(37d) Degradation Kinetics of a Liquid Mineral Oil
AIChE Annual Meeting
2019 AIChE Annual Meeting
Catalysis and Reaction Engineering Division
Reaction Engineering for Combustion and Pyrolysis
Sunday, November 10, 2019 - 4:08pm to 4:27pm
In the present study, fresh and degraded samples of a popular commercial paraffinic mineral oil (CAS number 64742-52-5) are used. The degraded mineral oil sample had undergone accelerated degradation at 370Â°C for 100 hours, above its rated operating temperatures. Each sample (0.5 Î¼l) is analyzed with two-dimensional gas chromatography coupled with time-of-flight mass spectrometry (GC x GC/ToFMS; LECO Pegasus 4D), giving excellent resolution of species. Initially, the species are identified solely by similarity with respect to the reference library mass spectra of the tentatively identified species. For the long linear and branched alkane chains, comparison of measured spectra is typically 70-75% similar. Adding GC elution times of standards will provide greater certainty.
The fresh mineral-oil sample mainly consisted of linear and branched alkanes having 15 to 28 carbons. Additional species were identified in the degraded mineral oil, notably smaller linear alkanes, branched alkanes having 5 to 14 carbon numbers, and cycloalkanes with 5, 6, and 8 carbons.
To probe the possible reactions underlying this degradation, the Reaction Mechanism Generator (RMG) code of Gao et al.  was used. Pyrolysis kinetics of 8-butyloctadecane, a possible major compound in this mineral oil, was estimated and tested at 370Â°C and 1 atm. Breakage of the branched alkane was predicted to occur through different radical-forming reactions, principally disproportionation, H abstraction, internal H transfer, and radical recombination.
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