Porterfield Jessica P, Bross David H, Ruscic Branko, Thorpe James H, Nguyen Thanh Lam, Baraban Joshua H, Stanton John F, Daily John W, Ellison G Barney
Chemical Sciences and Engineering Division, Argonne National Laboratory , Argonne, Illinois 60439, United States.
Computation Institute, The University of Chicago , Chicago, Illinois 60637, United States.
J Phys Chem A. 2017 Jun 22;121(24):4658-4677. doi: 10.1021/acs.jpca.7b02639. Epub 2017 Jun 9.
Two methyl esters were examined as models for the pyrolysis of biofuels. Dilute samples (0.06-0.13%) of methyl acetate (CHCOOCH) and methyl butanoate (CHCHCHCOOCH) were entrained in (He, Ar) carrier gas and decomposed in a set of flash-pyrolysis microreactors. The pyrolysis products resulting from the methyl esters were detected and identified by vacuum ultraviolet photoionization mass spectrometry. Complementary product identification was provided by matrix infrared absorption spectroscopy. Pyrolysis pressures in the pulsed microreactor were about 20 Torr and residence times through the reactors were roughly 25-150 μs. Reactor temperatures of 300-1600 K were explored. Decomposition of CHCOOCH commences at 1000 K, and the initial products are (CH═C═O and CHOH). As the microreactor is heated to 1300 K, a mixture of CH═C═O and CHOH, CH, CH═O, H, CO, and CO appears. The thermal cracking of CHCHCHCOOCH begins at 800 K with the formation of CHCHCH═C═O and CHOH. By 1300 K, the pyrolysis of methyl butanoate yields a complex mixture of CHCHCH═C═O, CHOH, CH, CH═O, CO, CO, CHCH═CH, CHCHCH, CH═C═CH, HCCCH, CH═C═C═O, CH═CH, HC≡CH, and CH═C═O. On the basis of the results from the thermal cracking of methyl acetate and methyl butanoate, we predict several important decomposition channels for the pyrolysis of fatty acid methyl esters, R-CH-COOCH. The lowest-energy fragmentation will be a 4-center elimination of methanol to form the ketene RCH═C═O. At higher temperatures, concerted fragmentation to radicals will ensue to produce a mixture of species: (RCH + CO + CH) and (RCH + CO + CH═O + H). Thermal cracking of the β C-C bond of the methyl ester will generate the radicals (R and H) as well as CH═C═O + CH═O. The thermochemistry of methyl acetate and its fragmentation products were obtained via the Active Thermochemical Tables (ATcT) approach, resulting in ΔH(CHCOOCH) = -98.7 ± 0.2 kcal mol, ΔH(CHCO) = -45.7 ± 0.3 kcal mol, and ΔH(COOCH) = -38.3 ± 0.4 kcal mol.
研究了两种甲酯作为生物燃料热解的模型。将乙酸甲酯（CH₃COOCH₃）和丁酸甲酯（CH₃CH₂CH₂COOCH₃）的稀样品（0.06 - 0.13%）夹带在（氦气、氩气）载气中，并在一组闪蒸热解微反应器中分解。通过真空紫外光电离质谱法检测和鉴定甲酯产生的热解产物。通过基质红外吸收光谱法进行互补产物鉴定。脉冲微反应器中的热解压力约为20托，通过反应器的停留时间约为25 - 150微秒。探索了300 - 1600 K的反应器温度。CH₃COOCH₃在1000 K开始分解，初始产物为（CH₂═C═O和CH₃OH）。当微反应器加热到1300 K时，出现CH₂═C═O和CH₃OH、CH₄、CH₂═O、H₂、CO和CO₂的混合物。CH₃CH₂CH₂COOCH₃的热裂解在800 K开始，生成CH₃CH₂CH═C═O和CH₃OH。到1300 K时，丁酸甲酯的热解产生CH₃CH₂CH═C═O、CH₃OH、CH₄、CH₂═O、CO、CO₂、CH₃CH═CH₂、CH₃CH₂CH₃、CH₂═C═CH₂、HCCCH₃、CH₂═C═C═O、CH₂═CH₂、HC≡CH和CH₂═C═O的复杂混合物。基于乙酸甲酯和丁酸甲酯热裂解的结果，我们预测了脂肪酸甲酯R - CH₂ - COOCH₃热解的几个重要分解通道。能量最低的碎片化将是甲醇通过4中心消除形成乙烯酮RCH═C═O。在较高温度下，将接着发生协同碎片化形成自由基，产生物种混合物：（RCH + CO + CH₃）和（RCH₂ + CO + CH₂═O + H）。甲酯β C - C键的热裂解将产生自由基（R和H）以及CH₂═C═O + CH₂═O。通过活性热化学表（ATcT）方法获得了乙酸甲酯及其碎片化产物的热化学数据，得到ΔH(CH₃COOCH₃) = -98.7 ± 0.2 kcal mol⁻¹，ΔH(CH₃CO) = -45.7 ± 0.3 kcal mol⁻¹，和ΔH(COOCH₃) = -38.3 ± 0.4 kcal mol⁻¹。
