CO2-binding Organic Liquids Research Articles

Efficient and Reversible Capture of CO2 in CO2-Binding Organic Liquids Formed by 1,1,3,3-Tetramethylguanidine and Glycerol Derivatives

A class of CO2-binding organic liquids (CO2-BOLs) composed of 1,1,3,3-Tetramethylguanidine (TMG) and Glycerol (Gly) and Gly’s amino derivatives were developed for highly efficient and reversible CO2 capture. These CO2-BOLs exhibited high gravimetric CO2 solubility up to 0.196 g CO2·g–1 at 313.2 K and 1.0 atm, superior to most functionalized ILs and other absorbents. The influential factors of CO2 absorption, such as components of CO2-BOLs, absorption temperature, and CO2 partial pressure together with water contents were investigated, and the recyclability of CO2-BOLs was verified to be excellent. The absorption mechanism of CO2-BOLs was explored with the help of spectral analysis, quantum chemical calculation, and thermodynamic analysis. All the results revealed that chemisorption took place once these CO2-BOLs were exposed to CO2, and alkyl guanidine carbonates were produced. Besides, it is illustrated that introducing the amino group to Gly could reduce the nucleophilic reactivity of CO2-BOLs, along with the absorption enthalpy simultaneously.

Energy-effective and low-cost carbon capture from point-sources enabled by water-lean solvents

Aqueous amines, as the most mature carbon capture technology, are subject to high energy and cost penalties due to the large water content in their formulations. Emerging technologies are in demand to enable a transition to a low-carbon global economy. However, rigorous process modeling and techno-economic analyses are limited for emerging carbon capture technologies. Here, four CO2-Binding Organic Liquids (CO2BOLs), all water-lean solvents were presented as promising options towards energy-effective and low-cost carbon capture from point sources. Rigorous solvent property and process models were developed in Aspen Plus for a coal-fired power plant with CO2BOL-based carbon capture unit. Techno-economic analyses were conducted in 2018 US pricing basis. The results suggest that water-lean formulations can minimize water condensation and vaporization, leading to a 36% energy saving compared with aqueous amines. Indeed, these CO2BOLs can capture up to 97–99% CO2 from coal fired plant. The estimated carbon capture cost is about $40/tonne CO2 at 90–97% carbon capture rate, about 12–23% less expensive than the conventional aqueous amine technology. The comparison between these CO2BOLs showed that in addition to vapor liquid equilibrium and kinetics (key properties for aqueous solvents), viscosity, volatility, and hydrophobicity, also have strong impacts on the performance of water-lean solvents. The methods presented in this work can be used to evaluate other emerging carbon capture technologies, while the results linking costs and performance of carbon capture solvents with their properties. Further, this work identifies research directions and targets for further reductions in total costs of capture from either cost or energy perspectives for these leading water-lean solvents.

Three-component 1,1,3,3-tetramethylguanidine based CO2-binding organic liquids: Statistical solvent design and thermodynamic modeling of CO2 solubility by LJ-Global TPT2 EoS

In this study, three-component CO2-binding organic liquids (CO2BOLs) are introduced for high pressure CO2 absorption. The non-aqueous, green solvents consist of a superbase (1,1,3,3-tetramethylguanidine (TMG)), a tertiary alkanolamine (Dimethylethanolamine (DMEA), Diethylethanolamine (DEEA) and N-methyldiethanolamine (MDEA)) and an alcohol (MeOH, n-BuOH, sec‑BuOH, tert‑BuOH and 1-HexOH). The best combination of solvent components was determined to be the TMG/DMEA/n-BuOH BOL (molar ration:1/1/1) based on both CO2 loading (αeq= 0.431 mol CO2/mol solvent) and absorption rate (αR= 0.225 mol CO2/mol solvent within 20 min) by implementing screening experiments. The mixture design approach was applied for the design of experiments, modeling and investigating the effect of components’ proportion on αeq and αR at the constant temperature of 35.0 °C and initial CO2 pressure of 25.0 bar. The highest αeq (0.573 mol CO2/mol BOL) and αR (0.362 mol CO2/mol solvent) were obtained using TMG/n-butanol (1/1) and DMEA BOLs, respectively. The CO2 solubility data in the two-component BOLs: TMG/n-BuOH, TMG/DMEA and DMEA/n-BuOH as well as the three-component TMG/DMEA/n-BuOH BOL were gathered at 25.0, 35.0 and 45.0 °C and the pressures up to 35.0 bar using equimolar solvent mixtures. The LJ-Global TPT2 EoS was used in the simultaneous VLE and chemical equilibrium calculation algorithm for the thermodynamic modeling of CO2 solubility in the BOLs. The AAD% in the modeling of TMG/n-BuOH, TMG/DMEA, DMEA/n-BuOH and TMG/DMEA/n-BuOH BOLs were calculated to be 11.5%, 12.4%, 10.5 and 12.9%, respectively. The enthalpies of CO2 absorption in BOLs and the speciation of the system components were predicted from reaction equilibrium constants and using LJ-Global TPT2 EoS.

Mass transfer mechanisms in CO2-binding organic liquids

Mass transfer mechanisms in CO2-binding organic liquids

Efficient Capture of Co2 In Co2-Binding Organic Liquids Formed by 1,1,3,3-Tetramethylguanidine and Glycerol Derivatives

Efficient Capture of Co2 In Co2-Binding Organic Liquids Formed by 1,1,3,3-Tetramethylguanidine and Glycerol Derivatives

CO2-binding organic liquids for high pressure CO2 absorption: Statistical mixture design approach and thermodynamic modeling of CO2 solubility using LJ-Global TPT2 EoS

CO2-binding organic liquids (CO2-BOLs) or switchable ionic liquids (SILs) are switchable polarity solvents (SPS) that can be used as non-aqueous, energy efficient solvents for CO2 absorption. In this study, the three-component CO2-BOLs comprised of a single-component CO2-BOL (tertiary alkanolamine) and a two-component CO2-BOL (superbase/alcohol) are introduced. The most efficient equimolar combination of superbase (1,8-diazabicyclo-[5.4.0]-undec-7-ene (DBU)), alcohol (methanol, n-butanol, sec-butanol, tert-butanol and hexanol) and amine (Dimethylethanolamine (DMEA), Diethylethanolamine (DEEA) and N-methyldiethanolamine (MDEA)) are obtained using screening experiments considering CO2 loading (αeq) and absorption rate (αR). The mixture design technique is employed for modeling of αeq and αR as a function of mole fraction of components at 35.0 °C and initial pressure of 25.0 bar. The DBU/DMEA/n-butanol CO2-BOL represented the best performance for CO2 uptake. The experimental CO2 solubility data in DBU/n-butanol, DBU/DMEA and DBU/DMEA/n-butanol BOLs were obtained in the temperature range of 25.0–45.0 °C and the pressure range of 1.0–45.0 bar. The DBU mole fraction was selected to be 0.1 and 0.2 while the molar ratio of DMEA to n-butanol was kept constant at 2 in the three-component BOL. The simultaneous vapor–liquid and chemical equilibrium calculation algorithm using LJ-Global TPT2 equation of state was used for the thermodynamic modeling of CO2 solubility in BOLs. The average absolute relative deviation error (AAD%) for the calculation of total pressure of DBU/n-butanol, DBU/DMEA and DBU/DMEA/n-butanol BOLs were obtained to be 8.5%, 5.8% and 8.6%, respectively.

CO2-Binding Organic Liquids Comprised of 1,1,3,3-Tetramethylguanidine and Alkanol for Postcombustion CO2 Capture: Water Inhibitory Effect of Amine Promoters

CO2-binding organic liquids (CO2-BOLs) are switchable polarity solvents that can be used as nonaqueous green solvents for energy-efficient CO2 capture. In this study, the novel three-component CO2-...

Towards water-insensitive CO2-binding organic liquids for CO2 absorption: Effect of amines as promoter

Abstract CO2-binding organic liquids (CO2-BOLs) or reversible ionic liquids (RILs), are non-aqueous CO2-triggered switchable polarity solvents which can be used for energy efficient CO2 capture. In this study, the novel three-component CO2-BOLs are introduced. They are comprised of 1,8-Diazabicyclo(5.4.0)undec-7-ene (DBU) as an organic superbase and an alkanol in conjunction with an amine as a promoter. Screening experiments were performed to find the best combination of CO2-BOL components based on CO2 loading and absorption rate. The variables were: the type of alcohol (methanol, n-butanol, sec-butanol, tert-butanol and 1-hexanol) and the type of amine (EEA, MEA, AMP, DEA, AEEA, PZ, TETA and DETA) using the DBU superbase. Statistical mixture design approach using Minitab 18 software was implemented for the design of experiments, modeling and optimization of CO2 loading at the fixed temperature of 35 °C and the initial CO2 pressure of 25 bar. It was found that DBU/MeOH/MEA system with the molar ratio of 0.3/0.17/0.53 has the maximum equilibrium absorption (αeq) and CO2 uptake within 30 min (αR) of 0.444 and 0.267 mol CO2/mol solvent, respectively. Amine additives promoted absorption efficiency and inhibited formation of solid precipitates (bicarbonate salt) in the presence of water impurity. Characterization of ionic species and explaining the water-inhibitory effect of MEA were obtained from FTIR, 1H NMR and 13C NMR spectroscopic analysis. Equilibrium CO2 solubility data in DBU/MeOH (1/2) and DBU/MeOH/MEA (0.3/0.6/0.1) CO2-BOLs were also obtained at temperatures of 308.2 and 318.2 K and pressure range of 0–33 bar. The results of present study can be used to effectively utilize CO2-BOLs in the wet conditions with higher absorption efficiency and lower regeneration energy.

Encapsulation of 2-amino-2-methyl-1-propanol with tetraethyl orthosilicate for CO2 capture

Carbon capture is widely recognised as an essential strategy to meet global goals for climate protection. Although various CO2 capture technologies including absorption, adsorption and membrane exist, they are not yet mature for post-combustion power plants mainly due to high energy penalty. Hence researchers are concentrating on developing non-aqueous solvents like ionic liquids, CO2-binding organic liquids, nanoparticle hybrid materials and microencapsulated sorbents to minimize the energy consumption for carbon capture. This research aims to develop a novel and efficient approach by encapsulating sorbents to capture CO2 in a cold environment. The conventional emulsion technique was selected for the microcapsule formulation by using 2-amino-2-methyl-1-propanol (AMP) as the core sorbent and silicon dioxide as the shell. This paper reports the findings on the formulated microcapsules including key formulation parameters, microstructure, size distribution and thermal cycling stability. Furthermore, the effects of microcapsule quality and absorption temperature on the CO2 loading capacity of the microcapsules were investigated using a self-developed pressure decay method. The preliminary results have shown that the AMP microcapsules are promising to replace conventional sorbents.

Evaluating the Performance of Micro-Encapsulated CO2 Sorbents during CO2 Absorption and Regeneration Cycling.

We encapsulated six solvents with novel physical and chemical properties for CO2 sorption within gas-permeable polymer shells, creating Micro-Encapsulated CO2 Sorbents (MECS), to improve the CO2 absorption kinetics and handling of the solvents for postcombustion CO2 capture from flue gas. The solvents were sodium carbonate (Na2CO3) solution, uncatalyzed and with two different promoters, two ionic liquid (IL) solvents, and one CO2-binding organic liquid (CO2BOL). We subjected each of the six MECS to multiple CO2 absorption and regeneration cycles and measured the working CO2 absorption capacity as a function of time to identify promising candidate MECS for large-scale carbon capture. We discovered that the uncatalyzed Na2CO3 and Na2CO3-sarcosine MECS had lower CO2 absorption rates relative to Na2CO3-cyclen MECS over 30 min of absorption, while the CO2BOL Koechanol appeared to permeate through the capsule shell and is thus unsuitable. We rigorously tested the most promising three MECS (Na2CO3-cyclen, IL NDIL0309, and IL NDIL0230) by subjecting each of them to a series of 10 absorption/stripping cycles. The CO2 absorption curves were highly reproducible for these three MECS across 10 cycles, demonstrating successful absorption/regeneration without degradation. As the CO2 absorption rate is dynamic in time and the CO2 loading per mass varies among the three most promising MECS, the process design parameters will ultimately dictate the selection of MECS solvent.

Attempting to Break the 2 GJ/tonne CO2 Barrier; Development of an Advanced Water-Lean Capture Solvent From Molecules to Detailed Process Design

Solvent-based post-combustion CO2 capture is an energy-intensive process primarily driven by the energy required to regenerate the CO2 capture solvent. Researchers are currently focused on developing drop-in solvent replacements for commercial amine solvents with lower regeneration energies. One approach to reducing the regeneration energy of a solvent is to reduce its water content, thereby reducing unnecessary condensing and consequent boiling in the process. There are a number of water-lean solvent formulations currently under development that allow for water contents below 10% by weight, versus more than 60% for commercial aqueous amines. One solvent class, CO2-Binding Organic Liquids (CO2BOLs), shows promise to reduce the parasitic load to a coal-fired power plant but has been impeded by high viscosities at high CO2 loadings. In this paper, we perform a preliminary modeling study of a new low-viscosity CO2BOL solvent and assess the energetics of different process stripper configurations. By tailoring the process configuration with the unique aspects of the solvent reboiler duties below 2 GJ/tonne CO2 could be achievable. Further, this study suggests that there is no one-size-fits-all process optimum configuration for solvents, and therefore optimal configurations will be solvent specific.

CO2 Controlled Catalysis: Switchable Homopolymerization and Copolymerization

The first versatile gas-controlled polymerization switch based on reversible absorption of CO2 by organic amidine was developed. The amidine/alcohol system, which originally belonged to CO2 binding organic liquids, served as an efficient CO2-responsive catalyst/initiator system for lactide polymerization. Chemoselective block copolymerization between polylactide and polycarbonate was further explored by opposite gas-controlled amidine and another CrIII catalyst, where an immortal strategy was developed for conjugated alternation of inverse polymerizations on different active species and permits many potential applications.

Investigation of glycerol-derived binary and ternary systems in CO2 capture process

Glycerol, an abundant byproduct in biodiesel industry process, has received a lot of attention in recent years. In this work, a series of glycerol-derived binary and ternary CO2 binding organic liquids (CO2BOLs), were proposed for carbon capture. Physical properties, 1H NMR spectra and FT-IR spectra of these systems were studied to describe the multiple interactions between constituents. The CO2 absorption performances were evaluated in details, and excellent CO2 uptake capacity was achieved. In order to systematically clarify the role of glycerol in superbase environment for CO2 capture process, binary systems were further explored to support the conclusions both theoretically and experimentally. The characteristic that glycerol could easily be deprotonated in superbase environment, was proved to be benefit to the efficient and homogeneous capture of CO2, and a corresponding absorption mechanism was put forward. In addition, the effects of superbase and ionic liquids on absorption were also investigated. The results in this work showed how green, economic and high performance absorbents could be designed for applications of carbon capture.

Pentaerythritol-Based Molecular Sorbent for CO2 Capturing: A Highly Efficient Wet Scrubbing Agent Showing Proton Shuttling Phenomenon

Pentaerythritol (PE) is considered a biodegradable material that combines the ease of synthesis, nonvolatility, and extra stability under basic conditions (acidic gas sequestration, e.g., CO2), which makes it a useful candidate for postcombustion capture (PCC) application. To overcome corrosion problems associated with CO2 binding organic liquids, a binary mixture comprised of PE/1,8-diazabicyclo-[5,4,0]-undec-7-ene (DBU) (1:4 molar ratio) dissolved in dimethyl sulfoxide (DMSO) was exploited for CO2 capturing. The formation of ionic alkyl organic carbonate (RCO3– DBUH+) was confirmed using 13C NMR (157.4 ppm) and ex situ attenuated total reflectance–Fourier transform infrared spectroscopy (ATR-FTIR) (two peaks were identified, viz., 1670 and 1630 cm–1, which were ascribed to the symmetric and asymmetric stretching of both C═O and O···C···O− within RCO3H and RCO3–, respectively). The charged adduct was measured using a thermostated beaker coupled with conductivity and pH meter probes. The sorption capacity...

Kinetics of reaction between CO2 and ionic liquid-carbon dioxide binding organic liquid hybrid systems: Analysis of gas-liquid absorption and stopped flow experiments

It is generally accepted that CO2 emissions from point sources – such as thermal power plants – can be controlled by gas-liquid absorption where the process is intensified significantly by introducing a reactantinto solvent. In this work, blends of 1-ethyl-3-methyl imidazolium bis (trifluoromethylsulfonyl) imide ([emim][Tf2N]) with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) (or 1,1,3,3-tetramethylguanidine (TMG)) in 1-hexanol were studied. Gas absorption experiments were carried out in a gas-liquid mini reactor for the hybrid systems containing different weight concentrations of organic bases while keeping the ionic-liquid weight percentage constant. Total amount of absorbed CO2 was measured as function of time and the absorption (or loading) capacities and the initial absorption rates have been obtained at 313K. It was found that increasing the amount of the organic base increased the loading capacity of CO2. Also, reusability and performance loss of hybrid solutions were investigated by using Fourier transform infrared spectrometry under sequential absorption-desorption cycles. The intrinsic reaction rates were measured in a stopped flow equipment for a temperature range of 283–303K. The empirical power law reaction orders with respect to DBU and TMG were found to be between 1.0 and 2.0 at different temperatures and the kinetic data could be interpreted satisfactorily by a modified termolecular reaction mechanism.Finally, the observed reaction rate constants inferred from heterogeneous gas absorption rates – through estimated solubility and diffusivity – were compared with the homogeneous – intrinsic – reaction rate constants obtained by a rapid mixing technique, namely stopped-flow conductimetry. The observed pseudo first order rate constants at 313K were found to be very similar and the deviations remained within 5–15%. Obtaining relevant data by these two very different techniques in the same laboratory provided pros and cons of each method and clarified – often – biased ambiguities.

New insights into the chemistry of ionic alkylorganic carbonates: a computational study.

A library of hydrogenated, perfluorinated aliphatic and aromatic (p-substituted) alcohols are selected together with a combination of superbases (SBs) and metal hydrides (MHs) to understand the thermodynamic parameters of the binary mixtures once serving as sorbents for the capture of CO2via ionic organic alkyl-carbonate (RCO3-) formation. Data are obtained using density functional theory (DFT) calculations with the B3LYP/6-31+G* level of theory and compared with the experimental results acquired from the literature using different spectroscopic techniques. It is found that the capturing process has a favourable enthalpic contribution and an unfavourable entropic penalty regardless the identity of the base, where the enthalpy values of alcohol/MH binary mixtures are almost two-fold higher compared to their SB-based mixtures. The utilisation of perfluorinated aliphatic alcohols instead of hydrogenated alcohols shows a negative impact on the formation of carbonate adducts, due to the less reactive alkoxide anion along the carbon skeleton, which is attributed to the low charge density of the nucleophilic oxygen atom. While perfluorinated phenol shows a higher reactivity than the parent phenol. The calculations indicate that the reactivity of phenolic compounds is highly affected by the electronic nature of the substituting groups, in which p-substituted phenols are more reactive towards CO2 capturing when electron releasing groups are utilised. A pronounced solvent effect is observed, in which the alkylcarbonate salts (RCO3- SBH+) are stabilized in solvents with high dielectric constant (e.g., DMSO and MeCN). Simulated NMR and IR spectra of RCO3- are consistent with those reported for the affiliated systems, which fortifies the results obtained for the unexplored substrate/MH mixtures, filling a gap in the literature of CO2 sequestration using CO2 binding organic liquids (CO2BOLs) and enabling a fair/quick prediction of potential substrates to be used as CO2 sorbents.

Dynamic Acid/Base Equilibrium in Single Component Switchable Ionic Liquids and Consequences on Viscosity.

The deployment of transformational nonaqueous CO2-capture solvent systems is encumbered by high viscosities even at intermediate uptakes. Using single-molecule CO2 binding organic liquids as a prototypical example, we present key molecular features that control bulk viscosity. Fast CO2-uptake kinetics arise from close proximity of the alcohol and amine sites involved in CO2 binding in a concerted fashion, resulting in a Zwitterion containing both an alkyl-carbonate and a protonated amine. The population of internal hydrogen bonds between the two functional groups determines the solution viscosity. Unlike the ion pair interactions in ionic liquids, these observations are novel and specific to a hydrogen-bonding network that can be controlled by chemically tuning single molecule CO2 capture solvents. We present a molecular design strategy to reduce viscosity by shifting the proton transfer equilibrium toward a neutral acid/amine species, as opposed to the ubiquitously accepted zwitterionic state. The molecular design concepts proposed here are readily extensible to other CO2 capture technologies.

Measuring Nitrous Oxide Mass Transfer into Non-Aqueous CO2BOL CO2 Capture Solvents

This paper investigates CO2 absorption behavior in CO2BOL solvents by decoupling the physical and chemical effects using N2O as a nonreactive mimic. Absorption measurements were performed using a wetted-wall contactor. Testing was performed using a “first generation” CO2-binding organic liquid (CO2BOL), composed of an independent base and alcohol. Measurements were made with N2O at a lean (0.06 mol CO2/mol BOL) and rich (0.26 mol CO2/mol BOL) loading, each at three temperatures (35, 45, and 55 °C). Liquid-film mass transfer coefficients (kg′) were calculated by subtracting the gas film resistance-determined from a correlation from literature–from the overall mass transfer measurement. The resulting kg′ values for N2O in CO2BOLs were found to be higher than that of 5 M aqueous MEA under comparable conditions, which is supported by published measurements of Henry’s coefficients for N2O in various solvents. These results suggest that the physical solubility contribution for CO2 absorption in CO2BOLs is great...

Bench-Scale Testing and Process Performance Projections of CO2Capture by CO2–Binding Organic Liquids (CO2BOLs) with and without Polarity-Swing-Assisted Regeneration

This manuscript provides a detailed analysis of a continuous-flow, bench-scale study of the CO2-binding organic liquid (CO2BOL) solvent platform with and without its polarity-swing-assisted regeneration (PSAR). This study encompassed four months of continuous-flow testing of a candidate CO2BOL with a thermal regeneration and PSAR regeneration using a decane antisolvent. In both regeneration schemes, steady-state capture of >90% CO2 was achieved using simulated flue gas at reasonable liquid/gas (L/G) ratios. Aspen Plus modeling was performed to assess process performance, compared to previous equilibrium performance projections. This paper also includes net power projections, and comparisons to DOE’s Case 10 amine baseline, and comments on the viability of the CO2BOL solvent class for post-combustion CO2 capture.

Microencapsulation of advanced solvents for carbon capture.

Purpose-designed, water-lean solvents have been developed to improve the energy efficiency of CO2 capture from power plants, including CO2-binding organic liquids (CO2BOLs) and ionic liquids (ILs). Many of these solvents are highly viscous or change phases, posing challenges for conventional process equipment. Such problems can be overcome by encapsulation. Micro-Encapsulated CO2 Sorbents (MECS) consist of a CO2-absorbing solvent or slurry encased in spherical, CO2-permeable polymer shells. The resulting capsules have diameters in the range of 100-600 μm, greatly increasing the surface area and CO2 absorption rate of the encapsulated solvent. Encapsulating these new solvents requires careful selection of shell materials and fabrication techniques. We find several common classes of polymers are not compatible with MECS production, but we develop two custom formulations, a silicone and an acrylate, that show promise for encapsulating water-lean solvents. We make the first demonstration of an encapsulated IL for CO2 capture. The rate of CO2 absorption is enhanced by a factor of 3.5 compared to a liquid film, a value that can be improved by further development of shell materials and fabrication techniques.