Capture of CO₂ in Confined Surfactant Geometries

-    Goal of the Project: The goal of the project is to design and validate a liquid crystalline phase for CO₂ post-combustion capture, transport, and aquifer injection, based on thermodynamic modelling, small scale experimentation, and economic cost estimation taking into consideration the kinetic uptake data obtained. Consideration of alternative concepts and development of alterative economic concepts is also an integral part of the project, based on the results of the economic analysis.

Update (October 2016): An economic analysis has shown the initial concept to be highly uneconomical, and a revised concept has been proposed and is being developed. New economic calculations are currently underway for the revised concept, and show promise for industrial CCS application.
2. Initially Proposed Concept:
-    Technical content: In the initial proposed non-reactive post-combustion CCS concept, a single complex fluid consisting of liquid crystals dispersed in water provides an integrated media for CO₂ capture, transport, and storage in aquifers. The single integrated complex fluid is consistent with a simplified equipment train during CO₂ capture. Liquid crystal phases provide reduced internal CO₂ chemical potentials. Hexagonal liquid crystal phases offer attractive phase ratios as well as stabilities for implementation with CCS. Subsequent dispersion with water provides flow-ability for transport and aquifer injection of the CO₂-loaded complex fluid. A double sealant mechanism during CO₂ storage in aquifers is provided by the hexagonal liquid crystals which thermodynamically capture CO₂. The primary sealant mechanism is thermodynamic stability of CO₂ inside chemically favorable cylindrical geometries. Geologic trapping comprises a secondary sealant mechanism. The liquid crystal trapping mechanism, transport, and geologic aquifer storage, using a single solution, would represent an entirely new concept for CCS. Technical advantages: Significant cost savings as well as energy savings are promised by utilizing inexpensive pumping (low energy input) instead of compression (high energy input) as well as avoiding regeneration costs, by utilizing a single integrated complex fluid medium. The reduced pressure requirements during CO₂ capture stem from the reduced Gibbs free energy of CO₂ in the liquid crystal phase. Therefore, the totality of the liquid crystal concept would promise a step change improvement in energy savings for CCS. The proposed concept exhibits beneficial qualities of being a non-reactive system, and does not contain slow pathways through fixed separation material. Instead, the concept exploits selective efficient interactions between CO₂ and atoms in the liquid crystals to efficiently capture CO₂ and maintain trapping through natural chemical potential, relative to CO₂ chemical potential in surrounding phases. Rheological flowability of the CO₂-loaded liquid crystals is assured by mild dilution, consistent with low-cost and low-energy conventional pipeline transportation. Finally, long-term volumetric utilization of aquifers is optimized by elevating effective CO₂ saturation and effectively preventing CO₂ leakages within the timescales relevant to global warming mitigation as well as continuing anthropogenic activities.

-    Initial R&D challenges:
o    Assure economic viability of the concept while accounting for feedstock costs
o    Implement thermodynamic calculations to guide and validate chemical design
o    Estimate orientation-dependent chemical potentials
o    Appropriate architectural selection of amphiphilic di-block copolymers for CCS
o    Establish stability of the liquid crystals with respect to dilution, impurities, temperature, pressure, pH, and salinity conditions relevant to CCS
o    Benchmark aggregate size and flowability dependencies on composition, dilution, impurities, temperature, pressure, pH, and salinity conditions relevant to CCS
o    Demonstrate swelling, CO₂ uptake, and phase equilibria, and verify successful economic performance of the liquid crystals for CCS, considering kinetic data
o    Minimize the toxicity of selected architecture
An economic analysis has shown the initial concept to be highly uneconomical (see section 4. Results to date). Therefore, the revised economic concept as follows is proposed.
3. Revised Economic Concept:
-    In the revised concept, liquid crystals are utilized/implemented in a post-combustive circulatory (cyclic) capacity to capture CO₂ into a purified CO₂ stream. The revised concept is compatible with conventional means of transporting CO₂, including possible dilution with water or condensate fluids. The revised concept is also compatible with conventional means of storing CO₂, including the new concept of mineralization of CO₂ in basaltic rock reservoirs (Matter et al., 2016)
-    The revised post-combustion concept comprises the following aspects
1.    Compression of post-scrubber flue gas streams to moderate pressure
2.    Selective absorption of CO₂ in a large absorption unit with
i.    Release of non-absorbed gas components via turbine to atmosphere
ii.    CO₂-saturated fluid stream exits the absorber
iii.    Pumping of CO₂-saturated fluid stream
iv.    Baric and/or thermal alteration of CO₂-saturated fluid stream
•    Disassembly of liquid crystal structure to free polymer solution
•    Phase separation of CO₂ and free polymer
v.    Release of CO₂ in pressurized separation unit
vi.    Baric and/or thermal reconditioning of liquid crystal stream exiting separator
•    Re-assembly of liquid crystals with appropriate heat integration.
vii.    Re-introduction of liquid crystals into absorption unit
3.    Conventional transport and storage of the pressurized CO₂ stream.
-    In the revised non-reactive post-combustion CCS concept, a smaller volume of liquid crystal solution is used in a circulatory manner to capture and release CO₂ into a purified CO₂ stream which may subsequently utilize conventional transport and storage technologies. The complex fluid consists of the same liquid crystal-forming amphiphilic polymers dispersed in water as in the original concept. Liquid crystal phases provide reduced internal CO₂ chemical potentials. Hexagonal liquid crystal phases offer attractive phase ratios as well as stabilities for implementation with CCS.

-    In the revised concept, the equipment train is somewhat more complicated during CO₂ capture, requiring heat integration equipment, a separator, and depending on the measured liquid crystal performance, also pressurization and depressurization equipment. Dispersion or dilution with water is largely avoided by recycling the liquid-crystal forming solutions. Flow-ability for use within the capture process is provided by conventional means, and the separated CO₂ may be also stored in conventional reservoirs rather than in only aquifers. In the revised concept, the double sealant mechanism is not relevant during CO₂ storage, because the liquid crystals do not follow the transported and stored CO₂ stream. The lack of a double sealant mechanism is a disadvantage for the revised concept. Technical advantages: Significant cost savings as well as energy savings are still realized by utilizing inexpensive pumping (low energy input) instead of compression (high energy input) as well as avoiding regeneration costs associated with carbamates, by utilizing a non-reactive single integrated recycled complex fluid medium. The reduced pressure requirements during CO₂ capture stem from the reduced Gibbs free energy of CO₂ in the liquid crystal phase. Therefore, even in the revised conception, the totality of the liquid crystal concept promises a step change improvement in energy savings for CCS. The proposed concept exhibits beneficial qualities of being a non-reactive system, and does not contain slow pathways through fixed separation material. Instead, the concept exploits selective efficient interactions between CO₂ and atoms in the liquid crystals to efficiently capture CO₂ and maintain trapping through natural chemical potential, relative to CO₂ chemical potential in an own CO₂ phase. Trapping is maintained within the capture process until the stream is thermally and/or barically modulated, disassembling the liquid crystal structure and releasing the CO₂ into a purified stream of CO₂. Rheological flowability of the CO₂-loaded liquid crystals is relevant to the internal cyclic CO₂ capture process. Subsequent transport may utilize water or condensate fluids, if available. Finally, the revised concept is compatible with mineralization processes for long term CO₂ storage in basaltic rock formations or other conventional storage technologies.
R&D challenges with revised concept:
o    Optimize effective CO₂ solubility differentials upon assembly/disassembly of the liquid crystals in solution. Saturation are amounts are somewhat less relevant as compared to the initial concept.
    Implement thermodynamic calculations to guide and validate chemical design
    Estimate orientation-dependent chemical potentials
    Appropriate architectural selection of amphiphilic di-block copolymers for CCS
    Establish stability of the liquid crystals with respect to impurities, dilution ratios, T, pressure, pH, and salinity conditions relevant to CCS.
o    Benchmark aggregate size and flowability dependencies on composition, dilution, impurities, temperature, pressure, pH, and salinity conditions relevant to CCS
o    Demonstrate swelling, CO₂ uptake, and phase equilibria, and verify successful economic performance of the liquid crystals for CCS, considering kinetic data


4. Results to date:
o    Experimental
o    Experimental pre-project literature review of relevant chemical functionalities
    Amine-based and non-amine-based functionalities have been considered
    Lessons learned from membrane polymers
o    Experimental pre-project synthesis of block copolymers containing relevant functionalities to capture CO₂
    Various synthesis routes attempted
o    Experimental phase behaviour investigations initiated with polarized light determination of liquid crystalline phases.

o    Theoretical Modelling
o    Theoretical Literature Review for CO₂-philic functional groups
    Modelling methods
o    Developed a new toolchain for setting up GPU-simulations including:
    Construction of models/molecules
    Parameterization
    Import into simulation software
o    Completed initial simulations on trial systems
o    Economic analysis initiated
    Modified polymeric surfactants cost about 1,000 USD per ton
    Equivalent weight basis of CO₂ captured per weight of modified polymeric surfactant
    Minimum net cost of capture in original conception is about 1,000 USD per tonne of CO₂ due to high feedstock costs
    Target cost for CO₂ capture is 40 USD per ton
    Initial proposed concept is not economical
•    A detailed report will be submitted showing the initial concept to be uneconomical
    Fast uptake kinetics do not justify original concept

o    New concept under development
    Circulatory use of liquid crystals to capture and release CO₂
    Proprietary new process/concept devised
•    Utilizes conventional transport and storage of CO₂
o    Not limited by surfactant toxicity
o    Capture solution not volatile  will not be released to the environment
•    Improved economics
•    Selection of baric and/or thermal cyclic modulation
o    Theoretical justification based on heat integration
    CapEx and OpEx costs are under calculation assuming pre-existing scrubber equipment at existing coal power plants
    Cost per tonne of CO₂ captured is currently being calculated.
    Various process systems are being devised based on heat integration, exergy considerations, and economic calculations.
    Thermal versus baric modulation will be established and justified based on technical as well as economic constraints.