Het gebruik van interfases voor de ontwikkeling van polyether gasscheidingsmembranen voor CO2-captatie

Reducing the emission of carbon dioxide (CO2), originating from the combustion of fossil fuels, is crucial in mitigating climate change, one of the major challenges of the 21st century. One way to reduce CO2 emissions is the use of post-combustion carbon capture, a process whereby CO2 emissions are separated from the combusted gas mixture at point emission sources, such as power plants, prior to release into the atmosphere and subsequently stored or used. Crucial in adopting post-combustion carbon capture is the ability to separate CO2 from other gasses in the gas stream (mostly nitrogen). A particularly promising separation technology for this application is the use of gas separation membranes, a technology where the membrane acts as a semi-permeable barrier which allows CO2 to pass through it whilst blocking passage of nitrogen. However, the gas streams generated by industrial processes targeted for carbon capture are large and a have a low CO2 concentrations, thus limiting the available driving force for the membrane separation. Therefore, there is a need for membranes with as high as possible CO2 permeances combined with a moderate CO2/N2 selectivity (30-50) to make membrane-based post-combustion carbon capture economically viable. Achieving high membrane CO2 permeances entails both optimizing the intrinsic CO2 permeability of the membrane material and processing the material into a thin film. Crosslinked poly(ethylene oxide) (XLPEO) is a polymeric material that fulfills both the adequate CO2/N2 selectivity requirement and has a high CO2 permeability, as a result of its CO2-philic ether bonds, but the crosslinked structure of XLPEOs makes it challenging to dissolve them and thus process them into thin films. This processability challenge can possibly be circumvented through the use of interfacial initiation of polymerization (IIP), a recently developed preparation technique for liquid separation membranes whereby an intrinsically crosslinked thin poly(epoxyether) (PEE) polymer layer is synthesized at the interface of two immiscible solvents. The PEE polymer is formed through a chain growth polymerization of epoxides initiated by a tertiary amine, resulting in an ether crosslinked polymer network containing quaternary ammonium (QA) groups, both known for their CO2-philicity. Their CO2-philicity, crosslinked nature and thin film preparation through IIP, make PEEs interesting materials for the development of novel carbon capture membranes. Therefore, the goal of this dissertation was twofold: to extend the IIP preparation of PEE membranes to gas separation carbon capture membranes and to develop the synthesis-structure-performance relationships for these PEE membranes. By preparing thin film composite (TFC) membranes out of the epoxide monomer poly(ethylene glycol) diglycidyl ether (PEGDE), a short PEO chain end-functionalized with epoxide groups, it was proven the IIP method of preparing PEE membranes could also be used for the development of gas separation membranes. A study of the effect of IIP conditions, such as densification strategy and time, as well as the monomer and initiator concentrations, on the gas separation performance of the corresponding membranes revealed at least one densification step, a threshold densification time, and a threshold reagent concentration were necessary to obtain a selective membrane with PEGDE. When these thresholds were surpassed, multiple reagent concentration combinations resulted in gas selective layers (CO2/N2 selectivity > 50) with tunable chemical composition. However, all PEGDE membranes, independent of synthesis conditions or chemical structure, showed low CO2 permeances, as a result of support pore impregnation. Pore impregnation could possibly be averted by using hydrophobic monomers with a high functional group density and bulky structure, as these are less likely to dissolve in the aqueous phase and ensure a fast polymer network formation. To verify this hypothesis TFC PEE membranes were prepared through IIP, using a glycidyl functionalized polyhedral oligomeric silsesquoixane (G-POSS) monomer and a pre-polymerized form of G-POSS as monomer. Selective G-POSS membranes could be prepared both with and without densification and had a 3-6 fold higher permeance than their PEGDE counterparts, as a result of reduced pore impregnation. Pre-polymerization of G-POSS, prior to IIP, further alleviated pore-impregnation issues and reduced the synthesis times required to obtain a selective membrane. However, pore impregnation was not completely averted for both monomers, possibly due to the long overall synthesis time of the membranes. In-depth characterization of G-POSS membranes revealed densification increased initiator incorporation in the membrane, reduced its gas permeance, increased its size selectivity and increased CO2 permeance for humidified gas streams (>100% for densified membranes with a high degree of initiator incorporation), most likely as a result of water induced swelling of the membrane. Combined these results reveal a significant impact of initiator incorporation in the membrane on its gas separation properties. To better understand the influence of the initiator content of the polymer on the gas separation performance of PEE, a facile, solvent-free synthesis procedure was developed to prepare self-standing PEE membranes, based on PEO functionalized G-POSS (EO-G-POSS) as epoxide monomer. Extensive physicochemical characterization confirmed that varying the epoxide-amine ratio during synthesis allowed control over the initiator content in the final membrane, with low epoxide-amine ratios resulting in an increased incorporation of initiator in the polymer structure, primarily as QA charges, whereas high epoxide-amine ratios resulted in more etherification and a higher residual epoxide content. Variations in initiator content did not impact the polymer chain flexibility, but resulted in an increasing polymer density with increasing initiator content. Additionally, membrane CO2, N2 and He permeability decreased with increasing initiator content, while membrane CO2/N2 selectivity was less affected. Remarkably, membranes prepared with a low epoxide-amine ratio showed exceptionally high CO2/N2 solubility selectivity at low pressures and a concurrently low CO2 diffusivity, whereas membranes prepared with higher epoxide-amine ratios had lower solubility selectivity, higher CO2 diffusivities. Finally, pore impregnation issues encountered during IIP inspired the development of interfacial transport (IT), a novel preparation method relying on transport of a selective compound across a liquid-liquid interface to fabricate thin film supported liquid membranes (SLM). A proof of concept for IT was established using poly(ethylene glycol) dimethyl ether (PEGDME). Subsequent optimization of IT conditions, such as IT time, PEGDME concentration, post-synthesis washing, organic phase solvent, and support structure and chemistry, allowed further improvement of membrane CO2 permeance. IT time and PEGDME concentration were found to be interconnected parameters, both characterized by a lower threshold required to obtain selective membranes. The IT SLMs maintained stable CO2/N2 separation factors during extended operation, but an increase in permeance over time suggested loss of some PEGDME. Furthermore, the membranes operated stably at N2 pressures up to 10 bar and CO2 pressures up to 20 bar, a remarkable achievement for SLMs, partly attributed to the use of a sealing layer.