Compositions based on ethylene-vinyl acetate copolymers and their use as anti-gelling additives of paraffinic crude oils

Abstract

A polymeric composition suitable for lowering the Pour Point of paraffinic crude oils comprising a synergic mixture including at least two ethylene-vinyl acetate copolymers respectively having an average molecular weight Mw lower than 130,000 Dalton (measured via GPC), a content of vinyl acetate monomer ranging from 15 to 50% by weight, with the proviso that the content of vinyl acetate monomer in the respective copolymers differs from one copolymer to another, by over 5%, on a weight basis.

Claims

1. A polymeric composition suitable for lowering the Pour Point of paraffinic crude oils comprising a synergic mixture comprising at least two ethylene-vinyl acetate (EVA) copolymers having an average molecular weight M.sub.w ranging from 25,000 to 100,000 Dalton (measured via GPC), a content of vinyl acetate (VA) monomer ranging from 15 to 50% by weight, respectively, with the proviso that the content of vinyl acetate monomer in the respective at least two ethylene-vinyl acetate copolymers differs from one another by a value higher than 5% on a weight basis, wherein the synergic mixture does not comprise an alkyl(meth)acrylate polymer.

2. The polymeric composition according to claim 1, wherein the number of EVA copolymers in the synergic mixture ranges from 2 to 6.

3. The polymeric composition according to claim 1, wherein the EVA copolymers have a weight average molecular weight M.sub.W ranging from 25,000 to 80,000 Dalton.

4. The polymeric composition according to claim 1, wherein the content of VA comonomers, on a weight basis, differs from one copolymer to another by a value from 7 to 22%.

5. The polymeric composition according to claim 1, wherein the synergic mixture comprises three EVA copolymers having a content of vinyl acetate comonomer of 20, 30 and 40% by weight, respectively.

6. The polymeric composition according to claim 1, wherein the synergic mixture comprises three EVA copolymers having a content of vinyl acetate comonomer of 24, 33 and 40% by weight, respectively.

7. The polymeric composition according to claim 1, wherein the concentration of a single EVA copolymer, in the synergic mixture, is equal to or higher than 5% by weight.

8. The polymeric composition according to claim 7, wherein the concentration of said single EVA copolymer in the synergic mixture ranges from 10 to 60% by weight.

9. A process for the lowering the Pour Point of a paraffinic crude oil having a paraffin content higher than 5% by weight, which comprises adding, to the paraffinic crude oil, from 50 to 1,500 ppm (by weight), with respect to the crude oil, a synergic mixture comprising at least two ethylene-vinyl acetate copolymers respectively having an average molecular weight M.sub.W ranging from 25,000 to 100,000 Dalton (measured via GPC), a content of vinyl acetate monomer ranging from 15 to 50% by weight, with the proviso that the content of vinyl acetate monomer in the respective at least two ethylene-vinyl acetate copolymers differs by a value higher than 5% on a weight basis, wherein the synergic mixture does not comprise an alkyl(meth)acrylate polymer.

10. The process according to claim 9, which comprises: a. dissolving the synergic mixture in an organic solvent to obtain a solution (a), b. adding the solution (a) to the paraffinic crude oil at the fluidification temperature of the crude oil, with a concentration of the synergic mixture in the crude oil ranging from 50 to 1,500 ppm.

11. The process according to claim 10, wherein the solution (a) comprises from 1 to 10% by weight of the synergic mixture.

12. The process according to claim 10, wherein the organic solvent is an aromatic hydrocarbon, an aliphatic hydrocarbon, a polar solvent, or mixtures thereof.

13. The process according to claim 9, wherein the synergic mixture is added to the paraffinic crude oil together with a surfactant with a hydrophilic lipophilic balance (HLB), higher than or equal to 10.

14. A paraffinic crude oil having a Pour Point lower than 10 C. comprising: i. a paraffinic crude oil with an average content of paraffins higher than 5% by weight; and ii. 50-1,500 ppm (by weight) with respect to the crude oil of a synergic composition comprising at least two ethylene-vinyl acetate copolymers having a weight average molecular weight M.sub.W ranging from 25,000 to 100,000 Dalton (measured via GPC), a content of vinyl acetate monomer ranging from 15 to 50% by weight, with the proviso that the content of vinyl acetate monomer in the respective at least two ethylene-vinyl acetate copolymers differs from one another by a value higher than 5% on a weight basis, wherein the synergic composition does not comprise an alkyl(meth)acrylate polymer.

Description

(1) An object of the present invention therefore relates to a synergic composition, also described in the enclosed claims, suitable for decreasing the Pour Point of paraffinic crude oils, also below 10 C., comprising (or consisting of) at least two ethylene-vinyl acetate copolymers, possibly dissolved in a solvent, respectively having a weight average molecular weight M.sub.W lower than 130,000 Dalton (measured via GPC), a content of vinyl acetate monomer ranging from 15 to 50% by weight, with the proviso that the content of vinyl acetate monomer in the respective copolymers, differs, with respect to each other, by over 5% on a weight basis. In other words, the difference in the concentration of the VA comonomer, between one EVA copolymer and another, is higher than 5% by weight.

(2) Alternatively, the synergic mixture comprising at least two ethylene-vinyl acetate copolymers having a different concentration of vinyl acetate monomer, can be substituted by a mixture, also synergic, comprising or consisting of one or more ethylene-vinyl acetate copolymers, as above, and at least one alkyl (meth)acrylate polymer wherein the alkyl group or alkyl side chain contains from 8 to 25 carbon atoms. The concentration of alkyl(meth)acrylate polymer in this second synergic composition, which is a further object of the present invention, ranges from 1 to 50% by weight.

(3) EVA copolymers are semi-crystalline polymeric resins synthesized through the copolymerization of ethylene with the second polar VA monomer, by means of a high-pressure process through radical synthesis. During the synthesis process, the comonomer is inserted in a purely random way inside the polymeric chains. As the reaction kinetics of ethylene and vinyl acetate are very similar, the content of comonomer in the EVA copolymers is in any case equal to the VA concentration in the reaction mixture, also under the experimental conditions adopted. As the comonomer is inserted randomly and not regularly in the chains, however, the EVA copolymers are characterized by polyethylene sections, between one molecule of VA and the next one, having a different length, i.e. by a distribution of polyethylene fractions composed of a different number of carbon atoms. The most probable length of the polyethylene sections, on which the distribution is centred, depends directly on the content of VA (Salyer, Kenyon, Journal of Polymer Science: Part A-1, Vol. 9 (1997), 3083-3103). Numerous properties of EVA copolymers depend on the percentage of VA comonomer and, among these, for example, also the crystallization point which decreases linearly with an increase in the content of VA in the chains.

(4) The polyethylene part of the EVA copolymers is capable of co-crystallizing with the paraffin fractions present within the crude oils, whereas the polar acetate group prevents the excessive growth of the crystals by altering or disturbing the crystalline structure. The co-crystallization will improve when the paraffins and polyethylene sections of the EVA copolymers have a comparable length.

(5) As crude oils are characterized by various paraffinic fractions having different lengths, the advantage of using the mixtures of EVA grades having a different VA content, instead of single grades, lies in the fact that the distribution of polyethylene sections that can co-crystallize with a wider range of paraffins, is enlarged, thus decreasing the PP more effectively. On the basis of what is specified above, the use of EVA with contents of VA which are such as to be at least partially immiscible with each other, i.e. each maintaining a distinct crystallization point when mixed with each other, proves to be particularly effective.

(6) According to a preferred aspect of the synergic composition object of the present invention, the number of EVA copolymers ranges from 2 to 6, more preferably from 3 to 5. EVA copolymers having a weight average molecular weight M.sub.W ranging from 15,000 to 100,000 Dalton, more preferably from 25,000 to 80,000 Dalton, are preferred. The minimum concentration of a generic EVA copolymer in the synergic mixture is at least 5% by weight, preferably from 10 to 60% by weight.

(7) Furthermore, according to the present invention, the content of vinyl acetate monomer in the EVA copolymer preferably ranges from 18 to 45% by weight, more preferably from 20 to 40% by weight, said content, on a weight basis, differs from one copolymer and another by over 5%, preferably from 7 to 22%.

(8) The mixtures of EVA copolymers object of the present invention, can be applied at a very low concentration, for example, from 50 to 1,500 ppm (weight) of overall copolymer with respect to the crude oil, preferably from 100 to 1,000 ppm, after being dissolved, for example, in a solution of a suitable solvent or carrier.

(9) In particular, mixtures of 3 EVA copolymers with a VA content of 20-30-40% or 24-33-40% respectively, for example, are considered as being particularly preferred. Preferably, the weight proportion of the copolymers of the mixture can be substantially defined empirically with reference to the molecular weight distribution of the waxes/paraffins of the crude oil (with reference to the linear paraffinic chains having a carbon atom content (C) of between 18 and 50). It is also effective to select the additives by testing them beforehand individually in a pre-determined amount (for example, 1,000 ppm (weight) each), and subsequently, after identifying the VA range which interferes most with the PP, adding the other two vicinal additives (with VA equal to about 7 in an amount of about of the most effective additive). The mixture thus formed can be re-used at 1,000 ppm (weight), for example, obtaining an improved result. It may also be convenient to use two vicinal additives having a VA content which is such as to comprise that of the most effective additive in equivalent amounts, obtaining an improved effect together with a third additive with a content equal to of the first two. Each of the above-mentioned copolymers can be substituted by a mixture of two copolymers having an average VA equal to that desired and with a VA of the single components which does not differ by more than 5% (therefore, for example, 20-(28-33)-40%).

(10) The presence of various EVA copolymers which co-crystallize with the n-paraffins present in the crude oil, allows disturbing elements to be introduced during the whole crystallization phase of the same petroleum waxes, obtaining the modification of the crystals of n-paraffins thus formed within the whole range of crystallization temperatures for crude oils characterized by a high content of waxes and a high Pour Point.

(11) The synergic mixture of EVA copolymers object of the present invention can be advantageously used together with a surfactant with a Hydrophilic Lipophilic Balance (HLB)10, preferably ranging from 10 to 15, such as, for example, an ethoxylated C.sub.8-C.sub.18 alkyl-phenol, ethoxylated or propoxylated C.sub.8-C.sub.18 alcohols, C.sub.2-C.sub.6 alkylates of sorbitol and mixtures thereof.

(12) The synergic mixture of EVA copolymers object of the present invention, can also be associated with the use of a different type of PPD, such as an alkyl(meth)acrylate polymer (adjuvant) wherein the alkyl group or alkyl side-chain contains from 8 to 25 carbon atoms, preferably from 12 to 22, in order to obtain particularly low PPs, lower than 0 C. In particular, adjuvants consisting of mixtures of said acrylic polymers are suitable, wherein from 10 to 40% by weight consists of polymers characterized by C.sub.12-C.sub.14 alkyl side-chains (alkyl radicals), from 40 to 80% by weight by C.sub.16-C.sub.18 alkyl side-chains (alkyl radicals) and from 0 to 30% by weight by C.sub.18-C.sub.22 alkyl side-chains (alkyl radicals).

(13) The PPD adjuvant, when present, is used in a quantity ranging from 1 to 50% by weight, preferably from 7 to 35% by weight of the overall synergic mixture with the EVA copolymers. Synergic mixtures containing from 10% to 30% by weight of polyalkyl(meth)acrylate adjuvant are particularly preferred.

(14) A further object of the present invention, as described in the enclosed claims, relates to a process for reducing the Pour Point of paraffinic crude oils having a content of paraffins>C.sub.5, for example C.sub.5-C.sub.100, ranging from 5 to 35% by weight, preferably from 10 to 25% by weight, said process comprising (or consisting in) adding, to the crude oil, the synergic mixture of EVA copolymers, also object of the present invention and previously described, possibly pre-diluted, according to methods well-known to skilled persons in the field, in an organic solvent, preferably aromatic, such as toluene, xylene, ethylbenzene, naphtha 100 solvent, naphtha 150 solvent; aliphatic solvent such as hexane, cyclohexane, decalin; polar solvents such as, for example, acetophenone, cyclohexanone; or mixtures thereof, preferably the acetophenone/aromatic mixture, in a 30/70 mixture (parts by weight).

(15) A third object of the present invention, also described in the enclosed claims, relates to a paraffinic crude oil characterized by a Pour Point also lower than 10 C. comprising (or consisting of): i. a paraffinic crude oil with an average content of paraffins higher than 5% by weight; and ii. 50-1,500 ppm (by weight) with respect to the crude oil, of a synergic composition comprising (or consisting of) at least two ethylene-vinyl acetate copolymers, possibly dissolved in a solvent, respectively having a weight average molecular weight M.sub.W lower than 130,000 Dalton (measured via GPC), a content of vinyl acetate monomer ranging from 15 to 50% by weight, with the proviso that the content of vinyl acetate monomer in the respective copolymers differs from one another by a value higher than 5% on a weight basis.

(16) The present invention will be now described with reference to the following examples which represent an illustrative and not limiting embodiment of the present invention.

(17) Mixtures of EVA grades were used, characterized by VA percentages ranging from 12 to 45% by weight, a fluidity index (ISO 1133) ranging from 3 g/10 to 800 g/10 and a weight average molecular weight (measured via high-temperature GPC) lower than 130,000 Dalton.

(18) Solutions of EVA copolymers were prepared in aromatic solvents (xylene, xylene/acetophenone mixtures 70/30) in concentrations ranging from 1% to 10% of the polymeric part; the mixture of EVA grades used (the VA percentage and the ratios between the components) is created in relation to the content and composition of the paraffinic fraction of the crude oil. The mixture of EVA copolymers was diluted in the solvent by hot mixing (70-85 C.) for at least 30-60 minutes. The additive and ethoxylated nonylphenol surfactant were added to the crude oil at room temperature, heating the crude oil only to the temperature sufficient for making it fluid (T=30-40 C.), or after exceeding its activation temperature, or at an intermediate temperature. The sample was then mixed by vigorous manual stirring. The surfactant can be added to the crude oil either individually or dissolved in solution with the EVA copolymers.

(19) In particular, the crude oil subjected to the test is a paraffinic crude oil having a PP of 27 C., characterized by a high paraffin fraction (21% m/m, concentration measured by applying the method BP237).

(20) The Pour Point of the crude oil as such and containing additives was measured according to the provisions of the standard ASTM D5853 and ASTM D97, after activation of the crude oil by thermal treatment at a temperature of about 85 C.

(21) The results obtained are provided hereunder. Blank tests were carried out to verify that the solvent did not influence the result.

(22) The Pour Point values measured for the EVA additives added individually are also indicated (comparative examples A-N and P) at two different concentrations in the crude oil (500 ppm and 1,000 ppm by weight).

(23) TABLE-US-00001 TABLE 1 (comparative results) Additive Surfactant PP (ppm) (ppm) ( C.) Paraffinic % 0 0 27 Crude oil A 1% Additive in EVA (18% VA, 150 g/10) 100 500 0 27 Xylene 1000 0 21 B 1% Additive in EVA (20% VA, 20 g/10) 100 500 0 24 Xylene 1000 0 27 C 1% Additive in EVA (23% VA, 5.5 g/10) 100 500 0 15 Xylene 1000 0 12 D 1% Additive in EVA (28% VA, 25 g/10) 100 500 0 18 Xylene 1000 0 15 E 1% Additive in EVA (28% VA, 40 g/10) 100 500 0 18 Xylene 1000 0 15 F 1% Additive in EVA (28% VA, 150 g/10) 100 500 0 15 Xylene 1000 0 12 G 1% Additive in EVA (28% VA, 800 g/10) 100 500 0 18 Xylene 1000 0 12 H 1% Additive in EVA (33% VA, 45 g/10) 100 500 0 18 Xylene 1000 0 27 I 1% Additive in EVA (39% VA, 60 g/10) 100 500 0 24 Xylene 1000 0 27 L 1% Additive in Polyacrylate C.sub.12-C.sub.18 100 500 0 27 Xylene 1000 0 21 M 1% Additive in Polyacrylate C.sub.12-C.sub.22 100 500 0 21 Xylene 1000 0 21 N 1% Additive in Polyacrylate C.sub.18-C.sub.22 100 500 0 24 Xylene 1000 0 24 P 1% Additive in Polyacrylate C.sub.12-C.sub.22 50 1000 200 18 Xylene EVA (28% VA, 800 g/100) 50

(24) TABLE-US-00002 TABLE 2 (Results according to the invention) Additive Surfactant PP (ppm) (ppm) ( C.) Paraffinic 0 0 27 Crude oil Surfactant 0 1000 27 1 5% Additive in EVA (20% VA, 20 g/10) 25% 50 1000 18 Xylene/Acetophenone EVA (28% VA, 40 g/10) 25% 70/30 EVA (33% VA, 45 g/10) 25% 1000 1000 9 EVA (40% VA, 60 g/10) 25% 2 8% Additive in EVA (20% VA, 20 g/10) 25% 1000 1000 9 Xylene/Acetophenone EVA (28% VA, 40 g/10) 25% 70/30 EVA (33% VA, 45 g/10) 25% EVA (40% VA, 60 g/10) 25% 3 10% Additive in EVA (20% VA, 20 g/10) 25% 1000 0 9 Xylene/Acetophenone EVA (28% VA, 40 g/10) 25% 70/30 EVA (33% VA, 45 g/10) 25% 1000 1000 9 EVA (40% VA, 60 g/10) 25% 4 5% Additive in Xylene EVA (20% VA, 20 g/10) 25% 200 1000 18 EVA (28% VA, 40 g/10) 25% 500 1000 12 EVA (33% VA, 45 g/10) 25% 1000 1000 9 EVA (40% VA, 60 g/10) 25% 1500 1000 9 5 5% Additive in EVA (18% VA, 150 g/10) 25% 50 1000 12 Xylene/Acetophenone EVA (28% VA, 800 g/10) 25% 70/30 EVA (33% VA, 45 g/10) 25% 1000 1000 9 EVA (39% VA, 60 g/10) 25% 6 5% Additive in Xylene EVA (18% VA, 150 g/10) 25% 200 1000 12 EVA (28% VA, 800 g/10) 25% 500 1000 12 EVA (33% VA, 45 g/10) 25% 1000 1000 9 EVA (39% VA, 60 g/10) 25% 1000 200 9 7 5% Additive in Xylene EVA (20% VA, 20 g/10) 17% 1000 1000 9 EVA (28% VA, 800 g/10) 35% EVA (39% VA, 60 g/10) 48% 8 5% Additive in Xylene EVA (20% VA, 20 g/10) 17% 1000 1000 6 EVA (28% VA, 800 g/10) 33% EVA (39% VA, 60 g/10) 17% Polyacrylate C.sub.18-C.sub.22 33% 9 5% Additive in Xylene EVA (20% VA, 20 g/10) 17% 1000 1000 3 EVA (28% VA, 800 g/10) 33% EVA (39% VA, 60 g/10) 17% Polyacrylate C.sub.12-C.sub.22 33% 10 5% Additive in Xylene EVA (20% VA, 20 g/10) 10% 500 200 9 EVA (28% VA, 800 g/10) 50% 750 200 3 EVA (39% VA, 60 g/10) 10% 1000 200 3 Polyacrylate C.sub.12-C.sub.22 30% 1500 200 3 11 5% Additive in Xylene EVA (18% VA, 150 g/10) 10% 1000 200 9 EVA (28% VA, 800 g/10) 32% Polyacrylate C.sub.12-C.sub.22 26% EVA (39% VA, 60 g/10) 32% 12 5% Additive in Xylene EVA (23% VA, 5.5 g/10) 52% 1000 200 0 EVA (33% VA, 45 g/10) 30% EVA (39% VA, 60 g/10) 18% 13 5% Additive in Xylene Polyacrylate C.sub.12-C.sub.18 25% 1000 200 3 Polyacrylate C.sub.18-C.sub.22 10% EVA (18% VA, 150 g/10) 7% EVA (23% VA, 5.5 g/10) 11% EVA (28% VA, 150 g/10) 13% EVA (33% VA, 45 g/10) 16% EVA (39% VA, 60 g/10) 18% 14 5% Additive in Xylene Polyacrylate C.sub.12-C.sub.22 26% 1000 200 3 EVA (18% VA, 150 g/10) 7% EVA (23% VA, 5.5 9/10) 12% EVA (28% VA, 150 g/10) 15% EVA (33% VA, 45 g/10) 20% EVA (39% VA, 60 g/10) 20% 15 5% Additive in Xylene EVA (20% VA, 20 g/10) 10% 1000 200 3 EVA (28% VA, 25 g/10) 50% EVA (39% VA, 60 g/10) 10% Polyacrylate C.sub.12-C.sub.22 30% 16 5% Additive in Xylene EVA (23% VA, 5.5 g/10) 47% 1000 200 6 EVA (33% VA, 45 g/10) 25% EVA (39% VA, 60 g/10) 18% Polyacrylate C.sub.12-C.sub.22 10%

(25) The mixtures of additives tested (examples 1-16), added to the paraffinic crude oil in concentrations equal to 1,000 ppm by weight, produced reductions in the Pour Point down to 6 C., whereas the EVA products or polyalkylacrylates added individually (final concentration in the crude oil of 1,000 ppm) led to poorer decreases in the Pour Point (examples A-N and P). This confirms the synergic effect of the EVA grades, characterized by different contents of VA comonomer, in reducing the gel point in the tested waxy crude oil for co-crystallization with a wider range of n-paraffins.

(26) It should be noted that some of the additives used proved to be almost completely inefficient if added alone, whereas they produced significant reductions in the PP when mixed with other products. In particular, in examples 1-2-3-4, it can be observed how the addition of as little as 250 ppm of an additive which individually proved to be poorly effective (example E), causes, when mixed with other EVA copolymers, a further lowering of the PP with respect to the additive used alone in a concentration equal to 1,000 ppm. It should be noted that the other EVA copolymers used in the mixtures of examples 1, 2, 3 and 4 proved to be ineffective (examples B-H-I) when used individually.

(27) The formulations were conceived according to the criteria described above, i.e. mixtures of EVA copolymers were prepared, consisting of copolymers characterized by differences in percentage of VA higher than 5% and, preferably equal to at least 7%. The PP tests carried out with mixtures consisting of copolymers having closer VA contents, in fact, indicated that the use of a greater number of EVA copolymers having similar percentages of comonomer (VA5%) does not imply a significant improvement in the efficacy of the additive (see examples 1-7), particularly if used in the absence of the polyalkylmethacrylate adjuvant.

(28) Finally, the best results in lowering the Pour Point were obtained by testing mixtures of EVA copolymers with different VA contents, to which polyalkylmethacrylates characterized by C.sub.12-C.sub.22 side-chains, were added. The addition of these products, in fact, led to a further enlargement of the distribution of polyethylene sections in the additive, capable of co-crystallizing with the n-paraffins present in the crude oil.