Graphene oxide membranes for gas separation

Recently, the carbon based materials1 attracted attention of the scientific community for applications in membrane gas separation. Tremendous number of carbon based materials such as carbon nanotubes, chemically modified graphene, graphene oxide (GO) or graphite (nano)particles in mixed matrix membrane (MMM) composites was tested within past decade2. It was found that even small loading of graphene and (GO) additives, i.e. 0.05 to 1 wt.%3, led to considerable changes of composite materials properties (elastic modulus, tensile strength, electrical conductivity, and thermal stability) compared to neat polymers. Please click Additional Files below to see the full abstract

Aging of polymers of intrinsic microporosity studied by sorption and permeation

Polymers of intrinsic microporosity (PIMs)1 seem to be effective materials for gas and vapor separations.2 However, gas separation efficiency of PIMs can be strongly influenced by the material aging process connected with the changes of PIMs inner structure.3 With respect to potential industrial applications, the investigation of such changes and their effect on gas and vapor transport is necessary. In this work, we present a detailed study of i) CO2 sorption in PIM-1 via momentary measurements during four years and ii) methanol permeation in PIM-11 and EA-TB-PIM2 via continuous and momentary experiments. Sorption experiments were performed gravimetrically using a self-developed apparatus equipped with McBain’s spiral balances. In this case, PIM-1 membranes were pre-treated (soaking in ethanol with consequent drying at different temperatures) in order to study the influence of temperature on PIM-1 aging. Methanol permeation experiments were performed using a differential flow permeameter with H2 and He as carrier gases. Permeation experiment were performed with PIM-1 and PIM-EA-TB methanol treated membranes. CO2 sorption measurements revealed that, assuming the validity of the solution-diffusion model, the decrease of permeability during aging can be attributed directly to the decrease of diffusivity, whereas solubility is time independent in the studied period of four years. Although higher preparation temperature led to the initial drop of diffusivity, this process stabilized separation performance of PIMs over time (Figure 1). MeOH permeation experiments confirmed previous findings from CO2 tests, that the permeability decrease during the aging is a diffusivity controlled process. Moreover, it was found that the momentary permeation data can be mathematically transferred to continuous data, which are more relevant for applications but more difficult to measure. The nature of aging process was studied by infrared spectroscopy. We have found that aging of PIMs does not influence their chemical structure and; therefore, they undergo only the so called physical-aging. Please click Additional Files below to see the full abstract

Effect of physical aging on the gas transport and sorption in PIM-1 membranes

Understanding of the properties over long time scales is a key requirement for the successful application of novel polymers as membrane materials. In this light, the physical aging of dense PIM-1 films with different previous histories was monitored for more than 4 years via parallel gas sorption and permeability measurements. The effect of aging on the individual transport parameters, permeability, solubility and diffusivity, was studied on alcohol treated membranes with high excess free volume. Thermal conditioning of these membranes led to accelerated aging and a reduction of the initial gas permeability and diffusivity of the membranes. A long-term CO2 sorption analysis showed aging affected the sorption kinetics much more than the total equilibrium sorption. This was confirmed by permeation studies with six different gases, showing that the reduction of the permeability coefficient of the samples as a function of time is almost entirely due to a reduction of the diffusion coefficient. A renewed alcohol treatment of the aged membrane led to significant rejuvenation of the membrane. To the best of our knowledge, this is the first systematic long term aging study on PIM-1 via simultaneous analysis of sorption and permeation kinetics. Mixed gas permeation measurements with a CO2/CH4 mixture and an N-2/O-2/CO2 mixture confirm the excellent permselective properties of the PIM-1 membranes even after long aging