NZ204590A - Gasoline composition containing dimethyl carbonate - Google Patents

Description

New Zealand Paient Spedficaiion for Paient Number £04590 2045 90 ^ 1^1 t'liiitif'iiiii Compfete Specification Filed: Cfaqs- CH>l~)h-Z\ ea>ncD.<^ V/IClOOt m-g ii«I Publication Date: .. H?. - No.: Date: NEW ZEALAND PATENTS ACT, 1953 COMPLETE SPECIFICATION FUEL COMPOSITIONS X/We, IMPERIAL CHEMICAL INDUSTRIES PLC a British Company of Imperial Chemical House, Millbank, London SwlP 3JF, England f 'J* hereby declare the invention for which / we pray that a patent may be granted to iffife/us, and the method by which it is to be performed, to be particularly described in and by the following statement: - (followed by page la) 2045 90 B 32361 Fuel oonrpooitieBB- This invention relates to fuel compositions and in particular to gasoline compositions for use in spark ignition internal combustion engines.

Such gasoline compositions comprise a mixture of hydrocarbons and other additives. The composition is required to vaporise over a range of temperatures to give satisfactory hot and cold starting characteristics and efficient engine operation. To this end the compositions generally have initial and final boiling points within the range 25-35°C and. 200-220°C respectively. The gasoline composition is often varied with the time of year and/or region to allow for variations in the average ambient temperature. The distillation and vapour pressure characteristics of typical gasolines are as follows. 1 Cold weather formulation Hot weather formulation initial boiling point" 28°C 32°C % boiling point 42 48-49 50% boiling point ASTM - 94-100 99-104 90% boiling point D-86 1 I64-I68 166-172 final boiling point I 207-210 209-213 Reid vapour pressure (ASTM D-323) 85-86 kPa 67-68 kPa For economic reasons the compositions generally contain as 25 much butane as is consistent with obtaining satisfactory vapour pressure and boiling range characteristics.

Spark ignition internal combustion engines, such as those used in aufccmofaQes, generally have, in the interests of efficiency, a relatively high compression ratio. For such engines a fuel having 30 a high octane rating is required: the Research Octane Number (RON) is normally above 80, more usually above 85, and in most cases above 90: indeed compositions having a RON in the range 95-100 are widely used for premium grade fuels. In order to achieve the desired octane rating, additives are gnerally incorporated into the composition: lead 35 compounds, e.g. lead tetraethyl, are the most widely used octane 2045 90 2 B 32361 rating improvers. However environmental considerations make the use of highly leaded gasolines undesirable: the discharge of exhaust gases from internal combustion engines into the atmosphere causes pollution and allegedly present health hazards. These exhaust gases 5 contain not only lead compounds which themselves give rise to pollution and alleged health hazards but also various nitrogen oxides which may also be objectionable. To reduce the nitrogen oxides emission it is often desirable to employ catalytic converters in the exhaust system to convert the nitrogen oxides to less objectionable 10 materials: however the catalysts in such converters are often poisoned by lead compounds in the exhaust gases.

For these environmental reasons the maximum amount of lead that can be incorporated into gasoline is often restricted: in many countries it is restricted to no more than 0.4 g Pb/Litre and in some 15 countries to no more than 0.15 Pb/litre. Indeed unleaded gasoline is used in some countries.

Alternative octane improving additives that have been employed include ethers and alcohols such as methyl t-butyl ether (MEBE) and t-butanol alone or in admixture with other alcohols such as 20 ethanol. The blending RON of these additives varies to some extent on the base gasoline used in the RON determination and on the amount of additive employed: typical blending RON are as follows: t-butanol ^ 108 ethanol 110-120 MEBE 115-133 While measurements indicate that methanol has a high blending RON, the benefit observed in normal automobile usage is markedly less than that predicted from its blending RON.

While MTBE has a high blending RON, it has a relatively low 30 boiling point (55°C) and so its use as an octane improver has the disadvantage that the amount of butane that can be included in the gasoline composition is reduced. Methanol suffers from the same disadvantage.

We have found that di-alkyl carbonates can be used to 35 improve the octane rating of gasoline without the aforementioned disadvantages. Di-alkyl carbonates have been proposed as gasoline 2 045 90 3 B 32361 additives in US-A-23313^6 which quoted a blending octane number of 96-98 for di-ethyl carbonate (DEC) when used in gasolines of octane number about 74 to 79 • Our measurements conducted on gasolines having higher EON indicate that DEC has a blending 5 RON of the order of 110-112 and that, surprisingly, di-methyl carbonate (DMC) has a much higher blending RON, of the order of 120-130 or more.

Compared with DEC and other di-alkyl carbonates, e.g. di- n-propyl carbonate (DiPC) and di-n-butyl carbonate (DBC), and 10 with other lead-free octane improving additives such as alcohols, e.g. methanol, ethanol, t-butanol, and MTBE, DMC has a number of disadvantages. Inter alia it has a significantly higher specific gravity and a much lower net calorific value (i.e. the heat of combustion excluding the heat liberated by condensation of the water 15 vapour formed during combustion, since in internal combustion engines this water vapour is not condensed but is emitted with the exhaust gases).

However, the unexpectedly high blending RON of DMC outweighs these disadvantages and renders IMC particularly useful as an octane 20 improving agent.

Accordingly the present invention provides a gasoline composition having a RON of at least 80 and comprising gasoline hydrocarbons and from 1 to 6% by volume, based on the volume of the composition, of DMC.

Another disadvantage of octane improving additives such as alcohols is their water miscibility. The use of water miscible additives presents storage problems, particularly the use of gasoline storage tanks having water providing a base level. Not only may water miscible additives tend to be leached from the gasoline 30 into the aqueous phase upon storage over a water base, but also their presence in the gasoline may increase the solubility of water in the gasoline.

The specific gravity, net calorific value, and water solubility of DMC in relation to other di-alkyl carbonates and other 35 gasoline additives are listed in the following table. # 2045 90 4 B 32561 Additive Specific gravity Net calorific value MJ/kg Water solubility g/LOO ml DMC 1.07 14.5 11.8 DEC 0.98 21.2 1.9 DPC 0-94 r-J 25 * 0.2 DBC 0.93 28 * X 0.02 methanol 0.79 19.8 OO ethanol 0.79 27.1 OO t-butanol 0-79 32.8 DO MTBE 0.75 34.9 ^ 5 gasoline 0.73 - 0.76 42.7 - 43 5 - * estimated Although IMC has an appreciable solubility in water, and this solubility is significantly greater than that of other di-alkyl carbonates, the partition coefficient of IMC between the gasoline and aqueous phases is strongly in favour of dissolution in the gasoline, phase. Furthermore, despite the greater solubility of IMC in water, the increase in solubility of water in gasoline resulting from incorporation of IMC into gasoline appears to be significantly less than that given by the incorporation of DEC into gasoline.

IMC can readily be produced from feedstocks other than crude oil and so its use enables a greater amount of fuel to be obtained from a given quantity of crude oil.

Thus IMC can be made fromnethanol by reaction with carbon monoxide and oxygen over a suitable catalyst, e.g. copper chloride: for example see Ind. Eng; Chem. Prod. Res. Dev. (1980) 19 . 396-403-It may also be made by reacting ethylene oxide with carbon dioxide to produce ethylene carbonate which is then reacted with methanol to produce DMC and ethylene glycol: for example see US-A-3642858 and 3803201.

The compositions of the present invention may contain other additives e.g. viscosity modifiers, gum suppressants and other octane improvers, e.g. other di-alkyl carbonates, alcohols or ethers, such 2 ,1 ! IJ B 32361 as t-butanol and MEBE, and lead compounds such as lead tetraalkyls e.g. lead tetraethyl and lead tetramethyl. However, for environmental reasons mentioned hereinbefore, the lead content is preferably not more than 0.4» preferably not more than 0.15, 5 g Pb/litre. In particular we prefer that the gasoline composition is substantially lead free.

Di-alkyl carbonates that can be used in combination with IMC (boiling point 90°C) are those di-alkyl carbonates of the 12 12 formula R -0-R in which R and R are alkyl radicals which may be the same or different and in which the total number of carbon atoms 1 2 in the alkyl groups R and R is from 3 "to 8. Examples of such di-alkyl carbonates include; Approx. boiling point (°C) di-ethyl carbonate (DEC) 127 ethyl methyl carbonate 109 di-n-propyl carbonate (DPC) 166 di-iso-propyl carbonate 147 di-n-butyl carbonate (DBC) 208 di-iso-butyl carbonate 190 1 2 Each of the alkyl groups R and R preferably contains less than 5 carbon atoms.

Since di-alkyl carbonates, and DMC in particular, have a poor calorific value when compared to hydrocarbons, the total amount of di-alkyl (including di-methyl) carbonates is preferably below 10% by 25 volume of the gasoline composition, while the amount of IMC employed, whether alone or in admixture with other di-alkyl carbonates and/or other octane improvers is between 1 and 6% by volume of the gasoline composition. The use of higher proportions of di-alkyl carbonates, and IMC in particular, would not only give less energy per litre of the 30 composition but also would necessitate modification of carburettor or fuel injector settings to allow for the different fuel/air ratio required for the combustion of di-alkyl carbonates relative to that required for hydrocarbons. The incorporation of IMC into gasoline has no unexpected adverse effect upon the distillation characteristics 35 or the Reid vapour pressure of the composition. 2 04 5 9 0 6 B 32361 Preferably the amount of DMC employed is 3 to 9% by volume. The use of such amounts of IMC generally increases the EON of unleaded gasoline or leaded gasoline containing up to 0.4 g Pb/l by about 1-2 units.

In some cases a mixture of EMC and one or more other di-alkyl carbonates may be preferable to IMC alone because the mixture has a higher calorific value, per unit volume, a range of boiling points and vapourisability, and less mutual solubility in water compared with IMC. All these properties are advantageous in gasoline 10 compositions for spark ignition interna], combustion engines.

However such a mixture will of course have a lower blending RON than IMC alone.

A mixture of di-alkyl carbonates may conveniently be made, when using a di-alkyl carbonate producing process, such as those 15 mentioned above, wherein the reactant providing the alkyl radicals is an alcohol, by using as the alcohol a mixture of alcohols.

Such a mixture of alcohols may be synthesised from a synthesis gas comprising carbon monoxide and hydrogen, by the use of a suitable catalyst. Processes for making such alcohol mixtures are well known 20 in the art.

The ratio of higher alcohols (mainly C^ to C^) to methanol and the structure, i.e. branched or straight chain, of the alcohols higher than ethanol produced by these processes will depend on the precise catalyst and synthesis conditions, including the E^/CO ratio 25 employed. r As mentioned hereinbefore one convenient method for the manufacture of di-alkyl carbonates is by reaction of an alkylene oxirane, e.g. ethylene or propylene oxide, with carbon dioxide to produce an alkylene carbonate which is then reacted with an alcohol to give the 30 di-alkyl carbonate and a glycol (for example as described in TJS-A-3642,858 and 3,803,201). Glycols, which have a variety of uses, are often made by the hydrolysis of alkylene oxiranes. Therefore, by modification of the conventional glycol production route of hydrolysis of alkylene oxiranes by replacing that hydrolysis step with 35 an alkylene carbonate formation step followed by reaction of the alkylene carbonate with an alcohol, a di-alkyl carbonate can be made 2045 9 7 B 32361 from the alcohol in addition to the production of the glycol from the alkylene oxirane.

One method that is employed for the production of alkylene oxiranes (for subsequent hydrolysis to the corresponding glycol) 5 involves the formation of an alkyl hydroperoxide by the reaction of an alkane with oxygen, i.e.

R-H + 02 —>R-00H followed by the reaction of the alkyl hydroperoxide with an alkene, e.g. propylene, e.g. 0 (see for example TJK-A-1,060,122 and 1,074*330). Generally the alkyl group R should be a tertiary alkyl group so that the hydroperoxide has sufficient stability for use in the reaction with the 15 alkene. A by-product of this reaction is thus the alcohol ROH corresponding to the alkyl hydroperoxide ROOH.

The nature of the by-product alcohol ROH will of course depend on the alkane feedstock employed to make the hydroperoxide ROOH. Depending on the alkyl group R the by-product alcohol ROH 20 can be put to a variety of uses including one or more of: i) directly as gasoline additives, ii) used in di-alkyl carbonate manufacture, iii) dehydrated to the corresponding alkene which is used as part of the alkene used to make the alkylene oxirane iv) dehydrated to the corresponding alkene which is used to make an ether v) used as an alcohol in the reaction of an alkene and an alcohol to produce an ether. i) Alcohols containing 4 "to 8 carbon atoms, particularly t-butanol, are useful as such as gasoline additives. By the use of a mixture of alkanes, e.g. a suitable petroleum fraction, a mixture of such alcohols can be produced. Hence by integrating the above-mentioned processes, a di-alkyl carbonate and one or more C^-Cg 35 alcohols can be produced and used as gasoline additives, and at the same time the glycol required for other applications is produced. 2 C45 90 8 B 32361 ii) As mentioned hereinbefore, the alkyl group R will generally be a tertiary alkyl group. Also since, even at the theoretical 10C% efficiency, only one mole of the alcohol ROH is produced for each mole of alkylene oxirane (which gives one mole of the alkylene 5 carbonate) and two moles of alcohol are required for the reaction with the alkylene carbonate to produce the di-alkyl carbonate, some additional alcohol, e.g. methanol, obtained from another source is required, over and above that produced in the oxirane-producing reaction, for the production of the di-alkyl carbonate. Hence by using a 10 suitable a1.ka.ne feedstock to produce the alcohol ROH, and another alcohol e.g. methanol is used as the additional alcohol, a gasoline additive comprising a mixture of di-alkyl carbonates and/or a di-alkyl carbonate in which the alkyl groups differ, can be produced. iii) Where the alcohol ROH has the same carbon skeleton as 15 the desired glycol, the alcohol can be dehydrated to the corresponding alkene. The alkene can be recycled to the oxirane-producing reaction and used as part of the alkene employed in the production of the alkylene oxirane as described in UK-A-1,111,945* I11 this way the amount of alkene feedstock employed to make the glycol can be 20 reduced, and consequently the amount of di-alkyl carbonate produced utilising a given amount of alkene feedstock is increased. iv) The alcohol ROH can be dehydrated to an. alkene which is then reacted with an alcohol to form an ether. Thus t-butanol (formed from isobutane via t-butyl hydroperoxide) dehydrates to 25 isobutene which, on reaction with methanol, gives methyl t-butyl ether (MTBE). Again, by use of a mixture of alkanes to give a mixture of alcohols and hence a mixture of alkenes, a mixture of ethers can be produced. MTBE and similar ethers, and ether mixtures, are useful as gasoline additives.

Therefore by this route both di-alkyl carbonates and ethers which are useful as gasoline additives, can be produced in addition to a glycol. v) The alcohol ROH can be used as part or all of the alcohol reacted with an alkene to give an ether, e.g. as described in 35 iv) above. Some or all of the alkene may be derived from part of 3 :z o r\ %j> if U B 32361 the alcohol ROH by dehydration as in iv) above while the remainder of the alcohol ROH is reacted, if desired in admixture with an alcohol, e.g. methanol, obtained from another source, with the alkene to give an ether, or ether mixture, suitable for use as gasoline 5 additives.

Where a mixture of alkanes is employed, giving a mixture of hydroperoxides and hence a mixture of alcohols, the latter mixture can be fractionated so that some alcohols are subjected to one or more of the uses outlined above while others are employed in other of 10 said uses. For example, considering uses iv) and v) above, an alcohol mixture produced from a mixture of hydroperoxides can be separated into "high" and "low" fractions: the "high" fraction can be dehydrated to the corresponding alkene or alkenes while the "low" fraction reacted with the alkene or alkene mixture obtained from the 15 "higfr" fraction to give the ether or ether mixture.

Which, if any, of the aforementioned uses of the alcohol is adopted will of course depend on the nature of the feedstock employed and on the desired end product: for example in some cases it may be desired to produce a liquid fuel material containing as additives, not 20 only at least one di-alkyl carbonate but also, at least one alcohol and at least one ether in specified proportions. By utilising a combination of uses i), iv) and/or v) and optionally ii) if necessary, in the appropriate proportions, the desired additives in their desired respective quantities can be obtained. Of course, where a mixture 25 of alkanes is used, giving a mixture of the alcohols ROH, it may be desirable to fractionate the alcohol mixture and subject the different fractions to the different uses.

Accordingly a further aspect of the invention provides a' process for the manufacture of i) a di-alkyl carbonate product 30 consisting of at least one cjj-al kyl carbonate, ii) an alcohol product A consisting of at least one alcohol and/or an ether product consisting of at least one ether, and iii) a glycol product consisting of at least one glycol, comprising a) reacting at least one alkyl hydroperoxide with an alkene feedstock B consisting of at least one alkene to produce at least one alkylene oxirane and an alcohol material C containing said 2 04590 B 32361 alcohol product A, b) reacting at least part of said at least one alkylene oxirane with carbon dioxide to form at least one alkylene carbonate, c) reacting said at least one alkylene carbonate with an 5 alcohol component D, consisting of at least one alcohol and which may contain part of said alcohol material C, to form said di-alkyl carbonate product and said glycol product, d) separating said glycol product from said di-alkyl carbonate product and, optionally e) dehydrating at least part of said alcohol material C to an alkene component E and etherifying said alkene component E by reaction with an alcohol component P, consisting of at least one alcohol and which may contain part of said alcohol material C, to produce said ether product.

The above process can thus upgrade an alkane feedstock into an alcohol product useful as a gasoline additive as such or as a reactant for the production of a gasoline additive, aind ah alkehe feedstock into a glycol product and also upgrade said alcohol product or a different alcohol component into a di-alkyl carbonate product 20 which is useful as a gasoline additive.

Accordingly a further aspect of the invention provides, in a process wherein an alkane feedstock and an alkene feedstock are upgraded to form an alcohol product and a glycol product by: 1) reacting said alkane feedstock with oxygen to form a hydroperoxide product, ii) reacting said hydroperoxide product with said alkene feedstock to form an alkylene oxirane product and said alcohol product, and iii) converting said alkylene oxirane product to said glycol product, the improvement comprising also upgrading an alcohol feedstock into a gasoline additive by converting said alkylene oxirane product to said glycol product by reacting .said oxirane product with carbon dioxide to form an. alkylene carbonate.'product and reacting said alkylene carbonate product with said alcohol feedstock to form said glycol product and a di-alkyl carbonate product.

The .catalysts^ and conditions suitable for effecting the above mentioned reactions are known and will be apparaent to those x. ~ J 90 11 B 32361 skilled in the art and so details thereof are here 'unnecessary.

In a preferred embodiment, isobutane is used as the alkane feedstock and the resulting hydroperoxide is reacted with propylene to give propylene oxide and t-butanol. The propylene oxide is 5 converted to propylene carbonate which is reacted with methanol to produce propylene glycol and BMC. Alternatively ethylene is used in place of propylene thus giving ethylene glycol and IMC. The t-butanol is preferably used as such, in admixture with the KMC, as a fuel additive, or some or all of the t-butanol is dehydrated to isobutene 10 which is etherified with methanol to give MTBE which is used in admixture with the IMC and the remainder, if any, of the t-butanol as a gasoline additive.

The invention is illustrated by the following examples.

EXAMPLE 1 Research Octane numbers (RON) of fuels were determined by the standard method (ASTM D2699) with a CFR-ASTM single-cylinder engine. Blends of 3 and 5% v/v of IMC in pure iso-octane were used. The values obtained were: % v/v IMC,blending RON =130 20 % v/v IMC, blending RON = 132 EXAMPLE 2 Example 1 was repeated using blends of 3 and 5% v/v of various di-alkyl carbonates in a gasoline composition comprising 8CP/0 v/v iso-octane and 2C% v/v n-heptane. Motor Octane Numbers (MON) 25 were also determined by the Standard Method (ASTM D2700). The results were as follows: ** j 9 0 12 B 32361 di-alkyl carbonate % additive (Vv) RON MON Average Blending No RON MON None IMC DEC DPC DBC { 0 3 5 3 5 3 5 3 5 80.0 81.5 82.6 81.0 81.4 80.8 81.7 80.1 80.2 80.0 80.6 81.0 80.7 81.1 80.3 81.1 80.0 80.1 131 110 110 84 100 103 96 81 EXAMPLE 3 Example 2 was repeated using leaded premium grade gasolines in place of the iso-octane/n-heptane mixtures. The gasolines, which differed for each di-alkyl carbonate, each contained 0.4 g Pb/L. The results were as follows: di-alkyl carbonate % Additive fv/v) RON MDN 0 97-0 87-7 3 97.9 88.3 98.3 88.8 ■ 0 98-5 88.1 3 98.9 88.3 99-2 88.5 0 97.4 88.6 3 97.8 89.0 98.3 89.1 0 97.7 88.1 3 97-7 88.1 97-7 88.2 Average Blending No RON MON IMC DEC DPC DBC I 125 112 113 98 109 95 104 88 It is seen from Temples 2 and 3 that DMC gives a much higher Research Octane No improvement than other di-alkyl carbonates, both in leaded and unleaded gasolines. 2 C 4 3 9 13 b 32361 EXAMPLE 4 The effectiveness of di-alkyl carbonates for lowering the surface and interfacial tension of a hydrocarbon fuel was tested as in US-A-2331386.

Precisely measured drops of a premium grade gasoline containing of the di-alkyl carbonate were allowed to fall 1.2 cm on to a polished metal surface. The diameter of the resultant droplet film was measured and is expressed in the table as a percentage of that formed from the gasoline containing no di-alkyl 10 carbonate.

Di-alkyl carbonate Relative spread (%) None 100 BMC 98 DEC 136 DPC 151 DBC 168 It is seen that there is reasonable agreement with the 20 results quoted for DEC and BBC in US-A-2331386 but IMC has only a little, but negative, effect on the degree of spreading.

EXAMPLE 5 The distribution of BMC between gasoline and water was determined by shaking together at ambient temperature equal volumes 25 of water on a commercial premium grade gasoline containing 0.4 g Pb/1 to which various amounts of BMC had been added. When equilibrium had been reached, samples of each phase were analysed for BMC. The results are given in the following table. 14 2 045 90 B 32361 Amount of KMC (% v/v) in Partition coefficient K Aaueous phase Gasoline phase 0.40 1.12 2.8 0.82 1.88 2.3 1.53 3.60 2.4 1.96 3.88 2 0 2.40 4.90 2.0 2.96 6.10 2.1 3.67 8.90 2.4 4.O4 9.20 2.3 concentration in gasoline phase K = concentration in aqueous phase By way of comparison K for t-butanol (at a level of 3% v/v 15 t-butanol in gasoline) is about 0.26 while that for methanol is very small.

EXAMPLE 6 The solubility of water in commercial premium grade gasolines containing 0.4 g Pb/l and various amounts of di-alkyl carbonates was 20 determined at -7°C and at 21°C. Since the base gasoline used for the different di-alkyl carbonates differed slightly the absolute solubilities are not strictly comparable. To obtain a realistic comparison the percentage increase in solubility given by incorporation of the.di-alkyl.carbonate is quoted in the following table. 2 04590 B 32361 Temperature IMC DEC Water concentration Increase in water °C (% v/v) (% v/v) (% v/v) concentration (%) 0 0.018 - 3 0.019 6 -7 6 0.02^5 28 0 0.019 - 3 0.026 37 0.030 58 0 0.039 - 3 0.045 21 6 0.054 38 0 0.035 3 0.046 31 0.057 63 It is clear that IMC, although appreciably soluble in water does not give a large increase in the solubility of water in gasoline, whereas DEC, which has a much lower solubility than IMC in water, gives a larger increase in the solubility of water in gasoline. 16 ae^ffo D 3C3frl

Claims (8)

WHAT WE CLAIM IS:

1. A gasoline composition for spark ignition internal combustion engines having a Research Octane Number of at least 80 comprising gasoline hydrocarbons and 1 to 6% by volume of said composition of di-methyl carbonate.

2. A gasoline composition according to claim 1 having a lead content of no more than 0.4 g Pb/Litre.

3> A gasoline composition according to claim 2 having a lead content of no more than 0.15 8 Pb/Litre.

4. A gasoline composition according to any one of claims 1 to 3 having a Research Octane Number of at least 90.

5. A gasoline composition according to any one of claims 1 to 4 also containing at least one other di-alkyl carbonate, the total amount of di-alkyl carbonates (including the di-methyl carbonate) being less than 10% by volume of the composition.

6. A gasoline composition according to any one of claims 1 to 5 also containing an alcohol, and/or an ether, containing a tertiary alkyl radical having from 4 to 8 carbon atoms.

7- A gasoline composition according to claim 6 wherein said alcohol is t-butanol.

8. A gasoline composition according to claim 6 wherein said ether is methyl t-butyl ether. DATED THIS DAY 18§r^ A. J. PARK & SON PER J AGENTS FOR THE APPLICANTS "\F S