Potential recovery of plastic waste

Potential Recovery of
Plastic Waste
May 6, 2014


Content
 Overview
 Techniques
• Mechanical Recycling
• Feedstock Recycling
• Energy Recovery

 Environmental Potential
 Economic Potential
 Other methods of treating plastic waste


Part 1

Overview


Overview of plastic waste
 What are plastics?
•

Polymers made from various
monomers

• Contains carbon, hydrogen,
oxygen, nitrogen, etc

Two main kinds
• Thermoplastics
• Thermosets


Plastic resin codes

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Second level
Third level
Fourth level
Fifth level


Plastic Industry

Plastic production from 1950-2012


Plastic consumption


Plastic waste in the world


Plastic waste in the Ocean

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Plastic waste imposes negative environmental externalities


Part 2

Techniques
i.

Mechanical Recycling

ii. Feedstock recycling
iii. Energy Recovery


Mechanical Recycling

(Source Burgdorf et al in 1997)


Plastic bottle recycle



Feedstock Recycling
• Depolymerization
• Hydrogenation
• Blast furnace
• Cracking
• Gasification

1. Depolymerisation
• Definition: The depolymerisation process is a technology for the
decomposition of mixed used plastics.
• End products: The oil (the so-called depolymerisate), HCl
• Application: Depolymerisation is used for the thermal conversion of used
plastic mixtures into oil which is utilized in existing refinery or energy
conversion plants.


Process

Advantages:
• The possibility of the use of
mixed used plastics containing
halogens.
• The possibility of the use of
heavy high chlorine factions
from the sorting of plastics.
• Insensitivity towards fluctuating
qualities of the material fed to
the system.
• Simple integration into existing
refinery and power conversion
plants.


2. Hydrogenation
• Definition: Hydrogenation of plastics is a potential alternative for breaking
down the polymer chain.

• End products: highly saturated products as fuels

• Process: using hydrogen with catalysts like palladium (Pt), nickel (Ni),
molybdenum (Mo) and iron (Fe), under high pressure during hydrogenation of
plastic.


3. Blast furnace
• Definition: The ‘feedstock recycling’ of plastics waste in
the metal blast furnace process provides a further option
for plastics at its end-of life.
• Application: Plastics convert iron ore to steel

• Process: plastic waste can roughly be described as a
hydrocarbon compound, is used as reducing agent.


4. Cracking
1. Hydrocracking

Polymers mixed

• 423–673 K
• 3–10 MPa
hydrogen

High quality
gasoline

catalyst

• Polyolefin
• PET
• polystyrene (PS)
• polyvinyl chloride
(PVC)
• mixed polymers
• …

• transition metals (e.g., Pt, Ni, Mo, Fe)
• acid solids (such as alumina,
amorphous silica–alumina, zeolites
and sulfated zirconia)


2. Thermal cracking (Pyrolysis)
• Degradation of the polymeric
materials by heating in the absence of
oxygen.

Four types of mechanisms:

• Conducted at 500- 800ºC
•
• Results in
 carbonized char
 volatile fraction:
- condensable hydrocarbon oil
- non-condensable high calorific
value gas.

• Chain-stripping

• End-chain scission or depolymerization
• Random-chain scission
• Cross-linking


2. Catalytic cracking
Introducing suitable catalysts could improve liquid hydrocarbons yield from
plastics pyrolysis.
There are two modes of catalyst usage:
•

liquid phase contact: the catalyst is contacted with melted plastics and acts mainly on the
partially degraded oligomers from the polymer chains.

•

vapor phase contact : the polymer is thermally degraded into hydrocarbon vapors which are
then contacted with the catalyst.


5. Gasification
The thermal conversion of any carbon-based material with a small amount of air or oxygen in a
heated chamber, into a mixture of combustible gases (hydrogen, carbon monoxide, carbon
dioxide and some trace compounds).


There are four different types of gasifiers:
• Updraft (counter-current flow gasifying agent and feedstock)

• Downdraft (co-current flow gasifying agent and feedstock)
• Crossdraft
• Plasma

Plasma gasification


Energy recovery
• MSWI (Municipal solid waste incineration) with energy recovery.
• Cement kiln
• Deriving fuel (petrol, diesel, LPG) from plastic.


1. MSWI with energy recovery
Slag
remain
at the
end of
kiln

Process

Plastic
waste
storage

Grid
kiln

Flue gas

and ash

Treated

Reuse in road
construction

cleaning

Flue gas cleaning
residues

NEUTREC
system

Disposal