GASOLINE COMPOSITION

Abstract: Gasoline composition comprising a major amount of a gasoline suitable for use in spark-ignition engines, and a minor amount of an alkali metal or alkaline earth metal salt of a succinic acid derivative having as substituent on at least one of its alpha-carbon atoms an unsubstituted or substituted aliphatic hydrocarbon group having from 20 to 200 carbon atoms, or of a succinic acid derivative having as substituent on one of its alpha-carbon atoms an unsubstituted or substituted aliphatic hydrocarbon group having from 20 to 200 carbon atoms which is connected to the other alpha-carbon atom by means of a hydrocarbon moiety having from 1 to 6 carbon atoms.

Description: The invention relates to a gasoline composition comprising a major amount of a gasoline suitable for use in spark-ignition engines and a minor amount of at least one additive. In spark-ignition engines malfunctioning may occur when the gasoline/air ratio is too lean for ignition. It would therefore be advantageous if gasoline additives would be available which are capable of improving the ignition of lean gasoline/air mixtures. To establish the influence of additives on the performance of spark plugs and on the early ignition, an experimental technique has been developed to measure flame speeds inside a cylinder of a spark-ignition engine. It was found that many alkali metal and alkaline earth metal compounds, either organic or inorganic, added to gasoline improved the development of an early flame and the flame speed in the cylinder. Use of such metal compounds in gasoline hence improves the combustion of lean gasoline/air mixtures and therefore improves the fuel economy without impairing the functioning of the engine and the driveability of the automobile containing the engine. Although the above effect of such metal compounds has not been recognized, it is known that such compounds may be added to gasoline. So, from British patent specification No. 785,196 it is known that monovalent metal salts, including alkali metal salts, of e.g. alkylsalicylic or naphthenic acids can be added to fuels, including gasoline, to prevent corrosion and clogging of filters. And from British patent specification No. 818,323 the addition of e.g. alkaline earth metal compounds to light hydrocarbon mixtures such as gasolines, is known. It was found that alkali or alkaline earth metal salts of alkylsalicylic acids do improve the development of an early flame in spark-ignition engines but it was also found that the inlet system of the spark-ignition engines is heavily fouled by these additives. Deposits especially accumulate in fuel induction systems of automobile spark-ignition engines, when the automobiles are driven under city driving conditions which include a stop-and-go way of driving. DE-A-2 029 804 discloses the use of an additive composition comprising (a) at least one oil-soluble carboxylic dispersant including a substantially saturated hydrocarbon-substituted carboxyl group having an average of at least thirty aliphatic carbon atoms in the hydrocarbon substituent, said carboxylic dispersant being a mono- or polycarboxylic acid or an anhydride, ester, metal salt, or acylated nitrogen derivative thereof, and (b) a bright stock petroleum fraction having a viscosity of at least 75 Saybolt Universal Seconds at 98.9°C and at least 550 Saybolt Universal Seconds at 37.8°C, for addition to hydrocarbons such as lubricants, hydraulic oils and fuels such as diesel fuel and gasoline. US-A-4 234 435 discloses substituted succinic acylating agents consisting of substituent groups and succinic groups, wherein the substituent groups are derived from polyalkene, said polyalkene being characterised by a Mn value of 1300 to about 5000 and a Mw/Mn value of about 1.5 to about 4, said acylating agent being characterised by the presence within its structure of an average of at least 1.3 succinic groups for each equivalent weight of substituent group; processes for their preparation; the preparation of carboxylic acid derivatives therefrom; and lubricant compositions and concentrates containing the succinic acylating agents or the carboxylic acid derivatives. It has now been found that alkali or alkaline earth metal salts of certain succinic acid derivatives do not give rise to any fouling in the engine whereas they do improve the flame speed in the cylinder. The invention therefore provides a gasoline composition comprising a major amount of a gasoline suitable for use in spark-ignition engines and, as spark-aider, a minor amount of a dibasic potassium salt of succinic acid derivative substituted on at least one of its alpha-carbon atoms with a polyolefin having from 35 to 150 carbon atoms derived from polyisobutylene. The polyolefin which is derived from polyisobutylene may contain substituents. One or more hydrogen atoms may be replaced by another atom, for example halogen, or by a non-aliphatic organic group, e.g. an (un)substituted phenyl group, a hydroxy, ether, ketone, aldehyde or ester. A very suitable substituent in the polyolefin is at least one other metal succinate group, yielding a hydrocarbon group having two or more succinate moieties. The chain length of the polyolefin is of importance, too, for the solubility of the alkali metal salts in gasoline. If chains with less than 20 carbon atoms are used the carboxylic groups and the alkali metal ions render the molecule too polar to be dissolvable in gasoline, whereas chain lengths above 200 carbon atoms may cause solubility problems in gasolines of an aromatic type. To avoid any possible solubility problem the polyolefin has from 35 to 150 carbon atoms. When a polyolefin is used as substituent the chain length is conveniently expressed as the number average molecular weight. The number average molecular weight of the substituent, e.g. determined by osmometry, is advantageously 490 to 2000. The succinic acid derivative may have more than one polyolefin group attached to one or both alpha-carbon atoms. Preferably, the succinic acid has one polyolefin group on one of its alpha-carbon atoms. On the other alpha-carbon atom conveniently no substituent or only a rather short hydrocarbon e.g. C₁-C₆ group is attached. The latter group can be linked with the polyolefin group, forming a ring structure. The preparation of the substituted succinic acid derivatives is known in the art. The substituted succinic acid salt can conveniently be prepared by mixing polyisobutylene with maleic acid or maleic anhydride and passing chlorine through the mixture, yielding hydrochloric acid and polyolefin-substituted succinic acid, as described in e.g. British patent specification No. 949,981. From the acid the corresponding potassium salt can easily be obtained by neutralisation with e.g. potassium hydroxide or carbonate. From e.g. Netherlands patent application No. 7412057 it is known to prepare hydrocarbon-substituted succinic anhydride by reacting thermally a polyolefin with maleic anhydride. The metal salts of the substituted succinic acids show the desired effect when they are included in the gasoline composition in a very small amount. From an economic point of view the amount thereof is as little as possible provided that the desired effect is evident. Suitably, the gasoline composition according to the invention contains from 1 to 100 ppmw of potassium present in the potassium salt of the succinic acid derivative. Apart from potassium salts of the above-mentioned substituted succinic acids the gasoline composition may contain other additives as well. Thus, it can contain a lead compound as anti-knock additive and accordingly, the gasoline composition according to the invention includes both leaded and unleaded gasoline. When the above-mentioned metal succinates are used in unleaded gasoline it was surprisingly found that the wear which was expected to occur at the seats of the exhaust valves of the engines, was either reduced considerably or completely absent. The gasoline composition can also contain antioxidants such as phenolics, e.g. 2,6-di-tert-butylphenol, or phenylenediamines, e.g. N,N'-di-sec- butyl-p-phenylenediamine, or antiknock additives other than lead compounds, or polyether amino additives, e.g. as described in United States patent specification No. 4,477,261 and European patent application No. 151,621. A very suitable additive combination in addition to the succinic acid derivative for the gasoline composition according to the present invention is described in United States patent specification No. 4,357,148. This additive combination comprises an oil soluble aliphatic polyamine and a hydrocarbon polymer. This additive combination reduces the octane requirement increase (ORI). The ORI-reduction is associated with the prevention of deposit formation in the combustion chamber and adjacent surfaces in spark-ignition engines and/or with the removal of such deposits therefrom. Although various types of polyamines and various types of polymers can be used, it is preferred to use a polyolefin, the monomers of which have 2 to 6 carbon atoms, in combination with a C 20-150 alkyl or alkenyl group-containing polyamine. Therefore, the gasoline composition according to the present invention preferably contains such a combination. A very advantageous species of the above polyolefin is polyisobutylene, having from 20 to 175 carbon atoms in particular polyisobutylene having from 35 to 150 carbon atoms. The polyamine used is preferably N-polyisobutylene-N',N'-dimethyl-1,3-diaminopropane. The contents of the polyolefin and of the alkyl or alkenyl group-containing polyamine in the gasoline composition according to the present invention is preferably from 100 to 1200 ppmw and from 5 to 200 ppmw, respectively. The composition may further suitably contain a non-ionic surfactant, such as an alkylphenol or an alkyl alkoxylate. Suitable examples of such surfactants include C₄-C₁₈-alkylphenol and C 2-6 -alkylethoxylate or C 2-6 -alkylpropoxylate or mixtures thereof. The amount of the surfactant is advantageously from 10 to 1000 ppmw. The gasoline composition according to the invention comprises a major amount of a gasoline (base fuel) suitable for use in spark-ignition engines. This includes hydrocarbon base fuels boiling essentially in the gasoline boiling range from 30 to 230 °C. These base fuels may comprise mixtures of saturated, olefinic and aromatic hydrocarbons. They can be derived from straight-run gasoline, synthetically produced aromatic hydrocarbon mixtures, thermally or catalytically cracked hydrocarbon feed-stocks, hydrocracked petroleum fractions or catalytically reformed hydrocarbons. The octane number of the base fuel is not critical and will generally be above 65. In the gasoline, hydrocarbons can be replaced up to substantial amounts by alcohols, ethers, ketones, or esters. Naturally, the base fuels are suitably substantially free of water, since water may impede a smooth combustion. The alkali or alkaline earth metal salts of the above-mentioned substituted succinic acids can be added separately to the gasoline or they can be blended with other additives and added to the gasoline together. A preferred method of adding these salts to gasoline is first to prepare a concentrate of these salts and then to add this concentrate in a calculated, desired amount to the gasoline. Such a concentrate suitable for addition to gasoline may comprise a gasoline-compatible diluent with from 20 to 50 %wt, calculated on the diluent, of a dibasic potassium salt as defined above. When a polyolefin and a polyamine as defined hereinabove are desired in the gasoline composition to be used, it is preferred that the concentrate further contains from 20 to 80%w of a polyolefin, the monomers of which have 2 to 6 carbon atoms and from 1 to 30%w of a C 20-150 - alkyl or alkenyl group- containing polyamine, in which the percentages have been calculated on the diluent. Suitable gasoline-compatible diluents are hydrocarbons, like heptane, alcohols or ethers, such as methanol, ethanol, propanol, 2-butoxyethanol or methyl tert-butyl ether. Preferably the diluent is an aromatic hydrocarbon solvent such as toluene, xylene, mixtures thereof or mixtures of toluene or xylene with an alcohol. Optionally, the concentrate may contain a dehazer, particularly a polyether-type ethoxylated alkylphenol-formaldehyde resin. The dehazer, if employed, can suitably be present in the concentrate in an amount of from 0.01 to 1%w, calculated on the diluent. The invention will now be illustrated with reference to the following Examples. EXAMPLE 1 To show the improved flame speed of lean mixtures tests were run using a 1.3 litre Astra engine which has been modified by a windows-containing plate to provide optical access to the combustion chamber of one of the cylinders. The compression ratio for the cylinder considered in the tests was 5.8. The engine was run at 2000 rpm at nearly stoichiometric conditions. After two hours of running, the time (T), taken by the flame to travel from the spark plug gap to a laser beam at a distance of 10mm, was frequently measured and an average (T) was determined. This technique has been described in Combustion and Flame, 49 : 163-169 (1983). The tests were run on unleaded gasoline without a potassium additive and on unleaded gasoline with 50,20 and 8ppm of potassium. The potassium was added as the dibasic salt of polyisobutylene-substituted succinic acid, in which the polyisobutylene chain had a number average molecular weight of 930, determined by osmometry. The structure of the polyisobutylene-substituted succinic acid derivative in this and the following Examples was that of the Diels-Alder adduct of the polyisobutylene and succinic acid. The results of the tests are indicated in Table I Amount of potasssium (ppmw) Average (T) (milliseconds) Improvement % - 1.59 - 50 1.37 14 20 1.45 9 8 1.46 8 EXAMPLE 2 The effect of the improved flame speed, caused by a potassium additive, on the fuel consumption is shown by the following experiments. A 2.0 litre Ford Pinto engine was run some time for conditioning. An acceleration was triggered at 1675 rpm and terminated at 2800 rpm. This was done ten times. The fuel consumed during the accelerations and the average acceleration time were measured. The procedure was carried out using three gasolines, differing in distillation ranges, characterized by the mid-points (50%-distillation temperature). The mid-points were 101,109 and 120°C. The additive used was the potassium salt of polyisobutylene succinic acid, in which the polyisobutylene had a number average molecular weight of 1000, in an amount of 50ppmw potassium. Results of experiments with and without the use of the potassium additive are shown in Table II. Fuel mid-point C° Fuel consumption, ml Acceleration Time, s No additive With additive Change % No additive With additive Change % 101 29.3 26.4 -9.8 10.92 10.50 -3.8 109 29.2 28.0 -4.1 11.30 10.84 -4.1 120 30.1 28.3 -6.0 12.18 11.26 -7.5 EXAMPLE 3 A 2.0 litre 4-cylinder Ford Sierra engine was subjected for 42 hours to test cycles comprising running the engine for 2 minutes at 900 rpm at a load setting of 2.5 Nm and for 2 minutes at 3000 rpm at a load setting of 52 Nm. At the end of the test the inlet valves of the cylinders were removed and rated visually according to a scale comprising a set of ten photographs representing different levels of cleanliness ranging in 0.5 unit intervals from perfectly clean (10.0) to very dirty (5.5). In the experiments a leaded gasoline was used. The additives used were: Additive I: polyisobutylene having a number average molecular weight of 650 determined by osmometry; Additive II: N-polyisobutylene-N',N'-dimethyl-1,3-diaminopropane, the polyisobutylene chain having a number average molecular weight of 750; Additive III: like additive II but with a polyisobutylene chain of a number average molecular weight of 1000; Additive IV: sodium alkyl salicylate in which the linear alkyl chain has between 14 and 18 carbon atoms. Additive V: potassium polyisobutylene succinate in which the polyisobutylene chain has a number average molecular weight of 930. In Table III the mean ratings of the four valves are given, together with the mean improvement, expressed as (It should be noted that the amounts of Additives IV and V are expressed as ppmw alkali metal). Amount of additive, ppmw Mean rating Mean Improvement % I II III IV V - - - - - 7.77 - 400 18 - - - 8.77 45 400 18 - 4 - 8.37 27 400 18 - 20 - 7.13 -29 400 - 16 - 4 9.02 56 400 18 - - 20 9.32 70 From Table III it is apparent that the addition of Additives I and II give a better cleanliness performance which is improved by Additive V. Additive IV tends to reverse the beneficial effect of Additives I and II. EXAMPLE 4 To assess the thermal stability of the alkali metal-containing additives 1.00g of the additive under investigation was put into a 5 cm diameter disk, which was placed on a hot plate kept at 280 °C, a temperature similar to the valve temperature of the test described in Example 3. After 20 min. the disk was removed and cooled before reweighing to determine the percentage of the contents remaining. A washing procedure then followed to simulate the solvent action of gasoline at the inlet ports of an engine. Thereto, a mixture of 50%w xylene and 50%w of petroleum ether (b.p. 80-120 °C) was used to rinse the disk. The remaining deposits were weighed to determine the percentage of these deposits, calculated on the starting additive. The results are presented in Table IV Additive Weight percentage after 20 min at 280°C Remaining deposits after rinsing potassium alkylsalicylate having a C₁₄₋₁₈- alkyl chain 25.1%w 16.5%w potassium-polyisobutylene succinate, having a polyisobutylene chain of 930 mol.wt. 20.3%w 0.45%w From the Table it is evident that the succinate additive leaves less deposits behind after exposure to 280 °C than the alkylsalicylate. Moreover, the deposits obtained from the succinate are easily rinsed off by liquid gasoline. It is thus clear that the inlet valves will be less fouled by the succinate additive than by the alkylsalicylate additive. EXAMPLE 5 To show the influence of the composition according to the invention on the wear reduction of the exhaust valve seats a 1.6 litre Ford Sierra and a 1.1 litre Ford Fiesta were subjected to a road test involving 10,000 Miles (16,000 km). The cars were run on unleaded gasoline in one series and on unleaded gasoline containing 30ppmw of Additive II of Example 3, 400ppmw of Additive I of Example 3 and 129ppmw of Additive V of Example 3, corresponding with 8ppmw potassium, in another series. After having run for 10,000 miles on unleaded gasoline, the valve seat showed some wear. No wear was detected at the valve seats having run for 10,000 miles on the composition according to the present invention. Example 6 Preparation of a ring-structured potassium succinate derivative. In a nitrogen atmosphere 1000 pbw of polyisobutylene, having an average number molecular weight of 1000, are introduced into a reactor. Maleic anhydride (167 pbw) is added thereto, and the mixture is stirred while being heated up to about 180 °C. Chlorine is passed into the reaction mixture over a period of five hours until 79 pbw of chlorine has been introduced. The reaction mixture is kept at 180 °C for four hours. Subsequently, excess and unreacted maleic anhydride is removed by distillation. After cooling down the succinic acid derivative is dissolved in xylene and mixed with a 30% solution of potassium hydroxide in methanol, the molar ratio of potassium to succinic acid derivative being about 2.04. The mixture is kept for 3 hrs at reflux temperature (about 70 °C). Subsequently the mixture was filtered to remove any solids, if present, yielding the desired salt. The ring structure of the obtained Diels-Alder adduct was confirmed by C¹³-NMR.

Claims: Gasoline composition comprising a major amount of a gasoline suitable for spark-ignition engines and, as spark-aider, a minor amount of a dibasic potassium salt of succinic acid substituted on at least one of its alpha carbon atoms with a polyolefin having from 35 to 150 carbon atoms derived from polyisobutylene. Gasoline composition according to claim 1, which contains from 1 to 100 ppmw of potassium, present as the potassium salt of the polyisobutylene substituted succinic acid. Gasoline composition according to claim 1 or 2, which further contains minor amounts of a polyolefin, the monomers of which have 2 to 6 carbon atoms, and of a C₂₀₋₁₅₀ alkyl or alkenyl group - containing polyamine. Gasoline composition according to claim 3, in which the polyolefin is polyisobutylene and the alkyl - group containing polyamine is N-polyisobutylene-N',N'-dimethyl-1,3-diaminopropane. Gasoline composition according to claim 3 or 4 which contains from 100 to 1200 ppmw of polyolefin and from 5 to 200 ppmw of the alkyl or alkenyl group - containing polyamine. Gasoline composition comprising a major amount of gasoline suitable for spark ignition engines and (a) 1 to 100 ppmw of potassium present as a dibasic potassium salt of succinic acid, bearing on one alpha-carbon a polyisobutylene substituent having from 35 to 150 carbon atoms; (b) 100 to 1200 ppmw of a polyisobutylene having from 35 to 150 carbon atoms; and (c) 5 to 200 ppmw of N-C₂₀₋₁₅₀ polyisobutylene-N',N'-dimethyl-1,3- diaminopropane.

Inventors: HELDWEG, RUDOLPH FRANK, KALGHATGI, GAUTUM TAVANAPPA, MCARRAGHER, JOHN STEVEN, MILES, RICHARD, VAN ES, CORNELIS
Applicants: SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1986
Main classification: C10L1
IPC codes: C10L1