Tag: recycling

Critical raw materials from electrolysers back into the cycle

Critical raw materials from electrolysers back into the cycle

Researchers succeed in recycling functional materials for hydrogen production

Hydrogen plays a central role in the energy transition. The gas is mainly produced with the help of electrolysers. This process requires critical raw materials such as platinum group metals, rare earths or nickel as catalysts. Researchers at the Helmholtz Institute Freiberg for Resource Technology (HIF), an institute of the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), have now been able to recover these functional materials using innovative flotation processes and liquid-liquid particle separation, thus returning them to the material cycle. The research is part of the H2Giga lead project of the German Federal Ministry of Education and Research (BMBF), which is investigating the longevity and recyclability of hydrogen electrolysers.

Hydrogen is considered a clean energy source that can help reduce CO2 emissions. The focus here is particularly on green hydrogen, which is produced through the electrolysis of water using renewable energies such as wind and solar power. Hydrogen is used in industry, for example as a raw material for the production of chemicals and steel, as well as in the transport sector, where it is used as a fuel for fuel cell vehicles. Hydrogen can also be used to store surplus energy from renewable sources, making it an important building block for a sustainable and climate-friendly energy future. According to the national hydrogen strategy, Germany is expected to need 95 to 135 terawatt hours of hydrogen in 2030.

Various processes can be used to produce hydrogen – one is water electrolysis: water is broken down into hydrogen and oxygen using an electric current. The catalysts in the electrolyser consist of critical metals, the so-called functional materials. Proton exchange membrane electrolysers (PEM) mainly use metals from the platinum group, such as platinum, iridium and palladium. High-temperature electrolysers use rare earths and nickel. These critical raw materials need to be secured. This is a project that HIF researchers are working on under the leadership of the TU Bergakademie Freiberg in the ReNaRe project.

ReNaRe stands for Recycling – Sustainable Resource Utilization and is part of the H2Giga flagship project. To implement the national hydrogen strategy, the BMBF has set up three flagship projects for Germany’s entry into the hydrogen economy. One of these is H2Giga, which focuses on the series production of hydrogen electrolysers. ReNaRe concentrates on the end of life of electrolysers in order to return the materials used, and in particular the critical metals, to the material cycle.

“We are involved in the recycling of PEM and high-temperature electrolysers, as they are easy to dismantle. We use ultra-fine particle separation techniques to recover the functional materials. This is because the critical anode and cathode materials are present as fine particles. Their size corresponds to approximately one hundredth of a human hair. Liquid-liquid particle separation and agglomeration flotation have proven to be suitable for separating the functional materials. The extraction of ultrafine particles uses a sustainable solvent-water circulation system for the effective separation of hydrophobic, i.e. water-repellent cathode catalysts and hydrophilic (water-attracting) anode catalysts. The complementary agglomeration flotation uses an innovative, sustainable hydrophobic binder to enable agglomeration of the particles into a uniform mass. The binder is based on a special emulsion technology, i.e. an oil-water mixture with a very high water content, which selectively agglomerates hydrophobic ultrafine particles. This enables the separation of hydrophilic ultrafine particles by adhesion to gas bubbles and discharge in the foam,” says Sohyun Ahn, PhD student at the HIF, describing the procedure. “With both processes, we were able to recover up to 90 percent of the critical functional materials and return them to the material cycle. An important step towards operating hydrogen electrolysis economically and sustainably.”

Read more on HZDR website

Image: Water drop (black) above a hydrophobic particle (grey are at the bottom)

Source: Ahn, Sohyun

Revolutionising plastic recycling: a breakthrough in enzyme-based depolymerisation

Revolutionising plastic recycling: a breakthrough in enzyme-based depolymerisation

The accumulation of plastic waste in the environment is an ecological disaster and will require multiple solutions to tackle the problem. Despite recent initiatives to close the plastics loop, only 9% of plastic was recycled in 2019, with the remaining waste either incinerated or accumulating in landfills or natural environments, posing hazards to both living and non-living systems. Bioplastics, derived from renewable sources, have been investigated as green alternatives to conventional fossil-based plastics. However, costly synthetic routes and low recyclability continue to challenge the growth of bioplastics. Poly(lactic acid) (PLA) is the most popular polymer for commercial bioplastics, but its recycling is limited by challenging mechanical recycling and slow biodegradation. A team of researchers from King’s College London has developed a generalisable biocatalysis engineering strategy to enhance the use of enzymes to depolymerise a broad class of plastics, in a publication recently published in Cell Reports Physical Science. This novel approach is 84 times faster than the 12-week-long industrial composting process currently used for recycling bioplastic materials 

The problem with plastic waste

The demand for conventional plastics such as Poly(lactic acid) (PLA) or poly(ethylene terephthalate) (PET) is increasing, with 460 million tons produced in 2019; a 230-fold increase from the 2 million tons produced in 1950. Plastic waste is a significant environmental issue, with millions of tons of plastic ending up in natural environments each year. Traditional recycling methods are often inefficient and unable to produce high-quality reusable materials. Bioplastics, derived from biological sources such as corn starch and sugarcane, are seen as a more sustainable alternative. However, current methods of bioplastic production are costly and compete with food-based agriculture for land use. Furthermore, mechanical recycling methods generate CO2 and are incapable of producing high-quality reusable materials, leading many retailers to revert to using oil and fossil-based materials. As an example, it takes up to 84 days at 60°C in industrial composting to recycle PLA, with very little valorisation possible. 

An innovative solution

In this publication, the team of researchers developed a new protocol to recycle PLA. This method involves different component to help depolymerise the material.  

First, they used ionic liquids to solubilise the plastic. Ionic liquids are salts in a liquid state that have unique properties, such as low volatility and high thermal stability. Ionic liquids have been shown to have the ability to solubilise polymers used in common plastics such as PET and PLA. Secondly, they used a commercially available enzyme, a lipase from Candida antarctica (CaLB) to degrade the plastic.  

As the enzyme may not be stable in ionic liquid, the researchers performed some chemical modifications in three different steps to preserve enzyme activity.

Researchers performed circular dichroism at Diamond Light Source on the B23 beamline to ensure that the secondary structure of the enzyme was intact after the chemical modifications. Measurements realised on B23 also showed that the thermostability of the modified protein was higher in ionic liquid (> 80°C) compared to the unmodified protein in aqueous solution. This parameter is important, as heat is required to help depolymerise plastics. 

Read more on Diamond website

Image: Graphical abstract of the publication

The World’s Most Efficient PET-Degrading Enzyme 

The World’s Most Efficient PET-Degrading Enzyme 

Polyethylene terephthalate (PET), which is used in drinking bottles, fibers, and many other applications, is one of a few plastics that can be broken down to its constituent monomers by naturally occurring enzymes. This study developed a landscape profiling method to identify and characterize the potential of microbial enzymes to degrade these plastics. Two enzymes were engineered with sequential mutagenesis and exhibited excellent performance relative to benchmarks, especially under the harsh conditions that are ideal for use in recycling applications..

Research Background and Objectives

PET (polyethylene terephthalate) is a representative general-purpose plastic widely used in various fields such as PET bottles, clothing, seat belts, takeout cups, and car mats. While most PET waste is separately collected and mechanically recycled into intermediate products, the recycled materials often degrade in quality, ultimately leading to incineration or landfill disposal. As a method to address this issue, chemical recycling technology has been developed to break down the PET polymer bonds using chemical catalysts and return them to the original raw materials. However, it has not been a perfect alternative due to the limitations of applying the method, which is caused by high temperature and high-pressure conditions. Therefore, the scientific community has turned to biological/biocatalytic recycling to solve these problems through enzymes. With complex bonding structures, enzymes react selectively with PET at low temperatures and in water solvent conditions to produce pure reactants. Thus, they are excellent at converting contaminated raw materials. There has been a fierce competition worldwide to develop PET-degrading enzymes using advanced technologies in various fields such as synthetic biology, computational chemistry, and AI-driven protein design. 

Research Approach

The research team attempted to experimentally determine the fitness landscape of various enzyme protein sequences. Since conducting experiments on all sequences was physically impossible, it was necessary to use a statistical sampling method through a landscape. To construct a landscape of the Polyesterase-Lipase-Cutinase Family, a neighborhood analysis module was devised to control the network’s rigidity using distance histogram data for each protein sequence. This analysis generated a two-dimensional semantic network. Based on this semantic network, the research team proposed an innovative approach to experimentally measure the fitness for PET degradation activity and thermal stability using hierarchization and cluster sampling. Also, to improve the selected enzymes, the team attempted a unique strategy of applying cross-template engineering to reflect natural diversity and fitness information in a rational design based on the protein’s 3D structural information. 

Results and Discussion

The new approach identified the most promising enzymes, Mipa-P and Kubu-P, among 158 nodes, which showed a superior PET-degradation rate and durability compared to other benchmarks. Cross-template engineering created heat-resistant variants MipaM19 (Mipa-PM19) and KubuM12 (Kubu-PM12) with melting temperatures exceeding 92 and 99°C, respectively. Surprisingly, Kubu-M12 withstood the condition of a minimum enzyme dosage of 0.58 g/mg and high PET loading of 20% and 30%, degrading more than 90% of the PET substrate within 8 hours. It showed overwhelming performance compared to other engineered benchmark enzymes. Moreover, Kubu-M12 withstood 99% ethylene glycol solvent and produced 30 mM level bis(2-hydroxyethyl) and terephthalic acid. For the first time in the world, the enzymatic catalytic glycolysis reaction was achieved at a significant level. 

Read more on PAL website

Recycling phosphorus from wastewater to grow better crops

Recycling phosphorus from wastewater to grow better crops

Scientists are helping close the loop on the sustainability cycle with research into nutrient-enhanced biochar — a charcoal-like material made by heating recycled biomass in the absence of oxygen (a process called pyrolysis). Biomass is any living or once-living material – including plants, trees, and animal waste — that can be used as a source of energy.

Daniel Strawn, Professor of Environmental Soil Chemistry at the University of Idaho, and his colleagues are interested in enhancing biochar – which can be used as an amendment to promote soil health — by adding phosphorus, a crucial nutrient for crops.

The research team, which also included scientists from the University of Saskatchewan and Washington State University, has focused its efforts on recovering phosphorus from wastewater.

“Phosphorus is a limited resource, taken out of the ground, processed to produce fertilizer, and eventually it ends up in wastewater,” says Strawn. “We are developing technology to recover it using biochar in a water treatment process.”

Biochar is an effective sponge ­that can soak up phosphorous and other nutrients, like nitrogen, from waterways. The team is testing this treatment process on municipal and agricultural wastewater systems.

With the help of the Canadian Light Source (CLS) at USask, Strawn and his colleagues confirmed in a recent paper which type of phosphorous had been absorbed by the biochar — a crucial step to understanding and refining their process.

Read more on the CLS website

Recycling alginate composites for thermal insulation

Recycling alginate composites for thermal insulation

Thermal insulation materials represent one the most straightforward, yet effective, technologies for improving the energy efficiency of buildings (and not only) – one of the key strategies for reducing carbon emissions. Natural-based materials and downcycled industrial and agricultural waste, thanks to their potentially reduced environmental footprint, have already made their way up to the market with the aim of limiting the ever-growing waste stream generated by the industrial sector. Research efforts on the topic are currently mainly focused on developing new insulation solutions, in which waste is reconverted as a new valuable resource. Carbohydrates, such as alginate, cellulose or chitosanare currently extensively studied base materials for thermal insulation systems, in the form of aerogels or as low-impact binding agents in waste-filled panels. Unfortunately, little or no attention has been paid to the end-of-life fate of these recycled materials; disposal (or incineration) still represents the only available option. This unprofitable scenario is even more critical in the case of polysaccharide-based composites specifically developed to reuse industrial waste. 


This was the starting point of our work, mainly conducted at the laboratories of the Engineering and Architecture department of the University of Trieste, in collaboration with TomoLab at Elettra. We developed a recycling process for an alginate-based thermal insulation foam, in which the original material is fully recovered and the thermal and acoustic insulation performances are maintained. The original foam is produced via a patented process in which alginate is used as the host poly-anionic matrix for industrial fiberglass waste. 

Read more on the Elettra website

Image: SEM and μCT image of oCAF

Credit: Figure reprinted from Carbohydrate Polymers, 251, Matteo Cibinel, Giorgia Pugliese, Davide Porrelli, Lucia Marsich, Vanni Lughi, Recycling alginate composites for thermal insulation, 116995, Copyright 2021, with permission from Elsevier.