Decarbonisation Technology - November 2023 Issue

Hydrogen through methane pyrolysis Methane pyrolysis is an important emerging technology that presents an economically attractive hydrogen production process with zero CO 2 emissions

MP Sukumaran Nair Centre for Green Technology & Management, India

T he message is clear. Greenhouse gases, especially carbon dioxide (CO 2 ), 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

H, CH

Fluidised bed reactor

Fresh carbon

Membrane

Carbon product

Grinder

Natural gas

Cooler

Carbon product storage

Figure 1 Methane pyrolysis schematic Courtesy: Wiley Online Library