CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from US Provisional Application No. 62/439,554 filed December 28, 2016, hereby incorporated by reference in its entirety for all purposes.

BACKGROUND

[0002] Commercial gasoline is a refined product of petroleum that is typically a mixture of hydrocarbons (base gasoline), additives, and blending agents. Additives and blending agents are added to the base gasoline to enhance the performance and the stability of gasoline, and can include anti-knock agents, anti-oxidants, metal deactivators, lead scavengers, anti- rust agents, anti-icing agents, upper-cylinder lubricants, detergents, and dyes.

[0003] When used in high compression internal combustion engines, gasoline has the tendency to "knock". Knocking occurs when combustion of the air/fuel mixture in the cylinder is not initiated correctly in response to ignition by the spark plug, and one or more pockets of the air/fuel mixture pre-ignite and explode outside the envelope of the normal combustion front causing a knocking noise. Anti-knocking agents reduce the engine knocking phenomenon by increasing the octane rating of the gasoline. An octane rating is a standard measure of the performance of an engine or aviation fuel. The higher the octane number, the more compression the fuel can withstand before detonating (igniting). In broad terms, fuels with a higher octane rating are used in high performance gasoline engines that require higher compression ratios.

[0004] Among the many types of anti-knocking agents, one notable compound is tetraethyllead (TEL) which has been blended with gasoline to boost octane levels since the early 1920s. By 1973, the first standards to phase out leaded gasoline had been implemented due to environmental and health reasons. By 2011, only six countries in the world were still using leaded gasoline.

[0005] Another notable anti-knocking additive that has been used in fuels is methylcyclopentadienyl manganese tricarbonyl (MMT), which became prevalent in response to the need to phase out lead. MMT, like TEL, is also a controversial gasoline additive in that it increases hydrocarbon emissions and has adverse effects on human health and catalytic converter systems in vehicles.

[0006] Decades later since the start of a global phasing out of leaded automotive fuel, oil companies continue to dedicate extensive research efforts towards the development of novel octane booster compounds, methods of enhancing the octane rating of a gasoline, and novel base gasoline formulations.

SUMMARY

[0007] In response to the phasing out of lead, gasoline sold in the United States and other countries was blended with up to 15 % volumes of an oxygenate, such as methyl -tertiary- butyl-ether (MTBE), in an effort to raise the octane rating and to reduce environmentally harmful exhaust emissions. Though large in octane number, MTBE is relatively low-boiling and light-natured. This means that blending of MTBE will produce a gasoline of a light nature even with a high octane requirement. While satisfactory start-ability of a cold engine can be expected with use of light gasoline, MTBE blending is reported susceptible to poor engine startup. Another but serious problem is that MTBE tends to increase nitrogen oxides (NOx) in exhaust gas.

[0008] Through research efforts made to eliminate the foregoing drawbacks of the prior art, it has now been found that a lead-free, high-octane gasoline with enhanced benefits for automotive use can be obtained by the use of a selected class of hydrocarbons combined with MTBE. The hydrocarbons are selected from C5 to C6 hydrocarbons and blended in specified amounts in the gasoline.

[0009] According to one aspect, there is provided a gasoline blend comprising at least 85 vol. % of a base gasoline having a research octane number of at least 90 and up to 15 vol. % of methyl tert-butyl ether (MTBE) having a purity of at least 96.5% by weight. In certain aspects the gasoline blend is substantially free of Ci aliphatic hydrocarbons. As used herein the term "substantially free of Ci aliphatic hydrocarbons" means the composition will contain Ci aliphatic hydrocarbons at less than 0.1 vol. %, 0.05 vol. %, 0.025 vol. %, or no more than 0.01 vol. % based on total volume of base gasoline. In a further aspect the methyl tert-butyl ether additive has a blending octane value of at least 110 and is effective in increasing the research octane number (RON) of the base gasoline by at least 2 units. RON can be determined by running the fuel in a test engine with a variable compression ratio under controlled conditions, and comparing the results with those for mixtures of iso-octane and n- heptane. In certain aspects the base gasoline in the gasoline blend is substantially free of Ci aliphatic hydrocarbons. In further aspects the methyl tert-butyl ether in the gasoline blend is substantially free of Ci aliphatic hydrocarbons. In still a further aspect the base gasoline and the methyl tert-butyl ether are substantially free of Ci aliphatic hydrocarbons.

[0010] Ci aliphatic hydrocarbons include, but are not limited to ^-heptane, 2- methylhexane; 3-methylhexane; 2,2-dimethylpentane; 2,3-dimethylpentane; 2,4- dimethylpentane; 3,3-dimethylpentane; 3-ethylpentane; 3-ethylpentane; 2,2,3- trimethylbutane; 1-heptene; 2-heptene; 3-heptene; 2-methyl-l-hexene; 3 -methyl- 1-hexene;

2.3 - dimethyl- 1-pentene; 2,4-dimethyl-l-pentene; 3,4-dimethyl-l-pentene; 3,3-dimethyl-l- pentene; 4,4-dimethyl- 1-pentene; 2,3-dimethyl-2-pentene; 2,4-dimethyl-2-pentene; 3,4- dimethyl-2-pentene; and/or 4,4-dimethyl-2-pentene. In certain aspects the Ci aliphatic hydrocarbons can be 2,2-dimethylpentane, 2,3-dimethylpentane, 2,4-dimethylpentane, 3,3- dimethylpentane, 2,2, 3 -trimethylbutane, 2,3-dimethyl-l-pentene, 2,4-dimethyl-l-pentene,

3.4- dimethyl-l-pentene, 3, 3 -dimethyl- 1-pentene, 4,4-dimethyl- 1-pentene, 2,3-dimethyl-2- pentene, 2,4-dimethyl-2-pentene, 3,4-dimethyl-2-pentene, and/or 4,4-dimethyl-2-pentene.

[0011] In certain aspects the gasoline blend comprises 90 to 92 vol. % of the base gasoline and 8-10 vol. % of the methyl tert-butyl ether. In particular aspects the gasoline blend comprises 90 vol. % of the base gasoline and 10 vol. % of the methyl tert-butyl ether. In certain aspects the methyl tert-butyl ether in the gasoline blend has a purity of at least 95.0, 96.0, 97.0, 98.0, 99.0, 99.5, or 99.8% by weight. In a particular aspect the methyl fert-butyl ether in the gasoline blend has a purity of at least 99.9% by weight.

[0012] In certain aspects the methyl tert-butyl ether in the gasoline blend has a blending octane value of at least 115 or 120. In a further aspect the methyl tert-butyl ether in the gasoline blend has a research octane number (RON) of at least 92 or 93. In certain aspects the base gasoline in the gasoline blend has a research octane number of at least 90, 91, 92, or 93. In a further aspect the base gasoline in the gasoline blend has an octane sensitivity of 7, 8, or 9, to 10, 11, or 12. In still a further aspect the base gasoline in the gasoline blend has an octane sensitivity of 8 to 10. [0013] Other embodiments of the invention are discussed throughout this application. Any embodiment discussed with respect to one aspect of the invention applies to other aspects of the invention as well and vice versa. Each embodiment described herein is understood to be embodiments of the invention that are applicable to all aspects of the invention. It is contemplated that any embodiment discussed herein can be implemented with respect to any method or composition of the invention, and vice versa. Furthermore, compositions and kits of the invention can be used to achieve methods of the invention.

[0014] The use of the word "a" or "an" when used in conjunction with the term "comprising" in the claims and/or the specification may mean "one," but it is also consistent with the meaning of "one or more," "at least one," and "one or more than one."

[0015] Throughout this application, the term "about" is used to indicate that a value includes the standard deviation of error for the device or method being employed to determine the value.

[0016] The use of the term "or" in the claims is used to mean "and/or" unless explicitly indicated to refer to alternatives only or the alternatives are mutually exclusive, although the disclosure supports a definition that refers to only alternatives and "and/or."

[0017] As used in this specification and claim(s), the words "comprising" (and any form of comprising, such as "comprise" and "comprises"), "having" (and any form of having, such as "have" and "has"), "including" (and any form of including, such as "includes" and "include") or "containing" (and any form of containing, such as "contains" and "contain") are inclusive or open-ended and do not exclude additional, unrecited elements or method steps.

[0018] In the context of the present invention, fifteen embodiments are now described. Embodiment 1 is a gasoline blend. The gasoline blend contains at least 85 vol. % of a base gasoline having a research octane number of at least 90; up to 15 vol. % of methyl tert-butyl ether having a purity of at least 96.5% by weight; and wherein the blend is substantially free of Ci aliphatic hydrocarbons and the methyl tert-butyl ether has a blending octane value of at least 110 and is effective in increasing the research octane number of the base gasoline by at least 2 units. Embodiment 2 is the gasoline blend of embodiment 1, wherein the base gasoline is substantially free of Ci aliphatic hydrocarbons. Embodiment 3 is the gasoline blend of embodiments 1 or 2, wherein the methyl tert-butyl ether is substantially free of Ci aliphatic hydrocarbons. Embodiment 4 is the gasoline blend of any one of embodiments 1 to 3, wherein the Ci aliphatic hydrocarbons are selected from the group consisting of ^-heptane, 2- methylhexane, 3-methylhexane, 2,2-dimethylpentane, 2,3-dimethylpentane, 2,4- dimethylpentane, 3,3-dimethylpentane, 3-ethylpentane, 3-ethylpentane, 2,2,3 -trimethylbutane, 1-heptene, 2-heptene, 3-heptene, 2-methyl-l-hexene, 3 -methyl- 1-hexene, 2,3 -dimethyl- 1- pentene, 2,4-dimethyl-l-pentene, 3,4-dimethyl-l-pentene, 3, 3 -dimethyl- 1-pentene, 4,4- dimethyl-l-pentene, 2,3-dimethyl-2-pentene, 2,4-dimethyl-2-pentene, 3,4-dimethyl-2-pentene and 4,4-dimethyl-2-pentene. Embodiment 5 is the gasoline blend of any one of embodiments 1 to 4, wherein the blend contains 90-92 vol. % of the base gasoline and 8-10 vol. % of the methyl tert-butyl ether. Embodiment 6 is the gasoline blend of any one of embodiments 1 to 5, wherein the blend contains 90 vol. % of the base gasoline and 10 vol. % of the methyl tert- butyl ether. Embodiment 7 is the gasoline blend of any one of embodiments 1 to 6, wherein the methyl tert-butyl ether has a purity of at least 99.5% by weight. Embodiment 8 is the gasoline blend of any one of embodiments 1 to 7, wherein the methyl tert-butyl ether has a purity of at least 99.9% by weight. Embodiment 9 is the gasoline blend of any one of embodiments 1 to 8, wherein the methyl tert-butyl ether has a blending octane value of at least 115. Embodiment 10 is the gasoline blend of any one of embodiments 1 to 9, wherein the methyl tert-butyl ether has a blending octane value of at least 120. Embodiment 1 1 is the gasoline blend of any one of embodiments 1 to 10, wherein the base gasoline has a research octane number of at least 92. Embodiment 12 is the gasoline blend of any one of embodiments 1 to 11, wherein the base gasoline has a research octane number of at least 93. Embodiment 13 is the gasoline blend of any one of embodiments 1 to 12, wherein the base gasoline has a research octane number of at least 95. Embodiment 14 is the gasoline blend of any one of embodiments 1 to 13, wherein the base gasoline has an octane sensitivity of 7 to 12. Embodiment 15 is the gasoline blend of any one of embodiments 1 to 14, wherein the base gasoline has an octane sensitivity of 8 to 10.

[0019] Other objects, features and advantages of the present invention will become apparent from the following detailed description. It should be understood, however, that the detailed description and the specific examples, while indicating specific embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

DESCRIPTION OF TH E DRAWINGS

[0020] The following drawings form part of the present specification and are included to further demonstrate certain aspects of the present invention. The invention may be better understood by reference to one or more of these drawings in combination with the detailed description of the specification embodiments presented herein.

[0021] FIG. 1 is a graph showing the effects of MTBE purity on the RONs of a base gasoline, the purity of MTBE being controlled by blending with ^-heptane. [0022] FIG. 2 is a graph showing the effects of MTBE purity on the RONs of a base gasoline, the purity of MTBE being controlled by blending with different MTBE commercial samples.

DESCRIPTION

[0023] Methyl Tertiary Butyl Ether (MTBE) has been accepted worldwide as a gasoline octane booster and it is being blended with gasoline in the range of 8 to 12 volume percent. The addition of MTBE affects the properties of gasoline in a positive way increasing the gasoline overall octane number for better combustion and improve performance of the automobile market. The present invention provides new lead-free, high-octane gasoline blend formulations that contain methyl tert-butyl ether (MTBE) and are substantially free of Ci aliphatic hydrocarbons.

[0024] MTBE belongs to a class of gasoline additive compounds called oxygenates. Oxygenates help engines burn gasoline more efficiently and reduce tailpipe or exhaust emissions by reducing the amount of carbon monoxide and soot that is created during the burning of the fuel. The production of compounds related to soot, such as volatile organic compounds (VOCs), polyaromatic hydrocarbons (PAHs) and nitrated PAHs, is also reduced.

[0025] Another important function of MTBE as a fuel additive is its anti-knocking properties. MTBE has the ability to raise the octane rating or octane number of the gasoline by increasing the oxygen content of the gasoline. The MTBE compound itself is large in octane number, with nominal blending octane values (BOVs) of 110-121 RON (Research Octane Number) and 98-106 MON (Motor Octane Number) and an octane sensitivity (RON - MON) of 17-18 octane numbers. The formula for BOV calculation is given below as Equation 2: = ON-ON _{bas e (1} -x) _{= Q Nbas e +} ON- _{(Equation 2)}

X X

where ON = RON or MON of base gasoline - MTBE-gasoline blend; ON _base = RON or MON of base gasoline; x = Volume fraction of MTBE.

[0026] Despite the large octane number, MTBE has a relatively low-boiling point (55.2- 55.5 °C), is light-natured, and has a low vapor pressure (260-280 mmHg at 25 °C), and therefore has superb miscibility with gasoline. Compared to alcohol-based oxygenate compounds such as methanol and ethanol, MTBE does not pose a phase-out separation problem when blended with gasoline. Per current ASTM D5983 standard (specification for MTBE for downstream blending for use in automotive spark-ignition engine fuel), the purity of MTBE should be 95%. However, the market demand of MTBE purity is 98%.

[0027] In order to account for differences in the performance quality of gasolines, two engine octane numbers or octane ratings are routinely used: RON and MON. RON is the most common type of octane rating and is determined by running the fuel in a test engine with a variable compression ratio at 600 rpm (simulation of the fuel performance under low severity engine operation). On the other hand, MON simulates the fuel performance under more severe engine operation using the same test engine but with a preheated fuel mixture, at 900 rpm and with variable ignition timing to further stress the fuel's knock resistance. The octane number is commonly reported as an anti-knock index, which is calculated using Equation 1 : AKI = (RON + MON)/2 (Equation 1)

[0028] An octane number is a measure of resistance of a gasoline to premature detonation when exposed to heat and pressure in the combustion chamber of an internal combustion engine. Although not directly correlating with the energy content of fuel, an octane number generally increases with any one or a combination of the following factors: a decrease in the carbon atoms especially with the length of a carbon chain, carbon chain branching and/or aromatics with same number of carbons. [0029] In certain embodiments, a gasoline blend according to the present invention comprises at least 85 vol. % of a base or raw gasoline that is substantially free of Ci aliphatic hydrocarbons and up to 15 vol. % of MTBE of at least 96.5% in purity (by weight), preferably at least 98.0%, more preferably at least 99.0%, more preferably at least 99.5%, even more preferably at least 99.9%.

[0030] In certain embodiments, a gasoline blend according to the present invention comprises at least 85 vol. % of a base or raw gasoline that is substantially free of Ci aliphatic hydrocarbons and up to 15 vol. % of MTBE that is substantially free of Ci aliphatic hydrocarbons and is of at least 96.5% in purity (by weight), preferably at least 98.0%>, more preferably at least 99.0%, more preferably at least 99.5%, even more preferably at least 99.9%.

[0031] As used herein, Ci aliphatic hydrocarbons include but are not limited to Ci aliphatic paraffins or alkanes such as ^-heptane; 2-methylhexane or isoheptane; 3- methylhexane; 2,2-dimethylpentane; 2,3-dimethylpentane; 2,4-dimethylpentane; 3,3- dimethylpentane; 3-ethylpentane; 3-ethylpentane; 2,2,3-trimethylbutane; Ci aliphatic olefins or alkenes such as 1-heptene; 2-heptene; 3-heptene; 2-methyl-l-hexene; 3 -methyl- 1-hexene; 2,3 -dimethyl- 1-pentene; 2,4-dimethyl-l-pentene; 3,4-dimethyl-l-pentene; 3,3-dimethyl-l- pentene; 4,4-dimethyl- 1-pentene; 2,3-dimethyl-2-pentene; 2,4-dimethyl-2-pentene; 3,4- dimethyl-2-pentene; and 4,4-dimethyl-2-pentene. In particular aspects Ci aliphatic hydrocarbons include but are not limited to 2,2-dimethylpentane; 2,3-dimethylpentane; 2,4- dimethylpentane; 3, 3 -dimethylpentane; 2,2,3-trimethylbutane; 2,3-dimethyl-l-pentene; 2,4- dimethyl-l-pentene; 3,4-dimethyl-l-pentene; 3, 3 -dimethyl- 1-pentene; 4,4-dimethyl- 1- pentene; 2,3-dimethyl-2-pentene; 2,4-dimethyl-2-pentene; 3,4-dimethyl-2-pentene; and 4,4- dimethyl-2-pentene. [0032] A base gasoline according to the present invention is a mixture of C4-C12 hydrocarbons with the exception of Ci aliphatic hydrocarbons. The base gasoline can be prepared by standard oil refinery processes wherein crude oil is separated into fractions by fractional distillation. The gasoline fraction distilled directly from crude oil serves as a hydrocarbon feed can be further subjected to another distillation process such as fractional distillation or extractive distillation in the presence of a polar solvent, so that a Ci cut comprising Ci aliphatic hydrocarbons can be separated. For example, to separate a Ci cut from a hydrocarbon feed, cut points can be set from 0.5 °C above the boiling point of C ₆ paraffins to 0.5 °C above the boiling point of Ci paraffins.

[0033] Being substantially or essentially free of Ci aliphatic hydrocarbons, a base gasoline according to the present disclosure should contain no more than 0.01 vol. % Ci aliphatic hydrocarbons based on the total volume of the base gasoline, preferably no more than 0.005 vol. %, more preferably no more than 0.0025 vol. %, even more preferably no more than 0.001 vol. %. The content of Ci aliphatic hydrocarbons in the base gasoline can be determined, for example, by gas chromatography (e.g. ASTM D6839 - incorporated herein by reference in its entirety) or gas chromatography/mass spectrometry (GC/MS) analysis.

[0034] In certain embodiments, the base gasoline substantially free of Ci aliphatic hydrocarbons according to the present invention meets ASTM D4814 standard specification for automotive spark-ignition engine fuel. The base gasoline can have a density of 0.720 to 0.760 g/cm ³ at 15 °C, preferably 0.725 to 0.755 g/cm ³ , more preferably 0.730 to 0.755 g/cm ³ . The Reid vapor pressure (RVP) of the base gasoline is 6.40 to 10.00 Psi, preferably 7.10 to 10.00 Psi, more preferably 8.50 to 10.00 Psi.

[0035] In some embodiments, in addition to being substantially free of Ci aliphatic hydrocarbons, the base gasoline may contain Cs and C ₆ hydrocarbons including but not limited to n-pentane; isopentane; neopentane; 1-pentene; 2-pentene; 2-methyl-l-butene; 3- methyl- 1-butene; 2-methyl-2-butene; cyclopentane; «-hexane; 2-methylpentane; 3- methylpentane; 2,2-dimethylbutane; 2,3-dimethylbutane; 1-hexene; 2-hexene; 3-hexene; 2- methyl- 1-pentene; 3 -methyl- 1-pentene; 4-m ethyl- 1-pentene; 2-methyl-2-pentene; 3-methyl-2- pentene; 3, 3 -dimethyl- 1-butene; 2,3-dimethyl-2-butene; cyclohexane; methylcyclopentane; cyclohexene; 1-methylcyclopentene; 3-methylcyclopentene; 4-methylcyclopentene; and/or benzene.

[0036] As described herein, the exclusion of Ci aliphatic hydrocarbons can enhance the octane rating of a MTBE-gasoline blend. A raw gasoline, as used herein, comprises a mixture of C4-C12 hydrocarbons. The Ci aliphatic hydrocarbon-free (or substantially free) base gasoline according to the present invention can have a RON of at least 90, 92, 93, or 95. The MON of the base gasoline can be at least 80, 82, 84, or 87. The octane sensitivity of the base gasoline (RON - MON) can be 7, 8, 9 to 10, 11, 12. In certain aspects the octane sensitivity of the base gasoline is 8 to 10. In other aspects the anti-knock index of the base gasoline is at least 85, 87, 89, or 90.

[0037] According to the present disclosure, the MTBE blended with the Ci aliphatic hydrocarbon-free or substantially Ci aliphatic free base gasoline has a purity (by weight) of at least or about 96.5%, 98.0%, 99.0%, 99.5%, or 99.9%. Impurities in MTBE include, for example, C ₄ hydrocarbons, Cs hydrocarbons, tert-butyl alcohol (TBA), diisobutylene and water. In certain aspects MTBE is substantially free of Ci aliphatic hydrocarbons.

[0038] MTBE is blended with the Ci aliphatic hydrocarbon-free or substantially free base gasoline at up to 15 vol. %, for example, 7, 8, or 9 to 10, 11, 12, 13, ^' 14, or 15 vol. %. In particular aspects MTBE is 8-12 vol. % or 8-10 vol. % of the blended composition. The MTBE used for gasoline blending has a BOV of at least 110, 115, or 120. The MTBE is effective in increasing the RON of the base gasoline by at least 2 units. Therefore, the MTBE-gasoline blend produced from the blending of MTBE and the Ci aliphatic hydrocarbon-free or substantially free base gasoline at specific volume ratios has an RON of at least 92, 93, 95, or 96. The octane sensitivity of the gasoline blend, like the base gasoline, is 7, 8, or 9 to 10, 11, or 12. In particular aspects the octane sensitivity is 7 to 11 or 8 to 10. The anti-knock index of the gasoline blend is at least 87, 89, 90, or 92.

[0039] The density and the Reid vapor pressure of the MTBE-gasoline blend produced herein remain substantially similar to the base gasoline.

[0040] In other embodiments of the invention the gasoline blend may consist of or consist essentially of the components disclosed herein. For example, in certain embodiments, the gasoline blend that is substantially free of Ci aliphatic hydrocarbons may consist or consist essentially of at least 85 vol. % of a base gasoline that is optionally substantially free of Ci aliphatic hydrocarbons and up to 15 vol. % of MTBE having a purity of at least 96.5% by weight that is also optionally substantially free of Ci aliphatic hydrocarbons. Gasoline blends that consist essentially of certain materials may include other components so long as the other components do not have a material effect on the basic and novel properties of the gasoline blend described herein. Such basic and novel properties include an increase octane number, reduced volatility, and/or otherwise reduced harmful combustion emissions. [0041] In the present disclosure, the inventors have also confirmed that the octane boosting effects of MTBE on a base gasoline and the final octane number of a gasoline- MTBE blend are dependent upon the following factors: MTBE concentration, MTBE stock purity, and compositions of the base gasoline stock. The behavior of MTBE varies when blended with different gasoline compositions at different concentrations. The amount of MTBE required for a certain octane number improvement depends on the purity of an MTBE stock, the composition of the impurities in the MTBE stock, and the composition of the base gasoline.

EXAMPLES

[0042] The following examples as well as the figures are included to demonstrate preferred embodiments of the invention. It should be appreciated by those of skill in the art that the techniques disclosed in the examples or figures represent techniques discovered by the inventors to function well in the practice of the invention, and thus can be considered to constitute preferred modes for its practice. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the spirit and scope of the invention.

[0043] The examples are intended to further illustrate the effects of impurities upon the blending octane value and the octane boosting effects of MTBE, and are not intended to limit the scope of the claims.

[0044] In both Examples 1 and 2, a base gasoline complying with the ASTM D4814 standard specification for automotive spark-ignition engine fuel, as shown in Table 1, was used for the octane number evaluation of MTBE. Per the ASTM D4814 specification, the base gasoline was subjected to two types of octane number evaluation, namely the research octane number (RON) and the motor research octane number (MON) using the ASTM D2699 and ASTM D2700 standard test methods, respectively. The base gasoline has an RON of 92.1 and a MON of 81.9. The anti-knock index (AKI) of the base gasoline is 87.

[0045] The density of the base gasoline was measured at 15 °C according to ASTM D4052 standard test method and the Reid vapor pressure (RVP) was measured using the ASTM D323 standard test method. Oxygenates, as measured by the ASTM D4815 standard test method, were not detected in the base gasoline. The base gasoline composition (paraffins, olefins, naphthenes, aromatics) was evaluated by gas chromatography according to ASTM D6839 standard test method. All ASTM D4814, ASTM D2699, ASTM D2700, ASTM D323, ASTM D4815 and ASTM D6839 standard specifications or test methods are incorporated herein by reference in their entireties.

[0046] The MTBE stock used in Examples 1 and 2 meets the ASTM D5983 standard, which is a standard specification for MTBE for downstream blending for use in automotive spark-ignition engine fuel. The MTBE stock has a purity of 99.49 wt. % based upon the total weight of the stock, with the 0.5 wt. % impurities, as measured by ASTM D5441 and ASTM D1364 standard test methods, comprising C ₄ hydrocarbons, Cs hydrocarbons, tert-butyl alcohol (TBA), diisobutylene and water.

EXAMPLE 1

[0047] The purity of the MTBE stock was reduced by mixing the stock with ^-heptane (purity > 99.9 wt. % based upon the total weight of the liquid). A 100% ^-heptane fuel is the zero point of the octane rating scale. Four MTBE samples with varying MTBE purities, as shown in Table 2, were each blended with the base gasoline at a concentration of 10 vol. % based upon the total volume of the gasoline blend (MTBE sample:base gasoline volume ratio of 1 :9). The MTBE sample 1 in Table 2, with a MTBE purity of 99.49 wt. %, was the original MTBE stock and had not been diluted with ^-heptane. After blending, the RON values of the four gasoline blends and the blending RON values (BOVs) of the four MTBE samples were obtained.

[0048] Results in Table 2 and FIG. 1 confirm that 99.49% MTBE boosts the octane number of the base gasoline having RON 92.1 to RON > 94.1 with the addition of 10 vol. % the MTBE stock. However by blending with ^-heptane, octane boosting power of MTBE decreases as the amount of ^-heptane in the blend increases. The quality of MTBE is one consideration when used as octane booster. The MTBE blend composition used as octane booster should be compatible with the base gasoline in all aspects, including the Reid vapor pressure. Table 2: Octane number evaluation of MTBE samples with the purity of an MTBE stock

EXAMPLE 2

[0049] In a similar fashion, the purity of the aforementioned MTBE stock was reduced by mixing the stock with commercial-grade MTBE from three different sources or suppliers. Four MTBE samples with varying MTBE purities, as shown in Table 3, were each blended with the base gasoline at a concentration of 10 vol. % based upon the total volume of the gasoline blend (MTBE sample:base gasoline volume ratio of 1 :9). The MTBE sample 1 in Table 3, with a MTBE purity of 99.49 wt. %, was the original MTBE stock that had not been mixed with any commercial-grade MTBE. After blending, the RON values of the four gasoline blends and the blending RON values (BOVs) of the four MTBE samples were obtained (see Table 3 and FIG. 2).

Table 3 : Octane number evaluation of MTBE samples with the purity of an MTBE stock

MTBE MTBE purity Blend RON BOV of MTBE sample (wt. %) (Base gasoline + MTBE sample) sample (RON)

1 99.49 94.5 116.1

2 98.51 94.3 114.1

3 97.63 94.3 114.1 4 96.58 94.3 114.1

[0050] Example 2 also confirms that MTBE of the highest purity (99.49 wt. %) gives the maximum octane boosting to the specific base gasoline. However by mixing the MTBE stock with different commercial-grade MTBE having different properties and compositions, the RON values of the gasoline blends were maintained the same at 94.3.