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Methane pyrolysis in molten salts has the potential to provide low-cost, low-CO2 emission H2 on an industrial scale. The alkali halides (NaBr, KBr, KCl, NaCl, (Na,K)Br) are inexpensive and environmental benign salts, which may facilitate sequestration or sales of the produced carbon even if low-to-moderate amounts of salt remain trapped in the carbon. In this novel work, alkali halides have been tested as the liquid reaction media, and the results of kinetic measurements and carbon characterisation are reported. The observed activation energies were found to be in the range 223.5–277.6 kJ mol−1, which is significantly lower than those measured during gas-phase methane pyrolysis (~422 kJ mol−1). After washing procedures with deionised water, the purity of the produced carbon was in the range 91.7–97.4 atom% or 55.0–91.6 wt%, with the carbon purities correlating well with the salt compounds size and salt-carbon wettability. The carbon samples generated in each salt are all low density (

Different technologies produce hydrogen with varying cost and carbon footprints over the entire resource supply chain and manufacturing steps. This paper examines the relative costs of carbon mitigation from a life cycle perspective for 12 different hydrogen production techniques using fossil fuels, nuclear energy and renewable sources by technology substitution. Production costs and life cycle emissions are parameterized and re-estimated from currently available assessments to produce robust ranges to describe uncertainties for each technology. Hydrogen production routes are then compared using a combination of metrics, levelized cost of carbon mitigation and the proportional decarbonization benchmarked against steam methane reforming, to provide a clearer picture of the relative merits of various hydrogen production pathways, the limitations of technologies and the research challenges that need to be addressed for cost-effective decarbonization pathways. The results show that there is a trade-off between the cost of mitigation and the proportion of decarbonization achieved. The most cost-effective methods of decarbonization still utilize fossil feedstocks due to their low cost of extraction and processing, but only offer moderate decarbonisation levels due to previous underestimations of supply chain emissions contributions. Methane pyrolysis may be the most cost-effective short-term abatement solution, but its emissions reduction performance is heavily dependent on managing supply chain emissions whilst cost effectiveness is governed by the price of solid carbon. Renewable electrolytic routes offer significantly higher emissions reductions, but production routes are more complex than those that utilise naturally-occurring energy-dense fuels and hydrogen costs are high at modest renewable energy capacity factors. Nuclear routes are highly cost-effective mitigation options, but could suffer from regionally varied perceptions of safety and concerns regarding proliferation and the available data lacks depth and transparency. Better-performing fossil-based hydrogen production technologies with lower decarbonization fractions will be required to minimise the total cost of decarbonization but may not be commensurate with ambitious climate targets.

In the near-to-medium future, hydrogen production will continue to rely on reforming of widely available and relatively low-cost fossil resources. A techno-economic framework is described that compares the current best practice steam methane reforming (SMR) with potential pathways for low-CO2 hydrogen production; (i) Electrolysis coupled to sustainable renewable electricity sources; (ii) Reforming of hydrocarbons coupled with carbon capture and sequestration (CGS) and; (iii) Thermal dissociation of hydrocarbons into hydrogen and carbon (pyrolysis). For methane pyrolysis, a process based on a catalytic molten Ni-Bi alloy is described and used for comparative cost estimates. In the absence of a price on carbon, SMR has the lowest cost of hydrogen production. For low-CO2 hydrogen production, methane pyrolysis is significantly more economical than electrochemical-based processes using commercial renewable power sources. At a carbon price exceeding $21 t(-1) CO2 equivalent, pyrolysis may represent the most cost-effective means of producing low-CO2 hydrogen and competes favorably to SMR with carbon capture and sequestration. The current cost disparity between renewable and fossil-based hydrogen production suggests that if hydrogen is to fulfil an expanding role in a low CO2 future, then large-scale production of hydrogen from methane pyrolysis is the most cost-effective means during the transition period while infrastructure and end-use applications are deployed. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Methane pyrolysis in molten salts could potentially provide a large-scale, low-cost and low-CO2 production route of H2 from CH4. The interplay of reaction and transport phenomena in molten pyrolysis reactors are currently poorly characterised and further understanding of the mass transfer and mechanistic pathways elucidated here may prove key to designing separation strategies that favour minimum carbon contamination and maximised production rates. Kinetic experiments were carried out at 850–1000 °C in a 590 mm bubble column of a eutectic mixture of molten NaBr and KBr. The use of four different injector sizes allowed for the variation of the mean surface area of the CH4 bubbles in the range of ~600–1200 m2 m−3 (0.77–2.9 cm2 per bubble). For the first time, a clear decoupling of bubble specific surface area and volume-based CH4 reaction rates in molten pyrolysis systems was demonstrated. These phenomena become more complex with catalyst particles present. Tests with γ-Al2O3 particles of varying sizes and with varying particle loadings were undertaken. The carbon depositing on the particles has a high catalytic activity and the material is thus a promising material for structured packings. Two clearly distinguishable kinetic regimes were identified, which transitioned at a γ-Al2O3 loading of ~1.25 wt%. We propose that the reaction is primarily enhanced by a shuttling mechanism of γ-Al2O3 adsorbing hydrocarbons (HC) in the HC-rich liquid-side film surrounding the bubble and desorbing it in the HC-lean liquid bulk. The findings provide a basis for (i) further models to extract kinetic parameters from CH4 pyrolysis in molten salt particle suspensions and (ii) for reaction rate modelling of industrial-scale pyrolysis reactors.

The economics of an integrated iron and hydrocarbon process utilizing molten salt electrolysis to produce 1850 kilotonnes per annum (kta) of reduced iron and 500 kta of higher hydrocarbons is presented. Capital and operating cost models based on Aspen Plus V8.6 sizing data were used to generate cash-flow and production costs for the proposed scheme. The process economics are most strongly dependent on the natural gas and electricity prices. The capital cost estimates include high contingency costs to reflect the higher investment risk for a first-of-a-kind (FOAK) process. At a carbon price of less than US $30/tCO2e, the process is competitive with traditional blast furnace smelting. Areas where a more complete understanding is needed of the barriers to the deployment of this technology are identified.

Methane pyrolysis using a molten metal process to produce hydrogen is compared to steam methane reforming (SMR) for the industrial production of hydrogen. Capital and operating cost models for pyrolysis and SMR were used to generate cash-flow and production costs for several different molten pyrolysis systems. The economics were most sensitive to the methane conversion and the value obtained for the solid carbon by-product. The pyrolysis system at 1500 °C is competitive with a carbon tax of $78 t−1; however, if a catalytic process at 1000 °C were developed using a conventional fired heater, it would be competitive with SMR without a carbon dioxide cost penalty. Several pyrolysis alternatives become competitive with increasing carbon dioxide taxes.

A promising production route for near CO2-free H2 from natural gas is methane pyrolysis in molten salts. During a screening of catalysts (containing La, Ni, Co and Mn) as particle suspensions in molten NaBr-KBr at 850 °C – 1000 °C, mixed Co-Mn catalysts were identified as being highly promising owing to their stability at pyrolysis conditions and fast kinetics. The catalysts, which contained Co-Mn nanocrystals (~8–9 ± 1 nm) that were prepared by colloidal chemistry were further tested in-depth, and their performance with varying molar Co:Mn ratios, particle sizes and temperatures were examined. The increase of the molar Co:Mn ratio from zero to two increased the CH4 conversion at 1000 °C from 4.8% to 10.4% for the smallest catalyst size range. Furthermore, we observed for all tested Co-Mn catalysts a stable performance over ca. 24 h of methane pyrolysis at 1000 °C and product selectivities for H2 near unity. While the Co-lean particles coked, the surface of the Co-rich particles remained largely carbon-free, and an increase in the Co-content was found to inhibit interactions between the support and the active phase (e.g. inhibited CoAl2O4 and MnAl2O4 formation). The rigorous procedure for the catalyst testing presented in this work enables the field to further investigate the use of catalysts for this process, and the insights gained from experiments with particle suspensions can be applied to the design of structured packings for an industrial-scale process.