Passive membrane dialysis

Passive membrane dialysis is usually applied batch-wise, since its driving-force is the difference in gradient concentration between the two solutions separated by the membrane. In this case, the solute (reactants and products small molecules) from a hypertonic solution (the resulting solution of the catalytic reaction) permeates through the membrane to the hypotonic side (pure solvent) until equilibrium has been achieved, whereas the nanosized catalyst remains confined inside the membrane (similar to a tea-bag see Fig. 3A). 

Fig. 3 Schematic representation of batch-wise passive membrane dialysis (A) and continuous membrane filtration dead-end-filtration (B) and loop reactor (C)...

Fig. 9 Passive membrane dialysis performed with catalyst G0-20 in a Michael 1,4-addition reaction. A Upper phase = Et20 + catalyst + product, lower phase = aqueous HC1 + side-products. B Organic phase addition into the membrane pocket . C Diffusion of the product into the beaker (charged with pure Et20), while the catalyst remains retained inside the tea-bag ...

At the end of a typical reaction, the reaction mixture was quenched with aqueous HC1 in order to form the product (Fig. 9A). The resulting organic phase was submitted to passive membrane dialysis (Fig. 9B,C) to recover the catalyst Go-20. The fraction retained by the membrane (Fig. 9C) was used in another run, where again the 1,4-addition product was formed quantitatively, proving the presence of active catalyst after recycling. 

The term dialysis covers separation methods that are based on the transport of molecules or ions through a semi-permeable membrane. A differentiation is made between various types of dialysis (passive dialysis, Donnan dialysis, and electrodialysis), according to the driving force and the type of separation membrane that is used. "... 

Although CFMR experiments have not yet been performed with these met-allodendritic assemblies, their purification using passive dialysis showed the potential application of these catalysts in a recycling process by means of membrane filtration techniques. 

Depending on the type of membrane used, dialysis may be either passive or active (Donnan type). Passive dialysis employs a neutral jwrous membrane with a fine pore structure. This type of dialysis is used primary to remove sample matrix materials such as proteins and/or fiber or other solids [8,9]. Donnan dialysis can do the same, but can also perform preconcentration of the ions in sample. In Donnan dialysis, an ion exchange membrane is used to exchange sample ions for receiving solution ions [10-13]. Each type of dialysis is described below. 

Conventional or passive dialysis. The driving force is the analyte concentration gradient across the membrane, which reflects the concentration difference between the donor and acceptor solutions. Ions and low-molecular-weight compounds are transferred, whereas dissolved and suspended material with high molecular mass is retained. 

Sulphur(IV) Atmospheric water Dialysis UV-Vis 1.6 x 10-7 mol L 1 Flow injection system passive ion-exchange tubular membrane for reagent addition [553]... 

Zinc Fertilisers Dialysis UV-Vis 4.75 mg L-1 Sequential injection system two holding coils related to the donor and acceptor channels dialysis through a passive neutral membrane [555]... 

This approach was further exploited in the spectrophotometric flow-injection determination of chloride in industrial effluents involving a passive neutral membrane [288]. The advantages inherent to passive dialysis were maintained and the mass transference was improved. Wide-range spectrophotometry was achieved by varying the applied voltage and/or the flow rates of donor and acceptor streams. 

A passive sampling device was constructed using the commercially available Twister sorbent stir bar by enclosing it inside a dialysis membrane. This device has been called a membrane-enclosed sorptive coating sampler or MESCO. Extraction efficiencies were three orders of magnitude lower than for SPMD due a lower sampling rate, however, the sensitivity was comparable because all of the collected analyte is desorbed into the GC whereas in SPMD, only a small sample in injected for analysis. Twister stir bars are also much smaller and can be deployed less conspicuously. 

As a proof of concept, the initial hypothesis has been illustrated along the text through two different applications focused on the recovery of heavy metals and mineral acids from industrial effluents (1) the recovery of zinc from spent chromium-based passivation baths and SPSs using the EPT and (2) the recovery of hydrochloric acid from SPSs by means of membrane diffusion dialysis. From the analysis previously undertaken, it is concluded that the process design needs the kinetic analysis of the separation and recovery... 

With the incorporation of a passive, neutral, semi-permeable dialysis membrane into the conduits of the sequential injection system, the contact time of the sample zone with the membrane had much influence on the... 

Sternberg et ai, 1991). For different vertical resolutions, the water is collected in multi-chamber samplers. The transport is performed across filter and dialysis membranes, either actively by suction via pumps and vacuums or passively driven by concentration gradients and diffusion. 

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