FR2673550A1 - Catalyst for cracking hydrocarbon feedstocks, including a zeolite MFI, a zeolite Y and a matrix - Google Patents

Abstract

Catalyst for cracking hydrocarbon feedstocks, containing: a) from 20 to 95 % by weight of at least one matrix, b) from 1 to 60 % by weight of at least one zeolite Y, of faujasite structure, and c) from 0.01 to 30 % by weight of at least one zeolite MFI, hydrogen form, synthesised in a fluoride medium, which has the following approximate formula: H<+>x(Si(96-x)AlxO192)<x->, where x is a number between 0.64 and 24, a fluorine content of between 0.01 and 2 % by weight and a nitrogen adsorption capacity measured at 77 K at a relative pressure P/Ps = 0.19 greater than 0.08 cm<3> (liquid)/g.

Description

The present invention relates to a catalyst for the conversion of hydrocarbon feeds comprising a Y zeolite of faujasite structure associated with an MFI zeolite in the form of hydrogen and with a matrix which is usually amorphous or poorly crystallized.

The catalyst of the present invention is particularly well suited to the cracking of petroleum fractions with a view to producing a large quantity of compounds having 3 and'or 4 carbon atoms per molecule and more particularly propylene and isobutane. The catalyst of the present invention is particularly well suited to the cracking of heavy petroleum fractions.

The present invention also relates to the process for cracking heavy petroleum feedstocks, in the presence of the catalyst defined above, as well as to the processes for preparing said catalyst. The cracking of hydrocarbon feedstocks, making it possible to obtain high yields of very good quality automobile gasoline, became essential in the oil industry from the end of the 1930s. The introduction of processes operating in a fluid bed (FCC or Fluid Catalytic Cracking) or in a moving bed (such as TCC) in which the catalyst constantly circulates between the reaction zone and the regenerator where it is freed of coke by combustion in the presence of a gas containing oxygen has introduced progress important compared to the fixed bed technique.

Fluid bed units (FCC) are now much more common than moving bed units. Cracking is usually carried out at around 500 ° C., under a total pressure close to atmospheric pressure and in the absence of hydrogen.

The catalysts most used in cracking units since the early 1960s have been zeolites, usually of a faujasite structure. These zeolites, incorporated in an amorphous matrix, for example consisting of amorphous silica-alumina, and which may contain variable proportions of clays, are characterized by cracking activities with respect to hydrocarbons 1000 to 10,000 times greater than those of silica-alumina catalysts. rich in silica used until the late 1950s.

In the late 1970s, the lack of availability of crude oil and the growing demand for high octane gasoline led refiners to process increasingly heavy crudes. The treatment of the latter constitutes a difficult problem for the refiner because of their high content of catalyst poisons, in particular of metal compounds (in particular nickel and vanadium), unusual Conradson carbon values and especially asphaltene compounds.

This need to deal with heavy loads and other more recent problems, such as the gradual but general elimination in gasoline of lead-based additives, the slow but appreciable evolution in certain countries of the demand for middle distillates (kerosene and gas oils), have moreover encouraged refiners to seek improved catalysts making it possible to achieve the following objectives in particular: - catalysts that are more thermally and hydrothermally stable and more tolerant to metals, - produce less coke with identical conversion, - obtain a gasoline of 'higher octane number, - improved selectivity for middle distillates.

In the majority of cases, one seeks to minimize the production of light gases, comprising compounds having 1 to 4 carbon atoms per molecule, and, therefore, the catalysts are designed to limit the production of such light gases.

However, there appears in certain particular cases a significant demand for light hydrocarbons with 2 to 4 carbon atoms per molecule or for some of them, such as C3 and / or C4 hydrocarbons and more particularly propylene and isobutane.

Obtaining a large quantity of isobutane is in particular advantageous in the case where the refiner has an alkylation unit, for example C3-C4 cuts containing olefins, with a view to forming an additional quantity of high octane gasoline.

Thus the overall yield of good quality gasoline obtained from the starting hydrocarbon cuts is appreciably increased.

Obtaining propylene is particularly desirable in certain developing countries, where there is significant demand for this product.

The catalytic cracking process can meet such demands to a certain extent, provided in particular that the catalyst is adapted for this production. An effective way of adapting the catalyst consists in adding to the catalytic masses an active agent having the following two qualities 1) cracking the heavy molecules with good selectivity in hydrocarbons with 3 and / or 4 carbon atoms per molecule, in particular in propylene and in isobutane; 2) be sufficiently resistant to the severe conditions of partial pressure of water vapor and temperature which prevail in the regenerator of an industrial cracker.

The significant research work carried out by the applicant on numerous zeolites led him to discover that, surprisingly, an MFI zeolite in the hydrogen form, characterized in particular in that it has been synthesized in a fluoride medium, makes it possible to obtain a catalyst having excellent stability and having good selectivity with respect to production of hydrocarbons with 3 and 4 carbon atoms per molecule. The use of such an MFI zeolite makes it possible to obtain a cracking catalyst making it possible to obtain a proportion of gas, and in particular of propylene and isobutane, which is greater than with the catalysts of the prior art.

The MFI zeolite, hydrogen form, used in the present invention is distinguished from the MFI zeolites of the prior art in particular by the fact that it was synthesized in a fluoride medium, according to the process described and claimed in French patent application No. 90. / 16529, a partial description of which is incorporated herein by reference.

The MFI zeolite as described and claimed in said French patent application is characterized by: a) the following approximate general formula: M + (x + y) (Sl ((x + y Alx Gay 0192) (x + Y) - where M represents an alkaline cation and / or an ammonium cation, x is a number between 0 and 24, y is a number between 0 and 24, (x + y) is a number between 0.64 and 24 and preferably between 1.88 and 19.2, b) an X-ray diffraction diagram, of its ammonium form, represented in table I of the description of French patent application No. 90/16529, said table being reproduced below , and c) a fluorine content of its ammonium form of between 0.01 and 2% by weight,
said zeolite having been synthesized in a fluoride medium and in the absence of organic agents.

The identification of the MFI type zeolites according to the invention can be done easily from their X-ray diffraction diagram. This diagram can be obtained using a diffractometer using the conventional powder method with the KX radiation of copper. An internal standard makes it possible to precisely determine the values of the angles 2a associated with the diffraction peaks. The different interreticular distances dhkl, characteristic of the sample, are calculated from the Bragg relation. The estimate of the measurement error d (dhk) on dhk is calculated as a function of the absolute error D (26) assigned to the measurement of 26 by the Bragg relation. In the presence of an internal standard, this error is minimized and commonly taken equal to +0.05 .. The relative intensity Illo assigned to each value of dhk is estimated from the height of the corresponding diffraction peak.

Table I represents the X-ray diffraction diagram of the ammonium form of zeolites of MFI type according to French patent application No. 90/16529. In the column of dhk, we have represented the values of the interreticular distances dhk ,. Each of these values must be affected by the measurement error generally between + 0.07 and +0.02 depending on the value of 2 (dh, is is expressed in Angstroms, 1 A = 10.10 m).

TABLE I

<tb> dhld <SEP> () <SEP> Vlo <SEP> dhkl <SEP> () <SEP> lilo <SEP>
<tb><SEP> 11.14 <SEP> 66 <SEP> 4.10 <SEP> 11
<tb><SEP> 9.99 <SEP> 43 <SEP> 4.01 <SEP> 14
<tb><SEP> 9.72 <SEP> 18 <SEP> 3.86 <SEP> 100
<tb><SEP> 7.44 <SEP> 7 <SEP> 3.82 <SEP> 94
<tb><SEP> 6.71 <SEP> 11 <SEP> 3.75 <SEP> 62
<tb><SEP> 6.37 <SEP> 11 <SEP> 3.73 <SEP> 66
<tb><SEP> 5.99 <SEP> 17 <SEP> 3.65 <SEP> 33
<tb><SEP> 5.70 <SEP> 13 <SEP> 3.60 <SEP> 10
<tb><SEP> 5.58 <SEP> 17 <SEP> 3.49 <SEP> 13
<tb><SEP> 5.38 <SEP> 6 <SEP> 3.45 <SEP> 14
<tb><SEP> 5.14 <SEP> 6 <SEP> 3.36 <SEP> 13
<tb><SEP> 4.98 <SEP> 11 <SEP> 3.32 <SEP> 17
<tb><SEP> 4.62 <SEP> 9 <SEP> 3.05 <SEP> 16
<tb><SEP> 4.37 <SEP> 16 <SEP> 2.98 <SEP> 21
<tb><SEP> 4.27 <SEP> 13 <SEP> 2.95 <SEP> 10
<tb>
The MFI zeolite in the hydrogen form, synthesized in a fluoride medium was prepared according to the process described and claimed in French patent application No. 90/16529, a process of which a partial description is given below by way of reference: a) a solution reaction mixture having a pH of less than 9 and comprising water, at least one source of silica, at least one source of aluminum and at least one source of gallium, at least one source of mobilizing agent containing ions fluoride (F-), at least one source of alkali metal cations (denoted A +); said alkali metal cations preferably being sodium cations (Na +), optionally at least one source of ammonium cations (NH4 +), said reaction mixture having a composition, in terms of molar ratio, included in the following ranges of values :: Si / ( Al + Ga): 7-60, preferably 14-50 F- / Si: 0.1-10, preferably 0.1-8 H2O / Si: 5-25, preferably 10-25 A + / Si: 0 , 1-10, preferably 0.1-8 A + / (A ++ NH4 +): 0.1-1, preferably 0.3-1 b) said reaction mixture is maintained at a heating temperature of between 90 and 300 C, preferably between 130 and 250 ° G until a crystalline compound is obtained.

In order to use said zeolite in the present invention, one or more ionic exchanges are carried out with a source of NH4 + cations (for example NH4NO3, NH4Cl) in order to be able to obtain the hydrogen form of the zeolite by calcination in air of the NH4 form. at a temperature above 3504C and preferably at 450ex.

The MFI zeolite can optionally be subjected, after the calcination step of its ammonium form, to a partial or total defluorination treatment, with NH4OH, as has been described in French patent application No. 90/16529.

The characteristics of the MFI zeolites are measured by the following methods: a) the overall Si / Al atomic ratios are determined by fluorescence analysis
X.

b) the fluorine content is determined by dosing using a specific electrode.

c) crystallinity is determined by X-ray diffraction.

d) the nitrogen adsorption capacity of the zeolite is determined at 77K for a relative pressure P / Ps = 0.19 (Ps being the saturated vapor pressure of nitrogen at 77K).

The MFI zeolite, hydrogen form, used in the present invention, is characterized by the following properties:
- the following approximate general formula:
H + x (si (9; x) Alx 0.92) X- where x is a number between 0.64 and 24 and preferably between 1.88 and 19.2,
- a fluorine content of between 0.01 and 2% by weight, usually between 0.01 and 1% by weight,
a nitrogen adsorption capacity measured at 77K under a relative pressure P / Ps = 0.19 greater than 0.08 and preferably 0.10 cm3 (liquid) / g.

The catalyst of the present invention also contains a Y zeolite of faujasite structure (Zeolite Molecular Sieves Structure, chemistry and uses,
DW BRECK, J. WILLEY and Sons 1973). Among the Y zeolites that can be used, a stabilized Y zeolite, commonly called ultrastable or USY, either in the form at least partially exchanged with metal cations, for example cations of alkaline earth metals and / or cations, will preferably be employed. cations of rare earth metals with atomic number 57 to 71 inclusive, or in the hydrogen form.

The catalyst of the present invention also contains at least one usually amorphous or poorly crystallized matrix chosen for example from the group formed by alumina, silica, magnesia, clay, titanium oxide, zirconia, combinations of at least two of these compounds and alumina-boron oxide combinations.

The matrix is preferably chosen from the group formed by Ima silica,
Alumina, magnesia, silica-alumina mixtures, silica-magnesia mixtures and clay.

The catalyst of the present invention contains: a) from 20 to 95%, preferably from 30 to 85% and even more preferably from 50 to 80% by weight of at least one matrix, b) from 1 to 60% , preferably from 4 to 50% and even more preferably from 10 to 40% by weight of at least one Y zeolite of faujasite structure, and c) from 0.01 to 30%, preferably from 0.05 to 20% and even more preferably from 0.1 to 10% of at least one MFI zeolite, hydrogen form, having the characteristics given above.

The catalyst of the present invention can be prepared by any of the methods well known to those skilled in the art.

Thus the catalyst can be obtained by simultaneous incorporation of the MFI zeolite in the hydrogen form and of the Y zeolite according to the conventional methods for preparing cracking catalysts containing a zeolite.

The catalyst can also be obtained by mechanically mixing a first product containing a matrix and a Y zeolite, and a second product comprising the MFI zeolite, hydrogen form, described above with a matrix which can be identical or different from that contained in said first product.

This mechanical mixing is usually carried out with dried products.

The products are preferably dried by spray-drying, for example at a temperature of 100 to 500 ° C., usually for 0.1 to 30 seconds.

After spray drying, these products may still contain 1 to 30% by weight of volatile matter (water and ammonia).

The MFI zeolite hydrogen-matrix mixture usually contains from 1 to 90% by weight and, preferably, from 5 to 60% by weight of zeolite MFI relative to the total weight of said mixture.

The zeolite Y-matrix mixture employed in the preparation of the catalyst of the present invention is usually a conventional cracking catalyst of the prior art (eg, a commercial catalyst); the MFI zeolite in the hydrogen form described above can then be considered as an additive which can be used as such with a view to its mixing with the conventional cracking catalyst defined above, or be incorporated beforehand in a matrix, the matrix assembly MFI zeolite then constituting the additive which is mixed with the conventional cracking catalyst defined above, for example, after adequate shaping, by mechanical mixing of the grains containing the zeolite
MFI forms hydrogen and conventional cracking catalyst grains.

The general conditions of catalytic cracking reactions are particularly well known not to be repeated here in the context of the present invention (see for example US Patents 3,293,192, 3,449,070, 4,415,438, 3,518,051 and 3,607,043).

In order to produce the largest possible quantity of gaseous hydrocarbons with three and four carbon atoms per molecule, and in particular of propylene and isobutane, it is sometimes advantageous to slightly increase the temperature at which the cracking is carried out, for example from 10 to 50 ° C. The catalyst of the present invention is however in the majority of cases sufficiently active so that such an increase in temperature is not necessary. The other cracking conditions are unchanged from those used in the prior art.

The following examples illustrate the present invention without, however, limiting its scope.

EXAMPLE 1
Preparation of an MFI zeolite in the form of hydrogen with an Si / Al ratio equal to 7.5.

In a 0.5 liter autoclave made of Monel (an alloy of copper and nickel), 50.4 g of NaF are dissolved at room temperature in 270 g of water; to this solution are then added with stirring and successively 74.45 g of "tixolex 28" exchanged with NH4 + of Si / Al ratio = 7.45 and 0.75 g of crystals of MFI zeolite synthesized in an uncalcined fluoride medium.

The composition of the reaction mixture, in terms of molar ratio is as follows:
Si / Al = 7.45; F / Si = 1.36; H2O / Si = 17; Na + / Si = 1.36
The pH of the reaction mixture is equal to 8.

The reaction mixture is brought to a temperature of 200 ° C. and is maintained at this temperature with slow stirring for 44 hours.

After this synthesis, the solid is collected by filtration, washed with distilled water, dried in an oven at 80 ° C. for 24 hours.

The product obtained is crystallized in the form of an MFI zeolite, as shown by its X-ray diffraction diagram of its ammonium form obtained by 2 successive exchanges with a 10 N solution of NH4NO3. Its SiO2JAI2O3 molar ratio is 15.1. The volume of its unit cell is 5.410 nm3. The fluorine content by weight of this ammonium form is 1%.

The hydrogen form of the MFI zeolite thus prepared is obtained by a calcination treatment in air at 550 ° C. under the following conditions: - stage for 2 hours at 550 G, nitrogen flow rate = 2 l / h / g, flow rate of air = 0.4 L / h / g; - level of 2 hours at 550 C, air flow = 2 I / h / g.

Lazéolite MFI forms hydrogen, then the following approximate chemical composition
H113 (si847Al11.3 O192) 11.3-
Its fluorine content by weight is 0.5%.

Its nitrogen adsorption capacity measured at 77K under a relative pressure of P / s = 0.19 is 0.19 cm3 (liquid) / g.

EXAMPLE 2
Preparation of a cracking additive based on MFI zeolite.

The MFI zeolite in the hydrogen form synthesized in Example 1 is used to prepare a cracking additive by mechanical mixing in a conventional manner at a rate of 30% by weight of MFI zeolite in the dry hydrogen form and 70% by weight of amorphous silica, previously calcined. , with a particle size comparable to that of the MFI zeolite in the hydrogen form.

The additive thus obtained is pelletized, then reduced into small aggregates using a crushing machine. The fraction of grains of size between 4 10-5 m and 2104 m is then collected by sieving. This additive is called A1 and contains 30% by weight of MFI zeolite.

EXAMPLE 3
Preparation of a cracking catalyst in accordance with the invention and condition for catalytic tests of the catalyst.

The additive A1 is mechanically mixed in a conventional manner at a rate of 20% by weight with a new industrial catalytic cracking catalyst called CAT for short. The CAT catalyst contains a siice-alumina matrix and 30% by weight of an ultrastabilized Y zeolite (USY) with a crystalline parameter of 2.45 nm.

The catalyst (CAT) and the additive were previously calcined for 6 hours at 750 ° C. in the presence of 100% water vapor.

The CAT catalyst, as well as the catalyst resulting from the mixture of the CAT catalyst and the additive A1 are then introduced into a MAT catalytic test micro-unit. The ability of each catalyst to convert a heavy load of hydrocarbons is then determined under the following conditions:
amount of catalyst = 6 g
catalyst / charge weight ratio = C / O = 6
charge injection duration = 40 seconds
WHSV = mass space velocity = 15 h- '
temperature = 510 C
The load used has the following characteristics:
density 15eC = 0.932% weight S = 1.8
% weight N = 0.2
Conradson Carbon% = 3.2
Ni + V = 8 ppm
viscosity 60 C = 46.2 mm2 / s
1R (60 C) = 1.5061 (refractive index of the load)
Saturated = 44.5% weight
Olefins = 1.7% by weight
Aromattic = 43.9% by weight
Resins = 8.6% by weight
Asphaltenes (insoluble in C5) = 1.3% by weight
Comparison of catalytic performance
The results contained in Table I are expressed as follows: - conversion of the feed in% by weight, - gas yield in% by weight (H2 + hydrocarbons from C1 to C4), - distribution of gases in% by weight (H2 + hydrocarbons from C1 to C4), - gasoline yield in% by weight C5 at 220 C, - yield in LCO (middle distillates: 220-380 C) in% by weight, - yield in coke in% by weight.

TABLE II

<tb><SEP> Catalysts <SEP> CAT <SEP> CAT + A1
<tb><SEP> conversion <SEP> 63.2 <SEP> 63.5
<tb><SEP> gas <SEP> totals <SEP> 14.8 <SEP> 18.6
<tb><SEP> gasoline <SEP> 42.3 <SEP> 38.3
<tb><SEP> LCO <SEP> 15.1 <SEP> 14.3
<tb><SEP> coke <SEP> 6.1 <SEP> 6.5
<tb><SEP> H2 <SEP> 0.06 <SEP> 0.07
<tb><SEP> Ci <SEP> + <SEP> C2 <SEP> 1.69 <SEP> 2.03
<tb><SEP> propane <SEP> 0.94 <SEP> 1.81
<tb><SEP> propylene <SEP> 3.51 <SEP> 4.52
<tb><SEP> n-butane <SEP> 0.69 <SEP> 0.91
<tb><SEP> isobutane <SEP> 2.60 <SEP> 3.50
<tb><SEP> butenes <SEP> 5.00 <SEP> 5.72
<tb> octane <SEP> search <SEP> base <SEP> + <SEP> 0.9
<tb>
These results show that the use of the additive based on MFI zeolite in hydrogen form, synthesized in a fluoride medium and in the absence of organic agents, makes it possible to produce larger quantities of propylene, butylene and isobutane. At the same time, the quality of gasoline, in terms of octane number, is improved.

Claims (9)

1) Catalyst containing: a) from 20 to 95% by weight of at least one matrix, b) from 1 to 60% by weight of at least one Y zeolite of faujasite structure and, c) from 0.01 to 30% by weight of at least one MFI zeolite, hydrogen form, synthesized in a fluoride medium, having the following approximate formula: H + x (Si (9; X) AlX 0192) X., Where x is a number between 0.64 and 24, a fluorine content between 0.01 and 2% by weight, a capacity nitrogen adsorption measured at 77K under relative pressure P / Ps = 0.19 greater than 0.08 cm3 (liquid) / g. 2) Catalyst according to claim 1 containing: a) from 30 to 85% by weight of matrix, b) from 4 to 50% by weight of Y zeolite of faujasite structure, and c) from 0.05 to 20% by weight of MFI zeolite in hydrogen form. 3) Catalyst according to one of claims 1 and 2 wherein said matrix is chosen from the group formed by alumina, silica, magnesia, clay, Titanium oxide, zirconium, combinations of at least two of these compounds and alumina-boron oxide combinations. 4) Catalyst according to one of claims 1 to 3 wherein said zeolite Y is an ultrastable Y zeolite in hydrogen form and / or in at least partially exchanged by cations of the metals or of the group rare earths with atomic number 57 to 71 inclusive. 5) Catalyst according to one of claims 1 to 4 wherein said zeolite MFI hydrogen form has the following approximate formula: H + x (Si (x) Alx0192) X-, where x is a number between 1.88 and 19.2, a fluorine content between 0.01 and 1% by weight, a capacity nitrogen adsorption measured at 77K under a relative pressure P / Ps = 0.19 greater than 0.10 cm3 (liquid) / g. 6) Catalyst according to claims 1 to 5 wherein said MFI zeolite hydrogen form is an MFI zeolite hydrogen form at least partially exchanged by cations of metals of the earth group rare with atomic number 57 to 71 inclusive. 7) Process for preparing a catalyst defined according to one of claims 1 to 6, characterized in that it comprises the following steps: a) a mixture dried by atomization of MFI zeolite is prepared in the form hydrogen te of a matrix, b) a mixture dried by atomization of zeolite Y of structure faujasite and a matrix, and c) the dried product from step a) is mixed with the dried product from step b). 8) Process for preparing a catalyst defined according to one of claims 1 to 6, characterized in that said MFI zeolite forms hydrogen and said Y zeolite are incorporated simultaneously into a matrix. 9) Use of a catalyst defined according to one of claims 1 to 6 or prepared according to one of claims 7 and 8 in a process for the catalytic cracking of a hydrocarbon feed with a view to to obtain a product containing a high proportion of propylene and of isobutane.