A Life Cycle Assessment Case Study of Coal-Fired Electricity Generation with Humidity Swing Direct Air Capture of CO2 versus MEA-Based Postcombustion Capture.

The potential of direct air capture using adsorbents in cold climates.

Limits to Paris compatibility of CO2 capture and utilization

CO2 electroreduction to multicarbon products from carbonate capture liquid

Carbon capture and utilization: More than hiding CO2 for some time

Integration of carbon capture with utilization technologies can lead the way to a net-zero carbon economy. Nevertheless, direct chemical conversion of chemically captured CO2 remains challenging due to its thermodynamic stability. Here, we demonstrate CO2 capture from flue gas/air and its direct conversion into syngas under solar irradiation without any externally applied voltage. The system captures CO2 with an amine/hydroxide solution and photoelectrochemically converts it into syngas (CO:H2 1:2 (concentrated CO2), 1:4 (simulated flue gas), and 1:30 (air)) using a perovskite-based photocathode with an immobilized molecular Co-phthalocyanine catalyst. At the anode, plastic-derived ethylene glycol is oxidized into glycolic acid over a Cu26Pd74 alloy catalyst. The overall process uses flue gas/air as carbon source and discarded plastic waste as electron donor, opening avenues for integrated carbon-neutral/negative solar fuel and waste upcycling technologies.

Current climate targets require negative carbon dioxide (CO2) emissions. Direct air capture is a promising negative emission technology, but energy and material demands lead to trade-offs with indirect emissions and other environmental impacts. Here, we show by life-cycle assessment that the commercial direct air capture plants in Hinwil and Hellisheiði operated by Climeworks can already achieve negative emissions today, with carbon capture efficiencies of 85.4% and 93.1%. The climate benefits of direct air capture, however, depend strongly on the energy source. When using low-carbon energy, as in Hellisheiði, adsorbent choice and plant construction become more important, inducing up to 45 and 15 gCO2e per kilogram CO2 captured, respectively. Large-scale deployment of direct air capture for 1% of the global annual CO2 emissions would not be limited by material and energy availability. However, the current small-scale production of amines for the adsorbent would need to be scaled up by more than an order of magnitude. Other environmental impacts would increase by less than 0.057% when using wind power and by up to 0.30% for the global electricity mix forecasted for 2050. Energy source and efficiency are essential for direct air capture to enable both negative emissions and low-carbon fuels. Direct air capture (DAC) of CO2 has garnered interest as a negative emissions technology to help achieve climate targets, but indirect emissions and other environmental impacts must be better understood. Here, Deutz and Bardow perform a life-cycle assessment of DAC plants operated by Climeworks, based on industrial data.

The current landscape of Carbon Capture and Storage (CCS) technologies is rapidly evolving, moving towards more cost-effective solutions to address the economic challenges associated with energy transition. Greenhouse gas emissions pose a significant threat to millions of people, as the global temperature continues to rise. Despite the close link between emissions and industrialization, many companies are actively engaged in developing high-performance, affordable CCS systems to reduce their carbon footprint without compromising their financial stability. As of early 2021, there were 24 operational commercial CCS and carbon capture and utilization (CCU) facilities worldwide, with the capacity to capture approximately 0.04 billion metric tons per annum (Gtpa) of CO2 emissions from energy and industrial processes. These facilities include natural gas processing plants, a coal power plant, chemical plants, hydrogen production facilities, and iron and steel plants. While some plants have ceased operations, 30 more are in various stages of development. Additionally, there are 16 small-scale pilot and demonstration plants currently in operation, with 19 in development and 24 already completed and closed. If all 30 commercial plants under development are completed, the capture capacity would increase to about 0.1 Gtpa. Notably, there are three operational commercial plants utilizing bioenergy with CCS (BECCS), with seven more in development. The current capture capacity of operational BECCS plants is relatively low, at 1.13 million metric tons per annum (Mtpa), but it could rise to 9.7 Mtpa if all the plants in development become operational. Furthermore, there are nine smaller-scale BECCS pilot and demonstration plants active, with six completed and four in various stages of development.2 There are several ways to capture CO2 and stabilize it under atmospheric conditions but the most studied systems commercially available are based on the formation of carbamate between CO2 and an amine in post combustion capture systems. First, the CCS systems can be divided in two main technological approaches, depending on the target application of such technology. There are direct air capture and industrially derived capture. Direct air capture, being the most ambitious and technological challenging approach, still requires plenty of work to deliver commercially scalable and economically viable solutions, as it accounts only for the 1% of total CCS technologies available. Currently, there are two plants using Direct air carbon capture and storage (DACCS), with one under development, in addition to 15 pilot and demonstration plants either in operation or in development; however, collectively, their capture capacities are quite limited. Capture technologies are at different levels of technological readiness (TRL), with some at TRL 1. Industrially derived capture is the most used one and can be further divided in three different technologies: Pre-Combustion Capture, Post-Combustion Capture and Oxy-fuel combustion capture. Post-combustion carbon dioxide (CO2) capture is mainly relevant to traditional natural gas and pulverized coal-fired (PC) power generation. In a typical PC power plant, fuel undergoes combustion with air in a boiler to produce steam, which then drives a turbine to generate electricity. The resulting boiler exhaust, or flue gas, primarily consists of nitrogen (N2) and CO2. The separation of CO2 from this flue gas stream poses significant challenges for several reasons: CO2 is present at a dilute concentration (typically 13 to 15 volume percent for PC power plants and 3 to 4 percent for natural gas-fired plants) and at low pressure (slightly above atmospheric), necessitating the treatment of a large volume of gas; trace impurities such as particulate matter, sulfur dioxide (SO2), and nitrogen oxides (NOx) in the flue gas can impair sorbents and reduce the efficiency of certain CO2 capture processes; CO2 is captured at low pressure, and compressing it from atmospheric to pipeline pressure (about 2,000 pounds per square inch absolute [psia]) will result in a substantial auxiliary power load on the overall power plant system.3

Mitigating anthropogenic CO2 emissions has been a subject of incredible urgency in recent years. Carbon capture and storage (CCS) has emerged as a promising means of cutting emissions, with post-combustion capture and direct air capture (DAC) both gaining traction as methods of offsetting emissions from point sources and the ambient atmosphere. Each of these carbon capture methods rely on absorbent or adsorbent materials to function, whose properties can vastly impact capture performance. In this work, 14 materials are analyzed, with qualitative descriptions and performance data of each material based on existing review papers and representative case studies being presented. The review highlights limitations in the field in standardizing the reporting of experimental data, complicating the direct comparison of different materials’ efficacies. While no single CCS technology is found to be unequivocally superior, the promising performances of certain materials in earlier stages of development emphasize the importance of investing further in emerging post-combustion capture materials. This study concludes that CCS technologies are a necessary tool in ultimately reaching net zero emissions due to their role in neutralizing sectors resistant to decarbonization, but they should not be relied upon to substitute the transition to renewable energy, as the prevention of emissions should take priority over the abatement of emissions.

Performance assessment of offshore wind energy integrated monoethanolamine synthesis system for post-combustion and potential direct air capture

Carbon Dioxide Emissions, Capture, Storage and Utilization: Review of Materials, Processes and Technologies

Negative emissions technologies are gaining widespread acceptance as crucial tools in achieving climate goals, such as keeping global temperatures below 2 °C of pre-industrial levels by 2100. Two technologies central to carbon dioxide removal efforts are direct air capture and Bioenergy with carbon capture and storage. While both technologies have undergone extensive study, only a few studies have explored the potential of using biomass as an energy source for direct air capture technology. This is despite bioenergy with carbon capture having the ability to provide carbon-negative heat and power, as well as its potential impact on the climate mitigation goals of the century. This study aims to investigate the feasibility of meeting the energy requirements of a direct air capture unit using bioenergy. Combining these units will result in compounded negative emissions for the integrated system. The objective is to examine the thermal and electrical requirements of the two primary approaches used in direct air capture design: the liquid solvent and solid sorbent direct air capture units, and to calculate the compounded negative emissions achieved by integrating them with bioenergy. The results of this study demonstrate that for a direct air capture plant capturing 1 mega ton of carbon dioxide per year, approximately 1200 and 2400 tons of biomass per day would be sufficient to meet the energy needs of the solid sorbent and liquid solvent direct air capture systems, respectively. The combined capture efficiency of both types of direct air capture systems integrated with bioenergy stands at 91.19% to 93.9% with overall carbon captured up to 1.51 mega tons of carbon dioxide per year. Over the century, integrating bioenergy into direct air capture units can remove gigaton levels of carbon from the atmosphere without disrupting the demand–supply dynamics of existing and future energy systems.

Proposed is an electrochemical nickel hydroxide based hydroxide exchange membrane carbon capture (HEMCC) device for Direct Air Capture (DAC) of CO2. DAC has been identified as one of the key net negative carbon technologies to achieve net zero carbon emissions. Net negative carbon technologies are required to offset continued emissions from dilute CO2 sources such as agriculture and construction. The majority of current DAC technologies at scale (>1 KT∙yr-1) are adsorbent based technologies with significant energy cost. The traditional DAC energy cost is primarily driven by the temperature swing required to regenerate the sorbent and has been shown to be 1.8 MWh·ton-1 at the system level.Electrochemical pH swing devices are a growing research area for carbon capture devices with the goal of lowering the energy cost required for DAC. A pH gradient is built by generating OH- at the cathode and consuming OH- at the anode. An acid-base equilibrium with CO2 allows for the capture of CO2 at the cathode and release at the anode. This extends from other electrochemical CO2 capture devices based on pKa shifts of an electrochemically active organic species allowing for the capture and release of CO2. Electrochemical CO2 capture is considered promising based on potentially low energy costs to capture CO2 in comparison with current temperature swing adsorption technologies.This work explores Ni(OH)2 electrodes to produce the pH gradient for CO2 capture and release. At the cathode NiOOH is reduced to Ni(OH)2 while at the anode Ni(OH)2 is oxidized to NiOOH. The symmetrical electrodes allow for a low voltage requirement; the thermodynamic potential difference of standard electrochemical reactions is zero. Most of the voltage observed is to produce the pH gradient with the remainder driving the polarization of the electrodes. There is a resistance component as well, but this is small in comparison due to the low current densities used in the device, nominally 2 mA·cm-1.Two similar devices are presented, a traditional MEA (membrane electrode assembly) and a flow-through MEA. The traditional MEA separates the two Ni(OH)2 electrodes with an 80μm Piperion® membrane. While the flow-through membrane separates the electrodes with a three piece membrane consisting of two 80μm Piperion® membranes with a porous membrane between them. In the traditional MEA system air is passed over the cathode for capture, while the flow-through MEA the air is passed through the porous membrane isolated from the electrodes.The traditional MEA has been used to establish a baseline performance of the device and has been shown to capture CO2 at an energy cost of 1 MWh·ton-1 at the device level. An understanding has been built around the components of that energy cost including the relationship of flux to current density, effect of a regeneration process, transient battery behavior, and gas losses coinciding with changing the polarization of the batteries.The flow-through MEA looks to address of transient battery behavior and gas losses. It allows for denser, higher capacity electrodes, which can lean on traditional Ni-MH battery technology used in alkaline batteries used today. The higher capacities, limit the transient battery effect on flux in the device. Gas losses are addressed by having a continuous inlet air stream to the device and continuous outlet product.

Aerosol-based emission, solvent degradation, and corrosion in post combustion CO2 capture

Reducing CO2 emissions alone will not suppress global warming, and it is necessary to capture the CO2 that has been cumulatively emitted into the atmosphere as well. For this reason, negative CO2 emission technology, a technology to capture CO2 from the atmosphere, is considered essential. Especially, direct capture of CO2 from the air, so-called direct air capture (DAC) has attracted much attention as one of promising technologies, because of the high potential capacity of CO2 capture. In general, absorption, adsorption, and membrane separation are known as representative CO2 capture technologies, and DAC is basically based on these technologies. In particular, DAC using absorption and adsorption methods has already reached the level of plant scale, but the desorption process of captured CO2 from the absorbent or adsorbent consumes a large amount of heating energy and water. On the other hand, membrane separation is generally considered as a most cost- and energy-efficient process among these capture technologies, but DAC by membrane separation has not been considered at all due to the immaturity of the membrane performance for CO2 capture, especially CO2 permeance. However, recent developments in membrane technology have brought the possibility that membrane processes can be considered as a new approach to DAC. In this article, the potential of membrane technologies as DAC is discussed and future technology target is proposed.Graphical abstract

Life cycle assessment of negative emission technologies for effectiveness in carbon sequestration