US2181037A - Method of sweetening hydrocarbon distillates - Google Patents

Description

Novyzl, 1939.

Filed March 4, 1937 2 Sheets-Sheet 1 Nov. 21, 19,39. v2.181,03',v

METHOD oF swEETENING HYDROCARBON DISTILLATES -v w. wlL'soN 2 sheets-sheet 2 Filed March 4, 1937 2 2 irma s 39 'mammal ammu on Nl aimons unnns Nvldvoaaw wwwmo y,

INVENTOR Y'xrdey uson,

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ATTORNEYS Patented Now-21, 1939 UNITED STATES PATENT ol-Fica i METHOD or' swEETENnva mnocAnBoN l nrsmn'rns Vir-den W. Wilson,

falo, N. Y.

Buffalo, Builalo Electro-Chemical Go N. Y., assignor to mpany, Inc., Buf- Application March 4, 1937, Serial No. 129,011

10A claims.

This invention relates to the sweetening of hydrocarbon distillates andmore particularly to sweetening of such distillates by the use of causticsolutions'of methanol in conjunction with materials, evolving hydrogen peroxide 'in solu- Inha vcopending application; Ser. No.` 123,481, ithas Vbeen pointed out that substantially water free alcoholic solutions of caustic alkalies and hydrogen peroxide used in conjunction are eiective sweetening agents -for hydrocarbon disally Water free solution the useV of methanol solutions of caustic alkali wherein substantial amountsof water may be` present, this solution being used in conjunction with hydrogen peroxide for the sweetening of hydrocarbon distillates that are designated as sour" and,. therefore, contain'sulphur as mercaptan or as hydrogen sulfide.

It is an object oi the present invention to provide a method for sweetening hydrocarbon distillates wherein an aqueous methanol solution of caustic is agitated with the distillate to be sweetened and wherein separation of the distillate and the alcoholic solution is readily secured without the necessity of adding large quantities of water and wherein, therefore, a large steam consumption for alcohol recovery is eliminated.

In thedrawings Fig. 1 is a iiow sheet illustrating the procedures of the 2 is a graph of the effect of aqueous methanol-` caustic solutions and hydrogen peroxide upon heptyl mercaptan. Fig. 3 the location of sulfur in a sample of unsweetened washed gasoline and Fig. 4 is a graph showing the location of the sulfur in a sweetened solution of the crude of Fig 3.

In general, therefore, it has been determined in accordance with the procedures of the present invention that a solution of sodium or potassium hydroxide or other caustic alkali in methyl alco- `hol containing from about 30 to 50 grams, more or less, of caustic alkali per liter of alcohol, when used in conjunction with suiilcient hydrogen peroxide, to react with the mercaptans present in the hydrocarbon distillate to be treated. will conpresent invention.. Fig.

is a graph showing,

vert substantially all the mercaptans therein to the corresponding organic disuldes, thus eiiecting sweetening of the sour hydrocarbon disillates. The treatment may be eiiected by agitatlng the methanol-caustic solution with the distillate and the hydrogen peroxide. The period of contact between the solutions will vary in accordance with the manner of treatment, in general, the more vigorous the agitation the more intimate the contact of the solutions. the more rapid the j sweetening. Upon completion oi the agitation, a considerable portion of the methanol solution. of caustic alkali will separate from the distillate and this maybe withdrawn and reused without further treatment since the disuliide, produced by the oxidation of the mercaptide willbe found in the hydrocarbon. A flu'ther quantity of recovered, if desired, from the preparation oi further quantities of `methanol caustic solutions.

As an eple of the efiicacy of the procedure of this invention, a synthetically sour gasoline was made from an unleaded, uncolored and sweet gasoline by adding heptyl mercaptan thereto and treating 100 cc.s of the synthetically soured gasoline with 1G cc.s of a methyl alcohol normal caustic solution and 0.2 cc.s of hundred volume hydrogen peroxide. i

Table I i Time ol treatment 0f methanol normal caustic alkali and nhydrogen |51 ten minutes as shown in Table H.

from@ n' l Percent Time oi Percent mag. ms converted ment mercaptan or removed 1o 0.000 10c 10 0.000 100 10 0.000 100 l 10 0.000 100 .As has shown above, the lower molecular the more readily removed of the presence of water in the methanol-caustic solution, a gasoline synthetically soured with lieptyl mercaptan was treated with aqueous methanol normal caustic of varying percentages of water by volume with the results set forth in Table III and in the graph in Fig. 2. It will be noted that with percentages of water above about 40 .volume percent very little sweetening action is observe'd. liis shown in the graph, the curve rises steeply and at about 60 volume percent ol' methanol conversion occurs. In each case the caustic concentration was maintained at 40 grams per liter of solution. A 100 cc. sample of the synthetically soured gasoline was treated for 10 minutes with l0 cc. of the treating solution and 0.2 cc. of 100 volume hydrogen peroxide.

. weight mercaptans are land to show the eii'ect Table III Percent Percent Volume percent methanol alcohol nslhqega converted I mwaptan or removed 40 O mercaptan 0. 07l7 None. 0. 000 100. 0. 0019 97. 3 0. 0066 49. l 0. 0454 36. 5 0. 0610 15.0 0. 0602 9. 0

In the copending application enumerated above it was shown that substantially water free water soluble mono-hydric alcohols containing caustic were effective in changing mercaptans to mercaptides, the latter being oxidized to disulnde by hydrogen peroxide or a subtsance liberating hydrogen peroxide. All of these alcohols form constant boiling mixtures with water except methyl alcohol.` In the instant invention, methyl alcohol which does not form a constant boiling mixture with water, may be used together withwater in solutions containing .above about 60 percent by volume of methyl alcohol as the solvent for the caustic alkali such essodlum or potassium hydroxide or other caustic alkali capable of forming `mercaptides as the treating solution.` The'greater .the amount of water originally present in the methanol solution the lesserv the quantity of methanol remaining in the distillate after agita` tion of the aqueous-methanol-caustic 'solution therewith and minimal quantities of wash water' are needed to extract the residual methanol from the distillate.

Although synthetically soured gasolines are representative of sour gasoline .encountered in the field, and sweetening procedures found successful upon gasoline containing the higher mercaptans can lbe used in refinery practice, a cracked distillate was treated as below.

A sample of a sour West Texas crude cracked fractions of collected and l enanos? l peroxide treatment in a contact time of less than Y gasoline, representative of the worts type of sour gasolines made in the United' States was treated successfully by agitating the gasoline -with a methanol-caustic solution and the appropriate amount of hydrogen peroxide.

Table IV Percent Treating solusuiiur regx Time of contact, minutes tion N caustic maining or com in methanol as mercaptan vetted Original gasoline 0.0162 l0.` 0.1 cc 0.0075 90. 2

100 vol. H110: l0 0.2 cc. Trace. 90. 9

lll) v01. H10: l0 0.2 cc. 0.0068 91.0

50 vol. H10: 10 0.3 cc. 0. 0032 95. 8

50 voi. H10: 10 0.4 cc. Trace. 90. 9

50 voi. H10 l0 0.5 cc. 0. 000 100.0

. 50 vol. HOi

The action of methanol-caustic-peroxide is a true sweetening of the sour West Texas cracked distillate as shown by the results set forth in Table through a fractionating column and succeeding the total sulfur and mercaptan sulfur determined. Another sample was agitated with methanol-causticperoxide for 10 minutes and then fractionated and the total sulfur and mercaptan sulfur determined on each fraction. The sulfur content of the original crude gasoline before sweetening was found to be 0.2760% sulfur by weight; the mercaptan content 0.078'l% by weight. The graph of the sulfur content of the various fractions is shown in Fig. 3. An integration of this graph shows the sulfur content to be 0.282% by weight, a figure in good agreement with that found by tests.

After sweetening, the sulfur was found to be 0.2555% Fig. 4. The fractions are shown by integration to contain 0;2490% sulfur by-weigl'rt. sulfur in the still bottoms oramples, hydrogen peroxide has been employed to oxidize the mercaptides to disulfides, other substances generating or liberating hydrogen peroxide in solution may be substituted in equivalent quantities, for instance, sodium peroxide, the perborates, percarbonates, persillcates and the like.

Referring to Fig. 1 of the drawings, cracking still products which have been passed through a hot oil separator l0 for removal of the liquid products and subsequently rstabilized for the removal of propane and hydrogen suliide are first contacted with a solution of caustic soda containing to 20% sodium hydroxide as will be discussed later. A portion, if not all of the caustic soda necessary for this initial, treatment maybe obtained as bottoms from themethanol recovery' the sulfur content Lofthe gasoline in proportion to the amount of low boiling mercaptan present in the cracked stock. The caustic-washed gasoline IV. The "crude gasoline was distilled' conversion of mercaptan to arance? v3 is then pumped through a mixing pump I2 either into a pipe coil or into a large turbulence pipe equipped with staggered oriiice plates. At the mixing pump a predetermined amount of meth- 5 anol caustic containing sufllcient sodium hydrox ide to react with all of the mercaptans present in the gasoline is added through one feed line into the pump, while an amount of vconcentrated hydrogen peroxide sufllcient to insure complete sweetening is added concurrently by means oi' a proportioning pump or other suitable methods. Such a procedure has been found to yield better results than contacting the alcoholic alkalles and hydrogen peroxide in series, although such a proc edure is entirely possible if advantages for this operation could be shown in plant operation.

The product discharged from the pipe coil or .mixing chamber I3 consists of a ilne dispersion of alcoholic"caustic in the gasoline together with small quantities of hydrogen peroxide which have not reacted. For economic reasons it is desirable to keep this amount of free peroxide at a minimum. The dispersion of caustic and gasoline is discharged into a settling tank Id where a considerableproportion i the alcoholic caustic settles to the bottom a d may be withdrawn for recirculation through the mixing pump and the pipe coil. The quantity of methanol separating at this point will depend upon theconcentration of water in the original methanol solution. The upper layer in the settling tank Id which contains the remainder of the'alcohol and a small amount 'of sodium hydroxide in dispersion in the gasoline is then passed into a washing 'tank I5 where it is contacted with a vigorous scrubbing spray of water. The volume of water is kept as low as practicable to insure complete removal of the alcohol from the gasoline and separation of the aqueous layer without detrimental emulsion for- 40 mation. 'I'he concentration of the alcohol in the v lower aqueous layer which settles in the washing tank will vary from v1i) to 50%, depending 'on the nature of the hydrocarbon from which the alcohol is removed. Such treatment will leave in the gasoline less than about one half of one per cent f of the methanol employed for the treatment, proalcoholic content of the settling tank bottoms is 60 recovered in the usual manner.

washed gasoline from which all traces of the treating reagents have been removed, is then run directly to storage without the customary 24 to 48 hour settling period necessitated in the doctor treatment for removal of the nely dispersed lead suliide sludge. The alcohol extracted by the water wash is then pumped through a series of heat exchangers I1 to a bubble plate fractionating column II. 'I'he '0 overhead from this alcohol fractions-ting column is condensed in a set of heat exchangers I8 to aliect maximum heat recovery. The recovered methanol is run to storage I9 from which it can be pumped to mixing tanks where fresh alcoholic 5 caustic is made up in quantities suicient to inl distillate with an oxidizin sure adequate caustic supply at the primary mixing pump at all times. The aqueous solution of caustic soda obtained as bottoms from the fractionating column maybe discarded or may be used in the primary cracked gasoline caustic s washers as mentioned in the preceding paragraph of this discussion. e process of treating and nous operation will remain substantially constant lo or gasoline carry-over losses become appreciable:

what is claimed is:

2. The method of sweetening sour hydrocarbon t' distillates which comprises treating the liquid ing hydrogen peroxide, and a methanol solution in greater amount than the water.

3. The method of sweetening sour h dr distillates which y 0cm-bon 25 tion of caustic alkali and water, and a suilicient at least by volume of methanol, iicient quantity of an oxidizing agent capable of of yielding hydrogen peroxide.

8. The method of sweetening sour hydrocarbon distillates which alkali, thereafter with a' methanol solution or 7g Y and hydrogen rcmde, per- 'e to settle and separate ianto d clowcr mex oi end withdrawing the alkali and water, mitting the mixtur en upper layer of distillate methanol caustic solution i lower layer.

water, and an oxidizing agent hydrogen peroxide, the mixture and sub c caustic alkali and capable of yielding the distillate from to e water wesh.

l0. A method oi distinctes which com distillate with e. methanol s sweetening sour hydrocarbon prises txeating the liquid elution of `a, caustic

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