pH and Design on n-Alkyl Alcohol Bulk Liquid Membranes for Improving Phenol Derivative Transport and Separation

Abstract

Regardless of the type of liquid membrane (LM) (Bulk Liquid Membranes (BLM), Supported Liquid Membranes (SLM) or Emulsion Liquid Membranes (ELM)), transport and separation of chemical species are conditioned by the operational (OP) and constructive design parameters (DP) of the permeation module. In the present study, the pH of the aqueous source phase (SP) and receiving phase (RP) of the proposed membrane system were selected as operational parameters. The mode of contacting the phases was chosen as the convective transport generator. The experiments used BLM-type membranes with spheres in free rotation as film contact elements of the aqueous phases with the membrane. The target chemical species were selected in the range of phenol derivatives (PD), 4−nitrophenol (NP), 2,4−dichlorophenol (DCP) and 2,4−dinitrophenol (DNP), all being substances of technical-economic and environmental interest. Due to their acid character, they allow the evaluation of the influence of pH as a determining operational parameter of transport and separation through a membrane consisting of n−octanol or n−decanol (n−AlcM). The comparative study performed for the transport of 4−nitrophenol (NP) showed that the module based on spheres (Ms) was more performant than the one with phase dispersion under the form of droplets (Md). The sphere material influenced the transport of 4−nitrophenol (NP). The transport module with glass spheres (Gl) was superior to the one using copper spheres (Cu), but especially with the one with steel spheres (St). In all the studied cases, the sphere-based module (Ms) had superior transport results compared to the module with droplets (Md). The extraction efficiency (EE) and the transport of 2,4−dichlorophenol (DCP) and 2,4−dinitrophenol (DNP), studied in the module with glass spheres, showed that the two phenolic derivatives could be separated by adjusting the pH of the source phase. At the acidic pH of the source phase (pH = 2), the two derivatives were extracted with good results (EE > 90%), while for pH values ranging from 4 to 6, they could be separated, with DCP having doubled separation efficiency compared to DNP. At a pH of 8 in the source phase, the extraction efficiency halved for both phenolic compounds.

Keywords: bulk liquid membranes; liquid membrane design; n–decanol membranes; n–octanol membranes; pH operational parameter; permeation module design; phenol derivative separation; phenol derivative transports.

Figure 1

Schematic presentation of extraction and membrane systems with organic solvent: (a) water 1 (W₁), organic solvent (OS), water extraction (W₂); or (b) liquid membranes (LM); (c) bulk liquid membranes (BLM); (d) supported liquid membranes (SLM); (e) emulsion liquid membranes (ELM). Legend: M = membrane; SP = source phase; RP = receiving phase.

Figure 2

Schematic presentation of the permeation module with dispersed phases: (a) general view; (b) cross-section detail. SP, source phase; RP, receiving phase; M, organic solvent membrane; m_np, magnetic nanoparticles; str, stirrer with magnetic rods.

Figure 3

Schematic presentation of the permeation module with dispersed phases with spheres: (a) the idea of positioning the spheres; (b) how to extend the surface of the aqueous phases from the drop, as a film on the considered spheres. SP, source phase; RP, receiving phase; M, organic solvent membrane; Sf, spheres.

Figure 4

Schematic presentation of the positioning of the distribution spheres (a); and of the aqueous phases (b). d, spheres for the distribution of the source phase (SP); D, sphere for the distribution of the receiving phase (RP) in the liquid membrane (M).

Figure 5

The decrease in concentration of p–nitrophenol for operation with the three types of materials: St, steel; Cu, copper; and Gl, glass; (a) for source phase with pH = 5; (b) with pH = 2; at the same value of the pH of receiving phase (pH = 13), for n–octanol membrane.

Figure 6

The decrease in concentration of p–nitrophenol for operation with the three types of materials: St, steel; Cu, copper; and Gl, glass; for the source phase with pH = 5 (a); and pH = 2 (b); at the same value of (pH = 13) of the receiving phase, for the n–decanol membrane.

Figure 7

The decrease in concentration of p–nitrophenol for operation in the drip module (Md) and in the module with spheres (Ms) of the three types of materials: St, steel; Cu, copper; and Gl, glass; for source phase (SP) with pH = 2 and receiving phase (RP) with pH = 13. (a) n–octanol membrane; (b) n–decanol membrane.

Figure 8

Morphology and composition of the surfaces of the spheres from: (a) glass; (b) copper; (c) titanium steel; obtained by scanning electron microscopy (SEM) and energy dispersive spectroscopy analysis (EDX).

Figure 9

Transformation of the aqueous phase drop into a film on the surface of the considered contact sphere.

Figure 10

The decrease in concentration of 2,4–dinitrophenol (DNP) and 2,4–dichlorophenol (DCP) for operation with the glass spheres module (Gl), of a source phase with: pH = 2 (a); pH = 4 (b); pH = 6 (c); and pH = 8 (d); for a receiving phase with the same pH (pH = 13), for n–octanol membrane.

Figure 11

The behavior of phenolic derivatives in the aqueous environment: (a) solubility variation of 2,4–dinitrophenol (DNP) depending on pH; (b) the degree of formation of 2,4–dichlorophenol (DCP).

Figure 12

The pH dependence of the source phase concentration for the two aromatic derivatives (2,4–dinitrophenol and 2,4–dichlorophenol), at four representative extraction times: 15; 30; 60 and 90 min.