Methane Pyrolysis Research Articles

Hydrogen and Solid Carbon Production via Methane Pyrolysis in a Rotating Gliding Arc Plasma Reactor.

Plasma-induced methane pyrolysis is a promising hydrogen production method. However, few studies have focused the decomposition of pure methane as a discharge gas. Herein, a rotating gliding arc reactor was used for the conversion of methane (discharge gas and feedstock) into hydrogen and solid carbon. Methane conversion, gaseous product selectivity, and energy usage efficiency(specific energy requirement for hydrogen production(SER)) were investigated as functions of operating parameters, e.g., specific energy input(SEI), residence time, and reactor design. SEI was positively(almost linearly)correlated with methane conversion and hydrogen yield and negatively correlated with SER. Conversion and efficiency of energy usage increased when reactor designs providing higher thermal densities were used. With the increasing flow rate of methane at constant SEI, the reaction volume and, hence, the residence time of the gas inside the reaction zone increased, which resulted in methane conversion and hydrogen selectivity enhancement. The solid carbon featured four distinct domains, namely graphitic carbon, turbostratic carbon, few-layer graphene, and amorphous carbon, which indicated a nonuniform temperature distribution in the reaction zone. But it seems that graphitic carbon dominates amorhphous one. This study highlights the potential of rotating gliding arc plasma systems for efficient methane conversion into hydrogen and valuable solid carbon products.

Characterization of particles generated by non-catalytic methane pyrolysis in a tubular flow reactor

Characterization of particles generated by non-catalytic methane pyrolysis in a tubular flow reactor

Current hydrogen production methods and their economic and environmental analysis

As global temperatures continue to rise due to the extensive use of fossil energy sources, concerns about the environment continue to deepen. Accelerating the energy transition is a major trend, and countries are continuously increasing the proportion of clean energy in the energy supply. Hydrogen energy is one of the most promising clean energy sources and a hot research topic in various countries. Hydrogen production is a key step in the use of hydrogen energy, this paper focuses on the current mainstream hydrogen production methods including electrolysis of water, solar decomposition of water, biomass hydrogen production, nuclear technology, steam methane reforming, coal gasification, methane pyrolysis, etc. And the economic and environmental benefits of each method. According to studies, the mainstream method of producing hydrogen today involves burning fossil fuels, and more recent methods—like the electrolysis of water—need a lot more testing and development before they can be used extensively. The implementation of CCS or CCUS technology can considerably lower the carbon emissions of the hydrogen production process when it comes to hydrogen produced from fossil fuels, but doing so will result in higher energy costs and hydrogen production costs. This paper is expected to support future research directions and help governmental decision-making in the energy transition.

CO2-free production of hydrogen via pyrolysis of natural gas: influence of non-methane hydrocarbons on product composition, methane conversion, hydrogen yield, and carbon capture

Methane pyrolysis represents a CO2-free hydrogen production route that enables simultaneous carbon capture. While the majority of previous studies in the field focus on pure CH4 as feed gas stream, commercial processes will typically rely on natural gas as feedstock that contains also non-methane hydrocarbons such as ethane, propane, and n-butane. Therefore, the present study evaluates how CH4 conversion, H2 selectivity, product composition, and solid carbon yield evolve when using either pure CH4 or synthetic natural gas (SNG) as feed gas stream for a thermal pyrolysis process in a lab-scale high-temperature reactor. For this, industrially viable conditions are applied, namely temperatures between 1000 °C and 1600 °C, residence times between 1 s and 7 s, and molar H2 dilution ratios between 1:1 and 4:1. Although the use of SNG results in slightly lower hydrocarbon conversions because the additional components in SNG result in a higher effective H2 dilution ratio compared to a CH4-only feed, the non-methane hydrocarbons in the SNG have a positive effect on both H2 selectivity and solid carbon yield. Taking existing mechanistic understanding into account, these positive effects are attributed to radicals formed from the non-methane hydrocarbons, which facilitate dehydrogenation steps from ethane to ethylene and hereby increase the relative amount of H2 originating from CH4. The introduction of a carbonaceous fixed bed further benefits the performance of the pyrolysis process and ultimately enables to capture more than 98% of carbon in its solid form under industrially viable process conditions.

A kinetic study of nonthermal plasma pyrolysis of methane: Insights into hydrogen and carbon material production

Nonthermal plasma-assisted methane pyrolysis has emerged as a promising approach for hydrogen production under mild conditions while simultaneously yielding valuable carbon materials. Herein, we develop a plasma chemical kinetic model to elucidate the underlying reaction mechanisms involved in methane pyrolysis to hydrogen and solid carbon within a gliding arc (GA) reactor. A zero-dimensional (0D) chemical kinetics model was developed to simulate the plasma chemistry during the GA-based methane pyrolysis process, incorporating reactions involving electrons, excited species, ions, and heavy species. The model accurately predicted methane conversion and product selectivity in agreement with the experimental data. A strong correlation between hydrogen production and methane conversion was observed, primarily driven by the reaction CH4 + H → CH3 + H2, contributing 44.2% to hydrogen formation and 37.7% to methane depletion. Electron impact collisions with hydrocarbons play a secondary role, accounting for 31.1% of H2 formation. This work provides a detailed investigation into the mechanism of solid carbon formation in GA-assisted methane pyrolysis. Most of the solid carbon originates from the electron impact dissociation of C2H2 through reactions e + C2H2 → e + C2 + H2/2H and subsequent C2 condensation. C2 radicals are highlighted as the major contributors to solid carbon formation, accounting for 95.0% of the total carbon yield, which might be due to the relatively low C–H dissociation energy in C2H2. This kinetic study offers a comprehensive understanding of the mechanisms behind H2 and solid carbon formation during GA-assisted methane pyrolysis.

Simulation of a Microwave Plasma Torch Used for Hydrogen Production via Methane Pyrolysis

ABSTRACTHydrogen is often envisioned as a green fuel and energy carrier. However, a greenhouse gas‐free production method is still needed for this purpose. A promising method is the pyrolysis of methane. In this study, we present the three‐dimensional simulation of methane pyrolysis in a microwave plasma torch operated in an argon–methane mixture. Due to the high gas temperatures, the chemistry is dominated by reactions between neutral particles. Therefore, the plasma is treated only as a heat source using space‐resolved gas temperature measurements as input. The end‐of‐pipe results of the simulation are compared to measured values, showing good agreement for methane conversion.

On the Role of Anions in Solid Catalysts with Ionic Liquid Layer (SCILL) for the Selective Hydrogenation of Highly Concentrated Acetylene Streams.

Electric plasma assisted pyrolysis of methane represents a highly promising greener alternative to produce ethylene from biogas and renewable energies compared to conventional steam cracking of naphtha. The mediocre performance of typical Pd-Ag catalysts for the downstream purification of the substantially higher concentrated acetylene impurities (≥15 vol.-%) in those ethylene streams via selective hydrogenation is yet limiting economic interest. Following the concept of solid catalysts with ionic liquid layer (SCILL), we have modified an intrinsically non-selective palladium catalyst with imidazolium based ionic liquids varying among 10 different anions and investigated them in this reaction. The best performing [C4C1IM][MeSO4]-SCILL reaches an outstanding average ethylene selectivity over 20 h on-stream of 82 % at full acetylene conversion without any sign of deactivation, clearly outperforming conventional Pd-Ag catalysts. By varying parameters like ionic liquid (IL) loading, temperature, feed gas composition, cations, and by using XPS for surface analysis we could gain a very comprehensive understanding of the underlying mechanisms that reduce the competing over-hydrogenation and oligomerisation side-reactions.

A Carbon Capture and Utilization Process for the Production of Solid Carbon Materials from Atmospheric CO2 - Part 2: Carbon Characterization.

This article is the second part of a study reporting the results of a novel carbon capture and utilization (CCU) process, which converts atmospheric CO2 into solid carbon materials. The CCU process combines direct air capture (DAC) with catalytic methanation, which is then followed by methane pyrolysis in a reactor filled with liquid tin. While Part 1 discussed the performance of the overall process and individual process steps regarding conversions and yields, Part 2 characterizes the solid carbon products obtained under various synthesis conditions. The effects of the pyrolysis temperature and the composition of the gas mixture from the methanation step on the solid carbon product are analyzed. Carbon powder is synthesized from methane with either H2 or CO2 as most important impurity. Carbon samples are characterized using SEM, TEM, Raman spectroscopy, XPS and XRD analysis. Very thin, disordered carbon flakes, soot aggregates and large carbon onions are identified as the main solid products of the process. Their formation mechanisms in the liquid metal-filled pyrolysis reactor are discussed.

A Carbon Capture and Utilization Process for the Production of Solid Carbon Materials from Atmospheric CO2 - Part 1: Process Performance.

The successful operation of a process that converts atmospheric CO2 into solid carbon products is presented as an alternative to fossil based solid carbon production. In a first step, CO2 is removed from the atmosphere by a direct air capture (DAC) unit. The gas is then mixed with hydrogen and enters a methanation unit. Depending on the operation conditions, gas mixtures consisting of mainly methane with either H2 or CO2 as side-component are obtained. After precipitating the water formed during the methanation step, the remaining gas mixture is fed into a bubble column reactor filled with liquid tin. During the rise of the gas bubbles, methane is thermally split up into hydrogen and solid carbon. The latter is continuously removed from the liquid metal surface as a fine powder by pneumatic conveying. This article is the first of two articles, focusing on the performance of the methanation and methane pyrolysis steps. The experimental results are complemented by thermodynamic analyses and reaction modelling. A detailed analysis of the solid carbon product of the process is presented in the second part.

Developing methane pyrolysis as a viable alternative for hydrogen production

Methane pyrolysis using molten media can produce hydrogen with no greenhouse gas emissions.

Literature Review on Thermodynamic and Kinetic Limitations of Thermal Decomposition of Methane

The state of the art in methane pyrolysis does not yet provide a definitive answer as to whether the concept of an elementary reaction is universally applicable to the apparently simple process of methane dissociation. Similarly, the literature currently lacks a comprehensive and unambiguous description of the methane pyrolysis process and, in particular, a single model that would well represent its course at both the micro and macro scales. Given the wide range of conditions under which this reaction can occur—whether thermal or thermo-catalytic, in solid or fluidized bed reactors—it is crucial to evaluate the usefulness of different kinetic models and their compatibility with basic thermodynamic principles and design assumptions. To address these research gaps, the authors analysed the thermodynamic and kinetic dependencies involved in the thermal decomposition of methane, using the synthesis of methane from its elemental components and its reversibility as a basis for exploring suitable kinetic models. Using experimental data available in the literature, a wide range of kinetic models have been analysed to determine how they all relate to the reaction rate constant. It was found that regardless of whether the process is catalytic or purely thermal, for temperatures above 900 °C the reversibility of the reaction has a negligible effect on the hydrogen yield. This work shows how the determined kinetic parameters are consistent with the Kinetic Compensation Effect (KCE) and, by incorporating elements of Transition State Theory (TST), the possibility of the existence of Entropy–Enthalpy Compensation (EEC). The indicated correspondence between KCE and EEC is strengthened by the calculated average activation entropy at isokinetic temperature (∆SB=−275.0 J·(mol·K)−1). Based on these results, the authors also show that changes in the activation energy (E=20–421 kJ·mol−1) can only serve as an estimate of the optimal process conditions, since the isoconversion temperature (Tiso=1200−1450 K>Teq) is shown to depend not only on thermodynamic principles but also on the way the reaction is carried out, with temperature (T) and pressure (P) locally compensating each other.

Investigating the formation of soot in CH4 pyrolysis reactor: A numerical, experimental, and characterization study

Methane pyrolysis is a promising method for eco-friendly hydrogen production, but soot formation and carbon interaction pose challenges for scaling up. Therefore, understanding the dynamics of soot formation and carbon deposition is crucial. This study delves into the intricacies of soot formation in methane pyrolysis under industrially relevant conditions, namely operations at atmospheric pressure, employing a H2:CH4 ratio of 2 and exploring a range of hot zone temperatures (1473 K, 1573 K, 1673 K, and 1773 K) with a 5 s residence time. Utilizing a detailed gas-phase kinetic model with direct carbon deposition reactions, the research adopts the method of moments coupled with a one-dimensional plug flow reactor model to simulate soot formation. The model is validated by characterizing soot particles that were produced in a pyrolysis reactor by means of transmission electron microscopy, Dynamic light scattering (DLS), and Raman spectroscopy. Results show that lower temperatures lead to nucleation-dominated growth, whereas higher temperatures significantly restrain particle growth due to carbon deposition. DLS data indicate a complex balance between particle growth and deposition processes. These findings provide insights into operational parameters that can enhance reactor performance and sustainability in hydrogen production processes by mitigating soot and carbon deposition.

Hydrodynamics of molten media bubble columns for hydrogen production through methane pyrolysis

Methane pyrolysis using a molten media bubble column reactor is a promising technique for hydrogen production with low carbon dioxide emissions at a feasible price. Understanding the bubble dynamics in molten media is essential to elucidate the reaction mechanisms and establish design requirements for efficient reactors. Computational fluid dynamics provides an effective means to understand the hydrodynamics in opaque molten media. This research used the volume of fluid method to study the effects of gas injection rate as well as variations in gas and molten media (iron, aluminum, and a salt mixture of sodium bromide and potassium bromide in a 48.7:51.3 molar ratio) properties on bubble dynamics. The computational model was first validated using existing experimental and empirical observations. This study makes fundamental contributions to the understanding of bubble dynamics in molten media. First, it was confirmed that gas properties had a small effect on bubble dynamics. The difference in bubble diameters between argon at ambient temperature and 1600 °C was less than 10%. Second, it was found that the volumetric gas injection rate and molten media properties significantly impacted the bubble dynamics, including the bubble diameter and flow regime. Future work will build on these findings to recommend appropriate operating conditions and molten media for specific pyrolysis reactor designs.

Nonprecious Single Atom Catalyst for Methane Pyrolysis.

The development of a suitable catalytic system for methane pyrolysis reactions requires a detailed investigation of the activation energy of C-H bonds on catalysts, as well as their stability against sintering and coke formation. In this work, both single-metal Ni atoms and small clusters of Ni atoms deposited on titanium nitride (TiN) plasmonic nanoparticles were characterized for the C-H bond activation of a methane pyrolysis reaction using ab initio spin-polarized density functional theory (DFT) calculations. The present work shows the complete reaction pathway, including energy barriers for C-H bond activation and dehydrogenated fragments, during the methane pyrolysis reaction on catalytic systems. Interestingly, the C-H bond activation barriers were low for both Ni single-atom and Ni-clusters, showing the energy barriers of ~1.10 eV and ~0.88 eV, respectively. Additionally, single-atom Ni-TiN showed weaker binding to adsorbates, and a net endothermic reaction pathway indicated that the single-atom Ni-TiN was expected to resist coke formation on its surface. However, these Ni single-atom catalysts can sinter, aggregate into a small cluster, and form a coke layer from the highly exothermic reaction pathway that the cluster takes despite the facile reaction pathway.

Performance Analysis of a Self-Decarbonizing Combustor

Abstract Hydrogen is envisioned to be a key decarbonization solution for fossil fuel-dependent power generation and aviation industries. At present, a significant fraction of the generated electrical power is derived from natural gas. As such, the external energy needed for hydrogen generation, often sourced from fossil fuels, results in CO2 emissions, compromising overall carbon neutrality. Instead, the processes of hydrogen generation can be energetically coupled with the combustion process, in situ, to eliminate external energy requirements. To that end, a novel self-decarbonizing combustor (SDC) has been conceptualized, integrating methane pyrolysis with the combustion process that can in principle decarbonize many contemporary power generation technologies. The underpinning methane pyrolysis process enables in situ pre-combustion capture of solid carbon, while simultaneously generating hydrogen. Consequently, CO2 emissions resulting from the combustion of processed, hydrogen-enriched fuel are mitigated. This study provides a comprehensive analysis, delineating the operating principle and the effect of some of the important governing parameters on the performance of the self-decarbonizing combustor. These parameters, including fuel temperature, residence time, pressure, and catalysis, are studied in the context of potentially applying the proposed concept to natural gas-based decarbonized electrical power generation. Investigating fuel chemistry, combustion exhaust, and carbon structure and morphology under varying process parameters enhances our comprehension of the SDC. Additionally, its self-sufficient nature eliminates the need for separate hydrogen production, storage, and transportation infrastructure, highlighting its potential as a scalable and realizable technology.

Solar methane pyrolysis in a liquid metal bubble column reactor: Effect of medium type and gas injection configuration

Solar methane pyrolysis in different molten media and reactor configurations was experimented to improve hydrogen production. Pure Sn, Ni0.18Sn0.82, Cu0.45Bi0.55, and KCl melts were compared at three different temperatures (1030–1130–1230 °C), and no significant difference was observed except for KCl and only at 1230 °C (XCH4 = 72 % vs. 57 % for pure Sn). This enhanced performance was attributed to possible carbon dispersion in the salt, which probably modified the physical properties and enhanced hydrodynamics. A porous quartz sparger (downward injection) did not significantly enhance the bubbles hydrodynamics, mainly because bubbles were trapped and coalesced below the sintered disc. A custom-made sparger (lateral bubbling) did not either improve conversion due to non-uniform pores. A sparger with an upward injection should be preferred to generate small bubbles with longer residence time. When a solid bed of tungsten carbide particles was placed around the injector, overlaid by molten tin, the conversion was improved even at a relatively low temperature (XCH4 = 17 % at 1030 °C). The immersed bed likely behaved as a porous device and increased the gas-solid surface contact. Combining particle bed and liquid bubbling system is very promising for further optimization of methane pyrolysis in molten media. The carbon collected above molten metals showed mostly a sheet-like structure with significant metal contamination. In case of KCl, most carbon was entrained with the gas, while the remaining was mixed with KCl in the reactor. The density of KCl is close to that of carbon, which prevented a good separation.

Catalytic and non-catalytic reactions of methane pyrolysis for hydrogen production in screening and electromagnetic levitation reactors using computational fluid dynamics

Molten metal (MM)-based methane (CH4) pyrolysis is a promising technology for clean hydrogen production with a minimal carbon footprint. Electromagnetic levitation (EMLR) and screening reactors (SR) were used to investigate the intrinsic catalytic reaction kinetics of MM-based CH4 pyrolysis. Heterogeneous catalytic reactions in the SR and EMLR occurred on the surfaces of the MM crucible and droplet, respectively. However, a homogenous non-catalytic reaction may occur just above the surface because the CH4 gas is preheated by the high-temperature MM. This study presents three-dimensional (3D) computational fluid dynamics (CFD) model coupled with chemical reactions to assess the extent to which non-catalytic reactions intervene in CH4 pyrolysis in both the SR and EMLR, which is difficult to measure experimentally. The CFD model validated against experimental data revealed that the non-catalytic reaction accounted for 4.0 % of CH4 pyrolysis in the CH4-Ni0.27Bi0.73 SR at 1045 °C, whereas it represented 0.02 % in the CH4-Sn EMLR at 1021 °C. This result highlights that the EMLR is suitable for studying the intrinsic catalytic reaction kinetics of MM-based CH4 pyrolysis because the non-catalytic reaction occurs to a lesser extent.

Dry Reforming of Methane to Syngas Mediated by Rhodium-Cobalt Oxide Cluster Anions Rh2CoO.

Dry reforming of methane (DRM) to syngas is an important route to co-convert CH4 and CO2. However, the highly endothermic nature of DRM induces the thermocatalysis to commonly operate at high temperatures that inevitably causes coke deposition through pyrolysis of methane. Herein, benefiting from the mass spectrometric experiments complemented with quantum chemical calculations, we have discovered that the bimetallic oxide cluster Rh2CoO- can mediate the co-conversion of CH4 and CO2 at room temperature giving rise to two free H2 molecules and two adsorbed CO molecules (COads). The only elementary step requiring the input of external energy (e.g., high temperature) is desorption of COads from the reaction intermediate Rh2CoOC2O2-. The doping effect of Co has also been clarified that the Co could tune the charge distribution and orbital energy of the active metal Rh, enabling the enhancement of cluster reactivity toward C-H activation, which is essential to facilitating the DRM to syngas. This work not only underlines the importance of temperature control over elementary steps in practical thermocatalysis but also identifies a promising active species containing the late 3d transition metal to drive DRM to syngas. The findings could provide novel insights into design of bimetallic catalysts for co-conversion of CH4 and CO2 at low temperatures.

Local Thermochemical Mechanisms in Direct Solar Graphite Synthesis from Methane.

Methane pyrolysis is known to produce hydrogen and solid carbon in a variety of thermal processes. However, the generated carbon product typically belongs to a low-value amorphous type. Here, we elucidate the thermochemical mechanisms of a reaction that produces high-quality graphite via direct solar methane pyrolysis on a porous substrate. By comparing graphite deposition rates and local reaction zone temperatures of exposed and shadowed regions from the same experiment, we clarify the effects of thermolysis and photolysis in this emission-free process that both decarbonizes a fuel and produces a critical material for the sustainable energy transition.

Near-zero emission trigeneration system coupling molten salt methane pyrolysis with solid oxide fuel cell based on carbon capture and utilization: Thermodynamic and exergoenvironmental evaluation

Natural gas-based energy systems have garnered widespread attention for their potential to facilitate the transition from traditional to renewable energy sources. Among these, methane pyrolysis technology stands out as a promising pathway. Consequently, a novel methanol-electricity-carbon trigeneration system featuring methane pyrolysis coupled with chemical looping combustion, methanol synthesis, and solid oxide fuel cell unit was designed. To validate this innovative concept, thermodynamic model of the process was developed. Compared to conventional single-generation system, the proposed system demonstrated superior thermodynamic performance, with energy efficiency of 69.51 %, representing improvement of 28.78 %. Sensitivity analysis indicated that optimal carbon utilization-to-storage ratio of 0.68 effectively balanced environmental benefits with energy conversion efficiency. Additionally, the CO2 capture rate and emission of the proposed system reached impressive 99.24 % and 2.15 kg/MWh, respectively, confirming its carbon mitigation potential. Based on this, exergoenvironmental analysis demonstrated that rb,k of the novel system was 21.14 %, indicating room for further environmental impact reduction. Moreover, due to the high rb,k of 16.61 % for the preheater-2 identified as a key component for optimization. Finally, the economic analysis verified the system’s feasibility, showing the annual net income of 6774.06 k$. This novel concept highlights the potential of natural gas-based systems in optimizing carbon utilization and energy efficiency, contributing to a more environmentally sustainable energy infrastructure.