The Transport of Nitrophenols Through Liquid Membranes

The paper presents the experimental results obtained at the separation of some phenolic derivatives: phenol, p-nitrophenol, o-nitrophenol, 2,4-dinitrophenol from aqueous medium through the technique of bulk liquid membrane. The influence of the solvent that forms the membrane on the efficiency of the transport of the studied phenolic compounds was investigated. The recuperation grade of the phenolic compounds varies in the receiving phase of the system from the point of view of the solvent used as membrane as follows: CHCl 3 >CH 2 Cl 2 >CCl 4 . Considering the partition equilibria at the interface of the transport system the optimum pH conditions (acid feed source, membrane-chloroform and alkaline receiving phase) were established. Transport efficiencies over 90 % were obtained. Membrane separations have an important role in the domain of environmental remediation and treatment of water contaminated with toxic material. In industrial wastewaters phenols are frequently encountered pollutants with a high toxic potential. Thus the separation and recuperation of these compounds represents an activity of total utility. For the separation of the phenolic compounds in membranary system the literature references regard mainly at the use of supported and emulsion liquid membranes. Both supported liquid membranes and emulsion liquid membranes were used with success in the separation of phenol from wastewater (1). Emulsion liquid membranes were successfully used at the recuperation of phenol from the effluent that results at the production of phenolic resins (1). In this case a study of the permeation of phenol derived from an installation of phenolic resins was realized. The membrane consisted of an aliphatic solvent and a non-ionic surfactant as an internal phase. The experimental results that indicate the efficiency of the emulsion liquid membrane were obtained at the removal of nitrophenols from wastewater. In optimum operating conditions (surfactant concentration in oil phase 2%, NaOH concentration in internal water phase 2%, the ratio oil phase to internal phase 2, the pH of the external water phase 2 and the ratio external water phase to emulsion phase 3) the total nitrophenol content in the effluent can be reduced from 1050 mg/L at less than 1 mg/L (2). An improved variant of the emulsion liquid membranes applied to the recuperation of phenol from wastewater is based on the use of a new polyamide type surfactant. This surfactant increases the stability of the emulsion (compared to SPAN 80). Therefore the breaking of the emulsion becomes difficult and decreases the efficiency of the process. In optimum conditions approximately 98% of the phenol can be removed in one stage and on the second stage the efficiency of removing the phenol increases up to 99, 8% (3). Many other examples mentioned in literature confirm that emulsion liquid membranes represent a promising alternative for the treatment of wastewaters that contain a large range of contaminants such as: phenol, chlorphenol, nitrophenols (4-8). In the case of supported liquid membranes a major concern was obtaining high transfer rates, high stability and high selectivity at transport so that it can be competitive with the methods applied in industry. Therefore supported liquid membranes have developed having a polymeric support (9-11). These membranes have the disadvantage that the selectivity is reduced due to the uneven pores. Most of the accomplishments in the field of supported liquid membranes applied to the separation of phenolic compounds are based on the use of membranes consisting of alumina foil coated with gold and then functionalized (for example with thiol groups). By this method self- assembled mono-layers, which permit the control of the hydrophobic properties of the membrane, are realized (12). Better transport rate was obtained with this type of membrane for the transport of 2, 4, 6-trichlorphenol. During the last years the technique of supported liquid membranes is based on fluid hydrophobic polymers, strongly permeable with a low viscosity. These polymers are functionalized with transporters capable of molecular recognition, thus increasing the selectivity of the process (13-16).