How greenhouse gasses and plastic waste can help save the world

Promise of solar power conversion

Among the different methods, conversion driven by solar power holds great promise, using the most renewable of all resources ­– sunlight – as its primary source of energy.

Researchers from the University of Cambridge have shown how CO2 can be captured from industrial processes – or even directly from the air – and be converted into clean and sustainable fuels using only solar energy. 

Researchers have also developed a solar-powered reactor that converts captured CO2 and plastic waste into sustainable fuels and other valuable chemical products.

In laboratory experiments, CO2 was converted into generated gas, a building block of sustainable liquid fuels, and plastic bottles were converted into glycolic acid, which is widely used in the cosmetics industry.

Advantages of new approach

Solar-driven CO2 conversion uses sunlight to drive chemical reactions that turn polluting gases into valuable fuels and chemicals. The new approach offers many advantages, including reduced reliance on fossil fuels and the use of solar and renewable energy.

By using sunlight as the only energy input, CO2 and plastic waste can be converted into clean fuels, while avoiding the need to bury the plastic underground or release it into the environment.

This approach is consistent with the principles of sustainability and circular economy, enabling waste recycling, reducing reliance on limited resources, and reducing the carbon footprint.

Reliance on energy-intensive steps, such as absorbing CO2 from the air and compressing it after capture, could be reduced because the new technology integrates solar energy into the CO2 conversion process.

How it works

Carbon capture is typically based on capturing CO2 emissions from power plants, refineries, cement production, and other industrial sources. The process involves three main steps: separation, capture, and storage.

In the first step, CO2 is separated from exhaust gas emitted by industrial processes by treating the gas after combustion using chemical agents that selectively capture CO2 while allowing other gases to pass.

Once CO2 is separated, it's concentrated for further processing or storage. Various capture techniques can be used, including chemical absorption by a solvent, such as amines. CO2 can then be released from the solvent through temperature or pressure changes.

Once captured, concentrated CO2 must be stored to prevent its release into the atmosphere,  but this process costs a lot of money and a huge amount of energy.

There is an alternative, however.

The "plant photosynthesis" process

For several years, Professor Erwin Reisner's research group worked on developing sustainable carbon fuels inspired by the photosynthesis process that plants use for energy,  using artificial products that resemble leaves.

Via photosynthesis plants absorb CO2 and convert it via sunlight into energy for growth, releasing oxygen into the air. Artificial leaves do the same,  converting CO2 and water into fuel using only sunlight.

There are also other new techniques that can mix carbon monoxide and hydrogen to use it to make industrial liquid fuels and chemicals rather than just releasing the carbon into the atmosphere.

The first phase of this process involves capturing CO2 from concentrated gas streams, post-combustion stack gas, or from the atmosphere, via various techniques. The captured CO2 is then treated with solar energy through a process that relies on specialised electrochemical cells including semiconductors or catalysts capable of converting the gas into valuable products.

From plastic waste to cosmetic products

The integrated system created by Cambridge University researchers contains a light cathode and anode. on the cathode side, the CO2 solution is captured and converted into generated gas, a simple fuel. Other plastics are converted into useful chemicals using only sunlight.

Because capturing CO2 from the air and using it makes the process so difficult, the researchers added plastic waste to the system. The plastic breaks down into glycolic acid, which is widely used in the cosmetics industry, and CO2 is converted into a simple fuel.

These green fuels could become the cornerstone of a sustainable future. The associated by-products add to the effect and promise of humanity being able to abandon traditional fossil-fuel-based materials.

So far, solar-powered researchers' experiments have used pure, concentrated CO2 from a cylinder, but for the technology to be of practical benefit, it must be able to capture CO2 from industrial processes or directly from the air.

Although improvements are needed before the technology is used on an industrial scale, a study on the research published in the journal Joule represents another important step toward producing clean fuels to support the economy, without the need to extract oil and gas.

But given that CO2 is just one of many types of molecules in the air we breathe, making this technology selective enough to convert highly diluted CO2 is a major technical challenge.

Completely eliminating fossil fuels

In a special statement to Al Majalla, one of the authors of the study in Joule, Sayan Kar, said that the team isn't only interested in decarbonising the air "but also in completely eliminating fossil fuels and creating a real circular economy."

Read more: How London is paving the way toward a circular future

Challenges and constraints

While the production of clean fuels from CO2 and renewables bodes well, there are many challenges and constraints that need to be addressed, most notably improving the overall efficiency of the conversion process.

The long-term stability and durability of system components – including catalysts and photovoltaic electrodes – must be improved, Kar says.

Long-term exposure to extreme operating conditions, such as high temperatures, corrosive environments, or solar radiation, can degrade the system's constituent materials, and thus lead to reduced performance and lifespan.

The cost of implementing carbon capture and conversion techniques remains a major challenge.

Long road ahead

The energy efficiency of the fuel produced by CO2 conversion technologies is still in the early stages of development. Speaking to Al Majalla, Kar adds that the efficiencies currently achieved are low, compared to mature renewable energy sources such as solar photovoltaic cells or wind energy.

However, it's important to note that the purpose of CO2 conversion technologies is not only to generate electricity but to use CO2 as an intermediate input to produce valuable fuels and chemicals. Kar said the focus is on recycling CO2 emissions and reducing reliance on fossil fuels, rather than directly generating electricity.

Converting CO2 into fuel can be combined with waste management strategies, especially the use of plastic waste.

By integrating selective oxidation of waste plastics in the process, such as converting ethylene glycol into glycolic acid, the technology helps boost the value of plastic waste, incentivising recycling.

The concept of circular economy aims to create a closed-loop system, where resources are kept in use as long as possible.  The new technology is compatible with this concept by using CO2 and plastic waste as valuable sources by integrating waste into the production cycle. This reduces the need for virgin resources and enhances the efficiency of the resources used.

Kar says the main result of that research is to demonstrate the concept of fuel production and waste management. instead of getting rid of excess CO2 and plastic waste in the atmosphere, we can harness the power of sunlight to turn both into valuable fuels.

This process offers a sustainable alternative to conventional fossil fuels and mitigates the environmental impact associated with CO2 emissions and plastic waste.

 "Our work confirms the possibility of providing a more sustainable and environmentally conscious future through the effective use of excess CO2 and the conversion of plastic waste into valuable resources," he says.