The pyrolysis product chemistry of triglycerides (TG) is still not well understood, though the subject has important implications for fuel production from TGs and food science.  Much past experimental progress has depended on batch reactor TG pyrolysis, with GC analysis of terminal products; the ingenuity and inductive powers of the experimenters are greatly put to test, to infer/predict key early chemistry based on terminal product analyses.  In contrast, cold gas expansion molecular beam methods, where pyrolysis products are analyzed in real time as they are entrained in gas expansions, offer some direct information on ongoing intermediate chemistry.  Soft photoionization of the products in free molecular flow then enables time-of-flight mass spectrometry.  Photoionization schemes can be selected for general product detection or for selective aromatic product detection.  The ongoing trends in the growth/diminution of various product mass peaks can be further clarified using methods of multivariate analysis.   These methods have been particularly useful in the analysis of PAH and high MW aromatic product chemistry.  Previous TG pyrolysis studies employing GC have been able to identify only relatively low MW aromatics.  Some surprising new results have emerged using molecular beam methods.  Rather large PAHs, up to 444 amu, have been detected, at non-trivial relative product fractions.  Indeed, a small number of PAHs with MW ≥ 276 amu increasingly dominate the aromatics product distribution.  Also surprisingly, PAH product detection ensues at rather low temperatures, as low as ~260 C. The obtained results were interpreted as the PAHs observed while using molecular beams do not make it into the liquid phase TG cracking products but instead serve as intermediates of coke/tar (solid phase) products, which could not be observed by other methods.

Real time studies of triglyceride thermal cracking chemistry using molecular beams

255th National Meeting (2018)

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