Newly devised spectrophotometric cell for measurements of solubility and slow reaction rate in supercritical carbon dioxide

A spectrophotometric cell for measurements of solubility and slow reaction rate in supercritical carbon dioxide (scCO2) up to 30 MPa was developed. A free piston made of a Teflon-coated magnet in the cell is moved up and down in the cell cylinder by an outside magnet, which is automatically driven by a gas cylinder at an arbitrary time interval. There is a one-way path in the free piston, and solution flow in the opposite direction is prevented; thus, the solution is stirred by circulating scCO2 in the looped pass. Using the developed cell, the solubilities of 5, 10, 15, 20-tetrakis(pentafluorophenyl)porphyrin (H2tpfpp) in scCO2 were determined at various temperatures and pressures. The dynamic process of copper(II) ion incorporation into the porphyrin core for the reaction of H2tpfpp with Cu(hfac)2 (hfac=1,1,1,5,5,5-hexafluoroacetylacetonate) was monitored by simultaneously dissolving both reagents in scCO2 in order to evaluate the applicability of the developed spectrophotometric cell for rate measurements of slow chemical reactions in scCO2.