Design and validate lyotropic liquid crystals for CO2 capture, transport and injection in aquifers, via thermodynamic modelling and small-scale experiments, involving selection of polymer architecture, investigation of water penetration into the structure, simple validation experiments, economic analysis and an overall technical concept review.
A low-energy post-combustion method for CO2 capture is studied utilizing nanostructured aqueous solutions, in the form of lyotropic liquid crystals, to capture CO2 from flue gas streams after compression to moderate pressures. Capture kinetics are fast due to an absence of fixed solid barriers to molecular diffusion pathways. After loading, nanostructured aqueous solutions contain an elevated molar content of CO2. After CO2 capture, pipelines transport CO2-loaded liquid crystals to underground aquifers for long-term storage. Liquid crystals provide a primary sealant mechanism against CO2 leakage out of the aquifer, with the aquifer cap rock providing a secondary sealant mechanism against CO2 leakage. An integrated aqueous solution is thereby provided to capture, transport and store CO2. Liquid crystals provide reduced chemical potentials of CO2 in a tailored internal phase. Substantial energy savings result from a reduction in the compressive energy required to capture CO2. Liquid crystals are designed using thermodynamic computational modelling and experimental synthesis, phase stability characterization, and small-scale concept validation. Thermodynamic computations involve molecular dynamics, including biased and brute force versions of Widom particle insertion techniques, to estimate orientation-dependent chemical potentials. Results of the thermodynamic computations guide functional group selection and architectural selection in tailoring internal chemical environments within the liquid crystal geometries. The experimental campaign involves phase equilibria mapping using polarized light microscopy, x-ray scattering, NMR and rheological assessment. Proof-of-concept validation measures swelling and provides quantifiable CO2 uptake rates using small-scale instrumentation and PVT measurements. Project activities encompass an overall review of the concept feasibility, including CapEx and OpEx costs, practical considerations and saturation data.
The project provides knowledge of CO2 saturation amounts in lyotropic liquid crystals as a function of pressure, providing general scientific usefulness by revealing thermodynamic aspects of CO2 affinity to specific polymeric moieties. Thermodynamic computational techniques developed in this project are universally transferable to a wide range of applications in CCS, including liquid crystal concepts, polymer membrane technologies and combined CCS-EOR technologies involving polymers.
Challenges are to implement thermodynamic calculations to guide chemical design and estimate orientation-dependent chemical potentials. Architectural optimization of amphiphilic di-block copolymers must establish stability and flowability of liquid crystals with respect to dilution, impurities, temperature, pressure and pH. CO2 uptake and phase equilibria must be demonstrated.
Lyotropic liquid crystals are not economically viable for CCS due to high material costs and low saturation amounts. At 5 bar pressure, the uptake is approximately 15 grams of CO2 per kilogram of liquid crystal solution. The practical feasibility of the concept is also precluded due to gelation and foaming phenomenon. Synthetic amine-modification of lyotropic liquid crystals was successfully performed in various architectural configurations. CO2 uptake occurs in modified liquid crystals by formation of chemical bonds as well as physical attractive interactions with ethylene oxide functional groups. Chemical bonds form by reaction of CO2 with amine groups. Physical bonds are attributed to quadrupole-dipole binding conditions highly unique to the oxygen molecule in the ethylene oxide groups of the liquid crystals. Both uptake mechanisms are evident in absorption measurements of CO2. However, absorption of pure CO2 in liquid crystal solutions imparts substantial osmotic water loss, eliminating the phase stability of the liquid crystals. NMR methods are insensitive to CO2 uptake. Pulsed field gradient NMR shows that liquid crystals contain bound and free water. Rheological measurements have demonstrated that CO2-loaded modified liquid crystals exhibit similar flowability to the unloaded modified liquid crystals. On the theoretical modelling side, a new toolchain has been set up for GPU simulations. Many challenges involved with setting up simulations have been overcome. Analytical methods and multi-dimensional presentation methods have been developed. Simulations have been run up to relatively long timescales for example systems utilizing ethers as the functional group with affinity towards CO2.
Lyotropic liquid crystals are not viable for integrated CO2 capture, transport and storage. At 5 bar pressure, saturation quantities are approximately 15 grams of CO2 per kilogram of lyotropic liquid crystals.
Lyotropic liquid crystals contain both bound and free H2O, precluding architectural designation of a kinetic barrier against water penetration. Hence, lyotropic liquid crystals will experience the same competitive binding of water to ethylene oxide functional sites as is known to occur in mixtures of dimethyl ethers of polyethylene glycol. As such, lyotropic liquid crystals will be unable to surpass the CO2 saturation uptake performance of mixtures of dimethyl ethers of polyethylene glycol. Lyotropic liquid crystals also suffer from problems of viscosity, gelling, and foaming.
A new toolchain was developed for setting up GPU simulations for CO2 in reference systems. The newly toolchain is highly applicable for performing thermodynamic modelling for other CCS applications.
The proposal represents a completely new and novel idea to utilize liquid crystals to capture CO2, providing thermodynamic stability and thereby circumventing natural restrictions on sealant rock integrity for long-term storage. The proposed approach uses a completely new chemical mechanism, and is therefore not a continuation of other ideas. Liquid crystal phases provide reduced internal CO2 chemical potentials. Significant energy savings are relevant during capture, compression, processing, transport, and injection stages of CCS processes. Hence, from a comprehensive perspective, significant potential exists for a step-change improvement in energy-saving as well as cost-savings.
The new liquid crystal concept provides a complete processing chain in one package - CO2 capture, dispersion with water, pumping for transport, and aquifer injection as an aqueous dispersion. Such an approach significantly reduces energy costs associated with capture, compression, processing, transport, and geologic injection. CapEx and OpEx costs are also substantially reduced by reducing the equipment train and associated processing steps. For example, the need for expensive membrane solutions is entirely eliminated.
The project represents a combination of thermodynamic modelling and experimental characterization and assessment. The modelling activities will include quantum mechanical methods as well as molecular dynamics simulations, to be performed by Bjørn Kvamme's group at UiB. The modelling work will be complemented by experimental activities including phase equilibria determination, dispersion stability, and bench-scale validation at Ugelstad Laboratory at NTNU.
A central part of the project will be assessment of the overall concept based on preliminary kinetic and saturation data. The review will be based on economic criteria as well as practical considerations such as transportability. Material and energy consumption will be included in the overall concept review.