US2744855A - Desulfurization process using alkali followed by extraction with liquid sulfur dioxide and a promoter - Google Patents

Description

H 9 M 8 w A". S 4 2D E 6 w 7 wm ww 6 MU HW R 5 H F O Tn" Fm n y 3 f mL f/ l .m 5 u M w nf msm mm L 1 0 DAwww a w w LnNuwml 2 5 I mmre, l :4J R MAY f AIDM A .EWMJ :./v CNEd .RODS H RPNTI. 0 NOX 7 AO C mRI 3 TTD ...AL AVA .f7 6 ZE s? on 2 3 I /y 4 2 lli 3 F fav 8 2 L 2 9 R Ww 2 E 4 E YJ 3 v/A l 3 D 4 anun M 2 HN b f wm 7 2 S d May 8, 1956 WML/M .w31 m MA V.. 7 0 m w. n/O 6 6 4, m Am 2 H a M Y m d m m w /F n W m m m E wm 3 P 9 9 6 9 m f w M utkm. @02W 7 8 7 B Y r .f 4 s M R/ 7/ JWM UW 27u D pn. 5 m m w H G 6 E2 x 2 oo 7 0 8 ha M :u/ 54 8 8 f 0^ L 6 ATTORNEY United States Patent O DESULFURIZATION PROCESS USING ALKALI FOLLOWED BY EXTRACTION WITH LIQUID SULFUR DIOXIDE AND A PROMOTER Robert C. Arnold, Park. Forest, Ill., assigner to Standard Oil Company, Chicago, Ill., a corporation-of Indiana Application July 9, 1953, Serial No. 366,957

Claims. (Cl. 196-32) This invention relates to a process for refining hydrocarbon materials containing one or more undesired impurities, such as coloring matter,.rnalodorous materials and organo-sulfur compounds. More particularly, this invention is concerned with'a process for desulfurizing mercaptan and other organo-sulfur compound containing hydrocarbon oils, particularly sour petroleum' oil distillates boiling in the heavier-than-gasoline range.

Patent application Serial Number 248,898, iiled September 29, 1951, now Patent No. 2,671,047, entitled Refining Hydrocarbon Materials with SO2 and BFa by Robert C. Arnold and Arthur P. Lien discloses a process for desulfurizing organo-sulfur compound containing hydrocarbon materials by the treatment thereof with an agent consisting essentially of liquid SO2 and BFa. This process gives a markedly greater amount of desulfurization than does an equivalent amount of liquid SO2 alone. Also, this processconverts a sour, i. e., mercaptan containing, oil into an oil that is sweet to the doctor test. These improved results are obtained with substantially no increase in the amount of hydrocarbons taken into the extract phase. However, it has been found that the raflinate oil from this process, although of markedly lower organo-sulfur compound content, contains appreciable amounts of elemental sulfur. The elemental sulfur is present in the raffinate oil even though none had been present in the sour oil feed to the process. The presence of elemental sulfur in hydrocarbon oils such as naphthas, kerosenes, vheater oils, or high solvency naphthas has an extremely bad effect on product quality as determined by the copper strip method.

One object of the present invention is to provide a process for rening and desulfurizing hydrocarbon oils containing organo-sulfur compounds. An additional object is to providel a process for decolorizing hydrocarbon materials, particularly hydrocarbon oils. A specic object of the invention is to provide a process for the treatment of a petroleum distillate containing objectionable amounts of organo-sulfur compounds to produce a product oil of low organo-sulfur compound content and also essentially free of elemental sulfur. These and other objects of the invention will become apparent from the following description. l

It has been discovered that elemental sulfur is not present in the product of the treatment of hydrocarbon material containing organo-sulfur'compounds with an agent consisting essentially of liquid SO2 and a promoter selected from the class of Lewis acids (Friedel-Crafts halides) when the hydrocarbon oil is treated to substantially eliminate mercaptans prior to undergoing the liquid SO2-promoter treatment. Thus the process of this invention comprises (l) treating a hydrocarbon material containing mercaptans and other organo-sulfur compounds to substantially eliminate the mercaptans, either by physical removal or conversion to the corresponding disuliides. (2) Contacting said substantially mercaptan-free oil with an agent consisting-essentially of liquid SO2 and ,a promoter selected from the class of Friedel-Crafts lcg halides consisting of BFa, AlCla, FeCls, TiCl4, HgClz, BCla and ZnClz. At least enough liquid SO2 is present in the agent to exceed the solubility of liquid SO2 in the oil undergoing treatment. The temperature of the treatment is below about 10 C. (3) A raiiinate oil of markedly lower organo-sulfur compound content and essentially free of elemental sulfur is separated from an extract phase comprising agent, sulfur compounds and extract hydrocarbons.

The SO2-promoter process is applicable to various liquid or liquefied hydrocarbon materials which contain organo-sulfur compounds. Thus it is applicable to various petroleum fractions for the purposes of removing sulfur, gums or other resinous materials, colored impurities and odoriferous compounds. feed stocks may comprise light naphtha fractions, gasolines, heavy naphthas, kerosenes, transformer oils, heater oils, furnace oils, diesel fuels, gas oils, lube oils and crude oils. Particularly suitable charging stocks are petroleum distillates boiling in the heaVier-than-gasoline range, i. e., between about 330 and 675 F.

This process can be applied for the purpose of desulfurizing various petroleum stocks which are to be subsequently treated .in refining yor conversion operations ,in which sulfur or sulfur compounds are undesirable, for example, catalytic cracking operations, catalytic reforming operations, catalytic hydrogenation in the presence of sulfur-sensitive catalysts and the like.

In addition the refining agents of the present inven-y y tion may be applied to the desulfurization and decolorization of aromatic hydrocarbon fractions, for example, crude ben'zols, toluols, xylols, naphthalene fractions'or the like. r

VThe process may also be applied to the refining of various coal tar fractions and coal tar distillates. In the refining of shale oil fractions the refining agentsserve not only to remove organic sulfur compounds from the feed stock, but also to remove oxygen compounds and nitrogen compounds. v

It is to be understood that the above specific examples of charging stocks which may be refined by the present invention are illustrative only and are not intended to limit the field of applicability of the process.

Any method which produces a substantially sweet oil may be utilized in the process of this invention. Although the mechanism is not understood, the mercaptans present in the feed oil appear to be the cause of the formation of elemental sulfur in the SO2-promoter process. A product oil that is free of elemental sulfur can be obtained if the mercaptans are eliminated from vthe oil.v

Any conventional process for the physical removal of mercaptans may be utilized, e. g., the sour oil may be contacted with an aqueous caustic-organic solvent solution. The organic solvent may be a monohydric alcohol ksuch as methanol or ethanol; a dihydric alcohol such as ethylene glycol; or a dihydric alcohol containing ether linkages such as diethylene glycol or triethylene glycol, Other organic solvents such as water-soluble aliphatic amines or alkanolamines may be used. The various soluti'zer processes may be used. In these processes the solution consists of aqueous caustic and a solubility promoter such as phenolic compounds, lower molecular weight fatty acids, wood tar oils, and tannins;

yAny conventional process for the Aconversion of the mercaptans to the corresponding disuliides wherein .the disuldes are dissolved in the oil may be used. Examples of these processes are: Contacting the sour oil with concentrated aqueous caustic solution in the presence of .free-oxygen. Contacting the' sour oil' with aqueous caustic solution, free-oxygenand catalysts for vthe oxidation of mercaptans such as hydroquinone, pyrogallol,

Suitable petroleum tannin, petroleum phenols, etc. Contact-ing the sour oil with concentrated aqueous caustic solution and freeoxygen in the presence of active copper catalysts such as CuSO4 and CuClz.

The most widely used processes for sweetening sour oils Vby the conversion of mercaptans to disuliides are the doctor process and the copper chloride process. ln the doctor process the sour oil is contacted with an aqueous caustic solution containing dissolved litharge and free-oxygen in the presence of elemental sulfur. In the copper chloride process the sour oil is contacted with free-oxygen in the presence of a catalyst mass consisting essentially of copper chloride, water and an inert support.

It is to be understood that any process which results in the production of a substantially sweet oil may be utilized and the process of this invention is not limited to the processes listed above.

In general, the proportion of liquid sulfur dioxide used varies depending upon vthe specific hydrocarbon material being treated. and the treating conditions, especially the temperature. The relative iniscibility of liquid sulfur dioxide and hydrocarbon charging stocks varies with temperature, greater' mutual miscibilities being encountered at higher temperatures and lower miscibilities at lower temperatures. At least a suiicient amount of sulfur dioxide is used to exceed its solubility in the hydrocarbon material being treated at the particular treating temperature, thereby forming two distinct liquid phases, i. e., a predominantly hydrocarbon liquid phase containing a relatively small proportion of dissolved sulfur dioxide or raffinate layer and a predominantly sulfur dioxide liquid phase or extract layer. Ordinarily, liquid sulfur dioxide is employed in the process in amounts between about percent and about 200 percent by volume or more, based on the volume of hydrocarbon charging stock. Preferably, between about and 75 volume percent of liquid SO2 is used.

,The sulfur-removing powers of liquid SO2 are remarkably` enhanced by the addition thereto of a promoter selected from the class of Lewis acids (Friedel-.Crafts-type halides). Not all the .members of the class of compounds known as the Friedel-Crafts-type halides can be used in this process. Some members are completely ineffective, for example, aluminum triuoride, or are only feebly eective, for example, antimony trichloride, aluminum bromide and stannic chloride. A high degree of solubility in the liquid SO2 is helpful. However, some members of low solubility are good promoters when used in the form of a liquid SO2-promoter slurry, for example, FeCls, HgClz, and ZnClz. The members of the class which are eifective as sulfur removal promoters in liquid SO2 extraction are AlCls, FeCla, TiCl4, BFs, HgCla, BC13, and ZnClz. With the exception of .BFg these promoters do not appear to give complete sweetening when a sour oil is contacted with the v.SO2-promoter agent. However, a suicient amount of sweetening occurs with all the promoters to produce a deleterious amount of elemental sulfur in the product oil if the sour oil is not sweetened prior to contacting with the SO2-promoter agent. Because of its solubility in liquid SO2, ease in recovery from the extract phase and superior desulfurization obtained therewith, BF3 is preferred.

The amount of promoter employed in the process will usually vfall within the range of about 0.5 to about 5 mols per gram atom of sulfur contained in the hydrocarbon charging stock. The proportions of promoter to sulfur within the above range, when employed with liquid sulfur dioxide, are sufficient not only to eiect substantial desulfurization of sulfur-,containing hydrocarbon materials but also to effect additional refining, particularly decolorization. For purposes of desulfurization it has been discovered that the optimum desulfurization can be eiected by the employment of between about 1 and about 3 mols of promoter per gram atom of sulfur contained in the hydrocarbon charging stock. (It is to bc understood that at least a suicient amount of liquid sulfur dioxide to form a liquid phase distinct from the raffinate hydrocarbon material is also present in the contacting zone.)

The SO2-promoter process may be conducted at temperatures between about -l-l0 C. and 85 C. The preferred temperature range is between about 10 C. and -40 C. The optimum temperature will vary not only with the type of charging stock but also with the desired product, i. e., maximum desulfurization and maximum color improvement may require different temperatures at otherwise constant conditions of operation.

The SO2-promoter process is conducted under pressure suicient at least to maintain a substantial proportion of the sulfur dioxide in the liquid state and likewise sufficient at least to maintain a substantial proportion of the gaseous promoters dissolved in the liquid phase. In the presence of liquid sulfur dioxide, BF3 forms extremely stable addition compounds with organo-sulfur compounds and, as a result, a substantial proportion of BFs which is originally introduced into the reiining zone as a gas is rapidly absorbed. The partial pressure of BFS in equilibrium with said BFS-sulfur compound addition compounds is very low at temperatures of 0 C. or less. In general, the SO2-promoter process can be operated at pressures which are commonly encountered in commercial process equipment, for example, between about l and about 300 p. s. i. g., although usually pressures between about l and about 15 p. s. i. g. are suiicient for the present purposes.

The contacting time required in the SO2-promoter process is dependent upon the intimacy of contacting with the refining agent of the hydrocarbon material being treated and upon the operating temperature. Ordinarily, the .contacting time may be between about l and 60 minutes. The operating temperature will, to some extent, aifect the intimacy of contacting by determining the liquid viscosities in the refining system and, probably to a more important extent, by determining the rate of interaction of sulfur compounds and other impurities in the feed stock with the refining agent.

Various diluents, countersolvents or co-solvents can be employed in the present process in addition to the refining agent. Especially in the case of viscous or relative high pour point hydrocarbon charging stocks it may be desirable to dilute said charging stocks with diluents or countersolvents such as liquefied propane, .butanes, pentanes, hexanes, saturated naphthas or the like. The use of Various co-solvents, particularly benzol with liquid sulfur dioxide, is well-known and these co-solvents may find application in the process.

It is possibleto heat the total extract phase from the process until substantially all the SO2 has been vaporized off without substantially decomposing the prornoter-sulfur compound adduct, lif the temperature of the extract phase does not exceed about 50 C. When using BF3 as the promoter, the free BF2., i. e., the BF3 existing insimple solution in the extract phase, passes off along with the gaseous SO2. Partial removal of the SO2 results in the separation of a second ralinate layer and the yield of the second raiiinate .reaches a maximum when substantially all the SO2 has been removed. When substantially all the SO2 has been removed from the first extract phase, the second railinate-consists essentially of all the aromatic hydrocarbons extracted from the feed stock and some sulfur compounds, as evidenced by the sulfur kcontent thereof; and the second extract phase consists substantially of an adduct of promoter and sulfur compounds. Theamount of SO2 present in the second extract phase may vary from about l to about l5 volume percent depending upon the temperature at which the irst extract phase was heated in order to remove SO2 and free BF3. The sulfur content of the aromatic hydrocarbon containing second raiiinate obtained by lthis SO2 removal technique is less than lthe sulfur contentvof ithe total extract materials; and may be in some cases as low as 0.1 weight percent.

When the extract phase is treated so as'to remove substantially all the SO2, the second extract material appears to consist essentially of organo-sulfur compounds. Treatment of a West Texas heater oil containing 0.6 Weight percent sulfur with 2 mols of BF3 per mol of sulfur dissolved in 25 volume percent of liquidv SO2, separation of the resultant extract phase, removal of the SO2 and free BFa from the extract phase at about 25 C. gave a second extract material with a sulfur content of 12.1%. The second raflinate consisted of aromatic hydrocarbons and enough organo-sulfur compounds to give a sulfur v content of 4%.

The SO2-promoter process can be carried out in batch, continuous or semi-continuous operating cycles, and-in one or more stages, employing contacting and separation equipment such as has heretofore been employed in the selective solvent refining of petroleum lubricating oil stocks or in effecting the alkylation of isoparatiinic hydrocarbons with oleiins in the presence of liquidacid catalysts. It should be understood that the -speciiic equipment employed forms no part of the present invention and that any equipment ladaptable for the purposes of contacting the refining agent with the hydrocarbon charging stock and thereafter separating spent refining agent from the rened charging stock can be employed for the purposes of the invention.

The invention is illustrated by one embodiment shown in the annexed drawing which forms a part of this specification. Numerous pumps, valves and other items of equipment have been omitted from this embodiment since these items may be Vreadily added thereto by those skilled in the art. l

The feed stock to the process is a heater oil derivedby distillation from West Texas crude. This feed boils be-v tween 375 and 560 F. and has a mercaptan number of 90. Since this feed is to be sweetened by thel copper chloride process, itshould be Has-free. The H2S has been removed by Washing with a dilute aqueous caustic solution. Other methods of removing Has may beiused. (Some sweetening methods do not require removal of the Has).

Caustic reacts with the copper catalyst and deactivates it. Therefore, it is necessary to remove any caustic which may be present in the feed. Thesour oil feed in this illustration is passed from source 11 through line 12 into salt iilter 13. Salt filter 13 consists of a cylindrical vessel filled with crushed rock salt. The rock salt removes any aqueous caustic that may be occluded, in the feed. Instead of using a salt drum, a vessel filled with steel wool, gravel, sand or other coalescing medium may be used.

The feed is passed out of salt lter 13, through line 14, into heat exchanger 16. In heat exchanger 16 the temperature of the sour oil is raised to about 80 F. In general, the temperature of operation should be between about 60 and 100 F. From heat exchanger 16 the sour oil is passed by way of line 17 into mixer 18. Mixer 18 may be any form of agitating device. In this case mixer 18 is provided with knothole orifice plates. Freeoxygen from source 21 is passed through line 22 into line 17 where it meets the main stream of sour oil. The free-oxygen and the sour oil 'are thoroughly intermingled in mixer 18.

Theoretically, the amount of free-oxygen needed in the process to insure substantially complete regeneration of the catalyst is 1 mol for each 4 mols of mercaptan present. However, normally a 100 or 200% excess is desirable.

A side stream of the sour oil is withdrawn from line 17 by way of line 24 and is passed into slurry tank 26. Slurry tank 26-is a cone-bottomed vessel provided with anagitator not shown. Fresh catalyst from source 27 or ammonium chloride.

is added by way of line 28 to slurry tank 26. The slurry of catalyst and oil is passed from tank l26 throughline 29 by way of pump 31 into line 32. The mainstream of sour oil is passed from mixer 18 by way of line 34 and pump 36 into line 37 where it meets the makeup catalyst slurry from line 32.

The catalyst comprises CuClz, water and a carrier. The carrier consists essentially of a nely powdered mixture, having a screen size of less than about mesh of fullers earth. Adsorbed on the carrier is an aqueous solution of CuClz. Based on the total catalyst, the catalyst should contain between about 5 and 30 weight percent of waterand between about l and 25 weight percent of CuClz. (However, the v CuClz may be' made by reacting in aqueous solution cupric sulfate and sodium chloride When forming the CuClz'by this reaction, it is preferred to use a small excess of the chloride salt.) f

The sour oil-oxygen-catalyst dispersion in-line 37 is passed into eductor 38 and from eductor 38 it is passed through line 39 into reactor 41. In some cases the eductor may be by-passed and the dispersion passed into line 39 by way of by-pass line 42. In reactor 41 the sour oil andthe catalyst are maintained in the dispersed condition until the oil is substantially sweet.

Reactor 41 has a conical shaped lower portion into which the catalyst settles. The dense slurry of catalyst and oil is withdrawn from the bottom of reactor 41 through line 46 and is passed into eductor 38 by way of line 47. ln Veductor 38 the recycle catalyst meets the stream of sour oil and makeup catalyst.` When the catalyst has become substantially inactive, catalyst is sent to recovery by way .of lines 46 and 49.

The substantially sweet oil contains a very slight amount of catalyst. The oil is withdrawn from reactor 41 through line 51 and is passed into line 52 wherev it meets water from source 53 and line 54. The amount of wash water used is dependent upon the amount of catalyst carried over from the reactor. In general, the amount of wash water may be between about 10 and 100 volume percent based on oil. The mixed stream of water and oil is passed into mixer 56. From mixer 56 the stream of oil and water is passed by way of line 57 into settler 58. The wash water separates in settler 58 and is sent to a sewer by way of line 59. The washed oil from settler 58 is passed into line 61. In some cases the washing operation is not necessary and the operation may be' bypassed by way of lines 51 and 62.

The washed oil from line 61v is passed through line 63, through cooler 64 and line 66 into salt tilter 67. Cooler 64 lowers the temperature of the washed oil in order to reduce the amount of water dissolved in the oil, and salt lter 67 dehydrates the washed oil. Brine from vessel 67 is passed to the sewer by way of line 68.l Salt filter 67 is similar in construction to salt lter 13.

Dehydrator 67 may comprise other conventional equip-I ment and drying reagents, for example, a vessel packed with calcium chloride, excelsior, fiber glass, magnesium silicate drying agents (Florisil), alumina gel or the like. Drying of the oil can also be effected by distillation, for example, vacuum distillation.

It should be understood that the specic vdrying treatment forms no part of the present invention and that any drying treatment may be used which substantially eliminates Water from the charging stock. The presence of water in the charging stock and in the treating system is extremely undesirable since water combines with BFs to form hydrates, which complicates the recovery of BFs, and since the corrosive tendencies of the" SO2-promoter agent tend to increase with increasing water concentration in the refining system.

The dried oil is passed through line 69 into deaeration equipment 71 wherein air dissolved incr entrained in the charging stock is,substantially removed. The specific deaeration process and equipment form no part of the 7 present invention. Vacuum deaeration equipment such as is ordinarily employed in commercial processes of liquid sulfur dioxideireiining of hydrocarbon oils can be employed. The deaerated oil is passed through line 72 into heat exchanger 73 wherein the temperature of the stock is lowered to the desired treating temperature.

The oil thus pretreated is introduced by way of line 7 into the lower portion of extraction tower 76. The extraction tower may be packed with suitable corrosionresistant packing materials to increase the efficiency of contacting of the charging stock and reiining agents. For example, the extraction tower can be packed with structural carbon in the form of Berl saddles, glass or porcelain spheres, Monel metal fragments, mild carbon steel jack chain o r the like, or may be provided with mechanically- 'or magnetically-actuated agitators.

If desired, ythe viscosity of the hydrocarbon charging stock may be reduced by dilution with a saturated hydrocarbon such as n-pentane, isopentane, n-octane, petroleum ether, methylcyclopentane, cyclohexane or the like diluent from source 77 may be introduced by way of valved line 78 into line 74.

In extractor 76 the oil is contacted with liquid sulfur dioxide and BFS. If desired the combined reagents may be introduced into the upper portion of tower 76 from storage drum 81 through line S2. Alternatively, liquid sulfur dioxide alone may be introduced through line 82 and BF3 may be introduced into the extraction Zone from source 84 by way of line 86 and manifold 37.

Contacting in extractor 76 is effected at a temperature of C. and at a pressureA of about 50 p. s. i. g. The amount of liquid sulfur dioxide introduced into extractor 76 is 70 percent by volume, based on the volume of oil. The amount of BF3 is 2.5 mols per gram atom of sulfur contained in the oil. Tower 76 may be operated rainaterich or extract-rich; the latter mode of operation is preferred. The contacting time in extractor 76 is about 5 minutes.

The rainate phase is withdrawn from the upper end of extractor 76 through line 88 into stripping tower S9 which is provided with internal reboiler 91. Stripper 89 may be unpacked or may optionally contain bubble trays, packing materials or other fractionating devices. Relatively small amounts of liquid SO2 and B133 which have been occluded in the rainate are vaporized in stripper 89 and are withdrawn through line 93 for reuse. Product oil is withdrawn through line 94 to storage not shown.

Further treatment of the product oil may be desired,

for example, treatment with concentrated sulfuric acid l or with selective solvents, alkali treatment, clay treatment, water washing or other refining treatment. If diluent has been used, this may be removed by distillation.

The extract phase is withdrawn from the lower portion of extractor 76 through line 96 for treatment to separate extract materials and the components of the agent, respectively. Herein the extract phase is passed from line 96 .into stripper 97 which is provided with internal reboiler 98. Stripper 97 is similar in construction to stripper $9. The extract phase is subjected to a sufficiently high temperature in stripper 97 to vaporize essentially its entire content of sulfur dioxide and BFa. Such temperatures fall within the range of about 50 C. to about 250 C. Suicient pressure must be maintained in stripper 97 to prevent vaporization of the lower boiling portions of the extract. The sulfur dioxide and BF3 are passed overhead from stripper 97 by way of line 101.

Stripped extract is withdrawn from stripper 97 and is passed to storage not shown by way of line 102. A portion of the extract may be recycled by way of valved line y103 to a lower point of extractor 76 as a reffux stream.

The SO2 Vand EP3 are passed from line 101 through valved line 106 and line 107 into purication zone 108. Here nonfcondensible gases, HzS, etc. are removed by means well known to the liquid SO2 extraction art. The purified SO2 and BF; are passed into line 109 where they meet the material from line 93 and the combined stream is passed by way of condenser 110 and line 111in storage drum 81.

Makeup SO2 from source 112 is passed by line 113 and makeup BFg from source 114 is passed by line `115 into storage drum 81.

When the stream in line 101 contains little or no H28, the purification zone may be by-passed and the SO2 and EP3 passed by way of valved line 116 directly to line 109.

It is desirable from time to time to dehydrate at least a portion of the stream passing through line 101. A part of this stream is passed by way of valved line 11S into dehydrator 119 which is provided with internal reboiler 121. Dehydrated SO2 and BFg are withdrawn overhead through line 122 and are passed by way of line 107 to purification zone 108. A liquid bottoms fraction comprising water, sulfur dioxide and B133 hydrates is withdrawn from the lower portion of dehydrator 119 by way of line 123 for discharge from the system.

The extract may be subjected to various rening operations. For example, it can be given a catalytic hydroning treatment, employing a conventional catalyst, e. g., cobalt molybdate, and conventional operating conditions. The extract is a surprisingly good feed to a catalytic cracking operation; a high yield of very high octane gasoline is obtained, which gasoline has the remarkably low sulfur content of less than 0.1 weight percent.

Numerous pumps, valves, heat exchangers and other engineering details have been omitted from the SO2-EP3 operation in the interests of simplifying the description. Common engineering process expedients, particularly those which have heretofore been employed in processes of refining hydrocarbon oils with liquid sulfur dioxide will readily suggest themselves to those skilled in the art; it is to beV understood that such engineering expedients are within the purview of the present invention.

The results obtainable with the process of this invention are illustrated by the following comparative experiments. The charging stock used in all the experiments below was a West Texas virgin heater oil distillate, characterized as follows:

API 40 Sulfur (total), wt. percent 0.62 Mercaptan Number 48.1 Color, Saybolt 16 Color, aged, ASaybolt 12 ASTM distillation, F.:

Initial 332 10% 390 50% 446 502 Max. 565

The aged color is a measure of the storage stability of an oil. The aged color is determined by exposing m1. of the oil to the atmosphere in an open beaker for 20 hours at a temperature of 200 F. The color of the oil at the end of the exposure is the aged color.

The extraction procedure consisted of adding 375 ml. of liquid sulfur dioxide to 750 ml. of oil contained in a reactor provided with a cooling jacket and mechanical agitator. The temperature of the reactor contents was maintained at 20 C. When used, 1.7 mois of EP3 per gram atom of sulfur in the oil were metered into the reactor and the reactor was closed. At this point a pressure of from l0 to 100 p. s. i. g., due largely to B173, prevailed in the reactor, but when agitation was started, the pressure fell rapidly to about 0 p. s. i. g. Agitation was continued for 20 minutes at -20 C. followed by a 30-minute settling period to furnish ample time for the extract and rafiinate phases to separate. The extract phase was drawn oli at the bottom of the reactor and the rainate phase was washed with water and then with caustic. Finally the raffinate was again washed with water and dried.

Run 1 v In this run the feed was contacted with liquid SO2 alone. The oil from the raflinate phase was sour to the doctor test. About one-half of themercaptans has been removed by the extraction. A reverse doctor test indicated that the product oil contained no free-sulfur.

Run 2 In this run the feed was contacted with liquid SO2-BF3 agent. The product oil wassweet to the doctor test. However, the reversedoctor test indicated that free-sulfur was present. y

y Run 3 v In this run the feed was contacted at 120 F. with a 50% aqueous KOH solution (2% based on feed) and air until the mercaptan number of the oil had been reduced to 4.8. The Saybolt color of the substantially sweet oil was 4; the aged oil was a tan color falling in the lower value of the ASTM-Union scale. No 'change had taken place in the total sulfur content and the oil contained no free-sulfur. v

Run 4 The substantially `sweet oil fromv Run 3`Was treated with liquid SO2 alone. An 88V volume percent "yie1d of carried out in the presence of a mercaptan oxidation catalyst.

5. The process of claim 1 wherein said mercaptan elimination process comprises the doctor process.

6. The process of claim l wherein the mercaptan elimination process comprises contacting said oil with a reagent solution comprising aqueous caustic and methanol and separating a substantially mercaptan-free oil from a mercaptide-reagent solution phase.

' 7. The process of claim 1 wherein said promoter is product oil was obtained. vThe product oil contained 0.36 weight percent sulfur (411%"reduction in sulfur content). The Saybolt color was 17 and the aged color was 9. The product oil was sour and contained no freesulfur.

Run 5 The substantially sweet oil from Run 3 was treated with liquid SO2- EP3 agent. An 86% yield of product 'poil was obtained.r The product oil contained 0.11 weight percent sulfur (82% lreduction in sulfur content).. The Saybolt color was 25 and the aged color was 2l; The product oil was sweet and contained no free-sulfur.

These runs show that the presence of free-sulfur can be avoided if the mercaptan containing oil is first rendered substantially doctor sweet prior to treatment With liquid SO2- EP3 agent. Further, the runs show that a remarkable improvement in color stability is obtained by treating an aqueous caustic-air sweetened oil with liquid SO2-EP3 agent as compared with treating saidk oil with liquid SO2 alone.

Thus having described theinvention, what is claimed 1. A process for refining a mercaptan-containing hydrocarbon oil, whichprocess comprises (1) treating said oil to substantially 'eliminate the mercaptans therefrom, (2) contacting said substantially mercaptan-free oil with an agent consisting essentially of liquid SO2 and a promotor, wherein the liquid SO2 is present in an amount at least sufficient to form 4an extract phase and the promoter is selected from the class of Friedel-Crafts metal halides consisting of A1C13, FeCla, TiCl4, BFs, HgClz, BC13 and ZnCl2 at a temperature below about |10 C., and (3) separating a rened rainate containing essentially no free-sulfur from an extract phase.

2. The process of claim whereinl said rnercaptanl 8. The process of claim 1 wherein said promoter is -9. The process of claim l wherein said promoter is FeCls.

10. A process for refining a hydrocarbon oil containing mercaptans and other organo-sulfur compounds, which process comprises l) treating said hydrocarbon oil by aA process that produces a substantially mercaptan-free and elemental sulfur-free oil, (2) contacting the oil from step (1) with an agent consisting essentially of liquid SO2, in an amount between about 15 and 200 volume percent based on oil, and a promoter selected from the class 'of Friedel-Crafts metal halides consisting of A1Cl3, FeCla, TiCLr, B133, HgCl2, BC13 and ZnC12, in an amount between about 0.5 and 5 mols per gram atom of sulfur in the oil, at a temperature between about 10 and 40 C., (3) separating a ranate phase from an extract phase, and (4) recovering a product oil markedly reduced in organo-sulfur compound content and containing essentially no free-sulfur as measured by the reverse doctor test from said raffinate phase.

11. The process of claim 10 wherein said hydrocarbon oil is a petroleum distillate boiling in the heavierthan-gasoline range.

j 12. The process of claim 10 wherein said promoter is BFa and the BFs'is present in an amount between about 1 and 3 mols per gram atom of sulfur in the oil.

13. The process of claim 10 wherein the oil from step (1) has amercaptan number below about 5.

14. A process for refining a high organo-sulfur compound containing sour petroleum distillates boiling in the heavier-than-gasoline range, which process comprises (l) contacting said distillate with a catalytic amount of an aqueous caustic solution in the presence of freeoxygen under conditions to reduce the mercaptan numl ber of said distillate to below about 5, (2) separating distillate is a heater oil boiling between about 330 and References Cited in the le of this patent UNITED STATES PATENTS 1,941,251 Davis Dec. 26, 1933 2,451,025 Ellenden Oct. 12, 1948 2,534,025 Howes et a1 Dec. 12, 1950 '2,560,330 Brandon July 10, 1951 2,626,893 Morrow Ian. 27, 1953 2,646,390 Arnold et al July 21, 1953 2,671,046 Arnold et a1. Mar. 2, 1954

Claims (1)

1. A PROCESS FOR REFINING A MERCAPTAN-CONTAINING HYDROCARBON OIL, WHICH PROCESS COMPRISES (1) TREATING SAID OIL TO SUBSTANTIALLY ELIMINATE THE MERCAPTANS THEREFROM, (2) CONTACTING SAID SUBSTANTIALLY MERCAPTAN-FREE OIL WITH AN AGENT CONSISTING ESSENTIALLY OF LIQUID SO2 AND A PROMOTOR, WHEREIN THE LIQUID SO2 IS PRESENT IN AN AMOUNT AT LEAST SUFFICIENT TO FORM AN EXTRACT PHASE AND THE PROMOTOR IS SELECTED FROM THE CLASS OF FRIEDEL-CRAFTS METAL HALIDES CONSISTING OF ALCL3, FECL3, TICL4, BF3, HGCL2, BCL3 AND ZNCL2 AT A TEMPERATURE BELOW ABOUT

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