POLYALKENYL SUCCINIMIDES AND USE THEREOF AS DETERGENTS FOR FUELS

The present invention relates to polyalkenyl succinim- ides and the use thereof as detergents for fuels . More specifically, the present invention relates to low-molecular-weight polyalkenyl succinimides and the use thereof as detergents in light distillate or middle distillate fuels such as diesel fuel, household heating oil, kerosene, jet fuel, fuels for gas turbines, etc. Even more specifically, the present invention relates to low-molecular-weight polyisobutenyl succinimides and the use thereof as detergents for fuels .

In the present description, all the conditions indicated in the text should be considered preferred conditions even if not expressly declared.

The use of small quantities of various additives for improving the properties and/or performances of gasoline fuels and middle distillates, is known. Small quantities of dispersing agents are used, for example, for improving en- gines cleaning and consequently obtaining with time a re-

auction in the emission of harmful substances which are formed during fuel combustion.

In internal combustion engines the formation of residues leads to the accumulation of deposits mainly in the injectors with a consequent imperfect fuel combustion, with all the consequences deriving therefrom (increased emissions, higher fuel consumption, etc.) . At the same time, other additives are used in these fuels, for example: antioxidants, corrosion inhibitors, antifoam agents, etc. Among the known detergent additives, polyalkenyl acy- lating agents possibly containing an imide group are utilized. These compounds are generally prepared either by classical synthesis, using chlorinated intermediates, or by direct thermal reaction of a "reactive" polyalkene, charac- terized by double terminal bonds of the vinylidene type, with an enophyl, at a temperature higher than 15O ⁰ C, generally higher than 200 ⁰ C, possibly followed by the reaction with an amine having at least one primary aminic group which can react to form the imide group. Examples of proc- esses for the preparation of these polyalkenyl acylating agents are provided in US patents 3,172,892, 3,912,764, 4,086,251 and 4,152,499.

In the case of products obtained via a thermal process, however, if a chlorine- free product is desired, the preparation processes of the known art are characterized,

when carried out at relatively low temperatures (around 200 ⁰ C) , by the drawback of having long reaction times and rather low yields and, in any case, they provide a product with a low functionalization degree. The Applicant has now found a detergent additive for fuels such as "light distillates" and "middle distillates", selected from the group of polyalkenyl succinimides, having a high functionalization degree which makes it particularly effective for this function, as illustrated in the enclosed examples.

An object of the present invention therefore relates to polyalkenyl succinimides produced starting from polyalkenyl succinanhydrides having a number average molecular weight, Mn, ranging from about 510 to 1,500 and a function- alization degree (FD) higher than 1, generally ranging from 1.50 to 2.50. The functionalization degree is calculated according to the procedure described in US patent 4, 952,328.

Alternatively, the functionalization degree of the polyalkenyl succinanhydrides can be calculated more directly and specifically, via H ^1- -NMR(FD _N MR) , by determining, in the reaction mixture, the formation of the various anhydride adducts, using the following formula: FD _NMR : (A/2 + B + 2C + 2D) / (A/2 +B+C+D) wherein A and B are the areas of mono-functionalized anhy-

drides and C and D are those of bis-functionalized anhydrides, calculated from the resonances attributed in the NMR spectra, according to what reported in the literature (Tessier M., Marechal E.; J. Polym. Sci., Part A: Polym. Chem. 1998; 26: 785-810). In this case the FD _NMR of the products can vary from 1 to 2, preferably from 1.2 to 1.9.

More specifically, an object of the present invention relates to polyalkenyl succinimides which can be obtained with a process which comprises: a. reacting a reactive polyalkene having a number average molecular weight, Mn, ranging from 400 to 1,300 and having terminal vinylidene groups content higher than or equal to 30%, with an enophyl selected from maleic anhydride or maleic acid, at a temperature higher than 180 ⁰ C; b. carrying out the reaction thermally for a time sufficient for having a conversion of the terminal vinylidene groups higher than 10%; c. completing the reaction in the presence of a reaction accelerator consisting of a Lewis acid selected from a tin, zinc, aluminum or titanium halide having the formula MX _y , wherein M is the metal, X represents a halide such as chlorine, bromine or iodine, y varies from 2 to 4. The metallic halide MX _y can also comprise a number of crystallization water molecules ranging from 1 to 5; d. reacting the reaction product of step (c) , the polyal-

kenyl succinanhydride, with an amine which has at least one primary aminic group capable of forming an imide group.

According to the present invention, the reagent mixture of the first reaction phase (a) - (b) is introduced into a reactor, suitable for performing batch reactions, in any- convenient way before heating to the reaction temperature. The reagents, for example, can be charged contemporaneously or sequentially in any order or pre-mixed in a mixing container and then transferred to the reaction vessel. Alter- natively, the reaction of phase (a) - (b) can be carried out in continuous.

The reaction is then completed (phase c) in the presence of a reaction accelerator consisting of the Lewis acid selected from a tin, zinc, aluminum or titanium halide. The reaction accelerator is preferably tin chloride SnCl ₂ -2H ₂ O.

The reaction accelerator is added to the reaction mixture when the conversion of the terminal vinylidene groups of the reactive polyalkene ranges from 20 to 90%, preferably from 30 to 80%. The accelerator is added to the reac- tion mixture in quantities corresponding to a molar percentage concentration, referred to the reactive double bonds of the polyalkene, ranging from 0.2 to 1.5%, preferably from 0.5 to 1.1%.

The reaction of phases (a) - (b) and (c) can be carried out without a solvent and the reaction products can be re-

covered after bringing the reaction mixture to room temperature. The products recovered are subsequently used for the reaction of step (d) . Alternatively, the reaction of step (d) can be effected in the same reaction environment as phases (a) - (c) .

The reactive polyalkenes differ from the conventional polyalkenes in the content of terminal vinylidene groups. A polyalkylene chain which has a terminal vinylidene group can be represented by the formula: POLY-C(R) = CH ₂ wherein R is an alkyl group, whose identity depends on the monomeric unit from which the polyalkene is obtained (for example R is a methyl group for polyisobutene) whereas POLY represents the remaining part of the polyalkenyl chain. Re- active polyalkenes are those which have a content of terminal vinylidene groups equal to at least 35%, preferably at least 40%, more preferably ranging from 50 to 95%.

The polyalkenes, according to the present invention, are generally reactive homopolymers of α-olefins, or co- polymers of α-olefins, such as, for example, the ethylene- α-olefins copolymer. Preferred α-olefins according to the present invention are those, linear or branched, having the general formula CH ₂ =CHR' wherein R' represents a linear or branched alkyl radical, containing from 1 to 10 carbon at- oms .

Preferred polyalkenes according to the present invention are reactive polyisobutene (PIB) and polybutene-1 with a content of terminal vinylidene groups preferably of at least 45%, for example between 55 and 99%, preferably from 55 to 90%. Methods for the preparation of reactive polyisobutene or polybutene-1 are described, for example, in US patents 4,152,499, 4,605,808, 5,674,955 and in the international patent application WO 01/19873.

Furthermore, the polyalkenes according to the present invention have a number average molecular weight, Mn, measured, for example, by means of GPC (Gel Permeation Chromatography) , osmometry, proton NMR or carbon-13 NMR, ranging from 400 to 1,300, for example from 600 to 1,100, preferably from 800 to 1,000. Particularly preferred polyalkenes are reactive polyisobutene (PIB) and polybutene-1, mentioned above, having an average molecular weight Mn ranging from 800 to 1,000.

The formation of the intermediate polyalkenyl succi- nanhydride is obtained through the reaction between the re- active polyalkene and an "enophyl" , preferably maleic anhydride or the corresponding acid. Analogous intermediate products, however, obtained from other anhy- drides/unsaturated polycarboxylic acids, used alone or mixed with the anhydride/maleic acid, fall within the scope of the present invention. Examples of these unsaturated

polycarboxylic acids are fumaric acid, itaconic acid, and their corresponding anhydrides or their corresponding C _x -C ₄ alkyl esters.

The reaction between the reactive polyalkene and the enophyl takes place at a temperature ranging from 180 to 300 ⁰ C, preferably from 190 to 25O ⁰ C and even more preferably at about 200 ⁰ C, at room pressure or under an inert gas, such as nitrogen, at pressures ranging from 0.1 to 1 MPa.

The reactive polyalkylene/enophyl molar ratios gener- ally range from 1:0.9 and 1:3, preferably from 1:1.3 to 1:2.5, for example from 1:1.5 to 1:2.4.

The polyalkenyl succinanhydride is reacted with an amine, or a polyamine, having at least one primary aminic group capable of forming an imide group, selected from mono-amines such as methyl amine, 2-ethylhexyl amine, n- dodecyl amine, stearyl amine, etc. or from polyamines such as, for example, propylene diamine. Particularly preferred are polyalkylene polyamines or polyamines having the general formula H ₂ N(CH ₂ CH ₂ NH) _n H wherein n is an integer ranging from 1 to 10. Examples of these polyamines are ethylene diamine, diethylene triamine (DETA) , triethylene tetramine (TETA) , tetraethylene pen- tamine (TEPA), etc. The reaction between the polyalkenyl succinanhydride

and the polyamine, for the formation of imides or, in particular, polyisobutenyl succinimides (PIBSI) , takes place at a temperature ranging from 100 to 200 ⁰ C, preferably from 140 to 17O ⁰ C, at atmospheric pressure, even if it is possi- ble to operate at pressures higher or lower than atmospheric pressure.

The water present in the system or generated during the reaction is preferably removed from the system by stripping under nitrogen. The removal can be facilitated by operating under conditions of reduced pressure.

The relative quantities of anhydride and polyamines are selected so that the ratio between the equivalents of succinic anhydride and polyamine (or amine) generally ranges from 0.5 to 2. In this way, by regulating the stoichiometry of the reaction, mono- or disuccinimides can be obtained.

The term imide, as used in the present description and claims, refers to the complete reaction product between the polyamine and the acylating agent (for example polyisobu- tenyl succinanhydride or PIBSA) which can comprise amides, amidines and possible saline species which can be formed from the reaction between the anhydride group and amine or polyamine .

The imidation reaction can take place in the same re- action environment as the anhydride, or the polyalkenyl

succinanhydride can be recovered with the known methods, for example by gear pumps, and can be transferred and reacted separately with the amine. The reaction can be carried out in the presence or absence of a solvent (mass imi- dation) and in the latter case the solvent can be added at the end. In this way, the final succinimide can be filtered, if necessary, moved, stored or more advantageously mixed with other components.

Suitable solvents for the purpose are aromatic sol- vents, for example, toluene or xylenes and light alkylate, Aromatic 100, Aromatic 150, Solvesso 150, Solvesso 200 and in general highly aromatic naphthas.

The polyalkenyl succinimides, object of the present invention, can be used as detergent additives for gasoline or diesel fuel or they can be used together with other components in "additive concentrates" or "packages" to be added to the fuel whose performances are to be improved. The final detergent is a highly desirable alternative with respect to analogous detergents produced according to the classical synthesis process of anhydrides by means of chlorinated intermediates .

Furthermore, the polyalkenyl succinimides, object of the present invention, generally have a higher functionali- zation degree than that obtained with the "classical" ther- mal reaction, which makes them more reactive with respect

to the detergents obtained with non-catalytic thermal processes.

A further object of the present invention relates to hydrocarbon compositions comprising polyalkenyl succinim- ides prepared as described above.

In particular, a further object of the present invention relates to hydrocarbon compositions comprising: i. a base fuel falling within the definition of light distillates with a boiling point ranging from 60 to 180 ⁰ C; and ii. a base fuel falling within the definition of middle distillates with a boiling point ranging from 180 to 400 ⁰ C; and iii. from 0.0001 to 0.15% by weight with respect to the to- tal weight of the composition, preferably from 0.01 to

0.15%, of a polyalkenyl succinimide, deriving from a polyalkenyl succinanhydride having a number average molecular weight Mn ranging from about 510 to 1,500 and a functionalization degree (FD) higher than 1.0 or FD _NMR ranging from 1 to 2 , obtained with the process comprising steps (a) - (d) described above.

Particularly preferred in the hydrocarbon compositions of the present invention are polyisobutenyl succinimides, deriving from polyisobutenyl succinanhydrides having a num- ber average molecular weight Mn ranging from 800 to 1,300

and a functionalization degree (FD) higher than 1.0 or FD _NMR ranging from 1 to 2 , obtained with the process comprising steps (a) - (d) described above.

Fuels for motor vehicles of the "gasoline" or "diesel fuel" type essentially consisting of blends of linear or branched paraffin, cycloparaffin, olefin, aromatic hydrocarbons and mixtures thereof, with a boiling point in the first case ranging from 60 to 18O ⁰ C and in the latter case from 180 to 400 ⁰ C, fall within the definition of base fuel. The present invention is now illustrated for illustrative and non- limiting purposes by means of the following examples . EXAMPLE 1 Synthesis of polyisobutenyl succinanhydride (PIBSA) In a generic experiment, 100 g of PIB (Glissopal 1,000, BASF; Mn 1,000) are introduced into a 250 mL cylindrical glass reactor, equipped with a mechanical stirrer and a reflux condenser.

The reactor is flushed with nitrogen, under stirring, until a temperature of 110 ⁰ C is reached. After 30 minutes, 14.7 g of maleic anhydride (MA) are added, under nitrogen, and the mixture is heated to 200 ⁰ C.

After at least 50% of the reaction has been completed,

SnCl ₂ -2H ₂ O is added, under stirring, and the reaction is kept under stirring for twenty-one hours. The temperature

is then lowered to 160 ⁰ C and the unreacted enophyl is stripped under vacuum (0.2 mm Hg) .

The weight conversion degree of the reaction was evaluated, by difference, by quantifying the weight of non- reacted polyisobutylene after its separation from the reaction mixture. A weighed quantity of polyisobutenyl succi- nanhydride (PIBSA) , dissolved in n-heptane, is eluted through a chromatographic column, containing silica gel. The eluted phase, containing only unreacted PIB, is then evaporated, dried under vacuum (0.2 mm Hg) and weighed.

The functionalization degree (FD) , expressed as grafted moles of succinic anhydride per mole of reacted polymer, was determined according to the procedure described in US patent 4,952,328, after determining the acid- ity of the PIBSA, by titration according to what is described in the method ASTM D 664

The NMR functionalization degree (FD _NMR ) was calculated after determining the adducts present in the PIBSA according to the method described in literature: ^" Tessier M., Marechal E. J. Polym. Sci., Part A: Polym. Chem. 1988; 26; 785-810.

Tables 1-3 show the yields and the FD of the products obtained at various times, in the presence and absence of catalyst .

Table 1

(1) Catalyst added at the beginning of the reaction

(2) Catalyst added after partial conversion of the PIB

Table 2

(1) Catalyst added after partial conversion of the PIB

Table 3

(1) Catalyst added after partial conversion of the PIB

Synthesis of polyisobutenyl succinimide (A)

The polyisobutenyl succinimide (PIBSI) is prepared by introducing 100 g of polyisobutenyl succinanhydride (PIBSA) into a jacketed cylindrical glass reactor, equipped with a mechanical stirrer, a lower drainage valve and a reflux condenser. 9.32 g of triethylene tetra-amine (TETA) are then added at a temperature of 130 ⁰ C, under a nitrogen blanket, the temperature is brought to 165 ⁰ C and the reaction is continued for about two hours. The water formed is stripped away by applying, for an hour, a nitrogen flow from the bottom of the reactor. Synthesis of polyisobutenyl succinimide (B)

The same procedure is followed as in the previous case (A) except for using 18.64 g of polyamine TETA per 100 g of PIBSA.

EXAMPLE 2

Evaluation of the products; Results obtained with the Peugeot XUD9 "Nozzle fouling" test (CEC F-23-a-01)

The Peugeot XUD9 "Nozzle Fouling" test (CEC F-23-a-01) was used for evaluating the "keep clean" properties (cleaning of the injectors of an internal combustion engine) of the detergents object of the present invention. Each test was carried out by introducing the polyisobutenyl succinim- ides, prepared according to what is described in examples IA and IB ₇ in a suitable "package" containing other addi-

tives appropriately mixed with diesel fuel having a very- low sulfur content (<10 ppm) . The results are compared with those obtained with a diesel fuel not containing additives.

Table 4 also shows the results obtained with the same diesel fuel containing a commercial detergent used in the same concentration.

The fouling percentage of the injector indicates the efficacy of the detergent. The lower the percentage, the better the capacity of the detergent to prevent the formation of deposits on the surface of injectors or to clean the latter from residues.

Table 4

The results of Table 4 show the existence of an effective detergent capacity of the polyalkenyl succinimides , object

of the present invention with respect to the fuel not containing additives and a more effective action with respect to that of a commercial detergent. Table 5 shows the results obtained from XUD- 9 engine tests obtained with diesel fuels, of very low sulfur content (<10 ppm) , added with detergents prepared according to what described in the examples IA and IB, compared with both a reference base fuel and a diesel fuel containing a polyalkenyl succinimide produced via a classical thermal reaction (without a catalyst) .

Table 5

Also in this case, the efficacy of the detergents, object of the present invention is evident, both with respect to

the pure fuel and also to the analogous products obtained via "classical" thermal reactions, i.e. produced without a catalyst .