Preparation of Nitrogen-Enriched Activated Carbons from Brown Coal

2015

Adsorption

A series of new carbonaceous adsorbents has been obtained by means of direct and physical activation of Polish brown coal, characterised by high mineral matter content. The influence of activation procedure on the porous structure development, acidic and basic surface groups generation as well as the sorptive properties of the adsorbents prepared toward liquid and gas pollutants was tested. Additionally the effect of mineral matter presence on the physicochemical and sorption properties of materials prepared was studied. The final products were micro/mesoporous activated carbons of medium developed surface area ranging from 407 to 674 m 2 /g, showing strongly basic or intermediate acidic-basic character of the surface. The results obtained during this study showed that direct and physical activation of low quality brown coal led to activated carbons with very good sorption capacity both toward gas contamination of acidic character (especially nitrogen dioxide) as well as toward methylene blue and inorganic pollutants of molecules of size similar to that of iodine molecules. It was also proved that demineralization of prepared activated carbons by hydrochloric acid significantly reduced their ability to toxic gases sorption, but simultaneously increased the efficiency of removing impurities from the liquid phase.

Section: Introductionmentioning

confidence: 99%

The effect of mineral matter on the physicochemical and sorption properties of brown coal-based activated carbons

2015

Adsorption

“…These changes are certainly related to the high temperature of the processes, which is responsible for breaking of the least stable chemical bonds present in the material, removal of heteroatoms in the form of simple gas or liquid compounds and consequently for the ordering of carbonaceous structure. The increase in nitrogen content observed for UPA and PUA samples is most probably related to the nitrogen building into the carbon structure during the reaction with urea, in the form of amines, amides, imines, lactams or nitriles [35,36]. Nevertheless, under the effect of high temperature (during pyrolysis or activation processes), a considerable part of these groups underwent decomposition or transformation to more thermally stable nitrogen species (e.g.…”

Section: Elemental Composition Of Materials Preparedmentioning

confidence: 99%

“…Nevertheless, under the effect of high temperature (during pyrolysis or activation processes), a considerable part of these groups underwent decomposition or transformation to more thermally stable nitrogen species (e.g. N-5, N-6 or N-Q [35,36]) and consequently the amount of nitrogen in the products of activation is not too high, especially for sample PUA, modified with nitrogen just before the activation process. High-temperature treatment of the demineralized coal causes also a significant increase in the ash content, as evidenced by the fact that the activation products are characterized by almost twice higher content of mineral substances than the starting material.…”

Section: Elemental Composition Of Materials Preparedmentioning

confidence: 99%

Effect of heat treatment on the physicochemical properties of nitrogen-enriched activated carbons

2016

J Therm Anal Calorim

A series of functionalized carbonaceous adsorbents were prepared by means of reaction with urea and chemical activation of Polish brown coal. In order to obtain nitrogen groups bonded in different ways to the carbon structure, the reaction with urea was performed at two different stages of processing, with precursor or char. Additionally, the influence of annealing under nitrogen atmosphere at 600 and 800°C or in hydrogen/nitrogen mixture at 600°C on the textural, acid-base and thermal properties of activated carbons prepared was tested. The resulting materials were characterized by elemental analysis, low-temperature nitrogen sorption, determination of the number of surface oxygen groups as well as by thermogravimetric study in helium atmosphere. The final products were microporous nitrogen-enriched activated carbons of very well-developed surface area reaching from 1303 to 2004 m 2 g -1 , showing different content of nitrogen (from 0.5 to 2.3 mass%) and different chemical character of the surface (from weakly acidic to intermediate acidic-basic), depending on the sequence of particular processes and variant of further thermochemical treatment. According to the results of thermal study, the nitrogen functional groups introduced into the carbon structure by the reaction with urea (especially at the char stage) show moderate thermal and chemical stability. Under the effect of high temperature, some of these groups underwent decomposition or transformation into more thermally stable nitrogen species. It was also proved that the thermochemical treatment of modified activated carbons led to considerable deterioration of their textural parameters as well as caused significant changes in the acid-base character of their surface.

“…So great differences in the content of N daf between the samples subjected to the reaction with urea at the stage of precursor (SUDAX, SUP6AX, SUP7AX- Table 1) and those subjected to this reaction at the stage of chars (SP6UAX, SP7UAX- Table 2), and the samples modified after activation (SDAXU, SP6AXU and SP7AXU- Table 3) are most probably a consequence of a low thermal resistance of nitrogen groups introduced into the carbon structure. Earlier studies by XPS (Pietrzak et al 2006;Nowicki et al 2010b;Burg et al 2002) have proved that the reaction of carbonaceous materials with urea or ammonia involves generation of considerable amounts of amine, amide, nitrile, imine and lactam groups, characterised by low thermal stability. An indirect evidence of formation of such groups is a simultaneous increase in the content of nitrogen and hydrogen after the reaction with urea.…”

Section: Pyrolysis 600ºc 700ºcmentioning

confidence: 99%

“…Efficiency of nitrogenation at this stage is about twice smaller than during precursor modification, but it is much higher than for chars SP6 and SP7. This result is probably a consequence of the presence of numerous oxygen groups on the surface of activated carbons which favours introduction of nitrogen groups (Pietrzak et al 2006;Bimer et al 1998). …”

Section: Pyrolysis 600ºc 700ºcmentioning

confidence: 99%

Nitrogen-enriched activated carbons prepared by the activation of coniferous tree sawdust and their application in the removal of Nitrogen dioxide

Int. J. Environ. Sci. Technol.

Kaźmierczak

Sawicka

et al. 2014

A technology of obtaining nitrogen-enriched activated carbons from coniferous tree sawdust by direct activation of the precursor and physical activation with CO 2 is described. The effect of activation time, pyrolysis temperature as well as modification with urea on the textural parameters, acid-base character of the surface and sorption properties of activated carbons has been tested. The resulting carbons were characterised by low-temperature nitrogen sorption and determination of the number of surface oxygen groups. The sorption properties of the materials obtained were characterised by nitrogen dioxide adsorption in dry and wet conditions. The final products were nitrogen-enriched microporous activated carbons of medium-developed surface, showing very diverse nitrogen content and acidic-basic character of the surface. The results obtained in our study have proved that through suitable choice of the activation and modification procedure of coniferous tree sawdust, activated carbons can be produced with high capacity towards nitrogen dioxide adsorption, reaching to 69 and 46 mg NO 2 /g in dry and wet conditions, respectively. The results of our study have also shown that the adsorption ability of carbonaceous adsorbents depends both on the method of preparation as well as on the textural parameters and acid-base properties of the adsorbents surface.