Lead-free aviation gasoline composition and preparation method thereof

Abstract

The invention relates to the field of fuel oil, and discloses a lead-free aviation gasoline composition and a preparation method of the lead-free aviation gasoline composition. The lead-free aviation gasoline composition comprises the following components in percentage by weight: 7.1 to 15 percent of C5 isoparaffin, 45 to 75 percent of C8 alkane, 0 to 2 percent of C4 alkane, 3 to 15 percent of C6-C7 alkane, 0 to 2.5 percent of C9 and C9 alkane, 1 to 10 percent of C7-C9 aromatic hydrocarbon and 1 to 23 percent of branched alkyl acetate with the carbon atom number of C4-C8. The lead-free aviation gasoline composition meets the requirements of various indexes such as antiknock property, vapor pressure, distillation range, calorific value, freezing point and the like, and does not contain high-toxic substances such as metal additives, aromatic amine compounds and the like. In addition, the lead-free aviation gasoline composition is simple in process and environment-friendly.

Description

Technical Field

[0001] This invention belongs to the field of fuel oil, specifically relating to an unleaded aviation gasoline composition and its preparation method. Background Technology

[0002] Aviation gasoline, also known as aviation piston engine fuel, is mainly used in aircraft equipped with reciprocating piston engines. The current standard is GB1787-2018, "Aviation Piston Engine Fuel." This standard specifies five categories of aviation gasoline, among which 95, 100, and 100LL aviation gasoline are leaded gasoline. The lead additives in aviation gasoline are highly toxic, and their combustion harms the environment and human health. Therefore, replacing leaded aviation gasoline with high-octane unleaded aviation gasoline is an inevitable trend.

[0003] Patent CN114149836B discloses a high-octane unleaded aviation gasoline and its production method. Although this unleaded aviation gasoline does not contain tetraethyl lead, its aromatic hydrocarbon content exceeds 70%. The use of a large amount of aromatic hydrocarbons will inevitably have an adverse effect on combustion performance and evaporation performance. Patent CN104593098B reduces the amount of aromatic hydrocarbons in its unleaded gasoline by adding aniline as a blending component. Although aniline components can increase the octane number of aviation gasoline, they are highly toxic and affect the vapor pressure of the base oil. In addition, patent CN104673409B adds methyl tert-butyl ether (MTBE), and patent CN 104593094B adds diethyl carbonate to improve the octane number of aviation gasoline. Dimethyl carbonate or diethyl carbonate can significantly increase the octane number, but they have low freezing points or pour points. Dimethyl carbonate has a melting point of 0.5°C, and diethyl carbonate has a melting point of -43°C, neither of which can meet the requirement that the freezing point of aviation gasoline should not be higher than -58°C.

[0004] Therefore, it is necessary to develop an unleaded aviation gasoline that meets the requirements, has low aromatic content, is free of amine compounds, and has a relatively simple composition. Summary of the Invention

[0005] The purpose of this invention is to overcome the aforementioned problems in the prior art and provide an unleaded aviation gasoline composition and its preparation method. This unleaded aviation gasoline composition meets the requirements for anti-knock properties, vapor pressure, distillation range, calorific value, and freezing point, while also being free of highly toxic substances such as metal additives and aromatic amine compounds. Furthermore, this unleaded aviation gasoline composition has a simple process and is environmentally friendly.

[0006] To achieve the above objectives, the present invention provides an unleaded aviation gasoline composition, wherein, based on the total weight of the unleaded aviation gasoline composition, the unleaded aviation gasoline composition contains: 7.1-15% by weight of C5 isoalkanes, 45-75% by weight of C8 alkanes, 0-2% by weight of C4 alkanes, 3-15% by weight of C6-C7 alkanes, 0-2.5% by weight of C9 and above alkanes, 1-10% by weight of C7-C9 aromatics, and 1-23% by weight of branched alkyl acetates.

[0007] A second aspect of the present invention provides a method for preparing an unleaded aviation gasoline composition as described in the first aspect, the method comprising the following steps:

[0008] 1) Distill alkylated gasoline to obtain a cutting oil composition with a distillation range of 40-120℃;

[0009] 2) Mix 60-90% by weight of the cutting oil composition, 4-19% by weight of isopentane, 1-10% by weight of C7-C9 aromatics and 1-23% by weight of branched alkyl acetate.

[0010] The above technical solution provides an unleaded aviation gasoline composition and its preparation method. The unleaded aviation gasoline meets the GB1787-2018 standard for 95-octane aviation gasoline, has good anti-knock properties, suitable vapor pressure, distillation range, calorific value and freezing point, and has low aromatic content. It does not contain lead compounds or aromatic amine compounds, and is environmentally friendly.

[0011] In addition, the method for preparing unleaded aviation gasoline provided by this invention requires fewer types of raw materials and has a simple preparation process, which greatly reduces production costs. Detailed Implementation

[0012] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0013] The first aspect of the present invention provides an unleaded aviation gasoline composition, wherein, based on the total weight of the unleaded aviation gasoline composition, the unleaded aviation gasoline composition contains: 7.1-15% by weight of C5 isoalkanes, 45-75% by weight of C8 alkanes, 0-2% by weight of C4 alkanes, 3-15% by weight of C6-C7 alkanes, 0-2.5% by weight of C9 and above alkanes, 1-10% by weight of C7-C9 aromatics, and 1-23% by weight of branched alkyl acetates.

[0014] During the research process, the inventors of this invention discovered that by adopting the above-mentioned scheme, it is possible to obtain an unleaded aviation gasoline composition with good anti-knock properties, suitable vapor pressure, distillation range, calorific value and freezing point without adding lead-containing compounds or aromatic amine compounds, which is environmentally friendly.

[0015] According to the present invention, preferably, based on the total weight of the unleaded aviation gasoline composition, the unleaded aviation gasoline composition contains: 8-13 wt% C5 isoalkanes, 49-70 wt% C8 alkanes, 0.5-1.1 wt% C4 alkanes, 6-11 wt% C6-C7 alkanes, and 0.5-2 wt% C9 and above alkanes. More preferably, the unleaded aviation gasoline composition contains: 9-12 wt% C5 isoalkanes, 54.3-64.5 wt% C8 alkanes, 0.65-0.9 wt% C4 alkanes, 7.5-9.5 wt% C6-C7 alkanes, and 1.3-1.8 wt% C9 and above alkanes. When the content of each component is within the above range, the overall performance of the obtained unleaded aviation gasoline composition is guaranteed to be better. It is understood that the hydrocarbons in the unleaded aviation gasoline composition are mostly isoalkanes, but may also inevitably contain small amounts of olefins, n-alkanes, etc.

[0016] According to the present invention, preferably, the unleaded aviation gasoline composition contains 2-10% by weight of C7-C9 aromatics. An aromatic content within this range can further reduce the environmental impact of aromatics, while also better ensuring the anti-knock performance of the unleaded aviation gasoline composition. More preferably, the unleaded aviation gasoline composition contains 5-8% by weight of C7-C9 aromatics.

[0017] According to the present invention, preferably, the unleaded aviation gasoline composition contains 5-20% by weight of branched alkyl acetates having a carbon number of C4-C8. A branched alkyl acetate content within the above range is more beneficial for improving the overall performance of the unleaded aviation gasoline composition. More preferably, the unleaded aviation gasoline composition contains 5-15% by weight of branched alkyl acetates having a carbon number of C4-C8.

[0018] According to the present invention, preferably, the C7-C9 aromatic hydrocarbon is one or more of toluene, xylene, ethylbenzene, cumene, and mesitylene; more preferably, the C7-C9 aromatic hydrocarbon is one or more of cumene and mesitylene. Using the scheme of the present invention, unleaded aviation gasoline compositions prepared by selecting cumene or mesitylene, which have lower toxicity, also meet the standards for 95-octane aviation gasoline.

[0019] According to the present invention, preferably, the branched alkyl acetate with C4-C8 carbon atoms is one or more selected from tert-butyl acetate, isobutyl acetate, ethylhexyl acetate, isoamyl acetate, and tert-butylamyl acetate; more preferably, the branched alkyl acetate with C4-C8 carbon atoms is tert-butyl acetate and / or isobutyl acetate. Using the preferred branched alkyl acetate of the present invention can further ensure the overall performance of the unleaded aviation gasoline composition.

[0020] According to the present invention, preferably, the content of aromatic amines in the unleaded aviation gasoline composition is less than 0.1% by weight; more preferably, the unleaded aviation gasoline composition does not contain aromatic amines, wherein the aromatic amines may be aniline, toluidine, or N-methylaniline. Using the solution of the present invention, unleaded aviation gasoline can meet the standard for 95-octane aviation gasoline with almost no use of aromatic amines.

[0021] The unleaded aviation gasoline composition provided by the present invention may further contain additives commonly used in the art to meet and improve the performance of unleaded aviation gasoline, such as antioxidants, which can delay the oxidation of unleaded aviation gasoline during use.

[0022] According to the present invention, preferably, the antioxidant can be one or more of 2,6-di-tert-butyl-p-cresol, 2,4-dimethyl-6-tert-butylphenol and 2,6-di-tert-butylphenol, more preferably 2,6-di-tert-butyl-p-methylphenol.

[0023] According to the present invention, preferably, the antioxidant content in the unleaded aviation gasoline composition is less than 12 mg / L, and more preferably 10-12 mg / L.

[0024] According to a particularly preferred embodiment of the present invention, the unleaded aviation gasoline composition contains only the components described above.

[0025] In this invention, there are no special requirements for the preparation method of the unleaded aviation gasoline composition; it can be prepared according to the above composition. The inventors of this invention have found that using a cut oil composition with a distillation range of 40-120°C makes it easier to obtain aviation gasoline that meets the standards compared to cut oils with other distillation ranges. Therefore, a second aspect of this invention provides a method for preparing unleaded aviation gasoline, which includes the following steps:

[0026] 1) Distill alkylated gasoline to obtain a cutting oil composition with a distillation range of 40-120℃;

[0027] 2) Mix 60-90% by weight of the cutting oil composition, 4-19% by weight of isopentane, 1-10% by weight of C7-C9 aromatics and 1-23% by weight of branched alkyl acetate.

[0028] According to the present invention, in step 1), the distillation conditions include: the bottom temperature of the distillation column is 110-120℃, the bottom pressure is 0.09-0.12MPa, the top temperature is 40-60℃, and the top pressure is 0.09-0.12MPa.

[0029] According to the present invention, the cutting oil is an alkylated oil cut under the above-mentioned distillation conditions, preferably, the distillation range of the cutting oil is 42-115°C.

[0030] The inventors of this invention have discovered that by distilling and cutting alkylated gasoline as described above, enriching C8 isoalkanes, and ensuring that the content of C8 isoalkanes in the cut oil is not less than 72% by weight, while reducing the content of C4 components, C9 components and components above C9, the distillation range of aviation gasoline can be adjusted, which is more conducive to obtaining unleaded aviation gasoline that meets aviation gasoline standards.

[0031] According to the present invention, the alkylated gasoline may be a common alkylated gasoline in the art, but the alkylated gasoline preferably contains 3-8% by weight of C4 hydrocarbons, 3-6% by weight of C5 hydrocarbons, 8-12% by weight of C6-C7 hydrocarbons, 65-72% by weight of C8 hydrocarbons, and 6-10% by weight of C9 and above hydrocarbons.

[0032] According to a preferred embodiment of the present invention, the alkylated gasoline contains 3-8% by weight of C4 hydrocarbon n-alkanes and 0-0.5% by weight of C4 hydrocarbon isoalkanes; the alkylated gasoline contains 3-6% by weight of C5 hydrocarbon isoalkanes; the alkylated gasoline contains 8-12% by weight of C6-C7 hydrocarbon isoalkanes; the alkylated gasoline contains 65-72% by weight of C8 hydrocarbon isoalkanes; and the alkylated gasoline contains 0-0.5% by weight of C9 and above hydrocarbon n-alkanes and 6-10% by weight of C9 and above isoalkanes.

[0033] According to the present invention, the distillation conditions are such that the cutting oil composition contains 0.5-2.5% by weight of C4 alkanes, 3-10% by weight of C5 alkanes, 8-15% by weight of C6-C7 alkanes, 72-85% by weight of C8 alkanes, and 1-2.5% by weight of C9 and above alkanes; more preferably, the distillation conditions are such that the cutting oil composition contains 0.8-1.6% by weight of C4 alkanes, 5-8% by weight of C5 alkanes, 9-13% by weight of C6-C7 alkanes, 75-83% by weight of C8 alkanes, and 1.5-2.5% by weight of C9 and above alkanes.

[0034] According to the present invention, the content of C4 n-alkanes in the cutting oil composition is 0.8-1.6% by weight; the content of C5 isoalkanes in the cutting oil composition is 5-8% by weight; the content of C6-C7 isoalkanes in the cutting oil composition is 9-13% by weight; the content of C8 isoalkanes in the cutting oil composition is 75-83% by weight; and the content of C9 and above isoalkanes in the cutting oil composition is 1.5-2.5% by weight. The cutting oil composition may also unavoidably contain small amounts of olefins, n-alkanes, etc.

[0035] According to a preferred embodiment of the present invention, the amount of the cutting oil composition is 65-85% by weight, preferably 70-83% by weight.

[0036] According to a preferred embodiment of the present invention, the amount of isopentane is 5-10% by weight, preferably 6-8% by weight.

[0037] According to a preferred embodiment of the present invention, the amount of the C7-C9 aromatic hydrocarbon is 2-10% by weight, preferably 5-8% by weight.

[0038] According to a preferred embodiment of the present invention, the amount of the branched alkyl acetate with C4-C8 carbon atoms is 5-20% by weight, preferably 5-15% by weight.

[0039] According to the present invention, the C7-C9 aromatic hydrocarbon can be one or more of toluene, xylene, ethylbenzene, cumene, and mesitylene, preferably one or more of cumene and mesitylene.

[0040] According to the present invention, preferably, the branched alkyl acetate with C4-C8 carbon atoms is one or more of tert-butyl acetate, isobutyl acetate, ethylhexyl acetate, isoamyl acetate and tert-butylamyl acetate, preferably tert-butyl acetate and / or isobutyl acetate.

[0041] According to the present invention, as described above, common additives, such as the aforementioned antioxidants, can also be added to aviation gasoline.

[0042] The present invention also relates to the application of the above-mentioned branched alkyl acetate in reducing the content of aromatics, lead compounds and aromatic amines in aviation gasoline.

[0043] The present invention will be described in detail below through embodiments, but the present invention is not limited to the following embodiments.

[0044] In the following examples and comparative examples, the alkylated gasoline, isopentane, and C7-C9 aromatics (toluene, cumene, and mesitylene) were sourced from China Petroleum & Chemical Corporation (Sinopec), while tert-butyl acetate and antioxidants were sourced from Beijing Innocare Technology Co., Ltd. The molecular composition of the alkylated gasoline was analyzed using gas chromatography.

[0045] Preparation Example

[0046] Alkylated gasoline (molecular composition shown in Table 1) was distilled. The bottom temperature of the distillation column was 120℃ and the pressure was 0.1MPa. The top temperature of the column was 40℃ and the pressure was 0.1MPa. Alkylated cutting oil was obtained, and its molecular composition is shown in Table 2. The initial boiling point of the cutting oil was 42℃ and the final boiling point was 115℃.

[0047] Table 1

[0048] carbon number n-Alkanes Isoalkanes Olefins Cycloalkanes Aromatics total 4 6.46 0.29 0.01 0.00 0.00 6.76 5 0.00 4.55 0.00 0.00 0.00 4.55 6 0.00 5.23 0.00 0.00 0.00 5.13 7 0.00 4.46 0.00 0.00 0.00 4.46 8 0.00 70.49 0.01 0.00 0.00 70.50 9 0.14 3.25 0.00 0.01 0.00 3.39 10 0.06 1.24 0.00 0.01 0.00 1.31 11 0.00 3.57 0.00 0.06 0.00 3.64 12 0.00 0.15 0.00 0.00 0.00 0.15 total 6.66 93.23 0.02 0.08 0.00 100

[0049] Table 2

[0050]

[0051]

[0052] Examples and Comparative Examples

[0053] Cutting oil or alkylated gasoline, isopentane, C7-C9 aromatics, tert-butyl acetate or carbonate or isobutyl acetate are mixed in a container to form formulations 1-16. The amounts of each component in the formulations are shown in Table 3. Among them, the hydrocarbons in formulations 1-12 and 14-16 are derived from cutting oil and isopentane, while the hydrocarbons in formulation 13 are derived from alkylated gasoline and isopentane.

[0054] Formula 14: Similar to Formula 3, except that tert-butyl acetate is replaced with dimethyl carbonate.

[0055] Formula 15: Similar to Formula 3, except that tert-butyl acetate is replaced with diethyl carbonate.

[0056] Formula 16: Similar to Formula 3, except that tert-butyl acetate is replaced with isobutyl acetate.

[0057] Table 3

[0058]

[0059]

[0060] Test Example 1

[0061] For a new type of unleaded aviation gasoline, the key physicochemical properties to be examined are motor octane number (MON), distillation range, vapor pressure, calorific value, and freezing point. Other properties are generally easy to meet the requirements. Therefore, the relevant properties of the above unleaded aviation gasoline compositions were tested according to the methods specified in GB1787-2018, and compared with the quality requirements of 95-octane aviation gasoline. The results are listed in Table 4.

[0062] Table 4

[0063]

[0064] The above results show that, by employing the technical solutions provided by this invention (formulas 3-5, 9-12, and 16), a 95-octane aviation gasoline composition that meets usage standards can be obtained without adding lead-containing compounds or aromatic amines, and with a simple composition. In particular, the more preferred solutions of this invention (formulas 3, 5, and 11-12) result in better overall performance of the unleaded aviation gasoline. Formulations 1-2, 6-8, and 13-15 are outside the scope of this invention, as at least one of their properties does not meet the quality requirements for 95-octane aviation gasoline. Formulations 14 and 15 alter the types of esters in the unleaded aviation gasoline composition, and their freezing point no longer meets the requirements of GB1787-2018 for 95-octane aviation gasoline.

[0065] Test Example 2

[0066] The antioxidant 2,6-di-tert-butyl-p-methylphenol was further added to the unleaded aviation gasoline prepared by formulations 3, 5 and 12, and the mixture was stirred evenly so that the content of 2,6-di-tert-butyl-p-methylphenol in the final unleaded aviation gasoline composition was about 10 mg / L. Since the amount of antioxidant added was very small, it can be considered that the content of each component in the final unleaded aviation gasoline is consistent with that in Table 3.

[0067] The unleaded aviation gasoline composition with added antioxidants was analyzed for other properties according to GB1787-2018, and all analytical results are shown in Table 5. Since the addition of antioxidants generally does not affect parameters such as motor octane number, initial boiling point, evaporation temperature, final boiling point, vapor pressure, calorific value, and freezing point, the tests were not repeated.

[0068] Table 5

[0069]

[0070] The results above show that the present invention can obtain a 95-octane aviation gasoline composition that meets the usage standards without adding lead-containing compounds or aromatic amines and with simple composition. The preparation process is simple and environmentally friendly.

[0071] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A composition of unleaded aviation gasoline, characterized in that, Based on the total weight of the unleaded aviation gasoline composition, the unleaded aviation gasoline composition contains: 7.1-15% by weight of C5 isoalkanes, 45-75% by weight of C8 alkanes, 0-2% by weight of C4 alkanes, 3-15% by weight of C6-C7 alkanes, 0-2.5% by weight of C9 and above alkanes, 1-10% by weight of C7-C9 aromatics, and 1-23% by weight of branched alkyl acetates having C4-C8 carbon atoms.

2. The unleaded aviation gasoline composition according to claim 1, wherein, The unleaded aviation gasoline composition contains: 8-13% by weight of C5 isoalkanes, 49-70% by weight of C8 alkanes, 0.5-1.1% by weight of C4 alkanes, 6-11% by weight of C6-C7 alkanes, and 0.5-2% by weight of C9 and above alkanes. Preferably, the unleaded aviation gasoline composition contains: 9-12% by weight of C5 isoalkanes, 54.3-64.5% by weight of C8 alkanes, 0.65-0.9% by weight of C4 alkanes, 7.5-9.5% by weight of C6-C7 alkanes, and 1.3-1.8% by weight of C9 and above alkanes.

3. The unleaded aviation gasoline composition according to claim 1 or 2, wherein, The unleaded aviation gasoline composition contains 2-10% by weight of C7-C9 aromatics; Preferably, the unleaded aviation gasoline composition contains 5-8% by weight of C7-C9 aromatics; And / or, the unleaded aviation gasoline composition contains 5-20% by weight of branched alkyl acetates having a carbon number of C4-C8; Preferably, the unleaded aviation gasoline composition contains 5-15% by weight of branched alkyl acetates with a carbon number of C4-C8.

4. The unleaded aviation gasoline composition according to claim 1 or 3, wherein, The C7-C9 aromatic hydrocarbons are one or more of toluene, xylene, ethylbenzene, cumene, and mesitylene; Preferably, the C7-C9 aromatic hydrocarbon is one or more of cumene and mesitylene.

5. The unleaded aviation gasoline composition according to claim 1 or 3, wherein, The branched alkyl acetate with C4-C8 carbon atoms is one or more of tert-butyl acetate, isobutyl acetate, ethylhexyl acetate, isoamyl acetate, and tert-butylamyl acetate. Preferably, the branched alkyl acetate with C4-C8 carbon atoms is tert-butyl acetate and / or isobutyl acetate.

6. The unleaded aviation gasoline composition according to any one of claims 1-5, wherein the content of aromatic amines in the unleaded aviation gasoline composition is less than 0.1% by weight; Preferably, the unleaded aviation gasoline composition does not contain aromatic amines; More preferably, the unleaded aviation gasoline composition does not contain aniline, toluidine, or N-methylaniline.

7. The unleaded aviation gasoline composition according to any one of claims 1-6, wherein the unleaded aviation gasoline composition further comprises an antioxidant; Preferably, the antioxidant is 2,6-di-tert-butyl-p-methylphenol; Preferably, the antioxidant content is 10-12 mg / L.

8. A method for preparing unleaded aviation gasoline, characterized in that, The method includes the following steps: 1) Distill alkylated gasoline to obtain a cutting oil composition with a distillation range of 40-120℃; 2) Mix 60-90% by weight of the cutting oil composition, 4-19% by weight of isopentane, 1-10% by weight of C7-C9 aromatics and 1-23% by weight of branched alkyl acetates with C4-C8 carbon atoms.

9. The method according to claim 8, wherein, In step 1), the distillation conditions include: the bottom temperature of the distillation column is 110-120℃, the bottom pressure is 0.09-0.12MPa, the top temperature is 40-60℃, and the top pressure is 0.09-0.12MPa. And / or, the distillation range of the cutting oil composition is 42-115°C.

10. The method according to claim 8 or 9, wherein, The distillation conditions are such that the cutting oil composition contains 0.5-2.5% by weight of C4 alkanes, 3-10% by weight of C5 alkanes, 8-15% by weight of C6-C7 alkanes, 72-85% by weight of C8 alkanes, and 1-2.5% by weight of C9 and above alkanes. Preferably, the distillation conditions are such that the cutting oil composition contains 0.8-1.6% by weight of C4 alkanes, 5-8% by weight of C5 alkanes, 9-13% by weight of C6-C7 alkanes, 75-83% by weight of C8 alkanes, and 1.5-2.5% by weight of C9 and above alkanes.

11. The method according to any one of claims 8-10, wherein, The amount of the cutting oil composition is 65-85% by weight, preferably 70-83% by weight; And / or, the amount of isopentane used is 5-10% by weight, preferably 6-8% by weight; And / or, the amount of the C7-C9 aromatic hydrocarbon is 2-10% by weight, preferably 5-8% by weight; And / or, the amount of the branched alkyl acetate with C4-C8 carbon atoms is 5-20% by weight, preferably 5-15% by weight.

12. The method according to claim 8 or 11, wherein, The C7-C9 aromatic hydrocarbons are one or more of toluene, xylene, ethylbenzene, cumene, and mesitylene; Preferably, the C7-C9 aromatic hydrocarbon is one or more of cumene and mesitylene; And / or, the branched alkyl acetate with C4-C8 carbon atoms is one or more of tert-butyl acetate, isobutyl acetate, ethylhexyl acetate, isoamyl acetate, and tert-butylamyl acetate; Preferably, the branched alkyl acetate with C4-C8 carbon atoms is tert-butyl acetate and / or isobutyl acetate.

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