Today, vinasse is usually used as fertilizer in the fertigation of crops, especially sugarcane, but transporting this residue to the plantations is expensive and laborious.

Researchers linked to the Research Center for Innovation in Greenhouse Gases (RCGI) are working on the development of a technology that aims to transform vinasse – a polluting residue generated during the production of ethanol – into green hydrogen.

Currently, when processed, vinasse is usually used as fertilizer in the fertigation of crops, especially sugarcane, as it is rich in potassium. “Transporting this residue to the plantations is an expensive and labor-intensive process for the mills. Not to mention that, if improperly applied, vinasse can damage the plantation and the soil, in addition to reaching groundwater. It is possible to improve this process”, says Thiago Lopes, a professor at the Polytechnic School of the University of São Paulo (Poli-USP) and a member of the RCGI, an Engineering Research Center funded by FAPESP and Shell do Brasil.

Heading the new Fuel Cells Laboratory, located at Poli-USP, Lopes intends to develop an electrolytic reactor aimed at the reality of the national sugar and ethanol industry. “Vinasse has 95% water in its composition. The idea is that through this reactor we can break water molecules to generate oxygen and green hydrogen”, says the researcher.

With wide application, green hydrogen can be used, for example, in the production of ammonia that enters the composition of fertilizers. “Today, ammonia is synthesized with hydrogen from natural gas, which generates a CO2 footprint”, he says. Pure oxygen, on the other hand, can be used for the combustion of sugarcane bagasse. “By condensing the water, you can easily and economically obtain pure CO2 for storage or to be converted into products.”

One of them is oxalic acid, an element that together with a biomonomer will enter the composition of the hydrogel that is being developed under the Hydrogel Program, financed by Shell Brasil, with resources from the R&D Investment Clause of the National Agency's Concession Contracts of Oil, Natural Gas and Biofuels (ANP). The project involves several research institutions at USP, under the leadership of the RCGI, as well as the Federal University of Rio Grande do Sul (UFRGS).

In this case, oxalic acid will be produced by the Fuel Cells Laboratory, in collaboration with the Energy and Nuclear Research Institute (Ipen) and the Brazilian Agricultural Research Corporation (Embrapa). The hydrogel generated at the end of the entire research process will be applied in the planting process in the form of granules, which will degrade and release carbon to be stored in the soil. “The idea is to create a virtuous cycle and enable new markets for the national sugar and alcohol sector.”

Another advantage of the reactor is to make the vinasse more concentrated – approximately 10 liters of vinasse are produced for each liter of ethanol. “It's a huge volume to store and transport. If it is more concentrated, free of a fraction of water, the vinasse will take up less space and demand less transport. It is worth mentioning that this transport, in general, is done by trucks powered by diesel oil, and this adds CO2 footprints to Brazilian ethanol”, points out Lopes.

According to the researcher, concentrated vinasse would also minimize the addition of synthetic fertilizer to the crop. “The mixture of vinasse and synthetic fertilizer causes higher CO2 emissions. Not to mention that, by reducing the volume of water, we prevent excess liquid from reaching the water table and polluting the rivers.”

Green hydrogen can also power fuel cell vehicles, one of the types of all-electric vehicles that circulate around the world today, especially in Japan. The other modality is electric vehicles powered by a rechargeable battery in special sockets.

“In a fuel cell vehicle, hydrogen reacts with oxygen that comes from the environment. The electrical energy released powers the vehicle and the process generates only heat and pure water as waste. Currently, this hydrogen is obtained worldwide through natural gas, which generates CO2 footprints. Hence the importance of finding ways to produce green hydrogen. This is what we intend to do in the laboratory through the vinasse electrolytic concentrator. Everything is interconnected”, explains Lopes.

According to the researcher, it is estimated that around 2040 the production of this type of vehicle will take off in Brazil. “This should happen, above all, in relation to fleets of buses and trucks, because the fuel cell is lighter than the batteries of an electric vehicle, in particular for vehicles that travel more than 450 kilometers a day”, he informs.

However, for this to happen, the technology needs to be improved in terms of performance and cost. According to Lopes, another objective of the laboratory is precisely to develop more efficient and cheaper parts for fuel cell vehicles. “The fuel cell layers can be optimized through advanced numerical models and topological optimization, for example. The catalyst, from the catalytic layer, is made of platinum, a rare metal that is worth more than gold and does not exist in Brazil, and the challenge is to find more affordable options,” he explains.

To seek these solutions, the laboratory will use a technique developed by Lopes during a season as an associate researcher at Imperial College London, in the United Kingdom, between 2012 and 2014.

“The fuel cell vehicle is powered on one side by oxygen and on the other by hydrogen. On the air side we put a mixture with about 1,000 ppm [parts per million] of ozone. In the catalytic layer, where the reaction of the fuel cell takes place, we place a pigment that, when interacting with ozone, emits light. This helps us to visualize, through a camera, and compare how the oxidizer is distributed in the fuel cell made with different types of materials, with different properties and under different conditions, thus promoting the development of advanced numerical models of the fuel cell. and topological optimization of them”, he continues.

The laboratory's transdisciplinary team, which includes researchers from Poli, the Institute of Physics (IF), the Institute of Chemistry (IQ) and the Institute of the Environment (IEE) at USP, will work together with Imperial College London in development of the different layers that make up fuel cells, as described above, and intends to move forward.

“In the catalytic layer, the idea is to find out if more accessible materials, such as a mixture of iron, carbon and nitrogen, can replace platinum and be used by the automotive industry,” says Lopes. “This is a worldwide demand. Today there is a research consortium in the United States, along the lines of the RCGI, focused on the development of these materials. Even because there is not enough platinum to change the entire world fleet of vehicles to fuel cell. We scientists have a lot of work ahead of us”, concludes Lopes.

Brazilian Scientists Develop Technology to Turn Vinasse Into Green Hydrogen