Wood-based activated carbon was modified by impregnation with urea and heat treatment at 450 and
950 °C. The chemical and physical properties of materials were determined using acid/base titration, FTIR,
thermal analysis, IGC, and sorption of nitrogen. The surface features were compared to those of a commercial
urea-modified carbon. Then, the H2S breakthrough capacity tests were carried out, and the sorption capacity
was evaluated. The results showed that urea-modified sorbents have a capacity similar to that of the
received material; however, the conversion of hydrogen sulfide to a water-soluble species is significantly
higher. It happens due to a high dispersion of basic nitrogen compounds in the small pores of carbons,
where oxidation of hydrogen sulfide ions to sulfur radicals followed by the creation of sulfur oxides and
sulfuric acid occurs. It is proposed that the process proceeds gradually, from small pores to larger, and
that the degree of microporosity is an important factor.
The H2S breakthrough capacity was measured on two
series of activated carbons of a coconut shell and a bituminous
coal origins. To broaden the spectrum of surface features
the samples were oxidized using nitric acid or ammonium
persulfate under conditions chosen to preserve their pore
structures. Then the carbons were characterized using
Boehm titration, potentiometric titration, thermal analysis,
temperature programmed desorption, sorption of nitrogen,
and sorption of water. It was found that the choice of
unimpregnated carbon for application as H2S adsorbent
should be made based on parameters of its acidity such as
number of acidic groups, pH of surface, amount of
surface groups oxygen, or weight loss associated to
decomposition of surface oxygen species. The results
obtained from the analyses of six unimpregnated carbon
samples suggest that there are certain threshold values of
these quantities which, when exceeded, have a dramatic
effect on the H2S breakthrough capacity.
Sewage sludge-derived materials were used as adsorbents of hydrogen sulfide from moist air. The adsorbent obtained by carbonization at 950 degrees C has a capacity twice of that of coconut-shell-based activated carbon. The capacity of the sludge-derived materials increases with increasing carbonization temperature. It is likelythatduring carbonization at 950 degrees C a mineral-like phase is formed that consists of such catalytically active metals as iron, zinc, and copper. The results obtained demonstrate that the presence of iron oxide significantly increases the capacity of commercial carbon and activated alumina. The sludge-derived adsorbents are efficient for hydrogen sulfide removal until the pore entrances are blocked with sulfur as the product of oxidation reaction. For materials in which the catalytic effect is predominant, hydrogen sulfide is adsorbed until all pores are filled with sulfur. There is also indication that chemisorption plays a significant role in the removal of hydrogen sulfide from moist air.
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