US2773805A - Desulfurization of cracked naphthas with formaldehyde and sodium - Google Patents

Description

DESULFURIZATION F CRACKED NAPHTHAS WITH FGRMALDEHYDE AND SGDIUl'Vl .Byron M. Vanderbilt, Westfielrl, and John P. Thorn, Elizabeth, N. 1., assignors to Esso Research .Zfllil Engineering Company, a corporation of Delaware Application February '1, 1954, Serial No. 407,592

4 Claims. (Cl. 19628) No Drawing.

'This invention is concerned with a novel process for the desulfurization of petroleum distillate products and particularly of application to the desulfurization of cracked naphthas. The invention concerns desulfun'zationof such distillates by contact with an alkali metal. In accordance with the invention, alkali metaldesulfurization is substantially improved by pretreating distillates to be desulfurized so as to remove reactive compounds which normally seriously reduce the efiiciency of alkali metal contacting. In particular the invention concerns pretreatment of distillates by means of a sulfuric acid treatment, clay treatment, formaldehyde treatment, or the like. 1

It has long been appreciated that removal of sulfur from petroleum products during refining is desirable. The presence of sulfur compounds in distillate fuels, ,fo'r, example, is objectionable for a number of reasons including the odor of such fuels,.the corrosion characteristics, etc. Consequently, specifications have been set up by'the refining industry which limit the amount of sulfur in petroleum products to what has been considered a low value. However, it has recently been appreciated that there are real incentives for lowering the sulfur content of petroleum products below present standards, approaching complete removal of all sulfur compounds.

"Even very minor amounts of sulfur have been found to be seriously detrimental when petroleum distillates are to be treated in certain catalytic processes such as platinum hydroforming, for example. Again, it has recently been determined that sulfur compounds in gasoline contribute to what has been called the octane requirement increase'of automobiles; that is, as the age of an automobile increases it has been found that a' progressively higher octane number fuel is required to satisfy the engine without knocking. For these and other reasons there is an extensive search under way 'in 'the petroleum industry at this time for improved desulfurization methods calculated to attain minimum sulfur levels in petroleum products well below the sulfur levels here toforeobtainable by conventional processing methods.

The-present invention is directed to this general field of eifort, employing treatment with alkali metals for sulfur removal. It is known that alkali metals have high atfinity for sulfur and on contact with sulfur-containing distillates will form reaction products serving to remove sulfur compounds as sludge material which can be separated. Because of the availability of sodium, sodium is the alkali metal which is considered preferable for use and this invention will be described with particular reference to sodium refining. Presumably sodium reacts with'sulfur constituents of petroleum distillates so asto form sodium sulfide which is insoluble and can be removed from the distillate. On the other hand it is possible that the sulfur combines with the sodium as a mercaptide, disulfide, a higher polysulfide, or in other combinations. However, there is evidence to indicate States Patent Patented Dec. ,11, 1956 sodium primarily forms sodium sulfide. As a basis for.

comparison in evaluating sodium refining processes, reference will be made to. the eificiency of sodium utilization, assuming that sodium combines with sulfur so as to form only the monosulfide. Thus, for example, ifin a given treat sufiicient sulfur is removed to provide the stoichiometric equivalent required to form NazS with all the sodium employed, then this would amount to 100% sodium efficiency.

inexperiments which have been conducted, it has been found that sodium refining of virgin distillates containing sulfur is very effective for sulfur removal. It is possible to refine such virgindistillates so as to attain remarkably low sulfur levels while appreciating high efficiencies of sodium utilization, However, when the attempt has been made to use sodium refining for the treatment: of cracked distillates, it has been found that very poor sodium efiicienciescan be attained. Much of the sodium is apparently uselessly expended in reaction with constituents of the cracked distillates other than sulfur compounds. It is presently theorized that sodium probably reacts with active olefim'c, phenolic, and aromatic materials present in cracked distillates so that sodium is consumed in these reactions rather than in the desulfurization reaction. This eifect is not only objec tionable in increasing the consumption and expense of the sodium requiredbut also in causing a loss of fuel constituents, further increasing the cost of such a refining operation,

It is therefore the principal purpose of this invention to improve the alkali metal refining of cracked distillates byproviding a pretreatment of the cracked distillates serving to increase the'efliciency of alkali metal utilization for desulfurization. In accordance with this invention the desired pretreatment may be carried out in a variety of ways operative to remove reactive constituents of cracked distillates, primarily other than sulfur compounds. At the present time a number of conventional methods are known for treating cracked'distillates so as to r emove the active olefinic, phenolic and aromatic compounds. Among the methods which can be employed are sulfuric acid treatment, phosphoric acid treating, clay refining, formaldehyde treatment or contact with a polymerization catalyst. treatments of this character serve to greatly increase the efficiency of sodium desulfurization. This process is particularly attractive in the case of cracked naphthas since there is a lower loss in clear octane number when a pretreated naphtha issodium treated than in the case infwhich the naphtha is simply sodium treated Without pretreatment. Theprocess is again valuable for the reason that the pretreatment converts reactive constitu- 4 cuts to the form of a liquid sludge having fuel or heating oil value. As opposed to this, if the active constituents are not removed in this manner, sodium refiningconverts these. constituents to solid form having virtually no value, or at best, being of utilization solely as coke.

While the invention is of application to light petroleum distillates generally, the invention is of particular application and will be described with reference to the treating of a cracked naphtha'fraction. By way of example, reference will be made to the treatment of cata-' lytically cracked gasolines. Such gasolines are obtained by the conventional catalytic cracking of petroleum feed stocks employing any of the known cracking procedures. Such gasolines are characterized by inclusion of active constituents formed in large part as a result of the crack ing process. Sulfur in these gasolines is primarily present as thiophene compounds and in conventional commer- It has been found that pre- 3 ciallycracked gasolines the sulfur concentration is ordinarily greater than about 0.03%.

In order to substantially completely remove these sulfur compounds from cracked gasolines in a first step of the invention, the gasoline is treated with a refining agent other than alkali metal so as to. remove the more active compounds which are present. The preferred agent for pretreatment is sulfuric acid which is' employed in concentrations of about 70 to 95% H2804; In generaL about 2 to 15 lbs. of'sulfuric acid, calculated as 100% H2804 per barrel of gasoline is to be employed in the pretreating step. It is onlynecessary to mix the, sulfuric acid with the'cracked gasoline in these proportions at ambient temtogether with the sulfuric acid after contacting. After the sulfuri'c'acid treatment, it is preferred to water-Wash the gasoline so as to remove any sulfuric acid, and for this purpose the gasoline may be treated with about of water in a single stage washing step. In the case'of the particular catalytic naphtha referred to'it was found that 2.4% of the original gas;

vperatures and atmospheric pressure tosecure the desired oline feed was lost during the sulfuric acid pretreatment and the water-wash, primarily as the liquid sludge referred to. As will be brought out hereinafter, alkali metal refining of this pretreated catalytic naphtha could he carried out successfully while attaining high treating cfficienciesr i In place of the sulfuric acidpretreatment, it isalso attractive to employ conventional clay treating. This is best carriedout by percolating the gasoline through a fixed bed of clay such as Attapulgus clay at temperatures up tol aboutSOO" F.-, and atmospheric pressures. In general,

about 5,000 to l0,000 barrels ofigasoline per ton of clay providea suitable pretreatment. i

As indicated, other pretreating steps maybeemployed in place of the sulfuric acid or clay pretreatment. Among gasoline may be carried out in'a variety "of ways. Sodium can be converted to a liquid by heating to a temperature above about 208 F., and at these temperaturesimaytbe. "effectively contacted'with the petroleum distillate for re fining. Contact may be carried out with the distillate in either vapor or liquid phase and may use the conventional vapor-liquid or liquid-liquid contacting devices. For example,so diu'rn in liquid phase may bepassed downwardly through a paclted contacting tower while" the cracked gasoline ,to be refined may be passed upwardly through the tower in vapor phase countercurreut to the sodium. f

Again sodium refining may be carried out by converting to 0.002l% H 145 these refining operations are formaldehyde treating, carwith finely divided inert materials the sodium serves to coat these particles. Thus, for example, in the case of'a low surface support such as sodium carbonate, up to about 4% of sodium can be deposited on 40 to 100 mesh sodium carbonate by this technique. In the case of high surface supports such as aluminum oxide or carbon, as much as 20% of sodium can be coated on such supports. Other material such as coke, glass beads, ground limestone and the like are particularly contemplated for use. However, it is presently felt that sodium carbonate is one of the most attractive supports for sodium in the refining process of this invention.

By whichevertechnique the sodium contacting is carried out, temperatures of about. 300 to 600 F. are preferably employed during the sodium refining. Although higher temperatures can be employed, ranging all the way up to 900 F., the deposition of carbonaceous materials on the sodium and support increases with temperature; However, excellentrefiningresults are obtained at tern; peratures in the range of 450 to 550 F., and this is the preferred temperature range to be employed. It is desira: ble during, contacting to maintain an inert atmosphere. Nitrogen may be used for this purpose although methaneor other low molecular weight hydrocarbon gases can be employed for this purpose.

In order to specifically illustrate the principlesand ad: vantages of this invention I reference will be made to typical experiments which were conducted to evaluate this process.

In one experiment a light catalytic naphtha obtained, from a commercial catalytic cracking operation was. subjected to sodium refining without the pretreatment step This catalytic naphtha boiled in the was evaporated in a preheater and passed vapor phase over the sodium and support at a rate of one volume of liquid per volume of Na-Na2CO per hour. It was found that the, sulfur content of the naphtha could be reduced. while achieving a sodium efiiciency of. 11.9%. If more naphtha were passed over the sodium and support, a sulfur content of 0.0447%.= couldbe ob I tained at a sodium efiiciency of 20.2%. i

This experiment was repeated at different temperatures,

andemploying different concentrations of sodium'on the,

sodium carbonate, support. For example, at 390? F., con; tactingtemperature using a, refining agent constituting 2.6% .of sodium on sodium carbonate it was found that the naphtha could be, reduced to a sulfur content-of;

0.001% at 5% sodiumefiiciency. Similarly, for ansul fur content of 0.014% a sodium efiiciency of l7.4% .wa s obtained,

' It will be ;noted from thesedata thatsodium refining,

. of a 'gcracked naphtha without any pretreatmentof the sodium to the form of finely divided or colloidal sodium' in a suitable .vehicle. Finely divided dispersions of sodium in a vehicle such as a hydrocarbon vehicle may then be mixed into hot liquid naphtha under pressure to achieve the desired refining.

While these and other methods of sodium refining may be employed in the practice of this invention it is particu-' larly preferred to employthe sodium' on a solid support. Whensodium is heated, above. its melting point and mixed naphtha ,is characterized by low efficiencies of sodium-t consumption. Thus, while the sodium served to effectively desulfurize the catalytic naphtha, much of the sodium. was expended in reactions other than the desulfurizationv reaction as evidenced by the formation of solid depositson, the refining agent. In the particular examples given, about, 1.5% of the original feed accumulated on thesodium. refining agent when desulfurizationwas carried. to. the; extent indicated.

Employing this same. catalytic naphtha, experiments, were carried out employing the process of this invention including pretreatment of the naphtha prior to thefsodium, refining. In a first experimentthe catalytic naphtha .was; treatedwithS lbs. of sulfuric acid per barrel-prior,

to the sodium refining. In this case the sodium vrefining;

The temperature of contacting in; thisexperiment was 465 F. The light catalytic naphtham could be reduced to a sulfur content of 0.0034% at a sodium efliciency of 16%. Similarly, the naphtha could be reduced to a sulfur content of 0.014% at a sodium efii- 'ciency of 36%. Comparing these results with those of the former examples, it will be noted that the sulfuric acid pretreatment served to substantially double the efficiency of sodium utilization. It was also found that the sulfuric acid pretreatments served to substantiallyminimize the deposits of solid constituents on the sodium refining agent. On a comparable basis the amount of deposit formed was only about as much.

In another experiment the same catalytic naphtha was pretreated by passage over burnt Attapulgas clay at room temperature. This naphtha was then treated at a temperature of 390 F., with 2.1% of sodium supported on sodium carbonate. Again, it was found that good sodium efliciencies were obtained in the refining. For example, the naphtha could be reduced to a sulfur content of 0.0086% at a sodium efiiciency of 20%. Pretreating with clay at elevated temperatures up to about 500 F. gave even superior results.

Again, to evaluate other pretreating steps, this same catalytic naphtha was pretreated with 0.75% formaldehyde by contact at 525 F. This naphtha was then passed over 2% of sodium supported'on sodium carbonate at 390 F. A substantial improvement in sodium efliciency again resulted.

In all these experiments it will be noted that the pretreatment of this invention served to materially improve the efi'iciency of sodium utilization. Of the different pretreatment steps employed, however, on the basis of economic considerations, it was concluded that sulfuric acid treatment was one of the most effective pretreating steps. Other experiments were therefore conducted to further evaluate sulfuric acid pretreatment of a stock to be refined with metallic sodium. In these experiments sulfuric acid of different concentrations was employed. For example, in a first run, 91% sulfuric acid lbs. per barrel) was employed followed by a refining step utilizing 0.3% of sodium based on the naphtha and contacted liquid phase. It was found that the resulting product contained 0.013% sulfur. In a comparative experiment sulfuric acid of 85% concentration was used resulting in a final product having a sulfur content of only 0.0056%. It is apparent from these data that in the process of this invention the concentration of sulfuric acid employed in the pretreating step is an important and critical factor of the process. It is apparent that dilute sulfuric acid is to be employed in preference to concentrated sulfuric acid. An acid having a concentration of about 75 to 85% is particularly contemplated for use.

When sodium is used on a support such as sodium carbonate, ground limestone, carbon, or the like, a preferred process is to use the reagent as a fluid bed. This may be either a batch fluid bed, or the spent reagent may be taken overhead, properly treated to remove the products of reaction, and the support reused. One problem which has been encountered when using the Na and support as a fluid bed, has been that carbonaceous deposits arising from the side reactions of the sodium with certain hydrocarbons cause the particles of the fluid bed to agglomerate and bogging or non-fluidization results. Whereas this is no problem when desulfurizing a virgin naphtha, it is a severe problem when treating either thermally or catalytically cracked naphthas.

Pretreating of the cracked feed stock prior to passing through a fluid bed of sodium on a solid support, has been found to greatly decrease the tendency of the bed to bog on use. Whereas consumption of 1% of sodium on sodium carbonate of 40100 mesh in size caused the bed to lose fluidity when treating catalytic naphtha, use of 3% of sodium on like sodium carbonate resulted in no bogging of the bed when this mixture was spent by passing pretreated catalytic naphtha to extinction of the sodium. This particular cracked naptha had been pre treated with 10 lbs. per barrel of sulfuric acid.

It is of interest to note that the pretreatment steps of this invention are of application to cracked distillates regardless of the original sulfur contents of these distillates; apparently the undesired compounds removed by the process of this invention are present in about the same concentration in either low or high sulfur stocks. This is shown by data obtained in treating a light catalytic naphtha having an original sulfur content of only about 0.055%. Even though this was a relatively low sulfur content, a sodium eificiency of only 9.5% was obtainable when treating this naphtha with 2% of sodium supported on sodiumcarbonate, at a temperature of 525 F., and at one w./hr./w.- When this same naphtha was pretreated with 5 lbs. per barrel of 85% sulfuric acid, a four-fold improvement of sodium efliciency was obtainable, comprising the products for comparable sulfur reduction, namely to a level of 0.013% sulfur.

In these same experiments, it was found that the untreated naphtha had a clear Research octane number of 93.0 or a leaded Research octane number of 97.0 (with 2 cc. TEL/ ga1.). When sodium treated without pretreatment, as indicated above, the octane numbers were 920' clear and 97.0 leaded, showing a loss in octane number attributable to the sodium treatment. However, when this naphtha was pretreated with sulfuric acid and then sodium treated, a clear octane number of 92.5 and a leaded octane number of 98.0 was obtainable. This data demonstrates the real octane number advantage attributable to the pretreatment step of the process of this invention.

The invention as described concerns treatment of a petroleum distillate, and particularly a cracked naphtha, prior to an alkali metal refining step so as to remove reactive compounds other than those containing sulfur. In using this invention, it is significant that the desulfurized products peroxidize much more rapidly when exposed to air than do corresponding untreated stocks. Consequently it is important in the practice of this invention to promptly inhibit the finished products prior to air contact. Suitable oxidation inhibitors which may be employed for this purpose are the trialkyl phenols or phenylene diamine type inhibitors. Sufficient inhibitor is employed to provide a concentration of about 0.1-4 lbs. per 5,000 gallons of product. Within this range, an inhibitor concentration of about 0.5-1.0 lb. per 5,000 gallons of fuel is preferably employed.

Of the trialkyl phenol inhibitors, it is particularly preferred to employ the 2,4,6 alkyl substituted phenols. 2,6- ditertiary-butyl-4-methyl phenol is an example of this class of inhibitors. Again, of the phenylene diamine type inhibitors, the preferred class is the N,N'-dialkyl-p-phenylenediamines.

To exemplify the tendency of unsaturated naphthas to peroxidize on treatment with sodium, polymeric gasoline obtained on polymerization of C3 and C4 olefins over solid phosphoric acid catalyst was contacted with finely divided sodium at 525 F. The sulfur content of the gasoline was reduced from 26 p. p. m. to 1. The A. S. T. M. Research Octane ratings for both the treated and untreated samples were 96.5. The two samples were then allowed to stand uninhibited in cans containing 50% air space for approximately three months. At the end of this storage period the untreated sample still had an octane number of 96.5, whereas that which had been sodium treated had fallen to 75.0. The latter gave a strong qualitative test for peroxides.

In another experiment, a light naphtha obtained by the vapor phase cracking of a virgin gas oil over a silicaalumina catalyst was passed over sodium deposited on sodium carbonate at a temperature of 525 F. The naphtha was reduced in sulfur content from 0.108% to 0.002%. Samples of the treated and untreated naphthas both uninhibited were then allowed to stand in loosely stoppered bottles for a period of two months, after which the; untreated anaphtha hada peroxide number of .,D.08 aIId'theJreatedp-ZGiO, r I V -,I t,..has:been,found that this peroxidationmf. sodium treatedznaphthascan be .preventedby prompt inhibition Off-I116 treatedhnaphthawith. conventional oxidation. inhibitors. These inhibitors areto be .employedlin. conyentionali amounts butare to be added. .to. the, naphtha immediatelyafter the sodium treatment.

I. To clearlydemonstrate this principle, a C7 polymer oi 0.002% sulfur was treatedin the, vapor phase. with sodium-supported'on NazCOs at a temperature of 485 to attain a sulfur content of.0.0001%.. After the sodiuin treatment theResearch. octanenumber of this materialw as 9 6.2. When this, product was stored; for six weeks: in the presence of air, Without-addition of. an oxidatiominhibitorgit Wasfound that the octane number hath-dropped ofi to.-93.5; However, prompt inhibition of the; product after, sodium treatment, eliminated any decrease in theoctane number when stored forthe same period. oftime. In this testN,Nf-di-sec-buty1-p phenylenediamine inhibitor was employedin the amount of 1 lb./5000 gallonsof product. This same result was securedby similarinhibition of sodium treated naphthas.

What'is claimed is:

. 111A process for desulfurizing'a cracked naphtha comprising-the steps of contacting ,-the,naphtha with dilute aqueous formaldehyde, forminga sludge material segregating the .said, sludge. .andspent sulfuric .acid, and icontacting .the' fsaidltreated naphtha Withan alkali .metalzon asolid" support. in. a. fluidized. solids operation at-.tempera-. turesof about30'0ito600" F. Y

2. The process defined by claim. 1- in .whichthe said alkalimetal constitutes about.2'% of sodium supported on NazCOs. 7 I

. .3..The'.process ofl refining. a light petroleum distil'late boiling-in thefmotor .fuel boiling range whichcomprises contacting said distillate with formaldehyde and then contacting the .distilIate ,in vapor phase Withl an metal on asolid' support. I I

.4. The. process defined by claim 3 in-Whibhthesaid light petroleum. distillate is a cracked naphtha.

; References Citedin the file of thispatent UNITEDQSTATES PATENTS" 1,865,235 Cross June 28,1932 1,952,616 Vose Mar..2 7, 1934 1,962,698 Vose June 12, 1934 2,059,542. Wait Nov. 3 1936 v FOREIGN PATENTS 421,235 Germany... Nov. 9', 1192s

Claims (1)

1. 3. THE PROCESS OF REFINING A LIGHT PETROLEUM DISTILLATE BOILING IN THE MOTOR FUEL BOILING RANGE WHICH COMPRISES CONTACTING SAID DISTILLATE WITH FORMALDEHYDE AND THEN CONTACTING THE DISTILLATE IN VAPOR PHASE WITH AN ALKALI METAL ON A SOLID SUPPORT.