Modelling Sorption and Transport of Gases in Polymeric Membranes across Different Scales: A Review

Professor Giulio C. Sarti has provided outstanding contributions to the modelling of fluid sorption and transport in polymeric materials, with a special eye on industrial applications such as membrane separation, due to his Chemical Engineering background. He was the co-creator of innovative theories such as the Non-Equilibrium Theory for Glassy Polymers (NET-GP), a flexible tool to estimate the solubility of pure and mixed fluids in a wide range of polymers, and of the Standard Transport Model (STM) for estimating membrane permeability and selectivity. In this review, inspired by his rigorous and original approach to representing membrane fundamentals, we provide an overview of the most significant and up-to-date modeling tools available to estimate the main properties governing polymeric membranes in fluid separation, namely solubility and diffusivity. The paper is not meant to be comprehensive, but it focuses on those contributions that are most relevant or that show the potential to be relevant in the future. We do not restrict our view to the field of macroscopic modelling, which was the main playground of professor Sarti, but also devote our attention to Molecular and Multiscale Hierarchical Modeling. This work proposes a critical evaluation of the different approaches considered, along with their limitations and potentiality

Modelling Sorption and Transport of Gases in Polymeric Membranes across Different Scales: A Review

Professor Giulio C. Sarti has provided outstanding contributions to the modelling of fluid sorption and transport in polymeric materials, with a special eye on industrial applications such as membrane separation, due to his Chemical Engineering background. He was the co-creator of innovative theories such as the Non-Equilibrium Theory for Glassy Polymers (NET-GP), a flexible tool to estimate the solubility of pure and mixed fluids in a wide range of polymers, and of the Standard Transport Model (STM) for estimating membrane permeability and selectivity. In this review, inspired by his rigorous and original approach to representing membrane fundamentals, we provide an overview of the most significant and up-to-date modeling tools available to estimate the main properties governing polymeric membranes in fluid separation, namely solubility and diffusivity. The paper is not meant to be comprehensive, but it focuses on those contributions that are most relevant or that show the potential to be relevant in the future. We do not restrict our view to the field of macroscopic modelling, which was the main playground of professor Sarti, but also devote our attention to Molecular and Multiscale Hierarchical Modeling. This work proposes a critical evaluation of the different approaches considered, along with their limitations and potentiality

Development of Atomistic Potentials for Silicate Materials and Coarse-Grained Simulation of Self-Assembly at Surfaces

This thesis is composed of two parts. The first is a study of evolutionary strategies for parametrization of empirical potentials, and their application in development of a charge-transfer potential for silica. An evolutionary strategy was meta-optimized for use in empirical potential parametrization, and a new charge-transfer empirical model was developed for use with isobaric-isothermal ensemble molecular dynamics simulations. The second is a study of thermodynamics and self-assembly in a particular class of athermal two-dimensional lattice models. The effects of shape on self-assembly and thermodynamics for polyominoes and tetrominoes were examined. Many interesting results were observed, including complex clustering, non-ideal mixing, and phase transitions. In both parts, computational efficiency and performance were important goals, and this was reflected in method and program development

Mass and Charge Transport in Hydrated Polymeric Membranes

Mass and charge transport through hydrated polymer membranes has significant importance for many areas of engineering and industry. Multi-scale modeling and simulation techniques were used to study transport in relation to two specific membrane applications: (1) food packaging and (2) additives for polymer electrolytes. Chitosan/chitin films were studied due to their use as a sustainable, biodegradable food packaging film. The effects of hydration on the solvation, diffusivity, solubility, and permeability of oxygen molecules in these films were studied via molecular dynamics and confined random walk simulations. With increasing hydration, the membrane was observed to have a more homogeneous water distribution with the polymer chains being fully solvated. Insight from this work will help guide molecular modeling of chitosan/chitin membranes and experimental synthesis of these membranes, specifically highlighting efforts to chemically tailor chitosan membranes to favor discrete as opposed to continuous aqueous domains to help reduce oxygen permeability. Additives for proton exchange membranes (PEMs) were studied to aid in the developing next-generation membrane materials for fuel cell applications. We calculate and present predictions of our analytical model that describes the fundamental relationship between the nanoscale structure of PEMs and their proton conductivity using a set of structural descriptors, accounting for nanopore size, functionalization and connectivity in order to predict proton conductivities in PEMs. The model reproduces experimentally determined conductivities in two current PEM materials. To extend the model based on structural descriptors of PEMs, we studied polyethylene glycol (PEG), a polymer used in electrochemistry applications due to it hydrophilicity and pH-dependent behavior in aqueous environments. We conducted ab initio molecular dynamics simulations of an excess proton in bulk water and aqueous triethylene glycol (TEG) solution and reactive molecular dynamics simulations of an excess proton in bulk water, aqueous TEG solution, and aqueous PEG solution. We determined differences in protonic defect structures, kinetics, thermodynamics, and hydrogen-bond networks associated with structural diffusion between systems. Driving forces for polymeric membrane design goals include economics, efficiency, energy consumption and sustainable production. Insight from this work hopes to aid in determining key design parameters and reduce time-to-discovery for developing next-generation polymeric membranes

Molecular Simulation of Diffusive Mass Transport in Porous Materials

Ever increasing control over the shape and form of a material's nanoscale features provokes the pursuit of a detailed understanding for the main factors influencing fluid transport. It is sought to facilitate the intelligent design of novel materials used in membrane separation processes. In addition to a strong dependence on molecular mobility, mass transport is heavily influenced by thermodynamic effects. Isolating thermodynamic and mobility effects is useful to understand the significant driving forces for mass transport through porous materials and their selective characteristics. However, experimental techniques are limited in probing this behaviour at the nanometre scale. In response to experimental challenges, the present study makes extensive use of the ability of molecular simulations to reflect the molecular character of nanoscale diffusion and identify equilibrium and transport properties individually. First, this work investigates diffusive mass transport inside a planar slit pore focusing on the influence of solid-fluid interactions, pore width, and fluid density. The influence of solid-fluid interactions, in particular, have often been neglected in studies of mass transport in porous solids. The vast variety of functionalised nano-materials is virtually endless and has spurred interest in this area. Equilibrium simulations were employed to determine self- and collective diffusivities and Grand Canonical insertions were used for the determination of thermodynamic factors. In addition, this work showcases the implementation of a highly efficient Non-Equilibrium Molecular Dynamics (NEMD) method through which effective transport was studied. The method was used to determine effective diffusivities which incorporate thermodynamic effects, the dominating contribution to transport for dense fluids. It is well suited to observe effective fluid transport in confined spaces as opposed to measuring self-diffusion, a measure for single-particle mobility only. The method is effective in studying mass transport in model systems as well as more realistic, complex geometries. As a second exemplary case, gas permeation through an atomistically detailed model of a high free-volume polymer was simulated explicitly with the NEMD approach. In addition to determining permeability and solubility directly from NEMD simulations, the results also shed light on the permeation mechanism of the penetrant gases, suggesting a departure from the expected pore-hopping mechanism due to the considerable accessibility of permeation paths.Open Acces

Thermodynamic and Molecular Simulation of Pure and Mixed Gas Sorption in Polymeric Membranes

The characterization of polymeric membranes for gas separation is often performed with pure-gas tests, which are poor predictors of the performance at multicomponent conditions. In this work, the Non-Equilibrium Lattice Fluid (NELF) model was applied to study mixed-gas sorption in traditional glassy polymers employed for CO2/CH4 separation, such as Cellulose Acetates, and innovative ones, such as polyimides (HAB-6FDA), Thermally Rearranged (TR) Polymers and Polymers of Intrinsic Microporosity (PIMs). The model results were validated against experimental data. Strong nonidealities are observed, due to competitive sorption and penetrant induced swelling, that radically modify the gas transport at multicomponent conditions compared to pure-gas cases. These effects were correctly predicted by the model, as well as temperature, pressure and concentration effects. The Dual Mode Sorption (DMS) model was tested for the same systems and a sensitivity analysis of its parameterization procedure revealed great uncertainty associated to its predictions of multicomponent sorption. A new measurement protocol was developed for the determination of sorption isotherms for gas mixtures with an arbitrary number of components. Mixed-gas sorption of binary C2H6/CO2 and C2H6/CH4 mixtures and of ternary C2H6/CO2/CH4 mixtures in PIM-1 was measured with this technique, finding strong competitive effects related to the presence of ethane. Predictions of the NELF model for binary and ternary sorption, performed using only pure-gas parameters as input, were in good agreement with the experimental data. Predictive Molecular Dynamics simulations were carried out to investigate the effect of CO2 up to high concentration on several properties of a polymeric material. A systematic evaluation of thermodynamic and structural properties, local dynamics, gas solubility and diffusivity yielded good agreement with the experimental data and meaningful trends with respect to temperature, gas concentration and polymer molecular weight were obtained, thus confirming the possibility to investigate the properties of materials at the molecular level with great accuracy

Flocculation kinetics using Fe(III) coagulant in water treatment: the effects of sulfate and temperature

This research focuses on the use of ferric nitrate as a coagulant to study flocculation kinetics including the fundamental mechanisms of orthokinetic flocculation, the impact of low water temperature, and the effect of sulfate ion. The kinetics of flocculation was studied for systems of kaolin dispersions destabilized by ferric nitrate coagulant in an 18 liter batch reactor under tightly controlled treatment conditions. Detailed measurement of the flocculation kinetics was done by assessing the rate of changes in total particle number concentration with an Automatic Image Analysis (AIA) system and by measuring the degree of turbidity fluctuation in a flowing suspension by a Photometric Dispersion Analysis (PDA) instrument;The overall objective of this research was (1) to investigate the kinetics of flocculating kaolin clay in water suspension under a number of treatment conditions, (2) to assess the effect of temperature on flocculation kinetics, spanning the full range of coagulation domains including the A/D and sweep floc mechanisms of coagulation, and (3) to investigate the role of sulfate ion in flocculation kinetics at two different temperatures;The conclusions of the flocculation kinetics studies using the 18 liter batch reactor are as follows: (1) Both the particle size distribution data obtained from the AIA and the on-line measurement of turbidity fluctuation by the PDA provided reliable and sensitive indications of flocculation kinetics. The AIA at high magnification gave the best indication of the primary particle disappearance, whereas, the PDA ratio values gave the best indication of the larger floc formation. (2) Sulfate ion added to the kaolin suspension played an important role in the flocculation process, not only in improving flocculation kinetics at more acidic pH levels at warm and cold water temperatures, but also in changing the surface charge of the particles. (3) Low water temperature had the pronounced effect on flocculation kinetics, slowing the rate of flocculation and enhancing the charge neutralizing ability of Fe(III) coagulant. The detrimental effect on the rate of flocculation was especially evident in the formation of larger aggregates as revealed by the PDA analysis. (4) The use of constant pOH at 5∘C and/or added sulfate ion was found to be partially effective for reducing the impact of low temperature on flocculation kinetics, but only in the acidic pH range studied (pH 6.0 to 6.8), but even under optimal adjustment of these provisions, the flocculation kinetics did not match the room temperature kinetics

En route to the industrial applications of ionic liquids for metal oxide production and biomass fractionation: A sustainable avenue to advanced materials

In the context of climate change, it is essential to use renewable materials and to reduce the environmental footprint of industrial processes. This work focuses on the feasibility of implementing a low-cost Ionic Liquid (IL) in a large-scale biorefinery for bioethanol production (the ionoSolv process). The selected feedstock was Eucalyptus red grandis, a fast-growing hardwood. The lignocellulosic biomass was fractionated at laboratory scale, using aqueous N,N,N-trimethylammonium hydrogen sulfate (20 wt% water), at different temperatures and reaction times, to maximize glucose recovery (86%). Experiments under CO2 atmospheres (sub and supercritical) revealed that the ionoSolv process is pressure insensitive. A detailed Techno-Economic Analysis (TEA) for a biorefinery using the ionoSolv pretreatment was performed and compared to one using the acid-catalysed steam explosion pretreatment. With the ionoSolv pretreatment, the composition of the cellulose-rich pulps can be tailored and high-purity lignins can be recovered. The economic performance of both pretreatments are similar. From a sustainability perspective there are trade-offs: the ionoSolv process consumes 25% more energy (with potential for optimization) but consumes less chemicals and produces less waste. These results indicate that this process can be a competitive alternative. During the development of this process, and other IL-based processes, the interaction of ILs (neat and aqueous) with metals was investigated to establish suitable materials of construction. It was observed that the corrosion behaviour of metals exposed to ILs is system dependent. Surprisingly, water can act either as a corrosion inhibitor or promoter. A semi-quantitative classification method for the different corrosion behaviours observed was developed. Some metals exposed to aqueous ILs formed particles, resulting in the inadvertent development of a novel process for metal-based materials at large-scale: Oxidative Ionothermal Synthesis (OIS). A high-level TEA suggests that OIS offers economic and environmentally advantageous production of bulk and advanced metal-based materials, such as zinc oxide.Open Acces