Aiming at a more thorough understanding of the influence of zeolite fillers in PDMS membranes on ... more Aiming at a more thorough understanding of the influence of zeolite fillers in PDMS membranes on the pervaporation of chlorinated hydrocarbons from aqueous solutions, the sorption aspect of this separation process was studied. Firstly, the sorption of water and five different chlorinated hydrocarbons was investigated in the zeolite and the polymer separately. Secondly, the composite system was considered and conclusions were drawn concerning interactions at the zeolite−polymer interphase. Finally, the sorption results obtained on the self-synthesized membranes were compared with measurements on commercially available PDMS membranes (GFT).
In order to study in more detail the influence of the filler on pervaporation performance, silica... more In order to study in more detail the influence of the filler on pervaporation performance, silicalite, ZSM-5, and zeolite Y were incorporated in poly(dimethylsiloxane) (PDMS) and tested in pervaporation experiments with binary mixtures of chlorinated hydrocarbons (Cl-HC's) in water. The results were compared with unfilled PDMS as a reference. The highest selectivities were obtained with the silicalite-filled membranes. However, these membranes showed a decrease in permeability for voluminous components due to molecular sieving effects. In this respect, the results with zeolite Y were rather disappointing, as its larger pore size was counteracted by its high polarity, whereas ZSM-5-filled membranes showed intermediate selectivities. Therefore, mesoporous silicas were synthesized, silylated to assure their apolarity, and incorporated in PDMS. The resulting membranes showed both improved organic fluxes and selectivities in comparison with all other membranes, even for voluminous or...
The free volume sizes and interstitial mesopore sizes in poly(1-trimethylsilyl-1-propyne) (PTMSP)... more The free volume sizes and interstitial mesopore sizes in poly(1-trimethylsilyl-1-propyne) (PTMSP)/silica nanocomposites and the correlation between nitrogen permeability and cavity sizes were studied with positron annihilation lifetime spectroscopy (PALS) at filler concentrations between 0 and 50 wt %. A bimodal free volume distribution was observed for PTMSP, and the size of the larger free volume cavities was significantly increased upon addition of hydrophobic fumed silica. Nanometer-sized interstitial cavities in filler agglomerates were observed in all PTMSP/fumed silica nanocomposites and in neat hydrophobic fumed silica. The radius of these interstitial mesopores in the nanocomposites decreased with decreasing filler concentration. A strong correlation between nitrogen permeability and the volume of the interstitial mesopores in the nanocomposite membranes was observed.
Bimetallic gold–palladium clusters, with an average size of 1.9nm and composed of 80mol% gold, pr... more Bimetallic gold–palladium clusters, with an average size of 1.9nm and composed of 80mol% gold, proved to be highly active and selective metal catalysts for the organic phase oxidation with O2 of aliphatic, allylic and benzylic alcohols to the corresponding carbonyl products. Polyvinylpyrrolidone stabilized gold–palladium clusters dispersed in N,N-dimethylformamide emerged as promising quasihomogeneous metal catalysts for the oxidation of benzyl alcohol to benzaldehyde with full selectivity; they could be efficiently recycled with unaffected catalytic performance by solvent-resistant nanofiltration. Highly active and durable heterogeneous catalysts for the amide phase or solvent-free alcohol oxidation were prepared by the quantitative immobilization of the optimized gold–palladium clusters on the high surface area basic BaAl2O4 spinel support with preservation of the bimetallic clusters’ nanodispersion.
Modified poly(ether ether ketone) (PEEK) was synthesized to produce ultrafiltration (UF) and nano... more Modified poly(ether ether ketone) (PEEK) was synthesized to produce ultrafiltration (UF) and nanofiltration (NF) membranes. The prepared polymer is soluble in some polar aprotic solvents, such as n-methyl-2-pyrrolidone and tetrahydrofuran, making it possible to prepare membranes from them via the phase inversion process. By introducing these films to a non-solvent bath, tight UF to open NF membranes could be prepared that were stable in water, alcohols and other solvents such as hexane and acetonitrile. A range of membranes was prepared and their performance was evaluated by filtration experiments with rose Bengal in isopropanol, while their morphology was investigated by scanning electron microscopy. In addition to the influence of polymer properties, such as molecular weight and polydispersity, the role of the PEEK concentration in the casting solution on membrane performance and morphology was investigated. The membranes were also tuned towards NF performance by introducing volat...
This review discusses many crosslinking methods for polyimide membranes that have been described ... more This review discusses many crosslinking methods for polyimide membranes that have been described in literature. Some important properties of polyimides and their synthesis reactions are first summarized. The important (commercialized) polyimide types that are now used in membrane technology, the preparation methods available for polyimide membranes and their main applications are listed. The effects of thermal annealing of polyimide membranes are briefly discussed, before giving an extensive review of the many crosslinking methods that have been described in literature. Thermal crosslinking, UV crosslinking and a range of chemical crosslinking methods, including diol and diamine crosslinking, are discussed in detail, focusing on the actual chemistry behind the crosslinking. Also, some new, not yet fully studied, crosslinking methods are listed.
ABSTRACT PEEK membranes with good stability in polar aprotic solvents are developed for the separ... more ABSTRACT PEEK membranes with good stability in polar aprotic solvents are developed for the separation of edible oils from acetone. PEEK membranes are hydrophobic in nature, and thus suitable to achieve high fluxes in organic solvents. Chemical crosslinking with amines provides the membranes with robust solvent stability. In this research, three types of modified PEEK were synthesized. All were crosslinked with both the well-known difunctional crosslinker hexanediamine as with the multifunctional polyallylamine. Performance of membranes prepared with both crosslinkers was compared for rose Bengal solutions in isopropanol and acetone, and for sunflower oil dissolved in acetone. Using polyallylamine as a crosslinker introduced free amines into the membrane structure, increasing the hydrophilicity of the membrane which improved the retention of edible oil significantly. (c) 2013 Elsevier Ltd. All rights reserved.
Thin film composite (TFC) membranes are used worldwide in aqueous applications. They mostly consi... more Thin film composite (TFC) membranes are used worldwide in aqueous applications. They mostly consist of a polyamide top-layer put on a polysulfone support via interfacial polymerization. Due to their thin and dense selective layer, these membranes are also interesting for filtrations in organic solutions. Polysulfone should then be replaced by a more solvent resistant material. The synthesis of solvent resistant nanofiltration TFC membranes via a newly developed method is reported: phase inversion, crosslinking and impregnation of a polyimide support are combined by adding amines to the aqueous coagulation bath. Next, a thin polyamide top-layer is formed on the support via interfacial polymerization. Several amines are tested as crosslinker for the support and as monomer for top-layer formation. The use of an amine mixture is also explored. Membrane stability, time in the coagulation bath, effect of solvent activation and mass and solvent intensity of the process are investigated. Th...
The phase inversion parameters of membranes prepared from lab-synthesized poly(ether ether ketone... more The phase inversion parameters of membranes prepared from lab-synthesized poly(ether ether ketone) polymers BPAPEEK and TBPEEK are investigated to tune their performance towards nanofiltration. These PEEK polymers are suitable for producing phase inversion membranes as they are soluble in polar aprotic solvents, thanks to the presence of alkyl side groups. Firstly, the influence of polymer concentration on membrane performance was investigated and a volatile co-solvent was added to improve the retention. Evaporation time was then tuned, in addition to coagulation bath composition and casting thickness. The membranes were also tested with a smaller solute. Additional to this phase inversion study, stability of the membranes in alkaline conditions was investigated. The prepared polymers proved to have potential as solvent resistant nanofiltration membranes or as hydrophobic support materials for thin film composite membranes.
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was e... more ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
Although transition-metal complexes are very attractive as homogeneous catalysts in fine chemistr... more Although transition-metal complexes are very attractive as homogeneous catalysts in fine chemistry, their high prices often limit their applications. A means to recycle those catalysts would solve this problem and would simultaneously facilitate the downstream purification of the product. This is now realized in a new concept in which homogeneous catalysis is coupled to dialysis. The advantages of homogeneous catalysis (off-the-shelf catalysts, high activities and selectivities) are thus combined with those of heterogeneous catalysis (easy catalyst separation from product solution, reuse of catalyst, and possibility for continuous operation). Since the heart of the process is the membrane, self-prepared membranes were preferred as they allow a better control and understanding of the separation characteristics. Rhodamine B was used as a probe molecule to define the working conditions of the membrane. The concept is proven to work for two relevant chiral reactions: a hydrogenation with Ru-BINAP and a hydrogen transfer reaction with Ru-TsDPEN [BINAP=(1,1'-binaphthalene)-2,2'-diylbis(diphenylphosphine); TsDPEN= tosyl-N,N'-diphenyl-1,2-ethanediamine].
Aiming at a more thorough understanding of the influence of zeolite fillers in PDMS membranes on ... more Aiming at a more thorough understanding of the influence of zeolite fillers in PDMS membranes on the pervaporation of chlorinated hydrocarbons from aqueous solutions, the sorption aspect of this separation process was studied. Firstly, the sorption of water and five different chlorinated hydrocarbons was investigated in the zeolite and the polymer separately. Secondly, the composite system was considered and conclusions were drawn concerning interactions at the zeolite−polymer interphase. Finally, the sorption results obtained on the self-synthesized membranes were compared with measurements on commercially available PDMS membranes (GFT).
In order to study in more detail the influence of the filler on pervaporation performance, silica... more In order to study in more detail the influence of the filler on pervaporation performance, silicalite, ZSM-5, and zeolite Y were incorporated in poly(dimethylsiloxane) (PDMS) and tested in pervaporation experiments with binary mixtures of chlorinated hydrocarbons (Cl-HC's) in water. The results were compared with unfilled PDMS as a reference. The highest selectivities were obtained with the silicalite-filled membranes. However, these membranes showed a decrease in permeability for voluminous components due to molecular sieving effects. In this respect, the results with zeolite Y were rather disappointing, as its larger pore size was counteracted by its high polarity, whereas ZSM-5-filled membranes showed intermediate selectivities. Therefore, mesoporous silicas were synthesized, silylated to assure their apolarity, and incorporated in PDMS. The resulting membranes showed both improved organic fluxes and selectivities in comparison with all other membranes, even for voluminous or...
The free volume sizes and interstitial mesopore sizes in poly(1-trimethylsilyl-1-propyne) (PTMSP)... more The free volume sizes and interstitial mesopore sizes in poly(1-trimethylsilyl-1-propyne) (PTMSP)/silica nanocomposites and the correlation between nitrogen permeability and cavity sizes were studied with positron annihilation lifetime spectroscopy (PALS) at filler concentrations between 0 and 50 wt %. A bimodal free volume distribution was observed for PTMSP, and the size of the larger free volume cavities was significantly increased upon addition of hydrophobic fumed silica. Nanometer-sized interstitial cavities in filler agglomerates were observed in all PTMSP/fumed silica nanocomposites and in neat hydrophobic fumed silica. The radius of these interstitial mesopores in the nanocomposites decreased with decreasing filler concentration. A strong correlation between nitrogen permeability and the volume of the interstitial mesopores in the nanocomposite membranes was observed.
Bimetallic gold–palladium clusters, with an average size of 1.9nm and composed of 80mol% gold, pr... more Bimetallic gold–palladium clusters, with an average size of 1.9nm and composed of 80mol% gold, proved to be highly active and selective metal catalysts for the organic phase oxidation with O2 of aliphatic, allylic and benzylic alcohols to the corresponding carbonyl products. Polyvinylpyrrolidone stabilized gold–palladium clusters dispersed in N,N-dimethylformamide emerged as promising quasihomogeneous metal catalysts for the oxidation of benzyl alcohol to benzaldehyde with full selectivity; they could be efficiently recycled with unaffected catalytic performance by solvent-resistant nanofiltration. Highly active and durable heterogeneous catalysts for the amide phase or solvent-free alcohol oxidation were prepared by the quantitative immobilization of the optimized gold–palladium clusters on the high surface area basic BaAl2O4 spinel support with preservation of the bimetallic clusters’ nanodispersion.
Modified poly(ether ether ketone) (PEEK) was synthesized to produce ultrafiltration (UF) and nano... more Modified poly(ether ether ketone) (PEEK) was synthesized to produce ultrafiltration (UF) and nanofiltration (NF) membranes. The prepared polymer is soluble in some polar aprotic solvents, such as n-methyl-2-pyrrolidone and tetrahydrofuran, making it possible to prepare membranes from them via the phase inversion process. By introducing these films to a non-solvent bath, tight UF to open NF membranes could be prepared that were stable in water, alcohols and other solvents such as hexane and acetonitrile. A range of membranes was prepared and their performance was evaluated by filtration experiments with rose Bengal in isopropanol, while their morphology was investigated by scanning electron microscopy. In addition to the influence of polymer properties, such as molecular weight and polydispersity, the role of the PEEK concentration in the casting solution on membrane performance and morphology was investigated. The membranes were also tuned towards NF performance by introducing volat...
This review discusses many crosslinking methods for polyimide membranes that have been described ... more This review discusses many crosslinking methods for polyimide membranes that have been described in literature. Some important properties of polyimides and their synthesis reactions are first summarized. The important (commercialized) polyimide types that are now used in membrane technology, the preparation methods available for polyimide membranes and their main applications are listed. The effects of thermal annealing of polyimide membranes are briefly discussed, before giving an extensive review of the many crosslinking methods that have been described in literature. Thermal crosslinking, UV crosslinking and a range of chemical crosslinking methods, including diol and diamine crosslinking, are discussed in detail, focusing on the actual chemistry behind the crosslinking. Also, some new, not yet fully studied, crosslinking methods are listed.
ABSTRACT PEEK membranes with good stability in polar aprotic solvents are developed for the separ... more ABSTRACT PEEK membranes with good stability in polar aprotic solvents are developed for the separation of edible oils from acetone. PEEK membranes are hydrophobic in nature, and thus suitable to achieve high fluxes in organic solvents. Chemical crosslinking with amines provides the membranes with robust solvent stability. In this research, three types of modified PEEK were synthesized. All were crosslinked with both the well-known difunctional crosslinker hexanediamine as with the multifunctional polyallylamine. Performance of membranes prepared with both crosslinkers was compared for rose Bengal solutions in isopropanol and acetone, and for sunflower oil dissolved in acetone. Using polyallylamine as a crosslinker introduced free amines into the membrane structure, increasing the hydrophilicity of the membrane which improved the retention of edible oil significantly. (c) 2013 Elsevier Ltd. All rights reserved.
Thin film composite (TFC) membranes are used worldwide in aqueous applications. They mostly consi... more Thin film composite (TFC) membranes are used worldwide in aqueous applications. They mostly consist of a polyamide top-layer put on a polysulfone support via interfacial polymerization. Due to their thin and dense selective layer, these membranes are also interesting for filtrations in organic solutions. Polysulfone should then be replaced by a more solvent resistant material. The synthesis of solvent resistant nanofiltration TFC membranes via a newly developed method is reported: phase inversion, crosslinking and impregnation of a polyimide support are combined by adding amines to the aqueous coagulation bath. Next, a thin polyamide top-layer is formed on the support via interfacial polymerization. Several amines are tested as crosslinker for the support and as monomer for top-layer formation. The use of an amine mixture is also explored. Membrane stability, time in the coagulation bath, effect of solvent activation and mass and solvent intensity of the process are investigated. Th...
The phase inversion parameters of membranes prepared from lab-synthesized poly(ether ether ketone... more The phase inversion parameters of membranes prepared from lab-synthesized poly(ether ether ketone) polymers BPAPEEK and TBPEEK are investigated to tune their performance towards nanofiltration. These PEEK polymers are suitable for producing phase inversion membranes as they are soluble in polar aprotic solvents, thanks to the presence of alkyl side groups. Firstly, the influence of polymer concentration on membrane performance was investigated and a volatile co-solvent was added to improve the retention. Evaporation time was then tuned, in addition to coagulation bath composition and casting thickness. The membranes were also tested with a smaller solute. Additional to this phase inversion study, stability of the membranes in alkaline conditions was investigated. The prepared polymers proved to have potential as solvent resistant nanofiltration membranes or as hydrophobic support materials for thin film composite membranes.
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was e... more ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
Although transition-metal complexes are very attractive as homogeneous catalysts in fine chemistr... more Although transition-metal complexes are very attractive as homogeneous catalysts in fine chemistry, their high prices often limit their applications. A means to recycle those catalysts would solve this problem and would simultaneously facilitate the downstream purification of the product. This is now realized in a new concept in which homogeneous catalysis is coupled to dialysis. The advantages of homogeneous catalysis (off-the-shelf catalysts, high activities and selectivities) are thus combined with those of heterogeneous catalysis (easy catalyst separation from product solution, reuse of catalyst, and possibility for continuous operation). Since the heart of the process is the membrane, self-prepared membranes were preferred as they allow a better control and understanding of the separation characteristics. Rhodamine B was used as a probe molecule to define the working conditions of the membrane. The concept is proven to work for two relevant chiral reactions: a hydrogenation with Ru-BINAP and a hydrogen transfer reaction with Ru-TsDPEN [BINAP=(1,1'-binaphthalene)-2,2'-diylbis(diphenylphosphine); TsDPEN= tosyl-N,N'-diphenyl-1,2-ethanediamine].
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