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Potential Chemicals from Plastic Wastes
Plastic is referred to as a “material of every application”. From the packaging and automotive industries to the medical apparatus and computer electronics sectors, plastic materials are fulfilling demands efficiently. These plastics usually end up in landfills and incinerators, creating plastic waste pollution. According to the Environmental Protection Agency (EPA), in 2015, 9.1% of the plastic materials generated in the U.S. municipal solid waste stream was recycled, 15.5% was combusted for energy, and 75.4% was sent to landfills.
2. Production of Chemicals from Plastic Wastes
|Polymer||Low-Temperature Products||High-Temperature Products|
|Polyethylene (PE)||Waxes, paraffin oil,
|Gases and light oils|
|Polypropylene (PP)||Vaseline, olefins||Gases and light oils|
|Polystyrene (PS)||Styrene and its oligomers||Styrene and its oligomers|
|Polymethyl methacrylate (PMMA)||Methylmethacrylate
|Low methyl methacrylate, more decomposition products|
|Polyethylene terephthalate (PET)||Benzoic acid (BA),
|Polyamide 6 (PA6)||ε-caprolactum (CPL)|
2.1. Polyethylene (PE) and Polypropylene (PP)
|S. No.||Plastics||Method||Conditions||Product Yields||Key Findings||Source|
|1.||PE||Noncatalytic pyrolysis||T = 602 °C||Paraffins 45%; Olefins 32%; Naphthalenes 17%;Aromatics 6%;||A whole spectrum of HCs, including paraffins, olefins, naphthalenes, and aromatics.|||
|PP||T = 602 °C||Paraffins 27%; Olefins 36%; Aromatics 11%;|
|PS||T = 477 °C||Styrene 63%|
|2.||HDPE||Thermal-catalytic two-step pyrolysis||T = 500 °C||Light olefin 59%||Higher efficiency of the two-step reaction system compared to the in situ catalytic pyrolysis (single-step) for production of 10 wt.% ethylene, 32 wt.% propylene, and 17 wt.% butenes.|||
|3.||PP and PE||Fluidized bed reactor||T =
|BTX 32–53%||Higher feed rates and gaseous fluidizing medium have a positive effect on liquid oil production.|||
|4.||PE||Mini-autoclave reactor (unstirred)||T = 280 °C,
t = 24 h, Pt/Al2O3
|Liquid product 80%||Tandem catalytic conversion produces a high yield of low-molecular-weight liquid/wax products.|||
|5.||PS||Fluidized bed reactor||T = 520 °C||Styrene 83%||Complete conversion of PS to styrene oil was reported, with only traces of aliphatic compounds|||
|6.||PS + organic compounds||Autoclave reactor||T = 400 °C,
t = 1 h
Residue < 4%
|Maximum styrene yield in the liquid was obtained with naphthalene as an organic compound with PS|||
|7.||PS||Flow reactor||T = 350 °C,
t = 3 h, Fe2O3
(in liquid oil)
|Barium oxide powder was found to be most effective catallyst for chemical recyling of PS waste|||
|T = 350 °C,
t = 3 h, BaO
(in liquid oil)
|T = 350 °C,
t = 3 h, HSM5
(in liquid oil)
|8.||PS||Fixed-bed reactor||T = 510 °C thermal||Liquid 91.8%;
|Other aromatic compounds can behave like a chain transfer agent and reduce the Tg of product polymer.|||
|T = 510 °C BaO (cat.)||Liquid 91.2%;
|T = 510 °C FCC cat.||Liquid 90.7%; Residue 7.1%|
|9.||PS||Two-stage auger and fluidized bed reactor||T = 780 °C||BTEX 26.3%||Product yields depend on the reaction temperatures and fluidizing mediums used.|||
|10.||PET||Glycolysis||T = 190 °C; atm pressure||BHET 100% conversion,
|Lewis acidic ionic liquids [Bmim]ZnCl3 catalyst was found to be effective.|||
|Hydrolysis||T = 200–250 °C; P = 1.4–2 MPa||TPA, EG|||
|Methanolysis||T = 200 °C||DMT 64%;
|The product yields depend on the solubility of PET.|||
|Aminolysis||T = 70–110 °C||Diamides of TPA 66–89%||The bifunctional 1,5,7-triazabicyclo [4.4.0]dec-5-ene activates the carbonyl group and catalyzes the reaction.|||
|Pyrolysis||T = 450–600 °C
ZSM-5 zeolite and NiCl2 used as catalyst
|Aromatic hydroxyl groups increased by 22%||ZSM-5 facilitated the decomposition of carboxyl, aliphatic groups, and ether bonds in the primary products produced from the PET pyrolysis.|||
|Pyrolysis||T = 400–700 °C||Phenyl carboxylic acid 44–79%||Pd loaded on activated carbon used as a catalyst and produced more environmentally friendly products|||
|11.||PET||Py-GCMS, EGA-MS, and TGA||T = 600 °C||4(vinyl oxy carbonyl) BA 27%;
|Wide range of liquid products obtained by different pyrolysis mechanisms.|||
|12.||PU||Glycolysis||T = 200–210 °C;
t = 2 h
|Acetone-soluble products 80.8%;
Amines in total acetone soluble products 58.3 mgKOH/g
|Polyol products produced from the process and used as initiators to produce oxy-alkylated polyols.|||
|13.||PA 6 and PA66||Aminolysis||T = 100 °C;
P = 3.5 MPa;
t = 5.6 h;
Raney® Co 2724
|ACN = 2; HMD = 32%; CPL = 46.2%; Other components = 13.6%||Raney® Co provided a better catalytic activity along with long catalyst life|||
|T = 100 °C;
P = 3.5 MPa;
t = 5.6 h;
Raney® Ni 2400
|ACN = 19.6; HMD = 15%; CPL = 46.5%; Other components = 14.7%|
|14.||PA66||Microwave irradiation||T = 200 °C;
t = 0.16 h; HCl:PA66 =
|AA 90%; HMDA 86%; with 100% purity||The rate of PA hydrolysis depended on the PA type and HCl/amide molar ratio. With microwave treatment, high-purity and high-quality products were formed.|||
2.2. Polystyrene (PS)
2.3. Polyethylene Terephthalate (PET)
2.4. Polyurethane (PU)
2.5. Polyamides (PA)
This entry is adapted from 10.3390/molecules26113175
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