FR2578979A1 - Method for rapidly determining the stability of petroleum residues and of fuel oils, as well as apparatus for implementing this method - Google Patents

Abstract

Method and apparatus for rapidly determining the flocculation of the products contained in fuel oils, in particular in visbreaking effluents. The apparatus comprises a mixing container or receptacle 100 connected by a sampling pipe 101 to the line 102 of the product to be analysed, and furthermore connected by two supply pipes to a tank 104 of solvent and to a tank 105 of non-solvent as well as a cell 20 of a device 110 for detecting the flocculation threshold and means 113 for measuring the quantities of product to be analysed, of solvent and of non-solvent supplied to the container.

Description

PROCESS FOR THE QUICK DETERMINATION OF THE STABILITY OF RESIDUES
OILERS AND OIL, AS WELL AS APPARATUS
FOR THE IMPLEMENTATION OF THIS PROCESS
The present invention relates to a process for the rapid determination of the flocculation of the products contained in visbreaking effluents and, more generally, in fuel oils. It also relates to an apparatus for implementing this process, in particular in a processing unit.

We know the value of a method for rapidly determining the flocculation of the products contained in visbreaking effluents and more generally in fuel oils. These flocculable species indeed condition the stability and compatibility of the fuel oils produced. One can consult on this subject the article "The behavior of asphaltene-hydrocarbon systems: an important factor for the stability and compatibility of residual fuel ojis" (written by WJ van Kerkvoort,
AJJ Nieuwstad and M. van der Waarden (Koniklijke / Shell lab. Amsterdam) and published in IV Cong. intern. ind. heating Paris 1952. Preprint
N 220, 8pp).

 Different tests have been proposed, tending to translate the phenomena of instability linked to the precipitation of flocculable products.

Some tests use the principle of filtration (ex. SHFT test: "Shell hot filtration test"), others sedimentation properties (Centrifugation test), others still rely on liquid chromatography on paper (Test ASTM D 2781).

 The tests using the principle of filtration are relatively long to implement (several hours, even 100 hours). They also require prior fluxing with diesel fuel in order to adjust the viscosity of the product to an acceptable value. This sensitivity to fluxing can lead to very different results depending on the final viscosity chosen and the nature of the diesel. Finally, these tests.

involve a large number of manipulations and weighings; they are difficult to automate and cannot be used directly on the operating site.

 Sedimentation tests also require prior dilution. They therefore have the same drawbacks as the filtration tests as to the nature of the fluxing agent. They last 2 to 5 hours.

 As for liquid chromatography tests on paper, they use either "straight run" diesel fuel (ASTM D 2781) or solvent / antisolvent couples with variable dilution rate, but independent of viscosity. In the latter case, the influence of the nature of the flux is overcome. The results are obtained relatively quickly (from ten minutes for simpl.fiSs tests to two hours for complete tests).

Their principle however calls for a visual observation, from which it follows a certain subjectivity of the results. The very nature of the analytical support makes automation difficult.

 The present invention uses the principle of the appearance of a flocculation threshold in a solvent / antisolvent mixture for a certain proportion of antisolvent; it provides a process allowing the implementation of an apparatus by which it is possible to automatically and continuously monitor the appearance of the flocculated products.

To clarify the role of the solvent / antisolvent couple, it should be remembered that a "heavy" petroleum product is composed of three kinds of products:
1. "Asphaltenes", products which tend to flocculate.

2. "Resins" which, when they are in quantity and quality
sufficient, peptize the asphaltenes (keep them in solution
tion).

 3. The "oil", the lighter remaining fraction constituting the solution.

 The solvent (xylene for example) does not disturb the weak bonds allowing peptization of asphaltenes by resins (due to their strong polarity).

 The other solvent, anti-solvent, on the other hand, (isooctane for example) because of its non-polarity will break the asphaltenes-resins continuity.

 At the appearance of the flocculate, the solvent-antisolvent ratio which caused the precipitation reflects the importance and the quality of the asphaltene-resin bonds. This is to say that if little antisolvent causes precipitation, the quality and / or quantity of the peptization bonds is / are weak and the product tends to be unstable; if, on the contrary, a large amount of antisolvent is required, these bonds are strong and / or numerous and the products stable.

Solvents are generally polar:
xylenes (aromatic)
carbon tetrachloride, CC14 methylnaphthalenes
Apolar anti-solvents are generally paraffins:
Heptane,
Isooctane,
Decane.

 ie method according to 1 invention for the rapid determination of the flocculation of the products contained in fuel oils uses the principle set out above and is characterized in that a sample is made of a mixture of the fuel oil to be analyzed and of a solvent at a chosen level of dilution, in that an anti-solvent is continuously added to this sample so as to precipitate the flocculable products, in that the flocculation threshold is detected and determines the amount of antisolvent added up to at the appearance of this threshold which is then quantified by the ratio: solvent / (solvent + antisolvent), indicative of the quality of the petroleum product analyzed, reported on a scale of 0 to 10 solvent / antisolvent.

 In one form of implementation of the method according to the invention for the detection of the flocculation threshold, the entire image of a light source is focused on a screen through a cell containing the sample of the mixture, collects on a large surface photoelectric detector disposed behind the screen the light flux diffused by said sample when flocculated products appear there and we observe the growth of the electric current delivered by this detector as a function of the volume of antisolvent.

This form of implementation is directly derived from the process described in the French patent application 84 09 127 filed on June 12, 1984 by the applicant for "Process and device for determining the cloud point of a gas oil".

 It allows automation of the measurement and can use a device which is also derived from the device described in the patent application mentioned above, this device comprising a light source and, aligned on the same axis, a diaphragm having a central hole. on said axis, an objective forming the image of the hole on a light trap and, behind this screen, a large diameter photoelectric detector capable of delivering an electric current when it receives a light flux, and, disposed between the objective and the screen, a cell containing a sample of the mixture to be analyzed.

 As will be seen below, this device in which the appearance of a flocculate results in a sudden rise in the current delivered by the detector, is particularly suitable for being used in an apparatus implementing the method according to the invention , for online measurement in a processing unit.

 The apparatus according to the invention is characterized in that it comprises a mixing capacity or container connected by a sampling line to the line of the product to be analyzed, and further connected by two respective supply lines provided with valves. to a solvent tank and to an antisolvent tank, as well as a cell of a flocculation threshold detection device which is arranged on a pipe connecting the sampling pipe to said mixing capacity, a pump circulation being placed on said pipe, the apparatus further comprising means for measuring the quantities of product to be analyzed, of solvent and of antisolvent brought to capacity.

 In a preferred embodiment, these measuring means consist of a balance on which the capacity or the mixing container rests.

 The flocculation threshold detection device is advantageously that derived from the device of the cited patent application.

The characteristics and advantages of the invention will emerge more clearly from the following description, given solely by way of example, with reference to the accompanying drawings in which:
- Figure 1 is a diagram of an apparatus intended for setting
work of the method according to the invention;
- Figure 2 schematically illustrates an embodiment of the
finculation threshold detection device
used in the apparatus of Figure i;
- Figure 3 is a section through a cell fitted to the device
of Figure 2;
- Figure 4 is a partial view on a larger scale of the
Figure 3 ;;
- Figures 5 and 6 are two examples of recording curves
Signai, issued by the device for detecting
Figure 2, as a function of time t.

- Figure 7 is a curve giving for the heavy product of a
example 4, the quality index according to the
dilution X;
- Figure 8 is a linearized form of the curve of Figure 7
using the parameter 1 / X on the abscissa;
- Figure 9 is a recording curve of the signal S in
depending on the volume of iso-octane added.

 In the embodiment chosen and represented in FIG. 1, the apparatus according to the invention comprises a mixing capacity or container 100 connected by a sampling pipe 101 to the line 102 of the product to be analyzed.

 A solvent tank 104 and an antisolvent tank 105 are connected to this capacity 100 by two pipes 106 and 107, - provided respectively with shut-off valves 108 and 109 and supply pumps 118 and 119. A cell detection 20 of a device 110 for detecting the flocculation threshold is placed on a pipe 111 connecting the sampling pipe 101 to the capacity 100 and a circulation pump 112 is placed on this pipe 111. The apparatus further comprises means of measuring the quantities of product, solvent and antisolvent brought to capacity.

 The means consist for example of a balance 113 on which the capacity 100 rests. The content of this capacity can be heated to a temperature chosen in advance by means of an electrical resistance 114.

 For rinsing the capacity, a tank 115 of a cleaning solvent is also provided, connected to the capacity 100 by a pipe 116 with a supply pump 117.

 In operation, after automatic or manual injection of the product to be analyzed by the line 101, the solvent from the reservoir 104 is injected in a necessary and sufficient quantity via the line 106, the whole being able to be checked using the balance 113. The mixture obtained in the capacity 100 is homogenized using the pump 112 and can be reheated to a selected temperature using the resistor 114.

 After homogenization, the addition of antisolvent to the reservoir 105 is carried out through the pipe 107 on a regular basis. Monitoring can also be carried out using the balance 113.

 Upon detection by cell 20 of the appearance of a flocculate as will be seen below, the amount of antisolvent added is measured and allows, using the appropriate formula, to determine the quality of the product. to analyze, fuel oil or residue. The uncertainty linked to the delay between the addition of antisolvent by line 107 and detection by cell 20 is minimized by reducing the distance between capacity 100 and cell 20 and by choosing appropriate flow rates on pumps 112 and 119.

 At the end of the measurement operation, the capacity 100 and the entire circuit are rinsed with the solvent from the reservoir 115 supplied by the pump 117.

 The flocculation threshold detection device 110 is shown in FIG. 2. It comprises a light source 10, for example a microscope lamp, and successively, aligned on the same axis, a diaphragm 11 comprising a central hole 12 on the said axis, this hole 12 having a reduced diameter (for example 2 min), a lens 14 forming the image of the hole 12 on a screen 15, opaque, serving as a light trap, and, behind this screen, a photoelectric detector 16, b large diameter (40 min for example), suitable for delivering a current I, in 17, when it receives a luminous flux.

 The cell 20 containing the product to be analyzed is placed between the objective 14 and the screen 15, this cell, the structure of which is given in more detail below, comprises on the path of the light beam 24, coming from the objective 14, two windows with parallel faces 21 and 22 which do not deflect this beam.

 When the product contained in the tank 20 does not contain flocculated products, all the light coming from the hole 12 is stopped by the opaque screen 15. The detector 16, which receives no light, delivers in 17 an electric current zero or substantially no.

 As soon as flocculent products appear, the light is diffused at the level of the cell (radius 25) and falls on the sensitive part of the detector 16, not masked by the screen 15, this detector then delivering a current I, this latter increasing very quickly depending on the appearance of flocculated products.

 This rapid growth makes it possible to measure with sufficient accuracy for use the volume of antisolvent creating the precipitation of flocculable products.

 The cell 20, in the embodiment shown in FIG. 3, consists of a metallic body 30 of cubic shape pierced right through along one of the axes of symmetry, in order to provide for the passage of light.

 This passage peddles from a central bore 31 and symmetrically with respect thereto a succession of concentric annular bearings 32, 35, 36, 38 which connect bores of increasing diameter 33, 35, 37 La- bearing 38 constitutes the external face of the body 30. FIG. 4 illustrates in detail this arrangement for the left part of the body 30.

 The innermost spans 32 receive transparent circular blades 21 22 with parallel faces, which constitute the windows of the cell 20 and have a diameter slightly smaller than that of the bore 33. Each blade is held in place by a ring 40 which is housed in the bores 35, 27. Means are provided for holding each ring 40 in its housing, for example by screws 43.

 Seals 48, 49 are arranged around the blades 21 and 22 and between them and the rings 40 to provide a sealed chamber 50 between these blades.

 A channel 54 connected to the pipe 111 for supplying the product to be analyzed is formed in the thickness of the body 30 and opens into the chamber 50; an evacuation channel 58 starts from this chamber 50 opposite the channel 54 and is connected to the pump 112.

 The electric current delivered by the detector 17 during the precipitation of the flocculable products is used to control the cycle of operations which has been defined above.

The originality of the process used with the above apparatus resides in the fact that:
1) The determination of the appearance of flocculated substance is measured
"continuous" compared to the addition of antisolvent which causes
this flocculation.

2) Detection itself no longer calls for subjective intervention
from the eye of the operator, but uses the principle that a subs
tance flocculated in a liquid produces the diffusion of rays
luminous which cross it.

3) The sensor itself is "drawn" in such a way that for
very black products "the measurement of the scattered light remains
possible.

This sensor measures this light scattered within the liquid in dynamic circulation.

 The choice of sensor and operating parameters makes it possible to work with a very short response time between the appearance of the flocculate in the solution and the detection in the cell.

 The apparatus according to the invention makes it possible to obtain, in a short time and in a precise manner, a rate of antisolvent causing flocculation.

This speed and this precision give access to a parameter, the peptization index, (as described in the article Oil and
Techniques n 310 - October 1984 by J. ROSSARIE and J. DEVANNEAUX).

Compared to known methods using nephelometry or opacimetry, the method according to the invention has the following advantages:
1) Work in direct light and not at 900, linked to optimization
of the thin cell, increases the intensity
of the transmitted signal and to overcome opacimetry problems
posed by a larger cell.

2) It is not necessary to have a dilution system too
complex.

3) Working in visible light (X = = 0.5 p) is possible thanks to the
low cell thickness and increases intensity
of the signal compared to an infrared operation (x = 1.5 u)
about a factor of 80 (because the variation is in
Examples of use of the apparatus according to the invention are given below without implied limitation.

EXAMPLE 1
10 g of product to be analyzed are introduced into the apparatus and diluted in 50 cm 3 of xylene used as solvent. A certain amount of antisolvent is added. From the curve for recording the cell output signal (cf. FIG. 5), it is possible to determine the quantity of antisolvent necessary to obtain precipitation of flocculable products, ie 37 cm 3.

 From the proportions of solvent and antisolvent, it is possible to determine the quality of the petroleum product to be analyzed, i.e. 5.7 on a scale from 0 to 10 xylene / iso-octane (50 / (50 + 37) .10 = 5.7).

EXAMPLE 2
5 g of product to be analyzed are introduced into the device and diluted in 50 cm3 of chloroform used as solvent. A certain amount of antisolvent is then added (here n-hexadecane). After recording the signal (FIG. 6) from the photoelectric detector, it is possible to deduce the quantity of n-hexadecane necessary to obtain precipitation of the flocculable products, ie 56 ces and to determine the quality of the petroleum product either 4.7 on a scale from 0 to 10 chloroform / n-hexadecane (50 / (50 + 56). 10 = 4.7).

EXAMPLE 3
This example aims to illustrate the effect of the severity of the visbreaking treatment on the stability of the residue and the corresponding development of the quality index. The residue treated with the visbreaker is a vacuum residue of light Arabian crude with characteristics:
. density at 15 C ................. 1.013
. viscosity at 100 C .............. 627 centistokes
. asphaltenes .................... 4.7%
. Conradson carbon .............. 19.6%
The viscosity of the residue is measured at time zero and after forty days of storage at 80 C. The change in viscosity is noted and is calculated as the viscosity 40 days minus the viscosity at time zero relative to the viscosity at time zero and noted in%.

@@ @ - @O
Or: = x 100
vo vo
The quality index is the solvent / solvent + antisolvent ratio
as defined above.

The performances obtained are collated in the table below
after.

Visbreaking temperature (C) 420 480 490 495
Conversion (%) 12 17 25 19 @ v / vo x 100 (%) 1.5 5 22 60
Quality index 4.3 6.2 7.4 8.3
EXAMPLE 4
This example illustrates the determination of the peptization index
of a heavy product. For heavy petroleum products, the appearance
of a flocculate when adding antisolvent depends on the dilution
of this petroleum product in the solvent-antisolvent mixture.

 In a diagram, Quality Index - Dilution, the curve of appearance of the flocculated substance is illustrated in Figure 7.

 As shown in Figure 8, the curve obtained for the quality index can be linearized by placing the inverse of the 1 / X dilution on the abscissa.

The line obtained in Figure 8 provides access to the following parameters:
FR max (quality index at defined dilution).

1 - (X minimum minimum dilution by Antisolvent without causing
X mini flocculation).

1 - FR max = Pa: Peptisability of asphaltenes (1-Pa) P = Po: Peptizing power of the medium
Po / 1 - Pa = P: Peptization index of the product.

Curve 9 illustrates the signal obtained during a practical example of analysis carried out on a residue obtained at the output of the visbreaker:
- curve I: From 5.7 g of residue + 50 ml xylene
- curve II: From 11.1 g of residue + 50 mi xylene
- curve III: From 15.6 g of residue + 50 ml xylene
Under the same operating conditions, 3 volumes of iso-octane are obtained which are necessary for flocculation.

V 1 = 26 ml Quality index 6.6
Y 2 = 32 ml Quality index 6.1
V 3 = 37 ml Quality index 5.7
Plotting the experimental curves will give access to the FR max parameters; 1 s Po; Pa; P
X mini
It should be noted that the method according to the invention ensures a very good correlation with the tests commonly used, but that for those skilled in the art it is more precise and above all allows a much faster measurement.

This measurement method according to the invention lends itself to different applications:
- control of a viscoreducer with downstream and upstream measurements,
- measurement of fuel oil stability,
- measurement of the compatibility of two fuel oils.

 Of course, the present invention is not limited to the embodiments described and shown and it is capable of numerous variants accessible to those skilled in the art without departing from the spirit of the invention. Thus, the balance 113 can be replaced by a metering pump and the apparatus has been described in application to petroleum residues but can be easily adapted by those skilled in the art to other applications.

Claims (7)

 1.- Method for the rapid determination of the flocculation of the products contained in fuel oils, in particular in visbreaking effluents, characterized in that a sample is made of a mixture of the fuel oil to be analyzed and of a solvent chosen level of dilution, in that an antisolvent is continuously added to this sample so as to precipitate the flocculabless products, in that the flocculation threshold is detected and determines the quantity of antisolvent added up to the appearance of this threshold which is then quantified by the ratio: solvent / tsolvant + antisolvent), indicative of the quality of the fuel oil analysis reported on a scale of 0 to 10 solvent / antisolvent.  2. A method according to claim 1, characterized in that, for the detection of the flocculation threshold, the focus is on a screen absorbing the entire image of a light source through a cell containing the sample of the mixture, the light flux diffused by said sample is collected on a large area photoelectric detector disposed behind the screen when flocculable products appear there and the growth of the electric current delivered by this detector is observed as a function of the volume of antisolvent.  3.- method according to one of claims 1 and 2, characterized in that the solvent is a polar solvent chosen from the group consisting of aromatic xylenes, methylnaphthalenes, carbon tetrachloride, while the solvent, apolar, is a paraffin chosen from group 6 - C16, in particular products such as n-heptane, iso-octane, cetane.  4.- Apparatus for the implementation of the method according to one of claims 1 to 3, characterized in that it comprises a capacity or a mixing container (100) connected by a sampling line (101) A the line (102) of the product to be analyzed, and further connected by two respective supply lines (106, 107) provided with shut-off valves (108, 109) to a solvent tank (104) and to a tank the anti-solvent (105) and a cell (20) of a flocculation threshold detection device (110) which is arranged on a pipe 31113 connecting the sampling pipe (101) to said mixing capacity (100), a circulation pump (112) being placed on said pipe, the apparatus further comprising means of measurement (113) of the quantities of product to be analyzed, of solvent and of anti-solvent brought to capacity.  5.- Apparatus according to claim 4, characterized in that the measuring means (113) consist of a balance on which-the rests the mixing capacity (100).  6.- Apparatus according to one of claims 4 and 5, characterized in that it further comprises a reservoir (115) of a cleaning solvent connected to the mixing capacity (100) by a pipe (116) provided a feed pump (117).  7.- Apparatus according to one of claims 4 to 6, characterized in that the detection device (110) comprises a light source (10) and successively aligned on the same axis, a diaphragm (11) having a hole central (12) on said axis, this hole (12) having a reduced diameter, a lens (14) forming the image of the hole (12) on an opaque screen (15), serving as a light trap, and, behind this notch, a photoelectric detector 516) of large diameter, capable of delivering an electric current (I in 17) when it receives a light flux.