Modeling Fischer–Tropsch kinetics and product distribution over a cobalt catalyst

A detailed kinetic model describing the consumption of key components and productdistribution in the Fischer–Tropsch synthesis (FTS) over a 20%Co/0.5Re γ-Al2O3commercial catalyst is developed. The developed model incorporates the H2O-assisted CO dissociation mechanism developed by Rytter and Holmen and a novelapproach to product distribution modeling. The model parameters are optimizedagainst an experimental dataset comprising a range of process conditions: total pres-sure 2.0–2.2 MPa, temperature 210–230C, CO conversion range of 10%–75% andfeed with and without added water. The quality of the model fit measured in termsof mean absolute relative residuals (MARR) value is 23.1%, which is comparable to lit-erature reported values. The developed model can accurately describe both positiveand negative effects of water on the rate kinetics, the positive effect of water on thegrowth factor, temperature and syngas composition on the kinetics and product dis-tribution over a wide range of process conditions, which is critical for the design andoptimization of the Fisher–Tropsch reactors.publishedVersio

Fischer-Tropsch reaction kinetics: Mathematical modeling and model fitting

I denne masteroppgaven er en matematisk modell for Fischer-Tropsch syntesen foreslått. Modellen inkluderer effektene av vann på reaksjonskinetikk, selektiviteter, og deaktivering av katalysator. Modellen er basert på 'consorted vinylene'-mekanismen. Fire katalysatorer med ulike karakteriseringer ble testet; tre av katalysatorene svarer til tre ulike Co/Re/γ-Al2O3 katalysatorer, og den fjerde svarer til en Co/Re/α-Al2O3 katalysator. Disse katalysatorene ble testet ved P = 20 bar, T = 210 C, og H2/CO = 2.1. Videre ble en kommersiell katalysator også testet ved P = 22-22 bar, T = 210 C, og H2/CO = 1.12, 1.72, og 2.1. Det konkluderes at den foreslåtte modellen klarer å beskrive hovedresponsene generelt veldig bra. Spesielt for den kommersielle katalysatoren ble metanselektivitetene i perioder hvor vann tilsettes bedre forklart med en modell for metandannelsen der vann er en aktiv del av dannelsesuttrykket. En andre ordens deaktiveringsmodell som inkluderer effekten av vann ble funnet til å beskrive katalysatorens deaktivering over tid på en tilfredsstillende måte. Modellen beskriver også den forventede effekten av vann, nærmere bestemt at vann øker katalysatorens deaktivering. Ved å studere hvordan ulike katalysator karakteriseringer påvirker de estimerte modellparameterne ble det observert at de fleste parameterne følger lineære trender når de plottes mot kobalt dispersjonene til katalysatorene. Den foreslåtte modellen for kjedevekst beskriver selektiviteten til C(5+) veldig bra, og modellen fanger også opp effekten av vann på riktig måte. Denne kjedevekstmodellen inkluderer ikke partialtrykket av hydrogen

The water assisted vinylene mechanism for cobalt Fischer-Tropsch synthesis assessed by multi-catalyst modelling of kinetics and deactivation

The paper describes development of a mechanism and a consistent rate expression for Fischer-Tropsch (FT) synthesis over cobalt-based catalysts. The developed mechanism relies on a two-step hydrogen assisted activation of CO. The carbon atom of CO is first hydrogenated by surface hydrogen to formyl; followed by the rate-limiting step whereby the oxygen atom is hydrogenated by adsorbed water. The produced CH* monomer is incorporated into the growing chain giving vinylene intermediate. The vinylene intermediate is either terminated to an olefin by adding hydrogen to the α-carbon atom or propagates by adding hydrogen to the β-carbon position. The resulting expression for CO consumption, the Fischer-Tropsch rate, can respond positively or negatively to the partial pressure of water, in agreement with experimental observations. A special feature is that the chain propagation probability does not depend on the partial pressure of hydrogen. The resulting kinetic model is tested on several cobalt catalysts supported on alumina; spanning from γ-alumina with average pore sizes ranging from 6.1 to 18.3 nm to α-alumina with a wide pore structure; and with cobalt particle sizes from 8 to 19 nm. Water was added sequentially to the syngas feed, causing enhanced deactivation, for testing the water response on activity and selectivity. A deactivation model comprising sintering and cobalt oxidation, and the FT-kinetics, describe the observed CO conversions with great precision for all catalysts. Selectivities are also well described, but with slight deviations at least partly due the effect of deactivation. Trends in some of the kinetic parameters are rationalized in terms of cobalt crystallite and pore sizes

Modeling Fischer–Tropsch

A detailed kinetic model describing the consumption of key components and productdistribution in the Fischer–Tropsch synthesis (FTS) over a 20%Co/0.5Re γ-Al2O3commercial catalyst is developed. The developed model incorporates the H2O-assisted CO dissociation mechanism developed by Rytter and Holmen and a novelapproach to product distribution modeling. The model parameters are optimizedagainst an experimental dataset comprising a range of process conditions: total pres-sure 2.0–2.2 MPa, temperature 210–230C, CO conversion range of 10%–75% andfeed with and without added water. The quality of the model fit measured in termsof mean absolute relative residuals (MARR) value is 23.1%, which is comparable to lit-erature reported values. The developed model can accurately describe both positiveand negative effects of water on the rate kinetics, the positive effect of water on thegrowth factor, temperature and syngas composition on the kinetics and product dis-tribution over a wide range of process conditions, which is critical for the design andoptimization of the Fisher–Tropsch reactors

Modeling Fischer–Tropsch kinetics and product distribution over a cobalt catalyst

A detailed kinetic model describing the consumption of key components and productdistribution in the Fischer–Tropsch synthesis (FTS) over a 20%Co/0.5Re γ-Al2O3commercial catalyst is developed. The developed model incorporates the H2O-assisted CO dissociation mechanism developed by Rytter and Holmen and a novelapproach to product distribution modeling. The model parameters are optimizedagainst an experimental dataset comprising a range of process conditions: total pres-sure 2.0–2.2 MPa, temperature 210–230C, CO conversion range of 10%–75% andfeed with and without added water. The quality of the model fit measured in termsof mean absolute relative residuals (MARR) value is 23.1%, which is comparable to lit-erature reported values. The developed model can accurately describe both positiveand negative effects of water on the rate kinetics, the positive effect of water on thegrowth factor, temperature and syngas composition on the kinetics and product dis-tribution over a wide range of process conditions, which is critical for the design andoptimization of the Fisher–Tropsch reactors

Modeling Fischer–Tropsch kinetics and product distribution over a cobalt catalyst

A detailed kinetic model describing the consumption of key components and productdistribution in the Fischer–Tropsch synthesis (FTS) over a 20%Co/0.5Re γ-Al2O3commercial catalyst is developed. The developed model incorporates the H2O-assisted CO dissociation mechanism developed by Rytter and Holmen and a novelapproach to product distribution modeling. The model parameters are optimizedagainst an experimental dataset comprising a range of process conditions: total pres-sure 2.0–2.2 MPa, temperature 210–230C, CO conversion range of 10%–75% andfeed with and without added water. The quality of the model fit measured in termsof mean absolute relative residuals (MARR) value is 23.1%, which is comparable to lit-erature reported values. The developed model can accurately describe both positiveand negative effects of water on the rate kinetics, the positive effect of water on thegrowth factor, temperature and syngas composition on the kinetics and product dis-tribution over a wide range of process conditions, which is critical for the design andoptimization of the Fisher–Tropsch reactors