FR2640994A1 - - Google Patents

Abstract

Process for the production of petrol having a low benzene content and a high octane number, characterised in that a. a material discharged from a reforming reaction is fractionated into a light fraction enriched in benzene and a heavy fraction depleted in benzene, b. the said light fraction is reacted with a cracking gas containing at least one C2-C5 monoolefin, in contact with a dealuminised mordenite catalyst having an overall atomic ratio Si/Al greater than 20, so as to give an alkylated fraction and c. the said alkylated fraction is mixed with the said heavy fraction. Use of the resulting mixture as a fuel.

Description

The present invention relates to a method of upgrading gases from the

  catalytic cracking and gasoline production with low benzene content and improved octane number. The gases from catalytic cracking, which can represent up to about 5% of products from a unit of F.C.C, are currently little or not valued, apart from their use as fuel to

  inside the refinery that produces them.

  These gases are generally composed mainly of hydrogen, methane, ethane, ethylene and nitrogen, accompanied by carbon monoxide and dioxide, propane, propene and some butanes, butes, pentanes and pentenes. The mono-olefin content of these gases (ethylene, propene, butenes, pentenes) is of the order of 20 to 30% by weight. Given the large capacity of the catalytic cracking units, it is therefore economically very interesting to

  to transform these olefins into products with higher added value.

  On the other hand, world and mainly European legislators will quickly impose, for reasons of public health, the limitation of the benzene content of gasoline and in particular reformat, and it is probable that from the beginning of the 1990s, the benzene limit, currently around 5% O, will have to be

  be strongly lowered to at most 3, and may be less.

  The method according to the invention solves these two problems jointly; it is therefore suitable for refiners having both a catalytic reforming unit and

  a catalytic cracking unit.

  According to the process of the invention, a reformate is fractionated into a benzene-enriched light fraction and a benzene-depleted heavy fraction, the light fraction is reacted with a cracking gas containing at least one C2-C5 monoolefin, contact of a mordenite catalyst defined below, so as to obtain an alkylated fraction, and said alkylated fraction is mixed with said

heavy fraction.

  This alkylation reaction is carried out in the presence of an acidic zeolite catalyst arranged in the form of a fixed bed, at a temperature of approximately 50 to 350 ° C. (preferably between 150 ° C. and 300 ° C.), under a pressure of from 2 ° to 10 MPa (preferably between 3 and 7 MPa), with a liquid hydrocarbon flow rate (space velocity) of about 0.5 to volumes per volume of catalyst and per hour, and with a molar ratio of benzene / olefins between 0 , 2 and 5 (preferably between

0.6 and 1.5).

  It has already been tried to valorize the olefins contained in the catalytic cracking gases by transforming them into gasoline or jet fuel by oligomerization, in the liquid phase or in the heterogeneous phase, in the presence of either a catalyst formed by the action of an alkylaluminium. on a nickel salt, a nickel-based catalyst deposited on silica-alumina. In both cases, the presence of carDone monoxide (for example 0.1 to 2 by weight) is very annoying, the latter being a poison nickel-carbon catalysts by formation of nickel-carbonyls. The use of such catalysts therefore requires a prior expensive separation by cryogenesis of the

  lightest fraction of the feedstock (hydrogen-CO-COO 2 -methane).

  In contrast, the zeolitic catalyst used in the invention, namely a dealuminated mordenite of Si / Al atomic ratio greater than 30, makes it possible to treat the gases resulting from catalytic cracking without any prior separation. These gases can

  contain, for example, 0.1 to 2 wt.% carbon monoxide.

  Several zeolite catalysts have already been proposed on the one hand, for the alkylation reaction of benzene with ethylene or

  on the other hand, for the alkylation reaction of benzene with propene.

  In the years 1975-1980, the use of zeolites under

  form H has been proposed, in particular ZSM5 from MCBIL (EP 0104729).

  More recently, other zeolites have been put forward, in particular certain mordenites, alone or mixed with faujasite (US 3,436,432), optionally with a Group VIII metal deposited thereon (US 3,851,400). Japanese patents (JP 582.16128 and JP 581 59427) advocate mordenites alone, of low Si / Al ratio (4.5 to 5), containing metal ions such as Mg, K, Ca, or

in H + form (JP 041670).

  Dealalized mordenites and their preparation are also known: EP-0084748, EP-0097552, EP-0196965 (small-pore mordenites) and FR8712932. These mordenites were used to

  convert methanol or isomerize olefins.

  These mordenites are preferably prepared as follows,

  to get the best results.

  In a first step, the non-cation is removed.

  decomposable, usually Na ', present in the starting mordenite.

  To do this, we can proceed to one or exchanges in dilute solutions of acids such as HCl or NH4 + solution. The important point is that at the end of this first step that can be described as de-cationization, almost all the alkaline cations are eliminated (% Na between 150- and 1000 ppm, and preferably between 300 and 800 ppm), and that the solid obtained is a form H or a precursor of form H (example NH4 +) not dealuminated

  substantially (% dealumination <10 and preferably <5%).

  In a preferred manner, the NH 4 + form will be chosen as precursor of the H form. In a second step, the H-form or the precursor of form H, little or not dealuminated, is subjected to a treatment under steam at a temperature above 450 C, for example at 450-650 ° C, and preferably , 550 to 600 -C. The water content (by volume) of the calcination atmosphere is advantageously greater than 20 and preferably 40. At the end of this second stage, a solid is obtained characterized by the presence of amorphous zones in small quantities, which are precursors of the secondary porous network, and by a crystalline framework practically free from structural defects. The presence of amorphous zones in zeolites treated at high temperature under water vapor is a known phenomenon. However, the operating conditions recommended make it possible to limit as much as possible the proportion of amorphous zone within the crystals. The crystallinity levels measured by X-ray diffraction are generally greater than 80% and, more specifically, 90%. The solids calcined under water vapor are also characterized by the presence, in the structural micropores, extra-network aluminum species, a subsequent acid attack is therefore necessary because these micropores are substantially clogged. However, to obtain a good alkylation catalyst, according to

  the invention this acid attack must be optimized.

  Acid etching is the third step in the preparation of the catalysts. At this point, it is important to preserve or release the strong acid sites of the solids. The acid attack must therefore be sufficiently strong to firstly eliminate the cationic aluminas formed during the treatment under steam, which are poisons strong sites and, secondly, to release the structural microporosity. The acid sites of the Brönsted type linked to extra-network species being of medium or low strength, it is not essential to proceed to their total elimination. The acid attack should not, however, be too strong, so as to avoid too much dealumination of aluminum frameworks. The force to be retained for the acid attack depends strongly on the characteristics reached after the calcination under water vapor and, in particular, the crystalline mesh. For Si / Al ratios ranging from 10 to 40, acid concentrations (HCl, H 2 SO 4, H 2 O 3, etc.) of between 0.5 and 5 N and preferably 1 to 3 NL will be used. For higher Si / Al framework ratios, acid solution concentrations of between 5 and N and preferably 7 to 12 N will be used (the Si / Al framework ratios are determined by infrared spectroscopy for ratios of 10 to 40, and 29Si NMR for higher ratios). On the other hand, to reach high Si / Al ratios, that is to say greater than 40 and more specifically greater than 60, it will be possible to use several calcination cycles under advantageous conditions.

water vapor-acid attack.

  The solids prepared according to the invention advantageously have Si / Al ratios greater than 30, preferably between 30 and 30; they have a mesh size between 2755 A3 and 2730 A3 (1A = 10 10m) and preferably between 2740 A3 and 2735 A3, they preferably have sufficient acid strength for structural AI-Hs to interact with a weak base such as ethylene (infrared measurement at 77-K), or a weakly acidic compound such as H2S (infrared measurement at 25 ° C). These solids must, in addition, preferably be free from extra-lattice cationic species which can be detected by a fine signal (half-width less than 5 ppm and preferably less than 2 ppm) at 0 ppm ( Al (H20) 63) on a spectrum of R.M1.N. of A1, measured with rotation technique

from the magic angle.

  The process according to the invention is designed so that: a reformate from a catalytic reforming unit is firstly fractionated in a first distillation column; at the bottom of the column is collected a benzene-depleted fraction of higher boiling point for example 85 -C, which is sent to storage; at the top of this first column is a light reformate enriched in benzene, for example C5-85 ^ C, which is mixed with gases from

  a catalytic cracking unit.

  the resulting mixture is first brought to the reaction temperature, both by heat exchange with the effluent from the alkylation reactor and by passing through an oven, and then sent to the alkylation section containing the catalyst mordenite mentioned above, the effluent of the alkylation section is then sent to a second stripping column, a light fraction consisting of hydrogen, carbon monoxide, carbon dioxide, nitrogen, d oxygen, methane and ethane, which can be flared off, or rather used as a fuel in the preheating furnace of the charge going to the alkylation section, the fraction drawn off at the bottom of this second column of stripping is sent to a third stabilization column; a light fraction enriched with propane and butanes, which can be marketed in the form of G.P.L. (liquefied petroleum gas) - the gasoline fraction scuttered at the bottom of this third column is sent to storage for mixing with the fraction of boiling point above 85 C approximately from the bottom of the first

  fractionation column of the reformate.

  The following nonlimiting examples illustrate the invention.

EXAMPLE 1A

  Three catalysts B1, B2, B3 are prepared.

  The raw material used to prepare these various catalysts is a small pore mordenite from the Chemical Society of the Greater Parish, referenced Alite 150; its chemical formula in the anhydrous state is Na, Al O 2 (SiO 2) 5.5, its benzene adsorption capacity is 1, by weight relative to the weight of dry solid, and its sodium content of 5, 3% by weight. Five hundred grams of this powder are dipped in a 2M solution of ammonium nitrate, and the suspension is heated at 95 ° C for 2 hours. The volume of the ammonium nitrate solution employed is equal to 4 times the weight of dry zeolite (V / P = 4). This cation exchange operation is repeated 3 times. After the 3rd exchange, the product is washed with water at 20 ° C. for 20 minutes, with a V / P ratio equal to 4. The sodium content expressed as a percentage by weight relative to the dry zeolite goes from 5.5 at 0.2%. The product is then filtered, and different batches are subjected to calcination in confined atmospheres, at a higher or lower temperature depending on the degree of dealumination of the framework that is to be obtained (Table 1). The duration of the calcination is fixed at 2 hours. The partial pressure of water vapor inside the reactor is of the order of 90% 0. The crystallinity of the various solids, after this step of

  calcination, is greater than or equal to 90%.

  Then, on each of the solids, an acid attack is carried out with nitric acid of concentration all the higher as the rate of dealumination of the framework obtained in the previous step is greater (Table 1). . During the acid attack, the solid is refluxed in the nitric acid solution for two hours, with a V / P ratio of 8. The product is

  then filtered, then washed thoroughly with distilled water.

2640 99 4

  The atomic Si / Al ratios obtained for each of the

are shown in Table 1.

  Each modified solid is then shaped by kneading with an aluminum-type binder, in a proportion of 20% by weight of binder, then through a die. The extrudates obtained, of diametre, 2 mm, are then dried and calcined between 150 and 550 ° C.

in about one hour.

TABLE I

CATALYST Bi B2 B3 Temperature of

510,560,600

  calcination (VC) 510 50 600 i '__ _ _ __ _ _! _ _ _ IR atomic ratio i5i / Al gloabl * 5.5 5, atomic ratio Si / Al IV il 49 86! framing _ _ _ __! _ _ The Formality of the 1 N 1 3, 5 N 10 N Nitric Acid Solution I i

__ _ _ _ _ I II!

  AtomicReport I I ISi / Al Global ** 1 l 1 49 86

1

* after calcination.

** after acid attack.

EXAMPLE 1B

  Three catalysts B'l, 8'2, B'3 are prepared. These catalysts differ from those described in Example 1A, in that the raw material used to prepare them is no longer the Alite 150 mordenite of the Chemical Society of the Greater Parish, but a large pore mordenite of the TOYO-SODA Company. , reference TSZ 600 NAA. Its chemical formula, in the anhydrous state, is Na, A102 (SiO2) 51, and its

sodium content of 5.7.

  All the stages of exchange, calcination, etching, shaping and calcination are carried out under the same conditions as those described in Example 1A. The atomic Si / Al ratios obtained are only slightly different

(Table II)

TABLE II

CATALYST B'1 B'2 B'3

Temperature of

1,510 5-60,600

  [calcination (C lC) 60 600 Atomic ratio SiAl gloDalw5,1 5.1 5.1

siSiA1 global-

  Atomic ratio Si / Al IV 10 47 83 jde framework Normality of the acid solution 1 N 3.5 N 10 N nitric Atomic ratio

47 83

SiA1p glooal- *

  * after calcination. ** after acid attack.

he

EXAMPLE 2A

  The three catalysts B1, B2, B3, described in Example 1A, were tested in alkylation of a top fraction (boiling point below 85 ° C) of a reformate from a catalytic reforming unit. by gases from a catalytic cracking unit. Before splitting the reformate had the composition

  weight and the characteristics presented in Table III.

  This reformate was then fractionated in an Oldershaw column of 60 theoretical plates, with a reflux ratio of 5/1, and two fractions were collected: an initial point fraction -85 C representing 32 by weight of the overall reformate, 85 C - end point representing 68 of the

global reformat.

  The main characteristics of these two fractions

  are shown in Table III.

  The gases from the catalytic cracking unit had the following weight composition: - hydrogen: 0.46 - carbon monoxide (CO): 4.49 carbon dioxide (CO2): 0.36 - nitrogen: 15.09 - oxygen: 0.26

TABLE III

REFORMAT FRACTION FRACTION

t GLOBAL PI-85: C 85 C - PF

I I)

MAIN ICARACTERISTICS

  Benzene content (wt%) 5.87 18.37 0 1- density at 20: C 0.787 0.687 0.838 distillation curve ASTM Starting point 2C 232 21-662 vol. 55, 309 1002 vol. 71 592 1135 50 vol. 111 62. 139:

flight. 139 I 66-145-

! 90 vol. 164: 765-176-

I 95 vol. 176-85- 185-

Final Point OC 194 ^ 97- 197-

  RON clear octane number 94.5 76 106 - methane 23.18 - ethane 23.62 ethylene 16.50 - propane 2.89 - propene 5.88 - butanes 1.58 - butenes 3, 31 - pentanes 0.76 The operating conditions used for the alkylation reaction were as follows: temperature: 230 ° C. pressure: 4.5 MPa-weight ratio of reformate (PI-85 OC fraction) liquid equal to 2.5 times the weight of the catalyst - molar ratio benzene (contained in the fraction

  PI-85 CC reformate) / olefins (C2 + C3 + B4 + C5) = 1.45 / 1.

  At the outlet of the reactor, and after 48 hours of operation, the products obtained on the three catalysts B1, B2 and B3 respectively had the main characteristics

presented in Table IV.

TABLE IV

CATALYSTS B1 B 2 3 '

  BENZENE PROCESSING RATIO 130.6 i46.8 J31.2% 1 J- FRACTION C5 +: weight 183.73% j86.50 S-! 88.0l% j86.56% 1 j- C5 + GAIN: ^ CHARGE 1 1 3.3 5.1 3.4% C5 + FRACTION ICARACTERISTICS 1 - density at 20 C 1 0.687 0.692 i 0.694 1 0.691; When the results are examined, it can be seen that it is preferable to work with the catalysts recommended by the invention, that is to say that it is necessary to use the RON clear octane number 176. dealuminated mordenites having an Si / Al ratio of between 30 and 80. Indeed, the mordenites having an Si / Al ratio of less than 30 are much less selective, and they lead to the formation of paraffins (methane, ethane, propane, butanes). pentanes); while the mordenites having an Si / Al ratio greater than 80 are a little more selective, but much less active since they do not completely transform the olefins (ethylene, propene, butenes, pentenes).

contained in the load.

  In the case of catalyst B2, the product obtained, at the bottom of the column 19 of the single figure, was mixed with the fraction drawn off at the bottom of column 2 of this same figure; and so ob

  obtained 104 Kg of gasoline is a yield increase of 4 ,.

  This species had the following characteristics: - density at 20: C: 0.785, - ASTM distillation curve, initial point 31: vol. 80 vol. 116 vols. 149: 90 vol. i78: C vol. 191 -C end point 238 ^ C - octane number: 98 instead of 94.5 for the initial reformate. the benzene content of the gasoline has been reduced from 5.87 to 0.36 by weight, ie a reduction of 94 S.

EXAMPLE 2B

  The three catalysts B'I, B'2 and B'3, described in Example 1B were also tested under the same operating conditions, and with the same load as the catalysts B1, B2 and B3, the results obtained, presented in Table V, are very close to those obtained with catalysts B1, B2 and B3. As in the case of Example 2A, we can see that it is better to work

  with mordenites whose Si / Al ratio is between 30 and 80.

TABLE V

  CATALYSTS B'lI B'2 B'3 TRANSFORMATION RATE OF BETIZEi E29.9 45.2 31 I FRACTION C5 +: weight 86.32 87.60 86.42 I

  GAIN IN C5 +: / LOAD 3.1,6 - 3,2%!

  ! CHARACTERISTICS OF FRACTION C5l density at 20: C 0.691 0.693 0.691 octane number: RON clear 82 81 83

Z640994

Claims (5)

  A process for the production of gasoline with a low benzene content, and a high octane number, characterized in that a) a reforming effluent is fractionated into a light fraction enriched in benzene and a heavy fraction depleted in benzene. b) the light fraction is reacted with a cracking gas containing at least one C2-C5 monoolefin, in contact with a dealuminated mordenite catalyst having an Si / Al atomic ratio of at least 30, so as to obtain an alkylated fraction, and   said alkylated fraction is mixed with the heavy fraction.   2. Process according to claim 1, wherein the cracking gas   contains 0.1 to 2 by weight of carbon monoxide.   The process according to claim 1 or 2, wherein the mordenite is the product resulting from: a mordenite H or NH 4 being treated with a gas containing water vapor at a temperature of 450 to 650 ° C b) the product of step (a) is treated with an acid of concentration 0.5 to 20 N. The method of claim 3, wherein the mordenite of   departure is a mordenite with small pores.   5. Method according to one of claims 1 to 4, wherein the   Si / Al ratio of the mordenite is 30 to 75.