US2413938A - Refining hydrocarbon distillates - Google Patents

Description

Patented Jan. 7, l947 REFINING HYDRO CARBON DISTILLATES Chester E. Adams, Highland, and Theodore B.- Tom, Hammond, Ind., assignors to Standard Oil Company, Chicago, 111., a corporation of Indiana No Drawing. Application November 20, 1944, Serial No. 564,410

9 Claims. 1

This invention relates to the extraction of weakly acidic substances from hydrocarbon solutions and more particularly it relates to the extraction of mercaptans from hydrocarbon oils such as petroleum distillates, naptha, gasoline, kerosene, etc. In the manufacture of gasoline and other petroleum distillates known in refinery practice as light oils, it has long been a problem to remove therefrom ill-smelling sulfur compounds which are primarily mercaptans. Certain processes such as the doctor treating process have been employed to convert mercaptans into other sulfur compounds such as disulfides'which are less objectionable from the standpoint of odor.

dimethyl ether, carboxy methylethylether, otherwise known as ethoxy acetic acid, carboxy diethyl ether, or, w dicarboxy glycol dimethylether, etc. The carboxy ethers of this invention include primarily the alkoxy acids of which the acid radical contains from 2 to 4 carbon atoms.

In addition to ethoxy acetic acid mentioned above, we may employ particularly propoxy acetic acid and butoxy acetic acid. We may also employ the methyl and ethyl ethers of malic, lactic and tartaric acids.

Other suitable ethers are the methyl and ethyl ethers of hydroxy valeric acid and anisic acid.

In a y g out our process, the hydrocarbon distillate containing mercaptans or other weakly acidic material is contacted preferably in a countercurrent extraction tower with a strong alkaline solution of the carboXy ether solutizer. For this purpose, sodium or potassium hydroxide may be used, preferably the latter, in a concentration However, this conversion does not decrease the of about 2 to 6 normal free caustic above that sulfur content of the gasoline and it has been combined with the solutizer agent. The conceniound that the disulfides themselves are quite obtration of solutizer employed will usually be jectionable from the standpoint of gasoline detowithin the range of about 5 to 40 percent on the nation characteristics. basis of free carboxy acid in the alkali solution. Numerous processes have been devised for ex- Usually the carboxy ether concentration falls tracting the mercaptans completely, thus prowithin the range of 1.5 to 4 molar. The extracducing a gasoline of higher knock rating and tion step is preferably carried out at ordinary higher susceptibility to knock rating improvetemperature, for example to F., and the ment resulting from the addition of tetraethyl solutizer solution containing dissolved mercaplead. In general, these processes have employed 5 tans or other weakly acidic substance is withstrong alkali solutions in conjunction with cerdrawn from the extractor and separately regentain mercaptan solubilizing agents known as erated after which it is recycled to the extracsolutizers. tion step. The regeneration operation consists in One of the objects of this invention is to proremoving from the caustic solutizer solution the vide an improved solutizer for the extraction of 3c dissolved mercaptans or other weakly acidic subweakly acidic substances from petroleum distilstances, and is preferably carried out by blowing lates. Another object of the invention is to prowith air, for example at a slightly elevated temvide a process of removing mercaptans more eiperature, e. g., to F. It is desirable to fectively from gasoline and other petroleum disavoid subjecting the solutizer solution to a temtillates by means of a solution which can be read- 35 peratule sufficiently high accelerate materially ily regenerated and recycled in the extraction hydrolysis of the carboxy ether employed; operation. A further object of the invention is In the regeneration operation, part of the merto provide a solutizer which is inexpensive and captans may be removed by dissociation and at the same time highly effective and which may evaporation and part by the oxidizing action of be employed in combination with other solutizers. =10 the air converting them to disulfides which are According to our invention we employ as a no longer soluble in the solutizer solution. These solutizer in our process the alkali metal salts of disulfides may be removed as an upper oily layer the carboxy ethers having from 3 to 8 carbon and, if desired, a hydrocarbon solvent may 'be atoms which we have discovered to be highly efemployed to assist in their removal from the reiective for the extraction of mercaptans occur- 45 generated solutizer solution. The solutizer soluring in light petroleum distillates, for example, tion is then recycled to the continuous extraction straight-run or cracked gasoline, heavy naptha, step of the process for the accumulation of more etc. We have found that carboxy ethers having mercaptans. from 4 to 6 carbon atoms are especially effective. The regeneration reaction may be accelerated Typical examples of our solutizers are carboxy 50 by employing catalysts which have the ability to speed the oxidation of the mercaptans. For this purpose certain alkali-soluble metal oxides may be employed, such as the oxides of lead, tin, etc. but we prefer to employ compounds of the character of phenols and polyphenols in accordance 3 with the teaching of the U. S. patent of Pevere, 2,015,038 (September 17, 1935). According to this method there is added to the solutizer solution a small amount of a phenol or polyphenol such as hydroquinone, catechol, pyrogallol, gallic acid, tannic acid, etc;, using a concentration of about 0.1 to 1 percent, thereby greatly increasing the rate of regeneration in the presence of air or oxygen. One very significant benefit resulting from the use of these phenolic catalysts is that they enable regeneration to be carried out at a lower temperature, for example room temperature, thereby reducing hydrolysis of the carboxy ether solutizer which would occur, were the solution re- 1 generated at substantially higher temperatures In the treatment of certain petroleum stocks, particularly cracked gasoline containing small amounts of phenolic compounds, especially cresols, it is desirable to precede the extraction with an alkali washing step to remove phenols, cresols, etc., thus preventing an excessive amount of such phenolic substances accumulating in the solutizer solution. In the treatment of such phenol-containing stocks, however, there is often a distinct advantage to permitting a controlled amount of such phenols, cresols, etc., accumulating in the solutizer solution, and we have found that the combination of cresols and our carboxy ethers provides a very effective reagent for extracting mercaptans. We prefer to control the amount of cresols in the range of about 1 to 3 normal concentration. Inasmuch as the distillate extracted by such a solution has been found to carry away in solution a small amount of cresols in the concentration which is in equilibrium with that in the solutizer solution, and inasmuch as cresols exert a valuable antioxidant effect on the treated gasoline, particularly in the case of cracked stocks, it is clearly desirable to employ a solutizer solution containing cresols. Other solutizers besides cresols may be employed with our carboxy ethers and a suitable proportion is a molar ratio of 0.2 to 0.8.

The following table gives the results obtained in the extraction of a sour naphtha containing primarily butyl mercaptan as an example of a weakly acidic substance. Removal of the butyl mercaptan is indicated by the copper number of the naptha. Extraction was carried out in the ratio of one volume of solutizer solution to five volumes of naptha in a single batch extraction step. The solutizer was ethoxy acetic acid, or isopropoxyacetic acid, alone or employed with cresol.

be seen from these data that excellent extraction of mercaptans was obtained in test 2 by the use of 3 normal potassium ethoxy acetate in 6 normal KO-H solution and that the combination betiveen ethoxy acetic acid and cresylic acid gave even more effective mercaptan extraction in tests 3 and 4. Isopropoxyacetate in test 8 was even more effective than the ethoxy compound in test 2. In a countercurrent operation it is easily possible to reduce the mercaptan concentration to a point at which the treated gasoline will react sweet to the doctor test. However, it may be more economical in practice to remove the major portion of the mercaptans from the stock by solutizer extraction and then treat the stock further in a separate sweetening operation with doctor, hypochlorite, etc., to produce a stock which will pass the doctor test where that is desired.

The copper number referred to above is determined by titrating a 100 ml. sample of naptha with standard ammoniacal copper solution, 1 ml. of which is equivalent to 1 mg. mercaptan sulfur per 100 ml. (1 copper number). The end point is observed when the blue color fails to be discharged after shaking.

Having thus described our invention, what we claim is:

1. The process of extracting weakly acidic SUD- stances from hydrocarbon distillates which comprises contacting said distillates with an aqueous solution of an alkali metal hydroxide and a solutizer comprising an alkali metal salt of a carboxy ether containing from 3 to 8 carbon atoms.

2. The process of removing mercaptans from a petroleum distillate which comprises contacting said distillate with an aqueous solution of an alkali metal hydroxide and a solutizer comprising an alkali metal salt of a carboxy ether containing from 3 to 8 carbon atoms.

3. The process of claim 2 wherein said alkali metal is potassium.

4. The process of extracting weakly acidic substances from hydrocarbon distillates which comprises contacting said distillates with an aqueous solution of an alkali metal hydroxide and a soluhydrocarbon distillate which comprises extracting said distillate with an aqueous solution of an alkali metal hydroxide and a solutizer comprising a mixture of alkali metal cresylate and an alkali metal salt of a carboxy ether containing from 3 to 8 carbon atoms.

Composition of solutizer solution 6N KOH, 2N EtOCH2COOK 6N KOH, 3N EtOCHzCOOK 5N NaOH, 3N EtOCHzCOONa... 4N KOH, 3N i-ProOCHzCOOK 5N KOH, 2N i-ProOOHzCOOK.-- 4N KOH, 2N i-ProOCHzCOOK, N cresylate 3N NaOH, 2N i-ProOCHzCOONa, 1.5N cresylate 1 The once-used solutizer was used again: copper No. 100 7.

The efficiency of extraction is indicated by the coefiicient, Kq which is the concentration of mar-- captans in the caustic solution divided by the concentration remaining in the naptha.

6. The process of removing mercaptans from a sour hydrocarbon distillate which comprises extracting said distillate countercurrently with It will an aqueous solution of an alkali metal hydroxide containing sufiicient alkali metal salt of ethoxy acetic acid to increase substantially the solubility of said mercaptans in said solution.

7. The process of claim 5 wherein the concentration of free alkali metal hydroxide in the said solution is about 2 to 6 normal and the concentration of the said ethoxy acetic acid is about 1 to 4 normal.

8. The process of removing mercaptans from a sour hydrocarbon distillate which comprises extracting said distillate countercurrently with an aqueous solution of an alkali metal hydroxide containing sufilcient alkali metal salt of propoxy acetic acid to increase substantially the solubility of said mercaptans in said solution.

9. The process of removing mercaptans from a sour hydrocarbon distillate which comprises extracting said distillate countercurrently with an aqueous solution of an alkali metal hydroxide containing sufiicient alkali metal salt of butoxy acetic acid to increase substantially the solubility 10 of said mercaptans in said solution.

CHESTER E. ADAMS. THEODORE B. TOM.