This dissertation investigates the pressing issue of climate change, identifying carbon dioxide as its main driver and introduces Direct Air Capture (DAC) as a crucial technology for achieving significant reductions in net global emissions. Through an extensive review of existing literature on DAC, it examines various methods and materials developed for this purpose, highlighting the ongoing efforts, advancements, and potential for real-world application. A novel sorbent, quaternary ammonium-functionalized poly(arylene ether sulfone) is explored for DAC via the moisture swing process. This sorbent exhibited the ability to capture and release atmospheric CO2 by a swing in moisture. Effects of form factors of powder, free standing dense membrane and thin film composite membrane were also evaluated for DAC. Furthermore, the dissertation explores modifications to poly(arylene ether sulfones) – polymers primarily used in desalination processes – to enhance water scarcity solutions by improving desalination membrane hydrophilicity and reducing fouling. This enhancement is achieved through the incorporation of zwitterionic groups into the polymer structure. Additionally, it investigates the synthesis of polysulfone polymers from lignin-derivable monomers, offering a greener alternative to traditional polysulfones used in desalination due to their environmental and health concerns. Polysulfones derivable from lignin exhibited comparable thermal properties and enhanced hydrophilicity compared to petroleum-derived polymers, showing considerable promise. Lastly, this dissertation investigates a potential hybrid system for desalination and direct ocean capture by integrating redox-active compounds into desalination membranes. This aims to achieve a pH swing that facilitates the formation of dissolved CO2.

Global emissions of carbon dioxide are reaching new heights every year since the Industrial Revolution. A major contributor to this is fossil fuel consumption. The consumption trend has indicated all this. It has also strengthened the argument for the need to cut down emissions and sweep out historical emissions through the implementation of Carbon Capture, Utilization, and Storage (CCUS) and Carbon Dioxide Removal (CDR) technologies respectively. This is required to control global warming. Direct Air Capture (DAC) is one of the CDR technologies. Extensive research and projections have suggested that DAC has tremendous potential to achieve global climate change mitigation goals. The feasibility of DAC is proven but work is required to bridge gaps in DAC research to make it affordable and scalable. Process modelling is an approach used to address these concerns. Current DAC research in system design and modelling is discrete and existing models have limited use cases. This work is focused on the development of a generalized process mass transfer model for the capture stage of solid sorbent DAC contactors. It provides flexibility for defining contactor geometry, selection of ambient conditions, and versatility to plug different sorbents in it for CO2 capture. The modelling procedure is explained, and a robustness check is performed to ensure model integrity. The results of the robustness check and sensitivity analysis are then explained. This research is part of a long-term effort to create a complete modelling package for the DAC community to boost research and development to large-scale deployments.

This paper will explore the existing relationship between direct air capture (DAC)technology and energy justice (EJ) principles. As DAC is a nascent technology that is transitioning from the R&D phase to the deployment phase, a standard for typical scaling practices has not yet been established. Additionally, since the industry of DAC aims to capture at least 10 gigatonnes of carbon dioxide per year by 2050, and at least 20 Gt/yr by 2100, the scaling practices of this technology will have a significant impact on communities around the world. Therefore, in this thesis I argue that if DAC is not scaled equitably, it will negatively impact the communities hosting the technology, and would develop a negative reputation which could slow down the overall scaling process. On the flip side, if DAC is scaled equitably, then it could create a positive effect by being deployed in underserved and marginalized communities and providing an economic benefit. This could result in DAC having a positive reputation and scaling more rapidly. In order to understand how the field viewed the integration of EJ principles into the scaling process, I interviewed representatives from DAC companies, experts in energy justice from NGOs and academia, and local government officials. These interviews were semi-structured, open-ended and conducted anonymously. Through these interviews I was able to refine my arguments and put forward a set of guidelines that the industry could use to scale DAC with equity and justice as core principles.

CO2 capture from ambient air (often referred to as direct air capture or DAC) is one of the Carbon Dioxide Removal methodologies that may limit Global Warming. High energy demand and high cost are currently serious barriers for large-scale DAC deployments. Moisture-controlled CO2 sorption is a novel technology for DAC, where CO2 sorption cycles are driven solely by changes in surrounding humidity. In contrast to traditional temperature-swing adsorption cycles, water is a cheaper source of exergy than high-grade heat or electricity and moisture-controlled CO2 sorption may reduce the cost of DAC. However, analytic models that describe this sorption system have not been well established, especially in a quantitative manner. In this dissertation the author first establishes both static and kinetic models analytically with bottom-up approaches from the governing equations. These models are of scientific interest and also of industrial importance. They were validated by literature data and custom experiments. In a second part of the dissertation, the author explores the application of moisture-controlled materials in the form of membranes that actively pump CO2 against a concentration gradient. These explorations are guided by the quantitative models developed in the first part of the dissertation. In CO2 separation technologies relying on actively pumping membranes, a moisture-controlled CO2 sorbent is used as either a gas-gas membrane contactor or a gas-liquid membrane contactor. The author experimentally and theoretically determined that a specific commercial anion exchange membrane that was considered a plausible candidate does not satisfy the requirements for such an active membrane as a consequence of its slow kinetics of carbon transport. Requirements for materials to serve as active membranes have been clarified, which is of great interest for industrial application and will provide a starting point for future material design and development.

Research confirms that climate change is primarily due to the influx of greenhouse gases from the anthropogenic burning of fossil fuels for energy. Carbon dioxide (CO2) is the dominant greenhouse gas contributing to climate change. Although research also confirms that negative emission technologies (NETs) are necessary to stay within 1.5-2°C of global warming, this dissertation proposes that the climate change problem has been ineffectively communicated to suggest that CO2 emissions reduction is the only solution to climate change. Chapter 1 explains that current United States (US) policies focus heavily on reducing CO2 emissions, but ignore the concentrations of previous CO2 emissions accumulating in the atmosphere. Through political, technological, and ethical lenses, this dissertation evaluates whether the management process of CO2 emissions and concentrations in the US today can effectively combat climate change.

Chapter 2 discusses the historical management of US air pollution, why CO2 is regulated as an air pollutant, and how the current political framing of climate change as an air pollution problem promotes the use of market-based solutions to reduce emissions but ignores CO2 concentrations. Chapter 3 argues for the need to reframe climate change solutions to include reducing CO2 concentrations along with emissions. It presents the scientific reasoning and technological needs for reducing CO2 concentrations, why direct air capture (DAC) is the most effective NET to do so, and existing regulatory systems that can inform future CO2 removal policy. Chapter 4 explores whether Responsible Innovation (RI), a framework that includes society in the innovation process of emerging technologies, is effective for the ethical research and deployment of DAC; reveals the need for increased DAC governance strategies, and suggests how RI can be expanded to allow continued research of controversial emerging technologies in case of a climate change emergency. Overall, this dissertation argues that climate change must be reframed as a two-part problem: preventing new CO2 emissions and reducing concentrations, which demands increased investment in DAC research, development, and deployment. However, without a national or global governance strategy for DAC, it will remain difficult to include CO2 concentration reduction as an essential piece to the climate change solution.

As the global community raises concerns regarding the ever-increasing urgency of climate change, efforts to explore innovative strategies in the fight against this anthropogenic threat is growing. Along with other greenhouse gas mitigation technologies, Direct Air Capture (DAC) or the technology of removing carbon dioxide directly from the air has received considerable attention. As an emerging technology, the cost of DAC has been the prime focus not only in scientific society but also between entrepreneurs and policymakers. While skeptics are concerned about the high cost and impact of DAC implementation at scales comparable to the magnitude of climate change, industrial practitioners have demonstrated a pragmatic path to cost reduction. Based on the latest advancements in the field, this dissertation investigates the economic feasibility of DAC and its role in future energy systems. With a focus on the economics of carbon capture, this work compares DAC with other carbon capture technologies from a systemic perspective. Moreover, DAC’s major expenses are investigated to highlight critical improvements necessary for commercialization. In this dissertation, DAC is treated as a backstop mitigation technology that can address carbon dioxide emissions regardless of the source of emission. DAC determines the price of carbon dioxide removal when other mitigation technologies fall short in meeting their goals. The results indicate that DAC, even at its current price, is a reliable backup and is competitive with more mature technologies such as post-combustion capture. To reduce the cost, the most crucial component of a DAC design, i.e., the sorbent material, must be the centerpiece of innovation. In conclusion, DAC demonstrates the potential for not only negative emissions (carbon dioxide removal with the purpose of addressing past emissions), but also for addressing today’s emissions. The results emphasize that by choosing an effective scale-up strategy, DAC can become sufficiently cheap to play a crucial role in decarbonizing the energy system in the near future. Compared to other large-scale decarbonization strategies, DAC can achieve this goal with the least impact on our existing energy infrastructure.

One of the key infrastructures of any community or facility is the energy system which consists of utility power plants, distributed generation technologies, and building heating and cooling systems. In general, there are two dimensions to “sustainability” as it applies to an engineered system. It needs to be designed, operated, and managed such that its environmental impacts and costs are minimal (energy efficient design and operation), and also be designed and configured in a way that it is resilient in confronting disruptions posed by natural, manmade, or random events. In this regard, development of quantitative sustainability metrics in support of decision-making relevant to design, future growth planning, and day-to-day operation of such systems would be of great value. In this study, a pragmatic performance-based sustainability assessment framework and quantitative indices are developed towards this end whereby sustainability goals and concepts can be translated and integrated into engineering practices.

New quantitative sustainability indices are proposed to capture the energy system environmental impacts, economic performance, and resilience attributes, characterized by normalized environmental/health externalities, energy costs, and penalty costs respectively. A comprehensive Life Cycle Assessment is proposed which includes externalities due to emissions from different supply and demand-side energy systems specific to the regional power generation energy portfolio mix. An approach based on external costs, i.e. the monetized health and environmental impacts, was used to quantify adverse consequences associated with different energy system components.

Further, this thesis also proposes a new performance-based method for characterizing and assessing resilience of multi-functional demand-side engineered systems. Through modeling of system response to potential internal and external failures during different operational temporal periods reflective of diurnal variation in loads and services, the proposed methodology quantifies resilience of the system based on imposed penalty costs to the system stakeholders due to undelivered or interrupted services and/or non-optimal system performance.

A conceptual diagram called “Sustainability Compass” is also proposed which facilitates communicating the assessment results and allow better decision-analysis through illustration of different system attributes and trade-offs between different alternatives. The proposed methodologies have been illustrated using end-use monitored data for whole year operation of a university campus energy system.

Carbon dioxide (CO2) is one of the most dangerous greenhouse gas. Its concentration in the atmosphere has increased to very high levels since the industrial revolution. This continues to be a threat due to increasing energy demands. 60% of the worlds global emissions come from automobiles and other such moving sources. Hence, to stay within safe limits, it is extremely important to curb current emissions and remove those which have already been emitted. Out of many available technologies, one such technology is the moisture swing based air capture technology that makes use of resin material that absorbs CO2 when it is dry and releases it when it is wet. A mathematical model was developed to better understand the mechanism of this process. In order to validate this model, numerical simulation and experimentation was done. Once the mechanism was proved, it was seen that there are many factors and parameters that govern this process. Some of these do not have definite value. To find the best fit value for these parameters, an optimized fitting routine needs to be developed that can minimize the standard deviation of the error. This thesis looks into ways in which the optimization of parameters can be done and the possible future work by using substantial data.