K.C. Khulbe

Preparation and characterization of polyvinylidene fluoride hollow fiber membranes for ultrafiltration

Polyvinylidene fluoride (PVDF) hollow fiber membranes were prepared using the solvent spinning method. N,N-dimethylacetamide was the solvent and ethylene glycol was employed as non-solvent additive. The effect of the concentration of ethylene glycol in the PVDF spinning solution as well as the effect of ethanol either in the internal or the external coagulant on the morphology of the hollow fibers was investigated. The prepared membranes were characterized in terms of the liquid entry pressure of water measurements, the gas permeation tests, the scanning electron microscopy, the atomic force microscopy, and the solute transport experiments. Ultrafiltration experiments were conducted using polyethylene glycol and polyethylene oxides of different molecular weights cut-off as solutes. A comparative analysis was made between the membrane characteristic parameters obtained from the different characterization techniques.

Characterization of synthetic membranes by Raman spectroscopy, electron spin resonance, and atomic force microscopy; a review

In this article an attempt is made to review critically the papers concerning novel membrane characterization methods. In particular, our focus on Raman spectroscopy, electron spin resonance (ESR) and atomic force microscopy. For each method the general principle is briefly outlined, followed by discussions on characterization of polymeric materials, in general, and synthetic polymeric membranes, in particular. After highlighting several examples, discussions are made on advantages for each method in order to identify specific area of applications. In general, Raman Spectroscopy is most adequate to obtain information on crystalline structure of the macromolecules and, change of polymeric structure in membrane, ESR on the mobility of molecules in membrane polymer matrixes and membrane pores, and Atomic Force Microscope for three-dimensional display of membrane surfaces.

Study on the effect of a non-solvent additive on the morphology and performance of ultrafiltration hollow-fiber membranes

Hollow-fiber membranes were prepared by the dry/wet spinning technique from polyvinylidene fluoride (PVDF) dope solutions containing the solvent N, N-dimethylacetamide and the non-solvent additive 1,2-ethanediol. Ethanol aqueous solution, 50% by volume, was used as internal and external coagulants. The effect of the non-solvent additive concentration on the morphological properties of the hollow fibers was studied in terms of atomic force microscopy (AFM) and scanning electron microscopy (SEM). The pore size, the nodule size and the roughness parameters at the inner and outer surfaces of the hollow fibers were studied by AFM. The liquid entry pressure of water (LEPw) and the porosity of the hollow fibers were evaluated. The pore size was also determined by the gas permeation test and by the solute transport using ultrafiltration of polyethylene glycol (PEG) and polyethylene oxides (PEO). A comparative study was made between the membrane characteristics parameters obtained from the different characterization techniques.

The effect of heat-treatment on the ultrafiltration performance of polyethersulfone (PES) hollow-fiber membranes

Polyethersulfone (PES) hollow-fiber membranes were prepared by the dry-wet spinning method and then heated in an oven at different temperatures to investigate the effect of heat-treatment on their ultrafiltration performance. It was found that the hollow-fiber membranes shrank by heat treatment, as evidenced by a decrease in flux and an increase in solute separation, although there was no visible change in the hollow-fiber dimension. The best results were obtained when the hollow fibers were heated at 150°C. A further investigation was made on the effect of the heating period, while the temperature was fixed to 150°C. It was found that the best combination of the temperature and the heating period was 150°C and 5 min.

Study of the surface of the water treated cellulose acetate membrane by atomic force microscopy

Water treated cellulose acetate (CA) membranes surface was studied by atomic force microscopy (AFM). It was observed that when CA membrane (water untouched) was treated with water, the morphology of the surface change was detected by AFM. The roughness parameter of the surface was increased. No significant change was observed on the surface on drying the water treated membrane at room temperature for four days. The results were discussed on the basis that CA membrane contains continuous channels (network pores), which were formed in water-swollen polymer matrix. These water channels are responsible for the rejection of salt in reverse osmosis (RO) phenomenon.

Hydrogenation of pyridine over NiWAl2O3 catalyst

Abstract The vapor-phase hydrogenation of pyridine was investigated in an integral flow reactor over NiW Al 2 O 3 catalyst. The effects of various parameters, viz., temperature, initial partial pressures of the reactants, and reciprocal of space velocity, were studied. The kinetics of the hydrogenation of pyridine to form piperidine have been investigated. A rate equation for pyridine hydrogenation was derived. The activation energy was found to be 13.69 kcal/mole. A plausible mechanism has been discussed.

TGA studies of asphaltenes derived from cold-lake (Canada) bitumen

Abstract The pyrolysis of the asphaltene fraction from Cold-Lake, Canada, bitumen in a nitrogen environment in the temperature range 20–845°C has been studied by TGA. A rate equation for the decomposition of asphaltenes was derived and a second order decomposition of asphaltenes was observed. The apparent activation energy and the Arrhenius constant for the decomposition of the asphaltenes were calculated and found to be 56.5 kcal/mol and 5.2 × 10 18 g −1 min −1 , respectively.

Thermal effect on the electron donating and accepting properties of Na-Y zeolite, and the reduction of SO2 and CO

Abstract A study was made of the formation of phenothiazine cation radical (TPQD+) and tetracyanoethylene anion radical (TCNE−) on the surface of Na-Y zeolite. It was observed using electron spin resonance (e.s.r.) that the number of cation formation sites decreased with higher activation temperature while the number of anion sites increased, the respective changes not being in proportion. The formation of the SO2− anion radical on Na-Y zeolite was studied at 450°C. It was observed that the e.s.r. line intensity of SO2− increased with the reaction time, and also with the length of degassing time during thermal activation. CO+ cation radicals were formed when the SO2-treated zeolite was heated at 450°C in contact with CO. The CO+ radicals disappeared either on prolonged heating or heating in the presence of air. The SO2 ions do not take part in the reduction of SO2− with the CO over zeolite. Mechanisms for the formation of CO+ and the other observed effects is discussed.

Electron spin resonance of vanadium pentoxide molybdenum trioxide catalysts

X‐ray, infrared, and electron spin resonance (ESR) studies were made on molybdenum trioxide catalysts doped with 0.25, 0.5, 2.0, 5.0, 10.0, and 20% by weight vanadium pentoxide. X‐ray diagrams indicate the existence of two kinds of patterns for catalysts containing more than 2% V2O5. All the samples produced ESR signals, including pure V2O5. For low dopant concentrations the signals were well resolved, and the paramagnetic center was identified as the VO2+ ion in the unit structure VO2+5O2−. The resonance lines increased in width as the dopant concentration was increased to 10%, and only a single broad line existed for 20% V2O5 or pure V2O5.

Electron spin resonance studies of some Canadian coals

Abstract Nine Canadian coals of different rank and composition were studied by electron spin resonance. For percentage of fixed carbon in the range of 43 to 78 wt%, the free radical g values were found to increase with decreasing carbon content, and did not level off for the low rank coals. The free radical linewidths are attributed to atomic species such as oxygen and not to protons of hydrogen.