Low pour crude oil compositions
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                                           
                           Point                                          
Pour Point Depressant*     (°F.)                                   
______________________________________                                    
Blank                      85                                             
75 Styrene/25 Acrylonitrile                                               
                           85                                             
68 Styrene/32 Acrylonitrile                                               
                           80                                             
79 Butadiene/21 Acrylonitrile                                             
                           90                                             
74 Butadiene/26 Acrylonitrile                                             
                           85                                             
63 Butadiene/37 Acrylonitrile (Hydrogenated)                              
                           85                                             
85 Ethylene/10 Vinyl Acetate/5 Methacrylonitrile                          
                           85                                             
69 Ethylene/18 Vinyl Acetate/13 Acrylonitrile                             
                           35                                             
82 Ethylene/18 Acrylonitrile                                              
                           20                                             
84 Ethylene/16 Acrylonitrile                                              
                           20                                             
85 Ethylene/5 Carbon Monoxide/10 Acrylonitrile                            
                           15                                             
79 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                                                     
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Pour Point      Pour Point                                                
Depressant      (°F.)                                              
______________________________________                                    
Blank           85                                                        
Shellswim 5X*   70                                                        
EAN 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         60                                                            
100         40                                                            
250         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                                                     
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        POUR POINTS (°F.)                                          
              EAN       CF      Shellswim                                 
        Blank 18        2315*   11T**                                     
______________________________________                                    
Umbarka   80      75        60    75                                      
Safir     65      20        30    35                                      
Agiba     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     70                                        
Henry Fritch*                                                             
            50          115     75                                        
DaQuing**  500          95      70                                        
Zohn UAN** 500          95      80                                        
Liao He**  100          75      40                                        
Hua Bei**  100          100     80                                        
Beatrice***                                                               
           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.                                           
                              Strength                                    
Crude                                                                     
     PPD     (ppm)                                                        
                 (°F.)                                             
                     (to °F.)                                      
                          (°F.)                                    
                              (lbs/100 ft)                                
__________________________________________________________________________
Bombay                                                                    
     --      --  122 98   68  312.0                                       
Bombay                                                                    
     EAN 18  100 122 98   68   1.7                                        
Bombay                                                                    
     Shellswim 5X                                                         
             150 122 98   68   5.2                                        
Safir                                                                     
     --      --  140 60   32  365.0                                       
Safir                                                                     
     EAN 18  100 140 60   32  130.3                                       
Safir                                                                     
     Shellswim 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                                                     
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                          Wax                                             
                  Conc.   Reduction                                       
PPD               (ppm)   (Percent)                                       
______________________________________                                    
EAN 18            1000    90                                              
EAN 18             50     80                                              
EAN 18             10     20                                              
Ethylene-vinylacetate-                                                    
                  1000    50                                              
methacrylic acid                                                          
terpolymer                                                                
Shellswim 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                                                     
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Sample  Ethylene      Acrylonitrile                                       
                                  Melt                                    
No.     Weight Percent                                                    
                      Weight Percent                                      
                                  Index                                   
______________________________________                                    
1       94.5           5.5          3                                     
2       89.0          11.0          8                                     
3       84.0          16.0          40                                    
4       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 Point                            
Sample Crude       PPM     Temp. (°F.)                             
                                    (°F.)                          
______________________________________                                    
1      Bombay      1000    74       85                                    
2      Bombay      1000    74       50                                    
3      Bombay      1000    74       40                                    
4      Bombay      1000    74       35                                    
1      Bombay       200    50       80                                    
2      Bombay       200    50       70                                    
3      Bombay       200    50       55                                    
4      Bombay       200    50       80                                    
2      Bombay       200    74       70                                    
3      Bombay       200    74       50                                    
4      Bombay       200    74       75                                    
       Ecopetrol.sup.(1)                                                  
2      Ecopetrol    50     40       75                                    
3      Ecopetrol    50     40       45                                    
4      Ecopetrol    50     40       75                                    
3      Ecopetrol    10     46       75                                    
3      Ecopetrol    50     46       70                                    
3      Ecopetrol    100    46       35                                    
2      Ecopetrol    100    46       65                                    
3      Ecopetrol    100    46       15                                    
4      Ecopetrol    100    46       65                                    
3      Ecopetrol    250    46       -30                                   
       Marathon.sup.(2)                                                   
3      Marathon    1000    70       80                                    
3      Marathon    1500    70       70                                    
3      Kotter.sup.(3)                                                     
                    50     74       45                                    
3      Kotter       500    74       55                                    
       Dulang.sup.(4)               95                                    
3      Dulang      1000    60       100                                   
4      Dulang      1000    60       100                                   
       Myton.sup.(5)                45                                    
3      Myton       1000    46       -10                                   
4      Myton       1000    46       -10                                   
       Daqing                       80                                    
3      Daqing      1000    60       60                                    
       Delhi.sup.(6)                70                                    
3      Delhi       1000    60       70                                    
4      Delhi       1000    60       70                                    
3      Delhi        200    46       65                                    
2      Delhi        200    46       70                                    
4      Delhi        200    46       70                                    
       Kalda.sup.(7)                75                                    
3      Kalda       1000    60       25                                    
4      Kalda       1000    60       40                                    
       New Zealand                  85                                    
2      New Zealand 1000    46       85                                    
3      New Zealand 1000    46       85                                    
4      New Zealand 1000    46       85                                    
       Ewing Banks.sup.(8)          40                                    
2      Ewing Banks 1000    46       20                                    
3      Ewing Banks 1000    46       10                                    
4      Ewing Banks 1000    46       -20                                   
       Myton Station       80/46    100                                   
3      Myton Station                                                      
                   1000    80/46    100                                   
4      Myton Station                                                      
                   1000    80/46    100                                   
       LSWR.sup.(9)                 125                                   
3      LSWR        1000    60       125                                   
4      LSWR        1000    60       125                                   
       Dickinson.sup.(10)           95                                    
3      Dickinson   1000    60       50                                    
4      Dickinson   1000    60       50                                    
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 .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