US2181036A - Method of treating hydrocarbon distillates - Google Patents

Description

' alkaline solution containng lead oxide, the

j group.

Patented Nov. 21, 1939 artists 2,18 3 PATENT .OFFICE'YI METHOD OF TREATING HYDBOCABBON DISTILLATES Virden w. Wilson, Buffalo, N. r., assignor to Buffalo Electro-Qhemical Company, Inc., Buffalo,

No Drawing. Application February Serial No. 123.481

10 Claims. (c1. res-2s) This invention relates to the treatment of hydrocarbon distillates andmore particularly to a mode of procedure whereby sour distillates are sweetened. I

.A hydrocarbon distillate obtainedby the distillation frompetroleum is sourf when upon treatment wtih an alkaline solution containing dissolved lead oxide, as, for instance, lead oxide,

dissolved in caustic soda, and elementary sulfur, a discoloration is produced at the interface of the gasoline and the aqueous solution. This test is generally designated as the doctor. test; the

doctor solution. A positive doctor test indicates that the distillates contain sulfur compounds, wherein the group SH is combined with an organic radical R or hydrogen.

As substantially all hydrocarbon distillates are sold according to rigid specification requiring that they be sweet, 1. e., show a negative doctor test, therefore, all distillates containing SH must be treated in some fashion to eliminate this Heretcfore, the method generally employed for sweetening sour distiilates comprised reacting the undesirable sulfur compounds of the type containing the SH group with a reagent obtained by dissolving lead oxide in caustic alkali, sodium plumbite and thereafter adding elementary sulfur. By this procedure RSH compounds are changed to innocuous di-sulfldes remaining in the distillate, or are removed from the distillate. In general, this sweetening procedure maybe illustrated by the following chemical equation It is generally recognized that the plumbite or doctor procedure is effective for sweetening gasoline or other sour distillates but suffers the disadvantage that the procedure is expensive and secondly, that it is necessary to add elementary sulfur in exact predetermined amounts in accordance withEquation 2 to prevent the addition of excess free sulfur which would produce a corrosive gasoline.

An object of the present invention, therefore, is the provision of a mode for sweetening sour petroleum distillates without the necessity of using sulfur with the production of a distillate showing a negative doctor test. Another object .01 the invention is toprovide a method for sweetening sour distillates that is relatively more ecobut not so vigorous as to attack unsaturated compounds present in the distillate. .qThus, an alcoholic caustic solution substantially free of water is preferably employed in the procedure of the present invention, the alkali being either caustic soda or caustic potash; dissolved in substantially anhydrous alcohol, as, for instance, methyl alcohol, ethyl alcohol, propyl alcohol, or other water soluble alcohol. The concentration ofcaustic hydroxide dissolved in the alcohol may be any quantity consistent with the solubility of' the caustic therein, although, in general, solutions of from about one-half normal to about two normal will be found to be practical for the procedure. The alcoholic caustic and the oxidizing agent may be added to the distillate concurrently or consecutively.

It is believed that upon the addition of the alcoholic caustic solution to the gasoline, any mercaptans contained in the gasoline are changed by the caustic alkali to meroaptides, the mercaptides being changed to dlsulfides upon reaction with the oxidizing agent.

In the-practical operation 0' he procedureit has been found preferable to u.-.e an amount of alcoholic caustic substantially in excess of that theoretically required for the content of me'rcaptans in the distillate 'to be sweetened, since the time of contact required to obtain complete conversion of the mercaptan is considerably reduced and is brought within practical operating limits. In general, two and a half to five fold excess of alcoholic caustic above that required by the mercaptan present in the gasoline has been found satisfactory. Representative results are outlined in Table 1 below where 100 cc.s of a crude gasoline containing 0.078% sulfur as mercaptan was agitated during a given time period of 10 minutes with the indicated normal caustic soda dissolved in substantially absolute methyl alcohol and the theoretical quantity of 100 volume hydrogen peroxide to oxidize the mercaptan sulfur.

Table I Percent of mercaptan Oc.'s ci-normal alcoholic caustic sum com verted Percent It will be noted that 2 cab of normal caustic soda represent approximately the theoretical quantity of caustic alkali required to exactlyreact with the amount of mercaptan present in the sample of gasoline and that within the given time limit a two and one-half fold excess of caustic alkali permits a substantially complete removal of the mercaptan sulfur.

In general, the alcohol used in making the alcoholic caustic. should be substantially anhydrous and contain less than about of water.

As is well known, the more acidic mercaptans, as, for instance, methyl and ethyl mercaptan and also hydrogen sulfide are readily removed by caustic wash and so are not troublesome in practice. In Table II is set forth the results of an investigation upon sweetening of a hydrocarbon distillate made sour by the addition thereto of specified mercaptans such as propyl, butyl, amyl and heptyl mercaptans. The sour distillate was treated with specified alcoholic alkali hydroxide solutions normal in strength and agitated minutes .and- 30 minutes in the presence of a slightexcess of hydrogen peroxide over that required for the conversion of -di-' sulfide.

The mode of-treatment on the experimental work was as follows: 100 cc. of the gasoline under test were pipetted into a clean glass bottle and 10 cc. of the caustic treating reagent were added. Immediately thereafter 0.2 cc. of 100 volume hydrogen peroxide was added. The

bottle was stoppered with a clean new cork stopper and was shaken for the appropriate length of time. In the conclusion of'this period of agitation the. bottle was removed and an amount of distilled water equivalent to the amount of alcohol originally added was pipetted "upper of which was decanted, filteredtoremove small amounts of still suspended alcohol and water and was then analyzed for mercaptan content, total sulfur, change inspecific gravity and other items of interest.' In the tablemethyl and ethyl alcohols are abbreviated in the usual way i 'asMeOH and EtOH respectively. p I

Table II Percent Percent of Percent Percent of of sulfur $capt-n of sulfur memptan I8 merl1! conll mer- 811 oon- 9" ca ten vested in carton vested in tin 10min. letln 30min. solution contact solution contact 'PRorYL MEROAPTAN on an 0100111000.-.. 0.1001 0.1001

Me 11400011---." 0.000 100 0.000 100 00 Ei0H-Na0H-' 00100 88.6 00002 01.0 00 Eton-K011"; I 0.000 100 M00 100 se sion-noun 0.00 100 0.000 100 turn. MERCAPTAN M0 n-Nson 11000 100 0.000 100 00% EtOH-NaOH... 0. 0212 01.1 0.0100 00.1 canton-noun" 0.000 100 0.000 100 AMYL MEROAPTAN.

i 0.1020 01020 in H-NeO 0. 000. 100 0.000 100 00% EtOH-NaOH.-- 0. 0001 n 2 0. 0214 70. 0 as. Et0H- KOH-..- 0. 000 100 0. 000 100 Harm. MEROAPTAII 11101. 0 1000 0.1000 MeOE-NaOH 0000 100 0.000 100 00% mon-xom. 0.000 100 0.000 100 at. EtOH-NaOH..- 0 0201 7a 1 0.0000 92. 0 abs'ston-xon..;; 0. 000 100 0 000 100 In Table m is set forth the results of an investigation of the effect of aqueous caustic soda upon various higher mercaptans dissolved in gasoline, 100 cc.s of the artificially soured gasoline being agitated with 10 cc.s of normal caustic for the time indicatedand the residual sulfur determined. The percent sulfur as mercaptan.

in the original samples was approximately 0.1%.

The mode of treatment contemplated in a plant process based on this experimentaleviden'ce would be as follows: Sour cracked gasoline which had been stabilized for the removal of most of the butane and all of the hydrogen sulfide is first contacted with a -=25 Be. solution of caustic soda. This may be obtained in part at least from the recovery still for methanol to be mentioned subsequently. The aqueous caustic treatment will remove the more acidic mercaptans andsucceed in lowering the sulfur content of the gasoline by the amount of low molecular weight mercaptan removed. The caustic washed gasoline is then pumped through a mixing pump into a pipe coil. At the mixing pump a mode-- termined amount of alcoholic caustic containing suflicient potassium or sodium hydroxide to react with all the mercaptans present in the gasoline is added andfan amount of concentrated hydrogen peroxide 's uiilcient to insure sweetening is added at the same time. It has been found that better results be obtained by such concurrent for recirculation throu8hthe process. The gasoline is then passed into a washer where it is contacted with a vigorous scrubbing spray oi! water, the volume of water being kept as low as possible, yet sufiicient employed to insure complete removal and separation of the aqueous alcoholic layer from the gasoline. The concentration ofthe alcohol in this layer will be 30-50%.

Buch treatment should leave less than one-half of 1% of the alcohol employed in the, gasoline.

Thisamount of loss willnot appreciably aifect treating costs since the volume of alcohol employed will be in the neighborhood of 5-7% of the volume of the gasoline treated. "The sweetened water-washed gasoline can then be passed directly to storage while the alcohol extracted by the final water wash would be returned to a free-- tionating column, the heat from which could be supplied by exchangers in connection with the cracking still column condenser. The'overhead from the alcohol fractionating column would be,

condensed in the second set oi heat exchangers to eilect maximum heat recovery and the recovered methanol run to storage, thence to. mixing tanks where iresh alcoholic caustic would be added in quantities sufllclent to insure adequate caustic present in the gasoline at all times. The process of treating and alcohol recovery can thereby be made cyclic and the amount of alcohol required ior'continuous operation will remain substantially constant and need be replaced only tor slight losses dueto carry-over in the gasoline or to such losses as may occur in tractionation.

From the foregoing it will be seen that the present invention provides a method for sweetening sour hydrocarbon distillate by the use of a substantially water free solution of caustic alkali in conjunction with an oxidizing agent capable of changing mercaptides to disulfldes, but not attacking unsaturated compounds in the gasoline, that is to say, the percompounds, which are materials capable oigenerating hydrogen peroxide in solution.

What is claimed is:

1. The method or sweetening sour hydrocarbon liquid distillates which comprises treating the distillate with an alcoholic solution of caustic aikali and an oxidizing agent yielding hydrogen peroxide.

2. The method of sweetening sour hydrocarbon distillates which comprises treating the liquid distillate with substantially water free alcoholic caustic alkali and an oxidizing agent capable of yielding hydrogen peroxid 3. The method of sweetening sour hydrocarbon distillates which comprises adding alcoholic caustic alkali to the liquid distillate and then treating the mixture with an oxidizing agent capable of yielding hydrogen peroxide. 4. The method of sweetening sour hydrocarbon distillates which comprises agitating the liquid distillate with alcoholic caustic alkali and an exidizing agent capable of yielding hydrogen peroxide and capable of oxidizing mercaptides to disulphides.

5. The method of sweetening so'ur hydrocarbon distillates which comprises treating, the liquid distillate with an amount of alcoholic caustic alkali having sufllcient caustic content to change the mercaptans in the sour distillate to mercaptides and treating the mixture with suflicient of suillcienthydrogen peroxide to render the distillate negative to the doctor test.

'7. The method of sweetening sour hydrocarbon distillates which comprises treating the liquid distillate with an amount of alcoholic caustic a1- kali having sufficient caustic content to change the mercaptans in the sour distillate to mercaptides and treating the mixture with sufiicient of an oxidizing agent capable oi yielding hydrogen peroxide to change the mercaptans to disulfldes and regenerate the alkali.

8. The method of sweetening sour hydrocarbon distillates which comprises treating the liquid distillate with 4-8% 01 an alcoholic caustic alkali, the alcohol being substantially anhydrous methanol, having a caustic content in excess of the amount required to react with the mercaptans in the distillate and adding thereto at the same time suflicient hydrogen peroxide to render the distillate negative to the doctor test.

'9. The method of sweetening sour hydrocarbon distillates which comprises treating the liquid distillate concurrently with 44% 01' a methanol solution of caustic alkali, having a caustic content sufiicient to react with all the mercaptans present in the distillate and a sufllcient quantity of hydrogen peroxide to render the distillate negative to the doctor test with subsequent removal of the excess'alcohol by water washing.

10. The method of sweetening sour hydrocarbon distillates which comprises adding to the liquid distillate an alcoholic caustic alkali solution, the alcohol being chosen from the water sol-' uble monohydrlc alcohols in substantial anhydrous condition, and concurrently treating the solution so obtained with an oxidizing agent capable oi yielding hydrogen peroxide.

VIRDEN W. WILSON.

CERTIFICATE 0F CORRECTION.' Patent No. 2,181,056. Novembr 21,- 19 9.

' YI RDE N w.- wI soNJ" .It is hereby certified. that prrorappeai'fa in the printed. specification of the above mmbered patent zjequiring corictioi; as follows: Page 2, first column, 1ine'l8,.f9r the aord -"of"-after "converaibn nqad to} page-5, first column, lin'e 26, claim 1,- ;trikdut "liquid? and insert the same before "ditil late' in lifie 27, same claim; andthgt the said Letters Patent should be read this correction thereiti that the same may corifom to the rec'ord of the case 111th; Patent @3190. I v v Signed and. sealed thiq 26th day of December; A.- D. .1959.

Henry Van Arsdle} (Sel) a 4 Acting onnnissioner 'bffatents.