US2478603A - Removal of sulfur - Google Patents

Description

Aug. 9, 1949. c. A. sTRATToN REMOVAL OF SULFUR Filed Dec. 29, 1945 I I l l l I JNVENTOR. CASTRAT ToN AT TORNE S Patented Aug. 9, 1949 Y' REMOVAL oF lSULFUR Charles A.v Stratton, Burgen: Tex., vassigner to Phillips Petroleum Company,.a corporation of Delaware Application December 29, 194.5,1sria1No- 638,402

i'nventionrelates to the treatment of hydrocarbons for the removal of sulfur compounds. V More particularly, the invention relates fto .the removal of sulfur compounds from lighter which they come in contact and, particularly in gasolines, for their influence on color land haze -`form'ation and their adverse effect on the susceptibility to fuel additives suchv as lead tetravethyl andvoxidation inhibitors. In conversions ofwhydrecarboncompounds the presence ofsulfur compoundsV is frequently detrimentalto the best results;` especially inthe vpoisoning and loss of,cata1yst, ifit be u-sed, and in the quality of th'evproduct whereA the sulfur originally present inthe feed is often concentrated, such as in polyf merization and alkylation processes in which light hydrocarbons are converted into motor fuels and the sulfur compounds .varecondensed into sulfur compound-s of similar Vvboiling range.Y

While sulfur compounds in hydrocarbon products,rjsuch as gasolines, may be rendered substantially innocuous by various refining treatments ,suchl as sweetening processes,A removal by absorption or adsorption, etc., it is preferable tovremove the sulfur constituents from theloriginal .mate

- rials Abefore lsubjecting the material to extensive reiiningor conversion processes in which the materials are involved. It is therefore an object of this inventionto provide Va Aprocess for the substantial removal of sulfur compounds vfrom hydrocarbons in which they are present.

lAnother object of the inventionis to remove sulfur compounds from light hydrocarbons in a novel combination of Washing treatments.

A'further object is toprovide for .the removal of 1 sulfur compounds from ,hydrocarbon mixtures `by a seriesfjof. lnterrelatedalkallne and plumbite treating operations.

.n 5 Claims. (crues- 33) Other objects will be apparent from the :specification and drawing in which the single gure is a schematic drawing of one embodiment of the invention. l

According to the present invention, a stream of hydrocarbons is consecutively contacted with a series of 'alkaline washes of progressively increasing strength, atleast the nal wash of Vwhich contains plumbitein solution. It is known that alkaline solutions are useful infreacting with and removing sulfur compounds and it has nowk been found expedient` and economical to include plumbite in the nal washing stage and to ad- Vance the washing solutions through the several stages 'until the alkaline solution'and/or plumbite is exhausted at which time the solutions may be regenerated. Y By the practice of the present method of treating and system of handling wash solutions, the effectiveness of the desulfurization is substantially increased. l-A better understanding of the invention may be hadv by reference to the drawing which illustrates an embodiment of the process in which a hydrocarbon mixture is introduced -by line I0 into a prewasher I I in which theV hydrogen sulde is substantiallyremoved by a solution of caustic. After contact with the'caustic solution the hydrocarbon is allowed to separatefrom the caustic solution which is removed with product soluble sulfur salts through line I2. Until depleted below a suitable caustic concentration, the mixture may be recycled to the inlet stream by line I3. Afterldepletion, the spent caustic solution may be withdrawn and fresh solution introduced. The treated hydrocarbon mixture is withdrawn via line I4 toa causticwasher I5 in whichl it is thoroughly contacted with an alkaline solutionwhich is recycledfrom the samefwasher by line I6.' Y"After `satisfactory contact,V the4 hydrocarbon mixture: is again separated and passed by line I1 tol asecond caustic washer I8 where it is again contacted with caustic'solution from recycle line 19, again" eiectedand the hydrocarbon is passed through line 20 to'a third washer 2| and con# tacted with recycle caustic introduced into the stream vialine 22. Aftertreatment. and separation therein the hydrocarbon is'conducted by line 23 toa fourth washer 24 in which it is contacted with' an alkaline plumbite solution from caustic Separation by stratification is storage 25 through line 26. During contact in this last washer mercaptans are converted to lead mercaptides as well as soluble alkaline mercaptides. The lead mercaptides of the lighter mercaptans precipitate and are collected in the alkaline aqueous layer upon the separation of the hydrocarbon. The desulfurized hydrocarbon is removed after separation and passed to further treatment and storage, as desired, by lineV 21. Solid lead mercaptide is collected in the lower portion of the washer 24 until it is desirable to augment the 'concentration of., plumbiterin the caustic solution or until a suiicient amount of precipitated mercaptide has accumulated for regeneration in regenerator 28 into which the mer-v captide is introduced through a funnel-.shaped passage 29 which i-s opened and closed by a valve 3B. Both expended caustic 'and lplumbite maybe regenerated simultaneously in the regeneration section as hereinafter described. solution containing unreactedplumbite and Yafter being substantially separated Ifrom precipitated lead mercaptides may be recycled and admixed with the hydrocarbons through line 3|. As the concentration or plumbitebecomes somewhat reducedby vreason of the removal of the lead through; reaction to form insoluble lead mercaptide salts, the caustic solution may be transferred by line 32 to caustic Washer 2| Whose caustic solution may at the same time be removed or transferred by line 33 :to the circulating system supplying the second caustic washer I8. Similarly the caustic. solution of washer Ij8 is transferred to the firstl washer I5 through line 34 and the 4substantially exhausted caustic solution -from washer l5 containing the soluble sulfur com Vpounds is removed by line 35 or passed to the regenerator via line 3S. Thus the caustic concentration in each. consecutive Washer isgprogressively higher for having been used a shorter llength, of time, the rstwasher l5 containing the Vlowest concentration. Air may beA introduced The caustic t into the regenerator through line t1V and Vspider Y distributor 38 and the regeneration may be accelerated by heating the solution being regenerated'. :Heat may be supplied through a heating coil 3.9 supplied with steam through line 4,0. Satisfactory regenerating temperature-s may be about 210 F. andfpreferably between 1D0-400 F. Entrained hydrocarbons and some disul-iides which form during regenerationare withdrawn as gases 'through line 4l while rthe major portionof the disuliides collects as an upper layer over :the caustic solution -in the regenerator and is. removed by line *42; AAny entrained liquid. materials may be removed from the overhead gas in trap 43. The regenerated caustic and plumbite are passed to storage through line 44 for recycle to Washer 24, YAdditional Water, litharge and caustic may be added as required by line 45.

The. system may be run through a series of abouttwenty-five "caustic changes without any attempt being made at regeneration vof the caustic :or lead, fresh lead and caustic solution rbeing added to Washer 24- at each change. The spent caustic in washer l5 may be dumped during Vthis period, and the lead 'mercaptide allowed to build up in the bottom of 'washer `24. Then, the washer may be cleaned out by any suitable means such as 'by hand and the lead mercaptide retained for use in regenerating future batches of caustic. Subsequently, each spent batch of caustic inthe ffirst washer "I5Jmay vbe regenerated by adding a portion of the stored lead mercaptide lowing equations:

Thegreaction between mercaptans and litharge (PbO). or plumbite (Na2PbO2) which is formed when litharge is dissolved in caustic may be expressed as follows:

Where R may be an alkyl group or hydrogen, in 'which latter case theV sulfur compound is hydrogen sulfide.

In regeneration the alkaline 'sulfur compounds vare oxidized to disuldswhich are removed. The

reactions occurring Vin 'the regeneration may be represented The disulde compounds Iare removed as described, leaving 4an aqueous solution of caustic `and litharge which willagain form plumbite sclution :suitable ffor recharging to the plumbitecaustic washer. OtherV reactions and products V'such as sulfates Vmay be forming'at the saine time but the principal Yreactions are assumed to be as described. The invention is not intended, however, to be limited by any discussion of theas- 'sumjed reaction andch'anges taking place. Y

By the practice of the present invention, vhvdrocarbonmix'tures which contain sulfur compounds are more effectively freed of those contaminating constituents. It is found that by desulfu'ri'zing according-to the present vprocess m'oreundesirable sulfur compounds are'r'emo'ved than by treating With'eitl'ierjcaus'tic :or plumbite solution alon'ea'nd that the final treatment Vwith caustic-containing -litharge reduces vthe 'sulfur 'con'te'nt of hydrocarbon stocks to a'point at which they may besatisfactorily utilized inVV particular conversions, such f'a's -alkylation and Vpolymerization where exceptionally -I'owsulfur content is desirable. Therefore limproved final conversion products rare 'possible without further treatment thereof.

As 'an example Viof the effectiveness ofthe 'invention "an alkylation 'stock consisting jmainly -of C4 hydrocarbons; with 'sorrre C3 and C5v constituents,V is liquefied and treated according to the presen-t. process. TheY untreated hydrocarbon mixture, containing 0108 per cen-t mer'capt'an sulfur and 0.0015 percent hydrogen sulfide sulfur, is treatedlin a prewasher with a CLD-per cents'olutionof caustic soda. Substantially'all ofthe hydrogen sulde lis converted to 'sodium sulfidewhich remains dissolved in the Vcaustic solution. The hydrocarbon vmixture V"is treated successively in the Icaustic washers, as described, V'andfis Icontactedfi'n the nal Washer'wiith :an-approximately twenty-five per centfcaiistic sodasolutionwhich contains 7.86 pounds of litharge (PbO) per barcal.

rel oroaustic solution. Atthe beginning ,of the :cycle with fresh caustic and plumbitel solution, :the:A liqueed light hydrocarbon. mixture isrecoveredfrom the processgwith,noghydrogen sulde suliureand lonly 0.001: percent of mercaptan sulfur. At the .point when thelead. salt has been substantially consumed as precipitated lead mercaptide'fand the mercaptan; sulfur conter'itroiA the .product hasarisen. to:'faboutf'0.0025'.` per "cent bf mercaptan sulfur, the solutions in eachiwashe aretransferredl tothe nextiin series before Ait,'"esh .plumbite-.caustic solution lis introduced inf; :the iinal washer and the solution from the iirstivasher is passed to the regenerator, mixed with the precipitated lead mercaptide and the mixture regenerated by heating and air blowing as described above. About 35 per cent of the caustic soda is spent in formation of sodium mercaptide and substantially all the lead content is consumed during the completion of the treating cycle. The mercaptan sulfur content of the product by this procedure averaged 0.0015 per cent which represents an improvement of 25 per cent over the product of a comparable treatment in which the litharge is omitted in the last washer.

If the hydrogen sulfide content of the original feed stock is negligible or for other reason a pretreatment of the stock is unnecessary, the prewasher may be omitted from the process and the hydrocarbon mixture treated as described thereafter. Similarly, additional or fewer caustic washers may be employed in the successive series of treatment and different concentrations o'f caustic may lbe used satisfactorily. Compounds, such as higher alcohols, stearates, etc. which are commonly used to prevent emulsication and which are not harmful to the process or its product may be used to prevent emulsiiication and foaming of the hydrocarbons in the caustic solutions. Likewise, caustic potash may be used in place of caustic soda if desired but the latter is usually more satisfactory and economi- Other minor changes will be recognized by those familiar with the art and may be made without departing from the spirit of the invention as disclosed and claimed below.

I claim:

1. A process for the substantial desulfurization of a relatively light hydrocarbon mixture containing sulfur compounds which comprises successively contacting a stream of said mixture with at least two concentrated caustic solutions of progressively increasing alkalinity in separate contact zones, contacting said stream in a final contact zone with a caustic solution containing litharge Without the addition of sulfur, separating the desulfurized hydrocarbon mixture and separating precipitated lead mercaptides in said nal contact zone, simultaneously transferring caustic solutions from each zone and said iinal zone to next preceding zone in line of hydrocarbon ilow upon the substantial depletion of lith- 6 and separating Yprec ipitaedleadrnfaeaptdes in saidnnal contact 'zongisimultaneously.transferring caustic solutions from each zone and 1*said nal zone -topnext precedirrgzone in line of hydrocarbon flow upon the substantial depletion of =litharge in iinal'zone',` .cycling spent caustic from the rst contact zone toa regenerating zone, adding said precipitated lead mercaptidesto fspent caustic in said regenerating zone, and regenerating the resulting mixture by blowingr the same withaini- Y .Y 3. A'p cess for substantially esulfurizingnor- :mally g'a'sousv hydrocarbons.' '.c ;tainingll` Vsul'rfiiir compounds "which comprises lidi'iefying said' hydrocarbons, successively contacting a stream of said hydrocarbons with at least two concentrated caustic solutions of progressively increasing alkalinity in separate contact zones, contacting said stream in a final contact zone with a caustic solution containing litharge Without the addition of sulfur, separating the desulfurized hydrocarbon mixture and recovering precipitated lead mercaptides in said nal contact zone, simultaneously transferring caustic solutions from each zone and said final zone to next preceding zone upon the substantial depletion of litharge in final zone, cycling spent caustic from first contact zone to a regenerating zone, adding said precipitated lead mercaptides to spent caustic in said regenerating zone, and regenerating the resulting mixture by blowing the same with air.

4. A process ior substantially desulfurizing a stream of gaseous hydrocarbons consisting substantially of butane which comprises liquefying said hydrocarbons, contacting said liquefied stream with a caustic solution in a prewasher to substantially remove hydrogen sulfide, successively contacting said stream with a concentrated caustic solution of progressively increasing alkalinity in at least three contact zones and with a plumbite solution comprising litharge dissolved in an approximate 25 per cent caustic solution in a iinal contact zone Without the addition of sulfur, separating the desulfurized hydrocarbon and recovering precipitated mercaptides from the caustic solution in the iinal contact zone after depletion of litharge therein, simultaneously transferring the caustic solution in each contact zone and said iinal zone to the next preceding contact zone in line of flow of hydrocarbons and transferring the spent solution from the first contact zone to a regenerating zone, removing said precipitated mercaptides from nal contact zone to said regenerating zone, simultaneously regeny erating said spent caustic and plumbite solutions,

and recycling the regenerated caustic litharge solution to the final contact zone.

5. A process for the substantial desulfurization of a relatively light hydrocarbon mixture containing sulfur compounds whic-h comprises successively contacting a stream of said mixture with at least two concentrated caustic solutions of progressively increasing alkalinity in separate contact zones, contacting said stream in a nal contact zone with a caustic solution containing litharge without the addition of sulfur, separating the desulfurized hydrocarbon mixture and separating precipitated lead mercaptides in said nal contact zone, simultaneously transferring caustic solutions from each zone and said nal zone to next preceding zone in line of hydrocarbon flow upon the substantial depletion of litharge in the nal zone, cycling spent caustic from the first contact zone to a regenerating zone, adding said precipitated lead mercaptides to spent caustic in umane' 8 said regeneratingzone, and regeneratingthe Number Y NameA VDate caustic litharge solution by blowing thel vsame 2,057,918 ARidgway Oct. 20, 1936 with air. Y' 150,170 `Keeling Mar. 14, 1939 CHARLES A. STRATTON. 2,164,665 Rogers et al. Julyf, 1939 5 2,314,217- Hyde et a1. Mar. 16, 1943 REFERENCE-s CITED f The followingl references arek of record in the me of this patent:

UNITED STATES. PATENTS Y GTI-IER REFERENCES VNiznrll': Systematic refining of cracked dis., tllates, JDur. Ind. Eng. Chem. (July 19265)', Pages 1.0 73310738.

N b N 4 Gruse et a1.: Chemical Technology of Petr uqw Stewf Jugelgg leum." McGraw-m1112001: co., New York c1942).

' Miner Aug. 25, 1936 P3593@

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