Startseite Self Diffusivity of n-Dodecane and Benzothiophene in ZSM-5 Zeolites. Its Significance for a New Catalytic Light Diesel Desulfurization Process
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Self Diffusivity of n-Dodecane and Benzothiophene in ZSM-5 Zeolites. Its Significance for a New Catalytic Light Diesel Desulfurization Process

  • María L. Ferreira , Saad A. Al-Bogami und Hugo I. de Lasa EMAIL logo
Veröffentlicht/Copyright: 13. Oktober 2015
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International Journal of Chemical Reactor Engineering
Aus der Zeitschrift International Journal of Chemical Reactor Engineering Band 14 Heft 3

Abstract

This study provides theoretical support to a recent promising ZSM5 catalyst used for the selective desulfurization of light diesel type compounds (Al-Bogami and de Lasa 2013; Al-Bogami, Moreira, and de Lasa 2013). With this end, Molecular Dynamics (MD) simulations employing a rigid silicalite structure are developed to calculate self-diffusivities of n-Dodecane (n-C12) and Benzothiophene (BZT) in a silicalite structure. The simulations are performed at 573 K, 623 K, 673 K and 723 K at a fixed loading of 1 molecule per unit cell to study the temperature effect on diffusivity coefficient. In addition, a number of simulations which are developed to investigate four molecule loadings (corresponding to 0.25, 0.5, 0.75 and 1 molecule per zeolite unit cell) at 723 K. MD simulations, show a self diffusivity of BZT one order of magnitude higher than that of n-C12 self diffusivity at all temperatures investigated. This is the case in spite of BZT having a critical molecular diameter of 6 Å when compared to the 4.9 Å diameter of n-C12. In addition, the self diffusivity coefficient is found to increase with temperature for both n-C12 and BZT. Furthermore, the results obtained show that the self diffusivity of n-C12 decreases as the number of n-C12 molecules per zeolite unit cell increases. On the other hand, it is observed that the self-diffusivity coefficient for BZT remains fairly constant and drops at a loading of 1 molecule per zeolite unit cell only. These coefficients show that differences in n-C12 and benzothiophene diffusivities favours desulfurization with selective benzothiophene adsorption and sulfur species removal as coke (Al-Bogami and de Lasa 2013).

Keywords: diesel; desulfurization; zeolite; catalyst; molecular simulation; self diffusion

Acknowledgments

The authors would like to acknowledge the financial contribution of the Natural Science and Engineering Research Council of Canada (NSERC). The authors also are very appreciative to Saudi Aramco Oil Company for providing the scholarship to Mr. Saad Al-Bogami and to the Consejo Nacional de Ciencia y Tecnologia (CONICET), for supporting Dr.M.L. Ferreira’s research at Plapiqui, Univ.Nacional del Sur,Argentina. In addition, we would like to thank Ms. F. de Lasa for her assistance on the preparation of this manuscript.

Notation

BZT

Benzothiophene

C

concentration

COMPASS

Condensed-Phase Optimized Molecular Potentials for Atomistic Simulation Studies

CREC

Chemical Reactor Engineering Centre

Ds

Self diffusivity coefficient

FCC

Fluid Catalytic Cracking

FTIR

Fourier Transform Infrared Spectroscopy

MD

Molecular Dynamics

MFI

Mordenite Framework Inverted

MSD

Mean square displacement

PFG NMR

Pulsed Field Gradient Nuclear Magnetic Resonance

NVE

constant number of particles, volume, and energy

NVT

constant number of particles, volume, and temperature

NHL

Nose-Hoover-Langevin

n-C12

n-Dodecane

QENS

Quasi-Elastic Neutron Scattering

r

coordinate of a particle

Si/Al

silica to alumina ratio

t

simulation time

TST

Transition State

u.c

unit cell

ΔR(t)

change of particle coordinates with simulation time

Units

Å

Angstrom

°C

Celsius

cm2

Squared centimetres

fs

Femtoseconds (10−15 s)

K

Kelvin

m2

Squared metres

nm

nanometre

ps

Picoseconds (10−12 s)

s

seconds

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Appendix I Thiophene Adsorption on ZSM5 Zeolite

  1. During the unsteady reaction of benzothiophene in the CREC Riser Simulator, the benzothiophene conversion has to comply with species balances in the ZSM5 crystallite as follows:

(4)εDsr2∂∂rr2∂Cbt∂r=∂Cbt∂t+ScρckadsCbt1−θbt−θd−kdesθbt

and

(5)ScρckadsCbt1−θbt−θd−kdesθbt=ρcKbt∂Cbt∂t+Catalytic Reaction Rate

With εDs in m2/s representing the effective diffusivity, kads the intrinsic rate adsorption constant in m/s, kdes the intrinsic rate desorption constant in moles/ (m2 s), Cbt the benzothiophene concentration in mole/m3, Kbt the benzothiophene equilibrium adsorption constant in m3/g, Sc the specific crystallite area per unit weight in m2/g, ρc the apparent crystallite density in g/m3 and θbt and θd the dimensionless site fraction occupied by benzothiophene and n-dodecane.

As a result, one can notice that both benzothiophene and the n-dodecane occupied sites influence the adsorption processes.

  1. However, during the early stages of adsorption, one can postulate a simplified (eq. (1)) with: i) no sites occupied by dodecane species, θd = 0, ii) very small fractions of sites being occupied by benzothiophene θbt<< 1, and iii) catalytic reaction being negligible.

Thus,

(6)ϵDsr2∂∂rr2∂Cbt∂r=ε∂Cbt∂t+ScρckadsCbt

and

(7)Sc ρc[kads cbt]=ρcKbt∂Cbt∂t

One should notice that under these early unsteady conditions a large εDsr2∂∂rr2∂Cbt∂r leads to significant selective benzothiophene adsorption with no n-dodecane occupied sites.

Published Online: 2015-10-13
Published in Print: 2016-6-1

©2016 by De Gruyter

Artikel in diesem Heft

  1. Frontmatter
  2. Editorial
  3. In Honour of Professor Serge Kaliaguine
  4. Research Articles
  5. Core/Shell Nanostructured Materials for Sustainable Processes
  6. Photodegradation Efficiencies in a Photo-CREC Water-II Reactor Using Several TiO2 Based Catalysts
  7. Hydrotreatment of Light Cycle Oil Over a Dispersed MoS2 Catalyst
  8. Hybrid Ionic Liquid-Chitosan Membranes for CO2 Separation: Mechanical and Thermal Behavior
  9. Photo-oxidation of Tributyltin, Dibutyltin and Monobutyltin in Water and Marine Sediments
  10. Contribution of Pd Membrane to Dehydrogenation of Isobutane Over a New Mesoporous Cr/MCM-41 Catalyst
  11. Self Diffusivity of n-Dodecane and Benzothiophene in ZSM-5 Zeolites. Its Significance for a New Catalytic Light Diesel Desulfurization Process
  12. Staggered Grid Finite Volume Approach for Modeling Single Particle Char Gasification
  13. High Efficiency CeCu Composite Oxide Catalysts Improved via Preparation Methods for Propyl Acetate Catalytic Combustion in Air
  14. Hydrodesulfurization of Dibenzothiophene in a Micro Trickle Bed Catalytic Reactor under Operating Conditions from Reactive Distillation
  15. Surface Modification of the ZnO Nanoparticles with γ-Aminopropyltriethoxysilane and Study of Their Photocatalytic Activity, Optical Properties and Antibacterial Activities
  16. One-Pot Isomerization of n-Alkanes by Super Acidic Solids: Sulfated Aluminum-Zirconium Binary Oxides
  17. Photocatalytic Decomposition of Metoprolol and Its Intermediate Organic Reaction Products: Kinetics and Degradation Pathway
https://doi.org/10.1515/ijcre-2015-0129
Schlagwörter für diesen Artikel
diesel; desulfurization; zeolite; catalyst; molecular simulation; self diffusion

Artikel in diesem Heft

  1. Frontmatter
  2. Editorial
  3. In Honour of Professor Serge Kaliaguine
  4. Research Articles
  5. Core/Shell Nanostructured Materials for Sustainable Processes
  6. Photodegradation Efficiencies in a Photo-CREC Water-II Reactor Using Several TiO2 Based Catalysts
  7. Hydrotreatment of Light Cycle Oil Over a Dispersed MoS2 Catalyst
  8. Hybrid Ionic Liquid-Chitosan Membranes for CO2 Separation: Mechanical and Thermal Behavior
  9. Photo-oxidation of Tributyltin, Dibutyltin and Monobutyltin in Water and Marine Sediments
  10. Contribution of Pd Membrane to Dehydrogenation of Isobutane Over a New Mesoporous Cr/MCM-41 Catalyst
  11. Self Diffusivity of n-Dodecane and Benzothiophene in ZSM-5 Zeolites. Its Significance for a New Catalytic Light Diesel Desulfurization Process
  12. Staggered Grid Finite Volume Approach for Modeling Single Particle Char Gasification
  13. High Efficiency CeCu Composite Oxide Catalysts Improved via Preparation Methods for Propyl Acetate Catalytic Combustion in Air
  14. Hydrodesulfurization of Dibenzothiophene in a Micro Trickle Bed Catalytic Reactor under Operating Conditions from Reactive Distillation
  15. Surface Modification of the ZnO Nanoparticles with γ-Aminopropyltriethoxysilane and Study of Their Photocatalytic Activity, Optical Properties and Antibacterial Activities
  16. One-Pot Isomerization of n-Alkanes by Super Acidic Solids: Sulfated Aluminum-Zirconium Binary Oxides
  17. Photocatalytic Decomposition of Metoprolol and Its Intermediate Organic Reaction Products: Kinetics and Degradation Pathway
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