Modeling mass transport in dense polymer membranes: cooperative synergy among multiple scale approaches

The modeling description of basic transport phenomena of either liquid, gas or vapor molecules in dense polymeric membranes is of tremendous impact for the separation industry, which relies on solid models for the design of optimal process conditions, for the selection of the most suitable membrane materials as well as for the development of novel ones. Such models need to deal with several physical aspects and phenomena, spanning over broad time and length scales, thus requiring multiple approaches. The solid frameworks now available mainly rely on the solution–diffusion theory, in which equation of state models and free volume theories are applied for the description of thermodynamic and kinetic properties, to be coupled in appropriate transport schemes

Examination of Several physiochemical characteristics of underground water collected from various wells situated south Baghdad-IRAQ

Underground water is subjected to contamination due to the wastewater of different agricultural and industrial activities .This work was designed to examine several physiochemical variables of well water situated in southern land of Baghdad that already used in such activities. Water samples were collected from different wells in January and July 2014. It has found that mean pH value were varying from 7.1 ± 0.4 to 7.5 ± 0.7 and these values for EC were  1.24±0.09 to 2.5±0.19 while mean values of turbidity were ranged from 0.01±0.0 to 7.01±1.54 . Mean values of each of BOD, COD and DO have been found to range from 7.0±2.44 to 13.24, 13.3±3.33 to 68.0±11.7 and 3.1±2.6 to 7.5±3.22 respectively. However, water samples had mean value of PO4 within a range of 0.30±0.01 to 0.66±0.12 and the mean of SO4 was placed between 93±24.69 to 371±35.27. For each of Cl, Ca and Mg ions had given mean values in a range of 0.01±0.0 to 1.9±0.36, 70.0±21.51 to 98.0±28.72, and 80.1±13.51 to 100.5±25.62 respectively. It seems clearly that there was no significant (<0.05) differences between the collecting periods for all examined variables except for water EC where mean values were significantly (P?0.05) higher in July than that of January. However, similar insignificant differences were recorded between mean values of   tested underground water samples in terms of all physiochemical variables. The mean values of certain examined variables were well above than those of fresh water of both rivers and lakes such as EC, BOD and Mg ions while the mean values of pH and DO were found to be within the range of similar variables, but the remaining variables were much lower than those reported for raw water. Furthermore, turbidity in water sample of well 5 was extremely higher in July than those of the remaining wells either in January and July. Key words: Water contamination, underground water, physiochemical variables, fresh water, water standards

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

Exploring the membrane-based separation of CO2/CO mixtures for CO2 capture and utilisation processes: Challenges and opportunities

The separation and removal of CO2 from its mixtures with CO2 is gaining increasing interest due to the novel processes in which these two gases are mixed, such as the non-thermal plasma activated reaction of CO2 splitting, a promising CO2 utilisation route that could be performed using renewable energy. The aim of this review is to propose a novel database suitable for membrane scientists to evaluate the feasibility of membrane-based separation processes involving such gas mixture, not included in the original Robeson’s works on the upper bound, nor in later developments. For this reason, we reviewed the data on the permeation, diffusion and sorption of these two gases in different classes of polymers, from polyolefins to polyimides and green polymers, spanning over a wide range of permeability values. Furthermore, we propose an upper bound for this separation, and provide a theoretical explanation for it. The separation mechanism is solubility-driven, and all polymeric membranes inspected in the literature show a CO2-selective behaviour, despite a very limited, or unfavourable, diffusion selectivity for CO2, which is consistent with empirical correlations. Consequently, the observed selectivity values are determined by the solubility-selectivity and are comprised mainly in the range 7–20, in agreement with known empirical correlations between the solubility and the critical temperature of the penetrants. Temperature has a detrimental effect onCO2/CO selectivity, as the activation energy for permeation of CO2 is always lower than that of CO. In general, while the permeability can vary over several orders of magnitude depending on the polymer nature, selectivity mostly ranges between 7 and 20, which makes the trade-off mechanism between permeability and selectivity rather weak in the case of this mixture. Such an effect provides a wider variety of design choices, and makes this separation attractive for polymeric membranes, if carried out at low temperatures and with CO2-philic materials. A preliminary calculation of the separation obtainable with single-stage membrane unit for a binary mixture is carried out for some representative polymers

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

How to describe and predict plasticization in glassy polymeric membranes for gas separations

In glassy polymeric membranes, gas permeability shows different trends as upstream pressure increases, including the monotonous decline, a monotonous increase, as well as an initial decline followed by a subsequent increase after a minimum permeability value is reached. The minimum value, whenever present, occurs at a pressure conventionally indicated as the plasticization pressure. It is currently accepted that permeability behavior can be conveniently well described by a transport model only below plasticization pressure, while above that value the onset of additional phenomena at higher pressures are responsible of the observed increase in permeability and decrease in selectivity. On the other hand, the plasticization phenomenon has not been further inspected thus far, in terms of material property variations. With the aim to reach to a deeper understanding of the phenomenon, we have experimentally inspected the behavior of Matrimid polyimide membranes, by analyzing both transport and mechanical properties. The permeability behavior and the “plasticization” effects induced by CO2 have been studied by increasing the upstream pressure at different fixed values of downstream pressure. The mechanical properties studied include elastic modulus and viscoelastic response of samples saturated at different CO2 pressures up to and above plasticization pressure. The trends obtained are rather interesting and actually not fully in line with what expected based on the current qualitative interpretation. We also show that the observed gas permeability behavior can be described by considering only a solution-diffusion model in which the penetrant mobility varies with its concentration in the polymer matrix through an exponential law, with two adjustable parameters only. Diffusivity is thus taken as the product of molecular mobility and a thermodynamic factor, calculated by using the NELF model for thermodynamic properties of the glassy phase. It is observed that by fitting the only two adjustable parameters to the initial branch of the permeability isotherm, the above solubility diffusivity model allows the prediction of the plasticization pressure, at all values of downstream pressures used, without introducing any additional physical phenomenon. The agreement observed between model calculations and experimental data of CO2 permeability in Matrimid, as well as in various glassy polymers, is very satisfactory. That allows us to offer a deeper insight on the so-called plasticization phenomenon. The analysis of the permeability and the solubility isotherms, and the evaluation of concentration and swelling profiles in the membrane, show that in some cases the plasticization phenomena take place after part of the membrane has turned into rubbery phase. However, in other relevant cases as in Matrimid, the minimum in permeability is observed when the entire membrane is still glassy (and characterized by mechanical behavior comparable to the pure “dry” material), but with a polymer swelling sufficient for a permeability increase. Finally, it is observed that all parameters used have a defined independent physical meaning, which might lead to the development of general correlations with both polymer and penetrant properties, based on which permeability predictions can be obtained

Study on ammonia transport and separation in Aquivion® perfluoro sulfonated acid membranes

The present study reports the results of a series of sorption and permeation tests of pure ammonia as well as nitrogen and hydrogen carried out on Aquivion C87-05 (short-side chain perfluoro sulfonic acid ionomer). Such material is indeed of interest for possible applications in sustainable processes for ammonia production, either as base material for polymer electrolyte membranes in low-temperature electrochemical ammonia synthesis or as a membrane for effective product separation. NH3, N2, and H2 permeation tests are performed at different temperatures (20, 35, and 50 ◦C) and both in dry and humid conditions (R.H. up to 80%), aiming to assess the influence of these parameters on the resulting permeabilities, while ammonia sorption is inspected at the same temperatures, and pressures up to near saturation conditions. Pure ammonia permeability reached outstanding values around 7000 Barrer in dry Aquivion membranes, revealing an increasing trend with upstream pressure, while it decreased with temperature. The same behavior is recorded for NH3 solubility, indicating that sorption drives the ammonia transport through the membrane. The obtained separation performances are found to be significantly better than those of other polymeric membranes proposed for the same separations, as compared to a permeability-selectivity plot

Geopolymer-zeolite composites for CO2 adsorption

Geopolymer-zeolite composites were produced mixing different geopolymer matrices with a synthetic commercial Na13X zeolite, to combine the functional microporosity of the zeolite with the mesoporosity of the geopolymer matrix, with the further possibility to consolidate the zeolite powder. The new materials were designed and produced in forms of monoliths to be used as adsorbents for low temperature CO2 capture applications. A potassium or sodium silicate activating solution was used to produce the metakaolin-based geopolymer matrices, then mixed with the synthetic zeolite used as a filler. As geopolymers can be regarded as the amorphous counterpart or precursor of crystalline zeolites, it is important to underline the chemical affinity between these two constituents. As a matter of fact, the morphological characterization evidenced the presence of geopolymer nanoprecipitates covering zeolite particles for the K-based composite, while in the Na-based composite the formation of a NaA zeolite phase was evidenced (Fig. 1). Please click Additional Files below to see the full abstract