Direct Air Capture of CO2 Using Amino Acid Solutions and Porous Catalysts

Abstract

Increasing CO2 in the atmosphere has led to an increase in global climate change, and this already has an observable effect on the environment. In recent years, there have been accelerated sea level rise, intense heat waves, loss of sea ice, plants flowering sooner, shrinking glaciers among other adverse effects. CO2 capture has the potential to reduce CO2 emissions from new and existing coal- and gas- fired power plants, industrial processes, and other sources of CO2. Aqueous monoethanolamine (MEA) mixtures for carbon capture have been widely popular for decades, due to their low cost, high absorption capacity and low regeneration heat requirement. However, they are also extremely volatile, they degrade in oxygen rich environments, and form degradation products that are toxic to human health and the environment. Recently, amino acids have emerged as an alternative to the use of monoethanolamine for CO2 capture. This is because of their stability, low toxicity, moderate capture performance, and that they are a naturally occurring substance.This research focuses on the capture performance of eight systems in comparison to MEA. Including, L-arginine, L-histidine, L-lysine, Glycine, L-arginine salt, L-histidine salt, L-lysine salt, and Glycine salt solutions. Attention is given to the cumulative absorption, cumulative desorption, desorption rate and breakthrough times of each system. The concentration of each solution studied is 10 mmol or 0.25 M, with the experiments occurring at atmospheric pressure 1 atm. The apparatus used in the experiment obtained data at room temperature (20 – 25 oC) during absorption and 70 – 95 oC during desorption. It was found that a number of amino acid and amino acid salt solutions tested could replace MEA, however the solutions of L-lysine and L-lysine salt showed the most promise. This thesis includes a brief introduction to the central issues of this work, explaining the relevance with global climate change in perspective. Then carbon management technologies are discussed, including the limits of the current technologies and the possibilities available with direct air capture using amino acids. Excerpts from a previously published review paper on post-combustion CO2 capture is included to provide more context for this work. The experimental process is also explained in detail, including absorbent selection, catalyst selection, absorbent and catalyst preparation, the experimental procedure and catalyst characterization. Finally, the results of the experiments are discussed, followed by the accomplishments of this project and future work.