
- Drainage pipes.
- Carpets.
- Railroad ties.
- Truck bed liners.
- Plastic roads.
The chemical recycling consists in the following
steps:
Step 1) Chemical depolymerization: it is a chemical
process by which the plastic waste is chemically
reduced to its original monomers or other
chemicals. It is suitable only for homogenous pre-
sorted plastic waste streams such as PET, PU, PA,
PLA, PC, PHA, and PEF. Chemical recycling can
be done by chemolysis, pyrolysis, fluid catalytic
cracking (FCC), hydrogen technologies,
Katalytische Drucklose Verölung (KDV) process or
Catalytic Pressureless Depolymerization process,
and gasification combined with methanol
production.
Step 2) Solvent-based regeneration: it is a
purification process based on dissolving polymers
in proprietary solvents, separating contaminants
and reconstituting the target polymer. The process
can be applied to several polymers.
Step 3) Thermal depolymerization and cracking
(gasification and pyrolysis): These processes heat
plastic waste in a low-oxygen environment to
produce molecules from mixed streams of
monomers that then form the basis of feedstock for
new plastic without degradation. The main output
is syngas or synthesis gas, [16]. Both gasification
and pyrolysis have been considered for decades to
create energy (syngas burned to drive steam
turbines) from municipal waste that didn’t get a
commercial success due to a combination of poor
economics, high energy consumption requiring
supplemental fuel, fires, explosions, emissions, and
residues. These processes are also used to create
‘plastic to fuels’ (fossil fuels), as oils and diesel can
be generated in addition to syngas. Most recently
biotechnology has been considered for plastic
degradation and waste management, thus the
depolymerization using enzymes, or bacteria is a
technique still at an experimental and research
stage. One if the studied techniques for example
uses a bacterial hydrolase enzyme to reduce PET to
its monomer, [17]. The bacterial enzyme is based
on a naturally occurring bacteria that has
subsequently been modified by scientists to
degrade PET more efficiently, claiming a 90%
depolymerization within 10 hours. More and more
examples of use of enzymes, bacteria but even
worms, insects and larvae for degradation of plastic
can be found in the literature evidencing the trend
for looking to natural, green chemistry,
biotechnological approaches for the plastic waste
treatment.
The last approach, we address is valorizing the
plastic waste for energy recovery, this is conducted
by burning plastic waste for electricity production,
this process reports an efficiency above 90%, [18].
The process is proposed for plastic waste that
cannot be recycled, but considering the need for
energy is widely applied even to recyclable plastic.
Main concern for incineration is the management of
ashes and air emissions making it difficult to get
population acceptance of an incineration plant
nearby. Most recent treatments consider the
transformation of plastic to fuels that might
‘substitute’ fossil fuels and offset oil, gas, and coal.
By the way the process still needs investigation and
upgrades, not to result in just compressed post
consuming plastic. One promising approach of this
process is the conversion of plastic waste to
hydrogen, which is a clean burning fuel. However,
to date, hydrogen production may require energy-
intensive processes that could even compromise the
benefits of reducing the carbon footprint.
3.1 Logistic and Distribution Solutions
Solutions must be studied starting from the entire
plastic waste production chain and researching how
each node in the supply chain can give its own help
to solve the problem. For example, industries are
expected to work together by creating and
implementing a plastic waste management system
using a reverse logistics system where plastic waste
is returned to the factories that produce it.
Afterwards, factories will manage the plastic waste
by recycling and reusing them. Reverse logistics is
the process of planning, implementing, and
controlling the flow of raw materials, work in
process, finished goods, and related information,
which flows from the point of consumption to the
point of origin efficiently, [19]. Logistics generally
bring products to customers.
Reverse logistics is the opposite of the previous
process, where the product or goods are brought
from the customer to the distributor, or to the
manufacturer, which includes reprocessing or
disposal. The transfer of the product or item is
carried out through a supply chain network, like the
one shown in previous Fig. 2. Another way to
manage plastic waste is to optimize the plastics
packaging supply chain. The plastics packaging
value chain starts along with the production and
continues with the distribution and utilization. On
the left side, indeed, there is the Plastics Packaging
Recovering Chain i.e., the packaging producers, the
WSEAS TRANSACTIONS on ENVIRONMENT and DEVELOPMENT
DOI: 10.37394/232015.2022.18.124
Antonio Pratelli, Patrizia Cinelli,
Maurizia Seggiani, Giovanna Strangis,
Massimiliano Petri