HFCLM membrane

The theory of a hollow-fiber contained liquid membrane (HFCLM) transport is described in detail by Sirkar et al. in Refs. [58,59,91]. Its modified model, (HELM), developed by Schlosser et al. [5,9-11,25,38,92] is presented below. 

The term contactor systems present only membrane devices, mosdy hollow-fiber, but not processes. The membrane in a contactor acts as a passive (not selective) barrier and as a means of bringing two immiscible fluid phases (such as gas and hquid, or an aqueous hquid and an organic hquid) in contact with each other without dispersion. The phase interface is immobihzed at the membrane pore surface, with the pore volume occupied by one of the two fluid phases that are in contact. Contactor devices are used in many of the above-mentioned BLM systems (HLM, HFCLM, HFLM, FLM, pertraction, membrane-based extraction, MHS) as construction units. Sometimes, selective hydrophobic, hydrophihc, or ion-exchange membranes are used as barriers for additional selective separation in the devices similar to contactors. 

The BOHLM term includes several similar LM systems, developed by different research groups, such as hybrid liquid membrane (HLM) by Kislik et al. [1-3] hoUow-fiber contained liquid membrane (HFCLM) by Sirkar et al. [4-8] and Schlosser et al. (HFLM) [9-11] pertraction... 

A number of reviews and articles have appeared on related subjects. Theoretical aspects of the hoUow-fiber Hquid membrane (HFCLM) selective separation processes have been covered in the reviews and articles by Sirkar et dl. [4-7, 55, 56], and with new modifications by Schlosser et al. [9-11, 25]. Theory for separations by the FLM is presented in the work by Teramoto et al. [31, 34-37] theoretical considerations for rotating film pertraction systems have been described by Boyadzliiev [18, 57-60], and for the multi-rnernbrane hybrid systems by Wodzki et al. [27, 29, 47, 48, 50, 52]. 

HFCLM hollow-fiber contained liquid membrane MELM microencapsulated liquid membrane... 

Figure 7.4 Drawing of the hollow-fiber contained liquid membrane (HFCLM) (A) configuration of HFCLM in a permeator shell and (B) side-view of the permeator (after modification from Ref. [12] Copyright 1996, reprinted with permission from Francis and Taylor).

Attempts to overcome the instability problems related to supported Hquid membranes used novel types of Hquid membranes with unique configurations such as the FLM [19-20] and HFCLM [21-23]. 

In the HFCLM configuration, the aqueous feed and strip solutions flow through the lumen side of the fibers. On the outside, an aqueous or organic solution was applied as the Hquid membrane phase as already described. This configuration was applied for facilitated the transport of CO2 over CH4. Stability up to 80 days was reported by the same authors. 

Recently, Bao et al. [68] compared the efficiency of facilitated transport of CO2 across a liquid membrane by different carriers (diethanolamine (DEA) and carbonic anhydrase (CA) + bicarbonate (NaHCO3) in a polypropylene HFCLM configuration. The hollow fibers used are made of polypropylene, pore size 0.04 pm. In all the experiments, the measured CO2 permeance and selectivity (CO2/O2) using CA bicarbonate as carrier was higher than in the case of DEA. The separation factor (CO2/O2) using DEA was about 152 which are 65% lower than the selectivity calculated with CA bicarbonate. 

Other configurations reported for simultaneous extraction and stripping include hollow fiber-contained liquid membrane (HFCLM) and ELMs in hollow fiber contactors. Neither technique has used microemulsion phases as the liquid membrane. The HFCLM configur-... 

HoUow Fiber Contained Liquid Membrane (HFCLM).130... 

A more recent liquid membrane technique is the hollow fiber-contained liquid membrane technique which is sometimes abbreviated as the CLM technique or the HFCLM technique. This technique has overcome most of the shortcomings of the SLM/ILM techniques. First introduced during 1986-1988 (, 5), the CLM-based permeation technique is undergoing evolution. This paper will provide a brief... 

In the basic HFCLM technique, the feed gas or liquid mixture flows through the lumen of a first set of microporous hollow fibers in the permeator shell. The sweep, strip or permeate stream (gas or liquid) flows through the lumen of a second set of identical hollow fibers in Ihe same permeator shell. Individual hollow fibers of the first set are intimately commingled with the individual fibers of the second set. The thin gap in the shell side between the outside surfaces of the contiguous hollow fibers of the two sets is filled with a liquid that keeps the feed fluid and the permeate fluid streams apart and acts as the selective liquid membrane (Figure 1). The shell-side liquid is connected to an external reservoir of the same liquid under pressure. Any loss of this membrane liquid to the flowing fluid streams is counteracted by an automatic and continuous supply from the external reservoir. 

In gas permeation through polymeric membranes, a sweep gas is not commonly employed. Only gas permeated through the membrane flows through the permeate channel. This mode of operation for a HFCLM permeator was studied by Guha et al. (7) for CO2-N2 separation. They demonstrated how one can pull a vacuum in the permeate channel and achieve high selectivity and stable performance... 

Figure 1. Basic hollow fiber-contained liquid membrane (HFCLM) permeator structure.

Figure 2. HFCLM configurations between two contiguous hollow fibers for gas separation. q feed gas pressure P liquid membrane pressure strip solution pressure.

Figure 3. HFCLM configurations between the walls of two contiguous hollow fibers for liquid-liquid separation. Pp feed pressure liquid membrane pressure Pj strip solution pressure.

Using a 20 cm long HFCLM permeator containing two sets of 180 Celgard X-10 fibers, Nguyen and Callahan (77) studied selective recovery of copper from zinc present in an aqueous ammonia solution by means of a liquid membrane of LIX 54 (phenyl alkyl beta-diketone, Henkel Corporation, Tucson, AZ). Nitrogen... 

In a flat membrane variation called flat-plate contained liquid membrane (FPCLM), Pakala et al. 24) studied and modeled SO2 separation from flue gas using liquid membranes of aqueous sodium citrate or aqueous sodium sulfite solutions. The measured SOj fluxes were predicted well by a nonequilibrium boundary layer analysis for SO2 transport. The SO2 fluxes for sodium citrate films were a few times higher than that for sodium sulfite as the reagent concentration was increased form 0.0 to 0.667 M. They also studied the same system in a HFCLM module which, unfortunately, had a large EMT. Therefore, the percentage of SO2 removal was much less than that in Majumdar et al (22). 

HFCLM-based Perstraction Processes. Perstraction, the combination of permeation and extraction, is selective permeation of a species from a liquid feed through a membrane into a strip or sweep liquid which selectively extracts the permeating species (Sirkar (30) has a brief review). Cahn and Li (31) report separation of toluene and n-heptane through an aqueous ELM and kerosene as the strip liquid. Papadopoulos and Sirkar (32) explored the separation of a 2 vol% isopropanol-n-heptane mixture through a highly polar liquid membrane in a HFCLM... 

HFCLM-based Isomer Separation Processes. Armstrong and Jin (33) studied liquid membrane permeation through an aqueous SLM in a cellulose filter placed in a batch cell. The feed consisted of a 50-50 mixture of organic isomeric solute systems (structural, stereoisomers, etc.) in an organic solvent with the same solvent present in the permeate side. They incorporated p-cyclodextrin (they also tested a-and y-) in the aqueous solution to develop selectivity for one isomer over the other. Considerable selectivity was achieved initially. With time the selectivity was lost due to the inherent nature of the batch system. 

HFCLM-based Membrane Reactors. A number of different types of reactor structures and reaction processes have been studied. Consider first HFCLM as a separator feeding a reactant to the permeate side. Basu and Sirkar (10) separated diltiazem (D) from an aqueous reaction mixture containing NaHC03 and NaCl through a HFCLM of decanol and fed it into an aqueous strip solution of L-malic acid to form diltiazem malate (D-M). The permeate side aqueous solution contained an overwhelming excess of L-malic acid. This solution was recirculated to build up the D-M concentration to many times over that possible in one continuous pass. A different example of HFCLM as a separator feeding a reactant is provided by... 

The versatile HFCLM technique can perform a variety of separations for gas mixtures and liquid solutions. It has been found to be stable for the gas and liquid separations studied. Larger modules (2" diameter and a total of iSOOO fibers) have been built. Production methods appear to be in place to achieve EMT values close to the theoretical limits (77). The liquid membrane may be organic or aqueous and the feed and strip phases may be organic, aqueous or gaseous. 

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