US2348623A - Refining mineral oils - Google Patents

Description

May 1944.

A. P.' HEWLETT ET AL REFINING MINERAL OIL Filed May 24, 1941 ZONE ALKAL/ .soLuT/o/v FAL-71572 /NC ZONE u-Lu STEAM r 1 OIL REGEIVERGTED ALKAL/ soLv-rro/ STO-RAGE (HL/YH L l STORAGE;

Patented May 9, 1944 REFINING MINERAL OILS Amiot P. Hewlett, Cranford, and Henry C. Paulsen, Elizabeth, N. J., assignors to Standard Oil Development Company, a corporation of Dela- Ware Application May 24, 1941, Serial No. 394,960

Claims.

The present invention is concerned with the refining of mineral oils. The invention is more particularly concerned with the removal of objectionable sulfur compounds from petroleum oils boiling in the motor fuel, kerosene and gas oil boiling ranges, utilizing an improved doctor sweetening operation. In accordance with the present process, the sulfur compounds are removed by means of a doctor sweetening operation in which an appreciable amount of the oil soluble lead mercaptides are removed with the spent doctor solution rather than with the treated oil.

It is known in the art to refine mineral oils by removing objectionable sulfur compounds therefrom utilizing various procedures. For example, it is known to use mineral acids as for example, a sulfuric acid, in order to reduce the sulfur concentration. It is also known to convert objectionable mercaptan compounds to disuliides by treating the feed oil with an alkali metal plumbite solution, termed a doctor solution,"

'which is prepared by dissolving lead oxide in an alkali metal hydroxide solution. When the mercaptan containing oil is contacted with the 'doctor solution, the mercaptans react with the doctor solution under conditions to form oil soluble lead mercaptides. Although a number of operations are employed to remove the lead from the treated oil, the usual process comprises precipitating the lead from the oil by adding free sulfur, whereby the lead is precipitated as lead sulde, resulting in the formation of alkyl disuliides with a corresponding improvement in odor. entirely satisfactory for improving odor, it does have the disadvantage that an overall sulfur reduction is not attained and octane number and 'leadsusceptibility are not improved. Another disadvantage of a process of this character is that considerable care must be exercised in the addition of the sulfur to the doctor treated oil. If an insufficient quantity of sulfur be added, some of the lead remains dissolved in the oil,

vwhich materially impairs the burning qualities of the oil. On the other hand, if an excess of sulfur be added, the excess sulfur will dissolve removes inherent difficulties heretofore present in conventional doctor treating operations. In accordance with our operation the oil is contactedv with a doctor solution containing dis- While an operation of this character is line I.

solved therein a solvent enhancing agent under conditions to convert the mercaptans to soluble lead mercaptides. By utilizing our doctor solution comprising the solvent enhancing agent, the lead mercaptides are rendered substantially completely soluble in the spent doctor solution and are thus removed with the spent doctor solution rather than with the treated oil. The spent doctor solution is separated from the treated oil and regenerated while the treated oil is removed and contacted in a secondary stage with a ltering medium comprising clay, or an equivalent medium, which completely removes the remaining lead mercaptides dissolved in the oil.

The process of our invention may be readily understood by reference to the attached drawing illustrating one embodiment of the same. For the purpose of description, it is assumed that the feed oil comprises a petroleum oil boiling in the motor fuel boiling range. The feed oil is introduced into the system by means of The oil is contacted with a quantity of an alkali metal plumbite solution containing an agent to promote solubility of lead mercaptide in the aqueous phase. For the purpose of description the solvent enhancing agent is taken to be potassium isobutyrate. The potassium isobutyrate may be introduced by means of line 6 or introduced directly into storage zone 2. Forv the purpose of description, the alkali metal plumbite is assumed to be a sodium plumbite solution or doctor solution which is withdrawn fromv doctor solution storage 2 then introduced into line I by means of line 3. The mixture is passed through mixing zone 4 and introduced into separation zone 5 wherein a separation is made between the aqueous spent doctor solution phase and the treated oil. By utilizing the doctor solution in conjunction with the solvent enhancing agent approximately to 90% of the lead mercaptides are dissolved in the aqueous doctor solution. The treated oil containing the remainder of the lead mercaptides is withdrawn from separation zone 5 by means of line 'l and passed through ltering zone 8 which contains a suitable filtering medium as, for example, fullers earth. The iiltered oil completely free of lead compounds is removed from zone 8 by means of line 9 and handled or further refined in any manner desirable.

After a time period, the clay becomes spent and the oil removed from zone 5 is passed into a secondary clay treating zone lll by means of line Il. This zone, likewise, comprises a suitable ltering medium, such as fullers earth,

which functions to free the oil completely of lead constituents. The treated oil is removed from zone l0 by means of line l2 and handled as described with respect to the oil removed by means of line 9. The spent clay containing adhered thereon the lead compounds in zone 8 is regenerated, preferably as follows:

The clay is rst subjected to oxidation by means of an oxidizing gas which is introduced by means of line i3 and withdrawn by means of line i4 under conditions to convert the lead sulfide to the corresponding lead oxide. The clay containing the lead oxide is then washed with a sodium hydroxide solution which is introduced by means of line I5 and withdrawn by means of line IG. This material is returned to doctor solution stcrage 2. The clay is then preferably washed with water and dried after which it is again suitable for contacting additional oil. The regeneration of spent clay in zone Il) is handled similarly to that described with respect to the regeneration of clay in zone 8. The spent doctor solution is Withdrawn from zone 5 by means of line l'i and introduced into regeneration zone I8 wherein the mercaptides are converted to mercaptans which are removed overhead by means of line i0. Regeneration of the spent doctor solution in zone I8 is preferably facilitated by steam which is introduced by means of line 2l. The regenerated doctor solution containing lead oxide is removed by means of line 20 and preferably handled as follows: The regenerated solution is introduced into treating zone 22 wherein the same is washed with a hydrocarbon solvent in order to remove small quantities of oil soluble sulfur compounds such as disulfides and thio-ethers which may be formed as by-products during the regeneration operation. The hydrocarbon wash solvent is inn troduced by means of line 23 and withdrawn by means of line 24. The washed regenerated solution is withdrawn from zone 22 by means of line 25 and preferably returned to storage zone 2. This solution may be employed in washing lead oxide from the regenerated adsorbent in zones 3 and l 0. If this latter operation be employed, the solution withdrawn by means of line 25 is passed through zone 8 by means of line 26 and returned to storage zone 2 by means of line l0.

The process of the present invention may be widely varied. It is to be understood that the respective zones may comprise any suitable number and arrangement of units. lThe operation may be adapted for the removal of mercaptan compounds from any feed oil containing the same. 4It is, however, particularly adapted for the removal of mercaptan compounds from petroleum oils boiling in the motor fuel and gas oil boiling ranges, such as oils boiling in the range from about 100 F. to about 400 F., from about 400 F. to '700 F., and in overlapping boiling ranges. The invention essentially comprises a method for removing a substantial proportion of the lead mercaptides with the spent alkaline solution. The remainder of the lead mercaptides may be removed from the treated oil after the same is separated from the spent alkaline solution by any suitable manner. Although the remainder of the mercaptides inthe treated oil may be removed by the addition of sulfur or by the use of an oxidizing agent, such as hydrogen peroxide or other known means, it is prefered not to precipitate lead sulfide in the oil but to remove the mercaptides by means of an adsorbent medium.

The plumbite solution may comprise any suitable alkaline solution but preferably comprises a sodium or potassium plumbite solution of a concentration from about to 40 Baume. The amount of plumbite used may be varied widely and will depend upon the particular feed oil being used and the concentration and character of the mercaptan compounds present therein. For example, when treating a petroleum oil boiling in the motor fuel boiling range, and when using a 10 to 40 Baume sodium plumbite solution, the amount of doctor solution used is generally in the range from about .O5 to about 1.0 volumes of doctor solution per volume of feed oil.

The solvent enhancing agent may be any substance which is characterized by being soluble in the aqueous spent doctor phase, and which is further characterized by having the ability to substantially increase the solubility of the lead mercaptides in the alkaline reagent. When utilizing reagents of this character, it is possible to remove lead compounds from the treated oil without precipitating lead sulfide therein. The solvent enhancing agent may be selected from a wide class of substances. Forinstance, the solvent enhancing agent may be a quaternary ammonium base, a sulfonium base, a glycol, as for example, butylene glycol, ethylene glycol, propylene glycol, butyl glycol, triethylene glycol, an alcohol, as for example, amino alcohol, salts such as alkali salts of amino or hydroxy aliphatic acids, preferably those aliphatic acids having from three to seven carbon atoms in the molecule, an alkali salt of phenyl acetic acid, an aliphatic amino glycol, and various ethers, such as mono, methyl or glyceryl ether. Desirable solvent enhancing agents are phenols and salts thereof, particularly alkylated phenols and alkylated phenolic salts, examples of which are tertiary butyl phenol, tertiary amyl phenols, tertiary propyl sodium phenolate, and the like. Preferred enhancing agents comprise salts of fatty acids, especially salts of low molecular Weight fatty acids which are characterized by having from 3 to 12 carbon atoms in the molecule. It is desirable that the salt be an alkaline salt, such as a fatty acid salt of an alkaline earth metal or an alkali metal as, for example, sodium and potassium fatty acid salts.

The amount of solvent enhancing agent used will depend upon the feed oil being treated, the concentration and character of sulfur compounds present, and the particular solvent enhancing agent employed. The amount is controlled so as to remove at least 50%, preferably from about 70% to 90%, of the lead mercaptides in the spent alkaline solution. In general, it is ypreferred to use from about 5% to about 100% of solvent enhancing agent, preferably from about 10% to about weight per cent of the agent, based upon doctor solution. For example, when using a salt of a low molecular weight fatty acid, it is preferred to use from about 40 to about '70 weight per cent of the solvent enhancing agent based upon the doctor solution.

The temperatures and pressures utilized in the treating zone may vary considerably. In general, the pressure is substantially atmospheric, While the temperature may be in the range from about 40 F. to about 1401 F., preferably in the range from about 60 F. to 80 F.

The adsorbent employed in the filtering zone when employing a preferred modification of the present process may comprise any suitable ,material as, for example, clay, fullers earth, bauxite, zeolite, diatomaceous earth, magnesium silicate (magnesol) and bentonites. Preferred materials comprise fullers earth and bentonites.

The filter adsorbent may be revivied by any suitable means. However, the adsorbent is pref.. erably reviviied by initially steaming to remove the occluded oil, followed by oxidizing the lead with an oxygen containing gas. The lead oxide is preferably reclaimed by passing the solvent enhancing agent through the clay bed. It is also desirable to wash the clay bed with Water, followed by drying the same.

In order to illustrate the invention further, the following example is given which should not be construed as limiting the same in any manner whatsoever:

Example In an operation a cracked oil boiling in the range from about 100 F. to about 400 F., and having a mercaptan concentration of 35 mg. per 100 ml., and 0.204 Weight per cent sulfur, was treated at 80 F. with 10% by volume of a solution comprising 6 normal potassium hydroxide and 3 normal potassium isobutyrate, containing 0.053 pound of lead oxide per gallon.

The plumbite solution was separated from the treated oil, which upon analysis was found to contain 8 mg. of mercaptan sulfur per 100 ml. of oil.

The treated oil free of spent plumbite solution was then percolated through a 16 inch bed (one inch I. D. tubes) of Attapulgas clay. The ltered oil was found to be completely free of mercaptan sulfur.

The operating conditions and results of this operation are summarized below:

Color, Saybolt Milligrams mercaptan sulfur per 100 milliliters Sulfur, weight percertr.-.

B. P., F Clay treating rate l v./v./hr

From the above it is apparent that a substantial proportion of the lead mercaptides, otherwise oil soluble, was removed with the spent alkali solution when employing the present invention of utilizing a solvent enhancing agent in conjunction with the alkali solution.

What we claim as new and Wish to protect by Letters Patent is:

1. Process for the removal of merca-ptan compounds from petroleum oils, which comprises contacting the same in an initial stage with an alkali metal plumbite solution containing dissolved therein a solvent enhancing agent comprising a salt of a fatty acid, under conditions to form lead mercaptides, separating a spent alkali metal solution phase containing dissolved therein a substantial proportion of the lead mercaptides, and an oil phase, separating the oil phase, and removing the remainder of the lead mercaptides therefrom by contacting the oil with a solid adsorbent.

2. Process as defined by claim 1 in which said petroleum oil boils in the motor fuel boiling range.

3. Process as dened by claim 1 in which said solvent enhancing agent comprises potassium isobutyrate.

4. Process as dened by claim 1 in which said spent alkali metal plumbite phase contains at least of the total amount of lead mercaptides formed.

5. Process as dened by claim 1 in which said spent alkali metal plumbite phase contains from to 90% of the lead mercaptides formed.

AMIOT P. HEWLETT. HENRY C. PAULSEN.

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