Removal using supported liquid membranes

A.M. Neplenbroek, D. Bargeman and C.A. Smolder, Nitrate removal using supported liquid membranes transport mechanism, J. Membr. Sci., 1992, 67, 107. 

We have Investigated the transfer of americium and, to some extent, plutonium from aqueous nitrate wastes using supported liquid membranes of the blfunctlonal organophosphorus extractants DHDECMP and 0()D(1B)CMP0 (+TBF). The results show good transfer and removal If the nitric acid In the feed Is first neutralized to O.IOM to minimize acid transfer and subsequent back transfer of the metal Ion. 

The removal of actinides from reprocessing acidic waste solutions is advantageous in terms of minimizing the radioactive discharge to the natural environment. The separation of plutonium using supported liquid membranes was extensively studied, as well as U(V1) and Pu(lV) selective transport over fission products and minor actinide contaminants (Lakshmi et al. 2004 Sriram et al. 2000 Kedari et al. 1999). 

The solubilities of the various gases in [BMIM][PFg] suggests that this IL should be an excellent candidate for a wide variety of industrially important gas separations. There is also the possibility of performing higher-temperature gas separations, thanks to the high thermal stability of the ILs. For supported liquid membranes this would require the use of ceramic or metallic membranes rather than polymeric ones. Both water vapor and CO2 should be removed easily from natural gas since the ratios of Henry s law constants at 25 °C are -9950 and 32, respectively. It should be possible to scrub CO2 from stack gases composed of N2 and O2. Since we know of no measurements of H2S, SO, or NO solubility in [BMIM][PFg], we do not loiow if it would be possible to remove these contaminants as well. Nonetheless, there appears to be ample opportunity for use of ILs for gas separations on the basis of the widely varying gas solubilities measured thus far. 

Affinity of MIP towards the target analyte should be examined prior to fabrication of the chemosensor. Batch binding assays are used to test selectivity of suitable MIPs. Especially, affinity of MIP to compounds, which are structurally related to the target analyte, should be tested. If MIP binds similarly with these compounds as the template, then cross-reactivity is manifested [156], This effect was exploited for determination of adenine and its derivatives with the use of MIP templated with 9-ethyladenine. Nevertheless, the cross-reactivity, if undesired, can be avoided by suitable sample pretreatment, e.g. by interferant extraction with a supported liquid membrane (SLM) coupled to the MIP-PZ chemosensor. The Fluoropore membrane filter of submicrometre porosity can serve that purpose. That way, this membrane holds interferants, thus eliminating the matrix effect. The SLM-involving determination procedure is cheaper than traditional laborious sample pretreatment used to remove the interfering substances. For instance, caffeine [143] and vanillin [157] in food samples have been determined using this procedure. 

Ho, W.S. and Wang, B., Inventors Commodore Separation Technologies Inc., Assinee. Combined supported liquid membrane/stripping dispersion process for removal and recovery of metals Dialkyl monothiophosphoric acids and their use as extractants, US Patent... 

Removal of unwanted high-molecular-weight substances by size exclusion chromatography, dialysis, ultrafiltration, precipitation, and use of supported liquid membrane. 

Promising results are shown by recently developed integrated SLM-ELM [84, 85] systems. These techniques are known as supported liquid membrane with strip dispersion (SLMSD), pseudo-emulsion-based hollow fiber strip dispersion (PEHFSD), emulsion pertraction technology (EPP), and strip dispersion hybrid Hquid membrane (SDHLM). AH techniques are the same the organic phase (carrier, dissolved in diluent) and back extraction aqueous phase are emulsified before injection into the module and can be separated at the module outlet. The difference is only in the type of the SLM contactors hoUow fiber or flat sheet and in the Hquid membrane (carrier) composition. These techniques have been successfuUy demonstrated for the removal and recovery of metals from wastewaters. Nevertheless, the techniques stiU need to be tested in specific apphcations to evaluate the suitabUity of the technology for commercial use. 

Nitric acid removal from an aqueous stream was accomplished by continuously passing the fluid through a hollow fiber supported liquid membrane (SLM). The nitric acid was extracted through the membrane wall by coupled transport. The system was modeled as a series of (SLM)-continuous stirred tank reactor (CSTR) pairs. An approximate technique was used to predict the steady state nitric acid concentration in the system. The comparison with experimental data was very good. 

Actinide Removal from Aqueous iste Using Solid Supported Liquid Membranes... 

Qin et al. (2003) used SLMs for the separation of acetic acid and butyric acid from their aqueous solution. Polypropylene hfs and silicon-coated, microporous hydrophobic polypropylene membranes were used as support. In another study, Qin et al. (2002) demonstrated PV by using a liquid membrane consisting of nonvolatile hydrocarbons immobilized in the micropores of hydrophobic hfs on the outer surface of the fibers. TCE was separated and concentrated from its aqueous solution at 25°C and essentially atmospheric pressure. The feed TCE concentration was varied between 50 and 950 ppm the permeate pressure range was 0.6-70 mmHg. A 78-flber, 30-33 cm long module could achieve as much as 98% removal of TCE. It was reported by them that the hexadecane SLM was permselective for TCE the experimental selectivity was 30,000 and the intrinsic selectivity could be as high as 2 x 10 much higher than the values obtained by any solid membranes. 

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