Kinetics and Mechanism for Hydrothermal Conversion of Polyhydroxybutyrate (PHB) for Wastewater Valorization
Kinetics and Mechanism for Hydrothermal Conversion of Polyhydroxybutyrate (PHB) for Wastewater Valorization
复制标题
聚羟基丁酸酯（PHB）水热转化废水增值的动力学和机理
DOI：
10.1039/c9gc02507c
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发表时间：
2019
期刊：
影响因子：
9.8
通讯作者：
Strathmann, T.J.
中科院分区：
文献类型：
--
作者：
Li, Y.;Strathmann, T.J.
传统的废水处理工艺可以定制为从废水中回收有机碳作为细胞内聚羟基丁酸酯（PHB）聚合物颗粒，同时满足流出物排放标准。PHB作为生物塑料的传统应用受到其次优性质（例如，脆性），缺乏从细胞中回收PHB的有效和可持续的方法，以及对废水来源的杂质的担忧。在这项研究中，我们报告了在水热条件下（在高温高压下的冷凝水中）转化PHB及其单体酸- 3-羟基丁酸（3 HBA）和巴豆酸（CA），以形成丙烯，一种有价值的化学中间体，自分离水。PHB解聚产生3 HBA和CA的混合物，其可以通过随主要反应条件变化的水合（脱）反应相互转化。单体酸的进一步水热转化产生丙烯和CO2。3 HBA的转化发生在比CA低的温度下，并且提出了一种新的协同脱水-脱羧途径，其不同于报道的用于干热转化的顺序脱水（3 HBA至CA）和脱羧（CA至丙烯和CO2）途径。一个动力学网络模型的实验结果表明，CA转化为丙烯和CO2的收益主要是通过水合到3 HBA，其次是协调的脱水脱羧途径，而不是通过直接脱羧CA。使用含聚羟基丁酸酯的甲烷氧化生物质的示范性实验表明，结果与模型一致，在较低的温度下，比以前报道的近理论产率产生丙烯。
Conventional wastewater treatment processes can be tailored to recover organic carbon from wastewater as intracellular polyhydroxybutyrate (PHB) polymer granules while simultaneously meeting effluent discharge standards. Traditional applications of PHB as a bioplastic are hampered by its suboptimal properties (e.g., brittle), lack of efficient and sustainable approaches for recovering PHB from cells, and concerns about wastewater-derived impurities. In this study, we report on the conversion of PHB and its monomer acids – 3-hydroxybutyric acid (3HBA) and crotonic acid (CA) – under hydrothermal conditions (in condensed water at elevated temperature and pressure) to form propylene, a valuable chemical intermediate that self-separates from water. PHB depolymerization results in a mixture of 3HBA and CA, which can interconvert via (de)hydration reactions that vary with prevailing reaction conditions. Further hydrothermal conversion of the monomer acids yields propylene and CO2. Conversion of 3HBA occurs at lower temperatures than CA, and a new concerted dehydration-decarboxylation pathway is proposed, which differs from the sequential dehydration (3HBA to CA) and decarboxylation (CA to propylene and CO2) pathway reported for dry thermal conversion. A kinetics network model informed by experimental results reveals that CA conversion to propylene and CO2 proceeds predominantly via hydration to 3HBA followed by the concerted dehydration-decarboxylation pathway rather than by direct decarboxylation of CA. Demonstrative experiments using PHB-containing methanotrophic biomass show results consistent with the model, producing propylene at near-theoretical yields at lower temperatures than reported previously.