Study of Preventing Oxidative Degradation of Monoethanolamine, and Benzene Adsorption onto Tetraethylenepentamine-impregnated Silica Surface

Coal-fired power plants contribute 31.7% of the total CO₂ emissions in the U.S. Therefore, it is necessary to develop technology that can be utilized by these plants to capture these emissions. One of the most researched technologies for removing the CO₂ is absorption/stripping with monoethanolamine (MEA). Studies showed that absorption/stripping with MEA removed 90 vol% CO₂ from the power plant flue gas, costing as little as $33/ton CO₂ avoided. However, much research was done to further reduce capital and operating costs. Some studies showed that oxidative degradation of MEA was a significant cost, and explored the reaction mechanisms, engineering concerns, and economics associated. In addition, other technologies for CO₂ capture using MEA were suggested. One technology would utilize a fluidized bed reactor, incorporating MEA-impregnated porous supports (solid sorbents). For these sorbents, amorphous silica (silica) is an attractive support due to low cost and high surface area. Characterization of the extent of MEA impregnation into the silica would be a valuable tool for silica/MEA ratio optimization.

In this study, the oxidative degradation of MEA is presented. Four additives at various concentrations were proposed to reduce the rate of oxidative degradation, which was performed at 100 °C for 18 h. This study also presents the characterization of the extent of tetraethylenepentamine (TEPA) impregnation into silica. Benzene adsorption was performed on silica, silica/TEPA-65/35 wt%, and silica/TEPA-48/46 wt% at 40, 70, and 120 °C under 150 cc/min Ar and 5.5 vol% benzene.

Results of the studies concluded that for the oxidative degradation of MEA, water reduced the average change in intensity of 1663 cm^-1 and 1597 cm^-1 the most, followed by ethyleneglycol. This indicated the greatest reductions in the oxidative degradation rate of MEA. Concentrations as low as 20-35 wt% water may be used instead of the 60-70% used in industry for the CO₂ capture solution. Results of this study also concluded that benzene adsorption proved a successful technique to characterize the extent of TEPA impregnation into silica. These results showed that benzene adsorption may also be a useful technique to characterize the extent of MEA impregnation into silica.