U.S. patent application number 12/475571 was filed with the patent office on 2010-12-02 for apparatus and method for measuring the properties of petroleum factions and pure hydrocarbon liquids by light refraction.
This patent application is currently assigned to UNIVERSITY OF KUWAIT. Invention is credited to Tareq Abduljahl Abahri.
Application Number | 20100305872 12/475571 |
Document ID | / |
Family ID | 43221178 |
Filed Date | 2010-12-02 |
United States Patent
Application |
20100305872 |
Kind Code |
A1 |
Abahri; Tareq Abduljahl |
December 2, 2010 |
Apparatus and Method for Measuring the Properties of Petroleum
Factions and Pure Hydrocarbon Liquids by Light Refraction
Abstract
A Method and apparatus to accurately measure and display various
properties of hydrocarbons and petroleum factions for a small
volume of sample in a short period of time in one test with less
cost and energy for the analysis by the method of light refection.
The refraction of light through the sample is measured and compared
to the refraction f the light through vacuum by the apparatus. The
method of the invention comprises a property estimation from the
apparatus to output a property estimate value. The property
estimation means is equipped with a property estimation model for
evaluating the property estimate value outputted from the property
estimation model. The method is incorporated into standard or
otherwise any refractive index test apparatus or refractometer to
provide accurate measure of the thermodynamic and transport
properties of pure hydrocarbons and undefined multicomponent
mixtures such as petroleum factions.
Inventors: |
Abahri; Tareq Abduljahl;
(US) |
Correspondence
Address: |
LITMAN LAW OFFICES, LTD.
PATENT LAW BUILDING, 8955 CENTER STREET
MANASSAS
VA
20110
US
|
Assignee: |
UNIVERSITY OF KUWAIT
|
Family ID: |
43221178 |
Appl. No.: |
12/475571 |
Filed: |
May 31, 2009 |
Current U.S.
Class: |
702/30 ;
356/128 |
Current CPC
Class: |
G01N 33/28 20130101;
G01N 2201/129 20130101; G01N 21/4133 20130101 |
Class at
Publication: |
702/30 ;
356/128 |
International
Class: |
G01N 21/41 20060101
G01N021/41 |
Claims
1. A method for measuring the chemical, performance, perceptual or
physical properties of a hydrocarbon sample which comprises at
least on for the following properties: the API gravity at
15.degree. C., the specific gravity, the density at 20.degree. C.,
the average boiling point, the Watson characterization factor, the
molecular weight, the critical volume, the Reid vapor pressure, the
kinematic viscosity at 37.8.degree. C. and 98.9.degree. C., the
true critical temperature, the pseudocritical temperature, the true
critical pressure, the pseudocritical pressure, the acentric
factor, the net heat of combustion at 25.degree. C., the isobaric
liquid heat capacity at 15.6.degree. C., the isobaric vapor heat
capacity at 15.6.degree. C., the liquid thermal conductivity at
25.degree. C., the research octane number, the motor octane
numbers, the heat of Vaporization at the Normal Boiling Point,` the
carbon to hydrogen content, the true vapor pressure, the flash
point, the freezing point, the surface tension of the liquid, the
aniline point, the cloud point, the critical compressibility
factor, the solubility parameter, and the compositional analysis
for paraffins, napthenes, aromatics, sulfur, mono-aromatics,
poly-aromatics: which comprises: a) placing said hydrocarbon sample
in a refractive index apparatus; analyzing a of said sample by
refractometry, under suitable and repeatable conditions, to
determine the refractive index of the of said hydrocarbon in the
refractive index apparatus; b) determining the API gravity of the
hydrocarbon sample by calculation form the first set of data of
step (a) or by analyzing the hydrocarbon sample by a suitable
method, under suitable and repeatable conditions; c) applying at
least the first set of data of step(a) or by analyzing the
hydrocarbon sample by a suitable method, under suitable and
repeatable conditions to determine the average boiling point of the
hydrocarbon sample; d) inputting the values of a least one set of
data from the first set of data of step (a), the second set of data
of step (b), and the third set of data of step (c) into a
computational model; e) applying a computational method to said
sets of data of step (d) comprising a mathematical model wherein
the computation method further performs a correlation between the
amounts of the detected values of said sets of data to the
properties of the hydrocarbon; and g) determining the physical and
chemical property that is derived from the hydrocarbon as a
function of that least the refractive index of its components
in-situ or in real time.
2. The method of claim 1, wherein the computational method in step
(e) comprises at least on of the following methods; optimization,
neural networks, multivariate regression, partial least square
regression, principal component regression, a topological approach,
genetic algorithms, or any computational method.
3. The method of claim 1, wherein the refractive index apparatus
conforms to at least one of the following standard or otherwise
non-standard test methods and its apparatus; (a) ASTM D1215 test
method for clear hydrocarbons' (b) ASTM D1218 test method using the
Bausch and Lomb refractometer; and (c) ASTM D1747 test method for
viscous oils.
4. The method of claim 1, wherein the refractive index in is
obtained from at least one of the following standard or otherwise
non-standard test methods and procedures; (a) ASTM D1215 test
method for clear hydrocarbons' (b) ASTM D1218 test method using the
Bausch and Lomb refractometer; and (c) ASTM D1747 test method for
viscous oils.
5. The method of claim 1, wherein said hydrocarbon is a petroleum
fraction such as naphtha, kerosene, middle distillated, heavy
distillate, vacuum distillate, gasoil, heavy gasoil, and cracked
feed.
6. The method of claim 1, wherein said hydrocarbon is a pure
hydrocarbon.
7. The method of claim 1 wherein said data from steps (a) to (c)
are stored in a standalone computer or in an integrated computer in
the refractive index apparatus.
8. The method of claim 1, wherein said data from steps (a) to (c)
are treated in a standalone computer or in an integrated computer
in the refractive index apparatus.
9. The method of claim 1 wherein computations in steps (d) to (g)
are performed and displayed in a standalone computer or in an
integrated computer in the refractive index apparatus.
10. The method according to claim 1 wherein said method for
predicting the fluid properties: (a) is powerful for simulation an
d predicting the properties of petroleum fluids; (b) is simple and
straightforward; (c) requires limited information from readily
available lab analysis and simple analytical characterizations to
describe the petroleum feedstock; (d) can predict the global
properties of molecular ensembles produced during various physical
and chemical processing scenarios as they progress; (e) can be
combined with or incorporated in process simulation packages thus
enhancing their information content; (f) provides a foundation for
developing property relationships and incorporating
well-established correlations to estimate mixture properties; (g)
the capability of predicting the physical and performance
properties of undefined multicomponent hydrocarbon mixtures during
processing; (h) can be incorporated as software in the refractive
index apparatus hardware to provide estimation of properties of
petroleum fractions using one single laboratory test; (i) leads to
large savings in terms of energy, tie and cost; (j) can predict the
properties of undefined multicomponent mixtures and petroleum
factions as well as pure hydrocarbons than the current methods and
can enhance the prediction performance of chemical process
simulation packages; (k) combines routine analytical test and a
modeling approach to provide direct measurement of the
thermodynamic and transport properties of a hydrocarbon sample; (l)
can calculate the properties of hydrocarbon with good accuracy when
at least one bulk property is available (i.e. the refractive
index); (m) is applicable to any hydrocarbon or petroleum faction;
and (n) can predict the properties of petroleum fuels from
refractive index date alone.
11. An apparatus for measuring the chemical, performance,
perceptual or physical properties of a hydrocarbon sample which
comprises at least on of the following properties: the API gravity
at 15.degree. C., the specific gravity, the density at 20.degree.
C., the average boiling point, the Watson characterization factor,
the molecular weight, the critical volume, the Reid vapor pressure,
the kinematic viscosity at 37.8.degree. C. and 98.9.degree. C., the
true critical temperature, the pseudocritical temperature, the true
critical pressure, the pseudocritical pressure, the acentric
factor, the net heat of combustion at 25.degree. C., the isobaric
liquid heat capacity at 15.6.degree. C., the isobaric vapor heat
capacity at 15.6.degree. C., the liquid thermal conductivity at
25.degree. C., the research octane number, the motor octane
numbers, the heat of Vaporization at the Normal Boiling Point,` the
carbon to hydrogen content, the true vapor pressure, the flash
point, the freezing point, the surface tension of the liquid, the
aniline point, the cloud point, the critical compressibility
factor, the solubility parameter, and the compositional analysis
for paraffins, napthenes, aromatics, sulfur, mono-aromatics,
poly-aromatics; which comprises: a) placing said hydrocarbon sample
in a refractive index apparatus; analyzing a of said sample by
refractometry, under suitable and repeatable conditions, to
determine the refractive index of the of said hydrocarbon in the
refractive index apparatus; b) determining the API gravity of the
hydrocarbon sample by calculation form the first set of data of
step (a) or by analyzing the hydrocarbon sample by a suitable
method, under suitable and repeatable conditions; c) applying at
least the first set of data of step(a) or by analyzing the
hydrocarbon sample by a suitable method, under suitable and
repeatable conditions to determine the average boiling point of the
hydrocarbon sample; d) inputting the values of a least one set of
data from the first set of data of step (a), the second set of data
of step (b), and the third set of data of step (c) into a
computational model; e) applying a computational method to said
sets of data of step (d) comprising a mathematical model wherein
the computation method further performs a correlation between the
amounts of the detected values of said sets of data to the
properties of the hydrocarbon; and g) determining the physical and
chemical property that is derived from the hydrocarbon as a
function of that least the refractive index of its components
in-situ or in real time.
12. The apparatus of claim 11, wherein the computational method in
step (e) comprises at least on of the following methods;
optimization, neural networks, multivariate regression, partial
least square regression, principal component regression, a
topological approach, genetic algorithms.
13. The apparatus of claim 11, wherein the refractive index
apparatus conforms to at least one of the following standard or
otherwise non-standard test methods and its apparatus; (a) ASTM
D1215 test method for clear hydrocarbons' (b) ASTM D1218 test
method using the Bausch and Lomb refractometer; and (c) ASTM D1747
test method for viscous oils.
14. The apparatus of claim 11, wherein said data from steps (a) to
(c) are stored in a standalone computer or in an integrated
computer in the refractive index apparatus.
15. The apparatus of claim 11 wherein computations in steps (d) to
(g) are performed and displayed in a standalone computer or in an
integrated computer in the refractive index apparatus.
16. The apparatus of claim 11 comprising a microprocessor to
execute the correlation means and a display screen to display said
predicted properties.
17. The apparatus of claim 11 comprising a microprocessor to
execute the correlation means and to display screen to display said
predicted properties.
18. The apparatus of claim 11 comprising wherein said apparatus for
predicting the fluid properties is a handheld analyzer.
19. The apparatus of claim 11 comprising wherein said apparatus for
predicting the fluid properties is a Laboratory bench-top
analyzer.
20. The apparatus of claim 11 comprising wherein said apparatus for
predicting the fluid properties is an inline process sample
analyzer.
21. The apparatus according to claim 11 wherein said method for
predicting the fluid properties: (a) is powerful for simulation an
d predicting the properties of petroleum fluids; (b) is simple and
straightforward; (c) requires limited information from readily
available lab analysis and simple analytical characterizations to
describe the petroleum feedstock; (d) can predict the global
properties of molecular ensembles produced during various physical
and chemical processing scenarios as they progress; (e) can be
combined with or incorporated in process simulation packages thus
enhancing their information content; (f) provides a foundation for
developing property relationships and incorporating
well-established correlations to estimate mixture properties; (g)
the capability of predicting the physical and performance
properties of undefined multicomponent hydrocarbon mixtures during
processing; (h) can be incorporated as software in the refractive
index apparatus hardware to provide estimation of properties of
petroleum fractions using one single laboratory test; (i) leads to
large savings in terms of energy, tie and cost; (j) can predict the
properties of undefined multicomponent mixtures and petroleum
factions as well as pure hydrocarbons than the current methods and
can enhance the prediction performance of chemical process
simulation packages; (k) combines routine analytical test and a
modeling approach to provide direct measurement of the
thermodynamic and transport properties of a hydrocarbon sample; (l)
can calculate the properties of hydrocarbon with good accuracy when
at least one bulk property is available (i.e. the refractive
index); (m) is applicable to any hydrocarbon or petroleum faction;
and (n) can predict the properties of petroleum fuels from
refractive index date alone.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to material analysis and, in
particular, the measuring method for rapidly predicting the
thermophysical property values of pure and complex hydrocarbon
mixtures by refractive index and its apparatus.
BACKGROUND OF THE INVENTION
[0002] Refractive index (n), also known as the Index of Refraction,
is defined as the ratio of the speed of light in a vacuum to the
speed of light in a material and is dimensionless quantity shown by
n:
n=velocity of light in the vacuum/velocity of light in the
substance.
[0003] In other words, when a light beam passes form one substance
(air) to another (a liquid), it is bent or refracted because of the
difference in speed between the two substances. The refraction
index indicates the degree of this refraction. Additional,
refractive index is measures as the sine of the angle of bending
(deflection) of light as it passes from one medium to another.
[0004] Refractive index is a property of optical materials that
determines how fast light travels through it. The numerical n value
indicates the light bending power of a medium such as a chemical.
The greater the bending power, the greater the refractive index. In
a medium, the speed of light depends on the wavelength and
temperature. For this reason refractive index is usually measured
and reported at 20.degree. C. with the D line sodium light.
[0005] The refractive index is a thermodynamic property and is a
state function, which for a pure fluid depends on temperature and
pressure. Since the velocity of light in a fluid is less than the
velocity of light in a vacuum, its value of a fluid is greater than
unity. Liquids have higher values of refractive index than that of
gases. For gases the values of refractive index are very close to
unity. The refractive index or refractivity (n) can be easily
measured by the sodium D line of a simple refractometer at a
temperature of interest. Values of n at 20 and 25.degree. C. are
given by the API Technical Data Book for many different
hydrocarbons.
[0006] All frequencies of electromagnet radiation (light) travel in
the same speed in vacuum (2.998.times.108 m/s); however, in a
substance the velocity of light depends on the nature of the
substance (molecular structure) as well as the frequency of the
light. For this reason, standard values of refractive index must be
measured at a standard frequency. Usually the refractive index of
hydrocarbons is measured by the sodium D line at 20.degree. C. and
1 atm. In some references the values of refractive index are
reported at 25.degree. C.; however, the refractive index is usually
measured at 20.degree. C. and 1 atm, and is usually used as a
characterization paramount for hydrocarbons and petroleum
factions.
[0007] Refractive index testing procedure is used to determine the
quality of every essential oil. Light behaves differently depending
upon the density of the material it is passing through. The reading
is compared to established literature; deviations are indicative of
adulteration. The index of air is 1.00 and all indices are referred
to the index of air, i.e. the index of water being 1.33 means that
the speed of light in air is 1.33 times greater as the speed of
light in water. Ice refractive index of 1.31, while air has a
refractive index of 1.000277. Refractive indexes of hydrocarbons
vary from 1.3 for propane to 1.6 for some aromatics; however,
aromatics have refractive index value greater than napthenes, which
in turn have refractive indexes greater than paraffins.
[0008] Refractive index (n) is a useful parameter to characterize
hydrocarbon systems and is needed to estimate the composition of
undefined petroleum factions. For example, the refractive index at
some reference conditions (i.e., 20.degree. C. and 1 atm) is a
useful characterization parameter to estimate the composition and
quality of petroleum factions. It is also used to estimate many
physical properties such as molecular weight, equation of state
paraments, the critical constants, or transport properties of
hydrocarbon systems.
[0009] For pure liquids and mixtures, refractive index is a bulk
property that can be easily and accurately measured by an optical
instrument called refractometer. Certain types of refractometers
can be used for measuring gases, liquids, and even transparent or
translucent solids such as gemstones.
[0010] Refractive index can be measured by digital refractometers
with a precision of 0.0001 and temperature precision of 0.1.degree.
C. The amount of sample required to measure refractive index is
very small and ASTM D1218 provides a test method for clear
hydrocarbons with values o f reflective indexes in the range of
1.33-1.5 and the temperature range of 20-30.degree. C. In the ASTM
D1218 test method the Baush and Lomb refractometers is used.
Refractive index of viscous oils with values up to 1.6 can be
measured by the ASTM D1747 test method. Samples must have clear
color to measure their refractive index; however, for darker and
more viscous sample in which actual refractive vale is outside the
range of application of refractometer, samples can be diluted by a
light solvent and refractive index of the solutions should be
measured. From the composition of the solution and refractive index
of pure solvent and that or the solution, refractive index of
viscous samples can be determined. A model Abbe refractometer
(Leica), for example, measure refractive index of liquids within
the temperature range of -20 to 100.degree. C. with temperature
accuracy of .+-.0.01.degree. C. Because of simplicity and
importance of refractive index it would be extremely useful if
laboratories measure and report its value at 20.degree. C. for a
petroleum product, especially if the composition of the mixture is
not reported.
[0011] There are four main types of fluid refractometers:
traditional handheld refractometers, digital handheld
refractometers, Abbe refractometers, and inline process
refractometers.
[0012] Ad traditional handheld refractometer is a handheld analog
instrument for measuring refractive index that works on the
critical angle principle. They utilize lenses and prism to project
a shadow line onto a small glass reticule inside the instrument,
which is then viewed by the user though a magnifying eyepiece. N
use, a sample is sandwiched between a measuring prism and a small
cover plate. Light traveling through the sample is either passed
through to the reticule or totally internally reflected. The net
effect is that a shadow line is formed between the illuminated area
and the dark area. It is at the point that this shadow line crosses
the scale that a reading is taken. Because refractive index is very
temperature dependent, it is important to use a refractometer with
automatic temperature compensation. Compensation is accomplished
through the use of a sample bi-metal strip that moves a lens or
prism in response to temperature changes.
[0013] In optics, a digital handheld refractometer is an instrument
for measuring the refractive index of materials. Most operate on
the same general critical angel principle as a traditional handheld
refractometer. The difference is that light for an LESD light
sources is focused on the underside or prism element. When a liquid
sample is applied to the measuring surface of the prism, some of
the light is transmitted through the solution and lost; while the
remaining light is reflected onto a linear array of photodiodes
creating a shadow line. The refractive index is directly related to
the position of the shadow line on the photodiodes. The more
elements there are in the photodiode array, the more precise the
readings will be, and the easier it will be to obtain readings for
emulsions and other difficult-to-read fluids that from fuzzy shadow
lines. Once the position of the shadow line has been automatically
determined by the instrument, the internal software will correlate
the position to refractive index, or to another unite of measure
related to refractive index, and display a digital readout on an
LCD or LED scale.
[0014] Digital handheld refractometers are generally more precise
than traditional handheld refractometers, but less precise than
most bench-top refractometers. Then also may require a slightly
larger amount of sample to read from (since the sample is not
spread thinly against the prism. Nearly all digital refractometers
feature automatic temperature compensation (for Brix at least).
Like most forms of electronics, this type of unit is always getting
smaller and more ergonomic.
[0015] Am Abbe or laboratory refractometer is a bench-top
refractometer that offers the highest precision of the different
types of refractometers. Nearly one and a half century after their
introduction, refractometers have come a long way in terms of
usefulness, though their principle of operation has changed very
little.
[0016] Ernst Abbe, working for the Zeiss Company in Jena, Germany
in the late 1800s, was the first to develop a laboratory
refractometer. These first instruments had built- in thermometers
and required circulating water to control instrument and fluid
temperatures. They also had adjustments for eliminating the effect
of dispersions. These first instruments had analog scales from
which the readings were taken.
[0017] There have been many refinements regarding teas of use and
precision to these instruments over the decades, but they still
operate on the same principle. They are still used today as an
inexpensive alternative to digital laboratory refractometers. They
are also possibly the easiest method to find the refractive index
of solid samples, such as glass, plastics, and polymer films. Some
Abbe refractometers utilize a digital display for the measurement,
to eliminate the need for discerning between small graduations. The
user still has to adjust the view to obtain the reading,
however.
[0018] The first truly digital laboratory refractometers began
appearing in the late 197s and early 19802, and no longer depended
on the user's eye to determine the reading. They still required the
use of circulating water baths to control instrument and fluid
temperature. They did, however, have the ability to electronically
compensate for the temperature differences of many laboratory
refractometers, while much more accurate and versatile than thief
analog Abbe counterparts, are not capable of reading solid
samples.
[0019] IN the late 1990s, Abbe refractometers with the capability
to read at wavelengths other than the standard 589 nanometers
became availability. These instruments utilize special filters of
the desired wavelength of light, well into the near infrared
(though a special viewer is required to see the infrared rays).
Multi-wavelength Abbe refractometers can be used to very easily
determine a sample's Abbe number.
[0020] The most advanced instruments of today use solid-state
Peltier effect devices to heat and cool the instrument and the
sample, eliminating the dependence on an external water bath. The
software on most of the current instruments is now very advanced
and offers features such as programmable user-defined scales and a
history function that recalls the last several measurements.
Several manufacturers provide easily usable controls, with the
capability to operate from and export readings to a linked
computer.
[0021] Previously refractive index readings from manual
refractometers were obtained by visual inspection. A sample is
placed in the refractometer and a knob that moved a graduated scale
is rotated until two lines representing light refection through the
material and space or air are aligned then the meter reading is
recorded using visual inspection. Currently lab-scale automatic
refractometers are being used which output the numeral value of the
refractive index using a digital display.
[0022] Inline process refractometers are a type of refractometer
designed for the continuous measurement of a fluid flowing through
a pipe or inside a tank throughout the manufacturing process. These
refractometers typically consist of a sensor, placed inline with
the fluid flow, couple to a control box. The control box usually
provides a digital readout as well as 4-20 mA analog outputs and
relay outputs for controlling pumps and valves.
[0023] Refractometers are widely used in oil industry, fat
industry, pharmaceutical factories, paint, and food processing,
among others. A refractometer can be used to determine the identity
of an unknown substance based on its refractive index, to assess
the purity of a particular substance, or to determine the
concentration of one substance dissolved in another. Most commonly,
refractometers are used for measuring fluid concentrations such as
the sugar content ((brix level) of fruits, vegetables, juices and
carbonated beverages, or of cutting fluids, urine specific gravity,
blood protein concentration, salinity, antifreeze, industrial
fluids, etc. Materials measured can be chemicals, syrups, Uren,
food, pharmaceuticals petroleum products and the like. For testing
refractive index, honey, coolants, specific gravity in urine, etc.
Measure soluble solids (BRIX) percentage in fruit, juices, cooking
oils and other various solutions. What current refractometers cant
do is directly measure and display the thermophysical properties of
the material being tested.
Prior Art Reference and Discussion
[0024] Various methods are known for the evaluation of fluid
properties indirectly. Conventional gas and liquid chromatography
(GLC), infrared and mass spectroscopy (IR), Nuclear magnetic
resonance (NMR), hydrogen ion nuclear magnetic resonance (HNMR),
nitrogen nuclear magnetic resonance (NNMR), and Fourier Transform
Infrared Spectroscopy (FTIR) techniques and the like enable
sampling and evaluation of a fuel's components but the equipment is
both expensive and ordinarily not available for evaluation of a
delivered product. It would therefore be highly desirable to have a
method for rapidly measuring the properties of pure hydrocarbons
and hydrocarbon mixtures using a single apparatus, and preferably
an apparatus that is so simple and widely used in the industry such
as the refractometer apparatus for example.
[0025] Gas chromatography has been used to predict petroleum
properties in gasoline-type petroleum products through indirect
measurements. Crawford and Hellmuth, Fuel, 1990, 69, 443-447,
describe a chromatographic analysis that is able to predict the
octane number of various effluents that come from the refinery, by
application of mathematical models that are based on the
statistical technique of principles component regression (PCR).
[0026] Japan Patent n. JP3100463 (1991) to TAKAMURA et al.
discloses a method and instrument for measuring cetane value or
cetane index in a sample from an extremely small volume of sample
oil in a short period of time by separating and eluting the
respective components contained in the sample to be measured by
using gas chromatograph couple to mass spectrometer. The cetane
value or cetane index is determined by substituting the variables
with the regression formula in which parameters are previously
determined.
[0027] Japan Patent n. JP9318613 (1997) to Sasnano discloses a
measuring method of research octane number of gasoline by gas
chromomatograph and its apparatus, by separating components of a
gasoline sample with a gas chromatograph using a specific column,
and by substituting a specific equation with a physical property of
a component which is selected by being only identified on a peak
area value equal to or more than a predetermined value.
[0028] U.S. Pat. No. 5,699,269 (1997) to Ashe, et al. discloses a
method for predicting chemical or physical properties of crude oils
or their boiling factions which comprise CG/MS analysis wherein the
often collinear data generated is treated by multivariate
correlation methods.
[0029] U.S. Pat. No. 6,275,775 (2001) to Baco, et al. discloses a
method for determining at least one physico-chemical property of a
petroleum fraction by gas chromatography couple with an atomic
emission detector (GC-AED) to determine the distribution of an
element from the group of carbon, hydrogen, sulfur, and nitrogen,
as a function of the boiling points of the components of the
sample, and the coefficients of the correlative model are
determined from all of the data. The petroleum fraction whose
property is to be determined is analyzed by chromatography under
the same conditions, and the data that obtained are multiplied by
the coefficients for the model to determine the value of said
property as a function of the boiling points of its components.
Application to the determination of the cetane number as a function
the distillation profile of the components of the petroleum
faction.
[0030] Near infrared spectrometric analysis has been used to
determine indirectly the qualitative properties of various
hydrocarbon samples. Examples are": "Prediction of Gasoline Octane
Number from Near Infrared Spectral Features in the Range 660-1215
nm" by Jeffery J. Kelly, et. Al., Analytical Chemistry, Volume 61,
Number 4, Feb. 15 1989, pp. 31320, and "Predicting Gasoline
Properties Using Near-IF spectroscopy" by Stephen J. Swarin and
Charles A. Drumm, Spectroscopy, Volume 7, number 7, September 1992,
both described a method of predicting the antiknock index of
gasoline using near infrared spectrometry. These methods described
passing energy in the near infrared region of the electromagnetic
spectrum through a sample of gasoline absorption at each
wavelength. This measurement results in a spectral profile, or
spectrum, which can then be compared to the spectrum of a data set
of samples having know antiknock indexes.
[0031] U.S. Pat. No. 4,800,279 (1889) to Heiftje, et al. discloses
methods and devices for near-infrared evaluation of physical
properties of samples. Methods are disclosed for quantifying
physical properties of gaseous, liquid or solid samples.
[0032] One method of evaluating fuel properties is known as near-IR
spectroscopy, in which a sample is excited with light from a
near-IR light source. Since known fuel components exhibit
characteristic vibrational mode overtones when excited in the
near-IF, the vibrations of unknown constituents can be evaluated
and classified accordingly. The typical evaluative process is
complex, involving substantial non-linear data comparisons. Kelly,
et al, describe such a method in "Prediction of Gasoline Octane
Numbers from Near-Infrared Spectral Features in the Range 660-1215
nm, "Vol. 61, Analytical Chemistry, No. 4, p313, Feb. 15 1989, in
which vibrational overtones and combination banks of CH groups of
methyl, methylene, aromatic, and olefinic functions were observed
in near-IF spectral region. With the ai of multivariate statistical
analysis, the spectral features were correlated to various fuel
quality parameters, include octane number. The property or yield is
usually determined by applying a correlation between the priority
or yield and the absorbance values. The correlation is determined
experimentally by multivariate regression or neural network and Is
dependent upon the type of spectrometer employed, the property or
yield to be determined, and the frequencies used.
[0033] U.S. Pat. No. 4,963,745 (1990) to Magard discloses an octane
measuring process and device comprising the near infrared
absorbance of the methyne band measures octane (pump, RON, and MON)
with excellent correlation and can be used for gasoline blending.
This patent is an example of near infrared absorbance evaluation
between 1200 and 1236 nm applied to the methyne bank along with the
tertiary butyl band, indicative of sources of free radicals which
seem to lead to smooth combustion. The signal processing techniques
used, however, are complex, including first, second, third, and
fourth or higher derivative processing as well as various known
curve fitting techniques.
[0034] U.S. Pat. No. 5,362,965 (1994) to Maggard discloses an
indirect method for determining oxygenate content and/or octane of
hydrocarbon fuels using near-infrared absorption spectra selecting
nanometer frequencies in the range 1,300 to 1,359 to reduces the
temperature dependence of calibration equations that predict values
representative of both oxygenate content and octane.
[0035] U.S. Pat. Nos. 5,349,188 and 5,349,189 both issued (1994) to
Maggard discloses a process and apparatus for analysis of
hydrocarbons by near-infrared spectroscopy to measure the weight
percent, volume percent, or even mole percent of each component,
e.g. PIANO (paraffin, isoparaffin, aromoatic, napthens, and
olefins), octane (preferably research, motor or pump), and percent
of various hydrocarbons, e.g. alpha olefins.
[0036] U.S. Pat. No. 5,121,785 (1992) to Maggard et al. discloses
determination of aromatics in hydrocarbons by near infrared
spectroscopy of mid-distillate hydrocarbon fuels. Preferred NIR
bands of 1650-1700 and 2120-2256 exhibit excellent correlation with
aromatics content.
[0037] U.S. Pat. No. 5,121,377 to Brown discloses a method for
correcting spectral data for dat due to the spectral measurement
process itself and estimating unknown property and/or composition
data of a sample using such method. The correction method is
preferably included in a method of estimating unknown property
and/or composition data of a sample under consideration.
[0038] U.S. Pat. No. 5,446,681 (1995) to Gethner, et al. discloses
a method of estimating property and/or composition data of a test
sample. A method of operating a spectrometer to determine property
and/or composition data of a sample compares an on-line spectral
measurement of the sample using a computer controlled spectrometer,
statistical analysis of the sample data based upon a statistical
model using sample calibration data, and automatically identifying
a sample if necessary based upon statistical and expert system
(rule-based) criteria.
[0039] U.S. Pat. No. 5,424,959 (1995) to Reyes, et al. discloses a
method for interpretation of fluorescence fingerprints of crude
oils and other hydrocarbon mixtures using neural networks. The
artificial intelligence system is used with a conglomeration of
fluorescence data to provide a method of improving recognition of
an unknown from its spectral pattern.
[0040] U.S. Pat. No. 5,218,529 (1993) to Meyer, et al. discloses a
neural network system and methods for analysis of organic materials
and structures using spectral data. Characteristic spectra are
obtained for the materials via spectroscopy techniques including
nuclear magnetic resonance spectroscopy, infrared absorption
analysis, x-ray analysis, mass spectroscopy and gas
chromatography.
[0041] Japan Patent no. JP9243634 (1997) to Sato and Fujimoto
discloses an apparatus for estimating properties for petroleum
product. The property estimation means is equipped with a property
estimation model using a neutral network and a property analyzed
value obtained by analyzing the petroleum product. In the property
estimation model, properties can be calculated from operation data
within a real time.
[0042] U.S. Pat. No. 5,452,232 (1995) to Espinosa, et al. discloses
a method and apparatus for determining a property or yield of a
hydrocarbon product based on Near Infra-Red (NIR) spectrum of the
feedstock.
[0043] U.S. Pat. No. 5,360,972 (1994) to DiFoggio, et al. discloses
a method for improving chemometric estimations of the physical
properties of materials. The invention discloses a method for
improving the estimation of physical properties of a material based
on the near and mid-infrared spectrum of the material. The method
further discloses use of a combination of Raman spectroscopy, gas
chromatography, and mid-infrared spectroscopy for the same purpose
of the invention.
[0044] U.S. Pat. No. 5,225,679 (1003) to Clarke, et al. discloses
methods and apparatus for determining hydrocarbon fuel properties.
Detection is made of absorption related to signature vibrational
modes associated with the fuel component molecules when excited in
the mid-IR. From the determined fuel component quantity and know
characteristics, the fuel solution properties are predicted. In one
embodiment, octane rating and vapor pressure for a fuel solution is
determined in-situ and in real time.
[0045] U.S. Pat. No. 5,412,581 (1995) to Tackett discloses method
for measuring physical properties of hydrocarbons using near
infrared spectrum measurements.
[0046] In all the above patents the property value for the
petroleum hydrocarbon mixture was calculated using a mathematical
correlation or neural network the impute parameters of which are
either the GC-measured pure component concentrations or the
spectral parameters. Since a property like octane number for
example can be estimated by fitting GC and IR characteristic output
data then the same can be done for all thero-physical properties as
well as using the characteristic output date from light
refraction.
[0047] All the above patents disclose using either infrared or gas
chromatography for the purpose of predicting one or more
proprieties of pure hydrocarbons or petroleum fractions.
[0048] None of the above patents claims or discloses using
refractive index or refractometry for that purpose. The method of
the present invention meets the novelty requirement.
[0049] European paten no. EP0071143 (1083) to Partky, discloses a
refractometer that measures the refractive index property but not
the other thermophysical properties. World Paten no. WO9509356
(19995) to Lawrence et al. and U.S. Pat. No. 5,482,076 (1995) to
Schopper, et al. both disclose a fluid detection system based on
the index of refraction which does not provide the fluid
thermophysical properties.
SUMMARY OF THE INVENTION
[0050] This invention relates to a method for predicting physical,
performance, perceptual and/or chemical properties of pure
hydrocarbons and hydrocarbon mixtures. The analytical method is
able to predict a set of date that consist of global petroleum
properties of pure hydrocarbons and hydrocarbon mixtures, form
correlative mathematical models which will be determined, according
to conventional analytical methods, ie. The refractive index.
[0051] It is a purpose of this invention to calculate the
properties of a hydrocarbon sample with high reliability. The
method of the invention comprises a property estimation apparatus
has a property estimation means estimating the properties of a
hydrocarbon product from the apparatus to output a property
estimate value. The property estimation means is equipped with a
property estimation model for a evaluating the property estimate
value outputted from the property estimation model and a property
analyzed value obtained by analyzing the hydrocarbon sample. The
property estimation model may comprise at least a regression
algorithm, a neural network algorithm, an optimization algorithm,
or generic algorithm, or the like.
[0052] In this invention a mathematical algorithm is used with
refractive index data to provide a method of improving recognition
of an unknown from its refractive as shown in FIG. 1. Customized
mathematical algorithms allow the ultimate organization and
resourceful use of assumption-free variables already existing in
refractive index apparatus for a much more comprehensive, discrete
and accurate differentiation and matching of thermo-physical and
transport properties than is possible with human memory. The
invention provides increased speed of fingerprinting analysis,
accuracy and reliability together with a decreased time, cost and
energy for the analysis.
[0053] The present invention is based on the recognition that the
molecules of components of a hydrocarbon solution each exhibit
physical and chemical characteristics that such signatures are
exhibited in terms of the refractive index and that such physical
and chemical characteristics can be correlated either linearly or
nonlinearly with said index of the solution.
[0054] Accordingly, in one embodiment of the invention, a know
volume of a hydrocarbon sample, placed in a refractometer and the
refractive index reading is recorded. The refractive index is
indicative of the characteristics of the hydrocarbon of interest.
The refractive index and that such physical and chemical
characteristics can be correlated either linearly or nonlinearly
with said index of the solution.
[0055] In another preferred embodiment the refractive index data is
plausibly correlated to the property of the hydrocarbon using
optimization algorithms. In another preferred embodiment the
refractive index data is correlated to the property of the
hydrocarbon using simple regression techniques. Yet in another
preferred embodiment the refractive index data is correlated to the
property of the hydrocarbon using neural networks.
[0056] In a preferred embodiment, the refractive index data is used
to compute the composition and the properties of the hydrocarbon
sample in the processing section within the refractive index,
apparatus, and a display output is then generated accordingly. In
another embodiment the refractive index data from the refractive
index apparatus is processed in a processing section out of the
device and a display output is then generated accordingly.
Likewise, other components and properties may be found and
quantified in a similar manner.
[0057] The refractive index method described above can be used to
predict a wide range of chemical and physical properties (including
performance and perceptual properties) of petroleum fuels such as,
API gravity @15.degree. C., Specific Gravity, Density @20.degree.
C., Average Boiling Point, Watson characterization factor,
Molecular Weight, Critical Volume, Reid Vapor Pressure, Kinematic
viscosity @37.8 & 98.9.degree. C., True critical temperature,
Pseudocritical temperature, True critical pressure, Pseudocritical
pressure, Acentric factor, Net heat of combustion @25.degree. C.,
conductivity @25.degree. C., Research octane number, Motor octane
numbers, Heat of Vaporization at the Normal Boiling point, Carbon
to hydrogen content, True vapor pressure, Flash point Freezing
point, Surface tension of liquid, Aniline point, Cloud point,
Critical compressibility factor, and Compositional Analysis for
sulfur, paraffin, naphthenes, and aromatics including
mono-aromatics, poly-aromatics, and the like, within the refractive
index apparatus in a shot time period and using one test.
[0058] Best of such simplicity, the invention enables hydrocarbon
properties to be easily determined and displayed. In fact, while
the ASTM methods of obtaining the physico-chemical properties
involved labor-intensive laboratory procedures, the present
invention provides an equivalent property measurement in-situ and
in real-time. The invention provides increased speed of
fingerprinting analysis, accuracy and reliability together with a
decreased learning curve and heighten objectivity for the
analysis.
[0059] Such apparatus is particularly useful for recognizing and
identifying organic compounds such as complex hydrocarbon, whose
analysis conventionally require a high level of training and many
hours of hard work to identify, and are frequently
indistinguishable from one another by human interpretation. The
present invention is therefore a valuable addition to the art of
fuels properties detection.
[0060] Upon further study of the specification and appended claims,
further objects and advantages of this invention will become
apparent to those skilled in the art.
BRIEF DESCRIPTION OF THE DRAWINGS
[0061] The above and other aspects, features, methods, processes
and advantages of the present invention will be better and more
fully understood by those skilled in the art with reference to the
following detailed and more particular description of specific and
preferred embodiments thereof, presented in conjunction with the
following drawings to show how the same may be carried into effect,
wherein:
[0062] FIG. 1 is shows a simplified block diagram of the invention
within its environment, wherein the measured properties of
petroleum fractions are illustrated.
[0063] FIG. 2 shows a simplified schematic representation of the
model, using the invention within its environment.
[0064] FIG. 3 shows a simplified block diagram of the components of
the apparatus for the invention within its environment.
[0065] FIG. 4 shows the API gravity of 424 pure hydrocarbon liquids
calculated using exponential expression and refractive index
measured at 25 degrees centigrade, evaluated in practice of the
invention.
[0066] FIG. 5 shows the solubility parameter of 287 pure
hydrocarbon liquids calculated using linear expression and
refractive index measured at 25 degrees centigrade, evaluated in
practice of the invention.
[0067] FIG. 6 shows the parity diagram for the solubility parameter
or 287 pure hydrocarbon liquids calculated using linear expression
and refractive index measured at 25 degrees centigrade, evaluated
in practice of the invention.
[0068] FIG. 7 shows the API gravity of 42 petroleum factions
calculated using linear expression and refractive index measured at
50 to 70 degrees centigrade, evaluated in practice of the
invention.
[0069] FIG. 8 shows the parity diagram for the API gravity of 42
petroleum factions calculated using linear expression and
refractive index measure at 50 to 790 degrees centigrade, evaluate
in practice of the invention.
[0070] FIG. 9 shows the API gravity of 43 petroleum fractions
collocated using quadratic expression and refractive index measured
at 50 to 70 degrees centigrade, evaluated in practice of the
invention.
[0071] FIG. 10 shows the parity diagram for the API gravity of 42
petroleum factions calculated using quadratic expressions and
refractive index measured at 50 to 70 degrees centigrade, evaluated
in practice of the invention.
[0072] FIG. 11 shows the API gravity of 15 petroleum factions
calculated using linear expression and refractive index measured at
20 degrees centigrade, evaluated in practice of the invention.
[0073] FIG. 12 shows the API gravity of 15 petroleum factions
calculated using linear expression and refractive index measured at
20 degrees for the API gravity of 15 petroleum factions calculated
sing linear expression and refractive index measured at 20 degrees
centigrade, evaluated in practice of the invention.
[0074] FIG. 13 shows the API gravity of 15 petroleum factions
calculated using quadratic expression and refractive index measured
at 20 degrees centigrade, evaluated in practice of the
invention.
[0075] FIG. 13 shows the parity diagram for the API gravity of 15
petroleum factions calculated using quadratic expression and
refractive index measured at 20 degrees centigrade, evaluated in
practice of the invention.
[0076] FIG. 15 shows the mid- (average) boiling point of 196
petroleum fraction calculated using exponential expression and API
gravity, evaluated in practice of the invention.
[0077] FIG. 16 shows the parity diagram for the Mid- (average)
boiling point of 196 petroleum factions calculated using
exponential expression and API gravity, evaluated in practice of
the invention.
[0078] FIG. 17 shows a handheld analyzer, a Laboratory bench-top
analyzer and an inline process sample analyzer.
DETAILED DESCRIPTION OF THE INVENTION
[0079] There will now be described, by way of example only, the
best mode contemplated by the inventor for carrying out the
invention. In the following description numerous specific details
are set forth in order to provide a thorough understanding of the
present invention. It will be apparent however, to one skilled in
the art, that the present invention may be practiced without
limitation to these specific details. In other instances, well
known methods and structures have not been described in detail so
as not to unnecessarily obscure the present invention.
[0080] It is therefore an object of the present invention to
provide a simple method and apparatus for hydrocarbon property
detection.
[0081] It is another object of the present invention to provide a
relatively inexpensive, real-time insitu detection method and
apparatus for detection of the properties of a pure hydrocarbon and
a hydrocarbon solution.
[0082] It is still another object of the present invention to
provide a simplified method and apparatus for obtaining refractive
index data relating to a pure hydrocarbon or hydrocarbon solution
and from which predicting fuel properties without complex
analytical processing techniques.
[0083] It is further an object of the present invention to provide
a method for predicting various properties of a pure hydrocarbon or
hydrocarbon solution based on the knowledge of the mixture's
refractive index that is easily measurable in the laboratory using
refractometers
[0084] Yet, it s further an object of the present invention to is
to provide a method to predict the various properties of a pure
hydrocarbon or hydrocarbon solution based on the knowledge of the
mixture's refractive index using refractometer which can be
incorporated into the ASTM reflective index apparatus to predict
and display the various prosperities for the petroleum faction
using one single laboratory text and apparatus.
[0085] It is further an object of the present invention to provide
a procedure for predicting the fluid properties that is simple and
straightforward.
[0086] It is further an object of the present invention to provide
a model that requires limited information form readily available
lab analysis and simple analytical characterization to describe a
petroleum feedstock.
[0087] It is further an object of the present invention to provide
a method for inline prediction the global properties of pure
hydrocarbon and hydrocarbon mixtures during various physical and
chemical processing scenarios as they progress.
[0088] It is further an object of the present invention to provide
a computerized procedure that can be incorporated as software in
the ASTM refractive index apparatus hardware to provide measurement
of the properties of pure components and of petroleum fractions
using one single laboratory test.
[0089] It is further an object of the present invention to provide
a method an apparatus that will leads to large savings in terms of
energy, time and cost whereby one refractometer test can replace
the test equipment needed to predict all of the properties of a
hydrocarbon or a hydrocarbon mixture such as petroleum.
[0090] It is further an object of the present invention to provide
a method that can calculate the properties of petroleum fractions
with good accuracy when at least one bulk property (e.g. ASTM
refractive index) is available.
[0091] It is further an object of the present invention to provide
a method that is applicable to any petroleum faction or pure
hydrocarbons.
[0092] The invention will now be explained with reference to some
exemplary equations and n)correlations whereby further objects and
advantages of this invention will become apparent to those skilled
in the art.
Pure Hydrocarbon Liquids
[0093] The value of the refractive index outputted from the
conventional digital refractometer incorporated(integrated) in this
invention is used to calculate the API gravity using the following
exponential expression,
API=5.times.10.sup.7 exp(-9.5788 n) (2)
[0094] This equation was developed using the experimental data for
the API gravity of 424 pure hydrocarbon liquids and refractive
index measured at 25 degrees centigrade. This equation applies for
pure hydrocarbon liquids with minimum refractive index of 1.3294
and a maximum of 1.6151 which corresponds to a minimum API of 6 and
maximum of 120. The question is applicable to different types of
hydrocarbons like paraffins, iso-paraffins, olefins, naphthenes and
aromatics. It has an average percentage error of 5 and a
correlation coefficient of 0.95 as shown in FIG. 4.
[0095] The specific gravity SG at 15 degrees centigrade can be
obtained from the following well know prior relation:
A P I = 141.5 S G - 131.5 ( 3 ) ##EQU00001##
[0096] Which upon rearrangement becomes as follows,
A P I = 141.5 A P I + 131.5 ( 4 ) ##EQU00002##
[0097] Numerical value of d.sub.20 for a given compound is very
close to the value of SG, which represents density at 15.5.degree.
C. in the unit of g/cm.sup.3. The most convenient way to estimate
d.sup.20 is through specific gravity. As a rule of thumb
d.sub.20=0.995 SG. One can use this equation to obtain a value of
density, d.sub.20, at 20.degree. C. (g/cm.sup.3) from the specific
gravity at 15.5.degree. C. from the prior art relation by Riazi et
al. as follows,
d.sub.20=SG-4.5.times.10.sup.-3(2.34-1.9 SG) (5)
[0098] Similarly, the value of the refractive index outputted from
the conventional digital refractometer incorporated (integrated) in
this invention is used to calculate the solubility parameter using
the following linear expression,
SP+12.838 n-10.542 (6)
[0099] This equation was developed using the experimental data for
the solubility parameter of 287 pure hydrocarbon liquids and their
refractive index measured as 25 degrees centigrade. This equation
applies for pure hydrocarbon liquids with minimum refractive index
of 1.3284 and a maximum of 1.6151 which corresponds to a minimum
solubility parameter of 6.2 and maximum of 10
(cal/cm.sup.3).sup.0.5. The equation is applicable to different
types of hydrocarbons like paraffins, iso-paraffins, olefins,
naphthenes, and aromatics. It has an average percentage error of
2.2% and a correlation coefficient of 0.92 as shown in FIG. 5. The
parity diagram for the same is shown in FIG. 6.
[0100] Petroleum Fractions
[0101] The global properties are calculated for the petroleum
fraction using well established methods in the literature or from
methods developed specifically for this purpose. The determination
of the petroleum fractions global properties involves either
accessing standard correlations or simulating various thermodynamic
experiments. Several charts and correlations in the literature
predict the physical, thermodynamic, and transport properties of
undefined mixtures, based on the boiling pint, specific gravity,
and some characterization factors. Examples of such chars and
correlations are available in the API-TDB [10] and other
references. The global properties determined by the present
invention as shown in FIG. 1.
[0102] The value of the refractive index outputted from the
conventional digital refractometer incorporated (integrated) in
this invention is used to calculate the API gravity using the
following linear expression,
API=-320.77 n+501.4 (7)
[0103] This equation was developed using the experimental data for
the API gravity of 42 petroleum fraction and refractive index
measured at 53 to 70 degrees centigrade. This equation applies for
petroleum fractions with minimum refractive index of 1.42 and a
maximum of 1.5227 which corresponds to a minimum API of 14 and
maximum of 47. The equation is applicable to different types of
petroleum fraction like naphtha, kerosene, middle distillated,
heavy distillate, vacuum distillate, gasoil, heavy gasoil, and
cracked feed. It has an average percentage error of 2.5% and a
correlation coefficient pf 0.992 as shown in FIG. 7. The parity
diagram showing the accuracy of the predictions is shown in FIG. 8.
Source of error in the calculated API related to different
temperature values at which the refractive index is measured
between 53 to 70 degrees C., but still the predictions are very
accurate.
[0104] Alternatively the following quadratic expression may be used
to obtain better predictions
API=836.17 n.sup.2-2775.4 n+2302.2 (8)
[0105] This equation predicts the API gravity with an average error
of 1.3% and a correlation coefficient of 0.997 as shown in FIG. 9
and the parity diagram in FIG. 10.
[0106] The value of the refractive index outputted from the
conventional digital refractometer incorporated(integrated) in this
invention is used to calculate the API gravity using the following
linear expression.
API=-394.12 n+615.12 (9)
[0107] This equation was developed using the experimental data for
the API gravity of 15 petroleum fractions and refractive index
measured at 20 degrees centigrade. This equation applies for
petroleum fractions with minimum refractive index of 1.9385 and a
maximum of 1.4976 which corresponds to a minimum API of 26 and
maximum of 66. The equation is applicable to different types of
petroleum fractions like naphta, kerosene, middle distillate, and
heavy gasoil. It has an average percentage error of 2/3% and a
correlation coefficient of 0.99 as shown in FIG. 11 which is very
accurate. The parity diagram showing the accuracy of the
predictions is shown in FIG. 12.
[0108] Alternatively the following quadratic expression may be used
to obtain better predictions
API=1.031.6 n.sup.2-3389.2 n+2788.1 (10)
[0109] This equation predicts the API gravity with an average error
of 1.3% and a correlation coefficient of 0.996 as shown in FIG. 13
and the parity diagram in FIG. 14.
[0110] The specific gravity SG at 15 degrees centigrade can be
obtained from Equation (4) described above.
[0111] When at least one additional property is available for a
liquid hydrocarbon or petroleum fraction such as the boiling point,
molecular weight, critical temperature, critical press, critical
volume, heat of vaporization, kinematic viscosity, or density, the
correlations present by Riaz (Ind. Eng. Chem. Res., 40, 8, 200,
1976-1984--Chem. Eng. Comm., 176 1999, 1750193) the teachings of
which are incorporated herein by reference, may be used to estimate
equation of state (EOS) parameters (for such property estimation as
density and specific volume in addition to phase behavior and
equilibrium calculations), critical constants, the composition of
petroleum fractions (in terms of paraffin, thermal conductivity,
diffusion coefficient) of hydrocarbon fluids using the refractive
index exclusively/alone. Said at least one additional property is
estimable by using correlations presented therein from refractive
index exclusively which may be obtained by refractometer using a
refractometer.
[0112] Recently Riazi et. Al. made an extensive analysis of
predictive methods and applications of refractive index in
prediction of other physical properties of hydrocarbon systems. An
evaluation of this method for some petroleum fractions is
demonstrated in detail therein. The limitation in these analyses is
that an additional parameter is required along with the refractive
index rendering the methods presented therein impractical.
[0113] To obtain the necessary additional correlating parameter,
the calculated API gravity value from the refractive index
outputted from the conventional digital refractometer incorporated
(integrated) in this invention is used to calculate the petroleum
fractions average boiling point using the following exponential
expression,
T.sub.b=(.degree. C.)=950.09 exp(-0.0335 API) (11)
[0114] Where T.sub.b is the ASTM-D86 temperature at 50% volume
vaporized in degrees centigrade.
[0115] This equation was developed using the experimental data for
the average boiling point of 196 petroleum fractions and the API
gravity. This equation applies for petroleum fractions with minimum
API gravity of 12.3 and a maximum of 75.1 which corresponds to a
minimum average boiling point of 64.4 and maximum of 544 degrees
centigrade. The equation is applicable to different types of
petroleum fractions like light naphtha, saturated naphtha,
unsaturated naphtha, heavy naphtha, kerosene, ATK, diesel, gasoil,
vacuum gasoil, coker gasoil, atmospheric residue, desulfurized
residue. It has an average percentage error of 2.8% (12.6 max.) and
a correlation coefficient of 0.98 as shown in FIG. 15 which is very
accurate. The parity diagram showing the accuracy of the
predictions is shown in FIG. 16.
[0116] Therefore, once the API of the petroleum fraction is
determined from RI, it can be used to determine the average
(middle) boiling point. Both the refractive index and the average
boiling point can e used as in FIG. 2 to calculate more properties
using prior art methods described herein and elsewhere.
[0117] The most commonly used characterization factor is that
proposed by Watson [10]. The Watson or UOP characterization factor
which is an index of paraffinicity of the sample requires the mean
average boiling point (MeABP) or simply the average boiling point
in Kelvin and the standard specific gravity (SG) at 15.6.degree. C.
of the petroleum fraction and is defined as follows,
K W = ( 1.8 Tb ) 1 / 3 S G ( 12 ) ##EQU00003##
[0118] The following relation can be used to determine the critical
constants, molecular weight, density, and boiling point,
.THETA.=a.sub.0
exp(b.sub.0T.sub.b+c0I20+d0T.sub.bI.sub.20)T.sub.b.sup.eoI.sub.20.sup.f0
(13)
[0119] where .THETA. is a property such as the critical
temperature, T.sub.c(K), critical pressure, P.sub.c(bar), critical
volume, V.sub.c(m.sup.3/kg), specific gravity at 15.5.degree. C.
(60.degree. F.), SG, and the heat of vaporization at the normal
boiling point in KJ/Kmol, .DELTA.H.sub.v.
TABLE-US-00001 Constants in Equation 13 for various properties:
.theta. = a.sub.0 exp (b.sub.0 T.sub.b + c.sub.0 I.sub.20 + d.sub.0
T.sub.b I.sub.20) T.sub.b.sup.e.sup.0 I.sub.20.sup.f.sup.0 .theta.
a.sub.0 b.sub.0 c.sub.0 d.sub.0 e.sub.0 f.sub.0 AAD % T.sub.c
4.4876 .times. 10.sup.5 -1.3171 .times. 10.sup.-3 -16.9097 4.5236
.times. 10.sup.-3 0.6154 4.3469 0.6 P.sub.c 8.4027 .times.
10.sup.23 -1.2067 .times. 10.sup.-2 -74.5612 0.0342 -1.0303 18.4330
2.6 V.sub.c 6.712 .times. 10.sup.-6 -2.72 .times. 10.sup.-3 0.91548
7.92 .times. 10.sup.-3 0.5775 -2.1548 1.8 MW 8.9205 .times.
10.sup.-6 15.5833 .times. 10.sup.-6 4.2376 0 2.0935 -1.9985 2.3 SG
2.4381 .times. 10.sup.7 -4.194 .times. 10.sup.-4 -23.5535 3.9874
.times. 10.sup.-3 -0.3418 6.9195 0.5 .DELTA.H.sub.v 39.741 0 0 0
1.13529 0.02414 1.6
[0120] The refractive index parameters I.sub.20, which is
considered as a size parameter (defined as the ratio of the actual
molar volume of molecules, R.sub.m (molar refraction), to the
apparent molar volume of molecules, V), is determined using the
following relation from the refractive index n measured
experimentally at 20.degree. C.,
I 20 = n 20 2 - 1 n 20 2 + 2 ( 14 ) ##EQU00004##
[0121] The density of the petroleum fraction at 20.degree. C. and 1
atm can be determined using one of the following relations
depending on the MW of the petroleum fraction,
For MW.ltoreq.300 d.sub.20=0.9837 T.sub.b.sup.0.002 SG.sup.1.005
(15)
For MW>300 d.sub.20=2.8309 MW.sub.b.sup.0.004 I.sub.201.1354
(16)
[0122] where T.sub.b is in degrees Kelvin.
[0123] Alternatively, the molecular weight of light petroleum
fractions (where the specific gravity is less than 0.9o7 and the
boiling point is less than 840 K) is determined using the API
recommended equation [19] which requires only the mean average
boiling point (T.sub.b) in Kelvin and the standard specific gravity
(SG) of the petroleum fraction.
MW=42.965(T.sub.b.sup.1.26007 SG.sup.4.98308) (17)
[exp(2.097.10.sup.-4 T.sub.b-7.78712 SG+2.08476.10.sup.-3
T.sub.bSG)]
[0124] The refractivity intercept, Ri and parameter, m are used to
characterize the petroleum faction. These parameters are both
defined in terms of the sodium D line refractive index at
20.degree. C., n.sub.20 as follows
Ri=n.sub.20-d.sub.20/2 (18)
M=MW(n.sub.20-1.475) (19)
[0125] Many properties can be determined using these parameters and
these are shown in the work of Riazi among others. The sulfur
content and the Paraffin, napthenes, and aromatic content of
petroleum fractions are show here just as an example. For fraction
with molecular weights of less than 250, the sulfur weight percent
(XS) can be calculated with an accuracy of about 0.15 using the
following relation:
X.sub.s=177.448-170.946 R.sub.i+0.2258 n+4.054 SG (20)
[0126] Correlations are also available for heavier petroleum
factions with MW more than 250 (Ind. Eng. Chem. Res. 1999, 38, 11,
4507).
[0127] For petroleum factions with a MW of less than 250, the
volume percent of paraffins, napthenes, and aromatics can be
determined using the following correlations with an average error
of about 5%,
X.sub.P=325.74-348.148+1.166 m (21)
X.sub.N=-195.71+363.853 SG-3.992 m (22)
X.sub.A=100-(XP+XN) (23)
[0128] Also for petroleum fractions with MW of less than 250, the
volume percent of monaromatics, (X.sub.MA) and polyardomatics
((X.sub.PA) can be determined using the following correlations with
an average error of about 5-6%,
X.sub.MA=-6282.45+5990.816 Ri-2.4833 m (24)
X.sub.PA=1188.175-1122.13 Ri+2.3745 m (25)
Where,
X.sub.A=X.sub.MA+X.sub.PA (26)
[0129] When the calculated value of any of XP, XN, XA is negative
then it should be set equal to zero and the other values should be
adjusted accordingly,
[0130] Other correlations are also available for heavier petroleum
fractions with MW more than 250 (Ind. Eng. Chem. Res 1986, 25, 4,
1009).
[0131] Alternatively, the molecular group-type (paraffins,
naphthenes and aromatics) fractional composition for the light
petroleum fraction may be determined using the generalized method
proposed by Riazi and Daubert. This method determined the mole
fractions of the paraffins, X.sub.P, napthenes, X.sub.N and
aromatics, X.sub.Ar using the following equations,
X.sub.P=-23.94+24.21 R.sub.i-1.092 VGF (27)
X.sub.N=41.14-39.43 R.sub.i+0.672 VGF (28)
X.sub.A=-16.2+15.22 R.sub.i+0.465 VGF (29)
R.sub.i=n-(d/2) (30)
n=[(1+2i)/(1-i)].sup.0.5 (31)
VGF=-1.816+3.484 SG-0.1156.upsilon..sub.37.8 (32)
Where R.sub.i is the refractivity intercept, n is the refractive
index at 20.degree. C., d is the density in g/cm.sup.3 at
20.degree. C. and 0.1 MPa, VGF is the viscosity gravity function,
SG is the specific gravity at 15.degree. C., and is the kinematic
viscosity at 38.degree. C. in mm.sup.2/s.
[0132] The viscosity of petroleum oil at the standard temperatures
of 37.58 and 98.9.degree. C. is determined using the following
relation by Abbot et. Al.
log v 37.8 = 4.39371 - 1.94733 K W + 0.12769 K W 2 + 3.2629 .10 - 4
A P I 2 - 1.18246 .10 - 2 K W A P I + ( 8.0325 .10 - 2 K W +
1.24899 A P I + 0.19768 A P I 2 ) ( A P I + 26.786 - 2.6296 K W ) (
33 ) log v 98.9 = - 0.463634 - 0.166532 A P I + 5.13447 .10 - 4 A P
I 2 - 8.48995 .10 - 3 K W A P I + ( 8.0325 .10 - 2 K W + 1.24899 A
P I + 0.19768 A P I 2 ) ( A P I + 26.786 - 2.6296 K W ) ( 34 )
##EQU00005##
[0133] where K.sub.w is Watson's characterization factor given by
Equation 12, API is API gravity given by Equation 3,
.upsilon..sub.37.8 is the viscosity at 37.8.degree. C. and U98.9 is
the viscosity at 98.9.degree. C. both in mm.sup.2/s, and log is the
common logarithm (base 10).
[0134] The liquid thermal conductivity at 25.degree. C. for the
petroleum factions is determined using the following
correlation,
.lamda.=2.540312 (SG/T).sup.0.5-0.0144485 (35)
[0135] where, .lamda. is the thermal conductivity in W/(m,K), T is
the temperature in Kelvin equal to 298 K, and SG is the specific
gravity.
[0136] The Reid vapor pressure (RVP) may be determined using the
Riazi-Albahri equation which predicts RVP with an accuracy of 0.06
bar.
R V P = P cp exp ( Y ) Y = - X ( T b S G T r ) ( 1 - T r ) 5 X = -
276.7445 + 0.06444 T b + 10.0245 S G - 0.129 T b S G + 9968.8675 T
b S G + 44.6778 ln T b + 63.6683 ln S G T r = .311 / T cp ( 36 )
##EQU00006##
[0137] where T.sub.cp and P.sub.cp are the pseudo critical
temperature and pressure of the petroleum faction in degrees Kelvin
and bar, respectably. SG is the specific gravity at 15.6.degree.
C., RVP is in bars and T.sub.b is the normal boiling point in
degrees Kelvin.
[0138] The pseudo-critical temperature (T.sub.cp), pseudo-critical
pressure (P.sub.cp) and the accentric factor (.omega.) of petroleum
oil are estimated by the methods of Lee-Kessler as follows,
T Cp = 189.8 + 450.6 S G + T b ( 0.4244 + 0.1174 S G ) + ( 14 , 410
- 100 , 688 S G ) T b ( 37 ) ln P Cp = 5.68925 - 0.0566 S G - 10 -
3 T b ( 0.436392 + 4.12164 S G + 0.213426 S G 2 ) + 10 - 7 T b 2 (
4.75794 + 11.819 S G + 1.53015 S G 2 ) - 10 - 10 T b 3 ( 2.45055 +
9.901 S G 2 ) ( 37 ) .omega. = - 7.904 + 0.1352 K W - 0.007465 K W
2 + 8.359 T br + ( 1.408 - 0.1063 K W ) T br T br = T b T c ( 39 )
##EQU00007##
[0139] where T.sub.cp is the pseudo critical temperature in Kelvin,
P.sub.cp pressure in bar, .omega. is the acentric factor, T.sub.b
is the normal boiling point in degrees Kelvin, SG is the standard
specific gravity, T.sub.br is the reduced boiling point temperature
from Equation 30 K.sub.W is Walton's characterization fact, T.sub.C
is the critical temperature Kelvin and in is the Napierian
logarithm.
[0140] The isobaric specific heat for a liquid petroleum fraction
is estimated by the 1933 correlation attributed to Watson and
Nelson.
Cp.sub.I=4.185(0.35+0.055
K.sub.W)(0.3065-0.16734SG+T(1.467.times.10.sup.-3-5.508.times.10.sup.-4SG-
)) (40)
where K.sub.W is Watson's characterization factor, SG is the
standard specific gravity, T is the temperature in Kelvin, and
Cp.sub.I is the isobaric mass specific heat for liquid in
KJ/kg,K).
[0141] The isobaric vapor heat capacity at 15.6.degree. C. is
determined using the method of Lee-Kesler also cited in the API
technical data book,
Cp g = 4.185 ( B + 3.6 CT + 9.72 DT 2 ) B = - 0.35644 + 0.02972 K W
+ .alpha. ( 0.29502 - 0.2846 S G ) C = - 10 - 4 2 ( 2.9247 - 1.5524
K W + 0.05543 K W 2 + .alpha. ( 6.0283 - 5.0694 S G ) ) D = - 10 -
7 3 ( 1.6946 + 0.0844 .alpha. ) .alpha. = 0 unless 10 < K W <
12.8 and 0.7 < S G < 0.885 then .alpha. = [ ( 12.8 K W - 1 )
( 1 - 10 K W ) ( S G - 0.885 ) ( S G - 0.7 ) .times. 10 4 ] 2 ( 41
) ##EQU00008##
[0142] where C.sub.pg is the specific heat of petroleum faction in
the ideal gas state in KJ/(kg.K), T is the temperature in Kelvin,
K.sub.w is Watson's characterization factor, SG is the standard
specific gravity, and B, C, and D are coefficients.
[0143] The research octane number (RON) is determined by the
graphical method of Nelson which we have digitized. The correlation
requires the mid-boiling point of gasoline and either the paraffin
content or the Watson characterization factor. The mote octane
number (MON) is determined from the following correlation derived
from that proposed by Jenkins for olefin free fuels,
MON=22.5+0.83 RON-20.0 SG
[0144] Where SG is the specific gravity of the fuel at 15.5.degree.
C.
[0145] The net heat of combustion is KJ/Kg is approximated by the
following API recommended equation as a function of the API gravity
and Watson Characterization factor (K.sub.W),
.DELTA.H.sub.c=19,783.6+1969.7 K.sub.w+267.3 API+0.2834
API.sup.2-23.146 K.sub.w API (43)
[0146] Another relation that provides equally good results but
better correlation is that of Gorenkov et al. for the net heat of
combustion of jet fuels in KJ/kg which is modified her for naphtha
in the following form,
.DELTA. H c = 35 , 696 + 94.87 ( X A ) - 9.44 ( T ave ) - 0.35 ( X
A ) ( T ave ) + 5 , 525 - 111.1 ( X A ) + 10.15 ( T ave ) + 0.377 (
X A ) ( T ave ) 0.001 d ( 44 ) ##EQU00009##
[0147] where X.sub.A is the content of aromatic hydrocarbons in wt
% and T.sub.ave is the average boiling point of the fuel (T.sub.b)
in .degree. C. and d is the fuel density at 20.degree. C. in
kg/m.sup.3.
[0148] The invention has been explained with reference to some
exemplary equation and correlations. It is understood that those
skilled in the art will be able to measure the same and other
properties, by calculating them using the above parameters, using
other equations and correlations which can be done without further
experimentations. Those are intended to be encompassed in the
claims of this invention.
[0149] The above procedure can be applied to measure other
properties of the petroleum faction by calculating through various
regression techniques from appropriate experimental data the values
of the constants of any appropriate equations and correlations. The
invention may as well be applied using prior art correlations or
digitization of the prior art figures and data tabulations the
accuracy of which has already been verified in the prior art
references. The refractive index may as well be the true refractive
index obtained for refractometer or any refractive index obtainable
from a refractive index device, a gas chromatograph, or infrared
spectroscopy and the like since these are well established in the
prior art or can be easily developed by those skilled in the art
without parting from the teachings of the present invention or
further experimentation.
[0150] When experimental data are available, one could easily
correlate the various properties of the petroleum fraction
disclosed hereinabove directly with the refractive index using
correlations, and algorithms like neural networks, and genetic
algorithms for example, or other correlating or data fitting
techniques for the purpose of the present invention.
[0151] An apparatus comprising such mathematical models is
particularly useful of recognizing and identifying organic
compounds such as complex hydrocarbons, whose properties
conventionally require a high level of training and may hours of
hard work to identify, and are frequently indistinguishable from
one another by human interpretation. The method and apparatus of
the present invention is useful for the measuring the properties of
pure hydrocarbon liquids and petroleum fractions in the laboratory
or (on-site) easily and rapidly in one single test from a small
sample with accurate results using a simple inexpensive
refractometer. It is also useful for property measurements in the
field in automatic inline analyzers for quality assurance and in
advanced control strategy systems to control production operations
to meet required product specifications. The said invention
provides increased speed of fingerprinting analysis, accuracy and
reliability together with a decrease learning curve and heightened
objectivity for the analysis.
[0152] Property measurement of petroleum fractions using neural
networks
[0153] An artificial intelligence system can be used with
refractive index data to provide a method of improving recognition
of an unknown from its boiling pattern by training the neural
networks from appropriate experimental data. Customized neural
network systems allow the ultimate organization and resourceful use
of variables already existing in the refractive index apparatus
(refractometer) for a much more comprehensive, discrete, and
accurate differentiation and matching of boiling point than is
possible with human memory.
[0154] Detail description of the neural network architecture that
can be used for the purpose of this invention is explained in
details in Albari the teaching of which are incorporated herein by
reference. Those experts in the art can easily ascertain that any
network type, network architecture, input range, training function,
adaptive learning function, and transfer function may be used
without departing from the spirit and scope of the present
invention and are all claimed herein.
PREFERRED EMBODIMENTS
[0155] The above and other aspects, features, and advantages of the
present invention will be better and more fully understood by
reference to the following detailed and more particular description
of the invention, present in conjunction with the following
examples which are provided to further define the invention and are
in non way meant to limit the scope of the invention to the
particulars of these examples, wherein:
[0156] FIG. 17 shows a handheld analyzer 10, a Laboratory bench-top
analyzer 20 and an inline process sample analyzer 30.
[0157] The Invention Handheld or Laboratory Bench-Top Digital
Analyzer
[0158] In a preferred embodiment with refereeing to the
accompanying figures, and in particular to FIG. 3, the present
invention uses the prior digital refractive index analyzer
(refractometer) which measures and digitally displays the
refractive index then using electronic circuit and software
comprising operating system, programming language, property
estimation algorithms and correlations to calculate the various
thermophysical properties of a hydrocarbon sample from its
refractive index property then output (display) said properties
instead of (or along with) displaying the refractive index
number.
[0159] The present invention may be used as a handheld 10 or
laboratory bench-top digital analyzer 20 wherein a small sample of
the product analyzed using refractometry and outputting the
measured property value to be displayed on an LCD screen on the
analyzer apparatus or on the screen of a computer 40 interfaced
with the analyzer apparatus.
[0160] As Inline Digital Analyzer
[0161] The present invention may be used as an inline analyzer 30
wherein an automatic system is used to automatically draw a small
sample of the product, analyze it using refractometry, then
disposing it and outputting the measured property value to the
advanced control strategy system or displaying it in the control
room to the operator for action.
[0162] A non-limiting example would be to control the crude oil
distillation units main fractionator overhead temperature using
output from such inline analyzer placed on the naphtha product to
provide set-point to the fractionator overhead temperature
controller to increase overhead temperature when naphtha API is
measured by an inline analyzer and found to be lower than required
specifications.
[0163] Another non-limiting example would be to control the crude
oil distillation unit main fractionator diesel product API using
output from such inline analyzer 30 for the diesel product, to
provide set-point to diesel draw-off rate controller from the
fractionator to increase the diesels draw-off rate when measured
API by such inline analyzer 30 is found to be lower than required
specifications.
[0164] Equivalents
[0165] From the foregoing description, one skilled in the art can
easily ascertain the essential characteristics of this invention
and, without departing from the spirit and scope thereof, can make
various changes and modifications of the invention to adapt it to
various usages and conditions.
[0166] Such variations and changes may include, but are not limited
to, using other mathematical or computational methods such as suing
other generalized correlations, neural networks algorithms, genetic
algorithms, or an other correlation method that can still represent
the chemical and physical behavior of the petroleum fraction. It is
believed that such can be accomplished without excessive
experimentation. In any case, any such variations are all claimed
under the scope of this invention.
[0167] Those experts in the art will also realize that the method
of invention as explained by exemplary equations, correlations, and
conditions and is not to be construed as limiting but only to
provide examples.
[0168] The methods of the present invention have been explained
with reference to plurality of references the teachings of which
are all incorporated herein by reference.
[0169] This invention has been described hereinabove, although with
reference to a plurality of illustrative exemplary and preferred
embodiments, it is to be understood that it is in no way to be
construed as limiting. However, it is readily appreciated that,
from reading this disclosure, the invention my be embodied in other
specific forms without departing from the spirit or essential
characteristics or attributes to bring modifications by replacing
some elements for this invention as practiced by their equivalents,
which would achieve the same goal and thereof and accordingly
reference should be made to the appended claims, rather than to the
foregoing specification, as indicating the scope of the invention.
Accordingly, those skilled in the art will recognize, or be able to
ascertain using no more than routine experimentation, many
equivalents to the specific embodiments and the scope of the
invention being indicated by the appended claims described herein.
Such equivalents, obvious variations, and all changes which come
within the meaning and equivalency of the claims are therefore
intended to be encompassed therein and are deemed covered by the
claims of this invention.
[0170] From the foregoing description, one skilled in the art can
easily ascertain the essential characteristics of this invention
and, without departing from the spirit and scope thereof, can make
various changes and modifications of the invention to adapt it to
various usages and conditions. Such variations and changes may
include, for example, altering the number of components in the
housing or using equivalents. It is believed that such can be
accomplished without excessive experimentation. In any case, any
such variations are all claimed under the scope of this
invention.
[0171] Nomenclature
[0172] .lamda.=Liquid thermal conductivity @25.degree. C.
[0173] .OMEGA.=Paraffin, Naphthene, or Aromatic content.
[0174] (.DELTA.H.sub.v).sub.Tb=Heat of vaporization @ NBP.
[0175] .sigma..sub.25=Surface tension for liquid @25.degree. C.
[0176] .DELTA.H.sub.c=Net heat of combustion @25.degree. C.
[0177] .PHI..sub.i=Surface fraction.
[0178] Cp.sub.g=Specific heat of petroleum fraction 15.6.degree. C.
in the ideal gas state.
[0179] Cp.sub.I=Isobaric mass specific heat for liquid 15.6.degree.
C.
[0180] d=Density in g/cm.sup.3 at 20.degree. C. and 0.1 MPa.
[0181] H.sub.2=Hydrogen content.
[0182] K=Liquid thermal conductivity at 25.degree. C.
[0183] K.sub.w=Watson characterization factor.
[0184] P.sub.c=Critical pressure.
[0185] Pc.sub.p=Pseudo-critical pressure.
[0186] P.sup.v.sub.37.8=Vapor pressure at 37.8.degree. C.
[0187] n=Refractive index at 20.degree. C.
[0188] R.sub.i=Refractivity intercept.
[0189] Ta=Aniline point.
[0190] T.sub.b=Normal boiling point at 1 atm.
[0191] T.sub.br=Reduced boiling point temperature.
[0192] T.sub.c=Critical temperature.
[0193] Tc.sub.m=True critical temperature of the mixture.
[0194] Tc.sub.p=Pseudo-critical temperature.
[0195] T.sub.f=Freezing temperature.
[0196] T.sub.r=Reduced temperature.
[0197] VGF=Viscosity gravity function.
[0198] X.sub.A=Mole fraction of aromatics.
[0199] X.sub.N=Mole fraction of naphthenes.
[0200] X.sub.P=Mole fractions of paraffins.
[0201] Zc=Critical compressibility factor.
[0202] .nu..sub.37.7=Viscosity at 37.8.degree. C.
[0203] .nu..sub.98.9=Viscosity at 98.9.degree. C.
[0204] .upsilon..sub.38=Kinematic viscosity at 38.degree. C. in
mm.sup.2/s.
[0205] .omega.=Acentric factor.
[0206] API=API gravity.
[0207] FBP=Final boiling point.
[0208] IBP=Initial boiling point.
[0209] MW=molecular weight.
[0210] NBP=Normal boiling point.
[0211] PNA=Paraffins, Naphthenes, and Aromatics.
[0212] P.sub.t=True vapor pressure of petroleum fraction.
[0213] RVP=Reid vapor pressure.
[0214] SG=Standard specific gravity for liquid at 15.6.degree.
C.
[0215] TVP=True vapor pressure.
* * * * *