Corrosion and degradation in amine based post-combustion CO2 capture
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Consumption of coal is expanding, and without CO2 capture and storage (CCS) or some other advanced coal combustion system, the most emission intensive gas, CO2, will continue to worsen climate change. Among the various CCS methods which have been proposed, CO2 capture and separation processes are some of the most promising. An effective CO2 capture process is CO2 post-combustion. Chemical absorption using aqueous alkanolamines solutions is the most commonly used method, and has already reached commercial stage. Monoethanolamine (MEA) is nowadays the benchmark solvent due to its good properties towards CO2 (fast absorption rate, cheap, non-volatile). Two of the big challenges in MEA based post-combustion CO2 capture are solvent degradation and equipment corrosion. The main aim of this thesis is to investigate which of the MEA degradation products cause corrosion and to what extent. Both oxidative and thermal degradation products were examined. In addition, focus was given on developing chromatographic methods for amines and degradation products of their reaction with CO2. Moreover, an alternative method for corrosion evaluation of amine solvents was developed. Finally, degradation and corrosion inhibitors and their potential use in MEA-based post-combustion CO2 capture was examined. Chromatographic techniques for fast and accurate determination of 12 amines and degradation products have been created by the use of Ion Chromatography (IC). All the methods were optimized and validated with a coefficient of determination greater than 0.99. The developed methods have been used in a pilot plant study, trace analysis and degradation experiments. Degradation and corrosion are closely tied and therefore all the research on this work studied both degradation product formation and corrosion. The effect of formic, propionic, oxalic, glycolic and acetic acid on corrosion was examined under thermal degradation conditions. Furthermore, the effect of 10 oxidative and thermal degradation products of MEA on corrosion was tested. ICP-MS used to determine Fe, Cr, Ni and Mo concentrations as an indication of corrosivity. LC-MS and IC were used to quantify the MEA loss and the degradation products formation. In addition, the surface morphology of 316 stainless steel was examined with SEM-EDS. Deposited corrosion products were identified by XRD. The advantages and disadvantages of three analytical techniques that can be used for corrosion evaluation i.e. ICP-MS, SEM-EDS and XRD were investigated. Development of a method for fast corrosion screening of amines was developed. The method is based on the solubility of ferrous in the solution and its association with FeCO3 (siderite) formation. Furthermore, ferrous solubility data for MEA, MDEA, DETA, EDA and PZ was obtained. Finally, various degradation and corrosion inhibitors were tested for 30wt% MEA. Among them, carbohydrazide showed excellent corrosion inhibition, and 1,3-Diaminopropane- N,N,N′,N′-tetraacetic acid showed remarkably high degradation inhibition performance.