Production of hydrogen from banana peels in milliseconds: Good replacement of fossil fuels

Our usage of fossil fuels rises in tandem with the world's energy demands. As a result, greenhouse gas emissions have skyrocketed, wreaking havoc on the ecosystem. To deal with this, scientists have been looking for alternate, renewable energy sources.

Hydrogen created from organic waste, or "biomass," of plants and animals is one of the most promising candidates. Biomass also absorbs, removes, and stores CO2 from the atmosphere, and breakdown of biomass can lead to negative emissions or the removal of greenhouse gases. Even while biomass represents a step forward, the optimal approach to maximise its conversion into energy remains a question. 

Gasification of biomass

Gasification and pyrolysis are the two main processes for turning biomass into energy currently available. Gasification converts solid or liquid biomass into gas and solid chemicals at temperatures around 1000°C; the gas is called "syngas," and the solid is called "biochar."

Syngas is a mixture of hydrogen, methane, carbon monoxide, and other hydrocarbons that are used to create electricity as "biofuel." Biochar, on the other hand, is frequently seen as a solid carbon waste, despite the fact that it can be used in agriculture.

Pyrolysis of biomass

Biomass pyrolysis, on the other hand, is identical to gasification except that biomass is cooked at lower temperatures, between 400 and 800°C, and at pressures up to 5 bar in an inert environment. Pyrolysis can be classified into three types: conventional, quick, and flash. The first two take the most time and produce the most char out of the three.

At 600°C, flash pyrolysis produces the greatest syngas and has the shortest residence time. Regrettably, it also necessitates the use of specialised reactors capable of withstanding high heat and pressures.

Splitting bananas for hydrogen production

Scientists at EPFL's School of Basic Sciences, led by Professor Hubert Girault, have invented a new process for biomass photo-pyrolysis that creates not only useful syngas but also solid carbon biochar that can be used in various applications. Chemical Science is the journal where the research was published.

The approach uses a Xenon lamp to produce flash light pyrolysis, which is often used to cure metallic inks for printed circuits. In recent years, Girault's group has employed the technology for additional applications, such as manufacturing nanoparticles.

The white flash light of the lamp provides both a high-power energy source and short pulses that encourage photo-thermal chemical reactions. The concept is to create a bright flash light shot that the biomass absorbs and activates a photothermal biomass conversion into syngas and charcoal in real time.

This flashing approach was applied to a variety of biomass sources, including banana peels, maize cobs, orange peels, coffee beans, and coconut shells, which were all dried for 24 hours at 105°C before being pulverised and sieved into a fine powder. At ambient pressure and under an inert atmosphere, the powder was placed in a stainless-steel reactor with a standard glass window. The Xenon light flashes, and the conversion is completed in a matter of milliseconds.

"Each kg of dried biomass can yield roughly 100 litres of hydrogen and 330g of biochar, which is up to 33% of the original dried banana peel mass," explains study co-author Bhawna Nagar. A positive computed energy result of 4.09 MJ per kilogramme of dried biomass was also obtained using this method.

The value of both the end products, hydrogen and solid-carbon biochar, shines out in this approach. The hydrogen can be utilised as a green fuel, whereas the carbon biochar can be buried and used as fertiliser or used to make conductive electrodes.

"The fact that we are indirectly extracting CO2stores from the environment for years adds to the relevance of our work," explains Nagar. "With the use of a Xenon flash lamp, we were able to convert that into useful end products in no time."

Reference:

1. Wanderson O. Silva, Bhawna Nagar, Mathieu Soutrenon, Hubert H. Girault. Banana split: biomass splitting with flash light irradiation. Chemical Science, 2022; DOI: 10.1039/d1sc06322g