Direct Production of Propene from the Thermolysis of Poly(β-hydroxybutyrate) (PHB). An Experimental and DFT Investigation
Direct Production of Propene from the Thermolysis of Poly(β-hydroxybutyrate) (PHB). An Experimental and DFT Investigation
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DOI：
10.1021/acs.jpca.5b09246
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发表时间：
2016-01-27
影响因子：
2.9
通讯作者：
Johnson, David K.
中科院分区：
文献类型：
--
作者：
Clark, Jared M.;Pilath, Heidi M.;Johnson, David K.
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，聚（β-羟基丁酸酯）是各种高分子量微生物聚羟基链烷酸酯中最常见的一种。丙烯是一种主要的商业碳氢化合物，通过 PHB 的解聚和随后巴豆酸单体的脱羧获得，收率良好（高达 75 mol%）。还利用密度泛函理论（DFT）研究了 PHB 解聚和巴豆酸气相脱羧的能量学。 R'C (O)O-R 键断裂的平均活化能为 163.9 +/- 7.0 kJ mol(-1)。 正如一些文献中所指出的，PHB 解聚的分子内自加速效应是由产品中巴豆酰基和羧基官能团的形成引起的，但 DFT 和微动力学模型的结果无法证实。然而，DFT 结果表明，涉及末端羧基的分子间催化可能会加速 PHB 解聚。该过程的活化能估计比非催化酯裂解的活化能（144.3 +/- 6.4 kJ mol(-1)）低约20 kJ mol(-1)。 DFT计算预测巴豆酸脱羧遵循二级动力学，活化能为147.5 +/- 6.3 kJ mol(-1)，与实验测量的146.9 kJ mol(-1)一致。 PHB 与丙烯整体反应的微动力学模型预测巴豆酸脱羧是限速步骤，与实验观察结果一致。结果还表明，为增强巴豆酸异构化为乙烯基乙酸而进行的改进将提高 PHB 向丙烯的直接转化率。
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.