Kinetic Modeling of Secondary Methane Formation and 1‐Olefin Hydrogenation in Fischer–Tropsch Synthesis over a Cobalt Catalyst

Abstract

A detailed kinetic model of Fischer-Tropsch synthesis (FTS) product formation, including secondary methane formation and 1-olefin hydrogenation, has been developed. Methane formation in FTS over the cobalt-based catalyst is well known to be higher-thanexpected compared to other n-paraffin products under typical reaction conditions. A novel model proposes secondary methane formation on a different type of active site, which is not active in forming C 2+ products, to explain this anomalous methane behavior. In addition, a model of secondary 1-olefin hydrogenation has also been developed. Secondary 1-olefin hydrogenation is related to secondary methane formation with both reactions happening on the same type of active sites. The model parameters were estimated from experimental data Correspondence to: Branislav Todic; e-mail: branislav.todic@ qatar.tamu.edu.Supporting Information is available in the online issue at www.wileyonlinelibrary.com. C 2017 Wiley Periodicals, Inc. 860TODIC ET AL.obtained with Co/Re/γ -Al 2 O 3 catalyst in a slurry-phase stirred tank reactor over a range of conditions (T = 478, 493, and 503 K, P = 1.5 and 2.5 MPa, H 2 /CO feed ratio = 1.4 and 2.1, and X CO = 16-62%). The proposed model including secondary methane formation and 1-olefin hydrogenation is shown to provide an improved quantitative and qualitative prediction of experimentally observed behavior compared to the detailed model with only primary reactions.

Competing Mechanisms in CO Hydrogenation over Co-MnOx Catalysts

“…It is interesting to note that high-pressure CO hydrogenation studies with the same nominal catalyst composition also showed little ethene formation . Similar observations were made with different catalyst compositions in both our laboratory and elsewhere. , We also note without showing (for details see Figure S3 in the Supporting Information) that the time constants for the decay of CO reactant and Ar reference in back-transients are very similar. Such behavior was previously observed for Co-MgO catalysts and places a strong argument in favor of a CO insertion mechanism being in operation under synthesis conditions. ,, …”

Superior Fischer-Tropsch performance of uniform cobalt nanoparticles deposited into mesoporous SiC

“…The relatively high methane yields over bulk Co, prepared via Co-oxalate decomposition, are possibly due to local overheating and surface carbon formation. Quite interestingly, and not well understood at present [44,45], the C 2 yields fall short for Co/pSiC and Co/Dav while they are close to ''ASF expectations" for Co/MCF and bulk Co. Just the opposite behavior is observed for the C 3 yields: while they fit the straightline dependency for Co/pSiC and Co/Dav, considerable ''positive" deviations are encountered for Co/MCF and bulk Co.…”

Microkinetic model validation for Fischer-Tropsch synthesis at methanation conditions based on steady state isotopic transient kinetic analysis

“…This can be attributed to the fast and reversible adsorption of CO on the Co surface, also referred to as the 'chromatographic effect' [11]. The In previous modeling studies of SSITKA data [13,37,[42][43][44][45], two different carbon species have been identified to contribute to the transient response of 12 CH4 and were denoted as Cα and Cβ. In recent density functional theory studies, multi-site models have been put forward was well to account for a site-dependent CO dissociation pathway [37,63,[68][69][70].…”

“…As such, more in-depth information is retrieved on metal particle size effects [14][15][16][17][18][19][20][21], promotor effects [22][23][24][25][26][27][28][29][30], and support effects [31][32][33][34][35][36]. SSITKA experiments are typically performed under methanation conditions (e.g., H2/CO = 10) to minimize the number of labeled compounds while relevant kinetic phenomena for the FTS can still be captured [16,37], even though such operating conditions significantly differ from what is encountered during industrial operation (e.g. H2/CO = 2).…”

“…For SSITKA data obtained for the FTS reaction, microkinetic modeling studies have pointed out that CO dissociates to two types of carbonaceous species which both participate in methane formation [13,37,[42][43][44][45]. The microkinetic models considered in these modeling studies are based on irreversible elementary reaction steps.…”