Andrey Bagreev

Pore structure and surface chemistry of adsorbents obtained by pyrolysis of sewage sludge-derived fertilizer

Abstract Terrene®, a fertilizer product derived from New York City municipal sewage sludge, was pyrolyzed at various temperatures between 400 and 950°C. The pore structure and surface chemistry of the adsorbent materials obtained were characterized using nitrogen adsorption, thermal analysis, potentiometric titration and FTIR. The adsorbents contain a high percentage of inorganic matter (up to 70%) and only up to 30% carbon. The results show that microporosity is developed within the carbon deposit and at the organic/inorganic interface with increasing temperature of heat treatment. An increase in the pyrolysis temperature also results in significant changes in the surface chemistry towards the development of basic nitrogen centers. In particular there was an increase in the pH values of adsorbents’ surfaces from 7 to 11.

pH of activated carbon surface as an indication of its suitability for H2S removal from moist air streams

Abstract Samples of activated carbons of different origins were tested as removers of hydrogen sulfide at room temperature. The breakthrough capacity was evaluated using a lab designed test. The surface properties of the carbons were studied using Boehm titration, nitrogen sorption and thermal analysis. The results obtained indicate that the choice of unimpregnated carbon for hydrogen sulfide removal should be based on the parameters describing surface acidity such as pH, number of acidic groups, or weight loss during thermal treatment associated with the presence of acidic functional groups. There are certain threshold ranges of these quantities which, when exceeded, have a dramatic effect on the H 2 S breakthrough capacity.

H2S adsorption/oxidation on unmodified activated carbons: importance of prehumidification

Three microporous activated carbons supplied by Norit® (of peat and bituminous coal origin) were used in this study as hydrogen sulfide adsorbents. Their surface properties were evaluated by means of nitrogen adsorption, Boehm titration, potentiometric titration, and thermal analysis. The results show that the carbons significantly differ in their pore structure and surface chemistry. This is reflected in their hydrogen sulfide breakthrough capacity. The breakthrough capacity is underestimated when not enough water is adsorbed on the carbon surface. The performance follows the expectations after extensive humidification of the sorbents’ surfaces. Moderately low pH in the acidic range of coal-based carbon, Vapure 612, promotes the oxidation of H2S to sulfur oxides which is important from the point of view of water regeneration. The high pH of peat-based carbon, RB 4, results in H2S oxidation to elemental sulfur.

Thermal regeneration of a spent activated carbon previously used as hydrogen sulfide adsorbent

The feasibility of thermal regeneration of spent coconut shell-based activated carbon previously used as hydrogen sulfide adsorbent was studied in three successive adsorption/thermal regeneration cycles. The regeneration of exhausted carbon was done by heating the samples at 300°C. The observed changes in the capacity were linked to changes in surface chemistry and porosity. Heating in air atmosphere resulted in the removal of sulfur dioxide and oxidation of elemental sulfur to sulfur oxides. All sulfur from small pores was removed and the pore structure was 100% regenerated. Good agreement in the balance of sulfur species removed from the carbon surface shows that during the treatment all desorbed gases can be collected minimizing the environmental hazard. The results show that the capacity of the carbons to adsorb hydrogen sulfide can be regenerated to at least 30% of its initial value.

Study of regeneration of activated carbons used as H2S adsorbents in water treatment plants

Abstract Regeneration of unmodified activated carbons used in New York City sewage treatment plants was carried out using cold water washing and thermal treatment at 300°C. The efficiency of the regeneration process was evaluated using adsorption of nitrogen, thermal analysis and dynamic measurement of hydrogen sulfide breakthrough capacity. Although differences in the behavior of samples from different locations exist, the results showed that thermal treatment is more efficient than cold water washing. The latter process was able to remove only a small percentage of sulfur species in the form of sulfuric acid, leaving the deposit of elemental sulfur intact. However, treatment at 300°C resulted in the removal of a significant amount of deposited sulfur species. The hydrogen sulfide adsorption capacity of regenerated samples was low due to the alterations in surface chemistry, which occurred during the treatment. The efficient regeneration of the carbon surface was not achieved due to the presence of significant amounts of volatile organic compounds adsorbed from effluent air.