Alkali emulsification

In buffered surfactant-enhanced alkaline flooding, it was found that the minimum in interfacial tension and the region of spontaneous emulsification correspond to a particular pH range, so by buffering the aqueous pH against changes in alkali concentration, a low interfacial tension can be maintained when the amount of alkali decreases because of acids, rock consumption, and dispersion [1826]. 

The product which distils during the initial heating and the three minutes of steam distillation is mainly satisfactory material the rest of the steam distillation yields only a small amount of pure product. The two portions of the distillate are, therefore, kept separate, since the second distillate always contains a considerable amount of high-boiling product which tends to cause emulsification of the alkali in the purification. No recovery of acetone is made. 

Silicates. Both sodium and potassium silicate solids or solutions have valued functionality including emulsification, buffering, deflocculation, and antiredeposition ability. Silicates also provide corrosion protection to metal parts in washing machines, as well as to the surfaces of china patterns and metal utensils in automatic dishwashers. Silicates are manufactured in liquid, crystalline, or powdered forms and with different degrees of alkalinity. The alkalinity of the silicate provides buffering capacity in the presence of acidic soils and enhances the sequestration ability of the builder system in the formulation. The sili-cate/alkali ratios of the silicates are selected by the formulator to meet specific product requirements. Silicate ratios of 1/1 are commonly used in dry blending applications with silicate ratios of 2/1 and higher commonly used in laundry and autodish applications. 

The surfactants so made have many interesting properties in addition to detergency. They are low-foaming, can tolerate alkalie, have emulsification and antistatic properties. They have rust Inhibition and are often used as lubricants. 

The saponification of triglycerides with an alkali is a bimolecular nucleophilic substitution (SN2). The rate of the reaction depends on the increase of the reaction temperature and on the high mixing during the processing. In the saponification of triglycerides with an alkali, the two reactants are immiscible. The formation of soap as a product affects the emulsification of the two immiscible reactants, which causes an increase in the reaction rate [1, 2, 5]. 

The difficulty of obtaining ready access of alkali to the mass of fats in soap manufacture has led to the introduction of various methods of emulsification reaction. Among these mention must be made of the Monsavon process. In this the chemical reaction is accelerated by passing the mixture of fats and alkali through a colloid mill the homogenized solution is subsequently heated to 100°C. to start the hydrolysis. The soap produced in this way contains a little free alkali, usually of the order 0.2%. 

The factors which lead to the formation of emulsions are not definitely known. The most permanent emulsions are formed when an insoluble oil is shaken with a solution which contains a substance that interacts with one of the constituents of the oil to produce a colloid. This occurs when an oil containing free fatty acids is shaken with an aqueous solution of an alkali. A layer of soap is formed around the particles of the oil, and it is probable that a layer of oil may surround the colloidal partides of soap. When a solution of egg albumin is shaken with olive oil, a layer of the coagulated protein is formed around the drops of the oil and emulsification takes place. 

Large quantities of alkalies are required for the scouring operation. Technical sodium hydroxide, sodium silicate, sodium carbonate, and trisodium phosphate are among the alkalies used. Occasionally ordinary soaps are employed to assist in penetration and emulsification, but more generally the cheaper soaps, such as pine oil soap, or synthetic detergents, though not cheap, can be used sparingly and economically. 

Chang (1976) showed that use of a polyphosphate, which is a buffer, improved recovery. Sodium tripolyphosphate (STPP) was used in laboratory tests for Cretaceous Upper Edwards reservoir (Central Texas). STPP was proposed to minimize divalent precipitation, for wettability alteration and emulsification (Olsen et al., 1990). Generally, it is not used as a primary alkali to generate soap for purposes of IFT reduction. Instead, it is used together with other alkalis such as sodium carbonate when divalents could be a problem (Harry Chang, Chemor Tech International, Plano, Texas, personal communication on June 16, 2009). 

The focus here is on these mechanisms. A high content of naphthenic acids in heavy oils is a good property for soap generation and emulsification. Therefore, this chapter also presents the synergy between alkali and surfactant in heavy oil reservoirs. First, it discusses the phase behavior of the mixed system of soap and surfactant. Then it describes how to build up a UTCHEM phase behavior model and how to use the model to analyze phase behavior. In addition, this chapter investigates a number of parameters related to phase behavior. 

Liu et al. (2006b) conducted bottle tests to emulsify a heavy oil using the alkali Na2C03. They used the surfactant S4, which is alkyl ether surfactant with a molecular weight of 441. The heavy oil viscosity was 1800 mPa s at 22°C. They first used 0.15 to 1.2% NaaCOs solution and 1 to 2000 ppm S4 solution separately. In these tests, the heavy oil could not be emulsified in either alkaline solution or surfactant solution. However, when they used 50 ppm S4 and 0.15 to 1.2% NaaCOs together, they observed emulsification. 

The other observations were reported elsewhere, however. Figure 13.3 shows polymer made the surfactant system emulsification better, and Figure 13.4 shows polymer slightly changed the value of electrophoretic mobility. The addition of polymer into an ASP system does not change IFT but shortens the phase separation time of emulsions. In these examples, when alkali concentration was below 1%, as the concentration was increased, the phase separation time decreased. When alkali concentration was above 1%, the phase separation time increased with the concentration. Thus, polymer apparently reduced the interaction between oil and alkali when alkali concentration was high. 

To avoid emulsification as much as possible it is advantageous to use warm water rather than cold, and dilute alkali rather than concentrated. The milkiness of the aqueous wash liquid represents only a very small loss of material. 

Emulsification is the most important act of the washing process. To prevent secondary soil deposition, formation of a coalescence-stable low-concentration emulsion is needed. As it is shown above (see section 6.4), the formation of such an emulsion is possible under real conditions considering the surfactant concentration in the washing solution and hydrodynamic conditions of the soil deposition process. As far as solid soils are concerned, the process of dispersion of particles is important here. To prevent their re-deposition on the surface washed, water-soluble polymers are used, e.g. carboxymethyl cellulose. Effective dispersion agents are also inorganic salts, e.g. alkali metal silicates. 

Several micellar-polymer flooding models as applied to the EOR are discussed in [237]. It is noted that the co-solvent ordinarily used in this process considerably influences not only the microemulsion stabilisation, but also the removal of impurities in the pores of the medium. The idea of using an alkali in micellar-polymer flooding is discussed in [238] in detail. The alkali effect on the main oil components was studied aromatic hydrocarbons, saturated and unsaturated compounds, light and heavy resin compounds and asphaltenes. It is demonstrated that at pH 12 surfactants formed from resins allow to achieve an interfacial tension value close to zero. For asphaltenes, such results are achieved at pH 14. In the system alkali solution (concentration between 1300 to 9000 ppm)/crude oil at 1 1 volume ratio a zone of spontaneous emulsification appears, which is only possible at ultra-low interfacial tensions. 

Chem. Descrip. Aromatic acid phosphate ester Uses Surfactant lubricant antirust antistat good emulsification detergency pigment dispersant polymerization emulsifier Features Acid and alkali resist. sol. to high cone, electrolyte Iiq. Properties Transparent Iiq. sp.gr. 1.11 pH 2.0 (3% aq.) anionic 100% solids... 

The importance of the properties of the interfacial region for spontaneous emulsification was first demonstrated by Gad (4), who observed that when a solution of lauric acid in oil was carefully placed on an aqueous alkaline solution, an emulsion spontaneously formed at the interface. The reason for this spontaneous emulsification is the formation of a mixed film of lauric acid and sodium laurate (produced by partial neutralization of the acid by alkali) which produces an ultra-low interfacial tension. 

Alkali refining is a complete refining process. The process must remove free fatty acids (without extra saponification of the oil), phospholipids, carbohydrates, colouring agents and proteineous substances, avoid loss of oil through emulsification and achieve effective colour removal. The alkali... 

In the alkaline flood process, the surfactant is generated by the in situ chemical reaction between the alkali of the aqueous phase and the organic acids of the oil phase The surface-active reaction products can adsorb onto the rock surface to alter the wettability of the reservoir rock and/or can adsorb onto the oil-water interface to lower the interfacial tension. At these lowered tensions (1-10 dyne/cm), surface or shear-driven forces promote the formation of stable oil-in-water emulsions or unstable water-in-oil emulsions the nature of the emulsion phase depends on the pH, temperature, and electrolyte type and concentration. These different paths of the surface-active reaction products have created different recovery mechanisms of alkaline flooding. The four alkaline recovery mechanisms which have been cited in the recent literature are (i) Emulsification and Entrainment, (ii) Emulsification and Entrapment, (iii) Wettability Reversal from Oil-to Water-Wet, and (iv) Wettability Reversal from Water- to Oil-Wet. These four mechanisms are similar in that alkaline flooding enhances the recovery of acidic oil by two-stage processes. 

Mechanistic interpretations The results of the dynamic and equilibrium displacement experiments are used to evaluate and further define mechanisms by which alkaline floods increase the displacement and recovery of acidic oil in secondary mode and the tertiary mode floods. The data sets used in the mechanistic interpretations of alkaline floods are (a) overall and incremental recovery efficiencies from dynamic and equilibrium displacement experiments, (b) production and effluent concentration profiles from dynamic displacement experiments, (c) capillary pressure as a function of saturation curves and conditions of wettability from equilibrium displacement experiments, (d) interfacial tension reduction and contact angle alteration after contact of aqueous alkali with acidic oil and, (e) emulsion type, stability, size and mode of formation. These data sets are used to interpret the results of the partially scaled dynamic experiments in terms of two-stage phase alteration mechanisms of emulsification followed by entrapment, entrainment, degrees and states of wettability alteration or coalescence. 

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