US3926579A - Petroleum crude oils containing polymers comprised of c' 18'+14 c' 40 'alpha-olefins have reduced tendency to deposit wax - Google Patents

Abstract

Paraffin deposition in flow systems handling petroleum crude oil is substantially reduced or inhibited by blending the crude oil with a polymer comprised of 20 to 100 wt. % of a C18-C40 alphaolefin and 0 to 80 wt. % of a C3-C16 alpha-olefin. The polymers have a number average molecular weight within the range between about 500 and 125,000 and are preferably copolymers containing 4 to 50 wt. % of a C3-C8 alpha-olefin and 50 to 96 wt. % of a C20C28 alpha-olefin.

Description

United States Patent Rossi et a1.

PETROLEUM CRUDE OILS CONTAINING POLYMERS COMPRISED OF C gC40 ALPHA-OLEFINS HAVE REDUCED TENDENCY TO DEPOSIT WAX Inventors: Albert Rossi, Jersey City; Norman Jacobson, East Brunswick; Harold N. Miller, Millington, all of NJ.

Exxon Research & Engineering Co., Linden, NJ.

Filed: Mar. 23, 1973 Appl. No.: 344,428

Related US. Application Data Continuation of Ser. No. 762,368, Sept. 16, 1968, abandoned.

Assignee:

US. Cl. 44/62; 44/80; 252/83 Int. Cl C101 1/16 Field of Search 44/62, 80

References Cited UNITED STATES PATENTS 4/1973 Miller 44/62 3,765,849 10/1973 llnyckyj et al. 44/62 3,776,247 12/1973 Choufoer et al 44/80 3,790,358 2/1974 Rossi et a1. 44/62 Primary Examiner Daniel E. Wyman Assistant Examiner-Y. H. Smith Attorney, Agent, or FirmR. J. Ott; Frank T. Johmann [57] ABSTRACT Paraffin deposition in flow systems handling petroleum crude oil is substantially reduced or inhibited by blending the crude oil with a polymer comprised of 20 to 100 wt. of a C C alpha-olefin and O to 80 wt. of a C C alpha-olefin. The polymers have a number average molecular weight within the range between about 500 and 125,000 and are preferably c0- polymers containing 4 to 50 wt. of a C -C alphaolefin and 50 to 96 wt. of a C -C alpha-olefin.

4 Claims, No Drawings PETROLEUM CRUDE OILS CONTAINING POLYMERS COMPRISED OF C g-C40 ALPI-IA-OLEFINS HAVE REDUCED TENDENCY TO DEPOSIT WAX This is a continuation of application Ser. No. 762,368, filed Sept. 16, 1968, now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to petroleum crude oils having a reduced tendency to deposit paraffin, i.e., wax, on the surfaces of handling systems. More particularly, the invention is concerned with petroleum crude oils containing hydrocarbon polymers comprised of alpha-olefins, which polymers reduce or inhibit the deposition of paraffin from the crude oil.

2. Description of the Prior Art Paraffin deposition on metal surfaces of oil-well pumps, rods, and other downhole equipment, as well as surface valves and flow lines, is a serious problem in petroleum crude oil production. Considerable expense is involved for periodic deposit removal, production losses resulting from restricted flow capacity, and unproductive down time.

The paraffin problem is found in virtually all the major oil-producing areas of the world. It is generally accepted that the major causes of paraffin deposition are the cooling of the crude oil during production, and the escape of light ends or gases which previously helped retain the paraffin in solution in the oil. Other contributing factors are:

. Alternate coating and draining of oil.

. Contact of oil with a cold surface.

. Spraying of oil as a mist.

. Flow of oil at a low rate.

. Agitation hastening paraffin particle growth.

. Sand, silt, water.

. Rough tubing surfaces.

. Viscosity of oil not so high as to prevent wax particles from settling out.

As a result of these influences, paraffin deposits occur at the bottom of the well, in tubing, and in surface equipment. Paraffin deposition in surface flow lines has been alleviated by the installation of largediameter lines, or the use of pumpable plugs. When such paraffin deposition occurs below the surface, however, its removal is more laborious and costly.

Remedial expense varies widely in different cases, depending on well conditions and severity of the problem. An average of from 2 to cents per barrel of crude is involved. In addition to the obvious costs of paraffin removal, decreased equipment life and increased lifting costs are also involved. Numerous methods have been developed for removing the paraffin plugging deposits. In general, these involve mechanical, thermal, and chemical methods, and combinations thereof.

The mechanical method involves the physical scraping of paraffin deposits from the tubing. Thermal methods include circulating hot oil or hot water down the well bore, or the use of bottomhole heaters. The chemical treatment method involves the use of special solvents that dissolve the paraffin so that it can be brought to the surface in liquid form.

In accordance with this invention, a new approach to the paraffin deposition problem is the development of a new class of polymeric wax crystal modifiers which 2 when blended with the crude oil reduce or inhibit the deposition of paraffin on the surface of flow lines. These additives also improve the (viscosity) flow properties of the crude, thereby facilitating production and handling of crude in pipelines, pumps, etc.

SUMMARY OF THE INVENTION Petroleum crude oils having a reduced tendency to deposit wax are prepared by incorporating into the crude oil from about 0.0001 to 2.00 wt. based on crude oil to be treated, preferably 0.0005 to 0.45 wt. of an oil-soluble polymer comprising at least 20 wt. of a C, C alpha-olefin, said polymer having a number average molecular weight in the range of about 500 to 125,000, preferably about 1000 to about 40,000 as measured by Vapor Phase Osmometry (VPO).

The C C alpha-olefin monomer which is used to prepare the polymer of the invention may be represented by the following general formula: H C CHR wherein R is a substantially linear aliphatic hydrocarbon radical containing from 16 to 38 carbon atoms. It is preferred, however, that R have the formula: CH (CI-l ),,-CH wherein n is a whole number ranging from about 14 to 36, more preferably from about 16 to 24. The term substantially linear is used herein to denote those aliphatic side chains, i.e., R, which contain no more than one lower alkyl side chain such as methyl, ethyl, etc., in the radical and wherein said lower alkyl side chain, when present in the radical, is located at a position such that R has a linear portion containing at least 16 carbon atoms. Examples of such monomers include, among others, n-eicosene-l, 3- methyl eicosene-l, n-docosene-l, n-tetracosene-l, 3- methyl tetracosenel n-hexacosene- 1 ntriacontenel and the like.

Polymers prepared from the aforedescribed C C alpha-olefins when blended in petroleum crude oils are effective for reducing or inhibiting the deposition of wax from the crude oil and for improving the flow properties of these oils. It has unexpectedly been found, however, that the polymers having the greatest ability to inhibit wax deposition in crude oils are prepared from the aforedescribed C C alpha-oletins and certain lower alphacletins. While not known with certainty, this unexpected improvement in the inhibition of wax deposition may be due to the fact that copolymerization with lower alpha-olefins results in a polymer of lower order thereby improving oil solubility and ability to co-crystallize with the wax to result in smaller wax crystals. Accordingly, the preferred polymer of this invention comprises 0 to wt. of a C C alpha-oleiin and 20 to wt. of the aforedescribed C -C alpha-olefin. Of these, copolymers containing 4 to 50 wt. of a C C alpha-olefin and 50 to 96 wt. of a linear C20-'C28 alpha-olefin are particularly effective. An especially preferred polymer comprises 20 to 40 wt. of a C C alpha-olefin and 60 to 80 wt. of a C ,C alpha-olefin.

The C -C alpha-olefins which are polymerized with the aforedescribed C -C alpha-oleiins may be represented by the following general formula: H C CI-IR' wherein R is a hydrocarbon radical containing from 1 to 14 carbon atoms. Since the lower alpha-oletin apparently serves only to disrupt the order of the polymer, there appears to be no criticality as to the configuration of R. Accordingly, R may be an alkyl, aralkyl, aryl, alkylaryl, or cycloaliphatic group. Examples of such monomers include propylene, butene-l,

hexene-l, octene-l, decene-l, 3-methyl decene-l tetradecene-l, styrene and styrene derivatives such as pmethyl styrene, p-isopropyl styrene, alpha-methyl styrene, etc.

The aforedescribed C, C alpha-olefins may be polymerized with various other monomers. For example, effective copolymers comprise 20l00 wt. of a C -C alpha-olefin of the invention and O8O wt. of a polymerizable C C diolefin. Similarly, the polymers of the invention may comprise 20 to 100 wt. of the aforedescribed C, C alpha-olefin, to 80 wt. of the aforedescribed C C, alpha-olefin and 0 to 80 wt. of a polymerizable C C diolefin. These diolefins which are useful for polymerization with the afore described alpha-olefins include the bicyclic, alicyclic or aliphatic diolefins containing from about 6 to about 28 carbon atoms, preferably from about 6 to 12 carbon atoms. Non-limiting examples of suitable monomers include 1,5-cyclooctadiene, methylene norbornene, dimethylene norbornene, 1,5-hexadiene dicyclopentadiene, -vinyl-2-norbornene, 1,5-cyclodecadiene, 2,4- dimethyl-Z ,7-octadiene, 3 2-methyll -propenyl) cyclopentene, 1,5-octadecadiene, and the like.

The polymers of this invention may be conventionally prepared by polymerizing the monomers under relatively mild conditions of temperatures and pressure in the presence of a Ziegler-type catalyst, i.e., a mixture of a compound derived from a Group IV, V or VI metal of the Periodic Table in combination with an organo metallic compound of a Group I, II, or III metal of the Periodic Table wherein the amount of the compound derived from a Group IV VI metal may range from 0.01 to 2.0 moles per mole of the organo metallic compound.

Effective catalysts for polymerizing the monomers of the invention include the following combinations: aluminum triisobutyl and vanadium trichloride; aluminum triisobutyl, aluminum chloride, and vanadium trichloride; vanadium tetrachloride and aluminum trihexyl; vanadium trichloride and aluminum trihexyl; vanadium triacetylacetonate and aluminum diethyl chloride; titanium tetrachloride and aluminum trihexyl; vanadium trichloride and aluminum trihexyl; titanium trichloride and aluminum trihexyl; titanium dichloride and aluminum trihexyl; etc.

The polymerization is usually carried out by mixing the catalyst components in an inert diluent such as a hydrocarbon solvent, e.g., hexane, benzene, toluene, xylene, heptane, etc., and then adding the monomers into the catalyst at atmospheric or superatmospheric pressure and temperatures within the range between about 50 and 180F. Usually atmospheric pressure isv employed when polymerizing the monomers containing more than 4 carbon atoms in the molecule and higher pressures are used for the more volatile C -C alphaolefins. The time of reaction will depend upon, and is interrelated to, the temperature of the reaction, the choice of catalyst, and the pressure employed. In general, however, /2 to 5 hours will complete the reaction.

Usually, based upon 100 parts by weight of polymer to be produced, about 120 to 100,000 parts by weight of solvent, and about 0.05 to 5 parts by weight of catalyst will be used in the polymerization.

Petroleum crude oils are often classified into asphaltbase, paraffin-base, and mixed-base, depending on whether they contain asphalt, wax, or a mixture of both in the distillation residue. The present invention is concerned with all petroleum crude oils containing wax 4 fractions which deposit from the crude oil when subjected to temperatures below the ASTM cloud point of the crude oil.

In accordance with the invention, reduction or inhibition of wax deposition can be effected by blending the oil with the polymeric wax crystal modifier of the invention at a point downhole, at the well head or a surface point downstream from the well site.

For ease in handling, the polymeric additive of the invention may be utilized in a concentrate form. For example, to facilitate storage and transportation, the polymer may be blended with a hydrocarbon solvent such as mineral oil to form a concentrate comprising from about 20 to about 80 wt. hydrocarbon solvent and from about 20 to about 80 wt. of the polymer of the invention.

The polymers of the invention may be used alone as the sole additive, or in combination with other additives such as corrosion inhibitors, demulsifying agents, scale inhibitors, etc.

The invention will be further understood by reference to the following examples which include preferred embodiments of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS EXAMPLE 1 A homopolymer of n-eicosene-l was prepared as follows:

Into a 500 ml. four-neck flask fitted with a mechanical stirrer, heating mantle, thermometer, condenser and gas inlet were charged under anhydrous conditions, 021 gram of TiCl .l/3AlCl 200 ml. of toluene as solvent and 0.4 gram of Al(nC I-I After stirring the catalyst-solvent mixture at room temperature for about 30 minutes, the mixture was heated to about C. under a nitrogen blanket and 20 grams of a C alpha-olefin (n-eicosene-l) dissolved in 10 grams of normal hexane was added thereto. After addition of the alpha-olefin solution was completed, the reaction mixture was heated to 70 to C. for about 2 hours, whereupon 1 ml. of isopropyl alcohol was added to stop the reaction. The product mixture was then cooled to room temperature and thereafter mixed with about 5 volumes of methanol to precipitate the solid C alphaolefin homopolymer which was then filtered off and dried for about 12 hours in an oven maintained at about 60C. and mm. pressure. The resulting polymer weighed 6.7 grams and had a number average molecular weight of 2100 as determined by Vapor Phase Osmometry (VPO).

EXAMPLE 2 A polymer of propylene and C C alpha-olefins was prepared in the following manner:

A I50 cc. stirred autoclave was charged under anhydrous conditions with 0.400 gram of triethyl aluminum, i.e., AI(C H 22 grams of xylene solvent and 0.424 gram of aluminum activated titanium trichloride, i.e., TiCl .l/ 3 AlCl with a dry nitrogen blanket. The catalyst-solvent mixture was then stirred at 70 to 80C. for 2 hours. To the reactor contents were then added 82.2 grams of a normal hexane solution containing 8 wt. of a C C alpha-olefin mixture containing 32 wt. nC alpha-olefin, 35 wt. nC alpha-olefin, 22 wt. n-C alpha-olefin, 7.8 wt. nC alpha-olefin and 3.2 wt. C alpha-olefins (wt. based on polymerizable material; 42 wt. inert material present). After addition of the C -C alpha-olefin solution was completed, propylene was pressured into the autoclave until the pressure was raised from atmospheric to 6 psig. Propylene pressure was maintained in the reactor for 2 hours at a temperature of 70 to 80C. Then, after adding 0.9 gram of isopropanol to kill the reaction, the reactor was opened and the contents were diluted with n-heptane and added to 4000 ml. of methanol to precipitate the polymer product. The empty reactor was rinsed with 30 ml. of n-hexane which was also added to the methanoLThe precipitated product was then dried for about 12 hours in an oven maintained at 60C. and 120 mm. pressure. The propylene/C C alpha-olefin polymer product weighed 5.2 grams and had a number average molecular weight of 1890 as measured by Vapor Phase Osmometry (VPO).

EXAMPLE 3 A copolymer of butene-l and n-C alpha-olefin was prepared by reacting 4.1 grams of liquefied butene- 1 in a stirred glass closed reactor containing 10.0 grams of C alpha-olefin dissolved in a catalyst-solvent mixture consisting of 122.5 ml. of toluene, 0.40 gram of Al(nC H and 0.21 gram of TiCl .1/3A1Cl which catalyst-solvent mixture was prepared in accordance with the method of Example 1. The polymerization was then carried out by reacting the reactants at 70 80C. for about 4 hours. Termination of the reaction and recovery of the product was then carried out in accordance with the steps given in the above examples. The butene-l/docosene-l copolymer product weighed 7.8 grams and had a number average molecular weight of about 4300 as measured by Vapor Phase Osmometry.

EXAMPLE 4 A number of polymers of lower alpha-olefins, higher alpha-olefins and cyclic olefins were prepared using the same general procedure as described in the above examples. In these runs, polymers prepared only from olefins containing 6 or more carbon atoms were made using the general process conditions set forth in Example 1, with the exception that different olefin-monomers and amounts were employed. Similarly, polymers prepared from propylene were made using the process described in Example 2. Polymers prepared from butene-l were made using the process described in Example 3. The resulting polymers were then tested in a Texas Austin County petroleum crude oil known as Racoon Bend crude and having an ASTM upper pour point of 75F. and lower pour point of 35F, a viscosity of 43 SUS at 100F., and an API gravity of 31.8. The crude oil-polymer blends were tested for pour depression since this is a measure of the ability of the polymer additive to keep the wax in suspension and in a fluid state, thereby eliminating or reducing the amount of wax which will deposit upon flow surfaces exposed to the crude. The results are given in the following table.

TABLE EVALUATION OF POLYMERIC ADDlTlVES IN RACOON BEND CRUDE OlL ASTM Pour TABLE-continued EVAL UATlON OF POLYMERlC ADDITIVES" IN RACOON BEND CRUDE on.

ASTM Pour Point, *"F.

Additive Upper Lower Tetradeeene-l homopolymer 65 30 Hexadecene-l homopolymer 65 45 Hexadecenel loctadecenel/C -C r polymer 20 1 5 Octadecenel lpropylenecopolymer" 65 10 Eicosene-l homopolymer -5 l5 Eicosene-l/propylene copolymer -5 -20 Docosene-l homopolymer 40 30 Amount of additive tested is 0.15 wt. 71 based on crude oil.

ASTM D-97, special procedure for black oils.

Number average molecular weight of about 17.000 (VPO).

" Number average molecular weight 20,000.

Number average molecular weight of about 3600 (VPO).

" Polymer prepared from 14 wt. 7: hexadccane-l. 11 wt. 7: octadeccne l. 7 wt. 7: cicosene-l. 35 wt. 7: ofC -C alpha-olefin mixture described in Example 2 and 33 wt. 7r of alpha-olefin mixture containing 2 wt. 7: C alpha olefin. 8 Wt. '71- C- alphaolefin, 18 Wt. 7n C alpha-olefin, 21 wt. 71 C alpha-olefin, 17 wt. 7r C alphaolefin, 13 wt. 7: C, alpha-olefin. 8 wt. 7: C alpha-olefin. 6 wt. 7 C alpha-olefin. and 7 wt. Z: of c alpha olefins.

Copolymer prepared from 44.4 grams octadecene-l and 4 psig. propylene using reactor system of Example 2 and having a number average molecular weight of about 6800 (VPO).

" Polymer of Example 1.

Copolymer prepared from 12.1 grams of cicosene-l and 6 psig. propylene using reactor system of Example 2 and having a number average molecular weight of about 1420 (VPO).

Number average molecular weight of about 7180 (VPO).

copolymer prepared from 67 wt. 7: docosene-l and 33 wt. 7: butene-l and having a number average molecular Weight of about 3350 (VPO).

Copolymer prepared from 40 wt. 7: docosenel and 60 wt. 7c hexene-l and having a number average molecular weight of about 5530 (VPO).

" Terpolymcr prepared from 60 wt. 7: docoscned, 38 wt. 7: hexene l and 2 wt. 7a dicyclopentadiene (DCPD) and having a number average molecular weight of about 3640 (VPO).

Terpolymer prepared from 56 wt. 7: docosenc-l. 36 wt. 71 hexene-l and 8 wt. 7: methylene norbomene (MNB) and having a number average molecular weight of about 2540 (VPO).

* Copolymer prepared from 72 wt. 7c docosene-l and 28 wt. 7: styrene and having a number average molecular weight of about 8005 (VPO).

Polymer prepared from 6.6 grams of C C alpha-olefin mixture described in Example 2 and 6 psig. propylene using reactor system of Example 2 and having a number average molecular weight of about 1890 (VPO).

" Copolymcr prepared from 72 wt. 71 of C -C alpha-0lcfin mixture of Example 2 and 28 wt. 71 styrene and having a number average molecular weight of about 8500 (VPO Copolymer prepared from 75 wt. 7! of (T -C alpha-olefin mixture of Example 2 and 25 wt. 7: of 4-mcthylpentcne-l and having a number average molecular weight of about 677 (VPO).

It can be seen from the data in the above Table that polymers prepared from alpha-olefins containing at least 18 carbon atoms in the molecule are very effective for lowering the pour point and thus increasing the flowability of petroleum crude oil. Of particular interest, is the surprising discovery that the effectiveness of these C alpha-olefin polymers is significantly improved by incorporating lower alpha-olefins, such as propylene, butene-l, hexene-l, etc., into the polymer molecule. For example, referring to the above Table. it is seen that homopolymers prepared from C or C alpha-olefin are substantially less effective than copolymers prepared from C C alpha-olefins and C or C alpha-olefin. While not known with certainty, this unexpected improvement is believed to be due to the dis rupting effect which the lower alpha-olefins have on the order of the polymer; Also, as is illustrated in the above Table. non-linear olefins, e.g., styrene, 4-methyl-- pentene-l, cyclicdienes, etcl, maybe advantageously copolymerized with the higher olefins.

It is not intended that this invention be limited to the specific examples presented by way of illustration. The scope of the invention is limited by the appended claims.

What is claimed is: I

1. An oil composition consisting essentially of a pea troleum crude oil containing in the range of 0.0005 to 0.45 wt. of a flow improving, oil-solublc copolymer prepared by using a Ziegler type polymerization catalyst and consisting essentially of 60 to 80 wt. of a higher alpha mono-olefin selected from the group con- 8 sisting of eicosene, docosene, andmixtures of C to C olefin; and 40 to 20 wt, of a lower alpha mono-olefin having 4 to6 carbon atoms, said copolymer being substantially free of diene monomers, and having a number average "molecular weight in the range of about 500 to 125,000. g

2. An oil composition according to claim 1, wherein said molecular weight is in the range of 1000 to 40,000.

3. An oilcomposition according to claim 2, wherein said copolymer consists essentially of docosene and butene-l. g

4. An oil composition according to claim 2, wherein said copolymer consists essentially of docosene and hxene-l

Claims (4)

1. AN OIL COMPOSITION CONSISTING ESSENTIALLY OF A PETROLEUM CRUDE OIL CONTAINING IN THE RANGE OF 0.0005 TO 0.45 WT. % OF A FLOW IMPROVING, OIL-SOLUTION COPOLYMER PREPARED BY USING A ZIEGLER TYPE POLYMERIZATION CATALYST AND CONSISTING ESSENTIALLY OF 60 TO 80 WT. % OF A HIGHER ALPHA MONO-OLEFIN SELECTED FROM THE GROUP CONSISTING OF EICOSENE, DOCOSENE, AND MIXTURES OF C22 TO C24 OLEFIN, AND 40 TO 20 WT. % OF A LOWER ALPHA MONOOLEFIN HAVING 4 TO 6 CARBON ATOMS, SAID COPOLYMER BEING SUBSTANTIALLY FREE OF DIENE MONOMERS, AND HAVING A NUMBER AVERAGE MOLECULAR WEIGHT IN THE RANGE OF ABOUT 500 TO 125,000.

2. An oil composition according to claim 1, wherein said molecular weight is in the range of 1000 to 40,000.

3. An oil composition according to claim 2, wherein said copolymer consists essentially of docosene and butene-1.

4. An oil composition according to claim 2, wherein said copolymer consists essentially of docosene and hexene-1.