Thermal Decomposition of 2,5-Dimethylfuran. Experimental Results and Computer Modeling

The thermal reactions of 2,5-dimethylfuran were studied behind reflected shock waves in a pressurized driver single pulse shock tube over the temperature range 1070−1370 K and overall densities of ∼3 × 10 -5 mol/cm 3 . A large number of products resulting from unimolecular cleavage of the ring and consecutive free radical reactions were obtained under shock heating. A methyl group migration from C(2) to C(3) in the ring with the elimination of CO produces four isomers of C 5 H 8 in unimolecular processes. An additional unimolecular process is the decomposition of 2,5-dimethylfuran to CH 3 CO and C 4 H 5 which is an important initiator of free radical reactions. Ejection of a hydrogen atom from the methyl group in the molecule is another channel for initiation of free radical reactions in the system. The 2,5-dimethylfuryl radical, which is obtained in the process of H-atom ejection, decomposes in channels similar to those of 2,5-dimethylfuran to produce, among other products, C 5 H 7, which is the precursor of cyclopentadiene. The major decomposition product found in the post shock mixtures is carbon monoxide. The rate constant of its overall formation is estimated as k CO = 10 15.81 exp(−75.1 × 10 3 / RT ) s -1 where R is expressed in units of cal/(K mol). Other products that were found in the postshock samples in decreasing order of abundance were C 4 H 4, C 2 H 2, and CH 4 in roughly the same abundance, C 2 H 4, C 2 H 6, CH 2 CH−CH CH 2, cyclopentadiene p -C 3 H 4, and a -C 3 H 4 and 2-methylfuran. Other isomers of C 4 H 6, C 5 H 6 and C 5 H 8, and some additional products were found in very small quantities. The total decomposition of 2,5-dimethylfuran in terms of a first-order rate constant is given by: k total = 10 16.22 exp(−77.5 × 10 3 / RT ) s -1 . An oxygen−carbon mass balance among the decomposition products is obtained. A reaction scheme composed of 50 species and some 180 elementary reactions accounts for the product distribution over the temperature range covered in this study. First-order Arrhenius rate parameters for the formation of the various reaction products are given, a reaction scheme is suggested, and results of computer simulation and sensitivity analysis are shown. Differences and similarities among the reactions of furan, 2-methylfuran, and 2,5-dimethylfuran are discussed.