Membrane adsorbers commercially available

A number of specialty companies have and are continuing to develop adsorbents to collect organic molecules from air samples. Industrial chemicals resulting, from syntheses or used in production processes, pesticides and emissions from exhaust towers are monitored routinely with commercially available adsorbents. Personnel monitoring can be accomplished without a pump using a system composed of a porous membrane through which air diffuses and compounds of interest are collected by an adsorbent. 

TABLE I Summary of Commercially Available Membrane Adsorbers... 

Commercially available flat sheet membranes were selected. The primary selection critetium was that the membrane be made of a hydrophilic material, which adsorbs less organics than more hydrophobic polymers. For comparison, the membranes used are listed in Table 4.2 with their pore size or molecular weight cut-off (MWCO) as specified by the manufacturer. 

Preparation of Ru-red in Nafion A commercially available Nafion membrane (4, thickness 180 pm, purchased from Aldrieh Chemical Co.) was swollen sufficiently by soaking in distilled water for 24 h. The swollen membrane (2x3 cm) was immersed in an aqueous solution containing of Ru-red (3, purchased from Wako Pure Chemieal Industries Ltd.) (3 mL of 5T0 mol dm solution, 1.5T0 mol) for 5 h, so that the complex was incorporated into the membrane by cation exchange. The amount of the complex incorporated into the membrane was estimated from the visible absorption spectral change of the aqueous solution before and after the incorporation of the complex. The molar concentration of the complex in the membrane (M) was calculated from the amount of the adsorbed complex and the membrane volume. 

The main disadvantage of flow EFT is the lack of commercially available membranes with flat non-adsorbing surfaces, uniform permeability, and batch-to-batch reprodu-cibihty. These features may affect retention time, separation efficiency, and sample recovery. Numerous studies and technical improvements have been done to ensure optimum performance. 

Isotherms for the interfacial tension at an aqueous/organic interface show that the new di-(p-alkylphenyl)phosphoric acids 3-6 adsorb at the interface stronger than do commercially available DEHPA (1) or Cyanex 272(2). From the interfacial fluxes for single transition metal cation species transport across a bulk kerosene membrane, the following selectivity orders were derived Zn(II) > Cu(II) > Co(II) > Ni(II) for 1, 5, and 6 Cu(II) > Zn(II) > CoJI) > Ni(II) for 2 and 3 and Cu(II), Zn(II) > CoJI) > Ni(II) for 4. Similar selectivity orders were observed in competitive transport of these transition metal cations across emulsion liquid membranes in which a high utilization degree of the carrier was demonstrated. The di-(p-alkylphenyl)phosphoric acids 3-6 are found to be efficient carriers for proton-coupled transport of transition metal cations from a weakly acidic aqueous source phase across an emulsion liquid... 

Adsorptive separation is a powerful technology in industrial separations. In many cases, adsorption is the only technology available to separate products from industrial process streams when other conventional separation tools fail, such as distillation, absorption, membrane, crystallization and extraction. Itis also demonstrated that zeolites are unique as an adsorbent in adsorptive separation processes. This is because zeolites are crystalline soUds that are composed of many framework structures. Zeolites also have uniform pore openings, ion exchange abiUty and a variety of chemical compositions and crystal particle sizes. With the features mentioned, the degree of zeoUte adsorption is almost infinite. It is also noted that because of the unique characteristics of zeoHtes, such as various pore openings, chemical compositions and structures, many adsorption mechanisms are in existence and are practiced commercially. 

---