GB2231582A - Process for catalytic cracking in the presence of a mordenite - Google Patents

Abstract

Fluidized or entrained bed cracking of a hydrocarbon charge is carried out in a substantially tubular vertical elongated reaction zone (1) into which a catalyst containing a mordenite is introduced, preferably at the lower base of the elongated zone, by a pipe (2) the charge is introduced by at least one pipe (3) and another hydrocarbonaceous fluid, e.g. a part of the petrol, motor spirit or light oil obtained by the cracking, is delivered by at least one pipe (3a) at an intermediate point between the catalyst admission and charge admission points. The catalyst comprises (a) 20-95% matrix, (b) 1-60% open structure zeolite and (c) 0.01 - 30% mordenite having a Si: Al atomic ratio of at least 4.5:1, a sodium content below 0.2% by wt, a unit cell volume below 2.80nm<3> and a nitrogen adsorption capacity higher than 0.09 cm<3> (liquid)/g measured at 77 DEG K under a relative pressure P/Ps of 0.19. <IMAGE>

Description

:2 2 3 1 -15 a: -2 1 PROCESS FOR CATALYTIC CRACKING IN THE PRESENCE OF A

MORDENITE The present invention relates to the catalytic cracking in the fluid state of hydrocarbon charges.

It is known that the petroleum industry conventionally uses cracking processes in which molecules of hydrocarbons of high molecular weight and high boiling point are split into smaller molecules, the resulting hydrocarbons boiling in lower temperature ranges appropriate for the intended use.

The most widely used process at present is Fluid Catalytic Cracking or FCC. In this type of process the hydrocarbon charge is vaporized by h ightemperature contact with a cracking catalyst, which is kept suspended in the vapours of the charge. After the desired molecular weight range has been reached by cracking and the corresponding reduction in boiling point, the catalyst is separated from the products obtained, stripped, regenerated by the combustion of the coke formed and then recontacted with the charge to be cracked. The charges to be cracked are normally injected into the reaction 20 zone at a temperature between 480 and 5400C and under a relative pressure of 0.7 to 3.5 bar, while the temperature of the regenerated catalyst entering the said zone can be approximately 600 to 9500C. In the process of the invention, the catalyst is introduced either at the top or at the bottom of a substantially vertical tubular zone serving as the reaction zone. Thus, this zone functions either as a riser or as a dropper. The quantity of catalyst introduced may be determined, for example, by the opening or closing of a valve. The catalyst grains are then accelerated towards the top or bottom of the tube by injection of a gaseous fluid at the bottom or top of the tube.

This injection takes place with the aid of a fluid distributor. The charge to be cracked is introduced downstream and vaporized as completely as possible with the aid of an appropriate device in the dense flux of catalyst grains.

At the end of the tube are provided enclosures in which the cracked charge is separated and the spent catalyst is stripped and optionally regenerated.

When the reaction zone is a riser, the catalyst is introduced at the base of the riser in a quantity that may be determined, for example, by the opening or closing of a valve. The grains of the catalyst are then conditioned and accelerated towards the top of the riser by injecting a gaseous fluid at the bottom of the riser. This injection takes place with the aid of a fluid distributor. The charge to be cracked is introduced at a higher level and is at least partly vaporized with the aid of an appropriate device in the dense flow of catalyst grains.

The top of the riser issues into an enclosure, which may be concentric with it and in which the cracked charge is separated and the spent catalyst is stripped. The catalyst is separated from the effluent, entrained by a cyclonic system, cleaned, and purified.

When the reaction zone is a dropper, the catalyst is introduced at the top of a tube of the dropper type in a quantity that may be determined, for example, by the opening of closing of a valve. The grains of catalysts are then accelerated towards the bottom of the' dropper by injecting a gaseous fluid into the top of the dropper.

The hydrocarbon charges that can be injected into units of the abovementioned type can contain hydrocarbons having boiling points above 2000C, e.g. between 200 and 5500C, and their density can vary between 10 and 350 API. These charges can also be heavy charges containing hydrocarbons whose boiling point can be, for example, up to 7500C and whose density can vary between 10 and 350 API, or between 1 and 250 API.

For example, charges may be those having final boiling points of approximately 4000C, such as vacuum diesel oils, as well as heavier hydrocarbon-containing oils, such as stabilized and/or crude oils, as well as vacuum distillation or atmospheric distillation residues. If appropriate, these charges may have undergone a prior treatment such as a heat treatment in the presence of catalysts, e.g. of the cobaltmolybdenum or nickel-molybdenum type. The preferred charges for the invention are those containing fractions, for example, those normally boiling up to 7000C, and that can contain high percentages of asphaltene products and have a Conradson carbon content, for example, up to 10%. These charges may or may not be diluted by conventional lighter cuts and may include hydrocarbon cuts that have already 3 undergone cracking, that are recycled, such as e.g. Light Cycle Oils or L. C.0 or Heavy Cycle Oils or H.C.O. According to the preferred embodiment of the invention, these charges are available and preheated in a temperature range of 300 to 4500C prior to their treatment.

The present invention makes it possible to improve the flexibility of the yields of products of a catalytic cracking process and simultaneously to improve the quality of the naphtha or petrol cut, i.e. the Research and Motor Octane Numbers. Thus, it is sometimes an objective of refining within the framework of catalytic cracking to obtain a maximum of Liquefied Petroleum Gas (C3-C4) or L.P.G. and, simultaneously, either a maximum of high-octane-number petrol or, more rarely, a maximum of light distillate, which is more generally called light cycle oil or L.C.O. In the latter case, such an operation is normally incompatible, because it is necessary to increase the severity of the catalytic cracking in order to obtain the maximum L.P.G. and to reduce it to maximize L.C.O. production.

The present invention makes it possible to achieve the above objectives and in particular to obviate the aforementioned incompatibility. For this purpose, the present invention provides a process for the catalytic cracking of a hydrocarbon charge in a fluidized or entrained bed in an essentially vertical tubular elongated reaction zone, in which the catalytic particles are introduced at one end of the elongated zone and the charge is introduced by at least one pipe into the elongated zone at a level downstream of the admission level of the catalytic particles, the latter being separated from the reaction effluent and fractionated with a view to obtaining various fractions, particularly LPGs, a petrol, a relatively light oil L.C.O. and a relatively heavy oil H.C.O; a petrol is injected into the elongated zone at a level intermediate between the admission level of the catalytic particles and the charge admission level, the said petrol representing 5 to 50% by volume of the charge; and the catalyst is constituted by at least one product containing by weight:

(a) 20 to 95 of a matrix, (b) 1 to 60% of at least one open structure zeolite, (c) 0.01 to 30% of a mordenite with the following properties:

a Si:Al atomic ratio equal to or higher than 4.5:1, 4 a sodium content below 0.2% by weight based on the dry mordenite weight, unit cell volume V below 2.80 nm3, nitrogen adsorption capacity higher than 0.09 cm3 (liquid)/g measured at 770K under a relative pressure P/Ps of 0.19.

The petrol may be at least part of the petrol obtained in the effluent of the catalytic cracking zone. It is pointed out that in general terms within the scope of catalytic cracking, the performance of the process is dependent on the nature of the hydrocarbon effluents which the user wishes to obtain as a function of the instantaneous refining objectives. Thus, in general terms, a catalytic cracking of an oil makes it possible to obtain:

light gases (hydrogen, hydrocarbons with 1 to 2 carbon atoms per molecule), propylene (C3=), saturated C4 hydrocarbons, including 'so C4 hydrocarbons, unsaturated C4 hydrocarbons, petrols or motor spirits, relatively light cycle oil of L.C.O., relatively heavy cycle oil or H.C.O., and residue or slurry generally purified from the entrained catalyst to obtain a Clarified Oil or C.O. or a Decantered Oil or D.O.

Certain users seek either to significantly increase the production of unsaturated C3 (propylene) and C4 without increasing the production of saturated dry gases (H2, Cl, C2), or to significantly improve the production of unsaturated C3 (propylene) and 'so C4 without notably increasing the production of saturated dry gases (H2, Cl, C2)s or to significantly increase the production of unsaturated C 3 (propylene) and unsaturated C4 without increasing the production of dry saturated gases (H2, Cl, C2). It is usual to associate all three cases with a maximum production of particularly High Octane Number petrol.

In the present invention it has been discovered that the addition of a dealuminated mordenite to a convention cracking catalyst makes it possible to increase its selectivity with respect to a production of hydrocarbons with 3 and 4 carbon atoms. The use of a mordenite with a Si:Al atomic ratio equal to or higher than 4.5:1 consequently makes it possible to obtain a cracking catalyst with an improved selectivity relative to gas production, in particular propylene and more especially isobutane production, compared with the prior catalysts, without significantly increasing coke production. The catalysts according to 5 the invention make it possible to obtain even better results when the mordenite used has a Si:Al atomic ratio equal to or higher than 12:1. The dealuminated or non-dealuminated mordenites are associated in the present invention with a Y zeolite, which may or may not be stabilized and as is e.g. described in EP-A-0 020 154 and US-A-4 137 152.

There are two types of mordenite, which differ with regard to their adsorption properties, namely the synthetic wide pore form, which adsorbs molecules such as benzene (kinetic diameter 6.6 X 10-10m) and the natural or synthetic small pore form, which only adsorbs molecules with a kinetic diameter smaller than approximately 4.4 x 10-10 M.

These mordenites also differ morphologically, i.e. needles for small pore mordenite and spherulites for wide pore mordenite, as well as structural differences, namely the presence or absence of defects. Mordenite is characterized by a Si:Al atomic ratio normally between 4.5:1 and 11:1. Its crystalline structure is constituted by 20 linkages of tetrahedra with an 5i04 and A104 base, which generate two types of channels, namely those having a dodecagonal opening or aperture (contour with 12 oxygens) and those having an octagonal opening or aperture (contour with 8 oxygens). Tetraethyl ammonium mordenites (TEA) synthesized in the presence of tetraethyl ammonium organic ions belong to the wide-pore category. Their adsorption properties, as described hereinbefore, can be determined only after eliminating, e.g. by calcination, the tetraethylammonium ions. The Si:Al atomic ratios thereof are usually from 7:1 to 1M. 30 It is possible to "open" the channels of the small pore mordenites, e.g. be treatment in a strong mineral acid and/or by calcination in the presence of water vapour, and thereby obtain an adsorption capacity close to that of wide pore mordenite. The different characteristics of the zeolites are measured by the following methods:

the overall Si:A1 atomic ratios are determined by X-fluorescence analysis and tne sodium contents by atomic absorption; 6 the volume of the lattice and the crystallinity are determined by X-diffraction, the sample being prepared in accordance with the standard ASTM D3942 80 drafted for faujasite; the nitrogen adsorption capacity of the mordenite being determined at 770K for a relative pressure P/Ps = 0.19 (Ps being the saturated steam pressure at a temperature of 770K).

The mordenite used for preparing the cracking catalyst according to the invention is either a wide pore, spherulite form, dealuminated mordenite, or an acicular mordenite in the case of open small-pore mordenites, the pore diameter being equal to or greater than 6.6 x 10-10m, i.e. the kinetic diameter of benzene.

The mordenite can be used in hydrogen form or in a form at least partly exchanged by metal cations, e.g. alkaline-earth metal cations or rareearth metal cations with atomic numbers of 57 to 71 inclusive.

The mordenites used in the present invention may for example be obtained from the following synthetic starting mordenites: small pore sodium mordenite, wide pore sodium mordenite and TEA-type mordenite.

The dealuminated mordenites used in the present invention are characterized by the following properties:

Si:Al atomic ratio above 4.5:1 and normally between 8:1 and 1000:1 and preferably between 15:1 and 500:1; sodium content below 0.2% by weight and preferably below 0.1% by weight compared with the dry mordenite weight; a lattice volume V of the unit cell below 2.80 nm3 and preferably between 2.650 and 2.745 nm3; and a nitrogen adsorption capacity measured att 770K under a relative pressure P/Ps of 0.19 that is higher than 0.09 cm3 (liquid)/g and preferably above 0.11 em3 (liquid)/g.

These mordenites can be obtained from small pore mordenites having a sodium content conventionally between 4 and 6.5% by weight compared with the dry mordenite weight, whose Si:Al atomic ratio is normally between 4.5:1 and 6.5:1 and whose lattice volume is between approximately 2.77 and 2.80 nm3, e.g. in accordance with the method described by the Applicant in European Patent EP-B-0 196 965. This starting mordenite adsorbs only molecules having a kinetic diameter below approximately 4.4 x 10-10m. After treatments, the mordenite is characterized by different specifications, whose determination methods

7 are described hereinafter. The mordenite obtained has all the characteristics referred to above and has a particular morphology, namely it is largely in the form of needles preferably having an average length of 5 microns (5 x 10-6m), whose hexagonal faces have a length of approximately 1 micron (1 x 10-6 m) and a "height" of approximately 0.3 micron (3 x 10-5m).

There are various methods for obtaining a wide pore dealuminated mordenite, like that defined above, from a small pore mordenite and reference should be made to EP-B-0 196 965.

The catalyst according to the invention contains at least one open-structure zeolite having dodecagonal channels of at least an aperture of 7 Angstroms (7 x 10-10m) and generally chosen from X, Y, L, omega and beta zeolites. Preference is given to the use of zeolites having a faujasite structure and in particular the Y zeolite (Zeolite Molecular Sieves Structure, Chemistry and Use, Donald W BRECK, John WILLEY & Sons, 1973). Among the Y zeolites that can be used, a stabilized Y zeolite, normally called ultrastable or USY, which may be in a partly exchanged form with metal cations, e.g. alkaline-earth metal and/or rare- earth metal cations with an atomic number between 57 and 71 inclusive, or in the form of hydrogen, is preferred.

The catalyst according to the invention also contains at least one normally amorphous or poorly crystallized matrix, e.g. alumina, silica, magnesia, clay, titanium dioxide, zirconium dioxide or a combination of at least two of these compounds, or an alumina - boron oxide combination.

Examples of combinations of at least two compounds of the aforementioned group include silica-alumina and silica-magnesia. The matrix is preferably chosen from silica, alumina, magnesia, silica- alumina combinations, silica-magnesia combinations and clay.

The catalyst used in the present invention consequently contains:

(a) 20 to 95%, preferably 30 to 85% and particularly advantageously to 80%, by weight of at least one matrix, (b) 1 to 60, preferably 4 to 50%, and particularly advantageously 10 to 40%, by weight of at least one so-called open structure zeolite, (c) 0.01 to 30%, preferably 0.05 to 20%, and particularly advantageously 0.1 to 10%, by weight of at least one mordenite 8, having the characteristics given herein.

The aluminosilicate structural framework of the modified or unmodified mordenite used in the preparation of the catalyst according to the present invention is solely constituted by aluminium atoms and silicon atoms. However, it is also possible to use in the preparation of the catalyst according to the invention, a modified or unmodified mordenite in which part of the aluminium and/or the silicon of the aluminasilicate structure is replaced, following synthesis, by other metal or non-metal elements, e.g. B, P, Ti, V, Cr, Fe, Mn, Ga, Ge and 10 Zr.

The catalyst according to the invention can be prepared by any known method.

Thus, the catalyst can be obtained by the simultaneous incorporation of the mordenite and the Y or open-structure zeolite by methods conventionally used in the preparation of zeolite-containing cracking catalysts.

The catalyst can also be obtained by mechanically mixing a first product incorporating a matrix and a Y zeolite and a second product incorporating the mordenite, e.g. a mixture of the mordenite with a matrix, which can be the same or different from that contained in the first product. This mechanical mixing is normally performed with dried products. The drying of the products is preferably carried out by atomization or spray drying, e.g. at a temperature of 100 to 4000C and normally for 0.1 to 30 seconds.

After spray drying these products can still contain approximately 1 to 30% by weight of volatile material (water and ammonia). The mordenite- matrix mixture normally contains 1 to 90 and preferably 5 to 60% by weight of mordenite based on the total weight of the mixture.

The mixture of matrix and open-structure zeolite used in the preparation of the catalyst according to the invention is normally a known cracking catalyst (e.g. a commercially available catalyst). The mordenite can be considered as an additive, which can be used as it is with a view to its being mixed with the conventional cracking catalyst defined above, or can have previously been incorporated into a matrix, the matrix-mordenite system then constituting the additive mixed with the conventional cracking catalyst defined hereinbefore, e.g. following an adequate shaping by mechanical mixing of the grains t 9 containing the mordenite and the conventional cracking -catalyst grains. In addition, the mordenite can be wholly or partly added during cracking upstream or downstream of the arrival of the catalytic material. 5 The general catalytic cracking reaction conditions are known and consequently need not be repeated here (cf. e.g. US-A-3 293 192; US-A-3 449 070; US-A- 4 415 438; US-A-3 518 051 and US-A-3 607 043). The association of the mordenite according to the invention with a conventional cracking catalyst in a fluidized bed makes it possible to obtain a catalyst with a higher activity and better selectivity for the production of C 3-4 light gases than conventional fluidized-bed cracking catalysts.

In the accompanying illustrative drawings, the single figure shows an elongated, tubular reaction zone 1 or riser with an upward flow of the charge and the catalyst (it being considered unnecessary to explain the operation of a dropper).

The catalyst is used jointly with the injection of a petrol upstream of the charge under conditions such that the petrol can again be cracked into lighter constituents (C 3, C4). It has been found that in order to be able to effectively crack the petrol, it should be passed into the lower part of the elongated, tubular reaction zone at a point below that where normal charge injection takes place. Thus, the temperature and C/0 conditions (catalyst to oil ratio) are such that cracking takes place under severe conditions.

The catalyst enters through pipe 2 at the bottom of the elongated zone, the charge entering in the form of a liquid dispersed in fine droplet form or atomized at the base of the riser, but at a level B higher than that at which the catalyst enters and using at least one opening 3. The catalyst enters the riser at a temperature Ti and flows at the bottom of it at a rate D1. The charge enters the riser at a temperature T2 and at a rate D2. The mixing of the charge and the catalyst takes place at the charge inlet 3. There is a heat exchange between the catalyst and the charge, so that at least part of the latter is vaporized. An equilibrium is reached at a temperature T 39 which is higher than T2, the charge-catalyst mixture flowing at this riser level at a rate D 3 The cracking reaction then takes place and as the reaction is endothermic, it leads to heat adsorption. In the upper part of riser 1, a device 4, which is called a T, is used for bringing about a separation of the gaseous reaction effluents from the catalyst particles.

Thus, as explained hereinbefore, the injection of the petrol fraction or LPG into the reactor 1 takes place through at least one pipe 3a. The cracking of this light fraction takes place under conditions of more favourable severity than if said injection had, for example, taken place through a pipe 3, because in the vicinity of level C of pipe 3a the catalyst temperature is at its highest level.

Thus, locally at level C there are severe cracking conditions (high temperature, high C/0), which are generally needed for the cracking of light charges (petrol, LPG). Thus, it is at level C that the injected petrol is cracked, so that at this level there is a drop in catalyst temperature. Thus, at the charge arrival point B, the temperature is lower, so that cracking can take place under gentler conditions (moderate temperature and already damped catalyst), which are very suitable for cracking the charge whilst obtaining an L.C.O. maximum. Petrol injection at 3a takes place at a temperature and under conditions that do not modify the temperature on leaving the reaction zone and also leads to a more fluid catalyst flow. In this way it is possible to reconcile two apparently incompatible objectives by the use of at least two zones of different severity, namely a first highseverity zone at the bottom of the riser between the petrol intake and the charge intake, where the maximum L.P.G. cracking production takes place by cracking a lighter petrol than L.C.0, and a less severe zone located in the riser above charge admission pipe 3, which latter zone can be subdivided into zones of differing severity as the temperature drops on ascending the riser.

The percentage of petrol and/or L.P.G. injected upstream of the charge according to the invention represents, by volume, 5 to 50% and preferably 10 to 30% of the charge.

The following examples illustrate the invention without limiting its scope.

1 11 EXAMPLE 1: Preparation of a Hydrogen Form Mordenite of Si:A1 Atomic Ratio above 100:1 The staring solid is a synthetic mordenite with a Si:C atomic ratio of SA:1 and marketed by the Societe Chimique de la Grande Paroisse under reference Alite 150. The approximate chemical formula of this zeolite in dehydrated form is Na20.A1203 10.8 Si02 In a first stage, the starting solid undergoes three successive exchanges at 1000C in 1ON ammonium nitrate solution (NH003) with a ratio of solution volume to dry mordenite weight (v/w) of 5 cm3/g. After the third exchange the solid is washed with distilled water and dried at 1000C for 10 hours. The solid obtained following this first series of treatments is designated NH4MO, its residual sodium content being below 500 ppm by weight.

In a second stage, the solid NH4M0 is calcined in moist air containing 85% by volume of water vapour at 6000C for 2 hours. It is then subjected to acid action in an aqueous OAN HCl solution at 1000C for 4 hours with a v/w ratio of 7 cm3/g. The mordenite is then washed with distilled water and dried at 1000C for 10 hours. It is designated HM1, its main physicochemical characteristics being given in Table 1.

This mordenite undergoes water vapour calcination at 6500C for 4 hours and then a treatment in a 4N HNO 3 nitric acid solution at 1000C for 4 hours, the v/w ratio being 5 cm3/g. The mordenite is then washed with distilled water and then dried at 1000C for 10 hours. This leads to a highly dealuminated solid with a Si:Al atomic ratio of 110:1 and designated HM2. The physicochemical characteristics of this solid are given in Table 1.

TABLE 1

Crystalline Parameter& (ra) Mordenit SifAl DX a h c M #2 Lattice PPO CM3/g r03 11 1.813 2.027 0.746 98 200 0.242 2.742 1.807 2.027 0.746 98 90 0.251 2.7320 12 EXAMPLE 2: Preparation of the Mordenite-Based Additive Prepared in Example 1 Into a 20-litre container equipped with a stirrer are introduced 14 litres of water, 600 g of dry pseudoboehmite gel marketed by CONDEA and containing approximately 75% by weight of alumina and 2.5 kg of a silica-alumina calcined and ground to a mean particle size of 6 microns. 160 cm3 of concentrated pure nitric acid is added, accompanied by stirring, to the preceding mixture, which is then heated to 500C for 45 minutes, accompanied by stirring. This is followed by the addition of 740 g of mordenite HM2 of Example 1 and stirring takes place for 15 minutes. The mixture is then atomized in a NIRO atomizer, at an intake temperature of 3800C and an outlet temperature of 1400C.

The finished catalyst is in the form of microspheres with a grain size comparable to that of commercially available fluidized bed cracking catalysts. It contains 20% by weight of mordenite based on the dry product.

Prior to testing, this product has previously been calcined for 16 hours at 7500C under an atmosphere constituted by 100% water vapour.

EXAMPLE 3 (not according to the invention: Carried out without injecting petrol and then with the injection of a light petrol at the bottom of the riser Two catalytic cracking tests were carried out on the basis of a hydrocarbon charge. The catalyst contained 70% of a conventional silica-alumina-based matrix rich in silica and kaolin and containing 30% of an ultrastable Y zeolite USY. The balanced catalyst flowing in the unit has the following characteristics: surface in J. g- 1 = 110 A120 3 % by weight: 27 30 rare earth oxides in % by weight = 1.4 Na20% by weight = 0.3 V (ppm) = 4800 Ni (ppm) = 2800 Fe (ppm) = 10200 35 In the first test, which is not in accordance with the invention, use is made of a conventional device for the injection of catalyst grains by means of a pipe 2 (Figure 1) and a heavy charge to be cracked 13 by a pipe 3. The second test was performed with the aid of the device recommended by the invention, involving the injection by a pipe 3a of 25% by weight petrol based on the petrol charge. However, this example is not in accordance with the invention, because the specific catalyst according to the invention is not used. The heavy charge common to both tests has the characteristics indicated hereinafter:

1 A CHARACTERISTICS OF HEAVY CHARGE USED Density (201C Viscosity (solid at 6000 (8000 est (10010 Conradson % by weight Na ppm Ni ppm V ppm C % by weight H by weight N by weight S by weight N basic % by weight C aromatic % by weight H aromatic % by weight Simulated distillation (OC) % by weight % by weight % by weight % by weight % by weight FBP 0.968 119.8 52.2 (52.2 mm 2 IS) 5.1 2 12 1 86.9 12.2 0.35 0.21 0.055 22.3 2.7 367 399 436 495 575 575 The direct distillation petrol used in the second test is a nonolefinic 50-160 cut with the following composition:

paraffins % by weight: 58 olefins % by weight: 0 naphthenes % by weight: 29.5 aromatics % by weight: 12.5 This petrol contains less than 2% by weight of compounds with 5 carbon atoms.

The following operating conditions were used during these two tests:

catalyst injection temperature 7710C heavy charged injection temperature 2100C -1 1 1 is riser temperature in the vicinity of pipe 3 5370C temperature at the top of the riser 5200C C/0 = 6, in which C is the mass flow rate or the catalyst and 0 the mass flow rate 6fthe heavy charge.

The results obtained in the two tests are given in table 2. The yields are in % by weight based on the heavy charge. The conversion of injected petrol in the second test is 56% by weight.

TABLE 2 lst Test 2nd Test (heavy charge) - % by weight (heavy charge + petrol) direct distillation H 2 S 0.10 0.10 H 2 + C 1 + C 2 4.6 5.5 C 1.4 2.0 C 3= 4.4 6.5 C 4 unsaturated 4.1 5.1 (Including iC 4 (3.3) (4.1) C 4 = total 5.9 9.3 Total of gases 20.5 28.5 C 5 petrol (221IC) 44.9 60.0 LCO(221-350OC) 15.1 15.8 Slurry (350+) 11.4 12.2 Coke 8.1 8.5 Conversion 73.5 - Total 100 125 Research Octane Number of petrol 92.2 90.9 Motor Octane Number of petrol 80.1 79.5 The system of injecting at the bottom of the riser on to a very hot catalyst a light first distillation petrol makes it possible to obtain an improved propylene and also 4 carbon atoms olefin yield.

1 16 EXAMPLE 4 (partly according to the Invention): Cracking Process with the Direct Injection of Light Distillation Petrol at the bottom of the Riser and use of a Catalyst containing an Offretite.

To the fluidized bed cracking catalyst used in example 3 are added 20% by weight or the additive catalyst according to the Invention prepared in example 2 and containing 20% by weight mordenite. Thus, there is 4% by weight of mordenite based on the total catalytic material.

The catalytic tests are carried under the conditions described in example 3, the C/0 ratio = 6 being defined by the ratio of the balanced catalyst flow (of example 3) and the heavy charge flow, whose characteristics were given in example 3.

The following table 3 gives the results obtained. It shows the results obtained in example 3 when petrol injection takes place, but without the use of a mordenite-containing catalyst. The addition of mordenite to a conventional catalyst leads to a significant propylene gain and a slight gain of butenes and isobutane.

1 17 TABLE 3

Test with the injection of a petrol and a conventional catalyst by weight) Test with the injection of a petrol and a catalyst according to the invention (% by weight) H 2 S 0.1 0.1 H 2 + C 1 + C 2 5.5 5.4 c 2.0 2.2 C 3 6.5 9.7 Total saturated C 4 5.1 8.2 (Including iC 4 (4.1) (6.2) c 4 = total 9.3 13.1 Total of gases 28.5 38.7 Petrol C 5 (221OC) 60.0 50.8 LCO (221-350OC) 15.8 15.3 Slurry (350+) 12.2 11.6 Coke 8.5 8.6 Total 125.0 86.3 Research Octane Number of petrol Motor Octane Number of petrol 90.9 93.8 79.5 82.2 18

Claims (6)

1. A process for the catalytic cracking of a hydrocarbon charge in a fluidized or entrained bed in an essentially vertical tubular elongated reaction zone, in which the catalytic particles are introduced at one end of the elongated zone and the charge is introduced by at least one pipe into the elongated zone at a level downstream of the admission level of the catalytic particles, the latter being separated from the reaction effluent and fractionated with a view to obtaining various fractions, particularly LPGs, a petrol, a relatively light oil L.C.O. and a relatively heavy oil H.C.O; a petrol is injected into the elongated zone at a level intermediate between the admission level of the catalytic particles and the charge admission level, the said petrol representing 5 to 50% by volume of the charge; and the catalyst is constituted by at least one product containing by weight:

(a) 20 to 95% of a matrix, (b) 1 to 60% of at least one open structure zeolite, (c) 0.01 to 30% of a mordenite with the following properties:

Si:Al atomic ratio equal to or higher than 4.5:1, sodium content below 0.2% by weight based on the dry mordenite weight, unit cell volume V below 2.80 nJ nitrogen adsorption capacity higher than 0.09 cm3 (liquid)/g measured at 770K under a relative pressure P/Ps of 0.19.

2. A process according to Claim 1, in which the catalyst contains by weight:

(a) 30 to 85% of the matrix, (b) 4 to 50% of the open-structure zeolite, (c) 0.05 to 20% of the mordenite.

3. A process according to Claim 1 or 2, in which the mordenite has the following characteristics: 35 a SiAl atomic ratio between 8:1 and 1000:1, a sodium content below 0.1% by weight, based on the dry mordenite weight, Z 19 1 a unit cell volume V between 2.650 and 2.760 nm3, a nitrogen adsorption capacity above 0.11 cm3 (liquid)/g, measured at 770K under a relative pressure P/Ps of 0.19.

4. A process according to any one of Claims 1 to 3, in which the open structure zeolite is an X, Y, faujasite, L, omega or beta zeolite.

5. A process according to any one of Claims 1 to 5, in which the catalyst is used as an additive to a conventional cracking catalyst.

6. A process according to Claim 1, substantially as hereinbefore described in Example 1 or 2.

P-bhshcd 1990 a The House 6671 High Holborn. London WC 1R 4TP. Flarther copies maybe obtained from The Patent Office Sa.es Branch, St Mary Cray, Orpington, Kent BR53RD. Printed by Multiplex techniques ltd, St Mary Cray, Kent. Con. 1.187