U.S. patent application number 11/847990 was filed with the patent office on 2008-03-06 for method for the measurement of water and water-soluble components in non-aqueous liquids.
Invention is credited to James E. Bruya, Thomas E. Coleman, Frederick R. Wolf.
Application Number | 20080057588 11/847990 |
Document ID | / |
Family ID | 37499462 |
Filed Date | 2008-03-06 |
United States Patent
Application |
20080057588 |
Kind Code |
A1 |
Coleman; Thomas E. ; et
al. |
March 6, 2008 |
METHOD FOR THE MEASUREMENT OF WATER AND WATER-SOLUBLE COMPONENTS IN
NON-AQUEOUS LIQUIDS
Abstract
A method for assigning a grade to a liquid hydrocarbon fuel in
relation to the potential for a water or water-based phase to form
is provided, comprising sensing the electrical resistance and the
capacitance of the fuel, determining the amount of water or
water-soluble compounds in the fuel based on comparing the
electrical resistance of the fuel to a plurality pre-determined
values of electrical resistance corresponding to a plurality of
concentrations of water or water-soluble compounds in the fuel;
identifying which water-soluble compound or compounds are present
based on comparing the capacitance to a plurality of pre-determined
values of capacitance corresponding to a water or a plurality of
water-soluble compounds that may be present; sensing the
temperature of the fuel, and calculating the potential for a water
or water-soluble phase to form during temperature conditions of
transportation or storage.
Inventors: |
Coleman; Thomas E.; (Yakima,
WA) ; Wolf; Frederick R.; (Seattle, WA) ;
Bruya; James E.; (Seattle, WA) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Family ID: |
37499462 |
Appl. No.: |
11/847990 |
Filed: |
August 30, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11156714 |
Jun 21, 2005 |
|
|
|
11847990 |
Aug 30, 2007 |
|
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Current U.S.
Class: |
436/40 ;
436/143 |
Current CPC
Class: |
G01N 33/2847 20130101;
G01N 33/2852 20130101; G01N 27/06 20130101; G01N 27/221 20130101;
G01N 27/048 20130101; G01N 27/223 20130101; Y10T 436/218 20150115;
Y10T 436/21 20150115 |
Class at
Publication: |
436/040 ;
436/143 |
International
Class: |
G01N 33/22 20060101
G01N033/22 |
Claims
1. A method for assigning a grade to a liquid hydrocarbon fuel in
relation to the potential for a water or water-based phase to form
in said fuel during transportation or storage of said fuel, said
method comprising the steps of: sensing the electrical resistance
of the liquid hydrocarbon fuel; sensing the capacitance of the
liquid hydrocarbon fuel; determining the composition of the fuel
and identifying any water-soluble compound or compounds are present
in said hydrocarbon fuel wherein the step of identifying which
compound or compounds are present includes the step of comparing
the capacitance to a plurality of pre-determined values of
capacitance corresponding to a water or a plurality of
water-soluble compounds that may be present; determining the amount
of water or water-soluble compounds in said liquid hydrocarbon fuel
wherein the step of determining the amount of water or
water-soluble compounds includes the step of comparing the
electrical resistance of the hydrocarbon fuel to a plurality
pre-determined values of electrical resistance corresponding to a
plurality of concentrations of water or water-soluble compounds in
the hydrocarbon fuel; sensing the temperature of said liquid
hydrocarbon fuel, and calculating the potential for a water or
water-soluble phase to form in said liquid hydrocarbon fuel during
anticipated temperature conditions of transportation or
storage.
2. The method of claim 1, further comprising assigning a grade to
said liquid hydrocarbon fuel based on said calculated potential for
a water or water-soluble phase to form.
3. The method of claim 1, wherein said liquid hydrocarbon fuel
comprises gasoline.
4. The method of claim 1, wherein said liquid hydrocarbon fuel
comprises diesel fuel.
5. The method of claim 1, wherein said liquid hydrocarbon fuel
comprises fuel oil.
6. The method of claim 1, wherein said liquid hydrocarbon fuel
comprises marine diesel fuel.
7. The method of claim 1, wherein said liquid hydrocarbon fuel
comprises bio-diesel fuel.
8. The method of claim 2, further comprising assigning a grade to
said liquid hydrocarbon fuel based on said calculated potential for
a water or water-soluble phase to form.
9. The method of claim 2, wherein said liquid hydrocarbon fuel
comprises gasoline.
10. The method of claim 2, wherein said liquid hydrocarbon fuel
comprises diesel fuel.
11. The method of claim 2, wherein said liquid hydrocarbon fuel
comprises fuel oil.
12. The method of claim 2, wherein said liquid hydrocarbon fuel
comprises marine diesel fuel.
13. The method of claim 2, wherein said liquid hydrocarbon fuel
comprises bio-diesel fuel.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional application of application
Ser. No. 11/156,714, filed Jun. 21, 2005.
BACKGROUND OF THE PRESENT INVENTION
[0002] It has long been difficult to determine the quality of
liquid fuels during transportation and storage. This has especially
been true due to the presence of water or water-soluble components
in non-aqueous liquid fuels, as the potential for water or
water-soluble components to cause harm may be less dependent upon
the amount of such components which are present than upon the
conditions of transportation and storage.
[0003] Conventional methods for measuring water content within
non-aqueous liquids usually fall into two categories, quantitative
methods that require expensive equipment and labor, and simple
methods that yield highly qualitative results. The quantitative
approaches include analytical laboratory equipment and industry
specific analyzers. While water-cut analyzers have been developed
for the crude oil industry, these instruments are designed to
measure water present in a separate phase from the crude oil.
Simple methods, such as color changing indicator chemicals, may be
highly portable and easy to use, but may not provide the
information desired.
[0004] The conventional laboratory-based method for the measurement
of water dissolved within non-aqueous liquids is Karl Fischer
titration (see ASTM D 1744). While very accurate, the use of the
Karl Fischer titration requires an expensive piece of equipment,
the Karl Fischer titrator, and a trained technician as operator. In
a facility or transport setting, standard analytical equipment is
expensive, complicated, fragile, maintenance intensive, and
requires trained technicians. Additionally, in a field setting, the
instrument machinery may not be sufficiently compact, portable, and
automated to permit practical use.
[0005] Indicator dye/colorimetric methods are known that use
indicator materials that undergo changes in color when water or
alcohol is present in a storage tank with petroleum fuels. U.S.
Pat. No. 4,699,885 to Melpolder and Victor describes a paste that
undergoes a change in color when exposed to a water phase. This
invention is only capable of detecting a distinct aqueous phase and
is not capable of detecting water dissolved within petroleum fuels.
U.S. Pat. No. 4,604,345 to Felder and Panzer describes a paste that
undergoes a change in color when exposed to a phase of alcohol or
to petroleum fuels containing dissolved alcohol. Any water
dissolved within the petroleum fuel must be removed by a drying
agent for the paste to properly indicate the presence of alcohol.
Neither invention is capable of producing reproducible quantitative
measurements of water or alcohol concentrations in petroleum fuels.
U.S. Pat. No. 5,229,295 to Travis describes colorimetric tests for
the presence of water and ethanol, and prescribes a separate step
for the volumetric determination of alcohol concentration. Due to
the reagent handling and restocking requirements, none of these
methods is well-suited for the automated measurement of the water
or alcohol content of petroleum fuels. While easy to use by a
non-technically trained operator, the information gained by these
inventions is very limited.
[0006] Several patents have been granted to inventions that
incorporate humidity sensors into their design. Modern relative
humidity sensors are composed of an interdigitated gold terminal on
an alumina substrate overcoated with a thermosetting hydrophilic
polymer. This polymer is a polyelectrolyte blend exhibiting a
change in ionic mobility as water of hydration is absorbed. The
ionic mobility is a direct function of the water vapor pressure in
the ambient environment as well as the ambient temperature. The
operating principle was patented by Martin Pope (Pope M., U.S. Pat.
No. 2,728,831, 1955) though recent iterations of his invention have
proven to yield sensors of greater stability.
[0007] According to Henry's Law, the partial pressure of water
vapor in equilibrium with a solution phase is directly proportional
to the moisture content of the solution provided the solution is
sufficiently dilute. The partial pressure of water vapor is equal
to the relative humidity (RH) multiplied by the saturated vapor
pressure of water at any given temperature. To a good
approximation, the solvent relative humidity (SRH) above any
hydrophobic liquid is equal to the relative humidity (RH) in air in
the absence of the vapors of that liquid.
[0008] Therefore, it is possible to determine the concentration of
dissolved water for hydrophobic liquids by the equation:
C=(Cs)*(SRH/100%) where C=water concentration in ppm
[0009] Cs=saturated water concentration in ppm at a given
temperature and pressure
[0010] SRH=solvent relative humidity as measured by the sensor
[0011] The measurement of SRH can either be made in the head space
above the liquid or within the liquid itself since the chemical
potential of the water is a function of either the concentration of
water or the water vapor pressure above the solution.
[0012] U.S. Pat. No. 6,138,674 to Gull and Hunt describes a module
which measures the humidity of a patient's expired respiratory
gases for the purpose of compensating for these variables in the
delivery of gaseous anesthetic. U.S. Pat. No. 6,039,696 to Bell
describes an adapter for the measurement of the humidity of
inspired and expired gases in a patient with an artificial airway.
The adapter may act as a control device to assist the delivery of
ventilating gases with physiological levels of moisture. The
apparatus also includes a display means which receives signals from
the humidity sensor, translates the signals, and displays the
results as percent relative humidity and/or moisture content. U.S.
Pat. No. 6,347,746 to Dage et al. describes the incorporation of a
humidity sensor into a system which monitors the temperature and
humidity of air in a vehicle for the purpose of detecting and
preventing conditions which lead to the fogging of vehicle
windows.
[0013] Patents have been issued to inventions which determine the
water content of materials by measuring the electrical properties
of the materials and relating these properties to water content.
U.S. Pat. No. 4,786,873 to Sherman describes a method to determine
the water content of hydrocarbon-containing porous earth formations
by measuring the dielectric permittivity of the earth formations.
U.S. Pat. No. 3,966,973 to Henry et al. describes a process by
which the moisture content of food is obtained by measuring the
impedance generated by the food passing through an alternating
current field. U.S. Pat. No. 6,388,453 to Greer describes a
swept-frequency shunt-mode dielectric sensor system is used to
measure complex impedance parameters such as capacitance and/or
dielectric loss of particulate materials in order to calculate
density and water content. U.S. Pat. No. 6,664,796 to Wang
describes a process by which the moisture content of a fuel
containing exclusively ethanol, and concentration of ethanol in the
fuel, is obtained by measuring the resistance of the fuel. Many
patents have been issued that employ sensors of dielectric
properties to measure the water content associated with hydrocarbon
liquids, especially crude oil. U.S. Pat. No. 5,070,725 to Cox et
al. describes a water-cut meter which measures the impedance
associated with crude oil and water mixtures. The percentage of
water may be determined in both water continuous and oil continuous
samples. U.S. Pat. No. 5,260,667 to Garcia-Golding et al. describes
a method for determining the water content of oil-in-water
emulsions by measuring the real part of a sample's specific
admittance and by making corrections for the sample temperature.
None of the above methods for determining the water content of
petroleum samples yield information specifically concerning the
dissolved water content, but only the water in a separate phase
from the petroleum or emulsified with it.
[0014] Methods of determining water content in oil streams also
include microwave technologies. U.S. Pat. Nos. 4,862,060 to Scott
et al. and 5,389,883 to Harper determine water content from the
frequency changes between emitted and received microwave signals
caused by the dielectric properties of oil and/or water samples.
These methods do not determine the dissolved water content of the
petroleum samples. Furthermore, microwave technologies are often
expensive to implement.
[0015] However, despite the above, a need still exists for a
single, field-capable, test method which can be used to determine
the amount of water in or degree of water saturation of non-aqueous
liquids (whose detailed composition can be changed without notice)
and assess the potential for such water to cause problems during
the storage and use of these liquids.
SUMMARY OF THE PRESENT INVENTION
[0016] The present invention is directed toward the measurement of
water or water-soluble liquids dissolved within non-aqueous liquids
by the analysis of responses from an array of low cost sensors
providing measurements of physicochemical properties.
[0017] Sensor responses to non-aqueous liquids are modeled and
integrated to extract qualitative and quantitative information. The
selection of sensors is based on the information desired, their
sensitivities to physicochemical properties, and the practicality
of their use.
[0018] In the preferred embodiment of this invention, sensors
capable of providing information on the relative humidity,
temperature, conductivity and capacitance are used to collect the
information needed to identify the type or composition of the
liquid present and then its water content. These data can be
further processed to predict the relative water content of the
liquid as it may either cool or warm. The liquid can then be given
a rating which identifies the potential for water-related problems
that are associated with the liquid such as the likelihood of
forming separate phases based on temperature change. If a rating
indicating a high potential for water-related problems is produced,
the practitioner will be informed before or soon after the problem
is manifest and suitable actions taken to remove the water before
serious consequences can become manifest.
[0019] A particular complication found with some non-aqueous
liquids, such as gasoline and diesel fuels, is that their chemical
composition and resulting physicochemical properties constantly
change due to the variability in the raw materials of their
manufacture, the variability in processing procedures and
parameters, and variability in the type and amounts of any blending
chemicals added.
[0020] For instance, Federal and state laws may require the
manufacture of gasoline that meets specific oxygen levels at
different times of the year. Such requirements can be met through
the use of various ethers or alcohols. The use of alcohols rather
than ethers can have an enormous effect on the ability of the
gasoline to dissolve water. K. Owen and T. Coley, "Oxygenated Blend
Components for Gasoline," Automotive Fuels Reference Book, pp.
275-281, Society of Automotive Engineers, Inc., 1995. The present
invention uses multiple physicochemical measurements to address the
variability caused by changes in the composition and temperatures
of these non-aqueous liquids to directly measure the water
dissolved within these liquids.
[0021] Many sensor types may provide information about the system
to be analyzed. The complementary response behaviors and
sensitivities of sensors may be combined to construct an accurate
representation of the physicochemical properties of interest. Many
sensor types useful for this purpose are compact, reliable, and
resistant to chemical degradation. Analytical instruments
incorporating such arrays of sensors night also be highly compact,
reliable, and durable. Such instruments can offer unique ease of
use due to designs tailored for specific applications. A device of
the invention might comprise sensors selected for their sensitivity
to water dissolved within non-aqueous liquids, their signal
transduction circuitry, a processing unit which applies an
algorithm to the sensor measurement data, and some type of
communication output, such as a visual display device, or an
electrical transmission.
[0022] One application of the invention is the measurement of water
dissolved within petroleum fuels. The contamination of fuels with
water cannot usually be avoided and is, therefore, an issue of
concern for the petroleum industry. Water dissolved within fuels
decreases their quality and poses a corrosion threat to handling
equipment. The corrosion of petroleum fuel handling equipment can
result in the leakage of fuel and is a major cause of environmental
damage. Fuels with a high water content burn poorly in combustion
engines. As the fuel changes temperature, water may separate from
the fuel causing combustion problems and may clog fuel filters. By
monitoring the water in the fuel, the level of water can be kept at
a low level, thereby avoid such storage and handling problems.
[0023] Another application of the invention is to avoid the
addition of one batch of fuel to another where the combined fuel
will have deleterious properties which neither of the original
fuels possess. Each fuel has a specific tolerance to the presence
of water that is based on its chemical composition. For example,
when conventional gasoline becomes saturated with water, a two
phase system will form consisting of water and gasoline where the
water layer consists primarily of water and the gasoline is
relatively unchanged. When an ethanol containing gasoline is
saturated with water, a two phase system will also form but the
water layer will contain mostly ethanol and the gasoline will be
depleted in the ethanol resulting in a loss of octane rating. By
providing a simple mechanism by which to readily identify the
composition of a fuel and the amount of water present, a
practitioner can prevent the mixing of fuels which, when combined,
would produce a mixture that may prove unuseable depending upon the
anticipated conditions of transportation, storage, and/or use.
[0024] For these reasons, it is desirable to monitor fuel stocks to
determine their moisture content and composition.
[0025] Another application of the invention is the monitoring of a
non-aqueous liquid to determine if unexpected changes have
occurred. Here, a baseline of the expected or normal
physicochemical properties is established. The properties are then
monitored to determine if and when unexpected changes have
occurred. If such changes occur, the liquid would undergo testing
to ensure that no deleterious material has been added to the
liquid.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 depicts the relationship between the electrical
resistance as determined by a humidity sensor and the solvent
relative humidity of conventional gasoline at a series of
temperatures.
[0027] FIG. 2 depicts the relationship between the electrical
resistance as determined by a humidity sensor and the solvent
relative humidity of 11% MTBE containing gasoline at a series of
temperatures.
[0028] FIG. 3 depicts the relationship between the electrical
resistance as determined by a humidity sensor and the solvent
relative humidity of 10% ethanol containing gasoline at a series of
temperatures.
[0029] FIG. 4 depicts the relationship between the oxygenate
content and the dielectric constant of oxygenated gasoline at
20.degree. C.
[0030] FIG. 5 depicts the relationship between the electrical
resistance of the gasoline and the solvent relativity humidity of
unoxygenated gasoline, and gasoline containing 1%, 3% and 10%
ethanol.
[0031] FIG. 6 depicts the relationship between the electrical
resistance as determined by a humidity sensor and the water content
(vol %) of ethyl alcohol.
DETAILED DESCRIPTION OF THE INVENTION
[0032] In order to derive an accurate measurement of the moisture
content of non-aqueous liquids, the responses from complementary
sensors are combined. The specific choice of constituent sensors is
based on performance characteristics, durability, cost, and other
practical considerations. In general, multiple sensors are required
to measure properties that depend on multiple factors. In the
simplest case of a non-aqueous liquid of a predetermined
composition, a single sensor sensitive to the presence of dissolved
water may be used for the measurement of dissolved water content.
However, if the composition of the non-aqueous liquid is unknown or
variable, additional sensors are required to produce an accurate
measurement of dissolved water content. A temperature sensor may
also be used to increase the accuracy of the measurement if sensor
responses vary with temperature.
[0033] The apparatus of the invention may therefore consist of a
sensor array, sensor transduction circuitry, a processing unit, and
electronic output for transmission to a display device. The sensor
array is a combination of sensors which detect moisture, physical
chemical properties, and temperature. The moisture sensor may be of
many types including, but not limited to, polymer film resistive
and capacitive sensors, infrared absorption sensors, and light
refractive sensors. The chemical property sensor may be of many
types including, but not limited to, capacitors of various
geometries (e.g., a parallel-plate capacitor), interdigitated
electrodes with or without film coatings, and sensors based on
light refraction or absorption. The temperature sensor may also be
of many types (e.g., mercury thermometers, thermistors,
thermocouples). The following sensors and sensor combinations are
suitable for use in the invention: moisture sensors, dielectric
property sensors and temperature sensors; moisture sensors and
dielectric property sensors; moisture sensors and temperature
sensors; moisture sensors; dielectric property sensors and
temperature sensors; and dielectric property sensors.
[0034] As one example of the application of the invention, a system
for the measurement of water content within petroleum fuels is
described below. The capacity of petroleum fuels to dissolve water
depends on the content of oxygenating chemicals in the fuel (such
as alcohols and ethers), the relative amounts of aromatic and
paraffin hydrocarbons, and the temperature of the fuel. Thus,
sensors sensitive to moisture, oxygenating chemicals,
aromatic/paraffin hydrocarbons, and temperature are combined
algorithmically to determine the moisture content of petroleum
fuels. Petroleum fuels and solvents (e.g., gasoline, diesel, fuel
oil, Stoddard solvent, and mineral spirits) may dissolve water
until their saturation limits are reached, at which point the water
will begin to form a separate layer, or phase.
[0035] The method comprises the collection of moisture, physical
chemical properties, and temperature measurements and determining
the dissolved water content or the likelihood that the petroleum
fuel or solvent might undergo a phase separation from water. The
water content can be determiined as a mass concentration or as the
solvent relative humidity (amount of water dissolved/maximum
possible dissolvable amount.times.100%). A "letter grade" can then
be assigned to the fuel based on the measurement. The letter grade
which is assigned (indicative of the likelihood of phase
separation) may be, for example, "A" through "E", where "A" would
indicate very little danger of phase separation and "E" would
indicate a high risk of phase separation.
[0036] Analysis of regular unleaded gasoline is an example of one
application of the invention. PIANO (paraffins, isoparaffins,
aromatics, naphthenes, and olefins) analysis (ASTM D 5443) of the
fuel investigated showed the absence of oxygenating chemicals
(e.g., alcohols and ethers). In order to re-create commercially
available gasoline, oxygenating chemicals were blended into the
gasoline. Methyl t-butyl ether (MTBE) was blended to simulate
ether-containing gasoline. Ethanol was blended to simulate
alcohol-containing gasoline. All reagents were dried thoroughly
with zeolite molecular sieves. Water was introduced into the
gasoline types by two different methods. For the unoxygenated
gasoline and the MTBE-containing gasoline, dry portions of gasoline
were mixed with portions of gasoline that were saturated with
water. For the ethanol containing gasoline, aliquots of water were
added to the gasoline.
[0037] Commercially available humidity sensors (EMD3000 and
EMD4000, General Eastern) were used as moisture sensors. Electrical
resistance of the gasoline samples was measured using these sensors
when immersed in unoxygenated gasoline, MTBE-containing gasoline,
and ethanol-containing gasoline. FIGS. 1, 2, and 3 depict the
relationship between the sample electrical resistance determined by
the humidity sensor and the solvent relative humidity of
non-oxygenated, 11% MTBE containing, and 10% ethanol containing
gasoline, respectively, at a series of temperatures. These
measurements are also listed in Tables 1, 2, and 3, respectively:
TABLE-US-00001 TABLE 1 EMD3000 humidity sensor measurements in
conventional gasoline Solvent Relative EMD3000 Temperature
(.degree. C.) Humidity (%) resistance (.OMEGA.) 15 30 6,550,000 15
50 170,000 15 70 4960 15 90 1400 25 30 7,044,000 25 50 292,000 25
70 16,400 25 90 2870 35 30 12,400,000 35 50 900,000 35 70 106,000
35 90 14,400
[0038] TABLE-US-00002 TABLE 2 EMD3000 humidity sensor measurements
in 11% MTBE gasoline Solvent Relative EMD3000 Temperature (.degree.
C.) Humidity (%) Resistance (.OMEGA.) 5 30 24,450,000 5 50 446,000
5 70 11,400 5 90 1250 15 20 69,500,000 15 50 307,000 15 70 10,400
15 90 1210 25 30 14,100,000 25 50 448,000 25 70 14,500 25 90
1720
[0039] TABLE-US-00003 TABLE 3 EMD3000 humidity sensor measurements
in 10% ethanol gasoline Solvent Relative EMD3000 Temperature
(.degree. C.) Humidity (%) resistance (.OMEGA.) 5 31 30,600,000 5
46 1,030,000 5 62 102,000 5 77 20,100 5 92 7240 15 30 5,650,000 15
40 450,000 15 50 87,000 15 60 24,500 15 70 9500 15 80 4590 15 90
2670 25 18 17,100,000 25 36 165,000 25 55 13,060 25 73 2555 25 91
1008
[0040] In general, moisture measurements determined by the humidity
sensor may be improved by correcting for the effects of temperature
and chemical content such as oxgenenting chemicals.
[0041] By measuring the temperature and physical chemical
properties, the relationship between the electrical resistance
determined by the humidity sensor and the solvent relative humidity
of the gasoline may be described by mathematical correlations.
These correltations may be of any form. One form of correlation
that solvent relative humidity=A.times.log(R)+B/log(R), where R is
the electrical resistance of the humidity sensor (W) and both A and
B may be functions of temperature and chemical content. These
functions may be of any form.
[0042] In the case of conventional gasoline, A=-0.1607T+0.634, and
B=8.7969T+155.08, where T is the temperature in degrees
Celsius.
[0043] When ethanol (1-10 vol %) is the oxygenating chemical
present, a good fit to data can be found with: A=-2.85, and
B=[-5.4605 log(EtOH %)-0.0496]T+[120.49 log(EtOH %)+287.7], where
EtOH % is the amount of ethanol blended with the gasoline (vol
%).
[0044] When MTBE is the oxygenating chemical present, a good fit to
data can be found with: A=5.16e.sup.-6T-2.3091
B=-4.37e.sup.-4T+323.91
[0045] This method of water content measurement can also be applied
to the measurement of water dissolved in ethyl alcohol. FIG. 6
depicts the relationship between the electrical resistance of the
humidity sensor and the solvent relative humidity of ethyl alcohol.
These measurements are listed in Table 4: TABLE-US-00004 TABLE 4
The relationship between the electrical resistance of the EMD4000
humidity sensor and the water content (vol %) of ethyl alcohol
Water (vol %) EMD4000 resistance (.OMEGA.) 1 7050 10 3250 30 1420
50 877
[0046] The electrical properties of the gasoline were measured with
a capacitor immersed within the gasoline. FIG. 4 depicts the
relationship between the oxygenate content in gasoline and the
dielectric constant measured from the capacitor at 20.degree. C. (1
kHz frequency of excitation). Table 5 lists these measurements.
TABLE-US-00005 TABLE 5 Dielectric constant measurements of gasoline
containing MTBE and ethanol, 20.degree. C. Oxygenate vol %
Dielectric constant MTBE: 0 2.06 5 2.15 11 2.25 15 2.30 Ethanol: 0
2.06 2 2.15 5 2.32 7.5 2.50 10 2.78
[0047] For ethanol containing gasoline this relationship has been
modeled as: oxygenate percentage=A.times.DC.sup.2+B.times.DC+C,
where DC is the dielectric constant of the gasoline. A good fit to
the data from ethanol-containing gasoline is possible when the
following formulas for A, B, and C are used: A=-1.554T-10.22,
B=8.133T+62.946, and C=-9.732-86.643, where T is the temperature
(.degree. C.) For MTBE containing gasoline, a good fit to the data
can be achieved with the following formulas for A, B, and C: A=0,
B=12.082T+46.977, and C=-22.82T+-98.125, where T is the temperature
(.degree. C.).
[0048] Other mathematical relationships are possible. For greater
accuracy, the effect of solvent relative humidity may be factored
into the model of oxygenate content.
[0049] A capacitor was also used to measure the bulk electrical
resistance (or conductance, equivalently) of the gasoline (20 Hz
frequency or excitation). FIG. 5 depicts the relationship between
the electrical resistance of the gasoline and the solvent
relativity humidity for non-oxygenated gasoline, as well as 1%, 3%
and 10% ethanol-containing gasoline. For a given oxygenate content,
the electrical resistance of the gasoline decreases as the solvent
relative humidity of the gasoline increases; Table 6 lists these
measurements: TABLE-US-00006 TABLE 6 Electrical resistance
measurements of gasoline with varying amounts of ethanol and
varying solvent relative humidity, 20.degree. C. Solvent relative
humidity Electrical resistance of test cell (%) (.OMEGA.)
Conventional: 0 .sup. 1.56e.sup.10 50 9.36e.sup.9 100 5.12e.sup.9
1% ethanol: 0 5.26e.sup.9 17 4.89e.sup.9 50 3.82e.sup.9 84
2.82e.sup.9 100 2.14e.sup.9 3% ethanol: 0 1.49e.sup.9 22
1.13e.sup.9 44 8.02e.sup.8 67 5.74e.sup.8 89 3.13e.sup.8 100
2.14e.sup.8 10% ethanol: 0 3.51e.sup.6 19 2.43e.sup.6 48
1.39e.sup.6 76 7.16e.sup.5 100 3.61e.sup.5
[0050] Thus, the electrical resistance of the gasoline may provide
water content information. One combination of measurements which
yields the solvent relative humidity for ethanol containing
gasoline is: solvent relative humidity=(A.times.log(Rc))+B, wherein
A=(35.243.times.log(Rc))-135.87, and
B=(-458.16.times.log(Rc))+1208.1 where Rc is the electrical
resistance (W) of the capacitor immersed in gasoline and EtOH % is
the amount of ethanol present in the gasoline (vol %). The
concentration of aromatic hydrocarbons also influences the
electrical properties of gasoline, including the dielectric
constant and the conductivity of gasoline. Higher concentrations
may yield larger dielectric constants and greater
conductivities.
[0051] The resistance and capacitance measurements from a capacitor
immersed in gasoline may provide oxygenate content and water
content information. These measurements are considered duplicative
to electrical impedance measurements (e.g., resistance and
reactance) of a test cell containing the sample. Pairing a
dielectric constant measurement with a phase angle difference from
a measurement circuit may yield oxygenate content and water content
information. Equivalent representations of the measurements may
include, but are not limited to, susceptance capacitance,
dielectric constant, complex permitivity, resistance, conductance,
admittance, reactance and impedance. Furthermore, parameters
derived from these property representations are considered to be
equivalent representations of the measurement information.
[0052] Water tolerance is the amount of water that a non-aqueous
liquid can dissolve before phase separation will occur with the
formation of distinct non-aqueous and aqueous phases (the aqueous
phase will also contain alcohols initially present in the solvent
phase). Water tolerance is related to liquid relative humidity in
that the water tolerance of a non-aqueous liquid is the
concentration of water in the non-aqueous liquid at 100% relative
humidity. In the case of petroleum fuels, water tolerance depends
on factors such as temperature, type of distillate, content of
blending components such as oxygenates, and aromatic hydrocarbon
content.
[0053] With knowledge of how the water tolerance of a non-aqueous
liquid varies with temperature, it is possible to predict its
relative humidity (or the likelihood of phase separation occurring)
at different temperatures. For example, if the relative humidity of
a non-aqueous liquid was determined to be 50% at 30.degree. C. and
the water tolerance of the liquid were known to be 1 vol % at
30.degree. C., then the water concentration would be estimated at
0.5 vol %. If the solvent were to cool to 10.degree. C., and if the
water tolerance of the liquid was 0.5 vol % at 10.degree. C., then
the relative humidity would be predicted to be at or near 100% and
phase separation would be likely to occur.
[0054] Such determinations are useful when a fuel is to be
transported, stored and/or used at different conditions from those
of the initial measurement.
[0055] The temperature dependence of the water tolerance of
conventional gasoline is estimated by the following correlation:
water tolerance,wt%=6.97e.sup.-4T+1.48e.sup.-2 where T is the
temperature in .degree. C.
[0056] The temperature dependence of the water tolerance of
gasoline containing 15 vol % MTBE is estimated by the following
correlation: water tolerance,wt%=1.33e.sup.-3T+5.96e.sup.-2 where T
is the temperature in .degree. C.
[0057] The water tolerance of gasoline is greatly increased by
blending with ethanol. The water tolerance of gasoline blended with
ethanol can be estimated by the following correlation: water
tolerance,wt%=aT.sup.2+bT+c where
a=(-8.052e.sup.-8(%EtOH).sup.2)+(4.545e.sup.-6.times.(%EtOH))+3.513e.sup.-
-4,
b=2.919e.sup.-5(%EtOH).sup.2+2.530e.sup.-4.times.(%EtOH)+6.736e.sup.--
4,
c=1.704e.sup.-3(%EtOH).sup.2+3.415e.sup.-2.times.(%EtOH)+1.220e.sup.-2-
, where % EtOH is the amount of ethanol blended into the gasoline
in vol % and T is the temperature in .degree. C.
* * * * *