Method of producing a process oil

Abstract: A method for producing a process oil comprises hydrotreating a naphthenic rich feed and enriching the hydrotreated feed by means of an aromatic extract oil. The enriched feed is then subjected to solvent extraction, thereby yielding a process oil of increased solvency. The aromatic extract oil employed is preferably derived from a portion of the stripped hydrotreated feed.

Description: This invention relates to a method of producing a process oil. Currently, light (30 mm 2 /s @ 40°C) (135 SSU @ 100°F), intermediate (215 mm 2 /s @ 40°C) (1000 SSU @ 100°F), and heavy (650 mm 2 /s @ 40°C) (3000 SSU @ 100°F) hydrofinished process oils are 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. FR 2273859, equivalent of GB 1518682, describes the preparation of process oils by addition of an aromatic extract of solvent extraction to any of several distillate streams, including naphthenic distillates, for subsequent solvent extraction, before or after blending these streams. Yield and quality are said to be improved without resorting to catalytic hydrogenation. End users of CPOs require still further increased solvency properties in 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. In essence, the 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, the aromatic extract oil is obtained by solvent extracting a portion of a hydrotreated naphthenic distillate. In one aspect the invention provides a method for producing a process oil comprising: hydrotreating a naphthenic rich feed at a temperature of from 300°C to 375°C, a hydrogen partial pressure of 2.07 to 17.24 MPa (300 to 2500 psia) and a space velocity of 0.1 to 2 (v/v/hr) to provide a hydrotreated feed; removing hydrogen sulfide and ammonia from the hydrotreated feed to provide a stripped hydrotreated feed; adding an aromatic extract oil to the stripped hydrotreated feed, preferably in a volume ratio ranging between 10% to 90% to provide an enriched feed; and solvent extracting the enriched feed to provide a process oil. In accordance with a modification, the invention provides a method for producing a process oil comprising: hydrotreating a naphthenic rich feed at a temperature of from 300°C to 375°C, a hydrogen partial pressure of 2.07 to 17.24 MPa (300 to 2500 psia) and a space velocity of 0.1 to 2 (v/v/hr) to provide a hydrotreated feed; removing hydrogen sulfide and ammonia from the hydrotreated feed to provide a stripped hydrotreated feed; dividing the stripped hydrotreated feed into a first part and a second part; solvent extracting the said first part with an aromatic extraction solvent to provide an extract; removing the solvent from the extract to provide an aromatic extract oil; adding the aromatic extract oil to the said second part to provide an enriched feed; and solvent extracting the enriched feed to provide a process oil. 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 300°C to 375°C and more preferably within the range of 340° to 365°C, a hydrogen partial pressure in the range of 2068 to 17237 kPa (300 to 2500 psia) and preferably in the range of 3447 to 8274kPa (500 to 1200 psia). The hydrotreating is usually done at a space velocity (v/v/hr) in the range of 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. HYDROFINED DISTILLATE AND EXTRACT LIGHT GRADE: 135 Hydrofined Distillate Extract From Hydrofined Distillate Viscosity SSU 37.7°C (100°F) 116.2 225.7 Viscosity SSU 98,8°C (210°F) 39.3 42.5 Viscosity Index VI 34.8 -57.8 Spec Gravity 15.6°C (60°F) 0.8957 0.9599 API Gravity 15.6°C (60°F) 26.5 15.9 Aniline Point °C (°F) 81.1 (178.0) 37.6 (99.7) Sulfur wt% 0.20 0.64 Basic Nitrogen ppm 71 266 Total Nitrogen ppm 262 951 Pour Point °C(°F) -30 (-22) -30 (-22) ASTM Color ASTM 1.5 2.0 Clay Gel Saturates wt% 63.7 25.9 Aromatics wt% 35.7 72.0 Polars wt% 0.6 2.1 COC Flash °C(°F) 176.7 (350) 193.3 (380) GCD 5 LV% °C(°F) 297.8 (568) 307.8 (586) 50 LV% °C(°F) 382.8 (721) 375.6 (708) 95 LV% °C(°F) 446.1 (835) 437.8 (820) HPLC Saturates wt% 65.7 31.1 1-Ring Aromatics wt% 20.4 30.9 2-Ring Aromatics wt% 8.2 21.3 3+ Ring Aromatics & Polars wt% 5.7 16.7 HYDROFINED DISTILLATE AND EXTRACT INTERMEDIATE GRADE 1000 Hydrofined Distillate Extract From Hydrofined Distillate Viscosity SSU 37,7°C (100°F) 725.4 2602.8 Viscosity SSU 98,8°C (210°F) 63.8 86.2 Viscosity Index VI 46.6 -65.0 Spec Gravity 15.6°C (60°F) 0.9171 0.9667 API Gravity 15.6°C (60°F) 22.8 14.9 Aniline Point °C (°F) 91 (195.4) 57.5 (135.5) Sulfur wt% 0.32 0.70 Basic Nitrogen ppm 240 575 Total Nitrogen ppm 762 1568 Pour Point °C (°F) -6 (21) ASTM Color ASTM 2.0 3.0 Clay Gel Saturates wt% 56.8 29.4 Aromatics wt% 40.7 65.6 Polars wt% 2.5 5.0 COC Flash °C (°F) 243.3 (470) 243.3 (470) GCD 5 LV% °C (°F) 383.9 (723) 377.2 (711) 50 LV% °C (°F) 461.7 (863) 448.9 (840) 95 LV% °C (°F) 522.8 (973) 508.3 (947) HPLC Saturates wt% 58.9 1-Ring Aromatics wt% 20.8 2-Ring Aromatics wt% 10.5 3+ Ring Aromatics & Polars wt% 9.7 HYDROFINED DISTILLATE HEAVY GRADE: 3000 Viscosity SSU 37.7°C (100°F) 1787.7 Viscosity SSU 98.8°C (210°F) 98.1 Viscosity Index VI 53.7 Spec Gravity 156.6°C (60°F) 0.9219 API Gravity 156.6°C (60°F) 22.0 Aniline Point °C (°F) 100 (210) Sulfur wt% 0.46 Basic Nitrogen ppm 401 Total Nitrogen ppm 1168 Pour Point °C (°F) ASTM Color ASTM 3.0 Clay Gel Saturates wt% 55.4 Aromatics wt% 40.2 Polars wt% 4.4 COC Flash °C (°F) GCD 5 LV% °C (°F) 414.4 (778) 50 LV% °C (°F) 514.4 (958) 95 LV% °C (°F) 573.8 (1065) HPLC Saturates wt% 54.1 1-Ring Aromatics wt% 20.1 2-Ring Aromatics wt% 11.8 3+ Ring Aromatics & Polars wt% 14.0 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 1:1 to 3:1. The extraction solvent preferably contains water in the range of 1 volume % to 20 volume %. Extraction temperatures are generally in the range of 40°C to 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 10:90 to 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 0.5:1 to 2:1. The extract solvent contains from 1 volume % to 30 volume % water. Extraction temperatures are in the range of 40°C to 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 37.8°C (100°F) was passed through two hydrotreating stages under the conditions outlined in Table 4 below. PROCESS VARIABLE PASS 1 PASS 2 Temperature, °C 355 315 H 2 Partial Pressure, kPa (psia) 3792.1 (550) 4516.1 (655) Gas Treat, M 3 /m 3 (SCF H 2 /Barrel) 80.1 (450) 80.1 (450) Space 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. Properties Comparative Example 1 50% Extract Example 1 Specific Gravity, 15.6/15.6°C (60/60°F) 0.8928 0.9100 Aniline Point, °C (°F) 81.7 (179) 70.6 (159) Sulfur, wt.% 0.11 0.23 Viscosity, 37.8°C (100°F), SSU 119 148 HPLC-2, wt.% Saturates 69.8 56.9 1-ring aromatics 21.9 28.5 2-ring aromatics 5.9 10.1 3+ ring arom. & Polars 2.4 4.5 Mutagenicity 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 62.8°C (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 37.8°C (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. Properties Comparative Example 2 50% Extract Example 2 Specific Gravity, 15.6/15.6°C (60/60°F) 0.9135 0.9230 Aniline Point, °C (°F) 93.1 (199.6) 87.0 (188.6) Sulfur, wt.% 0.20 0.32 Viscosity, 37.8°C (100°F), SSU 700.8 931.3 HPLC-2, wt.% Saturates 62.5 51.6 1-ring aromatics 21.8 27.7 2-ring aromatics 9.7 13.1 3+ ring arom. & Polars 6.1 8.5 Mutagenicity 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 79.4°C (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 37.8°C (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. Properties Comparative Example 3 50% 1000CH Extract Example 3 Specific Gravity, 15.6/15.6°C (60/60°F) 0.9197 0.9230 Aniline Point, °C (°F) 99.5 (211.1) 95 (203) Sulfur, wt.% 0.31 0.38 Viscosity, 37.8°C (100°F), SSU 1839.7 1574 HPLC-2, wt.% Saturates 55.6 49.8 1-ring aromatics 22.2 26.7 2-ring aromatics 11.5 13.5 3+ ring arom. & Polars 10.7 10.0 Mutagenicity Index 0.8 (Pass) 0.2 (Pass) IP 346, wt.% 3.4 1.9 Example 3 In this example, an intermediate (1000 SSU @ 38.7°C (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 79.4°C (175°F). After removal of the solvent, the aromatic extract oil was combined with an equal amount by weight of heavy (3000 SSU @ 38.7°C (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%.

Claims: A method for producing a process oil comprising: hydrotreating a naphthenic rich feed at a temperature of from 300°C to 375°C, a hydrogen partial pressure of 2.07 to 17.24 MPa (300 to 2500 psia) and a space velocity of 0.1 to 2 (v/v/hr) to provide a hydrotreated feed; removing hydrogen sulfide and ammonia from the hydrotreated feed to provide a stripped hydrotreated feed; adding an aromatic extract oil to the stripped hydrotreated feed, preferably in a volume ratio ranging between 10% to 90% to provide an enriched feed; and, solvent extracting the enriched feed to provide a process oil. The method of claim 1, wherein the aromatic extract oil has an aromatic content of 40% to 90% by weight. The method of claim 1 or claim 2, wherein the aromatic extract oil is obtained by solvent extracting a portion of the stripped hydrotreated feed. A method for producing a process oil comprising: hydrotreating a naphthenic rich feed at a temperature of from 300°C to 375°C, a hydrogen partial pressure of 2.07 to 17.24 MPa (300 to 2500 psia) and a space velocity of 0.1 to 2 (v/v/hr) to provide a hydrotreated feed; removing hydrogen sulfide and ammonia from the hydrotreated feed to provide a stripped hydrotreated feed; dividing the stripped hydrotreated feed into a first part and a second part; solvent extracting the said first part with an aromatic extraction solvent to provide an extract; removing the solvent from the extract to provide an aromatic extract oil; adding the aromatic extract oil to the said second part to provide an enriched feed; and solvent extracting the enriched feed to provide a process oil. The method of claim 4, wherein the said first part is solvent extracted at a solvent: first part volume ratio of from 1:1 to 3:1. The method of claim 4 or claim 5, wherein the said first part is solvent extracted at a temperature of 40°C to 80°C. The method of any one of claims 4 to 6, wherein the aromatic extract oil is added to the said second part in a volume ratio from 10% to 90%. The method of any preceding claim, wherein the enriched feed is solvent extracted with an aromatic extraction solvent at a solvent: feed volume ratio of from 0.5:1 to 2:1. The method of any preceding claim, wherein the enriched feed is solvent extracted at a temperature of 40°C to 80°C.

Inventors: ALDOUS KEITH K, ANGELO JACOB B, BOYLE JOSEPH PHILIP, ALDOUS, KEITH K., ANGELO, JACOB B., BOYLE, JOSEPH PHILIP
Applicants: EXXONMOBIL RES & ENG CO, EXXONMOBIL RESEARCH AND ENGINEERING COMPANY
Application year: 1998
Main classification: C10G67
IPC codes: C10G67