Article pubs.acs.org/EF
Inhibiting Hydrophobization of Sandstones via Adsorption of Alkyl Carboxyl Betaines in Surfactant−Polymer Flooding Using Poly Alkylammonium Bromides Zhenggang Cui,* Dan Qi, Binglei Song, Xiaomei Pei, and Xin Hu The Key Laboratory of Food Colloids and Biotechnology, Ministry of Education, School of Chemical and Material Engineering, Jiangnan University, 1800 Lihu Road, Wuxi, Jiangsu 214122, P. R. China S Supporting Information *
ABSTRACT: Alkyl carboxyl betaines are good surfactants for reducing crude oil/connate water interfacial tension (IFT) in the absence of alkali and are therefore potential surfactants for surfactant−polymer (SP) flooding. However, they suffer from high adsorption retention and hydrophobizing sandstones by forming a monolayer at the sandstone/water interface with head-on configuration, which brings a risk of making the sandstone surfaces oily wet. In this paper, a poly alkylammonium bromide, N1,N1′-(propane-1,3- diyl) bis(N1,N1,N3,N3,N3-pentamethylpropane-1,3-diaminium) bromide, abbreviated as tetra-N(3)-Br, was synthesized and its properties in inhibiting the hydrophobization of sandstones via adsorption of alkyl carboxyl betaines were examined. The results indicate that alkyl carboxyl betaines with either single or double long alkyl chains can hydrophobize significantly the negatively charged solid surfaces even in neutral aqueous media by forming a monolayer at solid/water interface with head-on configuration. The tetra-N(3)-Br, which has a high positive charge density, can adsorb strongly at negatively charged solid/water interface with the adsorption depending only on its equilibrium concentration regardless of the presence of alkyl carboxyl betaines. The negative charges on the solid surfaces are neutralized, the adsorption of alkyl carboxyl betaines is significantly inhibited, and the effective concentration of the tetra-N(3)-Br is as low as 10−6 mol/L. On the other hand the presence of tetra-N(3)-Br in aqueous solution does not affect the IFT behavior of alkyl carboxyl betaines in a wide concentration range up to 0.1 mM. Tetra-N(3)-Br is thus an excellent agent in inhibiting hydrophobization of sandstones via adsorption of alkyl carboxyl betaines in SP flooding. caustic alkalis3,8,17−19 or using SP flooding free of alkalis3,8,17,20−29 has been proposed recently. It has also been noticed that in absence of alkali the surfactants effective in ASP flooding, such as petroleum sulfonates and heavy alkylbenzenesulfonates, become ineffective or less effective17,28,29 due to lack of synergisms and the decrease of ionic strength in aqueous phase. As compensation the surfactants used in SP flooding should have higher hydrophilicity than those used in ASP flooding according to the Winsor’s R-ratio theory.30 Recent studies have shown that zwitterionic surfactants, both alkyl carboxyl betaines and alkyl sulfobetaines, are superior to anionic and nonionic surfactants in reducing crude oil/connate water IFT thanks to their high adsorption at oil/water interface.29,31−37 However, the achievement of ultra low IFT is not a guarantee of success of SP flooding. The adsorption retention of surfactants by sandstones and their effects on wettability of the sandstones are also crucial.38 On one hand the adsorption of surfactants on sandstones will reduce surfactant concentration in the flooding water and may result in chromatographic separation of mixed surfactants which are usually employed in surfactant flooding, making formulations ineffective; and on the other hand, if the surfactants have a head-on configuration at sandstone/water interface, the wettability of the sandstone surfaces will be
1. INTRODUCTION Enhanced oil recovery has been a sustained subject worldwide in the past decades1−3 due to nonrenewability of crude oils, especially in China,3,4 where nearly 60% of the crude oils consumed are imported whereas the outputs of the local giant oil fields are decreasing naturally.5 On the other hand, about 60% of the original oil in place (OOIP) remains underground after water flooding as oil droplets trapped in porous rocks by capillary force.3,6,7 Research works have indicated that by adding surfactants into the injected water to reduce crude oil/ water interfacial tension (IFT) to ultralow levels (99.8% and a BET surface area of 200 ± 20 m2/g was provided by Wuxi Jinding Longhua Chemical Co., China. Silica microparticles of 99.9% purity with a primary diameter 10 μm and a BET surface area of 0.8071 m2/g was purchased from Aladdin, China. The sandstone sample of 65−100 mesh composed of approximately 90% rocks and 10% clays39 was provided by Daqing oilfield, China, which was obtained by crushing nature cores followed by washing with benzene− ethanol (3:1) mixture and drying, milling, and sifting. The core discs with a diameter of 25 mm and thickness of 8−10 mm obtained by cutting a cylindrical natural core (after water flooding) were provided by Daqing oilfield, China. 2.2. Synthesis of Tetra-N(3)-Br. 2.2.1. Synthesis of 3-Bromopropyl-trimethylammonium Bromide. Cooled 1,3-dibromopropane (89 g, 0.44 mol), trimethylamine (20 g, 0.339 mol), and 300 cm3 acetone were added into a 500 cm3 reactor, which was then sealed and the mixture was allowed to react at room temperature for 24 h. After that the mixture was filtrated to collect white solid, which was washed three times with acetone, followed by drying under vacuum at 60 °C. 2.2.2. Synthesis of Tetra-N(3)-Br. N,N,N′,N′-tetramethylpropyl-1,3diamine (8 g, 0.06 mol), 3-bromo-propyl-trimethylammonium bromide (33 g, 0.13 mol) and 100 mL ethanol were added into a 250 cm3 flask equipped with a flux condenser. The reaction was performed at 79 °C for 20 h. The product was then cooled to room temperature with solid being precipitated from the solution. After filtration, the solid was recrystallized twice from a mixed solvent (methanol:ethanol (v/v) = 2:1), followed by drying under vacuum at 55 °C. A complete synthesis route is shown in Scheme 1.
alternated from water wet to oily wet, which are unfavorable to obtain a high oil recovery.38,39 The adsorption of surfactants on various solid/water interfaces has been extensively studied, as reviewed by many authors.40−45 The driving forces include mainly electrostatic attraction, ion-exchange, covalent bonding, chain−chain interaction, hydrogen bonding, and hydrophobic bonding, as well as solvation of various species,44,45 although not all interactions are involved in a specified system. It has been recognized that the sandstone in Daqing oil fields, China, is composed of various rocks (90%) and clays (10%), which are negatively charged in aqueous phase.39 Cationic surfactants are therefore not good candidates due to their high adsorption retention and hydrophobization to the sandstones at monolayer adsorption. The suitable surfactants are therefore anionics and nonionics, which unfortunately do not behave well in reducing IFT in absence of alkali. In previous studies we have shown that zwitterionic surfactants with double long alkyl chains, or didodecyl methyl carboxyl betaine is a good hydrophobic surfactants for SP flooding, which can reduce Daqing crude oil/ water IFT to ultra low by mixing with various hydrophilic surfactants, either homogeneous or different types.29 It is a pity that the carboxyl betaines, whether with single or double long hydrocarbon chains, have relatively high adsorption on sandstone,39 and further studies indicate that these surfactants can form a monolayer at sandstone/water interface with headon configuration even in neutral media at low concentration, giving a risk of converting sandstone surfaces to oily wet. To take advantage of the good performances of the alkyl carboxyl betaines in reducing IFT in SP flooding, it is quite crucial to inhibit their adsorption at sandstone/water interface and hydrophobization to the sandstones. Considering that carboxyl betaines can be converted to cationic surfactants in acidic media but not to anionic ones in alkaline media, it is predicted that the positive and negative charges in an alkyl carboxyl betaine molecule is not balanced. The positive charge on the ammonium may be stronger than the negative charge on the carboxyl group in neutral media, and thus have a head-on configuration on sandstone/water interface similar to cationic surfactants. To inhibit their adsorption at the sandstone/water interface the key is to screen the electrostatic interaction between the positive charge on ammonium and the negative changes on sandstone surfaces. Although adding counterions can screen significantly electrostatic interactions,46 this relies on addition of high concentration of monovalence electrolytes, which may significantly reduce the solubility of the surfactants used in aqueous phase. In this paper we report a novel protocol to inhibit the adsorption of alkyl carboxyl betaines on sandstone/water interface and corresponding hydrophobization to the sandstones by using a poly alkylammonium bromides, N1,N1′-(propane-1,3-diyl) bis(N1,N1,N3,N3,N3- pentamethylpropane-1,3-diaminium) bromide, abbreviated as tetra-N(3)-Br, as an inhibiting agent or sacrificial agent. It is found that in the presence of a trace amount of tetra-N(3)-Br, the adsorption of the alkyl carboxyl betianes at the sandstone/water interface and their hydrophobization to the sandstone surfaces is significantly inhibited, whereas their excellent performance in reducing crude oil/ connate water IFT keeps unaffected.
Scheme 1. Molecular Structure of N1,N1′-(Propane-1,3-diyl) bis(N1,N1,N3,N3,N3-Pentamethylpropane-1,3-diaminium) Bromide (Tetra-N(3)-Br) and Its Synthesis Route
2.3. Methods. 2.3.1. Contact Angle Measurement. Glass slides were cut to pieces of 25 mm × 15 mm, which were then immersed in 30% NaOH aqueous solution for 24 h, followed by rinsing with pure water and drying naturally. Then a piece of the glass slide or part of a core disc (cut from a core disc) was put in a glass cell (35 mm (L) × 25 mm (D) × 15 mm (H)) supported by a pair of glass trestles at two ends, and the cell was filled with aqueous solution of a surfactant until the slide piece was immersed. After 24 h (for reaching adsorption equilibrium) an oil (n-decane) drop was released from a U-shaped needle, which was captured by the slide piece to form an inverted sessile drop. The image of the drop was recorded and the contact angel of the aqueous phase was calculated by software. For a specified surfactant concentration at least three angles were measured and their average was taken as the result. The glass cell together with the apparatus was set in a plastic box with the temperature inside controlled at 25 °C by an Air-them heater (World Precision Instrument).
2. EXPERIMENTAL SECTION 2.1. Materials. 1,3-Dibromopropane, trimethylamine, and N,N,N′,N′-tetramethylpropyl-1,3-diamine were purchased from AladB
DOI: 10.1021/acs.energyfuels.5b02810 Energy Fuels XXXX, XXX, XXX−XXX
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Energy & Fuels 2.3.2. Adsorption of Surfactants at Particle/Water Interface. Approximately 1.0 g solid particles were weighed into a series of glass bottles (7.5 cm (h) × 2.5 cm (d)), followed by adding 20 cm3 aqueous solutions of a surfactant at different concentrations. The particles were dispersed using an ultrasound probe (JYD-650, Shanghai) for 1 min at 50 W output and the dispersion was then agitated by rotating the bottles on a tube rotator at 60 rpm for 24 h at constant temperature. After that the bottles were settled for 4 h at the same temperature, and the supernatant of the bottles was centrifuged at 5000 rpm for 20 min. The middle layer of solution was then taken for measuring surfactant concentration. The adsorbed amount of a surfactant at particle/water interface was calculated by Γ=
(C ini − Ceq)V W
(mmol/g)
then decrease with further increasing concentration to close to and beyond cmc.48−50 The contact angles of aqueous solutions of a series of alkyl carboxyl betaines on glass slides at 25 °C as a function of surfactant concentration were measured by captured oil (ndecane) drop method. The data are shown in Figure 1, and
(1)
3
Where V is the volume (20 cm ) of the solution, Cini and Ceq are the initial and equilibrium concentrations (M) of surfactant, respectively, and W is the weight (1.0 g) of the particle. For alkyl carboxyl betaines, Cini was measured by two-phase titration (C ≥ 1 mM) in the presence of excess sulfuric acid for ensuring all zwitterionic molecules being transformed to cationic ones. The methods for measuring Ceq depend on whether the system contains single or mixed components. For system containing a single alkyl carboxyl betaine, the two-phase titration was also applicable, but for system with mixed components, high performance liquid chromatography (HPLC) technique39 was preferred which enable to determine the concentration of two components simultaneously. A HPLC instrument (Waters 1525) equipped with an evaporation-light scattering detector (elsd, Waters 2420) and a column of Hedera ODS2 4.6 mm × 250 mm filled with SiO2 particles of 10 nm−5 μm was used, which was performed at a N2 pressure of 25 psi, tube temperature of 60 °C, and a detection temperature of 36 °C, using gradient elution with water/methanol as flow liquids. For removing small particles possibly present in the solution the supernatant was centrifuged at 5000 rpm for 20 min and forced to pass through a micro filter of 0.45 μm before it was injected into the column. The adsorption of surfactant at silica nanoparticle/water interface at low concentration (0.011
cationic diC12B 0.003746 164−170 >0.0093
surfactants and decreases with increasing POE chain length.46 Here the anionic surfactant SDS and nonionic surfactant LDGA do give a hydrophilic solid surface (θw/o = 10−15°) due to their low adsorption.39 It is thus clear that the adsorption behavior of alkyl carboxyl betaines at the slide/water interface is similar to that of cationic surfactants. For the alkyl carboxyl betaines tested, θmax w/o or plateau increases with increasing total hydrocarbon chain length, from 47° for C12B to 164−170° for diC12B, except that C18B gives a value (76°) lower than expected. The reason is probably that C18B has a longest single chain and very low cmc (0.0042 mM), which renders the molecule stronger chain−chain interaction and a double layer or hemimicelle adsorption may occurs at the interface before a dense monolayer is formed which thus limits further increase of the θmax w/o. In addition a Pickering decane-in-water emulsion can be stabilized by 0.5% silica nanoparticles in combination with C16B (at C < cmc), where both the silica nanoparticles48,49 and C16B at similar concentrations can not stabilize the emulsion solely, as shown in Figures S4 and S5, suggesting that alkyl carboxyl betaines are similar to cationic surfactants which are able to hydrophobize in situ silica nanoparticles by forming a monolayer with head-on configuration.48−50 In considering that these alkyl carboxyl betaines can be converted to cationic surfactants in acidic media, but not to anionic ones in alkali media, it is reasonable to predicted that the positive charge on ammonium and the negative charge on carboxyl group are not balanced, with the positive charge stronger than the negative charge. This makes them to have a constant adsorption at negatively charged surfaces46 even in neutral aqueous media and have a configuration in the monolayer similar to cationic surfactants. The adsorption of the alkyl carboxyl betaines at sandstone/water interface is thus much larger than that of anionic and nonionic surfactants,39 which causes not only high adsorption retention but also a worry of turning sandstone surface to oil-wet, which is an obstacle for success of SP flooding. 3.3. Effects of tetra-N(3)-Br on the Hydrophobization of Negatively Charged Surfaces by Adsorption of Carboxyl Betaine Surfactants. It is interesting to notice that when trace amount (0.01 mM) of tetra-N(3)-Br was added into aqueous solution of a carboxyl betaine, the peak or plateau in curve of contact angle vs surfactant concentration disappeared. For example, in Figure 1 C16B gives a θmax w/o of 154° at 0.02 mM, (cmc = 0.025 mM); whereas in the presence of 0.01 mM tetra-N(3)-Br, the θw/o decreases to less than 15° in a wide range of C16B concentration (0.001−0.1 mM), as shown in Figure 2. Similar θw/o values were obtained for diC12B in concentrations between 0.001 and 0.06 mM, (cmc = 0.0037 mM) where a plateau as high as 170° were measured in absence of tetra-N(3)-Br. This means that the hydrophobization of negatively charged surface by adsorption of alkyl carboxyl
CTAB 0.9246 156−163 0.03−0.6
diC12DMAB 0.0346 164−172 0.012−0.065
anionic
nonionic
SDS 6.028 13
LDGA 0.1528 14
Figure 2. Contact angles of aqueous solution of alkyl carboxyl betaines with 0.01 mM tetra-N(3)-Br on glass slides at 25 °C as a function of surfactant concentration measured by captured oil (n-decane) drop method.
betaines at low concentration is inhibited or avoided in the presence of trace amount of tetra-N(3)-Br. To find out the minimum effective concentration of tetraN(3)-Br in inhibiting hydrophobization, the concentration of C16B and diC12B was fixed at either Cmax (0.02 mM for C16B) or that at which the plateau of θw/o were obtained (0.005, 0.01, and 0.02 mM for diC12B) respectively, and the θw/o as a function of the concentration of tetra-N(3)-Br was examined. The results are shown in Figure 3, from which it is seen that for
Figure 3. Contact angles of aqueous solution of tetra-N(3)-Br without and with alkyl carboxyl betaine (concentration shown in the legend) as a function of concentration of tetra-N(3)-Br at 25 °C measured by captured oil (n-decane) drop method.
both C16B and diC12B, the minimum effective concentration of tetra-N(3)-Br is as low as 0.001 mM, beyond which the θw/o are all less than 20°. On the other hand at concentration lower than 0.001 mM, θw/o increases with decreasing the concentration of tetra-N(3)-Br, and the larger the concentration of the carboxyl betaine (diC12B) the higher the θw/o. 3.4. Mechanism of Tetra-N(3)-Br in Inhibiting Hydrophobization of Negatively Charged Surfaces by D
DOI: 10.1021/acs.energyfuels.5b02810 Energy Fuels XXXX, XXX, XXX−XXX
Article
Energy & Fuels Adsorption of Alkyl Carboxyl Betaines. The tetra-N(3)-Br, which has a molecular structure shown in Scheme 1, is a tetrameric quaternary ammonium bromides with a short methylene chain (−CH2CH2CH2−) between nitrogen atoms. It is quite soluble in water and dissociates to positively charged polycations and negatively charged Br−. The polycation, however, has no hydrophobization to the negatively charged slides, as shown by the low θw/o (
