Stability Of Sorbents Research Articles

Study on calcium precursors for CaO preparation to capture CO<sub>2</sub> at high temperature

As an abundant and cheap material,calcium oxide(CaO) is an efficient sorbent for CO2 capture at high temperature.The carbonation/calcination loop of CaO/CaCO3 is an effective process for CO2 capture and storage(CCS).However,both the gradual decline of the CO2 capture capacity and the poor stability,because of the pore filling and pore closure at the high calcination temperature,limit the industrial application of calcium-based sorbents.In this paper,study on calcium precursors was carried out in order to obtain CaO sorbents to capture CO2 with high efficiency.The candidate materials include seashell materials(oyster shells),natural minerals(calcite) and chemical reagents(calcium acetate hydrate).Oyster shell powder and calcite powder were analyzed by XRD,and CaO sorbents prepared from various precursors were characterized by nitrogen physisorption apparatus.The fresh CaO sorbents and CaO after multiple cycles to capture CO2 were characterized by scanning electron microscopy(SEM).The capture CO2 capability and the stability of CaO sorbents were investigated using a thermogravimetric analyzer(TGA),where multiple capture cycles were carried out alternatively in the simulation flue gas(10% CO2 in N2) and in decomposition purge gas(N2).Moreover,comparing the CO2 capture capability and the CaO stability with published works,and taking account of the market prices of precursors,calcium acetate hydrate is thought to be an economically appropriate calcium precursor,which has acceptable CO2 adsorption capacity and good stability at high temperature.

Effect of Zirconia Doping on the Structure and Stability of CaO-Based Sorbents for CO2 Capture during Extended Operating Cycles

A series of CaO-based sorbents are made using flame spray pyrolysis (FSP) and doped in situ by a wide range of zirconia loadings and tested for their CO2 capture during extended operating cycles. A...

Synthesis, stability, and chromatographic properties of silica gels modified by polyelectrolyte complexes

Methods are suggested for obtaining new sorbents for ionic chromatography (polyelectrolyte anion-exchangers) based on the modification of silica gels for HPLC by cationic polymer solutions. Advantages and faults of each method are pointed out. Factors that affect chromatographic characteristics and operating stability of polyelectrolyte sorbents are studied. Operating conditions are chosen for chromatographic columns based on polyelectrolyte sorbents that allow one to preserve the initial characteristics for more than 1.5 months.

Increasing Selective CO2 Adsorption on Amine-Grafted SBA-15 by Increasing Silanol Density

Two template removal methods were employed to create porosity in mesoporous silica SBA-15: ethanol extraction versus conventional high-temperature calcination. The resulting silicas were subjected to amine (3-aminopropyl) grafting and studied for their CO2 adsorption properties. The goal was to significantly increase the surface silanol density, and hence the grafted amine loading, leading directly to increased CO2 adsorption capacity and CO2/N2 selectivity. Thus, the silanol density was increased from 3.4 OH/nm2 for the calcined SBA-15 to 8.5 OH/nm2 for the SBA-15 by solvent extraction. Correspondingly, for these two samples, the grafted amine loading was increased from 2.2 to 3.2 mmol/g, and the CO2 adsorption capacity was increased from 1.05 to 1.6 mmol/g at conditions relevant to CO2 capture (0.15 bar and 25 °C), or a 52% increase. The CO2/N2 selectivity was increased from 46 to 131. The isosteric heats of adsorption, the sorbent stability during cyclic adsorption–desorption, and the (positive) effects of moisture on CO2 adsorption were also investigated and compared.

Improving the Stability of a CaO-Based Sorbent for CO2 by Thermal Pretreatment

Although the reversible absorption of CO2 by CaO at high temperature has been proposed as a promising method for capturing and removing CO2 from hot gas streams produced by the combustion of fossil fuels and other industrial processes, the activity of the sorbent has invariably declined when applied over many cycles of CO2 absorption and desorption. The objective of the present investigation was to extend the life cycle performance of the absorbent through improved thermal pretreatment as the absorbent was prepared from limestone, dolomite, calcium acetate, or plaster of Paris. The first three materials were converted to CaO by calcination, while the third being an impure form of CaSO4 required a combination of reduction and oxidation. The life cycle performance of an absorbent derived by calcination was found to depend on the calcination conditions including particle size, temperature, atmosphere, and length of treatment. Sorbent stability was favored by calcining fine-size particles (10 μm) at high temperature (1000 °C) in an atmosphere containing 50% CO2 or more. The sorbent derived from plaster of Paris by a cyclic process of reduction and oxidation at 1070 °C proved to be a very unusual material when applied because its activity increased rapidly and was still increasing after 200 cycles of absorption and regeneration.

Salen impregnated silica gel as a new sorbent for on-line preconcentration of cadmium(II)

A new sorbent – salen impregnated silica gel – was prepared and characterised for application as a minicolumn packing for flow-injection on-line preconcentration of cadmium(II). The system was coupled with flame atomic absorption spectrometer (FI-FAAS). The optimal pH for Cd(II) sorption was in the range of 7.4–8.8 and nitric acid (1%, v/v) was efficient as eluent. Sorption was most effective within the sample flow rate up to 7 mL min−1. Sorption capacity of the sorbent found in a batch procedure was 26.3 µmol g−1 (2.95 mg g−1). Enrichment factor (EF) and limit of detection (LOD) obtained for 120-second loading time were 113 and 0.26 µg L−1, respectively. The sorbent stability in the working conditions was proved for at least 100 preconcentration cycles. The evaluated method was applied to Cd(II) determination in various water samples.

Testing of hydrotalcite based sorbents for CO2 and H2S capture for use in sorption enhanced water gas shift

The sorption enhanced water-gas shift technology is attractive for pre-combustion decarbonisation of power production based on IGCC, but only when the SEWGS technology can be applied for sour syngas. To this extend, it was recently demonstrated that 2000 ppm of H2S did not influence the CO2 sorption behaviour of a potassium promoted hydrotalcite material at a relatively low pressure of 5 bar. This paper highlights ongoing sorbent testing at pressure swing operation between 30 bar adsorption and 2 bar regeneration, crucial for the successful development of the technology. The sorbent has good catalytic activity for the water-gas shift reaction during SEWGS conditions. At 30 bar pressure and 400 °C feed temperature, a CO, CO2 and H2S free H2-product is obtained when feeding a syngas containing 200 ppm H2S. This implies that mixing in a separate WGS catalyst is not needed, which significantly simplifies the technology. Moreover, multi-cyclic testing at 30 bar and 400 °C for 110 cycles shows good sorbent stability in the presence of 200 ppm H2S. Deliberately induced slips of CO2 and H2S stabilize within a limited number of cycles. By simply reducing the adsorption period, the mass-transfer zones for both CO2 and H2S are readily pushed back into the column, again producing a product free of CO2 and H2S. These observations suggest that reversibility of sorption processes on the material that have been tested is fully appropriate for the further development of the long-term operation of sour-SEWGS technology.

Assessment of Synthetic Protein-A MAbsorbents in Antibody Purification from Tobacco Plant Extract

Several plant-derived antibody (plantibody) purification approaches have been assessed demonstrating high purification capacities, but low recoveries (<30%) and poor sorbent stability. Thus, application of sorbents with high recovery, low ligand leakage and stable under harsh sanitization conditions could improve the efficiency antibody purification from this source. This paper reports for the first time MAbsorbents assessments in plantibody purification from tobacco plants. In conclusion MAbsorbent A1P is not suitable for plantibody HB-01 purification, while MAbsorbent A2P demonstrated high recovery (37.54 ± 15.15%) in 25 purification cycles. As recommendation, we consider that other elution conditions should be assessed before restudy the stability of this sorbent.

Preparation of a new Cd(II)-imprinted polymer and its application to determination of cadmium(II) via flow-injection-flame atomic absorption spectrometry

A new cadmium(II)-imprinted polymer based on cadmium(II) 2,2′-{ethane-1,2-diylbis[nitrilo( E)methylylidene]} diphenolate-4-vinylpyridine complex was obtained via suspension polymerization. The beads were used as a minicolumn packing for flow-injection-flame atomic absorption spectrometry (FI-FAAS) determination of cadmium(II) in water samples. Sorption effectiveness was optimal within pH range of 6.6–7.7. Nitric acid, 0.5% (v/v) was used as eluent. Fast cadmium(II) sorption by the proposed material enabled to apply sample flow rates up to 10 mL min −1 without loss in sorption effectiveness. Enrichment factor (EF), concentration efficiency (CE) and limit of detection (LOD, 3 σ) found for 120-s sorption time were 117, 39.1 min −1 and 0.11 μg L −1, respectively. Sorbent stability was proved for at least 100 preconcentration cycles (RSD = 2.9%). When compared to non-imprinted polymer the new Cd(II)-imprinted polymer exhibited improved selectivity towards cadmium(II) against other heavy metal ions, especially Cu(II) and Pb(II), as well as light metal ions. Accuracy of the method was tested for ground water and waste water certified reference materials and fortified water. The method was applied to Cd(II) determination in natural water samples.

Optimization of working conditions for polyelectrolyte sorbents

Matters affecting the working stability of polyelectrolyte sorbents are considered. The decrease in retention time during exploitation is found not to relate to desorption of the modifying polymer. It is found that dissociation of surface silanol groups influences significantly the extra retention of ionene on the surface of silica-based sorbents. Sorption of heavy metals and microbial contamination of the sorbent are identified as causes of decreased efficiency of polyectrolyte sorbents. The influence of organic additives on the chromatography behavior of a number of inorganic anions is studied. Finally, exploitational conditions for chromatography polyelectrolyte-containing columns are elaborated, allowing the initial parameters of separation to be maintained for a period of 1.5 months or longer.

Performance of sorption-enhanced water-gas shift as a pre-combustion CO2 capture technology

Abstract The sorption-enhanced water-gas shift (SEWGS) process is a promising technology for pre-combustion decarbonisation. It is well suited for decarbonising syngas produced from natural-gas and coal based fuels in combined-cycle power production schemes. Higher capture rates could be obtained by SEWGS at lower efficiency penalties and at lower costs than by absorption. In the SEWGS process, multiple reactor vessels are packed with mixtures of CO 2 sorption pellets and water-gas shift catalyst pellets. The technology is developed using potassium promoted hydrotalcite-based materials as the CO 2 sorbent. In a first series of experiments, the performance of this material is investigated under typical SEWGS process conditions. The sorbent was loaded in 2 m and 6 m tall fixed-bed reactor vessels. Breakthrough capacities of 1.3–1.4 mmol/g are reported. After breakthrough the sorbent continues to take up CO 2 , albeit at a much lower rate. Total sorption capacities exceeding 8 mmol/g are observed. This capacity is attributed to the formation of MgCO 3 in the bulk of the sorbent material and requires moderate to high partial pressures of CO 2 and steam. The stability of the sorbent material during cyclic operation was demonstrated for more than 4,000 adsorption and desorption cycles. A stable and low slip of CO 2 was established, corresponding to a carbon capture ratio of well above 90%. After investigation of the relevant sorbent characteristics, the reactor was loaded with sorbent and catalyst material in order to provide a proof-of-principle of the SEWGS technology and establish the performance and stability of sorbent and catalyst material. When the reactor was fed with a gas mixture that simulated a syngas typically produced by auto-thermal reforming of natural gas, it was demonstrated that carbon monoxide conversion can be enhanced from 55% in absence of a sorbent to 100% in the presence of a sorbent. Neither the change of gas composition nor the mixing of sorbent with catalyst did significantly impact CO 2 breakthrough capacity. In a cyclic duration test, the carbon capture rate and carbon monoxide conversion were confirmed to be above 98% without excessive steam demand, and reasonably stable for at least 500 cycles. The experimental data will be used for modelling, cycle optimization, and scale-up to a pilot unit.

Study on the Stability of Sorbents Removing H2S from Hot Coal Gas

Mixed metal oxide containing iron with the high-sulfur capacity and reactivity is considered as one of the most favorable sorbents for desulfurization in hot gas. The stability and life of iron-based sorbents are the main challenges for the hot gas cleanup techniques. Not only the effect of gas atmosphere but also the effect of ZnO and MgO on the stability of iron-based sorbent was studied in this work. The mechanism and factors influencing sorbent stability are discussed. The results showed that the coexistence of CO and H2 result in the instability of the zinc−iron-based sorbents. The reaction of carbon deposit is the crucial step affecting the stability of sorbent for hot gas desulfurization. ZnO in the sorbent is adverse to the physical stability of the iron-based sorbents. MgO in the sorbent hardly affects the physical stability of the iron-based sorbents but improves the capacity of removing the hydrogen sulfide from hot coal gas at 773 K.

Ethylene oxide removal by sorption on aluminium oxide

The dynamics of ethylene oxide sorption and desorption on Al2O3 sorbent were investigated. The investigations of ethylene oxide sorption on Al2O3 show that significant sorption appeared above 125?C. The removal of sorbed ethylene oxide from Al2O3 was achieved by continuous increasing of the temperature up to 450?C in air stream. The analysis of desorbed products show that 90% of adsorbed ethylene oxide is converted to CO2 and the rest consists of the three derivatives of ethylene oxide. The exact composition of desorbed organic products will be determined in further investigation. The desorption temperature profiles point out the presence of two exothermic picks, as was confirmed by detection of CO2 and derivates of ethylene oxide at these temperatures. Investigation of textural characteristics and thermal stability of Al2O3 sorbent show that there are no changes of any characteristics of Al2O3 in sorption/desorption operating temperatures regimes. Only at 700?C the specific surface area of Al2O3 decreases of about 10%. This indicates that the investigated Al2O3 is convenient material for removal of ethylene oxide by sorption.

EDTA modified LDHs as Cu 2+ scavengers: Removal kinetics and sorbent stability

EDTA modified layered double hydroxides (LDHs) were investigated as potential sorbents to remediate heavy metals pollution. The polidentate ligand was introduced by an exchange method in a Zn–Al-LDH, which takes place with partial erosion of the layers, causing the intercalation of [Zn(EDTA)] 2− complex instead of the ligand. [Cu(H 2O) 6] 2+ cation was selected as a model cation to study the uptake mechanism, exploring the elimination kinetics from the first minutes up to the steady state. A flow injection analysis system coupled to an amperometric detector (FIA-AM) was applied to perform fast and reliable [Cu(H 2O) 6] 2+ determinations in monodisperse solid–aqueous solution systems. Furthermore, the sorbent stability was determined as a function of the pH and the nitrate concentration. The [Cu(H 2O) 6] 2+ elimination is produced by an exchange reaction with [Zn(EDTA)] 2− anions placed either in the solid interlayer or in the aqueous solution, this last being released from the sorbent. Additional [Cu(H 2O) 6] 2+ removal is produced by Cu(OH) 2 precipitation at high copper concentrations due to the LDHs high pH buffering capacity. The sorbent removes [Cu(H 2O) 6] 2+ with high affinity in a wide concentration range. The elimination process reaches equilibrium in less than 30 min and leaves metal cation concentrations lower than 0.05 ppm in the supernatants.

Biosorption study in a mining wastewater reservoir

An in situ sorption was conducted to assess the behaviour of cations in a mining wastewater reservoir. Sorption experiments on test materials showed that biomass mainly bound uranium, copper, lead, zinc, and nickel, whereas goethite bound arsenic and chromium. Clay minerals bound both barium and rare earth elements. The lacustrine sediments mainly contained iron oxy-hydroxides. Desorption experiments using potentiometric titration were conducted to investigate the effect of pH variations on the stability of the test sorbents after immersion in the lake. Results indicated the presence of weak to very weak acidic functional groups in the sediments attributed to their high content of organic matter affecting the mobility and the behaviour of metals in the lake deposits.

Chemical stability of reversed phase high performance liquid chromatography silica under sodium hydroxide regeneration conditions

Chromatographic sorbents used within the purification of peptide or protein based active pharmaceutical ingredients (APIs) are commonly subjected to caustic regeneration procedures, so-called CIP treatments. While polymeric materials remain unaffected by this treatment, silica-based sorbents are at an intrinsic risk of dissolution under high pH conditions, such as, e.g. 0.1 M NaOH. It is common misconception that silica-based materials simply cannot be subjected to alkaline conditions above pH 9. Moreover, most studies covering the chemical stability of HPLC sorbents above pH 9 have been limited to the chromatographic conditions used for the separations themselves. Such studies have used buffered mobile phases up to pH 11 or 12. Very little focus has been put on the stability of the stationary phases when subjected to shorter but harsher pH conditions required for regeneration purposes, such as 0.1 M NaOH (pH 13). Knowledge about the amount of so-called leachables, degradation products originating from the stationary phase, is of growing importance for the registration of pharmaceuticals for human use and is addressed in this work. This study compares the chemical stability of different commercially available reversed phase silica materials (C18) that are used in industrial scale preparative HPLC. The silica materials were subjected to NaOH regeneration conditions and it is shown that some materials are able to withstand 0.1 M NaOH conditions without significant harm. It is demonstrated that contaminants present in the effluent in the range of 10–50 μg/mL can lead to significant contamination of API product fraction.

Removal of Cesium from Acidic Radioactive Tank Waste by Using Ionsiv IE‐911

IONSIV IE‐911, or the engineered form of crystalline silicotitanate (CST), manufactured by UOP Molecular Sieves, has been evaluated for the removal of cesium from Idaho National Engineering and Environmental Laboratory (INEEL) acidic radioactive tank waste. A series of batch contacts and column tests were performed by using three separate batches of CST. Batch contacts were performed to evaluate the concentration effects of nitric acid, sodium, and potassium ions on cesium sorption. Additional batch tests were performed to determine if americium, mercury, and plutonium would sorb onto IONSIV IE‐911. An equilibrium isotherm was generated by using a concentrated tank waste simulant. Column tests using a 1.5 cm3 column and flow rates of 3, 5, 10, 20, and 30 bed volumes (BV)/hr were performed to elucidate dynamic cesium sorption capacities and sorption kinetics. Additional experiments investigated the effect of CST batch and pretreatment on cesium sorption. The thermal stability of IONSIV IE‐911 was evaluated by performing thermal gravimetric analysis/differential thermal analysis. Overall, IONSIV IE‐911 was shown to be effective for cesium sorption from complex, highly acidic solutions; however, sorbent stability in these solutions may have a deleterious effect on cesium sorption.

Sorption of Metal Ions on Clay Minerals: II. Mechanism of Co Sorption on Hectorite at High and Low Ionic Strength and Impact on the Sorbent Stability

The mechanism of Co uptake from aqueous solution onto hectorite (a magnesian smectite) and its impact on the stability of this clay mineral were investigated as a function of Co concentration (TotCo = 20 to 200 μM, 0.3 M NaNO3) and ionic strength (0.3 and 0.01 M NaNO3, TotCo = 100 μM) by combining kinetics measurements and Co K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy. The morphology of the sorbent phase was characterized by atomic force microscopy (AFM) and consists of lath-type particles bounded by large basal planes and layer edges.At low ionic strength (0.01 M NaNO3), important Co uptake occurred within the first 5 min of reaction, consistent with Co adsorption on exchange sites of hectorite basal planes. Thereafter, the sorption rate dramatically decreased. In contrast, at high ionic strength (0.3 M NaNO3), Co uptake rate was much slower within the first 5 min and afterward higher than at 0.01 M NaNO3, consistent with Co adsorption on specific surface sites located on the edges of hectorite. Time-dependent isotherms for Co uptake at high ionic strength indicated the existence of several sorption mechanisms having distinct equilibration times. The dissolution of hectorite was monitored before and after Co addition. A congruent dissolution regime was observed prior to Co addition. Just after Co addition, an excess release of Mg relatively to congruent dissolution rates occurred at both high and low ionic strengths. At high ionic strength, this excess release nearly equaled the amount of sorbed Co. The dissolution rate of hectorite then decreased at longer Co sorption times.EXAFS spectra of hectorite reacted with Co at high and low ionic strengths and for reaction times longer than 6 h, exhibited similar features, suggesting that the local structural environments of Co atoms are similar. Spectral simulations revealed the occurrence of ∼2 Mg and ∼2 Si neighboring cations at interatomic distances characteristic of edge-sharing linkages between Co and Mg octahedra and corner-sharing linkages between Co octahedra and Si tetrahedra, respectively. This local structure is characteristic of inner sphere mononuclear surface complexes at layer edges of hectorite platelets. The occurrence of these complexes even at low ionic strength apparently conflicts with kinetics results, as exchangeable divalent cations are known to form outer sphere surface complexes. To clarify this issue, the amount of Co adsorbed on exchange sites was calculated from the solute Co concentration, assuming that cation exchange was always at equilibrium. These calculations showed that sorbed Co was transferred within 48 h from exchange sites to edge sorption sites.

STDS study for the identification of released compounds from commercial ion-exchange resins

Physical and chemical stability of polymeric sorbents, including ion-exchange resins, is among the main concern of both manufacturers and users. Different countries are gradually introducing regulations for the use of ion exchangers in water conditioning, food and beverage processing, separation of pharmaceutical products, and also for the use of reference materials as drugs and medical devices. Since all the applications mentioned may directly influence human health, the treated products must be free of any trace toxic compound potentially released by the polymeric matrix of the sorbent. The System for Thermal Diagnostic Studies (STDS) has recently been introduced commercially as a new versatile and powerful technique for the identification of the products evolved after thermal stress of solid phases. In this paper are presented the results of an STDS investigation to simulate the release of organic compounds from commercial weak and strong electrolyte anion and cation resins, differing for the type of polymeric matrix (polystyrene and polyacrylic based), porosity (gel and macroporous type), and functional groups, including sulfonic and carboxylate functionalities for the cation resins, and secondary, tertiary amine and quaternary ammonium functionalities for the anion resins. STDS determinations were carried out at 130, 200, 250 and 300°C by using a constant reaction time (10 min) and an inert (He) gas atmosphere. The thermally released compounds were cryofocused at −60°C and separated by temperature-programmed gas chromatography. The qualitative identification of the released compounds was made by searching the MS library NBS 54K. Thermogravimetric determinations were also carried out on a set of cation resins to complement STDS data.

Thermogravimetric study of regenerable sulphur sorbents for H 2S retention at high temperature

The behaviour of a series of mixed oxides including zinc titanate (ZT), zinc ferrite (ZF) and zinc ferrite doped with copper (ZFC) or titanium (ZFT) oxides as hot-gas desulphurizing sorbents was investigated by thermogravimetric techniques. The stability of sorbents against reduction was strongly affected by the temperature that limits the use of the prepared sorbents > 600°C. Intrinsic rate constants for the reaction between H 2S and the sorbents at 550°C were obtained in a thermal balance. The incorporation of titanium and copper oxides to zinc ferrite improved the sorbent reactivity. Five sulphidation-regeneration cycles were also carried out in order to provide information concerning the durability of sorbents. A loss of sorbent activity with the cycle number due to sintering in regeneration was found for zinc ferrite sorbents but not for titanium-containing sorbents.