Effect of surfactants on colloidal structure of lube distillates

Abstract

The use of NMR makes it possible to register fine effects at the micro level due to changes, caused by the presence of the surfactant, in the diffusional mobility of the molecules of disperse phase and dispersion medium in the lube fraction. Additional information on the influence of surfactants on the colloidal structure of lube fractions can be obtained by dielectric spectroscopy, since these fractions are dielectrics. In our work, the molecules of the oil fractions and their associates were subjected to polarization with subsequent reorientation under the influence of an ac electric field. The 350-420~ lube distillate that we investigated had been obtained from a 1:2 mixture of Tuimazy and West Siberian crudes. The physicochemical characteristics of the distillate were as follows: density 913 kg/m 3 at 20~ molecular weight 285, melting point 25~ refractive index 1.495 at 50~ viscosity 20 mm2/sec at 50~ hydrocarbon group composition (% by weight): paraffinic/naphthenic 33.7, monocyclic aromatics 21, bicyclic aromatics 13.4, polycyclic aromatics 28.7, resins 3.2; elemental composition (wt. %): H 13.3, C 85.4, S i.i. The additive used in this work, PMS-200A [methyl silicone], was added to the distillate at concentrations in the interval 0.005-0.02% by weight. This additive is used widely at concentrations from 0.002% to 0.005% as an antifoam additive in lube base stocks [2]. The test procedure consisted essentially of measuring the amplitude value and delay time of current passing through a sample when a sinusoidal voltage with an amplitude up to I0 V and a frequency of 20 to l0 s Hz was impressed on the sample, at temperatures from 30 ~ to 80~ The samples were thermostatted for 20 min before any measurements were made. On the basis of the results obtained in these measurements, calculations were performed in an ~lektronika DZ-28 microcomputer to determine the real E' and imaginary E" parts of the complex permittivity e* = e' + je", according to the formulas