CO2 Loading Research Articles

CO2 absorption enhancement of fluorinated ionic liquids on nonaqueous biphasic absorbents: Experimental and theoretical study

Nonaqueous biphasic absorbent decreasing the regeneration heat consumption by phase separation (lean-phase and rich-phase) and water evaporation elimination is a promising CO2 capture absorbent, but the low CO2 loading capacities are of great challenges. In this study, ionic liquids (IL) were proposed as catalysts for enhancing the CO2 loading in monoethanolamine (MEA)-1-Butanol nonaqueous biphasic absorbents. Three types of fluorinated IL including 1‑butyl‑3-methylimidazolium tetrafluoroborate ([Bmim][BF4]), 1‑butyl‑3-methylimidazolium hexafluorophosphate ([Bmim][PF6]), and 1‑butyl‑3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide ([Bmim][TF2N]) under different concentrations (0–10wt%) were detailly analyzed to explore the catalyzation of IL on phase separation behavior and absorption performance. Phase separation study showed that the MEA-1-Butanol-IL system exhibited the wonderful phase separation behavior with a volume ratio (rich-phase) between 30 and 40 %. Three phases were observed in MEA-1-Butanol-[Bmim][BF4] and MEA-1-Butanol-[Bmim][PF6] systems after CO2 absorption and the components of each phase were identified by 13C nuclear magnetic resonance (NMR) spectroscopy. In absorption study, the absorption enhancement of IL was in this order: [Bmim][TF2N] > [Bmim][BF4] > [Bmim][PF6]. MEA-1-Butanol-10wt% [Bmim][TF2N] system could improve 35.9 % CO2 loading and 24.2 % absorption rate compared to basic MEA-1-Butanol. A molecular scale understanding of the three-steps reaction mechanism of MEA-1-Butanol-IL absorbing CO2 was revealed, and the different catalyzation of three types of IL can be attributed to the different affinity for CO2. This study provides new insights into designing nonaqueous biphasic solvents and a promising MEA-1-Butanol-IL system with high CO2 capture performance.

In Situ Raman Methodology for Online Analysis of CO2 and H2O Loadings in a Water-Lean Solvent for CO2 Capture.

Carbon capture represents a key pathway to meeting climate change mitigation goals. Powerful next-generation solvent-based capture processes are under development by many researchers, but optimization and testing would be significantly aided by integrating in situ monitoring capability. Further, real-time water analysis in water-lean solvents offers the potential to maintain their water balance in operation. To explore data acquisition techniques in depth for this purpose, Raman spectra of CO2, H2O, and a single-component water-lean solvent, N-(2-ethoxyethyl)-3-morpholinopropan-1-amine (2-EEMPA) were collected at different CO2 and H2O concentrations using an in situ Raman cell. The quantification of CO2 and H2O loadings in 2-EEMPA was done by principal component regression and partial least squares methods with analysis of uncertainties. We conclude with discussions on how this simultaneous online analysis method to quantify CO2 and H2O loadings can be an important tool to enable the optimal efficiency of water-lean CO2 solvents while also maintaining the critical water balance under operating conditions relevant to post-combustion CO2 capture.

Catalytic desorption of CO2‐loaded solutions of diethylethanolamine using bentonite catalyst

AbstractThe absorption of CO2 gas into aqueous alkanolamine solutions is the most advanced CO2 separation technology and a key challenge in this technique is the energy‐intensive process of solvent regeneration. The tertiary amine N,N′‐diethylethanolamine (or DEEA) is a candidate CO2‐capturing solvent with potential. To improve the energy efficiency of regeneration of DEEA, several catalysts were used for desorbing CO2 from loaded solutions of DEEA (2.5 M) at T = 363 K. Desorption trials were conducted in batch mode. The initial CO2 loading varied in the 0.3–0.35 mol CO2/mol DEEA range. The performance was analyzed by calculating the rate of CO2 desorption, cyclic capacity, and reduction in sensible energy. The amount of thermal energy needed for amine regeneration was significantly lowered by using nine transition metal oxide catalysts and the hierarchy was as follows: Al2O3 < MoO3 < V2O5 < TiO2 < MnO2 < ZnO < Cr2O3 < SiO2 < ZrO2. Among the metal oxides, Al2O3 increased desorption efficiency compared to blank runs by 89%. A clay‐based powder bentonite was also used as catalyst and its efficacy was compared with the metal oxides. This cheap and easily available bentonite catalyst was tuned through simple ion‐exchange with four acids (HCl, H3PO4, HNO3, and H2SO4). Upon treatment with H2SO4, bentonite remarkably increased desorption efficiency by 100%. Furthermore, bentonite catalyst treated with sulphuric acid (denoted here as Bt/H2SO4) was characterized by Brunauer–Emmett–Teller (BET), scanning electron microscopy (SEM), Fourier transform infrared spectrometery (FTIR), X‐ray diffraction (XRD), and ammonia temperature‐programmed desorption (NH3‐TPD). In this way, a comprehensive study on catalytic desorption of DEEA was performed.

Speciation and gas-liquid equilibrium study of CO2 absorption in aqueous MEA-DEEA blends

The blending of primary amines, with fast reaction kinetic, together with tertiary amines, with a large loading capacity, is an increasingly popular approach to develop high-performance CO2 capture sorbents with low energy requirements for regeneration. In this study, we investigated the CO2 absorption performance of several aqueous solutions obtained by mixing ethanolamine (MEA) and diethylethanolamine (DEEA) and compared them with that of individual MEA and DEEA. CO2 loadings at equilibrium were measured experimentally under a wide range of operating conditions, at temperatures between 298 and 323 K, CO2 partial pressures in the range 5–60 kPa, and different amine mixing ratios. In addition, 13C NMR spectroscopy was employed to elucidate the reaction mechanisms and identify the species formed during CO2 capture. The results of the study reveal the intricate interplay of MEA and DEEA in CO2 capture, where MEA carbamate formation predominates in the early stages, gradually shifting to bicarbonate formation as the amine concentration decreases. Moreover, excess properties, which reflect non-ideal behaviors in amine blends, were introduced as a key parameter in the study. An excess property model, based on excess CO2 loading, was developed to accurately predict the CO2 equilibrium solubility without constant experimental measurement. As a result, good agreement was found between the experimental data and those calculated with the model (excess CO2 loading) under the same operating conditions, with a average relative deviation of 1.1%.

Molecular simulation of adsorption behaviors of methane and carbon dioxide on typical clay minerals

Knowledge of the interaction mechanisms between shale and CH4/CO2 is crucial for the implementation of CO2 sequestration with enhanced CH4 recovery (CS-EGR) in shale reservoir. As one of the main constituents of shale, clay minerals can profoundly affect the storage capacity of gases in nanopores. In this paper, the adsorption behaviors of both CO2 and CH4 on montmorillonite, illite as well as kaolinite under dry condition are investigated by Grand Canonical Monte Carlo (GCMC) simulation. The results exhibit that the maximum adsorption capacity of single-component CH4 and CO2 is associated with the types of clay crystals. Specifically, the montmorillonite has the strongest adsorption capacity for CO2, followed by illite and kaolinite, while the sequence in maximum adsorption capacity of CH4 is predicted in the order of kaolinite > montmorillonite > illite. These discrepancies are closely related to the characteristics of adsorbate molecules as well as the different structures of clay crystals. Meanwhile, the maximum adsorption capacity of CH4 in studied clay minerals gradually decreases as pore size increases, while nanopores with 2-nm basal spacing demonstrate the highest adsorption capacity for CO2. In addition, it is observed that the studied clay minerals tend to preferentially adsorb CO2 rather than CH4 during binary gas mixtures simulation. The selectivity of CH4/CO2 mixtures in montmorillonite and kaolinite exhibits various performances as the adsorption pressure increases, with the selectivity in montmorillonite being the largest, especially at low pressure. The cation exchange significantly enhances the electrostatic interaction with CO2 molecules, leading to a higher loading of CO2 as well as larger value of selectivity. These findings can provide basis and guidance for the CS-EGR project in shale reservoirs.

Volumetric and viscometric properties of aqueous choline chloride + methyldiethanolamine deep eutectic solvents

Amine-based deep eutectic solvents have the advantages of easy preparation, extremely low vapor pressure, stable biodegradation and high CO2 loading, which has become the most potential CO2 absorbent. In this work, the amine-based functionalized DES of choline chloride + methyldiethanolamine with different molar ratios were successfully prepared, and the densities and viscosities of DES aqueous solutions were measured from 303.15 K to 333.15 K. The effects of DES composition, water content and temperature on the excess molar volume, partial molar volume, apparent molar volume, limiting partial molar volume and viscosity deviation were investigated. The hydration and intermolecular interaction in DES solution were analyzed. The critical concentration of water in solution was determined under the premise of maintaining DES hydrogen bond network.

Comparative analysis of artificial neural network (ANN) models: CO2 loading in MDEA and blended MDEA/PZ solvents

CO2 loading plays a vital role in gauging a solvent's capability to absorb CO2 from combustion gases and natural gas flow. Yet, the customary approaches for measuring CO2 loading hinge on laborious and costly laboratory experiments. Therefore, researchers employed artificial neural network (ANN) approaches to estimate CO2 loading using various datasets, although case-specific methods and approaches restricted their attempts. This study employed two datasets with 303 (CO2 absorption via MDEA) and 361 (CO2 absorption via MDEA/PZ) acceptable experimental data to create ANN models to estimate CO2 loading in aqueous amine solvents. The CO2 loading is evaluated using a wide range of input parameters, including temperature, CO2 partial pressure, Methyldiethanolamine (MDEA) solvent, and Piperazine (PZ) solvent for cases A and B, respectively. Twelve distinct training algorithms, four distinct activation functions, and three hidden layers with neuron variations created the models. ANN models trained with a blend of PZ and MDEA solvents generated more accurate predictions compared to models trained with solely MDEA solvent. The sigmoidal activation functions (Tansig and Logsig) generated more precise predictions than the linear activation functions (Poslin and Purelin). In addition, “Levenberg-Marquardt (lm)” with the highest coefficient of determination (R2) was selected as the best training algorithm among the twelve training functions. The best average coefficients of determination were determined to be 0.964 for the tansig activation function with [25 18 10] number of neurons in case A and 0.967 for the logsig activation function with [30 20 12] number of neurons in case B. The statistical analysis (R2, MSE, RMSE, AAD, AARD, and run time) confirmed that the network provided accurate estimates of CO2 loading for both datasets. The prediction potential of the network is then further indicated by model generalization inside the training data set.

Dual Salt Cation-Swing Process for Electrochemical CO2 Separation.

Electrochemical CO2 separations, which use electricity rather than thermal energy to reverse sorption of CO2 from concentrated point sources or air, are emerging as compelling alternatives to conventional approaches given their isothermal, ambient operating conditions, and ability to integrate with renewable energy inputs. Despite several electrochemical approaches proposed in previous studies, further explorations of new electrochemical CO2 separation methods are crucial to widen choices for different emissions sources. Herein, we report an electrochemical cation-swing process that is able to reversibly modulate the CO2 loading on liquid amine sorbents in dimethyl sulfoxide (DMSO) solvent. The process exploits a reversible carbamic acid-to-carbamate conversion reaction that is induced by changing the identity of Lewis acid cations (e.g. K+, Li+, Ca2+, Mg2+, and Zn2+) coordinated to the amine-CO2 adduct in the electrolyte. Using ethoxyethylamine (EEA) as a model amine, we present NMR-based speciation studies of carbamic acid-to-carbamate conversion as a function of amine/salt concentrations and cation identity. The reaction is further probed using gas-flow reaction microcalorimetry, revealing the energetic driving forces between cations and the amine-CO2 adduct that play a key role in the described re-speciation. A prototype electrochemical cell was further constructed comprising a Prussian white (PW) potassium (K+) intercalation cathode, zinc (Zn) foil anode, and EEA/DMSO electrolyte containing a dual KTFSI/Zn(TFSI)2 salt. A low CO2 separation energy of ∼22-39 kJ/mol CO2 (0.1-0.5 mA cm-2) was achieved with a practical CO2 loading delta of ∼0.15 mol CO2/mol amine. Further optimizations in electrolyte design and cell architectures toward continuous CO2 capture-release are expected to enhance rate performance while retaining favorable separation energies.

Analytical first-principles-based model for sprays-based CO2 capture

CO2 removal from flue gases or air is directly proportional to the overall contact area between the solvent and gas flow. Spraying the solvent offers possibilities for large area/volume ratios resulting from the small size of solvent droplets. The overall mass transfer (KGAv) is a crucial indicator of the performance of the system and indicates the overall CO2 capture rate per unit volume at given working pressure. The maximum capture rate of spray systems considered in this study is 608 kmol/m3-hr. This study develops an analytical model to predict mass transfer in spray-based systems for CO2 capture by evaluating KGAv and capture efficiency. Model predictions are validated using two experimental studies for a range of liquid flow rate, inlet solvent loading, different nozzle types, and inlet CO2 partial pressure. The relative importance of the incorporation of equilibrium partial pressure of CO2 (P*) into amine with respect to CO2 partial pressure is also studied. It is found that its effect on KGAv is prominent in high liquid flow rate and low solvent loading regimes where the overall CO2 capture is high. Finally, the variation of key parameters such as KGAv, total mass transfer coefficient (KG), effective area (Av), solvent loading (α), and mole fraction of CO2 in the gas stream (XCO2) along the channel height is studied, which gives insights on optimization of the channel height for specified operating conditions.

Ultra-low temperature sono-assisted CO2 stripping/ carbon-rich solvent regeneration using different ultrasonic frequencies

ABSTRACT Carbon dioxide emission from anthropogenic sources plays a major role in global warming and climate change. Conventional amine-based carbon capture is matured technology that has limitations on high-temperature use imposed by solvent degradation and solvent loss during CO2 stripping/regenerating solvent. The present experimental investigation involves the application of tank-type (bath-type) sonication for CO2 stripping from aqueous carbon-rich 30 wt% MEA solvent in a low temperature-controlled environment, using ultrasonic frequencies of 25 kHz (cavitation-dominant), 360 kHz (streaming-dominant), and 58/132 kHz dual-mode (combined phenomena). The results are analyzed to understand the effects of carbon loading, CO2 stripping efficiency, stripping rate, temperature profile, and energy demand. The stripping rate is higher in the low-temperature range of 6°C to 12°C for all the frequencies due to the sonication effect. In the mid setpoint range of 15°C to 30°C, the CO2 stripping rate is lower due to the combination of sonication and temperature effect, and when the temperatures increase from 40°C to 45°C, the stripping rate increases gradually due to additional temperature effect. A high cyclic capacity of 1.12 mol CO2/kg. was observed for 360 kHz frequency at 12°C. The lowest energy of 3.94 kJ/mol CO2 was achieved for 360 kHz at a setpoint of 12°C. Factors such as sonication frequency, CO2 loading (mol CO2/mol soln.), temperature, and nominal power of ultrasonics play an important role in determining the sensible energy required for CO2 stripping. Specifically, CO2 stripping at the low temperature set point of 6°C and 12°C is found to be promising in all frequencies, indicating that CO2 stripping is primarily promoted by sonication, rather than by temperature.

A theoretical study on the separation of CO2/CH4 through MFI zeolite

The separation of carbon dioxide (CO2) and methane (CH4) is important in addressing global warming and energy shortages. Porous materials play a large role, of which MFI zeolite has received much attention. To better analyse mechanisms or guide experiments, the adsorption and diffusion properties of CO2 and CH4 in MFI zeolite have been studied by Monte Carlo and molecular dynamics simulations. Due to stronger interactions, the loading of pure CO2 is significantly higher than that of CH4. For mixtures (biogas or natural gas), CO2 dominates in competitive adsorption. Lower temperatures and higher pressures correspond to higher adsorption selectivity. In addition, the self-diffusion coefficients of guest molecules in MFI zeolite were also calculated. The diffusion performance of pure CH4 is superior to CO2 under the same conditions. And their self-diffusion coefficient increases with increasing temperature and decreasing load. For mixed components, CO2 greatly limits the diffusion of CH4.

Novel low energy mixed amine biphasic solvent for carbon dioxide capture in biogas upgrading

A low energy consumption aqueous mixed amine biphasic solvent consisting of monoethanolamine, N-methyldiethanolamine and 1-butyl-3-methylimidazolium tetrafluoroborate (BF) was prepared for CO2 capture in biogas upgrading process. The solvent could be divided into two phases after biogas upgrading: rich liquid phase and lean liquid phase, the rich liquid phase would enter the regeneration tower for regeneration, and the lean liquid phase could directly enter the absorber tower for biogas upgrading without regeneration, the methane purity of the upgraded biogas could reach 100 %, the energy consumption of regeneration would be lower than that of 30 wt% MEA by 44.07 %, and the carbon enrichment rate of the rich liquid phase could reach more than 98 % after the phase separation. A comprehensive study of the influence of the BF addition on CO2 capture and mass transfer was carried out Amplified by analyzing the physical parameters of mixed system and a beneficial conclusion was reached. In addition, the added BF could effectively reduce the free energy during the reaction and improve the efficiency of the reaction. The higher dipole moment of the BF also provided an effective impetus for the phase separation process to take place. Finally, an amplified phase separator was used to simulate the whole process of phase separation in real conditions and it was found that high CO2 loadings were effective in accelerating the rate of phase separation. This study provided a theoretical basis for the subsequent research of biphasic solvents in the field of biogas upgrading, as well as technical guidance for the wide application of biogas upgrading in industry, which had a broad research prospect.

A molecular dynamic insight into CO2 diffusion of type III porous liquids

As emerging materials, porous liquids have shown good performance in gas separations attributed to porosity and fluidity. In the present work, a microscopic insight into CO2 diffusion of type III porous liquids was revealed by molecular dynamic simulation. First, A model of [EMIm][NTf2]/ZIF-8 type Ⅲ porous liquids was constructed. The internal permanent, rigid, vacant pores in the porous liquids were demonstrated by molecular dynamics simulation. It was found these pores were still kept after 12 ns dynamic simulation, and the calculated specific surface area and the pore volume of the porous liquids were 0.139 cm3/g and 939 m2/g, respectively. Then the models of CO2-type Ⅲ porous liquids were constructed to study the diffusion behavior of CO2 molecules in porous liquids. It was found that ZIF-8 dominated the CO2 absorption by analyzing CO2 relative concentration. Subsequently, the effect of different parameters, including temperature, pressure, and CO2 loading on CO2 diffusion in porous liquids was studied. The results showed CO2 diffusion ability in the porous liquid enhanced with increasing temperature, and CO2 loading. and it was insensitive to pressure. Finally, the interaction energy was calculated, and the interaction energy between CO2 and [EMIm][NTf2], ZIF-8 followed the order CO2-ILs < CO2-ZIF-8. The research approach in this paper assists in obtaining the micro-informations of porous liquids.

Carbonic anhydrase textile structured packing for efficient CO2 absorption in methyldiethanolamine solvent

AbstractCarbonic anhydrase (CA) is an attractive biodegradable catalyst for CO2 absorption in solvent‐based CO2 capture. However, maintaining the stability of CA as a homogeneous component of the solvents is a challenge. Solvent regeneration temperature typically exceeds the enzyme thermal tolerance, which leads to CA deactivation. To reduce the need for frequent CA replenishment and to avoid inactive CA accumulation in the solvent, this work shows the benefits of an immobilization strategy where CA is fixed in a second‐generation design of textile structured packing (CATSP‐2) modules. The enzyme‐immobilized packing showed 1.5 times better performance in CO2 separation compared with traditional structured packing with a corresponding increased CO2 loading in the rich solvent. The modules exhibited good CA activity retention of ~80% during the tests without any CA replenishment. Applying CATSP‐2 could potentially decrease the packing height and absorber column size for a lower cost per amount of CO2 captured.

Aqueous Potassium Salt of L-Cysteine as Potential CO2 Removal Solvent: An Investigation on Physicochemical Properties and CO2 Loading Capacity

The operational and economic constraints suffered by amine solvents for CO2 removal have motivated the research on an alternative solvent with better performance and cost-effectiveness. Amino acid salt (AAS) has been identified as an interesting green solvent, an alternative to commercial amine solvents. The present work evaluated the physicochemical and CO2-solubility properties of potassium L-cysteine (K-CYS), a naturally occurring amino-acid-based solvent for CO2 removal from natural gas. Its physicochemical properties, including density, viscosity, and refractive index, were measured at different temperatures ranging between 298.15 and 333.15 K and a concentration range of 5 to 30 wt.%. Based on the experiment, all properties were found to decrease with increasing temperature and increase with increasing concentration. The experiments also demonstrated a significant reduction of CO2 loading from 2.4190 to 1.1802 mol of CO2/mol of K-CYS with increasing solvent concentration from 10 to 30 wt% at 313.15 K and 20 bar (g).

Effect of water on CO2 absorption by a novel anhydrous biphasic absorbent: Phase change behavior, absorption performance, reaction heat, and absorption mechanism

The ionic liquids (ILs)-based biphasic absorbents are viewed as promising substitutes for CO2 capture due to their remarkable CO2 absorption performance, excellent stability and low energy requirement for regeneration. Further decreasing the regeneration heat requirement can be achieved by utilizing ILs-based anhydrous biphasic absorbents, whose solid CO2-rich phase contained small volume and low specific heat capacity. Given the high hygroscopicity of ILs and the water present in the flue gas, comprehending the effect of water is crucial for post-combustion carbon capture using ILs-based anhydrous biphasic absorbents. In this work, the effect of water on CO2 absorption by an anhydrous biphasic absorbent, tetramethylammonium glycinate ([N1111][Gly])/ethanol, was studied. The experimental results demonstrated that the CO2 loading and absorption rate were decreased in the presence of water, but the CO2 desorption efficiency was enhanced. Besides, the presence of water slightly reduced the reaction heat of CO2 absorption by [N1111][Gly]/ethanol to 69.48 kJ/mol CO2, which was 20% lower than that of monoethanolamine (MEA) absorbent. Furthermore, the 13C NMR results indicated that the primary CO2-product was bicarbonate in the presence of water rather than carbamate. There were three possible pathways for bicarbonate generation: zwitterion hydrolysis, carbamate hydrolysis, and base-catalyzed CO2 hydration. Water and ethanol competed to react with carbamate. When a large amount of water was present (≥70 wt%), the reaction of ethanol with the carbamate hardly occurred.

Hybrid Smart Strategies to Predict Amine Thermal Degradation in Industrial CO2 Capture Processes.

CO2 emission reduction is an essential step to achieve the climate change targets. Solvent-based post-combustion CO2 capture (PCC) processes are efficient to be retrofitted to the existing industrial operations/installations. Solvent degradation (and/or loss) is one of the main concerns in the PCC processes. In this study, the thermal degradation of monoethanolamine (MEA) is investigated through the utilization of hybrid connectionist strategies, including an artificial neural network-particle swarm optimization (ANN-PSO), a coupled simulated annealing-least squares support vector machine (CSA-LSSVM), and an adaptive neuro-fuzzy inference system (ANFIS). Moreover, gene expression programming (GEP) is employed to generate a correlation that relates the solvent concentration to the operating variables involved in the adverse phenomenon of solvent thermal degradation. The input variables are the MEA initial concentration, CO2 loading, temperature, and time, and the output variable is the remaining/final MEA concentration after the degradation phenomenon. According to the training and testing phases, the most accurate model is ANFIS, and the reliability/performance of its optimal network is assessed by the coefficient of determination (R2), mean squared error, and average absolute relative error percentage, which are 0.992, 0.066, and 2.745, respectively. This study reveals that the solvent initial concentration has the most significant impact, and temperature plays the second most influential effect on solvent degradation. The developed models can be used to predict the thermal degradation of any solvent in a solvent-based PCC process regardless of the complicated reactions involved in the degradation phenomenon. The models introduced in this study can be employed for the development of more accurate hybrid models to optimize the proposed systems in terms of cost, energy, and environmental prospects.

Comprehensive performance of a diethylenetriamine/2-diethylaminoethanol biphasic absorbent for CO2 capture

The CO2 capture process based on amine absorption–regeneration is currently the most widely used technology, and the performance of absorbent is the key to this process. Biphasic absorbents have attracted considerable interest because of their strong potential to reduce the regeneration energy consumption and equipment investment costs. The mixed solution of diethylenetriamine (DETA) and 2-diethylaminoethanol (DEEA) has been proven to be a biphasic absorbent, but there is still a lack of comprehensive performance evaluation data. In this study, the ratio of the DETA/DEEA solution was optimized as 2 M DETA + 3 M DEEA, and its phase separation property, reaction mechanism, mass transfer kinetics, and desorption thermodynamics were investigated under various conditions. The comprehensive performance of the solution was then evaluated by further analyzing its oxidative degradation, thermal degradation, and metal corrosion characteristics. On this basis, the capital cost and operation cost of using DETA/DEEA biphasic absorbent were analyzed. Under typical coal-fired flue gas (CO2 concentration 12%), because of the high CO2 absorption capacity and excellent phase separation property, the minimal desorption energy consumption of the DETA/DEEA absorbent decreased to 2.14 GJ/t CO2, a 43.7% decrease compared with that of 5 M monoethanolamine (MEA). Under the same experimental conditions, DETA/DEEA exhibited an oxidative degradation rate of only 2.71%, which was 20.7% of 5 M MEA. In addition, the metal corrosion rate of DETA/DEEA was one order of magnitude lower than that of 5 M MEA. However, under a high CO2 loading, its thermal degradation resistance needed to be improved, and it was clear that the rates of oxidative degradation, metal corrosion, and thermal degradation of the CO2 rich lower phase were higher than those of the CO2 lean upper phase. The capital cost and operational capture cost of the DETA/DEEA biphasic process were approximately $107.8/t CO2 and $31.6/t CO2, respectively, which were 2.5% and 36.4% lower than those of the MEA process. These findings provide a theoretical basis for the industrial application of DETA/DEEA.

Energy-efficient non-aqueous biphasic solvent for carbon capture: Absorption mechanism, phase evolution process, and non-corrosiveness

High latent heat and corrosivity related to H2O inhibit the application of aqueous biphasic absorbents for CO2 capture. An energy-efficient non-aqueous biphasic solvent DETA-EG-PMDETA (D-E-P) was developed with EG-assisted CO2 absorption, interesting phase-transition behavior, and non-corrosiveness. EG could increase the absorption capacity through direct alcoholysis of carbamate and the complex reaction among EG, DETA, and CO2. When EG:PMDETA = 3.5:6.5, the CO2 saturated loading was as high as 2.02 mol/mol. Unlike common biphasic solvents, flue gas saturated-absorbent presented a denser CO2-rich phase with larger CO2 loading (6.01 mol/L) and smaller volume (26.7%), and more convenient homogeneous desorption, whereas the pure CO2-saturated absorbent exhibited an EG-diluted CO2-rich phase (4.34 mol/L, 43.5%) and heterogeneous desorption. Benefiting from low vapor pressure, vaporization enthalpy, and heat capacity of EG, and greatly reduced regeneration volume, the Qlatent (0.0208 GJ/t CO2) and Qsen (0.12797 GJ/t CO2) were considerably decreased, resulting in a regeneration energy of 1.87 GJ/t CO2. It's significantly lower than 30 wt% MEA and other aqueous biphasic absorbents. In addition, because the carbamate hydrolysis and CO2 hydration could not take place in non-aqueous absorbent, the content of H+ was considerably limited, leading to a non-corrosive feature, and the corrosion rate was only 3.70 E−3 mm/a.

Towards estimation and mechanism of CO2 adsorption on zeolite adsorbents using molecular simulations and machine learning

The earth's average temperature is being elevated owing to burning of fossil fuels, explicitly releasing enormous amounts of CO2 into the atmosphere. Therefore, effective collection strategies are needed to minimize the concentration of CO2. The current work presents use of molecular simulations to examine CO2 adsorption on zeolites from the zeolite database. Among the 218 zeolites, the Linde Type A zeolite (LTA) stands out as the best for CO2 adsorption with a percentage weight of 69.88% at 298 K and 1000 kPa. This calculated value is in agreement with a recent experimental study that reported 63.65% at 298 K and 0.1 MPa, indicating that our model could be reliable in predicting the CO2 loading capacity. The structural features of the zeolites were also calculated and their significance on CO2 adsorption, evaluated using a machine learning algorithm. Gravimetric surface area seemed to be the most significant structural features. Hence, its feature engineering may expedite adsorption of CO2. Quantum chemical calculations were further used to provide insights into the sorption mechanisms, whereby it is thermodynamically favorable for CO2 to adsorb through carbon bonding as opposed to dissociative adsorption or hydrogen bonding. Finally, the effect of doping the zeolites with selected cations on the loading capacity was investigated, whereby doping LTA with lithium significantly improved the adsorption of CO2.