23
A. Mwasha et al.: Management of Polystyrene Wastes Using a Supercritical Solvent - Propanone
ISSN 1000 7924
The Journal of the Association of Professional Engineers of Trinidad and Tobago
Vol.41, No.1, April/May 2013, pp.23-28
Management of Polystyrene Wastes Using a Supercritical Solvent - Propanone
Abrahams Mwashaa Ψ, Althea Armstrong-Richardsonb, and William Wilsonc
Department of Civil and Environmental Engineering, Faculty of Engineering, The University of the West Indies,
Trinidad and Tobago, West Indies
a
E-mail: [email protected]
b
E-mail: [email protected]
c
E-mail: [email protected]
Ψ
- Corresponding Author
(Received 4 October 2012; Revised 3 May 2013; Accepted 18 May 2013)
Abstract: Chemical densification method has recently gained popularity due to reduced waste management cost, energy
and other environmental impact such as pollution and gaseous emissions. Chemical densification is performed by
dissolution of polystyrene wastes in supercritical liquids. Today, there exists many supercritical solvents such as benzene,
toluene, xylene, tetrahydrofuran, chloroform, 1,3-butanediol, 2-butanol, linalool, geraniol, d-limonene, p-cymene,
terpinene, phellandrene, terpineol, menthol, eucalyptol, cinnamaldheyde, nitrobenzene, N,N-dimethylformamide which
could be used during the disposal and management of the plastic wastes. Most of these supercritical solvents are
extremely toxic and expensive to produce. The biodegradable solvents (such as Tapetane) can be used as a solvent for the
wastes. However, these solvent are currently being used as biofuel, making this form of disposal expensive. The
application of Propanone which can be easily produced in developing countries by fermenting agricultural wastes is
considered in this paper as a cost-effective solution for waste management of Expanded Polystyrene in Trinidad and
Tobago, as well as in other small islands of the Caribbean.
Keywords: Polystyrene wastes, Critical solvent, Propanone, Super critical solvent
1. Introduction
Waste management is the collection, transport,
processing, recycling or disposal, and monitoring of waste
materials after their usage. Proper waste management is
essential to preserve the environment and reduce the
harmful effects of waste on human health. Waste can be
classified as being solid, liquid or gaseous. The waste
management methods vary considerably due to factors
such as the type of wastes including volumetric or
compacted. In Trinidad and Tobago (T&T), landfilling is
the major form of waste disposal currently used. For small
islands like T&T, the price of land is too high to support
this practice.
Expanded polystyrene (EPS) is a voluminous
lightweight material. As a result, storage and disposal of
EPS in landfills would require a large space for only a
small mass. For example, the smallest common food
containers weighs 57 grams but has the volume equivalent
to 820 cubic centimeters (see Figure 1). If 500 such
polystyrene containers are used daily at The University of
the West Indies (UWI) St Augustine Campus, therefore
almost 410,000 cubic centimetres of land should be
available daily for the disposal of these containers.
Its lightweight property can be a disadvantage, as it
can become a nuisance when easily blown around by air.
Also, transportation of such a material will be costly due
to its large volume. Incineration of plastics releases many
toxic chemicals into the atmosphere hence this method of
disposal of EPS can have many disadvantages on the
environment (Estrellan and Lino, 2010). Reducing the
sizes of EPS waste will be important in preserving real
estate assets in small islands such as Trinidad and Tobago.
Figure 1. Common type of the containers used at food courts
Developing an efficient process to recycle EPS is
very important since this material is used in abundance
throughout the world for purposes such as packaging,
insulation and in the making of foam plates and cups
(Mwasha, 2011). According to Indexmundi (2003),
24
A. Mwasha et al.: Management of Polystyrene Wastes Using a Supercritical Solvent - Propanone
approximately fourteen millions kilograms were deposited
in T&T in 2010. Table 1 shows the cumulative amount of
polystyrene acquired in T&T from 2005 to 2010.
Table 1. The cumulative amount of polystyrene acquired in T&T,
2005-2010
Year
Amount
Cumulative amount of polystyrene consumed (1,000 Kgs)
2005
2006
2007
2008
2009
2010
840
2,.315 11,239
12,231
13,275
14,000
The four main waste management methods used
throughout the world are disposal, recycling, avoidance
and reduction. The reduction method can be implemented
by densification. Densification can be performed using
thermal method and chemical dissolution. As shown in
Table 2 chemical densification provides the best solution
for the disposal.
Chemical densification has recently gained popularity
due to reduced waste management cost, energy and other
environmental impacts such as pollutions and gaseous
emissions. Chemical densification is performed by
dissolution of polystyrene wastes in supercritical liquids.
García et al (2007) pointed out that the dissolution of
polymeric wastes with suitable solvents is one of the
cheapest and more efficient processes for polystyrene
waste management. The authors investigated the solubility
of polystyrene foams in several solvents benzene, toluene,
xylene, tetrahydrofuran, chloroform, 1,3-butanediol, 2butanol, linalool, geraniol, d-limonene, p-cymene,
terpinene, phellandrene, terpineol, menthol, eucalyptol,
cinnamaldheyde,
nitrobenzene,
and
N,Ndimethylformamide. However, most of these solvents
(such as benzene, toluene, xylene, chloroform and
tetrahyd rofuran) are carcinogenic.
Recently, Methyl methacrylate (MMA) solution has
been recommended for use in dissolution of plastics
during recycling, Moroka (2004). However, it should be
noted that the manufacturing of MMA is based on the
reaction of hydrogen cyanide (HCN) and acetone to give
acetone cyanohydrin. The cyanohydrin then undergoes
acid assisted hydrolysis and esterification with methanol
to give MMA. The toxicity caused by HCN compound
poses a threat to humans and the environment (US EPA,
1998).
On selecting the best solvent it is important to
consider the principles of green chemistry formulated by
Anastas (2004). It is better to prevent waste than to treat
or clean up waste after it has been created. It was argued
that synthetic methods should be designed to maximise
the incorporation of all materials used in the process into
the final product. Synthetic methods should be designed to
use and generate substances that possess little or no
toxicity to human health and the environment. A raw
material or feedstock should be renewable rather than be
technically and economically depleting.
Although a renewable solvent as the terpenic
(limonene and cymene) would have high capacity to
dissolve the polystyrene, terpenes have niche to serve as
advanced biofuel precursors (Harvey et al., 2007). For
example, the fully reduced form of the linear terpene
farnesene is being pursued as an alternative biosynthetic
diesel in the market (Renniger and McPhee, 2010). Based
on the principles of “green chemistry”, Terpene is a
valuable biofuel and is in high demand in a multitude of
oilfield applications, including wellbore cleanouts, matrix
stimulation, hydraulic fracture stimulation, sand control,
and cementing operations Curtis (2003). Therefore,
adding to 12 principles of green chemistry the availability
and the demand for the solvent should be considered when
selecting solvent for waste disposal.
Table 2. The comparisons in different methods of waste disposal and minimisation
Method of Disposal
Comparative Number of boxes to be deposited
Effective
disposal
Source
Separation and
disposal
0
Mechanical
Compaction
50
Baugh et al.
,1992;
Sabeeha
2011)
95
(Baugh et al.,
1992;
Sabeeha
2011)
heat
Densification
Chemical
densification
98.5
Proposed
method
using
Propanone
A. Mwasha et al.: Management of Polystyrene Wastes Using a Supercritical Solvent - Propanone
Propanone can be easily produced in most developing
countries using an abundant supply of fermatative
vegetation. It has also less competition as compared to
Terpenes. Gog et al. (2005) showed that Terpenes at high
concentrations can be toxic, and are thus important
defenses against herbivores and pathogens. Terpenes can
however be replaced by a readily available solvent such as
Propanone. In this paper, the advantage of using
environmentally friendly propanone for the disposal of
polystyrene wastes is discussed. The densification effects
of this method are compared with traditional methods of
waste densification.
2. Material and Methods
2.1 Propanone
Propanone for this experiment was supplied by Specialist
Chemical Limited (SCL) in T&T. Propanone sometimes
called 2-propanone is also systemically called acetone.
Acetone belongs to a group of organic molecules called
ketones or alkanones. Acetone is a colorless, flammable
liquid often used as a solvent as it is completely miscible
with water and nearly all other organic liquids such as
diethyl ether, methanol, ethyl alcohol and esters, in all
proportion. Acetone has a low boiling point 56.5 °C or
134 °F and readily vaporises and has a distinctive odor.
Propanone is used as a raw material for the chemical
synthesis of a wide range of products (such as ketene,
methyl methacrylate, bisphenol A, and methyl isobutyle
ketone) in chemicals, explosives and lacquer industries.
Most important is that this product can easily be produced
in developing countries such as Trinidad and Tobago by
fermentation of agricultural wastes. As a result of the
development of the petrochemical industry and the
increase in prices of the agricultural produce (especially
molasses used as substrate for the fermentation), the
fermentative acetone production became no longer
economically viable and came to a halt in the 1960’s
(Duerre, 1998). However, interest in the acetone
fermentation has resurfaced because of the new global
support for the exploitation of biomass as a sustainable
source of energy. In the present study, an attempt has been
made to utilise the abundant supply of cellulose and
25
hemicellulose in Domestic Organic Waste (DOW)
(Pieternel at el., 2000; López-Contrera et al., 2004).
Acetone has been proved to have low toxicity to
human beings at the same time having potential medical
benefits such as anticonvulsant effects in animal models
of epilepsy, in the absence of toxicity, when administered
at low (millimolar) concentrations (Likhodii et al. 2003).
It has been hypothesised that the high-fat, lowcarbohydrate, ketogenic diet used clinically to control
drug-resistant epilepsy in children works by elevating
acetone in the brain. It can, however, irritate and damage
skin. A break through to the medical world is that acetone
has been used successfully to remove superglue in the
human ear (Wasano et al., 2009; White and Broner, 1993).
There was no report on the damage to the tympanic
membrane. It has been reported that fatal damage can
happen only if there is a large intake of acetone.
2.2 Polystyrene Wastes
The EPS wastes were collected from discarded computer
packing on UWI St Augustine campus. The common
characteristics, handling and uses of polystyrene are
elaborated in Table 3.
2.3 Testing Procedure
A 9-step test procedure is proposed. These steps are:
1) The large volume of polystyrene wastes was collected
from different faculties at the UWI St Augustine
Campus.
2) EPS was then broken down into small pellets using a
metal grater attached to a wooden block for ease of
use.
3) Plastic container (of capacity of 11 liters) was filled
with grated EPS pellets.
4) Immediately after the pellets were dissolved, more
pellets were added to the mixture until all 11 litres of
pellets were used up.
5) After all the pellets were used it was observed that the
mixture contained residual acetone. The viscose
liquid of dissolved polystyrene was extracted and
extra acetone was separated and measured.
Table 3. Common characteristics, handling and uses of polystyrene
Physical Data
Molecular weight
Melting point
Solubility
Form supplied in
Purification
Handling, Storage, and
Precautions
Uses
Vary with molecular weight.
Varies g/mol
Varies widely; ranges from 190oC – 260oC
Soluble in most organic solvents (ethyl acetate, dichloromethane, benzene, chloroform, carbon tetrachloride
propanone (acetone), DMF, DMSO, tetrahydrofuran (THF), gasoline and toluene). Insoluble in water, low
molecular weight alcohols, in organic acids and bases, diethyl ether, and hexanes.
Colorless, viscous liquid (low molecular weight mixture); Solid - white power, flakes, sheets, rods, foams and
pellets (high molecular weight mixtures); widely available.
Precipitation from methanol or hexanes
No special handling or storage procedures are normally required.
Widely available as an excellent thermal and electrical insulator and packaging material. Used to manufacture
commercial, industrial, household and personal articles such as containers, cutlery, and trays, etc.
26
A. Mwasha et al.: Management of Polystyrene Wastes Using a Supercritical Solvent - Propanone
6) It was determined from the excess acetone that 0.35
litre was enough to dissolve 11 litres of polystyrene.
7) It was found that out of 11 litres of the polystyrene
0,5 litres of polystyrene viscose liquid was produced.
8) The viscose liquid of polystyrene was left to
evaporate in a metal container. After 3 weeks the
semi hardened polystyrene viscose liquid was
extracted from the metallic container and left to air
dry.
9) It was found that the volume of the polystyrene was
reduced to less than 0.10 litre from 11 litres of raw
polystyrene wastes.
2.4 Dissolution Procedure
Three hundred and fifty (350) milliliters of laboratory
grade acetone were measured using a measuring cylinder
and it was poured into a large container. Approximately,
six (6) litres of Styrofoam pellets were measured using a
graduated container. This material grated polystyrene
wastes (see Figure 2) were slowly added to the acetone in
the container, while constantly mixing using a mechanical
device (Cole Palmer Stirpak mixer). The mixing was
discontinued after all the material was dissolved. The
residual slurry formed was transferred to a graduated
cylinder to be measured volumetrically. The dissolution
process is elaborated in Figure 3.
of a massive quantity of material into a small volume of
liquid. Dissolving polystyrene in acetone demonstrates the
solubility of this plastic in an organic solvent, plus it
illustrates that polystyrene foam contains a large volume
of air within its physical structure.
The acetone breaks the polystyrene down into its
monomers. The polystyrene reforms as a polymer with a
different physical structure once the acetone-binding agent
evaporates. To explain further, some molecules are polar,
having electrically positive and negative sides, while
nonpolar molecules are electrically neutral. Since "Like
dissolves like" polar liquids generally dissolve polar
solids, while non-polar liquids dissolve non-polar solids.
As shown in Table 4, three litres of acetone can dissolve
100 litres of polystyrene pellets to produce 1.5 litres of
polystyrene slurry. The volume was reduced by 98.5%.
Table 4. The product of dissolution of polystyrene pellets in acetone
Solid wastes
Polystyrene pellets
(litres)
1,000
Solvent
Acetone
(litres)
30
Product
Polystyrene slurry
(litres)
15
A
B
C
D
Figure2. Collected polystyrene wastes (before recycling)
3. Results and Discussion
All the material completely dissolved rapidly
(approximately 1 minute) to form thick slurry. The
viscosity of the slurry changed to form a pliable solid
mass once the residual acetone evaporated and it was
found that the viscose liquid formed a crust on top. This
minimised the evaporation of water and remaining
acetone. The sample continued to decrease in volume as
long as it was left in the air.
3.1 Analysis
Polystyrene foam dissolves in the acetone to release the
air in the foam. This behaviour appears as the dissolution
A. Mixing proportions 0.5 litres of propanone for 11 litres of polystyrene beads
B. Mixing of the polystyrene beads with Propanone using Cole Palmer Stirpak mixer
C. The whitish slurry product after mixing polystyrene beads with Propanone
D. The hardened slurry
Figure 3. The process of dissolution of polystyrene using Propanone
In this paper, the densification of polystyrene wastes
was performed and it was found that 30 litres of acetone
can dissolve 1,000 litres of polystyrene which is converted
to 15 litres of slurry. The Polystyrene Reduction Ratio
(PRR) can be calculated following Equation.
PRR =
15
Slurry .
polystyrene = 1000 = 0.015 = 1.5%
In this case, using the method of densification is able
A. Mwasha et al.: Management of Polystyrene Wastes Using a Supercritical Solvent - Propanone
to reduce the volume of polystyrene wastes to 98.5%. As
was shown in Table 1, there are overwhelming advantages
on the use of Propanone to minimise the volume of the
polystyrene wastes as compared to that of mechanical
compaction and heat densification.
3.2 Economic Benefits
According US EPA (2012), the minimising of wastes and
reuse of contaminated land is a source of social and
economic concern. The spillage or release of hazardous
substances into the environment can have serious
economic consequences in terms of human health, damage
to natural ecosystems that provide valuable benefits to
society, and business operations within the contaminated
area. Therefore, the proposed method is vital in cleaning
up the environment and increasing the value of the real
estate and fostering overall sustainability in Trinidad and
Tobago. If one (1) litre of Propanone costs US$15.00,
then to clear one (1) square meter of polystyrene wastes
will only cost less then US$50.00. One square meter of
land at St Augustine costs more than US$200.00.
According to Mwasha (2011), there is potential for the
application of the product of the reaction between acetone
and polystyrene as construction material.
4. Conclusion and recommendations
The objective of this paper was to investigate the
possibility of using green technology for densification
polymeric wastes. The research found that Propanone can
be used effectively to minimise the volumetric
polystyrene wastes by 98.5%. The other advantage of
using this chemical is that it can be produced in
developing countries (e.g., T&T) by fermenting
agricultural wastes. From the literature it was found that
the other methods used in wastes disposal (such as heat
densification
and
compression)
have
adverse
environmental impacts and should be avoided. Using the
proposed chemical densification method, the accumulated
fourteen (14) million kilogrammes of polystyrene wastes
annually in T&T can be reduced to two hundred thousand
kilogrammes of polystyrene wastes which could be
converted to recycled materials with good economic
benefits, including construction materials.
It is recommended that a combination of legislation
and the enhancement of ecological consciousness through
education should be emphasised in various stages of
learning. The general public and the scientific community
also have the responsibility of ensuring that governments
and businesses change their attitudes towards the
consumption and disposal of all forms of wastes.
27
5 505 886 (Filed December 11, 1992; Issued April 9, 1996).
Duerre, P. (1998), “New insights and novel developments in
clostridial acetone/ butanol/ isopropanol fermentation”, Applied
Microbiology and Biotechnology, Vol49, pp.639-648.
Estrellan, C.R. and Lino, F. (2010), “Toxic emissions from open
burning”, Chemosphere, Vol.80, pp.201
Gog, L., DeLucia, E.H., Berenbaum, M.R. and Zangerl, A.R. (2005),
“Autotoxic effects of essential oils on photosynthesis in parsley,
parsnip, and rough lemon”, Chemoecology, Vol.15, pp.115-119
Harvey, B.G., Wright, M.E. and Quintana, R.L. (2010), “Highdensity renewable fuels based on the selective dimerisation of
pinenes”, Energy and Fuels, Vol.24, pp.267-273
Indexmundi (2003), “Trinidad and Tobago Yearly Imports in US
Dollars - Polystyrene, expansible, in primary forms”, available at:
http://www.indexmundi.com/trade/imports/?country=tt&commod
ity=390311 <Assessed April 2013>
James C. (2003), “Environmentally favaourale Terpene Solvent find
diverse applications in stimulation sand control and cementing
operations”, Proceedings of the SPE Annual Technical
Conference and Exhibition, Denver, Colorado, October, 8 pages
Likhodii, S.S., Serbanescu, I., Cortez, M.A., Murphy, P., Snead,
O.C. and Burnham, W.M. (2003), “Anticonvulsant properties of
acetone, a brain ketone elevated by the ketogenic diet”, Annals of
Neurology, Vol.54, No.2, pp.219-226
Moroka, A. (2004), “Basic properties of underwater polymer
mortars using waste expanded polystyrene-methyl methacrylatebased conference”, Proceedings of RILEM International
Symposium on Environment-Conscious Materials and Systems for
Sustainable Development, Bagneux, France, pp.203-210 (ISBN:
2-912143-55-1)
Mwasha, A. (2011), “Plastic wastes as engineering material”, UWI
Today, November 2011
Pieternel, A.M.C., Budde, M.A.W. and López-Contreras, A.M.
(2000), “Acetone, butanol and ethanol production from domestic
organic waste by solventogenic clostridia”, Journal of Molecules
Microbiology Biotechnology, Vol.2, No.1, pp.39-44
Renniger, N. and McPhee, D. (2008), “Fuel compositions
comprising farnesane and farnesane derivatives and method of
making and using same”, U.S. Patent No. 7399323.
Sabeeha, A (2011), Disposal and Applications of Polystyrene Waste
as a Construction Material, (Unpublished project report), The
University of the West Indies, St Augustine, Trinidad and Tobago
US EPA (1998), Toxicological Review of Methyl Methacrylate (CAS
No. 80-62-6) in Support of Summary Information on the
Integrated Risk Information System (IRIS). U.S. Environmental
Protection Agency/ National Center for Environmental
Assessment, Office of Research and Development, Research
Triangle Park, NC.
US EPA (2012), US Environmental Protection Agency National
Center for Environmental Economics Handbook on the Benefits,
Costs, and Impacts of Land Cleanup and Reuse, available at:
http://yosemite.epa.gov/ee/epa/eed.nsf/webpages/LandHandbook.
html#who <Assessed September 2012>
Wasano, Y., Sugimoto, T., Kitamura, K. and Maehara, H. (2006),
“Removal of superglue (cyanoacrylate) from the ear using
acetone (Review)”, Practica Oto-Rhino-Laryngologica, Vol.99,
No.2, pp.101-104
White, S.J. and Broner, S. (1994), “The use of acetone to dissolve a
styrofoam impaction of the ear”, Annals of Emergency Medicine,
Vol.23, No.3, pp.580-582
References:
Anastas, P. and Warner, J. (1998), Theory and Practice, Oxford
University Press, New York, NY
Baugh, M.R., Smithfield, R., Nielsen, M. and Goodwin, J.L. (1996),
Process for Densification of Low Density Polystyrene, US Patent
Authors’ Biographical Notes:
Abrahams Mwasha is a lecturer at the Department of Civil and
Environmental Engineering in The University of the West Indies
(UWI). He earned his PhD from the University of Wolverhampton in
A. Mwasha et al.: Management of Polystyrene Wastes Using a Supercritical Solvent - Propanone
West Midlands, United Kingdom (UK). His specific interests are on
Sustainable Construction and Environmental Management with
particular expertise in building materials and energy modelling;
life-cycle assessment processes and technologies including
sustainable refurbishment and modernisation. Dr. Mwasha is the
recipient and the winner of the Bizcom, UK award for the idea of
Novel and Sustainable Technology in 2006 and the author of a green
technology book titled “The practical Guide to Green Technology
for the Ground Engineering”.
Althea Armstrong-Richardson is currently a Senior Research
Technician in the Department of Civil and Environmental
Engineering at the UWI St Augustine. Ms. Armstrong-Richardson
has worked on the monitoring and laboratory testing of water and
wastewater systems for the past thirty-seven (37) years. She has
experience in hydrology from working at the Water Resources
Agency, quality control with the Water and Sewerage Authority and
teaching analytical skills, in water and wastewater testing, to
engineering undergraduate and post graduate students. She is the
holder of a BSc. Chemistry/Analytical Chemistry (UWI), an MSc
28
Environmental Engineering (UWI), and an MSc. Environmental
Science and Management (UTT). She is presently pursuing an
MHEd - Teaching and learning at UWI. Ms. Armstrong-Richardson
has a keen interest in the treatment and management of different
types of waste.
William Wilson is a lecturer at the Department of Civil and
Environmental Engineering in The University of the West Indies
(UWI). He earned his MSc and PhD from the Imperial College,
University of London, United Kingdom (UK). His specific interests
are in Structural and Geotechnical Engineering with particular
expertise in sustainable building materials including timber
engineering. Dr. Wilson is a Member of the American Society of
Civil Engineers (MASCE).
ƒ