THE EFFECT OF VISBREAKING CONDITIONS ON THE STABILITY OF SOME IRAQI LONG RESIDUES

A study has been done to investigate the change in the stability of residue during thermal process (visbreaking) at different cracking severity using flocculation ratio method. For this purpose, three long residues (350°C+) of different crude oils were used. The obtained results were discussed as a function of reaction temperature and residence time. Moreover, the stability was correlated with the nature and chemical composition of the feedstock.We observed that the intermediate paraffinic base feedstock (type A) was more stable than the other two asphaltenic base (Types B & C) when visbreaking temperature was 460°C. At higher temperatures, a sudden and large decrease in the stability of type A visbroken products was observed while only a gradual decrease in the stability of the other two products was noticed when visbreaking process was carried out at the same operating conditions.     

CHARACTERIZATION OF ARAB BERRI (EXTRA LIGHT) CRUDE FRACTIONŞ WITH EMPHASIS ON KINEMATIC VISCÓSITY-TEMPERATURE BEHAVIOR

The characterization data has been obtained for Arab Berri extra light crude oil (API° 46.9), which is one of the four crude oils being commercially produced by Saudi Arabia. Further, six true boiling point fractions (IBP-95°C, 95-205°C, 205-260°C, 260-34S°C, 345-455°C and 455°C+) of this crude were characterized in terms of API gravity, total sulfur, H₂S, merceptans, molecular weight, elemental analysis for total carbon, hydrogen and nitrogen, analysis of various metals and paraffin, aromatic and naphthalene contents of lighter fractions. The kinematic viscosity-temperature data have been obtained for 95°C+ TBP fractions for wide range of temperatures.     

ARAB LIGHT CRUDE STUDY FOCUSES ON KINEMATIC VISCOSITY

Arab light crude oil has been characterized in terms of API gravity, total sulfur content, Reid vapor pressure, ash content, heating value, salt content, viscosity SUS, vanadium content as V₂O₅, pour point and analyses of various metals. The crude oil was fractionated into six true boiling point (TBP) fractions (IBP-95°C, 95-205°C, 205-260°C, 260-345°C, 345-455°C and 455°C+). These fractions were characterized in terms of API gravity, total sulfur, H₂S, mercaptan contents, molecular weight, elemental analyses for total carbon, hydrogen and nitrogen, and analyses of various metals. The kinematic viscosity data have been obtained for 95°C+ TBP fractions for a wide range of temperature up to 200°C.     

STUDIES ON SLUDGE FROM STORAGE TANK OF WAXY CRUDE OIL PART - I : STRUCTURE AND COMPOSITION OF DISTILLATE FRACTIONS

Tank bottom sludge from storage tanks of Bombay High crude oil deposited during ten years have been studied. The yield of the sludge is approximately 0.1% wt. of the crude oil through-put. The residue boiling above 500°C amounts to over 50%. The distillate fractions collected at 50°C intervals have been analysed extensively and compared to fractions from whole crude of same boiling range. The sludge distillate are distinctly more paraffinic in nature.     

GEL FORMATION IN VACUUM GAS OIL. I. ROLE OF COMPOSITION

The compositional analysis of aromatics, saturates and urea non adductables obtained from vacuum gas oil (VGO) distillate (370-550°C) and its seven sub-fractions: (1) 370-400, (2) 400-425, (3) 425-450, (4) 450-475, (5) 475-500, (6) 500-525 and (7) 525-550°C, derived from both paraffinic and aromatic base crude oils have been done using thin layer chromatography/flame ionisation detection technique. The physico- chemical characteristics are measured using the ASTM/ standard test procedures and an attempt has been made to correlate the physico-chemical properties with the composition. The phenomenon of gel formation at low temperatures and the characteristics of the gel in these VGO sub-fractions have been studied by X-ray diffractometry and photomicrography. It is found that at low temperatures the gel formation takes place due to the development of a three dimensional network by the crystallizing n-paraffins, as well as by the agglomeration of molecules due to very high viscosity. Both processes proceed simultaneously and the concentration and composition of n-paraffins have been found to determine the dominance or otherwise of the crystallization process.     

CHARACTERIZATION OF SLUDGE WAXES FROM CRUDE OIL STORAGE TANKS HANDLING OFFSHORE CRUDE

The 300°C+ and 500°C+ vacuum residues of the sludge obtained from offshore crude oil storage tanks located at our onshore facilities have been subjected to dewaxing using MBK solvent. The yield of the refined waxes were 45.38% and 43.13% (sludge basis) and melting points 92-93°C and 95-96°C respectively The waxes were mainly n-parafTins. Their simulated boiling point distribution analysis reveals a distinct himodal distribution of n-paraffins, the even carbon number homologucs between C₅₀, to C₆₀ being present at preferentially higher ratio(l.4:1) than the odd ones. The present finding are expected to improve the understanding of waxes present in offshore crude. It is also expected to help in devising process to refine waxes of lank bottom sludge.     

STRUCTURAL CHARACTERIZATION OF SOLID n-PARAFFIN COMPONENTS DERIVED FROM MUKTA CRUDE OIL

The total solid paraffins (boiling 270°C+) separated from Mukta crude by urea adduction and its narrow fractions were analysed for their structural composition by proton NMR, infrared spectroscopy and gas chromatography. It has been observed that CH2/CH3 ratio in these samples varies from 7·9 to 13·8 while their average carbon number ranges from 17 to 29·6. The CH₂/CH₃ ratio and chain length of paraffins increases with increase in boiling range of the fractions.     

Rheology of Middle Distillate. I. Role of Composition

The rheological behavior of middle distillate (250-375°C) fraction, obtained from the waxy Bombay-High Off-shore crude oil, and its five narrow sub-fractions of 25°C interval each, i.e., Fr 1 (250-275°C), Fr 2 (275-300°C), Fr 3 (300-325°C), Fr 4 (325-350°C), and Fr 5 (350-375°C), have been studied below their ASTM pour point temperatures. The rheograms (the shear stress vs. rate of shear) of the fraction and sub-fractions, at various temperatures below their pour points, are recorded on a Haake RV-12 Co-axial Rota Viscometer fitted with a NV sensor and a temperature programmer (PG-20) and attached with a programmed heating/cooling system. From these rheograms the flow parameters like plastic viscosity, apparent viscosity, and yield stress are obtained and their variations with temperature and shear rate have been studied in terms of compositions of the fraction/sub-fractions. These results might be useful in devising methodology for overcoming the wax separation phenomenon from middle distillates at low temperatures.     

THE EFFECT OF ANTIOXIDANT ADDITIVE ON THE THERMOXIDATION STABILITY OF DISTILLATES FROM MEDIUM CRUDE OIL

Fractions 100-150, 150-200, 200-250°C were distilled from medium Iraqi crude oil. The thermo-oxidation stability experiments were carried out on original and inhibited (with Topanol 0) distillate fractions using the Alcor Jet Fuel Thermal Tester, over a temperature range 516-573 k. It was found that the antioxidant (Topanol 0) efficiency depends on the fractions composition and the oxidation temperature. Only 30 PPM of Topanol 0 stabilizes fraction 100-150°C to a considerable extent. Also, an inhibition effect is obtained in fraction 150-200°C but at a higher antioxidant concentration (90 PPM). Only, slight inhibition effect was observed in fraction 200-250°C at low oxidation temperature (below 551 K), while effect will be of no value at higher oxidation temperatures.     

Separation of Microcrystalline Waxes from Local Crude Petrolatums using Solvent-Antisolvent Mixtures

In order to separate and characterize the microcrystalline waxes from Suez and Alexandria crude petrolatums, multistage fractional crystallization technique has been used to fractionate Suez crude petrolatum by using n-hexane as a single solvent at different fractionating temperatures ranging from 20 to -20°C and at two different dilution and washing solvent ratios. Suez and Alexandria crude petrolatums were subjected also to multistage fractional crystallizations with solvent mixture at ambient temperature of 20°C and at fixed dilution and washing solvent ratios of 4:1 and 2:1 by weight, respectively. The solvent mixture composed of n-hexane as the main solvent and different percentages of absolute ethyl alcohol (ranging from 10 to 50 wt.%) as antisolvent. The solvent to feed ratios of dilution and washing were studied in the range of 2:1 to 8:1 and 2:1 to 6:1 by weight, respectively. Finally, one stage fractional crystallization has been done at the most suitable conditions to separate the microcrystalline waxes from Suez and Alexandria crude petrolatums followed by finishing via percolation in molten state through an activated bauxite column. The resulting finished microcrystalline waxes are evaluated according to the standard specifications of microcrystalline waxes, molecular type composition, degree of crystallinity, and scanning electron microscope (SEM).     

THE EFFECT OF VISBREAKING CONDITIONS ON THE STABILITY OF SOME IRAQI LONG RESIDUES

ABSTRACT

A study has been done to investigate the change in the stability of residue during thermal process (visbreaking) at different cracking severity using flocculation ratio method. For this purpose, three long residues (350°C+) of different crude oils were used. The obtained results were discussed as a function of reaction temperature and residence time. Moreover, the stability was correlated with the nature and chemical composition of the feedstock.We observed that the intermediate paraffinic base feedstock (type A) was more stable than the other two asphaltenic base (Types B & C) when visbreaking temperature was 460°C. At higher temperatures, a sudden and large decrease in the stability of type A visbroken products was observed while only a gradual decrease in the stability of the other two products was noticed when visbreaking process was carried out at the same operating conditions.     

OCCURRENCE AND DISTRIBUTION OF n-ALKANESAND n-FATTY ACIDS IN SAUDI ARABIAN CRUDE OILS

Ten crude oil samples, covering wide range of maturity (API gravity = 18·5-36·1), were assembled from Safaniya, Abqiq, Ain Dar, Wafra. Marjan and Zuluf oil fields in the area of Arabian Gulf. n-Alkanes of were separated from the petroleum distillate ((150°C-450°C) of the crude oils by urea adduction. n-Fatty acids were separated from the fraction of n-alkanes by treatment with aqueous solution of KOH. Distribution of n-alkanes and n-fatty acids has been investigated by means of gas chromatography. The studied crude oils showed symmetrical distribution curves of n-paraffins and fatty acids of low molecular weight were abundant as compared with n-paraffins. The n-paraffins distribution curve of Wafra/Iucene biodegraded immature crude oil showed three maxima at C₁₇, C₁₉, and C₃₁ whereas the maxima of n-fatty acids are located at C₁₄,C₂₂and C₂₄. The results were interpreted in terms of origin, maturation and depositional environments of the crude oils.     

ESMAOC AS POUR POINT DEPRESSANT FOR CRUDE OIL AND HEAVY OIL PRODUCTS

The synthesis of esterified copolymer of maleic anhydride/olefines mixture and its effect as pour point depressant for crude oil and heavy oil products were studied. The optimum ratio of the maleic anhydride/mixed a-olefines for the synthesis of EsMAOC is 1:6.29. On Daqing crude oil, the adequate addition amount of EsMAOC is 0·5-1.0 wt% when the decrease of pour point can reach to 8-10°C. To Anshan heavy diesel oil No. 20, the data are 1·0 wt%, 13°C respectively.     

PARAFFIN DEPOSITION AND VISCOSITY TEMPERATURE BEHAVIOUR OF ASSAM CRUDE OIL

The rate of paraffin deposition at equilibrium under different flowing conditions, viz, flow rate, oil and cold surface temperatures, and also viscosity temperature behaviour of Assam crude having wax content 11·0 % wt. and pour point 30°C has been studied. The effect of various diluents viz commercial kerosene and diesel oil on paraffin deposition and viscosity temperature behaviour have been determined. Deposition data has also been quantified in the form of a regression equation. It has been observed that added solvent significantly effect the paraffin deposition and viscosity temperature behaviour.     

KINEMATIC VISCOSITY-TEMPERATURE BEHAVIOR OF HEAVY TBP-FRACTIONS (455°C+) OF ARABIAN CRUDE OILS

A generalized kinematic viscosity-temperature correlation for undefined liquid heavy petroleum fractions has been developed to represent the data for a wide range of temperature from 100°C to 200°C. The correlation is based on the experimental kinematic viscosity data of true boiling point fractions of four Arabian crude oils. The characterization property required for estimation is 50% boiling point. The proposed correlation fits the experimental data with an overall absolute error of 6.1%. Experimental measurements of kinematic viscosity of heavy true boiling point fractions of Arabian crude oils were also obtained in order to develop the proposed correlation.     

FLOCCULATION OF ASPHALTENES IN HEAVY OIL AT ELEVATED TEMPERATURES

ABSTRACT

It has been observed that there is a dispersed phase of particles in vacuum residue that is associated with the heptane insoluble asphaltenes. The particles are in the size range of 100 Aˇ. In this paper we present rheological and small angle X-ray scattering(SAXS) data for the vacuum residue of Arabian Medium/Heavy crude oil that suggests the dispersed particles flocculate at elevated temperatures. We find the asphaltenic particles are stabilized below 200 ^° C against the attractive dispersion forces between asphaltenic particles by an adsorbed layer of non-asphaltenic molecules. However the strength of the interaction holding the adsorbed layer to the particles is only about 1.8 kcal/mole(3kT), and so this layer is dissipated as the temperature is increased. We estimate the particles are unprotected at 200 ^°C. The strength of the attraction due to the dispersion force is about 7kT in this state, and so the dispersion becomes thermodynamically unstable with respect to flocculation. Additionally, the driving force for flocculation is augmented by the formation of particles in the non-asphaltenic phase at elevated temperatures. The appearance of these particles increases the osmotic pressure, and forces the asphaltenic particles together. We suggest the asphaltenic phase formed by flocculation, well below the temperatures at which chemical reactions occur, is the precursor to the coke-producing phase in the reacting residue discussed by Wiehe.     

GENERALIZED KINEMATIC VISCOSITY-TEMPERATURECORRELATION FOR UNDEFINED PETROLEUM FRACTIONS OF IBP - 95°C TO 455°C+ BOILING RANGES

A generalized kinematic viscosity-temperature correlation for undefined petroleum fractions of all boiling ranges including 455^+°C fractions have been developed to represent the data for a wide range of temperature from 30 to 200°C. The correlation is based on experimental kinematic viscosity data for twenty TBP fractions of Arab heavy, Arab medium, Arab light and Arab extra-light crude oils. The proposed correlation has been found to fit all the eperimental data consisting of 248 measurements of the kinematic viscosity with an overall average absolute deviation of 9.07% compared to 15.47% given by ASTM method.     

Downhole Upgrading of Extra-heavy Crude Oil Using Hydrogen Donors and Methane Under Steam Injection Conditions

An extra-heavy crude oil underground upgrading process is described which involves the downhole addition of a hydrogen donor additive under steam injection conditions (280-315°C and residence times of at least 24-h). Laboratory experiments showed a 4° increase in the API gravity (from 9 to 12°) of the upgraded product, a two-fold reduction in the viscosity and, an approximately 8% decrease in the asphaltene content with respect to the original crude. Further increases on the temperature led to products with improved properties reaching 15°API at 315°C. It was found that the presence of the natural formation (catalysts) and methane (natural gas) is necessary to enhance the properties of the upgraded crude oil. From GC and GC-MS results a reaction pathway is proposed that involves hydrogen transfers from tetralin to the extra-heavy crude oil resulting in the formation of 1,2-dihydronaphthalene. This compound is then transformed into naphthalene, further upgrading of crude oil through hydrogen donation. The results of the experiments carried out in the presence and absence of the mineral formation and with an inert solid (SiC) strongly indicate that the former acts as a catalyst and not as a heat transfer matrix. Isotopic labeling studies (CD₄ and ¹³CH₄) give evidences that, most probably, methane is involved in the upgrading reactions.     

Characterization of Thermally Degraded Asphaltene Fractions Using Gel Permeation Chromatography

Petroleum asphaltene goes through three stages of mass reduction under thermogravimetric analysis from 25°C to 1,000°C at a heating rate of 1°C/min. The products from thermal degradation of asphaltene at three different temperature intervals are collected. Two residual fractions left in the sample cup are also obtained at two specific temperatures. The collected fractions and the residual fractions are characterized using gel permeation chromatography. The fraction collected between 25°C and 350°C demonstrates similar molecular weight distribution to that collected between 350°C and 450°C, with both fractions showing a typical molecular weight distribution for polymeric material. The fraction collected between 450°C and 650°C illustrates three different molecular weight distributions. The chromatogram of the residual fraction obtained at 350°C resembles that of the undegraded asphaltene. The residual fraction obtained at 450°C also demonstrates three different molecular weight distributions. The experimental data indicate that the mass reduction of asphaltene heated from 25°C to 350°C is mainly due to the evaporation of low boiling point and/or low molecular weight substances in asphaltene. Thermal decomposition and coke production occur significantly in the 350°C-450°C temperature interval. Thermal degradation continues to finish until 650°C.     

Correlation Between Properties of Asphaltenes and Precipitation Conditions

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%.