Evaluation of Potassium Iodide as Degradation Inhibitor

Abstract

Amine-based chemical absorption of CO2 is a mature technology that is or will be implemented in several industrial sites worldwide. Cost and energy efficiency has still potential for improvement. One way of reducing cost is reducing the loss of solvent due to degradation. Less loss of solvent could be obtained using for example more stable solvents, adding additives (inhibitors) that avoid the unwanted reactions or by optimising the operation to reduce solvent loss. This work focuses on development study of one inhibitor, potassium iodide (KI). Experiments have been conducted in batch reactors studying oxidative degradation and in cycled set-up investigating process degradation. The basis for the evaluation and discussions are experiments performed both at batch reactors four different amines (ethanolamine - MEA, 3-amino1-propanol – 3A1P, digylcolamine - DGA, 1-(2-Hydroxyethyl)pyrrolidine – 1-(2HE)PRLD) and one blend of 3A1P/1-(2HE)PRLD and in a cyclic degradation set-up for MEA. The experiments with the inhibitor in both experiments showed some promising effects. For example, a) the inhibitor reduced the amine loss for the three primary amines investigated in the batch experiment, b) in the cycled experiment under standard conditions (desorber temperature 120 °C, 5 ppm NOx), the presence of inhibitor reduced the build-up of all degradation compounds except the degradation compounds referred to as thermal degradation compounds, such as HEPO and HEGly as well as volatile components as ammonia, alkylamine and pyrazines, c) the inhibitor itself was not reduced, and d) in the cycled experiment and the batch experiment with the primary amines the discolouration was reduced. However, the tertiary and cyclic amine as well as the blend investigated in the batch experiments were not inhibited, and the cycled experiment showed that the impact of the inhibitor is strongly dependent on having a stable temperature throughout the campaign, temperature spikes for solvents with KI will provoke formation of thermal degradation products.

Keywords: MEA, degradation, inhibitor, solvent degradation rig, oxidative degradation