Kinetic Studies of Oxidative Coupling of Methane Reaction on Model Catalysts

Handle URI:
http://hdl.handle.net/10754/609454
Title:
Kinetic Studies of Oxidative Coupling of Methane Reaction on Model Catalysts
Authors:
Khan, Abdulaziz M. ( 0000-0002-6947-5704 )
Abstract:
With the increasing production of natural gas as a result of the advancement in the technology, methane conversion to more valuable products has become a must. One of the most attractive processes which allow the utilization of the world’s most abundant hydrocarbon is the oxidative coupling. The main advantage of this process is the ability of converting methane into higher paraffins and olefins (primarily C2) in a direct way using a single reactor. Nevertheless, low C2+ yields have prevented the process to be commercialized despite the fact that great number of attempts to prepare catalysts were conducted so that it can be economically viable. Due to these limitations, understanding the mechanism and kinetics of the reaction can be utilized in improving the catalysts’ performance. The reaction involves the formation of methyl radicals that undergo gas-phase radical reactions. CH4 activation is believed to be done the surface oxygen species. However, recent studies showed that, in addition to the surface oxygen mediated pathway, an OH radical mediated pathway have a large contribution on the CH4 activation. The experiments of Li/MgO, Sr/La2O3 and NaWO4/SiO2 catalysts revealed variation of behavior in activity and selectivity. In addition, water effect analysis showed that Li/MgO deactivate at the presence of water due to sintering phenomena and the loss of active sites. On the other hand, negative effect on the C2 yield and CH4 conversion rate was observed with Sr/La2O3 with increasing the water partial pressure. Na2WO4/SiO2 showed a positive behavior with water in terms of CH4 conversion and C2 yield. In addition, the increment in CH4 conversion rate was found to be proportional with PO2 ¼ PH2O ½ which is consistent with the formation of OH radicals and the OH-mediated pathway. Experiments of using ring-dye laser, which is used to detect OH in combustion experiments, were tried in order to detect OH radicals in the gas-phase of the catalyst. Nevertheless, noisy signals were obtained that prevented the ability of detecting OH at the expected few ppms concentrations. Further optimization of the experimental setup is required.
Advisors:
Takanabe, Kazuhiro ( 0000-0001-5374-9451 )
Committee Member:
Sarathy, Mani ( 0000-0002-3975-6206 ) ; Farooq, Aamir ( 0000-0001-5296-2197 )
KAUST Department:
Physical Sciences and Engineering (PSE) Division; Chemical and Biological Engineering Program
Program:
Chemical and Biological Engineering
Issue Date:
26-Apr-2016
Type:
Thesis
Appears in Collections:
Theses; Physical Sciences and Engineering (PSE) Division; Chemical and Biological Engineering Program

Full metadata record

DC FieldValue Language
dc.contributor.advisorTakanabe, Kazuhiroen
dc.contributor.authorKhan, Abdulaziz M.en
dc.date.accessioned2016-05-15T06:21:31Zen
dc.date.available2016-05-15T06:21:31Zen
dc.date.issued2016-04-26en
dc.identifier.urihttp://hdl.handle.net/10754/609454en
dc.description.abstractWith the increasing production of natural gas as a result of the advancement in the technology, methane conversion to more valuable products has become a must. One of the most attractive processes which allow the utilization of the world’s most abundant hydrocarbon is the oxidative coupling. The main advantage of this process is the ability of converting methane into higher paraffins and olefins (primarily C2) in a direct way using a single reactor. Nevertheless, low C2+ yields have prevented the process to be commercialized despite the fact that great number of attempts to prepare catalysts were conducted so that it can be economically viable. Due to these limitations, understanding the mechanism and kinetics of the reaction can be utilized in improving the catalysts’ performance. The reaction involves the formation of methyl radicals that undergo gas-phase radical reactions. CH4 activation is believed to be done the surface oxygen species. However, recent studies showed that, in addition to the surface oxygen mediated pathway, an OH radical mediated pathway have a large contribution on the CH4 activation. The experiments of Li/MgO, Sr/La2O3 and NaWO4/SiO2 catalysts revealed variation of behavior in activity and selectivity. In addition, water effect analysis showed that Li/MgO deactivate at the presence of water due to sintering phenomena and the loss of active sites. On the other hand, negative effect on the C2 yield and CH4 conversion rate was observed with Sr/La2O3 with increasing the water partial pressure. Na2WO4/SiO2 showed a positive behavior with water in terms of CH4 conversion and C2 yield. In addition, the increment in CH4 conversion rate was found to be proportional with PO2 ¼ PH2O ½ which is consistent with the formation of OH radicals and the OH-mediated pathway. Experiments of using ring-dye laser, which is used to detect OH in combustion experiments, were tried in order to detect OH radicals in the gas-phase of the catalyst. Nevertheless, noisy signals were obtained that prevented the ability of detecting OH at the expected few ppms concentrations. Further optimization of the experimental setup is required.en
dc.language.isoenen
dc.subjectmethane Oxidative Couplingen
dc.subjectCatalysisen
dc.subjectKineticsen
dc.subjectOH Mediateden
dc.subjectRing Dye Laseren
dc.titleKinetic Studies of Oxidative Coupling of Methane Reaction on Model Catalystsen
dc.typeThesisen
dc.contributor.departmentPhysical Sciences and Engineering (PSE) Divisionen
dc.contributor.departmentChemical and Biological Engineering Programen
thesis.degree.grantorKing Abdullah University of Science and Technologyen_GB
dc.contributor.committeememberSarathy, Manien
dc.contributor.committeememberFarooq, Aamiren
thesis.degree.disciplineChemical and Biological Engineeringen
thesis.degree.nameMaster of Scienceen
dc.person.id125265en
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