OIL DISPERSANT FORMULATION, METHODS AND USES THEREOF

Abstract

The present disclosure relates to an oil dispersant composition for dispersing a crude oil or a petrochemical spill comprising at least 20% (w/w) of a gum comprising a mannosylerythritol lipids mixture; at least 10% (w/w) polyethylene glycol sorbitan ester; and at least 20% (w/w) of a hydrophobic organic solvent, wherein said organic solvent has a flash point superior to the crude oil or the petrochemical spill flash point, preferably superior to 60 C. The disclosure also relates to a method for obtaining said composition as well as a method for dispersing an oil spill, comprising the step of applying the disclosed oil dispersant composition with an oil present in a body of water.

Claims

1. An oil dispersant composition for dispersing a crude oil or a petrochemical spill, comprising: at least 20% (w/w) of a gum comprising a mixture of mannosylerythritol lipids mixture; at least 10% (w/w) polyethylene glycol sorbitan ester; and at least 20% (w/w) of a hydrophobic organic solvent, wherein said organic solvent has a flash point superior to the crude oil or the petrochemical spill flash point.

2. The oil dispersant composition according to claim 1, comprising 35-45% (w/w) of the gum comprising a mannosylerythritol lipids mixture; 25-30% (w/w) of polyethylene glycol sorbitan ester; and 25-35% (w/w) of the hydrophobic organic solvent.

3. (canceled)

4. The oil dispersant composition according to claim 1, wherein the polyethylene glycol sorbitan ester is polyethylene glycol sorbitan monooleate.

5. The composition according to claim 1, wherein the number of carbons in the fatty chains of the mannosylerythritol lipids range from C8 to C12.

6. The oil dispersant composition according to claim 1, wherein at least 50% (w/w) of the fatty chains of mannosylerythritol lipids are C10 chain.

7. The oil dispersant composition according to claim 1, wherein the mannosylerythritol lipids are selected from a list consisting of di-acetylated mannosylerythritol lipid, mono-acetylated mannosylerythritol lipid, de-acetylated mannosylerythritol lipid, or mixtures thereof.

8. The oil dispersant composition according to claim 1, wherein the gum comprises a mixture of: at least 50% (w/w) of di-acetylated mannosylerythritol lipid; 15% (w/w) to 50% (w/w) of mono-acetylated mannosylerythritol lipid; and less than 35% (w/w) of de-acetylated mannosylerythritol lipid.

9. (canceled)

10. The oil dispersant composition according to claim 1, wherein the solvent comprises 65-70% (v/v) of a lighter fuel and 30-35% (v/v) of 2-ethylhexyl acetate.

11. (canceled)

12. The oil dispersant composition according to claim 1, wherein the mass ratio between mannosylerythritol lipids and polyethylene glycol sorbitan ester is 60:40.

13. The oil dispersant composition according to claim 1, wherein the hydrophilic-lipophilic balance ranges from 8 to 20.

14. (canceled)

15. A method for obtaining an oil dispersant composition, said oil dispersant composition comprising at least 20% (w/w) of a gum comprising a mixture of mannosylerythritol lipids, at least 10% (w/w) polyethylene glycol sorbitan ester, and at least 20% (w/w) of a hydrophobic organic solvent, wherein said organic solvent has a flash point superior to the crude oil or the petrochemical spill flash point, the method comprising the following steps: obtaining a gum comprising mannosylerythritol lipids mixture; blending the mannosylerythritol lipids mixture with polyethylene glycol sorbitan ester and with a solvent base.

16. The method for obtaining an oil dispersant composition according to claim 15, wherein the solvent base comprises 65-70% (v/v) of lighter fuel and 30-35% (v/v) of 2-ethylhexyl acetate.

17. A method for dispersing an oil spill, comprising a step of applying an oil dispersant composition into an oil in a body of water, wherein the oil dispersant composition comprises: at least 20% (w/w) of a gum comprising a mixture of mannosylerythritol lipids; at least 10% (w/w) polyethylene glycol sorbitan ester; and at least 20% (w/w) of a hydrophobic organic solvent, wherein said organic solvent has a flash point superior to the crude oil or the petrochemical spill flash point.

18. The method of claim 17, wherein the oil dispersant composition is applied to the oil in a dispersant to oil ratio ranging from 1:1000 to 1:20.

19. The method according to claim 17 wherein the oil dispersant composition is applied to the oil in a dispersant to oil ratio ranging from 1:900 to 1:500.

20. The method according to claim 17, wherein the dynamic dispersion effectiveness of the oil dispersant composition in the body of water ranges from 95 to 100% at 22 C.

21. The method according to claim 17, wherein the static dispersant effectiveness of the oil dispersant composition in the body of water ranges from 45 to 70% at 13 C.

22. The method according to claim 17, wherein the interfacial tension between the oil and the body of water, in the presence of the oil dispersant composition, is below 0.030 mN/m at 20 C.

23. The method according to claim 17, wherein the dynamic interfacial tension between the oil and the body of water, in the presence of the oil dispersant composition ranges between 0.04 to 0.002 mN/m at a dispersant to oil ratio of 1:20, from 5 C. to 60 C.

24. The method according to claim 17, wherein the body of water has a salinity ranging from 0 to 5 wt %.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The following figures provide preferred embodiments for illustrating the disclosure and should not be seen as limiting the scope of invention.

[0044] FIG. 1: Embodiment of the dynamic interfacial tension (IFT) of weathered 200 C.+ Troll B oil and IFO 180 bunker fuel oil in seawater (20-22 C.). Oils were premixed with Corexit 9500A (DOR 1:50) or with the MEL-based oil dispersant formulation (M+T) (DOR 1:20). DOR: dispersant-to-oil ratio.

[0045] FIG. 2: Embodiment of the effect of dispersant-to-oil ratio (DOR) on the interfacial tension (IFT) (0-300 s) of MEL-based oil dispersant formulation (M+T)Troll B or and Corexit 9500A-Troll B systems (20-22 C.).

[0046] FIG. 3: Embodiment of the dispersion effectiveness (DE) for the MEL-based oil dispersant formulation (M+T) or Corexit 9500A in fresh Troll B oil as obtained in the Baffled Flask Test (BFT) (25 C.). R1-3 are BFT replicates. DOR: dispersant-to-oil ratio.

[0047] FIG. 4: Embodiment of the dispersion effectiveness (DE) for the MEL-based oil dispersant formulation (M+T) and Corexit 9500A in weathered 200 C.+ Troll B oil and IFO 180 bunker fuel oil as obtained in the Mackay Nadeau Steelman Test (13 C.). DOR: dispersant-to-oil ratio.

[0048] FIG. 5: Embodiment of the total hydrocarbon content (THC) present after 7 days of incubation, at 25 C., in sea water and Bushnell-Haas (BH) media contaminated with crude oil (50 mg/L) (Control), contaminated with crude oil (50 mg/L) and mixed with the oil dispersant formulations: Corexit 9500A (I); disclosed MEL-based oil dispersant formulation (II), oil dispersant formulation inhere disclosed (TWEEN 80+solvent base), but without MELs (III), and MELs alone as dispersant (IV). Formulations I, II, III were used at a DOR of 1:20 and formulation IV at a DOR of 1:48 (ensuring formulation II and IV contain the same amounts of MELs).

DETAILED DESCRIPTION

[0049] The present disclosure relates to an oil dispersant composition for use in the treatment of marine or soil oil spills, wherein the resulting oil dispersed particles are biodegradable. This efficient and environmentally friendly oil dispersant can be used for many industrial applications, particularly for oil spill clean-up operations. In oil industry, oil dispersants and surfactants can be used for oil spill response applications, enhanced oil recovery processes and flow assurance operations.

[0050] The rising environmental concerns and emergence of stricter regulations on oil recovery, transportation, and clean-up operations has forced the oil and gas sector to seek alternatives to the use of synthetic oil dispersants. The disclosed oil dispersant composition, based on the mannosylerythritol lipid (MEL), exhibits excellent interfacial properties and dispersion effectiveness (DE) with crude oils under different environmental conditions. In particular, when applied to weathered and heavy fuel oils the, use of the MEL-based oil dispersant formulation exhibits considerably better DE results than when applied the more often commercially used oil dispersant, Corexit 9500A. Unlike synthetic oil dispersants, the MELs based dispersant is stable at a wide range of temperatures, pH and ionic strength, and have high biodegradability and low toxicity.

Example

[0051] In an embodiment, MELs used in the formulation of the disclosed MEL-based oil dispersant are produced from M. antarcticus using conditions previously described [12]. Cultivation starts with initial 40 g/l of D-glucose and after 4 days of cultivation, 20 g/l waste frying oil (WFO) is added. After 10 days, cultivation of M. antarcticus is extracted with ethyl acetate twice and the organic phase is collected and evaporated. The obtained orange gum has a purity in MELs of 88-90%. The ratio of the different MELs in this mixture is 68% (w/w) of di-acetylated (MEL-A), 28% (w/w) of mono-acetylated (MEL-B and -C) and 4% (w/w) of de-acetylated (MEL-D). The MELs' fatty acid chains range from C8 to C12 with 82% (w/w) of C10. The HLB for the MEL mixture is 8.6. MELs are then blended with polyethylene glycol sorbitan monooleate and the solvent base, at room temperature, for 2 h (500 rpm). Afterwards, the composition was stored at room temperature.

[0052] In an embodiment, the MEL-based oil dispersant formulation, comprises a blend of 42% w/w of a gum comprising a mixture of MELs (hydrophilic-lipophilic balance, HLB, 8.6), 28% w/w of polyethylene glycol sorbitan monooleate (HLB 15), and 30% w/w of a solvent base. The solvent base contains 66.7% (v/v) lighter fuel and 33.3% (v/v) of 2-ethylhexyl acetate.

Interfacial Tension Measurements of the MEL-Based Oil Dispersant Formulation.

[0053] In an embodiment, the IFT measurements are performed between crude oil and seawater in a Spinning Drop Tensiometer (SVT-20 N with SVTS 20 control and calculation software DataPhysics Instruments GmbH, Filderstadt, Germany) with a heating/refrigerated circulator for temperature control (F12-ED, Julabo GmbH, Seelbach, Germany). Prior to each measurement, the capillary tube is rinsed three times with dichloromethane, once with toluene, dried with nitrogen gas, rinsed three times with deionized water, dried with nitrogen gas, and then rinsed once with seawater. The capillary is carefully filled with seawater to ensure the absence of air bubbles. After the filling of capillary with seawater, closed the open side of the capillary with a septum held in the septum holder and inserted the fast exchange capillary into the measuring cell. Crude oil (10-30 L), premixed with dispersant, or crude oil without dispersant (control), is injected into the stationary capillary tube using a 1 mL syringe with a long needle. Rotation is then immediately started and IFT measurements are initiated immediately after placing the droplet in the capillary.

[0054] The spinning drop tensiometer works by measuring the radius of oil phase under the high rotational speed using an optical microscope connected to a computer for data acquisition and calculations. The IFT is calculated using the following expression:

[00002]$\begin{array}{cc}=\frac{{}^2{R}^3}{4}& \left(\mathrm{Equation}2\right)\end{array}$

Where (mN/m) is the interfacial tension (IFT) between oil and water phase; (g/cm3) is the density difference between the crude oil droplet and seawater; (rad/s) is the angular velocity, and R (cm) is the droplet radius.

[0055] During the first 5 min, IFT is measured after every 5 s and after this IFT is recorded after interval of 30 s. The IFT measurements are done on multiple droplets and standard deviations are typical 0.2 mN/m for high IFT values (1-20 mN/m) and 0.01 mN/m for low IFT values (0.001-0.9 mN/m).

[0056] In an embodiment, crude oils were pre-heated at 50 C. for 1 h and afterwards mixed with different formulations of oil dispersants at a specific DOR at room temperature for 3 h (500 rpm).

[0057] For the scope and interpretation of the present disclosure it is defined that room temperature should be regarded as a temperature between 15-30 C., preferably between 18-25 C., more preferably between 20-22 C.

[0058] In an embodiment, the MEL-based oil dispersant formulation was premixed with crude oils at a 1:20 DOR. Corexit 9500A was used at a 1:50 DOR as a reference since such dosage yielded the lowest IFT in previous laboratory studies. The overall results obtained, using the MEL-based oil dispersant formulation, indicate that with different types of crude oil, the initial (t=0 to t=100 s) and final IFT (after 60 min) vary between 0.006 to 0.070 mN/m, and between 0.002 to 0.070 mN/m, respectively (Table 1). No leaching from the oil/water interface is observed when used the MEL-based oil dispersant formulation with any type of crude oil. Furthermore, for all different types of crude oil assessed, the kinetics of the MEL-based oil dispersant formulation are very fast as the IFT is immediately reduced 1000 times. On the contrary, with Corexit 9500A, the initial and final IFT of different types of crude oil vary between 0.006 to 0.14 mN/m, and between 0.006 to 0.19 mN/m, respectively. Moreover, some leaching/desorption of Corexit 9500A is observed from the interface between IFO 180 bunker fuel oil and seawater (FIG. 1).

TABLE-US-00001 TABLE 1 Interfacial tension (IFT) of different types of crude, weathered and fuel oils in seawater measured at 20 C. Oils were premixed with Corexit 9500A or with the MEL-based oil dispersant formulation (M + T) at DOR of 1:50 and 1:20 respectively. IFT IFT IFT IFT (mN/m) (mN/m) (mN/m) (mN/m) 0-100 s 60 min 0-100 s 60 min Corexit Corexit M + T M + T 9500A 9500A (DOR (DOR (DOR (DOR Oil types 1:20) 1:20) 1:50) 1:50) Fresh Troll B 0.030 0.020 0.050 0.050 Weathered 200 C. + Troll B 0.004 0.002 0.010 0.006 Norne 2 0.030 0.008 0.020 0.010 Oseberg A 0.040 0.020 0.007 0.006 Diesel Fuel 0.070 0.070 0.050 0.040 IFO 180 Bunker Fuel 0.030 0.030 0.100 0.200 DOR: dispersant-to-oil ratio.

[0059] In an embodiment, for the naphthenic crude oil (fresh Troll B oil) with the MEL-based oil dispersant formulation, the IFT is reduced from an average value of 9 mN/m to 0.030 mN/m between t=0 to t=100 s, and after 1 h the IFT is further reduced to 0.02 mN/m. For fresh Troll B oil, a higher reduction in the IFT is observed with the MEL-based oil dispersant formulation than with Corexit 9500A. For weathered 200 C.+ Troll B oil, with the MEL-based oil dispersant formulation displays even lower IFT values are achieve than the ones obtained for fresh Troll B oil with the same formulation. For the waxy crude oil (Norne 2), the IFT results obtained with MEL-based oil dispersant formulation or Corexit 9500A. More precisely, the MEL-based oil dispersant formulation and Corexit 9500A reduced, respectively, the IFT to 0.03 mN/m and 0.02 mN/m (0-100 s) and to 0.008 mN/m and 0.010 mN/m (after 60 min). For the asphaltenic crude oil (Oseberg A) and the marine diesel oil (MDO), Corexit 9500A displayed lower IFT values than the MEL-based oil dispersant formulation (Table 1). Finally, for the high-density and highly asphaltenic IFO 180 bunker fuel oil, the MEL-based oil dispersant formulation displays much better IFT results than Corexit 9500A, with average IFT (after 60 min) of 0.03 and 0.20 mN/m, respectively.

[0060] In an embodiment, for high density, weathered, highly asphaltenic and highly viscous oils the results indicate that the MEL-based oil dispersant formulation works comparatively better than Corexit 9500A. These results are very surprising and encouraging as it is commonly difficult to reduce the IFT of highly asphaltenic, waxy and weathered oils.

[0061] In an embodiment, there is no apparent effect of the variable temperature on the IFT of naphthenic crude oil (fresh Troll B oil) premixed with MEL-based oil dispersant formulation (Table 2). The effect of temperature is also tested in weathered 200 C.+ Troll B oil premixed with MEL-based oil dispersant formulation or with Corexit 9500A. At 5 C., Corexit 9500A displays lower IFT values than the MEL-based oil dispersant formulation. Still, the IFT was significantly reduced by the MEL-based oil dispersant formulation, ranging from 0.007 to 0.009 mN/m. Interestingly, it was noticed a constant IFT along the experimental time, compatible with the absence of a leaching phenomenon. At 20 C., both Corexit 9500A and the MEL-based oil dispersant formulation display very low IFT values, but the IFT results were comparatively better with the MEL-based oil dispersant formulation, ranging from 0.002 to 0.004 mN/m. At 60 C. Corexit 9500A displays slightly better results than the MEL-based oil dispersant formulation. The IFT results indicate that the large variation among temperatures did not reduce the DE of the MEL-based oil dispersant formulation and IFT values were in the range of 0.002-0.02 mN/min.

TABLE-US-00002 TABLE 2 Interfacial tension (IFT) of the naphthenic crude oil (fresh and weathered 200 C. + Troll B oil) at different temperatures. Oils were premixed with Corexit 9500A and the MEL-based oil dispersant formulation (M + T) at DOR of 1:50 and 1:20 respectively. IFT IFT IFT IFT (mN/m) (mN/m) (mN/m) (mN/m) 0-100 s 60 min 0-100 s 60 min Corexit Corexit M + T M + T 9500A 9500A (DOR (DOR (DOR (DOR Oil types 1:20) 1:20) 1:50) 1:50) Fresh Troll B (5 C.) 0.040 0.040 0.020 0.003 Fresh Troll B (20 C.) 0.030 0.020 0.050 0.050 Fresh Troll B (60 C.) 0.050 0.040 0.010 0.010 Weathered 200 C. + Troll B 0.007 0.009 0.002 0.001 (5 C.) Weathered 200 C. + Troll B 0.004 0.002 0.010 0.006 (20 C.) Weathered 200 C. + Troll B 0.020 0.010 0.020 0.008 (60 C.) DOR: dispersant-to-oil ratio.

[0062] In an embodiment, the IFT between naphthenic oil (fresh Troll B) and seawater was also evaluated as function of the dispersant dosage or dispersant-to-oil ratio (DOR). The use of MEL-based oil dispersant formulation and Corexit 9500A were compared. The results clearly indicate that at low DOR (1:1000 and 1:500) the DE of the MEL-based oil dispersant formulation is better, while at moderate (1:100 to 1:250) and higher DOR (1:50 and 1:25), Corexit 9500A displays slightly better IFT results than the MEL-based oil dispersant formulation (FIG. 2).

Dispersibility Tests of the MEL-Based Oil Dispersant Formulation

[0063] Several standardized methods for evaluating the effect of dispersants have been developed over the last decades. The mixing energy input differs in different test methods, so the DE results obtained reflect the mixing energies.

[0064] Mackay-Nadeau-Steelman (MNS) test [13] is estimated to represent a moderate to high sea-state condition. Oil dispersibility requires high energy, which on the sea is generated by the breaking waves during dispersion. In the laboratory, the energy input is supplied by blowing air across the oil/water surface to produce a circular wave motion. In an embodiment, Troll B 200 C.+ and IFO 180 were included for dispersibility tests. Oil (10 mL) was applied to 6 liters of seawater and then the dispersant was injected on the oil surface at a DOR of 1:25 for Corexit 9500A and 1:20 for the MEL-based oil dispersant formulation. The oil is confined in a ring on the seawater surface. By removing the ring, the pre-treated oil is released and mixed naturally into the water column during the wave activity. After 5 min of mixing, 500 mL of the oil dispersion was sampled from the system, oil was extracted using dichloromethane liquid-liquid extraction and extracts were analyzed in an ultraviolet spectrophotometer at 410 nm for determining the dynamic dispersion effectiveness (%). After sampling for determining the dynamic DE, mixing was stopped, and another sample was taken 5 min later to determine the static dispersion effectiveness (%).

[0065] In an embodiment, Baffled Flask Test (BFT) was performed according to modifications introduced by Zhang et al. [14] to the method developed by Sorial et al. [15]. Moreover, in these assays natural seawater was used instead of artificial seawater. Initially, 120 mL of natural seawater was added to a baffled flask and then 100 L of fresh Troll B was carefully added to the seawater surface using a 100-L pipette. Afterwards, 4 L of either Corexit 9500A or MEL-based oil dispersant formulation was added onto the center of the oil slick. The flask was shaken at a rotation speed of 200 rpm on an orbital shaker (ELMI DOS-20L Digital Orbital Shaker 20 mm). After shaking for 10 min, the flask was left stationary for another 10 min. Then 2 mL of the mixture was discarded through a stopcock at the bottom of the flask before and then 30 mL of the sample was collected into a 50-mL measuring cylinder. The 30 mL sample was then poured into a separatory funnel and extracted with 5 mL dichloromethane (DCM, HPLC grade) for three times. Anhydrous sodium sulfate was added into the extract to remove water that may be contained in solvent. Afterwards, the extract was adjusted to a volume of 20 mL for determination of DE by ultraviolet spectrophotometry. The BFT was run in triplicate for each dispersant.

[0066] In an embodiment, standard crude oil solutions were prepared for calibrating the ultraviolet spectrophotometer (UVS). Volumes of 5, 10, 15, 20, and 25 L Troll B crude oil were added, using a syringe, to 30 mL of dichloromethane (DCM) (HPLC grade), respectively. These Troll B in DCM solutions were regarded as standard references representing DE of 20, 40, 60, 80, and 100%. UVS was employed to measure the absorbance. The absorbance of the extracts was measured at three wavelengths: 340, 370, and 400 nm. The area under the absorbance vs. wavelength curve between 340 and 400 nm was regarded as the relative concentration of dissolved oil [16], and was determined by the following equation using the trapezoidal rule:

[00003]$\begin{array}{cc}\mathrm{Area}=\frac{\left({\mathrm{Abs}}_{340}+{\mathrm{Abs}}_{370}\right)30}{2}+\frac{\left({\mathrm{Abs}}_{370}+{\mathrm{Abs}}_{400}\right)30}{2}& \left(\mathrm{Equation}3\right)\end{array}$

[0067] DE can be calculated as the ratio of the area of dispersed oil to the area of total oil added to the system (equals to the corresponding volume of oil dissolved in DCM). The standard curve was plotted using the value of area to DE. The coefficient of determination should be larger than 0.99.

Baffled Flask Tests

[0068] FIG. 3 shows the dispersion effectiveness (DE) of Corexit 9500A of the MEL-based oil dispersant formulation for fresh Troll B oil evaluated by the Baffled Flask Test (BFT). For the MEL-based oil dispersant formulation, DE ranges from 93 to 94%, whereas for Corexit 9500A DE ranges from 93 to 95%. The DE obtained for fresh Troll B oil alone (without dispersant) is usually below 10%. The BFT results indicate a high dispersibility of fresh Troll B oil both using MEL-based and the Corexit 9500A oil dispersants. The results may, however, be misleading because of the high shear imparted on the oil-water mixtures. The use of alternative dispersibility tests like the MNS test can help to elucidate differences between both dispersants' efficacy.

Mackay-Nadeau-Steelman Tests

[0069] For the Mackay-Nadeau-Steelman dispersibility test (MNS), weathered oil 200 C.+ Troll B and heavy IFO 180 bunker fuel oil were selected as target oils. The MNS results show a 100% dynamic DE with both dispersants. The control sample of weathered 200 C.+ Troll B oil (without oil dispersant) also shows 78% DE, indicating that the mechanical energy of the wave generated in the system for mixing, is a major contributor to the dynamic DE.

[0070] In addition to the dynamic DE, the static DE was also estimated 5 min after mixing has been stopped. The static DE shows a relatively high dispersibility of IFO 180 bunker fuel oil (i.e., >60%), both for the MEL-based oil dispersant formulation and Corexit 9500A (FIG. 4). For weathered 200 C.+ Troll B oil, Corexit 9500A had a higher DE (60%) than the MEL-based oil dispersant formulation (45%). A different DOR was used for each dispersant based on their effective dosage.

Mechanism for Interfacial Tension Reduction and Dispersibility by the MEL-Based Oil Dispersant Formulation

[0071] The overall results show that the MEL-based oil dispersant formulation exhibits excellent IFT and dispersibility results and are comparable with a standard and key dispersant for the industry (i.e., Corexit 9500A). Moreover, for the highly asphaltenic and high-density crude oils the IFT results are even better for MEL-based oil dispersant formulation than for Corexit 9500A.

[0072] In an embodiment, the results can be explained by providing the molecular level discussion of the synergy between MEL and polyethylene glycol sorbitan monooleate molecules. As explained earlier, MELs are hydrophobic and polyethylene glycol sorbitan monooleate is quite hydrophilic and water soluble. The HLB of the combination of the two surfactants can be calculated by the following expression:

[00004]$\begin{array}{cc}\mathrm{HLB}=8.6W_M+15W_{\mathrm{PGSE}}& \left(\mathrm{Equation}4\right)\end{array}$

[0073] Where, W.sub.M and W.sub.PGSE are, respectively, the weight fraction of MELs and polyethylene glycol sorbitan ester, in particular polyethylene glycol sorbitan monooleate, in the blend. Previous studies [17, 18] showed that HLB in the range of 9-12 may be optimal for creating the efficient dispersant for OSR application. In an embodiment, the lowest IFT with fresh Troll B oil (0.01 mN/m) was achieved at a 60:40 ratio (w/w) of MELs and polyethylene glycol sorbitan monooleate (TWEEN 80) (42% (w/w) MELs+28% (w/w) TWEEN 80+30% (w/w) Solvent base) where HLB is 11.6.

[0074] Previous studies by Athas et al. [17] and Jin et al. [18] reported that the dispersant mixture of Lecithin (L) and TWEEN 80 (T) at the 60:40 ratio (w/w) with an HLB value of 10.8 exhibited the best emulsification results with crude oil. They found that the L/T blend shows a synergistic effect, but neither L nor T is effective on its own. Moreover, Shah et al. [19] also studied that the stable O/W emulsion formed at an optimal ratio of 60:40 (w/w) of lactonic sophorolipid and choline laurate (ionic surfactant). Moreover, the minimum IFT achieved with L/T and sophorolipid/choline laurate mixtures against the crude oil/seawater interface was 0.075 mN/m and 1.5 mN/m respectively.

[0075] The synergy between MELs and T is likely due to the strong Van der Waals forces between the hydrocarbon chains of both surfactant molecules. Beside the tail interaction, there also exists a favorable interaction between the mannose and oxyethylene head groups of MELs and T molecules, respectively. Athas et al. [17] suggested that the oxyethylene head group of a T molecule also provides the steric stabilization to the oil droplet by extending into the water phase. The combination of both Van der Waals forces and stabilization of oxyethylene head groups creates a very stable interfacial film at the crude oil/water interface. Such stability prompts a quick decrease in the IFT and prevents the desorption of MEL and T molecules from the interface.

Comparison of the MEL-Based Oil Dispersant Formulation with Other Solutions

[0076] One of the main advantages of using the MEL-based oil dispersant formulation for OSR and EOR applications is the combination of both high DE in crude oil and stability of the resulting emulsions. In an embodiment, the MEL-based oil dispersant formulation was compared with two examples of green and/or efficient oil dispersants known from the state of the art: L/T-based oil dispersant [17, 18], and an ionic liquids-based oil dispersant (namely a combination of 1-butyl-3-methylimidazolium lauroylsarcosinate, 1,1-(1,4-butanediyl)bis(1-H-pyrrolidinium, which are environmentally problematic and not biobased) dodecylbenzenesulfonate, tetrabutylammonium citrate, tetrabutylammonium polyphosphate and tetrabutylammonium ethoxylate oleyl ether glycolate as described in Baharuddin et al. [20]). The L/T blend shows a synergetic action, when the two surfactants are combined at the oil/water interface, on further enhancing the emulsification capacity of the dispersant. The ionic liquids-based oil dispersant is presented as a biodegradable and non-toxic solution.

[0077] Unlike the L/T-based oil dispersant described in Jin et al. [18], the MEL-based oil dispersant formulation shows no desorption/release of surfactant molecules from the crude oil (fresh Troll B oil)/seawater interface, at temperatures between 5 and 60 C. and from high (1:25) to moderate DOR (1:100). The phenomenon of surfactant desorption (leaching) can be expressed as either an increase in the IFT of the oil dispersant mixture or an increase in the mean diameter of the emulsion, as reported by Jin et al. [18]. In addition, the formulation used by Jin et al. [18] contains an ethanol base which is not adequate for OSR application. Selected solvents should have a low toxicity, high flash point (i.e., >60 C.) and yield a good oil dispersion (low viscosity).

[0078] The MEL-based oil dispersant formulation exhibits much lower IFT values (0.002 mN/m) than the L/T blend (0.08 mN/m) and stable dynamic behavior for several types of crude oil and at a wide range of temperature values. This suggests that MEL and T molecules pack more closely at the oil/water interface. The condensed packing at the interface can be due to favorable interactions between the tail and head group of both MEL and T molecules. The common structure of MELs has two fatty acid tails, which are C8-C12 in length (hydrophobic chain), and a mannosylerythritol head group (hydrophilic head). On the other hand, T has an oleyl tail, which is C18 and three hydrophilic oxyethylene head groups.

[0079] The MEL-based oil dispersant formulation also shows higher DE (94%) for fresh Troll B oil at DOR 1:25, during BFT tests, than the ionic liquids-based oil dispersant for Arab and Ratawi crude oil. [20]. The MEL-based oil dispersant formulation presents ultra-low IFT values (0.010-0.002 mN/m) in weathered 200 C.+ Troll B oil after 1 h at 5 and 60 C. (DOR 1:20). Despite IFT measurements for the ionic liquids-based oil dispersant in Arab crude oil also showed ultra-low IFT values (0.006-0.004 mN/m) at 25 C. and 50 C. (DOR 1:10), Baharuddin et al. [20] do not specify the time considered for measurements. Baharuddin et al. [20] also report a considerable increase in the IFT between 25 to 50 C. at low salinity (i.e., <3 wt. %).

Evaluation of the MEL Based Oil Dispersant Formulations Toxicity in a Marine Environment

[0080] In an embodiment, a standardized protocol was used to evaluate the toxicity of the MEL-based oil dispersant formulation in a marine environment, following a 24 h LC.sub.50 bioassay using brine shrimp (Artemia) and its hatching. This bioassay was conducted according to the standard operational procedures of the marine toxicity screening test Artoxkit M, obtained from Microbiotests Inc., using instar II-III larvae of the brine shrimp Artemia franciscana hatched from cysts, standard seawater medium with a salinity of 35 ppt and a 24 multiwell test plate, provided in the commercial kit.

[0081] In an embodiment, the hatching of the cysts, carried out through exposure to a light source (minimum of 3000-4000 lux) during 30 h at 25 C., starts after about 18-20 h. After 30 h most of the larvae are in the desired instar II-III stage. The larvae are then transferred from the hatching medium to a rinsing well containing 1 ml of the test solution, thus exposing the larvae to the appropriate test solution before they entered the actual test well and minimizing dilution of the test solution during transfer. For each compound tested, the bioassay included one control and five concentrations of the tested compound, each of them with 3 replicates of 10 animals. The incubation was carried out in the dark at 25 C. and for 24 hours, then the dead larvae in each test solution well were counted to estimate the percentage of mortality. The median lethal concentration (LC.sub.50) was calculated from the five assays with different concentrations.

[0082] In an embodiment, the toxicity for the marine environment was evaluated for MEL-based oil dispersant formulation (42% (w/w) blend of MELs, 28% (w/w) TWEEN 80 and 30% (w/w) solvent base), against a formulation without MEL (i.e., with 48% (w/w) Tween 80 and 52% (w/w) solvent base), MEL and Corexit 9500. The results are presented in table 3.

TABLE-US-00003 TABLE 3 Artemia franciscana toxicity tests of MEL-based oil formulation, formulation components, MEL, Corexit 9500. Compound LC.sub.50 (mg/l) Corexit 9500 78.9 2.8 MEL-based oil dispersant 405.2 10.3 formulation TWEEN 80 + solvent base 182.2 4.4 (i.e. oil formulation without MEL) MEL 512.7 66.8

[0083] According to the results (Table 3), Corexit showed strong a toxicity (LC.sub.50 of 78.9), the mixture of Tween 80 and the solvent base (the developed formulation without MEL) exhibits a moderate cytotoxicity (LC.sub.50 of 182.2 mg/l) and MEL showed a weak toxicity in A. franciscana (LC.sub.50 higher than 400 mg/l). Surprisingly, the MEL-based oil dispersion formulation (MEL+TWEEN 80+solvent base) not only showed a much lower toxicity than Corexit, but also a weaker toxicity (LC.sub.50 of 405.210.3 mg/l) as compared to the formulation without MEL (LC.sub.50 of 182.24.4 mg/i), disclosing for the first time the surprising effect of MEL as an environmentally friendly agent not only when used alone, but also its positive effect when used in combinations with other dispersant agents.

Evaluation of the MEL-Based Oil Dispersant Formulations for Marine Environment Crude Oil Bioremediation

[0084] In an embodiment, biodegradation studies of crude oil were performed in 250 ml baffled shaking flasks with a working volume of 100 ml of seawater medium (i.e., 50% (v/v) seawater and 50% (v/v) Bushnell-Haas medium). Seawater was collected from coordinates 38 24.977N, 8 58.073W at a distance of 3 to 5 km from the coast of Setubal, Portugal at a depth of 74 m, placed at 25 C. and filtered using 25 m paper filter. In this assay, the oil biodegradation relies on endogenous microorganisms present on the seawater, as no additional microorganisms were inoculated. Troll B crude oil was used as sole carbon source, pre-mixed with the oil dispersant formulations, as previous described, and applied to the sea water media. The flasks containing these solutions were incubated at 25 C. for 7 days (150 rpm). At the end the experiment, 10 mL of HCl (15% v/v) was added for microbiological inactivation and the resulting aqueous solution samples were stored at 4 C. not more than up to 3 days. Then, two step extractions of the hydrocarbon contents in such aqueous samples were extracted by two step extractions using n-hexane (50 ml aqueous solution+25 ml of n-hexane, 95%, HPLC grade, Fisher Chemical), adding 0.1 mL of pristane (10 g/L in n-hexane) as an internal standard. The upper phases (organic) were concentrated by evaporation of n-hexane, using a rotary evaporator, until a volume of roughly 2 ml. The concentrated sample was filtered with a Pasteur pipette containing cotton, silica gel and anhydrous sodium sulphate and transferred to a glass vial. Its volume was further reduced to 0.9 ml using nitrogen stripping and then 0.1 ml of 5--androstane (10 g/l in n-hexane) was added as an external standard. Samples were stored at 20 C. prior to gas chromatography analysis.

[0085] In an embodiment, total hydrocarbon content (THC) samples taken from the bioremediation assay were assessed. THC comprises a large family of chemical compounds originally driven from crude oil. Crude oil comprises a very complex mixture made of many different chemicals. Therefore, for practical reasons, instead of measure each individual compound, THC is measured together to assess the evolution amount of crude oil present at an oil spill site. THC were analysed by a GC (Hewlett-Packard, HP5890) fitted with a flame ionization detector (FID) and with an oven temperature set to be held first at an initial value of 60 C., over 2 min, then to increase at a rate of 6 C./min until it reaches 310 C., and finally to be held at such value for a final 5 min. The injector and detector the temperatures were set to be was 300 C. and 310 C. respectively. Injected sample volume was 1 L. Calibration curves were made for both crude oil and alkane mixture standards using a series of dilutions (5 g/L, 2 g/L, 1 g/L, 0.5 g/L, 0.2 g/L in n-hexane) with 5--androstane as an internal standard. A relative response factor (RRF) was then calculated using equation 5 based on the concentrations (C) and areas (A) of the internal (andr) and external alkane standards (std). Moreover, the internal standards of pristane (prist) were added to the aqueous solution to quantify the percentage of hydrocarbons recovered in the extraction, using equation 5.

[00005]$\begin{array}{cc}\mathrm{RRF}=\frac{A_{\mathrm{andr}}{C}_{\mathrm{std}}}{A_{\mathrm{std}}{C}_{\mathrm{andr}}}& \left(\mathrm{Equation}5\right)\end{array}$$\begin{array}{cc}\mathrm{Recovery}\left(\%\right)=\frac{A_{\mathrm{andr}}}{A_{\mathrm{prist}}}& \left(\mathrm{Equation}6\right)\end{array}$

[0086] For the crude oil samples, the total area (A.sub.total) was obtained by integration of the GC-FID spectrum peaks. The THC area (A.sub.THC) was then calculated by subtracting the area of the internal standards (A.sub.andr, A.sub.pris) to the total area (equation 7) and the concentration of hydrocarbons in each sample (C.sub.THC) was then calculated using the equation 8.

[00006]$\begin{array}{cc}{A}_{\mathrm{THC}}=A_{\mathrm{total}}-A_{\mathrm{andr}}-A_{\mathrm{pris}}& \left(\mathrm{Equation}7\right)\end{array}$$\begin{array}{cc}{C}_{\mathrm{THC}}=\frac{A_{\mathrm{THC}}{C}_{\mathrm{andr}}}{A_{\mathrm{andr}}}\mathrm{RRF}\mathrm{Recovery}& \left(\mathrm{Equation}8\right)\end{array}$

[0087] In an embodiment, Corexit 9500 (I) was used as benchmarking, to assess the bioremediation efficiency of the MEL-based oil dispersant formulation (II) against the formulation without MEL (TWEEN+solvent base) (III) and MEL alone (IV). Troll B crude oil was pre-heated at 50 C. for 1 h and mixed with the oil dispersant at 500 rpm for 3 h at room temperature, employing 1:20 dispersant to oil ratio (DOR) for formulations I, II and III, and 1:48 DOR for formulation IV (formulations II and IV employs the same amount of MEL). The results on FIG. 5 shows, in comparison with the control, a decrease on C.sub.THC when any of the four oil dispersant formulations was used for 7 days. This result shows a clear efficiency of the four formulations assessed at laboratory scale. However, for applications on real settings, the efficiency and safety of those formulations rely on effective dispersion and low environment impact as evaluated, respectively, by IFT and LC.sub.50 values, pointing out for the superior performance of the MEL-based oil dispersant formulation.

[0088] The term comprising whenever used in this document is intended to indicate the presence of stated features, integers, steps, components, but not to preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

[0089] The disclosure should not be seen in any way restricted to the embodiments described and a person with ordinary skill in the art will foresee many possibilities to modifications thereof. The above-described embodiments are combinable.

[0090] The following claims further set out particular embodiments of the disclosure.

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