Kuniaki Inui

Permeation and separation of benzenecyclohexane mixtures through cross-linked poly(alkyl methacrylate) membranes

Abstract Poly(methyl methacrylate) (PMMA) and poly(ethyl methacrylate) (PEMA) which have strong affinity for benzene were selected as membrane materials and the characteristics of permeation and separation for the benzene cyclohexane mixtures through these poly(alkyl methacrylate) cross-linked with ethylene glycol dimethacrylate (EGDM) membranes by pervaporation were investigated. The cross-linked poly(alkyl methacrylate) membranes exhibited a benzene permselectivity for the benzene cyclohexane mixtures and the permeation rate increased with increasing benzene in the feed solution. The permselectivity of their membranes was strongly governed by the diffusion separation process depending on the difference of the molecular size between the benzene molecule and the cyclohexane molecule. The depression of swelling of those membranes with the increase of the cross-linker content in the benzene cyclohexane mixtures enhanced the benzene permselectivity. This result was attributed to the increase of the selectivity in the sorption separation process with the depression of swelling of the membrane. Furthermore, the cross-linked copolymer (PMMA-PEMA-EGDM) membranes showed excellent benzene permselectivity. These results suggested that both, the increase of affinity of the membrane for benzene and depression of swelling of the membrane, were very important in the separation of the benzene cyclohexane mixtures.

Permeation and separation of a benzene/cyclohexane mixture through benzoylchitosan membranes

Benzoylchitosans (BzCses) with a different degree of benzoylation were synthesized as membrane materials having a good durability for the separation of benzene/cyclohexane (Bz/Chx) mixtures. Characteristics of BzCs membranes such as contact angle, crystallinity and degree of swelling were significantly influenced by the degree of benzoylation. The BzCs membranes showed a high benzene-permselectivity for a Bz/Chx mixture of 50 wt% benzene in pervaporation and a difference of the benzene-permselectivity for the BzCs membranes with different degree of benzoylation corresponded to a difference in the physical structure of the membranes based on the characteristics of these membranes. When a Bz/Chx mixture of 50 wt% benzene was permeated through the BzCs membranes, permeation rate increased and benzene-permselectivity slightly decreased with increasing degree of benzoylation. These results are discussed from the viewpoints of chemical and physical structures of the BzCs membranes with different degree of benzoylation.

Pervaporation characteristics of methyl methacrylate–methacrylic acid copolymer membranes ionically crosslinked with metal ions for a benzene/cyclohexane mixture

Methyl methacrylate–methacrylic acid copolymer (MMA–MAA) membranes ionically crosslinked with Fe3+ and Co2+ ions (MMA–MAA–Fe3+ and –Co2+) were prepared, and characteristics of permeation and separation for a benzene/cyclohexane mixture of 50 wt % benzene through these membranes in pervaporation (PV) were studied. Although the introduction of the metal ions to the MMA–MAA membrane enhanced both benzene permselectivity and permeability for a benzene/cyclohexane mixture, the PV characteristics between the MMA–MAA–Fe3+ and –Co2+ membranes were significantly different. The difference in the PV characteristics between these membranes was strongly governed by the difference of these membrane structures based on the glass transition temperature, contact angle to methylene iodide, degree of swelling, and mixture composition absorbed in the membrane, and so on.

Pervaporation characteristics of a benzoylchitosan membrane for benzene‐cyclohexane mixtures

A benzoylchitosan was synthesized as a membrane material for separation of benzene/cyclohexane mixtures. When the benzoylchitosan membrane was applied to the permeation and separation of benzene/cyclohexane mixtures in pervaporation, both the permeation rate and benzene concentration in the permeate increased with increasing benzene concentration in the feed, and thus this membrane showed benzene permselectivity. Characteristics of permeation and separation of benzene/cyclohexane mixtures through the benzoylchitosan membrane were analyzed by the solution-diffusion model. It was found that the benzene permselectivity was dependent on both the sorption selectivity and diffusion selectivity but was significantly governed by the latter. Also a tentative model for the benzene permselectivity is discussed.

Permeation and separation of benzene/cyclohexane mixtures through liquid-crystalline polymer membranes

The side-chain liquid-crystalline polymer (LCP) was synthesized by the addition of the mesogenic monomer to poly(methylsiloxane) with Pt catalyst. When the benzene/cyclohexane mixtures were permeated through the LCP membranes by pervaporation at various temperatures, the permeation rate increased with increasing benzene concentration in the feed solution and permeation temperature. Though the LCP membranes exhibited a benzene permselectivity, a mechanism of the permeation and separation for the benzene/cyclohexane mixtures was different in the glassy, liquid-crystalline and isotropic state of the LCP membranes. These results suggested that the permselectivity was fairly influenced by the change of the LCP membrane structure, that is, a state transformation. It was found that a balance of the orientation of mesogenic groups and flexibility of siloxane chains is very important for the permeability and selectivity.

Effect of mesogenic groups on characteristics of permeation and separation for benzene/cyclohexane mixtures of side-chain liquid-crystalline polymer membranes

When benzene/cyclohexane (Bz/Chx) mixtures were permeated through nematic and smectic side-chain liquid-crystalline polymer (n- and s-LCP) membranes under various conditions in pervaporation, the n- and s-LCP membranes exhibited a benzene-permselectivity for the Bz/Chx mixtures. The benzene-permselectivity of the n-LCP membrane changed from the sorption selectivity to the diffusion selectivity by the state-transformation of the membrane with an increase in the permeation temperature but the benzene-permselectivity of the s-LCP membrane was governed by the diffusion selectivity regardless of the state of the s-LCP membrane. At the low permeation temperature, the n-LCP membrane in the liquid-crystalline state exhibited a lower permeability and a higher permselectivity than the s-LCP membrane. However, at the high permeation temperature the relationship between the permeability and permselectivity of the n-LCP and s-LCP membranes in the liquid-crystalline state was vice versa. These results were led by the difference of the chemical and physical structure of the n-LCP and s-LCP membranes.

Effect of permeation temperature on permeation and separation of a benzene/cyclohexane mixture through liquid-crystalline polymer membranes

When a benzene/cyclohexane mixture of 10 wt % benzene was permeated through side-chain liquid-crystalline polymer (LCP) membranes by pervaporation at various temperatures, the permeation rate increased with increasing permeation temperature. The LCP membranes also exhibited a benzene permselectivity. The permselectivity for the benzene/cyclohexane mixture through the LCP membrane was different in the glassy, liquid-crystalline, and isotropic states. The LCP membrane had different apparent activation energies for permeation at each state. LCP membrane in the liquid-crystalline state had the highest apparent activation energy of the three states. Results suggest that the benzene permselectivity was influenced by changes in the LCP membrane structure, i.e., a state-transformation. It was found that a balance of the orientation of mesogenic groups and the flexibility of the siloxane chains was very important for benzene permselectivity.

Permeation and separation of binary organic mixtures through a liquid-crystalline polymer membrane

When benzene/cyclohexane, toluene/cyclohexane and o-xylene/cyclohexane mixtures are subjected to pervaporation through a side-chain liquid-crystalline polymer (LCP) membrane in the liquid-crystalline state, the permeation rate increases with increasing temperature and the LCP membrane exhibits permselectivity for the aromatic hydrocarbon. The permeation rate and permselectivity of the LCP membrane for each mixture decreases with increasing molecular size of the aromatic hydrocarbon in the binary feed mixture.