Recovery, concentration and purification of phenolic compounds by adsorption: A review

Preparation and characterization of activated carbon from cotton stalk by microwave assisted chemical activation—Application in methylene blue adsorption from aqueous solution

Catalytic wet-air oxidation processes: A review

Preparation of activated carbons from cotton stalk by microwave assisted KOH and K2CO3 activation

Adsorption of Pb(II) on activated carbon prepared from Polygonum orientale Linn.: kinetics, isotherms, pH, and ionic strength studies.

The oxidation of aqueous ammonia to nitrogen by the catalytic wet air oxidation (CWAO) process with activated carbon as catalyst was studied. A commercial activated carbon CUDU1000 chemically modified by oxidation with HNO3 and/or reduction with H2 was used. The characterization of the activated carbons was carried out by N2 adsorption, thermal programmed decomposition (TPD), Fourier transformed infrared (FTIR) spectroscopy, Boehm titration and zero point charge (ZPC) techniques. Studies of aqueous ammonia adsorption on the activated carbons under atmospheric conditions showed that carboxylic, lactonic and anhydride surface groups increase both the rate and capacity of adsorption. The oxidized carbons had lower activity towards selective aqueous ammonia oxidation in CWAO process because of a strong ammonia adsorption. However, hydrogenated activated carbons had higher activity for selective aqueous ammonia oxidation. It is establish that a strong ammonia adsorption takes place onto carboxylic, lactonic and/or anhydride surface groups while the quinonic surface groups are responsible of the catalytic activity shown by these carbons.

Catalytic wet air oxidation of aqueous ammonia with activated carbon

BACKGROUND: A comparative study of the influence of preparation variables in the activation of pine sawdust and peach stones with phosphoric acid is presented. Adsorptive properties of these materials were tested for the clarification of apple juice and the decolorization of red wine. The main objective of this study was to identify the influence of the textural and chemical properties of activated carbons on clarification and decolorization processes.



RESULTS: The role of impregnation conditions in porosity development was more important for activated carbons originating from peach stones than in those originating from pine sawdust, mainly due to their morphological differences. The amount of phosphoric acid retained on the precursors was found to be a function of the impregnation variables. Furthermore, porosity development dependence on phosphoric acid content per gram of precursor was confirmed. For both precursors, the best microporosity development was obtained at a heat treatment temperature of 450 °C. Independently of the preparation variables used, activated carbons from pine sawdust and peach stones had the same type of surface functional groups: mainly phenolic, quinonic and phosphoric ester-like structures.



CONCLUSIONS: From the results of clarifications and decolorization tests, it was confirmed that to obtain good performance in these assays, the development of mesoporosity is crucial. However, when activated carbons had similar mesoporosities, the presence of surface functional groups contributed to improved performance in clarification and decolorization process. Copyright © 2008 Society of Chemical Industry

Activated carbons from peach stones and pine sawdust by phosphoric acid activation used in clarification and decolorization processes

Chemical activation of pine sawdust using aqueous solutions of phosphoric and boric acid was studied. Thermogravimetric analyses of the impregnated lignocellulosic precursor as well as their reactivities are presented. The role of the activating agents in the thermal decomposition of the precursor and their effects on the development of porosity in activated carbons is discussed. The use of boric acid as activating agent and a final heat treatment temperature (HTT) of 600 °C produced some porosity and activated carbons with a surface area of 600 m2 g−1. With a HTT of 450 °C, molecular sieve-like materials were produced. In contrast, phosphoric acid activation produced activated carbons with high surface areas. The amount of phosphoric acid retained in the precursor was, as expected, a function of the initial concentration as well as the impregnation time and temperature. The fact that the activated carbon porosity increases with the phosphoric acid content per gram of precursor was confirmed. The use of 6 M phosphoric acid solution and HTT of 450 °C produced the activated carbon with the highest surface area, about 1600 m2 g−1. The high degree of microporosity which developed in phosphoric acid-activated carbons is related to the low reactivity during the thermal treatment of chemical activation. The presence of up to 10% oxygen during HTT with phosphoric acid activation caused only small textural changes. Copyright © 2003 Society of Chemical Industry

Phosphoric and boric acid activation of pine sawdust

The catalytic wet air oxidation (CWAO) of methyl and dimethylamines was studied. A commercial peach stones activated carbon and its oxidized and reduced forms were used as catalysts. The observed catalytic behavior is related to the presence of oxygenated surface functional groups on the activated carbons. The N-compounds were selectively oxidized to nitrogen, water and carbon dioxide using these activated carbon catalysts. It is proposed that the quinonic surface groups are responsible for the selective catalytic oxidation of these amines. Carboxylic, lactonic and anhydride groups strongly adsorb the amine compounds producing inhibition of the catalytic activity of the activated carbon in the CWAO process.

http://www.ipb.pt/~htgomes/FCT110088-%5b12%5d.pdf

Catalytic oxidation of aqueous methyl and dimethylamines by activated carbon

The oxidation of an activated carbon prepared from peach stones as well as the adsorption of aqueous ammonia using untreated and modified carbons is described here in. Boehm method in conjunction with temperature-programmed desorption (TPD) were mainly used to assess the chemical changes. These methods were complemented by chemical analysis, pH measurements and FT-IR spectra. Textural characterization was obtained from CO2 and N2 adsorption. Chemical modifications performed under the same experimental conditions with aqueous solutions of HNO3 and H2O2 indicated evidences that carboxylic acids like group formation is enhanced by short periods of time of HNO3 treatment at temperatures about 353 K followed by a mild oven-dry process in atmospheric air. The activated carbon modified under such conditions resulted to be the best ammonia adsorbent

Gabriela Soto-Garrido

Papers

Catalytic wet air oxidation of aqueous ammonia with activated carbon

Activated carbons from peach stones and pine sawdust by phosphoric acid activation used in clarification and decolorization processes

Phosphoric and boric acid activation of pine sawdust

Catalytic oxidation of aqueous methyl and dimethylamines by activated carbon

A peach stone activated carbon chemically modified to adsorb aqueous ammonia