Abstract:
A method for producing a process oil is provided in which a napthenic rich feed is enriched with an aromatic extract oil. The enriched feed is then subjected to a solvent extraction thereby providing a process oil.

Description:
FIELD OF THE INVENTION 
     This invention is concerned with improved process oils and their method of preparation. 
     BACKGROUND OF THE INVENTION 
     A product line of light (135 SSU@100° F.), intermediate (1000 SSU@100° F.), and heavy (3000 SSU@100° F.) hydrofinished process oils are currently manufactured from the corresponding distillates of Gulf Coastal naphthenic crude oils. These products are known as Coastal Pale Oils (CPOs) and are used extensively as rubber extender oils. A parallel product line of Solvent Extracted Coastal Pale Oils (SECP) are also produced via solvent extraction of the same naphthenic crude distillates. The raffinates are used as general process oils while the extracts are downgraded to cat cracker feedstock. 
     End users of CPOs are requesting increased solvency of the products as indicated by a lower aniline point for a given viscosity grade. Simultaneously, the availability and quality of the Gulf Coast naphthenic crude oils is declining. Thus there is a need for a process which can produce CPOs and SECPs simultaneously, produce CPOs of higher solvency, require less naphthenic distillate for a given product make, and utilize lower quality Gulf Coast naphthenic crude oils. 
     SUMMARY OF THE INVENTION 
     Very simply stated, one embodiment of this invention comprises enriching a hydrotreated naphthenic distillate with an aromatic extract oil and thereafter solvent extracting the enriched distillate to provide a process oil. 
     In a particularly preferred embodiment of the present invention the aromatic extract oil is obtained by solvent extracting a portion of a hydrotreated naphthenic distillate. 
     These and other embodiments of the present invention will become apparent upon reading the Detailed Description in conjunction with the accompanying drawing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The accompanying FIGURE, is a simplified process flow diagram illustrating a preferred embodiment of the subject invention in which an initial naphthenic feedstock is passed via line 11 into a pipestill 12 where it is distilled. Volatile overheads and bottoms are taken off via lines 13 and 14 respectively. A naphthenic rich stream from the pipestill is fed through line 15 to a hydrotreating reactor 16 for hydrotreatment. The hydrotreated naphthenic distillate is passed via line 17 to a separation stage 18 where ammonia and hydrogen sulfide are removed via line 19. A portion of the hydrotreated naphthenic distillate is passed via line 20 to a solvent extraction unit 21. The aromatic extract oil is removed from solvent extraction unit 21 via line 22 where it is sent to the stripping zone 23 for removal of solvent via line 24. The aromatic extract oil is passed through line 25 and combined with a second portion of the hydrotreated naphthenic distillate from line 26 to provide a mixture which is extracted in a second liquid extraction unit 27 to provide a process oil removed via line 28 and extract removed via line 29. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Typically the naphthenic crude feedstock used is fed to a pipestill to produce a suitable naphthenic distillate useful in the present invention. Depending upon the operating parameters of the pipestill various cuts of naphthenic distillates can be obtained, each of which can be processed according to the invention; however, for simplicity, the present invention will be described in detail with respect to a single naphthenic distillate. 
     As indicated in the FIGURE, a naphthenic distillate is treated in a first hydrotreating stage to convert at least some of the sulfur and nitrogen present in the distillate to ammonia and hydrogen sulfide. Preferably the first hydrotreating stage is maintained within a temperature range of about 300° C. to 375° C. and more preferably within the range of about 340° to 365° C., a hydrogen partial pressure in the range of about 300 to 2500 psia and preferably in the range of about 500 to 1200 psia. The hydrotreating is usually done at a space velocity (v/v/hr) in the range of about 0.1 to 2 v/v/hr. 
     The catalyst used in hydrotreating is not critical. It may be any one of those known and used in the art such as nickel sulfides, cobalt sulfides, molybdenum sulfides, and tungsten sulfides and combinations of these. 
     After hydrotreating the naphthenic distillate, hydrogen sulfide and ammonia formed during the hydrotreating stage are removed by any convenient means from the feed. For example, the hydrotreated material may be passed to a stripping vessel and an inert stream such as steam can be used to strip the hydrogen sulfide and ammonia from the hydrotreated material by using techniques well-known in the art. 
     In accordance with the present invention, an aromatic extract oil is added to the hydrotreated naphthenic distillate to provide feed for further processing. Preferably the aromatic extract oil will have an aniline point of less than 40° C. in the case of light grades and less than 70° C. in the case of heavier grades. The properties for three typical grades of distillates are shown in Tables 1, 2 and 3. 
     
                       TABLE 1______________________________________HYDROFINED DISTILLATE AND EXTRACTLIGHT GRADE: 135                     Extract From             Hydrofined                     Hydrofined             Distillate                     Distillate______________________________________Viscosity    SSU 100° F.                   116.2     225.7Viscosity    SSU 210° F.                   39.3      42.5Viscosity Index        VI         34.8      -57.8Spec Gravity 60° F.                   0.8957    0.9599API Gravity  60° F.                   26.5      15.9Aniline Point        °F. (°C.)                   178.0 (81.1)                             99.7 (37.6)Sulfur       wt %       0.20      0.64Basic Nitrogen        ppm        71        266Total Nitrogen        ppm        262       951Pour Point   °F. -22       -22ASTM Color   ASTM       1.5       2.0Clay GelSaturates    wt %       63.7      25.9Aromatics    wt %       35.7      72.0Polars       wt %       0.6       2.1COC Flash    °F. 350       380GCD5 LV %       °F. 568       58650 LV %      °F. 721       70895 LV %      °F. 835       820HPLCSaturates    wt %       65.7      31.11-Ring Aromatics        wt %       20.4      30.92-Ring Aromatics        wt %       8.2       21.33+ Ring Aromatics &amp;        wt %       5.7       16.7Polars______________________________________ 
    
     
                       TABLE 2______________________________________HYDROFINED DISTILLATE AND EXTRACTINTERMEDIATE GRADE 1000                     Extract From             Hydrofined                     Hydrofined             Distillate                     Distillate______________________________________Viscosity    SSU 100° F.                   725.4     2602.8Viscosity    SSU 210° F.                   63.8      86.2Viscosity Index        VI         46.6      -65.0Spec Gravity 60° F.                   0.9171    0.9667API Gravity  60° F.                   22.8      14.9Aniline Point        °F. (°C.)                   195.4 (91)                             135.5 (57.5)Sulfur       wt %       0.32      0.70Basic Nitrogen        ppm        240       575Total Nitrogen        ppm        762       1568Pour Point   °F. 21ASTM Color   ASTM       2.0       3.0Clay GelSaturates    wt %       56.8      29.4Aromatics    wt %       40.7      65.6Polars       wt %       2.5       5.0COC Flash    °F. 470       470GCD5 LV %       °F. 723       71150 LV %      °F. 863       84095 LV %      °F. 973       947HPLCSaturates    wt %       58.91-Ring Aromatics        wt %       20.82-Ring Aromatics        wt %       10.53+ Ring Aromatics &amp;        wt %       9.7Polars______________________________________ 
    
     
                       TABLE 3______________________________________HYDROFINED DISTILLATEHEAVY GRADE: 3000______________________________________Viscosity       SSU 100° F.                     1787.7Viscosity       SSU 210° F.                     98.1Viscosity Index VI        53.7Spec Gravity    60° F.                     0.9219API Gravity     60° F.                     22.0Aniline Point   °F. (°C.)                     210 (100)Sulfur          wt %      0.46Basic Nitrogen  ppm       401Total Nitrogen  ppm       1168Pour Point      °F.ASTM Color      ASTM      3.0Clay GelSaturates       wt %      55.4Aromatics       wt %      40.2Polars          wt %      4.4COC Flash       °F.GCD5 LV %          °F.                     77850 LV %         °F.                     95895 LV %         °F.                     1065HPLCSaturates       wt %      54.11-Ring Aromatics           wt %      20.12-Ring Aromatics           wt %      11.83+ Ring Aromatics &amp;           wt %      14.0Polars______________________________________ 
    
     Such an aromatic oil suitable in the process of the present invention is readily obtained by extracting a naphthenic distillate with aromatic extraction solvents in extraction units known in the art. Typical aromatic extraction solvents include n-methyl pyrrolidone, phenol, n-n-dimethylformamide, dimethylsulfoxide, methylcarbonate, morpholine, furfural, and the like. Preferably, n-methylpyrrolidone or phenol is used as the solvent. Solvent to oil treat volume ratios are generally from about 1:1 to about 3:1. The extraction solvent preferably contains water in the range of about 1 volume % to about 20 volume %. Extraction temperatures are generally in the range of about 40° C. to about 80° C. Basically the extraction can be conducted in a counter-current type extraction unit. The resultant aromatic rich solvent extract stream is then solvent stripped to provide an aromatic extract oil having an aromatic content of about 40% to 90% by weight. Properties for two typical extract oils are given in Tables 1 and 2. 
     In a particularly preferred embodiment of the present invention, the aromatic oil is obtained by extracting a hydrotreated naphthenic distillate. Indeed it is particularly preferred in the practice of the present invention to produce the aromatic extract oil by utilizing a portion of the same hydrotreated naphthenic distillate that is to be enriched. 
     In any event, the aromatic extract oil is then mixed with a hydrotreated naphthenic distillate in the extract to distillate volume ratio in the range of about 10:90 to about 90:10. 
     The resultant mixture is then subjected to a solvent extraction using typical aromatic extraction solvents at solvent to oil volume treat ratios of about 0.5:1 to about 2:1. The extract solvent contains from about 1 volume % to about 30 volume % water. Extraction temperatures are in the range of about 40° C. to about 80° C. 
     As is shown herein the present invention has been found to produce a process oil having a substantially reduced aniline point and hence, increased solvency. Moreover, by enriching the naphthenic distillate with aromatic extract oil and re-extracting the admixture in accordance with the present invention, a substantially greater amount of process oil is obtained then when just distillate is employed. 
     COMPARATIVE EXAMPLE 1 
     In this Comparative Example, a naphthenic feedstock having a viscosity of 135 SSU at 100° F. was passed through two hydrotreating stages under the conditions outlined in Table 4 below. 
     
                       TABLE 4______________________________________PROCESS VARIABLE    PASS 1  PASS 2______________________________________Temperature, °C.               355     315H.sub.2 Partial Pressure, psia               550     655Gas Treat, SCF H.sub.2 /Barrel               450     450Space Velocity, V/V/HR               0.7     0.7______________________________________ 
    
     In this Comparative Example after hydrotreating under the conditions of stage 1 the material is stripped to remove hydrogen sulfide and ammonia. The product of the second stage represents a process oil having the properties shown in Table 5, Column 1, below. 
     
                       TABLE 5______________________________________             Comparative                       50% ExtractProperties        Example 1 Example 1______________________________________Specific Gravity, 60/60° F.             0.8928    0.9100Aniline Point, °F.             179       159Sulfur, wt. %     0.11      0.23Viscosity, 100° F., SSU             119       148HPLC-2, wt. %Saturates         69.8      56.91-ring aromatics  21.9      28.52-ring aromatics  5.9       10.13+ ring arom. &amp; Polars             2.4       4.5Mutagenicity Index             0 (Pass)  0 (Pass)IP 346, wt. %     3.2______________________________________ 
    
     EXAMPLE 1 
     In this Example a napthenic feedstock corresponding to that used in the Comparative Example 1 was passed through a single hydrotreating stage under the conditions set forth under Pass 1 of Table 4. The hydrotreated distillate was extracted using 9.2% water and phenol in a countercurrent extraction column in a treat ratio of 170% and at a temperature of 145° F. After removal of the solvent, the aromatic extract oil was combined with an equal amount by weight of hydrotreated distillate and the mixture was extracted using 9.7% water in NMP at a treat ratio of 110% and at a temperature of 55° C. After removal of the solvent a process oil having the properties set forth in Table 5, Column 2 was obtained. 
     This invention allows simultaneous production of CPOs and SECPs from given naphthenic distillates. Using the extract stream from the SECP allows increased solvency of the CPO which in turn allows use of lower quality naphthenic crude, and increases overall product (CPO+SECP) yield. The product derived from the distillate/extract blend passed the mutagenicity test. Assuming equal volumes of SECP and CPO products from a given distillate this invention reduces distillate requirements by 20%. 
     COMPARATIVE EXAMPLE 2 
     In this Comparative Example, a naphthenic feedstock having a viscosity of 1000 SSU at 100° F. was passed through two hydrotreating stages under the conditions outlined in Table 4 above. 
     In this Comparative Example after hydrotreating under the conditions of stage 1 the material is stripped to remove hydrogen sulfide and ammonia. The product of the second stage represents a process oil having the properties shown in Table 6, Column 1, below. 
     
                       TABLE 6______________________________________             Comparative                       50% ExtractProperties        Example 2 Example 2______________________________________Specific Gravity, 60/60° F.             0.9135    0.9230Aniline Point, °F.             199.6     188.6Sulfur, wt. %     0.20      0.32Viscosity, 100° F., SSU             700.8     931.3HPLC-2, wt. %Saturates         62.5      51.61-ring aromatics  21.8      27.72-ring aromatics  9.7       13.13+ ring arom. &amp; Polars             6.1       8.5Mutagenicity Index             0 (Pass)  0 (Pass)IP 346, wt. %     3.4       2.0______________________________________ 
    
     EXAMPLE 2 
     In this example, a naphthenic feedstock corresponding to that used in the Comparative Example 2 was passed through a single hydrotreating stage under the conditions set forth under Pass 1 of Table 4. The hydrotreated distillate was extracted using 2.4% water in phenol in a countercurrent extraction column in a treat ratio of 190% and at a temperature of 175° F. After removal of the solvent, the aromatic extract oil was combined with an equal amount by weight of hydrotreated distillate and the mixture was extracted using 7.0% water in NMP at a treat ratio of 110% and at a temperature of 66° C. After removal of the solvent a process oil having the properties set forth in Table 6, Column 2 was obtained. 
     This invention allows simultaneous production of CPOs and SECPs from given naphthenic distillates. Using the extract stream from the SECP allows increased solvency of the CPO which in turn allows use of lower quality naphthenic crude, and increases overall product (CPO+SECP) yield. The product derived from the distillate/extract blend passed both the mutagenicity test and the IP-346 (AMES) screening test for cancer potential of oil. Assuming equal volumes of SECP and CPO products from a given distillate this invention reduces distillate requirements by 20%. 
     COMPARATIVE EXAMPLE 3 
     In this Comparative Example, a naphthenic feedstock having a viscosity of 3000 SSU at 100° F. was passed through two hydrotreating stages under the conditions outlined in Table 4 above. 
     In this Comparative Example after hydrotreating under the conditions of stage 1 the material is stripped to remove hydrogen sulfide and ammonia. The product of the second stage represents a process oil having the properties shown in Table 7, Column 1, below. 
     
                       TABLE 7______________________________________           Comparative                     50% 1000 CH ExtractProperties      Example 3 Example 3______________________________________Specific Gravity, 60/60° F.           0.9197    0.9230Aniline Point, °F.           211.1     203Sulfur, wt. %   0.31      0.38Viscosity, 100° F., SSU           1839.7    1574HPLC-2, wt. %Saturates       55.6      49.81-ring aromatics           22.2      26.72-ring aromatics           11.5      13.53+ ring arom. &amp; Polars           10.7      10.0Mutagenicity Index           0.8 (Pass)                     0.2 (Pass)IP 346, wt. %   3.4       1.9______________________________________ 
    
     EXAMPLE 3 
     In this example, an intermediate (1000 SSU@100° F.) naphthenic feedstock corresponding to that used in the Comparative Example 2 was passed through a simple hydrotreating stage under the conditions set forth under Pass 1 of Table 4. The hydrotreated distillate was extracted using 2.4% water and phenol in a countercurrent extraction column in a treat ratio of 190% and at a temperature of 175° F. After removal of the solvent, the aromatic extract oil was combined with an equal amount by weight of heavy (3000 SSU@100° F.) hydrotreated distillate and the mixture was extracted using 7.0% water in NMP at a treat ratio of 110% and at a temperature of 66° C. After removal of the solvent a process oil having the properties set forth in Table 7, Column 2 was obtained. 
     This invention allows simultaneous production of CPOs and SECPs from given naphthenic distillates. Using the extract stream from the SECP allows increased solvency of the CPO which in turn allows use of lower quality naphthenic crude, and increases overall product (CPO+SECP) yield. The product derived from the distillate/extract blend passed both the mutagenicity test and the IP-346 (AMES) screening test for cancer potential oil. Assuming equal volumes of SECP and CPO products from a given distillate this invention reduces distillate requirements by 20%.