In Situ Raman Methodology for Online Analysis of CO2 and H2O Loadings in a Water-Lean Solvent for CO2 Capture.

Carbon capture represents a key pathway to meeting climate change mitigation goals. Powerful next-generation solvent-based capture processes are under development by many researchers, but optimization and testing would be significantly aided by integrating in situ monitoring capability. Further, real-time water analysis in water-lean solvents offers the potential to maintain their water balance in operation. To explore data acquisition techniques in depth for this purpose, Raman spectra of CO2, H2O, and a single-component water-lean solvent, N-(2-ethoxyethyl)-3-morpholinopropan-1-amine (2-EEMPA) were collected at different CO2 and H2O concentrations using an in situ Raman cell. The quantification of CO2 and H2O loadings in 2-EEMPA was done by principal component regression and partial least squares methods with analysis of uncertainties. We conclude with discussions on how this simultaneous online analysis method to quantify CO2 and H2O loadings can be an important tool to enable the optimal efficiency of water-lean CO2 solvents while also maintaining the critical water balance under operating conditions relevant to post-combustion CO2 capture.

Subtle changes in hydrogen bond orientation result in glassification of carbon capture solvents.

Water-lean CO2 capture solvents show promise for more efficient and cost-effective CO2 capture, although their long-term behavior in operation has yet to be well studied. New observations of extended structure solvent behavior show that some solvent formulations transform into a glass-like phase upon aging at operating temperatures after contact with CO2. The glassification of a solvent would be detrimental to a carbon-capture process due to plugging of infrastructure, introducing a critical need to decipher the underlying principles of this phenomenon to prevent it from happening. We present the first integrated theoretical and experimental study to characterize the nano-structure of metastable and glassy states of an archetypal single-component alkanolguanidine carbon-capture solvent and assess how minute changes in atomic-level interactions convert the solvent between metastable and glass-like states. Small-angle neutron scattering and neutron diffraction coupled with small- and wide-angle X-ray scattering analysis demonstrate that minute structural changes in solution precipitae reversible aggregation of zwitterionic alkylcarbonate clusters in solution. Our findings indicate that our test system, an alkanolguanidine, exhibits a first-order phase transition, similar to a glass transition, at approximately 40 °C-close to the operating absorption temperature for post-combustion CO2 capture processes. We anticipate that these phenomena are not specific to this system, but are present in other classes of colvents as well. We discuss how molecular-level interactions can have vast implications for solvent-based carbon-capture technologies, concluding that fortunately in this case, glassification of water-lean solvents can be avoided as long as the solvent is run above its glass transition temperature.

Water-Lean Solvents for Post-Combustion CO2 Capture: Fundamentals, Uncertainties, Opportunities, and Outlook.

This review is designed to foster the discussion regarding the viability of postcombustion CO2 capture by water-lean solvents, by separating fact from fiction for both skeptics and advocates. We highlight the unique physical and thermodynamic properties of notable water-lean solvents, with a discussion of how such properties could translate to efficiency gains compared to aqueous amines. The scope of this review ranges from the purely fundamental molecular-level processes that govern solvent behavior to bench-scale testing, through process engineering and projections of process performance and cost. Key discussions of higher than expected CO2 mass transfer, water tolerance, and compatibility with current infrastructure are presented along with current limitations and suggested areas where further solvent development is needed. We conclude with an outlook of the status of the field and assess the viability of water-lean solvents for postcombustion CO2 capture.

A novel high-temperature MAS probe with optimized temperature gradient across sample rotor for in-situ monitoring of high-temperature high-pressure chemical reactions.

We present a novel nuclear magnetic resonance (NMR) probe design focused on optimizing the temperature gradient across the sample for high temperature magic angle spinning (MAS) experiments using standard rotors. Computational flow dynamics (CFD) simulations were used to assess and optimize the temperature gradient across the sample under MAS conditions. The chemical shift and linewidth of 207Pb direct polarization in lead nitrate were used to calibrate the sample temperature and temperature gradient, respectively. A temperature gradient of less than 3 °C across the sample was obtained by heating bearing gas flows and adjusting its temperature and flow rate during variable temperature (VT) experiments. A maximum temperature of 350 °C was achieved in this probe using a Varian 5 mm MAS rotor with standard Vespel drive tips and end caps. Time-resolved 13C and 1H MAS NMR experiments were performed at 325 °C and 60 bar to monitor an in-situ mixed phase reverse water gas shift reaction, industrial synthesis of CH3OH from a mixture of CO2 and H2 with a Cu/ZnO/Al2O3 catalyst, demonstrating the first in-situ NMR monitoring of a chemical system at temperatures higher than 250 °C in a pressurized environment. The combination of this high-temperature probe and high-pressure rotors will allow for in-situ NMR studies of a great variety of chemical reactions that are inaccessible to conventional NMR setup.

Two coexisting liquid phases in switchable ionic liquids.

Switchable ionic liquids (SWILs) derived from organic bases and alcohols are attractive due to their applications in gas capture, separations, and nanomaterial synthesis. However, their exact solvent structure still remains a mystery. We present the first chemical mapping of a SWIL solvent structure using in situ time-of-flight secondary ion mass spectrometry. In situ chemical mapping discovers two coexisting liquid phases and molecular structures vastly different from conventional ionic liquids. SWIL chemical speciation is found to be more complex than the known stoichiometry. Dimers and ionic clusters have been identified in SIMS spectra; and confirmed to be the chemical species differentiating from non-ionic liquids via spectral principal component analysis. Our unique in situ molecular imaging has advanced the understanding of SWIL chemistry and how this "heterogeneous" liquid structure may impact SWILs' physical and thermodynamic properties and associated applications.

Homogeneous hydrogenation of CO2 to methyl formate utilizing switchable ionic liquids.

Combined capture of CO2 and subsequent hydrogenation allows for base/methanol-promoted homogeneous hydrogenation of CO2 to methyl formate. The CO2, captured as an amidinium methyl carbonate, reacts with H2 with no applied pressure of CO2 in the presence of a catalyst to produce sequentially amidinium formate, then methyl formate. The production of methyl formate releases the base back into the system, thereby reducing one of the flaws of catalytic hydrogenations of CO2: the notable consumption of one mole of base per mole of formate produced. The reaction proceeds under 20 atm of H2 with selectivity to formate favored by the presence of excess base and lower temperatures (110 °C), while excess alcohol and higher temperatures (140 °C) favor methyl formate. Known CO2 hydrogenation catalysts are active in the ionic liquid medium with turnover numbers as high as 5000. It is unclear as to whether the alkyl carbonate or CO2 is hydrogenated, as we show they are in equilibrium in this system. The availability of both CO2 and the alkyl carbonate as reactive species may result in new catalyst designs and free energy pathways for CO2 that may entail different selectivity or kinetic activity.

Tetrameric self-assembling of water-lean solvents enables carbamate anhydride-based CO2 capture chemistry.

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.

A US perspective on closing the carbon cycle to defossilize difficult-to-electrify segments of our economy.

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.

Enhancing CO2 Transport Across a PEEK-Ionene Membrane and Water-Lean Solvent Interface.

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.

Next steps for solvent-based CO2 capture; integration of capture, conversion, and mineralisation.

In this perspective, we detail how solvent-based carbon capture integrated with conversion can be an important element in a net-zero emission economy. Carbon capture and utilization (CCU) is a promising approach for at-scale production of green CO2-derived fuels, chemicals and materials. The challenge is that CO2-derived materials and products have yet to reach market competitiveness because costs are significantly higher than those from conventional means. We present here the key to making CO2-derived products more efficiently and cheaper, integration of solvent-based CO2 capture and conversion. We present the fundamentals and benefits of integration within a changing energy landscape (i.e., CO2 from point source emissions transitioning to CO2 from the atmosphere), and how integration could lead to lower costs and higher efficiency, but more importantly how CO2 altered in solution can offer new reactive pathways to produce products that cannot be made today. We discuss how solvents are the key to integration, and how solvents can adapt to differing needs for capture, conversion and mineralisation in the near, intermediate and long term. We close with a brief outlook of this emerging field of study, and identify critical needs to achieve success, including establishing a green-premium for fuels, chemicals, and materials produced in this manner.

Green chemistry: reversible nonpolar-to-polar solvent.

Imagine a smart solvent that can be switched reversibly from a liquid with one set of properties to another that has very different properties, upon command. Here we create such a system, in which a non-ionic liquid (an alcohol and an amine base) converts to an ionic liquid (a salt in liquid form) upon exposure to an atmosphere of carbon dioxide, and then reverts back to its non-ionic form when exposed to nitrogen or argon gas. Such switchable solvents should facilitate organic syntheses and separations by eliminating the need to remove and replace solvents after each reaction step.

Integrated Capture and Conversion of CO2 to Methane Using a Water-lean, Post-Combustion CO2 Capture Solvent.

Integrated carbon capture and conversion of CO2 into materials (IC3 M) is an attractive solution to meet global energy demand, reduce our dependence on fossil fuels, and lower CO2 emissions. Herein, using a water-lean post-combustion capture solvent, [N-(2-ethoxyethyl)-3-morpholinopropan-1-amine] (2-EEMPA), >90 % conversion of captured CO2 to hydrocarbons, mostly methane, is achieved in the presence of a heterogenous Ru catalyst under relatively mild reaction conditions (170 °C and <15 bar H2 pressure). The catalytic performance was better in 2-EEMPA than in aqueous 5 m monoethanol amine (MEA). Operando nuclear magnetic resonance (NMR) study showed in situ formation of N-formamide intermediate, which underwent further hydrogenation to form methane and other higher hydrocarbons. Technoeconomic analyses (TEA) showed that the proposed integrated process can potentially improve the thermal efficiency by 5 % and reduce the total capital investment and minimum synthetic natural gas (SNG) selling price by 32 % and 12 %, respectively, compared to the conventional Sabatier process, highlighting the energetic and economic benefits of integrated capture and conversion. Methane derived from CO2 and renewable H2 sources is an attractive fuel, and it has great potential as a renewable hydrogen carrier as an environmentally responsible carbon capture and utilization approach.

Amphilic Water-Lean Carbon Capture Solvent Wetting Behavior through Decomposition by Stainless-Steel Interfaces.

A combined experimental and theoretical study has been carried out on the wetting and reactivity of water-lean carbon capture solvents on the surface of common column packing materials. Paradoxically, these solvents are found to be equally able to wet hydrophobic and hydrophilic surfaces. The solvents are amphiphilic and can adapt to any interfacial environment, owing to their inherent heterogeneous (nonionic/ionic) molecular structure. Ab initio molecular dynamics indicates that these structures enable the formation of a strong adlayer on the surface of hydrophilic surfaces like oxidized steel which promotes solvent decomposition akin to hydrolysis from surface oxides and hydroxides. This decomposition passivates the surface, making it effectively hydrophobic, and the decomposed solvent promotes leaching of the iron into the bulk fluid. This study links the wetting behavior to the observed corrosion of the steels by decomposition of solvent at steel interfaces. The overall affect is strongly dependent on the chemical composition of the solvent in that amines are stable, whereas imines and alcohols are not. Moreover, plastic packing shows little to no solvent degradation, but an equal degree of wetting.

Catalytic coproduction of methanol and glycol in one pot from epoxide, CO2, and H2.

An atom (100%) and energy-efficient approach to coproduce two commodity chemicals, methanol and glycol, has been demonstrated for the first time using H2, CO2, and epoxide as feeds. A basic medium used for CO2 capture, polyethyleneimine (PEI600), is shown to facilitate the formation of a key reaction intermediate, cyclic carbonates. Upon hydrogenation of cyclic carbonates in the presence of a homogenous Ru-PNP catalyst, a 1 : 1 mixture of methanol and glycol is produced. This approach has been demonstrated in one pot by adding all the required reactants directly or stepwise. The stepwise addition of reactants resulted in good yields (>95% for PG and 84% for methanol) and selectivity of products.

Molecular-Level Overhaul of γ-Aminopropyl Aminosilicone/Triethylene Glycol Post-Combustion CO2 -Capture Solvents.

Capturing carbon dioxide from post-combustion gas streams is an energy-intensive process that is required prior to either converting or sequestering CO2 . Although a few commercial 1st and 2nd generation aqueous amine technologies have been proposed, the cost of capturing CO2 with these technologies remains high. One approach to decrease costs of capture has been the development of water-lean solvents that aim to increase efficiency by reducing the water content in solution. Water-lean solvents, such as γ-aminopropyl aminosilicone/triethylene glycol (GAP/TEG), are promising technologies, with the potential to halve the parasitic load to a coal-fired power plant, albeit only if high solution viscosities and hydrolysis of the siloxane moieties can be mitigated. This study concerns an integrated multidisciplinary approach to overhaul the GAP/TEG solvent system at the molecular level to mitigate hydrolysis while also reducing viscosity. Cosolvents and diluents are found to have negligible effects on viscosity and are not needed. This finding allows for the design of single-component siloxane-free diamine derivatives with site-specific incorporation of selective chemical moieties for direct placement and orientation of hydrogen bonding to reduce viscosity. Ultimately, these new formulations are less susceptible to hydrolysis and exhibit up to a 98 % reduction in viscosity compared to the initial GAP/TEG formulation.

Reversible uptake of COS, CS2, and SO2: ionic liquids with O-alkylxanthate, O-alkylthiocarbonyl, and O-alkylsulfite anions.

CO(2)-binding organic liquids (CO(2)BOLs) are mixtures of a base (typically an amidine or guanidine) and an alcohol, and have been shown to reversibly capture and release CO(2) with low reaction energies and high gravimetric CO(2) capacity. We now report the ability of such liquid blends to chemically bind and release other acid gases such as CS(2), COS, and SO(2) analogously to CO(2). These systems bind with sulfur-containing acid gases to form colored ionic liquids with new O-alkylxanthate, O-alkylthiocarbonyl, and O-alkylsulfite anions. The capture and thermal stripping of each acid gas from these systems and their applicability towards flue gas desulfurization is discussed.

Neutron powder diffraction and molecular simulation study of the structural evolution of ammonia borane from 15 to 340 K.

The structural behavior of (11)B-, (2)H-enriched ammonia borane, ND(3)(11)BD(3), over the temperature range from 15 to 340 K was investigated using a combination of neutron powder diffraction and ab initio molecular dynamics simulations. In the low temperature orthorhombic phase, the progressive displacement of the borane group under the amine group was observed leading to the alignment of the B-N bond near parallel to the c-axis. The orthorhombic to tetragonal structural phase transition at 225 K is marked by dramatic change in the dynamics of both the amine and borane group. The resulting hydrogen disorder is problematic to extract from the metrics provided by Rietveld refinement but is readily apparent in molecular dynamics simulation and in difference Fourier transform maps. At the phase transition, Rietveld refinement does indicate a disruption of one of two dihydrogen bonds that link adjacent ammonia borane molecules. Metrics determined by Rietveld refinement are in excellent agreement with those determined from molecular simulation. This study highlights the valuable insights added by coupled experimental and computational studies.

Assessing the impacts of dynamic soft-templates innate to switchable ionic liquids on nanoparticulate green rust crystalline structures.

This experimental and theoretical study investigates how dynamic solvation environments in switchable ionic liquids regulate the composition of nanoparticulate green rust. A custom microfluidic device enables in situ X-ray absorption spectroscopy to elucidate characterization of the solvent structure and speciation of reaction intermediates of air-sensitive nanoparticles growing in solution.

Coordination of aminoborane, NH(2)BH(2), dictates selectivity and extent of H(2) release in metal-catalysed ammonia borane dehydrogenation.

In situ(11)B NMR monitoring, computational modeling, and external trapping studies show that selectivity and extent of H(2) release in metal-catalysed dehydrogenation of ammonia borane, NH(3)BH(3), are determined by coordination of reactive aminoborane, NH(2)BH(2), to the metal center.

Mesoscopic Structure Facilitates Rapid CO2 Transport and Reactivity in CO2 Capture Solvents.

Mass transfer coefficients of CO2 are anomalously high in water-lean solvents as compared to aqueous amines. Such phenomena are intrinsic to the molecular and nanoscale structure of concentrated organic CO2 capture solvents. To decipher the connections, we performed in situ liquid time-of-flight secondary ionization mass spectroscopy on a representative water-lean solvent, 1-((1,3-Dimethylimidazolidin-2-ylidene)amino)propan-2-ol (IPADM-2-BOL). Two-dimensional (2D) and three-dimensional (3D) chemical mapping of the solvent revealed that IPADM-2-BOL exhibited a heterogeneous molecular structure with regions of CO2-free solvent coexisting with clusters of zwitterionic carbonate ions. Chemical mapping were consistent with molecular dynamic simulation results, indicating CO2 diffusing through pockets and channels of unreacted solvent. The observed mesoscopic structure promotes and enhances the diffusion and reactivity of CO2, likely prevalent in other water-lean solvents. This finding suggests that if the size, shape and orientation of the domains can be controlled, more efficient CO2 capture solvents could be developed to enhance mass-transfer and uptake kinetics.