ADDITION OF CO-SOLVENTS TO FURFURAL FOR AROMATIC EXTRACTIONS

Abstract: A process to improve the performance of furfural for aromatics extraction from gas oils and lube distillates by the addition of ethers and/or aldehydes, preferably having a dielectric constant less than about 40 @ 25 DEG C.

Description: ADDTTION OF CO-SOLVENTS TO FURFURAL FOR AROMATIC EXTRACTIONS The invention relates to separation of aromatic compounds from gas oil and lube oil fractions using a furfural/co-solvent mixture. Refining of crude oil to produce lubricating oil is one of the oldest refinery arts. Suitable crudes are fractionated to isolate a suitable boiling range material, usually in the 600 to 1100°F (316 to 593°C) range, to produce a distilled oil fraction. Various solvent purification steps are then used to reject components not suitable for lubricating stock. Aromatics are too unstable, and refiners resort to various means to remove aromatics from potential lube fractions. While many solvents were proposed for aromatics extraction, furfural has been a preferred solvent since about 1933 when the first commercial furfural extraction units were built. Furfural is denser than oil and related to formaldehyde. It is a solvent for aromatics. When furfural and a heavy oil fraction mix, the furfural dissolves much of the aromatics content of the heavy oil. Upon settling, an extract phase or dense furfural phase containing most of the aromatics separates from a raffinate phase of lighter hydrocarbons with a reduced amount of aromatics. As in most liquid/liquid extraction processes the separation is not perfect. Some aromatics remain in the raffinate and some furfural dissolves in the raffinate. Fractionation of the extract and raffinate recovers the furfural solvent for reuse. Some representative patents on preparation of lubricants by solvent extraction include US 2,698,276, US 3,488,283 and US 4,208,263 which are incorporated by reference. Dearomatization of lube distillates by furfural extraction is discussed in U.S. Patent 2,079,885. Since the furfural unit is often a bottleneck in the lube refining process, improvement in the capacity of furfural without loss of selectivity would be of value to the lube refining industry. Therefore, it is an object of the present invention to improve the furfural extraction performance. It has now been found that the addition of ethers and/or aldehydes, preferably having a dielectric constant less than about 40 @ 25°C, improves the capacity of furfural for extraction of nitrogen, sulfur compounds and aromatics. Nitrogen and sulfur compounds are sludge precursors. The process of the present invention results in improved thermal and oxidation stability of the lube basestock. The invention therefore includes a process for the separation of a mixture of organic compounds which comprises contacting the organic compound mixture with a mixed solvent comprising furfural and one or more ethers and/or aldehydes, preferably having a dielectric constant less than about 40 @ 25°C, to form two phases and subsequently separating the phases that formed. The invention further includes a process for the production of lubricant oil from an aromatic containing petroleum fraction comprising contacting the petroleum fraction with a solvent comprising furfural and one or more ethers and/or aldehydes, preferably having a dielectric constant less than about 40 @ 25°C, under extraction conditions, producing an aromatics reduced raffinate product. DETAILED DESCRIPTION OF THE PRESENT INVENTION Feedstock Hydrocarbons which may be separated according to the process of the present invention include hydrocarbon oil fractions obtained by direct distillation, by thermal or catalytic cracking or by hydrocracking. The extraction of low boiling aromatic containing hydrocarbon oil fractions with the solvent mixture of the present invention yields substantially pure aromatic hydrocarbons such as benzene and toluene. This process is particularly applicable to paraffinic feedstocks boiling in the lubricant boiling range. The feedstocks may typically comprise hydrocarbons having about a 600°F+ (316°C) initial boiling point and a final boiling point of about 1100°F (593°C) , particularly those having a boiling range of about 700°F (371°C) to 1050°F (566°C) , most preferably those fractions boiling in the range of 750°F (399°C) to 1000°F (538°C) . These distillate lubricant stocks are usually referred to as neutrals and are the distillate fractions of the vacuum tower. Solvent Extraction Solvent extraction is conducted by contacting the distillate fraction with a selective solvent. Since the feedstock contains aromatics usually ranging from at least about 25 wt.%, specifically from 25 to 80 wt.% and more specifically from 30 wt.% to 60 wt%, the feedstock is initially subjected to an extraction step. Extraction utilizes a solvent which is selective for aromatics, such as furfural, and removes the aromatics which contribute to poor stability and VI. The solvent extraction is conducted with a solvent to oil ratio in the range of from about 0.5:1 to 10:1, such as in the range of from about 0.75:1 to 5:1, depending on the feedstock. The operating conditions for furfural extraction cover a temperature range of about 75°F (24°C) to about 350°F (177°C), preferably from about 100°F (38°C) to 325°F (163°C) and more preferably from about 125°F(52°C) to 300°F(149°C) . The yield in terms of volume percent typically ranges from 30 to 80. The operation may be conducted as a batch or continuous operation. The characteristics of the product of solvent extraction are very important, and consideration of the solvent extraction conditions coupled with the choice of feed is necessary to achieve a product with the desired viscosity and VI, maximum yield of high VI product is achieved by adjusting the extraction severity. The resulting raffinate should have a VI of at least about 85, preferably 90. The aromatics-reduced raffinate should contain at most about 40 wt.% aromatics, preferably ranging from about 10 to 30 wt.%, even more preferably from 10-20 wt.%. The extractions may be performed by conventional means, such as in a multistage countercurrent system, in a column with packing material or provided with perforated plates or in a column with a rotating shaft provided with discs. Solvent The process of the present invention involves the addition of one or more ethers and/or aldehydes to furfural to enhance its extraction performance. In particular, aliphatic ethers, glycol ethers, aromatic ethers, cyclic ethers and diethers, and aromatic aldehydes, have a high capacity for aromatics as well as paraffins in lube distillates and are miscible with lube distillates at temperatures as low as 100°F. The ability of solvent to solvate ions is determined by it's polarity, which is usually reported as a dielectric constant. A highly polar solvent has a high dielectric constant. Ethers and aldehydes for use as co-solvents in the process of the present invention preferably have a dielectric constant § 25°C of less than about 40, preferably less than about 30, more preferably less than about 20 and even more preferably less than about 10. The process of the present invention involves the addition of small volumes of one or more co-solvents to furfural to enhance the extraction performance. Suitable co-solvents include aliphatic ethers such as dibutyl ether and tertiary arayl methyl ether (TAME) ; glycol ethers such as monoglyme, ethylene glycol diethylether (ethyl gly e) and diethylene glycol monoethyl ether; aromatic ethers such as methoxybenzene (anisole) and ethoxybenzene (phenetole) ; cyclic ethers and diethers such as tetrahydrofuran (THF) , 1,4 dioxane and 1,3 dioxolane; aromatic aldehydes such as benzaldehyde and salicylaldehyde; and mixtures thereof. Table 1 below lists some suitable co-solvents and their dielectric constants. TABLE 1 Generally, the co-solvent is added in an amount less than about 35 vol.% based on total solvent, such as less than about 25 vol.% based on total solvent, less than about 15 vol.% based on total solvent and less than about 10 vol.% based on total solvent, depending on the feedstock. For example, a 5 vol.% co-solvent/95 vol% furfural blend may be used in the extraction process of the present invention when the feedstock is Arab Light heavy neutral distillate. Co-solvents for use in the process of the present invention also have a boiling point in the range of from about 50 to 225°C, preferably in the range of from about 75 to 200°C and more preferably in the range of from about 100 to 175°C. The addition of co-solvents, such as THF, to furfural improves its capacity for extraction of aromatics from lube distillates without loss in selectivity. Use of co-solvents in furfural extraction may increase the raffinate yield at the same raffinate refractive index (RI) . The process of the present invention also allows for retrofitting existing equipment. The addition of the co-solvents of the present invention also reduces the temperature of miscibility of the resultant furfural/co-solvent blend with the organic compound mixture compared to furfural alone. The temperature of miscibility of the solvent and the oil is defined as the temperature at which the solvent and the distillate are miscible in all proportions. An additional advantage of the furfural/co-solvent mixtures of the present invention is that to reach the same extraction result as when using furfural alone the necessary quantity of furfural/co-solvent may be smaller. At the same selectivity as furfural, the furfural/co- solvent mixtures of the present invention generally have a better solvency than furfural alone. For example, when high boiling hydrocarbon oil distillates or residual hydrocarbon oil fractions are to be extracted, the solvency of furfural fails and relatively high solvent ratios have to be applied. Another advantage of the present invention is the somewhat higher solvency of the furfural/co-solvent mixtures renders it possible to perform extraction at lower temperatures than with furfural alone. Operation at lower temperature prevents undesirable conversions of thermally unstable compounds present in the mixture and enables the separation of any such products formed more efficiently. The following examples illustrate the process of the present invention. Arab Light heavy neutral distillate, having the properties as set forth below in Table 2, was used for each extraction example. TABLE 2 Properties of Arab Light Heavy Neutral Distillate Refractive Index 1.5062 API Gravity 18.8 Kinematic Viscosity @ 100°C 18.07 CS Kinematic Viscosity @ 300°F 6.036 CS Total Sulfur 2.9 Wt.% Aliphatic Sulfur 0.40 Wt.% Total Nitrogen 1200 ppm Basic Nitrogen 311 ppm Paraffins 12.2 wt.% Mono Napthenes 5.5 wt.% Poly Naphthenes 17.1 Wt.% Aromatics 65.2 Wt.% For each furfural/co-solvent blend to be tested single stage batch extraction was performed in a one liter jacketed glass extraction apparatus. Approximately 200 cc. of the Arab Light heavy neutral distillate were heated and loaded into the extraction apparatus. Solvent was added to the vessel to give the desired solvent treat (total solvent:oil volume ratios of 1:1, 2:1 and 3:1. These ratios are typically referred to as 100%, 200% and 300% solvent dosage) . The extractions were performed at temperatures ranging from 200-230°F (93-110°C) . Once the mixture of solvent and oil reached the extraction temperature, the mixture was agitated for 5 minutes at 1000 rpm. After agitation, the mixture was allowed to settle for 15 minutes at the extraction temperature and separted into a raffinate and extract phase. The two phases were weighed to ensure material balance closure. The solvent was stripped from the extract and raffinate with nitrogen under vacuum. The stripped raffinate and extract phases were weighed and the raffinate yield was obtained. Final raffinate samples were analyzed for API gravity and Refractive index (RI) . API gravity was measured on the final extracts. In Examples 1-3, furfural was used alone. The furfural/co-solvent blends tested were furfural/dibutyl ether (Examples 4-6), furfural/TAME (Examples 7-12), furfural/monoglyme (Examples 13-18) , furfural/ethyl glyme (Examples 19-21) , furfural/diethylene glycol monoethyl ether (Examples 22-25) , furfural/THF (Examples 26-34) , furfural/anisole (Examples 35-38), furfural/1,4 dioxane (Examples 39-41), furfural/1,3 dioxolane (Examples 42-44), furfural/benzaldehyde (Examples 45-46) and furfural/ salicylaldehyde (Examples 47-48). Vol.% furfural/vol.% co¬ solvent, extraction temperature and solvent dosage for each example are set forth in Table 3. TABLE 3 Example Extraction Temp. Solvent Dosage °F(C) 1 Furfural 230(110) 100% 2 Furfural 230(110) 200% 3 Furfural 230(110) 300% 4 90 Vol% Furf/10 Vol% Dibutyl Ether 210(99) 100% 5 90 Vol% Furf/10 Vol% Dibutyl Ether 210(99) 200% 6 90 Vol% Furf/10 Vol% Dibutyl Ether 210(99) 300% 7 95 vol% Furf/5 vol% TAME 220(104) 100% 8 95 vol% Furf/5 vol% TAME 220(104) 200% I H O 9 95 vol% Furf/5 vol% TAME 220(104) 300% I 10 95 vol% Furf/5 vol% TAME 210(99) 100% 11 95 vol% Furf/5 vol% TAME 210(99) 200% 12 95 vol% Furf/5 vol% TAME 210(99) 300% 13 95 vol% Furf/5 vol% Monoglyme 220(104) 100% 14 95 vol% Furf/5 vol% Monoglyme 220(104) 200% 15 95 vol% Furf/5 vol% Monoglyme 220(104) 300% 16 95 vol% Furf/5 vol% Monoglyme 210(99) 100% 17 95 vol% Furf/5 vol% Monoglyme 210(99) 200% 18 95 vol% Furf/5 vol% Monoglyme 210(99) 300% 19 95 vol% Furf/5 vol% Ethyl Glyme 210 (99) 100% The results from the batch extraction examples are shown below in Table 4. Commercially, lube extraction units are operated to a RI specification since for a particular lube crude and type of refining process, raffinate RI correlates with the viscosity index (VI) of the dewaxed oil (DWO) , with lower RI corresponding to higher VI. Analysis of the data in Table 4 shows that for extraction the furfural/co-solvent blends are more effective than furfural alone, resulting in a 2-3 volume % improvement in raffinate ield at constant raffinate RI. Example Solvent Raffinate Raffinate Raffinate Extract Yield, RI API API Vol% Gravity Gravity 18 95 vol% Furf/5 vol% Monoglyme 59.31 1.4808 25.06 10.88 19 95 vol% Furf/5 vol% Ethyl Glyme 76.6 1.4932 21.75 8.4 20 95 vol% Furf/5 vol% Ethyl Glyme 63.9 1.4851 23.86 9.61 21 95 vol% Furf/5 vol% Ethyl Glyme 57.7 1.4808 25.06 10.68 22 90 vol% Furf/10 vol% Diethylene 72.8 1.4927 21.7 10.2 Glycol Monoethyl Ether 23 90 vol% Furf/10 vol% Diethylene 66.6 1.4833 23.91 8.5 Glycol Monoethyl Ether 24 80 vol% Furf/20 vol% Diethylene 76.5 1.4940 21.6 8.9 I Glycol Monoethyl Ether I 25 80 vol% Furf/20 vol% Diethylene 61.8 1.4858 23.9 10.3 Glycol Monoethyl Ether 26 95 vol% Furf/5 vol% THF 75.27 1.4944 21.56 9.43 27 95 vol% Furf/5 vol% THF 61.35 1.485 23.98 11.42 28 95 vol% Furf/5 vol% THF 52.71 1.4802 25.3 12.3 29 95 vol% Furf/5 vol% THF 78.94 1.4935 21.76 8.95 30 95 vol% Furf/5 vol% THF 66.37 1.4856 23.86 9.91 31 95 vol% Furf/5 vol% THF 57.73 1.4806 25.14 11.08 32 95 vol% Furf/5 vol% THF 81.5 1.4923 21.74 7.42 33 95 vol% Furf/5 vol THF 69.71 1.486 23.72 8.79 Example Solvent Raffinate Raffinate Raffinate Extract Yield, RI API API Vol% Gravity Gravity 34 95 vol% Furf/5 vol% THF 59.8 1.4812 25.07 10.51 35 95 vol% Furf/5 vol% Anisole 75.97 1.4944 21.59 10.88 36 95 vol% Furf/5 vol% Anisole 61.62 1.4847 23.97 11.35 37 95 vol% Furf/5 vol% Anisole 65.92 1.4858 23.89 10.03 38 95 vol% Furf/5 vol% Anisole 58.24 1.4809 25.1 10.97 39 95 vol% Furf/5 vol% 1,4 Dioxane 81.44 1.4927 21.33 7.72 40 95 vol% Furf/5 vol% 1,4 Dioxane 67.93 1.485 23.47 9.24 41 95 vol% Furf/5 vol% 1,4 Dioxane 59.03 1.4799 24.77 10.53 42 90 vol% Furf/10 vol% 1,3 Dioxane 77.93 1.4928 21.65 8.72 σv I 45 90 vol% Furf/10 vol% Benzaldehyde 74 1.4917 22.34 8.21 46 90 vol% Furf/10 vol% Benzaldehyde 62.5 1.4840 24.15 9.71 47 90 vol% Furf/10 vol% 75.3 1.4922 21.97 8.48 Salicylaldehyde 48 90 vol% Furf/10 vol% 61.4 1.4844 24.16 10.08 Salicylaldehyde In summation, the present invention provides a process for the separation of a mixture of organic compounds which comprises contacting the organic compound mixture with a mixed solvent comprising furfural and one or more co- solvents, preferably having a dielectric constant less than about 40 § 25°C, to form two phases and subseguently separating the phases that formed. The present invention further provides a process for the production of lubricant oil from an aromatic containing petroleum fraction comprising contacting the petroleum fraction with a solvent comprising furfural and one or more ethers and/or aldehydes, preferably having a dielectric constant less than about 40 @ 25°C, under extraction conditions, producing an aromatics reduced raffinate product. The co-solvent may have a dielectric constant less than about 30 @ 25°C. The co-solvent may have a dielectric constant less than about 20 § 25°C. The co-solvent may have a dielectric constant less than about 10 @ 25°C. The co-solvent may be in an amount in the range of less than 35 vol.% total solvent. The process of the present invention may have a temperature in the range of from about 75 to about 350°F.

Claims: CLAIMS Claim 1. A method for the separation of an organic compound mixture comprising the step of contacting the organic compound mixture with a mixed solvent comprising furfural and one or more ethers or aldehydes to form two phases; and separating the phases that are formed. Claim 2. The method according to claim 1, where the ether or aldehyde has a dielectric constant of less than about 40 at a temperature of 25°C. Claim 3. The method according to claim 1, where the ether is selected from the group consisting of aliphatic ethers, glycol ethers, aromatic ethers and cyclic ethers, and the aldehyde is an aromatic aldehyde. Claim 4. The method according to claim 1, where the ether is selected is from the group consisting of dibutyl ether, tertiary amyl methyl ether, monoglyme, ethyl glyme, diethylene glycol monoethyl ether, anisole, phenetole, tetrahydrofuran, dioxane, dioxalane; and the aldehyde is selected from the group consisting of benzaldehyde and salicylaldehyde. Claim 5. A method for the separation of an organic compound mixture comprising the step of contacting the organic compound mixture with a mixed solvent comprising furfural and one or more one or more compounds selected from the group consisting of aromatic ethers and cyclic diethers to form two phases; and separating the phases that are formed. Claim 6. The method according to claim 5, where the aromatic ether and cyclic diether have a dielectric constant of less than 40 at 25°C. Claim 7. The method according to claim 5, where the aromatic ether is selected from the group consisting of anisole and phenetole; and the cyclic diether is selected from the group consisting of dioxane and dioxalane. Claim 8. A method for the separation of an organic compound mixture comprising the step of contacting the organic compound mixture with a mixed solvent comprising furfural and one or more compounds selected from the group consisting of aliphatic ethers and glycol ethers to form two phases; and separating the phases that are formed. Claim 9. The method according to claim 8, where the aliphatic ethers and glycol ethers have a dielectric constant of less than 40 at 25°C. Claim 10. The method according to claim 8, where the aliphatic ether is selected from the group consisting of dibutyl ether and tertiary amyl methyl ether, and the glycol ether is selected from the group consisting of monoglyme, ethyl glyme and diethylene glycol monoethyl ether. Claim 11. A method for the separation of an organic compound mixture comprising the step of contacting the organic compound mixture with a mixed solvent comprising furfural and one or more aromatic aldehydes to form two phases; and separating the phases that are formed. Claim 12. The method according to claim 11, where the aromatic aldehyde has a dielectric constant of less than about 40 at a temperature of 25°C. Claim 13. The method according to claim 11, where the aromatic aldehyde is benzaldehyde or salicylaldehyde.

Inventors: GUPTE ANAGHA AVINASH, LANDIS MICHAEL EUGENE, MARLER DAVID OWEN, GUPTE, ANAGHA, AVINASH, LANDIS, MICHAEL, EUGENE, MARLER, DAVID, OWEN
Applicants: MOBIL OIL CORP, MOBIL OIL CORPORATION
Application year: 1996
Main classification: C07C7
IPC codes: C10G21