Total Mass Balance

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Total mass balance is based on input and output amount in a simple process flow diagram, as shown in Figure 5.4. In this process, the optimization control condition is the maximum production of the oil product and the minimum production of the gas product and the sludge. Generally, the yields of gas and oil product are below 20% and above 70% respectively, based on 100% of feeding amount. Also, the sludge amount is much decreased to below 10%, which should be discharged in much smaller amounts, if possible. Increased amount of sludge discharged increases treatment cost and also decreases desired product yields, which has a great influence on economic decisions on the pyrolysis process of waste plastic.

As an example, the experimental data using stirred semi-batch laboratory-scale reactor [7] was obtained from the catalytic degradation of various plastics over spent FCC

Feeding material (100%)

Feeding material (100%)

Example Light Flow Diagram

Gas product Light oil product Heavy oil product (<20%) (A) (B)

Figure 5.4 Total mass balance of a simple process flow diagram in the pyrolysis of waste plastics

Gas product Light oil product Heavy oil product (<20%) (A) (B)

Figure 5.4 Total mass balance of a simple process flow diagram in the pyrolysis of waste plastics

Waste Polymers Feedstock Recycling

HDPE LDPE PP PS

Plastic type

Figure 5.5 Yield of liquid, solid and gas products in catalytic degradation of various plastics using spent FCC catalyst. (Reproduced with permission from Elsevier)

HDPE LDPE PP PS

Plastic type

Figure 5.5 Yield of liquid, solid and gas products in catalytic degradation of various plastics using spent FCC catalyst. (Reproduced with permission from Elsevier)

catalyst at 400°C, as shown in Figure 5.5. In general thermoplastics, the yield of liquid products is 80% or over, which is the following order; PS > PP > PE. Plastics with a polycyclic structure have higher liquid yield than that of polyolefinic structures. On the contrary, the gas yields in these types of plastics are in reverse order compared with those of liquid, which is below 20% yield. Also, the solid is much more produced from polycyclic polymer than polyolefinic polymer. Accordingly, the product distribution is very influenced by the type of plastic.

The pyrolysis of mixed waste thermoplastics in a pilot plant of 360 ton/year at the Korea Institute of Energy Research (KIER), as shown in Figure 5.6, has an oil yield of about 82% for continuous process control over two days. The distribution of oil product is 27% gasoline product and 73% heavy oil product. Also the yield, of gas product is 10-15% and consists of about 18.1% Ci, 15.2% C2, 30.3% C3, 21.9% C4 and 14.3% C5 components. Similar results were obtained by other researchers, as shown in Table 5.1.

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