Selective Absorption of Isoprene from C5 Mixtures by (pi)Complexation with Cu(I)

Selective absorption of isoprene from n-pentane mixtures was performed via reversible complexation with an aqueous solution of copper(I) nitrate, which was prepared by the disproportionation reaction between copper powder and cupric nitrate trihydrate [Cu(NO3)2·3H2O] in H2O in the presence of pyridine and nitric acid as stabilizers. The absorption of isoprene by the Cu(I) solution increased with an increase in the molar ratio of isoprene/Cu(I) up to 1 and remained nearly constant thereafter. The maximum isoprene pickup achieved at the molar ratio of isoprene/Cu(I) = 1 was around 0.5 equiv of Cu(I), implying that isoprene was complexed with Cu(I) in a 2 mode. The absorption ability of the Cu(I) solution was strongly dependent on the concentrations of the stabilizers, which prevent the oxidation of Cu(I) to Cu(II). The optimal molar composition of the solution was found to be Cu(I)/pyridine/HNO3 = 1/2.7/1.