liquid absorbents: panel members

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basic research needs workshop forCarbon Capture: Beyond 2020

Plenary Closing SessionMarch 5, 2010

Liquid Absorbents: panel members

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

* Panel co-lead

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Liquid Absorbents: current status

Flue gas ~40˚C, 1.1 bar, 22 kmol/s75% N2 13% CO2 6% H2O

5% O2

Pipeline RT, 150 bar≥95% CO2

>90% CO2 recovery

Large additional capital outlayOperation costs ~30% of generating capacity!

$$$$

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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, …

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Liquid Absorbents: technology challenges

• REDUCE ENERGY INTENSITY AND COST

• Availability of materials

• Cross-reactivity

• Decomposition and lifetime

• Corrosivity

• Reduce footprint

• Reduce infrastructure costs

• Reduce materials costs

Development of p

rocesses for

gas separations that a

re more

efficient th

an conventional

thermal and pressure swing

processes

Development of p

rocesses for

gas separations that a

re more

efficient th

an conventional

thermal and pressure swing

processes

p. 5



Liquid Absorbents: science challenges

• Challenges Develop new and novel:ChemistriesDesigned liquidsProcessesWays of controlling ∆µWays of driving ∆xTransport 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,

…

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Liquid Absorbents: science challenges

A + CO2 (g) ↔ A CO⋅ 2 Keq(T)

CO2

CO2

A-CO2

A-CO2A

PCO2

cCO2

µ

O2

N2

H2O

liquid

gas

ChallengeMaximize ∆x/∆µ

ChallengeMaximize ∆x/∆µ

WE NEED TO B

E ABLE TO C

ONTROL

THESE ISOTHERMS

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• 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

Liquid Absorbents: science needs

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Potential scientific impactPotential impact on Carbon Capture

Summary of research directionScientific challenges

Liquid Absorbents: Novel solvents and chemistries

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 situ characterization 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 absorbentsUnderstand 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

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 approachLower cost separationsHigh impact in 15-20 year timeframe

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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

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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 AnhydraseZn-OH- + CO2 ZnOH2 + HCO3

-

New nucleophiles

R2C: + CO2 R2C+-CO2-

New metallo-organic catalysts

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Potential scientific impact Potential impact on Carbon Capture


Liquid Absorbents: New uptake and release mechanisms

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?

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

More efficient CO2 capture 20+ years

Minimize energy consumption associated with CO2 capture 20+ years

Ability to identify promising scientific alternatives 5+ years

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Stimulus (heat, pH, hν, electric potential, etc…)

• Major challenges in efficient energy transfer, materials design, modeling free energy transformations

Liquid Absorbents: Stimulus responsive phase/structure changes

gas-philicGas-phobic

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• Major challenges in efficient energy transfer, materials design, modeling free energy transformations

Liquid Absorbents: Selective excitation and bond breakage

Selective excitation

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• 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?

Liquid Absorbents: Alternative approaches to chemical potential swings

hν e-

High pH

Low pH

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Liquid Absorbents: Coupled separation and reaction

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Liquid Absorbents: Interfacial processes and kinetics

• 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

• 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

• 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

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Very little is known about the chemical structure of liquid-gas interfaces. Surface composition is not a simple termination of the bulk structure.

Liquid Absorbents: Interfacial processes and kinetics

Maria J. Krisch, Raffaella D'Auria, Matthew A. Brown, Douglas J. Tobias, and John C. Hemminger, The Journal of Physical Chemistry C 111 (36): 13497-13509 (2007).

The gas-liquid interface is the gateway to bulk absorption. Transfer across this boundary is well known to limit many CO2 process rates.

Mass transfer considerations suggest that kinetic modifications of CO2 absorption processes are best targeted very near the surface to maximize flux into the bulk

New experimental and computational tools are now becoming available to study these interfaces.

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.

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Emerging theoretical and experimental tools can help guide rational design of novel interfaces

• 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,

Pavel Jungwirth and Douglas J. Tobias, Chem. Rev., 2006, 106 (4), pp 1259–1281

Snapshot of 1.2 M aqueous sodium iodide solution/air interface from molecular dynamics

Liquid-Jet x-ray photoelectron spectroscopy at BESSY

Brown et al. J. Am. Chem. Soc., 2009, 131 (24), pp 8354-8355

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Liquid Absorbents: Process Concepts Discovery

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

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

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• Example Liquid adsorption process

• Carbon capture process discovery critically dependent on properties Pure fluids, mixtures, complex

fluids, materials,…

Key sciencechallenge

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• 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 Capture Implementation

Carbon CaptureProcess

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• Where we are today Specify process, measure/estimate properties, optimize

• Where we need to be Specify desired outputs (cost, efficiency), find feasible process

alternatives

? Specified outputs

ProcessInputs:

semi-empiricalproperty estimation

Process cost, energy efficiency, operational parameters

Inputs:Quantitative properties

prediction for systemsof arbitrary complexity

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

Technology Maturation & DeploymentApplied Research Grand Challenges Discovery and Use-Inspired Basic Research

Designer Liquids Separation Breakthroughs

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

BESAC & BES Basic Research Needs Workshops

BESAC Grand Challenges Report DOE Technology Office/Industry Roadmaps

Designer Liquids … to … Separation Breakthroughs to … Carbon Capture Technologies for the 21st Century

Basic Energy SciencesBasic Energy Sciences Goal: new knowledge / understandingMandate: open-endedFocus: phenomenaMetric: knowledge generation

DOE Technology Offices: EERE, NE, FE, EM, RW…DOE Technology Offices: EERE, NE, FE, EM, RW… Goal: practical targetsMandate: restricted to targetFocus: performanceMetric: milestone achievement

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• 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.

Scientific Challenges: Achieve energy optimal separation of any gas mixture using liquid absorbents


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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.

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• 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 situ characterization 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.

Summary of Research Directions

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• 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.

Summary of Research Directions