Adsorption kinetics and equilibria of two methanol samples with different water content on activated carbon

To investigate the influence of fluid purity on the adsorption properties, adsorption kinetics and adsorption equilibria of two methanol samples with different water content on an activated carbon were studied. The purity of the methanol samples was 98.5% and 99.9%. Measurements were conducted at 298 K and 318 K using a magnetic suspension balance and cover a wide p/p0 range. To determine effective diffusion time constants and mass transfer coefficients, adsorption kinetics were evaluated using an isothermal and a nonisothermal Fickian diffusion model, and the linear driving force model. The pressure dependence of the kinetic parameters was studied and discussed. A small influence of sample purity on the adsorption equilibria was observed, as the purer methanol sample showed slightly higher equilibrium loadings than the less pure sample. However, significantly faster adsorption kinetics were observed for the purer sample at all temperature and pressure conditions. Compared to the less pure sample, the determined effective diffusion time constants and the mass transfer coefficients were up to 98% and 35% higher, respectively.

Modelling, kinetics and equilibrium studies of crystal violet adsorption on modified montmorillonite by sodium dodecyl sulfate and hyamine surfactants

Two novel adsorbents – montmorillonite (Mnt)-hyamine and Mnt-hyamine-sodium dodecyl sulfate (SDS) – were synthesized using Mnt nanoparticles. The modified Mnt and Mnt nanoparticles were used for the removal of crystal violet from water, and they were characterized using various techniques. The effects of pH, time, temperature, adsorbent dosage and initial dye concentration on the dye-removal efficiency were investigated using response surface methodology. The optimum conditions for maximum dye removal were obtained. The optimum conditions for crystal violet adsorption on Mnt-hyamine, Mnt-hyamine-SDS and Mnt nanoparticles are temperatures 25.00°C, 29.97°C and 27.28°C; pH values 9.00, 10.41 and 9.40; adsorbent dosages 1.00, 1.15 and 1.06 g L–1; and initial dye concentrations 30.00, 98.74 and 99.44 mg L–1, respectively. The adsorbent dosage is the most critical variable for dye removal. Temkin and Langmuir are the best isotherms for studying adsorption equilibria. In the kinetic study, the fractal-like integrated kinetic Langmuir model was the most appropriate model, and the thermodynamic parameters were also determined. The synthesized adsorbents could be easily separated from solution. The Mnt-hyamine-SDS adsorbent has a high adsorption capacity (690.69 mg g–1) for the removal of crystal violet.

Prediction of the Elution Profiles of Proteins in Mixed Salt Systems in Hydrophobic Interaction Chromatography

Hydrophobic interaction chromatography (HIC) is often used for purifying proteins. A mathematical model to describe the complex effects of salts on the adsorption equilibria in HIC has recently been introduced by our group. It describes not only the influence of single salts, but also salt mixtures, in which cooperative effects may occur. The influence of the salts is thereby modeled with a Taylor series expansion in the individual ion molarities. In the present study, the model of the adsorption equilibrium is coupled with a lumped kinetic model of the adsorption kinetics to obtain a model of the elution of proteins in HIC adsorption columns. The column model is tested using experimental data on the adsorption of bovine serum albumin (BSA) and lysozyme (LYS) on the mildly hydrophobic resin Toyopearl PPG-600M at pH 7. The studied salts are ammonium chloride, sodium chloride, ammonium sulfate, and sodium sulfate as well as binary and ternary mixtures of them. The parameters of the lumped kinetic model are protein-specific and were fitted to the elution profiles of the single proteins in presence of single salts. The model was then used to predict the elution profiles of BSA and LYS solutions containing both proteins, for single salts as well as for binary and ternary salt mixtures. Both isocratic and gradient elution were studied. Furthermore, the model was applied to identify the optimal overall ionic strength for the separation of the two proteins by isocratic elution and the optimal linear gradient of the salt concentration in a multicriteria approach where the conflicting goals are high separation yield and low elution volume.

Prediction of the Elution Profiles of Proteins in Mixed Salt Systems in Hydrophobic Interaction Chromatography

Hydrophobic interaction chromatography (HIC) is often used for purifying proteins. A mathematical model to describe the complex effects of salts on the adsorption equilibria in HIC has recently been introduced by our group. It describes not only the influence of single salts, but also salt mixtures, in which cooperative effects may occur. The influence of the salts is thereby modeled with a Taylor series expansion in the individual ion molarities. In the present study, the model of the adsorption equilibrium is coupled with a lumped kinetic model of the adsorption kinetics to obtain a model of the elution of proteins in HIC adsorption columns. The column model is tested using experimental data on the adsorption of bovine serum albumin (BSA) and lysozyme (LYS) on the mildly hydrophobic resin Toyopearl PPG-600M at pH 7. The studied salts are ammonium chloride, sodium chloride, ammonium sulfate, and sodium sulfate as well as binary and ternary mixtures of them. The parameters of the lumped kinetic model are protein-specific and were fitted to the elution profiles of the single proteins in presence of single salts. The model was then used to predict the elution profiles of BSA and LYS solutions containing both proteins, for single salts as well as for binary and ternary salt mixtures. Both isocratic and gradient elution were studied. Furthermore, the model was applied to identify the optimal overall ionic strength for the separation of the two proteins by isocratic elution and the optimal linear gradient of the salt concentration in a multicriteria approach where the conflicting goals are high separation yield and low elution volume.

Effect of Selected Anionic and Cationic Drugs Affecting the Central Nervous System on Electrical Properties of Phosphatidylcholine Liposomes: Experiment and Theory

Interactions between phospholipid membranes and selected drugs affecting the central nervous system (CNS) were investigated. Small, unilamellar liposomes were used as biomimetic cell membrane models. Microelectrophoretic experiments on two-component liposomes were performed using the electrophoretic light scattering technique (ELS). The effect of both positively (perphenazine, PF) and negatively (barbituric acid, BA) charged drugs on zwitterionic L-α-phosphatidylcholine (PC) membranes were analyzed. Experimental membrane surface charge density (d) data were determined as a function of pH. Quantitative descriptions of the adsorption equilibria formed due to the binding of solution ions to analyzed two-component membranes are presented. Binding constants of the solution ions with perphenazine and barbituric acid-modified membranes were determined. The results of our research show that both charged drugs change surface charge density values of phosphatidylcholine membranes. It can be concluded that perphenazine and barbituric acid are located near the membrane surface, interacting electrostatically with phosphatidylcholine polar heads.

Influence of Salts on the Adsorption of Lysozyme on a Mixed-Mode Resin

Mixed-mode chromatography (MMC), which combines features of ion exchange chromatography (IEC) and hydrophobic interaction chromatography (HIC), is an interesting method for protein separation and purification. The design of MMC processes is challenging as adsorption equilibria are influenced by many parameters, including ionic strength and the presence of different salts in solution. Systematic studies on the influence of those parameters in MMC are rare. Therefore, in the present work, the influence of four salts, namely, sodium chloride, sodium sulfate, ammonium chloride, and ammonium sulfate, on the adsorption of lysozyme on the mixed-mode resin Toyopearl MX-Trp-650M at pH 7.0 and 25°C was studied systematically in equilibrium adsorption experiments for ionic strengths between 0 mM and 3000 mM. For all salts, a noticeable adsorption strength was observed over the entire range of studied ionic strengths. An exponential decay of the loading of the resin with increasing ionic strength was found until approx. 1000 mM. For higher ionic strengths, the loading was found to be practically independent of the ionic strength. At constant ionic strength, the highest lysozyme loadings were observed for ammonium sulfate, the lowest for sodium chloride. A mathematical model was developed that correctly describes the influence of the ionic strength as well as the influence of the studied salts. The model is the first that enables the prediction of adsorption isotherms of proteins on mixed-mode resins in a wide range of technically interesting conditions, accounting for the influence of the ionic strength and four salts of practical relevance.