Extração de fenol, pela técnica de membranas líquidas surfatantes, tendo, com estudo de caso, o efluente da refinaria Gabriel Passos

Abstract

In this work, phenol extraction was studied in order to evaluate liquid surfactant membranes (LSM) technique potential for extraction of this solute from liquid effluents. For this purpose, two phenol solutions were used: a synthetic solution, containing 95 mg.L-1 of phenol, and an industrial liquid effluent from petroleum refinery from Gabriel Passos Refinery Plant - REGAP/PETROBRAS, containing 116.14 mg.L-1 of phenol. The LSM are prepared by making an emulsion of two immiscible phases, the resulting primary emulsion being dispersed in an external phase, of the same nature of the internal phase of such emulsion, resulting in a multiple emulsion. This three phase system, where the first and the third phases are miscible in each other, presents a membrane phase as an intermediate phase, which is responsible for the selective permeation of the solute from the donating external phase to the accepting internal phase. For the synthetic solution study, the investigated parameters were: external phase pH, extractant concentration, surfactant concentration, NaOH concentration of the internal phase and permeation time. The best results obtained for the phenol synthetic solution were: pH = 2,0, [CYANEX® 921] = 2,0% m/v, tpermeation = 10 min, [ECA 4360]MP = 1,0% v/v, [NaOH]IP = 0,50 mol.L-1, recovering 97% of the phenol initially present in the external phase, leaving the final external phase with a phenol concentration of 2,70 mg.L-1, in a single stage operation. Additionally, for the synthetic solution, the following results were obtained: the study for the evaluation of the extraction capacity of a membrane phase reused in contact with a fresh external phase, conducted in three complete and subsequent LSM extraction cycles, showed that the used membrane performance was similar to the fresh membrane phase; the study, aimed at the depletion of the external phase, showed the need of 3 extraction cycles, with a phenol concentration at the final external phase of 0.41 mg.L-1, lower than the required by the legislation for phenol disposal at watercourses (0.5 mg.L-1). The tests with the effluent were conducted by using the best conditions obtained for the synthetic solution study. Some parameters were reevaluated: permeation pH (pH 2.0, 4.0 and the natural pH of the effluent (pH 8.0) as a function of time. A higher phenol extraction was obtained for the pH 2.0 (68%) and for the effluent pH, an extraction of 56% was obtained. For the experiments for depletion of the external phase, 3 cycles were not enough to reach the required disposal levels. LSM technique showed a great potential for the desired application, further studies being necessary for this and other industrial effluents.