Showing papers on "Forward osmosis published in 1976"

Some transport characteristics of aromatic polyamide membranes in reverse osmosis

Abstract: The effects of solute concentration in the range of 0.0013 to 1.051 molality in the feed solution and operating pressure in the range of 100 to 900 psig on solute transport parameter DAM/Kδ in reverse osmosis have been studied for a class of laboratory-made aromatic polyamide membranes and aqueous sodium chloride feed solutions. The results showed that DAM/Kδ for NaCl increased both with increase in operating pressure and solute concentration in the concentrated boundary solution on the high-pressure side of the membrane. A general expression for DAM/Kδ for NaCl including the effects of both the above operating variables is given. These results are different from the corresponding results obtained for cellulose acetate membranes.

Reverse osmosis separations and concentrations of food sugars

Abstract: The physicochemical criteria approach offers a means of predicting quantitatively reverse osmosis separations of D-glucose, D-fructose, sucrose, maltose and lactose in aqueous solutions using porous cellulose acetate membranes. The presence of a small quantity of pectin in aqueous sucrose solution increases its viscosity and decreases its mass transfer coefficient during reverse osmosis. Reverse osmosis data with aqueous sucrose feed solutions containing small quantities of CaCl2 show that the latter does not exist as an independent entity in such solutions. A set of process design calculations is illustrated for reverse osmosis concentration of food sugars in aqueous solutions using a typical cellulose acetate membrane.

Membrane potential in reverse osmosis process

Abstract: It is well known that an electric double layer appears in the boundary phase of solid and solution whena macromolecular solid contacts an electrolyte solution, and the potential thus generated is called phase boundary potential or zeta potential. Reverse osmosis, which has received great attention as a method of desalting sea water2}, is a process of filtrating various electrolytes through membranes by a pressure gradient to produce pure water. Until now the cellulose acetate membranehas been one of the most successful for this purpose. The macromolecular segments such as cellulose acetate have a phase boundary potential on contact with electrolytes which affects the desalting ability of the membranein the reverse osmosis process. Little work has been done in this field, and in our studies we attempted to measure the streaming potential of the membraneand throw light on the desalting mechanism of membranes.

Performance of Some Reverse Osmosis Membranes and Their Application in the Separation of Metals in Acid Mine-Water

Abstract: Reverse osmosis separation behavior of some metal salts of Cu2 +, Ni2 +, Fe3+, and A13+ have been studied. The cellulose acetate membranes used were characterized in terms of pure water permeability constant, solute transport parameter, and mass transfer coefficient with a reference system of aqueous sodium chloride solution. The importance of the chemical species present in solution and its effect on the degree of separation has been illustrated. Correlation between the percent solute separation and the equilibrium constant for the formation of ion-pairs in solution has been established. Reverse osmosis treatment has been applied to an acid mine-water solution, and the suitability of this process is discussed.

Membrane methods of separating solutions and their possible uses in coking plants

Abstract: Semipermeable membranes have been increasingly used for solution separation processes over the last 10 to 15 years in a number of industrially developed countries, including the USA and the UK. The underlying principle is reversible osmosis, i.e., the preferential passage of solvent through the membrane under the action of an externally applied pressure exceeding the osmotic pressure of the solution to be separated. The reversible osmosis mechanism is based on the specific properties of water near the surfaces of a semipermeable membrane. The water adsorbed on and inside the membrane loses its ability to dissolve the solute. If the pore diameter in the membrane does not exceed the sum of the hydrated ion diameter plus twice the thickness of the adsorbed water film, only water can pass through the pores. Experiments on actual effluents from the Moscow plant have shown that membrane methods can be effectively used to purify effluents and separate various complex liquid mixtures encountered in coking plants.

The role of membrane in osmotic flow

Abstract: Osmosis as a phenomenon caused by internal forces goes on without the necessity for the presence of any external forces. Therefore pressure gradient plays no special role in osmotic flow. Membrane as a component of solution with its molecules possessing some kind of mobility ceases to be a passive obstacle to the flow of other components, but becomes also a co-determining factor in osmotic flow. This has been shown by using the methods of irreversible thermodynamics. In the state of osmotic equilibrium osmosis does not occur. So also the mobility of water molecules which may then be found in tracer experiment does not determine the osmotic permeability coefficient. The coefficientsσ andω as defined by the parameters of the system under the condition of zero volume flow are not directly connected to Lp.