Ionene - ionic liquid (IL) composites are promising materials for CO2 separation, yet a molecular-level understanding of their structure and its impact on CO2 speciation, solubility, rotation, and diffusivity remains unclear. Herein, using multimodal nuclear magnetic resonance (NMR), time-of-flight secondary ion mass spectrometry (ToF-SIMS), atomic force microscopy (AFM), and molecular dynamics (MD) simulations, we reveal that the composites contain IL-rich domains extending across hundreds of nanometres within the ionene matrix, and these bicontinuous domains span the entire membrane depth. CO2 also absorbs into the ionene matrix, with the distribution between two CO2 species varying with temperature and time. The rotational correlation times of these two species are on the timescale of 0.1 and 1 ns, respectively. As IL content increases, the ionic domains expand, resulting in higher CO2 solubility due to enhanced molecular dynamics and increased free volume in both ionene backbones and IL-rich regions. Although CO2 diffusion in the membranes is an order of magnitude slower than in bulk IL, the activation energy for CO2 diffusion remains comparable. Ionene-IL composites represent a promising platform for designing CO2 separation membranes, offering enhanced CO(2)diffusion and selectivity through IL-rich domains, and increased CO2 solubility and mechanical integrity from the ionene matrix.

Lignin is a plant-derived, the second most abundant natural polymer, and a waste byproduct of the pulp industry. Incorporation of lignin into plastic composites using scalable approaches is commercially favored and low carbon-cost. Potential end applications for lignin plastic composites (LPCs) could be found in buildings and furniture where wood plastic composites (WPCs) are used in various components. This study compares the mechanical properties of LPCs and WPCs, aiming at the examination of the viability of the use of LPCs as alternative materials to WPCs in the building industry. Sodium ligninsulfonate (SLS)-based LPC blended with high-density polyethylene (HDPE) (45 wt.%) and maleic anhydride grafted polyethylene (MAPE) as a compatibilizer (5 wt.%) reached flexural strength (35.17 and 30.92 MPa respectively) and moduli (2.87 and 1.79 GPa respectively) comparable to benchmarking WPCs. Lignin dealkaline (LD)-based LPC exhibited higher ultimate strain but lower strength than SLS-based LPC, probably due to fragmentation during the post-sulfite treatment steps.

Cryogenic time-of-flight secondary ion mass spectrometry (cryo ToF-SIMS) has emerged as a powerful tool for investigating molecular interactions, speciation, and dynamics in materials for CO2 capture. In this study, we apply cryo ToF-SIMS to probe interactions between CO2, water, and PEEK-ionene membranes—a promising material for direct CO2 capture due to its selectivity, durability, and efficiency. Despite this potential, the mechanisms governing CO2 diffusion and the influence of water vapor on CO2 behavior remain unclear. To address this, we loaded PEEK-ionene membranes with 13CO2 and D2O and employed cryo ToF-SIMS to visualize the 3D distribution of CO2 and water within the membrane. While prior studies suggest that 13CO2 is absorbed under ambient conditions, our cryo ToF-SIMS analysis revealed no enhancement of the 13C/12C ratio, suggesting weak CO2-membrane interactions. As a result, CO2 vaporizes even at low temperatures (−140°C) under vacuum conditions. In contrast, D2O displayed a relatively homogeneous distribution in the membrane, suggesting stronger water-membrane interactions via hydrogen bonding (18–20 kJ/mol). Interestingly, CO2 was not detected in D2O-loaded membranes, indicating minimal interference from water vapor on CO2 diffusion. As a comparison, the cryo ToF-SIMS data show that 13CO2 can readily react with a basic Na2CO3 aqueous solution to form NaH13CO3. These findings demonstrate cryo ToF-SIMS as a critical technique for understanding gas-water-membrane interactions, offering insights for membrane functionalization to improve CO2 capture efficiency.

Water-lean solvents, like N-(2-ethoxyethyl)-3-morpholinopropan-1-amine (EEMPA), show promise for postcombustion carbon capture, offering up to 36 and 25% energy and cost savings compared to 30 wt % MEA for a coal-fired power plant. Due to the increasing reliance on natural gas combined cycle (NGCC) power plants in the US, this study provides a conceptual design-level economic analysis of using water-lean solvents to capture 90-99.8% CO2 from NGCC flue gas. The higher capture rates correspond to resulting CO2 concentrations of <400 ppmv, which can be considered as "negative" emissions. The results indicate that EEMPA can achieve capture rates as high as 99.8% and an estimated minimum cost of $53.7/tonne CO2 (in 2018 U.S. dollar) at 90% capture. When applied as a negative emission technology with a postcapture exhaust gas CO2 concentration lower than 400 ppm, EEMPA proved economically attractive compared to direct-air capture technologies.

A series of doubly segmented (DS) poly(ether ether ketone)-ionenes (PEEK-ionenes) was synthesized through polycondensation via the Menshutkin reaction, followed by bistriflimide [Tf2N]- anion exchange. These newly designed tetracationic 2-methylimidazolium (C(2)-Me) linker groups employ a sequence of aromatic (p-xylyl) and aliphatic (hexylene) linkages between cations. The synthesized DS PEEK-ionenes exhibit good solubility in common organic solvents at room temperature, high number-average molecular weights ranging from 123 to 159 kDa, and thermal stability up to 410 degrees C, which are improved compared to their counterparts with C(2)-H imidazolium cations. The flexibility of the membranes depends on both the amount of free ionic liquid (IL) added to the PEEK-ionene materials and the characteristic features of the linker groups. The structure-property relationships within the series were established by comprehensively studying the physical properties and gas separation performances. All the newly developed PEEK-ionene + IL composites have moderate CO2 permeability up to 73 barrer, and the separation performance approaches the 1991 and 2008 upper bounds for O2/N2 and CO2/H2, respectively, with moderate selectivities for CO2/N2 and CO2/CH4. The elongated charged moieties per segment and the introduction of C(2)-Me are key factors for finely tuning and maximizing the separation performance of designed materials.

Molecular-level insights into reactive separations are crucial for the design of new conversion pathways of carbon dioxide (CO2). This work explores a postulated pathway that directs CO2 to undergo inverse-electron-demand Diels-Alder reactions to produce heterocycles using the CO2 chemically fixed on water-lean solvent molecules. Density functional theory calculations are applied to evaluate the lowest unoccupied molecular orbital (LUMO) energies of three types of reactants (1,3-butadiene, 1,3-cyclohexadiene, and 1,2,4,5-tetrazine) with various functional substituents. These calculations also provide a data set (5.8k data) for developing a machine learning model to efficiently predict LUMO energies. A computational screening of LUMO energies for an additional 47k diene and tetrazine candidates is performed, and a list of candidates with lowered LUMO energies by electron-withdrawing substituents is provided. These candidates are further examined by their reaction energy barriers computed from the interatomic potential or density functional theory. Two major energy barriers are identified, one for the proton transfer within the water-lean solvent and the other for the CO2 transfer from the solvent molecule to the reactant candidate (diene or tetrazine). The functional substituents have a more significant impact on the second barrier but a very slight one on the first barrier. This exploratory work demonstrates a new possibility for guiding experimental efforts toward the chemical conversion of fixated CO2 to value-added compounds.

We present here, the design, fabrication, and testing of a new "pressure, volume, temperature (PVT)" apparatus that enables rapid standardized testing for viscosity, vapor-liquid equilibria, and kinetics for water-lean carbon capture solvents. This unit is the first of its kind where equilibrium data are collected during operation as a PTx (pressure-temperature-composition) cell while kinetic data are collected simultaneously with an internal mini wetted-wall contactor (WWC) using controlled adjustments of CO2 injections to allow for measurements of gas flux (in and out of the liquid). Additionally, in situ measurements of viscosity data are also continuously collected while a solvent is in circulation during gas absorption. This cell empowers comprehensive testing of critical CO2 capture solvent properties in a single measurement, ensuring all data are collected at the same temperature, pressure, and CO2 loading. This apparatus also expedites screening of materials since less than 50 mL of sample is needed as compared to 2-3 L needed to get similar data from a conventional WWC. We describe here the methodology of data collected on this new PVT cell, nicknamed "Gary" in honor of Professor Gary Rochelle, for multiple water-lean amine solvents, which we compare to data collected from conventional instrumentation for amine testing.

N-(2-ethoxyethyl)-3-morpholinopropan-1-amine, also known as EEMPA, has recently been developed as a post-combustion capture CO2 solvent. In this application, EEMPA can operate as a water-lean solvent, containing less than 5 wt.% H2O, without a diluent component to manage viscosity. EEMPA may be able to achieve competitive specific reboiler duties (less than 2.5 GJ/tonne CO2 captured) and has several positive characteristics, including miscibility with water, low vapor pressure, and good thermal and oxidative stability. This paper reports initial data from an on-going test campaign in the Pilot Solvent Test Unit (PSTU) at the National Carbon Capture Center. The primary objective of this campaign is to measure the performance of the solvent at the engineering scale on both coal-relevant and natural gas flue gases. Preparations for the test and modifications to the PSTU to accommodate water-lean operation are discussed. Capture rates above 90% have been achieved, including periods above 95% capture. Water content was systematically varied from below 1 wt.% to above 10 wt.% without operational issues although peak solvent viscosity exceeded initial expectations. An unexpected fog has been observed in the regenerator vessel across most operating conditions.

Carboxylating lignin and lignite fillers to sequester CO 2 in composite materials.

Carbon capture, utilization and storage is a key yet cost-intensive technology for the fight against climate change. Single-component water-lean solvents have emerged as promising materials for post-combustion CO2 capture, but little is known regarding their mechanism of action. Here we present a combined experimental and modelling study of single-component water-lean solvents, and we find that CO2 capture is accompanied by the self-assembly of reverse-micelle-like tetrameric clusters in solution. This spontaneous aggregation leads to stepwise cooperative capture phenomena with highly contrasting mechanistic and thermodynamic features. The emergence of well-defined supramolecular architectures displaying a hydrogen-bonded internal core, reminiscent of enzymatic active sites, enables the formation of CO2-containing molecular species such as carbamic acid, carbamic anhydride and alkoxy carbamic anhydrides. This system extends the scope of adducts and mechanisms observed during carbon capture. It opens the way to materials with a higher CO2 storage capacity and provides a means for carbamates to potentially act as initiators for future oligomerization or polymerization of CO2.

Nitrogen oxides, present in flue gas, can cause negative impacts on amine carbon capture solvents by the formation of heat-stable salts and suspected carcinogens. Thus, to maximize the performance of water-lean solvents, a better understanding of this process in these systems is necessary. Here, a computational study for the fixation of the CO2 capture solvent N-(2-ethoxyethyl)-3-morpholinopropan-1-amine (EEMPA) to nitramine/nitrosamine was conducted. The first step involves the dissociation of the NH bond of EEMPA, in which the homolytic mechanism is energetically more favorable than the heterolytic mechanism. The second step involves radical recombination to form N-N bonds. While NO2 directly reacts with EEMPA, NO has almost no effect. However, in the presence of O-2, fixation of EEMPA by NO is enhanced via the formation of N2O4 species. Low reaction energies indicate that the formation of nitramine/nitrosamine may be a reversible process, suggesting that EEMPA could be recovered under thermal stripping conditions.

To meet performance requirements, the next generation of gas separation membranes will need both high gas permeability and selectivity, attainable if we could coax adsorbates to minimize random Brownian motion into direction-specific diffusion along a desired axis. In this first-principles computational study, we detail how direction-specific diffusion of CO2 can be achieved in chiral hexagonal boron nitride nanotubes (hBNNTs) where the chirality introduces a molecular-level “spin” on CO2 molecules to align the CO2 molecules along the nanotube axis and minimize interactions with the pore wall, resulting in increased axial diffusion. hBNNTs with chiral rifling patterns exhibit CO2 diffusion rates faster than non-chiral tubes of comparable and larger diameters. Of the hBNNTs studied, the (7,3) tube appears to be ideally sized (3.7 Å radius) and exhibits a spinning CO2 diffusing 2.06 times faster than a tumbling N2 by means of a new means of non-Knudsen mechanism. Calculations of a hypothetical sheet membranes prepared with the aligned chiral (7,3) hBBNT have a CO2/N2 permselectivity of 103 and a CO2 permeance of nearly 800,000 Barrer, providing potential to surpass the Robeson upper bound for CO2.

The primary objective of this CRADA activity is to use a combined molecular modeling and experimental validation approach to refine and develop transformational solvents for carbon capture. PNNL's role on this project is currently funded by the Department of Energy's (DOE) Office of Fossil Energy (OFE). PNNL is developing advanced molecular modeling based on their CO2BOLs solvent platform as a demonstration solvent for the activity; the model was developed and compared against measured data for CO2BOL derivatives. Here, a CRADA with PNNL and GE will leverage their current molecular models and apply them to solvent classes that operate on carbamate chemistry, specifically GE's aminosilicone solvent class. The molecular models will be used to predict physical and thermodynamic properties, such as viscosity, as a means to predict advanced formulations with reduced viscosity compared to current aminosilicone derivatives, enabling optimized thermodynamic and kinetic metrics for economical carbon capture for this class of materials. Together, PNNL and GE will develop a comprehensive means of linking molecular modeling parameters to intermediate physical properties as a means to improve solvent performance.

Static time-of-flight secondary ion mass spectrometry (ToF-SIMS) was performed for acquiring the high-resolution surface spectra of four types of synthesized imidazolium ionene membranes. These novel membranes have aromatic ether–ketone–ether linkages inspired by poly(ether ether ketone) (PEEK). The PEEK-ionenes synthesized for this study have imidazolium cations placed in the polymeric backbone with bistriflimide [Tf2N]− counterions. The attention given to synthetically modified PEEK derivatives, such as PEEK-ionenes, is considerable due to their ability to selectively capture CO2 molecules and other light gases. Therefore, it is important to characterize the surface of these synthesized novel PEEK-ionenes. In this work, characteristic and unique peaks were identified in the positive spectra of each sample. The differences in mass spectra among the samples provide insights for optimizing or fine-tuning the PEEK-ionenes synthesis to achieve a high-performance CO2 separation membrane with enhanced permeability, selectivity, and mechanical stability. The SIMS spectra and identified characteristic peaks of these synthesized ionenes will serve as a reference in the positive mode, complementing the corresponding spectra reported in the negative ion mode (Paper II).

Here, we demonstrate an integrated semibatch simultaneous CO2 capture and conversion to methanol process using a water-lean solvent, N-(2-ethoxyethyl)-3-morpholinopropan-1-amine (2-EEMPA), that serves as both the capture solvent and subsequent condensed-phase medium for the catalytic hydrogenation of CO2. CO2 is captured from simulated coal-derived flue gas at a target >90 mol % capture efficiency, with a continuous slipstream of CO2-rich solvent delivered to a fixed bed catalytic reactor for catalytic hydrogenation. A single-pass conversion rate >60 C-mol % and selectivity >80 C-mol % are observed for methanol at relatively low temperatures (<200 °C) in the condensed phase of the carbon capture solvent. Hydrogenation products also include higher alcohols (e.g., ethanol and propanol) and hydrocarbons (e.g., methane and ethane), suggesting that multiple products could be made offering adaptability with varied CO2-derived products. Catalyst activity and selectivity are directly impacted by the water content in the capture solvent. Anhydrous operation provides high catalyst activity and productivity, suggesting that water management will be a critical parameter in real-world operation. Ultimately, we conclude that the integrated capture and catalytic hydrogenation of CO2 are chemically viable and potentially more energetically efficient and cost-effective than conventional separate capture and conversion approaches.

An integrated CO2 capture and conversion to materials (IC3 M) implementation utilizing a CO2 capture solvent is an efficient approach to reduce the amount of CO2 in the atmosphere while producing value-added chemicals. Herein, we demonstrate that the advanced water-lean CO2 capture solvent, N-(2-Ethoxyethyl)-3-morpholinopropan-1-amine (EEMPA), can catalyze the cycloaddition reaction between CO2 and propylene oxide to produce the value-added chemical propylene carbonate in an IC3 M fashion. When excess propylene oxide is used relative to EEMPA, yields as high as 75% with 85% selectivity toward propylene carbonate can be achieved under solvent-free conditions without the need of additives/cocatalysts. The reaction temperature (120 degrees C) is comparable to that used in the thermal regeneration of the capture solvent under industrial conditions. Formation of an undesired amino alcohol side product was observed, but it may be reversible or avoidable with continued research despite the unsuccessful initial attempts. Lastly, we show that this can be applied to other epoxides for the production of various cyclic carbonates.

Electrification to reduce or eliminate greenhouse gas emissions is essential to mitigate climate change. However, a substantial portion of our manufacturing and transportation infrastructure will be difficult to electrify and/or will continue to use carbon as a key component, including areas in aviation, heavy-duty and marine transportation, and the chemical industry. In this Roadmap, we explore how multidisciplinary approaches will enable us to close the carbon cycle and create a circular economy by defossilizing these difficult-to-electrify areas and those that will continue to need carbon. We discuss two approaches for this: developing carbon alternatives and improving our ability to reuse carbon, enabled by separations. Furthermore, we posit that co-design and use-driven fundamental science are essential to reach aggressive greenhouse gas reduction targets. To achieve net-zero carbon emissions, we must close the carbon cycle for industries that are difficult to electrify. Developing the needed science to provide carbon alternatives and non-fossil carbon will accelerate advances towards defossilization.

Efficient direct air capture (DAC) of CO2 will require strategies to deal with the relatively low concentration in the atmosphere. One such strategy is to employ the combination of a CO2-selective membrane coupled with a CO2 capture solvent acting as a draw solution. Here, the interactions between a leading water-lean carbon-capture solvent, a polyether ether ketone (PEEK)-ionene membrane, CO2, and combinations were probed using advanced NMR techniques coupled with advanced simulations. We identify the speciation and dynamics of the solvent, membrane, and CO2, presenting spectroscopic evidence of CO2 diffusion through benzylic regions within the PEEK-ionene membrane, not spaces in the ionic lattice as expected. Our results demonstrate that water-lean capture solvents provide a thermodynamic and kinetic funnel to draw CO2 from the air through the membrane and into the bulk solvent, thus enhancing the performance of the membrane. The reaction between the carbon-capture solvent and CO2 produces carbamic acid, disrupting interactions between the imidazolium (Im(+)) cations and the bistriflimide anions within the PEEK-ionene membrane, thereby creating structural changes through which CO2 can diffuse more readily. Consequently, this restructuring results in CO2 diffusion at the interface that is faster than CO2 diffusion in the bulk carbon-capture solvent.