Tuesday, May 24, 2022

New technique produces hydrogen from banana peels within a few milliseconds

Over the last few decades, the high consumption of energy from fossil fuels has promoted a massive increase in greenhouse gas emissions worldwide. To address this, scientists have been searching for an alternative, renewable sources of energy.

One of the main candidates is hydrogen produced from organic waste, or biomass, of plants and animals. Biomass also absorbs, removes, and stores CO2 from the atmosphere, while biomass decomposition can also bring us ways to negative emissions or greenhouse gases removal.

Now, EPFL researchers have developed a way to maximize hydrogen yields from biowaste within a few milliseconds. The method uses rapid photo-pyrolysis to convert dried biomass powders such as banana peel into valuable gases and solids, including hydrogen and biochar.

The new method developed by EPFL scientists for biomass photo-pyrolysis produces not only valuable syngas but also biochar of solid carbon that can be repurposed in other applications. Syngas is a mix of hydrogen, methane, carbon monoxide, and other hydrocarbons, and those are what are used as “biofuel” to generate power, while biochar is often regarded as a solid carbon waste although it can be used in agriculture applications.

The method performs flashlight pyrolysis using a Xenon lamp, commonly used for curing metallic inks for printed electronics. The team has also used the system in the last few years for other purposes, like synthesizing nanoparticles.

The xenon-lamp flash photo-pyrolysis method.
The xenon-lamp flash photo-pyrolysis method. Credit: EPFL

The idea is to generate a powerful flashlight shot, which the biomass absorbs and which instantaneously triggers a photothermal biomass conversion into syngas and biochar. The banana peels were initially dried at 105°C for 24 hours and then ground and sieved to a thin powder. The powder was then placed in a stainless-steel reactor with a standard glass window at ambient pressure and under an inert atmosphere. The Xenon lamp flashes, and the whole conversion process is over in a few milliseconds.

“Each kg of dried biomass can generate around 100 liters of hydrogen and 330g of biochar, which is up to 33wt.% of the original dried banana peel mass,” says Bhawna Nagar, who worked on the study. The method also had a positive calculated energy outcome of 4.09 MJ·per kg of dried biomass.

Both the end products of the method, i.e., hydrogen and solid-carbon biochar, are valuable. The hydrogen can be used as green fuel, while the carbon biochar can either be buried and used as a fertilizer or can be used to manufacture conductive electrodes.

“The relevance of our work is further heightened by the fact that we are indirectly capturing CO2stores from the atmosphere for years,” says Nagar. “We have converted that into useful end products in no time using a Xenon flash lamp.”

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