Note: Descriptions are shown in the official language in which they were submitted.
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
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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,
-
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~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
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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
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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.
'~ In the preparation of a sample solution to be
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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
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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:
:
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
- 18 -
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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
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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
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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
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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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