Abstract Understanding ignition and extinction behavior is of crucial importance for oxidative coupling of methane (OCM). Therefore, for the first time the bifurcation behavior of OCM has been investigated while considering both homogeneous gas phase reactions and heterogeneous reactions using a detailed microkinetic model. Three different adiabatic reactor models are considered: a plug flow reactor (PFR), a continuously stirred tank reactor (CSTR) and a lumped thermal reactor (LTR) model. The latter represents the limiting case with zero backmixing (cf. PFR behavior) for species and perfect thermal backmixing (cf. CSTR behavior). For homogeneous processes this reactor type could for example be realized by adding a high thermal conductivity inert to the reactor tubes, for catalytic processes a high thermal conductivity catalyst could be used. The bifurcation behavior in these reactor types is compared with a focus on methane conversion, C 2 yields and their dependence on operating conditions such as inlet composition, inlet temperature and space time. Steady state multiplicity is observed for adiabatic CSTR and LTR models. This multiplicity of steady states is not observed for isothermal reactor models, indicating that it is caused solely by thermal backmixing and is not related to chemical feedback features such as autocatalysis. The start-up procedures or initial conditions determine the actual steady state that is obtained. Among the three investigated reactor types, a LTR shows the highest product yields and the lowest extinction temperatures, which allows autothermal operation at a much lower inlet temperature compared to a PFR and CSTR. For OCM without catalyst, autothermal operation on the ignited branch at ambient inlet temperatures and reasonable space times is only possible by using methane-to-oxygen ratios below 3 leading to low selectivities. For catalytic OCM compared to OCM without catalyst, the range for autothermal operation is much broader and it is much easier to find feasible operating conditions allowing autothermal operation at ambient inlet temperatures. By operating a LTR on the ignited branch at ambient inlet temperature of 300 K, methane-to-oxygen ratio CH 4 :O 2 = 6, space time V/F CH4,0 = 0.02 s, bulk density of Sn-Li/MgO = 1000 kg cat /m 3 and pressure P = 1 bar, overall C 2 selectivities (i.e. sum of ethane, ethylene and acetylene selectivity) of 80% can be obtained at methane conversions as high as 30%.

中文翻译：

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催化剂着火和熄灭：基于微动力学的甲烷氧化偶联绝热反应器分叉研究

摘要 了解点火和熄灭行为对于甲烷氧化耦合 (OCM) 至关重要。因此，首次使用详细的微动力学模型在考虑均相气相反应和非均相反应的同时研究了 OCM 的分叉行为。考虑了三种不同的绝热反应器模型：活塞流反应器 (PFR)、连续搅拌釜式反应器 (CSTR) 和集总热反应器 (LTR) 模型。后者代表物种零返混（参见 PFR 行为）和完美热返混（参见 CSTR 行为）的极限情况。对于均相过程，这种反应器类型可以例如通过向反应器管添加惰性的高导热性来实现，对于催化过程，可以使用高导热性催化剂。将这些反应器类型中的分叉行为与关注甲烷转化率、C 2 产率及其对操作条件（例如入口组成、入口温度和时空）的依赖性进行比较。对于绝热 CSTR 和 LTR 模型，观察到稳态多重性。在等温反应器模型中没有观察到这种稳定状态的多样性，这表明它仅由热返混引起，与化学反馈特征（如自催化）无关。启动程序或初始条件决定了所获得的实际稳定状态。在所研究的三种反应器类型中，LTR 显示出最高的产品收率和最低的消光温度，与 PFR 和 CSTR 相比，这允许在低得多的入口温度下进行自热操作。对于无催化剂的 OCM，只有通过使用低于 3 的甲烷与氧气比导致低选择性，才能在环境入口温度和合理的空间时间下在点燃分支上进行自热操作。与没有催化剂的 OCM 相比，催化 OCM 的自热操作范围要宽得多，并且更容易找到允许在环境入口温度下自热操作的可行操作条件。通过在 300 K 的环境入口温度下在点燃的分支上运行 LTR，甲烷与氧气的比率 CH 4 :O 2 = 6，时空 V/F CH4,0 = 0.02 s，Sn-Li/MgO 的堆积密度= 1000 kg cat /m 3 和压力 P = 1 bar，可以在高达 30% 的甲烷转化率下获得 80% 的总 C 2 选择性（即乙烷、乙烯和乙炔选择性的总和）。