Polymer Inclusion Membranes (PIM) for the Recovery of Potassium in the Presence of Competitive Cations

Potassium is an important nutrient used in fertilizers but is not always naturally available We investigated the properties of polymer inclusion membranes (PIM) regarding their selective recovery of K+ over competitive ions typically present in urine (Na+ and NH4+). The greatest flux was observed when the ratio of mass 2-nitrophenyl octyl ether (2-NPOE) used as plasticizer to cellulose triacetate (CTA) used as polymer was 0.25. The highest flux was achieved with a content of 24.8 wt % of dicyclohexan-18-crown-6 (DCH18C6) used as carrier, although the highest selectivity was observed with a content of 14.0 wt % of DCH18C6. We also studied whether the transport mechanism occurring in our system was based on co-transport of a counter-ion or ion exchange. Two different receiving phases (ultrapure water and 100 mM HCl) were tested. Results on transport mechanisms suggest that co-transport of cations and anions is taking place across our PIMs. The membrane deteriorated and lost its properties when the receiving phase was acidic; we suggested that this was due to hydrolysis of CTA. The greatest flux and selectivity were observed in ultrapure water as receiving phase

An easy method for the preparation of anion exchange membranes: Graft-polymerization of ionic liquids in porous supports

A novel way for anion exchange membrane (AEM) preparation has been investigated, avoiding the use of expensive and toxic chemicals. This new synthetic approach to prepare AEMs was based on the use of a porous polybenzylimidazole membrane as support in which functionalized ILs were introduced and subsequently grafted on the polymer backbone. These new AEMs were prepared and their chemical structures and properties including morphology, thermal stability, and ionic conductivity were characterized. The hydroxyl ionic conductivity of the synthesized membranes can reach values upto 6.62 × 10−3 S cm−1 at 20°C. Although the ionic conductivity is not very high yet, the work shows the strength of the concept. Membrane properties can be easily tailored toward specific applications by choosing the proper chemistry, i.e., porous polymer support, ionic liquid, and method of initiation and polymerizatio

Sorption induced relaxations during water diffusion in S-PEEK

This paper presents an analysis of the sorption kinetics of water vapor and liquid water in the glassy polymer sulfonated poly(ether ether ketone) (S-PEEK). Sorption isotherms are determined experimentally using a gravimetric sorption balance, and the relative contributions of Fickian diffusion and relaxational phenomena are quantified as a function of the water concentration in the polymer using the model of Hopfenberg and Berens.Analysis of the sorption isotherms and determination of the sorption kinetics prove the occurrence of both Fickian sorption behavior and relaxational phenomena already at very low water concentrations in the polymer. With increasing water concentration, the relative importance of relaxation phenomena increases, whereas the relative contribution of Fickian diffusion decreases.Based on the water vapor sorption kinetics only, the Fickian diffusion coefficient increases over two orders of magnitude with increasing water vapor concentration. Taking also the diffusion kinetics from liquid water sorption experiments into account reveals a change of even three orders of magnitude of the Fickian diffusion coefficient when the water concentration in the polymer increases

High pressure gas separation performance of mixed-matrix polymer membranes containing mesoporous FE(BTC)

Mixed-matrix membranes (MMMs), filled with inorganic particles, provide a means to improve the gas separation performance of polymeric membranes. In this work, MMMs containing the mesoporous metal organic framework (MOF) Fe(BTC) in a Matrimid®-PI matrix were characterized in terms of their carbon dioxide (CO2) and methane (CH4) separation performance at low and high pressures. Physical properties (density, thermal degradation, and glass transition) of Fe(BTC) and prepared MMMs were analyzed. An optimized priming and suspension mixing protocol resulted in a homogeneous distribution of MOF particles in the Matrimid®-PI matrix, as observed by scanning electron microscopy (SEM). Experimental results showed decreased thermal degradation but increased membrane density and glass transition with increased Fe(BTC) loading, as well as improvement in CO2 permeability and CO2/CH4 selectivity. At high pressures, the native Matrimid®-PI membrane showed typical plasticization behavior, but as the MOF loading increased gas transport properties seem to be controlled by MOF particles leading to reduced plasticization tendencies. The favorable performance of MOF containing membranes can be attributed to the strong increase in the sorption capacity and chain rigidity by the Fe(BTC) particles which suppressed plasticization. At a mixed gas feed pressure of 40 bar, MMMs with 30 wt% MOF showed a CO2/CH4 selectivity increase of 62% compared to the native Matrimid®-PI membrane, while the permeability was about 30% higher than that of native polyme

Performance and plasticization behavior of polymer–MOF membranes for gas separation at elevated pressures

Mixed matrix membranes (MMMs) based on three distinctively different MOFs (MIL-53(Al) (breathing MOF), ZIF-8 (flexible MOF) and Cu3BTC2 (rigid MOF)) dispersed in Matrimid®-PI have been investigated. MOF loading was varied between 0 wt% and 30 wt%. The fabricated MOF-MMMs were characterized for pure and binary gas mixture separations at low and high pressures and their performance in terms of CO2 permeability and CO2/CH4 selectivity was evaluated. The use of a less volatile co-solvent, optimized priming protocol to prepare the MMMs and thermal annealing resulted in a good dispersion of MOF particles in the Matrimid®-PI matrix. Incorporation of MOFs resulted in increased density, Tg and improved degradation behavior of the membranes confirming a good compatibility between the polymer and the MOFs. Low pressure gas separation showed moderate enhancement in CO2 permeability and CO2/CH4 selectivity of MOF-MMMs compared to native polymer membranes, but the improvement becomes pronounced at high pressures. At high pressures, the native Matrimid®-PI membrane showed typical plasticization behavior, while in MMMs, MOF particles limit the mobility of polymer chains thus suppressing CO2 induced plasticization and maintain large separation factors over a wide pressure range investigated. The respective increase in performance of MMMs is very much dependent on MOF crystal structure and its interactions with CO2 gas molecules. Among the three MOF-MMMs, membranes based on Cu3BTC2 showed highest selectivity while ZIF-8 based membranes showed highest permeability. In general it can be concluded that the high CO2 permeability and CO2/CH4 selectivity of MMMs is the combined effect of an increased sorption and diffusion selectivity and reduced plasticization. Overall, this work reveals that MOF-MMMs delay CO2 induced plasticization and show good separation performance even at high pressures, showing their potential to a wide range of newly emerging high pressure energy application