GB2254336A

GB2254336A - Hydrocarbon cracking

Info

Publication number: GB2254336A
Application number: GB9204212A
Authority: GB
Inventors: Christian Marcilly; Thierry Chapus; Jean-Francois Joly
Original assignee: IFP Energies Nouvelles IFPEN
Current assignee: IFP Energies Nouvelles IFPEN
Priority date: 1991-03-01
Filing date: 1992-02-27
Publication date: 1992-10-07
Anticipated expiration: 2012-02-27
Also published as: GB2254336B; DE4206270A1; FR2673385B1; FR2673385A1; GB9204212D0

Description

2 25 43 -56 1 CRACKING OF HYDROCARBON CHARGES WHOSE FINAL AND INITIAL

BOILING POINTS ARE BETWEEN 50 AND 2200C The present invention relates to the use in cracking of a 5 hydrocarbon conversion catalyst comprising a Y zeolite associated with a usually amorphous or poorly crystalline matrix.

The hydrocarbon fractions have initial and final boiling points between 50 and 2200C and particularly are fractions rich in naphthene and/or paraffin compounds, e.g. light hydrocracking petrols. They are cracked with a view to producing a large quantity of C 3 and/or C4 compounds, more particularly propylene, butenes and isobutane.

The term "hydrocarbon fractions rich in naphthene and/or paraffin compounds" means petroleum fractions whose total content of naphthene and/or paraffin compounds (i.e. the sum of the content of the naphthene compounds and the content of paraffins) exceeds 50% by weight and is usually at least 80% by weight. The usual content by weight of such paraffin fractions is 25 to 45 and preferably 35 to 45% and that of such naphthene fractions is 50 to 65 and preferably 50 to 60%.

The petroleum fractions, whose initial and final boiling points are between 50 and 2200C and that are in particular rich in naphthene and/or paraffin compounds, e.g. light hydrocracking petrols, normally have very mediocre combustion properties (low octane numbers). The main way to transform these 50 to 2000C petroleum fractions rich in naphthene and/or paraffin compounds is catalytic reforming, which leads to the formation of aromatics, whose content in the petrols will decrease very considerably in the medium or long term. In certain special cases there is a significant demand for light C2-4 hydrocarbons, or at least for certain of them, such as C 3 and/or C4 hydrocarbons and more specifically propylene, butenes and isobutane. 30 Obtaining a high isobutane quantity is more particularly of interest in the case where the refiner has an alkylation unit in which said compound is used as an alkylating agent, e.g. C 3-C4 fractions containing olefins, with a view to forming a supplementary quantity of petrol having a high octane number. 35 Obtaining propylene is more particularly desired in certain developing countries, where there is a large demand for this product. The process for the catalytic cracking of 50 to 2200C fractions, 2 which are rich in naphthene and/or paraffin compounds, e.g. 1 ight hydrocracking petrols, can to a certain extent satisfy such demands, provided that the catalyst is adapted to such production.

An effective way of adapting the catalyst, which contains a Y zeolite and a normally amorphous or poorly crystalline matrix, is to adapt the content of rare-earths of the Y zeolite contained in the catalyst in the new state, so as to (1) crack the hydrocarbon molecules of the family of naphthenes and paraff ins into C 3 and/or C4 hydrocarbons, particularly propylene, 10 butenes and isobutane; (2) limit the formation of aromatic compounds from naphthene compounds by hydrogen transfer reaction between these naphthenes and the olefins resulting from the cracking of the same naphthenes and paraffins.

US-A-4,969,987 describes the conversion of hydrocarbon fractions rich in naphthene and paraffin compounds. The catalysts described are constituted by zeolite and matrixes. The zeolites described are in particular characterized by constraint indexes such as defined in "Journal of Catalysis, 67, pp. 218-222, 198111, between approximately 1 and approximately 12.

Extensive research work carried out by the applicant on numerous zeolites has led to the surprising discovery that the use, in the cracking of hydrocarbon fractions with initial and final boiling points between 50 and 2200C, of a catalyst comprising a Y zeolite (constraint index equal to 0.4 in accordance with "Journal of Catalysis, 67, pp. 218- 222, 1981"), having a rare earth content, expressed as a percent by weight of oxide of rare earths T203 based on the Y zeolite (T is a rare earth of atomic number 57 to 71 inclusive) below 10% and preferably below 6%, in such a way that the lattice parameter of the Y zeolite of the catalyst in the equilibrium state within the catalytic cracking unit is below 2.435 nm and preferably below 2.430 nm, makes it possible to maximize the production of C 3 and/or C4 compounds and minimize the production of undesired aromatic compounds.

The catalyst used in the present invention contains a Y zeolite having a faujasite structure (Zeolite Molecular Sieves Structure, chemistry and use, D. W. Breck, J. Willey and Sons, 1973). Among the usable Y zeolites, preference is given to the use of a stabilized Y 3 zeolite, often referred to as ultrastable or USY, either in the partly exchanged form with cations of rare-earths of atomic numbers 57 to 71 inclusive in such a way that its rare-earth content expressed as a percent by weight of oxides of rare-earth metals is below 10%, preferably below 6%, or in hydrogen form. The rare-earth content of the Y zeolite used in the invention is therefore chosen in such a way that said Y zeolite of the catalyst in the equilibrium state within the catalytic cracking unit is characterized by a lattice parameter value below 2.435 nrn and preferably below 2.430 nm.

The catalyst used in the present invention also contains at least one normally amorphous or poorly crystalline matrix, e.g. one from the group formed by silica, alumina, magnesia, silica-alumina mixtures, silica-magnesia mixtures and clay.

Thus, the catalyst contains:

(a) approximately 25 to 99%, preferably approximately 40 to 95% and in a frequently advantageous manner approximately 50 to 85%, by weight of at least one matrix, (b) approximately 1 to 75%, preferably approximately 5 to 60% and in a frequently advantageous manner 15 to 50%, by weight of at least one faujasite structure Y zeolite whose rare earth content expressed as a percent by weight of oxides of rare-earth metals based on the Y zeolite is below 10% and preferably below 6%. This catalyst is known but is generally used for the catalytic cracking of conventional hydrocarbon charges, i.e. those having 25 initial and final boiling points between 300 and 7000C and it is e.g. described in EP-A-0 124 716. The aforementioned catalyst can be prepared by any known procedures. Thus, the catalyst can be obtained by the mechanical mixing of a first product containing the Y zeolite and a matrix. This mechanical mixture is normally dried, preferably by spray drying, e.g. at a temperature of approximately 100 to 5000C and normally for approximately 0.1 to 30 seconds. Following spray drying, the product obtained can still contain approximately 1 to 30% by weight of volatile matter (water and ammonia).

The present invention provides a process for the catalytic cracking of a hydrocarbon charge whose initial and final boiling points 4 are between 50 and 2200C, carried out in the presence of a catalyst containing:

(a) approximately 25 to 99% by weight of at least one matrix, (b) approximately 1 to 75% by weight of at least one faujasite structure Y zeolite, whose rare-earth content, expressed as percent by weight of oxides of rare-earth metals, based on the zeolite Y, is below 10%.

The catalytic cracking process according to the invention used for the selective transformation of hydrocarbon fractions rich in naphthene and/or paraffin compounds, e.g. light hydroerdeking petrols, is normally performed either in a fluidised bed (such as FCC or fluid catalytic cracking), or in a moving bed (such as TCC), in which the catalyst according to the invention permanently circulates between the reaction zone and the regenerator, where the coke is removed by combustion in the presence of an oxygen-containing gas. The term "hydrocarbon fractions rich in naphthene and/or paraffin compounds" means hydrocarbon fractions whose total content of naphthene and/or paraffin compounds (i.e. the sum of the content of naphthene compounds and paraffin compounds) is at least 50% by weight and normally at least 80% by weight.

The general conditions of the catalytic cracking reactions are too well known to be repeated within the scope of the present specification (cf. e.g. the following Patents: US-A-3,293,192,

US-A-3,449,070, US-A-3,607,043 and US-A-4,415,438).

However, with a view to producing the maximum quantity of gaseous C 3-4 hydrocarbons and in particular propylene, butenes and isobutane, it is often advantageous to use temperatures in the reaction zone between 400 and 8000C, preferably between 500 and 7000C. In the same way, the weight ratio of the catalyst weight to the charge weight can advantageously be between 3:1 and 15:1.

The following examples illustrate the invention without limiting its scope.

EXAMPLE 1: Catalyst according to the invention and test conditions.

The cracking catalyst has a Y zeolite weight content close to 35% and a matrix weight content of 65%. The weight content of rare-earths of said Y zeolite, expressed as percent by weight oxides of rare-earth metals based on the Y zeolite, is approximately 2% and its lattice parameter is 2.460 nm. This catalyst is designated CAT,.

A hydrothermal treatment under 100% steam, at 7000C and for 15 hours is applied to the catalyst CAT,, in order to simulate the aging.undergone by the catalyst in the catalytic cracking unit. The crystalline parameter of the Y zeolite of the CAT, catalyst following the hydrothermal treatment is 2.428 nm.

The aged catalyst is then introduced into the reactor of a MAT catalytic test microunit. The capacity of the catalyst to convert a charge rich in naphthene compounds and paraffins is then determined under the following conditions catalyst weight = 5 g, catalyst/charge weight ratio - C/0 = 6.2 for CAT,, charge injection time = 9 seconds, temperatures = 530, 560 and 600 0 C.

The percent by weight composition of the charge used is given in Table 1.

TABLE 1

Carbon Number c 5 c 6 c 7 c 8 c 9 c 10 c 11 Total per family Paraffins 0.17 6.03 12.08 12.80 7.38 1.58 40.04 Olefins - - - 0 Naphthenes 0.08 5.42 17.14 21.60 9.96 1.56 55.76 Aromatics - 0.45 1.14 1.61 0.88 0.09 0.03 4.20 Total 0.25 11.90 30.36 36.01 18.22 3.23 0.03 100 EXAMPLE 2: Catalyst not in accordance with the invention.

The cracking catalyst is here characterized by a Y zeolite weight content close to 20% and a matrix weight content close to 80%. The rare earth content of said Y zeolite, expressed as a percent by weight of oxides of rare earths based on the Y zeolite, is approximately 15.6% and its lattice parameter is 2.468 nm. This catalyst is designated CAT 2 A hydrothermal treatment under 100% steam, at 7300C and for 15 hours is applied to the catalyst CAT 2 in order to simulate the aging undergone by the catalyst in a catalytic cracking unit. The crystalline parameter of the Y zeolite of the catalyst CAT 2 after the hydrothermal treatment is 2. 436 nm.

The aged catalyst is then introduced into the reactor of a MAT catalytic test microunit. The capacity of the catalyst to convert a charge rich in naphthene compounds and paraffins is then determined under the same conditions as used for catalyst CAT 1 and which are described in Example 1, except that the catalyst/charge (equal C/0) weight ratio is 10 in this case. The two catalyst are tested at two different C/0, so that the zeolit'e/charge weight ratio is identical.

EXAMPLE 3: Comparison of the catalytic performance characteristics of catalyst CAT 1 and CAT 2 The results are given in Table 2 and very clearly show that the yields, based on the same hydrocarbon charge and under the same catalytic testing conditions, of isobutane and C 3 and C 4 compounds are significantly improved when using a catalyst containing a Y zeolite, whose rare earth content, expressed as percent by weight based on the Y zeolite, is below 10% and preferably below 6%.

TABLE 2

T=530 0 C T=560 0 C T=600 0 C Yields CAT 1 CAT 2 CAT 1 CAT 2 CAT 1 CAT 2 (% by weight) Total C 3 12.47 10.66 16.29 12.48 19.04 17.21 Total C 4 24.32 21.56 25.42 20.85 26.02 24.21 C 3 4.32 5.34 6.30 6.48 8.60 9.15 C 4 1.81 2.92 2.44 3.23 4.16 4.5 ic 4 17.38 14.31 17.72 13.20 16.29 14.52 C 3: propylene; C 4: butenes; ic 4: isobutane EXAMPLE 4: Comparison of the catalytic performance characteristics of the catalyst according to the invention on a conventional charge and on a 50 to 2200C fraction.

Use is made of the catalyst CAT, of Example 1 in accordance with the invention.

The capacity of the catalyst to convert a charge is determined under the following conditions:

catalyst weight: Sg, catalyst/charge weight ratio: C/0 = 6.2, charge injection time: 9 seconds, temperature: 530 0 C.

The MAT test is performed on a conventional charge (fraction obtained from a Kirkuk crude with an initial boiling point above 350 0 C) and then on a 50 to 220 0 C fraction (whose composition is given in Table 1). The results are given in Table 3.

TABLE 3

Conventional Charge FCC 50-220 0 C Fraction Total C 3 4.7 12.47 Total C 4 8.9 24.32 CS2 4.05 4.32 C 42-' 5.9 1.81 ic 4 2.1 17.38 In the case of use in accordance with the invention there is a significant isobutane yield improvement.

9

Claims

1. A process for the catalytic cracking of a hydrocarbon charge whose initial and final boiling points are between 50 and 2200C, 5 carried out in the presence of a catalyst containing:

2. A process according to Claim 1, in which the catalyst contains: (a) approximately 40 to 95% by weight of the matrix, (b) approximately 5 to 60% by weight of the zeolite.

is

3. A process according to Claim 1 or 2, in which the Y zeolite has a rare earth content, expressed as a percent by weight of oxides of rare earths, based on the Y zeolite, below 6%.

4. A process according to any one of Claims 1 to 3, in which the matrix is silica, alumina, magnesia, a silica-alumina mixture, a silica-magnesia mixture or clay.

5. A process according to any one of Claims 1 to 4, in which the 25 charge is rich in naphthene compounds and/or paraffins.

6. A process according to any one of Claims 1 to 5, in which the operating temperature is in the range 400 to 8000C.

7. A process according to any one of Claims 1 to 6, in which the weight ratio of the catalyst weight to the charge weight is in the range 3:1 to 15:1.

8. A process according to Claim 1, substantially as hereinbefore 35 described in the Examples with reference to the use of CAT, as therein defined with a 50 to 2200C fraction.