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The complete basis set method CBS-QB3 has been used to study the thermochemistry and kinetics of the esters ethyl propanoate (EP) and methyl butanoate (MB) to evaluate initiation reactions and intermediate products from unimolecular decomposition reactions. Using isodesmic and isogeitonic equations and atomization energies, we have estimated chemically accurate enthalpies of formation and bond dissociation energies for the esters and species derived from them. In addition it is shown that controversial literature values may be resolved by adopting, for the acetate radical, CH3C(O)O(.-), DeltaH(o)(f)298.15K) = -197.8 kJ mol(-1) and for the trans-hydrocarboxyl radical, C(.-)(O)OH, -181.6 +/- 2.9 kJ mol(-1). For EP, the lowest energy decomposition path encounters an energy barrier of approximately 210 kJ mol(-1) (approximately 50 kcal mol(-1)), which proceeds through a six-membered ring transition state (retro-ene reaction) via transfer of the primary methyl H atom from the ethyl group to the carbonyl oxygen, while cleaving the carbon-ether oxygen to form ethene and propanoic acid. On the other hand, the lowest energy path for MB has a barrier of approximately 285 kJ mol(-1), producing ethene. Other routes leading to the formation of aldehydes, alcohols, ketene, and propene are also discussed. Most of these intramolecular hydrogen transfers have energy barriers lower than that needed for homolytic bond fission (the lowest of which is 353 kJ mol(-1) for the C(alpha)-C(beta) bond in MB). Propene formation is a much higher energy demanding process, 402 kJ mol(-1), and it should be competitive with some C-C, C-O, and C-H bond cleavage processes.

Due to the world's over-reliance on fossil fuels there has been a developing interest in the production of renewable biofuels such as methyl and ethyl esters derived from vegetable oils and animal fats. To increase our understanding of the combustion chemistry of esters, the oxidation of methyl butanoate and ethyl propanoate, both with a molecular formula of C5H10O2, have been studied in a series of high-temperature shock tube experiments. Ignition delay times for a series of mixtures, of varying fuel/oxygen equivalence ratios (phi = 0.25-1.5), were measured behind reflected shock waves over the temperature range 1100-1670 K, and at pressures of 1.0, and 4.0 atm. It was found that ethyl propanoate was consistently faster to ignite than methyl butanoate, particularly at lower temperatures. Detailed chemical kinetic mechanisms have been assembled and used to simulate these experiments with good agreement observed. Rate of production analyses using the detailed mechanisms shows that the faster reactivity of ethyl propanoate can be explained by a six-centered unimolecular decomposition reaction with a relatively low activation energy barrier producing propanoic acid and ethylene. The elimination reaction itself is not responsible for the increased reactivity; it is the faster reactivity of the two products, propanoic acid and ethylene that leads to this behavior.

Co-pyrolysis of forestry wastes and waste tyres is carried out using different facilities: a fixed bed reactor and a continuous auger reactor. Remarkably, only one phase is found in the liquid fraction, which is not achieved by mixture of the pure liquids. In addition, positive effects between waste tyre and biomass are evidenced, being more notable even synergetic in the auger reactor. It is found that whilst acidity, density and oxygen content decrease, pH and calorific value increase with respect to the merely biomass pyrolysis liquid, leading to upgraded bio-oil. Upgrading process is linked to the presence of radical interactions between waste tyres and biomass pyrolysis products. In addition, it is observed that the addition of waste tyres to the feedstock blend is significantly decreasing the amount of aldehydes and phenolic compounds, which is beneficial for improving the stability of the new bio-oils.

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