Sorption-desorption Cycles Research Articles

Sugarcane bagasse-derived biochar modified by alkali for enriching surface functional groups to effectively treat ammonium-contaminated water.

In this study, sugarcane bagasse (SB), which was preliminarily treated with H3PO4, was utilized to produce biochar (SB-BC). The SB-BC was subsequently modified with KOH to enrich oxygen-containing functional groups (OCFGs) for the enhanced adsorption of NH4+ from wastewater. Batch tests revealed that KOH-modified SB-BC (SB-MBC) increased the maximum Langmuir adsorption capacity of NH4+ by approximately twofold, from 27.1mg/g for SB-BC to 53.1mg/g for SB-MBC. The optimal operational conditions for NH4+ adsorption onto SB-MBC were pH of 7.0 and a biochar dose of 3.0g/L for the removal of 50mg/L NH4+ at room temperature (25 ± 2°C) over 180min of contact. The enhanced adsorption capacity of NH4+ onto SB-MBC was due to the important contribution of the OCFGs enriched on the surface of biochar, which was increased by about fourfold, after being modified by KOH. The NH4+ adsorption dynamics were better fitted by the Elovich and the NH4+ adsorption isotherms were better described by Langmuir and Sips models, showing that the adsorption process was dominated by monolayer chemisorption. The properties of the adsorption materials before and after adsorption of NH4+ confirmed that cation exchange, electrostatic attraction and surface complexation were the main mechanisms controlling the adsorption process. The desorption and reusability tests of NH4+-saturated SB-MBC revealed that NH4+ adsorption slightly decreased after three successive sorption‒desorption cycles. The findings suggested that SB-MBC is a promising and feasible adsorbent for the effective treatment of NH4+-contaminated water sources. Future work should conduct tests for treatment of NH4+-rich real wastewater and utilize NH4+-saturated SB-MBC as slow releasing fertilizer for plants growth.

Extremely Fast Wicking Self‐Layered Interpenetrating Network Hydrogel for Rapid All Day Collection of Atmospheric Water

AbstractHygroscopic salt hydrogel photothermal composites and related technology are a promising pathway for water harvesting. However, due to the overly cumbersome preparation process, the distribution of the surface photothermal layer is difficult to control and the photothermal efficiency is low. In this paper, a method is proposed to greatly simplify the preparation process of photothermal layer hydrogels and improve their atmospheric water harvesting performance by constructing temperature‐sensitive interpenetrating networks. Due to the decomposition of some reversible hydrated structures in the network during heating and warming, carbon nanotubes move autonomously to form a layered structure with a photothermal effect on the upper surface, which can return to its original state after cooling and remain stable at room temperature or under solar illumination. Compared with hydrogels with general layered structure or overall distribution of photothermal materials, agar/GG/PAM/CNT hydrogel has faster moisture adsorption efficiency and higher desorption efficiency, and during the 24 h continuous sorption–desorption cycle is capable of achieving high water yield of 2.57 Lwater kgsorbents−1 day−1, superior to most recent hydrogel adsorbents. Simplifying the preparation process while maintaining high efficiency, while greatly improving photothermal performance, paves the way for cost‐effective mass production applications for a wide range of hygroscopic salt‐hydrogel photothermal composites.

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.

Enhanced capacity of thiol-functionalized sugarcane bagasse and rice husk biochars for arsenite sorption in aqueous solutions

The utilization of biowastes for producing biochar to remove potentially toxic elements from water represents an important pathway for aquatic ecosystem decontamination. Here we explored the significance of thiol-functionalization on sugarcane bagasse biochar (Th/SCB–BC) and rice husk biochar (Th/RH–BC) to enhance arsenite (As(III)) removal capacity from water and compared their efficiency with both pristine biochars (SCB–BC and RH–BC). The maximum As(III) sorption was found on Th/SCB–BC and Th/RH–BC (2.88 and 2.51 mg g−1, respectively) compared to the SCB–BC and RH–BC (1.51 and 1.40 mg g−1). Relatively, a greater percentage of As(III) removal was obtained with Th/SCB–BC and Th/RH–BC (92% and 83%, respectively) at a pH 7 compared to pristine SCB–BC and RH–BC (65% and 55%) at 6 mg L−1 initial As(III) concentration, 2 h contact time and 1 g L−1 sorbent dose. Langmuir (R2 = 0.99) isotherm and pseudo-second-order kinetic (R2 = 0.99) models provided the best fits to As(III) sorption data. Desorption experiments indicated that the regeneration ability of biochars decreased and it was in the order of Th/SCB–BC (88%) > Th/RH–BC (82%) > SCB–BC (77%) > RH–BC (69%) up to three sorption–desorption cycles. Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy results demonstrated that the thiol (-S–H) functional groups were successfully grafted on the surface of two biochars and as such contributed to enhance As(III) removal from water. Spectroscopic data indicated that the surface functional moieties, such as -S–H, − OH, − COOH, and C = O were involved to increase As(III) sorption on thiol-functionalized biochars. This study highlights that thiol-grafting on both biochars, notably on SCB–BC, enhanced their ability to remove As(III) from water, which can be used as an effective technique for the treatment of As from drinking water.Graphical

Concentration of heavy metal ions from aqueous media under dynamic conditions using a composite sorbent based on chitosan and silica

Objectives. The study set out to investigate the sorption, toxicological, and regeneration properties of a composite sorbent based on chitosan hydrogel and unsuspended silicon dioxide (chitosan–colloidal silica), which manifest themselves under dynamic conditions of purification of aqueous solutions, as a means of removing heavy metal ions.Methods. The total dynamic exchange capacity of a chitosan–colloidal silica composite sorbent was evaluated under dynamic sorption conditions by passing solutions containing Zn(II), Cd(II), Cu(II), and Cr(III) ions having a concentration of 240–251 mg/L through a fixed sorption bed. The method for determining acute toxicity using daphnia (Daphnia magna Straus) is based on the direct calculation of the mortality of daphnia exposed to toxic substances contained in the test aqueous extract in comparison with a reference culture in samples that do not contain toxic substances. The regeneration ability of the sorbent was assessed by counting the number of sorption–desorption cycles using 0.1 M NaOH and 0.1 M NaHCO3 eluents, as well as aqueous solutions of H2O2 (1 and 3%).Results. The effectiveness of the chitosan–colloidal silica composite sorbent in the process of dynamic purification of aqueous media to remove Cu(II), Zn(II), Cd(II), and Cr(III) ions was established. After determining the times of ion breakthrough and saturation of the developed sorbent, its dynamic exchange capacity was calculated by processing the kinetic curves of sorption of heavy metal ions under dynamic conditions. The results of regeneration of the sorbent were presented in the context of the possibility of its reuse. It is shown that the sorbent can withstand up to five sorption–desorption cycles while maintaining a level copper cation extraction above 90%.Conclusions. Analysis of the kinetic curves demonstrated that the driving force behind the removal of heavy metals from aqueous media by means of the obtained sorbent is the external diffusion mass transfer of ions from the mobile phase of the solution. Biotesting of samples showed that the developed chitosan-based sorbent does not have acute toxicity.

Magnetic composite chitosan/magnetite for removal of tetracycline from aqueous solutions

The synthesis of composites comprising chitosan (CS) and magnetite using the co-precipitation method yielded a compound denoted as CS/Fe3O4, which demonstrated magnetic properties. FTIR analysis confirmed the presence of magnetite nanoparticles within the composite. This CS/Fe3O4 composite proved to be highly efficient in adsorbing tetracycline (TC) from solutions of tetracycline hydrochloride (HTCCl), achieving an adsorption efficiency exceeding 65%. Moreover, the composite maintained its adsorption capacity over five cycles of sorption-desorption, indicating its robustness and reusability. The Langmuir isotherm provided a suitable description of the liquid-solid equilibrium of TC at 25 °C and 35 °C. Thermodynamic analysis revealed interesting insights into the nature of TC adsorption on CS. At low concentrations, the adsorption process was found to be exothermic, while at very high concentrations, it became endothermic. This observation suggests that the adsorption of TC at low concentrations is governed by protonation of chitosan and, at high concentrations, by entropic factors, highlighting the importance of considering thermodynamic parameters in understanding the adsorption mechanism. Overall, these findings contribute to the development of efficient and cost-effective adsorbents for the removal of TC from aqueous solutions.

Polystyrene-reduced graphene oxide composite as sorbent for oil removal from an Oil-Water mixture

This study enhanced the adsorptive capacity of polystyrene (PS) by infusing reduced graphene oxide (rGO) nanoparticles obtained from the synthesis of graphene oxide to produce PS-rGO composites via electrospinning method. Physicochemical characterization of as-synthesized rGO and PS-rGO were carried out through scanning electron microscopy, N2 physisorption among others. Oil sorption performance of synthesized rGO in crude oil, vegetable oil, fresh engine oil and used engine oil are 130.96 g/g, 121.77 g/g, 105.01 g/g and 100.56 g/g. Oil sorption capacities of electrospun pure PS in crude oil, vegetable oil, fresh engine oil and used engine oil were 46.32 g/g, 38.54 g/g, 35.14 g/g and 32.57 g/g and those of PS-rGO infused with 4 wt% of rGO were found to be 105.52 g/g, 98.86 g/g, 86.25 g/g and 83.47 g/g for crude oil, vegetable oil, fresh engine oil and used engine oil samples respectively. Pseudo second order (PSO) kinetic model fits the sorption data of the four oil samples on the four composite sorbents produced. Intra-particle diffusion (IPD) model evidently showed that sorption of the four oil samples on the four composite sorbents, occurred in three (3) phases. Composites demonstrate high oil adsorption capacity, and are reusable upto three sorption–desorption cycles.

Selective biosorption and recovery of scandium using the alga Fucus vesiculosus

The goal of this work was to study the viability of the application of biosorption using the brown alga Fucus vesiculosus in the recovery of scandium from red mud. The highest affinity of the biosorbent for scandium and aluminium was at pH 3. Sorption isotherms fitted to the Langmuir model for scandium and aluminium with adsorption capacities as high as 1.04 mmol·g−1 for both metals but with higher affinity for scandium than for aluminium. The performance of the biomass in fixed-bed columns was evaluated in different experimental conditions (flow rate, bed height and inlet metal concentration). Metal desorption was achieved with different inorganic and organic acids. After three consecutive sorption–desorption cycles using 0.1 N citric acid and deionized water during the regeneration step, the brown alga showed a progressive increase in scandium uptake due to the cross-linking citric acid and the alginate chains. The biomass was characterized before and after biosorption using Fourier transforms infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) coupled with an energy dispersive elemental analyser (EDS). The sorption involves different functional groups, such carboxylate and sulphonic groups by chelation and electrostatic interactions.

Hydrophobization of Reduced Graphene Oxide Aerogel Using Soy Wax to Improve Sorption Properties.

A special technique has been developed for producing a composite aerogel which consists of graphene oxide and soy wax (GO/wax). The reduction of graphene oxide was carried out by the stepwise heating of this aerogel to 250 °C. The aerogel obtained in the process of the stepwise thermal treatment of rGO/wax was studied by IR and Raman spectroscopy, scanning electron microscopy, and thermogravimetry. The heat treatment led to an increase in the wax fraction accompanied by an increase in the contact angle of the rGO/wax aerogel surface from 136.2 °C to 142.4 °C. The SEM analysis has shown that the spatial structure of the aerogel was formed by sheets of graphene oxide, while the wax formed rather large (200-1000 nm) clumps in the folds of graphene oxide sheets and small (several nm) deposits on the flat surface of the sheets. The sorption properties of the rGO/wax aerogel were studied with respect to eight solvent, oil, and petroleum products, and it was found that dichlorobenzene (85.8 g/g) and hexane (41.9 g/g) had the maximum and minimum sorption capacities, respectively. In the case of oil and petroleum products, the indicators were in the range of 52-63 g/g. The rGO/wax aerogel was found to be highly resistant to sorption-desorption cycles. The cyclic tests also revealed a swelling effect that occurred differently for different parts of the aerogel.

Facile preparation of cellulose nanofiber/ZSM-5 zeolite/polyethyleneimine aerogel for selective adsorption of Cu2+ in wastewater

The development of a cost-effective and environmentally friendly adsorbent is essential for effectively removing heavy metals from wastewater. This study presents the preparation of a recyclable cellulose nanofiber (CNF)/ZSM-5 zeolite/polyethyleneimine (PEI) aerogel through chemical crosslinking and freeze-drying techniques. The synthesized aerogel was applied for the highly selective adsorption of Cu2+. The characterization of the as-prepared aerogel indicates that its three-dimensional network porous structure, along with the abundance of active sites, contributes to the effective adsorption of Cu2+. The adsorption capacity was found to be 134.23 mg/g. Furthermore, it was observed that Cu2+ adsorbed by the composite aerogel could be efficiently eluted using 0.2 M EDTA-2Na. The adsorption kinetics and isotherm studies revealed consistency with the pseudo-second-order model and Langmuir model, indicating that the adsorption process was primarily governed by monolayer chemisorption. Mechanism analysis further confirmed that surface complexation, ion exchange, and electrostatic interaction were the primary driving forces behind the excellent adsorption capabilities of the prepared aerogel. Remarkably, the structural integrity and selective adsorption of the composite aerogel remained largely unchanged even after undergoing five sorption-desorption cycles. These findings strongly suggest that the CNF/ZEM-5/PEI composite aerogel holds significant promise for achieving efficient and selective removal of copper ions in wastewater.

Structural transformation investigations of δ to α manganese dioxides: Phosphate sorption and its mechanism

The elevation of environmental phosphate levels can negatively impact both the natural environment and human health. To address this issue, a series of MnO2 sorbents were investigated in this study. A facile one-pot synthesis method was employed to fabricate distinct morphologies and crystalline structures by controlling the hydrothermal duration. As the hydrothermal duration was prolonged, the samples demonstrated a pronounced enhancement of stability and crystalline phases, along with a corresponding increase in structural oxygen vacancies. A series of sorption performance tests were conducted, including pH effect, sorption isotherm, sorption kinetics, co-existing ions and sorption–desorption cycles experiments. It was revealed that manganese dissolution, the surface charge of the sorbents, and the phosphate species at different pH values collectively influenced the sorption process. The sorbent α-MnO2-120 h, with the highest oxygen vacancy ratio, exhibited the best sorption performance towards phosphate ions, with the maximum sorption capacity at pH 7. The highest removal rate and kd value were 82.63 % and 2.29 × 103 mL g−1, respectively, at the initial concentration of 30.7 mg PO4 g−1. The α-MnO2-120 h sorbent exhibited excellent selectivity in the presence of NO3−, SO42−, CO32−, and SiO32−. Furthermore, the regenerated material exhibited only a 6 % decrease in phosphate removal efficiency after five cycles, with no structural changes observed. A novel mechanism was proposed, highlighting the dominance of covalent chemical reactions in the sorption process. In particular, the participation of oxygen vacancies in sorbents contributed to enhancing the effective removal of phosphate ions. Overall, this study successfully demonstrated that synthesized α-MnO2 is a promising sorbent for phosphate removal.

An O/N/S-rich porous Fe-based metal-organic framework (MOF) for gold recovery from the aqueous phase with excellent performance

Recovering gold from wastewater has both economic and environmental benefits. However, how to effectively recover it is challenging. In this work, a novel Fe-based metal-organic framework (MOF) was synthesized and decorated with 2,5-thiophenedicarboxylic acid to have a well-developed porous architecture to effectively recover Au(III) from water. The maximum Au(III) sorption capacity by the finally-synthesized porous material MIL-101(Fe)-TDCA reached 2350 mg/g at pH = 6.00 ± 0.15, which is one of the highest among all literature-reported relevant materials including MOFs, and high sorption strength can be maintained within a wide pH range from 2.0 to 10.0. Besides, Au(III) sorption efficiency at low concentrations (i.e., 3.5 × 104 mg/mL) reached over 99%. Mechanically, outstanding Au(III) sorption by MIL-101(Fe)-TDCA resulted from the O/N/S-containing moieties on its surface, large surface area and porosity. The N- and S-containing functionalities (CS, CONH) served as electron donors to chelate Au(III). The O-containing (FeOFe, COFe, COOH, and coordinated H2O) and N-containing (CONH) moieties on MIL-101(Fe)-TDCA interacted with OH groups on the hydrolyzed species of Au(III) (AuCl3(OH)−, AuCl2(OH)2−, and AuCl(OH)3−) by hydrogen bond, which further increased Au(III) sorption. Furthermore, about 45.71% of Au(III) was reduced to gold nanoparticles by CS groups on the decorated 2,5-dithiophene dicarboxylic acid during sorption on MIL-101(Fe)-TDCA. Over 98.35% of Au(III) was selectively sorbed on MIL-101(Fe)-TDCA at pH 4.0, much higher than that of the coexisting heavy metal ions including Cu(II), Zn(II), Pb(II), and Ni(II) (< 5%), despite their same concentration at 0.01 mg/mL. Although sorption selectivity of a noble metal Pt(IV) by MIL-101(Fe)-TDCA is relatively poor (68.23%), it could be acceptable. Moreover, reusability of MIL-101(Fe)-TDCA is also excellent, since above 90.5% Au(III) still can be sorbed after two sorption-desorption cycles. Overall, excellent sorption performance and the roughly-calculated gold recycling benefits (26.30%) highlight that MIL-101(Fe)-TDCA is a promising porous material for gold recovery from the aqueous phase.

Fabrication of Fe-CoS2@N-doped C electrode for highly efficient and durable electrosorption of Yb(III) from aqueous solutions

In this study, the novel Fe-doped CoS2@nitrogen-doped carbon (Fe-CoS2@NC) composites were manufactured and investigated as the capacitive deionization (CDI) electrode materials for electrosorption of Yb(III). The as-prepared materials were characterized with X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, N2 adsorption–desorption test with Brunauer-Emmett-Teller method, Raman spectroscopy, and X-ray photoelectron spectroscopy. The electrochemical tests, including cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy, revealed that Fe-CoS2@NC exhibited the better electrochemical performance with a specific capacitance of 58.41 F g−1 than Fe-CoS2@0.5NC and Fe-CoS2. The electrosorption results demonstrated that Fe-CoS2@NC possessed the Yb(III) uptake of 129.4 mg·g−1 within 60 min at a voltage of 1.2 V and a flow rate of 20 mL·min−1. After five successive sorption–desorption cycles, the electrosorption efficiency of Fe-CoS2@NC remained at 98 %, exhibiting the robust durability for future industrial application. Furthermore, Fe-CoS2@NC also showed the favorable electrosorption performance towards various rare earth ions, especially for heavy rare earth ions. The mechanism analysis indicated that the impressive electrosorption performance is attributed to the synergistic contribution by the electric double layers of carbonaceous matrix and the pseudo-capacitance that induced by the redox reactions of Fe atom.

Utilization of water hyacinth (Eichhornia crassipes) biomass as eco-friendly sorbent for petroleum oil spill cleanup

Abstract This study focuses on the removal of spent engine oil (SEO) spill from the water surface using water hyacinth biomass (WHB)-based sorbents. The raw WHB was modified using extra virgin coconut oil (mainly consisting of lauric acid) to enhance the hydrophobicity and floating ability. With varying amounts of coconut oil and solvent, six diverse types of modified water hyacinth biomass (MWHB) were prepared. Among these MWHBs, an equal proportion of coconut oil and raw WHB with 10% methanol solution exhibited the highest removal of SEO reaching 96%. Various sorption kinetics and isotherm models were examined to understand the SEO sorption process on MWHB. The pseudo-second-order kinetics (R2 0.999) and both the Langmuir and Freundlich isotherm models (R2 0.992 and R2 0.999, respectively) were found to be the best-fitting models. These findings indicated a chemisorption mechanism involving the initial monolayer coverage of SEO molecules on the MWHB surface followed by the development of multilayers. The MWHB achieved a maximum sorption capacity of 4.75 g/g within 60 min. Furthermore, the reusability tests showed that MWHB maintained a sorption capacity of over 90% even after the third sorption–desorption cycle.

Synthesis and characterization of new generation of sorbent materials and their application in the elimination of diclofenac: Numerical analysis using Comsol software

This paper reports the preparation of a new class of eco- friendly sorbents as well as the study of the continuous dynamic sorption of diclofenac (DF) chosen as a model representative of pharmaceutical pollutants. Biomass based on palm waste was used as base material in the presence of 27% commercial polymer carbopol as granular support, 10% tween 80 as surfactant and NaOH in the preparation of hydrophobic and organophilic effective sorbent grains. Multiple experiments were conducted to investigate the impact of initial diclofenac concentration (20–50 mg/L), flow rate (1.11–1.82 L/h), and column height (10–15 cm) on the breakthrough curve. The maximum adsorption capacity was found to be 137 mg/g under a flow rate of 1.11 L/h, column height 15 cm and inlet concentration of diclofenac of 20 mg/L. The experimental data obtained data were fitted using the empirical models of Thomas, Yoon - Nelson and Adam-Bohart. The reusability assessment demonstrated the potential for reusing this active biomass for a minimum of three adsorption –desorption cycles. The breakthrough curves indicated a positive correlation between breakthrough time and column height, while initial diclofenac concentration and flow rate exhibited negative correlations. The utilization of the Thomas model effectively described the sorption process, supported by a highly satisfactory correlation coefficient (R² > 0.98). However, a marginal decrease in the sorption capacity of diclofenac was observed with the number of sorption-desorption cycles, with reductions of 24%, 10%, and 5%, respectively.

Carbon capture from low CO2 concentration stream through ternary alkali metal nitrates promotion of MgO sorbents at intermediate temperature and low space velocity

Many MgO sorbents exhibit high CO2 uptake in the presence of high concentration CO2 and aided by high space velocity, which unfortunately leads to low CO2 capture efficiency from the gas stream. This study investigates the effect of Li/Na/K ratio on sorption performance in dilute CO2 streams (15% CO2) using alkali metal nitrates-promoted MgO sorbents at a low space velocity of 20 ml/g·min in fixed bed reactor. Study shows that the ratio of Li/Na/K in ternary alkali nitrate salt mixture significantly affects the induction periods for the second phase CO2 sorption, which is a key contributor to high CO2 uptake. High LiNO3 content in ternary mixture leads to long induction period, and therefore lower CO2 capacity during the 4 h period. Conversely, high ratios of NaNO3 and KNO3 leads to shorter induction periods. Among the samples, MgO with 9 mol% (Li0.18Na0.52K0.3) exhibits the highest CO2 sorption capacity of 5.56 mmol/g at 240°C in 4 h (20.6% CO2 capture efficiency) and 3.18 mmol/g after 5 cycles (10.8% CO2 capture efficiency). Comparative studies show that optimal temperatures for CO2 sorption are higher when using pure CO2 (280 to 320°C) than when using 15% CO2 (240°C) due to the thermodynamic equilibrium. CO2-TPD results indicate that CO2 desorption proceeds in two phases similar to CO2 sorption, and the presence of alkali salt in MgO also promotes the decomposition of bulk carbonate to CO2. It is shown that molten salt migration and agglomeration of MgO particles are likely the factors that lead to decline in CO2 uptake over the sorption-desorption cycles.

The influence of chemical composition and preparation procedure on CO2 capture performance of NaNO3 /MgO-based sorbents

MgO based sorbents modified by 5–50 mol.% NaNO3 have been prepared by various methods and investigated in detail. It has been showed that optimal synthesis method is incipient wetness impregnation of MgO precursor with sodium nitrate water solution. The highest sorption capacity of 6.5 mmol CO2 g–1 sorb after 1 hour of sorption from the gas mixture with 50 vol.% CO2 at 320 °C was achieved using the MgO modified by 10 mol.% NaNO3. Sorption capacity for MgO modified by 10 mol.% NaNO3 during 10 consecutive sorption-desorption cycles is approximately 4.5–5.5 mmol CO2 g–1 sorb. The duration of the sorption stage is 30 min, the CO2 content in the feed gas is 50 vol.% and sorption-regeneration temperature is 300–350 °C respectively. It has been showed that increasing the sorption pressure to 10 bar allows reducing sorption temperature from 320 °C to 220–260 °C. The sorption capacity is reached up to 4.0 mmol CO2 g–1 sorb at 25 vol.% CO2 that is twice higher than that at 1 bar. It has been demonstrated that steam and hydrogen treatment before sorption doesn’t lead to a significant change in the sorption properties and phase composition of NaNO3 modified MgO-based sorbent.

A novel spherical micro-absorber for dehumidification systems

In this work, a novel design concept for absorbers used in dehumidification systems is proposed to overcome the practical challenges of the conventional packed-column absorbers. In the proposed design, spherical micro-absorbers (microcapsules) that contain a liquid LiBr desiccant inside a semi-permeable polymeric membrane shell are produced by using a custom-built microfluidic technique. The produced microcapsules are capable of containing the salt during crystallization. The X-ray diffraction analysis has confirmed that the observed crystals in the microscopes images were indeed for the encapsulated (LiBr) salt. Due to the indirect contact between the liquid desiccant and the process air, problems such as solution carryover and corrosion associated with packed-column absorbers can be eliminated. The collected sorption data show that the spherical microcapsules offer a high sorption capacity of 1 gw/gdry under 80% relative humidity. The proposed microcapsules offer surface-to-volume ratios between 6,000–12,000 m2/m3, which is up to two orders of magnitude higher than the conventional packed-column absorbers (200–600 m2/m3). The produced micro-absorbers can withstand a compression force up to 2 × 105 their weight, elastically expanded during the absorption process without rupture, and did not show a leakage or a reduction in capacity even after an accelerated test of 200 sorption-desorption cycles.

Effects of alkali-metal nitrate salts on hydrotalcite-based sorbents for enhanced cyclic CO2 capture at high temperatures

CO2 capture using solid-based adsorbents at high temperatures has been in the spotlight as a CO2 capture and storage (CCS) technology for solving global warming and climate change problems. Hydrotalcite is an anionic clay that is widely used as a CO2 sorbent at temperatures of 200–400 °C. In various methods to improve the relatively low CO2 uptake of hydrotalcite, the hydrotalcites with a high Mg/Al molar ratio achieved significantly increased CO2 sorption uptake. This was because the preparation method allowed incorporation of NaNO3 in the hydrotalcite structure; the maximum CO2 sorption uptake was measured as 28.4 wt% when the Mg/Al molar ratio was 30. The different degrees of NaNO3 melting, depending on the sorption temperature, led to different CO2 sorption kinetics and uptakes at 250, 275, and 300 °C. Over the repeated sorption-desorption cycles, the CO2 cyclic capacity continuously decreased under sorption at 250 and 275 °C, whereas it increased at 300 °C, regardless of the Mg/Al molar ratio. The partial melting of NaNO3 at 250 and 275 °C, below its melting temperature, provided insufficient rearrangement of molten NaNO3. This further caused sintering of the MgO structure, which also increased its crystallite size. Conversely, the accelerated rearrangement of molten NaNO3 at 300 °C, near its melting temperature, and the low CO2 uptake at the initial step inhibited sintering. Different changes in the strength of CO2 sorption on the hydrotalcite-based sorbents also appeared as the cycle number increased.

Doping birnessite as a method for synthesizing an ion exchanger selective to strontium and repeatedly working in sorption-desorption cycles

Manganese oxides represent an environmentally friendly and industrially scalable class of materials exhibiting sorption properties for Sr2+. However, there is a critical challenge of the drop in the exchange capacity in the processes of sorption and desorption. In the paper, there are proposed and have experimentally been tested the routes for enhancing stability of manganese oxides in the cycled ion exchange processes. There were analyzed the properties of the doped and “pure” birnessite in Sr-form and H-form. The strontium exchange capacity of doped Fe, Co, Ni samples increases with increasing cycling, whereas that of an undoped sample decreases. The samples doped with Fe and Co at 150°С proved to be most stable during cycling, with those doped with Ni and Co being such at modification temperature 360°С. Introduction of Ni and Co was evinced to favor preserving both the strontium exchange capacity and selectivity.