Enhanced CO2 separation membrane prepared from waste by-product of silk fibroin

Enhancement strategies of poly(ether-block-amide) copolymer membranes for CO2 separation: A review

Poly(ether-block-amide) (Pebax) membranes have become the preferred CO2 separation membrane because of their excellent CO2 affinity and robust mechanical resistance. Nevertheless, their development must be considered to overcome the typical obstacles in polymeric membranes, including the perm-selectivity trade-off, plasticization, and physical aging. This article discusses the recent enhancement strategies as a guideline for designing and developing Pebax membranes. Five strategies were developed in the past few years to improve Pebax gas transport properties, including crosslinking, mobile carrier attachment, polymer blending, filler incorporation, and the hybrid technique. Among them, filler incorporation and the hybrid technique were most favorable for boosting CO2/N2 and CO2/CH4 separation performance with a trade-off-free profile. On the other hand, modified Pebax membranes must deal with two latent issues, mechanical strength loss, and perm-selectivity off-balance. Therefore, exploring novel materials with unique structures and surface properties will be promising for further research. In addition, seeking eco-friendly additives has become worthwhile for establishing Pebax membrane sustainable development for gas separation.

A Strategical Improvement in the Performance of CO2/N2 Gas Permeation via Conjugation of L-Tyrosine onto Chitosan Membrane

Rubbery polymeric membranes, containing amine carriers, have received much attention in CO₂ separation because of their easy fabrication, low cost, and excellent separation performance. The present study focuses on the versatile aspects of covalent conjugation of L-tyrosine (Tyr) onto the high molecular weight chitosan (CS) accomplished by using carbodiimide as a coupling agent for CO₂/N₂ separation. The fabricated membrane was subjected to FTIR, XRD, TGA, AFM, FESEM, and moisture retention tests to examine the thermal and physicochemical properties. The defect-free dense layer of tyrosine-conjugated-chitosan, with active layer thickness within the range of ~600 nm, was cast and employed for mixed gas (CO₂/N₂) separation study in the temperature range of 25-115 °C in both dry and swollen conditions and compared to that of a neat CS membrane. An enhancement in the thermal stability and amorphousness was displayed by TGA and XRD spectra, respectively, for the prepared membranes. The fabricated membrane showed reasonably good CO₂ permeance of around 103 GPU and CO₂/N₂ selectivity of 32 by maintaining a sweep/feed moisture flow rate of 0.05/0.03 mL/min, respectively, an operating temperature of 85 °C, and a feed pressure of 32 psi. The composite membrane demonstrated high permeance because of the chemical grafting compared to the bare chitosan. Additionally, the excellent moisture retention capacity of the fabricated membrane accelerates high CO₂ uptake by amine carriers, owing to the reversible zwitterion reaction. All the features make this membrane a potential membrane material for CO₂ capture.

A lysine-based 2:1-[α/aza]-pseudopeptide series used as additives in polymeric membranes for CO2 capture: synthesis, structural studies, and application†

The current study presents for the first time the synthesis of a new 2:1-[α/aza]-pseudopeptide series possessing charged amino acids (i.e., lysine) and aims at studying the influences of chirality, backbone length, and the nature of the lysine side chains on the conformation of the 2:1-[α/aza]-oligomers in solution using NMR, FTIR spectroscopy and molecular dynamic calculations. The spectroscopic results emphasized the conservation of the β-turn conformation adopted by the trimers regardless of the chirality which demonstrated a noticeable effect on the conformation of homochiral hexamer (8c) compared with the hetero-analogue (8d). The molecular dynamic calculations predicted that the chirality and the side chain of the lysine residues caused a little distortion from the classical β-turn conformation in the case of short trimer sequences (7c and 7d), while the chirality and the backbone length exerted more distortion on the β-turn adopted by the longer hexamer sequences (8c and 8d). The large disturbance in hexamers from classical β-turn was attributed to increasing the flexibility and the possibility of molecules to adopt a more energetically favorable conformation stabilized by non-classical β-turn intramolecular hydrogen bonds. Thus, alternating d- and l-lysine amino acids in the 2:1-[α/aza]-hexamer (8d) decreases the high steric hindrance between the lysine side chains, as in the homo analogue (8c), and the distortion is less recognized. Finally, short sequences of aza-pseudopeptides containing lysine residues improve CO₂ separation when used as additives in Pebax® 1074 membranes. The best membrane performances were obtained with a pseudopeptidic dimer as an additive (6b′; deprotected lysine side chain), with an increase in both ideal selectivity α_CO2/N2 (from 42.8 to 47.6) and CO₂ permeability (from 132 to 148 Barrer) compared to the virgin Pebax® 1074 membrane.

A new 2:1-[α/aza]-pseudopeptide series based charged lysine amino acid was synthesized. Influences of chirality, backbone length, and lysine side chains on the oligomers conformation were investigated in solution using NMR, FTIR and MD calculations.