Note: Descriptions are shown in the official language in which they were submitted.
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REDUCED RVP OXYGENATED GASOLINE COMPOSITION AND METHOD
Background of the Invention
[01] This application claims benefit of provisional application Serial No.
611027,969
filed February 12, 2008, which is incorporated herein by reference in its
entirety.
[02] This invention relates to fuels, more particularly to oxygenated
gasolines including
gasolines containing ethanol. This invention provides an oxygenated gasoline
having a
reduced Reid vapor pressure (RVP) thereby allowing a higher proportion of low
boiling
components to be blended into the gasoline without exceeding RVP limits. This
invention
also provides a method for reducing the RVP of oxygenated gasolines.
[03] Gasolines are fuels which are suitable for use in a spark-ignition engine
and
which generally contain as a primary component a mixture of numerous
hydrocarbons
having different boiling points and typically boiling at a temperature in the
range of from
about 26 C to about 225 C under atmospheric pressure. This range is
approximate and
can vary depending upon the actual mixture of hydrocarbon molecules present,
the
additives or other compounds present (if any), and the environmental
conditions.
Typically, the hydrocarbon component of gasolines contain C4 to C10
hydrocarbons.
[04] Gasolines are typically required to meet certain physical and performance
standards. Some characteristics may be implemented for proper operation of
engines or
other fuel combustion apparatuses. However, many physical and performance
characteristics are set by national or regional regulations for other reasons
such as
environmental management. Examples of physical characteristics include RVP,
sulfur
content, oxygen content, aromatic hydrocarbon content, benzene content, olefin
content,
temperature at which 90 percent of the fuel is distilled (T-90), temperature
at which 50
percent of the fuel is distilled (T-50) and others. Performance
characteristics can include
octane rating (also called anti-knock index), combustion properties, and
emission
components.
[05] For example, standards for gasolines for sale within much of the United
States
are generally set forth in ASTM Standard Specification Number D 4814-01 a
("ASTM
4814") which is incorporated by reference herein. Additional federal and state
regulations
supplement this standard.
[06] The specifications far gasolines set forth in ASTM 4814 vary based on a
number
of parameters affecting volatility and combustion such as weather, season,
geographic
location and altitude. For this reason, gasolines produced in accordance with
ASTM
4814 are broken into volatility categories AA, A, B, C, D and E, and vapor
lock protection
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categories 1, 2, 3, 4, 5, and 6, each category having a set of specifications
describing
gasolines meeting the requirements of the respective classes. This
specification also
sets forth test methods for determining t he parameters in the specification.
[07] For example, a Class AA-2 gasoline blended for use during the summer
driving
season in relatively warm climates must have a maximum vapor pressure of 54
kPa, a
maximum temperature for distillation of 10% volume of its components (the
"Ti0") of 70
C, a temperature range for distillation of 50% volume of its components (the
'T50"') of
between 77 C and 121 C, a maximum temperature for distillation of 90% volume
of its
components (the "T90")of 190 C, a distillation end point of 190 C, a
distillation residue
maximum of 2% volume, a "Driveability Index" or "DI" maximum temperature of
597 C,
where DI is calculated as 1.5 times the T10 plus 3.0 times the T50 plus the
T90, and a
maximum vapor to liquid ratio of 20 at a test temperature of 56 C.
[08] One physical characteristic of gasolines that is addressed in ASTM 4814
and is
commonly regulated in many jurisdictions is RVP. RVP can be measured in
accordance
with ASTM Standard Specification D 5191-04a ("D 5191 ") which is incorporated
by
reference herein. RVP standards are typically expressed as a maximum RVP limit
which
gasolines sold commercially in a particular jurisdiction may be compelled to
meet. Such
RVP limits significantly constrain the composition of hydrocarbons in
gasolines because
RVP increases as the proportion of lighter hydrocarbons increases. Typically,
to produce
gasolines with reduced RVP, the proportion of lighter hydrocarbons, for
example C4
hydrocarbons, are reduced.
Reducing such lighter hydrocarbons can negatively impact gasoline
characteristics. For
example, decreasing the amount of butane in a gasoline fuel lowers the RVP of
that fuel,
but it also reduces the octane rating.
[09] By constraining the composition of gasolines, RVP limits also impose a
burden
upon refineries. Generally, refineries adjust the composition of gasolines by
controlling
the proportions of various refinery streams which are used to produce the
gasolines. For
example, to produce a gasoline with a higher boiling point, a refinery may
need to reduce
the proportion of low-boiling refinery streams used to produce the gasoline.
To produce
gasolines which will satisfy applicable RVP limits, refineries typically
reduce the
proportion of lighter boiling hydrocarbons in gasolines. RVP is typically
controlled or
adjusted using empirically determined RVP blending values. A RVP blend value
represent a particular composition's contribution to the RVP of a particular
mixture. One
consequence of such RVP constraints upon refineries is that less gasoline can
be refined
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from each barrel of petroleum. This can significantly impact the gasoline
supply available
to meet consumer demand.
[10]- The impact of RVP limits has intensified because of the increasing use
of
oxygenates in gasolines. Oxygenates are used in gasolines to increase the
chemical
oxygen content. Unfortunately, oxygenates have a non-linear effect upon RVP
when
blended into a fuel. Therefore, RVP blending values of oxygenates are
determined
empirically for a particular concentration of a particular oxygenate in a
particular fuel.
Many jurisdictions have oxygenate requirements for gasolines to promote more
complete
combustion. Methyl-tertiary-butyl ether (MTBE) was a commonly used as a
gasoline
oxygenate. However, many jurisdictions prohibit or severely limit the use of
MTBE and
similar ethers.
[11] Because of the restrictions on use of MTBE, other oxygenates with less
favorable
RVP are typically used in gasolines. Ethanol is widely used as a gasoline
oxygenate
because of a number of factors including tax credits offered by many
jurisdictions for use
of up to 10 vol% ethanol in gasoline. U.S. Patents 6,258,987 to Schmidt et al.
and
6,540,797 to Scott et al., which are incorporated by reference herein, discuss
blending
ethanol in gasolines. Unfortunately, many of the oxygenates permitted for
blending into
gasolines have significant detriments including an affinity for water which
causes
transportation and handling difficulties, and an increase in a gasoline's RVP
when
blended with the oxygenate. An affinity for water causes transport and
handling
difficulties. RVP increase amplifies the difficulty of producing gasoline
within applicable
RVP limits. Ethanol exhibits both of the foregoing effects.
[12] There is a need for a composition or method to lessen the detrimental
effects
which can result from blending oxygenates into gasolines. In particular, it
would be
desirable to counter at least some of the RVP increase attributable to
blending
oxygenates into gasolines.
[13] We have found that a certain compound exhibits unexpectedly low RVP
blending
values for blending with typical oxygenated gasolines. Surprisingly, in some
cases, such
compound can even exhibit negative RVP blending values.
[14] This invention lessens the RVP increase attributable to oxygenate
blending into
gasolines which allows refineries to use a higher proportion of low- boiling
hydrocarbons
in gasoline blend stocks thereby increasing the gasoline refining capacity of
the refinery.
This invention can be used to reduce the RVP of an oxygenated gasoline. In
certain
instances where an oxygenated gasoline is blended which has an RVP value
exceeding
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the applicable maximum RVP limit, this invention can be used to make the
oxygenated
gasoline comply with the RVP limit.
Summary of the Invention
[15] We have found that use of isobutanol can have a surprising RVP reducing
effect
upon oxygenated gasolines. Isobutanol can interact with an oxygenate to lower
the RVP
increase expected from blending the oxygenate with a gasoline blend stock. In
some
cases, isobutanol's effect is so dramatic that the RVP reducing compound
exhibits a
negative RVP blending value.
[16] This invention provides an oxygenated gasoline which can meet an
applicable
RVP limit and can still include a greater amount of lighter components than
would
otherwise be possible. This invention allows a refinery to use a greater
proportion of
crude for gasoline thereby increasing the supply of gasoline. This invention
also provides
a method of reducing the RVP of an oxygenated gasoline. Such reduction can be
performed at a terminal and can help reduce the necessity of obtaining waivers
for
gasoline which may otherwise have an RVP exceeding regulations. This invention
also
provides a method of reducing the RVP constraint upon gasoline blend stocks
for
oxygenate blending in the production of oxygenated gasolines for jurisdictions
having a
maximum RVP limit.
[17] In one embodiment, we provide a gasoline containing a gasoline blend
stock, a
suitable oxygenate, and an effective amount of isobutanol. Preferably, the
isobutanol
has a RVP blend value less than about 5.0 psi, more preferably less than about
3.0 psi
and most preferably less than about 0.0 psi. Optionally, the RVP value of a
mixture of the
gasoline blend stock and the suitable oxygenate is at least about 6.9 psi.
Preferably, the
suitable oxygenate is an alcohol, more preferably ethanol. Preferably greater
than I vol%
suitable oxygenates are present. Preferably, less than 20 vol% of isobutanol
is present.
More than one suitable oxygenate can be used.
[18] In another embodiment, a method of reducing the RVP of an oxygenated
gasoline
is provided. The method includes a step of blending a gasoline blend stock and
one or
more suitable oxygenates to form an oxygenated gasoline, and the step of
mixing the
oxygenated gasoline and isobutanol wherein the isobutanol has a RVP blend
value less
than about 5.0 psi, preferably less than about 3.0 psi and most preferably
less than about
0.0 psi. The suitable oxygenate can be an alcohol, preferably ethanol. Either
or both of
the blending or mixing steps can be performed at a terminal. Optionally, the
blending
step can be performed contemporaneously with the mixing step. Preferably
greater than
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1 vol% suitable oxygenates are present. Preferably, less than 20 vol% RVP
reducing
compounds are present.
[19] In another embodiment, a method of reducing the RVP constraint upon a
gasoline
blend stock in the production of oxygenated gasolines with a predetermined
maximum
RVP limit is provided. The method includes the step of blending a gasoline
blend stock
and one or more suitable oxygenates to form an oxygenated gasoline having a
RVP
value greater than the predetermined maximum RVP limit, and the step of adding
an
effective amount of one isobutanol to form a gasoline having a RVP value less
than or
equal to the predetermined maximum RVP limit. The blending step and the adding
step
can be performed contemporaneously. The suitable oxygenate is preferably
ethanol.
Preferably greater than 1 vol% suitable oxygenates are present. Preferably,
less than 20
vol% RVP reducing compounds are present.
[20] Relative absorbance, as described further herein, is a useful way to
measure
isobutanol's effectiveness in reducing RVP. Relative absorbance can also be
used to
identify oxygenated gasolines which are particularly amenable to RVP reduction
using
isobutanol. In any embodiment, a gasoline blend stock, one or more suitable
oxygenates
and isobutanol can be selected such that a mixture of the gasoline blend
stock, suitable
oxygenate(s) and isobutanol has a normalized relative absorbance less than
about
0.045. Preferably, a blend of the gasoline blend stock and suitable
oxygenate(s) has a
normalized relative absorbance greater than about 0.05.
Description of the Preferred Embodiment(s)
[21] Gasolines are well known in the art and generally contain as a primary
component
a mixture of hydrocarbons having different boiling points and typically
boiling at a
temperature in the range of from about 26 C to about 225 C under atmospheric
pressure. This range is approximate and can vary depending upon the actual
mixture of
hydrocarbon molecules present, the additives or other compounds present (if
any), and
the environmental conditions. Oxygenated gasolines are a blend of a gasoline
blend
stock and one or more oxygenates.
[22] Gasoline blend stocks can be produced from a single component, such as
the
product from a refinery alkylation unit or other refinery streams. However,
gasoline blend
stocks are more commonly blended using more than one component.
Gasoline blend stocks are blended to meet desired physical and performance
characteristics and to meet regulatory requirements and may involve a few
components,
for example three or four, or may involve many components, for example twelve
or more.
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[23] Gasolines and gasoline blend stocks optionally may include other
chemicals or
additives. For example, additives or other chemicals can be added to adjust
properties of
a gasoline to meet regulatory requirements, add or enhance desirable
properties, reduce
undesirable detrimental effects, adjust performance characteristics, or
otherwise modify
the characteristics of the gasoline. Examples of such chemicals or additives
include
detergents, antioxidants, stability enhancers, demulsifiers, corrosion
inhibitors, metal
deactivators, and others. More than one additive or chemical can be used.
[24] Useful additives and chemicals are described in US Patent No. 5,782,937
to
Colucci et al. which is incorporated by reference herein. Such additives and
chemicals
are also described in US Patent No. 6,083,228 to Wolf and US Patent No.
5,755,833 to
Ishida et al. both of which are incorporated by reference herein. Gasolines
and gasoline
blend stocks may also contain solvent or carrier solutions which are often
used to deliver
additives into a fuel. Examples of such solvents or carrier solutions include,
but are not
limited to, mineral oil, alcohols, carboxylic acids, synthetic oils, and
numerous other
which are known in the art.
[25] Gasoline blend stocks suitable for the composition of this invention are
typically
blend stocks useable for making gasolines for consumption in spark ignition
engines or in
other engines which combust gasoline. Suitable gasoline blend stocks include
blend
stocks for gasolines meeting ASTM 4814 and blend stocks for reformulated
gasoline.
Suitable gasoline blend stocks also include blend stocks having low sulfur
content which
may be desired to meet regional requirements, for example having less than
about 150
ppmv sulfur, more preferably less than about 100 ppmv sulfur, more preferably
less than
about 80 ppmv sulfur. Such suitable gasoline blend stocks also include blend
stocks
having low aromatics content which may be desirable to meet regulatory
requirements,
for example having less than about 8000 ppmv benzene, more preferably less
than
about 7000 ppmv benzene, or as further example, having less than about 35 vol%
total
aromatics content, more preferably less than about 25 vol% total aromatics
content. As
used herein "total aromatics content" refers to the total amount of all
aromatic species
present.
[26] "Oxygenate" as used herein means a C2 to C8 compound containing only
carbon,
hydrogen and one or more oxygen atoms. For example, oxygenates can be
alcohols,
ketones, esters, aldehydes, carboxylic acids, ethers, ether alcohols, ketone
alcohols and
poly alcohols. Ethanol is a preferred oxygenate for several reasons including
its
widespread availability. "Suitable oxygenate" as used herein means an
oxygenate which
has a RVP blend value of at least 6.5 psi and which is soluble in the
particular
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oxygenated gasoline being produced. Preferably greater than about 2 vol%
oxygenate is
present.
[27] "RVP blend value" or "blend RVP" is the effective RVP of a composition
when
blended into a fuel mixture. A blend RVP value represents the composition's
contribution
to the RVP of a mixture such that the RVP for the mixture equals the summation
of each
component's blend RVP multiplied by that component's volume fraction. For
example, for
a fuel mixture of [A] and [B], the RVP = (blend RVP of [A] x volume fraction
of [A]) +
(blend RVP of [B] x volume fraction of [B]).
[28] As used herein, a compound is soluble in a second compound if a mixture
of the
compounds exhibits a single liquid phase in the desired concentrations over
the
temperature range of interest which, unless stated otherwise, is from about -
40 C to the
initial boiling point of the mixture.
[29] Isobutanol is soluble in the selected oxygenated gasoline and reduces the
RVP of
the selected oxygenated gasoline containing no isobutanol when isobutanol is
blended
into the selected oxygenated gasoline. An effective RVP-reducing amount of
isobutanol
is an amount that reduces the RVP of the oxygenated gasoline by at least 0.05
psi for
the particular RVP reducing compound concentration. RVP can be determined in
accordance with ASTM D 5191 using sufficient measurements for a statistically
significant determination. Preferably, the total concentration of isobutanol
is less than
about 20 vol%, more preferably less than about 10 vol%, most preferably no
greater than
about 5 vol%. The isobutanol can be obtained from any suitable source,
including by
production from biomass. In addition to isobutanol, one or more additional RVP-
reducing
compounds can be added to the mixture with the oxygenated gasoline.
[30] Isobutanol's special effectiveness for reducing the RVP of oxygenated
gasolines
is illustrated by determining the normalized relative absorbance of a mixture
of the
oxygenated gasoline and the isobutanol. Additionally, suitable oxygenates
which are
particularly amenable to such especially effective RVP reduction can be
identified by
determining the normalized relative absorbance of the oxygenated gasoline
(without the
isobutanol).
[311 Without being limited to any particular theory, it is believed that
isobutanol
interacts with oxygenates in an oxygenated gasoline and increase the tendency
of the
oxygenate to remain in a liquid phase, thereby reducing the RVP of the
oxygenated
gasoline. Relative absorbance is an analytical technique that can be used to
identify
suitable oxygenates and isobutanol which are particularly amenable to such
interactions
with isobutanol which produce a synergistic reduction of RVP.
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[32] Relative absorbance employs the two-point baseline method, difference
method,
and infrared quantitative analysis techniques as described in ASTM Standard
Practices
for General Techniques of Infrared Quantitative Analysis Specification E 168-
99 ("E 168")
which is incorporated by reference herein.
[33] Relative absorbance of a mixture containing isobutanol and an oxygenated
gasoline is determined using the difference spectrum obtained by subtracting
the
absorbance spectrum of the oxygenated gasoline without any suitable oxygenate
from
the absorbance spectrum of the aforesaid mixture and using the two-point
baseline
method to calculate the ratio of the band area from 3680 cm-1 to 3550 cm-1, to
the band
area from 3680 cm-1 to 3100 cm-1. Use of the difference spectrum as described
minimizes variability due to use of different gasoline blend stocks.
[34] Relative absorbance of an oxygenated gasoline is determined using the
difference spectrum obtained by subtracting the absorbance spectrum of the
oxygenated
gasoline without the suitable oxygenate from the absorbance spectrum of the
oxygenated gasoline and using the two-point baseline method to calculate the
ratio of the
band area from 3680 cm-1 to 3550 cm-1, to the band area from 3680 cm-1 to 3100
cm-1.
[35] Table I below shows the relative absorbance of several oxygenated
gasolines
having differing concentrations of one oxygenate compound in a fungible
unleaded
regular gasoline meeting ASTM D 4814.
Table I
Relative Absorbance of Ethanol at
Varying Concentrations in an Unleaded Regular Gasoline
Oxygenate Concentration Relative
Compound wt% Absorbance
ethanol 1.05 0.104
ethanol 2.11 0.049
ethanol 5.27 0.009
iso-butanol 1.01 0.662
iso-butanol 2.00 0.137
iso-butanol 5.00 0.038
[36] As shown in Table I, relative absorbance varies by concentration. Table I
also
demonstrates the non-linearity between relative absorbance and concentration.
Relative
absorbance will generally be determined empirically. For the particular
unleaded regular
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gasoline used in Table I, ethanol would be a suitable oxygenate compound for
this
particular embodiment of the invention.
[37] Table II shows the relative absorbance of several mixtures of isobutanol
and an
oxygenated gasoline with the same fungible unleaded regular gasoline used for
Table I.
Table II
Relative Absorbance of Isobutanol in an
Oxygenated Gasoline (2 wt% Ethanol)
RVP Reducing Concentration Relative
Compound wt% Absorbance
none 0.049
Isobutanol 2.0 0.029
[38] As illustrated in Table I adding the isobutanol into the oxygenated
gasoline has a
significant impact on the relative absorbance of the mixture. The impact
varies with
different concentrations of isobutanol, but such changes in relative
absorbance indicate a
synergistic interaction between the components resulting in a surprising RVP
reducing
effect.
[39] In some embodiments, the normalized relative absorbance of a mixture
containing
isobutanol and an oxygenated gasoline is less than about 0.045, preferably
less than
about 0.030. Preferably, one or more suitable oxygenates are selected such
that the
normalized relative absorbance of an oxygenated gasoline containing such
suitable
oxygenate(s), (without the isobutanol) is greater than about 0.05, preferably
greater than
about 0.1.
[40] The term "normalized relative absorbance" of a mixture containing a
isobutanol
and an oxygenated gasoline is defined as the relative absorbance of the
mixture when
the isobutanol is present at more than about 0.5 wt% in the mixture at the
desired
concentration of suitable oxygenate.
[41] Normalized relative absorbance of an oxygenated gasoline (without
isobutanol) is
determined by calculating relative absorbance when the suitable oxygenate is
present at
about 1.0 wt% in an oxygenated gasoline.
[42] In another embodiment, the oxygenated gasoline includes a blend of
gasoline
blend stock, one or more suitable oxygenates, and isobutanol. In yet another
embodiment, the oxygenated gasoline is a blend of gasoline blend stock, one or
more
suitable oxygenates including ethanol, and isobutanol.
[43] Some properties of mixtures of gasoline blend stocks with oxygenate,
isobutanol
or both do not vary linearly with the amount of each component used. In
particular,
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volatility-related characteristics of such mixtures can diverge from linear
proportionality
with respect to the amount of each component used. This non-linear effect has
made it
particularly difficult to predict the actual impact upon RVP of oxygenates in
gasoline.
Actual RVP of an oxygenated gasoline varies with the gasoline blend stock
used, the
particular oxygenate used and the specific concentration of the oxygenate in
the
oxygenated gasoline. Because of this non-linear variability, RVP of an
oxygenated
gasoline is determined empirically. RVP data is typically empirically gathered
over a
range of oxygenate concentrations and over a range of gasoline blend stocks.
[44] The blend RVP of an oxygenate is typically calculated by measuring the
RVP of a
fuel before addition of such oxygenate and after addition of such oxygenate.
The
oxygenate blend RVP values which can be calculated from such empirical data
also
exhibit non-linear behavior with respect to concentration of the oxygenate in
the
particular oxygenated gasoline making such blend RVP values difficult to
predict.
Because of such non-linear effects upon RVP, the calculated blend RVP value is
particular to the concentration of a particular oxygenate added to a
particular fuel.
[45] The blend RVP of isobutanol when calculated as a function of volume
fraction of
isobutanol exhibit non-linear behavior making it more difficult to predict the
RVP of the
resulting mixture. The blend RVP of isobutanol is typically calculated by
measuring the
RVP of a fuel before addition of isobutanol and after addition of isobutanol.
Because
isobutanol exhibits non-linear effect upon RVP when added to a fuel, the
measured
blend RVP is particular to the concentration of isobutanol added to the
particular fuel.
[46] We have surprisingly found that the combination of one or more suitable
oxygenates and isobutanol can have a synergistic effect on the RVP value of
the
gasoline being produced.
[47] In any embodiment, gasoline blend stock, suitable oxygenates and
isobutanol can
be blended in any order. For example, Isobutanol can be added to a mixture,
including a
gasoline blend stock and suitable oxygenates. As another example, one or more
suitable
oxygenates and Isobutanol can be added in several different locations or in
multiple
stages. For further examples, Isobutanol can be added with the suitable
oxygenates,
added before the suitable oxygenates or blended with the suitable oxygenates
before
being added to a gasoline blend stock. In a preferred embodiment, Isobutanol
is added
to oxygenated gasoline. In another preferred embodiment, one or more suitable
oxygenates and Isobutanol are blended into a gasoline blend stock
contemporaneously.
[48] In any embodiment, more than one suitable oxygenate can be used in place
of a
single suitable oxygenate. Suitable oxygenates and Isobutanol can be added at
any point
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within the distribution chain. For example, a gasoline blend stock can be
transported to a
terminal and then suitable oxygenates and Isobutanol can be blended with the
gasoline
blend stock, individually or in combination, at the terminal. As further
example, a gasoline
blend stock, one or more suitable oxygenate and isobutanol can be combined at
a
refinery. Other components or additives can be added at any point in the
distribution
chain.
[49] In yet another embodiment, a method for reducing the RVP of an oxygenated
gasoline is provided. The method can be practiced at a refinery, terminal,
retail site, or
any other suitable point in the distribution chain. Preferably, the method is
practiced at a
terminal already designed for blending ethanol or some other oxygenate with a
gasoline
blend stock or at a terminal which can be adapted to accommodate such
blending.
[50] According to another embodiment, a gasoline blend stock is blended with
either
ethanol, another suitable oxygenate, or a combination of suitable oxygenates,
and
Isobutanol, to produce an oxygenated gasoline fuel having a lower RVP than the
oxygenated gasoline without the Isobutanol.
[51] The blend RVP value of the isobutanol is less than the RVP value of the
remaining mixture. Preferably the blend RVP of isobutanol is at most about 50%
of the
RVP of the remaining mixture. Alternatively, the blend RVP of the isobutanol
is less than
about 5.0 psi, more preferably less than about 3.0 psi, more preferably less
than about
0.0 psi.
[52] Regulations for gasolines set limits on various properties of the fuel
including,
typically, an upper limit on RVP. Such RVP limits may vary with country,
region, and
season. Such RVP limits place a constraint on the refinery product which can
be used as
gasoline. Typically, oxygenates, when blended into a gasoline blend stock,
will raise the
RVP of the resulting blend. Gasoline blend stocks for oxygenate blending
typically have
an RVP sufficiently below any applicable upper limits to account for the
anticipated effect
of the oxygenate. This further constrains the refinery product which can be
used for
gasolines because less high-volatility fuel components can used for gasoline
blend
stocks. Such RVP constraint can limit the amount of gasoline available for
consumption.
[53] In another embodiment, a method for reducing the RVP constraint on
refinery for
the production of gasoline blend stock for oxygenate blending is provided. The
RVP
constraint on a refinery is lessened because oxygenated gasoline that complies
with
regulatory RVP limits can be produced using gasoline blend stock which might
not
otherwise be useable to produce RVP compliant oxygenated gasoline. Another
embodiment provides a method to reduce the RVP of an oxygenated gasoline such
that
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some oxygenated gasoline which might not otherwise s meet regulatory RVP
limits might
be further blended to comply with such regulatory RVP limits.
[54] In yet another embodiment, an oxygenated gasoline is produced by blending
a
selected gasoline blend stock, a selected suitable oxygenate and isobutanol to
form an
oxygenated gasoline. The isobutanol reduces the RVP value of the oxygenated
gasoline.
For a particular suitable oxygenate and particular gasoline blend stock, use
of isobutanol
can allow use of a gasoline blend stock with a higher RVP value than could
typically be
used to produce an oxygenated gasoline meeting applicable RVP regulations.
[55] For a given maximum RVP value, a gasoline blend stock and a suitable
oxygenate are selected such that, even though the RVP value of the mixture of
the
gasoline blend stock and the suitable oxygenate would exceed the maximum RVP
value,
the RVP value of the oxygenated gasoline mixture containing the gasoline blend
stock,
the suitable oxygenate and isobutanol is less than or equal to the maximum RVP
value.
[56] Without limiting the scope, the following example illustrates various
embodiments
of our invention. The specific example below is discussed in the context of an
unleaded
gasoline fuel meeting the performance characteristics of ASTM D4814, but it
will be
appreciated by those in the art that the invention is not limited to such fuel
and can be
used with any gasoline blend stock or fuel consistent with the description
herein.
EXAMPLE
(57] An unleaded regular gasoline blend stock satisfying the performance
characteristics of ASTM D4814-01 a was blended with 10 vol% of a suitable
oxygenate.
Ethanol was used as the suitable oxygenate. The RVP of the resulting
oxygenated
gasoline was measured to be 9.69 psi when measured in accordance with ASTM
D5191.
Isobutanol (14% vol) was blended with the oxygenated gasoline and the RVP of
the
resulting mixture was 8.64 psi when measured in accordance with ASTM D5191.
The
blend RVP value calculated for the 14 vol% blend was 2.19 psi.
[58] The example above shows how isobutanol can reduce the RVP of an
oxygenated
gasoline. In regions which have a maximum RVP limit, refineries typically
produce
gasoline blend stocks significantly below such limit in anticipation of an RVP
increase
from oxygenate blending. Because isobutanol can be used to reduce the RVP of
an
oxygenated gasoline, refiners can utilize gasoline blend stocks to produce
oxygenated
gasolines which comply with applicable RVP limits which gasoline blend stocks
might not
otherwise be useable to produce RVP compliant oxygenated gasoline.
