US2677648A - Desulfurization of light oils with hydrogen fluoride-activated alumina - Google Patents

Description

lMay 4, 1954 A. P. LIEN ET AL DESULFURIZATION oF LIGHT ons WITH HYDROGEN FLUORIDE-ACTIVATED ALUMINA Filed Nov. 17, 1951 "O Enl mtut EUS 1 MI QN 1N VEN TORSI Arfhur P. Lien Harold Sha/if ATTORNEY Patented May 4, 1954 UNITED STATES PATENT OFFICE DESULFURIZATION OF LIGHT OILS WITH HYDROGEN FLUORIDE-ACTIVATED ALU- MINA Arthur P. Lien, Highland, and Harold Shalit, East Chicago, Ind., assignors to Standard Oil Company, Chicago, Ill., a corporation of Indiana Application November 17, 1951, Serial No. 256,868

5 Claims. l

This invention relates to the desulfurization of light oils with alumina which has been activated with hydrogen iiuoride. More particularly, it relates to the desulfurization of a high sulfur oleiinic naphtha such as coke still naphtha by a combination process which involves treating the high sulfur oleiinic naphtha with hydrogen iiuoride to obtain a raffinate, defluorinating the ramnate and then contacting the defluorinated railinate with HF-activated alumina under conditions to obtain high yields of highly oleiinic low sulfur gasoline.

It is known that gas oils which are higher boiling than naphtha may be extracted with HF prior to catalytic cracking in order to obtain desulfurization and to improve the effectiveness of the cracking operation (U. S. 2,525,812-3). It has also been proposed to effect HF alkylation of an alkylatable material with an alkylating inaterial, at least one of which is in the gas oil boiling range, and to catalytically crack the resulting allrylate with silica-alumina catalyst (U. S. 2,434,623). Such processes were not applicable to olenic charging stocks of the naphtha boiling range because excessive amounts of gasoline were lost in the extract and the initial HF treatment produced large amounts of alkyl fluorides and olen polymers, as well as alkylates. An object of our invention is to provide a process wherein the initial HF treatment of high sulfur oleiinic naphtha will be advantageous rather than disadvantageous, and to provide an improved method and means for processing the raiiinate product produced in the HF treating step. A further object is to provide an improved desulfurization process employing a relatively inexpensive catalyst which can be activated by alkyl iiuoride contaminants in charging stock undergoing treatment.

An important object is to desulfurize a high sulfur oleiinic naphtha by a combination of steps to obtain a higher yield of a more highly oleiinic naphtha product which is lower in sulfur content and higher in octane number than could be attained by processes heretofore known to the art. Hydrodesulfuriaation, for example, is not only an expensive process but it results in undue saturation of oleiins. Solvent extraction, acid treating, and many other types of processes have been proposed for effecting desulfurization of coke still naphtha but none of the prior proposals have given the desired product yield-quality relationship without unduly large operating costs. Another object of our invention is to attain such desired product yield-quality relationship at low cost. Other objects will b'e apparent as the detailed description ci our invention proceeds.

The invention is applicable to high sulfur olenic naphthas generally, i. e. to naphthas in which the oleiin to parain ratio is in the range of about 3:1 to 1:3, and it is particularly advantageous for charging stocks in which the olenic content exceeds the parafnic content. By high sulfur we mean a sulfur content which is at least about .25 weight percent and which is usually in the range of about 0.3 to 3 weight percent. By naphtha" we mean a normally liquid hydrocarbon fraction boiling below 450 F. and usually boiling almost entirely within the range of 100 to 400 F. An outstanding example of a high sulfur oleiinic naphtha is the naphtha produced by the coking of high sulfur reduced crude in any known manner, such, for example, as by continuously introducing heated charging stock into a coke drum at about atmospheric pressure to 50 p. s. i. g., at a temn perature in the range of about 850 to 950c7 F. and continuing the operating until coke solidiies E in the drum, the vaporous products from the drum being fractionated into a coke still naphtha fraction and one or more heavier fractions.

While our invention is applicable to high sulfurl` olenic naphthas produced by thermal cracking or by catalytic cracking, its outstanding advantage is in the rening of coke still naphtha because this charging stock is the most difficult of all to desulfurize or otherwise rene by conventional methods.

In accordance with our invention, a high sulfur olefinic naphtha is contacted with hydrogen uoa ride at a temperature lower than that heretofore employed for extraction of gas oil; the preferred contacting temperature is in the range oi about 60 F. to 30 F., or about 20 E. With higher contacting temperatures excessive valuable gasoline components are lost to the extract. The amount of HF, based on charging stock, should be in the range of about 5 to 200 volume percent, and preferably in the range of 10 to 100 volume percent. The pressure should be suiiicient to maintain the system in liquid state and the time of contact should be in the range of 6 to 60 minutes, e. g. about 30 minutes. Under such. conditions only about l0 to l5 percent of the charging stock is removed as extract and about 30 to 40 percent of the initial charge is converted by polymerization and alkylation to materials of the gas oil boiling range.

The total raffinate from the initial HF treating step is then contacted with alumina at a superatmospheric pressure which is preferably in the range of about 50 to 500 p. s. i. g. or more, with a space velocity in the range of about .1 to 3, e. g. about l, and at a temperature in the range of about 600 to 900 F., e. g. about 750 F. Under these conditions the raflinate is defluorinated and the alumina becomes activated by the released HF which it absorbs. The gas oil boiling range components of the charging stock are depolymerized and dealkylated, additional desulfurization is effected, and gas and coke formation are remarkably small, indicating that cracking takes place only to a very minor extent. The total product from this alumina treating step is characterized by a sulfur content of only about .04 weight percent and a fluorine content of the order of .001 weight percent or less. The naphtha boiling range portion of the product amounts to about 75 to 80 percent of the initial high sulfur naphtha and it is characterized by sulfur content of about .0l weight percent, a iiuorine content not higher than about .002 weight percent, a clear CFR-R, octane number of about 60 (slightly higher than that of the original charging stock), and a CFRf-R octane number with 2 cc. of lead tetraethyl upwards of 73, which is appreciably higher than the corresponding octane number of the original charge. oil boiling range product from the aiumina treat ing step amounts to about 8 to l0 percent of the original charge and it has a sulfur content oi about .17 and a negligible HF content.

After a run has been initiated, it is desirable to eliminate as much HF from the raninate as possible before the raiiinate is contactec with HF-activated alumina. We have found that the alumina is effective when it contains at least 10 to 15 weight percent of HF, but if the HF content of the alumina builds up to too great an extent, it may be necessary to eliminate HF from the catalyst. Although this may be done in the manner described, for example, in U. S. 2,397,085, We prefer to minimize the necessity of HF regeneration by removing as much as possible of the HF from the raiiinate before the rafnate contacts the alumina. Defluorination may be effected by the use of alkalized alumina, as described in U. S. 2,391,149, but we prefer to eiect the defluorination by heating and stripping in a raflinate-stripper deuorinator. The temperature of the deluorination in this de fluorinator should be in the range of about 400 to 600 F., the pressure should be suilioient to prevent loss of all but the lightest naphtha components of the overhead stream and the use of an inert stripping gas such as propane or butane adds to the eiiectiveness or the de fluorination.

The invention will be more clearly understood from the following description of a specic example thereof and by reference to the accompanying drawing which is a schematic flow diagram of a large scale plant for practicing the invention.

Coke still naphtha having a sulfur content of about .7 weight percent, a clear CFRf-R octane number of 59.7 and an olen content which exceeds its parain content was charged to a stirred reactor and contacted with 30 volume percent HF at about -20 F. for a period of approxiu mately one-half hour. About 87.7 percent of the charge was separated as a rainate and only about 12.3 percent was extracted, the extract after removal of HF being very high in sulfur but suitable for blending in certain fuel oils. The raffinate contained about 53.4 percent, based on original charge, of components in the naphtha boiling range and this intermediate product naphtha fraction had a CFR-R octane number of only 38. The remainder of the raflinate, about 34.3 percent based on original charge, consisted essentially of polymers and alkymers of the gas oil boiling range.

Total raffinate in this case was neutralized and then contacted. with activated alumina at about 750 to 800 F., under 400 pounds pressure, with a space velocity of about l and the product from the alumina contacting step was distilled into a 400 F. end point gasoline which was caustic washed and analyzed for sulfur and iuorine, The gasoline product amounted to 78.2 percent, based on initial charging stock, and it was characterized by a sulfur content of only .014, an HF content not exceeding .002 and a clear CFR-R octane number of 60.1. It is most remarkable that although the octane number of the naphtha portion of the original raffinate was only 38, that of the finished gasoline was 60.1. On a leaded basis, the improvement in Aoctane number was even greater, the original naphtha with 2 cc. of lead tetraethyl having a CFR-R octane number of 69.6 and the product gasoline having a corresponding octane number of 73.3. It will be noted that the alumina treat ing of the HF raiiinate increased the ultimate gasoline yield from 53.4 to 78.2 percent, an increase of about 25 percent, based on charge. The nished product had a sulfur content of only .014 percent, representing a 98 percent desulfurization. The octane number of the iinal gasoline and the lead response was better than that of the initial charge and the nal gasoline was still highly olenic.

Alumina activated by HF, as hereinabove described, Was employed for effecting desuliurization of virgin West Texas heater oil boiling in the range of about 325 to 575 F. by treatment at a space velocity of about l and at a tempera- I ture of about 725 F., under 600 pounds hydrogen pressure. This heater oil initially contained about .6 percent sulfur and by this treating step 72 percent desulfurization was obtained while the same stock, when treated under the same conditions with alumina which contained no HF, gave only about 62 percent desulfurization. It will, thus, be seen that the HF-activated alumina which is produced in our process may be used for desulfurization of other charging stocks or for isomerization of olens and then regenerated (U. S. 2,397,085) so that it may be subsequently used for treating additional HF raffinate.

Referring to the drawing, a coke still naphtha may be introduced by line I0 to extraction tower i l into the top of which HF is introduced through line l2. The tower may be provided with baiiles, trays, packing material. or the like and/or the naphtha may be introduced through atomizers or spray nozzles to insure thorough and intimate Contact. Alternatively, of course, mixers and settlers may be employed such, for example, as are used for effecting sulfuric acid alkylation. The extraction may be at any pressure sufficiently high to maintain liquid phase conditions therein, the important feature being to maintain a temperature lower than would be ernployed for gas oil extraction and preferably in the range of about 60 F. to +30 F., the temperature in this particular case being 20 F. and about 30 volume percent HF being employed.

Ybased on the naphtha charge, with a contact time of approximately one-half hour. The interface is preferably maintained at an intermediate or upper part of the tower.

The rainate is removed overhead through line I3 to raffinate stripper-defluorinator I4 which is provided at its base with a heater or reboiler I5 and into which a stripping gas such as propane and/or butane is introduced through line I 6. The stripper-deuorinator should be operated with a bottom temperature in the range of about 400 to 600 F., or approximately 500 F., and under a pressure suiciently high and a top temperature suificiently low to maintain most of the raiinate in the liquid phase. The top of the tower may be cooled or provided with reflux liquid (not shown). This heating and stripping not only removes dissolved HF from the rafnate but it deconiposes most of the alkyl fluorides so that the raffinate removed through line I1 may contain only about .l to .01 percent HF or less. During the start-up more HF may be allowed to `remain in the rainate in order to effect activation of the alumina as will be hereinafter described.

The extract phase withdrawn from tower I I 'I 'through line i8 is introduced into an extract stripper-deiiuorinator I9 provided with heater 20 which may operate under substantially the same conditions as stripper-defiuorinator I4. HF-free extract is withdrawn from the base of stripper-deuorinator IQ through line 2I and although this extract may contain 2 to 6 percent of sulfur, it may be utilized as a blending stock for certain fuel oils.

The overhead stream from stripper I4 is withdrawn through line 22 and combined with the overhead stream from stripper I9 which is discharged through line 23, the combined streams being introduced by line 24 to HF recovery system 25. Since no invention is claimed in the particular means for separating HzS, light hydrocarbons, and other contaminants from the HF ir this system, it will not be described in detail. Systems for this purpose are illustrated in U. Si. 2,532,492 and in copending application Serial Nos. 223,552 and 223,582, both filed on April 28, 1951. HF is recycled from the recovery system through line I2 along with make-up HF from line 20.

The substantially deiluorinated raffinate withdrawn through line Il is then passed through pipe still or heater 2'! wherein it is heated to a temperature of about 800 F. and it is then introduced into converter 23, which in this case is packed with activated alumina. Although fixed bed contacting is described in this example, it should be understood that moving beds and fluidized solids systems may be used. Also, instead of the commercial grade of alumina known as activated alumina, we may employ alumina in other forms although the gamma alumina is preferred. Advantageous results may be obtained with ordinary calcined bauxite. Catalysts made from alumina gels are most advantageous and since they are well known for the manufacture of hydroforming catalysts, it is unnecessary to describe them in any further detail. While silica or metal oxides may be employed along with alumina, their presence is preferably in minor amount and a feature of our invention is the avoidance of any necessity of employing expensive cracking catalysts such as silica-alumina or reforming catalysts, such as molybdena-alumina or chromia-alumina.

The contacting in converter 28 may be effected in either'gas phase or liquid phase condition although the latter is preferred. In other words, the contacting pressure is preferably superatmospheric and may be in the range of about 50 to 500 p. s. i. g. or more, at a temperature in the range of 600 F. to 900 F., preferably approximately 750 F. to 800 F. and with a space velocity in the range of about .1 to 3, preferably 1 to 1.5. In converter 28 residual alkyl uorides are decomposed, the liberated HF being absorbed by the alumina to effect activation of said alumina. The HF-activated alumina is remarkably effective for depolymerizing and dealkylating the high boiling components of the ranate while at the same time effecting further desulfurization and overall improvement of the octane number of the resulting gasoline-boiling range product. We prefer to maintain about 1 to 15 percent of I-lF on the alumina during the contacting step although activation is effected with even lesser amounts of HF and more HF than 15 percent may be tolerated. Coke deposition and gas formation are remarkably small in this operation which indicates that cracking in the usual sense occurs to only a very limited extent.

When the converter has been on stream for such period of time that it accumulates more than the desired amount of HF, the catalyst is preferably removed and utilized elsewhere, e. g. for desulfurizing heater oil or isomerizing olens, and in either case it may thereafter be regenerated and/or defluorinated and used again for treating HF raffinate.

The product stream from converter 2B next passes by line 29 to fractionator 3l] from which C4 and lighter hydrocarbons may be taken overhead, a portion of them being condensed and returned to the tower as reflux and the remainder thereof being returned to line i6 to serve as a stripping medium in rainate stripper-defluorinator I 4. The light hydrocarbons from the overhead of fractionator 30 are highly olenic in nature. A possible advantage to be realized by recycling them to stripper-deuorinator I4 is that part of these olens may be polymerized or alkylated in the stripper by catalytic action of the HF present. Much of the polymer or alkylate will eventually be taken as an overhead product from fractionator 32, increasing not only the ultimate yield of gasoline but also its octane number. When this source of stripping gas is inadequate, light hydrocarbons from the HF recovery system 25 or saturated hydrocarbons from an outside source may be used as a stripping gas.

The .fbottoms from tower 30 are introduced by line 3 I to fractionator 32 in which gasoline is taken overhead and heavier-than-gasoline materials are withdrawn as bottoms. For maximum gasoline production all or a part of the bottoms from tower 32 may be recycled to line I'I for passage through furnace 2'I and through converter 28. Likewise, the high sulfur extract leaving tower I9 through line 2|, after a hydrodesulfurization step, may be passed through furnace 27 and converter 28 for depolymerization and dealkylaton to gasoline-boiling-range product. It will be understood that any known product fractionation system may be employed and that the above description is diagrammatic and by way of example.

From the above description it will be seen that we have attained the objects of our invention and have provided a process wherein about 98 percent desulfurization of coke still naphtha may be eiiected while at the .same time obtaining gasoline yields of approximately 78 to 80 percent, with about 12 percent of the original charge being removed as extract in the HF treating step and about 8 to 10 percent of the original charge being converted into heavier-than-gasoline hydrocarbone having a sulfur icontent of only about .17 weight percent. The resulting gasoline is highly olenic and it is characterized by a higher octane number than the original charging stock and a much higher response to lead tetraethyl. While we have described a preferred example of our invention, it should be understood that the invention is not limited thereto since alternative procedural steps and operating conditions within the defined ranges will be apparent from the above description to those skilled in the art. Said description and drawing have been simpliiied for the purpose of clarity. It will be understood, of course, that heat exchangers, pumps, valves and safety precautions will be employed in accordance with known engineering standards and requireinents.

We claim:

1. The method of desulfurizing a high sulfur olenic naphtha, which method comprises intimately contacting said naphtha with hydrogen iluoride at a temperature in the range o1" 60 F. to +30" F. under conditions for obtaining a small amount of extract material containing a large amount of sulfur and for obtaining a large amount of raffinate, including polymers and alkymers of original charging stock components, removing most of the HF from said railinate, then heating said raimate to a temperature in the range of about 600 to 900 F. and contacting said raffinate at a temperature in said range with PIF-activated alumina for effecting further desulfurization and a reconversion of most of the polymer and alkylate into hydrocarbons of the gasoline boiling range.

2. The method of claim 1 wherein the high sulfur olenic naphtha is coke still naphtha.

3. The lmethod of rening a high sulfur olefinic naphtha which method comprises contacting said naphtha with hydrogen fluoride at a temperature in the range of -60 F. to +30 F. with an amount of HF in the range of 5 to 200 volume percent and for a time of contact IWithin the range of 6 to 60 minutes whereby extract and rainate phases are formed, stripping said rafnate phase at a sufficiently high temperature to decompose most of the alkyl luorides contained therein and to effect removal of liberated and dissolved HF therefrom, heating the stripped raffinate to a temperature in the range of about 60 to 900 F., contacting the heated railinate at a temperature in said range with HF-actvated alumina at a pressure in the range of about 50 to 500 p. s. i. g. and a space velocity in the range of .l to 3 volumes of railinate per hour per volume of HF-activated alumina and iractionating the products from the last-named contacting step to obtain a gasoline boiling range fraction which is olenic and substantiallyv free from sulfur and a small amount of a higher boiling hydrocarbon.

4. The method of claim 3 wherein the naphtha. is a coke still naphtha.

5. The method of claim 3 wherein the naphtha contacting with HIP-activated alumina is effected in liquid phase and wherein said alumina is associated with about 1 to l5 Weight percent of HF.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 2,336,165 Connolly Dec, '7, 1943 2,532,492 Giachetto et al. Dec. 5J 1950 2,537,620 Brandon Jan. 9, 1951 2,573,726 Porter et al Nov. 6, 1951

Claims (1)

1. THE METHOD OF DESULFURIZING A HIGH SULFUR OLEFINIC NAPHTHA, WHICH METHOD COMPRISES INTIMATELY CONTACTING SAID NAPHTHA WITH HYDROGEN FLUORIDE AT A TEMPERATURE IN THE RANGE OF -60* F. TO +30* F. UNDER CONDITIONS FOR OBTAINING A SMALL AMOUNT OF EXTRACT MATERIAL CONTAINING A LARGE AMOUNT OF SULFUR AND FOR OBTAINING A LARGE AMOUNT OF RAFFINATE, INCLUDING POLYMERS AND ALKYMERS OF ORIGINAL CHARGING STOCK COMPONENTS, REMOVING MOST OF THE HF FROM SAID RAFFINATE, THEN HEATING SAID RAFFINATE TO A TEMPERATURE IN THE RANGE OF ABOUT 600* TO 900* F. AND CONTACTING SAID RAFFINATE AT A TEMPERATURE IN SAID RANGE WITH HF-ACTIVATED ALUMINA FOR EFFECTING FURTHER DESULFURIZATION AND A RECONVERSION OF MOST OF THE POLYMER AND ALKYLATE INTO HYDROCARBONS OF THE GASOLINE BOILING RANGE.

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