Kinetic modeling and oprimization of fixed-bed reactorfor Fischer-Tropsch synthesis

by Branislav S Todić

Institution: Univerzitet u Beogradu
Year: 2016
Keywords: Fischer-Tropsch sinteza; kobaltni katalizator; gvozdenikatalizator; selektivnost proizvoda reakcije; raspodela proizvodareakcije; modelovanje kinetike; mehanizam reakcije; reactor sapakovanim slojem katalizatora
Posted: 02/05/2017
Record ID: 2134275
Full text PDF: https://fedorabg.bg.ac.rs/fedora/get/o:11518/bdef:Content/get


Technological Engineering (Chemical Technology) - Chemical Engineering / Tehnološko Inženjerstvo - Hemijsko Inženjerstvo / Fischer-Tropsch synthesis (FTS) is a heterogeneously catalyzed chemical reaction in which a mixture of hydrogen and carbon-monoxide is converted into an array of hydrocarbon products. These products can be used as synthetic liquid fuels (gasoline, diesel, kerosene) or feedstock for the chemical industry. As such, FTS is a key step in the conversion of coal, natural gas and biomass into liquids in large plants all over the world, including plants in Qatar, Malaysia, South Africa etc. Even though FTS has been commercially used for most of the 20th century, many fundamental aspects of this reaction are unclear. The main objectives of the work included in this thesis were: to study the effect of process conditions on FTS product selectivity and distribution with regards to hydrocarbon chain length, develop a detailed model of FTS kinetics (capable of predicting both reactant disappearance and product formation rates) and apply the detailed kinetic model in modeling and optimization of a multi-tubular fixed-bed reactor for FTS. Most often used catalysts for FTS are iron and cobalt. The experimental data used in this study were obtained in collaboration with Texas A&M University and Center for Applied Energy Research, University of Kentucky, for iron- and cobalt-based catalyst, respectively. The analysis of experimental data for both catalysts showed dependence of product selectivity from process conditions inside the reactor (temperature, pressure, reactant feed ratio and conversion level). These dependences were shown to be related to the chain-growth probability factor (α), which also varies with carbon number. Over the cobalt catalyst, the significant variation of C1 intermediate growth probability (α1) at different process conditions and a lack of the same variations for higher C2+ chain intermediates, was interpreted as evidence for the existence of separate methanation pathways. The same data presented evidence that the secondary 1-olefin readsorption does not play a major part in determining FTS selectivity. For the iron-based catalysts, similar correlations between variations of growth probability with process conditions were found. However, existence of additional pathways for methane formation and relevance of secondary olefin reactions could not be confirmed for that catalyst... Advisors/Committee Members: Nikačević, Nikola..