VISHNU RAJ R14CE63R09

Plastics are synthetic polymers derived from petro-fossil feedstock and made-up of long chain hydrocarbons with additives

Two types of plastics

Thermoplastics(Recyclable)-become soft when heated, can be moulded or shaped with pressure when in plastic state

Thermosets (Non Recyclable)-Once set cannot be remoulded /softened by applying heat.

Environmental Issues

Plastic waste disposal on land makes it infertile

Burning generates toxic emissions -CO, HCl, Dioxin, Furans

Leaching out of toxic chemicals added as additives

Littering

Affects waste processing facilities like composting

In efficient usage of crude oil resources

Plastic Waste Management

Recycling of plastics

Primary Recycling: involves processing of a waste into a product with characteristics similar to those of original product.

Secondary (Mechanical)Recycling: processing of waste plastics into products that have characteristics dissimilar from those of original plastic products

Tertiary(Chemical) Recycling: extraction of chemicals from plastic wastes

Quaternary Recycling: recovery of energy from wastes

Sorting Of Plastic Wastes Density sorting

Hydrocyclones- uses centrifugal force, enhance material wettability.

Heavy medium separation -using tetrabromoethane

Triboelectric separation- sorts materials on the basis of a surface charge transfer phenomenon

Speed accelerators

Paint Removal

Grinding & Solvent stripping

Mechanical RecyclingCan only be performed on single-polymer plastic

Steps involved

Crushing/Shredding

Contaminant separation:

Floatation

Milling

Washing and Drying

Agglutination

Extrusion

Mechanical recycling steps as described by Aznar et al. (2006).

Existing recycling processes & Issues

Selection of waste:

Toxic wastes are separated

Segregation of plastics waste: Segregation shall be done in accordance with IS 14535

Processing (extrusion process)

Washing generates waste water having high pollution load & needs treatment before proper disposal

Exposure of workers in reprocessing plant to toxic dyes and additives

CONVERTING WASTE INTO A RESOURCEquality concerns when converting waste plastics into fuel

resources are

Smooth feeding to conversion equipment

Effective conversion into fuel products

Well-controlled combustion and clean flue gas in fuel user facilities

plastics & fuel they produce

SOLID FUEL PRODUCTIONTwo types of solid fuel

refuse derived fuel (RDF)

refuse-derived paper and plastic densified fuel (RPF)

o Thermoplastics act as a binder for the other components

o Contamination of plastics with other plastics containing halogens (Cl, Br, F), N, S and other hazardous substances may cause air and soil pollution

Production method

Involves two steps- pretreatment and pellet production

Two types of commercial production systems

large-scale model(3 ton/hour)with pretreatment for the separation of undesirable contamination

small-scale model (150 kg/hour) without pretreatment equipment

Heating values

RDF: 4000 – 5000 kcal/kg

RPF: 6000 – 8000 kcal/kg

Schematic diagram of pretreatment process

Schematic diagram of a pelletizing process

Liquid Fuel Production

Based on the pyrolysis of the plastics and the condensation of the resulting hydrocarbons

Thermoplastics (PE, PP, and PS)are used for conversion.

Decomposition occur at 450 to 550 °C.

The products generated from include gasoline, diesel, benzene, naphtha, and fuel oil

The by-products from the process - sludge and gas are reused.

PVC plastics waste is not used as the chlorine can be converted into HCl as a by-product

Schematic diagram of a liquid fuel production plant (UNEP, 2009)

Gaseous Fuel Production Waste plastics undergo thermal decomposition

in a tank reactor for an extended time at a reaction temperature

Occurs at higher temperatures 800 -1000 °C

Two types of gaseous fuel are produced:

Gaseous hydrocarbon & Syngas

Calorific value of syngas ranges between the calorific value of biogas and LNG/LPG.

Gasification process for converting plastic wastes to chemicals (PCD, 2011)

Observations Impact, Los Angels Abrasion & Crushing Value

increased with the increase in the percentage of plastics.

Better skid resistance

Unevenness index values were low (3000 mm/km)

indicating good surface evenness.

Better resistance towards water stagnation i

Co-processing of Plastic waste in Cement Kiln Plastic waste is used as an alternative fuel in cement Kilns Primary fuel and raw material are substituted by waste

Pre-processing of plastic waste

Plastic waste is sun dried and subjected to shredding before feeding into cement kilns

PVC containing plastic waste is not used as it impair the cement quality

Plasma Pyrolysis Disintegration of organic compounds into gases and

non leachable solid residues in an oxygen-starved environment

Uses ions and excited molecules with high energy radiation to decompose chemicals

High temperature decomposes waste material into simple molecules

Efficient way of treating chlorinated plastics

Dioxins and furans emissions are below the prescribed limits ie, the range of 0.005-0.009 ng/m3

Ideal for decentralized disposal of plastic waste

Reduction in volume of organic matter > 99%

Segregation of the waste is not necessary

DEGRADABLE PLASTICSTypes

Poly-Lactic Acid (PLA)

produced in a two-step fermentation and chemical polymerization process

Polyhydroxyalkanoate (PHA)

synthesized by bacteria as intracellular carbon and energy storage compounds

Poly olefins modified by adding transition metals/compounds

Oxo-biodegradable plastics

Moisture and heat attack PLA polymer chains, splitting them apart through hydrolysis, to lactic acid monomers which are consumed by microbes

PHA plastics are attacked by microorganisms that secrete PHA depolymerizer, and most products take three to nine months to degrade

Polyolefins are decomposed by UV or heat-initiated oxidation

Plastic degradation processes

Photo degradation: Degradation caused through the action of sunlight on the polymer

Biodegradation :Degradation that occurs through the action of microorganisms such as bacteria, yeast, fungi, and algae etc.

Biodeterioration: Degradation that occurs through the action of microorganisms such as beetles, slugs, etc.

Autooxidation :Degradation caused by chemical reactions with oxygen.

Hydrolysis: Degradation that occurs when water cleaves the backbone of a polymer, resulting in a decrease in molecular weight and a loss of physical properties

Solubilization: Dissolution of polymers that occurs when a water-soluble link is included in the polymer

Compatibility of Degradable Plastics with Current SWM Practices Composting

Require specific levels of moisture and oxygen & inadequate temperatures may not initiate the key hydrolysis reaction for PLAs

Recycling

The increase in input heterogeneity will reduce the quality of the recovered plastic

Waste-to-Energy Incineration

Less CO2 emissions

Landfilling

Decay and release of more methane , production of higher strength leachate & sequestration of carbon,

Drawbacks Higher costs

Difficulty in recycling

concerns regarding potential later degradation of the end products

Requirement of specific levels of moisture and oxygen for initial reactions to occur

References

Recycling and recovery routes of plastic solid waste (PSW): A review, S.M. Al- Salem , P.Lettieri, J. Baeyens

Environmental evaluation of plastic waste management scenarios: L. Rigamontia, M.Grossoa, J. Møllerb, V. Martinez Sanchezb,S. Magnania, T.H. Christensen

A Review of Plastic Waste Management Strategies:JaveriyaSiddiqui and Govind Pandey, International Research Journal of Environment Sciences

Development of process for disposal of plastic waste using plasma pyrolysis technology and option for energy recovery: M. Puncochara, B. Rujb, P. K. Chatterjee

Degradable Plastics and Solid Waste Management Systems: David J. Tonjes ,Krista L. Greene

IS 14534 1998 -GUIDELINES FOR RECYCLING OF PLASTICS

Preliminary Study On The Conversion Of Different Waste Plastics Into Fuel Oil : Yasabie Abatneh, Omprakash Sahu

Biodegradability of Plastics : Yutaka Tokiwa, Buenaventurada P. Calabia ,Charles U. Ugwu and Seiichi Aiba

Recycling of plastic: accounting of greenhouse gases and global warming contributions : Thomas Astrup, Thilde Fruergaard, Thomas H. Christensen