Abstract
Nowadays, nearly 50% of the hydrogen produced worldwide comes from Steam Methane Reforming (SMR) at an environmental burden of 10.5 tCO2,eq/tH2, accelerating the consequences of global warming. One way to produce clean hydrogen is via methane pyrolysis using melts of metals and salts. Compared to SMR, significant less CO2 is produced due to conversion of methane into hydrogen and carbon, making this route more sustainable to generate hydrogen. Hydrogen is produced with high purity, and solid carbon is segregated and deposited on the molten bath. Carbon may be sold as valuable co-product, making industrial scale promising. In this work, methane pyrolysis was performed in a quartz bubble column using molten gallium as heat transfer agent and catalyst. A maximum conversion of 91% was achieved at 1119 °C and ambient pressure, with a residence time of the bubbles in the liquid of 0.5 s. Based on in-depth analysis of the carbon, it can be characterized as carbon black. Techno-economic and sensitivity analyses of the industrial concept were done for different scenarios. The results showed that, if co-product carbon is saleable and a CO2 tax of 50 euro per tonne is imposed to the processes, the molten metal technology can be competitive with SMR.
Highlights
On 12th December 2015, 195 countries set the basis of the Paris Agreement
Carbon was deposited on top of the molten metal's surface, and its segregation from the gas phase was gradually improved as more gallium was added to the reactor
This suggests that either gasphase thermal cracking occurred after the unconverted methane left the molten metal, or a portion of carbon deposited on the metal surface was dragged by the gas and accumulated on the walls, or a combination of the two
Summary
On 12th December 2015, 195 countries set the basis of the Paris Agreement They agreed to keep the mean global temperature increase below 2 C above pre-industrial levels by 2100. They committed to developing technologies that can limit the temperature rise to 1.5 C. 96% of the world's hydrogen production use fossil fuelbased technologies, emitting tremendous amounts of CO2. The current benchmark process for H2 production is Steam Methane Reforming (SMR), which consists of the chemical conversion of natural gas with steam to produce carbon monoxide and hydrogen. A subsequent reaction step known as water gas shift (WGS) is carried out in order to improve the production of hydrogen and the H2/CO ratio. The scientific community is currently working towards novel technologies for sustainable hydrogen production [3,5e9]
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