Plastic to hydrogen
Most recently, researchers from Swansea University have discovered a means of converting plastic waste into hydrogen fuel, which they say could one day be used to power cars.
The team added a light-absorbing photo catalyst to plastic products, a material that absorbs sunlight and transforms it into chemical energy in a process called ‘photoreforming’. The plastic and catalyst combination was then left in an alkaline solution exposed to sunlight, breaking down the material and producing bubbles of hydrogen gas in the process.
The new method would be a cheaper than current recycling options, as any plastic can be used without needing to be cleaned. According to The Balance Small Business, it currently costs around $4,000 to recycle a tonne of plastic bags, which often leads to plastic waste being burned or thrown in landfill to avoid expenses.
Dr Moritz Kuehnel, from the university’s chemistry department, said: “There’s a lot of plastic used every year – billions of tonnes – and only a fraction of it is being recycled. We are trying to find a use for what is not being recycled.
The beauty of this process is that it’s not very picky. It can degrade all sorts of waste.”
The team is now looking to scale up the process from current milligrams of plastic to use the photoreforming process on more sizeable pieces.
While it may be years before this plastic-to-fuel process can be rolled out on an industrial level, its development would work well in tandem with the advent of hydrogen vehicles. Currently, no such cars exist on our roads, though a number of companies have big plans in the pipeline. For instance, Toyota has stated its aim to sell one million electric and fuel cars worldwide by 2030, while it is also due to launch a fuel cell-powered bus in 2020.
Plastic to diesel
Chemists from the University of California, Irvine (UC), in collaboration with researchers from the Shanghai Institute of Organic Chemistry, have devised a plastic recycling method that allows them to dissolve the bonds of polyethylene plastic to create petroleum and other fuel products.
While untreated polyethylene can be broken down, it requires either a significant amount of heat or reactive, toxic chemicals, and results in the atomic bonds breaking in an unusable way. By contrast, the process developed by the researchers uses far less heat and allows the final product to be transformed into a new fuel source.
The team, led by UC Irvine chemist Zhibin Guan, used a type of hydrocarbon molecule known as alkanes, which are typically used to produce polymers, though they were here harnessed to break down polymers. In a gradual process of removing and adding bonds between the carbon and hydrogen atoms within the material, the team were able to restructure the polyethylene into a liquid fuel that can be used in cars or other industrial purposes.
The catalysts used are also compatible with various types of polyolefin additives, meaning plastic waste such as bottles, bags and film can all be converted into chemical feedstocks without the need for any pre-treatment.
Plastic to crude oil
In 2016, Illinois Sustainable Technology Center researchers B.K. Sharma and Kishore Rajagopalan, in collaboration with the US Department of Agriculture, successfully converted plastic bags into fuel.
The team used high-density polyethylene bags sourced from local retailers and fed them into a pyrolysis unit, creating plastic crude oil (PCO) in the process. They then distilled the PCO to make gasoline and two types of diesel. Following the addition of antioxidants, the resulting materials proved superior to conventional diesel fuels in terms of lubricity and derived cetane number, which demonstrates ignition quality.
Plastic to sulphur
US firm Plastic2Oil works to turn waste plastic into sulphur fuel, using the discarded material as feedstock to create an ‘ultra-low sulphur diesel’ that contains 15ppm or lower sulphur content.
Currently, ultra-low sulphur diesel is primarily produced from petroleum, though Plastic2Oil provides a viable alternative with its plastic-derived fuel. The firm’s processor accepts unwashed and unsorted plastic, generating around one gallon of fuel from 8.3 pounds of the material. The processor uses its own off-gases as fuel (approximately 10%-12% of process output), meaning minimal energy is required to run the machine. The fuel produced can also be refined and separated without the cost of a distillation tower.