Multiwavelength Speciation in Pyrolysis of n-Pentane and Experimental Determination of the Rate Coefficient of nC₅H₁₂ = nC₃H₇ + C₂H₅ in a Shock Tube

Abstract

We report the application of a multiwavelength speciation strategy to the study of n-pentane (nC5H12) pyrolysis behind reflected shock waves in a shock tube. Experiments were conducted with 2% nC5H12/0.8%CO2/Ar (by mole) between 1150 and 1520 K in the pressure range of 1–2 atm. Utilization of laser absorption spectroscopy at eight wavelengths allowed time-resolved measurements of n-pentane, ethylene, methane, heavy alkenes, and temperature. The measured time histories were compared against the predictions of four recently developed chemical kinetic models for heavy hydrocarbons. It was found that none of the models reconciled the measured species time histories simultaneously. Sensitivity analysis was conducted to identify key reactions influencing the evolution of ethylene and other major pyrolysis products. The analysis revealed that the unimolecular decomposition of n-pentane into n-propyl and ethyl radicals has a dominating influence over the evolution of ethylene in the temperature range of 1150–1450 K. The rate coefficient of this reaction was then adjusted to match the measured ethylene time histories for each experiment. The rate coefficients thus determined, were fit against temperature using an Arrhenius expression given by k 1(T) = 3.5 × 1014 exp­(−67.2 kcal/RT) s–1. The average overall 2σ uncertainty of the measured rate coefficient was found to be ±35%, resulting primarily from uncertainties in the rate coefficients of secondary reactions. The measured rate coefficient, when used with the models, leads to a significant improvement in the prediction of species time histories. Further improvements in the model are possible if the rate coefficients of relevant reactions pertaining to small hydrocarbon chemistry are determined with an improved accuracy, and less uncertainty. To the best knowledge of the authors, this is the first experimental determination of the rate coefficient of C5H12 → nC3H7 + C2H5.

Combustion in a Sustainable World: From Molecules to Processes

“…Specific reactions have also been investigated in the context of aromatics formation and pyrolysis . , For example, Hanamirian et al employed their automated kinetics code (EStokTP) and master equation lumping to obtain ab initio kinetic models for the H-abstraction reaction from methylcyclopentadiene and the unimolecular decomposition of the resulting methylcyclopentadienyl radical . Prompt dissociation of the radicals was shown to play a key role under combustion conditions .…”

“…Prompt dissociation of the radicals was shown to play a key role under combustion conditions . Biswas et al used a multiwavelength speciation experiment in a shock tube to determine the rate coefficient of n -pentane decomposition n C 5 H 12 = n C 3 H 7 + C 2 H 5 , a decisive step in the cracking of light naphtha, which is one of the key feedstocks to produce ethylene as a major building block in industrial chemical synthesis . Efficient reactor design and process conditions for future applications demand accurate chemical mechanisms for the relevant reactions …”

“…11 Biswas et al used a multiwavelength speciation experiment in a shock tube to determine the rate coefficient of n-pentane decomposition nC 5 H 12 = nC 3 H 7 + C 2 H 5 , a decisive step in the cracking of light naphtha, which is one of the key feedstocks to produce ethylene as a major building block in industrial chemical synthesis. 12 Efficient reactor design and process conditions for future applications demand accurate chemical mechanisms for the relevant reactions. 12 ■ FUELS AND MECHANISMS Chemical-kinetic combustion mechanisms are examined under a wide variety of conditions and for an ever-increasing range of fuels.…”

“…12 Efficient reactor design and process conditions for future applications demand accurate chemical mechanisms for the relevant reactions. 12 ■ FUELS AND MECHANISMS Chemical-kinetic combustion mechanisms are examined under a wide variety of conditions and for an ever-increasing range of fuels. Due to the hierarchical nature of combustion, various species (e.g., ketene and pentenes) are central to many combustion mechanisms.…”

Theoretical Kinetic Study on Hydrogen Abstraction Reactions from n-Pentane by NO2

“…n -Pentane is a representative component of gasoline fuel and has attracted much research attention. − In the present study, n -pentane was selected as the model compound. These H-abstraction reactions by NO 2 from n -pentane are listed as follows Here, the numbers (1, 2, and 3) denote the carbon site relative to the terminal carbon site, number “1” is located at the terminal carbon site, and so on.…”