Abstract:
A low pour point crude oil composition is prepared by incorporating in a waxy crude oil an effective pour point depressant amount of an oil soluble ethylene-acryonitrile copolymer or terpolymer. The copolymer or terpolymer is usually added as a solution. In one aspect the invention relates to the pipeline transportation of the low pour crude oil composition.

Description:
BACKGROUND AND SUMMARY OF THE INVENTION 
     Certain waxy, high-pour crude oils are known to have poor pipeline flow characteristics and, in addition, they exhibit a tendency to gel at temperatures encountered during transportation. This tendency is particularly troublesome when a pipeline containing these crudes is shut down under low ambient temperatures. 
     A number of processes have been suggested in the art for dealing with such flow problems. For example, the pour point of waxy curdes have been improved by the removal of a part of the wax by solvent extraction at low temperatures, with the attendant expense of recovering the solvent, and the problem of disposing of the wax and of providing the cooling requirements, which are substantial. In more recently proposed processes, wax has been removed without the use of a solvent by centrifuging a previously heated crude which has been cooled at a critically controlled and slow rate to a centrifuging temperature of around 35°-55° F. 
     Another widely practiced process involves cutting the waxy crudes with lighter fractions of hydrocarbons. This process suffers from a number of disadvantages, such as the fact that the procedure involves the use of relatively large amounts of expensive hydrocarbon solvents to transparent a relatively cheap product. Furthermore, this practice also necessarily requires that the cutting hydrocarbon solvents be available in suitable quantities which in some instances is inconvenient, and also that there be a ready market for the solvents at the other end of the pipeline. 
     In another method, heating equipment installed along the pipeline at frequent intervals is utilized to heat the crude and thus reduce its viscosity. Heaters employed for this purpose can be operated by withdrawing from the crudes being transported for use as fuels. As much as 5 percent of the crude may be utilized in providing the heating necessary for reducing the crude oil viscosity to a suitable value. Furthermore, most pipelines are not equipped with such heating installations. Also, there is the additional problem of contamination of the atmosphere when burning crude oils, since they may be difficult to burn completely. 
     According to this invention, an effective pour point depressant amount of a copolymer of ethylene and acrylonitrile is incorporated in a waxy crude oil to provide a composition having good pipeline flow characteristics and a reduced tendency to gel at temperatures encountered during transportation such crude oil. 
     PRIOR ART 
     British Patent No. 787,055 to Esso Research and Engineering Company discloses the use of oil soluble copolymers of ethylene and/or propylene and a nitrogen-containing unsaturated organic compound, such as acryonitrile as a detergent additive in lubricating oils. The reference further discloses that such copolymers, when modified by a side chain containing 8-18 carbon atoms, may impart additional properties, such as V.I. improving properties or pour point depressing properties in the refined products used as lubricants. 
     U.S. Pat. No. 4,062,796 to Gardner et al. discloses the use of the reaction product of a polyelectrolytic organic polymer and an organic surfactant to prevent the deposition of scale in aqueous solutions. The organic polymer may be an acrylonitrile copolymer with ethylene or propylene. 
     U.S. Pat. No. 3,693,720 to McDougall et al. discloses the use of a polymer comprising an ethylene moiety, a nonpolar moiety, such as acrylonitrile, and a polar moiety, such as acrylic acid to inhibit wax deposition on surfaces contacting crude oils. 
     U.S. Pat. No. 3,832,302 to Lansford et al. discloses a composition for inhibiting scale in an aqueous system formed by the reaction of a water soluble polyelectrolytic organic polymer having a molecular weight from 1,000 to 100,000 and a water-soluble organic cationic surface active compound. The organic polymer may be a copolymer of an olefin, such as ethylene with a compound having the formula ##STR1## in which R may be hydrogen and R 1  may be a nitrile radical. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The ethylene-arcylonitrile copolymers used in this invention may be prepared by polymerization of ethylene and acrylonitrile or by reacting acrylic acid with ethylene and pyrolyzing with ammonia to obtain the copolymer. These copolymers are well known in the art, and procedures for their preparation are readily available. The composition of the copolymers will vary. However, usually the amount of acrylonitrile in the copolymer is between about 1 and about 35 weight percent, and more usually between about 10 and about 20 weight percent. 
     The ethylene-acrylonitrile terpolymers may be prepared by polymerization of ethylene, acrylonitrile and a third monomer. Third monomers used non-exhaustively include vinyl acetate, carbon monoxide, alkyl acrylates, alkyl methacrylates, alkyl vinyl ethers, vinyl chloride, vinyl fluoride, acrylic acid and methacrylic acid. The various terpolymers used in the compositions of the invention are known in the art as are the procedures for their preparation. The amount of the third monomer in the terpolymers will vary from about 0.1 to about 10 weight percent, but usually is between about 1 and 5 weight percent. 
     It is possible to modify ethylene-acrylonitrile copolymers and terpolymers by adding hydrocarbon side chains to the polymers. However, in the crude oil compositions of this invention the ethylene-acrylonitrile copolymers and terpolymers are employed without such modification. 
     Depending on the polynmerization conditions used, particularly the temperature of polymerization, the copolymers and terpolymers may vary in melt index as measured by ASTM D1238-E (which is related to molecular weight). The melt index of the copolymers and terpolymers may be from as low as 1 to as high as 4000. More usually the melt index will be between about 1 and about 300. 
     The ethylene-acrylonitrile copolymers and terpolymers are usually solid or semi-solid at room temperature. While it is possible to introduce the copolymer or terpolymers to the waxy crude oil in the form of a solid, it is desirable for ease of handling to place the copolymer or terpolymer in solution before adding it to the waxy crude oil. This may be accomplished through the use of an aromatic solvent, such as toluene or xylene or, if preferred, a refinery stream high in aromatics, such as ethylene cracker bottoms, may be used for this purpose. 
     Although the crude oil compositions of this invention may be prepared using any crude oil containing wax, the ethylene-acrylonitrile copolymer and terpolymer pour point depressants are especially effective with high pour waxy crude oils. These copolymers and terpolymers find particular application in waxy crude oils obtained from areas such as India, Egypt and the British North Sea; however, they are useful in other waxy materials. 
     The amount of the ethylene-acrylonitrile copolymer or terpolymer incorporated in the crude oil compositions of this invention may be varied over a wide range. Generally, the amount of copolymer or terpolymer in the crude oil composition will be from about 1.0 to about 2000 parts per million by weight, and preferably between about 1 and about 500 parts per million. However, any amount of the copolymer or terpolymer which will provide a reduction in pour point may be used within the scope of the invention. 
     This invention is especially applicable to the pipelining of waxy crudes over substantial distances, particularly where the pipeline is subject to varying temperature conditions. It is also applicable, however, to situations where crudes are moved over short distances. For example, it may be used in off-loading of offshore platforms, in getting lines in oil fields and in the storage and transfer of crude oil in refineries. 
     The following examples illustrate the results obtained in carrying out the invention. 
     A number of polymers containing nitrile group (derived from acrylonitrile) were tested as pour point depressants in Bombay High, an Indian crude. One thousand parts pre million depressant material was added to the crude which was heated to a temperature of 122° F. The pour point of each crude sample was then determined by ASTM Method D-97. 
     
                       TABLE 1______________________________________                      Pour                      PointPour Point Depressant*     (°F.)______________________________________Blank                      8575 Styrene/25 Acrylonitrile                      8568 Styrene/32 Acrylonitrile                      8079 Butadiene/21 Acrylonitrile                      9074 Butadiene/26 Acrylonitrile                      8563 Butadiene/37 Acrylonitrile (Hydrogenated)                      8585 Ethylene/10 Vinyl Acetate/5 Methacrylonitrile                      8569 Ethylene/18 Vinyl Acetate/13 Acrylonitrile                      3582 Ethylene/18 Acrylonitrile                      2084 Ethylene/16 Acrylonitrile                      2085 Ethylene/5 Carbon Monoxide/10 Acrylonitrile                      1579 Ethylene/16 Vinyl Acetate/5 Acrylonitrile                      20______________________________________ *The numbers represent weight percent. 
    
     It is noted that the two ethylene-acrylonitrile copolymers tested both provided a substantial reduction in pour point. Both of the ethylene-vinyl acetate-acrylonitrile terpolymers also provided a similar reduction as did the terpolymer of ethylene, carbon monoxide and arcylonitrile. 
     An ethylene-acrylonitrile copolymer containing 18 weight percent acrylonitrile (EAN 18) was tested at various concentrations in Bombay High crude in a similar manner. The results are presented in Table 2. 
     
                       TABLE 2______________________________________  Conc. Pour Point  (ppm) (°F.)______________________________________   0    85   50   45  100   40  250   40  500   35  1000  20______________________________________ 
    
     The same ethylene-acrylonitrile copolymer was compared with Shellswin 5X in Bombay High crude. Shellswim 5X is a pour point depressant provided by Shell Oil Company. One hundred parts per million of each pour point depressant were used in the Bombay High crude which had been heated to 122° F. The results of the comparison are shown in Table 3. 
     
                       TABLE 3______________________________________Pour Point      Pour PointDepressant      (°F.)______________________________________Blank           85Shellswim 5X*   70EAN 18          35______________________________________ *Polyalkylacrylate polymer (containing C18 to C22 groups). 
    
     The pour point advantage of the ethylene-acrylonitrile copolymer is apparent from the data. 
     The same ethylene-acrylonitrile copolymer was tested in Geisum crude obtained from Egypt at several concentrations. The results are shown in Table 4. 
     
                       TABLE 4______________________________________Conc.       Pour Point - °F.(ppm)       EAN 18______________________________________ 0          85 50         60100         40250         10______________________________________ 
    
     A similar pour point advantage of the ethyleneacrylonitrile copolymer is seen here also. 
     The same ethylene-acrylonitrile copolymer was compared with two other pour point depressants in several Egyptian crudes. 150 parts per million of each material was added to crudes heated to a temperature of 122° F. The results are shown in table 5. 
     
                       TABLE 5______________________________________   POUR POINTS (°F.)         EAN       CF      Shellswim   Blank 18        2315*   11T**______________________________________Umbarka   80      75        60    75Safir     65      20        30    35Agiba     60      &lt;5        --    &lt;5______________________________________ *Polymer(s) containing ethylene, vinylacetate, alkyl acrylate and alkyl succinates. **Vinylpyridinealkylacrylate copolymer. 
    
     The same ethylene-acrylonitrile copolymer was tested in a number of crudes from N. Dak., The Peoples Republic of China, and the British North Sea. Various concentrations of the copolymer were tested in crudes heated to 165° F. The results are shown in Table 6. 
     
                       TABLE 6______________________________________    Conc.      POUR POINT (°F.)Crude      (ppm)        Blank   EAN 18______________________________________Henry Fritch*      1000         115     70Henry Fritch*       50          115     75DaQuing**  500          95      70Zohn UAN** 500          95      80Liao He**  100          75      40Hua Bei**  100          100     80Beatrice***      250          85      35______________________________________ *North Dakota. **Peoples Republic of China. ***British North Sea. 
    
     The same ethylene-acrylonitrile copolymer was tested for gel strength in Bombay and Safir crudes, along with two Shell materials (Shellswim 5X and Shellswim 11T). Pertinent test data and results are shown in Table 7. 
     
                                           TABLE 7__________________________________________________________________________            Prep.                Dynamic                     Hold                         Gel        Conc.            Temp.                Cooling                     Temp.                         StrengthCrudePPD     (ppm)            (°F.)                (to °F.)                     (°F.)                         (lbs/100 ft)__________________________________________________________________________Bombay--      --  122 98   68  312.0BombayEAN 18  100 122 98   68   1.7BombayShellswim 5X        150 122 98   68   5.2Safir--      --  140 60   32  365.0SafirEAN 18  100 140 60   32  130.3SafirShellswim 11T        250 140 60   32  195.5__________________________________________________________________________ 
    
     It is noted from the data that the ethylene-acrylonitrile copolymer, even in lower concentrations, provide better gel strength than the two Shell materials. 
     Wax depositions studies were made on Bombay High crude with the same ethylene-acrylonitrile copolymer and two other materials: Ethylene-vinylacetate-methacrylic acid terpolymer and Shellswim 5X. The results are shown in Table 8. 
     
                       TABLE 8______________________________________                     Wax             Conc.   ReductionPPD               (ppm)   (Percent)______________________________________EAN 18            1000    90EAN 18             50     80EAN 18             10     20Ethylene-vinylacetate-             1000    50methacrylic acidterpolymerShellswim 5X      1000    33______________________________________ 
    
     The data in Table 8 indicates the superiority of the ethylene-acrylonitrile copolymer as a paraffin deposition inhibitor. 
     Four ethylene-acrylonitrile copolymers were prepared. The composition of the copolymers and their melt indices are shown in Table 9. 
     
                       TABLE 9______________________________________Sample  Ethylene      Acrylonitrile                             MeltNo.     Weight Percent                 Weight Percent                             Index______________________________________1       94.5           5.5          32       89.0          11.0          83       84.0          16.0          404       69.0          31.0        &gt;100______________________________________ 
    
     The above copolymers were tested for pour point in a number of crudes obtained from around the world. The results of the tests are shown in Table 10. 
     
                       TABLE 10______________________________________                               Pour PointSample Crude       PPM     Temp. (°F.)                               (°F.)______________________________________1      Bombay      1000    74       852      Bombay      1000    74       503      Bombay      1000    74       404      Bombay      1000    74       351      Bombay       200    50       802      Bombay       200    50       703      Bombay       200    50       554      Bombay       200    50       802      Bombay       200    74       703      Bombay       200    74       504      Bombay       200    74       75  Ecopetrol.sup.(1)2      Ecopetrol    50     40       753      Ecopetrol    50     40       454      Ecopetrol    50     40       753      Ecopetrol    10     46       753      Ecopetrol    50     46       703      Ecopetrol    100    46       352      Ecopetrol    100    46       653      Ecopetrol    100    46       154      Ecopetrol    100    46       653      Ecopetrol    250    46       -30  Marathon.sup.(2)3      Marathon    1000    70       803      Marathon    1500    70       703      Kotter.sup.(3)               50     74       453      Kotter       500    74       55  Dulang.sup.(4)               953      Dulang      1000    60       1004      Dulang      1000    60       100  Myton.sup.(5)                453      Myton       1000    46       -104      Myton       1000    46       -10  Daqing                       803      Daqing      1000    60       60  Delhi.sup.(6)                703      Delhi       1000    60       704      Delhi       1000    60       703      Delhi        200    46       652      Delhi        200    46       704      Delhi        200    46       70  Kalda.sup.(7)                753      Kalda       1000    60       254      Kalda       1000    60       40  New Zealand                  852      New Zealand 1000    46       853      New Zealand 1000    46       854      New Zealand 1000    46       85  Ewing Banks.sup.(8)          402      Ewing Banks 1000    46       203      Ewing Banks 1000    46       104      Ewing Banks 1000    46       -20  Myton Station       80/46    1003      Myton Station              1000    80/46    1004      Myton Station              1000    80/46    100  LSWR.sup.(9)                 1253      LSWR        1000    60       1254      LSWR        1000    60       125  Dickinson.sup.(10)           953      Dickinson   1000    60       504      Dickinson   1000    60       50______________________________________ .sup.(1) Columbia .sup.(2) Tunisia .sup.(3) British North Sea .sup.(4) Peoples Republic of China .sup.(5) Utah .sup.(6) India .sup.(7) Egypt .sup.(8) Gulf Coast  USA .sup.(9) Malaysia  Low sulfur resid .sup.(10) North Dakota