Microemulsion-based organogels as matrices for lipase immobilization.

Analytical solution of the breakthrough curve for rectangular isotherm systems

The drying of hydrogel films formed by poly(ethylene oxide)-poly(propylene oxide) (PEO-PPO) block copolymers (Pluronic P105 and Pluronic L64) is investigated at various air relative humidity (RH) conditions in the range 11-94%. These amphiphilic block copolymers self-assemble to form a variety of ordered (lyotropic liquid crystalline) structures as the water content decreases. The amount of water lost increases linearly with the drying time initially (constant rate region, stage I). After this linear region, a falling rate is observed (stage II). The drying rate increases with decreasing RH, thus greatly shortening the drying time. A decrease of the initial film thickness or a decrease in the initial water content shortens the drying time; however, the drying mechanism remains the same. Analysis of the experimental data shows that the hydration level in the Pluronic hydrogel mainly determines the drying rate, rather than the type of ordered structure formed. Two distinct regions (liquid/gel and solid/crystalline) are observed in the drying isotherm for PEO-PPO block copolymers and homopolymer poly(ethylene glycol)s. A model for one-dimensional water diffusion is used to fit the experimental drying results at different RH, initial film thickness, and initial water content conditions. The model accounts for the shrinkage of the film during drying and for a water diffusion coefficient that is a function of the water concentration in the film. For the experimental conditions considered here, the Biot number (Bi) is less than unity and the drying is mainly limited by evaporation at the film surface. The diffusion model is used to obtain information for cases where Bi > 1.

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Drying of films formed by ordered poly(ethylene oxide)-poly(propylene oxide) block copolymer gels.

Intraparticle mass transfer of mutual ion exchange in MR-type resin was analyzed based on the assumption of parallel diffusion of counter ions in the solid phase and the macropore. Local equilibrium was also assumed between the concentration of counter ions in the solid phase and in the macropore, and the mass action law was applied. The Nernst-Planck equation was applied to the fluxes of ions diffusing through the solid phase and the macropore. The derived equations were solved numerically by using macropore and solid phase diffusivities obtained earlier by isotopic ion exchange. The theoretical lines agreed fairly well with the experimental uptake curves of R-H-NaCl, R-Na-HCl, R-Na-Zn(NO3)2, R-Zn-NaNO3 and R-H-ZnCl2 systems. The lower the concentration of bulk solution Co is, the smaller the effect of Co on the ion exchange rate becomes. The experimental uptake curves of Co ≤ 0.01 (mmole/cm3) were not affected by Co but agreed fairly well with the theoretical line for solid phase diffusion control. An approximate estimation method for obtaining the uptake curve was also proposed. This method gave fairly good approximation for equal valence ion exchange and for R-Na-Zn(NO3)2 systems.



On a analyse le transfert de masse intraparticulaire dans l'echange d'ions dans une resine de type MR; dans l'hypothese d'une diffusion parallele des contre-ions dans la phase solide et dans les macropores. On a aussi suppose l'equilibre local entre la concentration des contre-ions dans la phase solide et dans les macropores, et on a applique la loi d'action de masse. On a aussi applique l'equation de Nernst-Planck aux flux des ions diffusant par la phase solide et par les macropores. On a resolu numeriquement les equations etablies, en employant les diffusivites en phase solide et dans les macropores obtenues anterieurement par echange isotopique d'ions. Les courbes theoriques ont assez bien concorde avec les courbes d'adsorption experimentale pour les systemes de R-H-NaCl, R-Na-HCl, R-Na-Zn(NO3)2, R-Zn-NaNO3 et R-H-ZnCl2. Plus la concentration globale de la solution Co etait faible, et plus l'effet de Co sur la vitesse de l'echange d'ions est faible. Les courbes d'absorption experimentale a Co s 0,01 mmole/cm3 ne sont pas affectees par Co, mais elles sont en assez bon accord avec la courbe theorique pour un phenomene controle par la diffusion en phase solide. On propose aussi une methode approchee d'evaluation pour obtenir la courbe d'absorption; cette methode fournit une assez bonne approximation, dans le cas des systemes d'echange d'ions de meme valence et pour R-Na-Zn(NO3)2.

Intraparticle mass transfer in bidispersed porous ion exchanger part II: Mutual ion exchange

A perfectly mixed batch reactor was used for the determination of the intraparticle diffusivities of Na+ and K+ on commercial Amberlite IR-120 resin in different solvents:  water and solvents composed of different percentages of water and methanol, water and ethanol, and water and 2-propanol. A theoretical model was developed to describe the response of the system that includes the resistance to mass transfer inside the particle and the effect of the electric field (Nernst−Planck approximation). Equilibria were described using a homogeneous model based on the mass action law in which nonideal behavior for both the solution and the solid phase was taken into account. Simulations were performed to analyze the effect of the model parameters on the response curves. The values of intraparticle diffusivities of Na+ and K+ were obtained by nonlinear regression. Both the regression and the parameters were highly meaningful from the statistical point of view. A simple dimensionless relationship that relates diffus...

Determination of intraparticle diffusivities of Na+/K+ in water and water/alcohol mixed solvents on a strong acid cation exchanger

Resin-phase diffusivity in isotopic ion exchange was measured by the single-particle method. The effect of resin diameter, the degree of crosslinking and the concentration and valence of ionic species on resin-phase diffusivity were studied with a macroscopic model by which the diffusivity may be predicted. From these results, the estimating equation of resin-phase diffusivity for sulfonated styrene type resin in the range of the degree of crosslinking 3-16% was obtained.

Hideo Sanada

Papers

Estimation of the resin phase diffusivity in isotopic ion exchange