METHODS OF PREPARING NAPHTHENIC PROCESS OIL VIA EXTRACTION AND SEPARATION

Abstract

The methods described herein produce a naphthenic process oil, as classified by ASTM D-2226, containing 35-65% saturates and 35-65% aromatics as determined by ASTM D-2007. The produced naphthenic process oil also contains polyaromatic hydrocarbons (PAH), more specifically the EU/US EPA 8-regulated PAHs, less than 10 ppm. The naphthenic process oil is produced by first feeding gas oil ranging in viscosities up to 20 cSt at 100° C. through counter-current liquid-liquid extraction towers with a solvent having a selective affinity for aromatics. The extract is then cooled and either continuously processed through a coalescing separator or batch processed in a tank or decanter to produce a second raffinate, which can be further distilled to produce the naphthenic process oil.

Claims

1. A process for producing a naphthenic process oil, a primary paraffinic raffinate, and an aromatic secondary extract, comprising: feeding a hydrocarbon gas oil and an extraction solvent selective for aromatic hydrocarbons into a counter-current liquid-liquid extraction tower; performing counter-current solvent extraction of the hydrocarbon gas oil to produce a primary paraffinic raffinate and a primary extract, wherein the primary extract contains aromatic and naphthenic compounds separated and absorbed by the extraction solvent; collecting the primary extract; cooling the primary extract to produce a chilled primary extract; feeding the chilled primary extract to a separator for separation of the aromatic and naphthenic compounds in the chilled primary extract, wherein the separator is free of antisolvent during the separation; allowing the chilled primary extract to sit in the separator for an adequate period of time to allow the chilled primary extract to separate into two immiscible liquid phases, wherein the two immiscible liquid phases are a secondary raffinate and a an aromatic secondary extract, wherein the secondary raffinate contains naphthenic oil and solvent, and wherein the aromatic secondary extract is an aromatic process oil comprising aromatics greater than 65% by weight and solvent; and removing the solvent from the secondary raffinate by distillation to produce a naphthenic process oil.

2. The process of claim 1, wherein the naphthenic process oil comprises 35 to 65% saturates by weight and 35 to 65% aromatics by weight.

3. The process of claim 1, wherein the naphthenic process oil comprises less than 10 mg/kg of benzo(a)anthracene, chrysene, benzo(b)fluoranthene, benzoe(j)fluoranthene, benzo(k)fluoranthene, benzo(e)pyrene, benzo(a)pyrene, and dibenzo(a,h)anthracene and less than 1 mg/kg of benzo(a)pyrene.

4. The process of claim 1, wherein the hydrocarbon gas oil is distilled from crude oil and has a kinematic viscosity within a range of 0 cSt to 20 cSt at 100° C.

5. The process of claim 1, wherein the extraction solvent is selected from the group consisting of furfural, N-methyl-2-pyrrolidone, acetophenone, liquid SO2, acetonitrile, phenol, nitro-benzene, aniline, dimethyl sulfoxide, dimethyl formamide and mixtures thereof.

6. (canceled)

7. (canceled)

8. The process of claim 1, wherein the separator is a coalescing separator.

9. The process of claim 1, wherein the separator is a settler, a tank or a decanter.

10. The process of claim 1, wherein the counter-current liquid-liquid extraction tower has a top portion and a bottom portion, and wherein the top portion has a temperature in a range of 200° F. to 350° F. during the counter-current solvent extraction and wherein the bottom portion has a temperature in a range of 100° F. to 300° F. during the counter-current solvent extraction.

11. The process of claim 1, wherein the hydrocarbon gas oil and the extraction solvent fed into the counter-current liquid-liquid extraction tower have a ratio of extraction solvent to hydrocarbon gas oil ranging from 1:1 to 5:1.

12. The process of claim 1, wherein the primary raffinate has a viscosity index of at least 90.

13. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG. 1 shows a general schematic for methods of producing naphthenic process oils according to preferred embodiments disclosed herein.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0014] The present disclosure relates to methods for producing naphthenic process oils which are environmentally safe and meet regulations with regard to the amount of regulated polyaromatic hydrocarbons (PAH) they contain. The naphthenic process oils contain 35-65% saturates by weight and 35-65% aromatics by weight and less than 10 ppm of the 8 regulated PAH compounds. The naphthenic process oils are also characterized as containing less than 10 mg/kg of the 8 regulated PAH compounds and less than 1 mg/kg of benzo(a)pyrene and thus can be classified as non-carcinogenic oils.

[0015] FIG. 1 shows a general schematic for methods of producing naphthenic process oils according to preferred embodiments disclosed herein. The streams in FIG. 1 are labeled generally to show the flow of the process streams and where chemical separations are occurring. FIG. 1 illustrates a generic process and is not intended to limit the invention. Operational changes within this process can be made and are included in the scope of the invention.

[0016] Generally, the methods described herein include feeding gas oil (viscosity up to 20 cSt at 100° C.) produced by vacuum distillation of crude oil atmospheric residual bottoms and a solvent selective for aromatic hydrocarbons into a countercurrent liquid-liquid extraction tower. A primary raffinate is produced from the top of the tower and sent for further processing, which can result in profitable waxes and lubricating base oils. The distillate aromatic extract in solution with the extraction solvent produced from the bottom of the tower is then chilled in a cooling water exchanger or other form of chiller. This mixture is then fed to a vessel containing calming baffles and structured packing to aid in the separation/mild second extraction. This produces a secondary extract stream containing heavier aromatics and a pseudo-raffinate stream containing lighter aromatics, naphthenics, and low PAHs. Both product streams then pass through solvent recovery process units to produce solvent-free final products sent to tankage.

[0017] In particular, in preferred embodiments, a first step in the method is counter-current solvent extraction. The solvent used is selective for aromatic hydrocarbon compounds, particularly selective for polycyclic aromatics. Therefore, the solvent will separate and adsorb the aromatic compounds, including the PCAs and PAHs. Different solvents are available and capable of performing this separation. These include and are not limited to: furfural, NMP, acetophenone, liquid SO2, acetonitrile, phenol, nitro-benzene, aniline, dimethyl sulfoxide, dimethyl formamide, and mixtures thereof. The solvent is injected into the top of the extraction tower while the gas oil feed is injected into the middle/bottom. Multiple extraction towers can be operated in parallel in order to accomplish the same separation with more feed. Generally the internals of the extraction towers are either rotating circular disks or packing material. The gas oil feed is contacted with the solvent at a temperature ranging from 210° F. to 290° F. at a solvent to oil ratio in the range of 1:1 to 5:1, preferably 2:1 to 4:1. The temperature gradient in the extraction tower(s) is 40° F. to 70° F. depending on the desired extraction severity and the feed composition. The solvent removes the aromatic and naphthenic compounds and exits through the bottom of the tower while the paraffinic raffinate is removed from the top. This raffinate is no longer a part of the methods described herein after it is removed from the gas oil through extraction and sent to a solvent recovery train. This stream preferably has a viscosity index (VI) greater than 90 and is typically further processed by hydrotreatment or de-waxing to produce base oil and wax products. This first raffinate product stream can be further processed in a dewaxing unit that results in the production of a paraffinic base oil and a wax. Generally raffinate yields range from 45% to 80%. Operational controls of the solvent extraction tower(s) depends on the properties of the feed gas oil used, therefore the process conditions should be varied and not identical per different batches or feeds. It is preferable to set operating conditions to produce a raffinate with VI greater than 90.

[0018] The solvent extracted aromatics and naphthenics along with the majority of the solvent exit the bottom of the extraction tower(s) to be cooled 10° F. to 150° F. colder than the extractor bottom temperature. The cooling method can vary and examples include cooling water exchangers, process stream coolers, chillers, and a mixture in series or parallel. The colder temperature increases the selectivity of the solvent for aromatic compounds, therefore the colder the exiting stream, the more aromatics will be extracted in the next step. Therefore the exact cooling conditions to produce the desired oil described herein are determined by the concentration of aromatics and PAH compounds in the feed. The yields of each extraction and separation step are dependent on the feed and operating conditions chosen.

[0019] In preferred embodiments, the last step involves sending the cooled primary extract-solvent stream to a separator, such as a coalescing separator, to form two immiscible liquid phases. The coalescing separator contains internals comprised of one-stage packed coalescing material that aid in this second separation at the front and baffles for settling in the back. This process is continuous, producing the naphthenic oil and solvent mixture as well as a secondary extract and solvent mixture. Both of these streams are sent to separate solvent recovery trains ending with a final naphthenic oil and a secondary aromatic extract product. The final naphthenic oil in the pseudo-raffinate stream contains between 35% and 65% saturates and aromatics classifying the product as a Type 103 rubber petroleum oil according to industry standard ASTM D-2226. This product also contains PAH compounds less than 10 ppm, which satisfies the EU REACH regulation, making it a safe and non-carcinogenic process oil. The aromatic extract oil contains greater than 65% aromatics, which is classified as a Type 104 process oil. This second extract is a DAE with high PAH, which cannot be sold into the rubber industry due to the high aromatic content. If able, this stream can continue to be used in some rubber or other industrial applications that are not sensitive to carcinogenetic properties, such as the asphalt industry. In the methods described herein, a typical waste stream is converted to a naphthenic process oil that meets specifications and performance characteristics for safe use in rubber, polymers, and asphalt.

[0020] In alternate embodiments, gas oil is processed through liquid-liquid solvent extraction just as described above in the first preferred embodiments. The extract along with the majority of the solvent is cooled in a similar fashion to a temperature 10° F. to 150° F. colder than the extractor bottom temperature. Again, the exact cooling conditions to produce the desired oil of this invention are determined by the concentration of aromatics and PAH compounds in the feed so process conditions will vary. The last step consists of sending the extract-solvent stream to a separator, such as a settler, a tank or a decanter, where the two immiscible liquid phases will separate over time. The longer the oils sit, the better the separation will be. Generally, an adequate separation will occur in 24-48 hours. Once an adequate amount of time has passed the top phase containing the naphthenic oil and a small amount of solvent are removed. The two phases are then sent to separate solvent recovery trains producing a final naphthenic oil and a secondary aromatic extract oil.

[0021] An alternative step to further aid in the second separation, which takes place in the coalescing separator, settler, tank, or decanter, is the addition of an antisolvent, or solvent modifier, such as water. Adequate antisolvents are almost completely soluble in the extraction solvent and only slightly soluble in paraffinic oils. Water is the preferred antisolvent, but other effective antisolvents include alcohols and glycols. The use of antisolvent is not necessary to achieve the desired results.

[0022] Preferred embodiments of the present method do not require hydrotreatment or the use of naphthenic feeds. The primary existing methods for producing naphthenic oils require both of these things, which requires capital and higher operating expenses. One benefit of the present methods is the ability to produce multiple classifications of process oils in one or two processes. Just from the primary extract, 103 and 104 classes of rubber process oils are produced. There are also many options for further refining the primary raffinate. The naphthenic oil produced according to the methods disclosed herein can be used to replace carcinogenic DAE oils due to the low PAH content. This will be useful for both the polymer and rubber industries. The uses of this naphthenic oil are not restricted to any particular industries or products discussed herein.

EXAMPLE 1

[0023] The examples presented herein are not intended to limit the scope of the invention. Exemplary embodiments of the methods described herein are described with reference to the examples.

[0024] Various industry standard test methods exist to characterize relevant operating streams and physical properties of the products described herein. Table 1 below provides a list of industry standard test methods used in these examples.

TABLE-US-00001 TABLE 1 Property Test Method Viscosity (all ASTM D-445 temperatures) Density ASTM D-4052 API ASTM D-1250 Flash point, COC ASTM D-92 Refractive Index ASTM D-1218 Viscosity Gravity ASTM D-2501 Constant Pour Point ASTM D-5949 Refractivity Intercept ASTM D-2140 Carbon Analysis ASTM D-2140 Clay Gel, Composition ASTM D-2007 Simulated Distillation ASTM D-2887 EN 16143 PAH (ppm) GCMS

[0025] A crude mixture consisting mostly of West Texas Intermediate was distilled through an atmospheric distillation tower and two vacuum distillation towers to produce varying waxy distillates/gas oils. A bottom cut gas oil produced from the first vacuum tower and a middle cut gas oil produced from the second vacuum tower were chosen as the feeds. The properties of these waxy distillates were determined using the methods in Table 1 and are shown in Table 2 below.

TABLE-US-00002 TABLE 2 Property Gas Oil #1 Gas Oil #2 Viscosity @40 C. (cSt) 64.5 70.6 Viscosity @100 C. (cSt) 7.8 14.5 Density @15 C. (kg/L) 0.8998 0.9145 API 25.6 23.1 Flash (C.) 240 284 Refractive Index 1.5002 1.5032 Viscosity Gravity 0.838 0.841 Constant Pour Point (C.) 35 30 Refractivity Intercept 1.0519 1.0475 ASTM Color 5.0 8.0 Carbon Analysis C.sub.A, % 17 12 C.sub.N, % 22 31 C.sub.P, % 61 57 Simulated Distillation IBP 681 751  5% 771 814 10% 797 836 20% 824 866 30% 841 886 40% 855 904 50% 869 921 60% 882 937 70% 896 955 80% 913 976 90% 937 1005 95% 957 1029 FBP 1034 1105

[0026] The chosen gas oil (Gas Oil #1 or Gas Oil #2) was fed to three parallel liquid-liquid extraction towers where furfural was the selected solvent. The raffinate product was pulled from the top of the tower, processed through a mild hydrotreater and through a solvent recovery train. The primary raffinate was then sent for further processing. The primary extract and majority of the furfural was pulled from the bottom of the extractor towers and sent through a series of exchangers including a feed-effluent exchanger and a cooling water exchanger. The cooled extract-furfural stream was then sent to a coalescing separator to allow the furfural to further extract the heavy hydrocarbons and PAH compounds. From the coalescer the naphthenic stream containing a small portion of furfural and a secondary extract with the majority of the furfural were both sent to separate solvent extraction trains.

[0027] Two different runs using the same feed cut are discussed in this example. The process conditions of the extraction towers and separator for Gas Oil #1 are shown in Table 3. The process conditions of the extraction towers and separator for Gas Oil #2 are shown in Table 5. The resulting products of the invention separations were a primary raffinate, naphthenic oil, and an aromatic extract. The yields and physical properties of the subsequent products are shown in Table 4 and Table 6, respectively.

TABLE-US-00003 TABLE 3 Process Conditions-Gas Oil #1 Run #1 Run #2 Extractor top temperature 250 245 Extractor bottom temperature 175 175 Solvent to oil ratio 3.0 3.0 Separator temperature 145 100

TABLE-US-00004 TABLE 4 Run #1 Run #2 Primary Aromatic Primary Aromatic Property Raffinate Extract Naphthenic Raffinate Extract Naphthenic Yield 70% 26% 4% 68% 24% 8% Viscosity — 663.3 66 — 558.1 — @40 C. (cSt) Viscosity — — 26.5 — — — @60 C. (cSt) Viscosity 6.5 17.1 7.7 6.5 16.9 9.0 @100 C. (cSt) Density — 0.9812 0.9040 — 0.9842 0.9156 @15 C. (kg/L) API 31.46 12.57 24.83 31.19 12.14 22.89 Flash (C.) — 238 236 — 226 — Refractive — 1.5550 1.4988 — 1.5570 1.5060 Index Viscosity — 0.932 0.844 0.938 0.854 Gravity Constant Pour Point — 9 — 3 25 (C.) Refractivity — 1.0660 1.0480 — 1.0665 1.0497 Intercept Aniline Point 113.4  38.9 88.6 111.9  36.9 82.8 Carbon Analysis C.sub.A,% — 39 13 — 39 16 C.sub.N, % — 25 32 — 27 30 C.sub.P,% — 36 55 — 34 54 Clay Gel, Composition Aromatics — 72 39 — 75 50 Polars — 9 2 — 9 4 Saturates — 19 59 — 16 46 EN 16143 0   273 6.5 0   262 8.3 PAH (ppm)

TABLE-US-00005 TABLE 5 Process Conditions-Gas Oil #2 Run #1 Run #2 Extractor top temperature 280 280 Extractor bottom temperature 210 215 Solvent to oil ratio 3.75 3.85 Separator temperature 165 110

TABLE-US-00006 TABLE 6 Run #1 Run #2 Primary Aromatic Primary Aromatic Property Raffinate Extract Naphthenic Raffinate Extract Naphthenic Yield 54% 35% 11% 54% 28% 18% Viscosity — 288.1 — 365.9 @60 C. (cSt) Viscosity 10.6  32.8 15.2 10.6  36.9 16.5 @100 C. (cSt) Density — 0.9775 0.9170 — 0.9841 0.9233 @15 C. (kg/L) API 30.42 13.06 22.71 30.28 12.14 21.61 Flash (C.) — 277 268 — 259 Refractive — — 1.5079 — — 1.5097 Index Viscosity — — 0.842 — — 0.849 Gravity Constant Pour Point — 18 36 — 11 32 (C.) Refractivity — — 1.0510 — — 1.0496 Intercept Aniline Point 122.7  — 94.0 122.5  — 89.8 Carbon — Analysis C.sub.A,% — — 16 — — 15 C.sub.N, % — — 25 — — 29 C.sub.P,% — — 59 — — 56 Clay Gel, — Composition (wt %) Aromatics — 67 42 — 69 52 Polars — 12 4 — 12 6 Saturates — 21 54 — 19 42 EN 16143 — 64.7 3.6 — 90.0 2.3 PAH (ppm)

[0028] As seen in Table 4, the naphthenic oil produced from Gas Oil #1 contained, in Run #1, 39 wt % aromatics, 59 wt % saturates, and 6.5 ppm of the 8 regulated PAH compounds, and in Run #2, 50 wt % aromatics, 46 wt % saturates, and 8.3 ppm of the 8 regulated PAH compounds. As seen in Table 6, the naphthenic oil produced from Gas Oil #2 contained, in Run #1, 42 wt % aromatics, 54 wt % saturates, and 3.6 ppm of the 8 regulated PAH compounds, and in Run #2, 52 wt % aromatics, 42 wt % saturates, and 2.3 ppm of the 8 regulated PAH compounds.