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Method for Determining the Stability of a Petroleum Product Containing Asphaltenes

20170261446 · 2017-09-14

    Inventors

    Cpc classification

    International classification

    Abstract

    The invention relates to a method for determining a parameter representative of the stability of an asphaltene-containing petroleum product, said petroleum product being an effluent derived from a hydrocarbon feedstock conversion process or being a mixture of hydrocarbons, using proton NMR to determine a threshold value of said parameter representative of the stability, this threshold value constituting a boundary between a stability domain and an instability domain of a petroleum product. According to the invention, the parameter representative of the stability is a T.sub.2mean/T.sub.1mean or T.sub.1mean/T.sub.2mean ratio. The invention also relates to a method for monitoring a conversion process, in particular a deep conversion process, or a mixture of hydrocarbons, using this method of determination.

    Claims

    1.-13. (canceled)

    14. A method for determining a parameter representative of the stability of an asphaltene-containing petroleum product, a precipitation of which results in an instability of the petroleum product, the petroleum product being an effluent derived from a hydrocarbon feedstock conversion process or being a mixture of hydrocarbons, the method comprising: a. preparing one or more petroleum products either by implementing the process for the conversion of one and the same hydrocarbon feedstock at a plurality of conversion levels, or by mixing hydrocarbons in different proportions, b. measuring the longitudinal relaxation times T.sub.1 and the transverse relaxation times T.sub.2 of the petroleum products prepared in step a) by proton NMR, c. determining as parameter representative of the stability, a T.sub.2mean/T.sub.1mean or T.sub.1mean/T.sub.2mean ratio for each of the petroleum products prepared in step a), wherein T.sub.2mean and T.sub.1mean are the means of the values measured during step b), and d. determining a threshold value of the parameter representative of the stability, the threshold value constituting a boundary between a stability domain and an instability domain of the petroleum product.

    15. The method according to claim 14, wherein step c) comprises determining the ratio T.sub.2mean/T.sub.1mean as a parameter representative of the stability.

    16. The method according to claim 14, wherein the conversion process comprises a thermal conversion process, a fluid catalytic cracking process, a hydrocracking process, a hydrotreating process, a fixed-bed hydroconversion process, a moving-bed hydroconversion process, an ebullated-bed hydroconversion process, a slurry-phase hydroconversion process, a vacuum distillation residue desulfurization process or an atmospheric distillation residue desulfurization process.

    17. The method according to claim 14, wherein the petroleum product is a heavy fuel oil.

    18. The method according to claim 14, wherein the petroleum products have an asphaltene content of at most 50% by weight and of at least 0.1% by weight.

    19. The method according to claim 14, wherein step d) of determining a threshold value comprises a step of determining S-values of each of the petroleum products prepared in step a), an S-value being defined by the formula: S = S 0 1 - S a with Sa: stability of the asphaltenes and S.sub.0: solvency of the oily medium, the threshold value being chosen equal to the T.sub.2mean/T.sub.1mean or T.sub.1mean/T.sub.2mean ratio of the petroleum product whose S-value indicates a precipitation of the asphaltenes.

    20. The method according to claim 15, wherein step d) of determining a threshold value comprises a step of plotting a curve of the T.sub.2mean/T.sub.1mean ratios calculated as a function of the composition of the petroleum products prepared in step a), the threshold value corresponding to a value of the T.sub.2mean/T.sub.1mean ratio for which a plateau is arrived at.

    21. The method according to claim 20, wherein, when a petroleum product that is an effluent derived from a slurry-phase conversion process has a T.sub.2mean/T.sub.1mean ratio greater than or equal to 0.85, then the petroleum product is close to flocculation.

    22. The method according to claim 20, wherein, when a petroleum product derived from a slurry-phase conversion process and filtered has a T.sub.2mean/T.sub.1mean ratio greater than or equal to 0.27, then the mixture is close to flocculation.

    23. The method according to claim 1, wherein, in step b), a probe having a dead time of less than or equal to 11 μs is used.

    24. The method according to claim 1, wherein the NMR measurements are low-field proton NMR measurements.

    25. A method for monitoring a a deep conversion process comprising: a. converting a heavy hydrocarbon-based feedstock having an H/C ratio of at least 0.25, b. recovering the effluents produced by the conversion and separating at least one predetermined cut, c. measuring the T.sub.2mean/T.sub.1mean or T.sub.1mean/T.sub.2mean ratio of the predetermined cut by NMR, d. comparing the T.sub.2mean/T.sub.1mean or T.sub.1mean/T.sub.2mean ratio determined in step c) to a threshold value of the parameter representative of the stability previously determined by the method according to claim 1 using one or more conversion levels of the feedstock, e. deducing whether or not the predetermined cut is stable.

    26. A method for monitoring a mixture of hydrocarbons comprising mixing one or more hydrocarbons, the method comprises, during the mixing: a. measuring the T.sub.2mean/T.sub.1mean or T.sub.1mean/T.sub.2mean ratio of the mixture by NMR, b. comparing the T.sub.2mean/T.sub.1mean or T.sub.1mean/T.sub.2mean ratio determined in step a) to a threshold value of the parameter representative of the stability previously determined by means of the method according to claim 14 using mixtures of the same hydrocarbons in different proportions, c. deducing therefrom whether or not the mixture is stable.

    Description

    FIGURES

    [0183] FIG. 1 is a graphical representation of the T.sub.2mean/T.sub.1mean ratio as a function of the conversion level (example A).

    [0184] FIG. 2 is a graphical representation of the T.sub.2mean/T.sub.1mean ratio as a function of the value of Sa (example B).

    EXAMPLES

    [0185] The examples below aim to illustrate the effects of the invention and its advantages, but without limiting the scope thereof.

    Example A

    With a 250° C..SUP.+ TLP Derived from a Slurry-Phase Hydroconversion Process

    [0186] The estimation of the stability of a 250° C..sup.+ effluent (TLP) derived from a deep conversion process in a slurry reactor will be carried out as follows.

    [0187] Preparation of the samples: approximately 1 ml of the effluent/feedstock to be analyzed by NMR is withdrawn and poured into the bottom of an NMR tube. Since the feedstock and the effluents are very viscous at ambient temperature, it is necessary to heat the sample by passing into an oven at 110° C. for at least 5 min, in order to homogenize it and to liquefy it in order to be able to withdraw it.

    [0188] The measurements were carried out using a 0.47 T Bruker Minispec MQ20 spectrometer operating at 20 MHz for the proton, equipped with a 10 mm probe and having a dead time of 7 ps. The term “dead time” is understood to mean the time starting from which it is possible to record the signal. The mean duration of the 90° and 180° pulses is respectively 2.6 ps and 5.3 ps.

    [0189] Step a: The longitudinal relaxation time T.sub.1 is measured at 60° C. on various samples. In order to do this, a sample of the 250° C.+TLP (Total Liquid Product) is withdrawn at various conversion levels. [0190] Sample no. 1 corresponds to the feedstock derived from Safaniya crude oil, the asphaltene content of which is from 7% to 20% by weight. The asphaltenes are completely within the TLP samples used below [0191] Sample no. 2 corresponds to the effluent (TLP) at a conversion level of 22% [0192] Sample no. 3 corresponds to the effluent at a conversion level of 51% [0193] Sample no. 4 corresponds to the effluent at a conversion level of 73% [0194] Sample no. 5 corresponds to the effluent at a conversion level of 80.5% [0195] Sample no. 6 corresponds to the effluent at a conversion level of 92%.

    [0196] The T.sub.1 values are measured for the above samples and the weighted mean of these T.sub.1 values is produced for each of the samples as a function of the representation in % of the conversion levels of the sample using equation (2). These values are collated in table 2.

    [0197] Step b: The transverse relaxation time T.sub.2 of the samples is measured by low-field NMR and T.sub.2mean is calculated by weighting of the T.sub.2 as a function of the representation in % of the conversion levels of the sample using equation (4). These values are collated in table 2.

    [0198] Step

    [0199] A T.sub.2mean/T.sub.1mean ratio is determined, the values of which are presented in table 2.

    TABLE-US-00002 TABLE 2 % CONVERSION T.sub.2mean/T.sub.1mean Sample 525° C..sup.+ T.sub.1 mean (ms) T.sub.2 mean (ms) (within ± 5%) No. 1 0 78 0.2 0.003 No. 2 22% 57 2.2 0.04 No. 3 51% 87 25.0 0.29 No. 4 73% 192 156 0.81 No. 5 81% 497 481 0.97 No. 6 92% 786 787 1 The conversion level (or conversion) may be defined as being the ratio: [00006] wt .Math. .Math. % .Math. .Math. of .Math. .Math. the .Math. .Math. 525 .Math. ° .Math. .Math. C .Math. . + .Math. .Math. cut .Math. .Math. in .Math. .Math. the .Math. .Math. feedstock - wt .Math. .Math. % .Math. .Math. of .Math. .Math. 525 .Math. ° .Math. .Math. C .Math. . + .Math. .Math. cut .Math. .Math. in .Math. .Math. the .Math. .Math. effluents wt .Math. .Math. % .Math. .Math. of .Math. .Math. the .Math. .Math. 525 .Math. ° .Math. .Math. C .Math. . + .Math. .Math. cut .Math. .Math. in .Math. .Math. the .Math. .Math. feedstock

    [0200] A graphical representation of the T.sub.2mean/T.sub.1mean ratio is plotted as a function of the conversion level, as represented in FIG. 1.

    [0201] On this graph, it is seen that with the method in accordance with the invention, it is possible to determine the flocculation threshold of an asphaltene-containing petroleum product. This graphical determination is confirmed by a visual observation of the samples according to whether or not this product is precipitated.

    [0202] For an unfiltered effluent derived from the slurry-phase conversion process, it may be considered that if T.sub.2mean/T.sub.1mean is greater than 0.85 then the system is unstable and there is a risk of flocculation.

    [0203] For a predictive purpose, it is possible to consider that the T.sub.2mean/T.sub.1mean ratio may be up to 10% lower than said threshold value.

    Example B

    With a Filtered 250° C..SUP.+ TLP Derived from a Slurry-Phase Hydroconversion Process

    [0204] The estimation of the stability of a filtered 250° C..sup.+ effluent (TLP) derived from a deep conversion process in a slurry reactor will be carried out as follows.

    [0205] The preparation of the samples is in accordance with that used in the course of example A.

    [0206] The feedstock used to produce TLPs contains from 10% to 20% by weight of asphaltenes. The asphaltenes are completely within the TLPs. After filtration, the content of asphaltenes in the filtered TLP is from 8% to 18% by weight.

    [0207] The TLP contains both flocculated asphaltenes and asphaltenes that are at the flocculation limit. If the sample is filtered, the flocculated asphaltenes are removed from the sample and only non-flocculated, and therefore stable, asphaltenes remain.

    [0208] In order to carry out filtration, the TLP is diluted in toluene. After dilution, a vacuum filtration is carried out. It is possible to use a glass fiber filter having a porosity of 0.7 μm. The residual toluene is evaporated by a rotary evaporator under nitrogen.

    [0209] The measurement of the S-value, according to the ASTM D7157 standard, is carried out so as to obtain values of Sa, that is to stay the intrinsic stability of the asphaltenes.

    [0210] The results are collated in table 3 below.

    [0211] The value of T.sub.2mean and T.sub.1mean is determined in accordance with the method used during example A. These values are collated in table 3.

    [0212] The results obtained enable a correlation to be obtained between the T.sub.2mean/T.sub.1mean ratio and the value of Sa, represented in FIG. 2.

    [0213] It is known, for carrying out the process, that the stability threshold of the asphaltenes (Sa) determined by the S-value should be greater than 0.35.

    [0214] The determination of the T.sub.2mean/T.sub.1mean ratio and the correlation with the value of Sa makes it possible to observe that T.sub.2mean/T.sub.1mean should be kept below 0.27 in order to keep the system stable.

    TABLE-US-00003 TABLE 3 T.sub.2mean/ T.sub.1mean Sample Temperature Conversion (within no. (° C.) 525° C..sup.+ (% m) S Sa So T.sub.2mean T.sub.1mean ± 5%) 7 430 36% 2.14 0.57 0.92 4.3 55.7 0.08 8 433 39% 2.19  0.6 0.87 1.2 56 0.02 9 439 51% 1.40 0.44 0.78 13.8 76.3 0.18 10 435 58% 1.18 0.37 0.75 28.4 107 0.27 11 435 63% 1.30 0.32 0.89 50.9 141.1 0.36 The conversion level (or conversion) may be defined as being the ratio: [00007] wt .Math. .Math. % .Math. .Math. of .Math. .Math. the .Math. .Math. 525 .Math. ° .Math. .Math. C .Math. . + .Math. .Math. cut .Math. .Math. in .Math. .Math. the .Math. .Math. feedstock - wt .Math. .Math. % .Math. .Math. of .Math. .Math. 525 .Math. ° .Math. .Math. C .Math. . + .Math. .Math. cut .Math. .Math. in .Math. .Math. the .Math. .Math. effluents wt .Math. .Math. % .Math. .Math. of .Math. .Math. the .Math. .Math. 525 .Math. ° .Math. .Math. C .Math. . + .Math. .Math. cut .Math. .Math. in .Math. .Math. the .Math. .Math. feedstock