EP0421256A1 - Process for dewaxing waxy mineral-oil products - Google Patents

Abstract

The invention relates to a process for the solvent dewaxing of waxy mineral oil products, using at least one solvent suitable for dewaxing and a polyacrylate-based polymeric dewaxing aid, by mixing the product to be dewaxed with the solvent and with the polymeric dewaxing agent, cooling the resulting mixture and separating off the precipitated wax, the dewaxing aid used being a polymer mixture consisting of   I) a polymer P-1 of acrylic acid esters with C10-C40-alkanols and   II) a polymer P-2 of methacrylic acid esters with alkanols containing a proportion of more than 10% by weight of branched alkanols, with the proviso that the weight ratio of components I) and II) is 1:20 to 20:1.

Description

Subject of the invention

The invention relates to a method for dewaxing, in particular for solvent dewaxing of petroleum products containing wax using dewaxing aids (dewaxing aids) based on polyacrylate.

State of the art

The presence of paraffinic waxes in petroleum and petroleum products makes handling very difficult, primarily because of the tendency of the waxes to crystallize below certain temperatures, which vary from case to case. (See Ullmann's Enzyclopadie der techn. Chemie, 4th edition, vol. 20, p. 548 ff, Verlag Chemie 1981). Lighter petroleum fractions can be simply cooled down to the wax
Crystallization temperature of the waxes and pressing are removed via filters.
The predominantly technically used process for dewaxing wax-containing oils works with solvents, mostly low-boiling aliphatic hydrocarbons such as pentane, hexane, heptane, octane etc., ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and the like, also aromatic hydrocarbons such as benzene, toluene, xylene and the like. and mixtures of solvents. Here, too, the wax-containing oil that had been mixed with the solvent is cooled until the wax is deposited in the form of fine particles. The separated wax particles are placed on a wax separator, ie on a filter device, and thus separated from the oil and the solvent used to remove the wax.

Difficulties in practical implementation are caused by the by no means constant throughput capacity during filtration, which is determined, among other things, by the crystal structure of the wax to be separated. This is influenced by various parameters during the implementation, but most strongly by the type of cooling. The nature of the waxes, their crystal size and their appearance, give rise to a relatively wide range of variations in the texture and permeability of the filter cake, which of course makes it necessary to adapt the filtration conditions. There is a fear of the formation of very fine wax crystallites, which are very difficult to filter and sometimes migrate through the filters to cause cloudiness in the oil. The technique has developed dewaxing aids to improve filtration in general, particularly filtration speed and oil yield, which are added to the oils during the dewaxing process.

• A. einem Polyacrylat und
• B. einem n-Alkylmethacrylat-Polymeren,

wobei die Komponenten (A) und (B) in einem Gewichtsverhältnis von 1 : 100 bis 100 : 1 angewendet werden.Such dewaxing aids are usually polymers, for example of the type of the α-olefin copolymers (OCP), the ethylene-vinyl acetate copolymers (EVA) and the polyalkyl (meth) acrylic acid esters of C2-C20 alcohols. In US-A 4 451 353 a dewaxing process is proposed in which wax-containing oil distillates are mixed with a solvent (dewaxing solvent) and a dewaxing aid (dewaxing aid) based on polyacrylate, the mixture is cooled so that a thinner Porridge forms from solid wax particles and is separated by filtration from wax and the liquid parts from dewaxed oil and solvent. The dewaxing aid consists of:

• A. a polyacrylate and
• B. an n-alkyl methacrylate polymer,

wherein components (A) and (B) are used in a weight ratio of 1: 100 to 100: 1.

• I) einem Polymerisat P-1 aus Estern der Acrylsäure mit C10 - C40-Alkoholen und
• II) einem Polymerisat P-2 aus Estern der Methacrylsäure mit Alkanolen, die einen Anteil von mehr als 10 Gew.-% an verzweigten Alkanolen aufweisen,

verwendet, mit der Maßgabe, daß das Gewichtsverhältnis der Komponenten I) und II) im Gemisch 1 : 20 bis 20 : 1, vorzugsweise 1 : 10 bis 10 : 1 beträgt.
Im allgemeinen liegt die Zusatzmenge an den Polymerisaten P1 und P2 bei 0,01 bis 1 Gew.-% bezogen auf die wachshaltigen Substrate.
Das vorliegende Verfahren schließt vorteilhaft unmittelbar an dem Stand der Technik, beispielsweise in der US-A 4 451 353 angegebenen an.Claims and description of US-A leave no doubt that the methacrylate component should consist of esters of essentially linear, that is to say unbranched, alcohols having 10 to 20 carbon atoms.
Accordingly, the person skilled in the art had to assume that this group of methacrylic acid esters was particularly suitable as "dewaxing aids". Try the existing model ideas about the mode of action of such polymeric "dewaxing aids" to give plausible explanations for the influence of the polymer additive on the crystallization behavior of the waxes. However, they do not offer any selection rules for certain polymer compositions. (See for example Ullmann, loc.cit. Vol. 20, Verlag Chemie 1981).
It was therefore still the task to provide more effective "dewaxing aids" as far as possible on the basis of known starting materials, which on the other hand should not bring about any significant changes in the implementation of the dewaxing technology of petroleum or petroleum products. According to the present results, the method according to the invention can contribute significantly to solving this problem.
The invention thus relates to a process for solvent dewaxing of petroleum products containing paraffin, in particular mineral oil distillates, using at least one solvent suitable for dewaxing and a polymeric dewaxing aid (dewaxing aid) based on polyacrylate, the products to be dewaxed being treated with the solvent and the polymeric dewaxing agent mixes, the mixture obtained cools and the separated wax separates,
characterized,
that as a dewaxing aid, a polymer mixture consisting of:

• I) a polymer P-1 from esters of acrylic acid with C10 - C40 alcohols and
• II) a polymer P-2 from esters of methacrylic acid with alkanols which have a proportion of more than 10% by weight of branched alkanols,

used, with the proviso that the weight ratio of components I) and II) in the mixture is 1:20 to 20: 1, preferably 1:10 to 10: 1.
In general, the amount of polymer P1 and P2 added is from 0.01 to 1% by weight, based on the wax-containing substrates.
The present method advantageously follows directly from the prior art, for example given in US Pat. No. 4,451,353.

With regard to the petroleum-based wax-containing substrates suitable for dewaxing, there is no pronounced limitation of the process, but from a practical point of view, wax-containing distillate oils are particularly suitable, in particular those with a boiling range of approximately 300 to approximately 600 degrees C, a density of approximately 0.08 - 0.09 g / cc at 15 degrees C, a viscosity of approx. 10 - 20 cSt / 100 degrees C, a "pour point" of approx. 30 - 50 degrees C and a wax content (dry) of approx. 10 - approx. 25 wt. -%. Of particular importance are distillate oils from those fractions that include lubricating oils and special oils in the boiling range 300 - 600 degrees C, especially those with an average boiling point of approx. 400 - 450 degrees C.

The solvents L used according to the invention for solvent dewaxing also correspond to those which are conventionally used (see prior art).

For example:
aliphatic hydrocarbons with a boiling point <150 degrees C, including the self-cooling gases such as propane, propylene, butane, pentane, isooctane, etc. aromatic hydrocarbons such as
Toluene, xylene
Ketones such as
Acetone, dimethyl ketone, methyl ethyl ketone, methyl propyl ketone, methyl isobutyl ketone, optionally also
halogenated hydrocarbons such as methylene chloride, dichloroethane or N-alkylpyrrolidones such as N-methylpyrrolidone, N-ethylpyrrolidone.

Mixtures of solvents, for example ketones and aromatic hydrocarbons such as methyl ethyl ketone / toluene or methyl isobutyl ketone / toluene, are also advantageous.
The solvent L in the process according to the invention is added in the customary amounts, for example 0.5-10 parts by volume, preferably 2-7 parts by volume, based on the substrate to be dewaxed.

The polymers P-1 and P-2

The starting monomers for the polymerization P-1 and P-2 (which are already used in the art for the production of polyalkyl (meth) acrylates (PMMA)) are known per se. The polymerization of the monomers can also be carried out in a manner known per se.

The polyalkylacrylates P1 are composed of acrylic esters of C10-C40 alkanols, in particular of acrylic esters of C18-C24 alkanols, for example of the behenyl alcohol type. The molecular weight M is advantageously in the range from 10,000 to 1,500,000, preferably from 50,000 to 500,000. The determination can be carried out by means of gel permeation chromatography. (See Kirk-Othmer, Encyclopedia of Chemical Technology, 3rd Ed., Vol. 18, pg. 209, 749, J. Wiley 1982).
Characteristic of the polyalkyl methacrylates P-2 is that this more than 10 wt .-%, preferably more than 15 wt .-% esters of methacrylic acid contain branched alkyl groups.
In general, the polymers P-2 are esters of C1-C40 alkanols, with preference for the esters of C10-C24, in particular C12-C18 alcohols. The polymer P-2 can contain 0.1 to 20% by weight, in particular 1-15% by weight, of C1-C9-alkyl methacrylates. Alkanols with C12-C18 hydrocarbon radicals, for example with an average C number = 14, for example mixtures of ® DOBANOL 25L (product from Shell AG) and tallow fatty alcohol, and also mixtures of tallow fatty alcohol and other alcohols, for example i-decyl alcohol, are particularly mentioned.
The molecular weight M (see above) is generally in the range 3,000 to 500,000, preferably 50,000 to 300,000.

The radical polymerization is advantageously carried out in a solvent which is compatible with the substrate to be dewaxed, such as, for example, in mineral oil. Man uses conventional polymerization initiators such as per compounds, especially peresters such as tert-butyl perpivalate, tert-butyl peroctoate, tert-butyl perbenzoate and the like. in the usual amounts, for example 0.1 to 5, preferably 0.3 to 1% by weight, based on the monomers (cf. Th. Völker, H. Rauch-Puntigam, acrylic and methacrylic compounds, Springer-Verlag 1967).

Molecular weight regulators, in particular sulfur regulators, special mercaptans such as dodecyl mercaptan in the usual amounts, for example 0.01 to 2% by weight, based on the monomers, can also be added to the batches in a manner known per se.
Appropriately, you work under a protective gas such as CO₂.
The procedure is appropriately such that the monomers are dissolved in a suitable polymerization vessel equipped with a stirrer in the solvent, if appropriate together with the regulator and initiator and first degassed, for example using CO₂ snow, and then heated. For example, 80 ± 10 degrees C can be used as a guide. The initiator can also be added to the heated mixture in some cases. If necessary, further monomer and initiator and regulator are metered in. The temperature generally rises further, for example to 140 ± 10 degrees C. If necessary, suitable conditions for the postpolymerization can be established by adding heat and / or further addition of initiator. The total polymerization time is generally less than 12 hours.

The polymer components P-1 and P-2 can advantageously be used as separately prepared preparations. They are then mixed in the abovementioned weight ratios and the intended proportions of the substrates to be dewaxed, either in bulk or in a compatible solvent such as wax-free mineral oil or one of the solvents or mixtures L, taking care that the cloud point the oils to be dewaxed are exceeded, for example by heating to 50-120 degrees C. The polymers P-1 and P-2 can be added together or separately. The addition can take place before cooling or during cooling, but then in cooled solvents. The cooling can take place, for example, in accordance with US Pat. No. 3,773,650. The mixture of the polymers P-1 and P-2 is advantageously added together with the dewaxing solvent L in a cooling zone and at a temperature which is matched to the "pour point" of the dewaxed oil to be obtained.
The cooling step causes the formation of a fluid liquid slurry, which contains solid wax particles, dewaxed oil and solvent L. The wax particles usually contain polymer P-1 and P-2. The temperature to which cooling must depend on the type of substrate to be dewaxed and the overall procedure. In general, dewaxing is carried out in the temperature range from 0 degrees C to -50 degrees C, when using a solvent mixture L of a ketone and an aromatic hydrocarbon, the dewaxing temperature is to be set at -10 degrees C to -30 degrees C.

Special effects

Quite unexpectedly, the results obtained with the mixtures of the polymers P-1 and P-2 show that when using PAMA mixed components with more or less high degrees of branching of the alkyl radicals, significantly better effectiveness and more pronounced synergistic effects occur than with essentially linear ones Poly-alkyl (meth) acrylates. The findings were made on a wide variety of dewaxing solvents and paraffin-containing substrates, i.e. "Feedstocks" obtained, as evidenced by the following examples, so that general validity can be assumed.

The following examples serve to illustrate the invention. The specific viscosity η _sp / c is determined in accordance with DIN 7745 in chloroform as a solvent at 20 degrees C.

EXAMPLES A. Preparation of the polymers P-1 and P-2 example 1 Preparation of a poly (behenyl acrylate) P-1

51 kg of behenyl acrylate (C18-C24 acrylate), 9 kg of 100N oil and 0.051 kg of dodecyl mercaptan are placed in a 100 l stirred kettle, degassed with CO₂ ice and heated to 70 ° C. Then 0.191 kg of t-butyl perpivalate and 0.115 kg of t-butyl perbenzoate are added to start the polymerization. 1 hour after the temperature peak of 134 degrees C has been reached, 0.077 kg of dodecyl mercaptan and 0.051 kg of t-butyl perbenzoate are added and the polymerization is continued at 130 degrees C for 3 hours.
Mw (GPC, PMMA calibration) = 560,000 g / mol
ηsp / c (CHCl₃, 20 degrees C) 48 ml / g

Example 2 Preparation of poly (C12-C18-alkyl methacrylate) P-2-1

In a 150 l stirred kettle, 2.967 kg of a C12-C18-alkyl methacrylate (average C number 14, 17.9% are branched, for example based on a mixture of Dobanol 25 L ® from Shell and tallow fatty alcohol), 26.7 kg 100 N -Oil and 0.083 kg Submitted t-butyl peroctoate, degassed with CO₂ ice and heated to 85 degrees C. 37.033 kg of C12-C18-alkyl methacrylate and 0.0741 kg of t-butyl peroctoate are then metered in within 3.5 hours. 2 hours after the end of the feed, 0.08 kg of t-butyl peroctoate are again added. After a further 5 hours, the mixture is diluted with 33.3 kg of 100 N oil.
Mw (GPC, PMMA calibration) = 410,000 g / mol
ηsp / c (CHCl₃, 20 degrees C) 65 ml / g
Weight fraction of branched esters 17.9%

Examples 3-5 Production of poly (C12-C18-alkyl methacrylates) with different degrees of branching of the alkyl residues.

The preparation is carried out as described in Example 2. Instead of dobanol / tallow fatty alcohol, other alcohol mixtures are used. The following table summarizes the properties of the polymers. example Alkyl radicals C number Weight fraction of branched ester% ηsp / c (20 degrees C CHCl₃) 3rd 13-18 27.2 62 P-2-2 4th 13-18 38.9 64 P-2-3 5 12-18 46.7 63 P-2-4 Comparative example 12-18 0 61 V-2-1

Example 6 Preparation of a copolymer of i-C10 methacrylate and tallow fat methacrylate P-2-5

37 kg of 100 N oil, 4.111 kg of a methacrylic acid ester of an alcohol mixture of 57.9% by weight of tallow fatty alcohol and 42.1% by weight of i-decyl alcohol are placed in a 100 l stirred kettle and heated to 85 ° C. It is then degassed by adding CO₂ ice and 0.016 kg of dodecyl mercaptan and 0.032 kg of t-butyl peroctoate are added. A further 58.889 kg of the methacrylic acid ester, 0.236 kg of dodecyl mercaptan and 0.177 kg of t-butyl peroctoate are then metered in within 3.5 hours. 2 hours after the end of the feed, 0.126 kg of t-butyl peroctoate are again added. The polymerization is complete after a further 5 hours.
ηsp / c (CHCl₃, 20 degrees C) 22 ml / g
Weight fraction of branched esters = 45.2%

Example 7 Preparation of poly (Cl-C18 alkyl methacrylate) P-2-6

In a 100 l stirred kettle, 1.976 kg of C12-C18 alkyl methacrylate (average C number 14, 17.9 are branched, for example based on a mixture of Dobanol 25 L ® from Shell and tallow fatty alcohol), 0.0297 kg of methyl methacrylate, 17. 8 kg of 100 N oil and 0.0551 kg of t-butyl peroctoate are introduced, Degassed with CO₂ ice and heated to 85 degrees C. 24.664 kg of C12-C18 alkyl methacrylate, 6.223 kg of methyl methacrylate and 0.0494 kg of t-butyl peroctoate are then metered in within 3.5 hours. 2 hours after the end of the feed, 0.053 kg of t-butyl peroctoate are again added. After a further 5 hours, it is diluted with 22.18 kg of 100N-0l.
ηsp / c (CHCl₃, 20 degrees C) = 34 ml / g
Weight fraction of branched esters = 14.5%

Comparative Example 2 Preparation of an unbranched poly (C16-18 alkyl methacrylate) V2-2

In a 150 1 stirred kettle, 4,889 kg of C16-C18 alkyl methacrylate (e.g. based on Alfol 1618 S ® alcohol from Condea), 44.0 kg of 100 N oil and 0.172 kg of t Submitted butyl peroctoate. After degassing with CO₂ ice, the temperature is raised to 85 degrees C. Then 51.111 kg of C16-C18 alkyl methacrylate and 0.153 kg of t-butyl peroctoate are added by means of a metering pump within 3.5 hours. 2 hours after the end of the feed, 0.112 kg of t-butyl peroctoate are again added. The polymerization is complete after a further 5 hours.
Mw (GPC, PMMA calibration) = 220,000 g / mol
ηsp / c (CHCl₃, 20 degrees C) = 44 ml / g
Weight fraction of branched ester = 0%

B. Conduct a laboratory filtration test to determine oil yield and filtration rate

The filtration apparatus consists of a steel filter with a lid and cooling jacket and is cooled in circulation using a cryostat. Filter cloth from the dewaxing plant of the corresponding refinery is used. The filter volume is 100 ml. The filter is connected to a measuring cylinder via a glass attachment with a 2-way valve. A defined vacuum can be applied to the filtration apparatus using an oil rotary vane pump, a pressure reducing valve and a pressure gauge. The mineral oil distillate to be dewaxed is mixed with the dewaxing solvents in the heat (above the cloud point) and stirred until a clear solution results. This is carried out with the help of a cryostat with temperature control cooled down to the desired filtration temperature. The filter is pre-cooled to this temperature.

All filtration conditions such as solvent: feedstock ratio, solvent ratio for mixtures, cooling rates and filtration temperature correspond to the conditions used in the respective refinery. Since working with propane in the laboratory is problematic, isooctane was used instead of propane in such cases.

After the filtration temperature has been reached, the mixture is transferred to the precooled filter and a vacuum is applied. The filtrate volume is measured as a function of time and the filtration rate F is determined as the slope of the linear plot of V / 2S² against t / V, where V is the filtrate volume, t is the time in seconds and S is the filter area in cm².

After the solvents have been distilled off using a rotary evaporator, if appropriate azeotropically with the aid of a further solvent, the dewaxed oil obtained is dried to constant weight and the blue yield is determined gravimetrically. The oil content in the filtered paraffin is determined in accordance with ISO 2908. Example 8 Dewaxing Heavy Neutral 95 from a Spanish refinery Solvent = isooctane, HN 95: Solvent = 1: 4 (wt.). Cooling from +60 degrees C to +5 degrees C was carried out with stirring by placing in an O degrees C cooling bath and from +5 degrees C to -20 degrees C by placing in a -22 degrees C cooling bath. The mixture was then stirred for a further 20 minutes, then filtered. Dewaxing additives Dewaxing Polyalkyl acrylate Polyalkyl methacrylate % branches Mixing ratio Filterability F (cm² / s) Filtration time (sec.) Oil yield% - - - - 1.1 x 10⁻² 2460 73.7 P-1 - - 9 x 10⁻² 300 83.0 P-1 P-2-1 17.9 1: 1 26 x 10⁻² 90 83.9 P-1 P-2-1 17.9 2: 1 47 x 10⁻² 70 85.4 P-1 P-2-2 27.2 1: 1 48 x 10⁻² 60 84.6 P-1 P-2-3 38.9 1: 1 70 x 10⁻² 40 84.7 P-1 V-2-1 0 1: 1 18 X 10⁻² 150 83.7 Example 3 Dewaxing from Bright Stock 95 of a Spanish refinery Solvent: isooctane Conditions of the laboratory experiments as described in Example 8 Dewaxing additives Dewaxing Polyalkyl acrylate Polyalkyl methacrylate % branches Mixing ratio Filterability F (cm² / s) Filtration time (sec.) Oil yield% - - - - 0.09 x 10⁻² 3,300 83 P-1 - - - 14 x 10⁻² 180 83.4 - P-2-1 17.9 - 4 x 10⁻² 480 82.8 P-1 P-2-1 17.9 1: 1 24 x 10⁻² 90 83.2 P-1 P-2-1 17.9 3: 1 25 x 10⁻² 120 83.2 P-1 P-2-1 17.9 5: 1 28 x 10⁻² 90 83.4 P-1 P-2-1 17.9 10: 1 23 x 10⁻² 120 83.3 P-1 P-2-2 27.2 1: 1 28 x 10⁻² 90 82.8 P-1 P-2-3 38.9 1: 1 23 x 10⁻² 90 82.6 P-1 P-2-6 14.5 1: 1 23 x 10⁻² 100 83.3 - V-2-2 0 - 4 x 10⁻² 420 82.9 P-1 V-2-2 0 1: 1 14 x 10⁻² 180 82.8 P-1 V-2-1 0 1: 1 22 x 10⁻² 140 82.8 Example 10 Dewaxing of 500 N feedstock from a German refinery Ethyl methyl ketone solvent: toluene = 1: 1 (vol). The feedstock to solvent ratio was 1: 3. It was cooled from +70 degrees C to -17 degrees C at 3.5 degrees C / min., At -17 degrees C the filtration took place Dewaxing additives Dewaxing Polyacrylate Polymethacrylate % branches Mixing ratio dosage Filterability F (cm² / s) Filtration time (sec.) Oil yield% Paraffin Oil% - - - - - 1.5 x 10⁻² 1 100 42.4 63.4 P-1 - - - 250 3.6 x 10⁻² 420 57.3 - 500 3.6 x 10⁻² 480 57.4 58 - P-2-1 17.9 - 250 1.8 x 10⁻² 840 43.2 - 500 1.4 x 10⁻² 1 260 44.9 - P-1 P-2-1 17.9 1: 1 250 4.1 x 10⁻² 420 57.1 - 500 3.8 x 10⁻² 440 57.5 - P-1 P-2-1 17.9 2: 1 250 4.1 x 10⁻² 420 58.1 - 500 4.5 x 10⁻² 380 59.2 55.3 P-1 P-2-1 17.9 1: 2 250 3.6 x 10⁻² 480 53.5 - 500 3.95 x 10⁻² 420 57.2 56 P-1 P-2-1 17.9 1: 3 500 3.9 x 10⁻² 420 55.1 - P-1 P-2-2 27.2 1: 1 250 3.5 x 10⁻² 480 55.4 - P-1 P-2-3 38.9 1: 1 250 3.1 x 10⁻² 540 54.8 - 500 3.8 x 10⁻² 420 58.0 - P-1 P-2-4 46.1 1: 1 250 3.4 x 10⁻² 540 53.2 - 500 4.2 x 10⁻² 420 58.1 - P-1 P-2-5 45.2 1: 1 250 3.6 x 10⁻² 420 55.6 - P-1 V-2-2 0 1: 1 500 2.8 x 10⁻² 600 54.5 - - V-2-2 0 - 500 2.2 x 10⁻² 660 43.5 - P-1 V-2-1 0 1: 1 500 3.6 x 10⁻² 420 55.9 -

Claims (6)

1. A process for solvent dewaxing of petroleum products containing paraffin using at least one solvent suitable for dewaxing and a polymeric dewaxing aid based on polyacrylate, wherein the products to be dewaxed are mixed with the solvent and with the polymeric dewaxing agent, the mixture obtained is cooled and the separated product Separates wax,
characterized,
that as a dewaxing aid, a polymer mixture consisting of
I) a polymer P-1 from esters of acrylic acid with C10-C40 alkanols and
II) a polymer P-2 from esters of methacrylic acid with alkanols which have a proportion of more than 10% by weight of branched alkanols,
used, with the proviso that the weight ratio of components I) and II) is 1:20 to 20: 1. 2. The method according to claim 1, characterized in that the weight ratio of components I) and II) is 1:10 to 10: 1. 3. Process according to claims 1 and 2, characterized in that the polymers P-1 are composed of acrylic esters of C18-C24 alkanols. 4. Process according to claims 1 and 2, characterized in that the polymers P-2 are constructed from esters of methacrylic acid with C1-C40 alkanols. 5. The method according to claim 4, characterized in that the polymer P-2 is composed of at least 80 wt .-% of esters of methacrylic acid with C10-C24 alkanols. 6. The method according to claim 5, characterized in that the polymer P-2 is built up to 20 wt .-% of esters of methacrylic acid with C1-C9 alkanols.