CA1286521C - Rapid determination of asphaltene content and device therefor - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A method for determining an asphaltene content in a heavy hydrocarbon oil and a device therefor are disclosed.
The method comprises measuring absorbances of a sample solution having dispersed therein asphaltene particles at two different wavelengths selected from the range of from about 300 to 1000 nm and obtaining an asphaltene content from the measured values utilizing a relationship between known asphaltene contents and absorbances. The device comprises a dip probe to be dipped in a sample solution or a flow cell in which a sammple solution is made to flow, a two-wavelength absorbance detector by which absorbances of the sample solution at two different wavelengths are detect-ed and converted to electrical current values, and a com-puting means for converting the current values into an asphaltene content. The method and the device realize automatic asphaltene determination on a large number of samples in a reduced time per sample with high precision.

Description

RAPID DETERMI~ATION OF
ASPHA~TE~E CONTENT A~D DEVICE THEREFOR

IELD OF THE IMVENTIOM
This invention relates to a method o~ rapid determination of asphaltene content in heavy hydrocarbon oils, such a~ long residue, short residue, hydrocracked oil, thermally cracked oil, shale oil, tar sand oil, etc., and to a device for automatically carrying out such determination BACKGROUND OF THE INVE~TION
An asphaltene content in heavy hydrocarbon oil~ lS
: not only an indica~ion of combustibility and storage stabil-ity of heavy hydrocarbon oils but also an impor~ant: factor greatly influencing catalytic activity in a direct: disul-furization process. Therefore, it is required to carry out determination of asphaltene content in heavy hydrocarbon oils rapidly and precisely from considerations of product control and proces~ control.
Determination of asphaltene content (i.e., weight content o asphaltene) has been commonly carried out based ~ on a method of The Institute of Petroleum ~IP 143, herein-; . after referred to a~ IP method). IP method compri~es dis solving a sample in a pre~cribed amount of warm n-heptane, filtering the resulting mixture using a filter paper, washing an in~oluble matter collected by iltration with heptane at reflux in a Soxhlet'~ extractor, extracting the . : ' : -- 1 --~ ~ ' :: ~ , . ., . . , ... .. : .

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insoluble matter with toluene in the extractor, and deter-mining the extracted soluble matter. However, since the IP
method involves complicated operations and requires much time as long as 9 hours for analysis, it has been partly replaced by a method of Universal Oil Product Co. (UOP
614/80, hereinafter referred to as UOP method), in which a sample di~solved in a prescribed amount of warm n-heptane is filtered through a membrane filter and the insoluble matter collected on the filter is determined as an asphaltene content. The UOP method, however, still requires about 4 hours for analysis, and the measured values do not agrea with those obtained by IP method. Accordingly, it has been demanded to develop a simple and rapid method of asphaltene determination which gives measured values in good agreement with IP values.
Methods of rapid determination of asphaltene content so far proposed include (1) Ono method (Tastuo Ono, J~ of Japan Petrol. Inst., Vol. 14, ~o. 9, 504 (1971)), (2) ab-sorptiornetric methods (Tsutomu Kaibara et al., J. ~f Japan Petrol~ Inqt., Vol. 23, No. 3, -178 ~1980)) and Michel Bou~uet et al., Fuel, Vol. 64, 1625 tl985)), and (3) hydrogen flame ionization detection thin-layer chromatogra-phic methods ~FID-TLC) (Marc-Andre Poirier et al., J. of Chro~atographic Science, Vol. 21, No. 7, 331 (1983) and Yojiro Yamamoto et al., J. of Japan Petrol. Inst., Vol. 27, -,' ' ' : .. , ~o. 3, 269 (1984)).
The Ono method comprises the same pxocedures as IP
method except for omitting the toluene extraction, and the time required for analysis and measured values arP sub-stantially equal to those of t~e UOP method.
The h~drogen flame ionization detection thin-layer chromatographic method by ~amamoto et al. comprises spotting a sample ~olution on a silica ~el thin layer rod, developing the sample with a solvent, e.g., toluene, to separate asphaltene, and determining the asphaltene content by mean~
of a flame ionization detector. Although this methoa ~ : `
suaceeded to furnish measured values in correlation with I
values and to reduce the time re~uired for analysis to 30 to 60-minutes per 10 samples, it has disadvantages in that an ; 15 anal~st should always scan the system throughout measuremen~
and that analysis precision greatly depends on de-~elopment ¢onditions, resulting in poor reproducibility.
The absorptiometric method ~y Kaibara et al. com-prises dissolving a sample in n-heptane, measuril-lg absor-~0 bance o~ the solution at a wavelength of 700 nm by means ofa spectrophotometer, further measuring absorban~e of a iltrate obtained by filtration o the solution at a wave-length of 700 nm, and obtaining an asphaltene concentration ; from a difference in absorbance of the solution between before and after the iltration. According to this method, ':

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the time required or analysis is reduced to about 30 min-utes. However, the operation of filtration is complicated, and the measured values, though correlating with IP values, has a coefficient of correlation of 0.979, that is l~wer than a generally acceptable coefficient of correlation, i.e., not less than 0.99.
According to the method by Michel et al., .a sample is dissolved in toluene, and absorbance of the solution at a wavelength of 750 nm is measured. n-Heptane i5 added to another sample separately taXen from the same oil. while stirring, and asphaltene thus precipitated is removed by iltration. The resulting solution containing no asphaltene : i5 determined for absorbance at 750 nm using n-heptane as a control solu-tion. The asphaltene concentration is then obtained from a difference in absorbance between the two solutions. This method allows determination o~ asphaltene concentrations of up to 40~ by weight, but still requires complicated ~iltration operation.
SUMMARY OF THE I~VENTIO~
One object o this invention is to provide ~1 method o asphaltene determination by which asphaltene o a wider range o concentration can be determined more rapidly as compared with the conventional method~.
Another object of this invention is to provide a method o~ asphaltene determination by which a number o :
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samples can be analyzed surely and rapidly without requiring filtration operation.
A urther object o~ this invention is to provide a device for carrying out the above-described asphaltene determination.
It has now been found that the above objects can be accompli~hed by combining a means of sample preparation for precipitation of asphaltene and two-wavelength abscrptiome-try and by using a measurement device system composed of a sample feeder, a two-wavelength absorbance detec~or, and a microcomputer connected thereto. ~-BRIEF DESCRIPTIO~ OF THE DRAWINGS
- Figure 1 is an absorption spectrum each of a sampl2 solution and a sample solution having been filtered in a visible region.
Figure 2 is a sc~ematic view of the automatic determination device according to a dip probe syste~ of the present invention.
Figure 3 is an enlarged view of the two-wavelength -~
absorbance detector used in the device of Figure 2.
Figure 4 i~ a schematic view o~ the automatic determination device according to a ~low cell sy~tem o~ the present invention.
DETAILED DESCRIPTXON OF THE INVENTION
2S According to the general aspect of the present :` :

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invention, therefore, there is provided a method for determining an asphaltene content in a heavy hydrocaxbon oil, which comprises measuring- absorbances of a sample solution having dispersed therein asphaltene particles which is prepared from a sample oil to be determined at two wave-lengths selec-ted from a wavelength region of from about 300 to 1000 nm, and obtaining an asphaltene content of the sample oil from the measured values utili~ing a relationship between known asphaltene contents and absorbances at two wavelengths. According to the present invention, there .is also provided a device for determining an asphaltene content in a heavy hydrocarbon oil, which comprises a dip ~probe or flow cell for sampling a sample solution having dispersed therein asphaltene particles which is prepared from a sample oil to be determined, said dip probe or flow cell being set so as to face with the sample solution and being movable with up-and-down strokes so as to be in contac' with or apart from the sample solution, a two-wavelength al~sorbance detector including a light source, passages for light~to allow the light from the light source to pass 1:hrough a sample solution o~ a given thickness introduced in the dip probe or 10w cell, two interference filters each capable of tran3mitting the light having transmitted through the sample solution having a different wavelength selected from a range 2S of from about 300 to 1000 nm, and light-current transducers ~ - 6 -~, .

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each capable of converting the intensity of each of incident light and transmitted light having two different wavelengths into an electrical current, and a computing means capable of converting the electrical current values into an asphaltene content. This device can fur-ther include a means for con-trolling the dip probe or flow cell, two-wavelength absor-bance detector, and computing means so as to successively carry out determination of a plurality of sample solutions A basio technique o~ the determination method according to the present invention is as follows~ An appropriate amount (G) of a sample oil is weighed, and a ; prescribed amount of a solvent is added thereto, ~ollowed by ~tirring. The solution is then placed under prescribed conditions hereinafter described so as to precipitate asphaltene particles in particle size distribution as narrow as possible to prepare a sample solution having ~ispersed therein the asphaltene particles. Light is tr~nsmitted through the solution, and optical densities (hereinafter referred to as absorbance(s)) of the sample solution at two dif~erent wavelengths within a range o~ rom about 300 to 1000 nm. The absorption spectrum o~ the above-described ~ample ~olution having disper~ed therein asphaltene par-~icles in the wavelength region o from about 300 to 1000 nm does not have its maximum and shows a tendency of substan-tially linear drop in accordance as the wavelength becomes .~

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longer. Fig. 1 illustrates the principle of the determina-tion method according -to the presen~ invention, in which the axis o abscissa indicates a wavelength of light (nm) and ~he axi.s of ordinate indicates an absorbance. In Fig. 1, the solid line is the absorption spectrum of the sample solution before removal of asphaltene, while the dotted line is an absorption spectrum of the sample solution after removal of asphaltene.
Since the asphaltene particles do not substantially transmit light in a wavelength region o~ from about 300 to 1000 nm, the absorbance of a sample solution from w~ich the asphaltene particles have been removed by any means, such 2S
filtration, is lower than that of a sample solution before asphaltene removal by the absorbance correspondins to the asphaltene content. More specifically, it has been confirm-ed ~hrough investi~ations on various heavy hydrocar~on oils that there is a first-order correlation between (i) a ratio o (a diference between absorbance K4 of the sample solu~
tion before removal of asphaltene particles at wavelength ~
; 20 and absorbance K3 of the same solution at wavelength ~1) to absorbance K3, i.e. t (K4~K3) x 100/K3, (hereinafter referred to a~ rate of increase) and (ii) a ratio of absorbance Kl of ; the sample solution a~ter removal of a~phaltene particles at wavelength ~1 to absorbance K3, i.e., Kl x 100/K3, (herein-after referred to as blank rate) even if the kind or , ~; ' .

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asphaltene content of oil changes.
Therefore, absorbance Kl of a maltene ~soluble matter) at wavelength ~1 can be obtained by measuring absor-bances o a sample solution as having dispersed therein asphaltene particles at' two different wavelengths appro-priately selected and inserting the measured values 'in the correlation o rate o increase with blank rate. Further, absorbance K5 of the asphaltene particles can be ~btained rom a difference between K3 and Kl. ' ' Thus, once a calibration curve is prepared from a standard asphaltene, which is preferably prepared in accor- -dance with IP method or by a centrifugal separation tech nique, a weight of asphaltene (g) corresponding to absor-r . bance K5 is first obtain~d from the calibration cu:rve, and an asphaltene content of a sample oil is then obtained through equation:
' Asphaltene Content - g x 100/G twt%) ~1) :~ . . .
The asphaltene content may also be obtained by using one ca~ibration curve from ab~orbance~ K3 and K~. In this case, ~uch a calibration curve is based on a ~irst-order correlation between an absorbance ratio K4/K3 and a ratio of ~' ' gram of asphaltene ~g) in a sample ,solution to absorbance ~.
K3', g/K3. The asphaltene,gram in the sample solution can be _ 9 _ ... . .
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obtained in the same manner as described above.
Accordingly, if a relationship between the ratio K4/K3 and the ratio g/K3 for a known sample is once estab-lished, subsequent asphaltene determi.nations can be effected simply by measuring absorbances K3 and K4, obtaining an asphaltene weight g from a previously prepared calibration curve, and calculating an asphaltene conten-t from equation (1) ' In accordance with the above-described method of determination, determined values of about 50 kinds of heavy hydrocarbon oils having asphaltene contents between about 0.1 to about 30~ by weight correlate with IP and UC)P values with a coefficient of correlation o 0.99 or more and, in addition, with a coefficient o variation of 5~ or less, which indicates excellent analytical precision as compared with IP method having a coefficient of variation of 10% or less. Time required for a cycle of analysis is abou~ ~0 minutes:. However, since a large number of samples may be subjected to analysis all at once, the requisite time per sample is markedly reduced when compared with conventionally proposed rapid determination methods. For example, when ten samples are analyzed al} at once, the requisite time per ~ample is 10 minutes at the longest.
;I The preerred embodiment in carrying out the present invention will be described below.
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analy~ed, asphaltene particles present in a sample oil can be precipitated as fine particles with a narrow size dis-tribution by following specific procedures hereinafter de-scribed. The particle size and its distribution of precipi-tated asphaltene particles have great inEluences upon themeasurable range of asphaltene contents and precision of measurements in the subse~uent two-wavelength absorptiome-try. The sample solution should be stirred throughout th~
measurement so as to prevent sedimentation of asphaltene particles in the solution thereby to stably maintain the state of uniform dispersionO Light from a light source is led by optical fibers to the sample solution as incident light and then transmitted through the solution having a given thickness. Absorbances (optical densities~ of the sample solution at two different wavelengths within a range o from about 300 to 1000 nm, and preferably from about 50 to 1000 nm, are measured.
Intensity of each of the two transmitted light rays having diferent wavelengths is converted into an electrical ~0 current value by means of a light-current transducer, which is then put into a computer having a pre~cribed program I thereby to print out an asphaltene content in the sample oil.
The above-mentioned two-wavelength absorbance detec-tion can be carried out by either a dip probe system or a -~ , . .. . . . .
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flow cell system. In the former system, a dip probe equip-ped with an opening and a reflector at the end is dipped in a sample solution, and incident light and transmitted light are led through optical fibers incorporated in the probe.
S In the latter system, a sample solution is introduced by suction in a flow cell, with optical fibers for leading incident light and those for leading transmitted light being fixed on opposite sides of the flow cell. In either case, once a plurality of different sample solutions are prepared in advance, asphaltene contents of sample oils can be determined efficiently in a successive manner. It should ba noted, however, that it is necessary to wash the dip probe or flow c-ell with a washing solvent after every measurement to remove any remaining sample solution attached thereto.
The above-described operation can be controlled under a computer program at a great saving of labor.
The process for preparing samples whicn can be analyzed in the present inven-tion comprises pLacing an appropriate ~mount (e.g., from 0.3 to 5.0 g) of a sample oil - 20 in a beaker having a prescribed volume ~e.g., 100 ml), add-ing a small amount (e.g., rom 0.3 to 5.0 ml, and pr~ferably 1.0 ml~ of an aromatic hydrocarbon solvent (e.g., toluene) to the beaker to dis~olve the content, further adding a prescribed amount ~e.g., 100 ml) of an aliphatic hydrocarbon solvent (e.g., n-heptane) to the solution while stirriny to ,1 , .
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precipitate asphaltene, and allowing the contents of the beaker to cool at room temperature, preferably at a tempera-ture of from 15 to 30C, for about 30 minutes. The ali-phatic hydrocarbon solvent used above may be heated to a temperature of from about 40 to about 90C, and preferably 80~C. The aromatic hydrocarbon solvent to be used lncludes benzene, toluene, and xylene. The aliphatic hydrocarbon solvent to be used includes those having from 5 to 12 carbon atoms, such as pentane, hexane, heptane, octane, etc.
In order to ensure dispersion stability of the asphaltene particles by preventing a tendency of sedimenta-tion, the sample solution may further contain a surface active agent, a dispersant for engine oil, etc.
By the above-described process of preparing ~ sample 15 solution, asphaltene particles having a narrow size dis-tribution between about 1 ~m and about 3 ~m can be formed, which brings about great effects to widen the range of measurable asphaltene concentrations and increase precisîon in the subsequent two-wavelength absorbance detection.
The thus prepared sample sslution having dispersed ; therein the asphaltene particles i8 subjected to absorbance measurement, while being ~tirred by means of a magnetic stirrer, and the like, at two wavelengths being at a tance of at least about 50 nml and preferably rom about 2S 50 to lS0 nm, for example, at an analytical wavelength o `''`~ ' ' . `', ..

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800 nm and at a control wavelength of 675 nm. If the distance between the two wavelengths is less than about 50 nm, determination precision becomes poor.
Referring to Fig. 1, when the absorbance of a sample S solution at an analytical wavelength of 800 nm (K3) and that at a control wavelength of 675 nm (K4) are found to be 1.10 and 1.98, respectively, then the equation for rate of increase gives ~K~-K3) x 100/K3 = 80Ø From the correla-tion between rate of increase ana blank rate, one may obtain a blank rate of 29.1~ It follows that Kl ~absorbance o~ a maltene after removal of asphaltene at 800 nm) - 0~?2.
~ Therefore, K3 - Kl (absorbance of asphaltene) = K5 = 0.73.
; The weight of asphaltene can be obtained from a calibration curve of absorbance K5 and asphaltene weight g. From this value, the asphaltene content in the sample ~il can be obtained.
Table 1 below shows results of asphaltene determina-tions in accordance with the dip probe system of the present invention ln comparison with values obtained ~)y conven-~ionally Xnown determi.nation methods. It can be seen from~able 1 that the method and device in accordance with the presen~ inven~ion make it possible to determine a wide range o~ asyhaltene contents at high precision of analysis.
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The measured values given in Table 1 above were computed in accordance with the second me~hod of calculation using the relationship between K4/K3 and g/K3. In this particular case, there is established an equation:

Asphaltene Content (wt%) = 0.0287xt2.43K3-K4) x 100/G

; The coe~icient of variation in ~able 1 was calcu-lated for 6 mea~urements from equation:

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Coefficient of Variation (%) = (Standard Deviation e~pressed in Square Roo~ of Un~iased Variance) x 100/Mean When determinations are carried out on the same ~:
samples as used in Table 1 by a flow cell system according to the present invention, ~he results obtained are sub-stantially equal to those of Table 1.
The devices which can be used in carrying out ~he asphaltene determination of the invention will be illus-trated below.
I~ Dip Probe S~stem:
When a container containing a stirrer o~ a ~magnetic stirrer and a sample solutlon is carried to a predetermined position where the sample solution and a dip probe face to each other ~location of measurement), the magnetic stirrer - :
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is caused to rotate to agitate the sample solution and, at the same time, the probe and/or the container goes up or down whereby the end of the probe, i.e., the measurement part, is dipped in the sample solution to a depth necessary 5 and sufficient for absorbance measurement.
The dip probe contains therein optical fiber bundles leading incident light and transmitted light, respectively.
IJight having transmitted through the sample solution is passed through two interference filters differing in wave length that are placed in parallel at the outlet of the optical fiber bundle for transmitted light, wher~ optical densities ~absorbances) of the sample solution are deter~
mined at two dif~erent wavelengths falling wi~hin a range of from about 300 to 1000 nm.
The intensity of the light having transmitted through each filter is converted into electrical current by a light-current transducer, such as a phototube, a photo-cell, etc., and the resulting current value is introduced into a computer having a specified program to perform an 20 operation to print out the asphaltene content in the sample oil.
Upon completion of asphaltene determination, the dip probe and the container are æeparated from each other under instructions from the computer, and an electromagnetic valve ¦ 25 of a washing means is opened also on instructions of the . , ,~
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computer thereby to ~et a washing solvent fed from the washing means against the probe to wash away any sample solution attached to the measurement part of the probe. The washing solvent is introduced in the container containing the sample solution having been analyzed. After thorough washing of the probe, the electromagnetic valve is closed to stop washing, and the container is removed rom the location o measurement, while a container containing another sample solution and a magnetic stirrer is successively placed on the location of measurement. Through these procedures, one cycle of asphaltene determination is completed.
Figs. 2 and 3 show schematic views of a device which can be used for performing dip probe system asphaltene determination. Fig. 3 represents an enlarged vi~w of the dominant part of Fig. 2. In these figures, two-w~velength absorbance detector 1 is composed of a photometry ]?art com-prising light source 2 (e.g., a tungsten lamp), interference filters 3 (e.g., 675 nm and 800 nm), phototube (or solar cell) 4, and amplifier 5 and a measurement part (,i.e., dip probe 7) contained in elevator 6, both parts being connected to each other via optical iber bundle 8 for incident light and optical fiber bundles 9 for transmitted light. For details o the photometry part Fig. 3 can be referred to.
Dip probe 7 has an opening te.y., 3 mm in height and 8 mm in width) and reflector 10 at the lower end and is held by ~' ' ' . ' ' ' '~
~ , ' ' ' ' 2~ -holder 11 of elevator 6 (shown in Fig. 2). Probe 7 goes down to enter in a sample solution on measurement and goes up to stand apart from the sample solution during washing and rotation of turn table 12.
By reference to Fig. 2, elevator 6 is equipped with nozzles 13 for washing the dip probe that are aligned in a ring around ~he probe and connected to washing solvent-containing tank 16 equipped with miniature compressor 14 and electromagnetic valve 15 via a Teflon tube. Elevalor 6 is fixed to automatic sample feeder 17 having turn table 1~
(e.g., sett~ng 12 beakers~ and a magnetic stirrer at ~le location of measurement. Starting and stopping o~ elevator 6, miniature compressor 14, and turn table 12, ancl openiny . ~. . . .
; and closing of electromagnetic valve 15 are all controlled under instructions from microcompu~er 18. The current out~
put from two-wav01en~th absorbance detector 1 is introduc~d in the microcomputor, where the current is converted into an asphaltene content which is then printed out by printer 19~
More specifically, the magnetic stirrer of automatic sample feeder 17 starts to rotate at `a signal from micro-computor 18 to agitate a sample solution in a beaker set on a location o~ measurement. At the same time, elevator ~
starts to let probe holder 11 down so that the opening of the pxobe may be dipped in the sample solution. Light rays emitted rom light source 2 of two-waveleng~h absorbance ' -- ].9 --' `' . - ' ' ~ 6~2~ ~

detector 1 pass through optical fibers 8 ~or incident light to reach the dip probe and transmit through the sample solution from the opening. The light is partly absorbed in the sample solution and partly reflected on reflector 10.
The reflected light is again absorbed in the sample solution and passes through optical fibers 9 for t~ansmitted light to reach intererence filters 3, where transmitted light rays having two wavelengths are chosen by two interference filters 3 and each is converted into electrical current by respective phototube 4, amplified by respective amplifier 5, and then introduced in microcomputor 18.
In m.icrocomputor 18, the current input is conver~ed into transmittance T (ra-tio of transmitted light I,/incident light Io)~ which is then converted into absorbance K
(log101/T). The resulting absorbance values are applied to a correlation of rate of increase-blank rate and a calibra-tion curve of absorbance difference K3-Kl vs. a:phaltene content that have previously been put in the computor to calculate an asphaltene content, which is then put in printer 19. At the same time, the thus obtained asphaltene conkent is converted into an IP asphaltene contenk and an UOP asphaltene content by using a previously incorporated correlationships between asphalten~ content o the invention and that of IP method and between asphaltene content o the invention and that of UOP method. Upon completion of input, ' ,~
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~ignals are issued from microcomputor 18 to start miniature compressor 14, whereby the inner pressure of tank 16 is increased. Subsequently, elevator 6 starts to move, and as probe holder 11 goes up, electromagnetic valve 15 is opened to let a washing solvent (e.g., n--heptane) spout from nozzles 13 to clean dip probe 7.
Then, turn table 12 of automatic sample ;eeder 17 again starts to move to set the next sample solution to be analyzed on the location o~ measurement, and the same operations as described above are automatically repeated.
In the case where measurements are made on samples that are not easily washed of~ by jetting a solvent from nozzles, cLeaning effects may be assured by feeding a sample ~olution-containing beaker and a beaker containing a washing lS solvent (e.g., toluene) alternatingly on the turn table 12.
II. Flow Cell System~
A flow cell system device wherein a flow cell is used in place of the dip probe works in the sa~e manner aS
described or ~he dip probe system device except that the ends of optical iber bundles guiding incident light and transmitted light, respectivel~, are fixed to both sides ~
transparent 10w cell 80 as to face to each other and that the washing meanq as used in the dip probe sy~tem is re-placed with a pumping means to withdraw a sample solu~ion havin~ been analyzed.

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According to the ~low cell system, when the end of a suction pipe connected to a flow cell is dipped in a sample solution, the sample solution is introduced in the suction pipe by the action of a vacuum pump and then made to fl~w in the flow cell. Absorbances of the sample solution are measured while the solution stream passes between two ends of optical fiber bundles guiding incident liyht and tra~s-mitted light, respectively. The sample solution is then withdrawn into an enclosed waste liquor reservoir. The ; ~ 10 waste liquor reservoir is evacuated by removin~ a:Lr with a vacuum pump so as to permit the next sample solution be sucked into a suction pipe at a predetermined ~low xate.
- The evacuation is conducted via a cold trap so as t:o prevent contamination of the pump due to the waste liquor and gas.
After every de~ermination, any remaining sample solution attached to the suction pipe, flow cell, etc. can be washed away by replacing the beaker containing the sample solution with a container containing a washing solvent. Theref~re, the flow cell system eliminates the need of an independent washing means as required in the dip probe system.
Figure 4 illustrates a schematic view of a device for determining asphaltene content9 accordiny to the flow cell ~ystem. Elevator ~ starts to move at a signal from microcomputer 18, whereby flow cell 20 (e.g., a glass-made cell having a thickness of 3 mm) held by 10w cell holder 21 ',,: -. ,' : '' : ' ': ' ' ' ', ' : , .
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gne~ ~wn un~;' t~e en~ ef ~U~ pip~ 2~ (e.g. ~ fll~rin~-cont~ining po~ymer pipe having an inner diameter of 2 mm) connected to the lower end of flow cell 20 reaches a s~nple ~olution while being stirred with a magnetic stirrer, which i~ ~et on automatic sample feeder 17 at a location of measurement.
Vacuum pump 23 is then ~tarted to suck the sample ~olution at a certain flow rate (preferably from about 10 to 30 ml/
min) due to reduced pressure appropriately adjusted by means of pressure control valve 24. While the sample solution passed through flow cell 20, light having transmitted through the sample solution at two wavelengths (e.g., 675 nm and 8U0 nm) i8 detected by two-wavelength absorbance detec-tor 1, where measured intensities of transmi~ted light are converted into electrical current values. The resulting lS current outputs a~e inserted in microcomputer 18, where they are converted into absorbances. The input of current values in microcomputer 18 is preferably conducted after about 20 second~ from the state of vacuum pump 23.
Upon completion of one cycle of determination, ele-vator 6 goes up to lift suction pipe 22 and, ater several second~, vacuum pump 23 i~ stopped. The driving time o~
vacuum pump i~ preferably about 60 seconds. Then, automatic ~ample ~eeder 17 s~arts to cause turn table 12 to rotate, whereby a beaker containing a wa~hing solvent (e.g., toluene) i~ set on the location o~ mea~urement, followed by ; i;~`~

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suction of the solvent with vacuum pump 23 to wash the inner walls of suction pipe 22 and 10w cell 20. Af~er completion of washing, turn table 12 aqain rotates to carry the next sample solution to the location o measurement.
A series o the aoresaid operations is all control-led by programmed microcomputer 18. The re~;ults of asphaltene determinat.ion are succe~sively printed out hy printer 19 upon giv.ing instructions to computer 18.
The sample solution having been analyzecl and the washing solvent are collected in waste li~uor reservoir 25. .
In order to prevent contamination of vacuum pump 2'l, it is preferable to insert cold trap 26 between reservoir 25 ancl :
pump 23.
In Fig. 4, flow ¢ell holder 21 to which ~lo~ cell 20 is fixed and two-wavelength a~sorbance detector 1 are con- i ~;l nected to elevator 6. Flow cell 20 and holder therefor 21 may be fitted at.any position of the pipeline in which a sample solution fed from suction pipe 22 flows and should not be necessarily fixed to .elevator 6. Two~wavelength . 20 absorbance detector 1 also should not be necessari.ly fix~d to elevator 6. ~lat is required is that the end of suction pipe 22 moves with up-and-down strokes so as to be dipped in a. sample solut.ion and then lited. r~here~ore, in cases where 10w cell holder 21 is not ixed to elevator 6, suc-tlon pipe 22 may be ~ixed to elevator 6 at a site near to , ` , , ~ ~i , ', ' ' .

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the end thereof.
As described above, the present invention eliminates disadvantages associated with the conventional methods o determining asphaltene contents in heavy hydrocaxbon oils, such as time requirement per sample, complicated operations, labor requirement, narrow ranges of measurement, unsatis-factory precision in some cases, and the like. In other words, the present invention makes it possible to automat-ically carry out asphaltene determination on a larSIe number of samples in a reduced time per sample with high precision without requiring much labor.
~While the invention has been described in detail and - with reference to specific embodiments t~ereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from tbe spirit and scope thereof.
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Claims (12)

1. A method for determining an asphaltene content in a heavy hydrocarbon oil, which comprises measuring absorbances of a sample solution having dispersed therein asphaltene particles which is prepared from a sample oil to be deter-mined at two wavelengths selected from a wavelength region of from about 300 to 1000 nm, and obtaining an asphaltene content of the sample oil from the measured values utilizing a relationship between known asphaltene contents and ab-sorbances at two wavelengths.

2. A method as in claim 1, wherein the sample solution is prepared by adding an aromatic hydrocarbon to a sample oil to dissolve in each other, adding an aliphatic hydro-carbon to the solution to precipitate asphaltene particles, and allowing the solution to cool.

3. A method as in claim 2, wherein said aliphatic hydrocarbon is warmed to a temperature of from about 40 to 90°C.

4. A method as in claim 3, wherein said aliphatic hydrocarbon is warmed to 80°C.

5. A method as in claim 1, wherein the two wavelengths are selected from a range of from about 50 to 1000 nm.

6. A method as in claim 1, wherein the two wavelengths selected for absorbance measurement are at least 50 nm distant.

7. A method as in claim 6, wherein the distance between the two wavelengths is from about 50 to 150 nm.

8. A device for determining an asphaltene content in a heavy hydrocarbon oil, which comprises a dip probe or flow cell for sampling a sample solution having dispersed therein asphaltene particles which is prepared from a sample oil to be determined, said dip prove or flow cell being set so as to face with the sample solution and being movable with up-and-down strokes so as to he in contact with or apart from the sample solution, a two-wavelength absorbance detector including a light source, passages for light to allow the light from the light source to pass through a sample solu-tion of a given thickness introduced in the dip probe or flow cell, two interference filters each capable of trans-mitting the light having transmitted through the sample solution having a different wavelength selected from a range of from about 300 to 1000 nm, and light-current transducers each capable of converting the intensity of each of incident light and transmitted light having two different wavelengths into an electrical current, and a computing means capable of converting the electrical current values into an asphaltene content.

9. A device as in claim 8, wherein the two wavelengths selected for absorbance measurement are at least 50 nm distant.

10. A device as in claim 9, wherein the distance between the two wavelengths is from 50 to 150 nm.

11. A device as in claim 8, wherein the dip probe or flow cell is provided with a washing means for removing any remaining sample solution attached to the dip probe or flow cell.

12. A device as in claim 8, wherein said device further includes a means for controlling the dip probe or flow cell, two-wavelength absorbance detector, and computing means so as to successively carry out determination of a plurality of sample solutions.