CharacterizationsFTIRFigure 2 shows the FTIR spectra of the CSG1 and CSG2 nanocomposites reveal commonalities and differences in their functional groups. Both nanocomposites exhibit broad peaks between 3000 and 2500 cm−1, indicating the presence of O–H stretching vibrations and hydroxyl groups. Additionally, a peak at around 1600 cm−1 indicates the presence of C=O stretching vibrations and carbonyl groups in both nanocomposites. The distinguishing feature is a peak at approximately 1500 cm−1 in the spectrum of both CSG1 and CSG2, attributed to N–H bending vibrations.Fig. 2FTIR spectra of the matrix polymer of CSG1 and CSG2 nanocomposites.XRDFigure 3 described the X-ray diffraction (XRD) pattern of two materials, CSG1 and CSG2. The XRD pattern is a plot of the intensity of X-rays scattered by a material as a function of the angle of the scattered X-rays. The peaks in the pattern correspond to the spacing between atoms in the material. The XRD pattern for CSG1 and CSG2 shows that they have a similar crystalline structure. The peaks in the pattern are at the same angles for both materials, which suggest that the atoms are arranged in the same way in both materials. However, the intensity of the peaks is different for the two materials. This indicates that the materials have different crystal sizes or that there is a different amount of material in each sample. The XRD peaks for CSG2 are higher than the intensity of the peaks for CSG1. This suggests that CSG2 is more crystalline than CSG1. The higher crystallinity of CSG2 may be due to the higher concentration of graphene oxide in the nanocomposite. The XRD peaks for CSG1 and CSG2 can be assigned to the peak at around 2θ = 10° can be assigned to the (002) plane of CMCNa. The peak at around 2θ = 20° can be assigned to the (001) plane of SiO2. The peak at around 2θ = 40° can be assigned to the (002) plane of graphene oxide. The presence of these peaks indicates that the CMCNa, SiO2, and graphene oxide are well-dispersed in the nanocomposite. The XRD results illustrated that CSG2 is a more crystalline material than CSG1. This may be due to the higher concentration of graphene oxide in the nanocomposite. The higher crystallinity of CSG2 may lead to improved mechanical properties. The Scherer equation, Eq. (1)39, was used to estimate the mean particle size of the produced nano catalyst CSG1 and CSG2 was approximately 70.01 nm and 21.38 nm respectively.$$ {\text{D}} = \frac{0.89\lambda }{{\beta \cos \theta }} $$
(1)
where, D is the mean crystallite size, β is the broadening of the diffraction line measured at half-maximum intensity, λ is the wavelength of the X-ray radiation, and θ is the Bragg angle.Fig. 3X-ray diffraction (XRD) pattern of matrix polymer of CGS1 and CGS2 nanocomposites.BET, DLS and zeta potentialFigure 4 displays the adsorption–desorption isotherms of N2 of matrix polymer of CSG1 and CSG2 nanocomposites. The analysis of the porosity of the matrix polymer of CSG1 and CSG2 composites via adsorption–desorption isotherms of N2 at 273 K revealed specific surface areas of 0.577312 m2/g and 0.72164 m2/g, respectively, calculated using the Brunauer–Emmett–Teller (BET) model. Additionally, the average pore size diameter, determined by the Barrett-Joyner-Halenda (BJH) model, was found to be 46.963 nm and 58.704 nm for CSG1 and CSG2, respectively (Table 3).Fig. 4The isotherms (a) and pore size distribution (b) of matrix polymer of CSG1 and CSG2 nanocomposites.Table 3 BET/Z-average/zeta potential for matrix polymer CSG1 and CSG2 nanocomposites.Furthermore, measurements of Z-Average and Zeta potential in aqueous solutions, depicted in Fig. 5, provided valuable insights into the dispersion stability of colloids and the electrostatic interaction between different graphene oxide sheets. The results showed Z-Average values of 459.1 nm and 485.15 nm, and Zeta potential values of − 61.7 mV and − 64.1 mV for CSG1 and CSG2 nanocomposites, respectively. These highly negative values indicate that the nanocomposites are stable in aqueous suspensions due to strong electrostatic repulsion resulting from the presence of oxygen species on their surfaces. According to literature, a zeta potential absolute value higher than 30 mV indicates the stability of graphene oxide compound suspensions40. From these data, it was evident that the CSG1 and CSG2 nanocomposites possess high specific surface areas and large pore size diameters. Additionally, their stability in aqueous suspensions due to their negative zeta potential makes them promising candidates for various applications.Fig. 5Size distribution and zeta potential of matrix polymer of CSG1 and CSG2 nanocomposites.Morphological analysisFigure 6 utilizing the Scanning Electron Microscope (SEM), the morphologies of CSG1 and CSG2 nanocomposite matrix polymers. In Fig. 6a,b, the presented graphene oxide (GO) displays a carpet-like pattern, likely attributed to residual bound moisture and the presence of hydroxyl, epoxy, and carboxyl functional groups on the GO surface41. The graphene sheets exhibit intrinsic microscopic roughening and out-of-plane deformations (wrinkles), with some dispersed GO sheets connecting randomly to form a porous structure with numerous cavities or holes. This results in a cross-linked flaky structure with excellent dispersibility and an average size perspective of approximately (188–284 nm) and (223–264 nm) for composite matrix polymers CSG1 and CSG2, respectively.Fig. 6SEM and EdX of matrix polymer of CSG1 and CSG2 nanocomposites.SEM images of the CSG2 nanocomposite samples reveal superior dispersion, indicating a larger specific surface area that promotes enhanced catalytic activity. Additionally, Energy Dispersive X-ray (EDX) measurements were conducted for validation (Fig. 6). The CSG2 nanocomposite sample prominently exhibits C, O, and Si elements. Conversely, the expected C, O, and Si element peaks in the structure were confirmed by EDX investigation, providing evidence for the uniform distribution of C, O, and Si particles within the hybrid SiO2-GO-CMC nanocomposite material, forming SiO2-GO nanohybrids between the precursor and GO. The C, O, and Si content in the CSG1 EDX is higher than in CSG2 because EDX measures only the elements present on or near the surface. Therefore, the analysis may not fully reflect the overall composition of the samples. This can result in discrepancies between the surface layers and the bulk of the sample. Additionally, the distribution of nano silica in the sample may not have been homogeneous.Thermogravimetric analysis (TGA) of CSG1 and CSG2Figure 7 shows the TGA analysis and the thermal stability analysis of SiO2-GO/CMC nanocomposites. The TGA curves for SiO2-GO/CMC nanocomposites (CSG1 and CSG2) reveal a two-stage decomposition process. Moisture evaporates occurs around 100 °C, followed by the second stage involving organic component decomposition, which starts at 200 °C for the 10% composite and 250 °C for the CSG2composite. The CSG1 composite decomposes more rapidly than the CSG2, indicating higher thermal stability for the latter. At 900 °C, the CSG2 sample retains 56.79% weight, while the CSG1 sample retains 35.21%. This signifies greater thermal stability for the CSG2 composite due to lower organic content. Specific observations include moisture loss, GO surface decomposition (300–500 °C), CMC matrix decomposition (500–700 °C), and SiO2 nanoparticle decomposition (> 700 °C). The graphene oxide in CSG2 enhances stability, making it suitable for high-temperature applications. Therefore, CSG2, enriched with graphene oxide, is recommended for high-temperature applications due to its superior thermal stability compared to CSG1.Fig. 7TGA analysis for matrix polymer of CSG1 and CSG2 nanocomposites.Catalytic aquathermolysis resultsTo meet the future energy demands, heavy oil must be progressively upgraded into lighter and more valuable oil. Catalytic aquathermolysis is one of the most promising techniques in upgrading and decreasing the viscosity of the heavy crude oil in the presence of catalyst. The incorporation of nanomaterials as potential catalysts in the aquathermolysis process is vital and very efficient.Effect of CSG1 and CSG2 on the viscosity reduction of heavy oilThe role of CSG1 and CSG2 nanocomposites in the aquathermolysis process was investigated by comparing the viscosity reduction of each run. It is obvious that the orthogonal experiments were based on three factors: water content, temperature, and catalyst percent, as shown in Table 4. The time of each experiment was adjusted at five hours. The data in Table 4 reveals that the optimum conditions for both catalysts are 40%, 225 °C, and 0.5 wt% for the water concentration, temperature, and catalyst percent, respectively. In addition, the viscosity reduction using CSG2 is much better than that of CSG2, where the viscosity reduction reached 62% and 82%, respectively. This indicates that there is a considerable degree of viscosity reduction of the crude oil after using CSG2, even at relatively lower temperatures.Table 4 Designed experiments of catalytic aquathermolysis of the heavy crude oil.Group composition analysis (SARA)According to viscosity reduction data, it is clear that the optimal conditions referred to 0.5 wt% of catalyst at 225 °C in presence of 40% water concentration for both catalysts (CSG1 and CSG2). Consequently, the yielded oils under these conditions in the absence and the presence of catalysts were analyzed via SARA technique to study the difference in the group chemical composition. In which, four components were separated from the oil namely saturates, aromatic, resin and asphaltene using the column chromatography. Compared to the crude oil, the catalytic aquathermolysis using both CSG1 and CGS 2 samples show a substantial increase in lighter fractions, with saturates rising by 14.3% and 21.7% and aromatics by 12.8% and 26%, respectively as shown in Table 5. This is accompanied by a decrease in heavier components, with resins dropping by 7.7% and 17.9% and asphaltenes experiencing the most significant decline of 28.3% and 41.6% for CSG1 and CSG2, respectively. These results suggest that the catalytic aquathermolysis primarily targets asphaltene macromolecules, breaking them down into lighter and more desirable hydrocarbon fractions.Table 5 Group compositional analysis of the crude oil, the treated oil via aquathermolysis, and the treated oil via catalytic aquathermolysis using CSG1 and CSG2.FT-IR of the extracted asphalteneTo investigate the effect of catalytic aquathermolysis on the heavy crude oil, FT-IR spectroscopy was employed. The analysis focused on asphaltene extracted under the optimal experimental conditions and compared it to the original asphaltene before the treatment. As illustrated in Fig. 8, the FT-IR spectra reveal distinct differences between the two samples. Notably, the observed peaks at 3417 and 3412 cm−1 are attributed to the O–H stretching vibration, potentially indicating the presence of carboxylic, phenolic, or alcoholic groups within the asphaltene structure. Additionally, the FT-IR spectra showed peaks near 1609 and 1602 cm−1 for the untreated (AS1) and the treated (AS2) asphaltene, respectively, which are associated with the stretching vibrations of conjugated polyene C=C bonds and aromatic ketone C=O bonds in asphaltene. This shift towards lower wavenumbers in the treated asphaltene may be indicative of increased condensation of aromatic groups. In the untreated asphaltene, peak at 1712 cm−1 was observed, corresponding to aliphatic esters, aromatic esters, aliphatic carboxylic acids, and aromatic carboxylic acids. This peak disappeared in the treated asphaltene, suggesting the breaking of the C–C bond in the long alkyl chain influenced by the catalytic aquathermolysis process.Fig. 8FT-IR of the extracted asphaltene before (AS1) and after (AS2) aquathermolysis process at the optimum conditions.Gas chromatography analysis revealed that the composition of crude oil was significantly modified after undergoing catalytic aquathermolysis treatment with CSG2 (Fig. 9a,b). The most notable change was a dramatic increase in the light hydrocarbon fraction (C6 to C12), with their mole percent rising from 7.8, 9.8, 7.5, 8.5, 6.1, 2.7, and 2.9 to 8.0, 10.3, 8.3, 6.8, 8.0, 5.5, and 4.2 mol% as shown in Fig. 10. This is possibly due to the degradation of alkyl chains in the heavy components like asphaltenes. This is in a good agreement with the reported results obtained by Aliev et al., where they stated that the content of the low molecular weight hydrocarbon was increased during the in-situ catalytic upgrading of heavy crude oil using nickel tallate catalyst42. This is also supported by the decrease in mole percent of the heavy components (C13 and higher).Fig. 9Gas chromatograph for crude oil (a) before and (b) after catalytic aquathermolysis using CSG2 at the optimum conditions.Fig. 10Comparison between the composition analysis of the crude oil before and after catalytic aquathermolysis using CSG2 at the optimum conditions.Rheological behaviorCatalytic aquathermolysis aims to improve the flowability of heavy crude oil by reducing its viscosity, making it easier to transport within the reservoir or pipeline. The treated oil sample displayed shear thinning behavior as shown in Fig. 11. As the temperature rose from 25 to 50 °C, its apparent viscosity decreased. This behavior is likely due to the temperature-induced weakening of interactions between the heavy molecules, such as asphaltenes, which tend to clump together and increase viscosity. The results confirm that the treated oil exhibited a significantly lower viscosity compared to the untreated crude oil, where the viscosity of the crude oil at two different temperatures (25 and 50 °C) was decreased remarkably from around 420 and 110 cp to around 40 and 14 cp after using CSG2 at the optimum conditions of the catalytic aquathermolysis process. This is almost attributed to the effect of heat and the used catalysts, where they work together to break down the asphaltene molecules into smaller, lighter molecules. This enhances the overall viscosity reduction of the crude oil.Fig. 11Viscosity flow behavior of crude oil before and after catalytic aquathermolysis using CSG2 at 25 and 50 °C.A crucial tool for studying the viscoelastic behavior of the hydrocarbon liquids during investigating the rheological properties is the dynamic test, in which the impacts of oscillating stress on the oil samples. There are two key properties known as loss modulus (G′) and storage modulus (G″) which are calculated. The loss modulus is known as viscous modulus and it indicates the energy dissipated as heat due to internal friction within the material during deformation, which is not recoverable. On the other hand, the storage modulus (G″) is known as elastic modulus and it reflects the elastic portion of the material’s response. Moreover, represents the energy temporarily stored during deformation that can be recovered upon unloading.Figures 12 and 13 show the frequency dependence of the storage modulus (G′) and loss modulus (G″) for the heavy crude oil before and after aquathermolysis with CSG2. It is obvious that the storage modulus increases with increasing angular frequency. This indicates that the oil become stiffer as the oscillation rate increases. In addition, the treated oil with CSG2 has a storage modulus lower than the untreated crude oil at both temperatures 25 and 50 °C. The heavy crude oil exhibits a nearly linear response across the investigated frequency range. Importantly, the loss modulus (G″) consistently exceeds the storage modulus (G′), indicating that the energy stored within the heavy crude oil is less than the energy dissipated. This suggests a more viscous liquid-like behavior than a solid-like one.Fig. 12Storage modulus for crude oil before and after catalytic aquathermolysis using CSG2 at 25 and 50 °C.Fig. 13Loss modulus for crude oil before and after catalytic aquathermolysis using CSG2 at 25 and 50 °C.Table 6 compares the effectiveness of CSG1 and CSG2 against other published catalysts that were used in the catalytic aquathermolysis process. Notably, CSG2 achieved a significant 82% reduction in heavy crude oil viscosity. This catalyst holds promise for the petroleum industry due to its cost-effective preparation and the moderate temperature required for such high efficiency. The use of commercial-grade catalysts can improve the crude oil using aquathermolysis to a large extent, it has a negative effect represented by the synergetic effect of the ultrasonic and the catalyst43. However, the use of iron naphthenates in the catalytic aquathermolysis reduced the viscosity of heavy oil greatly it has a potential formation of stable emulsions. These stable emulsions can impede the interaction between the catalyst and the heavy oil, ultimately reducing the efficiency of the aquathermolysis process44.Table 6 A comparison demonstrates the effect of the prepared catalysts and the previously published on the viscosity reduction during the catalytic aquathermolysis of heavy crude oil.
In-situ upgrading of Egyptian heavy crude oil using matrix polymer carboxyl methyl cellulose/silicate graphene oxide nanocomposites
