|The traditional chemical dispersant formulations used in combating oil spills are comprised of mainly hydrocarbon solvents, petroleum-derived surfactants, and additives. The toxicity of these chemical dispersants to aquatic life and marine habitats has necessitated the search for alternative dispersant formulations that are environmentally benign. In this dissertation, low toxicity dispersants with high dispersion effectiveness were formulated for their application in crude oil spill remediation.
In chapter 2, the effectiveness on oil dispersions of a composite particle made of paraffin wax and the surfactant dioctyl sodium sulfosuccinate (DOSS) was compared to that of the same DOSS dissolved in a liquid solvent using the U.S. EPA’s baffled flask procedure. The solid dispersant composite particles are expected to release the surfactant exactly at the oil-water interface hence reducing surfactant wastage and toxicity. Solid dispersant composite particles were prepared by ultrasonically spray freezing paraffin wax and DOSS molten solution while varying the mass ratio. The amount of DOSS in the composite particle was determined by the methylene blue complexation procedure. Liquid delivery of DOSS was accomplished by dissolving the surfactant in propylene glycol (PG). The results from the study showed that the dispersion effectiveness of the DOSS-paraffin wax composite particles were dependent on particle size, the solubility of the matrix material (paraffin wax) in the crude oil and the DOSS-to-oil ratio (DOR, mg/g). This is because the paraffin wax would have to dissolve in the crude oil to release DOSS, which is then used for the dispersion of the crude oil. At 23 mg/g DOR, which was the maximum DOR used in the study, the dispersion effectiveness of the dispersant composite particles was 60 vol.% and 62.6 vol.% in the heavy Texas crude (TC) and the light crude (LC) oils, respectively. The dispersion effectiveness of the solubilized DOSS on TC was significantly higher than that of the dispersant composite particles; however, at DOR of 23 mg/g, the effectiveness of the dispersant composite particles on LC was just 1.8 vol.% below that of the solubilized DOSS. There was a significant increase in the dispersion effectiveness when the mixing energy was increased from 150 to 200 revolutions per minute (rpm); nevertheless, the effectiveness was almost the same at 200 and 250 rpm. Dispersion effectiveness was analyzed at different salinity environments, that is in brackish water (1.6 and 2.8 wt.% salt concentration) and saline water (3.5 wt.% salt concentration). The dispersant composite particles performed better at low salinities, however, the dispersion effectiveness almost leveled off at 2.8 and 3.5 wt.% salt concentrations. The dispersion effectiveness values of the formulated dispersant composite particles on light crude oil were almost the same as that of solubilized dispersants.
The possibility of formulating oil spill dispersants from food grade surfactants were explored in chapter 3. Soybean lecithin was used to formulate dispersants for crude oil spill application. Soybean lecithin was fractionated into phosphatidylinositol (PI) and phosphatidylcholine (PC) enriched fractions using ethanol. The fractionated PI was deoiled and characterized with Fourier Transform Infrared Spectroscopy (FT-IR). The crude soybean lecithin (CL) and the fractionated PI and PC were solubilized in water and their dispersion effectiveness determined using the U.S. EPA’s baffled flask test. The dispersion effectiveness of these solubilized dispersants was compared with that of solid crude lecithin (SL). The dispersion effectiveness of PC was found to be higher than SL, CL, and PI at all the dispersant-to-oil ratios (DORs) tested. However, when the fractionated PI was modified or “functionalized” (FPI) with additional hydroxyl groups to alter the hydrophilic-lipophilic balance (HLB), its dispersion effectiveness improved remarkably and was higher than that of PC. Comparing the dispersion effectiveness of FPI to that of the traditional chemical dispersant formulations (solubilized dioctyl sodium sulfosuccinate (DOSS) and Tween 80 in propylene glycol), it was observed that the dispersion effectiveness of solubilized DOSS and Tween 80 were higher than that of FPI at lower DORs ( ≤ 12.5 mg/g). However at higher DORs (>28 mg/g), the dispersion effectiveness of FPI was slightly higher than that of solubilized DOSS and Tween 80. The dispersion effectiveness of PC on Texas (TC) and light crude (LC) oil samples were almost the same. The same observation was made for FPI on TC and LC. The dispersion effectiveness of PC and FPI were also tested in different salinity environments. PC and FPI performed better at the higher salinity of 3.5 wt.% than the lower salinities of 0.8 and 1.5 wt.%. At higher DORs, oil spill dispersants formulated from soybean lecithin (FPI) were effective than solubilized DOSS and Tween 80 in propylene glycol.
To reduce the aqueous solubility and toxicity of oil spill dispersants and increase dispersion effectiveness, halloysite clay nanotubes (HNTs) loaded with different combination of surfactants were studied for possible application in crude oil spill remediation in chapter 4. Halloysite nanotubes were loaded with the surfactants; Tween 80, dioctyl sodium sulfosuccinate (DOSS, D), Span 80 (S) and modified soybean lecithin phosphatidylinositol (Lecithin FPI, LFPI) by vacuum suction method. The HNT loaded with the surfactants were then characterized with scanning electron microscopy (SEM), Fourier Transform Infrared Spectroscopy (FT-IR) and Thermogravimetric analysis (TGA). The release kinetics of nonionic and anionic surfactants from HNT were respectively studied with the cobalt thiocyanate and methylene blue active substance tests. The dispersion effectiveness of the raw HNT and the HNT loaded with the surfactant(s) were examined with the U.S. EPA’s baffled flask test procedure. The release kinetics of DOSS from HNT was slower than that of Tween 80 due to the interaction of the anionic head group of DOSS with the positively charged lumen of the HNT. The dispersion effectiveness of the raw HNT was lower than HNT loaded with surfactant(s) signifying the release of surfactants during the baffled flask test. For the dispersant formulated with a single surfactant loaded onto HNT, the highest and the lowest dispersion effectiveness were recorded by HNT loaded with Tween 80 (HNT-Tween 80) and HNT loaded with Span 80 (HNT-Span 80), respectively. Loading the HNT with binary surfactant mixtures improved the dispersion effectiveness. Notable among them was HNT loaded with DOSS and Tween 80 (HNT-DOSS-Tween 80) and HNT loaded with Lecithin FPI and Tween 80 (HNT-Lecithin FPI-Tween 80). The highest dispersion effectiveness values for all the dispersants formulated in this study were attained by HNT loaded with ternary surfactant mixtures. 100 and 99 vol.% dispersion effectiveness were obtained from HNT loaded with DOSS, Tween 80 and lecithin FPI (HNT-DOSS-Tween 80-Lecithin FPI) and HNT loaded with Span 80, Tween 80 and lecithin FPI (HNT-Span 80-Lecithin FPI), respectively. The petroleum based surfactant blend of DOSS, Span 80 and Tween 80 (HNT-DOSS-Tween 80-Span 80) recorded 96.2 vol.% dispersion effectiveness. An environmentally friendly oil spill dispersant was therefore formulated using naturally occurring HNT and FDA approved food grade surfactants (Span 80, Tween 80 and Lecithin FPI) with 99 vol.% dispersion effectiveness.