Schwartz William R, McEnally Charles S, Pfefferle Lisa D
Department of Chemical Engineering and Center for Combustion Studies, Yale University, New Haven, Connecticut 06520-8286, USA.
J Phys Chem A. 2006 Jun 1;110(21):6643-8. doi: 10.1021/jp0549576.
Biomass fuels are a promising renewable energy source, and so, the mechanisms that may produce toxic oxygenated byproducts and aromatic hydrocarbons from oxygenated hydrocarbons are of interest. Esters have the form R-(C=O)-O-R' and are components of biodiesel fuels. The five specific esters studied here are isomers of C5H10O2. The experiments were performed in atmospheric pressure coflowing methane/air non-premixed flames. A series of flames were generated by separately doping the fuel mixture with 5,000 ppm of each ester. This concentration is sufficiently large to produce measurable changes in intermediate hydrocarbon concentrations, yet small enough to not disturb the overall flame structure. Since the overall structure is not perturbed, the measured changes in the intermediate hydrocarbons can be directly attributed to the reactions of the esters. Analysis of these changes reveals that unimolecular six-centered dissociation is the primary decomposition pathway for the three esters with molecular arrangements capable of undergoing that mechanism. The remaining two esters exhibited decomposition rates and products that are consistent with simple fission as the dominant decomposition mechanism, though we do not exclude other pathways from playing a significant role in their decomposition. All of the esters produce aromatic hydrocarbons at higher rates than the undoped fuel, and the molecular arrangement of the ester isomers plays a role in the degree of aromatic formation. Isomer variations also influence the type and quantity of toxic oxygenates that are produced in the flames.
生物质燃料是一种很有前景的可再生能源，因此，由含氧烃类产生有毒含氧副产物和芳烃的机制备受关注。酯类的形式为R-(C=O)-O-R'，是生物柴油燃料的成分。这里研究的五种特定酯类是C5H10O2的异构体。实验在常压共流甲烷/空气非预混火焰中进行。通过分别向燃料混合物中掺入5000 ppm的每种酯类来产生一系列火焰。该浓度足够高，能够使中间烃浓度产生可测量的变化，但又足够低，不会干扰整体火焰结构。由于整体结构未受扰动，因此测得的中间烃类变化可直接归因于酯类的反应。对这些变化的分析表明，单分子六中心解离是三种具有能够经历该机制的分子排列的酯类的主要分解途径。其余两种酯类表现出的分解速率和产物与以简单裂变作为主要分解机制一致，不过我们并不排除其他途径在其分解过程中发挥重要作用。所有酯类产生芳烃的速率都高于未掺杂燃料，并且酯类异构体的分子排列对芳烃形成的程度有影响。异构体的变化也会影响火焰中产生的有毒含氧化合物的类型和数量。
