Low Asphaltene Research Articles

Effect of Crystal Modifiers and Dispersants on Paraffin-Wax Particles in Petroleum Fluids

Summary Petroleum fluids from shale light-oil and gas/condensate reservoirs generally have a high content of normal paraffins. Paraffin-wax deposition is among the challenges in shale gas and oil production and in offshore flow assurance. Low-dosage chemical additives can be effective in paraffin-wax mitigation because of their high efficiency and economics. These additives are divided into broad categories of crystal modifiers and dispersants with vastly different molecular structures and mechanisms in wax-crystal-particle stabilization and wetting. This investigation focuses on the understanding of the differences in the aggregate size and morphology of chemical additives, and it centers on (1) wax-particle sedimentation from diluted petroleum fluids in vial tests, (2) wax-crystal-particle-size distributions and morphology by dynamic light scattering (DLS) and polarized-light microscopy, and (3) the wetting state from the effect of water. In two of the three petroleum-fluid samples used in this work, there is no visible precipitation at the bottom of the vials at temperatures below the wax-appearance temperature (WAT). The microscopic image of fluids along the length of the tube shows that the wax-particle size and intensity increase from top to bottom. To observe precipitation, we dilute the crude with a hydrocarbon such as n-heptane. The sedimentation of wax is then observed. The petroleum fluids used in this work have very low asphaltene content, and there is no complication from asphaltene precipitation. Our study shows that a small amount of crystal modifier and dispersant can reduce crystal-particle size to the submicron scale, and change the crystal morphology. We investigate the differences in the mechanisms of dispersants and crystal modifiers in bulk. Water, which is often coproduced with petroleum fluids, can increase the effectiveness of dispersants significantly by altering the wetting state of the wax-particle surface. Such enhancement is not found in crystal modifiers. Both additives affect the rheology of petroleum fluids.

Combined interfacial shear rheology and microstructure visualization of asphaltenes at air-water and oil-water interfaces

Asphaltenes are surface-active polyaromatic molecules in crude oil that are known to deposit in pipelines or stabilize water droplets by flocculating at interfaces resulting highly viscous emulsions, leading to significant flow assurance problems. Commercial dispersants have been developed to disturb asphaltene aggregation to mitigate deposition, but their role on the interfacial properties of asphaltene films is unclear. In this study, we elucidate asphaltene interfacial rheology at air-water and oil-water interfaces at high and low asphaltene surface coverage and in the presence of dispersants. A modified Langmuir trough with double-wall ring rheometer is used to simultaneously visualize the microstructure of asphaltene interface and measure the rheological responses. Two surface coverages, 0.5 and 4 μg cm−2, show widely different rheological responses at air-water interfaces. Strong yielding behavior was observed for higher coverage while a less yielding behavior and wider linear viscoelastic regime we...

Pore-Scale Analysis of Residual Oil in a Reservoir Sandstone and Its Dependence on Water Flood Salinity, Oil Composition, and Local Mineralogy

Core-flooding of clay-containing reservoir sandstones can yield substantial tertiary recovery by reducing the flood brine salinity, associated with a shift toward water-wetting. Spontaneous imbibition experiments, in which this salinity-induced shift is the main driver for additional recovery, can provide insight into the extent and source of the wettability change, especially when combined with pore-scale imaging of changes in residual oil configurations using micro-CT. Spontaneous imbibition experiments were performed on two sister mini-plugs of a reservoir sandstone. To explore the influence of crude oil composition, each mini-plug used a different oil, of similar density and viscosity and of low asphaltene content, but primarily distinguished by their total acid number (TAN) of 3 and <0.1 mg KOH/g oil. Mini-plugs were imaged by micro-CT after each experiment. Additional insight into the origins of the apparent shift to more water-wetting were obtained by preparing polished embedded sections of the min...

Supercritical methanol as an effective medium for producing asphaltenes-free light fraction oil from vacuum residue

The upgrading of vacuum residue (VR) in supercritical methanol (scMeOH) was investigated without using catalysts. Various process parameters, including temperature (350–425°C), reaction time (30–90min), and additives (toluene and hydrogen) were explored to optimize the yield of light fraction oil (LFO) with few impurities. At a 400°C, 16.7wt% of VR in methanol for 60min, the LFO produced in scMeOH contained very low asphaltene content (0.74wt%) and a very low amount of heteroatom/metallic impurities (S, 3.58wt%;N, non-detectable; Ni, 10.4ppm;V, 36.9ppm, Fe, 7.3ppm). In addition, the naptha-to-diesel fraction increased from 1wt% (VR feed) to 15wt% and the saturate+aromatic content increased from 43.7 area% (VR feed) to 59.6 area% in the LFO. When the reaction time was extended to 90min at 400°C, a complete removal of asphaltenes could be achieved.

A new experimental investigation on upgrading of waxy crude oils by methacrylate polymers

Several methods have been used to reduce problems caused by wax precipitation during the production and/or transportation of waxy crude oil. Polymers are used to improve pour point and rheological behavior of waxy crude oils. In this work, the influence of the polymer inhibitors such as methacrylate polymers, as wax inhibitor, with different range of molecular weight and alkyl side chain carbons on the rheological behavior and pour point of two Iranian waxy crude oils were evaluated. Two Iranian waxy crude oils were selected on the basis of wax and asphaltene contents. The rheological behavior of these crude oils in absence and in presence of methacrylate polymer was studied. The rheological data cover the temperature range of–1 to 12°C. The results indicated that the performance of methacrylate polymer was dependent on the molecular weight, alkyl side chain carbons and the asphaltene content of crude oil. Methacrylate polymers with longer alkyl side chains than 18 carbons would perform best as wax inhibitors in two cases. Also, for crude oil with low asphaltene, higher molecular weight methacrylate polymer is the best flow improver and lower molecular weight methacrylate polymer showed good efficiency for crude oil with high asphaltene content.

Pyrolysis of a Low Asphaltene Crude Oil under Idealized in Situ Combustion Conditions

The coke formation is crucial to the crude oil in situ combustion (ISC) process. This study provided some insights through analyzing the influences of temperature and reaction atmosphere on the coke chemical–structural property. Thin coke films were produced on the polished single-crystal Si surface from the Xinjiang crude oil. Their functional groups were compared by Fourier transform infrared spectroscopy (FTIR), while the nanostructures were characterized through Raman spectroscopy, X-ray diffraction (XRD), and high-resolution transmission electron microscopy (HRTEM) techniques. In addition, the low-temperature oxidation (LTO) coke and the pyrolytic coke reactivities were investigated by thermogravimetric analyses. The results indicated that the main carbon structures in the pyrolytic coke were amorphous. No crystallization phenomena, such as the aromatic ring condensation and the planar stacking, were observed within the characteristic ISC pyrolytic temperature range. Despite the pyrolytic coke yield ...

In situ catalytic upgrading of heavy oil using a pelletized Ni-Mo/Al2O3 catalyst in the THAI process

Heavy oil and bitumen are difficult crudes to extract and upgrade, with additional transport and refining costs, because of their high viscosity, low API gravity, high asphaltenes, metals (V, Ni), and heteroatoms (N, S). Combining Toe-to-Heel Air Injection (THAI) with its catalytic add-on (CAPRI), a pelletized catalyst is incorporated along the outside of the horizontal producer well for in situ catalytic upgrading. This downhole upgrading process is one means to produce and partially upgrade heavy oil and bitumen with a reduced environmental footprint. In this study, the effectiveness of pelletized hydrodesulfurisation (HDS) Ni-Mo/Al2O3 catalyst for downhole catalytic upgrading was investigated at 350–425 °C, 20 bar, and 9 h−1 space velocity. The additional upgrading due to the presence of the catalyst was evaluated in terms of API gravity, viscosity, boiling point distribution, and sulfur and metals removals, before and after the experiment. The results indicate that the viscosity of the upgraded oil reduced by 1.7, 3 and 5 times less than the feed oil (0.49 Pa s) depending on the reaction temperature in the range 350–425 °C. The average increase in API gravity was approximately 2 to 5° while the gasoline yield showed an improvement of 2.5–13 wt.% above that of the original oil. There was also a modest reduction in the sulfur and metals (Ni + V) content of 2–8% and 1.3–9.2% (Ni + V), respectively. However, a possible limiting factor of the process was that rapid catalyst deactivation occurred due to coking.

Modeling and Scaling of the Viscosity of Suspensions of Asphaltene Nanoaggregates

The scaling and modeling of the viscosity of suspensions of asphaltene nanoaggregates is carried out successfully taking into consideration the solvation and clustering of nanoaggragates, and the jamming of the suspension at the glass transition volume fraction of asphaltene nanoaggregates. The nanoaggregates of asphaltenes are modeled as solvated disk-shaped “core–shell” particles taking into account the most recent small-angle neutron scattering (SANS), small-angle X-ray scattering (SAXS), and solid-state 1H NMR studies available on the size and structure of asphaltene nanoaggregates. This work is an extension of our earlier studies on modeling of asphaltene suspensions where solvation of asphaltene nanoaggregates was not considered. A new mathematical model is developed for estimating the aspect ratio (ratio of thickness to diameter of particle) and the corresponding intrinsic viscosity of suspension of solvated disk-shaped asphaltene nanoaggregates using the experimental relative viscosity data of suspensions at low asphaltene concentrations. The solvation of asphaltene nanoaggregates is found to be significant. The intrinsic viscosity increases with the increase in the degree of solvation of nanoaggregates. At high concentrations of asphaltenes, clustering of solvated nanoaggregates dominates resulting in large viscosities. A new scaling law is discovered to scale the viscosity data of different asphaltene suspensions. According to the new scaling law, a unique correlation is obtained, independent of the type of asphaltene system, when the data are plotted as ( η r − 1 ) / [ η ] S versus ϕ S where η r is the relative viscosity of suspension, [ η ] S is the intrinsic viscosity of suspension of solvated nanoaggregates, and ϕ S is the volume fraction of solvated nanoaggregates. Twenty sets of experimental viscosity data on asphaltene suspensions gathered from different sources are used to verify and confirm the scaling law and the viscosity model proposed in this work. Based on the experimental data, the glass transition volume fraction of solvated asphaltene nanoaggregates where jamming of suspension, and hence divergence of viscosity, takes place is found to be approximately 0.4. The viscosity model proposed in this work can be used to predict the viscosity of a new asphaltene system over a broad range of asphaltene concentrations provided that the intrinsic viscosity of the suspension is obtained from viscosity measurements at very low asphaltene concentrations.

Minimum miscibility pressure of CO2 and crude oil during CO2 injection in the reservoir

Recently, carbon dioxide (CO2) flooding into depleted reservoirs regardless of miscible or immiscible displacement is widely investigated not only to improve oil recovery but also to reduce the greenhouse effect of this gas produced by numbers of industries in the globe. In the light of this fact, in the first stage of this investigation, the minimum miscibility pressure (MMP) of CO2 and light crude oil (API°=35) with low asphaltene content was determined at temperatures of 30, 50 and 80°C using vanishing interfacial tension (VIT) method. The obtained results demonstrated that the MMP of the studied system is almost linear function of temperature with slope of 0.15MPa/K. The interesting point is that the results revealed a reduction in slope as the composition of light components of crude oil increases.

Surface Interaction of Water-in-Oil Emulsion Droplets with Interfacially Active Asphaltenes.

Adsorption of interfacially active components at the water/oil interface plays critical roles in determining the properties and behaviors of emulsion droplets. In this study, the droplet probe atomic force microscopy (AFM) technique was applied, for the first time, to quantitatively study the interaction mechanism between water-in-oil (W/O) emulsion droplets with interfacially adsorbed asphaltenes. The behaviors and stability of W/O emulsion droplets were demonstrated to be significantly influenced by the asphaltene concentration of organic solution where the emulsions were aged, aging time, force load, contact time, and solvent type. Bare water droplets could readily coalesce with each other in oil (i.e., toluene), while interfacially adsorbed asphaltenes could sterically inhibit droplet coalescence and induce interfacial adhesion during separation of the water droplets. For low asphaltene concentration cases, the adhesion increased with increasing asphaltene concentration (≤100 mg/L), but it significantly decreased at relatively high asphaltene concentration (e.g., 500 mg/L). Experiments in Heptol (i.e., mixture of toluene and heptane) showed that the addition of a poor solvent for asphaltenes (e.g., heptane) could enhance the interfacial adhesion between emulsion droplets at relatively low asphaltene concentration but could weaken the adhesion at relatively high asphaltene concentration. This work has quantified the interactions between W/O emulsion droplets with interfacially adsorbed asphaltenes, and the results provide useful implications into the stabilization mechanisms of W/O emulsions in oil production. The methodology in this work can be readily extended to other W/O emulsion systems with interfacially active components.

Study of asphaltene adsorption onto raw surfaces and iron nanoparticles by AFM force spectroscopy

The comprehension of dominant driving forces for Asphaltene self aggregation and adsorption onto surfaces are still under discussion. Experimental results point to combined effects of the local electrical fields, molecular polarization, and dispersion interactions play a relevant role in the adsorption. The nature and size of sorbent material has a determinant influence in the process, sorbent with size in the order of asphaltenes nanoaggregates could modificate the adsorption mechanism. This work focus to study the differences in asphaltenes adsorption driving forces of asphaltenes onto macro and nanosurfaces. AFM Force-displacement curves have been used to study the interaction forces between AFM tip and asphaltenes adsorbed onto macroscopy surfaces and Zero valent iron nanoparticles (FeNps). FeNps were prepared by laser ablation and used as sorbent material for Asphaltenes adsorption at very low Asphaltene in toluene concentration ranging from 1 to 10mg/g. The FeNps were characterized by Uv–Vis Spectroscopy, Dynamic Light Scattering (DLS) and Atomic Force Microscopy (AFM). AFM Force vs Separation of asphaltenes adsorbed onto macroscopic surface compared with adsorption onto NPs curves shown the importance of the surface size and morphology and asphaltenes molecular arrangement in the adsorption process. Properties as Force interaction, adhesion and Hamaker constant for each system were obtained.

A Mechanistic Understanding of Asphaltenes Precipitation From Varying-Saturate-Concentration Perspectives

Summary Asphaltenes precipitation within reservoir pores or production flowlines can severely hamper the petroleum-extraction process. Although the effect of temperature and pressure on asphaltene deposition is well-known, the manner in which the variations in oil composition affect the asphaltenes-precipitation mechanism requires more clarity. This work investigates the effect of crude-oil compositional change on asphaltene stability. The impact of oil composition is analyzed by preparing pseudocomponents through blending the crude oil with their own saturates fractions. A systematic characterization of 11 different bitumen and crude-oil samples was carried out by density and viscosity measurements and the determination of the elemental composition and saturates, aromatics, resins, and asphaltenes (SARA) contents. Further analyses were conducted on the asphaltenes separated by use of n-pentane. The cluster size was determined by a particle-size analyzer, and the stability of asphaltenes was evaluated by zeta-potential. The molecular structure of SARA fractions and bulk crude-oil samples was analyzed by Fourier-transform infrared (FTIR) spectroscopy. Onset-of-asphaltenes-precipitation (OAP) tests on crude-oil samples were achieved by the addition of different solvents (n-pentane, n-heptane, and crude-oil saturates fraction). While the physical characterization studies could only provide weak relations between the density/viscosity and the asphaltene content of the bulk samples, it has been found that mainly the ratio of the heavy (resins + asphaltenes) to light (saturates +aromatics) fractions controls the viscosity and the °API value of the crude oils. As this ratio increases, the crude oil becomes more viscous and dense. Also, the asphaltene/resin ratio was found to be critical because of its impact on asphaltene stability, which was determined through zeta-potential measurements. The high asphaltene/resin ratios result in low asphaltene stability; however, this effect is surpassed by the higher aromatics fraction in the bulk oil. Asphaltene stability was further studied with OAP tests. The OAP-test results provide the behavior of asphaltenes after the interaction of bulk oil samples with normal saturated hydrocarbons; however, our study improves the OAP-test procedure by conducting OAP tests with crude oil's own saturates fractions. The interaction of saturates fraction with crude oil resulted in more asphaltenes precipitation compared with interaction of n-pentane and n-heptane. The FTIR analyses indicate the presence of impurities in saturates fractions, and these impurities are believed to cause higher asphaltenes precipitation as a result of the polar nature of the impurities.

A non-catalytic, supercritical methanol route for producing high-yield saturated and aromatic compounds from de-oiled asphaltenes

Upgrading of de-oiled asphaltenes (DOAs), i.e., the heavy fraction obtained after solvent deasphalting of vacuum residue, was investigated in supercritical methanol (scMeOH) without using external catalysts and molecular hydrogen. Process parameters, including temperature (350–400°C), reaction time (30–120min), and additive (formic acid), were explored to optimize the yield of light oil with few impurities. As a result of the beneficial in-situ hydrogen-donation ability and reactivity of scMeOH, its use resulted in higher DOA conversion, increased light-fraction yield, and fewer impurities as compared to those obtained in supercritical water (scH2O). Higher reaction temperatures and residence times increased the DOA conversion to low-molecular-weight saturates and aromatics. With the addition of formic acid as a secondary source of H2 in scMeOH at 400°C, a 16.7wt% DOA concentration, and a 90min residence time, a remarkably high liquid oil yield of 83.9wt% was obtained. The produced light fraction oil contains a low asphaltene content (0.53wt%) and few impurities (S, 2.74wt%; Fe, 19.6ppm; Ni, non-detectable; V, 18ppm). In addition, the maltenes content (i.e., saturates+aromatics) was 78.3% and the naphtha-to-diesel fraction was 18wt% in the light-fraction oil; these results indicate effective cracking, desulfurization, and demetallization in the scMeOH medium with formic acid. A plausible reaction mechanism for scMeOH-based upgrading is discussed.

Rheological demonstration of alteration in the heavy crude oil fluid structure upon addition of nanoparticles

Nanotechnology offers potentially disruptive methods to improve the mobility of heavy oil through viscosity reduction. In this sense, the objective of this work is to probe changes in the viscoelastic network of asphaltenes intrinsic to heavy oil structure upon addition of fumed SiO2 nanoparticles, using dynamic rheological techniques. The effects of the addition of nanoparticle (100, 1000 and 10,000mg/L) on heavy oil are patently reflected as a viscosity reduction (for shear rates between 0 and 100s−1) and a non-Newtonian shear thinning behavior. The best concentration of nanoparticles over the wide range evaluated is obtained at 1000mg/L, which was evaluated at 288, 298 and 313K. The viscosity reductions were found to range from 12 to 45% in the shear rate range 0–100s−1. The linear viscoelastic region (LVR) was determined by running an amplitude sweep test at 10rad/s and 298K. Viscoelastic moduli were measured in dynamic tests in a frequency range from 0.1 to 100rad/s at a strain of 2% and at temperatures of 288, 298 and 313K. For heavy crude oil without nanoparticles, the magnitude of the loss modulus G″ and its growing trend suggest the existence of a viscoelastic network of asphaltenes and auto-associative behavior. For all tests, the loss modulus, G″, is always greater than the storage modulus G′, suggesting that the crude oil is more viscous than elastic, except at 313K and at a frequency > 30rad/s, where G′ is greater than G″. By adding 1000mg/L of nanoparticles, the magnitude of the viscoelastic moduli is reduced compared to values for crude oil without nanoparticles. The results conclusively prove that nanoparticles disrupt the viscoelastic network formed by asphaltenes aggregates in the presence of resins, and this causes the viscosity reduction in heavy crude oil. This conclusion is further supported by results obtained when nanoparticles were added to de-asphalted oil (DAO) and light oil with a low asphaltene content; in both cases the viscosity increases, suggesting that the nanoparticles interact directly with asphaltenes in crude oil. Effects are observed if asphaltenes are present at high enough concentration.

Mesoscale Simulation of Asphaltene Aggregation.

Asphaltenes constitute a heavy aromatic crude oil fraction with a propensity to aggregate and precipitate out of solution during petroleum processing. Aggregation is thought to proceed according to the Yen-Mullins hierarchy, but the molecular mechanisms underlying mesoscopic assembly remain poorly understood. By combining coarse-grained molecular models parametrized using all-atom data with high-performance GPU hardware, we have performed molecular dynamics simulations of the aggregation of hundreds of asphaltenes over microsecond time scales. Our simulations reveal a hierarchical self-assembly mechanism consistent with the Yen-Mullins model, but the details are sensitive and depend on asphaltene chemistry and environment. At low concentrations asphaltenes exist predominantly as dispersed monomers. Upon increasing concentration, we first observe parallel stacking into 1D rod-like nanoaggregates, followed by the formation of clusters of nanoaggregates associated by offset, T-shaped, and edge-edge stacking. Asphaltenes possessing long aliphatic side chains cannot form nanoaggregate clusters due to steric repulsions between their aliphatic coronae. At very high concentrations, we observe a porous percolating network of rod-like nanoaggregates suspended in a sea of interpenetrating aliphatic side chains with a fractal dimension of ∼2. The lifetime of the rod-like aggregates is described by an exponential distribution reflecting a dynamic equilibrium between coagulation and fragmentation.

How to select the right solvent for solvent-aided steam injection processes

Solvent-steam processes gained popularity in recent years in the extraction of high-asphaltenes-content heavy hydrocarbons. However, while solvent selection is key for the success of these processes, the criteria for solvent selection are still not fully established. In this study, three asphaltenes insoluble (propane, n-hexane, carbon dioxide) and one asphaltenes soluble (toluene) solvents were tested on solvent-aided steam processes to extract a bitumen sample from Alberta, Canada. Both steam flooding and SAGD performances were analyzed. The impact of clay presence was investigated by conducting experiments with and without the addition of clays, consisting of an illite-kaolinite mixture. The results of this study suggest that the produced oil samples from steam injection processes are in the form of water-in-oil emulsions. It has been observed that the amount of asphaltenes in produced oil determines the amount of water trapped in the form of emulsions. Co-injection of solvent with steam decreases the interfacial film between water and asphaltenes. However, asphaltenes insoluble solvents were found to be more effective to eliminate the forces at the oil-water interface. Presence of clays also reduced the water content of emulsions. The results of this study suggest that carbon dioxide, which is a non-hydrocarbon asphaltenes-insoluble solvent, yields the greatest quality oil with the lowest amount of water and clay in produced oil and provides high oil recovery. Hence, it is recommended to use asphaltenes-insoluble, non-hydrocarbon solvents for the extraction of low API gravity, high viscosity, and high asphaltenes content reservoirs.

On the effect of temperature on precipitation and aggregation of asphaltenes in light live oils

AbstractAsphaltene precipitation and deposition is a serious issue in all facets of petroleum production and processing. Despite the numerous experimental efforts concerning asphaltenes, the effect of temperature on asphaltene precipitation and aggregation in live oils remains an elusive and controversial subject in the available literature. In this work, a series of high pressure‐high temperature depressurization experiments were designed to assess the effect of temperature on asphaltene precipitation and aggregation in light live oils. Asphaltene related experiments were performed using a high pressure microscope and high pressure‐high temperature filtration setup on a light live oil with a low asphaltene content and a high potential of asphaltene formation. The results of the experiments were interpreted in terms of asphaltene onset pressure, size distribution and average diameter of the aggregates, fractal dimension of the asphaltene aggregates, and the amount of precipitated asphaltene. It was found that the depressurization process at higher temperatures resulted in higher asphaltene onset pressure or earlier formation of asphaltenes. Visualization experiments showed that asphaltene aggregates in light live oil are pressure‐temperature fractal structures. The depressurization process at lower temperatures led to the formation of highly porous and loose aggregate structures with relatively low fractal dimensions. As the temperature of the depressurization process decreases, the mechanism of asphaltene aggregation changes gradually from reaction‐limited aggregation to diffusion‐limited aggregation. This research reveals that temperature has crucial effects on the asphaltene aggregation process in light live oils at elevated pressures, which is of great importance for asphaltene handling and separation.

Bitumen heavy oil upgrading by cavitation processing: effect on asphaltene separation, rheology, and metal content

Cavitation processing has been proposed as a greener alternative to solvent dilution or heat treatment of bitumen and other heavy oils to reduce viscosity and hence, improve transportability. The effect of acoustic cavitation under different conditions of sonication frequencies (low- to high- frequency range) and power inputs on asphaltene content, rheological changes, and metal content of bitumen was investigated in this study. Ultrasonic treatment resulted in a decrease in asphaltene content in bitumen that lead to lower viscosity and shear stress over a wide range of shear rates. Over the range of sonication frequencies investigated (20 kHz–1.1 MHz), the sonication frequency of 574 kHz with 50 % power input resulted in low asphaltene content and lower viscosity suitable for improved transportability. Further, comparison of different conditions of sonication frequencies and power inputs were carried out to investigate the effect of ultrasound on properties of asphaltene (elemental analysis and metal content). It was observed that the sonication treatment of bitumen under different conditions of frequencies and acoustic power decreased the H/C ratio. These results showed higher content of aromatic hydrogen and lower content of aliphatic hydrogen in bitumen treated under different conditions of sonication frequencies and intensity. Characterization of asphaltene performed using ICP-MS and TXRF, revealed lower metal content (Ni, Fe, and V) in the asphaltene phase of processed (sonicated) bitumen. The lowered metal content can be attributed to the reduced asphaltene formation as a result of sonication treatment of bitumen.

Influence of presence/addition of asphaltenes on semi-coke textures and mesophase development in petroleum feed stocks

In this paper, effect of asphaltenes on optical textures of semi-coke and pitches prepared from vacuum residues (VRs) and their deasphalted oils (DAOs) during heat treatment at a temperature 390°C was investigated. Optical microscopic image analysis shows that VR-1 which contains 10.44wt% asphaltenes produces semi-coke VR-390-1 having 29vol% mesophase content and flow type coalescence. On the other hand, VR-2 which contains 24.57wt% asphaltenes produces semi-coke VR-390-2 having 27vol% mesophase content and mosaic type texture. Further, it was observed that deasphalting of these vacuum residues improve the optical textures as well as enhance the mesophase content in DAO-390-1 (48vol%) and DAO-390-2 (36vol%) semi-cokes. Furthermore, we have also concluded that asphaltenes molecules affect the growth of mesophase development in an adverse manner. In this study, we have prepared pitches from clarified oil (CLO) and aromatic extract (AE) having very low asphaltenes content at temperatures 380 and 390°C respectively without and with the addition of 3% asphaltenes. Optical microscopic images of these pitches show that mesophase contents were decreases with the addition of asphaltenes externally. In addition, semi-cokes and pitches were also characterized by using elemental analysis, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and thermogravimetric analyses (TGA). The study revealed that asphaltenes either present in the feed stock or externally added in the feed stock play a negative role on mesophase development as well as on coke texture.

Impact of oil compatibility on quality of produced fuel oil during start-up operations of the new residue ebullated bed H-Oil hydrocracking unit in the LUKOIL Neftohim Burgas refinery

During start-up operations of the new residue ebullated bed H-Oil hydrocracking unit in the LUKOIL Neftohim Burgas refinery oil incompatibility was registered in the process of production of heavy fuel oil. Тhat was the reason for obtaining high sediment off-spec heavy fuel oil product. The oil incompatibility was observed in the process of blending of high saturate, low asphaltene, high colloidal stability H-Oil unconverted vacuum residue with the high aromatic, and relatively high asphaltene visbroken residue. The use of antifouling additive was found to decrease the sediment level in the heavy fuel oil. However, it was not capable of reducing the heavy fuel oil sediment content after chemical and thermal artificial aging of the fuel oil. Considerable amount of high aromatic fluid catalytic cracking heavy cycle oil was needed to reduce the off-spec heavy fuel oil sediment content to the specified max. limit of 0.1% sediments. After deasphaltization of the visbroken residue with n-heptane and blending of the visbroken deasphalted oil with the H-Oil unconverted vacuum residue in a ratio of 1:1 the sediment content of the heavy fuel oil blend dropped from 2.5% to 0.01%. This suggests that the lower solubility of the visbroken residue asphaltenes in the high saturate H-Oil unconverted vacuum residue was the reason for the oil incompatibility during the production of off-spec heavy fuel oil in the LUKOIL Neftohim Burgas refinery when both the H-Oil residue hydrocracker and the visbreaker were in operation.