Miguel A. Alvarez-Merino

Chemical and physical activation of olive-mill waste water to produce activated carbons

Abstract Olive-mill waste water is produced in large quantities during the manufacture process of the olive oil in mills. This by-product has been used as raw material to produce activated carbons by both chemical and physical activation methods. In the first case, KOH and H3PO4 were used as activating agent, and in the second case, CO2 at 840°C for different periods of time. Results obtained indicate that the chemical activation with KOH at 800°C, in an inert atmosphere, yielded activated carbons with the highest surface area and more developed micro, meso and macroporosity.

Microporous activated carbons from a bituminous coal

A Spanish bituminous coal was used as raw material to prepare activated carbons both by CO2 and by chemical activation. The activated carbons were characterized by adsorption of N2 at 77 K, CO2 at 273 K and benzene and cyclohexane at 303 K, as well as by mercury porosimetry and helium density. The microporosity of the activated carbons was evaluated by the Dubinin-Astakhov equation applied to the adsorption isotherms and the α-plot method applied to the N2 adsorption data. All activated carbons studied were essentially microporous. The sample obtained by chemical activation with phosphoric acid had the widest micropores. The micropore volumes of activated carbons with medium to high activation determined by N2 and CO2 adsorption were quite similar, so both adsorbates measured the same type of micropores. Molecular sieve effects for benzene and cyclohexane were detected in activated carbons with low to medium activation.

Adsorption mechanisms of metal cations from water on an oxidized carbon surface.

Adsorption of Cr(III), Mn(II), Cu(II) and Zn(II) on an oxidized activated carbon cloth was studied. Its surface chemistry was characterized by potentiometric titration. This technique revealed the amount of surface oxygen functionalities and their acidity constant distribution. The acidity constant range involved in the metal cation adsorption was obtained from this distribution. Metal cation adsorption increased with higher adsorption temperature due to the increase in the negative surface charge of the oxidized activated carbon. Adsorption was by proton exchange and the number, amount and strength of the surface acid groups involved could be obtained. The proton exchange was by an inner-sphere or outer-sphere surface metal complex formation mechanism. In the case of divalent cation adsorption, the increase in temperature changed the adsorption mechanism from outer-sphere to inner-sphere. However, the adsorption mechanism of Cr(III) was outer-sphere and independent of temperature. Adsorption capacity augmented with the increase in the charge-to-size ratio of the hexa-aquo cations. In addition, the adsorption capacity of divalent cations increased with the rise in stability of the surface metal complex formed.

Nitroimidazoles adsorption on activated carbon cloth from aqueous solution

The objective of this study was to analyze the equilibrium and adsorption kinetics of nitroimidazoles on activated carbon cloth (ACC), determining the main interactions responsible for the adsorption process and the diffusion mechanism of these compounds on this material. The influence of the different operational variables, such as ionic strength, pH, temperature, and type of water (ultrapure, surface, and waste), was also studied. The results obtained show that the ACC has a high capacity to adsorb nitroimidazoles in aqueous solution. Electrostatic interactions play an important role at pH<3, which favors the repulsive forces between dimetridazole or metronidazole and the ACC surface. The formation of hydrogen bonds and dispersive interactions play the predominant role at higher pH values. Modifications of the ACC with NH3, K2S2O8, and O3 demonstrated that its surface chemistry plays a predominant role in nitroimidazole adsorption on this material. The adsorption capacity of ACC is considerably high in surface waters and reduced in urban wastewater, due to the levels of alkalinity and dissolved organic matter present in the different types of water. Finally, the results of applying kinetic models revealed that the global adsorption rate of dimetridazole and metronidazole is controlled by intraparticle diffusion.

Decomposition Reactions of Methanol and Ethanol Catalyzed by Tungsten Oxide Supported on Activated Carbon

Activity of the catalysts to obtain the dehydration products linearly increases with their total surface acidity. Results obtained seem to point out that the surface basicity of the support influences the acid strength of the tungsten oxide particles, especially at low tungsten loading.

Competitive adsorption of the herbicide fluroxypyr and tannic acid from distilled and tap water on activated carbons and their thermal desorption

A study was conducted on batch and column competitive adsorption of fluroxypyr (FLX) and tannic acid (TA) from distilled (DW) and tap water (TW) on activated carbon cloth (ACC) and granular activated carbon (GAC). Thermal desorption of the adsorbates from the spent ACC was also studied. FLX adsorption was higher from TW than from DW at low FLX equilibrium concentrations, and the inverse was observed at high FLX concentrations. The presence of TA diminished the amount of FLX adsorbed from both solvents due to partial blocking of the microporosity, but the same trends as before were observed at low and high FLX concentrations. Carbon consumption, obtained from the breakthrough curves, was lower as a function of superficial contact time with ACC than with GAC. The presence of TA increased carbon consumption, which was related to the microporosity of the adsorbents. Thermal desorption profiles of the spent ACC showed two peaks and one peak after adsorption from DW and TW, respectively. Desorption peaks shifted to higher temperatures with an increase in the heating rate, allowing the apparent activation energies and pre-exponential factors of the desorption processes to be determined.

Adsorption of SO2 from flowing air by alkaline-oxide-containing activated carbons

Abstract Adsorption of SO2 under dynamic conditions from an SO2-air mixture at 298 and 573 K on alkaline-oxide-containing activated carbons has been studied. The adsorption capacity of these samples at 298 K was, in general, lower than that in the original activated carbons and mainly governed by their microporosity accessible to benzene. However, at 573 K, the alkaline-oxide-containing activated carbons adsorbed a greater amount of SO2 than the original activated carbon, following the order Na ≥ K > Rb. At both adsorption temperatures, part of the SO2 adsorbed formed H2SO4 and Me2SO4, where Me = Na, K or Rb. When the SO2 adsorption was carried out at 573 K, this gas fixed additional oxygen complexes that evolved as CO2 under heating up to 873 K in He flow, probably by reaction of SO2 with carbon surface atoms of a basic nature that are not able to chemisorb oxygen from the air at the same conditions.

Application of ammonia intermittent temperature-programmed desorption to evaluate surface acidity of tungsten oxide supported on activated carbon

Intermittent temperature-programmed desorption of ammonia was used to study the strength and population of surface acid sites of tungsten oxide supported on activated carbon pretreated at 350 and 700 degrees C. Catalysts pretreated at 350 degrees C showed two types of surface acid sites and desorption occurred with free readsorption until a temperature of around 300 degrees C was reached. Pretreatment at 700 degrees C produced three different states of ammonia adsorbed on the catalysts and desorption occurred with free readsorption.

Effect of alkaline metal oxides on the adsorption of SO2 by activated carbons

Publisher Summary This chapter discusses the effect of alkaline metal oxides on the adsorption of sulfur dioxide (SO2) by activated carbons in flowing air and how it affect different SO2 adsorption–desorption cycles. Activated carbon used is prepared from a Spanish bituminous coal pyrolyzed in a nitrogen (N2) flow at 1273 Kelvin. Results showed that in such conditions, the SO2 adsorption process is governed mainly by a suitable developed microporosity and to a less extent by an adequate surface basicity of the adsorbent as measured by hydrochloric acid (HCl) titration. The experimental conditions used the SO2 adsorption capacity of samples containing alkaline metal oxides mainly governed by the microporosity of the samples accessible to benzene and other activated carbons, which did not contain metal oxides.