U.S. patent number 3,607,073 [Application Number 04/746,487] was granted by the patent office on 1971-09-21 for method and apparatus for analysis of fluid mixtures.
This patent grant is currently assigned to Texaco Inc.. Invention is credited to Ralph E. Stamm.
United States Patent |
3,607,073 |
Stamm |
September 21, 1971 |
METHOD AND APPARATUS FOR ANALYSIS OF FLUID MIXTURES
Abstract
A method and apparatus for continually monitoring a component of
a fluid mixture, such as the naphthene content of a hydrocarbon
mixture. The apparatus includes a microreactor for subjecting the
fluid mixture to a chemical reaction converting, at least in part,
a fluid component of the mixture so as to render the fluid
component of interest separable from the mixture, and detection
means for detecting the fluid component of interest. In a further
embodiment a unique computer is provided coupled with the detector
for computing the concentration of the fluid component of interest
in the fluid mixture. The method of the invention includes reacting
the fluid mixture in the aforementioned chemical reaction, and
detecting the fluid component of interest. In another version of
the method in which the reaction affects more than one component of
the mixture converting the affected components to still another
component of the mixture, the method includes the further steps of
detecting said other component in an unreacted sample of the fluid
mixture and generating a signal representative of the concentration
in the mixture of the fluid component of interest in accordance
with a predetermined relationship between the detected components
of the unreacted sample, the reacted sample, and the concentration
of the fluid component of interest in the fluid mixture.
Inventors: |
Stamm; Ralph E. (Port Arthur,
TX) |
Assignee: |
Texaco Inc. (New York,
NY)
|
Family
ID: |
25001060 |
Appl.
No.: |
04/746,487 |
Filed: |
July 22, 1968 |
Current U.S.
Class: |
436/140; 422/62;
422/89; 436/161; 702/25; 700/268 |
Current CPC
Class: |
G01N
31/00 (20130101); G01N 33/2835 (20130101); G01N
30/8603 (20130101); G01N 2030/8886 (20130101); Y10T
436/212 (20150115) |
Current International
Class: |
G01N
30/00 (20060101); G01N 31/00 (20060101); G01N
33/26 (20060101); G01N 33/28 (20060101); G01N
30/86 (20060101); G01n 031/08 (); G01n
031/10 () |
Field of
Search: |
;23/230,232,253,254
;73/25,190 ;235/151.12,151.35 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
cousins et al., "Dehydrogenation As An Aid To The Mass
Spectrometric Analysis of Naphtenes," Analytical Chemistry, Vol.
33, No. 13, Dec. 1961, PP 1875-1878..
|
Primary Examiner: Wolk; Morris O.
Assistant Examiner: Serwin; R. E.
Claims
I claim:
1. A method for detecting a naphthenes component of a hydrocarbon
fluid mixture consisting of said naphthenes component for detection
and at least a second aromatics component, said naphthenes
component having physical properties sufficiently similar to said
hydrocarbon fluid mixture rendering it difficult to distinguish
from said hydrocarbon fluid mixture, said aromatics component
having physical properties rendering said aromatics component more
readily distinguishable from said fluid mixture, comprising the
steps of:
a. detecting the concentration of said aromatics component in a
sample of said fluid mixture;
b. reacting a sample of said fluid mixture in a chemical reaction
converting at least a portion of said naphthenes component of said
mixture into said aromatics component;
c. detecting the concentration of said aromatics component in said
sample of said fluid mixture subsequent to said reacting step (b);
and
d. generating a first signal representative of the concentration of
said naphthenes component in said fluid mixture by generating said
first signal in response to said detecting steps (a) and (c) and in
accordance with a predetermined relationship relating said detected
aromatics components with the concentration of the same components
in a reference second fluid mixture.
2. The method of claim 1 wherein said detecting steps (a) and (c)
include generating second and third signals representative thereof
respectively,
3. The method of claim 2 wherein said predetermined relationship is
determined in accordance with the steps comprising:
e. detecting the concentration of said second component in a sample
of said reference second fluid mixture and generating a fourth
signal representative thereof;
f. reacting said sample of said reference second fluid mixture in a
chemical reaction converting at least a portion of said first
component into said second component, said reaction being performed
under substantially the same conditions as said reaction of step
(b);
g. detecting the concentration of said second component in said
sample of said reference second fluid mixture subsequent to said
reacting step (f) and generating a fifth signal representative
thereof; and
h. combining said second, third, fourth and fifth signals in a
proportional relationship relating the concentration of said second
component in said sample of said reference second fluid mixture
before and after said reacting step (f) with the concentration of
said second component in said sample of said first named fluid
mixture before and after said reacting step (b) and with said
predetermined concentration of said first component in said sample
of said reference second fluid mixture.
4. The method of claim 3 wherein said second, third, fourth and
fifth signals are combined in said step (h) substantially in
accordance with the following equation:
Y= Y.sub.1 (x.sub.2 - x.sub.1 )/(z.sub.2 - z.sub.1 )
where:
Y = the concentration of said first component for detection in said
first named fluid mixture,
Y.sub.1 = the concentration of said first component in said
reference second fluid mixture,
z.sub.1 = the concentration of said second component in said
reference second fluid mixture prior to said reaction thereof,
z.sub.2 = the concentration of said second component in said
reference second fluid mixture subsequent to said reaction
thereof,
x.sub.1 = the concentration of said second component in said first
named fluid mixture prior to said reaction thereof,
x.sub.1 = the concentration of said second component in said first
named fluid mixture subsequent to said reaction thereof.
5. The method of claim 4 wherein said first and second fluid
mixtures consist essentially of fluid components selected from the
group consisting of aromatics, naphthenes, and paraffins, wherein
said first fluid component of said fluid mixtures consists
essentially of naphthenes, wherein said second component of said
fluid mixtures consists essentially of aromatics, wherein said
reactions of steps (b) and (f) are performed in the presence of a
noble metal catalyst and in the presence of hydrogen for conversion
of at least a portion of said naphthenes to aromatics, wherein said
method includes the further steps of heating said samples of said
first and second fluid mixtures to a temperature in the range of
about 200.degree. to 400.degree. C. at least in part during said
respective reacting steps (b) and (f), and wherein each of said
detecting steps (a), (c) and (g) include the steps of; introducing
each respective sample of said fluid mixtures into a gas
chromatograph column of a sorbent material having a greater
affinity for said aromatics second component of said fluid
mixtures, urging said sample to pass into said column by passing a
carrier gas therethrough permitting the balance of said respective
fluid mixture to pass through said column in a forward direction
while said aromatics second component is retarded therein, sweeping
said column of said aromatics therein by reversing the flow
direction of said carrier gas therethrough, and at least in part
during said sweeping step detecting a physical property of the
effluent of the forward end of said column to detect the
concentration of said aromatics second fluid component in said
respective sample of said fluid mixtures.
6. The method of claim 2 comprising the further step of heating at
least in part during said reacting step (b) said first-named fluid
mixture to a temperature in a range at which said reaction of step
(b) is thermodynamically favored.
7. The method of claim 2 wherein said second component of said
first-named fluid mixture is distinguishable from said first-named
fluid mixture by selective sorbtion of at least one component of
said mixture, wherein said reacting step (b) is performed in the
presence of a catalyst for converting a substantial portion of said
first component into said second component, and wherein said
detecting steps (a) and (c) are each performed by the method of
chromatography.
8. The method of claim 2 wherein said first component for detection
of said first-named fluid mixture consists essentially of
naphthenes, wherein said reactions of step (b) is performed in the
presence of a noble metal catalyst and in the presence of hydrogen
for conversion of at least a portion of said naphthenes to
aromatics, and wherein said method includes the further step of
heating said sample of said first named fluid mixture to a
temperature in the range of about 200.degree. to 400.degree. C. at
least in part during said reacting step (b).
9. The method of claim 8 wherein said first fluid mixture consists
essentially of fluid components selected from the group consisting
of aromatics, naphthenes, and paraffins.
10. An apparatus for detecting a first component of a fluid mixture
from a source thereof, said fluid mixture consisting of at least a
first component for detection and at least another component said
first component having certain physical properties sufficiently
similar to those of said other components rendering it difficult to
separate or distinguish said first fluid component, comprising:
a. means including a chamber packed with a catalyst for subjecting
fluid mixture to a chemical reaction converting at least a portion
of said first component to a second component distinguishable from
said fluid mixture, said chamber having an inlet end and an outlet
end, said inlet-end being coupled with said source of said fluid
mixture for introduction thereof into said chamber said fluid
mixture passing through said outlet end of said chamber after
reacting therein;
b. a source of a carrier gas coupled with said inlet end of said
chamber for carrying said fluid mixture through said chamber;
c. heating means operatively coupled with said chamber (a) for
heating said fluid mixture at least in part during said reaction
thereof in said chamber to a temperature in a range at which said
reaction is thermodynamically favored;
d. means including a gas chromatograph column and a detector
operatively coupled with said outlet end of said chamber (a) for
detecting the concentration of said first component in said fluid
mixture by detecting said first component converted;
e. a source of a reference second fluid mixture having a
predetermined concentration therein of said first component,
and
f. valve means coupled with said source of said reference second
fluid mixture and operatively coupled with said inlet of said
chamber (a) for periodically introducing into said chamber said
reference second fluid mixture for reaction therein and detection
of said first component converted of said second fluid mixture
enabling periodic calibration of said apparatus in accordance with
a proportional relationship relating said detected first component
converted of said reference second fluid mixture with said
predetermined concentration therein of said first component, said
proportional relationship being representative of the relationship
between said detected first component converted of said first named
fluid mixture and the concentration therein of said first
component, said latter concentration being determinable from said
calibration-proportional relationship and said detected first
component converted of said first-named fluid mixture.
11. An apparatus according to claim 10 wherein said valve means (f)
are further coupled with said source of said first-named fluid
mixture and wherein said valve means (f) includes a valve having
first and second operative positions said valve when in its first
operative position permitting flow therethrough of said first-named
fluid mixture for detection of said first component thereof, said
valve when in its second operative position permitting flow
therethrough of said second fluid mixture for calibration of said
apparatus in accordance with said proportional relationship,
wherein said reacting means (a) further comprises:
a. (g) means including a sample measuring valve coupled with said
valve means (f) and operatively coupled with said inlet of said
chamber (a,a) for injecting into said chamber periodic samples of
substantially constant volume of said first and second fluid
mixtures, said sample measuring valve injecting said samples of
said first fluid mixture when said valve means (d) is in its second
operative position; and
a. (h) means including a vaporizer interposed between said sample
measuring valve means (a,g) and said chamber (a,a) and coupled with
said source of a carrier gas (a,b) for vaporization of said first
and second fluid mixtures prior to introduction thereof into said
chamber whereby said fluid mixtures are reacted therein in a
gaseous state.
12. An apparatus according to claim 11 wherein said first and
second fluid mixtures each include a second component
distinguishable from said respective fluid mixtures by gas
chromatography, the concentration of said second component in said
second fluid mixture being predetermined, wherein said first
component at least in part converted of said first and second fluid
mixtures is at least in part converted to said second component by
said respective reactions thereof, wherein said
proportional-calibration relationship relates the concentration of
said first component for detection in said first fluid mixture with
said detected converted first component converted to said second
component of said first and second fluid mixtures and with said
predetermined concentrations of said first and second components in
said reference second fluid mixture, and wherein said apparatus
further comprises:
g. means coupled with said source of said first fluid mixture and
coupled with said gas chromotograph for injecting into said gas
chromatograph vaporized samples unreacted of said first fluid
mixture for detection of said second component of said first fluid
mixture unreacted, the concentration of said first component in
said first fluid mixture being determinable from said detected
second component of said first fluid mixture unreacted, said
detected first component thereof converted, and said
proportional-calibration relationship.
13. An apparatus according to claim 12 wherein said first component
of said first and second fluid mixtures comprises naphthenes,
wherein said second component of said first and second fluid
mixtures comprises aromatics, wherein said catalyst in said chamber
(a,a) comprises a noble metal catalyst for conversion at least in
part of said naphthenes to aromatics, wherein said source (a,b) of
carrier gas includes hydrogen, wherein said chromatograph column
includes a sorbent material therein having a sorbent affinity for
aromatics, and wherein said chromatograph column means further
includes means including a backflush valve coupled with the inlet
and outlet ends of said chromatograph column and coupled with said
detector for backflushing said chromatograph column subsequent to
each respective injection therein of each of said samples of said
first and second fluid mixtures, said chromatograph column being
backflushed subsequent to sorbtion therein of at least a portion of
said aromatics and passage therethrough of at least a substantial
portion of the balance of said respective fluid samples, the
backflush flow of said column passing through said detector for
detection of the aromatics content of said samples, whereby the
concentration of said naphthenes first component in said first
fluid mixture is determinable in accordance with said calibration
relationship.
14. The apparatus of claim 13 wherein said chamber (a,a) comprises
a reaction chamber of about 5 feet of length of about 3/16-inch
diameter steel tubing packed with platinum reforming catalyst
having 35 to 80 mesh-particle size, wherein said heating means
(a,c) includes a temperature controlled enclosure in which is
mounted said reaction chamber, said enclosure including heating
means for heating said reaction chamber to a temperature in the
range of 200.degree. to 400.degree. C. wherein said chromatograph
column comprises a column of about 10 feet of length of about
1/4-inch diameter steel tubing packed with beta,
beta'-thiodipropionitrile deposited on a support of about 60 to 80
mesh-particle size for adsorbtion of said aromatics component and
detection thereof, wherein said detector includes means for
generating a detector signal the time integral of which is
representative of the concentration in said respective samples
passed therethrough of said aromatics component, said apparatus of
claim 24 further comprising:
h. means including a pressure regulator coupled with the outlet end
of said chromatograph column for regulating the pressure in said
reaction chamber and said chromatograph column in the range of 30
to 60 p.s.i.g.; and
i. computing means including integration means coupled with said
detector for computing the concentration of said naphthene first
component for detection in said first fluid mixture in accordance
with said proportional calibration relationship, said relationship
being substantially in accordance with the following equation:
Y= Y.sub.1 (x.sub.2 - x.sub.1)/(z.sub.2 - z.sub.1)
where:
Y = percent of said naphthene first component for detection in said
first fluid mixture,
Y.sub.1 = percent of said naphthene first component in said
reference second fluid mixture,
x.sub.2 = percent of said aromatics in said first fluid mixture
after said reaction thereof in said chamber,
x.sub.1 = percent of said aromatics in said first fluid mixture
prior to said reaction thereof,
z.sub.2 = percent of said aromatics in said reference second fluid
mixture after said reaction thereof,
and:
z.sub.1 = percent of said aromatics second component in said
reference second fluid mixture prior to said reaction thereof.
15. The apparatus of claim 14 wherein said computing means (i)
comprises:
ia. manual entry and signal-generating means for entering into said
computer the value of said predetermined concentration of said
naphthene first component in said reference second fluid mixture
and for generating a concentration second signal representative
thereof;
ib. integration means coupled with said detector for integrating
said detector signal and for generating third, fourth, fifth and
sixth signals representative of said respective concentrations of
said detected aromatics component in said fluid samples passed
therethrough, said signals being representative respectively of
said quantities: z.sub.1, z.sub.2, x.sub.1, and x.sub.2 ;
ic. first difference measuring means coupled with said integration
means (ib) for generating a difference seventh signal
representative of the difference (z.sub.2 - z.sub.1) between said
fourth and third signals;
id. second difference measuring means coupled with said integration
means (ib) for generating a difference eighth signal representative
of the difference (x.sub.2 - x.sub.1) between said sixth and fifth
signals;
ie. first multiplication means coupled with said second difference
measuring means (id) and coupled with said manual entry means (ia)
for generating a product ninth signal representative of the product
of said concentration second signal and said difference eighth
signal; and
if. division means including output means coupled with said first
multiplication means (ie) and coupled with said first difference
measuring means (ic) for generating an output first signal
representative of the quotient of said product ninth signal divided
by said difference seventh signal, said output first signal
corresponding to the concentration of said naphthene first
component for detection in said first fluid mixture in accordance
with said proportional-calibration relationship.
Description
BACKGROUND OF THE INVENTION
This invention relates to a method and apparatus for the analysis
of fluid mixtures, and more particularly to the analysis of
hydrocarbon mixtures.
In laboratory and industrial applications it is frequently
necessary to analyze a fluid mixture to determine the concentration
of its constituents. This is of particular importance in connection
with computer control and optimization of fluid processes in the
petroleum-refining industry where the economy of various processes
is often predicated upon accurate information of the composition of
fluid mixtures undergoing process treatment or the concentration
therein of selected fluid components.
Certain fluid mixtures, particularly the hydrocarbons, are
difficult to analyze or separate due to the similarity of the
physical properties of the fluid components. Thus, the components
of the fluid mixture may have similar boiling points, similar
adsorption characteristics, or they may be composed of similar
nonpolar molecules. Such similarities render the analysis or
separation of these fluid mixtures by presently known physical
methods, such as chromatography or fractionation, extremely
difficult.
An example of a fluid mixture difficult to analyze is found in
connection with the catalytic reforming process for the octane
improvement of fuels. The process charge stream usually comprises a
mixture of aromatics, naphthenes, and paraffins. Both the
naphthenes and the paraffins may be distinguished from the
aromatics by chromatographic analysis. But the naphthenes cannot be
easily distinguished from the paraffins due to the similar physical
properties of these components. One method by which such a mixture
may be analyzed is by use of a mass spectrometer. However, this
technique does not lend itself to online continuous process use in
its present state of development. Also, the use of prior art
chromatographic analysis techniques to analyze the fluid mixture
are unsatisfactory due to the inability of this method to
distinguish between certain fluid components having similar
physical properties.
For the purpose of computer or automatic control of the catalytic
reforming process, it is important to continuously analyze the
charge stream for its naphthene content since the naphthenes are
the main reactants in the process. The naphthene content of the
charge stream is therefore a key variable of the process. Hence, if
information thereof is continuously made available to a computer
control loop controlling other variables of the process, the
process may be optimized, improving its economy and the quality of
the product.
The invention as herein disclosed provides a solution to the
aforementioned problems by a unique and novel method and apparatus
for the continuous analysis of fluid mixtures suitable for many
process control applications.
SUMMARY
Briefly stated a preferred aspect of the invention provides a
method for continually monitoring a component of interest of a
fluid mixture having physical properties sufficiently similar to
those of other components of the fluid mixture rendering it
difficult to separate or distinguish the fluid component of
interest therefrom. The method includes reacting a sample of the
fluid mixture in a chemical reaction which affects at least one
component of the fluid mixture so as to alter at least in part the
chemical structure and at least one physical property thereof
rendering the fluid component of interest distinguishable from the
fluid mixture, and detecting the fluid component of interest. One
version of the method includes the step of separating at least a
portion of the fluid component of interest from the mixture and
then the fluid component of interest thus separated is detected. In
one aspect of the method for determining the concentration of the
fluid component of 60 interest in a fluid mixture which includes
one distinguishable component the reaction converts at least one
component of the mixture to the distinguishable component, the
separating step includes separating the distinguishable component
from the mixture subsequent to the reacting step, and the method
includes the further steps of detecting the distinguishable
component in an unreacted sample of the fluid mixture and
generating a signal representative of the concentration in the
mixture of the fluid component of interest in accordance with a
predetermined relationship relating the detected distinguishable
component of the unreacted sample and the reacted sample, with the
concentration of the fluid component of interest in the fluid
mixture. In a further aspect the method is adapted to monitor the
naphthene content of a hydrocarbon mixture comprising paraffin,
aromatic, and naphthene components.
Another aspect of the invention provides apparatus in novel
combination for continually monitoring a component of a fluid
mixture including a microreactor for subjecting a sample of the
fluid mixture to the aforementioned chemical reaction, and
detection means for detecting the fluid component of interest. Also
included are valve and conduit means for transmission of the fluid
mixture through the apparatus. In one version of the apparatus the
detection means include a chromatograph column and a detector. In a
preferred embodiment of the apparatus for monitoring the naphthene
content of a hydrocarbon mixture heating means are also provided
for maintaining suitable operating temperatures in the
microreactor, a noble metal reforming catalyst is employed in the
microreactor for converting naphthenes of the fluid mixture to
aromatics, and b, b' -thiodipropionitrile or other suitable polar
substrate is employed in the chromatograph column for separating
the aromatic component from the paraffin and naphthene components
of the fluid mixture. In a further embodiment a unique analog
computer is provided coupled with the detector for computing the
concentration of the fluid component of interest in the fluid
mixture.
In view of the foregoing it is an object of the invention to
provide an improved method for the analysis of fluid mixtures.
Another object of the invention is to provide a method for
detection of a component of a fluid mixture difficult to
distinguish from the mixture by employing a chemical reaction
producing identifiable components.
Another object of the invention is to provide a method for
determining the concentration in a fluid mixture of a component
difficult to distinguish from the mixture.
Another object of the invention is to provide a method for
monitoring the naphthene content of a fluid mixture of
hydrocarbons.
Another object of the invention is to provide embodiments of
apparatus to fulfill the aforementioned objectives.
These and other objects, advantages and features of the invention
will be more fully understood by referring to the following
descriptions and claims, taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic block diagram illustrating an embodiment of
apparatus for practicing the invention.
FIG. 2 is a schematic block diagram of a computer which may be used
in conjunction with the apparatus of FIG. 1 to compute the
concentration of the fluid component of interest in the fluid
mixture tested.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The fluid mixture being tested is introduced into the apparatus
through a conduit 10 from a source S.sub.1. Typically, this fluid
mixture can be associated with one of many hydrocarbon refining
processes. Thus, for example, the source S.sub.1 can be a sample
stream of the fresh feed of a catalytic-reforming process for the
octane improvement of fuels which usually includes a mixture having
components of naphthenes, aromatics, and paraffins. It is to be
understood that as used herein the term fluid component shall
signify any group of one or more similar chemical compounds such
as, for example, a component of naphthenes, a component of
paraffins, etc.
The fluid mixture being tested passes through the conduit 10 and
enters an electrically operated selection valve 11. For calibrating
the device a calibration standard fluid mixture of known
composition is provided from a source S.sub.2 which is coupled with
the selection valve 11, by a conduit 12, connected therewith. The
selection valve 11, when in its first operative position, permits
passage therethrough of the fluid mixture being tested, and when in
its second operative position, permits passage therethrough of the
calibration standard. Coupled with the outlet port of the selection
valve 11 is a conduit 14 which is in turn connected to the inlet
port of a sample-measuring valve 15 which incorporates an outlet
port through which flow measured samples of the fluid mixture being
tested. The sample-measuring valve 15 also incorporates a vent port
in fluid communication with its inlet port for uninterrupted flow
of the fluid mixture therethrough and out of its vent port. The
latter port is connected by a conduit 16 to a second sample
measuring valve 17 which also incorporates a measured sample outlet
port and a vent port, the latter port being connected to a vent
conduit 18 for flow of the fluid mixture out of the apparatus. In
this configuration either the fluid mixture being tested or the
calibration standard is present at all times in the bodies of the
sample measuring valves 15 and 17, the respective fluid flowing out
of the apparatus through the vent conduit 18.
The sample measuring valves 15 and 17 are conventional constant
volume liquid-sampling valves which when actuated measure and
release to their respective sample outlet ports single samples of
predetermined amounts of the fluid mixture present therein. Sample
valves providing samples ranging from 1 to 50 microliters can be
used in the apparatus. However, for the analysis of napthhenes it
is preferred to use sampling valves which provide liquid samples of
about 10 microliters.
Connected with the outlet port of the sample measuring valve 15 is
a conduit 19 which is in turn connected with a vaporizer 20 where
the samples are vaporized in the presence of a suitable carrier gas
such as hydrogen which is introduced into the vaporizer 20 through
a conduit 21 connected with a source of the gas S.sub.3. Generally,
many carrier gases can be used provided the gas is of a composition
which does not adversely affect to a substantial extent the
chemical reaction to which the fluid mixture is subjected. However,
the use of hydrogen is preferred in the analysis of the catalytic
reforming fresh feed to help prevent coking of the reforming
catalyst used in the microreactor discussed below. The vaporized
mixture passes from the vaporizer 20 through a conduit 22 connected
therewith and enters a microreactor 23. The microreactor 23
includes a section of tubing packed with a suitable catalyst to
effect a chemical reaction of the fluid samples converting a major
portion of the fluid component of interest thereof into a component
distinguishable or separable from the fluid mixture. For the
analysis of naphthenes in fluid mixtures comprising at least
naphthenes and aromatics, or naphthenes and paraffins, the
microreactor 23 is preferably comprised of about 5 feet of about
3/16-inch diameter steel tubing filled with 35-80 mesh
platinum-reforming catalyst. To further stimulate the reaction of
microreactor is in turn mounted within a temperature-controlled
enclosure, such as a regulated oven 24, which maintains the
microreactor at an elevated temperature. The choice of this
temperature and the operating pressure of the apparatus depend upon
the fluid mixture being analyzed and are generally not critical.
However, these operating conditions should be chosen such that the
desired chemical reaction will take place and is most favored
thermodynamically. For the analysis of naphthenes the preferred
value of the microreactor temperature is approximately in the range
of about 200 .degree. to 400.degree. C. when the pressure therein
is maintained in the vicinity of 45 p.s.i.g. In this case, a major
portion of the naphthene component of the samples is converted to
aromatics which can be separated from the paraffin and other
dissimilar components. Thus, the increase in the aromatic component
is indicative of the naphthene content of the samples.
Having thus reacted the samples in a manner rendering separable or
distinguishable the fluid component of interest, its concentration
in the samples can be determined by separating, or detecting, the
fluid component of interest in any of a number of ways, such as by
absorption spectroscopy or gas chromatography. For the analysis of
naphthenes it is preferred that the detecting be performed with a
gas chromatograph column employing a suitable polar substrate.
For this purpose a chromatograph column 25 and an electrically
operated conventional backflush valve 26 are provided. The outlet
flow of the microreactor 23 passes through a conduit 27 connected
with a first port 26a of the backflush valve 26 which incorporates
five further ports, 26b through 26f, respectively, to enable
forward or reverse flow through the chromatograph column 25. The
fifth port 26e of the backflush valve is connected with a vaporizer
28 by a conduit 29. The vaporizer 28 is in turn connected with the
inlet end of the chromatograph column 25 by a conduit 30. The third
port 26c is connected with the exit end of the chromatograph column
by a conduit 31; the fourth port 26d is connected with an outlet
conduit 32; and the second and sixth ports 26b and 26f,
respectively, are externally connected to each other by a loop
conduit 33.
When the backflush valve 26 is in its first operative position its
first port is in fluid communication with its second port, its
third port is in fluid communication with its fourth port and its
fifth port is in fluid communication with its sixth port. With the
valve in this operative position the fluid mixture including the
carrier gas from the microreactor entering the backflush valve
through its first port passes therethrough and out of its second
port, reenters the valve through its sixth port, passes out of the
valve through its fifth port, passes through the conduit 29,
through the vaporizer 28 and and thence passes through the
chromatograph column 25 in a forward direction. The fluid from the
chromatograph column passing through the conduit 31 reenters the
backflush valve through its third port, and exits therefrom through
its fourth port, and passes through the outlet conduit 32.
When the backflush valve 26 is in its second operative position its
first port is in fluid communication with its sixth port, its
second port is in fluid communication with its third port, and its
fourth port is in fluid communication with its fifth port. When the
backflush valve is in this operative position the chromatograph
column is backflushed by a flow of the carrier gas in the conduit
27 entering the backflush valve through its first port and exiting
through its sixth port, reentering the valve through its second
port, exiting through its third port and thence passing through the
conduit 31, the chromatograph column 25 and the vaporizer 28 in a
reverse direction, reentering the backflush valve through its fifth
port and exiting therefrom through its fourth port to the outlet
conduit 32. The outlet conduit 32 is in turn connected with a
pressure regulator 34, for regulating the pressure in the
apparatus. For the analysis of naphthenes the preferred pressure is
in the range of 30 to 60 p.s.i.g. The pressure regulator is in turn
connected with a suitable gas chromatography detector, such as a
thermal conductivity detector 35, for detecting the effluent of the
chromatograph column. The electrical signals developed by the
detector 35 are transmitted to a computer 38 which is further
discussed in reference to FIG. 2.
For the analysis of naphthenes in hydrocarbon mixtures the
preferred configuration of the chromatograph column 25 comprises a
length of about 10 feet of about 1/4-inch diameter steel tubing
packed with beta, beta'-thiodipropionitrile deposited by
conventional techniques on 60-80 mesh support, such as Chromosorb
P. In this configuration the column holds up the aromatic component
of the samples while permitting the saturates and other components
to pass through first. Then, when the column is backflushed the
held-up aromatics are detected as a group passing from the
chromatograph column in a reverse direction to the detector 35; the
area under the curve defining the detected thermal conductivity
response pulse occurring during backflushing of the aromatics being
proportional to the aromatics content of the respective fluid
samples.
The analysis of the foregoing fluid mixture involves converting the
naphthenes to aromatics. Should the fluid mixture initially contain
an appreciable amount of aromatics it is necessary to provide a
sampling by the chromatograph column of the fluid mixture in the
unreacted condition. Therefore, for the analysis of those fluid
mixtures wherein one component is converted to another by the
microreactor, it is necessary to provide the capability in the
apparatus for direct analytical sampling of the unreacted fluid
mixture. Hence, a flow of samples of the fluid mixture is provided
from the sample measuring valve 17 through the vaporizer 28,
connected with the sample-measuring valve 17 by a conduit 36, and
from the outlet of the vaporizer 28 to the conduit 30 at the inlet
end of the chromatograph column 25. The carrier gas is introduced
into the vaporizer 28 through the conduit 29 connected with the
backflush valve 26, which receives a flow of the carrier gas from
the source S.sub.3 passing through the vaporizer 20 and the
microreactor 24. The hydrogen source S.sub.3 is connected with the
detector 35 through a conduit 39 to provide a reference against
which the thermal conductivity response of the chromatograph column
effluent is measured by the detector 35.
The calibration characteristic, that is, the predetermined
relationship between the thermal conductivity response measured by
the detector 35, and the concentration of the fluid component of
interest in the fluid mixture tested may be determined
analytically. However, such a procedure is extremely difficult
since all of the fluid component of interest may not be converted
by the microreactor. Hence, a more suitable procedure is the use of
a calibration standard fluid mixture of well-known composition
having a concentration of the fluid component of interest similar
to, or in the expected range of, the concentration of the fluid
component of interest in the fluid mixture being tested. The
calibration standard is introduced from a source thereof S.sub.2,
through the conduit 12, through the selection valve 11, which when
in its second operative position permits a flow of the calibration
standard into the sample measuring valve 15, and thence into the
balance of the apparatus.
The calibration characteristic of the apparatus is initially
determined by two runs of the standard therethrough. In the first
run the standard passes through the microreactor and through the
chromatograph column for analysis. In the second run the
calibration mixture is introduced directly into the chromatograph
column for analysis. Once the first calibration is determined,
subsequent, or periodic calibrations need be performed only by
passing the calibration standard through the microreactor since any
subsequent changes in the operating characteristics of the
apparatus take place primarily in the microreactor due to changes
in the catalyst activity with age.
A time-cycle controller 37, which includes conventional
program-timing elements, is provided to control the actuation of
the various electrically operated valves through an appropriate
timing sequence. Generally, the timing sequence is not critical
provided that there is sufficient residence time of the samples in
the microreactor and the chromatograph column.
For the analysis of naphthenes in the fresh feed of catalytic
reforming processes it is preferred that the time cycle controller
37 provide for the following functions: the injection of a first
sample of the fluid mixture being tested into the microreactor for
reaction therein, permitting the sample to pass to the
chromatograph column and reside therein for a sufficient time
interval for adsorption of the aromatics and elution of the
saturates content of the sample in the forward direction,
thereafter, reversing the flow through the chromatograph column to
backflush the aromatics content of the sample and detecting the
aromatics content thereof. Subsequently, a second sample of the
fluid mixture is injected directly into the chromatograph column
and the aromatics detection sequence above is repeated. For the
aforementioned analysis of naphthenes a preferred timing sequence
is as follows: 1) for all normal operation, that is, absent
calibration, the selection valve 11 is kept in its first operative
position; 2) the sample measuring valve 15 is actuated for about 30
to 120 seconds while a single sample of the fluid mixture is
injected into the microreactor; 3) while the sample is reacted and
passes through the backflush valve into the chromatograph column,
the backflush valve is maintained in its first operative position
for a period of about 5 to 15 minutes and then is actuated to its
second operative position permitting backflushing of the
chromatograph column; 4) the backflush valve then remains in its
second operative position for a period of about 7 to 20 minutes
while the aromatics pass therethrough and are detected as a group;
5) the backflush valve is then returned to its first operative
position; 6) the sample-measuring valve 17 is then actuated for
about 30 to 120 seconds to release a single sample of the fluid
mixture, which bypasses the microreactor entering into the
chromatograph column; 7) the backflush valve 25 remains in its
first operative position for a period of about 5 to 15 minutes
permitting forward flow through the chromatograph column and
elution of the saturates; 8) then the backflush valve 25 is
actuated to its second operative position permitting reverse flow
through the chromatograph column and detection of the aromatics as
a group; 9) then the backflush valve 25 is returned to its first
operative position, and the operating cycle connecting with step
number 2 above is repeated. For the initial calibration of the
apparatus the selection valve 11 is actuated to its second
operative position and the aforementioned operating cycle
commencing with step number 2 is executed with respect to the
calibration standard fluid mixture. The periodic calibration
checks, for checking the catalyst aging, may be performed as often
as once a day or once a week depending upon the severity of use of
the apparatus. For this calibration check the sequence of steps
numbers 2 through 5 are executed while the selection valve 11 is
maintained in its second operative position. After the calibration
check the selection valve 11 is returned to its first operative
position and the normal sequence of operation is reinstated.
The output signals from the detector 35 are transmitted to the
computer 38, in which is programmed the predetermined calibration
relationship between the detected signals and the concentration in
the fluid mixture tested of the fluid component of interest. The
computer 38 also is responsive to the time-cycle controller 37 so
that is can interpret each of the thermal conductivity signals
generated by the detector 35 in proper order. I have found that the
following equation expresses the aforementioned predetermined
relationship, based upon the results of the calibration run, when a
first component of interest of the fluid mixture is analyzed for
which is converted to a second component of the fluid mixture by
the chemical reaction:
Y = Y.sub.1 (x.sub.2 -x.sub.1)/(z.sub.2 -z.sub.1) (1 )
where:
x.sub.2 = percent of the second component in the fluid mixture
being tested after the reaction,
x.sub.1 = percent of the second component in the fluid mixture
being tested before the reaction,
z.sub.2 = percent of the second component in the calibration
standard mixture after the reaction,
z.sub.1 = percent of the second component in the calibration
standard mixture before the reaction,
y.sub.1 = percent of the fluid component of interest in the
calibration standard mixture as determined independently such as by
mass spectrometetry,
y = percent of the fluid component of interest in the fluid mixture
being tested.
It should be noted that the time cycle indicated above is merely
the suggested time cycle for the analysis of naphthenes and
appropriate adjustments may be made with corresponding adjustments
of the length of the microreactor and the chromatograph column.
Furthermore, similar adjustments can be made for the analysis of
other fluid mixtures. Thus, for example, increasing the length of
the microreactor or of the chromatograph column results in an
increased residence time of the fluid mixture in these respective
items, whereby, the timing sequence should be modified accordingly.
It is also to be noted while the various automatic valves have been
described as electrically operated that pneumatically operated
valves may be used in their place. In this instance the time cycle
controller would be coupled to conventional electrical-to-pneumatic
valve operators. Also to be noted is that various of the conduits
illustrated in FIG. 1 may be eliminated by joining some of the
equipment items. Thus, for example, the sample-measuring valves and
the vaporizers may be combined into a single injector assembly. It
is also to be noted that since the device is calibrated as
discussed above the reaction in the microreactor need not be
complete, that is, the reaction need not affect the entire amount
in the fluid mixture of the component reacted. Also, the reaction
may affect more than one component in the fluid mixture. Thus, for
example, in a mixture containing naphthenes, paraffins, and
aromatics, a portion of the paraffins may be reformed while a
portion of the naphthenes are converted to aromatics. The device,
after calibration, is nonetheless able to solve for the naphthene
content of the mixture. Similarly, the device may be used to solve
for a component of the mixture other than the one reacted. For
example, in analyzing a mixture of naphthenes and paraffins to
determine the paraffin content, the device can be calibrated to
account for the reaction of the naphthenes and the paraffin
component may be solved for inferentially. It is also to be
appreciated by one skilled in the art that the device can be
adapted to analyze a variety of fluid mixtures by appropriate
modifications of the catalyst used in the microreactor and the
packing material of the chromatograph column. Thus, for example, a
noble metal may be used as a catalyst in conjunction with a
silicone rubber as substrate material for the analysis of
mercaptans as hydrogen sulfide in mixtures of hydrocarbons. Another
example is the identification of olefins and/or aromatics in a
hydrocarbon mixture by hydrogenation of said olefins and/or
aromatics.
Referring now to FIG. 2 which is a schematic block diagram of a
computer which can be used as the computer shown in FIG. 1, the
signals from the detector 35 are transmitted to an integrator 50
which also receives timing signals from the time cycle controller
37 so that the integrator is able to distinguish, by time
displacement, the electrical pulses received from the detector
during the timed sequence of operation. The integrator 50
integrates the area under each of the thermal conductivity response
pulses and provides four corresponding output signals, namely,
x.sub.2, x.sub.1, z.sub.2, and z.sub.1, as defined in reference to
equation (1 ) above. The x.sub.2 and x1 signals are transmitted to
a subtraction element 51 which subtracts the latter, x.sub.1, from
the former, x.sub.2, and provides an output signal corresponding to
this difference, namely, x.sub.2 -x.sub.1. This signal is in turn
transmitted to a multiplication operator 52. The z.sub.2 and
z.sub.1 signals from the integrator are transmitted to a
subtraction element 53 which subtracts the latter, z.sub.1, from
the former, z.sub.2, and provides an output signal corresponding to
z.sub.2 -z.sub.1. This signal is in turn transmitted to a division
element 54. For developing a signal corresponding to the percent of
the fluid component of interest in the calibration mixture a
standard voltage supply 55 is provided for applying a constant
voltage to a potentiometer 56 which is manually set to a position
corresponding to the value Y.sub.1. The Y.sub.1 signal, thus
developed, is transmitted to the multiplication element 52, which
multiplies the Y.sub.1 signal by the difference signal from the
subtraction element 51, and provides an output signal corresponding
to the product, namely, Y.sub.1 (x.sub.2 -x.sub.1 ). This signal is
transmitted to the division operator 54 which divides this signal
by the difference signal from the subtraction element 53, and
provides an output signal corresponding to the quotient. The output
signal from the division element 54 therefore corresponds to the
concentration of the fluid component of interest in the fluid
mixture being tested in accordance with equation (1 ). This signal
can be transmitted to a display device or a chart recorder and can
be utilized to control the process by application thereof to
suitable process control equipment.
It is to be appreciated by one skilled in the art that while
electrical computation elements have been discussed above,
pneumatic computation elements can be used in their place quite
advantageously. It is also to be appreciated by one skilled in the
art that a digital computer can be utilized to perform the
computational functions of the analog computer of FIG. 2. In this
instance, in place of the time-cycle controller, the computer can
be preprogrammed to control all the valve-switching functions,
including the calibration cycles, and the computer can synchronize
the integration steps with the operating sequence.
While the invention has been described with a certain degree of
particularity, it can, nevertheless be seen by the examples
hereinabove set forth that many modifications and variations of the
invention may be made without departing from the spirit and scope
thereof.
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