Banana peels

 

Scientists from the Swiss Federal Institute of Technology in Lausanne have developed a new method to obtain hydrogen and biochar from dried biomass. They obtained very encouraging results with banana peels.
 
At a time when the European Commission is still working on the future Euro 7 standard, which should open up the field more widely to biofuels and synthetic fuels, researchers located all over the world hope to multiply the sources of energy to be exploited in the mobility. On July 20, the institution should formulate a new proposal which this time will tackle various pollutants, and no longer just CO2 emissions. Waste of all kinds is more than ever at the heart of studies to obtain gas that can power heat engines and/or fuel cells. Thus green hydrogen which can be produced other than by electrolysis.
 

Current methods

The team of Professor Hubert Girault, from the School of Basic Sciences at EPFL, has just added a method to the range of possibilities for obtaining hydrogen by pyrolysis or gasification. With the latter, the waste is subjected to a temperature of around 1,000° C to transform solid or liquid biomass. The gas thus produced is a mixture of hydrogen, methane, carbon monoxide and other hydrocarbons. It is accompanied by biochar which can b​e exploited in agriculture. Pyrolysis, on the other hand, is divided into 3 processes, the classic and rapid variations of which are based on placing the biomass conditioned in an inert atmosphere under 5 bars of pressure. The temperature required for the transformation is lower, between 400 and 800° C. The share of biochar is however high. Flash pyrolysis releases more gas. With a shorter duration, the process requires the presence of reactors capable of withstanding high pressure and a temperature of 600°C

The photo-pyrolysis method developed by Professor Hubert Girault's team is very different from conventional, rapid and flash pyrolysis. First of all because it requires a first phase of drying at 105° C which lasts 24 hours. The biomass stripped of its moisture is then crushed and sieved to reduce it to a fine powder. The latter is then placed in a stainless steel reactor at ambient pressure and under an inert atmosphere. Through a standard glass window, the material will be flashed by a very powerful flashing beam provided by a xenon lamp. The transformation is instantaneous. The photo-thermal chemical reactions would last only a few milliseconds, according to Swiss scientists from EPFL. Output: synthetic gas and always biochar.
 

Bananas and other waste

Banana peel was not the only source tested by Professor Hubert Girault's team. She also experimented with photo-pyrolysis with coconut shells, coffee beans, orange peels and corn cobs. However, she seems to have preferred the first source and is delivering very encouraging results. One kilogram of dried banana skins would be enough to obtain 100 liters of hydrogen and 330 grams of solid matter. "  This represents up to 33% by weight of the initial mass of the dried banana peel ", insists the scientist Bhawna Nagar who participated in the experiments.

This biochar can still be used as a fertilizer for new crops. But its quality makes it possible to envisage a much more interesting exploitation in the manufacture of current-conducting electrodes. The work also uncovered a ratio of 4.09 MJ of energy per kilogram of dried biomass. It would have been relevant to also communicate the result from the mass before drying

with details for the different sources tested. These elements are probably in the full document published in the journal Chemical Science.

Small focus on the Xenon lamp

Professor Hubert Girault did not come by chance to use an overpowered Xenon flash lamp. He exploits this source of light and energy for other work. In particular for the synthesis of nanoparticles.

It is an already existing material and usually adopted for the curing of metallic inks in the field of printed electronics. A few questions remain concerning the study: How to collect in a differentiated way enough banana peels to obtain an interesting volume of hydrogen to be used for sustainable mobility? Even imagining a mix with orange peels and coconut shells, what company transforming these fruits into jams, composts, sweets and other finished products could provide sufficient quantities for an investment in a system of processing and collection appear profitable? Should this work be shelved, or is an opening to other sources of biomass possible?