5-7 OCTOBER

ISFR

2011

9

TOLEDO (SPAIN)CATALYSTS FOR THE CONVERSION OF WASTE PLASTICS: CHALLENGES FOR
THE DEVELOPMENT OF INDUSTRIAL PROCESSES
Thallada Bhaskar
Indian Institute of Petroleum (IIP), Council of Scientific and Industrial Research (CSIR), Haridwar Road,
Mohkampur, Dehradun 248005, India.
e-mail: tbhaskar@iip.res.in; thalladab@yahoo.com

Abstract
The utilization of plastics has been increasing and subsequently the volume of domestic and industrial waste plastics(municipal, production and e-waste) has been increasing significantly. The phenomenal growth of IT industry and exorbitant
use of plastics demands environmentally friendly solutions for recycling of waste plastics into value added materials andeffective recovery of non-renewable materials from the waste plastics. Novel and hybrid catalytic materials and processes
are the need of the hour to address the challenges for waste plastics (individual/commingled) conversion and upgradation
processes. The catalytic materials should address the value addition to the waste plastic streams, avoid the environmental
damage (soil, air, water) from the non-biodegradable plastics due to toxic/corrosive halogenated components added to theplastics.

Keywords: waste plastics, catalysts, fuels, halogenated compounds, recycling

1. Introduction
Worldwide plastic industry witnessed a steady growth inrecent years, which reflected in the increased
consumption of all types of plastic materials. World-wide,
the plastics and polymer consumption will have an
average growth rate of 5% and may touch a figure of 227
million tons by 2015.
In today’s modern world, plastics make a fundamental
contribution to all activities such as agriculture,
automobile industry, electricity and electronics, building
materials, packing and so on. This is primarily because of
the substitution of other materials with plastics as well as
their applications in new areas, and material’s durability
and versatility. The share of plastics in e-waste andmunicipal waste has seen a phenomenal increase in the
recent years. The rapid growth in plastics consumption
is increasing and subsequently plastic waste isaccumulated, and poses serious problems to theenvironment due to their non-biodegradable nature.
Recovery can be classified as material recycling(mechanical and feedstock) and energy recovery(gasification and combustion). Mechanical recycling islimited solely on single polymer thermoplastic waste andnot applicable to thermosets. Incineration of plastic waste
to produce heat may be a possibility, but its organic
content would totally be destroyed and converted intogreen house gas (CO2) and H2O. Due to the world’s
limited reserves of coal, crude oil and natural gases it
becomes very urgent to preserve the existing nonrenewable materials and to find other carbon sources(biomass) as feedstock materials or as fuels.

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Pyrolysis is one of the best methods to recover thematerial and energy from polymer waste, as only aboutca. 10% of the energy content of the waste plastic isused to convert the scrap into valuable hydrocarbons.
This is obtained by breaking down polymers at hightemperatures into petrochemical feedstock components
from which they originate. The main drawback to thermal
degradation is the requisite high temperatures (process
is highly endothermic) that results in a very broad rangeof products [1], which requires severe reaction conditions
and produces low value products. Hence, the role ofcatalysts and catalytic process are immense importancein producing very high value hydrocarbons from thewaste plastics in an environment friendly manner.

2. Catalysts for Plastics Pyrolysis
Catalysis is an interdisciplinary science and technology.
Catalysis is an integral component in any green
processing technology, serving as an important tool tosupportsustainable
development.
Sustainable
development is essential to deal with the challenges of afast changing world, where demands on natural resources,
the needs of a growing population and the accumulationof
waste will inevitably impose restriction upon how bussiness
operate. Where a manufacturing process is energy
intensive, a controlled recycle/reuse is an effective meansof decreasing overall negative environmental impacts [2].
The catalytic reactions take place in the solid-gas orsolid-liquid interface. The amazingly wide range ofchemical transformations in petroleum refining is based
mainly on two types of catalytic transformation.: hydrodehydrogenation and acidic hydrocarbon catalysis. The
first type controls the distribution of hydrogen among

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6th International Symposium on Feedstock Recycling of Polymeric Materials

hydrocarbon products while the second type, the acidcatalyst, controls the carbon number and boiling range,
the skeletal structure as well as the types ofhydrocarbons produced. Today’s advanced catalysts
combine these two catalytic functions with highly specificcatalyst structure features, called shape selectivity, which
control the size and other chemical features of molecules
produced.
The deployment of catalysts ensures lower operating
temperatures and/or pressures and a higher selectivity to
the target product with a resultant reduction in fuel usage
and waste production. A catalytic approach to waste
polymer reprocessing has the following positive features:(a) lower operating temperatures (relative to pyrolysis), nonoxidative process with lower energy requirements and no
directly associated NOx/SOx emissions; faster reaction
rate; selectivity increased towards similar type ofcompounds; (b) absence of thermally-induced free radical
reactions that can lead to toxic intermediates; (c) possibilityof selective Cl & Br removal (in the case of Chlorine andBromine containing polymers) with concomitant polymer
degradation to a target recyclable product; (d) operability ina closed system with no toxic emissions etc.,.
Plastics can be divided into two groups: (i) condensation
polymers; (ii) addition polymers (polyolefins).
Condensation polymers, which include such materials aspolyamides, polyesters and nylon can be“depolymerised” via reversible synthesis to the starting
diacids and diols or diamines. The solid catalysts(existing and newly developed) can provide solutions to
the first class of polymers (polyolefins) for effective
conversion. The novel and hybrid solvents has to be
developed for the depolymerization (for monomers andoligomers) of condensation polymers. In both thesecases the presence of additives and new combinations
will create the complications for the development of
catalysts and solvents.
Waste from Electrical and Electronic Equipment (WEEE)
contains plastics and metals in it. In 2009, India
generated approximately 330,000 tonnes of e-waste. Ewaste contains hazardous (lead, mercury, cadmium etc.,)
and precious material (gold, silver, copper etc.,). An
average PC approximately weighing 31.5 kg contains
7.24 kg of plastics, 1.98 kg of Pb, 0.693 g of Hg, 0.409 g
of As, 2.961 g of Cd, 1.98 g of Cr, 9.92 g of Ba, 4.94 g of
Be. In about 315 million computers about 550 X 106 kg ofPb, 900 000 kg of Cd, 180 000 kg of Hg and 0.5 X 106 kg
of Cr IV are present. It also has 1800 X 106 kg of plastic
and at least 159 X 106 kg of brominated flame retardants
from monitors [3]. With this present situation, thedevelopment of new catalysts, reactors, and processes
are highly desirable to address this important issue.

3. Present Status
There has been a plethora of research work in theconversion of waste plastics into fuels and chemicals.
The fundamental investigations and mechanistic
investigations of thermal decomposition of polymers havebeen published by Madorsky [4]. Kaminsky et al [5]reported that the plastic waste and tires can be converted

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into fuels and chemicals [5]. The initial catalytic cracking
research primarily focused on polyolefin feedstocks
because these polymers are the most abundant in plastic
waste [1-18]. In one of the first polymer catalytic
cracking studies using the noble metals on silicaalumina, Uemichi and co-workers reported the use ofsilica alumina, activated carbon, Pt/silica–alumina, andPt/alumina catalysts for poly(ethylene) (PE) cracking [6],Ayame et al [7] produced the branched polyethylene bycatalytic degradation-isomerization of high density
polyethylene (HDPE) using silica-alumina catalyst. The
comparative studies with the acidic and non-acidic
catalysts and mesoporous materials [17] have beenstudied to show the effect of acidity on the cracking ofpolyolefins [12, 14-15]. In the mixed waste streams, thehalogenated plastics cannot be avoided and poses
several problems in the thermal and catalytic pyrolysis inthepresenceofvariouscatalysts[4-18].
Dehydrochlorination of plastic mixtures was studied by
Bockhorn [18] and others [19-23] to provide the base forunderstanding the decomposition mechanism of PVC
containing mixed plastic waste, which has become thebase for the development of catalyst/sorbents for the
production of halogen free hydrocarbons from thecommingled waste plastics. Yoshioka et al. [20] showed
the mechanistic pathways for the two stage
decomposition of PVC and PVDC plastics for theeffective dehalogenation of PVC mixed plastics into
halogen free hydrocarbons [21] and Kamo et aldescribed the effect of pressure on the degradation of
PVC [22]. We have shown that the effect of HIPS-Br (ewaste plastic) in the mixed streams on the products
distribution and dehalogenation processes with thecarbon composite catalysts [24-25]. Serrano et al [26]showed the effectiveness of new generation catalysts
such as hierarchical zeolites for the pyrolysis of plastics.
Various above mentioned catalysts have been used forthe commercial processes for the conversion of waste
plastics with certain limitations. Due to the limitations andeconomics, the alternatives for the costly catalytic
materials has been looked by various groups andFujimoto et al [27] developed and utilized the disposable
catalysts (spent FCC) for the commercial processes.

4. Challenges
Catalysts are a class of compounds specially selected,
designed and optimized for influencing the reaction
mechanism, subsequently the high-value products.
Catalyst activity, selectivity, and stability are major
considerations. Theoretically, waste plastics haveexcellent fuel value, quite comparable to that of gas oil,when only polyolefins are considered. Introducing heteroatoms, such as oxygen, nitrogen, or chlorine, reduces theheating value. The major hetero-atoms appearing inpolymers are: oxygen, nitrogen, chlorine, bromine,
fluorine. After plastics pyrolysis, these elements either
appear as intermediate organic compounds still
incorporating the hetero-element, or as stable inorganic
compounds, i.e. water, ammonia and hydrogen cyanide,hydrogen chloride, hydrogen bromide and bromine,

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hydrogen fluoride. Most of these are hazardous andcorrosive components require a careful selection of
catalysts/sorbents for their effective removal/processing,as well as methods to neutralize or inhibit their effect.
A major problem in pyrolysis is in the rather
unpredictable specifications of both feedstocks(diffusion/steric hindrances of bulky molecules), if it is a
mix of plastics, and products. Hydrogenating conditions
lead to the elimination of hetero-atoms and yield moresaturated products as well, an important consideration
regarding the marketing of pyrolysis products.
Little is known on the effect of fillers or coke precursors(styrene, butadiene etc.,) on catalytic activity and catalyst
fouling, coking, or clogging. Another area of interest is
the effect of catalyst addition on the thermal
decomposition in the liquid phase. It seems unlikely thatthe macromolecules can contact the internal catalyst
surface in a productive fashion. Some additives may also
influence the product distribution by modifying thecracking mechanism and hence, product distribution.
Regeneration and life of the activity of catalysts is an
issue. Development of low cost materials for the specifictargeted production (light olefins, aromatics) from thewaste plastics is highly desirable.
Robust and stable catalytic materials for the effective
conversion of halogenated mixed plastic waste toproduce valuable hydrocarbons while recovering thevaluable halogen content. The non-renewable and very
precious metals present in the e-waste should beprocessed to recover both fractions (metallic andplastics). The energy efficient and environment friendly
methods for the closed loop systems and materials forthe waste plastics conversion to avoid any waste(residue) are highly desirable and challenging. The othertypical problems and possible solutions in industrial casestudies will be discussed during the presentation.

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