Environmental trade-offs of direct air capture technologies in climate change mitigation toward 2100

Economic and sustainable revolution to facilitate one-carbon biomanufacturing

One-carbon (C1) biomanufacturing serves as a substitute for fossil-based feedstocks, aiming to de-fossilize chemical production and foster a circular carbon economy by recycling waste greenhouse gases. Here, we review the key economic and technical barriers associated with the commercialization of C1 biomanufacturing through case studies. Additionally, a viable roadmap to enhance cost competitiveness is unveiled, underscoring its potential to facilitate carbon neutrality as scalable and sustainable alternatives to traditional chemical production.

Material needs for power-to-X systems for CO2 utilization require a life cycle approach

The world's transition from a fossil-fuel-driven society to a future net-zero or negative carbon dioxide emission society will require a significant scale-up of Power-to-X technologies to capture and convert CO2 to low carbon intensity fuels and chemicals. The deployment of Power-to-X technologies at gigawatt scales necessary to impact CO2 emissions and replace existing fossil-fuel-dependent processes will require vast quantities of raw materials and minerals. Many of the materials required in Power-to-X systems, such as rare earth metal yttrium and iridium, differ from those used to construct and operate petroleum-hydrocarbon-based processes for the last 100 years. Thus, electrolyzer manufacturers and mineral producers face significant challenges in matching supply to the growing demand. In this Perspective, we identify critical materials needed for Power-to-X electrolyzers and analyze the impacts and risks of these materials' existing global supply chains. We then provide an overview of methodologies for Environmental Life Cycle Assessment (LCA) and Social Life Cycle Assessment (SLCA) that we encourage scientific communities to adopt early in the research process to evaluate the multidimensional socio-environmental impacts throughout a product's life cycle, from raw material extraction and processing to manufacturing, use, and end-of-life disposal. We advocate that life cycle thinking is crucial for the informed, just and ethical development of disruptive technologies and systems such as Power-to-X technologies.

Strategic Design and Multiperiod Optimization under Uncertainty of Solid Sorbent Direct Air Capture Supply Chains in Europe

This study develops a multiperiod mixed-integer linear programming model for strategic planning of direct air capture (DAC) supply chains across Europe aiming at minimizing overall costs under uncertainty. DAC is pivotal for achieving net-zero targets and removing CO2 from the atmosphere to enable negative emissions. The optimization considers uncertainty in key parameters to ensure resilient decision-making. The model incorporates the influence of ambient air conditions on DAC performance, with temperature and humidity impacting productivity and energy consumption. Country-specific energy costs and greenhouse gas emission factors are accounted for, impacting the net cost of CO2 removal. Results indicate that with ambitious targets, technology learning curves, and renewable electricity transition, costs can fall to approximately 121 €/t CO2 by 2050, with 108 €/t attributed to capture costs. The findings highlight the importance of technological advancements and provide a systematic framework for policymakers to design resilient and cost-effective supply chains for large-scale deployment, positioning DAC as a potential decarbonization alternative for hard-to-abate emissions.

Prospective Life Cycle Assessment Suggests Direct Reduced Iron Is the Most Sustainable Pathway to Net-Zero Steelmaking

Decarbonizing the steel industry is essential due to its substantial contribution to climate change. This study explores pathways to achieve net-zero CO2eq emissions in the iron and steelmaking industry while minimizing environmental burdens beyond climate change. We conducted a comprehensive attributional life cycle assessment using the net-zero-CO2eq-emissions framework, incorporating both conventional and prospective life cycle assessment methods, to evaluate various decarbonization strategies within the United Kingdom. All value chains were constrained to achieve net-zero CO2eq emissions. Our findings indicate that, under a "current time" scenario, the natural gas-fired direct reduced iron with electric arc furnace is the most favorable option. This is mainly because hydrogen-based direct reduced iron production relies on the UK's current electricity grid, which has a carbon intensity of 293.28 g CO2eq per kWh. As greenhouse gas emissions decrease toward 2050 (approximately 70% for hydrogen-based direct reduced iron), the choice between natural gas and hydrogen will become increasingly region-specific. All net-zero-CO2eq steelmaking case studies perform similarly on human health indicators, while the direct reduced iron with electric arc furnace options have 60-82% lower impacts on the ecosystem end point indicator than the blast furnace basic oxygen furnace routes.

Efficient Direct Air Capture in Industrial Cooling Towers Mediated by Electrochemical CO2 Release

Direct air capture (DAC) is a promising technology for mitigating global climate change but suffers from low efficiency, small scale, and high cost due to the dilute atmospheric CO2, limited size of air contactors, and heat-driven CO2 release. Here, we propose combining DAC with widely used industrial cooling towers to extract CO2 from the air and using electrolysis to release the captured CO2 at room temperature. We first prepare a buffered absorbent solution consisting of sodium glycinate, glycine, and sodium chloride for effective CO2 capture from the air, solving the incompatibility problem of the cooling towers with conventional absorbents. Next, we employ a three-chamber electrolyzer for efficient release (≥95 %) of the captured CO2 with high purity (≥98 %) by constant current electrolysis at room temperature, bypassing the conventional energy-intensive heating process. The entire DAC system can operate stably for multiple cycles, and the mechanism for consecutive CO2 capture and release is uncovered. This work reveals the great potential of running DAC in industrial cooling towers coupled with electrochemically-driven CO2 release, opening up new avenues for curbing the increasingly severe climate change.

Life cycle environmental trade-off of decarbonising UK industrial clusters - A cradle to gate approach

The industrial sector is a major source of greenhouse gas (GHG) emissions due to process emissions and a heavy reliance on fossil fuels for heat and power. Methods exist to produce low carbon versions of products made in industrial clusters, including hydrogen, carbon capture and storage and alternative production methods, but these could increase burdens to other areas of the environment, such as resource depletion and water scarcity. This study compares different decarbonisation pathways for ammonia, cement, methanol and steel produced in the UK, to determine whether decarbonising could result in unintended environmental consequences. To determine this, life cycle assessment was applied to compare 267 different pathways to the conventional (fossil fuel) baseline. We find that most pathways lead to GHG emission reductions (43 to 78 % on average) but would increase impacts to other areas of the environment, including metal resources and ecotoxicity (8 % to 5-fold and 19 % to 24-fold, on average respectively). This study is the first to assess decarbonisation pathways for unintended environmental impacts and is of interest to industry, policy makers and anyone modelling industrial lifecycle emissions.

Mineral trapping of carbon dioxide: Rapid hydrothermal synthesis experiments and carbon sequestration potential of dawsonite

Dawsonite, as a natural CO2 tracing mineral, is intimately associated with CO2 injection and serves as a crucial mineral for geological carbon sequestration. The massive and stable presence of dawsonite in the geological background is a key consideration for CO2 mineralization capture and plays a significant role in identifying CO2 geological burial sites. To investigate the optimal conditions for the rapid synthesis of dawsonite using CO2, we conducted comparative experiments to examine the three primary influencing factors: temperature (100 °C, 120 °C, 140 °C, 160 °C, 180 °C, and 200 °C), pH (8.5, 9, 9.5, 10, and 10.5), and reaction time (6 and 12 h). Through scanning electron microscopy and X-ray diffraction analysis, the optimal conditions for dawsonite synthesis were determined. The experiments revealed that within the pH range of 8.5-10.5 and at temperatures of 100-180 °C, the dawsonite products obtained are consistently pure, which indicates that CO2 can be effectively mineralized and sequestered as dawsonite within these temperature and pH ranges. The synthesis yield increased and then decreased with increasing pH and temperature. At 200 °C, the crystallinity of dawsonite decreased and the content of pseudo-boehmite increased. This suggests that higher temperature conditions are not conducive to the mineralization and sequestration of CO2. Extending the reaction time did not have a significant promoting effect on the quality of the product. The maximum amount of dawsonite synthesis, good dispersion and homogeneity of crystals, and maximum ratio of mineralization of CO2 by dawsonite were achieved at a temperature of 140 °C and a pH of 9.5, indicating that these are the optimal conditions for the hydrothermal synthesis of dawsonite using CO2. Moreover, these are the optimal geological conditions for the mineralization sequestration of CO2 in the form of dawsonite.

Environmental Benefits of Circular Ethylene Production from Polymer Waste

The linear nature of the current plastics economy and increasing demand for polymers poses a pressing global problem. In this work, we explore the environmental and economic performance of a circular alternative for polymer production through chemical plastic recycling following the waste-to-methanol-to-olefins (WMO) route. We assess the life-cycle environmental impacts and techno-economic feasibility of this novel circular production route (CPR) in 2020 and 2050, and compare them to the existing linear production route (LPR), deploying naphtha steam cracking for olefin production, and a mix of landfill and incineration as end-of-life treatment. Our results showcase that CPR could enable significant impact reductions, notably in 2050 assuming a low-carbon electricity mix based on renewables. However, the shift from linear to circular comes with burden-shifting, increasing the impacts relative to LPR on five environmental indicators in 2020 (i.e., terrestrial and freshwater eutrophication, particulate matter formation, acidification, and metal/mineral resources use). From the techno-economic viewpoint, we found that ethylene from waste polymers could become competitive with fossil ethylene when deployed at large scale. Moreover, it is significantly cheaper than its green analogs, which deploy methanol-to-olefins with green methanol from captured CO2 and electrolytic H2, showcasing the potential of implementing high-readiness level technologies to close the loop for polymers.

Prospective environmental burdens and benefits of fast-swing direct air carbon capture and storage

Direct air capture (DAC) in combination with storage of CO2 can lower atmospheric CO2 concentrations. This study investigates the environmental impact of a new fast-swing solid sorbent DAC system, including CO2 transport and storage, over its life cycle, using prospective life cycle assessment. This DAC technology is currently on technology readiness level 5 and is expected to operate on an industrial scale by 2030. The technology was upscaled to the industrial scale and future changes in the background over the lifetime of the system were included, such as electricity grid mix decarbonization. Environmental trade-offs for the new DAC system were assessed by comparing environmental benefits from CO2 sequestration with environmental burdens from production, operation and decommissioning. We considered three electricity generation configurations: grid-connected, wind-connected, and a hybrid configuration. We found net environmental benefits for all configurations and background scenarios for ecosystem damage and climate change. Net human health benefits were observed when the electricity grid decarbonizes quickly and without the use of a battery. The environmental benefits increase with decreasing electricity footprint and are comparable with other DAC technologies. This illustrates that the new DAC system can help to meet the climate goals.

Assessment of Potential and Techno-Economic Performance of Solid Sorbent Direct Air Capture with CO2 Storage in Europe

Direct air capture with CO2 storage (DACCS) is among the carbon dioxide removal (CDR) options, with the largest gap between current deployment and needed upscaling. Here, we present a geospatial analysis of the techno-economic performance of large-scale DACCS deployment in Europe using two performance indicators: CDR costs and potential. Different low-temperature heat DACCS configurations are considered, i.e., coupled to the national power grid, using waste heat and powered by curtailed electricity. Our findings reveal that the CDR potential and costs of DACCS systems are mainly driven by (i) the availability of energy sources, (ii) the location-specific climate conditions, (iii) the price and GHG intensity of electricity, and (iv) the CO2 transport distance to the nearest CO2 storage location. The results further highlight the following key findings: (i) the limited availability of waste heat, with only Sweden potentially compensating nearly 10% of national emissions through CDR, and (ii) the need for considering transport and storage of CO2 in a comprehensive techno-economic assessment of DACCS. Finally, our geospatial analysis reveals substantial differences between regions due to location-specific conditions, i.e., useful information elements and consistent insights that will contribute to assessment and feasibility studies toward effective DACCS implementation.

Environmental problem shifting from climate change mitigation: A mapping review

Climate change mitigation will trigger major changes in human activity, energy systems, and material use, potentially shifting pressure from climate change to other environmental problems. We provide a comprehensive overview of such "environmental problem shifting" (EPS). While there is considerable research on this issue, studies are scattered across research fields and use a wide range of terms with blurred conceptual boundaries, such as trade-off, side effect, and spillover. We identify 506 relevant studies on EPS of which 311 are empirical, 47 are conceptual-theoretical, and 148 are synthetic studies or reviews of a particular mitigation option. A systematic mapping of the empirical studies reveals 128 distinct shifts from 22 categories of mitigation options to 10 environmental impacts. A comparison with the recent IPCC report indicates that EPS literature does not cover all mitigation options. Moreover, some studies systematically overestimate EPS by not accounting for the environmental benefits of reduced climate change. We propose to conceptually clarify the different ways of estimating EPS by distinguishing between gross, net, and relative shifting. Finally, the ubiquity of EPS calls for policy design which ensures climate change mitigation that minimizes unsustainability across multiple environmental dimensions. To achieve this, policymakers can regulate mitigation options-for example, in their choice of technology or location-and implement complementary environmental policies.

Geo-Spatial Economic Assessment of the Potential Development of Bioenergy Combined with Direct Air Carbon Capture (BEDAC) in the USA

This study presents a geo-spatial and economic framework to localize future bioenergy power plants combined with direct air capture (BEDAC). This framework is applied to two regions in the USA to assess the optimal use of forest biomass and in situ carbon sequestration under three specific short-term sequestration targets. Results show that there are many locations that have both the necessary biomass and geology required for storage. The Southeast has greater potential for forestry biomass due to both the rate of growth and forested areas, but the sequestration potential is mostly limited to a CO2 solution in saline aquifers. The Pacific Northwest has more sequestration potential than the Southeast given the location of managed forests and storage sites in carbonate mineralization in bedrock. The two combined regions have a total potential sequestration of 9.3 GtCO2 for the next 20 years that can be achieved under an implicit carbon value of $249/tCO2.

CO2 emissions of constructing China's power grid towards carbon-neutral target: Based on top-down and bottom-up integrated model

Power sector is the largest industrial emitter in China, and renewable energy development would contribute to the large-scale construction of power grid. Mitigating carbon emissions of power gird construction is extremely important. So, the objective of this study is to understand embodied carbon emissions of power grid construction under carbon neutrality target, and then put forward to policy implications of carbon mitigation. This study, based on top-down and bottom-up integrated assessment models (IAMs), investigates carbon emissions of power grid construction towards 2060, through identifying the key driving factors and forecasting their embodied emissions in line with China's carbon neutrality target. Our results show that, the increase of Gross Domestic Product (GDP) dominates the increase in embodied carbon emissions of power grid construction, while energy efficiency and energy structure improvement contribute to the decrease. Large scale renewable energy development promotes the power grid construction. In 2060, total embodied carbon emissions would increase to 1105.7 Million tons (Mt) under the carbon neutrality target. However, the cost and key carbon-neutral technologies should be re-considered to ensure the sustainable electricity supply. The results could provide data reference and decision-making of designing power construction and mitigating carbon emissions of power sector in future.

Turn air-captured CO2 with methanol into amino acid and pyruvate in an ATP/NAD(P)H-free chemoenzymatic system

The use of gaseous and air-captured CO₂ for technical biosynthesis is highly desired, but elusive so far due to several obstacles including high energy (ATP, NADPH) demand, low thermodynamic driving force and limited biosynthesis rate. Here, we present an ATP and NAD(P)H-free chemoenzymatic system for amino acid and pyruvate biosynthesis by coupling methanol with CO₂. It relies on a re-engineered glycine cleavage system with the NAD(P)H-dependent L protein replaced by biocompatible chemical reduction of protein H with dithiothreitol. The latter provides a higher thermodynamic driving force, determines the reaction direction, and avoids protein polymerization of the rate-limiting enzyme carboxylase. Engineering of H protein to effectively release the lipoamide arm from a protected state further enhanced the system performance, achieving the synthesis of glycine, serine and pyruvate at g/L level from methanol and air-captured CO₂. This work opens up the door for biosynthesis of amino acids and derived products from air.

Linking Life Cycle and Integrated Assessment Modeling to Evaluate Technologies in an Evolving System Context: A Power-to-Hydrogen Case Study for the United States

Carbon-neutral hydrogen (H₂) can reduce emissions from hard-to-electrify sectors and contribute to a net-zero greenhouse gas economy by 2050. Power-to-hydrogen (PtH₂) technologies based on clean electricity can provide such H₂, yet their carbon intensities alone do not provide sufficient basis to judge their potential contribution to a sustainable and just energy transition. Introducing a prospective life cycle assessment framework to decipher the non-linear relationships between future technology and energy system dynamics over time, we showcase its relevance to inform research, development, demonstration, and deployment by comparing two PtH₂ technologies to steam methane reforming (SMR) across a series of environmental and resource-use metrics. We find that the system transitions in the power, cement, steel, and fuel sectors move impacts for both PtH₂ technologies to equal or lower levels by 2100 compared to 2020 per kg of H₂ except for metal depletion. The decarbonization of the United States power sector by 2035 allows PtH₂ to reach parity with SMR at 10 kg of CO_2e/kg H₂ between 2030 and 2050. Updated H₂ radiative forcing and leakage levels only marginally affect these results. Biomass carbon removal and storage power technologies enable carbon-negative H₂ after 2040 at about -15 kg of CO_2e/kg H₂. Still, both PtH₂ processes exhibit higher impacts across most other metrics, some of which are worsened by the decarbonization of the power sector. Observed increases in metal depletion and eco- and human toxicity levels can be reduced via PtH₂ energy and material use efficiency improvements, but the power sector decarbonization routes also warrant further review and cradle-to-grave assessments to show tradeoffs from a systems perspective.

Catalytic Production of Functional Monomers from Lysine and Their Application in High-Valued Polymers

Lysine is a key raw material in the chemical industry owing to its sustainability, mature fermentation process and unique chemical structure, besides being an important nutritional supplement. Multiple commodities can be produced from lysine, which thus inspired various catalytic strategies for the production of these lysine-based chemicals and their downstream applications in functional polymer production. In this review, we present a fundamental and comprehensive study on the catalytic production process of several important lysine-based chemicals and their application in highly valued polymers. Specifically, we first focus on the synthesis process and some of the current industrial production methods of lysine-based chemicals, including ε-caprolactam, α-amino-ε-caprolactam and its derivatives, cadaverine, lysinol and pipecolic acid. Second, the applications and prospects of these lysine-based monomers in functional polymers are discussed such as derived poly (lysine), nylon-56, nylon-6 and its derivatives, which are all of growing interest in pharmaceuticals, human health, textile processes, fire control and electronic manufacturing. We finally conclude with the prospects of the development of both the design and synthesis of new lysine derivatives and the expansion of the as-synthesized lysine-based monomers in potential fields.