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15. Investigations on adsorption processes and pore structure development during solid fuel conversion

Author

Wedler, Carsten

Subjects
Adsorptionskinetik, 620 Ingenieurwissenschaften, Maschinenbau, Vergasung, Diffusionskoeffizient, Pyrolyse, Adsorption, ddc:620
Abstract

Um die Verbrennung von Festbrennstoffen beschreiben zu können, sind Informationen zum Stofftransport sowie zur Porenstruktur der Brennstoffe unerlässlich. Aus Mangel an diesen Informationen werden zur Modellierung des Verbrennungsprozesses allerdings oftmals stark vereinfachte Annahmen getroffen. Im Rahmen dieser Arbeit wurde daher die Porenstrukturentwicklung während der Pyrolyse und der Vergasung von Festbrennstoffen untersucht. Darüber hinaus wurde der Stofftransport anhand von effektiven Diffusionskoeffizienten mittels kinetischer Adsorptionsuntersuchungen von Verbrennungsgaskomponenten in den betrachteten Brennstoffen bestimmt. Klassische Stofftransportmodelle zur Bestimmung von effektiven Diffusionskoeffizienten können die Adsorptionskinetiken jedoch oft nur unzureichend beschreiben, sodass in dieser Arbeit zudem ein porenstrukturabhängiges Adsorptionskinetikmodell entwickelt und validiert worden ist.

Published
2020

16. Influence of Mineral Composition of Chars Derived by Hydrothermal Carbonization on Sorption Behavior of CO2, CH4, and O2.

Author

Wedler, Carsten, Lotz, Katrin, Arami-Niya, Arash, Xiao, Gongkui, Span, Roland, Muhler, Martin, May, Eric F, Richter, Markus, Wedler, Carsten, Lotz, Katrin, Arami-Niya, Arash, Xiao, Gongkui, Span, Roland, Muhler, Martin, May, Eric F, and Richter, Markus

Abstract

The doping of SiO2 and Fe2O3 into hydrochars that were produced by the hydrothermal carbonization of cellulose was studied with respect to its impact on the resulting surface characteristics and sorption behavior of CO2, CH4, and O2. During pyrolysis, the structural order of the Fe-doped char changed, as the fraction of highly ordered domains increased, which was not observed for the undoped and Si-doped chars. The Si doping had no apparent influence on the oxidation temperature of the hydrochar in contrast to the Fe-doped char where the oxidation temperature was reduced because of the catalytic effect of Fe. Both dopants reduced the micro-, meso- and macroporous surface areas of the chars, although the Fe-doped chars had larger meso- and macroporosity than the Si-doped char. However, the increased degree in the structural order of the carbon matrix of the Fe-doped char reduced its microporosity relative to the Si-doped char. The adsorption of CO2 and CH4 on the chars at temperatures between 273.15 and 423.15 K and at pressures up to 115 kPa was slightly inhibited by the Si doping but strongly suppressed by the Fe doping. For O2, however, the Si doping promoted the observed adsorption capacity, while Fe doping also showed an inhibiting effect.

Published
2020

21. Micropore Analysis of Biomass Chars by CO2Adsorption: Comparison of Different Analysis Methods

Author

Wedler, Carsten and Span, Roland

Abstract

Detailed knowledge of the pore structure evolution of fuel chars is essential for a sound description of the conversion process. The analysis of the chars by N2adsorption at 77.36 K according to the theory of Brunauer, Emmett, and Teller has been established as a standard in pore analysis. However, at this low temperature, the diffusion of N2in micropores is limited, and N2is therefore not suitable for an analysis of the microporous structure. For micropore analysis, CO2adsorption at 273.15 K can be used instead since CO2shows no limitation with regard to diffusion into micropores. For the evaluation of the CO2adsorption data, various analysis methods are available, which are commonly used in the literature. However, no consistent method has been established in the literature to determine micropore volume and surface area, and the used methods are often not described in a traceable way, which makes a comparison of results based on different analysis approaches hardly possible. To show and discuss the differences, CO2adsorption experiments were conducted in this study for four biomass chars. The data were analyzed according to Dubinin–Astakhov (DA), Dubinin–Radushkevich (DR), and nonlocal density functional theory (NLDFT) analysis. Because DA and DR are only able to determine the pore volume of the chars, an additional correlation is required to determine the surface area. Three different correlations for the relation between pore volume and surface area were compared within this study as well.

Published
2021
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22. Influence of Mineral Composition of Chars Derived by Hydrothermal Carbonization on Sorption Behavior of CO 2 , CH 4 , and O 2 .

Author

Wedler C, Lotz K, Arami-Niya A, Xiao G, Span R, Muhler M, May EF, and Richter M

Abstract

The doping of SiO 2 and Fe 2 O 3 into hydrochars that were produced by the hydrothermal carbonization of cellulose was studied with respect to its impact on the resulting surface characteristics and sorption behavior of CO 2 , CH 4 , and O 2 . During pyrolysis, the structural order of the Fe-doped char changed, as the fraction of highly ordered domains increased, which was not observed for the undoped and Si-doped chars. The Si doping had no apparent influence on the oxidation temperature of the hydrochar in contrast to the Fe-doped char where the oxidation temperature was reduced because of the catalytic effect of Fe. Both dopants reduced the micro-, meso- and macroporous surface areas of the chars, although the Fe-doped chars had larger meso- and macroporosity than the Si-doped char. However, the increased degree in the structural order of the carbon matrix of the Fe-doped char reduced its microporosity relative to the Si-doped char. The adsorption of CO 2 and CH 4 on the chars at temperatures between 273.15 and 423.15 K and at pressures up to 115 kPa was slightly inhibited by the Si doping but strongly suppressed by the Fe doping. For O 2 , however, the Si doping promoted the observed adsorption capacity, while Fe doping also showed an inhibiting effect., Competing Interests: The authors declare no competing financial interest., (Copyright © 2020 American Chemical Society.)

Published
2020
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