recycling of polymers.pptx includes pyrolysis which is a thermal decomposition of plastics

Covers both mechanical and chemical methods of recycling.

1. Topic: Recycling of Polymers BY GROUP 1 JERRY-OPARA VICTOR (G2023/MSc/CGRP/FT/148) ARINZE CHUKWU (G2023/MSc/CGRP/FT/145) RICHARD IRECHUKWU (G2023/MSc/CGRP/FT/147) CHARLES OGBONDA (G2023/MSc/CGRP/FT/153) EKEH LUCKY NNAMDI (G2023/MSc/CGRP/FT/162) ONOJA INNOCENT (G2023/MSc/CGRP/FT/159) CENTRE FOR GAS REFINING AND PETROCHEMICALS POLYMER TECHNOLOGY (RPE 811-1)

2. INTRODUCTION The term "plastic" often used interchangeably with "polymer," Plastics are a specific type of polymer, known for their moldability. Plastics are typically polymers of high molecular weight, and may contain other substances to improve performance and/or reduce costs. Plastic is one of the few new chemical materials which pose environmental problem. Polyethylene, polyvinyl chloride, polystyrene, PET are largely used in the manufacture of plastics.

3. Polymers Thermosets Cannot be melted Thermoplastics Can be melted Crystalline Ordered and tightly packed chains - opaque, strong, poor impact resistance eg Polypropylene, LDPE, HDPE . Amorphous Randomly arranged chains - transparent, brittle, good impact resistance eg Polystyrene, polycarbonate Semi- Crystalline A mix of both, offering a balance of properties eg Polybutylene terephthalate (PBT), PET CLASSIFICATION OF POLYMER

4. Why Recycle Polymers? slow decomposition times, taking from 20 to 500 years depending on the type of plastic and environmental factors Conservation of non-renewable fossil fuels Lowers greenhouse gas emissions associated with plastic production Conserves landfill space and prevents environmental pollution Creates new products from waste materials Reduced consumption of energy.

5. Types of Polymer Recycling Mechanical Recycling Most common method Sorts plastic waste by type Washes and grinds the plastic Melts the plastic into pellets Remolds pellets into new products Chemical Recycling Depolymerizes plastic waste into monomers Uses monomers to create virgin-quality plastic Pyrolysis

6. Mechanical Recycling Steps Sorting: Plastic waste is separated by polymer type (e.g., PET, HDPE, PP) Manual sorting Automated Sorting technique (NIR – Near IR/ Near Infared ) Washing: Contaminants like dirt and labels are removed Grinding: Plastic is shredded into small flakes Melting: Flakes are melted under controlled temperature and pressure. Here's a simplified equation representing this process for polyethylene (PE): PE + Heat → New PE Structure   Extrusion: Melted plastic is forced through a mold to create new shapes (pellets) Note: While mechanical recycling doesn't involve dramatic changes in the polymer's chemical structure, some rearrangement of the chains can occur during melting.

7. Recycling No. Abbreviation Polymer Name PETE or PET Polyethylene Terephthalate HDPE High-Density Polyethylene PVC or V Polyvinyl Chloride LDPE Low-Density Polyethylene PP Polypropylene PS Polystyrene OTHER Other plastics, including acrylic , polycarbonate , polylactic acid , nylon and fiberglass . To assist consumers and sorters, Society for plastic Industry (SPI) introduced recycling symbols . Numbering system for plastic recycling

8. Chemical Recycling Process Depolymerization : This is the heart of chemical recycling, breaking down polymers into monomers. C ommon techniques Thermal Decomposition: Uses high heat to break down polymers Solvolysis: Uses solvents to break down polymers Hydrogenolysis: Uses hydrogen gas to break down polymers

9. Thermal Decomposition (Pyrolysis): Chain-growth polymers can be degraded by heating in an oxygen-starved environment (around 400-800°C). This heat disrupts the polymer chains, converting them back into monomer. Example:  Polystyrene (PS) waste can be broken down into styrene monomer through pyrolysis. (PS)n → n(C₈H₈) (n represents the degree of polymerization, C₈H₈ represents styrene monomer) Solvolysis: Step-growth polymers like polyesters, polyamides and polycarbonates can be degraded by solvolysis and mainly hydrolysis to give lower molecular weight molecules. The hydrolysis takes place in the presence of water containing an acid or a base as catalyst. Example:  PET (polyethylene terephthalate) broken down into its monomers, terephthalic acid (TPA) and ethylene glycol (EG), through solvolysis. (C₁₀H₈O₄)n + nH₂O + nCH₃OH → nC₆H₄O ₄ + nC₂H₆O ₂ (C₁₀H₈O₄ represents PET, H₂O represents water, CH₃OH represents methanol, C₆H₄O₄ represents terephthalic acid (TPA), C₂H₆O₂ represents ethylene glycol (EG)) Hydrogenolysis:  PE waste is heated and exposed to hydrogen gas (H₂) in the presence of a catalyst. The H₂ breaks down the carbon-carbon bonds in the PE chain, producing a mixture of hydrocarbon gases with varying chain lengths. Example:  PE (polyethylene) waste can be depolymerized into various hydrocarbon molecules using hydrogenolysis. (C₂H₄)n + nH ₂ → Mixture of shorter hydrocarbon chains (C₂H₄ represents ethylene, the repeating unit in PE)

10. Purification: After depolymerization, the resulting monomers need purification to remove any impurities or byproducts. This ensures high-quality plastic production during repolymerization. Repolymerization: The purified monomers are then used to create new polymers through a process similar to virgin plastic production. Chemical recycling process

11. Pyrolysis in Focus: Breaking Down Polymers with Heat Pyrolysis, a form of thermal decomposition, deserves a closer look due to its growing importance in polymer recycling. Here's a breakdown of the process: Process:  Polymer waste is heated in a closed container (reactor) with little to no oxygen. The lack of oxygen prevents combustion and promotes thermal cracking of the polymer chains. The temperature range for pyrolysis can vary depending on the type of plastic waste being processed. Typically, it ranges from 400°C to 800°C. Products:  Pyrolysis yields a variety of products, including: Liquid hydrocarbons:  These can be further refined into new virgin plastic feedstock or used as fuels. The specific hydrocarbons produced will depend on the starting plastic material. Gases:  Depending on the plastic and process conditions, various gases like methane (CH₄), hydrogen (H₂), and carbon monoxide (CO) may be produced. Char:  This is a solid residue consisting of non-volatile components of the plastic waste. It can be used for energy recovery or further processing depending on its composition.

12. Pyrolysis for Polymer Recycling Process Advantages Feedstock versatility:  Pyrolysis can handle a wider range of plastic waste compared to other depolymerization methods, including mixed plastics. Energy efficient:  Pyrolysis can be a relatively energy-efficient process, especially when the recovered gases are used as fuel for the process itself. Potential for fuel production:  The recovered hydrocarbons can be a valuable source of renewable fuels. Limitations Product distribution:  The product distribution from pyrolysis can vary depending on the plastic feedstock and process conditions. Feedstock pre-treatment:  The plastic waste might require pre-treatment to remove impurities that could affect the product quality. Energy demand:  While potentially energy-efficient, pyrolysis still requires a significant amount of energy to reach the high temperatures needed.

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