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Adsorption: Journal of the International Adsorption Society (v.5, #3)
Neural Network Modeling of Adsorption of Binary Vapour Mixtures by M. Carsky; D.D. Do (pp. 183-192).
Three neural network models were used for prediction of adsorption equilibria of binary vapour mixtures on an activated carbon. The predictions were compared both with published experimental data and calculated values from the Ideal Adsorption Solution (IAS) model. The neural network was trained using both binary and single component experimental adsorption data. Even for a limited number of data points (about 60) the network models were capable of approximating experimental data very precisely.
Keywords: adsorption; activated carbon; neural network; ideal adsorption solution theory
An Equilibrium Relation for Gas Adsorption Applications by Bradley P. Russell (pp. 193-197).
A new multicomponent equilibrium relation is proposed for engineering applications. This relation is based on a lattice model for mixtures of unequally sized molecules. An approximation is introduced for loading-dependent enthalies of adsorption that simplifies the energy balance in fixed-bed models and allows efficient solution of the equation set in process simulations. Comparisons are made with nonideal binary data in the literature.
Keywords: adsorption equilibrium; lattice theory; pressure swing adsorption
Measurement of Gas Mixture Adsorption Equilibria of Natural Gas Compounds on Microporous Sorbents by J.U. Keller; F. Dreisbach; H. Rave; R. Staudt; M. Tomalla (pp. 199-214).
Physisorption equilibria of multicomponent gases on microporous solids like zeolites or activated carbons are considered. In view of lack of reliable and simple methods to calculate mixture adsorption isotherms from pure component data, experiments are still indispensable. An overview of classical and new methods to measure multicomponent gas adsorption equilibria is given. Some of the basic concepts like the Gibbs excess mass and the absolute mass adsorbed underlying these methods are discussed. Experimental data and a class of new adsorption isotherms for inhomogeneous microporous adsorbents of fractal dimension will be given in another subsequent paper (ADSO 635-98) by the same group of authors.
Keywords: coadsorption; gas adsorption equilibria; measurement technique; adsorption isotherm; natural gas
High Pressure Adsorption Data of Methane, Nitrogen, Carbon Dioxide and their Binary and Ternary Mixtures on Activated Carbon by F. Dreisbach; R. Staudt; J.U. Keller (pp. 215-227).
Adsorption equilibria of the gases CH4, N2, and CO2 and their binary and ternary mixtures on activated carbon Norit R1 Extra have been measured in the pressure range 0 ≤ P ≤ 6 MPa at T = 298 K. Pure gas adsorption equilibria were measured gravimetrically. Coadsorption data of the three binary mixtures CH4/N2, CH4/CO2, and CO2/N2 were obtained by the volume-gravimetric method. Isotherms of five ternary mixtures CH4/CO2/N2 were measured using the volumetric-chromatographic method. First, we present in a short overview the method and procedure of measurement. In a second part, the measured data of pressures, surface excess amounts adsorbed and absolute amounts adsorbed are presented and analyzed. In the last part of the paper the resulting pure gas adsorption data are correlated using a generalized dual-site Langmuir isotherm. Mixture adsorption can be predicted by this model using only pure component parameters with fair accuracy. Results are presented and discussed in several tables and figures.
Keywords: activated carbon; gas adsorption; coadsorption equilibria data; adsorption isotherm; Langmuir isotherm; dual-site
A General Package for the Simulation of Cyclic Adsorption Processes by Francisco A. Da Silva; José A. Silva; Alírio E. Rodrigues (pp. 229-244).
A general purpose package for simulation of fixed-bed and cyclic adsorption processes (PSA/VSA and TSA) has been developed. The package allows various models options depending on combinations of conservation equations: Equilibrium model, Macropore or Micropore model (LDF model), Bidisperse model (double LDF model). The fluid flow follows Ergun's equation locally and the operation of the column can be isothermal, adiabatic or non-isothermal, non-adiabatic. Two important industrial separation processes are considered: the propylene/propane and the n/iso paraffins systems. A three-step TSA and a four-step VSA are considered for propylene/propane mixture while a four-step PSA and two-step adsorption/purge-desorption processes are applied to the n/iso paraffins separation.
Keywords: cyclic adsorption simulator; PSA; VSA; TSA; bulk separation; fixed-bed
Analysis of Equilibrium PSA Performance with an Analytical Solution by Jong-Ho Park; Jong-Duk Kim; Jong-Nam Kim; Soon-Haeng Cho (pp. 245-259).
Five-step PSA cycles consisting of pressurization with product, adsorption, co-current depressurization, blowdown, and purge steps have been analyzed with equilibrium model assuming uncoupled linear isotherms and isothermal condition. Unlike the previous models, the proposed model is not restricted to the operating conditions that ensure a complete shock transition of concentration profile at the end of the high pressure adsorption step. The operating conditions could have two classifications: one is utilizing the column completely before blowdown, and the other is not. As the selectivity increases, it is more difficult to utilize the column completely before the blowdown step. There is an optimum co-current depressurization pressure which maximizes the recovery at the given extent of purge. The optimum co-current depressurization pressure decreases as the purge quantity decreases. On the less selective adsorbent, the recovery at the optimum co-current depressurization pressure increases with the decrease of purge quantity without much sacrifice of the throughput. But, on the highly selective adsorbent, there is an extent of purge and corresponding value of cocurrent depressurization pressure below which the recovery is not greatly improved while the throughput decreases rapidly, which limits the number of pressure equalization steps can be included.
Keywords: pressure swing adsorption; equilibrium model; analytical solution; optimum co-current depressurization pressure
Pressure Effects in Adsorption Systems by Bhaskar K. Arumugam; Jeanne F. Banks; Phillip C. Wankat (pp. 261-278).
A study of the occurrence of large pressure and flow transients when a strongly adsorbed gas is fed to a column which is initially loaded with a lightly adsorbed gas is presented here. Under certain conditions, these transients can cause premature breakthrough and change the shape of the breakthrough curve. This will result in improper estimation of adsorption parameters by the dynamic column loading method and lower apparent adsorption capacity in a full scale unit. A data acquisition system was used to record the pressure and flow transients. An isothermal PDE model developed to study these transients agreed reasonably well with the nonisothermal experimental results. The PDE model predicts that pressure and flow transients will occur during step and pulse~tests conducted to obtain adsorption and mass transfer parameters by the chromatographic method. For instance, lower adsorption capacity will be realized during step tests due to lowering in column pressure. Oscillations were observed when columns are connected in series. The PDE model also predicts these oscillations. Simulations indicate that the extent of oscillations is dependent on the dead volume between columns.
Keywords: adsorption; concentrated systems; pressure transients; flow transients
Heat Transfer Enhancement on the Adsorber of Adsorption Heat Pump by Lijun Wang; Dongsheng Zhu; Yingke Tan (pp. 279-286).
Three methods for improving the heat transfer of the adsorber have been developed in this paper. First, an electrically conductive polyaniline was applied for enhancing the thermal conductivity of adsorbent bed. A thermally conductive composite of polyaniline and adsorbent was prepared by chemical oxidative in situ polymerization of aniline onto the surface of adsorbent particles. A thin thermal conducting net on the surface of the adsorbent particles was grown. The experimental results indicated that the thermal conductivity of this composite could be increased to approximately 4 times that of the raw adsorbent. Second, the adsorbent bed was shaped by a compressing process. This process can reduce the thermal resistance among the adsorbent particles and the contact thermal resistance between the adsorbent bed and the heat exchanger. The thermal conductivity of the shaped adsorbent bed itself from the tests can be increased 30% when the density of the solid adsorbent bed is 1.5 times that of its original density. Furthermore, the adsorption capacity of the above treated adsorbent did not decrease obviously. Third, a proper design of adsorber has been introduced and analyzed. Further tests of this design will be conducted soon.
Keywords: adsorber; polyaniline; adsorbent bed-shaping; heat transfer enhancement