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Thermal decomposition mechanism of levoglucosan during cellulose pyrolysis
KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Energi- och ugnsteknik.
KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Energi- och ugnsteknik.ORCID-id: 0000-0002-1837-5439
KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Energi- och ugnsteknik.
2012 (Engelska)Ingår i: Journal of Analytical and Applied Pyrolysis, ISSN 0165-2370, E-ISSN 1873-250X, Vol. 96, s. 110-119Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Levoglucosan (1,6-anhydro-beta-D-glucopyranose) decomposition is an important step during cellulose pyrolysis and for secondary tar reactions. The mechanism of levoglucosan thermal decomposition was studied in this paper using density functional theory methods. The decomposition included direct C-O bond breaking, direct C-C bond breaking, and dehydration. In total, 9 different pathways, including 16 elementary reactions, were studied, in which levoglucosan serves as a reactant. The properties of the reactants, transition states, intermediates, and products for every elementary reaction were obtained. It was found that 1-pentene-3,4-dione, acetaldehyde, 2,3-dihydroxypropanal, and propanedialdehyde can be formed from the C-O bond breaking decomposition reactions. 1,2-Dihydroxyethene and hydroxyacetic acid vinyl ester can be formed from the C C bond breaking decomposition reactions. It was concluded that C-O bond breaking is easier than C-C bond breaking due to a lower activation energy and a higher released energy. During the 6 levoglucosan dehydration pathways, one water molecule which composed of a hydrogen atom from C3 and a hydroxyl group from C2 is the preferred pathway due to a lower activation energy and higher product stability.

Ort, förlag, år, upplaga, sidor
2012. Vol. 96, s. 110-119
Nyckelord [en]
Levoglucosan, Cellulose, Pyrolysis, Density functional theory
Nationell ämneskategori
Analytisk kemi
Identifikatorer
URN: urn:nbn:se:kth:diva-99223DOI: 10.1016/j.jaap.2012.03.012ISI: 000305719300014Scopus ID: 2-s2.0-84861687508OAI: oai:DiVA.org:kth-99223DiVA, id: diva2:541920
Anmärkning
QC 20120726Tillgänglig från: 2012-07-26 Skapad: 2012-07-23 Senast uppdaterad: 2017-12-07Bibliografiskt granskad
Ingår i avhandling
1. Micro-reaction Mechanism Study of the Biomass Thermal Conversion Process using Density Functional Theory
Öppna denna publikation i ny flik eller fönster >>Micro-reaction Mechanism Study of the Biomass Thermal Conversion Process using Density Functional Theory
2013 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

Biomass, or bio-energy, is one of the most important alternative energies because of environmental concerns and the future shortage of fossil fuels. Multi-scaled bioenergy studies have been performed in the division of Energy and Furnace Technology, which included studies of macroscopic systems such as systems and reactors, modeling of computational fluid dynamics (CFD), and atomic/molecular level studies. The present thesis focus on the atomic/molecular level that based on quantum chemistry methods.

The microscopic structure study of biomass is the first and an important step for the investigation of the biomass thermal conversion mechanism. Cellulose, hemicellulose, and lignin are the three most important components for biomass. The atomic interactions among these three main components were studied, including the hydrogen bond linkages between cellulose and hemicellulose, and the covalent bond linkages between hemicellulose and lignin.

The decomposition of biomass is complicated and includes cellulose decomposition, hemicellulose decomposition, and lignin decomposition. As the main component of biomass, the mechanism of cellulose pyrolysis mechanism was focused on in this thesis. The study of this mechanism included an investigation of the pathways from cellulose to levoglucosan then to lower-molecular-weight species. Three different pathways were studied for the formation of levoglucosan from cellulose, and three different pathways were studied for the levoglucosan decomposition. The thermal properties for every reactant, intermediate, and product were obtained. The kinetics parameters (rate constant, pre-exponential factor, and activation energy) for every elementary step and pathway were calculated. For the formation of levoglucosan, the levoglucosan chain-end mechanism is the favored pathway due to the lower energy barrier; for the subsequent levoglucosan decomposition process, dehydration is a preferred first step and C-C bond scission is the most difficult pathway due to the strength of the C-C bonds.

The biomass gasification process includes pyrolysis, char gasification, and a gas-phase reaction; Char gasification is considered to be the rate-controlling step because of its slower reaction rate. Char steam gasification can be described as the adsorption of steam on the char surface to form a surface complex, which may transfer to another surface complex, which then desorbs to give the gaseous products (CO and H2) and the solid product of the remaining char. The influences of several radicals (O, H, and OH) and molecules (H2 and O2) on steam adsorption were investigated. It was concluded that the reactivity order for these particles adsorbed onto both zigzag and armchair surfaces is O > H2 > H > OH > O2. For water adsorbs on both zigzag and armchair carbon surfaces, O and OH radicals accelerate water adsorption, but H, O2, and H2 have no significant influence on water adsorption.

It was also shown that quantum chemistry (also known as molecular modeling) can be used to investigate the reaction mechanism of a macroscopic system. Detailed atomic/molecular descriptions can provide further understanding of the reaction process and possible products.

Ort, förlag, år, upplaga, sidor
Stockholm: KTH Royal Institute of Technology, 2013. s. x, 58
Nyckelord
biomass thermal conversion, cellulose pyrolysis, char steam gasification, adsorption, interaction, mechanism, quantum chemistry, density functional theory
Nationell ämneskategori
Bioenergi
Identifikatorer
urn:nbn:se:kth:diva-120071 (URN)978-91-7501-656-6 (ISBN)
Disputation
2013-04-22, Sal F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (Engelska)
Opponent
Handledare
Anmärkning

QC 20130327

Tillgänglig från: 2013-03-27 Skapad: 2013-03-27 Senast uppdaterad: 2013-03-27Bibliografiskt granskad

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Yang, Weihong

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