Entrainer Effect of N,N-Dimethylformamide on Solubility of Monomers for Aromatic Polyimide in Supercritical Carbon Dioxide

Abstract

The solubilities of 4,4′-diaminodiphenyl ether (ODA) and pyromellitic dianhydride (PMDA) in supercritical carbon dioxide (scCO2) with N,N-dimethylformamide (DMF) were measured by a semibatch flow method, to accumulate new experimental data and to clarify the entrainer effect of DMF on the solubilities of the monomers of aromatic polyimide in scCO2. All measurements were carried out at 323 K and 20.0 MPa with DMF concentrations from 0 to about 20 mol %. The solubilities of both ODA and PMDA increased dramatically with increasing DMF concentration under our experimental conditions. For example, the addition of about 10 mol % of DMF increased the solubilities of ODA and PMDA to 54- and 115-fold, respectively, as compared to their solubilities in pure scCO2. The experimental results were correlated and predicted by the Peng–Robinson equation of state (PR-EOS). The critical temperatures and pressures of ODA and PMDA were estimated utilizing the group contribution method proposed by Constantinou and Gani, and the solid molar volumes of ODA and PMDA needed for calculation were obtained by the COSMO-RS method. The vapor pressures of ODA and PMDA, which are also required to calculate the solubilities, were obtained by correlating the solubilities of ODA and PMDA in pure CO2. The binary interaction parameters were estimated by correlating the phase equilibria and solubilities for each binary system. The predicted results approximately reproduced the experimental results for the solubilities of ODA in scCO2. As for the solubilities of PMDA, while a large deviation was observed between the predicted and experimental results, the correlated results approximately corresponded to the experimental data.