2 0 Plastics Recycling 9 7 8 3 Datchanee Pattavarakorn Industrial Chemistry, Science, CMU
Why recycle plastics? Waste emissions Industrial waste Domestic waste
Why recycle plastics? Waste emissions 640 kg/person in 2020
Why recycle plastics?
Why recycle plastics? Plastic problem
How to manage plastics waste?
How to manage plastics waste? Industrial waste Domestic waste
How to manage plastics waste? Landfill problem
How to manage plastics waste? Landfill problem
How to manage plastics waste? Landfill problem
Methods of plastic recycling Primary recycling Secondary recycling Tertiary recycling Quaternary recycling
Methods of plastic recycling using uniform & uncontaminated plastic waste to manufacture plastic products (reprocess) can be used alone or added to virgin resin at various ratios Main technical problems degradation Primary recycling loss in properties e.g., appearance, chemical resistance, processability, mechanical characteristics contamination of the processed plastic handling of low-bulk density scrap (film or foam)
Methods of plastic recycling Primary recycling Mechanisms : polymer structure change 1. Reduction of average MW. main chain scission the breaking of a molecular bond causing the loss of a side group or shortening of the overall chain
Methods of plastic recycling Mechanisms : polymer structure change 2. Increase of average MW. radical combination Primary recycling
Methods of plastic recycling Primary recycling Mechanisms : polymer structure change 3. Formation of unsaturation or cyclization dehydrohalogenation
Methods of plastic recycling Secondary recycling using recycled plastic waste to manufacture plastic products Mechanical recycling Chemical modification 2 nd recycling Coextrusion and Coinjection molding
Mechanical recycling Secondary recycling
Mechanical recycling : PET Secondary recycling
Coextrusion and Coinjection molding Secondary recycling
Methods of plastic recycling Tertiary recycling converts discarded plastic products into high-value petrochemical or fuel feedstocks Pyrolysis Tert. Recycling (Feedstock recycling) Chemical recycling (Chemolysis) Thermolysis Gasification Hydrogenation
Tertiary recycling : Chemical recycling Chemical recycling or Chemical depolymerization The breakdown of polymer by reaction with certain chemical agents, leading back to oligomer or even starting monomers identical to monomers used in the preparation of virgin polymers. suitable for treatment of clean mono-resin plastic waste especially applicable to condensation polymers such as polyesters, polyamides, polyacetals, polycarbonates, etc. < 15% of total plastic wastes
Tertiary recycling : Chemical recycling Chemical recycling or Chemical depolymerization Different decomposition routes can be envisaged, depending on The chemical agents used to breakdown the polymer. Hydrolysis Glycolysis Methanolysis Ammonolysis Alcoholysis Water Glycol Methanol Ammonia Alcohol
Tertiary recycling : Chemical recycling PET : Condensation polymerization Ethylene glycol (EG) Terephthalic acid (TPA) bis(hydroxyethyl) terephthalate (BHET) dimethyl terephthalate (DMT) PET
Tertiary recycling : Chemical recycling PET : Chemolysis alternatives
Tertiary recycling : Chemical recycling PET : Glycolysis simplest & oldest method of PET depolymerization reaction occurs under P & T (180-240 o C) with excess of low MW.; methylene glycol, ethylene glycol, propylene glycol requires catalyst; zinc or lithium acetate BHET purification - PET production - Unsaturated polyester Colors present in starting PET wastes are not usually removed.
Tertiary recycling : Chemical recycling PET : Glycolysis
Tertiary recycling : Chemical recycling PET : Methanolysis reaction occurs under P (20-40 atm)& T (180-280 o C) with excess of methanol requires catalyst; Zn or Mg or Co acetate or lead dioxide Products: DMT & EG organic impurities cannot be completely removed reaction can be run only in batch process Recently, PET methanolysis has been carried out with supercritical methanol condition. poor color
Tertiary recycling : Chemical recycling PET : Supercritical Methanolysis reaction occurs under P (> 80 atm)& T (300 o C) supercritical methanol much faster than liquid MeOH
Tertiary recycling : Chemical recycling PET : Supercritical Methanolysis www.petrecycling.cz/mhi_metanolyza.htm
Tertiary recycling : Chemical recycling PET : Hydrolysis reaction of PET with H 2 O TPA & EG process can be carried out under neutral, acidic and basic conditions requires severe condition long reaction times
Tertiary recycling : Thermolysis Thermolysis or Thermal depolymerization the chemical decomposition of condensed organic substances by heating Under pressure and heat, long chain polymers decompose into short-chain petroleum hydrocarbons with a maximum length of around 18 carbons oil & useful by products
Tertiary recycling : Thermolysis Pyrolysis physical & chemical decomposition of organic materials at elevated temperatures in the absence of oxygen or in low oxygen atmosphere typically occurs under pressure and at operating temperatures as high as 400-1000 C the production of basic chemicals and fuels from waste plastics
Tertiary recycling : Thermolysis Pyrolysis Gasoline, Diesel & heavy oil
Tertiary recycling : Thermolysis Pyrolysis
Tertiary recycling : Thermolysis Pyrolysis: Advantages a) most MSW can be converted into an economically viable forms b) volume of waste can be reduced by 90% or more c) does not cause air pollution & requires little space, thus it can be located in cities, resulting in lower transportation cost d) products are in convenient forms gas, oil and char e) Energy producer recover energy from waste
Tertiary recycling : Thermolysis Polymer as feedstock for fuel production
Tertiary recycling : Thermolysis Product types of some plastics pyrolysis
Tertiary recycling : Thermolysis Gasification A partial oxidation (incomplete combustion) process of carbonaceous materials leading predominantly to a mixture of carbon monoxide and hydrogen. Syngas or Synthesis gas Reaction of the raw carbonaceous material with O 2, air, steam or steam/o 2 and steam/air mixtures under T (700-1600 o C) & P (10-90 atm)
Tertiary recycling : Thermolysis Gasification
Tertiary recycling : Thermolysis Gasification : Utilization of Syngas Syngas a combustible gas mixture, carbon monoxide, hydrogen, nitrogen, carbon dioxide and methane a relatively low calorific value (100-300 BTU/SCF) can be used as a fuel to generate electricity or steam can be burned directly in internal combustion engines used to produce methanol and hydrogen
Tertiary recycling : Thermolysis Gasification : reactions in Gasifier
Tertiary recycling : Thermolysis Gasification : reactions in Gasifier Drying zone: all moisture must be removed H 2 O inability to produce clean fuel wet waste dry waste + H 2 O Pyrolysis zone: carbonaceous mat. decompose into tars (gasses and liquids) charcoal (high carbon content) waste + heat C+CO+CO 2 +H 2 O+CH 4 +C 2 H 6 +Acid+Tar
Tertiary recycling : Thermolysis Gasification : reactions in Gasifier Combustion zone: Oxidation zone combustion of the tars with O 2 to produces CO 2 & H 2 O C + O 2 ======> CO 2 2H 2 + O 2 ======> 2H 2 O adequate mixing and high temperature flame is required exothermic rxn. generates the heat to run reduction
Tertiary recycling : Thermolysis Gasification : reactions in Gasifier Reduction zone: reverts completely combusted hydrocarbons into a form that can be used as fuel endothermic removal of oxygen from HCs Combustion products become fuel gasses again and those fuel gasses can then be piped off C + CO 2 =====> 2CO C + H 2 O ===== > CO + H 2
Tertiary recycling : Thermolysis Gasification
Tertiary recycling : Thermolysis Gasification : Advantages efficient treatment for the degradation & conversion of plastic wastes, especially mixed plastics the process takes place under pressure and less poisonous gases are emitted into the atmosphere no hazardous heavy metals are generated during the process energy need of the process is significantly lower
Tertiary recycling : Thermolysis Hydrogenation : Hydrocracking plastic wastes are heated with H 2, usually in the presence of a catalyst to produce saturated liquid & gaseous hydrocarbons PE PP PS H 2 Methane, ethane, propane, Gasoline, diesel, lubricating oil PVC H Na 2 HC mixture + HCl 2 S NaCl
Quaternary recycling : Energy recovery The useful retrieval of the energy content of plastic wastes by its use as an energy source to produce products such as steam and/or electricity.
Quaternary recycling : Energy recovery
Quaternary recycling : Energy recovery INCINERATION a controlled combustion process for reducing solid, liquid, or gaseous combustible wastes primarily to gases e.g., carbon dioxide, water vapor, other gases relatively small & noncombustible residue that can be further processed or land-filled
Quaternary recycling : Energy recovery
Quaternary recycling : Energy recovery