A group of chemical engineers has come up with a new way to recycle polystyrene, possibly making it the first practical method for reusing this commonly used plastic.
This innovative technique promises to revolutionize the recycling of a material that has long posed environmental challenges due to its bulkiness and difficulty in recycling efficiently.
Developed by researchers at the University of Bath in the UK and Worcester Polytechnic Institute in Massachusetts, US, it promises to transform the recycling landscape by offering an economically viable and energy-efficient process.
Chemical recycling process
The collaborative team has unveiled a chemical process known as pyrolysis to break down polystyrene into its fundamental components. This method presents a promising solution to the ongoing problem of polystyrene waste. The technique not only enhances recycling efficiency but also proves to be both cost-effective and energy-efficient.
“Chemical recycling techniques are a major focus within chemical engineering right now, and cost- and energy-efficient ways to breakdown plastics to their primary building blocks such as polystyrene are urgently needed,” explains Dr. Bernardo Castro-Dominguez, a senior lecturer in chemical engineering at the University of Bath and a co-director of the Centre for Digital, Manufacturing & Design (dMaDe).
“Less than 5% of polystyrene is recycled at present—our work shows that as much as 60% of all polystyrene used today could be replaced by chemically recycled styrene,” he added.
The mechanics of pyrolysis
Pyrolysis is a process that involves subjecting polystyrene to extremely high temperatures in an oxygen-free environment. This prevents ignition and instead breaks down the polystyrene into monomers, which are then purified and reconstituted into new polystyrene.
Creating 2.2 pounds (one kilogram) of this new material requires less than 10 megajoules of energy—roughly enough to power a typical microwave for around 30 minutes. This efficient energy use is a key advantage of the process.
Michael Timko, professor of chemical engineering at WPI, underscores the potential impact of this technique, saying, “Our analysis finds polystyrene to be an ideal candidate for a chemical recycling process. Surprisingly, the process is energetically efficient and potentially economically competitive.”
He further added that investing in this process could reduce emissions as effectively as simple energy conservation measures.
The process breakdown
Traditional methods of recycling polystyrene involve heating, which degrades the material over time, compromising its strength and flexibility. The bulkiness of polystyrene also poses logistical challenges, leading to high transportation costs and limited recycling facility acceptance. Consequently, a mere fraction of polystyrene is recycled today.
The new process comprises a pyrolysis reactor, a heat exchanger, and two distillation columns. These components work together to decompose polystyrene into ‘monomer grade’ styrene, which can be reformed into new polystyrene, and ‘light’ and ‘heavy’ petroleum-like by-products that can be reused in various other applications.
The efficiency of this process is notable, with a yield of 60 percent. This means that from 1 kilogram of used polystyrene, approximately 600 grams of 99 percent pure monomer grade styrene can be recovered and used to create new polystyrene.
Environmental and economic benefits
The environmental benefits of this method are substantial. The research highlights that the cost to reduce carbon emissions through this process is about $1.5 per ton of CO2, significantly lower than many existing recycling methods.
Furthermore, the researchers advocate for policies that incentivize consumers to recycle polystyrene or divert it from landfills, which would enhance the economic attractiveness of this process. Such policies could play a crucial role in increasing the recycling rates of polystyrene, addressing a significant waste management challenge.
Interestingly, this is not the only innovative approach in polystyrene recycling. Earlier research led by Dr. Xiaodan Li and Professor Dirk Tischler explored biotechnological methods.
Their study, published in Nature Chemistry, identified a bacterial enzyme capable of degrading styrene, potentially paving the way for biological recycling methods. Tischler noted, “A new biological function of heme in proteins has been comprehensively described,” highlighting the potential of biotechnological advancements in sustainable plastic recycling.
Courtesy : Interestingengineering.com