Detailed Kinetic Modeling of NOx‑Mediated Oxidative Dehydrogenation of Propane

Shale gas is revitalizing America’s
chemical industry and
shifting ethylene production from oil-based naphtha to shale-derived
ethane, causing a short supply of propylene. Oxidative dehydrogenation
of propane mediated by NOx (NO and NO2) provides a potential route to convert propane into propylene
without solid catalysts. In this work, detailed kinetic modeling was
performed to simulate gas-phase homogeneous NOx-mediated oxidative dehydrogenation of propane. Consistent
with the experimental findings, our model suggests that propane conversion
increases with the amount of NO in the feed, with the selectivity
to propylene and ethylene decreased with increasing propane conversion.
Our modeling results also revealed that OH radicals are the major
species to consume propane. The addition of NOx in the system increases the production of OH radicals due
to additional pathways in the NO–NO2 cycle, including
(1) oxidation of NO by HO2 radicals, (2) reduction of NO2 by H radicals, and (3) formation and dissociation of HONO
and its isomers, facilitating propylene formation. The addition of
H2O further accelerates propane conversion by shifting
the equilibrium of OH quenching reactions. A reaction network consisting
of propane pyrolysis, propane oxidative dehydrogenation, and NOx mediation was sketched to explain the important
trends observed in the experiments.

页岩气的复苏正激活美国的化工产业，并将乙烯的生产从基于石油的轻烃转向页岩气制得的乙烷，导致丙烯供不应求。由氮氧化物（NO及NO2）催化的丙烷氧化脱氢反应提供了一种将丙烷转化为丙烯的潜在途径，且无需使用固态催化剂。在本研究中，我们进行了详细的动力学建模，以模拟气相均相氮氧化物介导的丙烷氧化脱氢反应。与实验结果一致，我们的模型表明，随着进料中NO含量的增加，丙烷转化率提高，而随着丙烷转化率的增加，丙烯和乙烯的选择性降低。我们的建模结果还揭示了羟基自由基是消耗丙烷的主要物种。系统中NOx的添加由于NO-NO2循环中的额外途径（包括：（1）HO2自由基氧化NO，（2）H自由基还原NO2，（3）HONO及其同分异构体的形成和解离）而增加了羟基自由基的产生，从而促进了丙烯的形成。H2O的添加通过改变羟基淬灭反应的平衡进一步加速了丙烷的转化。我们绘制了一个包含丙烷裂解、丙烷氧化脱氢和氮氧化物催化的反应网络，用以解释实验中观察到的关键趋势。