Characterization of Doba-Chad heavy crude oil in relation with the feasibility of pipeline transportation

A heavy crude oil was characterized in view of the recent commercial exploitation of Doba oilfield in landlocked Chad from where the crude oil is extracted and expected to be routed to the Atlantic shore through pipeline transportation. The elemental composition of Doba feedstocks is 86.25% C, 12.10% H, 0.25% N, 0.14% S and 1.16% O. Atmospheric distillation indicated an initial boiling point at 85 °C, a 10 vol% fraction distilling before 250 °C and an onset of crude thermal cracking at 300 °C. Crude API gravity is 18.8° API, corresponding to a specific gravity of 0.94 at 15.6 °C. The Doba crude oil was found to exhibit non-elastic purely viscous Newtonian behavior over the temperature range typical of crude transportation by pipeline. The crude was fractionated into 97.4% maltenes (n-pentane solubles), 1.8% asphaltenes (n-pentane insolubles), and 0.1% toluene insolubles. The maltenes were subsequently split into four sub-fractions: 45.0±1.2% saturates (MF1), 11.0±0.3% mono and diaromatics (MF2), 26.8±1.2% polyaromatics (MF3), and 12.8±0.8% polars (MF4). FT-IR characterization and proton nuclear magnetic resonance identification of the maltenic and asphaltenic fractions provided evidence of the chemical nature of the different fractions. The high values of the kinematic viscosity of crude oil (184.4cSt at 50 °C) and deasphalted crude oil (152.4cSt at 50 °C) suggest that partially upgrading the oil would be necessary to comply with the viscosity specifications recommended for crude transportation by pipeline.     

Correlating the chemical and physical properties of a set of heavy oils from around the world

Variations in the viscosity and other physical properties of heavy oils are poorly understood. The viscosities measured for different heavy oils can vary by orders of magnitude even at the same API gravity, which is the standard metric for lighter oils. Heavy oils are viscoelastic materials, and the shear modulus and the viscosity are coupled. Understanding what controls heavy oil viscosity will provide insight into what controls heavy oil shear modulus. Therefore, using rheology, ultrasonic measurements and molecular beam mass spectroscopy (MBMS) the physical and chemical properties of seven heavy oils from around the globe are explored. The viscoelastic nature of the oils is quantified as a function of temperature. Overall, the heavy oil samples show little correlation between the viscosity or shear modulus and the API gravity, separate resin content or separate asphaltene content as measured from SARA analysis. However, the total resin plus asphaltene content collapses the viscosity and modulus values to provide empirical relations between these quantities. Also, a partial least squares regression analysis provides tight correlations for the chemical signatures from the MBMS. The rapid and quantitative nature of the MBMS make it an attractive substitute for the inconsistencies endemic to SARA analysis.     

Testing various mixing rules for calculation of viscosity of petroleum blends

Seventeen mixing rules reported in the literature used for predicting kinematic viscosity of petroleum and its fractions were examined for accuracy by comparing the estimated values with the experimental viscosities of four crude oils (21.31, 15.93, 12.42 and 9.89°API gravity) and their blends with a diluent (diesel) at several proportion. Tested mixing rules were classified as pure mixing rules, mixing rules with a VBI parameter, and mixing rules with an additional parameter. The results indicated a general trend to fail as the crude oil API gravity decreased, although at high temperature of analysis the predictions improved. After calculating standard errors for all predictions, only four of these rules showed acceptable accuracy (Chevron, Walther, Einstein and Power law), nevertheless no rule was capable of estimating viscosity for all the crude oils, highlighting that predicting viscosity is a challenging task. This general result led a further analysis for testing the accuracy of mixing rules in predicting viscosity for light distillates (naphtha, diesel and vacuum gas oil) and their blends; basically the same results were found, although a fifth rule (Chririnos) showed good agreement with experimental values.     

In-situ combustion laboratory studies of Turkish heavy oil reservoirs

The purpose of this research was to perform dry and wet forward combustion experiments for Turkish heavy oil reservoirs (Raman, Adıyaman and Çamurlu and Batı Kozluca) under different experimental conditions. In the experiments, a vertical tube was packed with crushed limestone and saturated with crude oil and water. It was observed that peak temperatures were higher when stabilized combustion was achieved and decreased as the combustion front approached the outlet end of the tube. In wet combustion experiments, the rate of combustion reaction and therefore rate of heat generation were reduced with the resultant drop in peak temperatures. In dry and wet combustion experiments, excess carbon-dioxide productions were observed due to the decomposition of carbonate minerals. Atomic H/C ratio of the fuel consumed decreased as the average peak temperature increased. Fuel consumption rate was higher for dry combustion experiments as the °API gravity of the crude oils increased. A decrease is also observed in fuel consumption rate after the water–air ratio value is reached to optimum value. For high water–air ratio in wet combustion experiments, a general decrease was observed as the °API gravity of the crude oils increased.     

Catalytic pyrolysis of Athabasca bitumen in H2 atmosphere using microwave irradiation

Microwave-assisted catalytic pyrolysis was carried out for upgrading of Athabasca bitumen. The bitumen can be heated to the desired target temperature (430 °C) for pyrolysis with silicon carbide (SiC), a heating element, in approximately 10 min under microwave irradiation. However, the pyrolysis with SiC only resulted in heavy and viscous liquid product having an API gravity of 17.14°. Addition of Nickel and Molybdenum nanoparticles as catalysts enhanced the pyrolysis performance in terms of liquid yield and quality. In the pyrolysis with Mo nanoparticles, the yield and the API gravity of the liquid product were 72.0 wt% and 20.98°, respectively. However, the separate existence of nanoparticles and SiC in the reactor and the recovery problem of nanoparticles, might limit their application in microwave-assisted pyrolysis. In order to prepare a composite with microwave susceptibility and catalytic activity in one body, transition metals were loaded on alumina coated SiC. When it is compared to the direct application of metal nanoparticles to the pyrolysis of bitumen, the NiMo/Al₂O₃/SiC catalyst showed enhanced catalytic performance. The API gravity and sulfur contents of the liquid products from the pyrolysis with NiMo/Al₂O₃/SiC were 22.42° and 2.84 wt%, respectively.     

Non-catalytic hydrodesulfurization and hydrodemetallization of residua

Non-catalytic hydrodesulfurization (NHDS) and hydrodemetallization (NHDM) i.e. hydrothermal desulfurization and demetallization of heavy crude and atmospheric residue was studied in two different bench-scale units equipped with fixed-bed reactors in series operated in adiabatic and isothermal modes. The reactors were loaded with inert material (silicon carbide). Different feedstocks were used for thermal hydrodesulfurization tests: 13°API heavy crude oil, 21°API crude oil, atmospheric residue from the 13°API heavy crude oil, and atmospheric residue from the 21°API crude oil. The effects of pressure, residence time, temperature and type of feed on NHDS and axial reactor temperature profiles were examined. The effect of reaction variables is explained in terms of quenching of the reaction by hydrogen addition and changes in reaction selectivity. The results indicate that selectivity toward the reaction of NHDS as compared with NHDM do not show important changes when the temperature was increased. Temperature was found to be the main variable that affected the extent of thermal desulfurization and demetallization reactions. The different reactor temperature profiles were explained with the type of reaction occurring in the different sections of the reacting system.     

Potential for hydrogen generation from in situ combustion of Athabasca bitumen

The volume of heavy oil and bitumen in Alberta, Canada is estimated to be about 1.7 trillion barrels. The majority of the produced heavy oil and bitumen in Alberta is converted in surface upgraders to synthetic crude oil, a crude oil with API gravity typically between 31 and 33° API, which in turn can be converted to fuel, lubricant, and petrochemical products in standard refineries. To upgrade bitumen requires hydrogen. In current practice, much of this hydrogen is generated from catalytic steam reforming of methane together with the water-gas shift reaction. This means that heavy oil and bitumen upgrading, as is currently done, requires large amounts of natural gas to generate hydrogen. The potential for in situ generation of hydrogen by gasification of bitumen reservoirs offers an attractive alternative which can also have both economic and environmental benefits. For example, hydrogen generated from bitumen gasification can also be used for in situ upgrading as well as feedstock for ammonia and other chemicals. The water-gas shift reaction also generates carbon dioxide which could be potentially sequestered in an in situ gasification process so that emissions to the atmosphere are reduced. This technology provides a potential clean method to produce fuel and feedstock material from bitumen, a relatively “dirty” fuel and feedstock oil, in addition to more energy efficient ways of extracting in situ heavy oils. However, to design in situ bitumen gasification processes requires a reaction model that provides a reasonable representation of the gasification reactions. Here, a new kinetic model is developed to examine the potential for hydrogen generation from Athabasca bitumen. The kinetic model consists of thermal cracking, oxidation/combustion, hydrogen generation and hydrogen consumption reactions. A comparison of the simulation results and experimental data from the published literature reveal that the new model can predict hydrogen generation from gasification of methane, Athabasca bitumen, and coke.     

Effect of wax inhibitors on pour point and rheological properties of Iranian waxy crude oil

A variety of techniques have been employed in order to reduce problems caused by the crystallization of paraffin during the production and/or transportation of waxy crude oil. Flow improvers are used extensively to increase the mobility of crude oil. In this study, the influence of the ethylene-vinyl acetate copolymer (EVA), as flow improver, with different ranges of molecular weight on the viscosity and pour point of five Iranian waxy crude oils was evaluated. Five types of Iranian waxy crude oil were selected based on their similar wax (> 10%) but different asphaltene contents. Also, the effect of asphaltene content on the performance of this flow improver was studied. The rheological behavior of these crude oils, with middle range API gravity, in the absence/presence of flow improver was studied. The rheological data cover the temperature range of 5 to 40 °C. The results indicated that the performance of flow improver was dependent on the molecular weight and the asphaltene content. For crude oil with low asphaltene, higher molecular weight flow improvers are the best additive and lower molecular weight flow improvers showed good efficiency for crude oil with high asphaltene content. Addition of small quantities of asphaltene solvents such as xylene (1 wt.%), alone or in combination with flow improver, can improve viscosity of crude oil with high asphaltene content.     

The study on composition changes of heavy oils during steam stimulation processes

Using the heavy oils obtained from Liaohe oilfields in China, we have conducted the aquathermolysis reaction in laboratory at 240 °C. The results showed that Liaohe heavy oils have been undergoing visbreaking in the process of steam-drive and steam stimulation. After reaction with steam, the viscosity of the heavy oil was reduced by 28-42% and the amount of the saturated and aromatic hydrocarbons increased, while resin and asphaltene decreased. The gas partition chromatography showed that the accumulated amount of carbon numbers increased, after reaction, the accumulated amount of carbon numbers less than C₂₀ are 38.79-53.92%, and before reaction they are 13.30-20.92%. The results provided the basic data for heavy oil recovery by in situ catalytic method in production of heavy oil in oilfields.     

Hydrocarbon-type separation of heavy petroleum fractions

In this investigation the US Bureau of Mines — API method for the separation of heavy petroleum hydrocarbons into structural types — saturates, monoaromatics, diaromatics and polyaromatic-polar material — has been modified. The time of analysis is reduced drastically by applying pressure on the column and eliminating a time-consuming pretreatment of the samples with ion-exchange resins to remove the acidic and basic components of the oil. The polyaromatic-polar material, forming a substantial amount of the high-molecular-weight fractions of heavy oils, has been further separated into three concentrates of different composition, by using an additional two eluents. This step allows better characterization of the high-molecular-weight components of heavy oils and bitumens. The sample size, column volume and the weight of the adsorbing gels have also been scaled down first by a factor of 10 — for quantitative preparation of hydrocarbon classes in research laboratories for further analysis by Chromatographic or spectroscopic methods — and then 100 for chemical characterization of drill core extracts.     

Liquefaction of cellulosic wastes: III. Production,characterization and evaluation of pyrolytic oils

Liquefaction of municipal solid wastes has been achieved in an atmosphere of hydrogen gas and in the presence of boric acid which catalyzes the pyrolysis reaction. Two petroleum distillates, namely gas oil and residual fuel oil, were used as carrier media of solid refuse. The yield of pyrolytic oil was studied as a function of different operational conditions (temperature, pressure of hydrogen, carrier oil medium and concentration of boric acid). Hydrocarbon constituents of the oil mixtures, produced by liquefaction of cellulosic wastes slurried in fuel oil, were investigated by means of gas chromatography. It was found that the oil mixture, obtained at optimum reaction conditions, showed pronounced occurrence of low hydrocarbons in the range C₃-C₁₅ as compared with the original fuel oil and the oil resulting from the pyrolysis of carrier oil without solid refuse. The residual pyrolytic char exhibited catalytic activity towards hydrocracking. It was suggested that the activity of char is due to the presence of transition metals as evidenced by an electron dispersion system (EDS). The hydrocracking activity of char seemed to be dependent on the operational conditions of the liquefaction. Multiple analytical parameters including API gravity, calorific value, total acid number and wt% of residue over 450°C were used to evaluate the oil mixtures produced as a petroleum crude oil. Carrier oils, particularly fuel oil, seemed to be highly modified in the course of the pyrolysis process. Also, the oil mixtures produced were distinguished from the original carrier oils by a considerably higher acidity due to association with oxygenated compounds which could be derived from cellulose macromolecules.     

Influence of temperature and alumina catalyst on pyrolysis of corncob

Corncob has been investigated as an alternative feedstock to obtain fuels and chemicals via pyrolysis in fixed-bed reactor. The influence of pyrolysis temperature in the range 300-800 °C as well as the catalyst effects on the products was investigated in detail and the obtained results were compared. The results indicated that a maximum oil yield of 22.2% was obtained at a moderate temperature of 600 °C. The oil yield was reduced when the temperature was increased from 600 to 800 °C, whereas the gas yield increased.Pyrolysis oils were examined by using instrumental analysis, ¹H NMR spectroscopy and GC/MS. This analysis revealed that the pyrolysis oils were chemically very heterogeneous at all temperatures. It was determined that the most abundant compounds composing the bio-oil were phenolics.It was observed that the catalyst decreased the reaction temperature. Most of the components obtained using a catalyst at moderate temperatures was close to those obtained at high temperatures without using a catalyst. Moreover, the use of a catalyst and the high temperatures of the reactions also decreased the amount of oxygenated compounds produced.According to these results, corncob bio-oils can be used as fuel and constitute a valuable source of chemical raw materials.     

Regenerable MgO-based sorbents for high-temperature CO2 removal from syngas: 1. Sorbent development, evaluation, and reaction modeling

Highly reactive and mechanically strong low-cost regenerable MgO-based sorbents were prepared by modification of dolomite which involved partial calcinations followed by impregnation with a potassium-based salt. The sorbents are capable of removing CO₂ from gasification-based processes such as Integrated Gasification Combined Cycle (IGCC). The sorbents have high reactivity and good capacity toward CO₂ absorption in the temperature range of 300-450 °C at 20 atm. and can be easily regenerated at 500 °C. The reaction appears to be first order with respect to CO₂ concentration with an activation energy of 44 kJ/mol. The reactivity and the absorption capacity of the sorbents increase with increasing temperature, as long as the partial pressure of CO₂ is above the equilibrium value for sorbent carbonation. The reactivity of the sorbents appears to improve in the presence of steam, which is likely due to the increase in the BET surface area and the porosity of the sorbent. A two-zone expanding grain model, consisting of a high-reactivity outer shell and a low-reactivity inner core is shown to provide an excellent fit to the TGA experimental data on sorbent carbonation at various operating conditions.     

Influence of temperature on pyrolysis of recycled organic matter from municipal solid waste using an activated olivine fluidized bed

Pyrolysis of an organic concentrate from municipal solid waste was carried out using a bench-scale fluidized bed reactor at 350-540 °C comparing Al₂O₃ with activated olivine sand as bed materials. A maximum oil yield of 50 wt.% was obtained using the activated olivine sand at 400 °C while only 45 wt.% was obtained at 500 °C using Al₂O₃. The bio-oils using activated olivine sand at 400 °C had an H/C ratio of 1.50 and O/C ratio of 0.37 and were less aromatic and less nitrogenous compare to the oils obtained using Al₂O₃ at 400 °C where the H/C ratio was 1.32 and the O/C ratio was 0.44. The aromatic compounds were found to be reduced while the aliphatic compounds increased in the oils generated using activated olivine sand. The calorific value of the bio-oil at 500 °C was 29 MJ/kg using activated olivine sand while the bio-oil using Al₂O₃ was 23 MJ/kg. The presence of iron, magnesium and other oxides probably promotes the removal of oxygen, which indicates that the activation energy of C―O bond breakage is reduced compared to the C―C bonds, thus promoting dehydration, decarboxylation and alkalation reactions to produce aliphatic fatty acid at lower temperatures.     

Nonhydrogenative processing of a saskatchewan heavy oil under mild conditions using disposable additives

In this study, a nonhydrogenative process for partial upgrading of heavy oil was evaluated in a semi-continuous laboratory scale unit for producing a low viscosity oil which could be pipelined easily. The process was conducted at atmospheric pressure and over a temperature range of 400 to 470°C. Gas production was negligibly small (1-2 wt. % of the feed) and there was virtually no coking of reactor except at high coal concentrations (> 9.1 wt. %) and high reactor temperatures (470°C). The particulate content of the liquid product which contained unreacted coal, ash and coke (defined as toluene-insolubles) was less than 5 wt.% in the majority of the cases. In the presence of coal, iron oxide mixed with coal. and iron oxide alone, maximum reductions in viscosity were: from 1540 to 248 mPa.s, from 1540 to 192 mPa.s, and from 1540 to 80 mPa.s, respectively. A moderate improvement in API gravity (from 13.0 to 18.2) was obtained using 1 wt. % iron oxide additive at 470°C. However, apparent pitch (resid) conversion were of the order of only 20-30 wt. %.     

Nonhydrogenative co-processing of saskatchewan heavy oil and coal

A Saskatchewan heavy oil was processed with coal additives in a tubular reactor packed with procelain berl saddles at 400–480°C and atmospheric pressure. For comparison purposes, blank experiments in the absence of coal additive were also carried out. The results indicate that considerable reduction in viscosity and increased distillate yields can be achieved by processing heavy oil with coal additive. The API gravity of the liquid product is also improved. Increased amounts of gaseous products with changed composition are obtained in the presence of coal. Under certain conditions, significant dissolution of coal occurs even at the relatively mild conditions used.     

Kinematic viscosity of biodiesel components (fatty acid alkyl esters) and related compounds at low temperatures

Biodiesel, defined as the mono-alkyl esters of vegetable oils and animal fats is, has undergone rapid development and acceptance as an alternative diesel fuel. Kinematic viscosity is one of the fuel properties specified in biodiesel standards, with 40 °C being the temperature at which this property is to be determined and ranges of acceptable kinematic viscosity given. While data on kinematic viscosity of biodiesel and related materials at higher temperatures are available in the literature, this work reports on the kinematic viscosity of biodiesel and a variety of fatty acid alkyl esters at temperatures from 40 °C down to −10 °C in increments of 5 °C using the appropriately modified standard reference method ASTM D445. Investigating the low-temperature properties of biodiesel, including viscosity, of biodiesel and its components is important because of the problems associated with the use of biodiesel under these conditions. Such data may aid in developing biodiesel fuels optimized for fatty ester composition. An index termed here the low-temperature viscosity ratio (LTVR) using data at 0 °C and 40 °C (divide viscosity value at 0 °C by viscosity value at 40 °C) was used to evaluate individual compounds but also mixtures by their low-temperature viscosity behavior. Compounds tested included a variety of saturated, monounsaturated, diunsaturated and triunsaturated fatty esters, methyl ricinoleate, in which the OH group leads to a significant increase in viscosity as well as triolein, as well as some fatty alcohols and alkanes. Esters of oleic acid have the highest viscosity of all biodiesel components that are liquids at low temperatures. The behavior of blends of biodiesel and some fatty esters with a low-sulfur diesel fuel was also investigated.     

Thermal strength,deformation, and thermal fatigue characteristics of dinas products before and after service in the high-temperature zones of the hot-blast stoves

Conclusions The deformation and strength characteristics of the dinas specimens (drawn from the industrial walling and checkerwork products before and after service) were studied under uniaxial tension and compression at a temperature up to 1600°C.It was established that their ultimate strength decreases with increasing test temperature and that the load-bearing capacity is insignificant at 1570–1600°C; when subjected to cyclic heating (1250 1450°C) in the laboratory tests as well as during service in a hotblast stove operating under alternating oxidizing and reducing environmental conditions, dinas bricks exhibit embrittlement and softening (their tensile and compressive strength characteristics differ by almost 10 times).The obtained data showed that the limiting temperature at which the strength characteristics of dinas abruptly decrease under a constant stress and multiple cyclic action of alternating atmospheres amounts to 1600°C; this fact must be taken into account when designing and operating hot-blast stoves.Translated from Ogneupory, No. 6, pp. 19–22, June, 1986.     

Visualization of steam displacement of heavy oils in a Hele-Shaw cell

Experimental visualization of steam injection was performed at low pressure in a transparent Hele-Shaw cell. Synthetic (Dutrex 739) and natural heavy oils were displaced by steam under a variety of conditions. The results demonstrate the significant interplay between steam injection, steam condensation, viscous fingering, heat transfer, gravity and steam distillation effects. The experiments reveal that steam fronts may be neither smooth nor flat, but undergo constant rearrangements as a result of condensation and injection. These dynamics are substantially different from typical immiscible displacement processes. The injected steam was generally found to follow the path of the condensed water. The latter set the general displacement pattern, which was highly fingered. Also identified was a rather unusual viscoelastic response of the displaced heavy oils. Although novel and interesting, these results should be extrapolated with care to account properly for field effects of heat losses.     

A correlation for predicting liquid viscosities of petroleum fractions

A correlation has been developed for estimating the liquid viscosities of petroleum fractions at 100°F and at 210°F. When used with the ASTM viscosity chart (or its analytical equivalent), the new correlation provides a method for the prediction of viscosity-temperature behavior of fractions from the Watson characterization factor and specific gravity. Essentially an extension of an API Data Book viscosity nomograph, the proposed correlation substantially improves on the accuracy and increases the range of applicability of this method. Greatest accuracy is achieved for petroleum fractions in the kerosene to heavy gas oil range, although acceptable accuracy for most engineering calculations is also obtained for lube oils and for many complex pure heavy hydrocarbons.