EP0543356B1 - Process for making compositions with improved low temperature behaviour - Google Patents

Abstract

The invention relates to a process for making compositions with improved low-temperature behaviour for use as motor fuels or lubricants, starting from the esters of long-chain fatty acids obtained from natural sources with monohydric C1-C6-alcohols (FAE), a) additives PPD, known per se and used for improving the low-temperature behaviour of mineral oils, being added in quantities from 0.0001 to 0.1 % by weight, relative to the long-chain fatty acid esters FAE, and b) the mixture being cooled to a temperature below the cold filter plugging point (determined according to DIN 51 458) of the long-chain fatty acid esters FAE without additives, and c) the resulting precipitates (FAN) being separated off. s

Description

Field of the Invention

The invention relates to a process for the production of compositions with improved low-temperature behavior for use as fuels or lubricants based on longer-chain fatty acid alkyl esters, in particular rape oil methyl esters. According to the method, by adding additives based on polyalkyl (meth) acrylates (PAMA), both the Gold Filter Plugging Point (CFPP) and the Pour Point (PP) of e.g. Beet oil methyl esters or fuel mixtures or lubricants containing them can be improved.

State of the art

For some time now, the interest of technology has been on the one hand alternative energy sources that are not based on fossil resources, on the other hand so-called "renewable raw materials". These include, in particular, vegetable oils, ie fatty acid esters, usually triglycerides, which are generally classified as biodegradable and environmentally friendly. Rapeseed oil / rapeseed oil can serve as a prototype for such oils. The recommendations for using rape oil as a lubricant date back to the 1920s (cf. D. Holde, Chemiker-Zeitung 1922 (1), p. 4). Numerous property rights deal with the use of rapeseed oil or modified rapeseed oil in lubricants and fuels. (See Int. Appl. WO 88 05 808; DE-A 29 30 220, DE-A 30 23 372; FR-A 2 492 402; DE-A 3 404 243). Conventional rapeseed oil / rapeseed oil in its average composition has about 51% by weight erucic acid, 22% by weight linoleic acid, 18% by weight oleic acid, 2% by weight palmitic acid and in each case less than 1% by weight myristyl as fatty acid components -, stearyl and palmitolic acid. Newer breeds, on the other hand, have a low erucic acid content. Some of the technology has gone over to converting the naturally occurring triglycerides into fatty acid esters of monohydric alcohols, preferably into methyl esters, and using them in fuels (see DE-A 31 50 989, AT-B 387 399, M. Mittelbach et al. In Energy Agric 4 (3) 207-215 (1985), Chem. Abstr. 104 , 115 224j; Energy Agric. 2 , 369-84 (1983), Chem. Abstr. 100 , 106 496 q). Experience is particularly available when used as an extender for diesel fuels or synthetic esters. [JP-A 57.207.695, cf. Chem. Abstr. 99, 107 980 r; US-A 4 364 743; Klopfenstein et al. J. Am. Oil Chem. Soc. 60 , 1596 (1983)]. The solvent-mediating effect of the fatty acid esters of monohydric alcohols between methanol and gas oils is recommended (DE-A 31 49 170, FR-A 2 497 222). In addition, the use of fatty acid methyl esters as a component of lubricating oil mixtures is recommended (GB-A 1 177 568; PL-A 127 986, cf. Chem. Abstr. 107 , 118 152 g).

Task and solution

As an obstacle to the use of fatty acid esters of monohydric alcohols as a diesel fuel substitute alone or in a mixture with diesel fuel or synthetic esters, the flow behavior at low temperatures has been proven. For example, the beet oil methyl ester has an average "Cold Filter Plugging Point" (CFPP, determined according to DIN 51 428) of -15 degrees C. Similar to diesel fuel itself, this significantly affects the pourability and thus the fuel delivery at low temperatures.

The task was therefore to provide additives for improving the low-temperature behavior, in particular the cold filter plugging point of fatty acid esters of monohydric alcohols, especially the rape oil methyl ester. In the case of the beet oil methyl ester, for example, the aim was to reduce the CFPP from -15 degrees C to -22 degrees C. The additives should be in the range <0.1% by weight. The additives should also belong to a class other than that of the triglycerides.
The technique has long been used to reduce the pour point of lubricating oils and other mineral oil products, polymer compounds, so-called "pour point depressants", which as a structural feature have a large number of alkyl side chains with 8-40, in particular 10-28, carbon atoms as a rule.
Poly (meth) acrylic acid esters of long-chain alcohols (PAMA additives) are particularly important.
(See HF Mark et al. In Encyclopedia of Polymer Science and Engineering 2nd Ed. Vol. 11 , 26-30, J. Wiley; US-A 2 091 627; US-A 2 100 993; US-A 2 114 233 ; US-A 4 867 894) However, relevant experiments have shown that the addition of known cold filter plugging improvers Based on polyalkyl (meth) acrylates, the desired improvement in the low-temperature behavior alone does not result.

• a) an sich bekannte, zur Verbesserung des Tieftemperaturverhaltens von Mineralölen verwendete Additive PPD in Mengen von 0,0001 bis 10 Gew.-% bezogen auf die langkettigen Fettsäureester FAE zusetzt und
• b) auf eine Temperatur unterhalb des Cold Filter Plugging Point der nicht-additivierten langkettigen Fettsäureester FAE abkühlt und
• c) die entstehenden Niederschläge (FAN) abtrennt.

It has now been found that the desired improvement in the cold filter plugging point / pour point in fatty acid esters of monohydric alcohols, in particular rapeseed oil methyl ester, can nevertheless be achieved by a combination of appropriate measures. The invention thus relates to a process for the production of compositions based on esters of long-chain fatty acids obtained from natural sources with monovalent C1 to C6 alcohols (FAE) - preferably esters of fatty acids in the C12 to C26 range - with improved low-temperature behavior for use as fuels and lubricants, where one

• a) known additives used to improve the low-temperature behavior of mineral oils in amounts of 0.0001 to 10% by weight based on the long-chain fatty acid esters FAE and
• b) cools to a temperature below the cold filter plugging point of the non-additive long-chain fatty acid esters FAE and
• c) separating the resulting precipitates (FAN).

The long-chain fatty acid esters FAE

The expedient field of application of the method according to the invention results from the low-temperature behavior, in particular the values of the CFPP of the long-chain fatty acid esters from natural sources. These originally existed predominantly as triglycerides of mixtures of C10 (and lower) to approx. C26 fatty acids, namely saturated and unsaturated fatty acids. Depending on their composition or provenance, they are obtained as liquid vegetable oils, solid vegetable fats or as animal oils or animal fats. Overviews of the occurrences and compositions can be found in the literature (cf. Ullmann's Encyclopadie der Techn. Chemie, 4th edition, vol. 11 , pp. 458-459, Verlag Chemie; Kirk-Othmer, Encyclopedia of Chemical Technology, 3rd. Ed ., Vol. 9, pp. 795-831, pp. 804-805ff, J. Wiley 1980). Of particular interest is the esters of fatty acids derived from liquid vegetable oils with monohydric C1-C6 alcohols, especially the methyl esters (usually in the proportions of the natural occurrence of the acids). In general, they do not contain any noteworthy C10 fatty acid fractions, C12 fractions mostly only in traces and also relatively little C14 fractions, so that the main fractions are to be found in the area of saturated / unsaturated C16-C24 fatty acids, with a focus on unsaturated ones C18-C20 fatty acids. It can usually be assumed that the long-chain fatty acid esters FA-E are formed at least 95% by weight from C12-C26 fatty acids. The fatty acid alkyl esters to be used according to the invention are prepared from the naturally occurring esters, especially the triglycerides, by processes known per se. For example, the naturally occurring fatty acid esters, in particular the triglycerides, can be converted, for example, by transesterification.

The procedure can be such that the triglycerides are stirred with a 0.5 to 2-fold excess of the monohydric alcohol, for example methanol in about 1 atmosphere and about 50-100 degrees C. and in the presence of a preferably alkaline catalyst such as alkali hydroxide and / or alkali alkoxide in amounts of 0.05 to 0.2 parts by weight per 100 parts by weight of triglyceride. The working-up usually takes place by stripping off the excess alcohol, washing the residue one or more times with water or dilute acid and drying the ester after separating off the aqueous phase (cf. also AT-A 387 399).

The rape oil methyl ester is of particular interest in the context of the present invention. The following explanations exemplified are therefore preferably concerned with this ester, but they can easily be transferred to other fatty acid esters of the type claimed. The rape oil methyl esters are commercially available (source: e.g. from CASTROL, Austria; from HENKEL, Düsseldorf). A commercially available rape oil methyl ester (rape methyl ester "RME") can e.g. have the following composition: approx. 65% by weight oleic acid ester, approx. 19% by weight linoleic acid ester, approx. 2% by weight stearic acid ester, approx. 4% by weight palmitine ester, approx. 4% by weight <C14- Ester, approx. 6% by weight> C20 ester. Such an ester is hereinafter referred to as FEA-1.

The additive PPD

The additives used to improve the low-temperature behavior (“pour point depressants”) are generally the polymers used in particular, in particular those which are produced by a large number of long-chain ones Alkyl residues in the molecule are characterized or have a polyalkylene structure (cf. Ullmanns Encyclopadie der Technischen Chemie, 4th edition, vol. 20, pp. 548/549 Verlag Chemie 19; HF Mark et al. In Encyclopedia of Polymer Science and Engineering loc.cit. pg. 26 - 27)

• α) Polyalkyl(meth)acrylaten (PAMA s. unten)
• β) Polymere auf Basis von langkettigen Maleinsäure-, Fumarsäure, Itaconsäureestern (vgl. US-A 4 963 279)
• γ) Polyalkylenverbindungen ausgehend von α-Olefinen mit z.B. 6 - 24 C-Atomen, Isobutylen, Ethylen/Propylen, Ethylen/Butadien (vgl. US-A 4 132 663, US-A 2 895 915)
• δ) Carbonsäure-Vinylester, Homo- und Copoylmeren, insbesondere EVA (vgl. US-A 3 309 181) und Ethylen/Vinylacetat/Diisobutylen-Copolymere (US-A 2 721 877; US-A 2 876 213; US-A 3 250 715; US-A 4 127 138)
• ε) Ethylen/Fumarat und Ethylen/Maleinat-Copolymere, Ethylen/Acrylat- und Ethylen/Methacrylat-Copolymere
• ζ) 1,2-Epoxyalkancopolymere auf Basis von Ethylenoxid, Propylenoxid, Butylenoxid (US-A 3 382 055)
• η) Alkylierte Polystyrole und Maleinsäure-Styrol-Copolymere (GB-B 848 777)
• ϑ) Veresterungsprodukte mit Polyvinylalkohol (vgl. M.Ratsch, M. Gebauer, Erdöl u. Kohle Bd. 42(6) 238 - 241
• 
  Alkylierte Naphthaline (US-A 1 815 022)

The additives PPD to be used according to the invention are preferably selected from the group consisting of

• α) polyalkyl (meth) acrylates (PAMA see below)
• β) polymers based on long-chain maleic acid, fumaric acid, itaconic acid esters (cf. US Pat. No. 4,963,279)
• γ) polyalkylene compounds starting from α-olefins with, for example, 6-24 carbon atoms, isobutylene, ethylene / propylene, ethylene / butadiene (cf. US Pat. No. 4,132,663, US Pat. No. 2,895,915)
• δ) carboxylic acid vinyl esters, homo- and copolymers, in particular EVA (cf. US Pat. No. 3,309,181) and ethylene / vinyl acetate / diisobutylene copolymers (US Pat. No. 2,721,877; US Pat. No. 2,876,213; US Pat. No. 3) 250 715; US-A 4 127 138)
• ε) ethylene / fumarate and ethylene / maleinate copolymers, ethylene / acrylate and ethylene / methacrylate copolymers
• ζ) 1,2-epoxyalkane copolymers based on ethylene oxide, propylene oxide, butylene oxide (US Pat. No. 3,382,055)
• η) Alkylated polystyrenes and maleic acid-styrene copolymers (GB-B 848 777)
• ϑ) Esterification products with polyvinyl alcohol (see M.Ratsch, M. Gebauer, Erdöl u. Kohl, Vol. 42 (6) 238 - 241
• 
  Alkylated Naphthalenes (US-A 1 815 022)

The polymers α) -ϑ) mentioned can by definition be present as homopolymers or copolymers. They generally have the molecular weights recognized as appropriate in the conventional additives, generally in the range from 800 to 2,000,000 daltons. They can also be used in the form of graft (co) polymers, block polymers, but also as polymer mixtures. Mixtures with suitable alcohols, esters and / or carboxylic acids should also be considered.
In general, the content of the additives PPD is in the range from 0.0001 to 10% by weight, preferably in the range from 0.1 to 0.5% by weight, based on the esters to be added. The rape oil-methyl ester compositions produced according to the invention are distinguished by a significantly improved low-temperature behavior. With the method according to the invention, for example, the CFPP can be reduced from -15 degrees C to -22 degrees C with a maximum of 0,1 0.1% by weight of additive to the beet oil methyl ester.
Polyalkyl (meth) acrylates are particularly preferred in the context of the present invention.
The PAMA additives used as improvers in low-temperature behavior correspond to those used in the prior art.
In particular, they are polymers with molecular weights Mw in the range 800-1,000,000 daltons, in particular in the range 800-400,000 daltons (determination by gel permeation chromatography, cf. HF Mark et al. In "Encyclopedia of Polymer Science 2nd Ed. Vol. 10 , pg. 1-19, J. Wiley 1987) Suitable PAMA polymers are described, for example, in US Pat. No. 4,867,894.
The alkyl radicals of the ester units are in the C1-C28 range, with at least 75% by weight if the proportions of lower alkyl esters are in the C1-C2-alkyl range preferably ≥ 85% by weight of the monomers alkyl radicals above C6, while if the proportion of lower alkyl esters is in the C3-C6 range, the proportion of long-chain alkyl esters from C6 can be up to ≤ 40% by weight. They are preferably C12-C18-alkyl esters of (meth) acrylic acid.
The monomers to be used to prepare the PAMA additives are known. The polymerization is usually free radical.
The radical polymerization is advantageously carried out in a compatible solvent, for example in mineral oil. Usual polymerization initiators such as per compounds, especially peresters such as tert-butyl perpivalate, tert-butyl peroctoate, tert-butyl perbenzoate and the like are used. 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, for example, dodecyl mercaptan, can also be added to the batches in the usual amounts, for example 0.01 to 2% by weight, based on the monomers, in a manner known per se.
It is expedient to work under a protective gas such as CO ₂ .
The procedure is advantageously such that the monomers are dissolved in the solvent in a suitable polymerization vessel equipped with a stirrer, if appropriate together with the regulator and initiator and first degassed, for example by means of CO ₂ snow, and then warmed. 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 usually continues to rise, 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 amounts added when adding the rapeseed methyl ester are 10 to 0.0001% by weight, preferably 0.1 to 0.05% by weight.

Execution of the procedure

In step c), the process according to the invention provides for the removal of unsaturated and saturated fatty acid methyl esters of the C12-C30 acids. These fatty acid methyl esters tend to separate at low temperatures. The separation is expediently carried out in the temperature range 0 to -50 degrees C, in particular at -20 to -30 degrees C, by mechanical separation processes such as filtering, centrifuging, decanting and the like. The filtrate thus obtained has a cold filter plugging point from -23 to -41 degrees C, among others. depending on the oil provenance and the concentration of the additives.

The C12-C30 fatty acid methyl esters can also be separated off by fractional distillation. For economic reasons, however, the fractional Crystallization is preferred according to the procedure outlined above. The residues (preferably by filtration) are composed of unsaturated and saturated C12-C26 fatty acid methyl esters. These residues can advantageously be reused elsewhere. The PPD additives are preferably incorporated by mixing in, expediently with stirring into the beet oil methyl ester before separating off the fatty acid methyl ester according to c).

The forms of use of the compositions produced according to the invention can, in addition to the components mentioned, also other relevant polymers used, as well as low molecular weight compounds such as alcohols, long-chain iso-alcohols, fatty acid esters (esters of long-chain iso-alcohols) and the like. contain.

Beneficial effects

The beet oil-methyl ester compositions to be regarded as paradigmatic and produced by the process according to the invention come close to the technical requirements with regard to the “cold filter plugging point” or the “pour point”. They are environmentally friendly, sulfur-free additional fuels with higher efficiency than diesel fuel (see e.g. BE-A 889 140). It can be considered particularly advantageous that a soot filter can be dispensed with. But they are also suitable as lubricants or additives Lubricant components, the setting of the required viscosity is within the experience of the expert. The application in tribology follows the state of the art (see "State of the art").
The process according to the present invention, which is exemplified by the rape oil methyl ester, can also be used for other esters of naturally occurring fatty acids with monobasic alcohols having 1 to 4 carbon atoms. These can also be prepared so that they can be used, for example, as a fuel substitute or as a lubricant. The FAN products obtained by separation are suitable - if necessary. after appropriate preparation for the production of nutrients and / or for the substitution of the unsaturated fatty acids desired in the diet.

-1 (Vgl. Vieweg-Esser, Kunststoff-Handbuch, Band IX, S. 24, Carl Hanser 1975).
Die Porengröße der Filter wird nach ISO 4793 angegeben. Als Porengrößen werden Filter P40 bzw. P100 bevorzugt. Die Viskosität η wir nach DIN 51 398/ASTM D 2183 bestimmt.The following examples serve to illustrate the invention. The CFPP is determined according to DIN 51 428, the "pour point" in a HERZOG PP apparatus MC 850. Mw U stands for the non-uniformity U: $\frac{\text{Mw}}{\text{Mn}}$

-1 (See Vieweg-Esser, Kunststoff-Handbuch, Volume IX, p. 24, Carl Hanser 1975).
The pore size of the filter is specified according to ISO 4793. Filters P40 or P100 are preferred as pore sizes. The viscosity η is determined according to DIN 51 398 / ASTM D 2183.

EXAMPLES

In each case, the above-described rape oil methyl ester FAE-1 is used (see "the long-chain fatty acid esters FAE). The improvement in CFPP achieved can be seen from FIG. 1.

example 1

w von 9 100 und einer U = 0,73 gelöst (z.B. Produkt VISCOPLEX ® 0-050 der Röhm GmbH), die Lösung auf -25 Grad C abgekühlt und über eine auf Filtrationstemperatur vorgekühlte Glasfilternutsche P40 (Porengröße 16 - 40 µm) die auskristallisierten Fettsäuremethylester im Wasserstrahlvakuum abfiltriert. Das erhaltene Filtrat besitzt einen CFPP von -21 Grad C und einem PP von -36 Grad C. Die Ausbeutet beträgt 89 %.0.1 g of C12-C15 polymethacrylate with a $\overline{\text{M}}$

w of 9 100 and a U = 0.73 dissolved (e.g. product VISCOPLEX ® 0-050 from Röhm GmbH), the solution cooled to -25 degrees C and the crystals crystallized out via a P40 glass filter funnel (pore size 16 - 40 µm) that had been cooled to the filtration temperature Fatty acid methyl ester filtered off in a water jet vacuum. The filtrate obtained has a CFPP of -21 degrees C and a PP of -36 degrees C. The yield is 89%.

Example 2

w von 9 100 und einer U = 0,73 gelöst, die Lösung auf -30 Grad C abgekühlt und über eine auf Filtrationstemperatur vorgekühlte Glasfilternutsche G3 die auskristallisierten Fettsäuremethylester im Wasserstrahlvakuum abfiltriert. Das erhaltene Filtrat besitzt einen CFPP von -41 Grad C und einen Pour Point von -36 Grad C. Die Ausbeute beträgt 83 %.0.1 g of C12-C15 polymethacrylate with a $\overline{\text{M}}$

w of 9 100 and a U = 0.73 dissolved, the solution cooled to -30 degrees C and the crystallized fatty acid methyl esters filtered off in a water jet vacuum via a glass filter funnel G3 pre-cooled to filtration temperature. The filtrate obtained has a CFPP of -41 degrees C and a pour point of -36 degrees C. The yield is 83%.

Example 3

0.04% C12-C18 polymethacrylate (eg product VISCOPLEX ® 9-300 from Röhm GmbH) with a Mw of 364,000 and a U = 1.82 are dissolved in 100 g of rapeseed oil methyl ester, the solution is cooled to -30 ° C. and The crystallized fatty acid methyl esters are filtered off in a water jet vacuum via a glass filter funnel G3 pre-cooled to the filtration temperature. The filtrate obtained has a CFPP of -31 degrees C and a pour point of -33 degrees C. The yield is 86%.

Example 4

0.068% of a copolymer of C12-C18 methacrylate and methyl methacrylate = 90/10% by weight with a Mw of 300,000 and a U = 0.97 (for example product VISCOPLEX ® 1-810 from Röhm GmbH) are dissolved in 100 g of beet oil methyl ester. dissolved, the solution cooled to -25 degrees C and the crystallized fatty acid methyl esters filtered through a glass suction filter G3. The filtrate obtained has a CFPP of -24 degrees C and a pour point of -36 degrees C. The yield is 87.5%.

Example 5

0.05% of a C12-C15 polymethacrylate with an Mw of 9,100 and a U = 0.73 is dissolved in 100 g of rapeseed oil methyl ester, the solution is cooled to -30 degrees C and the crystallized fatty acid methyl ester is filtered off through a glass suction filter G3. The filtrate obtained has a CFPP of -25 degrees C and a pour point of -39 degrees C. The yield is 87%.

Example 6

0.5% of a C12-C15 polymethacrylate with a Mw of 9,100 and a U = 0.73 is dissolved in 100 g of rapeseed oil methyl ester, the solution is cooled to -20 ° C. and the crystallized fatty acid methyl ester is filtered off through a glass suction filter G3 that has been pre-cooled to the filtration temperature . The filtrate obtained has a CFPP of -23 degrees C and a pour point of -39 degrees C. The yield is 94%.

Example 7

In 100 g of beet oil methyl ester, 0.4% of a copolymer of C10-C18 fumarate and styrene (= 83/17% by weight) Mw approx. 20,000 is dissolved and cooled to -25 degrees C, the crystallized fatty acid methyl ester via one Filtration temperature pre-cooled G3 glass filter. The filtrate obtained has a CFPP of -22 degrees C and a pour point of -39 degrees C. The yield is 91%.

Example 8 (Comparison test)

A beet oil methyl ester without additive, which has a PP of -15 degrees C, was filtered at -10 degrees C. The filtrate obtained had a CFPP of -8 degrees C. The yield is 92%. By adding 0.5% C12-C15 polymethacrylate, the CFPP improved to -19 degrees C.

When carrying out the process on an industrial scale, separation by means of a cooling centrifuge is preferred.

Example 9 (Production of the Additives PPD (PAMA Additive According to Example 3)

The following mixture is placed in a 1 1 four-necked flask with stirrer, thermometer, reflux condenser and metering line: 200.00 g Mineral oil (n 100 degrees C = 3.9 mm ² / s) 17.11 g Methacrylic acid ester of a C12-C15 alcohol spectrum with 23% branched alcohols. 5.11 g Methacrylic acid ester of an unbranched C16-C18 alcohol spectrum 0.63 g tert-butyl peroctoate

The components are dissolved under nitrogen and the following mixture is metered in at 85 ° C. over a period of 210 minutes: 213.89 g Methacrylic acid ester of a C12-C15 alcohol spectrum with 23% branched alcohols 63.89 g Methacrylic acid ester of an unbranched C16-C18 alcohol spectrum 0.56 g tert-butyl peroctoate

A further 0.6 g of tert-butyl peroctoate are added 2 hours after the end of the feed. The polymerization time is 8 hours. The solution is then diluted to 40% by weight with 250 g of mineral oil (n 100 degrees C = 3.9 mm ² / s). A clear solution is obtained. The molecular weight (GPC) is 364,000, U = 1.82.

Claims (10)

1. A process for preparing compositions, based on the esters of naturally occurring long-chain fatty acids with monovalent C1-C6-alcohols (FAE), with improved low-temperature behaviour to be used as fuels or lubricants, characterised in that

   a) known PPD ("Pour Point Depressant") additives used for improving the low-temperature behaviour of mineral oils are added in amounts of 0.0001 to 10 wt.% based on the long-chain fatty acid esters FAE and

   b) cooled down to a temperature below the cold filter plugging point (determined according to DIN 51 458) of the long-chain fatty acid esters (FAE) without additives, and

   c) the resultant precipitates (FAN) are separated.
2. A process according to claim 1, characterised in that the long-chain fatty acids present in the esters are obtained from fluid vegetable oils.
3. A process according to claims 1 and 2, characterised in that the long-chain fatty acid esters (FAE) are formed, in an amount of at least 95 wt.%, from C12-C26 fatty acids.
4. A process according to claims 1 to 3, characterised in that the long-chain fatty acid esters (FEA) are methyl esters.
5. A process according to claim 4, characterised in that the long-chain fatty acid esters (FEA) are rape oil methyl esters.
6. A process according to claims 1 to 5, characterised in that the cold filter plugging point of the rape oil methyl esters is reduced from -15°C to -22°C.
7. A process according to claim 1, characterised in that the PPD additives are polymer compounds with a great number of alkyl side chains having 8 to 20 carbon atoms.
8. A process according to claim 7, characterised in that the PPD additives are polyalkyl(meth)acrylic acid esters (PAMA).
9. A process according to claim 8, characterised in that the polyalkyl(meth)acrylic acid esters are synthesised from monomeric esters of C1-C28 alcohols wherein at least 40 wt.% of the monomers contain alkyl groups above C8.
10. A process according to claims 1 to 9, characterised in that the process steps b) and c) are carried out within the temperature range of -20 to -30°C.

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