In this paper, we develop an xpression of Fick's law to be used in the diffusion-solution model when coupling exists. To derive this relationship we have manipulated the generalised Stefan-Mawell equation to get a more convenient generalised multicomponent Fick's law in which clearly defined diffusivities and coupling coefficients appear: the two equations are wholly equivalent. In the general accepted frame of hypotheses when using the solution-diffusion model we have written Fick's equation when coupling betwwen the fluxes exists. The order of magnitude of coupling is calculated, using previously published xperimental data, leading to the conclusion that coupling, in selective pervaporation process, can be neglected.

In order to improve the mass transfer characteristics, a coalescene-dispersion sieve plate was designed. Mass transfer experiments wer carried out in a coalescence-dispersion pulsed sieve extraction (PSE) column of 150 mm in diameter with a working system of 30% TBP (in kerosene)-nitric acid-water. Mass transfer direction was from the continuous phase to the dispersed phase,, namely form the aqueous phase to the organci phase. The mass transfer characteristics were evaluated by a dynamic tracer method. Three parameters, the 'true' height of the tranfer unit, the height of the dispersion unit and the apparent height ot the transfer unit, were estimated from the dynamic response curve. Compared woth that in a standard PSE column, the mass transfer formance in the coalescence-dispersion PSE column was greatly improved.

Sorption and pervaporation experiments were carried out with cellulose triacetate membranes for the separation of methyl tert-butyl ether and methanol mixtures. The sorption experiments show that with an increase of MeOH concentration in the feed, the membrane swelling ratio increases first until a maximum value is reached and then remains constant. On the other hand, the MeOH concentration in the sorped phase first decreases to a minimum value and then increases with the transition occurring near the azeotropic point. In the pervaporation experiments, the total and MeOH permeation fluxes were found to increase with the increase of MeOH concentration in the feed while the MTBE permeation flux first increases and then decreases. The total permeation fluxes are significantly enhanced with an increase in temperature. This temperature dependence is more pronounced at low MeOH concentration, but the extent of increase of the total permeate flux is relatively constant when MeOH concentrations are greater than 10%, and it can be described by the Arrhenius law. Selectivity decreases with the increase of MeOH concentration and becomes more or less constant at high MeOH concentrations.

Aqueous two-phase systems (ATPSs) formed by spontaneous phase separation of different water-soluble polymers are bio-compatible. Aqueous two-phase electrophoresis, coupling traditional solvent extraction with lectrophoresis, is a novel separation technique and provides a successful method for separating mixtures of biomolecules. In this work, the selective recovery of amino acids by aqueous two-phase electrophoresis was examined with dextran-polyethylene glycol-water as a working system. The experiment results show that glutamic acid can be separated from phenylalanine and tryptophan successfully. The influences of the electrophoresis time, field strength, and phase volume ratio were studied in an intermittent separation equipment.

Our previous work clearly showed that electro-eletrodialysis was an efficient way to concentrate a formic acid solution. Electro-electrodialysis can be easily scaIed up as electrodialysis, but the equipment cost is higher. Accordingly, an electrolysis process with a new cation-exchange membrane was tested in this work. The effects of concentration, electric current density, and concentration difference between the concentrated side and the dilute side were studied. The experimental results indicated that electrodialysis was also an effective method to concentrate formic acid solution. For the high concentration system the overall current efficiency was larger than 100%. The overall current efficiency for a low concentration system would be up to 90%. But the concentrated ratio is not as much as desired, which is limited by the operating system and conditions. In general, the overall current efficiency was increased to a maximum value with an increase ofthe current density. ARer a certain value, the overall current efficiency would begin to drop. The increase ofthe initial concentration helped to increase the overall current efficiency, but led to a decrease in the concentrated ratio. The volume change of the concentrated solution is seriously affected by the current density and the ratio of the initial concentration in the concentrated compartment compared to that in the dilute compartment.