EP0007590B1 - Middle distillates of petroleum, suitable as diesel fuel or as light heating oil, and with improved filtration properties - Google Patents

Description

The invention relates to middle distillates of petroleum, which are suitable as diesel fuels or light heating oil with improved filterability at temperatures above and below the cloud point and improved flow behavior. In addition to the copolymers known per se, monomers are added as solubilizers.

So-called middle distillates, such as gas oils, diesel oils or heating oils, such as those obtained from petroleum by distillation, have different paraffin contents depending on the origin of the crude oil. At low temperatures, paraffin wax is excreted in the form of platelet-shaped crystals, some of which also contain oil. As a result, the flowability of the petroleum distillate - fuels is significantly impaired. This leads e.g. in the case of diesel fuel, for clogging of filters and thus for interrupting or not evenly supplying the fuel to the combustion units, such as engines or jet engines. Malfunctions in heating oils can also occur in winter if such precipitations occur due to low temperatures. However, the pumping of middle distillates through pipelines over long distances can also be affected in winter by the precipitation of wax crystals.

It has long been known to add various additives as modifiers for crystal growth to petroleum distillate fuels, in particular middle distillates.

Such additives change the size and shape of the wax crystals so that the oil remains flowable even at low temperatures. Such additives are bsw under the name "pour point improver". "Flow improver" or "pour point improver" known. For this purpose e.g. according to US Pat. No. 2,189,924 condensation products also use chlorinated paraffins and naphthalene. In order to be sufficiently successful, however, such condensation products must be used in relatively large amounts. In addition, efforts have recently been made to switch off chlorinated hydrocarbons for this purpose as far as possible in order to avoid corrosive gases which are produced during combustion.

The use of oil-soluble or petroleum distillate-dispersible copolymers as pour point and / or flow improver is also well known (see e.g. U.S. Patent 38 32 150).

The polymers previously proposed as pour point and flow improvers now have the described properties as modifiers or growth inhibitors for paraffin crystals in practical use at low temperatures, ie temperatures below the cloud point, but in many cases they show up to temperatures above the cloud point considerable disadvantages at about plus 30 ° C. This applies in particular, for example, to copolymers of ethylene and fatty acid vinyl esters or ethylene and acrylic acid esters, which are prepared by known large-scale processes by solvent-free polymerization.

In particular, the diesel engines used in practice are equipped with filter materials of different pore sizes depending on the application. An unimpeded fuel supply must be guaranteed at all times, even under extreme conditions. In the military sector in particular, diesel engines have very narrow-pore fuel filters with pore sizes of 2 to 40 µ. Multi-layer filters made of materials with very different pore sizes for coarse and fine filtration are also frequently used.

Extensive tests have shown that copolymers of e.g. Ethylene and fatty acid vinyl esters, as well as ethylene and acrylic acid esters, which are produced by the known industrial processes, always contain small amounts of higher molecular weight polymerization products which are partly insoluble in petroleum distillate fuels and fuels.

These higher molecular weight polymerization products arise as by-products in the radical polymerization of ethylene and e.g. Fatty acid vinyl esters or acrylic acid esters. Depending on the type and amount of the higher molecular weight polymerization products, insoluble deposits can occur in the petroleum distillate fuels and fuels even at temperatures above the actual cloud point (i.e. the start of the separation of paraffin wax), which already clogs the narrow-pored filter materials being able to lead.

The object was therefore to change the known production processes for copolymers or to propose suitable measures in order to reduce or completely eliminate filter blockages due to small proportions of higher molecular weight polymerization products.

In the known manufacturing processes for copolymers of ethylene and e.g. Fatty acid vinyl esters or acrylic acid esters are e.g. according to the principle of solution or suspension polymerization under pressure at elevated temperatures. In these processes, after the reaction has ended, the solvent and the unreacted monomers are separated off by distillation, as is e.g. is described in German Patent 25 15 805.

In other processes for the preparation of the copolymers, one works, for example, completely without solvent at pressures of 500 to 2,000 bar and temperatures of, for example, 100 to 350 ° C., with the unreacted ethylene and the unreacted vinyl vinyl ester or acrylic acid ester being released by relaxation at the end of the reaction of the reactor are separated. Especially with the Solvent-free polymerization processes can lead to the formation of fractions that are insoluble in petroleum distillate fuels.

It has now been found that the solubility of the copolymers of ethylene and fatty acid vinyl esters or ethylene and acrylic acid esters produced by known processes in petroleum distillate fuels and fuels can be considerably improved by small amounts of the monomeric fatty acid vinyl esters or acrylic acid esters. The monomers acting as solubilizers essentially cause swelling of the waxy high molecular weight copolymers, which means that in practical use, i.e. the addition of these copolymers to petroleum distillate, fuels and fuels a strong improvement in the solubility for the copolymer and thus a considerable improvement in the filterability for the petroleum distillate is achieved at temperatures above the cloud point.

Accordingly, the invention consists in middle distillates of petroleum, which are suitable as diesel fuel or light heating oil, with improved fileability and improved flow behavior with a content of small amounts of modifiers in the form of copolymers, selected from the group of binary copolymers of ethylene and a vinyl ester of a C ₂ or C ₃ alkane carboxylic acid and binary copolymers of ethylene and a C _{1 to} C _s alkyl ester of a C ₃ or C ₄ alkene monocarboxylic acid, the copolymers comprising 60 to 95% by weight of ethylene and 5 to 40% by weight of the olefinically unsaturated ester polymerized in and have a viscosity in the melt, measured according to DIN 51 562 (ASTM D 445) at 120 ° C of 100 to 5000 mm ² / sec, which are characterized in that the middle distillates in addition to the copolymers 0.1 to 10 Vol.%, Based on the copolymer, the monomeric vinyl esters of a C _z - to C ₃ -alkane carboxylic acid or the monomeric C ₁ - to C _s -alkyl esters of a C ₃ - or contain C _4- alkenecarboxylic acid.

The monomers are preferably present in amounts of 0.5 to 5% by volume, based on the copolymer.

According to the invention, preference is given to using such binary copolymers which are obtained by polymerizing ethylene and vinyl acetate or alkyl acrylates without solvents at pressures from 500 to 2,000 bar and temperatures from 100 to 350 ° C., preferably 200 to 300 ° C., and the molecular weights from 500 to 10,000, preferably 1,000 to 5,000. The radical copolymerization can be started easily with air, but also with suitable peroxidic initiators or controlled by adding suitable regulators (e.g. aliphatic aldehydes).

After the polymerization has ended, the unreacted ethylene and the vinyl acetate and low-boiling oligomers are preferably separated off by depressurizing the reactor and the solvent-free monomers are subsequently added to the ethylene-free copolymer.

The monomers are preferably subsequently added to the copolymer. However, it is also possible to cool the polymerization mixture to temperatures below the boiling point of the monomers before the expansion, so that, apart from ethylene, the unreacted monomers do not or only partially evaporate during the expansion. A combination of both measures is also possible.

The monomers contained in the copolymers include, in particular, vinyl esters of carboxylic acids with 1 to 4 carbon atoms, preferably vinyl acetate with vinyl propionate, and acrylic and methacrylic acid esters of C ₁ to C _s alkanols, in particular butyl, isobutyl, 2-ethylhexyl and lauryl acrylate Consider.

Particularly suitable esters of maleic acid are dimethyl maleate or dibutyl maleate.

As already mentioned, the monomers serving as solubilizers are generally added alone or in combination with one another to the copolymers prepared by the known processes, which are generally of a very tough consistency and, for example, viscosities in the range from 100 to 5000 mm ² / s at 120 ° C.

In order to lower the viscosity and make it easier to use, the copolymers are usually dispersed in suitable solvents which have little or no solubility-improving effect; higher-boiling, highly aromatic products, e.g. contain polyalkylated benzenes, toluenes, xylenes, ethylbenzenes and optionally also higher alkylated naphthalenes. Another frequently used method is the dispersion of the copolymeric waxes in suitable petroleum distillates. Heavy gasoline, petroleum, diesel oil or gas oil fractions are used here in particular.

The monomers serving as solubility improvers can therefore be added to the copolymer waxes themselves, but also to the dispersions of these waxes in suitable dispersants; elevated temperatures e.g. 30 to 90 ° C and thorough mixing by stirring or pumping are advisable.

When using polymerization-sensitive unsaturated esters, such as vinyl acetate or acrylic acid esters or unsaturated oligomers, it is advisable to stabilize them by adding commercially available polymerization inhibitors in order to avoid subsequent polymerization of these components after they have been added as solubilizers. Typical polymerization inhibitors are, for example, polyalkylated phenols, nitrogen-containing aromatic heterocycles or alkylated aromatic aminophenols or substituted or unsubstituted phenylenediamines. The minimal discoloration of the petroleum distillates caused by the inhibitors is insignificant.

Depending on the molecular weight of the copolymer waxes used or the density and composition of the dispersants and the proportion of the copolymer waxes to be dispersed, the polymer waxes may settle in the dispersions. Especially when producing dispersions with a low proportion (for example 1 to 50% by weight) of copolymeric ethylene / fatty acid vinyl esters or ethylene / acrylic acid esters, the dispersions obtained are not as stable as with higher proportions (for example over 50% by weight) on copolymeric wax. It has now been found, in addition, that the above-described additions of monomers to copolymeric waxes in the stated concentrations also have a thickening effect for the dispersions of the copolymeric waxes.

By adding the monomers to the dispersions of the copolymeric waxes, the stability of the dispersions is also increased considerably in many cases. The copolymeric waxes do not settle or only to a very small extent.

From US-PS 36 27 838 it is known that a particularly good pour point improvement is obtained if the polymerization is carried out so that free vinyl acetate is always present, even at the end of the reaction. However, column 2, lines 29 and 30 show that the monomers are removed during the workup ("The product is stripped free of solvent and unreacted vinyl acetate under vacuum"). Accordingly, a product freed from monomers is used according to this patent specification, while according to the teaching of the present invention, the monomers are left in or added to the products.

To explain the invention, numerous filtration tests are given below, the viscosities of a large number of dispersants being measured with the addition of the monomers.

A suitable filtration test for petroleum distillate fuels and fuels that contain copolymeric flow improvers is carried out as follows:

Purpose of the determination

Testing the filterability of petroleum distillates containing copolymeric flow improvers at temperatures above the cloud point.

Brief description of the procedure

A certain amount of the petroleum distillate to be examined (e.g. kerosene, gas oil, diesel fuel, heating oil EL according to DIN 51 601) is filtered in a water jet vacuum in portions of 100 ml each through a membrane filter. The flow times are measured per 100 ml.

Equipment and chemicals

• 5 000 ml feeding bottle
• Water jet pump
• Paper pleated filter
• Blue band filter No. 589 ³ 0 15 cm
• 5 000 ml glass bottle
• 100 ml measuring cylinder
• Sartorius membrane filter attachment, type SM 16307
• Sartorius membrane filter type SM 11301 pore size 8 µ, n-pentane

Filtration

The selected petroleum distillate is filtered through a paper pleated filter to remove coarse suspended matter and dirt. The sample, which has been pre-cleaned in this way, is filtered in a water jet vacuum through a blue band filter.

A certain amount of flow improver dispersion or cow axis is mixed into 3,000 ml of the petroleum distillate pretreated in this way at room temperature. The petroleum distillate modified in this way is filtered through a membrane filter in portions of 100 ml each. The throughput time for 100 ml of liquid is measured and graphically plotted against the filtered volume. The time axis is divided logarithmically.

Evaluation of the determination

Method A: Comparison of the filtration curves obtained in this way.

Method B: Quantitative determination of the higher molecular proportions of copolymer wax insoluble in petroleum distillate.

Before filtration, the membrane filter is washed with 100 ml of n-pentane, dried and weighed. After filtration of the petroleum distillate to be examined, the membrane filter is washed again oil-free with 100 ml and n-pentane, dried and weighed out. The amount of higher molecular weight residue which is insoluble in petroleum distillate is given in% by weight based on copolymer wax.

The method described above allows the investigation of both unmodified Petroleum distillates, as well as petroleum distillates, which contain copolymeric waxes or dispersions or solutions of these waxes. Preliminary tests according to Method A with filters of different pore sizes ensure that when using a membrane filter with a pore size of 8 _j u, a distinction can be made between copolymer waxes with different contents of higher molecular weight.

In addition, method A ensures that the filtration curves of petroleum distillate fuels and fuels that do not contain copolymeric waxes do not show an increase in the filtration time with increasing filtration volume. The filtration time per 100 ml of filtered product depends only on the viscosity or density of the petroleum distillate. According to method A, petroleum distillates not modified with copolymer waxes do not indicate filter clogging.

The following examples illustrate the invention using the filtration test described above (methods A and B).

For copolymer waxes with extremely high proportions of higher molecular weight compounds, which can usually cause more filter blockages, the above filtration test can be varied by filtering smaller volumes (e.g. 20 ml portions). In this way it is possible to distinguish more clearly between very similar cow axes, which all result in a very bad filtration curve according to method A.

In the case of copolymer waxes with extremely low proportions of high molecular weight compounds, the membrane filter only clogs at higher throughputs of modified petroleum distillate. (e.g. 10 to 1001). In this case, larger sample volumes of 500 or 1,000 ml are recommended for the filtration test.

The effectiveness of the addition of monomers is retained at constant temperature even after the dispersions of copolymeric waxes have been stored for a long time.

However, the temperature is essential for the filtering behavior of petroleum distillates modified with flow improvers. It could be shown that the solubility of the small amounts of higher molecular weight compounds contained in the copolymer waxes is a function of the temperature.

In filtration tests according to method A, with decreasing filtration temperatures of the modified petroleum distillate for the same copolymer wax, the filtration curves are steeper and, according to method B, a correspondingly larger amount of higher molecular weight compounds in the copolymer wax which are insoluble under these conditions.

Nevertheless, the strong solubilizing effect of the monomers to be used according to the invention is retained even at lower temperatures; if necessary, only the amounts of the solubilizers added to the copolymer wax need to be increased.

The solubilizing effect of the monomers extends to temperatures from far above the natural cloud point of the petroleum distillates (e.g. 30 ° C) to far below the cloud point (e.g. -40 ° C). At or below the cloud point, the separation of paraffin crystals begins with petroleum distillates as the temperature continues to decrease. By adding ethylene / fatty acid vinyl esters or ethylene / acrylic acid esters as flow improvers, these paraffin crystals are modified and their growth is disturbed; the 61st is cloudy due to excreted paraffins, but remains flowable and pumpable. When using the copolymeric flow improvers, which still contain certain amounts of higher molecular weight polymers, these higher molecular weight portions become increasingly insoluble as the temperature decreases, so that they can precipitate with the paraffins either above or below the natural cloud point of the petroleum distillates and lead to disturbances in the Cold behavior of petroleum distillates. In these cases, filter and valve blockages are therefore not caused by the wax crystals modified in their crystal form below the cloud point, but rather above the cloud point by the precipitation of insoluble, higher molecular weight fractions in the copolymeric flow improver. For the perfect effectiveness of the copolymeric flow improvers, it is therefore necessary to keep the proportions of the higher molecular weight compounds which are always present due to the polymerization process as good as possible in solution. This is done by adding the solubilizers according to the invention.

example 1

Table 1 shows the physical data of various copolymer waxes based on ethylene / vinyl acetate. The table also shows the proportions of monomeric vinyl acetate still present in the copolymer waxes.

The cowaxes listed in Table 1 were adjusted as 50% dispersions in various dispersing agents and the filtering behavior of various gas oils after addition of 500 ppm by volume of the dispersions which act as flow improvers was investigated using Method A. The higher molecular weight components present in the 50% dispersions and determined by Method B are summarized in Table 2. 1 and 2 show the filtration curves of the cow axis from Table 2 determined according to method A, where here and in the following t denotes the filtration time in seconds and v the filtration volume in ml.

As Table 2 and FIGS. 1 and 2 show, all of the co-axes investigated in the dispersants used have poor filterability (according to method A) and correspondingly large proportions of higher molecular weight products according to method B. The following examples show the mode of action of the solubilizers claimed.

Example 2

The Cowachs No. 1 already mentioned in Table 1 and FIG. 1 was added as a 50% dispersion in C ₄ -oxoalcohol residue as a dispersant with the solubilizers according to the invention. The dispersions thus improved were added to a diesel fuel in an amount of 500 ppm by volume and investigated according to methods A and B.

The effect of the solubilizers on the amount of the higher molecular weight residue contained in Cowachs No. 1 is shown in Table 3. The residues were determined by Method B. 3 shows the filtration curves belonging to table 3.

Example 3

Cowachs No. 3 mentioned in Table 1 was adjusted as a 50% dispersion in C ₄ oxo alcohol residue. As shown in Table 2, the filtration test according to method B is one Amount of 3.6% higher molecular weight found. Curve 5 in Fig. 1 and A in Fig. 4 shows correspondingly poor filtering behavior (according to method A). When 1% by weight of vinyl acetate is added to the 50% dispersion of Cowachs No. 3 in the C _4- oxo alcohol residue, after addition of 500 ppm by volume of the dispersion which has been improved in this way, EL becomes a heating oil (according to DI N 51601) and the filter test found only 0.34% higher molecular weight by method B. Curve B in Fig. 4 shows the filtration curves according to method A.

Example 4

A copolymer wax made of ethylene and vinyl acetate with a vinyl acetate content of 28.5% by weight and a viscosity (120 ° C) of 210 mm ² / s; an average molecular weight of 1,880 and a content of 0.75% by weight of monomeric vinyl acetate (based on the copolymer) was adjusted as a 50% dispersion in a C ₄ -oxo alcohol residue.

The filtration test according to method A was carried out extra easily (according to DIN 51 601) after adding 500 ppm by volume of the 50% dispersion of the copolymer wax in C _4- oxo alcohol residue to a commercially available heating oil. Filtration curve No. 1 shown in FIG. 5 was obtained.

The dependency of the solubilizing effect on the content of monomeric vinyl acetate was subsequently shown by increasing additions of further amounts of monomeric vinyl acetate, likewise in the filtration test according to method A.

5 shows the dependence of the solubilizing action on the content of monomeric vinyl acetate in the dispersion in the filtration test according to method A. In filtration curves 2, 3, 4 and 5, the 50% dispersion of the copolymer wax was additionally 0.25, 0.50, 1.0 and 3.0% by weight of monomeric vinyl acetate were added.

Example 5

A copolymer wax made from ethylene and vinyl acetate by continuous polymerization without solvent at 220 ° C and 1,500 bar with a content of 27.2% by weight of vinyl acetate and a viscosity at 120 ° C of 365 mm ² / s and an average molecular weight of 2 230 and a residual monomeric vinyl acetate content of 0.55% by weight (based on the copolymer) is adjusted as a 40% dispersion in petroleum.

A filtration test is carried out according to methods A and B with the addition of 800 vol.ppm of the 40% dispersion to a commercially available heating oil extra light (according to DIN 51 601). The filter test is carried out immediately, as well as after 8 days and 30 days of the additive heating oil. The associated filtration curves 1, 2 and 3 in FIG. 6 and, according to method B, a proportion of higher molecular weight compounds of 9.5 (curve 1), 9.7 (curve 2) and 10.1% by weight (based on cowachs) are obtained. . Further filtration tests according to methods A and B are carried out after an amount of 0.5% by weight of monomeric vinyl acetate had previously been added to the dispersion. 800 vol.ppm of this improved flow improver dispersion were also added to the same heating oil.

The filter test of the heating oil additized in this way also takes place immediately or after 8 days and 30 days.

The associated filtration curves 4, 5 and 6 in FIG. 6 and, according to Method B, fractions of higher molecular weight compounds of 0.38% (curve 4) and 0.45% (curves 5 and 6) are obtained.

Example 6

• a) A copolymer wax prepared from ethylene and 2-ethylhexyl acrylate by continuous polymerization without solvent at a temperature of 245 ° C and a pressure of 1,500 bar with a content of 46.2% by weight of 2-ethylhexyl acrylate, a viscosity at (120 ° C) of 252 mm ² / s and an average molecular weight of 2,440 was stabled as a 58% dispersion in petroleum, heated to 80 ° C. for one hour with stirring, cooled to room temperature and subjected to a filtration test according to methods A and B. A commercial heating oil (extra light) was mixed with 500 ppm of the 58% ionic dispersion. The filtration test was repeated after 24, 48, 108 and 240 hours at room temperature. The amount of polymeric residues and the associated filtration curves are shown in Tables 4 and 7.
• b) 1% by weight of vinyl acetate (stabilized with 0.1%, 2.6 di-tert-butyl-p-cresol) was then added to the 58% dispersion, and the mixture was heated to 80 ° C. with stirring, to room temperature cooled and the filtration test A and B after addition of 500 ppm of the dispersion mixed with vinyl acetate after 24, 48, 108 and 240 hours at room temperature. The amounts of polymeric residues and the associated filtration curves are shown in Table 4 and Fig. 7. Therein, t filtration time in seconds, v filtration volume in ml, curves 1, 2, 3, 4 according to (a) after 24, 48, 108 and 240 Hours, curves 5, 6, 7, 8 according to (b) after 24, 48, 108 and 240 hours.

• Dispersion: 58% Wachs in Petroleum
• Dosierung: 500 ppm Dispersion in Heizöl (EL)
  

Effect of vinyl acetate as a solubilizer in a flow improver dispersion of a copolymer wax made of ethylene and 2-ethylhexyl acrylate

• Dispersion: 58% wax in petroleum
• Dosage: 500 ppm dispersion in heating oil (EL)
  

Example 7

In order to show the effect of the monomer addition when the filtration test was carried out near the cloud point of the modified petroleum distillate, the copolymer wax No. 1 described in Table 1 is adjusted as a 50% dispersion in an oxo alcohol residue from the butanol synthesis. The dispersion is heated to 80 ° C. with stirring, allowed to cool to room temperature and, after a standing time of 36 days at room temperature, used for filter tests A and B. For this purpose, a commercial heating oil (extra light) from the cloud point -2 ° C is mixed with 500 ppm by weight of the dispersion and cooled to 0 ° C in the course of 35 minutes. The oil thus obtained is filtered according to method B. A polymeric residue of 130 mg (= 26.2% based on the wax content in the dispersion) is obtained.

If the same test is carried out after the addition of 1% by weight of vinyl acetate (based on wax and stabilized with 0.1%, 2,6-di-tert-butyl-p-cresol) to the dispersion, the following is obtained: Method B only a polymeric residue of 44.2 mg (= 8.8%).

If the amount of vinyl acetate is increased to a total of 3% by weight and the same procedure is followed, only 5.5 mg (= 1.1%) of polymeric residue is obtained.

Example 8

• a) Eine Durchschnittsprobe des Wachses mit einem Gehalt an monomerem Vinylacetat von 0,6% wird dann als 50 %ige Dispersion in einem Oxoölrückstand aus der Butanolsynthese eingestellt. Man versetzt einen handelsüblichen Dieselkraftstoff mit einem cloud-point von -2°C bei Raumtemperatur mit 500 Gew.-ppm dieser Dispersion, kühlt die Mischung im Verlauf von 35 Minuten in einem Kühlbad auf 0°C ab und führt anschließend einen Filtrationstest nach Methode A und B durch. Es wird ein polymerer Rückstand von 37,2 mg (=₇,4 Gew.% bezogen auf den Wachsanteil in der Dispersion) erhalten.
• b) Werden der 50 %igen Dispersion 2 Gew.% Vinylacetat (bezogen auf Wachs und stabilisiert mit 0,1%, 2,6-Di-tert.-butyl-p-Kresol) zugesetzt und der oben beschribene Filtrationstest bei 0°C wiederholt, erhält man nur noch 4,1 mg polymeren Rückstand (= 0,83 Gew.% bezogen auf den Wachsanteil in der Dispersion). Die Filtrationskurven beider Filtrationsteste zeigt Fig. 8.

In a large-scale experiment, 30,000 kg of a copolymeric wax of ethylene and vinyl acetate with a content of 29.2% vinyl acetate and a viscosity (at 120 ° C) of are in a continuous polymerization plant at a temperature of 240 to 250 ° C and a pressure of 1,500 bar 247 mm ² / s and an average molecular weight of 1,940.

• a) An average sample of the wax with a content of monomeric vinyl acetate of 0.6% is then set as a 50% dispersion in an oxo oil residue from the butanol synthesis. A commercially available diesel fuel with a cloud point of -2 ° C. at room temperature is mixed with 500 ppm by weight of this dispersion, the mixture is cooled to 0 ° C. in a cooling bath over the course of 35 minutes and a filtration test is then carried out according to method A. and B through. There is obtained (referred = _7, 4 wt.% Of the wax content in the dispersion), a polymeric residue of 37.2 mg.
• b) 2% by weight of vinyl acetate (based on wax and stabilized with 0.1%, 2,6-di-tert-butyl-p-cresol) are added to the 50% dispersion and the above-described filtration test at 0 ° C. repeated, only 4.1 mg of polymeric residue are obtained (= 0.83% by weight based on the wax content in the dispersion). The filtration curves of both filtration tests are shown in Fig. 8.

Example 9

In an apparatus to be operated continuously as shown in FIG. 9, diesel oil is pumped through a commercially available fuel filter. The apparatus consists of an insulated storage vessel (B 1) with a volume of 110 I for the diesel oil, in which there is a cooling coil operated with cooling brine (s), a Bosch fuel pump (P-1) for 0-1.5 bar , a fuel filter (F), Bosch no. 1457434052, with differential pressure gauge (PI-2) and a continuous fuel flow measurement (FI). The pressure measuring points PI-1 and PI-3 as well as the temperature displays TI-1, TI-2 and TI-3 are also installed. The quantity of diesel oil pumped through the filter F is collected in the collecting vessel B-2 (volume 110 l). Pump and filter are in one with Dry ice-powered cool box to avoid temperature increases due to heat conduction and pump work.

In this apparatus, gas oils which had previously been cleaned using a paper filter were pumped through the filter F at a temperature of just above their cloud point at a flow rate of 10 l / h.

A criterion for covering the fuel filter with higher molecular weight components from the copolymeric flow improvers is the pressure increase of the differential pressure monometer PI-2.

• Kurve 1: Cowachs aus Äthylen-Vinylacetat mit 28,1 Gew.-% Vinylacetat, mittleres Molgewicht 2 160, Schmelzviskosität (120°C) 230 mm²/s, Gehalt an monomerem Vinylacetat 0,07 Gew.%, als 50 %ige Dispersion in Oxoölrückstand aus der Butanolsynthese. Dosierung der Dispersion in Dieselöl: 500 Vol-ppm - ohne weitere Zugabe von Lösungsvermittlern - Temperatur: ± 0°C.
• Kurve 2: wie 1, jedoch nach Zugabe von 0,5 Gew.% an monomerem Vinylacetat (stabilisiert), bezogen auf Cowachs.
• Kurve 3: wie 2, jedoch mit 1,0 Gew.% an monomerem Vinylacetat.
• Kurve 4: wie 2, jedoch mit 3,0 Gew.% an monomerem Vinylacetat.

The curves for the respective pressure curve (mm WS) are plotted against the test duration. The following FIG. 10, in which P denotes the pressure drop in mm of water and t the test duration in seconds, shows the results with various copolymeric ethylene-vinyl acetate waxes as flow improvers with and without the addition of monomeric vinyl acetate.

• Curve 1: Cowachs made of ethylene-vinyl acetate with 28.1% by weight of vinyl acetate, average molecular weight 2,160, melt viscosity (120 ° C.) 230 mm ² / s, content of monomeric vinyl acetate 0.07% by weight, as 50% Dispersion in oxo oil residue from butanol synthesis. Dosage of the dispersion in diesel oil: 500 vol ppm - without further addition of solubilizers - temperature: ± 0 ° C.
• Curve 2: as 1, but after adding 0.5% by weight of monomeric vinyl acetate (stabilized), based on cowachs.
• Curve 3: as 2, but with 1.0% by weight of monomeric vinyl acetate.
• Curve 4: as 2, but with 3.0% by weight of monomeric vinyl acetate.

Example 10

The Cowachs No. 1 mentioned in Table 1 and FIG. 1 was added as a 50% dispersion in C ₄ -oxoalcohol residue as a dispersant with the solubilizers according to the invention. The dispersions thus improved were added to a diesel fuel in an amount of 500 ppm by volume and investigated according to methods A and B.

The following table shows the effect of the solubilizers on the amount of the higher molecular weight residue contained in Cowachs No. 1. The residues were determined according to method B. 11 shows the filtration curves belonging to table 5.

Claims (6)

1. Middle distillates of petroleum suitable for use as diesel fuels or light fuel oil, having improved filterability and improved flow behaviour and containing small amounts of modifiers in the form of copolymers selected from the group consisting of binary copolymers of ethylene and a vinyl ester of a C₂- or C₃-alkanecarboxylic acid and binary copolymers of ethylene and a C₁- to C₈-alkyl ester of a C₃- or C_4-alkenemonocarboxylic acid, the copolymers containing 60 to 95% by weight of ethylene units and 5 to 40% by weight of units of the olefinically unsaturated ester and having a melt viscosity, measured according to DIN 51 562 (ASTM D 445) at 120°C, of from 100 to 5000 mm²/sec, characterized in that they contain, in addition to the copolymers, from 0.1 to 10% by volume, based on the copolymer, of the monomeric vinyl ester of a C₂- to C₃-alkanecarboxylic acid or a C₁- to C_s-alkyl ester of a C₃- to C_4-alkene- carboxylic acid.

2. Middle distillates as claimed in claim 1, characterized in that the binary copolymers have been prepared by solvent-free, free-radical polymerization at from 500 to 2,000 bar and from 100° to 350°C, preferably from 200° to 300°C, and have molecular weights of from 500 to 10,000, preferably from 1,000 to 5,000.

3. Middle distillates as claimed in claim 2, characterized in that toward the end of the polymermization reaction of the polymer to be added the unreacted ethylene together with the unreacted monomeric vinyl ester or monomeric C₁- to C₈-alkyl ester of a C₃- or C₄-alkenemono- carboxylic acid is first separated by venting the reactor and the said monomeric vinyl ester or monomeric C₁- to C₈-alkyl ester of a C₃- or C₄-alkenemonocarboxylic acid is added again to the copolymer now free from ethylene in an amount of from 0.1 to 10% by volume.

4. Middle distillates as claimed in claim 1, characterized in that they contain monomeric vinyl acetate.

5. Middle distillates as claimed in claim 1, characterized in that they contain monomeric acrylic acid esters of C₁- to C₈-alkanols.

6. Middle distillates as claimed in claim 1, characterized in that they contain monomeric C₁- to C₈- alkyl esters of maleic acid.

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