There is a possibility for a low-impact environmental breakdown of HFC-134a contained in end-of-life equipment by utilising an industrial byproduct from aluminium production.

The heat trapped in the atmosphere, forming almost a «blanket around the planet», defines the so-called “greenhouse effect,” whose harmful impacts are responsible for global warming and climate change.

Among the greenhouse gases responsible – along with carbon dioxide (CO2), methane, and nitrous oxide – are fluorinated gases, which include hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), sulfur hexafluoride, and nitrogen trifluoride.

These fluorinated gases are not natural byproducts but are synthetic gases produced intentionally and used in domestic, commercial, and industrial activities involving refrigeration (fridges), air conditioning, heat pumps, fire suppression systems, equipment containing solvents, and semiconductor manufacturing. They are characterised by a high Global Warming Potential (GWP), absorbing more energy per tonne emitted compared to CO2, thus trapping more heat and remaining in the atmosphere for periods ranging from a few to thousands of years [source: United States Environmental Protection Agency].

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TAKEAWAYS

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Hydrofluorocarbons: among the most potent greenhouse gases

Among fluorinated gases, hydrofluorocarbons (HFCs) are the most well-known. They were introduced as alternatives to the old chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs), which have been gradually phased out globally since 1989 under the Montreal Protocol (spearheaded by the UNEP – United Nations Environment Programme) due to their severe damage to the stratospheric ozone layer. While HFCs do not contain chlorine and thus do not harm the ozone layer, their carbon content makes them significant contributors to the greenhouse effect. Consequently, the Kyoto Protocol, which came into force in February 2005, classified HFCs among the seven most potent greenhouse gases to be reduced, alongside CO2, methane, nitrous oxide, perfluorocarbons, and sulphur hexafluoride.

Regarding the Global Warming Potential of hydrofluorocarbons, the study “Hydrolysis of HFC-134a using a red mud catalyst to reuse an industrial waste” (Journal of Industrial and Engineering Chemistry, August 2024 issue) by researchers from the Korea Institute of Energy Research and Korea University in Seoul highlights that their potential is 140-11,700 times greater than that of carbon dioxide, with a maximum atmospheric lifetime of 270 years.

Yet, despite this evidence, the authors note, «Worldwide, the consumption of hydrofluorocarbons is increasing, especially in automotive and electronic products, where HFC-134a is widely used as a refrigerant».

This underscores the urgency of developing an appropriate treatment process for this type of HFC to reduce its hazardous greenhouse effect at the end of its life cycle. Before delving into the regulatory frameworks governing their use at the European and international levels, let’s take a closer look at the context.

International agreements and reference regulations

In 2016, the Montreal Protocol was amended by the Kigali Amendment (also orchestrated by UNEP delegates), which came into effect in 2019. This amendment mandates all UN member states to reduce hydrofluorocarbon emissions by over 80% of historical levels by 2050.

Specifically, within the European context, on 11 March 2024, Regulation (EU) No. 573 on fluorinated greenhouse gases came into force, effectively repealing the old Regulation (EU) No. 517/2014 and amending Directive (EU) 2019/1937. The aim is to further limit emissions of these gases, in line with the EU’s agreement on climate neutrality by 2050 and the aforementioned international treaties.

The new EU Regulation stipulates the gradual and definitive elimination of all fluorinated gases, including HFCs, by introducing specific conditions for their production, importation, and market placement, alongside products and equipment containing them. The goal is to completely phase out their use within the next twenty-five years.

In the United States, the relevant legislation is the American Innovation and Manufacturing Act, enacted by the federal government in 2020. This law regulates the reduction of hydrofluorocarbons by 85% by 2036, gradually reducing their production and consumption, maximizing recovery, minimizing release from equipment, and facilitating the transition to next-generation technologies.

A brief overview of China and India shows that their approach to the harmful effects of HFCs primarily focuses on strengthening the implementation of the Kigali Amendment to the Montreal Protocol. Notably, China has tightened its Ozone Depleting Substances (ODS) regulations starting in early 2024, focusing on the progressive reduction of hydrofluorocarbons. Meanwhile, India has set a detailed roadmap until 2047, divided into four phases, aiming for cumulative reductions in HFCs of 10%, 20%, 30%, and 85%.

Current methods of reducing hydrofluorocarbons

Article 8 of the aforementioned Regulation (EU) No. 573/2024 stipulates that «operators of equipment containing fluorinated greenhouse gases, not contained in foams, must ensure that these substances are recoveredand, after deactivation of the equipment, are recycled, regenerated, or destroyed».

For equipment containing foams with fluorinated greenhouse gases, from 1 January 2025, the Regulation states that their treatment must «avoid emissions as much as possible and handle the foams in a way that ensures the destruction of the gases contained therein. If such gases are recovered, this must be carried out only by adequately qualified personnel».

Specifically, regarding the refrigerant gas HFC-134a, the Korean study mentioned at the outset states that its destruction at the end of the life cycle of the equipment containing it requires a significant amount of energy. The reason is that, among all HFCs, 134a «maintains a chemically stable state over time» the team explains, adding that «during its decomposition, hydrofluoric acid is generated, resulting in corrosion of the treatment plant. Therefore, various techniques are being studied to effectively destroy this type of HFC».

The current technologies for reducing this fluorinated gas, as described by researchers from the Korea Institute of Energy Research and Korea University, include:

• combustion
• thermal decomposition
• plasma decomposition
• catalytic decomposition

When reviewing these, the study group highlights their challenges, which are linked to the specific characteristics of HFC-134a. For instance, with combustion, there is a risk of generating pollutants such as fluorinated dioxins, CO2, and nitrogen oxide.

The thermal decomposition technique «has the disadvantage of high energy consumption. To achieve an 80% conversion of HFC-134a using this method, a temperature of at least 900°C is required».

Plasma decomposition also involves high energy costs and initial investment. Moreover, the larger the reactor, the greater the plasma density and decomposition efficiency must be.

Conversely, catalytic decomposition (using catalysts) is an approach capable of ensuring high destruction efficiency of HFC-134a at relatively low temperatures, up to 600°C, the authors highlight.

Currently, numerous studies are underway on the use of catalysts in the treatment of HFC-134a, including those focused on the use of waste materials, aluminium oxide-based materials, metallic oxides, and metallic phosphates, all aimed at reducing energy consumption during the decomposition process while generating minimal pollutants.

Catalytic decomposition of hydrofluorocarbons 134a using waste materials

A Korean research team has focused specifically on the use of catalysts derived from waste materials, which are considered both cost-effective and environmentally sustainable.

In this context, a Japanese study from 2011 titled “Simultaneous Decomposition and Fixation of F-Gases Using Waste Concrete” experimented with the decomposition reactions of HFC-134a. The study used a waste concrete-based catalyst that could lower the process temperature to 500 °C, while fixing hydrofluoric acid as calcium fluoride within the concrete.
Another study, published in the Journal of Industrial and Engineering Chemistry, examined the use of red mud, a by-product of the metallurgical industry, as a long-term catalyst. 

What is Red Mud? It is a waste product generated during aluminium production,  composed of iron, aluminium, and titanium oxides, with small amounts of silicon, calcium, and sodium oxides. These elements collectively contribute to its catalytic activity. The team highlighted that red mud «has an excellent particle size distribution, with 90% of its volume being less than 75 μm. Combined with the presence of active metals, this makes it advantageous as a catalyst for HFC-134a hydrolysis».

However, despite its positive properties, red mud is also highly alkaline and rich in heavy metals. If released untreated into the environment, it poses a toxic threat to soil, water, and human health. [Source: “Leaching of metals from red mud and toxicity in human cells in vitro” – Chemosphere, August 2023]. The researchers noted that «producing one tonne of aluminium generates 1 to 1.5 tonnes of red mud, which is then collected in industrial wastewater».

Therefore, the catalytic decomposition method using red mud serves a dual purpose: reducing powerful greenhouse gases in an eco-friendly manner and recycling a hazardous industrial waste.

Preparation and performance of red mud catalysts

The red mud catalysts for decomposing HFC-134a were produced using compression moulding. Initially, red mud, discharged as a liquid slurry during aluminium processing, was dried at 80 °C for 24 hours, resulting in a solid material. This material was then crushed and sieved to a size below 500 µm before being pressed.

«For the experiment, the compressed red mud was divided into pieces averaging about 5 mm. No chemical treatments were performed aside from physical solidification and compression» the Korean researchers stated, highlighting the eco-friendliness of their solution.

Initial hydrolysis tests of hydrofluorocarbon 134a showed excellent performance, maintaining a decomposition rate above 99% for 100 hours at temperatures between 550 and 700 °C, using 10,000 ppm of fluorinated gas.

Regarding temperature, it was observed that the gas decomposition rate increased with rising temperatures, reaching approximately 93% at 650 °C. To verify this phenomenon, hydrolysis was conducted at various temperatures:

«At 700 °C, the decomposition was similar to that at 650 °C, indicating that temperature had a negligible effect above 650 °C.”

Another key observation involved hydrofluoric acid, typically produced during HFC-134a decomposition and known for its corrosive nature. When reacting with the calcium oxide in red mud, hydrofluoric acid forms calcium fluoride, which creates a thin protective film on the catalyst surface, shielding it from external interference.

Glimpses of Futures

The aim of the study – to transform a waste product from the metallurgical industry into an effective environmental catalyst for the hydrolysis of hydrofluorocarbon 134a – has been achieved. Initial experiments have confirmed its suitability. 

Now, we must anticipate possible future scenarios by analysing the impacts of the catalytic decomposition technique for HFC-134a using red mud through the STEPS framework.

S – SOCIAL: globally, between 2040 and 2050, all types of hydrofluorocarbons (including refrigerant gas 134a) will be entirely phased out in terms of production, export, import, and market introduction, including the equipment that contains them. This scenario represents a monumental step towards climate neutrality. However, until HFCs are completely eliminated, disposal methods like the one developed by the Korea Institute of Energy Research and Korea University will help mitigate end-of-life damage of these potent greenhouse gases. Compared to other methods, this approach positively impacts energy consumption required for their destruction and reduces the generation of pollutants (especially hydrofluoric acid) released during their decomposition.

T – TECHNOLOGICAL: red mud is an exceedingly complex waste material composed of multiple elements. Consequently, its catalytic activity may vary depending on the preparation, moulding, and compression processes, as well as the dynamics occurring during performance. For this reason, the research team tested its catalytic functions using three different samples. The three catalysts were prepared following the same procedures but with a comparison of catalytic activity at different temperatures, ranging between 600 and 650 °C. The differences in the process of HFC-134a destruction were minimal (between 3-4 percentage points at 600 °C and 3-8 percentage points at 650 °C). Nevertheless, in the future, it will be useful to explore the performance of red mud catalysts obtained through different procedures, to evaluate their efficiency. Furthermore, should the catalytic decomposition technique of HFC-134a based on red mud be validated in the coming years, its application could be extended to the disposal of other greenhouse gases or substances harmful to the climate and environment.

E – ECONOMIC: in the future, the economic impact of a solution involving the decomposition of hydrofluorocarbon 134a using catalysts derived from red mud, a by-product of aluminium production, lies in the reduction of costs associated with treating this industrial waste. It is worth noting that 180 million tonnes of red mud are produced annually worldwide, «accumulated to the point of becoming one of the largest environmentally hazardous waste products, with an astonishing 4 billion tonnes amassed globally» [source: “Green steel from red mud through climate-neutral hydrogen plasma reduction” – Nature, January 2024], and the cost of its disposal represents approximately 2% of its total production value. «For example, Brazilians spend around 106 million dollars annually to ensure the safe disposal of red mud» [source: “Utilization of red mud in road base and subgrade materials: A review” – Science Direct].

P – POLITICAL: politically, the development of sustainable disposal methods aligns with global environmental policies and regulations aimed at reducing greenhouse gas emissions. Countries investing in such technologies may benefit from enhanced international standing and potential financial incentives or subsidies aimed at promoting green technologies. This alignment can facilitate smoother regulatory approvals and greater public support for environmental initiatives.

E – ENVIRONMENTAL: environmentally, using red mud as a catalyst helps address the dual issues of hazardous waste management and greenhouse gas reduction. The technique not only neutralises a harmful industrial by-product but also aids in the efficient breakdown of HFC-134a, a potent greenhouse gas. This dual benefit supports broader environmental goals and contributes to reducing the overall carbon footprint.

S – SUSTAINABILITY: for decades, environmental sustainability has been the guiding principle behind all actions related to political choices, legislative measures, research, and studies on the use of hydrofluorocarbons and, more broadly, fluorinated gases and greenhouse gases worldwide. The work illustrated here is yet another example of this trend. The conclusions drawn from the twenty-eighth United Nations Conference on Climate Change (COP 28) – held from 30 November to 13 December 2023 in Dubai – are very clear: «… to peak global greenhouse gas emissions by 2025, then reduce them with concrete actions by 43% by 2030 and by 60% by 2035 compared to 2019 levels, in order to limit global warming to 1.5 ºC». This is an urgent moral imperative. Recycling red mud for the reduction of HFC-132a, if it becomes a reality, would be a piece of the larger sustainability puzzle as we look towards 2050.