Sorption-desorption Cycles Research Articles

Water clustering in polychloroprene

Water sorption has been studied gravimetrically for polychloroprene rubber samples, first at a fixed hygrometric ratio (98% HR) and several temperatures (25, 40, 60 and 80 °C) for samples of 1.8 and 3.8 mm thickness (Constant Temperature and Hygrometry, CTH experiments), then at fixed temperature (40 °C) and several hygrometric ratios ranging from 0 to 95% HR on samples of 0.1 mm thickness (DVS experiments). CTH experiments reveal an abnormal sorption behavior: after an apparently fickian transient period, the water absorption continues at almost constant rate, no equilibrium is observed after more than 2500 h, whatever the temperature. DVS experiments reveal a very low Henry's solubility but the formation of clusters at water activities higher than 40%. The water diffusivity is almost independent of activity below 50% HR and decreases rapidly when activity increases above 50%. Contrary to CTH experiments, equilibrium is reached in DVS and the difference is not simply linked to the well-known effect of sample thickness on diffusion rate. The results allow hypotheses such as hydrolysis or osmotic cracking to explain the abnormal sorption phenomenon to be rejected. It is suggested that clusters could be polymer–water complexes having a linear/branched structure able to grow without phase separation that could explain the reversibility of sorption–desorption cycles. The difference of behavior between thin 0.1 mm and thicker 1.8 or 3.8 mm samples could be due to an effect of swelling stresses.

Recycled chitosan nanofibril as an effective Cu(II), Pb(II) and Cd(II) ionic chelating agent: Adsorption and desorption performance

Mechanically disassembled chitosan nanofibrils were prepared and used as metal ion chelating agents. Structure and morphology of nanofibrils were investigated and ionic adsorption or desorption performance were validated to establish related fitting models. In single metal ion solution, the saturated adsorption capacities of Cu(II), Pb(II), Cd(II), Zn(II), and Ni(II) were 168.66, 118.00 and 60.85, 143.67, and 63.32mg/g, respectively. In ternary metal ion solution, Cu(II) was more competitive to be adsorbed than Pb(II) and Cd(II) and its removal could arrive at 60%. Ions adsorbed by nanofibrils could be released by EDTA and the recovery could keep above 70% after 3 sorption–desorption cycles. Hence, renewable and recyclable nanofibrillar chitosan exhibited a great promising application in metal treatments attributed to its high adsorption capacity and chelation efficiency.

Application of Grafted Silica Gel for Improvement of FAAS Conditions of Copper(II) Determination in Water Samples

Silica gel was modified via silanization with 3-chloropropyltrimethoxysilane and subsequently Cu(II)-5- dodecylsalicylaldoxime was grafted. Obtained sorbent was applied to on-line copper(II) preconcentration and its FAAS determination. Effective copper(II) elution was observed for 2% v/v nitric acid. The new sorbent exhibits optimal sorption efficiency within pH 5.6 and 7.5. A portion of the sorbent may be used repeatedly for not less than 100 sorptiondesorption cycles. The sorbent indicates high sorption and elution effectiveness of ca. 96 and 99%, respectively. Introduction of a preconcentration step before flame atomic absorption spectrometry (FAAS) copper determination with 60 s loading time resulted in 12-fold increase in the measured absorbance. This could be further raised by extending the loading time. Metals, like Zn(II), Mn(II) and Pb(II) caused negative interference effect while presence of Ca(II) and Mg(II) caused increase in the obtained signals. Copper(II) in samples such as: well water, mineral water, river and tap water was determined via the standard addition method. Detection limit for the proposed procedure was estimated at 1.5 µg L-1 (3σ). Accuracy of the method was assessed via comparison of the results obtained for copper determination in ground water and waste water certificate reference materials with those obtained with the use of a reference method (ICP MS). Keywords: Copper determination, FI-FAAS, modified silica gel, on-line preconcentration, salicylaldoxime, solid-phase extraction.

Diffusion in polymers as investigated by two-dimensional correlation spectroscopy: The H2O/PCL system

Time-resolved FTIR spectra collected in situ during a sorption-desorption cycle constituted the experimental basis for a molecular level characterization of the H2O/PCL system. The data were analysed by a number of techniques (difference spectroscopy, least-squared curve-fitting (LSCF) and 2D-FTIR correlation spectroscopy (2D-COS) which provided relevant and complementary information on the diffusion mechanism and the molecular interactions formed (H-bonding). Particular attention was paid to the application of 2D-COS spectroscopy to diffusion studies and to the potential of this approach to disclose subtle details on the dynamic behaviour of the molecular specie involved. Its reliability was confirmed by comparison with simulation studies mimicking the system’s evolution during a sorption/desorption cycle. The conclusions drawn by 2D-COS were also supported by an analysis of the ν(OH) band of sorbed water with least-squared-curve-fitting techniques. The study has revealed two spectroscopically discernible water species – a first-shell, and a second-shell layer – which were quantified. It was concluded that on sorption, the concentration build-up of the first-shell layer is accelerated with respect to that of the second-shell, while the opposite occurs on desorption.

High temperature CO2 sorption with gallium-substituted and promoted hydrotalcites

Hydrotalcites (HTC) and gallium-substituted hydrotalcites (HTC-10Ga) were prepared by co-precipitation and modified by impregnation with alkali (K and Cs) and alkaline-earth (Sr) metals. The materials were tested and screened for CO2 sorption at 573K. The results indicate that the modification with potassium greatly enhanced the sorption capacity when compared with the original materials (both HTC and HTC-10Ga). An outstanding sorption capacity (2.01mmolcm−3 at 1.08bar) was obtained for the sample partially substituted with gallium and modified with potassium (HTC-10Ga–20K). Moreover, this material was also submitted to sorption–desorption cycles towards CO2 under low-pressure conditions (<0.0001–0.15bar) to assess its use in cyclic operation. An average working capacity of 0.97mmolcm−3 and 0.25mmolcm−3 was obtained after repeated cycles at 573K and 473K, respectively. The sorption kinetics was assessed through uptake measurements, showing two parallel resistances, which were well described by the proposed model.

New molecular basket sorbents for CO2 capture based on mesoporous sponge-like TUD-1

In this work, a new class of mesoporous and sponge-like TUD-1 materials have been explored as the support matrix for immobilizing a functional polymer, polyethylenimine (PEI), to prepare molecular basket sorbents (MBS) for CO2 capture. The performance of TUD-1 based MBS has been evaluated in a fixed-bed flow system using a simulated flue gas. Effects of the pore properties, PEI loading amount and moisture on the sorption capacity were examined. Compared to the well-known SBA-15, the TUD-1 based nano-porous MBS showed not only a comparable gravimetric capacity (∼115mg-CO2/g-sorb), but also a significantly higher volumetric capacity (as high as 68mg-CO2/mL-sorb). Both the pore volume and pore size play a crucial role in determining the CO2 sorption capacity of the TUD-1 based MBS. Furthermore, the TUD-1 supported PEI samples exhibited faster CO2 sorption kinetics than SBA-15 based MBS, due likely to the improved CO2 diffusion constant which was estimated by Parabolic diffusion equation. The highest CO2 sorption capacity of 116mg-CO2/g-sorb was obtained with PEI loading of 50wt% at 75°C under dry conditions, which was further enhanced to 130mg-CO2/g-sorb in the presence of moisture (3vol%). The PEI/TUD-1 sorbent was tested for 45 sorption–desorption cycles, showing a good regenerability and cyclic stability. Because of its high CO2 sorption performance and commercial availability of the support, the TUD-1 based MBS could be promising for cost-effective capture of CO2 from flue gas.

Biosorption of thorium from aqueous solution by Ca-pretreated brown algae Cystoseira indica

o C with pH of 3. The thermodynamic parameters indicated the biosorption of Th on the biomass was a feas- ible, spontaneous and endothermic process. Th sorption capacity remained unaffected or slightly affected (<10% in- hibition) in the presence of several interfering ions such as uranium (VI), nickel (II) and copper (II). The reusability of the biomass was also determined after five sorption-desorption cycles.

In-situ XRD Studies of dolomite based CO2 sorbents

Abstract Calcined dolomite (a CaOMgO material derivative of the natural mineral dolomite) has the potential as a CO 2 sorbent working at high temperatures (500-650 °C) in processes like post combustion carbonate-looping, or in sorbent enhanced reactions such as sorbent-enhanced water-gas shift (SEWGS) or sorbent-enhanced reforming (SER). However, deactivation and performance loss is inevitable and much effort has been aimed towards understanding and improving solid sorbents for various applications. This work presents a study of deactivation trends of calcined dolomite and Zr-modified versions of calcined dolomite that appears to possess better cyclic properties at rapid sorption-desorption cycling (which is a likely conditions in a real process using a CFB reactor). Surface area measurements, thermogravimetric analyses (TGA), fixed bed reactor studies, in-situ XRD and in-situ IR methods carried out at 600°C in a gas containing 1-2vol% steam in 10% CO 2 have been conducted to obtain fundamental information about the de-activation mechanisms taking place.

Arsenite and Arsenate Removal from Contaminated Groundwater by Nanoscale Iron–Manganese Binary Oxides: Column Studies

Abstract Fixed-bed sorption process can be very effective at removing arsenic from contaminated groundwater. In this study, a continuous operation was demonstrated for the removal of both arsenite [As(III)] and arsenate [As(V)] from aqueous media in a column packed with nanoscale iron–manganese binary oxides (NIM). Treatment performance of the sorbent was quantified by upflow column experiments at different flow rates and bed depth. Bed depth service time model was used for the prediction of column service time, and the predicted values were compared with experimental values. A study of competing ions showed that silicate caused the greatest decrease in the As removal rate relative to phosphate and sulfate. Column regeneration studies were carried out for three sorption–desorption cycles using 0.1 M NaOH as the eluent, the NIM bed saturated with arsenic could be efficiently regenerated and reused. We found that NIM could be used for different types of real groundwater. This column study revealed that NIM ...

Adsorption of rare earths (III) by calcium alginate-poly glutamic acid hybrid gels

BACKGROUND Adsorption is believed to be an effective and green technology for the removal and recovery of rare earths (III) from dilute solution. RESULTS A novel hybrid gel, abbreviated as ALG-PGA, has been prepared through crosslinking calcium alginate (ALG) and γ-poly glutamic acid (PGA), and its adsorption behavior towards whole rare earths (III) has been examined. Taking Nd(III) as a representative element, the adsorption capacity, kinetics, reusability, selectivity and mechanism have been investigated. Cation exchange is proposed as a possible adsorption mechanism. Doping PGA molecules into calcium alginate beads can significantly enhance the adsorption capacity and the selectivity of rare earths from non-rare earths. The maximum adsorption capacity obtained for Nd(III) was 1.65 mmol g−1. Reutilization of ALG-PGA gel was confirmed for up to eight consecutive sorption–desorption cycles with no damage to the gel. CONCLUSION The prepared biosorbent, ALG-PGA, was biocompatible and cost effective with a good adsorption ability for Nd(III), and provides a new approach to the recovery of rare earths (III) from rare earths-containing wastewater. © 2013 Society of Chemical Industry

Development of a new clay supported polyethylenimine composite for CO2 capture

A new inexpensive inorganic–organic composite sorbent for CO2 capture was prepared by the immobilization of a branched polyethyleneimine (PEI) onto porosity-enhanced clays using the wet impregnation method. In the composite, a low cost and naturally abundant clays (e.g. kaolinite and montmorillonite) was used as the supporting material, which was pre-modified by acid- or alkaline-treatment to improve its textural properties, i.e. pore volume and surface area, for accommodating the CO2-philic PEI. Among the modified clays, the montmorillonite modified by 6M HCl (Mon_HCl_6M) showed the highest porosity with the pore volume of 0.71cm3/g from 0.16cm3/g, and BET surface area of 253m2/g from 72m2/g. The cost of the Mon_HCl_6M was estimated as $0.14/kg, which was significantly lower than reported supporting materials for the amine-based sorbents for CO2 capture. At the optimal PEI loading of 50 wt% on the Mon_HCl_6M support, the CO2 sorption capacity reached 112mg CO2/g-sorbent at 75°C under dry condition, which can be further enhanced to 142mg CO2/g-sorbent with the moisture addition (ca. 3vol%) due to the change in the interaction mechanism between CO2 and amine in the presence of moisture. Moreover, the PEI/Mon_HCl_6M sorbent showed a good regenerability for 10 sorption–desorption cycles tested and a good thermal stability in the temperature range of CO2 sorption (75°C) and desorption (100°C).

Poly[1-(N,N-bis-carboxymethyl)amino-3-allylglycerol-co-dimethylacrylamide] brushes grafted onto siliceous support for preconcentration and determination of cobalt (II) in human plasma and environmental samples

A chelating matrix prepared by surface grafting of polymer containing a functional monomer, poly[1-(N,N-bis-carboxymethyl)amino-3-allylglycerol-co-methylacrylamide] (poly(AGE/IDA-co-DMAA) onto a modified silica. The silica surface was modified by silylation with 3-mercaptopropyltrimethoxysilane followed by graft polymerization. Monomer of allyl glycidyl ether-iminodiacetic acid was synthesized by reaction of allyl glycidyl ether with iminodiacetic acid. The chelating sorbent can be reused for 15 cycles of sorption-desorption without any significant change in sorption capacity. The profile of cobalt uptake on the sorbent reflects good accessibility of chelating sites in poly(AGE/IDA-co-DMAA)-grafted silica gel. The equilibrium adsorption data of Co(II) on modified sorbent were analyzed by Langmuir, Freundlich, Temkin and Redlich-Peterson models. The method was applied for cobalt ions determination in human plasma and sea water sample with satisfactory results.

Characterization and stability of a new, high-capacity amine-functionalized CO2 sorbent

Solid sorbents have received extensive research as an alternative to aqueous amine scrubbing to remove CO2 from gas streams due to their theoretically lower energy requirements. Amine-functionalized sorbents are among the solid sorbents with the highest CO2 capacity. In this study, a recently developed amine-functionalized sorbent with a high capacity for CO2 is characterized using multiple techniques, including 13C NMR. These characterizations show that the sorbent is thermally stable up to 200°C and is stable when used up to ten sorption–desorption cycles.

Effective removal of nitrate and phosphate anions from aqueous solutions using functionalised chitosan beads

Adsorption of nitrate and phosphate from aqueous solution on both the protonated cross-linked chitosan beads (PCB) and carboxylated cross-linked chitosan beads (CCB) was investigated in batch mode. Effects of various parameters such as contact time, dosage of adsorbent, pH of the aqueous solutions, competitive co-anions and temperature on the sorption capacity of the sorbents were studied. The reuse of sorbents was evaluated by sequential sorption–desorption cycles using 0.1M NaOH as regenerant. Three isotherms namely Langmuir, Freundlich and Dubinin–Radushkevich were used to fit the equilibrium data, whereas the pseudo-second-order equation was used for the kinetic data. The E values obtained from the D–R isotherm at 303 K for nitrate and phosphate adsorption on PCB were 0.036 and 0.107 kJ/mol, respectively, and on CCB were 0.029 and 0.114 kJ/mol, respectively, which confirms the physical adsorption between the anions and functional moieties in PCB and CCB. ΔH° values revealed that the adsorption of nitrate is exothermic process and adsorption of phosphate is endothermic process. The sorbents were characterised by SEM and FTIR.

Recovery of copper (II) absorbed in biomass of Cladosporium cladosporioides

The biosorption process, characterized by the use of biomass for removing metals from aqueous solutions, is an attractive technology using inactive and dead biomasses to remove heavy metals from aqueous solutions in the absence of metabolic activity necessary for intracellular accumulation. The desorption process, which concentrates the metal previously absorbed for possible reuse, is also important. The desorption of copper (Cu) (II) associated with the biomass of Cladosporium cladosporioides (Fres) de Vries was evaluated following the biosorption process (adsorption). Specifically, four eluents were used (all at a concentration 0.1 mol L-1), sulfuric acid, hydrochloric acid, ethylenediaminetetraacetate disodium and calcium chloride, as well as the recovery of Cu (II) desorbed as copper sulfate. After 120 h, 97 % of Cu in solution had been adsorbed. C. cladosporioides can efficiently adsorb Cu (II). Further, 0.1 mol L-1 sulfuric acid was viable and the most efficient for the desorption of the absorbed metal, while ensuring viability of C. cladosporioides after desorption, which is important for the reuse of the biomass in cycles of sorption-desorption.

Design and evaluation of chitosan/hydroxyapatite composite nanofiber membrane for the removal of heavy metal ions from aqueous solution

The performance of chitosan/hydroxyapatite (Cs/HAp) composite nanofiber membrane prepared by electrospinning process for the removal of lead, cobalt and nickel ions from aqueous solution was investigated. The prepared nanofiber membranes were characterized by FTIR, SEM and BET analysis. A response surface methodology based on Box–Behnken Design (BBD) was used to predict the average diameter of electrospun nanofibers. In optimum conditions (voltage of 18.90kV, tip-collector distance of 15.60cm and flow rate of 0.43ml/h), the minimum experimental fiber diameter was obtained 198nm which was in good agreement with the predicted value by the BBD analysis (200.6nm). Then, the adsorption experiments were carried out to investigate the effect of different adsorption parameters, such as contact time, initial concentration and temperature in a batch system. The kinetic and equilibrium data were well described by pseudo-second-order and Langmuir models, respectively. Thermodynamic parameters were evaluated to obtain the nature of adsorption process onto the Cs/HAp composite nanofibers. The obtained results of reusability of nanofiber membrane after five sorption–desorption cycles offer promising potential in industrial activities.

Removal of remazol yellow from aqueous solutions by unmodified and stabilized iron modified clay

The adsorption behavior of remazol yellow from aqueous solutions onto montmorillonite KSF and iron modified montmorillonite KSF samples was investigated as a function of initial concentration of remazol yellow, contact time and pH. The regeneration of the dye saturated material was also considered.The sorption showed that the montmorillonite KSF removed about 10% more dye than the iron modified montmorillonite KSF but the standard deviations of the experiments were very high for the unmodified material. The kinetic experiments showed that the equilibrium time was reached in less than an hour for both materials and the experimental data were adjusted to the pseudo first order model (Lagergren), which is based on a surface reaction.The experimental data could be adjusted to the Langmuir, Freundlich and Langmuir–Freundlich models, but according to the characteristics of the adsorbents only the two last models should be considered because the adsorbents are heterogeneous. It was also observed that the sorption capacities for the iron modified montmorillonite were not affected by pH from 2 to 12.The results on the desorption processes showed that the best regenerator agent was Fenton's reagent, the sorption capacities were a little higher for iron modified montmorillonite KSF than for montmorillonite KSF in the first 7 sorption–desorption cycles and then the sorption of the dye increases almost 3 times in the 8–10 sorption–desorption cycles.

Enhanced irreversible sorption of carbaryl to soils amended with crop-residue-derived biochar

The irreversible sorption–desorption of carbaryl in five soil types with crop-residue-derived biochar (CBC) amendment was determined. CBC has lower surface area and micropores volume than wood-based biochar and charcoal. However, CBC amendment (0.5%) still significantly enhanced the hysteresis effect on soils, with a 1.7- to 2.8-fold increase in the hysteresis index (HI) values. The HI values increased exponentially with the increased amount of CBC but decreased exponentially with the increased amount of soil organic matter (SOM%). Furthermore, the irreversible carbaryl sorption (qirr) and the irreversibility index (Iirr) values were proportional to the amount of CBC (0–1.0%) in soils. Likewise, the SOM-rich soil (S3) was washed ten times to reduce its SOM% to evaluate the influence of the dissolved organic matter (DOM) in the soils on the irreversible sorption. The Iirr values of the unamended S3 increased as the number of sorption–desorption cycles increased, whereas those of the 1.0% CBC-amended S3 decreased. In addition, the Iirr values of the unwashed S3 were lower than those of the washed S3. By contrast, the Iirr values of the 1.0% CBC-amended S3 soil were higher in the unwashed samples than in the washed samples. These results suggested that DOM had opposite effects on the irreversible carbaryl sorption by unamended and CBC-amended soils. The DOM release may expose more irreversible adsorption sites in the soils and may cover the surface of the CBC to form a desorption-resistant fraction in its mesopore or macropore regions, thereby preventing the desorption of adsorbed carbaryl molecules.

Physico-chemical study for zinc removal and recovery onto native/chemically modified Aspergillus flavus NA9 from industrial effluent

Zinc biosorption characteristic of locally isolated Aspergillus flavus NA9 were examined as a function of pH, temperature, pulp density, contact time and initial metal ion concentration. The maximum zinc uptake was found to be 287.8 ± 11.1 mg g−1 with initial metal concentration 600 mg L−1 at initial pH 5.0 and temperature 30 °C. The equilibrium data gave good fits to Freundlich and Florry models with correlation coefficient value of 0.98. The contribution of the functional groups and lipids to zinc biosorption as identified by chemical pretreatment was in the order: carboxylic acids > hydroxyl > amines > lipids. The mechanism of biosorption was also studied using Fourier transform infrared (FTIR) spectrometry, scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). The biosorbent was regenerated using 0.01 M HCl with 83.3% elution efficiency and was reused for five sorption–desorption cycles with 23.5% loss in biosorption capacity. The order of co-cations showing increased inhibitions of zinc uptake by A. flavus NA9 was Pb > Cu > Mn > Ni. The biosorption assays conducted with actual paint industry effluents revealed efficiency of 88.7% for Zn (II) removal by candidate biomass.

MgO/CaO-Loaded Activated Carbon for Carbon Dioxide Capture: Practical Aspects of Use

Porous carbons loaded with CaO and MgO were prepared through a one-step process from mixtures of poly(ethylene terephthalate) and dolomite mineral. Obtained hybrid materials were examined as sorbents for CO2 gas contained in air. The influence of pore structure, loadings of the oxides, moisture, and temperature on the efficiency of gas removal is presented and discussed. Performance of the materials during CO2 capture was confirmed to be influenced by all mentioned factors. As a rule, efficiency of CO2 removal increased along with loading of the oxides. CO2 uptake increased also with moisture content and temperature of the bed. On the basis of attained results, optimal parameters for operational use are suggested and probable mechanisms of the CO2 removal from dry and humid air are proposed. Cyclic sorption–desorption experiments confirmed capability of the material for several-times use. Superior performance of the hybrid materials over a mixture of CaO and MgO is confirmed and discussed.