A. Mwasha et al.: Management of Polystyrene Wastes Using a Supercritical Solvent - Propanone 23

ISSN 1000 7924The 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: Abrahams.Mwasha@sta.uwi.edu b E-mail: Althea.Richardson@sta.uwi.edu

c E-mail: william.wilson@sta.uwi.edu 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),

A. Mwasha et al.: Management of Polystyrene Wastes Using a Supercritical Solvent - Propanone 24

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 Cumulative amount of polystyrene consumed (1,000 Kgs)

Year 2005 2006 2007 2008 2009 2010 Amount 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, 2-butanol, linalool, geraniol, d-limonene, p-cymene, terpinene, phellandrene, terpineol, menthol, eucalyptol, cinnamaldheyde, nitrobenzene, and N,N-dimethylformamide. 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

Effective disposal Method of Disposal Comparative Number of boxes to be deposited Source

Separation and disposal

0

Baugh et al. ,1992; Mechanical

Compaction

50

Sabeeha 2011)

heat Densification

95

(Baugh et al., 1992; Sabeeha 2011)

Proposed method using

Chemical densification

98.5

Propanone

A. Mwasha et al.: Management of Polystyrene Wastes Using a Supercritical Solvent - Propanone 25

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

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, low-carbohydrate, 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 Vary with molecular weight. Molecular weight Varies g/mol Melting point Varies widely; ranges from 190oC – 260oC Solubility 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.

Form supplied in Colorless, viscous liquid (low molecular weight mixture); Solid - white power, flakes, sheets, rods, foams and pellets (high molecular weight mixtures); widely available.

Purification Precipitation from methanol or hexanes Handling, Storage, and Precautions

No special handling or storage procedures are normally required.

Uses 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.

A. Mwasha et al.: Management of Polystyrene Wastes Using a Supercritical Solvent - Propanone 26

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.

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

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 Solvent Product Polystyrene pellets

(litres) Acetone (litres)

Polystyrene slurry (litres)

1,000 30 15

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.

Slurry . 15 PRR = polystyrene = 1000 = 0.015 = 1.5%

In this case, using the method of densification is able

A B

C D

A. Mwasha et al.: Management of Polystyrene Wastes Using a Supercritical Solvent - Propanone 27

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.

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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

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), “High-density 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&commodity=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 methacrylate-based 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

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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

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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

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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

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).