Abstract:
A process for improving the deasphalting of a heavy hydrocarbon feedstock with a solvent by subjecting the feedstock to shearing alternatively after and/or before the addition of at least a portion of the solvent to the feedstock is disclosed. Alternative means for effecting the shearing and desired ranges of shear are also disclosed.

Description:
The present invention relates to a process for deasphalting a heavy hydrocarbon feedstock. 
     A heavy hydrocarbon feedstock within the meaning of the present invention is a feedstock having a density at 15° C. greater than about 930 kg/m 3  and composed essentially of hydrocarbons but containing also other chemical compounds which have, in addition to carbon and hydrogen atoms, heteroatoms such as oxygen, nitrogen and sulfur, and metals such as vanadium or nickel. 
     This feedstock may consist, in particular, of a crude petroleum or of a heavy oil having the aforesaid density. 
     The feedstock may also come from the fractionation or treatment of crude petroleum, of a heavy oil, of oil shales or even of coal. Thus it may be the residuum from vacuum distillation or the residuum from atmospheric distillation of the starting products cited above or, for example, products obtained by the thermal treatment of these starting products or their distillation residua. 
     BACKGROUND OF THE INVENTION 
     The trend in recent years has been to seek to upgrade high-density hydrocarbonaceous products more and more, which was not the case before. The need to upgrade heavy products has become more pressing since it is anticipated that the demand for light products such as motor fuels will increase at a relatively faster pace than the demand for heavier products, such as fuel oils. 
     The heaviest portion of heavy hydrocarbon feedstocks consists of a mixture of an oil phase and an asphaltic phase. 
     The asphaltic phase is the phase which precipitates upon the addition of a hydrocarbon with a low boiling point (for example, propane, butane, pentane, hexane, or heptane), the oil phase being soluble in said hydrocarbon. 
     The oil phase, that is, the light phase, is economically more worthwhile than the asphaltic phase. It fact, it may be used as a catalytic cracking feedstock that will yield light products. It may also serve as a feedstock for the production of lubricating-oil bases. These products are more valuable than the fuels and bitumens obtained from the asphaltic phase. 
     As has been pointed out above, heavy hydrocarbon feedstocks contain compounds which have, in addition to hydrogen and carbon atoms, heteroatoms such as oxygen, nitrogen and sulfur as well as metals. Some of these compounds, and particularly those containing metals, are present especially in the asphaltic phase. 
     Two groups are customarily distinguished among the compounds which make up the asphaltic phase: the resins and the asphaltenes. Both the asphaltenes and the resins have polycyclic aromatic structures. Apart from aromatic rings, thiophene and pyridine rings are present. However, the resins have less-condensed structures than the asphaltenes and lower molecular weights. 
     The name &#34;asphaltenes&#34; is generally applied to compounds which are precipitated by the addition to the feedstock of a saturated aliphatic hydrocarbon having from 5 to 7 carbon atoms, such as pentane, hexane, or heptane. Under French standard AFNOR NFT 60-115, the asphaltene content of a product thus is determined by precipitation with normal heptane upon boiling. 
     The resins precipitate at the same time as the asphaltenes when a hydrocarbon with a lower boiling point, for example, propane, is used. In fact, this is a conventional differentiation, and it is obvious that when a given hydrocarbon is employed at a given temperature to treat a feedstock, precipitation of asphaltene-type compounds can be obtained if the hydrocarbon and the temperature are appropriate. If the feedstock freed from the asphaltenes is then treated with the same hydrocarbon at a higher temperature, precipitation of the resins is obtained. 
     In the well-known deasphalting process, the oil phase and the asphaltic phase are separated by an operation which consists in extracting the oil phase from a hydrocarbon feedstock by means of a substance known to those skilled in the art as a solvent. The solvent is both a solvent for the oil phase and a precipitant for the asphaltic phase. Hereinafter it will be referred to simply as a solvent. 
     The solvent may be selected from the group consisting of: 
     saturated or unsaturated aliphatic hydrocarbons having from 2 to 8 carbon atoms, alone or in admixture; 
     mixtures of hydrocarbons, known as distillates, with molecular weights close to those of the hydrocarbons having from 2 to 8 carbon atoms; and 
     mixtures of all of the aforesaid hydrocarbons. 
     Deasphalting may be carried out in a single stage, in which case an oil phase and an asphaltic phase are obtained, the latter containing both the asphaltenes and the resins. It may also be carried out in two stages, using two different solvents and/or different operating conditions in the two stages. In the two-stage process, the oil phase, the resins and the asphaltenes are obtained separately. (See, for example, French patent application No. 86 06994, filed on May 15, 1986, in the name of the Applicant; and correspond-U.S. patent application Ser. No. 050,912 filed May 15, 1987). 
     As mentioned above, it is the oil phase that is more worthwhile economically. In a deasphalting process, whether single- or two-stage, it is therefore advisable to endeavor to obtain a maximum yield of the oil phase. Of course, this striving for a maximum oil-phase yield should not be at the expense of the characteristics of the oil phase. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention thus is directed to increasing in a deasphalting process the yield of the oil phase while preserving the characteristics of the oil phase which are desirable for the contemplated use. For example, for its use as a catalytic cracking feedstock, a Conradson residue (determined in conformity with standard AFNOR NFT 60-116) of less than 10 weight percent is desirable. 
     To this end, the invention has as a preferred embodiment a process for deasphalting a heavy hydrocarbon feedstock by means of a solvent, said process being characterized in that the feedstock is subjected to shearing, optionally before and/or after the addition of at least a portion of the solvent. 
     For the purposes of the present invention, shearing means the application of high stress to the diluted or undiluted feedstock. 
     The shearing action may be produced in particular by the forced passage of the feedstock, which optionally contains at least a portion of the solvent, through a restriction, a convergent die, a gap between two parts, one of which is moving relative to the other, a pipe of smaller cross-sectional area than the feed pipe for the feedstock, or any equivalent contrivance. 
     The shearing action may also be produced by the use of a turbine or of any other agitating means, optionally in the deasphalting tower. 
     In the case of the passage of the feedstock through a gap bounded by a stationary part and a coaxial part rotating within the stationary part, the shearing action expressed as a rate is given by the ratio du/dx, where du is the velocity difference between the walls of the gap, and dx the distance separating the parts bounding the gap. This shearing may then be at a rate ranging from 10 3  to 10 6  s -1  and preferably ranges from 10 4  to 2·10 5  s -1 , where s is time in seconds. 
     The result of the shearing action is surprising since one skilled in the art would be inclined to think that shear would cause the asphaltenes to be dispersed rather than precipitated. It is well known, for example, that to obtain an emulsion of fine water droplets in an oil it is advisable to agitate the oil/water mixture vigorously, in other words, to produce strong shearing action. 
     The deasphalting operation which follows shearing or is concurrent with it may be carried out in one or two stages. 
     In the former case, an oil phase and an asphaltic phase are obtained, and in the latter case, an oil phase, a resin phase and an asphaltene phase. 
     The solvent used in the extraction stage or stages may be selected from the group consisting of 
     saturated or unsaturated aliphatic hydrocarbons having from 2 to 8 carbon atoms, alone or in admixture; 
     mixtures of hydrocarbons, known as distillates, with molecular weights close to those of the hydrocarbons having from 2 to 8 carbon atoms; 
     mixtures of all of the aforesaid hydrocarbons; and 
     other chemical compounds which have, in addition to carbon and hydrogen atoms, heteroatoms such as oxygen, for example, alcohols and phenols, alone or in admixture with the aforesaid hydrocarbons. 
     The operating conditions in the deasphalting stages may be as follows: 
     Pressure ranging from 20·10 5  to 1·10 7  pascals abs. 
     Temperature ranging from 30° to 300° C. 
     Mass ratio of solvent to feedstock ranging from 1 to 10. 
     These conditions will vary, of course, depending in particular on the nature of the feedstock and on the nature of the solvents used. 
     A better understanding of the invention will be provided by the detailed description which follows, with reference to the accompanying drawing, which is nonlimitative. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 diagrammatically shows as a preferred embodiment a deasphalting unit including a shearing installation. 
    
    
     DETAILED DESCRIPTION 
     In this embodiment of the invention, the heavy hydrocarbon feedstock to be deasphalted, for example, an oil having a density at 15° C. greater than 930 kg/m 3 , is introduced through line 1 into the midsection of a liquid-liquid extractor 2. 
     In the extractor 2, the oil phase is extracted from the feedstock by means of a solvent introduced into the extractor through line 3. The solvent may be, in particular, a saturated or unsaturated aliphatic hydrocarbon having from 2 to 8 carbon atoms, and preferably from 3 to 5 carbon atoms, or mixtures of hydrocarbons, known as distillates, having from 2 to 8 carbon atoms, or mixtures of all of the aforesaid hydrocarbons. 
     The starting solvent of the unit comes from a source external to the unit through line 4. The solvent losses may be compensated by means of an external makeup supplied through line 4. 
     The pressure in the interior of the extractor 2 may range from 20·10 5  to 1·10 7  pascals abs, the temperature from 30° to 300° C., and the mass ratio of solvent to feedstock from 1 to 10. 
     At the top of the extractor 2, through line 5, the oil phase in solution in the solvent is recovered. This mixture is piped through line 5 to a fractionating section 6. For simplicity, this section is not shown in detail, but it generally comprises a regulator controlling a pressure drop, as well as evaporators. 
     At the outlet of section 6, solvent is recovered through line 7 and recycled to the extractor 2 through line 3, and the oil phase is withdrawn through line 8. 
     At the bottom of the extractor 2, the precipitated asphaltic phase as well as solvent are withdrawn. This mixture is conducted through line 10 to a fractionating section 11, which generally comprises a furnace or an exchanger with a hot fluid, an evaporator, and a steam stripping column. 
     At the outlet of section 11, solvent is recovered through line 12 and recycled to the extractor 2 through line 3, and the asphaltic phase is withdrawn through line 13. 
     A portion of the solvent from line 3 may be piped to line 1 through line 14 to predilute the feedstock, if desired. 
     In accordance with the invention, at least one restriction may be located at 20 in line 1 to induce shear in the feedstock. (There might be several such restrictions in parallel, depending on the flow rate of the feedstock.) This restriction could also be located downstream or upstream of the intersection of lines 1 and 14, ahead of the deasphalting tower 2. 
     In addition to or in place of the device 20, an agitating means such as a turbine may be provided in tower 2. 
     The examples which follow will illustrate how the invention is carried out as well as its advantages. 
     EXAMPLE 1 
     This example relates to deasphalting tests run with a vacuum-distillation residuum of the atmospheric-distillation residuum of a Safaniya crude petroleum with and without prior shearing of the residuum. 
     The characteristics of this charge stock are as follows: 
     
         ______________________________________Density at 15° C.: 1042 kg/m.sup.3(Determined in conformity with standard AFNORNFT 60-101)Viscosity at 100° C.:                     6250 mm.sup.2 /s(Determined in conformity with standard AFNORNFT 60-200)Conradson residue:        22.9 wt. %(Determined in conformity with standard AFNORNFT 60-116)Asphaltene content:       15.1 wt. %(Determined in conformity with standard AFNORNFT 60-115)Sulfur content:           5.46 wt. %(Determined by x-ray fluorescence)Nickel content:           45 ppm(Determined by x-ray fluorescence)Vanadium content:         149 ppm(Determined by x-ray fluorescence)______________________________________ 
    
     This feedstock is subjected to: 
     deasphalting control tests T1 and T2 without prior shearing of the charge stock, and 
     tests A11, A12 and A2 in accordance with the invention after prior shearing of the feedstock and without prior solvent addition. 
     The deasphalting solvent used in all tests is a solvent having the following composition (in percent by volume): 
     
         ______________________________________  Propane   0.82  Isobutane 43.99  n-Butane  23.01  n-Butene-1            8.08  Isobutene 9.17  cis-Butene-2            9.16  trans-Butene-2            5.70  Isopentane            0.07______________________________________ 
    
     The conditions of the tests are given in Table 1 which follows. 
     
                       TABLE 1______________________________________Temper-  Pressure Mass ratioature    10.sup.5 pas-                  solvent toTest °C.         cals abs feedstock                          Nature of prior shearing______________________________________T1   70       40       4       No shearingA11  70       40       4       Machine: Emulsifier.                          Gap: 1 mm.                          Speed of rotation: 7000                          rpm.                          Temperature: 150° C.                          Recycling time: 2 min-                          utes.A12  70       40       4       Machine: Emulsifier.                          Gap: 1 mm.                          Speed of rotation: 7000                          rpm.                          Temperature: 150° C.                          No recycling. Single                          pass.                          Very short time.T2   70       40       6       No shearing.A2   70       40       6       Machine: Emulsifier.                          Gap: 0.35 mm.                          Speed of rotation: 7000                          rpm.                          Temperature: 130° C.                          Recycling time: 10 min-                          utes.______________________________________ 
    
     At the end of these tests and after separation of the solvent, an oil phase and an asphaltic phase are obtained. The yields obtained and the characteristics of these phases are determined. They are presented in Table 2 which follows. 
     
                                           TABLE 2__________________________________________________________________________           T1       A11      A12           Oil Asphaltic                    Oil Asphaltic                             Oil AsphalticTest            phase               phase                    phase                        phase                             phase                                 phase__________________________________________________________________________Yield, wt. %    46.2               53.8 49.6                        50.4 50  50Density at 15° C., kg/m.sup.3         (1)           967.3    966.7    965.2Index of refraction at 60° C.           1.5290   1.5296   1.5288Softening point, °C.         (3)   122.5    119      122Viscosity at 100° C., mm.sup.2 /s         (4)           108.9    111.7    100.7Conradson residue, wt. %         (5)           6.4 37.5 6.05                        37.1 6.6 36Asphaltene content, wt. %         (6)           0.05               31.6 0.05                        29.6 0.08                                 34.5Sulfur content, wt. %         (7)           3.71               7.58 3.70                        6.54 3.75                                 7.14Nickel content, ppm         (7)           4   92   3   93   3   87Vanadium content, ppm         (7)           6   296  8   260  7   269__________________________________________________________________________                    T2       A2                    Oil Asphaltic                             Oil Asphaltic    Test            phase                        phase                             phase                                 phase__________________________________________________________________________    Yield, wt. %    62.5                        37.5 66.6                                 33.4    Density at 15° C., kg/m.sup.3                  (1)                    969.6    968.5    Index of refraction at 60° C.                    1.5305   1.5299    Softening point, °C.                  (3)    Viscosity at 100° C., mm.sup.2 /s                  (4)                    121.3    114.5    Conradson residue, wt. %                  (5)                    6.7 37.4 6.6 36    Asphaltene content, wt. %                  (6)                    0.045                        32.3 0.13                                 31.7    Sulfur content, wt. %                  (7)                    3.76                        7.15 3.82                                 6.76    Nickel content, ppm                  (7)                    3   90   3   98    Vanadium content, ppm                  (7)                    6   285  7   271__________________________________________________________________________ (1) In conformity with standard AFNOR NFT 60-101 (3) In conformity with standard AFNOR NFT 66-008 (4) In conformity with standard AFNOR NFT 60-100 (5) In conformity with standard AFNOR NFT 60-116 (6) In conformity with standard AFNOR NFT 60-115 (7) Determined by xray fluorescene 
    
     In discussing Example 1 (including Tables 1 and 2), the published French priority application (No. 86.11638 filed Aug. 12, 1986 and from which priority was claimed in the original application papers in this case) made the following observations: 
     From these results, it can be seen that with identical operating conditions, better yields of oil of a substantially similar quality are obtained by the process of the invention. 
     For example, if one compares tests T2 and A2, the oil yield increases from 62.5% to 66.6%, which means an increase of 4.1%. It can be seen, also, that the quality of the resulting oil is almost identical for the two tests: 
     Conradson residue (wt %): 6.5 and 6.6, 
     Viscosity at 100° C. (mm 2  /s): 119.3 [sic., actually 121.3 in Table 2] and 114.5. 
     It should also be noted that the advantageous effect of the shearing subsists even if the deasphalting step is not conducted immediately after the shearing step. 
     EXAMPLE 2 
     This example relates to deasphalting tests run with two feedstocks C 1  and C 2 , with and without prior shearing of the feedstocks. When it is effected, shearing takes place in the presence of solvent. 
     Feedstock C 1  identical to that used in Example 1 and therefore consists of a vacuum-distillation residuum of an atmospheric-distillation residuum of a Safaniya crude petroleum. Its characteristics are given in Example 1. Feedstock C 2  consists of an atmospheric-distillation residuum of a Maya crude petroleum. 
     The characteristics of this feedstock are as follows: 
     
         ______________________________________Density at 15° C.: 1026 kg/m.sup.3(Determined in conformity with standard AFNORNFT 60-101)Viscosity at 100° C.:                     876 mm.sup.2 /s(Determined in conformity with standard AFNORNFT 60-100)Conradson residue:        19.7 wt. %(Determined in conformity with standard AFNORNFT 60-116)Asphaltene content:       16.2 wt. %(Determined in conformity with standard AFNORNFT 60-115)Sulfur content:           4.57 wt. %(Determined by x-ray fluorescence)Nickel content:           91 ppm(Determined by x-ray fluorescence)Vanadium content:         480 ppm(Determined by x-ray fluorescence)______________________________________ 
    
     These feedstocks are subjected to: 
     deasphalting control tests T 3  (with C 1 ) and T 4  (with C 2 ) without prior shearing of the feedstock, and 
     tests A 3  (with C 1 ) and A 4  (with C 2 ) in accordance with the process of the invention after prior shearing of the feedstock, with addition of solvent prior to shearing. 
     The addition of solvent, n-heptane, is made with agitation at a temperature 10° C. higher than the softening temperature of the feedstock: 60° C. for C 1 , and 34° C. for C 2  (determined in conformity with standard AFNOR NFT 66-008). 
     Shearing is effected at a temperature of 95° C. in a turbine having a gap of 0.6 mm and a notched head (with the teeth spaced 2 mm apart) at a speed of rotation of 17,000 rpm. 
     For the tests T 3  and A 3 , a solvent composed of 89 weight percent n-pentane and 11 weight percent n-heptane is used. 
     For the tests T 4  and A 4 , the solvent contains 78.1 weight percent n-pentane and 21.9 weight percent n-heptane. 
     In these compositions, allowance is made for the n-heptane previously added. 
     The conditions of the tests are given in Table 3  below. 
     
                       TABLE 3______________________________________                           Mass ratio  Temperature,   Pressure, solvent toTest   °C.     pascals abs                           feedstock______________________________________T.sub.3  175           4 · 10.sup.6                           3A.sub.3  175           4 · 10.sup.6                           3T.sub.4  175           4 · 10.sup.6                           3A.sub.4  175           4 · 10.sup.6                           3______________________________________ 
    
     At the end of these tests and after separation of the solvent, an oil phase and an asphaltic phase are obtained. The yields obtained and the characteristics of these phases are determined. They are presented in Table 4 which follows. 
     
                                           TABLE 4__________________________________________________________________________           T.sub.3  A.sub.3  T.sub.4           Oil Asphaltic                    Oil Asphaltic                             Oil AsphalticTest            phase               phase                    phase                        phase                             phase                                 phase__________________________________________________________________________Yield, wt. %    57.7               42.3 61.7                        38.3 72.5                                 27.5Density at 15° C., kg/m.sup.3         (1)           986      984      974Index of refraction at 60° C.           1.5433   1.544    1.5362Viscosity at 100° C., mm.sup.2 /s         (4)           200      197.1    59.5Conradson residue, wt. %         (5)           9.8 40.2 10.2                        41.9 8.1 45.0Asphaltene content, wt. %         (6)           1.82               51.3 1.60                        62.7 3.8 70.8Sulfur content, wt. %         (7)           4.14               7.00 4.03                        7.2  3.74                                 6.94Nickel content, ppm         (7)           7   117  7   104  15  262Vanadium content, ppm         (7)           22  332  24  348  95  1299__________________________________________________________________________                             A.sub.4                             Oil Asphaltic             Test            phase                                 phase__________________________________________________________________________             Yield, wt. %    75.3                                 24.7             Density at 15° C., kg/m.sup.3                           (1)                             975             Index of refraction at 60° C.                             1.5381             Viscosity at 100° C., mm.sup.2 /s                           (4)                             62.9             Conradson residue, wt. %                           (5)                             7.8 45.7             Asphaltene content, wt. %                           (6)                             2.8 75.1             Sulfuir content, wt. %                           (7)                             3.73                                 7.03             Nickel content, ppm                           (7)                             15  248             Vanadium content, ppm                           (7)                             99  1310__________________________________________________________________________ (1) In conformity with standard AFNOR NFT 60-101 (4) In conformity with standard AFNOR NFT 60-100 (5) In conformity with standard AFNOR NFT 60-116 (6) In conformity with standard AFNOR NFT 60-115 (7) Determined by xray fluorescene 
    
     The same conclusions may be drawn as with respect to Example 1.