Molecular Changes in Asphaltenes within H2 Plasma - Energy

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Molecular changes in asphaltenes within H2 plasma Juan Carlos Poveda, Daniel Molina, Horacio Martinez, Oswaldo Florez, and Bernardo Capillo Energy Fuels, Just Accepted Manuscript • Publication Date (Web): 05 Jan 2014 Downloaded from http://pubs.acs.org on January 7, 2014

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Molecular changes in asphaltenes within H2 plasma Juan C. Poveda1 †, Daniel Molina1, Horacio Martínez2, Oswaldo Florez2 and Bernardo Campillo3 1

Laboratorio de Espectroscopia Atómica Molecular, Escuela de Química, Universidad Industrial de Santander, Bucaramanga, Santander, Colombia A.A. 678 2 Instituto de Ciencias Físicas, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México C.P. 62210 3 Facultad de Química, Universidad Nacional Autónoma de México, Cd. Universitaria D.F., México C.P. 04510

ABSTRACT In the present work, the chemical changes in asphaltenes, solid residues, when they are treated with hydrogen plasma were analyzed. H2 plasma was characterized by the presence of electrons, H and H ions, at kinetic energies as low as 30 eV. These species can interact with the asphaltenes to produce changes in the chemical structure by different mechanisms such as bond cleavage, recombination, and condensation. Asphaltene samples were exposed to different treatment times (up to 120 minutes). The plasma was characterized by Optical Emission Spectroscopy (OES) as well as by the different products created in the reactions of asphaltenes. The presence of C , CH , C , NH , and V was confirmed. Spectroscopic techniques such as Fourier Transform Infrared spectroscopy (FT-IR), Matrix-Assisted Laser Desorption Ionization Time of Flight - Mass Spectrometry (MALDI-TOF-MS), Nuclear Magnetic Resonance spectroscopy (1H-NMR and

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C-NMR), and X-Ray Diffractometry (XRD), were used to

characterize the chemical composition of asphaltenes at the different treatment times. Chemical changes were analyzed from the molecular structural parameters calculated by the abovementioned spectroscopic techniques. Possible changes in the asphaltene cluster structures were analyzed using XRD. This work explores the application of plasma technologies to modify the chemical composition of asphaltenes and obtain valuable chemical products resulting of plasma treatment process. †

Corresponding author E-mail: [email protected]

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Keywords: Asphaltenes, Plasma Treatment, Molecular Characterization, Spectroscopic Techniques, Heavy Crude Oils Fractions. 1. INTRODUCTION The main global production of crude oils is currently focused on heavy crude oils, which are rich in heavier compounds corresponding to the resin and asphaltene fractions.1,2 These compounds are important in the thermodynamic properties of crude oils and their fractions.3-5 Changes in the downstream conditions, pressure and temperature, of heavy crude oils can dramatically affect the properties of the fluids, with the asphaltenes being deposited in the many of cases. Deposition of asphaltenes in pipelines has serious implications for the transport of crude oils.6-8 Significant additional effort is required to maintain production efficiency because of the deposition of asphaltenes. Higher amounts of the heavy fractions in crude oils have forced the technological development of new strategies to overcome the limitations imposed by heavier fractions in the thermal cracking reactors, hydrogenation processes and other processes that require catalysts. Chemical changes in the asphaltenes and resins have been studied because it is very important to know how these compounds behave when samples are exposed to different gases as oxygen under various experimental conditions.9,10 Other reports have considered the chemical changes that occur when samples are thermally treated under different reaction conditions such as temperature, pressure and time for reaction.11-13 Few studies have been reported regarding the chemical changes in asphaltenes when these compounds are exposed to plasmas under low energy conditions where the electrons reach kinetic energies of a few electron volts (eV), lower than the ionization energies of asphaltene molecules.14-16 We are interested in knowing the chemical changes that occur when asphaltenes are exposed to plasmas produced by different gases under low pressure regimes. We analyzes actually in a new set of experiments the chemical changes when asphaltenes are exposed to oxygen, methane and hydrogen plasmas at different exposure times and gases pressures. When heavy oil or its fractions are treated by plasma technologies, several advantages can be observed. First, treatment favors molecular breaking under gentle conditions requiring no high pressures and high temperatures, with a consequent energy saving. Second, the products of molecular breakdown of heavy ends can be used in later stages of the refining processes and increased production of fractions and products of higher economic value. And third, these technologies can be applied equally to any fraction regardless of the chemical nature of crude


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oils used. To our knowledge, technologically feasible implementation of these processes requires additional effort and more research to try to understand the complex processes occurring at the molecular level. In the present work, asphaltenes from a Colombian heavy crude oil, obtained by the ASTM procedure D6560-12,17 were exposed to plasma produced in a hydrogen atmosphere. The plasma and the chemical species resulting from the decomposition of samples were characterized using optical emission spectroscopy. The decomposition efficiency of samples and the chemical changes were analyzed as a function of the exposure time. Chemical changes were interpreted using the structural parameters calculated from the above-mentioned spectroscopic techniques such as 1H- and 13C-NMR spectroscopy, MALDI-TOF, FT-IR, and XRD. 2. EXPERIMENTAL SECTION 2.1. Plasma generation and asphaltenes erosion. The experimental setup and technique to generate the plasma was recently reported and it is shown in Figure 1.18 A brief description is reported here. Two stainless steel circular plates plasma electrodes were used, 1 mm thick and 30 mm in diameter. The electrodes are located at the center of the reaction chamber with 7 mm gap spacing. The amount of 200 mg of asphaltene samples was pressed into flake on electrode and exposed to H2 plasma glow discharge. A continuous dynamic flow of H2 gas (99.99% purity) was let in the system through Matheson flowmeter model FM1000 at 1.5 l/min. The H2 gas was introduced into the reaction chamber using a lateral flange. The same gas connection was used for the pressure sensor (MKS, Type 270 signal conditioner and 690A11TRC MKS Baratron). A DC discharge was used to generate the plasma in H2 gas. Plasma particles were monitored by plasma emission spectroscopy through a quartz window using an optical fiber (Solarizationresistant UV and fiber diameter size of 400 µm) that was connected to the entrance aperture of a high-resolution Ocean Optics Inc. Spectrometer Model HR2000CG-UV-NIR (101.6 mm focal length, 5 µm inlet and outlet slits, and 300 lines-mm-l) in the spectral region 200-1100 nm at a resolution of ~0.35 nm (an OFLV-200-1100 order-sorting filter was installed to eliminate second- and third-order effects) with a Sony ILX511B linear silicon CCD array (2048 individual pixels with 14 µm x 200 µm of pixel size and sensitivity of 75 photons/count at 400 nm). The low noise level (with 250:1 signal-to-noise ratio at full signal) of the CCD allows long integration times (resolution times between 1 ms to 20 s) and therefore the detection of very low emission intensities. The spectrometer was calibrated using an Ar Source (Ocean Optics Inc.).


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The spectra data were obtained with 10 s integration time. The fiber optic was positioned to collect the emission light appearing on the asphaltene-H2 plasma. The H2 pressure was 5.0 Torr, with a flow of 1.5 l/min. The discharge power supply was maintained at an output of 340 Volts (VD) and a current (ID) of 0.15 A (50 W), which was measured using a digital Tektronix multimeter model DM2510. To avoid any contamination due to particles and gases deposition into the experimental apparatus, the entire chamber (window, electrodes, walls, wires) was cleaned. Inside surface of plasma chamber was cleaning with a volatile solvent as chloroform and the electrodes and wires were sonicated, washed and dried at a temperature of 70 °C. Before each experiment the chamber was maintained at the base pressure for a period of time of two hours to remove residual solvent and moisture. The base pressure of the plasma chamber of 6.3 x 10-3 m3 volume was 7.5x10-3 Torr (measured with a Thermovac sensor TR211 connected to a Thermovac TM20 digital controller), achieved using a mechanical pump (Trivac D10, Leybold Pump with nominal pumping speed of 11.8 m3 h-1). With the present pressure conditions, the signal corresponding to background pressure (water vapor, hydrogen, etc.) contribution was estimated to be in the order of 0.015%. In order to observe the erosion of the asphaltene exposed to H2 plasma, an asphaltene sample was placed on one of the electrodes inside the discharge zone. Before exposing it to the plasma, the sample was kept under vacuum of 7.5 x 10-3 Torr. Since asphaltene has a vapor pressure, some material could evaporate; it is estimated that the amount exposed of asphaltene has a maximum reduction of 10% during the time exposure to vacuum environment, which was considered in the measurements. The asphaltene mass loss (mL) was determined in % of the sample, which is calculated according to the equation mL= (Δm)100%/m0, where Δm is the mass of asphaltene lost from the initial mass (m0) during the plasma treatment. Mass measurements were carried out using a LECO 250 Balance. 2.2. Infrared spectroscopy of asphaltenes. Infrared spectra of the asphaltene samples were collected on a Bruker TENSOR-270 FT-IR spectrometer, spectral range from 370 to 7500 cm-1. We use in the analysis the spectral range from 500 to 4000 cm-1, 64 scans per spectra and resolution of 1 cm-1. The FT-IR spectrometer was equipped with a low noise DLATGS (Deuterated L-α-Alanine doped TriGlycine Sulphate) detector with KBr windows. FT-IR spectra


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were measured by the attenuated total reflectance (ATR) technique using a Bruker ATR A225 sample cell equipped with a diamond crystal of quadrate area of 2 x 2 mm2, spectral range of crystal 10000 to 10 cm-1. The FT-IR spectrometer was controlled using the OPUS software. Calculated areas of main observed signals in the FT-IR spectra are reported in Table 2. 2.3. Matrix Assisted Laser Desorption Ionization. MALDI-TOF spectra were acquired using a Bruker Reflex II MALDI-TOF Mass Spectrometer equipped with an Nd:YAG laser emitting at the third harmonic 355 nm and repetition rate of 500 Hz, with a pulse width of 3.5 ns. Ions were extracted and accelerated from the ionization region by a pulsed ion extraction system designed by Bruker with a delay of 1.2 ns and extraction voltage of 20 kV. The voltages of the Einzel lens and deflection plates in the ion optics region were optimized to obtain the best possible resolution. The TOF-MS analyzer was operated in the reflector mode equipped with a microchannel plate detector. Reflection plates were polarized at 25 kV to obtain a potential gradient according to the kinetic energy of the ions, allowing the best reflection properties and refocusing the ions close to the detector. The mass spectrometer was calibrated prior to measurements. The asphaltenes were dissolved completely in chloroform to yield solutions of approximately 3 wt%. No matrix was used because the chemical nature of the asphaltenes can absorb the ionizing radiation as well as the chromophores used in the main MALDI experiments. The sample was deposited in a sample holder in amounts of 4 L, and the chloroform evaporated in the air. This procedure was repeated five times to concentrate the sample in the ionization region. The sample holder was then placed in the spectrometer, and measurements were made. 2.4. NMR spectroscopy. The 1H- and 13C-NMR spectra were measured on a Bruker Advance III spectrometer operating at 400 and 100 MHz, respectively. The 1H-NMR samples were 4 wt% solutions in CDCl3 (99.8 % D). The 30° pulses (Bruker zg30 pulse sequence) were used, sweep width 49000 Hz, 32K points, and delay time was 2 s. Sixteen scans were averaged for each spectrum. The 13C-NMR samples were in 10 wt% solutions in CDCl3 (99.8% D) using Cr(acac)3 as the paramagnetic relaxation reagent at a 0.05 M concentration. The 30° pulses (Bruker zgig30 pulse sequence) were used, sweep width 22400.0 Hz, 32K points, and delay time was 20 seconds. The zgig30 pulse sequence suppresses the Overhauser effect and the C-H coupling with a inverse gated decoupling sequence, Composite Pulse Decoupling (CPD). Three thousand scans were averaged for each spectrum. In both cases, spectra were recorded using a 5 mm probe with


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a spinning rate of 10 Hz and 298.15 K temperature. Free induction decays (FID) were processed using MestreNova.19 2.5. X-Ray Diffraction. X-ray diffractograms were measured using a Bruker D8 Advance automated diffractometer on finely ground powders of asphaltenes. In this ground-powdered form the quality of the diffraction pattern is improved. The diffractometer uses an X-ray tube with a copper target (Kα1 1.5406 Å) operating at 40 kV and 30 mA, a nickel filter as a monochromator, an autodivergent slit at 0.6 mm, a soller slit at 2.5° and is equipped with a lynxeye linear detector. A two-theta angle was scanned from 5 to 80° in steps of 0.015° with 5 s per step. The baseline was corrected using the data points outside rectangle method with a second order function to connect outside points of rectangles. Data were smoothed using Savitzky-Golay filtering. Peak profile analysis was performed to fit the diffraction profile and determine the peak positions, full widths at half-maximum (FWHM), background profiles, and peak areas. Single peaks were assumed to have Gaussian profiles. The characteristics of peaks γ , 002, 100, 004, and 110 were calculated. 3. RESULTS AND DISCUSSION. 3.1. OES measurements. Throughout the plasma irradiation process the OES arrangement was adapted to measure spectra every 5 min. Figure 2 shows a selected survey spectra and represents a typical OES measurement of the H2-plasma glow discharge of the asphaltene, at various exposed times ranging from 5 to 30 min. The OES spectrum obtained after 5 min of plasma exposure is relatively low. The identified species in the spectra shown in figure 4 are listed and reported in Table 1.20 Then at 30 min of plasma exposed, the OES spectrum is considerable extensive, showing the NH, CH, C2 and V, as the dominant species in the spectra. In addition to the species aforementioned, appears an emission of Hγ arising from the H2 plasma discharge. We can see from Figure 2 that the molecular bands intensities observed gradually increase during the initial 10 min of plasma treatment, followed by an increment in the subsequent 30 min, reaching their highest intensity. As the treatment time increases the band intensities decrease. That means that asphaltene reacts and produced similar products during all increments of the treatment time. The discharge time of maximum erosion was at 30 min. Therefore, the intensity of the product generated in the plasma coming from the asphaltene decreased with increasing discharge time, being correlated with the mass loss.


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Plasma processing opens the possibility for changing the chemical structure of asphaltenes, many processes with different reaction kinetics occur. A variety of species such as excited molecules, free radicals and ions are generated by free electrons impacts and H2 plasma, and asphaltenes. The reactions can comprise numerous products: electrons (e), positive molecular ions (H ), radicals (H), atoms (C, H, N, O, V) and hydrogen molecule. The base experimental data of the rate constants for electron collision dissociation in such plasma at low energies can implicate a substantial atoms and molecules produced from asphaltene and H2, which are not well determined. On the other hand, the rate constants can be calculated, when the dependence of cross-sections as a function of the energy are well established. Any chemical kinetic model requires the electron collision ionization and dissociation cross sections of the reactions involved. It is also required to consider the neutral gas (H2) reactions, photoreactions and recombination. Therefore, we propose a qualitative interpretation of the way that the observed species were formed. In the present conditions in this experiment, the OES spectra observed consists of the emission of the hydrogen molecular and lines of hydrogen atomic (Hα and Hβ). The radiating species (H2 and H2+) are produced by electron impact excitation followed by: H C Π → H B Π "

(1)

H B Σ → H X Σ "

(2)

The mechanism of H2 plasma-initiated erosion is produced by the interaction of the (e), H2 , H2, H, H+ and energetic photons with the asphaltene surface (several research has been +

performed on the molecular nature of asphaltenes).21-24 Regarding to their natural complexity of asphaltene, the molecular arrangement is difficult to describe their structures, so asphaltene has been defined by ASPH. We can propose the possible reactions may be: , H , H , H , H , ASPH →

CH NH C V H , H , H , H, H , ASPH ∗

(3)

Equation 3 display the proposed reaction that produced the erosion of the asphaltenes and the formation of the products observed in OES measurements (molecules of C2, CH and NH, and the atoms V, and H). From the experimental conditions: 50 W of discharge power, 6.3 x 10-3 m3 of discharge volume and ~5.0 Torr of pressure, a low ionization degree (~10-7) of molecular hydrogen was


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found. As a result, the specie more abundant in the plasma composition is the precursor (H2) and only small intensity of other compounds (CH, NH, C2, V, and Hγ) as display in Figure 2. The H2 plasma (without asphaltene) displays only signals coming from the H2, so the background of the system produced a low signal. Interactions with the discharge wall may affect the intensity of several products in a low-pressure discharge. These signals are important in low pressures, especially when the chamber radius (250 mm) is approximately equal to the ion mean free-path. In the present experiment, the electrodes (30mm) are 8.3 times smaller than the chamber radius. We expected a low contribution from the wall background to the emission spectra. It was measured asphaltene mass loss (mL) at 15, 30, 60 and 120 min of treatment times. Figure 3 shows the asphaltene mass loss (mL) versus treatment time. The final asphaltene mass loss-time data obtained was the result of 5 independent measurements. Increasing the treatment time in H2 discharge, the asphaltene has an erosion rate of 0.63 mg/min throughout the first 45 min. Between 60 and 240 min of treatment time, the mass loss is approximately constant because the erosion rate of the asphaltene was low in that particular period, and significant changes in the spectroscopic data are not observed. From J=ID/S, where ID is the current discharge (0.15 A) and S is the electrode surface (7.07 x 104

m2), the plasma-ions flux (J) reaching the cathode was obtained. The plasma- ions flux was

~7.95 x 1022 m-2 min-1. Considering that the principal ion product was H2+, the J was approximately 0.26 g m-2min-1. It is observed for the first 45 min, that the treatment time and asphaltene mass loss has a linear correlation. 3.2. FT-IR Spectroscopy. Fourier Transform Infrared Spectroscopy was used for the determination of the main chemical groups of asphaltenes. Quantitative analysis was possible on basis of the calculated areas of signals of chemical groups of interest. The most commonly observed absorption bands in asphaltenes are found at frequencies of 700, 780, 840, and 880 cm-1, for the aromatic C-H bending vibrations, out-of-plane. Signals at 725 and 760 cm-1 correspond to rocking vibrations of long (CH )n moieties with n>2, which can overlap with the C-H bending vibrations of aromatics. The sharp peak at 1306 cm-1 could be due to the presence of ethers or esters. The peak near 1030.5 cm-1 can be assigned either to ester linkages or sulphoxides present in the asphaltenes.25,26


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At frequencies of 1510 and 1580 cm-1 deformation vibrations of a benzene ring are detected, and the band at 1610 cm-1 is assigned to the C=C bond of an aromatic ring (see Figure 4). Stretching vibrations of the C-H bond appears at 1625 and 1650 cm-1, typical C-H stretching vibrations in condensed aromatic hydrocarbons are observed at 3040 and 3060 cm-1. The bands observed at 1373.3 and 2872.0 cm-1 correspond to symmetrical bending and stretching vibrations, respectively, of methyl groups in which all of the C-H bonds extend and contract in phase. The bands at 1459.5, and 2924.5 cm-1 are due to methylene groups of alkyl side-chains in aromatic hydrocarbons and naphthenes, the absorption bands at 1441.3 and 1459.5 cm-1 assigned to CH2 groups can present contributions of CH3 bending modes.27 Other bands can be assigned to heteroatoms in the molecular structure, i.e. the absorption band centered at 3440 cm-1, are characteristic of nitrogen-containing groups. In the region 3500-3750 cm-1, signals assigned to the OH stretching vibrational mode appears. The bands at 3652 and 3668 cm-l are assigned to OH groups in the surface of asphaltene layers sandwiched between two of them. Other bands around 3700 cm-1 are also assigned to OH stretching contributions: some of which are assigned to hydroxyl groups in the surface of the micro-crystals, including hydroxyl groups at the broken edges.28,29 From a quantitative point of view, the FT-IR data are used to obtain information about the ratio of groups into the sample. Some authors analyze asphaltenes and observe the linear relationship of the relative intensities of alkane vibrational frequencies between 1380 and 1460 cm-1 and the ratio (CH2/CH3) of the aliphatics.30-33 Direct applications of the methodology have been reported by Benkheda and Landais to analyses the change of the average aliphatic chain length of mature coals, by deconvolution of the FT-IR spectra, in the region of 1360-1390 cm-1 (see Figure 4).33 The relation "CH ⁄#CH "CH was used to calculate the ratio of methyl to methylene groups obtained from the peak intensities at 1373.0 cm-1 and 1459.5 cm-1, as follows: %&'(

)&'* %&'(

, -(.(.0

+ ,-123.2

(4)

calculated ratios are reported in Table 3. FT-IR deconvolution analysis in the range 2700 to 3100 cm-1 allows us to characterize the CH 456% , CH456% , CH, CH 56% and CH56% vibrational modes. From calculated areas of 2924.5 and 2954.9 cm-1 signals is possible to obtain the #CH⁄"CH ratio (see Table 3).34 Deconvolution analysis must be applied to different regions in the FT-IR spectra to the


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determination of intensities of signals where signals cannot be differentiated. Yen et al. calculated the ratio of HMe (number of hydrogen atoms in methyl groups) to Hsat (number of hydrogen atoms attached to saturated carbon atoms) using the following equation:35 '78

'9:;

+

?-(.(.( ?*3*0.0

@, where K´ is 2.4

(5)

Also, we calculate the #CH⁄"CH ratio by using the signals at 2851.9, 2924.5, and 2954.7 cm-1, as the ratio ABCD.E AEF.C ⁄AECF.G, results are reported in Table 3.

In Figure 4 we present the differential spectra of asphaltene samples after subtracting the FT-IR spectrum of asphaltene sample before plasma exposure as is suggested by Chang.35 Changes in the chemical structure of asphaltenes were analyzed through the groups of signals, 700-900 cm-1, 1030 cm-1, 1300-1500 cm-1, 2900-3000 cm-1, and 3500-3750 cm-1. The three absorption bands from 700 to 900 cm-1 are assigned to the aromatic C H H out-of-plane bending vibrations, in these region also appear the signals of long alkyl chains (CH2)n, 725-760 cm-1. So, the analysis of aromatic cores is difficult because the overlapping of signals in this region. As can be seen in Figure 4, when asphaltene samples are exposed to the plasma, the relative intensities of signals changes, indicating chemical changes occurring when interaction with plasma particles takes place, but there a clear tendency in not observed. The signals of CH and CH groups appear from 1300 to 1500 cm-1, and the relative areas changes as the treatment time increases (see Table 3). The ratio of hydrogens in CH to the hydrogens in CH groups can also be analyzed using the region between 2900 and 3000 cm-1. Analyzing the reported data in Table 3, we can see that results allows us to observe a progressive increment of CH2 groups when they are compared with CH3. This indicates that CH2 groups are produced as the plasma particles (H , H , H ) interact with asphaltenes. During the first 30 minutes the signals of CH2 bending and symmetric stretching of CH3 increases but decreases at longer times. A similar behavior was observed to the signals between 2850-2970 cm-1 assigned to the symmetric CH2 and antisymmetric CH3 stretching. One possible mechanism involves the hydrogenation of aromatics units in the periphery to form cyclic paraffins before the formations of linear paraffins, which can explain the changes in the calculated ratios reported in Table 3. In the region at 3500 to 3750 cm-1 appears amines and hydroxyl groups.28,29 The presence of free OH groups can be observed beyond 3600 cm-1. These signals appear changing their intensities as the plasma treatment is prolonged. The signal at 3750 cm-1 is attributed to free OH on the surface of the material, most likely outside the aromatic cores of the asphaltenes. From


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Figure 4, we observe that signals of OH groups increases progressively as the exposure time to the plasma also increases. The increment in the OH signal can be the result of either ether or keto to alcohol functionalities conversion, R-O-R´ to ROH or R´OH, and R-CO-R´ to R-CH(-OH)-R´. Chemical changes in the aromatic core were observed in the region 700 to 900 cm-1, signals 748.34, 808.13, and 864.07 cm-1 are more prominent at 30 min, at this exposure time the aromatic core being richer in hydrogen than substitutions of alkyl groups. Two of the possible reaction mechanisms can be either the aromatization of naphthenic rings joined to aromatics, by hydrogen elimination via C-H bond break, or by the alkyl elimination via C-C bond break and inclusion of hydrogen form plasma particles. So, the above-mentioned mechanisms need to be supported on the basis the structural parameters using data from NMR and XRD spectroscopies. When plasma particles-asphaltenes interacts C-H and C-C bond break occurs. If hydrogen elimination takes place from cyclic paraffins there is an aromatization process, resulting in an increment of the signals of aromatics at 700 to 900 cm-1, also supported by the growth observed of signals at 1565 to 1600 cm-1 (C-C stretch of aromatics). Otherwise, if hydrogen interacts either with cyclic paraffins or outside of aromatic structures, and it is linked to the structure a hydrogenation process takes place and the ratios of CH2 to CH3 increases as the treatment time also increases (see Table 3). Also, if C-C bond breaks occur this process facilitates the removal of low molecular fragments, which are evacuated by the vacuum system of plasma chamber. Signal at 1030 cm-1 increases as the exposition time to plasma also increases, this signal is assigned to sulphoxides possibly due to the oxidation of thiophenes. 3.3. Matrix Assisted Laser Desorption Ionization Mass Spectrometry. MALDI-TOF spectra of asphaltene without plasma erosion and after 15 minutes of exposure to plasma are displayed in Figure 5. Spectra were analyzed making a deconvolution of envelopes and calculating the minimum number of Gaussians required for reconstruction. For all cases the number of Gaussian functions needed to obtain a good correlation with experimental data was four. From deconvolution processes we observe that the Gaussian functions were centered in the ranges 1616-1655, 2096-2164, 2867-3110 and 5139-5597 Daltons, corresponding to the range of mass profile distributions; results of deconvolution are presented in Table 4. Because the laser radiation desorb the sample by a fast thermal heating, there is possible to obtain clusters with several molecules per cluster unit, the ionization occurs by proton transfer mechanisms, being registered de ions M-H+. From the results was possible to observe that the interactions of


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molecules into the molecular masses ranges of 1616-1655 and 2096-2164, can produce clusters with two and three molecules per cluster unit, observed in the region of masses of 2867-3110 and 5139-5507, respectively. To our knowledge, the MALDI-TOF-MS has been useful in determining the molecular profile distributions of heavy fractions from crude oils, but many aspects of processes taking place during the desorption and ionization remain unrevealed.37,38 Desorption and ionization processes are very sensitive to the radiation intensities and wavelengths because the wavelength can promote either resonant or nonresonant photon absorption, as has been reported by other authors.39-42 In the present study was difficult follow the changes of molecular weight distributions because the formation of cluster darkness the analysis. From data in Table 4 we observe that the relative amount of mass distribution centered at 1616-1655 Da and 2096-2164 Da, decreases as the treatment time increases, while the higher mass clusters, 2867-3110 Da and 5139-5507 Da, increases. Interaction of asphaltenes with plasma particles favors the formation of larger clusters. 3.4. Nuclear Magnetic Resonance Spectroscopy. NMR spectroscopy yields information about the hydrogen and carbon distribution in the molecular environments like different regions for aromatics, unsaturated and alkyl chains. Because asphaltenes are a mixture of thousands of compounds, the NMR spectra are difficult to be analyzed. So, the NMR spectra would be divided into regions, with each region assigned to a chemical group. In the NMR spectra, the integrated areas are commensurate to the relative amount of atomic nucleus of the different chemical groups presents in the sample. Quantitative experimental conditions are needed to obtain useful structural data. The main chemical groups present in asphaltenes and the spectral ranges where these chemical groups appear in 1H and 13C-NMR spectra are shown in Table 5, with normalized integrated areas also presented. Chemical changes of asphaltenes can be inferred from these data analyzed on basis of the time in the plasma. From 1H-NMR data, changes were observed in the naphthenic and paraffinic structure. The amount of hydrogen in mono-aromatic rings changes as the treatment time increases, but no clear tendency was observed. The main changes were observed in the relative number of hydrogen atoms located in polycyclic aromatic rings, the number increases as the exposure time to the plasma also increases. In examining the carbon data in Table 5, important changes were observed for the carbons in naphthenic structures and the number of aromatic carbons bonded to either naphthenic or paraffinic carbons. Small changes were also observed for the number of catacondensed aromatic carbons, which increase as the


12

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Energy & Fuels

treatment time is prolonged. We can argue that the chemical changes occurring during the plasma treatment as a result of the interaction between atomic and molecular hydrogen and asphaltenes involve two different pathways. One pathway could be the I J or IK bond cleavage for paraffinic or naphthenic structures joined to aromatic rings (mainly polyaromatic rings), decreasing the number of carbon atoms in those groups. Small neutral fragments resulting from the processes are evacuated by the vacuum system, decreasing the amount of sample in the chamber. The other pathway could be the hydrogenation of aromatic carbons in the polyaromatic ??? structures, resulting in small changes in the pericondensed and catacondensed carbons (I?L , ?? W ??? I?L , respectively). Because the I?L and I?L appear in the same 13C-NMR spectral region, we

cannot distinguish the changes from these data. But, the addition of hydrogen on the ??? ?? , I?L . polyaromatic structures diminishes the number of I?L

From the analysis of the data reported in Table 5, we observe that the main structural changes occur within the first 30 minutes of treatment with plasma. As observed in Figure 3, when the time increases, the mass loss becomes stabilized and no more sample is either thermal desorbed or plasma degraded. 3.5. X-Ray Diffraction. Vacuum residues and heavy fractions such as asphaltenes and resins can be characterized using X-ray diffraction. Ordered structures in the solid phase such as the stacking of aromatic layers in asphaltenes have crystal characteristics that can be characterized using the measured diffraction profiles. The measured diffraction pattern for asphaltenes without plasma exposure (black line) and differential XRD patterns of samples exposure to different plasma times are shown in Figure 7. Yen43 proposed the method for the calculation of aromaticity and crystallinity parameters many years ago. The calculation procedure is found elsewhere and improvements have not been made during this time.43 The calculation is briefly summarized as follows: Two main bands designated as γ and graphene [002] bands appearing at 2θ near 20° and 25° are attributed to reflections of paraffinic and aromatic structures in the material. Areas are proportional to the amounts of these structures present in the sample. The aromaticity (fa) can be calculated from the areas (A) of the integrated bands for γ and graphene using the ratio: X4 +

YZ Y

+ Y

YZ

Z Y[

+ ?

?\]:^_8`8

\]:^_8`8 ?a

(6)

where Ib , and I? , are the saturated and aromatic carbon atoms in the sample.


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The distance between aromatic layers cd was calculated from the 2-Theta position of maximum of the graphene band [002] using the Bragg relation:41 cd +

e

(7)

5f)g

where λ is 1.54056 Å (high-resolution) for the Cu Kα radiation, and θ is the Bragg angle. The equation 8 gives the distance between saturated chains of the asphaltene molecules: Ce

ch + B5f)g

(8)

The average diameter of the aromatic units can be calculated using the Scherrer crystallite size formula: D.BFe

m.E

i4 + jkl5g + n

(9)

-/*

where pD/ is the full width at half-maximum using the band [110], and ω is the bandwidth. The average thickness of the asphaltene cluster measured perpendicularly to the aromatic layers was calculated from the full width of the [002] band at half-maximum using the ratio: m.FC

iY + 0.9 s tuvw + n

(10)

-/*

The number of aromatic layers in an asphaltene cluster, M, was calculated from the above values of Lc and dm: x+

yz

{|

1

(11)

The structural parameters as determined by XRD are presented in Table 6. X-ray diffraction patterns need to be processes to calculate the main characteristics of the observed bands. Baseline was corrected by a linear combination of two-second order polynomials. In this procedure, three points are defined on the basis of the observed pattern. Two points define the lower and higher points in the pattern, and a third point defines a minimum located between the [002] and [100] bands. Change in baseline, had little influence on the results such as the aromaticity. Nevertheless, all of the patterns needed to be processed using a similar procedure. Changes in the XRD patters were observed when differential patterns were calculated as are presented in Figure 7. Relative areas of γ and (002) bands as well the (100) and (004) bands decreases as the exposure time being longer. Main changes were observed as the time reach 60 to 120 minutes of plasma exposure. The three major bands (γ, 002, and 100) at 2θ values of 20, 25, and 44° were used as the


14

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Energy & Fuels

initial parameters for the analysis. At high 2 θ values, the 004 band was observed, approximately 53°. The structural parameters of samples were calculated using data obtained from XRD patterns, peak positions, FWHM, and areas into the equations reported in Table 6, the results are reported in Table 7. Changes in the structural parameters were observed as the exposure time to the plasma was increased. The inter-planar distance between aromatic layers does not reflect significant changes, being of the order of 3.53 Å. Likewise, the average distance of paraffinic side chains being of the order of 5.85 Å, the increments in distances compared to the aromatic moieties can be attributed to steric hindrance of the chains, having many different possible orientations. More visible structural changes were observed when we analyzed the diameters of the aromatic layers. The diameters of the aromatic layers were reduced from 20.46 Å to 15.15 Å at plasma exposure times of 120 minutes. Indicating that atomic hydrogen from plasma interacts with asphaltenes to introduce hydrogen in the aromatic cores, resulting in the increment of paraffinic side chains, afterward paraffins can experiences a C-C bond break being evacuated from plasma chamber. FT-IR data shows that the ratio #CH "CH ⁄"CH decreases as the exposure time increases (see Table 3), but also from NMR data the calculated structural parameters shows that ~? the aromatic cores increases the alkyl substitution, see the I?L parameter in Table 5. From 1H-

NMR data the ?L,l6 parameter shows that the number of hydrogens on polyaromatics ring W ??? increases at longer exposure times. Comparatively with the I?L , I?L parameter, the initial and

final values shows in Table 5 do not present important changes, indicating that the number of ??? I?L must decrease to be consistent with the observed values of ?L,l6 and ?L,%l)l (see

Table 5). Without considering the paraffinic units, we can define the i4 ⁄ik ratio, which can be useful to define a shape factor for aromatic cores of clusters. In the original sample, the i4 ⁄ik ratio reaches values of 0.71, indicating a cylindrical shape not conspicuously changing in plasma exposure times up to 30 minutes. At longer exposure times, the shapes of clusters are more cylindrical than the shapes observed at short exposure times. The i4 ⁄ik ratio can reach values of 0.51 and 0.49 at 60 and 120 minutes of plasma exposure time, respectively. Analyzing parameters such as M, I? , I? , and N, we can conclude that structural changes occur at the periphery of aromatic moieties, changing their diameters as well the number of aromatic carbons. We do not observe significant changes in the number of aromatic layers per cluster. Compared


15

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Page 16 of 32

with the MALDI-TOF experiments, where energy is transferred to sample from laser radiation and dissociation of clusters is possible, in the XRD measurement asphaltenes clusters do not dissociate, so the MALDI-TOF mass spectra do not shows evidence of higher size clusters as those are measure in XRD experiments. 4. CONCLUSIONS The results of the work are summarized as follows: the chemical changes in asphaltenes when they are treated with hydrogen plasma were analyzed as increases the exposure time. Chemical changes were followed at exposure times of 0, 15, 30, 60 and 120 minutes using the data from OES, MALDI-TOF-MS, FT-IR, XRD, and 1H- and 13C-NMR spectroscopy. Mass loss in the samples can be the result of two different processes, one is the thermal desorption of low volatile compounds in the plasma vacuum chamber, resulting from heating of sample at the first stages of process by the plasma particles-asphaltenes interactions. The second is the chemical degradations of asphaltenes, the results of the chemical bond breaks when plasma particles interact with asphaltenes. Under these conditions different processes could take place, i.e. hydrogenation of aromatic cores, naphthenes ring opening, and other several dissociation processes activated by collisional processes when plasma particles interact with asphaltenes. Using OES, the products of the decomposition of asphaltenes were identified (C , CH , C , NH , V+). By comparing the asphaltene decomposition products with species found in the pure hydrogen plasma, the asphaltene decomposition species were shown to result exclusively from chemical decomposition of asphaltenes. FT-IR data show that the ratio of CH2 to CH3 in asphaltenes decreases as the times for exposure to plasma increase, indicating a decrease in the average length of paraffinic chains. Changes in the aromatic cores were observed by analyzing the patterns of signals at 700 to 800 cm-1. MALDI-TOF data had shown that the formation and detection of clusters in the TOF spectra were possible. From NMR data, relative quantities of different structural fragments reveal that changes in the numbers of aromatic hydrogens indicate that this number of aromatic hydrogens increases as exposure time increases. The results of 1H-NMR and

13

C-NMR indicate

changes in the aromatic structure results of the plasma exposure. X-Ray diffraction was useful to characterize changes in the clusters when asphaltene samples were either chemically or physically modified. The main changes were analyzed on the


16

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Energy & Fuels

basis of the shape factor determined from i4 and iY parameters for clusters. Evidence for the change in the clusters of the aromatic units was obtained. Chemical changes were analyzed using the average molecular parameters (AMP) calculated by compiling the structural information obtained by different spectroscopic techniques. Possible changes in the asphaltene cluster structures were analyzed using XRD. Plasmas under different conditions, operating pressures, types and energy of particles can be used satisfactorily to recover amounts of heavy fractions as gases from lighter fractions. Additional work is needed to find an industrial way for these procedures to be used. ACKNOWLEDGEMENTS The authors, D. Molina and J.C. Poveda, thank the support of the Escuela de Química-UIS by the FT-IR measurements, and Vicerectoria de Investigaciones (VIE) of the Universidad Industrial de Santander to measurements of NMR spectroscopy, XRD, and MALDI-TOF-MS at the facilities of Parque Tecnológico de Guatiguara. Authors H. Martínez, B. Campillo, and O. Flores thank the financial support of CONACyT 128714, DGAPA-UNAM 105010 and to Mr. Anselmo Gonzalez and Mr. Ivan Puente for their technical support. Also, we thank the technician support of Jose Luis Pinto and Mari Helena Torres at XRD and NMR facilities. REFERENCES (1) Sims, R. A. H.; Hastings, A.; Schlamadinger, B.; Taylor, G.; Smith, P. Global Change Biology 2006, 12, 2054-2076. (2) Poddar, S. K.; Ragsdale, R.; Geosits, R. F.; Hood, R. L.; Lynch, K. Z. ROSE asphaltenes, a fuel with a future, Proceedings of the 1994 National Petroleum Refiners Association (NPRA) annual meeting, San Antonio, TX (United States), Mar 20-22, 1994. (3) Schabron, J. F.; Speight, J. G. Petroleum Science and Technology 1998, 16, 361-375. (4) Erickson, D. D.; Niesen, V. G.; Brown, T. S.; Thermodynamics measurement and prediction of paraffin precipitation, Paper No. SPE 26604, Proceedings of the SPE Annual Technical Conference and Exhibition, Houston, TX, Oct 3-6, 1993. (5) Andersen, S. I.; Keul, A.; Stenby, E. Petroleum Science and Technology 1997, 15, 611-645. (6) Thanh, N. X.; Hsieh, M.; Philp, R. P. Organic Geochemistry 1999, 30, 119-132.


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(7) Zaki, N; Butz, Th.; Kessel, D. Petroleum Science and Technology 2001, 19, 425-435. (8) Ramirez-Jaramillo, E.; Lira-Galeana, C.; Manero, O. Energy Fuels 2006, 20, 1184-1196. (9) Boukir, A.; Aries, E.; Guilliano, M.; Asia, L.; Doumenq, P.; Mille, G. Chemosphere 2001, 43, 279-286. (10) Ciajolo, A.; Barbella, R. Fuel 1984, 63, 657-661. (11) Seki, H.; Kumata, F. Energy Fuels 2000, 14, 980-985. (12) Ancheyta, J.; Centeno, G.; Trejo, F.; Marroquin, G. Energy Fuels 2003, 17, 1233-1238. (13) Trejo, F.; Ancheyta, J.; Rana, M. Energy Fuels 2008, 23, 429-439. (14) Martínez, H.; Flores, O.; Poveda, J. C.; Campillo, B. Plasma Science and Technology 2012, 14, 303-311. (15) Gambús, G.; Patiño, P.; Méndez, B.; Sifontes, A.; Navea, J.; Martín, P.; Taylor, P. Energy Fuels 2001, 15, 881-886. (16) Salmanova, Ch. K.; Akhmedbekova, S. F.; Mamedov, A. P.; Kyazimov, S. M.; Abdulova, Sh. N. Chemistry and Technology of Fuels and Oils 2007, 43, 415-421. (17) American Society for Testing and Materials (ASTM). ASTM method D6560-12. Determination of asphaltenes (Heptane insolubles) in crude petroleum and petroleum products; ASTM: West Conshohocken, PA, 2001. (18) Martínez, H.; Avellaneda, D. Nuclear Instruments and Methods 2012, B272, 351-356. (19) MestReNova, version 8.1.0-11315; software for NMR data processing; Mestrelab Research S.L. Chemistry Software Solutions, Santiago de Compostela, Spain, 2012. (20) Pearse, R. W. B.; Gaydon, A. G., The identification of molecular spectra; University Printing House Cambridge: Great Britain, 1976. (21) Poveda, J.C.; Molina, D. Petroleum Science and Technology 2012, 84-85, 1-7.


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(22) Morgan, T. J.; Álvarez-Rodríguez, P.; George, A.; Herod, A. A.; Kandiyoti, R. Energy Fuels 2010, 24, 3977-3989. (23) Garcia, D. M.; Murgich, J.; Andersen, S. I. Petroleum Science and Technology 2004, 22, 735-758. (24) Mullins, O. C.; Sabbah, H.; Eyssautier, J.; Pomerantz, A. E.; Barré, L.; Ballard Andrews, A.; Ruiz-Morales, Y.; Mostowfi, F.; McFarlane, R.; Goual, L.; Lepkowicz, R.; Cooper, T.; Orbulescu, J.; Leblanc, R. M.; Edwards, J.; Zare, R. N. Energy Fuels 2012, 26, 3986-4003. (25) Michels, R.; Langlois, E.; Ruau, O.; Mansuy, M.; Elie, M.; Landias, P. Energy Fuels 1996, 10, 39-48. (26) Wilt, B. K.; Welch, W. T. Energy Fuels 1998, 12, 1008-1012. (27) Malhotra, V. M.; Buckmaster, H. A. Preprints from ACS Symposium on Trace Elements in Petroleum Geochemistry, Dallas, TX, April 9-14, 1989. (28) Brown, F. R.; Friedman, S.; Makovsky, L. E.; Schweighardt, F. K. Applied Spectroscopy 1977, 31, 241-243. (29) Siddiqui, M. N. Petroleum Science and Technology 2003, 21, 1601-1615. (30) A-Liang, W.; Que, G.; Chen, Y.; Liu, C. ‘‘Asphaltenes and asphalts’’ Chapter 10, in: T.F. Yen, G.V. Chilingarian (Eds.), Chemical Composition and Characteristics of Residues of Chinese Crude Oils Development in Petroleum Science, Vol. 2, Elsevier, New York, 2000; p. 287. (31) Bellamy, L. J. The Infrared Spectra of Complex Molecules, John Wiley & Sons Inc.: New York, 1957; pp. 18–20. (32) Liu, D.; Wang, Z.; Zhou, J.; Deng, W.; Liang, S.; Que, G. Symposium on General Papers Presented before the Division of Petroleum Chemistry, Inc., 222nd ACS National Meeting,


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American Chemistry Society Chicago, IL, August 26 – 30, 2001. (33) Benkhedda, Z.; Landais, P. Energy Fuels 1992, 6, 166–172. (34) Coelho, R.R.; Hovell, I.; de Mello Monte, M.; Middea, A.; Lopez de Souza, A. Fuel Processing Technology 2006, 87, 325-333. (35) Yen, T. F.; Wu, W. H.; Chilingar, G. V. Energy Sources 1984, 7, 203-235. (36) Chang, Ch.-L.; Fogler, S. Langmuir 1994, 10, 1758-1766. (37) Poveda, J. C.; Guerrero, A; Álvarez, I.; Cisneros, C. Photochem. Photobio. A: Chemistry, 2010, 215, 140-146. (38) Tanaka, R.; Saato, S.; Takanohashi, T.; Hunt, J. E.; Winans, R. E. Energy Fuels 2004, 18, 1405-1413. (39) Qian, K.; Edwards, K. E.; Siski, M.; Olmstead, W. N.; Mennito, A. S.; Dechert, G. J.; Hoosain, N. E. Energy Fuels 2007, 21, 1042-1047. (40) Hortal, A. R.; Hurtado, P.; Martínez-Haya, B.; Mullins, O. C. Energy Fuels 2007, 21, 28632868. (41) Tanaka, R.; Sato, S.; Takanohashi, T.; Hunt, J. E.; Winans, R. E. Energy Fuels 2004, 18, 1405-1413. (42) Pomerantz, A. E.; Hammond, M. R.; Morrow, A. L.; Mullins, O. C.; Zare, R. N. Energy Fuels 2009, 23, 1162-1168. (43) Yen, T. F. Anal. Chem. 1961, 33, 1587-1594. Figure Captions. Figure 1. Plasma Chamber. Figure 2. Emission spectra of asphaltene-H2 plasma. Figure 3. Time profile of mass loss of asphaltenes sample treated by air plasma. Figure 4. Differential FTIR spectra of asphaltenes after subtracting FTIR spectra of reference sample of asphaltenes.


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Figure 5. MALDI-TOF spectra of asphaltenes without plasma erosion and after 15 minutes. Figure 6. a. 1H-NMR and b.13C-NMR spectra of original asphaltenes (Reference sample). Figure 7. XRD pattern of asphaltenes without plasma treatment (black line) and differential XRD patterns of asphaltenes with different plasma erosion times.


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Table 1. Identified species from emission spectra. λ(nm)

Species

Systems

Transitions

315.7 337.1

CH NH

A2∆-X2Π A3Π-X3Σ-

358.8

C2

4300 Å system 3360 Å system Deslandres-D’Azambuja system

c1Πg-b1Πu

388.9

CH

3900 Å system

B2Σ-X2Π

405.0

V

431.4 653.3

CH H

1s 2 2s 2 2 p 6 3s 2 3 p 6 3d 3 4s 24 F3/ 2 A2∆-X2Π

4300 Å system

Table 2. Integrated intensities of main signals in the IR spectra of asphaltenes. cm-1

Group CH out-of-plane (Aromatics)

CH3 symm. bending CH2 bending CH2 bending+ CH3 asymm.

Time to the H2 Plasma (min)

748.3 808.1 864.1 total 1373.3 1441.3

0 0.3701 0.4507 0.4660 1.2868 0.2323 0.7490

15 0.5700 0.9851 0.6791 2.2342 0.3318 1.2804

30 0.6197 1.0698 0.7093 2.3988 0.3798 1.4624

60 0.4725 0.5494 0.6203 1.6418 0.3486 1.2652

120 0.4963 0.9058 0.6435 2.0393 0.3177 1.2210

1459.5

0.5453

0.8066

0.9899

0.9182

0.8541

2831.6 2851.9

2.9895 1.3230

3.2145 3.3816

4.1549 3.7817

4.7494 3.1806

3.8019 3.5433

2900.8

4.8184

6.0978

6.0564

6.8474

3.9541

2924.5 2954.9

1.1942 1.4192

4.3372 2.2610

6.4232 2.7213

3.9976 2.4820

6.6808 2.0892

*

bending

Aliphatic C-H CH2 symm. stretching **

C-H stretching CH2 symm. stretching CH3 asymm. stretching *

748.3 cm-1 overlapping with rocking vibrations of long (CH2)n, n>2.

symm. Symmetrical; asymm, asymmetrical. ** C-H stretching of branched–chain alkanes.


22

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Table 3. Structural parameters calculated from IR data. Time to the H2 Plasma (min)

Parameter ⁄"CH

1 #CH

2

"CH ⁄#CH "CH 3 4

H&'( ⁄H54

#CH⁄"CH

Reference

0 1.91

15 4.65

30 5.77

60 3.87

120 7.89

Cohelo34

0.44

0.43

0.40

0.39

0.38

Benkeda31

0.48

0.19

0.15

0.21

0.12

Yen32

1.77

3.41

3.75

2.89

4.89

Authors

1

Using the 2924.5 cm-1 and 2954.9 cm-1 peaks. Using the 1373.0 cm-1 and 1459.5 cm-1 peaks. 3 Using the 1373.0 cm-1 and 2924.5 cm-1 peaks. 4 Using the 2924.5 cm-1, 2851.9 cm-1, and 2954.7 cm-1 peaks. 2

Table 4. Deconvoluted molecular weight distribution profiles* of asphaltenes. Time to the H2 plasma (min) 15 30 60

Band 0 x

*

Area

x

Area

x

Area

x

120 Area

x

Area

1

1625.5 22.88 1662.9 19.50 1616.4 20.12 1625.6 14.57 1655.2 17.32

2

2164.2 34.55 2150.5 35.46 2102.4 36.51 2096.3 25.75 2112.9 33.61

3

3109.7 27.39 3108.9 27.75 3074.9 27.14 2867.9 25.78 3003.9 29.46

4

5139.0 15.17 5193.9 17.29 5190.5 16.23 5596.6 33.90 5234.7 19.61

Measured using MALDI-TOF mass spectrometry, area is reported in percent.


23

Energy & Fuels

Table 5. Normalized integrated areas in the NMR spectra.

0

15

30

60

120

4L~YW(

0.10-1.00

17.98

18.42

13.98

18.30

17.84

4L~YW* ,YW

1.00-1.50

32.13

33.84

28.63

32.79

31.73

4L,4~YW* ,YW

1.50-2.14

24.89

21.49

30.47

22.72

22.89

2.14-2.33

2.61

2.94

2.30

2.63

2.67

∝~?L 4L,4

2.33-5.00

11.68

12.94

12.29

11.77

12.64

?L,%l)l

5.00-7.16

3.85

3.44

4.74

4.07

3.93

?L,l6

7.38-9.00

6.85

6.93

7.60

7.73

8.30

3.0-18.5

6.14

6.08

6.39

6.99

6.39

18.5-21.5

4.12

4.04

4.20

4.07

3.86

21.5-60.0

38.60

35.51

35.82

33.72

33.98

85.0-129.2

29.42

29.00

27.81

26.29

29.35

129.2-137.0

12.81

13.50

13.76

14.14

13.30

137.0-160.0

8.91

12.36

12.02

14.79

13.11

h~?L

K~?L

1H-NMR

Time to the H2 Plasma (min)

Spectral range, ppm

Chemical group

K~?L

∝~?L 4L~YW (

h~?L

I4L

13C-NMR

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 32

K~?L I4L~YW( YW* ,YW I4L,4 W ??? I?L , I?L ?? I?L

~?

h~?L

I?L

4L~YW( : methyl hydrogens in paraffin’s in gamma positions or more to

K~?L aromatics, 4L~YW : CH and CH in paraffin’s beta position to aromatics, * ,YW K~?L 4L,4~YW*,YW : CH and CH in paraffin’s and naphthenes beta positions to ∝~?L ∝~?L aromatics, 4L~YW : methyl hydrogens alpha to aromatics, 4L,4 : hydrogens ( in paraffins and naphthenes alpha to aromatics, ?L,%l)l : hydrogens in h~?L monoaromatics, ?L,l6 : hydrogens in polyaromatics, I4L : paraffinic carbons K~?L gamma or more to aromatics, I4L~YW : methyl in paraffinic chains beta to ( YW* ,YW W ??? aromatics, I4L,4, : CH2 or CH in paraffin or naphthenic chains, I?L , I?L : ?? aromatic carbons joined to hydrogens or in pericondensed structures, I?L : ~? aromatic carbons in catacondensed structures, I?L : aromatics carbons alkyl substituted.


24

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Energy & Fuels

Table 6. Structural parameters that can be obtained from X-ray data. X4

cd

Amm ⁄Amm Ah

Factor of aromaticity

⁄2sin w

Distance between aromatic sheets

Ec. 6 Ec. 7

ch

Distance between paraffinic chains

⁄2 sin w

Ec. 8

i4

Average diameter of aromatic layers, alpha carbons included.

0.92⁄pD⁄ [110]

Ec. 9

iY x

Average diameter of the clusters. Number of aromatic layers per cluster.

0.45⁄pD⁄ [002] iY ⁄c% 1

Ec. 10 Ec. 11

I?

Aromatic carbons per molecule.

i4 ⁄2.62

Ec. 12

I?

Number of aromatic carbons per aromatic unit, including alpha carbons

i4 1.23 ⁄0.615

Ec. 13

Number of aromatic centers per molecule.

I? ⁄I?

Ec. 14

Table 7. Structural parameters calculated from X-ray data. Time to the H2 plasma (min)

Parameter fa dm, Å dγ , Å La, Å Lc, Å M I? I? N

0

15

30

60

120

0.14 3.53 5.87 20.46 28.76 9.15 159.8 35.3 4.53

0.14 3.53 5.86 20.42 28.92 9.19 159.2 35.2 4.52

0.13 3.54 5.93 20.44 28.65 9.10 159.5 35.2 4.53

0.12 3.54 5.94 15.86 31.04 9.77 96.0 27.8 3.45

0.12 3.53 5.88 15.15 30.72 9.69 87.6 26.6 3.29


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Energy & Fuels

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Page 26 of 32

Electrical circuit Power supply Electrodes

~

A

~

V

A

Probe Asphaltene

MKS Baratron

V

Ocean Optics Spectrometer Lens Optical System

Termovac T20

Exhaust Vacuum pump Trivac D10

Figure 1. Plasma Chamber.


26

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Energy & Fuels

t =120 min

t = 45 min

t = 30 min

t = 15 min

t = 0 min

Figure 2. Emission spectra of asphaltene-H2 plasma.


27

Energy & Fuels

0

5

mL (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 32

10

15

20 0

50

100

150

200

t (min)

Figure 3. Time profile of mass loss of asphaltenes sample treated by air plasma.


28

Page 29 of 32

0,12

ASF 15 min - ASF reference ASF 30 min - ASF reference ASF 60 min - ASF reference

0,10

CH2 sym stretching

OH

ASF 120 min - ASF reference

stretching in ASF surface and microcrystals

-CH2-

0,08 Asample-Areference

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

bending

CH3 asym stretching

CH3

0,06

sym bending

Ar-H

0,04

out of plane

0,02

0,00 500

1000

1500

2000 2500 Wavenumber (cm-1)

3000

3500

4000

Figure 4. Differential FT-IR spectra of asphaltenes after subtracting FTIR spectra of reference sample of asphaltenes.


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Energy & Fuels

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Figure 5. MALDI-TOF spectra of asphaltenes without plasma erosion and after 15 minutes.


30

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Energy & Fuels

Figure 6. a. 1H-NMR and b.13C-NMR spectra of original asphaltenes (Reference sample).


31

Energy & Fuels

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γ (002) Reference ASF 15 min - ASF reference ASF 30 min - ASF reference ASF 60 min - ASF reference ASF 120 min - ASF reference

(100) (004)

0

10

20

30

40

50

60

70

80

2 Theta Figure 7. XRD pattern of asphaltenes without plasma treatment (black line) and differential XRD patterns of asphaltenes with different plasma erosion times.


32

Molecular Changes in Asphaltenes within H2 Plasma - Energy

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