REDUCED RVP OXYGENATED GASOLINE COMPOSITION AND METHOD

Background of the Invention

[01] This appfication claims benefit of provisional application Serial No. 61/027,969 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 ⁰ C to about 225 ⁰ 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 C ₄ to C ₁₀ 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 environmenta! 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

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 "TV) of 70 0C, a temperature range for distillation of 50% volume of its components (the "T ₅₀ "') of between 77 ⁰ C and 121 ⁰ C, a maximum temperature for distillation of 90% volume of its components (the "TW)Of 190 ⁰ C, a distillation end point of 190 ⁰ C, a distillation residue maximum of 2% volume, a "Driveability Index" or "Dl" maximum temperature of 597 ⁰ C, where Dl is calculated as 1.5 times the T ₁₀ plus 3.0 times the T ₅₀ plus the T ₉₀ , and a maximum vapor to liquid ratio of 20 at a test temperature of 56 ⁰ 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 C ₄ 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

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.

[1 1] 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

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 gasofine 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 iess than about 0.0 psi. Optionally, the RVP value of a mixture of the gasoline biend 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 1 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

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 isobutanoi'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 ^α 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.

[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 detrimentai 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 lshida 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 gasoiines 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 C ₂ to Cg 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

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 ⁰ C to the initial boiling point of the mixture.

[29] lsobutanol 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 voi%, 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). [31] 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.

[32] Relative absorbance employs the two-point baseline method, difference method, and infrared quantitative analysis techniques as described in ASTM Standard Practices for Genera! Techniques of Infrared Quantitative Analysis Specification E 168-99 ("E 168") which is incorporated by reference herein.

[33] Relative absorbance of a mixture containing isobutano! 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

gasoline used in Table I, ethanoi would be a suitable oxygenate compound for this particular embodiment of the invention.

[37] Table Il shows the relative absorbance of several mixtures of isobutanoi and an oxygenated gasoline with the same fungible unleaded regular gasoline used for Table I.

Table Il

Relative Absorbance of Isobutanoi in an Oxygenated Gasoline (2 wt% Ethanoi)

RVP Reducing Concentration Relative Compound wt% Absorbance none 0.049 Isobutanoi 2.0 0.029

[38] As illustrated in Table I adding the isobutanoi into the oxygenated gasoline has a significant impact on the relative absorbance of the mixture. The impact varies with different concentrations of isobutanoi, 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 isobutanoi 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 isobutanoi) is greater than about 0.05, preferably greater than about 0.1.

[40] The term "normalized relative absorbance" of a mixture containing a isobutanoi and an oxygenated gasoline is defined as the relative absorbance of the mixture when the isobutanoi 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 isobutanoi) 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 isobutanoi. In yet another embodiment, the oxygenated gasoline is a blend of gasoline blend stock, one or more suitable oxygenates including ethanoi, and isobutanoi.

[43] Some properties of mixtures of gasoline blend stocks with oxygenate, isobutanoi or both do not vary linearly with the amount of each component used. In particular,

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 fuef.

[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 isobutanoi is typically calculated by measuring the RVP of a fuel before addition of isobutanol and after addition of isobutanol. Because isobutanoi 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

within the distribution chain. For example, a gasoline blend stock can be transported to a terminal and then suitable oxygenates and lsobutanol 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

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 iimit 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.