Oct-2023

Hydrogen through methane pyrolysis

Methane pyrolysis is an important emerging technology that presents an economically attractive hydrogen production process with zero CO2 emissions.

MP Sukumaran Nair
Centre for Green Technology & Management, India

Article Summary

The message is clear. Greenhouse gases, especially carbon dioxide (CO2), emitted from human activities using fossil fuels and feedstocks, currently and over the past 150 years, significantly contribute to global warming. Therefore, a global consensus has been reached that we must reduce greenhouse gas emissions and foster a sustainable, low-carbon economy.

The potential for hydrogen to play a significant role in the transition from carbonaceous fuels to clean energy resources without CO₂ emissions is widely recognised. Hydrogen can serve directly as a fuel in fuel cells, internal combustion engines, or furnaces for industrial processes that are difficult to electrify. Hydrogen can also be used as a building block in decarbonised chemicals and transport fuels where a higher energy density is required.

Hydrogen is abundant in nature, but only in the combined form (with oxygen as water and carbon as hydrocarbons), which requires the intervention of high-order energy reactions for its liberation to the free molecular form. Hitherto, most manufacturing processes involving hydrogen – ammonia, methanol, power, and chemicals – used the energy from fossil fuels for its separation and downstream uses, which invariably resulted in emissions of large quantities of CO₂. Around 90% of the hydrogen produced today is from steam methane reforming (SMR), autothermal reforming (ATR), or gasification processes using methane, naphtha, fuel oil, petroleum coke, or coal as feedstock – all of fossil origin.

The production of hydrogen from the electrolysis of water (WE) is a known technology and was the main industrial source of hydrogen during the 1960s. In present times, the term ‘green hydrogen’ has been coined to denote hydrogen produced using electricity generated from renewable sources. As such, a prerequisite for the use of the term green hydrogen is either an uninterrupted supply of renewable electricity from the grid or a dedicated supply of renewable electricity (from wind, solar, geothermal, hydropower, or biomass) as part of the project.

While water electrolysis processes are in early commercialisation, further research and development are needed to design larger capacity plants with improved economies of scale.

During the energy transition period, hydrogen production from fossil sources can support the growing hydrogen economy, providing the carbon intensity of the process is comparable with that of water electrolysis. Many existing SMRs are being revamped to add carbon capture equipment. The captured carbon can then be used for the synthesis of chemicals or fuels or sent to certified sites for sequestration and permanent storage, thus avoiding emissions to the atmosphere. This requires additional facilities with the consequential investment for the management of the CO₂. Hydrogen produced using fossil fuel feed to an SMR with carbon capture is termed ‘blue hydrogen’.

Critical challenges developing green hydrogen technologies include the development of cost-effective and efficient electrolysers and building the necessary infrastructure for handling, storage, and distribution of hydrogen. The Green Hydrogen Catapult (GHC), formed in 2020, is a coalition of industry leaders organised with the support of the UN High Level Champions for Global Climate Action. The GHC has targeted the deployment of 25 GW electrolysers with the aim of reducing the cost of green hydrogen below $2/kg, which will allow the clean fuel to be cost-effective in the short term (Climate Champions, 2030).

Pyrolysis technologies for methane
An emerging technology for generating clean hydrogen is the pyrolysis of methane to produce hydrogen and solid carbon (char). Compared with SMR with CCUS, the methane pyrolysis process has a major advantage: the carbon produced is in the elemental solid form. As the methane pyrolysis process does not produce CO2, it avoids the need for carbon capture and sequestration infrastructure. Compared with water electrolysis, the methane pyrolysis  process does not need renewable electricity or water as a feedstock.

Currently, methane pyrolysis is at a lower technology maturity level than electrolysis or SMR with CCUS. Development is focused on improving the reliability of the pyrolysis process and attaining economy of scale operations. Several companies are commercialising methane pyrolysis technology, moving from the pilot plant (200kg H₂ per day) and demonstration unit levels (200kg H₂ per day) through to the first commercial-scale plants (>5kt p.a. H₂) (see Figure 2)(Monolith, 2021) (BASF, 2023), (Ekona, 2023), (Monolith hydrogen, 2023).

The methane source can be in the form of conventional natural gas or as bio-methane from anaerobic digestion of manure and other forms of biomass waste. The hydrogen so produced is termed ‘turquoise’, on the colour spectrum between blue and green.

The main developmental challenges include the cost of hydrogen produced, energy efficiency, and operational reliability. Uses for the solid carbon by-product are also an important consideration. In the interim, while capital costs will be higher, the cost of hydrogen production will likely be lower than that of SMR with CCS or water electrolysis.

As the technology matures with larger commercial plants providing economies of scale, methane pyrolysis will have an edge over other competing technologies. Methane pyrolysis is an active area of research that is now attracting interest from some of the leading engineering technology companies, including BASF, Ekona, Baker Hughes, and Mitsui. The pyrolytic decomposition of methane can be affected in three ways: thermal, plasma, and catalytic.

Thermal pyrolysis
Pyrolysis of methane in the absence of oxygen yields carbon (solid) and hydrogen (gas) as per the reaction below:

CH₄ (gas) ® C (solid)+ 2H₂ (gas) ΔH -76KJ/Mole