Solvent extraction of penicillin - a study of electrostatic spraying behaviour during enhanced extraction in a spray column

The conditions required for generation of electrostatic sprays in a liquid-liquid extraction column have been experimentally studied. In particular the time dependent variation of column conductance due to space charge migration, mass transfer, and due to large changes in dispersed phase hold-up were examined. It is shown that the minimum voltage required for electrostatic spray generation was significantly affected by the electrical history of the column in the absence of dispersed phase flow, and that pre-charging of the extraction column allows spray generation at reduced voltages. It was also shown that the major factor influencing changes in column conductance during the extraction of penicillin from a 25 g/1 aqueous solution, as dispersed phase into dichloromethane, is solute trasfer into the organic phase. At high degrees of extraction it was shown that the effect of dispersed phase hold-up and the transfer of buffer components and water make relatively minor contributions to changes in column conductance. Preliminary drop size measurements made in the extraction column indicate the significant presence of droplets of less than 1µm in diameter.