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Adsorption: Journal of the International Adsorption Society (v.12, #3)
Removal of heat of adsorption from adsorbent by forced convection by Shivaji Sircar (pp. 167-174).
An analytical mathematical model is used to investigate the effectiveness of forced convection for removal of the heat of adsorption from an adsorbent mass undergoing a differential adsorption process in a flow system. An example of such a process is measurement of gas adsorption kinetics using a differential adsorption bed. Isothermal operation may not be achieved even when a high gas flow rate is used, particularly if the sorption kinetics is relatively fast. Very small changes in the adsorbent temperature can cause significant departure from the isothermal uptake behavior when the heat of adsorption is moderately large. A criterion for validity of isothermal data analysis is given.
Keywords: Adsorption; Kinetics; Non-isothermal; Forced convection; Heat removal
New method for evaluation of heavy metal binding to alginate beads using pH and conductivity data by Ahmet Karagunduz; Dilsad Unal (pp. 175-184).
Extensive research has been conducted for removal and recovery of heavy metals from wastewater and industrial wastewater in recent years. Due to its low cost and high sorption efficiency, alginate was extensively investigated as a biosorbent. It is known that the sorption of metals to alginate is rate limited. However, the sampling in the beginning of experiments, from 30 seconds to few minutes, is very difficult, if not impossible. In this study, a nontraditional experimental method was used to determine the removal kinetics of metals for short time periods. A relationship among pH, conductivity, and metal concentration was established. It was shown that the sorption mechanism was ion exchange for all metals investigated in this study. A series of experiments was conducted to determine the ion exchange kinetics of different metals at varying pH conditions. Second order pseudo rate kinetics was shown to define the experimental findings well. Results also showed that the extent of exchange significantly reduced as the pH decreased. The selectivity of metal exchange to alginate beads was determined. It was observed that the extent of the ion exchange was greatest for Cu2 + and lowest for Mn2 + and Fe2 +, following the order of Cu2 + > Zn2+≅ Co2 +≅ Ni2+ > Mn2+≅ Fe2+.
Keywords: Second order pseudo rate; Ion exchange; Kinetics; Alginate; Metal sorption; Biosorption
Adsorption of Fe(III) from water by natural and acid activated clays: Studies on equilibrium isotherm, kinetics and thermodynamics of interactions by Krishna G. Bhattacharyya; Susmita Sen Gupta (pp. 185-204).
The present work investigates the removal of Fe(III) ions from an aqueous solution by kaolinite, montmorillonite and their acid activated forms. The specific surface areas of kaolinite, acid activated kaolinite, montmorillonite and acid activated montmorillonite were 3.8, 15.6, 19.8 and 52.3 m2/g respectively whereas the cation exchange capacity (CEC) was measured as 11.3, 12.2, 153.0, and 341.0 meq/100 g for four clay adsorbents respectively. Adsorption increased with pH till Fe(III) became insoluble at pH > 4.0. The kinetics of the interactions is not certain, but the second order kinetics (k 2 = 4.7 × 10− 2 to 7.4 × 10− 2 g mg− 1 min− 1) appears to give a better description. Langmuir and Freundlich isotherms were applied and isotherm coefficients were computed. The Langmuir monolayer capacity of the clay adsorbents was from 11.2 to 30.0 mg g− 1. The process was exothermic with Δ H in the range of −27.6 to −42.2 kJ mol− 1accompanied by decrease in entropy (Δ S = −86.6 to −131.8 J mol− 1 K− 1) and decrease in Gibbs energy. The results have shown that kaolinite, montmorillonite and their acid activated forms could be used as adsorbents for separation of Fe(III) from aqueous solution. Acid activation enhanced the adsorption capacity compared to the untreated clay minerals.
Keywords: Adsorption; Kaolinite; Montmorillonite; Acid activated clay; Kinetics; Isotherm; Temperature
Adsorption of acrylonitrile and methyl acrylate on activated carbon in a packed bed column by Fengsong Wang; Jun Li; Jiarong Wang; Haoqi Gao (pp. 205-212).
The adsorption equilibrium and dynamics of acrylonitrile (ACN), methyl acrylate (MA) and the ACN-MA mixture on activated carbon were investigated in a packed bed column at 40∘C. The study indicated that the adsorption isotherms of the pure components belong to the classical Langmuir type; in the case of the binary mixture adsorption, the Ideal Adsorption Solution Theory (IAST) could predict better than the Extended Langmuir (E-L) equation in particular for the MA component. The mass balance equations were established to describe the adsorption dynamic behaviors of the gas phase in the packed bed column, and the linear driving force (LDF) approximation was adopted to estimate the absorbate adsorption kinetics onto the adsorbent. The coupled partial differential equations of the model were numerically solved by the orthogonal collocation (OC) method. The correlated results showed that the model could give an acceptable description of the breakthough curves of the pure ACN and MA in the packed bed column. The prediction of the breakthough curves for the binary CAN-MA system at different inlet concentrations was also implemented, indicating a good agreement with the experimental data.
Keywords: Adsorption equilibrium; Dynamics; Acrylonitrile; Methyl acrylate; Packed bed column
Introduction of new functions to speed up sorption measurements by J. A. Poulis; C. H. Massen; A. Dábrowski; E. Robens (pp. 213-217).
The procedure suggested by Jäntti enables estimation or calculation of the values of adsorption parameters in an early stage of adsorption measurements. The procedure may also give information about the validity of models used for the explanation of the measurements. In the present paper new functions are introduced to get results easier.
Keywords: Adsorption; Dynamic; Fast measurement; Sorption; Surface
Removal of ammonia from waste air streams with clinoptilolite tuff in its natural and treated forms by Karel Ciahotný; Lenka Melenová; Hana Jirglová; Olga Pachtová; Milan Kočiřík; Mladen Eić (pp. 219-226).
Natural and impregnated clinoptilolite tuffs were studied to assess their potential to remove ammonia from air and, in a subsequent application, to use the spent adsorbent as a fertilizer. H2SO4, H3PO4 and HNO3, as agents containing important plant nutrients compatible with soil, were selected for impregnation to enhance sorption capacity of the natural clinoptilolite tuffs for ammonia removal. Sorbents were characterized using N2 adsorption isotherms at 77 K, X-ray analysis and high pressure mercury porosimetry. Ammonia breakthrough curves on fixed beds of sorbent were determined using appropriate NH3 and H2O input concentrations, flow rates and temperatures similar to the conditions in animal breeding farms. Impregnated clinoptilolite tuffs showed adsorption capacities comparable to SSP-4, an activated carbon that is commercially used for NH3 removal. Impregnations with H2SO4 and HNO3 are particularly important, since such modified adsorbents exhibit relatively high breakthrough capacities, thus rendering them potentially useful for practical applications in controlling ammonia emissions. The main contribution to the sorption capacity enhancement on impregnated clinoptilolite tuff samples seems to be due to the chemical reaction of ammonia with acids remaining in the macro- and mesopores.
Keywords: Clinoptilolite tuffs; Ammonia; Adsorption; Impregnation
Natural gas storage cycles: Influence of nonisothermal effects and heavy alkanes by Krista S. Walton; M. Douglas LeVan (pp. 227-235).
A mathematical model is developed for examining the influence of nonisothermal effects and accumulation of heavy alkanes on natural gas storage cycles. The model is solved for the charge and discharge steps of the cycle. This is the first study to solve the natural gas storage problem for a nonisothermal charge of natural gas containing impurities. We examine both adiabatic and isothermal operation of natural gas and pure methane storage cycles on BPL carbon and an activated carbon prepared from coconut shells. Our simulations show for both carbons that the adiabatic gas storage cycles operate under subcooled conditions with respect to the feed temperature due to long discharge times and the desorption heat. It is also shown that degradation of gas storage performance due to impurities depends more on selectivity of the material for heavy alkanes than on adsorption capacities.
Keywords: Natural gas storage; Simulation; Multicomponent