[Guest feature] Can pyrolysis help to tackle the plastic pollution?

In 2017, BBC premiered “Blue Planet II”, a nature documentary series on marine life. The documentary had a significant impact on the public and it highlighted the issue of plastic pollution as shown in Figure 1. The “blue planet effect” is the term described by many researchers as the change in the plastic consumption behavior of the public after watching the documentary. The plastic pollution has ever since become a major concern for many organizations and institutions. Some key facts about the issue are:

• Half of all plastics ever produced have been made in the last 15 years.
• 448 million tons of plastic were produced in 2015 which is expected to double by 2050.
• Every year, about 8 million tons of plastic waste escapes into the oceans from coastal nations.
• Plastics contain additives which extend the life of the products to at least 400 years before it breaks down.

The major concerns regarding plastic pollution are the improper disposal and recycling of the products. In places where there is an inefficient garbage collection system, plastic pollution becomes quite visible such as the developing nations of Asia and Africa. When plastic is thrown in rivers and landfills it greatly affects the wildlife. Millions of animals are killed by plastics every year due to entanglement or starvation, and nearly 700 species are known to have been affected by it. The pollution has become so evident that nearly every species of seabirds eat plastic, plastics can be found in municipal drinking water systems, drifting through the air and henceforth in human blood.

How to Reduce Plastic Pollution?

There are two things necessary to reduce plastic pollution: reduce the production of non-degradable plastics and recycle the already manufactured non-degradable plastics. Many initiatives have been undertaken all over the world to reduce the demand and production of non-degradable plastics. Companies have substituted plastics with more sustainable products such as bamboo straws and governments have banned the production of single-use plastics. But the bigger issue has been the consistent treatment of the non-degradable plastics which are already manufactured and thrown away in landfills that can survive up to 500 years or longer as shown in Figure 2.

How to treat non-degradable plastics?

There are essentially three ways to treat plastics:

• Pyrogenesis: It is the destruction of combustible waste through the use of a plasma torch. It also involves the process of Pyrolysis where extreme thermal process helps to convert organic matter into synthetic gases.
• Bioremediation: It is the use of living organisms, like microbes and bacteria, to break down hazardous substances into less toxic or non-toxic.
• Phytoremediation: Similar to bioremediation, this process uses a living organism, specifically green plants, to detoxify soil and water contaminated with heavy metals or excess minerals.

Pyrogenesis and Pyrolysis are the most popular ways to treat plastic as it converts waste into energy. The other two processes are comparatively restrictive as they require specific conditions to function effectively. Pyrogenesis, specifically pyrolysis, on the other hand, can be more profitable, environmentally sound and can be implemented on large scale.

What is Pyrolysis?

Pyrolysis is a thermochemical process where any organic (carbon-based) product is decomposed. In this treatment, the material is exposed to high temperature (typically above 430°C), and in the absence of oxygen or air it goes through chemical and physical separation into different molecules. Pyrolysis process always produces solid (charcoal, biochar), liquid (in case of plastic- plastic oil) and non-condensable gases (H₂, CH₄, CnHm, CO, CO₂ and N). Usually, there are three types of pyrolysis:

• Slow Pyrolysis: This is characterized by lengthy solids and gas residence, low temperatures (500°C) and slow biomass heating rates.
• Flash Pyrolysis: It occurs as rapid heating rates and moderate temperatures between 400 and 600°C.
• Fast Pyrolysis: It involves rapidly heating biomass to temperatures of 650 to 1000°C. This process is often used to produce bio-oil and gas.

How does Pyrolysis work on plastics?

For plastic pyrolysis, the heat breaks plastic polymers down into smaller hydrocarbons, which can be refined to diesel fuel and even into other petrochemical products—including new plastics. Figure 3 illustrates the 7 steps involved in the pyrolysis process of plastics. The main barriers for pyrolysis of plastic waste are “unavailability and inconsistent quality of feedstock, inefficient and hence costly sorting, non-existent markets citing lack for standardized products, and unclear regulations around plastic waste management.” But there have been successful start-ups which are applying pyrolysis on plastics efficiently such as Paterson Energy while also being cost-effective and sustainable.

Who are Paterson Energy and what do they do?

Paterson Energy is an Indian start-up which commenced its operations in the year 2016, with its pilot plant in Chennai. It was initially a 5 TPD test plant which was upgraded later to a larger capacity plant upon successful results. Paterson Energy was founded by Mr Amarnath & Ms Vidya, with a passion for the environment and has been innovating with various technologies for a cleaner & better environment. Their vision is to protect the environment by developing technologies and processes for the mitigation of inorganic waste, with a specific focus on plastics.

They use a continuous type thermochemical depolymerization process to convert the otherwise hazardous plastic waste into a high-grade diesel oil variant. They have a completely zero-emission and zero effluent treatment process thereby providing a complete circular economy. Figure 4 shows the stages involved in the process such as shredding the plastic, reaction, gas separation, oil condensation and carbon discharge.

How efficient is their process?

• The technology introduced by Paterson Energy is a complete Green Technology as it produces zero effluent and zero discharge. The excess fuel is collected in a balloon and is routed back into the reactor as a heating agent.

• The thermochemical depolymerization plants set-up are efficient as any energy that is let out from the process is duly captured and routed back into the system as heating agents.

• The process is continuous, run in optimum pressure thereby, drastically reducing the escape and mix of carbon together with the fumes preventing them from coming out with the Thermo Chemical Depolymerization oil.

What can the plastic oil be used for?

Paterson Energy are setting a standard of plastic treatment throughout the industry in India. It has been proved challenging in some places such as the USA, where there seven projects involving pyrolysis of plastics. But Paterson Energy are showing how when done effectively, the process can not only reduce plastic waste but also generate sufficient profits to keep the business sustaining. As the plastic production is expected to double by 2050, proper recycling and treatment of plastics are crucial. Even with proper waste collection systems and recycling initiative, there is always going to be a need for processes such as pyrolysis.