15 Feb 2019...

15 Feb 2019

https://www.chemistryworld.com/news/microwave-process-decarbonises-fossil-fuels-and-generates-hydrogen/3010124.article

Microwave process decarbonises fossil fuels and generates hydrogen.
Researchers in the UK and Saudi Arabia have devised a technique to generate high purity hydrogen from fossil fuels that doesn’t liberate carbon dioxide into the atmosphere. Their microwave-initiated dehydrogenation process uses inexpensive iron particle catalysts and works on heavy crude oil through to diesel, petrol and methane.

The byproduct of the process is solid carbon in the form of multi-walled carbon nanotubes, which can be converted into high value products such as catalysts, carbon electrodes or building materials. Alternatively, the solid carbon can be stored underground.

However, other researchers in the field remain skeptical about how efficient the technique is.

Edwards’ team claims that larger-scale microwave systems would be designed to achieve 99.9% efficiency using renewable sources of primary electricity, however, other researchers seem unconvinced.

‘At present, 0.5% of the energy from the microwaves is making it through to hydrogen. The best case scenario, where they are only looking at the energy absorbed from the microwaves, gives around a 4% efficiency,’ comments Paul Fennell, a professor of clean energy at Imperial College London, UK. He notes that electricity is used to power the microwave generator, which inevitably decreases the net efficiency, adding that the process is 50% less efficient when used on a crude oil rather than a refined diesel (requiring significant energy to produce) feedstock, highlighting that the work may be far from being practical.

The catalyst suffers a significant decrease in activity due to the build-up of carbon residues after approximately 10 cycles. These residues can be removed by combustion, however, the original high activity is never fully recovered due to iron oxide being present post-combustion.

Nazim Muradov, from the Florida Solar Energy Centre, US, who has been working in the fossil fuel decarbonisation area for two decades, says the work ‘provides valuable information on the impact of microwave radiation on the kinetics and selectivity of the studied process.’ However, he also is cautious about implementing the technology: ‘The practical realisation of the process is likely to face many challenges of technological and economic nature. The energy efficiency of the process has to be improved by at least one order of magnitude, and the catalyst deactivation problem has to be fundamentally addressed,’ explains Muradov. He suggests that the process may face competition from other electricity-driven fossil fuel decarbonisation routes that are closer to commercialisation.’