NO304077B1 - Petroleum intermediate distillates with improved flow properties in cold - Google Patents

Abstract

Petroleum middle distillates having improved cold flow characteristics contain small quantities of A) conventional ethylene-based flow improvers and B) copolymers, which consist of at least 70% by weight of one or more monomers of both formulae I and II <IMAGE> and H2C=CH-O-R<3> (II), R<1> being hydrogen or methyl, R<2> being C8- to C18-alkyl and R<3> being C18- to C28-alkyl, and the A/B weight ratio being 40/60 to 95/5.

Description

The present invention relates to petroleum middle distillates with improved flow properties in the cold, and the peculiarity of the middle distillates according to the invention is that they contain 50-50 00 ppm of a mixture of A) common ethylene-based flow improvers and

B) copolymers, consisting of at least 70% by weight of one or

several monomers of formula I and formula II,

where

R<1> stands for hydrogen or methyl, R<2> for C8- to C18-alkyl, and

R<3> for C18- to C28-alkyl, the weight ratio between A and B being

40 : 60 to 95 : 5.

These and other features of the invention appear in the patent claims.

The invention thus relates to petroleum middle distillates

which contain small amounts of a common ethylene-based flow-improving agent and copolymers of ethylenically unsaturated esters of carboxylic acids and long-chain n-alkanols with long-chain alkyl vinyl ethers, and which are distinguished by improved flow properties in the cold.

Intermediate distillates, such as gas oils, diesel oils or heating oils, which are obtained by distilling petroleum oils, have different contents of paraffins depending on the origin of the petroleum oil, and depending on the processing method in the refinery. In particular, the cold flow conditions for such distillates are determined by the proportion of long-chain n-paraffins. On cooling, the n-paraffins are separated as plate-shaped crystals which mesh with each other like gears and which build up a three-dimensional network (house of cards structure) in which large quantities of distillate are enclosed which are still liquid and which are thus rendered immobile. Parallel to the crystallization of the n-paraffins, there is a reduction in buoyancy and an increase in viscosity. Because of this, the supply of the intermediate distillates to the combustion units is made difficult, the precipitated paraffins clog filters in front of the combustion units, so that in extreme cases the supply can stop completely.

It has long been known that the clogging of filters at low temperatures can be counteracted by the addition of so-called flow improvers. During nucleation, the additives ensure that many small paraffin crystals are formed instead of a few large ones. At the same time, the crystal modification of the paraffin crystals changes, so that the small plates described above are not formed. The paraffin crystals that are formed in the presence of flow-improving agents are so small that they can pass the filters, or a filter cake is built up that is permeable to the still liquid part of the middle distillate, so that operation is ensured without disturbances even at low temperatures.

Increasingly, mid-distillate cuts are occurring at the refineries where the standard flow improvers show insufficient effect or no effect at all. This is particularly the case with so-called high-cut oils, that is, fractions with a high final boiling point (final boiling point > 370°C). However, the cooking properties are not the only criterion. It thus occurs that the standard flow improver exhibits a good effect in one of two fractions with boiling curves that are similar to each other, but where the base crude oils have different places of origin, but not in the other. According to DIN 51 428, the effect of the flow improvers is determined indirectly by measuring the "cold filter plugging points" ("Cold Filter Plugging Points" CFPP).

As standard cold flow improvers, known ethylene copolymers are used per se, above all copolymers of ethylene and unsaturated esters, such as those e.g. is described in DE-A-2 102 469 or in EP-A-84 148.

In the technique, however, new flow improvers or combinations of such are needed, which also show good effects with the critical oils described above.

From DE-A-1 645 785 the use of polymers with unbranched, saturated side chains with at least 18 carbon atoms for lowering the pour point of waxy fuel oil is known. These are e.g. homo- or copolymers of alkyl esters of unsaturated mono- or dicarboxylic acids, as well as homo- or copolymers of various alkyl vinyl ethers.

DE-A-2 047 448 describes the addition of a mixture consisting of polyvinyl ethers and ethylene-vinyl acetate copolymers to paraffin-based crude oils.

EP-A-360 419 describes middle distillates containing polymers of vinyl ethers with hydrocarbon residues with 1

to 17 carbon atoms. As comonomers are mentioned, among others respectively alkyl acrylates and methacrylates. In the examples, however, only polymers of alkyl vinyl ethers with up to 4 carbon atoms in the side chain are described. These Cx to C4 vinyl ethers are copolymerized with respectively maleic and fumaric acid derivatives. Examples of copolymers with acrylic acid derivatives are not indicated. The relevant additives can be used together with other flow-improving agents.

However, when it comes to the agents' effect as cold flow improvers in middle distillates, these polymers are not satisfactory.

The task is therefore to find additives that show a better effect as cold flow improvers for middle distillates.

Accordingly, it was now found that petroleum middle distillates containing small amounts of A known ethylene-based flow improvers and B copolymers which to an extent of at least 70% by weight consist of one or more monomers of both formula I and formula II

where

R<1> means hydrogen or methyl,

R<2> means C8- to C18-alkyl, and

R<3> means C18- to C28-alkyl,

meets these requirements, and this is the basis for the present invention.

The weight ratio between monomers according to formula I and monomers according to formula II lies advantageously between 10:90 and 95:5, preferably between 40:60 and 95:5, and particularly preferably between 60:40 and 90:10. The ratio between flow improver A and copolymer B is between 40:60 and 95:5, preferably between 60:40 and 95:5, and particularly preferred between 70:30 and 90:10.

The alkyl radicals R<2> and R<3> are preferably straight-chain and unbranched. However, they can contain up to 20% by weight of cyclic and/or branched components.

Examples of monomers according to formula I are n-octyl(meth)acrylate, n-decyl(meth)acrylate, n-dodecyl(meth)acrylate, n-tetradecyl(meth)acrylate, n-hexadecyl(meth)acrylate and n-octadecyl-(meth)acrylate, as well as mixtures thereof.

Examples of monomers according to formula II are n-octadecyl vinyl ether, n-eicosyl vinyl ether, n-docosyl vinyl ether, n-tetracosyl vinyl ether, n-hexacosyl vinyl ether and n-octacosyl vinyl ether, as well as mixtures thereof.

The copolymers B consist to a degree of at least 70% by weight of monomers according to the formulas I and II. In addition, they can contain up to 30% by weight of other ethylenically unsaturated monomers, such as e.g. styrene, alkylstyrenes, straight-chain or branched olefins with 2-16 carbon atoms, vinyl esters of C±- to C5-carboxylic acids, acrylonitrile, N-alkyl-substituted acrylamides, N-containing, ethylenically unsaturated heterocyclic compounds, such as vinylpyrrolidone, vinylimidazole or vinyl pyridine, hydroxyl or amino group-containing monomers such as butanediol monoacrylate, hexanediol monoacrylate, dimethylaminoethyl acrylate, diethylaminoethyl acrylate, as well as (meth)acrylic acid esters of C1 to C8 alkanols, such as e.g. methyl methacrylate, ethyl acrylate, isobutyl acrylate, as well as maleic acid, fumaric acid and itaconic acid esters of Cx- to C18-alkanols.

Examples of flow improvers A are the polymers already mentioned and described in DE-A-2 102 469 and EP-A-84 148, such as copolymers of ethylene with vinyl acetate, vinyl propionate, vinyl butyrate, vinyl pivalate, respectively. with esters of (meth)acrylic acid, which are derived from alkanols with 1-12 carbon atoms. Mixtures of several copolymers of ethylene and vinyl acetate (EP-A-261 951, Additive A), copolymers of ethylene with α-olefins (EP-A-

261 957, additive D), as well as the mixtures of terpolymers of ethylene, vinyl acetate and diisobutene with oxidized polyethylene wax specified in DE-A-3 624 147 are also suitable. Particularly preferred are copolymers of ethylene with vinyl acetate or vinyl propionate or ethyl hexyl acrylate.

The copolymers B exhibit synergistic effects together with flow improvers. Although the copolymers B alone do not show any flow-improving effect or only a small such effect, the combination of A and B surpasses the individual effect to a high degree.

The monomers according to formula I are readily available. They can e.g. is achieved using the known methods for esterification. For example, a solution of (meth)acrylic acid and an alkanol or a mixture of different alkanols is heated in an organic solvent while adding the usual polymerization inhibitors, e.g. hydroquinone derivatives, and esterification catalysts, such as sulfuric acid, p-toluenesulfonic acid or acidic ion exchangers, to boiling and removes the reaction water formed by azeotropic distillation. As vinyl ether can polymerize cationically under acidic conditions, resp. breaks down in the presence of water and acid with the formation of acetaldehyde, which destroys the radical polymerization, it is necessary for the production of the copolymers B to neutralize the catalyst acid as well as the excess of (meth)acrylic acid with e.g. amines or remove these compounds by washing the ester solution with alkaline agents and water. Particularly pure esters can be obtained by distillation of the contaminated ester solution.

Further possibilities for producing the monomers according to formula I are the reaction of (meth)acrylic acid chloride or anhydride with the appropriate alkanols, as well as the reaction known as transesterification between lower (meth)acrylic acid esters and the appropriate C8 to C18 alkanols with the addition of acidic or basic catalysts and distillative removal of the lower alkanol. Also with this production method, the ester should be oxidized to such an extent that there is no more acid present.

The vinyl ethers according to formula II can be obtained according to known methods by reacting alkanols with acetaldehyde and subsequent water splitting, or by catalytic addition of acetylene to alkanols. Particularly pure monomers can also be obtained here by distillation. In the case of vinyl ethers with more than 20 - 22 carbon atoms in the alkyl part, it is technically difficult to carry out a distillation where decomposition does not take place. In such cases, purification by filtration, extraction or recrystallization is recommended to remove the catalysts.

The production of the copolymers (B) takes place according to known discontinuous or continuous polymerization methods, such as mass, suspension, precipitation or solution polymerization, and with initiation with common radical donors, such as acetylcyclohexanesulfonyl peroxide, diacetylperoxydicarbonate, dicyclohexylperoxydicarbonate, di- 2-ethylhexyl peroxydicarbonate, tert-butyl perneodecanoate, 2,2 '-azobis(4-methoxy-2,4-dimethylvaleronitrile), tert-butyl perpivalate, tert-butyl per-2-ethyl hexanoate, tert-butyl permaleinate, 2,2'-azobis(isobutyronitrile), bis-(tert-butyl peroxide) cyclohexane, tert-butyl peroxyisopropyl carbonate, tert-butyl peracetate, dicumyl peroxide, di-tert-amyl peroxide, di-tert-butyl peroxide, p- menthane hydroperoxide, cumene hydroperoxide or tert-butyl hydroperoxide, and mixtures of these with each other. Generally, these initiators are used in amounts of from 0.1 to 20% by weight, and preferably 0.2 to 15% by weight, based on the monomers.

The polymerization usually takes place at temperatures from 40 to 400°C, preferably 70 to 300°C, since when using solvents that have boiling temperatures below the polymerization temperature, it is appropriate to work under pressure. If it is not possible to work under boiling conditions, it is appropriate to carry out the polymerization under the exclusion of air, e.g. under nitrogen or carbon dioxide, as oxygen delays polymerization. By co-using redox coinitiators, such as benzoin, dimethylaniline, ascorbic acid and also soluble organic complexes of heavy metals, such as copper, cobalt, manganese, iron, nickel and chromium, the turnover can be accelerated. The amounts usually used are 0.1 to 2000 ppm by weight, preferably 0.1 to 1000 ppm by weight. When choosing initiators or initiator systems, it is appropriate to ensure that the half-life of the initiator or initiator system is less than 4 hours at the selected polymerization temperature.

In order to obtain low molecular weight copolymers, it is often appropriate to work in the presence of chain transfer agents. Suitable chain transfer agents are, for example, allyl alcohols, such as 1-buten-3-ol, and organic mercapto compounds, such as 2-mercaptoethanol, 2-mercaptopropanol, mercaptoacetic acid, mercaptopropionic acid, tert-butyl mercaptan, n-butyl mercaptan, n-octyl mercaptan , n-dodecyl mercaptan and tert.-dodecyl mercaptan, which are usually used in amounts from 0.1 to 10% by weight.

Apparatus suitable for the polymerization are e.g. ordinary stirrers with, for example, armature, blade, paddle wheel or multi-stage impulse counter-current stirrers, and for continuous production stirrer cascades, tubular reactors and static mixers.

The simplest polymerization method is mass polymerization. In this method, the vinyl aromatic compounds and monomers containing acid groups are polymerized in the presence of an initiator and in the absence of solvents. It is appropriate to mix all monomers in the desired composition and to place a small portion, e.g. about. 5 - 10%, in the reactor in advance, heat with stirring to the desired polymerization temperature and evenly dose in the rest of the monomer mixture and the initiator and possibly co-initiator as well as chain transfer over the course of 1 - 10 hours, preferably 2-5 hours. It is therefore appropriate to dose the initiator and also the co-initiator separately in the form of solutions in a small amount of a suitable solvent. The copolymer can then, together with the flow improver, be added directly to the intermediate distillate as a solidified melt or after absorption in a suitable solvent.

A continuous high-pressure process, which allows space-time yields from 1 to 50 kg of polymer per liter reactor and hour, is also suitable for the production of the desired copolymers. As polymerization equipment, e.g. a pressure boiler, a pressure boiler cascade, a pressure tube or also a pressure boiler with a downstream reaction tube which is equipped with a static mixer is used. The monomers of (meth)-acrylic acid esters and vinyl ethers are preferably polymerized in at least 2 successively connected polymerization zones. In this case, one reaction zone can consist of a pressure-resistant boiler, and the other of a static mixer that can be heated. This results in conversions of more than 99%. A copolymer of (meth)acrylic acid esters and vinyl ethers can, for example, be produced by continuously adding the monomers and a suitable initiator to a reactor or to two successively connected reaction zones, for example a reactor cascade, and removing the reaction product continuously from the reaction zone after a residence time of from 2 to 60, preferably from 5 to 30 minutes, at temperatures between 200 and 400°C. It is appropriate to carry out the polymerization at a pressure of more than 1 bar, preferably between 1 and 200 bar. The copolymers obtained have a solids content of over 99%, and can be added to the middle distillate without further treatment.

A further simple method for producing the copolymers B is solution polymerization. In solution polymerization, solvents are used in which the monomers and the copolymers formed are soluble. For this, all solvents which meet this condition and which do not react with the monomers are suitable. Examples of such are toluene, xylene, ethylbenzene, cumene, high-boiling aromatic mixtures, such as e.g. Solvesso<®>100, 150 and 200, aliphatic and cycloaliphatic hydrocarbons, such as e.g. n-hexane, cyclohexane, methylcyclohexane, n-octane, iso-octane, paraffin oils, Shellsol<®>TD, T and K, as well as tetrahydrofuran and dioxane, tetrahydrofuran and dioxane being particularly suitable for obtaining low molecular weight copolymers. When carrying out the solution polymerization, it is appropriate to introduce the solvent and part of the monomer mixture in advance (e.g. approx. 5 - 20%), and then dose the rest of the monomer mixture together with the initiator and possibly co-initiator, chain transfer and solvent. The monomers can also be added individually and at different rates. This is recommended for monomers with greatly different reactivity, which is the case with (meth)acrylates and vinyl ethers, and if a particularly even distribution of the less reactive vinyl ether is desired. In this case, the less reactive monomer is added faster and the more reactive monomer more slowly. It is also possible to place the entire amount of one monomer, preferably the less reactive vinyl ether, in the reaction vessel and only add the (meth)-acrylate. Finally, it is also possible to place all the monomers and the solvent in the reaction vessel and only add the initiator and possibly the co-initiator and the chain transfer

("rate" operation). When carrying out this method on a larger scale, however, problems may arise with removing the heat so that this method should only be used with a low concentration of the monomers to be polymerised. The concentration of the monomers to be polymerized is between 20 and 80% by weight, preferably between 30 and 70% by weight. The solid copolymer can be easily recovered by evaporation of the solvent. However, it is appropriate for the polymerization to choose a solvent that is compatible with the middle distillate, so that the polymer solution can be added directly to the middle distillate. Solution polymerization is the preferred form of production for the copolymers of (meth)acrylic acid and vinyl ethers.

In the technique, it is necessary that the additives according to the invention, consisting of a flow improver A and a copolymer B, are available in an easily manageable form. For this purpose, the polymers A and B should be present together in the form of one concentrate, because the use of two concentrates - one of each of the polymers A and B - makes handling difficult. Due to the possible incompatibility between the polymers A and B, phase separation can occur when the two polymers are mixed together in a common solvent. This can possibly be suppressed with the help of suitable solvents and/or additives. Suitable is e.g. alkanols, such as iso-butanol, n-hexanol, 2-ethylhexanol, iso-decanol and adducts of these with ethylene oxide, propylene oxide and/or butylene oxide, alkylphenols and adducts of these with ethylene oxide, propylene oxide and/or butylene oxide, as well as half-esters or diesters of dicarboxylic acids with alkanols or (oligo)alkylene oxide half ethers, such as mono- or dibutyl phthalate, mono- or di-2-ethylhexyl phthalate or di(2-methoxyethyl) phthalate.

A further method to avoid possible phase separation consists in grafting copolymer B at least partially onto the flow improver. For grafting, the mass or solution polymerization is preferably used. The polymerization may take place according to a "batch" or batch process. In the "batch" method, the entire amount of flow improver A on which the grafting is to be carried out is placed in the reaction container together with the monomer, and initiator, as well as possibly coinitiator and chain transfer agent are dosed. In the addition method, the entire quantity of flow improver A to be grafted onto, possibly together with part of the monomer, is placed in the reaction vessel, and the rest of the monomers, initiator, and possibly coinitiator and chain transfer are dosed to.

As already mentioned, it is not necessary to graft the copolymer B onto the entire proportion of flow improver A. For example, at a ratio A : B of 90 : 10, due to space-time exchange, the copolymer B is grafted only on a proportion of 2 to 20% by weight of the total amount of A. At a ratio of A : B of 40 : 60, however, a proportion of 30 - 100% by weight of the total amount of A is grafted.

It is also not necessary to graft the copolymer B completely onto a part of the flow improver A. This is in all cases difficult, as a seed yield of 100% is not usually achieved, so that in the described concentrates next to graft polymers and unreacted or admixed flow improver A cannot also be grafted copolymer B.

The K values [according to H. Fikentscher, Cellulosechemie, vol. 13, pp. 58-64 and 71-74 (1932)], determined in a 2% (w/v) xylene solution of the copolymers B, lie between 10 and 50, preferably between 10 and 40 and particularly preferably between 13 and 30. The particularly preferred range corresponds to molecular weights between approx. 5,000 and 25,000 g/mol (number average values, determined by gel permeation chromatography against polystyrene standards).

Additives A and B according to the invention are added together to the petroleum middle distillates in quantities of 50 - 5,000 ppm, preferably 100 - 2,000 ppm.

The intermediate distillates according to the invention, which contain small amounts of a flow improver A and a copolymer B, may, depending on the intended use, also contain other additives or additives, such as dispersants, anti-foam additives, corrosion protection agents, antioxidants, dyes, e.g.

The invention shall be explained with the help of the following examples: Preparation of the copolymers B according to the invention Example 1

In a reactor equipped with a stirrer, heating and addition device, 144 g of lauryl acrylate, 16 g of n-octadecyl vinyl ether, 0.16 g of 2-mercaptoethanol, 65 mg of triethylamine and 69 g of toluene were heated to 100°C in a gentle stream of nitrogen with stirring , and over the course of 4 hours a solution of 0.64 g of tert-butyl per-2-ethylhexanoate in 38.2 g of toluene was added evenly. The mixture was then reheated for another 1 hour at 100°C and diluted with approx. 54 g of toluene. A clear, yellowish, approx. 50% by weight solution. The K value of the polymer was 24.8.

Example 2

In a reactor according to example 1, 144 g of lauryl acrylate, 16 g of n-octadecyl vinyl ether and 68.6 g of Solvesso® 150 (high-boiling aromatic mixture from the company Esso) were heated to 80°C in a weak stream of nitrogen with stirring and during 4 hours evenly added a solution of 0.48 g azoisobutyronitrile in 30 g Solvesso<®>150. A solution of 0.16 g of azoisobutyronitrile in 8.5 g of Solvesso<®>150 was then added, reheated for 2 hours at 80°C and diluted with 53.5 g of Solvesso<®>150. A clear, colorless, viscous, approx. 50% by weight solution. The K value of the polymer was 2 8.3.

Example 3

In a reactor according to example 1, 29.2 g of lauryl acrylate, 7.3 g of n-octadecyl vinyl ether and 55.4 g of Shellsol<®>K

(high-boiling n- and iso-paraffin mixture from the company Shell)

heated to 100°C in a weak stream of nitrogen with stirring and over the course of 2 hours a solution of 102.1 g of lauryl acrylate, 26.0 g of n-vinyl octadecyl ether and 14.6 g of Shellsol<®>K, and over the course of 4 hours a solution of 0.5 g of tert.-butyl-per-2-ethyl hexanoate in 25 g of Shellsol<®>K. Then it was

added a solution of 0.17 g of tert-butyl per-2-ethyl hexanoate in 4.2 g of Shellsol<®>K, reheated at 100°C for 1 hour and diluted with 67.5 g of Shellsol<®>K. A clear, colorless, slightly viscous polymer solution was obtained. The K value of the polymer was 19.6.

Examples 4-18 were prepared according to methods which corresponded to the methods in example 3.

LA Lauryl acrylate = n-alkyl acrylate mixture, prepared from a commercial fatty alcohol mixture, consisting of a maximum of 1.5% by weight n-decanol, 51 - 57% by weight n-dodecanol, 41 - 47% by weight n-tetradecanol and

max. 1.5% by weight n-hexadecanol.

A8-18 n-Alkyl acrylate mixture, prepared from a fatty alcohol mixture of the usual commercial type, consisting of 5 - 8% by weight n-octanol, 5-7% by weight n-decanol, 44 - 50

wt% n-dodecanol, 14-20 wt% n-tetradecanol, 8-10 wt% n-hexadecanol and 8-12 wt% n-octadecanol.

V18 n-Octadecyl vinyl ether

V1822 n-Alkylvinyl ether mixture, prepared from a commercial fatty alcohol mixture, consisting of 41-43% by weight n-octadecanol, 9-13% by weight n-eicosanol and

43 - 46% by weight n-docosanol.

V20+ n-Alkylvinyl ether mixture, prepared from a commercial grade fatty alcohol mixture, consisting of a maximum of 6% by weight n-octadecanol, 40 - 60% by weight n-eicosanol, 23 - 35% by weight n-docosanol, 10 - 18% by weight n- tetracosanol and 2-8% by weight n-hexacosanol.

Vpr Vinyl Propionate

SK Shellsol<®>K

V i-4 Isopropyl vinyl ether

C-hex Cyclohexane

TBPO tert-butyl per-2-ethyl hexanoate

AIBN Azoisobutyronitrile

Example 19

(Comparison test analogous to EP-A-360 419, example C4)

In a reactor according to Example 1, 51.4 g (about 0.1 mol) of di-n-tetradecyl fumarate and 10.0 g (0.1 mol) of n-butyl vinyl ether were heated to 90°C with a weak stream of nitrogen and stirring. Then 0.4 g of AIBN was added and polymerized for 6 hours, with a further 0.1 g of AIBN being added every hour. A viscous, 99% by weight polymer solution with a K-value of 11.5 was obtained.

Example 2 0

(Comparison test analogous to DE-A-1 645 785)

In a reactor according to example 1, 1.5 g of boron trifluoroetherate was placed in 187.5 g of toluene and at 30°C a solution of 90 g of n-octadecyl vinyl ether in 22.5 g of toluene was added evenly over the course of 1 hour; it was stirred for another 10 minutes, and the polymerization was terminated by the addition of 5 ml of methanol. The polymer solution was precipitated in acetone and dried in vacuum. The K value was 15.4.

Examples 17 - 20 are comparative examples and not part of the present invention.

Example 21

Grafting of lauryl acrylate and n-octadecyl vinyl ether on a flow improver consisting of 60% by weight ethylene and 40% by weight vinyl propionate with an average molecular weight of approx. 2,500 (determined by vapor pressure osmometry) = Fl(A).

In a reactor according to example 1, 215 g of the flow improver Fl(A) and 86 g of Shellsol<®>K were heated to 100°C in a weak stream of nitrogen and with stirring. To this was added 86 g of a mixture of 516 g of lauryl acrylate, 129 g of n-octadecyl vinyl ether and 73.1 g of Shellsol<®>K, and the rest of the mixture was added evenly over the course of 2 hours. At the same time, 1.94 g of tert-butyl per-2-ethyl hexanoate, dissolved in 64.5 g of Shellsol<®>K, was added evenly over the course of 4 hours. Then a solution of 0.65 g of tert.-butyl per-2-ethylhexanoate in 21.5 g of Shellsol<®>K was added, it was reheated for 1 hour and diluted with 615 g of Solvesso<®>150 (high-boiling aromatic mixture from Esso). An approx. 50% by weight, slightly cloudy polymer solution with K-value 25.2. Of this, 80 g were mixed with 110 g Fl(A) and 110 Solvesso® 150 at 60°C. At room temperature, a cloudy mixture was obtained which consists of a total of approx. 80 parts flow improver Fl(A) and 20 parts copolymer B. The mixture is stable for more than 10 weeks at room temperature.

Application examples

In the following means:

Fl = flow improver, esp

Fl(A) ethylene/vinyl propionate (with approx. 40% by weight vinyl propionate) with an average molecular weight of approx. 2,500

(determined by vapor pressure osmometry)

Fl(B) ethylene/vinyl propionate (with approx. 30% by weight vinyl propionate) with an average molecular weight of approx. 2,500 Fl(C) ethylene/vinyl acetate (with approx. 30% by weight vinyl acetate)

with an average molecular weight of approx. 2,500

The flow improvers Fl(A), Fl(B) and Fl(C) are products of the usual commercial type, e.g. The Keroflux<®->brands from the company BASF.

As middle distillates, fuel oils and diesel fuels of West German refinery quality of the type usually available in the trade were used. They are designated as middle distillates I, II, III and IV.

Test method:

The "Cold Filter Plugging Point" ("Cold Filter Plugging Point"), CFPP) was examined according to DIN 51428. The results are summarized in the following table.

As the above-mentioned examples show, the usual flow improvers Fl(A), Fl(B) and Fl(C) only work unsatisfactorily in middle distillates. Addition of only the copolymers according to the invention rather leads to a deterioration of the CFPP of the middle distillates. The synergistic effect of flow improvers and copolymers according to the invention is made clear by means of examples 7-40.

As the comparative examples show, neither the polyacrylate (Example 42) nor the polyvinyl ether (Example 45) together with the usual flow improvers cause a satisfactory lowering of the CFPP. Also the copolymers with short-chain vinyl ethers described in EP-A-360 419 (examples 43 and 44) proved to be ineffective in the above-mentioned oils, while the copolymers according to the invention of alkyl acrylates, long-chain vinyl ethers and possibly a further monomer in combination with Fl( A), Fl(B) or Fl(C) significantly lowered CFPP at low dosage.

Claims (5)

1. Petroleum middle distillates with improved flow properties in cold, characterized in that they contain 50-5000 ppm of a mixture of A) common ethylene-based flow improvers and B) copolymers, consisting of at least 70% by weight of one or several monomers of formula I and formula II, where R<1> stands for hydrogen or methyl, R<2> for C8- to C18-alkyl, and R3 for C18- to C28-alkyl, the weight ratio between A and B being 40:60 to 95:5. 2. Petroleum middle distillates according to claim 1, characterized in that the quantity ratio between the monomers according to formula I and the monomers according to formula II in the copolymers B is 10:90 to 95:5. 3. Petroleum middle distillates according to claim 1, characterized in that the alkyl substituents in the copolymers B are straight-chain and unbranched. 4. Petroleum middle distillates according to claim 1, characterized in that the copolymers contain up to 30% by weight of other ethylenically unsaturated monomers. 5. Petroleum middle distillates according to claim 1, characterized in that copolymers of ethylene with vinyl acetate, vinyl propionate or ethylhexyl acrylate are used as common flow improvers.