CA2044103A1 - Crystalline silicate catalyst and a reforming process using the catalyst - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
The preferred reforming catalyst has a high silica to alumina molar ratio and a small crystallite size. The reforming process using the catalyst is prefer-ably run without added hydrogen, and at low pressures and temperatures.

Description

~ ..&~

A CRYSTALLINE SILICAT~ CATALYST
AND A REFORMING PROCESS ~SING THE CATALYST
SBACKGROUND OF THE INVENTION

The present invention relates to a cry~talline silicate reforming catalyst and a process using the cata-lyst. More speciically, a ccmbination o process condi~
tions and improvements in the catalyst result in a low 1~ fouling rate.
Catalytic reforming is well known in the petroleum industry and refers to the treatment of naphtha fractions to improve the octane rating by the production of aromatics. The more important hydrocarbon reactions occurring during reforming include dehydrogenation of cyclohexanes to aromatics, dehydroisomerization of alkyl-cyclopentanes to aromatics, and dehydrocyclization of acyclic hydrocarbons to aromatic~;. A number of other reactions also occur, including t:he following: dealkyla-tion of alkylbenzenes, isomerization of paraffins, and hydrocracking reactions which prc~duce light gaseous hydro-carbons, e.g., methane, ethane, propane and butane.
Hydrocracking reaction~ are to be particularly minimized during reforming as they decrease the yield of gasoline boiling products and hydrogen.
Because of the demand for high octane gasoline for use as motor fuels, etc., extensive research is being devoted to the development of improved reforming catalysts and catalytic reforming processes. Catalysts for success-ful reforming processes must possess good selectivity.
That is, they must be able to produce high yields of liquid products in the gasoline boiling range which con-tain large concentrations of high octane aromatic hydro-carbons and low concentrations of light gaseous hydrocarbonsu Also, the catalysts should possess good acti~ity in order that the ~emperature required to produce a certain quality product need not be too high It is also necessary that catalysts either possess good stability in order that the activity and selectivity characteristics can be retained during prolonged periodsof operation, or be sufficiently regenerable to allow fre-05 quent regeneration without loss of performance.
Reforming catalysts are usually composed of a highly dispersed transition metal(s) on a metal oxide sup-port. Typically, the transition metal i5 a noble metal, most notably platinum. However, there are numerous metal oxide supports. Examples are: silica, alumina, and a plethora of natural and man-made zeolites. Silicalite is one of those zeolites.
Silicalite is an intermediate pore zeolite and has a high silica:alumina (SiO2:AlO3) ratio. Examples of its methods of manufacture can be shown in: Dwyer et al, U.S. Patent Nos. 3,941,871, issued March 2, 1976 and 4,441,991, issued April 10, 1984; and Derouane et al, EPO
Application No. 186,479, published February 7, 1986, all of which are incorporated by reference in their entirety.
Dwyer et al suggest that a platinum-loaded sili-calite catalyst can be used in reforming hydrocarbons, as well as other typss of reactions~, The process conditions in Dwyer et al are listed as: a temperature between 700F
and 1000F; a pressure between 100 psig and 1000 psig (preferably 200-700 psig); a liquid hourly space velocity ~LHSV~ between 0.1 and 10 (preferably between 0.5 and 43;
and a hydrogen to hydrocarbon (H2/HC) mole ratio between 1 and 20 (preferably 4 and 12). Detz et al, U.S. Patent No, 4,347,394, issued ~ugust 31, 1982, disclose a process for selectively producing benzene using a catalyst having platinum on an intermediate pore zeolite which is sub-stantially free of acidity (such as silicalite)~ The process conditions can be: temperatures greater than 480C (more preferably at relatively high temperatures, such as between 510C and 595C); pressures of between atmospheric and 10 bar; an LHSV between 0.1 to 15; and hydrogen may or may not be added. P. Jacobs et al, "Comparison of Acid to Metal Catalyzed Conversion of N-decane and Cyclodecane on ZSM-5 and Faujasite-type ~eolites", J. Mol. Cat., 27, 11 (1984) show reacting a

2 ~ .... L ~

~1 -3-platinum silicalite catalyst with the test compounds n-decane and cyclodecane.
05 Reforming at low pressure in the absence of added hydrogen produces a relatively high liquid yield of relatively high octane reformate. Unfortunately, conven-tional catalysts foul quickly at these conditions which makes this operation impractical. Accordingly, the need has arisen for a reforming catalyst which has an accept-able run length under the conditions noted above.
SUMMARY OF THE INVENTION
The present invention is a reforming catalyst and a process for using the catalyst. The process com-lS prises contacting a hydrocarbon feedstream with a catalystwhich comprises at least one Group VIII metal and a crys-talline silicate having a silica to alumina molar ratio of at least 500:l and a crystallite size less than 10 microns.
More preferably, the crystallite size is less than 5 microns, most preferably the crystallite size is less than 2 microns. Silicalite is the preferred crystalline sili-cate and platinum is the preferred Group VIII metal. It is also preferred that the silicalite catalyst have at least 80% crystallinity, more preferably at least 90~
crystallinity, most preferably at least 95% crystallin-ity. Furthermore, the process is preferably run at tem-peratures bet~een 599F and 1058F, in the absence of added hydrogen, and at a pressure below l00 psig.
Among other factors it has beerl discovered that reforming using a crystalline silicate catalyst comprising small crystallites and a high degree of crystallinity results in surprisingly long run lengths in the reforming process. Also, when the crystalline silicate has small crystallites, it can run at lower pressures and tempera-tures without added hydrogen. A further advantage is thatwhen hydrogen is not added and the reforming pressure is low, a high yield is achieved.
The process more specifically comprises contact-ing a hydrocarbon feedstream having less than 0.1 ppm sulfur wi~h a silicalite reforming catalyst at a pressure of less 01 _4_ than 100 psig, a temperature between 644 and 1004~F, and in the absence of added hydrogen; the reforming catalyst com-prises platinum, silicalite having at least 90% crystallin-ity, a silica to alumina mole ratio of at least 1000:1 and a crystallite size of less than 5 microns and an alkali or alkaline earth metal. Preferably, at least 70 wt.% of the crystallites are less than 10 microns, more preferably at least 80 wt.% are less than 10 microns, most preferably at least 90 wt.% are less than 10 microns.
BRIEF DESCRIPTION OF THE DRAWI~G
FIG. 1 is a graph showing the performance of different catalysts.
DETAILED DESCRIPTION OF THE INVENTION
There are operating and economic advantages in obtaining longer, yield-stable run lengths from reforming catalysts. One way to attain this, is by improvements in the catalyst itself. I have found that when platinum is ~ added to a crystalline silicate, such as silicalite, which has a small crystallite size, and a high degree of crys-tallinity, longer run lengths can be achieved.
Crystalline Silicates The catalyst of the present invention contains a crystalline silicate. '7Crystalline silicate" as used herein refers to silicates havin~ rigid, three-dimensional network of SiO4 tetrahedra in which the tetrahedra are crosslinked by the sharing of oxygen atoms. The crystalline silicates are substantially alumina-free, but they may contain minor amounts of alumina resulting from impurities in the starting materials or contamination of the reac~ion vessels. The preferred crystalline silicate is silicalite, examples of which are disclosed in U.S. Patent No. 4,061,724 and U.S.
Patent No. Re. 29,948 which are hereby incorporated by reference in their entireties. The silica:alumina molar ratio of the crystalline silicates of the present invention are preferably greater than about 500:1, more preferably greater than about 1000:1 and most preferably greater than about 2000:1. The crystalline silicates also preferably ~ have specific gravities, in the calcined form, between about rS !~ e~ 3 5 ~

l.S0 and about 2.10 g/cc and a refractive index between about 1.3 and about 1.5.

The following sets forth the relevant details and methodq of manufacture for the preferred catalyst As noted above, crystalline silicates which can be used in the process of the present invention have been reported in the literature. As synthesized, silicalite (U.S. Patent a No. 4~061,724) has a specific gravity at 77F of 1.99~0.05 g/cc as measured by water displacement. In the calcined form (1112F in air for one hour), silicalite has a specific gravity of 1.70~0.05 g/cc. With respect to the mean refractive index of silicalite crystals, values obtained by measurement of the as synthesized form and the calcined form (1112F in air for one hour) are, 1.48~0.01 and 1.39~0.01, respectively.
The X-ray powder diffraction pattern of silica-lite (1112F calcination in air for one hour) has six strongest lines (i.e., interplanar spacings). They are set forth in Table A ("S"-strongt and "VS"-very strong):

TABLE A

d-A Relative Intensity 11.1 t 0.2 VS
10.0 ~ 0.2 VS

3.85 ~ 0.07 VS
3.82 ~ 0.07 S
3.76 ~ 0.05 S
303.72 0.05 S
Table B shows the X-ray powder diffraction pattern of a typical silicalite co~po~ition containing 51.9 mols of sio2 per mol of tetrapropylammonium oxide (TPA)2O, prepared according to the method of U.S. Patent 3~ No. 4,061,724, and calcined in air at 1112F for one hour.

~3 TABLE B
Relative Relative 05d-A Intensity d-A Intensity 11.1 100 4.35 5 10.02 64 4.25 7 9.73 16 4.08 3 8.99 1 4.00 3 8.04 0.5 3.85 59 7.42 1 3.82 32 1~7.06 0.5 3.74 24 6.68 5 3.71 27 6.35 ~ 3 D 64 12 5.98 14 3.59 0.5 5.70 7 3.48 3 5.57 8 3.44 5 5.36 2 3.34 11 5.11 2 3.30 7 `
5.01 4 3.25 3 ~.98 5 3.17 0.5

4.86 0.5 3.13 0.5 4.60 3 3.05 5 4.44 0.5 2.98 10 ~ Silicalite crystals in both the "as synthesized"
and calcined forms are ~enerally orthorhombic and have the following unit cell parameterso a=20.05 A, b=19.86 A, c=13.36 A (all values +0.1 A).
~he pore diameter of silicalite is about 6A and its pore volume is 0~18 cc/gram as determined by adsorp-tion. Silicalite adsorbs neopentane (6.2 A kinetic diameter) slowly at ambient room temperature. The uniform pore structure imparts size-selective molecular sieve pro-perties to the composition, and the pore size permits separation of p-xylene from o-xylene, m-xylene and ethyl-benzene as well as separations of compounds having quater-nary carbon atoms from those having carbon-to-carbon linkages of lower value ~e.g. normal and slightly branched paraffins).
The crystalline silicates of U.S. Patent No. Re. 29,948 are disclosed as having a composition, in the anhydrous state:
0.9 ~ 0.2 [xR2O ~ (1 - x)M2/nO]: <.005 Al2o3:>l sio2 ~,f~

01 ~7~
where M is a metal, other than a metal of Group IIIA, n is the valence of said metal, R is an alkyl ammonium radical and x is a number greater than 0 but not exceeding 1~ The crystalline silicate is characterized by the X-ray diffraction pattern of Table CO

TABLE C
Interplanar Spacin~ d(A) Relative Intensity 11.1 S
10.0 S
7.~ W
7.1 W
6.3 W
IS 6.4

5.97 W
5.56 W
5.01 W
4~60 W
4.25 W
3.85 VS
3.71 S
3.04 W
2.99 W
2.94 W

The following discloses crystalline silicates that are related to silicalite. The crystalline silicate polymorph of U.S. Patent No. 4,073,865 is disclosed as having a specific gravity of 1,70 ~ 0.05 g/cc and a mean refractive index of 1.39 + 0.01 after calcination in air at 600C, as prepared by a hydrothermal process in which fluoride anions are included in the reaction mixture. The crystals, which can be as large as 200 microns, exhibit a substantial absence of infrared adsorption in the hydroxyl-stretching region and also exhibit an exceptional degree of hydrophobicity. They exhibit the X-ray diffrac-tion pattern of Table D.

~0 d(A) Intensity 11.14 91 10.01 100 05 9.75 8.01 0.5 7.44 0.5 7.08 0.2 :
~69

6.36 6 5.99 10 5.71 5 5.57 5 5.33 5.21 0-3 5.12 1.5 lS 54 927 6 4.92 0.6 4.72 0.5 4.62 2 4.47 0.6 4.36 3 4.25 4 ~0 4.13 0.5 4.08 1.5 4.00 3 3.85 44 3.82 25 3.71 21 3.65 5 3.62 3.59 3.48 1.5 3.45 3 3.44 3 3.35 3 3.31 5 3.25 1.5 3.23 0.8 3.22 0 5 The literature also describes other crystalline silicates and their method of preparation. The following method discloses the preparation of the crystalline sili-cate called "silicalite-2" (Nature, August, 1979~:
The silicalite-2 precursor is prepared using tetra-n-butylammonium hydroxide only, although adding ammonium hydroxide or hydrazine hydrate as a source of .

i J ~

~1 _9_ extra hydroxyl ions increases the reaction rate consid-erably. It is stable at extended reaction times in a 05 hydrothermal system. A successful preparation is to mix 8.5 mol sio2 as silicic acid (74g SiO2), 1.0 mol tetra-n-butylammonium hydroxide, 3.0 mol NH40H and 100 mol water in a steel bomb and heat at 338F for 3 days. The pre-cursor crystals will be ovate in shape, approximately 2-3 micromillimeters long and 1-1.5 micromillimeters in diameterr It is reported that the silicalite-2 precursor will not form if 1i, Na, K, Rb or Cs ions will be present, in which case the precursor of the U.S. Patent No. 4,061,724 silicalite is formed. It is also reported that the size of the tetraalk~lammonium ion is critical because replacement of the tetra-n-butylammonium hydroxide by other quaternary ammonium hydroxides tsuch as tetra-ethyl, tetrapropyl, triethylprop~l, and triethylbutyl hydroxides) will result in amorphous products. The amount of Al present in silicalite-2 depends on the purity of the starting materials and is reported as being less than 5 ppm. The precursor contains occluded tetraalkylammonium salts which, because of their size, are removed only by thermal decomposition. Thermal analysis and mass spectro-metry show that the tetraalkylammonium ion decomposes at approximately 572F and is lost as the tertiary amine, alkene and water. This is in contrast to the normal thermal decomposition at 392F of the same tetraalkylammo-nium salt in air.
The Nature article further reports that the major differences between the patterns of silicalite and silicalite-2 are that peaks at 9006~ 13.9, 15.5, 16.5 20.8, 21.7, 22.1, 24.~, 26.6 and 27.0 degrees 2~ (CuK
alpha radiation) in the silicalite X-ray diffraction pattern are absent from the silicalite-2 pattern. Also, peaks at 8.8, 14.8, 17.6, 23.1, 23.9 and 29.9 degrees are singlets in the silicalite-2 pattern rather than doublets as in the silicalite pattern. These differences are reported as being the same as those found between the ~0 ,J

diffraction patterns of the aluminosilicalites, orthor-hombic ZSM-5 and tetragonal ZSM-ll. Unit cell dimensions 05 reported as calculated on the assumption of tetragonal symmetry for silicalite-2 are a = 20.04; b = 20.04;
c = 13.38. The measured densities and refractive indices of silicalite-2 and its precursor are reported as 1.82 and 1.98 g/cc and 1.~1 and 1.48 respectively.
Preparation of Crystalline Silicates The preparation of crystalline silicates o the present invention generally involves the hydrothermal crystalli~ation of a reaction mixture comprising water, a source of silica and an organic templating compound at a pH of 10 to 1~. Representative templating moieties include quaterna~y cations such as XR4 where X is phos-phorous or nitrogen and R is an alkyl radical containing from 2 to 6 carbon atoms, e.g., tetrapropylammonium hydroxide (TPA-OH) or halide, as well as alkyl hydroxy-alkyl compounds, organic amines and diamines, and hetero-cycles such as pyrrolidine.
When the organic templating compound (i.e., TPA-O~) is provided to the system in the hydroxide form in sufficient quantity to establish a basicity equivalent to the pH of 10 to 14, the reaction mixture need contain only water and a reactive form of silica as additional ingredi-ents. In those cases in which the pH must be increased to above 10, ammonium hydroxide or alkali metal hydroxides can be suitably employed for that purpose, particularly the hydroxides of lithium, sodium, and potassium. The ratio R~
R+ + M+, where R+ is the concentration of organic templating cation and M+ is the concentration of alkali metal cation, is preferably between 0.7 and 0.98, more preferably between 0.8 and 0.98, most preferably between 0.85 and 0.98.
The source of silica in the reaction mixture can be wholly, or in part, alkali metal silicate but should not be employed in amounts greater than that which would change the molar ratio of alkali metal to organic 0 1 ~
templating compound set forth above. Other silica sources include solid reactive amorphous silica, eDg., fume 05 silica, silica sols, silica gel, and organic orthosili-cates. One commercial silica source is Ludox AS-30 avail-able from Du Pont.
Aluminum is easily incorporated as an impurity into the crystalline silicate, so, care should be exer-cised in selecting the silica source to minimize aluminauptake. Commercially available silica sols can typically contain between 500 and 700 ppm A12O3, whereas fume silicas can contain between 80 and 2000 ppm of A12O3 impurity. As explained above, the silica to alumina molar ratio in the crystallina silicate is preferably greater than 500:1, more preferably greater than 1000:1, most preferably 2000:1. Aluminum in the synthesis contributes a~idity to the catalyst, which is undesirable~
The ~uantity of silica in the reaction system is ~0 preferably between about 1 and 10 mols SiO2 per mol-ion of the organic templating compound. Water should be gener-ally present in an amount between 20 and 700 mol per mol-ion of the quaternary cation. The reaction preferably occurs in an aluminum-free reaction vessel which is resis-tant to alkali or base attack, e.g., Teflon.
Strong acidity is undesirable in the catalystbecause it promotes cracking, resulting in lower selec-tivityO To reduce acidity, the catalyst preferably con-tains an alkali metal and/or an alkaline earth metal. The alkali or alkaline earth metals are preferably incorpo-rated into the catalyst during or after silicalite syn-thesis. Preferably, at least 90~ of the acid sites are neutralized by intrGduction of the metals, more preferably at least 95~, most preferably at least 100%.
Crystalline silicates are conventionally syn -thesized largely in the sodium or potassium form. These cations are exchangeable, so that a given silicalite can be used to obtain silicalites containing other cations, such as alkaline earth metals or other alkali metals, by subjecting the silicalite to ion exchange treatment in an ~L ~

aqueous solution of appropriate salts. The preferredalkali and/or alkaline earth metals are: lithium; sodium;
05 potassium; rubidium; cesium; strontium; and barium; more preferred metals are: sodium, potassium; rubidium; and cesium.
The crystalline silicate is preferably bound with a matrix or porous matrix. The terms "matrix" and "porous matrix" include inorganic compositions with which the silicate can be combined, dispersed, or otherwise intimately admixed. Preferably, the matrix is not-cataly-tically active in a hydrocarbon cracking sense, i.e., contains substantially no acid sites. The matrix porosity can either be inherent or it can be caused by a mechanical or chemical means. Satisfactory matrices include pumice, firebrick, diatomaceous earth and inorganic oxides. Pre-ferred inorganic oxides include alumina, silica, naturally occurring and conventionally processed clays, for example bentonite, kaolin, sepiolite, attapulgite, and halloysite.
The preferred matrices have few, if any, acid sites and therefore have little or no cracking activity~ Silica or alumina are especially preferred, The use of a non-acidic matrix i5 preferred to maximize aromatics production.
Compositing the crystalline silicate with an inorganic oxide matri~ can be achieved by any suitable known method wherein the silicate is intimately admixed with the oxide while the latter is in a hydrous state (for example, as a hydrous salt, hydrogel~ wet gelatinous pre-cipitate, or in a dried state, or combinations thereof).
A convenient method is to prepare a hydrous mono or plural oxide gel or cogel using an aqueous solution of a salt or mixture of salts (for example aluminum sulfate and sodium silicate)~ Ammonium hydroxide carbonate (or a similar base) is added to the solution in an amount sufficient to precipitate the oxides in hydrous form. Then, the preci-pitate i5 washed to remove most of any water soluble salts and it is thoroughly admixed with the silicate which is in a finely divided state. Water or a lubricating agent can ~1 -13-be added in an amount sufficient to facilitate shaping of the mix (as by extrusion).
05 The preferred crystalline silicate is silicalite.
Assuming that the only crystalline phase in the silicalite prep is silicalite, the silicalite preferably has a percent crystallinity of at least 80~, more preferably at least 90%, most preferably at least 95%. To determine percent crys-tallinity, an X-ray diffraction ~XRD) pattern of the sili-calite is made and the area under the 8 major peaks ismeasured in the angle interval between 20.5 and 25.0 degrees. Once the area under the curve is calculated, it is compared with the area under the curve for a 100% crys-talline ~tandard for silicalite.
The preferred crystallite size of the crystalline silicate is less than 10 micronsl more preferably less than 5 microns, most preferably less than 2 microns. When a crys-tallite size is specified, preferably at least 70 wt.% of the crystallites are that size, rnore preferably at least 80 wt.~, more preferably 90 wt.%o Crystallite size can be controlled by adjusting synthesis conditions, as known to the art. These conditions include temperature, pH, and the mole ~a~ios H2o/SiO2, R+/SiO2, and M+/SiO2 where R+ is the ~5 organic templating cation and ~ an alkali metal cation.
For small crystallite size, i.e., less than 10 microns, typical synthesis conditions are listed below:
More Most Preferred Preferred Preferred Temperature, F176-392 144-356 212-302 pH 12-14 12~ 5-14 13-13.5 H2O/Sio2 5-100 10-50 10-40 Rt/Sio2 0~ 1) O~ l~Oa 50~ 2--0~ 5 M+/Sio2 0.01-0.3 0O01-0.15 0.01-0.08 other techniques known to the art, such as seeding with silicate crystals, can be used to reduce crystallite size.
Group_VIII Metals The catalysts according to 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, andparticularly platinum. They are more selective with 05 regard to dehydrocyclization and are also more stable under the dehydrocyclization reaction conditions than other Group ~III metals. The preferred percentage of the Group VIII metal, such as platinum, in the catalyst is between 0.1 wt.% and 5 wt.%, more preferably from 0.3 wt.%
to 2.5 wt.%.
Group VIII metals are preferably introduced into the crystalline silicate by impregnation, occlusion, or exchange in an aqueous solution or exchange in an aqueous solution of an appropriate salt. When it is desired to introduce two Group VIII metals into the crystalline sili-cate, the operation may be carried out simultaneously or se~uentially. Preferably, the Group VIII metal is finely dispersed within, and on, the crystalline silicate~
By way of example, platinum can be introduced by ~U impregnation with an aqueous solution of tetraammineplati-num (II) nitrate, tetraammineplatinum (II) hydroxide, dinitrodiamino-platinum or tetraammineplatinum (II) chlo-ride. In an ion exchange process, platinum can be intro-duced by using cationic platinum complexes such as tetraammineplatinum (II) nitrate. When platinum is intro-duced into the silicalite by occlusion a platinum complex is preferably introduced into the crystalline silicate during its formation.
After the desired metal or metals have been introduced~ the catalyst is preferably treated in air, or air diluted with an inert gas, and reduced in hydrogen.
Catalysts containing platinum are typically subjected to halogen or halide treatments to achieve or maintain a uni-form metal dispersion. Typically, the halide is a chloride compound. The catalysts of our invention can be subjected to similar treatments although the preferred catalyst does not contain chloride in the final form.
other metals can be added to the catalyst.
These metals are preferably selected from Groups VIII, ~0 IVA, IB or VIB. More preferably, additional metals may include: rhenium, tin, gold, or chromium.
~5 Reforming and Dehydrocy~lizing once the Group VIII metal has been deposited on the catalyst, it can be employed in any of the conven-tional types of equipment known to the art. It may be employed in the form of pills, pellets, granules, broken fragments, or various special shapes, disposed as a fixed bed within a reaction zone, and the charging stock may be passed therethrough in the liquid, vapor, or mixed phase and in either upward, downward, or radial flow~ Alter-natively, it may be prepared for use in moving beds, or in fluidized-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 of well-known opera-tional advantages either a fixed bed system or a dense-~ phase moving bed system are preferred. In a fi~ed bedsystemr the feed is preheated (by any suitable heating means) to the desired reaction temperature and then passed into a dehydrocyclization zone containing a fixed bed of ~he catalyst. This dehydrocyclization zone may be one or ~5 more separate reactors with suitable means to maintain the desired temperature at the entrance to each reactor. The temperature must be maintained because the dehydrocycli-zation reaction is endothermic in nature. Afterward, the reaction products from any of the foregoing processes are separated from the catalyst, vented to atmospheric pres-sure, and fractionated to recover the various componentsthereof.
The feed to the reformer is preferably a naphtha fraction, boiling within the range of 70 to S50F and 3~ preferably from 120 to 400F. This can include, for example, straight run naphthas, paraffinic raffinates from aromatic extraction or adsorption, and C6-C10 paraffin-rich f0eds, as well as paraffin-containing naphtha products from other refinery processes, such as hydrocracking or conv0ntional reforming. The actual reforming conditions ~ 3 ~1 -16-will depend in large measure on the feed used, whetherhighly aromatic, paraffinic or naphthenic and upon the ~5 dcsired octane rating of the product. Furthermore, the temperature and pressure can be correlated with the liquid hourly space velocity (LHSV) to favor any particularly desirable reforming reaction as, for example, aromatiza-tion, isomerization or dehydrogenation. The catalyst of the present invention is preferably used to dehydrocyclize acyclic hydrocarbons to form aromatics.
The reforming process is preferably conducted inthe absence of added hydrogen. The absence of added hydrogen favors aromatics formation and increases liquid yield at a given octane.
A low sulfur feed is especially preferred in the present process. The feed preferably contains less than 10 ppm, more preferably less than 1 ppm, and most prefer-ably 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 hydrogenating the feed in a presaturation zone with a hydrogenating catalyst which is resistant to sulfur poisoning. An example of a suitable catalyst for this hydrodesulfurization process is an alumina-containing support and a minor catalytic proportion of molybdenum oxide, cobalt oxide and/or nickel oxide. A platinum on alumina hydrogenating catalyst can also work. A sulfur sorber is preferably placed downstream of the hydrogen-ating catalyst, but upstream of the silicalite reforming catalyst. Examples of sulfur sorbers are alkali or alkaline earth metals on porous refractory inorganic oxides, æincr etc. Hydrodesulfurization is typically conducted at 599F to 951F, 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 in the feed to less than 10 ppm nitrogen, or more preferably less than 1 ppm. Preferably, water in the feed is limited to less than 100 ppm H2O, more preferably less than 10 ppm H2O. Catalysts and processes which are suitable for these purposes are known to those skilled in the art.

~J J '~

In the process of the present invention, the pressure is preferably between 0 psig and 200 psig, more ~5 preerably between 0 and 100 psig, and most preferably between 25 psig and 75 psig. The liquid hourly space velocity (LHSV) is preferably between about 0.1 to about 10 hr. 1 with a value in the range o about 0.3 to about 5 hr. 1 being preferred. The temperature is preferably between about 599F and about 1058F, more preferably between 644F and 1004F. As is well ~nown to those skilled in the dehydrocyclization art, the initial selec-tion of the temperature within this broad range is made primarily as a function of the desired conversion level of the acyclic hydrocarbon considering the characteristics of the feed and of the catalyst. Thereafter, to provide a relatively constant value for conversion, the temperature is slowly increased during the run to compensate for the inevitable deactivation that occurs.
~ After a period of operation the catalyst can become deactivated by sulfur or coke. Sulfur and coke can be removed by contacting the catalyst with an oxygen-con-taining gas at an elevated temperature. If the Group VIII
metal(s) have agglomerated, then it can be redispersed by contacting the catalyst with a chlorine gas under condi-tion~ effective to redisperse the metal(s). The method ofregeneratlng the catalys~ will depend on whether there is a fixed bed, moving bed, or fluidized bed operation.
Regeneration methods and conditions are well known in the art. An example of an oxychlorination regeneration proce-dure is shown in U.S. Serial No. 944,403 which is herebyincorporated by reference in its entirety. An example o~
a sulfur removal procedure is shown in U.S. Serial No. 944,392 which i5 hereby incorporated by reference in its entiretY.

~1 -18-The present invention will be more fully under-stood by reference to the following examples. They are 05 intended to be purely exemplary and are not intended to limit the scope of the invention in any way.
EXAMPLES
Example 1 A Pt-occluded silicalite catalyst was made as 10 follows: 4.6 grams NaN03, 10.0 grams EDTA, and 1.0 grams Pt(NH3)4 (NO3)2 were mixed into 20 cc of distilled water.
This mixture was added to 200 grams of a 25% aqueous solu-tion of TPA-OH with rapid stirring, and stirred an addi-- tional 10 minutes. 160 Grams of Ludox AS-30 were then added with rapid stirring and stirred for an additional 15 minutes. The pH of the mixture was reduced to 11,0 using HCl. The mixture was placed in a Teflon bottle in an autoclave under autogeneous pressure at 150C for three da~s. The product was filtered, dried overnight in a ~
~U vacuum oven at 110C, and calcined for 8 hours in dry air at 454C. The sieve was identified as silicalite by X-ray diffraction analysis~ The average crystallite size was about 40x15x15 microns troughly rectangular) as determined by scanning election micros~opy. The percent silicalite was determined by X-ray dif~raction (XRD) analysis to be 100%. The Pt content was 0.6 w~
Example 2 A Pt-occluded silicalite was prepared as follows: 9.2 grams of NaNO3, 20 grams of EDTA, and 30 2-0 ~rams Pt(NH3)4 (NO3)2 were mixed into 40 ml of dis-tilled water in a polyethylene beaker. Four hundred (400) grams of a 25~ aqueous solution of TPA-OH were added and the mixture stirred well for 15 minutes. Three hundred twenty (320) grams of Ludox AS-30 were added with rapid stirring and the mixture stirred an additional 15 minutes.
The pH of the mixture was 13.2. The mixture was poured 4~

into a Teflon bottle and kept at 100C for 7 days. The product was filtered, dried overnight in a vacuum oven at 05 120C, and then calcined in dry air at 454C. The average crystallite size was about 0.5 microns in diameter (roughly spherical). The Pt content was 0.6 wt.%. The Al content was 397 ppm. Na was OL68 wt.~.
Example 3 The catalysts of Examples 1 and 2 were tested for conversion of n-hexane to benzene under various condi-tions. The results in Table I show that the catalyst having 0O5 microns crystallites is more selective for benzene than the catalyst having 40x15x15 crystallites.

TABLE I
Conversion of N-Hexane over 0.6% Pt (occ)/Silicalite at 1 LHSV

Silicalite, microns40x15x15 0.540x15x15 0.5 Pressure, psig 100 100 100 100 Temperature, F 980 980 950 950 Gas H2 H2 N2 N2 Gas/HC4 4 4 7 7 Product, Wt.%
Cl 10.0 11.2 0.9 17.8 C2 1~.8 15.3 1.5 14.1 C3-c4 39.9 37.6 4.4 7.6 C5+ 30~3 35.9 93.2 60.5 Benzene 23.9 25.9 17.0 56.8 MCP 0 0.1 6~2 0 C6 Paraffins + Olefins 0.3 1.5 65.4 0 Wt.% Selectivity to Benzene from C6 Paraffins and Olefins 24.0 26.3 49.1 56.8 S)l -20-The catalyst of Example 2 was used to reform a ~5 light straight run naphtha feed (Table II) at 875F, 100 psig, 1 LHSV, and 7 N2/HC. Throughout the 140-hour run, the benzene yield was 22-25 wt.~ at about 85 wt.~ C5+
yield. The toluene yield was 11-12 wt.%.
At the 140-hour point, N2 flow was stopped and replaced by H2 at the same rate. The benzene yield dropped within four hours to 8.7 wt.%.
The product properties in Table III, show that the catalyst is quite selective for conversion of low octane normal paraffins. The research octane number was increased from 71.7 to 92.1.

TABLE II
Li~ht Straight Run Naphtha ;~0 Gravity, API 70.7 Sulfur, ppm <0.05 Octane, RON/MON 71.7/69.7 P/N/A, LV~ 60.3/35.0/4.7 Composition, LV%
C5 19.7 C6 41.9 C7 30.5 C8 7.6 Cg 0~3 D86 Distillation, LV%, F
.

10/30 13~/147 ~0 Example 5 A catalyst identical to that of Example 2 was S prepared, with the exception that it contained 0.8 wt.%
Pt. This catalyst was used to reform the feed of Table II
at 875F, 0 psi~, 1 L~SV, and no diluent gas. During a 20-hour period, the benzene yield was 30 wt.~ at a C5~
yield of about 76 wt.%. At the 20-hour point, the reactor temperature was lowered to 850F and the pressure was increased to 10Q psig. Over the next 72 hours, the ben-zene yield was about 24-25 wt.%. The product properties at these condition~ are shown in Table III.

TABLE III
Reforming Light ~ ht Run Naphtha over Pt/Sil Ex. 4 Ex. 5 Eeed_0-140 hrs.)(20-72 hrs.) ~0 Temperature, F 875 850 Pressure (psig) 100 100 LHSV
C5+' LV% 84 71 H2, SCF/bbl 400 H2/CH4 1.2 C5+ Composition, LV%

P/O/ 60.3/0/49.1/4.8/50.0/2.8/
N/A 35.0/4.718.8/27.39.0/38.2 nC5 12.0 14.6 16.3 nC6 12.3 1.9 2.2 nC7 5.0 0.5 0.2 C6P Conversion, 0~
nC6 87 87 Octanes, RON/MON 71.7/69.792.1/81.0 92.3/83.8 Example 6 A Pt-occluded silicalite catalyst was prepared as follows: 18.4 grams of NaNO3, 40 grams of EDTA, and 4.0 grams of Pt tNH2)4 (NO3)2 were mixed into 80 ml of distilled water. Eight hundred (800) grams of a 25%
aqueous solution of TPA-OH were added and mixed well for 15 minutes. Six hundred forty (640) grams of Ludox AS-30 were added with rapid stirring and stirred an additional 15 minutes. The pH of the mixture was 12.9. This was ;20 raised to 13.2 by the addition of about 5 ml of a 50%
aqueous solution of NaOH. The mixture was poured into a Teflon bottle and kept at 100C for 7 days. The product was filtered and then dried overnight in a vacuum oven at 100C. It was then calcined at 232C for 4 hours, 371C
for 2 hours, and finally 454C for 4 hours. The catalyst contained 0.85% Pt, 1.17~ Na, and 433 ppm Al. The average crystallite size was about 0.9 microns in diameter (roughly spherical). The percent silicalite was deter-mined by XRD analysis to be 91%.
ExamPle ?
A Pt-impregnated silicalite catalyst was made as follows: 9.2 grams of NaNO3 and 20.0 grams of E~TA were mixed into 40 ml of distilled water. To this were added 400 grams of a 25% aqueous solution of TPA-OH and mixed well for 15 minutes~ Three hundred twenty (320) grams of Ludox AS-30 were then added with rapid stirring, and the mixture stirred for an additional 15 minutes. The pH of the mixture was 13.2. The mixture was poured into a O Teflon bottle and kept at 1003C for 7 days. The product was filtered, and then dried overnight in a vacuum oven at C2 ~3 r 2 3~~

120C. It was then calcined for 8 hours at 427C and another 8 hours at 566C. The percent silicalite was 99%
05 as determined by XRD analysis. The sieve, which had an average crystallite size of about 0.8 microns in diameter (roughly spherical), was then impregnated with 008% Pt by the pore-fill method using an aqueous solution of Pt(NH3)4(NO3)2. The catalyst was then dried overnight in a vacuum oven at 110C and calcined in air for 4 hours at 232C and 8 hours at 454C.
Example 8 A platinum-impregnated silicalite catalyst was prepared as follows: 8.4 grams of NaNO3 and 40 grams of EDTA were mixed into 80 ml of distilled water. Eight hundred ~800) grams of a 25~ aqueous solution of TPA-OH
were added and mixed well for 15 minutes. Six hundred forty (640) grams of Ludox AS-30 were added and mixed with rapid stirring for 15 minutes. The pH of the mixture was 13.1. The mixture was poured into a Teflon bottle and kept at 100C for 7 days. The product was filtered and then dried overnight in a vacuum oven at 120C. It was then calcined for 8 hours at 566C in air. The percent silicalite was 100% as measured by XRD analysis. The sieve, which had an average crystallite size of about one micron in diameter (roughly spherical) r was then impreg-nated with 0.8 wto~ platinum by the pore-fill method using an aqueous solution of Pt(NH3)4(NO3)2. The catalyst was then dried overnight in a vacuum oven at 120C and calcined in dry air for 4 hours at 204C, 4 hours at 288C, 4 hours at 371C, and 4 hours at 427C.
Example 9 The catalyst of Example 8 was exchanged once with a 5 wt.~ aqueous solution of KNO3 at 82C for 2 hours. It was then filtered, washed with distilled water, and dried overnight in a vacuum oven at 120C. The catalyst was then calcined in dry air for 4 hours at 204C
and 4 hours at 288C. The K+ level of the catalyst was 0O69 wt.~. Na+ was 239 ppmO
~0 Example 10 A large crystal, platinum-impregnated silicalite catalyst was prepared as follows: 6.25 grams of NaOH was dissolved in 400 grams of distilled water. Then, 41.25 grams of tetrapropylammonium bromide was added and mixed well. Next r 200 grams of Ludox AS-30 were add~d with rapid stirring. HCl was added to half of this mix-0 ture to reduce the pH to 11.0 and it was poured into aTeflon bottle and kept at 150C for 4 days. It was fil tered, then dried overnight in a vacuum oven, and then calcined for 8 hours at 566C in air. The silicalite was identified as 100~ silicalite as determined by XRD anal-ysis. It had an SiO2/A12O3 ratio of about 2000 and 0.16~
Na. Its size was about 30x10x10 microns. It was impreg-nated with platinum, dried, and calcined by the same pro-cedure as used with the catalyst of Example 8.
Example 11 The catalysts of Examples 6-10 were used to reform the light straight naphtha feed of Table II at 52 psig, 1 LHSV, and no diluent gas. The reactor temper-ature was adjusted to maintain an n-C6 conversion of 60%.
Plots of reactor temperature versus time are shown in FIG. 1.
Example 12 A platinum-occluded silicalite catalys~ was made as follows. 18,4 grams of NaNO3, 40 grams of EDTA, and 4 grams of Pt(NH3)4(NO3)2 were dissolved in 80 ml of dis-tilled water. This solution was added with stirring to800 grams of a 25% aqueous solution of TPA hydroxide in a polyethylene beaker and stirred for 15 minutes. 640 grams of Ludox AS-30 were added with rapid stirring and stirred for an additional 15 minutes. The pH of the mixture was 3~ 13~1, The mixture was poured into a Teflon bottle and placed in an oven for 24 hours at 70C. The temperature was then raised to 100C and held there for 6 more days.
The product was collected by both filtration and centri-fugation~ It was water washed and dried for three days in Ql -25-a vacuum oven at 90C. It was then calcined in dry air for 8 hours at 454C. The percent silicalite as deter-05 mined by X-ray diffraction analysis was 74%~ The Pt con-tent was 0.80 wt.%. The average crystallite size was about 0.2 microns.
Example 13 The catalyst of Example 12 was used to reform lC the light straight run naphtha feed of Table II at the same conditions as in Example 10. At 24 hours onstream, a temperature of 870F was required for 60~ n-C~ conversion, considerably higher than with a catalyst of greater than 90~ crystallinity (i.e., Examples 6-3).
lS The foregoing disclosure has taught some speci-fic examples of the present invention. 8Owever, there are many modifications and variations within the spirit of the disclosure. It is intended that the embodiments are only illustrative and not restrictive, reference being made to the following claims to indicate the scope of the invention.

~0

Claims (40)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for reforming hydrocarbons comprising:
contacting a hydrocarbon feed under reforming condi-tions with a catalyst which comprises:
(a) at least one Group VIII metal; and (b) a crystalline silicate having a silica:alumina molar ratio of at least 500:1 and a crystallite size of less than 10 microns.

2. A process for reforming in accordance with Claim 1 wherein the crystalline silicate is silicalite.

3. A process for reforming in accordance with Claim 2 wherein the silicalite crystallite size is less than 5 microns.

4. A process for reforming in accordance with Claim 1 wherein the silicalite crystallite size is less than 2 microns.

5. A process for reforming in accordance with Claim 2 wherein the Group VIII metal is platinum.

6. A process for reforming in accordance with Claim 1 wherein the catalyst comprises silicalite of at least 80% crystallinity.

7. A process for reforming in accordance with Claim 1 wherein the catalyst comprises silicalite of at least 90% crystallinity.

8. A process for reforming in accordance with Claim 1 wherein the catalyst comprises silicalite at least 95% crystallinity.

9. A process for reforming in accordance with Claim 1 wherein at least 70 wt.% of the crystallites are less than 10 microns.

10, A process for reforming in accordance with Claim 1 wherein at least 80 wt.% of the crystallites are less than 10 microns.

11. A process for reforming in accordance with Claim 1 wherein at least 90 wt.% of the crystallites are less than 10 microns.

12. A process for reforming in accordance with Claim 2 wherein the catalyst further comprises at least one alkali or alkaline earth metal.

13. A process for reforming in accordance with Claim 2 wherein the catalyst further comprises a metal selected from the group consisting of sodium, potassium, rubidium, or cesium.

14. A process for reforming in accordance with Claim 5 wherein the silicalite is impregnated with platinum.

15. A process for reforming in accordance with Claim 5 wherein the silicalite is grown in the presence of platinum.

16. A process for reforming in accordance with Claim 2 further comprising contacting the hydrocarbon feed with the catalyst in the absence of added hydrogen.

17. A process for reforming in accordance with Claim 16 further comprising contacting the hydrocarbon feedstream with the catalyst at a pressure less than 100 psig.

18. A process for reforming in accordance with Claim 17 further comprising contacting the hydrocarbon feedstream with the catalyst at a temperature between 593°F and 1058°F.

19. A process for reforming in accordance with Claim 18 further comprising contacting the hydrocarbon feedstream with the catalyst at a temperature between 644°F and 1004°F.

20. A process for reforming in accordance with Claim 2 wherein the catalyst further comprises a promoter metal selected from the group consisting of: rhenium, tin, gold, and chromium.

21. A process for reforming in accordance with Claim 2 wherein the hydrocarbon feedstream has less than 1 ppm sulfur.

22. A process for reforming in accordance with Claim 2 wherein the hydrocarbon feedstream has less than 0.1 ppm sulfur.

23. A process for reforming hydrocarbons, comprising:
contacting a hydrocarbon feedstream having less than 0.1 ppm sulfur at a pressure of less than 100 psig and a temperature between 644 and 1004°F, and in the absence of added hydrogen;
with a catalyst comprising platinum, an alkali or alkaline earth metal, and silicalite, which silicalite has at least 90% crystallinity; a silica to alumina mole ratio of at least 1000:1, of which at least 80 wt.% are crystallites less than 5 microns.

24. A process for reforming in accordance with Claim 23 wherein the catalyst further comprises a promoter metal selected from the group consisting of rhenium, tin, gold, and chromium.

25. A process for reforming in accordance with Claim 23 wherein the silica to alumina molar ratio of the catalyst is at least 2000:1.

26. A process for reforming in accordance with Claim 23 wherein the silicalite crystallite size is less than 2 microns.

270 A crystalline silicalite reforming catalyst comprising a Group VIII metal and silicalite which has a silica to alumina ratio of at least 500:1 and a crys-tallite size less than 10 microns.

28. A reforming catalyst in accordance with Claim 27 wherein the crystallite size is less than 5 microns.

29. A reforming catalyst in accordance with Claim 27 wherein the crystallite size is less than 2 microns.

30. A reforming catalyst in accordance with Claim 27 wherein the Group VIII metal is platinum.

31. A reforming catalyst in accordance with Claim 27 wherein the silicalite has at least 80% crystallinity.

32. A reforming catalyst in accordance with Claim 27 wherein the silicalite has at least 90% crystallinity.

33. A reforming catalyst in accordance with Claim 27 wherein the silicalite has at least 95% crystallinity.

34. A process for reforming in accordance with Claim 27 wherein at least 70 wt.% of the crystallites are smaller than 10 microns.

35. A process for reforming in accordance with Claim 27 wherein at least 80 wt.% of the crystallites are smaller than 10 microns.

36. A process for reforming in accordance with Claim 27 wherein at least 90 wt.% of the crystallites are smaller than 10 microns.

37. A reforming catalyst in accordance with Claim 27 further comprising an alkali or alkaline earth metal.

38. A reforming catalyst in accordance with Claim 27 wherein the silica to alumina ratio is at least 1000:1.

39. A reforming catalyst in accordance with Claim 27 wherein the silica to alumina ratio is at least 2000:1.

40. A reforming catalyst comprising.
silicalite, which has:
a silica to alumina ratio of at least 1000:1;
crystallites, of which at least 80 wt.% are less than 5 microns; and at least 90% crystallinity, an alkali or alkaline earth metal, and platinum.