POLYMER COMPOSITIONS

Abstract: Polymer compositions comprising a dispersion of at least one polymer A obtained by polymerisation of at least one olefinically unsaturated compound, which polymer contains aliphatic hydrocarbon side chains of at least 10 carbon atoms, in a continuous aqueous phase comprising a surfactant and at least one polymer B which comprises a thixotropic hydrophilic polymer, a process for the preparation of the compositions, and their use as pour point depressants.

Description: POLYMER COMPOSITIONS This invention relates to polymer compositions, their preparation and their use as pour-point depressants . Crude oils (crude mineral oils) and certain fuels (oils) derived therefrom, e.g. wax-containing fuel oils and diesel fuels, may contain considerable amounts of wax. This wax gradually separates out as such materials are cooled, and at sufficiently low temperatures these materials may solidify completely. The lowest temperature observed during a standard laboratory test (ASTM D.97) at which the waxy material still flows is called the "pour-point" of the material. In order to overcome the problems arising from cooling of such materials in storage or in transport, whether in tankers or by pipeline, certain polymers have been developed which when added to such materials depress the pour-point of the material. Such polymers are typically polymers obtained by polymerisation of at least one olefinically unsaturated compound, which polymers contain aliphatic hydrocarbon side chains of at least 10 carbon atoms, e.g CIQ-30 aliphatic hydrocarbon side chains. Typically these polymers have molecular weights (M n ) in the range of 10,000 to 1,000,000. Examples of such polymers are described in GB-A-1154966, GB-A-1161188, GB-A-1285087, GB-A-1410819, EP-A-0120512, EP-A-0236844 and US-A-4547202. Whilst these polymers have proved to be very effective pour point depressants, and hence useful fluidity improvers, they are typically sold as concentrated solutions in solvents such as toluene or xylene, which solutions may themselves have relatively high pour points. For dispersion in tanks of crude oil and fuel oil, this normally presents no significant problem. Examples of commercially available fluidity improvers include those available from the Royal Dutch/Shell Group of companies under the trade mark "SHELLSWIM - 5X", a 50%w solution of an alkyl acrylate polymer in xylene (having a pour point of 27°C) , and under the trade mark "SHELLSWIM - 11T", a 50%w solution of an alkyl acrylate/vinyl pyridine copolymer in toluene (having a pour point of 18°C) . However, there are circumstances, for example where it may be desired to pass the fluidity improvers themselves along a pipeline in cold environments, e.g. in North Sea or Arctic areas, when it would be advantageous to have concentrated formulations of pour point depressants which would remain readily flowable at low ambient temperatures. In EP-A-0448166, concentrated formulations have been disclosed containing an alkylacrylate polymer, a surfactant, a polyol and various amounts of water. It appears from said document that the best results (long term storage stability) are obtained when use is made of formulations containing a limited amount of water. Surprisingly, it has now been found that formulations which may contain high amounts of water constitute attractive pour point depressants, when they contain a thixotropic hydrophilic polymer. According to the present invention there is provided a polymer composition comprising a dispersion of at least one polymer A obtained by polymerisation of at least one olefinically unsaturated compound, which polymer contains aliphatic hydrocarbon side chains of at least 10 carbon atoms, in a continuous aqueous phase comprising a surfactant and at least one polymer B which comprises a thixotropic hydrophilic polymer. The polymer compositions according to the present invention advantageously display a low viscosity under transport conditions and a long term " storage stability. Suitable polymers A are described in GB-A-1154966, GB-A-1161188, GB-A-1285087 , EP-A-0120512 , EP-A-0236844 and US-A-4547202. These polymers typically have molecular weights (M n ) in the range 10,000 to 1,000,000 and contain CIQ-30 aliphatic hydrocarbon side chains. Preferably polymer A has a molecular weight (M n ) in the range 20,000 to 250,000, more preferably 25,000 to 100,000, e.g. 30,000 to 80,000. Polymer A is preferably a homo- or copolymer of one or more (C^g-30 n-alkyl) acrylates or methacrylates, e.g. 1-docosyl acrylate (C22) > 1-octadecyl acrylate (C_g) and 1-eicosyl acrylate (C20) • Suitable copolymers are copolymers of one or more (C_g-30 n-alkyl) acrylates or methacrylates with a monoolefinically unsaturated compound having a nitrogen containing group, such as acrylonitrile, acrylamide, p-aminostyrene, N-vinylpyrrolidone or 4-vinylpyridine . Most preferably polymer A is a polymer of one or more (Cιg_26 n-alkyl) acrylates or a copolymer of one or more (C_g-26 n-alkyl) acrylates and 4-vinyl- pyridine) . Various non-ionic and ionic surfactants are suitable for incorporation in compositions according to the invention. Preferably the surfactant is selected from alcohol ethoxy sulphate surfactants and lignosulphonate surfactants. Such surfactants are typically alkali metal or ammonium salts. Alcohol ethoxy sulphate surfactants typically have the formula RO- (CH 2 CH 2 0) n -S0 3 -M where m is sodium or ammonium, R is C_2-18 alkyl and n is 2 or 3. Compositions according to the invention suitably contain 0.1 to 20, preferably 1 to 15, more preferably 1 to 10 parts by weight of surfactant per 100 parts by weight of polymer A. Polymer B comprises a thixotropic hydrophilic polymer. Solutions of such polymers are known to have a high viscosity at a low shear rate and to have a low viscosity at a high shear rate. Suitable polymers B include for instance polysaccharides (e.g. Xanthan Gum) and partly hydrated polyacrylamides . These polymers typically have number average molecular weights (M n ) in the range 1 x 10^ to 1 x i F , preferably m the range 5 x 10 5 to 5 x 10 6 . Suitably, tnese polymers have a molecular weight distribution (M w /M n , whereby M w is defined as the weight average molecular weight) m the range 1 to 5, preferably 1 to 2, most preferably 1 to 1.5. Polymer B is preferably a polysaccharide . Most preferably polymer B is Xanthan Gum. Compositions according to the invention suitably contain 0.01 to 20, preferably 0.1 to 10, more preferably 0.2 to 5, parts by weight of polymer B per 100 parts by weight of polymer A. These amounts include any minor amounts of solvents such as ethanol which may be present m the surfactant chosen for incorporation m the composition. Other additives may be incorporated m minor amounts m the compositions of the invention such as anti-oxidants, anti-corrosion agents or metal deactivators . Compositions according to the invention suitably contain more than 20, preferably more than 50, more preferably more than 80, parts by weight of water per 100 parts by weight of polymer A. The presence of even small amounts of thixotropic polymers have a beneficial effect n terms of viscosity reduction under transport conditions. Suitably, the continuous aqueous phase may comprise two or more different types of thixotropic hydrophilic polymers . The invention further provides a process for the preparation of polymer compositions of the invention, which process comprises emulsifying a mixture of polymer A, the surfactant and polymer B at a temperature above the melting point of the polymer A, and cooling the resulting emulsion to a temperature below the melting temperature of polymer A. The upper temperature limit for the process will be determined by the lowest decomposition temperature of the various components of the mixture. '.s.ing acrylate polymers as polymer A, alcohol ethoxy sulphate surfactants and/or lignosulphonate surfactants, and temperatures for emulsifying mixtures in the range 50°C to 100°C has been found to be very effective, temperatures in the range 60 to 100°C being preferred. Further in accordance with the invention there is provided the use of a composition of the invention in depressing the pour point of a crude mineral oil or a wax-containing fuel oil or diesel oil. The polymer compositions of the invention have particularly useful application according to the invention in inhibition and/or reduction of wax deposition in crude oil pipelines. The fact that the present aqueous compositions are fluid at lower temperatures than simple solutions of the relevant polymer at corresponding concentrations in solvents such as toluene or xylene confers significant improvements in handleability in lower temperature environments. Moreover, since the present aqueous formulations contain little or none of such solvents they constitute very attractive materials from the safety standpoint (flashpoint), when compared with conventional formulations. The invention will be further understood from the following illustrative Examples, in which: - Polymer I is an alkyl acrylate polymer, mp 51°C, of molecular weight (Mn) in the range 49,000 to 76,000 measured by gel permeation chromatography (GPC) (polyacrylate scale) prepared from a blend of linear alkyl acrylates comprising 1-docosyl acrylate, 1-octadecyl acrylate and 1-eicosyl acrylate. "DOBANOL 25-3A/60" (trade mark) ethoxy sulphate is a 60%w solution in aqueous ethanol (2:1 w/w) of ammonium (C 2-15 alcohol) ethoxy sulphates containing 3 mol ethylene oxide/mol (density at 20°C 1.04 kg/1). Examples 1 to 6 Water (44.6 g) , "DOBANOL 25 - 3A/60" ethoxy sulphate (5 g) and partly hydrated polyacrylamide (PHAM) (0.4 g) were stirred to give a homogenous solution at ambient temperature (20°C) in a 150 ml beaker. Polymer I (50 g) was added and the bottle was transferred to a thermostatic oil bath at 80°C. The two- phase mixture was emulsified using an "ULTRA TURRAX T25" (trade mark) laboratory emulsifier (1.8 cm dispersing tool, at 24,000 r.p. .) for 1 minute. The resulting emulsion of Polymer I in the aqueous phase was cooled by removing the bottle from the oil bath and allowing it to cool in air to ambient temperature (20°C) , to yield the desired composition as a readily flowable suspension. Additional suspensions (Examples 2 to 6) were prepared in a similar manner to the above suspension, except that in Example 4 Xanthan gum was used instead of PHAM and that hexadecyltrimethylammonium bromide (HDTMAB) was used instead of ethoxysulphate; in comparative Example 5 glycerol was used instead of water and PHAM, the temperature of the thermostatic oil bath was 96°C and the mixture was emulsified for 2 minutes; and in comparative Example 6 glycerol was used instead of PHAM, the temperature of the thermostatic oil bath was 101°C and the mixture was gently emulsified for 1 minute, after which water was added. Details of all six suspensions and their preparation are given in Table 1. In each case the suspensions were stable at ambient temperature (20°C) for at least one month. The suspensions were all liquid at least down to 5°C . The suspensions were tested by addition to a Far East crude oil and assessment of the pour point according to ASTM D.97. The pour point of the undoped crude oil was 24°C, for examples 1-3, and 30°C for examples 4-6. The test results of the suspensions of Examples 1 to 6 are summarised in Table II. Viscosity was measured at 20 °C with a cone and plate system in a Carri-Med "CSL 500" Rheometer. It will be clear from Table II that the suspensions in accordance with the invention (Examples 1-4) display an attractive pour point activity together with an improved low viscosity when compared with suspensions falling outside the scope of the present invention (Examples 5 and 6) . Table I pbw = parts by weight/100 parts polymer I Table II

Claims: C L A I M S 1. A polymer composition comprising a dispersion of at least one polymer A obtained by polymerisation of at least one olefinically unsaturated compound, which polymer contains aliphatic hydrocarbon side chains of at least 10 carbon atoms, in a continuous aqueous phase comprising a surfactant and at least one polymer B which comprises a thixotropic hydrophilic polymer. 2. A composition according to Claim 1 wherein the at least one polymer B is a polysaccharide or a partly hydrated polyacrylamide . 3. A composition according to Claim 1 or 2 wherein polymer A has a molecular weight (Mn) in the range 20,000 to 250,000. 4. A composition according to Claim 1, 2 or 3 which contains 0.1 to 20 parts by weight of surfactant per 100 parts by weight of polymer A. 5. A composition according to any one of Claims 1 to 4 which contains 0.01 to 20 parts by weight of polymer B per 100 parts by weight of polymer A. 6. A composition according to any one of Claims 1 to 5 which contains more than 20 parts by weight of water per 100 parts by weight of polymer A. 7. A composition according to any one of Claims 1 to 6 wherein polymer A is a polymer of one or more (C g_26 n-alkyl) acrylates or a copolymer of one or more (C g-26 n-alkyl) acrylates and 4-vinyl pyridine. 8. A composition according to any one of Claims 1 to 7 wherein the surfactant is an alcohol ethoxy sulphate surfactant or a lignosulphonate surfactant. 9. A process for the preparation of a composition according to any one of Claims 1 to 8 which comprises emulsifying a mixture of polymer A, the surfactant and polymer B at a temperature above the melting point of polymer A, and cooling the resulting emulsion to a temperature below the melting temperature of polymer A. 10. Use of a composition according to any one of Claims 1 to 8 in depressing the pour point of a crude mineral oil or a wax-containing fuel oil or diesel oil.

Inventors: BRAAMS JOHANNES FRANCISCUS HEN, IN T VEEN BERNARDUS CORNELIS M, REYNHOUT MARINUS JOHANNES, BRAAMS, JOHANNES, FRANCISCUS, HENDRIKUS, IN 'T VEEN, BERNARDUS, CORNELIS, MARIA, REYNHOUT, MARINUS, JOHANNES
Applicants: SHELL INT RESEARCH, SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1997
Main classification: C08J3
IPC codes: C08J3, C08L33, C08L39, C08L101, C10L1, C10L10, C10M157, C10M161, C10M173