Environmentel Chemistry
H. M. L. Dieteren and A. P. H. Schouteten Technical College Heerlen Dr. Jaegersstraat 40 Heerlen, Netherlands
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Removal of Crude Oil from Marine Surfaces An ecological lecture experiment
O n e of the methods to remove crude oil from marine surfaces is to sink the oil by means of an impregnated powder to which the oil adheres. I n a characteristic method developed by Shell Oil Company1 the powder (sand) suspended in water is treated with a diamine, such as RNH(CH&NH,, or one of its derivates which adhere to the sand, thus providing a hydrophobic surface. The suspension is then sprayed on the oil, adheres to it and the oil sinks. The features of this procedure include that sand is usually unlimitedly available a t sea and that the oil-wetting agents are harmless to fish, plankton, and other organisms living in the water of the sea.z The goal of our investigations was to demonstrate this procedure on a laboratory scale and to investigate some aspects in order to increase the student's insight in its theoretical background. Furthermore the experiments could contribute to an increased "environmental conscience" of the students. Experimental Part
The experiments can be performed in two ways: the thorough mixing of water, sand, amine, and oil in a volumetric flask, and an imitation of the spraying method on a laboratory scale. With the aid of the thorough mixing method the relationship between the amount of adsorbed oil, the concentration of amine, the chemical composition of the amine, and the pH of the mixture is determined. The sand used is the fraction 0.20 < d < 0.50 mm. For the oil toluene and hexadecane are substituted in order to diminish the amount of Darameters. For the same reason the easy available monoamines aniline, 1-aminohexane, 1-aminododecane, 1-(N,N-dimethylarnino)dodecane, and 1-aminooctadecane are used instead of the mixtures of diamines applied in the technical performance. Furthermore it turned out that the oil wetting properties of 1-aminooctadecane and the mixture of diamines are quite similar. Procedure I n the thorough mixing experiments 10.00 g of sand is mixed with a known quantity of toluene or hexadecane, 95 ml of water snd 5 ml of a suspension of the amine in a volumetric flak. After shaking and settlement of the sand, the remaining amount of oil on the surface of the water is determined quite easily by measur-
I'AN LAAR,H. G., Coastnl Water Pollution, C.C.M.S., 1, (1970). k o m e e n C is manufactured by A m o u r Hess Chemicals
ing the height of the oil column in the neck of the flask. With the aid of this method the following aspects can be investigated. The Effect of Amine Concenlmtion. For this purpose different quantities of I-aminododecane or 1-aminoaotadeeane are used as oil-wetting agents. The relationship between the amount of adsorbed hydrocarbon to the amount of amine on the sand gives rise to a curve similar to Figure 1. This curve consists of a stable
Figure 1. Relationship between the amovnl of adsorbed hyrocerbon 10 the amount of amino on the sand.
send'm'a stable conglomerate. The amine co&entration st M is about 2 X lo-' g of amine/g of sand, the concentration in the stable region about I0 times as much. The labile type of oilsand bond consists of a n oil droplet that is made heavier by some attached sand particles. A conglomerate of this type proves to be very sensitive to movement or shock, sometimes releasing part of its adhered oil upon slight rocking. The stable conglomerate consists of a rigid slimy structure composed of sand nartides wetted with oil. r~ Duomeen C,$ a mixture of diamines, that is used in the technical performance, shows an adsorption curve similar to Figure 1. The quantity of adsorbed oil however is increased. l'he Effect of the Chemical Composition of the Amines. The sdsorpti"n cu&e is determined, using various amines as oil-wetting agents. I n contrast with 1-aminododecane and l-aminofail oetadecane. aniline .and 1-(N.N-dimethvlamino)dodecane . to give a well-defined maximum in their curve up to a concentration of 0.01 g of amine/g of sand. The I-sminohexane shows s n optimum hut s t a concentration of about 0.01 g of amine/g of sand. The conglomerates of all three amines are of the labile type up to a concentration of about 0.1 g of amine/g of sand. The Effect of pH. The pH of the mixture of l-aminooctadecrtne. sand. and water is varied by adding different amounts of hydr&hlorio' acid to several sodium -hydroxide solutions before the hydrocarbon is added. The concentration of amine amounts to 0.005 g of amine/g of sand. The effect of the pH is represented by Figure 2. Spraying Test. As clogging ocours, the imitation of the technicd performance on small scale with the aid of miniaturized spraying nozzles is not possible. Therefore 230 g of sand, containine 0.26 e of 1-sminooctsdecane is ~ u ont a sieve (hole diameter 0.71 mm) and rinsed down into a. beaker containing 73 ml ~~~~
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Volume
49, Number I, January 1972 / 19
Environmental Chemistry
place if the apolar group of the amine is sufficiently extended. So the oil-wetting properties of an amine depend on the number of carbon atoms in the arnine's fatty chain. The effect of pH upon the activity of an amine also reveals the mechanism of adsorption. At low pH the adsorbed RNHa+ ions are replaced by H30+ ions, while a t hieher V H the number of R N H 3 + ions is strongly decreased. Further it appears that the structure of the stable oilsand conglomerates differs entirely from the usual adsorption mechanisms. The experiment shows that 1 g of treated sand is capable of adsorbing 0.25 g of hexadecane. Taking into account an area of 90 cm2/g of sand and assuming that all hydrocarbons are parallel and perpendicular to the surface, this means that about 15,000 layers of molecules should be present on the sand. The data clearly indicate that 1 molecule of amine causes the adsorption of 250 molecules of hexadecane. From these facts it may he concluded that the classical adsorption theory is not fit to describe this phenomenon. An explanation of the phenomenon is subject to further investigations.
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Figure 2.
The effect of pH on the amount of oil adsorbed.
of hexadeeane above a water surface (area 175 cm2)by means of a movable water hose. The adsorbed amount of hydrocarbon is about 60% of the original amount. If the amount of aminetreated sand is doubled, the adsorbed amount of oil will rise to about 80% of the original amount.
Discussion
From the preceding data one may conclude that the amine molecule; on ionizing in water, liberates a long chain of fatty ion carrying a positive charge. The R N H 3 + ion will attach itself most readily to the surface that carries a high proportion of negative charge thus providing a hydrophobic surface to which the oil adheres. The failure of 1-(N,N-dimethy1amino)dodecane to establish a stable conglomerate probably stems from steric hindrance by the methyl groups. Furthermore it is established that a reasonable interaction between the amine and the oil can only take
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Acknowledgment
We thank the students W. H . G. Daniels and F. G. Wolffs for the performance of the experiments that were part of their graduation assignments.
