Methane Pyrolysis: Design and Modeling of a Liquid Metal Bubble Column Reactor
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gilleland-bhgillel-msme-meche-2026-thesis.pdf
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Author(s)
Gilleland, Braden
Advisor(s)
Henry, Asegun
Barton, Paul
Date Issued
February 2026
Publisher
Massachusetts Institute of Technology
Abstract
Hydrogen is an important commodity, and a potential carrier of the renewable energy needed to mitigate climate change. However, contemporary hydrogen processes contribute more than 2% of global CO₂ emissions. To realize hydrogen’s potential, a CO₂-free process is needed. While electrolysis is the typical solution, it requires large amounts of electricity and expensive catalysts. Hydrocarbon or Methane pyrolysis (HP or MP) is a process which requires less energy than even today’s processes, while having virtually no CO₂ emissions. It does this by heating a hydrocarbon feedstock – typically natural gas – in an anoxic environment, decomposing it into hydrogen and solid carbon. Despite decades of effort, HP hasn’t yet been deployed at scale. This thesis introduces a novel reactor concept which overcomes past challenges and develops a reactor model to use in later design optimization. The goal of this work is to design an HP process that leverages HP’s attributes to approach cost-parity with today’s processes. To inform the reactor design, the hydrocarbon pyrolysis literature is first surveyed. This includes the thermodynamics and kinetics of the reaction, as well as previous efforts. Using the insights from this review, the proposed system design is next introduced. It is a liquid metal bubble column (LMBC) reactor which uses entirely ceramic materials to enable operation at ~1300 °C, which the thermodynamics and kinetics showed is necessary to achieve the highest purities (~98%) and short residence times (< 1 sec.). To reduce energy costs associated with operating at such high temperatures, the reactor is designed to enable direct heat recuperation. This is done by making the reactor essentially a shell and tube heat exchanger, where a counterflow stream of tin provides the sensible and reaction heat needed in the reactor. The cold tin stream is then partially reheated by the hydrogen. Other details of the process design are also discussed, including carbon separation, recovery of tin contaminating the carbon, heat exchanger design, hydrogen purification, and the potential of using biomass or plastic as feedstocks. Discussion of the reactor model follows. It begins with a review of past efforts to model bubble dynamics and bubble columns, and includes surveys of bubble formation dynamics, bubble drag coefficients, bubble column flow regimes, and modeling approaches for bubble columns, for which there is no standard approach. A new Single Bubble Model (SBM) is then introduced which applies some of the methods surveyed. It considers the transit of a single bubble through a liquid tin column, resolving: the initial bubble size, the kinematics of the bubble, conductive heat transfer within the bubble, the reaction, and bubble growth. It assumes that bubbles do not interact with each other or the liquid, that no convection occurs within the bubble, and that the bubble is spherical. This gives a conservative impression of the performance, and it has a negligible computational cost, allowing for large parametric studies. This allows us to select experimental conditions and consider the design of an industrial system. Despite the simplifying assumptions, the SBM is also used to give an impression of how coalescence and liquid circulation might degrade the performance. Nonetheless, it cannot predict the actual performance of an industrial system. Accordingly, plans for more advanced model incorporating bubble coalescence, breakage, and liquid circulation are discussed at the end.
MIT Department
Massachusetts Institute of Technology. Department of Mechanical Engineering
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