ISOMERIZATION CATALYST AND PROCESS FOR ITS USE

Abstract: The present invention is a process and a catalyst for isomerizing normal and slightly branched C4 to C7 hydrocarbons. The catalyst comprises a Group VIII metal on Beta zeolite.

Description: ISOMERIZATION CATALΪST AND PROCESS FOR ITS USE FIELD OF THE INVENTION The present invention is a process for al ane isomerization. More specifically, the present invention is a process for isomerizing C, to C_ paraffins to increase their octane rating. BACKGROUND OF THE INVENTION The petroleum distillate fraction that contains C. to C_ hydrocarbons is relatively low in octane because it contains substantial amounts of low octane, normal paraffins. For example, normal C , has a blending RON of 62 and normal C g has a blending RON of 19 (blending RON will be hereinafter called "RON"). However, when these paraffins are isomerized to form branched paraffins, thei RON increases dramatically. For example, isopentane ( 2-methyl butane) has a RON of 99 and isohexane (2-methyl- pentane) has a RON of 83. Generally, the RON will increa with even higher branching (e.g., 2, 2-dime thy 1 butane has RON of 89). Several catalysts have been used to isomerize these lower octane paraffins into the branched, higher octane paraffins. Examples are shown in U.S. Patent No. 4,374,296 issued February 15, 1983 to Haag et al.; U.S. Patent No. 3,432,568 issued March 11, 1969 to Miale et al.; U.S. Patent No. 3,673,267 issued June 27, 1972 to Chen et al.; and U.S. Patent No. 4,665,272 issued May 12, 1987 to Bakas et al. Haag et al . disclose isomerizing paraffins using intermediate pore zeolites, which have a constraint index between 1 and 12. Miale et al. describe hydroisomerizing saturated aliphatic and cyclic hydro¬ carbons by contacting them with a dual functional catalys comprising mordenite and a catalytic metal. Chen et al. describe a process for isomerizing paraffins using mordenite having a silica to alumina ratio between 20:1 and 60:1. Bakas et al . disclose isomerizing paraffins using a crystalline aluminosilicate having a catalytic metal. However, even though these prior art catalysts are useful, there remains a need for a new catalyst that is: (1) highly active; (2) highly selective for producing high octane liquid product; and (3) sulfur tolerant. That need is satisfied by the invention that is detailed below. SUMMARY OF THE INVENTION According to the present invention, a catalyst and a process for using the catalyst are provided for isomerizing C. to Cy hydrocarbons. The catalyst comprises a Group VIII metal and Beta zeolite and the process com¬ prises contacting the catalyst with a feed having normal and branched C4 o C 7 hydrocarbons under isomerization conditions. Preferably, the Group VIII metal is platinum and the feed substantially comprises normal and singly branched lower octane C- and Cg hydrocarbons. To improve catalytic activity the catalyst is preferably calcined in a steam/air mixture at an elevated temperature after impregnation with the Group VIII metal. Among other factors, the present invention is based on my finding that a catalyst comprising Beta zeo¬ lite and a Group VIII metal is highly active and highly selective for isomerizing C5 and Cg hydrocarbons. The catalyst is also surprisingly selective for isomerizing Cη hydrocarbons. Additionally, the catalyst is relatively sulfur tolerant. Furthermore, when the catalyst is calcined in a steam/air mixture, higher activity and selectivity are* achieved. More specifically, the process for alkane isomerization comprises contacting a feed containing low octane normal and singly branched C5 and Cg hydrocarbons and less than 0.1 ppm sulfur with a catalyst which comprises Beta zeolite and between 0.1% and 1.0% platinum, at a temperature between 400°F and 600°F, at a pressure between 100 and 500 psig, a H2/HC ratio between 1 and 8, and between 1 and 4 LHSV. . DETAILED DESCRIPTION OF THE INVENTION The following discussion presents a more detailed discussion of the present catalyst. The Catalyst Beta zeolite is a large pore zeolite. Large pore zeolites typically have effective pore diameters e between 6 and 8 Angstroms (A). Beta zeolite has a pore o opening of approximately 7 A. Although its present struc ture is unknown, it is believed to have pore windows formed by twelve-membered rings of silicon and aluminum a toms . Beta zeolite is substantially shown and described in U.S. Patent No. 3,308,069 and Re 28,341 to adlinger et al., and Breck, "Zeolite Molecular Sieves", p. 309 (1984), which are all hereby incorporated by refer ence in their entireties. These references describe a process for making Beta zeolite, its elemental compositio and formula. Preferably, the Beta zeolite of the present invention has a silica to alumina molar ratio between 10 and 1000, more preferably between 15 and 100. It is also preferable that the catalyst have high acidity. The cata lyst's acidity can be increased by ammonium ion exchange and subsequent calcination to yield the hydrogen form. I addition to the hydrogen form, other forms of the zeolite can be used if they are sufficiently acidic. Preferably, the catalyst is substantially free of alkali or alkaline earth metals. Preferably, catalysts of the present invention contain one or more Group VIII metals, e.g., nickel, ruthenium, rhodium, palladium, iridium or platinum. The preferred Group VIII metals are iridium, palladium, and most preferably platinum. The preferred percentage of t Group VIII metal in the catalyst is between 0.05% and 5%, more preferably between 0.1% and 2.5%, most preferably between 0.1% and 1.0%. Group VIII metals are preferably introduced in Beta zeolite by impregnation, occlusion, or exchange in -4- 01 aqueous solution of an appropriate salt. When it is desired to introduce two Group VIII metals into Beta zeo¬ lite, the operation may be carried out simultaneously or 05 sequentially. Preferably, the Group VIII metal is highly dispersed within, and on, the zeolite. By way of example, platinum can be introduced by impregnation with an aqueous solution of tetraammineplati- num (II) nitrate, tetraammineplatinum (II) hydroxide, 10 dinitrodi ami no-platinum or tetraammineplatinum (II) chloride. In an ion exchange process, platinum can be introduced by using cationic platinum complexes such as tetraammineplatinum (II) nitrate. On the other hand, when platinum is introduced into the zeolite by occlusion a 15 platinum complex is preferably introduced into the zeolite during its synthesis. After the desired metal or m tals have been introduced, the catalyst is preferably calcined in air, or air diluted with an inert gas. More preferably, the cata¬ 20 lyst is calcined in a steam/air mixture at an elevated temperature after platinum impregnation. Promoter metals can be added to the catalyst in the manner described above. These metals are preferably selected from Groups VIII, IVA, IB or VIB. 25 The zeolite is preferably bound with a porous matrix. The term "porous matrix" includes inorganic compositions with which the zeolite will effectively bond after appropriate thermal treatment. The matrix porosity 30 can either be inherent or it can be introduced by chemical means. Satisfactory matrices include pumice, firebrick, diatomaceous earth and inorganic oxides. Preferred inor¬ ganic oxides include alumina, silica, naturally occurring or synthetic clays (for example, bentonite, kaolin, ..,. sepiolite, attapulgite, and halloysite). Silica or alumina are especially preferred. Compositing the zeolite with an inorganic oxide matrix can be achieved by any suitable known method wherein the zeolite is intimately admixed with the oxide « Q while the latter is in a hydrous state (for example, as a 01 -5- hydrous salt, hydrogel, wet gelatinous precipitate, or in a dried state, or combinations thereof). A convenient 05 method is to prepare a hydrous mono or plural oxide gel o cogel using an aqueous solution of a salt or mixture of salts (for example, sodium silicate). Ammonium hydroxide (or a similar base) is added to the solution in an amount sufficient to precipitate the oxides in hydrous form. 10 Then, the precipitate is washed to remove most of the water soluble salts and it is thoroughly admixed with the zeolite which is in a finely divided state. Water or lubricating agents can be added in an amount sufficient t facilitate shaping of the mix (e.g., by extrusion). 15 The Process Once the catalyst has been formed it can be employed in any of the conventional types of process equipment known to the art. It may be employed in the form of pills, pellets, granules, broken fragments, or 20 various special shapes. It can be disposed as a fixed or moving bed within a reaction zone, and the charging stock can be passed therethrough as a liquid, vapor, or mixed phase, and in upward, downward, or radial flow. Alternatively, it could be prepared for use in fluidized- 2 ~ solid processes, in which the charging stock is passed upward through a turbulent bed of finely divided catalyst However, in view of the danger of attrition losses of the valuable catalyst and the well-known advantages of plug flow reactors either a fixed bed system or a dense-phase - 0 moving bed system is preferred. In a fixed bed system, the feed is preheated (by any suitable heating means) to the desired reaction temperature and then passed into a isomerization zone containing the catalyst. This isomer ization zone may be one or more separate reactors with - } " > suitable means to maintain the desired temperature at th entrance to each reactor. After reaction, the products from any of the foregoing process variants are separated from the catalyst, reduced to atmospheric pressure, and fractionated to recover the various components thereof. 40 Additionally, the process can be operated in once-throug -6- or, preferably, with recycle of normal paraffins. Recycle operations are within the knowledge of skilled prac itioners. As discussed above, the petroleum distillate fraction preferably contains normal and singly branched C . to Cη Paraffins. The feed preferably contains few multiply branched components such as 2,2-dimethylbutane and 2,3- imethylbutane. However, when the low octane paraffins are isomerized to form multiply branched paraf¬ fins (such as the di ethylbutanes, for example), the octane number increases dramatically. This is the function of the present catalyst. The present catalyst is highly active and highly selective for isomerizing C 4 to Cη hydrocarbons. This hig selectivity means that in comparison to prior art cata¬ lysts, such as mordenite, a higher product yield can be achieved when the two catalysts are run to a given octane. It also means that a higher octane can be achieved when the two catalysts are run to produce a given liquid yield. The present process comprises contacting the isomerization catalyst with a hydrocarbon feed under isomerization conditions. The feed is preferably a light straight run fraction, boiling within the range of 30°F to 250°F and preferably from 60°F to 200°F. Preferably, the hydrocarbon feed for the process comprises a substantial amount of C^ to C 7 normal and singly branched hydrocarbons more preferably low octane C^ and Cg hydrocarbons. The pressure in the process is preferably between 50 psig and 1000 psig, more preferably between 100 and 500 psig. The liquid hourly space velocity (LHSV) is preferably between about 1 to about 10 with a value in the range of about 1 to about 4 being more preferred. It is * j also preferable to carry out the isomerization reaction in the presence of hydrogen. Preferably, hydrogen is added to give a hydrogen to hydrocarbon ratio (H ^ /HC) of between 0.5 and 10, more preferably between 1 and 8. The tempera¬ ture is preferably between about 200°F and about 1000°F, Q more preferably between 400°F and 600°F. As is well known to those skilled in the isomerization art, the initial selection of the temperature within this broad range is made primarily as a function of the desired conversion level considering the characteristics of the feed and of the catalyst. Thereafter, to provide a relatively constant value for conversion, the temperature may have to be slowly increased during the run to compensate for any deactivation that occurs. The present catalyst is relatively sulfur tolerant. Nonetheless, a low sulfur feed is especially preferred ih the present process. The feed preferably contains less than 10 ppm, more preferably less than 1 ppm, and most preferably less than 0.1 ppm sulfur. In the case of a feed which is not already low in sulfur, acceptable levels can be reached by hydrotreating the feed in a pretreatment zone with a hydrotreating catalyst which is resistant to sulfur poisoning. Sulfur can be subse¬ quently removed as hydrogen sulfide in the gas phase after condensation of the liquid product. An example of a suitable catalyst for this hydrodesulf urization process is an alumina-containing support and a minor catalytic pro¬ portion of molybdenum oxide, cobalt oxide and/or nickel oxide. Hydrodesulf urization is typically conducted at 315°C to 455°C, at 200 to 2000 psig, and at a liquid hourly space velocity of 1 to 5. It is also preferable to limit the nitrogen level and the water content of the feed. Catalysts and processes which are suitable for these purposes are known to those skilled in the art. After a period of operation the catalyst can become deactivated by sulfur or coke. Sulfur and coke can be removed from the catalyst using procedures that are known to those skilled in the art. The present invention will be more fully understood by reference to the following examples. They are intended to be purely exemplary and are not intended to limit the scope of the invention in any way. EXAMPLES Example 1 5 In a 2-l i ter glass liner, 8.29 g s of Mallinkrodt sodium aluminate (Na2θ. A^^ . S^O) was dissolved i n 259.6 gms of an aqueous solution containing 20% tetraethyl ammonium hydroxide (Aldrich ) . 207.5 Grams of Ludox AS-30 colloidal silica was added in a thin stream while the 0 solution was vigorously stirred . The liner was placed in a 2-liter Parr stainless steel bomb and statical ly heated for 6 days at 150°C. The solid, precipitate product was > washed and dried, after which it was determined to be Beta zeolite by X-ray dif fraction. , c Be ta zeoli te was made more catalytical ly active by converting it into its hydrogen (proton ) form as follows . Beta zeoli te was layered in a thin bed and incrementally heated to 1000°F at a rate of 150°/hr. The temperature was maintained at 1000°F for 5 hours and then 20 it was increased to 1100°F for 4 more. The calcined zeo¬ l ite was ion-exchanged by 4 successive treatments with NH4NO3. Each trea tment used the same mass of H^ O^ to zeolite (a slurry of about 50 gr. zeolite/l iter H2 0 ) and the solution was re fluxed for at leas t 2 hours. The 25 sodium content of the zeolite was low after the fourth exchange . The zeolite was f iltered, washed , dried and recalcined as above wh ile omi tting the 1100°F heating ste . The f inal Beta zeolite was impregnated wi th 30 enough tetraamine plati num nitrate to achieve 0.8 wt . % platinum. Thereafter, the impregnated catalyst was dried at 250°F for approximately 14 hours then calcined a t 500°F for 3 hours , and then reduced. Example 2 35 The catalyst of Example 1 was used to isomerize a feed which substantially comprised normal and branched C 5 and Cg hydrocarbons. The isomerization conditions were 1 LHSV, 200 psig, 6 H 2 /HC, and 520°F. The feed compo¬ sition and the isomerization results are shown in Table I. 40 Example 3 A commercial mordenite (Zeolon 10OH) was obtained from Norton Chemical Company and platinum impreg¬ nated as in Example 1. The final catalyst contained 0.8 wt.% platinum. Example 4 This example compares the liquid yields achievable with the catalysts of Example 1 and Example 3, which both contained 0.8% platinum. Both catalysts were used to iso erize normal C5, Cg, and Cγ pure component feeds at 500°F, 100 psig, and 6H2/HC. The liquid yields and corresponding octanes that were obtained for the two catalysts are shown in FIG. 1. Example 5 Pla tinum was impregnated onto samples of Be ta zeoli te and mordeni te at va ryi ng levels . Both catalysts were used to isome rize a normal hexane feed at 510°F , 100 ps ig , 3 LHSV, and 6H 2 HC. The results are shown i n -10- 1 Table II. The relative intrinsic activity for each catalyst at low conversion was calculated and is shown in FIG. 2. 5 *Temp. raised to 540°F due to low activity. Example 6 0 This example demonstrates the effect of sulfur on platinum/Beta zeolite and platinum/ mordenite catalysts. Each catalyst was contacted with the feed of Table I at 520°F, 200 psig, 6H 2 HC, and 1 LHSV for 24 hours. Then H-s was continuously added to the reactor inlet H 2 and into 5 the feed for 24 hours. The H 2 S addition rate was sufficient to give approximately 250 ppm sulfur on a feed weight basis. Thereafter, the H 2 s was removed and the catalysts were only contacted with clean feed and clean hydrogen. The results are shown in Table III. 0 5 0 -11- 1 The conventional platinum on mordenite catalyst suffers a relatively larger loss in liquid yield than platinum on Beta zeolite catalyst. Additionally, when 5 sulfur is withdrawn, both catalysts recover from sulfur poisoning, but the liquid yield from the platinum/Beta zeolite is relatively higher. Example 7 This example demonstrates a preferred method of 10 platinum loading which includes a steam calcination step after platinum impregnation. Beta zeolite was prepared in the manner set forth in Example 1. Platinum was impregnated onto the Beta zeolite to achieve 0.3 wt.% and then samples of the 15 catalyst were subjected to different calcination treatments. The different catalysts were then used to isomerize the feed of Table I at 200 psig, 1 LHSV, 6 H 2 /HC, for 20 hours. The results are shown in Table IV. 20 TABLE IV Isomerate Properties Calcination Reaction 2,2-DMB/ Yield TON Catalyst Conditions Temperature i/nC,. nCg (LV%) (Calc.) 25 0.3% Pt/ 500°F in 520°F 1.7 0.6 97.4 79.5 Beta Air 0.3% Pt/ 500°F in 515°F 1.8 1.0 97.8 79.9 Beta 50% Steaπ 50% Air 30 0.3% Pt/ 600°F in 520°F 2.1 0.9 97.0 80.1 Beta 50% Steam/ 50% Air When the catalysts were calcined in a steam/air 35 mixture, the product ratios of iso to normal C 5 hydrocar¬ bons (i/nC 5 ) and 2, 2-dimethylbutane to normal C g hydrocar bons ( 2,2-DMB/nCg) increased, which in turn increased the product RON. Additionally, this increase was achieved at 40 a lower reaction temperature which indicated an increase in catalyst activity. The embodiments of this invention which are exemplified above are intended solely as illustrations of the invention. They should not be interpreted as limiting the scope of the invention to just those features which are shown or disclosed. As those familiar with this area of research will appreciate, there are numerous variations of the invention as defined in the following claims which may have not been exemplified but which will achieve equivalent results.

Claims: -13- WHAT IS CLAIMED IS: 1. A process for isomerizing C^ to C hydrocarbons, 5 comprising contacting a catalyst, comprising at least one Group VIII metal and Beta zeolite, with a feed having C. to C 7 hydrocarbons under isomerization conditions. 0 2. A process in accordance with Claim 1 wherein the catalyst has been calcined in a steam/air mixture at an elevated temperature after impregnation of the Group VIII metal. 5 3. A process in accordance with Claim 1 wherein th Group VIII metal is platinum. 4. A process in accordance with Claim 3 wherein th catalyst comprises between 0.05% and 5% platinum. 0 5. A process in accordance with Claim 3 wherein th catalyst comprises between 0.01% and 2.5% platinum. 6. A .process in accordance with Claim 1 wherein th feed comprises normal and singly branched C,. and Cg hydrocarbons . 7. A process in accordance with Claim 6 wherein th temperature is between 200°F and 1000°F, the pressure is 0 between 50 and 1000 psig, the LHSV is between 1 and 10, and a H 2 /HC ratio between 0.5 and 10. 8. A process for alkane isomerization, comprising: contacting a feed containing normal and singly branched C j c, and Cg hydrocarbons with a catalyst, which comprises Beta zeolite and between 0.1% and 1.0% platinum, at a tempera¬ ture between 400°F and 600°F, at a pressure between 100 and 500 psig, a H 2 /HC ratio between 1 and 8, and between and 4 LHSV. 40 9. A process for alkane isomerization, comprising: contacting a feed containing normal and singly branched Cc and C hydrocarbons and less than 0.1 ppm sulfur with a catalyst, which comprises Beta zeolite and between 0.1% and 1.0% platinum, at a temperature between 400°F and 600°F, at a pressure between 100 and 500 psig, a H 2 /HC ratio between 1 and 8, and between 1 and 4 LHSV. 10. An alkane isomerization catalyst for isomerizing C 4 to Cη hydrocarbons, comprising a Group VIII metal and Beta zeolite wherein the catalyst has been calcined in a steam/air mixture at an elevated temperature after impregnation with the Group VIII metal. 11. A catalyst in accordance with Claim 10 wherein the Group VIII metal is platinum. 12. A catalyst in accordance with Claim 11 wherein the catalyst comprises between 0.05% and 5% platinum. 13. A catalyst in accordance with Claim 12 wherein the catalyst comprises between 0.1% and 2.5% platinum. 14. A catalyst in accordance with Claim 10 wherein the Beta zeolite has a silica to alumina ratio between 15 and 100.

Inventors: HOLTERMANN DENNIS L, HOLTERMANN, DENNIS, L.
Applicants: CHEVRON RES & TECH, CHEVRON RESEARCH AND TECHNOLOGY COMPANY
Application year: 1990
Main classification: C07C5
IPC codes: B01J29, C07B61, C07C5, C07C9, C07C15, C10G35