Supercritical carbon dioxide extractions of agricultural chemicals from aqueous solutions

Examination was made on the supercritical carbon dioxide extraction of agricultural chemicals from aqueous solutions. In the case of the semi batch extraction blowing supercritical carbon dioxide into the aqueous solutions at a concentration of 5 mg L-1, the dependencies of the removal ratios of four kinds of agricultural chemicals on temperature and pressure were shown in different patterns depending on the agricultural chemicals. For simazin (CAT), no unusual phenomena were observed. On the other hand, isoprothiolane (IPT) exhibited unusual phenomena. That is, the removal ratios decreased, as the pressure increased above 100 kg cm(-2) at temperatures of 45 degrees C and 50 degrees C. A similar phenomenon was observed for fenitrothion (MEP) or napropamide (NPP). Complicate pattern was shown for MEP. The removal ratios at pressures of 80 kg cm(-2) and 90 kg cm(-2) had maxima at 40 degrees C and 45 degrees C, respectively. These phenomena were discussed in terms of equilibrium and mass transfer. It was referred to that consideration should be given to such phenomena when the extraction technique is used for analysis. The order of the easiness of the separation of agricultural chemical from aqueous solution (that was estimated by the removal ratio at temperature of 35 degrees C and pressure of 100 kg cm(-2)) was IPT > NPP > MEP > CAT. Correlation was seen between the removal ratio and the solubility of agricultural chemical in water, and in hexane or the melting point.