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Plastic Waste for Fuel Production

Every year, more than 380 million tonnes of plastic are produced around the globe which greatly contribute to global pollution as a large part of it remains in the environment or enters the oceans. Only a small percentage of the plastic waste produced is subjected to some form of recycling. About 12 percent is incinerated and the remaining 79 percent is left to decay without receiving any further treatment. One viable solution to utilising this large amount of plastic waste is to convert it into fuel.

Now (2021), scientists from the University of Delaware's (UD's) Center for Plastics Innovation (CPI) have developed a technology that enables recycling of waste plastic, such as food packaging, foil and other plastic waste from households, and converting it into fuel products, such as diesel, jet, and petrol.

For this purpose, they designed a method to selectively transform polyolefins into branched liquid fuels. In this process a novel catalyst which consisted of a WO3/ZrO2 and HY zeolite and process were used to break down chains of plastic polymers, known as polyolefins. The team used hydrocracking to split up the plastic solids into smaller carbon molecules. Then, hydrogen molecules were added on both ends to stabilise the material. The hydrocracking converted the material into branched molecules which allowed for more direct transformation into an end product. The process could be adapted individually so that different plastic wastes, such as low and high-density polyethylene, as well as composite plastics, could conveniently be converted into fuels or lubricants.

In the past, there have been several attempts to design catalytic processes for fuel production. In 2019, scientists designed a process for the catalytic pyrolysis of different types of plastics wastes, such as PS, PE, PP, and PET, using modified natural zeolite (NZ) catalysts and a small pyrolysis reactor. As a result of the catalytic pyrolysis of PS, a higher liquid oil was received than from PP and PE. The final product contained a mixture of aromatics, aliphatic and other hydrocarbon compounds. Also, it had a high heating value (HHV) range close to that of conventional diesel. The scientists were convinced that the oil produced by means of this process was a promising candidate as an alternative source of energy and transportation fuel after refining.

In 2020, a method for liquefaction of waste plastic was created that produced reusable oil from waste materials which are or cannot be recycled, such as plastics with metal elements, including computer cables and keyboards, as well as non-recyclable packaging materials. Moreover, the technology could remove resin and recover rare metals from waste. It employed convection control which could reduce the temperature difference between the bottom of molten plastic and the liquid surface. This enabled the reduction of the effective vaporisation area, thus compensating for energy loss.

The new conversion process for plastic waste has several advantages: the technology needs a lot less energy than other technologies and does not contribute to increasing global CO2 emissions. The process cycle is accomplished within a couple of hours at relatively low temperatures around 250°C. Also, the methods can be used to process different kinds of plastics at the same time, so previous sorting of the plastic waste is not required. Moreover, the catalysts used consist of common and abundant materials.

The next step of the research will be to find out what other plastic materials can be treated using this method and what additional kinds of materials the resulting products can be turned into. Whatever insights the scientists will gain in the course of these studies, one thing is certain: it will be a valuable contribution to making the civilizational impact on earth more sustainable.