CA1094496A

CA1094496A - Process for sweetening sour hydrocarbon distillates

Info

Publication number: CA1094496A
Application number: CA269,199A
Authority: CA
Inventors: Kenneth M. Brown
Original assignee: UOP LLC
Current assignee: Honeywell UOP LLC
Priority date: 1976-01-14
Filing date: 1977-01-05
Publication date: 1981-01-27
Also published as: GB1566052A; DE2700850B2; BR7700156A; YU39982B; AU505893B2; AU2113077A; IT1076210B; ZA7740B; FR2338322B1; FR2338322A1; DE2700850C3; JPS52101206A; ES455004A1; SU689623A3; YU5377A; DE2700850A1; JPS558116B2

Abstract

ABSTRACT OF THE DISCLOSURE

An improved process for sweetening of sour hydrocar-bons in a fixed bed treating process wherein the hydrocarbons, containing mercaptans, contact a phthalocyanine catalyst on charcoal in the presence of a basic medium and oxygen. The improvement is use of a quaternary ammonium compound as the basic medium, instead of the aqueous sodium hydroxide solution customarily used. A process for recovery of quaternary ammon-ium in a compound and its reuse in the process is also dis-closed.

Description

?6 BACKGROUND OF THE INVENTION

lQ Field Of The Invention The invention relates to an improvement in the treat-ment of hydrocarbon distillates, and particularly to an improved method of sweetening sour hydrocarbon distillates by oxidizing mercaptans in the distillate to disulfides in the presence of a phthalocyanine catalygt on a charcoal carrier in the presence of a basic medium and oxygen. An improved basic medium is disclosed, along with a process for recovery and reuse of a basic medium which dissolves in the treated hydrocarbon.

Prior Art The fixed bed sweetening of hydrocarbons is well known in the art. A typical fixed bed sweetening process is disclosed ~ J

~0~ 6 in U. S. Patent 2,9~8,50~ ~
In this patent, a sour petroleum distillate is contacted with a fixed bed of a metal phthalo-cyanine catalyst composited with a charcoal carrier in the presence of oxygen and an alkaline reagent. The patentee teaches that any alkaline reagent may be used, but that aqueous sodium hydroxide solution is preferred because it is cheapest. The other alkaline reagents taught were aqueous solutions of lithium hydroxide, rubidium hydroxide, and cesium hydroxide O The patentee taught ~10 that it was 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 referring to a non-,.~ .
!" ' aqueous solvent, rather than a non-alkaline solvent. See 2 lines 46-69.
;15 The advantage of a fixed bed treating process is that the refiner has a high degree of control over the sweetening opexation, 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 this patent is that it does not add any significant amount of harmful materials - to the treated hydrocarbon. 'rhis 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 produ~ts.
~5 Another type of sweetening process~ and one that occurs almost by accident in a number of refineries~ is inhibitor sweet-ening. This is a phenomena observed when a refiner adds an , .
~ -2-,~

10~4496 inhibitor such as phenylene diamine to his 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 differ-entiate 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, was exceedingly satisfactory for many hydrocarbon charge stocks, there were a few problems encountered in the practice of that invention. Specifically, a number of feeds contained naphthenic acids and other oxidation products which would react with the strong caustic solutions used to pro-vide an alkaline reagent. The reaction product of the naphthenic acid and alkaline reagent formed 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 insure removal of all caustic from the hydro-carbon 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 pxesence of caustic solution can be eliminated by passing the treated hydrocarbon throug}l a two-phase separator, then passing the hydrocarbon phase through a water-wash zone to remove caustic, followed by another two-~hase 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 insure that the last traces of water are removed from the process.

Another problem encountered in the treating arts, is that the desirable fixed bed sweetening process is being used to treat very refractory sour hydrocarbon distillates. The hydro--carbon distillates encountered by refiners today are becoming !, ' more difficult to treat because, with the worldwide demand for o~l, reiners are encountering distillates which are exceedingly difficult to sweeten. With some hydrocarbon distillate, the only ; way to sweeten them in a conventional fixed bed unit is to pro-vide for frequent replacement of the catalyst in the bed, and even more frequent placement of the strong caustic used to wet :~ 20 the charcoal bed.
Accordingly, I realized that it would be very desir-able to find a way to operate the fixed bed treating process without using an aqueous solution of sodium hydroxide. It :j would also be desirable if a substitute could be found which would be soluble in hydrocarbons, and perhaps eliminating the necessity for a separate alkaline phase in the fixed bed - sweetening process.

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: ~ ' `., 4~6 I also realized that it would be desirable to eliminate, if possible, the waste disposal problem associated with the use of aqueous sodium hydroxide solutions.
I conducted a series of tests, and discovered that the ~ 5 use of quaternary ammonium hydroxides would permit 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 in a pro-`~ cess for treating a sour hydrocarbon distillate containing mer-captans by reacting the mercaptans with an oxidizing agent by - passing the distillate, oxidizing agent and an alkaline medium through a fixed bed of a phthalocyanine catalyst composited with a carbon carrier at a liquid hourly space velocity of 0.1 to 20, the improvement which comprises use of a quaternary ammonium compound as the alkaline medium.
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 10~ 96 water from step (c) to step (b); and (e) recycling the concen-trated organic alkaline reagent from step (c) to step (a).
It is believed that any highly alkaline quaternary ammonium compound may be used. The preferred compound is a quaternary ammonium hydroxide, and 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 ; 10 hydroxide is another excellent alkaline reagent for use in the present invention.
The quaternary ammonium compounds may be used in an ; aqueous or alcoholic solution, and substitute for 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 alkaline - solution of the quaternary ammonium compound. In the preferred embodiment, the quaternary ammonium compounds are dissolved in the hydrocarbon feed to the fixed bed unit. This permits elim-ination of an aqueous or alcoholic phase within the fixed bed treating reactor.
When the quaternary ammonium compounds are used in an aqueous or alcoholic solution, the concentration should be 0.1 to 10 normal. The upper limit is a function of how much quater-nary amine will dissolve in the aqueous or alkaline medium usedto contain the alkaline reagent, while the lower limit is set 10~

by the minimum concentration required to provide a basic medium.
Optimum concentration secms to bc around 1 n~mal.
In th~ preferre~ embodiment, quaternary ammonium hydroxide is used without any solvent, i.e., dissolved in the feed. Thus, small amounts of QAH, or quaternary ammonium hy-droxide, may be added to a storage tank supplying feed to the unit, or to the feed as it comes to the unit, or injected in the reactor upstream of the charcoal. The QAH may be dissolved in a hydro-carbon, aqueous or alcoholic solvent to permit easy metering of the QAH into the charge stock. However, once injected into the feed, the QAH would dissolve in the feed.
The fixed bed of catalyst will operate in substantially the same way as in prior art units, i.e., the temperatures, LHSV, pressure, and amounts of oxidizing agents added will be conven-'~ 15 tional. 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 may range from 0.1 to 20. The amount of oxidiz-ing agent added should be at least enough to satisfy the stoichio-metric 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 catalyst which will speed up the rate of mercaptan oxidation in the presence of an alkaline ~0~44~6 reagent enough to permit sweetening of a sour hydrocarbon dis-tillate 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 phthalo-~- 5 cyanines. Especially preferred are the monosulfonated deriva-, tives of cobalt phthalocyanine. ~he sulfonation of the cobalt phthalocyanine makes the material soluble enough in various sol-vents 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 impuri-tles permitting the leeching away of catalyst from the bed.
Recent work done with polyphthalocyanine catalysts, and mixtures of different metal phthalocyanines, indicates that these catalyst too may be acceptable for use in the present invention, although ,~ forming no part thereof.
The catalyst material may be composited with any suit-able form of charcoal by conventional means. An excellent way of preparing the catalyst is to dissolve, e.g., cobalt phthalo-cyanine monosulfonate in methanol and pass the methanol-catalyst solution repeatedly over a bed of activated charcoal. The pre-cise type of catalyst used, its method of preparation and its incorporation onto a bed of charcoal support form no part of - the present invention.
EXA~PLES
To evaluate the effectiveness of the alkaline medium of the present invention, a number of experiments were run. A

10~4~6 , ' kerosene which was very difficult to sweeten was used as the ` reference feedstock. The kerosene contained 180 wt. ppm mer-captan sulfur.
The test procedure used was not meant to be indicative ; 5 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 i 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 con-tent of the hydrocarbon determined.
To insure the validity of the test, a number of blanks were run, i.e., operation with charcoal which contained no metal phthalocyanine catalyst on it, and operation with and without conventional alkaline reagent (aqueous sodium hydroxide solution).
The same lot 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 phthalo-cyanine sulfonate in 100 cc of methanol. The cobalt phthalo-cyanine was difficult to dissolve, so to insure that all of it _9_ , ~ ~ ,~ ,. :., .

! ~ went into solution, the dissolu-tion proceeded step-wise, i.e , one-fourth of the alcohol was mixed with the phthalocyanine, then decanted, then the next o,ne-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 yrams (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, ., .

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109 1~96 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 convcntional fixed bed process. Surprisingly, the use of an alcoholic NaO~I
solution gives much better results than use of an aqueous NaOH
solution, however, the use of an alcoholic sodium hydroxide solu-tion forms no part of the present invention. Not all solutions showed an improvement in going from an aqueous to an alcoholic phase, as can be observed by comparing the results of aqueous NH40H to alcoholic NH40H. The alcoholic NH40H 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.

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10~4496 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 hy-drocarbon feed to the unit, to provide the alkalinity needed.
The catalyst rapidly deactivated, probably due to formation of , 15 gum or other polymeric material upon the bed of charcoal cata-lyst. In addition, the gasoline product contained an unacceptable ~ gum content. The gum content was probably due to over oxidation 3 of treated feed. At the very start of a run, air injection equiv-alent to 150~ of stoichiometric would convert mercaptans to di-sulfide, while at the end of a run, the gasoline product would not be doctor sweet even with a 400 or 500 percent of stoichio-metric air condition. Even increasing the temperature~ 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 effected by steaming of the catalyst bed with 50 psig plant steam to desorb gum material.
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The treating unit was designed to process about 20,000 barrels per day of a heavy gasoline from an FCC unit. The tem-perature 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 of 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 refineryO Ac-cordingly, the feed composition varied during day-to-day opera-tion. On average, the boiling range of the charge stock was 125,180, 285, 382 and 434 F for an initial boiling point, 10 LV %
distilled, 50 LV %, 90 LV % and end point respectively. The feed contained from 40 to 70 ppm basic nitrogen. The gum con-tent 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 con-tent ranged from 0 to 1 mg/100 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. T~H has a molecular weight of 91.15 and is soluble in water and hydrocarbons. It was available as a 26 wt. % solution in methanol. Reagent grade material was used for this test, though it is believed that ~chnical grade of TM~H will work as well.

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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 sequenc~ of operation did illustrate how the unit worked with and without TMAH injection. The reason for the discontinuous addition of TMAII was more accidental than intended. Three 55 yallon drums of the 26 wt. ~ solution of TMAII in methanol were readily available, while de]ivery of two or more drums required several days. Consequently, the amount of TMAI-I 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 be~t available.

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10!~ 6 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 = 117F
Air rate = 1.1 x theory RSH-S = 310 ppm Color = +19 Saybolt T~iAH injection rate = 6 gal/hr T~H concentration in gasoline = 8.8 ppm as N or ` 10.7 ppm as OH
"Within an hour of initiating Tl~AH 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 Tl~AH 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 summary this plant trial confirmed previous pilot plant trials conducted at Des Plaines.

10~'t4~36 hile waiting for the remaining two drums of TMAH
to arrive at the unit, the effect of deleting T~H injection on the unit performance was noted. Product gasoline remained sweet for 10 hours at 1.1 x theory air rate after TMAH injec-tion stopped. It was then necessary to raise air rate to 2.1x 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 T~H
were added to the unit at reduced injection rate.
"TMAH injection at 3 ppm as Nitrogèn 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 T~H 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 Ti~H 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 T~H in the product. The test run, however, was of short duration, and on only one feedstock.

~0~ 6 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 or-ganic alkaline reagent dissolved in the feed, this can beaccomplished by washing the organic alkaline reagent from the treated product with water. The washwater can then be frac-tionated 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 sati~fy some or substantially all of the process's requirement for alkaline reagent. The water recovered from the fractionation zone may be reused to wash ~09~96 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 impuri-;~ ties such as naphthenic acids, phenols, aliphatic acids, and the like, and dispose of it by mixing it with fuel oil forburning in the refinery. The net consumption of organic alkaline reagent will then be only a function of the non-mer-captan 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 50~ 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 specifica-tions, and the price of organic alkaline reagent will deter-mine the exact percentage recovery of organic alkaline reagent desired, and the ratio of wash-water to treated product needed.

'

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a process for treating a sour hydrocarbon dis-tillate containing mercaptans by reacting the mercaptans with an oxidizing agent by passing the distillate, oxidizing agent and an alkaline medium through a fixed bed of a phthalocyanine catalyst composited with a carbon carrier at a liquid hourly space velocity of 0.1 to 20, the improvement which comprises use of a quaternary ammonium compound as the alkaline medium.

2. Improved process of Claim 1 wherein the quaternary ammonium compound is a quaternary ammonium hydroxide.

3. Improved process of Claim 1 wherein the quaternary ammonium compound comprises tetramethyl ammonium hydroxide.

4. Improved process of Claim 1 wherein the alkaline medium is contained in a separate aqueous or alcoholic phase within the reaction zone.

5. Improved process of Claim 1 wherein the alkaline medium is dissolved in the hydrocarbon distillate.

6. Improved process of Claim 5 wherein the alkaline medium is dissolved in a fluid and continuously injected into the hydrocarbon distillate.

7. Improved process of Claim 5 wherein the alkaline medium is tetramethyl ammonium hydroxide.

8. Improved process of Claim 5 wherein the alkaline medium is benzyltrimethyl ammonium hydroxide.

9. Improved process of claim 1 wherein the alkaline medium is present in an amount equivalent to 1 to 500 wt. ppm, based upon the weight of sour hydrocarbon distillate.

10. 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 a quaternary ammonium compound at a liquid hourly space velocity of 0.1 to 20 to produce a treaded 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 hydro-carbon;
(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).

11. Process of claim 10 wherein the oxidizing agent is air and the metal chelate catalyst is a cobalt phthalocyanine sulfonate supported on charcoal.

12. Process of claim 10 wherein the quaternary ammonium compound is a quaternary ammonium hydroxide.

13. Process of claim 10 wherein the quaternary ammonium compound is tetramethyl ammonium hydroxide.

14. Process of claim 10 wherein the quaternary ammonium compound is benzyltrimethyl ammonium hydroxide.

15. Process of claim 10 wherein the quaternary ammonium compound is present in an amount equivalent to 1 to 500 wt. ppm, based upon the weight of liquid hydrocarbon.