Modeling and Validating Fixed‐Bed Reactors: A State‐of‐the‐Art Review

Theoretical and experimental investigation of the influence of intraphase diffusion on the oxidation of toluene over manganese-based oxide

The influence of intraphase diffusion on the oxidation of toluene over manganese-based oxide, MnFeOx, under isothermal conditions was investigated. The one-dimensional (1D) heterogeneous model was developed to explain the experimental results. The model can be applied under certain operating conditions, i.e. conditions with negligible resistance to external mass transfer. The article describes the numerical solution of the equations of the proposed model. The relevance of the 1D heterogeneous model compared to the 1D pseudohomogeneous model was also emphasized. Validation of the proposed models was carried out by comparing with experimentally measured results. Both models were found to describe the experimental system studied quite well, with the 1D heterogeneous model providing better insight into the relationship between the rate of chemical reaction and the rate of intraphase diffusion.

High-performance fixed-bed in situ mass analyzer-ISMA

We demonstrate a newly developed high-performance fixed-bed reactor combined with an in situ mass analyzer (ISMA). The ISMA is particularly relevant to sub-second time-resolved studies where mass changes occur due to, e.g., chemical reactions and process conditions such as choice of solid, temperature, gas atmosphere, and pressure. The mass is determined from the optically measured oscillation frequency of a quartz element, yielding a mass resolution below 10 μg-typically 2-3 μg-for samples up to ∼500 mg. By placing the quartz element and optical sensor inside stainless steel pipes and providing heat from the outside, the instrument is applicable up to ∼62 bars and 700 °C. By surrounding this core part of the instrument with a suitable feed system and product analysis instruments, in combination with computer control and logging, time-resolved studies are enabled. The instrument with surrounding feed and product analysis infrastructure is fully automated. Emphasis has been put on making the instrument robust, safe, operationally simple, and user-friendly. We demonstrate the ISMA instrument on selected samples.

State-of-the-art in methane-reforming reactor modeling: challenges and new insights

The reforming of methane is an important industrial process, and reactor modeling and simulation is frequently employed as a design and analysis tool in understanding this process. While much research work is devoted to catalyst formulations, reaction mechanisms, and reactor designs, this review aims to summarize the literature concerning the simulation of methane reforming. Applications in industrial practice are highlighted, and the three main approaches to representing the reactions are briefly discussed. An overview of simulation studies focusing on methane reforming is presented. The three central methods for fixed-bed reactor modeling are discussed. Various approaches and modern examples are discussed, presenting their modeling methods and key findings. The overall objective of this paper is to provide a dedicated review of simulation work done for methane reforming and provide a reference for understanding this field and identifying possible new paths.

Connecting theory and simulation with experiment for the study of diffusion in nanoporous solids

Nanoporous solids are ubiquitous in chemical, energy, and environmental processes, where controlled transport of molecules through the pores plays a crucial role. They are used as sorbents, chromatographic or membrane materials for separations, and as catalysts and catalyst supports. Defined as materials where confinement effects lead to substantial deviations from bulk diffusion, nanoporous materials include crystalline microporous zeotypes and metal–organic frameworks (MOFs), and a number of semi-crystalline and amorphous mesoporous solids, as well as hierarchically structured materials, containing both nanopores and wider meso- or macropores to facilitate transport over macroscopic distances. The ranges of pore sizes, shapes, and topologies spanned by these materials represent a considerable challenge for predicting molecular diffusivities, but fundamental understanding also provides an opportunity to guide the design of new nanoporous materials to increase the performance of transport limited processes. Remarkable progress in synthesis increasingly allows these designs to be put into practice. Molecular simulation techniques have been used in conjunction with experimental measurements to examine in detail the fundamental diffusion processes within nanoporous solids, to provide insight into the free energy landscape navigated by adsorbates, and to better understand nano-confinement effects. Pore network models, discrete particle models and synthesis-mimicking atomistic models allow to tackle diffusion in mesoporous and hierarchically structured porous materials, where multiscale approaches benefit from ever cheaper parallel computing and higher resolution imaging. Here, we discuss synergistic combinations of simulation and experiment to showcase theoretical progress and computational techniques that have been successful in predicting guest diffusion and providing insights. We also outline where new fundamental developments and experimental techniques are needed to enable more accurate predictions for complex systems.