GB2293177A - Gasoline compositions containing carbamates - Google Patents

Abstract

Gasoline compositions are provided whose antiknock properties are improved by the addition of a small amount of a carbamate ester, of the formula R<1>-O(CO)NR<2>R<3> wherein R<1> is hydrocarbyl of up to 20 C atoms, or furfuryl optionally C1-C6 alkyl-substituted; and R<2>, R<3> are H or a group as defined for R<1>. All Rs may be the same or different.

Description

Gasoline Compositions Containing Carbamates This invention relates to improved fuels for internal combustion engines. More particularly, it relates to improving the anti-knock properties of the fuel by the addition of novel metal-free ashless anti-knock agents.

The petroleum industry has long recognized the need for greater fuel economy and efficiency in the operation of gasoline powered spark-ignition engines. It is also recognized that the most economical burning of the fuel is obtained at the higher compression ratios, and so to obtain high performance in high compression ratio engines without the risk of knock damage, fuels need to be used with a high octane number and good anti-knock properties.

While octane ratings of fuels can be improved by additional refining operations, the additional necessary refinery processes are extremely costly. Refiners have therefore blended anti-knock additives into their fuels to increase the octane number of the fuel.

Numerous compounds have been suggested as anti-knock additives for fuel compositions. Anti-knock agents that have been used most are those of the organometallic type, and the most successful of these have been the organo-lead agents. However, their use is now severely limited by incompatibility with exhaust catalysts, and their use may be prohibited in future. Numerous non-lead, anti-knock compounds have been suggested as alternatives, including organo-iron derivatives such as iron pentacrbony; and ferrocene, and organo-manganese products such as methylcyclopentadienyl manganese tricarbonyl (MMT). However, these additives have their own associated problems when blended into fuels for internal combustion engines, such as increased engine wear and alleged toxic emissions into the environment.

U.S. Pat. 3,770,397 claimed the use of alkali metal salts of alkyl and dialkylaminoalkylphenols as effective anti-knock agents, while U.S. Pat. 3,771,979 claimed the use of alkali metal salts of diarylcarbamates of the general formula:

in which Rl to Rlo is hydrogen or alkyl having from 1 to 12 carbon atoms, and M is an alkali metal.

The use of metal salts of N,N-disubstituted diselenocarbamates as anti-knock agents was claimed in U.S. Pat. 3,976,439. The compounds generally conformed to the following formula:

wherein M is a metal selected from the group consisting of nickel, zinc, copper, manganese and iron, X is the valence state of the metal, and R, and R2 are alkyl, cycloalkyl, or aryl groups.

The art has for some time now been looking for anti-knock agents of the non-metallic type, which will not pollute the environment with toxic metals following their combustion.

The most widely known organic metal-free anti-knock agents that have been proposed include aniline and alkyl derivatives thereof such as N-methylaniline and Nethylaniline, phenylenediamines, aminocresol derivatives, nitriles such as proprionitrile, tertiary alkyl ethers, and alcohols such as ethanol and tertiary butanol.

U.S. Pat. 3,083,086 claimed the use of propionate and butanoate esters as anti-knock agents, while U.S. Pat. 4,444,567 claimed the use of alkoxy-substituted benzaldehydes and alkoxy-substituted benzoic esters. The use of malonate esters was claimed in U.S. Pat. 4,602,919.

The use of dialkyl carbonates (i.e., diesters of carbonic acid) as antiknock agents was described, for example in European Pat. Appl. Nos. 82,688, 98,691, 112,172 and 474,342, Jpn. Pat. No. 60-46473, and U.S. Pat. Nos. 2,331,386, 3,001,941, 3,382,181, 4,302,215, 4,380,455, 4,600,408, 4,891,049 and 4,904,279.

Gasoline detergent molecules containing a carbamate functionality have been extensively patented. For instance, US patents US 4,160,648, US 4,191,537, US 4,236,020, US 4,233,168, US 4,288,612 and US 4,247,301 describe the use of hydrocarbyl poly(oxyalkylene)amino carbamates, of which the following structure is typical:

where R is hydrogen or hydrocarbyl, R' and R3 are selected from hydrogen or lower alkyl of 1 to 6 carbon atoms, R2 is alkylene of from 2 to 10 carbon atoms, and n and p are integers of at least one, preferably between 2 and 20.

US patent 4,904,278 describes the use of modified succinimides as dispersants in lubricating oils, gasolines, and other oils. In particular, polyamino alkenyl or alkyl succinimides with carbamate functionalities were described.

US patents US 4,936,868, US 4,946,982 and US 4,946,473 describe the use of poly(olefin)-N-substituted carbamates of the following formula to prevent or reduce engine deposits either alone or in combination with certain poly(olefin) polymers or hydrogenated forms of polymers:

wherein R is an olefinic polymer chain having an average molecular weight from about 500 to about 9,900; Rl is hydrocarbyl group containing up to 20 carbon atoms; and R2 is hydrocarbyl group or a hydrocarbylaminohydrocarbyl group, each containing up to 20 total carbon atoms in the hydrocarbyl group(s).

US patent US 3,717,447 described the use of nitrogen heterocyclic-substituted carbamates as additives for hydrocarbon fuels. 2-(2-Alkenyl-2-imidazolin-l-yl)ethyl carbamates of the following formula were claimed to reduce the interfacial tension of the fuel, increase the carburettor detergency effectiveness, improve the antirust properties of the fuel, without adversely affecting the fuel stability:

PCT Int. Appl.WO 88 10,250 described-the use of carbamates as detergent additives for gasoline, having the formula ROC(:O)NXY [X and Y are independently either H, a (hetero-substituted) hydrocarbyl group, or ZNHC(:O)OR (I), where Z is a divalent hydrocarbyl, a substituted hydrocarbyl, or (alkylene),(NH),(alkylene), in which n = 0-4, m = 1-4, and R is a (substituted) hydrocarbyl group, provided that if either one of X or Y is I, the other of X or Y is H]. Reduced valve deposits using the additive were claimed.

It should be stressed that in none of the above patents describing the use of carbamates as detergent fuel additives were the use of carbamates claimed as antiknock or octane enhancing additives.

In accordance with the present invention, new and improved gasoline compositions are provided containing a minor amount (less than 20% by volume) of one or more carbamate esters, which are compounds represented by the following formula:

wherein R' is hydrocarbyl group containing up to 20 carbon atoms, or a furfuryl or C,-C6 hydrocarbyl substituted furfuryl group, and, R2 and R3 are hydrogen or groups as defined for R'.

Also covered within the scope of the invention is an additive composition containing on a volume basis, from say 30-70% of one or more carbamates as described above, and the remainder a suitable liquid carrier or diluent miscible with gasoline.

When hydrocarbyl, typical values for R', R2 and R3 are straight or branched chain alkyl, alkenyl, cycloalkyl (including combinations such as alkylcycloalkyl, cycloalkylalkyl, etc.), aryl (including mono- and fused ring structures e.g. naphthyl, and alkyl-substituted aryl, e.g. xylyl, tolyl, etc.) and aralkyl, e.g. benzyl (including alkyl-substituted aralkyl). The preferred hydrocarbon values for R', R2 and R3 are straight or branched chain C,-C,0 alkyl, especially C,-C6, and phenyl.

Additive compounds having the above structure are generally referred to as alkyl-Nalkyl carbamates (when R3 is a hydrogen radical) or alkyl-N,N-dialkyl carbamates (when both R2 and R3 are alkyl radicals), such as methyl-N-rert-butyl carbamate or phenyl-N,N-dimethyl carbamate.

Also covered within the scope of the invention is an additive composition containing on a volume basis, from say 30-70% of one or more carbamates as described above, and the remainder a gasoline miscible liquid carrier or diluent. The carrier or diluent can be a liquid hydrocarbon, alcohol or ether, or mixture of two or more thereof, or can also be itself a gasoline blend, or base oil stock.

As used herein, 'gasoline' refers to fuels meeting ASTM standard D439, and includes blends of distillate hydrocarbon fuels with other additives such as antioxidants, detergents, demulsifiers, corrosion inhibitors, metal de-activators, dyes, deposit modifiers, anti-knock additives (e.g., tetraethyl lead and MMT), oxygenates such as MTBE and alcohols (e.g., ethanol, TBA) and the like.

Anti-knock characteristics of an additive are typically evidenced by an increase in the research and motor octane numbers of the fuel when the additive is admixed therewith. The research (RON) and motor (MON) octane numbers of fuel compositions are typically measured by ASTM D 2699 and ASTM D 2700 respectively. While RON and MON are by themselves good indicators of the antiknock characteristics of an additised fuel, another measure of the anti-knock characteristics of a fuel is the average of the two numbers (RON + MON)/2, which provides a fairly good approximation of the octane number required by engines under typical driving conditions. This average is often quoted as the typical rating used for commercial products.

The fuel composition may be comprised of any amount of the additive compound of this invention which enhances the anti-knock characteristics of the fuel to the level desired by the end user. Usually, the anti-knock additive comprises a minor amount (i.e. less than 20 percent by volume) of the fuel composition. Preferably the fuel composition comprises from about 0.1 volume percent to about 15 volume percent of the additive compound of this invention, more preferably from about 0.2 to about 5 volume percent of the additive compound.

The compounds of this invention can be prepared by methods well known in the art.

They can be made by reacting the appropriate amine with a chloroformate as disclosed by Pirkle, Simmondsand Boeder [J. Org. Chem., 44,4891(1979)]; by the reaction of an alcohol with an isocyanate as disclosed by Satchell and Satchell [Chem.

Soc. Rev., 4, 231(1975)]; and for ten'alkyl carbamates, R2N-CO-OCR'3 (R = H, alkyl, R' = alkyl) which cannot be made by either of the above methods, the reaction of di-terr-alkyldicarbonates with the appropriate amine is disclosed by Tarbell, Yamamoto and Pope [Proc. Nat. Acad. Sci. USA, 69, 730 (1972)].

The following examples and comparative data will serve to illustrate the preparation of the anti-knock compounds of the present invention and their efficacy in improving the octane number of liquid hydrocarbon fuels. It will be understood, however, that it is not intended that the invention be limited to the particular antiknock compounds.

Various modifications of these additives can be effectively employed, as will be readily apparent to those skilled in the art.

EXAMPLE 1 Methyl-N-methyl carbamate Methyl isocyanate (94.6g) was added dropwise to a solution of methanol and triethylamine (150ml) in methylene chloride (400ml) under a nitrogen atmosphere.

The reaction was warmed to reflux for 6 hours, cooled to room temperature and the solvent evaporated. The crude residue was distilled at 790C/47mmHg to give methyl N-methyl carbamate (91.3g, 61.7%) as a colourless oil. This compound had the following structure:

EXAMPLE 2 Ten-butyl-N-methyl carbamate A solution of 40% by weight aqueous methylamine (36ml) was added dropwise to a solution of di-tert-butyl-dicarbonate (100g) and triethylamine (70ml) in methylene chloride (400ml). The reaction was then heated at reflux for 6 hours, cooled to room temperature, and the layers separated. The aqueous phase was extracted with methylene chloride (1 x 100ml) and the combined organic phases washed with water (2 x 100ml), dried over magnesium sulphate and the solvent evaporated.The residue was distilled at 610C/IOmmHg to give ten-butyl-N-methyl carbamate, (38.5g 70%) as a colourless oil. This compound had the following structure:

EXAMPLE 3 Methyl-N-tert-butyl carbamate Tert-butylisocyanate (100g) was added to a solution of methanol (32.3g) and triethylamine in methylene chloride (l50ml) under a nitrogen atmosphere. The mixture was warmed to reflux for 6 hours, cooled, and washed with water (3 x 100ml). The organic phase was dried over magnesium sulphate, the solvent evaporated, and the residue distilled at 55 C/lSmmHg to give methyl-N-(ert-butyl carbamate (65.7g, 50%) as a colourless oil that solidified on standing.This compound had the following structure:

EXAMPLE 4 Tert-butyl-N-tert-butyl carbamate A solution of tert-butylamine (25.6g) and triethylamine (36g) in methylene chloride (l00ml) was added slowly to a solution of di-tert-butyl-dicarbonate (85g) in methylene chloride (250ml) at 0-50C. The mixture was then warmed to 20-250C for 2 hours before evaporation of the solvent. Purification by column chromatography using silica gel (200g), using chloroform as eluant gave tert-butyl-N-tert-butyl carbamate (5 lug, 84%) as a clear colourless oil.This compound had the following structure:

EXAMPLE 5 Iso-butyl-N-tert-butyl carbamate Tert-butyl isocyanate (29.7g) was added to a solution of iso-butanol (2-methylpropan I-ol) (22.2g) and triethylamine (30.3g) in methylene chloride (100ml) and the mixture warmed to reflux for 4 hours. After cooling to ambient temperature, the solvent was evaporated and the residue purified by column chromatography on silica gel (200g) eluting with chloroform. Evaporation of the relevant fractions gave iso-butyl-N-tertbutyl carbamate (43.lug, 83%) as a colourless oil.This compound had the following structure:

EXAMPLE 6 Phenyl-N-tert-butyl carbamate Tert-butyl isocyanate (29.7g) was added to a solution of phenol (28.2g) and triethylamine (30.3g) in methylene chloride (lOOml) and the mixture heated at reflux for 6 hours. The solution was allowed to cool to ambient temperature, the solvent evaporated and the residue purified by column chromatography on silica gel (200g) eluting with chloroform. Evaporation of the relevant fractions gave phenyl-N-tertbutyl carbamate (42.lug, 72%) as a white solid. This compound had the following structure:

EXAMPLE 7 Furfuryl-N-tert-butyl carbamate Tert-butyl isocyanate (29.7g) was added to a solution of furfuryl alcohol (29.4g) and triethylamine (30.3g) in methylene chloride (lOOml) and the mixture warmed to reflux for 4 hours. After evaporation of the solvent, the residue was purified by column chromatography on silica gel (200g) eluting with chloroform. The relevant fractions were evaporated to give furfuryl-N-tert-butyl carbamate (42.5g, 72%) as a white solid. This compound had the following structure:

EXAMPLE 8 Methyl-N-iso-butyl carbamate A solution of sec-butylamine (2-butylamine, 92g) and triethylamine (120ml) in methylene chloride (500ml) was stirred at 0-50C under a nitrogen atmosphere. To this was added a solution of methyl chloroformate (132.3g) in methylene chloride (250ml) dropwise at this temperature. After completion of the addition, the reaction was heated at reflux for 3 hours and then cooled to room temperature.The solid was filtered and the filtrate washed with water (3 x 200ml), dried over magnesium sulphate and the solvent evaporated. The residue was purified by column chromatography, eluting with chloroform hexane (1:1). Evaporation of the relevant fractions gave methyl-N-sec-butyl carbamate (56.5g, 34.2%) as a colourless oil. This compound had the structure:

EXAMPLE 9 lso-butyl-N-iso-butyl carbamate A solution of iso-butyl chloroformate (49.2g) in methylene chloride (loom) was added dropwise at 0-5 C to a solution of iso-butylamine (21.9g) and triethylamine (35ml) in methylene chloride (250ml). The mixture was heated to reflux for 3 hours and then cooled and the solid filtered off.The filtrates were washed with water (5 x 50ml), saturated sodium chloride solution (50ml) and water (50ml). Drying over magnesium sulphate, evaporation of the solvent and purification of the residue by column chromatography on silica gel (200g) using gradient elution (hexane to chloroform) gave, after evaporation of the appropriate fractions, iso-butyl-N-iso-butyl carbamate (36g, 58%) as a colourless oil.This compound had the following structure:

EXAMPLE 10 Phenyl-N-iso-butyl carbamate A solution of phenyl chloroformate (47g) in methylene chloride (100ml) was added dropwise to a solution of iso-butylamine (18.3g) and triethylamine (35ml) in methylene chloride (250ml), at OOC. The mixture was warmed to reflux for 3 hours, cooled, and the resulting solid filtered off and washed with methylene chloride (50ml). The filtrates were washed with water (5 x 50ml), saturated sodium chloride solution (50ml), and water (SOml) before drying over magnesium sulphate and evaporating the solvent. The residue was slurried in hexane (lOOml) to give phenyliso-butyl carbamate (38.6g, 8096) as a white crystalline solid.This compound had the following structure:

EXAMPLE 11 Tert-butyl-N-furfuryl carbamate A solution of 2-furfurylamine (19.4g) in methanol (50ml) was added slowly to a solution of di-tert-butyl-dicarbonate (48g) and triethylamine (20ml) in methanol (200ml). The reaction mixture was heated at reflux for 45 minutes and then cooled, and the solvent evaporated. Purification by column chromatography on silica gel (200g) with chloroform as eluant gave, after evaporation of the solvent, tert-butyl-Nfurfuryl carbamate (32g, 81 %) as an oil which solidified on standing.This compound had the following structure:

EXAMPLE 12 Tert-butyl-N, N-dimeth yl carbamate A solution of 40% by weight aqueous dimethylamine (52.3ml) was added to a solution of di-tert-butyl dicarbonate (100g) and triethylamine (SOml) in methylene chloride (400ml) with cooling. The reaction was then warmed to reflux for 5 hours, and then cooled. The two layers were separated and the aqueous phase extracted with methylene chloride (100ml), and the combined organic phases washed with water, dried over magnesium sulphate and evaporated. The residue was distilled at 39"C/10mmHg to give tert-butyl-N,N-dimethyl carbamate (44g, 72 %) as a colourless oil.The compound had the following structure:

TEST DATA The anti-knock performance of several gasoline samples was determined by measuring the research octane number (RON) and the motor octane number (MON) of each sample. The samples tested contained the carbamate esters of this invention and the conventional octane enhancers MTBE and N-methylaniline for the purpose of comparisons.The base gasoline used in these tests had the following properties: Inspection Property Mean Value Density &commat; 15 C, g/ml 0.7239 Reid Vapour Pressure, mbar 341 FIA, % volume Saturates 82.0 Olefins 0.2 Aromatics 17.8 Distillation &commat;, C IBP 43.8 2 % 60.8 5 eye 69.4 10 % 76.0 20 % 84.7 30 % 91.8 40 % 95.8 50 % 97.4 60% 98.4 70 % 99.4 80 % 100.4 90 % 101.1 95 % 102.4 FBP 109.6 % vol recovery 98.8 % vol residue 0.6 % vol loss 0.6 The results of these tests are shown in Table 1 below.

Run Additive Molar Treat RON ARON MON AMON (RON + (RON + Conch. Rate MON)12 AMON)/2 (mol/l) (Sbwthol) Run 14 none 0 0 92.2 87.2 89.95 5 Example 1 0.225 2.00 93.0 0.8 87.3 0.1 90.15 0.45 6 Example 3 0.125 1.65 92.7 0.5 87.8 0.6 90.25 0.55 7 Example 3 0.225 2.95 92.9 0.7 87.8 0.6 90.35 0.65 8 Example 4 0.125 2.16 92.9 0.7 87.7 0.5 90.3 0.60 9 Example 5 0.125 2.16 92.7 0.5 87.9 0.7 90.3 0.60 10 Example 5 0.225 3.89 93.1 0.9 88.0 0.8 90.55 0.85 11 Example 7 0.125 2.46 93.1 0.9 87.9 0.7 90.5 0.80 12 Example 7 0.225 4.43 93.9 1.7 88.4 1.2 91.15 1.45 13 Example9 0.125 2.16 92.8 0.6 87.5 0.3 90.15 0.45 14 Example 10 0.025 0.48 92.4 0.2 87.8 0.6 90.1 0.40 15 Example 11 0.150 3.00 92.9 0.7 87.7 0.5 90.3 0.60 16 Example 11 0.255 5.00 93.9 0.7 88.8 1.6 91.35 1.65 17 Example 11 0.510 10.0 95.8 3.6 89.7 2.5 92.75 3.05 18 none 0 91.9 86.9 89.4 19 N-methylaniline 2.70 93.5 1.6 87.6 0.7 90.55 1.15 20 do. 5.00 94.2 2.3 88.2 1.3 91.2 1.70 21 do. 10.0 96.2 4.3 89.1 2.2 92.65 3.25 22 none 0 92.1 86.8 89.45 23 MTBE 3% vol 93.0 0.9 87.6 0.8 90.3 0.85 24 do. 5% vol 93.9 1.8 88.1 1.3 91.0 1.65 25 do. 1OSvo vol 95.4 3.3 89.1 2.3 92.25 2.80 The data in Table 1 show that carbamate esters of this invention are effective octane enhancers. In particular, additives described in examples 5, 7 and 11 show significant octane enhancement properties relative to conventional oxygenates such as MTBE.

Claims (10)

1. An anti-knock additive composition for gasolines comprising one or more carbamates of the formula:

where Rl is a hydrocarbyl group containing up to 20 carbon atoms, or a furfuryl and R2 and R3 are selected from the group consisting of hydrogen, hydrocarbyl or furfuryl or Cí-C6 hydrocarbyl substituted furfuryl group, and, R2 and R3 are hydrogen or groups as defined for R', R', R2 and R3 being the same or different; in admixture with a gasoline miscible liquid carrier or diluent.

2. An additive composition according to claim 1, containing on a volume basis, from 30-70% carbamate, and from 70-30% carrier or diluent.

3. An additive composition according to claim 1 or 2, wherein the carrier or diluent is a liquid hydrocarbon, alcohol or ether or mixture of two or more thereof.

4. An additive composition according to claim 3, wherein the carrier or diluent is itself the gasoline blend, or an aromatic hydrocarbon.

5. An additive composition according to any one of the preceding claims additionally containing one or more gasoline additives, e.g. antioxidants, rust prevention agents, detergents, etc. etc.

6. A gasoline containing as an anti-knock agent, a compound of the formula:

where R' is a hydrocarbyl group containing up to 20 carbon atoms, or a furfuryl and R2 and R3 are selected from the group consisting of hydrogen, hydrocarbyl or furfuryl or Cl-C6 hydrocarbyl substituted furfuryl group, and, R2 and R3 are hydrogen or groups as defined for R', R', R2 and R3 being the same or different; in admixture with a gasoline miscible liquid carrier or diluent.

7. A gasoline according to claim 6 wherein the said compound(s) is or are present in an amount up to 20 vol. % based on the volume of the gasoline, preferably from 0.2 to 5%.

8. A method of improving the anti-knock rating of a gasoline blend, which comprises incorporating into the blend, one or more compounds of the formula:

where R' is a hydrocarbyl group containing up to 20 carbon atoms, or a furfuryl and R2 and R3 are selected from the group consisting of hydrogen, hydrocarbyl or furfuryl or C,-C6 hydrocarbyl substituted furfuryl group, and, R2 and R3 are hydrogen or groups as defined for R', R', R2 and R3 being the same or different; in admixture with a gasoline miscible liquid carrier or diluent.

9. A method according to claim 8, wherein the said compound(s) is or are incorporated into the blend in an amount of up to 20% by volume, preferably from 0.2 to 0.5%.

10. A method according to claim 8 or 9, wherein the said compound(s) is or are incorporated into the blend as a preformed additive or concentrate as claimed in any one of claims 1 to 5.