Energy & Fuels 2008, 22, 4077–4086
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Characterization and Pyrolysis Behavior of Novel Anthracene Oil Derivatives ´ lvarez,† M. Granda,*,† J. Sutil,† R. Menendez,† J. J. Ferna´ndez,‡ J. A. Vin˜a,‡ P. A T. J. Morgan,§ M. Millan,§ A. A. Herod,§ and R. Kandiyoti§ Instituto Nacional del Carbo´n, Consejo Superior de InVestigaciones Cientı´ficas (CSIC), Apartado 73, OViedo 33080, Spain, Industrial Quı´mica del Nalo´n, S.A. AVda. de Galicia 31, OViedo 33005, Spain, and Department of Chemical Engineering, Imperial College London, London SW7 2AZ, United Kingdom ReceiVed July 4, 2008. ReVised Manuscript ReceiVed September 9, 2008
The characterization and pyrolysis behavior of a set of pitches prepared from anthracene oil have been described. The pitches were obtained from four successive cycles of a sequential process that begins with blowing air through the heated anthracene oil, to bring about recombination reactions. Reaction products are distilled to give a pitch residue and a lighter fraction. Thermal treatment/distillation cycles of this reaction product yield a pitch and a distillate fraction (unreacted anthracene oil) during each subsequent stage. Products obtained during the process have been characterized by elemental analysis, Fourier transform infrared (FTIR) and ultraviolet (UV)-fluorescence spectroscopy, and size-exclusion chromatography (SEC). The pyrolytic behavior of the anthracene oil derivatives was examined using a thermogravimetric balance. Thermal treatment of the anthracene oil and its (distilled) reaction products at 440-460 °C under 5 bar pressure leads to a partially anisotropic pitch with the formation of a liquid crystal phase (mesophase). The formation and evolution of these mesophases were analyzed by optical microscopy.
1. Introduction Anthracene oil (AO) is a low-value distillation fraction of coal tar, largely made up of polycyclic aromatic hydrocarbons of 3-5 rings. It is mostly used in the manufacture of carbon black. One option to obtain higher value products is the transformation of AO into pitch, through partial polymerization. The process is usually reported to take place in the presence of AlCl3 or BF3/HF as a catalyst.1,2 However, the elimination of the catalyst after polymerization is not straightforward, and the catalyst tends to contaminate the pitches in this manner. An alternative route for the polymerization goes through a partial oxidation process,3,4 involving polymerization and condensation reactions within the heated mass through a set of recombination reactions.5,6 It is known the treatment first causes the homolytic cleavage of C-H bonds, leading to new C-C bonds via intermediate oxy and peroxy moieties.7 Under controlled conditions, the final pitches obtained by this method are able to give * To whom correspondence should be addressed. E-mail: mgranda@ incar.csic.es. † Consejo Superior de Investigaciones Cientı´ficas (CSIC). ‡ Industrial Quı´mica del Nalo ´ n. § Imperial College London. (1) Fernandez, A. L.; Granda, M.; Bermejo, J.; Menendez, R. Carbon 1999, 37 (8), 1247–1255. (2) Bermejo, J.; Fernandez, A. L.; Granda, M.; Suelves, I.; Herod, A. A.; Kandiyoti, R.; Menendez, R. J. Chromatogr., A 2001, 919 (2), 255–266. (3) Bermejo, J.; Fernandez, A. L.; Granda, M.; Rubiera, F.; Suelves, I.; Menendez, R. Fuel 2001, 80 (9), 1229–12381. (4) Fernandez, A. L.; Granda, M.; Bermejo, J.; Menendez, R. Carbon 2000, 38 (9), 1315–1322. (5) Bermejo, J.; Menendez, R.; Fernandez, A. L.; Granda, M.; Suelves, I.; Herod, A. A.; Kandiyoti, R. Fuel 2001, 15, 2155. (6) Dominguez, A.; Blanco, C.; Santamaria, R.; Granda, M.; Blanco, C. G.; Menendez, R. J. Chromatogr., A 2004, 1026 (1-2), 231–238. (7) Metzinger, T.; Huttinger, K. J. Carbon 1997, 35 (7), 885–892. (8) Taylor, G. H. Fuel 1961, 40, 4651.
rise to an anisotropic liquid crystal phase called mesophase, which in turn, may serve as a carbon material precursor.9,10 Recently, Fernandez et al. reported the preparation of an AOderived pitch through an innovative two-step oxidation process.11 The procedure requires a first-step oxidative treatment to produce a reaction product that is subsequently thermally treated to produce the final pitch. The method served to prepare suitable binder and impregnating pitches. Because of the novelty of these pitches, little information is available about their compositions and pyrolysis behavior. The information would be of interest in establishing relationships between AO-processing conditions and pitch properties. This paper describes a study of four AO-based pitches obtained by partial oxidation steps, followed by thermal treatment. The structures and chemical compositions of the pitches have been studied using elemental analysis, Fourier transform infrared (FTIR) and ultraviolet-fluorescence (UV-F) spectrometry, and size-exclusion chromatography (SEC). Finally, thermogravimetric analysis was used to monitor the pyrolytic behavior of these materials, and optical microscopy was used to examine their value as a precursor for preparing graphitizable carbons. 2. Experimental Section 2.1. Raw Materials. An anthracene oil (AO-1) was used as the raw material (elemental analysis: C, 93.6%; H, 4.4%; N, 1.0%; S, 0.5%; and O, 0.5%). During the first process step, AO-1 was partially oxidized and reaction products (RP-1) were then heat(9) Granda, M.; Santamarı´a, R.; Mene´ndez, R. Chemistry and Physics of Carbon; Marcel Dekker: New York, 2003; Vol. 28, p 263. (10) Perez, M.; Granda, M.; Garcia, R.; Santamarı´a, R.; Romero, E.; Mene´ndez, R. J. Anal. Appl. Pyrolysis 2002, 63 (2), 223–229. (11) Fernandez, J. J.; Alonso, M. Light Met. 2004, 449–450.
10.1021/ef800537a CCC: $40.75 2008 American Chemical Society Published on Web 11/07/2008
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Figure 1. Schematic diagram showing the steps followed in the preparation of pitches from AO (air, air-blowing; TT, thermal treatment).
treated, giving rise to a distilled product (AO-2) and the first product pitch (P-1). The cycle was repeated using AO-2 to make RP-2, which was heat-treated and distilled to make P-2 and AO-3. AO-3 was then oxidized to make RP-3, which was heat-treated to produce P-3 and AO-4. Finally, AO-4 was partially oxidized to make RP4, which was heat-treated to distilled off AO-5, leaving P-4 as the residue. The temperatures of thermal treatment increased in successive cycles, ranging from ∼240 °C in the first cycle to ∼300 °C in the fourth cycle. Figure 1 shows a schematic diagram of the preparation of pitches from AO. All samples were supplied by Industrial Quı´mica del Nalo´n, S.A. 2.2. Sample Characterization. 2.2.1. Elemental Analysis. The carbon, hydrogen, sulfur, and nitrogen contents of the samples were determined with a LECO-CHNS-932 micro-analyzer. The oxygen content was obtained directly using a LECO-VTF-900 furnace coupled to the micro-analyzer. The analyses were performed with 1 mg of sample ground and sieved to P-1. In addition to the highest intensity peak, the P-4 sample also gave the earliest eluting retained peak. The chromatograms of the set of reaction products covered almost identical ranges in both the retained and excluded regions. The only difference between the RP-x samples was an increase in intensity of the lowest mass region of the retained peak as the number of cycles increases (Figure 4b). This suggests that reactions with the oxygen also involved some cracking reactions, with this later being more likely to occur under the more severe reaction conditions. In summary, the SEC chromatograms showed the expected increases in the molecular size (as suggested from IR and elemental analysis results) from the AOs to their corresponding pitches. Larger molecular sizes were observed in the pitch samples recovered from the later processing cycles. This indicates that samples were becoming progressively heavier with the increasing severity of partial oxidation and heat-treatment stages. Meanwhile, a clear trend of increasing molecular size was observed for the pitches produced from the later stages. The wide polydispersity of the reaction products and the pitches, however, does not allow for more detailed comparisons.21 A more detailed characterization of solubility fractions of these pitches, in terms of mass distribution and structural features, has been undertaken and will be submitted for publication in due course. 3.1.4. UV-F Spectroscopy. Large shifts toward longer wavelengths have been observed in the UV-F spectra of pitches in comparison to those from the corresponding AOs and reaction products. Figure 5 shows the UV-F spectra of the samples from the first cycle, AO-1, RP-1, P-1, and AO-2. Parts a-c of Figure 6 present the results for samples from equivalent stages of different cycles. The UV-F spectra have been peak-normalized.
(20) Morgan, T. J.; Millan, M.; Behrouzi, M.; Herod, A. A.; Kandiyoti, R. Energy Fuels 2005, 19, 164.
(21) Islas, C. A.; Suelves, I.; Li, W.; Morgan, T. J.; Herod, A. A.; Kandiyoti, R. Fuel 2003, 82, 1813.
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Figure 5. UV-F spectra at 350 nm, area-normalized, of the samples from the first cycle: anthracene oil (AO-1), reaction product (RP-1), pitch (P-1), and the unreactive anthracene oil (AO-2).
Figure 4. SEC curves at 300 nm, area-normalized, of the anthracene oils (a) AO-x, (b) reaction products RP-x, and (c) pitches P-x obtained in the first (x ) 1), second (x ) 2), third (x ) 3), and fourth (x ) 4) processing cycle of the AO.
The spectra point at the presence of larger aromatic groups in the pitches compared to the AOs. This interpretation is reinforced by the lower fluorescence intensities exhibited by the pitch samples. It is likely that similar large fused aromatic compounds are also present in the reaction products, but their presence would be masked by the presence in larger amounts of lighter material. Smaller molecules (carrying smaller polynuclear aromatic groups) are expected to fluoresce more intensely than the larger molecules and affectively mask the signal from the larger molecules. This reduction in sensitivity toward longer wavelengths in complex hydrocarbon mixtures has been previously discussed.20 A comparison between the UV-F spectra of the AO-x samples (Figure 6a) shows that all of the AOs exhibit fluorescence in the same regions of the spectrum. Differences in relative intensity are observed as the number of processing cycles
increases, shifting toward shorter wavelengths (smaller polynuclear aromatic groups). AO-1 showed a more intense signal at the longest wavelengths, with a large peak centered around 390 nm. The latter peak significantly diminished in intensity from AO-1 to AO-3 and then remained nearly constant from AO-3 to AO-5. A similar trend was observed for the peak centered at 360 nm. The most intense fluorescence for samples AO-1 and AO-2 were observed as two peaks at 320 and 340 nm, which progressively decreased in intensity after the second cycle. From AO-3 onward, the most intense florescence was observed at 300 nm, which grew in intensity with increasing process cycles. For AO-5, a new peak appeared as a shoulder at 280 nm. These data suggest that molecules with the largest conjugated aromatic systems are the more reactive species and are consumed in the first two stages of the process. This leaves molecules with smaller aromatic ring systems in the AOs of the later cycles, which apparently are more stable compounds. AO-3 and AO-4 also show a small amount of signal in the 600-700 nm region, which is not observed in the other oils. A similar signal between 600 and 700 nm is observed for RP-2, RP-3, and RP-4. This signal is reproducible and suggests the presence of larger molecular mass materials produced during the process. The UV-F spectra for the reaction products closely resembled those for the AOs. Almost identical trends were observed, with shifts in maximum intensity from longer to shorter wavelengths as the number of cycles increased. The similarity of the corresponding AO-x and RP-x samples highlights the influence of the smallest molecules over the observed UV-F spectra. UV-F spectra of P-1, P-2, P-3, and P-4 are presented in Figure 6c. The main feature was a large peak at 390 nm, which decreased in relative intensity compared to the rest of the spectrum, with successive stages of processing. The signal at both higher wavelengths (∼460 and ∼490 nm) and lower wavelengths (between 310 and 370 nm) increased in relative intensity. Taking into account the SEC results showing larger molecules in the pitches obtained from successive cycles, these data suggest that these pitches contain broader spreads of molecular sizes as well as broader distribution of polycyclic aromatic units. To confirm these findings, a more detailed NMRbased study has been undertaken on solubility fractions of these pitches; this work is being prepared for publication. The findings of the UV-F study are consistent with earlier findings from SEC and elemental analysis, all of which point toward higher concentrations of larger polynuclear aromatic
NoVel Anthracene Oil DeriVatiVes
Figure 6. UV-F spectra of the anthracene oils (a) AO-x, (b) reaction products RP-x, and (c) pitches P-x obtained in the first (x ) 1), second (x ) 2), third (x ) 3), and fourth (x ) 4) processing cycle of the AO.
groups being produced in the pitches obtained from successive cycles, alongside an incremental increase in oxygen functionalities. 3.2. Pyrolysis Behavior of AO Derivatives. 3.2.1. ThermograVimetric Analysis. The thermal stability of the products obtained was studied by thermogravimetric analysis (Figure 7). Three regions of weigh loss can be defined for these coal-tarderived products: (i) 550 °C, where the pitch has already been transformed into a semi-coke and weight loss is due to the removal of gases from solid mass.10 In the latter case, light gases (e.g., H2, CH4, etc.) are evolved as a consequence of cyclization and aromatization reactions, which lead to greater structural order within the coke. The TGA profiles obtained for all samples indicate that the unreacted anthracene oils (AO-1, AO-2, AO-3, AO-4, and AO5) and reaction products (RP-1, RP-2, RP-3, and RP-4) undergo
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weight loss in a single step at temperatures below 450 °C. Parts a and b Figure 7 shows that weight loss takes place between 150 and 350 °C for anthracene oils (AO-x) and between 150 and 450 °C for reaction products (RP-x). In contrast, the pitch samples exhibited multi-step weight loss, with a temperature of initial weight loss of ∼200 °C. Thus, the weight loss behavior of the AOs and “reaction products” were associated with the release of volatiles. The high volatile contents observed for these two sets of samples relate directly to their low carbonaceous residue at 350 °C: 10-12% for reaction products and 0% for unreacted AOs. On the other hand, once the residual volatile matter had been released, the weigh loss behavior of the pitch samples can be attributed to the release of the volatile matter formed during the carbonization of the material. The carbon residue at 350 °C for the pitches (P-x) was much greater, nearer the 70-75% mark. At 1000 °C, these values decreased to ∼5-6 wt % for the reaction products and 35-50% for the pitches. From these results, it can be inferred that the oxidative treatment of the anthracene oils (AO-x) leads to reaction products that mainly consist of volatile compounds. On the other hand, the subsequent thermal treatment produces the most polymerized material. Thermogravimetric curves of the all AOs are shown in Figure 7a. As it can be seen, the final temperature of weight loss decreased from ∼290 °C for AO-1 to ∼280 °C for AO-2 and to ∼260 °C for AO-3, indicating that the thermal stability of the AOs seems to decrease in the first and second cycles. However, a small shift toward higher temperatures (∼280 °C) is observed for the unreacted AOs of the third and fourth cycles (AO-4 and AO-5). These results suggest that the most reactive species are the less volatile and are consumed in the first cycles. These findings also match those of the SEC and UV-F results, which show smaller aromatic clusters in the AOs from the later stages. In the case of the reaction products, the TG and DTG profiles reveal that the temperature of maximum weight loss continuously decreased with the processing cycles, following the trend: RP-1 > RP-2 > RP-3 > RP-4 (Figure 7b). This suggests that the increment in the severity of the oxidative treatment leads to reaction products containing volatile compounds that distill at lower temperatures. In the case of the pitches, their TG/DTG curves revealed that during the early stages of pyrolysis (below 375 °C), the pitches present the same thermal trend as the reaction products (Figure 7c). The temperature of the first maximum rate of weight loss decreased as the severity of each treatment increased. However, above this temperature, there was a change in thermal reactivity and the amount of residue obtained at 1000 °C followed the trend P-3 > P-2 > P-1. This suggests the presence of lighter compounds that coexist with more polymerized compounds. At 1000 °C, the carbon residue of the whole pitch (P-x) increased with the severity of processing conditions. This trend is not observed in P-4. This could be related to the fact that P-4 also exhibits an unusually high oxygen content compared to the other pitches (Table 1), recalling the lower thermal stability of P-4 at temperatures above 380 °C. 3.2.1. Mesophase from AO DeriVatiVes. To evaluate the ability of the samples to generate mesophase, reaction products and pitches were pyrolyzed in the 440-460 °C range for 1-3 h. Taking into account the results obtained by thermogravimetric analysis and to avoid the massive release of volatiles, the reaction products (RP-x) were pyrolyzed under a constant flow
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Figure 7. TG (left) and DTG (right) curves of the (a) anthracene oils (AO-x), (b) reaction products (RP-x), and (c) pitches (P-x) obtained in the first (x ) 1), second (x ) 2), third (x ) 3), and fourth (x ) 4) processing cycle of the AO. Table 3. Main Characteristics of the Pyrolysis Products of Reaction Products (RP-x) and Pitches (P-x) at Different Temperatures and Soaking Times
a
sample
treatment
RYa
MYb
RP-1 RP-1
440 °C, 3 h, 5 bar 460 °C, 3 h, 5 bar
57 11
63
RP-2 RP-2
440 °C, 3 h, 5 bar 460 °C, 3 h, 5 bar
54 11
62
RP-3 RP-3
440 °C, 3 h, 5 bar 460 °C, 3 h, 5 bar
48 9
60
RP-4 RP-4
440 °C, 3 h, 5 bar 460 °C, 3 h, 5 bar
20 5
58
sample P-1 P-1 P-1 P-2 P-2 P-2 P-3 P-3 P-3 P-4 P-4 P-4
treatment 440 440 450 440 440 450 440 440 450 440 440 450
°C, °C, °C, °C, °C, °C, °C, °C, °C, °C, °C, °C,
1 3 2 1 3 2 1 3 2 1 3 2
h h 81 70 h h h h h h h h h h
RYa
MYb
84 81 53 80 66 45 74 59 39 61 57 26
15 70 57 15 50 36 11 40 35 10 37 32
RY ) reaction yield (wt %). b MY ) mesophase yield (wt %).
of nitrogen at a pressure of 5 bar. Table 3 shows the experimental conditions used and the amounts of the mesophase generated. The results show that, under the same experimental conditions (temperature and soaking time), the reaction products (RP-x) gave considerably less mesophase than the corresponding pitches. Thus, at 440 °C for 3 h, P-1 developed 70% mesophase. Under the same conditions, RP-1 did not show any trace of mesophase formation. In fact, it was observed that RP-1 requires the use of 460 °C, 3 h, and 5 bar to form a similar amount of mesophase. This is consistent with the fact that pitches are
produced with an additional thermal treatment step compared to the “reaction products” and, consequently, contain polymerized material that form mesophase under less severe conditions (lower temperature and absence of pressure). According to the results obtained over the temperature and soaking time range, the capacity to form mesophase follows the order P-1 > P-2 > P-3 > P-4, in the case of the pitches, and RP-1 > RP-2 > RP-3 > RP-4, in the case of the reaction products (Table 3). Thus, the increase in the severity of the processing conditions in successive cycles was observed to lead to samples with lower capacity for mesophase formation. This is consistent with the
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Figure 8. Optical micrographs of the pyrolysis products obtained from the reaction products (a) RP-1, (b) RP-2 (c) RP-3, and (d) RP-4 at 460 °C for 3 h under 5 bar and pitches (e) P-1, (f) P-2 (g) P-3, and (h) P-4 at 440 °C for 3 h.
fact that the AOs obtained at the end of each processing cycle (AO-x) were somewhat lighter, more oxygenated, and less reactive than those in the previous processing stage. The microstructures of the pyrolysis products from reaction products (RP-x) and the pitches (P-x) were studied by optical microscopy to assess the capacity of the samples to generate mesophase. This is a powerful technique that allows us to evaluate the formation of the anisotropic liquid crystal phase (mesophase) because of the properties of this mesophase to refract the polarized light. Figure 8 presents optical micrographs of the pyrolysis products. As mentioned before, all of the samples could generate mesophase under the different conditions studied. These mesophases ranged from small to large spheres that coexist with regions of coalesced mesophase. The presence of these coalesced regions appears related to the absence of primary quinoline insolubles in this type of pitch, because of the fact that the AO is obtained as a distillate. Reaction products and pitches were also pyrolyzed at 900 °C to study the optical texture of the cokes and to establish possible relationships between the compositions of the samples and microstructures of the resultant cokes. Figure 9 shows optical micrographs of the cokes obtained from these samples. It is worth noting that the optical textures of the cokes (parts a-h of Figure 9) reflect the progression of the mesophase (parts a-h of Figure 8). Both, reaction products and pitches, corresponding to the same processing cycle (i.e., RP-1/P-1, etc.), exhibited similar optical textures, suggesting that the structural order in the cokes could be mainly defined by the sequence of thermal events. Optical textures of large regions of coalesced mesophase (domains) are obtained in samples from cycles 1 and 2 (parts a, b, e, and f of Figure 9). The formation and development of these large domains is more restricted in samples produced in the last stages of AO processing (RP-3/P-3 and RP-4/P-4), and cokes from these cycles exhibited optical textures of mosaics (parts c, d, g, and h of Figure 9). It is well-known that the optical texture of cokes is governed by the viscosity of the mixture
during carbonization, especially during the formation and development of the mesophase.22,23 The larger domains were thus observed to originate from samples containing larger mesophase spheres in a less viscous environment. The decrease in the size of the domains observed for samples from cycles processed under more severe conditions (cycles 3 and 4) appear related to changes in the molecular structures of the samples (pitches and reaction products). These samples show more complex and cross-linked structures, which would tend to delay the formation of mesophase. Therefore, the required initial cracking of the molecules and subsequent reorganization of this kind of configuration proceeds thorough structures giving higher viscosities, which produces cokes with a preferential optical texture of mosaics. Thus, samples from cycles 1 and 2 that generate cokes that exhibit optical textures of broader flow domains might be used as precursors for needle coke and mesophase-based carbon fibers.24 On the other hand, samples from cycles 3 and 4 that produce cokes with optical textures of mosaics would serve as suitable precursors for high-density polygranular carbons.25 These results highlight the versatility of the AO-based pitches as precursors of carbon materials with a variety of microstructures and a broad spectrum of potential applications. 4. Conclusions AO can be easily transformed into AO-based pitches through a sequential process of increasing severity, consisting of cycles of oxidation and thermal treatment. The increase in the average molecular size observed from the AOs to their corresponding (22) Fernandez, J. J.; Figueiras, A.; Granda, M.; Bermejo, J.; Parra, J. B.; Menendez, R. Carbon 1995, 33 (9), 1235. (23) Marsh, H.; Walker, P. L. Chemistry and Physics of Carbon; Walker, P. L., Thrower, P. A., Eds.; Marcel Dekker: New York, 1979; Vol. 15, p 229. (24) Mochida, I.; Yoon, S. H.; Takano, N.; Fortin, F.; Korai, Y.; Yokogama, K. Carbon 1996, 34 (8), 941. (25) Fanjul, F.; Granda, M.; Santamaria, R.; Menendez, R. J. Mater. Sci. 2004, 39 (4), 1213.
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Figure 9. Optical micrographs of the cokes obtained from the reaction products (a) RP-1, (b) RP-2, (c) RP-3, and (d) RP-4 and pitches (e) P-1, (f) P-2, (g) P-3, and (h) P-4 at 900 °C for 30 min.
pitches provides evidence of AO polymerization. Larger molecular sizes and larger polynuclear aromatic ring systems were observed in the pitch samples recovered from the later processing cycles, indicating that samples were becoming progressively heavier with the increasing severity of the oxidative and thermal treatments. Examination of oxygen functionalities in the samples from the successive stages of the process indicated that oxygencontaining structures are formed in the oxidation stages. The results also suggest that, in this process, molecules with the largest conjugated aromatic systems are the most oxygenreactive species and are mostly consumed in the first two cycles. Most of the oxygen is then eliminated during the thermal treatment, which leads to a pitch with a more polymerized structure. The amount of oxygen introduced into the samples increased with the severity of the oxidation conditions. However, during the fourth cycle, the pitch obtained exhibited an unusually high oxygen content compared to the pitches from the earlier cycles. The higher oxygen content of P-4 can be correlated with its decreased thermal stability compared to pitches P-1, P-2, and P-3.
Upon pyrolysis, both the reaction products and the pitches gave rise to mesophase formation. However, “reaction products” require more severe reaction conditions to produce mesophase contents similar to those from the corresponding pitches. The optical textures of the cokes obtained at 900 °C varied gradually from flow domains in the first cycle to mosaics in the latter. Because the microstructure is related to the properties of the materials, the AO derivatives studied in this work offer the possibility of designing precursors for a variety of carbon materials. Acknowledgment. Authors thank the European Union (Project RFC-PR04001) and FICYT (Project PC-04-13) for their financial support. Dr. Patricia Alvarez also thanks the Spanish Council for Research for her I3P PS grant. Juan Sutil thanks the Spanish council for research for his I3P postgraduate grant.
EF800537A
