Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Micro-reaction Mechanism Study of the Biomass Thermal Conversion Process using Density Functional Theory
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Energy and Furnace Technology.
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
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.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. , x, 58 p.
Keyword [en]
biomass thermal conversion, cellulose pyrolysis, char steam gasification, adsorption, interaction, mechanism, quantum chemistry, density functional theory
National Category
Bioenergy
Identifiers
URN: urn:nbn:se:kth:diva-120071ISBN: 978-91-7501-656-6 (print)OAI: oai:DiVA.org:kth-120071DiVA: diva2:613329
Public defence
2013-04-22, Sal F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20130327

Available from: 2013-03-27 Created: 2013-03-27 Last updated: 2013-03-27Bibliographically approved
List of papers
1. Modeling Study of Woody Biomass: Interactions of Cellulose, Hemicellulose, and Lignin
Open this publication in new window or tab >>Modeling Study of Woody Biomass: Interactions of Cellulose, Hemicellulose, and Lignin
2011 (English)In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 25, no 10, 4786-4795 p.Article in journal (Refereed) Published
Abstract [en]

Lignocellulosic biomass pretreatment and the subsequent thermal conversion processes to produce solid, liquid, and gas biofuels are attractive solutions for today's energy challenges. The structural study of the main components in biomass and their macromolecular complexes is an active and ongoing research topic worldwide. The interactions among the three main components, cellulose, hemicellulose, and lignin, are studied in this paper using electronic structure methods, and the study includes examining the hydrogen bond network of cellulose-hemicellulose systems and the covalent bond linkages of hemicellulose-lignin systems. Several methods (semiempirical, Hartree-Fock, and density functional theory) using different basis sets were evaluated. It was shown that theoretical calculations can be used to simulate small model structures representing wood components. By comparing calculation results with experimental data, it was concluded that B3LYP/6-31G is the most suitable basis set to describe the hydrogen bond system and B3LYP/6-31G(d,p) is the most suitable basis set to describe the covalent system of woody biomass. The choice of unit model has a much larger effect on hydrogen bonding within cellulose-hemicellulose system, whereas the model choice has a minimal effect on the covalent linkage in the hemicellulose-lignin system.

National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-51431 (URN)10.1021/ef201097d (DOI)000296212900060 ()2-s2.0-80055053770 (Scopus ID)
Funder
Swedish Research Council
Note
QC 20111213Available from: 2011-12-13 Created: 2011-12-12 Last updated: 2017-12-08Bibliographically approved
2. Levoglucosan Formation Mechanism during Cellulose Pyrolysis
Open this publication in new window or tab >>Levoglucosan Formation Mechanism during Cellulose Pyrolysis
(English)Article in journal (Other academic) Submitted
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-120080 (URN)
Note

QS 2013

Available from: 2013-03-27 Created: 2013-03-27 Last updated: 2013-03-27Bibliographically approved
3. Formation Mechanism of Levoglucosan and Formaldehyde during Cellulose Pyrolysis
Open this publication in new window or tab >>Formation Mechanism of Levoglucosan and Formaldehyde during Cellulose Pyrolysis
2011 (English)In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 25, no 8, 3739-3746 p.Article in journal (Refereed) Published
Abstract [en]

Biomass pyrolysis is an efficient way to transform raw biomass or organic waste materials into useable energy, including liquid, solid, and gaseous materials. Levoglucosan (1,6-anhydro-beta-D-glucopyranose) and formaldehyde are two important products in biomass pyrolysis. The formation mechanism of these two products was investigated using the density functional theory (DFT) method based on quantum mechanics. It was found that active anhydroglucose can be obtained from a cellulose homolytic reaction during high-temperature steam gasification of the biomass process. Anhydroglucose undergoes a hydrogen-donor reaction and forms an intermediate, which can transform into the products via three pathways, one (path 1) for the formation of levoglucosan and two (paths 2 and 3) for formaldehyde. A total of six elementary reactions are involved. At a pressure of 1 atm, levoglucosan can be formed at all of the temperatures (450-750 K) considered in this simulation, whereas formaldehyde can be formed only when the temperature is higher than 475 K Moreover, the energy barrier of levoglucosan formation is lower than that of formaldehyde, which is in agreement with the mechanism proposed in the experiments.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-38956 (URN)10.1021/ef2005139 (DOI)000294077100044 ()2-s2.0-80051953095 (Scopus ID)
Funder
Swedish Research Council
Available from: 2011-09-06 Created: 2011-09-05 Last updated: 2017-12-08Bibliographically approved
4. Thermal decomposition mechanism of levoglucosan during cellulose pyrolysis
Open this publication in new window or tab >>Thermal decomposition mechanism of levoglucosan during cellulose pyrolysis
2012 (English)In: Journal of Analytical and Applied Pyrolysis, ISSN 0165-2370, E-ISSN 1873-250X, Vol. 96, 110-119 p.Article in journal (Refereed) 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.

Keyword
Levoglucosan, Cellulose, Pyrolysis, Density functional theory
National Category
Analytical Chemistry
Identifiers
urn:nbn:se:kth:diva-99223 (URN)10.1016/j.jaap.2012.03.012 (DOI)000305719300014 ()2-s2.0-84861687508 (Scopus ID)
Note
QC 20120726Available from: 2012-07-26 Created: 2012-07-23 Last updated: 2017-12-07Bibliographically approved
5. Kinetics of levoglucosan and formaldehyde formation during cellulose pyrolysis process
Open this publication in new window or tab >>Kinetics of levoglucosan and formaldehyde formation during cellulose pyrolysis process
2012 (English)In: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 96, no 1, 383-391 p.Article in journal (Refereed) Published
Abstract [en]

The mechanisms and kinetics studies of the formation of levoglucosan and formaldehyde from anhydroglucose radical have been carried out theoretically in this paper. The geometries and frequencies of all the stationary points are calculated at the B3LYP/6-31+G(D,P) level based on quantum mechanics, Six elementary reactions are found, and three global reactions are involved. The variational transition-state rate constants for the elementary reactions are calculated within 450-1500 K. The global rate constants for every pathway are evaluated from the sum of the individual elementary reaction rate constants. The first-order Arrhenius expressions for these six elementary reactions and the three pathways are suggested. By comparing with the experimental data, computational methods without tunneling correction give good description for Path1 (the formation of levoglucosan); while methods with tunneling correction (zero-curvature tunneling and small-curvature tunneling correction) give good results for Path2 (the first possibility for the formation of formaldehyde), all the test methods give similar results for Path3 (the second possibility for the formation of formaldehyde), all the modeling results for Path3 are in good agreement with the experimental data, verifying that it is the most possible way for the formation of formaldehyde during cellulose pyrolysis.

Keyword
Rate constant, Cellulose pyrolysis, Levoglucosan, Formaldehyde
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-93901 (URN)10.1016/j.fuel.2012.01.006 (DOI)000301853900043 ()2-s2.0-84862831380 (Scopus ID)
Funder
Swedish Research Council
Note
QC 20120504Available from: 2012-05-04 Created: 2012-05-03 Last updated: 2017-12-07Bibliographically approved
6. Kinetics study on thermal dissociation of levoglucosan during cellulose pyrolysis
Open this publication in new window or tab >>Kinetics study on thermal dissociation of levoglucosan during cellulose pyrolysis
2013 (English)In: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 109, 476-483 p.Article in journal (Refereed) Published
Abstract [en]

The mechanisms and kinetics studies of the levoglucosan (LG) primary decomposition during cellulose pyrolysis have been carried out theoretically in this paper. Three decomposition mechanisms (C-O bond scission, C-C bond scission, and LG dehydration) including nine pathways and 16 elementary reactions were studied at the B3LYP/6-31 + G(D, P) level based on quantum mechanics. The variational transition-state rate constants for every elementary reaction and every pathway were calculated within 298-1550 K. The first-order Arrhenius expressions for these 16 elementary reactions and nine pathways were suggested. It was concluded that computational method using transition state theory (TST) without tunneling correction gives good description for LG decomposition by comparing with the experimental result. With the temperature range of 667-1327 K, one dehydration pathway, with one water molecule composed of a hydrogen atom from C3 and a hydroxyl group from C2, is a preferred LG decomposition pathway by fitting well with the experimental results. The calculated Arrhenius plot of C-O bond scission mechanism is better agreed with the experimental Arrhenius plot than that of C-C bond scission. This C-O bond scission mechanism starts with breaking of C1-O5 and C6-O1 bonds with formation of CO molecule (C1-O1) simultaneously. C-C bond scission mechanism is the highest energetic barrier pathway for LG decomposition.

Place, publisher, year, edition, pages
Elsevier, 2013
Keyword
Rate constant, Cellulose pyrolysis, Levoglucosan decomposition, Dehydration
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-120082 (URN)10.1016/j.fuel.2013.03.035 (DOI)000320651700061 ()2-s2.0-84879100732 (Scopus ID)
Funder
Swedish Research Council
Note

QC 20130802. Updated from accepted to published.

Available from: 2013-03-27 Created: 2013-03-27 Last updated: 2017-12-06Bibliographically approved
7. Formation and Characterization of Carbon-Radical Precursors in Char Steam Gasification
Open this publication in new window or tab >>Formation and Characterization of Carbon-Radical Precursors in Char Steam Gasification
2010 (English)In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 24, 6513-6521 p.Article in journal (Refereed) Published
Abstract [en]

Highly reactive radicals play an important role in high-temperature gasification processes. However, the effect of radicals on gasification has not been systematically investigated. In the present study, the formation of carbon-radical precursors using atomic radicals such as OH, O, and H and molecules such as H-2 and O-2 was characterized, and the effect of the precursors on the adsorption step of steam char gasification was studied using quantum chemistry methods. The results revealed that the radicals can be chemisorbed exothermically on char active sites, and the following order of reactivity was observed: O > H-2 > H > OH > O-2. Moreover, hydrogen bonds are formed between steam molecules and carbon-radical complexes. Steam molecule adsorption onto carbon-O and carbon-OH complexes is easier than adsorption onto clean carbon surfaces. Alternatively, adsorption on carbon-O-2, carbon-H-2, and carbon-H complexes is at the same level with that of clean carbon surfaces; thus, OH and O radicals accelerate the physical adsorption of steam onto the char surface, H radical and O-2 and H-2 molecules do not have a significant effect on adsorption.

National Category
Materials Engineering Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-28601 (URN)10.1021/ef101144f (DOI)000285266000038 ()2-s2.0-78650343292 (Scopus ID)
Note
QC 20110117Available from: 2011-01-17 Created: 2011-01-17 Last updated: 2017-12-11Bibliographically approved

Open Access in DiVA

No full text

Search in DiVA

By author/editor
Zhang, Xiaolei
By organisation
Energy and Furnace Technology
Bioenergy

Search outside of DiVA

GoogleGoogle Scholar

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 496 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf