Chem. Eng. J. Biochem. Eng. J.

Extraction of penicillin G from the filtrate of fermentation broth indicates that neutral phosphorus esters can be used to substitute butyl acetate as the extractant and that the equilibrium pH can be controlled at 3.0-4.0 because of the higher extraction capability of neutral phosphorus esters. The equilibrium constants of the extraction, the molar ratios of tributyl phosphate to penicillin G in the extract and the bonding structures of the extracted species have been established using chemical analysis and the absorbance shift of Fourier transform IR spectra of the functional groups in penicillin G