Hydrotreating of Furrial Crude Oil Using NiMoS Supported on Alumina: Study of the Asphaltene and Their Fractions in Cyclohexane

Abstract

The Furrial crude oil originated in northern Monagas State. This shows problems such as the colloidal instability of the asphaltenes fraction present in them, causing its precipitation. This work is oriented to achieve an interpretation of the colloidal behavior of the asphaltenes through the study of the effect of the hydrotreating reactions (HDT) on the asphaltenes of the Furrial crude oil, using NiMoS/γ-Al₂O₃ as a catalyst. The results obtained after HDT reactions were analyzed to know the percentage of asphaltene and their fractions in cyclohexane, the measurement of flocculation thresholds and molecular weights by the VPO technique, and ¹³C NMR as well as the determination of the total sulfur content. Appreciable changes on the asphaltene of the Furrial crude oil and its fractions in cyclohexane after HDT, under conditions used, were observed. In general terms, the amount of asphaltene diminished and the percentage of distribution for insoluble fraction in cyclohexane (IFC) and for soluble fraction in cyclohexane (SFC) was affected causing an increase in the stability of the asphaltene. The asphaltene and IFC were observed to be a pronounced variation of the molecular weight average in number, in comparison with SFC. ¹³C NMR spectra indicate that the hydrotreated asphaltene shows structural change, and IFC presents a variation of the percentage of sulfur minor in comparison to SFC.     

A Thermodynamic Model for the Prediction of Asphaltene Precipitation

Abstract

Asphaltene precipitation in reservoirs, wells, and facilities can have a severe and detrimental impact on the oil production. Due to the extreme chemical complexity of the asphaltene and crude oil and the lack of comprehensive experimental data, the modeling of asphaltene precipitation in crude oil remains as a challenging task. In this article, a compositional thermodynamic model was developed to predict asphaltene precipitation conditions. The proposed model is based on a cubic equation of state with an additional term to describe the association of asphaltene molecules. Extensive testing against the literature data, including asphaltene precipitation from crude oil and solvent injection systems, concludes that the proposed model provides reasonable predictive results.     

Correlation Between Properties of Asphaltenes and Precipitation Conditions

Abstract

Asphaltenes from three crude oils were precipitated by using a pressurized system. Different conditions during the precipitation of asphaltenes were studied: pressure was varied between 15 and 45 kg/cm² and temperature between 40°C and 100°C. The effect of contact time and solvent-to-oil ratio was also studied in the range of 0.5–6 hr and 2:1 to 5:1 mL/g, respectively. Asphaltenes properties were analyzed as a function of pressure and temperature. It was found that in a deeper way temperature influences the asphaltenes properties than pressure in the range studied in this work. Asphaltenes properties were highly dependent on the nature of crude oil. Various correlations were developed and experimental and calculated asphaltenes contents and properties were in good agreement with absolute error less than 0.2%.     

Study of Asphaltene Precipitation Using Refractive Index Measurement

Abstract

The measurements of the refractive index of crude oils were utilized in this work to enhance the understanding of the behavior of asphaltenes in crude oil, specifically, their tendency to precipitate from crude oil. The onset of asphaltene precipitation was measured in eight crude oil samples, which were titrated with either heptane or pentane in order to induce precipitation of the asphaltenes. The refractive index of each sample was measured to find its relationship to asphaltene precipitation. The assumption that refractive index of a mixture is a linear combination of the refractive indexes of the individual components was verified. It was also found that mixtures of heptane or pentane and crude oil also followed this same behavior. However, as asphaltenes began to precipitate from the solution, the refractive index no longer followed this linear mixing rule. Careful analysis of the refractive index data for each of the crude oil samples revealed many interesting relationships between the refractive index data and the content of the different polar asphaltene fractions present. The refractive index of asphaltenes was predicted from the refractive index data of crude oils. The results suggest the possibility predicting the properties and characteristics of the asphaltenes contained in a crude oil simply by measuring the refractive index.     

MATHEMATICAL MODELLING OF WAX DEPOSITION IN CRUDE OIL PIPELINES (COMPARATIVE STUDY)

ABSTRACT

In this research, wax deposition in different crude oil pipeline systems was studied. In oil pipelines, the main mechanism for wax appearance is the temperature change along the pipeline. A computer program was developed to simulate the wax precipitation phenomena. Temperature profile along the pipeline was determined and solid liquid equilibrium constant, wax mole fraction and wax thickness along the pipeline were calculated. This computer program was applied to different crude oil pipeline systems in Iraq (Baiji-Daura, Rumaila-Zubair-Fao and Hadttha-Rumailia). In Haditha-Rumaila crude oil pipeline system, it was observed that wax thickness after a year is approximately 0.1 mm and temperature declined from 303 K to around 300.5 K. The wax mole fraction after a year is approximately 0.2. The solid-liquid equilibrium constant for the first component around 0.228 and around 165 for the second component after a year. Similar results were observed in other crude oil pipeline systems studied.     

By-Products Formation in the Dehydrogenation of Methylcyclohexane

Abstract

The selectivity of the by-products' formation for the dehydrogenation of methylcyclohexane (MCH) is studied under varying conditions of temperature, pressure, and feed composition. Benzene, cyclohexane, and ring-closed products (dimethylcyclopentanes and ethylcyclopentane) were found as the major by-products. The yield of these major by-products increased with an increase in the total pressure as well increased hydrogen concentration in the feed. Analyses of benzene and cyclohexane formation reveal cyclohexane is an intermediate in the formation of benzene.     

Effect of Crude Oil Composition and Blending on Flowing Properties

Abstract

The effect of crude oil n-paraffin molecular weight distribution on wax crystallization risk was studied. Sixteen highly paraffinic crude oils from Eastern Venezuela were characterized, in terms of hydrocarbon family distribution, by High Temperature Simulate Distillation (HTSD), Gel Permeation Chromatography (GPC), and wax content. n-Paraffin chain length was correlated with crude oil cloud point and pour point. It was demonstrated that high molecular weight linear paraffins are responsible for crude oil wax precipitation. A quantitative correlation between molecular weight distribution and crude oil flowing properties was also obtained. It was found that the wider the molecular weight distribution, the lower is the wax crystallization risk. Blends of different paraffinic crude oils were prepared and their flowing properties were evaluated in comparison with the original crudes. Cloud points below the mean value were obtained. In some cases, a synergistic effect was observed (cloud points below the minimum of the two crude oils). Blends of some of these crudes with condensates afforded improvements on crude oil flow and a reduction of wax crystallization tendency (cloud point). This phenomenon can be attributed to a combination of two factors: I. increases in C24-n-paraffins, and II. a wider molecular weight distribution.     

An Experimental Investigation of Asphaltene Precipitation During Natural Production of Heavy and Light Oil Reservoirs: The Role of Pressure and Temperature

Abstract

Many oil reservoirs encounter asphaltene precipitation as a major problem during natural production. In spite of numerous experimental studies, the effect of temperature on asphaltene precipitation during pressure depletion at reservoir conditions is still obscure in the literature. To study their asphaltene precipitation behavior at different temperatures, two Iranian light and heavy live oil samples were selected. First, different screening criteria were applied to evaluate asphaltene instability of the selected reservoirs using pressure, volume, and temperature data. Then, a high pressure, high temperature filtration (HPHT) setup was designed to investigate the asphaltene precipitation behavior of the crude samples throughout the pressure depletion process. The performed HPHT tests at different temperature levels provided valuable data and illuminated the role of temperature on precipitation. In the final stage, the obtained data were fed into a commercial simulator for modeling and predicting purposes of asphaltene precipitation at different conditions. The results of the instability analysis illustrated precipitation possibilities for both reservoirs which are in agreement with the oil field observations. It is observed from experimental results that by increasing the temperature, the amount of precipitated asphaltene in light oil will increase, although it decreases precipitation for the heavy crude. The role of temperature is shown to be more significant for the light crude and more illuminated at lower pressures for both crude oils. The results of thermodynamic modeling proved reliable applicability of the software for predicting asphaltene precipitation under pressure depletion conditions. This study attempts to reveal the complicated role of temperature changes on asphaltene precipitation behavior for different reservoir crudes during natural production.     

The Colloidal Characteristics of Blended Crudes

Abstract

Iran and Saudi crude oils were selected to be studied in this article. The characteristics of colloid were investigated at the optimum active status (the distillation yield is higher than the theoretical distillation yield). The experimental results show that at optimized blending ratio, vacuum residue becomes denser, the precipitation point of vacuum residue advances, and the aggregation of colloidal particles becomes strong. It was found that the interaction of the functional groups after blending was similar to previous blending. However, at the optimized blending ratio the signals of hydrogen bond and condensed aromatic rings weakened.     

Methodology for Predicting the Phase Envelope of a Heavy Crude Oil and Its Asphaltene Deposition Onset

Abstract

We have presented general ideas to develop a new theoretical methodology, based on molecular simulation and equations of state, for obtaining the phase envelope and to predict pressure, volume, temperature (PVT) conditions of asphaltene precipitation by only taking into account the composition of the heavy crude oil and an asphaltene average molecular structure. Those results show that asphaltene precipitation is a reversible thermodynamic process. The precipitated phase is a liquid phase which consists of mainly asphaltene and some heavy fractions from the crude. This methodology can be applied to find complete phase diagrams of different crude oils based on an asphaltene average molecular structure and the composition of crude oil.     

PRECIPITATION OF ASPHALTENES AT HIGH PRESSURES; EXPERIMENTAL TECHNIQUE AND RESULTS

ABSTRACT

Precipitation of asphaltenes in crude oil has been measured both as a function of pressure and composition. The onset of precipitation has been determined by the measurement of conductivity. A specially designed high pressure conductivity cell has been constructed. Due to the low conductivity of most crude oils the electrode spacing has to be very narrow and the effective electrode area as large as practical. The cell has a coaxial design with inlet and outlet on opposite sides on the cylinder. The cell is rated to 700 bar and 120 deg.C but can be constructed for both higher pressure and temperature. The onset of precipitation is detected by a maximum in the weight normalized conductivity, i.e. the conductivity divided by the weight fraction of oil

By using normal alkanes from ethane to pentane the precipitation onset is shown to increase linearly as a function of n-alkane carbon number. A smaller but significant increase in the onset is found by increasing the hydrostatic pressure. For monophasic live crude the onset is shown by a break in the conductivity curve.     

ASPHALTENE PRECIPITATION AND SOLVENT PROPERTIES OF CRUDE OILS

ABSTRACT

Improved prediction of the onset of asphaltene precipitation may be achieved using refractive index (RI) to characterize crude oils and their mixtures with precipitants and solvents. Experimental measurements of RI for mixtures of several crude oils with the precipitant n-heptane, are reported at ambient conditions. Theoretical developments are described that will permit extension of these observations to reservoir conditions

Measurements of RJ at the onset of precipitation have shown that the onset occurs at a characteristic RI for each oil/ precipitant combination, supporting the premise that precipitation is dominated by London dispersion interactions and thus, that RI can be used to predict the onset of precipitation. Reports in the literature showing that the onset of precipitation occurs at constant solvent-to-precipitant ratios provide additional confirmation

The theory is developed on the assumption that London dispersion forces dominate aggregation and precipitation of asphaltenes. The interaction energy of asphaltene molecules or aggregates in a medium of oil can be expressed as a function of the difference between the RI of asphaltene and oil. The RI of live crude oil during pressure depletion can be calculated from the RI of the stock tank oil, the molar refraction of the separator gas, the formation volume factor B_o and the solution gas/ oil ratio R_s     

Gemini Surfactant as a New “Green” Demulsifier for Treating Oilfield Emulsions

Abstract

Surface tension and interfacial tension (IFT) were the key factors asso- ciated with the stability of crude oil emulsion. Investigation of interfacial tension behavior related with the demulsification of crude oil emulsions can have a great impact on the development of crude oil demulsification processes and products. This article presents the surface and interface behaviors of Gemini surfactants (12-2-12, (12)-2-(12), (14)-2-(14)). The results indicated that (12)-2-(12) could exhibit higher surface and interface active properties. The demulsification efficiency and related factors were also discussed. It showed that as an environmentally friendly and safer demulsifier, Gemini surfactant could exhibit better demulsification efficiency.     

Dispersion of Asphaltene Precipitation in Egyptian Crude Oil Using Corrosion Inhibitors

Three corrosion inhibitors are examined in this work to control asphaltene precipitation in Egyptian heavy crude oil. Dodecylbenzenesulfonic acid (DBSA), 4-nonylphenyl-polyethylene glycol, and synthetic cationic gemini surfactant: N₂,N₃-didodacyl-N₂,N₂,N₃,N₃-tetramethylbutane diaminium bromide displayed highest capacity to inhibit asphaltene deposition. The H¹-NMR spectroscopy was used to confirm the chemical structure of the synthetic inhibitor. The efficiency of the studied additives as corrosion inhibitors are evaluated by weight loss method using the same crude oil. The effect of the mentioned corrosion inhibitors as asphaltene inhibitors is studied. The studied inhibitors are with dual nature for inhibition of both corrosion and asphaltene precipitation.     

Test Methods for Determining Asphaltene Stability in Crude Oils

Abstract

The high cost of remediating asphaltene deposition in crude oil production and processing has necessitated the development of test methods for determining the stability of asphaltenes in crude oils. In the current work, the stability of asphaltenes in crude oils of varying API gravity is predicted using the Oliensis Spot Test, the Colloidal Instability Index, the Asphaltene–Resin ratio, and a solvent titration method with NIR solids detection. The test methods are described in detail and experimental data from them presented. The experimental stability data were validated via correlation with field deposition data. The effectiveness of the various tests as predictors of the stability of asphaltenes in oils is discussed. The Colloidal Instability Index and the solvent titration method were found to predict a crude oil's propensity towards asphaltene precipitation better than both the Asphaltene–Resin ratio and the Oliensis Spot Test. For oils with low asphaltene content where most stability tests fail, live oil depressurization is proposed as the test for predicting the stability of asphaltenes.     

Reactions of Cyclohexane on Platinum,Palladium, or Iridium-loaded H-ZSM-5 Zeolite Hydrohalogenated Catalysts

Abstract

The catalytic hydroconversion of cyclohexane using catalysts containing H-ZSM-5 zeolite loaded with 0.35 wt% platinum, palladium, or iridium was studied in a pulse-type microreactor/GC system at atmospheric pressure. These catalysts were also either doped with 3.0% of HCl or HF. The activities of these catalysts and the distribution of the products formed were found to depend on the dispersion of the metallic component as well as on the acidity, acid sites number, and strength in the catalysts. TPD of ammonia and hydrogen chemisorption were applied to evaluate acid site strength distribution and metals dispersion, respectively, in the catalysts. In case of the Pt- and Pd-containing catalysts, hydrochlorination enhanced the isomerization and dehydrogenation activities and selectivities of cyclohexane, but decreased its hydrocracking activity. However, catalyst hydrofluorination resulted in the reverse effects. Nevertheless, for the Ir-loaded catalyst, both hydrohalogenation treatments decreased the isomerization and dehydrogenation of cyclohexane. The Ir/H-ZSM-5 catalyst exhibited higher hydrogenolysis activities than did those acquired by the Pt- and Pd-containing catalysts.     

Intelligent Modeling of Asphaltene Precipitation in Live and Tank Crude Oil Systems

Abstract

The study of asphaltene precipitation properties has been motivated by their propensity to aggregate, flocculate, precipitate, and adsorb onto interfaces. The tendency of asphaltenes to precipitation has posed great challenges for the petroleum industry. The most important parameters in asphaltene precipitation modeling and prediction are the asphaltene and oil solvent solubility parameters, which are very sensitive to reservoir and operational conditions. The driving force of asphaltene flocculation is the difference between asphaltene and the oil solvent solubility parameter. Since the nature of asphaltene solubility is yet unknown and several unmodeled dynamics are hidden in the original systems, the existing prediction models may fail in prediction the asphaltene precipitation in crude oil systems. One of ways in modeling such systems is using intelligent techniques that need some information about the systems; so, based on some intelligent learning methods it can provide a suitable model. The authors introduce a new implementation of the artificial intelligent computing technology in petroleum engineering. They have proposed a new approach to prediction of the asphaltene precipitation in crude oil systems using fuzzy logic, neural networks, and genetic algorithms. Results of this research indicate that the proposed prediction model with recognizing the possible patterns between input and output variables can successfully predict and model asphaltene precipitation in tank and live crude oils with a good accuracy.     

Experimental Investigations of the Mitigation of Paraffin Wax Deposition in Crude Oil Using Chemical Additives

Abstract

Wax deposition from crude oil is a very expensive problem for oil producers around the world. The objective of this study is to understand the characteristics of paraffin wax deposition and to test the effectiveness of solvents in the inhibition of the crystallization and subsequent precipitation of the paraffin wax and to test the most effective concentration of the solvent used. The oil used here is from the Dakota formation from the Fourteen Mile Field in the Big Horn Basin of Wyoming. Two paraffin inhibitors were tested for this crude oil on a horizontal flow system. The inhibitors are mixtures of solvents, pour point depressants, and wax crystal modifiers. These inhibitors were tested at different concentrations and temperatures and the deposition rates were obtained for each. One inhibitor especially designed for this crude oil was relatively successful, reducing the deposition by up to 59% depending on the temperature.     

Prediction of Asphaltene Precipitation during Pressure Depletion and CO2 Injection for Heavy Crude

Abstract

In this work, a thermodynamic approach is used for modeling the phase behavior of asphaltene precipitation. The precipitated asphaltene phase is represented by an improved solid model, and the oil and gas phases are modeled with an equation of state. The Peng-Robinson equation of state (PR-EOS) was used to perform flash calculations. Then, the onset point and the amount of precipitated asphaltene were predicted. A computer code based on the solid model was developed and used for predicting asphaltene precipitation data reported in the literature as well as the experimental data obtained from high-pressure, high-temperature asphaltene precipitation experiments performed on Sarvak reservoir crude, one of Iranian heavy oil reserves, under pressure depletion and CO₂ injection conditions. The model parameters, obtained from sensitivity analysis, were applied in the thermodynamic model. It has been found that the solid model results describe the experimental data reasonably well under pressure depletion conditions. Also, a significant improvement has been observed in predicting the asphaltene precipitation data under gas injection conditions. In particular, for the maximum value of asphaltene precipitation and for the trend of the curve after the peak point, good agreement was observed, which could not be found in the available literature.