Middle distillate hydrocarbon compositions containing thermal stability additive
FIELD OF THE INVENTION 
     This invention relates to a middle distillate hydrocarbon composition particularly characterized by thermal stability. More particularly it relates to a novel extended middle distillate such as a jet fuel composition. 
     BACKGROUND OF THE INVENTION 
     As is well known to those skilled in the art, middle distillate fuels such as aviation jet fuels form gums and deposits on storage, particularly when storage is at elevated temperature. These gums and deposits are undesirable in that they may interfere with operation by partially or wholly clogging narrow passageways through which the fuel is to pass. The standard test method for determining the amount of thermal degradation products of middle distillate hydrocarbon fuels such as Jet Fuels is ASTM, Jet Fuel Thermal Oxidation Test D-3241. In this JFTOT test, a fuel is maintained at elevated temperature; and the amount of gum and deposit is determined. The results are measured in terms of the amount of deposit on an aluminum heater tube and the rate of plugging of a 17 μm nominal porosity precision filter; and a visual rating of 0-2 is good and 3-4 is unsatisfactory by comparison with a standard. Preliminary screening testing may be carried out using a test temperature of 400° F. (in a Modified JFTOT Test) rather than the standard temperature of 500° F. 
     It is an object of this invention to improve the thermal stability of a middle distillate. Other objects will be apparent to those skilled in the art. 
     STATEMENT OF THE INVENTION 
     In accordance with certain of its aspects, this invention is directed to a middle distillate composition comprising 
     (a) a major portion of middle distillate fuel containing a hydrocarbon boiling in the middle distillate boiling range; 
     (b) an extending portion of a shale oil diesel fraction; and 
     (c) a minor effective amount of, as thermal stability additive, an (alkyl polyoxyalkyl) amino alkanoic acid. 
     DESCRIPTION OF THE INVENTION 
     The fuels which may be used in practice of the process of this invention include middle distillate fuels which boil above gasolines and below heavier lube oil fractions. Middle distillate fuels contain hydrocarbons which boil in the middle distillate boiling range. Typically these fuels have an ibp of 270° F.-400° F., typically 340° F.-400° F., sy about 350° F.; a 50% bp of 400° F.-670° F., typically 420° F.-520° F., say about 425° F.; and an ep of 500° F.-660° F., typically 525° F.-640° F., say about 525° F. 
     Typical middle distillates may include kerosene, diesel fuel, light cycle gas oil, intermediate light cycle gas oil, etc. 
     A typical gas oil may be characterized by an ibp of 358° F., a 50% bp of 500° F., an ep of 580° F., and an API Gravity of 40.5. 
     A typical light cycle gas oil may be characterized by an ibp of 356° F., a 50% bp of 500° F., an ep of 640° F., and an API Gravity of 32.8. 
     A typical diesel oil may be characterized by an ibp of 357° F., a 50% bp of 418° F., an ep of 550° F., an API Gravity 45.1, and a Cetane No. of 50. 
     A typical intermediate light cycle gas oil may be characterized by an ibp of 270° F., a 50% bp of 664° F., an ep of 690° F., and an API Gravity of 21.2. 
     The advantages of this invention may be particularly advantageous when it is carried out in connection with a middle distillate hydrocarbon, such as jet fuel, which has been extended with a shale oil diesel fraction. 
     The base jet fuel in which the additive of the invention may be used to form a jet fuel composition may comprise a mixture of hydrocarbons boiling in the jet fuel boiling range. This base fuel may contain straight chain or branched chain paraffins, cycloparaffins, olefins, and aromatic hydrocarbons and any mixture of these. The base fuel may be derived from straight-chain naphtha, polymer gasoline, natural gasoline, catalytically cracked or thermally cracked hydrocarbons, catalytically reformed stocks, etc. 
     The jet fuels which may be used in practice of this invention may be characterized by the fact that they contain hydrocarbons which boil in the jet fuel boiling range which is characterized by an ibp of 320° F.-360° F., say about 350° F., a 50% bp of 400° F.-430° F., say bout 425° F.; and an ep of 500° F.-530° F., say about 525° F. 
     A typical jet fuel may be Avjet A characterized as follows: 
     
                       TABLE                                                       
______________________________________                                    
                Jet Fuel A                                                
______________________________________                                    
Gravity, ° API                                                     
                  42.4                                                    
ASTM Distillation °F.                                              
ibp               350                                                     
10%               376                                                     
30%               400                                                     
50%               423                                                     
90%               486                                                     
95%               504                                                     
EP                526                                                     
Flash Point °F.                                                    
                  126                                                     
Cloud Point, °F.                                                   
                  -56                                                     
Pour Point, °F.                                                    
                  -55                                                     
Cetane            43.0                                                    
Kin Vis cs @ 40° C.                                                
                  1.5                                                     
% S, X-ray        0.04                                                    
JFTOT @ 400° F.*                                                   
                  2                                                       
______________________________________                                    
 *Modified Jet Fuel Thermal Oxidation Test, ASTM D3241                    
 
    
     It is a feature of this invention that it is possible to extend middle distillates such as jet fuels by the addition thereto of a shale oil diesel fraction prepared by distillation of shale oil. A shale oil diesel fraction may typically have the following properties: 
     
                       TABLE                                                       
______________________________________                                    
                   Paraho Derived Diesel Fuel                             
                   (From Shale Oil)                                       
            Broad  Typical                                                
______________________________________                                    
Gravity, ° API                                                     
              30-40    32.6                                               
ASTM Distillation °F.                                              
ibp           500-520  510                                                
10%           525-535  530                                                
30%           560-570  568                                                
50%           590-600  593                                                
90%           650-660  659                                                
95%           670-680  676                                                
EP            670-680  678                                                
Flash Point °F.                                                    
              180-190  184                                                
Cloud Point, °F.                                                   
                       Unsuitable                                         
Pour Point, °F.                                                    
              45-55    50                                                 
Cetane        60-65    62.8                                               
Kin Vis cs @ 40° C.                                                
              5.0-5.5  5.30                                               
% S, X-ray    0.50-0.60                                                   
                       0.58                                               
JFTOT @ 400° F.*                                                   
              3-4      4                                                  
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 *Modified Jet Fuel Thermal Oxidation Test, ASTM D3241                    
 
    
     Middle distillate hydrocarbons such as jet fuel may be blended with shale oil diesel fraction to form an extended Jet fuel containing 80-95 v%, say 90 v% of Jet fuel. It is found that the thermal stability of such extended jet fuels may be unsatisfactory. For example in a typical instance a jet fuel having a JFTOT rating of 2 may be blended with a shale oil diesel fraction having a rating of 4 (90:10 by volume) to give a product having a rating of 4+ which is unsatisfactory. 
     An extending portion of the shale oil diesel fraction is typically 5-15 parts, say 10 parts by volume of the shale oil diesel fraction per 100 parts by volume of jet fuel. In a typical mixture, this corresponds to about 80-95 v%, say 90 v% of jet fuel and 5-20 v%, say about 10 v% of shale oil diesel fraction. 
     The compositions of this invention may contain any of the additives normally employed in middle distillates. 
     In accordance with practice of this invention, there may be added to a major portion of the extended middle distillate, typically a jet fuel, a minor effective amount of, as a thermal stability additive, an (alkyl polyoxyalkyl) amino alkanoic acid. 
     Preferably the additive has the formula 
     
         R(OR&#39;).sub.a NR&#34;COOH 
    
     In the above formula, 
     R may be an alkyl group typified by methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, amyls, hexyls, octyls, etc. R may contain 1-20 carbon atoms, preferably 10-15, more preferably 10-12 carbon atoms. 
     R&#39; and R&#34; may each be a divalent alkylene group containing 1-8 carbon atoms, typically 1-4, say 2-3 carbon atoms. Preferably R&#34; is --C 2  H 4  -- and R&#39; is ##STR1## 
     a maybe 1-20, preferably 1-5, say 1-2. 
     Illustrative compositions may be the following, the first noted being preferred: 
     
                       TABLE                                                       
______________________________________                                    
 ##STR2##                                                                 
 ##STR3##                                                                 
 ##STR4##                                                                 
 ##STR5##                                                                 
 ##STR6##                                                                 
These composition may be commercially available under Jeffamine           
trademarks typified by Jeffamine Experimental surfactant MA-300. One      
preferred commercially available product is the first noted in the above  
table, available under the trademark Jeffamine Surfactant MA-300. It is   
possible to readily prepared these compositions. For example, the         
preferred composition may be prepared by the reaction of equimolar        
portions of acrylic acid with the Jeffamine M-300 brand of                
 ##STR7##                                                                 
wherein R is a mixture of linear C-10 and C-12 alkyl groups and x has the
 average value of 2.
 ##STR8##
 
    
     In practice of this invention according to certain of its aspects, the additive may be added to the base fuel in minor effective amount. The additives are particularly effective in amount of 0.01-1 w% (ca 26-2600 PTB), preferably 0.1-0.3 w% (ca 260-785 PTB), of the total fuel composition. Preferred range may be 0.1-0.3 w%, (ca 260-785 PTB) more preferably 0.15-0.25 w%, (ca 390-650 PTB), say 0.2 w% (ca 520 PTB). PTB stands for pounds per thousand barrels. 
     It is a feature of this invention that the fuel composition as prepared is characterized by improved ratings on the Modified JFTOT Test ASTM D-3241. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Practice of this invention will be apparent to those skilled in the art from the following examples wherein, as elsewhere in this specification, all parts are parts by weight unless otherwise specified. 
     EXAMPLE I 
     In this example which illustrates the best mode known to me of practicing the process of this invention, the reference fuel is the Jet Fuel A hereinbefore tabulated. There is added to this Jet Fuel A, a shale oil diesel fraction, identified as a Paraho Derived Diesel Fuel, having the specific properties set forth as typical in the table supra. The final composition contained 90 v% Jet Fuel A and 10 v% of Paraho Derived Diesel Fuel. The additive is 0.2 w% of the Jeffamine MA-300 brand of Component A of the Table: ##STR9## 
     EXAMPLE II* 
     In this control example, the Modified JFTOT test was carried out on the charge Jet Fuel alone. 
     EXAMPLE III* 
     In this control example, the Modified JFTOT test was carried out on the Paraho Derived Diesel Fuel alone. 
     EXAMPLE IV* 
     In this control example, the Modified JFTOT test was carried out on the 90:10 v mixture of Jet Fuel and Paraho Derived Diesel Fuel alone. 
     The results are as follows: 
     
                       TABLE                                                       
______________________________________                                    
       Modified                                                           
       JFTOT                                                              
Example                                                                   
       Rating     Composition                                             
______________________________________                                    
I      1          Jet Fuel (90 v %)                                       
                  Shale oil Diesel Oil Fraction (10 v %)                  
                  Additive (0.2 w %)                                      
II*    2          Jet Fuel                                                
III*   4          Shale oil Diesel Oil Fraction                           
IV*     4+        Jet Fuel (90 v %)                                       
                  Shale oil Diesel Oil Fraction (10 v %)                  
______________________________________                                    
 
    
     From the above table, it is apparent that the presence of the additive permits attainment of outstanding results. For example, as may be seen by comparing Example I with Example IV*, it is possible to upgrade an extended jet fuel having an undesirable Modified JFTOT rating of 4+; by addition of 0.2 w% additive the rating is upgraded to 1. 
     The novel products of this invention are characterized by improved (i.e. decreased) formation of gums and deposits after standing at elevated temperatures. 
     Results comparable to those of Example I may be obtained if the additive is 
     
                       TABLE                                                       
______________________________________                                    
EXAMPLE     ADDITIVE                                                      
______________________________________                                    
             ##STR10##                                                    
  VI                                                                      
             ##STR11##                                                    
  VII                                                                     
             ##STR12##                                                    
  VIII                                                                    
             ##STR13##                                                    
______________________________________                                    
 
    
     Results comparable to those of Example I may be obtained if the middle distillate is: 
     
                       TABLE                                                       
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Example       Middle Distillate                                           
______________________________________                                    
IX            Gas Oil        40.5 API                                     
              ibp            358° F.                               
              50% bp         500° F.                               
              ep             580° F.                               
              Pour Point (D-19)                                           
                             +10° F.                               
              Cetain No. (D-613)                                          
                             55.2                                         
X             Light Cycle Gas Oil                                         
                             32.8 API                                     
              ibp            356° F.                               
              50% bp         500° F.                               
              ep             640° F.                               
              Pour Point (D-19)                                           
                             +25° F.                               
              Cetain No. (D-613)                                          
                             42.2                                         
XI            Diesel Oil     45.1 API                                     
              ibp            357° F.                               
              50% bp         418° F.                               
              ep             550° F.                               
              Pour Point (D-19)                                           
                             -25° F.                               
              Cetane No. (D-613)                                          
                             50                                           
XII           Intermediate Light                                          
                             21.2 API                                     
              Cycle Gas Oil                                               
              ibp            270° F.                               
              50% bp         664° F.                               
              ep             690° F.                               
              Pour Point (D-19)                                           
                             74° F.                                
              Cetane No. (D-613)                                          
                             39.7                                         
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     Although this invention has been illustrated by reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made which clearly fall within the scope of this invention.