Presentation Title

Thermal Decomposition Mechanisms of Cyclopentane, Cyclohexane, and Cycloheptane by Flash Pyrolysis Time-of-Flight Mass Spectrometry

Faculty Mentor

Jingsong Zhang

Start Date

17-11-2018 12:30 PM

End Date

17-11-2018 2:30 PM

Location

CREVELING 13

Session

POSTER 2

Type of Presentation

Poster

Subject Area

physical_mathematical_sciences

Abstract

Cycloalkanes are hydrocarbon molecules characterized by a ring structure containing three or more carbon atoms. Many cycloalkanes are found in heavy oils such as motor fuel, natural gas, petroleum gas, kerosene, and diesel. Thermal decomposition, or pyrolysis, of cycloalkanes is an important process heavily used in the chemical industry to yield many forms of hydrocarbon products. The thermal decomposition of cycloalkanes is also important in combustion, as cycloalkanes decompose upon exposure to heat or an ignition source by various pathways. Herein, flash pyrolysis experiments were conducted on cyclopentane, cyclohexane, and cycloheptane via vacuum ultraviolet single photoionization time-of-flight mass spectrometry (VUV-SPI-TOF-MS) to devise mechanisms of their thermal decomposition by assessing their production of free radicals and other reactive intermediates in the early stages of thermal decomposition reactions. The species of interest were diluted in Helium (an inert carrier gas) to undergo fast flow through a heated micro-reactor followed by immediate supersonic expansion into high vacuum resulting in a molecular beam, effectively cooling and isolating reactive intermediates before detection by VUV-SPI-TOF-MS. The pyrolysis of hydrocarbons is known to follow a radical chain mechanism initiated by the cleavage of carbon to carbon bonds, and is difficult to study due to the highly reactive nature of the free radical intermediates. By setting the sample to heater contact times in the range of 20 - 100 μs (significantly shorter than those in traditional methods) the direct detection of species produced in early unimolecular decomposition reactions is possible. This information could help to better understand and optimize the mechanisms of combustion, verify and improve current kinetic models, and elucidate novel decomposition reaction pathways for the molecules understudy.

Summary of research results to be presented

The thermal decomposition of the cyclopentane, cyclohexane, and cycloheptane systems were found to decompose through the biradical and alkene isomer intermediates. Some fragments may not have been detected if they had an ionization energy higher than the photon energy of the laser.

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Nov 17th, 12:30 PM Nov 17th, 2:30 PM

Thermal Decomposition Mechanisms of Cyclopentane, Cyclohexane, and Cycloheptane by Flash Pyrolysis Time-of-Flight Mass Spectrometry

CREVELING 13

Cycloalkanes are hydrocarbon molecules characterized by a ring structure containing three or more carbon atoms. Many cycloalkanes are found in heavy oils such as motor fuel, natural gas, petroleum gas, kerosene, and diesel. Thermal decomposition, or pyrolysis, of cycloalkanes is an important process heavily used in the chemical industry to yield many forms of hydrocarbon products. The thermal decomposition of cycloalkanes is also important in combustion, as cycloalkanes decompose upon exposure to heat or an ignition source by various pathways. Herein, flash pyrolysis experiments were conducted on cyclopentane, cyclohexane, and cycloheptane via vacuum ultraviolet single photoionization time-of-flight mass spectrometry (VUV-SPI-TOF-MS) to devise mechanisms of their thermal decomposition by assessing their production of free radicals and other reactive intermediates in the early stages of thermal decomposition reactions. The species of interest were diluted in Helium (an inert carrier gas) to undergo fast flow through a heated micro-reactor followed by immediate supersonic expansion into high vacuum resulting in a molecular beam, effectively cooling and isolating reactive intermediates before detection by VUV-SPI-TOF-MS. The pyrolysis of hydrocarbons is known to follow a radical chain mechanism initiated by the cleavage of carbon to carbon bonds, and is difficult to study due to the highly reactive nature of the free radical intermediates. By setting the sample to heater contact times in the range of 20 - 100 μs (significantly shorter than those in traditional methods) the direct detection of species produced in early unimolecular decomposition reactions is possible. This information could help to better understand and optimize the mechanisms of combustion, verify and improve current kinetic models, and elucidate novel decomposition reaction pathways for the molecules understudy.