Bridging the Commercialization Gap for the Direct Air Capture of Atmospheric CO2

Abstract

The present work is a systematic investigation that addresses the primary concerns associated with scaling Direct Air Capture (DAC) technology. Chapter 2 provides a non-technical communication about the value of DAC relative to other forms of Carbon Dioxide Removal (CDR). If CDR systems are compared on a simple cost basis, DAC will be more expensive per tonne of CO2 due to technology’s nascency relative to nature-based forms of CDR such as afforestation/reforestation. Chapter 2 reasons that a simple accounting framework neglects the inherent value of long-duration CO2 sequestration, which is a possibility when DAC is paired with carbon mineralization or geological sequestration but is not possible with afforestation/reforestation. Chapter 2, therefore, argues for the implementation of a more complex pricing framework that accounts for the value of long duration storage in CDR solutions. Chapter 3 begins this thesis’ examination of chemical sorbents for DAC. The chapter describes a novel, green mechanochemical synthesis for a zirconium-based metal-organic framework (MOF), UiO-66-NH2, which was believed to be a potential sorbent for DAC. UiO-66-NH2 was synthesized at a rate of 4.52 g per 90 minutes with a 43% yield at a levelized cost of $6,498/kg of MOF. It became clear through CO2 gas sorption results, however, that the MOF itself was not a sufficient adsorbent material. As a result, Chapter 4 describes the mechanochemical impregnation of UiO-66-NH2 with a redox active guest, 9,10-phenanthrenequinone. The composite material exhibited the desired electrochemical behavior after a rapid 30-minute mechanochemical impregnation where the redox-active guest comprised approximately 13% of the composite material’s mass. This chapter demonstrates that mechanochemical impregnation is a rapid functionalization technique that can be leveraged with other porous materials for many industrial applications including and beyond CO2 capture. Overall, Chapter 4 examines this novel functional material as a solid-state cathode for electrochemical CO2 capture, and the chapter demonstrates that mechanochemical functionalization is a useful technique for rapidly introducing desired chemical properties for various industrial applications. After examining solid-state materials for DAC in Chapters 3 and 4, Chapter 5 is a technological pivot away from solid-state sorbents toward a solution-state electrochemical DAC process. iv Chapter 5 describes the investigation of several types of archetypal redox active organic molecules—such as diazines and quinones—for a continuous, non-aqueous electrochemical CO2 capture process. The highest performing organic molecule was phenazine, which maintained a 100% coulombic efficiency over 9.5 hours of testing with a theoretical minimum energy of 77.2 kJ/mol of CO2 captured. Additionally, this chapter describes the development of a 3D printed zero-gap electrochemical flow cell, which was designed to reduce the engineering costs associated with facilitating a continuous electrochemical reaction. In Chapter 6, the technology further evolves toward a green, aqueous electrochemical DAC process. The system demonstrated reversible electrochemical behavior over 100 cycles or 205 hours and maintained an average coulombic efficiency of 100% and an average capacity retention of 99.8%. Additionally, the system has an estimated theoretical minimum energy of 24.6 kJ/mol. Chapter 6 also includes further optimization of the electrochemical flow cell, which was performed with computational fluid dynamics (CFD) software to improve the flow of solution to the surface of the electrode, and it also includes a techno-economic analysis (TEA) to analyze variables that facilitate the commercialization of a redox flow DAC process.