CO2 Loading Research Articles

Unraveling the influence of CO2 and Ce loading over ZSM-5 for oxidative dehydrogenation of propane

Utilization of CO2 as a soft oxidant for oxidative dehydrogenation of propane to propene (ODHP) is of great importance to attain net-zero carbon emissions and to reduce greenhouse gases contributing to global warming. Here, Ce was impregnated into ZSM-5 (denoted as CZ-5 catalyst) to enhance the C3H8 conversion and C3H6 selectivity due to the redox properties of Ce to activate CO2 into CO and O* and induce propane bond cleavage (C-H). After characterization of the catalyst’s physicochemical properties, NH3-TPD and pyridine IR analysis revealed that introducing Ce regulates the acidic properties of ZSM-5 catalysts by increasing the number of Lewis acid sites while simultaneously decreasing the amount of Brönsted acid sites. The increment in Lewis’s acid sites considerably improved the C3H6 selectivity. The oxygen transfer from Ce4+ to Ce3+ during the reaction also contributed to the outstanding performance of the 12 %CZ-5 catalyst. Regarding optimum conditions, 2 % CO2 concentration and 12 % Ce loading were the optimum amount of oxidant and Ce content that produce the highest C3H6 yield of 34.08 %. The catalytic effectiveness and stability were preserved despite several hours of propane conversions at 550 °C. Therefore, modifying ZSM-5 with Ce could be a feasible way for improving propene selectivity and catalyst stability for ODHP.

Functional ionic liquid as phase separation trigger in biphasic absorption of CO2

An amino acid based ionic liquid ([N1111][Ala]) was employed as a trigger to start the phase separation of 2-(2-aminoethylamino) ethanol (AEEA) and 1-ethylimidazole (Eim) solutions (AEH) and to enhance CO2 capture. Due to the accompanying phase change, the CO2 load of AEEA-Eim-H2O-[N1111][Ala] (AEHI) is 1.47 times higher than that of AEH. The interaction mechanism between AEHI and CO2 was elucidated by spectroscopic analysis and molecular simulation. The water-shell layer around [Ala]–CO2 and hydrogen-bonding were first proposed and demonstrated to be the key reasons for the phase separation. The formation of the water-shell layer expelled Eim from the rich phase and thus facilitated the proton transfer process, which not only accelerated the phase separation process but also reduced the regeneration energy consumption. After successive absorption–desorption cycles, the CO2 uptake decreased slightly. The innovative mechanism provides important guidance for the design of excellent biphasic absorbents with good performance and low energy consumption.

Evaluation of the effect of water on CO2 absorption in AMP and DMSO systems

Non-aqueous precipitating amine systems for carbon capture allows for CO2 desorption at lower temperatures than conventional aqueous amine systems and can potentially reduce the energy requirement for regeneration. In this work, the influence of water accumulation that may arise from humid gases entering the absorption column was investigated for absorption systems containing 2-amino-2-methyl-1-propanol (AMP) and dimethyl sulfoxide (DMSO). The physical solubility of CO2 decreased with increasing water concentration, as expected from the lower solubility of CO2 in water than in DMSO. The CO2 loading capacity was increased with the addition of water, resulting from formation of bicarbonate with water present in the system. Low lean loadings of 0.1 mol CO2/mol AMP and precipitation was observed in 23 wt% AMP/DMSO with 9 wt% added water, suggesting that some water accumulation might be tolerable while still maintaining the desired properties of the absorption system. NMR was used to study the CO2 reaction products at 30–88 °C. The results suggested that 88 °C can be used for regeneration of the system even with water accumulated in the system. At 80 °C formation of the tentatively assigned species 4,4-dimethyl-1,3-oxazolidin-2-one was observed, indicating that thermal degradation of AMP may occur above this temperature.

Research on CO2 capture performance and reaction mechanism using newly tetraethylenepentamine (TEPA) + monoethanolamine (MEA) mixed absorbent for onboard application

Large–scale CO2 emissions have raised international concerns as they lead to global temperature rise. Consequently, mitigating CO2 emissions has emerged as a central focus of interdisciplinary research. Although onboard carbon capture technology proves effective in reducing a ship's CO2 emissions, challenges persist in the form of high desorption energy consumption and low CO2 loading of the absorbents. In this study, a novel polyamine–based mixed amine system based on marine engine exhaust CO2 capture technology has been developed to reduce desorption energy consumption and enhance CO2 loading. Additionally, the reaction mechanisms of CO2 with polyamine–based mixed amine were investigated using a combination of quantum chemical calculations and nuclear magnetic resonance (NMR) techniques. The results indicated that compared to monoethanolamine (MEA) with the same mass fraction, the CO2 loading of the new mixed absorbent tetraethylenepentamine (TEPA) + MEA increased by 7 % and the desorption heat duty reduced by 18.1 %. The analytical approach results showed that in the case of 7.5 wt% TEPA + 7.5 wt% MEA solution, proton transfer was predominantly governed by TEPA, whereas MEA primarily engaged in the reaction with CO2. During desorption at 368 K, the released CO2 primarily arose from HCO3− and CO32−. These findings hold academic and practical significance for the advancement of more efficient carbon capture technologies in maritime applications.

Corrosion Investigation of Carbon Steel in Different Amine-Based CO2 Removal System

The steel industry is a major source of CO2 emissions, which is affecting the corrosion behavior of carbon steel. The corrosion behavior of carbon steel (C1018) absorbed for CO2 removal is examined in different blends of amine solution by adding a heat-stable salt neutralizer and increasing amine concentration. Corrosion of carbon steel using different methyldiethanolamine (MDEA)/ (5% piperazine amine solution) which had 26% amine solution that contained heat stable amine salts treated with neutralizer at 80 °C and CO2 loading was investigated. The effect of the treated solutions on the corrosion behavior was observed using either the K2CO3 treatment solution to reach 30% amine or increasing the concentration to 33% amine solution using weight loss, potentiodynamic polarization, cyclic voltammetry, and impedance measurements. A visual examination of the corroded samples of the different amine solutions was performed. XRD for phase identification and SEM for microstructure examination were used to describe the corroded surfaces and analyze the corrosion products on the specimen surfaces under different conditions. After nine days in the 30% amine solution, these analyses showed the formation of the FeCO3 protective layer. The carbon steel in 30% amine solution provides better protection, and the lowest corrosion resistance (39.9 µm/Y).

Adsorption Characteristics of CO2/CH4/H2S Mixtures in Calcite Nanopores with the Implications for CO2 Sequestration

Summary Injecting CO2 into reservoirs for storage and enhanced oil recovery (EOR) is a practical and cost-effective strategy for reducing carbon emissions. Commonly, CO2-rich industrial waste gas is used as the CO2 source, whereas contaminants such as H2S may severely impact carbon storage and EOR via competitive adsorption. Hence, the adsorption behavior of CH4, CO2, and H2S in calcite (CaCO3) micropores and the impact of H2S on CO2 sequestration and methane recovery are specifically investigated. The Grand Canonical Monte Carlo (GCMC) simulations were applied to study the adsorption characteristics of pure CO2, CH4, and H2S, and their multicomponent mixtures were also investigated in CaCO3 nanopores to reveal the impact of H2S on CO2 storage. The effects of pressure (0–20 MPa), temperature (293.15–383.15 K), pore width, buried depth, and gas mole fraction on the adsorption behaviors are simulated. Molecular dynamics (MD) simulations were performed to explore the diffusion characteristics of the three gases and their mixes. The amount of adsorbed CH4, CO2, and H2S enhances with rising pressure and declines with rising temperature. The order of adsorption quantity in CaCO3 nanopores is H2S > CO2 > CH4 based on the adsorption isotherm. At 10 MPa and 323.15 K, the interaction energies of CaCO3 with CO2, H2S, and CH4 are −2166.40 kcal/mol, −2076.93 kcal/mol, and −174.57 kcal/mol, respectively, which implies that the order of adsorption strength between the three gases and CaCO3 is CO2 > H2S > CH4. The CH4-CaCO3 and H2S-CaCO3 interaction energies are determined by van der Waals energy, whereas electrostatic energy predominates in the CO2-CaCO3 system. The adsorption loading of CH4 and CO2 are lowered by approximately 59.47% and 24.82% when the mole fraction of H2S is 20% at 323.15 K, reflecting the weakening of CH4 and CO2 adsorption by H2S due to competitive adsorption. The diffusivities of three pure gases in CaCO3 nanopore are listed in the following order: CH4 > H2S ≈ CO2. The presence of H2S in the ternary mixtures will limit diffusion and outflow of the system and each single gas, with CH4 being the gas most affected by H2S. Concerning carbon storage in CaCO3 nanopores, the CO2/CH4 binary mixture is suitable for burial in shallower formations (around 1000 m) to maximize the storage amount, while the CO2/CH4/H2S ternary mixture should be buried as deep as possible to minimize the adverse effects of H2S. The effects of H2S on CO2 sequestration and CH4 recovery in CaCO3 nanopores are clarified, which provides theoretical assistance for CO2 storage and EOR projects in carbonate formation.

Modeling CO2 loading capacity of triethanolamine aqueous solutions using advanced white-box approaches: GMDH, GEP, and GP

The equilibrium solubility of carbon dioxide (CO2) in the solvents is a key essential characteristic that has to be evaluated for successful absorption-based CO2 capture procedures. In this study, the CO2 loading capacity of triethanolamine (TEA) aqueous solutions was estimated using three famous white-box algorithms namely gene expression programming (GEP), genetic programming (GP), and group method of data handling (GMDH). For achieving the aim of this study, 258 data in a wide range of pressure, temperature, and amine concentration were collected from literature. Temperature, partial pressure of CO2, and amine concentration were used as input parameters. The results demonstrated that GMDH correlation is more accurate than GEP and GP with a determination coefficient (R2) of 0.9813 and root mean square error of 0.0222. The R2 values of 0.9713 and 0.9664 for the GEP and GP, respectively, demonstrated that the GEP and GP also showed accurate predictions. In addition, GMDH approach accurately predicted the anticipated trends of the CO2 loading in response to changes in the partial pressure of CO2 and temperature. The Pearson and Spearman correlation analyses were also incorporated in this research which showed that temperature and CO2 partial pressure have almost the same relative effect on CO2 loading, while amine concentration has the lowest effect on it.

Enhanced capturing of acidic components (CO2/SO2) from Flue gas by MAF-66 produced by a facile and one pot synthetic procedure: Experimental, isotherms and modeling

This study focuses on the synthesis and characterization of MAF-66, a metal-organic framework with excellent adsorption properties for the flue gases containing carbon dioxide (CO2) and sulfur dioxide (SO2) impurities. The sol-gel method was employed using various sources of zinc to approach to the qualified product with the highest yield. The best results were achieved by mixing zinc nitrate solution, ammonia, and amitrol at room temperature, followed by washing the product with methanol at 40 °C and drying it under vacuum conditions at 200 °C. The characterization analyses, confirmed the desired crystalline phase structure of MAF-66, with the specific surface area of 1226 m2/g and pore volume of 0.65 cm3/g. The synthesized material exhibited the presence of N-H functional groups on the surface. Equilibrium adsorption measurements at the two temperatures of 35 and 45 °C showed high loading and selectivity of CO2 and SO2 over nitrogen, at low and moderate pressures. The ideal selectivities of CO2/N2 and SO2/N2 were obtained 194 and 357, respectively, at 35 °C. The isosteric heats of adsorptions were determined as − 25.4 kJ/mol for CO2 and − 36.1 kJ/mol for SO2. The synthesized material demonstrated good stability and reliability during regeneration and reuse, making it suitable for cyclic adsorption-desorption processes in flue gas refining.

Feature analysis of generic AI models for CO2 equilibrium solubility into amines systems

AbstractReported models have disadvantages such as poor prediction accuracy and time‐consuming. And they can not reflect the impact of chemical reactions on CO2 solubility. To compensate for these deficiencies, parameters representing operational parameters, physical properties, chemical properties, and molecular properties are introduced as input variables. A series of models are constructed by three algorithms: back propagation neural network, radial basis function neural network, and random forest. The model with the best prediction performance is level OPCM (RBFNN), with the AARE of only 1.52%. By ranking the importance of the features using the RF algorithm, PCO2, was found to be the key parameter affecting the CO2 loadings, with M being the least important. Using the screened key parameters to model the model, as well as optimizing the structure, can further improve the predictive performance of the model. The full process development and optimization model framework constructed in this article can provide practical guidance for the development of machine learning models.

Experimental and computational study of the thermal degradation of primary amines used in CO2 capture

CO2 loaded amine polymerizes during solvent regeneration at temperatures above 100 °C, resulting in the deterioration of solvent performance. Herein, five primary amines were heated to 120, 135 and 150 °C with CO2 loading of 0.4C/N to study thermal degradation. It was found that 2-amine-1-butanol showed the greatest amine loss of 38.5 % after heating to 135 °C for 672 hrs while 2-amino-2-methyl-1-propanol was most stable with amine loss of 17.4 % under the same conditions. The degradation products were identified and the reaction pathway was studied through density functional theory (DFT) calculation. Furthermore, the transition state for ring closure and opening reactions was analyzed. The ring closure reaction to form oxazolidinones had a higher energy barrier, showing that it was the limiting step. This is further supported by the good agreement with experimental results. The structure–activity relationship showed the strong steric hindrance effect and the methyl group at β-carbon improved the amine stability.

A Coupling Calculation Method of Desorption Energy Distribution Applied to CO2 Capture by Chemical Absorption

The pursuit of low-energy-consumption CO2 capture technology has promoted the renewal and iteration of absorbents for chemical absorption. In order to evaluate the regeneration energy consumption of absorbents and obtain the distribution of energy consumption, a coupling method combining rigorous energy balance and simple estimation is proposed in this study. The data regarding energy balance and material balance from process simulation are transformed into the model parameters required in the simple estimation model. Regenerative energy consumption and distribution are determined by the empirical estimation formula. Two CO2 capture processes of an MEA aqueous solution and MEA–n-propanol aqueous solution (phase-change absorbent) were used to verify the feasibility and applicability of the coupling method. The effects of n-propanol concentration, CO2 loading in the lean solution, and temperature on energy consumption were discussed. The results show that the energy consumption of 30 wt% MEA aqueous solution is the lowest at 3.92 GJ·t−1-CO2 when CO2 load in the lean solution is 0.2 mol CO2·mol−1-MEA, and the reaction heat Qrec, sensible heat Qsen, and latent heat Qlatent were 1.97 GJ·t−1-CO2, 1.09 GJ·t−1-CO2, and 0.86 GJ·t−1-CO2, respectively. The lowest energy consumption of the phase-change absorbent with CO2 loading of 0.35 mol CO2·mol−1-MEA in the lean solution is 2.32 GJ·t−1-CO2. Qrec, Qsen, and Qlatent were 1.9 GJ·t−1-CO2, 0.29 GJ·t−1-CO2, and 0.14 GJ·t−1-CO2, respectively. This study provides a simple and meaningful method for accurately assessing absorber performance and process improvement, which can accelerate the development of economically viable, absorption-based CO2 capture processes.

A mass transfer study of CO2 absorption in aqueous solutions of isomeric forms of sodium alaninate for direct air capture application

Direct air capture (DAC) of CO2 is a critical emerging technology required to achieve ambitious net-zero emissions. Aqueous amino acid absorbents are ideal candidates for DAC and this work describes the investigation of the CO2 absorption performance of sodium salts of β- and α-alaninate under relevant conditions for DAC by utilising synthetic CO2 gas streams at concentrations levels found in the atmosphere (200–600 ppm). The effects of solution concentration, temperature, gas flowrate, liquid flowrate, and dissolved CO2 concentration (i.e., CO2 loading) on CO2 mass transfer coefficients were investigated. The overall mass transfer coefficient was found to be independent of the gas and liquid flowrates, with larger values determined for β-alaninate solutions (0.75–1.16 mmol m−2 s−1 kPa−1) than that of α-alaninate (0.65–0.87 mmol m−2 s−1 kPa−1), under similar experimental conditions. The results showed that the overall mass transfer coefficient increases with increasing temperature, conversely decreasing steadily with increasing CO2 loading. The maximum CO2 loading capacity of the 5.0 M solutions was ∼10 % higher for β-alanine (0.651 mol CO2/mol alaninate) than α-alanine (0.607 mol CO2/mol alaninate) at 25.0 °C. Precipitation was found to play an important role in the CO2 absorption processes here. Interestingly, beyond CO2 loadings >0.12 mol CO2/mol α-alaninate, the 5.0 M solution of α-alaninate begins to develop precipitate(s) while precipitation in the β-alaninate solution is only initiated at much higher CO2 loadings >0.52 mol CO2/mol β-alaninate. This study provides valuable insights into the suitability of β-alanine and α-alanine for CO2 capture directly from the ambient air.

Analysis and insights of the second-generation ternary AMP-PZ-MEA solvents for post-combustion carbon capture: Absorption-regeneration performance

This work comprehensively investigates absorption and regeneration performance of the second-generation AMP-PZ-MEA in comparison with the first-generation AMP-PZ-MEA, the benchmark 5 M MEA, and the conventional MEA at the same amine concentration. The performance indicators include CO2 absorption capacity, mass transfer coefficient, CO2 removal percentage, amount of desorbed CO2, initial CO2 desorption rate, and regeneration heat duty. Both 6 M (i.e., 2:2.5:1.5, 1.3:3.2:1.5, and 0.95:3.55:1.5) and 7 M (i.e., 2:2.5:2.5, 1.3:3.2:2.5, and 0.95:3.55:2.5) second-generation blends show more promising overall absorption and regeneration performance than 5 M, 6 M, and 7 M MEA. In comparison with the first-generation blend, 6 M and 7 M second-generation blends deliver more favorable mass transfer rate. Interestingly, an increase of PZ:AMP molar ratio accelerates mass transfer and absorption capacity but unfavorably affects solvent regeneration. Also, high viscosity of the second-generation 7 M blend (especially, at its equilibrium CO2 loading) retards the solvent regeneration. The key success for a formulation of AMP-PZ-MEA is appropriate PZ:AMP molar ratio and total amine concentration. Too high and too low PZ:AMP molar ratio lead to (i) solvent precipitation and (ii) imbalance of absorption and regeneration performance. Three standouts are recommended. 2.5:0.5:3 is attractive due to its low regeneration heat duty (42.1% lower than that of 5 M MEA). In terms of mass transfer coefficient, 0.95:3.55:1.5 shows 148.6% higher than 5 M MEA. 2:2.5:1.5 is also favorable according its high mass transfer coefficient (91.3% greater respecting 5 M MEA) and low regeneration heat duty (16.3% less than 5 M MEA).

The impact of trace amounts of CO2 on the high-pressure adsorption of CH4 on 5A zeolite

The impact of trace amounts of CO2 on CH4 adsorption in a zeolite at elevated pressure was examined using experimental, binary adsorption isotherms, and molecular simulations. CH4 upgrading is important for a variety of applications, and the use of zeolites for CH4 upgrading has been considered previously but, to the best of our knowledge, not at pressures between 60 and 70 bar. The non-ideality of the adsorption was examined by comparing the experimental loadings to predicted loadings from the Ideal Adsorbed Solution Theory (IAST). When adsorption occurs at a total pressure of 58–66 bar, and a CO2 fraction below 0.42 mol %, there was less than 5 % error in the CH4 IAST predicted loading compared to the experimental value, but the deviation in CO2 loading between IAST and experiments, even at these low CO2 mole percentages, varied nominally from 4 to 13 %. Above 0.42 mol % deviations from IAST were more severe. Grand Canonical Monte Carlo simulations captured the trends in the adsorption data and illustrated how CO2 molecules align in the pore when adsorbed such that oxygens on both ends of the molecule can interact with cations in the zeolite. The results highlight the applicability of adsorbent materials to separate CO2 from process streams at elevated pressure and provide molecular insights that can aid the design of adsorbent structures.

Optimization of K2CO3 exposure conditions using response surface methodology for CO2 capture with 2-methylpiperazine and monoethanolamine as promoters

In this study, the optimization of potassium carbonate (K2CO3) exposure conditions for CO2 capture with the use of 2-methypiperazine (2MPz) and monoethanolamine (MEA) as promoters was investigated. The tested operating conditions for the CO2 capture process included the pH, temperature, K2CO3 dose, gas flow rate, and pressure, and their effect on the CO2 absorption/desorption rate and CO2 absorption efficiency was assessed. Response surface methodology (RSM) was also employed to determine the equations for the optimal long-term operating conditions. The results showed that the CO2 absorption rate and efficiency increased under K2CO3 exposure with an increase in the pressure and loading rate. Moreover, for the temperature the absorption efficiency first increase and then decreases with increase in temperature, however, the with increase in temperature the faster absorption were observed with lower absorption loading rate. Furthermore, pH had a more complex effect due to its variable effects on the speciation of bicarbonate ions (HCO3−) and carbonate ions (CO32−). Under higher pH conditions, there was an increase in the concentration of HCO3−, which has a higher CO2 loading capacity than CO32−. Contouring maps were also used to visualize the effect of different exposure conditions on the CO2 absorption rate and efficiency and the role of 2MPz and MEA as promoters in the K2CO3 solution for CO2 absorption. The results showed that the mean CO2 absorption rate was 6.76 × 10−4 M/L/s with an R2 of 0.9693 for the K2CO3 solution containing 2MPz. The highest absorption rate (6.56–7.20 × 10−4 M/L/s) was observed at a temperature of 298–313 K, a pressure of >2 bar, a pH of 8–9, and a loading rate of 80–120 L/h for a concentration of 1–3 M K2CO3 and 0.05–1.5 M 2MPz. The CO2 absorption efficiency exhibited a variation of 56–70% under the same conditions.

Inhibiting effect of 2-amino-2-methyl-1-propanol on gelatinous product formation in non-aqueous CO2 absorbents: Experimental study and molecular understanding

Diamines or polyamines with two or more amino groups are suitable for formulating non-aqueous absorbents (NAAs) with high CO2 loading capacity and low regeneration energy consumption. However, these two types of amines in NAAs are prone to produce insoluble gelatinous products after absorbing CO2, resulting in difficult operation of the CO2 capture system. In this study, by using 2-amino-2-methyl-1-propanol (AMP) as an inhibitor, the insoluble gelatinous products of the aminoethylethanolamine (AEEA)-N-methyl-2-pyrrolidone (NMP) (A-A-N) and 3-(methylamino)propylamine (MAPA)-NMP (M-A-N) NAAs were successfully eliminated. The experimental results showed that the AMP-regulated NAAs possessed a high absorption rate, high CO2 loading capacity, excellent desorption efficiency, and stable recyclability. The reaction mechanism of CO2 absorption and the inhibitory mechanism of AMP on the formation of gelatinous products were comprehensively elucidated. Taking the A-A-N system as a representative, AEEA reacted with CO2 to form zwitterionic protonated carbamate species (AEEACO2−(P)H+(S)), which tended to self-aggregate via hydrogen-bond interaction, resulting in the formation of insoluble gelatinous products. With the introduction of AMP, the AMP-derived products could combine easily with AEEACO2−(P)H+(S) via strong electrostatic attraction to form ion pairs, preventing the AEEACO2−(P)H+(S) molecules from self-aggregating to form insoluble gelatinous products. The regeneration heat duty of the A-A-N system was 1.89 GJ∙ton−1 CO2, which was 49.9 % lower than that of the benchmark 30 wt% MEA. Overall, introducing AMP as a gelatinous product inhibitor was beneficial for the development of NNAs with high CO2 absorption capacity and low-energy consumption.

Characterization of Loading Rate of CO2 with Mono Ethanol Amine Continuous Reactor Experimentation & Titrimetric CO2 Loading Evaluation

This study delves into leveraging a continuous reactor experiment setup for CO2 Capture using Mono Ethanol Amine (MEA). A series of experiments were conducted utilizing various concentrations of MEA from 10% to 30% wt/wt under controlled conditions to determine their CO2 loading rates. The continuous reactor system offered insights into the kinetics and equilibrium behaviours of the MEA-CO2 interaction. The CO2 loading with MEA solvents is estimated using a titrimetric method, the UOP 829-821 which consumes less resources for research in a laboratory setup. This enabled repetitive and reciprocal loading rate assessments of CO2 loading rate analysis with MEA solvents. The CO2 content in the experimented amine samples ranged from 0.13 to 0.45 mol CO2 / mol MEA while varying the CO2 concentration between 10% to 20% and MEA Concentration from 10% to 30% for a range of absorption time periods. The CO2 loading performance showed only a marginal performance improvement was found between 20% and 30% MEA concentration. The results of this study can help pave pathways for more efficient MEA based CO2 Capture Technologies.

Optimizing continuous medium-chain fatty acid production from biohydrogenic palm oil mill effluent: Operational parameters and microbial dynamics

Palm oil mill effluent (POME) was dark fermented into biohydrogen for clean energy production with volatile fatty acids (VFAs) as a byproduct. The VFAs remaining 70% in hydrogenic POME offer potential substrate for conversion into valuable medium-chain fatty acids (MCFA), presenting an opportunity for resource recovery and environmental mitigation. This study investigated the influence of varying operating parameters on continuous MCFA production from biohydrogenic POME through a stirred tank reactor. Optimizing MCFA production necessitates a 5.4 g/L ethanol load supplemented with 2.6 g/L NaHCO3 and 1.5 L-CO2/L/d while maintaining a pH of 6.5 and a temperature of 35 °C. Under optimized conditions, a maximum MCFA production of 2.2 g-COD/L was achieved, consisting primarily of 1.8 g-COD/L caproic acid, 0.2 g-COD/L heptanoic acid, and 0.2 g-COD/L caprylic acid, translating to a total MCFA yield of 0.5 g-COD/g-COD and MCFA selectivity of 51% with Caproiciproducens sp. (45%), Lactobacillus sp. (21%), and Clostridium sp. (14%) as predominant bacteria. Notably, CO2 loading significantly enhances MCFA production, particularly caproic and heptanoic acids. Remarkably, the system maintained stable MCFA production for an impressive 220 days. The microbial community in the reactor effectively removed total solids, volatile solids, chemical oxygen demand (COD), suspended solids of 42%, 61%, 31%, and 95%, respectively. Key bacteria like Caproiciproducens sp., C. kluyveri, Clostridium sp., and Sporanaerobacter sp. possess most of the enzymes required for the reverse β-oxidation pathway, an energy-efficient pathway for MCFA generation. This study makes a significant contribution to the field of biowaste valorization, specifically focusing on anaerobic fermentation for bio-based chemical production. Despite challenges related to butyric acid accumulation and inhibition, these findings offer promising potential for scaling up the fermentation process.

Enhancements of monoethanolamine CO2 absorption rate and degradation in the presence of nickel nanoparticles catalysts

In the study of the catalytic effect of nickel nanoparticles (NiNPs) on amine-based CO2 capture systems, monoethanolamine (MEA) was subjected to a CO2 loading at greatly varying concentrations (3–30 wt%) at two temperatures (20 °C and 50 °C) for the first time in a lab study to the best of our knowledge. This study shows that NiNPs can enhance the rate of CO2 absorption into MEA and that its enhancement is greater at 20 °C than at 50 °C. Solutions were loaded with CO2 until full saturation and the mass gain was recorded. At 20 °C the overall enhancement ranged between 4.0–7.4% with the optimum (>7.0%) observed at concentrations of 5 wt% and 20 wt% of MEA with NiNPs. In addition, there were large reductions in the time that it takes to fully saturate the MEA with CO2, (up to a 42% reduction) and there were differences in peak loading (molCO2/molmea) between the NiNPs solution and the control (without NiNPs) (of up to 12.5% for the same time at 20 °C and 30 wt% of MEA with NiNPs). For the first time to the best of our knowledge, the degradation of MEA with and without NiNPs was studied; an oxidative degradation experiment (30 wt%, 0.4 molCO2/molmea, 7.5 mL/min CO2, 0.35 L/min air, 55 °C) based on typical absorber conditions and a thermal degradation experiment based on typical stripper conditions (30 wt%, 0.5 molCO2/molmea, 135 °C) were carried out. Gas chromatography-mass spectrometry was used to identify and quantify the major degradation compounds. It is found that NiNPs increase the rate of both oxidative and thermal degradation.

3D models guide the design of hollow fiber membrane contactors with complex internal structures for CO2 capture

AbstractMembrane contactors have good prospects in the field of CO2 capture. In this study, the effects of operation conditions (gas velocity, liquid flow, CO2 pressure, amine concentration, and CO2 loading) on CO2 absorption flux (JCO2) for CO2 absorption into N‐methyl‐4‐piperidinol (MPDL) solution in membrane contactors were investigated through experiments and simulations. A three‐dimensional (3D) model was developed using COMSOL Multiphysics software to study the comprehensive CO2 mass transfer process in the multifiber membrane contactor and the effect of the number of fibers on the flow and CO2 concentration distribution without simplifying the geometry compared with those of traditional one‐dimensional (1D) and two‐dimensional (2D) models. Non‐ideal effects occurring in hollow fiber membrane contactors can be explained using a 3D modeling. By comparing the simulated with the experimental , the effectiveness of the model was determined. The simulation results emphasize that the spatial concentration distribution has a great correlation with the corresponding velocity distribution. Additionally, reducing the uneven velocity distribution of gas and liquid is a very important factor to improve the mass transfer performance of CO2. Increasing the number of fibers with a constant total volumetric flux can reduce the thickness of the boundary layer and promote the mass transfer.