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We present here an overview of water-lean solvents that compares their projected costs and performance to aqueous amine systems, emphasizing critical areas of study needed to evaluate their performance against their water-based brethren. The work presented here focuses on bridging these knowledge gaps. Because the majority of water-lean solvents are still at the lab scale, substantial studies are still needed to model and assess their performance at full scales. This presents a significant challenge as each formulation has different physical and thermodynamic properties and behavior, and quantifying how these different properties manifest themselves in conventional absorber-stripper configurations, or identifying new configurations that are specific for a solvent's signature behavior. We identify critical areas of study that are needed, and our efforts (e.g. custom infrastructure, molecular models) to predict, measure, and model these behaviors. Such findings are critical for determining the rheology required for heat exchanger design; absorber designs and packing to accommodate solvents with gradient changes (e.g. viscosity, contact angle, surface tension), and stripper configurations without direct steam utilization or water reflux. Another critical area of research need is to understand the molecular structure of the liquid interface and bulk as a function of CO2 loading, and to assess whether conventional film theories accurately quantify solvent behavior, or if thermodynamic models adequately quantify activity coefficients of ions in solution. We conclude with an assessment of our efforts to aid in bridging the knowledge gaps in understanding water-lean solvents, and suggestions of what is needed to enable large-scale demonstrations to meet the United States Department of Energy's goals.

We present novel design strategies for reduced viscosity single-component, water-lean CO 2 capture organic solvent systems. Through molecular simulation, we identify the main molecular-level descriptor that influences bulk solvent viscosity. Upon loading, a zwitterionic structure forms with a small activation energy of ca 16 kJ/mol and a small stabilization of ca 6 kJ/mol. Viscosity increases exponentially with CO 2 loading due to hydrogen-bonding between neighboring Zwitterions. We find that molecular structures that promote internal hydrogen bonding (within the same molecule) and suppress interactions with neighboring molecules have low viscosities. In addition, tuning the acid/base properties leads to a shift of the equilibrium toward a non-charged (acid) form that further reduces the viscosity. Based on the above structural criteria, a reduced order model is also presented that allows for the quick screening of large compound libraries and down selection of promising candidates for synthesis and testing.

Aqueous amines-based absorption is the most mature and scalable technology for post-combustion carbon capture, but subject to high energy and capital investment costs. Water-lean solvents, with associated advanced process configurations, show promise of significantly reducing both energy and capital costs via lower solvent recirculation and lower water condensation and vaporization. Even though advanced process configurations have been intensively studied for aqueous amines, few discussions can be found in the open literature for water-lean solvents. In order to fill the gap, the present study focuses on the process designs towards lower carbon capture cost enabled by water-lean solvents. N-(2-ethoxyethyl)-3-morpholinopropan-1-amine (EEMPA), a single-component water-lean solvent, was selected as an archetypical water-lean solvent. A property package was developed for the H2O−CO2-EEMPA system based on experimental data. Process models were developed in Aspen Plus for 90% CO2 capture in a 550 MW supercritical pulverized coal power plant, with optimal operating conditions determined by sensitivity studies. Techno-economic analyses were performed to compare seven process configurations: simple stripper, two-stage flash, lean vapor compression, inter-heated column, advanced flash stripper, low-pressure steam heater, and advanced heat integration. The results show a two-stage flash configuration, has a carbon capture cost of $47.1/tonne CO2 (in 2011 US dollars), about 19% lower than the industrial benchmark, Cansolv. While considerable capture cost reductions have been proven for aqueous amine using lean vapor compressor and advanced flash stripper, those configurations were shown to have negligible impacts with water-lean solvents due to differences in solvent’s physical properties.

Broad research is underway on developing transformational solvents that can capture of CO 2 from flue gas with lower energy compared to aqueous amines. Water-lean, or non-aqueous, solvents are being considered as a class of transformational solvents due to the prospect of lower energy duties by not having to heat and condense water. To date, little is known about the real world performance of water-lean solvent systems compared to commercial aqueous amine technologies, and whether or not they can utilize existing or at least similar processing infrastructure. This paper provides the key results from a comprehensive three-year study of the water-lean CO 2 -Binding Organic Liquids (CO 2 BOL) solvent platform coupled with Polarity-Swing Assisted Regeneration (PSAR). We present here thermodynamic, kinetic, and bench-scale data, followed by Aspen Plus projections of full-scale process performance for three CO 2 BOL/PSAR cases. This paper also provides discussions on materials performance and identifies viscosity as a critical property that most greatly limits the viability of water-lean solvent platforms. We provide results from a new effort spanning molecular modeling and synthesis and experimental testing to decipher the critical material properties needed to address this challenge. We conclude with implications for development of other water-lean solvent systems.

A new solvent-based CO2 capture process couples the unique attributes of non-aqueous, CO2-binding organic liquids (CO2BOLs) with the newly discovered polarity-swing-assisted regeneration (PSAR) process that is unique to switchable ionic liquids. Laboratory measurements with PSAR indicate the ability to achieve a regeneration effect at 75˚C comparable to that at 120˚C using thermal regeneration only. Initial measurements also indicate that the kinetic behavior of CO2 release is also improved with PSAR. Abstract cleared PNWD-SA-9743

Carbon capture and storage (CCS) is one of a suite of technology options that might play a significant role in reducing greenhouse gas emissions. However, outside of traditional enhanced oil and gas recovery operations with a well established business model, CCS project deployments are struggling with adoption of a federal or international climate policy driver appearing unlikely for the foreseeable future. As part of a feasibility study for an industrial CCS project at the Boise White Paper mill in Washington State, a business model and CCS system design was developed that provided financial surety for the project developers while recognizing that uncertainty in revenue forecasts for CO2 storage would persist for the foreseeable future. Key to the business model was installation of a new 37 MWe biomass-fueled power island at the plant that would replace antiquated boilers and that could still supply the necessary steam to run pulp and paper production operations when capturing CO2 emissions under favorable market conditions for monetizing CO2 storage credits. Under unfavorable market conditions, CO2 capture would be suspended and excess power generated from the plant would reduce external electrical energy purchases required for paper mill operations. The net CO2 reduction for the project versus current operations is 1.0 MMT of CO2 per year with the CCS system online, and 139 ktons per year with the CCS system offline due to reduced natural gas co-firing. So, both operational modes offered a significant net reduction in CO2 emissions. Based on assumptions regarding electricity and natural gas pricing, and CO2 storage revenue generated through an open market mechanism priced at $15 per metric ton CO2, the payback period for the project capturing 0.5 MMT/yr (62% of total CO2 production) was estimated at 6.7 years versus 7.4 years with the CCS system offline. Geologic storage was evaluated in the deep flood basalt formations that dominate the storage capacity in Eastern Washington. Sub-basalt sediments were also examined at the site to provide alternative or supplemental storage capacity in the event that storage in the basalt sequences did not prove technically or economically feasible.

We report the performance of multiple CO2 binding organic liquids (CO2BOLs) as solvent systems for post combustion gas capture. Alkanolguanidines and alkanolamidines are single component CO2BOLs that reversibly bind CO2 chemically as liquid zwitterionic amidinium/guanidinium alkylcarbonates. Select alkanolguanidines/alkanolamidines and guanidine/alcohol mixtures were tested for CO2 capacity and solvent lifetime. Solvent performance of these three CO2BOLs was assessed by batchwise CO2 uptake and release over multiple cycles. We report each CO2BOL's activity and solvent durability with and without water.