RU2779617C2 - Prediction of solvent power of light oils - Google Patents

Abstract

FIELD: oil industry.

SUBSTANCE: invention relates to a method for calculation of solvent power of light oil, SP _{(LO calculated)}. The above-mentioned method provides for: titration of light oil with reference oil, optionally in the presence of titrant, for the determination of a volume fraction of light oil in the beginning of asphaltene deposition, V _{(onset fraction LO)}, a volume fraction of reference oil in the beginning of asphaltene deposition, V _{(onset fraction RO)}, and, if titrant is present, a volume fraction of titrant in the beginning of asphaltene deposition, V _{(onset fraction T)}, and determination of calculated solvent power of light oil, SP _{(LO calculated)}, according to the following formula: SP _{(LO calculated)}=(CSP_(RO) - SP_(RO) × V _{(onset fraction RO)} - x × SP_(T) × V _{(onset fraction T)}/V _{(onset fraction LO)}. In the formula: CSP_(RO) is critical solvent power of reference oil, SP_(RO) is solvent power of reference oil, SP_(T) is solvent power of titrant, and x is 1, when titrant is present, and 0 in other conditions. In this case, critical solvent power is solvent power, below which asphaltenes begin to deposit from crude oil, and reference oil is heavy oil, which has asphaltene content, which is more than asphaltene content in light oil.

EFFECT: accurate determination or prediction of solvent properties of light crude oil in such a way that light crude oil can be combined with heavy crude oil in amount, which does not lead to asphaltene deposition.

19 cl, 7 dwg, 1 tbl, 4 ex

Description

TECHNICAL FIELD OF THE INVENTION

The present invention relates to methods for predicting the solvency of light oils. In particular, the present invention relates to methods for predicting the solvency of light crude oils.

Background of the Invention

It is often desirable to blend crude oils from various sources prior to processing in a refinery. There are a number of reasons for combining crude oils in this way.

For example, there may be a period when a large supply of a particular type of crude oil is present, resulting in a relatively low cost. However, certain types of crude oil may have properties that make them less attractive for processing or for subsequent sale. In these situations, it is desirable to combine a crude oil having one set of properties with a crude oil having a different set of properties such that the resulting blended crude oil provides properties that are preferred by the market. In many cases, it is desirable to add light crude oil to heavy crude oil.

Heavy crude oils usually contain asphaltenes. Asphaltenes are organic heterocyclic macromolecules that are usually the heaviest compounds in crude oils. Asphaltenes are defined as a class of solubility and are generally soluble in aromatic solvents such as toluene and insoluble in paraffinic solvents such as n-heptane.

Under normal refining conditions, asphaltenes in heavy crude oils are usually stable and remain in solution. However, when light crude oil, which typically contains a high proportion of paraffinic components, is added to heavy crude oil, asphaltenes can precipitate. When sediment begins to attach to metal surfaces in a refinery, contamination occurs.

Fouling of process equipment can lead to clogging of flow lines and loss of heat transfer efficiency due to poor heat transfer through the contaminant layer. Contamination can occur in any refinery process equipment that comes into contact with blended crude oil. Such process equipment includes tanks, pipelines, heat exchangers, fired heater tubes (furnaces), fractionating columns and reactors.

Accordingly, one of the most difficult problems that arise in crude oil refineries is the ability to ensure that the asphaltenes in the crude oil remain stable and remain in solution during refining.

Useful properties for predicting the occurrence of asphaltene precipitation include the critical solvency power (CSP) and solvency power (SP) of crude oil. When the solvency decreases below the critical solvency, asphaltenes begin to precipitate out of the crude oil. Increased asphaltene precipitation is observed when the solvency continues to decrease below the critical solvency.

US 5,871,634 discloses a process for mixing two or more oil streams, of which at least one contains asphaltenes. Within the framework of this method, the insolubility index and the solubility index of the mixture of each stream are determined. The method provides for the possibility of mixing oil flows without precipitation of asphaltenes from the solution.

US 2004/0121472 discloses a process for mixing two hydrocarbon liquids. Within this process, the solvency power of each liquid is determined by the characteristic factor K. Heptane and toluene are used as solvency standards, with heptane having a solvency power of 0 and toluene having a solvency power of 100. The two hydrocarbon liquids are then mixed such that the solvency the mixture is more than the critical solvent power of the crude oil having the highest critical solvent power in the mixture.

Although the characteristic factor K is a convenient and simplified means for evaluating dissolving power, it does not always correspond to experimentally determined values. Accordingly, precipitation of asphaltenes can be observed when some light crude oil is added to a heavy crude oil, although precipitation has not been predicted using the characteristic factor K. Similarly, in some cases, more light crude oil can be added to a heavy crude oil without causing start of asphaltene precipitation than the amount predicted using the characteristic factor K.

Accordingly, there is a need for a method for accurately determining or predicting the solvent properties of light crude oil so that light crude oil can be combined with heavy crude oil in an amount that does not result in precipitation of asphaltenes.

Brief summary of the present invention

The present invention provides a method for recalculating the solubility power of light oil, SP _{(LO recalculated)} , and the above method provides:

titration of light oil with reference oil, optionally in the presence of a titrant, to determine the volume fraction of light oil at the onset of asphaltene precipitation, V _{(onset fraction LO)} , the volume fraction of reference oil at the onset of asphaltene precipitation, V _{(onset fraction RO)} , and, if titrant is present , the volume fraction of the titrant at the beginning of asphaltene precipitation, V _{(onset fraction Т)} , and

determination of the recalculated solubility power of light oil, SP _{(LO recalculated)} , according to the following formula:

SP _{(LO recalculated)} =(CSP _(RO) -SP _(RO) ×V _{(onset fraction RO)} -x×SP _(T) ×V _{(onset fraction T)} /V _{(onset fraction LO)}

wherein:

CSP _(RO) is the critical solvent power of the reference oil,

SP _(RO) is the solvent power of the reference oil,

SP _(T) is the solubility of the titrant, and

x is 1 when the titrant is present and 0 otherwise.

In addition, the present invention provides a method for determining the relationship between recalculated solubility and bulk properties of light oils, the aforementioned method comprising:

determining the converted solvency for a plurality of light oils using the method described herein, and

determination of the relationship between the recalculated solvency and bulk properties of a variety of light oils.

In addition, a method is provided for predicting the recalculated solvent power of light oil, the aforementioned method using a relationship determined according to the method described herein to predict the recalculated solvent power of light oil from its bulk properties.

In addition, a method is provided for reducing the precipitation of asphaltenes from a mixture of light oil and heavy oil in a refinery, the aforementioned method comprising:

determining the converted solvent power of light oil or predicting the converted solvent power of light oil using the method described herein;

calculating, based on the calculated solvent power of light oil, the maximum possible relative content of light oil in a mixture of light oil and heavy oil, which does not cause precipitation of asphaltenes in the refinery; and

sending a mixture of light oil and heavy oil, having a relative content of light oil up to the maximum level, to the refinery.

The solvency of light oils can be accurately predicted by measuring the solvency of light oils relative to a reference oil and optionally a titrant. Accurate prediction of the dissolving power of light oils enables improved oil blending operations that minimize the risk of asphaltene settling.

In addition, the present invention makes it possible to predict the solvent power of light oil only from its bulk properties. This can facilitate informed crude oil purchasing decisions as well as refinery blending and planning when a real oil sample is not available for laboratory analysis.

Brief description of the figures

In FIG. 1 is a graph illustrating the weight percentage of sludge that forms at various ratios in blends of light crude oil (Oil A) with heavy crude oil (Oil B);

in fig. 2a-c are optical microscope images of mixtures of oils A and B;

in fig. 3 is a graph illustrating the weight percentage of sludge that forms at various ratios in blends of light crude oil (Oil A) with heavy crude oil (Oil C);

in fig. 4 is a graph illustrating the weight percentage of sludge that forms at various ratios in blends of light crude oil (Oil A) with heavy crude oil (Oil D); and

in fig. 5 is a graph comparing predicted converted solubility and converted solubility when determined using titration according to the method of the present invention for 150 light crude oils.

Detailed disclosure of the present invention

Determination of Solvent Power and Critical Solvent Power of Reference Oil

The formula for determining the recalculated solubility power of light oil, SP _{(LO recalculated)} , is derived from the following relationship:

CSP _(LO+RO) =(CSP _(RO) +SP _(LO) ×V _{(onset fraction LO)} -x×SP _(T) ×V _{(onset fraction T)}

CSP _(LO+RO) is the critical solvent power for a mixture of light oil and reference oil.

For the purposes of the present invention, it is assumed that CSP _(LO+RO) is equal to the greater of the critical solvent power of light oil, CSP _(LO) , and the critical solvent power of reference oil, CSP _(RO) . Since light oils will have low or no critical solvency power, it is assumed that CSP _(LO+RO) equals CSP _(RO) .

Any known method can be used to determine the solvent power of the reference oil, SP _(RO) , and the solvent power of the titrant, SP _(T) . The dissolving power of the titrant, SP _(T) , is usually known in the art. The solubility of the reference oil, SP _(RO) , as well as the solubility of the titrant, SP _(T) , if unknown, can be calculated using the method disclosed in US 2004/0121472 (Nemana, S. et al.; Predictive Crude Oil Compatibility Model), incorporated herein by reference. According to this method, the dissolving power is evaluated using the characteristic factor K.

The characteristic factor K, K _(RO) , is calculated according to the following formula:

K _(RO) =VABP _(RO) ^1/3 /SG _(RO)

where VABP _(RO) is the volume average boiling point of the reference oil in degrees Rankine, and

SG _(RO) is the standard relative gravity of the reference oil.

The volume average boiling point of a reference oil VABP _(RO) can be determined using known methods. In some cases, VABP _(RO) can be determined from the output profile of the reference oil.

The reference oil yield profile can be determined by physical distillation, for example, according to ASTM D 2892 or ASTM D 5236. Alternatively, the reference oil yield profile can be determined using gas chromatography (GC) and high temperature simulated distillation (HT-SIMDIS) . The use of GC analysis makes it possible to determine the hydrocarbon composition of oil for components boiling in the C _1-9 hydrocarbon range. The GC analysis can be performed according to the standard test method IP 601. The HT-SIMDIS analysis can be performed according to the standard test method IP 545.

Reference Oil Standard Relative Gravity, SG _(RO) , is the ratio of reference oil density to water density at 60°F (ie, 15.6°C). SG _(RO) can be determined using known methods. For example, the density of a reference oil can be measured experimentally according to ASTM D 4052 or ASTM D 5002. The solvent power of a reference oil, SP _(RO) , can be determined from the characteristic factor K using linear interpolation. For example, SP _(RO) can be determined from K _(RO) based on the relationship between the characteristic factor K and the solubility parameter of heptane and toluene. The characteristic factor K and the solubility parameter of heptane and toluene are known in the art.

The critical solvent power of a reference oil, CSP _(RO) , can be determined by titrating the reference oil with the precipitant. In some cases, CSP _(RO) can be determined according to the following formula:

CSP _(RO) = V _{(onset fraction RO(P))} ×SP _(RO) /100

where V _{(onset fraction RO(P))} is the volume fraction of the reference oil at the beginning of asphaltene precipitation by the precipitator; and

SP _(RO) is the solvent power of the reference oil, which can be determined as described above, for example, based on the characteristic factor K.

The precipitant used to determine CSP _(RO) preferably has a low solvency, such as a solvency of less than 5 and preferably less than 2. In some cases, the precipitant may have a solvency of about 0. Suitable precipitants include alkanes such as C _4-20 alkanes and preferably C _4-20 n-alkanes or C _4-20 isoalkanes. In some cases, precipitants are selected from heptane, undecane and pentadecane.

The reference oil and precipitant may be held to equilibrium for 20 minutes to 40 minutes, such as 30 minutes. In some cases, the reference oil and precipitant remain undisturbed during this time, i.e. they are not subjected to any mixing or shaking. Titration intervals of less than 15% by volume, such as less than 10% by volume and preferably less than 5% by volume, may be used.

Mixtures of hydrocarbon fluid and precipitant can be observed under an optical microscope to determine when asphaltenes precipitate. Alternatively, mixtures can be centrifuged, washing any solids (eg using a precipitant) and weighed to determine the amount of asphaltenes precipitated.

Titration of light oil with reference oil

Preferably precipitation of asphaltenes is observed when light oil is titrated with a reference oil in the absence of a titrant. In these cases x is 0 and the recalculated light oil solubility, SP _{(LO recalculated)} , can be determined according to the following formula:

SP _{(LO recalculated)} =(CSP _(RO) -SP _(RO) ×V _{(onset fraction RO)} )/V _{(onset fraction LO)} .

These embodiments advantageously reduce the need for experimentation with artificial precipitants such as n-heptane.

However, in some cases asphaltene precipitation may not be observed when light oil is titrated with reference oil alone. In these cases, light oil can be titrated with a reference oil in the presence of a titrant (i.e., x=1). This can be achieved, for example, by mixing a light oil with a titrant and then combining different amounts of reference oil and mixture; or by mixing a reference oil with a titrant and then combining different amounts of light oil and mixture. Preferably, the light oil is titrated with a mixture containing reference oil and titrant, where the reference oil and titrant are present in the mixture in a ratio of 2:1 to 1:2 and preferably 1.5:1 to 1:1.5. In some cases, reference oil and titrant are present in the mixture in a ratio of approximately 1:1.

In these cases, the titrant preferably has a low solvent power, such as a solvent power of less than 5 and preferably less than 2. In some cases, the precipitant may have a solvent power of about 0. Suitable titrants include alkanes such as C _4-20 alkanes and preferably C _4-20 n-alkanes or C _4-20 isoalkanes. In some cases, the titrants are selected from heptane, undecane and pentadecane. The use of a titrant with low solvent power promotes precipitation of asphaltenes and the effect of the titrant's solvent power on SP _{(LO recalculated)} is minimal. Thus, the formula for determining the recalculated solubility power of light oil, SP _{(LO recalculated)} , is as described in connection with embodiments that do not use a titrant (ie, x=0). Unlike embodiments that do not use a titrant, the sum of V _{(onset fraction RO)} and V _{(onset fraction LO)} will be less than 1.

Titration of a light oil with a reference oil, optionally in the presence of a titrant, can be carried out at titration intervals of less than 15% by volume, including less than 10% by volume and preferably less than 5% by volume. The authors believe that a titration interval of 2% by volume gives results that can be used to obtain a highly accurate estimate of the solvent power of light oils.

The titration may include mixing the light oil with a reference oil. Mixing can be carried out using an ultrasonic or vortex mixer.

The mixtures may be held to equilibrium for a period of at least 1 minute, for example 3 minutes to 5 hours and preferably 5 minutes to 1 hour. The achievement of equilibrium can occur at a temperature of from 0°C to 100°C, including from 10°C to 80°C and preferably from 20°C to 60°C.

Mixtures can be observed, for example, after reaching equilibrium, using an optical microscope to determine whether asphaltenes have precipitated or precipitated. An optical microscope can be used at magnifications from 10 to 1000, including 50 to 750 and preferably 100 to 500. Gravimetric analysis of mixtures can also be used, for example, as disclosed in US 2004/0121472.

In some cases it may be desirable to carry out a first titration with long titration intervals and a second titration with short titration intervals. Thus, long titration intervals can be used to obtain a rough estimate of the volume fractions of the reference oil and light oil at the beginning of asphaltene precipitation, V _{(onset fraction RO)} and V _{(onset fraction LO)} , and then small titration intervals can be used to perform accurate measurements V _{(onset fraction RO)} and V _{(onset fraction LO)} . The second titration should only be carried out in intervals centered at the crude estimate of V _{(onset fraction RO)} and V _{(onset fraction LO)} that was obtained from the first titration, for example, up to 25%, including up to 15% by volume on each side of the rough estimate of V _{(onset fraction RO)} and V _{(onset fraction LO)} .

In some cases, the method of the present invention involves titrating a light oil with a plurality of reference oils, predicting the solvent power of the light oil based on each of the plurality of reference oils, and determining the average predicted solvent power of the light oil.

By titrating a light oil with multiple reference oils, multiple predicted solvency values can be obtained. These predicted solvency values can then form the basis for the average predicted solvency of the light oil.

Light oils can be titrated using at least 5, at least 10, or at least 20 reference oils. The greater the number of reference oils, the more accurate is the average predicted solvent power of the light oil.

The average predicted solvent power of a light oil is usually defined as the mean square predicted solvent power. However, it should be understood that other averages may be available in some circumstances, for example to account for outliers. Various methods for calculating averages are known in the art.

Determination of the relationship between the recalculated solubility and bulk properties of light oil

In some cases, a plurality of light oils may be titrated with a reference oil such that the recalculated solvency for each of the light oils can be determined. The recalculated solvent powers can then be correlated with the bulk properties of the light oils. This makes it possible to predict the recalculated dissolving power of light oil only by its bulk properties.

In some cases, at least 5 light oils can be titrated with the reference oil, for example at least 10 light oils and preferably at least 20 light oils.

It should be understood that each of the plurality of light oils may be titrated with a single reference oil (with the reference oil being the same or different for each of the oils being tested) or with a plurality of reference oils. By titrating each of the light oils with a plurality of reference oils, average recalculated solvent powers can be determined for each of the light oils.

In some instances, a method for predicting the relationship between recalculated solvent powers and light oil bulk properties may include the step of measuring the bulk properties of a plurality of light oils.

The person skilled in the art is aware of methods for determining the relationship between recalculated solvent powers and bulk properties of a variety of light oils. To implement these methods, there is readily available software. Examples include the Nutonian® Eureqa software (a registered trademark of Nutonian, Inc.), although other software packages may be used. In these cases, data on bulk properties and recalculated solubility properties of light oils are used as input, and the software generates a formula relating the recalculated solubility and bulk properties of light oils. Many different formulas can be derived, in which case the operator can select from among them the formula that is most suitable for use, for example, includes bulk properties that can be easily or reliably measured.

Bulk properties may include: yield, for example, light oil fractions such as vacuum gas oil (VGO) fraction; characteristic factor K, for example, light oil; total acid number (TAN), for example, light oil or its fractions; nitrogen content, for example, light oil or its fractions; the API gravity of, for example, light oil or its fractions, such as the VGO fraction; the content of aromatic compounds, for example, light oil or its fractions; and density, for example, light oil or its fractions. Some or all of these properties may be taken into account when determining the relationship between the bulk properties of a light oil and its recalculated solvent power. Other bulk properties may also be used.

The yield of various cuts, such as the VGO cut, can be determined by distillation of the residual fraction (typically components boiling above 300°C) of light oil according to ASTM D 5236. The residue is formed by distillation of light oil according to ASTM D 2892. GC analysis SIMDIS (according to IP 545 and IP 507) of residual fractions can be used to determine the yield of the following fractions, including the VGO fraction.

The characterization factor K can be calculated using the volume average boiling point and density of the light oil, as discussed above in connection with the reference oil.

The nitrogen content of light oils can be measured according to ASTM D 4629, IP 379 or an equivalent standard.

TAN can be measured according to ASTM D 664 (IP 354) or ASTM D 974 (IP 139).

API gravity, such as VGO fraction, may be measured according to ASTM D 4052, ASTM D 5002, IP 365, or equivalent standards.

The aromatic content can be measured according to IP 548.

Density can be measured according to ASTM D 4052 or ASTM D 5002.

VGO is usually defined as a material boiling in the range of 350 to 580°C.

Although the bulk properties of oils can be measured, for example, as described above, they can often be easily obtained from oil analysis data that was carried out prior to purchasing the oil for use in a refinery. Also, in the absence of measured data, a crude oil property modeling tool such as CrudeSuite® (registered trademark of Spiral Software Limited) can be used to predict properties using limited crude oil property measurements.

Once the relationship between recalculated solubility and bulk properties of light oils has been determined, it can be used to predict the recalculated solubility of light oils from its bulk properties. The bulk properties of light oils can be measured, or they can be readily available.

Reducing asphaltene deposition in a refinery

The calculated solvent power of light oil can be used in a method to reduce the precipitation of asphaltenes from a mixture of light oil and heavy oil in a refinery. In particular, from the recalculated light oil solvent power, the maximum relative light oil content that can be present in a mixture of light oil and heavy oil can be calculated without causing asphaltene precipitation in the refinery. The refinery may then receive a mixture of light oil and heavy oil having a relative content of light oil up to a maximum level.

The reduction in asphaltene deposition can be observed in at least one of tanks, pipelines, heat exchangers, fired heater tubes, fractionators and reactors. Preferably, asphaltene deposition is reduced on the surfaces of heat exchangers in a refinery.

In some cases, precipitation of asphaltenes from a mixture can be reduced by at least 80%, preferably at least 90%, and more preferably at least 95% by weight compared to the precipitation that would be observed from the same mass of heavy oil.

Light oil and reference oil

Light oils typically have an asphaltene content of less than 1% by weight, and preferably less than 0.5% by weight. Light oils may also have a gravity greater than 35° API.

The reference oil is preferably a heavy oil. The heavy oil has an asphaltene content that is greater than the asphaltene content of the light oil, for example greater than 3% by weight, and preferably greater than 5% by weight. In addition, heavy oils typically have a gravity of less than 25° API and optionally have a heavy residue content (components boiling above 1000° F. i.e. 537.8° C.) of greater than 30% by weight.

The content of asphaltenes in the test oil and the reference oil can be determined using known methods. For example, the asphaltene content of each oil can be measured according to the IP 143 standard.

API gravity of light oil and reference oil can be determined using known methods. For example, the API gravity of each oil is preferably determined according to ASTM D 4052, although ASTM D 1298 may also be used.

The content of heavy residues of heavy oil can be determined using known methods. For example, the content of heavy oil residues can be determined according to ASTM D 5236 by distillation of the residue (boiling above 300°C) obtained by distillation according to ASTM D 2892.

The light oil and reference oil are preferably crude oils. Accordingly, they are preferably free of any asphaltene inhibitor and any dispersing agents. In addition, the light oil and reference oil are preferably free of drilling fluid or any other contaminants.

Examples

Example 1: Conversion of Solvent Power of Light Crude Oil

Experiments were performed to convert the solvent power of oil A (light crude oil). Oil B (heavy crude oil) was used as the reference oil.

Based on the characteristic factor K, oil A had a dissolving power of 21 and a critical dissolving power of 0. Oil A had a density of 0.7945 g/cm ³ at 15°C. Based on the characteristic factor K, oil B had a solvent power of 37 and a critical solvent power of 24. Oil B had a density of 0.9136 g/cm ³ at 15°C.

According to the method disclosed in US 2004/0121472, oil A could be mixed with oil B in an amount of up to 80% by weight without observed precipitation of asphaltenes.

To determine the converted solvent power, oil A was titrated with oil B to experimentally determine the point of observed precipitation of asphaltenes. Initial titration experiments were carried out using titration intervals of 10% by weight, with asphaltene precipitation measured using gravimetric analysis of mixtures. In FIG. 1 it can be seen that the minimum asphaltene precipitation was observed in the region of approximately 50% by weight of oil B.

Then carried out high-precision titration. Clean glass tubes containing 5 g of oil B were prepared. Various weights of oil A were added to the tubes. The oils were mixed and brought to equilibrium. Aliquots from the tubes were viewed with an optical microscope (200x magnification) to check for asphaltene precipitation. The results are presented in the following table:

The images of test tubes 2-4 obtained using an optical microscope are shown in Figs. 2a-c, respectively. It can be seen that little precipitation was observed in tube 2 and increased levels of precipitation were observed in tubes 3 and 4 as the proportion of oil A in the mixture increased.

The results show that the mixture of oil A and oil B remained stable at 50.9% v/v of oil A.

The recalculated solvent power of oil A was determined using formula I:

SP _{oil A (recalculated based on oil B)} \u003d (24-37 × 0.491) / 0.509 \u003d 11.46

This is significantly lower than the predicted value based on the characteristic factor K.

Example 2: Confirmation of the recalculated solvent power of light crude oil

The recalculated solvent power of Oil A was confirmed by additional experiments involving titration of Oil A with various heavy oils (Oils C and D).

Based on the characteristic factor K, oil C had a solvency of 36 and a critical solvency of 18. Based on the characteristic factor K, oil D had a solvency of 55 and a critical solvency of 27.

Initial titration experiments were carried out using titration intervals of 10% by weight, with asphaltene precipitation measured using gravimetric analysis of mixtures. In FIG. 3 shows that the minimum asphaltene precipitation was observed in the region of approximately 30% by weight of oil C, and FIG. 4 shows that the minimum asphaltene precipitation was observed in the region of approximately 50% by weight of oil D.

Then carried out high-precision titrations. Oil A was mixed with oil C up to 74% by volume and with oil D up to 65% by volume until asphaltene precipitation was observed.

The recalculated solvent power of oil A was determined using formula I:

SP _{oil A (recalculated based on oil C)} = (18-36 × 0.26) / 0.74 = 11.68

SP _{oil A (recalculated based on oil D)} = (27-55 × 0.35) / 0.65 = 11.92

It can be seen that the calculated solvent power of oil A based on oils C and D corresponds to that based on oil B, demonstrating that the method of the present invention provides consistent results when using different reference oils.

Example 3: Determining the Relationship Between Converted Solvent Power and Bulk Properties of Light Crude Oils

Experiments were performed on a wide variety of light oils to determine the relationship between the recalculated solvency and bulk properties of light crude oils.

More than 200 light crude oils were titrated with a heavy reference oil or a heavy reference oil and n-heptane as a titrant to determine their recalculated solvent power. Titrations were carried out using titration intervals of 2% by weight. The start of asphaltene precipitation was observed using a microscope.

In addition, standard experiments were carried out to determine the bulk properties of light crude oils.

Data from about 150 light crude oils were examined for correlations between scaled solubility and oil bulk properties using the Nutonian Eureqa software. The following dependency has been defined:

Dissolving power=

0.50 × vacuum gas oil yield (vol.%)

+2.6×10 ^-3 × characteristic factor K × total nitrogen content (ppm)

0.77 × [total acid number (mg KOH/g)] ²

-0.024 × total nitrogen content (ppm)

-22.9 × characteristic factor K

-0.018 × vacuum gas oil yield (vol.%) × vacuum gas oil density (°API)

-7.18×10 ^-7 × [total nitrogen content (ppm)] ²

+288.7

Example 4: Predicting the Recalculated Solubility Power of Light Crude Oil

The formula defined in Example 3 was used to predict the recalculated solvent power of 200 light crude oils. Approximately 150 of these oils have already been used in developing the formula as described above, with datasets from the remaining oils also being used to investigate the accuracy of the formula.

The converted solvency predicted using the formula defined in Example 3 was compared with the converted solvency determined using titrations according to the method of the present invention. The data is presented in the form of a graph in Fig. 5. Associated with the predicted recalculated solvency is a rms error of 0.17 solubility units, demonstrating the accuracy of the methods disclosed herein.

Claims (34)

1. A method for calculating the dissolving power of light oil, SP _{(LO calculated)} , and the above method provides: titration of light oil with reference oil, optionally in the presence of a titrant, to determine the volume fraction of light oil at the onset of asphaltene precipitation, V _{(onset fraction LO)} , the volume fraction of reference oil at the onset of asphaltene precipitation, V _{(onset fraction RO)} , and, if titrant is present , volume fraction of titrant at the beginning of asphaltene precipitation, V _{(onset fraction Т} ), and determination of the calculated dissolving power of light oil, SP _{(LO calculated)} , according to the following formula: SP _{(LO calculated)} =(CSP _(RO) - SP _(RO) × V _{(onset fraction RO)} - x × SP _(T) × V _{(onset fraction T)} )/V _{(onset fraction LO)} wherein: CSP _(RO) is the critical solvent power of the reference oil, SP _(RO) is the solvent power of the reference oil, SP(T) is the solubility of the titrant, and x is 1 when the titrant is present and 0 otherwise, where the critical solvency is the solvency below which asphaltenes begin to precipitate out of the crude oil, and The reference oil is a heavy oil that has an asphaltene content greater than that of the light oil. 2. The method of claim 1 wherein titration intervals of less than 15% by weight are used to titrate the light oil with the reference oil. 3. The method of claim 1 wherein the light oil is titrated with a reference oil in the presence of a titrant and x is 1. 4. The method of claim 1, wherein the method comprises titrating the light oil with a plurality of reference oils, predicting the solvent power of the light oil for each of the plurality of reference oils, and determining the average predicted solvent power of the light oil. 5. The method of claim 4 wherein the light oil is titrated using at least 5 reference oils. 6. The method of claim 1, wherein the solvent power of the reference oil, SP _(RO) , is estimated from the characteristic factor K of the reference oil. 7. The method of claim 1, wherein the critical solvent power of the reference oil, CSP _(RO) , is determined by titrating the reference oil with a precipitant. 8. The method of claim 1, wherein the light oil has an asphaltene content of less than 1% by weight. 9. The method of claim. 1, in which the reference oil has an asphaltene content of more than 3% by weight. 10. The method of claim 1 wherein the light oil and the reference oil are crude oils. 11. A method for determining the relationship between the calculated dissolving power and the bulk properties of light oils, the aforementioned method comprising: determining the calculated dissolving power for a plurality of light oils using the method according to any one of paragraphs. 1-10; and determining the relationship between the calculated solvency and bulk properties of a variety of light oils. 12. The method of claim 11, wherein the method comprises measuring the bulk properties of a plurality of light oils. 13. The method of claim 11 wherein the plurality of light oils consists of at least 5 light oils. 14. The method according to p. 11, in which the bulk properties include at least one of the following: output, for example, fractions of light oil, such as a fraction of vacuum gas oil (VGO); characteristic factor K, for example, light oil; total acid number (TAN), for example, light oil or its fractions; nitrogen content, for example, light oil or its fractions; and API gravity, for example, light oil or its fractions, such as the VGO fraction; the content of aromatic compounds, for example, light oil or its fractions; and density, for example, light oil or its fractions. 15. A method for predicting the calculated dissolving power of light oil, and in the above method, the use of a dependence determined according to any one of paragraphs is provided. 11-14 to predict the calculated solvent power of light oil from its bulk properties. 16. The method of claim 15, wherein the method comprises measuring the bulk properties of the light oil. 17. A method for reducing the precipitation of asphaltenes from a mixture of light oil and heavy oil in a refinery, the above method comprising: determination of the calculated dissolving power of light oil using the method according to any one of paragraphs. 1-10 or predicting the calculated dissolving power of light oil using the method according to p. 15 or 16; calculating, based on the calculated solvent power of the light oil, the maximum possible relative content of light oil in the mixture of light oil and heavy oil that does not precipitate asphaltenes in the refinery; and sending a mixture of light oil and heavy oil, having a relative content of light oil up to the maximum level, to the refinery. 18. The method of claim 17, wherein the precipitation of asphaltenes from the mixture can be reduced by at least 80%, preferably at least 90%, and more preferably at least 95% by weight compared to the precipitation that would be observed from the same mass of heavy oil. 19. The method of claim 17, wherein asphaltene deposition is reduced on the surface of heat exchangers in a refinery.

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