A new generation of confined palladium(II) catalysts covalently attached inside of porous organic polymers (POPs) has been attained. The synthetic approach employed was straightforward, and there ...was no prerequisite for making any modification of the precursor polymer. First, POP-based catalytic supports were obtained by reacting one symmetric trifunctional aromatic monomer (1,3,5-triphenylbenzene) with two ketones having electron-withdrawing groups (4,5-diazafluoren-9-one, DAFO, and isatin) in superacidic media. The homopolymers and copolymers were made using stoichiometric ratios between the functional groups, and they were obtained with quantitative yields after the optimization of reaction conditions. Moreover, the number of chelating groups (bipyridine moieties) available to bind Pd(II) ions to the catalyst supports was modified using different DAFO/isatin ratios. The resulting amorphous polymers and copolymers showed high thermal stability, above 500 °C, and moderate–high specific surface areas (from 760 to 935 m2 g–1), with high microporosity contribution (from 64 to 77%). Next, POP-supported Pd(II) catalysts were obtained by simple immersion of the catalyst supports in a palladium(II) acetate solution, observing that the metal content was similar to that theoretically expected according to the amount of bipyridine groups present. The catalytic activity of these heterogeneous catalysts was explored for the synthesis of biphenyl and terphenyl compounds, via the Suzuki–Miyaura cross-coupling reaction using a green solvent (ethanol/water), low palladium loads, and aerobic conditions. The findings showed excellent catalytic activity with quantitative product yields. Additionally, the recyclability of the catalysts, by simply washing it with ethanol, was excellent, with a sp2–sp2 coupling yield higher than 95% after five cycles of use. Finally, the feasibility of these catalysts to be employed in tangible organic reactions was assessed. Thus, the synthesis of a bulky compound, 4,4′-dimethoxy-5′-tert-butyl-m-terphenylene, which is a precursor of a thermal rearrangement monomer, was scaled-up to 2 g, with high conversion and 96% yield of the pure product.
A new nucleophilic monomer (2,2-bis(3-amino-4-hydroxyphenyl)adamantane, ADHAB) having bulky adamantane groups has been synthesized following an efficient synthetic methodology. The main target of ...this work was to employ a high thermal stable bulky cycloaliphatic moiety as adamantane to obtain aromatic ortho-hydroxypolyimides (poly(o-hydroxyimide)s) able to thermally rearrange to give polybenzoxazole (TR-PBO) materials that could be tested as gas separation membranes. Thus, an array of ortho-acetylcopolyimides, o-acetyl PIs) were prepared by reaction of ADHAB and 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (APAF) with 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) via chemical imidization. Copolyimides and homopolyimides showed inherent viscosities ranging from 0.49 to 0.70 dL/g and provided good-quality dense membranes. Glass transition temperatures of these o-acetyl copolyimides were higher as the amount of ADHAB increased. The thermal stability of the adamantane moiety during the TR process was evaluated by directly synthesizing PBOs, which were made from the reaction, and ulterior thermal cyclization, of 2,2-bis(4-chlorocarbonylphenyl)-hexafluoropropane with ADHAB/APAF. TR-PBO membranes made through a thermal treatment at 450 °C for 30 min showed excellent gas separation properties for the CO2/CH4 gas pair with values close to the 2008 Robeson limit.
A new generation of porous polymer networks has been obtained in quantitative yield by reacting two rigid trifunctional aromatic monomers (1,3,5-triphenylbenzene and triptycene) with two ketones ...having electron-withdrawing groups (trifluoroacetophenone and isatin) in superacidic media. The resulting amorphous networks are microporous materials, with moderate Brunauer–Emmett–Teller surface areas (from 580 to 790 m2 g–1), and have high thermal stability. In particular, isatin yields networks with a very high narrow microporosity contribution, 82% for triptycene and 64% for 1,3,5-triphenylbenzene. The existence of favorable interactions between lactams and CO2 molecules has been stated. The materials show excellent CO2 uptakes (up to 207 mg g–1 at 0 °C/1 bar) and can be regenerated by vacuum, without heating. Under postcombustion conditions, their CO2/N2 selectivities are comparable to those of other organic porous networks. Because of the easily scalable synthetic method and their favorable characteristics, these materials are very promising as industrial adsorbents.
A set of mixed matrix membranes (MMMs) has been prepared by incorporating a triptycene-isatin porous polymer network (PPN) to three aromatic polyimides (one commercial, Matrimid, and two synthesized ...by us: 6FDA–6FpDA and 6FDA–TMPD) covering a wide range of performances for gas separation. The triptycene-isatin PPN is a highly microporous network having a high CO2 uptake and high chemical and thermal stability. The good compatibility between the components (PPN content of 15 and 30% w/w) was supported by the increase in the glass transition temperature of MMMs relative to the pure polyimide membranes. The addition of the PPN particles improved the permeability of all the gases tested, by increasing diffusivity and, in some cases, gas solubility. The improvements were particularly noticeable in Matrimid-based MMMs, where gas permeability increased by 700%, whereas CO2/N2 and CO2/CH4 ideal selectivities decreased by a mere 4% and 12%, respectively.
The present work aims to investigate the effect of chlorine on the surface of the polysulfone (PSF) layer uncovered in the transformed ultrafiltration (UF) membranes (recycled from end-of-life ...reverse osmosis (RO) membranes). With this purpose, 6 end-of-life RO membranes used previously during their useful life to treat brackish water or seawater were transformed using two higher exposure doses of free chlorine (50,000 and 300,000 ppm h). On one hand, the end-of-life membranes were first characterized in terms of the type of fouling identified by TGA, ICP and bacteria detection. On the other hand, to determine the stability of the PSF layer, the transformed PSF UF membranes were then characterized by means of its permeability and molecular weight cut-off (MWCO). In addition, membrane surface characterization was performed by ATR-FTIR, SEM and AFM. The results show that all the end-of-life RO membranes with organic and inorganic fouling were effectively transformed to PSF UF membranes at the ppm∙h values studied. However, one of the analysed sea water membrane model (HSWC3) showed more resistance to be transformed and the pores of the uncovered PSF layer only appeared at 300,000 ppm h. This membrane showed different surface appearance, with bigger pores after 300,000 ppm h exposure dose that might have affected the PSF UF membrane performance. This study indicates that a complete characterization of transformed PSF UF membrane surface is crucial for a deep understanding of the recycling process of end-of-life membranes.
•PSF UF membranes were obtained after degrading polyamide layer when exposing RO end-of-life membranes to NaOCl.•Reduction of transformation process time allows its implementation at pilot scale.•Complete characterization of transformed PSF UF membranes surface was performed.•Biofouling and type of PA layer hindered significantly the transformation process.•Recycling of end-of-life membranes would avoid their disposal in landfills.
A series of new diamine monomers, with systematic variations in their chemical structure, by introducing various substituents onto the polymer backbone, have been made to react with two commercial ...dianhydrides: a very rigid one, pyromellitic dianhydride, (PMDA) and a more flexible one, 2,2′-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA), to obtain a series of polyimide membranes with high fractional free volume (FFV), and their gas separation properties have been studied. In order to gain insight into the relationship between structure and gas separation properties of the polymers, a computer simulation of the polymers has been carried out, by a combination of molecular mechanics and molecular dynamics, to study the effect of the polymeric structure on the permeability and selectivity of the membranes. Moreover, the effect of the probe size on the accessible free volume, which cannot be experimentally determined, has been simulated and related with experimental gas separation parameters as permeability and selectivity. The use of FFV (that corresponds to a probe of zero-radius) cannot predict the behavior of several polymers, which have similar FFV values but different values of permeability and selectivity. However, simulation has permitted to correlate accurately permeability and selectivity with the accessible free volume to probes of different radii.
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•Changes in the structure of new diamines permit to control fractional free volume.•Computer simulation relates polymer structure with free volume distribution.•Permeability and selectivity correlated with the accessible free volume to different probes.
Three novel polyimides have been successfully synthesized from 3,8-diphenylpyrene-1,2,6,7-tetracarboxylic dianhydride (DPPD), and three commercial diamines by solution polycondensation. All polymers ...exhibited high molecular weight, high thermal stability and high rigidity (no glass transition was detected up to 400°C) and free volume. The new polymers have been tested as gas separation membranes, showing very good combination of permeability and selectivity, especially in the case of the polymer derived from trimethyl-m-phenylenediamine (TMPD), which overpassed the 1991 Robeson upper bound for the gas pairs O2/N2 and CO2/CH4 and was near the 2008 upper bound for CO2/N2.
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•A planar and rigid dianhydride has been used to prepare gas separation polyimides.•PCO2/PHe and PCH4/PN2 ratios are reversed compared to glassy polymers (as in PIMs).•Very high permeability has been attained by combining with ortho-substituted diamines.•Meta-substitution in diamine significantly improves permeability.•New polyimides show excellent combination of permeability and selectivity for CO2/N2.
Two new polyimides have been obtained from commercial and inexpensive pyromellitic dianhydride and two affordable meta-substituted diamines bearing ortho methyl substituents (i.e., ...2,4,6-trimethyl-1,3-phenylene diamine (TMPD) and 5,7-diamino-1,1,4,6-tetramethylindane (TMID)). Due to a combination of dianhydride rigidity and meta substitution, in addition to the influence of the ortho substituents on the orthogonal placement of the amine and imide planes, the two polyimides exhibited a high fractional free volume and a high rigidity. Therefore, these polyimides were able to produce gas separation membranes with an excellent balance between permeability and selectivity, and these membranes performed similar to many polymers with intrinsic microporosity (PIMs) and surpassed the 1991 Robeson upper bound for all gas pairs. The behavior is more favorable than that for similar polyimides based on 6FDA, which is considered to be the best dianhydride for gas separation polyimides.
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•Pyromellitic anhydride and ortho-substituted meta-diamines give contorted structures.•Membranes from these polyimides behave as polymers with intrinsic microporosity.•PMDA polyimides give significantly better gas separation efficiency than 6FDA ones.•Substituents size and asymmetry improve permeability without selectivity losses.
A series of experimental aramid-g-PEO copolymers was employed to fabricate ultrafiltration (UF) membranes by the conventional method of phase inversion, using N,N-dimethylformamide as the solvent and ...water as the coagulating medium. By adjusting the dope concentration for each polymer, porous membranes were attained which were suitable for UF operations and were tested using a laboratory-scale cross-flow test unit. The water flux of the membranes showed a strong dependency on the chemical composition, with water permeability increasing with increasing PEO content in the copolymer. Their separation potentials were investigated using standard solutions of poly(ethylene oxide) (PEO) as the feed, and the performance of the membranes in UF operations was systematically compared. A relationship between the dope concentration and the molecular weight cut-off (MWCO) could be observed, with higher concentrations resulting in a lower MWCO. In contrast, it was observed that the higher the content of PEO in the copolymer the greater the MWCO. In fouling tests performed using a bovine serum albumin (BSA) solution, aramid-g-PEO UF membranes exhibited very good antifouling properties compared to a commercially sourced polysulfone membrane and to polyamide UF membranes. The results of this work indicate that aramid-g-PEO copolymers are promising materials for the fabrication of fouling resistant membranes for biomacromolecules' separations.
New liquid absorbents (LA) consisting of water solutions of CO2-complexing agents have been developed and tested in an experimental lab-scale to be used in CO2 separation from gas mixtures. The ...results here presented concern the preparation of these amino acid based new liquid absorbents and the studies carried out to determine their performance as CO2 scrubbers. The novel systems show good performance in terms of sorption and stability compared to the standard alkanolamines. Moreover, the experimental results have shown that among the studied carriers, arginine and ornithine are the natural amino acids with greater affinity towards CO2 and that some of the here synthesized amino acids show outstanding absorption capacities, superior to MEA or any other amino acid tested. The developed materials have a direct use as mobile carrier membranes for facilitated transport and present a great potential for application in gas separation processes. Computational (DFT) and spectroscopic (1H and 13C-NMR) methods have been applied to make clear the mechanism of carbamate formation from the amine group of amino acids and CO2.
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