US2337467A - Refining mineral oils - Google Patents

Description

Dec. 21, 1943. P, HEWLETT 2,337,467

A v REFINING MINERAL OILS Original Filed Mai-ch 1, 1941 FEED GIL name I s :e onwan Y zoms sncaprn/vs- Jon/0N Hvazza x102 l FEC YCLE' CAUS TIC MFWJW Patented Dec. 21, 1943 REFINING LIINERAL OILS Amiot P. Hewlett, Cranford, N. J., assignor to Standard Oil Development Company, a corporation of Delaware Continuation of application Serial No. 381,248,

March 1, 1941. This application December 11, 1942, Serial No. 468,610

2 Claims.

The present invention is concerned with the refining of mineral oils. The invention more particularly relates to the refining of petroleum oils boiling in the motor fuel, kerosene, and gas oil boiling ranges, and is especially directed to an improved process for the removal of objectionable acidic compounds therefrom, In accordance with the present process oils of this character are treated with an alkali metal hydroxide solution utilizing a particularly novel sequence and arrangement of stages by which desirable acidic constituents are retained in the oil while objectionable acidic constituents are removed in an eflicient and economical manner.

This invention has as its purpose, the refining of motor fuels particularly catalytically cracked motor fuels without'impairing gum stability to the extent that a satisfactory product cannot be obtained by the use of commercial gum inhibitors. Catalytically produced motor fuels are peculiar as compared with the thermally cracked motor fuels and are quite abnormal in their behavior toward alkaline refining agents. The unrefined catalytically cracked motor fuels have extremely high breakdown periods. This is due to the presence, in these gasolines, of large quantities of naturally occurring phenolic gum inhibitors; The concentration of these gum inhibitors, naturally occurring, will generally vary between 0.1 and 0.3%. Since these compounds are acidic in nature, they are readily removed by treatment with alkaline solutions and as a result, the motor fuel loses stability. Treatment with alkaline reagents is necessary in finishing a gasoline in order to remove other acidic and objectionable compounds. It is, therefore, the

purpose of this invention to supply means for applying the necessary caustic finishing without impairing the stability of the product, that is, without removing desirable, naturally occurring, phenolic gum inhibitors. This is accomplished by taking advantage of the varying strengths of the acdio materials present. The principal types of naturally occurring acidic compounds occurring in petroleum oils boiling in the motor fuel boiling rang'e, particularly in catalytically cracked gasoline, .in the order of increasing acidity are as follows:

Mercaptans Undesirable in motor fuels Phenols Desirable.in motor fuels Hydrogen sulfide Undesirable in motor fuels Naphthenic and fatty acids Undesirable in motor fuels Since the constituents are tabulated in the order of increasing acidic strength, any lower enumerated constituents will displace from its salts, any higher enumerated constituent. For example, hydrogen sulfide will react with sodium mercaptide and with sodium phenolate forming sodium sulfide and sodium acid sulfide, liber-' ating the mercaptans or the phenols. Salts of all these constituents can exist in the same solu- 5 tion, up until the point where all the free sodium hydroxide is neutralized or reacted. Beyond this point, the addition of further quantities of the stronger acids will result in the liberation of an equivalent quantity of the Weaker acids. My invention utilizes this principle in the process which may be readily understood by reference to the drawing illustrating an embodiment of the same.

For purposes of description, it is assumed that the feed oil comprises a petroleum oil boiling in the motor fuel boiling range and that the same has been secured from a catalytic cracking operation. The feed oil containing various quantities of naturally occurring acidic constituents, such as phenols and naphthenic acids, hydrogen sulfide and mercaptans is removed from zone I and introduced into initial alkali metal hydroxide tretaing zone 2 by means of line 3, wherein it contacts an alkali metal hydroxide solution introduced by means of line 4. For purposes of description, it is assumed that the alkali metal hydroxide solution comprises a sodium hydroxide solution. In zone 2 the feed oil is contacted 2 1 with the sodium hydroxide solution which is substantially completely free of mercaptans, hydrogen sulfide, naphthenic and fatty acids.

The quantity of caustic introduced into zone 2 is regulated so that the naphthenic acids, the 4 fatty acids and the hydrogen sulfide are cornpletely neutralized and removed with the spent caustic. The amount of caustic is also carefully regulated with respect to the character of the feed oil so that no free caustic is present in the spent caustic. Under these conditions the nat-" 40 urally occurring phenolic constituentspresent in the feed oil as well as] the mercaptans present are not affected. i Y J The caustic treated oil from which 'subs'tane: tially no weakly acidic (phenolic) compounds are removed is withdrawn from zone 2 by means'of lines 6 and introduced into a secondary caustic treating zone i. In zone I, the oil contacts a sodium hydroxide solution which is introduced by means of line l4 and withdrawn by means of line 9. Conditions are adjusted in zone 1 to secure the complete removal of all mercaptan compounds from the oil. Since the caustic utilized in zone I secured as hereinafter described, is saturated with naturally occurring phenolic constituents and is substantially completely free of mercaptan salts, complete removal of the, mercaptans from the oil will be secured without affecting the concentration of the desirable naturally occurring phenolic constituents present.-

A treated oil substantially completely free of objectionable acidic compounds and containing desirable naturally occurring phenolic constituents is removed from zone 1 by means of line In and handled or further refined in any manner desirable. The spent caustic solution withdrawn by means of line 9 is passed to zone ll wherein the caustic is treated for the removal of the mercaptan compounds therefrom. This is preferably secured by steaming the caustic solution and removing overhead by means of line l2 the volatilized mercaptans. The caustic solution containing dissolved therein acidic phenolic compounds present in the feed oil is withdrawn by means of line l3 and passed to zone 2 by means of line 4 as described. Since this caustic solution contains the acidic phenolic compounds and is substantially saturated with the same, it will not function to remove similar constituents from Zone 1 presents a condition where the phenol content of the caustic solution is sufficiently great to be in equilibrium with the phenol content of the gasoline, so that phenols are not removed from the oil in this stage. Thus I have a system for removing hydrogen sulfide and more strongly acidic material without losing the valuable Weakly acidic phenolic inhibitors. In zone 1 the mercaptans are extracted by the phenolcontaining caustic solution due to the fact that this solution contains some free alkalinity. Un-

der these conditions, extraction is aided by the the feed oil and. will, function only to free the oil.

plete removal of the naphthenic acid and hydrogen sulfide constituents as described while the remainder is passed to secondary treating zone I..' Fresh caustic equivalent to the amount utilized in initial zone '2' is supplied to the system by meansof line 8. The process of the present invention may bewidely varied. It is to be understood that zones I, 2-, I and H may comprise any suitable num-. her and arrangement of units. Although the in-. vention may be adapted for the complete re-.' moval of-objectionable acidic compounds from any-type of petroleum oil, it is particularly useful' in the removal of these compounds which are present in motor fuels, gas oil fractions, heating.

oil fractions, and the like. It is particularly-suitablefor the treatment of catalytically produced motor fuels. a 5 In. the operation of this process, caustic solu-l tion isrecirculated through zone I and its con-. necting lines, This caustic would react with all types of acidic compounds present and would dissolve desirable inhibitors from the gasoline. until an equilibrium concentration is reached following which no further inhibitor will be ex-- tracted. If hydrogen sulfide is present in the gas-; olineventering this part of the system, however,.. the caustic solution becomes converted to sodium; sulfide, with; the. result that it will have to, be rejected. from. thesystem, and replaced with fresh; caustic whlch-would up-set the existing equilib-'. rium. Forfthe removal of hydrogensulfide, zone 2 has been provided and a portion of thejcaustic recirculated throughlzone l and connecting lines, is passed; tozone 2- where this solution removes hydrogen sulfide and strong acids. The quan tity of. the solution is so adjusted that the spent caustic withdrawn through line .5 is free of sodiumhydroxide. ,A maximum hydrogen sulfide. removal is obtained when converting the sodium. hydroxide entirely to sodium hydrosulfide; however, this is not practicable when removing all. the hydrogen sulfide from the oil. Since the solution effect of phenols for sodium mercaptide. The quantity of mercaptans which can be dissolved by this alkaline solution is limited and regeneration zone I l is provided for the purpose of continually stripping mercaptans from this alkaline solution so that the mercaptan content will remain low in order to facilitate mercaptan removal from the oil.

The process of the present invention essentially comprises the particular arrangement and utilization of two zones in which objectionable acidic constituents are completely removed without affecting the removal of desirable acidic constituents in any manner. This is secured by utilizing in the initial zone the entire amount of caustic solution. The feed oil is treated in a secondary zone with recycled and fresh caustic under conditions to remove the mercaptan compounds from the oil. The spent sodium hydroxide solution is passed to a tertiary zone and handled to secure the removal of the mercaptain constituent. without removing any of the desirable acidic compounds, which caustic solution is then passed to. the respective zones as described.

Although the invention may be adapted to the employment of various alkali metal hydroxide solutions, it is particularly useful when employing a sodium hydroxide or a potassium hydroxide solution. The concentration and quantity of alkali used will vary depending upon the character of the feed oil and the character and concentration of impurities present. In general, I prefer tointroduce first caustic of from about 10 to 20 Baum.

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

EXAMPLE 1 The stability of a motor fuel produced by a catalytical cracking-operation was determined before and after treating with a custic wash.

The stability was also determined utilizing com-.

caustic solution is entirely converted to a 70 Motor fuel washed 10%, 10 B. NaOH+2 ture. of sodium sulfide and sodium hydrosulfide andsalts of strong acids, the phenols and mercaptans will bedisplaced from this solution, redissolvedinthe; gasoline phase and carried to zone- I.

Breakdown Motor fuel before washing 635 Motor fuel washed 10%,: 10 B. NaOH 45 Motor fuel washed 10%, 10 B. NaOH-l-5 .mg. inhibitor A/100 cc 50 Motor fuel washed 10%, 10 B. NaOH+10 mg. inhibitor A/100 cc 55 Motor fuel washed 10%, 10 Be. NaOH+20 mg. inhibitor A/100 cc mg. inhibitor B/lOO cc Motor fuel washed 10%, 10 B. NaOH+6 mg. inhibitor B/ cc Motor fuel washed 10%, 10 B. NaOH+10 15 mg. inhibitor B/lOO cc 110 Motor fuel .B

V Breakdown Motor fuel before washing 310 Motor fuel washed with 10% of 10 B. soda 55 Motor fuel after addition of 30 mgs. in-

hibitor A/100 cc 120 Measure of stability of cit-25 cc. of oil are placed in a bomb at a temperature of 212 F. under oxygen pressure at 100 pounds per square inch. The time in minutes is measured during which the pressure drops two pounds and is taken as the breakdown.

From the above it is apparent that the caustic washing considerably impairs the stability of the catalytically produced motor fuel which cannot be rectified utilizing known inhibitors.

EXAMPLE 2 A qualified material balance is given as applied to the drawing which will clearly demonstrate the results secured by utilizing the arrangement and sequence of stages as taught in the present invention.

Initial zone Feed 'ithdrawn Spent caustic (line 5) Caustic Treated (line 4 11 0 (line 6) Oil Mercaptans Salts of naphthenic and fatty acids What I claim as new and wish to protect by Letters Patent is:

1. Process for the removal of acidic compounds including naphthenic acids, hydrogen sulfide and mercaptans from a petroleum oil while retaining phenolic acidic compounds therein, which comprises passing the oil successively through two treating zones, the first being a preliminary treating zone in which the naphthenic acids and hydrogen sulfide are removed, and the second being the main treating zone in which the mercaptans are removed, the treating agent in both zones being an aqueous caustic soda solution of substantially the same caustic soda concentration in the approximate range of 10 to 20 Baum, the treatment in the main zone being effected with a relatively large amount, sufficient to completely remove mercaptans from the oil, of treating solution in the approximate proportion of 25 parts by weight of caustic soda solution to 100 parts by Weight of oil, said caustic soda solution also containing dissolved therein a sufficient amount of soda salts of petroleum phenols so that when contacted with the oil containing phenolic compounds not more than a minor proportion of the phenolic compounds dissolved in the oil will be removed therefrom into the caustic soda treating agent, the spent caustic solution from said main treating zone being then passed to a regenerating zone where mercaptans are removed by steam stripping and the thus regenerated caustic solution still containing dissolved phenolic salts is divided into major and minor portions, the major portion, comprising about 25 times as much as the minor portion, being recycled to serve as treating agent in the main treating zone, along with the addition of a small amount of 10 to 20 B. fresh caustic soda solution approximating /25 the amount of recycled solution, the minor portion of regenerated caustic solution containing phenolates being passed to the preliminary treating zone in which it is contacted with fresh oil in the approximate proportions of 1 part of treating solution to 100 parts of oil, the exact amount of said treating solution used being just sufiicient to remove hydrogen sulfide and naphthenic acids Without leaving any excess of caustic soda, whereby hydrogen sulfide and naphthenic acids are substantially completely removed from the oil and the phenolic salts present in the treating Secondary zone Feed Withdrawn Fresh Recycled caustic Recycled Trealted 0 (line 10) Hydrogen sulfide. Naphthenic and fatty acids. Sodium hydroxide a. Water Salts of mercaptans Salts of hydrogen sulfide. Salts of naphthenic and fatty acids From the above it is apparent that desirable phenolic type constituents ar retained in the oil and that the undesirable acidic constituents are removed.

This application is a continuation of application Serial No. 381,248, filed March 1, 1941.

agent dissolve in the oil, thereby leaving a spent aqueous caustic solution substantially entirely free of caustic soda and containing essentially sodium sulfide and naphthenates with not more than a relatively minor proportion of salts of the phenolic compounds originally present in the petroleum oil treated is a catalytically cracked naphtha which, when washed with a treating agent consisting or a caustic soda solution, is greatly impaired in stability and does not recover its stability upon addition of customary oxidation inhibitors, but when treated according to th process of claim 1 retains a major proportion of its original stability.

ANHOT P. HEWLETT.

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