US3066087A - Process of reducing sulfate content in stock feed - Google Patents

Description

R. J. PHILLIPS Nov. 27, 17962 PROCESS 0E REDUCING SULFATE CONTENT IN STOCK FEED Filed oct. 12, 1959 2 Sheebs--Sheei'I l Nov. 27, 1962 R. J. PHILLIPS PROCESS OF REDUCING SULFATE CONTENT IN STOCK FEED Filed Oct. 12, 1959 2 Sheets-Sheet 2 QQIOOIOOOI. tlnolcclnoonns lacca oobcooooo'oooocq BY 7n#- ArroRA/Ew United States This invention relates to new and useful improvements in methods of and apparatus for treating hydrocarbon streams to reduce the sulfur content, and relates particularly to the treatment of the products of distillation which comprise petroleum fractions.

This application is filed as a continuation-in-part of my co-pending application Serial No. 601,919, filed August 3, 1956, and now abandoned.

In refining operations, certain products of distillation contain undesirable or deleterious components as, for example, in the case of catalytic reformer feed stock, which stock is high in sulfur content. The presence of sulfur in the feed stock, unless removed, causes corrosion in the reformer units due to the formation of hydrogen sulfide, a reaction product of hydrogen and sulfur.

Industry has recognized the problem of sulfur content and various methods and treatments directed toward reduction and removal of sulfur content have been employed, but such prior treatments have involved specially designed and economically expensive apparatus without providing a completely satisfactory solution to the problem.

Prior to the present invention it has not been believed possible to accomplish the result with a relatively simple type electrical treater, but I have found that by proper control of the electrical treating zone as to voltage and electrode spacing, and also by accurately controlling the contact time of the material both Within an initial mixing zone and within the electrical treater, an efficient process for effectively reducing the sulfur content of the hydrocarbon feed may be carried out.

It is therefore one object of this invention to provide a very simple and improved practical method or process for effectively reducing the sulfur content of hydrocarbon streams such as reformer feed stocks, whereby the damaging effects of corrosion to the equipment through which the stream or feed stock is subsequently directed are eliminated.

An important object is to provide an improved treatingmethod, of the character described, wherein sulfuric acid is intimately admixed with the feed stream for a controlled period of time and the mixture is thereafter directed through an electrical precipitator and is subjected to the action of a single electrical treating zone with the contact or residence time of the stream within the precipitator being accurately controlled so that the sulfur content of the stream is reduced and other deleterious components such as nitrogencompounds are removed or reduced.

arent A particular object is to provide an improved treating method wherein the electrical treatment of the hydrocarbon-acid dispersion performs adual function in that it subjects said mixture to electrostatic mixing to assure completion of the oxidation reaction of the sulfur comf field which is created by spaced electrodes located between 6 and l2 inches from each other, with electrode potentials of 1900 to 2500 volts per inch of electrode spacing; the current being supplied by a three-phase system whereby the deviation of the maximum voltage from the average voltage, normally referred to as the ripple factor is reduced to a low substantially steady state. It has been found through actual practice that when the above arrangement is employed, an efficient separation of the sulfur content is effected. Y

Still another object is to provide an improved method, of the character described, which includes not only the initial sulfur-removing step, but which also may include a subsequent caustic-neutralizing step followed by a water wash to provide a complete process for producing a desulfurized product. Y

The construction designed to carry out the invention will be hereinafter described, together with other features thereof.

The invention will be more readily understood from a reading of the following specication and by reference to the accompanying drawings forming a part thereof, wherein an example of the invention is shown, and wherein:

FIGURE l is a diagrammatic View or flow diagram of the apparatus for carrying out the improved method or process; and,

FIGURE 2 is a horizontal, cross-sectional view of the electrical treating apparatus which is employed in the process; and,

FIGURE 3 is a transverse, vertical sectional view, taken on the line 3 3 of FIGURE 2.

In the drawings (FIGURE l) the numeral 10 indicates an inlet conductor through which the hydrocarbon stream which is to be treated is directed. The invention has been found particularly applicable to the treatment of catalytic reformer feed stocks or streams for the purpose of reducing the sulfur content of such streams. As is well known, a catalytic reformer feed stream contains a relatively high sulfur content which creates deleterious effects in the equipment, such as the reformer units, through which the stream is subsequently directed. Although the invention is particularly adapted for the treatment of this type of hydrocarbon stream and will be described herein as applied thereto, the invention has application in the treatment of other hydrocarbon streams.

The inlet conductor 10 conducts the hydrocarbon stream containing sulfur components into a mixer 11 which is illustrated as a vessel having rotatable mixer blades 12 therein. For controlling the flow or volume of the hydrocarbon stream a suitable flow controller 13 is connected in the inlet conductor 10 in advance of the mixer 11. Sulfuric acid is introduced into the mixer il through a line 14 and within the mixer the acid-hydrocarbon solution is vigorously and intimately mixed to reduce the acid particle size to an optimum diameter and to cause the acid to begin reaction with the sulfur components in the stream. As is well known, an oxidation reaction of said sulfur components occurs which converts the components to the disulfide form, in which form the re-action products are preferentially soluble in the acid. The residence time of the hydrocarbonand acid in the mixer is important since it is desirable to reduce the size of each acid particle suiiiciently to obtain maximum contact area and also to assure mobility of the particle within an electrical field when said particle is subsequently subjected to electrical treatment; however, if the acid particles are too small, efficient subsequent separation of the acid from the hydrocarbon cannot be etiiciently carried out. Thus, to obtain optimum particle size the energy imparted to the mixer and the residence time of the hydrocarbon-acid in the mixture is controlled and is related i to the through-put through the system so that the particle size of the acid is reduced to assure maximum contact area without such a great reduction in size as to cause diculty in subsequent separation. Actual tests have shown that with a through-put of approximately 10,000 bbls. per day, a residence time in the mixer of from 3 to 6 minutes is satisfactory. With such assumed throughput sulfuric acid having a strength lying between the limits o-f 85 to 98% titratable acidity is introduced to the mixture in a volume which depends upon the concentration of contaminants in the hydrocarbon. Such volume may v ary from 2 pounds of acid per barrel of hydrocarbon stream to 25 pounds of acid per barrel.

The hydrocarbon stream containing the acid dispersion is conducted from the mixer through a line 15 into the lower end of the vessel 16 of an electrical precipitator A. During its passage from thepmixe'r some re-action of the sulfur components and the acid will occur, and such reaction products will enter into solution with the acid. Continued rek-action takes place within the lower portion, which may be termed a settling zone, of the vessel 16. As will be explained, the dispersion is conducted upwardly through the vessel and passes through an electrical treating zone, wherein it isV subjected to suiicient electrostatic mixing to enhance contact between the acid and sulfur components and thereby insure completion of the oxidation reaction of the sulfur components in the hydrocarbon to the disulfide form, whereby the reaction products may move into the acid phase. Not only does the electrical treating zone kfunction to insure completion of the oxidation reaction, but it also accomplishes a rapid coalescence of the acid droplets to effect a rapid separation of the acid from the hydrocarbon. The precipitator A may be referred to -as the reaction stage and within this stage the sulfur is substantially removed from the stream. The stream is vdischarged from the upper'end of the vessel 16 through an outlet conductor 17.

The acid having the reacted disulfides in solution therewith is coalesced within the vessel V16 and precipitates downwardly to be collected in the bottom of the vessel, being discharged therefrom through a conductor 13. lf a recirculation of the acid, which may be said to be only partially spent, is desired, the ilow is through line 18 and then through `a recycling line 18a which extends to an acid supply vessel 19, such vessel also having connection with a fresh `acid supply line 20. From vessel 19 the acid is circulated by means of a pump 21 to the line 14 which extends to the mixer and which has a suitable flow controller 22 connected therein whereby the volume of acid which is conducted to the mixer is controlled.

A predetermined liquid level is maintained, in the vessel 16 of the precipitator by means of a float 23, controller 24 and outlet valve 2S, the latter being mounted in an acid outlet line 26 extending from the discharge 18. When valve 25 is opened by reason of the float rising above the pre-set level, the acid is removed from vessel 16 through outlet line 26; the reaction products are, of course, removed along with the acid. So long as the level is below that for which the controller is set, the acid which is partially spent and containing the reacted disulfides is recirculated by means of conductor 18 and re-cycling line 18a.

Although the re-circulation of acid has been found satisfactory, it is not essential since good results can be obtained with a once-through circulation of the acid through the system. In such case, the re-cycling line 18a between the discharge conductor 18 and vessel 19 would be eliminated and fresh acid would be furnished to the mixer at all times. The spent acid having the reaction products therein would, of course, be removed through outlet 26. k .p Y

The electrical precipitator A which has been found to perform the dual function of electrostatic mixing and coalescence and which effectively carries out the present process is illustrated in FIGURES 2 and 3. Such precipitator includes the vessel 16 having the line 15 and conductor 18 connected in its bottom. Line 15 projects upcoalescence of the acid droplets.

wardly into the vessel and has connection with a distribution header 27 which is shown as constructed of a longitudinal pipe having outlet openings 28 spaced along its length. Thus, the acid-hydrocarbon stream is evenly distributed by the header 2'7 throughout the length of the vessel 16 and an upward flow of the mixture within the vessel occurs.

The hydrocarbon outlet conductor 17 extends from the upper end of the vessel andV between this outlet and the inlet the electrode system, which forms the electrical treating Zone, is mounted. As will be explained, the position of the electrode system is predetermined with respect to the inlet header 27 so as to control the size of the settling zone therebelow; by controlling the size or area of the settling zone the residence time of the mixture within the zone and within the electrical treat ing zone is controlled. The electrode system comprises a plurality of live electrodes 29 which are grid-like in structure and which are suspended through electrical conducting rods 30 from an electrode bar 31 located in the upper portion of the vessel. The electrodes are supplied with direct current by means of electrical power unit P which receives its supply from `a three-phase A.C. power source. Between the live grid-like electrodes 29 are longitudinally extending ground electrodes 32 which are `also grid-like in structure; below the lowermost live electrode 29 is a grid-like ground electrode 33. Thus, a D.C. lelectrical field zone is created within the vessel and such zone extends substantially throughout the upper portion of the vessel. Suitable baffles 34 (FIG. 2) and 3S (FIG. 3) are mounted within the vessel adjacent the sides and ends of the lowermost electrode 33 and function to direct the ilow of liquid upwardly through the electrical iield zone formed between the electrodes.

The particular spacing of the electrodes has been found of importance in carrying out the present method and actual practice has shown that the spacing between the electrodes may vary between 6 and l2 inches; a normal spacing of approximately 8 inches between electrodes has been found satisfactory. Satisfactory results are obtainable with electrode potentials of between 1900 and 2500 volts per inch of electrode spacing and actual tests have indicated that potentials outside of these limits are unsatisfactory for the purpose. The use of a three-phase system is of importance to the invention because with the three-phase system the deviation of the maximum voltage from the average voltage, generally known as the ripple factor, ris reduced so as to effect a reduction in pulsation. For example, a single-phase system pulses constantly with the ripple factor being approximately 52%; with the three-phase system the ripple factor is reduced to 4%.

Although the exact action which takes place in the electrical precipitator is not fully understood, it is believed that the electrical treating zone performs a dual function; first, it subjects the mixture to electrostatic mixing which insures completion of the oxidation reaction of the sulfur components, and second, it effects rapid Electrostatic mixing may be defined as the employment of the electrical energy to accelerate the motion of an electrically conductive particle or ion within the body of a non-conductive medium. The conductive particle which is the sulfuric acid is reduced by this mechanical mixing to a very small particle sizewith a correspondingly large increase in surface area which greatly enhances the contact between the sulfuric acid and the lsulfur components. 'Ihe predetermined electrical potential is applied to the properly spaced elec- 'which greatly enhances and encourages the probability of contact between any rgiven molecule of sulfur and any given molecule of sulfuric acid; second, Yelectrolysis of `chanical design of said Vessel.

the sulfuric acid molecule increases the speed and efficiency of the reaction. Actual experience with the process indicates that substantially complete oxidation reac `tion of the sulfur components to the disulfide form is accomplished, thereby assuring conversion of the components into the acid phase.

The electrical field also hastens and rapidly eects the coalescence of the droplets of sulfuric acid containing reaction products to accomplish rapid settling and efficient separation of the hydrocarbon on the one hand and the acid-reaction product on the other.

In addition to the proper spacing of the electrodes and the electrode potentials in the electrode system, the total residence or contact time of the mixture being treated is carefully controlled throughout the entire process to pre- Ivent the formation of undesirable reaction products, such as esters and sulfones. As has been noted, the contact time in the mechanical mixer is in the range of 3 to 6 minutes whereby a reduction of acid particle size to a previously determined optimum diameter is accomplished. The residence time of the acid-hydrocarbon mixture within the vessel 16 may vary between the limits of 20 to 40 minutes in accordance with the particular size and me- The effective residence time of the mixture within the settling zone which iS formed below the bottom live electrode 29 is preferably about 40% of the total residence time of the mixture within the vessel. The contact time is controlled by controlling the flow rate of the main hydrocarbon stream which is introduced through the inlet conductor and also by properly locating the electrode System within said vessel in relationship to the settling zone. In this manner the mixture is retained in the settling zone and in the electrical treating zone for the predetermined time which has been found most satisfactory to accomplish the improved results.

The operating temperature ofthe vessel 16 may vary from 40 F. to approximately 150 F. Below 40 F. the reaction does not proceed with the desirable speed, and above 150 F. the sulfuric acid will begin to react with other compounds in the stream to produce undesirable reaction products. As to operating pressure, the mini mum operating pressure is that which would be required to maintain the hydrocarbon phase as a liquid; there is no upper limit on the operating pressure except that which might be imposed by economical design of the vessel and associated equipment.

The process has been found extremely satisfactory when applied to a feed stock stream which is generally characterized as napthas, having ASTM boiling ranges of approximately 150 F. to 450 F. The sulfur content may vary from 25 to 1500 ppm. As heretofore mentioned, a treating agent which has been found satisfactory is sulfuric acid having an optimum strength lying between the limits of 85 to 98% titratable acidity, and the rate of acid addition varies with the nature and concentration of contaminants in the hydrocarbon. The particular process and its manner of functioning is believed evident from the foregoing. The sulfuric acid is intimately and vigorously mixed with the hydrocarbon stream in the mixer 12, and mixing is controlled to reduce the particle size of the acid to the point Where maximum surface area is presented for contact with the sulfur components. Oxidation reaction of the sulfur componentsto the disulfide form begins in the mixer and continues as the stream is distributed longitudinally within the Vlower portion of the vessel 16 by the header 27. The mixture is retained in the settling zone formed by the area between the headers and the lowermost live electrode 29 to permit the oxidation to proceed and to convert the reaction product to the acid phase; also some precipitation of the acid-reaction product occurs in the settling zone.

The mixture then flows upwardly and is subjected to the action of the direct current electrical field in the electrical treatment zone wherein the dispersion is subjected to suticient electrostatic mixing to insure completion of the oxidation reaction of the sulfur components in the hydrocarbon to the disulfide form, and to subsequently move such reaction products into the acid phase. At the same time, the action of the electrical iield continuously and rapidly coalesces the acid containing the reaction products and said acid is collected in the bottom of the vessel 16 from which it is discharged through the conductor 18. If the partially spent acid containing the reaction products is to be recirculated, it is conducted through re-cycling line 18a to the vessel 19. If, however, a once-through passage of acid through the vessel is being carried out, the spent acid containing the reacted disultides is withdrawn through outlet 26. The hydrocarbon stream leaving the vessel 16 which forms Ythe reaction stage is conducted therefrom Vthrough the outlet conductor 17.

Actual experience with the process has indicated that the sulfur content of catalytic reformer feed stock has been reduced to the point of eliminating corrosion or other difliculties in the reformer units through which the stream is subsequently conducted. As an example, actual tests were made on a Mid-Continent naphtha under exactly identical conditions, except that in one case the acidnaphtha mixture was passed through the reaction stage vessel 16, and in the other case it was not. Without the electrical treatment as above described, the sulfur was reduced from about 400 parts per million in the feed to about parts per million in the product. With the application of electrical treatment as above described, the sulfur in this same feed stock was reduced in the product to approximately 25 parts per million. It is believed that the improved results may be best explained by j the phenomena of electrolysis. However, electrolysis is conventionally employed with very high current and` low voltage, but the present apparatus has reversed this and employs very high voltage and very low current. The reduction of ripple factor by reason of the three-phase system is believed to be important because the reduction in pulsation provides for a steady state for the electrolysis to occur.

It has also been found that the total residence, or contact time, of the mixture in its passage through the vessel is of importance. By properly controlling the rate of flow the mixture may be retained within a vessel a predetermined length of time to permit the efficient separation of the sulfur components from the hydrocarbon stream.

It is ordinarily desirable to treat the product from the reaction stage with a caustic to neutralize the carry-over of sulfuric acid, and also to neutralize the acidic reaction products and naturally occurring acids which may be present in the feed stock. For this purpose, the hydrocarbon product from the reaction stage is conducted through the outlet conductor 17 and to the lower end of an electrical precipitator B. A suitable caustic, such as mild sodium hydroxide, is introduced through an inlet line 36a to a supply vessel 37. From this vessel a pump 36 directs the caustic through line 38 into the outlet conductor 17, the connection being made in advance of a mixer 39. A suitable ow controller 40a controls the volume of caustic being introduced through line 38. Mixer 39 thoroughly admixes the caustic with the stream under treatment and the mixture is conducted into the precipitator B.

Within the precipitator the admixed stream and caustic are subjected to a direct current electrical field whereby a neutralizing action is carried out. The precipitate from the precipitator B may be re-circulated through line 40, or may be discharged through line 41. It is pointed out that the electrical precipitator B may be of any standard construction, and this step of the process may be referred to as the neutralization stage.

The neutralized hydrocarbon may thereafter be Water washed to remove any carry over of caustic and in such instance is conducted from the neutralization stage precipitator B through line 42 which has connection with the lower end of a third electrical precipitator C. Water is introduced through inlet line 43 and is pumped by means of pump 44 through a line 45 which connects with the outlet conductor 42 extending from the neutralization stage. Flow controller 46 controls the volume of water so introduced and the water is mixed by means of a suitable mixer 47 with the neutralized hydrocarbon stream.

Within the precipitator C the water is electrically coalesced and the nal de-sulfurized product is conducted from precipitator C through outlet line 48. The separated water is removed through outlet line 49.

In some instances it may not be necessary to include the neutralization stage and water wash, although in most instances it is desirable to neutralize the product from the reaction stage. Actual experience with the process has indicated that the sulfur content of the catalytic reformer feed stock can be readily reduced to the point of eliminating corrosion or other difficulties in the reformer units through which the stream is subsequently conducted. As mentioned above, although the 'invention is particularly adapted to products of distillation, it is suitable for the treatment of any hydrocarbon stream in which the reduction of sulfur content is desirable. By means of the present process, a "simple type electrical treater in which the electrodes are properly spaced and the electrode potentials controlled may be employed. As noted, the intimate mixing of the acid with the hydrocarbon, together with the reaction time or residence time of the mixture within the reaction stage,lis of importance.

details of the illustrated construction, may be made within the scope of the appended claims without departing from the spirit of the invention.

I claim:

1. A process of treating a hydrocarbon stream containing sulfur components which comprises intimately and vigorously admixing with such hydrocarbon stream sulfuric acid having a strength of between 85 and 98% titratable acidity in proportions of 2 to 25 pounds of said acid per barrel of hydrocarbon for a period of 3 to 6 minutes, conducting the acid-hydrocarbon mixture into a settling zone, allowing said mixture to remain in said settling zone for a period of time sufficient to bring about the formation of sulfur-containing reaction products which dissolve in the acid, passing the mixture through an electrical field zone wherein the electrical field is generated by la direct current of approximately 1900 to 2500 volts per inch of electrode spacing with the electrode spacing being between 6 and 12 inches, while maintaining a temperature in the settling and electrical eld zones within the range of and 150 F. and a combined residence time of the acid-hydrocarbon mixture within the settling and electrical field zones between 20 and 40 minutes, removing acid from the settling zone, and removing a desulfurized hydrocarbon stream from the electrical iield zone.

2. A process as claimed in claim 1 in which the residence time of the mixture in the settling zone is approximately 40% of the combined residence time of the acidhydrocarbon mixture in the settling and electrical field zones.

References Cited in the file of this patent UNITED STATES PATENTS 2,101,168 Deutsch Dec. 7, 1937 2,382,697 Deutsch Aug. 14, 1945 2,412,791 Waterman Dec. 17, 1946 2,721,833 Defoe et al Oct. 25, 1955 2,855,357 Stanzel Oct. 7, 1958 2,974,095 Gordon Mar. 7, 1961

Claims (1)

1. A PROCESS OF TREATING A HYDROCARBON STREAM CONTAINING SULFUR COMPONENTS WHICH COMPRISES INTIMATELY AND VIGOROUSLY ADMIXING WITH SUCH HYDROCARBON STREAM SULFURIC ACID HAVING A STRENGTH OF BETWEEN 85 AND 98% TITRATABLE ACIDITY IN PROPORTIONS OF 2 TO 25 POUNDS OF SAID ACID PER BARREL OF HYDROCARBON OF A PERIOD OF 3 TO 6 MINUTES, CONDUCTING THE ACID-HYDROCARBON MIXTURE INTO A SETTLING ZONE, ALLOWING SAID MIXTURES TO REMAIN IN SAID SETTLING ZONE FOR A PERIOD OF TIME SUFFICIENT TO BRING ABOUT THE FORMATION OF SULFUR-CONTAINING REACTION PRODUCTS WHICH DISSOLVE IN THE ACID, PASSING THE MIXTURE THROUGH AN ELECTRICAL FIELD ZONE WHEREIN THE ELECTRICAL FIELD IS GENERATED BY A DIRECT CURRENT OF APPROXIMATELY 1900 TO 2500 VOLTS PER INCH OF ELECTRODE SPACING WITH THE ELECTRODE SPACING BEING BETWEEN 6 AND 12 INCHES, WHILE MAINTAINING A TEMPERATURE IN THE SETTLING AN ELECTRICAL FIELD ZONES WITHIN THE RANGE OF 40 AND 150*F. AND A COMBINED RESIDENCE TIME OF THE ACID-HYDROCARBON MIXTURE WITHIN THE SETTLING AND ELECTRICAL FIELD ZONES BETWEEN 20 AND 40 MINUTES, REMOVING ACID FROM THE SETTLING ZONE, AND REMOVING A DESULFURIZED HYDROCARBON STREAM FROM THE ELECTRICAL FIELD ZONE.

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