COMPOSITIONS OF HYDROCARBONS FROM REFINING, HAVING IMPROVED FLUIDITY AT LOW TEMPERATURES

Abstract: The fluidity at low temperatures of compositions based on liquid hydrocarbons from refining is improved by means of the addition, preferably in solution, of ethylene/propylene/(conjugated diene) copolymers or terpolymers, containing 20-55% of propylene, optionally degraded by thermo-oxidation, and structurally characterized by values of at least one of X₂ and X₄ parameters, which are equal to, or lower than, about 0.02, indicative of the absence in the polymeric chain of propylene linking inversions.

Description: The present invention is concerned with compositions based on liquid hydrocarbons from refining, such as, e.g., gas oils and fuel oils in general, and from a more general standpoint, the products known as the "middle distillates" which, with decreasing temperature, show undesired alterations in their physical properties, which can be detected, e.g., by means of measurements of the following parameters: the cloud point (C.P.), the pour point (P.P.) and the cold filter plugging point (C.F.F.P.), as respectively defined in ASTM D2500-81 ASH D97-66 and IP 309/83 standards. For example, the gas oils used for automobile, naval and aeronautical internal combustion engine feeding or for heat generation purposes, are known to become less fluid with decreasing temperature, causing serious drawbacks in their use. Such a phenomenon is mainly due to the precipitation of n-paraffins contained in the gas oil. Obviating such a drawback by adding to the above said hydrocarbons suitable substances, generally of polymeric type, is known as well. The additives commonly used for such a purpose are represented by ethylene-vinyl acetate copolymers having suitable molecular weight values and compositions, or, according to as disclosed in IT-A- 811,873 and 866,519, by ethylene-propylene-(non-conjugated) diene copolymers or terpolymers, prepared with homogeneous-phase catalysts (based on vanadium compound, and organometallic aluminum compounds). In US-A- 3,374,073 and 3,756,954, as such additives ethylene-propylene-conjugated or non-conjugated diene terpolymers are proposed, which are prepared with homogeneous-phase catalysts, and are subsequently degraded by thermo-oxidation until suitable values of molecular weight are reached. The present Applicants have found that certain particular ethylene-propylene copolymers, or terpolymers of such monomers with a conjugated diene are endowed with exceptionally favourable characteristics as additives for improving the physical behaviour, as detected by means of C.P., P.P. and C.F.P.P. values, of the above-mentioned hydrocarbons, in particular at low temperatures. The copolymers or terpolymers used as additives according to the present invention are structurally characterized by the substantial absence in their polymeric chain of inversions in propylene linking pattern (also known as propylene "head-head", "tail-tail" inversions). It is known in this regard that propylene may enter in the polymeric chain with insertions of either primary or secondary type, such as disclosed, e.g., by I. Pasquon and U. Giannini in "Catalysis Science and Technology" vol. 6, pages 65-159, J.R. Anderson & M. Boudart Eds., Springer Verlag, Berlin 1984. By "inversion in propylene linking pattern", the change in insertion modality (from primary to secondary), which the molecule of propylene may show in the macromolecule is herein meant. Methods for determining the distribution of ethylene-propylene sequences, and in particular the absence of the above said inversion, in ethylene-propylene copolymers, are well known from technical literature. They comprise well-defined procedures for qualitative and quantitative investigations, based on ¹³C Nuclear Magnetic Resonance, according to as disclosed, e.g., by J.C. Randall in "Polymer Sequence Determination by C-13-NMR Method" (Academic Press, N.Y. 1977) and in "Macromolecules", 11 , 33 (1978); or by H.N. Cheng in "Macomolecules", 17 , 1950 (1984); or by C.J. Charman et al. in "Macromolecules", 10 , 536 (1977). Such procedures can be transferred as well to ethylene/propylene/diene terpolymers, in which the dienic termonomer is contained in relatively low amounts, generally lower than 10% by weight. Ethylene-propylene copolymers and ethylene-propylene-conjugated diene terpolymers, in whose macromolecules propylene linking inversions are essentially absent, are characterized by very low values of absorption in ¹³C-NMR spectrum (obtained in solution in ortho-cloro-benzene at the temperature of 120°C, by using dimethyl-sulphoxide (DMSO) as the external reference) at about 34.9; 35.7 and 27.9 p.p.m. (chemical shift, referred to tetramethyl-silane (TMS) = 0), typical of the presence of sequences of type (head-head or tail-tail inversion of X₂ type); and of type (head-head or tail-tail inversion of X₄ type). The substantial absence of propylene linking inversions in such copolymers and terpolymers is expressed by the fact that at least either of X₂ and X₄ parameters, and preferably both of them, have a value equal to, or smaller than, about 0.02. It is known that X₂ and X₄ parameters represent the fraction of methylenic sequences containing uninterrupted sequences of respectively 2 and 4 methylene groups between two successive methyl or methin groups in the polymeric chain, as computed relative to the total of the uninterrupted sequences of methylene groups, as determined by means of ¹³C-NMR. The value of such a fraction is computed according to the method as described by J.C. Randall in "Macromolecules" 11 , 33 (1978). It was also found that from among the copolymers and terpolymers endowed with such a feature, those containing from 20 to 55%, and preferably from 25 to 45% by weight of propylene, and from 0 to 10%, and preferably from 1 to 7% by weight of monomeric units deriving from a conjugated diolefin, can be advantageously used as additives. Such copolymers and terpolymers can be used in amounts comprised within the range of from 0.005 to 0.25%, preferably of from 0.01% to 0.15% by weight relatively to their mixture with the hydrocarbon, and can be added to the liquid hydrocarbons from refining preferably as solutions in suitable solvents constituted by hydrocarbons and/or their blends, having an aromatic, paraffinic, naphthenic character, and so forth, such as, e.g., those known on the market under the trade name Solvesso 100, 150, 200, HAN, Shellsol R, AB, E, A, and so forth, Exsold, Isopar, and so forth. Therefore, the object of the present invention are liquid hydrocarbons from refining, comprising from 0.005% to 0.25% by weight, relatively to the mixture of such hydrocarbons, of a copolymer of ethylene with propylene, or of a terpolymer of ethylene with propylene and a conjugated diolefin, characterized in that they contain from 20 to 55% by weight of propylene, and from 0 to 10% by weight of monomeric units deriving from such a diolefin, and by values of at least one of said X₂ and X₄ parameters, as above defined, equal to, or lower than, 0.02. The copolymers and terpolymers suitabie for being used as additives according to the present invention are preferably obtained by means of a copolymerization of the monomers carried out in the presence of catalysts based on titanium compounds supported on a magnesium halide, and of catalysts are disclosed, e.g., in US-A- 4,013,823; in EP-A- 202,550; in IT-A- 1,185,555 and 1,173,240; and in Italian patent application No. 20,203, A/81 which is the priority document of EP-A- 60090. As the conjugated diolefins, suitable for forming the terpolymers to be used as the additives according to the invention, the following are herein cited: butadiene, isoprene, piperylene, 1,3-hexadiene, 1,3-octadiene, 2,4-decadiene and cyclopentadiene. Butadiene is the preferred diolefin. The copolymers and terpolymers preferred for use as additives according to the present invention have a' viscosimetric molecular weight (Mv) comprised within the range of from 1,000 to 200,000, and preferably comprised within the range of from 3,000 to 150,000. According to a further preferred aspect of the present invention, the above disclosed copolymers and terpolymers are submitted to a thermo-oxidative degradation before being used as additives. Such a degradation can be carried out according to known techniques, e.g., by heating the polymer under an atmosphere consisting of an oxygen-containing gas, at temperatures of at least 100°C, and of up to 400°C, preferably comprised within the range of from 300 to 350°C, for a long enough time for the (viscosimetric) molecular weight to be reduced down to a value comprised within the range of from 1000 to a value 5% lower than the original molecular weight value. The so-oxidated polymer has a content of groups comprised within the range of from 0 to 10 per each 1,000 carbon atoms, as determined by I.R.-spectroscopy. The degradation of the polymer can be advantageously and preferably carried out inside extruders, or similar devices, with the possible addition of degrading substances, such as a peroxide, or of polymer-modifying substances, such as, e.g., amines. The degradation of the polymer can be also carried out in solution, according to routes well known in the art. The copolymer or terpolymer containing at least one, and preferably both X₂ and X₄ parameters equal to, or lower than 0.02, is particularly suitable for improving the physical behaviour at low temperatures of the liquid hydrocarbons from refining, obtained by distillation at a temperature comprised within the range of from about 120°C to about 400°C, and which have a cloud point (C.P.) comprised within the range of from +10°C to -20°C, a pour point (P.P.) comprised within the range of from +10°C to - 30°C, and a C.F.P.P. comprised within the range of from +10°C to -25°C. The compositions according to the present invention can also contain other types of generally mixed additives, such as anti-oxidant agents, basic detergents, corrosion inhibitors, rust inhibitors, pour-point depressants. The copolymers and terpolymers used according to the present invention are generally compatible with these additives. Such additives can be directly added to the compositions, or they can be contained in the polymeric solution which is added to the hydrocarbon from refining. The following examples are given in order to illustrate the finding according to the present invention, and do not have a limitative value. In the examples, the P.P. is measured according to ASTM D97-66 standard; the C.P. is measured according to the ASTM D2500-81 Standard; and the C.F.P.P. is measured according to the IP 309/83 Standard. Example 1 An ethylene/propylene copolymer is used, which contains 28% by weight of propylene prepared by using a heterogeneous-phase catalyst based on TiCl₄ supported on MgCl₂, and of tri-isobutyl-aluminum, as disclosed in Italian patent application No. 20,203 A/81 (priority document of EP-A- 60090), having a viscosimetric molecular weight of 100,000, and characterized by values of X₂ and X₄ parameters equal to 0.01. Different amounts of such a solution were added in solution to a same number of samples of a gas oil having the following characteristics: In Table 1 the amounts of copolymer contained in gas oil compositions and the values of P.P., C.P. and C.F.P.P. of the so-formulated compositions are reported. Example 2 (Comparative Example) An ethylene-propylene copolymer containing 28% by weight of propylene is used. It was prepared by means of a homogeneous-phase catalytic system based on VOCl₃ and Al₂(C₂H₅)₃Cl₃, as disclosed in Example 1 of IT-A- 866,519, having a viscosimetric molecular weight of 120,000. Such a copolymer was characterized by values of X₂ and X₄ parameters of 0.05. In Table 1, the values of P.P., C.P. and C.F.P.P. of the same gas oil as of Example 1 after the addition of different amounts of such copolymers, added in solution, are reported. Example 3 By following the same procedure, and using the same catalytic system as of Example 1, an ethylene/propylene copolymer was prepared, which contained 38% by weight of propylene, and had a viscosimetric molecular weight of 100,000. At ¹³C-NMR analysis, the values of X₂ and X₄ of such a copolymer resulted to respectively be of 0.02 and 0.005. The ¹³C-NMR spectrum of the copolymer is attached with the instant patent application as Figure 1. Such a spectrum was determined in ortho-dichlorobenzene at 120°C (chemical shift relatively to TMS). In Table 1, the characteristics of the gas oil disclosed in Example 1 are reported after the addition of different amounts of such a copolymer, added in solution. Example 4 (Comparative Example) By means of the same catalyst and process as disclosed in (comparative) Example 2, an ethylene/propylene copolymer was prepared, which contained 38.5% by weight of propylene, and had a viscosimetric molecular weight of 120,000. At ¹³C-NMR analysis, the values of X₂ and X₄ parameters of such a polymer resulted to respectively be of 0.13 and 0.06. The ¹³C-NMR spectrum of the copolymer is attached with the instant patent application as Figure 2. Such a spectrum was determined in ortho-dichlorobenzene at 120°C (chemical shift relatively to TMS). In Table 1, the characteristics of the gas oil of Example 1 are reported after the addition of different amounts of such a copolymer, added in solution. Example 5 By using the same catalytic system and process as disclosed in Example 1, an ethylene/propylene/butadiene terpolymer was prepared, which contained 36% by weight of propylene, and 6% by weight of butadiene, and had a viscosimetric molecular weight of 100,000. From ¹³C-NMR analysis, the values of X₂ and X₄ parameters of such a polymer resulted to respectively be of 0.02 and 0.01. In Table 1, the characteristics of the gas oil of Example 1 are reported after the addition of such a copolymer, added in solution. Example 6 The terpolymer prepared in Example 5 was degraded by being submitted to heating in air at the temperature of 320°C for about 1 minute, inside a twin-screw Werner-Pfleiderer extruder, having a diameter of 33 mm and with a ratio of length to diameter of 33. The so-obtained polymer had a viscosimetric molecular weight of 44,000, and a content of groups of 0.15 per each 1,000 carbon atoms, as determined by means of I.R. spectrometry. In Table 1, the characteristics of the gas oil of Example 1 are reported after the addition of such a copolymer, added in solution. Example 7 By means of the same catalytic system and process as disclosed in Example 5, an ethylene/propylene/butadiene terpolymer was prepared, which contained 28.5% by weight of propylene, and 3.5% of butadiene, and had a viscosimetric molecular weight of 80,000. The ¹³C-NMR analysis showed that such a terpolymer had values of X₂ and X₄ parameters respectively of 0.02 and 0.005. By following the same procedure as disclosed in Example 6, such a terpolymer was degraded until a molecular weight of 20,500 and a content of groups of 0.2 per each 1,000 carbon atoms were reached. In Table 1, the characteristics are reported, which were measured on the gas oil of Example 1 after the addition of such a copolymer, added in solution. Example 8 Different amounts of the non-degraded polymer disclosed in Example 7 were added to a gas oil having the following characteristics: In Table 1 the characteristics of the so-formulated gas oil, with the additive being added in solution, are reported. Example 9 The degraded terpolymer prepared according to Example 7 was used as an additive for the gas oil described in Example 8. The data relevant to the so obtained composition is reported in Table 1.

Claims: 1. Compositions of liquid hydrocarbons from refining, comprising from 0.005% to 0.25% by weight, relative to the hydrocarbon, of a copolymer of ethylene with propylene, or of a terpolymer of ethylene with propylene and a conjugated diolefin, said copolymer and terpolymer being characterized in that they contain from 20 to 55% by weight of propylene, and from 0 to 10% by weight of monomeric units deriving from such a diolefin, and by values of at least one of X₂ and X₄ parameters, which are equal to, or lower than, 0.02, X₂ and X₄ parameters representing the fraction of methylenic sequences containing uninterrupted sequences of respectively 2 and 4 methylene groups between two successive methyl of methin groups in the polymeric chain, as conputed relative to the total of the uninterrupted sequences of methylene groups, as determined by means of ¹³C-NMR. 2. Compositions according to claim 1, wherein both X₂ and X₄ parameters of the copolymer or terpolymer are equal to, or lower than, 0.02. 3. Compositions according to claim 1 or 2, wherein the conjugated diolefin is butadiene. 4. Compositions according to any of the preceding claims, wherein the copolymers and terpolymers are prepared by means of the copolymerization of the monomers in the presence of catalysts based on titanium compounds supported on magnesium halides and on organometallic aluminum compounds. 5. Compositions according to any of the preceding claims, wherein the terpolymer has a content of conjugated diolefin comprised within the range of from 1 to 7% by weight. 6. Compositions according to any of the preceding claims, wherein the copolymers and terpolymers have a viscosimetric molecular weight comprised within the range of from 1,000 to 200,000, preferably of from 3,000 to 150,000. 7. Compositions according to any of the preceding claims, wherein the copolymers or terpolymers are degraded at temperatures of at least 100°C, and have a content of groups comprised within the range of from 0 to 10 per each 1,000 carbon atoms. 8. Compositions according to claim 7, wherein the degradation of the copolymer or terpolymer is carried out at a temperature comprised within the range of from 300 to 350°C. 9. Compositions according to any of the preceding claims, wherein the copolymer or terpolymer is added in solution. 10. Compositions according to claim 9, wherein the solvent is constituted by hydrocarbons and/or their blends, of aromatic, paraffinic or naphthenic character.

Inventors: ALBIZZATI, ENRICO, CANOVA, LUCIANO, FALCHI, PAOLO, MILANI, FEDERICO, SANTORO, ETTORE
Applicants: AUSIMONT S.P.A., SOCIETA' ITALIANA ADDITIVI PER CARBURANTI S.R.L.
Application year: 1989
Main classification: C10L1
IPC codes: C09K3, C10L10, C10L1