ArticlePublisher preview available

Life-cycle assessment of an industrial direct air capture process based on temperature–vacuum swing adsorption

To read the full-text of this research, you can request a copy directly from the authors.

Abstract and Figures

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.
This content is subject to copyright. Terms and conditions apply.
1Institute for Technical Thermodynamics, RWTH Aachen University, Aachen, Germany. 2Institute of Energy and Climate Research, Energy Systems
Engineering (IEK-10), Forschungszentrum Jülich, Jülich, Germany. 3Energy and Process Systems Engineering, ETH Zurich, Zurich, Switzerland.
Fossil energy is still important to most societies, which led to
36.8 Gt yr1 of carbon dioxide (CO2) emissions in 2019 (refs. 1,2).
Moving from fossil energy to renewable energy will reduce
greenhouse gas (GHG) emissions. However, there is broad scientific
consensus that the target of the Paris Agreement of the 2015 Climate
Conference (COP 21)3 requires not only a massive reduction in
GHG emissions but even up to 30 Gt yr–1 of negative emissions46.
Negative emissions could be provided by direct air cap-
ture (DAC) of CO2 with subsequent storage for carbon dioxide
removal (CDR)7,8. Captured CO2 can be stored geologically or via
mineralization9,10. DAC not only allows us to remove GHG emis-
sions from our past use of fossil fuels but also enables future fuels
with a closed carbon cycle. The captured CO2 could serve as a
carbon feedstock for fuels11,12 and other value-added products
like chemicals13,14 and building materials15,16 via carbon capture
and utilization.
The most developed DAC concepts separate CO2 from the air
by either absorption or adsorption1719. DAC based on absorption
typically uses aqueous hydroxy sorbents like alkali and alkali-earth
hydroxides. By contrast, DAC based on adsorption can employ
a wide range of solid sorbents, for example, alkali carbonates20,21,
amines supported on oxides22,23, solid organic materials22,2426 and
metal–organic frameworks22,27. Absorption by aqueous sorbents
allows for low costs and continuous operation28 but leads to high
water loss29. Furthermore, sorbent regeneration requires high tem-
peratures19,30. By contrast, DAC by adsorption can operate at low
regeneration temperatures (<100 °C)19,28,31,32. The first commercial
DAC system employs solid adsorbents in cyclic temperature–vac-
uum swing adsorption3335.
While DAC removes CO2 directly from the atmosphere, the
potential climate benefits of DAC are partly offset by indirect
environmental impacts due to the supply of energy and materials.
So far, a detailed assessment of this trade-off is only available for
GHG emissions for a DAC process with aqueous hydroxy sorbents,
where high-temperature heat is usually obtained from natural
gas, and the resulting CO2 emissions are recaptured12,29. Available
assessments for adsorption-based DAC systems consider energy
requirements but use proxy data for plant construction and adsor-
bent36,37. Currently, requirements for water and land38 as well as
energy and materials for sorbent production39,40 are intensely
debated as key issues for the potential large-scale deployment of
DAC. Thus, a comprehensive environmental assessment is missing
for adsorption-based DAC but urgently needed to establish the role
of DAC in climate change mitigation41.
Herein, we comprehensively evaluate the environmental impacts
of adsorption-based DAC using the method of a life-cycle assess-
ment (LCA)42,43. Temperature–vacuum swing adsorption is stud-
ied based on data from the first commercial DAC plants. Climate
impact reductions depend strongly on the energy supply, while the
adsorbent and infrastructure become important when low-carbon
energy is used. Even large-scale deployment of DAC, capturing 1%
(ref. 44) of the global annual CO2 emissions, is not constrained by
material and energy supply for plant construction and operation,
nor would it lead to substantial trade-offs in other environmental
impact categories.
LCA goal and scope
LCA accounts for all flows of energy and materials exchanged with
the environment throughout the life cycle. The DAC system con-
sidered captures CO2 from the air by cyclic temperature–vacuum
swing adsorption. The climate benefit of removing CO2 from the
atmosphere is reduced by indirect emissions, for example, due to
the construction and operation of the DAC plant, for which the
company Climeworks provided industrial data.
Life-cycle assessment of an industrial direct air
capture process based on temperature–vacuum
swing adsorption
Sarah Deutz 1 and André Bardow 1,2,3 ✉
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.
NATURE ENERGY | VOL 6 | FEBRUARY 2021 | 203–213 | 203
Content courtesy of Springer Nature, terms of use apply. Rights reserved
... Evidently, for DACCS facilities connected to electric power grids, their environmental performance will depend on the electricity system context in which they will operate. Previous studies have shown that DACCS can achieve negative emissions, but capture efficiencies are sensitive to the operational efficiency and the energy source [22][23][24][25] . A recent life cycle assessment (LCA) of DACCS technologies also identified potential environmental trade-offs in increased land transformation if DACCS is operated by solar electricity (as compared to using grid electricity) 26 . ...
... Merely shifting to low-carbon energy sources for DACCS plant operation could lead to environmental trade-offs. These findings are in-line with other DACCS LCA studies 22,24,26 . We find that solvent-based DACCS generally has lower impacts than sorbentbased DACCS in five (climate change, human toxicity, freshwater CCI HTI FEI FTI TAI TTI MD WD 2020 2060 2100 2020 2060 2100 2020 2060 2100 2020 2060 2100 2020 2060 2100 2020 2060 2100 2020 2060 2100 2020 eutrophication, freshwater ecotoxicity, and metal depletion) out of eight impact categories studied herein. ...
... These differences appear to be linked to the study's optimistic electricity (180 kWh/ t CO 2 ) and heat (2.6 GJ/t CO 2 ) consumption assumptions for sorbent-based DACCS (under the reference case). These are less than half of those reported by several other studies 24,26,41 and the ones used herein (470-700 kWh/t CO 2 for electricity and 5.4-5.8 GJ/t CO 2 for heat). ...
Full-text available
Direct air capture (DAC) is critical for achieving stringent climate targets, yet the environmental implications of its large-scale deployment have not been evaluated in this context. Performing a prospective life cycle assessment for two promising technologies in a series of climate change mitigation scenarios, we find that electricity sector decarbonization and DAC technology improvements are both indispensable to avoid environmental problem-shifting. Decarbonizing the electricity sector improves the sequestration efficiency, but also increases the terrestrial ecotoxicity and metal depletion levels per tonne of CO2 sequestered via DAC. These increases can be reduced by improvements in DAC material and energy use efficiencies. DAC exhibits regional environmental impact variations, highlighting the importance of smart siting related to energy system planning and integration. DAC deployment aids the achievement of long-term climate targets, its environmental and climate performance however depend on sectoral mitigation actions, and thus should not suggest a relaxation of sectoral decarbonization targets.
... However, its large-scale deployment may negatively impact ecosystems, create water stress, or drive biodiversity loss (mainly if energy crops are employed) [21]. These impacts could be alleviated with DACCS, but the chemical process requires large amounts of energy to operate, making it costly today and entailing associated environmental impacts [22]. What is clear is that there is no "silver bullet" (single technology or strategy) to solve the climate problem and deliver CDR at the scale and pace required [23]. ...
... To mention some prior studies, Minx et al. [5] and Fuss et al. [4] provided a thorough techno-economic assessment of several CDR alternatives. Other works investigated the CDR potentials and environmental impacts on the environment [29,30]; most of them focused only on BECCS [31][32][33][34][35] or DACCS [22,36,37], while other alternatives have received much less attention [9,11]. Another active research direction consists of assessing the role of the different CDR options in the climate change mitigation pathways and the broad implications of their large-scale deployment of the CDR [3,[38][39][40][41]. ...
Full-text available
Carbon dioxide removal (CDR) will be a key component of the climate change mitigation efforts to achieve the carbon-neutrality goals. Hence, a comprehensive assessment of the CDR potential at national and local levels is crucial to identify regional opportunities and deploy practical actions timely. This study focuses on the potential function of olive agroecosystems in delivering CDR in the European Mediterranean countries. Relying on a geospatial assessment of existing olive groves (and associated residual biomass) combined with statistical, process systems engineering, and life cycle emissions data, the CDR potential considering five promising actions linked with the olive agroecosystems was here estimated. These actions are i) conservation measures protecting tree carbon sequestration, ii) agricultural practices increasing soil carbon sequestration, iii) biochar production and utilization, iv) biomass conversion routes coupled with carbon capture and storage (CCS), and v) development of bio-based and CO2-based materials. Overall, the bottom-up assessment highlights the value of the olive groves, currently storing around 0.22 Gt CO2-eq in standing trees and potentially sequestering 0.03 Gt CO2-eq annually in soils. Moreover, exploiting the abundant biomass wastes in biorefineries coupled with CCS could deliver gigatonne-scale CDR while producing various value-added products, achieving above 0.01 Gt CO2-eq per year only using prunings for biochar or power, while other pathways show lower potential (e.g., 0.52 MtCO2eq yr⁻¹ for fermentation). These results may promote the large-scale deployment of CDR actions, stimulate new policy initiatives to exploit opportunities associated with the olive groves, and ultimately contribute to the transition toward the net-zero targets.
... The authors claim that the new plant will capture 4000 tons of CO 2 per yearmaking it the world's most extensive climate-positive facility to date [141]. Recently, Deutz and Bardow [142] analyzed the carbon footprint of Climeworks' DAC plant construction, considering the materials used, the energy required, the use of sorbents etc., to capture 1% of the global CO 2 emissions (see Fig. 5). It is clear that this approach requires a high amount of adsorbent and energy. ...
... The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. [142]. ...
Since carbon dioxide (CO2) is the primary greenhouse gas emitted due to human activities into the atmosphere, strong research efforts have been developed towards capturing and decreasing its production. Unfortunately, specific processes and activities make it impossible to avoid CO2 emissions. Among the different strategies scientists propose for CO2 reduction, direct CO2 capture from the atmosphere, also known as direct air capture (DAC), represents a promising alternative in which sorbents have been mainly used. Recently, gas separation membranes have also been speculated to carry out such a separation, thanks to their smaller footprint and simpler setup and operation; however, their application remains a proposition in the field. This paper gives a perspective of the ongoing research and attempts of DAC applications via membrane separation and introduces the main membrane materials and types used for CO2 separation. Finally, the process considerations for DAC using membranes are stated to guide the new researchers in the field.
... In contrast, their side-effects and co-benefits beyond global warming have often been overlooked. Some studies have quantified the environmental impacts of DACCS and BECCS, but their results are hard to interpret from an absolute sustainability viewpoint [15][16][17][18][19] . Only recently, the impacts of BECCS were assessed against the Earth's biophysical limits 20,21 , i.e., the Planetary Boundaries (PBs) within which humanity could safely operate 22 . ...
... Nonetheless, previous studies suggest that the contribution of infrastructure to the total impacts of NETs might be minor. Notably, the impacts of constructing and decommissioning biomass power plants are negligible 62 , whereas the impacts related to the infrastructure of LTSS-DACCS are small relative to other life-cycle impacts 15 . ...
Full-text available
Meeting the 1.5 °C target may require removing up to 1,000 Gtonne CO 2 by 2100 with Negative Emissions Technologies (NETs). We evaluate the impacts of Direct Air Capture and Bioenergy with Carbon Capture and Storage (DACCS and BECCS), finding that removing 5.9 Gtonne/year CO 2 can prevent <9·10 ² disability-adjusted life years per million people annually, relative to a baseline without NETs. Avoiding this health burden—similar to that of Parkinson’s—can save substantial externalities (≤148 US$/tonne CO 2 ), comparable to the NETs levelized costs. The health co-benefits of BECCS, dependent on the biomass source, can exceed those of DACCS. Although both NETs can help to operate within the climate change and ocean acidification planetary boundaries, they may lead to trade-offs between Earth-system processes. Only DACCS can avert damage to the biosphere integrity without challenging other biophysical limits (impacts ≤2% of the safe operating space). The quantified NETs co-benefits can incentivize their adoption.
... The reason is that the environmental performance of NETs depends not only on the technology but also on local conditions and spatial restrictions. For example, Lefebvre et al. (2019) found that transportation (distance from quarry to field) was a key limitation to enhanced weathering in soils, whereas Deutz and Bardow (2021) studied the environmental sustainability of the DAC plants in Hinwil and Hellisheiði, operated by Climeworks, and noted that the LCA results are very sensitive to the energy sources. Furthermore, when comparing different NETs, a wide range of environmental impacts should be considered (McQueen et al., 2021b) as well as other aspects of each technology. ...
Full-text available
Over the previous two decades, a diverse array of geochemical negative emissions technologies (NETs) have been proposed, which use alkaline minerals for removing and permanently storing atmospheric carbon dioxide (CO2). Geochemical NETs include CO2 mineralization (methods which react alkaline minerals with CO2, producing solid carbonate minerals), enhanced weathering (dispersing alkaline minerals in the environment for CO2 drawdown) and ocean alkalinity enhancement (manipulation of ocean chemistry to remove CO2 from air as dissolved inorganic carbon). CO2 mineralization approaches include in situ (CO2 reacts with alkaline minerals in the Earth's subsurface), surficial (high surface area alkaline minerals found at the Earth's surface are reacted with air or CO2-bearing fluids), and ex situ (high surface area alkaline minerals are transported to sites of concentrated CO2 production). Geochemical NETS may also include an approach to direct air capture (DAC) that harnesses surficial mineralization reactions to remove CO2 from air, and produce concentrated CO2. Overall, these technologies are at an early stage of development with just a few subjected to field trials. In Part I of this work we have reviewed the current state of geochemical NETs, highlighting key features (mineral resources; processes; kinetics; storage durability; synergies with other NETs such as DAC, risks; limitations; co-benefits, environmental impacts and life-cycle assessment). The role of organisms and biological mechanisms in enhancing geochemical NETs is also explored. In Part II, a roadmap is presented to help catalyze the research, development, and deployment of geochemical NETs at the gigaton scale over the coming decades.
... One of the benefits of DAC over PCC is the capturing of environmental CO 2 such as transportation system emissions and other activities associated with CO 2 release into the atmosphere. Deutz et al. [90] . presented a life cycle assessment of DAC on an industrial scale using the pilot study project in Hinwil and Hellisheiði that Climeworks operates as a case study. ...
Full-text available
Carbon neutrality is an ambitious goal that has been promulgated to be achieved on or before 2060. However, most of the current energy policies focus more on carbon emission reduction, efficiency and high penetration of renewable energy. Thus, this paper presented a review strategy towards carbon neutrality by presenting the concept of a multi-energy system (MES) in terms of its technologies, configuration, modelling and feasibility as zero-emission equipment. The paper addressed some prominent challenges associated with zero-carbon multi-energy systems (ZCMES). Various proven solutions in the extant studies that have been affirmed to alleviate some of these challenges were presented. In the end, we identified and summarised the current research gaps, and the future directions to ensure the feasibility of ZCMES as a primary strategy towards the actualization of carbon neutrality. Hence, this review work serves as a reference for revising the current energy policies to incorporate a carbon neutrality framework.
... Used in conjunction with renewable (but relatively intermittent) energy sources, direct air capture sites may be an efficient way to use otherwise curtailed electricity production, ramping up when energy demand is saturated and energy storage is full. To benefit from these advantages, however, direct air capture technology will have to overcome significant challenges with technological readiness, high energy demand, high financial costs, and social acceptance (Budinis, 2021;Deutz and Bardow, 2021;Erans et al., 2022;Fasihi et al., 2019). ...
Full-text available
Direct Air Capture with Carbon Storage (DACCS) technologies represent one of the most significant potential tools for tackling climate change by making net-zero and net-negative emissions achievable, as deemed necessary in reports from the Intergovernmental Panel on Climate Change and the European Green Deal. We draw from a novel and original dataset of expert interviews (N=125) to distil ten recommendations for future DACCS policy. After providing a literature review on DACCS and explaining our methods of data collection, we present these recommendations as follows: (1) follow governance principles that ensure “negative” emissions; (2) prioritize long-term carbon storage; (3) appreciate and incentivize scale; (4) co-develop with capture, transport, and storage (5) phase in a carbon price; (6) couple with renewables; (7); harness hub deployment; (8); maintain separate targets; (9) embrace certification and compliance; and (10) recognize social acceptance. All ten recommendations are important, and all speak to the urgency and necessity of better managing and shaping the potentially impending DACCS transition.
Negative emission technologies (NETs) could play a key role in ensuring net-zero and longer-term net negative emission ambitions are met. However, greenhouse gas emissions (and other pollutants) will occur over the life cycle of a NET and will need to be taken into consideration when developing schemes to roll out their use. We compare five NETs: afforestation/reforestation (AR), enhanced weathering (EW), mangrove restoration (MR), bioenergy and direct air capture with carbon storage (BECCS and DAC), using life cycle assessment to determine their environmental impacts (global warming, freshwater, toxicity etc.). We find that there is a wide range in the environmental impacts estimated across the NETs and the context in which they are used will directly impact which NET has low or high environmental impacts. This is an important aspect to consider when deciding which NET to prioritise in strategies to roll out their use on large scales. If consistent removal of CO2 from the atmosphere is the goal, then AR and MR have the lowest environmental impacts. However, if large and quick CO2 removal is the goal then EW, DAC and BECCS have similar, if not lower, environmental impacts.
Electromicrobial production (EMP) processes, in which electricity or electrochemically-derived mediator molecules serve as energy sources to drive biochemical processes, represent an attractive strategy for the conversion of CO 2 into carbon-based...
Vehicle lightweight and carbon neutrality turn out to be the critical goals in developing new energy vehicles. As an important part of electric vehicles, power battery packs have an impact on the environment. In this study, Multiple environmental assessment indicators were grouped into a comprehensive index, namely the green characteristic index, and the green characteristic index was used to comprehensively evaluate the environmental impact of 11 kinds of battery packs. This study calculates and analyzes the environmental impact values of battery packs in different regions for four types of small, medium, intermediate, and limousine cars. Finally, the uncertainty analysis was carried out. Research has found that micro battery packs have a lower potential environmental impact than advanced battery packs, so smaller, more energy‐efficient BEVs generally perform better than larger BEVs for vehicle models. During the operation stage of the battery pack, the environmental impact value of carbon footprint and ecological footprint is greatly affected by the regional power structure. Running the battery pack in China will generate higher carbon footprint and ecological footprint. In addition, the green characteristic index is more affected by the stage of use. When the scene is switched, the larger the model of the electric vehicle, the more obvious its environmental emission reduction capability. This highlights the benefits of high‐efficiency electrical structures in large electric vehicles, which can reduce environmental impact by increasing lifetime and charging efficiency, reducing the loss of transport power in the area, and improving the weight‐to‐energy relationship for BEVs. This article is protected by copyright. All rights reserved.
Full-text available
Scenarios for meeting ambitious climate targets rely on large-scale deployment of negative emissions technologies (NETs), including direct air capture (DAC). However, the tradeoffs between food, water and energy created by deploying different NETs are unclear. Here we show that DAC could provide up to 3 GtCO2 yr−1 of negative emissions by 2035—equivalent to 7% of 2019 global CO2 emissions—based on current-day assumptions regarding price and performance. DAC in particular could exacerbate demand for energy and water, yet it would avoid the most severe market-mediated effects of land-use competition from bioenergy with carbon capture and storage and afforestation. This could result in staple food crop prices rising by approximately fivefold relative to 2010 levels in many parts of the Global South, raising equity concerns about the deployment of NETs. These results highlight that delays in aggressive global mitigation action greatly increase the requirement for DAC to meet climate targets, and correspondingly, energy and water impacts.
Full-text available
Government policies during the COVID-19 pandemic have drastically altered patterns of energy demand around the world. Many international borders were closed and populations were confined to their homes, which reduced transport and changed consumption patterns. Here we compile government policies and activity data to estimate the decrease in CO2 emissions during forced confinements. Daily global CO2 emissions decreased by –17% (–11 to –25% for ±1σ) by early April 2020 compared with the mean 2019 levels, just under half from changes in surface transport. At their peak, emissions in individual countries decreased by –26% on average. The impact on 2020 annual emissions depends on the duration of the confinement, with a low estimate of –4% (–2 to –7%) if prepandemic conditions return by mid-June, and a high estimate of –7% (–3 to –13%) if some restrictions remain worldwide until the end of 2020. Government actions and economic incentives postcrisis will likely influence the global CO2 emissions path for decades. COVID-19 pandemic lockdowns have altered global energy demands. Using government confinement policies and activity data, daily CO2 emissions have decreased by ~17% to early April 2020 against 2019 levels; annual emissions could be down by 7% (4%) if normality returns by year end (mid-June).
Full-text available
Negative emissions technologies will play an important role in preventing 2°C warming by 2100. The next decade is critical for technological innovation and deployment to meet mid-century carbon removal goals of 10 – 20 GtCO2 /yr. Direct air capture (DAC) is positioned to play a critical role in carbon removal, yet remains under paced in deployment efforts, mainly due to high costs. This study outlines a roadmap for DAC cost reductions through the exploitation of low-temperature heat, recent US policy drivers, and logical, regional end-use opportunities in the US. Specifically, two scenarios are identified that allow for the production of compressed high-purity CO2 for costs  $300/tCO2, net delivered with an opportunity to scale to 19 MtCO2/yr. These scenarios use thermal energy from geothermal and nuclear power plants to produce steam and transport the purified CO2 via trucks to the nearest opportunity for direct use or subsurface permanent storage. While some utilization pathways result in the re-emission of CO2 and cannot be considered true carbon removal, they would provide economic incentive to deploying DAC plants at scale by mid-century. In addition, the federal tax credit 45Q was applied for qualifying facilities, (i.e., producing  100 ktCO2/yr).
Full-text available
Direct Air Capture (DAC) separates carbon dioxide (CO2) from ambient air either chemically or physically. As such, it could be a potential climate mitigation tool when paired with geological sequestration of CO2 or downstream conversion to produce lower-carbon products. In this study, we conduct a life cycle assessment (LCA) of the greenhouse gas (GHG) emissions of a DAC system paired with Fischer-Tropsch synthesis (FTS) to produce transportation fuel (i.e., diesel). This is the first LCA study of a DAC process based on data from an operating pilot plant. This study presents a mass and energy balance of the combined DAC and FTS system for the design of a commercial scale operation informed by pilot and design data. The base case scenario, including fuel use, is estimated to emit 0.51 gCO2e/gCO2 captured from air or 29 gCO2e/MJ FTS fuel combusted. The impact of changing uncertain and variable parameters on the end product carbon intensity reveals that this process is most sensitive to the electricity grid emission factor, followed by the type of calciner. We conclude that a combined DAC and FTS process can produce fuel that is lower in carbon than current fossil systems.
Full-text available
The CarbFix method was upscaled at the Hellisheiði geothermal power plant to inject and mineralize the plant’s CO2 and H2S emissions in June 2014. This approach first captures the gases by their dissolution in water, and the resulting gas-charged water is injected into subsurface basalts. The dissolved CO2 and H2S then react with the basaltic rocks liberating divalent cations, Ca²⁺, Mg²⁺, and Fe²⁺, increasing the fluid pH, and precipitating stable carbonate and sulfide minerals. By the end of 2017, 23,200 metric tons of CO2 and 11,800 metric tons of H2S had been injected to a depth of 750 m into fractured, hydrothermally altered basalts at >250 °C. The in situ fluid composition, as well as saturation indices and predominance diagrams of relevant secondary minerals at the injection and monitoring wells, indicate that sulfide precipitation is not limited by the availability of Fe or by the consumption of Fe by other secondary minerals; Ca release from the reservoir rocks to the fluid phase, however, is potentially the limiting factor for calcite precipitation, although dolomite and thus aqueous Mg may also play a role in the mineralization of the injected carbon. During the first phase of the CarbFix2 injection (June 2014 to July 2016) over 50% of injected carbon and 76% of sulfur mineralized within four to nine months, but these percentages increased four months after the amount of injected gas was doubled during the second phase of CarbFix2 (July 2016–December 2017) at over 60% of carbon and over 85% of sulfur. The doubling of the gas injection rate decreased the pH of the injection water liberating more cations for gas mineralization. Notably, the injectivity of the injection well has remained stable throughout the study period confirming that the host rock permeability has been essentially unaffected by 3.5 years of mineralization reactions. Lastly, although the mineralization reactions are accelerated by the high temperatures (> 250 °C), this is the upper temperature limit for carbon storage via the mineral carbonation of basalts as higher temperatures leads to potential decarbonation reactions.
Full-text available
Carbon Capture and Utilization (CCU) is an emerging field proposed for emissions mitigation and even negative emissions. These potential benefits need to be assessed by the holistic method of Life Cycle Assessment (LCA) that accounts for multiple environmental impact categories over the entire life cycle of products or services. However, even though LCA is a standardized method, current LCA practice differs widely in methodological choices. The resulting LCA studies show large variability which limits their value for decision support. Applying LCA to CCU technologies leads to further specific methodological issues, e.g., due to the double role of CO2 as emission and feedstock. In this work, we therefore present a comprehensive guideline for LCA of CCU technologies. The guideline has been development in a collaborative process involving over 40 experts and builds upon existing LCA standards and guidelines. The presented guidelines should improve comparability of LCA studies through clear methodological guidance and predefined assumptions on feedstock and utilities. Transparency is increased through interpretation and reporting guidance. Improved comparability should help to strengthen knowledge-based decision-making. Consequently, research funds and time can be allocated more efficiently for the development of technologies for climate change mitigation and negative emissions.
Our LCA-based assessment showed that all considered CCU technologies for mineralization can reduce climate impacts over the entire life cycle due to the permanent storage of CO 2 and the credit for substituting conventional products.
Several greenhouse gas removal technologies (GGRTs), also called negative emissions technologies (NET) have been proposed to help meet the Paris Climate Agreement targets. However, there are many uncertainties in the estimation of their effective greenhouse gas (GHG) removal potentials, caused by their different levels of technological development. Life Cycle Assessment (LCA) has been proposed as one effective methodology to holistically assess the potential of different GGRT removal approaches but no common framework is currently available for benchmarking and policy development. In this article, challenges for LCA are reviewed and discussed together with some alternative approaches for assessment of GGRTs. In particular, GGRTs pose challenges with regards to the functional unit, the system boundary of the LCA assessment, and the timing of emissions. The need to account within LCA of GGRTs for broader implications which involve environmental impacts, economic, social and political drivers is highlighted. A set of recommendations for LCA of GGRTs are proposed for a better assessment of the GGRTs and better accounting of their carbon removal potentials to meet the targets established within the Paris Agreement.