Process Operability Analysis of Membrane-Based Direct Air Capture for Low-Purity CO2 Production

Addressing climate change constitutes one of the major scientific challenges of this century, and it is widely acknowledged that anthropogenic CO2 emissions largely contribute to this issue. To achieve the "net-zero" target and keep the rise in global average temperature below 1.5 °C, negative emission technologies must be developed and deployed at a large scale. This study investigates the feasibility of using membranes as direct air capture (DAC) technology to extract CO2 from atmospheric air to produce low-purity CO2. In this work, a two-stage hollow fiber membrane module process is designed and modeled using the AVEVA Process Simulation platform to produce a low-purity (≈5%) CO2 permeate stream. Such low-purity CO2 streams could have several possible applications such as algae growth, catalytic oxidation, and enhanced oil recovery. An operability analysis is performed by mapping a feasible range of input parameters, which include membrane surface area and membrane performance metrics, to an output set, which consists of CO2 purity, recovery, and net energy consumption. The base case for this simulation study is generated considering a facilitated transport membrane with high CO2/N2 separation performance (CO2 permeance = 2100 GPU and CO2/N2 selectivity = 1100), when tested under DAC conditions. With a constant membrane area, both membranes' intrinsic performances are found to have a considerable impact on the purity, recovery, and energy consumption. The area of the first module plays a dominant role in determining the recovery, purity, and energy demands, and in fact, increasing the area of the second membrane has a negative impact on the overall energy consumption, without improving the overall purities. The CO2 capture capacity of DAC units is important for implementation and scale-up. In this context, the performed analysis showed that the m-DAC process could be appropriate as a small-capacity system (0.1-1 Mt/year of air), with reasonable recoveries and overall purity. Finally, a preliminary CO2 emissions analysis is carried out for the membrane-based DAC process, which leads to the conclusion that the overall energy grid must be powered by renewable sources for the technology to qualify within the negative emissions category.

Insect tracheal systems as inspiration for carbon dioxide capture systems

Membrane technology advancements within the past twenty years have provided a new perspective on environmentalism as engineers design membranes to separate greenhouse gases from the environment. Several scientific journals have published articles of experimental evidence quantifying carbon dioxide (CO2), a common greenhouse gas, separation using membrane technology and ranking them against one another. On the other hand, natural systems such as the respiratory system of mammals also accomplish transmembrane transport of CO2. However, to our knowledge, a comparison of these natural organic systems with engineered membranes has not yet been accomplished. The tracheal respiratory systems of insects transport CO2at the highest rates in the animal kingdom. Therefore, this work compares engineered membranes to the tracheal systems of insects by quantitatively comparing greenhouse gas conductance rates. We demonstrate that on a per unit volume basis, locusts can transport CO2approximately ∼100 times more effectively than the best current engineered systems. Given the same temperature conditions, insect tracheal systems transport CO2three orders of magnitude faster on average. Miniaturization of CO2capture systems based on insect tracheal system design has great potential for reducing cost and improving the capacities of industrial CO2capture.

Recent Progress on Porous Carbons for Carbon Capture

High emission of carbon dioxide (CO2) has caused CO2 levels to reach more than 400 ppm in air and led to a serious climate problem. In addition, in confined spaces such as submarines and aircraft, the CO2 concentration increase in the air caused by human respiration also affects human health. In order to protect the environment and human health, the search for high-performance adsorbents for carbon capture from high and low concentration gas is particularly important. Porous carbon materials, possessing the advantages of low cost and renewability, have set off a boom in the research of porous adsorbents, which have the opportunity to be utilized on a large scale for industrial carbon capture in the future. In this review, we summarize the recent research progress of porous carbons for carbon capture from flue gas and directly from air in the last five years, including activated carbon (AC), heteroatom-modified porous carbon, carbon molecular sieves (CMS), and other porous carbon materials, with a focus on the effects of temperature, water content, and gas flow rate of industrial flue gas on the performance of porous carbon adsorbents. We summarize the preparation strategies of various porous carbons and seek environmental friendly porous carbon materials preparation strategies under the premise of improving the CO2 adsorption capacity and selectivity of porous carbon adsorbents. Based on the effects of real industrial flue gas on adsorbents, we provide new ideas and evaluation methods for the development and preparation of porous carbon materials.

Membrane Separation Technology in Direct Air Capture

Direct air capture (DAC) is an emerging negative CO2 emission technology that aims to introduce a feasible method for CO2 capture from the atmosphere. Unlike carbon capture from point sources, which deals with flue gas at high CO2 concentrations, carbon capture directly from the atmosphere has proved difficult due to the low CO2 concentration in ambient air. Current DAC technologies mainly consider sorbent-based systems; however, membrane technology can be considered a promising DAC approach since it provides several advantages, e.g., lower energy and operational costs, less environmental footprint, and more potential for small-scale ubiquitous installations. Several recent advancements in validating the feasibility of highly permeable gas separation membrane fabrication and system design show that membrane-based direct air capture (m-DAC) could be a complementary approach to sorbent-based DAC, e.g., as part of a hybrid system design that incorporates other DAC technologies (e.g., solvent or sorbent-based DAC). In this article, the ongoing research and DAC application attempts via membrane separation have been reviewed. The reported membrane materials that could potentially be used for m-DAC are summarized. In addition, the future direction of m-DAC development is discussed, which could provide perspective and encourage new researchers' further work in the field of m-DAC.

Upscaling DAC Hubs with Wind Energy and CO2 Mineral Storage: Considerations for Large-Scale Carbon Removal from the Atmosphere

Continued fossil fuel emissions will increase CO2 concentrations in the atmosphere and could require removal of 10 Gt of CO2 per year or more to reach IPCC global climate goals. Large-scale construction of direct air capture (DAC) hubs to scrub CO2 from the atmosphere paired with geological storage is a prominent approach to potentially meet this target. We consider one location for theoretical scale-up of a DAC hub: the Kerguelen plateau in the Southern Indian Ocean which has high-potential renewable energy resources (wind) and large volumes of basalt rock for mineral storage. With consistent wind, previous studies indicate a hub in this location could collect approximately 75 Mt of CO2 annually, with conservative storage resources for 150-300 Mt of CO2 each year. Even with its immense wind and storage potentials, 14 Kerguelen-scale hubs would be needed to capture and store 1 Gt of CO2 per year. This brings into focus the important social, economic, and environmental trade-offs that must be considered in finding an acceptable balance between climate solutions, renewable energy requirements, and nature. Engaging public groups on these trade-off considerations will be crucial for gigaton scale-up of CO2 removal in just and responsible ways.

Expanding the Library of Ions for Moisture-Swing Carbon Capture

Developing materials that can more efficiently and cheaply capture carbon dioxide from ambient atmospheric conditions is essential for improving negative emission technologies. This study builds on the promising moisture-swing modality for direct air capture of carbon dioxide by investigating the use of several new anions─orthosilicate, borate, pyrophosphate, tripolyphosphate, and dibasic phosphate─that when introduced into ion-exchange resins allow for the cyclable capture of CO2 under dry conditions and its release under wet conditions. These ions, as well as many others that failed to show moisture-swing performance, are tested and directly compared thermodynamically and kinetically to understand their differences. This includes the use of analytical approaches new to the carbon capture field, such as the correlation of adsorption isotherms to moisture-swing performance, the use of phase lag kinetics, the examination of the humidity-carbon capture hysteresis of the sorbents, and the precise quantification of ion loading using inductively coupled plasma-optical emission spectroscopy. Phosphate dibasic was found to have the largest mass-normalized CO2 moisture-swing capacity, whereas phosphate tribasic had the best performance when factoring in kinetics, and pyrophosphate had the highest swing capacity when normalizing on a per-ion or per-unit-charge basis. This work not only sheds light on ways to improve DAC but also provides insights pertinent to the advancement of gas separation, negative emission technologies, and sorbent materials.

Methanol production and purification via membrane-based technology: Recent advancements, challenges, and the way forward

Industrail revolution on the back of fossil fuels has costed humanity higher temperatures on the planet due to ever-growing concentration of CO₂ emissions in Earth's atmosphere. To tackle global warming demand for renewable energy sources continues to increase. Along renewables, there has been a growing interest in converting carbon dioxide to methanol, which can be used as a fuel or a feedstock for producing chemicals. The current review study provides a comprehensive overview of the recent advancements, challenges, and future prospects of methanol production and purification via membrane-based technology. Traditional downstream processes for methanol production, such as distillation and absorption, have several drawbacks, including high energy consumption and environmental concerns. In comparison to conventional technologies, membrane-based separation techniques have emerged as a promising alternative for producing and purifying methanol. The review highlights recent developments in membrane-based methanol production and purification technology, including using novel membrane materials such as ceramic, polymeric, and mixed matrix membranes. Additionally, integrating photocatalytic processes with membrane separation has been investigated to improve the conversion of carbon dioxide to methanol. Despite the potential benefits of membrane-based systems, several challenges need to be addressed. Membrane fouling and scaling are significant issues that can reduce the efficiency and lifespan of the membranes. Furthermore, the cost-effectiveness of membrane-based systems compared to traditional methods is a critical consideration that must be evaluated. In conclusion, the review provides insights into the current state of membrane-based technology for methanol production and purification and identifies areas for future research. The development of high-performance membranes and the optimization of membrane-based processes are crucial for improving the efficiency and cost-effectiveness of this technology and for advancing the goal of sustainable energy production.

Ionic Liquid Mixtures for Direct Air Capture: High CO2 Permeation Driven by Superior CO2 Absorption with Lower Absolute Enthalpy

This paper reports a series of liquid materials suitable for use as high-performance separation membranes in direct air capture. Upon mixing two ionic liquids (ILs), namely N-(2-aminoethyl)ethanolamine-based IL ([AEEA][X]) and 1-ethyl-3-methylimidazolium acetate ([emim][AcO]), the resulting mixtures with a specific range of their composition showed higher CO₂ absorption rates, larger CO₂ solubilities, and lower absolute enthalpies of CO₂ absorption compared to those of single ILs. NMR spectroscopy of the IL mixture after exposure to ¹³CO₂ allowed elucidation of the chemisorbed species, wherein [AEEA][X] reacts with CO₂ to form CO₂-[AEEA]⁺ complexes stabilized by hydrogen bonding with acetate anions. Supported IL membranes composed of [AEEA][X]/[emim][AcO] mixtures were then fabricated, and the membrane with a suitable mixing ratio showed a CO₂ permeability of 25,983 Barrer and a CO₂/N₂ selectivity of 10,059 at 313.2 K and an applied CO₂ partial pressure of 40 Pa without water vapor. These values are higher than those reported for known facilitated transport membranes.

Enhanced recombinant carbonic anhydrase in T7RNAP-equipped Escherichia coli W3110 for carbon capture storage and utilization (CCSU)

Sulfurihydrogenibium yellowstonense carbonic anhydrase (SyCA) is a well-known thermophilic CA for carbon mineralization. To broaden the applications of SyCA, the activity of SyCA was improved through stepwise engineering and in different cultural conditions, as well as extended to co-expression with other enzymes. The engineered W3110 strains with 4 different T7 RNA polymerase levels were employed for SyCA production. As a result, the best strain WT7L cultured in modified M9 medium with temperature shifted from 37 to 30 °C after induction increased SyCA activity to 9122 U/mL. The SyCA whole-cell biocatalyst was successfully applied for carbon capture and storage (CCS) of CaCO₃. Furthermore, SyCA was applied for low-carbon footprint synthesis of 5-aminolevulinic acid (5-ALA) and cadaverine (DAP) by coupling with ALA synthetase (ALAS) and lysine decarboxylase (CadA), suppressing CO₂ release to -6.1 g-CO₂/g-ALA and -2.53 g-CO₂/g-DAP, respectively. Harnessing a highly active SyCA offers a complete strategy for CCSU in a green process.

Facilitated transport membrane with functionalized ionic liquid carriers for CO2/N2, CO2/O2, and CO2/air separations

CO₂ separations from cabin air and the atmospheric air are challenged by the very low partial pressures of CO₂. In this study, a facilitated transport membrane (FTM) is developed to separate CO₂ from air using functionalized ionic liquid (IL) and poly(ionic liquid) (PIL) carriers. A highly permeable bicontinuous structured poly(ethersulfone)/poly(ethylene terephthalate) (bPES/PET) substrate is used to support the PIL-IL impregnated graphene oxide thin film. The CO₂ separation performance was tested under a mixture feed of CO₂/N₂/O₂/H₂O. Under 410 ppm of CO₂ at 1 atm feed gas, CO₂ permanence of 3923 GPU, and CO₂/N₂ and CO₂/O₂ selectivities of 1200 and 300, respectively, are achieved with helium sweeping on the permeate side. For increased transmembrane pressure (>0 atm), a thicker PIL-IL/GO layer was shown to provide mechanical strength and prevent leaching of the mobile carrier. CO₂ binding to the carriers, ion diffusivities, and the glass transition temperature of the PIL-IL gels were examined to determine the membrane composition and rationalize the superior separation performance obtained. This report represents the first FTM study with PIL-IL carriers for CO₂ separation from air.

Membrane Separation Processes and Post-Combustion Carbon Capture: State of the Art and Prospects

Membrane processes have been investigated for carbon capture for more than four decades. Important efforts have been more recently achieved for the development of advanced materials and, to a lesser extent, on process engineering studies. A state-of-the-art analysis is proposed with a critical comparison to gas absorption technology, which is still considered as the best available technology for this application. The possibilities offered by high-performance membrane materials (zeolites, Carbon Molecular Sieves, Metal Oxide Frameworks, graphenes, facilitated transport membranes, etc.) are discussed in combination to process strategies (multistage design, hybrid processes, energy integration). The future challenges and open questions of membranes for carbon capture are finally proposed.

Porous Liquids: Computational Design for Targeted Gas Adsorption

In this Perspective, we present the unique gas adsorption capabilities of porous liquids (PLs) and the value of complex computational methods in the design of PL compositions. Traditionally, liquids only contain transient pore space between molecules that limit long-term gas capture. However, PLs are stable fluids that that contain permanent porosity due to the combination of a rigid porous host structure and a solvent. PLs exhibit remarkable adsorption and separation properties, including increased solubility and selectivity. The unique gas adsorption properties of PLs are based on their structure, which exhibits multiple gas binding sites in the pore and on the cage surface, varying binding mechanisms including hydrogen-bonding and π-π interactions, and selective diffusion in the solvent. Tunable PL compositions will require fundamental investigations of competitive gas binding mechanisms, thermal effects on binding site stability, and the role of nanoconfinement on gas and solvent diffusion that can be accelerated through molecular modeling. With these new insights PLs promise to be an exceptional material class with tunable properties for targeted gas adsorption.

Crown Nanopores in Graphene for CO2 Capture and Filtration

With growing concerns about global warming, it has become urgent and critical to capture carbon from various emission sources (such as power plants) and even directly from air. Recent advances in materials research permit the design of various efficient approaches for capturing CO₂ with high selectivity over other gases. Here, we show that crown nanopores (resembling crown ethers) embedded in graphene can efficaciously allow CO₂ to pass and block other flue gas components (such as N₂ and O₂). We carried out extensive density functional theory-based calculations as well as classical and ab initio molecular dynamics simulations to reveal the energetics and dynamics of gas transport through crown nanopores. Our results highlight that the designed crown nanopores in graphene possess not only an excellent selectivity for CO₂ separation/capture but also fast transport (flow) rates, which are ideal for the treatment of flue gas in power plants.

Environmental Performances of Various CCU Options in the Framework of an Integrated Chemical Plant

Several carbon capture processes are investigated to separate a part of the CO₂ contained in the flue gas of a coal-fired power plant located in a chemical integrated plant, with the objective of using it as a raw material in a production process. The expected results are to reduce the impact on global warming potential (GWP) and to increase the productivity of the plant. The study is based on the modelling of the combination of systems in the plant using a process simulation software and using life cycle assessment to evaluate both technical feasibility and environmental aspects. Models for the power plant, the production processes, amine chemical absorption, membrane separation and adsorption on activated coal are developed and validated against industrial and literature data. The life cycle inventory is obtained from the mass and energy balances given by the systems model. A first set of calculations is launched with a high purity requirement for the CO₂ stream (95%) recycled into the process. Those calculations show a 12% increase in productivity for the chemical process considered, but result in no significant gain in terms of GWP. Conversely, scenarios with a lower CO₂ purity (40%) show a drop around 9% of the impacts on GWP using membrane separation and activated coal adsorption, while keeping the other impacts at about the same level.

Circular Carbon Economy (CCE): A Way to Invest CO2 and Protect the Environment, a Review

Increased levels of carbon dioxide have revolutionised the Earth; higher temperatures, melting icecaps, and flooding are now more prevalent. Fortunately, renewable energy mitigates this problem by making up 20% of human energy needs. However, from a “green environment” perspective, can carbon dioxide emissions in the atmosphere be reduced and eliminated? The carbon economic circle is an ideal solution to this problem, as it enables us to store, use, and remove carbon dioxide. This research introduces the circular carbon economy (CCE) and addresses its economic importance. Additionally, the paper discusses carbon capture and storage (CCS), and the utilisation of CO2. Furthermore, it explains current technologies and their future applications on environmental impact, CO2 capture, utilisation, and storage (CCUS). Various opinions on the best way to achieve zero carbon emissions and on CO2 applications and their economic impact are also discussed. The circular carbon economy can be achieved through a highly transparent global administration that is supportive of advanced technologies that contribute to the efficient utilisation of energy sources. This global administration must also provide facilities to modernise and develop factories and power stations, based on emission-reducing technologies. Monitoring emissions in countries through a global monitoring network system, based on actual field measurements, linked to a worldwide database allows all stakeholders to track the change in greenhouse gas emissions. The process of sequestering carbon dioxide in the ocean is affected by the support for technologies and industries that adopt the principle of carbon recycling in order to maintain the balance. This includes supporting initiatives that contribute to increasing vegetation cover and preserving oceans from pollutants, especially chemicals and radioactive pollutants, which will undoubtedly affect the process of sequestering carbon dioxide in the oceans, and this will contribute significantly to maintaining carbon dioxide at acceptable levels.