CHEMICAL BREAKTHROUGH COULD END THE PLASTIC POLLUTION CRISIS
A new chemical process can liquify plastic. The next challenge? Creating a machine that can recycle the sludge on an industrial scale
One single-use plastic bag takes at least 450 years to degrade. Give Miranda Wang three hours and she can reduce ten of them into liquid.
Wang is the first to discover a chemical process that tackles the end-of-life of plastic. She first learned the scale of the problem in eighth grade with her friend, Jeanny Yao, when they visited a city waste recycling plant in Vancouver, Canada where they grew up. “That’s when we learnt that even plastics that are put into a curbside recycling bin end up being exported overseas in developing countries where they become ocean pollution,” she says.
Since the 1950s, 8.3 billion tons of plastic has been produced. It’s now found in toys, car parts, in donor organs and in the oceans. Because of the centuries-long degradation period, most of it still exists: 6.3 billion tons of it as waste. While many are trying to curb the inconceivably big problem of plastic pollution by collecting it from oceans and placing bans on certain products, Wang says it is commendable, but it is not enough: “If we can not just outlaw plastics altogether immediately, if we’re always going to produce this plastic, what do we do about it, how do we pragmatically handle it?”
Recycling plastic today is a mechanical process. It is sorted by colour, shredded, cleaned, and melted. But this is limited to only certain types of plastics: PET, used in water bottles, and HDPE, used in milk jugs. The five other types of commonly used plastics usually contain colourants and plasticisers that mean they cannot be recycled.
These are the plastics Wang has her sights on. “Our technology can turn these dirty films that have food or dirt or any kind of grime or any kind of contamination on it and we turn this material into a combination of four different kinds of chemicals, called organic acids,” says Wang.
In 2015, Yao and Wang, while they were still at college, founded BioCellection. The startup was based on their discovery of a bacteria that has evolved to eat plastic. But, it did not take long to realise that the bacteria would always prefer to eat whatever food contamination was on the plastic surface, and when it did eat the plastic, the speed at which it could digest it was far too slow.
They shifted their thinking towards using chemicals with a focus on film plastic. Used for plastic bags or food packaging, it is made from the extremely cheap material polyethylene. In the US, it is the number one produced plastic by quantity, above PET plastic created for plastic bottles, and more than 97 per cent of it is not recycled. “Film is the worst type of plastic because it’s so easy to catch surface contamination,” says Wang. “You can have such a small amount by mass, by weight of plastic, and its entangled and wrapped around everything in the waste bin and it just catches all the liquids and the oil.”
Rather than using bacteria to breakdown the plastic, Wang uses a clear liquid catalyst. To prove that it works, she used plastic waste taken from a city waste plant in San Jose. “We shred this plastic, we put it into a flask and then we add our liquid catalyst,” she says. It is a relatively conventional chemical process – something she prioritised during its design so that it can be scaled. The reaction occurs at 120 degrees Celsius in common glass equipment with no added pressure. While the surface contamination on the plastic bathes in the catalyst, it does not react. The plastic itself, made up of a long carbon chain of polymers, destabilises and collapses on itself to create other chemicals with four to seven carbons in the chain link.
“So instead of having one extremely long carbon chain, it forms many chemicals with shorter chains with four to eight carbons in size,” says Wang. “That is what is in the liquid at the end of the reaction.”
The liquid catalyst is then boiled off and re-captured by the system, recovering it so it is constantly used to break down the plastic and cause a chain reaction. “The chemical identity of the content changes. That is why the plastic becomes a liquid in the end,” says Wang. “It is not a plastic liquid, it is a chemical liquid, because the plastic polymer has changed into chemicals.” After this, another chemical separation can be done to turn the liquid into a white chemical powder.
One of these chemicals is adipic acid, a precursor for materials like nylon and polyamines used in fashion, for electronic parts and in the automotive industry for car parts. “Our vision is to transform a polyethylene, which right now does not have any downstream market value once its consumed and is used for one life cycle, and we turn it into a chemical that is of the same quality as what is immediately made from petroleum – adipic acid,” says Wang. “This first helps us not allow film plastics from becoming pollution and second is that it actually displaces petroleum from being needed to be extracted to make new materials.”
Now, Biocellection is ready to scale. From the initial 10 plastic bags in a 500 milliliter flask breaking down in three hours, she is creating a continuous five litre system. In October, they will conduct a demonstration pilot at a plant in San Leandro, California, where over three months, 17 metric tons of plastic film waste will be converted into six metric tons of organic chemicals. Crucially, it will also provide much needed data about how the system will work at a larger scale. “At the moment it is impossible for us to know exactly how our reaction will work on an industrial scale what the exact economics will be,” says Wang.
In 2019, they plan to build an even larger machine that will process five metric tons of plastic waste per day. This will be standardised, replicated and transported anywhere in the world where there is a lot of waste, where it can be plugged into a wall and left to run. The next move is to expand beyond film plastics. “We can actually deal with any kind of polyethylene, even if its in a rigid form, as long as its shredded we can use it. But there are also opportunities in polypropylenes that we’re interested in,” she says.
Wang sees plastic pollution in two parts: first is the collection and centralisation of the materials that are the problem. “Especially in the context of oceans, like how do we get that back?” she says. The other is what to do with the material once its been collected.