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Plastic waste poses a serious threat to the environment and it has been increasing at an alarming rate. In 2022, global plastic waste generation was reported to be around 380 million tonnes as compared to 353 million tonnes in 2019. Production of liquid fuel from plastic waste is regarded as a viable method for disposing of the plastic and utilizing its energy. A wide range of technologies have been explored for turning plastic waste into fuel, including the conventional pyrolysis, incineration, gasification and advanced oxidation.
S. No. |
Feed |
Reactor |
Temperature (°C) |
Yield (wt%) |
Reference |
||
---|---|---|---|---|---|---|---|
Liquid |
Gas |
Char |
|||||
1. |
HDPE |
Fixed bed |
550 |
70 |
23 |
7 |
[23] |
2. |
Mixed |
Semi batch |
500 |
75.8 |
10 |
14.2 |
[24] |
3. |
HDPE |
Batch |
440 |
74 |
9 |
17 |
[25] |
4. |
PE |
Steel micro |
350 |
80.9 |
17.2 |
1.9 |
[26] |
5. |
PP |
Steel micro |
350 |
67.8 |
30 |
1.6 |
[26] |
6. |
Mixed |
Semi batch |
500 |
65.2 |
34 |
0.8 |
[27] |
7. |
PET |
Fixed bed |
500 |
38.89 |
52.13 |
8.98 |
[28] |
8. |
PET |
Parr mini bench top |
500 |
15.0 |
32.0 |
53.0 |
[29] |
9. |
HDPE |
Horizontal steel |
350 |
80.88 |
17.24 |
1.88 |
[26] |
10. |
HDPE |
Semi batch |
450 |
91.2 |
4.1 |
4.7 |
[30] |
11. |
HDPE |
Batch |
550 |
84.70 |
16.30 |
- |
[31] |
12. |
HDPE |
Fluidized bed |
650 |
68.50 |
31.50 |
- |
[32] |
13. |
HDPE |
Semi-batch |
400 |
82 |
16 |
2 |
[33] |
14. |
HDPE |
Fluidized bed |
500 |
85 |
10 |
5 |
[34] |
15. |
PS |
Batch |
581 |
89.5 |
9.9 |
0.6 |
[35] |
16. |
PS |
Semi-batch |
400 |
90 |
6 |
4 |
[33] |
17. |
PP |
Batch |
380 |
80.1 |
6.6 |
13.3 |
[36] |
18. |
PS |
Batch |
500 |
96.73 |
3.27 |
- |
[37] |
19. |
LDPE |
Batch |
430 |
75.6 |
8.2 |
7.5 |
[38] |
20. |
PP |
Semi-batch |
400 |
85 |
13 |
2 |
[33] |
21. |
HDPE |
Semi-batch |
450 |
91.2 |
4.1 |
4.7 |
[30] |
22. |
LDPE |
Fluidized bed |
600 |
51.0 |
24.2 |
- |
[39] |
23. |
HDPE |
Batch |
450 |
74.5 |
5.8 |
19.7 |
[40] |
24. |
PP |
Semi-batch |
450 |
92.3 |
4.1 |
3.6 |
[41] |
25. |
HDPE |
CSBR |
650 |
46.0 |
18.0 |
- |
[42] |
26. |
Mixed |
CSBR |
450–600 |
- |
- |
100% wax |
[43] |
27. |
LDPE and PP |
Fluidized bed |
680 |
56.7 |
42.8 |
0.5 |
[44] |
28. |
Mixed |
Fluidized bed |
677 |
57.8 |
35.3 |
6.9 |
[45] |
29. |
Mixed |
Fluidized bed |
600 |
49.0 |
43.0 |
8.0 |
[46] |
30. |
LDPE |
Fixed bed |
500 |
95.0 |
5.0 |
- |
[47] |
31. |
PP |
Batch |
430 |
80.7 |
4.3 |
6.1 |
[48] |
32. |
LDPE |
Batch |
550 |
93.1 |
14.6 |
- |
[31] |
33. |
HDPE |
Fluidized bed |
650 |
68.5 |
31.5 |
- |
[32] |
S. No. |
Feed |
Microwave Power Range (kW) |
Yield (wt.%) |
||
---|---|---|---|---|---|
Liquid |
Gas |
Char |
|||
1. |
HDPE |
3 |
83.92 |
15.68 |
0.40 |
2. |
PP |
3 |
70.82 |
13.29 |
15.89 |
3. |
PVC |
3 |
3.44 |
81.87 |
14.69 |
4. |
PET |
1.8–3 |
35.32 |
26.48 |
38.20 |
5. |
PS |
3–6 |
89.25 |
8.92 |
|
S. No. |
Parameter |
Fixed or Moving Bed |
Fluidized Bed |
Entrained Bed |
---|---|---|---|---|
1. |
Feed size |
Less than 51 mm |
Less than 6 mm |
Less than 0.15 mm |
2. |
Tolerance for fines |
Limited |
Good |
Excellent |
3. |
Tolerance for coarse |
Very good |
Good |
Poor |
4. |
Gas exit temperature |
450–650 °C |
800–1000 °C |
Greater than 1200 °C |
5. |
Feedstock tolerance |
Low rank coal |
Low rank coal and excellent for biomass |
Any coal including caking but unsuitable for biomass |
6. |
Oxidant requirements |
Low |
Moderate |
High |
7. |
Reaction zone temperature |
1090 °C |
800–1000 °C |
1990 °C |
8. |
Steam requirement |
High |
Moderate |
Low |
9. |
Nature of ash produced |
Dry |
Dry |
Slagging |
10. |
Cold-gas efficiency |
80% |
89% |
80% |
11. |
Application |
Small capacities |
Medium size units |
Large capacities |
12. |
Problem areas |
Tar production and utilization of fines |
Carbon conversion |
Raw-gas cooling |
Reaction Type |
Reaction |
Heat of Reaction (kJ/mol) |
---|---|---|
R1: Combustion reaction |
C + ½ O2 |
−122 |
R2: Combustion reaction |
CO + ½ O2 |
−283 |
R3: Combustion reaction |
H2 + ½ O2 |
−248 |
R4: Water gas reaction |
C + H2O |
+136 |
R5: Water gas shift reaction |
CO + H2O |
−35 |
R6: Steam reforming of methane |
CH4 + H2O |
+206 |
R7: Boudouard reaction |
C + CO2 |
+171 |
R8: Hydrogasification |
C + 2H2 |
−74.8 |
S. No. |
Feed |
Reactor Type |
Conditions [Equivalence Ratio (ER), Temperature (T), Steam to Plastic (S/P)] |
Gasifying Medium |
Gas Yield (m3kg−1) |
Gas Composition (% vol) |
Reference |
---|---|---|---|---|---|---|---|
1. |
PE |
Bubbling fluidized bed |
ER: 0.2–0.31, T: 845–897 °C |
Air |
3–4.3 |
H2: 9.1–9.5, CO: 2.2–2.8, CO2: 9.1–10.4, CH4: 7.1–10.4 |
[65] |
2. |
PE |
Bubbling fluidized bed |
ER: 0.3, T: 750 °C |
Air |
3.6 |
H2: 2.7, CO: 6.1, CO2: 8.8, CH4: 7.0 |
[66] |
3. |
PP |
Fluidized bed |
ER: 0.32–0.36 T: 850 °C |
Air |
4.5 |
H2: 5, CO: 5, CO2: 12, CH4: 3 |
[67] |
4. |
PP |
Fluidized bed |
ER: 0.2–0.45 T: 690–950 °C |
Air |
2.0–3.8 |
H2: 4–5, CO: 15–20, CO2: 9–15, CH4: 4–6 |
[58] |
5. |
Waste PE |
Bubbling fluidized bed |
ER: 0.3, T: 750 °C |
Air |
3.7 |
H2: 3, CO: 8.7, CO2: 7.4, CH4: 8.7 |
[66] |
6. |
Mixed plastic wastes |
Bubbling fluidized bed |
ER: 0.25, T: 887 °C |
Air |
3.3 |
H2: 5.9, CO: 4.5, CO2: 10.3, CH4: 6.6 |
[68] |
7. |
PE |
Bubbling fluidized bed |
ER: 0.2–0.29 T: 807–850 °C |
Air |
4.2–6.2 |
H2: 30, CO: 18.4–20.9, CO2: 1.6–2.2, CH4: 3.4–1.5 |
[65] |
8. |
Waste plastic mixture |
Fixed bed |
ER: 0.15–0.6 T: 700–900 °C |
Air |
1.2–1.5 |
H2: 29–41, CO: 22–33, CO2: 8.2–22, CH4: 4.3–10 |
[69] |
9. |
Waste polyolefins |
Bubbling fluidized bed |
ER: 0.25–0.35, T: 750 °C |
Air |
3.2–4.4 |
H2: 3, CO: 8.5–10, CO2: 6.5–7.8, CH4: 8.5–10 |
[66] |
10. |
Waste plastic mixture |
Bubbling fluidized bed |
ER: 0.22–0.31 T: 869–914 °C |
Air |
2.5–3.2 |
H2: 6.6–6.8, CO: 3.7–4.8, CO2: 11–11.6, CH4: 6.3–7.3 |
[65] |
11. |
PP |
Fluidized bed |
ER: 0.32–0.36 T: 850 °C |
Air |
5.3 |
H2: 6, CO: 7, CO2: 16, CH4: 8 |
[67] |
12. |
Mixed plastic and cellulosic material |
Bubbling fluidized bed |
ER: 0.24, T: 869 °C |
Air |
2.73 |
H2: 6, CO: 6.6, CO2: 12.7, CH4: 6.5 |
[68] |
13. |
Recycled plastic |
Bubbling fluidized bed |
ER: 0.25, T: 877 °C |
Air |
3.5 |
H2: 6, CO: 6.6, CO2: 12.7, CH4: 6.5 |
[70] |
14. |
PE |
Fluidized bed |
S/P: 2, T: 850 °C |
Steam |
1.2 |
H2: 38, CO: 7, CO2: 8, CH4: 30 |
[71] |
15. |
PP |
Fluidized bed |
S/P: 2, T: 850 °C |
Steam |
1 |
H2: 34, CO: 4, CO2: 8, CH4: 40 |
[71] |
16. |
PP + PE |
Fluidized bed |
S/P: 2, T: 835 °C |
Steam |
2.1 |
H2: 46, CO: 22, CO2: 5, CH4: 16 |
[71] |
17. |
PE + PET |
Fluidized bed |
S/P: 1.2, T: 850 °C |
Steam |
1 |
H2: 27, CO: 20, CO2: 29, CH4: 15 |
[71] |
18. |
PE + PS |
Fluidized bed |
S/P: 1.8, T: 850 °C |
Steam |
1.4 |
H2: 52, CO: 24, CO2: 7, CH4: 12 |
[71] |
19. |
PE |
Spouted bed |
S/P: 1, T: 800–900 °C |
Steam |
2.5-3.4 |
H2: 57–60, CO: 24–28, CO2: 1–3, CH4: 6–7 |
[57] |
20. |
PE |
Spouted bed |
S/P: 1, T: 900 °C |
Steam |
3.2 |
H2: 58, CO: 27, CO2: 3, CH4: 7 |
[57] |
21. |
PE |
Spouted bed |
S/P: 1, T: 900 °C |
Steam |
3.3 |
H2: 59, CO: 26, CO2: 2, CH4: 8 |
[57] |
22. |
PP |
Fixed bed |
T: 850 °C |
Steam |
1.9 |
H2: 38, CO: 45, CO2: 8, CH4: 9 |
[72] |
23. |
HDPE |
Fixed bed |
T: 850 °C |
Steam |
2.4 |
H2: 35, CO: 43, CO2: 10, CH4: 11 |
[72] |
24. |
PS |
Fixed bed |
T: 850 °C |
Steam |
1.3 |
H2: 29, CO: 43, CO2: 26, CH4: 1.7 |
[72] |
25. |
Waste plastic |
Plasma |
T: 1200 °C |
Steam |
3.5 |
H2: 62, CO: 34 |
[73] |
26. |
PP |
Fixed bed/fixed bed |
T: 400/580–680 °C |
Pyrolysis and steam reforming |
5.4-8.8 |
H2: 70, CO: 9–11, CO2: 16–19, CH4: 1.4–1.5 |
[74] |
27. |
PP |
Fixed bed/fixed bed |
T: 400–600/630 °C |
Pyrolysis and steam reforming |
5.4-5.6 |
H2: 71–72, CO: 8–9, CO2: 19, CH4: 0.9–1.5 |
[74] |
28. |
PS |
Spouted bed/fluidized bed |
T: 500/700 °C |
Pyrolysis and steam reforming |
5 |
H2: 65, CO: 14, CO2: 21, CH4: <0.1 |
[75] |
29. |
PE |
Fixed bed/fixed bed |
T: 500/800 °C |
Pyrolysis and steam reforming |
4.35 |
H2: 67, CO: 24, CO2: 9, CH4: 1 |
[76] |
30. |
PP |
Fluidized bed/fluidized bed |
T: 650/850 °C |
Pyrolysis and steam reforming |
4.1 |
H2: 65, CO: 12, CO2: 21, CH4: 1.6 |
[62] |
Conversion of plastics through electrocatalytic oxidation can be brought about using two different methods: direct oxidation and indirect oxidation. Direct oxidation refers to the electrophilic attack on a polymer by ·OH produced by water discharge on the anode surface. When strong oxidising intermediates dominate in the plastic conversion process, it is referred to as indirect oxidation. With an external voltage (0.55 V) applied in H3PO4 solution at 200 °C, polyvinyl alcohol (PVA) was successfully converted to H2 (9.5 mol/min) [77]. Also, for the production of carboxylic acid (75%), electrocatalytic degradation of PVC was carried out on TiO2/C cathode (−0.7 V) at 100 °C [78].
A plastic polymer is reduced when it receives electrons from the cathode (TiO2/C), which undergoes dechlorination at a high temperature. Additionally, the polymer is oxidised with ·OH to produce carbonyl and hydroxyl groups, which subsequently breaks down into tiny molecules (e.g., alcohols, carboxylic acids and esters). Finally, these chemicals partially mineralize to CO2 and H2O. Electrocatalytic breakdown of plastic wastes may result in a single product that could be turned directly into fuels. Electrolysis alone cannot yield as many fuel components as pyrolysis and electrolysis combined.