US2631121A

US2631121A - Hypochlorite sweetening process

Info

Publication number: US2631121A
Application number: US110172A
Authority: US
Inventors: Norman F Linn; Arthur K Scott; Walter H Rupp
Original assignee: Standard Oil Development Co
Current assignee: Standard Oil Development Co
Priority date: 1949-08-13
Filing date: 1949-08-13
Publication date: 1953-03-10
Anticipated expiration: 1970-03-10

Description

March 10, 1953 N. F. I INN ET AL HYPOCHLORITE SWEETENING PROCESS Patented Mar. 10, 1953 UNITED STATES PATENT OFFICE HYPOCHLORITE SWEETENING PROCESS Application August 13, 1949, Serial No. 110,172

3 Claims. l

This invention is concerned with an improved hypochlorite sweetening process in which particular operating features are involved and in which particular concentrations of treating agents are maintained. 'I'he invention is concerned with the conversion of mercaptan compounds present in petroleum oils using a treating reagent consisting of ahypochlorite solution containing high quantities of sodium hydroxide and sodium chloride. A novel feature of the process is the manner in which it is continuously conducted so as to provide for the recirculation of the main body of the treating reagent with provision for the discard of a portion of the agent and for the addition of makeup constituents so as to maintain optimum quantities of the treating constituents at all times. A particular advantage of the process is the economy of operation provided by a novel manner of treating spent hypochlorite solution so as to provide suitable sodium hydroxide solutions for preliminary caustic washing operations.

As disclosed in United States application No. 86,152 led April 5, 1949, now U. S. Patent No. 2,550,668, improved sweetening results may be obtained by using a hypochlorite sweetening solution containing an excess quantity of sodium hydroxide and a high proportion of sodium chloride. Such a solution is operative to cause a marked reduction in sulfur content when using a comparatively small treat. The present invention is related to this type of operation by providing an improved procedural method for conducting this type of sweetening adapted for economic commercial utilization. It is therefore to be understood that while the identied application U. S. 86,152 broadly concerns the concentrations of constituents to be used in hypochlorite sweetening, this application relates to improved steps and procedures for conducting this type of sweetening.

In the refining of petroleum oils, a common refining step is to treat the oils by various procedures in order to remove objectionable compounds such as sulfur compounds therefrom. One manner of accomplishing this which has been known is to treat particular hydrocarbon fractions with a hypochlorite solution containing, for example, either sodium or calcium hypochlorite. Mercaptans present in the petroleum fraction react with the hypochlorite solution to form alkyl disuldes,

a metal chloride, and water. The conversion of the mercaptans to disuldes has the effect of sweetening the petroleum fraction so as to eliminate the malodorous mercaptans and so as to form the relatively harmless disuldes.

This general type of sweetening operation using hypochlorite solutions has not been particularly attractive for a number of reasons. First, a prime disadvantage of the older method of sweetening with hypochlorite solutions containing only relatively minor amounts of free sodium hydroxide is that considerable amounts of chlorine are introduced into the hydrocarbons with a resulting degradation in product quality. Secondly, the corrosion of equipment has been severe so that high replacement rates and costs have discouraged the wide adoption of the hypochlorite process. Thirdly, in prior methods of sweetening with hypochlorite solutions containing minor amounts of free sodium hydroxide as in. U. S. Patent 1,552,830, it was necessary to follow the sweetening operation with a caustic washing step in order to obtain a marketable product. By conducting the sweetening operation according to the improved process described hereafter, no caustic afterwash is required. It is therefore the principal object of this invention to provide an improved hypochlorite sweetening process in which relatively low treats of the treating reagent are required, in which product degradation is substantially reduced and in which the corrosivity of the treating solution is substantially eliminated.

A still more specific object of this invention is to provide an effective continuous process for conducting the sweetening operations in a manner to permit maintenance of the optimum quantities of sweetening reagents.

A still further object of the invention is to provide a recovery operation for treating the spent hypochlorite sweetening solution so as to economize the consumption of the treating reagent.

The manner in which these and other objectives of this invention are attained will be understood from the following description developed with relation to the accompanying drawing in which a suitable iiow plan of the hypochlorite sweetening process of this invention is diagrammatically illustrated.

In accordance with the process of this invention, a sweetening solution is used consisting of particular proportions of hypochlorite, of sodium hydroxide, and of sodium chloride. The hypochloritc in the solution may consist of either sodium or potassium hypochlorite, although, other alkali metals or alkali earth metals having soluble hydroxides may be used, if desired. The amount of the hypochlorite solution employed is not critical and may vary appreciably in the ranges, for example, of about 2% to 50% and higher, based upon the volume of oil being treated. According to the preferred procedure, in order to maintain the quantity of treating solution as low as possible, the percent treat is maintained at about 5%. Similarly, the concentration of the hypochlorite in thel sweetening solution may vary appreciably, and, to some extent, the concentration will be a function of the amount of solution utilized. Thus, While the concentration of the hypochlorite may be chosen from the range of about l to 6o grams of sodium hypochlorite or equivalent, per liter, it is preferred that the concentration be in the range of about l to l2 grams per liter of treating solution. More, narrowly still, it is preferred that about l to 5 grams per liter of hypochlorite be utilized. These specific concentrations of hypochlorite limit the oxidizing power of the solution so as to minimize undesired reactions.

The concentration of sodium hydroxide maintained in the sweetening solution is a critical factor which must be assiduously maintained above 90 grains per liter. A preferred concentration of the sodium hydroxide is 100 to 360 grams per liter, and, more specifically, may be said to be about 200 grams per liter. The concentration 0I" the sodium hydroxide is critically chosen in the range indicated for three reasons. First, the sweetening effect obtainable is critically related to the sodium hydroxide content, as indicated by the fact that improved sweetening results are obtained in the case in which an excess of sodium hydroxide is maintained over the case in which less than 50 grams per liter of sodium hydroxide 'is maintained. Secondly, by maintaining a high concentration oi caustic, the equilibrium between hypochlorite and hypochlorous acid is controlled so that only a small concentration of hypochlorous acid will be present. This aids in limiting 'the oxidation potential of the treating solution lrosivity of the sweetening solution is critically related tothe concentration of the sodium hydroxide. Thus, it has been discovered that when the sodium hydroxide is present in concentrations of less than about 9G grams per liter, the sweetening solution begins to exhibit corrosive tendencies towards ferrous materials. However, When the concentration of the sodium hydroxide is greater than about 90 grams per liter, the sweetening solution is substantially non-corrosive to ferrous materials. Consequently, for these three reasons, the concentration of sodium hydroxide is maintained above 90 grams per liter, and preferably, at about l0() to 300 grams per liter so as to maintain the hydroxide content on the safe side of the corrosive limits and so as to maintain the hydroxide content in the range in which improved sweetening results may be obtained.

Similarly, the 'concentration 'of the sodium tive to remove hydrogen Ystunde and a particular caustic.

4 chloride maintained in the sweetening solution is a critical factor which is carefully controlled by the process of this invention. Thus, improved sweetening results are obtained by maintaining the sodium chloride content in the range of about 50 to 250 grams per liter, the upper limit being set by the solubility of sodium chloride. It is apparent that should reagents other than sodium hypochlorite and sodium hydroxide be used, the concentration of the corresponding salt should similarly be maintained below saturation conditions. Iii the preferred operation of this process, the sodium chloride content is maintained at about 10G grams per liter. This range is particularly preferred in order to keep the sodium chloride at a concentration level adapted for effective s weeteningbut so as to maintain the sodium chloride content below the level at which the sodium chloride begins to precipitate from the sweetening solution. rihis precipitation point is at about 170 grams per liter of sodium chloride whenthe treating solution contains 200 g./l. of NaOH and 5 g./l. of NaOCl. A practical advantage of operating considerably below the saturation limit of sodium chloride, at about grams per liter for example, is that localized salt buildups may be tolerated without likelihood of Salt precipitation.

Other operating parameters` of the sweete'ning operation are not particularly critical and may be controlled within wide limits. Thus', the time of Contact may be more or less arbitrarily chosen, but should preferably be below' about 10 minutes to limit possibility of undesirable side reactions. A contact time of about 2 to 5 minutes is preferred. The temperature of treatment may be chosen from the range of about ambient temperatures to about 150 F. Any temperature greatly in excess of about F'. is undesirable since the sodium hypochlorite in the sweetening solution becomes unstable at higher temperatures.

With this general indication of the critical factor and principles of hypochlolite sweetening, the process of this invention may be appreciated by reference to the accompanying drawing. Referring to this-drawingtbe numeral I designates a feed introductionline for petroleum fractions to be treated in accordance with this invention. The fraction to be treated may broadly be any `hyd'rocarbon fraction boiling below about '700 F. The process is of particular application to the treatment of uncracked hydrocarbon fractions although it is also effective in the sweetening of cracked stocks. The process is particular-ly apE plicable to those hydrocarbons boiling in approximately the kerosene boiling range. as, for example, in the range of about 3D0 to 690 F, It is to be understood that the fraction to be treated con tains malodorous mercaptans to be converted by the sweetening operation. Consequently, a suitable feed stock is conducted through line' l to a mixing zone 2, wherein the feed hydrocarbons are mixed with a caustic solution introduced through line 3. As illustrated, the caustic washing facilities may comprise the orifice mixers or equivalent mixing means indicated by the numeral 2 operated in conjunction With the separation zone 33. Suitable caustic washing will be provided by utilizing a single stage caustic contacting of the feed employing about 4 to 20 percent of a caustic solution containing` about 3 to 20 percent of It is preferred to utilize about 10% of a caustic solution comprising about 5` Baume caustic solution. This caustic washing is operaother sulfur compounds from the feed. The particularpurpose of the caustic washing is to remove the hydrogen sulde which otherwise could be converted to elemental sulfur in later sweetening steps.

The caustic washed feed hydrocarbons may be removed from the upper portion of separation zone 33 through line 5 while the spent caustic solution may be removed from the lower portion of zone 33 through line G, containing the abstracted sulfur compounds. The caustic washed feed hydrocarbons are then conducted through line 5 to mixing zone 'l and sweetening zone 8. Again, the-mixing means utilized in zone l may, if desired, consist of simple orice mixers or equivalent means operative to thoroughly mix the feed hydrocarbons of line 5 with sweetening solution conducted through line S. As will be developed, the sweetening solution of line 9 principally consists of the sweetening reagents withdrawn from the sweetening zone t through line IG for recycle back to zone 8 through line il. Makeup sweetening constituents are also introduced to line 9 from line II leading from storage zone I2. Thus, storage zone I2 contains a solution containing fresh hypochlorite, sodium hydroxide and sodium chloride. This solution may be made up in the solution makeup vessel i3 in which caustic, Water, and chlorine are combined. Thus, caustic solution may be introduced to zone I3 through line Id while water and chlorine are respectively introduced to zone I3 through lines I5 and IS. 1n a specific embodiment of this invention, caustic of about 50 Baume is introduced through line Ill While sufcient water is introduced through line I5 to dilute the caustic to a concentration of about 29 Baum. Sucient chlorine is then introduced through line I6 to provide a desired concentration of sodium hypochlorite. As an example of preferred conditions, sufficient reagents are introduced to zone I3 so as to provide a sweetening solution consisting of 200 grams per liter of sodium hydroxide, 65 grams per liter of sodium hypochlorite and about 51 grains per liter of sodium chloride. Sodium chloride is formed as a by-product of the hypochlorite formation and subsequently in the sweetening zone is formed as a by-product of the sweetening reaction. It is important that cooling coils or equivalent means I7 be provided in zone I3 so as to maintain the temperature of the solution below about 125 F. The sweetening solution as made up may then be conducted to storage zone I2 for subsequent addition lto sweetening zone 8, as will be described.

In the operation vof sweetening zone 8, as indicated, the feed hydrocarbons to be sweetened are mixed with the sweetening reagents in mixer 'I and are then passed to the separation zone 8. Zone 3 may simply consist of a settling zone operated to permit withdrawal of sweetened hydrocarbons from the upper part thereof through line I8 and to permit the Withdrawal of partially spent sweetening solution from the lower part of the zone through line lll. The temperature of zones l' and 8 is maintained below about 150 F., preferably below 125 F. The Contact of the indicated sweetening solution and the feed hydrocarbon converts mercaptans present to disuldes with the consequent formation of sodium chloride. Thus, the concentration of sodium chloride in line iii will be greater than the concentration of sodium chloride in line II. Similarly, the concentration of the sodium hypochlorite 4in line I0 will be lower than the concentration of sodium chloride in line II. It is apparent that with continuous recycle of the sweetening solutions through line I0 back to the sweetening zone, the concentration of sodium chloride would build up to prohibitive levels, While the concentration of the sodium hypochlorite would drop to insufficient levels. Consequently, a portion of the solution of line I0 is periodically or continuously Withdrawn through line I9 while a substantially equivalent amount of fresh sweetening solution is introduced to the system through line II. In the preferred operation of this process, the withdrawal of sweetening solution through line I9 is maintained so as to hold the sodium chloride content of the solution at a desired level. Thus, for example, sufcient solution is withdrawn from line I0 through line I9 so that this solution has a composition of about 200 grams per liter of sodium hydroxide, about 31/2 grams per liter of sodium hypochlorite, and about grams per liter of sodium chloride. By this method of withdrawing partially spent sweetening solution while continuously adding fresh sweetening solution, it is possible to maintain the concentrations of sweetening reagents at optimum levels at all times. Thus, by the specific Withdrawal and introduction of sweetening compositions having the concentrations indicated, at all times the sweetening reagents present in zone 8 will consist of a solution containing about 200 grams per liter of sodium hydroxide, from 31/2 to 5 grams per liter of sodium hypochlorite, and from 98 to 100 grams per liter of sodium chloride. As will be developed, sweetening solutions of this composition are best adapted for the sweetening of hydrocarbons While having minimum corrosivity towards ferrous materials so that conventional steel tank and apparatus facilities may be utilized in the sweetening.

To complete the processing of the sweetened hydrocarbons removed through line I8, these hydrocarbons are preferably subjected to a water wash in mixer 20= and settling zone 2|. For this purpose, about 30 volume percent of Water may be introduced through line 22 for admixture with the hydrocarbons in mixer 20. The water Washed sweetened product may then be removed through line 23 from the separation zone 2| While the water utilized may be discarded through line 24.

A particular feature of this invention is the manner in which the abstracted sweetening solution of line I9 is treated. The solution of line I9 is preferably contacted with steam in jet mixing zone 25 yand is then Aconducted to decomposing zone 25. The contact of the spent sweetening solution with steam in zones 25 and 2:6 decomposes the greater part of the sodium hypochlorite. As indicated, the decomposition may be carried out by utilizing steam as a source of heat input provided the temperature be increased to about 200 F. Alternatively the solution of line I9 may be passed into decomposing zone 26 and there be contacted with steam to promo-te decomposition of residual sodium hypochlorite. The steam is also effective to dilute the sweetening solution sufciently to prevent crystallization of salt present. It is preferred that the sweetening solution be maintained in zones 25 and 2-6 for a period about l0 minutes in order to permit satisfactory decomposition of the sodium hypochlorte to sodium chlorate and sodium chloride.' 'I'he resulting solution, to be removed through line 21, will therefore consist of a'sodium-hydroxide solution 7 Y a containing tolerable concentrations of vsodium titles of sodium hydroxide. These experiments chlorate, sodium hypochlorite and sodium chloset forth in the table ybelow showed that if causride. This caustic solution on suitable dilution tic concentration was maintained above about may -then be recycled through line .2T for utiliza- 90 grams per liter, substantially no corrosion tion as the caustic washingagent employed in occurred.

caustic washing zones 2 and 3. If desired, a por- Corrosion tests on steel tion of the sodium hydroxide solution of line 21 may be withdrawn for use as desired in other re- Composition of S0. ning operation-s. fslllmffypochlm'ie Having now fully described a preferred manner 10 o u lo rime on Cogofin Nt. of conducting the process of this invention ex- I. Test Inr. l mg `ree Available amples of treating operations will be given to NaOH, Chlorine, more clearly denne rthe nature and scope of this g-/lgJl' invention.

tt 23 32 838% t3 EXAMPLE l 100 45 25 0 0001 No An uncracked kerosene fraction con-taining 15g g mercaptans and boiling in the range from about g 34D to 530'o F. was contacted with hypochlorite as si i9 0 0030 Yes solutions containing diierent quantities of sodium hydroxide for contact times of about 2 EXAMPLE 3 minutes.

The results of these operations are listed as An uncracked kerosene secured from a West follows: Texas crude and boiling in the range from about Eleot of concentration of sodium hydroxide in hypochlorite sweetem'ng of kerosene in two minutes Contact time Hypocmome Analysis Treat, Acidty Chlorine, Operation Vol. Doctor Test MLN/1OKH/ Wt.

N800), gn. NaOH, gli. Percent 100 m1. Percent 10.7 2. i 10. 7 2. l 50 10. 7 26 10 l10.7 2e 25 10.-8 51 l0 10. 6 78 l() 10. 5 1'07 5 10. 5 107 10 These results show that the kerosene can be 350 to 530 F. which contained 99 milligrams of sweetenedwith progressively mauer amou-ms 9i mercaptan sulfur per 100 milliliters was treated hypochlorite as excess sodium hydroxide is L utilized. 1n various operations with the following results:

Ejeot of sodium hydromz'cte concentration in .hy-

pochlortte sweetenirtg of West Texas kerosene in two minutes contact time Hypoclilorite Analysis Treat I operano PQE-m Dom Test KOH/'ion m1. wt. Percent Na() Cl, g.,l. NaOH, g./l.

55. v 0. o 100 2o. 1 o. 0341 55.1 9. o 13. 5 0. 0204 10. 6 7s. o 50 3. a .021

From the albove it is apparent that very desi-r- From the above data it is apparent that for a able results are secured by utilizing a hypochloxed NaOH concentration, as the quantity of rite .solution containing a relatively high QOIICBH- treat increased lthe tendency to form undesirable 'traton'of Sodlumhydmxdesulfonic acids and sulfonyl chlorides increased EXAMPLE 2 prohibitively as evidenced by the increase in Corrosion experiments were conducted to deacldlt on the other hand m Operamon 5 termine `the corrosivi'ty toward steel test panels wherein an excess of `sodium hydroxide Was emof sweetening solutions containing variablequanployed, the acidity was appreciably lower.

junction with Vanfex'ces's of sodium hydroxide.

rIVhe results of these operations are as follows:

Effect of excess sodium chloride in hypochlorite sweetenmg of Iraq kerosene (14 mg. mercaptan sulfur/100 ml.)

Hypoohlorite Composition! Chlorine Operation Treat V 01' Doctoi.l Test Rcs-@ual Wt.Per-' Percent Acldity e t Nacre/1. Na0H,g./1. Naooi, g./1. c

s 1.0 10.4 s0 1.0 10.4 s 107 10.0 1(5) 80 105 10.6 5

1 Amounts of sodium chloride shown were weighed into the solutions; NaOH and NaOCl were determined by analysis.

and boiling in the range from" '35010 500 F. with the following results:

From the above, it is readily apparent that when excess vsodium Achloride is used in conjunc- Hypochlorite Analysis Treat, l Operation V01. DOCOI TUS Alslgglovl eelxt Naool, g./1; Noon, g./1. Percent 10. 8 156 2 DNP 10.8 156 5 Pass 2. 03 0. 0044 10.5 166 2 dO 0.48 0.0014 10, 3 220 2 .do 0.58 O. 0014 It is apparent from this data that excellent 35 tion with a'hypochloite solutidn which contains results are secured when the amount of hypochlorite is maintained relatively low, when excess sodium hydroxide is employed, and also when a relatively low volume of treat is utilized.

EXAMPLE 4B a relatively low concentration of sodium hydroxide, no marked eiect is secured. However, when excess sodium chloride is used in conjunction Was a hypochlorite solution which has a high concentration of sodium hydroxide, unexpected and desirable results are secured.

EXAMPLE 6 A solution containing about 2.3 grams per liter of sodium hypochlorite was heated to 210 F. After maintaining this temperature for one minute, it was found that the hypochlorite concentration had been reduced to about 0.8 gram per It will be noted that as the concentration of caustic is increased, the weight percent of chlorine in the product is progressively reduced. By operating therefore with solutions containing signicant amounts of caustic no strong caustic afterwash is required in order to obtain an acceptable product. Further, it will be observed that the ratio of actual consumption of sodium hypochlorite to theoretical is significantly reduced as the caustic concentration is increased.

EXAMPLE 5 Additional operations were conducted wherein an excess of sodium chloride was used .in oonsweetening solution is particularly controlled in accordance with-this invention so as to maintain a given concentration of sodium chloride such as 100 grams per liter in the discarded sweetening solution. The discarded sweetening solution is then decomposed by heating to a temperature above 200 F. and is diluted to provide a usable caustic solution, at least a part of which is used to pre-wash the hydrocarbons to be sweetened. As indicated, this novel treating process is par ticularly adapted for the treatment of hydrocarbons of the kerosene boiling range.

What is claimed is;

1. A sweetening process in which hydrocarbons are contacted in a sweetening zone with a sweetening solution having a hypochlorite content of about 1 to 12 grams per liter, a sodium hydroxide content of about 100 to 300 grams per liter, and a sodium chloride content of about 50 to 100 grams per liter, said sweetening solution being maintained to have this composition by substantially constant recirculation through the said sweetening Zone, while withdrawing partially spent sweetening solution substantially constantly characterized by containing about 100 grams per liter of sodium chloride, and While introducing fresh svveetening solution substantially constantly to the said sweetening zone, said fresh sweetening solution having about 1 to 12 grams of hypochlorite per liter, a sodium hydroxide content of about 100 to 300 grams per liter, and a sodium chloride content of about 50 grams per liter.

2. The process of claim '1 in which the feed l2 hydrocarbons are pre-Washed with caustic solution.

3. The process of claim 2 in which the withdrawn sweetening solution is heated to temperatures above about 200 F., is diluted with Water, and at least a portion thereof is utilized in the caustic washing steps.

NORMAN F. LINN. ARTHUR K. SCOTT. WALIER H. RUPP.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,435,824 Dunstan Nov. 14, 1922 1,600,845 Reinhold Sept. 21, 1926 1,636,946 Weber July 26, 1927 1,658,171 McMichael Feb. 7, 1928 1,784,215 Ziser et al. Dec, 9, 1930 2,028,998 Schulze et al, Jan. 28, 1936 2,379,228 Gilbert June 26, 1945 2,488,855 Denton Nov. 22, 1949 2,550,668 Brandon et al May l, 1951 FOREIGN PATENTS Number Country Date 288,931 Great Britain Apr. 13, 1928 OTHER REFERENCES Wood et al., Ind. and Eng. Chem.. 18, 823-826 (1926).

Claims

1. A SWEETENING PROCESS IN WHICH HYDROCARBONS ARE CONTRACTED IN SWEETENING ZONE WITH A SWEETENING SOLUTION HAVING A HYPOCHLORITE CONTENT OF ABOUT 1 TO 12 GRAMS PER LITER, A SODIUM HYDROXIDE CONTENT OF ABOUT 100 TO 300 GRAMS PER LITER, AND A SODIUM CHLORIDE CONTENT OF ABOUT 50 TO 100 GRAMS PER LITER, SAID SWEETENING SOLUTION BEING MAINTAINED TO HAVE THIS COMPOSITION BY SUBSTANTIALLY CONSTANT RECIRCULATION THROUGH THE SAID SWEETENING ZONE, WHILE WITHDRAWING CONSTANTSPENT SWEETENING SOLUTION SUBSTANTIALLY CONSTANTLY CHARACTERIZED BY CONTAINING ABOUT 100 GRAMS PER LITER OF SODIUM CHLORIDE, AND WHILE INTRODUCING FRESH SWEETENING SOLUTION SUBSTANTIALLY CONSTANTLY TO THE SAID SWEETENING ZONE, SAID FRESH SWEETENING SOLUTION HAVING ABOUT 1 TO 12 GRAMS OF HYPOCHLORITE PER LITER, A SODIUM, HYDROXIDE CONTENT OF ABOUT 100 TO 300 GRAMS PER LITER, AND A SODIUM CHLORIDE CONTENT OF ABOUT 50 GRAMS PER LITER.