Branko Kunst

Porosity of some commercial reverse osmosis and nanofiltration polyamide thin-film composite membranes

Abstract The objective of this study was to determine porosity parameters of some commercial polyamide thin-film composite membranes, and to explain their influence on membrane performance. Experiments were performed at two operating pressures using model inorganic and organic aqueous solutions. Pore size distributions and the effective number of pores in the upper membrane layer were calculated from the experimental results. The performances of the examined membranes were explained using the calculated porosity parameters.

Removal of organics from aqueous solutions by commercial RO and NF membranes of characterized porosities

Removal of organic pollutants of petrochemical and agrochemical origin by some commercial reverse osmosis (RO) and nanofiltration (NF) membranes of characterized porosity was investigated. The rejection of organics was shown to depend on both the membrane properties like pore size, membrane material, membrane charge and solute characteristics such as molecule size, charge and polarity. The rejection of the small nonionized organic molecules by the tight pore membranes is influenced by both the sieving parameters (solute and pore size) and by the physicochemical interactions. The rejection of the same pollutants by the wider pore membranes is dominantly influenced by the physicochemical interactions. The rejection of pesticides is prevalently governed by the sieving mechanism based on the size of the solute molecule and the membrane pore size. However, the physicochemical effects cannot be totally neglected, and they can contribute to the rejection of some pesticides by certain membranes.

Preparation and porosity of cellulose triacetate reverse osmosis membranes

Good cellulose triacetate reverse osmosis membranes have been prepared by the phase separation technique. The membrane properties were influenced by the membrane casting dope composition, mostly by the dioxane/acetone ratio and the maleic acid content in the casting dope. The distinctive membrane performances were caused by different pore size distributions and various numbers of pores in the membranes skin. The improved pore size distribution analysis and the calculation of both the effective number of pores and the active part of the membranes surface area have shown a wide spectrum of the network pore sizes and usually one size group of bigger aggregate pores.

FT30 membranes of characterized porosities in the reverse osmosis organics removal from aqueous solutions

Removal of some organic pollutants from aqueous solutions by reverse osmosis using commercial FT30 membranes of characterized porosities was investigated. The pore size distribution analysis and calculation of the effective number of pores have shown the presence of numerous narrow unimodally distributed pores in the upper selective membrane layer. The organic pollutant removal by reverse osmosis is governed mostly by mutual interactions between the membrane material, solute and water molecules.

On the skinned cellulose triacetate membranes formation

Abstract The effect of casting dope parameters like a dioxane to acetone ratio and a maleic acid content in the process of asymmetric cellulose triacetate membrane preparation were investigated. The results were considered in terms of possible pore size distribution in the membranes skin. It was found that the second parameter, the maleic acid content, played a significant role in the formation process, affecting strongly the performance of membranes.

On the calculation of stream concentrations in reverse osmosis processes

Abstract A modification of the design equations used for the calculation of expected performance of reverse osmosis units has been proposed. The product water and brine concentrations have been calculated as functions of the product recovery and a variable salt rejection coefficient of the membrane. The calculated data compare favorably with the experimentally obtained results.

On the comparison of reverse osmosis membrane performance

Abstract The conditions for the performance comparison of different reverse osmosis membranes have been analyzed. The inherent porosity of a membrane has been shown to affect systematically the extent of concentration polarization at the high pressure side of the film. A method has been proposed to determine the proper value of membrane flux necessary for the exact performance comparison of various reverse osmosis membranes.

Asymmetric membrane formation. Is the evaporation step necessary

Abstract In order to shed more light on the role and necessity of the solvent evaporation step the experiments comparing performances of the membranes made with the evaporation step and corresponding membranes prepared without it, have been carried out. The results have shown that the evaporation step improves the membrane performance and slightly decreases the reproducibility of the preparation method.

Technoeconomic considerations in reverse osmotic concentration of seawater

Abstract Conditions of reverse osmotic concentration of seawater as the first step in the salt production are analysed. By separating out two third of the total water content of seawater the bulkiest phase in the salt production could be remarkably accelerated. Reverse osmotic concentration can be accomplished in a two-stage process with a moderate membrane rejection factor in the first stage. The seawater concentration is accompained by the fresh water production in the second stage. The analysis of the technoeconomical data justifies the principle, and shows that it could be successfully implemented.

Reverse osmosis in seawater concentration

Abstract Reverse osmosis as the first step in the process of seawater concentration has been investigated. The brine of up to 10 % TDS was aimed at applying pressures not higher than 60 bars. Such a process was shown to be feasible when reverse osmosis membranes of moderate solute rejections were used. The effects of various operating pressures and membranes of various characteristics have been evaluated using the model and the real system. The results were compared in terms of energy requirements for the concentration process.