Sacrificial adsorbates

Ethoxylated methylcarboxylates Propoxyethoxy glyceryl sulfonate Alkylpropoxyethoxy sulfate as surfactant, xanthan, and a copolymer of acrylamide and sodium 2-acrylamido-2-methylpropane sulfonate Carboxymethylated ethoxylated surfactants (CME) Polyethylene oxide (PEG) as a sacrificial adsorbate Polyethylene glycols, propoxylated/ethoxylated alkyl sulfates Mixtures of sulfonates and nonionic alcohols Combination of lignosulfonates and fatty amines Alkyl xylene sulfonates, polyethoxylated alkyl phenols, octaethylene glycol mono n-decyl ether, and tetradecyl trimethyl ammonium chloride Anionic sodium dodecyl sulfate (SDS), cationic tetradecyl trimethyl ammonium chloride (TTAC), nonionic pentadecylethoxylated nonylphenol (NP-15), and nonionic octaethylene glycol N-dodecyl ether Dimethylalkylamine oxides as cosurfactants and viscosifiers (N-Dodecyl)trimethylammonium bromide Petrochemical sulfonate and propane sulfonate of an ethoxylated alcohol or phenol Petrochemical sulfonate and a-olefin sulfonate... 

T. Austad, O. Rorvik, T. A. Rolfsvag, and K. B. Oysaed. Adsorption Pt 4 An evaluation of polyethylene glycol as a sacrificial adsorbate towards ethoxylated sulfonates in chemical flooding. J Petrol Sci Eng, 4(6) 265-276, January 1992. 

This section discusses three approaches that may be used to minimize surfactant adsorption matching surfactant type to specific reservoir rock type based on surfactant ionic character and solid surface charge, application of surfactant mixtures, and sacrificial adsorbates (128). 

Sacrificial Adsorbates. The idea of preflushing a reservoir with cheaper chemicals in order to block the adsorption sites and reduce subsequent surfactant adsorption has been extensively studied. However, an inherent problem with all reservoir preflushes is that it is extremely difficult to place the sacrificial chemical in the same zones that will make contact with the surfactant that follows it. This problem can be attributed to a change in fluid mobilities caused either by the higher viscosity of the injected fluids or by the fact that residual oil is being mobilized and moved ahead of the surfactant bank. In fact, the function of a foam is precisely to change the flow pattern to previously unswept areas. 

Effectiveness of sacrificial adsorbates is based on two basic assumptions No significant desorption of the sacrificial agent takes place when the surfactant solution makes contact with the surfaces with the preadsorbed materials, and the sacrificial agent adsorbs on the same adsorption sites as the surfactant. 

From the previous discussion, it may be seen that many uncertainties are associated with the use of sacrificial adsorbates. Although preflushes with sacrificial adsorbates may show some improvement in chemical flooding processes (149), it remains to be demonstrated that the additional costs related to sacrificial materials can be fully compensated for by lowering the requirements for the primary surfactant. 

Some of the techniques used to minimize surfactant adsorption include mixing of different types of surfactants and the use of sacrificial adsorbent [64], At the low pH environment encountered during acidizing, mutual solvent was found to minimize the loss of surfactant due to adsorption in sandstone reservoirs [65]. 

Reduction of two different precious metal ions by refluxing in ethanol/water in the presence of PVP gave a colloidal dispersion of core/shell structured bimetallic nanoparticles. In the case of Pd and Au ions, e.g., the colloidal dispersions of bimetallic nanoparticles with a Au core/Pd shell structure are produced. In contrast, it is difficult to prepare bimetallic nanoparticles with the inverted core/shell (in this case, Pd-core/Au-shell) structure. The sacrificial hydrogen strategy was used to construct the inverted core/shell structure, where the colloidal dispersions of Pd-cores are treated with hydrogen and then the solution of the second element, Au ions, is slowly added to the dispersions. This novel method, developed by us, gave the inverted core/shell structured bimetallic nanoparticles. The Pd-core/Au-shell structure was confirmed by FT-IR spectra of adsorbed CO [144]. 

Various metal and metal oxide nanoparticles have been prepared on polymer (sacrificial) templates, with the polymers subsequently removed. Synthesis of nanoparticles inside mesoporus materials such as MCM-41 is an illustrative template synthesis route. In this method, ions adsorbed into the pores can subsequently be oxidized or reduced to nanoparticulate materials (oxides or metals). Such composite materials are particularly attractive as supported catalysts. A classical example of the technique is deposition of 10 nm particles of NiO inside the pore structure of MCM-41 by impregnating the mesoporus material with an aqueous solution of nickel citrate followed by calicination of the composite at 450°C in air [68]. Successful synthesis of nanosized perovskites (ABO3) and spinels (AB2O4), such as LaMnOs and CuMn204, of high surface area have been demonstrated using a porous silica template [69]. 

Infrared Spectroscopy. Infrared (1R) spectroscopy is also used for understanding the structure of the bimetallic nanoparticles. Carbon monoxide can be adsorbed on the surface of metals, and the 1R spectra of the adsorbed CO depend on the kind of metal. These properties are used for analyzing the surface structure of metal nanoparticles. The inverted core/shell structure, constructed by sacrificial hydrogen reduction, was probed by this technique (44). 

Electron Transfer Between Co-adsorbed Species. So far, the most notable examples for photo-induced electron transfer on clay surfaces occur between co-adsorbed species as illustrated by the sacrificial oxidation of water. In water the system is the following (31) ... 

Another dye, hydroxoaluminiumtricarboxymonoamide phthalocyanine (AlTCPc), adsorbed on Ti02 particles at different loadings was tested for Cr(VI) photocatalytic reduction under visible irradiation in the presence of 4-CP as sacrificial donor. Direct evidence of the one-electron reduction of Cr(VI) to Cr(V) was also obtained by EPR experiments. The inhibition... 

Particulate soil is removed from fibres by a two-step process. First, a thin layer of wash liquid penetrates between the particle and the fibre surface, enabling surfactants to adsorb onto the particle surface (Fig. 7.1). Then, the particle becomes solvated and is transported away from the fibre and into the bulk of the wash liquid by mechanical action. Finishes that are hydrophilic (enhancing penetration of the fibre-soil interface) with low adhesion to soil under washing conditions should improve particulate soil release. Ablative or sacrificial finishes... 

In photochemical reduction of CO2 by metal complexes, [Ru(bpy)3] is widely used as a photosensitizer. The luminescent state of [Ru(bpy)3] is reductively quenched by various sacrificial electron donors to produce [Ru(bpy)3] . Metal complexes used as catalyst in the photochemical reduction of CO2 using [Ru(bpy)3] are prerequisites which are reduced at potentials more positive than that of the [Ru(bpy)3] " redox couple (-1.33 V vs SCE) (72). Irradiation with visible light of an aqueous solution containing [Co (Me4(14)-4,ll-dieneNJ], [Ru(bpy)3], and ascorbic acid at pH 4.0 produces CO and H2 with a mole ratio of 0.27 1 (73). Similarly, photochemical reduction of CO2 is catalyzed by the [Ru(bpy)3] /[Ni(cyclam)] system at pH 5.0 and also gives H2 and CO. However, the quantum efficiency of the latter is quite low (0.06% at X = 400 nm), and the catalytic activity for the CO2 reduction decreases to 25% after 4 h irradiation (64, 74, 75). This contrasts with the high activity for the electrochemical reduction of CO2 by [Ni(cyclam)] adsorbed on Hg. 

A so-called sacrificial flush is a solution containing cheap surfactant substitutes (e.g. lignosulphonates) likely to adsorb on the rock surface. Such a slug could be injected to prevent or reduce the adsorption from the surfactant slug, thus reducing losses (and cost) and formulation alterations. It also prepares the reservoir fluids to reach the optimal formulation in an easier and faster way. 

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