Sorbent Performance Research Articles

Performance evaluation of porous sodium aluminate sorbent for halide removal process in oxy-fuel IGCC power generation plant

Integrated coal gasification combined cycle power generation that adopts oxy-fuel concept has potential to achieve thermal efficiency of 44% at lower heating value besides its CO2 separation ability. Halide control as well as dry gas sulfur removal is inescapable process to the proper operation of the plant. This study investigates performance of dry halide sorbents to establish suitable halide control procedure for the power plant. The most appropriate position of the process is considered to be in the upper stream of the dry sulfur removal process, where the process is able to prevent both corrosion of gas turbine and halogenation of zinc in the desulfurization sorbent. Preproduction sorbents for the dry-gas halide removal process were prepared as pellets containing sodium aluminate as a main ingredient. The sorbents could absorb stoichiometric amount of hydrogen chloride at 450 °C and 0.98 MPa absolute in a simulated coal derived gas environment. The fresh and spent sorbents were examined for dependence of kinetics of halide removal reaction on their pore structures. The results showed that the pore structure comprising of macropore peak at around 5.0 μm and smaller peaks at 1.0 μm or below was suitable to attain affordable kinetics on halide removal and sodium conversion of the sorbent.

Performance of new mesoporous carbon sorbent prepared from grape industrial processing wastes for malachite green and congo red removal

Sorptive properties of a novel activated carbon (GWAC) prepared at optimized conditions from grape processing waste (GW) by ZnCl2 activation were tested using the textile dyes as cationic dye, malachite green (MG) and anionic dye, congo red (CR), from aqueous solutions. Batch experiments were conducted to study the effects of sorbent dose, initial dye concentration, agitation time and temperature at natural pH of dyes in aqueous solution on GWAC-dyes sorption systems. Equilibrium sorption isotherms and kinetics were investigated. The equilibrium experimental data were analyzed by the Langmuir and Freundlich models. Kinetic experiments revealed that the sorptions of MG and CR onto GWAC can be described with pseudo-second order model and the equilibrium isotherm data were well described by the Langmuir model. The sorption diffusion mechanisms were determined from the intra-particle diffusion model. Thermodynamic parameters showed that the process was spontaneous and endothermic. The sorption capacities of GWAC for the MG and CR removal were found to be 667 and 455mg/g, respectively. These results clearly indicate the efficiency of GWAC as a promising sorbent for treatment of wastewater containing MG and CR.

Effect of cerium oxide doping on the performance of CaO-based sorbents during calcium looping cycles.

A series of CaO-based sorbents were synthesized through a sol-gel method and doped with different amounts of CeO2. The sorbent with a Ca/Ce molar ratio of 15:1 showed an excellent absorption capacity (0.59 gCO2/g sorbent) and a remarkable cycle durability (up to 18 cycles). The admirable capture performance of CaCe-15 was ascribed to its special morphology formed by the doping of CeO2 and the well-distributed CeO2 particles. The sorbents doped with CeO2 possessed a loose shell-connected cross-linking structure, which was beneficial for the contact between CaO and CO2. CaO and CeO2 were dispersed homogeneously, and the existence of CeO2 also decreased the grain size of CaO. The well-dispersed CeO2, which could act as a barrier, effectively prevented the CaO crystallite from growing and sintering, thus the sorbent exhibited outstanding stability. The doping of CeO2 also improved the carbonation rate of the sorbent, resulting in a high capacity in a short period of time.

Adsorption of perfluoroalkyl acids by carbonaceous adsorbents: Effect of carbon surface chemistry

Adsorption by carbonaceous sorbents is among the most feasible processes to remove perfluorooctane sulfonic (PFOS) and carboxylic acids (PFOA) from drinking and ground waters. However, carbon surface chemistry, which has long been recognized essential for dictating performance of such sorbents, has never been considered for PFOS and PFOA adsorption. Thus, the role of surface chemistry was systematically investigated using sorbents with a wide range in precursor material, pore structure, and surface chemistry. Sorbent surface chemistry overwhelmed physical properties in controlling the extent of uptake. The adsorption affinity was positively correlated carbon surface basicity, suggesting that high acid neutralizing or anion exchange capacity was critical for substantial uptake of PFOS and PFOA. Carbon polarity or hydrophobicity had insignificant impact on the extent of adsorption. Synthetic polymer-based Ambersorb and activated carbon fibers were more effective than activated carbon made of natural materials in removing PFOS and PFOA from aqueous solutions.

Incorporation of CaO into novel Nd2O3 inert solid support for high temperature CO2 capture

A novel inert solid support of Nd2O3 was introduced to enhance the cyclic carbonation/calcination performance of CaO-based sorbents. CaO particles were incorporated into Nd2O3 by a wet-mixing method, using three organometallic precursors (OMPs) as calcium precursors and neodymium(III) acetate hydrate as inert support precursor. For comparison, CaO-based sorbents directly produced from precursors and the naturally occurring sorbent (limestone) were also investigated. FSEM and EDAX results revealed that the ultrafine active specie of CaO particles were homogeneously dispersed into Nd2O3 inert support. As a result, an improved durability and higher carbonation conversion were observed owing to the retarded sintering and the delayed diffusion controlled stage respectively for the sorbents investigated. The performance of the synthetic sorbents also relies on the precursor. When calcium dl-lactate pentahydrate (CaL) was used to incorporate CaO into the inert support Nd2O3, the highest conversion and best durability were obtained. The effect of calcination temperatures on the sorbent durability was also investigated. Under a relatively severe calcination temperature of 900°C, a high conversion of about 67% were obtained after 100 carbonation/calcination cycles for a sorbent synthesized from calcium dl-lactate pentahydrate (CaL) and neodymium(III) acetate hydrate. When the calcination temperature was changed to a mild one of 800°C, a significantly high conversion (>92.5%) was maintained over 100 carbonation/calcination cycles. Besides, no apparent capacity decline was observed for the sorbents after granulation.

Evaluation of process variables on the performance of Sorption Enhanced Methane Reforming

The joint performance of a synthetic Ca-based sorbent and a 10%wt.NiO/NiAl2O4 catalyst is tested under Sorption Enhanced Reforming (SER) of CH4 in a fixed bed reactor. The effects of the mass hourly space velocity (MHSV, mol CH4 h−1 (gcatalyst + gsorbent−1)), the sorbent-to-catalyst proportion (Z) for diverse steam-to-methane ratios (S/C) and the behavior of cycled solids under different regeneration conditions (by calcination under inert, oxidant, with steam and CO2 atmospheres) are studied.An H2 concentration close to equilibrium (≈95 vol.% for S/C = 3.2) is achieved working at both lower (0.01 mol CH4 h−1 (gcatalyst + gsorbent)−1 or 769 h−1) and higher MHSV (0.04 mol CH4 h−1 (gcatalyst + gsorbent)−1 or 3000 h−1). The practical operation window for the combination of the sorbent and catalyst used should be below 0.044 mol CH4 h−1 gsorbent−1, and around 0.44 mol CH4 h−1 gcatalyst−1. The stabilities of both solids (sorbent and catalyst) working cyclically are demonstrated, despite the demanding and realistic regeneration environments used. Thus, H2 purity close to equilibrium (≈88 vol.% for S/C = 2) is attained under SER conditions and no carbon deposition is found. In summary, the results obtained confirm the good joint performance of the synthesized solids in the SER process even when working under demanding conditions.

Calcium-based regenerable sorbents for high temperature H 2 S removal

Abstract Ca–Al–O regenerable sorbents with various calcium contents have been prepared by co-precipitation method for H 2 S removal at 850 °C. For the sorbent with a calcium content of 52.5 wt%, its sulfur capacity reached 36 g S/100 g sorbent. The saturated S/Ca molar ratios of the sulfided sorbents changed from 0.82 to 0.88, depending on the Ca content of sorbent. They are much higher than the case of pure CaO. Regeneration by diluted air, a cyclic oxidation/reduction process, or water vapor was applied for the regeneration of sulfided sorbents. The sulfided sorbent cannot be regenerated completely in the diluted air regeneration operation. It was completely regenerated in the oxidation/reduction process, in which the oxidation used 3% O 2 and the reduction used 10% H 2 . Repeating the oxidation/reduction 4 times, CaS was completely converted to CaO. Under such regeneration conditions, the sorbent performance was stable during 5 sulfidation–regeneration cycles. Sintering was observed in high O 2 concentration regeneration due to the strong exothermic reaction, which resulted in activity drop. During 6 cycles of steam regeneration with 81% H 2 O at 850 °C, the sulfur capacities of the regenerated sorbents with an initial calcium content of 61.2 wt% remained stable at 36 g S/100 g sorbent.

Inhibition and elimination of carbon deposition in dry gas desulfurization process under oxy-fuel IGCC derived coal gas environment

Oxy-fuel IGCC is a concept of new coal fueled power generation with CO2 capture capability without large penalty on thermal efficiency. It is estimated that thermal efficiency will attain 44% at lower heating value, LHV along with 99% CO2 capture capability. An imperative issue to be solved to realize this concept is to reconcile pre-combustion sulfur removal and retaining the inorganic gas composition of the coal derived gas. Although introduction of dry gas sulfur removal is desired to protect gas turbine from corrosion and to preserve the gas composition, the sulfur removal sorbent containing zinc ferrite installed in the process may suffer from the severe side reaction of carbon deposition. Although it was found that mixing the coal gas with the circulating exhaust in the plant would effectively prevent the carbon deposition in the process, exhaust will not be available until gas turbine comes into normal operation after the plant start-up.The amount of deposited carbon was evaluated and its behavior was examined during the reduction and succeeding regeneration steps performed under expected starting up condition of the plant, which is severe condition for carbon deposition. While carbon deposition occurs during reduction step under start-up conditions, the deposit can be released as carbon dioxide during succeeding regeneration step of scheduled duration. The deposited carbon totalling 0.8wt% as maximum can be eliminated by regeneration to sufficiently low level below 0.03wt% for the range of expected operating conditions. The carbon deposition may not affect the desulfurization performance of the zinc ferrite sorbent for the expected condition range at plant start-up. It was confirmed that the carbon deposition and elimination from the sorbent would be adequate measure for operating the dry gas purification process in the oxy-fuel IGCC power generation plant.

CO 2 capture performance of synthetic sorbent prepared from carbide slag and aluminum nitrate hydrate by combustion synthesis

A new CO2 sorbent was prepared from carbide slag, aluminum nitrate hydrate and glycerol water solution by combustion synthesis method. The effects of the sorbent preparation conditions (glycerol addition, combustion synthesis temperature, ratio of carbide slag to aluminum nitrate hydrate) and carbonation/calcination conditions (temperature, atmosphere and time) on CO2 capture performance of the synthetic sorbent were investigated in the calcium looping cycles. The addition of glycerol during the sorbent preparation exhibits an improvement on the cyclic CO2 capture capacity. It was also found that the optimal combustion synthesis temperature for the synthetic sorbent was in the range of 750–800 °C. The synthetic sorbent contained the mass ratio of CaO derived from carbide slag to Al2O3 derived from aluminum nitrate hydrate = 90:10 exhibited higher CO2 capture capacity (0.38 g CO2/g sorbent after 50 cycles). X-ray diffraction analysis showed that the main compounds of the synthetic sorbent were CaO and Ca3Al2O6 by X-ray diffraction analysis. The synthetic sorbent showed higher CO2 capture capacity than the carbide slag under severe calcination conditions (950 °C, CO2) and at short carbonation time (<5 min). From the present investigation, it shows that a high active synthetic CO2 sorbent could be obtained using the carbide slag in the calcium looping technology.

Wet mixing combustion synthesis of CaO-based sorbents for high temperature cyclic CO2 capture

CaO-based sorbents are considered suitable candidates for cyclic CO2 capture at high temperatures. However, the CO2 capture capacities of natural CaO-based sorbents decrease sharply after only a few cycles. This paper presents a novel wet mixing combustion synthesis to improve the cyclic CO2 capture performance of CaO-based sorbents. Results show that preparation conditions significantly affected the cyclic performance of the sorbents. The optimal molar ratios of calcium to magnesium and fuel to metal oxides were 2 and 0.5, respectively, for the preparation process. The wet mixing combustion synthesis did not show the highest CO2 capture capacity in comparison to the sol–gel combustion synthesis, however, the proposed method is still valid due to the low cost of the materials used. The sorbent prepared by the new method could achieve relatively stable cyclic CO2 capture behavior, and showed a porous microstructure that can be maintained during cyclic reactions. The capture capacity of the sorbent obtained a 0.4g CO2/g sorbent after 50 cycles.

Carbon dioxide adsorption thermodynamics and mechanisms on MCM-41 supported polyethylenimine prepared by wet impregnation method

Amine-functionalized sorbents prepared by wet impregnation method shows great promises for CO2 capture from real flue gas in power plants. The objective of this work is to understand CO2 adsorption thermodynamics and mechanisms at varied polyethylenimine (PEI) loadings on mesoporous MCM-41 by wet impregnation method using a computational approach for the first time. The structures of PEI/MCM-41 sorbents were optimized using molecular dynamics (MD), and the CO2 adsorption thermodynamics at varied PEI loadings was simulated using Grand Canonical Monte Carlo (GCMC) method. Results showed a good agreement between experiments and simulation. On the surface of the MCM-41, there are high CO2-philic sites for CO2 adsorption, which were firstly covered by PEI molecular. The functionalization groups increased the interactions of the CO2 with more PEI molecular deployed on the surface of the MCM-41, then to the center of the pore. The adsorption performance of the composite sorbents depended on the adsorption cites and the space for CO2 diffusion. The CO2 adsorption thermodynamics and mechanisms at varied PEI loadings shed lights on tuning CO2 capture performance with amine-functionalized sorbents for power plant greenhouse gas control.

Cyclic CO&lt;SUB align="right"&gt;2 capture performance of CaO-based sorbents obtained from various precursors

The effects of pore morphology and crystal structure of CaO–based sorbents derived from various precursors were investigated to elucidate the property dependence of CaO–based sorbent performance for cyclic CO2 capture. The results indicate that CO2 capture capacity of the first carbonate looping cycle is dependent on the specific surface area of CaO–based sorbents. The carbonation conversions of the initial calcined sorbent are restricted from 29% to 83% due to the limitations in the small pores with diameter range from 20 to 70 nm. The initial calcination of CaO–based sorbents obtained from the inorganic precursors leaves an 'imprint' in the following carbonation/calcination cycles, which leads to greater decay rate of carbonate conversion than the organic precursors. Increase of carbonate conversion with cycle number is found for CaO–based sorbent obtained from calcium L–lactate hydrate and this reactivation phenomenon is probably due to its special crystal structure.

Selective Determination of 2,4,6-Trinitrotoluene in Water Samples Based on Magnetic Imprinted Nanoparticles via Grafting Polymerization

The magnetic surface imprinted polymer was effectively synthesized based on polymerization for selective determination of 2,4,6-trinitrotoluene (TNT) as template molecule. The grafting procedure was performed by copolymerizing of vinyl modified magnetic substrate with methacrylic acid (MAA) and ethylene glycol dimethacrylate (EGDMA) as functional monomer and cross-linking agent, respectively. The morphology, structure and polymeric properties of imprinting polymers were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transforms infrared spectroscopy (FT-IR). In order to improve on the adsorption capacity amount, the various parameters were considered. The resulting sorbent exhibited a high capacity with appropriate selectivity for TNT molecules. The evaluation demonstrated a linear range of 10-500 µg L−1 with the detection limit of 3.0 µg L−1. Moreover, the performance of the present sorbent was studied for extraction and determination of TNT compound in environmental waters and acceptable recoveries ranging from 91.7 to 100.8% were achieved.

Key factors for optimum performance in phosphate removal from contaminated water by a Fe–Mg–La tri-metal composite sorbent

Eutrophication is typically due to excessive discharge of phosphate-containing wastewater into natural waters. In this study, a novel Fe–Mg–La trimetal composite sorbent with a Fe:Mg:La molar ratio of 2:1:1 was developed through a cost-effective co-precipitation approach for phosphate removal in contaminated water. It was found that the adsorption was greatly affected by solution pH. The experimental data was better described by Langmuir isotherm model, and the maximum adsorption capacity of 415.2mg-P/g was achieved under pH 6.0, much higher than most of sorbents previously reported. Nitrate, sulfate, bicarbonate, fluoride and humic acid widely exist in natural water, and their presences would slightly retard the adsorption of phosphate. The adsorption kinetics experiment showed that most of adsorption occurred in the first 1h and the adsorption equilibrium was achieved in 10h; the adsorption history was well described by the intraparticle diffusion model. The performance of sorbent was further confirmed by treating phosphate contaminated lake water. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis indicated that hydroxyl group on the sorbent surface (M–OH) played the most key role in the phosphate adsorption. The presence of sulfate group was important in the uptake as well.

Performance and mechanism study on phosphate adsorption onto activated carbon fiber loading lanthanum and iron oxides

A hybrid sorbent of lanthanum and iron oxides doped onto activated carbon fiber (ACF–LaFeO) was developed for the removal of phosphate from water. The effects of n (La)/n (Fe), total metal ion concentration, activation time, and activation temperature on the sorbent performance were studied by single-factor method. Response surface method (RSM), based on three-variable, three-level Box–Behnken design (BBD), was used to optimize the preparation parameters. The phosphate adsorption mechanism was investigated by Brunauer–Emmett–Teller (BET) analysis, Fourier transform infrared (FT–IR) spectroscopy analysis, and the test of adsorption amount dependence on the solution pH. The possible adsorption mechanisms could be a combination of electrostatic interaction, ion exchange, and Lewis acid–base interactions, depending on solution pH.

Elemental mercury capture and oxidation by a regenerable manganese-based sorbent: The effect of gas composition

A regenerable synthetic sorbent based on MnOx impregnated on high surface area γ-alumina and supported onto cordierite honeycomb monolith was tested for elemental mercury capture in different gas environments. Hg removal tests were performed in a lab-scale quartz reactor operated at 50–350°C, with Hg concentration in the range 50–250μg/m3, and GHSV=3.6·105h−1. The sorbent was tested in air (reference case), nitrogen and air with added CO2, CO, NO, SO2 and HCl. Results were analyzed in terms of the apparent initial Hg removal rate. In the absence of oxygen, the sorbent gradually deteriorated its performance. Both CO2 and CO moderately and reversibly worsened the Hg capture performance, while NO did not show any appreciable effect. On the other hand, SO2 adversely impacted on the sorbent performance and most importantly the Hg capture capacity was permanently deteriorated. No release of oxidized Hg was observed in tests containing the above components both during adsorption and desorption stages. In the presence of HCl (50ppm in air) the sorbent both adsorbed elemental Hg and catalyzed its heterogeneous oxidation giving an overall outstanding performance. During desorption only oxidized mercury was released.

Sponges with covalently tethered amines for high-efficiency carbon capture

Adsorption using solid amine sorbents is an attractive emerging technology for energy-efficient carbon capture. Current syntheses for solid amine sorbents mainly based on physical impregnation or grafting-to methods (for example, aminosilane-grafting) lead to limited sorbent performance in terms of stability and working capacity, respectively. Here we report a family of solid amine sorbents using a grafting-from synthesis approach and synthesized by cationic polymerization of oxazolines on mesoporous silica. The sorbent with high amount of covalently tethered amines shows fast adsorption rate, high amine efficiency and sorbent capacity well exceeding the highest value reported to date for low-temperature carbon dioxide sorbents under simulated flue gas conditions. The demonstrated efficiency of the new amine-immobilization chemistry may open up new avenues in the development of advanced carbon dioxide sorbents, as well as other nitrogen-functionalized systems.

Performance of a combined CaO-based sorbent and catalyst on H2 production, via sorption enhanced methane steam reforming

The performance of an hybrid material CO2-sorbent and reforming catalyst under Sorption Enhanced Reforming of methane has been assessed. The material was synthesised through physical mixing of CaO, NiO and calcium cement aluminate (varying the proportion CaO/NiO to produce three different solids). The materials, that presented a stable CO2 carrying capacity of 20wt.% of the total CaO in the solid, were able to reach gas product composition very close to thermodynamical equilibrium (at 650°C, steam to carbon ratio, S/C, of 3 and 1200h−1 CH4 spatial velocity), with H2 composition over 94vol.% (dry basis). In addition, it has also been demonstrated that the hybrid materials with NiOwt.% contents of 14 and 18.5 can fulfill the thermodinamical equilibrium at S/C ratios as low as 1.5. Finally the 18.5% NiO material has been tested in cyclic operation, under realistic conditions by regenerating the sorbent in oxidizing conditions. The cycled material showed slight increase of NiO crystal size that resulted in slight loose of activity after cycling. However, H2 percentages over 90vol.% (dry basis) were always obtained.

Amine-modified ordered mesoporous silica: The effect of pore size on CO2 capture performance

The objective of current research is to investigate the effect of pore size of mesoporous silica supports on the CO2 capture performance of solid amine sorbents. Two ordered mesoporous silicas (OMS) with different pore sizes (5.6nm and 7.6nm) were synthesized as tetraethylenepentamine (TEPA) supports. A serious of techniques, such as physical adsorption, infrared spectroscopy and thermal gravimetric analysis were used to characterize the solid amine sorbents. The CO2 capture performances of the sorbents were evaluated using breakthrough method with a fixed-bed reactor equipped with an online mass spectrometer. The experimental results indicate that the pore size has significant influence on CO2 capture performance. Larger pore size could decrease the mass transfer resistance and increase the interaction between CO2 and TEPA. Therefore, OMS-7.6 is better than OMS-5.6 as amine support. The highest CO2 sorption capacities achieved with OMS-7.6 with 50wt% TEPA loading (OMS-7.6-50) in the absence and presence of moisture are 3.45mmol/g and 4.28mmol/g, respectively, under the conditions of 10.0% CO2/N2 mixture at 75°C. Cyclic CO2 adsorption–desorption experiments indicate that the solid amine sorbents are fairly stable and regenerable.

Increasing oxygen functional groups of activated carbon with non-thermal plasma to enhance mercury removal efficiency for flue gases

To improve mercury removal efficiency of activated carbon (AC), a simple and efficient non-chemical treatment method was proposed: AC was treated by non-thermal plasma in air environment and characterized with ultimate analysis, Brunauer–Emmett–Teller (BET) surface area and X-ray photoelectron spectroscopy (XPS) technique. Mercury removal performance of AC was tested in a bench-scale quartz tube reactor. AC samples with different treatments were used as contrast sorbents for adsorption and desorption experiments. The results showed that AC treated with non-thermal plasma had higher mercury removal efficiency than others, and longer treatment time resulted in higher efficiency, the main reason was that non-thermal plasma treatment increased active sites, carbonyl groups (CO) and ester groups (C(O)OC) of AC, which played an important role in mercury absorption. By further analysis, it was found that increasing the active sites of AC was more effective than increasing the surface area for improving the mercury removal efficiency. And ester groups dominated mercury removal efficiency at higher temperature. Moreover, the results of the temperature programmed desorption (TPD) experiments indicated that the mercury desorption peak of carbonyl groups and ester groups should occur at 230°C and 320°C, respectively. By removing the functional groups of AC, mercury desorption peak desorbed by sorbent’s pore at 130°C was found. The non-thermal plasma treatment is a potential method for improving the mercury adsorption performance of sorbents.