US2727849A - Sweetening of catalytically cracked naphthas with alkali, alkyl phenol, oxygen, and sulfur - Google Patents

Description

Dec. 20, 1955 M. D. NAPPER 2,727,849

SWEETENING OF CATALYTICALLY CRACKED NAPHTHAS WITH ALKALI, ALKYL PHENOL, OXYGEN AND SULFUR Filed March 7, 1952 GOALESER A TTOHNEY United States Patent O SWEEENNG F CATALYTCALLY CRACKED NAPHTHf/S WITH Aile-MI, ALKYL PHENOL, XYGEN, AND SULFUR Max D. Napper, Casper, Wyo., assignor to Standard Gil Compmy, Chicago, El., a corporation of Indiana Application Mami 7, 1952, serial No. 275,321

1e calms. (ci. 19e-29) This invention relates to the sweetening of catalytically cracked sour naphthas. More particularly, the invention relates to the sweetening of catalytically cracked sour naphthas having an ASTM end point (760 mm.) between about 400 F. and 425 F.

Virtually all naphthas derived from the distillation of crude petroleum or from cracking of petroleum fractions contain objectionable amounts of mercaptans. Such mercaptan-containing naphthas are commercially spoken of as being sour. A naphtha which has been treated to remove substantially all these mercaptans is known as sweet. in the petroleum industry a sweet oil is one which gives a negative doctor test; a more quantitative description of a sweet naphtha is one which has a so-called copper number of less than l. Many processes for sweetening sour naphthas are known. A particularly effective procedure is to contact the sour naphtha with an aqueous caustic solution containing al catalytic amount of phenolic compounds in the presence of a free-oxygencontaining gas, usually air. This procedure Works very well on sour naphthas of comparatively low copper nurnber. lt has been discovered that this procedure is ineffective on catalytically cracked sour naphthas having a copper number greater than about l2.

Another procedure for sweetening sour naphthas is to contact the sour naphtha with aqueous caustic and freesulfur. While this method is relatively effective on virtually all stocks, it has been found to have a Very serious disability, namely, the sweet naphtha almost always contains corrosive sulfur. It is very diflicult to control the sulfur addition to just the amount needed for sweetening; when using this procedure the excess free-sulfur appears as corrosive sulfur in the product naphtha.

it is an object of this invention to sweeten a catalytically cracked naphtha that contains objectionable amounts of mercaptans. Another object of this invention is to sweeten catalytically cracked sour naphthas that have an ASTM end point between about 400 and 425 F. Still another object is to sweeten catalytically cracked naphthas which have a Cu number of less than about 26. A particular object is to sweeten a catalytically cracked sour naphtha in the presence of an aqueous treating agent and free-sulfur without introducing corrosive sulfur into the sweet naphtha. Other objects of the invention will be apparent in the following description thereof.

It has been discovered that a catalytically cracked sour naphtha having a Cu number of less than about 26 and boiling within the range of about 80 and 425 F. can be sweetened by contacting said sour naphtha in the presence of free-oxygen with an aqueous solution of caustic and alkylphenols wherein the total caustic content is at least about l weight percent and the alkylphenol content is at least about 2 volume percent, in an amount sucient at least to form a separate aqueous phase, followed by adding an amount of free-sulfur effective for sweetening, but insuicient to render the product -naphtha corrosive, such as between about 0.0011 and 0.04 lb./bbl. of naphtha, maintaining Athe free-'sulfur-containing mixalkylhydroxybenzene, such as, cresol, Xylenol, etc.

ture at a temperature of at least about 120 F. for a time sucient to complete the sweetening reaction and then separating the sweet non-corrosive product naphtha from the separate aqueous phase.

The feed to this process is a sour naphtha derived from the catalytic cracking of an organic sulfur-containing hydrocarbon. The sour naphtha feed to this process should boil within the range of about to 425 F. Naphthas having an ASTM end point (760 mm.) of between about 400u and 425 P. are a particularly suitable feed to this process. The sour naphtha feed to this process must have a Cu number of less than about 26, and preferably less than about 24. The process may be used on any catalytically cracked naphtha having a Cu number less than about 26, but it is particularly suitable for sour naphthas having a Cu number greater than about l2. The preferred range of Cu numbers is between about 16 and 24. The catalytically cracked sour naphtha that is a suitable feed to this process can be derived from any one of the many catalytic cracking processes now in commercial use. Examples of these processes are the uidized catalytic cracking process, the thermofor catalytic cracking process, the Houdri-ow process, the Houdry process. The catalyst used in these processes may be silica-alumina, silica-magnesia, fullers earth and acid treated clays, etc.

The aqueous treating agent used in this process must be present in an amount at least sucient to form a separate aqueous phase. For most operating conditions and feed naphthas the amount of aqueous treating agent used may be between about l0 and 200 volume percent based on the feed naphtha. In general phase separation is aided and emulsion difficulties are reduced if the amount of aqueous treating agent used is between about 25 and 50 volume percent. The aqueous treating agent contains caustic and alkylphenols as the predominant constituents other than water.

The caustic component of the aquous treating agent may be either sodium hydroxide or potassium hydroxide. The caustic is present in the treating agent in the form of free alkali and in the form of a compound with the alkylphenols. The total caustic content should be at least about l0 weight percent and preferably about l5 weight percent. The alkylphenol content should be such that some free caustic is present in the aqueous treating agent, e. g., about 2%. Higher caustic concentrations can be used and in come cases a saturated solution is desirable, e. g., about 50% of NaOH. In general, the total alkalinity of the aqueous treating agent should be between about l5 and 25 weight percent.

The alkylphenols present in the aqueous treating agent act as solutizers for the mercaptans and as catalysts for the conversion of the mercaptans to disullides. The alkylphenols also have the very important function of preventing the presence of corrosive sulfur in the product oil; they do this, itis believed, by reacting with the excess freesulfur.

It has been found that at least about 2 Volume percent of alkylphenols must be present in the aqueous treating agent and preferably at least about 5 volume percent. It is advantageous to have even more of the alkylphenols present and, in some cases, a saturated solution may be desirable, e. g., about 30 volume percent. However, in general, the use of aqueous treating agent containing more than about 20 volume percent of alkylphenols will result in phase separation diculties because of the increased viscosity of the aqueous treating agent. It is preferred to use between about 5 and 20 volume percent of the alkylphenols.

The alkylphenols used in this invention may be any the preferred alkylphenols are those naturally occurring in petroleum hydrocarbons, .particularly in hydrocarbonsv derived from thermal cracking and catalytic cracking processes. Petroleum cresols occur in cracked naphthas and may be obtained therefrom readily by contacting the naphtha with aqueous causticsolution of about 10 or more weight percent. These petroleum cresols derived from naphthas have an VVASTM boiling Vrange. from about 370 to 440 F. Alltylphenols occur in petroleum hydrocarbons boiling in the heavier-than-gasoline range, i. e., hydrocarbons boiling from about 350 to'about 600 F. These alkylphenols arevusuaily called heavy xylenols and may be obtained by contacting cracked gas oils and many virgin gas oils with concentrated aqueous caustic solution such as a 40% solution. These heavy xylenols have an ASTM boiling range between about 375 and 550 VF. The petroleum cresols present in the sour naph'tha being treated may be extracted by the aqueons treating agent and used asA the alkylphenol in the sweetening process. Thus the fresh treating agent may contain no alkylphenols but will quickly extract petroleum cresols from the sour naphtha and will in time attain a state of saturation, i. e., will contain as much as 30 volume percent of petroleum cresols. The concentration of cresols in the treating agent can be maintained by removing a portion of the treating agent and replacing said portion with fresh aqueous caustic solution.

It has been found that the presence of free-oxygen is necessary even when treating a sour naphtha having a Cu number lower than about 12. The presence of freeoxygen in the process appears to have some beneficial effect on the overall sweetening reaction. The free-oxygen may be introduced into the process either in the form of substantially pure oxygen, i. e., cylinder oxygen or in the form of a free-oxygen-containing gas, e. g., air. Very slight amounts of free-oxygen are needed. However, it is preferred to add between about 0.2 and 2 standard cu. ft. of free-oxygen per barrel (42 gallons) of sour naphtha. When air is the source of the free-oxygen, from about 1 to l0 s. c. f. of air are added per bbl. of sour naphtha. in general the amount of free-oxygen added will increase with increase in Cu number of the sour naphtha. Usually 5 s. c. f. of air will be sufficient for the production of a sweet product and for the production of a reusable aqueous treating agent.

It has been found that a catalytically cracked sour naphtha having a Cu number in excess of about 14 cannot be sweetened by contacting said naphtha with an aqueous caustic-cresol solution in the presence of air even though the temperature of the contacting is maintained at about 200 F. for a prolonged period of time. However, the addition of a minor amount of free-sulfur to this system will produce a sweet product naphtha. W'hile it is possible to sweeten naphthas having a Cu number lower than about 12 by the use of free-sulfur in the presence of the aqueous treating agent Without the use of free-oxygen as explained above, the presence of free-oxygen is preferred. The amount of sulfur added in this process varies with the Cu number of the particular feed naphtha but is not directly related to said Cunumber. It is not necessary to control closely the amount of free-sulfur added to the process in order to avoid a corrosive product. The amount of free-sulfur added may be as little as 0.001 and as much as .04 1b./bbl. of sour naphtha. in general satisfactory results are obtained for most sour naphthas by the use of between about 0.01 and 0.03 lb. of free-sulfur per bbl. of sour naphtha.

It has been found that the order in which the various reagents are added to the process is important. The aqueous treating agent, the sour naphtha feedand the free-oxygen should be brought together and thoroughly intermingled prior to the addition of the free-sulfur. The

free-sulfur-containing-agent-naphtha mixture should be maintained at a temperature of at least about 120 F. and

maintained in an agitated condition for a time suficientv ditions the preferred temperature range is lso to complete the sweetening reaction. The free-oxygenmay be added to the aqueous treating agent prior to contacting the sour naphtha, or it may be added to the sour naphtha, or it may be added to the agent-naphtha mixture.

When operating on sour naphthas having a Cu number of less than about 12, comparatively low temperatures may be used in the process. However, a temperature of at least about 120 F. is preferred. The reaction temperature may be as high as 210 F., but such temperatures are used only when processing a very refractory sour naphtha. For most feed stocks and operating conbetween about 140 and 190 F.

The mixture of sulfur-agent-naphtha should be maintained intermingled for a time suflicient to complete the sweetening reaction, i. e., to produce a product naphtha having a Cu number of less than l. The contacting time is dependent upon primarily the temperature of operation and may vary from about 1 minute to as much as 60 minutes. For most feed stocks and operating conditions, a contact time of between about 2 and 15 Vminutes will be suicient.

After the completion of the sweetening reaction the mixture of treating agent and naphtha is settled for a time suicient to separate the product naphtha from the lower aqueous phase. This lower aqueous phase is'suitable usually for recycle to the initial contacting step. However, in the course of time there is a buildup of thiosulfates and other by-product salts which interferes with the catalytic activity of the treating agent and more particularly with the ease of phase separation between the product naphtha and the aqueous phase. At this point the aqueous treating agent is discarded and a fresh aqueous caustic solution charged to the process. Another method of operating is to withdraw continuously an aliquot portion of the separated aqueous phase and adding thereto fresh aqueous caustic solution before recycling the total mixture to the initial contacting step.

A large scale embodiment of this process is illustrated in the accompanying figure which is made a part of this specication. The embodiment illustrated is vschematic in nature;l all pumps, many valves and other pieces of equipment have been omitted as anyone skilled in the art can readily add these items to the embodiment shown in the figure.

The sour naphtha feed to this embodiment was derived by the treatment of a high sulfur gas oil in a fluid catalytic cracking process. The catalyst was a silica alumina and the' gas oil was passed through the catalyst at a temperature of 925 F. The cracked products were fractionated. The sour naphtha from the fractionator had an ASTM distillation range between and 422 F., a total sulfur content of 0.21 Weight percent and a Cu nurnber of 20. l

The aqueous treating agent used in this embodiment had a total caustic content, as NaOH, of 15 weight percent and contained 7 volume percent of petroleum cresols.

Fresh aqueous NaOH solution from source 11 is passed into line 12 where it meets recycle aqueous treating agent. The total aqueous treating agent is passed through line 12 at a rate of 70 bbls. per hour. Air from source 13 is passed through line 14 into line 12 where it intermingles with the aqueous treating agent. The amount of air used in this embodiment is 2 s. c. f /bbL of sour naphtha. The air-containing treating agent is passed from line 12 into heater 16 where the temperature of the treating agent is raised to about F. The hot treating agent is passed from heater 16 into line 17. Sour naphtha from source 21 is passed through line 22 into line 17.

The sour naphtha auditreating agent in line 17 are passed into mixer 23 wherein the sour naphtha and treating agent are thoroughly intermingled. Mixer 23 may be any Yconventimal typeof mixer, e. g., a, knothole mixer..

The sour naphtha-agent mixture is passed from mixer 23 into line 24. An aliquot portion of the sour naphtha in line 22 is withdrawn by way of valved line 26 through sulfur pot 27 and valved line 28 into line 24. Sulfur pot 27 is a small vessel lled with lump sulfur. The amount of naphtha passing through the sulfur pot is so arranged that about 0.015 lb. of sulfur per bbl. of total fresh feed is passed into line 24. The total sour naphtha feed present in line 24 amounts to about 200 b. p. h.

The contents of line 24 are passed into mixer 29, which mixer is identical in construction to mixer 23. The thoroughly intermingled sulfur-agent-naphtha mixture is passed through line 31 into vessel 32. Vessel 32 is provided with heating means 33 and mixing means not shown.

The sulfur-agent-naphtha mixture is maintained in vessel 32 at a temperature of 155 F. for a total time of about minutes. This time is sucient to complete the sweetening reaction. The contents of vessel 32 are passed through line 34 into settler 36.

In settler 36 the mixture separates into an upper naphtha layer and a lower aqueous phase. The lower aqueous phase consists of treating agent and reaction products of the excess sulfur. The aqueous phase is withdrawn from settler 36 by way of line 37 and is recycled through valved line 38 to line 12 for reuse in the process. An aliquot portion of the aqueous phase is withdrawn to waste from line 37 by way of Valved line 39.

The upper naphtha phase in settler 36 is withdrawn by way of line 41 to coalescer 42. Coalescer 42 may be a simple separator or it may be packed with a coalescng medium, such as, steel wool, glass wool, gravel, sand, etc. In this embodiment coalescer 42 is packed with steel wool supported on a grid 43. Occluded aqueous material carried over from settler 36 by the naphtha phase is coalesced and withdrawn from the bottom of coalescer 42 by way of line 44. A sweet non-corrosive product naphtha is passed out of coalescer 42 by way of line 46 and is sent to storage not shown.

In order to illustrate the results obtainable by our process, a catalytically cracked naphtha boiling between about 90 and 420 F. and having a Cu number of 16 was contacted with 50% of aqueous treating agent. The aqueous treating agent had a total NaOH content of and a cresol content of 30%. To the mixture of treating agent and sour naphtha, air was added at the rate of 5 s. c. f./bbl., while the temperature of the reagents was held at 160 F. The agent-naphtha mixture was settled and the upper naphtha phase withdrawn. The product naphtha had a Cu number of 3.

A catalytically cracked sour naphtha having a boiling range between 90 and 422 F. and a Cu number of 20 was contacted with volume per cent of aqueous treating agent. The aqueous treating agent had a total caustic content as NaOH or" 15% and a cresol content of 7 volume percent. Air was added to the agent-sour naphtha mixture at the rate of l s. c. f./bbl. Into the air-containing mixture .025 lb./ bbl. of Howers of sulfur were added. The sulfur-containing mixture was maintained at 145 F. for about 5 minutes. The naphtha phase was separated from the aqueous phase and found to be sweet to the Doctor Test with a Cu number of 0.

Having described this invention what is claimed is:

l. A process for sweetening a catalydcally cracked feed naphtha having a copper number of between l2 and 26, which process comprises the steps of contacting said feed, in the presence of free-oxygen, with an aqueous treating agent containing at least 10 weight percent of total caustic and at least 2 volume percent of alkylphenols, wherein said agent is present in an amount suicient to form a separate aqueous phase, adding to said feed-agent mixture an effective amount of free-sulfur, which amount is insutiicient to render said naphtha corrosive, maintaining said feed- 6 l agent-sulfur mixture at a temperature of at least F. for a time suicient to reduce the copper number of said feed to less than 1, and separating a sweet, non-corrosive product naphtha from an aqueous phase.

2. The process of claim 1 wherein said aqueous treating agent contains between 10 and 50 weight percent of total caustic and between 2 and 30 Volume percent of alkylphenols.

3. The process of claim 1 wherein said temperature is between 120 and 210 F.

4. The process of claim 1 wherein the amount of aqueous treating agent present is between about 10 and 200 volume percent based on said feed.

5. A process for sweetening a catalytically cracked feed naphtha having a copper number between 12 and 26, which process comprises the steps of contacting said feed, in the presence of at least 0.2 s. c. f. of free-oxygen per barrel of said feed, with an aqueous caustic treating agent containing between 15 and 50 weight percent of total caustic and between 2 and 30 volume percent of alkylphenols, in an amount between 10 and 200 Volume percent based on said feed, adding to said feed-agent mixture free-sulfur in an amount between 0.001 to 0.04 lb. per barrel of said feed, wherein said free-oxygen and said free-sulfur addition are adjusted to give a sweet but noncorrosive product naphtha, maintaining said feed-agentsulfur mixture at a temperature between and 190 F. for a time suthcient to reduce the copper number of said feed to less than l, and separating a sweet, non-corrosive product naphtha from an aqueous phase.

6. The process of claim 5 wherein said alkylphenols are cresols derived by caustic extraction from cracked petroleum naphthas.

7. The process of claim 5 wherein said alkylphenols are xylenols derived by caustic extraction of petroleum oils boiling between about 350 and 600 F.

3. The process of claim 5 wherein said treating agent is present in an amount between 25 and 50 volume percent.

9. A process for producing a sweet, non-corrosive product naphtha from a catalytically cracked sour naphtha having a copper number between i6 and 24, which process comprises the steps of contacting said sour naphtha, in the presence of between 1 and 5 s. c. f. of a free-oxygen containing gas per barrel of said sour naphtha, with an aqueous treating agent comprising essentially between l5 and 25 weight percent of total alkalinity as sodium hydroxide, between 5 and 20 volume percent of petroleum cresols and the remainder essentially water, in an amount between 25 and 50 volume percent based on said sour naphtha, adding to said sour naphtha-agent mixture between 0.01 and 0.03 lb. of free-sulfur per barrel of sour naphtha, maintaining said sulfur-sour naphtha-agent mixture at between 140 and 190 F. for a time sucient to substantially sweeten said sour naphtha and separating a sweet, non-corrosive product naphtha from an aqueous phase.

l0. The process of claim 9 wherein said sour naphtha has au A. S. T. M. end point (760 mm.) between about 400 and 425 F.

References Cited in the le of this patent UNITED STATES PATENTS 1,767,356 Fischer June 24, 1930 1,955,607 Rees et al. Apr. 17, 1934 1,970,583 Stagner Aug. 21, 1934 2,329,615 Hoover Sept. 14, 1943 2,600,465 Bond .Tune 17, 1952 2,604,437 Conner et al. July 22, 1952 OTHER REFERENCES Kalichevsky, Chemical Rening of Petroleum, 2nd ed. (1942), page 190.

Claims (1)

1. A PROCESS FOR SWEETENING A CATALYTICALLY CRACKED FEED NAPHTHA HAVING A COPPER NUMBER OF BETWEEN 12 AND 26, WHICH PROCESS COMPRISES THE STEPS OF CONTACTING SAID FEED, IN THE PRESENCE OF FREE-OXYGEN, WITH AN AQUEOUS TREATING AGENT CONTAINING AT LEAST 10 WEIGHT PERCENT OF TOTAL CAUSTIC AND AT LEAST 2 VOLUME PERCENT OF ALKYLPHENOLS, WHEREIN SAID AGENT IS PRESENT IN AN AMOUNT SUFFICIENT TO FORM A SEPARATE AQUEOUS PHASE, ADDING TO SAID FEED-AGENT MIXTURE AN EFFECTIVE AMOUNT OF FREE-SULFUR, WHICH AMOUNT IS INSUFFICIENT TO RENDER SAID NAPHTHA CORROSIVE, MAINTAINING SAID FEEDAGENT-SULFUR MIXTURE AT A TEMPERATURE OF AT LEAST 120* F. FOR A TIME SUFFICIENT TO REDUCE THE COPPER NUMBER OF SAID FEED TO LESS THAN 1, AND SEPARATING A SWEET, NON-CORROSIVE PRODUCT NAPHTHA FROM AN AQUEOUS PHASE.

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