The experimental investigation of effect of microwave

Journal of Analytical and Applied Pyrolysis 128 (2017) 92–101

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The experimental investigation of effect of microwave and ultrasonic waves on the key characteristics of heavy crude oil

MARK

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Jaber Taheri-Shakiba,b, Ali Shekarifarda,b, , Hassan Naderic a

School of Chemical Engineering, College of Engineering, University of Tehran, Tehran, Iran Institute of Petroleum Engineering, College of Engineering, University of Tehran, Tehran, Iran c Research Institute of Petroleum Industry, Department of Research and Technology of the Rock and Fluid Reservoirs, Tehran, Iran b

A R T I C L E I N F O

A B S T R A C T

Keywords: Heavy oil Ultrasonic Microwave Viscosity Asphaltene

This study examined the effects of microwave (MW) and ultrasonic (US) waves on an heavy crude oil sample from a reservoir in southwest Iran. The waves irradiated the sample from two to 10 min at two-minute steps. MW caused the temperature of the crude-oil sample to rise by selective heating of polar components and creation of hot zones; under US, heating was accompanied by a cavitation effect. MW at 2 and 4 min reduced the sample’s viscosity by inducing hot zones. At 2 min, the viscosity declined 16% due to cracking of heavy components such as asphaltenes, which have a higher capacity to absorb MW. As the radiation time increased after 4 min, the viscosity increased because light components escaped from the sample. However, US reduced the viscosity of the heavy crude oil sample at all time durations. The greatest reduction of viscosity was around 19%, at 4 min. The viscosity increased with irradiation time and then remained constant. Ultrasonic waves altered the viscosity by creating bubbles, which disintegrated the resin intermolecular bonds and cracked the large molecular particles of the asphaltene. The reduction in sulfur content under US was much greater than under MW. At all time durations, sulfur content fell as radiation time increased. Due to its high potential to absorb MW, creates active sulfur that can be emitted from the crude oil as sulfide and hydrogen sulfide, with the sulfur level falling to 0.39%. Furthermore, US waves also reduced sulfur content to around 0.46% as the asphaltene flocks disintegrated. Reduction of sulfur content from asphaltene agglomerates under MW and US was observed using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). In addition to reducing the effect of sulfur by affecting its nitrogen and oxygen elements, irradiation also reduced the polarity of the asphaltene particles and prevented reaggregation of cracked particles. Results of SARA (saturation, aromatic, resin and asphaltene) analysis showed that asphaltene particles have a higher capacity to absorb MW than resin components, as after the amount of asphaltene components declined in the early stages of irradiation, resin components began to change, falling to 34% at 10 min. The decrease in asphaltene content in samples under US was more evident, reaching 34% at 8 min. According to Fourier transform infrared (FTIR) spectra results, MW irradiation caused cracking of large-chain molecules and drove light components from heavy crude sample. These two phenomena are a function of radiation time. The rate of cracking of heavy components was continuously greater than the rate of light components leaving the sample at early time intervals; ultimately, this resulted in an upgraded heavy oil. In some cases, despite cracking of large-chain molecules and creation of light components, the output values of light components were higher. Under US, the cracking of large-chain molecules occurred, but due to the departure of heavy components from the crude oil, peak intensities increased and the resulting crude oil had purer components.

1. Introduction The increase in energy consumption worldwide and the decline of global light-oil reserves necessitates more attention to heavy/ultraheavy oil reservoirs. Heavy-oil reservoirs remain intact or are producing with low efficiency using old technology. Hence, extensive

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research in the field of heavy/ultra-heavy oil using more-efficient processes needs to be conducted. Novel methods and techniques are of great importance to remove barriers and increase production from such reservoirs. Developing and presenting new methods in the field of heavy oil is an issue of great importance, as the large volume of these reserves can help meet the world's ever-increasing energy needs.

Corresponding author at: School of Chemical Engineering, College of Engineering, University of Tehran, Tehran, Iran. E-mail address: [email protected] (A. Shekarifard).

https://doi.org/10.1016/j.jaap.2017.10.021 Received 1 September 2017; Received in revised form 22 October 2017; Accepted 28 October 2017 Available online 04 November 2017 0165-2370/ © 2017 Elsevier B.V. All rights reserved.


J. Taheri-Shakib et al.

Fig. 1. Schematic of microwave oven.

Fig. 2. Schematic of ultrasonic device.

Some studies have been performed on the effects of MW and US on crude oil. Changes in oil viscosity under US waves have been an issue of great importance to researchers [1]. US can be used as an alternative to or intensifier of some chemical reactions [2], extraction [3] and removal of some components from oil [4]. In oil-water emulsions, US can be used to determine the presence of oil particles in water [5] and to separate oil and water [6]. Using US technology increases oilfields’ productivity [7–9]. Various experimental studies examining US-based enhanced oil recovery have shown the ability of these waves to increase production [10,11]. Other research has studied the parameters of the reduction and removal of formation damage factors and the effect of US on these parameters. US can remove polymeric particles [12], asphaltene precipitates near wellbore [13], filtrates penetrating into the formation with drilling fluid [14] and the intensification of the impact on inorganic scales [15]. Amani et al. investigated the impact of US on asphaltene particles and showed that these waves could break asphaltene flocks and reduce asphaltene content in crude oil [16]. Moreover, studies have examined the effect of US on the asphaltene rheology of crude oil and the kinetics of asphaltene aggregation and deposition [17,18]. Shedid et al. examined the impact of US waves on asphaltene deposits in the presence of chemical solvents and concluded that increasing the time of exposure reduces viscosity and asphaltene agglomerate size [19]. Most of the literature on MW in the petroleum-engineering field is related to oil shales [20–23]. MW can assist in the separation of oil and water in stable oil-water emulsions [24], and enhances the effect of desulfurization and upgrading of heavy oil [25]. MW can also be applied in enhanced oil recovery (EOR) operations that increase oil production [26]. Hascakir et al. showed in his experiments that MW raises production by heating specific components and reducing viscosity [27]. Ranji et al. investigated the mechanism of MW effectiveness and stated that the existence of some heavy elements in oil with different absorption coefficients for MW creates hot zones [28]. Jackson incorporated some additives high capability to absorb microwaves into heavy oil, finding that this improves the upgrading process [29]. The current study examines the effect of MW and US on Ahwaz heavy crude oil from a reservoir in southwest Iran. The heating mechanism,

Fig. 3. Oil temperature under different MW and US time intervals of radiations.

Fig. 4. Crude oil viscosity under different MW and US time intervals of radiations (@ 22 °C).

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Fig. 5. Microscopic images of asphaltene particles of oil samples under different time intervals of MW and US radiations:. A: Asphaltene particles of heavy crude oil. B: Asphaltene particles under MW irradiation 2 min. C: Asphaltene particles under US irradiation 4 min. D: Asphaltene particles under MW irradiation 4 min. E: Asphaltene particles under US irradiation 6 min.

is shown in Fig. 2. The crude-oil sample was subjected to US radiation at 20 KHz frequency and 300 W power at different time ranges. The viscosity and temperature of the sample were measured after each time interval of wave radiation. The irradiated oil was cooled for one day at ambient temperature to allow it to stabilize. The samples’ sulfur contents were measured using a Vario Max-CHNS elementar (ASTM D4294). FT-IR spectra were also used to determine the bonds and functional groups within the samples. SARA (Saturation, Aromatic, Resin, and Asphaltene) experiments identified saturations, aromatics, resins (ASTM D-4124) and asphaltenes (IP-143). SEM images of asphaltene agglomerates showed changes in their structure. Moreover, the EDS of the asphaltene agglomerates helped determine the samples’ CSNO (carbon, sulfur, nitrogen and oxygen) compositions during

desulfurization and viscosity changes due to MW and US irradiation are studied. Variations in the composition of the heavy oil after exposure to these waves is also investigated. 2. Experimental setup and procedures A 100 mL sample of heavy crude oil of an oilfield in southwest Iran was subjected to MW and US for 2, 4, 6, 8 and 10 min. The reason for stopping after 10 min is that after this period the values for the measured components remained almost constant. A schematic of the MW apparatus used in this study is shown in Fig. 1. Samples were exposed to MW at various time durations at a 2450 MHz frequency and 300 W power. A schematic of the MW irradiation apparatus used in this study 94



amounts of these components, MW creates local regions that absorb a higher percentage of energy, resulting in microzones with higher temperatures. These microzones, also called “hot zones”, contribute to the upgrading phase at earlier points in the irradiation process [33]. In MW radiation, the hot spots formed in the crude oils raised the overall temperature. In addition to the benefits of superheating phenomena in increasing the temperature at hot zones, there are additional advantages such as impeding the liquid’s change of phase above its normal boiling point and decreasing the cohesion force between molecules in the liquid phase to the minimum level possible. By reducing the attractive force and not letting the volatile molecules approach evaporation phase, superheating decrease viscosity to its minimum: when the heated components exceed their boiling point close to the hot zones and other regions, a movement to the liquid surface occurs, and the components may escape from the crude-oil surface, which results in a zone of increasing viscosity [34]. Heavy components concentrate closest to the hot zones, so the superheating acts to prevent evaporation in MW heating. In the current study, when MW irradiation time was increased past 2 min, these components could leave the sample, leading to an increase in viscosity. At 4 min, light components exited the sample, but increased amounts of cracked light components and longchain molecules from heavy components were created. In samples under US at 2 and 4 min, viscosity reduces and then increases, after which it remained nearly constant. For almost all irradiated samples under US, viscosity did not increase. US irradiation has a large impact on both the physical and rheological properties of crude oil. As mentioned earlier, as US exposure time continues, bubbles within the crude oil will grow to a critical size and then collapse. Increasing the bubble size up to, but not past, the point of collapse will expand the volume of crude oil and decrease the viscosity of the fluid. Moreover, the implosion of the bubble can also break the viscosifying chain and facilitate crude-oil movement. Both the ultrasonic and implosion energy will result in disintegration of resin intermolecular bonds and the breakdown of large asphaltene molecular particles to smaller. This breakdown of asphaltene particles will consequently degrade and demolish the high molecular chain that is the main factor in viscosity [35]. However, there is an optimum irradiation time; until that time, irradiation will lead to the reintegration of asphaltene particles and the reformation of the viscosifying high molecular chain. Nevertheless, raising the crude oil temperature during irradiation can intensify the viscosity reduction through the effects of cavitation and ultrasonic energy conversion [36]. An enhancement in cavitation phenomena could decrease viscosity by improving molecular mobility. Microscopic images of asphaltene particles are shown in Fig. 5. In Fig. 5A, larger asphaltene conglomerates of crude oil are observable. When a heavy crude oil sample was subjected to MW at 2 min irradiation, viscosity varied from 935.51 mPa to 781.44 mPa. Flocculated asphaltene particles in n-heptane were exposed to MW at 2 min. The average size of asphaltene particles after 24 h reached 46.6 μm (Fig. 5B), while this value was around 51.3 μm in the crude-oil sample (Fig. 5A). Thus, one reason for viscosity reduction due to MW irradiation at 2 min is the crushing and cracking of asphaltene flocks. Moreover, it is important to note that at 4 min irradiation viscosity was increasing and the average size of asphaltene particles was approaching 41.3 μm (Fig. 5D). This could be due to the dissolution of the suspended particles when irradiated using MW. On the other hand, these fine particles increase viscosity by increasing the internal friction between the components of the crude oil. Among all investigations carried out on all samples under MW, neither reaggregation of crushed particles into asphaltene conglomerates nor formation of long-chain flocks took place. In samples under US at 4 min the average size of asphaltene particles approached 20.7 μm (Fig. 5C) and viscosity declined to 184.3 mPa. In the sample under US at 6 min, an increase in the size of asphaltene particles compared with the previous sample was observed after 24 h of cooling. The average size of

Fig. 6. Sulfur content under different MW and US time intervals of radiations.

irradiation using MW and US. To study the effect of MW and US on the size of asphaltene particles, 60 mL of n-heptane was added to 40 mL of crude oil; this ratio of crude oil/n-heptane ensures flock formation. After mixing the solution, it was left to stand for sufficient time for the flocculation to form. Four drops from each sample were observed using magnification times microscope. The optical polarizing microscope used in this study consisted of a high-resolution video camera, a PC and a high-resolution image monitor, and images were stored at high resolution. The samples were radiated with MW and US radiation for time intervals ranging from 2 to 10 min, at two-minute intervals. Twenty photos were taken for each sample and stored.

3. Results and discussion The temperatures of the oil samples at each interval of MW and US irradiation are shown in Fig. 3. In samples under MW no particular change was observed in the sample’s temperature at 2–4 min; however, after 4 min a steep increase in temperature was observed. Under US, sample temperatures rose between 2 and 6 min, after which the rising slope of the sample temperature declined; after 8 min the sample temperature ceased to rise. MW heating is based on the ability of materials such as oil to absorb microwave energy and efficiently convert the electromagnetic energy to heat (kinetic energy). Since MW heating is dependent on the dipole moment of a molecule, it is logical that more polar components convert microwave irradiation into heat than do nonpolar components [30]. In MW heating, energy is supplied directly to the oil sample by the interaction between an electric field and the electric charges of molecules, or molecular interaction with the electromagnetic field generated [31]. As the petroleum is exposed to the ultrasonic waves, cavitation takes place, in which large bubbles formed by the heating collapse; the mechanical effect of this collapse leads to the disintegration of suspension conglomerates. Increases in temperature can be observed during the treatment time. Macromolecules are disrupted by the hydro-mechanical shear forces resulting from ultrasonic cavitation and the resulting increase in temperature. Collapsing the expanded bubble causes shear shockwaves and micro-jets of solvent, which may generate turbulence at the interfacial film around the solid particle. As mentioned earlier, collapsing the growth bubble will produce localized high temperatures [32]. Fig. 4 shows the viscosity variations for the heavy crude oil samples at various time ranges under MW and US at 22 °C. Under MW irradiation at 2 min, oil viscosity declined, after which it began to increase. At 2 and 4 min the viscosity of the samples under MW was lower than untreated crude oil. Some components play a fundamental role in carrying charges in heavy crude oil and have higher dielectric properties, and, because they are good microwave receptors, contribute to temperature increases under irradiation; thus, in samples with large 95



Fig. 7. SEM and EDS of asphaltene particles:. A: Crude asphaltene. B: Asphaltene under 10 min MW irritation. C: Asphaltene under 10 min US irritation.

asphaltene particles was 30.5 μm in this case. One reason for the increase in viscosity at 6 min was the integration of the broken-chain asphaltene particles into long-chain conglomerates. In samples under US at 2 and 4 min, reaggregation of asphaltene particles to asphaltene flocks did not occur. However, with an increase in US radiation time, the integration of broken-chain asphaltenes particles into long-chain conglomerates was observed; this integration increased viscosity. This could be due to higher fragmentation of asphaltene particles and an

increase in their contact area, and with the creation of turbulence using US waves, thus intensifying the aggregation of crushed particles into asphaltene conglomerates [37]. Crude oil consists of hydrocarbons of various molecular weights and sulfur-containing compounds. Desulfurization of crude oil is one of the most important processes in the oil industry. Changes in sulfur content in the heavy crude oil samples at different times under MW and US are shown in Fig. 6. In all samples, desulfurization occurred. Under MW at

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Fig. 8. SARA compounds of crude oil during different MW and US time intervals of radiations.

for treating the crude oil, increasing the irradiation time decreased the crude oil’s sulfur content [42]. The results suggest that the disintegration of asphaltene conglomerates facilitates this reduction in the sulfur content. As irradiation continues, increasing the temperature of the sample will result in higher rate of vaporization. The resulting vapors will strip the sulfur fragment from the crude oil. While vapors cannot transport high-molecular-weight suspended components from the sample, implementation of US will break large conglomerates down and assist in the removal process. However, increasing the exposure time up to an optimum will lead to desegregation. The discrepancy between the sulfur content beyond 8 min’ irradiation could be attributed to the distribution of the asphaltenes’ sulfur flocks [43,44]. Thus, sonication has a considerable effect on the disintegration of asphaltene flocks and the reduction in their mean diameter due to mechanical force created by the ultrasonic waves themselves and the resulting bubble implosion. Fig. 7 shows the SEM and EDS of the asphaltene particles in the nheptane solution after MW and US irradiation. The hot zones resulting from MW created microcracks in the asphaltene particles. MW reduced the sulfur content of asphaltene in this study’s samples from 15.52 wt.% to 10.09 wt.%. Similarly, US reduced sulfur the content of asphaltene up to 8.16 wt.%. Polar components of asphaltene that contain nitrogen, oxygen and sulfur cause asphaltene particles to absorb more MW, which leads to the creation of hot zones, and ultimately to cracking. EDS results for the asphaltene particles showed that along with reduction in sulfur content, nitrogen and oxygen values also fell to 22% and 44%, respectively. The polarity of asphaltene particles is the critical factor for their aggregation with each other [45]. MW prevents reconglomeration of asphaltenes by removing their polar components, which have a high capacity to absorb these waves (Fig. 5D). Fig. 8 shows the SARA results for samples under MW and US irradiation. In samples under MW the lowest amount of asphaltene content was observed at 2 min (9.54 wt.%). With increased irradiation time, asphaltene content remained almost constant. Resin content was almost constant up to 4 min, after which a decreasing trend was observed. Asphaltene and resin play a key role in carrying charges in heavy crude oil due to their higher dielectric properties. This causes the heavier carbon chain molecules to reach their cracking threshold, increasing the values for the lighter component fractions. MW also induced

all time durations, sulfur content decreased. At 10 min sulfur content had declined to 32%. Oils with higher concentrations of sulfur-bearing components as well as heavy molecules (i.e. asphaltenes and resin) have high absorption coefficients, which can increase the oils’ total absorption of microwaves and rapid increases in temperature [38]. The results of the current study show that sulfur content from the heavy oil selected was about 1.11 mass%. MW heating decreased the sulfur content is decreased. The rapid heating of heavy crude oil activated desulfurization. However, in conventional heating, the rise in temperature was not sufficient to activate this reaction [39]. The results of the current study show that the content of sulfur was directly proportional to the asphaltene fraction in the crude oil; this indicates that sulfur exists at the center of the heating zones produced by MW irradiation. The increased heat causes sulfur-bearing components to crack and ultimately produce sulfide. Another possible reason for decreases in the sulfur content of heavy crude oil under MW irradiation is related to bonding activation [40,41]. It is accepted that microwave particularly affects the sulfur bonds in polar or hydrocarbon components, breaking the bonds and producing active sulfur. The activated sulfur can react with the hydrogen present in the crude oil to create hydrogen sulfide. Hydrogen bonds between sulfur and carbon are smaller and weaker than other hydrocarbon bonds. Thus, the decrease in sulfur content during the cracking phase in MW heating most probably is the result of the bonds’ relatively low energy. Production of hydrogen sulfide from these reactions resulted in decreases in the hydrogen and sulfur content and increases in the carbon content in the samples. However, because of the low sulfur content and intermediate rate of this reaction, the decrease in the hydrogen fraction was not significant. Desulfurization occurred to a greater degree in samples under US. Increase in irradiation time up to 8 min decreased the sulfur content. The highest level of desulfurization − around 41% − was measured at 8 min. The cavitation process, including the growth and collapse of bubbles due to the propagation of mechanical and shear waves through the crude oil, can disintegrate conglomerate and concentrated sulfur within the asphaltene. As the asphaltene conglomerate breaks down, the temperature increases, mostly likely because the ultrasonic energy can intensify the liberation of sulfur from the treated crude oil. Based on the results of the current study and other research into the use of US 97



Fig. 9. FTIR spectra of crude oil under different MW time intervals of radiations.

(1630–1680). Moreover, similar dual peaks were not detected at 1370. Thus, it can be concluded that right-chain alkane molecules are present in the crude-oil sample. Beside alkanes, there are also aromatic molecules in the crude-oil structure, as indicated by the presence of a peak at 1600 and low-intensity peaks at frequencies under 1000. In samples under MW at 2–6 min irradiation, CH3 asymmetric vibration gradually increased such that at 6 min the intensity of this peak equalled that of CH2 asymmetric vibration. The ratio of intensities of these two peaks can be an indication of hydrocarbon chains' length. At 6 min, the length of hydrocarbon chains declined and the intensity of peaks became equal, which indicates small molecule chains. The peaks gradually rose between 2 min and 6 min. The intensity of the peak is indicates the concentration of the functional group associated with the composition. Peaks showed more intensity at 6 min MW irradiation than at 2 min MW irradiation and the baseline was higher. This is because with MW radiation, some components evaporated from the sample and the associated bonds (related to each frequency) were more concentrated. Furthermore, aromatic bonds at 6 min MW were more intense than at 2 and 4 min due to the cracking of long-chain molecules such as asphaltene, and the consequent creation of short-chain molecules created. This upgrading was shown in the SARA results (Fig. 8) where

secondary cracking adjacent to the hot zones. In hot zones, the concentration of resin and asphaltene is higher than in other areas of the crude oil, and thus, the possibility of cracking of heavier components in this regions is higher than usual [46,47]. The temperature in hot zones is a great deal higher than in other areas; therefore, the temperature of materials adjacent to the hot zones also increases due to both thermal exchange with hot zones and higher direct absorption of microwave energy. Moreover, after the normal point of condensation is passed, temperatures increase further in samples heated with microwaves; this superheated condition causes the light components to remain trapped in the oil and upgrades the heavy crude. This is the reason that the saturation components increased at 2 and 4 min, and why at other time intervals higher values for the crude oil samples were observed. Asphaltene agglomerates have a greater capacity to absorb microwaves than resin components. Thus in MW irradiation the asphaltene components first changed and then declined. Afterward, with an increase in radiation time and the cracking of asphaltene particles, the resin components also began to change, approaching 15.73 wt.% at 10 min. FTIR spectra results for crude oil under MW are shown in Fig. 9. CH2 and CH3 peaks have the highest intensity in the spectrum. Peaks were observed for CH2 and CH3, but no not in ranges related to alkenes 98



Fig. 10. FTIR spectra of crude oil under different US time intervals of radiations.

time to more than 8 min will greatly reduce the saturate-group content. According to the analysis above, it can be concluded that most of the growth of bubbles to the critical size occurred at or before 8 min, and a higher rate of cracking on the asphaltene chain and flocks could be expected. This means that the components generated by the cracking process of asphaltene distribute to the other fractions. However, beyond 8 min’ irradiation, the mass fraction of asphaltene increased; this can be attributed to the reduction of the saturated fraction [50,51]. These results suggest that at every sonicating time interval, the crude oil temperature increases. The temperature during 10 min’ irradiation time approached 240 °F. Saturate fractions have a lower vapor point because of their lower molecular weight; thus, increasing the sonicating time to more than 10 min will cause the saturates to vaporize. At 4 min, US showed more peak intensity than 2 min at all frequencies. Moreover, the peak intensity of the CH3 asymmetric bond gradually increased to the point where it was equal to the CH2 asymmetric bond; this suggests a shortening of the length and dimension o9f

asphaltene components showed the largest reduction, and saturation components had the highest values. However, at 8 and 10 min these results were not observed, and the ratio of the CH2 asymmetric vibration peaks to the CH3 were similar to those for the crude-oil samples. Increased irradiation time drove the light and short-chain components from the crude oil, causing the concentration of heavy components to rise in turn. However, light components were still present in the sample due to the cracking of heavy components, which had a concentration similar to the light components in the crude-oil samples [48,49]. US irradiation reduced asphaltene contents in all samples (Fig. 10). At 8 min, the lowest asphaltene content was observed (8.35 wt.%). Unlike the samples under MW irradiation which showed a decreasing trend in resin content at 6–10 min, there was no defined trend for resin components in samples under US. At 10 min resin-component contents approached 31.35 wt.% and saturation components reached their lowest amount (9.26 wt.%). It is evident from the SARA results that increasing the sonication

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molecules. The peak intensity of the C]C bond was greater at 1600. Other peaks also showed an increasing trend, which could be due to the increasing purity of the sample, because peak intensity increases as the concentration of bonds rises. Furthermore, at 1030 the sulfo-oxide peak was observed, which could be due to the lighter components escaping from the crude sample as the temperature rose under US irradiation. No additional bonds were indicated at 6 min compared to 4 min under US, but the peak intensity of existing bonds increased; however, because this increase was not balanced and did not take place for all bonds, it cannot be considered a significant change in the structure. In contrast, at 8 min US, the intensity was lower than in other samples, and no bonds were added or destroyed; regardless, these bonds were of low intensity in the sample. From the point of view of molecular length, the ratio of peak intensities of CH2 and CH3 resembled those in previous samples. At 10 min US, the bonds were also similar to previous bonds, but with greater peak intensity of peaks. This increase was not associated with a particular peak, but occurred across all frequencies.

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4. Conclusion

• The heating mechanisms and performance of MW and US waves are

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different. MW works according to its effect on polar components and its selective heating of the crude oil sample. This heating mechanism created hot zones in the crude sample in areas that contained those components with a higher capacity to absorb these waves. The cavitation associated with US further increased the temperature of the samples. Macromolecules with high molecular mass were disrupted by the hydro-mechanical shear forces generated by ultrasonic cavitation; this further increased the temperature of the samples. It might be a result of molecular friction due to wave propagation that generates. Reduction in the viscosity of heavy oil under MW irradiation was due to cracking in hot zones. Constituent components in these regions were heavy-chain molecules, such as asphaltenes, which contained elements with a high capacity to absorb microwaves. Superheating phenomena in these areas impeded the liquid’s change in phase above the normal boiling point and decreased the cohesion force between molecules in the liquid phase to the minimum level; at this assisted in the upgrading of heavy crude oil by preventing the removal of light components. Moreover, the heating time was a major factor because as MW irradiation continued, the light components left the sample and the concentration of heavy components increased, which in turn increased the viscosity. US radiation reduced the viscosity of the crude-oil samples. This reduction in viscosity differed in that it was a function of irradiation time. At the early time intervals, the value of viscosity was lower. The mechanism of bubble creation to disintegrate the intermolecular bonds in the resin and crack the large molecular particles of the asphaltene through US-induced cavitation changed the viscosity. The reintegration and reformation of asphaltene particles also interrupted the decrease in viscosity. This phenomenon was not observed in the samples treated with MW. MW and US irradiation caused desulfurization of heavy oil. Reductions in the samples sulfur content under US was greater than that under MW. Microwaves particularly affected the sulfur bonds in the polar or hydrocarbon components, resulting in breakage of the current bonds and the production of active sulfur. Sulfur exists at the heating zones under MW irradiation as sulfide and hydrogen sulfide. As the asphaltene conglomerate broke down under US irradiation, the temperature increased because the ultrasonic energy could intensify the liberation of sulfur from the treated crude oil. Also, the disintegration of asphaltene flocks would facilitate reductions in the crude oil’s sulfur content, as indicated by the fact that the content of sulfur was directly proportional to the asphaltene fraction in the crude oil. SEM and EDS images of asphaltene agglomerates show that US

waves reduced the sulfur content of these particles, while MW not only reduced the sulfur content but also affected other polar components of asphaltene. In this case, the reaggregation of cracked asphaltene particles did not occur. Early in the treatment process, MW reduced the asphaltene content in the crude oil samples. The increase in irradiation time affected the resin components. Asphaltenes have a higher capacity to absorb MW, and the results of this study showed that because they did so early in the irradiation process, resulting in the cracking of these particles, later in the process the resin components began to absorb the MW. FTIR spectra results show that early in the irradiation process under MW, the large-chain molecules cracked, leading to an increase in light components in the crude oil. This process continued throughout each experiment; in some time ranges, the cracking of heavy components was more obvious, and in others the escape of light components from the samples was more visible. US was more efficient at reducing asphaltene components than MW. US was shown to reduce asphaltene content in the heavy crude oil samples. This indicates that the viscosity of crude oil samples under US is not a function of asphaltene content, because despite the fact that the greatest reduction of asphaltene contents, the lowest amount of viscosity was not simultaneously observed. The US-induced changes in the heavy crude oil sample indicated the cracking of coarse chains and an increase in the intensity of peaks. In addition, the purity of the crude oil increased and the peak intensities increased due to the driving off of some specific components.

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