Energy Fuels 2010, 24, 3144–3149 Published on Web 05/04/2010
: DOI:10.1021/ef901302y
Reduction of Paraffin Precipitation and Viscosity of Brazilian Crude Oil Exposed to Magnetic Fields Jose L. Gonc-alves,*,† Antonio J. F. Bombard,† Demetrio A. W. Soares,† and Glaucia B. Alcantara‡ †
Laborat orio de Reologia Dr. Hans Martin Laun, Instituto de Ci^ encias Exatas, Universidade Federal de Itajub a (UNIFEI), Itajub a, Minas Gerais (MG) 37500-001, Brazil, and ‡Laborat orio de Resson^ ancia Magn etica Nuclear (RMN), Instituto de Quı´mica, Universidade Federal de Goi as (UFG), Goi^ ania, Goi as (GO) 74001-970, Brazil Received November 6, 2009. Revised Manuscript Received April 9, 2010
The problems related to organic deposition on pipeline walls are well-known and have been challenging the petroleum industry since the primordial days. Some problems can result in a decrease of the production rate or a rise in the pumping power. Motivated by these problems, the present work tried to understand the influence of magnetic fields on paraffin crystallization and the reduction of crude oil viscosity. A mixture of paraffin (C15-C58) was diluted in n-hexane, and the solvent was evaporated slowly, under the influence of a 0.3 T magnetic field, and also naturally, without the influence of magnetic fields. The micrographs of paraffin crystals show that the magnetic field influenced the crystallization process. Further, for a better understanding of the reduction of crude oil viscosity, some experiments were made to show the influence of a magnetic field (1.3 T) on the viscosity of three samples with different paraffin contents. Sample 1 had its viscosity reduced. Originally, its viscosity was 69 cP. After exposure to the magnetic field, its viscosity was reduced to 39 cP. The other samples maintained the same viscosity before and after magnetic field exposure. Therefore, the reduction of oil viscosity does not happen for all types of crude oils. In an attempt to detect the factors in sample 1 that probably affect the reduction of oil viscosity, the samples were analyzed by the techniques of 1H nuclear magnetic resonance (NMR) and vibration sample magnetometer (VSM) and next compared to each other.
and magnetorheology principles.9-14 Von Flatern5 reported that paraffinic crude oils have a reduction in their viscosity after exposure to magnetic fields. Rocha et al.1 and Tao and Xu2,3 performed some experiments with crude oils and magnetic/electric fields and reached the conclusion that paraffinic crude oils interact with magnetic fields in a strong way. Paraffin is an organic component responsible for causing the problems described before, and it is worth understanding a little more about the influence of magnetic fields on its properties. On the basis of that, the present work shows that a sample of crude oil has its viscosity and wax appearance temperature (WAT) reduced after having been exposed to a 1.3 T magnetic field for 1 min. The present work also shows that a 0.3 T magnetic field can modify the crystallization process of a paraffin mixture. To acquire more information concerning the magnetic behavior of samples, we measured their magnetization. Information about the kind of hydrocarbon molecules present in samples was obtained by nuclear magnetic resonance (NMR) spectroscopy.
1. Introduction The problems related to the organic resin accumulation and the treatment of high-viscosity crude oils are well-known and have been challenging the petroleum industry since its primordial days. Recently, some researchers have claimed that magnetic/electric fields may affect the quality of some crude oil beneficially.1-7 Here, some authors suggest a “new physical mechanism”2,3,8 of viscosity reduction based on electro*To whom correspondence should be addressed: Laborat orio de Reologia, Universidade Federal de Itajuba, Av. BPS 1303, Itajuba, MG 37500-903, Brazil. Telephone: þ55-35-3629-1222. Fax: þ55-353629-1140. E-mail:
[email protected]. (1) Rocha, N.; Gonzalez, G.; Marques, L. C. do C.; Vaitsman, D. S. Pet. Sci. Technol. 2000, 18, 33–50. (2) Tao, R.; Xu, X. Energy Fuels 2006, 20, 2046–2051. (3) Tao, R. Int. J. Mod. Phys. B 2007, 21, 4767–4773. (4) Tung, N. P.; Vinh, N. Q.; Phong, N. T. P.; Long, B. Q. K.; Hung, P. V. Phys. B 2003, 327, 443–447. (5) Von Flatern, R. Offshore 1997, 57, 3. (6) Gonc-alves, J. L.; Bombard, A. J. F. Proceedings of the Rio Pipeline Conference and Exposition, Rio de Janeiro, Brazil, 2009; IBP1329_09. (7) Evdokimov, I. N.; Kornishin, K. A. Energy Fuels 2009, 23, 4016– 4020. (8) Tao, R.; Huang, K.; Tang, H.; Bell, D. Energy Fuels 2009, 23, 3339–3342. € L. Energy Fuels 2009, 23, 591–592. (9) G€ ulder, O. (10) Bombard, A. J. F.; Knobel, M.; Akantara, M. R. Int. J. Mod. Phys. B 2007, 21, 4858–4867. (11) Bombard, A. J. F.; Antunes, L. S.; Gouvea, D. J. Phys. 2009, 149, No. 012038. (12) Fang, F. F.; Choi, H. J.; Jhon, M. S. Colloids Surf., A 2009, 351, 46–51. (13) Choi, H. J.; Jhon, M. S. Soft Matter 2009, 5, 1562–1567. (14) Choi, H. J.; Jhon, M. S. Ind. Eng. Chem. Res. 1996, 35, 2993– 2998. r 2010 American Chemical Society
2. Materials and Methods In an attempt to observe the influence of the magnetic field on the paraffin crystallization process, a mixture of paraffin (C15C58) was diluted on n-hexane. The paraffin was evaporated on an acrylic plate with the influence of a 0.3 T magnetic field and naturally, without the magnetic field influence. The crystals were observed by optical microscopy. After that, we analyzed the influence of a high-intensity magnetic field (1.3 T) on the viscosity of paraffinic crude oil. A stresscontrolled rheometer (Physica MCR-301, Anton Paar, Germany) was used to measure the viscosity of samples. The rheometer was equipped with a Peltier cell to control the temperature and 3144
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Energy Fuels 2010, 24, 3144–3149
: DOI:10.1021/ef901302y
Gonc-alves et al.
Figure 1. (a-c) Paraffin crystals formed naturally, without the magnetic field influence. (d-f) Paraffin crystallized under the influence of a 0.3 T magnetic field.
One can see in panels a-c of Figure 1 some black points that are clusters of paraffin surged during the volatilization of solvent. Panels d-f of Figure 1 show the paraffin crystallized under the influence of a 0.3 T magnetic field. Visually, the amount of paraffin crystals formed under the 0.3 T magnetic field action was less than crystals formed naturally, without the magnetic field influence. Moreover, using the optical microscope, it was possible to observe paraffin clusters formed during the solvent volatilization. In this case, the paraffin clusters were observed just on the plate that was not exposed to the magnetic field. This experiment was repeated 3 times, and the 0.3 T magnetic field appeared to interfere with the paraffin crystal formation. Because paraffin is present in crude oils and the magnetic field appeared to interfere with the paraffin crystal formation, we tried to measure the intensity of the interaction between the magnetic fields and some samples. The magnetization curves were measured by a VSM and are shown in Figure 2. Panels a-c of Figure 2 show that the samples with a paraffin content of 11, 6, and 11% (w/w) has a diamagnetic behavior under high-intensity magnetic fields, which means a feeble interaction between them, compared to paramagnetic and ferromagnetic substances. Besides the interference of magnetic fields on paraffin crystallization, the literature also reports the reduction of WAT and viscosity of paraffinic crude oils after they were exposed to magnetic fields.1,2 To corroborate that, some experiments were performed. WAT and viscosity of three crude oils were measured by rheometry, before and after they were exposed to a 1.3 T magnetic field. The three samples were divided into samples 1-3, and the results are as follows. 3.1. Sample 1. The paraffin content in this sample is 11% (w/w), and its WAT was measured by rheometry. The
cone-plate geometry (50 mm in diameter and 1° cone angle). For the reason that the magnetic field interferes with Peltier systems, an external electromagnet was used to generate the magnetic field (1.3 T). The crude oil samples were placed in 150 17 mm test tubes, and their temperatures were kept constant in a thermostatic bath. The samples were supplied by Petrobras and named samples 1-3. According to the supplier, the paraffin content for samples 1 and 2 was 11 and 6% (w/w), respectively. Originally, sample 3 was 1% (w/w) paraffin content, and 10% (w/w) paraffin was added, resulting in a crude oil mixture with 11% (w/w) paraffin. During all processes, the temperature of the samples was kept constant around their WAT. Basically, the viscosity of the sample was analyzed before and after exposure to a 1.3 T magnetic field for 1 min. The magnetic behavior of samples was analyzed by the vibration sample magnetometer (VSM), Lakeshore 7404. To measure the aliphatic/aromatic hydrocarbon ratio in samples, Bruker Avance III 500 (11.75 T) NMR spectroscope was used.
3. Results and Discussion In the paper by Rocha et al.1, it is shown that the magnetic fields alter the morphology of paraffin crystals. We attempt to analyze what would be the influence of a 0.3 T magnetic field on the process of paraffin crystal formation. A blend of average weight (550 g/mol) with a molecular distribution from C15 to C58, with 75% aliphatic and 25% branched and cyclic hydrocarbons, was dissolved in n-hexane. A total of 2 mL of this mixture was deposited on an acrylic plate, and the solvent was evaporated at ∼25 °C and room pressure. The process of solvent evaporation occurred sometimes under the 0.3 T magnetic field influence and sometimes naturally, without the magnetic field influence. The paraffin crystals were observed by reflected optical microscopy and are shown in Figure 1. 3145
Energy Fuels 2010, 24, 3144–3149
: DOI:10.1021/ef901302y
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Figure 2. Magnetization curves of three samples: (a) sample 1, (b) sample 2, and (c) sample 3.
Figure 3. WAT of sample 1 measured by rheometry before and after its exposure to a 1.3 T magnetic field.
Figure 4. Viscosity of sample 1 before, immediately after, and 150 min after being exposed to a 1.3 T magnetic field.
sample was heated until 80 °C and cooled to 15 °C at 2 °C/ min, and the WAT of the sample is observed at the inflection point of the curve. Figure 3 shows the WAT of sample 1 before and after it has been exposed to a 1.3 T magnetic field.
According to Figure 3, before the sample exposure, the WAT of the sample is clearly visible at approximately 45 °C and, after its exposure, it is observed at 41 °C. There was a further reduction of sample WAT of 4 °C. Subsequently, after the WAT of sample 1 had been measured, a new amount of sample 1 was prepared. It was 3146
Energy Fuels 2010, 24, 3144–3149
: DOI:10.1021/ef901302y
Gonc-alves et al.
alteration was not observed on the viscosity of sample 2 after its exposure to the magnetic field. Its viscosity was the same, even though it presented a 6% (w/w) paraffin content. 3.3. Sample 3. In a comparison of the results obtained from samples 1 and 2, one can observe a reduction of 40% in viscosity for the first and nothing for the second. According to some authors,1,2 the reduction of the viscosity of some crude oils is caused by the presence of paraffin in the oil and the higher the paraffin content in the oil, the stronger the interaction between the magnetic field and the sample. On the basis of that, we prepared a mixture of crude oil and paraffin (sample 3). This crude oil already had 1% (w/w), and thus, we added a 10% (w/w) blend with 550 g/mol average weight, molecular distribution between C15 and C58, with 75% (v/v) aliphatic and 25% (v/v) cyclic and branched molecules, resulting in a mixture of crude oil with 11% (w/w) paraffin content. The WAT of sample 3 was measured by rheometry, and the inflection point became visible at 39 °C. Similar to the other samples, sample 3 was exposed to a 1.3 T magnetic field for 1 min, at a constant temperature of 39 °C, and its viscosity measurement is shown in Figure 6. In the figure, 0 and 9 are the average of measured points and the bars are the standard deviation. According to this figure, any meaningful alteration of the viscosity of sample 3 was not observed, even though this sample has 11% (w/w) paraffin content. Considering the mentioned works of Rocha et al.1 and Tao and Xu,2 which reported that the reduction of oil viscosity is caused by the interaction of paraffin with a magnetic field, a reduction of the viscosity of sample 3 would be expected, as observed in sample 1. In view of the fact that the paraffin was not the crucial factor responsible for promoting the reduction of the viscosity of the samples, we attempted to describe the substances and structures of molecules present in the samples that interact with the magnetic field. With concern to that, we analyzed the types of major molecules in samples by NMR, as shown in Figure 7. The peaks observed in the chemical shift in Figure 7 between 0 and 4 ppm correspond to the aliphatic hydrocarbons, while peaks observed in the chemical shift between 6 and 9 ppm correspond to aromatic hydrocarbons. The peak at 4.6 ppm, more notable in sample 1, corresponds to water. In quantitative chemical analysis by 1H NMR, the integral of the peak area corresponds to the quantities of chemical constituents. Hence, the proportion of molecule types was obtained by the integration and shown in Table 1. Among the samples described on Table 1, sample 1 presented the biggest aromatic/aliphatic ratio and also the major water concentration (10%, v/v). Furthermore, this was the unique sample which presented a significative viscosity reduction. The supplier of sample 1 provided some additional data, which are described in Table 2. Table 2 shows some features and properties of sample 1 after its dehydration.
Figure 5. Viscosity of sample 2 before and after being exposed to a 1.3 magnetic field.
Figure 6. Viscosity of sample 3 before and after exposure to a 1.3 T magnetic field.
conditioned at 45 °C, and its viscosity was measured at a constant shear rate of 50 s-1. The viscosity of sample 1 were measured before and after being exposed to a 1.3 T magnetic field for 1 min, and the result is in Figure 4. In Figure 4, 0, 9, and 2 represent the average of measured points and the bars represent the standard deviation. According to the figure, the viscosity of sample 1 before its exposure to the magnetic field was 66 cP and, immediately after that, it was reduced to approximately 39 cP. There was a reduction of 40%. Nevertheless, the reduction was not stable. Slowly the sample 1 viscosity returned to the original state. After 150 min, the viscosity of sample 1 was measured again and presented at 46 cP. In the oil field, far from laboratory conditions, these results could have interesting applications. For oil transportation, energy could be saved in oil pumping, and because the oil viscosity returns to the original oil very slowly, it could reach 10 km in 150 min, because the oil velocity in pipe is 4 km/h.2 3.2. Sample 2. According to the supplier, this oil has a paraffin content of 6% (w/w). It was exposed to a 1.3 T magnetic field for 1 min at 28 °C. Its viscosity was measured before and after being exposed to the magnetic field, and the results are in Figure 5. In the figure, 0 and 9 are the average of measured points and the bars are the standard deviation. Any meaningful
4. Conclusion According to the optical micrographics of crystallized paraffin, the magnetic field influenced the process of paraffin crystal formation. Visually, the amount of paraffin crystallized under the 0.3 T magnetic field was less than that crystallized naturally, without the magnetic field action. 3147
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: DOI:10.1021/ef901302y
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Figure 7. 1H NMR spectra from some crude oils: (a) sample 1, (b) sample 2, (c) sample 3, and (d) comparative spectra of the three samples. Table 1. Aromatic/Aliphatic Ratio of Hydrocarbon Molecules Present in Samples Described in Figure 7 crude oil samples
aromatic/aliphatic
sample 1 sample 2 sample 3
1:444.46 1:28.13 1:175.12
Table 2. Features of Sample 1 properties density (API) pour point WAT asphaltene (insoluble in heptane) sulfur nitrogen saturated hydrocarbons aromatic hydrocarbons resins asphaltenes salt
Moreover, the magnetic field did not allow the formation of paraffin clusters. Another fact observed was the reduction of the viscosity of sample 1. Notwithstanding, it presented a diamagnetic behavior under magnetic fields. There was a reduction in its viscosity of almost 40% after it had been exposed to a 1.3 T magnetic field. Also, there was a reduction in the WAT of sample 1 of 4 °C. In an oil field situation, it is possible that these structural changes on sample 1 could make the oil transportation easier, saving energy required for its pumping. Even though the viscosity of sample 1 could return to its original value, it occurred very slowly. At 150 min after its exposure, it was 30% of its original viscosity.2
value
method
36.5° 33.0 °C 48.3 °C
