Elena Tocci

A highly permeable polyimide with enhanced selectivity for membrane gas separations

A highly gas permeable polyimide with improved molecular sieving properties is produced by using a bisanhydride monomer based on the rigid ethanoanthracene unit. The polymer (PIM-PI-EA) demonstrates enhanced selectivity for gas separations so that its gas permeability data lie above the 2008 Robeson upper bounds for the important O2–N2, H2–N2, CO2–CH4 and CO2–N2 gas pairs.

A molecular simulation study on gas diffusion in a dense poly(ether–ether–ketone) membrane

Abstract Results of molecular dynamics (MD) simulations on transport and solubility of small molecules in amorphous cardo poly–ether–ether–ketone membranes are discussed. Atomistic simulation techniques have proven to be a useful tool for the understanding of structure–property relationships of materials. Although MD are still not an ideal tool for the quantitative prediction of gas permeation properties, this methodology can be used for a detailed description of the complex morphologies and transport mechanisms associated with rigid glassy structures. The diffusion process results from jumps of penetrant molecules between adjacent holes in the polymer matrix. The free volume and the occurring jump mechanism are characterized and visualized with different methods. Constants of diffusion and solubility coefficients have been calculated by the Transition State Gusev–Suter Monte Carlo method revealing a considerable agreement between simulated and calculated data.

Thermal treatment effect on the structure and property change between hydroxy-containing polyimides (HPIs) and thermally rearranged polybenzoxazole (TR-PBO).

In this study, we report on the effect of thermal treatment on polyimide precursors (HPIs) and on the resulting thermally rearranged polybenzoxazole (TR-PBO) polymer membranes as investigated through the use of molecular dynamics (MD) simulations. For this purpose, we have first analyzed the structures of hydroxy-containing polyimides before thermal treatment and those of the thermally rearranged polybenzoxazoles after the thermal treatment, according to their temperature conditions. As expected, HPIs and TR-PBOs always show very limited motion of their polymer chains, indicated by the radius of gyration, due to their well-known thermal stability. In particular, the very rigid and stiff PBO linkages did not undergo significant change in their torsional angle distribution. On the other hand, in regards to intrachain movement, HPI chains were significantly affected by temperature. Their conformational changes were notably observed, which affected the distances between possible reaction sites, oxygen atoms in hydroxyl groups, and carbon atoms in the imido-ring. The free volume analysis, performed on both polymers and during thermal treatment, indicates that HPIs have a unimodal distribution of free volume areas, which partially coalesce in larger areas having, however, a relatively narrow size. Further, TR-PBO shows a bimodal cavity distribution, and after thermal treatment and TR reaction, the free volume structures in TR-PBO are maintained. The cavity size distributions determined by simulation were also consistent with free volume distributions determined by positron annihilation lifetime spectroscopy.

Diffusion of gases in PEEKs membranes: molecular dynamics simulations

Abstract Results of molecular dynamics (MD) simulations on transport process of small molecules in amorphous cardo poly-ether-ether-ketone membranes, namely PEEK-WC, sulfonated PEEK-WC and nitrated PEEK-WC are discussed. Atomistic simulations techniques have proven to be a useful tool for the understanding of structure–property relationships of materials and in particular MD can be used for detailed descriptions of the complex morphologies and transport mechanisms associated with rigid glassy structures. The diffusion process results from jumps of penetrant molecules between adjacent holes in the polymer matrix. The occurring jump mechanism is characterised and visualised. Constants of diffusion and solubility coefficients have been calculated by the transition state Gusev–Suter Monte Carlo (MC) method.

Physicochemical characterization of solute retention in solvent resistant nanofiltration: the effect of solute size, polarity, dipole moment, and solubility parameter.

Growing interest in nanofiltration for solvent purification requires a fundamental understanding of the physicochemical mechanisms of solute retention in organic solvent nanofiltration. In this study, the retention of a similar series of azo dyes with approximately similar molar mass (around 350 Da) by four nanofiltration membranes was studied. The membranes used are commercially available polymeric nanofiltration membranes with molecular weight cutoff between 150 and 300 Da (DuraMem150, StarMem122, NF270 and Desal-Dk). In order to correlate the retention with the size of the molecules, which is assumed to be one of the main factors that determines the retention, use was made of different parameters for the molecular size: molar mass, the Stokes diameter, the equivalent molar diameter, and the cavity surface in methanol and ethanol. All parameters were calculated by using molecular dynamics simulations. For each size parameter, the correlation with retention in nanofiltration experiments was calculated. For the StarMem122 membrane, zero retentions were observed due to the swelling of the membrane and pore size enlargement in methanol and ethanol. For the three other membranes, a fairly good correlation of the retention with the size could only be observed if the size difference between compounds is sufficiently large. Two other factors were studied by using molecular dynamics, i.e., the polarity of the molecule and the electron density of the molecule. The importance of these factors depends on the structure of the molecule as well as the functional groups of the polymer. A very good correlation has been observed for retention of dyes versus their dipole moment. Finally, the effect of solubility parameters of dyes on their retention did not show any significant effect.

A highly rigid and gas selective methanopentacene-based polymer of intrinsic microporosity derived from Tröger's base polymerization

Polymers of intrinsic microporosity (PIMs) have been identified as potential next generation membrane materials for the separation of gas mixtures of industrial and environmental relevance. Based on the exceptionally rigid methanopentacene (MP) structural unit, a Polymer of Intrinsic Microporosity (PIM-MP-TB) was designed to demonstrate high selectivity for gas separations. PIM-MP-TB was prepared using a polymerisation reaction involving the formation of Trogers base linking groups and demonstrated an apparent BET surface area of 743 m2 g−1 as a powder. The microporosity of PIM-MP-TB was also characterized by chain packing simulations. PIM-MP-TB proved soluble in chlorinated solvents and was cast as a robust, free-standing film suitable for gas permeation measurements. Despite lower gas permeability as compared to previously reported PIMs, high selectivities for industrially relevant gas pairs were obtained, surpassing the 2008 Robeson upper bound for H2/CH4 and O2/N2, (e.g., PO2 = 999 Barrer; αO2/N2 = 5.0) and demonstrating a clear link between polymer rigidity and selectivity. Upon aging, the permeability data move parallel to the Robeson upper bounds with a decrease of permeability, compensated by a related increase in selectivity. Mixed gas permeation measurement for CO2/CH4 and CO2/N2 mixtures confirmed the excellent selectivity of PIM-MP-TB for potentially relevant separations such as biogas upgrading and CO2 capture from flue gas. Importantly, unlike other high performing PIMs, PIM-MP-TB is prepared in four simple steps from a cheap starting material.

Pure And Modified Co‐poly(amide‐12‐b‐ethylene oxide) Membranes For Gas Separation Studied By Molecular Investigations

A combined experimental and theoretical study has been performed to investigate transport properties in a pure and modified poly(amide‐12‐b‐ethylene oxide) (PEBAX®2533) block copolymer membrane with N‐ethylo,p‐toluenesulphonamide (KET) as additive molecules. MD simulations using COMPASS force field, Gusev‐Suter Transition State Theory (TST) and Monte Carlo methods have been used. Bulk models of PEBAX®2533 and PEBAX/KET in different copolymer/additive compositions have been assembled and analysed to evaluate gas permeability and the morphology to characterize structure‐performance relationships.