Development of Novel Mixed Membranes using Organic Fillers for the Separation of CO2 from CH4

Abstract

The recent research by the world energy landscape established that the fossil fuels including the natural gas (CH4) and petroleum products are still accounted as the world’s primary sources of energy. These fossil fuels are accountable for the 65% of the world energy supply, and this behavior of significant share of world energy demand is expected to continue from the coming century as well. Natural gas which majorly composed of methane, is a significant renewable energy source. However, the raw natural gas contains impurities including majorly CO2 which results to the corrosion in natural gas pipelines and successive reduction in the heating value of natural gas as a fuel. Therefore, there is need to process the natural gas streams to separate CO2 from CH4 for improvements in energy value and economic efficiency along with significant contribution to fight against global warming due to Greenhouse Gases (GHGs) emissions. This study deals with the synthesis of different fillers including acid treated MWCNTs, amine and deep eutectic solvent functionalized MWCNTs, perylene, poly(ethylene oxide) (PEO), and porphyrin and polysulfone (PSf) polymer-based MMMs via solution casting approach. The fillers uniform distribution, symmetricity uniformity, amorphous nature, and successful bond formation. MMMs demonstrated high thermal stability with high glass transition temperature. The presence of π-π bonds and Lewis’s basic functionalities between filler-polymer resulted highly CO2-philic structure. The pure and mixed gas permeabilities and selectivities were successfully improved and surpass the tradeoff of the Robeson’s upper bound curve. The MMMs revealed improved pure and mixed gas selective transport properties. Additionally, the temperature influence on CO2 permeability revealed lower activation energies at higher temperatures leading to the gas transport facilitation. In case of oxygen rich functionalized multi-walled carbon nanotubes (MWCNTs) incorporated MMMs, the CO2 permeation results demonstrated that the with the successful incorporation of the oxygen rich functionalized MWCNTs, the CO2 ermeability improved for raw-MWCNTs-PSF-MMMs (75.52%), and OH-MWCNTsPSF-MMMs (65.5%). For N2 functionalized multiwalled carbon nanotubes (MWCNTs) based MMMs, the CO2 permeation results revealed that the with the successful incorporation of the N2 rich functionalized MWCNTs, the CO2 permeability improved for Amine-MWCNTs-PSF-MMMs (197.36%), and DES-MWCNTs-PSFMMMs (152.05%). The perylene filler based MMMs resulted improved permeabilities of CO2 (138%), CH4 (59%), and N2 (60%) without any significant variation in selectivities CO2/CH4 (3%) and CO2/CH4 (7%). Similarly, mixed gas permeabilities were improved for (CO2-CH4 – 119%) and (CO2-N2 – 116%) along with enhanced selectivities (CO2-CH4 – 50%) and (CO2-N2 – 46%). Dealing with the fabrication of MMMs using PEO filler and PSf polymer resulted improved permeabilities of CO2 (96%), CH4 (80%), and N2 (78%) with significant improvements in selectivities CO2/CH4 (84%) and CO2/CH4 (86%). Similarly, mixed gas permeabilities were improved for (CO2-CH4 – 97%) and (CO2-N2 – 96%) along with enhanced selectivities (CO2-CH4 – 85%) and (CO2-N2 – 85%). The implementation of the solution casting method to synthesize the MMMs based on porphyrin filler and PSf polymer. The filler was incorporated into polymer matrix at three different weight fractions of 5 wt%, 10 wt%, and 20 wt%. The MMMs revealed increased gas permeation properties of CO2 (97%), CH4 (82%), and N2 (81%) Similarly, mixed gas permeabilities were increased to (CO2-CH4 – 97.53%) and (CO2-N2 – 97.23%). The pure gas selectivities were improved CO2/CH4 (84%) and CO2/N2 (86%). the mixed gas selectivities raised to (CO2-CH4 – 85%) and (CO2-N2 – 85%). Precise prediction of the gas permeability behavior through the mixed matrix Composite membranes (MMMs) composed of the tubular fillers using existing theoretical approaches are infrequent. In this work, raw- and functionalized MWCNTs filler based MMMs in polysulfone (PSF) matrix were synthesized successfully, followed by morphological analysis on matrix interfacial layers parameters. KJN model was modified by introducing pseudo-dispersed phase fillers that influenced the interfacial layer and consequently overall gas permeabilities, which was ignored in existing models. The new proposed theoretical model is able to predict the gas permeability behavior with significantly reduced average absolute relative error (%AARE) of 1.26% compared to 52.43% and 42.71% for unmodified KJN and HC models, respectively. Furthermore, the mKJN model revealed that the interfacial layer thickness is a unique characteristic and is independent of the penetrant gas molecules which may be influenced by the heterogeneity in the experimental conditions. The cross-sectional morphology and mKJN model revealed that the filler functionalization may lead to the improvement in filler-polymer interaction which thus reduced interfacial layer thickness.