Ridder Harm, Sinn Christoph, Pesch Georg R, Dreher Wolfgang, Thöming Jorg
Chemical Process Engineering (CVT), Faculty of Production Engineering, University of Bremen, Leobener Str. 6, 28359 Bremen, Germany.
Center for Environmental Research and Sustainable Technology (UFT), Post box 330 440, 28334 Bremen, Germany.
ACS Meas Sci Au. 2022 Jul 26;2(5):449-456. doi: 10.1021/acsmeasuresciau.2c00022. eCollection 2022 Oct 19.
Catalytic hydrogenation reactions are important in a modern hydrogen-based society. To optimize these gas-phase reactions, a deep understanding of heat, mass, and momentum transfer inside chemical reactors is required. Nuclear magnetic resonance (NMR) measurements can be used to obtain spatially resolved values of temperature, gas composition, and velocity in the usually opaque catalytic macrostructures. For this, the desired values are calculated from measured NMR parameters like signal amplitude, , or . However, information on how to calculate target values from these NMR parameters in gases is scarce, especially for mixtures of gases. To enable detailed NMR studies of hydrogenation reactions, we investigated the relaxation of methane and hydrogen, which are two gases commonly present in hydrogenation reactions. To achieve industrially relevant conditions, the temperatures are varied from 290 to 600 K and the pressure from 1 bara to 5 bara, using different mixtures of methane and hydrogen. The results show that hydrogen, which is usually considered to be nondetectable in standard MRI sequences, can be measured at high concentrations, starting at a pressure of 3 bara even at temperatures above 400 K. In the investigated parameter range, the absolute values of hydrogen show only small dependence on temperature, pressure, and composition, while of methane is highly dependent on all three parameters. At a pressure of 5 bara, the measured values of for methane agree very well with theoretical predictions, so that they can also be used for temperature calculations. Further, it can be shown that the same measurement technique can be used to accurately calculate gas ratios inside each voxel. In conclusion, this study covers important aspects of spatially resolved NMR measurements of gas-phase properties during hydrogenation reactions at industrially relevant conditions to help improve chemical processes in the gas phase.
催化加氢反应在现代氢基社会中至关重要。为了优化这些气相反应，需要深入了解化学反应器内部的热量、质量和动量传递。核磁共振（NMR）测量可用于获取通常不透明的催化宏观结构内温度、气体组成和速度的空间分辨值。为此，通过测量的NMR参数（如信号幅度等）来计算所需值。然而，关于如何从这些气体中的NMR参数计算目标值的信息很少，尤其是对于气体混合物。为了能够对加氢反应进行详细的NMR研究，我们研究了甲烷和氢气的弛豫，这两种气体是加氢反应中常见的。为了达到工业相关条件，使用不同的甲烷和氢气混合物，温度在290至600 K之间变化，压力在1巴至5巴之间变化。结果表明，通常认为在标准MRI序列中无法检测到的氢气，即使在温度高于400 K时，从3巴的压力开始，在高浓度下也可以测量。在所研究的参数范围内，氢气的绝对值仅对温度、压力和组成有很小的依赖性，而甲烷的则高度依赖于所有这三个参数。在5巴的压力下，甲烷的测量值与理论预测非常吻合，因此它们也可用于温度计算。此外，可以证明相同的测量技术可用于准确计算每个体素内的气体比例。总之，本研究涵盖了在工业相关条件下加氢反应过程中气相性质的空间分辨NMR测量的重要方面，以帮助改进气相化学过程。
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