US2514997A - Method for removing sulfur and its compounds from nonaromatic hydrocarbon fractions - Google Patents

Description

July 11, 1950 c. M. FLOYD 2,514,997

METHOD FOR REMOVING SULFUR AND ITS COMPOUNDS FROM NONAROMATIC HYDROCARBON'FRACTIONS- Filed June 1, 1948 SULFUR FREE I0 bonnsuszn couoznssa EXTRACT RAFFINATE non-Anounlc mnnocnaon FEED MERE-UP SOLVENT I H SOLVENT r --'-l 4 Z' I a 6 F I6. I.

Ex'rnAc'r' F IG. 2.

26 RAFFINATE non-noun"; nvnnocmaou FEED 'a e ,INVENTOR.

MAKE-UP SOLVENT Patented July 11, 1950 UNITED STATE-1s PATENT oFFlscli';

M'ETHQD FOR REMOVING SULFUR AND ITS COM-POUNDS FROM NONAROMATIG HY- DROCARBON; FRACTIONS Clyde M ..F;Ioyd;,Woost.er, Tex-., .assignor, by mesne assignments,. to Standard. Oil Development Company, Elizabeth, N. J.,. a corporation of Delaware Application J-unel, 1948,. Serial No... 30,236:

I 6 Claims. (01. 196"2 4')' sulfur and its compounds. from non-aromatic hydrocarbon. fractions. The invention has. particularly to-do withthe solvent extraction of .nonaromatic hydrocarbons to remove. sulfur compounds therefrom.

Heretofore, it.has been known to. remove sulfur and its, compounds from. hydrocarbon. fractions containing them by contacting the sulfurcontaining fraction with strong. sulfuric acid. While. the. strong. sulfuric acid effectively reduces the: sulfur content of hydrocarbon. fractions, it also converts desirable hydrocarbons to less desirable. compoundssuch as sulfonated derivatives of sulfuricacidr Thesulfuric. acidmay also polymerize low boiling. hydrocarbons. to less desirable. high. boiling hydrocarbons. In effect, while the sulfuric acid reducesthe sulfur content of hydrocarbon fractions, it alsocauses. aloss in yield of the hydrocarbons by conversion. to less desirable-products.

Another method of reducing sulfur contents.

pounds, but convertathe sulfur compounds to a form. where they do not. cause. detrimental resultswhen the'hydrocarbon fraction. is employed as a motor fuel. However, conversion. of the. sulfur compounds by: the so-called sodium plumbite treatmentusually requires some after treatment, such-as distillation. andthelike, to. separate the converted sulfur compounds from the desirable hydrocarbons.

Itisalso well known in the: art to treat petroleumoils; with various solvents. to segregate the relatively more. paraffinic constituents. from the relatively lesssaturated constituents. Conditions are selected-in the process so thatthemineral oil contactedwith the solvent at a temperature below that at which complete miscibility. occurs. The solvent. usually selected. is. from the class whichhas-a preferential selectivity for the more aromatic compounds as. compared with the more parafiinic. compounds. Solvents. of. this class are, for example, phenoL. furfural, sulfur dioxide, nitro-benzene', aniline, organic esters and. the like. Allzof. these solvents have the disadvantage theta: separation betweenthe aromatic constituents and. the olefinic: constituents is not ob.-

tainedwith. anyhigh. degree of selectivity. Itis.

2. possible to. obtain alseparationbetween the. more or less, unsaturated compounds; which are. representedrby the aromatic and olefin hydrocarbons and the: aliphatic compounds as. represented by the paraffins but itv has been. impractical to segregate the aromatic hydrocarbons from the ole,- fins..when employing solvents. of the class. enumerated hereinabove.

The prior art Workers have also taught. that aromatic hydrocarbons. may. be separated! from mixtures thereof with other hydrocarbons by selective solvent extraction with. a poly-olefin-glycol. having a molecular weight above about? 1,000. The poly-olefin glycol is quite eff ecti've, in obtaining substantially pure. aromatic hydrocarbons from. mixtures thereof.

I have now discoveredthatsulfur andQitsderivatives may be removed. from hydrocarbon fractions. containing. themby extracting;- the. sulfur-containing hydrocarbon with a poly-olefin glycol. having: a molecular weight-in the range from. about 400130 4,000..

In accordance with the-presentdnvention hydrocarbon fractions such as those. boiling. below about.1- F. and those containing .sub'stam tially no aromatic hydrocarbonsjand those. from which. the aromatic hydrocarbons have been. removedgaboiling. up. to. about 60.0? may be. extracted-.with a poly-olefin. glycol, such.- as poly ethylene g-lycol,. having a molecular Weight. in the 1 rangefrom about 400 to 4,000 so thata fraction comprising, essentially non-aromatic.- hydrocarbons and, substantially; free: of sulfur compounds. is obtained;

In the present invention; mineral, oilrandLother hydrocarbon fractions. boiling below: about 1.65? F. andhigh boiling hydrocarbon fractions from which. aromatics have. beenremoved. are. con! tacted. -wi.t h a poly-olefin glycol; ofv high molecularweightso that the'sulfur. compounds. are dis: solved. in the solvent. and arev thereby segregated and. removed. fromthe olefinic.andIpar-affihiccQn: stituents...

In. the. present. invention. the. solvent. and". the hydrocarbon. being treated. are. contacted; with each; other at) temperature from. about; F1

up to the boilingpoint of! the distillate being treated.- In distinction.-.to.tlie conventional treati-v ing processesheretofore employed. in the.- solvent extraction art, the present-invention.is conduoted at temperatures substantiallyabove. atmospheric, whereas. other. solvents require. low-- temperature operationwhichentails considerable-refrigeration orlhigh temperature. operations which 11.60.65.511 tate employing; excessively, high pressures. and

3 special equipment. Even with the best solvents employed before, removal of sulfur from the hydrocarbon distillates was not obtained.

The present invention may be conducted with both thesolvent and the hydrocarbon being treated in the liquid phase or it may be conducted with the solvent in the liquid phase andthe hydrocarbon in the vapor phase.

In operating with the solvent in the liquid phase and the hydrocarbon in the liquid phase, it is preferred to contact the hydrocarbon with the solvent in an extraction system in which a temperature gradient is maintained so that fresh solvent contacts the partially strippedroil at the highest temperature and the extract contacts th solvent at the lowest temperature. In general, a temperature gradient say in the range of about 4 referred to as a wet extract. The rafilnate leaving tower 8 in vapor form is passed through condenser l wherein the temperature of the hydrocarbons is lowered to below its dew point and a liquid'stream which may v comprise paraffins and naphthen'es is withdrawn from the system through line H for further treatment. If olefins are present in the feed mixture they may be dis- 40 to 80 F. may be employed. Usually the maximum temperature at which treating occurs will range toabout 180 F. while the lowest temperature in the extraction system will be about 120 F. In operating with the hydrocarbon in the vapor phase and the solvent in the liquid phase, the reverse is generally true. The vaporized hydro carbons are initially contacted with the solvent at the boiling point temperature of the heaviest hydrocarbon in the fraction, whereas the temperature at which the extract finally leaves the extract system is somewhat higher, generally in the neighborhood of from to 50 F. higher. Temperatures of about F. higher than the boiling point of the heaviest constituents in the rafiinate may be found suitable as a maximum temperature at which the extract finally con: tacts the solvent in the extraction tower. V

The invention will be better understood by reference to the following drawings in which Fig. 1 is a diagrammatic flow plan of one em bodiment in which the liquid solvent is contacted with the vaporized hydrocarbon; and Fig. 2 illustrates another embodiment of my invention in which both the hydrocarbon and the solvent are maintained in the liquid phase and the apparatus illustrated in the flowdiagram is a front elevation of equipment found suitable for conducting the invention.

Referring now specifically to Fig. 1, a hydrocarbon feed containing sulfur compounds and havinga boiling range below 165 F., for example betweenj 80 and 150 F., is introduced, from a source not shown, into the system through line I and pump 2 and is thereby routed through heating coil 3 in which the temperature of the hydrocarbon fraction, is raised to its boiling point so that when it ,is injected by means of line 4 into solvent extraction tower 5 it immediately vaporizes. Solvent extraction tower 5 may comprise any suitable extraction equipment but preferably it is a packed tower so that intimate contact between the vaporized hydrocarbon and the solvent introduced thereto by means of line 6 is effected. Solvent extraction tower 5 is equipped with heating means I for maintenance of a suitable temperature therein. As mentioned before, it is preferred to maintain the bottom of solvent extraction tower 5 at a temperature about 30" higher than that maintained in the top of said tower. The temperature in the top of the tower should be about the boiling point of the hydrocarbon introduced thereto.

Solvent extraction tower 5 is equipped with line B for withdrawalof rafiinate consisting of hydrocarbons and line 9 for withdrawal of the sulfur compounds, which are dissolved in the solvent. This latter mixturewill hereinafter be solved inthe solvent with the sulfur compounds. The wet extract discharged from tower 5 through'line 9' is introduced thereby into extract stripper l2, in which conditions are so adjusted that-the sulfur compounds are removed from the solvent, leave extract stripper I2 through line [3, condensed in line [4, and discharged from the system by way of line I 5. This latter stream comprises substantially all of the sulfur compounds originally present in the fraction charged to the system. This material may be discarded or used as desired.,. f V

The solvent stripped free of sulfur constituents leaves extract stripper I2 by way of line i! and accumulates in solventstorage tank" l8. Solvent storage tank I8 is equipped with-a heating means l9 to maintain the, solvent: in a fluid state since at ordinary temperature it isa solid. As men tioned hereinbefore solvent is introduced in the top of extraction tower 5 by way of line- 6--which connects to tank l8 and line 20; in which make up solvent is introduced'as required. Line 6 is equipped with pump 2 and heater 22 for insuring the proper temperature of the solvent introduced into extract tower 5. With respect to the embodiment-represented in Fig. 2, a hydrocarbon feed containing sulfur compounds and having a boiling range between about and 400 E, which has been freed of aromatic hydrocarbons, is introduced intothe system by means of line 23 and pump '24, connecting to extractiontower 25. The extraction tower 25 may be any suitablecontacting device to insure intimate coni'lact between the liquid solvent and liquid hydrocarbon fraction. Preferably, extraction tower 25 is a bafile d or packed tower. It may be equipped with bell cap plates, Raschig rings or any other suitable packing or contacting means. The hydrocarbon fraction is introduced into extraction tower 25 about midway'thereof so that the tower is thereby divided into extraction andstripping stages, the portion of the tower above the'feed inlet being the extracting stage and that below the feed inlet'being the stripping stage."

Polyethylene glycol inthe liquid state is introduced into thetop of extraction tower 25 by means of line 26 and countercurrently contact the hydrocarbon ascending therein. The rain: nate fraction may comprise paraffins andnaphthenes andis withdrawn" from; the top offextraction tower 25 through line ,2? for further treatment as will be described hereinafter while the wet extract fraction is removed from thebottom of extract tower 25 by wayo'f line 28 and injected thereby into extract stripperf29L olefins which may ,be present. in the feed will also be dissolved in theffsolventg The wet extract discharged into extract stripper Z9 is separated therein into' a solvent phase and an extract phase free of solvent' which comprises *su'uur compounds. Thisis accomplished by adjusting temperatures in eXtract'stripperQS by means of heating means 30. The extract is fdistilled from the top of extract stripper 29, and is discharged therefrom through line'ilhand is condensed-in condensing means not shown and a portion oft he air-meow condensed fraction is withdrawn-from the system. mentioned. before; only a. portionrof the extract is withdrawn from the system whileua second portion is recycled by. way of line 32. and pump 33 to extraction tower '25 for maintenance of reflux therein. I

It is understood that extraction tower 25 is operated so; that the highest-temperaturesare obtained in the top of-the-tower" and the lowest in the bottom of the tower.- 'I n-general atemperature of about 180 F. is maintained in the top of extraction tower 25 and a temperature of about 120 F. in the bottom thereof.

The rafinate leaving extraction tower 25 discharges by way of line 31 into raffinate stripper 34 which is equipped with heating means 35 so that the temperature in raffinate stripper 34 may be adjusted for distillation of raffinate from the solvent. The raffinate distilling overhead from stripper 34 leaves through line 36 and is condensed by means not shown and may be utilized or further treated in any manner desired. This raffinate is substantially free of sulfur and its compounds. Solvent is withdrawn from the bottom of rafiinate stripper 34 by means of line 31 and combined in line 38 with the solvent discharged from the bottom of extract stripper 29 by means of line 39. The combined stream of solvent in line 38 then recycles to extraction tower 25 through line 26. Make-up solvent can be introduced into line '26 by opening valve 40 located therein.

In practicing the present invention it will be obvious to those skilled in the art that the ratio of solvent to liquid will vary with the concentration of sulfur and/or its compounds in the fraction being extracted. In general, good results may be obtained while operating with liquid to liquid extraction with ratios of solvent to liquid of 4:1 to 20:1, while in vapor-liquid extraction, the ratio of solvent to liquid will be somewhat higher of the order of about :1 to 50:1. The reflux ratios employed will likewise vary with the concentration of sulfur compounds in the feed stock but good results may be obtained in both liquid-liquid and vapor-liquid extraction with reflux ratios of the order of about 1:1 to about 10:1.

A preferred solvent specified for use in the present invention has been described as a polyethylene glycol having a molecular weight in the range of about 400 to 4,000. Solvents of this nature having molecular weights in excess of about 800 are solids at ordinary temperature. They are advantageously employed at elevated temperatures at which they are in a liquid state.

A typical solvent employed in the present invention has the following characteristics:

Table Density (grams/cc. at 20 C.) 1,15 Melting point, C 30-40 Viscosity, Saybolt Universal at 210 F 60-90 Mol. wt. (Cryoscopicmethod) 1200 (approx) In general, glycols in the higher portion of the range from about 1,000 to 4,000 molecular weight will be employed. These glycols usually have a specific gravity slightly above that of water and melt in the neighborhood of about 100 to 130 F. The higher molecular weight poly-olefin glycols are usually solids, but like the lower molecular weight poly-olefin glycols, have a melting point in the range given. For example,

6. a pory-olenn glycol-having a. molecular weight of 4.000 has a melting point of about-" In order to illustrate the practice'ofi the: pres! ent' invention further; a kerosene fraction which had been substantially freed an aromatic en:- st'ituents by extraction withliquid sulfur dioxide and havinga sulfur content-of 0.25% weight was extracted with polyethylene glycol at a temperature of F. to obtain a raifinate and an extract phase.- The rafilnate wastested and foundto= contain 0.125% by weightof sulfur.

A light naphtha boiling below about and substantially free of aromatic hydrocarbons was contacted at about 225 F. with polyethylene glycol having a molecular weight of approximately 1,200. A rafllnate phase and an extract phase was obtained. Sulfur determinations were then made on the original charge, the raffinate, and the extract. The original charge showed a sulfur content of 0.11% by weight while the sulfur content of the rafiinate was 0.025% and the sulfur content of the extract was 0.2%. It was also found that the mercaptan sulfur content of the charge was 18 mg. per 100 ml., that of the raffinate was 0, and the mercaptan sulfur content of the extract was 16 mg. per 100 ml. indicating that the mercaptan sulfur had all been concentrated in the extract.

The present invention may be employed in conjunction with conventional solvent extraction processes. For example, sulfur dioxide and/or similar solvents may be employed to remove aromatic constituents from naphthas and a poly-olefin glycol extraction may follow the sulfur dioxide extraction to remove sulfur compounds from the substantially aromatic-free rafilnate resulting from the extraction with sulfur dioxide.

The nature and objects of the present invention having been fully described and illustrated, what I wish to claim as new and useful and to secure by Letters Patent is:

1. A process for removing sulfur and its compounds from a non-aromatic hydrocarbon fraction containing them which comprises contacting the'sulfur-containing fraction with a poly-olefin glycol having a molecular weight in the range between 400 and 4,000 under conditions to form a rafiinate phase and an extract phase, and recovering substantially sulfur-free hydrocarbons from said raflinate phase.

2. A method for removing sulfur and its compounds rrom a non-aromatic hydrocarbon boiling below F. containing them which comprises contacting said hydrocarbon with a polyolefin glycol having a molecular weight in the range between 400 to 4,000 under conditions to form a rafiinate phase and an extract phase, separating said phases, and recovering substantially sulfur-free hydrocarbons from said raffinate phase.

3. A method for removing sulfur and its compounds from non-aromatic hydrocarbons containing them which comprises heating a sulfuroontaining non-aromatic hydrocarbon fraction boiling in the range between100 F. and 600 F. to a temperature no lower than 120 F. and no higher than 50 F. above the boiling point of the heaviest hydrocarbon in said non-aromatic hydrocarbon fraction, contacting said heated hydrocarbon fraction with a poly-olefin glycol having a molecularweight in the rang between 1,000 and 4,000 under conditions to form a raffinate phase and an'extract phase, separating said phases, and recovering a substantially sul- REFERENCES CITED The following references are of record in the file of this patent:

} f NI'rEDHsTATEs PATENTS Number Name Date 2,007,114 gstratford June 2, 1935 2,013,663 Malisoff: Sept. 10, 1935 2,402,799 'Arnold'et al. June 25, 1946 Ashbum Jan. 14, 1947'

Claims (1)

1. A PROCESS FOR REMOVING SULFUR AND ITS COMPOUNDS FROM A NON-AROMATIC HYDROCARBON FRACTION CONTAINING THEM WHICH COMPRISES CONTACTING THE SULFUR-CONTAINING FRACTION WITH A POLY-OLEFIN GLYCOL HAVING A MOLECULAR WEIGHT IN THE RANGE BETWEEN 400 AND 4,000 UNDER CONDITIONS TO FORM A RAFFINATE PHASE AND AN EXTRACT PHASE, AND RECOVERING SUBSTANTIALLY SULFUR-FREE HYDROCARBONS FROM SAID RAFFINATE PHASE.

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