The Interaction Between Welan Gum And Sodium Fatty Alcohol Polyoxyethylene Ether Sulfate

The complex system of water-soluble polymer and surfactant has always attracted much attention. The interaction between the polymer and surfactant allows changes in the conformation of the polymer chains. Meanwhile, the presence of the polymer affects the physicochemical properties of the surfactant solution. The coexistence of the polymer and surfactant often brings in some unique characteristics and functions which are superior to any pure-component. Consequently, it is so great significant to study the interaction between the polymer and surfactant. The research not only enriches the theories of the colloid and interface science, but also guides the practical application of the complex system in many industrial areas, such as biology, chemical, pharmaceutical and oil development. Especially in the oil development, the water-soluble polymer is always used in polymer flooding, polymer/surfactant binary combination flooding and polymer/surfactant/alkali ternary combination flooding. The interaction between the polymer and surfactant can significantly affect the oil displacement effect.There are many advantages for the polysaccharide, such as natural, non-toxic, sustainable and safety. The interaction between polysaccharide and surfactant not only simulates the signs of life, but also guides the formulation design of products. Therefore, the physicochemical properties of the polysaccharide and surfactant complex system as well the mechanism of interaction have attracted much attention. Anionic-nonionic surfactant combines the advantages of nonionic and anionic surfactant, and it is more and more popular for its mild, safe, biodegradable and multi-functional characteristics. However, the interaction between the polysaccharide and anionic-nonionic surfactant has rarely reported so far. In this thesis, the properties of welan gum, xanthan gum, and sodium fatty alcohol polyoxyethylene ether sulfate (AES) have been investigated respectively by the surface tension, fluorescence, and rheological technology firstly, and then the synergistic effects of welan/AES and xanthan/AES complex systems on surface, bulk, foaming, and foam stability have been investigated. We expect that our research can provide the basic data and theoretical guidance for the application of welan gum, AES, and welan/AES complex in the enhanced oil recovery and other industries. There are five parts in this thesis.In the first section, the research status of microbial polysaccharides and the interaction of the polysaccharide with different types of surfactant have been summarized. Meanwhile, the significance and purpose of the thesis are clarified.In the second section, the effects of the concentration, temperature and salinity on the rheological properties of welan gum have been systematically investigated, comparing with that of xanthan gum at the same time. Welan gum solution shows an excellent rheological performance on shear resistance capacity, temperature resistance and salt resistance than xanthan gum. Moreover, the oil displacement efficiency of welan gum is higher than that of xanthan gum in the simulated flooding experiment. The distinction in rheological behavior of welan gum and xanthan gum depends on the difference of the molecular interaction. Welan gum molecules are easier to form the double helix structure which arranges in a different way with that of xanthan gum. Due to intra-and intermolecular attraction, adjacent double helices of welan gum arrange in parallel as the zipper model. The network structure is more firm for the greater molecular entanglement than that of xanthan gum, and can resist higher shear, temperature and inorganic ions.In the third section, the aggregation behaviors of AES in aqueous solution with different inorganic salts have been investigated by surface tension, fluorescence and rheological methods. The wormlike micelle can be formed in AES solution by the addition of inorganic salt, in which EO groups in AES play an important role. At the same concentration of inorganic salt, the order of the efficiency and effectiveness reducing the surface tension is CaCl2> MgCl2> NaCl, and as for the mineralized water, the order of the efficiency and effectiveness reducing the surface tension is Simulated Seawater> Simulated Formation Water> Pure Water. The steady shear viscosity of AES/salt complex solution can be described by the Cross empirical equation. There is an optimal ratio of AES and salt at which the apparent viscosity and the viscoelasticity of the complex solution are both highest. The apparent viscosity and the viscoelasticity reduce gradually with the increase of the temperature, and the shear activation energy is proportional to the viscosity of the solution. The interaction of AES with salt is different, the effect of Ca2+、Mg2+is stronger than that of Na+at the same concentration, while the result is contrary at the same ionic strength. The formation of AES wormlike micelle is generally dependent on the hydration radius of counter ions and the electric charge, and the latter one is the main factor. The complexation between multivalent cation and EO groups of AES plays an active role as well.In the forth section, the properties of welan/AES complex system have been investigated, and compared with that of xanthan/AES complex system. The shear-thinning behavior is shown for the welan/AES complex solution. The concentration of AES has a little effect on the apparent of welan/AES complex solution, the dynamic modulus increased slightly, and the elasticity is the dominant property. The apparent viscosity, complex modulus, storage modulus and loss modulus of welan/AES are higher than those of xanthan/AES, indicating that the anti-interference ability of welan/AES complex system is stronger. There is no hydrophobic interaction between welan gum or xanthan gum and AES, since there are no hydrophobic groups in the molecular structures of welan gum and xanthan gum. The same charge hinders the interaction between welan gum or xanthan gum and AES due to the electrostatic repulsion. The addition of AES has little effect on the rheological properties of welan gum and xanthan gum. On the whole, the welan/AES complex solution can get a low surface tension, and maintain a high apparent viscosity, and the viscoelasticity is higher than those of xanthan/AES complex solution. The welan/AES complex system combines the advantages of welan gum and AES. This complex system used as binary combination flooding can theoretically enhance oil recovery by expanding the swept volume and improving the efficiency of oil displacement.In the fifth section, the foamability and foam stability of welan/AES complex system have been investigated by the Foamscan, and the factors influencing them are also discussed. At the room temperature, the optimum foaming concentration of AES is500mg·L-1. The foaming capacity of AES can be enhanced by adding the welan gum, and the optimum adding concentration of welan gum is80mg·L-1, at which the least foaming time can be realized. Meanwhile, the addition of welan gum can enhance the foam stability of AES. Foam conductance and liquid volume in the foam of the welan/AES complex solution are both higher than those of AES solution. Welan gum can enhance the viscoelasticity of AES foam membrane and prevent the drainage of the foam membrane. The dilational viscoelasticity of AES is enhanced by adding welan gum. The dilational viscosity is higher than the dilational elasticity, indicating that the interface viscosity is the dominant factor in stabilizing the foam. The molecules of welan gum tend to form a regular double helix structure due to the Vander Waals force and hydrogen bond between side chains and main chain. This double helix structure increases the interfacial viscosity of liquid membrane and improves the self-repair capacity. The foam properties of welan gum is poor, but after combining with AES, the foaming ability and foam stability are both better than pure AES solution and pure welan gum, indicating a synergy effect occurs through compounding.