US2746989A

US2746989A - Separation of naphthenic acids

Info

Publication number: US2746989A
Application number: US336550A
Authority: US
Inventors: James L Jezl
Original assignee: Sun Oil Co
Current assignee: Sunoco Inc
Priority date: 1953-02-12
Filing date: 1953-02-12
Publication date: 1956-05-22
Anticipated expiration: 1973-05-22

Description

May 22, 1956 Petroleum Material Naphfhenic Acids J. L. JEZL 2,746,989

SEPARATION OF NAPHTHENIC ACIDS Filed Feb. 12, 1953 Sodium Forma're a Sodium Acetate ggggr z /lO j l2 Treating Zone \H Separating Zone /|5 l7 Hydrocarbon I9 l8 Regenerahon Zone Separating Zone 2| Distlllatlon Zone 23 INVENTOR.

JAMES L. JEZL o SPA ATTORNEY SEPARATION OF NAPHTHENIC ACIDS James L. Jezl, Swarthmore, Pa., assignor to Sun Oil Company, Philadelphia, Pa., a corporation of New Jersey Application February 12, 1953, Serial N 0. 336,550

4 Claims. (Cl. 260--514) This invention relates to the separation of naphthenic acids from other petroleum constituents such as hydrocarbons, petroleum phenols, mercaptans, etc.

The present invention provides a separation of naphthenic acids from petroleum materials containing naphthenic acids by contact with a regenerable treating agent. The petroleum materials which can be so contacted according to the invention include materials containing relatively small amounts of naphthenic acids, as for example crude petroleum, topped crude, lubricating oil distillates, gas oil distillates, etc., and also materials containing relatively large amounts of naphthenic acids, as for example crude naphthenic acids obtained by preliminary separation from petroleum but containing substantial amounts of hydrocarbon material, or deoiled mixtures of naphthenic acids and petroleum phenols. The present invention provides a manner of separating naphthenic acids from petroleum phenols and/or mercaptans and other petroleum constituents, as well as from hydrocarbon materials.

According to the present invention, a petroleum material containing naphthenic acids and other petroleum constituents from which it is desired to separate the naphthenic acids is contacted with a treating agent comprising an alkali metal salt of an organic acid having a dissociation constant in the range from l 1() to 3 10- and having boiling point substantially below the boiling point of the naphthenic acids which are to be separated, thereby to react the naphthenic acids in the petroleum material with the alkali metal salt to form alkali metal naphthenate. Free organic acid is also formed by liberation from the salt in the reaction, and is removed from the treating zone in order to drive the reaction toward completion.

According to a particularly advantageous embodiment of the present invention, an excess of organic acid salt may be employed, in which case a two-phase reaction product is obtained, one phase comprising the excess salt and the other the oil phase. It has been found that the alkali metal naphthenates which are formed in the reaction dissolve in the salt phase, leaving the oil phase generally substantially free from naphthenates, and that the salt phase can be separated from the oil phase by stratification and decantation of the oil phase. The naphthenic acids can then be removed from the salt phase by acidification.

In recovering naphthenic acids by acidification of alkali metal naphthenate, it is often advantageous to use for this acidification the free organic acid which was evolved in the original treating step. In this way, the organic acid is converted back to the salt, which can be re-used in the treating stage, and a naphthenic acid product of high quality is obtained.

The process of the invention can thus be used to accomplish a separation of naphthenic acids from petroleum by means of a regenerable treating agent without producing any waste products such as are obtained in conventional processes for naphthenic acid removal.

2 ,746,989 Patented May 22, 1956 As mentioned previously, the process of the present invention can be used to separate naphthenic acids from petroleum phenols and mercaptans. Thus, naphthenic acids can be separated from a deoiled mixture of naphthenic acids and phenols and/or mercaptans, or naphthenic acids can be separated from both hydrocarbons as well as phenols and/or mercaptans, beginning with a hydrocarbon-containing material. The separation between naphthenic acids on the one hand and phenols and mercaptans on the other proceeds through the reaction of the organic acid salt with naphthenic acids rather than with the phenols or mercaptans, the latter being Weaker acids than the naphthenic acids, and therefore less capable. than naphthenic acids of displacing the organic acid from the organic acid salt. Thus, in the treating step the phenols and mercaptans remain in the petroleum material phase, and are separated therewith from the salt-naphthenate phase. The term petroleum phenols, is used herein to indicate the petroleum constituents which are known in the art by that name. Whether or not they are actually phenols, in the strict sense, is a matter of some doubt, but they have previously been regarded as phenolic in nature.

The treating agent employed according to the invention is an alkali metal salt of an organic acid having dissociation constant of at least 1x10 and having boiling point substantially below the boiling point of the naph thenic acids which are to be separated. For suitable reaction with petroleum naphthenic acids, the treating agent should contain a salt of an organic acid having dissociation constant not greater than 3X10- and preferably not greater than 3 X 10- In addition to such salt, the treating agent may also contain another salt of a stronger organic acid, whose purpose is primarily to provide a carrier for the other, more reactive salt.

Suitable salts for use according to the invention include salts of aliphatic, cycloaliphatic, aromatic, heterocyclic organic acids, etc. Suitable saturated aliphatic salts include sodium formate, potassium formate, sodium acetate, potassium acetate, sodium propionate, sodium butyrate, sodium caproate, etc. Suitable saturated cycloaliphatic salts include cyclohexanecarboxylic acid, cyclohexylacetic acid, petroleum naphthenic acids, etc. In connection with the use of naphthenic acid salts, it is pointed out that it is possible to use such salts when the average molecular weight of the naphthenic acids which are to be removed from the oil is greater than the average molecular weight of the naphthenic acids whose salt is used as treating agent.

Although aliphatic and cycloaliphatic acid salts generally exhibit superior properties for use according to the invention, the essential characteristics of the salt to be used are the dissociation constant and boiling point of the acid involved, rather than the chemical structure of the acid, and other well-known types of organic acid salt, e. g. aromatic and heterocyclic, may be employed, insofar as they possess the required dissociation constant and boiling point properties.

The treating agent used according to the present invention preferably comprises an alkali metal salt of an organic acid, which acid has normal boiling point or normal average boiling point not substantially greater than 450 F., since the use of such treating agent facilitates the removal of vapors of the acid from the treating zone. However, salts of acids having much higher boiling point may be used, provided that the boiling point or average boiling point is substantially less, preferably at least 50 F. less, than the average boiling point of the naphthenic acids which are to be separated. Preferably, there is used a salt of an acid having boiling point or endpoint substantially less than the boiling point or initial boiling point of the naphthenic acids to be separated.

Preferably the number of carbon atoms in the salt employed in the treating agent according to the invention is not greater than 7, though considerably higher molecular weight salts may be used in some instances, e. g. up to '14 carbon atoms or more; more preferably, the number of carbon atoms is not greater than 3.

The invention will be further described with reference to the attached drawing, which is a schematic illustration of the process. Anhydrous, molten salt, e. g. a mixture of 25 weight per cent sodium acetate and 75 Weight per cent sodium formate, which mixture has previously been melted by means not shown, is introduced at 450 F. through line 10 into treating zone 11. Petroleum material, e. g. lubricating oil, containing naphthenic acids, which material has been preheated by means not shown, is introduced at 450 F. through line 12 into treating zone 11, which is maintained at approximately atmospheric pressure. The relative amounts of treating agent and petroleum material are such that there is an excess of sodium acetate over the stoichiometric amount required for reaction with naphthenic acids. Upon contact of the naphthenic acids in the oil with the sodium salt, the acids react with the sodium salt to form sodium naphthenate and aliphatic acid, the latter vaporizing at the temperature in the treating zone and being removed through line 13. The removal of the aliphatic acid tends to drive the reaction of naphthenic acid with sodium acetate toward completion. The reaction tends to be with sodium acetate rather than with sodium formate, since formic acid, being a stronger acid than acetic acid, is more diflicult to displace from its salts.

The reaction mixture, comprising unsaponified petroleum material, excess sodium salt, and sodium naphthenate, is removed from treating zone 11 through line 14 into separating zone 15, wherein it is allowed to settle at atmospheric pressure and still at elevated temperature into a lower layer comprising excess sodium salt containing sodium naphthenate in solution and an upper layer comprising unsaponified petroleum material containing little or substantially no sodium napthenates.

The upper layer is removed through line 16, and if it is desired to remove whatever small amount of sodium naphthenates may be contained therein, the removed material may be Washed with a solvent such as aqueous ethanol to extract such sodium naphthenates. The lower layer is removed through line 17 and introduced into regeneration zone 18.

Aliphatic acid vapors, predominantly acetic acid, are also introduced into regeneration zone 18 through line 13, and contacted with the sodium salt and sodium naphthenate mixture to react with the sodium naphthenate and form naphthenic acid and additional sodium salt. The temperature in the regeneration zone is maintained at 450 F. and the pressure therein at a level at least somewhat above the pressure in treating zone 11, e. g. 2 atmospheres. A hydrocarbon material less viscous than the naphthenic acids formed by sufiiciently nonvolatile to remain in liquid phase under the conditions prevailing in regeneration zone 18 is introduced there into through line 19; a petroleum fraction, such as kerosene, may be used. As naphthenic acid is formed in regeneration zone 18, it dissolves in the hydrocarbon material. The use of the hydrocarbon material is not strictly necessary, but aids in subsequent layer separation, particularly if the naphthenic acids are highly viscous.

The products of the regeneration step are removed through line 20 and introduced into separating zone 21, wherein, upon settling at atmospheric pressure and still at elevated temperature, an upper hydrocarbon layer containing naphthenic acids and a lower sodium salt layer are formed. The upper layer is removed through line 22 and introduced into distillation zone 23 wherein the hydrocarbon is distilled off through line 24, leaving as residue naphthenic acids, which are removed through line 25. The lower layer formed in separating zone 21 is removed through line 26, and re-introduced into treating zone 11.

It is noted that the reaction involved in the regeneration step described above is essentially the reverse of the reaction involved in the initial contacting, or treating step. The reaction may be represented as follows where the alkali metal is sodium:

RCOOH+ R'COONER RCOONEI +R'COOH where RCOOH is naphthenic acid, and RCOONa is sodium salt of aliphatic acid. In the treating step, the reaction proceeds toward the right due to removal of the aliphatic acid by vaporization, and therefore conditions favoring such reaction are employed in the treating step. in the regeneration step, the reaction proceeds to the left, and therefore conditions different from those in the treating step and favoring such reaction, are employed in the regeneration step.

An important condition which aifects the equilibrium is the aliphatic acid concentration. High pressure tends to increase the aliphatic acid concentration and therefore favors the reaction going to the left in the above equation, and therefore it is preferred that the pressure be higher in the regeneration step than in the treating step. This may be accomplished by maintaining a vacuum in the treating step or elevated pressure in the regeneration step or both. High temperature tends to increase the vaporization of aliphatic acid and therefore favors the reaction going to the right, and therefore a higher temperature in the treating step than in the regeneration step favors the overally regenerative process. However, the temperature should be maintained high enough in both steps and throughout the process to maintain the alkali metal salt of the aliphatic acid in molten state.

High aliphatic acid concentration favors the reaction going to the left, and therefore it is preferred to remove aliphatic acid as rapidly as possible from the treating step in order to drive the reaction to the right. High temperature and low pressure contribute to this result. The removal of aliphatic acid from the treating step may also, if desired, be promoted by use in the treating step of a distillation entraining agent such as iso-octane, benzene, toluene, or xylene, etc., which forms with the aliphatic acid a minimum boiling mixture. In the regeneration step, on the other hand, a high concentration of aliphatic acid is preferably maintained in order to drive the reaction to the left.

In the preceding description of the drawing, the temperatures in the treating and regeneration zones were equal, and the difference in reaction equilibrium was maintained by a pressure differential between the two zones. A temperature differential can be used instead of, or in addition to, the pressure differential.

In the process as described in connection with the drawing, the temperature should be maintained, in all steps where sodium acetate and formate are present, at a temperature above the melting point of the mixture of sodium acetate and sodium formate. Such temperature is readily determined, in the light of the present specification, by a person skilled in the art. The temperatures used should be less than those which would cause decomposition or vaporization of the original petroleum material or the naphthenic acids removed therefrom. Generally, temperatures below 600 F. are favored. In the treating zone, a temperature within the range from 300 F. to 500 F. is preferred. In the regeneration zone, the same temperatures are generally suitable, though it may be desired to employ a lower temperature, say at least 25 F. lower in the regeneration zone than in the treating zone.

In the treating zone, the pressure is preferably not substantially above atmospheric. Considerably lower pressures, e. g. down to 10 mm. Hg absolute or lower, may

advantageously be used. In the regeneration zone, the pressure is preferably not substantially below atmospheric. Considerably higher pressures, e. g. up to 500 p. s. i. g. or higher, may advantageously be used. However, highly satisfactory results can be obtained with pressures not greater than 100 p. s. i. g. Preferably, the pressure in the regeneration zone is at least 1.5 times as great as the pressure in the treating zone.

The treating agent employed in the process described with reference to the drawing is maintained in substantially anhydrous, molten form. The substantial exclusion of water minimizes the tendency for emulsion formation in any stage of the process. The temperature required to maintain the treating agent molten varies for the different treating agents according to their melting points. The melting points of single anhydrous salts vary with the salt. Various eutectic mixtures of a plurality of salts within the scope of the invention have substantially lower melting points than those of the corresponding single salts and may advantageously be used according to the invention. For example, a mixture of about 60 percent potassium acetate and 40 percent sodium acetate has a melting point of about 220 C. as compared with 324 C. for sodium acetate and 292 C. for potassium acetate and can therefore be used at a lower temperature than either of the latter. Preferably, the melting point of the treating agent used according to the invention is not greater than 350 C.

It is particularly advantageous to employ as treating agent a mixture of a minor proportion of a higher molecular weight salt and a major proportion of a formate salt, e. g. sodium acetate and sodium formate, or sodium propionate and sodium formate, since the lower molecular weight salt is less miscible with the petroleum material and facilitates phase separation after the treating, while the higher molecular weight salt reacts more readily with naphthenic acids. The relative proportions of the salts may vary widely. Generally, when mixtures of salts are employed, it is preferred that the higher molecular weight salt be present in to 50 weight percent concentration, more preferably to weight percent concentration. Mixtures of more than two salts may be employed. Preferably, at least a stoichiometric amount of the higher molecular weight salt is used, based on the naphthenic acids which are to be separated.

In the process described in connection with the drawing, acetic acid vapors removed from treating zone 11 were used to acidify the alkaline material, i. e. sodium naphthenate, in regeneration zone 18. It is to be understood that, alternatively, the sodium naphthenate could be acidified with some other acid introduced into the process, e. g. aqueous mineral acid, with subsequent separation of naphthenic acid phase from the aqueous salt phase. Such operation, however, requires further treatment of the salt phase to regenerate it for use in the treating zone, and such operation is therefore not preferred. Also if the acetic acid removed from treating zone 11 is not used to acidify the sodium naphthenate, it must be reacted with some other alkaline-reacting material, e. g. sodium hydroxide, before re-introduction into treating zone 11.

In the process described in connection with the drawing, an excess of molten sodium salt was employed. It is also possible, according to the invention to employ only an approximately stoichiometric amount of molten sodium salt, in which case a solvent for sodium naphthenate, e. g. aqueous ethanol or molten sodium formate, etc., must be added to the reaction products before they can be separated. Use of aqueous solvents introduces water into the process and is therefore not preferred operation. It is also possible to use an aqueous salt solution in the treating step, rather than molten salt, but this is not preferred in view of the fact that the conditions in the treating zone must be such as to 6 volatilize and remove the aliphatic acid liberated in the reaction, and under such conditions water will also be volatilized and removed.

The following examples illustrate the invention:

Example I A mixture of naphthenic acids and lubricating oil was treated with a molten anhydrous mixture of potassium formate and potassium acetate at atmospheric pressure and a temperature of about 450 F. for 3 hours to obtain a salt phase containing potassium naphthenate and an oil phase substantially free from potassium naphthenate. The naphthenic acids employed had been previously separated from petroleum by conventional methods and deoiled by solvent extraction, and had saponification number of 169 mg. KOH per gram, and bromine number (A. S. T. M. 87546T) of 5. The original reaction mixture contained 1 part by weight of naphthenic acids, 10 parts of lubricating oil, and 11 parts by weight of the formate-acetate mixture, 10 parts of which were potassium formate.

During the 3 hours at 450 F., vapors of fatty acid, probably mostly acetic acid, were removed from the contacting zone. At the end of the three hours, the products were cooled to room temperature, and the oil layer was decanted from the salt phase. The decanted oil layer was washed with 50 percent aqueous ethanol to determine whether there was any substantial amount of potassium naphthenates therein; no substantial amount was removed by the washing. The oil layer was then titrated with caustic soda to determine the amount of naphthenic acids remaining in the oil; it was found that the oil contained fifty percent of the naphthenic acids originally present, indicating that fifty percent had been removed in the salt layer. More complete removal of naphthenic acids is obtained by treating under vacuum, by using a treating agent containing a greater proportion of sodium acetate as in Example II, or by other suitable means.

This example shows that naphthenic acids can be removed from oil by contact with excess molten fatty acid salt, with removal of evolved fatty acid and separation of excess salt from oil.

Example II Naphthenic acids similar to those used in Example I and containing substantial amounts of materials known in the art as petroleum phenols, Were treated with molten anhydrous sodium acetate, in the presence of a hydrocarbon material comprising equal amounts of a petroleum fuel oil (boiling range about 400 F. to 550 F.) and a petroleum spirits fraction (boiling range about 300 F. to 400 F.), the latter acting as an entraining agent, at a temperature in the neighborhood of 420 F. for 2 hours. 25 grams (0.0755 moles) of naphthenic acid, 10 grams (0.122 moles) of sodium acetate, and 250 ml. of hydrocarbon were employed. During the 2 hour period, hydrocarbon entraining agent and acetic acid were removed from the treating zone as vapor. At the end of the 2 hour period, the reaction products were cooled to room temperature and contacted with 100 ml. of 60 percent aqueous ethanol and 250 ml. of naphtha to obtain an aqueous layer containing sodium acetate and sodium naphthenate and a naphtha layer containing residual hydrocarbon and unreacted constituents of the original naphthenic acids. After repeated extractions with additional amounts of aqueous alcohol and naphtha, a composite aqueous layer was obtained which, upon acidification yielded naphthenic acids constituting about percent of the original charge and having bromine number of 3.2, indicating substantial reduction from the original bromine number of 5. The reduction of bromine number indicates removal from the naphthenic acids of materials contributing to high bromine number, probably materials known in the art as petroleum phenols.

This example shows that contaminating materials can be removed from naphthenic acids by contact with molten anhydrous sodium acetate.

The invention claimed is:

1. Method for separating naphthenic acids from other petroleum constituents which comprises: contacting in a treating zone a petroleum fraction containing naphthenic acids with an alkali metal salt of an organic acid having dissociation constant in the range from 1X10" to 3 l0" and having boiling point less than the boiling point of said naphthenic acids; maintaining in said treating zone conditions effective to vaporize said organic acid; reacting naphthenic acids with said salt in said treating zone to form alkali metal naphthenate and free organic acid; removing said free organic acid in vapor form from said treating zone; separating said alkali metal naphthenate from the petroleum fraction; reacting said free organic acid with alkalinereacting material to form alkali metal salt of said organic acid; and introducing the salt thus formed into said treating zone to contact additional such petroleum fraction.

2. Method for separating naphthenic acids from other petroleum constituents which comprises: contacting in a treating zone a petroleum fraction containing naphthenic acids with an excess of a molten, substantially anhydrous treating agent comprising an alkali metal salt of. an organic acid having dissociation constant in the range from 1 l0 to 3X10- and having boiling point less than the boiling point of said naphthenic acids; maintaining in said treating zone conditions eiiective to vaporize said organc acid; reacting naphthenic acids with said salt in said treating zone to form alkali metal naphthenate, which dissolves in the excess treating agent, and free organic acid; removing said free Organic acid in vapor form from said treating zone; separating said excess treating agent from the petroleum fraction; introducing the separated treating agent into a regenerating zone; introducing said free organic acid into said regenerating zone; contacting said free organic acid and said treating agent in said regenerating zone to form alkali metal salt of said organic 8 acid and free naphthenic acids; separating said naphthenic acids from said alkali metal salt; and returning the separated salt to said treating zone to contact additional such petroleum fraction.

3. Method according to claim 2 wherein said treating agent comprises alkali 'metal formate and alkali metal acetate.

4. Method for removing naphthenic acids from petroleum oil which comprises: contacting petroleum oil containing naphthenic acids with a molten, substantially anhydrous treating agent comprising a major proportion of alkali metal formate and a minor proportion constituting at least a stoichiometric amount of alkali metal acetate at a temperature within the range from 300 F. to 500 F. and a pressure within the range from 10 mm. Hg absolute and 1 atmosphere in a treating zone, thereby to form alkali metal naphthenate, which dissolves in said treating agent, and free acetic acid; removing said free acetic acid in vapor form from said treating zone; separating said treating agent from the petroleum fraction; introducing the separated treating agent into a regenerating zone; introducing said free acetic acid into said regenerating zone; contacting said free acetic acid and said treating agent in said regenerating zone at a temperature within the range from 300 F. to 500 F. and a pressure Within the range from 1 atmosphere to 500 p. s. i. g. and at least 1.5 times as great as the first-named pressure, thereby to form alkali metal acetate and free naphthenic acids; separating said free naphthenic acids from the treating agent; and returning the separated treating agent to said treating zone to contact additional such petroleum oil.

References Cited in the file of this patent UNITED STATES PATENTS 2,093,001 Blount a- Sept. 14, 1937 2,136,608 Blount Nov. 15, 1938 2,277,315 Galstaun Mar. 24, 1942

Claims

1. METHOD FOR SEPARATING NAPHTHENIC ACIDS FROM OTHER PETROLEUM CONSTITUENTS WHICH COMPRISES: CONTACTING IN A TREATING ZONE A PETROLEUM FRACTION CONTAINING NAPHTHENIC ACIDS WITH AN ALKALI METAL SALT OF AN ORGANIC ACID HAVING DISSOCIATION CONSTANT IN THE RANGE FROM 1X10-6 TO 3X104 AND HAVING BOILING POINT LESS THAN THE BOILING POINT OF SAID NAPHTHENIC ACIDS; MAINTAINING IN SAID TREATING ZONE CONDITIONS EFFECTIVE TO VAPORIZE SAID ORGANIC ACID; REACTING NAPHTHENIC ACIDS WITH SAID SALT IN SAID TREATING ZONE TO FORM ALKALI METAL NAPHTHENATE AND FREE ORGANIC ACID; REMOVING SAID FREE ORGANIC ACID IN VAPOR FORM FROM SAID TREATING ZONE; SEPARATING SAID ALKALI METAL NAPHTHENATE FROM THE PETROLEUM FRACTION; REACTING SAID FREE ORGANIC ACID WITH ALKALINE-REACTING MATERIAL TO FORM ALKALI METAL SALT OF SAID ORGANIC ACID; AND INTRODUCING THE SALT THUS FORMED INTO SAID TREATING ZONE TO CONTACT ADDITIONAL SUCH PETROLEUM FRACTION.