Thermal Degradation of Piperazine in Sulfolane Aqueous Solution in CO2 Capture Process

Abstract

Thermal degradation of piperazine (PZ) in aqueous and mixed sulfolane (SFL) (30% by weight) + H₂O solution as a hybrid context was investigated as a function of temperature and two levels of piperazine concentrations and two levels of carbon dioxide loadings. Degradation of PZ in aqueous solution has been found to be first order. The pseudo rate constants for 5%wt solution of piperazine at 145, 160 and 175 °C in aqueous solution are 2.24 × 10^–9, 1.09 × 10^–8 and 2.27 × 10^–7 and in the hybrid media are 3.56 × 10^–8, 7.67 × 10^–8 and 1.19 × 10^–7 per second, respectively, and the activation energies for the aqueous and hybrid media were estimated 238.71 and 62.77 kJ/mole, respectively. Considering the most abundant degradation products identified; 3-(hydroxyethyl)-2-oxazolidone (HEOD), N,N-bis-(2-hydroxyethyl)-piperazine (BHEP), N,N’,N-tris-(hydroxyethyl) ethylenediamine (THEED), 1-[2-[(2-Aminoethyl) amino] ethyl] piperazine (AEAEPZ) and 1-Methylpiperazine (1-MPZ), the degradation pathway of PZ in both media is expected to proceed through ring opening of protonated PZ with the attack of other piperazine molecules on its alpha carbon. The presence of SFL only accelerates the reactions without changing the degradation mechanism.