pyrolysis
TRANSCRIPT
PYROLYSIS - A PIONEER IN PLASTIC WASTE
RECYCLING
Triveni chandrika. A*a, Lalitha deepthi. Mb
a IV B.Tech, dept of chemical engineering ,M V G R College of engg..,
E-mail: [email protected] b III B. Tech, dept of chemical engineering ,M V G R College of engg..,
E-mail: [email protected]
KEY WORDS: plastic wastes, chemical recycling, and pyrolysis
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ABSTRACT:
The need for efficient plastic waste disposal introduced new technologies
for plastic waste treatment. Among the various technologies available, pyrolysis
appears to be a technique that is able to reduce a bulky high polluting waste while
producing energy and/or valuable chemical compounds.
In this paper, pyrolysis of plastic wastes with and without the use of
catalysts and example of one commercial technology in use today is discussed in detail.
The yields of oil and plastic monomers from each technology are compared.
At the end, the future prospects for this technology are presented and
India’s progress in developing innovative technologies for plastic recycling is briefly
mentioned.
INTRODUCTION:
The need for the biodegradable plastics and recovery of plastic waste has assumed
increasing importance in the last few years. Various treatment technologies can use waste plastics as
the valuable resources. Mechanical recycling or production using the same material can be
recommended as a desired method. But chemical recycling technologies are the objects of interest
today, as alternatives for the mechanical recycling techniques.
PLASTIC AND ENVIORNMENT:
Plastics are fundamental in promotion of efficient use of natural resources
including energy. Advancement in our understanding on biodegradation has shown that the
plastic is environmental friendly compared to many conventional materials with
biodegradable label. Some of the eco-friendly aspects of the plastics are listed in table-1
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SOME ECO-FRIENDLY ASPECTS OF PLASTICS
Energy efficient manufacturing, 50% lower energy consumption and 35% less
pollution generation compared to paper manufacturing.
Light weight product.
Energy saving applications, such as home insulation and in automobile
manufacturing.
Conservation of natural resources.
Prevent generation of methane and CO2.
PLASTIC WASTE MANAGEMENT STRATEGIES:
Up to 1985 plastics were considered to be a macro pollutant with low
toxicity and side effects. The visible plastic waste has created major disposal problem,
therefore, an efficient plastic waste management will be the great significance. This lead to
the demand from the environmental lobby to ban the use of plastics.
Plastic wastes are of two types namely:
1. RECOVERABLE PLASTICS
2. NON-RECOVERABLE PLASTICS
The non-recoverable plastics waste is of most nuisance value and creates maximum
environmental problems due to their long persistence in the nature. A large amount of waste is of
non-recoverable and is disposed-off in landfill. A very small fraction of plastic produced is photo-
oxidizable or biodegradable grade and 10% each is recycled. Various strategies for plastics waste
management are listed in table-2
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TYPES OF PLASTIC WASTE AND WASTE MANAGEMENT STRATEGIES
Types of waste strategies
Non-recoverable plastics source reduction
Degradation in environment
Land filling and composting
Recoverable plastics reduction and recycling
Incineration
Feed stock recovery
Energy recovery
The process steps include: 1. Pretreatment, 2. Liquefaction, 3.Pyrolysis, 4. Co-processing, 5.
Hydrocracking.
Among all these technologies, pyrolysis may be favorably used for oil and monomer
recovery from waste plastics.
TYPES OF PYROLYSIS TECHNIQUES:
In our study, we intended to divide pyrolysis into pyrolysis with the use of catalysts
and pyrolysis without the use of catalysts. Pyrolysis process, which uses catalysts, can take place in two
different kinds of batch reactor
3-1: Pyrolysis using expensive catalysts:
Here the catalysts used are metal promoted silica-alumina or mixtures of metal
hydrogenation catalysts with HZSM-5. The optimization of waste plastic as a function of
temperature in a batch mode reactor gave liquid yields of about 80% at a furnace temperatures of
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about 600 degrees centigrade and one hr residence time. The pyrolysis oil obtained at the
temperature of maximum yield are relatively heavy in nature. However, hydroprocessing at
relatively low hydrogen pressures (200-500psiag) at 430-450 degrees centigrade either thermally or
catalytically converts them into a much lighter product. Sodium carbonate or lime addition to the
pyrolysis and coprocessing reactors results into an effective chlorine capture and the chlorine content
of pyrolysis oil reduces to about 50-200ppm and that of the hydroprocessed oils to 1-10ppm. The
volatile product from this process is scrubbed and condensed yielding about 10-15%gas and 75-80%
of a relatively heavy oil product.
3-2 Pyrolysis using synthesized catalysts from fly ash:
Table 2 shows chemical compositions of the catalysts and fly ash
obtained from coal fired power plants. To use fly ash as synthesized catalyst it was treated in
NaOH solution for more 24 hrs, washed by distilled water and dried. To make another
synthesized catalysts this catalyst can be impregnated in the nickel nitrate solution. So two
types of catalysts were made for the pyrolysis of PE and PP of olefin series.
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Component Mordenite HY SilicaAlumina Fly Ash
SiO2 91.7 74.9 87 53.56
Al2O3 8.23 24.0 13 27.71
Na2O3 0.03 1.1 - 0.37
Fe - 0.03 - 5.53
SiO2/Al2O3 (-)18.9 5.31 6.69 1.93
The setup of the pyrolysis batch reactor is shown in Figure 1. The mechanical
agitator was installed in the batch type reactor wrapped around with electric heater for controlling the
pyrolysis temperature of waste plastic. The organic vapor pyrolyzed from waste plastics can pass the
catalytic cracker bed or not when catalyst is charged with waste plastics in the reactor. After that, the
vapor is discharged through 1st and 2nd condenser for product oil conversion. These two condensers
are maintained at different temperatures, 70 and 10. Pyrolysis oil collected from each condenser was
analyzed by SIMDIS GC to investigate the catalytic properties and the pyrolysis conditions. The yields
of pyrolysis oil from polyethylene and polypropylene were 75 89%
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3-3: Pyrolysis without the use of catalysts:
The process carried out is the same in this case also but catalysts are not
used. Instead the temperature parameters are varied.
3-4: Commercial technology (CFFLS pyrolysis technology):
CFFLS (Consortium for fossil fuel liquefaction science) technology is
implemented by USA.Here; plastic is subjected to a very simple pretreatment process of
shredding of waste to 1-10cm size. The shredded materials are then subjected to magnetic and
eddy current cleaning steps. In pyrolysis at about 600 degrees centigrade for 1hr about 80% of
oil yield is obtained, which is relatively low in chlorine content (1-10ppm).
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Future prospects of pyrolysis technology:
Pyrolysis is a very promising and reliable technology for the chemical
recycling of plastic wastes. Countries like UK, USA, and Germany etc have successfully
implemented this technology and commercial production of monomers using pyrolysis has
already begun there.
Pyrolysis offers a great hope in generating fuel oils, which are heavily priced
now. This reduces the economical burden on developing countries. The capital cost required
to invest on pyrolysis plant is low compared to other technologies. So, this technology may be
the beacon light in the future to a world, which is now on the verge of acute fuel shortage.
Indian scenario and conclusion:
According to one estimate in India about 80000 tons of municipal solid waste
is generated everyday of which plastics comprise of only 4-6%. A scientific and systematic
approach in recycling the plastic waste in India is still in its infancy. Unscientific and
haphazard landfilling is in operation in urban areas and in rural areas practically there is
absence of any treatment.
The reasons are many. Both the government and private industrial sectors
failed to initialize the development of indigenous technologies related to this area. Except
well-established industries like Reliance polymers etc, others are not investing in a venture
like this.
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Nevertheless, India has already taken its first step in this direction. In the
course of time, with the potential that our country has, India will surely make the most of
chemical recycling methods and achieve great profits and progress by adapting pyrolysis.
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oil