US2913390A

US2913390A - Urea-dewaxing method for producing low cold-test oils

Info

Publication number: US2913390A
Authority: US
Publication date: 1959-11-17
Anticipated expiration: 1976-11-17

Description

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m w m R. mSSS M m wm V am m m mm. \\U ld. 'MMI MQ @www MN t3: .mmm 3S wm. w SEEE SQ BY fe/ur?? wai-r ATTORNEY United States Patent O UREA-DEWAXING METHOD FOR PRODUCING LOW COLD-TEST OILS USING FEED OIL TO DE- COMPOSE THE FORMED ADDUC'IS Lawrence C. Brnnstrnm, Flossmoor, Ill., assignor to aindard Oil Company, Chicago, Ill., a corporation of rana Application September 21, 1956, Serial No. 611,129

4 Claims. (Cl. 208-25) This invention relates to the dewaxing of oils. More particularly, it relates to the preparation of low coldtest oils from wax-containing petroleum stocks. This application is a continuation-in-part of my prior copending application Serial Number 474,517, filed on December 10, 1954, now abandoned.

A number of methods are disclosed in the prior art for removing waxes from hydrocarbon oils and for obtaining treated oils of reduced pour point therefrom. One of the more recent developments in this iield is urea dewaxing, in which the wax-containing stock is contacted with urea under conditions to form solid, crystalline adducts of urea and straight-chain waxes, which can be readily separated from the unreacted oil. A major diculty in the prior-art processes lay in the recovery of the urea from the adducts in reusable form. An object of the present invention is to decompose the urea adducts in such a manner as to regenerate the urea in a form suitable for direct recycle.V

In one prior-art method, the urea adducts were decomposed by contact with a hot, inert hydrocarbon liquid such as a petroleum naphtha, pentane, isooctane, benzene, or the like. The waxes were extracted in this way from the adducts, liberating the urea; but the urea occluded the extracting solvent and carried it into the succeeding cycle, where it contaminated the treated oil. Another object of my invention is to decompose urea adducts without using solvents which would contaminate the urea or the treated oil, and which do not need to be recovered and recycled.

A further object of my invention is to eiect the def waxing of petroleum oils in an integrated cyclic process, while avoiding the problems of solvent and wax recovery. Other objects will be apparent from the appended description and claims.

In a simple embodiment of my invention, a wax-containing hydrocarbon fraction in the low cold-test viscosity range, suitably a solvent-dewaxed lubricating oil stock having a viscosity up to about 300 SSU at 100 F., is subjected to contact with urea under adduct-forming conditions in the presence of an activator, usually comprising water and methanol. The urea and wax form an insoluble adduct, which is readily iiltered from the oil, leaving a treated oil within the low cold-test range (i.e., having a pour point below F.). The urea adduct is commingled and heated with an additional quantity of the wax-containing charging stock to a temperature above the decomposition point of the adduct but belowthe melting point of urea, whereby the adduct decomposes and the liberated wax is dissolved bythe oil. The urea is regenerated thereby in the form of a finely divided slurry, from which the urea is readily recovered by iiltration or the like, and is reused for contacting additional charging stock. The wax-oil solution is virtually unchanged in pour point, and can conveniently be disposed of by return to the refinery pool of low-wax stocks of similar viscosity.

It has been observed that hydrocarbon oils ranging in viscosity from about 40 to 300 SSU at 100 F. and in 2,913,390 Patented Nov. 17, 1959 ice pour point from about 0 to 100 F. and containing up to about 20 weight-percent or more of waxes are reduced in pour point to the range of about -10 to 70 F. by urea dewaxing according to the described technique. These viscosities correspond in general to the SAE 10, SAE 5, and lighter grades. The process is effective, for example, in treating a mineral seal oil of 45 SSU viscosity at 100 F. and pour point around 35 F., yielding a treated oil having a pour point of 75 F., which is more than adequate for most uses. The minimum pour point attainable appears to depend on the viscosity of the oil, varying directly as a logarithmic function thereof. Previous solvent dewaxing, in some cases, also atects the pour point obtained by urea dewaxing. Oils having viscosities of 40 to 150 SSU at 100 F. urea-dewax to the same low pour point whether previously dewaxed by other means or not. -In the viscosity range of 150-200 SSU, urea dewaxing produces oils in the low coldatest range only from oils which have been previously dewaxed by other means-eg., by cold pressing, or by solvent dewaxing with liquid propane, methyl ethyl ketone, ethylene dichloride, Freon, or the like. From 200 to 300 SSU, urea forms adducts with the waxes in both distillates (undewaxed) and cold-pressed oils, but the improvements in pour point are not as great. Urea dewaxing also tends to increase the viscosity of the treated oil, ordinarily up to about 10 percent.

In the adduct-forming step of my process, the charging stock may be subjected with advantage to contact with urea in the presence of about 0.05 to 0.5 mole of methanol per mole of urea and about 2 to l0 volume-percent of water based on the methanol. Although the concurrent use of methanol and water in a volume ratio between about :10 and 98:2 is preferred in the treatment of oils of SAE l0 viscosity and lower, the use of other proportions of methanol and water and other types of methanol activation, including the use of an anhydrous methanol activator, as generally known to the art, is contemplated. I ordinarily employ methanol in the proportion of about 0.5 to 4 gallons per 100 pounds of urea, and I prefer to employ aqueous 94-97 percent methanol in the propo-rtion of about 1 to 2 gallons per 100 pounds of urea. The urea and wax form an insoluble adduct at temperatures below about 130 F., ordinary temperatures in the range of about 75 to 80 F. being preferred. Temperatures above F. are less satisfactory, because the methanol tends to be driven off, and temperatures below about 50 F. are less satisfactory because of contacting and filtering diculties arising from increased Viscosity of the reaction mixture. For substantially complete wax removal from any given charging stock, a certain minimum proportion of urea is necessary, depending upon the wax content of the stock. Ordinarily, about 4 pounds of urea are sucient to ecct complete removal of 1 pound of wax. F or example, a propane-dewaxed oil such as a Mid-Continent SAE 10 stock, which contains approximately 0.4 po-und of adductible material per gallon, requires at least about 1.6 pounds of urea per gallon of oil for best results. A smaller urea:wax ratio tends to give incomplete wax removal and less than the maximum pour-point lowering. In most cases, I use between about 4 and 8 pounds of urea per pound of adductible wax contained in the stock.

In the adduct decomposition step of my process, the urea-wax adduct is dispersed in a further quantity of the wax-containing charging stock, suilicient to form a iluid slurry with the adduct and to dissolve the waxes contained therein, and the resulting slurry is heated to a temperature sufficiently high to decompose the adducts and to release the waxes and the urea. The waxes are dissolved by the charging-stock liquid, and the wax-oil solution is separated from the regenerated urea by iiltration, centrifugation, settling and decantation, or the like. Surprisingly, the pour point of the wax-enriched oil is practically unaffected, and as a result the said oil can be returned to the refinery pool of low-wax oils without detriment to the latter. Thus, the process can be visualized as a means for transferring the wax from a portion (e.g., 20 to 50 volume-percent) of a low-wax oil pool to the remainder of the pool yielding a quantity of low cold-test oil while avoiding any substantial effect on the properties of the remainder of the pool. This advantageous result is feasible apparently because the removal of the last traces of wax from the oil produces a very large decrease in the pour point thereof, while adding the same amount of wax to the oil has practically no eiect in raising the pour point.

lt will be understood that a given batch of urea can be used to treat one or a number of batches of oil before regeneration of the urea may become necessary. rThis will depend upon the quantity of urea employed and the quantity of wax present in each batch of oil, as the art recognizes. It will also be apparent that the quantity of wax which can be taken up in the decomposition step is not unlimited; however, in treating an average low-wax oil, the quantities of wax involved are so small that the posibility of saturating the solvent oil in the decomposition step will not arise.

The attached drawing illustrates a batch-type embodiment of my invention, in `which a propane`dewaxed Mid- Continent SAE 5 distillate is urea-treated in the presence of aqueous methanol, the dewaxed oil is withdrawn from the resulting urea-Wax adduct and any unreacted urea, the dewaxed oil is stripped of methanol and water to produce a low cold-test oil of the desired flash point, the adduct is decomposed by heating with additional charging stock, which dissolves the liberated wax, the waxenriched oil is filtered from the regenerated urea, and the regenerated urea is employed to dewax a further quantity of the charging stock. n

In the drawing, the charging stock, supplied through line 11, together with methanol and water in the desired amount, supplied through line 12, is introduced by pump 13 through valved line 14 into reaction vessel 15, containing solid, finely divided urea. the charged materials and urea are intimately commingled by agitator 16 until adduct formation has reached substantial completion Thereafter, an inert gas is introduced through line 17 into the top of the reactor, and pressure is applied thereby, forcing the liquid phase through filter medium 18 (suitably canvas supported on a screen) and out through valved lines 19 and 20 into storage vessel 21.

From storage vessel 21, the dewaxed oil is conveyed by pump 22 through heater 23 into low-pressure stripper column 24 at an upper point. Therein, the oil is stripped of low boilers (e.g., methanol) to the desired flash point with steam, introduced into a lower section of the column through line 25. The low boilers emerge overhead through line 26, leading to a vacuum pump or other suitable vacuum-proclucing means. From the bottom of column 24, the desired oil of low pour point emerges through cooler 27. lt can be further treated if desired to remove any entrained water or other haze-forming substances, employing methods well known in the art.

Remaining within reactor 15 is a filter cake, consisting essentially of urea-wax adducts, methanol, Water, and unreacted urea. The adducts are decomposed by introducing an additional quantity of charging stock, suitably in a proportion between about 0.5 and 5 pounds of oil per pound of solids, by way of line 11, pump 13, and valved line 14 into reactor 15 and recirculating the resulting slurry by way of line 23, pump 29, heater 30, and line 31 to permit the stream to be heated to a temperature above the decomposition point of the adducts but below the melting point of the ureai.e., above about 160 F. and below about 270 F., preferably be- Within the reactor,

tween about and 250 F. Overheating tends to decompose the urea, but not to an objectionable extent below about 270 F. During the heating cycle, methanol is driven off overhead through valved line 32, and is condensed by cooler 33 and led through line 34 into storage tank 35. Make-up methanol and water are supplied tothe said tank respectively through lines 36 and 37.

After the adduct decomposition is substantially complete, pump 30 is stopped, and the urea slurry is again filtered by introducing inert gas under pressure through line 17. The resulting filtrate, consisting essentially of charging stock slightly enriched in wax, is withdrawn through valved lines 19 and 38 and cooler 39 for disposal as desired. It can conveniently be returned to the propane-dewaxed oil pool, where its added wax content has a virtually negligible' effect on the pour point of the composite. l

Reaction vessel 15 is left with a filter cake of finely divided, solid, crystalline urea, suitable for immediate reuse in treating another batch of charging stock according to the procedure outlined above. Make-up urea is supplied as needed.

My invention will be more clearly understood from the following specific examples.

Example 1 A phenol-extracted, propane-dewaxed SAE l0 Mid- Continent lube-oil stock having a pour point of 0 F. was subjected to urea dewaxing according to the following procedure. Into an agitated reaction vessel were charged 57 pounds of the lube-oil stock, 12 pounds of urea, and 2 pounds of aqueous 97 percent methanol, and the mixture was agitated for 3 hours at ordinary temperatures around 75 F. The resulting reaction slurry was filtered, and the treated oil (filtrate) was found to have a pour point of 25 F., well within the low cold-test range. The lter cake, containing urea-wax adducts, was reslurried with 5 gallons of the untreated lube-oil stock, heated to 220 F. for 5 minutes, and filtered while hot. The filtrate had a pour point of 10 F. The filter cake was substantially waxfree urea, ready for recycle.

The recovered urea was used in a Second cycle of adduct formation and decomposition according to the same procedure, using fresh portions of the same charging stock. The urea-dewaxed oil had a pour point of 20 F., and the oil from the adduct-decomposition step had a pour point of 5 F.

Two additional cycles of adduct formation and decomposition under substantially the same conditions gave the following results:

Example 2 A phenol-extracted, propane-dewaxed SAE 5 Mid- Continent lube-oil stock having a pour point of 0 F. was urea-dewaxed according to the procedure described in Example 1, 5 gallons of the oil being treated with approximatelyrlZ pounds of recovered urea and 1 pound of aqueous 97 percent methanol. The treated oil had a pour point of 35 F. The urea adducts were reslurried with 2 gallons of the untreated SAE 5 stock, heated to 235 F. under 20 to 25 inches of vacuum, and filtered hot. The wax-enriched filtrate had a pour point of 0 F., unchanged from its original level.

Example 3 SSU at 100 F., and containing around 18 weight-percent waxes, was contacted with approximately 12 pounds of recovered urea and one pound of aqueous 97 percent methanol according to the procedure described in Example 1, and a treated oil was obtained having a pour point of 25 F. and a visocosity of 63 SSU at 100 F. The urea adducts obtained thereby were reslurried with 2 gallons of untreated charging stock, heated to 225 F., and filtered hot. The filtrate had a pour point of 20 F. and a viscosity of 60 SSU at 100 F.

In a second cycle of adduct formation and decomposition, using the recovered urea, fresh 2gallon portions of the pale parain oil charging stock, and only 0.5 pound of aqueous 97 percent methanol, a urea-dewaxed oil was obtained having a pour point of -25 F. and a viscosity of 63 SSU at 100 F. The wax-enriched oil from the adduct-decomposition step had a pour point of 25 F., unchanged, and a viscosity of 57 SSU at 100 F.

In a third cycle, using only 0.4 pound of aqueous methanol, the dewaxed oil had a pour point of -15 F. and a viscosity of 62 SSU at 100 F., while the waxenriched oil had a pour point of 30 F. and a viscosity of 56 SSU at 100 F.

While I have described my invention with reference to certain specific charging stocks, operating conditions, and processing techniques, it is to be understood that such details are included only by way of illustration, and not by way of limitation. For example, it will be apparent that my process can be carried out in a continuous or semi-continuous manner, utilizing for this purpose reaction vessels and auxiliary equipment of the types described in and available to the art. Numerous modications and equivalents of the invention will be apparent from the foregoing description to those skilled in the art.

In accordance with the foregoing description, l claim as my invention:

1. A cyclic process for dewaxing a solvent-dewaxed wax-containing hydrocarbon oil having a viscosity between about 40 and 300 SSU at 100 F. and a pour point between about v and 100 F. and obtaining a low coltitest oil therefrom having a pour point in the range of about to about 70 F., which comprises contacting said oil with urea under urea-adduct forming conditions in the presence of a methanol activator, whereby urea adducts are formed from the waxes contained in said oil, separating urea adducts and any unreacted urea from the resulting slurry, stripping said activator from the treated liquid resulting therefrom, whereby the desired low cold-test oil is obtained, commingling the residual solids containing the urea-wax adducts with a further quantity of said wax-containing hydrocarbon oil and exposing the mixture thereof to a temperature in the range above the decomposition point of said urea-wax adducts and below the melting point of urea, whereby the waxes are liberated from said adducts and are dissolved and recovered in said oil, and whereby solid urea is regenerated in active condition for further adduct formation, separating the regenerated urea from the resulting mixture at a temperature within said range, and reusing the regenerated urea for dewaxing a further quantity of said wax-containing hydrocarbon oil.

2. A cyclic process for treating a solvent-dewaxed Waxcontaining lubricating-oil stock of not greater than SAE 10 viscosity and pour point between about O and 100 F. and obtaining a low cold-test oil therefrom having a pour point in the range of about -10 to about -70 F., which comprises contacting said stock with urea in the presence of between about 0.05 and 0.5 mole of aqueous methanol per mole of urea, said aqueous methanol containing between about 2 and 10 volume-percent of water, the urea being employed in a quantity sufficient to react with substantially all of the straight-chain waxes con-l tained in said stock, continuing said contacting under conditions and for a sufficient time to form urea adducts with the straight-chain waxes contained in said stock, separating urea adducts and any unreacted urea from the resulting slurry, stripping methanol and Water from the treated liquid resulting therefrom, whereby the desired low cold-test oil is obtained, reslurrying said urea adducts and any unreacted urea with a further quantity of said solvent-dewaxed lubricating-oil stock and exposing the mixture thereof to a temperature between about and 270 F., whereby the methanol contained therein is liberated and withdrawn as a vapor stream and the waxes are liberated and dissolved in said further quantity of said solvent-dewaxed wax-containing lubricating-oil stock, while the urea is regenerated in active condition for further adduct formation, separating the resulting mixture at a temperature within said range into a solid, regenerated urea phase and a wax-enriched oil phase having substantially the same pour point as the original stock, and reusing said methanol and said regenerated urea for treating a further quantity of said solvent-dewaxed wax-containing lubricating-oil stock.

3. The process of claim 2 wherein between about 20 and 50 percent of a quantity of a propane-dewaxed waxcontaining lubricating-oil stock is subjected to further dewaxing with urea under the defined conditions, and the resulting urea-wax adducts are decomposed with the remainder of said stock, whereby the desired low cold-test oil is obtained and the wax content of the original oil is recovered in the remainder of the original oil without substantially raising the pour point of said oil, and whereby the urea is regenerated in active form, free from materials not contained in the treated oil.

4. A cyclic process for treating a solvent-dewaxed waxcontaining Mid-Continent lubricating oil of not greater than SAE-10 viscosity and pour point between about 0 and 100 F. and obtaining a low cold-test oil therefrom having a pour point in the range of about -10 to about -70 F., Which comprises contacting said solventdewaxed wax-containing lubricating oil with urea in a proportion of at least about 4 pounds of urea per pound of wax contained therein and between about 0.5 and 4 gallons of methanol activator per 100 pounds of urea, containing said contacting under conditions and for a sufficient time to form adducts with the waxes contained in said oil, separating the reaction mixture into a solid adduct phase and a liquid raffinate phase, stripping the activator from said liquid raffinate to obtain said low cold-test oil, commingling said solid adduct phase with a further quantity'of said solvent-dewaxed wax-containing lubricating-oil stock in a proportion between about 0.5 and 5 pounds of oil per pound of solids and exposing the reaction mixture to a temperature between about and 250 F., whereby the waxes contained therein are liberated and dissolved in said stock Without substantially raising the pour point thereof, and solid urea is regenerated in active condition for further adduct formation, separating said regenerated urea from the resulting mixture at a temperature within said range, and reusing the regenerated urea for the treatment of a further quantity of said solvent-dewaxed wax-containing lubricating-oil stock.

References Cited in the le of this patent UNITED STATES PATENTS 2,653,123 Kirsch et al. Sept. 22, 1953 2,663,671 Wiles et al. Dec. 22, 1953 2,672,457 Weedman Mar. 16, 1954 2,681,335 Gorin June 15, 1954 2,731,455 Salzmann et al. Jan. 17, 1956 2,861,941 Jancosek et al Nov. 25, 1958

Claims

1. A CYCLIC PROCESS FOR DEWAXING A SOLVENT-DEWAXED WAX-CONTAINING HYDROCARBON OIL HAVING A VICOSITY BETWEEN ABOUT 40 AND 300 SSU AT 100* F. AND A POUR POINT BETWEEN ABOUT 0 AND 100* F. AND OBTAINING A LOW COLDTEST OIL THEREFROM HAVING A POUR POINT IN THE RANGE OF ABOUT -10 TO ABOUT -70* F., WHICH COMPRISES CONTACTTING SAID OIL WITH UREA UNDER UREA-ADDUCT FORMING CONDITIONS IN THE PRESENCE OF A METHANOL ACTIVATOR, WHEREBY UREA ADDUCTS ARE FORMED FROM THE WAXES CONTAINED IN SAID OIL, SEPARATING UREA ADDUCTS AND ANY UNREACTED UREA FROM THE RESULTING SLURRY, STRIPPING SAID ACTIVATOR FROM THE TREATED LIQUID RESULTING THEREFROM, WHEREBY THE DESIRED LOW COLD-TEST OIL IS OBTAINED, COMMINGLING THE RESIDUAL SOLIDS CONTAINING THE UREA-WAX ADDUCTS WITH A FURTHER QUANTITY OF SAID WAX-CONTAINING HYDROCARBON OIL AND EXPOSING THE MIXTURE THEREOF TO A TEMPERATURE IN THE RANGE ABOVE THE DECOMPOSITION POINT OF SAID UREA-WAX ADDUCTS AND BELOW THE MELTING POINT OF UREA, WHEREBY THE WAXES ARE LIBERATED FROM SAID ADDUCTS AND ARE DISSOLVED AND RECOVERED IN SAID OIL, AND WHEREBY SOLID UREA IS REGENERATED IN ACTIVE CONDITION FOR FURTHER ADDUCT FORMATION, SEPARATING THE REGENERATED UREA FROM THE RESULTING MIXTURE AT A TEMPERATURE WITHIN SAID RANGE, AND REUSING THE REGENERATED UREA FOR DEWAXING A FURTHER QUANTITY OF SAID WAX-CONTAINING HYDROCARBON OIL.