The prior art When a fluid, such as a liquid hydrocarbon, is fed through a conduit, friction result- ing from the fluid stream causes a pressure drop increasing with the distance from the point (s) of feeding. Such a friction loss, also called drag, causes very high fluid transportation costs.

In order to reduce drag, a variety of polymeric materials have been used as additives in the fluid to be transported. Suitable materials have been polymers (= homopoly- mers and copolymers) of olefins, in particular very high molecular weight, non- crystalline and hydrocarbon soluble polymers of C-C30-oc-olefins.

In order to reduce drag effectively, a drag reducing olefin polymer must be of very high molecular weight, but at the same time soluble in and compatible with the fluid to be transported. These properties are only achieved with the right kind of catalysts.

Ziegler-Natta catalysts have been modified to produce polymers having said proper- ties. In the methods of Mack and Mack et nul., see columns 11-18 of US 4,415,714, columns 7-10 of US 4, 358,572 and column 4 of US 4,289,679, a-olefins are polym- erized in the presence of a Ziegler-Natta system comprising titanium chloride, an electron donor, and an alkyl aluminium cocatalyst and the polymerization is stopped at below about 20% conversion. Such polymers are soluble in hydrocarbon fluids and act as drag reducing agents.

However, none of these documents teach or suggest a method for obtaining an ul- trahigh molecular weight polymer having all properties suitable for use as a drag re- ducing agent. Especially, the drag reducing agents of these documents tend to loose their effect when exposed to high shear forces caused e. g. by a centrifugal pump.

The purpose of the invention is to obtain a drag reducing agent, which in addition to reducing the fluid stream friction also retains that property when exposed to high shear forces.

The invention The purpose of the invention has now been fulfilled by means of a new process for the production of a drag reducing agent wherein a monomer or monomer mixture comprising one or more C4-C30 monoolefins, preferably C6-C20 monoolefins, is po- lymerized into an essentially non-crystalline, hydrocarbon-soluble, ultrahigh mo- lecular weight drag reducing polymer in the presence of a polymerization catalyst system comprising a Group 4-6 (IUPAC 1990) transition metal compound and an organoaluminium compound.

In the process, said transition metal compound has been prepared by providing a support comprising an atomized complex of a magnesium halide and a monohydric C-C4 alcohol and contacting the support with a halogenous titanium compound and a C6-Cl8 alkyl carboxylic acid ester. The contacting takes place under conditions which deposit the halogenous titanium compound on the support and cause trans- esterification between the monohydric Cl-C4 alcohol and the C6-C18 alkyl carboxylic acid ester.

Detailed description of the invention The support has preferably been prepared by contacting and heating magnesium chloride and ethanol to form a molten complex, preferably MgCl2-n C3HsOH, wherein n is 2-6, and atomizing and solidifying the molten complex. The atomiza- tion can e. g. be accomplished by heating the components in a hot, inert liquid, whereby a dispersion of molten complex droplets is formed, after which the disper- sion is poured into another cooled liquid for the precipitation of small complex par- ticles. Preferably, however, MgCl2 and C2HgOH are melted and reacted together and the molten complex is sprayed into a cooled gas medium (spray-crystallizing), whereby small support particles are formed having sufficient alcohol on their sur- face to adhere the transition metal compound thereto and engage in transesterifica- tion with the carboxylic acid ester.

Next, the contacting between the support and the transitional metal compound takes place under conditions, which deposit the transitional metal compound on the sup- port and cause transesterification between the monohydric C, C4 alcohol and the C6- Cl8 alkyl carboxylic acid ester. This is preferably accomplished by preparing a hy- drocarbon slurry of the support, adding titanium tetrachloride and a Ce-Cjg alkyi phthalate to the slurry, preferably at a temperature below + 120°C, and heating the resulting mixture to an elevated temperature, preferably over +120°C, at which transesterification takes place.

The organoaluminium component of the polymerization catalyst system may be any compound known in the field of Ziegler-Natta catalysis for acting as a so called co- catalyst. It preferably has the following composition: RmAlnX3n-m wherein R is a Cl-C8 alkyl, X is a halogen, m > 1 and n = 1 or 2. Most preferably, the organoaluminium compound is a tri-Cl-C2-alkyl aluminium such as triethyl alu- minium or triisobutyl aluminium.

According to one embodiment of the invention, a so called external donor may be used with the organoalumonium compound. A preferred external donor is a di-C,- CI2 alkyl-di-Cl-C6 alkoxy silane, e. g. cyclohexyl methyl dimethoxy silane.

The C4-C30 monoolefins used in the production process of the invention are typically higher monoolefins capable of undergoing polymerization by a Ziegler-Natta cata- lyst system. There are tens of such polymerizable C4-C30 monoolefins and their se- lection on the basis of the prior art is easy for a person skilled in the art. When se- lecting the monomers, they should be chosen on the basis of their capability to form high molecular weight non-crystalline and hydrocarbon soluble polymers.

Typical a-olefin monomers are hexene-1, octene-1, decene-1, dodecene-1, tetrade- cene-l, hexadecene-1 and eicosene-1. Preferably, the C4-C30 monoolefin (s) of the invention is (are) selected from C6-C12 alkene-1 compounds and their mixtures.

Typical such a-olefin monomers and their combinations include propene-dodecene- 1, butene-l-dodecene-1, butene-l-decene-1, hexene-l-dodecene-1, octen-1- tetradecene-1, butene-1-decene-1-dodecene-1, propene-hexene-l-dodecene-1, etc.

Preferred monomers and monomer mixtures are hexene-1, octene-1, decene-1, do- decene-1, propene-dodecene-1, butene-l-decene-1, butene-1-dodecene-1 and hex- ene-l-dodecene-1. Especially preferred monomers are hexane-l and octene-l.

Preferably, the monomer or monomer mixture is polymerized into an essentially non-crystalline, hydrocarbon-soluble, ultrahigh molecular weight drag reducing polymer by carrying out the polymerization essentially in the absence of chain trans- fer agents, such as hydrogen, and/or stopping the reaction at a low conversion such as 10-30 mol-%, preferably 10-20 mol-%. The reaction can suitably be stopped by adding a substance, e. g. acetone, which deactivates the catalyst system. By using such a measure, ultra high molecular weight (UHMW, Mw > light scatteling1°6 g/mol) non-crystalline C4-C30 oc-olefin polymers are produced.

The above mentioned drag reducing properties and especially the good shear force resistance obtained with the above defined catalyst system can be further improved by polymerizing the C4-C30 monoolefins in the presence of 0.0001-10%, based on of the weight of the C4-C30 monoolefin (s), of a polyunsaturated aliphatic hydrocarbon which is copolymerized with the C4-C30 monoolefin (s). By"aliphatic"is here meant non-aromatic. In the invention, preferably 0.001-1%, most preferably 0. 01-0. 1% of the polyunsaturated aliphatic hydrocarbon, based on the weight of the C4-C30 monoolefin, is copolymerized with the C4-C30 monoolefin (s).

Thanks to the polyunsaturation of the comonomer, some crosslinking takes place, which improves the high shear force resistance of the drag reducing agent. Thanks to the aliphatic character of the comonomer, the solubility of the drag reducing agent in the fluid to be transported is very high. A polymer is best dissolved by sol- vents having the same chemical structure as the polymer. Equally high solubilities are not to be expected of the drag reducing agents of Gessell et al. (US 5,276,116), which uses the non-aliphatic divinyl benzene or divinyl siloxane as polyunsaturated comonomers. Besides, Gessell et al. uses another catalyst system than the invention.

The polyunsaturated aliphatic hydrocarbon comonomer used to prepare the drag re- ducing agent of the invention may be any compound which copolymerizes and crosslinks either during or after the copolymerization. The art of olefin polymeriza- tion knows a large number of such polyunsaturated hydrocarbons which easily can be selected for the invention. Terpenes (isoprene oligomers and polymers) and re- lated compounds such as dicyclopentadiene and 2-ethylidenenorborn-2-ene can be selected. According to a preferred embodiment of the invention, the polyunsaturated hydrocarbon is selected among linear C4-C30 dienes, preferably linear non- conjugated C6-C0 dienes. Typical such dienes are hexa-1, 4-diene, octa-1, 4-diene, octa-1, 6-diene, octa-1, 7-diene, and deca-1, 9-diene.

In addition to one polyunsaturated aliphatic hydrocarbon comonomer, mixtures of two and more of such comonomers may also be used.

The copolymerization of the C4-C30 monoolefin (s) and the polyunsaturated aliphatic hydrocarbons can be carried out at any convenient reaction conditions. As the drag reducing effect is better if the molecular weight of the copolymer is high, the co- polymerization, just like the polymerization mentioned above, is preferably carried out at conditions which give high molecular weights. In the art of olefin homo-and copolymerization, the means for obtaining high molecular weight are generally known. Such means are, e. g., the elimination of all chain transfer agents, such as hydrogen, and impurities acting as chain transfer agents, see above.

More preferably, the copolymerization is carried out under conditions which pro- duce ultrahigh molecular weight (Mw > 106 g/mol) polymer, most preferably by car- rying out the copolymerization rapidly to a monomer conversion of only 10-30 mol- %, advantageously 10-20 mol-%. See above. Then, the copolymerization is prefera- bly finished by adding a substance such as acetone, which deactivates the catalyst system. If an ultrahigh molecular weight copolymer of an olefin and a polyunsatu- rated aliphatic hydrocarbon is produced in this manner, a superior combination of drag reduction, solubility and high shear force resistance is achieved.

Further, it is preferable, if the homo-or copolymerization of the invention to a ultra- high molecular weight polymer is carried out in a hydrocarbon solvent. The homo- or copolymerization can e. g. be carried out at a starting temperature of between -30°C and +20°C, preferably about-10°C to-5°C and a final temperature of be- tween-5°C and +30°C, preferably about +10°C to +15°C. Then, the pressure is preferably 1-20 bar, most preferably 2-5 bar.

After the copolymerization, the product is preferably recovered as a gel containing the copolymer, the solvent and/or unreacted monomer. The gel may then be added as such to the hydrocarbon fluid, the drag of which is to be reduced. Advanta- geously, the gel contains 4-10% by weight of the polymer or the copolymer, 30-50% by weight of the monomer and 50-65% by weight of the solvent. Alternatively, the monomer may be removed and recovered for reuse.

The gel may also be transformed into a drag reducing powder, slurry, solution or dispersion, which is then added to the conduit or fluid to be transported.

In addition to the above described process for preparing a drag reducing agent, the invention also relates to a method for reducing the drag of hydrocarbon flowing.

In the claimed drag reducing method, (a) a drag reducing agent prepared of the above described type is provided, and (b) the drag reducing composition is fed into a conduit or the like, in which the hydrocarbon is or will be flowing, or, alternatively to a fluid to be transported in the conduit or the like. Preferably, the drag reducing composition is fed in an amount of 1-200 ppm, preferably 10-100 ppm, most pref- erably 20-80 ppm, based on the amount of the flowing hydrocarbon.

The invention also relates to the use of a transition metal compound, which has been prepared by contacting an atomized solid complex of a magnesium halide and a monohydric C, C4 alcohol with a halogenous titanium compound and a C6-C, 8 alkyl carboxylic acid ester under conditions depositing the halogenous titanium com- pound on the complex and transesterifying the monohydric Cl C4 alcohol and the C6-CI8 alkyl carboxylic acid ester, in the polymerisation of one or more C4-C30- monoolefins for improving the high shear force resistance of resulting drag reducing polymers. In the use according to the invention, essentially the same parameters are used as described in connection with the claimed production process.

The following examples, in which the parts and percentages are on a weight basis, unless otherwise indicated, are merely provided to illustrate the invention.

Examples Measuring methods The methods used for characterizing the drag reducing agents (compositions), henceforth called DRA, can crudely be subdivided into the physical properties (dry matter, viscosity) and the actual performance properties (DPT, Visko 50).

The dry matter of a gel sample is determined by removing the gel solvent (s) by evaporating in a heating chamber. In addition to the polymer, the gel hardly contains other solids, so, the dry matter gives the polymer content of the product. The dry matter of the gel is a remarkable physical property in so far as the performance reached at the site of use depends on the amount of polymer dissolved in the fluid, i. e. when feeding to the fluid equal masses or volumes of different products, most effective agent is fed with the product having the larges dry matter.

The viscosity is the dynamic viscosity (cP) was measured by a Brookfield viscome- ter using different shear rates (e. g. 0.5,1,2.5,5,10,20,50 and 100 rpm).

The DPT (= delta pressure vs. time) is a kind of life span analysis. The sample to be tested is fed to a solvent circulation system maintained by a gear pump. By measur- ing the productivity pressure, the dissolution of the sample can be followed and thereafter the gradual disappearance of the drag reducing effect can be followed as the sample one time after another passes the pump. In DPT measurements, attention is especially paid to the percent DPT, which is obtained as an integral by summing up the differences between the reference pressure and the momentary pressures dur- ing the measurement. The drag reduction can be calculated using the following equation: % drag reduction = (po-ps)/po X 100 wherein po is the measured drop occurring when hexane without drag reducing agent was pumped through the test line, and ps is the measured pressure drop occur- ring when hexane containing the drag reducing agent was pumped through the test line.

The Visko 50 test is based on measuring the kinematic viscosity of the sample.

A 50 ppm solution of the DRA is prepared, the viscosity of which is compared to the viscosity of pure solvent. The result of a Visko 50 test contains information about the solubility of the DRA as well as its ability to alter the viscoelastic proper- ties of the hydrocarbon fluid. The DRA is considered the better, the larger the Visko 50 value is.

Preparation 1. General The process is based on batch polymerization of a mixture of C6, C8 and C12 linear alpha olefins using a saturated hydrocarbon as solvent and Ziegler-Natta catalyst as a polymerization catalyst system. The used catalyst system has been prepared by re- acting and heating TiCl4 and C ? SOH to produce a molten complex and spray crys- tallizing the complex (see below). The polymerization process is a rapid one, partly because only about 15% of monomers will polymerize. When the proper molecular weight has been obtained, the polymerization product is pumped out of the reactor injecting simultaneously acetone to it for"killing"the catalyst. A monomer recovery process may eventually be included in the unit to improve the production econom- ics.

2. Catalyst preparation The catalyst was prepared essentially as follows : 102 kg of spray-chrystallized solid complex MgCl2-nC2H5OH wherein n = 2-4, con- taining 438 mol of Mg, was mixed in a reactor under inert conditions with 600 1 of hydrocarbon medium (LIAV 110, Neste Oy) having a boiling point of 110°C. The obtained slurry was cooled to-15°C. Then, 1200 1 of cold Tical4 was added and the temperature was allowed to rise gradually to 20°C. Next, 24. 8 kg (63.6 mol) of dioc- tyl phthalate (DOP) was charged to the reactor. The temperature was elevated to 130°C for transesterification between the C2H5OH and the DOP, and the solution was removed from the reactor after half an hour. Next, 1200 1 of fresh Tical4 was charged to the reactor for a second titanation. Subsequently, the mixture was ther- mostated at 120°C. After one hour, the solid catalyst was washed three times with hot hydrocarbon (LIAV 1110) and dried under nitrogen at 50-60°C. The analyzed composition was Ti 2.0 wt-%, Mg 15.2 wt-%, DOP 0.1 wt-%, DEP 14. 3 % and Cl 50.3 wt-%.

3. Raw material supply and specifications The monomers C6, C$ and Cl2 alpha olefins as well as 1,9-decadiene can be pur- chased as ready made blends or as such. They have the following specifications:

Monomer 1-hexene 1-octene 1-dodecene 1,9-decadiene Average molecular weight 84 112 168 138 Density at 20 °C, kg/l 0.673 0.715 0.758 0.750 Purity, alpha olefin 98.5 98.5 >96 >95 content, wt-% A non-aromatic hydrocarbon solvent distillate is the solvent used in the production of the DRA gel.

Distillation, °C Specification Typical Value IBP min 200 200-205 95 % reported 239-241 FBP max 250 246-250 Dry point reported 244-249 Density, 15 °G reported 800-810 A Ziegler-Natta catalyst is used for the polymerization. Its specifications are: Magnesium chloride, wt-% 40-60 TiCl4, wt-% 5-16 Hydrocarbon distillate, wt-% 10-25 Dialkyl esters of 1,2-benzene dicarboxylic acid, wt-% 5-15 4. Catalyst Aluminium alkyl is used as a cocatalyst with Ziegler catalyst. The DRA polymeriza- tion uses TIBA (triisobutyl aluminium) as a 25 wt-% solution in heptane as a cocata- lyst. The cocatalyst has the following specifications: Chemical Name Triisobutylaluminium Abbreviation TIBA Concentration, wt-% in heptane 25 Density, kg/1 0.7248 5. External donor The external donor is cyclohexyl methyl dimetoxy silane. The donor is diluted with a solvent (bp. 950 °C) for a 15 wt-% solution.

6. Quencher Any catalyst deactivating compound, e. g. acetone, can be used for stopping the po- lymerization reaction. The quencher is mixed with the polymerized product when the polymerized DRA product is transferred from the reactor to the storage tank.

7. Polymerization The polymerization of C6, C$ and Cl2 monomer blend is performed in said saturated hydrocarbon solvent with said Ziegler-Natta catalyst in a series of two batch reac- tors. Chilled monomer blend, solvent, initiator and catalyst are charged into the first prepolymerization reactor with an agitator running in order to obtain a homogeneous mixture at all times. The initial temperature is 5 °G to-10 °C. The first 15 most crucial minutes of the polymerization process take place in the prepolymerization reactor. After these initial 15 minutes of the polymerization process when the tem- perature has risen to about 0 °C, the contents of a batch are still quite easily flowing and the batch is then transferred to the actual polymerization reactor where the final part of the polymerization takes place in an hour during which the temperature rises to about +10 °C to +15 °C. The amounts of monomer are adjusted to obtain the fol- lowing product composition.

8. Product specifications The obtained product, DRA gel, is a mixture of monomers, solvent and 7 wt-% of polymer with the following properties:

Composition, wt-% -polymer 5-7 -monomer 40-42 -solvent 52-54 -acetone 0.08 Average molecular weight > 5 000 000 (typical) Viscosity (Brookfield 7/20) at 20 °C, cP > 20 000 The amounts of used reactants and the analytical results of the examples are given in the following table.

Table The results of the reference and working examples Bench scale Pilot scale Formula-Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 8 tion Solvent 1400 ml 1400 ml 1750 kg 1750 kg 0 0 1500 kg 1750 kg C6 700 ml 700 ml 875 kg 875 kg 650 kg 650 kg 750 kg 875 kg C8 350 ml 350 ml 437. 5 kg 437.5 kg 0 0 375 kg 438 kg C12 350 ml 350 ml 437.5 kg 437.5 kg 0 0 375 kg 438 kg Catalyst0.3 g 0.36 g 340 ml 460 ml 125 ml 125 ml 195 ml 380 ml TIBA 10. 4 ml 10.4 ml 7110 ml 7200 ml 1263 ml 1263 ml 4331 ml 7146 mi Donor 0.4 ml 0. 4 ml 1065 ml 1150 ml 188 ml 188 ml 427 ml 1100 ml 1,9-decadie- 0 0.84 g 0 2000 ml 0 560 ml 0 2000 ml ne Analysis Visko 50 0.227 0.263 0.175 0.17 0.229 0.307 0.182 0.199 DPT % 5.69 9.03 7. 8 9. 7 9. 3 10.1 6 9.1 Dry matter 4. 1 4.7 6. 9 6.8 9.9 65.5 6. 6 7. 8