Dissertation
Designing catalysts and tuning reaction conditions to enlarge the feedstock platform of functionalized hydrocarbons in the Fischer Tropsch synthesis
Doctor of Philosophy (PhD), Washington State University
01/2020
Handle:
https://hdl.handle.net/2376/112129
Abstract
The need for high-value added chemicals, such as functionalized hydrocarbons is growing rapidly. Among such functionalized hydrocarbons, olefins, alcohols, nitriles and amines with varying chain lengths are of prime interest. Traditionally, functionalized hydrocarbons are synthetized from petroleum feedstocks and are further processed by homogeneous catalysis. The major drawback of these traditional synthesis routes are: i) lack of regioselectivity, ii) use of expensive reagents, iii) multi-step processes and iv) formation of toxic by-products. In the present work, we synthetized functionalized hydrocarbons with a high regioselectivity in a “one-step one-pot” process employing Fischer Tropsch (FT) chain lengthening technology with a syngas (CO+H2) rich in CO, similar to compositions received from biomass feedstocks. Because nitrogenates are not observed during traditional FT synthesis, we used FT technology as a vehicle for producing long-chain hydrocarbon skeletons and ammonia as a co-reagent to provide terminal nitrogen functionalization. We showed that the reaction can be tuned via adjustments of the H2/CO ratio so as to favor the production of either terminal amines or nitriles over a promoted Co/MnOx catalyst. Up to 80% combined selectivity of chain-lengthened terminal olefins/amines/nitriles with high regioselectivity was reached. The physicochemical characterization of the spent Co/MnOx catalyst showed that the bulk of the catalyst was composed of Co2C while the surface contained Co-C-N complexes. We demonstrated using Chemical Transient Kinetics (CTK) that the formation of nitrogen-containing compounds during FT synthesis results from a surface polymerization involving a C1 monomer. We also showed that ammonia inhibits the formation of methane and increases the selectivity of alkenes over cobalt-based catalysts. Ammonia also enhances the water gas shift reaction over catalysts containing transition metal oxides. \nOlefins and oxygenates were also synthetized using well dispersed colloidal iron-based nanoparticles as catalyst. We showed that the combined functionalized hydrocarbon selectivity over pure colloidal iron nanoparticles is as high as 82% (72 % olefins + 10% alcohols) at H2/CO=0.3, while this selectivity over promoted colloidal iron nanoparticles is 78% (43% olefins, 35% alcohols) at H2/CO=0.3. Commercial iron bulk catalysts used in FT plants lead to a selectivity up to 6% of oxygenates, making our catalysts promising candidates for industrial applications.
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Details
- Title
- Designing catalysts and tuning reaction conditions to enlarge the feedstock platform of functionalized hydrocarbons in the Fischer Tropsch synthesis
- Creators
- Hafsa Karroum
- Contributors
- Norbert NK Kruse (Advisor)Hongfei Lin (Committee Member)Steven R. Saunders (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- Chemical Engineering and Bioengineering, School of
- Theses and Dissertations
- Doctor of Philosophy (PhD), Washington State University
- Number of pages
- 273
- Identifiers
- 99900581410101842
- Language
- English
- Resource Type
- Dissertation