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Adsorption: Journal of the International Adsorption Society (v.10, #1)
Structural and Adsorptive Characteristics of Pyrocarbon/Silica Gel Si-60 by V.M. Gun'ko; V.V. Turov; J. Skubiszewska-Zięba; B. Charmas; R. Leboda (pp. 5-18).
Pyrocarbon/silica gel adsorbents (carbosils, CS) with mesoporous Si-60 (Merck, granule size 0.2–0.5 mm) modified by pyrolysis of CH2Cl2 at 823 K and reaction time from 0.5 to 6 h and then hydrothermally treated at 473 K for 6 h were studied by means of TEM, adsorption and 1H NMR methods. Changes in the structural and adsorptive characteristics of hybrid adsorbents before and after hydrothermal treatment, which depend on pyrocarbon content (C C), were analyzed on the basis of TEM micrographs and p-nitrophenol and nitrogen adsorption isotherms treated using a constrained regularization method. Interfacial water layers in aqueous suspension of CS were investigated by means of 1H NMR with freezing-out of bulk water at T < 273 K showing nonlinear changes in the Gibbs free energy of interfacial water with increasing C C because of nonlinear dependence of the structural characteristics of pyrocarbon deposits and CS as a whole on C C.
Keywords: mesoporous silica gel; pyrocarbon/silica gel; nitrogen adsorption; pore size distribution; p-nitrophenol adsorption; interfacial water; 1H NMR; Gibbs free energy
Retention of Progesterone by an Activated Carbon: Study of the Adsorption Kinetics by Cristobal Valenzuela-Calahorro; Antonio Navarrete-Guijosa; Mostafa Stitou; Eduardo M. Cuerda-Correa (pp. 19-28).
The process by which progesterone in an ethanol solution is retained by Merck granular activated carbon involves a reversible mechanism that conforms to a kinetic equation of unity partial order in both the progesterone concentration in solution, the coverage fraction (θ) of the adsorbing surface and (1−θ). Over the temperature range 10–40°C, the specific adsorption rate varies from 5.8·10−5 to 1.3·10−4 s−1. The thermodynamic activation functions for the process are ΔH*=41.6 kJ/mol and ΔS*=−0.20 kJ/K· mol. The rate of the adsorption-desorption process is primarily determined by diffusion of progesterone molecules in the pores of the sorbent.
Keywords: adsorption; activated carbon; kinetics; progesterone
Measurement and Modeling of Water Vapor Adsorption on Zeolite 4A—Equilibria and Kinetics by A. Gorbach; M. Stegmaier; G. Eigenberger (pp. 29-46).
The adsorption of water vapor on Zeolite 4A has been analyzed. Both equilibrium and kinetics are examined. The equilibrium is measured with a static-volumetric method in a wide range of partial pressure and temperature and is modeled by several conventional approaches and a new type isotherm model, which fitted the obtained data best. Kinetics are determined by measuring breakthrough curves. The breakthrough curves are matched by a detailed model based on a modified linear driving force (LDF) approximation for the mass exchange. An analytic expression for the corresponding LDF-coefficient is designed in order to describe its dependency on water concentration, temperature and pressure. For the practical range of operating conditions the dependency on concentration can be described by the nonlinearity of the adsorption isotherm. The dependency on temperature and pressure corresponds to that of molecular diffusion. The presented data and models for equilibria and kinetics provide a basis for modeling and optimizing air-drying processes containing Zeolite 4A.
Keywords: adsorption; zeolites; water vapor; equilibria; kinetics; modeling
Adsorption Heat Pump Using an Innovative Coupling Refrigeration Cycle by Shengwei Wang; Dongsheng Zhu (pp. 47-55).
An adsorption heat pump system using a new binary coupling adsorptive cycle is developed and tested. Experimental results show that the COP of the binary coupling cycle is higher than that of a pure zeolite-water system. The system operating pressure is found to be moderate (close to the ambient pressure) when a proper concentration of ammonia is used in the system. The moderate operating pressure of the new coupling cycle results in low leakage to the system, achieving long life and the light design of the system vessels. The use of the new binary adsorption cycle greatly improves the feasibility and reliability of the adsorption heat pumps, providing essential benefits for the industrialisation of adsorption heat pumps.
Keywords: adsorption heat pump; binary coupling; thermodynamics and operating pressure
Performance of a Diesel Locomotive Waste-Heat-Powered Adsorption Air Conditioning System by Y.Z. Lu; R.Z. Wang; S. Jianzhou; M. Zhang; Y.X. Xu; J.Y. Wu (pp. 57-68).
An innovative exhausted-heat-powered solid adsorption air conditioning system with zeolite-water as working pair is designed for providing air-conditioning for the driver's cab of a diesel locomotive. Only one adsorber is used in the system and a cold storage water tank is attached to provide cooling during generation process to ensure the continuous cooling output. Experiments on the laboratory prototype have been carried out and a mean cooling power output of about 3.3 kW is obtained when the condensing temperature and the evaporating temperature are 40°C and 7°C respectively. The influences of some operating conditions on the system performance are analyzed by simulation and experiments. The results of the performance testing of the prototype installed in a diesel locomotive are also discussed as well. An average cooling power of 4.1 kW is got under typical summer condition. It is proved that such a system is quite competitive even if a little bit heavier.
Keywords: adsorption; zeolite; air conditioning; exhausted heat; diesel locomotive
Research on the BET Surface Area and Packing of Molecules on the Activated Carbon by Sirous Nouri; F. Haghseresht (pp. 69-77).
Adsorption of different aromatic compounds (two of them are electrolytes) onto an untreated activated carbon (F100) is investigated. The experimental isotherms are fitted into Langmuir homogenous and heterogeneous Model. Theoretical maximum adsorption capacities that are based on the BET surface area of the adsorbent cannot be close to the real value. The affinity and the heterogeneity of the adsorption system observed to be related to the pKa of the solutes. The maximum adsorption capacity (Q max) of activated carbon for each solute dependent on the molecular area as well as the type of functional group attached on the aromatic compound and also pH of solution. The arrangement of the molecules on the carbon surface is not face down. Furthermore, it is illustrated that the packing arrangement is most likely edge to face (sorbate-sorbent) with various tilt angles.For characterization of the carbon, the N2 and CO2 adsorption were used. X-ray Photoelectron Spectroscopy (XPS) measurement was used to surface elemental analysis of activated carbon.
Keywords: BET surface area; molecular size; Langmuir equation; activated carbon; spectrophotometer; characterization of activated carbon
Adsorption of p-Nitrophenol in Untreated and Treated Activated Carbon by Sirous Nouri; F. Haghseresht (pp. 79-86).
The adsorption of p-nitrophenol in one untreated activated carbon (F100) and three treated activated carbons (H2, H2SO4 and Urea treated F100) was carried out at undissociated and dissociated conditions.To characterize the carbon, N2 and CO2 adsorption were used. X-ray Photoelectron Spectroscopy (XPS) was used to analyze the surface of the activated carbon.The experimental isotherms are fitted via the Langmuir homogenous model and Langmuir binary model. Variation of the model parameters with the solution pH is studied. Both Q max and the adsorption affinity coefficient (K 1) were dependent on the PZC of the carbons and solution pH. The Effect of pH must be considered due to its combined effects on the carbon surface and on the solute molecules. Adsorption of p-nitrophenol at higher pH was found to be dependent on the concentration of the anionic form of the solute.
Keywords: adsorption; p-nitrophenol; treated activated carbon; langmuir equation; characterization of activated carbon
Applications of Inorganic Ion Exchangers: II—Adsorption of Some Heavy Metal Ions from Their Aqueous Waste Solution Using Synthetic Iron(III) Titanate by M.M. Abou-Mesalam (pp. 87-92).
Adsorption of Zn2+ and Cd2+ ions from aqueous waste solutions on iron(III) titanate as inorganic ion exchange material was investigated to determine the effect of contact time, pH of solution and the reaction temperatures. Batch kinetic studies were carried out and showed that the time of equilibrium for both Zn2+ and Cd2+ ions was attained within three hours, and the order of kinetic reaction is the first order reaction. Batch distribution coefficients of Zn2+ and Cd2+ ions on iron(III) titanate as a function of pH have been studied at 25, 40 and 60 ± 1°C. From the obtained results we found that the K d values decreased with increasing reaction temperatures. Enthalpy change (ΔH) values for Zn2+ and Cd2+ ions were found to be −8.19 and −22.49 kJ/mol, respectively. The data of adsorption of Zn2+ and Cd2+ ions at various concentrations were fitted with the Freundlich isotherm. Finally, separation of the above mentioned cations on iron(III) titanate in a column was performed.
Keywords: adsorption; heavy metals; waste; synthetic; iron(III) titanate