Advancements in Direct Air Capture Technologies: Engineering Solutions for Scalable CO₂ Removal

 Corresponding author: Hikmat Ayoola Sodiq; Email: Copyright © 2025 Author(s) retain the copyright of this article. This article is published under the terms of the Creative Commons Attribution License 4.0. Advancements in Direct Air Capture Technologies: Engineering Solutions for Scalable CO₂ Removal Hikmat Ayoola Sodiq 1, *, Temitayo Oluwaseyi Ogunwoye 2, Nicodemus Chidera Omekawum 3, Oluwabusayo Adetunji Agboola 4, Patrick Ebelechukwu Akuagwu 5, Miracle Chiemerie Umeh 6 and Maryam Abdullahi Umar 7 1 Department of Public Health, Fountain University, Osun Osogbo, Nigeria. 2 Department of Materials and Metallurgical Engineering, University of Ilorin, Nigeria. 3 Department of Chemical Engineering, Federal University of Technology, Owerri, Nigeria. 4 Department of Materials Science and Engineering, Kwara State University, Nigeria. 5 Department of Petroleum Engineering, Federal University of Petroleum Resources Effurun, Nigeria. 6 Department of Petroleum and Gas Engineering, Federal University Otuoke, Bayelsa State, Nigeria. 7 Environmental Standards Node, Abubakar Tafawa Balewa University, Bauchi, Nigeria. Global Journal of Engineering and Technology Advances, 2025, 24(01), 045-066 Publication history: Received on 10 May 2025; revised on 05 July 2025; accepted on 08 July 2025 Article DOI: https://doi.org/10.30574/gjeta.2025.24.1.0214 Abstract Direct Air Capture (DAC) is an innovative technology that extracts carbon dioxide (CO₂) directly from the atmosphere, offering a vital tool to combat climate change by reducing greenhouse gas levels. This review explores advancements in DAC systems to support large-scale CO₂ removal, targeting 1–10 billion tons annually by 2050 to achieve global netzero emissions. Recent progress includes improved methods using solid materials and liquid solutions, which have increased efficiency by 15–20% and lowered costs to $200–600 per ton of CO₂ removed. Operational facilities now capture up to 1 million tons of CO₂ yearly, demonstrating practical success. Engineering solutions, such as modular designs and renewable energy use, reduce costs by 15% and energy needs by 10–20%, enabling expansion to larger scales. DAC can achieve net CO₂ reductions of up to 0.9 tons per ton captured, but its environmental benefits depend on clean energy sources to minimize emissions during operation. Challenges include high costs, significant energy requirements, and limited global infrastructure for CO₂ storage and transport. Future efforts should focus on developing durable materials, building 10–20 DAC hubs worldwide by 2035, and introducing stronger financial incentives to cut costs to $100 per ton. This study highlights DAC’s potential to significantly contribute to climate goals, provided technological and policy barriers are overcome. By advancing engineering and fostering global cooperation, DAC can complement emissions reduction efforts, ensuring a sustainable path to net-zero. Keywords: Direct Air Capture; CO₂ Removal; Chemical Engineering; Scalability; Sorbent Technology; Renewable Energy; Techno-Economic Analysis; Environmental Sustainability 1. Introduction Direct Air Capture (DAC) technologies represent a critical component of global strategies to achieve net-zero carbon dioxide (CO₂) emissions by 2050, addressing residual and historical atmospheric CO₂ concentrations that contribute to climate change [1,2]. With atmospheric CO₂ levels reaching approximately 420 parts per million (ppm) in 2025, the Intergovernmental Panel on Climate Change (IPCC) projects a need for 1–10 gigatons of CO₂ removal annually by 2050 to limit global warming to 1.5°C [3]. Unlike point-source carbon capture, DAC extracts CO₂ directly from ambient air, offering flexibility for deployment in diverse locations and integration with storage or utilization systems. However, DAC’s current global capacity remains limited to approximately 0.01 megatons of CO₂ per year (MtCO₂/year), Global Journal of Engineering and Technology Advances, 2025, 24(01), 045-066 46 constrained by significant engineering challenges, including high energy requirements (1–10 GJ/ton CO₂), elevated costs ($200–600 per ton of CO₂ captured), and substantial land use demands [4,5]. These barriers necessitate advancements in capture technologies and engineering solutions to enable scalable, cost-effective deployment. Recent developments in DAC technologies have focused on improving capture efficiency and reducing operational costs through innovations in sorbent and solvent materials. Solid sorbent systems, such as those utilizing aminefunctionalized materials, have achieved efficiency gains of up to 20% by enhancing CO₂ adsorption capacity and reducing regeneration energy [6]. Liquid solvent systems, often employing potassium hydroxide (KOH), have demonstrated cost reductions of approximately 15% through optimized absorption cycles [7,8]. Engineering approaches, including modular reactor designs and integration with renewable energy sources, further contribute to scalability by lowering energy consumption by 10–20% and enabling decentralized deployment [8]. Real-world implementations, such as Climeworks’ Orca facility in Iceland (capturing 4,000 tCO₂/year), illustrate the feasibility of DAC but underscore the need for significant scale-up to meet global removal targets [7]. To contextualize DAC within the broader landscape of carbon dioxide removal (CDR) technologies, Figure 1 illustrates various CDR approaches, highlighting DAC’s unique role in achieving negative emissions through atmospheric CO₂ capture. The primary challenges to DAC deployment include not only technical and economic barriers but also environmental and infrastructural considerations. High capital costs for DAC facilities, estimated at $500–1,000 per ton of annual capture capacity, limit investment, while energy-intensive processes raise concerns about lifecycle emissions if powered by non-renewable sources [5,9]. Additionally, the land footprint required for large-scale DAC plants, particularly for air contactors, poses challenges in densely populated or ecologically sensitive regions [10]. Policy frameworks, such as carbon pricing and subsidies, are essential to incentivize adoption, yet global coordination remains limited. Addressing these challenges requires a multidisciplinary approach, integrating advanced materials, optimized engineering designs, and supportive policies to enhance DAC’s viability. Figure 1 Types of Carbon Dioxide Removal. This schematic outlines key CDR methods—Afforestation, Soil Carbon Sequestration, Biochar, BECCS, DACCS, Enhanced Weathering, Peatland Restoration, Blue Carbon, Ocean Alkalinity Enhancement, and Ocean Fertilisation—each paired with storage mediums (Buildings, Vegetation, Soils, Geological Formations, Minerals, Marine Sediment) and timescales (decades to centuries, centuries to millennia, or ten thousand years or longer), highlighting DACCS among diverse carbon removal strategies. Reproduced with permission from Ref [9] This review aims to provide a comprehensive analysis of advancements in DAC technologies, with a focus on engineering solutions to achieve scalable CO₂ removal. The objectives are fourfold: (1) to evaluate innovations in DAC capture technologies, including solid sorbents, liquid solvents, and hybrid systems; (2) to assess engineering strategies for scalability, such as modular designs and renewable energy integration; (3) to analyze the techno-economic and environmental impacts of DAC deployment; and (4) to identify research gaps and propose future directions for global Global Journal of Engineering and Technology Advances, 2025, 24(01), 045-066 47 implementation. By synthesizing recent literature and case studies, this article offers a roadmap for researchers, engineers, and policymakers to advance DAC as a cornerstone of climate change mitigation. 1.1. Global Context and Importance of DAC The urgency of CO₂ removal is driven by the need to address emissions from hard-to-abate sectors, such as aviation and agriculture, and to offset historical emissions [10,11]. DAC’s ability to capture CO₂ anywhere, independent of emission sources, positions it as a versatile tool for negative emissions. Projects like Carbon Engineering’s 1 MtCO₂/year facility in Canada highlight DAC’s potential, yet scaling to gigaton levels remains a formidable challenge [12]. This section contextualizes DAC within global climate goals, emphasizing its complementary role alongside other carbon capture and renewable energy strategies. 1.2. Scope and Objectives This review focuses on engineering advancements that enhance DAC’s scalability and efficiency, drawing on case studies such as Climeworks Orca and 1PointFive’s megaton-scale hub [13,14]. By examining technological, economic, and environmental dimensions, the article seeks to guide the development of DAC systems capable of meeting IPCC removal targets. 2. Background Direct Air Capture (DAC) technologies are engineered to extract carbon dioxide (CO₂) from ambient air, offering a pathway to achieve negative emissions essential for meeting net-zero targets by 2050 [1,10]. Unlike point-source carbon capture, which targets concentrated CO₂ streams from industrial facilities, DAC operates at atmospheric CO₂ concentrations of approximately 420 parts per million (ppm), requiring highly efficient capture mechanisms to overcome low partial pressures [15,16]. This section provides an overview of DAC technologies, their underlying engineering principles, and the scalability challenges that shape current research and deployment efforts. 2.1. DAC Technologies and Processes DAC systems primarily employ two capture approaches: solid sorbents and liquid solvents, each governed by distinct engineering principles. Solid sorbent systems utilize materials, such as amine-functionalized silica or metal-organic frameworks (MOFs), which adsorb CO₂ onto their surfaces during air contact [17]. The process involves passing air through contactors, where CO₂ binds to the sorbent, followed by regeneration through temperature or pressure swings to release concentrated CO₂ for storage or utilization. These systems typically require 1–3 GJ/ton CO₂ for regeneration, with recent advancements achieving up to 20% efficiency gains through optimized sorbent designs [18]. Liquid solvent systems, often based on aqueous potassium hydroxide (KOH) or sodium hydroxide (NaOH), absorb CO₂ via chemical reactions, forming carbonate compounds [19]. The CO₂ is then released through a high-temperature calcination process, consuming 5–10 GJ/ton CO₂ due to the energy-intensive regeneration step [20]. Hybrid systems, combining sorbent and solvent advantages, are emerging to reduce energy use by approximately 12% while maintaining high capture rates [21]. The DAC process concludes with CO₂ compression for geological storage or utilization, such as in enhanced oil recovery or synthetic fuel production [22]. Key engineering components of DAC systems include air contactors, regeneration units, and CO₂ collection systems. Air contactors, designed to maximize surface area for CO₂ capture, vary from packed beds in solid sorbent systems to spray towers in liquid solvent systems [23]. Regeneration units, such as vacuum-temperature swing adsorption for sorbents or calciners for solvents, are critical for energy efficiency and material durability. The integration of these components determines the overall performance, with current systems capturing 0.8–0.9 tons of CO₂ per ton of material processed [24]. Case studies, such as Climeworks’ Mammoth plant (36,000 tCO₂/year capacity) and Carbon Engineering’s megaton-scale facility, demonstrate operational feasibility but highlight the need for energy optimization [13,14]. 2.2. Engineering and Scalability Challenges The scalability of DAC technologies is constrained by several engineering and systemic barriers. Energy intensity remains a primary challenge, with solid sorbent systems requiring 1–3 GJ/ton CO₂ and liquid solvent systems up to 10 GJ/ton CO₂, compared to 0.5–1 GJ/ton for point-source capture [25]. This high energy demand, often met by fossil-based grids, can negate DAC’s environmental benefits unless paired with renewable energy sources [22]. Material durability is another concern, as sorbents degrade after 1,000–2,000 cycles, and solvents require periodic replacement, increasing operational costs by 5–10% annually [23]. Land use is a significant constraint, with large-scale DAC facilities requiring 1–10 km² per MtCO₂/year captured, posing challenges in urban or ecologically sensitive areas [24]. Infrastructure Global Journal of Engineering and Technology Advances, 2025, 24(01), 045-066 48 limitations, such as the lack of CO₂ transport pipelines and storage sites, further hinder deployment, with only 27 operational DAC facilities globally in 2025 [22]. Economic barriers are equally formidable, with current DAC costs ranging from $200–600 per ton of CO₂ captured, far exceeding the $50–100/ton needed for economic viability [25]. Capital costs for DAC plants, estimated at $500–1,000 per ton of annual capture capacity, deter investment, particularly in developing regions [26]. Policy support, such as carbon pricing or subsidies, is critical but inconsistent, with only a few jurisdictions offering incentives above $100/ton CO₂ [27]. These challenges underscore the need for engineering innovations, such as modular designs and process automation, to reduce costs and energy use, alongside policy frameworks to accelerate global adoption. 2.3. Role of Engineering in DAC Advancement Engineering plays a pivotal role in addressing DAC’s challenges through advancements in materials, system design, and energy integration. Research efforts focus on developing high-capacity sorbents, such as MOFs with 15–20% higher CO₂ selectivity, and low-energy regeneration processes, such as microwave-assisted desorption [28]. Modular contactor designs enable cost reductions of 10–15% by allowing prefabrication and deployment in diverse settings [24]. Integration with renewable energy sources, such as solar thermal or wind, reduces lifecycle emissions by up to 20% and aligns DAC with sustainable energy systems [22]. These advancements set the stage for subsequent sections, which explore capture technologies (Section 3), scalability solutions (Section 4), and their impacts (Section 5). 3. Advancements in Direct Air Capture Technologies The efficacy of Direct Air Capture (DAC) technologies hinges on the performance of capture systems, which must efficiently extract CO₂ from ambient air at concentrations of approximately 420 parts per million (ppm) while minimizing energy and cost inputs [29]. Recent advancements in capture technologies—solid sorbents, liquid solvents, and hybrid systems—have significantly improved efficiency, reduced costs, and enhanced scalability, positioning DAC as a viable tool for achieving net-zero emissions by 2050 [10]. This section examines these innovations, focusing on material developments, process optimizations, and their practical implementation in operational DAC facilities. By synthesizing recent literature and case studies, such as Climeworks’ Mammoth and Carbon Engineering’s megaton-scale plant, this analysis highlights the engineering breakthroughs driving DAC’s evolution. 3.1. Solid Sorbent Systems Solid sorbent-based DAC systems utilize materials, such as amine-functionalized silica or metal-organic frameworks (MOFs), to adsorb CO₂ onto their surfaces during air contact [15]. These systems operate via a cyclic process: air is passed through contactors, CO₂ binds to the sorbent, and the sorbent is regenerated using temperature-vacuum swing adsorption (TVSA) to release concentrated CO₂. Recent advancements have achieved efficiency gains of up to 20% through nanostructured sorbents with enhanced CO₂ selectivity and adsorption capacity [30]. For instance, MOFs with tailored pore structures have increased CO₂ uptake by 15–20% compared to conventional amines, reducing regeneration energy from 2.5 GJ/ton CO₂ to 1–2 GJ/ton CO₂ [5,31]. Additionally, novel sorbents, such as zeolites modified with quaternary ammonium groups, exhibit improved durability, maintaining performance over 2,000 cycles [21]. These improvements have lowered operational costs by approximately 10%, with capture costs for solid sorbent systems ranging from $250–400/ton CO₂ in 2025 [31]. The Climeworks Mammoth facility in Iceland, capturing 36,000 tCO₂/year, exemplifies these advancements, utilizing optimized TVSA cycles to achieve a 15% reduction in energy use compared to earlier plants [32]. 3.2. Liquid Solvent Systems Liquid solvent-based DAC systems employ aqueous solutions, typically potassium hydroxide (KOH) or sodium hydroxide (NaOH), to chemically absorb CO₂, forming carbonate compounds [33]. The process involves air contact in spray towers or packed columns, followed by regeneration through calcination at 800–900°C, which releases CO₂ and regenerates the solvent [34]. Recent optimizations have reduced costs by 15% through improved absorption cycles and heat recovery systems, lowering capture costs from $400–600/ton CO₂ to $300–450/ton CO₂ [35]. For example, advanced KOH-based systems have decreased energy requirements from 8–10 GJ/ton CO₂ to 5–7 GJ/ton CO₂ by integrating waste heat from industrial processes [36]. Innovations in solvent formulations, such as amino acid-based solutions, have enhanced CO₂ absorption rates by 10% and reduced corrosion, extending equipment lifespans by 5–8 years [5]. Carbon Engineering’s 1 MtCO₂/year facility in Canada demonstrates these advancements, achieving a 12% cost reduction through a novel pellet reactor design that minimizes solvent loss [24]. To elucidate the operational mechanism of liquid solvent-based DAC, Figure 2 provides a detailed process flow diagram of the liquid-precipitate cycle, showcasing the chemical reactions and regeneration steps critical to efficient CO₂ capture. Despite these gains, Global Journal of Engineering and Technology Advances, 2025, 24(01), 045-066 49 liquid solvent systems remain energy-intensive, requiring integration with renewable energy to ensure environmental benefits [22]. To provide a comprehensive overview of DAC capture technologies, Table 1 compares solid sorbents, liquid solvents, hybrid systems, and emerging electrochemical approaches across multiple performance metrics. This detailed analysis includes capture efficiency, energy requirements, costs, scalability, and environmental considerations, drawing from recent advancements and operational case studies to highlight their potential for large-scale CO₂ removal. Figure 2 Process Flow Diagram for Liquid-Precipitate DAC Cycle. Technical specifications are shown in blue, while power requirements are marked in red, expressed in megawatts (MW), aligned with industry-standard conditions. Reproduced with permission from Ref [10] under the terms and conditions of the Creative Commons Attribution (CC BY) license Global Journal of Engineering and Technology Advances, 2025, 24(01), 045-066 50 Table 1 Detailed Comparison of DAC Capture Technologies Technology Capture Efficiency (tCO₂/ton) Energy Requirement (GJ/ton CO₂) Cost ($/ton CO₂) Material Lifespan Scalability (tCO₂/year) CO₂ Selectivity (%) Regeneration Method Environmental Impact Case Study Reference Solid Sorbents 0.85–0.90 1.0–3.0 250– 400 2,000– 3,000 cycles 10,000– 100,000 90–95 TemperatureVacuum Swing Low water use (0.1–1 t/ton) Climeworks Mammoth (36 ktCO₂/year, Iceland) [5, 24, 31] Liquid Solvents 0.75–0.80 5.0–7.0 300– 450 5–8 years 100,000– 1,000,000 85–90 Calcination (800–900°C) High water use (1–10 t/ton) Carbon Engineering (1 MtCO₂/year, Canada) [7, 8, 23] Hybrid Systems 0.80–0.85 2.0–3.5 350– 500 1,500– 2,500 cycles 10,000– 50,000 88–92 MoistureSwing Adsorption Moderate water use (0.5–2 t/ton) Heirloom (100 ktCO₂/year, USA) [10, 37, 38] Electrochemical 0.60–0.70 0.5–1.5 500– 700 Unknown <1,000 80–85 Electric Potential Low water use (0.1–0.5 t/ton) Verdox (pilot, <1 ktCO₂/year, USA) [36, 39, 40] AmineFunctionalized MOFs 0.90–0.95 1.5–2.5 200– 350 3,000– 5,000 cycles 50,000– 200,000 95–98 MicrowaveAssisted Low lifecycle emissions Global Thermostat (10 ktCO₂/year, USA) [28, 30, 74] Amino Acid Solvents 0.80–0.85 4.0–6.0 280– 400 6–10 years 200,000– 800,000 87–90 LowTemperature Calcination High water use (2–8 t/ton) Heirloom (pilot, USA) [5, 35, 75] Global Journal of Engineering and Technology Advances, 2025, 24(01), 045-066 51 3.3. Hybrid and Emerging Systems Hybrid DAC systems combine solid sorbent and liquid solvent advantages to optimize energy use and capture efficiency [10]. These systems employ solid-supported solvents, such as amine-impregnated resins, to achieve high CO₂ uptake (1.8–2 mol/kg) with lower regeneration energy (2–3 GJ/ton CO₂) compared to liquid solvents alone [37]. Recent developments have yielded 12% energy savings through hybrid designs that integrate moisture-swing adsorption, reducing reliance on thermal regeneration [38]. Emerging technologies, such as electrochemical DAC, use electric potentials to capture and release CO₂, potentially lowering energy requirements to 0.5–1 GJ/ton CO₂, though scalability remains limited [36,39,40]. These systems, while promising, face challenges in material stability and high upfront costs, necessitating further research. 3.4. Practical Implementation and Case Studies Operational DAC facilities provide insights into the practical application of capture advancements. Climeworks’ Mammoth plant leverages solid sorbents with a modular contactor design, achieving a capture efficiency of 0.9 tCO₂/ton processed and a 10–20% cost reduction compared to its Orca facility [41]. Carbon Engineering’s megaton-scale plant employs liquid solvents with a pellet reactor, reducing energy use by 12% and targeting costs below $300/ton by 2027 [8]. Emerging projects, such as Heirloom’s renewable-powered DAC facility, integrate hybrid systems with solar energy, demonstrating a 10% lifecycle emission reduction [9]. These case studies highlight the importance of material innovation, process optimization, and energy integration in advancing DAC technologies. To complement the practical insights from operational DAC facilities, Figure 3 provides a schematic overview of the Direct Air Capture process, illustrating the use of liquid and solid sorbents, energy inputs from geothermal, natural gas, and solar sources, and the diverse reuse options including synthetic fuel, building materials, enhanced oil recovery, and carbon sequestration, highlighting the integrated engineering approach driving current implementations. Figure 3 Schematic Overview of the Direct Air Capture Process with Sorbent Technologies and CO₂ Reuse Options. Reproduced with permission from Ref [5] under the Creative Commons CC-BY-NC-ND4.0 license Global Journal of Engineering and Technology Advances, 2025, 24(01), 045-066 52 4. Engineering Solutions for Direct Air Capture Scalability Achieving the Intergovernmental Panel on Climate Change (IPCC) target of removing 1–10 gigatons of CO₂ annually by 2050 through Direct Air Capture (DAC) requires overcoming formidable engineering challenges, such as high energy demands, substantial capital costs, and limited infrastructure [6]. While advancements in capture technologies (Section 3) have enhanced efficiency, scaling DAC to megaton or gigaton levels demands innovative engineering solutions that improve system modularity, optimize energy use, and integrate with global CO₂ management systems. This section examines engineering strategies—modular designs, renewable energy integration, process automation, and infrastructure development—that enable DAC scalability, drawing on case studies such as 1PointFive’s megaton-scale DAC hub and Occidental Petroleum’s STRATOS project [8,10]. By addressing technical and systemic barriers, these solutions facilitate cost-effective, large-scale CO₂ removal. 4.1. Modular System Designs Modular DAC systems, featuring prefabricated and scalable contactor units, are critical for reducing capital and operational costs while enabling flexible deployment. According to Deutz et al. [25], traditional DAC plants incur capital costs of $500–1,000 per ton of annual capture capacity due to custom-built infrastructure. Modular designs address this issue by utilizing standardized air contactor modules that can be mass-produced, significantly lowering costs. From the findings of Sabatino et al. [21], such designs reduce construction costs by 15–20% and deployment time by 30% through prefabrication. For example, Climeworks employs modular contactors, each capturing 500–1,000 tCO₂/year, which can be stacked to achieve megaton-scale capacity, as demonstrated by 1PointFive’s DAC hub in Texas, targeting 1 MtCO₂/year by 2026 [24]. McQueen et al. [24] note that modular systems also reduce land use by 20–30% per ton of CO₂ captured compared to conventional designs, addressing spatial constraints. According to Keith et al. [23], innovations in contactor geometry, such as cross-flow configurations, enhance air-CO₂ contact efficiency by 10%, further reducing energy requirements. These advancements collectively improve DAC’s economic and spatial viability. 4.2. Renewable Energy Integration The high energy intensity of DAC systems, ranging from 1–10 GJ/ton CO₂, necessitates integration with renewable energy sources to minimize lifecycle emissions and operational costs [22]. According to IEA [22], renewable energy integration is essential to ensure DAC’s environmental benefits. From the findings of Möllersten et al. [42], coupling DAC with solar thermal or wind power achieves 10–20% energy savings, reducing costs by $50–100/ton CO₂. For instance, Heirloom’s DAC facility in California, as reported by Ozkan et al. [5], uses solar-powered calcination, lowering energy use by 15% and achieving a lifecycle emission reduction of 0.1 tCO₂/ton captured. Similarly, Occidental [43] highlight Occidental’s STRATOS project, which employs wind power to support megaton-scale capture, resulting in a 12% reduction in operational costs. Keith et al. [23] note that innovations in energy storage, such as high-capacity batteries, address renewable intermittency, ensuring continuous DAC operation. These developments align DAC with sustainable energy systems, a prerequisite for gigaton-scale deployment. Table 2 summarizes scalability metrics, including energy and cost reductions achieved through these engineering solutions. Table 2 Scalability Metrics of DAC Systems Solution Capacity Cost Reduction Energy Savings Land Use Case Study Modular Design 100 kt–1 MtCO₂/year 15–20%; $50– 80/ton 10%; 0.1–0.3 GJ/ton 0.5–1 km²/MtCO₂ 1PointFive (1 MtCO₂/year, Texas) Renewable Energy 500 kt–2 MtCO₂/year $50–100/ton 10–20%; 0.2– 0.5 GJ/ton 1–2 km²/MtCO₂ Heirloom (100 ktCO₂/year, California) Automation 50–500 ktCO₂/year 5–10%; $20– 40/ton 8%; 0.1–0.2 GJ/ton 0.8–1.5 km²/MtCO₂ Global Thermostat (10 ktCO₂/year, USA) 4.3. Process Automation and Optimization Automation and process optimization are pivotal for enhancing DAC efficiency by streamlining operations and reducing labor costs. According to Sabatino et al. [21], advanced control systems employing machine learning algorithms optimize air flow, regeneration cycles, and CO₂ compression, achieving efficiency gains of 8–10%. For example, from the findings of Sabatino et al. [21], Global Thermostat’s DAC plant uses real-time monitoring to adjust sorbent regeneration, reducing energy use by 8% and operational costs by 5%. McQueen et al. [8] report that heat recovery systems, which Global Journal of Engineering and Technology Advances, 2025, 24(01), 045-066 53 recycle waste heat from calcination or compression, lower energy requirements by 10–15% in liquid solvent systems. Ma and Liu [44] highlight innovations in CO₂ compression, such as multi-stage compressors, which reduce energy use by 5% and improve system reliability. These optimizations are particularly critical for large-scale plants, where operational costs dominate [44]. From the findings of Buratto et al. [45], Carbon Engineering’s automated pellet reactor demonstrates a 10% reduction in downtime, enhancing scalability by minimizing maintenance interruptions. Such advancements ensure DAC systems are both efficient and economically viable at scale. 4.4. Infrastructure and Global Deployment Scaling DAC to gigaton levels requires robust CO₂ transport and storage infrastructure, alongside coordinated global deployment strategies. According to IEA [22], current CO₂ pipeline networks, spanning only 8,000 km globally, are insufficient for gigaton-scale capture. From the findings of Kuby et al. [46], modular CO₂ collection systems that integrate with existing pipelines can reduce infrastructure costs by 10%, facilitating scalability. de Coninck et al. [47] estimate that global geological storage capacity, primarily in saline aquifers, is 1–2 GtCO₂, necessitating expansion to support DAC growth. Projects like 1PointFive’s DAC hub, as described by International Energy Agency [48], integrate capture with dedicated storage, targeting 1 MtCO₂/year by 2030, demonstrating a model for infrastructure synergy. IEA [48] propose establishing DAC hubs in regions with abundant renewable energy and storage, such as the Middle East and North America, to optimize deployment. Stavins [50] emphasize that policy incentives, such as carbon pricing at $50/ton, are essential to drive infrastructure investment. These strategies ensure DAC transitions from megaton-scale pilots to global networks. The global deployment of DAC facilities is a critical step toward achieving gigaton-scale CO₂ removal. Table 3 provides a detailed overview of operational and planned DAC facilities as of 2025, including their locations, technologies, capacities, energy sources, and integration with storage or utilization systems, highlighting the current state and future potential of DAC infrastructure. Likewise, to illustrate the spatial requirements of DAC facilities, Figure 4 compares the land area needed for DAC plants using different sorbents and energy sources. This visualization highlights the compact nature of DAC systems, aiding in understanding their feasibility for deployment in diverse geographic contexts. Global Journal of Engineering and Technology Advances, 2025, 24(01), 045-066 60 the deployment of large-scale DAC facilities globally, with plans for at least 130 facilities currently in development, to meet the necessary capture capacities [97]. To achieve the IPCC’s target of 1–10 gigatons of CO₂ removal by 2050, a structured roadmap for DAC development is essential. Table 6 outlines key milestones, research focuses, expected impacts, and capacity targets through 2050, integrating technological, engineering, and policy advancements to guide global DAC scale-up. Table 6 Roadmap for DAC Technology and Infrastructure Development Timeline Milestone Research Focus Expected Impact Capacity Target (MtCO₂/year) Cost Target ($/ton CO₂) Key Technologies Case Study Reference 2025– 2030 Material durability (+30%) MOFs, electrochemical systems 15% cost reduction 10–20 150– 250 Advanced sorbents, automation Verdox Pilot [71, 73, 76] 2030– 2035 Modular design optimization Compact contactors, automation 20% capacity increase 70–100 100– 200 Modular systems, renewable integration Global Thermostat [21, 79, 81] 2035– 2040 Infrastructure expansion 10–20 DAC hubs, CO₂ pipelines 100 MtCO₂/year 100–200 80–150 CO₂ transport, storage 1PointFive Hub [48, 88, 89] 2040– 2050 Global carbon pricing $150–200/ton CO₂ 3x deployment 980–1,000 50–100 Hybrid systems, electrochemical Occidental STRATOS [83, 94, 95] 2025– 2050 Socioeconomic integration Technology transfer, public engagement 40% cost reduction in developing regions 500–1,000 50–150 Localized manufacturing Climeworks Orca [90, 92, 93] 2030– 2050 CO₂ utilization Synthetic fuels, cement Revenue streams (+20%) 200–500 100– 200 Utilization systems Heirloom [9, 70, 93] 7. Conclusion Direct Air Capture (DAC) technologies are essential for achieving net-zero emissions by 2050, offering a scalable solution to remove 1–10 gigatons of CO₂ annually from the atmosphere. This review has comprehensively evaluated advancements in DAC systems, engineering strategies, and their techno-economic and environmental implications, highlighting pathways to overcome existing barriers. Despite significant progress, high costs, energy demands, and infrastructure limitations continue to challenge DAC’s global deployment, underscoring the need for sustained innovation and coordinated policy efforts. Recent developments in capture technologies have enhanced efficiency and reduced costs. Solid sorbent and liquid solvent systems have achieved notable improvements, enabling operational facilities like those capturing 36,000 tons of CO₂ per year or targeting megaton-scale capacities. These advancements demonstrate DAC’s practical feasibility, with modular designs, renewable energy integration, and automation further driving cost reductions and energy savings. Projections suggest capture costs could approach $100–200 per ton by 2030, making DAC increasingly viable for largescale implementation. Environmentally, DAC delivers negative emissions, removing up to 0.9 tons of CO₂ per ton captured, provided renewable energy sources are utilized to minimize lifecycle impacts. Nevertheless, critical research gaps persist, including the need for more durable materials, compact system designs, and expanded global infrastructure. Establishing 10–20 DAC hubs by 2035, particularly in regions with abundant renewable Global Journal of Engineering and Technology Advances, 2025, 24(01), 045-066 61 resources, could significantly boost capture capacity. Policy incentives, such as higher carbon pricing, are vital to accelerate investment and deployment, while integrating DAC with CO₂ utilization offers economic and socio-economic benefits. Addressing these gaps requires a multidisciplinary approach, combining technological breakthroughs with equitable deployment strategies to ensure DAC supports climate justice goals. This review emphasizes DAC’s potential as a cornerstone of climate change mitigation, provided ongoing challenges are addressed. Researchers should focus on developing cost-effective materials and scalable systems, while policymakers must prioritize infrastructure development and international collaboration. Achieving capture targets of 10 million tons per year by 2035 and 1 billion tons by 2050 is attainable with concerted efforts. Crucially, DAC must complement, not replace, emissions reduction strategies to secure a sustainable future. By bridging technological, economic, and policy divides, DAC can play a transformative role in global efforts to combat climate change. Compliance with ethical standards Acknowledgments The authors would like to thank all of the participating academics and colleagues who worked together to co-author and co-edit this review article. This work was completed solely by the authorship team's academic and intellectual contributions; no external money or help from any person, group, or institution was required. Disclosure of conflict of interest The authors declare that they have no conflict of interest to be disclosed. References [1] Sovacool, B. K., Baum, C. M., Low, S., Roberts, C., and Steinhauser, J. (2022). Climate policy for a net-zero future: ten recommendations for Direct Air Capture. Environmental Research Letters, 17(7), 074014. [2] Motlaghzadeh, K., Schweizer, V., Craik, N., and Moreno-Cruz, J. (2023). Key uncertainties behind global projections of direct air capture deployment. 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