Succinic acid has been pertracted with TOA using free liquid membranes without or with 1-octanol. The addition of the alcohol led to the increase of up to 2.83 times of the acid's initial and final mass flows. At the same time, the influence of 1-octanol on the transport capacity of the pertraction system was negative, its addition inducing the accumulation of succinic acid into the liquid membrane. A mathematical model describing the acid accumulation inside the liquid membrane has been developed for pertraction systems without and with 1-octanol and offers good concordance with the experimental data. (c) 2012 Canadian Society for Chemical Engineering