(201e) Suitable Characteristics for Surfactants Substituent of Antifoam Silicon Oil
Among the methods for foam control, the more efficient is the application of antifoamers or defoamers, chemicals with properties to avoid foam to form or to break it in a short time. The standard product used in this case is silicone oil, specifically polydimethylsiloxane (PDMS). Although it is very efficient as an antifoam agent, the silicon present in PDMS structure is converted to silicon oxide in the petroleum refining step, causing the poisoning of the hydro-treatment catalyst and the yield reduction. Much research has been done to reduce the amount of silicon in the antifoamers, but none with satisfactory results1. Therefore, another approach has been made to understand what properties of PDMS make it a so effective antifoamer, and with those, been able to design a silicon-free polimer or a low-quantity silicon polimer with such characteristics.
In this manner, 5 Polydimethylsiloxane (PDMS) commercial samples with distinct viscosities had their viscosimetric molar mass determined. For each sample, 6 solutions of different concentrations were prepared in toluene and their viscosity was analyzed in a rotational rheometer Haake MARS 60, with shear rate defined at 300 s-1 at 25Â°C.The parameters K and a applied in the equation [Î·] = K Ma were acquired from the literature2. Formulations of these samples were prepared and the interfacial tension with petroleum 19Â°API and the antifoam efficiency3 were tested. Physical-chemical properties, such as dielectric constant, density at 20°C and 4°C, viscosity at 25°C and permeability of gas were also investigated. In order to determine the formulation with the most effective performance, different solvents were used in this study.
So far, it can be inferred that for samples with lower viscosity, or lower molar mass, the antifoam effect is almost null, despite been a silicon oil sample. With increasing the viscosity, the antifoam effect increases to a maximum and starts to decrease at even higher viscosities. As for this behavior, it is known that the higher the molecular weight, the greater the likelihood of entanglements, which may alter the dispersion of the surfactant, decreasing its antifoam potential.
Moreover, viscosity should be adjusted so the agent may be properly solubilized. For that, the solvent has a major role, as it may synergize with the agent so to improve its access to the oil, allowing a faster time of action avoiding the formation of the foam.
The interfacial tension allowed to observe how the samples modify the elasticity of the foam film by comparison of the entrance, spreading and bridge coefficients. The calculations shown a slight difference in spreading, indicating that the smaller molar mass samples access the oil medium easier. No changes were observed in the other 2 coefficients.
Surface rheology is being investigated, together with solubility parameters to understand how cohesion and adhesion of the antifoamers with the oil will affect the tensoactive behavior.
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- Rezende, D. A. Bittencourt, R. R., Mansur, C. R. E. Petrol. Sci. Eng. 2011, 76, 172-177.