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FISCHER-TROPSCH STUDIES WITH ACETYLENIC COMPOUNDS AS PROBES

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Hou, Li (2005) FISCHER-TROPSCH STUDIES WITH ACETYLENIC COMPOUNDS AS PROBES. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

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Abstract

Incorporation of probe molecules has been widely used in elucidation of the mechanism of the Fischer-Tropsch (F-T) reaction. In this study, we used acetylenic molecules, including 1-hexyne, 2-hexyne, 4-phenyl-1-butyne, and 1-phenyl-1-propyne as well as acetylene as probes with cobalt and iron catalysts. Experiments were carried out in a tubular microreactor of 3/8 inch diameter. Long chain alkynes were added via a saturator or a syringe pump. Acetylene was introduced from a cylinder containing carbon monoxide and hydrogen plus 1% of acetylene. We found that acetylenic compounds can initiate the F-T synthesis at temperatures more than 100oC lower than those at which normal F-T reactions are carried out. Since products obtained from linear alkyne-initiated F-T and those from normal F-T synthesis are indistinguishable, we used phenyl-substituted acetylenes as probes to distinguish the alkyne initiated products from normal F-T products. At low temperatures, only alkyne-initiated F-T reactions take place; at normal F-T temperatures, both alkyne initiated reactions and normal initiated F-T reactions occur. Although the degree of incorporation of internal alkynes is much less than that of the terminal alkynes, they can also initiate F-T chain growth to form mostly branched products. Under the same reaction conditions, internal olefins have little effect on the F-T reaction.When an acetylenic probe molecule is added to cobalt catalyzed F-T reactions, aldehydes or alcohols with one carbon more than the added probe molecule are the only oxygenates formed, perhaps by a hydroformylation type of reaction. Incorporation of alkynes (with carbon number n) on iron catalysts increased the rate of formation of Cn+1+ oxygenates, via Anderson-Schulz-Flory distribution. The F-T synthesis is a complex process in which a large number of hydrocarbon and oxygenated species are present on the catalyst surface. The nature of these adsorbates and how they react differ as reaction conditions and the nature of the catalyst changes. This work, combined with results of experiments on incorporation of ethylene, lends credence to the postulation that unsaturated two-carbon entity, possibly vinylidenes or ethylidynes, may be involved in initiation of the F-T synthesis.


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Details

Item Type: University of Pittsburgh ETD
Status: Unpublished
Creators/Authors:
CreatorsEmailPitt UsernameORCID
Hou, Lilih12@pitt.eduLIH12
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairWender, Irving
Committee MemberMorsi, Badie I.
Committee MemberCobb, James T.
Committee MemberTierney, John W.
Committee MemberOukaci, Rachid
Date: 21 June 2005
Date Type: Completion
Defense Date: 10 February 2005
Approval Date: 21 June 2005
Submission Date: 15 February 2005
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Institution: University of Pittsburgh
Schools and Programs: Swanson School of Engineering > Chemical Engineering
Degree: PhD - Doctor of Philosophy
Thesis Type: Doctoral Dissertation
Refereed: Yes
Uncontrolled Keywords: 1-Hexyne; 1-Phenyl-1-propyne; 2-Hexyne; 4-Phenyl-1-butyne; Acetylene; Acetylenic compounds; Alkynes; Chain initiation; CO hydrogenation; Cobalt; Fischer-Tropsch synthesis; Fixed-bed reactor; Iron; Probe molecules
Other ID: http://etd.library.pitt.edu/ETD/available/etd-02152005-204329/, etd-02152005-204329
Date Deposited: 10 Nov 2011 19:31
Last Modified: 15 Nov 2016 13:36
URI: http://d-scholarship.pitt.edu/id/eprint/6356

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