Sorbent Performance Research Articles

Study on the sorption and desorption behavior of La3+ and Bi3+ by bis(2-ethylhexyl)phosphate modified activated carbon.

The separation of 213Bi from its parent radionuclide 225Ac via radionuclide generators has proven to be a challenge due to the limited performance of the current sorbents. This study evaluated the separation performance of La3+ (as a surrogate for 225Ac) and Bi3+ using bis(2-ethylhexyl)phosphate monofunctionalized activated carbon (HDEHP/AC). The potential applications of phosphate groups as active sites and the carbon structure as a sorbent support were confirmed and validated. Various factors, including pH values, salt concentration, halide ions, contact time, solid-to-liquid ratio, initial La3+/Bi3+ concentration, and gamma irradiation were examined through batch sorption experiments in both single and binary systems. HDEHP/AC had a high sorption capacity for La3+ via electrostatic attraction, with the sorption data fitting well to the pseudo-second-order kinetic equation and Langmuir model. The sorption performance of La3+ on HDEHP/AC was minimally affected as the NaCl/NaI concentrations increased at pH = 2, whereas the sorption capacity for Bi3+ decreased significantly. Additionally, selective desorption of La3+ and Bi3+ was achieved using HNO3 and NaI solutions, respectively. These results backed up by a conceptual separation process point toward a potential use of these materials in a direct/inverse 225Ac/213Bi radionuclide generator. Further optimization of the material and separation process will be required to bring this class of promising materials into an actual generator for medical applications.

Phase transition behaviors of Sr0.72Ca0.28Fe1-xNixO3-δ perovskite oxygen sorbents in a fixed bed reactor

Perovskite oxides have emerged as promising materials for oxygen storage applications, with their phase transitions being a key area of research. This study reports on the unique oxygen absorption and desorption breakthrough curves observed in the Sr0.72Ca0.28Fe1-xNixO3-δ series (x = 0.05) during fixed-bed experiments, featuring a distinct plateau. Through in situ X-ray diffraction (XRD) analysis, we demonstrated the reversible phase transition between the perovskite and brownmillerite (BM) structures. High Resolution Transmission electron microscopy (HR-TEM) further revealed the coexistence of these two phases within a granule. Focusing on the Sr0.72Ca0.28Fe0.95Ni0.05O3-δ sample at 550 °C, we conducted a detailed analysis of the oxygen absorption curve. Our findings indicate that the plateau arises from the oxygen-deficient BM phase absorbs oxygen to form the oxygen-saturated BM phase, followed by further oxygen absorption, leading to the formation of the perovskite phase. The inflection point in the oxygen absorption curve marks a critical oxygen concentration, signifying the threshold for effective oxygen absorption. This critical concentration is influenced by both material composition and operation temperature. Based on our observations, a phase diagram for x = 0.05 was drawn, encompassing both oxygen concentration and temperature. This diagram allows for the rational selection of operation temperatures and oxygen concentration swing ranges to enhance the performance of the oxygen sorbent. Our study highlights the crucial role of phase transition in oxygen storage, offering insights into the design and development of high-performance perovskite-based materials for various applications.

CO2 gas-liquid equilibrium study and machine learning analysis in MEA-DMEA blended amine solutions

The combination of primary and tertiary amines represents a promising approach to improve sorbent performance in CO2 capture by enhancing absorption efficiency and reducing regeneration energy. This study focuses on investigating the absorption performance of binary mixtures of ethanolamine (MEA) and N,N-dimethylethanolamine (DMEA) at temperatures between 298–323 K and CO2 partial pressures between 5–60 kPa. The species generated during the absorption were analyzed using 13C NMR spectroscopy, to clarify the intricate role of MEA and DMEA in the capture process. A developed excess property model for MEA-DMEA, based on excess CO2 loading, predicted equilibrium CO2 solubility data with an average absolute relative deviation (AARD) of 1.6 %. Additionally, the machine learning models XGBoost, RBFNN, and SVR were applied, providing AARD values between 0.86 % and 1.28 %, demonstrating strong agreement between experimental and predicted outcomes. These comprehensive findings enhance our understanding of mixed amines’ mechanisms and practical applications, contributing to ongoing research development.

Interactions between antibiotic removal, water matrix characteristics and layered double hydroxide sorbent material

Sorption by layered double hydroxides (LDH) is gaining substantial interest for remediating emerging contaminants, including pharmaceuticals from wastewaters. Findings from a sorbent material performing successfully in lab-based studies using non-environmental (laboratory-sourced) water cannot be assumed to translate to equal performance under environmental downstream applications. However, studies evaluating sorbent material performance for removal of pollutants and understanding material interactions with environmental waters are limited. This study evaluates the removal of the antibiotic amoxicillin (AMX) using a Mg2Al–NO3-LDH sorbent material from laboratory-grade water and wastewater effluent (WWE). AMX is successfully removed (94.53 ± 4.30 % within 24 h) in laboratory-grade water (under batch sorption conditions: 100 μg/L AMX, 0.2 g/L LDH, 20 °C). The comparison of LDH removal performance in laboratory grade and WWE shows a decreased maximum removal of AMX in WWE (13.39 ± 5.53 %). A lower final AMX concentration is observed in the WWE without the presence of LDH, compared to the ‘removal’ experiments in WWE with the presence of LDH, indicating a contribution of non-sorption removal pathways of AMX. This is proposed to be due to the difference in metal concentrations in the WWE with and without LDH present. The presence of LDH is found to decrease concentrations of metal pollutants in WWE, such as Zn concentration decreasing by 85 % over 24 h, changing water characteristics. Overall, this paper reports that an LDH performs differently in laboratory-sourced water and a wastewater effluent. This provides evidence that sorbent material performance needs to be evaluated in complex water matrices to ensure that it is representative of how a sorbent material will perform in an environmental application, which is the end goal of developing such technologies. Finally, good practice recommendations are provided for future lab-scale sorption experiments evaluating the performance of any new sorbent materials for water treatment applications.

Region specific economic model for solid sorbent direct air capture using geothermal energy resources (S-DAC-GT)

Low temperature geothermal resources, ranging from 80° to 120 °C, may substantially lower both the cost and the CO2 emissions footprint of CO2 direct air capture (DAC) systems. This paper provides a model for determining a region-specific economic analysis for DAC with solid sorbent (S-DAC) using geothermal resources (S-DAC-GT).This paper provides a methodology and program for calculating estimated cost and carbon emissions for potential S-DAC facilities on a region-specific basis. The paper outlines the necessary region-specific characteristics required as parameters for the techno-economic model. The region-specific characteristics are then applied to an S-DAC energy and cost model based on existing literature to calculate the levelized cost per tonne of CO2 captured and stored. Further, the model provides a reasonable approximation of the carbon intensity of the S-DAC-GT system. These calculations allow selecting and prioritizing regions appropriate for potential S-DAC-GT facilities operating at a scale of ∼1 Mt CO2 captured and stored per year.This paper presents a novel approach that addresses several gaps in current DAC techno-economic analyses found in literature. First, the model is highly customizable, allowing the user to apply their own proprietary sorbent properties and region specific parameters to determine precise costs and carbon emissions for their hypothetical S-DAC-GT facility. Second, the overwhelming majority of DAC techno-economic analyses in literature assume away variability of ambient conditions, presuming stable temperature and humidity during operations. This paper directly integrates these large local ambient effects on sorbent performance and evaluates S-DAC-GT costs and carbon emissions based on specific and variable conditions dictated by the user. Third, the flexibility of the model allows the user to rapidly compare S-DAC-GT costs and carbon emissions in different user selected regions, with custom sorbent characteristics. The model provides visualizations of the sensitivity of S-DAC-GT costs and carbon emissions to different parameters and provides visualizations of the cost and carbon emissions due to variability in ambient conditions.Existing techno-economic analyses are either region agnostic or constrain their results to a specific region. The novelty of this paper and its model is the deeper technical and economic analysis of using geothermal energy as the thermal resource, coupled with customizability and visualizations that enable accelerated differentiation of S-DAC-GT costs and carbon intensity by region.

Bentonite clay reinforced alginate grafted composite hydrogel with remarkable sorptive performance toward removal of methylene green

The rapid industrial progress in today's world has led to an alarming increase in water pollution caused by various contaminants such as synthetic dyes. To address this issue, a new hydrogel sorbent, BC-r-Na-Alg-g-p(NIPAm-co-AAc), was developed by combining bentonite clay, sodium alginate, and poly(N-isopropyl acrylamide-co-acrylic acid) through one-pot free radical polymerization at 60 °C. The developed sorbent was characterized using several analytical techniques including SEM, FTIR, TGA, UTM, and swelling studies. The swelling capacity of the sorbent was observed to increase remarkably with an increase in pH, reaching a maximum of 9664 % at pH 11. In batch mode sorption experiments, the sorbent's performance toward methylene green (MG) was investigated by analysing the effects of contact time, pH, temperature, and concentration. The experimental data were fitted to pseudo-second-order kinetic and Langmuir isotherm models, indicating chemisorption as the dominant interaction mode between the anionic sorbent and cationic MG. However, physisorption may also occur to a lesser extent, indicated by the significant R2 of the pseudo-first-order kinetic and Freundlich isotherm models. Additionally, the sorbent exhibited very little decrease (approximately 5 %) in sorptive performance for six sorption-desorption cycles. Overall, the facile fabrication, excellent swelling (9664 %), promising sorption performance (2573 mg.g−1), and good recyclability (6 cycles) make the developed sorbent a potential candidate for various industrial applications.

Performance evaluation and sensitivity analysis of polyethyleneimine-based sorbent in a circulating fluidized bed carbon dioxide capture unit

Greenhouse gases, particularly carbon dioxide, have increased the Earth’s average temperature by 1 °C, which has resulted in significant consequences for human life. To prevent further global warming and maintain a stable lifespan, it is imperative to achieve carbon neutrality. Post-combustion capture using an amine-based aqueous solvent is an advanced technology that has gained attention, but there are challenges such as corrosion, environmental impact, and energy consumption associated with it. This study aims to evaluate the performance of a polyethyleneimine-based sorbent in a circulating fluidized bed carbon dioxide capture unit and to determine the optimal operating conditions through sensitivity analysis. Various variables, including carbon dioxide concentration, water vapor content, desorber temperature, and sorbent residence time, were analyzed. The unit was continuously operated for 128 h even under challenging conditions with higher oxygen concentrations than the actual flue gases, and sorbent degradation was negligible. The results showed a 55 % carbon dioxide removal efficiency, a dynamic sorption capacity of 0.041 g-CO2/g-sorbent, and a regeneration heat energy of 4.2 GJ/tCO2. Sensitivity analysis revealed that there was minimal improvement even with changes in the absorber structure and physical properties of the sorbent. Only an increase in the sorbent reaction rate had a significant effect. If the reaction rate were to double, the carbon dioxide removal efficiency would reach 90 %, with a dynamic sorption capacity of 0.068 g-CO2/g-sorbent and regeneration heat energy of 2.9 GJ/tCO2.

Understanding the influences and mechanism of water vapor on CO2 capture by high-temperature Li4SiO4 sorbents

Li4SiO4 sorbent attracts wide attention due to its high and stable CO2 adsorption. However, the process of CO2 capture is significantly affected by various impurities under the circumstance of industrial applications, and water vapor is one such impurity that needs to be well studied. Herein, we aim to evaluate the effect of water vapor on physicochemical characteristics of Li4SiO4-based sorbents during cyclic CO2 adsorption and desorption and to understand the action mechanism of H2O molecules on CO2 adsorption by Li4SiO4. Reaction tests show that water vapor can significantly enhance CO2 adsorption performance of sorbents, but the promotion effect varies with the different presence of water vapor during reactions. Material characterization and DFT calculation reveal that although the presence of water vapor leads to deterioration of internal pore structure of the sorbent, H2O molecule will form OH– on the surface of Li4SiO4 and further react with CO2 to generate HCO3–, thus the adsorption energy with water vapor presenting is increased with an observation of promoted CO2 adsorption.

Towards a sustainable recovery of polyphenols from agrifood waste: Performance of polymeric sorbents with natural deep eutectic solvent extracts

Olive oil production generates large amounts of waste, which contains phenolic compounds at relevant concentrations. In recent years, interest in the recovery of these compounds has grown to take advantage of their natural antioxidant properties. Natural deep eutectic solvents (NaDESs), considered as green solvents, have proved their efficiency to extract phenolic compounds from agri-food waste. The resulting extracts must be purified before being used in pharmaceutical, food, or cosmetic applications. In this study, the performance of several non-functionalized polymeric sorbents (PuroSorb PAD900, PAD950 and PAD610, and Macronet MN202) was evaluated for the purification of NaDES extracts (choline chloride-glycerol (1:5); 30% water) from olive tree leaves. It is important to highlight that these types of characterization studies are common for conventional solvent extracts but are very novel and scarce for their NaDES counterparts. Sorption was investigated at the natural conditions of the extracts (pH 5.3), and ethanol-water mixtures were used in the desorption experiments. Overall, the four sorbents displayed good sorption characteristics, with MN202 being particularly suited to retain 3-hydroxytyrosol. Ethanol levels above 70% were appropriate for desorption of most phenolic compounds, while mixtures with ethanol content below 50% were more efficient for small polar molecules such as 3-hydroxytyrosol.

Thermodynamic and CO2 sorption investigations on improved Li3BO3-based sorbents by NaOH addition

The development of new solid sorbents with high carbon capture capacity and good reversible sorption properties is considered a key factor for mitigating CO2 emissions. Tri-lithium borate (Li3BO3) has shown to be a high-capacity CO2 sorbent adequate for an intermediate temperature range (500–650 °C). However, the performance of this sorbent has been little studied in particular at low CO2 concentrations, requiring the introduction of changes in Li3BO3 to make it competitive. Here, highly efficient NaOH-modified Li3BO3 sorbents were synthesized by a simple two-step mechano-thermal method at low temperature using different amounts of NaOH. For the first time, the influence of increasing amounts of an additive on the standard enthalpy change of Li3BO3 as well as on the relation between CO2 pressure and temperature equilibrium was determined. A progressive rise in the standard enthalpy change and a decrease in the equilibrium CO2 pressure at a fixed temperature were observed with the increase in the amount of additive. Moreover, the NaOH addition to Li3BO3 improves its CO2 capture capacity, CO2 absorption rate and stability during carbonation/regeneration cycles. The CO2 capture capacity ranges between 50 wt% and 35 wt% at pure CO2 and 15 % CO2, respectively, for low amounts of NaOH added. Further studies showed that CO2 capture/desorption efficiency is kept high after 20 cycles at 525 °C and 15 % CO2. The improved performance of NaOH-modified Li3BO3 sorbents and the changes in the thermodynamic properties were associated with two factors: the partial substitution of boron by carbon in the Li3BO3 structure, and the formation of Li2CO3-Na2CO3 molten carbonates. Therefore, these NaOH-modified Li3BO3 materials represent attractive CO2 sorbents for moderate temperatures, applicable for post-combustion industrial processes.

Mercury Capture Performance and Kinetics of CCl4-Adsorbed Activated Carbon Pretreated by the Mechanochemical Method.

In the present work, CCl4-adsorbed activated carbon pretreated by the mechanochemical method (CCl4-AC) was produced for gas-phase mercury capture. The physicochemical properties of the CCl4-AC sorbent were analyzed via N2 adsorption, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The mercury capture performance of the CCl4-AC sorbent under different flue gas components was investigated in a fixed-bed experimental device. The programmed temperature desorption of mercury was used to determine the mercury capture product of the spent CCl4-AC. Finally, the mass transfer factor model proposed by Fulazzaky was used to analyze mercury capture on the CCl4-AC for clarifying its characteristics. The results showed that the prepared CCl4-AC can be used as a mercury sorbent because of its high mercury capture performance. Mercury capture by the CCl4-AC was interfered by SO2 and promoted by O2 and H2O. Hg-temperature programmed desorption (Hg-TPD) analysis indicated that the main mercury capture products of the CCl4-AC were HgCl2 and HgO. Because of the presence of SO2 in flue gas, there was a little Hg2SO4 formation on the sorbent. XPS analysis showed that the functional group of C-Cl played the dominant role in Hg0 capture, and part of the C-Cl groups were converted into Cl- after mercury capture. The mercury desorption energy of the spent CCl4-AC was 50.49 kJ/mol and stronger compared with that of raw activated carbon. Mass transfer analysis displayed that surface adsorption was the main form at the beginning of mercury adsorption, and the external mass transfer was the mercury adsorption rate-controlling step. Then, mercury adsorption entered the second stage; internal diffusion adsorption stage with internal mass transfer became the adsorption rate control step.

Supramolecular Complexation-Enhanced CO2 Chemisorption in Amine-Derived Sorbents.

A supramolecular complexation approach is developed to improve the CO2 chemisorption performance of solvent-lean amine sorbents. Operando spectroscopy techniques reveal the formation of carbamic acid in the presence of a crown ether. The reaction pathway is confirmed by theoretical simulation, in which the crown ether acts as a proton acceptor and shuttle to drive the formation and stabilization of carbamic acid. Improved CO2 capacity and diminished energy consumption in sorbent regeneration are achieved.

Investigation of multiple cyclic pressure loading on the service life and sorption performance of a composite sorbent

Investigation of multiple cyclic pressure loading on the service life and sorption performance of a composite sorbent

Infusion of Fly Ash/MgO in CaO-based sorbent for high-temperature CO2 capture: Precursor selection and its effect on uptake kinetics

Calcium Looping Technology for high-temperature CO2 capture suffers from a gradual decline of uptake capacity over repeated cycles caused by the sintering-induced agglomeration of CaO particles. The latter is typically inhibited by infusing inert into the sorbent to disperse CaO grains. In this respect, current work investigates the infusion of inerts like Fly ash (FA) and Magnesium salt in CaO-based sorbent through sol-gel combustion, assessing sorbent performance under harsh conditions: carbonation at 650 °C for 30 min and calcination at 950 °C for 15 min under a CO2 (100%) atmosphere. The study includes (i) in-depth characterization of various sorbents: both unsupported and modified with inert, synthesized using inorganic (InOP) and organometallic (OMP) precursors for different fuel-to-metal oxide molar ratios (MR = 2 and 3), (ii) thermogravimetric analysis for evaluating uptake kinetics based on carbonation conversion (XCBN) and cyclic stability and (iii) kinetic modeling to evaluate rate parameters. Kinetic analysis after a single cycle revealed the highest XCBN (78%) for unsupported InOP (MR = 2 and 3) and OMP (MR = 2) among thermally pre-treated sorbents. MgO-modified InOP (MR = 2) performed better (XCBN = 66%) than its OMP counterpart, while both MgO-modified sorbents (MR = 3) performed similarly (XCBN = 66%). Cyclic stability studies conducted for 30 cycles established higher stability of FA-modified OMP with lower deterioration by 13.47% (XCBN = 22.60%) than unsupported OMP by 62.99% (XCBN = 15.06%). Overall, the results showcase FA infusion in OMP as a viable route to develop stable modified CaO-sorbents with considerable carbonation conversion.

Promotional effect of NaNO3/NaNO2 on CO2 adsorption performance of MgO sorbents

The magnesium oxide (MgO) sorbents doped with different NaNO3/NaNO2 molar ratios were prepared to improve their stability over multiple cycles. Regulating the NaNO3/NaNO2 molar ratio effectively improved the CO2 adsorption performance of the sorbent. The MgO sorbent with the NaNO3/NaNO2 molar ratio of 0.8 exhibited outstanding performance and stability. Characterization and density functional theory calculations confirmed the positive effects of the appropriate NaNO3 amount in improving the adsorption activity, whereas the suitable NaNO2 amount slowed the sintering step and improved stability. Notably, the molten salt remained stable during cycling and did not decompose even at high regeneration temperatures, guaranteeing the cyclic stability of the sorbent. Further characterization showed that the CO2 sorption drop in the first few cycles was ascribed to the decline in the active surface owing to the aggregation of MgO particles, incomplete regeneration of sorbents, and segregation of molten salt on the sorbent surface.

Synthesis and multi-objective optimization of fly ash-slag geopolymer sorbents for heavy metal removal using a hybrid Taguchi-TOPSIS approach

This study develops and evaluates a highly effective geopolymer sorbent specifically designed for the removal of heavy metals from wastewater. Single and binary blends of fly ash and slag were utilized as the binding material. The geopolymer composite was activated using either sodium hy solely or in combination with sodium silicate. The Taguchi method was employed to design the geopolymer mixes, having four factors, each with four levels of variation. These factors included the fly ash-to-slag ratio (FA), binder content (BC), the molarity of the sodium hydroxide solution (M), and the sodium silicate-to-sodium hydroxide ratio (SS/SH). The performance of the geopolymer sorbent was rigorously assessed against a comprehensive set of criteria, including metal sorption capacity, setting time, flowability, density, compressive strength, abrasion resistance, water absorption, permeable voids, sorptivity, carbon footprint, and cost. The TOPSIS methodology was applied to aggregate the response criteria and determine the optimal mix for superior performance. The results showed that the optimum mix consisted of an FA of 33 %, BC of 1050 kg/m3, M of 10, and SS/SH of 3. A sensitivity analysis confirmed that changes in the weighting of the performance criteria did not significantly impact the proportioning of the optimum mix. Furthermore, the analysis of variance (ANOVA) revealed that the FA contributed the most to the sorbent’s performance, followed by the SS/SH, BC, and M. The development of this geopolymer sorbent not only addresses a critical environmental concern but also offers great potential for practical applications in industries and municipalities worldwide.

Solar photovoltaic refrigeration system coupled with a flexible, cost-effective and high-energy-density chemisorption cold energy storage module

Owing to the environmental pollution and high costs associated with lead-acid batteries, this paper proposes a solar photovoltaic (PV) refrigeration system coupled with a flexible, cost-effective and high-energy-density chemisorption cold energy storage module. Its operation mode includes daytime solar PV refrigeration/cold energy charging mode and nighttime cold energy discharging mode. A novel composite sorbent SrCl2 is developed using expanded natural graphite as matrix and carbon coated aluminum as additive, exhibiting superior heat and mass transfer performance. A sorbent performance test bench is constructed, demonstrating that the cold energy storage density reaches 503.6 kJ/kg at an evaporating temperature of −15 °C, 1.5 times of ice storage. Compression-assisted desorption is adopted to regulate desorption temperature, so that 75–90 °C solar hot water from low-cost non-concentrating solar collectors can be utilized as the driving heat source. For an evaporating temperature of −10 °C and a solar hot water temperature of 90 °C, the electrical coefficient of performance for cold energy storage unit reaches 3.72, representing a 33 % improvement compared to conventional solar PV refrigeration systems. This novel system features characteristics such as low cost, high efficiency and eco-friendliness, offering a promising solution for solar refrigeration.

Experimental and DFT study of Na4SiO4 doped with oxysalts for high-temperature CO2 capture

Eutectic doping has been considered as one of the most efficient ways to modify the Na4SiO4-based CO2 sorbent. Nevertheless, the effects of different acid radical ions and alkali metal cations of the oxysalts on the CO2 capture performances of Na4SiO4 have never been explored. In this study, Na4SiO4-based CO2 sorbents were prepared using four kinds of oxysalts as the dopants. The effects of acid radical ions/alkali metal cations, doping ratios and sorption/desorption temperatures on the CO2 capture performances of sorbents were investigated. The results showed that the promotion effects of CO32− and Li+/K+ ions were stronger than others, the maximum CO2 sorption capacity of Na4SiO4-30Li2CO3 and Na4SiO4-30K2CO3 at 700 °C reached 20.6 wt% and 19.5 wt%, respectively. The cyclic sorption capacity of Na4SiO4-30Li2CO3 was 8.5 wt%, which was 40.0% higher than that of Na4SiO4. Further, the oxysalt dopants could enhance the CO2 adsorption energy on the Na4SiO4 surfaces and reduce the energy level of the systems using density functional theory calculation, which were consistent with the experimental values. Finally, the effects of water vapor on the sorption of Na4SiO4 and Na4SiO4-K2CO3 were simulated, which could enhance the activity of O atoms on sorbent surfaces and promote rapid carbonization during the sorption progress. Thus, Na4SiO4 doped with oxysalts exhibit promising potential for high-temperature CO2 capture application.

On Comparing Packed Beds and Monoliths for CO2 Capture from Air Through Experiments, Theory, and Modeling.

This study compares the performance of amine-functionalized γ-alumina sorbents in the form of 3 mm γ-alumina pellets and of a γ-alumina wash-coated monolith for CO2 capture for direct air capture (DAC). Breakthrough experiments were conducted on the two contactors to analyze the adsorption kinetics and performance for different gas feeds. A constant pattern analysis revealed dominant mass transfer resistances in the gas film and in the pores, with axial dispersion also observed, particularly at higher concentrations. A 1D, physical model was used to fit the experiments and thus to estimate mass transfer and axial dispersion coefficients, which appear to be consistent with the hypotheses derived from constant pattern analysis. A dual kinetic model to describe mass transfer was found to better describe the tail behavior in the monolith, whereas a pseudo-first-order model was sufficient to describe breakthroughs on packed beds. A substantial two-order magnitude decrease in mass transfer coefficients was noted when reducing the feed concentration from 5.6% to 400 ppm CO2, thus underscoring the significant mass transfer limitations observed in DAC. Comparison between the contactors revealed notably higher mass transfer coefficients in the monolith compared to the packed beds, which are attributed to shorter diffusion lengths and lower equilibrium capacity. While the faster mass transfer coefficients observed in the monolith experiments led to reduced specific energy consumption and increased adsorption productivity compared to the packed bed at 400 ppm, no significant improvement was observed for the same process at the higher concentration of 5.6% CO2 in the feed. This finding highlights the need to tailor the contactor design to the specific gas separation requirements. This research contributes to the understanding and quantification of mass transfer kinetics at DAC concentrations in both packed bed and monolith contactors. It demonstrates the crucial role of the contactor in DAC systems and the importance of optimizing the adsorption step to enhance productivity and DAC performance.

Lignocellulosic waste biosorbents infused with deep eutectic solvents for biogas desulfurization

This paper introduces an innovative method for treating biogas streams, employing lignocellulosic biosorbents infused with environmentally friendly solvents known as deep eutectic solvents (DES). The primary focus of this study was the elimination of volatile organosulfur compounds (VSCs) from model biogas. Biosorbents, including energetic poplar wood, antipka tree, corncobs, and beech wood, were used, each with varying levels of lignin and hemicellulose content. The selection of the DES with the greatest potential for VSC removal was carried out using COnductor-like Screening MOdel for Realistic Solvents (COSMO-RS) modeling. The chosen DES consisted of quaternary ammonium salts and glycols, specifically, tetrapropylammonium bromide and 1,2-hexanediol (1:3). The physicochemical properties of the new DES, such as the viscosity, density, and melting point, were evaluated. The biosorbents were treated with the selected DES after shredding, purifying, and sieving. Comprehensive analysis techniques, including thermogravimetric analysis, scanning electron microscopy, and X-ray diffraction, were employed on the modified biosorbents both before and after modification. The subsequent step involved the adsorption of VSCs from biogas. The results of this study demonstrated the superior performance of a novel sorbent based on corn cob modified by DES compared to commercially available alternatives. The sorption capacity ranged from 103.8 to 112.1 mg/g for various VSCs. The adsorption process using the new biosorbent can be described by the pseudo second order kinetic model, as well as the Yoon-Nelson and Adams-Bohart models. The high efficacy of the VSCs removal was attributed to the concurrent operation of the absorption and adsorption processes. The resulting sorbent was also characterized by its ability to regenerate repeatedly without significant loss of sorption capacity of the new sorbents.