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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Direct Production of Propene from the Thermolysis of Poly(beta-hydroxybutyrate) (PHB). An Experimental and DFT Investigation
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Direct Production of Propene from the Thermolysis of Poly(beta-hydroxybutyrate) (PHB). An Experimental and DFT Investigation

机译：由聚（β-羟基丁酸酯）（PHB）的热解直接生产丙烯。实验和DFT研究

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摘要

We demonstrate a synthetic route toward the production of propene directly from poly(beta-hydroxybutyrate) (PHB), the most common of a wide range of high-molecular-mass microbial polyhydroxyalkanoates. Propene, a major commercial hydrocarbon, was obtained from the depolymerization of PHB and subsequent decarboxylation of the crotonic acid monomer in good yields (up to 75 mol %). The energetics of PHB depolymerization and the gas-phase decarboxylation of crotonic acid were also studied using density functional theory (DFT). The average activation energy for the cleavage of the R'C (O)O-R linkage is calculated to be 163.9 +/- 7.0 kJ mol(-1) Intramolecular, autoacceleration effects regarding the depolymerization of PHB, as suggested in some literature accounts, arising from the formation of crotonyl and carboxyl functional groups in the products could not be confirmed by the results of DFT and microkinetic modeling. DFT results, however, suggest that intermolecular catalysis involving terminal carboxyl groups may accelerate PHB depolymerization. Activation energies for this process were estimated to be about 20 kJ mol(-1) lower than that for the noncatalyzed ester cleavage, 144.3 +/- 6.4 kJ mol(-1). DFT calculations predict the decarboxylation of crotonic acid to follow second-order kinetics with an activation energy of 147.5 +/- 6.3 kJ mol(-1), consistent with that measured experimentally, 146.9 kJ mol(-1). Microkinetic modeling of the PHB to propene overall reaction predicts decarboxylation of crotonic acid to be the rate-limiting step, consistent with experimental observations. The results also indicate that improvements made to enhance the isomerization of crotonic acid to vinylacetic acid will improve the direct conversion of PHB to propene.
机译：我们展示了直接从聚（β-羟基丁酸酯）（PHB）生产丙烯的合成路线，这是广泛的高分子量微生物聚羟基链烷酸酯中最常见的一种。丙烯是主要的商业烃，是通过PHB的解聚和巴豆酸单体的后续脱羧得到的，收率很高（最高75 mol％）。还利用密度泛函理论（DFT）研究了巴豆酸的PHB解聚和气相脱羧的能量。 R'C（O）OR键断裂的平均活化能经计算为163.9 +/- 7.0 kJ mol（-1）与PHB解聚有关的分子内，自加速效应，如某些文献所述DFT和微动力学建模的结果无法确定产物中巴豆酰基和羧基官能团的形成。然而，DFT结果表明，涉及末端羧基的分子间催化可加速PHB解聚。估计该过程的活化能比未催化酯裂解的活化能低约20 kJ mol（-1），为144.3 +/- 6.4 kJ mol（-1）。 DFT计算预测巴豆酸的脱羧反应遵循二级动力学，其活化能为147.5 +/- 6.3 kJ mol（-1），与实验测得的活化能为146.9 kJ mol（-1）。 PHB对丙烯总体反应的动力学模型预测，巴豆酸的脱羧是限速步骤，与实验观察结果一致。结果还表明，为增强巴豆酸向乙烯基乙酸的异构化所做的改进将改善PHB向丙烯的直接转化。

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