Aleksandra Janusz-Cygan

This study presents interphase-engineered Pebax-based thin composite membranes incorporating magnetite-zeolitic imidazolate framework-8 (Fe3O4@ZIF-8) hybrid fillers for highly selective CO2/N2 separation under dry and humid conditions. The combined effects of filler loading, operating humidity and pressure, and magnetic-field-assisted membrane formation were systematically investigated to elucidate their impact on gas transport behaviour. The optimized membrane, containing 4 wt.% Fe3O4@ZIF-8, fabricated under an external magnetic field, achieved an outstanding CO2/N2 selectivity of 117.9 with a corresponding CO2 permeability of 34.2 Barrer under humid conditions. These enhancements are attributed to magnetic alignment-induced interphase engineering, leading to the formation of rigid Pebax regions that preferentially suppress N2 transport over CO2, resulting in an overall decrease in gas permeability accompanied by a pronounced increase in selectivity. Furthermore, Fe3O4 nanoparticles promote a differential-sorption effect, limiting N2 transport, while the ZIF-8 frameworks contribute molecular sieving, synergistically enhancing separation performance. Comprehensive structural and physicochemical characterisation using scanning electron microscopy (SEM), differential-scanning calorimetry (DSC), and positron annihilation lifetime spectroscopy (PALS) reveals a clear correlation between morphology, free-volume architecture, and gas-transport properties.

Biomethane is one of the controllable Renewable Energy Sources. It may be derived from biogas, a multicomponent gas mixture, using, among others, membrane processes. The proper optimization of such a process requires the knowledge of the phenomena accompanying each specific biogas–membrane separation system. Therefore, the solubility, permeance and diffusion of CO₂, CH₄, O₂ and N₂ in a polyimide-based sample were described and analyzed using the Dual Mode Sorption and partial immobilization models. The parameters of the models were determined based on pure gas sorption isotherms measured gravimetrically and experimental permeances of the four gases. The membrane swelling caused by CO₂ was observed at temperatures of 293 and 303 K and for pressures higher than 3 bar. The adsorption of CH₄, O₂ and N₂ in the fractional free volume (FFV) has a dominant (>50%) share in their total solubility in the entire pressure range. This makes them sensitive to the presence of CO₂, whose affinity is the strongest towards the tested polyimide-based sample. The diffusion of O₂ is the fastest which makes it competitive with CO₂ in permeation through the membrane, despite its low solubility. The ideal CO₂/O₂ selectivity is thus relatively low (2.3–5.1). Methane, which is competitive in solubility compared to CO₂, was found to diffuse the slowest and as a result, it is also the slowest permeating gas. This translates into the very high CO₂/CH₄ ideal selectivity (33–95.7), which is, however, strongly dependent on temperature and pressure.

The research problem was to determine the possibility of aqueous mineral carbonation using fly ash from lignite fluidized bed combustion. Both direct and indirect routes were used. The innovative nature of the research consisted of conducting experiments at atmospheric pressure and ambient temperature (20 °C). The synthetic gas mixture with composition analogical to the flue gas (nitrogen and up to 16 vol.% of carbon dioxide) was used. The experiments proved that almost all CO₂ from the gas was chemically bound at pH > 12. The sequestration capacity of studied fly ash is about 55–76 g CO₂ per 1 kg of ash in the case of the indirect method, and 80–95 g CO₂ per 1 kg of ash for the direct route. These values are similar to those presented in the literature, but unlike most publications, they were obtained under ambient conditions, which can significantly reduce the costs of the process.

Biogas, one of the important controllable renewable energy sources, may be split into two streams: bio-CH₄ and bio-CO₂ using, among others, membrane processes. The proper optimization of such processes requires the knowledge of phenomena accompanying each specific CH₄–CO₂–membrane system (e.g., competitive sorption or swelling). The phenomena were analyzed for the polysulfone-based membrane used in a developed adsorptive–membrane system for biogas separation. The Dual Mode Sorption and partial immobilization models were used to describe the solubility and diffusion of CO₂, CH₄ and their mixtures in this material. The parameters of the models were determined based on pure-gas sorption isotherms measured gravimetrically and permeances of CO₂/CH₄ mixture components from our previous studies. It was found, among other things, that the membrane swelling caused by CO₂ was observed for pressures higher than 5 bar. The real selectivity (permselectivity) of CO₂ vs. CH₄ is significantly lower than the selectivity of pure gases (ideal selectivity), while the solubility selectivity of CO₂ vs. CH₄ in the mixture is higher than that of pure gases. This is due to the better affinity of CO₂ towards the tested polysulfone membrane, making CO₂ the dominant component in competitive sorption. The reduction in the permselectivity is mainly due to an approximately two-fold decrease in the CO₂ diffusion rate in the presence of CH₄. It was also found that the fraction of solubility in the fractional free volume (FFV) is dominant for both gases, pure and mixed, reaching 65–73% of the total solubility. Moreover, in CO₂/CH₄ mixtures, the mobility of methane in FFV disappears, which additionally confirms the displacement of methane by CO₂ from FFV.

Membrane processes continue to attract significant interest, as reflected in the growing number of studies focused on the development of innovative membrane materials. Novel membranes are frequently designed for specific separation processes, in which they demonstrate enhanced transport properties and improved resistance to fouling. In this study, a methodology was proposed to evaluate the transport properties of novel membrane materials with respect to their resistance to hydrogen sulfide, a common contaminant in biogas. To this end, the permeance, solubility, and diffusivity of CH4, CO2, N2, and O2 were experimentally determined both before and after exposure of a glassy polyimide membrane to hydrogen sulfide. Exposure to H2S resulted in a reduction of both permeation and diffusivity coefficients for all investigated gases. It was also observed that hydrogen sulfide exposure did not significantly affect the overall gas solubility. Notably, only for CO2 an increase in gas mobility within the fractional free volume was detected, whereas the mobility of the remaining gases was effectively diminished. To describe the solubility and diffusivity behavior of the gases in the glassy polyimide membrane, the Dual Mode Sorption and partial immobilization models were applied. The parameters of the DMS model were determined based on gravimetric sorption experiments.

The paper discusses the application possibilities of ceramic foam in a thermal combustion process of a lean methane-air mixture. The experiments were done in a ceramic foam bed. The foam (Vukopor ® A) was made mainly of Al 2O 3. The foam samples were packed in a tubular reactor symmetrically placed in a laboratory furnace. It was assumed that the tested foam should have a surface close to the monolith surface area which was tested in a previous work (Pawlaczyk and Gosiewski, 2015). Pore density of the tested foam was 10 PPI. The tested air mixture contained 0.51 - 0.76 vol. % of methane. The results show that thermal methane oxidation in foam is possible in the acceptable range of temperatures. The combustion process in foam is characterized by similar ignition temperature to tests carried out in monolith, a more intense course, and better methane conversion at lower temperatures.

The agriculture sector in Poland could provide 7.8 billion m³ of biogas per year, but this potential would be from dispersed plants of a low capacity. In the current study, a membrane process was investigated for the upgrading biogas to biomethane that conforms to the requirements for grid gas in Poland. It was assumed that such a process is based on membranes made from modified polysulfone or polyimide, available in the market in Air Products PRISM PA1020 and UBE UMS-A5 modules, respectively. The case study has served an agricultural biogas plant in southern Poland, which provides the stream of 5 m³ (STP) h⁻¹ of biogas with a composition of CH₄ (52 vol.%), CO₂ (46.3 vol.%), N₂ (1.6 vol.%) and O₂ (0.1 vol.%), after a pretreatment. It was theoretically shown that this is possible to obtain the biomethane stream of at least 96 vol.% of CH₄ purity, with the concentration of the other biogas components below their respective thresholds, as required in Poland for gas fuel “E”, with methane recovery of up to 87.5% and 71.6% for polyimide and polysulfone membranes, respectively. The energetic efficiency of the separation process is comparable for both membrane materials, as expressed by power excess index, which reaches up to 51.3 kW_th kW_el⁻¹ (polyimide) and 40.7 kW_th kW_el⁻¹ (polysulfone). In turn, the membrane productivity was significantly higher in the case of the polyimide membrane (up to 38.3 kW_th m⁻²) than those based on the polysulfone one (up to 3.13 kW_th m⁻²).

Commercially available polymeric membrane materials may also show their potential for CO₂ capture by the association of the membrane process with other separation techniques in a hybrid system. In the current study, PRISM PA1020/Air Products and UBE UMS-A5 modules with membrane formed of modified polysulfone and polyimide, respectively, were assessed as a second stage in the hybrid vacuum swing adsorption (VSA)–membrane process developed in our laboratory. For this purpose, the module permeances of CO₂, N₂, and O₂ at different temperatures were determined, and the separation of CO₂/N₂ and CO₂/N₂/O₂ mixtures was investigated in an experimental setup. An appropriate mathematical model was also developed and validated based on experimental data. It was found that both modules can provide CO₂-rich gas of the purity of > 95% with virtually the same recovery (40.7−63.6% for maximum carbon dioxide content in permeate) when fed with pre-enriched effluent from the VSA unit. It was also found that this level of purity and recovery was reached at a low feed to permeate the pressure ratio (2−2.5) in both modules. In addition, both modules reveal stable separation performance, and thus, their applicability in a hybrid system depends on investment outlays and will be the subject of optimization investigations, which will be supported by the model presented and validated in this study.