Kopač Drejc, Jurković Damjan Lašič, Likozar Blaž, Huš Matej
Department of Catalysis and Chemical Reaction Engineering, National Institute of Chemistry, Hajdrihova 19, SI-1001 Ljubljana, Slovenia.
Association for Technical Culture of Slovenia (ZOTKS), SI-1000 Ljubljana, Slovenia.
ACS Catal. 2020 Dec 18;10(24):14732-14746. doi: 10.1021/acscatal.0c03197. Epub 2020 Dec 1.
Propane (CH) and butane (CH) are short straight-chain alkane molecules that are difficult to convert catalytically. Analogous to propane, butane can be dehydrogenated to butenes (also known as butylenes) or butadiene, which are used industrially as raw materials when synthesizing various chemicals (plastics, rubbers, etc.). In this study, we present results of detailed first-principles-based multiscale modelling of butane dehydrogenation, consisting of three size- and time-scales. The reaction is modelled over CrO(0001) chromium oxide, which is commonly used in the industrial setting. A complete 108-step reaction pathway of butane (CH) dehydrogenation was studied, yielding 1-butene (CHCHCHCH) and 2-butene (CHCHCHCH), 1-butyne (CHCCHCH) and 2-butyne (CHCCCH), butadiene (CHCHCHCH), butenyne (CHCHCCH), and ultimately butadiyne (CHCCCH). We include cracking and coking reactions (yielding C, C, and C hydrocarbons) in the model to provide a thorough description of catalyst deactivation as a function of the temperature and time. Density functional theory calculations with the Hubbard model were used to study the reaction on the atomistic scale, resulting in the complete energetics and first-principles kinetic parameters for the dehydrogenation reaction. They were cast in a kinetic model using mean-field microkinetics and kinetic Monte Carlo simulations. The former was used to obtain gas equilibrium conditions in the steady-state regime, which were fed in the latter to provide accurate surface kinetics. A full reactor simulation was used to account for the macroscopic properties of the catalytic particles: their loading, specific surface area, and density and reactor parameters: size, design, and feed gas flow. With this approach, we obtained first-principles estimates of the catalytic conversion, selectivity to products, and time dependence of the catalyst activity, which can be paralleled to experimental data. We show that 2-butene is the most abundant product of dehydrogenation, with selectivity above 90% and turn-over frequency above 10 s at = 900 K. Butane conversion is below 5% at such low temperature, but rises above 40% at > 1100 K. Activity starts to drop after ∼6 h because of surface poisoning with carbon. We conclude that the dehydrogenation of butane is a viable alternative to conventional olefin production processes.
丙烷（CH）和丁烷（CH）是短直链烷烃分子，难以通过催化进行转化。与丙烷类似，丁烷可脱氢生成丁烯（也称为丁基烯）或丁二烯，它们在工业上用作合成各种化学品（塑料、橡胶等）的原料。在本研究中，我们展示了基于详细的第一性原理的丁烷脱氢多尺度建模结果，该建模涵盖三个尺寸和时间尺度。该反应在工业环境中常用的CrO(0001)氧化铬上进行建模。研究了丁烷（CH）脱氢的完整108步反应路径，生成1-丁烯（CHCHCHCH）和2-丁烯（CHCHCHCH）、1-丁炔（CHCCHCH）和2-丁炔（CHCCCH）、丁二烯（CHCHCHCH）、丁烯炔（CHCHCCH），最终生成丁二炔（CHCCCH）。我们在模型中纳入了裂解和结焦反应（生成C、C和C烃），以全面描述催化剂失活与温度和时间的关系。使用含Hubbard模型的密度泛函理论计算来研究原子尺度上的反应，得出脱氢反应的完整能量学和第一性原理动力学参数。这些参数被纳入使用平均场微观动力学和动力学蒙特卡罗模拟的动力学模型中。前者用于获得稳态下的气体平衡条件，将其输入后者以提供准确的表面动力学。使用全反应器模拟来考虑催化颗粒的宏观性质：它们的负载量、比表面积、密度以及反应器参数：尺寸、设计和进料气流。通过这种方法，我们获得了催化转化率、产物选择性和催化剂活性随时间变化的第一性原理估计值，这些值可与实验数据进行对比。我们表明，2-丁烯是脱氢的最主要产物，在 = 900 K时选择性高于90%，周转频率高于10 s。在如此低的温度下，丁烷转化率低于5%，但在 > 1100 K时升至40%以上。由于碳的表面中毒，活性在约6小时后开始下降。我们得出结论，丁烷脱氢是传统烯烃生产工艺的可行替代方案。
