Better than the landfill: Pyrolysis turns plastic bags into crude oil
Researchers at the University of Illinois have found a way to make diesel and gas out of used plastic bags
Walk down any city street and you’ll undoubtedly see an underlying commonality: plastic bags. Either littered about the gutter or being used by a passer–by, plastic bags are everywhere. Plastic bags are inexpensive to produce, easy to transport, and take about half a millennia to biodegrade. Recently, researchers at the University of Illinois’ Sustainable Technology Center have come up with a process that doesn’t make plastic bags biodegrade faster, but uses the petroleum composition of plastic bags (what keeps them from breaking down) to make fuels like diesel and gasoline. Dr. Sriraam R Chandrasekaran, a research and development engineer from the Sustainable Technology Center who helped develop the process, took some time to speak with me about his findings.
Could you walk me through the process of creating fuel from plastic bags?
Dr. Sriraam R Chandrasekaran: “Standard plastic bags are basically made from petroleum by–products. What we do is collect plastic bags and put them through a process called pyrolysis. Pyrolysis is basically combusting all these materials in an oxygen deficient atmosphere. When you do that it produces syn–gas [synthetic gas], when you condense the syn–gas it forms crude oil. If you want to further distillate it you can get diesel, or gasoline.”
How many plastic bags does it take to make 1 gallon of crude oil?
SC: “The plastic bags have a very low density, 8 lbs. of grocery bags yield about 1 gallon of crude oil. A pound of plastic bags contains approximately 75-100 bags, about 700–800 plastic bags will produce roughly a gallon of crude oil.”
Is there any difference between the crude oil that comes out of the ground and the crude oil produced with plastic bags?
SC: “The crude oil from the plastic bags has slightly better properties than the crude oil you get from underground. The reason being is the plastic bags are made from petroleum, so crude oil made from plastic bags have fewer trace metals, such as sulfur.”
Is this process scalable?
SC: "Yes. There are technologies available to scale up. We are currently working on the scale up process, we’ve been conducting small-scale batch experiments and we’ve gone a little higher for the pilot scales too. Whatever we produce in our lab, as an integral part of the Sustainable Technology Center, we expand to the pilot scale and also work to transfer the technology to the industry."
Is the process dangerous?
SC: "No. Pyrolysis is one of the only high temperature processes where not much pressure is involved. And it’s a closed system so net emissions are almost zero. There are definitely no harmful emissions since it’s a closed system."
What’s the future of creating fuels from plastic?
SC: "Right now we’ve been concentrating on grocery bags, but we are slowly expanding our research studies to other types of plastics that are not recyclable, and end up in landfills. We’re trying to optimize the process, combining different plastics and see if we can get the same results. There are a lot of plastics available that are not recyclable and ideal for energy conversion. Our work is expanding into all these plastics, instead of concentrating on high–density or low–density plastics we are trying to expand it to all non–recyclable plastics."
What chemical by–products are produced as a result of the pyrolysis?
SC: "The by–products of the pyrolysis process are very minimal. Most of the hydrocarbons that are produced by the process are condensed and collected in the form of liquid. Some of the gasses produced that could be volatile and escape, we have a process of catalytic conversion where any unburned hydrocarbons are completely converted to carbon dioxide."
What else are you working on?
SC: "It is not just plastics we are doing; we are also trying to convert biomass materials, using the pyrolysis process, into biochar and biofuel. We do a lot of work related to energy stuff. Getting biochar uses the same process as getting crude oil, only the raw material is biomass and not plastic bags."
Lab photos courtesy of Dr. Chandrasekaran.
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