Process for deasphalting and demetallizing crude petroleum or its fractions

Abstract: A process is described for deasphalting and demetallizing crude petroleum or a fraction thereof containing asphaltenes and metals, in which: said crude or its fraction is brought into contact with an organic carbonate, the operation being conducted in the homogeneous liquid phase, until a solid residue rich in asphaltenes and asphaltenic metals precipitates; and said solid residue is separated from the homogeneous liquid phase. After separating the solid the homogeneous liquid phase can be cooled to separate an oil-rich refined liquid phase from an extracted liquid phase rich in organic carbonate. The separation of the extracted and refined liquid phases can also be achieved by adding a liquid solvent more polar than the carbonate, with or without cooling.

Description: This invention relates to a process for deasphalting and demetallating crude petroleum or its fractions containing asphaltenes and metals. Vanadium and other metals, such as nickel and iron, are present in crude petroleum mainly in the form of porphyrinic and asphaltenic complexes. The metal content and the ratio of the two types of complex depend essentially on the age of the crude and the severity of conditions during its formation. In some crudes the vanadium content can reach 1200 ppm [J.M. Sugihara et al., J. Chem. Eng. Data 10, No. 2, April 1965 (190-194)], and the porphyrinic vanadium content can vary from about 20% to about 50% of the total vanadium [Fish and Komlenic, Anal. Chem., 56, (3), 1984 (510-517)]. The vanadium present in the crude has a deleterious effect on the refinery operations in that it represents a poison for catalysts used in catalytic cracking, hydrogenation and hydrodesulphurization. Vanadium present in fuel oil combustion catalyzes the oxidation of sulphur dioxide to sulphur trioxide, leading to corrosion and the formation of acid rain. In addition metal porphyrins are relatively volatile and when the crude is vacuum-distilled tend to pass into the heavier fractions of the distillate; Hence traces of vanadium are usually found in vacuum gas oil. Deasphalted oil is the usual feedstock in refinery runs, since the asphaltenes tend to form coke and/or consume large amounts of hydrogen and the removal of asphaltene also reduces the content of asphaltenic vanadium and nickel and of heteroatom-containing organic compounds, especially those which contain N and S. US-A-2 587 643 considers the liquefied hydrocarbons as the major deasphalting agents and the suggests the use of organic carbonates as mere modifiers: moreover, this document does not consider the problem of a concurrent demetalating at all. Industrial practice is specifically to deasphalt the crude distillation residues (resid) with propane or by the ROSE (residual oil solvent extraction) process, which uses n-butane or n-pentane. In this respect reference should be made to H.N. Dunning and J.W.Moore, "Propane Removes Asphalts from Crudes", Petroleum Refiner, 36 (5), 247-250 (1957); J.A. Gearhart and L. Garwin, "ROSE Process Improves Resid Feed", Hydrocarbon Processing, May 1976, 125-128; and S.R. Nelson and R.G. Roodman, "The Energy Efficient Bottom of the Barrel Alternative", Chemical Engineering Progress, May 1985, 63-68. Specifically, deasphalting with propane is conducted in RDC (rotating disk contactor) columns at an overhead temperature of about 90°C, thus close to the propane critical temperature (about 97°C), with a bottom temperature of about 40°C and a propane/oil ratio of between about 5/1 and about 13/1. Under these conditions a stream rich in light components and solvent is released as column overhead and a heavy stream consisting essentially of asphalt and solvent as column bottom product. This second phase is rich in aromatics and contains nearly all the asphaltenes present in the feedstock. Both the exit streams are subjected to a series of isothermal flash evaporations at decreasing pressure until a propane/oil ratio of the order of 1/1 is obtained. Further lowering of the propane content requires stripping usually with steam. The vaporized propane is condensed, compressed and recycled. The ROSE process uses n-butane or n-pentane at high temperature and pressure, to produce two streams similar to those of the propane process. To recover the solvent the temperature is raised beyond the solvent critical temperature to cause separation of a condensed oily phase and a gaseous solvent phase. The deasphalting efficiency in the process using propane is of the order of 75-83%, with an overall deasphalted oil recovery yield of the order of 70%. In the ROSE process these values are 75-90% and 70-86% respectively. These processes are mostly costly and complicated, requiring very large solvent quantities in relation to the hydrocarbon feedstock to be treated, their efficiency and yield are not completely satisfactory, they produce asphaltic by-products and are unable to separate metals such as porphyrinic vanadium and nickel which are not eliminated with the asphaltene fraction. To offset these drawbacks, processes have been proposed in the art based on the use of solvents other than hydrocarbon solvents, in particular processes based on the use of polar solvents possibly used under supercritical conditions, but these have not shown significant development. US-A-4,452,691 describes a process for transforming a high-boiling hydrocarbon feedstock into one with a lower boiling range which comprises contacting the initial feedstock with an oxygenated ether or alcoholic solvent to precipitate the asphaltenes from a liquid phase, this latter being fed without solvent separation to a zeolite catalyst. US-A-4,618,413 and US-A 4,643,821 describe the extraction of porphyrinic vanadium and nickel from an oil product by extracting with various solvents including ethylene carbonate, propylene carbonate and ethylene thiocarbonate. It has now been found that an organic carbonate chosen from dialkyl carbonates and cyclic carbonates, under temperature conditions which allow mutual solubility with the crude petroleum or its fraction, produces rapid precipitation of an easily separable solid residue which is rich in asphaltenes, asphaltenic vanadium and nickel and heteroatomic sulphur and nitrogen organic compounds. It has also been found that when said homogeneous solution from which the precipitated solid has been removed is cooled to a temperature below mutual solubility temperature and/or a liquid solvent more polar than the organic carbonate is added, it separates into a refined liquid oil phase and a denser extracted liquid phase rich in porphyrinic vanadium and nickel and in heteroatomic organic compounds. Finally, it has been found that this precipitation and phase separation take place under mild conditions, requiring only small solvent quantities, and result in a deasphalting efficiency and a deasphalted oil yield which are unexpectedly good. Thus according to the present invention an oil can be deasphalted with the simultaneous removal of the porphyrinic V and Ni, the asphaltenic V and Ni, and the heteroatom-containing compounds, all these results being obtained simply and conveniently. To overcome the drawbacks of the prior art, this invention, therefore, provides a process for concurrently deasphalting and demetalating crude petroleum or a crude petroleum fraction containing asphaltenes and metals, by treating said crude petroleum or fraction with an organic carbonate, characterized by comprising the steps of: (a) contacting said crude petroleum or fraction thereof with an amount of an organic carbonate selected from the dialkyl carbonates having the formula: wherein R and R', equal to, or different from one another, are C₁-C₃ alkyls, and the cyclic carbonates having the formula: wherein R'' is the hydrogen atom or a methyl, as the sole deasphalting and demetalating agent, in a weight ratio of said organic carbonate to said crude oil or fraction thereof of from 0,5: 1 to 4:1, at a temperature of from 20°C to 150°C until a homogeneous liquid phase is obtained and the precipitation of a solid residue takes place thereupon; (b) physically separating said solid residue from said homogeneous liquid phase; (c) condensing and collecting the volatiles during said physical separation and combining them with said homogeneous liquid phase; (d) cooling said homogeneous liquid phase, and/or adding thereto an optionally cooled liquid solvent more polar than the organic carbonate, and (e) allowing the combined liquids exiting step (d) to split into two discrete phases, which are a lighter refined liquid phase predominantly containing crude oil or a fraction thereof plus the balance organic carbonate and asphaltenes, and a heavier extracted liquid phase predominantly containing the organic carbonate and the balance crude oil. Step (a) of the process is carried out at a temperature equal to or higher than the mutual solubility temperature. Preferred organic carbonates are dimethyl carbonate, diethyl carbonate, dipropyl carbonate, diisopropyl carbonate, ethylene carbonate, and propylene carbonate and any admixtures thereof: mixed dialkyl carbonates, such as methyl ethyl carbonate, can also be used. More preferred are dimethyl carbonate and diethyl carbonate and most preferred is dimethyl carbonate. The critical weight ratio range of the organic carbonate is from 0,5:1 to 4:1. In fact, if the ratio is lower than 0,5:1, the deasphalting efficiency is unacceptably poor, whereas, if a ratio over 4:1 is adopted, a tacky solid precipitate is formed. The preferred ratio range is from 1,5:1 to 2,5:1, the optimum being at 2:1. The homogeneous liquid phase obtained in step a) is maintained at a temperature equal to or higher than the mutual solubility temperature. In particular, if dimethyl carbonate is used with a weight ratio of dimethyl carbonate to crude of between 1.5/1 and 2.5/1, mutual solubility conditions (formation of a homogeneous liquid phase) are obtained above about 45°C, depending on the ratio itself. If diethyl carbonate is used, mutual solubility is already obtained at ambient temperature (20°C-25°C). With propylene carbonate a homogeneous liquid phase is obtained at a temperature of the order of 150°C, which phase-separates rapidly on cooling to a temperature below 120°C. With ethylene carbonate a homogeneous liquid phase is obtained at a temperature exceeding 150°C. Consequently the temperature at which precipitation occurs can generally vary from ambient temperature (20-25°C) to 150°C or more, depending on the particular organic carbonate used, and if necessary employing greater than atmospheric pressure to maintain the system in the liquid phase. When the organic carbonate is dimethyl carbonate, the operating temperature is preferably within the range of 60°C-90°C, with an optimum preferable value of 80°C. When the organic carbonate is diethyl carbonate the operating temperature is ambient or close to ambient. In all cases, a solid residue rich in asphaltenes, asphaltenic vanadium and nickel and heteroatomic compounds rapidly separates from the homogeneous liquid phase. It should be noted that when operating below the mutual solubility temperature the deasphalting efficiency is undesirably low. The contact time for precipitation can vary generally from a few minutes, for example 2 minutes, to several hours, for example up to 6 hours. Generally, subtantially complete precipitation is obtained in a time of from a few minutes (for example 1 min-2 min) to 1 hour. In stage b) of the process of the present invention, the solid precipitated in stage a) is physically separated from the homogeneous liquid phase. It has been found in practice that when operating under the aforedescribed conditions the precipitated solid settles easily because of the density difference between the solid and the homogeneous liquid phase and the low viscosity of the liquid phase due to the solvent, possible combined with the effect of temperature. In the practical implementation of stage b) of the process any known method for separating a solid from a liquid can be used, such as gravimetric sedimentation, centrifuging, filtration or hydrocyclone treatment. The temperature at which the separation takes place must be such as to maintain the liquid phase homogeneous. Consequently, the temperature used must be within the range indicated for stage a). After the separation of the solid the homogeneous liquid phase obtained in stage b) is separated [stage e)] into an extracted liquid phase and a refined liquid phase. This can be achieved by two different variants. In one of these variants, said homogeneous liquid phase is cooled to a temperature below the mutual solubility temperature to separate an oil-rich refined liquid phase from an extracted liquid phase rich in organic carbonate. In the other variant, a liquid solvent more polar than the organic carbonate is added with or without cooling to the separate liquid homogeneous phase of stage b), to separate said refined and extracted liquid phases. A suitable liquid solvent more polar than the carbonate is water or a lower aliphatic alcohol, preferably methanol, or their mixtures. The quantity of this solvent added can generally vary from 0,1% to 10% by weight of the organic carbonate. In the case of water, these quantities also comprise the water which may be present in a small quantity in the crude. Preferably a solvent quantity of the order of 2%-3% by weight of the organic carbonate is added, preferably with simultaneous cooling to induce separation of the extracted and refined liquid phases. The temperature at which this phase separation occurs varies according to the organic carbonate used and the presence or absence of the liquid solvent more polar than the carbonate. In general the phase separation temperature can vary from -10°C to 120°C. However when using dimethyl carbonate the phase separation temperature is preferably of the order of 25°C-35°C, irrespective of the fact that the liquid solvent more polar than dimethyl carbonate is present, or not. When using diethyl carbonate, the phase separation is preferably effected at ambient or close to ambient temperature, by adding said more polar liquid solvent, especially methanol. In all cases the phase separation is rapid and produces a well separated refined liquid phase and extracted liquid phase of composition which, other conditions being equal, depends on the phase separation temperature. To this end reference should be made to the accompanying Figure which shows the variation of the solubility, as determined experimentally, of a binary system consisting of dimethyl carbonate (DMC) and Egyptian Belaym crude dried and free of asphaltenes (curve ). In the plot the horizontal axis represents the composition of the binary system and the vertical axis represents temperature in °C. In the portion of the plot above the curve, there is complete miscibility, and the system is in the homogeneous liquid phase, with a complete solubility temperature near to 47°C. The precipitation of the solid in stage a) of the process is effected under these conditions of homogeneousness. In the portion the plot below the curve, there are two liquid phases in equilibrium, specifically a refined liquid phase (to the left) and an extracted liquid phase (to the right). This situation occurs when the homogeneous liquid phase is cooled, after solid separation, to a temperature below the total solubility temperature, at which the system separates into two liquid phases, namely an oil-rich refined liquid phase and a solvent-rich extracted liquid phase. For example, when a system formed from 50 wt% of oil and 50 wt% of dimethyl carbonate is cooled to 25°C, as shown in the Figure, it splits typically, into a refined liquid phase with about 73 wt% of oil, the remainder being essentially dimethyl carbonate. Under these conditions, the corresponding extracted liquid phase contains about 83 wt% of dimethyl carbonate, the balance being essentially oil. It is also possible to choose a phase separation temperature below 25°C, for example down to -10°C, to obtain a refined liquid phase still more rich in oil (about 90% by weight) and an extracted liquid phase still more rich in dimethyl carbonate (95% by weight). Alternatively the refined liquid phase and extracted liquid phase obtained at 25°C can be individually subjected to further cooling. For example, further cooling the extracted liquid phase obtained at 25°C to -5°C results in the separation of a second extract formed substantially of dimethyl carbonate only, and a second refined phase formed substantially of oil only, as shown graphically in the Figure. Figure 1 also shows the variation for the dimethyl carbonate (DMC) system and Belaym crude freed of asphaltenes, to which a water quantity of 0.4 wt% (curve ), 2 wt% (curve ) and 3 wt% (curve ) on the dimethyl carbonate has been added. It can be seen that the addition of water raises the temperature of complete solubility of the system and that this system containing water separates to produce an extracted phase richer with dimethyl carbonate and a refined phase richer with oil, consistently with the water content. It has been found, in practice, that, operating as described heretofore, the porphyrinic vanadium and nickel initially present in the crude remain to a large extent dissolved in the extracted liquid phase, the refined liquid phase being consequently depleted of both porphyrinic and asphaltenic vanadium and nickel. It has also been found that the oil present in the extracted phase is lighter (average molecular weight typically 66% of the feedstock value), whereas the average molecular weight of the oil in the refined phase is practically unchanged from the initial value. The solid physically separated in stage b) is rich with asphaltenic vanadium and nickel and organic compounds having sulphur and nitrogen heteroatoms. Specifically, the average molecular weight of the asphaltenic precipitate is typically 2100, ie of the order of magnitude of the average molecular weight of a heavy asphalt and close to the typical value for asphaltenes (2200-2300). Operating according to the present invention it is therefore possible to obtain the fractionation of the components initially present in the crude, with a concentration of the lighter components in the extracted phase. In addition this phenomenon of fractionation at the various temperatures, due to the different affinity of the polar and non-polar compounds for the organic carbonate solvent at the various temperatures, can be governed, within certain limits, on the basis of the phase separation temperature and/or by repeated phase separation. Finally, the extracted and refined liquid phases can be subjected to the usual treatment for recovering their components. Any crude or a fraction thereof can be treated by the process of the present invention, such as crudes reduced by atmospheric or reduced pressure distillation containing asphatenes and having a density generally of from 10° to 45° API. The asphaltene content of such crudes can reach values near to 20% by weight. The process is preferably carried out on a crude or fraction with an initial boiling point of 20°C-40°C above the boiling point of the organic carbonate used. In the case of heavier crudes or distillation residues, which are difficult to treat under the conditions of this process, such crudes or residues can be diluted with a hydrocarbon component before being treated with the organic carbonate. Hydrocarbon components suitable for this purpose can be selected from those which do not significantly modify the natural state of the oil-asphaltene dispersion, such as C₁₀-C₂₀ paraffin cuts, gas oils and kerosenes of the type usually used for I.E. engines. The quantity of the selected hydrocarbon component is such as to provide sufficient fluidity for conducting the operations of the instant process. At the end of the process, the added hydrocarbon component is recovered from the refined and extracted liquid phases conventionally, such as by flash evaporation. The process of the present invention is both simple and convenient. In particular, it can be conducted at moderate temperatures,without applying overpressure and with a low ratio of organic carbonate to crude, or crude fraction. In addition, the process provides high deasphalting efficiency generally in the range of 85%-99%, these values being higher than those of the commercial processes. The total deasphalted oil yield is generally greater than 90%, this value being equal to, or better than, that of the known processes. The following experimental examples are provided to better illustrate the present invention. EXAMPLE 1 In this example an Egyptian Belaym crude (land/off-shore blend) of the following characteristics is subjected to deasphalting: 208,2 g of dimethyl carbonate and 98,9 g of crude of the abovesaid characteristics are fed into a flask fitted with a stirrer. The mixture is heated to 80°C and kept stirred at this temperature for 1 hour to obtain in the flask a homogeneous liquid phase and a solid precipitate suspended in said liquid phase. The suspension obtained in this manner is filtered under hot conditions (80°C) through a Whatman filter paper with vacuum applied by a water pump, to collect 14,5 g of a solid residue. A cold trap is connected between the filtrate collection vessel and the vacuum pump to condense the dimethyl carbonate and other light compounds which vaporize during filtration. After the filtration, the contents of the cold trap are added to the filtrate, which is then placed in a separator funnel and allowed to cool at ambient temperature (25°C). At this temperature the liquid separates into two phases, namely an upper (refined) oil phase of 83,5 g and a lower denser (extracted) phase of 209 g. The separated solid residue consists of 6,4 g (44% by weight) of asphaltenes and 8,1 g (56% by weight) of a retained refined phase consisting of 6,4 g of deasphalted oil and 1,4 g of dimethyl carbonate. The refined liquid phase consists of 69,2 g of oil (82,8% by weight), 13,8 g of dimethyl carbonate (16,5% by weight) and 0,5 g of asphaltenes (0,6% by weight). The extracted liquid phase consists of 16,7 g of oil (8% by weight) and 192 g of dimethyl carbonate (92% by weight). The crude deasphalting efficiency is therefore 92,4%. The total oil recovery yield is 87% by weight of the crude, with 70% recovery in the refined phase and 17% recovery in the extracted phase. The total deasphalted oil yield, evaluated relative to the oil content of the crude, is 93,4% by weight. Table 1 summarizes the characteristics of the initial crude (G), the solid residue (RS), the refined liquid phase (LR) and the extracted liquid phase (LE). The asphaltene content of the crude and the various separated phases is determined gravimetrically, in accordance with ASTM D-2007, modified in accordance with IP-143, operating with a weight ratio of 10 parts of n-heptane per part of sample, with asphaltene precipitation in 2 hours under reflux conditions. The vanadium and nickel content is evaluated by atomic absorption analysis on samples previously subjected to acid digestion. The vanadium content is confirmed by vanadium (IV) electron-spin resonance spectroscopy. The sulphur content is evaluated by X-ray fluorescence. The nitrogen content is evaluated by the usual Kjeldahl method. The carbon/hydrogen atomic ratio is evaluated by elemental analysis under oxygen flow. From the data given in Table 1 it can be seen that the efficiency of vanadium removal from the crude is 59% (52,6% in the solid precipitate and 6.4% in the extracted liquid phase). The efficiency of nickel removal is 60% (57,3% in the solid precipitate and 2,7% in the extracted liquid phase). The sulphur removal is 56% (22,5% being the extraction contribution) and the nitrogen removal is 64% (11% being the extraction contribution). The C/H weight ratio in the solid residue (8,77/1) is clearly higher than that of the initial crude (6,97/1). From elemental analysis and weight balances it can be confirmed that oxygen is not incorporated preferentially into the refined oil. No dimethyl carbonate decomposition was noted during the treatment. When the extracted liquid phase, obtained as described, is cooled from 25°C to -5°C, a further oil phase separates in an amount of 6% by weight on the extracted liquid phase. EXAMPLE 2 A series of tests are conducted by bringing, the Belaym crude of Example 1 into contact at different temperatures with dimethyl carbonate in a weight ratio of 1:1. In each case stirring is maintained for 1 hour. After stirring, the residual solid is separated by filtration at the precipitation temperature. The filtered liquid phase is cooled to 25°C (except for the first test, which is conducted at this temperature) and an extracted liquid phase and refined liquid phase separate. Tests 1 to 4 are outside the scope of the present invention, in that, at the precipitation temperatures used there, there is an incomplete miscibility between the crude and the dimethyl carbonate. In tests 5 to 8 a complete miscibility between the crude and the dimethyl carbonate in the precipitation stage is obtained, these tests, therefore, falling within the scope of the invention. Table 2 shows for each test the temperature (°C) during the precipitation stage, the weight percentage of residual asphaltenes in the refined liquid phase (%A-R) and the deasphalting efficiency (%Eff-D) expressed as the weight percentage of precipitated asphaltenes on the asphaltene content of the crude. EXAMPLE 3 A series of tests are conducted by bringing dimethyl carbonate into contact with the Belaym crude of Example 1 at different mutual weight ratios, stirring for 1 hour at 80°C, separating the residual solid at this temperature by filtration and finally cooling the filtrate to 25°C to separate an extracted liquid phase from a refined liquid phase. Tests 1 to 4 are conducted in accordance with the invention. Tests 5 and 6 are comparison tests, in that at these dimethyl carbonate/crude weight ratios the precipitated solid is tacky and unfilterable. The test results are summarized in Table 3, which shows the weight ratio (WR) of dimethyl carbonate to crude during the extraction stage, the weight percentage of residual asphaltenes in the refined liquid phase (%A-R) and the deasphalting efficiency (%Eff-D) expressed as the weight percentage of precipitated asphaltenes relative to the asphaltene content of the crude. EXAMPLE 4 A series of tests are conducted by bringing the Belaym crude of Example 1 into contact for different times with dimethyl carbonate in a weight ratio of 1/2, stirring at 80°C, separating the residual solid at this temperature by filtration and finally cooling the filtrate to separate an extracted liquid phase from a refined liquid phase. Table 4 summarizes the results of tests 1 to 5, showing the contact time in hours between the crude and the dimethyl carbonate at 80°C, the weight percentage of residual asphaltenes in the refined liquid phase (%A-R) and the deasphalting efficiency (%Eff-D) expressed as the weight percentage of precipitated asphaltenes relative to the asphaltene content of the crude. EXAMPLE 5 A Rospo di Mare crude (11,8° API) with an asphaltene content of 20.3% by weight is diluted with gas oil of the type used commercially for I.E. engines, the mixtures thus obtained being contacted with dimethyl carbonate, stirring for 1 hour at 80°C. The dimethyl carbonate/crude/gas oil weight ratio is 2,2:1:1. At 80°C a homogeneous liquid phase exists, and a residual solid precipitates which is filtered off at the precipitation temperature. The filtrate separates at 25°C into a refined liquid phase and an extracted liquid phase. In the refined liquid phase a residual asphaltene quantity of 4,7% by weight is found (value already corrected for the dilution with gas oil). The deasphalting efficiency is thus 76%, as evaluated relative to the asphaltene content of the crude. For comparison, three tests of asphaltene extraction from the crude are conducted operating under the aforesaid conditions, but without dimethyl carbonate, and with a ratio of gas oil to crude of 0.6:1, 1:1 and 3:1 respectively. In the three tests a refined phase is obtained with an average asphaltene content of 19,3% by weight and an average crude deasphalting efficiency of 4,9%. EXAMPLE 6 27,75 g of dimethyl carbonate are added to 13,35 g of the Belaym crude of Example 1 (dimethyl carbonate/oil weight ratio 2,08/1) and the mixture kept stirring for 30 minutes at 80°C. The solution obtained is adjusted to 60°C and maintained at this temperature for 20 minutes. The asphaltene solid is separated by filtration, 0,60 g of deionized water (2,1% by weight relative to the dimethyl carbonate) are added to the filtrate and the mixture cooled to 35°C with stirring. When the stirring is interrupted, an extracted liquid phase rich in dimethyl carbonate (density 1,039 g/ml), and an oil-rich refined phase (density 0,759 g/ml) quickly separate. These values and the composition of the phases are comparable with those of the anhydrous system, but separated at 20°C. A residual asphaltene content of 0,3% by weight is determined in the refined phase. The deasphalting efficiency is thus 93%. When the test is repeated heating initially to 60°C instead of 80°C the deasphalting efficiency is 47,1%. EXAMPLE 7 A series of tests are conducted by bringing diethyl carbonate into contact with the Belaym crude of Example 1 at different mutual weight ratios, stirring for 10 minutes at ambient temperature (20°C-25°C), allowing the solid to settle for 20 minutes and separating the solid by centrifuging at 2500 rpm for 5 minutes. The test results are summarized in Table 5, which shows the weight ratio (WR) of diethyl carbonate to crude during the extraction stage, and the deasphalting efficiency (%Eff-D) expressed as the weight percentage of precipitated asphaltenes on the asphaltene content of the crude. EXAMPLE 8 In this example an RA370 + Belaym (RA atmospheric residue) is treated with dimethyl carbonate, stirring at 80°C for 30 minutes, filtering the precipitate and phase-separating at ambient temperature to obtain a refined liquid phase and an extracted liquid phase. RA370 + Belaym has the following characteristics: asphaltene content 8,8% by weight; density 15/4°C 0,9865 g/ml; kinematic viscosity at 50°C: 10⁻⁴. 29,68 m²/s (2968 cSt), at 100°C: 1,175.10⁻⁴ m²/s (117,5 cSt); yield on crude feed to atmospheric distillation 60% by weight. The test results are summarized in Table 6, which shows the weight ratio (WR) of dimethyl carbonate to the RA370+Belaym during the extraction stage, and the deasphalting efficiency (%Eff-D) expressed as the weight percentage of precipitated asphaltenes on the asphaltene content of the crude.

Claims: Process for concurrently deasphalting and demetalating crude petroleum or a crude petroleum fraction containing asphaltenes and metals by treating said crude petroleum or fraction with an organic carbonate, characterized by comprising the steps of: (a) contacting said crude petroleum or fraction thereof with an amount of an organic carbonate selected from the dialkyl carbonates having the formula: wherein R and R', equal to, or different from one another, are C₁-C₃alkyls, and the cyclic carbonates having the formula: wherein R'' is the hydrogen atom or a methyl, as the sole deasphalting and demetalating agent, in a weight ratio of said organic carbonate to said crude oil or fraction thereof of from 0,5: 1 to 4:1, at a temperature of from 20°C to 150°C until a homogeneous liquid phase is obtained and the precipitation of a solid residue takes place thereupon; (b) physically separating said solid residue from said homogeneous liquid phase; (c) condensing and collecting the volatiles during said physical separation and combining them with said homogeneous liquid phase; (d) cooling said homogeneous liquid phase, and/or adding thereto an optionally cooled liquid solvent more polar than the organic carbonate, and; (e) allowing the combined liquids exiting step (d) to split into two discrete phases, which are a lighter refined liquid phase predominantly containing crude oil or a fraction thereof plus the balance organic carbonate and asphaltenes, and a heavier extracted liquid phase predominantly containing the organic carbonate and the balance crude oil. Process according to Claim 1, further comprising the steps of recovering the crude oil and the organic carbonate from each of the discrete phases exiting step (e). Process according to Claim 1, wherein said dialkyl carbonate is selected from dimethyl carbonate, diethyl carbonate, dipropyl carbonate, diisopropyl carbonate, ethylene carbonate, propylene carbonate, and any admixtures thereof. Process according to Claim 1, wherein the weight ratio of said organic carbonate to said crude oil or fraction thereof is from 1,5:1 to 2,5:1. Process according to Claim 1, wherein said dialkyl carbonate is dimethyl carbonate, and the temperature of step (a) is of from 60°C to 90°C. Process according to Claim 1, wherein said dialkyl carbonate is diethyl carbonate and the temperature of step (a) is from 20°C to 25°C. Process according to Claim 1, wherein the physical separation stage (b) is carried out by a procedure selected from gravity sedimentation, centrifuging, filtration and hydrocycloning.

Inventors: SAVASTANO CESAR, SAVASTANO, CESAR
Applicants: ENIRICERCHE SPA, ENIRICERCHE S.P.A.
Application year: 1991
Main classification: C10G21
IPC codes: C10C3, C10G29, C10G21