US2297751A - Sweetening hydrocarbon distillates - Google Patents

Description

Oct. 6, 1942.l c. DRYER Erm.

SWEETENING I-IYDROCLARBON` Y DISTILLATES Filed Sept. 8, 1939 Patented Oct. 6, 1942 SWEETENING HYoRooARoN Dis'riLLA'rEs Charles G. Dryer and Charles Wirth, III, Chicago,

Ill., assignors to Universal Oil Products Company, Chicago, Ill., a corporation of Delaware Application September 8, 1939, Serial No. 293,894

2 Claims.

This invention relates to an improved method for sweetening hydrocarbon distillates.

Distillates which may be treated according to the present process include those of petroleum origin obtained by various methods such as the primary distillation of crude hydrocarbon oils, the cracking of crude petroleum or fractions thereof, the polymerization of normally gaseous oleiins from cracking or other processes, etc. Distillates from other hydrocarbon sources, such as coal tars, shale oils, etc., may also be treated by the present method.

`Practically all hydrocarbon distillates require some form of treatment to render them of marketable quality, Vand this is particularly true of cracked products of motor fuel boiling range. Many distillates require little or no treatment other than sweetening which is often supplemented, in the case of cracked gasolines, by the addition of inhibitors to increase storage stability and prevent the formation of color, gum, and other objectional products during the storage period.

Among the sweetening methods which have been used'with considerable success is the socalled doctor process employing alkaline solutions of sodium plumbite. Another method is the hypochlorite process wherein gasolines are sweetened by means of solutions or suspensions of sodium or calcium hypochlorite. The copper sweetening process has been developed in recent years to overcome many of the disadvantages of these methods. It is with improvements in this process that the present invention is concerned.

In one specific embodiment the present invention comprises contacting sour hydrocarbon distillate with a dilute solution of an acidic substance, separating the distillate, contacting it with a drying agent to remove water, mixing the dried distillate with air, contacting the mixture with a solid copper-containing sweetening reagent in a primary sweetening step, passing the sweetened gasoline and residual air intoY a Vertical contactor the upper section of which is vented and' serves as a means of separating the residual air, passing the gasoline through the lower section of said vertical contactor wherein is disposed a layer of a secondary treating agent to remove copper from the sweetened distillate, and recovering the finished distillate.

Any relatively low boiling hydrocarbon distillate such as natural, straight run, cracked or polymer gasoline, naphtha, kerosene, furnace oil,

etc., may be sweetened according to the present process.

The distillate is contacted with a dilute solution of an acidic substance, this term being intended to include materials which yield a solution having a pI-I of less than 7 and which in the state of dilution in which they are used are relatively unreactive with the hydrocarbons. Ineluded are mineral acids such as sulfuric, phosphoric and hydrochloric acids; acid salts such as sodium and ammonium acid-sulphate or acidphosphate; heavy metal halides such as aluminum chloride, iron chloride, zinc chloride, etc.; and organic acids such as acetic acid. Normally, the concentration of the solution is less than 20% in order to prevent undue reaction of the acidic substance with hydrocarbon components of the distillates undergoing treatment. This depends to a large extent on the acidic substance being used. Solutions of sulfuric or phosphoric acid of 1-20% and preferably 1-10% may be satisfactorily used. When using hydrochloric acid, solutions of less than 10% concentration are preferred. When using acid sulfates such as sodium acid-sulphate somewhat stronger solutions may be employed without effecting undesirable secondary reactions. Contacting is carried out at substantially atmospheric temperature.

Treatment with dilute acidic substance may be effected in any suitable manner such as for example mixing the acidic substance with the gasoline in an eductor or Venturi type mixer, by mechanical agitation, by counter-current contacting in a packed column, or similar equivalent devices. A separation step follows in which the hydrocarbon is substantially freed of suspended aqueous solution. In certain cases this is followed by treatment with alkali although this is not always done.

The effect of treatment with dilute acidic substances is to remove colored or color-forming materials which tend to accumulate on the sweetening reagent and later under the influence of air, to redissolve thus throwing the distillate off color and depreciating its other desirable properties such as storage stability.

The clear hydrocarbon distillate is withdrawn from the settler and passed through a drying step, which comprises contacting it with a solid drying agent cap-able of absorbing Water from the hydrocarbon. The reagent may consist of activated alumina, silica gel, calcium sulphate, rock salt, calcium chloride, solid sodium or potassium hydroxide, etc.

The dried distillate is then mixed with air and passed into a primary treating tower wherein the sweetening reaction occurs by means of a coppercontaining sweetening reagent.

The purpose of the drying step is to minimize migration of soluble copper salts through the reagent bed which results when water is formed during the sweetening reaction. The dried gasoline dissolves a major part of the water formed and removes it so that it cannot accumulate and migration of the salts is stopped.

The sweetening reagent may comprise any suitable solid copper-containing material such as, for example, a mixture of copper sulfate with sodium or ammonium chloride, and an inert filler such as pumice, fullers earth, rebrick, etc. Impregnated sweetening reagents are also used, these consisting of an adsorbent granular carrier impregnated with mixtures of copper sulfate and an alkalinous chloride, or with cupric chloride or other suitable copper compounds. The

term alkalinous chloride is intended to mean chlorides of alkali or alkaline earth metals including the hypothetical metal ammonium.

The secondaryV treating tower may comprise any suitable elongated vertical vessel in the lower section of which is disposed a bed of secondary reagent. I'he top section of the tower is empty and serves as an air separator. It has a vent controlled by a valve to release residual air. A liquid level controller is used to maintain a layer of liquid over the reagent bed. The liquid level is kept suliciently below the vent to prevent mechanical loss of distillate with the released air.

The advantage of this particular step is that it dispenses with a separate air separator which is normally used in connection with the copper sweetening process between the primary and secondary treating steps. A further advantage is that it shortens the lapse of time between the primary sweetening step and contacting of the sweetened distillate with the secondary reagent. This has been found to be of particular importance when sweetening cracked gasolines. Results wherein the copper sweetened gasoline has been allowed to stand for even a relatively short time after leaving the primary sweetening tower have shown that the gasoline is no longer readily treated for copper removal and that it has suffered a loss in some of its desirable properties such as color and storage stability. The effects on the gasoline in even as short a time as minutes to 1/2 hour is often sufficient to bring about irreparable damage unless expensive expedi'ents such as redistillation are resorted to. By using the secondary tower as a combination air separator and treating tower the gasoline from the primary sweetening step is contacted immediately with the secondary reagent and the residual air is removed from contact with the gasoline as eiciently as in the formerly used air separator.

The secondary reagent may suitably comprise a heavy' metal sulfide deposited on a liller, for example, zinc sulfide on pumice. Other suliides such as iron sulde, lead sulfide, etc., or alkalior alkaline-earth metal suliides deposited on a carrier vsuch as pumice or fullers earth may be used.

One embodiment of our process is shown diagrammatically by the accompanying drawing, although this should not be interpreted as restricting the invention to the exact apparatus shown.

Referring to the drawing, hydrocarbon distillate such asl gasoline is introduced through line I, valve 2, pump 3, valve 4, which joins with line 5 and is commingled with a dilute acidic solution passing through valve 6, pump I and valve 8. Mixing is accomplished in line 9 and mixer I0 which may comprise any suitable type of mixing apparatus. The Inixture passes through settler II, from which spent acidic solution is withdrawn through valve I2 and line I3. Clear gasoline passes through line I4 valve I5 to gasoline drier I6 which may be, for example, a vertical tower packed with a suitable drying agent in solid form. The dried gasoline is removed through line I'I and valve I8. Line I9 and valve 2i! serve as a means of draining the drier. Air is introduced through line 2 I, valve 22 and air drier 23. The air drier may be similar to the gasoline drier IS or may comprise merely a knockout drum for removing entrained water. It is not necessary to dry the air completely so that almost any suitable packing material such as steel wool, rock salt, fullers earth, etc., may be used. Water may be removed from the bottom of the drier through line 24, valve 25. The dried air passes through line 26 and valve 21 which joins with line I1. The air and gasoline are mixed in mixer 28 and enter primary treating tower 29 through distributor 30. Line 3l and valve 32 serve as a means of venting the primary treating tower. The tower is equipped with pressure gauge 33. The tower contains 'a solid Copper-containing sweetening reagent such as one of those previously described. The hydrocarbon distillate and air under pressure of 30-100 pounds per square inch approximately are passed through the sweetening reagent and are removed through line 34 and valve 35 to secondary treating tower 36. Line 3l and valve 38 serve as a means of draining tower 29. TreatirgV tower 3E comprises a vertical tower, the upper section of which is empty and serves as an air separator. Air is withdrawn from the top of the tower through line and valve 46. The gasoline passes downwardly through a layer of granular secondary sweetening reagent such as Zinc sulphide deposited on pumice or other suitable material. The tower is equipped with liquid level controller 3.9 which actuates valve 4I), said valve being contained in line 4I. The tower may be drained through line 42 and valve 43. The tower is equipped with pressure gauge 44.

The following example is given to illustrate the usefulness and practicability of our invention but should not be construed as limiting it to the exact conditions or materials used therein.

A sour West Texas cracked gasoline was contacted with 5% by volume of a 21/2% solution of sulfuric acid, the gasoline was separated and passed into a drying step where it was contacted with activated alumina. The dryer consisted of two towers which were used alternatively, the material in one reactor being dried and regenerated while the other was in operation. Regeneration was carried out by heating the activated alumina while passing dry air through it continuously to remove water.

'Ihe dried gasoline was mixed with approximately 6 cubic feet of air per barrel of gasoline and passed into a copper sweetening step. The sweetening reagent consisted of a mixture of copper sulphate, ammonium chloride and pumice. The gasoline was passed downwardly through the reagent under a pressure of pounds per square inch. The sweetened gasoline containing residual air was passed to the secondary treating tower. The upper section of the tower was used as an air separator from the top of which the air was released. In this way there was a minimum lapse of time between sweetening with the copper reagent and the treatment of the gasoline to remove dissolved copper therefrom, which is one of the advantages of the present process. Residual air was withdrawn from the top of the tower. The gasoline passed through the secondary treating agent which comprised zinc sulfide deposited on pumice. The nished treated gasoline was withdrawn from the bottom of the secondary treating tower and passed to storage.

The properties of the sweetened product are compared in the following table with those of the original sour gasoline, the gasoline copper-sweetened but not previously treated with dilute acid, and the gasoline which has been pretreated with dilute acid, copper-sweetened, passed through an air separator and then through the secondary treater to remove dissolved copper.

The results show that the acid pretreatment with an air separator and secondary treater yielded a gasoline of improved properties over those obtained when the gasoline was not acid pretreated, but that the properties other than the doctor test were slightly poorer than those of the original sour gasoline. When using the combined air separator and secondary treater following copper-sweetening of acid pretreated gasoline, the properties of the sweetened gasoline were improved still further.

During the operation of the plant, the advantage of drying the gasoline prior to copper sweetening was demonstrated by the fact that migration of the copper salts through the reagent bed was minimized. When operating without an air dryer, it Was necessary to remove the sweetening reagent at intervals of approximately 30-40 days, remix it in order to produce a uniform reagent mass, and return it to the tower. This was necessitated by migration of salts resulting in the development of channelling due to migration of the salts. When operating according to the present invention, a period of 60-90 days operation was possible without the development of channelling.

We claim as our invention:

1. In the treatment of sour hydrocarbon distillates with a copper-containing sweetening agent in the presence of oxygen-containing gas, the method which comprises introducing the mixture of distillate and gas from the sweetening step into the upper portion of a vertical chamber having a free space in its upper portion and a layer of copper-removing agent in its lower portion, separating the gas from the distillate in said free space of the chamber and permitting the separated distillate to gravitate through said layer, whereby to minimize the time interval between the sweetening of the distillate and the removal of dissolved copper therefrom.

2. A process for sweetening sour hydrocarbon distillates which comprises treating the ldistillate with an aqueous mineral acid solution of a concentration not substantially above 20%, whereby to remove colored and color-forming bodies without undue reaction on the hydrocarbon components of the distillate, drying the thus treated distillate to remove water therefrom, mixing an oxygen-containing gas with the dried distillate and contacting the resultant mixture with a copper-containing sweetening agent, introducing the mixture of distillate and gas from the sweetening step into the upper portion of a vertical chamber having a free space in its upper portion and a layer of copper-removing agent in its lower portion, separating the gas from the distillate in said free space of the chamber and permitting the separated distillate to gravitate through said layer, whereby to minimize the time interval between the sweetening of the distillate and the removal of dissolved copper therefrom.

CHARLES G. DRYER. CHARLES WIRTl-I III.

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