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Plastic waste: transforming a problem into energy

23 March 2022/0 Comments/in Energy, Environment, In the News/by I'MTech

The linear life cycle of plastics, too rarely recycled, exerts a heightened pressure on the environment. The process of gasification makes it possible to reduce this impact by transforming more waste – currently incinerated or left in landfill – into useful resources like hydrogen or biomethane. Javier Escudero, process engineering researcher at IMT Mines Albi, aims to perfect this approach to make it easier to implement locally.

Plastic waste is so abundant, it is practically like rain. While we know well that it is piling up in landfills and oceans, an American study published in the journal Science has also shown that plastic particles are even in the air we breathe. Despite increased levels of pollution, international plastic production continues its explosive growth. However, at the end of the chain, the recycling industry has never managed to keep up with consumption. In France, the average recycling rate for all plastics is 28%, a percentage mainly obtained from bottle recycling (54.5% of the total). The vast majority of these materials is therefore incinerated or sent to landfill.

In order to respond efficiently to the plastic crisis, other forms of reuse or recycling must be developed. “Gasification means we can transform this waste into useful energy vectors, while losing as little material as possible”, explains Javier Escudero, Process Engineering Researcher at IMT Mines Albi. It is an alternative that contributes to a circular economy approach.

Some plastics not so fantastic

Rigid plastics used for bottles are generally made from a single material, which makes it easier to recycle them. For plastic films, which represent 40% of waste deposits, this is not the case. They are made from a multilayer combination of various plastics, such as polyethylene, polyurethane, and so on, sometimes joined with other materials like cardboard. The complex configuration of chemicals makes recycling such packaging too expensive. This means that in recycling centers, these products are overwhelmingly used for solid recovered fuel (SRF) – non-hazardous waste used for energy production. They are incinerated to feed turbines and generate electricity.

Another kind of waste that is ineligible for recycling is packaging from chemical products (industrial and mass market), considered hazardous. Some of the toxic compounds (chorine, sulfur, metals, etc.) are removed from the surface by pre-washing. However, certain atoms are absorbed into the material and cannot be removed by prewashing. This is where the advantages of gasification come in. “It makes it possible to process all plastics – SRF and contaminated ones – with less prewashing beforehand, as well,” emphasizes Escudero.

Moreover, this process has greater capacity for recycling plastic waste than incineration, as it produces chemical compounds that can be reused by industry, The synthesis gases can be burnt to generate energy (heat, electricity) with better yield than combustion. They can also be reprocessed and stored in the form of gas to be used as fuel (biomethane, hydrogen). To achieve this, one of the challenges of research is to observe the influence of pollutants, and therefore the composition of plastics, on products obtained from gasification.

Transforming materials down to the last crumb

Ground-up waste is compacted in the form of pellets, all the same size, to facilitate their transformation into gas in the gasifier. But if you want to recycle as much waste as possible, you need to adapt the gasification operating parameters, depending on the types of plastics contained in the pellets. For example, processing at a low temperature will break the long chains of polymers in plastic films. The molecules are then broken up again in the next step, as is done in petrochemistry. This produces a wide variety of products: hydrogen, methane, acetylene, and heavier molecules as well.

Processing at a higher temperature will produce more synthesis gas. However, it also produces more aromatic molecules like benzene and naphthalene. These compounds have a very stable structure and are very difficult to break into useful molecules. They may turn into soot – solids that build up in pipes – representing a significant loss of materials. The objective of Escudero’s research into gasification is therefore to combine the advantages of these two methods of processing, to avoid solid residue forming while producing as much gas as possible.

To do so, the researcher and his team are mainly focusing on gas injection, which breaks the molecular bonds of the materials being processed. Where and at which point in the process should injection take place? In connection to what? How does the material react? These questions, and many others, must be answered to improve the process. The gasifier at the Valthera technological platform, located at IMT Mines Albi and used for the tests, can process around 20 kilograms of material per hour. The process recycles not only the materials but also their energy. “Gasification reactions require energy to occur. This means that we use the energy stored in the materials to power their transformation,” explains the researcher.

Use less, convert more

Hydrogen and biomethane obtained through gasification directly power the goals of the French energy transition. Gasification therefore transforms materials made from fossil fuels into renewable energy. However, this process remains restricted to the context of research. “There are still many small aspects to study in designing gasifiers, to make them higher-performing and more mature for a certain amount of material. We are also going to concentrate on purifying synthesis gases with the aim of finding even cheaper solutions,” concludes Escudero. Gasification could supplement waste management channels at a local level. However, cost remains the greatest obstacle to small industrial actors adopting this method.

Anaïs Culot

An oasis of waste reconverted into ceramic materials

14 February 2022/0 Comments/in In the News, Materials/by I'MTech

Transforming industrial waste and unused by-products could make it possible to respond to issues of scarcity for civil engineering resources, recyclability and even reducing use of fossil fuels. Doan Pham Minh, process engineering researcher at IMT Mines Albi, explains several avenues for recycling and reusing materials explored by his work.

One man’s trash can be another man’s treasure. Turning rubbish into resources is the aim of the circular economy. And it is also the issue at the heart of the Innovative Ceramic Materials for Energy Storage and Construction (MACISEB)^[1] project, launched in 2019, with the participation of researchers from IMT Mines Albi^[2]. “Our objective is to transform inorganic, industrial waste and by-products, which can be found around us, into something that is useful for society,” describes Doan Pham Minh, process engineering researcher. The solutions identified as part of the project will then be transferred to companies in the Occitania region. From finding other uses for unrecyclable waste to replacing raw materials that are running out, the principle of ‘second life’ can be applied to a large range of unexpected situations.

Sand reserve seeks replacement for time to rest and recuperate

The French Agency for Ecological Transition (Ademe) reports that between 27 and 40 billion tons of sand are extracted each year around the world. It can be found in our buildings and windows, as well as our computers. “The demand for this resource is even more critical than that for noble metals. And the reserves are running out so quickly that they are arriving at breaking point,” emphasizes Pham Minh. Extracted from quarries or taken from riverbeds, natural sand is formed by the lengthy process of erosion. Too long, therefore, to meet society’s needs. However, this material is indispensable for the civil engineering sector (its main consumer) and therefore the economic stability of many countries.

Read more on I’MTech: Sand, an increasingly scarce resource that needs to be replaced

This is why the MACISEB project is seeking sand replacement products from inorganic by-products, i.e. industrial waste that is not currently being used. “The idea is not to completely change our means of manufacturing, but to replace a critical raw material using a circular economy approach,” specifies Pham Minh. With his team, the researcher has created resource maps for the entire Occitan territory. He identified and located deposits with high potential and similar properties to sand. He also ensured that these products are sustainable, by noting the quantity and availability of this waste. In this way, multiple candidates were selected, including glass residue.

During the recycling process, glass is ground up into grains fine enough to be reused by glass factories. However, a portion of this glass, too fine, coarse or contaminated, is not reused. “We are recovering this leftover glass to replace part or all of the sand needed to make ceramic bricks or tiles,” specifies Pham Minh. Sand from foundries, slag from blast furnaces, and ashes from biomass thermal power plants are also promising.

Using these materials, researchers have suggested formulas to create bricks and tiles with the same mechanical and thermal properties as those made with clay and natural sand. Moreover, the formulas comply with industrial specifications. The products are therefore guaranteed to be able to be manufactured using equipment that companies already possess, without extra investment. The first bricks will be made in 2022, and then tested by the Scientific and Technical Center for Building (CSTB).

From wind to heat: reusing wind turbine blades

The operating lifespan of a wind turbine is estimated at around twenty years. This means that the first French facilities are now arriving at end-of-life, and there will have to be more dismantling in the coming years. In short, recycling is becoming a major challenge for the wind energy industry. While the parts made from metal (pole and rotor) and concrete (base) recycle well, the blades – made from glass fiber mixed with organic resin – are not so lucky. Another part of the MACISEB project involves researchers recycling this waste into thermal storage materials. “Our objective is to reuse glass fiber from the blades to develop ceramics used by concentrated solar power (CSP) plants,” explains the researcher. This means of energy production transforms solar energy first into heat, then electricity. To do so, it uses systems made up of mirrors that concentrate the sun’s rays at one point, generating extremely high temperatures (from 200 to 1,500°C). The heat is transported by fluid, to propel the turbines and produce. It can be stored in ‘thermal batteries’, to later be released during the night to ensure continuity of service.

At present, thermal power plants store heat using molten salt – a mixture of potassium nitrate and sodium nitrate. “These compounds can also be found in agricultural fertilizer. There is therefore a conflict of use between the two sectors. However, there is currently no commercial alternative that is economically and environmentally viable,” explains Pham Minh. Transforming turbine blades into ceramics would therefore provide a new solution for this sector. With this in mind, researchers are developing materials capable of handling intense, repeated cycles of heating and cooling for multiple years. This solution would eventually make it possible to reuse a waste product that promises to grow. But it will also give a technological boost to the thermodynamic solar energy sector, which could allow it to establish itself in the renewable energy market. As part of the MACISEB project, this research is being undertaken by the PROMES laboratory, a partner of the project and academic reference body in the area of thermal storage. ART-DEV, partner and social sciences laboratory, is also looking into the social conditions for recycling wind turbine blades and the possibility of implementing a recycling ecosystem for the blades at a regional scale.

Industrial fumes: an idea to get the turbines going

Another application could make use of ceramic materials made from inorganic waste to capture heat. At present, the industry squanders over 30% of the energy it consumes in the form of so-called waste heat, released into the atmosphere in industrial fumes. Researchers at IMT Mines Albi are collaborating with company Eco-Tech Ceram, specialist in thermal storage, in order to recover this energy, store it and use it to supply industrial processes. For example, ceramicists and metal-working factories use high-temperature ovens, often running on natural gas. Reusing the heat captured from their fumes would make it possible to partially heat their equipment and therefore reduce their fossil fuel consumption.

Like for thermodynamic solar, the challenge is therefore to develop ceramic materials adapted for companies’ conditions of use. “Nevertheless, here another issue arises: industrial fumes contain pollutants. Such acidic, corrosive gases accelerate the aging of ceramics and therefore alter their performance,” explains the researcher. Moreover, the composition of fumes varies according to the industrial operations. The first thing to do will therefore be to characterize the kind of fumes, their temperature, etc. sector by sector, in order to develop sustainable materials while keeping costs under control^[3].

Anaïs Culot

[2] The project brings together researchers from the RAPSODEE center, the PROcesses, Materials and Solar Energy (PROMES) laboratory, the Actors, Resources and Territories in Development (ART-DEV) laboratory and the company Eco-Tech Ceram.

[3] This is part of the objectives of certain projects, Eco-Stock® solutions to recycle complex industrial waste heat (SOLUTEC, launched in 2021) and developing monolithic materials from local clay blends to reuse industrial waste heat in Occitania (CHATO, launched in 2021), led by IMT Mines Albi.

hydrogène décarboné carbon-free hydrogen

Carbon-free hydrogen: how to go from gray to green?

16 February 2021/0 Comments/in Energy, In the News/by I'MTech

The industrial roll-out of hydrogen production only makes sense if it emits little or no carbon dioxide. Researchers at IMT schools are working on various alternatives to the use of fossil fuels, such as electrolysis and photocatalysis of water, plasma pyrolysis of methane, and pyrolysis and gasification of biomass.

Currently, the production of one ton of hydrogen results in 12 tons of CO₂ emissions and 95% of the world’s hydrogen is produced from fossil resources. This is what we call gray hydrogen. A situation that is incompatible with the long-term roll-out of the hydrogen industry. Especially since, even if the CO₂ emitted by current processes can be captured in a controlled environment, fossil resources will not be able to meet the government’s ambitions for this energy. It is therefore essential to develop other modes of “carbon-free hydrogen” production. Within the Carnot H₂Mines network, researchers from the different IMT schools are working on processes that could turn the color palette of today’s hydrogen to green.

From blue to green

One process in line with the French government’s plan published last September is water electrolysis. This consists in separating an H₂O molecule into hydrogen and oxygen using an electricity supply. This is a carbon-free solution, provided the electricity comes from a renewable source. But why turn an already clean energy into gas? “Hydrogen enables the storage of large amounts of energy over the long term, which batteries cannot do on a large scale to power an entire network,” explains Christian Beauger, a researcher in materials science at Mines ParisTech. Gas therefore partly responds to the problem of intermittent renewable energies.

Researchers therefore want to improve the performance of electrolyzers in order to make them more competitive on the market. The goal is to find the best possible balance between yield, lifespan and reduced costs. Electrolyzers are made up of several electrochemical cells containing two electrodes and an electrolyte, as in the case of fuel cells. There are three main families: alkaline solutions with liquid electrolyte, polymer membrane technologies (PEM) and high-temperature systems based on ceramic solid oxide (SOC). Each presents its own problems.

At Mines ParisTech, Christian Beauger’s team is seeking to increase the lifespan of PEM electrolyzers by focusing on the materials used at the anode. “We are developing new catalyst supports in the form of metal oxide aerogels which must be electronically conductive and capable of resisting corrosion in a humid environment, at a temperature of 80°C and subjected to potentials often higher than 2 volts“, says the researcher. Another major problem also affects the materials: the cost of an electrolyzer. The catalyst present on PEM electrodes is iridium oxide, a compound that is too expensive to encourage widespread use of future high-power electrolyzers. For this reason, researchers are working on catalysts based on iridium oxide nanoparticles. This reduces the amount of material and thus the potential cost of the system.

Shedding light on photocatalysis

In the laboratory, an alternative using solar energy to break water molecules into hydrogen and oxygen is also being considered. This is photocatalysis. The semiconductors used can be immersed in water in powder form. Under the effect of the sun’s rays, the electron-hole pairs created provide the energy needed to dissociate the water molecules. However, the energy levels of these charge carriers must be controlled very precisely to be useful.

“We form defects in materials that introduce energy levels whose position must be compatible with the energy required for the process,” explains Christian Beauger. This ultra-precise work is delicate to carry out and determines the efficiency of photocatalysis. There is still a long way to go for photocatalysts, the most stable of which hardly exceed 1% in efficiency. But this method of hydrogen production should not be dismissed too quickly, as it is cheaper and easier to set up than a system combining a renewable energy source and an electrolyzer.

Turquoise hydrogen using methane pyrolysis

At Mines ParisTech, Laurent Fulcheri’s team, which specializes in plasma processes, is working on the production of hydrogen not from water, but from the pyrolysis of methane. This technique is still little known in France, but has been widely explored by our German and Russian neighbors. “This process requires electricity, as for the electrolysis of water, but its main advantage is that it requires about seven times less electricity than water electrolysis. It can therefore produce more hydrogen from the same amount of electricity,” he says.

In practice, researchers crack molecules of methane (formula CH₄) at high temperature. “To do this, we use a gas in the plasma state to provide thermal energy to the system. It is the only alternative to provide energy at a temperature above 1,500°C without CO₂ emissions and on an industrial scale,” says Laurent Fulcheri. The reaction thus generates two valuable products: hydrogen (25% by mass) and solid carbon black (75% by mass). The latter is not to be confused with CO₂ and is notably used in tire rubber, batteries, cables and pigments. The carbon is thus stored in the materials and can theoretically be recycled ad infinitum. “The production of one ton of carbon black by this method avoids the emission of 3 tons of CO₂ compared to current methods”, adds the researcher.

This process has already proven itself across the Atlantic. Since 2012, researchers at Mines ParisTech have been collaborating with the American start-up Monolith Materials, which has developed a technology directly inspired by their work. Its location in Nebraska is not insignificant, as it gives it direct access to wind energy in the heart of the corn belt, a major agricultural area in the United States. The hydrogen produced is then transformed into ammonia to fertilize the surrounding corn farms.

Although the machine is working, the research of Laurent Fulcheri’s team, a major player in the start-up’s R&D, is far from over. “Hydrogen production is the simplest task, because the gas purification processes are fairly mature. On the other hand, the carbon black produced can have drastically different market values depending on its nano-structure. The objective is now to optimize our process in order to be able to generate the different qualities of carbon black that meet the demands of consumer industries,” says the researcher. Indeed, the future of this technology lies in the short-term valorization capacities of the two co-products.

Biomass processing: a local alternative

At IMT Mines Albi, Javier Escudero‘s team is working on thermochemical processes for the transformation of biomass by pyrolysis and gasification. Organic waste is heated to high temperatures in a reactor and converted into small molecules of synthesis gas. The hydrogen, carbon monoxide, methane and CO₂ thus produced are captured and then recombined or separated. For example, the CO₂ and hydrogen can be used to form synthetic methane for use in natural gas networks.

However, a scientific issue has yet to be solved: “The synthesis gas produced is always accompanied by inorganic molecules and large organic molecules called tars. Although their concentration is low, we still require an additional gas purification stage,” explains Javier Escudero. The result is an increase in processing costs that makes it more difficult to implement this solution on a small scale. The researcher is therefore working on several solutions. For example, the exploration of different catalyst materials that could accelerate certain reactions to separate molecules from waste, while eliminating tars.

This approach could be envisaged as a form of local energy recovery from waste. Indeed, these technologies would enable a small and medium-scale territorial network with reactor sizes adapted to those of the collection centers for green waste, non-recovered agricultural residues, etc. However, there is also a need to clarify the regulations governing this type of facility. “For the moment, the law is not clear on the environmental constraints imposed on such structures, which slows down their development and discourages some manufacturers from really investing in the method,” says the researcher.

There is no shortage of solutions for the production of carbon-free hydrogen. Nevertheless, the economic reality is that in order to be truly competitive, these processes will have to produce hydrogen cheaper than hydrogen from fossil fuels.

By Anaïs Culot

Power-to-gas, when hydrogen electrifies research

15 February 2021/0 Comments/in Energy, In the News/by I'MTech

Hydrogen is presented as an energy vector of the future. In a power-to-gas system, it serves as an intermediary for the transformation of electricity into synthetic methane. The success of this energy solution depends heavily on its production cost, so IMT researchers are working on optimizing the different processes for a more competitive power-to-gas solution.

Increasing production of renewable energy and reducing greenhouse gas emissions. What if the solution to these two ambitions were to come from a single technology: power-to-gas? In other words, the conversion of electricity into gas. But why? This method allows the storage of surplus electricity produced by intermittent renewable sources that cannot be injected into the grid. The energy is then used to produce hydrogen by electrolysis of water. The gas can then be consumed on site, stored, or used to power hydrogen vehicles. But these applications are still limited. This is why researchers are looking at transforming it into other useful products such as methane (CH₄) to supply natural gas networks. What is the potential of this technology?

Costly hydrogen?

“The main issue with the development of power-to-gas today is its cost,” says Rodrigo Rivera Tinoco, a researcher in energy systems modeling at Mines ParisTech. If we take into account the cost of producing hydrogen using a low-temperature electrolyzer (PEM), the technology envisaged in power-to-gas installations, a 1 GW hydrogen reactor (almost the power equivalent of a nuclear reactor) would today cost €3 billion.” In September, the French government allocated a budget of €7 billion in aid for the development of the national hydrogen industry. A reduction in the production cost of this gas is therefore necessary. All the more so since power-to-gas technologies are destined to compete with other energy modes on the market.

France wants to reach a cost of €50 per megawatt-hour in 2030. However, a low-cost but short-lasting technology would not be suitable. “To be cost-effective, systems must have a minimum 60,000 to 90,000 hour operating guarantee,” adds Rodrigo Rivera Tinoco. Currently, low-temperature electrolyzers (PEMs) have an operating life of between 30,000 and 40,000 hours. This is where research comes in. The objective is to optimize the energy efficiency of low-cost technology.

Which technology for which use?

Digital modeling enables the identification of the strengths and weaknesses of technologies prior to their installation. “We carry out technical and economic studies on the various water electrolysis processes in order to increase their efficiency and reduce their cost,” says Chakib Bouallou, an expert in digital modeling and energy storage at Mines ParisTech. Several technologies exist, but which one is the most suitable for storing renewable energy? On an industrial scale, low-temperature electrolyzers are mature and seem to respond to the intermittent nature of these energy sources.

However, in the evaluation phase, no technology is being ruled out. As part of the ANR MCEC project and in collaboration with Chimie ParisTech, Chakib Bouallou’s team is currently working on a solution based on molten carbonates that relies on the co-electrolysis of water and CO₂. “Using performance curves of materials depending on the current, we estimate the efficiency of the systems under different usage scenarios. The overall analysis of this technology will then be compared to other existing techniques”, says the researcher. Indeed, the adaptability of a system will depend above all on the intended use. To complete these studies, however, experiments are essential.

Minerve: a demonstrator for research purposes

In order to gain the knowledge needed to make the transition to power-to-gas, the Minerve demonstrator was installed in 2018 on the Chantrerie campus north of Nantes. “The platform is first and foremost a research tool that meets the needs of experimentation and data collection. The results are intended to help develop simulation models for power-to-gas technologies,” explains Pascaline Pré, a process engineering researcher at IMT Atlantique. Equipped with solar panels and a wind turbine, Minerve also has an electrolyzer dedicated to the production of hydrogen converted, with CO₂ in cylinders, into methane. This is then redistributed to a fuel distribution station for natural gas vehicles (CNG) and used for mobility. The next step is to integrate CO₂ capture technology from the combustion fumes of the site’s heating network boilers to replace the cylinders.

Carbon dioxide is very stable in the air. Turning it into useful products is therefore difficult. Pascaline Pré’s team is developing a new process to capture this gas by absorption using a solvent. The gas collected is purified, dried, compressed and sent to the methane plant. However, some hurdles need to be overcome in order to optimize this approach: “Solvent regeneration consumes a lot of heat. It would be possible to improve the energy efficiency of the device by developing an electrified microwave heating system,” explains the researcher. This concept would also reduce the size of the facilities needed for this process for a future industrial installation.

In the long term, Minerve should also serve as a basis for the study of many issues in the Carnot HyTrend project, which brings together part of the French scientific community to look at hydrogen. Within three years, initial recommendations on the different technologies (electrolysis, methanation, CO₂capture, etc.) will be published to improve the existing situation, as well as studies on the risks and environmental impacts of power-to-gas.

What about power-to-gas-to-power?

It is possible to go beyond current power-to-gas techniques by adding an oxycombustion step. As part of the ANR project FluidStory, Chakib Bouallou’s team focused on modeling a device based on three advanced technologies: low-temperature PEM electrolysis, methanation (allowing the storage of electricity in the form of gas) and oxycombustion power plants for the destocking stages. The first two steps are therefore the same as in a classical power-to-gas infrastructure as mentioned above. The difference here is that oxygen and CH₄, obtained respectively by electrolysis of water and methanation, are stored in caves for an indefinite period of time. Thus, when the price of electricity rises, the oxy-fuel combustion process reuses these gases to produce electricity. The CO₂ also emitted during this reaction will be reused by the methanation process in the next cycle.

This closed-cycle design therefore allows autonomous operation with regard to the required reagents, which is not possible in conventional power-to-gas setups. However, analyses aimed at better understanding its mechanics and the nature of the interactions between its components have yet to be conducted.

Looking towards power-to-X

The methanation at the heart of the processes mentioned so far is only one example of the transformation of hydrogen in contact with CO₂. Indeed, these reactions, called hydrogenation reactions, are used to synthesize many chemicals usually obtained from fossil resources. At IMT Albi Mines, Doan Pham Minh’s team is working on the optimization of these processes. As well as methane production, researchers are targeting the synthesis of liquid biofuels, methanol, ethanol and other carbon-based chemicals. All these “X” compounds are therefore obtained from hydrogen and CO₂. Two factors determine the nature of the result: the operating conditions (temperature, pressure, residence time, etc.) and the catalyst used. “This is what drives the reaction to a target product. Thus, by developing active, selective and stable catalytic materials, we will improve yields in synthesizing the desired product,” the researcher explains.

Methanol is of particular interest to industries. Indeed, this compound is everywhere around us and is used in particular for the surface materials of furniture, in paints, plastics for cars, etc. The same is true for ethanol, biofuels or chemical intermediates of renewable origin. Beyond the role of hydrogen in the national energy mix, the researcher therefore insists on its use by other high-consumption sectors: “It is widely used by the chemical industry and we must be ready to develop competitive and high-performance processes by anticipating future uses of hydrogen and power-to-X.”