US2465964A - Treatment of cracked petroleum distillates - Google Patents

Description

March 29, 1949. L. F. BROOKE ETAL 2,465,964

TREATMENT OF CRACKED PETROLEUM DISTILLATES Filed Sept. 24, 1945 CA MST/C [XTRACT O/L Patented Mar. 29, 1949 UNITED STATES PATENT OFFICE TREATMENT OF CRACKED PETROLEUM DISTILLATES Application September 24, 1945, Serial No. 618,208

4 Claims.

This invention relates to the treatment of cracked distillates and more particularly to the treatment of cracked distillates from high-sulfur oils under such conditions as to remove the major portion of the sulfur compounds with minimum degradation or loss of the more valuable hydrocarbon materials present in said distillates.

More specifically the invention has reference to the treatment of cracked distillates to produce maximum yields of high octane number gasoline refined sufiiciently to meet commercial specifications for sulfur in motor fuels.

Refining of cracked hydrocarbon materials, particularly cracked distillates from high sulfur oils, is necessary to reduce the sulfur content to a specified minimum and remove highly unsaturated hydrocarbons which tend to form gums on storage and evaporation. Sulfuric acid treatment has been most commonly used for this purpose. Many modifications of treating methods as to quantity of acid, temperature of treatment and contact time have been applied to produce the desired degree of refinement economically. In many cases these methods are only partially successful and in other cases cracked distillates cannot be economically desulfurized by sulfuric acid treatment. Sulfuric acid readily attacks unsaturated hydrocarbons causing them to become oxidized and polymerized and often results in excessive losses of valuable hydrocarbon materials possessing good anti-knock properties. Some of the oxidation and sulfation products formed during the sulfuric acid treatment dissolve in the treated cracked istillate, and upon redistillation decompose yielding products that give rise to color, instability and gum in the gasoline,

Mixtures of sulfuric acid with other acids and acid reagents other than sulfuric acid have been proposed to remove undesirable materials such as diolefins and sulfur compounds without at the same time degrading appreciable amounts of valuable unsaturated hydrocarbons in cracked naphthas, but only very limited success has been achieved.

Anhydrous hydrogen fluoride, boron trifluoride dissolved in hydrogen fluoride and spent hydrofluoric acid alkylation catalyst have been proposed for the treatment of cracked distillates. In these processes sulfur compounds, aromatic and olefin hydrocarbons are removed simultaneously from petroleum fractions containing these materials in addition to saturated hydrocarbons. These constituents are removed simultaneously from saturated hydrocarbons and it is not possible by the above processes to remove only one of them selectively when two or more are present. By means of the present invention it is possible to effect a substantially complete removal of undesirable sulfur compounds from cracked distillates without substantial simultaneous removal of valuable olefinic and aromatic hydrocarbons of high anti-knock value and relatively stable characteristics.

Hydrogen fluoride alone and in combination with boron trifiuoride has been proposed for treating hydrocarbon materials in such a manner as to catalyze the polymerization of unsaturated hydrocarbons. After treatment with amounts of catalyst too small to permit formation of a second liquid layer the catalyst is removed by means such as caustic washing or fractional distillation. The present invention involves formation of a second liquid layer and separation of treated hydrocarbon and acid extract layers in the liquid phase. The hydrofluoric acid used is often diluted with water and employed under such conditions that reduce its catalysis of polymerization and alkylation reactions to the extent that valuable gasoline constituents are substantially unaffected.

It is with improvements in the method of refining cracked distillates that the present invention is concerned.

One specific embodiment of the invention comprises treating hydrocarbon oils with hydrofluoric acid under optimum conditions of temperature, concentration of hydrofluoric acid, quantity of acid and contact time to obtain maximum desulfurization with minimum polymerization and/or alkylation of high octane number olefinic and aromatic hydrocarbons.

An object of the invention is to remove from cracked distillates objectionable sulfur compounds and diolefins having odor-forming, corrosive, and gum-forming characteristics without substantially affecting the relatively more stable unsaturated hydrocarbons or the paraffin, naphthene and aromatic hydrocarbons.

A further object of the invention is to provide a process for maximum production of gasoline whereby sufiicient proportions of impurities are selectively removed from cracked distillates, to meet commercial gasoline specifications, by the application of treating agents readily and economically recoverable from the extracted impurities.

Still another object of the invention is to provide a practical commercial process for removing sulfur from cracked gasolines without degrading the valuable olefin and isoparafiin hydrocarbons, removing the aromatic hydrocarbons, or seriously affecting the knock rating.

Additional objects and advantages of the invention will become apparent from the accompanying description and illustrations.

In accordance with the present invention cracked hydrocarbon distillate materials, whether normally gaseous or liquid, are treated with liquid hydrofluoric acid at temperatures and pressures chosen so that the major portion of the hydrocarbon material is in the liquid phase. The hydrocarbon distillate materials and the hydrofluoric acid are preferably in liquid phase, to economize on space, but the invention is not limited to treating only in the liquid phase. Other treating conditions such as concentration of hydrogen fluoride in the treating acid, ratio of treating acid to hydrocarbon material, time and method of contacting acid and stock, etc., are chosen to cooperate toward \the desired optimum removal of sulfur compounds and other undesirable impurities with minimum degradation of hydrocarbon materials.

The concentration of hydrofluoric acid preferred for treating purposes in this invention is in the range of about 70 to about 90 per cent by weight of hydrogen fluoride in aqueous solution. Best selective extraction of sulfur compounds is achieved with treating acids in this range but in some cases satisfactory results may be obtained with as low as 60 per cent by weight hydrogen fluoride in aqueous solution and in other cases as high as 99 per cent may be used with success. The higher water content hydrofluoric acid is usually used with very high olefin content cracked distillates and the acids containing only small proportions of Water are used to treat cracked hydrocarbon materials containing relatively small amounts of unstable olefin hydrocarbons. Thus the amount of water in the treating acid bears a close relation to the type and proportion of olefln hydrocarbons in the oil being treated.

Sufficient amounts of hydrofluoric acid solution should be used to form a second layer that can be settled and withdrawn from the hydrocarbon layer. The amount needed may vary depending on the chemical composition of the cracked distillate treated, especially on the concentration and types of sulfur compounds, the degree of refining desired, the type of treating equipment employed, and upon the concentration of hydrogen fluoride in the acid. For most cases a volume ratio of 0.1 to 2.0 volumes of hydrofluoric acid toone volume of oil is adequate and convenient.

The selective removal of sulfur compounds by this process is generally not very sensitive to temperature variations. However, to minimize polymerization and losses of valuable hydrocarbon material having desirable anti-knock properties the temperature should not be above about 100 F. The temperature of operation chosen will be dependent upon the concentration and proportion of treating agent employed as well as its water content. If the hydrocarbon material being treated contains considerable amounts of unstable olefinic material, temperatures below atmospheric are employed. These reduced temperatures are brought about and maintained by precooling the cracked distillate and the hydrofluoric acid prior to mixing them and removing the heat generated by exothermic chemical reactions during the treatment. This may be done by immersing refrigerating coils in the reaction mixture. Temperatures in the range of about .10 F. to about F. are used with good results when treating most cracked naphthas with aqueous acids containing about 80 per cent hydrogen fluoride by weight in the mixture.

The optimum time of contacting the treating acid with the hydrocarbon material for obtaining an optimum yield and quality of gasoline depends upon the water content of the treating acid, the degree of desulfurization desired, the volume ratio of treating acid to hydrocarbon material and the type of contacting employed. In general, longer times of contacting are desirable when more dilute treating acids, particularly with respect to the water content of the acid, and smaller volume ratios of treating acid to hydrocarbon are employed. It is understood that the invention is not limited to batch treatment but is applicable to any of the continuous methods of treatment such as multistage and/or conflow or counterflow contacting.

The operating pressure should be sufficient to maintain substantially all of the treating material and hydrocarbon material in the liquid state.

The set of treating conditions brought to bear on a given cracked distillate will be largely dependent upon its sulfur content. The proper treating temperature, contact time, concentrartion of acid, quantity of acid, and ratio of treating material to distillate must be chosen to accomplish the desulfurization necessary to meet commercial gasoline specifications. In addition to the sulfur content, the type and content of unsaturated hydrocarbons in the distillate will have a .bearing on the treating conditions required to remove the more unstable conjugated diolefins selectively from the more stab-1e and high anti-knock quality mono-olefins contained in the stock. In severely cracked naphthas, for example, having a high proportion oi very unstable oleflnic hydrocarbon material it may be desirable to dilute the cracked distillate with a light inert hydrocarbon such as normal pentane before treatment with hydrofluoric acid in order to further minimize losses of gasoline through polymerization. The use of low temperatures and relatively more water in the aqueous hydrofiuoric acid treating material also assists in achieving this aim.

The process of this invention may be understood by reference to the attached drawing illustrating a preferred method of operating the same. Dried cracked naphtha is fed into the bottom of HF treater 12 through feed line H and thoroughly contacted with hydrofluoric acid being fed into HF treater I2 via valved line 13. The oil or raffinate phase because of its lower density, rises toward the top of the extractor as the acid or extract phase settles toward the bottom where it is drawn ofi through line l4 and fed into YEW regenerator 15. The hydrofluoric acid is recovered from the extract by distillation with reflux. To reduce losses of hydrofluoric acid in the extract oil to a minimum the extract oil bottoms in regenerator l5 are stripped by passing streams of light hydrocarbon fractions, suchas C5 parafhns, through the heated bottoms. The stripping medium and hydrofluoric acid mixture is drawn from regenerator l5 through line 55 leading to gas separator l! where a separation of condensed hydrofluoric acid and stripping medium is effected and accumulated gases are vented. The hydrofluoric acid is recycled to'HF treater l2 through lines is and i3 anda portion of the stripping medium is supplied as reflux to Hl regenerator through lines l9 and Y20. The remaining portion of stripping medium from gas separator H is recycled throughlines l9 and 2!. Fresh stripping ,medium is introduced into the extract oil near the bottom of HF regenerator I 5. The stripped extract oil is led out of HF regenerator l5 through line 22.

The raflinate phase rising to the top of HF treater I2 is withdrawn through line 23 and fed to catalytic defluorinator 24. In catalytic defiuorinator 25 the raflinate phase comes in contact with etched aluminum rings at 200 F. to 450 F. Under these conditions dissolved hydrofluoric acid is vaporized and chemically combined fluorine is split off as hydrogen fluoride from the hydrocarbon molecules in the raifinate. The separated hydrofluoric acid with some of the lighter fractions of the treated hydrocarbon material is removed from catalytic defiuorinator 24 via line 25 and recycled to HF treater 12 through line l3.

The defluorinated naphtha containing only small amounts of residual fluorine is removed from catalytic defluorinator 2A through line 25 and passed through lime defluorinator 2'1 at 350 F. to 500 F. The lime removes the major portion of the residual fluorine and fixes it as calcium fluoride. Bauxite defiuorination may also be used instead of the lime defluorination. The lime treated naphtha is led out of lime defluorinator 27 through line 28 in which it comes in contact with a stream of fresh aqueous caustic being fed into line 28 via line 29. The mixture or" gaso line and caustic proceeds into caustic scrubber 39 through line 59. The spent caustic containing the removed fluorine in the form of sodium fluoride is settled to the bottom of caustic scrubber 39 and drawn off through line 3|. The caustic scrubbed naphtha is led into Water washer 32 by way of line 33. Water is introduced through inlet line the wash water is removed from water washer 32 through line 35 and the washed gasoline is charged to rerun still 36 through line 37. From rerun still 36 naphtha of the desired boiling range is distilled with the aid of steam introduced through line 49. Rerun bottoms are withdrawn from rerun still 35 through line 38. The rerun naphtha is taken from the still via line 39 and introduced into reflux drum 40 along with caustic introduced in the naphtha stream in line 39 through line 4!. The spent caustic is withdrawn from reflux drum 40 through line 52. The rerun product is withdrawn from reflux drum 40 through line 43 and a major portion of it is taken out of the process through line 44. Some of the rerun product is fed into rerun still 36 as reflux through line 45.

Certain cracked distillates would require prohibitive amounts of sulfuric acid to effect an extensive removal of sulfur before gasoline meeting sulfur content specifications could be produced. The yields of gasoline are often very low for these distillates. The octane values of these treated gasolines are often greatly reduced and enormous quantities of sulfuric acid sludge present serious disposal problems. These cracked distillates may be satisfactorily treated with hydrofluoric acid in that sulfur removal may be effected with less polymerization and alkylation than in the case of sulfuric acid. Higher yields of better octane number gasoline are produced from hydrofluoric acid treatment and the recovery of used acid is very convenient and economical as compared to the regeneration of sulfuric acid.

Contacting the treating acid with the cracked distillate may be batchwise or continuous, and may be concurrent employing mixing devices of conventional types, but continuous counterflow contacting of the treating material and hydrocarbon material is preferred.

In order to control contacting time more sharply, any of the well-known accelerated methods for separating the acid treating material from the treated stock, such as centrifuging, for example, may be practiced.

To facilitate the maintenance of the desired treating temperature by offsetting the heat developed during the treating process, both the cracked distillate and the treating acid may be precooled before they are mixed in the treating device and/ or internal refrigeration employed in the treater.

The following examples are given merely in order to more clearly illustrate the invention and its advantages, and should not be taken as limitations of its scope.

A quantity of raw deoetanized cracked naphtha, produced by thermal cracking, and having a gravity of 37.6 A. P. I., a bromine number of 39.6 and a sulfur content of 0.58% was treated at F. with 80% aqueous hydrofluoric acid. The quantity of hydrogen fluoride in the acid was equivalent to 0.20 volume of 99% hydrogen fluoride to one volume of cracked naphtha. The hydrofluoric acid and cracked naphtha were charged to a mixing device and thoroughly mixed for 5 minutes. The resulting mixture was transferred to a separatory vessel and permitted to separate into an acid (extract) layer and a naphtha (raffinate) layer. The hydrocarbons in the naphtha layer were recovered after Washing with water to remove the dissolved hydrofluoric acid and the extracted material was recovered from the acid layer by diluting with water before extracting the organic matter with isopentane. The isopentane was separated from the extract by fractional distillation. Inspection data on the rafiinate and extract fractions are summarized in the following table as run No. 4K-222 along with similar data for several other hydrofluoric acid treats on the same cracked naphtha performed with different concentrations of hydrofluoric acid.

The gasoline in each case was obtained by fractional distillation of the raiflnate in a true boiling point still. The fluorides present in the raiflnate fraction were decomposed during the distillation With the regeneration of olefines.

Table 1 214, 216, Run Number, 4K-

Cone. of acid, percent HF 99 80 70 40 Raffinate Charge Bromine No 39. 6 1.8 14. 7 22.0 23. 2 39. 4 Sulfur, percent. 0.58 0.12 0.38 0.51 O. 57 0.58 Desulfurization,

percent 79 35 12 2 0 Extract:

Percent of charge 12. 4 2. 9 1.0 0. 7 0. 1 Bromine No 150 168 183 169 Sulfur, percent. 3.1 4. 9 2. 7 2. 6 0.99 Gasoline, 400 F. E. P

Yield, percent of charge 60.2 38. 5 52. 2 55. 4 55.9 58. 5 Bromine N0 53. 8 3. 7 35. 6 41. 3 46. 4 49. 5 Sulfur, percent 0. 56 0. 004 0. 092 0.28 0.38 0. 54 Octane No., CFR- M M 3 47. 0 63. 4 63. 6 65.6 65 6 Desulfurization,

percent 99. 3 84 50 32 4 Desulfurization Ratio 1 .80 .42 .24 .06

1 This ratio is computed by dividing the percent desulfurization of raffinate by the corresponding percent desulfurization of gasoline from the data above.

It will be observed from Table 1 that the use of 99% hydrofluoric acid (approaching anhydrous hydrogen fluoride) resulted in the removal of 99.3 per cent of the sulfur from the charge material and the production of a raifinate containing only 0.12 per cent sulfur and gasoline of 0.004 per cent sulfur content. However, the desulfurization in this case was accompanied by excessive losses of good anti-knock hydrocarbon material due to the catalysis of polymerization and alkylation reactions by the hydrogen fluoride. This is illustrated by the low gasoline yield from cracked naphtha charged of 38.5 per cent, the high per cent (12.4) of charge material extracted by the hydrogen fluoride and the low bromine numbers, 1.8 and 3.7, respectively, of the rafiinate and the gasoline.

Aqueous hydrofluoric acid extractions, on the other hand, resulted in sufficient desulfurization for the production of gasoline meeting commercial specifications for sulfur, without accompanying excessive losses of hydrocarbon material. The use of 80 per cent hydrofluoric acid, for example, resulted in the production of gasoline containing only 0.092 per cent sulfur. The much higher yield from cracked naphtha charged of 52.2 per cent gasoline having a bromine number of 35.6 is due to the selective removal of only the more unstable unsaturated hydrocarbons along with the sulfur and illustrates one of the advantages of the invention. Another important advantage of practicing the invention is illustrated by the fact that the gasoline produced by the use of 80 per cent aqueous hydrofluoric acid had an octane number of 63.4 as compared to only 47.0 for gasoline produced when substantially anhydrous hydrogen fluoride (99% hydrogen fluoride) was used in the treatment. Furthermore, 80% hydrofluoric acid is a more selective treating agent for sulfur compounds than liquid 99% hydrogen fluoride, as evidenced by a 4.9 per cent sulfur content in the extract from the former compared to 3.1 per cent sulfur in the extract from the latter.

The desulfurization ratio obtained by dividing the per cent desulfurization of the rafiinate in each case by the percent desulfurization of the gasoline is an index to the particular step in the process in which the sulfur was removed from the cracked naphtha. A portion of it is separated in the hydrofluoric acid extract and another portion is removed in the residue resulting from the fractional distillation or" the raffinate to produce the 400 F. end point gasoline. If the major portion of the total sulfur removed in the extraction and distillation steps taken to gether is removed in the extraction step, the value of the percent desulfurization of the rafiinate will be high and the desulfurization ratio will be above 0.5. If, on the other hand, most of the sulfur removed by the process occurs in the distillation step, the desulfurization ratio will be lower than 0.5.

In Table 1 it will be seen that a desulfurization ratio of 0.80 was obtained when the extraction operation was conducted with essentially anhydrous hydrogen fluoride whereas the use of hydrofluoric acid containing substantial amounts of water gave desulfurization ratios below 0.5 In the case of 80% hydrofluoric acid, for example, the desulfurization ratio of 0.42 indicates that more than half of the sulfur removal occurred in the distillation step.

The observations pointed out in discussing the examples presented in Table l serve to illustrate the essential characteristic differences and distinctions between anhydrous liquid hydrogen fluoride on the one hand and aqueous hydrofluoric acidon the other, in their behavior toward sulfur compounds and unsaturated hydrocarbons in cracked hydrocarbon distillates.

Additional improvements may be obtained in the treatment of cracked distillates by carefully controlling the treating conditions. The effect on octane number of varying the temperature, for example, is illustrated by the data in the table below. A series of treatments were made with 80% aqueous hydrofluoric acid on a deoctanized cracked-naphtha, using the equivalent of 0.2 volume HF per volume of naphtha, through a range of treating temperatures, as shown below. The octane number .of the 400 F. end point gasoline from the untreated naphtha was 65.3.

Higher octane numbergasolines resulted from treatments made in the 11 to 26 range than at 50 F. and above.

In order to illustrate the excellent practical results obtainable by applying the present invention to the production of motor gasoline from cracked distillates, the following treatments, comparing 80% aqueous hydrofluoric acid with spent alkylation sulfuric acid are given. The stock used for both treats was a caustic treated dehexanized cracked naphtha having a gravity of 466 A.P. I., a bromine number of 59.6 and a sulfur content of 1.10 per cent by Weight. The hydrofluoric acid treatment was done with aqueous hydrofluoric acid containing 80% hydrogen fluoride by weight in the mixture and the sulfuric acid treatment performed with a sample of spent .alkylation acid containing 88.8% E2804, 6.0% carbon and 2.9% water by weight. The optimum conditions for both treats to produce 425 F. end point gasoline containing 0.3%

. sulfur were determined by a series of experiments.

The hydrofluoric acid treat was made at 30 F. a contact time of 20 minutes. The treated naphtha was distilled to 450 vapor temperature in a fractionatingcolumn to producea gasoline of 425 F. endpoint on an ASTM basis. Partial defluorinathion occurred during the distilla tion and the gasoline was bauxite treated at 350-375" F., atmospheric pressure, and 5 volumes of liquid per volume of v8-14 mesh bauxite (dried for 2 hours at 1200-1400) F. per hour. The fluorine content of .thegasoline was reduced from 0.05 to 0.001%.

The hydrofluoric acid in the extract material was recovered by a simple flash distillation and stripping by nitrogen. The bottoms material remaining after recovery of the hydrofluoric acid contained approximately 6.3% sulfur and 0.12 fluorine. Hence, the recovery of hydrofluoric acid from the spent treating acid is a simple and convenient operation as compared to the serious problem involved in disposing of large quantities of sulfuric acid sludge.

The sulfuric acid treat was also done at 30 F., the optimum temperature for this stock, and at 20 minutes contact time. The treated naphtha was distilled using fire and steam at a maximum still temperature of 375 F., with caustic in the still, to produce 435 F. end pointgasoline containing 0.3 sulfur.

Table 3 30 Per Cen pent Alky- Hydrofluorir laiiou Sul- Acid uric Acid Treating temperature, T .1 30 30 Acid rate, lbs. per bbl h 67 33 Gasoline loss, percent 1 8.8 11.4

1 Defined as ((per cent gasoline in ori inal charge-per cent gasoline after treatment based on original chargeflgasoline in original charge) X100.

A lower loss of gasoline components resulted in the hydrofluoric acid treatment than in the cold sulfuric acid treatment. The quality of the hydrofluoric acid treated gasoline with regard to sulfur content; anti-knock value and susceptibility to octane number improvement by the addition of tetraethyl lead is equal to that of the sulfuric acid treated gasoline. In addition to greater over-all gasoline yields of equal quality obtainable by the present invention the hydrocarbon material recovered from the hydrofluoric acid extract may be marketed as a raw material for synthetic chemicals and for use in various products such odorants. These advantages added to the fact that spent hydrofluoric acid is readily recoverable by simple distillation and stripping and catalytic defluorination of the treated naphtha make the present invention very attractive from the standpoint of economy.

The examples referred to in describing the in vention are for purposes of illustration only, and the application of the present invention is not limited to the particulars of any of said examples nor to the use of the arrangements of the apparatus referred to, and is of the full scope set forth in the following claims.

We claim:

1. The process of selectively removing sulfur compounds from a sulfur-containing cracked distillate having a substantial content of monoolefinic and aromatic hydrocarbons of high antiknock value, which comprises extracting said distillate with aqueous hydrofluoric acid containing about 70 to 90% HP in sufi'icient amount to form two phases, separating an acid phase containing an extract comprising sulfur compounds and a hydrocarbon raflinate phase having a sulfur content substantially lower than that of said distillate. and adjusting the water content of the aqueous hydrofluoric acid within said specified range to produce a substantially unsaturated rafinate phase comprising the major proportion of the mono-olefinic and aromatic hydrocarbons contained in said distillate.

2. The process of claim 1 wherein the volume ratio of aqueous hydrofluoric acid to said distillate ranges from 0.1 to 2.0.

3. The process of selectively removing sulfur compounds from a, sulfur-containing cracked petroleum distillate having a substantial content of mono-olefinic and aromatic hydrocarbons of high antiknock value which comprises extracting a quantity of said distillate with between about 0.1 and 2 times its volume of aqueous hydrofluoric acid containing between about and HF, the extent of dilution with water of the acid within said specified range being dependent upon the mono-olefin content of the distillate selected for treatment and bein reater in proportion to said content, separating a rafflnate phase having a sulfur content substan tially lower than that of said distillate and containing a major amount of the mono-olefin and of the aromatic hydrocarbons originally present in said distillate.

4. A process as defined in claim 3 including the additional step of subjecting said raifinate phase to fractional distillation to separate an overhead fraction boiling within the gasoline boiling range of substantially lower sulfur con tent than the bottoms fraction.

LLOYD F. BROOKE. MELVIN M. HOLM. LAVERNE P. ELLIOTT.

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

OTHER REFERENCES The Condensed Chemical Dictionary, page 350, Reinhold Pub. Corp. 3rd ed. (1942).

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