Ability to easily produce fuel from discarded plastic waste

Dr.Sumith Baduge, Phd.

PUBLISHED ON June 10, 2021

Is the discarded plastic waste in the last region still a headache for the country? This article will explore the recycling potential of plastic waste.

As shown in the figure below, crude oil is used as the main ingredient in the manufacture of plastics. Therefore, the basic constituents of plastics are carbon (C) and hydrogen (H2).

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Figure 1: Crude Oil Into Plastic

The plastics currently in use in the world can be divided into Thermoplastic and Thermosetting plastics. Of these, thermoplastic is the most widely used type for home appliances and packaging. Most of them can be recycled. Thermosetin plastics are widely used in the manufacture of various equipment in factories, many of which are difficult to recycle.

Elastomer and Compounds composite plastics are used for a variety of purposes. Here the queue can be made by mixing different types of fibers (Glass fiber, Carbon fiber, etc) using very strong (Composites) plastics which are similar in strength to aluminum and iron. They are used in the construction of automotive spacecraft, ships and boats, and in the building industry. The high use of plastics in the world today makes it impossible to think of a world without plastics.

Although plastics are very beneficial to human beings, their disposal after disposal has created huge environmental problems. It has been found that the amount of plastic waste that enters the oceans by 2050 is currently estimated to be equal to the number of fish in the oceans. It has been found that the environmental damage caused by plastics is very high as it takes about 100 years for them to decompose. Plastics are easily combustible but burning in open spaces releases the highly toxic gas dioxins (Dioxins, C4 H4 O2). Considering all these, it is advisable to be very careful in disposing of plastics after use and handing over for sorting and recycling.

Currently, there are two basic methods of recycling discarded plastics in the world. That is, mechanical recycling methods. Disposable plastics must first be classified in the mechanical system. To this end, the Society of the Plastic Industry introduced the Plastic Classification System in 1988. The plastics were given the code numbers Resin Identification Code (RIC) and Fyda Plastic Identification Code (PIC), taking into account the plastic manufacturing unit.

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Figure 2: Plastic Recycling

Accordingly, recyclable plastics are divided into 07 categories as shown in the table below. During mechanical recycling, all discarded plastics should be segregated and cleaned according to the RIC number. These are then heated and melted into pellets. The pellet can be reheated and reusable. When making pellets without grading, the density of the various plastics changes, and as they solidify, they solidify into layers, thus reducing the strength of the product. Similarly, in the manufacture of plastics, various dyes are added to plastics with chemicals, making them difficult to recycle.

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Figure 3: Categorisation of plastics in Resin Identification Code (RIC)

At present Sri Lanka collects about 500 tons of discarded plastic per day and out of this about 75 tons are recycled daily. This recycling method is expensive as it involves the separation, washing and melting of plastics

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Figure 4: Plastic Waste Generation in Sri Lanka

However, years of research by the Department of Mechanical and Product Engineering at the University of Ruhuna have found that about 70% to 80% of the plastic waste collected using thermochemical recycling can be converted into liquid fuel without being completely purified.

It has been shown that about 97% of the currently produced plastic waste can be converted into fuel after the use of discarded plastics. It has been proven that when the temperature and pressure of the reactor in this machine are controlled correctly, about 66% of the resulting liquid fuel and 31% of the gaseous fuel can be obtained. Post Images

Figure 5: about 97% of the currently produced plastic waste can be converted into fuel after the use of discarded plastics

Thus, 1 kg of discarded plastic can hold about 650 g of liquid fuel and 300 g of fuel. The gaseous fuels we produce are similar to the petroleum gas (LP) we currently use, and the liquid fuel has the same properties as the diesel fuel. Therefore, the liquid fuel obtained from these discarded plastics was used as fuel for a compression ignition engine and the efficiency and exhaust emissions of the engine were tested.

Our tests have shown that this liquid fuel has the ability to mix and operate with diesel up to 50%.

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Here it was possible to obtain an efficiency similar to that of diesel. It was confirmed that this output was similar to that of the diesel engine only when the engine was running. We are preparing to further develop this machine manufactured by our department in the future and introduce it to the market.

If this waste disposal machine is provided to all local authorities, the problems currently caused by the waste plastics in those institutions can be solved very successfully and the liquid fuel generated from this can be used as fuel for the existing diesel vehicles in those institutions to save a lot of money.

Eng. Lanka Ramanayaka - CEO
Design Knigdom Lk
BSc(Eng), PG Dip.(BSE), CEng., MIE(SL), MEC(SL)
Chartered Engineer