Liquid Absorbents: panel members

1. Bill Schneider* Peter Cummings* Joan Brennecke Bruce Kay John Kitchin Roger Aines Ellen Stechel John Hemminger Carol Fierke Jeff Siirola Mike Malone Rich Noble Evan Granite Abhoyjit Bhown Liquid Absorbents: panel members * Panel co-lead

2. Liquid Absorbents:current status $$$$ Flue gas ~40˚C, 1.1 bar, 22 kmol/s 75% N2 13% CO2 6% H2O 5% O2 Pipeline RT, 150 bar ≥95% CO2 >90% CO2 recovery Large additional capital outlay Operation costs ~30% of generating capacity!

3. Liquid Absorbents: current status • Liquid absorbents leading post-combustion CCS technology • Liquids have major advantages in terms of practical experience, ease of deployment, heat integration, chemical tailoring, high selectivity • Only incremental advances in absorbent chemistry over the last 80 years • 1˚, 2˚, 3˚ aqueous amine and NH3 chemistry • Physical solvents • Carbonates • Thermal and pressures swings are primary methods used to drive separation • Liquid absorbents much less/not used for other separations, e.g. air to O2, air capture, …

4. Liquid Absorbents: technology challenges Development of processes for gas separations that are more efficient than conventional thermal and pressure swing processes • REDUCE ENERGY INTENSITY AND COST • Availability of materials • Cross-reactivity • Decomposition and lifetime • Corrosivity • Reduce footprint • Reduce infrastructure costs • Reduce materials costs

5. Liquid Absorbents: science challenges • Challenges • Develop new and novel: • Chemistries • Designed liquids • Processes • Ways of controlling ∆µ • Ways of driving ∆x • Transport mechanisms • Separation “Paradise” • 100% selectivity to X • High affinity to X + low regeneration cost • Maximize composition change while minimizing work (∆x/∆µ) • Low molecular weight • Non-volatile • Chemically stable • Fast chemical kinetics • Fast transport • Dirt cheap, abundant, safe, …

6. Liquid Absorbents: science challenges A + CO2 (g) ↔ A⋅CO2 Keq(T) gas O2 PCO2 H2O CO2 CO2 N2 WE NEED TO BE ABLE TO CONTROL THESE ISOTHERMS A A-CO2 µ A-CO2 cCO2 liquid Challenge Maximize ∆x/∆µ

7. Liquid Absorbents:science needs • Infrastructure to design, synthesize, characterize absorbent systems with optimal physical/chemical characteristics • Ability to control and model novel energy transfer processes for absorption/desorption • Ability to interrogate and manage liquid/gas interface • Data-driven methods  synthesize new processes

8. Liquid Absorbents:Novel solvents and chemistries Scientific challenges Summary of research direction • Develop highly selective, efficient, stable, and reversibly reactive absorbents tailored to specific conditions: • Develop inverse design methodology for absorbent systems • Develop efficient and versatile liquid absorbent synthesis and in situcharacterization capabilities • Exploit non-traditional chemical systems: • Biomimetics, aqueous and non-aqueous solvent systems, hybrid solvent systems, new functional groups, cooperativity • Redox vs. acid-base • Hybrid and composite systems (e.g., supported liquid membranes) • Understand and learn to independently control thermodynamic (H and S), kinetic, and transport characteristics of absorbents • Understand relationships between intra- and intermolecular interactions and all absorbent properties • Achieve energy optimal separation of any gas mixture using liquid absorbents • How to control equilibria and rates of gas/liquid interactions as a function of any external variable? • What are the fundamental relationships between the structure of materials, their properties, and separation performance? • How to predict and exploit non-ideal solution behavior in mixtures? • How to make materials chemically and thermally stable while maintaining high and reversible reactivity and specificity • How do we use both enthalpy AND entropy for separations? How do we vary these ‘independently’? ∆G = ∆H – T∆S Potential scientific impact Potential impact on Carbon Capture New design tools linking structure, properties, and gas separation performance New, generally applicable synthesis & characterization methods Energy optimal gas separation systems that take advantage of well developed separation approach Lower cost separations High impact in 15-20 year timeframe

9. Liquid Absorbents: Integrating experiment and theory for rational absorbent design • Inverse design of highly selective, efficient, stable, and reversibly reactive absorbents tailored to specific conditions • Aqueous, non-aqueous, ionic liquids, … • Exploit non-ideal behavior and cooperative effects • Understand and manage properties far from equilibrium

10. Liquid Absorbents:Chemistries for gas separation processes Reversible and rapid chemical capture/release of gases R-X: + CO2 R-X+-CO2- Biological and biomimetic approaches: e.g. Carbonic Anhydrase Zn-OH- + CO2 ZnOH2 + HCO3- New nucleophiles R2C: + CO2 R2C+-CO2- New metallo-organic catalysts

11. Liquid Absorbents:New uptake and release mechanisms Scientific challenges Summary of research direction Devise new mechanisms for the efficient capture/release of gases in liquids using chemical potential swings, e.g. created by combinations of chemical transformations, photo/electrochemical methods, pH, phase changes, pressure, temperature, concentration gradients, etc… Understand and model novel energy transfer processes at every scale How to manipulate chemical potential swings to affect the capacity and rates of the capture/release of gases in solvents? How to efficiently direct energy into and out of systems to drive the capture/release of gases when away from equilibrium? Potential scientific impact Potential impact on Carbon Capture More efficient CO2 capture 20+ years Minimize energy consumption associated with CO2 capture 20+ years Ability to identify promising scientific alternatives 5+ years Development of new design principles that would drive large changes in properties with small or no energy penalty. New concepts in efficient energy transfer would impact catalysis, solar energy, conversion of chemical energy to work in biology, and other separations

12. Liquid Absorbents:Stimulus responsive phase/structure changes • Major challenges in efficient energy transfer, materials design, modeling free energy transformations Stimulus (heat, pH, hν, electric potential, etc…) gas-philic Gas-phobic

13. Liquid Absorbents:Selective excitation and bond breakage • Major challenges in efficient energy transfer, materials design, modeling free energy transformations Selective excitation

14. Liquid Absorbents:Alternative approaches to chemical potential swings hν e- • Photoelectrochemically driven, spatio-temporal pH gradients coupled with gas separations • Major challenges in • Ion-selective membranes • Materials for pH swing • Hybrid membrane/solvent approach • Modeling photoelectrochemical processes • What are intrinsic performance limits? High pH Low pH

15. Liquid Absorbents:Coupled separation and reaction

16. Liquid Absorbents:Interfacial processes and kinetics Scientific challenges Summary of research direction • Gas liquid interfaces; gateway to bulk • Potential kinetic bottlenecks • Understand structure and dynamics of complex liquid-gas interfaces • Understand linkage between composition, structure and chemistry of the interface • Capability to probe liquid interfaces, especially in situ chemical reactivity • Develop tools to characterize dynamic and chemically complex interfaces • Determine interface composition and chemistry with spatio-temporal resolution • Understand molecular vs. reactive adsorption • Depth profile of interfacial reactivity • Tailor surface chemistry to enhance reactivity and improve reversibility/switchability • Strong coupling of experiment and theory, computer simulations of liquids Potential scientific impact Potential impact on Carbon Capture • Fundamental understanding of liquid-gas interfaces and complex solutions. • Achieve capture device performance near thermodynamic limit • Potentially important in catalysis, atmospheric science, ocean acidification • Rational design of new materials and processes with enhanced capture and reduced energy demand • Minimization of reaction and mass transfer kinetic limitations to process design

17. Liquid Absorbents:Interfacial processes and kinetics The gas-liquid interface is the gateway to bulk absorption. Transfer across this boundary is well known to limit many CO2 process rates. Very little is known about the chemical structure of liquid-gas interfaces. Surface composition is not a simple termination of the bulk structure. Mass transfer considerations suggest that kinetic modifications of CO2 absorption processes are best targeted very near the surface to maximize flux into the bulk Understanding the structure and dynamics of this interface is key to tailoring uptake and release kinetics and will allow controlled design of future sorption materials. New experimental and computational tools are now becoming available to study these interfaces. Maria J. Krisch, RaffaellaD'Auria, Matthew A. Brown, Douglas J. Tobias, and John C. Hemminger, The Journal of Physical Chemistry C 111 (36): 13497-13509 (2007).

18. Emerging theoretical and experimental tools can help guide rational design of novel interfaces Brown et al. J. Am. Chem. Soc., 2009, 131 (24), pp 8354-8355 Liquid-Jet x-ray photoelectron spectroscopy at BESSY Snapshot of 1.2 M aqueous sodium iodide solution/air interface from molecular dynamics Pavel Jungwirth and Douglas J. Tobias, Chem. Rev., 2006, 106 (4), pp 1259–1281 Tools are becoming available to probe time-averaged structure and composition (sum frequency generation, photoemission from liquids, x-ray and neutron scattering) Advances are required to achieve temporal resolution requisite to studying kinetics and dynamics. Petascale computing and new experimental methods will permit development of fundamental understanding necessary to allow rational design of novel liquid interfaces for CO2 capture and other separation processes (e.g. O2) Fundamental understanding broadly applicable in areas such as catalysis and climate change,

19. Liquid Absorbents: Process Concepts Discovery Scientific challenges Summary of research direction Use data-driven algorithms to discover and screen novel process configurations for gas separations Develop new theory and computational tools for modeling intermolecular interactions in complex environments, effectively utilizing computational resources through the exascale. Discovery of new process configurations for gas separations Develop the scientific understanding that enables de novo molecular-specific physical and chemical properties of arbitrary mixtures Potential scientific impact Potential impact on Carbon Capture New methods will enable the discovery and virtual prototyping of novel process concepts Thermodynamic limits of new process concepts can be rapidly evaluated New, non-intuitive, disruptive carbon capture processes will be discovered 19

20. Liquid Absorbents: Process Concepts Discovery Example Liquid adsorption process Carbon capture process discovery critically dependent on properties Pure fluids, mixtures, complex fluids, materials,… Key sciencechallenge

21. Liquid Absorbents: Process Concepts Discovery • Why enable process concept discovery? • Cost-effective carbon capture processes are as yet unknown • Current estimated costs of $20-$100 per tonne of CO2 removed not acceptable • Best solutions will not be universal • At source or air-capture • Site-specific • Pre-/post- and oxy- combustion • Flue gas • Coal-fired vs natural gas-fired • High or low pressure/temperature process • No effective way to screen enormous number of alternatives • Choices • CC mechanism (biological, physical, chemical, hybrid,…) • Flowsheet (process architecture) • Materials, solvents, phases, surfactants, • Inverse problem • Operating conditions…. Importance of Early Evaluation Carbon CaptureProcess Carbon Capture Implementation

22. Liquid Absorbents: Process Concepts Discovery Where we are today Specify process, measure/estimate properties, optimize Where we need to be Specify desired outputs (cost, efficiency), find feasible process alternatives Process cost, energy efficiency, operational parameters Inputs: semi-empiricalproperty estimation Process Inputs: Quantitative properties prediction for systemsof arbitrary complexity Specified outputs ?

23. Grand Challenges Discovery and Use-Inspired Basic Research Designer Liquids Separation Breakthroughs Applied Research Technology Maturation & Deployment Designer Liquids … to … Separation Breakthroughs to … Carbon Capture Technologies for the 21st Century • Design and perfect atom- and energy- efficient synthesis of revolutionary new forms of matter with tailored properties • Master energy and information on the nanoscale to create new technologies with capabilities rivaling those of living things • Characterize and control matter away from equilibrium • Develop experimental and computational tools with sufficient spatio-temporal resolution to characterize structure, dynamics and kinetics at gas-liquid interface • Design separations-specific reactive chemistry • Develop new theory and methods to predict relevant properties from atomic composition for systems of arbitrary complexity • Develop new mechanisms that result in large changes in separations properties at small energy cost • Rational design of energy-efficient separations concepts for at-source carbon capture • Concepts and methodologies for energy-efficient air separations • Research with the goal of meeting technical milestones, with emphasis on the development, performance, cost reduction, and durability of materials and components or on efficient processes • Proof of technology concepts • Scale-up research • At-scale demonstration • Cost reduction • Prototyping • Manufacturing R&D • Deployment support BESAC & BES Basic Research Needs Workshops DOE Technology Office/Industry Roadmaps BESAC Grand Challenges Report Basic Energy Sciences Goal: new knowledge / understanding Mandate: open-ended Focus: phenomena Metric: knowledge generation DOE Technology Offices: EERE, NE, FE, EM, RW… Goal: practical targets Mandate: restricted to target Focus: performance Metric: milestone achievement

24. Liquid Absorbents: Novel solvents and chemistries Scientific Challenges: Achieve energy optimal separation of any gas mixture using liquid absorbents • How to control equilibria and rates of gas/liquid interactions as a function of any external variable? These variables are traditionally T and P, but other variables (e.g., pH, electrical potential could also be important; see second PRD) • What are the fundamental relationships between the structure of materials, their properties, and separation performance? This is the key issue. If this were understood then we could design absorbent materials and mixtures a priori. For single classes of compounds (e.g., traditional liquid absorbents that selectively dissolve a particular gas by physical dissolution) we have a reasonable handle on this by both extensive experimentation and by molecular simulation. However, for more complex systems such as electrolyte systems (e.g., aqueous, ionic liquids) or structured liquids (e.g., microemulsions), and especially those that react with the target compound (e.g., CO2), the relationship between structure, properties and performance is very poorly understood. Theory, molecular simulation and experimentation would be needed to address this challenge. • How to predict and exploit non-ideal solution behavior in mixtures? Here we are concerned about the fact that absorption of gases when they are present in a mixture (as is the case when you are trying to do a separation) are not necessarily the same as when the gas is pure. These mixed gas solubility issues is important. In general, we do have models to describe liquid phase nonideality. However, accurately describing weak interactions (van der Waals interactions, hydrogen bonding) is more difficult. In addition, when the target compound reacts with the absorbent then the nature of the absorbent has changed substantially and this can be the origin of the effect on the solubilization of the minority compound. This can not be accurately predicted at the moment.

25. Liquid Absorbents: Novel solvents and chemistries Scientific Challenges: Achieve energy optimal separation of any gas mixture using liquid absorbents • How to make materials chemically and thermally stable while maintaining high and reversible reactivity and specificity? We need the absorbents to be extremely stable so that they can be reused continuously. This means we don’t want them to react with any other components of the gas mixture than the target gas and we don’t want weak linkages in the absorbent itself that could lead to thermal decomposition. This will be especially important for new materials that are likely to be more expensive than compounds like monoethanolamine. This is a serious challenge since we want the absorbents to interact (react) strongly with the target gas. In other words, the challenge is to design extremely specific reactivity. • How do we use both enthalpy AND entropy for separations? How do we vary these ‘independently’? ∆G = ∆H – T∆S The capacity of an absorbent for a gas is directly related DG. (e.g., if the absorbent reacts with the gas ln K = -DG/RT, where K is the equilibrium constant). For an efficient separation system, the adsorbent should have a high capacity and selectivity for the species being separated,. However, the energy penalty for regeneration should be as low as possible, which means we want a relatively low DH. For thermodynamically-based separations, these two objectives are at odds with one another: high selectivity and capacity typically means a large enthalpy of sorption (usually via chemical complex formation). This high enthalpy must be paid back during the regeneration step. On the other hand, one can also take advantage of changes in the entropy, DS. This means using differences in sizes and shapes (entropy) of components to be separated as an alternative strategy to using differences in interaction energy (enthalpy). The challenge with liquid absorbents, then, is to be able to design in and control the changes in enthalpy and entropy in as independent a manner as possible.

26. Liquid Absorbents: Novel solvents and chemistries Summary of Research Directions Develop highly selective, efficient, stable, and reversibly reactive absorbents tailored to specific conditions: Develop inverse design methodology for absorbent systems; this means identifying a list of chemical and physical criteria that would lead to a lower energy gas separation system and then designing the absorbent a priori. The goal is new materials discovery. Experimentation, theory and simulation is vital to developing the database for the structure, property, performance relationships needed to do this. Then computational methods are needed to do the reverse design activity. Develop efficient and versatile liquid absorbent synthesis and in situcharacterization capabilities. Once the new materials or molecules are discovered by the reverse design methodology, then we need synthesis strategies to be able to actually make the new materials. Once they are made, then we need to be able to characterize the new absorbents for all the important properties (e.g., gas capacities, DH, DS, viscosity, thermal stability, chemical stability, etc.) and how these properties change in response to external stimuli (T, P, pH, electrical potential, etc.). Being able to do the characterization of these properties in situ and, potentially, simultaneously, would greatly speed the development of new absorbents.

27. Liquid Absorbents: Novel solvents and chemistries Summary of Research Directions Exploit non-traditional chemical systems: Traditionally, we have looked to acid-base chemistry in aqueous solutions for CO2 separation. For air separation, cryogenic distillation is still the industry standard. We need to look to other chemistries and methods. A few examples are expanded on below. Biomimetics, aqueous and non-aqueous solvent systems, hybrid solvent systems, new functional groups, cooperativity. Nature (e.g., carbonic anhydrases) may provide some inspiration for alternative chemistry. We shouldn’t feel bound to aqueous systems (e.g., ionic liquids). We should definitely consider mixtures of absorbents, where different components serve different purposes. We should consider complex system that may include micelles or microemulsions. We should consider new functional groups to bind with CO2 other than amines (e.g., carbenes). And we should work to exploit nonideal interactions to enhance selectivity. Redox vs. acid-base. Most current CO2 capture systems use acid-base chemistry. We need to consider redox chemistry as an alternative. Hybrid and composite systems (e.g., supported liquid membranes). Combining absorbents with other materials (such as membranes or adsorbents) may overcome some of the barriers inherent to liquid absorbents. Suported liquid membranes or liquid absorbents coated on solid adsorbents should be considered.