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 ß-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 ß-turn conformation in the case of short trimer sequences (7c and 7d), while the chirality and the backbone length exerted more distortion on the ß-turn adopted by the longer hexamer sequences (8c and 8d). The large disturbance in hexamers from classical ß-turn was attributed to increasing the flexibility and the possibility of molecules to adopt a more energetically favorable conformation stabilized by non-classical ß-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.

Grafting cellulose acetate with ionic liquids for biofuel purification membranes : Influence of the anion.

Membranes made from cellulose acetate grafted with imidazolium or ammonium ionic liquids (ILs) containing different anions were considered for ethyl tert-butyl ether biofuel purification by pervaporation. The new cellulosic materials were obtained after bromide (Br-) exchange by different anions (Tf2N-, BF4-, AcO-). IL structure-membrane property relationships revealed that the membrane properties were strongly improved by varying the anion structure, molecular size and hydrogen bonding acceptor ability ß in the Kamlet-Taft polarity scale. The grafted ammonium IL with AcO- anion combined the highest parameter ß with big cation/anion sizes and finally led to the best membrane properties with a normalized pervaporation flux of 0.41 kg/h m2 (almost 20 times that of virgin cellulose acetate) for a reference thickness of 5 µm and a permeate ethanol content of 100%. Such properties thus corresponded to an outstanding separation factor at 50 °C.

Multiblock Copolymer Grafting for Butanol Biofuel Recovery by a Sustainable Membrane Process.

Biobutanol is an attractive renewable biofuel mainly obtained by the acetone-butanol-ethanol (ABE) fermentation process. Nevertheless, the alcohol concentration has to be limited to a maximum of 2 wt % in ABE fermentation broths to avoid butanol toxicity to the microorganisms. The pervaporation (PV) membrane process is a key sustainable technology for butanol recovery in these challenging conditions. In this work, the grafting of azido-polydimethylsiloxane (PDMS-N3) onto a PDMS-based multiblock copolymer containing alkyne side groups led to a series of original membrane materials with increasing PDMS contents from 50 to 71 wt %. Their membrane properties were assessed for butanol recovery by pervaporation from a model aqueous solution containing 2 wt % of n-butanol at 50 °C. The membrane flux J50µm for a reference thickness of 50 µm strongly increased from 84 to 192 g/h m(2) with increasing PDMS content for free-standing dense membranes with thicknesses in the range of 38-95 µm. At the same time, the intrinsic butanol permeability increased from 1.47 to 4.68 kg µm/h m(2) kPa and the permeate butanol content was also strongly improved from 38 to 53 wt %, corresponding to high and very high membrane separation factors of 30 and 55, respectively. Therefore, the new grafted copolymer materials strongly overcame the common permeability/selectivity trade-off for butanol recovery by a sustainable membrane process.

Grafting of cellulose acetate with ionic liquids for biofuel purification by a membrane process: Influence of the cation.

A new strategy was developed for grafting ionic liquids (ILs) onto cellulose acetate in order to avoid IL extraction and improve its performance for ethyl tert-butyl ether (ETBE) biofuel purification by the pervaporation membrane process. This work extended the scope of IL-containing membranes to the challenging separation of organic liquid mixtures, in which these ILs were soluble. The ILs contained the same bromide anion and different cations with increasing polar feature. The membrane properties were strongly improved by IL grafting. Their analysis in terms of structure-property relationships revealed the influence of the IL content, chemical structure and chemical physical parameters α, ß, π* in the Kamlet-Taft polarity scale. The ammonium IL led to the best normalized flux of 0.182kg/m(2)h for a reference thickness of 5µm, a permeate ethanol content of 100% and an outstanding infinite separation factor for the azeotropic mixture EtOH/ETBE at 50°C.