NZ207823A - Cloud point decreasing additives for middle distillates - Google Patents

Description

New Zealand Paient Spedficaiion for Paient Number £07823 Fat. Appn07823 Piv.Apf5n^wit of Appn.

I o'.yfjy^i 4 207823 Priority Date{sh Complete Specification Piled: !. )£. , Class: j-pp^ _ .gp.TQp^' •CP>.QQ| Under the provisions of RefU* lation 23 (I) the Specification has been ante-datedj to __ |9<g2 v % '"""v. inti Publication Date: .., ■ & $ MYj9j9§ P.O. Journal, No: .'.9X3....

Hi If §ISh Patents Form No:5 NEW ZEALAND PATENTS ACT 1953 COMPLETE SPECIFICATION "NITROGEN-CONTAINING ADDITIVES USABLE AS AGENTS FOR DECREASING THE CLOUD POINT OF HYDROCARBON MIDDLE DISTILLATES AND COMPOSITIONS OF HYDROCARBON MIDDLE DISTILLATES CONTAINING THESE ADDITIVES" We, INSTITUT FRANCAIS DU PETROLE, of 4, Avenue de Bois-Preau, 9250 2 Rueil-Malmaison, France, a body corporate and ELF FRANCE of 137, rue de 1'Universite, 75007 Paris, France, a body corporate, hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- 207823 It has now been discovered that certain chemicals, whose definition is given hereinafter, when added to middle distillates^ have the property to make the first paraffin crystals appear at a lower temperature than that observed in the absence of these additives. This property is the more unobvious as it is still maintained after several cycles of heating and cooling and operates according to a mechanism which has not yet been explained.

This class of chemical compounds also has an action on other properties of middle distillates (particularly gas oils), by modifying the behaviour of the medium which contains the precipitated paraffins.

Thus, the compounds proposed in this invention have a substantial effect on the limit filterability temperature and the pour point.

When paraffin crystals have formed by cooling, their normal tendency is to assemble by gravity at the bottom.

This phenomenon, generally called settling, results in the plugging of ducts and filters and is detrimental to a safe use of middle distillates, particularly gas oils. The chemicals proposed in the invention can decrease substantially the settling rate of the paraffins formed by cooling of gas oils and other middle distillates.

Finally, the proposed products for having the above mentioned properties, also confer to the gas oils and middle distillates, to which they are added, anti-corrosion properties with respect to metal surfaces.

As a general rule, the additives of the invention can be defined as products having an average molecular weight of about 300 to 10,000, obtained by condensation of at least one compound comprising a primary amine function, complying with the following general formula: H (I) r 2 with at least one dicarboxylic compound as hereinafter defined. 2 078 2 3 In formula (I),R is generally a monovalent saturated aliphatic radical comprising from 1 to 30 carbon atoms; Z can be, depending on the case, a divalent group of the type > -NH-, or - NR' -, R* being a monovalent aliphatic radical ; n is an integer from 2 to 4 and m may be zero or an integer from 1 to 4.

The compounds of the above formula (I) may consist of primary amines of the formula R^" - NI^ (in that case, in formula (I), Z represents a - NH - group and the value of m is zero).

The radical R^" is preferably linear and comprises from 12 to 30, particularly from 16 to 25 carbon atoms.

Specific examples of these amines are : dodecylamine, tetradecylamine, hexadecylamine, octadecylamine, eicosylamine and docosylamine, hexadecylamine and octadecylamine being preferred.

The compounds of the formula (I) may also consist of polyamines obtained from saturated aliphatic amines of the formula : R1 - NH- (CH0) NH- l n- H m corresponding to the general formula (I) wherein Z is a - NH - group; m may have a value from 1 to 4 and n a value from 2 to 4, preferably 3.

Preferably, the radical R^ is linear and comprises from 12 to 30 and particularly from 16 to 25 carbon atoms.

Specific compounds are : N-dodecyl 1,3-diamino propane, N-tetradecyl 1,3-diamino propane, N-hexadecyl 1,3-diamino propane, N-octadecyl 1,3-diamino propane, N-eicosyl 1,3-diamino propane, N-docosyl.1,3-diamino propane, N-hexadecyldipropylene triamine, N-octadecyl dipropylene triamine, N-eicosyldipropylene triamine and N-docosyl dipropylene triamine. There are more advantageously used N-docosyl-, N-eicosyl-, N-octadecyl-, N-hexadecyl- or N-dodecyl 1,3-diamino propane, as well as N-hexadecyl- and N-octadecyl- dipropylene - triamine. 207823 The compounds of formula (I) may also consist of polyamines of the formula: N- R3/ (CH,)- NH l n m 2 3 wherein R and R , identical or different, are each an alkyl 2 radical with 1 to 24 and preferably 8 to 22 carbon atoms, R 3 and R preferably comprising together from 16 to 32 carbon atoms ; n has a value from 2 to 4 and m a value from 1 to 4.

Specific compounds are : N, N-diethyl 1,2-diamino ethane, N, N-diisopropyl 1,2-diamino ethane, N, N-dibutyl 1,2-diamino ethane, N,"N-diethyl 1,4-diamino butane, N, N-dimethyl 1,3-diamino propane 10 N-diethyl 1,3-diamino propane, N, N-dioctyl 1,3-diamino propane N, N-didecyl 1,3-diamino propane, N, N-didodecyl 1,3-diamino propane, N, N-ditetradecyl 1,3-diamino propane, N, N-dihexadecyl 1,3-diamino propane, N, N-dioctadecyl 1,3-diamino propane, N, N-didodecyldipropyle-netriamine, N, N-ditetradecyldipropylene 15 triamine, N, N-dihexadecyldipropylene triamine and N, N-diocta- decyldipropylenetriamine.

It must be understood that, without departing from the invention, it is possible to operate with one or more compounds of formula (I) associated with one or more other compound(s) having a primary 20 amine function, and canplying with one of the forrmilae (II) and (III) described hereinafter, the ccnpound(s) of formula (II) and/or the canpound(s) of formula (III) being used in a total proportion of at most 50% with respect to the cumulated amounts of ccnpounds of formulae (I), (II) and (III).

The compounds of formula (II) which may be used in minor 25 proportion consist of ether-amines, more particularly those complying with the formula : R4 - O (CH2>ir (II) tn 4 wherein the radical R comprises 1 to 24, preferably 8 to 22 carbon atoms, m is an integer from 1 to 4 and n an integer from 2 to 4, preferably 2 or 3.

Specific compounds of the ether-amine type are : 2-methoxy ethylamine, 3-methoxy propylamine, 4-methoxy butylamine, 3-ethoxy propylamine, 3-octyloxy propylamine, 3-decyloxy propylamine, 3-hexadecyloxy propylamine, 3-eicosyloxy propylamine, 3-docosyloxy propylamine, N-(3-octyloxy propyl) 207823 1,3-diamino propane, N-(3-decyloxy propyl) 1,3-diamino propane, 3-(2,4,6-trimethyl decyl) oxy propylamine and N- 3 —(2,4,6-trimethyl decyl) oxy propyl 1,3-diamino propane.

The compound of formula (III) which may be used in minor proportion may also consist of an aminoalcohol of formula : HO - CH2 - R5 - NH2 (III) wherein R^ is a divalent saturated aliphatic radical, linear or branched, preferably linear, comprising 1 to 18 and preferably 10 to 18 carbon atoms.

Specific examples are : monoethanolamine, 1-amino 3-propanol, 1-amino 4-butanol, 1-amino 5-pentanol, 1-amino 6-hexanol, 1-amino 7-heptanol, 1-amino 8-octanol, 1-amino 10-decanol, 1-amino 11-undecanol, 1-amino 13-tridecanol, 1-amino 14-tetradecanol, 1-amino 16-hexadecanol, 2-amino 2-methyl 1-propanol, 2-amino 1-butanol and 2-amino 1-pentanol.

The dicarboxylic compounds on which is effected the condensation of a compound of formula (I) and optionally a compound of formula (II) and/or (III) such as described hereinbefore are more particularly selected from the anhydrides of aliphatic, preferably unsaturated, a, 8- dicarboxylic acids, such as, for example, maleic anhydride, alkylmaleic anhydrides, for example methylmaleic (or citraconic) anhydride, or from the alkenyl-succinic anhydrides, for example those obtained by reacting at least one a -olefin, preferably linear, (having, for example, 10 to 30 carbon atoms) with maleic anhydride. Specific examples are n-octadecenyl succinic anhydride or dodecenyl succinic anhydride. It is obviously possible to use mixtures of two (or more) of these compounds. 207823 The above mentioned anhydrides may be replace d by the corresponding dicarboxylic acids, or by the C-^ -alkyl diesters thereof (e.g. methyl, ethyl, propyl and butyl esters).

The compounds with a primary amine function of the formulas (I) and optionally (II) and/or (III) are commonly used in a proportion of 1.02 to 1.2 mole, preferably 1.05 to 1.1 mole, per mole of the dicarboxylic compound. The compound with a primary amine function (I) and optionally (II) and/or (III) may also be used in slight defect, down to 0.9 mole per mole of the dicarboxylic compound. The proportion is thus generally from 0.9 to 1.2 mole/mole.

The condensation of the compounds of formula (I) and optionally (II) and/or (III) on the dicarboxylic compounds (for example dicarboxylic acids, esters or preferably anhydrides) may be effected without solvent ; but preferably with a solvent, consisting more particularly of an aromatic or naphteno-aromatic hydrocarbon having a boiling point of for example, from 70 to 250°C : toltiene, xylenes, diisopropylbenzene or an oil cut having the appropriate distillation range.

The additive compositions of the invention can be prepared, in practice, as follows : the compound of formula (I) and optionally (II) and/or (III) is introduced progressively into a reactor containing the dicarboxylic compound, while maintaining the temperature between 30 and 80°C. The temperature is then raised tol20-200°C while eliminating the resultant volatile products (water or alcohols) , either stripping with a stream of inert gas or by azeotropic distillation with the selected solvent ; the content of dry substance is, for example, from 40 to 7.0 % more often about 60%. This leads predominantly to the formation of imide linkages.

The reaction time, after addition of the reactants, is, for example, from 1 to 8 hours, preferably 3 to 6 hours. 2 078 2 3 The additives contemplated in this invention are particularly efficient for improving the cloud point of oil middle distillates (particularly gas oils), thus decreasing the temperature at which appear the first crystals of paraffin contained therein.

Although the action of these additives on the temperature at which the paraffin crystals appear in the aiddle distillates has not yet been clearly elucidated, a positive improvement of the cloud point of the Diiddle distillates treated with these additives is observed, when the latter are added in a proportion of, for exaaple, from 10 20 to 2000 p per ton of middle distillate. The preferred concentrations range from 100 to 2000 g/t. The decrease of the cloud point may reach, for example, 5°C, sometimes nore.

It is also remarkable that the additives of the invention, which improve efficiently the cloud point of middle distillates, have also the properties of inhibiting the settling of n-paraffins contained in saddle distillates, at rest, of improving the limit filterability tc-poraturc and the pour temperature and of inhibiting the corrosion of metal surfaces in contact with these distillates.

Thus, in the ran^e of additive concentrations from 20 to 20 2000 g per ton, it is possible to observe a decrease the filterability terrperature of, for example, up to 12°C, a decrease of the pour point of up to 20°C, a decrease of the proportion of settled paraffins and a clear anticorrosion effect particularly on ferrous metals.

The middle distillate compositions according to the invention my be prepared by dircctly adnixing additives to the middle distillate^ It is however often advantageous to introduce them in the fona of "mother-solutions" previously prepared in the above-mentioned solvents.

The "mother-solutions" can contain, for example, from 20 50 to 60 Js by weight of additive. 2D7S23 The following examples illustrate the invention and nrust not bo considered as linitative thereof in any respect.

- EXAMPLE 1 2,700 g of a polyamine of the trade (containing, in adnix ture, about 27 f- of palrsityl 1,3 propane diamine and 70 £ of stearyl 1,3 propane dia.-^Lne^ irith a 570 g equivalent of primary anine) and 2,700 g of zylene are introduced into a 20 liter reactor provided with an efficient stirrer ; the amine is dissolved at 50°C ; after cooling to 30°C, a solution of 699 g of mleic anhydride in 10 1,050 g of xylene is added, while maintaining the inner temperature at 40°C. The addition lasts one hours ; heating at xylene reflux is then performed for 3 hours, the inner tenperature being 144°C ; 157 g of water, corresponding to 123 g of reaction water and 29 g of vater contained in the anine, are reaoved by distillation ; once the reaction is conplete, 500 g of xylene are distilled to obtain a 50 f; b.-„*. solution of additive I in xylene.

Additive I has been analyzed after evaporation of the solvent. Its molecular weight, by nuaber, ceasured by tonometry, aaounts to 180C. The thin layer infra-red spectrin shoifs the presence 20 of imde bands at 1700 and 1780 cn~\ secondary amide bands at 1635 and 1560 cn~^ and a secondary p-tt' tip band at 3300 cn ^ . The secondary amide bands are however very weak in intensity.

Additives II to VII have the sare bands as additive I. Their nolecular weigits range between 1500 and 3000.

The activity of edditive I is detemined vith two gas oil cuts of Aranco origin, uhose characteristics are given in Table I beloi? : 2 078 TABLE I § § § § 1 DISTILLATION AS® ! £ DISTILLED 1 V VOLIL-IIC I-1ASS AT § § § °C IN (Kg/l) § 6 i F?oc ! AT 350°C £ § Gas oil Ho. 1 § 181 • 382 ! 89 t I 0.846 § § S ! § Gas oil Ho. 2 ! 186 f ! ! 385 ! 67 f a 0.847 § § The effect of additive I on the decrease of the cloud point of each of the two gas oil cuts, in relation vdth the additive concentration, determined according to standard NF T 60105, is shown Table II belo-.j.

TABLE II S ! T f ADDITIVE COIJCEITTRATIO:: J CLOUD POEIT (CC) j CLOUD POIET (°C) | x Cr-; b.w.) : oas on, n0. 1 • gas oil ii0. 2 ? S ! ! § § 0 ! +2 ! +6 § § ! ! § § 0.01 ! +1 ! +5 § § ! ! § § 0.05 » 0 J +4 § § 1 j § § 0.1 » - 1 ! +2 § § ! ! S § 0.15 ! - 1 ! +2 § § ! ! § § 0.2 ! - 2 ! + 1 § § ! ! § - EIAJiPLE 2 Additives differing mainly by the starting amine are used in an amount of 0.1 £ b.w. in the two gas oil cuts of example 1, the method of manufacture being the same as in example 1. 2 078 2 Additive I : product used in example 1 ; Additive II : product obtained by condensing N-stearyl-dipropylene trianxne on isaleic anhydride ; Additive HI : product obtained by condensing stearyl amine on maleic anhydride.

The results are given in Table in belo"-; : TA2LE III § | CLOUD KHET (°c) § : § ^ Additive-free I § § + 0.1 /j additive I € f 6 £ + 0.1 Jc additive II I i> § + 0.1 p additive III $ OAS. OIL No. 2 | It is found that the effect of decreasing the cloud point is narmus in the case of additive I, vrherein the starting anine is a laixturc of two N-a3iyl 1,3 propane diamines. - example 3 Additives differing essentially by the length of the alkyl chain of the starting amine are used in this example, in an amount of 0.1 f- b.w. in the cane two gas oils as above.

There are thus used : Additive I : product used in ej-iasple 1 2 078 2 3 Additive IV : product obtained by condensing H-behepyl 1,3 propane diandne on naleic anhydride (behenyl = C22^ Additive V : product obtained by condensing H-lauryl 1,3 propane dicr±ne on maleic anhydride (lauryl = C^) The results of the determinations of the cloud point are given in Table TV below TABLE IV §—— £ £ CLOUD POINT (°C) I ' § q Additive-free § GAS OIL Ho. 1 GAS OIL Ho. 2 | § § § § § § § § + 2 + 6 § v + 0#1 y> additive I § |+0.1 £ adiitive IV $ - 1 + 2 - 1 + 2 § + 0.1 £ additive V § + 1 + 5 § § § It can be observed that the additive obtained from a diamine vdth an aliyl chain of 12 carbon atoas has a lower efficiency than the additives obtained from a dianine with a longer chain of 16, IB or 22 carbon a tons.

- E X A K P L E 4 Additives differing essentially by the nature of the starting dicarboxylic compound are used in this example, in a proportion of 0.1 b.v;. in the same two gas oils as above.

There are thus vised : 2 07823 ■Additive I : product used in example 1t obtained from maleic anhydride.

Additive VI j product obtained by condensing N-steaiyl 1,3 propane diamine on methylmaleic (citraconic) anhydride.

Additive VII : product obtained by condensing U-stearyl 1,3 propane diamine or. n-octadecenyl succinic anhydride.

The determined cloud points are shown in Tabic V below : TA3L2 V § CLOUD POIIJT (CC) § f 6 ^ Additive-free § § § ^ + 0.1 additive I £ + 0.1 £ additive VI I + 0.1 additive VII - EXAKPLS 5 The inhibiting effect of an additive conforming- to the invention on the settling of n—paraffins crystallising in a gas oil cut maintained at rest at lovr temperature is determined in this example.

The additive is additive I already used above.

Two 100 cc test tubes are filled with the already used 20 gas oil No. 2 (distillation range : IP = 186°C, FP = 385°C).

No additive is introduced into the first test tube. 2 07-8 23 0.1 < b.w* of additive is introduced into the second test tube.

The two test tubes are closed hermetically, then left at rest in a cold room at — 10°C for one week.

After one week, the settling rate of the settled paraffins erpressed as the volume of the upper linpid phase, is reported in the folloviing Table : table vi £ TEST TUBS No. 1 | AHDITIVS-FHE3 GAS OIL § 50 £ vcl TEST TUBS Ho. 2 GAS OIL + ADDITIVE I 1? /' vol =§ i § _§ § § All the precipitated paraffins are thus present in 50 by volume of the additive-free gas oil, wMch makes the lower portion more difficult to use as the result of the pTu^gins of the jumps, filters and pipes.

As concerns the additive-containing gas oil, the upper limpid phase amounts tc only 15 5^. The paraffins are thus in 85 of the tctal volume. They are in a state of better dispersion and can be transported more easily.

- EXAMPLE 6 The effect of an additive conform^ to the invention is tested, in this example, on the limit filterability temperature (LIT) of the ttro gas oil cuts described abeve.

The LPT values are determined according to standard IIP II 07-042. 2 07823 TABLE VII r coijcsjjtratio:-: TLF | OF ADDITIV2 I (</= b.u.) J GAS OIL Ho. 1 - E7.AKPLS 7 The anti-corrosion effect of additive I of example 1 is tested in tliis esanple.

Product I has been used in the two gas oils Ho. 1 and No. 2, as hereinbefore described, at e concentration of 0.01 £ by weight.

The corrosion test consists of determining the rate of corrosion, by synthetic sea water, cf cylindrical test pieces of polished steel or iron, according to the AST!"; standard D 665 modified in the folio.ring manner I The tenperature is J2.2°C ; the test time is 20 hours.

The additive-free gas oils IIo. 1 end No. 2 cause 100 ^ of the surface of the test pieces to rust ; the tiro gas oils contai-20 ning 0.01 b.u. of additive do not cause any rusting of the test pieces. — e I A K ? l I B In this exanple, the effect of additive I, according to the invention, on the pour point of gas oil cuts is tested. The pom-points are determined according to the Frcnch standard 1IFT 60105 ; 2 078 23 The additive is tested in en amount of 0.1 by weight. The results are given in Table VIII below. table viii | GAS oil § § distillation ASTIi $> distilled M1 350° i voluiitc 1IASS ha/l AT 15°c pour p0ii7t without additive ! with additive ip°c f?cc S § § »>■ 1 § | *• 2 § No. 3 § | Ho. 4 § 181 186 201 166 382 3B5 366 386 89 87 93 89 0.846 0.847 0.833 0.833 - 6°C - 3°c - 3°c - 3°c - 9°c - 9°c - 15°C - 21 °c - E I A I '. P L E 9 A solution consisting of 294 g (3 Holes) of naleic anhydri de dissolved in 500 g of xylene is introduced into a 3 liter reactor provided with a Dean and Stark water-separation system and an efficient stirrer. While maintaining the temperature of the solution between 30 and 40°C, a solution of 1230 g (3 moles) of N,I3-didodecyl 1,3-diB-rino propane in 1000 g of xylene is added thereto in 1.5 h. The whole is heated for 3 hours at xylene reflux, during tine 55 g of water discharged from the reaction medium are collected. The reaction product constitutes additive viii which is present as a solution is xylene at a concentration very close to 50 ^ b.w.

- EXAMPLE 10 Although operating as in example 9, 532 g (2 moles) of dodecenylsuccinic anhydride are condensed on 820 g (2 moles) of II, 13-didodecyl 1,3-diamino propane. The condensation product constitutes additive ix whose concentration in xylene is so adjusted as to attain 50 £ b.u. 207823 The effect of the so-obtained additives VIII and IX has been tested on the cloud point (determined according to standard Iff" T 60 — 105), the linit filterobility tesperatuxe (determined accorcir.5 to standard NF K 07 - 042) and the pour point (determined eccorr.in~ to standard HF T 60 - 105) of the two pas oils Jio. 1 nnd Ko. 2, the concentration of the additive boirvj 0.1 J; b.:r. in cach cffio.

The results are given in Table J7. belo;.' : TABLE IX "T T i f, r | ADDITIVES § § cloud poi:rr (°c) t.l.f.. (°c) poui? poii^r (°c) 1 ci j g2 gi G2 g1 G2 § 0.1 £ viii § § 0.1 £ iz § '» 0.1 fl! v - 1 \~' + 3 - 2 ! ^ 2 1 \ 1 - 4 - 5 7 0 - 3 - 9 - 12 - 1 7 _ q — 9 n § § 'without § + 2 ! + 6 * 0 + 3 - 6 "■ y - 3 207823

Claims (13)

WHAT WE CLAIM IS:

1. An additive, useful, in particular, to decrease the cloud point of middle distillates, characterized as having a molecular weight of 300 to 10,000 and resulting from the condensation of at least one aliphatic dicarboxylic compound selected from the maleic and alkylmaleic and alkenylsuccinic acids, anhydrides, and alkyl diesters thereof, and at least one compound having a primary amine function, complying with the general formula: R - Z (CH.) 2 n -NH- m (I) wherein R represents a monovalent saturated aliphatic radical of 1 to 30 carbon atoms, Z is selected from - NH - and - NR' -groups, wherein R' is a monovalent saturated aliphatic radical containing 1 to 30 carbon atoms, n is an integer from 2 to 4, m is zero when Z is - NH or an integer from 1 to 4 in all cases; said compound of formula (I) being used in a proportion of 0.9 to 1.2 mole per mole of said dicarboxylic compound(s), the reactants being brought in contact at 30 - 80c and then heated at 12 0-2 00°C.

2. An additive according to claim 1, characterized in that the compound having a primary amine function (I) consists of at least one mono-amine of the formula R^" NH£ where R"*" represents a linear alkyl radical of 12 to 30 carbon atoms.

3. An additive according to claim 1, characterized in that the compound having a primary amine function (I) consists of at least one polyamine of the formula: R1 - NH- -(CH_ ) NH- 2 n -H wherein R^" represents a linear alkyl radical with 12 to 30 carbon atoms, n is an integer from 2 to 4 and m is an integer from 1 to 4. - 17 - .20788.3

4. An additive according to claim 1, characterised in that the compound having a primary amine function (I) consists of at least one polyamine of the formula: r2\ ^ N- R3" (CH2)n NH m wherein R2 and R3 are each a linear alkyl radical of 8 to 22 carbon atoms, R2 and R3 together comprising from 16 to 32 carbon atoms, n is an integer from 2 to 4 and m is an integer from 1 to 4.

5. An additive according to claim 1, characterized in that the compound having a primary amine function (I) is used together with at least one ether-amine of the formula: R4 - 0- -(CH ) NH- 2 n m (II) 4 wherein R represents an alkyl radical of 8 to 22 carbon atoms, n is an integer from 2 to 4 and m is an integer from 1 to 4 and/ or at least one amino-alcohol of the formula: HO - CH2 R5 - NH2 (III) where R~* represents a linear alkylene radical containing 10 to 18 carbon atoms, said at least one ether-amine of formula (II) and/or said at least one amino-alcohol of formula (III) being used in a total proportion of at most 50% with respect to the cumulated amounts of said compounds of formulae (I), (II), and (III)

6. An additive according to one of claims 1 to 5 characterized in that said aliphatic dicarboxylic compound is selected from maleic anhydride, methylmaleic anhydride, and n-octadecenyl and dodecenyl succinic anhydrides.

7. An additive according to one of claims 1 to 6, characterized in that the reaction performed to prepare it comprises admixing, at a temperature of 30 to 80°C, (a) said at least one dicarboxylic compound with (b) said at least one compound having a primary amine function comprised of at least 50% of at least one compound of formula (I) and at most 50% of at least one compound of formula (II) and/or (III), said compounds (a) and (b) being in substantially equimolecular proportion with respect to each other, and heating the resultant mixture at a temperature of 120 to 200°C for 1 to 8 hours. 207823

8. A middle distillate composition, characterized in that it comprises a major proportion of middle distillate of distillation range from 150 to 450°C, and a minor proportion, sufficient to decrease the cloud point thereof, of at least one additive according to one of claims 1 to 7.

9. A middle distillate composition according to claim 8, characterized in that said middle distillate consists of a gas oil cut distilling between an initial temperature of 160 to 190°C and a final temperature of 350 to 390°C.

10. A middle distillate composition according to claim 8 or 9, characterized in that the proportion of said additive is from 20 to 2000 g/ton.

11. A middle distillate composition according to claim 10, characterized in that the proportion of said additive is about 1000 g/ton.

12. An additive as claimed in claim 1 substantially as described herein in any one of the Examples.

13. A middle distillate composition as claimed in claim 8 substantially as described herein in any one of the Examples.