Chemical Absorption Of CO2 Research Articles

CO2 absorption performance of biogas slurry enhanced by biochar as a potential solvent in once-through CO2 chemical absorption process

Carbon capture, utilization, and storage (CCUS), offers a promising avenue for mitigating CO2 emissions, in which the big challenge is the high CO2 capture cost. A novel CCUS technology called once-through CO2 chemical absorption using biogas slurry, could potentially reduce the CO2 capture cost through decreasing the energy consumption greatly during CO2 capture. This technology, however, is constrained by the CO2 absorption capacity of biogas slurry. To enhance the CO2 capture capacity of this innovative technology, we proposed a method to enhance CO2 absorption by integrating biochar into biogas slurry. Results indicated that the CO2 absorption capacity of biogas slurry improved by biochar varied with the type of biochar adopted. Among all the investigated biochar, the wood biochar like sea buckthorn and sand willow exhibited the lowest CO2 capture enhancement, with 0.82±0.19 mmol/g and 0.81±0.30 mmol/g, respectively. Biochar from C4 plants like corn stalks and cobs demonstrated the highest enhancement, with 2.11±0.24 mmol/g and 2.47±0.86 mmol/g, respectively. The enhancement driven by C3 plant biochar like millet stalks and shells was intermediate, with 1.62±0.47 mmol/g and 1.62±0.46 mmol/g, respectively. The primary factor for promoting CO2 absorption in the biochar-based biogas slurry was the increase in pH of biogas slurry. The total pore volume of biochar was the principal material property that enhanced CO2 absorption, followed by the EC and BET surface areas of biochar. Increasing the carbonization temperature of biochar could also enhance the CO2 absorption capacity by biogas slurry. In CO2-rich biochar-based biogas slurry, CO2 primarily existed as HCO3− and carbamate. However, for the influence of the biochar's pore structure, CO2 in the CO2-rich biochar-based biogas slurry was more stable than that in CO2-rich biogas slurry.

Computational modelling and optimization of physicochemical absorption of CO2 in rotating packed bed

AbstractThe current study developed a novel computational fluid dynamics (CFD) model that accounted for both physical and chemical absorption in the multiphase flow and captured the relative dominance of chemical absorption over physical by employing a tunable model parameter ‘enhancement factor’. The CFD model was validated against experimental data in a rotating packed bed, and then the validated model was used to investigate the effect of operational parameters such as rotational speed, monoethanolamine (MEA) concentration, inlet velocity, and MEA‐packing contact angle on the physiochemical absorption. The significance of each operational parameter was then evaluated by the ANOVA analysis, which inferred that the enhancement factor is sensitive to rotational speed, MEA concentration, inlet velocity, and contact angle. The p‐value of MEA concentration and inlet velocity was less than 0.05, which implies that these two variables are the most significant variables for the chemical absorption of CO2. The response surface methodology (RSM) and the artificial neural network (ANN) were also employed to develop the predictive model for the enhancement factor. Among the employed techniques, ANN resulted in R2 closer to 0.99 and could better predict the enhancement factor. The modelling approach and findings of the current study are useful in optimizing the operation of rotating packed‐bed reactor (RPB) for CO2 absorption on the industrial scale.

Waste heat recovery in carbon capture process using a novel amphipathic inorganic membrane

To reduce the CO2 regeneration heat requirement in the CO2 chemical absorption process, a novel amphipathic ceramic membrane-based transport membrane condenser was developed in this study to act as a heat transfer medium in the rich solvent-split mechanism for enhancing the waste heat recovery performance from the stripped gas (i.e., mainly the gas mixture of CO2 and water vapor). Both hydrophobic and hydrophilic segments coexisted on one membrane surface of amphipathic ceramic membrane, while the other surface was totally hydrophilic. The surface characterization and waste heat recovery performance of the flat sheet amphipathic membrane were investigated, and the original hydrophilic ceramic membrane was adopted as the control. Results showed that the water contact angle with 108.9 ± 4° was screened for the hydrophobic surface of the ceramic membrane to achieve the best waste heat recovery performance. Additionally, the waste heat recovery performance of amphipathic membrane firstly increased and then dropped with an increase in the area ratio of hydrophobic surface to the total membrane surface. The maximum waste heat recovery of 13.39 MJ/(m2·h) was achieved at a hydrophobic area ratio of 37.5 % without segmenting by the hydrophilic surface, which was 5.6 % higher than that of the original hydrophilic ceramic membrane. Furthermore, the maximum water recovery of amphipathic membrane was 8.24 % higher than the original hydrophilic ceramic membrane. When the total area of hydrophobic surface was fixed, dividing the hydrophobic surface into two equally sized hydrophobic segments spaced by the hydrophilic segments could further improve the waste heat recovery performance of amphipathic membrane. This study might provide a new insight on improving the waste heat recovery performance of ceramic membrane.

Deciphering the transfer mechanisms for CO2 absorption into binary blended solutions

A thorough understanding of the mechanisms involved in CO2 chemical absorption is crucial for the development of efficient CO2 capture technologies. Due to the insufficient insight into the interaction mechanism of different components in blended solutions, CO2 absorption reactions were often categorized as unidirectional transfer between absorption products. In this study, the CO2 absorption performance of binary blended solutions, including piperazine (PZ)/n-methyldiethanolamine (MDEA), ethanolamine (MEA)/MDEA, ammonia (NH3)/MDEA, PZ/potassium carbonate (K2CO3), and NH3/K2CO3, was investigated using a combination of experimental and computational methods. The CO2 absorption mechanisms of “competitive reaction”, “transfer reaction” and “parallel reaction” in the binary blended solution system were proposed. Kinetic experiments revealed that different blended solutions had varying impacts on the process of CO2 absorption. Among them, PZ/MDEA and MEA/MDEA solutions reduced the absorption rates by an average of 8% and 25%, respectively, compared to PZ or MEA component solutions. NH3/MDEA and PZ/K2CO3 solutions had absorption rates similar to those of single NH3/PZ component solutions. NH3/K2CO3 solutions, on the other hand, exhibited an average increase of 17% in absorption rates compared to NH3 solutions. Quantum mechanical (QM) methods were employed to evaluate of the absorption products and key processes in terms of kinetics and thermodynamics. Quantitative 13C NMR analyses were conducted to further investigate the interactions between components and the pathways of mass transport in blended solutions, which demonstrated proton transfer and CO2/-COO transfer between adsorption products. This study highlights an accurate description of the transfer mechanisms of various blended systems for the enhanced CO2 capture.

Experimental and theoretical investigation of CO2 solubility in amine-based deep eutectic solvents

Deep eutectic solvents (DESs) have appealed increasing research interest across various scientific and industrial applications, notably in relation to efforts in CO2 capture. This study presents a novel series of DESs were synthesized on the basis of monoethanolamine (MEA) and N-methyldiethanolamine (MDEA) as hydrogen bond donors with tetrabutylammonium bromide (TBAB) and tetrabutylphosphine bromide (TBPB) salt as hydrogen bond acceptors. A gas solubility measurement experimental system based on pressure drop method has been established to evaluate the solubility of CO2 in amine-based deep eutectic solvents. The evaluation was performed over a temperature range of 303.15 to 323.15 K and a pressure range of 100 to 1000 kPa. The results indicated that as the molar ratio of hydrogen bond donors increases, the solubility of CO2 in DESs increases, while it was found to be less affected by the hydrogen bond acceptor. Of these, the solubility of CO2 is strongest at a 1:10 molar ratio of TBAB and MEA. The nuclear magnetic resonance spectroscopy spectra (NMR) and FTIR spectroscopy revealed that the MEA-based DES mixture primarily exhibited chemical absorption of CO2, while the MDEA-based DES predominantly showed physical dissolution of CO2. In addition, it was observed that both temperature and pressure significantly influenced the CO2 solubility, and a successful correlation was developed using different semi-empirical models.

Two Different Pathways from CO2 to HCO3− in Aqueous Solutions of Arginine Sodium Salt

AbstractAmino acids and their salts are amine compounds with great potential for the chemical absorption of CO2 via the amine method. The CO2 absorption properties of various amino acids and their salts have been previously reported. However, the detailed reaction mechanism of CO2 with basic amino acids in aqueous solutions has not yet been clarified. In this study, we focused on arginine (Arg), which has the highest basicity among the standard amino acids, and its monohydrochloride (ArgCl) and sodium (NaArg) salts for the dissolution of CO2 in the aqueous solutions of Arg, ArgCl, and NaArg. CO2 was chemically dissolved in aqueous Arg and NaArg solutions but not in the aqueous ArgCl solution. One‐dimensional 1H and 13C and two‐dimensional 1H‐13C heteronuclear multiple bond correlation nuclear magnetic resonance spectroscopy indicated that the final products in the aqueous Arg and NaArg solutions were protonated Arg and HCO3−. HCO3− was formed from both CO2‐bonded Arg/Arg− and CO32− intermediates in the aqueous NaArg solution but only from the CO2‐bonded Arg/Arg− intermediate in the aqueous Arg solution. In addition to their high environmental and biological compatibility, Arg and NaArg exhibit high CO2 absorption capacity, demonstrating their potential for practical use as naturally derived CO2 chemical absorbents.

Prediction of CO2 absorbing performance of amine aqueous solution using random forest models

Designing an amine(s) solution for the chemical absorption of CO2 for carbon capture, utilization and storage is a significant challenge. To accelerate the development of high-performance amine solutions, a method for predicting the CO2 loading of amine(s) solution is studied. Available literature data are curated (45 amines, 3151 data points), and random forest regression is conducted using the data with descriptors calculated using HSPiP or RDkit software. The CO2 loadings of single amine aqueous solutions are regressed with high accuracy (R2 = 0.943, RMSE = 0.072–0.073 for the validation data). Feature importance analysis suggests that the partial charge of atoms in the amine is an important descriptor, as well as process parameters such as CO2 partial pressure and temperature. Based on the analysis, a simpler descriptor list is developed with temperature, CO2 partial pressure, and partial charges of N atoms calculated by density functional theory. CO2 loading of a single amine solution is regressed with an accuracy comparable to that of the above models (R2 = 0.931, RMSE = 0.079) with only 5 descriptors. Moreover, data including both single and blended amine solutions are regressed with high accuracy (R2 = 0.944, RMSE = 0.073) with only 8 descriptors. The generalization performances of the models are evaluated using the leave-one-group-out procedure. Although some outliers exist, the overall trend of almost all amines can be predicted using the procedure in this study.

Process simulation and optimization for post-combustion CO2 capture pilot plant using high CO2 concentration flue gas as a source

This work mainly focuses on process simulation and optimization of a high-concentrated CO2 chemical absorption process using aqueous amine solutions based on both pilot plant data and process modeling. To optimize operating parameters for reducing energy consumptions, this study explores the influence of process structure and operational parameters on the product purity, capture rate, and energy consumption, which would provide theoretical and technical support for optimizing high-concentration CO2 capture. At first, the rate-based absorption/desorption models are established and well-verified by a total of 25 sets of pilot plant data, which shows high accuracy for reliable model predictions. Under an annual absorption capacity of 50 tons at a 90% capture rate and 95% product purity, the optimal case using Monoethanolamine (MEA) solution shows an increased CO2 capture rate of 12.37% and a decreased unit energy consumption of 22.5%. After flowsheet optimization, a new system of blended MEA, Methyl diethanolamine (MDEA), and 2-Amino-2-methyl-1-propanol (AMP) solution is designed to capturing high-concentrated CO2 under the same conditions. Compared with the MEA system, its specified energy consumption is reduced by 10.35% and its CO2 capture capacity increases by 11.6 tons annually.

Structure effects of imidazolium ionic liquids on integrated CO2 absorption and transformation to dimethyl carbonate

The integration of chemical absorption of CO2 and in situ transformation to highly valuable chemicals is a promising process as an alternative toward fossil fuels. Here, three imidazolium ionic liquids (ILs), 1-butyl-3-methylimidazolium acetate, 1-butyl-3-methylimidazolium 1,2,4-triazole ([Bmim][Tz]), and 1-butyl-2,3-dimethylimidazolium 1,2,4-triazole were synthesized to absorb and activate CO2 by the formation of CO2-adducts, which can be in situ converted into dialkyl carbonates with alcohols (ROH, R = CH3, C2H5, and C4H9) in solvent diiodomethane under ambient temperature and pressure. The results show [Bmim][Tz] exhibits the best CO2 absorption capacity and dimethyl carbonates (DMC) yield, where CO2 capacity is up to 0.216 gCO2/gIL and DMC yield (based on methanol) is as high as 20.2 %. The structures of imidazolium ILs have significant effects on the absorption of CO2 and subsequent transformation process. Fourier transform infrared and carbon nuclear magnetic resonance spectroscopies demonstrate ILs structures influence binding sites for CO2 absorption, which can combine with CO2 to form CO2-adducts, zwitterion [Bmim-CO2], and [Tz-CO2]−. Furthermore, density functional theory calculations verify the structure effects (binding sites and steric hindrance) of ILs on the activation of CO2 and methanol, through the elongated CO bond lengths of CO2-adducts and O-H bond lengths of methanol in IL-methanol complexes, respectively, leading to different DMC yields. The integrated process is promising for the energy-efficient capture and utilization of CO2 under ambient conditions.

Study on design strategies and on new structure-performance relationships for CO2 capture in gas-liquid hollow fiber membrane contactors

The urgent need for carbon dioxide (CO2) capture technologies motivates this chemical engineering study, which systematically investigates the influence of macroscopic and microscopic structure on the CO2 absorption performance of hydrophobic alumina (Al2O3) hollow fiber membrane (A-HFMs) contactors. Six different A-HFMs prepared using the non-solvent-induced phase separation (NIPS) method with select solvents followed by sintering at 1300°C were then tested for chemical CO2 absorption in an A-HFM contactor using a monoethanolamine (MEA) solution. The hydrophobicity of the coatings applied on the A-HFM surfaces was confirmed by the water contact angle and thermogravimetric (TGA) analysis. Pearson's statistical analysis of a correlation matrix revealed the strength of relationships between nine variables, including outer diameter (mm), inner diameter (mm), percentage of sponge layer (%), pore size (nm), maximum pore size (nm), mechanical strength (MPa), surface porosity (m−1), overall porosity (%), and CO2 absorption flux (mol m−2 s−1). Building upon these findings, this study unveils a novel non-linear function linking three specific microscopic characteristics— pore size, surface porosity, and a geometric sponge layer factor—to CO2 absorption flux, offering valuable insights for optimizing hydrophobic A-HFM design and enhancing CO2 capture efficiency. The A-HFM, characterized by the combination of three factors (higher pore size, increased surface porosity, and a thicker sponge layer), achieved a CO2 absorption flux of 6.36 ×10−3 mol m−2 s−1 at room temperature, showcasing its exceptional performance in capturing CO2. The resulting empirical morphological factor provides a novel approach for enhancing the performance of CO2 absorption through A-HFM design optimization.

Adopting green absorbent for CO2 capture and agricultural utilization: Biogas slurry and biomass ash case

Previously, the once-through CO2 chemical absorption process by biogas slurry was experimentally verified to offer the unique advantages like low energy consumption, cost-effectiveness, and feasibility of CO2 fixation in plants. However, this technology also faces some challenges and limitations, including a low CO2 absorption rate and performance. To improve the effectiveness and reliability of this innovative carbon capture, utilization, and storage (CCUS) technology, this study proposes a novel method to enhance the CO2 absorption performance without affecting agricultural applications of CO2 by mixing biogas slurry with biomass ash as the green CO2 absorbent. The results indicate that when the solid-liquid mass ratio of biomass ash to biogas slurry is 5:10, the CO2 loading of the biomass ash and biogas slurry mixture (BA-BS) reaches 936.7 ± 59.1 mmol/kg. Furthermore, the pH of the BA-BS remains stable at 6.9, meeting the rhizosphere pH requirements for plant cultivation. The CO2 absorption of the BA-BS liquid phase, referred to as improved biogas slurry (IBS), reaches its maximum at 230.4 ± 3.5 mmol/L, which is 126.8% higher than that of the unimproved biogas slurry. The nitrogen content in the BA-BS solid phase, calling improved biomass ash (IBA), also reaches its maximum at 4.24 ± 0.74 mg/g, thereby expanding the agricultural utilization of biomass ash. The most reasonable and effective way of utilizing CO2-rich mixed biogas slurry and biomass ash involves use IBA as the base fertilizer for tomato cultivation, supplemented later with IBS to promote growth. This optimal application allows for substantial utilization of CO2, introduced into the tomato cultivation environment by IBA and IBS. The carbon fixation of a single tomato has improved by 108.2%. This study thus provides a feasible solution for high-value negative carbonization of biogas slurry and biomass ash.

Dynamics of Taylor bubble under chemical reaction enhanced mass transfer in minichannel

Taylor bubble dynamic characteristics of CO2 chemical absorption into MEA aqueous solution in a vertical minichannel were systematically investigated in this study. The generation, movement, and shrinkage of bubbles in the minichannel were visualized and monitored using a high-speed camera, and their dynamic behaviors were characterized by image analysis method. The effects of gas and liquid Re numbers and absorbent concentration on two-phase flow patterns, bubble generation frequency, initial bubble length, bubble length decrease rate, and bubble velocity were examined and analyzed. Results showed that chemical reaction-enhanced mass transfer hindered the bubble cap penetration into the main channel, and alleviated the bubble neck thinning, both effects inhibiting the bubble generation. A new Damköhler number (Da)-based correlation has been proposed to predict the initial Taylor bubble length, showing good prediction accuracy for experimental data in the literature using different absorbents. Results also showed that before the formation of sphere bubble at the end of absorption, an approximate linear relationship exists between bubble length decrease rate and bubble velocity, with the slop decided by chemical reaction rate that could be characterized by the Da number. Finally, a simple model has been developed to determine the effective channel length at a given operating condition, providing design guidelines for microchannel-based miniaturized CO2 absorbers.

Experimental study on single CO2 bubbles freely rising in MEA/DEEA blended solutions: Bubble behavior and mass transfer

CO2 absorption into amine solutions is an important method for reducing carbon emissions. The influence mechanism of chemical reactions on the bubble behavior and mass transfer needs to be comprehensively investigated. In this study, firstly, we measure the bubble behavior and mass transfer of single CO2 bubbles freely rising in monoethanolamine (MEA)/N,N-diethylethanolamine (DEEA) blended solutions and DEEA solutions by high-speed photography. Moreover, we investigate the effect of amine concentration on the bubble shape, aspect ratio, rising trajectory, rising velocity, and mass transfer coefficient. The results show that CO2 bubbles in MEA/DEEA blended solutions experience significant shape deformation, oscillation damping, surface contamination, and mass transfer deterioration. In contrast, CO2 bubbles in DEEA solutions behave similarly to those in ultrapure water, i.e. negligible surface contamination and mass transfer enhancement. Furthermore, we consider the differences in the bubble behavior and mass transfer from the viewpoint of the chemical reaction kinetics and bubble surface contamination degree. The location where a chemical reaction occurs is close to the bubble surface with a fast reaction, and as a result, the bubble surface is likely to be contaminated. Finally, this study provides insights into the intensification of amine-based CO2 chemical absorption processes.

Direct Esterification of Alkylcarbamic Acids with Alcohols over CeO2 Catalyst.

Alkylcarbamic acids, which are easily produced via chemical absorption of CO2 into amines, have a great potential to be substrates for producing value-added chemicals. In this research, the esterification of various alkylcarbamic acids with alcohols into alkyl N-alkylcarbamates was demonstrated by using a heterogeneous catalyst as well as the corresponding amine additives. In the model reaction, the esterification of benzylcarbamic acid (BZA-CA) and methanol (MeOH), the target product of methyl N-benzylcarbamate was obtained in 64 % CO2 -based yield at 413 K in 12 h over a CeO2 catalyst, which also exhibited good reusability. In this catalytic system, the corresponding amine additive (i. e., benzylamine for BZA-CA) had the important role in the improvement of CO2 -moiety-based balance, allowing the precise kinetic study, in contrast to the cases without such additive. The detailed kinetic study on the target catalytic system and control systems suggested that BZA-CA underwent the esterification by MeOH directly. The current catalytic system using the combination of CeO2 catalyst and corresponding amine additive was also demonstrated to be applicable to the synthesis of alkyl N-alkylcarbamates from alkylcarbamic acids and alcohols with short, linear alkyl chains (≤C3 ).

Improved prediction of reaction kinetics for amine absorbent-based carbon capture using reactive site-based transition state conformer search method

There is no doubt that carbon emissions are one of the greatest challenges facing humanity today. Carbon capture, utilization, and storage is an effective way to achieve carbon neutrality. However, the commonly used commercial absorbents for post-combustion captures still have some limitations such as low chemical absorption rate constants. In this paper, a universal reaction kinetic model is developed for amine-based carbon capture based on the transition state theory, density functional theory, and hybrid solvation model. The developed reaction kinetic model is applicable to a wide range of amine-solvent solutions involving primary/secondary/tertiary amines and aqueous/nonaqueous solvents. The key contribution of this work is developing a reactive site-based search method for the GENeration of Conformers for Transition States (GENConf-TS). GENConf-TS has greatly improved the prediction accuracy of the reaction kinetic model from R2 = 0.882 to R2 = 0.950 based on a dataset of 23 various amine-solvent solutions. The results highlight the critical impacts of the transition state conformational isomers on amine-based CO2 chemical absorption rate constants.

Target-specific modification of diethylenetriamine with hydroxyalkyls: Efficient absorbents for CO2 capture

Chemical absorption of CO2 by amine solutions is an industrialized operation and currently represents the most practical technology worldwide. However, the development of amine absorbents with high efficiency and energy-saving benefits remains a major challenge. Here, we developed a novel class of amines through the target-specific modification of the secondary amine group in diethylenetriamine (DETA) with various hydroxyalkyls. The obtained amines present enhanced overall efficiency for CO2 capture, especially with regards to the absorption/desorption rates and recyclability. Significantly, the regeneration energy consumption for the developed amines can be reduced to a remarkable low value of 2.78 GJ t-1 CO2. Moreover, the CO2 absorption and desorption processes were closely monitored by nuclear magnetic resonance (NMR). Combined with density functional theory (DFT) calculations, the mechanism of the developed amine for CO2 capture was fully elucidated. This targeted modification strategy provides a new avenue for the development of efficient amine absorbents for practical CO2 capture.

Research of novel polyamine-based biphasic absorbents for CO2 capture using alkanolamine to regulate the viscosity and mechanism analysis

Biphasic solvent has attracted widespread attention in CO2 chemical absorption technology due to its significant potential for reducing capture energy consumption. However, the high viscosity of CO2-rich phase after phase split could lead to issues such as high flow resistance, low heat transfer efficiency, and phase separation instability in application. To address these limitations, a strategy of using alkanolamine as a viscosity regulator for biphasic solvents was proposed. Diethanolamine(DEA), an alkanolamine regulator, was introduced to a system of polyamine/amide absorbent, and then a novel biphasic solvent of diethylenetriamine (DETA)/diethanolamine(DEA)/N, N-Dimethylacetamide(DMAC)/water(H2O) was developed. The viscosity of the CO2-rich phase solvent was reduced to 19.02 mPa⋅s, a significant decrease compared to the solution without DEA regulation. The novel solvent exhibited a high cyclic capacity of 2.08 mol/kg, which was 43.4 % higher than that of the solution without DEA, and a desorption rate twice as high as 30 wt% monoethanolamine(MEA). Quantitative 13C Nuclear Magnetic Resonance (NMR) and Molecular Dynamics (MD) simulations revealed the phase split and viscosity regulation mechanisms. It was proved that DETA species, especially carbamates, tend to self-aggregate with each other due to intermolecular hydrogen bonding with the CO2 loading increases, which leads to phase split and high viscosity of the saturated solution. Through DEA regulation, the protonation of carbamates and the generation of HCO3–/CO32– were promoted, which weakened the self-aggregation of carbamates species, decreasing the viscosity and the regeneration energy of saturated CO2-rich phase solution. The regeneration energy reached 2.19 GJ/ton CO2, which exhibited a 42.4 % reduction compared with that of 30 wt% MEA.

A combined genetic algorithm and active learning approach to build and test surrogate models in Process Systems Engineering

In Process Systems Engineering, computationally-demanding models are frequent and plentiful. Handling such complexity in an optimization framework in a fast and reliable way is essential, not only for generating meaningful solutions but also for providing decision support. Indeed, optimization results need to be obtained efficiently without compromising accuracy or solution quality. Surrogate models are a cheap way of replacing complex ones, while still capturing the intrinsic features that make them unique and valuable. In this work, a methodology to build surrogate models is developed. It combines a genetic algorithm with an active learning method, harvesting the benefits of both approaches — on the one hand leveraging nature-inspired optimization procedures that explore the optimization space area, and conversely a ‘smart’ approach to adding meaningful sample points to the training stage. The methodology, coined GA-AL, is tested and validated for chemical absorption of CO2 in a biogas mixture inserted in a utility superstructure framework. Nine surrogate modes are tested, with Artificial Neural Networks, Random Forest and Kringing outperforming other approaches, assessed via four performance criteria.

Organic-inorganic composite membrane-based transport membrane condenser: Performance of waste recovery from hot gas mixture of CO2 and water vapor

Recovering the waste heat from the stripped gas (i.e., the gas mixture of CO2 and water vapor) using the transport membrane condenser is an effective approach to reduce the regeneration heat consumption in CO2 chemical absorption process. To decrease the capital expenditure of transport membrane condenser, this study prepared an inexpensive organic–inorganic composite membrane through adding the hydroxylated boron nitride (BN-OH) into the polyvinylidene fluoride (PVDF) during membrane preparation via nonsolvent induced phase separation. Then the composite membrane was placed in a membrane cell as the transport membrane condenser to recovery the waste heat of simulated stripped gas. The results showed that when compared to the single PVDF membrane, the addition of BN-OH improves the pore uniformity, thermal conductivity, and porosity of membrane. Among all the prepared composite membranes, the composite membrane adding 5 wt% nano-sized BN-OH particles exhibits the best waste heat recovery performance. Furthermore, a decrease in the membrane thickness in addition to an increase in polyvinylpyrrolidone dosage during membrane preparation enhances the waste heat recovery performance, however deteriorates the mechanical strength of membrane. Moreover, the organic–inorganic composite membrane prepared in this study demonstrated a good stability of waste heat recovery performance during a long-term operation, showing a potential in the rich solvent-split modified carbon capture process to achieve a low capital expenditure and a high waste heat recovery performance.

Effects of structures of lower aliphatic alcohols and concentrations on CO2 chemical absorption and desorption reactions in various alcohol solutions of 1,8-diazabicyclo[5.4.0]undec-7-ene

Alcohol solutions of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) have received considerable interest as chemical absorbers of CO2 and switchable solvents because of their reversible reaction with CO2 and the polarity change triggered by CO2 absorption/desorption. However, there have been only a few systematic studies on the CO2 absorption and desorption behaviors of DBU–alcohol solutions. In this study, we determined the solubility of CO2 in binary solutions of DBU and various lower aliphatic alcohols at different temperatures. Except for the 2-methyl-2-propanol solution, which showed very low reactivity with CO2, all the DBU–alcohol solutions exhibited almost the same solubilities of CO2 at 298.2 K, independent of the alkyl groups present on the alcohols. However, their solubilities varied with DBU concentration. Moreover, we examined the amounts of CO2 recovery from the CO2-saturated solutions at high temperatures up to 393.2 K or the boiling points. The amount of CO2 per mole of DBU desorbed by heating was markedly influenced by both the alkyl group on the alcohols and the DBU concentration, indicating that at the studied concentrations, the temperature dependence of CO2 solubilities is strongly affected by the type of alcohol. To clarify this unique desorption behavior, we measured the 1H, 13C, and 15N nuclear magnetic resonance spectra of the DBU–alcohol solutions with and without CO2 at 298.2 K. In the absence of CO2, the nitrogen atoms at the 8-position of the DBU molecules strongly interact with the hydroxyl hydrogen atoms of the alcohol molecules via hydrogen bonding. As the DBU–alcohol solutions were saturated with CO2, the formation of protonated DBU ([DBUH]+) and alcohol-CO2 adduct (alkyl carbonate, [ROCO2]–) was confirmed. [DBUH]+ is stabilized by the solvation of free alcohol molecules, and the reverse reaction of [DBUH]+ with [ROCO2]– for CO2 release is hindered. Our findings are beneficial for designing and tuning DBU–alcohol systems for CO2 separation.