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.

Emulsion Liquid Membranes Based on Os–NP/n–Decanol or n–Dodecanol Nanodispersions for p–Nitrophenol Reduction

“…Catalytic systems based on osmium nanoparticles, coupled with polymer or liquid membrane processes, have been less frequently reported [19][20][21]30,31]. In these hybrid membrane-catalytic processes, p-nitrophenol is reduced to p-aminophenol with osmium nanoparticles.…”

“…This hybrid process involves both the conversion of p-nitrophenol in the source phase and the separation of p-aminophenol in the receiving phase through a membrane process. Previously, bulk liquid membranes based on osmium nanoparticles were tested [20,21,30], as well as liquid membranes on support (SLMs) [19,31].…”

“…The reactive membrane systems recently tested for the reduction and separation of p-nitrophenol (pNP) from source aqueous solutions use polymers as membrane phases (Figure 1c) or medium-chain n-alcohols, in which nanoparticles are dispersed [19][20][21][22][23].…”

“…The reduction reaction takes place in a column-type reactor fed at the base with the emulsion containing the receiving phase, and the source phase is introduced either at the base of the column (co-current) (Figure 7a) or at the top (counter-current) (Figure 7b). The conversion (η%) or extraction efficiency (EE%) for the species of interest using the concentration of the solutions [19][20][21] was calculated as follows:…”

Three- and Multi-Phase Extraction as a Tool for the Implementation of Liquid Membrane Separation Methods in Practice

“…Liquid membrane separations (bulk [ 1 , 2 , 3 ], supported [ 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 ], emulsion [ 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 ]) combining extraction and stripping processes in a single mass-transfer unit allow the separation of species on their partition between two aqueous phases. Mass transfer occurs through an intermediate organic phase (mass-transfer medium).…”