Method for Monitoring a Process for Refining a Hydrocarbon Feedstock by NMR Measurement of Transverse Relaxation time T2

Abstract

The invention relates to a method for monitoring a process for refining a feedstock of hydrocarbons, in which: a) a signal representative of the transverse relaxation time of the different entities of an effluent resulting from said refining process, in particular an effluent comprising solid entities, is acquired by proton NMR, b) the signal measured is modeled using a mathematical function comprising several components, each component corresponding to a dynamic range of the entities of said effluent, c) the following are extracted from each of the components of the mathematical function: the transverse relaxation time of each of the components, the intensity of each of the components, d) a value of parameter characteristic of said effluent is determined from at least one intensity determined in stage c), e) a signal for controlling the refining process is generated as a function of said characteristic parameter.

Claims

1.-7. (canceled)

8. A method for monitoring a process for refining a feedstock of hydrocarbons, comprising: a) acquiring a signal representative of the transverse relaxation time of the different entities of an effluent resulting from said refining process, in particular an effluent comprising solid entities, by proton NMR, b) modeling the signal using a mathematical function comprising several components, each component corresponding to a transverse relaxation time T.sub.2 and to an intensity which is related to the amount of spins having this transverse relaxation time T.sub.2, c) extracting from each of the components of the mathematical function: the transverse relaxation time of each of the components, the intensity of each of the components, d) determining a value of parameter characteristic of the solid entities of said effluent from the intensity determined in stage c), said characteristic parameter being a ratio of intensities, e) generating at least one signal for controlling the refining process as a function of said value of said characteristic parameter, the control signal being chosen from a signal for directing the operating conditions of the refining process and a signal for destination of the effluent, said stage of generation of a control signal comprising a stage of comparison of the value of the characteristic parameter of said effluent with at least one threshold value, determined according to one of the following ways: i) operating said refining process at different levels of conversion or under different operating conditions for one and the same feedstock of hydrocarbons, and by carrying out stages a) to d) of the monitoring method, or ii) carrying out stages a) to d) of the monitoring method on an effluent obtained during the operation of the refining process under known predetermined conditions.

9. The monitoring method as claimed in claim 8, in which the intensities are estimated by modeling the acquired signal by a mathematical function exhibiting two components.

10. The monitoring method as claimed in claim 8, in which the mathematical function is chosen from: a function comprising at least one Gaussian part and at least one exponential part, a polynomial function, any other mathematical function suitable for adjusting the acquired NMR signal.

11. The monitoring method as claimed in claim 8, in which, during stage a), the signal representative of the transverse relaxation time is acquired by low field proton NMR.

12. The monitoring method as claimed in claim 8, in which the refining process is chosen from a vacuum or atmospheric distillation, 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 ebullating bed hydroconversion process, a slurry-phase hydroconversion process or a process for the desulfurization of a vacuum distillation residue or of an atmospheric distillation residue.

13. The monitoring method as claimed in claim 8, in which the refining process is a slurry-phase hydroconversion process and in which process stage a) of acquisition of the NMR signal is carried out on the 350° C.+ or 525° C.+ cut of the effluent resulting from a slurry-phase hydroconversion process.

14. The monitoring method as claimed in claim 13, in which the control signal generated in stage e) comprises a signal for destination of the 350° C.+ or 525° C.+ cut, the destination of the 350° C.+ or 525° C.+ cut being chosen from the recycle as feedstock of the refining process, the use as fuel or the use as base for the formulation of an asphalt.

Description

FIGURE

[0133] FIG. 1 is a graphical representation of the A/A+B ratio as a function of the level of conversion of a vacuum residue (example 1).

[0134] FIG. 2 is a graphical representation of the A/A+B ratio as a function of the degree of conversion of a pitch feedstock (example 2).

EXAMPLES

[0135] The examples below are targeted at illustrating the effects of the invention and its advantages, without limiting the scope thereof.

[0136] In the examples, a refining process is carried out at different degrees of conversion.

[0137] Preparation of the samples: approximately 1 ml of the effluent to be analyzed by NMR is withdrawn and poured into the bottom of an NMR tube.

[0138] 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 μs. The mean duration of the 90° and 180° pulses is 2.6 μs and 5.3 μs respectively.

[0139] The transverse relaxation signal was measured by a sequence of FID type.

[0140] The signal obtained was modeled by a mathematical function (1) comprising a Gaussian part and an exponential part and which can be written:

[00001]$\begin{array}{cc}{M}_x\left(t\right)=A\times \exp \left(-\frac{t^2}{T_{21}^2}\right)+B\times \exp \left(-\frac{t}{T_{22}}\right)& \left(1\right)\end{array}$

[0141] where:

[0142] M(x) is the transverse magnetization measured

[0143] t represents the time

[0144] T.sub.21 corresponds to the transverse relaxation time of the least mobile entities in the sample

[0145] T.sub.22 corresponds to the transverse relaxation time of the most mobile entities in the sample

[0146] A represents the intensity corresponding to the spins having the transverse relaxation time T.sub.21

[0147] B represents the intensity corresponding to the spins having the transverse relaxation time T.sub.22.

[0148] The proportion of the (100×A)/(A+B) fraction, also known as Gaussian fraction, is measured for different degrees of conversion of a refining process.

[0149] The level of conversion (or conversion) can be defined as being the ratio:

[00002]$\frac{\begin{array}{c}\%.Math..Math.\mathrm{by}.Math..Math.\mathrm{weight}.Math..Math.\mathrm{of}.Math..Math.\mathrm{the}.Math..Math.525.Math.°.Math..Math.C..Math.+\mathrm{cut}.Math..Math.\mathrm{in}.Math..Math.\mathrm{the}.Math..Math.\mathrm{feedstock}-\\ \%.Math..Math.\mathrm{by}.Math..Math.\mathrm{weight}.Math..Math.\mathrm{of}.Math..Math.525.Math.°+\mathrm{cut}.Math..Math.\mathrm{in}.Math..Math.\mathrm{the}.Math..Math.\mathrm{effluents}\end{array}}{\%.Math..Math.\mathrm{by}.Math..Math.\mathrm{weight}.Math..Math.\mathrm{of}.Math..Math.\mathrm{the}.Math..Math.525.Math.°.Math..Math.C..Math.+\mathrm{cut}.Math..Math.\mathrm{in}.Math..Math.\mathrm{the}.Math..Math.\mathrm{feedstock}}$

Example 1

[0150] The refining process considered in the present example is a slurry-phase hydroconversion process.

[0151] The tests were carried out on a feedstock which is a vacuum residue of Ural-type crude, the characteristics of which are described in table 2 below. The catalyst employed is a fat-soluble molybdenum octoate salt injected at a content of 1000 ppm with respect to the feedstock. The tests are carried out at temperatures between 410 and 450° C. with a residence time of between 1 and 5 h under 150 bar of hydrogen. The effluents recovered are fractionated (naphtha, gas oil, vacuum distillates and vacuum residue). The low field NMR analysis is carried out on the vacuum residue cut corresponding to the 525° C.+ cut. The asphaltene content of this effluent varies, according to the level of conversion, from 10 to 60% by weight.

[0152] A graphical representation of the Gaussian fraction defined above is plotted as a function of the level of conversion, as represented in FIG. 1.

[0153] In this graph, it is seen that the Gaussian fraction suddenly increases from a certain level of conversion, which indicates a high risk of formation of coke. It is thus possible to direct the process by watching the Gaussian fraction of the effluent and to act on the parameters of the process in order to keep this Gaussian fraction in a value range where the risk of formation of coke is low.

Example 2

[0154] The refining process considered in the present example is a slurry-phase hydroconversion process.

[0155] Catalytic tests in an autoclave reactor were carried out with a pitch feedstock, the characteristics of which are described in table 3 below. The catalyst employed is a fat-soluble molybdenum octoate salt injected at a content of 500 ppm (metal/feedstock ratio). The catalytic tests were carried out at temperatures between 410 and 440° C. and a residence time of between 20 minutes and 170 minutes under 150 bar of hydrogen.

[0156] The low field NMR analysis is carried out on the nonvolatile liquid fraction of the TLP (Total Liquid Product, 170° C.+ cut) effluents. The level of 525° C.+ conversion (or conversion) can be defined as being the ratio:

[00003]$\frac{\begin{array}{c}\%.Math..Math.\mathrm{by}.Math..Math.\mathrm{weight}.Math..Math.\mathrm{of}.Math..Math.\mathrm{the}.Math..Math.525.Math.°.Math..Math.C..Math.+\mathrm{cut}.Math..Math.\mathrm{in}.Math..Math.\mathrm{the}.Math..Math.\mathrm{feedstock}-\\ \%.Math..Math.\mathrm{by}.Math..Math.\mathrm{weight}.Math..Math.\mathrm{of}.Math..Math.525.Math.°+\mathrm{cut}.Math..Math.\mathrm{in}.Math..Math.\mathrm{the}.Math..Math.\mathrm{effluents}\end{array}}{\%.Math..Math.\mathrm{by}.Math..Math.\mathrm{weight}.Math..Math.\mathrm{of}.Math..Math.\mathrm{the}.Math..Math.525.Math.°.Math..Math.C..Math.+\mathrm{cut}.Math..Math.\mathrm{in}.Math..Math.\mathrm{the}.Math..Math.\mathrm{feedstock}}$

[0157] A graphical representation of the Gaussian fraction defined above is plotted as a function of the level of 525° C.+ conversion, as represented in FIG. 2. This level of conversion is adjusted by varying the reaction temperature and the reaction time.

[0158] In this graph, it is seen that the Gaussian fraction reaches a plateau from a level of conversion equal to approximately 70%. This means that the Gaussian fraction is substantially constant from this degree of conversion, which indicates the imminent formation of coke. It is thus possible to direct the process by watching the Gaussian fraction of the effluent and to act on the parameters of the process in order to keep this Gaussian fraction in a value range where the risk of formation of coke is low.

TABLE-US-00002 TABLE 2 characteristics of the feedstock of example 1 Ural VR TBP cut 450-750° C. SP-160° C. (% by weight) 0.0 160-350° C. (% by weight) 0.0 350-525° C. (% by weight) 2.6 +525° C. (% by weight) 97.2 Density at 15° C. (kg/m.sup.3) 1031.8 CCR (% by weight) 21 Viscosity 100° C. in cSt 4189.0 Viscosity 135° C. in cSt 458.5 Elemental analysis Carbon (% by weight) 85.50 Hydrogen (% by weight) 10.24 Nitrogen (% by weight) 0.74 Oxygen (% by weight) 0.52 Sulfur (% by weight) 3.14 Ni (ppm) 72 Va (ppm) 280 Chlorine (ppm) 15 TAN in mg KOH/g 0 Basic nitrogen (ppm) 2046 S-value (standard ASTM D7157) 4.42 Sa 0.77 So 1.02 Xylene sediments (ppm) (standard ISO10307-2) 316 Asphaltenes (% by weight) 7.00

TABLE-US-00003 TABLE 3 characteristics of the feedstock of example 2 Description C3-C4 pitch TBP cut 470-750° C. SP-160° C. (% by weight) 0 160-350° C. (% by weight) 0 350-525° C. (% by weight) 7.13 +525° C. (% by weight) 92.88 Density at 15° C. (kg/m.sup.3) 1093.2 Elemental analysis S (% by weight) 5.61 H (% by weight) 9.15 Fe, ppm 17 Ni, ppm 58.6 V, ppm 173 CCR (% by weight) 30.14 Ntotal, ppm 3582 Nbasic, ppm 1671 S-value (standard ASTM D7157) 5.06 Sa value 0.75 So value 1.29