Methane Pyrolysis in a Liquid Metal Bubble Column Reactor: A Model Approach Combining Bubble Dynamics with Byproduct and Soot Formation

Abstract

Methane pyrolysis is a promising bridging technology to mitigate the effects of climate change. By decarbonizing natural gas, hydrogen can be produced from fossil fuels without creating CO2 emissions. The focus of future process optimization should not only be on the hydrogen yield and the energy efficiency but also on the carbon products and possible byproduct formation. During methane pyrolysis in a liquid metal (LM) bubble column reactor, at least two very distinct types of carbon are synthesized: soot particles and graphene‐like carbon sheets. A model is presented that couples a description of bubble dynamics in a LM bubble column reactor with a kinetic mechanism, originally developed for the combustion of natural gas that includes byproduct and soot formation. The model is validated by comparing it with an experimental dataset that covers a broad range of process conditions and the implications for carbon and byproduct formation are discussed. The good agreement of model results and experimental data shows that the combustion kinetic mechanism may be applied to methane pyrolysis and that the selected way of modeling bubble fluid dynamics in LM results in a good estimation of the actual bubble residence time in the optically nonaccessible liquid.

Recent progress in melt pyrolysis: Fabrication and applications of high‐value carbon materials from abundant sources

“…33 In a recent study using molten Sn, Uhlenbruck et al identified two types of carbon structures formed during high-temperature methane pyrolysis in molten tin. 34 Employing a mathematical model they developed to encapsulate methane pyrolysis, they observed the formation of lamellar graphite carbon and carbon black aggregates via C 2 H x species pyrolysis. In Wang's study, it was determined that in the presence of Mg, XRD and SEM analyses identified the produced carbon as amorphous carbon (Figure 5B,C).…”

Emerging Liquid Metal Catalysts

“…Because the liquid metal has a higher density than the pyrolytic carbon, carbon can accumulate on the surface of liquid metal, and then it can be easily separated. Wetzel et al proposed a liquid metal bubble column reactor, in which liquid Sn is used as the working fluid profited from the high density in contrast to carbon, high thermal conductivity, good chemical stability, and nontoxicity . In addition, the influencing factors, including the temperature distribution of liquid metal, gas flow rate, and so on, were thoroughly investigated. − Furthermore, the liquid metal can be used as a low-temperature solvent to combine with the active metal to form a liquid alloy.…”

Technology Development for the Pyrolysis of Hydrocarbons in Liquid Metal

“…Many chemical compounds can act as intermediates, such as ethane, ethylene, acetylene, etc. [8]. The composition of the pyrolysis products in the gas mixture depends on the temperature, pressure and other conditions under which the process is operated.…”

“…The use of liquid metals in the bubble column not only avoids clogging of the chemical reactor, but also results in a number of other advantages. Thus, the use of a bubble column, where the reagent gas rises from the bottom in the form of numerous bubbles, results in the continuous renewal of the active surface area for the reaction, as the chemical reactions are assumed to take place at the bubble interface and inside of the gas bubble as discussed in publications [8] addressing the formation of different kinds of carbon. In addition, the good thermal conductivity of metals and the hydrodynamics of popping bubbles intensify the heat exchange within the reactor, which also has a beneficial effect on methane pyrolysis.…”

“…The process is currently under investigation and the results including the selectivity of the entire process will be published in detail in a separate publication in the near future. The hydrogen selectivity of the methane pyrolysis process at various process parameters has also been considered in [8,10]. In general, only small amounts of by-products (ethane, ethene) have been detected in the product gas in previous studies.…”