Norit model

Figure. 3.3. (a) A Norit model indicating a structure in activated carbon made up of layers of carbon atoms (defective graphene layers) stacked so as to create porosity between them. 

In general, the model can represent the experimental data fairly well as seen in Figure 3. The adsorption isotherms for the other binary systems on Filtrasorb-400, and Norit ROW 0.8 are available elsewhere [9]. In order to test the importance of the incorporation of the pore network connectivity concept, the ideal adsorbed solution theory was also applied without considering the connectivity of the pore network. For this purpose, we also used the binary... 

The pure component adsorption equilibrium of ethane and propane are measured on Norit AC at three temperatures (30, 60 and 90 °C). All experimental data of two species at three temperatures are employed simultaneously to fit the isotherm equation to extract the isothermal parameters. Since an extended Langmuir equation is used to describe the local multicomponent isotherm, the maximum adsorbed capacity is forced to be the same for ethane and propane in order to satisfy the thermodynamic consistency. The saturation capacity was assumed to be temperature dependent while the other parameters, bo and u], are temperature independent but species dependent. The derived isotherm parameters for ethane and propane are tabulated in Table 1. The experimental data (symbols) and the model fittings (solid lines)... 

Fig. 2. Adsorption isotherm data and model fitting of ethane and propane in Norit activated carbon ------ MPSD model -------------Energy distribution model...

Having obtained the adsorption equilibrium and mass transfer parameters of single component systems (Tables 1 to 2), we are ready to examine the predictability of the model in simulating the sorption kinetics of multicomponent systems on Norit activated carbon. 

Several modifications of the OPDA procedure have been reported for automated analysis. Kirk and Ting (16) described a continuous flow analysis in which DCIP was substituted for Norit in the oxidation step. TAA and DHA can be determined directly RAA is calculated as the difference between TAA and DHA. Good agreement between the manual and automated procedures was achieved, with a considerable decrease in analytical time for the automated assay. Kirk and coworkers (17 19) have used the continuous flow analysis for studies of the kinetics of ascorbic acid degradation in model systems. 

More recently, Ustinov and coworkers [72, 73] developed a thermodynamic approach based on an equation of state to model the gas adsorption equilibrium over a wide range of pressure. Their model is based on the Bender equation of state, which is a virial-like equation with temperature dependent parameters based on the Benedict-Webb-Rubin equation of state [74]. They employed the model [75, 76] to describe supercritical gas adsorption on activated carbon (Norit Rl) at high temperature, and extended this treatment to subcritical fluid adsorption taking into account the phase transition in elements of the adsorption volume. They argued that parameters such as pore volume and skeleton density can be determined directly from adsorption measurements, while the conventional approach of He expansion at room temperature can lead to erroneous results due to the adsorption of He in narrow micropores of activated carbon. 

To elucidate consequences of all four different model assumptions (P1...P4) for the volume of a porous sorbent/sorbate system, adsorption data (Q) of nitrogen N2 (5.0) on activated carbon (AC) Norit R1 Extra which have been measured gravimetrically at 298 K, and the adsorbed masses calculated from these data are shown in Figure 1.22, [1.50]. The lowest curve presents the Q-data. Note that these decrease at high gas densities as then seemingly the increase in buoyancy of the sorbent/sorbate sample is larger than the uptake of nitrogen gas, cp. Eq. (1.31). The other curves present data as follows ... 

Table 1.7. Adsorption equilibria of nitrogen N2 (5.0) on activated carbon (AC) Norit R1 Extra at T = 298 K. Parameters of data correlation for different models of V = V + V using a generalized Langmuir adsorption isotherm Eqs. (1.41, 1.42).

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