Ethylene-based copolymers and their use as flow improvers in mineral oil middle distillates

Abstract

Ethylene-based copolymers which are suitable as flow improvers for mineral oil middle distillates are composed ofa) from 50 to 94% by weight of ethylene,b) from 3 to 30% by weight of one or more vinyl esters of C.sub.2 -C.sub.6 -monocarboxylic acids,c) from 3 to 20% by weight of one or more aminoalkyl acrylates of the general formula I ##STR1## where R.sup.1 is hydrogen or methyl, R.sup.2 and R.sup.3 may be identical or different and are each hydrogen or C.sub.1 -C.sub.6 -alkyl and A.sup.1 is straight-chain or branched C.sub.2 -C.sub.10 -alkylene, andd) from 0 to 10% by weight of one or more monomers which are copolymerizable with the monomers a) to c),copolymers in which monomer b) is vinyl acetate and which have a number average molecular weight of from 5000 to 50,000 being excluded, or are composed ofa') from 50 to 95.5% by weight of ethylene,b') from 4 to 30% by weight of one or more vinyl esters of C.sub.2 -C.sub.6 -monocarboxylic acids,c') from 0.5 to 20% by weight of one or more vinylimidazoles of the general formula II ##STR2## where R.sup.4, R.sup.5 and R.sup.6 may be identical or different and are each hydrogen or C.sub.1 -C.sub.6 -alkyl, orfrom 0.5 to 20% by weight of one or more aminoalkyl vinyl ethers of the general formula IIIR.sup.7 R.sup.8 N--A.sup.2 --O--CR.sup.9 .dbd.CR.sup.10 R.sup.11(III)whereR.sup.7 and R.sup.8 are each C.sub.1 -C.sub.6 -alkyl,R.sup.9, R.sup.10 and R.sup.11 are each hydrogen or C.sub.1 -C.sub.6 -alkyl andA.sup.2 is C.sub.2 -C.sub.6 -alkylene, andd') from 0 to 10% by weight of one or more monomers which are copolymerizable with the monomers a') to c').

Description

The present invention relates to novel ethylene-based copolymers, the use of these and of copolymers known per se as flow improvers in mineral oil middle distillates, and furthermore mineral oil middle distillates which contain these copolymers.

Middle distillates, such as gas oils, diesel oils or fuel oils, which are obtained from mineral oils by distillation, have different contents of paraffins, depending on the origin of the crude oil. At relatively low temperatures, solid paraffins separate out (cloud point, CP). On further cooling, the lamellar n-paraffin crystals form a house-of-cards structure, and the middle distillate sets although the predominant part of the middle distillate is still liquid. The flow of the fuels obtained from the mineral oil distillate is considerably impaired by the precipitated n-paraffins in the temperature range between cloud point and pour point. The paraffins block filters and cause nonuniform fuel feed to the combustion units or completely stop the feed. Similar problems occur in the case of fuel oils.

It has long been known that the crystal growth of the paraffins in the combustion and power fuels obtained from the mineral oil middle distillates can be modified by means of suitable additives. Effective additives on the one hand prevent middle distillates from forming such house-of-cards structures and becoming solid at temperatures as low as a few degrees Celsius below the temperature at which the first paraffin crystals crystallize out and, on the other hand, form fine, well-crystallized, separate paraffin crystals which pass through filters in motor vehicles and heating systems or at least form a filter cake which is permeable to the liquid part of the middle distillates, thus ensuring trouble-free operation.

Ethylene/vinyl carboxylate copolymers as disclosed, for example, in U.S. Pat. No. 3,048,479 and U.S. Pat. No. 3,627,838 have long been used as flow improvers.

A disadvantage of these additives is that, because they have a higher density than the liquid part, the precipitated paraffin crystals tend increasingly to settle out on the bottom of the container during storage. Consequently, a homogeneous phase having a low paraffin content forms in the upper part of the container and a two-phase paraffin-rich layer at the bottom. Since, both in vehicle tanks and in the mineral oil dealers' storage or delivery tanks, the middle distillate is generally withdrawn slightly above the bottom of the container, there is a danger that the high concentration of solid paraffins will lead to blockages of filters and metering means. This danger is all the greater the further the storage temperature is below the precipitation temperature of the paraffins, since the amount of paraffin precipitated is a function of the temperature and increases with decreasing temperature.

JP-A 83/80386 describes flow improvers comprising ethylene, vinyl acetate and N-vinyl-2-pyrrolidone, which however do not give satisfactory results in all cases in practice since the mineral oil fractions to be treated differ greatly in composition, depending on their origin. According to EP-A 405 270, the action of the terpolymers disclosed in the Japanese patent application can be improved by mixing with an ethylene/vinyl acetate copolymer; on the other hand, the addition of a plurality of polymers to the mineral oil middle distillates is technically very complicated.

U.S. Pat. No. 2,787,459 discloses copolymers made from monomers which carry a basic nitrogen atom, such as aminoalkyl acrylates, and those monomers which carry no amino group but a hydrocarbon radical of 8 to 18 carbon atoms. They are used for dispersing sludge, as may be obtained from fuel oils.

EP-A 340 975 describes copolymers of ethylene and aminoalkyl acrylates, which may contain up to 20% by weight of vinyl acetate and have a number average molecular weight of from 5000 to 50,000. The copolymers are used for reducing the concentration of metal ions in aqueous solution.

It is an object of the present invention to provide copolymers which ensure the flow of mineral oil middle distillates at low temperature and which have a dispersing effect such that settling out of precipitated paraffins is delayed or prevented. The flow improvers should display their action independently of the composition of the mineral oil middle distillates.

We have found that this object is achieved by ethylene-based copolymers which are composed of

a) from 50 to 94% by weight of ethylene, b) from 3 to 30% by weight of one or more vinyl esters of C.sub.2 -C.sub.6 -monocarboxylic acids, c) from 3 to 20% by weight of one or more aminoalkyl acrylates of the general formula I ##STR3## where R.sup.1 is hydrogen or methyl, R.sup.2 and R.sup.3 may be identical or different and are each hydrogen or C.sub.1 -C.sub.6 -alkyl and A.sup.1 is straight-chain or branched C.sub.2 -C.sub.10 -alkylene, and d) from 0 to 10% by weight of one or more monomers which are copolymerizable with the monomers a) to c), copolymers in which monomer b) is vinyl acetate and which have a number average molecular weight of from 5000 to 50,000 being excluded, or are composed of a') from 50 to 95.5% by weight of ethylene, b') from 4 to 30% by weight of one or more vinyl esters of C.sub.2 -C.sub.6 -monocarboxylic acids, c') from 0.5 to 20% by weight of one or more vinylimidazoles of the general formula II ##STR4## where R.sup.4, R.sup.5 and R.sup.6 may be identical or different and are each hydrogen or C.sub.1 -C.sub.6 -alkyl, or from 0.5 to 20% by weight of one or more aminoalkyl vinyl ethers of the general formula III R.sup.7 R.sup.8 N--A.sup.2 --O--CR.sup.9 .dbd.CR.sup.10 R.sup.11(III) where R.sup.7 and R.sup.8 are each C.sub.1 -C.sub.6 -alkyl, R.sup.9, R.sup.10 and R.sup.11 are each hydrogen or C.sub.1 -C.sub.6 -alkyl and A.sup.2 is C.sub.2 -C.sub.6 -alkylene, and d') from 0 to 10% by weight of one or more monomers which are copolymerizable with the monomers a') to c').

The abovementioned number average is determined by measuring the viscosity (cf. EP-A 340 975).

We have also found the use of the stated copolymers as additives for mineral oil middle distillates, and mineral oil middle distillates which contain these copolymers.

The novel copolymers have, as a rule, a weight average molecular weight of from 300 to 8000, and, in view of their use as flow improvers, those having a molecular weight of from 500 to 5000, especially from 1000 to 3000, are preferred. The molecular weight is determined by gel permeation chromatography. The novel copolymers generally have a viscosity of from 1000 to 2000, preferably from 250 to 1000, mm.sup.2 /s, determined according to DIN 53 019 at 120.degree. C.

The copolymers are composed of at least three monomers:

a) in the case of aminoalkyl acrylates I as monomers c), the amount of ethylene is preferably from 50 to 92, in particular from 65 to 87, % by weight, or a') in the case of vinylimidazoles II or aminoalkyl vinyl ethers III as monomers c'), the amount of ethylene is preferably from 65 to 94% by weight. b) Preferred components b) are vinyl acetate and vinyl propionate and mixtures thereof, or compounds such as vinyl butyrate. Preferably, the amount of monomers b) is from 5 to 30, in particular from 10 to 23, % by weight in the case of aminoalkyl acrylates I as monomers c), and from 4 to 23% by weight in the case of vinylimidazoles II or aminoalkyl vinyl ethers III as monomers c'). c) Monomer c) of the general formula I comprises aminoalkyl acrylates and methacrylates. Examples of alkyl radicals A.sup.1 are ethylene, n-propylene, n-butylene, dimethylethylene and sec-butylene.

R.sup.2 and R.sup.3 may be, for example, hydrogen, methyl, ethyl, n-propyl, isobutyl and n-butyl, among which methyl is preferred. Examples of suitable monomers c) are aminoethyl acrylate, amino-n-butyl acrylate, N-methylaminoethyl acrylate, N,N-di-n-butylamino-n-propyl acrylate and the corresponding methacrylates, dimethylaminoethyl acrylate and dimethylaminoethyl methacrylate being preferred.

The monomers are commercially available or can be prepared by known methods, for example by esterifying acrylates with aminoalcohols in the presence of a titanium catalyst (cf. EP-A 188 639).

The preferred amount of aminoalkyl acrylates I as monomers c) is from 3 to 12% by weight.

c') Monomer c') of the general formula II comprises vinylimidazoles.

R.sup.4, R.sup.5 and R.sup.6 may be, for example, hydrogen, methyl, ethyl, n-propyl, isopropyl and n-butyl, among which hydrogen is preferred. Examples of suitable monomers c') are 2-methylvinylimidazole, 4-methylvinylimidazole and 5-methylvinylimidazole, the parent structure vinylimidazole being preferred.

The monomers are commercially available or can be prepared by known methods.

The preferred amount of vinylimidazoles II as monomers c') is from 1 to 4% by weight.

Monomer c') of the general formula III comprises aminoalkyl vinyl ethers.

R.sup.7, R.sup.8, R.sup.9, R.sup.10 and R.sup.11 may be identical or different and are each C.sub.1 -C.sub.6 -alkyl, e.g. methyl, ethyl, n-propyl, isopropyl and n-butyl. R.sup.9, R.sup.10 and R.sup.11 may furthermore be hydrogen. The C.sub.2 -C.sub.6 -alkylene radical A.sup.2 is straight-chain or branched alkylene, for example ethylene, n-propylene, dimethylmethylene, methylethylmethylene and dimethylethylene. Preferred compounds are those in which R.sup.7 and R.sup.8 are identical and are each C.sub.1 -C.sub.3 -alkyl, A.sup.2 is a straight-chain C.sub.2 -C.sub.4 -radical and R.sup.9, R.sup.10 and R.sup.11 are each hydrogen, as in diethylaminoethyl vinyl ether and dimethylaminopropyl vinyl ether.

These monomers are obtainable, for example, according to Liebigs Ann. Chem. 601 (1956), 81.

The preferred amount of aminoalkyl vinyl ethers III as monomers c') is from 0.5 to 5% by weight.

d) Suitable monomers d) and d') are monomers which are copolymerizable with components a) to c), and a') to c'), respectively, and which may replace these without substantially influencing the properties of the copolymers, e.g. propene. The amount of monomer d) or d') is preferably from 0 to 2% by weight.

The copolymers are prepared in a manner known per se by polymerizing the monomers a) to d) or a') to d'). The vinylimidazole II or the aminoalkyl vinyl ether III is incorporated in preference to ethylene, so that the content of said vinylimidazole or of said aminoalkyl vinyl ether in the novel copolymers is increased compared with the starting monomer mixture. In a preferred embodiment, the monomers are polymerized in the absence of a solvent at from 50 to 400, preferably from 100 to 300, MPa and at from 150.degree. to 350.degree. C., preferably from 180.degree. to 280.degree. C., in the presence of compounds which form free radicals. The average residence time is in general from 60 to 120 seconds. Examples of suitable free radical initiators are peroxides, such as di-tert-butyl peroxide, tert-butyl peroxypivalate or tert-butyl peroxy-3,5,5-trimethylhexanoate, the amount of which is as a rule less than 5% by weight, based on the monomers used in the course of polymerization. In order to prepare low molecular weight copolymers, it is often advantageous to carry out the copolymerization in the presence of regulators, such as C.sub.1 -C.sub.4 -aldehydes, e.g. propionaldehyde, or organic SH-containing compounds, the amount of which is in general from 0.1 to 5% by weight, based on the sum of the monomers. The polymerization can be carried out, for example, in an autoclave, a tube reactor or a combination of tube reactor and autoclave.

The novel copolymers are used as additives for mineral oil middle distillates, which are understood as meaning petroleum, fuel oil and diesel fuels having a boiling point of from about 150.degree. to 400.degree. C. The copolymers may be added to the middle distillates directly or, preferably, as a 20-70% strength by weight solution. Suitable solvents are aliphatic or aromatic solvents, such as xylene or mixtures thereof, as well as high-boiling mixtures of aromatics, and middle distillates. The amount of copolymers in the mineral oil middle distillates is as a rule from 10 to 10,000, preferably from 50 to 5000, ppm. Depending on the intended use, the middle distillates may contain further additives, such as flow improvers, dispersants, antifoams, corrosion inhibitors, antioxidants, conductivity improvers and dyes.

Regardless of their origin, the copolymers result in a substantial improvement in the low-temperature flow properties in middle distillates. In addition, they keep precipitated paraffin crystals effectively in suspension, so that there is no blockage of filters and lines by paraffin which has settled out.

EXAMPLES

1. General Preparation Method I

Ethylene, vinyl propionate or acetate and dimethylaminoethyl acrylate or vinylimidazole are polymerized in an autoclave, with the addition of propionaldehyde as a regulator. The free radical initiation of the polymerization was carried out by continuously metering in an isododecane solution which contained 0.2% by weight of tert-butyl peroxypivalate and 0.5% by weight of tert-butyl peroxy-3,5,5-trimethylhexanoate. The autoclave had an internal volume of 1l and a length/diameter ratio of 5:1. The average residence time of the reaction mixture in the autoclave was about 90 seconds.

The polymerization conditions and the ratios of the monomers are listed in Tables 1 and 2 below.

Table 3 shows the composition of the copolymers prepared by the above method with the concomitant use of vinylimidazole.

TABLE 1__________________________________________________________________________Example No. Reaction Reaction Composition of the reaction Freeaccording to pressure temperature reaction mixture.sup.a) radicalthe invention �MPa! �.degree.C.! C.sub.2 H.sub.4 VPr.sup.d) VAc.sup.e) DMAEA.sup.f) DMAEMA.sup.g) initiator.sup.b) Regulator.sup.c)__________________________________________________________________________1 150 250 85.6 10.2 -- 4.2 -- 13.7 2.12 150 250 85.8 10.0 -- 4.2 -- 10.6 1.293 150 235 75.0 18.2 -- 6.8 -- 19.1 0.804 150 250 79.0 -- 15.4 5.6 -- 9.4 1.785 150 235 80.5 13.2 -- 5.9 -- 13.3 0.436 150 235 80.1 13.6 -- 6.3 -- 8.3 1.237 150 250 75.8 19.0 -- 5.2 -- 22.7 1.068 150 250 73.5 22.1 -- 4.4 -- 19.7 0.309 150 230 94.0 -- 3.0 -- 3.2 12.2 0.4210 150 230 88.2 -- 4.1 -- 7.7 14.1 0.5911 150 230 91.9 -- 4.9 -- 3.2 13.2 0.5112 150 230 90.5 -- 6.5 -- 3.0 13.9 0.7213 150 235 75.9 16.9 -- -- 7.2 18.3 0.80Comparison 150 250 93.7 -- -- 6.3 2.3 8.1 2.3V 1V 2 150 250 94.0 -- -- 6.0 1.8 13.4 1.8V 3 190 200 68.9 -- 11.1 -- 2.1 0.96 2.1__________________________________________________________________________ .sup.a) % by weight, based on the reaction mixture .sup.b) ppm by weight, based on ethylene .sup.c) % by weight, based on monomers .sup.d) VPr = vinyl propionate .sup.e) VAc = vinyl acetate .sup.f) DMAEA = dimethylaminoethyl acrylate .sup.g) DMAEMA = dimethylaminoethyl methacrylate TABLE 2__________________________________________________________________________Example No. Reaction Reaction Composition of theaccording to pressure temperature reaction mixture.sup.a) Free radicalthe invention �MPa! �.degree.C.! C.sub.2 H.sub.4 VPr.sup.d) VAc.sup.e) VI.sup.f) initiator.sup.b) Regulator.sup.c)__________________________________________________________________________14 150 236 93.2 6.1 -- 0.8 33.1 2.815 150 234 93.5 5.8 -- 0.7 6.5 2.916 151 231 90.9 8.4 -- 0.7 17.7 3.117 151 235 87.9 11.4 -- 0.7 23.8 3.118 150 232 85.9 13.5 -- 0.6 27.4 2.719 151 235 88.3 10.4 -- 1.3 24.5 2.820 151 234 94.1 5.2 0.7 4.7 2.921 149 234 66.9 29.4 -- 3.7 193.3 0.922 151 236 73.9 23.2 -- 2.9 139.4 1.223 150 234 83.8 14.4 -- 1.8 32.9 2.9Comparison 190 200 88.9 -- 11.1 -- 1.0 2.1V 4__________________________________________________________________________ .sup.a) % by weight, based on reaction mixture .sup.b) ppm by weight, based on ethylene .sup.c) % by weight, based on monomers .sup.d) VPr = vinyl propionate .sup.e) VAc = vinyl acetate .sup.f) VI = vinylimidazole TABLE 3______________________________________Composition of the copolymersExample No. C.sub.2 H.sub.4 VPr VAc VIaccording to �% by �% by �% by �% by Viscosity*.sup.)the invention weight! weight! weight! weight! �mm.sup.2 /s!______________________________________14 76.5 22.1 -- 1.4 46015 93.9 4.7 -- 1.4 42016 91.7 6.9 -- 1.4 25017 89.9 6.8 -- 1.3 25018 86.9 12.0 -- 1.1 24019 88.9 8.6 -- 2.5 23020 92.9 -- 5.7 1.4 24021 68.1 24.9 -- 7.0 46022 75.3 1.3 -- 5.4 48023 85.9 10.6 -- 3.5 250Comparison 88.9 -- 11.1 -- 280V 4______________________________________ *.sup.) in the rotary viscometer according to DIN 53 019 at 120.degree. C.; vinylimidazole is more readily incorporated into the copolymer than i ethylene 2. General Preparation Method II

Ethylene, vinyl propionate or acetate and diethylaminoethyl vinyl ether were polymerized in an autoclave, with the addition of propionaldehyde as regulator. The free radical initiation of the polymerization was carried out at 235.degree. C. and 150 MPa by continuously metering in an isododecane solution which contains 0.2% by tert-butyl peroxypivalate and 0.5% by weight of tert-butyl peroxy-3,5,5-trimethylhexanoate. The autoclave had an internal volume of 1l and a length/diameter ratio of 5:1. The average residence time of the reaction mixture in the autoclave 90 seconds.

The polymerization conditions and the ratios of the monomers in the reaction mixture are listed in Table 4 below. Table 5 shows the composition of the copolymers prepared by the above method.

TABLE 4______________________________________Example No. Composition of theaccording to reaction mixture.sup.a) Free radicalthe invention C.sub.2 H.sub.4 VPr.sup.d) DEAEVE.sup.e) initiator.sup.b) Regulator.sup.c)______________________________________24 93.7 5.7 0.6 1.8 2.725 83.4 15.0 1.6 9.9 1.926 74.6 23.0 2.4 32.6 0.427 86.6 7.8 3.6 6.9 2.028 82.5 10.9 5.0 10.6 1.729 78.7 13.9 6.3 18.6 1.130 75.4 16.3 7.4 18.9 0.931 72.2 18.8 8.6 42.5 0.4Comparison 78.8 21.2 -- 2.0 1.9V 5______________________________________ .sup.a) % by weight, based on reaction mixture .sup.b) ppm by weight, based on ethylene .sup.c) % by weight, based on monomers .sup.d) VPr = vinyl propionate .sup.e) DEAEVE = diethylaminoethyl vinyl ether TABLE 5______________________________________Composition of the copolymersExample No. C.sub.2 H.sub.4 VPr DEAEVEaccording to �% by �% by �% by Viscosity*.sup.)invention weight! weight! weight! �mm.sup.2 /s!______________________________________24 94.4 5.1 0.5 45025 87.0 12.0 1.0 48026 84.9 13.6 1.5 40027 93.1 5.1 1.8 46028 89.3 8.1 2.6 41029 86.5 10.0 3.4 42030 82.6 13.3 4.1 41031 79.3 16.0 4.7 390Comparison 86.8 13.2 -- 460V 5______________________________________ *.sup.) in the rotary viscometer according to DIN 53 019 at 120.degree. C.; DEAEVE is more readily incorporated into the copolymer than is ethylene. 3. Use Examples

The novel copolymers and the comparative compounds were tested in a number of middle distillates. These are diesel fuels of commercial German refinery quality; they are referred to as DK 1 to DK 7:

______________________________________ DK 1 DK 2 DK 3 DK 4 DK 5 DK 6 DK 7______________________________________Cloud point -8 -7 -4 -7 -8 -7 -7(.degree.C.)CFPP (.degree.C.) -12 -10 -7 -14 -10 -9 -9Density at 0.831 0.829 0.832 0.814 0.831 0.831 0.82620.degree. C. (g/ml)Initial 175 183 171 164 175 172 172boiling point(.degree.C.)20% boiling 223 211 220 206 223 216 217point (.degree.C.)90% boiling 314 317 332 306 314 325 321point (.degree.C.)Final boiling 352 364 363 337 352 343 356point (.degree.C.)______________________________________ 3.1 Description of the Test Methods

The appropriate amounts of the novel examples 1 to 31 and Comparative Examples V1 to V5 (50% strength in Solvesso.RTM. 150, a high-boiling aromatic hydrocarbon mixture from Esso) were added to the middle distillates at 40.degree. C. with stirring, and the mixture was then cooled to room temperature.

Test 1

The middle distillates containing the additive were stored in 100 ml measuring cylinders for 20 hours in a refrigerator at -13.degree. C. The volume and appearance of the paraffin phase which had settled out and the oil phase above this were then determined and evaluated visually. In addition, the cold filter plugging point (CFPP) of each sample was measured according to DIN EN 116.

The results are shown in Tables 6 to 14. It is evident that the novel copolymers 1 to 31 have not only a good CFPP-improving effect but also an excellent effect as paraffin dispersants. In contrast, the comonomeric Comparative Examples V1 and V2 based on ethylene/amino acrylate lead only to an insufficient improvement in the CFPP, and Example V3 based on ethylene/vinyl propionate is ineffective as paraffin dispersant. Comparative Example V4 based on ethylene/vinyl acetate leads only to an insufficient paraffin-dispersing effect. Comparative Example V5, too, does not lead to sufficient dispersing of the paraffins.

TABLE 6______________________________________Dispersing tests (Test 1) in DK 1, CP: -8.degree. C., CFPP: 12.degree.C. Paraffin phase Oil phase Dose CFPP (% (%Ex. (ppm) (.degree.C.) by vol.) Appearance by vol.) Appearance______________________________________1 300 -24 95 dispersed 5 clear2 300 -23 95 dispersed 5 clear3 300 -22 100 dispersed 0 --4 300 -24 90 dispersed 10 clear5 300 -26 85 dispersed 15 clear6 300 -25 100 dispersed 0 --7 300 -29 90 dispersed 10 clear8 300 -25 85 dispersed 15 clearComp. 300 -17 100 dispersed 0 --V1V2 300 -18 100 dispersed 0 --V3 300 -25 55 flocculent 45 clear______________________________________ TABLE 7______________________________________Dispersing tests (Test 1) in DK2, CP: -7.degree. C., CFPP: -10.degree.C. Paraffin phase Oil phase Dose CFPP (% (%Ex. (ppm) (.degree.C.) by vol.) Appearance by vol.) Appearance______________________________________2 300 -23 80 dispersed 20 clear5 300 -26 100 dispersed 0 --6 300 -25 100 dispersed 0 --8 300 -25 80 dispersed 20 clear______________________________________ TABLE 8______________________________________Dispersing tests (Test 1) in DK 3, CP: -4.degree. C., CFPP: 7.degree. C. Paraffin phase Oil phase Dose CFPP (% (%Ex. (ppm) (.degree.C.) by vol.) Appearance by vol.) Appearance______________________________________1 300 -18 95 dispersed 5 clear2 300 -17 100 dispersed 0 --4 300 -19 95 dispersed 5 clear5 300 -19 100 dispersed 0 --6 300 -18 95 dispersed 5 clear9 300 -17 100 dispersed 0 --10 300 -18 95 dispersed 5 clear11 300 -18 100 dispersed 0 --12 300 -19 100 dispersed 0 --13 300 -17 100 dispersed 0 --Comp. 300 -19 30 flocculent 70 clearV3______________________________________ TABLE 9______________________________________Dispersing tests in DK 5, CP: -8.degree. C., CFPP: -10.degree. C. Paraffin phase Oil phase Dose CFPP (% (%Ex. (ppm) (.degree.C.) by vol.) Appearance by vol.) Appearance______________________________________14 300 -24 90 dispersed 10 clear15 300 -19 85 dispersed 15 clear16 300 -24 80 dispersed 20 cloudy17 300 -22 95 dispersed 5 clear18 300 -25 70 dispersed 30 clear19 300 -20 80 dispersed 20 cloudy20 300 -24 100 dispersed 0 --Comp. 300 -25 55 flocculent 45 clearV4______________________________________ TABLE 10______________________________________Dispersing tests in DK 6, CP: -7.degree. C., CFPP: -9.degree. C. Paraffin phase Oil phase Dose CFPP (% (%Ex. (ppm) (.degree.C.) by vol.) Appearance by vol.) Appearance______________________________________15 300 -14 100 dispersed 0 --16 300 -13 100 dispersed 0 --17 300 -14 100 dispersed 0 --18 300 -14 100 dispersed 0 --19 300 -14 100 dispersed 0 --20 300 -13 100 dispersed 0 --Comp. 300 -19 30 flocculent 70 clearV4______________________________________ TABLE 11______________________________________Dispersing tests DK 7, CP: -7.degree. C., CFPP: -9.degree. C. Paraffin phase Oil phase Dose CFPP (% (%Ex. (ppm) (.degree.C.) by vol.) Appearance by vol.) Appearance______________________________________14 300 -14 100 dispersed 0 --15 300 -12 100 dispersed 0 --16 300 -13 100 dispersed 0 --17 300 -13 100 dispersed 0 --18 300 -13 90 dispersed 10 clear19 300 -12 100 dispersed 0 --20 300 -13 100 dispersed 0 --______________________________________ TABLE 12______________________________________Dispersing tests in DK 5, CP: -8.degree. C., CFPP: -10.degree. C. Paraffin phase Oil phase Dose CFPP (% (%Ex. (ppm) (.degree.C.) by vol.) Appearance by vol.) Appearance______________________________________24 300 -18 90 dispersed 10 clear27 300 -20 97 dispersed 3 clear28 300 -20 85 dispersed 15 clear29 300 -24 90 dispersed 10 clear30 300 -25 90 dispersed 10 clear31 300 -26 95 dispersed 5 clearComp. 300 -25 55 flocculent 45 clearV5______________________________________ TABLE 13______________________________________Dispersing tests in DK 2, CP: -7.degree. C., CFPP: -10.degree. C. Paraffin phase Oil phase Dose CFPP (% (%Ex. (ppm) (.degree.C.) by vol.) Appearance by vol.) Appearance______________________________________25 300 -20 70 dispersed 30 clear26 300 -27 70 dispersed 30 clear______________________________________ TABLE 14______________________________________Dispersing tests in DK 7, CP: -7.degree. C., CFPP: -9.degree. C. Paraffin phase Oil phase Dose CFPP (% (%Ex. (ppm) (.degree.C.) by vol.) Appearance by vol.) Appearance______________________________________24 300 -12 100 dispersed 0 --25 300 -12 75 dispersed 25 clear______________________________________ Test 2

The additive-containing middle distillates were cooled in 500 ml glass cylinders in a cold bath from room temperature to -18.degree. C. and stored for 20 hours at this temperature. The amount and appearance of the paraffin phase were then determined and evaluated visually. The cold filter plugging point (CFPP) of each sample of the 20% by volume of bottom phase separated off at -18.degree. C. was determined according to DIN EN 116 and the cloud point (CP) according to ASTM D 2500.

TABLE 15______________________________________Dispersing tests (Test 2) in DK 4, CP: -7 .degree. C., CFPP: -14.degree.C. 20% bottom phaseDose CFPP Paraffin phase CFPPEx. (ppm) (.degree.C.) (% by vol.) Appearance (.degree.C.) CP (.degree.C.)______________________________________1 300 -26 100 dispersed -25 -112 300 -25 100 dispersed -24 -105 300 -25 100 dispersed -25 -13______________________________________ The measured values in Table 5 show that the novel copolymers have not only a good CFPP-improving effect but also an excellent effect as paraffin dispersants, which is evident from the good agreement of the CFPP values (20% bottom phase) with the total CFPP values.

Claims

1. An ethylene-based copolymer which is suitable as a flow improver for mineral oil middle distillates and is composed of:

a') from 50 to 95.5% by weight of ethylene,

b') from 4 to 30% by weight of one or more vinyl esters of C.sub.2 -C.sub.6 -monocarboxylic acids,

c') from 0.5 to 20% by weight of one or more vinylimidazoles of the formula II ##STR5## wherein R.sup.4, R.sup.5 and R.sup.6 may be identical or different and are each hydrogen or C.sub.1 -C.sub.6 -alkyl, or

from 0.5 to 20% by weight of one or more aminoalkyl vinyl ethers of the formula III

R.sup.7 R.sup.8 N--A.sup.2 --O--CR.sup.9 .dbd.CR.sup.10 R.sup.11(III)

where

R.sup.7 and R.sup.8 are each C.sub.1 -C.sub.6 -alkyl

R.sup.9, R.sup.10 and R.sup.11 are each hydrogen or C.sub.1 -C.sub.6 -alkyl and

A.sup.2 is C.sub.2 -C.sub.6 -alkylene, and

d') from 0 to 10% by weight of one or more monomers which are copolymerizable with the monomers a') to c').

2. The copolymer as claimed in claim 1, wherein monomer b') is vinyl acetate or vinyl propionate.

3. The copolymer as claimed in claim 1, wherein R.sup.4 to R.sup.6 of the vinylimidazole II are each hydrogen.

4. The copolymer as claimed in claim 2, wherein R.sup.4 to R.sup.6 of the vinylimidazole II are each hydrogen.

5. The copolymer as claimed in claim 1, wherein diethylaminoethyl vinyl ether is the aminoalkyl vinyl ether III.

6. The copolymer as claimed in claim 2, wherein diethylaminoethyl vinyl ether is the aminoalkyl vinyl ether III.

7. A method of improving the flow of mineral oil middle distillates, comprising:

incorporating the copolymer of claim 1 into said middle oil distillates.

8. The method of claim 7, wherein said copolymer has a weight average molecular weight of from 500 to 5,000.

9. A mineral oil middle distillate containing an effective flow improving amount of the copolymer of claim 1.