Title of Invention

"A COMPOSITION OF COPOLYMERS OF ALKYL ACRYLATES OR OF ALKYL ACRYLATES / VINYLPYRIDINE AND PROCESS THEREOF"

Abstract

ACRYLIC COPOLYMERS AS ADDITIVES FOR INHIBITING THE DEPOSITION OF PARAFFINS IN CRUDE OILS AND COMPOSITIONS CONTAINING THE OILS AND THE SAID ADDITIVES Acrylic copolymers which can be used as additives for inhibiting the deposition of paraffins in crude oils and compositions containing the oils and the said additives. The present invention relates to polymeric additives which can be used for inhibiting the deposition of paraffins and improving the flow properties of crude oils, as well as to compositions containing crude petroleum oils and the said additives. These are essentially copolymers of acrylates of alcohols containing from 10 to 50 carbons, with specific chain distributions which are given in the patent, as well as the corresponding terpolymers of 2- and/or 4-vinylpyridine.

Full Text

TECHNICAL FIELD The field of the invention described here is that of crude petroleum oils and additives intended to improve the conditions for their exploitation. Crude oils may contain large fractions of paraffins, the amount and exact nature of which are variable depending on the fields from which they are extracted. At the temperature of the well, paraffins are liquid and dissolved in the crude oil. During the raising of the oil to the surface, its temperature falls and the paraffins, on crystallizing, form a three-dimensional network of needles and flakes. This results in a loss of fluidity which makes the production, transportation, storage and even the treatment of these oils very difficult. Blockages in the pipelines and in the processing equipment are frequent. PRIOR ART Many processes have been proposed to solve this problem, such as mechanical scraping or heating of the walls. These processes are expensive and they cannot always be used. To improve the rheology of crude petrols, Shell has carried out pioneering work in FR 1,575,984: this teaches that macromolecular compounds of "comb" type constructed on the model of a main hydrocarbon chain on which are grafted side chains which are themselves fairly long hydrocarbons, that is to say atleast 14 carbon atoms and not more than 30 carbon atoma, may disrupt the crystallization cf heavy paraffins. This property is well developed in macromolecules whose average molecular mass (number-average molecular mass Mn, the definition of which is recalled where the Mi values are the molecular masses of the Ni individual species present in the polymer) is between 1000 and 1/000,000 and preferably between 4000 and 100,000. It has thus been suggested to use additives, usually polymeric additives, whose role is to retard or to modify the crystallization of the paraffins and consequently to improve the flow properties of the oil and to prevent agglomeration of the crystals formed on the walls. Many studies have subsequently attempted to improve the efficacy of these first additives of polymeric nature either by synthesis or by formulation, in order to adapt them to the various types of crude oils encountered, and successively to overcome the difficulties in the synthesis and/or handling of the various generations of products such as, for example, among the most effective, copolymers of C18.30, preferably mainly C20.22/ acrylates with a heterocyclic monomer, in particular vinylpyridine [Patents US 2,839,512 (1958) and FR 2,128,589 (1972) from Shell]. The presence of polar units imparts a dispersing nature to the copolymer, which makes it possible to prevent deposition of the paraffins on the walls. However, on account of the higher reactivity of long-chain acrylates when compared with that of polar comonomers, these acrylates are generally very difficult to incorporate and the dispersing effect associated with the level of incorporation of the polar comonomer therefore often remains very low. Despite these successive improvements, these additives cannot be applied universally to all crude oils, since each one is a particular case and poses its own specific problem. ACCOUNT OF THE INVENTION It has just been found, very unexpectedly, that the performance of paraffin inhibitors of alfcyl acrylate copolymer or alkyl acrylate/vinylpyridine copolymer type can be improved considerably when some of the alkyl acrylate monomer units participating in the polymer chain, which units can be represented by (Formula Removed)residues of in which the groups Ri are saturated linear aliphatic alcohol residues Ri-OH, the number of carbon atoms of which ranges from about 10 to about 50, originate from an acrylic fraction having a specific distribution of the alkyl chains, referred to for the purpose of the present patent as a "U" distribution. The term "U" distribution is understood to mean a distribution of the alkyl chains as a function of the length of the chains, here all in an even number of carbons, the envelope of which is very uniform/ the weight-aver age molecular mass Mw of which is between 375 and 700, the number-average molecular mass Mn of which is between 375 and 840, and the polydispersity factor Mw/Mn of which is between 1.0 and 1.2 (Mw is the weight-average molecular mass, the formula for calculation of which is recalled Mw = Zj NiMi2/ Ij NiMi, where the values Mi are the molecular masses of the Ni individual species present in the polymer). Figure 1 gives a representation of the distribution of alcohols distributed according to such a law of "U" distribution with an average molecular mass of 425 (for the production of such alcohols, see US 4,426,329). The acrylate polymers obtained by polymerization only of monomers with a "U" distribution are not particularly distinguished from those which are obtained from arbitrary monomers, this term being understood to mean5 products usually available to those skilled in the art and in which no specific pendant chain length distribution is sought, in other words products whose distribution is random and, in any case, is not a "U" distribution. The feature which is very surprising, and from which the Applicant is extracting all the advantageous consequences, is that powerful synergism develops as regards the inhibition of crystallization of the paraffins in the petroleum oils when products of the "U" class and of the "non-U" class are distributed in the same polyacrylic or polyacrylic/vinylpyridine copolymer. As with any synergism in mixtures which may be of highly variable composition, the rules are difficult to determine, but the directing principles thereof may be stated, which will be of the greatest use to those skilled in the art: the "U" components are centred on average pendant chain lengths iu which are higher than those inu of the "non-U" components, and the weight in the copolymer of all of the units containing "U" chains is relatively low relative to that of all of the "non-U" units. For the purposes of the invention, vinylpyridine is understood to refer to 2-vinylpyridine, 4-vinylpyridine or a mixture of both. The copolymers of the invention contain from 1 to 10% thereof. In terms of structural description, it may be stated that alkyl acrylate copolymers or alkyl acrylate/vinylpyridine copolymers of weight-averagemolecular mass Mw between 5000 and 500,000, preferably between 40,000 and 350,000, form part of the invention, in which the acrylate monomer units which participate in the polymer chain (Formula Removed)in which the groups Ri are saturated linear aliphatic alcohol residues Ri-OH where i represents the number of carbons of these residues, which ranges between 10 and 50 carbon atoms, and follow a distribution law which is the superposition of a "U" distribution law, in which the values i are even numbers developed on the high part 24-50 of the range, the centre value of which is iu, and of a "non-U" distribution law, in which the values i are even or odd numbers developed on the low part 10-22 of the range and the centre value inu of which is such that inu (Formula Removed)containing Ri distributed according to the "U" law to all of the units distributed according to the "non-U" law ranging from 1:99 to 50:50, and preferably from 5:95 to 50:50. The paraffin-inhibitory formulations incorporating these copolymers as essential components overcome the drawbacks mentioned above and allow the production of a series of additives with a broad spectrum of use which are endowed with good solubility in the crude oils, and which moreover have an effect both on the crystallization of paraffins and on the dispersion of crystals which are already formed. They retard the crystallization of paraffins whose distribution generally ends between C60 and C70, allow lowering of the flow point and the viscosity of these oils and facilitate their transportation, storage and processing. They are readily incorporated into crude oils of very diverse origins. EMBODIMENT OP THE INVENTION The copolymers according to the invention may be obtained according to a simple and relatively non-restricting polymerization process. The invention also offers those skilled in the art the possibility of selecting, by simple routine tests, the polymer alkanol fraction which will be of greatest similarity with the crude oil to be treated and which will correspond to the best efficacy. Results in this sense are presented in the examples. The best results are obtained with random copolymers of acrylates of "U" and "non-U" alcohols or of acrylatea of "U" and "non-U" alcohols and vinylpyridine which contain from 5 to 50% "U" monomers centred on C24 to C50, the characteristics and efficacy of the copolymers being defined by the choice of solvent/initiator couple. The preferred "U" comonomers are acrylates of alcohols centred between C30 and C40. The polymeric additive is obtained according to the invention either by polymerization of monomers in toluene, xylene and, generally, in any aliphatic or aromatic solvent with a boiling point below 300°C, which is chemically inert towards the monomers, in which both the monomers and the copolymer are soluble, or, in the case of purely acrylic copolymers, by mixing acrylic homopolymers obtained separately in the same solvents. The polymerization temperature may vary fairly widely as a function of the radical initiator used, for example between 50 and 150°C and preferably between 70 and 120°C. The pressure may vary between atmospheric pressure and pressures below or equal to 30 bar. The presence of 1 to 10% of 2-vinylpyridine and/or 4-vinylpyridine units in the chains of the copolymers according to the invention substantially improves the efficacy thereof, at least with respect to certain types of oils. One example thereof is reported later, (x) counted on the total weight of "U" and "non-U" monomers, The catalysts are generally chosen from free-radical-generating compounds which are soluble in the reaction medium, such as, for example, peroxides such as benzoyl, acetyl or di-tert-butyl peroxide/ tert-butyl perbenzoate/ tert-butyl peroctoate or azo compounds such as azobisisobutyronitrile. 10"5 to 10"1 mol of catalyst and preferably from 5x10"4 to 10"2 mol per mole of monomer is generally used. The overall concentration of monomer in the solvent may range from 10 to 90% by weight, the preferred concentrations ranging from 20 to 70%, in order to control the molecular mass and the pumpability of solutions containing the polymeric additive. The degree of polymerization is measured by gel permeation chromatography (6PC), which makes it possible to achieve the weight-average molecular masses Hw and number-average molecular masses Mn of polystyrene equivalent and the polydispersity value Pd of the polymer. The weight-average molecular masses Mw and the number-average molecular masses Mn of the final copolymer used, alone or in combination with a second copolymer according to the invention, may vary within a wide range depending on the nature of the crude to be treated, i.e. between 5,000 and 500,000 for the Hw, preferably from 40,000 to 350,000, for a polydispersity Pd which may range between 1.5 and 7.5. INDUSTRIAL APPLICATION The copolymers according to the invention are used in crude oils at doses which may vary within a wide range depending on the nature, structure and molecular mass of the copolymer to be used, the nature and amount of paraffin waxes present in the crude oil and the desired performance in terms of lowering of the flow point; these doses may range from 5 to 5000 ppm by weight, preferably from 10 to 2000 ppm. They have a favourable influence on the rheology of the crude oils, in particular on their characteristics of viscosity as a function of the temperature and of the shear modulus, which controls in particular the pressure required to restart a plant (pipeline and wells) which has been stopped, on their flow point or setting temperature, on their starting point of crystallization, on their flow by simple gravity, and on the deposits which form on contact with cold walls. These are all highly important characteristics for the extraction, transportation and storage of the oils, and a few illustrations of these will be found in the laboratory tests intended to evaluate the efficacy of these additives. The antiparaffin compositions according to the invention consist of solutions of these copolymers or additives at concentrations ranging from 2 to 90% by weight, preferably from 20 to 70%, in solvents which are soluble in the crude petroleum oils which it is desired to treat and which may advantageously be the11 solvents used during the polymerization. EXAMPLES The production methods leading to various home-polymer/ copolymer or terpolymer compositions are described below to serve as examples or counterexamples, along with the characteristics of the copolymers obtained, these being collated later in Table I. In these examples, the "non-IP monomer acrylates 18-22 are acrylates of alcohols containing about 18-22 carbon atoms (marketed by Elf-Atochexn S.A. under the name Norsocryl® 18-22), the composition by weight of which is 0 "u""425 is a fraction of monomer acrylates of alcohols obeying the "U" distribution law, centred on 28-30 carbon atoms, the average molecular mass of which is 425. "U"550 likewise denotes a fraction of monomer acrylates of alcohols obeying the "U" distribution law, centred on C40, the average molecular mass of which is 550. m.18 denotes a supposedly pure stearyl methacrylate. The acrylates of alcohols are obtained by methods well known to those skilled in the art; direct esterification or transesterification catalysed byzirconium acetylacetonate. In Table I, the Mn, Mw and Pd columns reproduce the number-average molecular masses, weight-average molecular masses and the coefficient of dispersion, which is a ratio of Mw to Mn, respectively. EXAMPLE I - C18-C22 "non-U" acrylate homopolymer (Mw - 56,000) 438 kg of acrylate of n-alkyl with an average chain length of C18 to C22 in 359 kg of Solvantar 340® (i.e. a reaction medium containing about 55% solids) are introduced into aim3 reactor. The temperature of the reactor is subsequently brought to 40°C under vacuum while bubbling nitrogen through, and is maintained for 30 minutes, then at 100°C while the bubbling with nitrogen is maintained. 3 kg of tert-butyl perbenzoate (Luperox P® or Trigonox C®) are added continuously over 1 h 30 between 100 and 105°C, while monitoring the viscosity of the medium which is stable 2 to 3 hours after the end of the introduction of the initiator. The total polymerization time is 6 hours for a polymerization yield of greater than 98%. The product is then brought to 37% active material by addition of Solvantar 340®. EXAMPLE la - C18-C22 acrylate homopolymer (Mw - 119,000) The same operating conditions as those which are described in composition I are repeated, replacing the Solvantar 340® with xylene. EXAMPLE II - C18-C22 acrylate homopolymer (Mw - 104,000) 438 kg of acrylate of n-alkyl with an average chain length of C13 to C->o in 359 kg of Solvantar 340-are introduced into aim3 reactor. The temperature of the reactor is subsequently brought to 40°C under vacuum while nitrogen is bubbled through, and is maintained for 30 minutes, then at 80°C while maintaining the bubbling with nitrogen. 8 kg of dibenzoyl peroxide (Lucidol CH 50®) are added continuously over 1 h 30 between 80 and 85°C, while monitoring the viscosity of the medium which is stable 1 hour after the end of the introduction of the initiator. The total polymerization time is 4 hours for a polymerization yield of greater than 98%. The product is then brought to 37% active material by addition of Solvantar 340®. EXAMPLE III - C18-C22 acrylate homopolymer (Mw - 128,000) 558 kg of acrylate of n-alkyl with an average chain length of C18 to C22 in 239 kg of Solvantar 340® (reaction medium containing 70% solids) are introduced into aim3 reactor. The temperature of the reactor is subsequently brought to 40°C under vacuum while nitrogen is bubbled through, and is maintained for 30 minutes, then at 100°C while maintaining the bubbling with nitrogen. 3 kg of tert-butyl perbenzoate (Luperox P® or Trigonox C®) are added continuously over 1 h 30 between 100 and 105°C, while monitoring the viscosity of the medium which is stable 2 to 3 hoursafter the end of the introduction of the initiator. The total polymerization time is 6 hours for a polymerization yield of greater than 97%. The product is then brought to 37% active material by addition of Solvantar 340®. EXAMPLE IV - C18-C22 acrylate homopolymer {Mw - 268,000) 518 kg of acrylate of n-alkyl with an average chain length of C18 to C22 in 222 kg of xylene (reaction medium containing 70% solids) are introduced into a 1 m3 reactor. The temperature of the reactor is subsequently brought to 40°C under vacuum while bubbling nitrogen through, and is maintained at this temperature for 30 minutes and then at 100°C while maintaining the bubbling with nitrogen. 3 kg of tert-butyl perbenzoate (Luperox P® or Trigonox C®) are added continuously over 1 h 30 between 100 and 105°C, while monitoring the viscosity of the medium which is stable 2 to 3 hours after the end of the introduction of the initiator. The total polymerization time is 6 hours for a polymerization yield of greater than 97%. The product is then brought to 37% active material by addition of xylene. EXAMPLE V - Copolymer of C1B-C22 acrylate and of "U" type acrylate centred on C28-C30 - "U"425 in the table (ratio 90/10 - Mw - 123,000) - reaction performed in xylene (solids - 65%). EXAMPLE VI - Copolymer of C18-C22 acrylate and of "UM25 acrylate (ratio 80/20 - MW - 134,000} - reaction15 performed in xylene (65% solids). EXAMPLE Via - Copolymer of Cla-C-,-, acrylace and of "U"425 acrylate (ratio 80/20 - MW - 64,000) - reaction performed in xylene (solids - 55%). EXAMPLE VII - Copolymer of Cig-C22 "non-U" acrylate and of "U"425 acrylate (ratio 70/30 - MW - 146,000). 363 kg of acrylate of n-alkyl with an average chain length of C18 to C22 and 155 kg of "Un425 acrylate (ratio 70/30) in 279 kg of xylene (solids - 65%) are introduced into aim3 reactor. The temperature of the reactor is subsequently brought to 40°C under vacuum while bubbling nitrogen through, and is maintained for 30 minutes, then at 100°C while maintaining the bubbling with nitrogen. 30.3 kg of tert-butyl perbenzoate (Luperox P® or Trigonox C®) are added continuously over 1 h between 100 and 105°C, while monitoring the viscosity of the medium, which is stable 2 to 3 hours after the end of the introduction of the initiator. The total polymerization time is 6 hours for a polymerization yield of greater than 97%. The product is then brought to 37% active material by addition of xylene. EXAMPLE VIII - Copolymer of C18-C22 acrylate and of "U"425 acrylate (ratio 50/50 - Mw not measurable) EXAMPLE IX - "U"425 acrylate homopolymer (Mw not measurable) The same operating conditions as those described in composition III are repeated. The total16 polymerization time is 6 hours for a polymerization yield of greater than 95%. The product is then brought to 37% active material by addition of xylene. EXAMPLE X - Copolymer of C18-C22 acrylate and of a "U"550 acrylate of "U" alcohol centred on C40 (ratio 90/10 - Mw - 162,000) - reaction performed in xylene (65% solids). EXAMPLE XI - Copolymer of C18-C22 acrylate and of "U"550 acrylate (ratio 95/5 - Mw - 150,000) - reaction performed in xylene (solids - 65%). EXAMPLE XII - Copolymer of stearyl methacrylate and of BD"425 acrylate (ratio 70/30 - Mw - 317,000) EXAMPLE XIII - Terpolymer of stearyl methacrylate, C18-C22 acrylate and "U"425 acrylate (ratio 14/56/30 -Mw - 180,000). EXAMPLE XIV - Terpolymer of stearyl methacrylate, C18-C22 acrylate and "U'II425 acrylate (ratio 28/42/30 -Mw - 214,000). EXAMPLE XV - Terpolymer of 4-vinylpyridine, C18-C22 acrylate and "Un425 acrylate (ratio 5/66.5/28.5) - Mw - 221,000) . EXAMPLE XVI (counter-example): copolymer of 4-vinylpyridine and C18-C22 acrylate (ratio 5/95 -solubility failure, Mw not measurable) EXAMPLE XVII (counter-example): copolymer of 4-vinylpyridine and "U"425 acrylate (ratio 5/95 -solubility failure, Mw not measurable).17 EXAMPLES XVIII TO XXII In these examples, various compositions containing 37% additives were incorporated into crude oils - i.e. 20°C above the flow point of the crude with stirring - at concentrations ranging from 100 to 1500 ppxn. The performances obtained for the polymers according to the invention were compared relative to the control with Shellswimm 5X® and Shellswimm 11T®, two well-known paraffin inhibitors marketed by the Shell Oil Company. (Table Remved) Several types of approaches exist to determine the efficacy of these polymers known as paraffin-deposit inhibitors, among which are the Theological behaviour of the crudes and the lowering of their flow point. By modifying the phenomena of crystallization of the crude oils, the paraffin inhibitors directly influence their rheological characteristics. It is clear that during the industrial use of these products in production/transportation, the rheological measurements will take their performance directly into account. The viscosity as a function of the shear is measured in particular. The crude oils generally have a rheological behaviour of Binghamian plastic fluid type, that is to say that the shear tension varies linearly with the shear rate. In contrast with Newtonian fluids, it is necessary to apply a minimum force in order to set the fluid into motion. This force corresponds to the minimum shear tension (yield value or yield point). This measurement is commonly carried out on production sites, since it makes it possible by a simple calculation to evaluate the pressure required to restart a plant (pipe and wells) which has been stopped. It is this starting pressure which paraffin-inhibitor additives are capable of lowering considerably, by disorganizing the crystalline lattices20 in formation. A Farm-type viscometer is used to measure this yield value, and the stress is measured as a function of the rate gradient applied to the spindle. The curve obtained has an asymptote, and it suffices to extrapolate the straight line of the asymptote to zero shear in order to obtain the flow threshold value: AP=4Z-D The flow point or setting temperature of the crudes is also a very important characteristic for evaluating the rheological properties of a crude oil. This characteristic is measured under very precise conditions dictated by ASTM standard O97B. It is generally accepted that a compound belongs to the class of flow point decreases if it is capable of bringing about an at least 6°C lowering of the flow point for a dose used not exceeding 0.2% by weight of polymeric additives. The non-limiting examples which follow show the advantages provided by the invention on different crudes. EXAMPLE XVIII: Modification of the flow point of a crude from Gabon The oil tested is a crude with a density of 852 kg/m3 (15°C) and whose paraffin content (determined by gas chromatography) is 15%. Its flow point, measured21 under the conditions of ASTM standard D 97 B, is 18°C. The flow points obtained with two compositions containing 37% additives described in Examples I to XVII above and the flow temperature differences observed relative to the untreated crude are reported in Table II below. It is noted that the optimum efficacy obtained with copolymer VII (70/30) is considerably improved with terpolymer XV, which can, all in all, be considered as a copolymer between 4-vinylpyridine and copolymer VII in a 5/95 (or more precisely 5/66.5/28.5) mass ratio, to the point that the lowering of the flow temperature can no longer even be measured by the tests commonly adopted (flow point below -45°C).22 (Table Remved) a - Shellswimm 5X® is a composition containing 50% by weight of a homopolymer of acrylate of C18-C22 "non-U" alcohol, marketed by Shell. b - Shellswimm 11T® is a composition containing 50% by weight of a copolymer of acrylate of C18-C22 "non-U" alcohol and of vinylpyridine, marketed by Shell. The graph in Figure 2 shows the lowering of the flow point of this Gabon crude with 100 ppm of a composition containing 37% "non-U"18-22 acrylate/acrylate of "U" alcohols centred on C30 copolymer as a function of the percentage of C30 acrylate in the copolymer. This graph clearly shows the advantage of copolymers containing from 5 to 50% of acrylate of "U" alcohols centred on C30 on this type of crude oil, and more particularly that of the copolymer of Example VII containing 30% acrylate of "U" alcohol centred on C30, as well as the 50% threshold beyond which a considerable reduction in efficacy, associated with the decreased solubility of the copolymer, is observed. This efficacy is not as considerable with the corresponding 70/30 weight mixture of the C18-22 "non-U" and C30 "IT" homopolymers respectively for the same reasons. The graph shown in Figure 3 is a curve of the increase in flow point of the same Gabon crude as a function of the addition of variable amounts of the products of Examples IV and VII (37% compositions). It makes it possible to evaluate the improvement obtained with the composition of Example VII of the invention on this crude oil, compared with one of the references currently on the market, Shellswimm 5X®. An additional increase in efficacy is obtained by means of the addition of 4-vinylpyridine according to Example XV. EXAMPLE XIX: Modification of the flow point of an Egyptian crude I The oil tested is a crude with a density of 845 kg/m3 (15°C) and whose paraffin content is 15%. Its flow point, measured under the conditions of ASTM standard D97B, is +15°C. The flow points obtained with various compositions containing 37% additive, for two contents, described in the above example, and the differences in flow temperature relative to the untreated crude are reported in Table III. (Table Remved)The same comments as in Example XVIII may be made for this crude oil which is harder to process, the working doses here being between 1000 and 1500 ppm. EXAMPLE XX: Modification of the flow point of an Egyptian crude II. The oil tested is a crude with a density of25 820 kg/m3 (15°C) and whose paraffin content is 20-25%. Ita flow point is 27-30°C. The flow points obtained with various compositions containing 37% additive, for two contents, described in the above example, and the differences in flow temperature relative to the untreated crude are reported in Table IV. TABLE IV (Table Remved) The same comments as in Example XIX may be made for this other example of a crude oil having a flow point of 30°C, the working doses here also being between 1000 and 1500 ppm. The curves in Figures 4 and 5 illustrate, on the one hand, the improvement in the susceptibility to heac of the viscosicy of a crude oil by addition of 1000 ppm of composition VII (containing 37% polymer), the benefit of which is a significant decrease in its viscosity at low temperatures, and/ on the other hand, the beneficial influence on the flow threshold (yield value) at 15°C. EXAMPLE XXI: Modification of the flow point of an Egyptian crude III The oil tested is a crude with a density of 843 kg/m3 (15°C) and whose paraffin content is 10.4%. Its flow point is +9°C. The flow points obtained with 30 ppm of various compositions containing 37% additive and the differences in flow temperature relative to the untreated crude are reported in Table VI. (Table Remved) Here also, the noteworthy efficacy of additive VII and that of terpolymer XV are noted. EXAMPLE XXII: Modification of the flow point of a Syrian crude The oil tested is a crude with a density of 870 kg/m3 (15°C) and whose paraffin content is 6%. Itsflow point is 18°C. The flow points obtained with various compositions containing 37% additive described in the above example, for two contents, and the differences in flow temperature relative to the untreated crude are reported in Table VII. (Table Remved) The purpose of this new example is merely to confirm the broad spectrum of activity of the additives according to the invention and their superiority compared with the products existing on the market. All these examples show the noteworthy and unexpected efficacy of the copolymers of acrylates of primary fatty alcohols with "u" distribution and of compositions containing them according to the invention, with regard to the improvement in the overall behaviour of the crude oils, with, in particular, a considerable lowering of the flow point and of the flow threshold of the crude oila containing these additives. 1. Copolymers of alkyl acrylates or of alkyl acrylates/vinylpyridine of weight -average molecular mass Mw between 5000 and 500,000, preferably between 40,000 and 350,000, in which the acrylate monomer units which participate in the polymer chain are units (Formual Removed)in which R is H or CH3/ in which the groups Ri are saturated linear aliphatic alcohol residues Ri-OH where i represents the number of carbons of these residues, which ranges between 10 and 50 carbon atoms, and which have the feature that they follow a distribution law which is the superposition of a "U" distribution law, in which the values i are even numbers developed on the high part 24-50 of the range, and of a "non-U" distribution law, in which the values i are even or odd numbers developed on the low part 10-22 of the range, the weight ratio of all of the units30 (Formual Removed)distributed according to the "U" law to all of the units distributed according to the "non-U" law ranging from 1:99 to 50:50, and preferably from 5:95 to 50:50. 2. Copolymers according to Claim 1, in which the "non-U" units and the "U" units are units of acrylates, 3. Alkyl acrylate copolymers according to Claims 1 or 2, containing, besides the acrylate units, from 1 to 10% by weight of vinylpyridine units relative to the copolymer. 4. Process for the production of the \ copolymers described in Claim 1, characterized in that a mixture of monomers is made to polymerize, in which mixture one part of the acrylic or xnethacrylic ester monomers (Formual Removed)obeys a "U" distribution law and the complementary par of the ester monomers obeys a "non-U" distribution law, the weight ratio between the set of esters distributed according to the "U" law and the set of esters distributed according to the "non-U" law ranging approximately from 5:95 to 50:50. 5. Process according to Claim 4, in which the mixture of acrylic or methacrylic esters is obtained by mixing together the esters of each of the "U" and "non-U11 distribution categories in a weight ratio of 1:99 to 50:50 and preferably from 5:95 to 50:50. 6. Process according to Claim 4, in which the mixture of the acrylic or methacrylic esters is obtained by prior mixing of the alcohols of each of the "U" and "non-U" distribution categories, followed by esterifying them with acrylic or methacrylic acid. 7. Process according to Claim 4, characterized in that it is performed in a solvent in which the monomers and the copolymer are soluble and the boiling point of which solvent is below 300°C. 8. Process according to Claim 7, characterized in that the solvent is xylene. Additive intended to lower the flow point of crude petroleum oils and to improve the rheological behaviour thereof, characterized in that it consists of copolymers described in Claim 1 and of aromatic and/or aliphatic solvent, the weight concentration of the copolymer in the additive being 32 between 2 and 90%, preferably between 20 and 70%. 10. Composition comprising a crude petroleum oil and a copolymer as described in Claim 1, in which the copolymer content is between 5 and 5000 ppm, preferably between 10 and 2000 ppm. 11. Copolymers of alkyl acrylates or of alkyl acrylates/ vinylpyridine/ substantially as hereinbefore described with reference to the foregoing examples and accompanying drawings. 12. Process for the production of the copolymers, substantially as hereinbefore described with reference to the foregoig examples and accompanying drawings. 13. Additive intended to lower the flow point of crude petroleum oils and to improve the rheological behaviour thereof, substantially as hereinbefore described with reference to the foregoing examples and accompanying drawings.

Documents:

615-del-1997-abstract.pdf

615-del-1997-claims.pdf

615-del-1997-corresponcene-po.pdf

615-del-1997-correspondence-others.pdf

615-del-1997-description (complete).pdf

615-del-1997-drawings.pdf

615-del-1997-form-1.pdf

615-del-1997-form-19.pdf

615-del-1997-form-2.pdf

615-del-1997-form-3.pdf

615-del-1997-form-4.pdf

615-del-1997-form-6.pdf

615-del-1997-gpa.pdf

615-del-1997-peition-137.pdf

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