Dubinin-Serpinski equation

Dubinin-Serpinski Equation for Water Adsorption on Carbon... 

Figure 4.2-5 Plot of the Dubinin-Serpinski equation versus P/Pq with c = 3, C o = 1 mmol/g...

Being a three parameter equation, the Dubinin-Serpinsky equation (4.2-15) can be used directly in a nonlinear optimisation routine to determine the optimal parameters. Alternatively, the initial adsorption data can be used with eq. (4.2-17) to determine the constant c and the concentration of the primary site, and the equation for the maximum capacity (4.2-19) then can be used to determine the remaining parameter k. 

Figure 4.2.6 shows plots of the above data as well as fitted curves (obtained from the ISO FITl program) from the Dubinin-Serpinski equation and the DA equation. Both of these equations fit the data reasonably well although the Dubinin-Serpinski equation provides a better fit in the lower range of the pressure. This could be attributed to the correct description of the water clustering in the lower pressure range. 

Figure 4.2-6 Fitting the Dubinin-Serpinski equation to water/activated carbon data...

The adsorption of water vapour has been studied with a range of microporous carbons, zeolites and aluminophosphates in order to elucidate the relative influence of surface chemistry, pore size and pore shape upon the form of the water isotherm. It was possible to separate the adsorbents into three groups on the basis of their affinity and capacity for water vapour. The porous carbons were further examined using the BET and Dubinin-Serpinsky equations. The results show that the adsorption of water vapour at low p/p° is largely dependent upon specific adsorbent-adsorbate interactions whilst at higher relative pressures the micropore size and shape control the extent of adsorption. It is proposed that hydrogen-bonded layers of water can be more readily accommodated in the narrow slit shaped pores (-0.5nm) of molecular sieve carbons than in tubular pores of similar width (e.g. Silicalite/ZSM-5). 

Fig. 5. Quadratic fit of the Dubinin-Serplnsky fjg g. Quadratic fit of the Dubinin-Serpinsky equation to JF144 experimental data. equation to KCC1 experimental data.

The Dubinin-Serpinski (DS) equation, which was based on this model, can be expressed in the form... 

This adsorption equation, known as the Dubinin-Serpinsky (D-Se) equation, exhibits a type V isotherm as shown in Figure 4.2-5 for c mmole/g and three... 

Serpinski, V.V., and Jakubov, T.S., Dubinin-Radushkevich equation as the equation for the excess adsorption isotherm, Adsorpt. Sci. Technol., 10, 85-92 (1994). 

In order to further elucidate the complex pore filling process in microporous carbons, the empirical Dubinin-Serpinsky (DS) equation (refs. 14-15) was used to assess the influence of polar sites on the shape of the isotherm. This equation was developed from the concept of adsorption of water molecules at uniform high energy primary adsorption centres. Molecules adsorbed on these sites act as secondary adsorption centres via a hydrogen-bonding mechanism. Thus, this model does not refer explicitly to the role played by pore size. The DS equation may be written in its modified form (ref. 15) as ... 

The adsorption of water by activated carbons follows Equation (4.18) (Dubinin and Serpinsky, 1981) ... 

Dubinin MM, Serpinsky VV. Isotherm equation for water vapour adsorption by microporous carbonaceous adsorbents. Carbon 1981 19(9) 402-403. 

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