Isotherm, adsorption continuous

Whittaker, K. F., 1980, Adsorption of selected pesticides by activated carbon using Isotherm and continuous flow column system, Ph.D. Thesis, Purdue Unlveslty, West Lafayette, Indiana. 

Qualls, R., and B. L. Haines. 1992b. Measuring adsorption isotherms using continuous, unsaturated flow through intact soil cores. Soil Science Society of America Journal 56 456-460. 

The continuous approach is more recent and is not yet widely used. In contrast to a discontinuous procedure, the adsorptive is now continuously feeding the adsorbent, so that the point on the adsorption isotherm is continuously moving along the path of the isotherm. By using the term adsorption isotherm we imply that the adsorption system is always at thermodynamic equilibrium. Since the system is now continuously changing we should stricdy speak of quasi-equilibrium (Rouquerol et at., 1988). The fact that this condition was not fulfilled in the first experiments of this type (Innes, 1951 Lange, 1963) unfortunately delayed the development of this procedure. 

C12SO.) are shown in Figure 2. All of the " adsorption isotherms were continuous in Regions II and III, which suggests that the distribution of energy level patches on o the surface of the alpha aluminum oxide was nearly... 

Rouquerol et al. (11, 12) have recently described the experimental determination of entropies of adsorption by applying thermodynamic principles to reversible gas-solid interactions. Theoretically, the entropy change associated with the adsorption process can only be measured in the case of reversible heat exchange. The authors showed how isothermal adsorption microcalorimetry can be used to obtain directly and continuously the integral entropy of adsorption by a slow and constant introduction of adsorbate under quasi-equilibrium conditions (11) or by discontinuous introduction of the adsorbate in an open system (12). 

In Fig. 9a), isotherms for nitrogen gas adsorption at 77 K are compared for three ACFs [23,24] the coiTespondii PSDs are shown on F. 10. For activated carbon liber AS, the adsorption of nitrogen gas reached almost saturation at P/Po below 0.05. For A20, however, a gradual increase in adsorption continues up to P/Pg of 0.3, after an abrupt initial increase in adsorption. These abrupt initial adsorptions are due to filling of micropores with size <1 nm. 

Pore volume The pore volume is frequently also determined from the gas adsorption isotherm. The value of low-temperature nitrogen adsorption at the relative pressure p/ps 1 is generally accepted to be equal to the pore volume of the sorbent. However, this is valid only for type IV isotherms (Fig. 3.1.b), which clearly level off in the vicinity of pjp = 1. Leveling of the isotherm indicates that all pores in the sorbent are already filled with the liquid sorbate. If the isotherm has a different shape in this ultimate range of relative pressures and adsorption continues to rise at pjps 1 as in Fig. 3.1.a, the estimation... 

Presented section of the adsorption isotherm is continued till the value p p = 1. Thus, the next third section of the adsorption isotherm is characterized by the transition of polymeric chains from the concentrated solution in the concentrated adsorption layer. 

The basis of this intuitive assertion is the shape of the concentration profiles in Fig. 15.3-3. On the left-hand side of this figure, the results for a linear isotherm show that dispersion grows with time as the solute moves down the bed. On the right-hand side, the results for a favorable isotherm show that the dispersion stays the same as the adsorption continues. This favorable isotherm is self-sharpening, with the effects of dispersion and adsorption in balance. Thus the length of unused bed / is a constant, found easily from the fraction of bed saturated, 9... 

As stated in the introduction to the previous chapter, adsorption is described phenomenologically in terms of an empirical adsorption function n = f(P, T) where n is the amount adsorbed. As a matter of experimental convenience, one usually determines the adsorption isotherm n = fr(P), in a detailed study, this is done for several temperatures. Figure XVII-1 displays some of the extensive data of Drain and Morrison [1]. It is fairly common in physical adsorption systems for the low-pressure data to suggest that a limiting adsorption is being reached, as in Fig. XVII-la, but for continued further adsorption to occur at pressures approaching the saturation or condensation pressure (which would be close to 1 atm for N2 at 75 K), as in Fig. XVII-Ih. 

The multilayer isotherms illustrated thus far have all been of a continuous appearance—it was such isotherms that the BET, FHH, and other equations treated. About 30 years ago, however, multilayer adsorption on smooth sur-... 

Continuing the formal development of the influence of the adsorption isotherm on the apparent reaction kinetics, we next consider the case of a reac-... 

Fig. 230 Adsorption of nitrogen at 77 K on a silica powder a) adsorption isotherms b) /-plot. Broken line, uncompacted powder continuous line, power compacted at 2-00 x 10 N m (130 ton in ). (—>—) adsorption (—<-) desorption. / is the ratio of the amount adsorbed on the powder to the amount adsorbed on the compact at the same relative...

Both kinetic and equilibrium experimental methods are used to characterize and compare adsorption of aqueous pollutants in active carbons. In the simplest kinetic method, the uptake of a pollutant from a static, isothermal solution is measured as a function of time. This approach may also yield equilibrium adsorption data, i.e., amounts adsorbed for different solution concentrations in the limit t —> qo. A more practical kinetic method is a continuous flow reactor, as illustrated in Fig. 5. 

It is seen that at high concentrations (a) becomes unity and the surface is completely covered with the more strongly adsorbed solvent. The adsorption isotherm of chloroform on silica gel, determined by Scott and Kucera (5) is shown in figure 1. It is seen that the monolayer of chloroform collects on the surface continuously until the chloroform content of the mobile phase is about 50%. At this concentration the monolayer appears complete. Thus, between 0 and 50% chloroform in the n-heptane, the interactions between the solute and the chloroform in the mobile phase are continuously increasing. 

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