CO2 Capture and Concentration using Alkoxides and Photoacids

With the increase of CO2 and other greenhouse gases emissions into the atmosphere, research into methods to mitigate these emissions is gaining more attention. The use of various capture agents to absorb CO2 from either waste gas streams or directly from air can lead to completely carbon-neutral or carbon-negative technologies. This work studies two new methods for CO2 capture: a direct capture method using alkoxides, and an indirect capture method using photoacids for creating localized pH swings. CO2 capture using alkoxides was verified through the formation of alkyl carbonates. The CO2 absorption capacity was then measured for each alkoxide synthesized or purchased, showing a general trend for higher CO2 absorption capacity correlating with higher pKa values. The effect of the counter cation for alkoxides in CO2 capture was also investigated, showing that changing the counter cation does in fact alter CO2 absorption capacity for hydroxide (0.39-0.85 mole CO2 absorbed per mole of hydroxide). The second capture system investigated used photoexcitation of photoacids to release captured CO2 from solution. The initial setup to test CO2 capture and release for this system shows effective CO2 capture into solution and release of CO2 after the photoacid is excited. However, this process’s efficiency could be improved through use of a higher intensity photon source

CO2 Capture and Concentration using Alkoxides and Photoacids

With the increase of CO2 and other greenhouse gases emissions into the atmosphere, research into methods to mitigate these emissions is gaining more attention. The use of various capture agents to absorb CO2 from either waste gas streams or directly from air can lead to completely carbon-neutral or carbon-negative technologies. This work studies two new methods for CO2 capture: a direct capture method using alkoxides, and an indirect capture method using photoacids for creating localized pH swings. CO2 capture using alkoxides was verified through the formation of alkyl carbonates. The CO2 absorption capacity was then measured for each alkoxide synthesized or purchased, showing a general trend for higher CO2 absorption capacity correlating with higher pKa values. The effect of the counter cation for alkoxides in CO2 capture was also investigated, showing that changing the counter cation does in fact alter CO2 absorption capacity for hydroxide (0.39-0.85 mole CO2 absorbed per mole of hydroxide). The second capture system investigated used photoexcitation of photoacids to release captured CO2 from solution. The initial setup to test CO2 capture and release for this system shows effective CO2 capture into solution and release of CO2 after the photoacid is excited. However, this process’s efficiency could be improved through use of a higher intensity photon source

Inverse Molecular Design of Alkoxides and Phenoxides for Aqueous Direct Air Capture of CO2

Aqueous direct air capture (DAC) is a key technology toward a carbon negative infrastructure. Developing sorbent molecules with water- and oxygen-tolerance and high CO2 binding capacity is therefore highly desired. In this work, we analyze the CO2 absorption chemistries on amines, alkoxides, and phenoxides with density functional theory (DFT) calculations and search for the optimal sorbent using an inverse molecular design strategy. The alkoxides and phenoxides are found to be more suitable for aqueous DAC than amines thanks to their water-tolerance and capture stoichiometry of 1:1 (2:1 for amines). All three molecular systems are found to obey the same linear scaling relationship (LSR) between pK_(CO_2 ) and pK_a, since both CO2 and proton are bonded to the nucleophilic binding site through a majorly σ bonding orbital. Several high-performance alkoxides are proposed from the computational screening. In contrast, phenoxides have relatively poor correlation between pK_(CO_2 ) and pK_a, showing promise for optimization. We apply genetic algorithm (GA) to search the chemical space of substituted phenoxides for the optimal sorbent. Several promising candidates that break the LSR are discovered. The most promising off-LSR candidate phenoxides feature bulky ortho substituents forcing the CO2 adduct into a perpendicular configuration with respect to the aromatic ring. In this configuration, CO2 utilizes a different molecular orbital for binding than does the proton, and the pK_(CO_2 ) and pK_a are thus decoupled. The pK_(CO_2 )-pK_a trend and off-LSR behaviors are then confirmed by experiments, validating the inverse molecular design framework. This work not only extensively studies the chemistry of the aqueous DAC, but also presents a transferrable computational workflow for understanding and optimization of other functional molecules

Inverse molecular design of alkoxides and phenoxides for aqueous direct air capture of CO2.

Aqueous direct air capture (DAC) is a key technology toward a carbon negative infrastructure. Developing sorbent molecules with water and oxygen tolerance and high CO2 binding capacity is therefore highly desired. We analyze the CO2 absorption chemistries on amines, alkoxides, and phenoxides with density functional theory calculations, and perform inverse molecular design of the optimal sorbent. The alkoxides and phenoxides are found to be more suitable for aqueous DAC than amines thanks to their water tolerance (lower pKa prevents protonation by water) and capture stoichiometry of 1:1 (2:1 for amines). All three molecular systems are found to generally obey the same linear scaling relationship (LSR) between [Formula: see text] and [Formula: see text], since both CO2 and proton are bonded to the nucleophilic (alkoxy or amine) binding site through a majorly [Formula: see text] bonding orbital. Several high-performance alkoxides are proposed from the computational screening. Phenoxides have comparatively poorer correlation between [Formula: see text] and [Formula: see text], showing promise for optimization. We apply a genetic algorithm to search the chemical space of substituted phenoxides for the optimal sorbent. Several promising off-LSR candidates are discovered. The most promising one features bulky ortho substituents forcing the CO2 adduct into a perpendicular configuration with respect to the aromatic ring. In this configuration, the phenoxide binds CO2 and a proton using different molecular orbitals, thereby decoupling the [Formula: see text] and [Formula: see text]. The [Formula: see text] trend and off-LSR behaviors are then confirmed by experiments, validating the inverse molecular design framework. This work not only extensively studies the chemistry of the aqueous DAC, but also presents a transferrable computational workflow for understanding and optimization of other functional molecules

Electrochemical Carbon Dioxide Capture and Concentration

Electrochemical carbon capture and concentration (eCCC) offers a promising alternative to thermochemical processes as it circumvents the limitations of temperature-driven capture and release. This review will begin by discussing the history of eCCC, describing early work in the field and the motivation for pursuing such a process. We will then transition towards discussing more recent approaches, with a heavier emphasis on methods that employ redox mediators to facilitate CO2 capture and release. These methods rely more on optimization through chemical design and include pH-mediated systems, electrochemically-mediated amine regeneration, and direct capture with redox-active molecules. For each approach, we provide a general overview of the system, discuss redox mediator chemistries that have been studied in literature, and highlight requirements for future generations of redox mediators. We also describe previous demonstrations of each method and current cell/system designs that have been used at the lab-scale. To conclude, we summarize achievements in the field, current challenges, and opportunities for improving these technologies. Overall, this review is a comprehensive survey of the eCCC field and evaluates the chemical, theoretical, and electrochemical engineering aspects of this approach. We hope this work can be used to assist the community in the development of modern economical eCCC technologies that can be utilized in large-scale CCS processes

Electrochemical Carbon Dioxide Capture and Concentration

Electrochemical carbon capture and concentration (eCCC) offers a promising alternative to thermochemical processes as it circumvents the limitations of temperature-driven capture and release. This review will discuss a wide range of eCCC approaches, starting with the first examples reported in the 1960s and 1970s, then transitioning into more recent approaches and future outlooks. For each approach, the achievements in the field, current challenges, and opportunities for improvement will be described. This review is a comprehensive survey of the eCCC field and evaluates the chemical, theoretical, and electrochemical engineering aspects of different methods to aid in the development of modern economical eCCC technologies that can be utilized in large-scale carbon capture and sequestration (CCS) processes