Casting call: ions and polymer combine to produce gas separation membranes

Significance 

New gas separation membranes using plastic crystal composites.

The power industry is one of the main carbon dioxide producers. Thus, it has become the main target for most of the greenhouse effects mitigation strategies. One of the most commonly used strategies to reduce CO2 emission is separating it from the flue gas stream and reusing it in other industrial applications such as polymer synthesis. The presently used technologies to capture and store carbon dioxide downstream the combustion systems are mainly based on chemical absorption favorable for enhancing performance and gas selectivity. Unfortunately, these technologies require the use of solvents and are energy-intensive, thus reducing fuel efficiency. Therefore, the development of cost-effective and more efficient CO2 capture and storage (CCS) technologies is highly desirable.

Membrane separation is arguably one of the most efficient gas separation technology. Unlike the traditional CCS technologies, it is more energy-efficient and requires mainly pressure gradient to operate. However, the effectiveness of this technology for CCS is compromised by several factors, including the large stream flow rates associated with most power industries and the low CO2 concentration. Lately, membrane separation technologies based on room-temperature ionic liquids (RTILs) have been identified as promising solutions. They exhibit competitive permeability and remarkable solubility-driven selectivity. Consequently, organic ionic plastic crystals (OIPCs) that exhibit similar ionic structures to RTILs have drawn significant research attention. However, use of OIPCs for developing efficient gas separation membrane technologies requires a thorough understanding of the various types of OIPCs and how to optimize the mechanical and physical properties of their associated polymer composites.

On this account, Mr. Fernando Ramos (Ph.D. Candidate), Professor Maria Forsyth and Professor Jennifer Pringle from Deakin University in Australia investigated the potential application of OIPCs for developing highly efficient and cost-effective gas separation technologies. Specifically, the authors investigated the feasibility of using a new membrane preparation method and a different type of OIPC to design novel and more selective membranes for CO2/N2. Their research work is currently published in the research journal, ChemSusChem.

In their approach, the research team used two OIPCs: methyl (diethyl)isobutylphosphonium hexafluorophosphate ([P122i4][PF6]) and N-methyl-N-ethyl pyrrolidinium bis(fluorosulfonyl)imide ([C2mpyr][FSI]), fabricated via solvent-casting or co-casting with poly(vinylidene difluoride) (PVDF). The former was studied in their previous research and was used as a benchmark in this study, while the latter was studied for the first time., Their gas transport properties were determined and compared, with the [C2mpyr][FSI]-based membrane recording a remarkable selectivity of aCO2/N2 > 40. The impact of the ion type and the casting method was studied in detail using various experimental techniques such as gas permeation experiments using N2 and CO2.

The main difference between the two OIPCs reside in the chemistry. Whilst both OIPCs contain fluorinated anions associated with the CO2-philicity, the degree and nature of the ionic interactions determine the structure, thermal behavior, and the capacity to absorb and diffuse gas. The co-casting method resulted in improved thermophysical properties of the composites and was identified as the most feasible method for producing mechanically stable and durable membranes. It also resulted in higher permeation reproducibility and an increase in the CO2 solubility than the solvent-casting method. Additionally, co-casting allowed the production of tougher, thinner and more homogenous membranes by enhancing robustness and reducing OIPC flow in the membranes. Furthermore, the thermal behavior of the composites fabricated via co-casting depended on the chemical interaction between the OIPCs and PVDF. All the evidence suggests that the polymer should not be consider as a mere support, and the authors are investigating this impact of polymer, and a wider range of OIPCs, as part of their future work in this exciting new area.

In summary, the authors demonstrated the potential application of OIPCs for developing novel gas separation membrane technologies. Co-casting proved to be effective for preparing thin OIPC-based composite membranes with improved thermophysical properties. The OIPC/PVDF co-cast composites also demonstrated improved molecular interactions, providing a new approach for synthesizing highly selective membranes for light gas separation.

In a statement to Advances in Engineering, Professor Jennifer Pringle said that the insights from the study are very exciting as they show that the types of OIPC used, the polymer content and the method of fabrication of the membrane can all have an impact on the properties and performance. This information paves the way for designing and synthesizing more high-performance OIPC-based membranes, and for further optimization of their performance in gas separation applications.

Casting call: ions and polymer combine to produce gas separation membranes - Advances in Engineering

About the author

Prof Jenny Pringle works in the Institute for Frontier Materials at Deakin University, Melbourne, Australia. She is a chief investigator in the ARC Centre of Excellence for Electromaterials Science and in the Industrial Transformation Training Centre “StorEnergy”. She received her degree and PhD at The University of Edinburgh in Scotland before moving to Monash University in Melbourne, Australia in 2002. From 2008-2012 she held an ARC QEII Fellowship, investigating the use of ionic electrolytes for dye-sensitized solar cells. Prof Pringle moved to Deakin University in 2013. There she leads research into the development and use of ionic liquids and organic ionic plastic crystals for applications including thermal energy harvesting, CO2 separation membranes, sodium and lithium batteries.

About the author

Professor Maria Forsyth “FAA” (Fellow Australian Academy of Sciences), is the Director of ARC Industrial Transformation Training Centre for Future Energy Storage Technologies, StorEnergy, past ARC Laureate fellow and currently an Alfred Deakin Professorial Fellow at Deakin University and an Ikerbasque Visiting Professorial Fellow at University of the Basque Country. Professor Forsyth is a world leader in electrolyte materials research. She has worked at the forefront of energy materials research since her Fulbright Research Fellowship in 1990 and has consistently made breakthrough discoveries, including in polymer electrolytes, ionic liquids and organic plastic crystals. Her research has focused on understanding the phenomenon of charge transport in these materials and at metal/electrolyte interfaces present in all electrochemical applications. This extensive body of work provides the basis for understanding the behaviour of these materials and thus, provides clarity on how to overcome their performance limitations and design and develop improved applications.

About the author

Mr Fernando Ramos Saz is currently working on his PhD in the Institute for Frontier Materials at Deakin University. He studied his BSc. Honours (Mechanical Engineering) at EU Ford Spain University 2004-2008; and his MSc. by Coursework (Materials Engineering) and MSc. by Research (Mechanical and Materials Engineering) at Polytechnic University of Valencia 2008-2012. He completed a MSc Thesis about ultra-fast annealing treatments for low-alloy high-strength steels at Ghent University.

He worked for 3 years in AIMPLAS (Plastic technology institute of Valencia) from 2013-2015 focusing his formal training in the field of Polymers Science (Compounding and Transformation Processes). He worked on sustainable high-density composite alternatives for lead substitution in 2016-2017. Then he started his current PhD research on permeation and capture of carbon dioxide in Organic Ionic Plastic Crystals based composite membranes.

Reference

Ramos, F., Forsyth, M., & Pringle, J. (2020). Organic Ionic Plastic Crystal‐Based Composite Membranes for Light Gas Separation: The Impact of Varying Ion Type and Casting MethodChemsuschem, 13(21), 5740-5748.

Go To Chemsuschem

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