Two activated carbons from different sources were oxidized with nitric acid and hydrogen peroxide and the effects of this on their porous structure and sorption of water and methanol were studied. The microstructural properties were derived from analysis of N2 isotherms. The surface acidity was assessed using Boehm titration and potentiometric titration. Changes in the surface chemistry were also monitored using difference reflectance IR Fourier transform. From the potentiometric titration the pKa distributions were calculated and the surface density of acidic groups was evaluated. The structural and surface chemical results demonstrate that carbons derived from different sources can have wide variation in their oxidation susceptibility. To further evaluate the impact of the recorded changes due to oxidation in the carbons studied, sorption uptake of water and methanol was measured and correlated with the acidity of the carbon surfaces.
Type, amount and composition of gases which form in rocks and coals during a metamorphism process depend on a number of factors in particular genetic type of original matter, way and conditions of its gathering, temperature, pressure and geological time. Sorption tests were done by the volumetric method, with the use of adsorption micro-burettes. A major advantage of the measurement set-up is that the surplus amounts of adsorbate can be used in experiments, which is of particular importance when handling sorbents with heterogeneous structure, such as hard coals. Sorbates used in the test program were the vapours of hexane, hex-1-ene, heptane, hept-1-ene, octane and benzene. Measurement results seem to corroborate the hypothesis that sorption of polar substance vapours is chiefly a surface process. Polarity of hard coals, mostly associated with the presence of reactive oxygen groups (nitrogen and sulphuric groups), largely affects the sorption of polar substances and in a most characteristic manner controls the sorption of apolar ones. In the case of the latter, sorption is induced by the action of the dispersive interaction force between the coal surface and the sorbate's polar molecules. The pattern of sorption isotherms indicates that the presence of dual bond affects the sorbent-sorbate interactions and hence the sorption capacity of investigated coals.
This paper summarises the results of methanol sorption on three selected coal samples from Polish collieries. These coals differ in terms of their degree of metamorphism (coal rank), petrography and elemental composition. It was found out that during the sorption of methanol, the sorption capacity is closely related to the structure of the coal surface and the amount of sorbed polar substance tends to decrease with the higher degree of metamorphism. Experimental data were plotted as isotherms. Empirical measurements were supported by thermodynamic analysis of aliphatic hydrocarbons sorption. The procedure is based on the Multisorption Model (MSM) designed for describing small molecules sorption in different types of carbonaceous materials (hard coals, lignites, active carbons).
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