Properties Of Sorbents Research Articles

Regenerable potassium-based alumina sorbents prepared by CO2 thermal treatment for post-combustion carbon dioxide capture

Potassium carbonate supported on alumina is used as a solid sorbent for CO2 capture at low temperatures. However, its CO2 capture capacity decreases immediately after the first cycle. This regeneration problem is due to the formation of the by-product [KAl(CO3)(OH)2] during CO2 sorption. To overcome this problem, a new regenerable potassium-based sorbent was fabricated by CO2 thermal treatment of sorbents prepared by the impregnation of δ-alumina with K2CO3 in the presence of 10 vol% CO2 and 10 vol% H2O. The CO2 capture capacities of the new regenerable sorbents were maintained over multiple CO2 sorption tests. These results can be explained by the fact that the sorbent prepared by CO2 thermal treatment did not form any by-product during CO2 sorption. Based on these results, we suggest that the regeneration properties of potassium-based sorbents using δ-alumina could be significantly improved by the use of the CO2 thermal treatment developed in this study.

Hydrogen sulfide removal using CeO2/NaOH/PSAC: Effect of process conditions and regeneration study

Present investigations reported in the literature on the preparation of activated carbon that can be used effectively to remove H2S from biogas. However, apart from the synthesis of a reactive sorbent, the process conditions can also significantly influence the performance of the sorbent. Therefore, the aim of this study is to investigate the effect of process conditions; sorption temperature, H2S concentration, sorbent loading, flow rate and the presence of other gas components on the performance of activated carbon based sorbent for H2S removal. In this study, palm shell activated carbon was impregnated with CeO2 and NaOH. H2S sorption capacity of the optimized sorbent was found to be increasing with decreasing sorption temperature, minimum at 2000ppm H2S, increasing with increasing sorbent loading, maximum at 500mL/min and maximum at 25% relative humidity. CO2 and CH4 were found to affect sorption capacity in a different extent. Regeneration efficiency as high as 78% was achieved using heat treatment at 500°C regeneration temperature and four hours regeneration time. Selected sorbents were characterized in order to further understand the sorbent properties and characteristics of the reaction.

Agricultural Drainage Filters. II. Phosphorus Retention and Release at Different Flow Rates

Granular drainage filters may provide new innovative solutions for removing phosphorus (P) from agricultural tile drainage water. The influence of filter sorbent properties is well recognized; however, intragranular diffusion may be critical for the P retention efficiency in drainage filters, where convective velocities are generally high. This was investigated in granular materials (Leca, Filtralite-P®, granulated Limestone, crushed Seashells, calcined diatomite earth (CDE), and poorly ordered Fe hydroxide aggregates (CFH)) with known solute transport behavior at variable flow rates. Phosphorus retention and release were investigated during continuous P loading with a constant inlet concentration of 0.3 mg P L−1 followed by a subsequent P release phase. A parallel batch sorption experiment ranked the materials according to strength of P retention CFH > Filtralite-P® > Seashells > Limestone > Leca, while CDE was a P source at low solution concentrations. Column experiments demonstrated that filters with non-equilibrium transport (CFH and Seashells) attained higher P retention rates and lower P release rates compared to filters with equilibrium flow (Filtralite-P® and Limestone). This behavior was even more pronounced as flow rate increased and was attributed to intragranular diffusion of P in CFH and Seashells, which would maintain concentration gradients between mobile convective water and immobile domains. This facilitated further diffusion and thus increased P retention. In addition, the release of previously retained P was limited in filters with non-equilibrium transport ( 5 %). The results demonstrated that intragranular diffusion was an important mechanism increasing P retention.

Removal of perfluorinated surfactants from wastewater by adsorption and ion exchange — Influence of material properties, sorption mechanism and modeling

Perfluorooctane sulfonate (PFOS) has attracted increasing concern in recent years due to its world-wide distribution, persistence, bioaccumulation and potential toxicity. The influence of sorbent properties on the adsorptive elimination of PFOS from wastewater by activated carbons, polymer adsorbents and anion exchange resins was investigated with regard to their isotherms and kinetics. The batch and column tests were combined with physicochemical characterization methods, e.g., N2 physisorption, mercury porosimetry, infrared spectroscopy, differential scanning calorimetry, titrations, as well as modeling. Sorption kinetics was successfully modelled applying the linear driving force (LDF) approach for surface diffusion after introducing a load dependency of the mass transfer coefficient βs. The big difference in the initial mass transfer coefficient βs,0, when non-functionalized adsorbents and ion-exchange resins are compared, suggests that the presence of functional groups impedes the intraparticle mass transport. The more functional groups a resin possesses and the longer the alkyl moieties are the bigger is the decrease in sorption rate. But the selectivity for PFOS sorption is increasing when the character of the functional groups becomes more hydrophobic. Accordingly, ion exchange and hydrophobic interaction were found to be involved in the sorption processes on resins, while PFOS is only physisorptively bound to activated carbons and polymer adsorbents. In agreement with the different adsorption mechanisms, resins possess higher total sorption capacities than adsorbents. Hence, the latter ones are rendered more effective in PFOS elimination at concentrations in the low μg/L range, due to a less pronounced convex curvature of the sorption isotherm in this concentration range.

Evolution of sorptive and textural properties of CaO-based sorbents during repetitive sorption/regeneration cycles

The evolution of sorptive and textural properties of CaO-based sorbents during repetitive sorption/regeneration cycles has been mathematically simulated. The proposed model takes into account the morphology of nascent CaO, sorbent sintering physics and CO2 sorption kinetics. The results show that the model is in good agreement with the experimental data for real sorbents and predicts the dependence of the recarbonation extent on the number and duration of the sorption/regeneration cycles well. The model obtained allows predicting the change of the textural properties of the sorbent (e.g. the values of specific surface area and mean pore size) during the sorption/regeneration cycles.

Organosilatranes with Acylthiourea Derivatives – Metal‐Ion Binding, Substituent‐Dependent Sensitivity, and Prospects for the Fabrication of Magnetic Hybrids

A variety of topologically interesting acylthiourea‐tethered organosilatranes (AcTu‐OS) were prepared, and their function as metal‐ion binding sites was investigated. The prepared compounds have been characterized by elemental analysis; FTIR, UV/Vis and NMR (1H and 13C) spectroscopy; and mass spectrometry. The organosilicon complexes 4a–4e possess diverse coordination abilities for the surveyed metal ions (Cu2+, Cd2+, Hg2+ and Pb2+), as was appraised by the corresponding absorption shifts in the UV/Vis spectra. In addition, a facile preparatory route for the covalent grafting of the most efficient receptor 4e onto a silica‐encrusted magnetic nanosupport was implemented. The resultant organic–inorganic hybrid nanoparticles (H‐NPs) were characterized by physicochemical techniques such as FTIR spectroscopy, XRD, thermogravimetric analysis (TGA), TEM, field‐emission SEM (FE‐SEM) and energy‐dispersive X‐ray spectroscopy (EDX). The grafting of the sensory module afforded active sites for the adsorption of metal ions from the aqueous solution which is outlined using the Langmuir adsorption isotherm. The potential in sensing, sorbent properties and facile magnetic recovery of the hybrid evinces the separation process practical to undertake environmental issues.

Magnetic Nanocomposites as Efficient Sorption Materials for Removing Dyes from Aqueous Solutions.

Magnetic composite sorbents based on saponite clays with different content of magnetite (2–7 wt%.) were synthesized. The samples were analyzed by X-ray diffraction methods, and it was found that the Fe3O4 in composites is in the nanorange. It has been shown that the magnetic nanocomposites have more developed microporosity and mesoporosity compared to saponite clay. The sorption properties of magnetic nanocomposite sorbents were determined, and the results evidenced that their efficiency is significantly higher than the individual phases of the composite. It was shown that all waste composite magnetic sorbents are successfully removed from the water environment by magnetic separation.

Potassium-based dry sorbents for removal of sulfur dioxide at low temperatures

The SO2 sorption properties of dry potassium-based sorbents, prepared by impregnation of various supports with potassium carbonate, were investigated at the various water vapor concentrations at a level of 5000ppm of SO2. It was found that alkali metal-based sorbents promoted with potassium carbonate could be used as a sorbent for SO2 sorption at low temperatures (between 30°C and 60°C). In particular, the potassium-based sorbents showed an excellent SO2 sorption capacity of about 310mg SO2/g sorbent in the presence of water vapor, while in the absence of water vapor, their SO2 sorption capacities decreased.

Improved performance of electrodes based on carbonized olive stones/S composites by impregnating with mesoporous TiO2 for advanced Li—S batteries

Carbons obtained from biomass have attracted a lot of attention for use as electrodes for Li-ion batteries. Less attention has been paid to their use in LiS batteries in spite of the higher energy densities. Here, we optimized the electrochemical properties of an activated carbon (OSAC) obtained from olive stones with the help of mesoporous TiO2. The OSAC@TiO2/S hybrid composite exhibited improved electrochemical performance compared with the OSAC/S composite. The presence of TiO2 increased the delivered capacity of the cell by more than 60%, and the rate capability was notably improved. The cell could operate at current densities of 3350 mA g−1 (2 C), releasing an average capacity of 500 mAh g−1 with a coulombic efficiency close to 100%. This improvement in the electrochemical performance is attributed to the sorbent properties of TiO2 towards Li polysulfides and its facility to insert Li, which enhances the electronic and ionic conductivity of the hybrid composite.

Effect of microwave irradiation on the preparation of iron oxide/arenaceous clay sorbent for hot coal gas desulfurization

For applications in the high temperature coal gas desulfurization process, iron oxide/arenaceous clay sorbents were prepared by microwave irradiation and conventional heating, respectively. The desulfurization performances of sorbents were evaluated using a fixed-bed reactor with simulated coal gas. The effects of calcination temperature and microwave heating time on the properties of sorbents were also investigated. The microwave-irradiated sorbents exhibit sulfur capacity and reactivity greater than those prepared by conventional heating. X-ray diffraction, X-ray photoelectron spectroscopy, a scanning electron microscope, a transmission electron microscope and N2 adsorption were used to characterize the physical and structural properties of the sorbents. Several benefits have been observed using microwave heating rather than conventional heating for the preparation of sorbents. The results indicate that microwave irradiation leads to better inner structure of sorbent and more uniform distribution of the active component with smaller particle size, which facilitate chemical reaction and mass transfer. Microwave irradiation also results in greater outer layer electron density and higher contents of surface metal element, both of which are beneficial to the increase of absorption efficiency and desulfurization reactivity. Then the microwave-irradiated sorbents were tested for three successive sulfurization–regeneration cycles, the 3rd regenerated sorbent still performed well with no apparent deterioration, it proved that the sorbent has good regenerability and is suitable for hot gas desulfurization.

Effect of temperature-programmed pyrolysis pre-treatment on desulfurization performance of Zn-based sorbent prepared by lignite as support

A series of Zn-based sorbents were prepared by high-pressure impregnation with lignite as precursor of support and zinc nitrate as the precursor of active component, followed by temperature-programmed pyrolysis of the impregnated lignite sample in a fixed-bed quartz reactor. The H2S removal performances of sorbents prepared under different pyrolysis conditions such as temperatures, holding time as well as heating rates were evaluated. The physical and chemical properties of sorbents were characterized by atomic absorption spectroscopy (AAS), X-ray diffraction (XRD), transmission electron microscope (TEM) and nitrogen adsorption techniques. The results show that the process of pyrolysis can improve the pore structure dramatically, which lead to the high specific surface area and large pore volume. The good desulfurization performance of sorbent was attributed to both of the proper porous structure of sorbents, the content and distribution of active component. The optimal operating conditions of temperature-programmed pyrolysis for the impregnated lignite sample were the heating rate of 10°C/min, holding time of 180min in N2 atmosphere and pyrolysis temperature of 550°C. The sulfidation time could hold for over 720min before reaching 1ppm H2S in outlet gases and the sulfur capacity was up to 25.91g S/100g ZnO for sorbent prepared under this optimized condition.

Sorbents for Extracorporeal Removal of Toxic Substances and Molecules with Adverse Biological Activity (Review)

The review devoted to sorbents and sorbentbased medical devices used in clinical practice for extracorporeal detoxification using a hemoperfusion technique. Clinical data have confirmed the effectiveness of this approach for removal of bacterial endotoxins, lowdensity lipoproteins, and bilirubin. Other studies demonstrated successful application of sorbents to treat autoimmune diseases. Special attention is paid to hemoperfusion in as a possible treatment for severe sepsis and septic shock. The review justifies importance of development and application of novel multimodal sorbents, which combine both properties of selective and nonselective sorbents. The review discusses clinical efficacy of hemoperfusion and key molecular interactions between the sorbent and circulating molecules pathogenetically relevant to developing critical illness and severe diseases. The reference list: 137.

Effects of microwave irradiation on H2S removal activity from hot coal gas by modified semicoke-supported ZnO sorbents

To improve the desulfurization performance of sorbents at a low cost, modified semicoke-supported zinc oxide sorbents were prepared for hot coal gas by calcining the precursors using microwave and conventional heating. The desulfurization performances of these sorbents were evaluated over a fixed-bed reactor. The effects of microwave-assisted calcination temperature and time on the properties of sorbents were also investigated. These sorbents were characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, and nitrogen adsorption. The results show that the sorbents calcined by microwave exhibited a much higher sorbent utilization and desulfurization efficiency than those heated by conventional method. Compared to conventional heating, even and rapid heating of microwave led to smaller crystal size and better dispersion of active species. The Brunauer–Emmett–Teller results confirm that microwave irradiation modified the microstructure improved the pore structure (an increase in the specific surface area and pore volume), thus facilitating the gas–solid interactions during the desulfurization processes. A higher concentration of elements Zn and O was observed on the surface of sorbents by XPS analysis, facilitating the reaction of active species with H2S. The performance of the sorbents heated by microwave irradiation appeared to be stable over multiple sulfidation–regeneration cycles.

Effect of regeneration atmosphere on the properties of an iron oxide desulphurisation sorbent for high-temperature coal gas desulphurisation

Desulphurisation sorbent properties, including desulphurisation activity and mechanical strength, are important in the sulphidation/regeneration cycle for high-temperature coal gas desulphurisation. In this paper, α-Fe2O3 desulphurisation sorbent was prepared and the changes in its mechanical strength and the surface morphology after regeneration in O2, SO2 and SO2–O2 atmospheres were measured with a particle strength tester and by scanning electron microscopy. The mechanical strength of the sorbent was generally higher after regeneration, although the formation and decomposition of sulphate during regeneration decreased the mechanical strength of the sorbent. The sulphate formation and decomposition depended on the O2 and SO2 concentration and the regeneration temperature. The mechanical strength was also increased by the sorbent sintering.

MECHANISMS OF THE COMPLEX FORMATION BY d-METALS ON POROUS SUPPORTS AND THE CATALYTIC ACTIVITY OF THE FORMED COMPLEXES IN REDOX REACTIONS

The catalytic activity of supported complexes of d metals in redox reactions with participation of gaseous toxicants, PH3, CO, O3, and SO2, depends on their composition. Owing to the variety of physicochemical and structural-adsorption properties of available supports, their influence on complex formation processes, the composition and catalytic activity of metal complexes anchored on them varies over a wide range. The metal complex formation on sup-ports with weak ion-exchanging properties is similar to that in aqueous solutions. In this case, the support role mainly adds up to the ability to reduce the activity of water adsorbed on them. The interaction between a metal complex and a support surface occurs through adsorbed water molecules. Such supports can also affect complex formation processes owing to protolytic reactions on account of acidic properties of sorbents used as supports. The catalytic activity of metal complexes supported on polyphase natural sorbents considerably depends on their phase relationship. In the case of supports with the nonsimple structure and pronounced ion-exchanging properties, for instance, zeolites and laminar silicates, it is necessary to take into account the variety of places where metal ions can be located. Such location places determine distinctions in the coordination environment of the metal ions and the strength of their bonding with surface adsorption sites and, therefore, the catalytic activity of surface complexes formed by theses metal ions. Because of the energy surface inhomogeneity, it is important to determine a relationship between the strength of a metal complex bonding with a support surface and its catalytic activity. For example, bimetallic complexes are catalytically active in the reactions of oxidation of the above gaseous toxicants. In particular, in the case of carbon monoxide oxidation, the most catalytic activity is shown by palladium-copper complexes in which copper(II) is strongly fixed on a support surface as a result of the ion exchanging and palladium(II) is bound with copper(II) through a water molecule or some other ligands. The formation of surface complexes can occur as a result of the covalent binding of 3d metals with ligands preliminarily immobilized on supports. However, the examined complexes with aerosol immobilized Schiff bases are catalytically active only in the reaction of ozone decomposition.

Hollow Fe3O4@mesoporous carbon core–shell microspheres for efficient sorption of radionuclides

Hollow Fe3O4@mesoporous carbon (h-Fe3O4@mC) microspheres have been synthesized using silica nanospheres as the sacrificial matrix. Physiochemical properties, surface morphology, and internal structures of the as-prepared products have been carefully characterized. The synthesized h-Fe3O4@mC microspheres have been applied to adsorb radionuclides from aqueous solutions and can be easily separated by an external magnetic field. Effects of contact time, pH, and initial concentrations on the interaction of h-Fe3O4@mC with U(VI), Eu(III), Co(II), and Sr(II) have been studied. The sorption is strongly dependent on pH and can reach equilibrium within 2 h. Dependence of sorption on pH is relevant to both the surface properties of sorbents and the relative distribution of radionuclides species in solutions. Due to the mesoporous structure, carboxyl-functionalized surface, and low density, h-Fe3O4@mC shows efficient sorption for radionuclides even in acidic solutions. The maximum sorption capacities of U(VI), Eu(III), Co(II), and Sr(II) on h-Fe3O4@mC at pH 3.0 and T = 298 K calculated from the Langmuir model are 0.566, 1.013, 0.860, and 0.733 mmol g−1, respectively. Findings of the present work suggest that h-Fe3O4@mC can serve as a promising candidate for recovery and removal of radionuclides from aqueous solutions in the environmental pollution management.

Physicochemical and adsorption properties of carbonaceous sorbents prepared by activation of tropical fruit skins with potassium carbonate

A series of new carbonaceous adsorbents has been obtained by means of chemical activation of common tropical fruit peels with potassium carbonate. The influence of the precursor on the porous structure development, acidic and basic surface group generation, as well as the sorptive properties of the adsorbents prepared towards liquid pollutants, was tested.The products of thermo-chemical treatment of grapefruit, mandarin, pomelo and banana peels were microporous carbonaceous sorbents with relatively high contribution of mesopores (of diameters within the range of 2–10nm), characterised by well-developed surface area ranging between 836 and 1198m2/g, containing mainly acidic surface functional groups. Moreover, the results obtained during the study proved that a proper selection of biomass treatment process allows getting adsorbents with a very high sorption capacity towards methylene blue and methyl red as well as inorganic pollutants of molecules of size similar to that of iodine molecules.

Sorption and selective chromatographic properties of isomer-selective composite sorbent based on a eutectic mixture of nematic liquid crystals and perbenzoylated β-cyclodextrin

Mesomorphic, sorption, and selective properties of a three-component sorbent based on a mixture of nematic (N) liquid crystals of 4-methoxy-4′-ethoxyazoxybenzene (MEAB) and 4,4′-diethoxyazoxybenzene (azoxyphenetol, AOP) of an eutectic composition and heptakis-(2,3,6-tri-O-benzoyl)-β-cyclodextrin (Bz-β-CD) are studied. For 30 organic compounds of different classes with linear and cyclic molecular structures, including optical isomers of limonene, pinene, camphene, and butanediol-2,3, thermodynamic functions are determined for their gas-phase sorption using a three-component MEAB-AOP-Bz-β- CD sorbent (62: 28: 10 wt %). It is found that the investigated sorbent possesses high structural selectivity (αp/m = 1.128–1.059, 100–130°C, N) and moderate enantioselectivity (1.07–1.02) within a broad temperature range (95–170°C) including both mesomorphic and isotropic phases of the sorbent. It is shown that the enantioselectivity of the sorbent is apparent under conditions of both increasing retention when a chiral Bz-β-CD additive is introduced into the MEAB–AOP system (limonenes, pinenes, camphenes) and decreasing retention (butanediols-2,3).

Adsorption properties of magnetic ferrospinel and sorbents on its basis

Adsorption of heavy metal ions (Cu2+ and Pb2+) on various samples of a manganese-zinc nano ferrospinel of composition Mn0.7Zn0.3Fe2O4, produced by the coprecipitation method, was studied. Samples of the starting ferrospinel and that modified with zinc and obtained in the presence of thermally treated agricultural wastes of cereal crops were examined. It was shown that all the three samples are effective sorbents. It was also found that the adsorption process on these sorbents is of complex type, depending on the nature of a metal ion being sorbed.

Carbon sorbent from carbonized peat

The physicochemical and adsorptive properties of a carbon sorbent obtained by the microwave carbonization of peat were studied. With the use of IR spectroscopy and elemental analysis, it was found that, under the action of microwave radiation, the concentration of functional groups in peat decreased and, as a result, the carbon content of peat increased. It was established that the adsorption activity of the carbon sorbent for iodine considerably increased as a result of carbonization, and that for methylene blue and methanyl yellow decreased. The carbon sorbents obtained by the microwave carbonization of peat had a total pore volume of 1.02 cm3/g and a specific surface area of no smaller than 1350 m2/g.