TRANSPORT OF FATTY-ACIDS FACILITATED BY NORMAL-HEXADECYLTRIMETHYLAMMONIUM BROMIDE MICELLES THROUGH A LIQUID MEMBRANE

Transport of various fatty acids (FA) by micelles of n-hexadecyltrimethylammonium bromide (HTAB) in a liquid membrane system was examined experimentally, and the mechanism of the transport is proposed. The system consists of three phases: a heptane solution of FA as a source phase, an aqueous HTAB solution as a membrane phase, and heptane as a receiving phase. The effect of HTAB concentration on the transport rate of each FA was investigated. The shorter the hydrocarbon chain of FA is, the larger the transport rate is. HTAB transports FA at larger concentrations than its critical micelle concentration, which is clear evidence that micelles of HTAB dissolve and carry FA through the aqueous membrane. The transport rates increase with increasing HTAB concentration but then pass through maxima and decline again with more concentrated HTAB solutions. On the other hand, FA concentration in the aqueous phase at the steady state increases nearly proportional to the HTAB concentration. These behaviors were analyzed kinetically. It is shown that the rate constant of uptake increases to reach a maximum value and that of release decreases with an increase in the HTAB concentration. These changes in rate constants are naturally derived by assuming a mechanism in which FA dissolves at first in water and then is uptaken by HTAB micelles at the source/membrane interface; FA goes out of the micelles to water and then to the receiving oil phase at the membrane/receiving-phase interface. This model is also consistent with the other transport characteristics, such as that the transport rate of shorter FA reaches the maximum value at higher HTAB concentration and the maximum rate is larger. © 1990 American Chemical Society.