Expanded Polystyrene Volume Reduction
Out of the massive quantities of polystyrene waste roaming around the planet, a major volumetric proportion of it can be found in the expanded polystyrene (EPS) form. This form presents a problem to the recycling processes of the plastic as it makes it economically inconvenient to clean out.
It is apparent that polystyrene, unlike other plastics, has the ability to dissolve in organic solvents. This property allowed us to chemically prepare it by freeing up the air molecules trapped within EPS once dissolved, making it a suitable method for reducing the unnecessary volumes of air found in EPS and allowing the pure polystyrene mass to be prepared for further processing.
Table 1: Polystyrene solvents (Garcia et al, 2009)
Some of the strongest organic solvents for EPS turn out to be acetone, methanol, chloroform and toluene (García et al., 2009). Although these possess high dispersity values, they are highly polluting, toxic and inconvenient to use as they pose threat to the environment. Thus, we went on to test more ecological alternatives such as limonene and cymene. Both limonene and cymene are naturally occurring compounds, but accordingly, to their natural presence, limonene is a more ubiquitous, more easily accessible molecule.
Limonene is a naturally occurring hydrocarbon found in the zest (outer peel) of citrus fruits, ranging in concentrations from highest in oranges and grapefruits and lowest in lemons and limes. It is a monoterpene molecule, which can often be found used as an oil in food, perfumery and pharmaceutical industry. Although about 4 times weaker than acetone’s dissolving capability, limonene’s accessible and eco-friendly nature makes it optimal for use as an EPS deairifying compound, so we decided to test the methods of extracting it and using it as a polystyrene solvent.
Limonene can be found in the outer peel of citrus fruits. To obtain the purest yield of limonene, other essential oils found in citrus peels need to be evaded by scraping only the outermost surface of the fruit. Oranges and grapefruits contain the thickest surface and thus should contain the highest yield of limonene.
Two methods that can generally be used to separate limonene from peels are steam distillation and soxhlet extraction (Students2Science, 2011).
The Soxhlet extraction kit (figure 3) is a laboratory apparatus commonly used for the extraction of partially soluble compounds and lipids from solid media. The steam distillation kit, on the other hand, is an assembly used for easy and fast extraction of immiscible oils with boiling points higher than water from solid compounds (normally plants) at boiling temperatures of water. It has been a commonly well-known method used for the extraction of essential oils from plants, which due to its good accessibility and high purity values in contrast to the soxhlet, got used in this experiment.
A steam distillation apparatus was assembled and a steam distillation procedure was performed at two different masses of citrus peel fruits (25g and 50g). The peel masses were distributed accordingly to table 1 and the tests were carried out one after another. To ensure variety in the samples by age and origin, two different types of zest were obtained from two different stores (Tesco and Marks&Spencer). The samples were mixed with distilled water (100 mL with the 25g sample and 200 mL with the 50g sample. The steam distillation was performed until the medium volume boiled down to a half of its initial volume. The aim of the experiment was to determine the amount of limonene that can be obtained from steam distillation of the three citrus fruits.
Figure 4: Steam distillation kit
A steam distillation apparatus was assembled according to the provided protocol and distillation procedure was performed at two different masses of citrus peel fruits (25g and 50g). The peel masses were distributed accordingly to table 1 and the tests were carried out one after another. To ensure variety in the samples by age and origin, two different types of zest were obtained from two different stores (Tesco and Marks & Spencer). The samples were mixed with distilled water (100 mL with the 25g sample and 200 mL with the 50g sample). The steam distillation was performed until the medium volume boiled down to a half of its initial volume. The aim of the experiment was to determine the amount of limonene that can be obtained from steam distillation of the four given citrus fruits.
The fruits samples were done each on a different day following the table. The peel zest was grated strictly along the surface to ensure that as much of the limonene-containing samples are present. The procedure was done in a fume hood to reduce exposure to toxic gasses.
Table 2: Volume of the hydrophobic compound extracted from ½ volume steam distillation.
Once the distillation procedures were finished, a hydrophobic layer could be visible in each of the tested samples. Because the liquids contained multiple compounds aside from limonene, the presence of limonene had to be tested. It was taken out of the tubes with a syringe and tested for the presence of covalent bonds using the was obtained, further testing on the composition of the it has the appearance of a transparent liquid. The liquid was tested out for its polystyrene dissolving abilities through a second series of experiments.
In order to test the efficiency of limonene dissolving, multiple samples of varying limonene volumes were tested against a constant volume of polystyrene and their dissolving ability was recorded through time. Control samples contained acetone.
250 mL of polystyrene was dissolved in 5 mL of limonene and 5 mL of acetone were dissolved as a control to compare the speed of limonene dissolving.
The provided videos compare the dissolving time between acetone and limonene.
The collected mix of polystyrene and limonene is a dense, white, half-transparent gel that possesses a few other interesting properties that could offer it alternative usage.
Further preparation of this gel requires vacuum distillation at boiling water temperatures
Pyrolysis of polystyrene and preparation of styrene feedstock 12/08/18
Dissolving expanded polystyrene (EPS) in organic solvents is a physical reaction that proves the solubility of polystyrene materials and also the large amounts of air that EPS contains. When dissolved, 98% of its initial volume is reduced, offering an efficient method of cutting down the amounts of its disposed waste, while additionally preparing it for more cost-efficient recycling. Since natural degradation of the dense polystyrene mass yet remains an issue, new favorable methods in both reusing and disposing its waste are yet to be discovered. Since one of the main insights of our project states that bacterial degradation of polystyrene occurs only at monomer levels, our favourable next step was depolymerising it. Little did we know, the remaining high density polystyrene is able to be further depolymerised at temperatures between 350° - 450°C. The aim of this experiment was to collect a high yield of styrene monomers and prepare them for bacterial digestion.
Figure 8: materials
-Two round bottom flasks
-1/20 mols of high density polystyrene
-2 distillation heads
Cut 5.2 grams of polystyrene parts and fit them inside the 25ml glass flask. Construct the apparatus shown on picture 1 inside the fume cupboard. Connect the round bottom flask to a distillation head and place it into the glass tube. Fix the assembly above the bunsen burner. Put a condenser tube onto the other end of the glass tube and connect it to a 25ml glass flask using a distillation head and put it in the ice bath. There should be a small hole just above the collecting tube of the distillation apparatus to make sure air can escape it. Make sure that the condenser tube goes directly inside the 25ml collecting flask and that the small air hole is above it (this is because styrene is heavier than air 104.15g/mol:28.9g/mol so it will go to the bottom of the flask and air will escape at the top). For this distillation experiment, you do not need to run water in the glass tube as the temperature will be high enough to damage the glass if cold water is running through it.
Start heating polystyrene inside the flask with a bunsen burner (roaring flame). Heat the flask from all of its sides to make sure all of the polystyrene heats up.
The distillation starts within a minute. A cloudy gas of styrene can be seen travelling through the condenser down to the round bottom flask where it stays at the bottom and condenses. As styrene cools down, a white-yellow oily liquid with a strong and unpleasant smell is formed. Results showed successful depolymerisation and distillation of our polystyrene parts into a liquid compound. The distillation process can have leftover impurities which vary in their appearance depending on what plastic is used. In our experiment, highly impure leftovers were present in polystyrene cups, while almost completely pure styrene was obtained from transparent polystyrene utensils. This is a huge issue as the contaminating materials will not be digested by the styrene degrading bacteria.
García, M.T., Gracia, I., Duque, G., de Lucas, A., Rodríguez, J.F. (2009). Study of the solubility and stability of polystyrene wastes in a dissolution recycling process. Waste Management. 29 (6), 1814-1818. Available from: https://www.semanticscholar.org/paper/Study-of-the-solubility-and-stability-of-wastes-in-Garcia-Gracia/5f7a7fbabad7d0fe90512c7fde103367280c5a7c