Continuous Stripping with Dense Carbon Dioxide

The integration of flow chemistry into continuous manufacturing requires efficient, controllable, and continuous methods for the concentration of diluted solutions on relatively small scales. The design and application examples of a new continuous solvent removal process are presented. The continuous stripping method employing dense carbon dioxide is based on the formation of homogeneous mixtures of dilute organic solutions of the target molecules with a large excess of carbon dioxide at temperatures as low as 35 °C and pressures around 10 MPa. Subsequent pressure reduction results in the quick release of carbon dioxide and vaporization of a significant fraction of the organic solvent. The concentration of the solute in the separated liquid phase can be up to 40 times higher than in the feed. Among the many controllable process parameters, the most significant ones are the mass-flow rate ratio of carbon dioxide to the feed and the temperature of the phase separator. By careful setting of the operational parameters, the degree of concentration enhancement may be accurately controlled. The new apparatus-despite consisting of laboratory equipment and being built in a fume hood-could easily support pilot-scale synthetic flow chemistry, being a continuous, efficient alternative to thermal concentration methods.