Inhibiting Hydrophobization of Sandstones via Adsorption of Alkyl Carboxyl Betaines in Surfactant–Polymer Flooding Using Poly Alkylammonium Bromides

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, <i>N</i>¹,<i>N</i>¹′-(propane-1,3- diyl) bis­(<i>N</i>¹,<i>N</i>¹,<i>N</i>³,<i>N</i>³,<i>N</i>³-penta­methyl­propane-1,3-diaminium) bromide, abbreviated as tetra-<i>N</i>(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-<i>N</i>(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-<i>N</i>(3)-Br is as low as 10^–6 mol/L. On the other hand the presence of tetra-<i>N</i>(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-<i>N</i>(3)-Br is thus an excellent agent in inhibiting hydrophobization of sandstones via adsorption of alkyl carboxyl betaines in SP flooding

Dioctyl Glyceryl Ether Ethoxylates as Surfactants for Surfactant–Polymer Flooding

Enhanced oil recovery by chemical flooding has been a main measure for postponing the overall decline of crude oil output in China, and surfactant–polymer (SP) flooding may replace alkali–surfactant–polymer flooding in the future for avoiding the undesired effects of using caustic alkali. In this paper, a series of double alkyl non-ionic surfactants, 1,3-dioctyl glyceryl ether ethoxylates (diC₈GE-E_<i>n</i>, where <i>n</i> = 4.6–15.8), were synthesized and characterized and the effects of the ethylene oxide (EO) number on their properties were evaluated. The results show that diC₈GE-E_<i>n</i> are highly surface-active, as reflected by their low critical micelle concentration (cmc) (<2 × 10^–5 mol/L) and low γ_cmc (<30 mN/m). Specifically, the member with the shortest EO chain (diC₈GE-E_4.6), which gives a saturated adsorption (5.81 × 10^–10 mol/cm²) nearly double that of others (2.94–2.63 × 10^–10 mol/cm²) at the air/water interface, can reduce Daqing crude oil/connate water interfacial tension (IFT) to ultralow (<0.01 mN/m) solely at 5 mM at 45 °C. The members with larger EO numbers, although cannot reduce Daqing crude oil/connate water IFT to ultralow solely, are very good hydrophilic components superior to a typical monoalkyl non-ionic surfactant, such as polyoxyethylene (10) monododecyl ether (C₁₂E₁₀), when mixed with a hydrophobic surfactant, didodecyl methyl hydroxylpropyl sulfobetaine (diC₁₂HSB), for SP flooding free of alkali. At optimum formulation, the molar fraction of diC₈GE-E_<i>n</i> can be decreased from 0.85 to 0.45 with increasing <i>n</i> from 8.0 to 15.8 and ultralow IFT can be easily achieved at a wide effective concentration range (0.3–10 mM) thanks to the larger interaction of the double alkyl chains in the molecules with the oil. Derived from commercially available materials and produced by commercially realizable technology, these surfactants are therefore practically significant for SP flooding

Photoresponsive Foams Generated by a Rigid Surfactant Derived from Dehydroabietic Acid

Innovation in the structure of surfactants is crucial to the construction of a surfactant-based system with intriguing properties. With dehydroabietic acid as a starting material, a nearly totally rigid azobenzene surfactant (R-azo-Na) was synthesized. The <i>trans</i>-R-azo-Na formed stable foams with half-lives of 636, 656, 976, and 872 min for 0.3, 1, 2, and 4 mmol·L^–1 aqueous solutions, respectively. Under UV light irradiation, a fast collapse of the foams was observed, showing an in situ response. The excellent foam stability of <i>trans</i>-R-azo-Na leads to the extremely high photoresponsive efficiency. As revealed by dynamic surface tension and pulsed-field gradient NMR methods, an obvious energy barrier existed in the adsorption/desorption process of <i>trans</i>-R-azo-Na on the air/water interface. The foams formed by <i>trans</i>-R-azo-Na are thus stable against coarsening processes. The results reveal the unique photoresponsive behavior of a surfactant with a rigid hydrophobic skeleton and provide new insights into the structure causing aggregation of surfactants

Photoresponsive Foams Generated by a Rigid Surfactant Derived from Dehydroabietic Acid

Innovation in the structure of surfactants is crucial to the construction of a surfactant-based system with intriguing properties. With dehydroabietic acid as a starting material, a nearly totally rigid azobenzene surfactant (R-azo-Na) was synthesized. The <i>trans</i>-R-azo-Na formed stable foams with half-lives of 636, 656, 976, and 872 min for 0.3, 1, 2, and 4 mmol·L^–1 aqueous solutions, respectively. Under UV light irradiation, a fast collapse of the foams was observed, showing an in situ response. The excellent foam stability of <i>trans</i>-R-azo-Na leads to the extremely high photoresponsive efficiency. As revealed by dynamic surface tension and pulsed-field gradient NMR methods, an obvious energy barrier existed in the adsorption/desorption process of <i>trans</i>-R-azo-Na on the air/water interface. The foams formed by <i>trans</i>-R-azo-Na are thus stable against coarsening processes. The results reveal the unique photoresponsive behavior of a surfactant with a rigid hydrophobic skeleton and provide new insights into the structure causing aggregation of surfactants