Solvent-resistant nanofiltration for product purification and catalyst recovery in Click chemistry reactions

The quickly developing field of "click" chemistry Would undoubtedly benefit from the availability of an easy and efficient technology for product purification to reduce the potential health risks associated with the presence of copper in the final product. Therefore. solvent-resistant nanofiltration (SRNF) membranes have been developed to selectively separate "clicked" polymers from the copper catalyst and solvent. By using these solvent-stable cross-linked polyimide membranes in diafiltration, up to 98% of the initially present copper could be removed through the membrane together with the DMF solvent, the polymer product being almost completely retained. This paper also presents the first SRNF application in which the catalyst permeates through the membrane and the reaction product is retained

Free Volume Expansion of Poly[1-(trimethylsilyl)-1-propyne] Treated in Supercritical Carbon Dioxide As Revealed by Positron Annihilation Lifetime Spectroscopy

The free volume changes of poly[1-(trimethyl-silyl)-1-propyne] (PTMSP) treated in supercritical CO2 (scCO(2)) were investigated with positron annihilation lifetime spectroscopy (PALS). CO2 is known to plasticize and increase the free volume size of a broad range of polymers. In this work dense PTMSP films were treated with scCO(2) under different pressures and temperatures, resulting in the enlargement of the characteristic channel-like holes (R-3) and the larger free volume cages (R-4) up to 39% and 19%, respectively. The free volume enlargement was found to have a relaxation time of similar to 30 years. At higher temperatures (110-150 degrees C), the o-Ps intensities and gel permeation chromatography (GPC) data revealed chemical changes of the scCO(2)-treated polymer due to the onset of PTMSP's degradation. However, at lower temperatures (40-70 degrees C), significant free volume cavity size increases to 25% for R-3 and 9% for R-4 were also observed

Enhanced performance in pervaporation of supercritical carbon dioxide treated poly[1-(trimethylsilyl)-1-propyne] membranes

The effect of a supercritical carbon dioxide (scCO(2)) treatment on the free volume of poly[1-(trimethylsilyl)-1-propyne] (PTMSP) and PTMSP-silica nanohybrid membranes was investigated with positron annihilation lifetime spectroscopy (PALS) and correlated with their performance in pervaporation. Treatment of dense unfilled PTMSP and silica filled PTMSP (2.5, 10 and 20 wt.% silica) membranes with scCO(2) at different pressures and temperatures, resulted in a clear increase in the mean free volume size and an enhanced performance in the pervaporative separation of an aqueous ethanol mixture. Specific permeation rate increases up to 76% were observed for the unfilled membranes treated with scCO(2) at 70 degrees C and 24 MPa. The scCO(2)-treatment could thus be seen as an effective alternative to PTMSP-silica (50 wt.%) membranes, which cause a 72% increase in specific permeation rate. Moreover, the ethanol concentration in the permeate increases significantly upon treating the membranes with scCO(2). (C) 2011 Elsevier B.V. All rights reserved

Ag-0 and Co-0 nanocolloids as recyclable quasihomogeneous metal catalysts for the hydrogenation of alpha,beta-unsaturated aldehydes to allylic alcohol fragrances

The hydrogenation of the alpha,beta-unsaturated aldehydes cinnamaldehyde (trans-3-phenyl-2-propenal), citral (3,7-dimethyl-2,6-octadienal) and leaf aldehyde (trans-2-hexenal) was investigated with metal colloids as quasi homogeneous catalysts in organic solvents. Using polyvinylpyrrolidone-stabilized Ag-0 and Co-0 nanoclusters, the carbonyl compounds were chemoselectively hydrogenated to the desired allylic alcohol fragrances. Particularly the Ag-0 nanosols emerged as a worthwhile alternative for Pt or Ru based catalysts. Amides proved to be excellent solvents for the synthesis as well as for the application of the metal nanocolloids in the hydrogenation of alpha,beta-unsaturated aldehydes. In the challenging hydrogenation of citral, a selectivity exceeding 70% towards the doubly unsaturated alcohol isomers (geraniol and nerol) was attained at 90% conversion using Ag-0 nanocolloids dispersed in N,N-dimethylacetamide. Reactions were performed under mild conditions (2.0 MPa H-2, 323 K) at a molar citral/silver ratio of 200/1. The addition of Lewis acid cations, such as Fe3+ or Zn2+ resulted in a further improvement of the catalytic activity and chemoselectivity. Finally, by application of membrane filtrations, an efficient separation of the metallic nanocolloids from the reaction mixtures was realized. In the recycling of the metal nanosols, the metal catalysts' nanodispersion and performance were satisfactorily preserved. (C) 2007 Published by Elsevier B.V.status: publishe

Crosslinked poly[1-(trimethylsilyl)-1-propyne] membranes: Characterization and pervaporation of aqueous tetrahydrofuran mixtures

To enhance their applicability in a broader range of pervaporation feed streams, poly[1-(trimethylsilyl)-1-propyne] (PTMSP) membranes have been successfully crosslinked, using a 3,3'-diazido-diphenylsulfone crosslinker. Both photochemical and thermal processes were used to activate the bis(azide) and thus initiate the crosslink reaction. The presented photochemical crosslink process, has an insufficient efficiency, due to the unreacted bis(azide) and the formation of by-products such as carboxylic acids. On the other hand, thermal annealing at temperatures of at least 160 degrees C allows successful crosslinking of FTMSP. In contrast to photochemical crosslinking, the bis(azide) completely decomposes after thermal treatment, rendering the membranes insoluble in solvents that dissolve the uncrosslinked polymer, such as tetrahydrofuran (THF), n-heptane and methyl-tert-butyl ether. All membranes were extensively characterized by means of infrared analysis, solid-state H-1-wideline NMR, positron annihilation lifetime spectroscopy, swelling capacity measurements and pervaporation measurements. These techniques, allowed to gain insight in the crosslink reaction mechanism, crosslinking density of the crosslinked polymer network, changes in the free volume cavity sizes, solvent resistance and pervaporation performance, respectively. The potential of the thermally crosslinked PTMSP membranes in the removal of demanding solvents from aqueous mixtures was illustrated by pervaporation tests on dilute THF/water mixtures. The membrane containing 15 wt.% of crosslinker and treated at 180 degrees C during 1.5 h showed specific permeation rates that are approximately 4 times higher than those of the commercially available polydimethylsiloxane-based membranes, combined with competitive THF/water separation factors. Feed streams containing 10 wt.% THF could be enriched up to 84 wt.% THF in the permeate. (C) 2011 Elsevier B.V. All rights reserved

Ag-0 and Co-0 nanocolloids as recyclable quasihomogeneous metal catalysts for the hydrogenation of alpha,beta-unsaturated aldehydes to allylic alcohol fragrances

The hydrogenation of the alpha,beta-unsaturated aldehydes cinnamaldehyde (trans-3-phenyl-2-propenal), citral (3,7-dimethyl-2,6-octadienal) and leaf aldehyde (trans-2-hexenal) was investigated with metal colloids as quasi homogeneous catalysts in organic solvents. Using polyvinylpyrrolidone-stabilized Ag-0 and Co-0 nanoclusters, the carbonyl compounds were chemoselectively hydrogenated to the desired allylic alcohol fragrances. Particularly the Ag-0 nanosols emerged as a worthwhile alternative for Pt or Ru based catalysts. Amides proved to be excellent solvents for the synthesis as well as for the application of the metal nanocolloids in the hydrogenation of alpha,beta-unsaturated aldehydes. In the challenging hydrogenation of citral, a selectivity exceeding 70% towards the doubly unsaturated alcohol isomers (geraniol and nerol) was attained at 90% conversion using Ag-0 nanocolloids dispersed in N,N-dimethylacetamide. Reactions were performed under mild conditions (2.0 MPa H-2, 323 K) at a molar citral/silver ratio of 200/1. The addition of Lewis acid cations, such as Fe3+ or Zn2+ resulted in a further improvement of the catalytic activity and chemoselectivity. Finally, by application of membrane filtrations, an efficient separation of the metallic nanocolloids from the reaction mixtures was realized. In the recycling of the metal nanosols, the metal catalysts' nanodispersion and performance were satisfactorily preserve