US2729592A - Air sweetening process - Google Patents

Description

Jan. 3, 1956 E. J. NIEHAUS, JR

AIR SWEETENING PROCESS Filed Feb. 3, 1953 Edward J. Niehaus, Jr. Inventor Byaw .-7MWD/1ttorney United States Patent O AIR SWEETENING` PROCESS Application February 3, 1953, serial No. 334,365 claims. (c1. 19a- 29) This invention concerns a process for the sweetening of naphtha compositions. In acocrdance with this invention sour gasoline stocks are sweetened by contact with air and ammonia in the presence of a phenylenediamine oxidation inhibitor. The invention is of particular application to the sweetening of cracked gasolines including blends of cracked gasolines and virgin gasoline.

The removal of undesired sulfur compounds from petroleum products is a perennial problem in the petroleum refining industry. While there have been many suggestions made as to processes for removing undesired sulfur compounds, the desire for simplified sulfur removal processes remains. Again new problems are encountered in the processing `of novel feed stocks or unusual blends of stocks.

Comparatively recently it has been discovered that cer-` tain stocks are susceptible to what is known as air sweetening. For example, certain gasolines during simple storage under conditions to expose the gasolines to oxygen will undergo a process in which mercaptans are converted to` disultides. This conversion of sulfur compounds from mercaptans to disuliides is called sweetening by virtue of the fact that the disullides, unlike the mercaptans, are not malodorous. The basic simplicity of the air sweetening process holds great promise as a `finishing procedure for stocks susceptible to this treatment in order to provide the last incremental improvement in sweetening which is often required. The present invention is concerned with an improvement in air sweetening techniques providing for increased rates of sweetening of those stocks` which respond to air sweetening. It is a particular feature of the process that it has been found to be of particular application to the sweetening of blends of cracked gasolines with virgin gasolines, since virgin gasolines are normally unresponsive to air sweetening.

In` accordance with this invention a naphtha to be sweetened is subjected to a pre-caustic wash. This caustic wash is primarily used to eliminate hydrogen sulfide since hydrogen sulfide would be converted to objectionable free sulfur in the subsequent air treating step. Hydrogen sultide would also react with and poison theinhibitor. The caustic pre-wash also serves to remove at least some of the sulfur compounds so that the following air sweetening step requires less storage or treating time. It also prevents hydrogen sulfide and mercaptans accumulating in the ammonia solution. While the caustic pre-wash step of the process is required it is to be understood that other sweetening operations may be conducted prior to the caustic pre-wash or the air sweetening process to be described. Thus, the process of this invention is not intended as a single step sweetening operation, but is rather intended as a supplemental sweetening `operation effective to eliminate residual mercaptan content after prior f sweetening operations. example, the so-called solutizer sweetening operation is now well known. In a solutizer operation a petroleum distillate is contacted with a caustic solution containing agents which increase the extractive power of the caustic In this connection, for` Patented Jan. 3, 1956 solution for mercaptan compounds. In many cases however, it is difiicult to secure a mercaptan-free product by this type of processing. This then isone example of the field of application of this invention.

The naphthas to be sweetened by this process may be identified by reference to the mercaptan content of the stock. As indicatedby the copper number of the gasoline, the invention is of particular application to those gasolines having a copper number ranging from about l, or less, to 15. As will be understood, such gasolines may constitute gasolines obtained from prior sweetening operations or from relatively low sulfur crude oils.

It should be understood that this: process is not of application to stocks which are essentially virgin in character. Thus, gasolines which are derived by the distilla- 2` tion or fractionation of crude oils are not susceptible to the process of this invention. Rather, the invention `is of application to gasolines derived from thermal or catalytic cracking operations. Itis a particular feature of this process that when cracked gasolines are blended with Virgin gasolines in substantial proportions, the resultant blend also responds to the treatment of this invention. The gasolines to be treated may therefore be identified as gasolines containing at least about 1/3` of cracked naphthas. p

After the caustic pre-wash of the gasoline to be treated, the gasoline is simply contacted with air and ammonia in thepresence of a phenylenediamine compound, so as to secure the desired sweetening. Phenylenediamine com pounds are commonly classed as anti-oxidants. Particularly effective compounds in this class are the N,N- dialkyl-p-phenylenediamnes, and of these compounds phenylenediamines which are preferred for use are N,N- di-sec-butyl-pphenylenediamine, and N,N'dinbutylpphenylenediamine. The amount of the phenylenediamine compound to be included in the gasoline to be treated ranges from about 0.1 to 2 lbs. per 5,000 gallons of gasoline.

in carrying out this process it is convenient to incorporate the phenylenediamine inhibitor in the gasoline after the hydrogen suliide has been reacted with caustic soda. Air and ammonia may be introduced to the gasoline by any desired type of mixer. Orifice mixers may conveniently be employed. Thereafter it is only necessary to store the gasoline for a period of about l to 3 days to secure the desired sweetening. After the storage period the ammonia may be recovered from the gasoline and recycled for continuous use if desired. The process may thus be identified as a regenerative sweetening operation.

This invention may be fully understood and the preferred practice of the invention will be described with reference to the accompanying drawing which diagrammatically illustrates an operative flow plan embodying the invention.

In the drawing, a caustic pre-wash zone is identified by the numeral 2. A naphtha to be sweetened, of the character heretofore described, is passed through line 3 for entrance to zone 2. Caustic soda employed for the caustic wash may be introduced through line 4 for mixture with the sour naphtha in an orifice mixer or the like identified by numeral 5. The caustic soda to be employed may constitute about l to l0 volume percent of 5 to 30 percent caustic. Aqueous solutions of other alkali metal hydroxides may of course be employed if desired. The phenylenediamine inhibitor may conveniently be added to the naphtha through line 6 before passage of the naphtha to the caustic settler. However, it is only necessary that the phenylenediamine compound be added to thenaphtha prior to air contact, and thus it may be added if desiredv after the caustic pre-wash.

The sour naphtha of line 3 after admixture with caustic soda from line 4 passes through mixer 5, and after admixture with inhibitor added through line 6, is then brought in to the settling zone 2. Here the naphtha separates from the caustic solution so that naphtha may be wihdrawn through line 7' and spent caustic may be discharged through line 8. This entire .caustic washing operation must be conducted in the absence of oxygen. For this purpose oxygen-free contacting solutions are to be employed and a closed system must be used to prevent any access of air or oxygen.

The caustic washed naphtha of line 7' is then mixed f with an aqueous ammonia solution obtained from ammonia storage zone 9. The aqueous ammonia may have a concentration'of about l to 28 percent, and is employed in quantities of about l to volume percent, based on the naphtha with which it lis mixed. Ammonia withdrawn from storagefzone 9 and passed through line 10 may be mixed with the naphtha in orifice mixer 1l or thelike. Air is also introduced to the naphtha of line -.7 prior to passage through mixer 11. Air maybe introduced through line 12 yby means of a compressed air line containing a meter such as arotameter. The air injected should be not less than 0.05 of a standard cubic foot per copper number per barrel of gasoline treated. Thus, for a gasoline of 10 copper number 0.50 s. c. f. of air vper barrel would be the minimum requirement, but

about 1.5 s. c. f. would be preferable to speed up the sweetening rate. The process may be operated continu ously but throughput must be controlled so that the holdup time in zone 13 is sufficient to complete sweetening.

The naphtha containing the phenylenediamine admxed with the air and ammonia is then conducted to storage zone 13. Depending upon the quantity of mercaptan sulfur in the untreated naphtha, a holdup period of about 1 to 3 days is to be employed. As the aqueous ammonia solution accumulates on the bottom of storage tank 13, it may be drained off through line 14 and can be returned to storage zone 9 for re-use.

The gasoline is withdrawn through line 15 and is subjected to a water-wash to eliminate any residual traces of ammonia. Thus, the gasoline in line 15 may be mixed with water from line 16 to orifice mixer 17. About 2 to 25 volume percent of water is preferably employed in this washing operation. The gasoline is separated from the water in settling zone 1 8 so that ythe VVfinished sweet naphtha may be Withdrawnthrough line 19. Water settling from the naphtha is removed from zone 18 through line 20 and may be transferred to ammonia recovery facilities through line 21 to be described.

In this process it is practical and desirable to vent the storage Zone 13 through a line 30 leading to a'simple water scrubber 31. Scrubber 31 may constitute an elongated vessel preferably illed with packing material or the equivalent to secure effective contact of water with vapors rising through the tower. Thus, air ventedlfrom storage zone 13 is introduced to the bottom of scrubber 31 while water is introduced to the top of scrubber 31 through line 32. This operation removes any ammonia from the air so that a weak ammonia solution may be withdrawn from the bottom of the scrubber through line 34. In order to avoid a pressure on tank 13 and to induce flow through vent line 30 and the scrubber 31, a

slight vacuum vin line 33 is desirable and can be developed by a small exhaust fan. VThe ammonia solution withdrawn through line 34 is combined with the ammonia of line 21 and is passed to the ammonia recovery still 35. A portion of the ammonia may be introduced to still 35 through line 36 so as to pass in heat exchange relation with the water derived as a bottoms product of the still through line 37. A second portion of the ammonia solution of line 21 may be introduced t'o still 35 through line 47 to asto pass in heat exchange relation with ammonia removed from the top of still 35 through line 38. The ammonia recovered from line 38 may then be passed through a cooler 39 and may be returned to ammonia storage zone 9 by Way of line 48 for continued re-use. It will be seen that this process provides for the complete regeneration ofthe ammonia' solution employed in the process.

Although the process as here described is a continuous' operation, it must be understood that it can also be operated batchwise. In such a case tank 13 would simply be filled with gasoline, which had been treated as described above, where it could be stored for as long a period as desired.

Another way of conductingk the process is to recycle the gasoline from tank 13 to the inlet of mixer 11 and TABLE I Air-ammonia-z'nhbtor sweetenng of various naphthas Catalytic Naphths Light Light Virgin Ther- 'rype or Naphtha 'logl Light catalytic mal Inspections: v v

Boiling Range, F 97-304 110-330 123-406 10U-353 10B-348 98-346 98-346 91-346 Gravity, API 67. 64. 53. E 65. 0 64. 8 63. 4 63. 4 60. 6 Copper No.-

Raw 12 12 Caustic Wash (3 Vol. Percent 15 Be.) 23 54 l0 13 10 6 5 l 20 Treating Conditions:

Inhibitor Added, lb./5,000 Gal 1 0 1 0 1 0 1.0 1 0 1 0 1 0 1 0 Ammonia Solution Added, V

cent 1 1 l 1 1 1 1 l NH; Concentration, wt. Percent NH:

in water 28 28 1 4 28 14 28 1 4 28 Aix' Space, Vol. Percent.. 50 50 50 50 50 50 50 50 Agitation, Min 2 2 2 2 2 2 2 2 Temperature, F 75 75 72 75 72 100 75 75 Rate of Sweetening: Copper Number- Initially After 24 hrs. storage- After 48 hrs. storage- After 72 hrs. storage- After hrs. storage; Percent Mercaptan Reduction in 48 hours.

l Raw naphtha, uoteaustc washed. I Washed with 25 B. caustic soda.

back to tank 13. This can be done while pumping in fresh feed or the fresh feed can be held out and the gasoline in tank 13 recycled until sweet.

The application of this invention to different types of naphtha is illustrated in Table I. Complete data as to the operations conducted are there given in applying the process to the treatment of a light virgin naphtha, a catalytic naphtha, a thermal naphtha, a blend of light catalytic naphtha with light virgin naphtha, and a blend of light thermal naphtha with light virgin naphtha. In each case 1.0 1b. of N-Ndisec-butyl paraphenylene diamine per 5000 gallons of naphtha was employed. One volume percent of ammonia solution was mixed with the naphtha containing this concentration of inhibitor. The ammonia solution in most cases had a concentration of 28 weight percent ammonia as shown in the table. In these experiments, air contact was achieved by shaking the ammonia and naphtha together in a bottle containing an air space followed by a storage period. The shaking period was two minutes and the air space in the bottle g was equal to the volume of naphtha being treated. The results of these experiments are given in Table I.

It will be observed from these data that the process of this invention was relatively ineffective in the sweetening of the light virgin naphtha. However, the cracked naphthas subjected to this operation were very effectively sweetened by the process.

Additional data showing the application of this process to mixtures of virgin naphtha with cracked naphthas are indicated in Table II.

TABLE II Comparison of air-caustic with air-ammonainhibitor sweetening of mixed naphthas N aphtha Mixture 50% Light 50% Light Virginl; Virgin u; 50% Light 50% Light Thermal b. Catalytic d.

Inspections:

Boiling Range L1F... 95330 l05-342 Gravity, mp1' es. 6 e4 9 Copper No. after Cans Soda ash 22 A B A B Treating Conditions:

Inhibitor Added, Lb. duPont #22/5,000 gal 1. 0 1.0 1. 0 1. 0 Caustic Soda Solution Added,

Vol. Percent of 15 B 1 0 l 0 Ammonia Solution Added, Vol.

Percentofzm NH3 o i o i 50 Air Space, Vol. Percent 50 50 50 Agitation, min-.. 2 2 2 2 Temperature, F 75 75 75 75 Rate of sweetening:

Copper N umber- Initial 22 22 34 34 After 24 hrs. storage..` 11 1 l5 l1 55 After 48 hrs. storage... 7 1 14 1 Percent Mercaptan Reduction n 48 hours 08.2 +95. 59 0 +97 No. 1 under light virgin-Table I. b No. 1 under light thermal-Table I. c No. 2 under light virgin-Table I. d No. l under light catalytic-Table I.

It will be noted from these data that the process of this invention serves to sweeten these blends even though this result appears paradoxical in view of the data of Table I. Thus, as shown by Table I, virgin naphthas are not responsive to the sweetening process of this invention.` However, as shown by the data of Table II, blends of virgin naphthas with either thermally cracked or catalytically cracked naphthas can be effectively sweetened.

Table II also brings out the superiority of the present air-ammonia sweetening process of this invention over a process in which caustic is substituted for the ammonia. On a strictly comparable basis, it will be noted that the use of ammonia in this process i's much more effective than the use of caustic.

Table III presents additional data comparing an aircaustic sweetening process and an air-ammonia sweetening process as applied to cracked naphthas.

TABLE III Comparison of arr-caustic with arr-ammonz'a-inhibitor sweetemng of cracked naphthas Type o Naptlm Light Light Thermal Catalytic Inspections:

Boiling Range, F 91-346 103-348 Gravity, API 60. 6 64.8 Copper Number after Caustic Soda Wash 20 l0 A B A B Treating Conditions:

Inhibitor Added, Lb. duPont #Z2/5,000

gal 1 0 l 0 1.0 1 0 Caustic Soda Solution Added Vol Percent of 15 B 1 0 l 0 Ammonia Solution Added, Vol. Percent 0 1 0 l Nla Concentration, Wt., Percent NH3 1n Water 28.0 14.0 Air Space, Vol. Percent 50 50 50 50 Agitation, Min 2 2 2 2 Temperature, "F 75 75 72 72 Rate of sweetening:

Copper Number- Initially 20 20 10 10 After 24 hrs. storage.. 5 O 2. 5 1 After 48 hrs. storage. 2.0 1 After 72 hrs. storage 1. 0 0 Percent Mercaptan Reduction in 24 hours 75 100 75 90 Again, the air-ammonia sweetening process of this invention is shown to be superior. However, a comparison of Table II with Table III shows that the superiority is particularly evident in the ability of this process to sweeten blends of virgin naphthas with cracked naphthas.

What is claimed is:

l. A process for sweetening gasoline containing substantial portions of cracked stocks in which the gasoline is contacted with air in the presence of a phenylenediamine inhibitor and ammonia.

2. The process defined by claim l .in which the said inhibitor is an N,N'dialkyl-p-phenylenediamine.

3. The process dened by claim l in which the said inhibitor is selected from the group consisting of N,N' di-sec-butyl-p-phenylenediamine and N,Ndinbutylpphenylenediamine.

4. The process deiined by claim l in which about 0.1 to 2 lbs. of the said inhibitor is employed per 5000 gallons of gasoline.

5. The process deiined by claim l in which about 1 to 10 volume percent of aqueous ammonia is employed having a concentration ofabout l to 28%.

6. The process defined by claim 1 in which the said gasoline contains about 331/s% of cracked stock.

7. An improved sweetening process for gasoline produced by cracking characterized by a copper number of about 1 to l5 in which the gasoline is admixed with air, ammonia, and a phenylenediamine inhibitor, employing more than about 0.05 standard cubic feet of air per copper number per barrel, about 0.1 to 2 lbs. of the said inhibitor per 5000 gallons of gasoline, and about l to l0 volume percent of aqueous ammonia having a concentration of about 1 to 28%.

8. The process defined by claim 7 in which the said gasoline constitutes a catalytically cracked gasoline.

9. The process defined by claim 7 in which the said gasoline constitutes a thermally cracked gasoline.

l0. The process defined by claim 7 in which the said gasoline includes virgin naphtha blended therewith.

References Cited in the tile of this patent UNITED STATES PATENTS 2,616,831 Rosenwald Nov. 4, 1952

Claims (1)

1. A PROCESS FOR SWEETENING GASOLINE CONTAINING SUBSTANTIAL PROTIONS OF CRACKED STOCKS IN WHICH THE GASOLINE IS CONTACTED WITH AIR IN THE PRESENCE OF A PHENYCLENEDIAMINE INHIBITOR AND AMMONIA.

Images