Monomer extraction from polymers using supercritical CO2

Abstract

Polymerization reactions often leave unreacted monomers in the polymer. These unreacted monomers can emit vapors at ambient temperatures that cause unpleasant odors, pose both environmental and safety risks, and negatively impacts polymer properties. Therefore, a purification step is necessary after polymerization to remove these residual monomers. High temperature devolatilization is the currently applied technique of removing these monomers, however this treatment can also negatively impact the properties of the polymer. In this study the possibility of using supercritical CO₂ (scCO₂) as an extraction medium of these residual monomers, which are considered as Volatile Organic Compounds (VOCs), has been investigated experimentally. Polymer samples of either PS or PMMA with 4–7 wt% of residual monomers were extracted continuously with scCO₂ at temperatures ranging from 50 to 90 °C and pressures of 100–400 bar. The measured extraction efficiencies, based on ¹H NMR analysis, were 99+% and was reached between 4 and 16 h depending on the experimental conditions. In general, higher temperatures and higher pressures lead to enhanced extraction rates and thus higher efficiencies at shorter process times. The experimental results were successfully modelled with an empirical extraction simulation model as originally proposed by Sovová.