Liquid adsorption and immersion of two alcohol–water mixtures on carbon molecular sieves

Abstract

The adsorption excess isotherms of ethanol–water and propanol–water mixtures are studied on a series of carbon molecular sieves with well-separated micro- and mesoporosity at 298.15 K. The preferential adsorption of one component from a mixture is measured by using vibration densitometry for the concentration analysis. Microcalorimetrically measured enthalpies, which are released upon immersion of the carbon materials in the binary mixtures, complement the adsorption excess data. It is shown that (i) density measurements are well applicable for studying liquid-phase adsorption, (ii) liquid-adsorption isotherms are sensitive to smallest chain length differences of the adsorptives, (iii) the calculated separation diagrams depend strongly on the assumptions about the adsorbed phase, and (iv) the combined determination of gas, vapor and liquid adsorption isotherms and immersion enthalpies offers advantages for the analysis of complex adsorption systems.

How Important Is the Internal Hydrophobicity of Metal–Organic Frameworks for the Separation of Water/Alcohol Mixtures?

“…The reduced surface excess, Γ σ( n ) , for the liquid multicomponent mixtures was calculated by normalΓ i σ ( n ) = n m a ( x i − x i ′ ) where n is the total amount of fluid in the system, m a is the adsorbent’s mass, x i is the mole fraction of i in the real system, i.e., corresponding to the mole fraction of i in the pores (simulation) or the initial liquid mixture (experiment) , and x i ′ is the mole fraction of i in the reference system, i.e., the equilibrium mole fraction of i in the liquid mixture. The simulated reduced surface excess obtained for each system was fitted to the bi-Langmuir function normalΓ i σ ( n ) = ȟ 2 ( ȟ 1 K 1 x i ′ 1 + false( K 1 − 1 false) x i ′ + false( 1 − ȟ 1 false) K 2 x i ′ 1 + false( K 2 …”

One hundred years of the Ostwald—de Izaguirre theory for adsorption from solution. Its connection with carbon adsorbents

“…The Ostwald-de Izaguirre equation continues to be applied in the 21st century, for instance in works on adsorption energy distribution functions [42,43] (functions whose calculation still poses difficulties [44]). Besides carbon-based adsorbents such as lignin chars [35], ordered mesoporus carbons [45] and carbon molecular sieves [46], it is being applied to adsorption by zeolites [47] or layered silicates [48,49,50]. The variety of adsorption systems involved undeniably shows the potential of Ostwald-de Izaguirre theory in the entire area of adsorption from solution despite the fact that it was validated with experimental data corresponding to a narrow set of (nowadays obsolete) carbonaceous adsorbents.…”