Thermal decomposition of t-amyl methyl ether (TAME) studied by flash pyrolysis/supersonic expansion/vacuum ultraviolet photoionization time-of-flight mass spectrometry

Thermal decomposition of the oxygenated fuel component tert-amyl methyl ether (TAME) has been studied by flash pyrolysis up to 1250 K in a 20–100 μs time scale. Pyrolysis was followed by supersonic expansion to isolate intermediates and products, which are monitored by vacuum ultraviolet single-photon ionization time-of-flight mass spectrometry (VUV-SPI-TOFMS). The species detected, such as CH3, C2H4, C2H5, C4H8, C5H10, C3H6O, and C4H8O, show competition between molecular elimination and bond fission pathways. The alkenes 2-methyl-1-butene (1) and 2-methyl-2-butene (2), the primary molecular elimination products of TAME, were separately pyrolyzed to evaluate the extent of secondary decompositions, as were the ketones (acetone and 2-butanone) produced by losses of two alkyl radicals. While vicinal elimination of methanol from TAME to form 1 and 2 in an approximate 3:1 ratio begins around 600 K and continues to dominate at higher temperatures, homolysis of TAME to form radicals onsets >825 K, yielding more acetone than 2-butanone. Contributions from secondary dissociations of the ketone and alkene products are evaluated.

Figure optionsDownload high-quality image (119 K)Download as PowerPoint slideResearch highlights▶ Molecular elimination is the predominant unimolecular dissociation of neutral TAME below 1000 K. ▶ MeOH elimination from neutral TAME gives 2-methyl-1-butene and 2-methyl-2-butene in a ≈3:1 ratio. ▶ 118.2 nm photoionization shows that neutral TAME begins to pyrolyze to CH3 and C2H5 radicals >850 K. ▶ Ketones from successive loss of 2 radicals from neutral TAME are detected at the onset of homolysis. ▶ Acetone and butanone (ratio ≈2:1) give photoion intensities less than those of C2H5 or CH3 radicals.