Solubility behavior of ethyl cellulose in supercritical fluid solvents

Solubility data to 180 °C and 1200 bar are reported for ∼1.0 wt.% ethyl cellulose (50% ethoxyl content, 2.5 average degree of substitution) (EC) in neat supercritical fluid (SCF) chlorodifluoromethane (F22); difluoromethane; 1-chloro-1,1-difluoroethane; 1,1-difluoroethane; and dimethyl ether (DME). The pressures needed to dissolve EC in the polar fluorocarbons decreases with increasing solvent size. The exception in this trend is F22 which is the best fluorocarbon solvent of the series likely due to its ability to hydrogen bond to the oxygens in EC. Data are also reported for EC in CO2 with up to 30 wt.% ethanol and methanol showing that, on a weight basis, methanol is a much better cosolvent although on a mole basis methanol is only slightly better. DME is the highest quality solvent for EC of the series of SCF solvents investigated. Although the EC+DME system exhibits lower critical solution temperature behavior similar to the EC+F22 system, EC dissolves in DME at lower temperatures and pressures compared with F22. Solution density data at the phase boundaries are reported for the EC+SCF solutions. The EC+DME solutions exhibit the lowest densities which suggests that EC-DME cross interactions are very strong and likely dominated by hydrogen bonding.