The extraction fraction E and overall volumetric mass transfer coefficient k(L)a of TBP extracting butyric acid process in confined impinging jet reactors (CUR) with two jets were investigated. The main variables tested were the concentration of tri-butyl-phosphate (TBP) and butyric acid, the impinging velocity V, the impinging velocity ratio of two phases V-org/V-aq, the nozzle inner diameter d, and the distance L between the jet axes and the top wall of the impinging chamber. The results showed that E and k(L)a increase with an increase of the impinging velocity V, the concentration of TBP C-org and the impinging velocity ratio V-org/V-aq. However, E and k(L)a decrease with an increase of the inner diameter d(i) from 1 to 2 mm the concentration of butyric acid C-aq from 0.5% (v, v) to 2% (v/v). The factor L ranging from 3 to 11 mm has a negligible effect on E and k(L)a. A correlation on these variables and k(L)a was proposed based on the experimental data. These results indicated good mass transfer performance of ay in the extraction operation. (C) 2015 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. All rights reserved.