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The present work investigates the permeation properties of Aquivion® perfluorosulfonic acid (PFSA) membranes, commercialized by Solvay Specialty Polymers, in view of its possible application in the field of natural gas separation or biogas sweetening. Results have been focused on the measurement of CH 4 , CO 2 , propane and butane permeabilities at different temperatures and relative humidity, focusing the attention on investigating the material performance for CO 2 separation in different experimental conditions. Aquivion®, similarly to other PFSA materials, is highly hydrophilic, and swells consistently in humid conditions increasing its gas permeability of more than one order of magnitude with respect to value prevailing in dry conditions. Present data confirm such a behavior being the permeability of all gases and vapors tested substantially increased in presence of water. Interestingly the increase in permeability results to be similar for all the gases inspected, hence such enhanced permeation capability is not associated to a selectivity loss, as usually happens in polymeric membranes. In humid condition, therefore, the ideal separation ability of Aquivion® is maintained, while the potential membrane productivity increases considerably. In addition to the experimental work, a simple model derived by the analysis of permeability in heterogeneous materials has been applied to the experimental data and showed to be suitable for the description of the observed behaviors for all the gases considered.

In this work, we studied CO 2 sorption and transport in two series of aliphatic-aromatic copolyimide membranes, as a function of chemical formulation, pressure and temperature. Such materials are formed by two distinct phases with rather different properties: the first one is formed of rubbery polyether segments (poly(propylene oxide) (PPO) or poly(ethylene oxide) (PEO)), characterized by favorable energetic interactions with CO 2 and high flexibility, which endows the copolymers with high CO 2 permeability, suitable for capture processes. The second phase is formed by hard glassy polyimide blocks, randomly distributed at the microscopic level, which provide the necessary thermal, chemical and mechanical stability. Previous studies indicate that CO 2 permeability increases with increasing the amount of polyether phase in the copolymers; in the present work we investigate more deeply the interactions and synergies occurring between the two phases, by focusing separately on the CO 2 solubility and diffusivity terms that contribute to permeability. In particular, by studying the shape of the solubility isotherm, as well as the values of diffusivity, sorption enthalpy and activation energy, we were able to monitor the transition from a glassy-like to a rubbery-like behavior as the fraction of rubbery component in the copolymer increases. The data indicate that polyether enhances CO 2 permeability by acting mostly on diffusivity, while the solubility contribution is less affected on a quantitative basis. However, the qualitative behavior of solubility allows understanding the nature of interactions between the two phases. In particular, by using a simple additive approach to estimate the CO 2 solubility of the copolymer, and the Non-Equilibrium Lattice Fluid (NELF) to evaluate the CO 2 solubility in the pure homopolymers, one concludes that the copolymers sorption behavior is “ideal”, i.e. purely additive, indicating a good combination of the two phases. The copolymer volume, on the other hand, shows a contraction upon combination of the two phases. The NELF modeling of solubility data allows attributing such a contraction only to the glassy phase, whose excess free volume is reduced in the presence of the rubbery portion in the copolymer, which possibly partly occupies such excess volume, indicating a strong interpenetration of the two phases.

The permeability of various low molecular weight species (both gases and vapors) in a series of glassy polymers has been extensively analyzed by means of a thermodynamic based approach for solubility and diffusivity, recently proposed and already applied to a few penetrant/polymer systems. The model relies on the thermodynamic description of the solubility behaviors of the solutes provided by the nonequilibrium thermodynamic model for glassy polymers (NET-GP), while the diffusivity is the product of the mobility coefficient, a purely kinetic quantity, and the thermodynamic factor, accounting for the dependence of the penetrant chemical potential on its concentration in the glassy polymer matrix. The model is applied to permeability data of many penetrant species from very light gases, such as hydrogen or helium, to hydrocarbons and fluorocarbons, in several different glasses, including very high free volume materials, polyimides and fluoropolymers. The model proved to be effective in the representation of all types of permeability behaviors with respect to penetrant upstream pressure, which may be either decreasing, increasing, or with a nonmonotonous trend showing a minimum value at the so-called plasticization pressure.

Solubility and permeability of gases in glassy polymers have been considered with the aim of illustrating the applicability of thermodynamically-based models for their description and prediction. The solubility isotherms are described by using the nonequilibrium lattice fluid (NELF) (model, already known to be appropriate for nonequilibrium glassy polymers, while the permeability isotherms are described through a general transport model in which diffusivity is the product of a purely kinetic factor, the mobility coefficient, and a thermodynamic factor. The latter is calculated from the NELF model and mobility is considered concentration-dependent through an exponential relationship containing two parameters only. The models are tested explicitly considering solubility and permeability data of various penetrants in three glassy polymers, PSf, PPh and 6FDA-6FpDA, selected as the reference for different behaviors. It is shown that the models are able to calculate the different behaviors observed, and in particular the permeability dependence on upstream pressure, both when it is decreasing as well as when it is increasing, with no need to invoke the onset of additional plasticization phenomena. The correlations found between polymer and penetrant properties with the two parameters of the mobility coefficient also lead to the predictive ability of the transport model.

The present invention relates to a process, and relevant plant (1), for separating at least one key component (KC) from a multicomponent gas stream (GS) that is caused to flow on a composite membrane (20) comprising dense domains (21) permeable to the key component (KC) and porous domains (22) intended to adsorb preferentially the key component (KC). A permeate stream (PS), separated from the multicomponent gas stream (GS) and containing the key component (KC), is extracted through a discharge line (5) depending on the measured value of the pressure (P) downstream the membrane (20), Upon reaching a predetermined maximum value (pmax) of such pressure (P), the permeate stream (PS) is extracted until reaching a predetermined minimum value (pmin) of such pressure (P) downstream the membrane (20), and upon reaching such predetermined minimum value (pmin), the extraction of the permeate stream (PS) is stopped. Thus by repeating such operations extracting and stopping the extraction downstream the membrane (20), alternated cycles are generated and a pseudo-steady state condition is accomplished, where the plant (1) receives the feed stream (GS) in the continuous mode and releases the permeate stream (PS) in an intermittent manner, while a retentate stream (RS), containing the components of the feed stream (GS) that have not been collected in the permeate stream (PS) is discharged with continuity. By handling the predetermined maximum value (pmax) and minimum value (pmin) of the pressure (P) downstream the membrane (20), that is of the extraction cycle of the permeate stream (PS), it is possible to considerably vary the efficacious permeance value and the separation factor of the process without modifying the membrane (20), the module (10) where it is contained or the feeding conditions.

Affinity membranes have been prepared by immobilizing D-PAM, a synthetic ligand that exhibits affinity for the Fc portion of antibodies, onto poliethersulfone microporous membranes. The ligand density has been measured and the ligand utilization was evaluated and compared with literature data available for chromatographic beads. The resulting new affinity membranes have been experimentally characterized and tested by using pure murine IgG solutions and mouse serum. Equilibrium and kinetic parameters have been obtained in batch experiments using pure protein solutions. The highest binding capacity measured for murine IgG was 45 microg/cm(2) obtained at 1.2 mg/mL protein concentration at equilibrium, while the maximum static binding capacity calculated with the Langmuir model was 81 microg/cm(2). The adsorption of murine IgG on the affinity membranes was described using different isotherms: Freundlich and Temkin models have been considered and critically compared with the Langmuir adsorption model. A dynamic binding capacity of 21 microg/cm(2) was obtained by feeding a solution of 0.3 mg/mL of murine IgG, confirming the results obtained in batch experiments at the same concentration. The affinity membranes considered are endowed with good binding capacity for murine IgG and good selectivity for immunoglobulins and can be considered for the capturing step of an antibody production process.

Recovery of antibodies with Protein A affinity chromatography columns has become the standard for the biotechnology industry. Membrane affinity chromatography has not yet experienced extensive application due to the lower capacity of membrane supports compared to chromatographic beads. In this work, new affinity membranes endowed with an interesting binding capacity for human IgG are studied in view of their application in the capturing step of a monoclonal antibody production process. The membranes have been extensively tested with pure IgG solutions and with a cell culture supernatant containing IgG1. The effects of feed flow rate and IgG concentration on the separation performances have been studied in detail, considering in particular binding capacity, selectivity and recovery. These new high capacity affinity membranes appear good candidates to avoid the throughput limitations and other well-known drawbacks of traditional bead-based chromatographic columns.

A mathematical model for the adsorption of biomolecules on affinity membranes is presented. The model considers convection, diffusion and adsorption kinetics on the membrane module as well as the influence of dead end volumes and lag times; an analysis of flow distribution on the whole system is also included. The parameters used in the simulations were obtained from equilibrium and dynamic experimental data measured for the adsorption of human IgG on A2P-Sartoepoxy affinity membranes. The identification of a bi-Langmuir kinetic mechanisms for the experimental system investigated was paramount for a correct process description and the simulated breakthrough curves were in good agreement with the experimental data. The proposed model provides a new insight into the phenomena involved in the adsorption on affinity membranes and it is a valuable tool to assess the use of membrane adsorbers in large scale processes.