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Experimental and kinetic modeling of Fischer–Tropsch synthesis over nano structure catalyst of Co–Ru/carbon nanotube

  • Ali HaghtalabEmail author
  • Jafar Shariati
  • Amir Mosayebi
Article
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Abstract

In this work, the nanostructure catalyst of Co–Ru/CNTs is prepared by chemical reduction technique. Then, a set of catalytic experiments are designed and conducted for the Fischer–Tropsch synthesis (FTS) using the synthesized catalyst in a fixed bed reactor. The physical and chemical properties of the support and the synthesized catalyst were determined using the BET, XRD, H2–TPR, TEM, and H2-chemisorption characterization techniques. Based on the alkyl mechanism and using the Langmuir–Hinshelwood–Hougen–Watson (LHHW) isotherm, a kinetic model is developed for FTS. In most of the previous kinetic models, the primary reactions have merely been used, but in the current derivation of the developed kinetic model, the secondary reactions (adsorption, hydrogenation and chain-growth) and re-adsorption of primary olefins at the secondary active sites are considered. The present comprehensive kinetic model is applied for the product distribution such that the rate equations parameters are acquired via optimization. To estimate the kinetic model parameters, FTS was accomplished via a series of tests under the operating conditions as pressure (P): 10–20 bar, temperature (T): 483–513 K, gas hourly space velocity (GHSV): 1400–2400 h−1 and the H2/CO ratio of 1–2. The rationality and significance of the suggested model were checked through the statistical and correlation tests. The obtained results indicated that the outcomes of the current kinetic model were in good agreement with the experimental data. Using the present kinetic model, the average absolute deviations (AAD%) for the prediction of methane, ethylene and heavier hydrocarbons (C5+) formation rates are obtained as 7.06%, 11.57% and 14.74%.

Keywords

Co–Ru/CNTs catalyst Fischer–Tropsch synthesis Kinetic modeling Langmuir–Hinshelwod–Hougen–Watson Secondary active sites 

Abbreviations

FTS

Fischer–Tropsch synthesis

LHHW

Langmuir–Hinshelwood–Hougen–Watson

CNTs

Carbon nanotubes

ASF

Anderson–Schulz–Flor

F-B

Fixed-bed reactor

TPR

Temperature-programmed reduction

XRD

X-ray diffractometer

TEM

Transmission electron microscopy

RDS

Rate-determining step

FWHM

Full width half maximum

List of symbols

R

Universal gas constant (8.314 × 10−5 bar m3/mol K)

x

Position within the catalyst bed

T

Reaction temperature (K)

t

Time consuming for Fischer–Tropsch reaction (s)

Mw,j

Molecular weight of component j

P

Productivity (kg) (mass of produced hydrocarbon in liquid phase product)

F

Molar flow of product in gas phase (mol/s)

rj

Formation rate of component j (mol/kg s)

yj

Molar fraction of component j in gas phase

wj

Weight fraction of component j in the liquid phase

W

The catalyst weight (kg)

FCO,in

Molar flow of carbon monoxide in the reactor inlet (mol/s)

FCO,out

Molar flow of carbon monoxide in the reactor outlet (mol/s)

B

FWHM of the Co3O4 at diffraction peak of 2θ = 36.8

MC,out

Mass of output carbon

MC,in

Mass of input carbon

NC

Total number of the species

Fj

Mole flow rates of jth component (mol/s)

Ri

Rate of ith reaction (mol/kg s)

NR

Number of total considered reactions

XCO

CO conversion (%)

PT

Total pressure in the reactor (bar)

Pj

Partial pressure of j component (bar)

O

Objective function of FTS reaction

K1

Equilibrium constant for the H2 adsorption on the primary active site

E

Reaction activation energy (kJ/mol)

k3

Rate constant of chain growth in FTS mechanism for primary active site (mol/kg s)

k3,0

Pre-exponential factor of chain growth in FTS mechanism for primary active site (mol/kg s)

k5

Rate constant of the formation of methane (mol/kg s)

k5,0

Pre-exponential factor of the formation of methane (mol/kg s)

k4

Rate constant of the formation of paraffins on primary active site (mol/kg s)

k4,0

Pre-exponential factor of the formation of paraffins on primary active site (mol/kg s)

k6

Rate constant of the formation of olefins (mol/kg s)

k6,0

Pre-exponential factor of the formation of olefins (mol/kg s)

K7

Equilibrium constant for the CO adsorption on the secondary active site

k10

Rate constant for the forward reaction of olefin re-adsorption (mol/kg s bar)

k10,0

Pre-exponential factor for the forward reaction of olefin re-adsorption (mol/kg s bar)

k−10

Rate constant for the reverse reaction of olefin re-adsorption (mol/kg s)

k−10,0

Pre-exponential factor for the reverse reaction of olefin re-adsorption (mol/kg s)

k11

Rate constant of chain growth in FTS mechanism for secondary active site (mol/kg s)

k11,0

Pre-exponential factor of chain growth in FTS mechanism for secondary active site (mol/kg s)

k12

Rate constant of the formation of paraffins on secondary active site (mol/kg s bar)

k12,0

Pre-exponential factor of the formation of paraffins on secondary active site (mol/kg s bar)

Greek letters

ψ

Primary active site on catalyst surface

θ

Secondary active site on catalyst surface

σji

Stoichiometric coefficient of jth component in ith reaction

αn

Chain growth factor of FTS reaction for carbon number (n > 1)

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Notes

Supplementary material

11144_2019_1535_MOESM1_ESM.docx (353 kb)
Supplementary material 1 (DOCX 354 kb)

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Copyright information

© Akadémiai Kiadó, Budapest, Hungary 2019

Authors and Affiliations

  1. 1.Department of Chemical EngineeringTarbiat Modares UniversityTehranIran
  2. 2.Department of Chemical EngineeringTafresh UniversityTafreshIran

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