National Centre for Catalysis Research

Methods for Plastic Waste RemovalMethods for Plastic Waste Removal

M. BANU

Plastic is the general common term for a wide range of synthetic or semisynthetic organic amorphous solid materials suitable for the manufacture of industrial products. Plastics are typically polymers of high molecular weight , and may contain other substances to improve.

Plastics' versatility allow it to be used in everything from car parts to doll parts, from soft drink bottles to the refrigerators they are stored in.

From the car we drive to work in to the television watch when we get home, plastics help make your life easier and better.

Plastics are the material that can provide the things consumers want and need.

Plastics have the unique capability to be manufactured to meet very specific functional needs for consumers.

IntroductionIntroduction

The development of plastics is believed to have started around 1860, when Phelan and Collander, a U.S. pool and billiard ball company, offered a prize of $10,000 to the person who could design the best substitute for natural ivory.

John Wesley Hyatt who developed a cellulose derivative for the contest. Leo Hendrik Baekeland, a Belgian-American chemist, developed the first completely synthetic plastic which he sold under the name Bakelite.

In 1920, a major breakthrough occurred in the development of plastic materials. A German chemist, Hermann Staudinger, hypothesized that plastics were made up of very large molecules held together by strong chemical bonds.

Plastic HistoryPlastic History

Nylon was first prepared by Wallace H. Carothers of DuPont. In 1938, Roy Plunkett was discovered the Teflon.

During World war II, sientist from Germany and japan discovered te plastics from rubber.

Karl Ziegler, a German chemist developed polyethylene in 1953, and the following year Giulio Natta, an Italian chemist, developed polypropylene.

These are two of today’s most commonly used plastics. During the next decade, the two scientists received the 1963 Nobel Prize in Chemistry for their research on polymers.

Thermosets are formed by cross-linking of molecules, and cannot be reused.

Thermoplastics are held together by Van der Walls forces, resulting in a molecular structure can be reformed with heat. Both of them, in most cases, are derived from oil—and both are present the Tomahawk missile. Oil is drilled in regions around the world, though the primary sources are currently

Classification of PlasticsClassification of Plastics

There are two basic types of plasticThere are two basic types of plastic

Packaging

Construction Automobile Manufacture

Electronic Devices Around the House

Clear low-density polyethylene plastic wrap coverings account for most of the plastic packaging materials, followed closely by igh-density polyethylene plastic films used in trash bags and containers.

high-density polyethylenes and polyvinyl chlorides are used for pipes and siding sheets

Air-intake manifolds, fuel lines, brake linings, windshield wipers, tires, bumpers, speedometer gears, emission canisters, headlights, steering wheels, and fuel pumps all contain tough plastics. More flexible plastics are used for interior paneling, seats, and trim.

plastics are used in the outer casings of telephones, lighting fixtures, electric mixer housings, fans, radio cabinets, coffee makers, computers, and clocks.

shower heads, dishes, skylights, eye glasses, cameras, floor waxes, carpets, piano keys, switch cover plates, buttons, door knobs, papers, shoe heels, toothbrush handles, pen and pencil barrels, beads, toys, fisherperson's floats and tackle, cutlery handles, combs, washing machines, detergent dispensers.

ApplicationsApplications

Extreme versatility and ability to be tailored to meet very specific technical needs.

Lighter weight than competing materials, reducing fuel consumption during transportation.

Extreme durability.

Resistance to chemicals, water and impact.

Good safety and hygiene properties for food packaging.

Excellent thermal and electrical insulation properties.

Relatively inexpensive to produce.

Benefits of plasticsBenefits of plastics

Disposal of plastic wastes in the land

Disposal of plastic wastes in the land

Accumulation of plastic bags over and around caper bushesAccumulation of plastic bags

over and around caper bushes

Decay of plastic and precipitation of heavy

metals in soil

Decay of plastic and precipitation of heavy

metals in soil

Absorption of heavy metals from soil by the plant root

system

Absorption of heavy metals from soil by the plant root

system

Plant eaten by animals or man, or used by Bedouin for treatment of rheumatoid

Plant eaten by animals or man, or used by Bedouin for treatment of rheumatoid

Heavy metals cause toxicity, cancer and death to man

Heavy metals cause toxicity, cancer and death to man

ToxicityToxicity

What can we doWhat can we do

Separate plastic waste at home

Recycle plastic bags and bottles

Reduce use of plastic bags and bottles

Separate plastic waste at home

Recycle plastic bags and bottles

Reduce use of plastic bags and bottles

Screening techniquesScreening techniques

Trommel screening utilises a (usually inclined) rotating drum, with progressively larger holes arrayed across the drum.

Improved separation is achieved by collecting the different size fractions separately.

Oversize material also passes right through the drum for further sorting.

Separation techniquesSeparation techniques

Low speed, high torque “shredders” have been developed that is will reduce the size of both organic compostable materials and the contaminants.

Shredders are designed more to tear apart large particles (for example meat joints) rather than cut objects into smaller pieces.

Shredding technologyShredding technology

Shredders must not reduce the particle size below optimum size if they are to maintain a suitably “open” fibrous structure capable of sufficient air exchange and general circulation to maintain aerobic conditions.

However, if the particles created by shredding remain too large, the composting process may become excessively dry, or be incapable of generating sufficient temperature rise for sanitization.

Primary recycling is the processing of scrap plastics into similar types of product from which it has been generated, using standard plastics processing methods.

Secondary or mechanical recycling where the polymer is separated from its associated contaminants and can be readily reprocessed into granules by conventional melt extrusion. Secondary recycling includes the sorting and separation of the wastes, size reduction and melt filtration.

Plastic RecyclingPlastic Recycling

Tertiary or chemical or feedstock recycling involves the transformation of polymeric materials by means of heat or chemical agents to yield a variety of products ranging from the starting monomers, to oligomers or mixtures of other hydrocarbon compounds. The resulting raw materials are then reprocessed into plastics materials or other products of the oil refining process.

Quaternary recycling or energy recovery is an effective way to reduce the volume of organic materials by recovering the latent energy content of plastic materials by incineration. Although polymers are actually high-yielding energy sources, this method has been widely accused as ecologically unacceptable owing to the health risk from air born toxic substances such as dioxins and hydrogen chloride, airborne particles and carbon dioxide.

PETE Polyethylene Terephthalate (PET) -   Soda & water containers, some waterproof packaging.

HDPE High-Density Polyethylene -  Milk, detergent & oil bottles, Toys and plastic bags

Vinyl/Polyvinyl Chloride (PVC) - Food wrap, vegetable oil bottles, blister packages.

LDPE Low-Density Polyethylene - Many plastic bags. Shrink wrap, garment bags.

Plastic Recycling CodePlastic Recycling Code

PP Polypropylene - Refrigerated containers, some bags, most bottle tops, some carpets, some food wrap.

PS Polystyrene – Throun away utensils, meat packing, protective packing.

OTHER Usually layere or mixed plastic.  No recycling potential - must be landfilled.

Overview of the main form feedstock recycling for waste plastics by thermolysis

Overview of the main form feedstock recycling for waste plastics by thermolysis

Pyrolysis of plastic waste into crude oil and dieselPyrolysis of plastic waste into crude oil and diesel

Pyrolysis, also termed thermolysis is a process of chemical and thermal decomposition, generally leading to smaller molecules.

Semantically, the term thermolysis is more appropriate than pyrolysis, since fire implies the presence of oxygen and hence of reactive and oxygen-bearing intermediates.

In most pyrolysis processes, however, air is excluded, for reasons of safety, product quality, and yield. Pyrolysis can be conducted at various temperature levels, reaction times, pressures, and in the presence or absence of reactive gases or liquids, and of catalysts.

Plastics pyrolysis proceeds at low (<400°C), medium (400–600°C) or high temperature (>600°C). Some preparation of the waste plastics feed is required before pyrolysis, including size reduction and removal of most nonplastics.

This feed is charged into the heated fluidized bed reactor, operating at 500°C, in the absence of air.

The plastics thermally crack to hydrocarbons, which leave the bed together with the fluidizing gas.

Solid impurities and some coke either accumulates in the bed or are carried out as fine particles and captured by cyclones.

The decomposition of PVC leads to HCl formation, which is eventually neutralized by contacting the hot gas with solid lime, resulting in a CaCl2 fraction to be landfilled.

The process shows very good results concerning the removal of chlorine. With an input of 1% Cl2, the products contain 10 ppm Cl2, somewhat higher than the 5 ppm typical of refinery use. Also, metals like Pb, Cd and Sb can be removed to very low levels in the products. Tests have shown that all hydrocarbon products can be used for further treatment in refineries.

The purified gas is cooled, condensing to a distillate feedstock, tested against agreed specifications before transfer to the downstream user plant.

The light hydrocarbon pyrolysis gases are compressed, reheated and returned to the reactor as fluidizing gas.

Part of this stream could be used as fuel gas for heating the cracking reactor, but as it is olefin-rich, recovery options were also considered.

Plastics waste disposal through Plasma Pyrolysis Technology (PPT)Plastics waste disposal through Plasma Pyrolysis Technology (PPT)

In plasma pyrolysis, firstly the plastics waste is fed into the primary chamber at 850°C through a feeder. The waste material dissociates into carbon monoxide, hydrogen, methane, higher hydrocarbons etc.

Induced draft fan drains the pyrolysis gases as well as plastics waste into the secondary chamber, where these gases are combusted in the presence of excess air. The inflammable gases are ignited with high voltage spark.

The secondary chamber temperature is maintained at around 1050°C. The hydrocarbon, carbon monoxide and hydrogen are combusted into safe carbon dioxide and water.

The process conditions are maintained so that it eliminates the possibility of formation of toxic dioxins and furans molecules (in case of chlorinated waste).

The conversion of organic waste into non toxic gases (CO2, H2O) is more than 99% . The extreme conditions of Plasma kill stable bacteria such as Bacillus stereothermophilus and Bacillus subtilis immediately.

Segregation of the waste is not necessary, as very high temperatures ensure treatment of all types of waste without discrimination.

Power and Fuel From Plastic WastesPower and Fuel From Plastic Wastes

Collection and segregation of plastics waste

Collection and segregation of plastics waste

Storing of Plastic wasteStoring of Plastic waste

Shredding of wasteShredding of waste

Feeding into hopperFeeding into hopper

Liquid/Movement of liquid-vapor into condenserLiquid/Movement of liquid-vapor into condenser

Trapping of vessels tarry waste

Trapping of vessels tarry waste

Trapping of Liquid fuel (as a product)Trapping of Liquid fuel (as a product)

Flow of waste into heating vessel in presence of catalyst (2700-3000)

Flow of waste into heating vessel in presence of catalyst (2700-3000)

• The odour of volatile organics has been experienced in the processing area due to some leakages or lack of proper sealing.

• Absolute conversion of liquid-vapour was not possible into liquid, some portion of gas (about 20%) is connected to the generator. However, the process will be improved in full-scale plant. PVC plastics waste is not used and if used, it was less than 1%.

• In case PVC is used, the chlorine can be converted into hydrochloric acid as a by-product.

• The charcoal (charcoal is formed due to tapping of tarry waste) generated during the process has been analysed and contain heavy metals, poly aromatic hydrocarbon (PAH) which appears to be hazardous in nature.

• The source of metals in charcoal could be due to the presence of additives in plastics and due to multilayer and laminated plastics.

Environmental Related Problem during this ProcessEnvironmental Related Problem during this Process

The gasifier consists of the pyrolysis is zone(vertical furnace) and the partial combustion and gasification zone (horizontal furnace).

Before gasification, waste plastics were fragmented under 8 to 25 mm with a shredder in order to promote their devolatilization.

Gasification of plasticsGasification of plastics

Gasification of plastics

If the gasification process, crushed plastics transferred with air were at first pyrolyzed and partially, combusted and then converted into synthesis gases.

Ash contained in wastes, was melted at the lower portion of the vertical furnace and flowed out through the slag hole of the horizontal CPC. The estimated residence gasifier was approximately a second.

The synthesis gases with impurities were purified in the next gas clean up process, which consisted of the gas quencher, the hot cyclone, the bag filters and the dehydrocholorination water scrubber.

The hot cyclone separated ashes and char particles from the gas stream. A couple of bag filter was operated in turn and effectively catches fine particle.

Polyvinyl chrolide was dechlorinated at 380°C and 30 min in nitrogen gas ventilatin. Nickel, KOH or NaOH weresss used for the gasification catalyst.

The plastic, distilled water and catalyst were loaded into the reactor. Then the air in the reactor was replaced with nitrogen gas.The reactor was closed and heated to a reaction temperature in an electric furnace.

It took about 15min for the reactor to increase from the room temperature to the setting reaction temperature around 700°C.

Gasification of Plastics in supercritical waterGasification of Plastics in supercritical water

Degradable plastics

After reaching the reaction temperature, small amount of distilled water was added into the reactor using a high pressure pump in order to adjust the reaction pressure.

After a given reaction time, the furnace was turned off and opened, and the reactor was cooled quickly with the electric fan.

The gaseous product was collected into a sampling bag and analyzed using gas chromatographs equipped with thermal conductivity detectors.

Degradable plasticsDegradable plastics

Hydro-degradable

Some degradable plastic products are based on starch , and whilst non-food uses of agriculture may seem attractive, they are not the best way forward. Some of these plastics perforate over time but do not totally degrade, because the starch constituent is consumed by microbial activity, but not the plastic. The plastic residues can be harmful to the soil and to birds and insects.

Aliphatic Polyester

These products have the same disadvantage as starch. They are also expensive.

Photo-degradableThese plastics degrade after prolonged exposure to sunlight. They will not therefore degrade if buried in a landfill, a compost heap, or other dark environment, or if heavily overprinted.

Bio-plastics

A number of manufacturers have been exploring alternatives to plastics made from non-renewable fossil-fuels. Such alternative 'bio-plastics' include polymers made from plants sugars and plastics grown inside genetically modified plants or micro-organisms. Health and safety concerns have arisen over potentially hazardous chemical additives to plastics and consumer pressure has contributed to manufacturers switching to plant-based plastics in such cases.

Plastics are very useful because of their lighter weight, extreme durability, hygiene properties for food packaging and less expensive to produce.

However plastics are non degradable and it contains many toxic additives like polyvinyl chloride, polycarbonates which would leach out into the food causing many diseases.

The recycling technologies like pyrolysis, gasification processes are very useful for the production of valuable fuels and chemicals from waste plastics.

However the products of above processes contain some poisonous gases and metals.

So the best method of reducing waste disposals negative effect on society is simply to prevent its generation.

ConclusionConclusion

We shall make the Earth a little beautiful Everyday

Thank You