US2417308A - Desulphurization and hydroforming - Google Patents

Description

March ll, 1947. M. w. LEE

DESULPHURIZATION AND HYDROFORMING Filed April 12, 1943 Patented Mar. 11, 1947 DESULPHURIZATION AND HYDROFORRIING Milton W. Lee, Palos Verdes Estates, Calif., as-

signor to Union Oil Company of California, Los Angeles, Calif., a corporation of California Application April 12, 1943, Serial No. 482,717 7 Claims. (Cl. 196-2`4).

This application relates to the catalytic conversion of hydrocarbony mixtures containing sulfur compounds and especially to the production of improved motor fuels from high sulfur, volatile petroleum fractions by a two-stage vapor phase desuliurization and hydroforming process.

It has long been known that sulfur compounds are objectionable in motor fuels Ifor various reasons, particularly because of deleterious effects on odor, anti-knock ratingv and lead susceptibility or improvement in octane number in response to the addition of anti-detonants such as tetraethyl lead. f'

Various types of treating methods have been proposed for eliminating sulfur compounds from petroleum distillates. For example, mercaptan's, which are principally responsible for the objectionable odor, have been converted to less odorous disulfides by familiar sweetening processes such as doctor treatment. Such treatment, however, does not reduce the total sulfur content of the distillate, and since disuldes are as deleterious in their effects on octane number and lead susceptibility as the parent mercaptans, such processes do not improve the gasoline in these respects, i

Another type of treatment which has been employed particularly as a sweetening process involves the extraction of sulfur compounds with various reagents, usually alkaline. These methods are generally effective only for the mercaptans and in some instances with the thioethers, but not for the thiophenes, which are normally the predominating sulfur compounds present in cracked gasolines. Sulfuric acid has been commonly used for the reduction of total sulfur content of gasolines, and is partially effective on alll types of sulfur compounds. However, wherethe total sulfur content of a cracked gasoline oontaining substantial amounts of olefins, such as over about20% for example, must be reduced from high values such as 2% to values around .2% or less, so much loss is experienced in the treatment due to polymerization of desired olefinic hydrocarbons that in most instances this type of treatment is uneconomical.

Another treatment method involves vapor phase catalytic treatmentin the absence of hydrogen, by which means mercaptans and in some cases thioethers are destroyed, but thiophenes are unaffected. Recently, methods have been developed which involve catalytic treatment in the presence of hydrogen. These processes I shall refer to as hydroforming processes, where there is an'overall production of hydrogen or substantial conversion or reaction such as crack- 2 ing, aromatization and dehydrogenation, or catalytic desulfurization processes where there is an overall consumption of hydrogen. Both `of these processes have been found to be sucprocess and the single stageprocesses, a brief description of each will be given.

In a single stage desulfurization process, the feed stock is vaporized and mixed with hydrogen, and the resulting vapor is passed over a desulfurization catalyst such as cobalt molybdate at a temperature `between about 650 F. and 850 F. Under these conditions the sulfur compounds present in the feed stock are largely decomposed with the formation of hydrogen sulfide, and when olens are present, these are largely hydrogenated. Catalyst life between regenerations is extremely long, and hydrogen 'sulfide is present in the product gas throughout a1- most the entire catalyst life.

In a single stage hydroforming operation the feed stock is vaporized and mixed with hydrogenl in a similar manner and the resulting vapor mixture is passed over a hydroforming catalyst such as molybdic oxide on alumina, chromic oxide and the like at a temperature of approximately 900 F. or above Under these conditions the sulfur compounds present in the feed stock may also be largely decomposed, but such reactions as cracking, dehydrogenation, aromatization and the like result in an overall production of hydrogen. The catalyst life is relatively short compared to the desulfurization catalyst life, because of relatively rapid deposition of carbonaceous material on its surface. Generally, no hydrogen sulfide is produced, since the catalyst is usually able to absorb some hydrogen sulfide by the conversion of oxides present lto sulfides, and the catalyst usually loses its effectiveness as a hydroforming catalyst before its capacity for absorbing hydrogen sulfide is exceeded.

.According to a preferred form of the present invention, the two single stagey processes outlined above are combined by passingthe vaporized feed stock in ladmixture with hydrogen first over a bed of desulfurization catalyst maintained at a relatively low temperature in the neighborhood' of 700 F., and thereafter, without removal of hydrogen sulfide or other reaction products, the resulting products are cooled'and separated. e. g. `by fractional distillation, to obtain a liquid fraction sub- 1 stantially free from sulfur compounds and a, hydrogen-rich gas fraction part of which is freed of hydrogen sulde by treatment with iron oxide, or tripotassium phosphate, etc., and recycled to the first stage with fresh feed vapors. Other desired fractions, such as a butane-butene cut, etc., may also be segregated.

The two-stage process of the present invention may be carried out as illustrated in the accompanying drawing, which represents a flow diagram of one method of carrying out the process. Re-

i ferring to the drawing, feed stock is introduced through line I and control valve 2 to vaporization and preheating system 3. Hydrogen-rich gas introduced through line 4 and control valve 5 may also be preheated in system 3, separately or together with the feed stock. The mixture of vapor'ized feed stock and hydrogen from system -3 is passed through line 6 to the first catalytic stage 1, into which additional hydrogen may also be introduced through lines 4 and B and valve 9. In

, the first stage 1, the gaseous mixture is contacted with a catalyst as describedherein, and the resulting product gases, without condensation or removal of any of their constituents are passed successively through line I0, heat exchanger II, compressor I2, control valve I3 and line I4 to second catalytic stage I5. Heat'exchanger II may be operated either as a heater or a cooler, de-

pending on vwhether the second stage is operated at a higher or` lower temperature than the rst stage as described later. If the second stage is operated at a sumciently lower pressure than the yf'lrst stage, compressor I2 may bel omitted. If

desired, additional hydrogen may be introduced into line I through lines 4 and I6 and. control valve I1, or other gases such as hydrocarbon gases, steam, carbon oxides, nitrogen, etc may be introduced into line I0 through line I8 and control valve I 9. In the second stage I 5, the gaseous mixture is contacted with a second catalyst as described herein, and the resulting product gases are passed through line 20 into separation system 2I, where they are separated by conventional methods of cooling, absorption and fractiona1 distillation, to obtain at least two fractions, one a hydrogen-rich gas, drawn olf through line 22 and the other a liquid product, drawn offthrough line 23 and control valve 24. If desired, other fractions, such as intermediate hydrocarbon fractions, butenes, propene, etc., or heavy gas oil fractions, etc., may be drawn 01T, as through lines y25 and 2B and valves2'l and 28. Fractions not desired as final product may be recirculated if desired, either to the rst stage, through line 29 and control valve 30 to line I, etc., or to the second stage through line I8 and control valve I9 to line III, etc. Part of the hydrogen-rich gas may be withdrawn as make gas through line 3l and valve 32, and the remainder is passed through line 22 and control valve 33 to the hydrogen sulde removal system 34 from which it is pumped through .line 4 by means of compressor 35. If additional hydrogen is required as make-up gas, it may be introduced into line 4 through line 36 and valve 31.

One of the chief advantages of the two-stage process over the single-stage desulfuri'za-tion process as described above lies in its production of gasolines containing larger proportions of olens high-sulfur stocks. In the hydroforming process,-

when treating high-sulfur stocks, the catalyst life may be limited by its capacity to absorb the H28 produced; and when treating stocks containing large amounts of oleflns, such as cracked stocks, the catalyst life may be limited by the rapid rate of depositionof coke on the catalyst. In the twostage process, there is no limitation on the sulfur content of the feed stock, and olefins` are largely hydrogenated in the rst stage. This results in excellent catalyst life with all types of feed stocks. Cracked stocks containing as much as 3.5% sulfur (as organic sulfur compounds) may readily be handled, whereas hydroforming of cracked stocks containing over about 2% sulfur is not commercially feasible. given quality such as octane number, may be ob` tained by the two-stage process from both cracked, high sulfur stocks, and straight-run low sulfur stocks, whereas the yields from hydroforming of thesetwo types of stocks are markedly different, being much lower for the cracked, highsulfur stocks. Such exibility of voperation and uniformity of product quality are most desirable. The longer catalyst lifev also provides for greater uniformity of product quality, ease of operation, and lower equipment costs.l By longer catalyst life it is meant to convey not only longer life between regenerations, but also at least as many effective regenerations, resulting in a longer overall period of usefulness of the catalyst.

There are many other advantages of the twostage process over simple hydroforming of high i sulfur cracked stocks,vsuch as for example the improved susceptibility of the product to the action of gum inhibitors or antioxidants, the greater concentration of hydrogen in the gaseous product obtained, which reduces the minimum desirable recycle rate and the permissible use of catalysts which do not absorb hydrogen sulfide.

The presence of hydrogen sulfide in either stage apparently has no deleterious effect, and apparently has a benecial effect. It is believed that the lack of exposure to air, the elimination of handling operations such as condensation,

and theshortness of the time interval between stages also contribute to the quality of the product and the improved life of the hydroforming catalyst.

In the generally preferred mode of operation,

. from the liquid product, andthe remainder resteam, etc. The rates of addition of these materials and the amounts-of catalysts employed may be varied to obtain the desired conditions.

High yields, for prociuctsl of For example, hydrocarbon feed stocks of For The catalyst for the desulfurization stage may be any effective desulfurization catalyst such as cobalt molybdate, chromic oxide, or vanadium oxide, with or without gel carriers. Catalysts comprising cobalt molybdate are especially effective.

follows:

A cobalt molybdate catalyst was prepared by dissolving 7.7 gram-mols of cobalt nitrate in 19 liters of cold water, and stirring thesolution while slowly adding a solution containing 1.1 mols of ammonium paramolybdate, (NHosMovO-nAHzO, and 12 mols of ammonium hydroxide, dissolved in 6 liters of cold water. The grey-pink precipitate was filtered, washed, dried for 48 hours at 220 F., ground, and pelleted.

A catalyst consisting of 20% cobalt molybdate precipitated on 80% undried alumina gel is preferable even to the above catalyst in some respects. One such catalyst was prepared by dissolving 8 gram-mols of aluminum nitrate in 10 liters of hot water, and slowly stirring in 24 mols of ammonia in the form of concentrated ammonium hydroxide solution, to form a gelatinous alumina precipitate. After filtering and washing this precipitate to free it of soluble salts, it was resuspended in 6 liters of hot water, and 2 liters of hot water containing V0.9 mol of dissolved cobalt nitrate was added thereto. Then a solution containing 0.13 mol of ammonium paramolybdate (NH4)6MovO24.4H2O, and 0.98,mol of ammonia, both dissolved in a total of 2 liters of hot water, was slowly stirred into the above cobalt nitrate solution containing the suspended alumina, precipitating cobalt molybdate on the` Two such catalysts may be prepared as Temperature,

alumina. The resulting solid product was filtered oil', washed, dried for 48 hours at 200 F. to 400 F., and ground to 10 to 20 mesh slate-blue granules. j

The catalyst for the hydroformin'g stage may be any effective cracking or hydroforming catalyst such as molybdic oxide on alumina, but is preferably one which is not adversely affected by hydrogen sulfide. Various clays, Activated Alumina, silicates and gels impregnated with activating metal oxides such as chromic oxide and cobalt molybdate for example, are suitable.

The desulfurization catalyst, when employed under the mild conditions prescribed for the first stage above will require only infrequent regeneration. A cobalt molybdate catalyst used under the conditions described forpthe rst stage, in the specific example below desulfurized over 180,0 A

times its own volume of a moderately high-sulfur cracked gasoline without perceptible loss in activity. The catalyst for the hydroforming stage will probably require more frequent regeneration than the desulfurization catalyst. Suitable arrangements of multiple reaction chambers substantial de-alkylation of high-boiling aro` matics, nitrogen bases, etc., to form low-boiling similar type compounds. Thus, the process is of importance in the production of toluene, etc.

The approximate'ranges of operating conditions in the two stages of the preferred process of this invention are as follows:

Second stage (hydroforming) Feed rate, volumes of liquid per volume of catalyst per hour.

Hydrogen, cubic feet per barrel of liquid feed l to10, preferably l 0.1 to l0, preferably to 8. 0.2 to 5.

to 10,000, prcfcrably 2,000 to 6,000.

000 to 850, preferably Pressure, lb. per 'Oto 1,500, preferably square inch gage. 100 to 800.

100 to 10,000, preferably 1,000 to 6,000.

850 to 1,500, preferably 000 to 1,100.

0 to 1,500, preferably As a specific example of the process of this invention an operation was conducted in which a single vertical ltube was used as a reaction chamber for both stages. The lower section of the vertical reaction tube was charged with 50 ml. of a cobalt molybdate catalyst prepared 4as above, and was maintained at a temperature of about 700 F. The upper section of the same tube was charged with 50 ml. of chromic oxide gel catalyst prepared by ammonia precipitation of chromic oxide from a dilute chromic nitrate solution, and was maintained at a temperature of about 950 F. A heavy gasoline fraction derived from cracking of a heavy naphthenic California crude oil was employed as feed stock. This was introduced into the lower end of the reaction tube at a rate of 200 ml. (liquid) per hour (4 volumes per volume of each catalyst per hour) in admixture with liters/hr. (3370 cu. ft./bbl. feed) of hydrogen, and at a pressure of 250 lb. gage the vaporized mixture was passed upward through the two successive catalyst beds. were cooled to room temperature under pressure, whereby the bulk of the liquid was condensed. The uncondensed gases were depressured and led through a trap chilled by an acetone bath cooled with excess solid carbon dioxide, to the meters used to estimate the hydrogen flow rate. The pressure condensate and trap condensate were collected periodically, measured, combined and washed with about 10% of their volume of about 2% strength caustic to remove any dissolved hyedrogen suliide. A composite of the condensate obtained during the rst 121/2 hours of operation compared with the feed stock, tested as shown below. Shown also are the characteristics of the product from the first stage as determined in a separate operation conducted Without the high temperature second stage of hydroforming catalyst.

First Second Feed stage stage product product Gravity, A. P. I. at 60 F 47. 7 50. 6 51.3 Engler distillation, F.:

Init 141 151 '96 107 214 218 168 sofi 299 291 272 90%. 380 373 380 Max 407 410 442 Olen content, per cent 5i 6 26 Sulfur content, per cent by wt 0.63 0.01 0.01 Octane No. (Motor):

No TEL 72.0 61.5 74. 5 m1. TEL/gal 78.0 79.0 84. 5 Estlmated ml. TEL/gal to 80 octane. 6.0 3. 5 0. 8

The yield of nal product in the above operation was 87% of the feed. Using this as a basis of comparison between this operation and conventional hydroforming, it is estimated on the basis of extensive pilot plant hydroforming operations employing a molybdic oxide on alumina catalyst that the product obtained in an 87% yield at 950 F. and similar pressure and hydrogen recycle flow would contain about .04% sulfur The resulting productsv Max; Sulfur content, per cent by wt.

and have an octane number of about 72 and 74, respectively, for a two-hour cycle on high sulfur cracked gasoline and a six-hour cycle on low sulfur straight run gasoline, respectively. l Besides permitting a much longer cycle, and producing a somewhat better quality product, this combination desulfurization-hydroforming operation was carried out at feed rates 6 to 7 times as high as the normal hydroforming feed rates, making the life of the hydroforming catalyst, expressed in volumes of feed per volume of catalyst, at least 12 to at least 40 times that obtained in the conventional hydroforming operation,

The hydrogen sulfide in the hydrogen-rich gaseous product from the second stage of the operation need not be quantitatively removed before recycling this gas, since small amounts of hydrogen sulfide do not usually greatly affect the efliciency of the process. Where products of extremely low sulfur content are desired; it is pref- 4 rable that the hydrogen sulfide content of the recycle gas should be below about 0.2% by volume, but normally this value may be as high as 1% or even 5% in many instances.

A modification of the two-stage process.f this invention has also been carried out in-Which the f hydroforming is carried out in the first stage and the desulfurization in thesecond stage. Conditions of operation for the two stages may be approximately as described above, except for the reversal in order. The catalystsare also reversed, the catalyst used in the first stage being of the cracking or hydroforming type, and the catalyst tion with fresh catalysts while regenerating spent catalysts.

In a specific example of this modification of I the process the same equipment described in the previous example was used. In this operation the same type of feed stock used in the previous example was' Vaporized and mixed with hydrogen, and passed upward through' a reaction tube, the lower section of which contained ml. of cobalt molybdate catalyst maintained at a temperature of 900l F. and the upper section of Which contained a similar amount of the same catalyst maintained yat 720 F. The feed rate was maintained at about 200 ml. (liquid) per hour (8 volumes per volume of catalyst for each stage), the hydrogen ow was approximately 120 liters per hour (3370 cu. ft. per barrel), and the pressure in the reactor was 250 lb. gage. The gases from the top of the reactor were cooled to room temperature under pressure, and the liquid product was condensed, recovered and treated asin the previous example. A composite of the condensate obtained during the introduction of approximately the rst 1.8 liters of feed (9 hours of operation) compared with the feed stock, tested as follows:

Gravity. u.. P. I. at 66 F Engleiiistillation, F.:

Copper dish gum, nig/100 ml..

`Octane No. (Motor):

i No TEL 3 ml. TEL/gal Estimated TEL/gal. to 80 octane Multiple catalyst beds The yield of product in the above operation was approximately 96%. based on the feed voli ume, and its octane number, lead susceptibility and sulfur content are better than'.` those of the product obtainable in a similar yield by singlestage hydroforming, even of a low sulfur straightrun gasoline, at a similar condition of temperature, pressure, and hydrogenv iiow, with an effii called base stocks for aviation gasoline of extremely high anti-knock rating, since large proportions of desirable anti-knocking hydrocarbons such as aromatics, etc., may be formed in the first stage, together with oleiins which are less desir- 1 ab-le on the` basis of oxidation resistance, etc. The t olens, however, may be almost completely hygenating the aromatics,

drogenated in the second stage to form more desirable saturated hydrocarbons. without hydro- The presence of hydrogen sulfide in the product leaving the first stage and entering the second stage appears to promote this olefin hydrogenation. Furthermore, the sulfur content is reduced in both stages, and

` a product of excellent anti-knock rating and excellent response to the addition of anti-detonants such as tetraethyl lead may be obtained. Pure aromatics such as benzene, toluene, xylenes, etc.

, which are unusually free from contaminating sulfur compounds may also be prepared from the products of this type of process.

Other modifications of the process which would occur to one skilled inthe art and are not disclosed previously are to be included in the invention as dened in the following claims.

I claim: f

1. A process for treatment of a volatile hydrocarbon feed mixture containing sulfur compounds, which comprises subjecting said mixture to vapor phase catalytic desulfurization at a ternperature between about 600 F. and 850 F. in one stage and subjecting the resulting gaseous mixi ture without substantial removal of any of its constituents to vapor phase hydroforming with a different catalyst in a succeeding stage at a temperature between about 850 F. and 1500 F.,

employing superatmospheric pressures and hytaining over about 2% sulfur as organic sulfur compounds.

3. A process according to claim 1 in which the desulfurization catalyst comprises cobalt molybdate.

4. A process according to claim 1 vin which the desulfurization catalyst is cobalt molybdate on a gel carrier.

5. A process according to claim 1 in which a low-sulfur hydrocarbon mixture of low olefin content is introduced between stages.

6. A process according to claim 1 in which a gaseous fraction rich in hydrogen is separated from the product of they hydroforming stage and a portion thereof is treated to reduce its hydrogen sulfide content, and the resulting gas is recycled to the desulfurization stage.

7. A process for the treatment of a cracked naphtha boiling below about 500 F. and having a sulfur content above about 0.5% which comprises forming a mixture of the vapors of said naphtha and hydrogen; desulfurizing said naphtha by contacting the said mixture with a catalyst comprising cobalt molybdate, at a temperature between about 650 F. andy 800 F.; and hydroforming the so desulfurized naphtha by contacting the resultlng gaseous mixture, without substantial removal of any of its constituents, with a different catalyst comprising an oxide selected from the class consisting of molybdic oxide and chromic oxide, at a temperature between about 900 F. and 1100 F., employing in both the desulfurization and the hydroforming operations, pressures in excess of 100 pounds per sq. in. gage, and amounts of hydrogen in excess of 1000 cubic feet per barrel of liquid naphtha.

MILTON W. LEE.

REFERENCES CITED ile of this patent:

Number Number UNITED STATES PATENTS Name Date Watson Mar." 30, 1943 Drennan Nov. 3, 1942 Boyd May 20, 1941 Gwynn Oct. 3, 1939 Penisten Aug. 25, 1942 Brooks May 12, 1942 Rosen May 28, 1940 Schulze Dec. 19, 1939 Gwynn Mar. 9, 1937 Buell et al Mar. 30. 1937 Heard June 18, 1940 Byrns July 27, 1943` Smith l Nov. 29, 1932 Chickinoii Mar. 23, 1943 Liedholm et al June 29, 1943 Marshall Sept. 1, 1943 Szeszlch Feb. 6, 1934 Welty etal. June`30, 1942 Byrns '-July 27, 1943 Conn Aug. 8, 1944 FOREIGN PATENTS Country Date British Aug. 16,1935 British Nov. 2, 1934

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