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Igor N. Evdokimov,* and Konstantin A. Kornishin Department of Physics, Gubkin Russian State University of Oil and Gas, Leninsky Prospekt, 65, Moscow B-296, GSP-1, 119991, Russia Abstract.
magnet with a high-homogeneity field in the 12 mm gap between parallel circular poles. The magnetic field strength was 0.12 T as measured by proton resonance meter. In each of eleven experiments, we employed four 2 ml oil samples in sealed glass tubes inclined by ca. 20o to the horizontal plane. After filling the tubes, the samples were allowed to equilibrate for 30 minutes. One pair of samples was placed into the pole gap of the magnet; another pair remained outside magnetic field. In each pair, one sample remained stationary; the other was rotated with a frequency of 55-60 revolutions per minute (cf. the scheme of experimental setup in Figure 1). This oil treatment procedure continued for 1 hour at 20-23 oC; afterwards optical properties of all samples were measured within 2-3 minutes. Figure 1. Experimental setup for magnetic treatment of the crude oil (for details – cf. text).
observed lower RI values in magnetically treated samples may be reliably attributed to well- known density (specific gravity) decrease in fluids via bond break-up and deaggregation,43,44 Computer simulations have shown that these processes should be accompanied by a decrease of fluid’s viscosity.44 An exception is a case where colloidal particles are stabilised by strongly absorbed solvent molecules. In such system structure-breaking in colloidal aggregates is counteracted by structure-building at the increased interface area; hence the net effect is an increase of bulk density.45-47 The data of Table 1 suggest that such stabilization/absorption effects are negligible in a colloidal system of the studied crude oil. Additional proof of disaggregation in magnetically treated oil was provided by measurements of optical extinction. Figure 2 shows Shimadzu UV-2201 extinction spectra of non-treated oil (1) and of a crude oil sample rotated in a magnetic field (2); note a log scale for extinction. Clearly seen is a decrease of extinction after magnetic treatment at all wavelengths. The details of this effect were emphasized by computing the ratio of extinction in a treated sample to extinction in the original crude oil, as illustrated in Figure 3. Solid line – the data from Figure 2; open circles connected by dashed line – the data from KFK-2 Photocolorimeter. Figure 2. Optical extinction spectra of the original (1) and of magnetically treated (2) crude oil.
where λ is the wavelength of the incident light and n is the ratio of the particle RI to the RI of continuous phase.49 Accordingly, the overall decrease of extinction may be regarded as a qualitative proof of magnetic field - induced decrease of the size of suspended colloidal particles. It should be noted, however, that the relative decrease of Rayleigh scattering is expected to be independent on the incident wavelength, while Figure 3 shows a step-like change from a value of ∼0.875 below 300 nm, to another fairly constant level of ∼0.95-0.96 above ca. 370 nm. A plausible interpretation may be a different degree of magnetic action on smaller and larger crude oil molecules. The most effective absorbers below 300 nm are known to be low molecular weight species with 1-2 ring aromatic chromophores, while absorbance in the visible and in the near-IR ranges is due to the presence of heavier asphaltene molecules with multiple-ring aromatic Figure 3. Relative decrease of crude oil’s optical extinction after magnetic treatment.
The appearance of two local minima in the longer-wavelengths part of Figure 3 may be regarded as an additional support of the above interpretation as these are indicative of relatively stronger magnetic field effects on the specific molecular species. In particular, the position of these minima coincide with positions of the strong Soret and the weaker Qα and Qβ absorption bands in vanadyl porphyrins51 (at 410, 553 and 573 nm as indicated by vertical lines in Figure 3). Furthermore, it has been experimentally demonstrated that vanadyl porphyrins are accumulated only in asphaltene sub-fractions with the lowest molecular weights.
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