Rasmus Fehrmann

Abstract:

Atmospheric pollution and climate changes are now recognized to be severely influenced by the emission of acidic gasses; for example, NOX, SOX and COX from the combustion of fossil fuels in instances such as power plants, cement factories and ships. Accordingly, these gases have to be effectively removed from flue gasses. Presently, this is mainly achieved by relatively energy intensive and resource demanding technologies via selective catalytic reduction (SCR) of NOX with ammonia, SO2 wet-scrubbing by lime obtaining gypsum and CO2 wet-scrubbing with organic amines. The latter leads to particular concern about, e.g. intensive energy requirements for desorption, corrosion of steel pipes and pumps, CO2 absorption capacity and thermal decomposition of the amine. The structures of ionic liquids (ILs) are well-ordered even in the liquid state with regular cavities which can host selected solute species depending on the IL ion composition or contain reversible binding functionalities. This makes the materials promising for selective, reversible absorption of gaseous pollutants, such as in industrial off-gases. In this work, we demonstrate how more environmental friendly ILs as amino acid based ones can be applied as selective, high-capacity absorbents of CO2, exemplified by a tetraalkylphosphonium prolinate IL. In the context of CO2 removal, ILs are considered environmentally friendly because they are not emitted to the environment due to their negligible vapor pressure. In addition, an imidazolium nitrate IL is also investigated regarding absorption of NO. Few publications deal with possible interferences of other flue gas components with the IL absorbers. Thus we here also investigate the interaction of the selected ionic liquids with SO2, CO2, NO and air. Furthermore, different porous, high surface area carriers like mesoporous silica have been applied as supports for the ionic liquids to obtain Supported Ionic Liquid-Phase (SILP) absorber materials. These materials benefit from low mass transport resistance of the often very viscous ILs by the distribution of the liquid as a thin film (or small droplets) on the surface of the highly porous carrier materials enabling fast absorption/desorption rates of the particular gas to be removed by the SILP absorber. These powderous SILP materials may also be extruded with appropriate binders to multichannel rotating filters that might be installed in the flue gas duct of the industrial unit or used as filters for sweetening of bio- and natural gas by reversible selective gas absorption. The gaseous pollutant is then desorbed and obtained in concentrated form for further processing on site to e.g. commercial grade mineral acids or stored in underground reservoirs.