Oxidative Degradation of Amine Solvents for CO2 Capture

Abstract

The oxidative degradation of diamines was measured in a stirred reactor at 70, 98kPa O2, and 2kPa CO 2 . Amines studied include ethylenediamine (EDA), propylenediamine (PDA), 1,4-diaminobutane (putrescine), hexamethylenediamine (HMDA), propanolamine (MPA), Diglycolamine® (DGA®), and bisaminoethyl ether (Jeffamine EDR-104®). Amine solutions with an initial concentration of 10 m alkalinity, an initial loading of 0.4 mol CO 2 /mol alkalinity, and an initial metals concentration of 0.4 mM Fe, 0.2 mM Mn, 0.1 mM Ni, and 0.05 mM Cr were oxidatively degraded. The purpose of these experiments was to study the structural effect of diamines on their degradation rates. At high metals concentration of 4 mM Fe, 2 mM Mn, 1 mM Ni, and 0.5 mM Cr, PDA does not show signs of significant degradation. This is also true for PDA at the normal metal concentration of 0.4 mM Fe, 0.2 mM Mn, 0.1 mM Ni, and 0.05 mM Cr. PDA was tested with antifoam and it did not show measurable degradation. EDA degradation follows zeroth order kinetics with a rate constant of 9.79 mmol/kg-hr and is likely mass transfer controlled. Putrescine degradation follows first order kinetics with a rate constant of 0.00104 1/hr and is likely kinetically controlled at experimental conditions. The degradation of HMDA follows first order kinetics with rate constant k = 0.01/hr. The degradation of bisaminoethyl ether follows first order kinetics with rate constant k = 0.023/hr. DGA® degradation also follows first order kinetics with rate constant k = 0.008/hr. HMDA, Jeffamine EDR-104®, and DGA® degradation are all kinetically controlled. MPA showed negligible degradation after 260 hours of run time. There was no significant degradation observed for PDA with normal and high metals concentration in previous experiments.