- Email: [email protected]
A laboratory screening study on the use of solidifiers as a response tool to remove crude oil slicks on seawater
Chemosphere 80 (2010) 389–395
Contents lists available at ScienceDirect
Chemosphere journal homepage: www.elsevier.com/locate/chemosphere
A laboratory screening study on the use of solidifiers as a response tool to remove crude oil slicks on seawater Pablo I. Rosales a, Makram T. Suidan a,*, Albert D. Venosa b a b
Department of Civil and Environmental Engineering, University of Cincinnati, Cincinnati, OH 45221-0071, United States Land Remediation and Pollution Control Division, National Risk Management Research Laboratory, US EPA, Cincinnati, OH 45268, United States
a r t i c l e
i n f o
Article history: Received 10 March 2010 Received in revised form 12 April 2010 Accepted 13 April 2010 Available online 7 May 2010 Keywords: Gas chromatography Infrared spectroscopy Oil spills Oil solidifiers Prudhoe Bay crude oil UV–Vis spectroscopy
a b s t r a c t The effectiveness of five solidifiers to remove Prudhoe Bay crude oil from artificial seawater in the laboratory was determined by UV–Vis and GC/MS. The performance of the solidifiers was determined by UV– Vis as a function of solidifier-to-oil mass ratios (SOR), water volume and surface area, and contact time. An SOR of 1:4 solidified crude oil from 58% to 84%. Under more severe test conditions (SOR 1:16) the material with better performance solidified 28% of the oil initially added to water. The percent mass of free oil remaining on the seawater at the end of the contact time was the same when measured by either UV–Vis or by GC/MS. Analyses performed using GC/MS revealed that oil solidification is not a selective process; n-alkenes and polycyclic aromatic hydrocarbons reacted at a similar rate for each solidifier. Infrared Spectroscopy was used to investigate the functional groups in the materials as received. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction Solidifiers are materials that react with oil and change oil from liquid to solid state. Use of solidifiers as a response technique for oil spills on water has been investigated since the early 1970s (Dahl et al., 1996). However, use of solidifiers for oil spill response has some drawbacks. For example, the effectiveness of the treating agents depends on the type and composition of the crude oil tested (Fingas et al., 1990; Fingas and Tennyson, 1991). Another disadvantage of the use of solidifiers in oil spills is the large amount of material that needs to be applied. It has been reported that 16% to over 200% by weight (solidifier–oil mass ratio) is required to solidify crude oil (Fingas et al., 1993, 1995). Therefore, the use of solidifiers to remove slicks of crude oil has received little attention due to a lack of practical application methods and appropriate tests under various conditions and environments (Delaune et al., 1999). Different laboratory effectiveness test have been developed for solidifiers (Fingas et al., 1990). Effectiveness is a major problem with treating agents, since it is generally a function of oil type and composition. For example, solidifiers that are effective on aromatic compounds may not be applicable to polar compounds (Fingas and Tennyson, 1991). Fingas et al. (1993) tested three different solidifiers. The effectiveness test was carried out by adding solidifier (at 1-min intervals) to an oil under constant stirring until the oil * Corresponding author. Tel.: +1 513 556 3695; fax: +1 513 556 2599. E-mail address: [email protected] (M.T. Suidan). 0045-6535/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.chemosphere.2010.04.036
solidifies. The product that performed better in the laboratory tests was tested in a larger scale. They found that it was necessary double the amount used in laboratory to solidify the oil in a real spill. An important factor for testing solidifiers is the aquatic toxicity. Fingas et al. (1995) reported that many products tested by Environment Canada have high and unacceptable aquatic toxicities. The aquatic toxicity for the solidifiers tested by Fingas and coworkers showed that the products were relatively non-toxic. The toxicity was carried out using a standard acute 96-h Rainbow Trout procedure. Cardello (1996) investigated the use of oil spill solidifiers for land applications. The researcher evaluated the final consistency and solidification time for solidifier-to-oil mass ratios (SOR) from 1:1 to 1:4. The solidifiers were tested in laboratory and in field with different oils. The results showed that some solidifiers performed better in field than in laboratory tests. The effect of temperature on the solidification time was also tested and the results showed some solidifiers performed better at lower temperature (1.6 °C), while others performed better at a higher temperature (20 °C). Ghalambor (1996) investigated the performance of 23 solidifiers to remove three crude oils. The solidifiers were tested under static and dynamic (200–400 rpm) conditions and the heat released during the solidification reaction was measured by a solution calorimeter. Ghalambor conclude that the effectiveness of the solidifiers may depend on the level of oil asphaltenes, the paraffin wax content, and the sulfur content. The researcher found
390
P.I. Rosales et al. / Chemosphere 80 (2010) 389–395
that the level of solidifier consumption depends on the kind of crude oil used. Walker et al. (1999) review the effectiveness and environmental considerations for non-dispersant chemical countermeasures and reported that the effectiveness probably decreases for emulsified, weathered, thick, or heavy oils due to the difficulty of mixing the product into viscous liquids. They reported also that salinity has no effect on the solidification of oil. It appears that the performance of solidifiers is unaffected by salinity as reported by Walker et al. (1995) and Fingas (2008). Delaune et al. (1999) also tested a commercial solidifier (Nochar A650) on open water to remove South Louisiana crude oil. The effectiveness test consisted of applying one part of solidifier by two parts of crude oil and let them react for 4 d. After 4 d, the researchers found that over 70% of the crude oil was solidified. More recently, Fingas (2008) reviewed the literature on oil spill solidifiers. Fingas pointed out that the use of solidifiers in recent times is not well-documented and the lack of scientific assessment of solidifier effectiveness at spill scenes. Despite the disadvantages stated above, better knowledge of the chemistry involved in the solidification of oil slicks can lead to the manufacture of cost-effective solidifiers and the development of protocols for testing the appropriateness of using solidifiers to respond to crude oil spills. This paper discusses the effectiveness of five solidifiers to cleanup crude oil spills, as well as the chemical changes during the solidification of crude oil. We analyzed the results found when a solidifier reacts with crude oil, using analytical techniques such as GC/MS, Infrared Spectroscopy (IR) and UV–Vis. 2. Materials and methods Five commercial solidifiers (referred to as S1, S2, S3, S4, and S5) were examined in this study for their effectiveness in removing Prudhoe Bay crude oil from artificial sea water. Artificial seawater, modified GP2 (Bidwell and Spotte, 1985), was used as the exposure medium. The artificial seawater had pH values in the 7.6 ± 0.1 range and its temperature value was 21 ± 1 °C. Pesticide quality dichloromethane (DCM) served as the extraction solvent. The experiments were carried out in silanized beakers to minimize adherence and spreading of crude oil on the walls of the glassware. 3. Experimental procedure A volume of 0.5 mL of Prudhoe Bay crude oil was added to silanized beakers containing 80 mL of artificial seawater. Crude oil and artificial seawater volumes were kept constant in the experiments, while the mass of solidifier changed depending on the SOR tested. Each commercial solidifier was added to a slick of crude oil on artificial seawater and the mixture stirred at 30 rpm with a magnetic stirring bar. The preliminary conditions used to evaluate the effectiveness of solidifiers were: oil surface area (the area changes as a function of the beaker capacity), SOR, and solidifier/oil contact time. Beaker volumes used were 100, 400, and 800 mL. SOR ratios of 1:4, 1:8, and 1:16 were used during the evaluation of solidifiers to estimate the optimized SOR, and the solidifier/oil contact times were 30, 60, 120, and 180 min. The experiments were carried out in triplicate. The resulting data were plotted as the average of triplicate samples; the acceptance criterion for the triplicate samples was a Relative Standard Deviation 625%. All residual crude oil concentrations remaining on the seawater after the solidified oil was removed were measured by UV–Vis spectroscopy. The effectiveness of five solidifiers was also determined by GC/ MS. Each of the solidifiers was added to a slick of crude oil on arti-
ficial seawater in 400-mL silanized beakers at an SOR of 1:16 (0.027 g solidifier–0.447 g of crude oil). After stirring the mixtures at 30 rpm for 30 min, the solidified oil was carefully removed from the artificial seawater with tweezers. The artificial seawater with the remaining oil was transferred from the beakers to 250-mL separatory funnels and spiked with 200 lL of surrogate solution. The experiments were carried out in triplicate for each solidifier. The solutions in the funnels were extracted three times with 20 mL of DCM and the final volume adjusted to 60 mL. A volume of 1 mL of the solution and 20 lL of internal standard were added to a vial, and the sample was later injected into the GC for analysis. This procedure was repeated for residual crude oil samples unexposed to solidifier to determine the recovery of the crude oil. DCM was injected as a blank. 4. UV–Vis spectroscopy An Agilent 8452 UV–Vis spectrophotometer (Agilent Technologies, Palo Alto, CA) was used to measure the residual crude oil concentration remaining on the seawater after removal of the solidified oil. Six standard solutions of oil were prepared to calibrate the UV–Vis spectrophotometer (Srinivasan et al., 2007). The crude oil remaining on the seawater surface was determined by extracting the entire contents of the beaker with DCM after the solidified oil was removed. The solution was extracted three times with 20 mL of DCM, and, if necessary, the final volume of the extract was adjusted to 60 mL by adding DCM. DCM was used as a blank, and the calibration curve was determined by measuring the concentration of the six standard solutions from the lowest to the highest concentration. The crude oil remaining on artificial seawater after being extracted was diluted with DCM when the concentration exceeded the maximum concentration value generated with the calibration curve. The diluted sample was prepared by adding 24 mL of DCM to 1 mL of the extracted solution. The absorbance measurements were recorded at 340, 370, and 400 nm. The concentration was calculated using the trapezoidal rule (Srinivasan et al., 2007). 5. IR The spectra were collected with a Nicolet Magna IR equipment model 760 (Thermo Fisher Scientific, Walthman, MA) with a ZnSe prism and a deuterated triglycine sulfate detector. The horizontal attenuated total reflection technique was used to generate the spectra in the middle infrared region (400–4000 cm1) averaging 64 scans at a resolution of 4 cm1. 6. GC/MS The GC/MS analyses were done using an Agilent 6890 GC with an Agilent 7683 auto sampler (Agilent Technologies, Palo Alto, CA, USA) coupled to an Agilent 5973N mass selective detector. 1 lL of the crude oil extracted was injected for GC/MS analysis in the pulsed splitless mode. A 4 mm id Liner (Agilent Technologies, Palo Alto, CA, USA) with a glass wool tap was used. The inlet initial temperature was 290 °C and high purity helium was the carrier gas. The initial GC oven temperature was 45 °C; the temperature was ramped to 200 °C at 4 °C min1 and then to 310 °C at 10 °C min1. The oven was kept a 310 °C for 10 min. The carrier gas was ultra-high purity helium (0.9 mL min1) with chromatographic separation in a DB-5 ms column (30 m, 0.25 mm internal diameter, 0.25 lm film thickness, J&W Scientific, Folsom, CA, USA). Selected ion monitoring mode was used for the detection and data acquisition. An interface temperature of 300 °C, ion source of 230 °C, and quadrupole of 150 °C were the parameters
391
P.I. Rosales et al. / Chemosphere 80 (2010) 389–395
of the mass spectrometer. Analytical grade n-decane, n-hexane, neicosane, n-triacontane, naphthalene, anthracene, chrysene, perylene, and androstane were used as internal standards. The internal standards were added prior to injection of extract. Analytical grade n-heptadecane, tetracosane, n-dotricontane, 1-methylnaphthalene, phenanthrene, and pyrene were used as surrogates.
7. Results and discussion The initial set of experiments was carried out using an SOR of 1:16 (0.0279 g solidifier–0.447 g crude oil) to determine the effectiveness of the five solidifiers under the worst case scenario. Three different container sizes (100-, 400-, and 800-mL beakers) were used to determine the effect of the surface area of the slick of crude oil on the effectiveness of the solidifiers. The size of the beaker determines the depth and surface area of the water and the thickness of the oil slick (see Supplementary material). Results (see Supplementary material) indicated that the performance of the solidifiers under the conditions tested did not depend on the surface area of the oil slick or the thickness of the crude oil slick. The intermediate container size of 400 mL was selected for subsequent experiments to determine the effects of SOR and the solidifier–crude oil contact time. Again, SOR ratios of 1:4, 1:8, and 1:16 were used in these experiments. As expected, an SOR of 1:4 (0.112 g solidifier–0.447 g crude oil) removed the highest amount of crude oil from the water (Fig. 1a); the smaller the percentage remaining, the greater was the performance. The concentration of crude oil remaining on the artificial seawater ranged from 16% to 43% for solidifiers tested with an SOR of 1:4. These results generally agree with the work done by Delaune et al. (1999) who reported a 70% removal of crude oil using an SOR of 1:2. In our experiments, the crude oil and the artificial seawater volumes were held constant while varying only the amount of solidifier added. The results for a 1:8 SOR (0.0558 g solidifier–0.447 g crude oil) revealed that S2 and S3 performed slightly better than the
other three solidifiers with an average percent remaining unsolidified being approximately 50% for these two solidifiers. At this SOR, the amount of unsolidified crude oil remaining after S1, S4, and S5 reacted was 61.4%, 62% and 58%, respectively, of the crude oil originally added. Similarly, for a 1–16 SOR (0.0279 g solidifier–0.447 g crude oil), unsolidified oil remaining after treatment with the five solidifiers was in the range 72–81% of the initial crude oil. The effectiveness of solidifiers as a function of time was investigated using an SOR of 1–16 in a 400-mL beaker. The results (Fig. 1b) showed that a contact time of 30 min was enough to allow solidification to take place for all five solidifiers tested. Longer contact times resulted in moderate increases in performance in terms of amount of crude oil remaining unsolidified on the water. We concluded that the longer the stirring time, the greater was the likelihood that exposure of all the oil to the solidifier took place. The initial solidification prevented full exposure of the oil to the action of the solidifier, and this resulted in a longer exposure time to achieve the higher performance. The mass of crude oil remaining on the artificial seawater at an SOR of 1:16 was also quantified by GC/MS with results similar to those obtained by UV–Vis spectroscopy. Fig. 2 shows the concentration ratios of the individual n-alkanes and polycyclic aromatic hydrocarbons (PAH) and initial crude oil. The light alkanes volatized during the 30 min exposure of the oil and solidifier, as can seen from the values for nC10, nC11, and nC12 for all five solidifiers. Beyond nC12, the abundance ratios remained constant for all five solidifiers. The ratio of abundance of n-alkanes on seawater and in crude oil was in the range 0.7–0.8 for the five solidifiers. These levels were similar to the percent of crude oil left in artificial seawater obtained by UV–Vis spectroscopy (See Fig. 1a). The concentration ratios of PAH/crude oil were similar to the values obtained for n-alkanes. The GC/MS results indicate that oil solidification is not a selective process in terms of oil components. Attempts to identify the functional groups used in the solidifiers can provide information that might help explain the differences in the performance of the solidifiers observed. To understand better
100
a(a)
1:16 1:8 1:4
b
(b)
30 min 60 min 120 min 180 min
Percent %
80
60
40
20
0 S1
S2
S3
Solidifier
S4
S5
S1
S2
S3
S4
S5
Solidifier
Fig. 1. Percent of the oil remaining unsolidified on artificial seawater as a function of: (a) SOR, and (b) reaction time. Solidifiers reacted for 30 min in the experiments carried out as a function of SOR; the experiments as a function of reaction time were carried out at an SOR of 1:16.
392
P.I. Rosales et al. / Chemosphere 80 (2010) 389–395
Concentration relative to initial crude oil
1.2
1.0
0.8
0.6
0.4 S1 S2 S3 S4 S5
0.2
S1 S2 S3 S4 S5
Naph C1-N C2-N C3-N C4-N Biphenyl Phen F C1 F C2 F C3 F Diben C1 D C2 D C3 D Naphdibthph C1 Naphdibthph C2 Naphdibthph C3 Naphdibthph C1 Phenanthrene C2 Phenanthrene C3 Phenanthrene C4 Phenanthrene C1 Pyrene C2 Pyrene Chrysene C1 Chrysene C2 Chrysene C3 Chrysene C4 Chrysene Coprostane Hopane
nc10 nc11 nc12 nc13 nc14 nc15 nc16 nc17 nc18 nc19 nc20 nc21 nc22 nc23 nc24 nc25 nc26 nc27 nc28 nc29 nc30 nc31 nc32 nc33 nc34 nc35
0.0
Fig. 2. Concentration ratio of the oil remaining unsolidified on artificial seawater and initial crude oil for n-alkanes and polycyclic aromatic hydrocarbons (PAH). The experiments were carried out at an SOR of 1:16. The solidifier was in contact with crude oil for 30 min and the mix was stirred at 30 rpm.
the oil solidification process, the infrared spectra of the materials as they were received were determined to identify the chemical functional groups present before the solidification of oil. The infrared spectrum of Prudhoe Bay crude oil (Fig. 3a) was very similar to the crude oil infrared spectra reported in the literature (Coates and Setti, 1985; Tjomsland et al., 1996). Although crude oil is a mixture of multiple compounds, the infrared spectrum of crude oil identified mainly the presence of methyl and methylene functional groups. The main absorption bands observed in the spectrum were located at 2952, 2921, and 2852 cm1, assigned to asymmetric stretch CH3, asymmetric stretch CH2, and symmetric stretch CH2, respectively (Colthup et al., 1990). The other two main absorption bands observed in the spectrum were located at 1456 and 1377 cm1, assigned to CH in CH3 and CH2 groups in the crude oil. The absorption bands near 1614, 870, 810, and 750 cm1 are characteristic of aromatic groups (Akrami et al., 1997; Guo et al., 2006). The infrared spectrum obtained for S1 as received is shown in Fig. 3b. The spectrum showed absorption bands at 2921 and 2842 cm1, assigned to CH3 and CH2 groups, respectively. The spectrum also revealed a shoulder near 2948 cm1, assigned to CH3. Absorption bands characteristic of carbonates were observed in the infrared spectrum such as the bands located at 1450 and 1376 cm1. Slager et al. (1972) reported doublet absorption bands located at 1460 and 1380 cm1 for silver carbonate. The bands located at 1018 and 873 cm1 in Fig. 3b are also characteristic of carbonates. Slager and coworkers exposed silver oxide to a 50 662 Pa pressure of CO2 and found the formation of new bands at 1020, 880, 1410, and 690 cm1. These bands correspond to vibrations of carbonate species (Slager et al., 1972). The absorption band around 1410 cm1 became a doublet at 1460 and 1380 cm1 when the carbonate was exposed to moisture. Since our experiments were carried out under ambient conditions, S1 adsorbed moisture as seen from the bands near 1450 and 1376 cm1 in Fig. 3b.
The infrared spectrum of S2, an organic solidifier, is plotted in Fig. 3c. The infrared spectrum for S2 showed a broad absorption band near 3300 cm1 assigned to intermolecular hydrogen bonds (Bellamy, 1958). It has been reported that the broad shape is usually attributed to association of alcohol in various polymeric forms, where the broad band is a composite of a number of sharper bands. This absorption band can be assigned to polymeric association in cellulose (Bellamy, 1958). Functional groups that contain CO were found in the spectrum of S2 as shown by the absorption bands located near 1380, 1150, and 1040 cm1, which were assigned to OCH2, CO, and CH2OCH2, respectively. The infrared spectrum of S2 also showed absorption bands associated with carbonyl compounds (ketones). Ketones have characteristic absorption bands near 1715 cm1; the infrared spectrum of S2 showed an absorption band near 1710 cm1 and another band near 1625 cm1, which can be assigned to di-ketones (Colthup et al., 1990). Fig. 3d shows the infrared spectrum of S3, whose features are similar to the spectrum for S1. Methylene functional groups were observed in the infrared spectrum in the 2920–2850 cm1 region, while functional groups associated with carbonate were found by the absorption bands at 1411, 870 and 1020 cm1. The infrared spectrum for S4 (Fig. 3e) is characteristic of a polymer formed by chains of methyl and methylene groups. This spectrum had absorption bands near 2920, 2850, 1470, 1380, and 720 cm1, assigned to methyl and methylene groups. Absorption bands in the 720– 780 cm1 region have been used by many researchers to estimate the presence of methylene groups of different types and length in a given sample. Ramaswamy and Singh (1987) summarized the methylene assignments as a function of the position of the absorption band in the spectrum: R–(CH2)nP6 (721 cm1); R–(CH2)4,5–CH3 (724 cm1); R–(CH2)3–CH3 (728 cm1); R–(CH2)3–R0 (735 cm1); R–(CH2)2–CH3 (739 cm1). The absorption band at 720 cm1 indi-
393
Absorbance (arbitrary units)
P.I. Rosales et al. / Chemosphere 80 (2010) 389–395
4000
A a
D d
B b
E
c
F
e
f
3500
3000
2500
2000
1500
1000
Wavenumber (cm-1)
4000
3500
3000
2500
2000
1500
1000
Wavenumber (cm-1)
Fig. 3. Infrared spectrum of: (a) crude oil as received; (b) S1; (c) S2; (d) S3; (e) S4; and (f) S5.
cates that the polymer was formed by short chains of methylene groups. The infrared spectrum for S4 is characteristic of polyethylene. Due to the high intensity of the main absorption bands in the spectrum for S4, it was difficult to identify the presence of additives or carbonates in the polymer. The infrared spectrum of S5 is shown in Fig. 3f. The spectrum showed functional groups similar to those found in the spectra for S1 and S3 (Fig. 3b and d, respectively). From the position of the absorption bands found in the spectrum near 1419 cm1, S5 also has carbonates. Thus, carbonate was found in the spectra of S1, S3, and S5. Guo et al. (2006) reported the use of sodium carbonate as an alkali component in polymers to enhance oil recovery. In our research, solidifiers that contained carbonate as a functional group performed slightly better than those without carbonate. The infrared spectra of the solidifiers after reacting with Prudhoe Bay crude oil were evaluated as above. The solidifiers were in contact with crude oil for 30 min. After the reaction occurred, the solidified oil was removed from the mixture and rinsed with acetone for 15 min. The whole solidified product was stirred with 20 mL of acetone to remove un-reacted crude oil. Since the solidified oil was rinsed with acetone, the solidifiers as received were also rinsed with acetone, and the infrared spectra were compared with the spectra of solidified oil. In the infrared region for aliphatic methyl and methylene groups, there were no significant changes in the absorption spectrum other than the change in intensity of the bands. Therefore, the analysis of the infrared spectra was focused on the 1800–650 cm1 region. The infrared spectrum of S1 as received, after rinsing with acetone for 15 min, is shown in Fig. 4a. The spectrum showed absorption bands near 1430, 1020, and 873 cm1, indicating the presence of carbonate in the polymer. The spectrum of S1 after reacting with crude oil and rinsing with
acetone is plotted in Fig. 4b. The main difference indicated in Fig. 4a and b was the sharper absorption band at 1450 cm1, which indicates that part of the carbonate reacted with crude oil. The absorption band at 1377 cm1 was also sharper due to the decrease in the band associated with carbonates. The absorption band at 1377 cm1 is characteristic of CH2 CH2CH3 (the propylene group) (Roeges, 1994). Fig. 4c and d shows the infrared spectra of S2 before and after reacting with crude oil, respectively. Methyl and methylene groups were not observed in the spectrum of S2 as received and rinsed in acetone (lack of absorption bands in the 3000–2800 cm1 region). The spectrum from the solidifier after reacting with crude oil showed the absorption bands at 2850, 2920, and the shoulder at 2954 cm1. The absorption bands at 1460 and 1375 cm1 are due to methyl and methylene groups. These presence of these absorption bands in the spectrum indicated that chains of methyl and methylene groups are formed at the surface of the solidified oil. The solidification of crude oil by S3 was investigated (Fig. 4e and f). The spectrum for S3 after reacting with crude oil showed an increase on the absorption bands associated with methyl and methylene groups (2960, 2920, and 2860 cm1). Similar to S1, the band at 1376 cm1 increased in intensity after the solidifier reacted with crude oil. The band at 725 cm1 in Fig. 4f (not shown in Fig. 4e) indicates the formation of methylene chains in the solidified oil. The spectra in Fig. 4g and h was obtained for S4 and oil solidified by S4, respectively. Both infrared spectra are very similar, suggesting that the crude oil was removed from the solidifier surface when the sample was rinsed with acetone. The absorption band at 1600 cm1 in the spectrum is due to aromatic groups in the solidified oil sample. Other slight differences in the spectra were found in the absorption bands near 813 and 873 cm1 associated to aromatic CH groups.
394
P.I. Rosales et al. / Chemosphere 80 (2010) 389–395
e
b
f
c
g
i
Absorbance (arbitrary units)
Absorbance (arbitrary units)
a
j
4000
3000
2000
Wavenumber
d
4000
1000
(cm-1)
h
3000
2000
Wavenumber
1000
(cm-1)
4000
3000
2000
1000
Wavenumber (cm-1)
Fig. 4. Infrared spectrum of (a) S1 rinsing with acetone; (b) oil/S1 after reacting for 30 min and rinsing with acetone; (c) S2 rinsed with acetone; (d) oil/S2 after reacting for 30 min and rinsing with acetone; (e) S3 rinsed with acetone; (f) oil/S3 after reacting for 30 min and rinsing with acetone; (g) S4 rinsed with acetone; (h) oil/S4 after reacting for 30 min and rinsing with acetone; (i) S5 rinsed with acetone; and (j) oil/S5 after reacting for 30 min and rinsing with acetone.
The infrared spectrum for S5 rinsed in acetone is shown in Fig. 4i. The sample absorbed moisture as seen in the broad band around 3400 cm1 and the band near 1640 cm1. The presence of carbonate in the solidifier after rinsing with acetone is shown by the absorption band at 1430 cm1. The rest of the absorption bands were already described by the solidifier as received. The spectrum of S5 after reacting with crude oil is shown in Fig. 4j. The main differences in the spectrum were found in the absorption bands near 1260, 1220, 1174, and 1160 cm1. These bands are associated with stretching of CO bonds in the solidified oil. 8. Conclusions The effectiveness of commercial solidifiers is dependent on the test conditions. In this research the dimensions of the test vessel
(which may account for either water surface area, oil thickness, or water depth), SOR, and solidifier/oil contact time were tested. The results showed no significant changes in the concentration of oil remaining in the vessel (decrease in solidification of oil) as the container size (crude oil surface area) or oil slick thickness increased. Solidifiers removed from 58% to 84% of the crude oil when the SOR was 1:4. For lower solidifier application rates, such as an SOR of 1:16, less solidification by all five products was observed and the crude oil solidified was in the 19–28% range. An increase in the contact time slightly reduced the crude oil remaining in solution (or increased the performance of the solidifiers), although most of the solidifiers reached a stable value after 30 min of contact time. The GC/MS results showed that the solidification process is not selective in terms of oil components. The abundance ratio of n-al-
P.I. Rosales et al. / Chemosphere 80 (2010) 389–395
kane/crude oil and PAH/crude oil showed that solidification of crude oil components is not preferential. Infrared spectroscopic results for the solidifiers used in this study showed similarities among S1, S3, and S5, and the performance of these products was similar under some conditions. The IR spectra of these three solidifiers revealed the presence of carbonate as a functional group in the product formulation, although S3 had the best performance under the experimental conditions tested. Further investigations are needed to determine the mechanisms of the solidification of crude oil by solidifiers and to develop a testing protocol to quantify effectiveness of commercial solidifier products. Acknowledgments This research was supported by the US Environmental Protection Agency’s National Risk Management Research Laboratory, Cincinnati, OH under Contract No. EP-C-05-056. Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.chemosphere.2010.04.036. References Akrami, H.A., Yardim, M.F., Akar, A., Ekinci, E., 1997. FT-IR characterization of pitches derived from Avgamasya asphaltite and Raman-Dinçer heavy crude. Fuel 76, 1389–1394. Bellamy, L.J., 1958. The Infra-red Spectra of Complex Molecules. Methuen, London, UK. Bidwell, J.P., Spotte, S., 1985. Artificial Seawaters. Formulas and Methods. Jones and Bartlett Publishers, Boston, MA. Cardello, E.A., 1996. Oil spill solidifiers for upstream/downstream land applications. Petroleum Environmental Research Forum PERF 94-14. Coates, J.P., Setti, L.C., 1985. Oil, Lubricants, and Petroleum Products. Characterization by Infrared Spectra. Marcel Dekker, New York, NY. Colthup, N.B., Daly, L.H., Wiberley, S.E., 1990. Introduction to Infrared and Raman Spectroscopy. Academic Press, San Diego, CA. Dahl, W.A., Lessard, R.R., Cardello, E.A., 1996. Solidifiers for oil spill response. In: The 1996 3rd International Conference on Health, Safety and Environment in Oil
395
and Gas Exploration and Production. Part 1 (of 2), New Orleans, LA, USA, pp. 803–810. Delaune, R.D., Lindau, C.W., Jugsujinda, A., 1999. Effectiveness of ‘‘Nochar” solidifier polymer in removing oil from open water in costal wetlands. Spill Sci. Technol. Bull. 5, 357–359. Fingas, M., 2008. A review of literature related to oil spill solidifiers 1990–2008. Prince Williams Sound Regional Citizens’ Advisory Council (PWSRCAC), Anchorage, AK. Fingas, M.F., Kyle, D.A., Larouche, N.D., Fieldhouse, B.G., Sergy, G., 1993. Oil-spilltreating agents. Spill Tech. Newslett. 18, 6–14. Fingas, M.F., Kyle, D.A., Larouche, N., Fieldhouse, B., Sergy, G., Stoodley, G., 1995. Effectiveness Testing of Oil Spill-treating Agents. ASTM Special Technical Publication 1252, pp. 286–298. Fingas, M.F., Stoodley, R., Laroche, N., 1990. Effectiveness testing of spill-treating agents. Oil Chem. Pollut. 7, 337–348. Fingas, M.F., Tennyson, E.J., 1991. Chemical treating agents for oil spill responserecent 370 research results. In: Coastal Zone ’91. The Seventh Symposium on Coastal and Ocean 371 Management. Part 3 (of 4), Long Beach, CA, USA, pp. 2491–2500. Ghalambor, A., 1996. The effectiveness of solidifiers for combating oil spills. Louisiana Applied and Educational Oil Spill Research and Development Program. Baton Rouge, LA. Guo, J., Liu, Q., Li, M., Wu, Z., Christy, A.A., 2006. The effect of alkali on crude oil/ water interfacial properties and the stability of crude oil emulsions. Colloids Surf. A 273, 213–218. Ramaswamy, V., Singh, I.D., 1987. Determination of n-paraffinic structure in petroleum fraction by infrared spectroscopy. Fresenius Z. Anal. Chem. 327, 774–776. Roeges, N.P.G., 1994. A Guide to the Complete Interpretation of Infrared Spectra of Organic Structures. John Willey, New York, NY. Slager, T.L., Lindgren, B.J., Mallmann, A.J., Greenler, R.G., 1972. The infrared spectra of the oxides and carbonates of silver. J. Phys. Chem. 76, 940–943. Srinivasan, R., Lu, Q., Sorial, G.A., Venosa, A.D., Mullin, J., 2007. Dispersant effectiveness of heavy fuel oils using the baffled flask test. Environ. Eng. Sci. 24, 1307–1320. Tjomsland, T., Hilland, J., Christy, A.A., Sjöblom, J., Riis, M., Friisø, T., Folgerø, K., 1996. Comparison of infrared and impedance spectra of petroleum fractions. Fuel 75, 322–332. Walker, A.H., Kucklick, J.H., Steen, A.E., Fritz, D., 1995. Oil spill chemicals in freshwater environments: technical issues. In: Proceedings of the 1995 International Oil Spill Conference. American Petroleum Institute, Washington, DC, pp. 1–15. Walker, A.H., Kucklick, J.H., Michel, J., 1999. Effectiveness and environmental considerations for non-dispersant chemical countermeasures. Pure Appl. Chem. 71, 67–81.
Contents lists available at ScienceDirect
Chemosphere journal homepage: www.elsevier.com/locate/chemosphere
A laboratory screening study on the use of solidifiers as a response tool to remove crude oil slicks on seawater Pablo I. Rosales a, Makram T. Suidan a,*, Albert D. Venosa b a b
Department of Civil and Environmental Engineering, University of Cincinnati, Cincinnati, OH 45221-0071, United States Land Remediation and Pollution Control Division, National Risk Management Research Laboratory, US EPA, Cincinnati, OH 45268, United States
a r t i c l e
i n f o
Article history: Received 10 March 2010 Received in revised form 12 April 2010 Accepted 13 April 2010 Available online 7 May 2010 Keywords: Gas chromatography Infrared spectroscopy Oil spills Oil solidifiers Prudhoe Bay crude oil UV–Vis spectroscopy
a b s t r a c t The effectiveness of five solidifiers to remove Prudhoe Bay crude oil from artificial seawater in the laboratory was determined by UV–Vis and GC/MS. The performance of the solidifiers was determined by UV– Vis as a function of solidifier-to-oil mass ratios (SOR), water volume and surface area, and contact time. An SOR of 1:4 solidified crude oil from 58% to 84%. Under more severe test conditions (SOR 1:16) the material with better performance solidified 28% of the oil initially added to water. The percent mass of free oil remaining on the seawater at the end of the contact time was the same when measured by either UV–Vis or by GC/MS. Analyses performed using GC/MS revealed that oil solidification is not a selective process; n-alkenes and polycyclic aromatic hydrocarbons reacted at a similar rate for each solidifier. Infrared Spectroscopy was used to investigate the functional groups in the materials as received. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction Solidifiers are materials that react with oil and change oil from liquid to solid state. Use of solidifiers as a response technique for oil spills on water has been investigated since the early 1970s (Dahl et al., 1996). However, use of solidifiers for oil spill response has some drawbacks. For example, the effectiveness of the treating agents depends on the type and composition of the crude oil tested (Fingas et al., 1990; Fingas and Tennyson, 1991). Another disadvantage of the use of solidifiers in oil spills is the large amount of material that needs to be applied. It has been reported that 16% to over 200% by weight (solidifier–oil mass ratio) is required to solidify crude oil (Fingas et al., 1993, 1995). Therefore, the use of solidifiers to remove slicks of crude oil has received little attention due to a lack of practical application methods and appropriate tests under various conditions and environments (Delaune et al., 1999). Different laboratory effectiveness test have been developed for solidifiers (Fingas et al., 1990). Effectiveness is a major problem with treating agents, since it is generally a function of oil type and composition. For example, solidifiers that are effective on aromatic compounds may not be applicable to polar compounds (Fingas and Tennyson, 1991). Fingas et al. (1993) tested three different solidifiers. The effectiveness test was carried out by adding solidifier (at 1-min intervals) to an oil under constant stirring until the oil * Corresponding author. Tel.: +1 513 556 3695; fax: +1 513 556 2599. E-mail address: [email protected] (M.T. Suidan). 0045-6535/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.chemosphere.2010.04.036
solidifies. The product that performed better in the laboratory tests was tested in a larger scale. They found that it was necessary double the amount used in laboratory to solidify the oil in a real spill. An important factor for testing solidifiers is the aquatic toxicity. Fingas et al. (1995) reported that many products tested by Environment Canada have high and unacceptable aquatic toxicities. The aquatic toxicity for the solidifiers tested by Fingas and coworkers showed that the products were relatively non-toxic. The toxicity was carried out using a standard acute 96-h Rainbow Trout procedure. Cardello (1996) investigated the use of oil spill solidifiers for land applications. The researcher evaluated the final consistency and solidification time for solidifier-to-oil mass ratios (SOR) from 1:1 to 1:4. The solidifiers were tested in laboratory and in field with different oils. The results showed that some solidifiers performed better in field than in laboratory tests. The effect of temperature on the solidification time was also tested and the results showed some solidifiers performed better at lower temperature (1.6 °C), while others performed better at a higher temperature (20 °C). Ghalambor (1996) investigated the performance of 23 solidifiers to remove three crude oils. The solidifiers were tested under static and dynamic (200–400 rpm) conditions and the heat released during the solidification reaction was measured by a solution calorimeter. Ghalambor conclude that the effectiveness of the solidifiers may depend on the level of oil asphaltenes, the paraffin wax content, and the sulfur content. The researcher found
390
P.I. Rosales et al. / Chemosphere 80 (2010) 389–395
that the level of solidifier consumption depends on the kind of crude oil used. Walker et al. (1999) review the effectiveness and environmental considerations for non-dispersant chemical countermeasures and reported that the effectiveness probably decreases for emulsified, weathered, thick, or heavy oils due to the difficulty of mixing the product into viscous liquids. They reported also that salinity has no effect on the solidification of oil. It appears that the performance of solidifiers is unaffected by salinity as reported by Walker et al. (1995) and Fingas (2008). Delaune et al. (1999) also tested a commercial solidifier (Nochar A650) on open water to remove South Louisiana crude oil. The effectiveness test consisted of applying one part of solidifier by two parts of crude oil and let them react for 4 d. After 4 d, the researchers found that over 70% of the crude oil was solidified. More recently, Fingas (2008) reviewed the literature on oil spill solidifiers. Fingas pointed out that the use of solidifiers in recent times is not well-documented and the lack of scientific assessment of solidifier effectiveness at spill scenes. Despite the disadvantages stated above, better knowledge of the chemistry involved in the solidification of oil slicks can lead to the manufacture of cost-effective solidifiers and the development of protocols for testing the appropriateness of using solidifiers to respond to crude oil spills. This paper discusses the effectiveness of five solidifiers to cleanup crude oil spills, as well as the chemical changes during the solidification of crude oil. We analyzed the results found when a solidifier reacts with crude oil, using analytical techniques such as GC/MS, Infrared Spectroscopy (IR) and UV–Vis. 2. Materials and methods Five commercial solidifiers (referred to as S1, S2, S3, S4, and S5) were examined in this study for their effectiveness in removing Prudhoe Bay crude oil from artificial sea water. Artificial seawater, modified GP2 (Bidwell and Spotte, 1985), was used as the exposure medium. The artificial seawater had pH values in the 7.6 ± 0.1 range and its temperature value was 21 ± 1 °C. Pesticide quality dichloromethane (DCM) served as the extraction solvent. The experiments were carried out in silanized beakers to minimize adherence and spreading of crude oil on the walls of the glassware. 3. Experimental procedure A volume of 0.5 mL of Prudhoe Bay crude oil was added to silanized beakers containing 80 mL of artificial seawater. Crude oil and artificial seawater volumes were kept constant in the experiments, while the mass of solidifier changed depending on the SOR tested. Each commercial solidifier was added to a slick of crude oil on artificial seawater and the mixture stirred at 30 rpm with a magnetic stirring bar. The preliminary conditions used to evaluate the effectiveness of solidifiers were: oil surface area (the area changes as a function of the beaker capacity), SOR, and solidifier/oil contact time. Beaker volumes used were 100, 400, and 800 mL. SOR ratios of 1:4, 1:8, and 1:16 were used during the evaluation of solidifiers to estimate the optimized SOR, and the solidifier/oil contact times were 30, 60, 120, and 180 min. The experiments were carried out in triplicate. The resulting data were plotted as the average of triplicate samples; the acceptance criterion for the triplicate samples was a Relative Standard Deviation 625%. All residual crude oil concentrations remaining on the seawater after the solidified oil was removed were measured by UV–Vis spectroscopy. The effectiveness of five solidifiers was also determined by GC/ MS. Each of the solidifiers was added to a slick of crude oil on arti-
ficial seawater in 400-mL silanized beakers at an SOR of 1:16 (0.027 g solidifier–0.447 g of crude oil). After stirring the mixtures at 30 rpm for 30 min, the solidified oil was carefully removed from the artificial seawater with tweezers. The artificial seawater with the remaining oil was transferred from the beakers to 250-mL separatory funnels and spiked with 200 lL of surrogate solution. The experiments were carried out in triplicate for each solidifier. The solutions in the funnels were extracted three times with 20 mL of DCM and the final volume adjusted to 60 mL. A volume of 1 mL of the solution and 20 lL of internal standard were added to a vial, and the sample was later injected into the GC for analysis. This procedure was repeated for residual crude oil samples unexposed to solidifier to determine the recovery of the crude oil. DCM was injected as a blank. 4. UV–Vis spectroscopy An Agilent 8452 UV–Vis spectrophotometer (Agilent Technologies, Palo Alto, CA) was used to measure the residual crude oil concentration remaining on the seawater after removal of the solidified oil. Six standard solutions of oil were prepared to calibrate the UV–Vis spectrophotometer (Srinivasan et al., 2007). The crude oil remaining on the seawater surface was determined by extracting the entire contents of the beaker with DCM after the solidified oil was removed. The solution was extracted three times with 20 mL of DCM, and, if necessary, the final volume of the extract was adjusted to 60 mL by adding DCM. DCM was used as a blank, and the calibration curve was determined by measuring the concentration of the six standard solutions from the lowest to the highest concentration. The crude oil remaining on artificial seawater after being extracted was diluted with DCM when the concentration exceeded the maximum concentration value generated with the calibration curve. The diluted sample was prepared by adding 24 mL of DCM to 1 mL of the extracted solution. The absorbance measurements were recorded at 340, 370, and 400 nm. The concentration was calculated using the trapezoidal rule (Srinivasan et al., 2007). 5. IR The spectra were collected with a Nicolet Magna IR equipment model 760 (Thermo Fisher Scientific, Walthman, MA) with a ZnSe prism and a deuterated triglycine sulfate detector. The horizontal attenuated total reflection technique was used to generate the spectra in the middle infrared region (400–4000 cm1) averaging 64 scans at a resolution of 4 cm1. 6. GC/MS The GC/MS analyses were done using an Agilent 6890 GC with an Agilent 7683 auto sampler (Agilent Technologies, Palo Alto, CA, USA) coupled to an Agilent 5973N mass selective detector. 1 lL of the crude oil extracted was injected for GC/MS analysis in the pulsed splitless mode. A 4 mm id Liner (Agilent Technologies, Palo Alto, CA, USA) with a glass wool tap was used. The inlet initial temperature was 290 °C and high purity helium was the carrier gas. The initial GC oven temperature was 45 °C; the temperature was ramped to 200 °C at 4 °C min1 and then to 310 °C at 10 °C min1. The oven was kept a 310 °C for 10 min. The carrier gas was ultra-high purity helium (0.9 mL min1) with chromatographic separation in a DB-5 ms column (30 m, 0.25 mm internal diameter, 0.25 lm film thickness, J&W Scientific, Folsom, CA, USA). Selected ion monitoring mode was used for the detection and data acquisition. An interface temperature of 300 °C, ion source of 230 °C, and quadrupole of 150 °C were the parameters
391
P.I. Rosales et al. / Chemosphere 80 (2010) 389–395
of the mass spectrometer. Analytical grade n-decane, n-hexane, neicosane, n-triacontane, naphthalene, anthracene, chrysene, perylene, and androstane were used as internal standards. The internal standards were added prior to injection of extract. Analytical grade n-heptadecane, tetracosane, n-dotricontane, 1-methylnaphthalene, phenanthrene, and pyrene were used as surrogates.
7. Results and discussion The initial set of experiments was carried out using an SOR of 1:16 (0.0279 g solidifier–0.447 g crude oil) to determine the effectiveness of the five solidifiers under the worst case scenario. Three different container sizes (100-, 400-, and 800-mL beakers) were used to determine the effect of the surface area of the slick of crude oil on the effectiveness of the solidifiers. The size of the beaker determines the depth and surface area of the water and the thickness of the oil slick (see Supplementary material). Results (see Supplementary material) indicated that the performance of the solidifiers under the conditions tested did not depend on the surface area of the oil slick or the thickness of the crude oil slick. The intermediate container size of 400 mL was selected for subsequent experiments to determine the effects of SOR and the solidifier–crude oil contact time. Again, SOR ratios of 1:4, 1:8, and 1:16 were used in these experiments. As expected, an SOR of 1:4 (0.112 g solidifier–0.447 g crude oil) removed the highest amount of crude oil from the water (Fig. 1a); the smaller the percentage remaining, the greater was the performance. The concentration of crude oil remaining on the artificial seawater ranged from 16% to 43% for solidifiers tested with an SOR of 1:4. These results generally agree with the work done by Delaune et al. (1999) who reported a 70% removal of crude oil using an SOR of 1:2. In our experiments, the crude oil and the artificial seawater volumes were held constant while varying only the amount of solidifier added. The results for a 1:8 SOR (0.0558 g solidifier–0.447 g crude oil) revealed that S2 and S3 performed slightly better than the
other three solidifiers with an average percent remaining unsolidified being approximately 50% for these two solidifiers. At this SOR, the amount of unsolidified crude oil remaining after S1, S4, and S5 reacted was 61.4%, 62% and 58%, respectively, of the crude oil originally added. Similarly, for a 1–16 SOR (0.0279 g solidifier–0.447 g crude oil), unsolidified oil remaining after treatment with the five solidifiers was in the range 72–81% of the initial crude oil. The effectiveness of solidifiers as a function of time was investigated using an SOR of 1–16 in a 400-mL beaker. The results (Fig. 1b) showed that a contact time of 30 min was enough to allow solidification to take place for all five solidifiers tested. Longer contact times resulted in moderate increases in performance in terms of amount of crude oil remaining unsolidified on the water. We concluded that the longer the stirring time, the greater was the likelihood that exposure of all the oil to the solidifier took place. The initial solidification prevented full exposure of the oil to the action of the solidifier, and this resulted in a longer exposure time to achieve the higher performance. The mass of crude oil remaining on the artificial seawater at an SOR of 1:16 was also quantified by GC/MS with results similar to those obtained by UV–Vis spectroscopy. Fig. 2 shows the concentration ratios of the individual n-alkanes and polycyclic aromatic hydrocarbons (PAH) and initial crude oil. The light alkanes volatized during the 30 min exposure of the oil and solidifier, as can seen from the values for nC10, nC11, and nC12 for all five solidifiers. Beyond nC12, the abundance ratios remained constant for all five solidifiers. The ratio of abundance of n-alkanes on seawater and in crude oil was in the range 0.7–0.8 for the five solidifiers. These levels were similar to the percent of crude oil left in artificial seawater obtained by UV–Vis spectroscopy (See Fig. 1a). The concentration ratios of PAH/crude oil were similar to the values obtained for n-alkanes. The GC/MS results indicate that oil solidification is not a selective process in terms of oil components. Attempts to identify the functional groups used in the solidifiers can provide information that might help explain the differences in the performance of the solidifiers observed. To understand better
100
a(a)
1:16 1:8 1:4
b
(b)
30 min 60 min 120 min 180 min
Percent %
80
60
40
20
0 S1
S2
S3
Solidifier
S4
S5
S1
S2
S3
S4
S5
Solidifier
Fig. 1. Percent of the oil remaining unsolidified on artificial seawater as a function of: (a) SOR, and (b) reaction time. Solidifiers reacted for 30 min in the experiments carried out as a function of SOR; the experiments as a function of reaction time were carried out at an SOR of 1:16.
392
P.I. Rosales et al. / Chemosphere 80 (2010) 389–395
Concentration relative to initial crude oil
1.2
1.0
0.8
0.6
0.4 S1 S2 S3 S4 S5
0.2
S1 S2 S3 S4 S5
Naph C1-N C2-N C3-N C4-N Biphenyl Phen F C1 F C2 F C3 F Diben C1 D C2 D C3 D Naphdibthph C1 Naphdibthph C2 Naphdibthph C3 Naphdibthph C1 Phenanthrene C2 Phenanthrene C3 Phenanthrene C4 Phenanthrene C1 Pyrene C2 Pyrene Chrysene C1 Chrysene C2 Chrysene C3 Chrysene C4 Chrysene Coprostane Hopane
nc10 nc11 nc12 nc13 nc14 nc15 nc16 nc17 nc18 nc19 nc20 nc21 nc22 nc23 nc24 nc25 nc26 nc27 nc28 nc29 nc30 nc31 nc32 nc33 nc34 nc35
0.0
Fig. 2. Concentration ratio of the oil remaining unsolidified on artificial seawater and initial crude oil for n-alkanes and polycyclic aromatic hydrocarbons (PAH). The experiments were carried out at an SOR of 1:16. The solidifier was in contact with crude oil for 30 min and the mix was stirred at 30 rpm.
the oil solidification process, the infrared spectra of the materials as they were received were determined to identify the chemical functional groups present before the solidification of oil. The infrared spectrum of Prudhoe Bay crude oil (Fig. 3a) was very similar to the crude oil infrared spectra reported in the literature (Coates and Setti, 1985; Tjomsland et al., 1996). Although crude oil is a mixture of multiple compounds, the infrared spectrum of crude oil identified mainly the presence of methyl and methylene functional groups. The main absorption bands observed in the spectrum were located at 2952, 2921, and 2852 cm1, assigned to asymmetric stretch CH3, asymmetric stretch CH2, and symmetric stretch CH2, respectively (Colthup et al., 1990). The other two main absorption bands observed in the spectrum were located at 1456 and 1377 cm1, assigned to CH in CH3 and CH2 groups in the crude oil. The absorption bands near 1614, 870, 810, and 750 cm1 are characteristic of aromatic groups (Akrami et al., 1997; Guo et al., 2006). The infrared spectrum obtained for S1 as received is shown in Fig. 3b. The spectrum showed absorption bands at 2921 and 2842 cm1, assigned to CH3 and CH2 groups, respectively. The spectrum also revealed a shoulder near 2948 cm1, assigned to CH3. Absorption bands characteristic of carbonates were observed in the infrared spectrum such as the bands located at 1450 and 1376 cm1. Slager et al. (1972) reported doublet absorption bands located at 1460 and 1380 cm1 for silver carbonate. The bands located at 1018 and 873 cm1 in Fig. 3b are also characteristic of carbonates. Slager and coworkers exposed silver oxide to a 50 662 Pa pressure of CO2 and found the formation of new bands at 1020, 880, 1410, and 690 cm1. These bands correspond to vibrations of carbonate species (Slager et al., 1972). The absorption band around 1410 cm1 became a doublet at 1460 and 1380 cm1 when the carbonate was exposed to moisture. Since our experiments were carried out under ambient conditions, S1 adsorbed moisture as seen from the bands near 1450 and 1376 cm1 in Fig. 3b.
The infrared spectrum of S2, an organic solidifier, is plotted in Fig. 3c. The infrared spectrum for S2 showed a broad absorption band near 3300 cm1 assigned to intermolecular hydrogen bonds (Bellamy, 1958). It has been reported that the broad shape is usually attributed to association of alcohol in various polymeric forms, where the broad band is a composite of a number of sharper bands. This absorption band can be assigned to polymeric association in cellulose (Bellamy, 1958). Functional groups that contain CO were found in the spectrum of S2 as shown by the absorption bands located near 1380, 1150, and 1040 cm1, which were assigned to OCH2, CO, and CH2OCH2, respectively. The infrared spectrum of S2 also showed absorption bands associated with carbonyl compounds (ketones). Ketones have characteristic absorption bands near 1715 cm1; the infrared spectrum of S2 showed an absorption band near 1710 cm1 and another band near 1625 cm1, which can be assigned to di-ketones (Colthup et al., 1990). Fig. 3d shows the infrared spectrum of S3, whose features are similar to the spectrum for S1. Methylene functional groups were observed in the infrared spectrum in the 2920–2850 cm1 region, while functional groups associated with carbonate were found by the absorption bands at 1411, 870 and 1020 cm1. The infrared spectrum for S4 (Fig. 3e) is characteristic of a polymer formed by chains of methyl and methylene groups. This spectrum had absorption bands near 2920, 2850, 1470, 1380, and 720 cm1, assigned to methyl and methylene groups. Absorption bands in the 720– 780 cm1 region have been used by many researchers to estimate the presence of methylene groups of different types and length in a given sample. Ramaswamy and Singh (1987) summarized the methylene assignments as a function of the position of the absorption band in the spectrum: R–(CH2)nP6 (721 cm1); R–(CH2)4,5–CH3 (724 cm1); R–(CH2)3–CH3 (728 cm1); R–(CH2)3–R0 (735 cm1); R–(CH2)2–CH3 (739 cm1). The absorption band at 720 cm1 indi-
393
Absorbance (arbitrary units)
P.I. Rosales et al. / Chemosphere 80 (2010) 389–395
4000
A a
D d
B b
E
c
F
e
f
3500
3000
2500
2000
1500
1000
Wavenumber (cm-1)
4000
3500
3000
2500
2000
1500
1000
Wavenumber (cm-1)
Fig. 3. Infrared spectrum of: (a) crude oil as received; (b) S1; (c) S2; (d) S3; (e) S4; and (f) S5.
cates that the polymer was formed by short chains of methylene groups. The infrared spectrum for S4 is characteristic of polyethylene. Due to the high intensity of the main absorption bands in the spectrum for S4, it was difficult to identify the presence of additives or carbonates in the polymer. The infrared spectrum of S5 is shown in Fig. 3f. The spectrum showed functional groups similar to those found in the spectra for S1 and S3 (Fig. 3b and d, respectively). From the position of the absorption bands found in the spectrum near 1419 cm1, S5 also has carbonates. Thus, carbonate was found in the spectra of S1, S3, and S5. Guo et al. (2006) reported the use of sodium carbonate as an alkali component in polymers to enhance oil recovery. In our research, solidifiers that contained carbonate as a functional group performed slightly better than those without carbonate. The infrared spectra of the solidifiers after reacting with Prudhoe Bay crude oil were evaluated as above. The solidifiers were in contact with crude oil for 30 min. After the reaction occurred, the solidified oil was removed from the mixture and rinsed with acetone for 15 min. The whole solidified product was stirred with 20 mL of acetone to remove un-reacted crude oil. Since the solidified oil was rinsed with acetone, the solidifiers as received were also rinsed with acetone, and the infrared spectra were compared with the spectra of solidified oil. In the infrared region for aliphatic methyl and methylene groups, there were no significant changes in the absorption spectrum other than the change in intensity of the bands. Therefore, the analysis of the infrared spectra was focused on the 1800–650 cm1 region. The infrared spectrum of S1 as received, after rinsing with acetone for 15 min, is shown in Fig. 4a. The spectrum showed absorption bands near 1430, 1020, and 873 cm1, indicating the presence of carbonate in the polymer. The spectrum of S1 after reacting with crude oil and rinsing with
acetone is plotted in Fig. 4b. The main difference indicated in Fig. 4a and b was the sharper absorption band at 1450 cm1, which indicates that part of the carbonate reacted with crude oil. The absorption band at 1377 cm1 was also sharper due to the decrease in the band associated with carbonates. The absorption band at 1377 cm1 is characteristic of CH2 CH2CH3 (the propylene group) (Roeges, 1994). Fig. 4c and d shows the infrared spectra of S2 before and after reacting with crude oil, respectively. Methyl and methylene groups were not observed in the spectrum of S2 as received and rinsed in acetone (lack of absorption bands in the 3000–2800 cm1 region). The spectrum from the solidifier after reacting with crude oil showed the absorption bands at 2850, 2920, and the shoulder at 2954 cm1. The absorption bands at 1460 and 1375 cm1 are due to methyl and methylene groups. These presence of these absorption bands in the spectrum indicated that chains of methyl and methylene groups are formed at the surface of the solidified oil. The solidification of crude oil by S3 was investigated (Fig. 4e and f). The spectrum for S3 after reacting with crude oil showed an increase on the absorption bands associated with methyl and methylene groups (2960, 2920, and 2860 cm1). Similar to S1, the band at 1376 cm1 increased in intensity after the solidifier reacted with crude oil. The band at 725 cm1 in Fig. 4f (not shown in Fig. 4e) indicates the formation of methylene chains in the solidified oil. The spectra in Fig. 4g and h was obtained for S4 and oil solidified by S4, respectively. Both infrared spectra are very similar, suggesting that the crude oil was removed from the solidifier surface when the sample was rinsed with acetone. The absorption band at 1600 cm1 in the spectrum is due to aromatic groups in the solidified oil sample. Other slight differences in the spectra were found in the absorption bands near 813 and 873 cm1 associated to aromatic CH groups.
394
P.I. Rosales et al. / Chemosphere 80 (2010) 389–395
e
b
f
c
g
i
Absorbance (arbitrary units)
Absorbance (arbitrary units)
a
j
4000
3000
2000
Wavenumber
d
4000
1000
(cm-1)
h
3000
2000
Wavenumber
1000
(cm-1)
4000
3000
2000
1000
Wavenumber (cm-1)
Fig. 4. Infrared spectrum of (a) S1 rinsing with acetone; (b) oil/S1 after reacting for 30 min and rinsing with acetone; (c) S2 rinsed with acetone; (d) oil/S2 after reacting for 30 min and rinsing with acetone; (e) S3 rinsed with acetone; (f) oil/S3 after reacting for 30 min and rinsing with acetone; (g) S4 rinsed with acetone; (h) oil/S4 after reacting for 30 min and rinsing with acetone; (i) S5 rinsed with acetone; and (j) oil/S5 after reacting for 30 min and rinsing with acetone.
The infrared spectrum for S5 rinsed in acetone is shown in Fig. 4i. The sample absorbed moisture as seen in the broad band around 3400 cm1 and the band near 1640 cm1. The presence of carbonate in the solidifier after rinsing with acetone is shown by the absorption band at 1430 cm1. The rest of the absorption bands were already described by the solidifier as received. The spectrum of S5 after reacting with crude oil is shown in Fig. 4j. The main differences in the spectrum were found in the absorption bands near 1260, 1220, 1174, and 1160 cm1. These bands are associated with stretching of CO bonds in the solidified oil. 8. Conclusions The effectiveness of commercial solidifiers is dependent on the test conditions. In this research the dimensions of the test vessel
(which may account for either water surface area, oil thickness, or water depth), SOR, and solidifier/oil contact time were tested. The results showed no significant changes in the concentration of oil remaining in the vessel (decrease in solidification of oil) as the container size (crude oil surface area) or oil slick thickness increased. Solidifiers removed from 58% to 84% of the crude oil when the SOR was 1:4. For lower solidifier application rates, such as an SOR of 1:16, less solidification by all five products was observed and the crude oil solidified was in the 19–28% range. An increase in the contact time slightly reduced the crude oil remaining in solution (or increased the performance of the solidifiers), although most of the solidifiers reached a stable value after 30 min of contact time. The GC/MS results showed that the solidification process is not selective in terms of oil components. The abundance ratio of n-al-
P.I. Rosales et al. / Chemosphere 80 (2010) 389–395
kane/crude oil and PAH/crude oil showed that solidification of crude oil components is not preferential. Infrared spectroscopic results for the solidifiers used in this study showed similarities among S1, S3, and S5, and the performance of these products was similar under some conditions. The IR spectra of these three solidifiers revealed the presence of carbonate as a functional group in the product formulation, although S3 had the best performance under the experimental conditions tested. Further investigations are needed to determine the mechanisms of the solidification of crude oil by solidifiers and to develop a testing protocol to quantify effectiveness of commercial solidifier products. Acknowledgments This research was supported by the US Environmental Protection Agency’s National Risk Management Research Laboratory, Cincinnati, OH under Contract No. EP-C-05-056. Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.chemosphere.2010.04.036. References Akrami, H.A., Yardim, M.F., Akar, A., Ekinci, E., 1997. FT-IR characterization of pitches derived from Avgamasya asphaltite and Raman-Dinçer heavy crude. Fuel 76, 1389–1394. Bellamy, L.J., 1958. The Infra-red Spectra of Complex Molecules. Methuen, London, UK. Bidwell, J.P., Spotte, S., 1985. Artificial Seawaters. Formulas and Methods. Jones and Bartlett Publishers, Boston, MA. Cardello, E.A., 1996. Oil spill solidifiers for upstream/downstream land applications. Petroleum Environmental Research Forum PERF 94-14. Coates, J.P., Setti, L.C., 1985. Oil, Lubricants, and Petroleum Products. Characterization by Infrared Spectra. Marcel Dekker, New York, NY. Colthup, N.B., Daly, L.H., Wiberley, S.E., 1990. Introduction to Infrared and Raman Spectroscopy. Academic Press, San Diego, CA. Dahl, W.A., Lessard, R.R., Cardello, E.A., 1996. Solidifiers for oil spill response. In: The 1996 3rd International Conference on Health, Safety and Environment in Oil
395
and Gas Exploration and Production. Part 1 (of 2), New Orleans, LA, USA, pp. 803–810. Delaune, R.D., Lindau, C.W., Jugsujinda, A., 1999. Effectiveness of ‘‘Nochar” solidifier polymer in removing oil from open water in costal wetlands. Spill Sci. Technol. Bull. 5, 357–359. Fingas, M., 2008. A review of literature related to oil spill solidifiers 1990–2008. Prince Williams Sound Regional Citizens’ Advisory Council (PWSRCAC), Anchorage, AK. Fingas, M.F., Kyle, D.A., Larouche, N.D., Fieldhouse, B.G., Sergy, G., 1993. Oil-spilltreating agents. Spill Tech. Newslett. 18, 6–14. Fingas, M.F., Kyle, D.A., Larouche, N., Fieldhouse, B., Sergy, G., Stoodley, G., 1995. Effectiveness Testing of Oil Spill-treating Agents. ASTM Special Technical Publication 1252, pp. 286–298. Fingas, M.F., Stoodley, R., Laroche, N., 1990. Effectiveness testing of spill-treating agents. Oil Chem. Pollut. 7, 337–348. Fingas, M.F., Tennyson, E.J., 1991. Chemical treating agents for oil spill responserecent 370 research results. In: Coastal Zone ’91. The Seventh Symposium on Coastal and Ocean 371 Management. Part 3 (of 4), Long Beach, CA, USA, pp. 2491–2500. Ghalambor, A., 1996. The effectiveness of solidifiers for combating oil spills. Louisiana Applied and Educational Oil Spill Research and Development Program. Baton Rouge, LA. Guo, J., Liu, Q., Li, M., Wu, Z., Christy, A.A., 2006. The effect of alkali on crude oil/ water interfacial properties and the stability of crude oil emulsions. Colloids Surf. A 273, 213–218. Ramaswamy, V., Singh, I.D., 1987. Determination of n-paraffinic structure in petroleum fraction by infrared spectroscopy. Fresenius Z. Anal. Chem. 327, 774–776. Roeges, N.P.G., 1994. A Guide to the Complete Interpretation of Infrared Spectra of Organic Structures. John Willey, New York, NY. Slager, T.L., Lindgren, B.J., Mallmann, A.J., Greenler, R.G., 1972. The infrared spectra of the oxides and carbonates of silver. J. Phys. Chem. 76, 940–943. Srinivasan, R., Lu, Q., Sorial, G.A., Venosa, A.D., Mullin, J., 2007. Dispersant effectiveness of heavy fuel oils using the baffled flask test. Environ. Eng. Sci. 24, 1307–1320. Tjomsland, T., Hilland, J., Christy, A.A., Sjöblom, J., Riis, M., Friisø, T., Folgerø, K., 1996. Comparison of infrared and impedance spectra of petroleum fractions. Fuel 75, 322–332. Walker, A.H., Kucklick, J.H., Steen, A.E., Fritz, D., 1995. Oil spill chemicals in freshwater environments: technical issues. In: Proceedings of the 1995 International Oil Spill Conference. American Petroleum Institute, Washington, DC, pp. 1–15. Walker, A.H., Kucklick, J.H., Michel, J., 1999. Effectiveness and environmental considerations for non-dispersant chemical countermeasures. Pure Appl. Chem. 71, 67–81.