Shinohara Yuji, Tsubouchi Naoto
Center for Advanced Research of Energy and Materials, Hokkaido University, Sapporo, Hokkaido 060-8628, Japan.
ACS Omega. 2020 Jan 10;5(3):1688-1697. doi: 10.1021/acsomega.9b03780. eCollection 2020 Jan 28.
Our previous experimental study showed that Na-exchanged coal prepared from low-cost natural soda ash is an excellent catalyst for steam gasification of low-rank coals using fixed-bed quartz reactors. However, it is difficult to experimentally clarify the effect of Na ion exchange on low-rank coal. In order to investigate the influence of Na ions on low-rank coal, this study determined the electronic state between the Na-exchanged coal model and raw coal model and compared them using RHF/6-311G* and B3LYP/6-31G*. The experiments revealed that Na ion exchange has a significant effect on low-rank coal gasification. The model structure of low-rank coal is considered to change significantly in terms of the electronic state before and after Na exchange even with a simple main molecular structure. Molecular models where H of COOH/OH was ion-exchanged with one, two, and three Na ions were developed, and quantum chemical calculations were performed. The results showed that when the number of Na-exchanged sites is increased, the electron state on the coal molecule becomes more negatively charged in the case of the Na-exchange coal model. It is presumed that this contributes to enhancing the reactivity of low-rank coal and water vapor. In addition, weak bonds in the Na-exchanged coal molecule were examined by calculating the difference in the value of the Mulliken and Löwdin bond orders before and after Na exchange. The results showed that the increase in the number of exchanged Na in the low-rank coal molecule model increased the number of weak bonds in the molecule. It is presumed that this contributes to enhancing the decomposition of low-rank coal.
我们之前的实验研究表明，由低成本天然纯碱制备的钠交换煤是使用固定床石英反应器对低阶煤进行蒸汽气化的优良催化剂。然而，通过实验阐明钠离子交换对低阶煤的影响是困难的。为了研究钠离子对低阶煤的影响，本研究确定了钠交换煤模型和原煤模型之间的电子态，并使用RHF/6-311G和B3LYP/6-31G对它们进行了比较。实验表明，钠离子交换对低阶煤气化有显著影响。即使低阶煤的主要分子结构简单，其模型结构在钠交换前后的电子态方面也被认为发生了显著变化。构建了羧基/羟基中的氢与一、二、三个钠离子进行离子交换的分子模型，并进行了量子化学计算。结果表明，在钠交换煤模型中，当钠交换位点的数量增加时，煤分子上的电子态变得更带负电。据推测，这有助于提高低阶煤和水蒸气的反应活性。此外，通过计算钠交换前后穆利肯键级和洛丁键级值的差异，研究了钠交换煤分子中的弱键。结果表明，低阶煤分子模型中交换钠数量的增加增加了分子中弱键的数量。据推测，这有助于促进低阶煤的分解。
