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Adsorption: Journal of the International Adsorption Society (v.16, #3)
A new Gaussian adsorption isotherm model: test data is methane-5A zeolite by Dana Abouelnasr; Kevin F. Loughlin (pp. 93-101).
An adsorption isotherm model is deduced based on the Gaussian cumulative frequency distribution principles. This isotherm has three parameters: q max, the 50% adsorbate loading pressure P 50, and the standard deviation σ. The isotherm development hinges on establishing P 50 and σ. These are deduced from a log plot of the isotherm pressure P versus the inverse Gaussian cumulative frequency distribution plot. The slope of this plot is σ and the y-intercept is P 50. The temperature dependency of P 50 is deduced from a plot of log P 50 versus 1/T: this is actually the isosteric plot at 50% loading with slope equal to the heat of adsorption at 50% loading.The model is tested using the literature methane data for 5A zeolite. Twenty-four isotherms from six different studies are fitted with the model using a q max of 9 g/100 gZ applicable to methane 5A isotherms in the temperature range of the study, as reported in the literature. The standard deviation σ is observed to be 0.98±0.088. The isostere of P 50 indicates a heat of adsorption between 4.62–4.97 kcals/mole consistent with literature values. All 24 isotherms reduce to one characteristic curve when θ is plotted against (P/P 50)1/σ . The θ values approaching zero (<0.05) are shown to be consistent with reported Henry constant data using the heat of adsorption value calculated at 50% loading as is expected for homogeneous adsorption.
Keywords: Isotherm; Gaussian model; Log normal probability distribution; Methane; 5A zeolite
Adsorption technology for direct recovery of compressed, pure CO2 from a flue gas without pre-compression or pre-drying by Michael G. Beaver; Shivaji Sircar (pp. 103-111).
The effects of the sorption and the regeneration temperatures on the performance of a novel rapid thermal swing chemisorption (RTSC) process (Lee and Sircar in AIChE J. 54:2293–2302, 2008) for removal and recovery of CO2 from an industrial flue gas without pre-compression, pre-drying, or pre-cooling of the gas were mathematically simulated. The process directly produced a nearly pure, compressed CO2 by-product stream which will facilitate its subsequent sequestration. Na2O promoted alumina was used as the CO2 selective chemisorbent, and the preferred temperatures were found to be, respectively, 150 and 450 °C for the sorption and regeneration steps of the process. The specific cyclic CO2 production capacity of the process and the pressure of the by-product CO2 gas were substantially increased over those previously achieved by using the sorption and regeneration temperature of, respectively, 200 and 500 °C (Lee and Sircar in AIChE J. 54:2293–2302, 2008). The net compressed CO2 recovery from the flue gas (∼92%) did not change. However, substantially different amounts of high and low pressure steam purges were necessary for comparable degree of desorption of CO2. A first pass estimation of the capital and the operating costs of the RTSC process was carried out for a relatively moderate size application (flue gas clean up and CO2 recovery from a ∼80 MW coal fired power plant). Both costs were substantially lower than those for a conventional absorption process using MEA as the CO2 solvent (Desideri and Paolucci in Energy Convers. Manag. 40:1899–1915, 1999).
Keywords: Thermal swing chemisorption; Flue gas; Carbon dioxide removal and recovery; Promoted alumina; Comparative cost
Arithmetic approach for complex PSA cycle scheduling by Amal Mehrotra; Armin D. Ebner; James A. Ritter (pp. 113-126).
An algebraic model was derived for obtaining complex pressure swing adsorption (PSA) cycle schedules. This new approach involves a priori specifying the cycle steps, their sequence and any constraints, and then solving a set of analytical equations. The solution identifies all the cycle schedules for a given number of beds, the minimum number of beds required to operate the specified cycle step sequence, the minimum number and location of idle steps to ensure alignment of coupled cycle steps, and a simple screening technique to aid in identifying the best performing cycles that deserve further examination. The methodology was tested successfully against 10, 12 and 16 bed PSA systems in the literature that all utilized the same 13 step cycle sequence that has four pressure equalization steps. It completely resolved all the corresponding cycle schedules for these 13 step multi-bed PSA systems with ease, and showed that the number of cycle schedules was hundreds to thousands of times greater than the few ever reported in the literature for each one. Overall, this new methodology for complex PSA cycle scheduling can be applied to any number of cycle steps, any corresponding cycle step sequence, and any number of constraints, with the outcome being the complete set of cycle schedules for any number of beds greater than or equal to the minimum number it determines.
Keywords: Pressure swing adsorption; PSA; Cycle scheduling; Cycle sequencing; PSA cycle schedules
Palladium and platinum sorption using chitosan-based hydrogels by Dalila Sicupira; Karol Campos; Thierry Vincent; Versiane Leao; Eric Guibal (pp. 127-139).
Two chitosan hydrogels (prepared by NaOH neutralization and by polyphosphate ionotropic gelation) have been tested in the dry state for Pd(II) and Pt(IV) sorption at pH 2. Similar sorption isotherms with maximum sorption capacities close to 190 mg Pd g−1 and 235 mg Pt g−1 were achieved. The sorption mechanism involves electrostatic attraction of the chloro-anionic species onto protonated amine groups; the drastic decrease of sorption capacity with the addition of chloride ions supports this hypothesis. SEM-EDAX analysis suggests that sorption proceeds, in kinetic terms, through a shrinking core mechanism. Metal ions can diffuse throughout all the sorbent volume. The main differences between the sorbents are revealed by kinetics. The hydrogels prepared by ionotropic gelation in polyphosphate (C-PPh) allows reaching equilibrium much faster than the hydrogels prepared by the neutralization process (C-NaOH). While for C-PPh sorbent the chemical reaction rate seems to control sorption profiles, in the case of C-NaOH a combination of mechanisms including intraparticle diffusion resistance controls uptake kinetics. Metal desorption from loaded sorbents is possible using thiourea alone or in association with HCl solutions. The recycling of the sorbents is possible but for a limited number of cycles.
Keywords: Chitosan; Ionotropic gelation; Sodium polyphosphate; Hydrogels; Drying; Sorption isotherms; Intraparticle diffusion; Uptake kinetics; Desorption
Water adsorption on zeolite 13X: comparison of the two methods based on mass spectrometry and thermogravimetry by F. B. Cortés; F. Chejne; F. Carrasco-Marín; C. Moreno-Castilla; A. F. Pérez-Cadenas (pp. 141-146).
Two different experimental methods have been used for studying equilibrium adsorption of water vapour on zeolite 13X based on thermogravimetry and a novel technique using mass spectrometry. Good agreement can be found between experimental data of the adsorption isobars from these two methods. Also the isosteric heat of adsorption of this system has been determined from the equilibrium data. Water adsorption has been measured under a variety of operation conditions of the cooling systems, i.e. pressures from 12.28 to 73.84 mbar and temperatures from 50 to 230 °C.
Keywords: Adsorption; Zeolite 13X; Water; Thermogravimetry; Mass spectrometry
Modeling breakthrough curves of volatile organic compounds on activated carbon fibers by Line Fournel; Pierre Mocho; Ross Brown; Pierre le Cloirec (pp. 147-153).
Granular activated carbon (GAC) and more recently activated carbon fibers (ACF) are used for the treatment of volatile organic compounds (VOC) in industrial processes. The purpose of this study was to investigate the adsorption kinetics of ACF to eliminate VOC from polluted air. This approach is carried out by modeling experimental breakthrough curves with two kinds of models: an equilibrium model and a mass transfer model based on a linear driving force (LDF) in conjunction with the Langmuir equilibrium model. The results show the influence of the intraparticle diffusion on the adsorption kinetics of ACF, in spite of their small fiber diameter. Moreover, external diffusion kinetics is fast because of the influence of the large external surface area of ACF on the VOC mass transfer.
Keywords: Adsorption; VOC; Activated carbon fibers; Breakthrough curve; Model
Kinetic evaluation of sorption and desorption by Mats Jansson; Mats Jonsson; Joel Mohlén (pp. 155-159).
Sorption is often quantified by a distribution coefficient, K d , which is the equilibrium ratio between species sorbed to the rock and species in solution. Traditionally K d -values are determined in batch experiments from equilibrium concentrations.In this work we describe an approach to determine rate constants for sorption and desorption from data obtained in ordinary batch sorption experiments. By varying the surface area to solution volume ratio in experiments where the dynamics for sorption equilibration is monitored, the rate constants (and consequently the K d -value, which is the quota between forward and backward reactions) can be determined.To demonstrate the method, sorption of strontium to crushed granite was studied. The K d -value obtained with the kinetic approach was in good agreement with that obtained from equilibrium concentrations.
Keywords: Sorption; Kinetics; Cation; Mineral; Sr2+ ; Granite
Preparation of activated carbon from sawdust by zinc chloride activation by Huiping Zhang; Ying Yan; Lichun Yang (pp. 161-166).
A series of activated carbons were prepared from sawdust by zinc chloride activation in different operation conditions. The effects of operation parameters such as impregnation ratio, activation temperature and time on the adsorption properties of activated carbons were measured and analyzed in order to optimize these operation conditions. The experimental results show that under the experimental circumstances studied, both the yield and the adsorption for iodine and methylene blue of activated carbon can reach a relatively higher value in the chemical activation process with the impregnation ratio of 100% ZnCl2/sawdust in the activation temperature of 500 °C carbonized for 60–90 minutes which are the optimum activation conditions in making wood activated carbon. The most important operation parameter in chemical activation with zinc chloride was found to be the impregnation ratio.
Keywords: Activated carbon; Activation; Carbonization; Adsorption
Competitive sorption of Cu(II) and Eu(III) ions on olive-cake carbon in aqueous solutions—a potentiometric study by Maria Konstantinou; Ioannis Pashalidis (pp. 167-171).
The competitive sorption of Cu(II) and Eu(III) ions from aqueous solutions by olive-cake carbon, has been investigated by potentiometry at pH 6, I=0.1 M NaClO4, 25°C and under normal atmospheric conditions. Evaluation of the experimental data supports the formation of inner-sphere surface complexes and results in the calculation of the formation constant of the surface complexes ((=S–O)2Cu), which is found to amount log β Cu=5.3±0.3. Addition of competing Eu(III) ions in the aqueous system leads to replacement of the Cu(II) by the competitor metal ion. Evaluation of the potentiometric data obtained from competition experiments indicates an ion-exchange mechanism. The formation constant of the Eu(III) species sorbed on olive cake carbon is found to be log β Eu=5.1±0.5. Comparison of the complex formation constants of the olive-cake carbon with the corresponding complex formation constants for of olive cake and humic acid with the two metal ions, indicates that the same type of active sites is responsible for the metal ion complexation on the surface of the different types natural organic matter (e.g. olive-cake carbon, olive-cake and humic acid).
Keywords: Metal ions; Olive-cake carbon; Surface complexes; Competition; Formation constants
Adsorption kinetic, thermodynamic and desorption studies of phosphate onto hydrous niobium oxide prepared by reverse microemulsion method by Liana Alvares Rodrigues; Maria Lúcia Caetano Pinto da Silva (pp. 173-181).
A type of Nb2O5⋅3H2O was synthesized and its phosphate removal potential was investigated in this study. The kinetic study, adsorption isotherm, pH effect, thermodynamic study and desorption were examined in batch experiments. The kinetic process was described by a pseudo-second-order rate model very well. The phosphate adsorption tended to increase with a decrease of pH. The adsorption data fitted well to the Langmuir model with which the maximum P adsorption capacity was estimated to be 18.36 mg-P g−1. The peak appearing at 1050 cm−1 in IR spectra after adsorption was attributed to the bending vibration of adsorbed phosphate. The positive values of both ΔH° and ΔS° suggest an endothermic reaction and increase in randomness at the solid-liquid interface during the adsorption. ΔG° values obtained were negative indicating a spontaneous adsorption process. A phosphate desorbability of approximately 68% was observed with water at pH 12, which indicated a relatively strong bonding between the adsorbed phosphate and the sorptive sites on the surface of the adsorbent. The immobilization of phosphate probably occurs by the mechanisms of ion exchange and physicochemical attraction. Due to its high adsorption capacity, this type of hydrous niobium oxide has the potential for application to control phosphorus pollution.
Keywords: Adsorption; Hydrous niobium oxide; Phosphate; Desorption