A short-cut method for the design and simulation of two-phase hollow fiber (HF) contactors with variable mass-transfer and distribution coefficients taking into account reaction kinetics is presented. A parametric study of membrane based solvent extraction (MBSE) and stripping (MBSS) of butyric acid (BA) based on experimental data is given. For the systems with concentration dependent mass-transfer and distribution coefficients a method dividing the length of fibers into segments with the same inlet to outlet concentration difference in the feed phase is suggested. The mean values of mass-transfer and distribution coefficients are estimated for each segment independently. For the tested system with BA, convergence of the simulation results was achieved for more than 20 segments. Dependences of the total number of contactors (length of fibers) on the shell Reynolds number and approach to the equilibrium at the raffinate end of the HF contactor exhibit a minimum at about 0.9 and 0.40, respectively. The overall number of contactors in MBSE and MBSS is very sensitive to the increase in BA yield in MBSE above 0.85. For following process parameters: volumetric flow rate 1 m(3) h(-1), feed concentration 350 mol m(-3), yield of BA in MBSE 85%, Re-shell =0-9, approach to equilibrium at the raffinate end of the HF contactor 0.40, and concentration factor of 10, the number of contactors of Liqui-Cel type 10 in. x 28 in. (Celgard) in series, without parallel lines of contactors, is five in MBSE and eight in stripping. In case when two parallel lines of contactors are used the number of contactors in series is two in extraction and four in stripping. (C) 2004 Elsevier B.V. All rights reserved.