Residual Monomer Reduction in Polymer Latex Products by Extraction with Supercritical Carbon Dioxide

Extraction of residual monomer from a latex product with supercritical carbon dioxide ((sc)CO2) in a column was studied. Operating conditions were chosen at 35 degrees C and 100 bar. For reducing the residual styrene level in a polystyrene latex from 10(4) ppm to 100 ppm and from 10(4) ppm to 10 ppm, a countercurrent bubble column with latex as continuous and (sc)CO2 as dispersed phase is suggested. Monomer partitioning was demonstrated to be a key parameter in the equipment design. Monomer transport was found to be governed by the shuttle effect, caused by Brownian motion of the latex to and from the H2O/CO2 interface. The drift-flux approach was followed to determine the column flooding conditions. Small column volumes are obtained. (sc)CO2 is a promising extraction medium for residual monomer reduction in latex products. Performance towards steam stripping is better as the final residual monomer level becomes lower.