US2208591A - Process of refining petroleum distillates - Google Patents

Description

July 23, 1940 E. E. LYDER PROCESS 0F REFINING PETROLEUM DISTILLATES Filed oct. 11, 1937 /Nl/ENTOR frnes E. gde/ A 7'7'ORNEV Patented July 23, 1940 UNITEDv STATES PnooEss oF REFINING PETROLEUM DIs'rILLATEs Ernest E. Lyder, Richmond, Calif., assignor to Standard Oil Company of California, San

Francisco, Calif., a corporation of Delaware Application October 11, 1937, Serial No. 168,313

9 Claims.

This invention relates to a process of refining hydrocarbon oils and especially to a process of sweetening petroleum distillates containing mercaptans. The invention involves a process of the type disclosed in United States Patent No. 2,049,423 granted to Brown et al. August 4, 1936 and is more particularly concerned with maintaining the lead sulfide catalyst utilized in such a process in an active condition.

Accordingly, an object ofthe invention is to provide an improved process for sweetening petroleuni hydrocarbons.

Another object of the invention is to provide an eiective method for reactivating a lead suliide catalyst for use in sweetening processes.

A further object of the invention is to provide a process for reactivating or regenerating a lead sulde treating agent in processes which require that the treating agent be maintained in a balanced condition, i. e. substantially free from either soluble suliides or soluble lead compounds.

The drawing is a diagrammatic illustration of an apparatus for carrying out the process and attaining the objects of the invention.

In the type of process with which the invention is primarily concerned, a petroleum distillate is intimately contacted with an aqueous caustic treating solution containing insoluble lead suliide in suspension. The proportions of caustic soda and lead sullide present in the treating agent may vary through a considerable range of proportions. The aqueous solution of Yalkali preferably comprises a 20 to 30 B. caustic soda solution, although as low a concentration as 1 B. is operative. The more dilute caustic solutions give a slower sweetening reaction rate. This slower rate is particularly noticeable and often objectionable when the hydrocarbons being treated have a relatively high mercaptan content. The amount of lead suliide in suspension in the caustic solution may vary from 01.1 to 2.0 pounds of lead sulde per gallon of reagant. The preferred proportions are from 0.5 to 1 other than sodium or potassium may be used in the aqueous portion of the treating agent. Additional ingredients, such as agents which reduce the interfacial tension between oil and water, may also be present in the treating agent. The sodium salts of phenols or other acidic bodies present in petroleum are an example of such interfacial tension reducing agents.

This treating agent alone; will sweeten large quantities of hydrocarbon distillates Without the pound of lead sulfide per gallon. Alkali hyroxides addition of extraneous air or oxygen vwhen the hydrocarbon distillates beingv treated contain less thanapproximately .O2-.03 percent of mercaptan sulfur. When the distillate to be treated contains greater amounts of mercaptan sulfur, the `f5 introduction of air or other oxygen containing gas is generally required. However, the amount of air added in the treating zone should be carefully controlled so that the treating agent is maintained in a balanced condition.

By the term balanced condition it is intended to signify a treating agent free from substantial amounts of either water-soluble metal sulfide compounds .for water soluble lead compounds. Although a very small -amount of water soluble lead compounds is desirable in some instances, for yexample approximately .003 pound of lead per gallon of reagent when the distillatev being treated is relatively high in mercaptan content, the vtreating agent should generally be kept free Lfrom all but traces of soluble lead. It should be understood `that the treating agent is to be regarded as in an essentially balanced condition when it contains .no more than approximately .003 pound of soluble lead compounds per gallon. Similarly, only traces of soluble suldes should be permitted in the balanced reagent to avoid the presence of free or corrosive sulfur'in the treated gasolines.

Amounts of air required for sweetening gasoline distillates containing 0.1 to 0.12% of mercaptan sulfur usually comprise about 0.8-.10, cubic feet per gallonof oil treated. These proportions illustrate the careful control of amounts of air, which is essential to maintaining the treating agent in a balanced condition.

If an excess of air should be added by accident or if for some other reason thereagent becomes unbalanced and contains either an excess of soluble lead compounds or an excess of soluble sulfides, the treating lagent can be brought back into a balanced condition by addition of either a proper amount of doctor solution to remove the soluble suliides or a proper amount of sodium sulfide, hydrogen sulfide or other soluble suldes to react vwith soluble lead and precipitate the same as insoluble lead sulfides. The technique of maintaining the treating agent in a balanced condition is disclosed in detail in United States Patent No. 2,049,423, previously mentioned.

In operating the above type of process it has been found that the lead sulde eventually loses its catalytic activity. This is particularly true when cracked gasolines arebeing treated. The present invention provides a method for maintaining the lead sulfide in an active condition by reactivating or regenerating the same. The reactivating process comprises the following principal steps:

(l) Adding sodium sulde or other soluble sulfide to the caustic solution until there is a slight excess of soluble sulfide present;

(2) Separating the lead sulde from the caustic solution;

(3) Thoroughly steaming and/or water-washing the separated lead sulfide;

(4) Again suspending the treated lead sulde in a caustic solution to obtain an effective and active treating agent.

In some cases it is also found desirable to throw the reagent entirelyr oi balance by blowing the lead sulfide while suspended in strong caustic solution with an excess of air at elevated temperatures. This blowing operation oxidizes the lead. sulfide and converts the same to soluble lead compounds which dissolve in the cautic s0- lution. This last type of treatment is generalltr utilized in addition to the above mentioned steaming and/or washing operations, although it can be adopted in lieu thereof. The air blowing vis preferably continued until at least a major portion of the lead sulfide is oxidized and is therefore fundamentally different from air blowing operations in which the reagent is kept in an essentially balanced condition and where only a Very small portion of the PbS is accidentally oxidized. The unbalanced reagent is then again balanced by addition of sodium sulfide in the proportion required to precipitate all of the soluble lead as lead sulfide. Excess sodium sulfide is, of course, avoidedas'is always done where a balanced reagent is desired.

Referring to the drawing:

Sour distillates such as gasoline flow from storage through valve controlled conduit I to chargingpump 2, and ow control 3 in line 4 to contactor 5 driven by suitable means such as an electric motor 5. Treating agent from conduitv I5 is thoroughly contacted with the sour gasoline in contactor 5 and the mixture passed through line 1 to settler 8. Air from conduit 9 mayfalso be introduced into contactor 5 to aid in the sweetening reaction.

VSodium sulfide is supplied to the system through pipe I!! to blowcase II. Compressed air from receiver I2 enables the removal of the sodium sulfide solution from blowcase Il, and metering blowcase I3 permits the careful control of quantities of solution supplied to line I4; Sodium sulfide solution ows from line I4 through ow control device I5 and conduit I6 into the reagent supply pipe 6. The amount of sodium sulfide introduced at this point is very carefully controlled in order to maintain the treating agent in a balaneed condition.

As has previously been stated, the gasoline and treating agent mixture is introduced into settler 8 after thorough agitation in contactor 5. The sweetened gasoline separates to the top of settler il` and is-removed through conduit I1 to rock packed clarifier I8.

Clarifier I8 is packed with rock of any suitable type and removes final traces of caustic soda solution and oil-wetted lead sulfide which are suspended in the oil and carried over from settler 8. The rock effectively removes the suspended lead sulfide and caustic soda solution, presumably subsequently drain. Various types of rock resistant to alkali may be used in the clarifier. Weathered rock such as found in gravel deposits is very satisfactory and is more eilicient than crushed rock which has not been subjected to weathering action. Quartz is also a satisfactory packing material.

The claried gasoline passes from the top of clarifier I8 through valve controlled line I9 to storage.` Conduits 20 and 2| are provided for recirculating gasoline from the top of clarier I8 or from the top of settler 8 to charging pump 2, when desired.

Settler 8 is provided with a lower drum 22 and is connected therewith through restricted passages 23. The sweetening system is operated so that the greater portion of the treating agent separates to the bottom portion 22 of settler 8 and so that the gasoline-caustic soda interface, that is the dividing line between the settled treating agent and the separated gasoline, is within the lower portion 22 of the settler.

Drum 22 is equipped with agitating means comprising an inner circulation tube 24 at one end of which is provided a circulation screw impeller 25 for the purpose of maintaining a iiow velocity down the central tube and through the annular space between the circulation tube and the outer shell of the drum at suflicient velocity to bring about adequate turbulence in the iluid for maintaining a homogeneous mixture of lead sulfide, caustic solution and oil. Pump 26 driven by motor 2 is in communication with drum 22 and recirculates the homogenized treating agent through line 28 controlled by Valve 29 and iiow meter 38.

The agitating means provided in drum 22 is desirable for the reason that it has been found that the lead sulfide becomes oil-wetted and a portion thereof tends to gather at the oil-caustic soda solution interface. If an ordinary settler is utilized and the treating agent withdrawn from a region below the interface, it is apparent that a considerable portion of the PbS will not be eiectively recirculated and will therefore not be utilized in the sweetening zone. At the beginning of operations, drum 22 is charged with the proper amount of 32 B. caustic solution containing lead sulfide. At this initial stage of operations the caustic should ll no more than approximately half of drum 22. As the sweetening is continued water is generated by the sweetening reaction and gradually dilutes the caustic soda solution, thereby increasing its volume and raising the caustic level in drum 22. Dilution also occurs from the addition of the solution of soluble sulfide. Thus it is seen that the caustic may be diluted to a considerable extent without rais ing the level of the interface above the agitating zone in drum 22. No claim is made in the present application to this agitating feature per se, since it comprises the invention of another. However, this feature in combination with the revivification or activation features of the present invention enables more ecient operation of lead sulfide sweetening processes. i

As will be readily understood from previous discussion, the treating agent is continuously re- 'circulated throughy line 28 -to contactor 5 for long rperiods of time and effects a satisfactory sweetening action. The relative proportions of oil and sweetening agent entering the mixing zone in contactor 5 may vary considerably. Amounts of treating agent from lo to 60% by volume of the n aphtha ,are satisfactory, and in general it is found that higher rates of recirculation are de` sirable where higher Ymercaptan content inthe distillate being sweetened is encountered.

` Even with very careful control of the quantities of air used and of the soluble lead or soluble sulfide content of the treating agent, the lead sulfide catalyst eventually loses some of its activity and if recirculated long `enough without any reactivation treatment the catalyst maybecome entirely inactive. In order to maintain the catalyst in active form the treating agent may be passed through conduit 3l controlled by valve 32 to separator 33. `Sufficient sodium suliide is introduced through valve controlled line 34 to provide a slight excess in the treating agent and precipitate all soluble lead compounds which may be present. The separator as illustrated is of the gravity type and is provided with three outlets. As has been previously mentioned, a certain amount of the lead sulfide becomes oilwetted and tends to float on the caustic soda solution. For this reason it is necessary to provide a conduit 35 at the -top level of the caustic solution to remove this floating lead sulfide which passes to mixing tank 3G. A portion `of the lead sulfide also gravitates to the bottom'of the separator and is removed therefrom through lines 31 and 31. Caustic soda solution with the lead sulde removed therefrom may be withdrawn' through valve controlled line 38. This caustic solution may .be passed to tanks and again mixed with the lead sulde after the latter has received its reactivation treatment. The caustic may also be given a ,purification and concentration treatment when desired, as for example by heating and boiling off a substantial portion of the water present therein, which will simultaneously remove certain organic materials dissolved in the reagent.

Attention is directed to the fact that the term oil-wetted lead sulfide is used herein to designate that form of lead sulfide which has the f property of floating on the caustic soda solution the same. The lead sulfide is first washed with hot water or steam or both at temperatures. within the range of approximately 180 to 240 F. After this washing treatment the lead sulfide may again be suspended in caustic soda solution of the proper strength admitted through line 4|. This caustic soda solution may be either a fresh supply Aor the caustic soda solution removed from separator 36 with or without a purication and concentration treatment is desired.

This reactivated treating agent can be returned to the system through conduit 42. An intermediate storage tank `llt isprovided in line 42 so that a supply of active lead sulde may be kept on hand at all times.

On those occasions where it is found that-the lead sulfide catalyst is particularly resistant to reactivation, it is necessary to throw the reagent ofi balance by blowing with air supplied through line 44. This air blowing operation is carried out at elevated temperatures, such as F. or above, and preferably above F. while the lead sulfide is suspended in strong caustic soda solution. The lead sulfide-caustic suspension should be blown with air until at least a substantial portionfof the PbS has been oxidized and converted to soluble lead dissolved in the aqueous phase. Preferably, all of the lead sulfide is so oxidized and dissolved. Before introducing the treating agent into the sweetening system after the air blowing step, the soluble lead is reprecipitated in active form and the entire agent converted to a vbalanced condition by addition of sodium sulfide through conduit 45. The doctor solution supply conduit 46 is also provided in order that the reagent may be balanced .by precipitation of the soluble suldes as lead sulfide in the event that an excess of sodium ,sulfide should .be accidentally introduced.

V It is apparent that the reactivation process can be operated concurrently with the sweetening operation merely by splitting the reagent into two portions, one flowing through Valve 29 and the recirculation conduit including iiow meter 30 to y the ksweetening zone, and the other portion owing through valve 32 and line 3| to separator 33 for reactivation treatment. In general, it is more desirable to shut off recirculation by closing valve 29 entirely and removing .the old treating agent from the system. While the old treating agent is being removed, fresh active lead sulfide suspended in caustic may .be supplied from storage 43 through valve controlled line 4B to the sweetening system.

f within the spirit and teaching of this invention.

I claim:

1. In a process of sweetening petroleum distillates with lead sulfide suspended in a treating agent in a balanced condition, said agent comprising an aqueous solution of an alkali hydroxide substantially free of water-soluble lead compounds, whereby said lead sulfide normally beof inl.

comes at least partially poisoned and loses some of its catalytic activity, a process of maintaining the lead sulfide in active condition which coml prises separating lead sulfide from the aqueous solution, treating the lead sulfide with H2O at elevated temperatures alcove approximately 180 F., suspending the lead sulfide in an aqueous solution of an alkali hydroxide, converting the last meny to precipitate dissolved lead formed by the airblowing process and recirculating the balanced treating agent with the petroleum distillate to be sweetened.

2. In a process of sweetening petroleum distilvlates with lead sulfide suspended in a treating .agent in a balanced condition, said agent 'comprising an aqueous solution of an alkali hydroxide substantially free of water-soluble lead compounds, whereby said lead sulfide normally becomes at least partially poisoned and loses some of its catalytic activity, a process of reactivating the lead sulfide which comprises adding a soluble sulfide to the aqueous solution in an amount sufficient to produce an excess thereof, separating lead sulfide from said aqueous solution, treating the separated lead sullide'with' water and steam at elevated temperatures, suspendingV the lead y sulfide in an aqueous solution of anv alkali hydroxide, converting said treating agent to an unbalanced condition byheating to elevated temperatures and blowing with air in the presence of said suspended' lead sulfide, and balancing the treating agent by addition of a soluble sulfide to precipitate dissolved lead formed by the air-blowing process.

3. In a process of sweetening petroleum distillates with lead sulfide. suspended in a treating agen-t in a balanced condition, said agent comprisingan aqueous solution of an alkali lhydroxide substantially free of water-soluble lead compounds, whereby said lead sulfide normally bel comes at least partially poisoned and loses some Athe treating agent by adding sufficient soluble sulfide to precipitate the soluble lead compoundsr so formed.

4. In a process of sweetening petroleum distillates with lead sulfide suspended in a treating agent in a balanced condition, said agent comprising an aqueous solution of an alkali hydroxide substantially free of water-solubleV lead compounds, whereby said lead sulfide normally becomes at least partially poisoned and loses' some of its catalytic activity, a process o f reactivatlng the lead sulfide which comprises separating lead sulfide contained in caustic suspension from the sweetening zone, suspending lthe separated lead sulfide in strong alkali solution, heating said suspension to an elevated temperature, blowing said suspension with an excess of air while at said elevated temperature and while out of contact with the oil being sweetened, and balancing the treating agent by adding sufficient sodium sulfide to precipitate the soluble lead compounds formed by the air-blowing operation.

. oughly washing said lead sulfide with lH2O at elef pended in an aqueous solution of an alkali hydroxide containing no more than approximately .003'pound of water-soluble lead compounds per gallon, said process comprising converting at least a major portion of the lead sulfide to soluble lead compounds -while suspended in hot caustic solution by blowing with air while out of contact with the distillate to oxidize the insoluble lead sulfide, precipitating the lead in the soluble lead compounds so formed by adding a soluble sulfide to the solution, and recirculating Ithe treated agent to a petroleum sweetening zone.

8. A process of treating petroleum distillates which comprises.: intimately contacting a sour distillate in a sweetening zone with a catalytic treating agent comprising lead sulfide suspended in an aqueous solution of an alkali hydroxide;

separating the distillate from said treating agent; recycling said treating agent to said sweetening zone; maintaining said treating agent in a substantially balanced condition when in said sweetening zone, whereby said recycled treating agent does not ycause color reversion in the distillate being processed but `becomes poisoned to the extent that it loses at least some of its catalytic activity; restoring catalytic activity -to said poisoned treating agent, without causing color reversion in distillate to be treated, by blowing said lead sulfide with air while suspended in hot caustic solution to oxidize a substantial portion of said lead sulfide to soluble lead compounds and balancing said air-blown suspension by adding soluble sulfide to precipitate the soluble lead compounds; and returning said balanced treating agent to said sweetening zone.

9. A process of reactivating a lead sulfide cata'- lytic sweetening agent which has accumulated catalyst poisons of the type produced by catalytic sweetening of petroleum distillates with a b'alanced treating agent comprising lead sulfide suspended in an aqueous solution of an alkali hydroxide, said reactivating process comprising blowing said lead sulde with air while suspended in hot caustic solution, to oxidize a substantial portion of said lead sulfide to soluble lead compounds, and balancing the resulting solution by vadding a soluble sulfide in an amount not ysubstantially greater than necessary to precipitate the soluble lead compounds as a reactivated lead sulfide sweetening catalyst.

ERNEST E. LYDER.

CERTIFICATE-OF CORRCTION. Patent No. 2,208,591. Ju1y`25, 191m.

ERNEST E. LYDER.

It is hereby certified that error appears in the Aprinted specification of the above numbered patent requiring correctionas follows: Page l, second column, line 52, for "O.8.lO read -.O8.lO-; and that the said Letters Patent should be'read with this correction therein that the same may conform to the record of the oase in the Patent Office.

Signed and sealed this 19th day of November, A. D. l9li0.

Henry Van Arsdale, (Seal) Acting Commissioner of Patents.

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