Cerciello, Francesca (2017) Oxidation of solid carbon materials : Structural and Thermochemical Analysis. [Tesi di dottorato]


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Item Type: Tesi di dottorato
Lingua: English
Title: Oxidation of solid carbon materials : Structural and Thermochemical Analysis
Cerciello, Francescafrancesca.cerciello@unina.it
Date: 10 December 2017
Number of Pages: 150
Institution: Università degli Studi di Napoli Federico II
Department: dep08
Dottorato: phd038
Ciclo di dottorato: 30
Coordinatore del Corso di dottorato:
Mensitieri, Giuseppegiuseppe.mensitieri@unina.it
Salatino, PieroUNSPECIFIED
Senneca, OsvaldaUNSPECIFIED
Scherer, ViktorUNSPECIFIED
Date: 10 December 2017
Number of Pages: 150
Uncontrolled Keywords: char properties, surface oxides, pyrolysis, combustion, oxy-combustion
Settori scientifico-disciplinari del MIUR: Area 03 - Scienze chimiche > CHIM/02 - Chimica fisica
Area 09 - Ingegneria industriale e dell'informazione > ING-IND/25 - Impianti chimici
Additional Information: cell : 3393452397
Date Deposited: 08 Jan 2018 01:16
Last Modified: 22 Mar 2019 10:11
URI: http://www.fedoa.unina.it/id/eprint/12168


This Thesis project aimed at giving a contribution to further unravel selected aspects of the chemistry and physics of carbon combustion and gasification relevant to implementation of novel clean coal technologies for Carbon Capture and Storage (CCS)-ready conversion. Aspects that have been specifically scrutinized are: a) surface oxides as intermediates of carbon combustion and gasification; b) Chemico-physical characterization of chars generated under oxyfiring conditions. The chemical nature of carbon oxides that populate the char surface and their evolution throughout thermochemical processing has been clarified combining C1s and O1s core-level XPS Spectra acquired at high-resolution using Synchrotron radiation and thermoanalytical analysis. Results are consistent with the hypothesis represented by a semi-lumped kinetic model based on four steps: formation of ‘metastable’ surface oxides by oxygen chemisorption, rearrangement of metastable oxides into stable complexes either by thermally activated rearrangement/isomerization or by complex-switch-over driven by molecular oxygen, desorption of surface oxides with release of CO and CO2. The “metastable” oxides may prevailingly consist of epoxy functionalities, whereas the more stable oxides would be composed by ether and carbonyl moieties. Results are helpful not only in view of applications to stationary combustion or gasification of carbons, but also to shed light on the dynamical patterns of carbon chemisorption/desorption under alternating oxidizing conditions, relevant to “looping combustion” of carbon, as in the “Carboloop” concept proposed by the Naples group. Along a different path, it is recognized that coal combustion is significantly changed in CO2-rich atmospleres as oxyfiring. In an international collaboration between three institutions from Aachen, Bochum and Naples, pyrolysis experiments have been carried out to investigate the influence of inert (N2) vs reactive (CO2) gas atmospheres as well as reactor type (and associated test conditions) on properties of gas, tar and char. At low heating rates/ temperature or high heating rates /temperature, the differences between N2 and CO2 pyrolysis products were marginal. A CO2 rich atmosphere, instead, impacted severely the properties of pyrolysis products under the fast heating-short residence time conditions in drop tube reactor. In particular, in the course of pyrolysis experiments in drop tube reactor in CO2, the appearance on the wall of the ceramic filter of a fluffy carbonaceous solid material was noticed. What emerged is that such fine carbon particulate is mostly ash-free, suggesting that its formation occurs in the gas phase. In order to investigate chemical and structural effects on char reactivity, DTR chars prepared in N2 and CO2 were subjected to combustion and oxy-combustion experiments in TGA. The CO2 chars resulted to be less reactive than the N2 chars by one order of magnitude in combustion, oxy combustion and gasification TGA experiments. The difference in reactivity between the two chars seems to correlate well with differences in the C-O functionalities which reside on their surface, as detected by XPS. Finally, in order to investigate the effect of substituting N2 with CO2 under ‘realistic’ combustion conditions, combustion and oxy-combustion experiments of coal have been carried out in a drop tube reactor. Chemico-physical analysis suggests an enhanced degree of char burn out and graphitization in CO2 rich atmospheres. XPS analysis supports the hypothesis that CO2 could be involved in some cross-linking reactions enhanced by the formation of carboxyl and lacton surface oxide complexes.


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