In this publication, the performance of a slurry bubble column reactor (SBCR) and a tube bundle reactor (TBR) are compared for steady-state and transient Power-to-Gas (PtG) operation. Transient PtG conditions are modeled using gas load step changes between 25 and 100% of the reactor maximum capacities in 1 s. For steady-state operation the TBR facilitates much higher gas hourly space velocities (GHSV) as compared to the SBCR. A sensitivity analysis shows that the TBR is limited by heat transfer, while the SBCR is limited by gas/liquid mass transfer. For transient PtG operation the TBR undergoes significant temperature changes within a short time resulting in out of specification product gas qualities and unacceptable temperature hot spots; the SBCR temperature shows marginal changes upon transient operating conditions, and the outlet gas composition sticks to the gas quality requirements. Finally, measures to improve the efficiency of both reactors are proposed considering dimensionless numbers. The GHSV of the SBCR can be enhanced by increasing the specific interfacial area controlling gas/liquid mass transfer, while the transient behavior of the TBR can be improved by reducing the catalyst concentration/activity or by mixing the catalyst with high heat capacity inert material in detriment of the GHSV. (C) 2019 Elsevier Ltd. All rights reserved.

The reaction kinetics of the three-phase CO2 methanation for a commercial Ni/SiO2 catalyst suspended in a liquid phase is studied in a continuous stirred-tank slurry reactor at a CO2 partial pressure of 1 bar and temperatures from 220 degrees C to 320 degrees C. By applying different liquids, namely squalane, octadecane, and dibenzyltoluene, showing different gas solubilities, it is found that the gas concentration in the liquid phase and not the partial pressure in the gas phase is the driving force for the CO2 methanation reaction kinetics. The liquid phase does not influence the reaction kinetics but reduces the available gas concentrations and H-2/CO2 ratio on the catalyst surface. Based on these findings, a kinetic rate equation for the three-phase CO2 methanation is developed additionally incorporating the chemical equilibrium limitations relevant in the temperature regime.

In a previous publication related to three-phase CO2 methanation (3PM) reaction kinetics (Lefebvre et al., 2018) it was postulated that (i) the liquid phase influences the effective reaction rate but not the intrinsic chemical reaction rate and (ii) gas concentration in the liquid phase, not gas partial pressure, is the relevant parameter to describe 3PM reaction kinetics. In this earlier publication, it was also reported that (iii) measurement uncertainties related to gas concentration in the liquid phase are high and (iv) catalyst reoxidation during the starting procedure of the three-phase experiments may not have been fully excluded. The aim of the present publication is to prove the postulates (i) and (ii). To achieve this, the two-phase CO2 methanation (2PM) reaction kinetics is investigated in a plug flow laboratory reactor. Using the data of 213 validated experiments, a power law kinetic rate equation is developed, which describes 2PM reaction kinetics on a commercially available catalyst for inlet CO2 partial pressures of 1 bar and temperatures between 200 degrees C and 300 degrees C. This two-phase kinetic rate equation is applied to calculate 3PM reaction rates using temperatures and gas concentrations in the liquid phase from previous 3PM experiments. It is shown that the two-phase kinetic rate equation can describe 3PM experiments with good agreement, i.e. a liquid phase does not influence the intrinsic reaction rate but the concentration of reacting species on the catalyst surface and gas concentration, not gas partial pressure, is the relevant parameter to describe the CO2 methanation reaction kinetics.

The CO₂ methanation reaction is highly exothermic, which makes reactor temperature control under dynamic operation conditions challenging. To tackle this challenge, a slurry bubble column reactor (SBCR) is an attractive reactor concept: The high heat capacity of the heat transfer liquid allows for isothermal process conditions and efficient heat extraction. To assess the dynamics of such a reactor and its potentials for the PtG process, dynamic SBCR simulation will be compared with the results of a dynamic simulation of a state-of-the-art adiabatic fixed-bed reactor. In order to clarify the influence of a liquid phase on the CO₂ methanation kinetics kinetic experiments with different heat transfer liquids are carried out in a CSTR at the same partial pressures or gas concentrations in the liquid phase. It will be shown that the gas concentration in the liquid phase is the rate determining factor for the description of the three-phase methanation kinetics. Additionally, experimental data on CO₂ methanation kinetics in a two-phase system will be provided and compared to results from three-phase system. It will be shown that the two-phase methanation kinetics can be applied to describe the three-phase methanation kinetics when the gas solubility in the heat transfer liquid is known.

Chemie Ingenieur TechnikVolume 88, Issue 9 p. 1261-1261 Vortrag CO2 Methanation in a Slurry Bubble Column Reactor – Influence of the Liquid Phase on the Reaction Kinetics and Reactor Design J. Lefebvre, Corresponding Author J. Lefebvre jonathan.lefebvre@kit.edu Karlsruher Institut für Technologie, Engler-Bunte-Institut, Chemische Energieträger Brennstofftechnologie, Engler-Bunte-Ring 1, 76131 Karlsruhe, DeutschlandKarlsruher Institut für Technologie, Engler-Bunte-Institut, Chemische Energieträger Brennstofftechnologie, Engler-Bunte-Ring 1, 76131 Karlsruhe, DeutschlandSearch for more papers by this authorDr.-Ing. S. Bajohr, Dr.-Ing. S. Bajohr Karlsruher Institut für Technologie, Engler-Bunte-Institut, Chemische Energieträger Brennstofftechnologie, Engler-Bunte-Ring 1, 76131 Karlsruhe, DeutschlandSearch for more papers by this authorProf. Dr.-Ing. T. Kolb, Prof. Dr.-Ing. T. Kolb Karlsruher Institut für Technologie, Engler-Bunte-Institut, Chemische Energieträger Brennstofftechnologie, Engler-Bunte-Ring 1, 76131 Karlsruhe, DeutschlandSearch for more papers by this author J. Lefebvre, Corresponding Author J. Lefebvre jonathan.lefebvre@kit.edu Karlsruher Institut für Technologie, Engler-Bunte-Institut, Chemische Energieträger Brennstofftechnologie, Engler-Bunte-Ring 1, 76131 Karlsruhe, DeutschlandKarlsruher Institut für Technologie, Engler-Bunte-Institut, Chemische Energieträger Brennstofftechnologie, Engler-Bunte-Ring 1, 76131 Karlsruhe, DeutschlandSearch for more papers by this authorDr.-Ing. S. Bajohr, Dr.-Ing. S. Bajohr Karlsruher Institut für Technologie, Engler-Bunte-Institut, Chemische Energieträger Brennstofftechnologie, Engler-Bunte-Ring 1, 76131 Karlsruhe, DeutschlandSearch for more papers by this authorProf. Dr.-Ing. T. Kolb, Prof. Dr.-Ing. T. Kolb Karlsruher Institut für Technologie, Engler-Bunte-Institut, Chemische Energieträger Brennstofftechnologie, Engler-Bunte-Ring 1, 76131 Karlsruhe, DeutschlandSearch for more papers by this author First published: 29 August 2016 https://doi.org/10.1002/cite.201650028AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume88, Issue9Special Issue: ProcessNet-Jahrestagung und 32. DECHEMA-Jahrestagung der Biotechnologen 2016September, 2016Pages 1261-1261 RelatedInformation

Methane can be produced via CO and CO2 methanation. However, the CO2 methanation is more relevant in the context of Power-to-Gas (PtG) applications. The two methanation reactions are accompanied by further reactions such as the reverse water gas shift reaction and the Boudouard reaction. Looking at the overall stoichiometry the CO2 methanation can be seen as the combination of the CO methanation with the reverse water-gas shift. The Boudouard reaction producing unwanted carbon deposits on methanation catalysts is a big challenge especially for the CO methanation but of minor importance for the CO2 methanation and therefore PtG applications.

The gas holdup is an important parameter for the design of slurry bubble columns. However, there is no correlation in literature to calculate the gas holdup of such reactors for industrially relevant conditions if the reactor is operated in the homogeneous regime. In this article, a novel correlation for calculating the gas holdup in the homogeneous and in the pseudo-homogeneous regimes is proposed. The correlation takes the relevant parameters into account: gas, liquid, and solid properties, sparger design, reactor diameter, and gas velocity. The correlation is also applicable for systems operated at elevated pressure and temperature.The correlation is based on 1199 data points, and it was developed by using the method of least squares. About two thirds of the data used were taken from literature (more than 20 research papers). The data from literature were carefully checked for confidence before using them for the correlation. >90 % of the data points are covered by the new correlation with a relative error of less than 30 %, the standard deviation is 17.8 % and the averaged relative error is 9.5 %. Finally, the correlation was successfully validated with measurements which were not used to fit the correlation.An Excel file for using the developed correlation can be found in the Supplementary material.

Hydrodynamics (e.g. gas holdup, bubble size, and flow regime) significantly influences the performance of slurry bubble column reactors. In this work, the influence of gas, liquid, and solid phase properties on the hydrodynamics was investigated at temperatures up to 573K and pressures up to 0.5MPa. Amongst the investigated liquids, the hydrodynamic behavior of ionic liquids at elevated temperatures is ruled by their high surface tension leading to small gas holdups and formation of large bubbles compared with heat transfer oils.The solids strongly influence the hydrodynamics but their effects are still not fully understood. Therefore, the behavior of solids was investigated in this work. The results indicate that small concentrations of fine particles reduce bubble coalescence and subsequently stabilize the homogeneous regime. However, the primary bubble size increases with the addition of solids. Furthermore, it has been shown that the gas holdup decreases with an increasing difference between particle and liquid density.

Methane production from syngas goes back to more than 100 years of research and process development. Early developments (1970-1980) using syngas from coal gasification plants primarily focused on fixed-bed and fluidized-bed methanation technologies. Temperature control and catalyst deactivation, e.g. caused by fouling and mechanical stress, were key issues of investigation.Due to the debate about a sustainable energy supply, research on methanation has been intensified during the last ten years. Novel reactor developments comprise e.g. micro reactors and three-phase reactors aiming at an advanced temperature control and a reduced complexity of future methanation plants. The developments are supported by detailed modeling and simulation work to optimize the design and dynamic behavior.To accompany and facilitate new methanation developments, the present work is aimed at giving researchers a comprehensive overview of methanation research conducted during the last century. On one hand, application-orientated research focusing on reactor developments, reactor modeling, and pilot plant investigation is reviewed. On the other hand, fundamentals such as reaction mechanisms and catalyst deactivation are presented. (C) 2015 Elsevier Ltd. All rights reserved.

The performance of a slurry bubble column reactor was evaluated for its application as a methanation reactor. The influences of the reactor pressure (5 to 20 bar), temperature (275 to 325 degrees C), gas velocity (0.8 to 1.6 cm/s), catalyst concentration (1.6 to 9 vol.%) as well as reactant partial pressures (H-2/CO2 ratio from 3.8 to 6.3) on the reactor performance were assessed and optimal process conditions for substitute natural gas production were identified. An increase in pressure, temperature, and H-2/CO2 ratio improves the reactor performance. The optimal catalyst concentration depends on the operating conditions. Under the experimental conditions of the work presented in this paper, a concentration of 6.5 vol.% led to the highest conversion rates. Additionally, the dynamic behavior of the three-phase methanation reactor was investigated using inlet gas velocity step changes to simulate load variation of a power-to-gas facility. The reactor showed rapid adaptation while maintaining an isothermal temperature profile. (C) 2014 Elsevier B.V. All rights reserved.

The Power-to-Gas (PtG) process chain could play a significant role in the future energy system. Renewable electric energy can be transformed into storable methane via electrolysis and subsequent methanation.This article compares the available electrolysis and methanation technologies with respect to the stringent requirements of the PtG chain such as low CAPEX, high efficiency, and high flexibility.Three water electrolysis technologies are considered: alkaline electrolysis, PEM electrolysis, and solid oxide electrolysis. Alkaline electrolysis is currently the cheapest technology; however, in the future PEM electrolysis could be better suited for the PtG process chain. Solid oxide electrolysis could also be an option in future, especially if heat sources are available.Several different reactor concepts can be used for the methanation reaction. For catalytic methanation, typically fixed-bed reactors are used; however, novel reactor concepts such as three-phase methanation and micro reactors are currently under development. Another approach is the biochemical conversion. The bioprocess takes place in aqueous solutions and close to ambient temperatures.Finally, the whole process chain is discussed. Critical aspects of the PtG process are the availability of CO2 sources, the dynamic behaviour of the individual process steps, and especially the economics as well as the efficiency.

Conversion of electric power into chemical energy carriers plays a key role in many concepts for a future energy supply based on renewable sources. ́Power-to-X ́ technologies like the methanation of CO2 allow long-term energy storage and compensation of fluctuations in renewable energy. Structural characterization of methanation catalysts under realistic and dynamic reaction conditions [1] using methods like X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) provides valuable information for a knowledge-based optimization. Ni-based catalysts for the methanation of CO2 were characterized in quartz capillaries heated by a gas blower with operando XAS at the KIT synchrotron (XAS and CAT-ACT beamlines, [2]), and with Quick Scanning XAS at the Swiss Light Source (SuperXAS, [3]). A fluctuating H2 supply was simulated by temporary removal of H2 from the feed gas [4]. Within the German BMBF project “Kopernikus Power-to-X” these studies were continued at elevated pressure to approach industrial relevant conditions and by including a commercial Ni-based catalyst used in three-phase methanation of CO2 [5]. At CAT-ACT, a set-up for combined XAS and XRD was implemented. Operando XAS studies on Ni-based catalysts for twoand three-phase methanation of CO2 at atmospheric pressure provided insights into deactivation mechanisms during methanation under dynamic feed conditions. The results revealed that all investigated catalysts were stable under methanation conditions at atmospheric pressure. H2 dropouts caused partial oxidation of the catalytically active Nito Ni-species resulting in a lower activity during subsequent methanation cycles. XRD data indicated formation of a NiO phase. No NiCO3 reflections were observed. A regeneration of the catalysts without a loss in activity was achieved by reduction in H2/N2. The combined XAS-XRD experiments provided detailed complementary structural information about the changes in Ni-based catalysts during methanation of CO2 and under more dynamic feed conditions. All catalysts were stable during CO2 methanation but immediately oxidized in CO2/N2 (H2 dropout, technical CO2). A regeneration to restore the initial activity was achieved by reduction in H2/N2. In order to further approach industrially relevant conditions (elevated pressure, low space velocity) a new high pressure operando cell for combined XAS-XRD is now tested, and the operando studies on Ni-based catalysts for twoand three-phase methanation of CO2 will be continued to further investigate the structural changes. More complex processes like three-phase methanation will be studied in liquid phase using an in situ batch cell based on ref. [6].