The influence of nitrogen groups introduced onto activated carbons by high- or low-temperature NH3 treatment on SO2 sorption capacity (original) (raw)
Related papers
Adsorption of SO2 on Activated Carbons: The Effect of Nitrogen Functionality and Pore Sizes
Langmuir, 2002
Activated carbons of different origins were studied as sulfur dioxide adsorbents. The materials were characterized using adsorption of nitrogen, titration, X-ray photoelectron spectroscopy, and thermal analysis. The investigation was focused on the role of nitrogen functionality and pore sizes in the process of SO2 adsorption/oxidation. The results showed that quaternary and pyridinic type nitrogen significantly enhance the adsorption capacity. It happens when catalytic centers are located in the small pores, which is likely to help in achieving high dispersion of these centers. Besides an oxidation effect due to the formation of active oxygen radicals, the nitrogen-containing centers attract the SO4 2ions causing the gradual pore filling which is the most effective usage of the carbon pore space.
Chemical Physics Letters, 2013
The influence of the gradual oxidation of carbons on SO 2 physisorption was studied, by comparison of experimental and simulated SO 2 adsorption isotherms. The results confirmed a significant impact of surface groups on the SO 2 adsorption. The simulations also revealed a similar, to that observed experimentally, effect of the increase in the percentage of the smallest micropores on adsorption isotherms. The isotherms were analysed using the CMMS model. The conclusion is that this model seems to be a good and sensitive tool for studying SO 2 physisorption mechanism since a very good qualitative agreement between the experimental and simulated data was observed.
The effect of low-concentration SO2 on the adsorption of NO from gas over activated carbon
Fuel, 1997
The effect of low-concentration SO2 on the adsorption of NO over activated carbon was studied using adsorption--desorption profiles obtained during thermal analysis-mass spectrometry. Using three different gas mixtures and adsorption temperatures between 293 and 413 K with NO and SO2 as the reactants, it was determined that NO2 and SO 2 were the primary adsorbed species. The uptake of NO2 decreased with increasing temperature, whereas the uptake of SO2 was independent of temperature. Except at the highest adsorption temperatures, the amount of NO 2 adsorbed was greater than that of SO 2 adsorbed. The presence of SO2 inhibited adsorption of NO2, but the co-adsorption of NO 2 promoted the adsorption of SO2. These data point to the possibility that the SO 2 binding sites on the carbon are associated with the reaction NO + ½ 02 ~ NO2, and to the different adsorption mechanisms which control NO 2 and SO2 uptake. © 1997 Elsevier Science Ltd.
Materials
The textural properties and surface chemistry of different activated carbons, prepared by the chemical activation of olive stones, have been investigated in order to gain insight on the NO 2 adsorption mechanism. The parent chemical activated carbon was prepared by the impregnation of olive stones in phosphoric acid followed by thermal carbonization. Then, the textural properties and surface chemistry were modified by chemical treatments including nitric acid, sodium hydroxide and/or a thermal treatment at 900 • C. The main properties of the parent and modified activated carbons were analyzed by N 2-adsorption, scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR) techniques, in order to enlighten the modifications issued from the chemical and thermal treatments. The NO 2 adsorption capacities of the different activated carbons were measured in fixed bed experiments under 500 ppmv NO 2 concentrations at room temperature. Temperature programmed desorption (TPD) was applied after adsorption tests in order to quantify the amount of the physisorbed and chemisorbed NO 2. The obtained results showed that the development of microporosity, the presence of oxygen-free sites, and the presence of basic surface groups are key factors for the efficient adsorption of NO 2 .
Adsorption of H 2S or SO 2 on an activated carbon cloth modified by ammonia treatment
Carbon, 2003
The aim of this research is to investigate how ammonia treatment of the surface can influence the activity of a viscose-based activated carbon cloth (ACC) for the oxidative retention of H 2 S and SO 2 in humid air at 25 8 C. Surface basic nitrogen groups were introduced either by treatment with ammonia/air at 300 8 C or with ammonia/steam at 800 8 C. The pore structure of the samples so prepared was examined by adsorption measurements. Changes in the surface chemistry were assessed by X-ray photoelectron spectroscopy, X-ray absorption spectroscopy and temperature programmed desorption (TPD). The change of ACC activity could not be merely attributed to surface nitrogen groups but to other changes in the support. Ammonia/steam treatment improved ACC performance the most, not only by introducing nitrogen surface groups, but also by extending the microporosity and by modifying the distribution of surface oxygen groups. Successive adsorption-regeneration cycles showed important differences between oxidative retention of H 2 S and SO 2 and the subsequent catalyst/support regeneration process.
Applied Surface …, 2010
A commercial granular activated carbon (GAC) was subjected to thermal treatment with ammonia for obtaining an efficient carbon dioxide (CO 2 ) adsorbent. In general, CO 2 adsorption capacity of activated carbon can be increased by introduction of basic nitrogen functionalities onto the carbon surface. In this work, the effect of oxygen surface groups before introduction of basic nitrogen functionalities to the carbon surface on CO 2 adsorption capacity was investigated. For this purpose two different approaches of ammonia treatment without preliminary oxidation and amination of oxidized samples were studied. Modified carbons were characterized by elemental analysis and Fourier Transform Infrared spectroscopy (FT-IR) to study the impact of changes in surface chemistry and formation of specific surface groups on adsorption properties. The texture of the samples was characterized by conducting N 2 adsorption/desorption at −196 • C. CO 2 capture performance of the samples was investigated using a thermogravimetric analysis (TGA). It was found that in both modification techniques, the presence of nitrogen functionalities on carbon surface generally increased the CO 2 adsorption capacity. The results indicated that oxidation followed by high temperature ammonia treatment (800 • C) considerably enhanced the CO 2 uptake at higher temperatures.
Carbon, 2016
In this work, an equation for the prediction of the low pressure region of the water adsorption isotherms of activated carbons, based on their amount of surface groups, has been further developed in order to account for porous carbonaceous materials with an oxygen-rich surface chemistry. To attain this goal, highly hydrophilic carbon materials were selected and their surface chemistry was modified by several techniques (mainly thermal and plasma treatments) in order to obtain a series of samples with a surface oxygen content up to 45 wt. %. Then, their water sorption isotherms were measured and the amount of surface groups obtained by fitting them by the proposed equation was compared with the one resulting from direct X-ray photoelectron spectroscopy (XPS) measurements. Based on the obtained results, it seems that beyond a certain concentration of surface oxygen, there is a change in the sorption mechanism (from clustering to layering) and consequently, on the size of the water cluster formed before the micropore filling. These findings have allowed us to go a step further in the modelling of this part of the water sorption isotherms and to find a correlation between the surface oxygen content and the water cluster size.
Nitromethane-water competitive adsorption over modified activated carbon
Adsorption-journal of The International Adsorption Society, 2011
Modifications of texture and surface properties of a commercial activated carbon (Norit GF-40) were performed by several treatments in order to study their effects on the selective adsorption of nitromethane from nitromethane/water vapor mixtures. Characterisation of the samples by nitrogen adsorption and thermal analysis showed that HNO 3 treatments produce important losses of porosity and surface area, accompanied of an increase of oxygenated functional groups on the surface of carbon, which are progressively removed by heating at temperatures between 573 and 1073 K. All this leads to a drastic decrease of the adsorption capacity per gram of adsorbent with respect to the raw carbon, which offers, on the other hand, the best adsorptive performance. Oxidation by H 2 O 2 does not practically affect its textural properties and introduces an important amount of oxygen functional groups at the surface, but changes in the adsorptive properties of carbon are insignificant. Sample oxidised by H 2 O 2 and subsequently treated by diethylentriamine shows a decrease in adsorption capacity, without any relevant loss of surface area. The raw carbon treated at high temperature that exhibits the highest surface area and where surface functional groups are absent, showed the greatest adsorption capacity for nitromethane, being much more selec-
Adsorption of Ammonia on Regenerable Carbon Sorbents
Proceedings of the 45th International Conference on Environmental Systems, 12-16 July, 2015, Bellevue, WA, Paper No. ICES-2105-179, 2015
Results are presented on the development of reversible sorbents for the combined carbon dioxide, moisture, and trace-contaminant (TC) removal for use in extravehicular activities, and more specifically in the Primary Life Support System. The currently available life support systems use separate units for carbon dioxide, trace contaminants, and moisture control, and the long-term objective is to replace the above three modules with a single one. Data on sorption and desorption of ammonia, which is a major TC of concern, are presented in this paper. The current TC-control technology involves the use of a packed bed of acid-impregnated granular charcoal, which is non-regenerable. The carbon-based sorbent under development in this project can be regenerated by exposure to vacuum at room temperature. In this study, several carbon sorbents were fabricated and tested for ammonia sorption. Ammonia-sorption capacity was related to carbon pore structure characteristics, and the temperature of oxidative carbon-surface treatment was optimized for enhanced ammonia sorption performance.