US 3865716 A
The olefinic components of hydrocarbon streams containing both olefins and aromatics can be selectively hydrogenated using a catalyst comprising (1) an amorphous base component, (2) a crystalline aluminosilicate component preferably comprising 10 to 30 wt.% of the total catalyst and having a silica/alumina mole ratio of at least 2.5 and an alkali metal content of less than about 2.0 wt.% and (3) a transition metal hydrogenation component.
Description (OCR text may contain errors)
Un ted States Patent 1191 1111 Sosnowski 1451 Feb. 11, 1975 PROCESS FOR THE SELECTIVE 3,379,640 4/1963 Chen et a1. 208/111 HYDROGENATION 0F OLEFINS 3,547,807 12/1970 Hansford et 1111. 208/1 1 1 3,600,301 8/1971 Rausch 208/255 John Sosnowski, Westfield, NJ.
Exxon Research and Engineering Company, Linden, NJ.
Filed: Sept. 13, 1973 Appl. No.: 397,001
U.S. c1 208/255, 260/683.9, 208/143 1111. c1. Cl0g 23/06 Field Of Search 208/255, 134, 111, DIG. 2,
References Cited UNITED STATES PATENTS Primary Examiner-Delbert E. Gantz Assistant ExaminerJuanita M. Nelson Attorney, Agent, or Firm-A. D. Litt  ABSTRACT The olefinic components of hydrocarbon streams con taining both olefins and aromatics can be selectively hydrogenated using a catalyst comprising l an amorphous base component, (2) a crystalline aluminosilicate component preferably comprising 10 to 30 wt.7( of the total catalyst and having a silica/alumina mole ratio of at least 2.5 and an alkali metal content of less than about 2.0 wt.% and (3) a transition metal hydrogenation component.
10 Claims, No Drawings PROCESS FOR THE SELECTIVE HYDROGENATION OF OLEFTNS BACKGROUND OF THE INVENTION Field of the Invention This invention relates to hydrocarbon conversion processes. More particularly, this invention relates to processes for the selective hydrogenation of olefinic compounds in hydrocarbon streams containing both olefinic and aromatic compounds.
DESCRIPTION OF THE PRIOR ART Mixtures of hydrocarbons resulting from various hydrocarbon conversion processes often contain unsaturated compounds (primarily monoolefins and diolefins) and various aromatics compounds. It is desirable for many purposes to convert the olefinic compounds to saturated compounds by hydrogenation. At the same time, however, it is not usually desired to hydrogenate the aromatic compounds. For example, in the production of gasoline, it is necessary to hydrogenate the olefinic constituents in order to assure stability. However, hydrogenation of the aromatic components would be detrimental in that the octane value of the gasoline would be lowered. Also, it is desired for some purposes, for example the manufacture of lead-free gasoline, to extract aromatics from catalytically cracked naphthas and cycle oils. Most polar solvents and adsorbents would remove olefins along with the aromatics. Since olefins are not desirable in low emissions gasoline, it would be advantageous to saturate the olefins prior to the extraction step. For this purpose, one would require a saturation process which would hydrogenate only the olefins and not the aromatics.
Various processes have been proposed to achieve the selective hydrogenation of olefins. These involve, typically, multi-step operations such as that illustrated in U.S. Pat. No. 3,580,837. As such, they are not economically attractive.
SUMMARY OF THE INVENTION It is therefore the principal object of this invention to provide a single step process for selectively hydrogenating olefinic compounds in hydrocarbon streams containing both olefins and aromatics while, at the same time, not hydrogenating the aromatic compounds.
According to this invention, olefinic compounds present in mixed hydrocarbon streams containing olefins and aromatics are selectively hydrogenated in a single step process using a catalyst comprising (1) an amorphous base component, (2) a crystalline aluminosilicate component preferably comprising to wt.% of the total catalyst and having a silica/alumina mole ratio of at least 2.5 and an alkali metal content of less than about 2.0 wt.% (as alkali oxide) and (3) a transition metal hydrogenation component selected from the oxides and sulfides of Group VI-B and/or VIII metals of the Periodic Table.
Feedstocks usable in the practice of this invention can be any mixed hydrocarbon stream containing both olefins and aromatic compounds. By olefins is meant compounds having a single ethylenic double bond (monoolefins) as well as those containing multiple ethylenic double bonds (diolefins, etc.) and including conjugated diolefins. Specific feedstocks include steam cracked naphthas, catalytically cracked naphthas,
cycle oils, raw mineral oils, various hydrocarbon distillates, etc. The present invention is applicable to finished products where it is desired to selectively hydrogenate olefinic compounds as well as to hydrocarbon streams intended for further conversion processes.
The process of this invention can be effected at reaction conditions hereinafter set forth and in contact with the catalyst herein described in any conventional or otherwise convenient manner. For example, the hydrocarbon stream to be treated can be charged to a high pressure vessel utilized as a hydrotreater. The hydrocarbon stream can be commingled with hydrogen prior to its being charged to the hydrotreater or the hydrocarbon stream and the hydrogen can be charged thereto in individual and separate streams. Preferably, the catalyst is disposed in one or more fixed beds within a reaction zone of the hydrotreater and the hydrocarbon stream and hydrogen being charged upf|ow or down-flow in contact therewith. The hydrotreater effluent is preferably cooled and then passed to a high pressure separator where it is separated into a normally liquid hydrotreated product and a normally gaseous stream. The gaseous stream, which comprises princi pally hydrogen, is suitably recycled to the hydrotreater; although, if desired, it may be vented for the purpose of maintaining hydrogen purity. In addition, either this gaseous stream or cooled liquid product or both can be recycled to the reaction zone to remove the exothermic heat of reaction and thereby maintain the desired operating temperatures.
The operative and preferred hydrogenation condi tions in the process of this invention are as follows:
Contact time of the catalyst, hydrocarbon feedstock and hydrogen can vary widely, being dependent in part upon the temperature and space velocities employed. In general, contact time may range from 15 minutes to about 8 hours, preferably from about I hour to 2 hours.
The choice of inlet temperatures is based on economic and safety considerations and is dictated by reactor design rather than by catalyst limitations. High inlet temperatures will result in rapid temperature increases due to the exothermic nature of the hydrogenation reaction and large quantities of a cold quenching medium will be required to prevent excessively high temperatures. On the other hand, ultra low temperatures will not initiate the reaction. The inlet temperatures should be as low as possible, but suitable to initiate the reaction. As the catalyst deactivates with use, the inlet temperatures can be raised as required to initiate the reaction. The exothermic nature of the reaction will then cause the temperature of the reacting mixture to rise to the desired levels.
A further reason for maintaining low inlet tempera tures is to minimize polymerization of highly unsaturated compounds which may be present in the feed. These polymerized compounds could be deposited within the catalyst pore structure and thereby deactivate the catalyst, or could be deposited within the interstices between the catalyst particles and thereby plug the catalyst beds. The severity of these problems will depend on the degree of unsaturation of the feed.
Reactor outlet temperatures should be maintained below 700F to prevent excessive hydrogenation of the aromatics. With highly active fresh catalyst, hydrogenation of aromatics will occur at 650F with a long residence time of the reaction mixture within the catalyst zone. Therefore, the residence time should be minimized at temperatures above 450F with relatively fresh catalyst if total saturation of the olefins is desired.
With highly unsaturated feeds, i.e., greater than 50 Bromine Number, and/or containing large amounts of sulfur, i.e., greater than 400 wppm, the process conditions employed to prevent aromatics saturation may not be sufficient to prevent formation of mercaptan within the reaction zone. In these instances, it may be desirable to include a bed of conventional hydrodesulfurization catalyst at the outlet of the reactor. This bed would operate at reactor outlet or higher temperatures, and at space velocities greater than about 2 V/V/Hr. ln addition, it may be desirable to introduce a stream of hot recycle gas to this last catalyst bed to further increase temperature for any required desulfurization.
Using the catalysts described herein under preferred conditions, the following product quality improvements can be expected upon hydrogenating an olefinic naphtha derived from steam cracking a vacuum gas oil.
Feed Product Bromine No., eg/gm 80 1.5 Dicue No. 20 Sulfur, wppm 1510 7 Gum Tests, mg/l00 ml Existent 85* 1 Copper Beaker 170* 4 Clear Octane Numbers RON 100.5 99 MON 86.5 86.5 Benzene Content, wt% 32 30 Inhibited with Tenamene- 2 using 1 lb. of inhibitor per 5000 gal. of feed.
With olefinic naphthas derived from steam cracking light feeds, such as virgin naphthas, the totally hydrogenated C /375F product (1.0 Bromine Number) can still contain 79 wt.% total aromatics (34 wt.% benzene).
In many situations, the degree of olefin saturation cited in the aforementioned examples may not be necessary. Within the scope of the present invention, naphthas having satisfactory stability as gasoline components can be produced without total saturation of the olefins. For example, a naphtha containing 100 Bromine Number could be partially saturated to 66 Bromine Number. Existent gum should be reduced from 1000 to about 5 mg/100 ml and copper beaker gum from 620 to about mg/100 ml. This partially hydrogenated naphtha could still be suitable for use in gasoline.
Critical to the practice of this invention is the nature of the catalyst, which will now be more fully described.
The catalyst used in the process of this invention comprises a mixture of (1 an amorphous component, (2) 5 to 70 wt.% (based on total catalyst) of a crystalline aluminosilicate component and (3) a hydrogenation component. Catalysts of this type are exemplified and described more completely in US. Pat. Nos. 3,547,807 and 3,304,254, the disclosures of which are incorporated herein by reference.
Preferably, the catalyst comprises a mixture of 1 a major component, i.e. greater than 50 wt.%, comprising an amorphous support upon which is deposited one or more transitional metal hydrogenation components, preferably selected from Groups Vl-B and V111 metals of the Periodic Table and/or the oxides and/or sulfides thereof and (2) a minor component comprising a crystalline aluminosilicate zeolite having a silica/alumina mole ratio greater than about 2.5 and an alkali metal content of less than 2.0 wt.% (as alkali metal oxide) based on the final aluminosilicate composition, and containing deposited thereon or exchanged therewith one or more transitional metal hydrogenation components preferably selected from Groups Vl-B and V111 metals of the Periodic Table and/or the oxides and/or sulfides thereof.
The amorphous component (support) of the catalyst can be one or more of a large number of non-crystalline materials having high porosity. The support is desirably inorganic; however, it may be an organic composition. Representative materials that can be employed include metals and metal alloys; sintered glass; firebrick; diatomaceous earth; inorganic refractory oxides; organic resins, such as polyesters, phenolics and the like; metal phosphates such as boron phosphate, calcium phosphate and zirconium phosphate; metal sulfides such as iron sulfide and nickel sulfide; inorganic oxide gels and the like. Preferred inorganic oxide support materials include one or more oxides of metals selected from Groups ll-A, lll-A and IV of the Periodic Table. Nonlimiting examples of such oxides include aluminum oxide, titania, zirconia, magnesium oxide, silicon oxide, titanium oxide, silica-stabilized alumina and the like.
Suitable hydrogenation components that can be added to the support are the transitional metals and/or the oxides and/0r sulfides thereof. The metals are prefer ably selected from Groups Vl-B and V111 of the Periodic Table and are exemplified by chromium, molybdenum, tungsten, cobalt, nickel, palladium, iron, rhodium, and the like. The metals, metal oxides or sulfides may be added alone or in combination to the support. The preferred hydrogenation components are nickel, tungsten and molybdenum metals and the oxides and- /or sulfides thereof. In use, the hydrogenation components probably exist in a mixed metal/metal oxide or metal/metal oxide/metal sulfide form. The hydrogenation components are added to the support in minor pro portions ranging from about 1 to 25% by weight based on the total amorphous component of the catalyst.
Preferably, the catalyst composition comprises a silica/alumina support containing molybdenum trioxide and nickel oxide hydrogenation components. The silica/alumina weight ratio in the amorphous support can range from 20:1 to 1:20 and preferably from 1:4 to 1:6. The molybdenum trioxide/nickel oxide weight ratio in the amorphous support can range from about 1:25 to 25:1 and preferably from 10:1 to 4:1. Finally, the weight ratio of the support to the hydrogenation component can range from about 20:1 to 1:20 and preferably from 4:1 to 8: 1. A particularly preferred catalyst composition comprises:
The catalyst is preferably presulfided by conventional methods such as by treatment with hydrogen sulfide or carbon disulfide prior to use. The precise chemical identity of the hydrogenation constituents present on the support during the course of the hydrogenation operation is not known. However, the hydrogenation components probably exist in a mixed elemental metal/metal oxide/metal sulfide form.
The amorphous component of the catalyst can be prepared in any suitable manner. Thus, for example, if silica-alumina is employed, the silica and alumina may be mechanically admixed or, alternatively, chemically composited with the metal oxides such as by cogelation. Either the silica or alumina may, prior to admixture with the other, have deposited thereon one or more of the metal oxides. Alternatively} the silica and alumina may first be admixed and then impregnated with the metal oxides.
The crystalline aluminosilicate (sieve component) employed in the preparation of the crystalline component of the catalyst comprises one or more natural or synthetic zeolites. Representative examples of particularly preferred zeolites are zeolite X, zeolite Y, zeolite L, faujasite and mordenite. Synthetic zeolites have been generally described in US. Pat. Nos. 2,882,244, 3,130,007 and 3,216,789, the disclosures of which are incorporated herein by reference.
The silica/alumina mole ratio of useful aluminosilicates is greater than 2.5 and preferably ranges from about 2.5 to 10. Most preferably this ratio ranges between about 3 and 6. These materials are essentially the dehydrated forms of crystalline hydrous siliceous zeolites containing varying quantities of alkali metal and aluminum with or without other metals. The alkali metal atoms, silicon, aluminum and oxygen in the zeolites are arranged in the form of an aluminosilicate salt in a definite and consistent crystalline structure. The structure contains a large number of small cavities, interconnected by a number of still smaller holes or channels. These cavities and channels are uniform in size. The pore diameter size of the crystalline aluminosilicate can range from 5 to A and preferably from 5 to lOA.
The aluminosilicate component may comprise a sieve of one specific pore diameter size or, alternatively, mixtures of sieves of varying pore diameter size. Thus, for example, mixtures of 5A and 13A sieves may be employed as the aluminosilicate component. Synthetic zeolites such as type-Y faujasites are preferred and are prepared by well-known methods such as those described in US, Pat. No. 3,130,007.
The aluminosilicate can be in the hydrogen form, in the polyvalent metal form, or in the mixed hydrogen polyvalent metal form. The polyvalent metal or hydrogen form of the aluminosilicate component can be prepared by any of the well-known methods described in the literature. Representative of such methods is ion exchange of the alkali metal cations contained in the aluminosilicate with ammonium ions or other easily decomposable cations such as methyl-substituted quaternary ammonium ions. The exchanged aluminosilicate is then heated at elevated temperatures of about 300-600C. to drive off ammonia, thereby producing the hydrogen form of the material. The degree of polyvalent-metal or hydrogen exchange should be at least about 20%, and preferably at least about 40% of the maximum theoretically possible. In any event. the crystalline aluminosilicate composition should contain less than about 6.0 wt.% of the alkali metal oxide based on the final aluminosilicate composition and, preferably, less than 2.0 wt.%, i.e. about 0.1 wt.% to-0.5 wt.% or less.
The resulting hydrogen aluminosilicate can be employed as such, or can be subjected to a steam treatment at elevated temperatures, i.e. 427 to 704C. for example, to effect stabilization thereof against hydrothermal degradation. The steam treatment, in many cases, also appears to effect a desirable alteration in crystal structures resulting in improved selectivity.
The mixed hydrogen-polyvalent metal forms of the aluminosilicates are also contemplated. In one embodiment the metal form of the aluminosilicate is ionexchanged with ammonium cations and then partially back-exchanged with solutions of the desired metal salts until the desired degree of exchange is achieved. The remaining ammonium ions are decomposed later to hydrogen ions during thermal activation. Here again, it is preferred that at least about 40% of the monovalent metal cations are replaced with hydrogen and polyvalent metal ions.
Suitably, the exchanged polyvalent metals are transition metals and are preferably selected from Groups VI-B and VII] of the Periodic Table. Preferred metals include nickel, molybdenum, tungsten and the like. The most preferred metal is nickel. The amount of nickel (or other metal) present in the aluminosilicate (as ion-exchanged metal) can range from about 0.1 to 20% by weight based on the final aluminosilicate com position.
In addition to the ion-exchanged polyvalent metals, the aluminosilicate may contain as non-exchanged constituents one or more hydrogenation components comprising the transitional metals, preferably selected from Groups Vl-B and VIII of the Periodic Table and their oxides and sulfides. Such hydrogenation components may be combined with the aluminosilicate by any method which gives a suitably intimate admixture, such as by impregnation. Examples of suitable hydrogenation metals, for use herein, include nickel, tungsten, molybdenum, platinum, and the like, and/or the oxides and/or sulfides thereof. Mixtures of any two or more of such components may also be employed. Particularly preferred metals are tungsten and nickel. Most preferably, the metals are used in the form of their oxides. The total amount of hydrogenation components present in the final aluminosilicate composition can range from about 1 to 50 wt.%, preferably from 10 to 25 wt.% based on the final aluminosilicate composition. The final weight composition of the crystalline component of the total catalyst will range from about 10 to wt.% and preferably from about 10 to 30 wt.%, eg 20 wt.% based on total catalyst.
The amorphous component and the crystalline aluminosilicate component of the catalyst may be brought together by any suitable method, such as by mechanical mixing of the particles thereby producing a particle form composite that is subsequently dried and calcined. The catalyst may also be prepared by extrusion of wet plastic mixtures of the powdered components followed by drying and calcination. Preferably, the
complete catalyst is prepared by mixing the metalexchanged zeolite component with alumina or silicastabilized alumina and extruding the mixture to form catalyst pellets. The pellets are thereafter impregnated with an aqueous solution of nickel and molybdenum or tungsten materials to form the final catalyst.
Other modifications of the present invention will occur to those skilled in the art upon a reading of the present disclosure. These are intended to be included within the scope of this invention.
What is claimed is:
l. A process for selectively hydrogenating olefins in a hydrocarbon stream containing both olefins and aromatic compounds, which comprises contacting the hydrocarbon stream with hydrogen under hydrogenation conditions in the presence of a catalyst comprising a mixture of 1) an inorganic non-crystalline base component, (2) a crystalline aluminosilicate component comprising from to 70 wt.% of the total catalyst and having a silica/alumina mole ratio of at least 2.5 and an alkali metal content of less than about 2.0 wt.% (as alkali oxide), based on the total aluminosilicate component, and (3) a transitional metal hydrogenation component.
2. The process of claim 1 wherein hydrogenation is effected at a temperature ranging from about 150 to about 700F, a pressure ranging from about 100 to about 1000 psig., a hydrogen feed rate of greater than about 500 SCF/B and a contact time ranging from about minutes to about 8 hours.
3. The process of claim 1 wherein the crystalline aluminosilicate component of the catalyst comprises from 10 to 30 wt.% of the total catalyst.
4. The process according to claim 3 in which the inorganic non-crystalline base component of the catalyst comprises alumina.
5. The process according to claim 4 in which the amorphous base component of the catalyst is silicastabilized alumina in which the ratio of silica to alumina is from 1:4 to 1:6.
6. The process according to claim 4 in which the amorphous base component of the catalyst is silicastabilized magnesia in which the ratio of silica to magnesia is from 1:4 to 1:6.
7. The process according to claim 1 in which the transitional metal hydrogenation component is a Group Vl-B or Vlll metal of the Periodic Table and/or an oxide and/or a sulfide thereof.
8. The process according to claim 1 wherein the hydrogenation component is present in amounts ranging from 1 to about 25% by weight based on the total inorganic non-crystalline component of the catalyst.
9. The process of claim 7 in which the hydrogenation component is selected from the group consisting of the oxides and sulfides of nickel, molybdenum and tungsten and mixtures thereof.
10. The process according to claim 1 wherein the catalyst comprises:
NiO 2 wt.% M00 16 wt.% S10 14 wt.% M 0 66.4 wt.% Na O 0.08 wt.%