Pertraction

Pertraction A process for removing organic pollutants from industrial wastewater. The water is contacted with an organic solvent via a hollow-fiber membrane. Developed in 1994 by TNO Institute for Environmental and Energy Technology, in collaboration with Tauw Environmental Consultancy and Hoechst. 

A very effective way to improve the pertraction performances in permeability and selectivity is to incorporate extractants into the hydrophobic phase, which react with a given solute reversibly and selectively. 

Boyadzhiev, L. Lazarova, Z. Liquid membranes (liquid pertraction) In Membrane Separations Technology, Principles, and Applications, R.D. Noble and S.A. Stem (Eds.), Elsevier Science B.V., Amsterdam (1995). 

Mohapatra, P.K. Lakshmi, D.S. Mohan, D. Manchanda, V.K. Uranium pertraction across a PTFE flat sheet membrane containing Aliquat 336 as the carrier, Sep. Pur. Technol. 51 (2006) 24-30. 

In membrane extraction, the treated solution and the extractant/solvent are separated from each other by means of a solid or liquid membrane. The technique is applied primarily in three areas wastewater treatment (e.g., removal of pollutants or recovery of trace components), biotechnology (e.g., removal of products from fermentation broths or separation of enantiomers), and analytical chemistry (e.g., online monitoring of pollutant concentrations in wastewater). Figure 18a shows schematically an industrial hollow fiber-based pertraction unit for water treatment, according to the TNO technology (263). The unit can be integrated with a him evaporator to enable the release of pollutants in pure form (Figure 18b). 

Figure 18 Pertraction technology for wastewater treatment from the TNO Institute (a) scheme of the hollow-fiber pertraction unit (b) integration of pertraction with film evaporation. (Courtesy TNO.)...

TNO Environment, Energy and Process Innovation. Pertraction for Water Treatment. Technical information brochure, 2002. 

Wang Y, Zhu S, Dai Y. Removal of VOCs from wastewater using pertraction. In Cox M, Hidalgo M, Valiente M, eds. Solvent Extraction for the 21st Century. Proceedings of ISEC 99, Barcelona. London Society of Chemical Industry, 2001 177-182. 

Partitioning of components between two immiscible or partially miscible phases is the basis of classical solvent extraction widely used in numerous separations of industrial interest. Extraction is mostly realized in systems with dispergation of one phase into the second phase. Dispergation could be one origin of problems in many systems of interest, like entrainment of organic solvent into aqueous raffinate, formation of stable, difficult-to-separate emulsions, and so on. To solve these problems new ways of contacting of liquids have been developed. An idea to perform separations in three-phase systems with a liquid membrane is relatively new. The first papers on supported liquid membranes (SLM) appeared in 1967 [1, 2] and the first patent on emulsion liquid membrane was issued in 1968 [3], If two miscible fluids are separated by a liquid, which is immiscible with them, but enables a mass transport between the fluids, a liquid membrane (LM) is formed. A liquid membrane enables transport of components between two fluids at different rates and in this way to perform separation. When all three phases are liquid this process is called pertraction (PT). In most processes with liquids membrane contact of phases is realized without dispergation of phases. 

Pertraction (PT) can be realized through a liquid membrane, but also through a nonporous polymeric membrane that was applied also industrially [10-12]. Apart from various types of SLM and BLM emulsion liquid membranes (ELM) were also widely studied just at the beginning of liquid membrane research. For example, an emulsion of stripping solution in organic phase, stabilized by surfactant, is dispersed in the aqueous feed. The continuous phase of emulsion forms ELM. Emulsion and feed are usually contacted in mixed column or mixer-settlers as in extraction. EML were applied industrially in zinc recovery from waste solution and in several pilot-plant trials [13,14], but the complexity of the process reduced interest in this system. More information on ELM and related processes can be found in refs. [8, 13-16]. 

H F contactors with planar elements with flowing head of fibers and crossflow of one phase in three and more phases contactor have been suggested in a patent [35] and their scheme is shown in ref. [8]. A two-phase H F contactor with planar elements was developed at TNO and tested in pilot plants [36, 37]. Reviews on two-phase HF contactors are presented in refs. [27, 38-40]. Mass-transfer characteristics of two-phase contactors are presented in ref. [30]. Three-phase HF contactors for pertraction are described in refs. [6-9, 41]. They are not produced commercially. 

Mass transfer occurs from the feed films into the stripping solution films through the bulk liquid membrane. Pertraction in RD contactors has been widely studied in the Boyadzhiev group for recovery of organic acids [50-53], antibiotics [54], alkaloids [55-58], biosurfactant [59] and metals [60-64],... 

The functions of contactors in the simultaneous MBSE and MBSS with an arrangement as shown in Figure 23.4, are coupled. They react similarly as a pertractor with a S LM. The differences are only in the overall resistance, which is smaller in the pertractor where there is only one support wall. In addition, it is not necessary to pump the solvent in its circulation loop in PT, as is used in the simultaneous MBSE and MBSS process [30]. On the other hand, in pertraction through SLM its limited lifetime could be problem which is not the case in M B S E and MBSS where it is easy to keep the constant properties of the solvent phase. 

A schematic flowsheet of the fermentation unit with integrated MBSE and MBSS circuit for recovery of acid(s) product from the fermentation broth is presented in Figure 23.5. Martak et al. [73] ran a semicontinuous fermentation of lactic acid with Rhizopus arrhizus with a periodical bleed and feed operation without a decrease in LA productivity for 152 h. Such a process could be integrated with separation of lactic acid, for example, by MBSE studied in ref. [74] or by pertraction [44,45], Recovery of vanilline from a fermentation broth is presented in ref. [75] aiming at formation of an integrated system. A combination of MBSE of phenol from saline solution in HF contactor with bioreactor with Pseudomonas putida to remove phenol is studied in ref. [76],... 

Modeling and optimization of MBSE and MBSS of a multicomponent metallic solution in HF contactors is discussed in ref. [77]. A short-cut method for the design and simulation of two-phase HF contactors in MBSE and MBSS with the concentration-dependent overall mass-transfer and distribution coefficients taking into account also reaction kinetics was suggested by Kertesz and Schlosser [47]. Comparison of performance of the MBSE and MBSS circuit with pertraction through ELM in case of phenol removal presented Reis [78] and for copper removal Gameiro [79]. 

Modeling and optimization of pertraction into emulsion in HF contactors is discussed in refs. [77, 138]. The design and optimization of a network of HF contactors with minimum cost that permits the selective separation and recovery of anionic pollutants, for example, Cr(VI), using BLME process for groundwater remediation is presented in ref. [139] and for waste-water treatment in ref. [140]. 

Comparison of PT through BLME and MBSE with MBSS both inCF HFmodules is given in ref. [ 138]. Galan et al. [ 119] compared techniques for removal of chromium by MBSE with ion exchange and pertraction through BLME. 

An overview of selected papers on pertraction through BLME is presented in Table 23.3. 

Table 23.3 Selected papers on recovery or removal of metals and organics by pertraction through BLME.

Copper catalyst was recovered from waste water from the wet peroxide oxidation process by pertraction through BLME and copper sulfate from stripping solution can be recycled to the reactor without loss in performance [144]. 

Ho et al. [141-143,146,151] published a series of papers on removal/recovery of several metals from waste solutions by pertraction through B LM E in H F contactors as shown in Table 23.4. For some metals, such as zinc and copper, scale-up of this system to pilot plant with a HF module with a surface area of fibers of 19 m2 (with diameter 10.2 and length 71.1 cm) was done and mass-transfer characteristics have been estimated [142]. Separation of phases in the dispersion from the stripping was satisfactory. 

Phosphonium ionic liquids can be a reactive carrier of organic acids and form effective SLM, as was found recently [183]. SLM with ionic liquid trihexyl-(tetradecyl) phosphonium bis 2,4,4-trimethylpentylphosphinate (Cyphos IL-104) had stable performance in pertraction of lactic acid for 5.3 days [44, 45], which is promising. 

Pertraction through SLM is widely used in analytical chemistry for separation and preconcentration of solutes before application of selected analytical method and it is discussed in refs. [32-34, 184, 185]. 

A simulation of the hybrid fermentation-pertraction process for production of butyric acid shows that the pH of fermentation and pertraction should be optimized independently [198]. It is advantageous to have the pH of the feed into pertraction at about 4.0 for both IL and TOA carriers. Choosing a proper carrier in the supported liquid membrane between IL and TOA should be made according to actual operation conditions, because of the different transport properties of these carriers in respect to the concentration of undisociated form of BA. While at lower BA concentrations the IL is better, at higher concentrations of above 20kgm 3 and pH equal to 4.0, the membrane area needed is lower for TOA. An important factor will be the toxicity of the carrier to biomass. TOA is not very good in this respect and data for IL used are not available, but it is hoped that IL will be less toxic. 

Comparison of Extractive Processes in HF Contactors and Pertraction through ELM... 

The advantages and disadvantages of membrane based processes and pertraction through various types of liquid membranes are summarized in Table 23.5. HF contactors are supposed in these processes with the exception of pertraction into stable emulsions (ELM) where mixed column contactors or mixer-settlers are used. 

Table 23.5 Advantages and disadvantages of membrane-based processes and pertraction through various types of liquid membranes in two- and three-phase systems.

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