Composite hollow fiber membranes for CO2 capture

Composite hollow fibers membranes were prepared by coating poly(phenylene oxide) (PPO) and polysulfone (PSf) hollow fibers with high molecular polyvinylamine (PVAm). Two procedures of coating hollow fibers outside and respective inside were investigated with respect to intrinsic PVAm solution properties and hollow fibers geometry and material.The influence of operating mode (sweep or vacuum) on the performances of membranes was investigated. Vacuum operating mode gave better results than using sweep because part of the sweep gas permeated into feed and induced an extra resistance to the most permeable gas the CO₂. The composite PVAm/PSf HF membranes having a 0.7–1.5 μm PVAm selective layer, showed CO₂/N₂ selectivity between 100 and 230. The selectivity was attributed to the CO₂ facilitated transport imposed by PVAm selective layer. The CO₂ permeance changed from 0.006 to 0.022 m³(STP)/(m² bar h) in direct correlation with CO₂ permeance and separation mechanism of the individual porous supports used for membrane fabrication. The multilayer PVAm/PPO membrane using as support PPO hollow fibers with a 40 nm PPO dense skin layer, surprisingly presented an increase in selectivity with the increase in CO₂ partial pressure. This trend was opposite to the facilitated transport characteristic behaviour of PVAm/porous PSf. This indicated that PVAm/PPO membrane represents a new membrane, with new properties and a hybrid mechanism, extremely stable at high pressure ratios. The CO₂/N₂ selectivity ranged between 20 and 500 and the CO₂ permeance from 0.11 to 2.3 m³(STP)/(m² bar h) depending on the operating conditions.For both PVAm/PSf and PVAm/PPO membranes, the CO₂ permeance was similar with the CO₂ permeance of uncoated hollow fiber supports, confirming that the CO₂ diffusion rate limiting step resides in the properties of the relatively thick support, not at the level of 1.2 μm thin and water swollen PVAm selective layer. A dynamic transfer of the CO₂ diffusion rate limiting step between PVAm top layer and PPO support was observed by changing the feed relative humidity (RH%). The CO₂ diffusion rate was controlled by the PPO support when using humid feed. At low feed humidity the 1.2 μm PVAm top layer becomes the CO₂ diffusion rate limiting step.     

Viscous splitting approximation of mixed hyperbolic-parabolic convection-diffusion equations

Summary. We first analyse a semi-discrete operator splitting method for nonlinear, possibly strongly degenerate, convection-diffusion equations. Due to strong degeneracy, solutions can be discontinuous and are in general not uniquely determined by their data. Hence weak solutions satisfying an entropy condition are sought. We then propose and analyse a fully discrete splitting method which employs a front tracking scheme for the convection step and a finite difference scheme for the diffusion step. Numerical examples are presented which demonstrate that our method can be used to compute physically correct solutions to mixed hyperbolic-parabolic convection-diffusion equations. Received November 4, 1997 / Revised version received June 22, 1998     

Properties and characterization of hydrophobized microfibrillated cellulose

Microfibrillated cellulose (MFC) obtained by disintegration of bleached softwood sulphite pulp in a homogenizer, was hydrophobically modified by surface silylation with chlorodimethyl isopropylsilane (CDMIPS). The silylated MFC was characterized by Fourier transform infrared spectroscopy (FT-IR), atomic force microscopy (AFM), transmission electron spectroscopy (TEM), X-ray photoelectron spectroscopy (XPS) and white light interferometry (WLI). The degree of surface substitution (DSS) was determined using Si concentrations from XPS survey scans, as well as deconvoluted peaks in high-resolution C1s XPS spectra. The DSS values obtained by the two methods were found to be in good agreement. MFC with DSS between 0.6 and 1 could be dispersed in a non-flocculating manner into non-polar solvents, TEM observations showing that the material had kept its initial morphological integrity. However, when CDMIPS in excess of 5 mol CDMIPS/glucose unit in the MFC was used, partial solubilization of the MFC occurred, resulting in a drop in the observed DSS and a loss of the microfibrillar character of the material. The wetting properties of films cast from suspension of the silylated MFC were also investigated. The contact angles of water on the films increased with increasing DSS of the MFC, approaching the contact angles observed on super hydrophobic surfaces for the MFC with the highest degree of substitution. This is believed to originate from a combination of low surface energy and surface microstructure in the films.     

A kinetic study of the polymerization of pure meta-divinylbenzene and pure para-divinylbenzene

The kinetics of the polymerization of pure meta-divinylbenzene (DVB) and pure para-divinylbenzene at 70°C have been studied in the presence of toluene and 2-ethylhexanoic acid. The apparent rate constant ratios (k_p/k_t)^1/2 for these systems have been calculated. meta-Divinylbenzene polymerizes at a higher rate than the para-isomer in both toluene and 2-EHA, and the polymerization rates of meta-DVB and para-DVB before the gel point were both higher in the presence of 2-EHA than in toluene. The monomer conversion at the visual gel point is higher for para-DVB than for meta-DVB. The gel point has also been determined indirectly by size exclusion chromatography, and these results are consistent with the gel times observed visually. The conversion of pendant vinyl groups during the polymerization has been determined by bromination. It is found that the homopolymers of poly(para-DVB) have a substantially higher content of pendant vinyl groups than poly(meta-DVB) both during and at the end of the polymerization. The molecular weight distribution (MWD) prior to gelation has been determined by size exclusion chromatography (SEC). Weight average (M̄_w); and number average (M̄_n) molecular weight prior to gelation and of the sol fractions after gelation have also been measured by SEC. There are larger fractions of high molecular weight polymers prior to gelation, when the polymerization was run in the presence of toluene, than in 2-EHA, mainly due to the differences in solvating power of the two diluents. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3345–3359, 1999     

Adaptive Exponential Smoothing Revisited

Adaptive exponential smoothing models are designed to improve performance by letting the smoothing parameter vary according to the most recent forecasting accuracy. This paper argues that the constant exponential smoothing results used in two comparative studies are inadequate as benchmarks. A reexamination does not indicate that adaptive exponential smoothing methods provide superior forecasts compared to those obtainable from constant exponential smoothing with a considerate choice of the smoothing constant. No support was found for the alleged advantages of the Dennis run based adaptive procedure.     

Direct access to functional (Meth)acrylate copolymers through transesterification with lithium alkoxides

A straightforward and efficient synthetic method that transforms poly(methyl methacrylate) (PMMA) into value‐added materials is presented. Specifically, PMMA is modified by transesterification to produce a variety of functional copolymers from a single starting material. Key to the reaction is the use of lithium alkoxides, prepared by treatment of primary alcohols with LDA, to displace the methyl esters. Under optimized conditions, up to 65% functionalization was achieved and copolymers containing alkyl, alkene, alkyne, benzyl, and (poly)ether side groups could be prepared. The versatility of this protocol was further demonstrated through the functionalization of both PMMA homo and block copolymers obtained through either radical polymerization (traditional and controlled) or anionic procedures. The scope of this strategy was illustrated by extension to a range of architectures and polymer backbones. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 1566–1574     

Hydrophobic monolayer preparation by Langmuir-Blodgett and chemical adsorption techniques

Alkylsiloxane and perfluoroalkylsiloxane monolayers are prepared on siliceous surfaces using the techniques of Langmuir-Blodgett deposition and solid-liquid chemical adsorption. Acid-catalyzed hydrolysis and polycondensation reactions provide two-dimensional siloxane networks at the liquid-vapor interface, which can be compressed to mean molecular areas of approximately 22 and approximately 32 A(2) for pendent hydrocarbon and fluorocarbon chains, respectively. Subsequent Langmuir-Blodgett transfer onto glass substrates at moderate surface pressures leads to compact monolayers for single-component precursors, while mixed alkyl- and perfluoroalkylsilanes produce nonhomogeneous films characterized by transfer ratios greater than unity. As an alternate monolayer preparation technique, silane polymerization was performed directly on siliceous surfaces via a chemical adsorption mechanism. XPS analysis of a chemically adsorbed 1H,1H,2H,2H-perfluorodecylsiloxane film confirms a single adsorbed monolayer thickness in which the pendent fluoroalkyl chains align nonperpendicularly with respect to the surface. The surface free energy was determined to be 11.4 dyn cm(-1) based on static contact angle measurements. AFM imaging shows the presence of surface defects due to oligomer deposition during the drying process. The use of solubilized trichloro-based silane coupling agents under anhydrous conditions is shown to produce surfaces with a minimal number of surface defects. The presence of undissolved silane material in the bulk solution significantly increases the number of surface defects.     

Syntheses and Structures of Four New Tellurium(II) Complexes

The four Te^II complexes, cis‐[TeCl₂{(ⁱPrNH)₂CS}₂] ( 1 ), cis‐[TeCl₂{(ⁱBuNH)₂CS}₂] ( 2 ), trans‐[TeCl₂{(PhNMe)₂CS}₂] ( 3 ), and trans‐[TeCl₂{(Et₂N)₂CS}₂] ( 4 ), have been synthesised and their molecular structures solved by means of X‐ray crystallography. All four complexes are square planar, those with disubstituted thiourea ligands have a cis configuration, those with tetrasubstituted thioureas have a trans configuration. The Te–S bond lengths in 1 and 2 average 2.4994 and 2.5213 Å, respectively. The Te–Cl bonds trans to the Te–S bonds have average lengths of 2.8754 and 2.8334 Å, reflecting the trans influence of the two disubstituted thioureas. In 3 and 4 with identical ligands trans to each other, the average Te–S and Te–Cl bond lengths are 2.6834 and 2.5964 Å, respectively.     

Determination of benzo[a]pyrene tetrols by column-switching capillary liquid chromatography with fluorescence and micro-electrospray ionization mass spectrometric detection

The present work displays capillary liquid chromatographic column switching methodology tailored for determination of benzo[a]pyrene tetrol isomers in biological matrices using on-line fluorescence and micro-electrospray ionization mass spectrometric detection. A well-established off-line crude solid phase extraction procedure was used in order to make the method compatible with several biological matrices. The solid phase extraction eluates were evaporated to dryness, redissolved in 1.0 ml methanol:water (10:90, v/v), loaded onto a 0.32 mm I.D. x 40 mm 5 microm Kromasil C(18) pre-column for analyte enrichment and back-flushed elution onto a 0.30 mm I.D. x 150 mm 3.5 microm Kromasil C(18) analytical column. The samples were loaded with a flow rate of 50 microl min(-1) and the tetrols were separated at a flow rate of 4 microl min(-1) with an acetonitrile:10 mM ammonium acetate gradient from 10 to 90%. A sample loading flow rate up to 50 microl min(-1) was allowed. The fluorescence excitation and emission were set to 342 and 385 nm, respectively, while mass spectrometric detection of the benzo[a]pyrene tetrols was obtained by monitoring their [M - H](-) molecular ions at m/z 319. The method was validated over the concentration range 0.1-50 ng ml(-1) benzo[a]pyrene tetrols in a cell culture medium with 100 microl injection volume, fluorescence detection and the first eluting tetrol isomer as model compound, resulting in a correlation coefficient of 0.993. The within-assay (n= 6) and between-assay (n= 6) precisions were determined to 2.6-8.6% and 3.8-9.6%, respectively, and the recoveries were determined to 97.9-102.4% within the investigated concentration range. The mass limit of detection (by fluorescence) was 3 pg for all the tetrol isomers, corresponding to a concentration limit of detection of 30 pg ml(-1) cell culture medium. The corresponding mass spectrometric mass limits of detection were 4-10 pg, corresponding to concentration limits of detection of 40-100 pg ml(-1) cell culture medium.