Decomposition of refrigerants: new frontiers and discoveries
The decomposition of refrigerants is becoming an increasingly important issue, especially in light of the urgent need to reduce greenhouse gas emissions and protect the environment. Refrigerants such as HFC-134a are widely used in air conditioning and refrigeration systems, but their disposal poses significant challenges due to their chemical stability and high global warming potential.
Recent advances in the catalytic decomposition of refrigerants have opened up new opportunities for managing these compounds more efficiently and reducing their environmental impact. The most common methods currently used to treat these substances are combustion and high temperature decomposition via plasma. Although very different, both are valid solutions, but each entails certain disadvantages which should not be underestimated. These can be summarised as follows:
- the first method (although efficient at destroying the compounds), causes the formation of secondary pollutants such as nitrous oxides (NOx), which add to atmospheric pollution;
- while the second requires high temperatures and significant energy expenditure, which compromise its sustainability. Furthermore, the efficiency of this method tends to diminish as the reactor size increases, presenting challenges in terms of scalability.
Innovative catalyst use in the decomposition of refrigerants
In order to tackle these limitations, a group of researchers led by Dr. Ryi Shin-kun at the Hydrogen Convergence Materials Lab of the Korea Institute of Energy Research (KIER) has developed an innovative catalyst using ‘red muds’ (a by-product of aluminium production). Red muds, generated during the extraction of aluminium oxide from bauxite, are known for their high alkalinity and heavy metal content and, if not disposed of properly, can cause ground and water pollution.
The research involved the use of metallic components present in these residues, such as iron and aluminium, to create a catalyst capable of decomposing the refrigerant HFC-134a with over 99% efficiency. This technology offers the advantage of being able to operate at lower temperatures compared to conventional methods, thereby reducing energy costs and minimising the formation of secondary pollutants.
The characteristics of the catalyst and the role of red mud
Red muds have a porous structure and a large surface area relative to their mass, which makes them ideal for catalytic reactions. Their thermal stability enables the reactants to flow easily through the catalyst, improving decomposition efficiency and extending the lifespan of the catalyst itself. They also offer an optimum environment for interfacial processes such as absorption, essential for the chemical reaction needed for refrigerant decomposition.
In order to further improve the catalyst’s performance, the research team used a thermal treatment process, which enabled the creation of composite materials like tricalcium aluminate (C3A) and gehlenite (C2S). These compounds increase the catalyst’s resistance and widen the reaction surface, leading to more efficient decomposition of the refrigerants.
During the decomposition of HFC-134a, one of the by-products produced is the corrosive compound known as hydrogen fluoride (HF). The catalyst developed by the researchers is capable of handling that problem too. The calcium oxide (CaO) present in the red muds reacts with the hydrogen fluoride to form a chemically stable mix called calcium fluoride (CaF2). This process neutralises the HF and a thin film of CaF2 is formed on the catalyst’s surface, protecting it from disactivation and extendg its useful life.
Environmental and economic benefits of the new technology
The technology of catalytic decomposition using red muds is not only an important step forward in the sustainable management of refrigerants, it also offers considerable environmental and economic benefits.
By using a process which recycles an industrial waste product, the volume of material destined for landfill is reduced, which contributes towards the reduction of ground and water pollution. Furthermore, the use of waste products from industrial processes brings a reduction in the catalyst’s production costs, making this technology more competitive from a financial point of view.
Translated by Joanne Beckwith
