Forgot your password?
New user?
New Window Opens on the Secret Life of Microbes: Scientists Develop First Microbial Profiles of Ecosystems
CAS announces the release of SciFinder Scholar for Mac OS X
Press Releases
Press Releases
| Check out our New Publishers' Select for Free Articles |
Adsorption: Journal of the International Adsorption Society (v.11, #2)
Adsorption Equilibrium of Alkanes on a High Surface Area Activated Carbon Prepared from Brazilian Coconut Shells by Krista S. Walton; Célio L. Cavalcante Jr.; M. Douglas Levan (pp. 107-111).
Adsorption equilibria of methane, ethane, and n-butane on a high surface area activated carbon prepared from Brazilian coconut shells is examined in this study. The material shows high capacities for the alkanes tested. A group-contribution theory is used to predict adsorption isotherms for all three components with very good accuracy employing one set of model parameters. The theory is also used to observe trends in isosteric heat of adsorption as a function of loading at various temperatures.
Keywords: adsorption equilibrium; alkanes; nanoporous; group-contribution theory; carbon; coconut shells
A New Numerical Method for Accurate Simulation of Fast Cyclic Adsorption Processes by Hyungwoong Ahn; Stefano Brandani (pp. 113-122).
In the simulation of fast cyclic adsorption processes, to apply the Fickian diffusion model it is necessary to include an increasing number of numerical discretization points as the cycle time is reduced in comparison to the characteristic diffusional time constant.We propose a new numerical method based on the definition of two distinct regions within an adsorbent particle: an outer layer where the concentration varies significantly with large internal gradients leading to enhanced mass fluxes, and an internal region where the concentration profile is virtually flat. The proposed method leads to the automated generation of a numerical grid that has a constant number of elements independent of the process cycle time. The procedure is demonstrated on a model for the simulation of a heatless dryer pressure swing adsorption process.
Keywords: diffusion model; adsorption; numerical simulation; cyclic adsorption processes
Chromatographic Separation of Bupivacaine Enantiomers by HPLC: Parameters Estimation of Equilibrium and Mass Transfer Under Linear Conditions by Ivanildo José Da Silva Jr; Vinícius De Veredas; Marcos José Souza Carpes; Cesar Costapinto Santana (pp. 123-129).
Bupivacaine is an amide type local anesthetic widely used in surgery and obstetrics because of its sustained peripheral and central nerve blockade. R-(+)-bupivacaine is more toxic to the central nervous and the cardiovascular systems than S-(−)-bupivacaine. To obtain S-(−)-bupivacaine with high degree of purity using a continuous simulated moving bed (SMB) unity, equilibrium and mass transfer parameters under dilute conditions were obtained by pulse experiments using 0,0′-bis[4-terc-butyl-benzoyl]-N,N′-diallyl-L-tartar diamide immobilized in silica (Kromasil® CHI-TBB). The linear equilibrium constants were found to be 2.12 and 2.91 for R-(+)-and S-(−)-bupivacaine, respectively. Axial dispersion coefficients were found to be practically the same for both enantiomers. A fast kinetic of mass transfer was observed. The internal resistance to the mass transfer controls all the mass transfer process in this chiral column and the pore diffusion coefficients were of the order 10−7cm2/s. The equilibrium and mass transfer parameters will be employed in future simulation and design of operating conditions of SMB unity.
Keywords: Chiral separations; preparative liquid chromatography; mass transfer; equilibrium; bupivacaine
Lysozyme Adsorption onto Different Supports: A Comparative Study by Kátia Cecília De Souza Figueiredo; Vera Maria Martins Salim; Tito LíVio Moitinho Alves; José Carlos Pinto (pp. 131-138).
The interaction between proteins and solid surfaces has been investigated. The aim of this work is to compare three different materials (hydroxyapatite, polystyrene with core-shell structure (PE-CS) and a functionalized styrene divinylbenzene copolymer) to be used as adsorbents for lysozyme, known as a “hard” protein. Tests were performed according to an experimental design in order to compare the effects of pH, lysozyme and phosphate buffer concentration onto the adsorbed amount of protein. A 23 factorial design and a cross design, which was performed in triplicate, were used to distinguish the most important variables and to infer about the interaction between them. Hydroxyapatite showed the best performance—higher adsorbed amount of lysozyme and smaller dispersion (72.2 ± 0.9 mg/g). However, PE-CS can be regarded as a promising support as high amounts of lysozyme are adsorbed onto this material with relatively small dispersion.
Keywords: adsorption; lysozyme; hydroxyapatite; polystyrene; amberlite
Desorption Processes: Supercritical Fluid Regeneration of Modified Clays by Marisa F. Mendes; Gerson L. V. Coelho (pp. 139-146).
The main objective of this work is the study of the regeneration capacity of modified clays using carbon dioxide. These modified clays are used as organic compounds adsorbents. Modified clays were used to remove ethyl acetate from aqueous solutions. Structural changes on the montmorillonite clay after a treatment with quaternary amines were investigated. The experimental step was also done using a packed column with the clay contaminated by ethyl acetate and toluene. Different pressures and temperatures were employed, leading to different fluid conditions (gas, liquid and supercritical). The results obtained showed the influence of the density of the supercritical CO2 and of the organic modifier in the desorption process. These data were modeled with a simple model and with models of first and second orders. The better results were reached using the second-order model. This study allows the scale-up of the desorption process for the regeneration of solid matrices using supercritical fluids. The modified clay capacity as a pollutant attenuator remained almost unchanged after a regeneration cycle.
A Theoretical and Experimental Study of Charge and Discharge Cycles in a Storage Vessel for Adsorbed Natural Gas by Moisés Bastos-Neto; A. Eurico B. Torres; Diana C. S. Azevedo; Célio L. Cavalcante Jr. (pp. 147-157).
This study presents experimental data of storage and delivery tests of methane on activated carbon carried out in a prototype vessel at pressures up to 40 atm. Adsorption equilibrium data at high pressure were measured using a gravimetric apparatus. Experimental data obtained from the storage/delivery tests are compared to those obtained from process simulation using a dynamic model. The simulation model was run using the measured equilibrium data as input parameters. A good agreement was observed between experimental and simulated results. Histories of pressure and stored mass were satisfactorily well predicted. Despite heat effects, not precisely taken into account in the model, there was a reasonably good agreement between simulation and experiment for the average temperature inside the vessel.
Keywords: natural gas; activated carbon; storage and delivery; heat effects
Crystallization of ZSM-12 Zeolite with Different Si/Al Ratio by Antonio S. Araujo; Antonio O. S. Silva; Marcelo J. B. Souza; Ana C. S. L. S. Coutinho; Joana M. F. B. Aquino; José A. Moura; Anne M. G. Pedrosa (pp. 159-165).
In this work the acid properties of a series of HZSM-12 zeolites with different Si/Al ratio were studied. The ZSM-12 crystals were synthesized by the hydrothermal method starting from a gel with the following molar composition: 20MTEA:10Na2O:x Al2O3:100SiO2:2000H2O, with x = 0.50, 0.67, 1, 1.25 and 2, respectively. The gels were crystallized at 140∘C for 6 days, then washed, dried and calcined to remove the MTEA template. The samples were ion-exchanged with an ammonium chloride solution and calcined again to obtain the zeolites in the acid form. The materials thus obtained were characterized by XRD, SEM, BET, TG and n-butylamine adsorption. The Si/Al ratio in the reaction mixture affects the amount of zeolite produced and the size of the particles. The XRD analysis indicated that the ZSM-12 zeolite crystallizes in a pure form only with Si/Al ratio above 33. The SEM analysis showed the presence of crystallites with very well defined prismatic shapes. The removal of the MTEA of the pores of the ZSM-12 by TG indicated that there are two kinds of internal sites occupied by MTEA inside the structure. The BET area of the ZSM-12 decreases proportionally with the crystallinity of materials. The desorption of n-butylamine showed that the acid site density is proportional to aluminum content, but the Si/Al ratio shows little influence on the relative strengths of these sites.
Keywords: ZSM-12 zeolite synthesis; hydrothermal crystallization; different Si/Al ratio; aluminum concentrationn-butylamine adsorption
Adsorption of Phenolic Compounds from Water on Activated Carbon: Prediction of Multicomponent Equilibrium Isotherms using Single-Component Data by Anabela Leitão; Rosalina Serrão (pp. 167-179).
Batch-type experiments were carried out to obtain equilibrium isotherms for the adsorption of phenol and m-cresol in aqueous solutions on activated carbon. Single solute systems, at 20 and 40∘C, were tested for Langmuir, Freundlich and Sips adsorption isotherms in the range of concentrations up to 200 mg/L. Equilibrium data were more closely followed by the Freundlich and Sips equations for all cases. Adsorption isotherms for bisolute systems at 20∘C, with two different initial concentrations of phenol and m-cresol, were predicted solely on the basis of single solute equilibrium parameters by using the equations of Butler and Ockrent and the IAS theory. The best agreement with the experimental loading values was afforded with the IAS theory based on Sips isotherm for pure compounds. However, this theory is found to be not able to predict with success the binary isotherms in this work where significant displacement of one solute by the other is observed. Chemical interactions in the adsorbed phase, estimated by a modified Butler–Ockrent model, can be responsible for this lack of success of the conventional IAS theory. The predictions based on the IAS theory are compared with the results of some empirical models.
Keywords: binary adsorption; phenol and m-cresol; prediction of mixture isotherms; IAS theory
Study of the Adsorption Properties of MCM-41 Molecular Sieves Prepared at Different Synthesis Times by Antonio S. Araújo; Marcelo J. B. Souza; Antonio O. S. Silva; Anne M. G. Pedrosa; Joana M. F. B. Aquino; Ana C. S. L. S. Coutinho (pp. 181-186).
The variation of surface properties of SiMCM-41 and AlMCM-41 nanoporous materials as function of synthesis time was examined. The main properties studied were: surface area, pore diameter, pore volume, mesoporous parameter, and wall thickness. Siliceous MCM-41 molecular sieves were synthesized starting from hydrogels with the following molar compositions: 4.58SiO2:0.435Na2O:1 CTMABr:200 H2O for SiMCM-41, and 4.58SiO2:0.485 Na2O:1 CTMABr:0.038 Al2O3:200 H2O, for AlMCM-41. Cetyltrimethylammonium bromide (CTMABr) was used as the structural template. The crystallographic parameters were obtained from XRD data and by nitrogen adsorption using the BET and BJH methods. The results obtained showed a significant variation of the surface properties of the MCM-41 materials as a function of the synthesis time reaching silica wall thickness of ca. 2 nm on the fourth day.
Keywords: MCM-41; synthesis time; wall thickness