Toshio Masuoka

PERVAPORATION OF ETHANOL/WATER THROUGH A POLY (VINYL ALCOHOL)/CYCLODEXTRIN(PVA/CD) MEMBRANE

Abstract A poly(vinyl alcohol)/cyclodextrin (PVA/CD) membrane was utilized in the pervaporation of ethanol/water mixtures. The membrane was prepared by casting an aqueous solution of PVA and β-cyclodextrin oligomer. The CD oligomer was successfully immobilized in the membrane by the crosslinking of PVA with glutaraldehyde for 1 h. The content of CD was up to 33%. The effect of CD on the pervaporation performances of water/ethanol was investigated by measurements of the sorption equilibrium and the calculations of the diffusion coefficient of the permeants in the membrane. The addition of CD increased the water selectivity of the pervaporation of water/ethanol, especially at lower (

Pervaporation membranes for ethanol-water mixture prepared by plasma polymerization of fluorocarbons. II. Perfluoropropane membranes☆

Abstract Pervaporation membranes for ethanol-water binary mixtures were prepared by plasma polymerization of perfluoropropane (PFP). The plasma-polymerized thin films were deposited onto porous polysulfone (PS) filters as substrates with an average pore size from 0.1 to 0.45 μm. By adding argon carrier to PFP system, fluorine/carbon elemental ratios (F/C) of the produced membranes evaluated by X-ray photoelectron spectroscopy (XPS), showed a maximum value, then slightly decreased at higher partial pressure of Ar. This tendency was recognized more clearly by comparing the summation of −CF3 and −CF2-peak area percentages based on a whole C18 peak area. As a measure of hydrophobicity, this value is more intelligible than the direct F/C ratio. The influence of substrate pore-size, plasma-treatment time and hydrophobicity of the membranes on the separation capability were studied. The ethanol-separation coefficient, (αEtOH), of PFP membranes increased slightly with decrease of the average pore-size of the substrates, but treatment time did not apparently affect the αEtOH. We classified the prepared membranes into two classes, i.e. the membranes showing higher and lower permeation fluxes than 0.5 kg/m2-hr. The αEtOH was more evidently observed to increase with membrane hydrophobicity for the former class of PFP membranes. We suggest that, at least, three separation schemes might be necessary to understand the correlations found in each group.

Relationship between permselectivity and permeability in pervaporation of water/alcohol mixture

Abstract The evaporation mechanism of a water/alcohol mixture with a polymeric membrane was investigated. Flory-Huggins thermodynamics was adopted to introduce the selective dissolution factor, R . It was shown that the value of R of a water permselective membrane increases as permeability decreases, and that it has no upper limit. For an ethanol permselective membrane, R has a maximum value at a certain value of the swelling ratio. Making some assumptions for R , a semi-quantitative relationship between permselectivity and permeability, J , was derived for a water permselective membrane and examined experimentally. When the swelling ratio is changed, it can be said that selectivity is proportional to J 1− ( 1 s ) depending on s , the molecular volume ratio of water to alcohol.

Preparation of a cyclophane-bonded stationary phase and its application to separation of naphthalene derivatives

A cyclophane (CP44)-bonded silica gel stationary phase was prepared and elution behaviour of hydrophobic solutes was investigated in the reversed-phase mode. Aromatic compounds were retained on the stationary phases more strongly than the corresponding alicyclic compounds, as was expected by the complex-forming ability of the cyclophane. The stationary phases also showed isomer-selective separation for monomethyl- and dimethylnaphthalenes. The isomers having methyl groups at the α-position were eluted prior to those having methyl groups at the β-position, i.e., the retention order for methylnaphthalene was, α<β and that for dimethylnaphthalene, α,α<α,β<β,β. Moreover, some dimethylnaphthalene isomers which cannot be separated on ordinary reversed-phase stationary phases were separated finely on this stationary phase. The separation mechanism is discussed on the basis of the structure of the cyclophane-involved complex.

Simple thermodynamics of macroscopic phase separation in shrinking gels

The shrinking process induced in spherical gels by an abrupt change in temperature has been investigated qualitatively. The phase diagram of the gel system has been found to be helpful in classifying a variety of shrinking processes. When the solvent quality is lowered within the region between the volume transition and coexistence temperatures, the local swelling ratio of the inner portion, which is divided by a moving interface from the outer shrunk phase, declines in the course of the shrinking process. On the contrary, the local swelling ratio of the inner portion of the shrinking gel is enlarged when the solvent quality is lowered into the region between the coexistence and spinodal temperatures. In this latter case, owing to large local swelling of the inner portion in the vicinity of the interface, spherical symmetry will imply mechanical instability. This instability will be the origin of transient spatial patterns on the surfaces of shrinking gels.