PIM-PI-1 and Poly(ethylene glycol)/Poly(propylene glycol)-Based Mechanically Robust Copolyimide Membranes with High CO₂-Selectivity and an Anti-aging Property: A Joint Experimental–Computational Exploration

Abstract

Polymer membranes with excellent thermomechanical properties and good gas separation performance are desirable for efficient CO2 separation. A series of copolyimide membranes are prepared for the first time using PIM-PI-1, a hard segment with high CO2 permeability, and poly­(ethylene glycol)/poly­(propylene glycol) (PEG/PPG), a soft segment with high CO2 selectivity. Two different unit polymers are combined to compensate the limitations of each polymer (e.g., the fast aging and moderate selectivity of PIM-PI-1 and the poor mechanical properties and lower permeability of PEG/PPG). The corresponding PIM-(durene–PEG/PPG) membranes exhibit an excellent combination of mechanical properties and gas separation performance compared to the typical PI-PEG-based copolymer membrane. The improved mechanical property is attributed to the unique chain threading and the reinforcement between the spiro unit of PIM and the flexible PEG/PPG at the molecular level, which has not previously been exploited for membranes. The PIM-(durene–PEG/PPG) membranes show a high CO2 permeability of 350–669 Barrer and a high CO2/N2 selectivity of 33.5–40.3. The experimental results are further evaluated with theoretical results obtained from molecular simulation studies, and a very good agreement between the experimental results and simulation results is found. Moreover, the PIM-(durene–PEG/PPG) copolymer membranes display excellent anti-aging performance for up to 1 year.

Mixed Matrix Membranes for Efficient CO2 Separation Using an Engineered UiO-66 MOF in a Pebax Polymer

“…With this relationship in mind, various methods have been proposed to improve the separation performance of polymeric membranes, including polymer blending, crosslinking, copolymerization, and the incorporation of fillers [6,7,12,13]. Incorporating nonporous or porous fillers into a polymer matrix leads to the formation of mixed matrix membranes (MMMs), which have great potential as high-performance membranes.…”

Biphenyl(isatin-co-trifluoroacetophenone)-Based Copolymers Synthesized Using the Friedel–Crafts Reaction as Mechanically Robust Membranes for Efficient CO2 Separation

“…We have identified membrane technology as one of the most effective ways to address industry-related environmental problems, such as CO 2 capture and sequestration processes, and to promote sustainable living. − A polymer membrane for CO 2 separation has several advantages, such as energy efficiency, low cost, eco-friendliness, flexible operation, compact modules, and the ability to form sheets or modules. − Consequently, this form factor has attracted greater attention than other techniques (e.g., amine scrubbing or cryogenic distillation) currently in use. , …”

“…Additional properties determine whether the polymer is suitable for industrial applications, such as high mechanical stability for processing into hollow fibers or flat membranes, chemical and physical resistance to support aggressive environmental applications (swelling, CO 2 plasticization, and aging), and low cost. However, most commercial polymer membrane materials in use today, such as cellulose acetate (CA), polyimide (PI, e.g., Matrimid), polyphenylene oxide (PPO), polycarbonate (PC), and polysulfone (PSf), are subject to one or more of the abovementioned restrictions. − Furthermore, the most common limitation of polymer-based gas separation membranes is the trade-off between permeability ( P ) and selectivity (α). ,, Simply put, highly permeable polymers have lower selectivity and vice versa, as defined by the Robeson upper limit. , Therefore, developing polymeric materials for use in membranes for efficient CO 2 separation is a great challenge.…”

“…Most of these studies have developed gas separation membranes based on glassy polymers with high-free volume and rigid backbones, such as polyimides (PIs), intrinsically microporous polymers (PIMs), and PIM-PIs. ,− These polymer membranes are very promising because of their superiority over other glassy polymers, i.e., high thermal and mechanical strength and high permeability. ,,,, However, these materials have not yet achieved the high CO 2 /light gas selectivity and CO 2 permeability required for industrial commercialization. Specifically, the major disadvantage of high-free volume polymers is physical aging, which results from the shrinkage of nonequilibrium free volume with operating time. ,, This shrinkage leads to deterioration of the long-term stability of the gas permeability of the membrane. Also, these highly porous polymers (PIM and PIM-PI) exhibit poor elongation properties, which makes their practical application in the form of hollow fibers or flat-plate modules challenging.…”

“…Also, these highly porous polymers (PIM and PIM-PI) exhibit poor elongation properties, which makes their practical application in the form of hollow fibers or flat-plate modules challenging. In addition, the high cost of starting materials (initial reagents) and the multistep synthesis of these polymers increase the difficulty of using them for large-scale industrial applications. ,,, …”