Direct Yellow and Methylene Blue liquid–liquid extraction with alkylene carbonates

Propylene and 1,2-butylene carbonates enable very effective extraction of Methylene Blue. The use of a more hydrophobic 1,2-butylene carbonate is preferred for practical application. Separation is enhanced by addition of an electrolyte (NaCl). Partition coefficients for solutions containing Methylene Blue and 1 M NaCl are at least a hundred times higher than for Direct Yellow solutions. The recovery of Methylene Blue with propylene and 1,2-butylene carbonates is significantly better, compared with the cloud point technique. Cloud point technique yields to almost 100% only in the case of low concentrations of Methylene Blue in the feed (0.5 mg dm−3). For higher initial concentrations (0.01–0.25 g dm−3) of Methylene Blue, this method of recovery provides low extraction percentages (10–40%). Alkylene carbonates are not appropriate extractants for recovery of very hydrophilic Direct Yellow.