depends on the membrane counter-ion and that this dependence is probably linked to the interactions taking place at the nanoscale inside the membrane matrix. In this paper, a computational approach is carried out, combining quantum mechanics and molecular mechanics to determine the interactions occurring at the nanoscale, taking a cation exchange membrane as example. Building blocks are first accurately studied at high level of quantum theory, before being merged in macromolecular models. The computed interactions are then compared to the experimental values of the solute flux in order to point out the nanoscale mechanisms governing the solute transfer. The computed glucose-polymer fragment interactions, related to the sugar solubility inside the membrane, are found to be almost independent from the membrane counter ion. On the contrary, significant variations of the chain-chain interaction, i.e. the interaction energies per trapped water molecule or hydrogen bonding wire connecting the polymer fragments, were observed according to the cation. Moreover, a correlation was pointed out with the experimental sugar fluxes obtained with 3 different sugars. Increasing chain-chain interactions inside the membrane was found to give decreasing sugar flux. Then this work shows that the cohesion energy between the polymer fragments fixes the dependence of the sugar flux versus the membrane counter-ion. The crucial role of the water molecules coordinating the cations is also highlighted

Structural properties of cation exchange membranes: characterization,electrolyte effect and solute transfer

Experimental investigations have shown that the presence of electrolytes has a strong influence on the transfer of neutral organic solutes through ion exchange membranes used in electrodialysis. It was further demonstrated that this influence is due to the impact of the membrane counter-ions on the noncovalent interactions existing between the hydrated and charged polymer chains in the membrane. The aim of this work is to investigate the structural properties of hydrated CMX membranes equilibrated with different counter-ions. Different methods, such as Infrared spectra (IR), contact angle and Differential Scanning Calorimetry (DSC) measurements, were used to characterize the membrane samples soaked in different electrolytes. In addition, IR spectra were calculated using a quantum mechanics approach and compared with the experimental ones. Shifts of characteristic IR peaks as function of membrane ionic form were observed in both experimental and computed spectra. Both spectra present shifts to lower wavenumber in presence of cations with higher hydration number. The contact angle of CMX membranes also increases in presence of more hydrated ions revealing a decrease of the hydrophilicity of the membrane. Concerning DSC, the freezing temperature of the water entrapped in the membrane polymeric network soaked with different electrolytes was measured. A shift at lower temperature was found for more hydrated trapped ions. The computational and experimental membrane structural properties were correlated with the corresponding transfer properties (sugar fluxes) and a good agreement was obtained

Scheduling: modelli, algoritmi e simulazione

A partire da una classificazione dell’architettura delle linee produttive, viene proposto un caso applicativo per mostrare le potenzialità degli algoritmi di simulazione delle sequenze di operazioni su un determinato parco macchin

Microporous Organic Polymers: Synthesis, Characterization, and Applications

The presence of a certain degree of porosity in polymers is a feature that provides them with unique properties and with opportunities to be exploited in a number of technologically important applications [...

Plastic breeze: Volatile organic compounds (VOCs) emitted by degrading macro- and microplastics analyzed by selected ion flow-tube mass spectrometry

Pollution from microplastics (MPs) has become one of the most relevant topics in environmental chemistry. The risks related to MPs include their capability to adsorb toxic and harmful molecular species, and to release additives and degradation products into ecosystems. Their role as a primary source of a broad range of harmful volatile organic compounds (VOCs) has also been recently reported.In this work, we applied a non-destructive approach based on selected-ion flow tube mass spectrometry (SIFT-MS) for the characterization of VOCs released from a set of plastic debris collected from a sandy beach in northern Tuscany.The interpretation of the individual SIFT-MS spectra, aided by principal component data analysis, allowed us to relate the aged polymeric materials that make up the plastic debris (polyethylene, polypropylene, and polyethylene terephthalate) to their VOC emission profile, degradation level, and sampling site. The study proves the potential of SIFT-MS application in the field, as a major advance to obtain fast and reliable information on the VOCs emitted from microplastics. The possibility to obtain qualitative and quantitative data on plastic debris in less than 2 min also makes SIFT-MS a useful and innovative tool for future monitoring campaigns involving statistically significant sets of environmental samples

Correlation between Computed Ion Hydration Properties and Experimental Values of Sugar Transfer through Nanofiltration and Ion Exchange Membranes in Presence of Electrolyte

The widespread use of nanofiltration and electrodialysis membrane processes is slowed down by the difficulties in predicting the membrane performances for treating streams of variable ionic compositions. Correlations between ion hydration properties and solute transfer can help to overcome this drawback. This research aims to investigate the correlation between theoretically evaluated hydration properties of major ions in solution and experimental values of neutral organic solute fluxes. In particular, ion hydration energies, coordination and hydration number and the average ion-water distance of Na+, Ca2+, Mg2+, Cl− and SO42− were calculated at a high quantum mechanics level and compared with experimental sugar fluxes previously reported. The properties computed by simple and not computationally expensive models were validated with information from the literature. This work discusses the correlation between the hydration energies of ions and fluxes of three saccharides, measured through nanofiltration and ionic-exchange membranes. In nanofiltration, the sugar flux increases with the presence of ions of increasing hydration energy. Instead, inverse linear correlations were found between the hydration energy and the sugar fluxes through ion exchange membranes. Finally, an empirical model is proposed for a rough evaluation of the variation in sugar fluxes as function of hydration energy for the ion exchange membranes in diffusion experiment

Glassy PEEK‐WC vs Rubbery Pebax®1657 Polymers: Effect on the Gas Transport in CuNi‐MOF Based Mixed Matrix Membranes

Mixed matrix membranes (MMMs) are seen as promising candidates to overcome the fundamental limit of polymeric membranes, known as the so‐called Robeson upper bound, which defines the best compromise between permeability and selectivity of neat polymeric membranes. To overcome this limit, the permeability of the filler particles in the MMM must be carefully matched with that of the polymer matrix. The present work shows that it is not sufficient to match only the permeability of the polymer and the dispersed phase, but that one should consider also the individual contributions of the diffusivity and the solubility of the gas in both components. Here we compare the gas transport performance of two different MMMs, containing the metal-organic framework CuNi‐MOF in the rubbery Pebax®1657 and in the glassy poly(ether‐ether‐ketone) with cardo moiety, PEEK‐WC. The chemical and structural properties of MMMs were investigated by means of FT‐IR spectroscopy, scanning electron microscopy and EDX analysis. The influence of MOF on the mechanical and thermal properties of both polymers was investigated by tensile tests and differential scanning calorimetry, respectively. The MOF loading in Pebax®1657 increased the ideal H2/N2 selectivity from 6 to 8 thanks to an increased H2 permeability. In general, the MOF had little effect on the Pebax®165 membranes because an increase in gas solubility was neutralized by an equivalent decrease in effective diffusivity. Instead, the addition of MOF to PEEK‐WC increases the ideal CO2/CH4 selectivity from 30 to ~48 thanks to an increased CO2 permeability (from 6 to 48 Barrer). The increase in CO2 permeability and CO2/CH4 selectivity is maintained under mixed gas conditions