Effect Of Structure Differences In Surfactant On The Retention Of Phenol During Micellar-Enhanced Ultrafiltration

Micellar-enhanced ultrafiltration ( MEUF ) is a new purification technique combining surfactants and ultrafiltration membrane,and can be used to remove organic mater and metal ions from wastewater. The technology is of higher retention, lower energy consumption, simple equipment, easily operation and lower cost. The aqueous contains lower content of phenol was disposed with MEUF using spiral polysulfone ultrafiltration membrang. Orthogonal experiment in three factor and three levels was conducted to research the solubilization of phenol on three different cationic surfactants, and analyse the results through range analysis. In the second part, some different parameters such as feed OTAB concentration, K2CO3 concentration, feed phenol concentration, pressure, temperature were adapted to analyse the effect on solubilization of phenol on OTAB micelles.The research results showed that: (1) the retention of phenol increased in the order as follows: hexadecyltrimethylammonium bromide ( CTAB ) < octadecyl trimethyl ammonium bromide ( OTAB ) < cetylpyridinium chloride ( CPC ), namely, this obviously indicates that the surfactant with hydrophilic pyridinium head group has better effect on solubilization of phenol in micelles. In the case of surfactant with the same hydrophilic head group, the surfactant with longer hydrophobic tail does better influence on the solubilization of phenol. (2) Dodecyl trimethyl ammonium bromide(DTAB) was selected to discuss the effect of hydrophobic tail on the solubilization of phenol, and the optimal retention is only 63% compared with some other surfactants. (3) It is observed that the apparent hydrodynamic diameters of micelles in the presence of phenol are larger than that of in the absence of phenol by a Zetasizer Nano ZS instrument (Malvern), and the particle diameter of OTAB ( 6.48 nm ) is the biggest of three kinds of surfactants due to the longest hydrophobic tail, and increased in the order as follows: CPC < CTAB < OTAB. The effect of phenol solubilization on the CPC micelle is the best but with the smallest particle diameter, so we can conclude that the particles diameter selected are all beyond the hole diameter of membrane. Considering separation efficiency and economically acceptable after orthogonal experiment, OTAB was selected in the following Single factor test and analyse the effect of feed OTAB concentration, K2CO3 concentration, feed phenol concentration, pressure, temperature on solubilization of phenol. With the introduction of surfactant OTAB continuously, the corresponding retention of phenol increases, and then the slope levels off. So the effect of OTAB addition becomes less significant when the feed OTAB concentration is higher than 60 mM. Though the CMC of OTAB decreases upon the addition of electrolyte K2CO3, at higher electrolyte concentration, phenol has to compete with excessive CO32- ions to get adsorbed on the OTAB micelle, which may be attributed to strong electrostatic force between anionic phenol and cationic OTAB micelles. Solubilization capability of OTAB micelle increases with the increase of feed phenol concentration: the retention of phenol, however, seems independent of the feed phenol concentration which is just comparatively in accordance with a model proposed by Mulder, 1996 (as to the low levels of contamination, the retention do not change with the feed contamination concentration.). Increasing in pressure can accelerate the permeate flux and also can diminish the pollution, however, micelles may become compact at high pressure and therefore solubilization capability of micelles decreases. With the increase of temperature, the solute may be evenly dissolved. Besides, the increase of temperature can expand membrane pores, consequently, more OTAB and phenol molecules pass through the membrane and go into permeate. The MEUF has such a few advantages: being simply operated, being easily industrialized, being suitable to remove organic mater and metal ions with lower molecular weight and concentration from wastewater independently or simultaneously.So the environmental profit of the MEUF is highly significant. In the meantime, in comparison with the method of adsorption, distillation and extraction. The MEUF also has such several advantages:being nophase variation, the disposed wastewater can be directly reused, valuable organic mater or heavy metals can be recovered and reused from concentrating fluid with certain measures.Therefore,the MEUF has significantly economic profit and considerably practical value. The study provides foundation for application and popularization of organics–containing wastewater treatment by MEUF.