ISSN 1070-4272, Russian Journal of Applied Chemistry, 2012, Vol. 85, No. 12, pp. 1905−1909. © Pleiades Publishing, Ltd., 2012. Original Russian Text © D.V. Batov, V.N. Kartsev, S.N. Shtykov, 2012, published in Zhurnal Prikladnoi Khimii, 2012, Vol. 85, No. 12, pp. 2018−2023.
TECHNOLOGICAL PROCESSES IN HETEROGENEOUS SYSTEMS
Preparation, Heat Capacity, and Combustion Characteristics of Water–Surfactant–Halogenated Hydrocarbon Microemulsions Suitable for Combined Fire-Extinguishing Means D. V. Batova, V. N. Kartsevb, and S. N. Shtykovb a
Krestov Institute of Solution Chemistry, Russian Academy of Sciences, Ivanovo, Russia e-mail:
[email protected] b Chernyshevsky Saratov State University, Saratov, Russia Received October 1, 2012
Abstract—Water–sodium dodecyl sulfate–triethanolamine–1-pentanol–1,1,2,2-tetrafluorodibromoethane (С2F4Br2) microemulsions differing in the Н2О/С2F4Br2 ratio and content of surfactants were prepared. The principal possibility of combining halogenated hydrocarbons with water for developing new fire-extinguishing formulations was demonstrated. The emulsions obtained are of the oil-in-water type and are incombustible. The flash point and heat capacity of the systems were determined. DOI: 10.1134/S107042721212018X
Diphilic nature of surfactant molecules imparts to them unique capability to dissolve both in water and in a wide range of nonaqueous solvents. In both cases, surfactant molecules and ions under definite conditions form in solutions direct and inverse micelles and microemulsions (MEs), self-organizing nanosized aggregates of surfactant molecules or ions. Owing to the formation of these aggregates, constituting the basis for solubilization (dissolution) of both polar and nonpolar substances, surfactants are widely used in daily life, in various branches of industry, agriculture, medicine, pharmacology, biotechnologies, and even in firefighting [1, 2]. For the use in firefighting, the key property of surfactants is their capability to form a large amount of foam containing, e.g., carbon dioxide and preventing access of atmospheric oxygen to the flame [3]. Today, instead of hydrocarbon surfactants, it is suggested to use their more hydrophobic fluorinated analogs. Efforts are also made to develop high-performance fire-extinguishing formulations combining different mechanisms of fire extinguishing [4]. In this respect, it is promising to use mixtures of hydrocarbons with water, allowing flame cooling with water to be combined
with inhibition of combustion with a halogenated hydrocarbon. One of such combustion inhibitors is 1,1,2,2-tetrafluorodibromoethane (C2F4Br2) tested on a laboratory installation of automatic autonomous fireextinguishing unit [5]. Its mixture with water in 1 : 70 ratio showed high fire-extinguishing performance in extinguishing of model seats of fire of acetone, gasoline, and diesel fuel. It should be noted that this mixture was used at a temperature exceeding by 30– 60°C the boiling point of both liquids. It would be more efficient and convenient to use such liquid mixtures at common temperatures, because it would create conditions for additional cooling of the fire zone due to heat consumption for heating of the liquid to the boiling point and for its evaporation. However, under common conditions halogenated hydrocarbons are practically immiscible with water. For example, the solubility of tetrachloromethane in water is 0.08 g/100 ml [6]. The solubility of water in halogenated hydrocarbons is of approximately the same order of magnitude. Therefore, it is topical to search for the ways to combine halogenated hydrocarbons with water with the aim to prepare stable combined mixtures in a wide range of compositions and temperatures.
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BATOV et al.
One of the ways to solve the problem of combining halogenated hydrocarbons with water with the aim to obtain combined fire-extinguishing formulations at room temperature is the use of microemulsions. Microemulsions are transparent, optically isotropic solutions spontaneously forming from water, oil, a surfactant, and a co-surfactant [1, 7]. In this case a halogenated hydrocarbon will act as “oil.” Analysis shows that publications concerning the use of microemulsions as fire-extinguishing means are very few. In this context, we should note a US patent [8] whose author suggests using oil-in-water (o/w) microemulsions as a fire-extinguishing means. Emphasis is made on ensuring more finely dispersed state of water near the flame or directly in the flame by pulverizing water in the course of evaporation of a low-boiling hydrocarbon (heptane, octane), which is a dispersed (oil) phase of the microemulsion. The same author [8] suggests using a chemical fire-extinguishing agent as a liquid immiscible with water and water-soluble organic and inorganic (borates, phosphates) chemical fire-extinguishing agents as additives. This approach ensures combined effect of microemulsions. Physicochemical properties and structure of ternary [9], quaternary [10], and quinary [11] microemulsions containing halogenated hydrocarbons have been studied. Mukherjee et al. [9] obtained total phase diagrams of water–surfactant–chloroform ternary microemulsions with anionic [sodium bis(2-ethylhexyl) sulfosuccinate, AOT], cationic (cetyltrimethylammonium bromide, CTAB; cetylpyridinium chloride, CPC), and neutral (Triton X-100, TX-100) surfactants as emulsifiers. It follows from the phase diagrams given in [9] that single-phase systems are microemulsions of either o/w or w/o type, existing in a relatively narrow concentration interval. At high surfactant concentrations, viscous liquid crystal systems or gels are formed. The water– CTAB–chloroform system is worth noting, because in this system a single-phase solution is formed at a CTAB content of approximately 25 wt % in a wide interval of Н2О : СНCl3 ratios. The thermodynamics of water and chloroform dispersion in the corresponding surfactant solutions was also studied. Sineva et al. [11] reported on formation of microemulsions in the water–sodium dodecyl sulfate–1-pentanol–n-octane–chloroform system. The goal of this study was to prepare water– surfactant–co-surfactant–tetrafluorodibromoethane
microemulsions with various H2O : С2F4Br2 ratios, stable in the temperature range 10–40°С, and to examine their properties. EXPERIMENTAL To prepare microemulsions, we used double-distilled water (specific conductivity 1 × 10–5 s cm–1), sodium dodecyl sulfate (NaDDS; Amresco) of biotechnology grade (main substance content >98%), 1-pentanol (PenOH) of chemically pure grade, and triethanolamine (TEA) of pure grade. The chemicals were used without additional purification. The amount of water in 1-pentanol and triethanolamine, determined by Fischer titration, was 1.3 and 2.7 wt %, respectively, and was taken into account in microemulsion preparation. The microemulsions were prepared by adding the components in the order indicated in Table 1 and vigorously shaking the vessel. Triethanolamine in the microemulsions acts both as surfactant and as hydrotropic compound. At 25°C, throughout the examined concentration range, the microemulsions remained macroscopically single-phase and transparent. Visual monitoring for 5 months showed that all the three microemulsion systems remained macroscopically homogeneous, with no macrophase segregation in the temperature interval 12–40°С. Below 12°С, the systems got noticeably turbid, and their viscosity increased. The microemulsions were stored in glass flasks with two ground-glass stoppers. Owing to the presence of TEA, all the microemulsions are strongly alkaline (рН 10.4, 10 and 10.7 for ME-1, ME-2, and ME-3, respectively). The pH was determined with an I-500 pH meter at 17.3°С, using glass and silver chloride electrodes. The microemulsion type (o/w or w/o) was determined by the method suggested in [12] and used in [11]. Table 1. Composition of water–sodium dodecyl sulfate–triethanolamine–1-pentanol–1,1,2,2-tetrafluorodibromoethane microemulsions ME
Content, wt % NaDDS
Н2О
TEA
PenOH
C2Br2F4
МE-1
8.41
28.14
7.55
6.22
49.69
МE-2
8.29
38.44
7.66
6.16
39.44
МE-3
7.08
48.81
7.42
7.10
29.59
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 85 No. 12 2012
PREPARATION, HEAT CAPACITY, AND COMBUSTION CHARACTERISTICS
A drop of a microemulsion was added to a test tube filled with water. In all the cases, microemulsion drops in the course of sinking were uniformly distributed in the bulk of water without stirring. This behavior allowed us, to a first approximation, to assign all the examined microemulsions to the o/w type. With further addition of microemulsion drops to water, the formation of a new phase was detected as turbidization of the lower layer of the solution. Noticeable turbidization was observed on adding to 5 ml of water three drops of ME-1, five drops of ME-2, and ten drops of ME-3. This trend is consistent with an increase in the water content of the microemulsions. To evaluate the combustion properties of the microemulsions, we estimated their flash point using a Vspyshka-A automatic flash point recorder for petroleum products (BMTs Private Joint-Stock Company, Minsk, Belarus). This device allows measurement of the flash point of liquids in the interval 102–280°С in the open crucible mode (absolute uncertainty ±5°C) and in the interval 30–260°С in the closed crucible mode (absolute uncertainty ±2°C at Тfl ≤ 104°С and ±5°C at Тfl > 104°С). To check the device performance and absence of systematic error, we measured the closedcrucible flash point of pure grade pentadecane without preliminary purification. According to [13], Тfl of this compound is 115°С (the mode is not indicated). The mean value that we obtained from seven measurements was Тfl(С15Н32) = 120 ± 1°С, which is consistent with the reference value within the indicated device uncertainty. The flash points of the microemulsion systems were measured in the accelerated closed crucible mode. Heating of liquids in a crucible to 80–95°С led to their vigorous boiling and evaporation. Further heating to 120°С was accompanied by complete evaporation of the liquid from the crucible. The flash tests performed at 5°С intervals throughout the heating period gave negative result for all the systems under consideration. This fact allows the microemulsions obtained to be classed with incombustible fluids. The isobaric heat capacity of the microemulsions was measured with a Netzsch DSC 204 F1 differential scanning calorimeter. RESULTS AND DISCUSSIONS The starting point in preparation of the desired microemulsions with high content of both water and oil
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was the previously studied system water–sodium dodecyl sulfate (surfactant)–1-pentanol (co-surfactant)–n-octane [14, 15]. As we showed in [14–17], at 7.77 wt % content of sodium dodecyl sulfate and 14.5 wt % content of 1-pentanol, water and n-octane are miscible in any ratios at temperatures close to standard temperature. However, on replacing n-C8H18 by С2F4Br2, i.e., in going to the water–sodium dodecyl sulfate–1-pentanol–С2F4Br2 system, we obtained only two-phase systems. Also, the presence of a large amount of combustible 1-pentanol (flash point Тfl = 48°С [13]) is unnecessary. It is also known that water–sodium dodecyl sulfate–1-pentanol– n-octane microemulsions containing approximately 30 wt % water have relatively high viscosity (15 cSt at 25°С [17]). A search for surfactants and co-surfactants for preparing homogeneous liquid mixtures water– surfactant–co-surfactant–С2F4Br2 showed that TEA additions gave good results. The addition of TEA allowed the content of 1-pentanol to be decreased and the fire hazard of the system to be reduced, because the flash point of TEA (Tfl = 179°С [13]) is considerably higher than that of 1-pentanol. An important property characterizing both the structural features of a substance and its fireextinguishing performance is the heat capacity. The results of measuring the isobaric heat capacity of the microemulsions obtained are given in Fig. 1. As can be seen, the specific heat capacity of all the microemulsions monotonically increases in the interval 15–40°С. This fact suggests the absence in this temperature interval of phase transitions and sharp structural changes in the systems. Mutual arrangement of isoconcentrates in Fig. 1 shows that the specific heat capacities of the microemulsions in the examined temperature interval increase with an increase in the water content. The trend is more pronounced for the isotherm recorded at 293.15 K (Fig. 2). The reduced weight percentage of water was calculated by the formula red, H2O
where wH2O and wC2F4Br2 are the weight percentages of the microemulsion components. For other temperatures, we obtained similar
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BATOV et al.
ME-2 ME-1 ME-3
cp, J g–1 K–1
CpE, J mol–1 K–1
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T, °C
w, %
Fig. 1. Temperature dependence of the isobaric heat capacities cр of microemulsions (1) ME-1, (2) ME-2, and (3) ME-3.
Fig. 3. Excess heat capacities CEp of microemulsions as (1) 298.15 and (2) 313.15 K.
H2O
microemulsions, calculated by formula (2) using the necessary data for the components from [18–20] (Table 3):
cp, J g–1 K–1
ME-3 ME-2 ME-1
where Cp and C 0p, i are the molar heat capacities of the microemulsions and their components at a given temperature, and Хi is the mole fraction of the component. As can be seen, the values of C Ep are positive and tend to decrease with increasing temperature.
w, % Fig. 2. Isobaric heat capacity cр of microemulsions at 293.15 K as a function of their composition. (w) Reduced weight percentage of water; the same for Fig. 3. Points are experimental data, and the line is fitting by second-degree polynomials; the extreme points correspond to the heat capacities of tetrafluorodibromoethane and water.
dependences, which were approximated by seconddegree polynomials. The equation coefficients are given in Table 2. The correlations include the heat capacities of С2F4Br2 and H2O. Figure 3 shows the excess heat capacities of the Table 2. Coefficients of the equationsa cр = а0 + а1 wred, H
2O
Kopylov et al. [21] distinguished heptafluoroiodopropane (R 217I1) among environmentally friendly halogenated hydrocarbons for microemulsions. They showed that, in firefighting, heptafluoroiodopropane is an analog of tetrafluorodibromoethane. Another aspect is the choice of a surfactant, an emulsifier with high solubilizing power. Compounds with branched hydrocarbon chains can be promising in this respect. For example, sodium 2-hexyldecyl sulfate taken in an amount
+ а2 w2red, H O, J g–1 K–1 2
Т, K
а0
а1
а2
R
sd
n
293.15
0.664 ± 0.010
0.062 ± 0.000
–0.00027 ± 0.00000
1.0000
0.01
5
298.18
0.665 ± 0.022
0.063 ± 0.001
–0.00028 ± 0.00001
0.9999
0.02
5
303.15
0.667 ± 0.023
0.063 ± 0.001
–0.00028 ± 0.00001
0.9999
0.02
5
313.15
0.666 ± 0.040
0.063 ± 0.002
–0.00028 ± 0.00002
0.9995
0.04
5
a (R) Correlation coefficient, (sd) standard deviation, and (n) number of approximated points.
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PREPARATION, HEAT CAPACITY, AND COMBUSTION CHARACTERISTICS Table 3. Molar heat capacities of microemulsion componentsa Molar heat capacity, J mol–1 K–1 Т, K
NaDDS Н2О TEA PenOH C2Br2F4 b b b 288.380 18.015 149.200 88.150b 259.824b
298.15
380.7
75.4
389.0
208.4
173.9
303.15
389.3
75.3
389.0
216.0
174.6
313.15
406.6
75.3
389.0
241.1
176.0
a Heat capacities of crystalline NaDDS were determined in this study. b
Molar weight.
of 1.54 wt % is capable to “mix” 49.2 wt % aqueous phase (NaCl solution) with 49.2 wt % heptane [1]. CONCLUSIONS (1) Principal possibility of combining halogenated hydrocarbons with water with formation of microemulsions was confirmed. (2) Н2О–sodium dodecyl sulfate–triethanolamine– 1-pentanol–С2F4Br2 microemulsions with various Н2О : С2F4Br2 ratios and 22 wt % content of surfactants were obtained, their type was determined, and the flash point and heat capacity were measured. ACKNOWLEDGMENTS The study was supported in part by the Russian Foundation for Basic Research, project no. 12-0300450а. REFERENCES 1. Holmberg, K., Jönsson, B., Kronberg, K., and Lindman, B., Surfactants and Polymers in Aqueous Solution, Chichester: Wiley, 2003, 2nd ed. 2. Lange, K.R., Poverkhnostno-aktivnye veshchestva: sintez, svoistva, analiz, primenenie (Surfactants: Synthesis, Properties, Analysis, Use), St. Petersburg: Professiya, 2004. 3. Kazakov, M.V., Primenenie poverkhnostno-aktivnykh veshchestv dlya tusheniya pozharov (Use of Surfactants for Firefighting), Moscow: Stroiizdat, 1977. 4. Sharovarnikov, A.F. and Sharovarnikov, S.A.,
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Penoobrazovateli i peny dlya tusheniya pozharov. Sostav. Svoistva. Primenenie (Foaming Agents and Foams for Firefighting. Composition. Properties. Use), Moscow: Pozhnauka, 2005. Ershov, A.V., Efficiency of Firefighting in Closed Volumes of Ships with Combined Water-Based Fire-Extinguishing Formulations, Cand. Sci. Dissertation, St. Petersburg, 2002. Spravochnik khimika (Chemist’s Handbook), Moscow: Khimiya, 1964, vol. 2, p. 1020. Rusanov, A.I., Mitselloobrazovanie v rastvorakh poverkhnostno-aktivnykh veshchestv (Micellization in Surfactant Solutions), St. Petersburg: Khimiya, 1992. US Patent 7004261. Mukherjee, K., Mukherjee, D.C., and Moulik, S.P., J. Colloid Interface Sci., 1997, vol. 187, pp. 327–333. Fletcher, P.D.I., Galal, M.F., and Robinson, B.H., J. Chem. Soc., Faraday Trans. 1, 1985, vol. 81, pp. 2053–2065. Sineva, A.V., Ermolat’ev, D.S., and Pertsov, A.V., Kolloidn. Zh., 2007, vol. 69, no. 1, pp. 96–101. Emulsion Science, Sherman, P., Ed., London: Academic, 1968. Baratov, A.N., Korol’chenko, A.Ya., Kravchuk, G.N., et al., Pozharovzryvoopasnost’ veshchestv i materialov i sredstva ikh tusheniya: Spravochnoe izdanie (Fire and Explosion Hazard of Substances and Materials and FireExtinguishing Means: Handbook), Moscow: Khimiya, 1990, book 2.
14. Batov, D.V., Kartsev, V.N., Shtykov, S.N., and Shtykova, L.S., Izv. Vyssh. Uchebn. Zaved., Khim. Khim. Tekhnol., 2003, vol. 46, no. 6, pp. 80–82. 15. Batov, D.V., Kolloidn. Zh., 2004, vol. 66, no. 1, pp. 123– 125. 16. Kartsev, V.N., Shtykov, S.N., Tsepulin, V.V., and Shtykova, L.S., Kolloidn. Zh., 2000, vol. 62, no. 6, pp. 860–862. 17. Kartsev, V.N., Shtykov, S.N., Sineva, A.V., et al., Kolloidn. Zh., 2003, vol. 65, no. 3, pp. 429–432. 18. http://webbook.nist.gov. 19. Minadakis, C. and Sabbah, R., Thermochim. Acta, 1982, vol. 55, pp. 147–159. 20. Vesely, F., Zabransky, M., Barcal, P., and Svoboda, V., J. Chem. Thermodyn., 1988, vol. 20, pp. 1283–1285. 21. Kopylov, S.N., Kol’tsov, S.L., and Igumnov, S.M., Pozharn. Bezopasn., 2005, no. 2, pp. 51–55.
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