Basic Study Reveals How Different Crude Oils Influence Dispersant Performance

BASIC STUDY REVEALS HOW DIFFERENT CRUDE OILS INFLUENCE DISPERSANT PERFORMANCE

Gerard P. Canevarij Downloaded from http://meridian.allenpress.com/iosc/article-pdf/1987/1/293/2349609/2169-3358-1987-1-293.pdf by guest on 24 September 2021 Exxon Research and Engineering Company P.O. Box 101 Florham Park, New Jersey 07016

ABSTRACT: Previous research has shown that crude oils contain var- In order to more directly establish the role of the indigenous ious amounts of indigenous surface active agents that stabilize water-in- surfactants in the crude, the surfactant phase was successfully sepa- oil emulsions. It is also known that crude oils stabilize such emulsions rated from nine of the crude oils. The amount of this surfactant phase to different extents. One aspect of the study was to investigate the was measured and then added to the tetradecane in the same propor- relationship between the emulsion forming tendency of the various tions as contained in the crude oil. The performance of this surfactant crude oils and the level of performance of a chemical dispersant on the spiked tetradecane was then tested and compared with the crude oil. particular crude oil. Thus, the two major laboratory aspects of the study were: (1) The results of the extensive laboratory test program indicated that construction of the Labofina test stand to measure the effectiveness of dispersant effectiveness is a function of both dispersant type and the four chemical dispersants on ten selected crude oils and tetradecane; specific crude oil. However, there is no apparent correlation between and (2) separation of the surfactant fraction residue from nine crude the degree of emulsion-forming tendency of the crude oil, which is a oils for further analysis of its effect: on dispersant performance. function of the indigenous surfactant content, and effectiveness. A "clean" hydrocarbon, tetradecane (C14), was also tested in order to evaluate the absence of any indigenous surfactants on performance. Labofina test selected for laboratory It was found that tetradecane exhibited a higher level of effectiveness compared to the crude oils for each of the dispersants tested. effectiveness evaluation In essence, the indigenous surfactants in the crude oil, in every instance, reduce dispersant effectiveness but to an unpredictable level. The Labofina Laboratory Effectiveness Test method was selected This is probably due to the fact that these agents present in crude oil as the means to compare the effectiveness of the four dispersants on promote a water-in-oil emulsion. Since the chemical dispersant is for- the ten crude oils. This method was selected because of its simplicity mulated to produce an oil-in-water dispersion, the interference of these crude oil surfactants is apparent. Hence, tetradecane would be an ideal test oil since the degree of dispersion of tetradecane by a particular dispersant represents the maximum dispersion effectiveness for that product. In order to establish more definitively the role of the indigenous surfactants, this surfactant phase was successfully separated from nine crude oib representative of different emulsion forming tendencies. It was found that the amount of surfactant residue extracted from the crude oil did correlate with the emulsion forming tendency of the crude oil. Finally, the above separated surfactant residue was added to tetradecane at the same concentrations as in the respective crude oil. As expected, in every instance, the surfactant residue decreased dispersant performance compared to "pure" tetradecane.

Ten crude oils with varying levels of emulsion forming tendency ranging from very weak to very strong were selected for dispersant effectiveness testing.4 Four dispersants of known formulation also were selected. A simple Labofina test stand was constructed so that the dispersibility of the crude oil-dispersant systems could be determined under identical conditions. In addition, a "clean," surfactant free oil, tetradecane (CH ), was tested to obtain additional data on the influence of the crude oil indigenous surfactants. Tetradecane has been found by William Wade, University of Texas,6 to have many of the physical characteristics of crude oil.

1. Current address: G. P. Canevari Associates, 104 Central Ave., Figure 1. Labofina laboratory effectiveness test—motor speed can Cranford, N.J. 07016 be adjusted by small Variac, but is normally set at 33 rpm 293 294 1987 OIL SPILL CONFERENCE

Table 1. Relative water emulsifying tendencies of crude oils

Extremely Relatively strong Very strong Strong Intermediate weak Very weak Kuwait Iranian Heavy Sunniland Nigerian Lt. Berri Goose Creek La Rosa Iranian Light North Slope Skikda W. Texas Sour Saharan Blend Arabian Heavy Maya Lagunillas Jobo Ekofisk Arabian Med. Arabian Lt. Loolaan Brent Jay Kirkuk Basrah Sirtic Flotta Tía Juana Med. Tia Juana Lt. Murban Mubarek Sag River Guanipa Zakum So. Louisiana Talco Minas Loretto Qatar Bachaquero Alik Forties Cold Lake Downloaded from http://meridian.allenpress.com/iosc/article-pdf/1987/1/293/2349609/2169-3358-1987-1-293.pdf by guest on 24 September 2021 Agip 100 Ardjuna Sassan Hondo Monterey Hondo Mix Tapis Loudon San Joaquín

.. Hondo Sandstone Suez Mix Romashkino

in view of the large numbers of tests required to generate the needed forming tendency is associated with the indigenous surfactant content data base. During the course of this program, it was also found to be of the particular crude oil, a representative slate of crude oils was a test that could be readily replicated.3 selected. This indigenous surfactant content also could have an influ- Basically, the method consists of adding the oil spill dispersant ence on dispersant performance. The following are the ten crude oils (0.2 ml) dropwise to a measured volume of the test oil on the surface with emulsion-forming tendency shown: (1) Kuwait (extremely of sea water contained in a conical separatory funnel resulting in a strong), (2) La Rosa (extremely strong), (3) North Slope (strong), (4) dispersant to oil ratio of l-to-25. The separatory funnel is rotated Guanipa (strong), (5) Loudon (strong), (6) Murban (intermediate), about a horizontal axis at right angles to its longitudinal axis for a (7) So. Louisiana (relatively weak), (8) Goose Creek (very weak), (9) period of two minutes at 33 ± 1 revolutions per minute (rpm). After Saharan Blend (very weak), and (10) Ekofisk (very weak). rotation has ceased, the flask is unstoppered and after one minute In addition, a clean hydrocarbon, tetradecane (Q4), also was tested standing time 50 ml of oily water are withdrawn through the bottom so that the effect of the absence of any indigenous surfactants on tap. The quantity of oil in the water sample is then determined spec- dispersant performance could be evaluated. trophotometrically following extraction into methylene chloride. The dispersants used are designated Dispersant A, B, C, and D for The test stand constructed at Exxon Research and Engineering Co. ease of reference. They were selected because of their known com- Florham Park laboratory is shown in Figure 1. positions and/or being a well established commercial product.

Ten crude oils selected for testing based on Dispersant effectiveness varies for both dispersant type emulsion forming tendency and the specific crude oil

Table 1 lists the emulsion forming tendencies for a large number of The results of the extensive laboratory test program indicated that crude oils of interest to Exxon. The table is based on extensive work dispersant effectiveness is a function of both dispersant type and of in this field by J. E. Shewmaker. Since it is believed that the emulsion the crude oil. The overall summary of Labofina effectiveness data is

Table 2. Labofina effectiveness results—standard 1 minute delay before sampling

Crude oil Emulsion tendency Dispersant A Dispersant B Dispersant C Dispersant D Kuwait Extremely strong 25 12 8 21 La Rosa Extremely strong 24 — — 20 North Slope Strong 26 — — 30 Guanipa Strong 18 — — 35 Loudon Strong 23 4 5 21 Murban Intermediate 17 10 10 21 South Louisiana Relatively weak 20 11 4 15 Ekofisk Weak 26 12 7 34 Saharan Blend Weak 19 — 38 Goose Creek Weak 31 — 29 Ci4 None 46 39 24 50 Note: Average of differences for all tests is one percentage point DISPERSANTS 295

Schematic Of Chemical Surfactant

Water Soluble Oil Soluble

£ Downloaded from http://meridian.allenpress.com/iosc/article-pdf/1987/1/293/2349609/2169-3358-1987-1-293.pdf by guest on 24 September 2021

Water Drop in Oil Media

Figure 2. Indigenous surfactants in crude oil can be seen as plastic-like film at interface

shown in Table 2 for ten crude oils based on a minimum of 3 tests. In Indigenous surfactants successfully extracted from addition to the 10 crude oils representing various degrees of emulsion forming tendency, a "clean" hydrocarbon, tetradecane, was tested. representative crude oils From the data presented in Table 2, it is evident that the effectiveness of a given dispersant (for example, Dispersant A) varies In order to establish more definitively the role of indigenous surfac- significantly for the different crude oils. Secondly, there is no appar- tants, this surfactant phase was separated from nine crude oils repre- ent correlation between the degree of emulsion forming tendency of sentative of different emulsion forming tendencies. the crude oil—a function of the indigenous surfactant content—and The initial attempts to separate the surfactant phase from the vari- effectiveness. Possibly, the actual composition of the indigenous sur- ous crude oils by Soxhlet extraction were not successful. A fiber factants influences dispersant effectiveness in a different manner than thimble, and later a latex rubber sac, were used as the dialysis mem- emulsion formation. brane with toluene, and later cyclohexane, used as the solvent but neither membrane retained any material. A method published in 1960 by Max Hill, was then tried.5 Some modifications to the Soxhlet extractor glassware were made and a small thin-walled rubber sac (medically termed "finger cotts") was used as shown in Figure 3. Effectiveness data indicate tetradecane could be The high molecular weight surfactant residue which probably con- ideal test oil tains some non-surfactant high molecular weight compounds extracted from the crude oil is a black solid residue at room tempera- Table 2 shows that the "clean" surfactant-free tetradecane exhibits ture. As can be seen from Table 3, the amount of this surfactant phase the highest level of effectiveness for each of the four dispersants. In does correlate with the emulsion forming tendency of the crude oil. essence, the indigenous surfactants in the crude oils, in every in- Apparently, the total amount of the surfactant residue, regardless of stance, reduced dispersant effectiveness but to an unpredictable de- composition, does influence the level of emulsion stability. gree. This is probably due to the fact that these agents present in crude oil promote a water-in-oil emulsion. Since the chemical dispersant is formulated to produce an oil-in-water dispersion, the inter- Further insight on indigenous surfactant ference of these crude oil surfactants is apparent.1 The presence of these surfactants at the oil-water interface can be seen clearly in behavior developed Figure 2.2 Since the dispersant is formulated to treat the crude oil- water interface, the presence of these foreign surfactants at that inter- Finally, the indigenous surfactant residues for five selected crude face can hinder its performance. Hence, the degree of dispersion of oils were added to tetradecane in the same proportion as each had in tetradecane by a particular dispersant represents the maximum dis- its respective crude. Tetradecane has been found by William Wade to persion effectiveness for that product. The dispersante effectiveness have many of the physical characteristics of crude oil.6 The objective on a crude oil will be less but to an unpredictable amount. was to determine if the pure Q4 hydrocarbon with the various surfac- 296 1987 OIL SPILL CONFERENCE

Table 4. Comparison of dispersant effectiveness for crude oil surfactant residue + C14 versus C,4 (all tests with Dispersant A; standard Labofina test)

Percent of oil dispersed Surfactant extracted with a blend of from Surfactant residue -I- d4 Kuwait 16 La Rosa 14 No. Slope 20 Murban 13 So. Louisiana 14 C14 46 Downloaded from http://meridian.allenpress.com/iosc/article-pdf/1987/1/293/2349609/2169-3358-1987-1-293.pdf by guest on 24 September 2021 Note: Average of differences for all tests is one percentage point

parison of the pure Cu versus Q4 with the various surfactant residues. It can be seen that in every case this surfactant residue decreased the performance of Dispersant A.

Conclusions

In summary, the experiments indicated that testing dispersants with tetradecane in the laboratory defines an upper limit on relative dispersant performance. The indigenous surfactants present in crude will reduce dispersibility but the magnitude of the reduction could not be correlated with crude properties (e.g., emulsion forming tendency) based upon these limited experiments. Furthermore, in an attempt to establish the role of indigenous surfactants in the crude, the surfactant phase was successfully separated from nine of the crude oils. The amount of surfactant phase present did correlate directly with the emulsion forming tendency of the crude. The addition of the surfactant extracts to tetradecane in the same proportions as contained in the crude, caused the dispersibility of the tetradecane to be reduced. However, the amount of the reduction was unpredictable and did not correlate with the amount of the Figure 3. Modified Soxhlet extraction shown disassembled surfactant phase present in the synthetic blend. tant residues is similar to the original crude oil as regards dispersant performance. References The results are summarized in Table 4. A key result is the corn- 1. Bancroft, W. D., 1915. Journal of Physical Chemistry, vl9, p275 Table 3. Amount of surfactant phase extracted 2. Berridge, S. A., Matthew Thew, and A. Loriston Clarke, 1968. from various crude oils The Formation and Stability of Emulsions of Water in Crude Pe- troleum and Similar Stocks. Paper presented at the Institute of Petroleum Symposium on the Scientific Aspects of Pollution of the Surfactant residue Sea by Oil, October 2 Crude oil Emulsion tendency (weight percent) 3. Byford, Derek C. and Peter Green, 1982. A View of the MacKay and Labofina Laboratory Tests for Assessing Dispersant Effec- Kuwait Extremely strong 19.5 tiveness with Regard to Performance at Sea. in Oil Spill Chemical La Rosa Extremely strong 16.8 Dispersants. ASTM publication North Slope Strong 6.7 4. Canevari, Gerard P., 1985. The effect of crude oil composition on Murban Intermediate 3.3 dispersant performance. Proceedings of the 1985 Oil Spill Confer- So. Louisiana Relatively weak 2.8 ence, American Petroleum Institute, Washington, D.C. Ekofisk Very weak 1.1 5. Hill, Max W. and Monroe W. Munsell, 1960. Dialysis of petro- Jay Very weak 1.9 leum products. Proceedings of the American Petroleum Society, Goose Creek Very weak .6 Division of Petroleum Chemistry Meeting, New York, N.Y., Sept. Saharan Very weak 1.2 11-16 C14 None 0.1 6. Wade, William, July 1976. Personal communication