Energy Costs Of Pelletizing Pet Plastic: What's The Verdict?

Plastic pelletizing is the process of converting scrap plastic into pelletized plastics. The process involves cutting plastic scraps into small pieces and heating them until they melt. The molten plastic is then passed through a die, which produces cylindrical pellets. The total energy required to produce, package, and transport a 16 oz. PET container is 32 MJ compared to 34 MJ for a 16 oz. glass container. Producing a pound of plastic resin uses nearly nine times the energy of producing a pound of glass.

The total energy required to produce, package, and transport a 16 oz. PET container is 32 MJ

The energy used in the production of plastics for packaging comes from non-renewable resources, such as natural gas or crude oil. Researchers have been working on ways to reduce the amount of non-recyclable plastic that ends up in landfills. One technique involves combining plastic with paper fibre to form pellets with an energy content similar to coal. This process, known as torrefaction, uses heat to convert biomass into a coal-like material.

Producing a pound of plastic resin uses nine times the energy of producing a pound of glass

The plastic resin manufacturing process involves heating hydrocarbon raw materials to form resin pellets. These pellets are then melted and blown into a mould to form the shape of a bottle. The energy used to make and process plastic is equivalent to 3.8 grams of CO2 per 1.0 gram of plastic.

Glass, on the other hand, is produced through an extremely heat-intensive process. A furnace heats the raw materials to 2600-2800° F for melting. The temperature is then reduced as the molten glass is cut, moulded, and blown into its final bottle form. The glass-making process requires energy that is equivalent to 3.0 grams of CO2 per 1.0 gram of glass.

The amount of energy required to manufacture plastic bottles differs from the amount required for glass manufacturing. Glass melts at between 1400-1600° C, while plastic melts at a much lower temperature of around 170° C. This means plastic requires significantly less energy to shape and manufacture.

In addition, the advanced recycling process ensures that the resulting virgin resin is identical to virgin resin produced with fossil fuels. This process creates a circular economy by transforming post-consumer waste into a pyrolysis oil feedstock.

Plastic pelletizing involves cutting plastic scraps into small pieces and heating them until they melt

The energy consumption of plastic production is largely due to the energy required to heat and refrigerate the materials, as well as the feedstock of natural gas or crude oil that is burned to generate energy.

To reduce the environmental impact of plastic production, researchers have been working on techniques to combine non-recyclable plastics and paper fibre that would otherwise end up in landfills. One such technique is torrefaction, which uses heat between 200°C and 320°C to convert biomass into a coal-like material. This process removes chlorine and other compounds that can produce harmful gases during combustion, making it a more sustainable alternative to traditional plastic production.

The molten plastic is then passed through a die, which produces cylindrical pellets

The process of pelletizing PET plastic involves passing molten plastic through a die to create cylindrical pellets. This process requires a significant amount of energy, with the total energy required to produce, package, and transport a 16 oz. PET container being 32 MJ. This is comparable to the energy required to produce a glass container, which is 34 MJ. However, it is important to note that producing a pound of plastic resin uses nearly nine times the energy of producing a pound of glass.

The pelletizing process for PET plastic typically involves using a plastic recycling machine that consists of a feeder, double-screw extruder, strand pelletizer/granulator, and collection silo. This machine melts the PET flakes to produce plastic pellets. The molten plastic is then passed through a die, which gives the pellets their cylindrical shape.

The shape and size of the die play a crucial role in determining the final shape and size of the pellets. By adjusting the dimensions and design of the die, manufacturers can control the diameter and length of the cylindrical pellets. This step ensures that the pellets are uniform and consistent in size, which is essential for their subsequent use in various applications.

It is worth mentioning that researchers have also explored alternative methods for pelletizing non-recyclable plastics. One such technique, developed by Idaho National Laboratory (INL) in collaboration with Michigan Technological University (MTU) and Convergen Energy, involves combining non-recyclable plastics with paper fibre to form pellets with energy content similar to bituminous coal. This process, known as torrefaction, uses mild heat between 200°C and 320°C to homogenize and consistentize the biomass while removing harmful compounds.

The new polymer is extruded, pelletized, or flaked; the product is called a “resin”

The process of pelletizing PET plastic involves melting PET flakes to produce plastic pellets. This process requires a significant amount of energy, comparable to the energy consumption of resin manufacturing.

The energy required to produce, package, and transport a 16 oz PET container is 32 MJ, which is only 6 MJ less than what is needed for a new glass container. However, producing a pound of plastic resin uses nearly nine times the energy of producing a pound of glass. This energy consumption is largely due to the use of non-renewable resources, such as natural gas or crude oil, for heating and refrigeration during the production process.

To reduce energy consumption, researchers have developed techniques to combine non-recyclable plastics and paper fibres that would otherwise end up in landfills. By using torrefaction, a thermal process, they can convert these materials into pellets with an energy content similar to bituminous coal. This process involves applying mild heat, typically between 200°C and 320°C, to homogenize and purify the materials while removing harmful compounds.

Overall, the pelletization of PET plastic is an energy-intensive process, but advancements in technology are being made to improve energy efficiency and reduce the environmental impact of plastic production.

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