GB2056961A - Synthetic chromia silicate catalyst and hydrocarbon processing using the same - Google Patents

Abstract

A synthetic crystalline chromia silicate catalyst having an X-ray diffraction pattern similar to known aluminosilicates (eg ZSM-5) is prepared by hydrothermally crystallizing an aqueous reaction mixture containing sources of quaternary alkylammonium oxide, chromium oxide, silica and an alkali metal oxide. The chromia silicate has a SiO2:Cr2O3 mol ratio greater than 20:1. The crystalline chromia silicate is useful as a catalyst in hydrocarbon conversion processes such as dewaxing and olefin production.

Description

SPECIFICATION Synthetic chromia silicate catalyst and hydrocarbon processing using the same This invention relates to novel species of crystal line silicates containing chromia and methods for preparing same. These compositions are useful as catalysts for hydrocarbon processes, particularly in dewaxing operations and olefin production.

Molecuiar sieve crystalline zeolites are aluminosilicates comprised of a rigid three dimensional framework of SiO4 and AlO4 tetrahedra joined by common oxygen atoms. The inclusion of aluminum atoms in the framework produces a defi ciency in electrical charge which must be locally neutralized by the presence of additional positive ions within the structure. In natural zeolites and many of the synthetic zeolites, these ions are nor mally alkali metal or alkaline earth cations which are quite mobile and readily exchanged in varying degrees by conventional techniques for other cations. The cations occupy channels and interconnected voids provided by the framework geometry.

U.S. Patent No.3,702,886, incorporated herein by reference, discloses a new family of crystalline zeol ites, designated as ZSM-5. The ZSM-5-type zeolites have a composition expressed in mol ratios of oxide as follows.

0.90.2N2z,0:W203:5-100YO2:ZH20 wherein M is at least one cation, n is the valence thereof, W is either aluminum or gallium, Y is either silicon or germanium, and z is between 0 and 40.

Members of the ZSM-5 family are disclosed to possess a random powder X-ray diffraction pattern hav ing the following significant lines: TABLE 1 Interplanar Spacing d(A): Relative Intensity 11.1 +0.2 s.

10.0 0.2 s.

7.4 +0.15 w.

7.1 + 0.15 w.

6.3 +0.1 w.

6.04) w.

5.97) t 0.1 5.56 t 0.1 w.

5.01 t0.1 w.

4.60 t 0.08 w.

4.25 t 0.08 w.

3.85 t 0.07 v.s.

3.71 0.05 s.

3.04 t 0.03 w.

2.99 a 0.02 w.

2.94 o 0.02 w.

The above values were determined by conventional techniques described in the patent.

The patent teaches that ZSM-5-type zeolites are prepared by hydrothermally crystallizing a reaction mixture of tetrapropylammonium hydroxide, sodium oxide and an oxide of aluminum or gallium and an oxide of silicon or germanium.

U.S. Patent No.3,941,871, incorporated herein by reference, discloses a crystalline metal organosilicate having the composition, in its anhydrous state, as follows: 0.9-0.2 xR2Ot(1 -x)M400U : < .005A12O3: lSiO2 wherein M is a metal, other than a metal of Group IIIA, n is the valence thereof, R is an alkylammonium radical and x is between 0 and 1. The disclosed compositions are synthesized by hydrothermally crystallizing a reaction mixture of alkylammonium oxides, sodium oxides, water and oxides of a metal other than Group IIIA. Alumina appears in the product in small quantities due to reactant impurities and/or the equipment used in the synthesis. Random X-ray powder diffraction analysis shows the following significant lines: TABLE2 Interplanar Spacing d(A): Relative Intensity 11.1 0.2 s.

10.0 0.2 s.

7.4 0.15 w.

7.1 -t- 0.15 w.

6.3 0.1 w.

6.04)t 0.1 w.

5.56 0.1 w.

5.01 0.1 w.

4/7- /08 w.

4.25 t 0.08 w.

3.85 t 0.07 v.s.

3.71 t 0.05 s.

3.04 ~ 0.03 w.

2.99 ~ 0.02 w.

2.94 ~ 0.02 w.

U.S. Patent No. 4,061,724, also incorporated herein by reference, discloses a crystalline silica, denominated as "silicalite". Silicalite is prepared by hydrothermal crystallization of a reaction mixture containing water, silica and an alkylonium compound such as tetraethylammonium hydroxide, tetrapropylammonium hydroxide, or the salts corres ponding thereto, such as tetrapropylammonium bromide. Silicalite, after calcination in air at 600"C for one hour, exhibits the following X-ray diffraction pattern: TABLE3 d-A Relative Intensity 11.1 +0.2 vs.

10.0 t 0.2 v.s.

3.85 t 0.07 v.s.

3.82 t 0.07 s 3.76 t 0.05 s 3.72 a 0.05 s Table 4 presents the results of an X-ray diffraction analysis of a silicalite composition aftercalcination containing 51.9 mols of SiO2 per mol of tetrap ropylammonium oxide: TABLE 4 Relative Relative d-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 7.06 0.5 3.74 24 6.68 5 3.71 27 6.35 9 3.64 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 4.98 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 All of the above compositions have a pore diameter of approximately 6 Angstroms and are individually useful in certain hydrocarbon processing applications.However, ZSM-5-type aluminosilicates are "overly" active in hydrocracking services, for example, in cracking normal paraffins from a feedstock for dewaxing purposes. This high activity results in high gas production and low liquid yields. Silicalite per se, in contrast, is much less active and is used primarily as an absorbent for oil from oil-water mixtures.

It is, therefore, an object of the present invention to provide a novel composition which is useful for dewaxing feedstocks with high liquid yields, for the production of olefins, and for other hydrocarbon conversion processes.

The present invention relates to a novel crystalline chromia silicate which is hydrothermally crystallized from a reaction mixture containing chromium. The chromia silicates of the present invention have a chromia:silica ratio, in terms of mol ratios of oxides of greater than about 20:1, and an X-ray diffraction pattern characterized by the diffraction lines of Table 5.

TABLE 5 d-A Relative Intensity 11.1 + 0.2 v.s.

10.0 -e 0.2 v.s.

3.85 t 0.07 v.s.

3.82 t 0.07 s 3.76 t 0.05 s 3.72 + 0.05 s The chromia silicates, hereinafter referred to as CZM, have a composition, expressed in the anhydrous state in terms of mols of oxides which comprises: R2O:aM20:bCr2O3:cSiO2 wherein R2O is a quaternary alkylammonium oxide, preferably tetrapropylammonium oxide, M is an alkali metal selected from the group of alkali metals consisting of lithium, sodium, potassium or mixtures thereof, preferably sodium, a is between 0 and 1.5, c is greaterthan or equal to 12, and c/b is greater than 20. The ratio c/b will normally range between 20 and 3000, and is preferablyin the range of 50 to 1000.

Said chromia silicate exGribits the random powder X-ray diffraction lines shown in Table 6.

TABLE 6 InterplanarSpacing 2e Normalised d {Angstrom) (Double Bragg angle) Intensities 11.2 + .2 7.90 100 10.0512 8.80 70 9.75.11 9.07 17 8.99 t .09 9.84 1 7.44 ~ .06 11.90 1 6.71 05 13.20 7 6.36 t .05 13.92 11 5.99 t .04 14.78 14 5.7104 15.53 7 5.57t.04 15.91 10 5.36 +.03 16.54 3 5.14t.03 .03 17.25 1 5.02 .03 17.65 5 4.98t.03 17.81 5 4.61+.02 .02 19.25 4 4.36 .02 20.37 5 4.25 .02 20.88 8 4.08 .02 21.78 2 4.01 .02 22.18 3 3.86 t .02 23.07 52 3.82 +.02 23.29 32 3.75 + .02 23.73 17 3.72 t .02 23.73 26 3.65 1.02 24.40 12 3.60 t .02 24.76 2 3.48 1.01 25.58 2 3.44 1.01 25.88 4 3.40 .01 26.24 1 3.35 .01 26.60 3 3.31 1.01 26.95 6 3.25 +.01 27.43 2 3.05 1.01 29.28 4 2.99 1.01 29.90 9 2.96 +.01 30.22 4 The X-ray diffraction patterns were obtained by standard diffractometer methods using a copper target X-ray tube, a graphite crystal monochromato r set to select the K-alpha doublet radiation of copper, and a proportional countertube operating to selectively measure the reflected K-alpha doublet radiation.The patterns were recorded with a strip chart recorder and the diffraction peak intensities normalized to a scale of 0 to 100. The interplanar spacings, d (measured in angstroms), corresponding to the recorded diffraction peaks were calculated.

The crystalline chromia silicate is prepared by hydrothermally crystallizing an aqueous reaction mixture containing quaternary alkylammonium oxide, chromium oxide, silica and an oxide of an alkali metal from the group of alkali metals consisting of lithium, sodium, potassium or mixtures thereof, preferably sodium.

The reaction mixture preferably has a composition expressed in terms of mols of oxides, as follows: R2O:aM2O:bCr2O3:cSiO2:dHO wherein a is greaterthan 0 but less than 5, c is in the range 1 to 100, the ratio c/b is greater than 12 but less than 800, and d is in the range, 70-500. Preferably, a is in the range 0.05 to I, c is in the range 2-20, the ratio c/b is in the range 30 to 600 and d is in the range 100 to 300. Hydrothermal crystallization is preferably conducted at a temperature in the range of 100 to 200 C, more preferably at 125 to 175 C, and still more preferably at 150 C. The crystallization is conve nientlyconducted at the autogenous pressure of the reaction mixture.

CZM is useful as a hydrocarbon processing catalyst and is particularly useful in dewaxing operations and olefin production.

In such processes, a hydrocarbon charge, such as a reformate, is contacted with CZM catalyst under conversion conditions.

Normal paraffins in the reformate are cracked and yield substantial quantities of olefins, even in the presence of hydrogen.

Preferably, the reformate is contacted with the CZM catalyst in the presence of hydrogen at a hydrogen partiai pressure in the range of 10 to 27 atmospheres and at a temperature in the range of 450 to 510 C. These conversion conditions permit the catalyst to be placed to receive the entire reformer effluent either in a separate vessel following the reformer unit or as a layered bed of catalyst in the last reformer reactor. A liquid hourly space velocity in the range of 0.5 to 3 should preferably be maintained.

The CZM catalyst of the present invention may be used with or without a matrix or blinder. If a matrix is used, the CZM may be conventionally bound there with in a weight ratio of catalyst to matrix of from about 95:5 to 1:100. The matrix in such cases should comprise substantially nonacidic materials such as alumina or silica. A preferred binder is alumina which may be peptized, comulled with the catalyst, and extruded.

The chromia silicates of the present invention comprise crystalline structures identified by random powder X-ray diffraction patterns similar two those patterns exhibited by ZSM-5 aluminosilicates and silicalite. In the present invention, the chromia must be present in the reaction mixture during hydrothermal crystallization. The mol ratio of silica to chromia in the product composition is greater than 20 and is preferably in the range 50 to 1000.

CZM may be hydrothermally crystallized from a reaction mixture containing appropriate sources of chromium, silicon and sodium oxides, water, and quaternary alkylammonium cations having the formula (R4N) + in which R represents an alkyl group containing 1 to 4 carbon atoms.

Preferably R is an ethyl, propyl or normal butyl alkyl group, especially propyl. Illustrative compounds which supply the derived cation in solution, include tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, and the salts corresponding to these hydroxides, such as the chloride, bromide and iodide salts.

Suitable sources of silica for the reaction mixture include alkali metal silicates, such as sodium silicate solution, as well as reactive forms of the silica so Is, silica gels and fumed silicas. Silica sols, such as the commercially available, Ludox brand silica sol which contains 30% SiO2 by weight, are especially preferred. Since alumina will be readily incorporated into the crystalline lattice, care should be taken to minimize the sources of alumina impurities. Commercially available silica sols typically contain 500 to 700 ppm Al203, and at least a portion of the alumina will appear in the final product.

Generally, sodium, potassium or lithium may be added to the reaction mixture in the form of hydroxides or the corresponding salts thereof. Alkali metal silicates may also provide all or a portion of the required metals in addition to serving as a source of silica. Preferred reaction sources include sodium hydroxide, sodium nitrate and sodium silicate solution or water glass.

Chromium sources include soluble chromium salts such as chromium chloride, chromium sulfates, and chromium nitrates, the nitrates being especially preferred. The chromium silicates in the present invention are preferably crystallized from a basic reaction mixture having a pH in the range from 10 to 13. To obtain a mixture in this pH range, it may be necessary, depending upon the source of reactants, to raise the pH by adding additional base to the mixture (e.g. ammonium hydroxide or alkali metal hydroxides) orto lowerthe pH into the desired range using an acid (e.g. mineral acids). Sodium, lithium or potassium hydroxides are particularly useful in adjusting the pH upwards since the alkali metals are also required as reactants in the crystallization pro cess.

The reaction mixture should preferably comprise, in terms of ratios of mols of oxides, 0.05 to 5 mols of sodium, potassium or lithium oxide, 1 to 100 mols of SiO2, 70 to 500 mols of water and a ratio of mols of silica to mols ofchromia equal to or greater than 12 for each mol. Preferred reaction mixtures have from 0.05 to 1 mol of sodium, potassium or lithium oxide, preferably sodium oxide, 2 to 20 mols of silica, 100 to 300 mols of water and a ratio of mols of silica to mols of chromia in the range 30 to 600.

After the reaction mixture is prepared, the mixture is heated to a temperature in the range 100 to 200"C, preferably 125 to 175"C, and more preferably at a temperature of 1500C, and maintained at said temperature and at autogenous pressure until the hydrated forms of CZM are formed. Crystalline hydrated CZM will normally form and precipitate from the reaction mixture within 6 hours to 6 days, and normally within 48 hours. The product crystals are separated from the mother liquor, such as by cooling to room temperature, filtering and washing.

Low sodium or dehydrated forms of the product may be prepared by conventional techniques from the synthesized crystals.

The following examples are provided to more fully illustrate the nature of the invention.

EXAMPLE 1 A reaction solution was prepared by dissolving 47.9 grams of tetrapropylammonium bromide in 35 ml of water and adding to the solution 7.2 grams of sodium hydroxide dissolved in 30 ml. of water. 8 grams of Cr(NO3)3.9H2O dissolved in 20 ml of water and 116 grams of Ludox brand (30 weight percent SiO2) silica sol were added to the TPA BR-NaOH mixture with rapid stirring. The total reaction mixture was autoclaved in an open Teflon bottle at a temperature of 1500C and at autogenous pressure for 48 hours. At the end ofthe hydrothermal crystallization period, the product crystals were filtered from the solution and washed with water.The crystals were dried overnight at 121 0C and then calcined for 8 hours at 450"C. They had the X-ray diffraction pattern shown in Table 6 and had a composition in terms of mols of oxide as 0.6Na20:Cr203: 280SiO2 after washing with aqueous NH4NO3.

EXAMPLE 2 2.3 grams of sodium nitrate dissolved in 10 ml of water and 5.5 grams of Cr(NO3)3.9H2O dissolved in 10 ml of water were sequentially added to 100 grams of a 25 weight percent solution of tetrapropylammonium hydroxide with rapid stirring. 80 grams of Ludox brand8(30 weight percent SiO2) silica sol were added to the above solution and the total mixture was placed in an autoclave maintained at 144 C for two days at the solution vapor pressure. The product crystals were filtered from the solution and recovered, exchanged with ammonium nitrate, waterwashed, dried at 121 "C overnight, and calcined for 8 hours at 450CC. X-ray analysis revealed the diffraction pattern shown in Table 6, above.

The crystals had a composition expressed in terms of mol oxides as follows: 0.5Na20:Cr203:66SiO2 EXAMPLE 3 In testing the CZM catalyst, a sample of the chromia silicate, prepared in accordance with Example 2, was mixed with a binder (peptized Ziegler alumina-Catapal) in a weight ratio of 1 to 1, extruded, exchanged with ammonium acetate, dried, and calcined at450CC for 8 hours. The exchange and calcination were repeated twice. The non-alumina portion of the catalyst had a composition, expressed in terms of mol oxides, as follows: 0.01 Na2O:Cr2O3:225SiO2.

A 385 C+ isosplitter bottoms feedstock, having a pour point of -P33 C was passed over the catalyst with hydrogen at a pressure of 68 atmospheres, a temperature of 350"C and a liquid hourly space velocity of 2. Hydrogen feed to the reactors was maintained at 17.8 liters per liter of feed. Under these conditions a 370"C - product yield of 83.8 weight percent, having a pour point of-30 C was obtained.

For comparison purposes, a similar test was conducted using the same weight ratio of silicalite, prepared in accordance with U.S. Patent No. 4,061,724, to Catapal binder. However, in orderto obtain a comparable C4 f' product, an operating temperature of 406CC was required, thus dramatically demonstrating the greater activity of the chromia silicate overthe prior art.

EXAMPLE 4 A series of experiments were performed to examine the activity of CZM, silicalite, and silicaiite impregnated with chromium after synthesis using Cr(NO3)3.9H2O and standard techniques.

The CZM catalyst was prepared as follows: The sieve of Example 2 was exchanged five times with 25% ammonium acetate solution at 80 C, waterwashed, dried overnight at 121 C, and calcined at 450"C for 8 hours. The exchange, drying, and calcination was repeated.

Silicalite was prepared using the techniques of U.S.

4,061,724. The catalyst was prepared by exchanging silicalite four times with 20% ammonium nitrate solution at 80"C, water-washing, drying overnight at 1210C, andcalciningat4500Cfor8hours.

The chromium impregnated silicalite was prepared by impregnating the above catalyst with a solution of Cr(NO3)3.9H2O by the pore-fill method. The catalyst was dried overnight at 121 CC, and calcined at 450"C for 8 hours.

Inspections of the three catalysts are given in Table 7.

TABLE 7 Altppm) NatppmJ Cr(wt%) CZM 380 < 50 0.56 Silicalite 400 < 50 0 Silicalite impregnated 400 100 0.5 with chromium The catalysts were bound with Catapal alumina, extruded, dried, and calcined 8 hours at 450"C. Samples of each were placed in porcelain crucibles in a calcination pot and treated at 1400"F with a 100% steam atmosphere.

Steamed and unsteamed catalyst samples were then tested in a "pulse decane cracking test" to determine their cracking activity. The test procedure was as follows: 0.1-0.5g of catalyst were mixed with 1g of acid-washed and neutralized alundum and packed in a 3/16" stainless steel reactor tube with the remaining space filled with alundum. The reactor contents were calcined for one hour at 450"C. The reactor was then placed in a clam-shell furnace and the reactor outlet connected to the inlet of a gas chromatograph. The inlet was connected to the carrier gas line of the GC.Helium was passed through the system at 30 cc/min. 0.04 Microliter pulses of n-decane were injected through a septum above the reactor and reaction products were determined by standard GC analysis. Blank runs with alundum showned no conversion under the experimental conditions, nor did a 100% Catapal alumina catalyst.

A pseudo-first-order, cracking rate constant, k, was calculated using the formula K= 1 A 1-x where A is the weight of zeolite in grams and x is the fractional conversion to products boiling below decane.

Table 8 shows the resulting values of the 1 n ofkas a function of steaming time at 1400"F.

TABLE 8 Ln kaftersteaming at 1400"F 0 hers. 6 hrs. 24 hrs.

CZM -0 -1.85 -2.70 Silicalite -1.40 -3.00 -4.35 Silicalite impregnated 0 -2.65 -4.20 with chromium With no steaming, both chromium containing catalysts were very active. After 6 hours steaming, CZM was about three times as active as silicalite, while the chromium-impregnated silicalite was only about 1.4 times as active. After 24 hours steaming, CZM was five times as active as silicalite, while the silicalite impregnated with chromium had only slightly improved activity. These data illustrate the significantly different catalytic activity obtained by the CZM chromia silicates from low alumina silicates which have and have not been impregnated with chromium.

EXAMPLE 5 ESCA Analysis ofCrSllicalites A series of tests were performed to show the differences between the chromium in CZM chromia silicates and in silicalite impregnated with chromium.

Samples of CZM and chromium impregnated silicalite prepared as in Example 4 (but unsteamed) were examined in a Hewlett-Packard 5950A ESCA (Electron Spectroscopy for Chemical Analysis) Spectrometer. The samples were not bound in a composite. Both samples were powders and were mounted in the spectrometer by dusting them onto doublesided sticky tape. Al Ka radiation that had been passed through a monochromator was employed as the excitation source. 2 eV electrons from an electron fiood gun with an emission setting of 0.3 mAmp were used to compensate for sample charging effects. The pressure in the spectrometer during analysis was about 2x1 Cr8 torr. For chromium a 50 eV window with 256 points was scanned, while for silicon, carbon and oxygen 20 eV windows with 256 points were scanned.The various windows were scanned several times and then signal averaged to obtain good signal-to-noise ratios and resolution.

The analyzer was calibrated by setting the Au(4f 7/2) binding energy (BE) at 84.0 10.1 eV. After accounting for the sample charging effects the Cr (2p3/2) BE was 2 eV lower in CZM than in chromium impregnated silicalite, while the Si(2p) and O(is) BE's of the two samples were the same within experimental accuracy (+0.1eV). The accompanying drawing shows the difference in the Cr(2p) lines for CZM and chromium impregnated silicalite. The large difference in Cr BE's indicates that the chromium, surprisingly, is in different oxidation states in the two samples.

Visual inspection ofthe CZM and the chromium impregnated silicalite gives further evidence of differences between the samples. After the calcination step ofthe preparation (450"C; 8 hr), the CZM sample was light green in color while the chromium impregnated silicalite was yellow. This shows the increased stability of the chromium in the CZM chromia silicate as compared to the chromium impregnated silicalite.

The synthetic chromia silicates can be used as synthesized or can be thermally treated (calcined).

Usually, it is desirableto remove alkali metal cation by ion exchange and replace it with hydrogen, ammonium, or any desired metal ion. The chromia silicate can be used in intimate combination with hydrogenating components, such as tungsten, vanadium, molybdenum, rhenium, nickel, cobalt, chromium, manganese, or a noble metal, such as palladium or platinum, for those applications in which a hydrogenation-dehydrogenation function is desired. Typical metal cations can include rare earth, Group IIA and Group Villi metals, as well as their mixtures; cations of metals such as rare earth, Mn, Ca, Mg, Zn, Cd, Pt, Pd, Ni, Co, Ti, Al, Sn, Fe and Co are particularly preferred.

The hydrogen, ammonium and metal components can be exchanged into the chromia silicate. The chromia silicate can also be impregnated with the metals, or, the metals can be physically intimately admixted with the chromia silicate using standard methods known to the art.

Typical ion exchange techniques involve contacting the synthetic chromia silicate with a solution containing salt of the desired replacing cation or cations. Although a wide variety of salts can be employed, chlorides and other halides, nitrates, and sulfates are particularly preferred. Representative ion-exchange techniques are disclosed in a wide variety of patents including U.S. Patent Nos.

3,140,249; 3r140,251; and 3,140,253. Ion-exchange can take place either before or after the zeolite is calcined.

Following contact with the salt solution of the desired replacing cation, the chromia silicate is typically washed with water and dried at a temperature ranging from 65 C to about 315"C. After washing, it can be calcined in air or inert gas attemperatures ranging from about 200"C to 820 C for periods of time ranging from 1 to 48 hours, or more, to produce a catalytically-active product especially useful in hydrocarbon conversion processes.

Regardless of the cations present in the synthesized form of the chromia silicate, the spatial arrangement of the atoms which form the basic crystal lattice remains essentially unchanged. The exchange of cations has little, if any, effect on the lattice structures.

The chromia silicates can be manufactured into a wide variety of physical forms. Generally speaking, they can be in the form of a powder, a granule, or a molded product, such as extrudate having particle size sufficient to pass through a 2-mesh (Tyler) screen and be retained on a 400-mesh (Tyler) screen.

In cases where the catalyst is molded, such as by extrusion with an organic binder, the chromia silicate can be extruded before drying, or, dried or partially dried and then extruded.

The chromia silicate can be composited with other materials resistant to the temperatures and other conditions employed in organic conversion processes. Such matrix materials include active and inactive materials and synthetic or naturally occurring zeolites as well as inorganic materials such as clays, silica and metal oxides. The latter may be either naturally occurring or in the form of gelatinous precipitates, sols or gels including mixtures of silica and metal oxides. Use of a material in conjunction with the synthetic chroma silicate, i.e., combined therewith, which is active, tends to improve the conversion and selectivity of the catalyst in certain organic conversion processes. Inactive materials suitably serve as diluents to control the amount of conversion in a given process so that products can be obtained economically without employing other means for controlling the rate of reaction. The chromia silicates can be incorporated into naturally occurring clays, e.g., bentonite and kaolin. These materials, i.e., clays, oxides, etc., function, in part, as binders for the catalyst. It is desirable to provide a catalyst having good crush strength, because in petroleum refining the catalyst is often subjected to rough handling. This tends to break the catalyst down into powder-like materials which cause problems in processing.

Naturally occuring clays which can be composited with the chromia silicates of this invention include the montmorillonite and kaolin families, which families include the sub-bentonites, and the kaolins commonly known as Dixie, McNamee, Georgia and Florida clays or others in which the main mineral constituent is halloysite, kaolinite, dickite, nacrite, or anauxite. Fibrous clays such as sepiolite and attapulgite can also be used as supports. Such clays can be used in the raw state as originally mined or initially subjected to calcination, acid treatment or chemical modification.

In addition to the foregoing materials, the chromia silicate can be composited with porous matrix materials and mixtures of matrix materials such as silica, alumina, titania, magnesia, silica alumina, silicamagnesia, silica-zirconia, silica-thoria, silica-beryllia, silica-titania, titania-zirconia as well as ternary compositions such as silica - alumina -thoria, silica alumina - zirconia, silica - alumina - magnesia and silica - magnesia - zirconia. The matrix can be in the form of a cogel.

The chromia silicates can also be composited with other zeolites such as synthetic and natural faujasites, erionites, and mordenites (e.g. X and Y). They can also be composited with synthetic zeolites.

The relative proportions of the crystalline chromia silicates of this invention and the inorganic oxide gel matrix can vary widely. The chromia silicate content can range from about 1 to about 90 percent by weight but is more usually in the range of about 2 to about 50 percent by weight of the composite.

Chromia silicates are useful in hydrocarbon conversion reactions. Hydrocarbon conversion reactions are chemical and catalytic processes in which carbon-containing compounds are changed to different carbon-containing compounds. Examples of hydrocarbon conversion reactions include catalytic cracking, hydrocracking, and olefin and aromatics formation reactions. The catalysts are useful in other petroleum refining and hydrocarbon conversion reactions such as isomerizing n-paraffins and naphthenes, polymerizing and oligomerizing olefinic or acetylenic compounds such as isobutylene and butene-1, reforming, alkylating, isomerizing polyalkyl substituted aromatics (e.g., ortho xylene), and disproportionating aromatics (e.g. toluene) to provide a mixture of benzene, xylenes and higher methylbenzenes.

The chromia silicates can be used in processing hydroca rbonaceous feedstocks. Hydroca rbonaceo us feedstocks contain carbon compounds and can be from many different sources, e.g., virgin petroleum fractions, recycle petroleum fractions, shale oil, liquefied coal, tar sand oil, and in general any carbon containing fluid susceptible to zeolitic catalytic reactions. Depending on the type of processing the hydrocarbonaceous feed is to undergo, the feed can be metal-containing or without metals, it can also have high or low nitrogen or sulfur impurities. It can be appreciated, however, that in general the processing will be more efficient (and the catalyst more active) the lower the nitrogen content of the feedstock.

The conversion of hydrocarbonaceous feeds can take place in any convenient mode, for example, in fluidized bed, moving bed, or fixed bed reactors depending on the types of process desired. The formulation ofthe catalyst particles will vary depending on the conversion process and method of operation.

Using chromia silicates containing hydrogenation components, heavy petroleum residual stocks, cyclic stocks, and other hydrocrackable charge stocks can be hydrocracked at temperatures from 300 C to 525"C using molar ratios of hydrogen to hydrocarbon charge from 1 to 100. The pressure can vary from 10 to 5000 psig and the liquid hourly space velocity from 0.1 to 30. For these purposes, the chromia silicates can be composited with mixtures of inorganic oxide supports as well as with faujasites such as X and Y.

The chromia silicates can be used for catalytic cracking using temperatures from about 260 C to 625"C, pressures from subatmospheric to several hundred atmospheres, and other standard conditions.

Chromia silicates can be used to dewax hydrocarbonaceous feeds by selectively removing straight chain and slightly branched chain paraffins. The process conditions can be those of hydrodewaxing - a mild hydrocracking, or they can be at lower pressures in the absence of hydrogen. Dewaxing produces significant amounts of olefins from the cracked paraffins.

Chromia silicates can also be used in reforming reactions using temperatures from 360"C to 600"C, pressures from atmospheric to 500 psig, and liquid hourly space velocities from 0.1 to 20. The hydrogen to hydrocarbon mol ratio can be generally from 1 to 20.

The catalyst can also be used to hydroisomerize normal paraffins, when provided with a hydrogenation component, e.g., platinum. Hydroisomerization is generally carried out at temperatures from 200 C to 3750C, and liquid hourly space velocities from 0.01 and 5. The hydrogen to hydrocarbon mol ratio is from 1:1 and 5:1. Additionally, the catalyst can be used to isomerize olefins using temperatures from 140 C to 320"C.

Other reactions which can be accomplished employing the catalyst of this invention containing a metal, e.g., platinum, include hydrogenationdehydrogenation reactions, denitrogenation and desulfurization reactions.

Chromia silicates can be used in hydrocarbon conversion reactions with active or inactive supports, with organic or inorganic binders, and with and without added metals. These reactions are well known to the art as are the reaction conditions.

Claims (20)

1. A synthetic crystalline chromia silicate catalyst having a SiO2:Cr2O ) mol ratio greater than 20:1 and haviang a random powder X-ray diffraction pattern characterized by the following diffraction lines: d-A

11.1 t 0.2

10.0 + 0.2

3.85 + 0.07

3.82 t 0.07

3.76 t 0.05

3.72 + 0.05

2.A synthetic crystalline chromia silicate catalyst expressed in the anhydrous state in terms of mols of oxides comprising: R2O:aM2O:bCr2O:cSiO2 wherein R2O is a quaternary alkylammonium oxide, M is an alkali metal selected from lithium, sodium and potassium or mixtures thereof, a is greaterthan 0 but less than 1.5, c is greater than or equal to 12, and c/b is greater than 20; and said chromia silicate having a random powder X-ray diffraction pattern characterized by the diffraction lines shown in the foregoing Table 6.

3. Acrystalline chromia silicate catalyst as claimed in Claim 2, wherein R2O is tetrapropylammonium oxide and M is sodium.

4. A process for preparing a crystalline chromia silicate catalyst, which comprises: hydrothermally crystallizing a reaction mixture containing a quaternary alkylammonium oxide, an oxide of an alkali metal selected from lithium, sodium and potassium or mixtures thereof, chromium oxide and silica, said reaction mixture having a composition expressed in terms of mols of oxides of: R2O:aM2O:bCr3O2:cSiO2:dH, wherein R2O is a quaternary alkylammonium oxide, M is an alkali metal selected from lithium, sodium and potassium or mixtures thereof, a isgreaterthan 0 but less than 5, c is in the range 1-100, c/b is greater than 12, and d is in the range 70-500.

5. A process according to Claim 4, wherein R2O is tetrapropylammonium oxide and M is sodium.

6. A process according to Claim 4 or 5, wherein a is in the range of 0.05-1, c is in the range 2-20, c/b is in the range 30-600 and d is in the range 100-300.

7. A process according to Claim 4, 5 or 6, wherein the hydrothermal crystallization is conducted at a temperature in the range from 100 to 200"C.

8. A process according to Claim 4, 56 or 7, wherein the hydrothermal crystallization is conducted at autogenous pressure.

9. A process for preparing a crystalline chromia silicate substantially as described in the foregoing Example 1 or2.

10. A process for preparing a crystalline chromia silicate as claimed in Claim 1, substantially as described in the foregoing Example 4.

11. A hydrocarbon conversion process which comprises contacting a hydrocarbonaceous feed with a catalyst as claimed in Claim 1, 2 or 3, under hydrocarbon conversion conditions.

12. A hydrocarbon conversion process according to Claim 11, wherein said process is hydrocracking.

13. A hydrocarbon conversion process according to Claim 11, wherein said process is dewaxing.

14. A hydrocarbon conversion process according to Claim 11, wherein said process is reforming.

15. A hydrocarbon conversion process according to Claim 11, wherein said process is olefin polymerization or oligomerization.

16. A hydrocarbon conversion process according to Claim 11, wherein said process is isomerization.

17. A hydrocarbon conversion process according to Claim 11, wherein said process is disproportionation.

18. A hydrocarbon conversion process according to Claim 11, wherein said process is alkylation.

19. A hydrocarbon conversion process according to Claim 11, wherein said process is catalytic cracking.

20. A hydrocarbon conversion process in accordance with Claim 11, substantially as described in the foregoing Example 3 or 4.