Masako Maekawa

PARALLEL TRANSPORT BY SURFACE AND PORE DIFFUSION IN A POROUS MEMBRANE

Abstract To investigate parallel transport by surface and pore diffusion within a porous material, we measured uptake curves and concentration profiles for adsorption of a direct dye on a cellulose membrane. A surface diffusion model, a pore diffusion model, and a homogeneous model each predicted well the uptake curves but not the concentration profiles, although the surface diffusion model gave a better agreement than the pore diffusion model. The surface diffusivities determined by assuming surface diffusion control, pore diffusivities assuming pore diffusion control, and the effective diffusivities for the homogeneous model (Deff) obtained from the uptake curves varied with the concentration of the dye and the stimulator (NaCl). The experimental concentration profiles were predicted well by the parallel surface and pore diffusion model. The surface diffusivities for the parallel diffusion model (Ds) were determined from the values of the intercepts of the plots of Deff[1 + (epCo/qo)] vs epCo/qo. The pore diffusivities (Dp) were obtained by matching the theoretical concentration profiles for the parallel diffusion model with the experimental data. The values of Ds and Dp were independent of the concentrations of the dye and the stimulator (NaCl), although the stimulator significantly increased the extent of adsorption. When qo/epCo ⪢ 260, surface diffusion was the rate-controlling step. For lower qo/epCo, the adsorption rate increased concomitantly because of the contribution of pore diffusion.

Surface diffusion of direct dyes in porous cellulose membranes

Abstract Adsorption of C.I. Direct Yellow 12 and C.I. Direct Blue 15 from aqueous solution onto cellulose membranes was carried out in an ultrafiltration-type cell. The dyeing process was analysed on the basis of the parallel transport mechanisms of surface and pore diffusion using Langmuir and Freundlich isotherms. The equilibrium isotherm was represented by Langmuir-type adsorption more accurately than Freundlich-type adsorption when the solution concentration of the dye was less than 0.3 mol m −3 . The differences between the theoretical concentration profiles obtained on the assumption of surface diffusion control for the Langmuir and Freundlich isotherms was negligibly small. In contrast there is a difference between the theoretical concentration profiles of pore diffusion control for Langmuir and Freundlich isotherms. The experimental uptake curves and the concentration profiles showed better agreement with the theory for surface diffusion control than for pore diffusion control. The concentration of NACl influenced the equilibrium isotherm but had little effect on the surface d

Transport phenomena of sulfonated dyes into cellulose membranes: parallel diffusion of a sulfonated dye with a high affinity onto cellulose

Abstract Transport phenomena of C.I. Direct Red 2 into water-swollen cellulose membranes have been studied at 55°C. We reasoned that the dye has a high affinity on cellulose. The transport phenomena were analyzed on the basis of a parallel transport theory of surface and pore diffusion. The transport of the dye into a cellulose membrane was characterized and factors that affect the pore diffusivity of the parallel diffusion model were considered by comparing stimulated data.

Effects of type of adsorption isotherms on parallel diffusion of sulfonated dyes into porous cellulose membrane

Transport phenomenon of three sulfonated azo dyes, C.I. Acid Red 88, C.I. Direct Yellow 12, and C.I. Direct Blue 15 into water-swollen cellulose membranes has been analyzed on the basis of parallel transport theory by surface and pore diffusion. Langmuir equation was applied into the mass balance equation to estimate dye concentration in the pores. The results were compared with the results obtained by applying Freundlich equation in our previous papers. The surface diffusivity (Ds) and the pore diffusivity (Dp) for the parallel diffusion model obtained by applying Langmuir equation agreed with those obtained by applying Freudlich equation. The theoretical concentration profiles for parallel diffusion calculated usingDs andDp coincided accurately with the experimental data when we applied either Langmuir or Freundlich equations.

Effects of affinity and aggregation on parallel diffusion of tri-sulfonated azo compounds into water-swollen cellulose membranes

Adsorption and diffusion of tri-sulfonated azo dyes, C.I. Acid Red 18 and C.I. Acid Red 27 onto waterswollen cellulose membrane has been studied at 25°C. Affinities of these dyes onto cellulose were evaluated by the coefficients of Freundlich equation. Diffusion behavior of these days was analyzed on the basis of a parallel transport theory by surface and pore diffusion. The results could be described by the parallel diffusion model provided that adsorption was stimulated by addition of NaCl. The surface diffusivities for the parallel diffusion model were correlated by the affinity of the dyes, on the other hand, the pore diffusivities for the model were affected by aggregation of the dye depending on its structure and NaCl concentration.

Mixture diffusion of sulfonated dyes into cellulose membrane. III. Application of parallel diffusion model to binary system of direct dyes with different affinity

Abstract Mixture diffusion of two dyes (C.I. Direct Blue 15 (DB15) and C.I. Direct Yellow 12 (DY12)) with different affinity onto the substrate into cellulose membrane from the binary solution was studied at 55°C. Uptake curves and concentration–distance profiles were measured experimentally in the ratios (DB15:DY12) 1:0.5, 1:1 and 1:2. It was examined whether the diffusion of the dyes could be analyzed based on the parallel diffusion theory of surface and pore diffusion. It was revealed that the diffusion of DB15 with higher affinity could be analyzed based on the model in the ratios 1:0.5 and 1:1, although the theoretical value deviated slightly from the data in the concentration–distance profile in the ratio 1:1. On the other hand, the diffusion of DY12 with smaller affinity could not be described by the model, because the diffusivity of the dye changed during the adsorption process against the assumption of the model.

Adhesion of polystyrene latex particles to cotton fibers in aqueous sodium alkylate solutions

The adhesion of polystyrene latex (PSL) particles to cotton fibers was investigated in aqueous sodium alkylate solutions. The PSL particles were polymerized in a surfactant-free system. The sodium alkylates used were sodium octanoate, sodium decanoate, and sodium dodecanoate. The number of particles adhering to the cotton fibers from an aqueous suspension containing sodium alkylate was determined spectroscopically. The rate constant of particle adhesion and the apparent equilibrium amount of the PSL particles adhering to the fibers were obtained. The total potential energies of interaction between the particle and fiber were calculated using the electrokinetic potentials and the thickness of the adsorbed layer on the basis of the heterocoagulation theory. A plot of the logarithmic rate constant of adhesion against the maximum potential energy was found to be linear. The relation between the equilibrium amount of adhesion and the depth of the primary well was also linear. The adhesion of PSL particles to c...

MIXTURE DIFFUSION OF SULFONATED DYES INTO CELLULOSE MEMBRANE. II. EFFECTS OF ADDITION OF A DYE WITH LOWER AFFINITY ON PARALLEL DIFFUSION OF A DYE WITH HIGH AGGREGATION PROPERTY

Abstract Transport phenomena of C.I. Direct Red 2 (DR2) from a binary mixture of dyes with a different affinity to cellulose were studied at 55°C. Diffusion of DR2 with a higher affinity into water-swollen cellulose membrane in the presence of C.I. Direct Yellow 12 (DY12) with a lower affinity was analyzed based on a parallel transport theory of surface and pore diffusion. It was revealed that the diffusion of DR2 in the presence of DY12 could be described by the parallel diffusion model, and pore diffusion for DR2 was enhanced owing to increased pore diffusivity by addition of DY12.

Mixture diffusion of sulfonated dyes into cellulose membrane. I. Application of parallel diffusion model to binary system of acid dyes with small affinity onto cellulose

Transport phenomena of binary mixture of dyes with a small affinity onto cellulose into a water-swollen cellulose membrane were studied at 55°C. The results were analyzed on the basis of a parallel transport theory of surface and pore diffusion. The diffusion of dye molecules in a binary dye system could be described by the parallel diffusion model. Although existence of the other dye decreased the equilibrium adsorption of both dyes onto cellulose, the surface and pore diffusivities for the model of both dyes were same as those in the single dye system.

Peroxide decoloration of azo dyes catalyzed by manganese chlorophyll derivative in micellar solutions

A manganese chlorophyll derivative (MnChlorophyll a) with hydrogen peroxide efficiently catalyzed the decoloration of C. I. Acid Orange 7, in various micellar solutions under mild conditions such as pH 6–8 and 25°C. In the experiment, peroxide decoloration was dependent on the structures of the surfactants and the presence of imidazole. The maximum decoloration rate was observed for MnChlorophyll a in hexadecyltrimethylammonium chloride (HDTAC) micellar solution, especially in the presence of imidazole.