US3451922A - Method for hydrogenation - Google Patents

Description

June 24, 1969 R. J. PARKER METHOD FOR HYDROGENATION Filed April 28. 1967 xuQNM mEu B Q5390 simk /V V EN TOR Rob/n J. Parker /\V l 1 mm t Nv I/QV 4111K? mm. NM vw hwy T$N 3 mm w m .h .0 Q J m m Q m w W J 0 MM. w w M Q u. a a 0 9 l U U I a a a w mm 1 m w w mm m t m mm 0 u 0. U .1 W N I M w W m Q w 1 w mm mm\ m Q N h w t I. x 9 Wm T Mm Wm. m f f k I QTm Q fM Q fiwm b. A TTOFP/VEYS 9141 0509 s sl o/l United States Patent 3,451,922 METHOD FOR HYDROGENATION Robin J. Parker, Western Springs, 111., assignor to Universal Oil Products Company, Des Plaines, 111., a corporation of Delaware Filed Apr. 28, 1967, Ser. No. 634,554 Int. Cl. C10g 23/04, 23/02, 31/14 US. Cl. 208-57 3 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION This invention relates to the hydrogenation of hydrocarbons. It particularly relates to the stabilization of pyrolysis gasoline. It specifically relates to a method for selectively removing diolefins and olefins from the product gasoline obtained in light olefin manufacture.

It is known in the art that one of the commercially attractive routes to the production of valuable normally gaseous olefinic hydrocarbons such as ethylene, propylene, etc. is the thermal cracking or pyrolysis of hydrocarbons such as the light parafiin hydrocarbons and/or naphtha fractions obtained from petroleum. Usually, the pyrolysis reaction is effected in the substantial absence of a catalyst at high temperatures often in the presence of a diluent such as superheated steam utilizing a tubular reactor or a plurality of cracking furnace coils. Depending upon the charge stock and specific pyrolysis operating conditions employed, the effluent from the cracking zone may comprise light olefinic hydrocarbons such as ethylene, propylene, butylene, etc. or mixtures thereof, all of which may constitute the principal product or products. In addition to these light olefinic gases there is also produced a significant quantity of pyrolysis gasoline which contains undesirable quantities of diolefin hydrocarbons and/ or sulfur compounds. The pyrolysis gasoline frequently is rich in aromatic hydrocarbons, but it has been found that usually the aromatic portion of the pyrolysis gasoline is also heavily contaminated with olefin hydrocarbons which renders recovery of the aromatics in high purity extremely diflicult.

Conventional prior art schemes for producing light olefin gases, such as ethylene, may charge ethane, propane, or a straight-run naphtha fraction containing about 5% aromatic hydrocarbons, to a pyrolysis unit. The pyrolysis efiluent is separated into desired fractions, one fraction of which usually comprises a C 400 F. pyrolysis gasoline which represents, for example, approximately 1% to 40% by weight of the original naphtha feed depending upon the charge stock and severity of cracking. Since the pyrolysis gasoline is heavily contaminated, as previously mentioned, it is hydrotreated for saturation of olefin and/or diolefin compounds and for removal of sulfur compounds. Not infrequently the prior art schemes also charge the hydrotreated pyrolysis gasoline fraction to an aromatic extraction unit for recovery of the aromatic hydrocarbons such as benzene, toluene, and xylene therefrom. Typical extraction procedures utilizing a solvent such as sulfolane or the glycols are well known to those skilled in the art for aromatic extraction purposes.

However, as is known by those skilled in the art, the diene content of such pyrolysis gasoline, as measured by its well known Diene Value, is usually within the range Patented June 24, 1969 from 20 to 70 for C -400" F. gasolines. The diolefin compounds pose particular difiiculty in the operation of the hydro-treating facilities since these compounds cause extensive equipment fouling and catalyst bed fouling. So far as is known, the prior art, hydrotreating process will experience this fouling from polymer formation to some extent. Usually, the prior art will attempt to improve the on-stream efiiciency of the hydrotreating unit by either promoting the polymerization reaction prior to the hydrotreating step thereby preventing the polymer from reaching downstream equipment and/ or utilizing operating techniques and schemes which tend to minimize polymer formation. None of the prior art approaches are completely successful in overcoming the fouling difiiculty resulting from the diolefin compounds present in the pyrolysis gasoline.

More important, however, the prior art schemes do not povide selectivity in the hydrotreating unit. For example, the hydrogenation reaction may not stop with the conversion of diolefins to olefins but will frequently saturate the amount of olefins completely and even hydrogenate substantial portions of aromatic hydrocarbons. Such nonselectivity, of course, results in a decreased yield of desirable products in the pyrolysis gasoline. Even though aromatic hydrocarbons may not be hydrogenated, more frequently, olefin hydrocarbons are completely saturated, thereby significantly decreasing the octane blending value of that portion of the pyrolysis gasoline which is normally utilized in motor fuel.

Therefore, it would be desirable to provide a process for selectively hydrogenating pyrolysis gasoline which minimizes polymer formation, minimizes product degradation, and operates in a facile and economical manner.

SUMMARY OF THE INVENTION Accordingly, it is an object of this invention to provide a method for hydrogenating hydrocarbons.

It is another object of this invention to provide a method for stabilizing pyrolysis gasoline.

It is a specific object of this invention to provide a method for removing diolefins from. pyrolysis gasoline without destroying the olefins while simultaneously removing diolefins, olefins, and sulfur compounds from the aromatic portion of the pyrolysis gasoline in a facile and economical manner.

Therefore, the practice of the present invention provides a method for hydrogenating hydrocarbons which comprises introducing a relatively heavy hydrocarbon feedstock containing diolefin and olefin compounds into a first reaction zone maintained under hydrogenation conditions including a relatively low temperature and the presence of a palladium-containing catalyst suflicient to convert diolefin compounds to olefin compounds; passing the total eflluent from the first reaction zone into a second reaction zone maintained under hydrogenation conditions including a relatively high temperature and the presence of a desulfurization catalyst sufiicient to substantially saturate olefin compounds and convert sulfur compounds to hydrogen sulfide; admixing the total efliuent from the second reaction zone with a relatively light hydrocarbon feedstock containing diolefin and olefin compounds; passing said admixture into a third reaction zone maintained under hydrogenation conditions including a relatively low temperature and the presence of a palladium-containing catalyst sufficient to convert diolefin compounds; to olefin compounds; and recovering hydrogenated hydrocarbons in high concentration from the efiluent of the third reaction zone.

Another embodiment of the invention includes the method hereinabove wherein said relatively heavy hydrocarbon feedstock comprises the C -40O" F. fraction of pyrolysis gasoline and said relatively light hydrocarbon feedstock comprises the C fraction of said pyrolysis gasoline.

A particular embodiment of this invention includes the methods hereinabove wherein said desulfurization catalyst comprises a nickel-containing catalyst.

The selectivity of the present invention is based on the discovery that the unique three-stage system for hydrogenation accomplishes the desired results of removing diolefins, selectively removing olefins, and removing sulfur compounds simultaneously from various fractions of pyrolysis gasoline so that maximum recovery of desired products may be obtained from the pyrolysis of ethane, propane and naphthas to produce, for example, ethylene. This invention achieves these results in an economical and facile manner. For example, the use of the palladium catalyst in the first reaction zone achieves selectively the conversion of diolefins to olefins without substantial desulfurization. This is accomplished by maintaining the temperature in the first stage below desulfurization temperatures. Satisfactory operation may be achieved in the first reaction zone at a temperature from 200 F. to 400 F., a pressure from 200 p.s.i.g. to 1200 p.s.i.g., a liquid hourly space velocity from 1 to based on combined feed, and a molar excess of hydrogen. Usually, hydrogen in an amount from 500 to 5,000 standard cubic feet per barrel (s.c.f./b.) based on combined or total feed to the reactor will be satisfactory.

The operation performed in the second reaction zone of the present invention is primarily one of desulfurization utilizing any of the well known desulfurization catalysts. It was found that the conventional nickel-containing desulfurization catalyst was particularly satisfactory in removing sulfur from the relatively heavy fraction of pyrolysis gasoline while simultaneously saturating the olefin compounds. By proper selection of operating conditions it was found that no substantial aromatic saturation was achieved. Particularly satisfactory operating conditions for the second reaction zone include a temperature from 600 F. to 800 F., a pressure substantially the same as the pressure in the first reaction zone and a catalyst particularly useful for desulfurization such as, for example, nickel-molybdate supported on alumina.

The operating conditions for the third reaction zone are particularly important. It is noted that in the practice of the invention the entire hydrocarbon efiluent from the second reaction stage is admixed with the relatively light fraction obtained from the pyrolysis gasoline. The purpose of this admixing is to reduce the Diene Value of the total feed to the third reaction zone to a relatively low figure. It has been found that the C fraction of pyrolysis gasoline contains, for example, from 50% to 80% by weight conjugated diolefin hydrocarbons. These diolefins would contribute significantly to polymer formation in the third reaction zone. Accordingly, it was found that the use of the substantially saturated hydrocarbon efiluent from the second reaction zone as diluent was particularly advantageous. Again, the third reaction zone utilizes the particularly satisfactory palladium catalyst. The diolefins are selectively converted to olefins at a temperature from 290 F. to 550 F., preferably, 360 F. to 500 F. It was found that operating outside of these temperature limits did not produce a particularly desirable result. Therefore, it is important that the temperature of the third reaction zone be maintained within these temperature limits for otherwise the olefin hydrocarbons would be unduly saturated and/ or the dienes would be converted to undesirable dicyclopentadiene which is extremely difficult to remove from the gasoline fraction. Frequently increased liquid hourly space velocity (LHSV) over those of the first reaction zone may be utilized herein. An LHSV of from 5 to based on combined feed is satisfactory. Again, the pressure on the third reaction zone is substantially the same as that on the other two reaction zones allowing for normal pressure drop through the system.

Normally, the entire fresh hydrogen is added to the system only through the first reaction zone; although, the

addition of fresh hydrogen to the other two reaction zones may be desirable from time to time.

By way of emphasis, it is to be noted that the present invention is based on the discovery that the palladiumcontaining catalyst is particularly useful in selectively converting dienes to olefins. Contrary to teachings found in the prior art a platinum-containing catalyst was not satisfactory in the practice of the present invention. It was also distinctly discovered that palladium deposited on lithiated alumina support produced excellent results. The amount of lithium on the support achieved remarkable results in reducing gum formation caused by polymerization of the dienes on the acid sites of the catalyst.

The palladium-containing catalyst employed in the present invention is prepared utilizing spherical alumina particles formed in accordance with the well known oil drop method as described in US. Patent No. 2,620,314 issued to James Hoekstra. These preferred catalysts contain either 0.75% or 0.375% by weight of palladium incorporated by way of an impregnation technique using the proper quantities of dinitro-dianisole palladium. Following evaporation to visual dryness and drying in air for about an hour at F., the palladium impregnated alumina is calcined at about 1100 F. for about two hours. The lithium component is then incorporated using the necessary quantities of lithium nitrate to produce catalysts of 0.33% and 0.5% lithium in an impregnation procedure and the composite again is dried and calcined. A distinctly preferred diene hydrogenation catalyst includes 0.4 weight percent palladium, 0.5 weight percent lithium on a inch spherical base. Broadly, then, the particularly preferred catalyst for the first and third reaction zones of the present invention comprises lithiated alumina containing from about 0.05% to about 5.0% by weight of palladium.

The practice of the present invention as previously noted is particularly applicable to a feedstock obtained from the pyrolysis of naphthas for the production of light olefinic gases such as ethylene. The pyrolysis reaction for the conversion of hydrocarbons into normally gaseous olefinic hydrocarbons is obtained at operating conditions including a temperature from 1000" F. to 1700 R, preferably, 1350" F. to 1550 F., a pressure from 0 to 20 p.s.i.g., preferably 5 to 10 p.s.i.g., and a residence time in the reaction zone of from 0.5 to 25 seconds, preferably, from 3 to 10 seconds. In order for the pyrolysis reaction to proceed subsequently without undue plugging of the reaction tube, an inlet diluent such as steam, light gases, and the like, is used. The prior art distinctly prefers to use superheated steam as the diluent which is added to the reaction zone in an amount from 0.2 to 1.0 pound of steam per pound of hydrocarbon, preferably, from 0.3 to 0.7 pound per pound, and typically, about 0.5 pound per pound.

The invention may be more fully understood with reference to the appended drawing which is a schematic representation of apparatus which may be utilized in practicing one embodiment of the invention.

DESCRIPTION OF THE DRAWING Referring now to the drawing, a typical pyrolysis gasoline comprising C material separated from the effluent of a steam pyrolysis reaction zone is passed via line 10 into depentanizer tower 11. Suitable conditions are maintained in depentanizer tower 11 to separate the feed to a C fraction and a (3 fraction. The C fraction contains primarily hydrocarbons comprising C paraffius and naphthenes, C olefins and C diolefin hydrocarbons. There may in some cases be small amounts of light hydrocarbons such as the 0., present, but usually this light hydrocarbon contaminant is not significant. The C fraction is removed from depentanizer tower 11 for further use in the third reaction zone more fully discussed hereinbelow. The heavy portion of the feed is removed via line 12 and, preferably, is introduced into rerun column 13. The purpose of column 13 is to produce a distinctly desired fraction, namely, a C -370 CF. fraction of the pyrolysis gasoline which contains the greatest concentration of desirable aromatic hydrocarbons such as benzene, toluene, and xylene. In some instances columns via line 32 and a normally liquid hydrocarbon fraction containing the desired hydrogenated products is removed via line 35. The hydrogenated product containing stream i line .35 is then passed into post-fractionation facilities 36 for separation into desired fractions. A C gasoline 11 and 13 may be merged into a single column, but genfraction 1s removed via line 37 and 1s suitable for gasoerally, it is preferable to maintain them as separate colline blending since it still contains a substantial quantity umns. The undesirable 370 F.+ material is removed of olefin hydrocarbons. An aromatics fraction rich in from rerun column 13 via line 14 and disposed of by benzene, xylene, and toluene (BTX) is withdrawn via means known to those skilled in the art. line 38 and is suitable for feed to a, for example, sulfo- The desired C -370 P. fraction is passed via line 16 lane solvent extraction unit since the material in line 38 into admixture with a hereinafter described diluent i substantially olefin-free. stream from line 40 through line 17 into reactor 18 mm The remaining portion of the hydrogenated hydrocartaining the preferred palladium catalyst. The total efilubons represents recovered C material and is withdrawn ent from reactor 18 is withdrawn via line -19, heated in via line 39, If desired, a portion of this material is reeXchangel raised considerably in temperature y moved via line 41 and since it is substantially sulfur-free heater 21, and the heated efiluent passed via line 22 into and diolefin-free, it may be mixed with th C gasoline reactor 23. It is to be noted that the entire efiluent infraction from line 37 and passed into gasoline motor fuel eluding y gen is passed directly from reactor 18 t0 blending facilities, not shown. Preferably, however, the reactor 23 without any intervening separation thereof. 20 material in line 39 is admixed with hydrogen from sepa- Normally, Sufficient y g has been added to the 3/ rator 31 which has been compressed in compressor 34 tern, as hereinbelow discussed, so that additional quanand being recycled via line 32 The combined hydrogen tities of hydrogen are not needed for the desulfurization and C material is passed via line 40 through heat reaction in reactor 23. changer 25 wherein it is heated significantly to reaction The effluent from reactor 23 is passed through heat 25 temperature and passed into admixture with the C -370 exchanger 20 wherein it gives up heat to the effluent F. material from line 16 as discussed hereinabove. The from reactor 18 in line 19, passes through heat exchange amount of material returned via line 39 into reactor 18 25 Where it gives p additional heat to the hereinafter is chosen so that the Diene Value of thecombined feed to described diluent stream and into admixture with the prereactor 18 is less than 15, preferably, less than 12, and viously mentioned C fraction in line 15. Generally, the t i ll f 5 t 10, It was f nd th t .b operating entire efihlenll from reactor 23 is Passed ly into in this manner that polymer and 'gum formation in reac reactor 27; however, in some cases, it may be advisable to 18 did ot cc to an significant extent, to remove, y means not Shown, y g Sulfide g Thus, it is seen that in substance the present invention prior to introduction to reactor 27 since an excessive provides method for stabilizing pyrolysis gasoline whereamount of hydrogen Sulfide y Cause mercaptan in diolefins are removed from the gasoline fraction withmat n in the third a n ZOIley, however, out destroying the olefins while simultaneously removing as long as the feed in line 16 contains below 1,000 parts diolefins, olefins, and sulfur compounds from the BTX per million by weight (p.p.m.) of hydrogen sulfide, and aromatic fraction. yp y, less than about 500 P-P- 110 Separation of The following example is furnished to demonstrate the H 8 between reactor 23 and reactor 27 is nec ssarv. 4O operation of the present invention. These typical operat- The combined mixture of C hydrocarbons from line i diti r h en; 15 and (3 saturated hydrocarbons in line 24 is passed via line 26 into reactor 27 wherein conditions are main- Reactor #18 Reactor #23 Reactor #27 tained to selectively convert the C diolefins and C ole- Temperature; F 300 650 360 cfin hydrocarbons. The presence of the saturated eflluent E V 801 803 802 in line 24 effectively reduces the Diene Value of the com- HS Pd Pd bined feed to reactor 27 so that polymer and gum formation in the third reaction zone are minimized. The T f d to reactor 18 was a C -370 F. fraction sep effl ent from reactor 27 1S e y Vla line 23, rated from pyrolysis gasoline and the fresh feed to reactor 1 cooler and Passed Vla 11116 Into separatlon 27 was a C fraction separated from the same pyrolysis zone 31. gasoline. The following material balances were obtained COnditiOnS are maintained in Separation Zone 31 Wherewhile operating under the conditions above and with the by a gaseous fraction comprising hydrogen is removed distinctly preferred catalyst previously mentioned:

TABLE I Reactor #27 Reactor #18 Reactor #23 Raw Reactor #18 Fresh Charge Fresh Charge Tot. Product Charge, Fresh Charge, Product, Wt. Product, Wt. 05 Charge, (F.C.) Wt. Wt. Percent Wt. Percent Percent Percent Wt. Percent Percent Chemical Hydrogen Consumption 0.09 C5Pplus N 0.30 C O 2.10

4.80 1.80 1.80 4.70 4.70 1.60 1.60 26.40 26.40 1.20 1.20 1.10 1.10 1.20 1.20 25. 40 25.40 0.70 0.70 0.60 0.60 0.60 0.60 13. 70 18. 70 0.40 0. 4o 0. 40 0. 40 0.40 0.40 8. 50 8.50 8. 370 F. Plus- 4.10

Rerun C01. Bottoms 4.10.

It was noted from the above example that BTX available was not reduced, the olefin content of the gasoline portion of the C s was not significantly lessened, and the olefin content for the aromatic portion was eifectively removed.

PREFERRED EMBODIMENT Thus, a preferred embodiment of the present invention provides a method for stabilizing pyrolysis gasoline which comprises the steps of: (a) separating pyrolysis gasoline into a relatively light fraction and a relatively heavy fraction; (b) introducing said heavy fraction into a first hydrogenation reaction zone under conditions including the presence of a palladium-containing catalyst sufiicient to convert diolefins to olefins; (c) passing the total effluent from the first reaction zone into a second hydrogenation reaction zone under conditions including the presence of a desulfurization catalyst sufficient to substantially saturate olefins and convert sulfur compounds to hydrogen sulfide; (d) admixing the total efiluent from said second zone with said relatively light fraction; (e) passing said admixture into a third hydrogenation reaction zone under conditions including the presence of a palladium-containing catalyst sufficient to convert diolefins to olefins; and, (f) recovering stabilized pyrolysis gasoline from the effluent of the third reaction zone.

Another preferred embodiment of the invention includes the preferred embodiment hereinabove wherein a portion of said stabilized gasoline from Step (f) is returned to Step (b) as diluent in said heavy fraction in an amount sufficient to maintain the combined feed to said first reaction zone at a Diene Value of less than 12.

A distinctly preferred embodiment of this invention provides a method for hydrogenating a sulfur-containing pyrolysis gasoline which comprises the steps of: (a) separating said gasoline into a relatively light fraction comprising C hydrocarbons and a relatively heavy fraction comprising C to 400 F. hydrocarbons; (b) admixing said heavy fraction with hydrogen and 'a hereinafter specified recycle stream and introducing said admixture into a first reaction zone containing hydrogenation catalyst comprising palladium on lithiated alumina under conditions including a temperature from 300 F. to 400 F., a pressure from 200 p.s.i.g. to 1200 p.s.i.g., a liquid hourly space velocity from 1 to 10 based on combined feed and a molar excess of hydrogen sufficient to convert dienes to olefins without substantial conversion of sulfur compounds to hydrogen sulfide; (c) introducing the total efiluent from the first reaction zone into a second reaction zone containing desulfurization catalyst comprising nickel-molybdate on alumina under conditions including a temperature from 600 F. to 800 F. suflicient to substantially convert olefins to saturates and sulfur compounds to hydrogen sulfide; (d) passing the total effiuent from the second reaction zone together with said relatively light fraction into a third reaction zone containing hydrogenation catalyst comprising palladium on lithiated alumina under conditions including the presence of hydrogen at a temperature from 290 F. to 550 F. and a liquid hourly space velocity from 5 to based on combined feed sufiicient to convert dienes to olefins; (e) separating the total efiluent from the third reaction zone into a gaseous fraction comprising hydrogen, a C olefin containing hydrocarbon fraction suitable for gasoline blending, an olefin free aromatic hydrocarbon rich fraction suitable for aromatics extraction, and a gasoline fraction comprising 0 4- hydrocarbons; (f) returning at least a portion of said gasoline fraction to the first reaction zone as said specified recycle stream; and, (g) recycling gaseous fraction of Step (e) to the first reaction zone of Step (b).

The invention claimed:

1. Method for hydrogenating sulfur-containing pyrolysis gasoline which comprises the steps of:

(a) separating said gasoline into a relatively light tfraction comprising C hydrocarbons and a relatively heavy fraction comprising C to 400 F. hydrocarbons;

(b) admixing said heavy fraction with hydrogen and a hereinafter specified recycle stream and introducing said admixture into a first reaction zone in the presence of a palladium-containing catalyst under conditions including a temperature from 200 F. to 400 =F., a pressure from 200 p.s.i.g. to 1200 p.s.i.g., a liquid hourly space velocity from 1 to 10 based on combined feed, and a molar excess of hydrogen, sufficicnt to convert dienes to olefins without substantial conversion of sulfur compounds to hydrogen sulfide;

(c) introducing the total efiluent from the first reaction zone into a second reaction zone containing desulfurization catalyst comprising nickel-molybdate on alumina under conditions including a temperature from 600 F. to 800 F. sufficient to substantially convert olefins to saturates and sulfur compounds to hydrogen sulfide;

(d) passing the effluent from the second reaction zone together with said relatively light fraction into a third reaction zone under conditions including the presence of a palladium-containing catalyst, a molar excess of hydrogen, a temperature from 290 to 550 F., and a liquid hourly space velocity from 5 to 20 based on combined feed, suflicient to convert dienes to olefins;

(e) separating the total effluent from the third reaction zone into a gaseous fraction comprising hydrogen, a C olefin-containing hydrogen fraction suitable for gasoline blending, an olefin-free aromatic hydrocarbon-rich fraction suitable for aromatics extraction, and a gasoline fraction comprising C hydrocarbons;

(f) returning at least a portion of said gasoline fraction to the first reaction zone as said specified recycle stream; and,

(g) recycling gaseous fraction of Step (e) to the first reaction zone of Step (b).

2. Method according to claim 1 wherein the hydrogen admixed with the heavy fraction in Step (b) is in an amount from 500 to 5,000 s.c. f./b. based on combined feed.

3. Method according to claim 1 wherein said palladiumcontaining catalyst com-prises palladium on lithiated alumina.

References Cited UNITED STATES PATENTS 3,133,013 5/1964 Watkins 208-143 3,161,586 12/1964 Watkins 208-143 3,221,078 11/1965 Keith et al. 208-143 3,239,454 3/1966 Streed et al 208-143 3,388,055 6/1968 Craig et al. 208-143 HERBERT LEVINE, Primary Examiner.

U.S. Cl. X.R.

Images