FR2463746A1 - CHROMIUM SILICATE CATALYST, PROCESS FOR PRODUCING THE SAME AND APPLICATION THEREOF TO HYDROCARBON TREATMENT - Google Patents

Abstract

THE INVENTION RELATES TO A NEW CATALYST OF THE TYPE OF A CRYSTALLINE SILICATE CONTAINING CHROME OXIDE. THE CATALYST OF THE INVENTION SHOWS AN X-RAY DIFFRACTION DIAGRAM SIMILAR TO THAT OF KNOWN ALUMINOSILICATES, BUT IT IS PREPARED BY HYDROTHERMAL CRYSTALLIZATION OF A WATER-BASED REACTIONAL MIXTURE CONTAINING SOURCES OF ALKOATNAIREMONIUM, DE CHRISTIAN SILICA AND AN ALKALINE METAL OXIDE. APPLICATION TO THE TRANSFORMATION OF HYDROCARBONS.

Description

The present invention relates to new varieties of silicates

  containing chromium oxide and methods for obtaining them. These compositions are useful as catalysts for hydrocarbon processing processes, particularly in

  dewaxing operations and for the production of olefins.

  Crystalline zeolites called molecular sieves are aluminosilicates formed from a rigid three-dimensional network of SiO and AlO4 tetrahedra bonded by common oxygen atoms. The inclusion of aluminum atoms in the network produces a deficiency of electric charge which must be compensated locally by the presence of additional positive ions in the structure. In natural zeolites and in many synthetic zeolites, these ions are normally alkali metal or alkaline earth metal cations which are highly mobile and are easily exchanged to other degrees by other conventional techniques. Cations occupy interconnected channels and voids created by the

network geometry.

  U.S. Patent No. 3,702,886 discloses a novel family of crystalline zeolites, referred to as ZSM-5 zeolites. Zeolites of the ZSM-5 type have a composition in which the molar ratios of the oxides are expressed by the equation: Of 9 + O 2 M 2 / nO: W 2 Q 3: 51 OO y O 2: zH 2 O wherein M represents at least one cation, n is the valence of this cation, W is aluminum or gallium, Y is silicon or germanium and z has a value of 0 to 40. Representatives of the ZSM-5 zeolite family are considered as having a statistical X-ray diffraction pattern (methods using a powder) which has the following characteristic lines: Interplanar spacing

TABLE I

(d / nm): Relative intensity

1.11 + 0.02

1.00 + 0.02

0.74 + 0.015

0.71 + 0.015

0.63 + 0.01

0.604)

) + 0.01

0.597)

0.556 + 0.01

0.501 + 0.01

0.460 + 0.008

0.425 + 0.008

0.385 + 0.007

0.371 + 0.005

0.304 + 0.003

0.299 + 0.002

0.294 + 0.002

  strong, low, very high, very low, n values The values given above have been determined by conventional techniques described in US Pat.

aforementioned patent.

  This patent teaches that zeolites of the ZSM-5 type are prepared by hydrothermal crystallization of a reaction mixture of tetrapropylammonium hydroxide, sodium oxide, aluminum oxide or gallium oxide.

  an oxide of silicon or germanium.

  U.S. Patent No. 3,941,871 discloses a crystalline metal organosilicate whose composition, in the anhydrous state, has the following formula: 0.9 + 0.2 (xR2O + (1-x) M2 / nO1): <0, 005Al2O3:> 1SiO2 in which M is a metal other than a Group metal

  IIIA, n is the valence of this metal, R is an alkyl radical

  ammonium and x has a value between 0 and 1. The synthesis of the described compositions is carried out by crystallization

  hydrothermal reaction mixture of alkyl oxides

  ammonium, sodium oxides, water and oxides of a metal other than a Group IIIA metal. Alumina appears in the product in small amounts due to the presence of impurities in the reactants and / or equipment used in the synthesis. Statistical diffraction analysis of X-rays (powder) shows the following characteristic lines:

TABLE II

  Interplanar spacing (d / nm): Relative intensity

1.11 + 0.02

1.00 + 0.02

0.74 + 0.015

0.71 + 0.015

0.03 + 0.01

0.604)

) + 0.01

0.597)

0.556 + 0.01

0.501 + 0.01

0.4 / 0.7- + / 0.008

0.425 + 0.008

0.385 + 0.007

0.371 + 0.005

0.304 + 0.003

0.299 + 0.002

0.294 + 0.002

  strong you weak I1 It is very strong strong weak It II The patent of the United States of America N 4,061,724

  discloses a crystalline silica called "silicalite".

  Silicalite is prepared by hydrothermal crystallization of a reaction mixture containing water, silica and

  an alkylonium compound such as tetraethylhydroxide

  ammonium, tetrapropylammonium hydroxide, corresponding salts, such as tetrapropylammonium bromide. Silicalite, after calcination in air at 600 ° C for 1 hour, shows the following X-ray diffraction pattern:

TABLE III

Relative intensity

1.11 + 0.02

1.00 + 0.02

0.385 + 0.007

0.382 + 0.007

0.376 + 0.005

0.372 + 0.005

  Table IV reproduces the results of an X-ray diffraction analysis of a silicalite composition after calcination, containing 51.9 moles of SiO per mole of tetrapropylammonium oxide:

TABLE IV

  d (nm) Relative intensity d (nm) Relative intensity 1,11 1,002

0.973

0.899 0.804 0.742 0.706

0.668

0.635 0.598 0.570 0.557

0.536

0.511 0.501 0.498 0.486

0,460

  0.444 0.5 0.5 0.5 0.5 0.435 0.425 0.408 0.400 0.385 0.382 0.374 0.371 0, 364 0.359 0.348 0.344 0.334 0.330 0.325 0.317 0.313 0.305 0.298 0.5 -5 1 1 0.5 0.5 d (nm) ) All the above compositions have a

  pore diameter of about 0.6 nm and are useful

  in some applications for hydrocarbon processing. However, aluminosilicates of the ZSM-5 type are "excessively" active in hydrocracking operations, for example in the cracking of normal paraffins in a feed, for purposes of dewaxing. This high activity leads to high gas production and produces low liquid yields. Silicalite, on the other hand, is much less active and is used mainly to absorb oil in

oil and water mixtures.

  One of the aims of the present invention is therefore to find a new composition which can be used to dewax fillers giving high yields of liquid, for the production of olefins and for other

  hydrocarbon processing processes.

  The single figure of the accompanying drawing illustrates the electronic spectra of chemical analysis (ESCA spectra) of metallic chromium in the CZM chromium silicates of the present invention (CZM curve) and in a silicalite

  impregnated with chromium obtained in Example 5 (CR curve).

  (The binding energy is expressed in attojoules).

  The present invention relates to a new

  crystalline chromium silicate which is formed by crystalliza-

  hydrothermal reaction of a reaction mixture containing chromium. The chromium silicates of the present invention have a ratio of chromium oxide: silicon oxide, expressed as a function of the molar proportions of the oxides, of more than about 20: 1 and an X-ray diffraction pattern characterized by the diffraction lines indicated on the

table V.

TABLE V

  d (nm) Relative intensity 1.11 + 0.02 very strong

1.00 + 0.02

0.385 + 0.007

0.382 + 0.007 strong

0.376 + 0.005

0.372 + 0.005 "

  The chromium silicates, hereinafter referred to as CZM, have a composition, expressed in the anhydrous state by the number of moles of oxides, corresponding to the formula: R20: aM2O: bCr203: cSiO2 in which R20 is an oxide of quaternary alkylammonium, preferably tetrapropylammonium oxide, M is an alkali metal selected from the group of alkali metals formed of lithium, sodium, potassium or their mixtures, preferably sodium, has a value between 0 and 1 , 5, c is greater than or equal to 12 and the c / b ratio is greater than 20. The c / b ratio is normally in the range of 20 to 3000 and is preferably in the range of 50 to 1000. This chromium silicate exhibits the X-ray (powder) random diffraction lines indicated on

the following table VI.

  Interplanar spacing d (nanometers)

TABLE VI

  (Bragg angle multiplied by 2) Normalized Intensities

1.12 + 0.02

1.005 + 0.012

0.975 + 0.011

0.899 + 0.009

0.744 + 0.006

0.671 + 0.005

0.636 + 0.005

0.599 + 0.004

0.571 + 0.004

0.557 + 0.004

0.536 + 0.003

0.514 + 0.003

0.502 + 0.003

0.498 + 0.003

0.461 + 0.002

0.436 + 0.002

0.425 + 0.002

0.408 + 0.002

0.401 + 0.002

0.386 + 0.002

0.382 + 0.002

0.375 + 0.002

0.372 + 0.002

0.365 + 0.002

0.360 + 0.001

0.348 + 0.001

0.344 + 0.001

0.340 + 0.001

0.335 + 0.001

0.331 + 0.001

0.325 + 0.001

0.305 + 0.001

0.299 + 0.001

0.296 + 0.001

  7.90 8.80 9.07 9.84 11.90 13.20 13.92 14.78, 53, 91 16.54 17.25 17.65 17, 81 19.25, 37, 88 21.78 22.18 23.07 23.29 23.73 23.73 24.40 24.76, 58, 88 26.24 26.60 26.95 27.43 29.28 29.90, 22 1 1 Determined X-ray diffraction patterns by normal diffractometric methods

  using a copper-target X-ray tube, a mono-

  a graphite crystal chromator selectively tuned from the copper K-alpha doublet radiation and a proportional counting tube operating to selectively measure the reflected radiation of the K-alpha doublet. The diagrams were recorded using a graphical recorder and the maximum diffraction intensities were reduced to a standard scale from 0 to 100. The interplanar spacings d (measured in nanometers) corresponding to the

  recorded diffraction peaks, were calculated.

  The crystalline crystalline silicate is prepared by hydrothermal crystallization of an aqueous reaction mixture containing a quaternary alkylammonium oxide, chromium oxide, silica and an alkali metal oxide selected from the group of alkali metals comprising lithium, sodium, potassium or their mixtures,

preferably sodium.

  The reaction mixture preferably has a composition which is expressed, as a function of the moles of oxides,

by the formula: -

  R20: aM2O: bCr203: cSiO2: dH20 where a is greater than 0, but less than 5, c is in the range of 1 to 100, the ratio c / b is greater than 12, but less than 800, and is preferably in the range of 70 to 500. Preferably, a is in the range of 0.05 to 1, c is in the range of 2 to 20, the ratio c / b is in the range of 30 to 600 and da range from 100 to 300. The hydrothermal crystallization is preferably conducted at a temperature in the range of 100 to 2001C, preferably in the range of 125 to 1751C and especially at the temperature of 1500C. The crystallization is advantageously carried out under the autogenous pressure of the mixture

reaction.

  CZM is useful as a hydrocarbon processing catalyst and is particularly preferred in dewaxing operations and in the

olefin production.

  In these processes, a hydrocarbon feedstock, for example a reforming product, is brought into contact with a

  CZM catalyst under transformation conditions.

  The normal paraffins found in the reforming product are cracked and give

  appreciable olefins, even in the presence of hydrogen.

  Preferably, the reforming product is contacted with the CZIN catalyst in the presence of hydrogen at a hydrogen partial pressure in the range of 1.0 to 2.7 MPa and a temperature in the range of 450. at 510WC. These transformation conditions make it possible to make the catalyst capable of receiving all of the effluent from the reforming tower either in a separate container arranged after the reforming plant, or in a laminate bed of catalyst in the latter. reforming reactor. We should preferably maintain a

  hourly space velocity of the liquid from 0.5 to 3.

  The CZM catalyst of the present invention can be used with or without a matrix or binder. If a matrix is used, the CZM catalyst can be conventionally bonded to this matrix in a weight ratio of catalyst to matrix of about 95: 5 to 1: 100. In these cases, the matrix must contain substantially non-acidic materials such as alumina or silica. A binder

  appreciated is the alumina that can be peptized, put into

  suspend with the catalyst, then extrude.

  The chromium silicates of the present invention have crystalline structures identified by X-ray statistical diffraction patterns (powder)

  similar to the diagrams presented by alumino-

  silicates of the ZSM-5 type and silicalite. In the present invention, chromium oxide must be present in the

  reaction mixture during the hydrous crystallization

  thermal. The molar ratio of silica to chromium oxide in the product composition is greater than 20 and is preferably in the range of 50 to 1000. The CZM product can be formed by hydrothermal crystallization from a mixture reaction mixture containing suitable sources of chromium, silicon and sodium oxides, water and quaternary alkylammonium cations of the formula (R4N) + wherein R represents an alkyl group containing 1 to 4 carbon atoms. Preferably, R is an alkyl group such as a normal ethyl, propyl or butyl group, preferably the propyl group. Examples of compounds that provide the

  desired cation in solution include tetrahydroxide

  ethylammonium, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide and the salts corresponding to these hydroxides, such as chlorides, bromides and

iodides.

  Suitable sources of silica for the reaction mixture include alkali metal silicates such as sodium silicate solution, as well as reactive forms of silica sols, silica gels and silica "fumes". Silica sols such as the commercially available "Ludox" brand silica sol, which contains 30% by weight of SiO 2, are particularly preferred. Since silica is easy to incorporate into the crystal lattice, efforts should be made to minimize sources of impurities such as alumina. Commercially available silica sols normally contain 500 to 700 parts per million of Al 2 O 3 and at least a portion of

  alumina is found in the final product.

  Generally, sodium, potassium or lithium may be added to the reaction mixture as hydroxides or corresponding salts. Alkali metal silicates may also provide all or a portion of the desired metals, in addition to being a source of silica. Preferred reaction sources include sodium hydroxide, sodium nitrate, and a solution of sodium silicate also called water glass. Sources of chromium include soluble chromium salts such as chromium chloride, chromium sulfates and chromium nitrates, with nitrates being particularly preferred. The chromium silicates used in the present invention are preferably obtained by crystallization from a basic reaction mixture whose pH is in the range of 10 to 13. To obtain a mixture in this pH range, it may be necessary to depending on the source of the reactants, to raise the pH by adding additional base to the mixture (for example ammonium hydroxide or alkali metal hydroxides) or to lower the pH to the desired range using a acid (chosen for example between mineral acids). The

  hydroxides of sodium, lithium or potassium are particularly

  useful for adjusting pH to increasing values, since alkali metals

  in the crystallization process.

  The reaction mixture should preferably contain molar proportions of oxides of 0.05 to 5 moles of sodium, potassium or lithium oxide, 1 to 100 moles of SiO 2, 70 to 500 moles of water and it should have a ratio of moles of silica to moles of chromium oxide equal to or greater than 12 for each mole. Preferred reaction mixtures contain 0.05 to 1 mole of sodium, potassium or lithium oxide, preferably sodium oxide, 2 to 20 moles of silica, 100 to 300 moles of water and a ratio of moles of silica to the number of moles of chromium oxide in the

range from 30 to 600.

  After the reaction mixture has been prepared, this mixture is heated to a temperature in a range of 100 to 2000C, preferably 125 to 1750C and especially at a temperature of 1500C and is maintained at this temperature and at autogenous pressure until the hydrated forms of CZM have been produced. The crystalline hydrated CZM product is formed and normally precipitates in the reaction mixture over a period of 6 hours to 6 days, normally over a period of 48 hours. The crystals produced are separated from the mother liquor, for example by cooling to room temperature, filtration and washing. Low sodium forms or dehydrated forms of the product can be prepared by conventional techniques from the synthesized crystals. Other details of the present invention

emerge from the following examples.

EXAMPLE 1

  A reaction solution is prepared by dissolving 47.9 g of tetrapropylammonium bromide in ml of water and adding to the solution 7.2 g of sodium hydroxide dissolved in 30 ml of water. To the mixture of tetrapropylammonium bromide and sodium hydroxide is added, with rapid stirring, 8 g of Cr (NO3) 3.9H2O dissolved in 20 ml of water and 116 g of "Ludox" brand silica sol (30% by weight of SiO2). The total reaction mixture is autoclaved in an open "Teflon" bottle at a temperature of 1500C and under autogenous pressure for 48 hours. At the end of the hydrothermal crystallization period, the product crystals are separated from the solution by filtration and washed with water. The crystals are dried for about

  18 hours at 1211C, then calcined for 8 hours at 4501C.

  They exhibit the X-ray diffraction pattern reproduced in Table VI and, after washing with an aqueous solution of ammonium nitrate, their composition expressed in moles of oxide corresponds to the formula 0.6Na 2 O: Cr 2 O 3: 28 OSiO 2.

EXAMPLE 2

  2.3 g of sodium nitrate dissolved in 10 ml of water and 5.5 g of Cr (NO3) 3. 9H20 dissolved in 10 ml of water are successively added to 100 g of a 25% solution by weight

  of tetrapropylammonium hydroxide, with rapid stirring.

  80 g of "Ludox" brand silica sol (30% by weight of SiO 2) are added to the above solution and the total mixture is maintained in an autoclave set at 14 ° C. for 2 days at the vapor pressure of the solution . The product crystals are filtered from the solution and collected, treated by ammonium nitrate exchange, washed with water, dried for about 18 hours at 12 ° C. and calcined for 8 hours at 450 ° C. X-ray analysis reveals the diffraction pattern reproduced on the chart

VI above.

  The crystals have the following composition, expressed in moles of oxides: 0.5 Na 2 O: Cr 2 O 3: 66 SiO 2

EXAMPLE 3

  To test the CZM catalyst, a sample of the chromium silicate prepared in accordance with Example 2 is mixed with a binder ("Catapal" Ziegler alumina) in a weight ratio of 1: 1, the mixture is extruded and exchanged with ammonium acetate, dried and calcined at 4500C for 8 hours. The exchange and calcination are repeated twice. The portion of the foreign alumina catalyst has the following composition, expressed in moles of oxides: OOlNa 2 O: Cr 2 O 3: 225SiO 2 The tails of a fractionated isocarbon fractionation apparatus, boiling at 3350 ° C., are passed as a filler onto the catalyst. and having a pour point of + 330C, with hydrogen at a pressure of 6.8 MPa, at a temperature of 3500C and at a liquid hourly space velocity equal to 2. The hydrogen charge introduced into the reactors is maintained at a rate of 17.8 liters per liter of charge. Under these conditions, a product boiling at 37 ° C., having a pour point of -30 ° C., is obtained in a yield of 83.8% by weight. For comparison purposes, a similar test was conducted using the same weight ratio of silicalite (prepared in accordance with US Patent No. 4,061,724 supra) and "Catapal" binder. However, in order to obtain a comparable C4 + product, a working temperature of 4060C was required, which demonstrates remarkably the highest

  activity of chromium silicate compared to the prior art.

EXAMPLE 4

  A series of experiments were conducted to observe the activity of the CZM product, silicalite and chromium impregnated silicalite after synthesis using Cr (NO3) 3.9H2O and conventional techniques. The CZM catalyst was prepared as follows: The sieve of Example 2 was exchanged five times with a 25% solution of ammonium acetate at 800 ° C, washed with water, dried for about 18 hours at 12 ° C. and calcined at 4500C for 8 hours. Exchange, drying and calcination are repeated. Silicalite is prepared using the techniques described in U.S. Patent No. 4,061,724. The catalyst is prepared by treating the silicalite by four-fold exchange with a 20% solution of ammonium nitrate at 800 ° C. washing with water, drying for about 18 hours at 1210C and calcination at 4500C for

8 hours.

  The chromium impregnated silicalite is prepared by impregnating the above catalyst with a solution of Cr (NO3) 3.9H20 by the pore filling method. The catalyst is dried for about 18 hours at 12 ° C. and

calcined at 4500C for 8 hours.

  Analytical data on the three

  Catalysts are reproduced in Table VII.

TABLE VII

Al (ppm) Na (ppm) Cr (% by weight)

CZM 380 <50 0.56

  Silicalite 400 <50 0 Silicalite impregnated with chromium 400 100 0.5 The catalysts are bonded with "Catapal" alumina, extruded; dried and calcined for 8 hours at 4500C. Samples of each of them are placed in porcelain crucibles in a calcination pot and processed

  at 7600C in an atmosphere with 100% water vapor.

  Treated and untreated steam catalyst samples are then tested in a "pulse decane cracking test" to determine their cracking activity. The test method is as follows: a quantity of 0.1 to 0.5 g of catalyst is mixed with 1 g of acid-washed and neutralized alundum and the mixture is loaded into a stainless steel tubular reactor. 4.76 mm, the remaining space being filled with alundum. The reactor contents are calcined for 1 hour at 450WC. The reactor is then placed in a shell furnace and the reactor outlet is connected to the inlet of a gas chromatograph. The inlet is connected to the gas train of the gas chromatograph. Helium is passed into the apparatus at a rate of 30 cm 3 / min. 0.04 microliter volumes of n-decane were pulsed through a membrane above the reactor and the reaction products were assayed by conventional gas chromatographic analysis. Witnesses

  made with alundum do not show any transfor-

  in experimental conditions, no more than in

  the case of a catalyst with 100% alumina "Catapal".

  A pseudo-first-order cracking rate constant k is calculated using the formula 1 k = -A-1-x-1 where A is the weight of zeolite in grams and x is the fraction of transformation into products of more low point

boiling as the decane.

  Table VIII shows the values obtained for the common logarithm (ln) of k as a function of the duration of

Steam treatment at 7600C. -

TABLE VIII

  ln k after steaming at 7601C 0 hours 6 hours 24 hours

CZM> 0 -1.85 -2.70

  Silicalite -1.40 -3.00 -4.35 Chromium Impregnated Silicalite> 0 -2.65 -4. In the absence of steam treatment, the two chromium-containing catalysts are very active. After steaming for 6 hours ,. the CZM catalyst is about three times as active as the silicalite, while the chromium impregnated silicalite is only about 1.4 times as active. After steam treatment for 24 hours, the CZM catalyst is five times as active as silicalite, while the chromium impregnated silicalite shows only a slight improvement in activity. These results demonstrate the distinctly different catalytic activity of CZM chromium silicates compared to low alumina silicates

  have and have not been impregnated with chromium.

EXAMPLE 5

  ESCA Analysis of Chromium Impregnated Silicalites A series of tests were conducted to demonstrate the differences in chromium in CZM chromium silicates and in chromium impregnated silicalite. Samples of CZM and chromium impregnated silicalite prepared as in Example 4 (but without steam treatment) are examined in an ESCA spectrometer.

  (Electron Spectroscopy for Chemical Analysis) Hewlett-

  Packard 59A0A. The samples are not bonded into a composite. Both samples are powders and are introduced into the spectrometer by dusting a double-sided tape. As the excitation source, the Kct radiation of the aluminum is used after passing through a nochromator. Electrons of 0.32 aJ produced by an electron gun whose emission is set at 0.3 mA are used to compensate for the charge effects of the samples. The pressure in the spectrometer during the analysis is equal to approximately 2.67 x 10 6 Pa. For chromium, a window of 8.01 to 256 points is explored, whereas for silicon, carbon and oxygen , we explore windows from 3, 20 to 256 points. The various windows are scanned several times, then the average of the signals is calculated in order to obtain proper signal-to-noise ratios and correct resolution. The analyzer is calibrated by adjusting the binding energy <EL) of Au (4f 7/2) to 13.46 + 0.016 aJ. After offsetting the charge effects of the samples, the EL energy of Cr (2p3 / 2) was 0.32 aJ lower in the CZM catalyst, compared with the chromium impregnated silicalite, while the Si binding energies ( 2p) and O (1s) of the two samples were the

  same within the limits of the experimental error (+0.016 ai).

  The single figure of the appended drawing shows the difference which exists between the Cr (2p) lines for CZM and for chromium impregnated silicalite. The great difference in the binding energies of chromium indicates that this metal exists surprisingly at different degrees of oxidation in

both samples.

  Visual inspection of the CZM catalyst and chromium-impregnated silicalite further highlights the differences between the samples. After the calcination step of the preparation (450 ° C, 8 hours), the CZM sample has a light green tint, while the chromium impregnated silicalite is yellow. This shows the higher stability of chromium in CZM chromium silicate

  compared to silicalite impregnated with chromium.

  Synthetic chromium silicates can be used as synthesized or they can be

  can be heat treated (calcined), Ordinary-

  It is desirable to remove the alkali metal cation by ion exchange and replace it with hydrogen, ammonium ion or any desired metal ion. The chromium silicate may be used in intimate admixture with hydrogenating components such as tungsten, vanadium, molybdenum, rhenium, nickel, cobalt, chromium, manganese or a noble metal such as palladium or platinum, for applications in which a function hydrogenation-dehydrogenation type is desired. Representative examples of metal cations include Group IIA and VIII rare earth metals as well as mixtures thereof; Particularly preferred are cations of metals such as rare earths, Mn, Ca, Mg, Zn, Cd, Pt, Pd, Ni, Co, Ti, Al, Sn, Fe and Co. Hydrogen and ammonium components and metals can be introduced by exchange in chromium silicate. The latter can also be impregnated with metals or the metals can be intimately mixed with chromium silicate by

  classics known in the prior art.

  Conventional ion exchange techniques involve contacting the synthetic chromium silicate with a solution containing a salt of the desired replacement cation (s). Although a wide variety of salts can be used, chlorides and other halides, nitrates and sulphates are particularly preferred. Representative examples of ion exchange techniques are given in a wide variety of patents such as US Pat. Nos. 3,140,249, 3,140,251 and 3,140,253. place before or after the zeolite has been calcined. After contact with the salt solution of the desired replacement cation, the chromium silicate is normally washed with water and dried at a temperature between 65 and about 3151C. After washing, it may be calcined in air or in an inert gas at temperatures of from about 200 to 8200C for periods of from 1 to 48 hours or more, so that

  obtain a product endowed with particular catalytic activity

  useful in hydrocarbon processing processes. Whatever the cations present in the form of chromium silicate obtained by synthesis, the spatial arrangement of the atoms that constitute the network

  crystalline base remains essentially unchanged.

  The exchange of cations has little or no influence

on network structures.

  Chromium silicates can be produced in a wide variety of physical forms. In general, they may be in the form of a powder, granules or a molded product, for example an extruded product whose particles have sufficient diameters to pass through a sieve of about 8.00 mm diameter. mesh opening and to be retained by a screen of 0.037 mm mesh opening. When the catalyst is molded, for example by extrusion with an organic binder, the chromium silicate can be extruded before drying, or it can be dried or

  partially dried, then extruded.

  The chromium silicate can be compounded with other materials resistant to the temperatures and other conditions used in transformation processes in organic chemistry. These matrices include active and inactive materials and synthetic or natural zeolites as well as inorganic materials such as clays, silica and metal oxides. The latter may be natural oxides or may be in the form of gelatinous precipitates, sols or gels comprising mixtures of silica and metal oxides. Use in conjunction with synthetic chromium silicate, i.e. together with it, of a material that is active, tends to improve the conversion rate and selectivity of the catalyst in certain organic transformations. Inactive materials advantageously serve as diluents to limit the degree of conversion in a given process so that products can be obtained economically without using other means of limiting the rate of reaction. The chromium silicates can be incorporated into natural clays, for example bentonite and kaolin. These materials, i.e., clays, oxides, etc., behave in part as binders for the catalyst. It is desirable to obtain a catalyst having good crush strength, because in refining the

  oil, the catalyst is often handled without softness.

  This tends to disintegrate the catalyst into pulverulent materials, which causes problems during treatment. The natural clays that can be compounded with the chromium silicates of the invention include the clays of the montmorillonite and kaolin families, these families including the sub-bentonites and kaolins commonly referred to as Dixie clays, of McNamee, Georgia and Florida, or other clays whose main mineral constituent is halloysite, kaolinite, dickite, nacrite or anauxite. Fibrous clays such as sepiolite and attapulgite may also be used as supports. These clays can be used in the raw state as initially extracted from the mine, or they can be first subjected to calcination,

  an acid or a chemical modification.

  In addition to the above materials, the chromium silicate may be compounded with porous matrices and matrix mixtures such as silica,

* alumina, titania, magnesia, silica-alumina, silica

  magnesia, silica-zirconium oxide, silica-thorium oxide, silica beryllium oxide, silica-titania, titania-zirconium oxide as well as ternary silica-alumina oxide compositions

  thorium, silica-alumina-zirconium oxide, silica-alumina

  magnesia and silica-magnesia-zirconium oxide. The matrix

  can be in a cogelled form.

  Chromium silicates can also be formulated with other zeolites such as synthetic and natural forms of faujasites, erionites and mordenites (eg X and Y). We can also put them in

  composition with synthetic zeolites.

  The relative proportions of the crystalline crystalline silicates of the invention and the matrix of gels

  inorganic oxide can vary within wide limits.

  The chromium silicate content may range from about 1 to about 90% by weight, but is more usually in the range of about 2 to about 50% by weight of the

composite.

  Chromium silicates are useful in hydrocarbon conversion reactions. Hydrocarbon conversion reactions are chemical and catalytic processes in which carbon-containing compounds are converted to different carbon compounds. Examples of hydrocarbon conversion reactions include catalytic cracking, hydrocarbon, and olefin and aromatic hydrocarbon formation reactions. The catalysts are useful in other petroleum refining and hydrocarbon conversion reactions such as reactions.

  isomerization of n-paraffins and naphthenes, polymeric

  and oligomerization of olefinic or acetylenic compounds such as isobutylene and butene-1, reforming, alkylation, isomerization, polyalkylated aromatic hydrocarbons (eg ortho-xylene) and disproportionation of aromatic hydrocarbons (eg toluene) to form a mixture of benzene, xylenes and

higher methylbenzenes.

  The chromium silicates can be used in the treatment of hydrocarbon feeds. Hydrocarbon feedstocks contain carbon compounds and can come from many different sources, such as virgin petroleum fractions, petroleum recycle fractions, shale oil, liquefied coal, oil sand oil, and in general, any carbon-containing liquid susceptible to zeolite catalyzed reactions. Depending on the type of treatment that the hydrocarbon feedstock must undergo, this feed may or may not contain metals, it may also have high or low levels of nitrogenous or sulphurous impurities. However, it should be noted that, in general, the treatment is all the more effective (and the catalyst even more so

  active) that the nitrogen content of the feed is lower.

  Transformation of hydrocarbon feeds can take place in any convenient way, for example in fluidized bed, moving bed or fixed bed reactors depending on the type of treatment desired. The formulation of the catalyst particles varies according to the method of

  transformation and the mode of driving.

  Using chromium silicates containing hydrogenation components, petroleum heavy residues, cyclic charges and other hydrocrackable feedstocks can be hydrocracked at temperatures of 300 to 5251C using molar ratios of 1: 1 to 1: 1. hydrogen with a hydrocarbon feed of 1 to. The manometric pressure can range from 70 kPa to 35 MPa and the hourly space velocity of the liquid can range from 0.1 to 30. For such purposes, chromium silicates can be compounded with mixtures of carriers formed from inorganic oxides as well as with faujasites such as X and Y forms. Chromium silicates can be used for catalytic cracking at temperatures of about 260 to 6250C, at pressures below atmospheric pressure. at values up to several tens of MPa as well as in other conventional conditions. Chromium silicates can be used

  to dewax hydrocarbon feedstocks by removing

  selective selection of right-chain paraffins and slightly branched chain paraffins. The operating conditions can be those of hydrodewaxing (moderate hydrocracking) or can be operated at lower pressures in the absence of hydrogen. Dewaxing produces appreciable amounts of olefins from

cracked paraffins.

  The chromium silicates can also be used in reforming reactions using temperatures of 360 to 6000 ° C., pressure pressures ranging from 0 to 3.5 MPa and hourly space velocities of the liquid of 0.1 to 20. The molar ratio of hydrogen to

  the hydrocarbon can generally be between 1 and 20.

  The catalyst can also be used for

  isomerize normal paraffins, when it contains a

  hydrogenation component, for example platinum. The hydro-

  Isomerization is generally conducted at temperatures of 3751C and hourly space velocities of the liquid of 0.01 to 5. The molar ratio of hydrogen to hydrocarbon is from 1: 1 to 5: 1. In addition, the catalyst can be used to isomerize the olefins to

temperatures from 140 to 320WC.

  Other reactions that can be carried out using the catalyst of the invention containing a metal, for example platinum, include hydrogenation-dehydrogenation type reactions, elimination reactions.

  nitrogen and desulfurization reactions.

  Chromium silicates can be used in hydrocarbon conversion reactions with active or inactive carriers, with organic or inorganic binders and with and without the addition of metals. These reactions are well known in practice, as are

  also the reaction conditions.

Claims (9)

  1. Crystalline chromium silicate in which the molar ratio of SiO 2: Cr 2 O 3 oxides is greater than about 20: 1 and which exhibits the following X-ray (powder) random diffraction lines: d (nm) Relative intensity 1,11 + 0.02 very strong 1.00 + 0.02 0.385 + 0.007 " 0.382 + 0.007 strong 0.376 + 0.005 " 0.372 + 0.005 "   2. A crystalline chromium silicate whose composition, expressed in the anhydrous form, in moles of oxides, corresponds to the formula: R20: aM2O: bCr203: cSiO2 in which R20 is a quaternary alkylammonium oxide, M is a alkali metal selected from the group of alkali metals including lithium, sodium, potassium or mixtures thereof, a is greater than 0, but less than 1.5, c is greater than or equal to 12 and the c / b ratio is greater than with this chromium silicate having the following X-ray powder diffraction pattern (powder): d (nm) Relative intensity 1.11 + 0.02 very strong 1.00 + 0.02 " 0.385 + 0.007 " 0.382 + 0.007 strong 0.376 + 0.005 " 0.372 + 0.005   Crystalline chromium silicate according to Claim 2, characterized in that R20 is the oxide of   tetrapropylammonium and M is sodium.   4. A process for converting hydrocarbons, characterized in that it consists in introducing a hydrocarbon feedstock into contact with the catalyst according to the   claim 1 under transformation conditions.   5. Process for enriching a reforming product containing normal paraffins, characterized in that it comprises bringing said product into contact with the catalyst according to claim 1 under processing conditions, so that an appreciable portion of said normal paraffins is cracked into gaseous products lighter.   6. Process according to claim 5, characterized in that the gaseous products comprise olefins, the conversion being preferably carried out in the presence of hydrogen under a partial pressure of 0.1 to 3 MPa, a temperature in the range of 400.degree. at 550WC   and a space velocity in the range of 0.1 to 10 hr-1.   7. A method for producing a crystalline chromium silicate, characterized in that it consists in carrying out the hydrothermal crystallization, preferably at a temperature in the range of 100 to 2001C and under autogenous pressure, of a reaction mixture containing a quaternary alkylammonium oxide, an alkali metal oxide selected from the group of alkali metals including lithium, sodium, potassium or mixtures thereof, chromium oxide and silica; said reaction mixture   having a composition, expressed in moles of oxides, corresponding to   wherein R 20 is a quaternary alkylammonium oxide, preferably tetrapropylammonium oxide, M is an alkali metal selected from the group consisting of lithium and alkali metal, and R 20: aM 2 O: bCr 2 O 3: cSiO 2: dH 2 O the sodium, the potassium or their mixtures, preferably sodium, has a value greater than 0, but less than 5, preferably between 0.05 and 1, ca a value lying in a range from 1 to 100, preferably in the range of from 2 to 20, the ratio c / b is greater than 12, preferably in the range of 30 to 600, and in a range of 70 to 500, preferably in the range from range from 100 to 300.   8. A crystalline crystalline silicate obtained by the   process according to claim 7.   9. Application of the composition according to   claim 1 to a process for converting hydro-   carbides such as hydrocracking, dewaxing, reforming, polymerization or oligomerization of olefins, isomerization, disproportionation, alkylation, catalytic cracking, etc., by contacting a hydrocarbon feedstock with said composition   under hydrocarbon transformation conditions.