Modeling of on-line catalyst addition effects in a short contact time reactor

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Recently developed short-contact-time reactors (SCTR), consisting of porous alumina monoliths coated with platinum, have been shown to produce ethylene from rich ethane/oxygen(hydrogen) mixtures with yields and selectivities comparable to conventional steam cracking, using a reactor of much smaller size. Although the overall mechanism is clearly autothermal and catalytic, the details, in particular the relative contributions of heterogeneous and homogeneous chemistry, are a matter of considerable debate. Recent experiments show that reactor performance can be further enhanced by dripping a dilute platinum solution onto the SCTR front face during reaction, resulting in catalyst deposition within only a short (several millimeter) zone ... continued below

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22 p.

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Zerkle, D. K.; Allendorf, M. d.; Wolf, M. & Deutschmann, O. July 30, 2000.

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  • Sandia National Laboratories
    Publisher Info: Sandia National Labs., Albuquerque, NM, and Livermore, CA (United States)
    Place of Publication: Albuquerque, New Mexico

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Description

Recently developed short-contact-time reactors (SCTR), consisting of porous alumina monoliths coated with platinum, have been shown to produce ethylene from rich ethane/oxygen(hydrogen) mixtures with yields and selectivities comparable to conventional steam cracking, using a reactor of much smaller size. Although the overall mechanism is clearly autothermal and catalytic, the details, in particular the relative contributions of heterogeneous and homogeneous chemistry, are a matter of considerable debate. Recent experiments show that reactor performance can be further enhanced by dripping a dilute platinum solution onto the SCTR front face during reaction, resulting in catalyst deposition within only a short (several millimeter) zone of the reactor. The authors have undertaken a computational study of this system, using two-dimensional computational fluid dynamics simulations with full heat and mass transport and detailed heterogeneous and homogeneous kinetic mechanisms. The results indicate that front-face catalyst loading enhances reactor performance by limiting the opportunity for heterogeneous ethane reactions that produce methane. As a result, ethylene selectivity increases and CH{sub 4} selectivity decreases. The results strongly support a mechanism recently proposed by the authors, in which rapid, heterogeneous oxidation of adsorbed hydrogen consumes most of the oxygen. The resulting heat is then released to the gas phase, causing homogeneous pyrolysis of ethane to occur in an environment containing much less oxygen. This mechanism explains not only the effects of on-line catalyst addition, but also the increase in ethylene selectivity observed upon addition of hydrogen to the reactant mixture.

Physical Description

22 p.

Notes

OSTI as DE00755924

Medium: P; Size: 22 pages

Source

  • Twenty-Eighth International Combustion Symposium, Edinburgh, Scotland (GB), 07/30/2000--08/04/2000

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  • Report No.: SAND2000-8677C
  • Grant Number: AC04-94AL85000
  • Office of Scientific & Technical Information Report Number: 755924
  • Archival Resource Key: ark:/67531/metadc703178

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  • July 30, 2000

Added to The UNT Digital Library

  • Sept. 12, 2015, 6:31 a.m.

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  • April 10, 2017, 3:15 p.m.

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Zerkle, D. K.; Allendorf, M. d.; Wolf, M. & Deutschmann, O. Modeling of on-line catalyst addition effects in a short contact time reactor, article, July 30, 2000; Albuquerque, New Mexico. (digital.library.unt.edu/ark:/67531/metadc703178/: accessed September 23, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.