Organic solutes using membranes

Reverse Osmosis Separation of Various Organic Solutes Using Membranes of Different Porosities. Since Rj for all membranes, g and Q for all solutes Involved in this work are now available (Table I and II), it is possible to calculate the solute separation, f, for all membranes other than those used for the determination of B and D and for all solutes other than the reference solute. 

A historical perspective on aqueous-organic extraction using membrane contactor technology is available in Refs. [1,6,83]. The mechanism of phase interface immobilization was first explored in Ref. [84], while application of membrane solvent extraction for a commercial process was first explored in Ref. [85]. Two aspects of liquid-liquid contact in membrane contactors that are different from typical gas-liquid contact are (1) the membrane used could be hydrophobic, hydrophdic, or a composite of both and (2) the membrane mass transfer resistance is not always negligible. Ensuring that the right fluid occupies the membrane pores vis-a-vis the affinity of the solute in the two phases can minimize membrane resistance. These aspects have been discussed in detail in Refs. [6,86,87]. 

To remove water from organic solutions, hydrophilic membranes are used. These types of membranes are typically made of polymers with glass transition temperatures above room temperatures. PVA is an example of a hydrophilic membrane material. 

UF Membranes as a Substrate for RO An important use of UF membranes is as a substrate for composite reverse-osmosis membranes. After the UF membrane (usually polysulfone) is prepared, it is coated with an aqueous solution of an amine, then dipped in an organic solution of an acid chloride to produce an interfacially polymerized membrane coating. 

Pervaporation membranes are of two general types. Hydrophilic membranes are used to remove water from organic solutions, often from azeotropes. Hydrophobic membranes are used to remove organic compounds from water. The important operating charac teris-tics of hydrophobic and hydrophihc membranes differ. Hydrophobic membranes are usually used where the solvent concentration is about... 

Organic solutions can be obtained in high yield by extracting HOCl from Cl -containing aqueous solutions into polar solvents such as ketones, nitriles or esters. Electrodialysis using semiper-meable membranes affords an alternative route. 

Flow-injection (FI) on-line analyte preconcentration and matrix removal techniques greatly enhance the performance of atomic spectrometry [348], By using USN with membrane desolvation (MDS) as the interface, FI sorbent extraction can be directly coupled with ICP-MS for the analysis of organic solutions [349]. 

The interface consists of (a) the nebulizer (b) the chamber (c) the membrane separator and (d) the torch. Organic solutions are fed to the nebuhzer via a peristaltic pump and the aerosol chamber is heated by a 2S0 W heating tape around the chamber. The membranes used are made from siHcone rubber and this is supported by high density polyethylene supports. A vacuum pump provides the vacuum on the membrane to remove the solvent vapour. 

Determination of Pore Size Distributions on the Surface of CA Membranes and Aromatic PAH Membranes. The organic solutes listed in Table IV were chosen as reference solutes, and then D and B values with respect to CA-398 and PAH materials were obtained by step 4. The results are listed in Table IV. Then, by using these B and D values, the average pore size and the pore size distribution on surfaces of membranes under study were calculated by following step 5. In these calculations, B and D values for CA-400 material were assumed to be equal to those of CA-398 material because of the closeness of acetyl content. The results are listed in Table II. 

Concentration and Recovery of Solutes. The RO method was evaluated by using small-scale concentrations and selected model organic solutes. Similar concentrations were performed by other researchers by using alternate sampling methods as part of a comparison study. The concentration provided a 50-fold volume reduction (500 L down to 10 L). Field applications of the RO method usually involve sample volumes of 2000-8000 L. No steps were taken to condition membranes and equipment prior to the laboratory tests. This laboratory performance evaluation was conducted, in many respects, as a worst case exercise. 

---