GB1566052A - Process for sweetenging sour hydrocarbon streams - Google Patents

Description

(54) IMPROVED PROCESS FOR SWEETENING SOUR HYDROCARBON STREAMS (71) We, UOP INC, a corporation organized under the Laws of the State of Delaware, United States' of America, of Ten UOP Plaza, Algonquin & Mt.

Prospect Roads, Des Plaines, Illinois, United States of America, do hereby declare the invention, for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to a process for sweetening sour hydrocarbon streams, particularly distillates, by oxidizing mercaptans contained therein to disulfides.

The fixed bed sweetening of hydrocarbons is well known in the art. A typical fixed bed sweetening process is disclosed in U.S. Patent 2,988,500. In that patent, a sour petroleum distillate is contacted with a fixed bed of a metal phthalocyanine catalyst composited with a charcoal carrier in the presence of oxygen and an alkaline rdsage{lt. The patent states that any alkaline reagent may be used, but that aqueous sqiurn hydroxide solution is preferred because it is cheapest. The other .alkali! reagents mentioned are aqueous solutions of lithium hydroxide, rubidium hydroxide, and cesium hydroxide.The patent states that it is possible to have the alkaline reagent as an alkaline solution, but that a solution in a non-alkaline solvent may be used. It is believed that the patentee is intending to refer there to a non- aqueous solvent, rather than a non-alkaline solvent. (See column 2 lines 46-69).

The advantage of a fixed bed treating process is that the refiner has a high degree of control over the sweetening operation, and can be reasonably sure that all of the hydrocarbon passing through his fixed bed treating unit will be treated.

The advantage of a fixed bed process as disclosed in the above patent is that it does not add any significant amount of harmful materials to the treated hydrocarbon.

This is in contrast to some other treating processes, e.g., the plumbite process, wherein sulfur is one of the treating reagents used, leading to the possibility of sulfur contamination in the hydrocarbon products.

Another type of sweetening process, and one that occurs almost by accident in a number of refineries, is inhibitor sweetening. This is a phenomenon observed when a refiner adds an inhibitor such as phenylene diamine to this petroleum products and stores the products in a large tank. After several days the mercaptan content of the product declines, and the product may eventually become doctor sweet. In such a process, it is necessary to contact the mercaptan with oxygen.

usually in the presence of an alkaline reagent. Perhaps the best way to differentiate between inhibitor sweetening and fixed bed treating is the time of treating. In a fixed bed treating unit, the duration of contact of hydrocarbon and catalyst is almost always less than one hour, i.e., these fixed beds typically operate at a 1.0 or higher liquid hourly space velocity. In contrast, in inhibitor sweetening, the reaction takes several days to occur.

Although the fixed bed sweetening process, as disclosed in U.S. Patent 2,988,500, has been exceedingly satisfactory for many hydrocarbon charge stocks, there are a few problems encountered in the practice of that invention.

Specifically, a number of feeds contain naphthenic acids and other oxidation products which react with the strong caustic solutions used to provide an alkaline reagent. The reaction product of the naphthenic acid and alkaline reagent forms a soap which could plug the charcoal bed on which the catalyst is supported.

Another problem associated with the use of strong caustic solution is that means must be provided to ensure removal of all caustic from the hydrocarbon product.

These deficiencies can be overcome without too much difficulty, however. The naphthenic acids can be removed from the feed with a simple prewash of the feed with a dilute caustic material, Similarly, the presence of caustic solution can be eliminated by passing the treated hydrocarbon through a two-phase separator, then passing the hydrocarbon phase through a water-wash zone to remove caustic, followed by another two-phase separator, followed by passage of the hydrocarbon stream through a bed of salt which will remove any water remaining in the charge stock. Finally, passage of the treated hydrocarbon through a bed of sand will ensure that the last traces of water are removed from the process.

Another problem encountered in the treating art is that the desirable fixed bed sweetening process is being used to treat very refractory sour hydrocarbon distillates. The hydrocarbon distillates encountered by refiners today are becoming more difficult to treat because, with the worldwide demand for oil, refiners are encountering distillates which are exceedingly difficult to sweeten. With some hydrocarbon distillates, the only way to sweeten them in a conventional fixed bed unit is to provide for frequent replacement of the catalyst in the bed, and even more frequent placement of the strong caustic used to wet the charcoal bed.

Accordingly, we realized that it would be very desirable to find a way to operate the fixed bed treating process without using an aqueous solution of sodium hydroxide. It would also be desirable if a substitute could be found which would be soluble in hydiocarbons, perhaps eliminating the necessity for a separate alkaline phase in the fixed bed sweetening process. We also realized that it would be desirable to eliminate, if possible, the waste disposal problem associated with the use of aqueous sodium hydroxide solutions.

Having conducted a series of tests, we found that the use of organic bases, especially quaternary ammonium bases, as alkaline reagent permitted complete elimination of the conventional alkaline reagent, i.e., aqueous sodium hydroxide solution, used in a fixed bed treating process.

Accordingly, the present invention provides a process for treating a sour hydrocarbon stream, particularly a distillate containing mercaptans, which comprises contacting the stream with an oxidizing agent in the presence of a metal chelate catalyst and an organic base, e.g. by passing the distillate, the oxidizing agent and an alkaline medium comprising the base, particularly a quaternary ammonium base, through a fixed bed of metal phthalocyanine catalyst, particularly one composited with a carbon carrier, suitably at a liquid hourly space velocity of 0.1 to 20.

In one embodiment, the present invention provides a process for oxidizing mercaptans present in a liquid hydrocarbon stream comprising: (a) contacting the hydrocarbon stream with an oxidizing agent in the presence of a metal chelate catalyst and an organic alkaline reagent to produce a treated hydrocarbon stream with reduced mercaptan content and containing dissolved organic alkaline reagent: (b) contacting the treated hydrocarbon phase with water and recovering an aqueous phase containing at least 50% of the organic alkaline reagent present in the treated hydrocarbon; (c) passing the aqueous phase from step (b) to a fractionation means and separately recovering therefrom water and concentrated organic alkaline reagent; (d) recycling the water from step (c) to step (b); and (e) recycling the concentrated organic alkaline reagent from step (c) to step (a).

The organic base is preferably a quaternary ammonium base. Any highly alkaline quaternary ammonium compound may be used as the quaternary ammonium base. The preferred compound is a quaternary ammonium hydroxide, particularly tetrabutyl ammonium hydroxide.

Another excellent quaternary ammonium hydroxide is one.in which a benzene ring is at least one of the substituents on the ammonium hydroxide. Thus, benzyl trimethyl ammonium hydroxide is another excellent quaternary ammonium base for use in the present invention.

Advantageously, from 1 to 500 wt ppm of the organic alkaline reagent (quaternary ammonium base) is employed based on the weight of sour hydrocarbon distillate (liquid hydrocarbon stream).

'The quaternary ammonium bases may be used in an aqueous or alcholic solution, and are used instead of the conventional aqueous solution of sodium hydroxide. Thus, the fixed bed of catalyst used in the sweetening process may be wetted, either continuously or intermittently with an aqueous or alcoholic solution of the quaternary ammonium base. In the preferred embodiment, the quaternary ammonium base is dissolved in the hydrocarbon feed to the fixed bed unit. This permits elimination of an aqueous or alcoholic phase within the fixed bed treating reactor.

When the quaternary ammonium base is used in an aqueous or alcoholic solution, the concentration is suitably from 0.1 to 10 normal. The upper limit is a function of how much quaternary amine will dissolve in the aqueous or alcoholic medium used to contain the alkaline reagent, while the lower limit is set by the minimum concentration required to provide a basic medium. The optimum concentration is around 1 normal.

In a preferred embodiment, a quaternary ammonium hydroxide is used without any solvent, i.e., dissolved in the feed. Thus, small amounts of QAH (quaternary ammonium hydroxide) may be added to a storage tank supplying feed to the unit or to the feed as it comes to the unit, or may be injected in the reactor upstream of the charcoal. The QAH may be dissolved in a liquid, particularly a hydrocarbon, aqueous or alcoholic solvent, to permit easy metering of the QAH into the charge stock. However, once injected into the feed, the QAH dissolves in the feed.

The fixed bed of catalyst can be operated in substantially the same way as in prior art units, i.e., the temperatures, LHSV, pressure, and amounts of oxidizing agents added will be conventional. In practice, the preferred conditions are a low pressure, but sufficient to maintain liquid operation within the reactor, typically one to ten atm. absolute. Temperatures will generally be ambient, or slightly above ambient, which will speed up the rate of reaction somewhat. Temperatures of 20 to 60"C work well. The LHSV is usually in the range from 0.1 to 20. The amount of oxidizing agent added is in general at least enough to satisfy the stoichiometric amount needed to oxidize the mercaptans contained in the feed to disulfides.

Usually air is added in an amount equal to 100 to 250 percent of the amount of air required to oxidize all of the mercaptans.

The catalyst used can be any metal chelate catalyst which will speed up the rate of mercaptan oxidation in the presence of an alkaline reagent enough to permit sweetening of a sour hydrocarbon distillate over a fixed bed of the catalyst.

Some metal chelates possess sufficient activity to permit their use as in such a process. Preferred among the metal chelates are the phthalocyanines. Especially preferred are the monosulfonated derivatives of cobalt phthalocyanine. The sulfonation of the cobalt phthalocyanine makes the material soluble enough in various solvents to permit the impregnation of a fixed bed of charcoal with the catalyst. The monosulfonate derivative is preferred because the more highly sulfonated derivatives are more soluble in the water which is periodically used to wash out accumulated impurities, thus permitting the leeching away of catalyst from the bed. Recent work done with polyphthalocyanine catalysts, the mixtures of different metal phthalocyanines, indicates that these catalysts too may be acceptable for use in the process of the present invention.

The catalyst material may be composited with any suitable form of charcoal by conventional means. An excellent way of preparing the catalyst is to dissolve e.g.

cobalt phthalocyanine monosulfonate in methanol and pass the methanol-catalyst solution repeatedly over a bed of activated charcoal. The precise type of catalyst used, its method of preparation and its incorporation onto a bed of charcoal support are not crucial to the present invention.

Examples To evaluate the effectiveness of the alkaline medium of the present invention, a number of experiments were run. A kerosene which was very difficult to sweeten was used as the reference feedstock. The kerosene contained 180 wt. ppm mercaptan sulfur.

The test procedure used was not meant to be indicative of commercial operation, rather It was meant to be a simplified procedure which would quickly separate good alkaline reagents from bad ones. The test procedure was to put 2 grams of catalyst, wetted with 5 ml of the alkaline reagent being tested, plus 100 ml of feedstock in a 300 ml flask. The flasks were then capped and placed in an automated shaking device. Temperature was not measured, but all tests were conducted at ambient temperature in a room maintained at about 25 C. so changes in temperature are not believed to be significant. The contents of the flasks were sampled at uniform intervals and the mercaptan sulfur content of the hydrocarbon determined.

To ensure the validity of the test, a number of blanks were run, i.e., operation with charcoal which contained no metal phthalocyanine catalyst on it, the operation with and without conventional alkaline reagent (aqueous sodium hydroxide solution). The same brand of charcoal material was used throughout the test, a vegetable derived charcoal sold by the Westvaco Co. known in the trade as Nuchar WA. The catalyst was prepared by impregnating the charcoal with a cobalt phthalocyanine monosulfonate.The catalyst was prepared by dissolving 0.15 grams of cobalt phthalocyanine sulfonate in 100 cc of methanol The cobalt phthalocyanine was difficult to dissolve, so to insure that all of it went into solution, the dissolution proceeded step-wide, i.e., one-fourth of the alcohol was mixed with the phthalocyanine, then decanted, then the next one fourth portion was added to the cobalt phthalocyanine remaining in the bottom of the flask with grinding of the cobalt compound. This was repeated a third and a fourth time to make sure that all of the active material was dissolved in the alcohol. The alcohol was then placed in a container with 15 grams (100 cc) of charcoal, stirred slightly, and allowed to stand overnight. The alcohol was then drained from the material, and the charcoal dried under a water pump vacuum. The filtrate had only a faint blue color, but did not contain any significant amount of cobalt, so the catalyst contained 1 wt. % of the cobalt phthalocyanine sulfonate. This catalyst was divided into several 2 gram portions for use in carrying out the activity tests. The bases used, and the results of the test are reported in the following table.

TABLE I: INORGANIC BASES TEST 1 2 3 4 5 6 Wt. % Catalyst -0- 1.0 1.0 1.0 1.0 1.0 M1 Base -0- -0- 5 5 5 5 Base Description - - * Aqueous ** Alcoholic *** Aqueous **** Alcoholic NaOH NaOH NH4OH NH4OH NH4OH -------------------- wt - ppm RST ---------------- Shaking Time (Minutes) 0 180 180 180 180 180 180 5 167 158 44 5 - 15 164 152 16 2 78 44 30 164 146 11 1 53 38 60 164 137 7 1 30 33 90 - - 3 - 26 22 120 - - 3 - 25 * 1 N NaOH in H2O ** 1 N NaOCH3 Solution Made Up Reacting Na Metal With Methyl Alcohol *** 1 N NH4OH In H2O *** 1 N NH4OH Solution Made Up Using Reagent Grade Aqueous NH4OH and Methyl Alcohol A dash indicates that the mercaptan content was not tested. The results reported under test 3, i.e. use of aqueous NaOH solution, indicate the standard activity for a conventional fixed bed process.Surprisingly, the use of an alcoholic NaOH solution gives much better results than use of an aqueous NaOH solution: however, the use of an alcoholic sodium hydroxide solution forms no part of the present invention. Not all solution showed an improvement in going from an aqueous to an alcoholic phase, as can be observed by comparing the results of aqueous NH4OH to alcoholic NH4OH. The alcoholic NH4OH appeared to give slightly higher initial activity, but after a 60 minute period, the mercaptan content was 100 to 20% higher for the alcoholic solution than for the aqueous solution.

A number of organic bases were tested. The results are presented in Table II.

TABLE II TEST 7 8 9 10 Wt. % Catalyst 1.0 -0- 1.0 1.0 Ml Base 5 5 5 5 Base Description *Aqueous **Alcoholic **Alcoholic ***Alcoholic TMAH TMAH TMAH BT MAH ----------------- wt - ppm RSH -------- Shaking Time (Minutes) ~~ 0 180 180 180 180 5 - - 2 3 15 16 10 2 3 30 11 5 2 2 60 5 2 1 1 90 3 1 1 1 120 2 - 1 * 1 N Aqueous Tetramethyl-Ammonium Hydroxide (TMAH) ** 22% TMAH in Methyl-Alcohol *** 1 N Benzyltri-Methyl Ammonium Hydroxide (BT MAH) Solution Made Up Using Pure Base And Methyl Alcohol.

In addition to this accelerated testing, a test of one embodiment of the present invention was conducted at a refinery. The refiner had experienced extreme difficulty in sweetening a heavy gasoline produced from an FCC unit. The gasoline contained large amounts of materials which would oxidize to form gum, which would plug the bed, and color bodies, which made the gasoline unacceptable. In addition, the gasoline contained very high levels of mercaptan sulfur, which were difficult to oxidize. The refiner's treating unit was a fixed bed sweetening system using a catalyst similar to that prepared for the batch shake test discussed previously in this specification. The refiner used naturally occurring basic nitrogen compounds present in the hydrocarbon feed to the unit to provide the alkalinity needed.The catalyst rapidly deactivated, probably due to formation of gum or other polymeric material upon the bed of charcoal catalyst. In addition, the gasoline product contained an unacceptable gum content. The gum content was probably due to over oxidation of treated feed. At the very start of a run, air injection equivalent to 150% of stoichiometric would convert mercaptans to disulfide, while at the end of a run, the gasoline product would not be doctor sweet even with a 400 to 500 percent of stoichiometric air condition. Even increasing the temperatures to 125 F and decreasing the throughput to 45% of design capacity could not produce a sweet gasoline. In addition, the catalyst appeared to lose activity irreversibly because operation between regenerations went from eight days, to about three days, to one day.Catalyst regeneration was affected by steaming of the catalyst bed with 50 psig plant steam to desorb gum material.

The treating unit was designed to process about 20,000 barrels per day of a heavy gasoline from an FCC unit. The temperature of the gasoline entering the unit was 117 F. Oxygen was added by adding compressed air in an amount equivalent to 1.1 times the amount of air required to convert mercaptan sulfur to disulfides.

The Saybolt color df the feed was, on average, about +20. The feed did not come from storage, but came primarily from another operating unit, the FCC unit in the refinery. Accordingly, the feed composition varied during day-to-day operation.

On average, the boiling range of the charge stock was 125, 180, 285, 382 and 434 F for an initial boiling point, 10 LV Ó distilled, 50 LV %, 90 LV % and end point respectively.The feed contained from 40 to 70 ppm basic nitrogen. The gum content of the feed was determined by two methods, air jet gum and nitrogen jet gum. The air jet gum content of the gasoline feed ranged from 12 to 33 mg/100 ml, while the nitrogen jet gum content ranged from 0 to l mg/l00 ml. The great difference in gum content by the two methods indicated that the feed contained an exceptionally large amount of material which would oxidize in the presence of air to form gum.

The quaternary ammonium compound used was tetramethyl ammonium hydroxide, or TMAH. TMAH has a molecular weight of 91.15 and is soluble in water and hydrocarbons. It was available as a 26 wt. 0) solution in methanol.

Reagent grade material was used for this test. though it is believed that technical grade of TMAII will work as well.

The test was conducted in several phases, the first phase was with injection of TMAH, the second phase was without, and the third phase was again with TMAH injection. This sequence of operation did illustrate how the unit worked with and without TMAH injection. The reason for the discontinuous addition of TMAH was more accidental than intended. Three 55 gallon drums of the 26 wt. Oo solution of TMAH in methanol were readily available, while delivery of two or more drums required several days. Consequently, the amount of TMAH available was used. and when more came in later, it was also used. The data taken during this test run are presented in greater detail in Table III. These data are averages for each day of operation, and are the best available.

TABLE III TEST DAY 1 2 3 4 5 6 FEED: RSH (Mercaptan), ppm 320 300 270 263 280 280 Saybolt Color +21 +20 +19 +21 +22 +21 Air Jet Gum, mg/100 ml 33 30 27 12 14 N2 Jet Gum mg/100 ml 1 0 1 1 1 BPD (Barrels Per Day) 29,760 28,450 19,600 23,800 27,200 27,600 Air, SCFH (FT /HR) 1,900 2,930 2,930 Air, % of minimum 120 260 320 210 160 250 Rx Temp. F. 120 120 120 120 121 120 Rx Pressure, PSIG 102 102 102 101 102 102 Rx LHSV* 1.79 1.71 1.18 1.43 1.65 1.68 TREATED GASOLINE:: RSH-S (Mercaptan-Sulphur), ppm 2.2 22 28 28 15 10 Saybolt Color +10 +1 to -7 -13 -13 +10 to -7 +4 Air Jet Gum, mg/100 ml 1 11 4 5 2 N2 Jet Gum mg/100 ml 0 1 0 3 1 Peroxide Number LT 0.01 0.13 1.22 2.41 0.06 0.02 Doctor Test Neg Pos/Neg Neg Pos/Neg Slightly Slightly Positive Positive TMAH Injection, ppm N 5.6 0 0 3.0 3.0 3.0 *Reactor's Liquid Hourly Space Velocity As a supplement to the data, the notes made by a chemical engineer supervising the test run are also reported.

"Initially, the following conditions were established on the unit: Heavy FCC gasoline flow = 19,500 BPD Gasoline temperature = 117 F Air rate = 1.1 x theory RSH-S = 310 ppm Color = +19 Saybolt TMAH injection rate = 6 gal/hr TMAH concentration in gasoline = 8.8 ppm as N or 10.7 ppm as OH "Within an hour of initiating TMAH injection, gasoline product RSH-S was reduced to 20 ppm. Air rate was increased to 1,3 x theory and within five hours the product gasoline was doctor negative.

"The unit charge rate was increased to 29,800 BPD which reduced the fixed TMAH injection to a concentration of 5.6 ppm. as nitrogen or 6.8 ppm. as OH in the gasoline charge to the reactor. The air rate was reduced to 1.1 x theory. The above conditions were maintained for about 16 hours until the first three drums of TMAH had been used.

"The effect of the small quantity of alkali added was dramatic. Color loss during the above trial was only 3 to 6 Saybolt numbers. Product mercaptan was 1 to 2 ppm. Existent gum and peroxide number were minimal. Product alkalinity was low, e.g., pH= 6.1. In sumary this plant trial confirmed previous pilot plant trials conducted at Des Plaines.

"While waiting for the remaining two drums of TMAH to arrive at the unit, the effect of deleting TMAH injection on the unit performance was noted. Product gasoline remained sweet for 10 hours at 1.1 x theory air rate after TMAH injection stopped. It was then necessary to raise air rate to 2.1 x theory to maintain sweet product another 10 hours at which time reactor LHSV was halved and air rate increased to 3 x theory to maintain sweet product for another 12 hours. The gasoline remained sour for another day during which time product color loss, existent gum and peroxide number quickly increased. At that time the additional two drums of TMAH were added to the unit at reduced injection rate.

"TMAH injection at 3 ppm as Nitrogen and 4 ppm as Nitrogen even at 3 x theory air rate failed to sweeten the gasoline, e.g., 10 ppm. RSH-S. This no doubt results from the short duration of TMAH injection after the bed had been allowed to become fouled following the first TMAH trial. From the reduced existent gum and peroxide number and improved color in the product, the TMAH was benefiting operation at the reduced injection rate." In the refinery test of the present invention wherein tetramethylammonium hydroxide was continuously added to the feed to the treating unit, no complaints were noted of any objectionable odor or characteristics imparted to the feed via dissolution of the TMAH in the product. The test run, however, was of short duration, and on only one feedstock.Because many organic alkaline reagents, and especially the quaternary ammonium compounds, are soluble in the oil, they may appear in the treated product. A significant amount of the organic alkaline medium may be present in the treated product when a highly alkaline medium is required for the treating process. Similarly, the end use of the treated hydrocarbon may put very stringent limitations of the amounts of organic alkaline reagent which may be present. This is particularly true when using tetramethylammonium hydroxide which can impart a "fishy" odor to some types of hydrocarbon stocks.

It also may be desirable to recover the organic alkaline medium used to permit its reuse within the process. In general, it is believed that the small quantities of QAH used in the process of the present invention will not normally justify elaborate QAH recovery facilities, but the economics of each refinery unit will be different.

When it is desired, for reasons of economics, or to meet a stringent product specification, to remove the organic alkaline reagent dissolved in the feed, this can be accomplished by washing the organic alkaline reagent from the treated product with water. The washwater can then be fractionated to recover a water phase and an alkaline reagent rich phase. The alkaline reagent rich phase may be recycled to the feed to the unit to satisfy some or substantially all of the process's requlrement for alkaline reagent. The water recovered from the fractionation zone may be reused to wash organic alkaline reagent from the treated product.It will probably be necessary to continuously remove a small portion of the alkaline reagent rich stream, containing acidic impurities such as naphthenic acids, phenols, aliphatic acids, and the like, and dispose of it by mixing it with fuel oil for burning in the refinery. The net consumption of organic alkaline reagent will then be only a function of the non-mercaptan acidic components of the feed to the unit, in addition to any loss of organic alkaline reagent in the dissolved product. In general, it will not be worthwhile to recover organic alkaline reagent unless at least about 500/0 of the alkaline organic reagent remaining in the treated product is removed therefrom in the water-wash step.

The relative solubilities of the organic alkaline reagent in water and in hydrocarbon, the product specifications, and the price of organic alkaline reagent will determine the exact percentage recovery of organic alkaline reagent desired, and the ratio of wash-water to treated product needed.

Claims (20)

1. WHAT WE CLAIM IS:

   l. A process for sweetening a sour hydrocarbon stream which comprises contacting the sour hydrocarbon stream with an oxidizing agent in the presence of a metal chelate catalyst and an organic base.
2. 2. A process as claimed in claim l, wherein the organic base is a quaternary ammonium base.
3. 3. A process as claimed in claim 1 or 2. wherein the metal cheiate catalyst is a metal phthalocyanine catalyst.
4. 4. A process for treating a sour hydrocarbon distillate containing mercaptans to react the mercaptans with an oxidizing agent by passing the distillate, the oxidizing agent and an alkaline medium through a fixed bed of a metal phthalocyanine catalyst, wherein the alkaline medium comprises a quaternary ammonium base.
5. 5. A process as claimed in any of claims 2 to 4 wherein the quaternary ammonium base is a quaternary ammonium hydroxide.
6. 6. A process as claimed in any of claims 2 to 4 wherein the quaternary ammonium base comprises tetramethyl ammonium hydroxide.
7. 7. A process as claimed in any of claims 4 to 6 wherein the alkaline medium is contained in a separate aqueous or alcoholic phase within the reaction zone.
8. 8. A process as claimed in any of claims 4 to 6 wherein the alkaline medium is dissolved in the hydrocarbon distillate.
9. 9. A process as claimed in claim 8 wherein the alkaline medium is dissolved in a liquid and continuously injected into the hydrocarbon distillate.
10. 10. A process as claimed in any of claims 4 to 9, wherein the metal phthalocyanine catalyst is composited with a carbon carrier.
11. 11. A process as claimed in any of claims 4 to 10 wherein the distillate, oxidizing agent and alkaline medium are passed through the fixed bed of metal phthalocyanine catalyst at a liquid hourly space velocity of 0.1 to 20.
12. 12. A process as claimed in any of claims 4 to 11 wherein the quaternary ammonium base is present in an amount equivalent to 1 to 500 wt. ppm, based upon the weight of sour hydrocarbon distillate.
13. 13. A process for oxidizing mercaptans present in a liquid hydrocarbon stream comprising: (a) contacting the hydrocarbon stream with an oxidizing agent in the presence of a metal chelate catalyst and an organic alkaline reagent to produce a treated hydrocarbon stream with reduced mercaptan content and containing dissolved organic alkaline reagent (b) contacting the treated hydrocarbon phase with water and recovering an aqueous phase containing at least 50% of the organic alkaline reagent present in the treated hydrocarbon: (c) passing the aqueous phase from step (b) to a fractionation means and separately recovering therefrom water and concentrated organic alkaline reagent: (d) recycling the water from step (c) to step (b); and, (e) recycling the concentrated organic alkaline reagent from step (c) to step (a).
14. 14. A process as claimed in claim 13 wherein the oxidizing agent is air and the metal chelate catalyst is a cobalt phthalocyanine sulfonate supported on charcoal.
15. 15. A process as claimed'in claim 13 or 14 wherein the organic alkaline reagent is a quaternary ammonium hydroxide.
16. 16. 'A process as claintedin claim 15 wherein the organic alkaline reagent is tetramethyl ammonium hydroxide.
17. 17. A process as claimed in claim 15 wherein the organic alkaline reagent is benzyltrimethyl ammonium hydroxide.
18. 18. A process as claimed in any of claims 13 to 17 wherein the organic alkaline reagent is present in an amount equivalent to 1 to 500 wt. ppm, based upon the weight of liquid hydrocarbon.
19. 19. A process as claimed in claim 1, 4 or 13 carried out substantially as hereinbefore described or exemplified.
20. 20. A sweetened hydrocarbon stream when obtained by a process as claimed in any of claims 1 to 19.