Patent Publication Number: US-4547201-A

Title: SRC Residual fuel oils

Description:
The Government of the United States of America has rights in this invention pursuant to Contract No. DE-AC05780RO3054 (as modified) awarded by the U.S. Department of Energy. 
    
    
     This invention relates to a composition of matter which has utility as a fuel oil substitute. 
     More specifically, this invention relates to a blend of solvent refined coal in a mixture of distillate oils. The resulting composition exhibits long term stability as a fuel oil and it may be used with only minor modification in existing infrastructures. 
     PRIOR ART 
     Coal refining consists of adding hydrogen to coal and removing its principal pollutants, sulphur and ash. First, raw coal is pulverized, mixed with a solvent derived from the refining process and heated under pressure. Hydrogen is added and the hydrogenated coal-solvent mixture is sent to a reactor vessel where liquefaction occurs. The resulting mixture is passed to a separator, naphtha and distillate liquids are drawn off, sulphur is removed as hydrogen sulphide and ash is eliminated by a conventional deashing step. 
     The principal product of this operation is solvent refined coal, that is, SRC which at ambient temperature is a shiny, black solid. Upon subjecting SRC to hydrogenation in a catalytic hydrocracker there is also produced TSL SRC a solid residual fuel having very low sulphur content and more naphtha and distillate liquids. 
     Compositions comprised of solvent refined coal and distillate oils have been reported in the literature but their use as fuel oil substitutes has not been widely accepted due to their instability over the long term. It has heretofore been believed that the asphaltenes and preasphaltenes content of the SRC would always result in an unstable mixture of SRC and coal derived liquids. 
     In Annual Reports by the Electric Power Research Institute (EPRI) entitled &#34;Upgrading of Coal Liquids For Use as Power Generation Fuels,&#34; published October, 1977, December 1978, and December 1979 as Reports AF444, AF873 and AF1255 there are described blends of SRC fuel in recycled solvents. With these blends complete solubilization was not achieved due to the presence of two phases at temperatures up to 300° F. and/or benzene insoluble compounds which separated from solution over extended periods attributed to oxidation and degradation at high SRC concentrations. 
     In an article captioned &#34;Viscosity of Coal Liquids--The Effect of Character and Content of the Non-Distillable Portion&#34; (Journal of the American Chemical Society, Division of Fuel Chemistry, Volume 22: pages 33-48; 1977) J. Schiller describes a simulated fuel oil comprised of finely ground distillation residues derived from SRC and anthracene oils. These compositions exhibit a low viscosity which Schiller attributes to the synergistic effect of asphaltene on anthracene oil. 
     Asphaltenes are polar compounds which are found in distillation residues. They are high in heteroatom content and they possess hydroxy and nitrogen moieties which contribute to the formation of insoluble residues; however, Schiller observed, surprisingly, that the synergistic effect of asphaltene resulted in a composition free of undissolved solids. Unfortunately, however, the distillation residues in these liquids do not remain in solution indefinitely and, therefore, the synergistic effect of asphaltene cannot explain fully the undissolved solids which have been observed over extended storage periods. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1-6 graphically depict the viscosity characteristics of solvent refined coal-distillate oil blends as well as the viscosity characteristics of No. 6 fuel oil in relation to temperature and storage time. 
    
    
     THE INVENTION 
     It has been discovered that deashed solvent refined coal (SRC or TSL SRC) can be combined with the distillate oils of solvent refined coal to provide compositions which are uniquely stable over long periods, a feature which makes them suitable as simulated fuel oils. The term `SRC` is used herein to jointly and severally refer to the various sources of non-distillate solvent-refined coal products, nominally, 850° F.+ coal, for example, SRC, HSRC and TSL SRC. 
     Accordingly, it is an object of this invention to describe novel blends of SRC and SRC distillate oils which can be used as a No. 6 fuel oil substitute and which remain homogeneous in a single phase over extended periods. 
     It is a further object to describe novel means for producing single-phase homogeneous blends of SRC and SRC distillate oils by utilizing parameters which make it possible to customize the blend to specification. 
     A unique feature of this invention lies in the discovery that a correlation exists between the homogeneity of SRC fuel oil and the heteroatom composition of the distillate oils and the particular SRC which are mixed. 
     The evaluation of residual SRC oils as fuel oil substitutes led to the discovery that homogeneity and stability depend to a large extent on component characterization. SRC solids, for example, are rich in nitrogen, oxygen and sulphur, that is, heteroatoms which exert a high degree of polarity within the molecule. A contributor to this effect are the preasphaltenes which are present in solvent refined coal in appreciable amounts. The preasphaltenes are pyridine solubles rich in polar functional groups and it has been found that solubilization of SRC requires solvents having a polarity at least equal to or greater than pyridine. 
     This invention provides guidelines for optimizing the solubility of SRC solids in distillate oils. It identifies the polarity requirement of the solvent necessary to form homogeneous residual oil blends and specifies the compositions of heteroatom rich first-stage oil to be added to make SRC and second-stage oil homogeneous blends. 
     More specifically, this invention relates to a homogeneous, single-phase blend of fuel oil consisting essentially of deashed solvent-refined coal and distillate oils derived from the liquefaction of coal, said oils having a heteroatom content greater than about 25 wt% of the heteroatom content of said solvent-refined coal. 
     The distillate oils employed in this invention are first- and second-stage distillate oils having a boiling range of 400°-1000° F.; they are comprised nominally of 400°-650° F. middle oil, 650°-850° F. heavy oil and 450°-850° F. process solvent. These distillate oils can be used individually or they can be used in various combinations with deashed SRC to provide a homogeneous single-phase SRC residual oil blend having viscosity-temperature characteristics which make it suitable for use of substitute for No. 6 fuel oil. 
     The amount of distillate oil combined with deashed solvent-refined coal depends upon the heteroatom content of the distillate oil employed. At concentrations equal to or greater than 40 wt% deashed solvent refined coal cannot be mixed even at temperatures close to its flash point to form homogeneous blends with middle oil, heavy oil or process solvent of the second stage. 
     Generally, first stage distillate oils contain the greatest concentration of heteroatoms and, therefore, deashed solvent-refined coal (SRC) forms homogeneous blends with first-stage distillate oils at all concentrations. 
     On the other hand, homogeneous blends of SRC (above 40 wt%) and second-stage middle oil require the addition of first-stage heavy oil in quantities greater than 15 wt%. According to another embodiment a homogeneous blend of SRC and second-stage heavy oil can be made only if first-stage heavy oil is present in an amount at least equal to or greater than 10 wt%. 
     Accordng to still another embodiment homogeneous blends of SRC (above 40 wt%) and second-stage process solvent can be effected only if first-stage process solvent is present in amounts of at least 20 wt%. 
     Deashed SRC is a product derived from the first and/or second stage liquefaction of solvent refined coal (SRC-I) and it can be dissolved with SRC distillate oils in pulverized (solid) form or in molten form. 
     The following is a list of SRC solids and distillate oils referred to in this application. 
     SRC SOLIDS (850° F.+ BOILING RANGE) 
     SRC: A first-stage solvent-refined coal product (nominally greater than 850° F.) obtained after a deashing process. 
     HSRC: Heavy SRC; a first-stage solvent-refined coal product recovered from the SRC-I process after critical solvent deashing. 
     TSL SRC: A product obtained via the two-stage liquefaction of SRC (i.e., hydrocracked SRC). 
     Note: The term &#34;SRC&#34; is often used as an abbreviation for all solvent-refined coal non-distillate products such as one or all three of the above as well as the first-stage product only. 
     DISTILLATE OILS 
     Middle Oil: 400°-650° F. (first and second stage oil) 
     Heavy Oil: 650°-850° F. (first and second stage oil) 
     Process Solvent: 450°-850° F. (first &amp; second stage oil) 
     The SRC solids of this invention may be dissolved in coal liquid distillates in solid form or liquid form. They are prepared by first forming an SRC mineral ash slurry and subjecting the mixture to a separation procedure, optionally followed by a hydrocracking step. This procedure is described in detail below. 
     MOLTEN SRC AND SRC SOLIDS (DEASHED) 
     SRC Mineral Ash Slurry: Dry pulverized coal slurried with process solvent was pumped to reaction pressure. The slurry was heated against hot process solvent in coal exchangers, hot hydrogen-rich recycle gas was added to the pressurized slurry and the mixture was heated to reaction temperature. There was thus obtained a slurry containing low-sulphur solvent-refined coal (SRC) and mineral ash residue with distillate liquid and gaseous by-products. 
     The distillate liquid by-products were separated into medium and heavy oil fractions for the recovery of process solvent and unreacted hydrogen was recovered, purified and recycled to the coal exchanger for re-use in the preparation of additional slurry. 
     Deashed Molten SRC: The SRC mineral ash slurry of the previous step was mixed with proprietary solvent and pumped to a first-stage settler in which a heavy phase and a light phase separated. The light phase was passed into a second stage settler where a heavy phase and light phase again separated. 
     The light phase from the second stage settler was passed into a third stage settler where light SRC was separated from the mixture and critical solvent was removed from the remaining heavy phase to afford deashed molten SRC. 
     Deashed SRC Solids: Deashed molten SRC from the prior step can be divided into three streams. One stream was sent to a hydrocracker for liquid distillate production, another was passed into a coker-calciner for coke production and the remaining stream was sent to a molten SRC tank where SRC was cooled and solidified. 
     The SRC solids are pulverized according to the following procedures depending upon whether a small scale (laboratory) or large scale (pilot-plant) preparation of residual oil blends is desired. 
     BLENDING PROCEDURES 
     Small Scale Blends of SRC Solids: Deashed SRC solids were pulverized 100% to 140 mesh (approximately 105 μm) and this material was added with stirring to preheated distillate oil in a three-necked round-bottomed flash (500 ml) equipped with a thermometer. The solid was added slowly over a 4 hour period at the required blending temperature (i.e., 200±5° F. for SRC and 150±5° F. for TSL SRC) to assure complete dissolution and homogeneity and stirring was continued for an additional 12 hours. 
     Large Scale Blends of SRC Solids: Deashed SRC solids were pulverized to -200 mesh were quckly added through a closed solids feed port to distillate oil which had been preheated to 150°-220° F. in a closed steam-heated vessel equipped with a reflux condenser. The mixing step was effected using a low shear circulating pump and a nitrogen atmosphere was maintained in the vessel to prevent contact between the blended flue and ambient air. A homogeneous blend was obtained within about 45-60 minutes following the addition of SRC solids. 
     Molten SRC Blends: Molten TSL SRC (200 lbs) maintained at about 600° F. was passed at a flow-rate of approximately 100 lbs per/hr into a 55 gallon closed head drum containing 200 lbs of a 1:1 mixture of first and second-stage process solvents at ambient temperature. The resulting mixture reached a maximum temperature of 350° F. and upon cooling there was obtained an SRC single-phase residual oil blend which exhibited the viscosity characteristics of a homogeneous mixture. 
     HETEROATOM CONTENT 
     The following examples illustrate the effect of heteroatom concentration on SRC solubility. All first- and second-stage solids and all distillate oils employed in these studies exhibited the following heteroatom content: 
     
                       TABLE 1                                                     
______________________________________                                    
Properties of Fuel Oil Blend Components                                   
       1st-Stage    2nd-Stage                                             
                 Mid-                 Mid-                                
                 dle    Heavy         dle  Heavy                          
Component:                                                                
         HSRC    Oil    Oil   TSL SRC Oil  Oil                            
______________________________________                                    
Ultimate                                                                  
analysis                                                                  
(wt %)                                                                    
C        85.86   86.24  86.89 89.95   88.89                               
                                           89.40                          
H         6.03    8.98   7.81  6.98   10.28                               
                                            9.11                          
N         1.78    0.60   1.25  1.34    0.39                               
                                            0.85                          
O         5.15    3.93   3.28  1.56    0.44                               
                                            0.61                          
S         1.08    0.25   0.77  0.17    0.00                               
                                            0.03                          
Ash       0.10   --     --    --      --                                  
H/C, atomic                                                               
         0.843   1.249  1.079 0.931   1.388                               
                                           1.223                          
ratio                                                                     
______________________________________                                    
 
    
     This data shows that the first stage components and lower H/C ratios and a higher heteroatom content than their second-stage counterparts. The boiling point distribution for the distillate oils of Table 1, determined by the standard ASTM D2887 simulated distillation method, is given in Tables 2-5: 
     
                       TABLE 2                                                     
______________________________________                                    
Boiling Point Distribution of 1st-Stage                                   
Middle Oil by ASTM 02887                                                  
% Dist.  Temp. (°F.)                                               
                      % Dist.  Temp. (°F.)                         
______________________________________                                    
IBP      391          60       540                                        
 5       416          70       574                                        
10       424          80       607                                        
20       438          90       641                                        
30       462          95       664                                        
40       486          99       729                                        
50       516          FBP      783                                        
______________________________________                                    
 
    
     
                       TABLE 3                                                     
______________________________________                                    
Boiling Point Distribution of 1st-Stage                                   
Heavy Oil by ASTM D2887                                                   
% Dist.  Temp. (°F.)                                               
                      % Dist.  Temp. (°F.)                         
______________________________________                                    
IBP      660          60       781                                        
 5       682          70       806                                        
10       692          80       841                                        
20       710          90       899                                        
30       726          95       952                                        
40       743          99       1010                                       
50       761          FBP      1027                                       
______________________________________                                    
 
    
     
                       TABLE 4                                                     
______________________________________                                    
Boiling Point Distribution of 2nd-Stage                                   
Middle Oil by ASTM D2887                                                  
% Dist.  Temp. (°F.)                                               
                      % Dist.  Temp. (°F.)                         
______________________________________                                    
IBP      375          60       587                                        
 5       422          70       606                                        
10       450          80       626                                        
20       489          90       647                                        
30       520          95       658                                        
40       541          99       681                                        
50       562          FBP      708                                        
______________________________________                                    
 
    
     
                       TABLE 5                                                     
______________________________________                                    
Boiling Point Distribution of 2nd-Stage                                   
Heavy Oil by ASTM D2887                                                   
% Dist   Temp. (°F.)                                               
                      % Dist.  Temp. (°F.)                         
______________________________________                                    
IBP      640          60       759                                        
 5       663          70       783                                        
10       674          80       813                                        
20       691          90       862                                        
30       705          95       906                                        
40       722          99       1010                                       
50       739          FBP      1035                                       
______________________________________                                    
 
    
     The foregoing shows that the second stage middle oil and first stage heavy oil contain a preponderance of heavy components and, as a result, they are more viscous than their respective first-stage middle oil and second-stage heavy oil counter parts. 
     Tables 6 and 7 show the relationship between temperature and viscosity for the first and second stage middle and heavy oils. The liquids exhibited Newtonian behavior over all temperature ranges: 
     
                       TABLE 6                                                     
______________________________________                                    
Variation of Viscosity with Temperature,                                  
1st-Stage Middle and Heavy Oils                                           
        Temperature   Shear Rate                                          
                                Viscosity                                 
Oil     (°F.)  (sec.sup.-1)                                        
                                (cP)                                      
______________________________________                                    
Middle   70           79.20      9.6                                      
                      39.60      9.6                                      
         80           79.20      7.2                                      
                      39.60      7.0                                      
         90           79.20      4.8                                      
                      39.60      4.7                                      
Heavy   100           2.04      8288                                      
                      1.02      8292                                      
                      0.51      8300                                      
        110           4.08      3019                                      
                      2.04      3021                                      
                      1.02      3025                                      
        120           10.20     1343                                      
                      4.08      1350                                      
                      2.04      1350                                      
        125           20.40      925                                      
                      10.20      935                                      
                      4.08       938                                      
        135           20.40      500                                      
                      10.20      500                                      
                      4.08       500                                      
        145           15.84      274                                      
                      7.92       273                                      
                      3.96       275                                      
        155           39.60      163                                      
                      15.84      164                                      
                      7.92       164                                      
        165           79.20      103                                      
                      30.60      104                                      
                      15.84      104                                      
        180           79.20     57.9                                      
                      39.60     58.0                                      
                      15.84     57.9                                      
        200           79.20     30.4                                      
                      39.60     30.5                                      
______________________________________                                    
 
    
     
                       TABLE 7                                                     
______________________________________                                    
Variation of Viscosity with Temperature,                                  
2nd-Stage Middle and Heavy Oils                                           
        Temperature   Shear Rate                                          
                                Viscosity                                 
Oil     (°F.)  (sec.sup.-1)                                        
                                (cP)                                      
______________________________________                                    
Middle  70            79.20     10.6                                      
                      39.60     10.7                                      
        80            79.20      7.7                                      
                      39.60      7.6                                      
        90            79.20      5.9                                      
                      39.60      5.9                                      
Heavy   74            1.98      2915                                      
                      0.79      2917                                      
        80            3.96      1715                                      
                      1.98      1730                                      
                      0.79      1738                                      
        85            7.92      1178                                      
                      3.96      1180                                      
                      1.98      1185                                      
        90            7.92      829                                       
                      3.96      833                                       
                      1.98      835                                       
        95            15.84     584                                       
                      7.92      591                                       
                      3.96      593                                       
        100           15.84     441                                       
                      7.92      444                                       
                      3.96      443                                       
        110           15.84     256                                       
                      7.92      258                                       
                      3.96      260                                       
        120           39.60     152                                       
                      15.84     154                                       
                      7.92      155                                       
        140           79.20     66.8                                      
                      39.60     66.8                                      
                      15.84     66.9                                      
        165           79.20     29.9                                      
                      39.60     30.0                                      
                      15.84     30.0                                      
______________________________________                                    
 
    
     The data of Tables 6 and 7 show that the viscosity of the liquid is related to its structural composition and heteroatom content. 
     This invention will now be illustrated by reference to specific embodiments. 
     EXAMPLE 1 
     Single-Phase Solid/Liquid Blends 
     HSRC and TSL SRC solids were pulverized to a fineness of 100% through 140 mesh, approximately 105 μm. Single-phase blends were prepared in a three-necked, round-bottomed flask (500 ml) equipped with a thermometer and a glass stirrer. Fifty percent by weight of pulverized solids were added to preheated distillate liquids with constant stirring as described below. To assure complete dissolution and homogeneous mixing, the solids were added slowly over a 4 hr period at the required blending temperature (i.e., 200±5° F. for HSRC and TSL SRC, respectively) maintained for at least 12 hours. 
     The following blends of 50 wt% solid composition were prepared: 
     HSRC/1st-stage middle oil 
     HSRC/1st stage heavy oil 
     TSL SRC/1st-stage middle oil 
     TSL SRC/2nd stage middle oil 
     TSL SRC/1st-stage heavy oil 
     TSL SRC/2nd-stage heavy oil 
     The viscosities of the blends at specific temperatures and shear rates, as determined by a Brookfield viscometer, are listed in Tables 8-13. The range of applied shear rates varied with the viscosity of the blend and the spindle used. The blends behaved like a Newtonian liquid within experimental error. All blends were solid at ambient temperature and showed no separation of a liquid phase. 
     
                       TABLE 8                                                     
______________________________________                                    
Variation of Viscosity with Temperature,                                  
50 wt % HSRC in 1st-Stage Middle Oil                                      
Temperature    Shear Rate                                                 
                         Viscosity                                        
(°F.)   (sec.sup.-1)                                               
                         (cP)                                             
______________________________________                                    
 100           0.20      68,500                                           
               0.10      69,000                                           
115            1.02      16,600                                           
               0.51      16,800                                           
               0.20      17,000                                           
130            4.08      5,125                                            
               2.04      5,175                                            
               1.02      5,200                                            
145            10.20     1,938                                            
               4.08      1,956                                            
               2.04      1,963                                            
160            20.40       859                                            
               10.20       868                                            
               4.08        869                                            
175            15.84       382                                            
               7.92        385                                            
               3.96        388                                            
190            39.60       200                                            
               15.84       201                                            
               7.92        204                                            
215            79.20     82.1                                             
               39.60     83.0                                             
               15.84     83.1                                             
240            79.20     41.5                                             
               39.60     41.3                                             
               15.84     41.9                                             
265            79.20     22.6                                             
               39.60     23.0                                             
______________________________________                                    
 
    
     
                       TABLE 9                                                     
______________________________________                                    
Variation of Viscosity with Temperature,                                  
50 wt % HSRC in 1st-Stage Heavy Oil                                       
Temperature    Shear Rate                                                 
                         Viscosity                                        
(°F.)   (sec.sup.-1)                                               
                         (cP)                                             
______________________________________                                    
220            0.84      31,350                                           
               0.42      31,533                                           
               0.17      31,750                                           
230            1.68      14,950                                           
               0.84      14,950                                           
               0.42      15,000                                           
240            3.36      7,450                                            
               1.68      7,467                                            
               0.84      7,467                                            
250            1.98      3,700                                            
               0.79      3,725                                            
               0.40      3,750                                            
270            7.92      1,201                                            
               3.96      1,213                                            
               1.98      1,220                                            
290            15.84       463                                            
               7.92        464                                            
               3.96        468                                            
310            39.60       209                                            
               15.84       211                                            
               7.92        214                                            
335            79.20     95.0                                             
               39.60     95.0                                             
               15.84     96.3                                             
360            79.20     48.4                                             
               39.60     48.3                                             
385            79.20     27.9                                             
               39.60     28.3                                             
415            79.20     16.1                                             
               39.60     16.0                                             
______________________________________                                    
 
    
     
                       TABLE 10                                                    
______________________________________                                    
Variation of Viscosity with Temperature,                                  
50 wt % TSL SRC in 1st-Stage Middle Oil                                   
Temperature    Shear Rate                                                 
                         Viscosity                                        
(°F.)   (sec.sup.-1)                                               
                         (cP)                                             
______________________________________                                    
 75            2.04      6,738                                            
               1.02      6,775                                            
               0.51      6,900                                            
 85            4.08      3,300                                            
               2.04      3,325                                            
               1.02      3,350                                            
 95            10.20     1,683                                            
               4.08      1,700                                            
               2.04      1,725                                            
105            20.40       931                                            
               10.20       943                                            
               4.08        956                                            
120            15.84       423                                            
               7.92        428                                            
               3.96        433                                            
135            39.60       212                                            
               15.84       215                                            
               7.92        219                                            
155            79.20     99.1                                             
               39.60       100                                            
               15.84       102                                            
180            79.20     47.6                                             
               39.60     47.5                                             
               15.84     48.8                                             
200            79.20     28.8                                             
               39.60     29.3                                             
               15.84     30.6                                             
225            79.20     17.4                                             
               39.60     18.0                                             
______________________________________                                    
 
    
     
                       TABLE 11                                                    
______________________________________                                    
Variation of Viscosity with Temperature,                                  
50 wt % TSL SRC in 2nd-Stage Middle Oil                                   
Temperature    Shear Rate                                                 
                         Viscosity                                        
(°F.)   (sec.sup.-1)                                               
                         (cP)                                             
______________________________________                                    
 75            2.04      11,188                                           
               1.02      11,300                                           
               0.51      11,350                                           
 85            4.08      5,231                                            
               2.04      5,300                                            
               1.02      5,300                                            
 95            4.08      2,694                                            
               2.04      2,700                                            
               1.02      2,700                                            
105            10.20     1,465                                            
               4.08      1,469                                            
               2.04      1,471                                            
120            15.84       607                                            
               7.92        615                                            
               3.96        618                                            
135            15.84       305                                            
               7.92        306                                            
               3.96        308                                            
155            39.60       137                                            
               15.84       137                                            
               7.92        138                                            
180            79.20     60.3                                             
               39.60     60.8                                             
               15.84     61.3                                             
200            79.20     35.8                                             
               39.60     35.8                                             
225            79.20     20.6                                             
               39.60     20.8                                             
______________________________________                                    
 
    
     
                       TABLE 12                                                    
______________________________________                                    
Variation of Viscosity with Temperature,                                  
50 wt % TSL SRC in 1st-Stage Heavy Oil                                    
Temperature    Shear Rate                                                 
                         Viscosity                                        
(°F.)   (sec.sup.-1)                                               
                         (cP)                                             
______________________________________                                    
170            0.20      58,125                                           
               0.10      58,500                                           
185            1.02      15,825                                           
               0.51      15,850                                           
               0.20      15,875                                           
200            4.08      5,200                                            
               2.04      5,225                                            
               1.02      5,225                                            
215            10.20     1,980                                            
               4.08      1,981                                            
               2.04      1,988                                            
230            20.40       861                                            
               10.20       861                                            
               4.08        863                                            
245            15.84       408                                            
               7.92        409                                            
               3.96        410                                            
260            39.60       221                                            
               15.84       221                                            
               7.92        221                                            
275            39.60       129                                            
               15.84       129                                            
               7.92        129                                            
295            79.20     69.0                                             
               39.60     69.4                                             
315            79.20     40.6                                             
               39.60     40.6                                             
340            79.20     23.4                                             
               39.60     23.3                                             
365            79.20     14.6                                             
               39.60     14.5                                             
______________________________________                                    
 
    
     
                       TABLE 13                                                    
______________________________________                                    
Variation of Viscosity with Temperature,                                  
50 wt % TSL SRC in 2nd-Stage Heavy Oil                                    
Temperature    Shear Rate                                                 
                         Viscosity                                        
(°F.)   (sec.sup.-1)                                               
                         (cP)                                             
______________________________________                                    
150            0.20      56,750                                           
               0.10      56,750                                           
170            2.04      11,100                                           
               1.02      11,125                                           
               0.51      11,150                                           
190            4.08      2,994                                            
               2.04      3,000                                            
               1.02      3,000                                            
210            20.40     973                                              
               10.20     978                                              
               4.08      975                                              
220            20.40     601                                              
               10.20     603                                              
               4.08      606                                              
240            39.60     247                                              
               15.84     248                                              
               7.92      250                                              
265            79.20     106                                              
               39.60     106                                              
               15.84     105                                              
290            79.20     52.5                                             
               39.60     52.5                                             
310            79.20     32.4                                             
               39.60     32.3                                             
330            79.20     17.9                                             
               39.60     17.9                                             
______________________________________                                    
 
    
     The foregoing shows that HSRC forms homogeneous blends with first stage distillate oils at all concentration levels. This is attributable to the presence in HSRC of high concentrations of preasphaltenes, that is, pyridine solubles rich in highly polar functional groups. Accordingly, the complete solubilization of HSRC requires a solvent having a polarity equal to or greater than pyridine. First-stage distillate oils possess an essentially identical profile, that is, they are relatively high in heteroatom content and possess high polarity as a result of which they solubilize the highly polar HSRC. 
     On the other hand, second-stage distillate oils are not sufficiently rich in heteroatom content and their low polarity make it impossible to solubilize HSRC. This conclusion is supported by the observations reported in Example 2 and the accompanying Tables 14 and 15. 
     By contrast, TSL SRC has a negligible concentration of preasphaltenes. Accordingly, it is compatible with the low heteroatom content of the second-stage oil and is solubilized thereby. See in this regard the reduced heteroatom content (polarity) of the second-stage distillate oil as compared to the first stage oil in Table 1. 
     Indeed, TSL SRC forms homogeneous blends with first-and second-stage distillate oils or mixtures of same at all concentration levels. 
     Example 2 illustrates the limited solubility of HSRC in second-stage oils even when additions are made close to the flash point temperatures. The inability of the second-stage oils to completely solubilize HSRC is attributed to the low heteroatom content (i.e., low polarity) of the second-stage oil. 
     EXAMPLE 2 
     Dual-Phase HSRC Blends 
     The procedure of Example 1 was repeated except that 50 wt% of pulverized HSRC was added to second-stage middle oil and second-stage heavy oil. 
     A partial separation of the oil phase in both preparations was observed at ambient temperature. 
     The variation in viscosity and shear rates over a range of temperatures are listed in Tables 14 and 15. 
     
                       TABLE 14                                                    
______________________________________                                    
Variation of Viscosity with Temperature,                                  
50 wt % HSRC in 2nd-Stage Middle Oil                                      
Temperature    Shear Rate                                                 
                         Viscosity                                        
(°F.)   (sec.sup.-1)                                               
                         (cP)                                             
______________________________________                                    
115            0.79      8,125                                            
               0.40      12,100                                           
130            1.98      2,170                                            
               0.79      3,925                                            
               0.40      6,242                                            
145            7.92      788                                              
               3.96      1,043                                            
               1.98      1,257                                            
160            15.84     372                                              
               7.92      496                                              
               3.96      719                                              
175            39.60     228                                              
               15.84     281                                              
               7.92      405                                              
250            79.20      67                                              
               39.60     102                                              
               15.84     216                                              
______________________________________                                    
 
    
     
                       TABLE 15                                                    
______________________________________                                    
Variation of Viscosity with Temperature,                                  
50 wt % HSRC in 2nd-Stage Heavy Oil                                       
Temperature    Shear Rate                                                 
                         Viscosity                                        
(°F.)   (sec.sup.-1)                                               
                         (cP)                                             
______________________________________                                    
240            0.20      9,738                                            
               0.10      16,150                                           
265            20.40       686                                            
               10.20     1,217                                            
               4.08      2,569                                            
290            20.40       529                                            
               10.20     1,018                                            
               4.08      1,738                                            
315            20.4        341                                            
               10.20       425                                            
______________________________________                                    
 
    
     The observed decrease in viscosity with shear rates is indicative of a multi-phase composition rather than a homogeneous blend of components. 
     Moreover, the observed viscosities in second-stage middle oil (Table 14) and the viscosities observed in second-stage heavy oil (Table 15) indicate that at the specified temperatures the viscosity of each mixture depended on the applied shear rate. The non-Newtonian behavior of these mixtures suggests that the blends do not exist as single phase compositions due to the limited solubility of HSRC in second-stage oils. Partial separation of the oil phase was also observed when mixtures were allowed to cool to ambient temperature, further substantiating the non-homogeneous nature of these mixtures. 
     A major portion of HSRC consists of pyridine-soluble preasphaltenes, that is, compounds rich in polar functional groups. Accordingly, the complete solubilization of HSRC requires the use of solvents having a polarity equal to or greater than that of pyridine. Unfortunately, the low heteroatom second-stage oils do not possess this property. 
     EXAMPLE 3 
     Single-Phase HSRC Blends 
     The procedure of Example 1 was repeated except that HSRC was combined with mixtures of first-stage heavy oil and second-stage heavy oil. 
     Table 16 lists the viscosities observed for a blend of 40 wt% HSRC solids with 10 wt% first-stage heavy oil and 50  wt% second-stage heavy oil over a range of temperatures and shear rates: 
     
                       TABLE 16                                                    
______________________________________                                    
Variation of Viscosity with Temperature,                                  
(HSRC - 40 wt %, Heavy Oil 1st-Stage - 10 wt %,                           
Heavy Oil 2nd-Stage - 50 wt %)                                            
Temperature    Shear Rate                                                 
                         Viscosity                                        
(°F.)   (sec.sup.-1)                                               
                         (cP)                                             
______________________________________                                    
180            0.20      54,750                                           
               0.10      54,750                                           
200            2.04      7,350                                            
               1.02      7,350                                            
               0.51      7,400                                            
220            10.20     1,755                                            
               4.08      1,763                                            
               2.04      1,775                                            
230            20.40     1,055                                            
               10.20     1,066                                            
               4.08      1,069                                            
240            20.40       628                                            
               10.20       628                                            
               4.08        631                                            
260            39.60       238                                            
               15.84       239                                            
               7.92        240                                            
280            79.20       110                                            
               39.60       110                                            
               15.84       113                                            
305            79.20     50.9                                             
               39.60     51.0                                             
330            79.20     27.4                                             
               39.60     28.0                                             
______________________________________                                    
 
    
     Table 17 lists the viscosities observed for a blend of 50 wt% HSRC solids with 10 wt% first-stage heavy oil and 40 wt% second-stage heavy oil over a range of temperatures and shear rates: 
     
                       TABLE 17                                                    
______________________________________                                    
Variation of Viscosity with Temperature,                                  
(HSRC - 50 wt %, Heavy Oil 1st-Stage - 10 wt %,                           
Heavy Oil 2nd-Stage - 40 wt %)                                            
Temperature    Shear Rate                                                 
                         Viscosity                                        
(°F.)   (sec.sup.-1 1)                                             
                         (cP)                                             
______________________________________                                    
220            0.20      52,500                                           
               0.10      53,250                                           
240            2.04      9,188                                            
               1.02      9,175                                            
               0.51      9,200                                            
255            4.08      3,100                                            
               2.04      3,125                                            
               1.02      3,125                                            
265            10.20     1,685                                            
               4.08      1,688                                            
               2.04      1,688                                            
275            20.40       980                                            
               10.20       983                                            
               4.08        988                                            
295            20.40       379                                            
               10.20       380                                            
315            39.60       165                                            
               15.84       167                                            
               7.92        168                                            
335            79.20     87.5                                             
               39.60     87.5                                             
360            79.20     45.1                                             
               39.60     45.2                                             
390            79.20     23.4                                             
               39.60     23.4                                             
______________________________________                                    
 
    
     Both HSRC mixtures provided single-phase homogeneous blends. These observations and the supporting data support the view that a homogeneous blend of HSRC and second-stage heavy oil can be made if first-stage heavy oil is added in amounts at least equal to or greater than 10 wt%. 
     The addition of first-stage oil is necessary to solubilize the HSRC solids because the low-heteroatom content of the second-stage oils is not sufficient to solubilize HSRC. By contrast, the first-stage oils are rich in heteroatom content and their addition to second-stage oil results in an increase in polarity to the extent that it solubilizes HSRC. 
     EXAMPLE 4 
     HSRC-Middle Oil Blends 
     By following the procedure of Example 1 using HSRC, second-stage middle oil and first-stage heavy oil in various combinations, it was determined that homogeneous blends of HSRC and second-stage middle oil require the addition of first-stage heavy oil in amounts greater than 15 wt%. 
     Table 18 lists the viscosities for a blend of HSRC with second-stage middle oil and first-stage heavy oil over a range of temperatures and shear rates: 
     
                       TABLE 18                                                    
______________________________________                                    
Variation of Viscosity with Temperature,                                  
(HSRC - 40 wt %, Heavy Oil 1st-Stage - 15 wt %,                           
Middle Oil 2nd-Stage - 45 wt %)                                           
Temperature    Shear Rate                                                 
                         Viscosity                                        
(°F.)   (sec.sup.-1)                                               
                         (cP)                                             
______________________________________                                    
120            10.20     2,155                                            
               4.08      2,775                                            
               2.04      3,738                                            
150            20.40       843                                            
               10.20       898                                            
               4.08      1,181                                            
180            20.40       329                                            
               10.20       345                                            
______________________________________                                    
 
    
     Due to the small heteroatom content of second-stage middle oil relatively high concentrations of first-stage heavy oil (rich in heteroatom content) are needed to prepare single-phase HSRC blends. The data in Table 18 indicates that first-stage oil concentrations in excess of 15 wt% should be added to HSRC and second-stage middle oil in order to prepare a 40 wt% HSRC single-phase blend in second-stage middle oil. 
     The blend in Table 18 developed a partial separation of a oil phase at ambient temperature. Moreover, the decrease in viscosity and concomitant increase in shear rate is indicative of multi-phase mixture rather than a homogeneous blend. 
     EXAMPLE 5 
     HSRC/Process Solvent Blends 
     Blends containing more than 40 wt% of HSRC and second-stage process solvent require the addition of first-stage process solvent in amounts at least equal to 20 wt% in order to afford homogeneous fuel oil blends. 
     Table 19 summarizes the viscosity/temperature data for the single-phase blend of 50 wt% HSRC in a 2:3 mixture of first-and second-stage process solvents. 
     
                       TABLE 19                                                    
______________________________________                                    
Variation of Viscosity with Temperature,                                  
HSRC: 50 wt %, Process Solvent 1st-Stage: 20 wt %,                        
Process Solvent 2nd-Stage: 30 wt %                                        
Temperature    Shear Rate                                                 
                         Viscosity                                        
(°F.)   (sec.sup.-1)                                               
                         (cP)                                             
______________________________________                                    
169            4.08      5056                                             
               2.04      5113                                             
               1.02      5125                                             
179            4.08      2500                                             
               2.04      2525                                             
               1.02      2550                                             
189            10.20     1345                                             
               4.08      1356                                             
               2.04      1363                                             
194            20.40     1005                                             
               10.20     1015                                             
               4.08      1019                                             
204            20.40      616                                             
               10.20      620                                             
219            15.84      294                                             
               7.92       294                                             
               3.96       300                                             
240            39.60      133                                             
               15.84      132                                             
               7.92       133                                             
260            79.20     69.0                                             
               39.60     69.0                                             
               15.84     69.4                                             
286            79.20     35.4                                             
               39.60     35.3                                             
291            79.20     33.8                                             
               39.60     33.8                                             
311            79.20     23.8                                             
               39.60     23.8                                             
______________________________________                                    
 
    
     The foregoing data supports the view that the rich heteroatom content of the first-stage process solvent is required in amounts of at least 20 wt% in order to fully solubilize the HSRC solids. 
     EXAMPLE 6 
     Storage Stability Test 
     The following residual fuel oils were subjected to storage stability testing: 
     
         ______________________________________                                    
            Fuel composition (wt %)                                       
Component     #1         #2      #3                                       
______________________________________                                    
HSRC          50         --      --                                       
1st-stage middle oil                                                      
              40         30      --                                       
1st-stage heavy oil                                                       
              10          5      --                                       
TSL SRC       --         50      --                                       
2nd-stage middle oil                                                      
              --         12      --                                       
2nd-stage heavy oil                                                       
              --          3      --                                       
No. 6 Fuel Oil                                                            
              --         --      100                                      
______________________________________                                    
 
    
     The above HSRC and TSL SRC blend compositions simulate, respectively, the first-stage and second-stage SRC-I Demonstration Plant total blended products (excluding naphtha and anode coke). Table 20 shows that the H/C ratio and heating values increase in the following order: HSRC blend &lt;TSL SRC blend &lt;No. 6 Fuel Oil. 
     
                       TABLE 20                                                    
______________________________________                                    
Properties of Residual Fuel Oils                                          
Used for Stability Tests                                                  
                                    No. 6                                 
            HSRC Blend TSL SRC Blend                                      
                                    Fuel Oil                              
Residual Oil                                                              
            #1         #2           #3                                    
______________________________________                                    
Ultimate Analysis, wt %                                                   
C           85.60      88.40        86.34                                 
H           7.23       8.13         11.48                                 
N           1.24       1.01         0.27                                  
O           4.81       2.23         0.87                                  
S           1.04       0.23         0.99                                  
Ash         0.08       --           0.05                                  
H/C (atomic ratio)                                                        
            1.014      1.104        1.596                                 
Higher Heating                                                            
            16.849     17.343       18.749                                
Value, Btu/lb                                                             
______________________________________                                    
 
    
     After 1 day there was sufficient evaporation of volatile components within the vapor space of the storage bottle as to require a 3° F. higher temperature to maintain the original viscosity. As shown in FIG. 1 the temperature required for the residual oils to reach viscosities of 30 cP (atomizing) and 1,000 cp (pumping) are as follows: 
     
         ______________________________________                                    
                Temperature (°F.) at:                              
Residual Oil      30 cP    1,000 cP                                       
______________________________________                                    
HSRC blend (#1)   282      180                                            
TSL SRC blend (#2)                                                        
                  217      121                                            
No. 6 Fuel Oil (#3)                                                       
                  203       92                                            
______________________________________                                    
 
    
     The residual oils were then subjected to a 4-5 month storage stability test at 150° F. in controlled nitrogen and air atmospheres. Various 1 oz. vials, each containing approximately 10 ml of the residual oil, were capped after flushing with the desired gas and then stored in a 150° F. isothermal oven. The temperature and atmosphere of the oven were maintained by the slow circulation of the gas. At specified intervals, one vial of each residual oil was taken from the oven to measure viscosities at three temperatures used to monitor fuel aging with time. FIGS. 2-4 depict the resulting changes in viscosity. Although the residual oils were stored in closed vials of the same size, some loss of volatiles undoubtedly occured during high-temperature storage, and such losses contribute to an increase in the viscosity. However, since storage conditions, temperatures, and viscosity measurement procedures were the same, the loss of material and its impact upon viscosity should be considered constant for the same residual oil stored under air or nitrogen. Therefore, it is apparent that storage in air had some adverse effect on the stability of No. 6 Fuel Oil and HSRC residual oil, but virtually no effect on TSL SRC residual oil. 
     The air-stored HSRC residual oil, the most rapid increase in viscosity occurred during the 20-60 day storage period; after 60 days, viscosity increased less rapidly. FIG. 5 shows that the temperature increases required to bring 140-day air- and nitrogen-aged HSRC residual-oil samples to the original pumping viscosity of 1,000 cP were 10° and 6° F., respectively. FIG. 6 shows that the temperature increases required to bring the 120-day air- and nitrogen-aged No. 6 Fuel Oil samples to the original pumping viscosity of 1,000 cP were 8° and 4° F., respectively. These results indicate that the storage stability of HSRC residual oils is comparable to that of No. 6 Fuel Oil, and the nitrogen blanketing during storage is important in maintaining the specified viscosity characteristics of the residual oils. An almost identical change in the viscosity of TSL SRC residual oil with storage time in nitrogen and air atmospheres suggests that such oils are relatively more stable than No. 6 Fuel Oil and HSRC residual oil, and that the viscosity increase during storage is mainly due to the loss of volatile components rather than to any associated aging effect.