EnabledPower Feature

EnabledFuture: Metal Recovery in Photovoltaic Modules

Michelle

EnabledFuture: Metal Recovery in Photovoltaic Modules

Anaïs Engelmann, Researcher, Enabled Future Limited

1. The Market for Solar PV Technology

Solar power is playing a major role in the global renewable energy transition with new capacity installations accounting for more than all other renewable technologies in 2021 combined. (Solar Power Europe, 2022) However, the success of solar comes with a dark side – the deployment of solar photovoltaic (PV) modules is forecasted to result in 78 million tonnes of module waste in landfill by 2050. (IRENA, 2016) Immediate action is required to prepare for this incoming waste stream and to divert it from contributing to the electronic waste crisis.

2. Drivers and Challenges for Tackling Solar PV Waste

Currently, only 10% of PV modules are reused and/or recycled worldwide with the rest ending up in landfill, creating significant environmental issues given the presence of hazardous metals including lead and tin, and the depletion of virgin materials. (Koch, 2015) This can be primarily attributed to a lack of economic incentives, due to the low value of the currently recovered material components, coupled with the high recycling costs of their separation and processing. This section examines the current drivers and challenges to implementing circularity within the end-of-life (EoL) solar PV supply chain.

2.1 Recovery Economics

A major barrier to higher PV recycling rates is the lack of profitability, which is demonstrated in the case of crystalline polysilicon (c-Si) modules, making up 95% of the PV technology market share. (IEA, 2022) With the recovered value of secondary materials taken into account, it currently costs around $20-30 to recycle a single c-Si panel, versus the $1-2 of sending it to landfill. (Wesoff & Betz, 2020) Other estimates put the relative costs of recycling and landfill in the USA at $15-45 per panel and $1-5 per panel respectively. (Deng, Chang, & Green, 2021)

However, the current value extracted from commercial PV recycling methods focuses on glass and aluminium components and does not fully exploit the potential value recovered from the present metals such as silver, copper, and silicon. There is an opportunity here for emerging PV chemical recycling technologies to focus their efforts on obtaining these lower content, yet higher value materials, which could result in lower net recycling costs or even a profit. However, there are several challenges currently faced in the recovery of such metals which are preventing their full value from being extracted.

In the case of silver, the relatively small amount found in EoL modules means its recovery is only economically feasible in large single-lot quantities of around 30-40 tonnes, due to freight expenses. Therefore, due to current waste stream volumes, the financial benefits are insufficient to justify silver-specific recovery schemes. R&D efforts are ongoing to increase silver recovery yields to improve the business case for its recovery.

In addition, for recovery to be scalable, a grading system must be put in place to classify types of PV waste and their associated silver values. However, silver content varies greatly between different panel types, particularly within amorphous crystal panels, ranging between 4 and 10 grams per panel in quantity. This creates issues in terms of standardisation, creating a further barrier to scalability. (Marchisio, 2022)

A well organised recycling facility with appropriate analytical and diagnostic capabilities should also be able to categorise and stream solar panel waste and this approach is normal in other types of recycling e.g., catalysts and batteries. However, it will be some time before such state-of-the-art facilities become commonplace.

In the case of metallic silicon, research shows potential for its waste stream to be made fully circular, but challenges are faced in terms of its purity when recovered. Silicon must be fully purified to be reinserted back into the PV supply chain, requiring high energy and complex understanding of impurities left in the recycled silicon. (Hutchins, 2022) As a result, the relative value of silicon metal is currently too low to be economically feasible, leading to a lack of silicon recovery supply chains and infrastructure.

2.2 Collection Systems and Frameworks

Key activities in creating a scalable, circular PV supply chain are the decommissioning, collection, and transportation of modules from the owner to recycling facilities, relying on participation from several stakeholders. Implementation of collection into supply chains enables this activity, with existing services typically falling under one of two categories. The first is the original equipment manufacturer (OEM) take-back schemes, where the module manufacturer has an established internal recycling infrastructure. For instance, US-based module manufacturer First Solar offers a recycling service agreement for an added fee, wherein the customer can drop off an EoL module at a region-designated collection point. (First Solar, 2022)

The second service model is where collection systems are provided by a third-party recycler, who engages with the EoL module on behalf of OEMs. (H. Salim, 2019) For instance, PV Cycle offers their Distributor Take-back Scheme in the UK, where quantities of under 20 modules can be taken to dedicated collection facilities free of charge. (PV Cycle, 2022) However, in cases where services rely on owner responsibility to uninstall and transport modules to their nearest facility, customer motivation and a lack of incentive can be barriers. Collection of EoL electronic products has proved to be significantly more effective in countries where legislation ensures that responsibility falls on the OEMs as opposed to the product owner. (OECD, 2022)

At present, only the EU has implemented a fully legislative approach, by incorporating solar waste into the Waste Electrical and Electronic Equipment Directive (WEEE) (2012/19/EU) as of 2012. This directive obligates manufacturers to collect at least 85% of their PV modules. Each EU member state has been required to transform this legislation into national law and define the rules behind collection and recycling, falling into two financial model categories. Firstly, producer-financed compliance cost models, where the producer finances EoL management through joining a compliance scheme and either paying a recycler directly or joining a stewardship programme. Secondly, consumer-financed upfront recycling fee models, where the consumer pays an additional fee at the time of module purchase, to go towards either offsetting current recycling costs or to set aside as an estimate for future recycling costs. (IRENA, 2016) These different models have been summarised in Figure 1.

Figure 1. Frameworks for EoL Module Recovery (Engelmann, 2022)

Countries outside of the EU’s mandatory framework operate under a voluntary framework, where producers either take a direct management approach and implement their own recycling infrastructures and services, or an indirect management approach. Under indirect management, the producer’s involvement can range from contracting service providers to handle waste management, to leaving the responsibility completely up to the consumer, which inevitably results in higher landfill rates. (IRENA, 2016)

2.3 Recycling Infrastructure

Alongside having collection systems in place, recycling infrastructure is another fundamental component for supporting the transition to a circular PV system. Module designs and the difficulty in material separation mean that distinct industrial processes are needed to recycle them. (Vekony, 2021) This creates the challenge of providing the necessary infrastructure to accommodate such process, and on a large enough scale to meet demands. Pilot projects of varying scale have been rolled out both privately and by research initiatives; a 2015 review of recycling infrastructure found that eight laboratory processes, two industrial pilot plants, one industrial plant and one patent had been developed thus far, with only three of those reaching an industrial level. (CucchiellaIa, D’Adamo, & Rosa, 2015)

Progress has been made within this space. For instance, the PV Producer Responsibility Organisation Soren (previously PV Cycle France, an organisation dedicated to the circularity of solar modules) has been working on several industrial-scale projects. It operates by calling for tenders and commissioning partner recycling companies. Soren partnered with the French utilities company Veolia in 2017 to open an industrial scale solar panel recycling site in Rousset, France with a capacity of 4,000 tons of PV waste annually. In September of 2022, another recycling plant was inaugurated by Soren in Saint-Loubès, France in partnership with Envie 2E Aquitaine, a French company offering WEEE collection and management services for authorities and professionals. Again, this has a capacity of 4,000 tonnes of PV waste annually and reports 95% recycling rates. This progress demonstrates the identified value potential within waste-focused industries.

3. Value Potential in Metal Recovery

Two EoL scenarios – early-loss and regular-loss – from a recent IRENA study are presented to examine value potentials whilst accounting for different uncertainties. Under the regular-loss scenario, a 30-year solar panel lifespan is assumed with no early attrition, projecting 1.7 million tons of PV waste by 2030 and 60 million tons by 2050. Under the early-loss scenario, infant and midlife failures are considered, projecting 8 million tons of PV waste by 2030 and 78 million tons by 2050 respectively. These two scenarios would amount to a cumulative $248 million and $1.1 billion of recoverable crystalline silicon value respectively becoming available for recycling. (IRENA, 2016)

Today, materials such as silicon, silver, and copper are not separated out in recycling methods, but rather just shredded and sold with the recovered glass. (Calma, 2022) The implementation of the aforementioned legislative and infrastructural drivers, coupled with continuous R&D in efforts in these areas, could unlock a huge amount of recovered material value from PV waste, considering silicon, silver, and copper account for two-thirds of the monetary material value. (Peplow, 2022) Given the material composition of a c-Si module as shown in Table 1, estimates can be made for the total recoverable value potential of the metal contents with regards to future waste streams. An average weight of 22kg per module has been used in calculations. (Latunussa, Mancini, Blengini, Ardente, & Pennington, 2016)

In the case of crystalline silicon, metallurgical-grade silicon with 99% purity has a value of approximately $4 per kg. (Peplow, 2022) Assuming the 99% purity can be achieved, that would amount to around $3.12 of recovered secondary silicon sold per module, and $146 per ton of PV waste processed. However, for silicon to be reinserted into PV production supply chains, solar-grade silicon with a minimum of 6N grade purity is required. If such purity in secondary silicon is attained, the total recoverable value could soar to around $30 per kg, meaning $1,095 per ton of PV waste processed. Under IRENA’s regular-loss and early-loss scenarios, this would equate to $1.86 billion (1.7 million tons of PV waste) and $8.76 billion (8 million tons of PV waste) respectively by 2030. (IRENA, 2016) Such high purity is yet to be achieved, but several R&D projects are already in motion to work towards unlocking this full value through soft chemistry mechanisms. These are described in the following section.

Table 1. PV Module Material Composition and Recoverable Values. (1) (H&S Metals, 2022) (2) (Statista, 2021) (3) (Bullion By Post, 2022)

In the case of silver, assuming a conservative 4 grams recovered per solar module and a current market value of $0.66 per gram (Bullion By Post, 2022), there is a total potential value of up to $2.64 per module in resale value. Under IRENA’s regular-loss and early-loss scenarios, this would equate to $594 million (1.7 million tons of PV waste) and $2.8 billion (8 million tons of PV waste) respectively by 2030. Current silver recovery yields are around 95%, and so with continued R&D these values could be further maximised. (Latunussa, Mancini, Blengini, Ardente, & Pennington, 2016)

In the case of copper, the material is found in both the copper wires connecting the cells (soldered on with tin and lead), and the internal conductor material. Assuming a full recovery of 0.47kg of copper per module and a scrap market resale value of $3.49 per kilogram (H&S Metals, 2022), there is a total potential value of $1.65 per module. Under IRENA’s regular-loss and early-loss scenarios, that would equate to approximately $127 million (1.7 million tons of PV waste) and $597 million (8 million tons of PV waste) respectively by 2030.

In the case of aluminium, the material is predominantly found in the frame, as well as the internal conductors within the solar cells. Assuming a full recovery of 4.08kg of aluminium per module and a scrap resale value of $0.51 per kilogram (H&S Metals, 2022), there is a resale value of $2.08 per module, equating to regular and early loss scenarios of $160.7 million (1.7 million tons of PV waste) and $756.4 million (8 million tons of PV waste respectively by 2030.

In total, this would amount to between 0.4 and 1.9 million tons of solid PV waste recycled worth based on today’s metal prices between $1 and $2.2 billion in value recovered.


Table 2. Regular and Early Loss Scenarios for PV Module Material Value Recovery

While the metal recovery revenues are attractive, when solar panel recycling is mandated by legislation, or where OEMs choose to take responsibility for EoL panel disposal for ESG compliance, certified recyclers can charge panel OEMs treatment and processing charges which alone make it a valuable business for them. Material recovery values are more important when there are voluntary systems for PV module recycling.

4 Recovery Methods

To capture the identified value potential in metal recovery, improved recycling methods are required to increase metal yields and to decrease processing costs. Though still in their early stages across the industry, there are now several companies with emerging technologies and research working towards improving these factors.

The Full Recovery End-of-Life Photovoltaic (FRELP) process is an EU-funded project that ran between 2013 and 2016 with a €‎4.7 million budget. (FRELP, 2022) The project was coordinated by Sasil S.p.A, Stazione Sperimentale del Vetro, and PV Cycle, with the objective of achieving 100% recyclability rates. This is considered one of the most advanced methodologies for material recovery in c-Si PV waste panels, with precious metal recovery rates of 74.5% (copper), 38.6% (metallic silicon) and 11.3% (silver). (Markert, Celik, & Apul, 2020) Though the initial objectives were not fully achieved, partial results were achieved in the form of a pre-prototype. (European Commission, 2021)

The FRELP process has the following steps: the PV frames, cables and glass are removed, leaving behind the remaining layers of polymers and cells which are treated in an incineration plant. The obtained ashes are sieved and treated by acid leaching with nitric acid, then filtered to recover the metallic silicon which is further treated with electrolysis to recover the silver (using graphite rods) and copper. (Ardente, Latunussa, & Blengini, 2019) Following the EU’s most recent technical report of the FRELP method in 2015, it was found that for 1 ton of PV waste, 36.5kg of silicon metal could be recovered by filtration after leaching and resold in the metallurgical sector, and 1.67kg of copper and silver could be recovered at cathodes following electrolysis also for market resale. (FRELP, 2022)

Other efforts to improve current metal recovery rates and costs are emerging from different private companies. The recycling start-up TG Companies, based in Tucson, Arizona in the US, has developed a patent-pending chemical process used to extract silver, tin, copper, and lead from PV cells, leaving behind just the metallic silicon. Their method includes heat treatment to boil off the EVA protective layer, using temperatures below 500°C to operate the oven and avoiding the leaching of iron and copper into the solar cell. The company predicts the recovery of $15 worth of silver per module by achieving 95% recovery at 99.9% purity. They aim to have their first pilot plant running by 2024 with a recycling target of 100,000 PV modules annually. (Hanley, 2022) (Ferrell, 2022)

ROSI Solar, headquartered in Grenoble, France, is a company offering innovative solutions for recycling and revalorization of raw materials in the PV industry. Its CEO is physicist and entrepreneur – Yun Luo and co-founder is silicon product expert – Daniel Bajolet, former VP of Rhodia. Its Chief Technology Officer (CTO) is Guy Chichignoud. ROSI’s technologies enable recovery of ultra-pure silicon and other metals currently lost during the production of photovoltaic cells and at the end-of-life (EoL) of solar panels. (ROSI Solar, 2022) They belong to the consortium ICARUS and are financially supported by the EU’s Horizon programme.

ROSI Solar is developing technology to improve the efficiency and costs of material separation, allowing them to recover ultra-pure silicon as well silver fingers from a cell, using a combination of physical, thermal, and soft chemistry mechanisms.

In solar panel production, waste is created when silicon ingot raw material is sawed using a diamond wire into wafers (less than 200 µm thick). Some 40% of the material is lost into a sludge (“kerf”) created as micro-chips of silicon mix with the sawing liquid and historically this has been disposed of rather than recovered. An estimated 200,000 tons of silicon worth $1.5 bn is lost in this way and the amounts will increase as solar panel production rates increase. ROSI’s kerf recovery technology helps manufacturers to save on kerf disposal costs and creates value by separating out the silicon from the sawing liquid. The silicon particles can be washed and used to make ultra-pure silicon granules for fresh silicon ingot and the liquid can be reused in the sawing process. (ROSI Solar, n.d.)

A patent family (WO2020007720A1) assigned to CNRS with ROSI’s CTO as one of the inventors describes a treatment process involving high temperature melting and granulation of the kerf. Silicon melts at 1,410 °C and the process requires temperatures of ~1450°C to obtain molten silicon. A first pre-granulation step using a crucible and capillary to form a discontinuous flow of molten silicon droplets which are atomised to form solid metal granules by fragmenting and solidifying the droplets received on a cooled rotating disc to form solid metal granules. (Chichignoud & Faveau, 2020)

Figure 2. ROSI Solar’s Process for Recovery of Silicon and Sawing Fluid from Kerf Waste (Chichignoud & Faveau, 2020)


ROSI Solar differentiate themselves from silicon recyclers by offering higher purity silicon, achieving up to 5N (99.999%) purity. 5N grade silicon both exceeds the 3N purity requirement for metallurgical-grade silicon and provides the environmental advantage of requiring less energy in the purifying process for higher grade application such as battery semiconductors (5-6N) and reuse in the PV supply chain (9-11N).

Furthermore, there is a current gap in the market for local European suppliers, with most high-grade silicon being imported from Asia. ROSI intends to fill this gap through PV metal recovery, particularly given market trends towards an increase in silicon demand, such as batteries which are starting to see silicon incorporated into anode technologies. Though still in their pilot phase, ROSI Solar will launch their first industrial site in 2024 in collaboration with French solar panel producer responsibility organisation Soren and Saint-Loubès based waste service provider Envie 2E Aquitaine. The facility has an expected treatment capacity of 3,000 panels per year, eventually increasing to 10,000 per year. ROSI also has ambitions to expand sites to Germany and eventually other European countries. Battery and semiconductor manufacturers are predicted to be the main secondary market customers, and a key activity soon will be working with those customers to identify what state of recycled silicon best meets their needs.

It has also been suggested that diverting silicon to applications with lower purity requirements is the best option for maximising recovery, as recovery costs for lower purity would be significantly cheaper. For instance, a team of scientists from the Agency for Science, Technology and Research (A*STAR) and Nanyang Technological University, Singapore (NTU Singapore) has proposed using such silicon for high-performance thermoelectric devices that convert heat into electricity, as thermoelectric devices which are tolerant to defects and impurities, making them suitable for recycled silicon. Their proposed technique would include pulverising polycrystalline silicon into powder and pelletising it into ingots, using spark plasma sintering to dope the silicon with germanium and phosphorus. (Bellini, 2022)

Similarly, Korean company MGInnovation Ltd. filed a patent in 2021 for the use of silicon recovered from polycrystalline silicon wafers, as a raw material for anode material additives for lithium ion batteries (LIBs). This invention uses silicon sludge recovered during the manufacturing process (as opposed to EoL silicon), and this sludge contains 30% or more of ultra-high purity silicon nanoparticles. (Korea Brevet n° KR20210152604A, 2021) Using silicon derived from the sludge in battery anodes provides several benefits over silicon powder, such as higher purity, higher reactivity, and ease of chemical bonding due to the energy generated during silicon wafer manufacturing. This shows great potential for redirecting silicon from PV waste streams into different applications.

While there is much promising activity as described in this article, many of the solutions are still in a relatively early stage development. Companies with existing pyrometallurgical scrap material who can specialise in large volume/low grade scrap recovery hold the most promise with handling future PV waste streams, given their pre-existing market expertise and infrastructure. To facilitate this, manufacturers have also started working with recyclers to improve the module designs for disassembly. For instance, Solarge is a Dutch PV manufacturing company whose modules are designed for improved extraction of materials, having already achieved better extraction results for silicon and silver compared to conventional PV modules. This can be attributed to easier material separation, no cross contamination or dangerous by-products, and less energy required for separation, also leading to lower costs and improved scalability. Their initial production capacity will be 100 MW/year, with ambitions to scale up beyond 350 MW/year. (Gerven, 2022)

A summary of the key companies with promise for future scale-up of solar PV recycling is summarised in Table 3.

Table 3. Summary of Solar PV Recycling Case Studies (Engelmann, A using data from public domain sources quoted in this article)

5 The Future for PV Recycling

Forecasted PV waste streams will significantly add to the global electronic waste production crisis unless PV recycling at scale is achieved within the next 10 years. Future implementation of regulatory approaches and infrastructure will be key enablers to avoiding large PV landfilling volumes, however complete reliance on this is insufficient. Recycling economics must also be improved to reduce processing costs and increase recoverable value.

Capturing the value of the metals present in PV modules provides a great opportunity, both for driving business within secondary raw material waste streams and diverting panels away from landfill. If higher recovery rates can be achieved through R&D for materials such as silicon metal, copper and silver, processing costs can be significantly decreased. This will be further enabled by scales of economy as PV waste streams increase over the coming years.

This can be accelerated by improved regulatory measures globally regarding extended producer responsibility for PV waste. Mandating manufacturers to handle their EoL modules would incentivise R&D for higher value recovery as well as improved collection infrastructures.

About The Author

Anaïs Engelmann is a recent graduate of Design Engineering at Imperial College London, now working at Enabled Future Limited researching solar panel recycling technologies. This work is a continuation of her Masters’ project, where she developed a web tool to facilitate recycling decisions for solar panel supply chain stakeholders. Alongside her work at EFL, she is working on the startup Team Repair, which she co-founded during her time at university. Team Repair is a circular business aimed at engaging children with STEM subjects through teaching them how to repair electronics.

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Approaches to Improving Manganese Circularity in Lithium Ion Batteries

Michelle

Approaches to Improving Manganese Circularity in Lithium Ion Batteries

Dr Michelle K. Lynch CChem FRSC, CEO, Enabled Future Limited

Snapshots of Battery Chemistries

The chemical formulations of cathode materials for lithium ion batteries (LIB) have changed over the last decade to meet the evolving needs of different applications. For instance, in electric vehicles (EVs) driving range, power performance, low temperature operation, battery life requirements and many other parameters have dictated the need for LIB technology improvements. One of the major trends in recent years was to reduce the amount of cobalt (Co) in LIB and to increase the amount of nickel (Ni). This had a two-fold benefit – reducing the demand for Co to a level where responsible supply could be managed and increasing the energy density of the battery by incorporating higher levels of Ni. However, as discussed in this month’s EnabledCircular feature, Ni prices have seen volatility and all time high prices over the last two years.

As a result of the market dynamics of Co and Ni, there is a desire to use more earth abundant metals in LIB and other rechargeable battery types. One way this can be achieved is by using higher levels of manganese (Mn) in place of the Ni. There are two main types of battery chemistry with predominantly Ni and Mn – the spinel-type lithium nickel manganese oxide (LNMO) and layered-oxide types (NMx) and high Mn NCM. Doping of lithium iron phosphate (LFP) to produce LMFP is another source of Mn demand.

The percentage by weight of Ni, Co and Mn in different battery chemistries are summarised in Figure 1 and Table 1. NB in this analysis, NCA and LFP are not included as they do not contain Mn. The trajectory of cathode chemistry development as discussed above moved from formulations with relatively high levels of cobalt e.g. NCM111 to those with higher nickel e.g. NCM811 and NCM955. To those unfamiliar with these codes, the numbering system corresponds to the relative amount of Ni, Co and Mn on a molar basis. The percentages in the chart and table refer to weight content of the pure cathode material powder prior to mixing with any coatings, binders or additives. The highest Ni content is seen in NCM955 (54 wt%) which contains only 3% Mn.

Figure 1. Metal Mass Content in LIB by Chemistry and Key High Mn LIB Innovators (Source: Enabled Future Limited)

Forecasted Manganese Demand

With most EV batteries coming onto the market expected to be high-nickel NCMs, it could be assumed that Mn would not have the level of supply criticality as do Ni and Co. However, this is not predicted to be the case. A recent analysis from Benchmark Mineral Intelligence indicates that for the NetZero scenario, Mn demand is set to rise by almost 600% between 2025 and 2040 with over 1.2 million tons of Mn required per annum by the end of that forecast period. Even more interesting, is that the largest portion of 2040 demand is expected to be for non-NCM Mn rich LIB chemistries. (Fleming, 2023) (See Figure 2 below). This has implications, not just for sourcing sufficient battery grade Mn to produce the batteries, but also for incorporating recycled content in those battery formulations in the near term and recycling them in the long term.

Table 1. Metal Mass Content in LIB by Chemistry (Source: Enabled Future Limited)
Figure 2. Manganese Demand Requirements for LIB (Fleming, 2023) republished with permission

Sources of Mn Supply

Manganese is supplied from primary mining operations. In total 20 million tons of Mn was mined in 2022 with South Africa being the largest producer (35%), followed by Gabon (22%) and the USA 16.5%. (USGS, 2023) There is no European country with a significant primary manganese mine supply – only Ukraine and Kazakhstan produce and this is from concentrates.

While the amount of Mn mined globally is much higher than that required for LIBs, there is currently insufficient capacity for producing enough high purity Mn (HPM) suitable for battery grade cathode material to meet future demand. Only 1% of the ore produced goes to HPM and most HPM is produced in China. The remainder is for steel ferroalloys (91%) and lower grades of electrolytic manganese and Mn sulphate (8%). (Fleming, 2023) In addition, while Mn is not part of the current draft of EU regulations for recycled content in LIB, the ESG goals of battery and EV OEMs may require it anyway. Therefore, there is a need to find secondary and sustainable sources of Mn for future LIB demand.

Figure 3 shows three different secondary sources of Mn – recycled LIB, other recycled batteries and sustainable mine sources along with their advantages and disadvantages. Considerations for these options are discussed in the proceeding sections of this article.

Figure 3. Sustainable Sources of Manganese and their Relative Advantages and Disadvantages

Manganese from Recycled Batteries

LIB cathodes need to have recycled content in line with the forthcoming EU Battery Passport regulations. (Popp, 2022) Although Mn is not included in these regulations currently, cell makers and EVs also require recycled content in LIBs to meet their ESG goals and this includes the Mn content – especially for Mn rich batteries. Therefore, cathode material producers in Europe are looking to source recycled content for their products. Recycled content is generated at metal refineries across all the key battery metals in the form of metal salts e.g. Ni, Co, Mn sulphates from so-called “black mass” generated from shredded waste batteries. These salts can also be recovered from treating other types of waste Mn e.g. non-LIB that contain Mn as well as scrap from metallurgical operations, catalysts and other industrial materials. The refiners then supply the cathode material producers with metal salts and solutions that have a % of recycled content mixed with virgin content.

One issue with this system is that the metal salts are generated from the output of central hydrometallurgical processing of both mixed waste streams and primary concentrates. Some cell OEMs would like a closed loop supply – whereby only their battery waste is put into the hydromet unit. However, this could only work for the largest companies, so that refineries could justify a separate line just for that OEM’s materials. This isn’t possible yet as there is not enough hydromet capacity in Europe and not enough waste batteries. However, this will change over time as that capacity comes online and waste battery levels rise. One challenge is that refining projects are only bankable if they have green electricity sources – so refiners are competing for “green-electrons”. Many new wind farms in Scandinavia are attracting battery metal refining capacity for this reason.

A second issue is the need to develop specifications for material provided from recyclers/refiners. For well-established battery chemistries such as NCM622 and NCM811, there are already well understood specifications. It should be noted that, according to leading industry contacts, the Mn coming back from recycled materials is not sufficient to be used in high-nickel NCM batteries – and it is not clear how those materials will be supplied. However recycled Mn may be good enough for LNMO. Currently for LNMO there is no long-term data on the battery performance in the end-use application and as yet, not a clear understanding therefore of the exact cathode specifications.

LNMO cathode material producers such as Topsoe in Denmark are working from the existing NCM811 specifications and learning how they should be tailored for LNMO through extensive R&D work on cathode materials containing recycled content.

Some impurities cause more trouble than others for LNMO. For instance, Co isn’t as bad as Fe – it doesn’t reduce performance, it simply doesn’t contribute to it. Whereas for Fe, which can cause self-discharge and shelf-life issues in cells, more specification development is required and testing in end-use applications. Other problem contaminants include Zn, Ca, Mg, P and F.

The pragmatic approach for producing recycled cathode materials is to start with the cheapest recycled salts available in the largest quantities. These are evaluated first and after that smaller and/or more expensive feeds are considered. The ideal is to have a constant supply of material within a range of specifications.

Recycled materials are unlikely to contribute enough to meet the rapidly growing demand for battery grade Mn. The batteries reaching their EoL over the next 10-20 years have only small quantities or no Mn at all i.e., nickel rich NCM, LCO and LFP. A second issue is that it might be difficult to keep recycled materials in Europe as cars have a habit of being sold outside the region – first going to East Europe, then South to Africa for instance. Once this happens it is unlikely that the batteries would be exported back. Attempts to force vehicle batteries to be kept and recycled in Europe are problematic from a sustainability perspective and as discussed in the EnabledMetals news insight, would do little to relieve the pressure on metal demand requirements given the growth in the battery industry.

Manganese from Sustainable Mine Sources

Production of metals from former working mines is another method to generate sustainable battery materials. Euro Manganese, headquartered in Vancouver, Canada is a producer of battery materials with a focus on producing sustainable battery grade manganese chemicals for the EV industry. Its project at Chvaletice, Czech Republic is aimed at large scale reprocessing of Mn from old mine tailings at a decommissioned mine site. The site is reportedly Europe’s largest Mn resource hosted in tailings and is a 25-year project looking to produce 50,000 tons per annum of high purity battery grade products. The output is intended to provide much needed material to plug the current and increasing Mn supply gap. The project involves no hard rock mining is cleaning up a site which is already polluted and produces Mn chemicals at around one-third the carbon footprint of industry incumbents, thereby contributing to the EU’s decarbonisation goals. (Votava, 2022)

In spite of the very positive outlook for Mn in LIB, it is not considered a desirable metal to collect and recycle from LIBs. In fact Mn is currently the last priority for a hydromet after Ni, Co and Li have been recovered. According to industry contacts, it costs as much to recycle Mn as it does Ni and Co combined. When it is recycled, most Mn is not purified back to the grade needed for most batteries i.e., NCM, NCA. The usual output is Mn hydroxide salts when the carbonates would be preferable.

Therefore, there is an industry need to take in a range of Mn-rich precipitates from different industries and process them centrally. According to Euro Manganese, this could be carried out at Chvaletice. Pyrometallurgical units have a Mn-containing slag which is in the form of oxides and silicates. This goes into construction materials currently. With some upgrading, industry contacts believe this could be viable for LNMO/LMFP battery chemistries.

As long the feeds don’t have too much Fe or F, they can be viable for upgrading – companies can also choose to do an extra upgrade themselves then send them for refining – this needs discussion and collaboration between the companies and the refiners. Blending of Mn salts from different recycled materials with purer feeds of Mn e.g., from the mine tailings can be a useful strategy although it needs to be demonstrated.

Patent Landscape for Manganese Recycling

There are relatively few patent publications for recycling manganese-rich batteries compared with NCM/NCA which is not surprising given their early phase of commercialisation. However selected patents and key details are provided for Mn recycling from LIB and other secondary sources in Table 2 below. Most of the patent literature comes from Chinese assignees and amongst those – key universities and institutes as well as the larger recycling companies with hydrometallurgical capacity i.e., GEM and Brunp.

Table 2. Selected Patents and Key Details for Mn Recovery from Waste Batteries and Other Secondary Sources (Source: Enabled Future Limited)

Enabled Future Limited provides ongoing analysis of patents related to the production and recycling of LIB for Mn rich formulations and these are available as a monthly download via subscription.

Key Takeaways

  • Cathodes with lower Ni/Co-Free chemistries are growing rapidly e.g., LNMO, NMx, LMFP
  • LNMO will be the largest user of Mn in batteries by 2040, even more than high nickel formulations
  • The need to meet demand for recycled materials in line with sustainability/ESG goals will require that much more secondary Mn is available
  • Recycled Mn is expensive to produce and could be detrimental to battery price competitiveness in the EU – there is a large need to bring down the price.
  • Sustainable mine sources can seriously help to bridge the supply gap – and projects such as Euro Manganese Chvaletice, Czech Republic are looking promising.
  • Much of the effort needed isn’t necessarily technical – it’s logistical and requires cooperation between different stakeholders.

    There is a need to ensure that Mn doesn’t end up in landfill and is actually recycled – ESG practices ought to benefit the industry here.

    There are opportunities – however we must be proactive and collaborative in order to realise them.

About The Author

Michelle Lynch is a PhD in Chemicals and Catalysis and is a Chartered Chemist and Fellow of the Royal Society of Chemistry (FRSC). Her 26 years of post-doctoral experience span catalyst R&D, catalyst and precious metals market research, patent analysis and consulting. She is currently the CEO and Owner of Enabled Future Limited (EFL). Prior to setting up EFL, Michelle worked with IHS (S&P Global), Nexant and Johnson Matthey. Michelle is a regular speaker at conferences, editor and contributor to industry magazines including the new Enabled Future magazine. Her publications have also appeared in the IHS Chemical Bulletin, IHS Quarterly, The Catalyst Review, Recycling & Waste World and The Catalyst Group subscriber reports. She lives and runs her consultancy in the West Midlands, UK.

Fleming, A. (2023). Manganese Panel. Benchmark Week (pp. 1-6). Benchmark Mineral Intelligence.
Popp, D. (2022, December 9). Batteries: deal on new EU rules for design, production and waste treatment. Retrieved from Europarl: https://www.europarl.europa.eu/news/en/press-room/20221205IPR60614/batteries-deal-on-new-eu-rules-for-design-production-and-waste-treatment
USGS. (2023). Manganese. Retrieved from USGS: https://pubs.usgs.gov/periodicals/mcs2023/mcs2023-manganese.pdf
Votava, J. (2022, May 17-18). The Chvaletice Manganese Project. Retrieved from re-mine.eu: https://re-mine.eu/wp-content/uploads/2022/06/3_13_EMN-corporate-presentation_2022_05_18-_Conference-Micheleen_Belgium-combined-1.pdf

H2 Economy: Recycling Solutions for the Future

Michelle

H2 Economy: Recycling Solutions for the Future

Anna Marchisio, Business Development Manager, Hensel Recycling GmbH

Anna Marchisio is Business Development Manager from Hensel Recycling GmbH, based in Aschaffenburg, Germany. Hensel Recycling was founded in 1998 and it is due to celebrate its 25th anniversary this year. Its main business is in recycling of platinum group metal (PGM) containing products including automotive pollution control catalysts, oxygen-sensors, and e-scrap. More recently it has begun to work on recycling of PGM-containing fuel cells.

Anna gave a presentation as part of a webinar hosted by Hydrogen Moves on February 28th along with her colleague from Hensel Recycling’s daughter company IDO-Lab GmbH, Orhun Dedici – project manager of fuel cell recycling. The presentation covered the different stages of recycling loops from a product’s end-of-life (EoL) to its re-usage in new items. The stages in between require fastidious processes for collection, dismantling, homogenization, sampling and analysis, PGM value estimation, refining and precious metal recovery.

This process reduces the CO2 footprint of PGM by around 12-fold compared to if PGM is not recycled.

Hensel Recycling is a participant of a consortium with eight other partners on the European funded Clean Hydrogen Project – BEST4Hy which focuses on the development of new technologies to recover critical raw materials from EoL fuel cells – both PGM and SOFC, with Hensel Recycling focusing on the PGM fuel cells. The BEST4Hy project is aiming to scale the process from technology readiness level 3 (TRL3) to TRL5. Hensel Recycling has three key areas of interest: disassembly of stacks, closed loop recycling of PGM via its HRT process and recovery and reuse of the ionomers.

Some slides from this presentation are provided here and the full recording of the webinar and slides are available on the Hydrogen Moves web site (https://www.hydrogen-universe.com/) (registration required):

Sorption-enhanced processes for simultaneous waste utilisation, CO2 capture and hydrogen production

Sorption-enhanced processes for simultaneous waste utilisation, CO2 capture and hydrogen production

Michelle

Sorption-enhanced processes for simultaneous waste utilisation, CO2 capture and hydrogen production

Dr Dawid Hanak, Associate Professor in Energy and Process Engineering, Cranfield University

Rapid development and commercialisation of energy efficiency measures, renewable energy production and low-carbon technologies, such as carbon capture and utilisation (CCU) and low carbon hydrogen (LCH), are critical to meeting commitments made by country signatories to the Paris Agreement for reducing greenhouse gas (GHG) emissions. In addition, companies are looking to remove fossil fuels from their supply chains and meet consumer-driven demand for greener products.

Waste-to-energy (WTE) coupled with sorption-enhanced processes is forecasted to be a promising approach for reducing GHG, the amount of waste sent to landfill and our dependence on fossil fuels. Yet, this technology is still at an early stage of development, and further R&D activities are necessary for its rapid commercialisation.

In addition, replacing fossil fuels with alternative energy vectors, such as LCH and hydrogen-derived fuels (i.e., ammonia, methanol, synthetic natural gas and synthetic aviation fuels), form a key part of technology-based strategies for decarbonising industry, transportation and heating. Over 50 countries globally have already devised a dedicated hydrogen strategy and are investigating how to obtain hydrogen at scale. Currently, nearly the entire global hydrogen supply (70 million tons per annum, tpa) still depends on the conversion of fossil fuels¹. Furthermore, the International Energy Agency (IEA) forecasted that hydrogen demand will grow to more than 200 million tpa by 2030 and 500 million tpa by 2050¹. As such a large amount of LCH is required, different sources and production methods need to be pursued.

Biomass is widely considered as an alternative feedstock to fossil fuels for energy and hydrogen production, given its low carbon characteristics. As a result, a significant amount of R&D has been undertaken over the past decades to develop conversion technologies such as gasification and associated syngas upgrading processes.

However, there are major challenges to using traditional virgin biomass, e.g., food crops, as the backbone for the hydrogen economy, not least the significant land and water requirement to produce it at the necessary scale and the potential competition with food supply chains. Therefore, more sustainable sources of biomass, e.g., non-food crops, crop waste, forestry waste and municipal solid waste (MSW) have also been considered as alternative feedstocks.

Notably, approximately 2 billion tpa of MSW are generated worldwide and this is forecasted to increase to 3.4 billion tpa by 2050³. In the UK, 7.2 million tons of MSW were produced in 2018⁴. The organic content of MSW varies between 40–70%, with developing countries being at the highest end of this range⁵. Approximately 4% of the UK GHG emissions are still associated with MSW, mostly due to its deposition in landfills⁶, which accounted for UK emissions of 12.8 million tons of CO2 equivalent (tCO2eq) in 2020⁷.

MSW streams have an average energy content between 5–22 MJHHV,ar/kg²,⁸, which is comparable to biomass (i.e. rice straw – 13.4 MJHHV,ar/kg; manure – 13.6 MJHHV,ar/kg²) and some fossil fuels (i.e. peat coal – 10.9 MJHHV,ar/kg; lignite – 6.8 MJHHV,ar/kg²) (Figure 1). Consequently, MSW can be converted into valuable fuel products using novel technologies, such as sorption-enhanced processes. These can efficiently convert MSW into thermal energy and/or clean fuels at near-zero CO2 emissions, when linked with carbon capture, contributing to the decarbonisation of the energy and industrial sectors. This is explained in the proceeding sections.

Hydrogen production via conventional gasification and sorption-enhanced gasification

Although hydrogen production from MSW can be achieved via biological or thermochemical processes, the latter are most attractive because they offer faster process kinetics and lead to higher H2 yields9. Among the main thermochemical routes, gasification offers better results in terms of H2 yield when compared with pyrolysis10.

Figure 1: Comparison of MSW heating value (green bars) with other biomass types (amber bars) and fossil fuels (orange bars) (Data source: ECN Phyllis database²)

MSW conversion to H2 via gasification occurs at temperatures between 700°C and 1200°C, which is necessary to support the endothermic gasification reactions. A gasifying agent, such as air, oxygen, steam or CO2 is normally required. Pure oxygen (up to 64 gH2/kg biomass) rather than air (~15 gH2/kg biomass) leads to higher H2 yield and more concentrated product streams with higher calorific values because there is no nitrogen dilution11. Steam gasification (up to 128 gH2/kg biomass) leads to even higher H2 yields when compared with O2 gasification. This can be attributed to the decomposition of water, the water gas shift (WGS), and methane reforming reactions. The addition of steam also moves the equilibrium of the WGS reaction
(CO+H2O<->CO2+H2) to the right, enhancing the H2 yield (Table 1).

The products of biomass gasification are tars, chars, and syngas, with the typical syngas composition being 30–50%vol of H2, 25–40%vol of CO, 8–20%vol of CO2 and 6–15%vol of CH412. It can be further upgraded in the WGS reactors and pressure swing adsorption (PSA) processes to produce H2 with 99.9% purity. Yet, the endothermic characteristic of conventional gasification means that energy needs to be supplied from an external source. This is usually done via combustion of fuel, resulting in CO2 emissions.

Table 1: Summary of levelised cost of hydrogen for different technologies11,15

In contrast to conventional gasification, a sorption-enhanced gasification (SEG) process combines the solid fuel gasification process with simultaneous CO2 removal to produce H2-rich syngas (Figure 2). This is achieved by the presence of a CO2 capture sorbent, such as calcium oxide (CaO), in the gasification chamber which is held at approximately 600–700°C. This temperature has been shown to maximise the CO conversion and CO2 capture rate13. The so-called carbonation reaction (CaO+CO2<->CaCO3) is exothermic and releases enough heat to balance the heat demand needed to drive the endothermic gasification reaction. Consequently, the SEG process does not require an external combustor to drive the gasification process, avoiding the corresponding CO2 emissions.

Figure 2: Operating principle of sorption-enhanced gasification of solid fuels and waste (Source: Dr Hanak)

Moreover, the underlying premise of such a process is an enhancement of the H2 yield by removing CO2 from the gasification environment, shifting the equilibrium of the water gas-shift (WGS) reaction further to the right14. For example, considering the same feedstock composition and input, the study by Santos and Hanak15 revealed that SEG will result in a substantial increase in the H2 yield (up to 80 gH2/kg MSW), and thus concentration (Figure 3), compared to the conventional gasification process (up to 70 gH2/kg MSW).

It is also important to highlight that the SEG process uses natural sorbents, such as calcium oxide (CaO). This sorbent is considered a promising catalyst and CO2 capture material due to its high availability, low cost, and potential use of the spent material in the cement industry16. SEG would produce about 146 kg of spent sorbent per each tonne of CO2 captured. However, stream can contain sulphur compounds (i.e., CaSO4) and ash15 that may prevent its industrial re-use.

Figure 3: Comparison of syngas composition produced in conventional gasification and SEG before the final pressure swing adsorption process (Data source: Santos and Hanak15)

The main downside of the emerging SEG process is that the sorbent needs to be regenerated, in the so-called calciner, at a temperature above 900°C. The state-of-the-art process designs assume that high-grade heat to drive the calcination reaction is supplied via oxy-combustion of fuels directly in the calciner. This, in turn, results in an added energy penalty for producing pure oxygen of about 200 kWh/tO2. Alternative options to supply high-grade heat to drive the calcination reaction, including indirect heat transfer from air-fired combustor17 and solid-oxide fuel cell18, were considered. However, such concepts are still in the early stage of development.

Figure 4: Degeneration of sorbent conversion (XCaO) with number of carbonation and calcination cycles (Source: Grasa and Abanades19)

Another major challenge of using Ca-based sorbents for SEG is a reduction in the sorbent CO2 carrying capacity (Figure 4) on cycling operation due to sintering, attrition and sulphation20. Consequently, the deactivated sorbent needs to be partially replaced by fresh sorbent to keep acceptable sorbent conversion in the carbonator. This further increases both the demand for high-grade heat and the operating cost. To reduce fresh sorbent requirement and improve the cyclic performance of SEG, the Ca-based sorbents can be enhanced via hydration (CaO+H2O<->Ca(OH)2), doping with salts or acids, and thermal pre-treatment. Synthetic sorbents were also shown to deliver much better cyclic performance21. However, the economic viability and commercial scalability of alternative sorbents have not yet been proven22.

Energy and environmental benefits

The core premise for integrating CO2 capture and H2 production is to enhance the energy performance of the gasification process while reducing the amount of CO2 released into the atmosphere. Higher H2 yields achieved through the enhancement of the WGS reaction will naturally result in syngas of a higher quality that, in turn, requires less purification effort. Yet, the actual energy performance of the process is highly dependent on the gasification operating conditions, such as the steam to MSW ratio that stands for the amount of steam needed to gasify a unit amount of solid fuel.

The primary function of the gasification process is to convert MSW into a high-purity hydrogen stream. The energy performance of such a conversion process is usually characterised by the ratio of the hydrogen energy produced and the amount of energy input with MSW. This performance metric is substantially influenced by the amount of steam used in the gasification process. For the conventional gasification process, the optimum operating point is at the steam-to-MSW ratio of about 1.2, which results in the H2 production efficiency of 47.7%. This is because any further addition of steam would not improve the H2 production efficiency, increasing the energy demand and water demand for the process. On the contrary, the H2 production efficiency for the sorption-enhanced process has increased proportionally to the steam-to-MSW ratio, achieving 51.2% at the steam-to-MSW ratio of 2. This is because, in this case, MSW gasification takes place simultaneously with the WGS reaction, which promotes steam conversion to hydrogen. Despite the 3.5%-point increase in hydrogen production efficiency, the optimum steam-to-MSW ratio for SEG is about 1.8–1.9. Operation under higher steam-to-MSW ratios would result in an electricity deficit and SEG would need to draw electricity from the grid.

Given that both conventional gasification and SEG operate at elevated temperatures above 650°C, waste heat can be recovered to generate electricity that can then offset some (or all) of the process electricity requirement. This usually takes place in a conventional superheated steam cycle. Such a practice allows avoiding the need for electricity import from the grid and increases the overall energy efficiency of the process. However, the additional equipment required in SEG to supply pure O2 for the calcination process and the compression of captured CO2 results in an additional electricity requirement. Consequently, the net electric efficiency, and thus the amount of electricity exported to the grid, tends to be lower for SEG than for conventional gasification (Figure 5). Therefore, it is expected that SEG would result in an overall energy penalty of about 4% points15.

Figure 5: Comparison of energy efficiency15

Regardless of marginally lower energy efficiency, the key advantage of SEG over conventional gasification is a reduction in the carbon intensity associated with hydrogen production. The conversion of MSW using conventional technology would result in specific CO2 emissions of about 181 gCO2/MJH2. This is due to the char and tail gas combustion to supply heat for the gasification process and produce electricity for the auxiliary equipment. The carbon intensity would drop by more than 90% (11.67 gCO2/MJH2) for the sorption-enhanced process15. SEG achieves such a reduction in the carbon intensity because the char and tail gas combustion takes place in the oxy-fired calciner (Figure 2). A small fraction of tail gas is used in the gas turbine to supply electricity to drive the auxiliary equipment, hence the carbon intensity is still positive15. However, considering the UK’s Low-Carbon Hydrogen Standard23, which specified that hydrogen can be considered low-carbon when the specific CO2 emissions of its production is less than 20 gCO2/MJH2, the SEG of MSW will produce LCH that meets this standard. Therefore, such processes can substantially contribute to improving waste management and reduce our reliance on fossil fuels to increase the LCH supply.

Economic viability

Based on 20 years of past research and development activities, we know that carbon capture is expected to increase the cost of hydrogen production compared to conventional production technologies due to increased capital and operational expenditures24. This also applies to SEG processes, although the cost estimations for this technology are scarce due to its low technology maturity.

Considering the layout of the SEG process, it benefits from a simplified syngas processing train because the WGS reaction takes place simultaneously with the gasification reaction in the sorption-enhanced gasifier. In addition, the syngas clean-up unit, which includes a liquid oxidation catalyst process and zinc oxide bed for hydrogen sulphide (H2S) removal, is not required. This is because of the strong affinity of CaO to sulphur compounds, these will be removed in the sorption-enhanced gasifier and then removed with the purged spent sorbent. However, the resulting CaSO4 would reduce the quality of the purged sorbent and reduce it market appeal. Moreover, the SEG plant needs an air separation unit (ASU) and CO2 compression unit, and a calciner for sorbent regeneration. Consequently, its capital cost is 20–50% higher than that of conventional biomass gasification. Moreover, the operating cost of the SEG will be higher due to the need to factor in the cost of fresh CO2 capture sorbent and the cost of CO2 transport and storage.

Consequently, the initial economic assessments of the SEG of MSW (Figure 6) showed that the levelised cost of hydrogen produced via this route is expected to be nearly double (3.9–6.1 €/kgH2) than that produced from the conventional MSW gasification (2.0–3.4 €/kgH2)15. This corresponds to the cost of CO2 avoided, which stands for the minimum CO2 price to offset the difference between the low-carbon and conventional hydrogen production, of about 115 €/tCO215. As of September 2022, such a figure is still above the CO2 emission allowance price on the EU Emission Trading Scheme, which stands at about 90–100 €/tCO225. Consequently, the carbon tax or price alone there may not provide sufficient financial incentives yet for the technology developers to pursue deploying this technology. However, the amount of allowed CO2 emissions in the EU Emission Trading System is expected to decrease gradually over time, in line with the EU’s “Fit For 55” plan to achieve at least 55% greenhouse gas reductions by 203026. In turn, this is expected to push the prices of CO2 emission allowances above 140 €/tCO227. Furthermore, the recent survey by the International Emission Trading Association (IETA) found that to limit global warming to 2°C, the global average carbon price needs to be about €124.35/tCO2 and €200.50/tCO2 by 2030 and 2050, respectively28. Such a level of the carbon price (or tax) is significantly higher than the tax credits introduced recently in the US through the Inflation Reduction Tax that assume €85/tCO2 and €60/tCO2 when CO2 is stored and utilised, respectively29.

Figure 6: Levelised cost of hydrogen estimated for different technologies (solid orange bars – unabated fossil fuels; pattern orange bars – fossil fuels with CO2 capture; solid amber bars – unabated biomass; pattern orange bars – biomass with CO2 capture; solid green bars – unabated municipal solid waste; pattern green bars – municipal solid waste with CO2 capture)

Nevertheless, there is an alternative option to the ETS and carbon tax credits that can make CCUS technologies financially viable. Industrial use of CO2 can provide a valid business opportunity for developers of the MSW SEG process. Taking the UK food industry as an example, the CO2 price has surged from €235/tCO2 (£200/tCO2) in September 202130 to €1,183/tCO2–€5,324/tCO2 (£1,000/tCO2–£4,500/tCO2) in September 202231. Even at the lowest end of this scale, the CO2 price is still substantially above the carbon price necessary for MSW SEG to be financially viable, and products which tie up the CO2 captured such as polyols for polyurethanes, and olefins for polyolefins would go further than simple fossil fuel displacement. As the majority of CO2 supply in the UK comes from the fertilizer industry, such a drastic increase in CO2 market price is associated with a sharp increase in the natural gas price. Although the latter figure comes from an uncertain source, using CO2 from SEG of MSW can provide a financially viable supply for industrial utilisation. Moreover, the waste treatment facilities can attract a gate fee, which can vary between 40–60 € per tonne of waste processed15. Such a carbon price and gate fee would promote investment in MSW utilisation technologies via the sorption-enhanced route.

Table 2: Summary of levelised cost of hydrogen for different technologies15,32

Still, the levelised cost of hydrogen (LCOH) production for the SEG of MSW does not appear to be economically competitive when compared to more established hydrogen production technologies (Table 2), such as steam methane reforming (SMR; 1.0–1.5 €/kgH2 w/o capture; 1.2–2.7 €/kgH2 w/ capture), coal gasification (0.9–1.8 €/kgH2 w/o capture; 1.2–3.4 €/kgH2 w/ capture) or biomass gasification (1.4–3.2 €/kgH2 w/o capture; 2.1–3.3 €/kgH2 w/ capture). It is, however, competitive with the SEG of biomass, for which the low fidelity estimate of the LCOH falls between 6.1–10.1 €/kgH215. This can be attributed to the fact that, in contrast to biomass, there is a potential gate fee that the plant operator can receive in return for processing MSW. SEG of MSW process will also result in a competitive LCOH to variable renewables integrated with electrolysis, such as wind and solar, which currently is about 4-9 €/kgH2, but is expected to reach less than 2 €/kgH2 after 2030 and to below 1.5 €/kgH2 by 20501.

Current development status

Although the SEG of MSW has resulted in a higher cost of hydrogen production, this technology is still in a relatively early stage of development. Much R&D activity is focused on designing and optimising sorption materials and reducing sorbent deactivation during cyclic operation. However, the pilot and demonstration scale experience are scarce. At the pilot plant scale, the SEG was performed in a dual fluidised bed unit at the Technical University Wien. The design fuel input of this pilot plant is 100 kW. Moreover, 20 kW and 200 kW pilot plants were developed and tested at the Institute of Combustion and Power plant Technology of the University of Stuttgart. Finally, a 71 kW pilot plant was developed by the Gas Technology Institute (GTI) in the US. The pilot-scale experiments showed that about 70–80% volume fraction of H2 was achieved33. This was in line with the figures reported by Santos and Hanak15. It is important to emphasise that, to date, no demonstration scale units have been operated for the SEG of solid fuels. The first 1.5 MW demonstration plant is currently being developed at Cranfield University in collaboration with GTI, Doosan Babcock and the UK Department for Business, Energy and International Strategy (BEIS)34. However, some of the existing dual-fluidised-bed gasifiers were adopted to operate under the SEG, including the 8 MW gasification plant in Güssing, Austria and the 8.5 MW gasification plant in Oberwart, Austria. As these units were not designed specifically for the sorption-enhanced process, the maximum hydrogen purity reached 52–57%33.

Future development needs and perspective

There is no simple answer to whether the SEG of MSW is a viable technology to supply LCH to support the decarbonisation of our economy. On the one hand, such a process would allow us to efficiently utilise MSW and significantly reduce the amount of MSW ending up in landfills. It also has the capability of supplying LCH that meets the requirements of the UK’s Low-Carbon Hydrogen Strategy. Furthermore, SEG of MSW could reduce the reliance on fossil fuels of, and the cost of CO2 supply to, various sectors of our economy. This is especially critical considering the current supply crisis associated with soaring prices of natural gas. Notably, if all MSW generated in the UK (7.2 million tpa) was processed in SEG, it could supply about 35% (0.25 million tpa) of current UK H2 production (0.7 million tpa)35. Therefore, SEG of MSW can play a crucial role in the decarbonisation of large cities and industrial clusters, reducing the need for MSW and H2 transport. However, as with other carbon capture technologies, the challenge is a high economic penalty. A higher energy requirement and capital cost of the SEG process than that of the conventional gasification process results in an uncompetitive LCOH.

Notably, SEG is currently at a relatively early stage of development, with the technology readiness level assessed to be about 3–5. The mature hydrogen production technologies, such as steam-methane reforming, coal gasification or electrolysis, have already reached commercialisation deployment and are well established. This is equivalent to the technology readiness level of 9. Therefore, further development of the sorption-enhanced processes and new sorbents with better cycling performance can bring further cost reductions. This, combined with policy and subsidy support from the government and the development of carbon markets, can make the SEG of MSW competitive with well-established processes.

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