EP0685552A1 - Process and installation for the selective hydrogenation of catalytic cracking gasoline - Google Patents

Abstract

A new method is used for the selective hydrogenation of petrol, obtd. from a catalytic cracking process, with a di-olefin content less than 5%, cyclopentadiene less than 1%, mercaptans 1-300 ppm. The petrol cut C5 - 210 degrees C is contacted with a catalyst comprising 0.1-1% Pd deposited on a support contg. at least 50% Al2O3, at 4-25 bar, 80-200 degrees C and LHSV of 1-10h<-1>. Figures (1) and (2) illustrate the nature of the process. In figure (1), a C3-180 degrees C cut is delivered to the de-butaniser (3) to separate the C3-C4 fraction. The C5-180 degrees C (or C5-160 degrees C or C5-210 degrees C, where applicable), i.e. the C5 + petrol cut from catalytic cracking is introduced in a zone (4) of selective hydrogenation and H2 in also introduced (5). The hydrogenated cut passes into (6) of sepn. which is a de-pentaniser (C5 sepn.) or de-hexaniser (C5 + C6 sepn.). Thus a C5 or C5 + C6 fraction is obtd., sent to an etherification unit and a C7+ fraction sent to a petrol stock. The catalytic hydrogenation reactor, shown in figure (2), (10) is arranged in two catalytic zones (11) and (12); the first is traversed by the liq. charge and some H2 (less than the stoichiometric amt. necessary to convert all diolefins to mono olefins). In this zone the sweetening process also takes place. The second zone receives the charge from the first zone (and the remainder of the H2 required to convert diolefin to olefins and to isomerise prim. and sec. olefins to tert olefins). The proportion (vol.) of the first zone is at most 50% of the sum of the two zones (pref. 15-30%). The hydrogenation unit operates at pressures lower than the de-butaniser, and the de-pentaniser (or de-hexaniser) requires only 13-15 bar. Charge circulation can thus be effected by a slight de-pressurisation at the exit of the hydrogenation unit. The high temp. at the base of the de-butaniser and the high activity of the hydrogenation catalyst allows the unit (4) to be operated without further pre-heating of the charge.

Description

The production of reformulated petrol meeting new environmental standards requires in particular that their concentration of olefins, aromatics (especially benzene) and sulfur be reduced.

The decrease in the concentration of olefins is often obtained by etherification of 2-methyl butenes into tertioamylmethyl ether or even sometimes of 2-methylpentenes and 3-methylpentene-2 into tertiohexylmethylether.

Etherification is therefore an elegant way of reducing the content of olefins while transforming them into ethers with high research and motor octane numbers.

However, the presence of diolefins in the catalytic cracking gasolines leads to deactivation of the etherification catalyst by the formation of gums, these also causing a degradation in the quality of the ether produced.

A process has therefore been developed which makes it possible to selectively hydrogenate the diolefins to corresponding olefins, and to carry out, together with the hydrogenation of the diolefins, isomerization at least in part of the primary and / or secondary olefins to tertiary olefins and for example the isomerization of non-etherifiable 3-methylbutene-1 into etherifiable 2-methylbutene-2.

It has also been discovered that it is possible to at least partially soften the gasoline of catalytic cracking by transformation of the mercaptans into other sulfurized products thanks to the particular conditions of the invention and a particular arrangement of the catalytic reactor of the present invention. By softening, we understand an olefin addition reaction on a mercaptan.

More specifically, the subject of the invention is a method of treatment by selective hydrogenation of catalytic cracking gasoline, by bringing the C₅ -210 ° C cut into contact with a catalyst comprising 0.1 to 1% of palladium deposited on a support, under a pressure of 4-25 bar, at a temperature of 80-200 ° C, with an hourly space velocity of the liquid (LHSV) from 1 to h⁻¹.

The catalyst must comprise palladium (0.1 to 1% by weight, and preferably 0.2-0.5% by weight) deposited on a support containing at least 50% of alumina, and preferably at least 90%, and advantageously this support is pure alumina.

Another metal can be combined to form a bimetallic catalyst, such as gold (Au / Pd expressed by weight greater than or equal to 0.1 and less than 1, and preferably between 0.2 and 0.8).

The catalyst thus essentially comprises palladium or palladium and gold.

The choice of operating conditions is particularly important. Most generally, it will be operated under pressure in the presence of a quantity of hydrogen in slight excess relative to the stoichiometric value necessary for hydrogenating the diolefins. The hydrogen and the feed to be treated are injected in ascending or descending currents into a reactor preferably with a fixed bed of catalyst. The temperature is most generally between 80 and 200 ° C, in particular between 130 and 200 ° C and preferably between 150 and 170 ° C.

The pressure is sufficient to keep most of the gasoline to be treated in the liquid phase in the reactor, namely most generally between 4 and 25 bar and preferably above 10 bar. An advantageous pressure is between 10-20 bar, and preferably between 12-16 bar.

The space speed is in these conditions established between 1-10 h⁻¹, preferably less than 10 h⁻¹ and better between 4 and less than -10 h⁻¹.

It is also possible to inject with this essence traces of oxygen in very low concentration, namely of the order of 100 to 500 ppm mole.

The invention relates exclusively to catalytic cracking gasolines.

Unlike pyrolysis essences which contain around 50% of diolefins, the catalytic cracking gasoline fraction generally contains from 15 to 40% of olefins (olefins, diolefins and cycloolefins) with a content of conjugated diolefins of less than 5% and generally of at least plus 4%. After hydrogenation, the content of dienes is reduced to less than 1000 ppm. The diene content in cuts C5 and C6 after selective hydrogenation is generally reduced to less than 250 ppm.

The content of cyclopentadiene in a catalytic cracking gasoline is less than 1% by weight, and generally less than 0.5% by weight, while it can be 20% by weight in a steam cracking gasoline.

The mercaptan content is between 1 and 300 ppm, and generally less than 200 ppm.

These particular conditions make it possible to operate directly downstream of the debutanizer of the catalytic cracking gasoline without the need to add a preheater or a charge pump, and preferably with a single reactor.

The subject of the invention is also an installation for the treatment by selective hydrogenation of a catalytic cracking gasoline comprising a catalytic cracking unit followed by a fractionation unit for separating the fraction C₃-210 ° C, a debutanizer, then a separation unit chosen from a depentanizer and a dehexanizer, said installation comprising a selective hydrogenation unit placed between the debutanizer and the separation unit.

Figure 1 shows schematically the method and the installation according to the invention.

From the catalytic cracking unit 1, for example a catalytic cracking in a fluid bed, an effluent leaves which is fractionated in a unit 2 for fractionation into a diesel cut (LCO), a heavy cut (HCO) and a cut containing the hydrocarbons. C₃ at 210 ° C, preferably C₃ at 180 ° C and advantageously C₃ at 160 ° C and most preferably C₃ at <160 ° C (that is to say cutting end point of 160 ° C).

In Figure 1, a C₃-180 ° C section is sent to the debutanizer 3 to separate the C₃-C₄ fraction.

The cut C₅-180 ° C obtained (or the cut C₅-160 ° C or C₅-210 ° C depending on the fractionation carried out), called gasoline cut C _{5 +} of catalytic cracking, is introduced into a zone (or unit) 4 of selective hydrogenation according to the invention, hydrogen is also introduced for example by line 5.

The hydrogenated cut obtained enters the separation unit 6 which is a depentanizer (C₅ separation) or a dehexanizer (C₅-C₆ separation). A C₅ fraction or a C₅-C₆ fraction is therefore obtained, which is advantageously sent to the etherification unit, and a C ₇ fraction. ₊ sent to petrol storage.

According to one embodiment of the invention, the catalytic hydrogenation reactor 10 comprises a crossed catalytic reaction zone by the total charge and the quantity of hydrogen necessary to carry out the desired reactions.

According to a preferred embodiment of the invention, the catalytic hydrogenation reactor 10 is arranged in a particular way as indicated in FIG. 2, namely two catalytic zones 11 and 12, the first 11 being crossed by the liquid charge (and a quantity of hydrogen, supplied by a pipe 5, less than the stoichiometry necessary to convert all the diolefins into mono olefins) entering through the pipe 15; in this first zone, softening also takes place; the second 12 receiving the liquid charge coming from the first zone (as well as the rest of the hydrogen, that is to say a quantity of hydrogen sufficient to convert the remaining diolefins into mono olefins and to at least partially isomerize the primary and secondary olefins into tertiary olefins) for example injected through a lateral tube 13 and dispersed using an appropriate diffuser 14.

The proportion of the first zone (by volume) is at most equal to 50% of the sum of the 2 zones and preferably from 15 to 30%.

Since the hydrogenation unit can operate at pressures lower than those required by the debutanizer and since the depentanizer (or dehexanizer) does not require a pressure of 13 to 15 bar, the circulation of the charge through the installation is obtained by a slight depressurization at the outlet of the hydrogenation unit. This allows operation without additional pumps.

The high temperature of the debutanizer base and the high activity of the catalysts used in the invention allow the selective hydrogenation unit to cut C _{5 +} catalytic cracking to operate without a charge preheating furnace and to be very compact. This leads to a unit with low investment and great flexibility which gives it unique advantages.

Compared with conventional hydrogenation units, the new process according to the invention for the selective hydrogenation of catalytic cracked petrol requires neither charge or recycling pumps, nor preheating furnace. Compared to a selective hydrogenation unit in a distillation column, the new process offers much greater flexibility by isolating the catalyst from the distillation column, allowing the catalyst to be replaced without stopping the units located downstream. It also allows the catalyst to provide greater activity, thanks to higher temperatures and pressures than those obtained in the depentaniser.

In addition, the new process makes it possible to simultaneously treat cuts C₅, C₆ and C₇-210 ° C. This therefore allows the pretreatment before etherification of the C₅ and C₆ cuts thanks to a selective flexible and inexpensive hydrogenation. This process makes it possible to obtain the maximum of precursors of ethers in C₅ and C₆ and moreover decreases the quantity of antioxidants to be used in the treated gasoline.

According to the present invention, it is indeed carried out not only the selective hydrogenation of diolefins but also the isomerization of primary and secondary olefins into tertiary olefins (eg 3-methylbutene-1 into 2-methylbutene-2 and 2-methylbutene -1).

This process therefore makes it possible to improve the quantity of etherifiable products, therefore the production yield of ethers such as tertioamyl ether for example. It also improves the quality of the gasoline produced, which has better oxidation stability and an improved octane number.

The example below illustrates the invention.

We have 100 cm³ of catalyst LD265 from the company Procatalyse containing 0.3% by weight of palladium supported on alumina in a stainless steel tube 1.9 cm in diameter. This catalyst is commonly used for the hydrogenation of C₃ and C₄ cuts of FCC and steam cracking.

The catalyst is activated by reduction under hydrogen at a flow rate of 30 l / h for 5 hours at 200 ° C. The installation is cooled under nitrogen to 150 ° C. before injecting the FCC gasoline having the properties indicated in table 1. The reactor is then pressurized to 14 bar and the gasoline is injected into the bottom of the reactor (100 cm³ / hour so a VVH of 1 h⁻¹).

A quantity of hydrogen corresponding to a H₂ / diolefin molar ratio of 1.6 is injected. The charge / hydrogen mixture crosses the catalytic bed in upward flow. The results obtained according to the invention are shown in Table 2.

The effect of space velocity is determined by increasing the VVH at 5 h⁻¹ (example 2) then at 10 h⁻¹ (example 3) while keeping the H₂ / diolefin molar ratio to 1.6.

The effect of reducing the H₂ / diolefin molar ratio is shown in Example 4 where this ratio is 1.4 and the liquid VVH is 10 h⁻¹.

Another series of catalytic tests was carried out to illustrate the present invention. The catalytic zone is cut into two separate beds, therefore 25 cm³ in the first zone and 75 cm³ of LD265 in the second. The procedure is as previously described in Example 4 except the quantity of hydrogen injected into the reactor with the feed represents a molar ratio of 0.9. An injection device between the two beds allows adding an additional quantity of hydrogen corresponding to a molar ratio of 0.5 relative to the quantity of diolefins initially present in the raw FCC gasoline, Example 5.

It is found that the staged addition of hydrogen under the conditions recommended in the present invention not only improves the conversion of diolefins (show by increasing the induction period) but also increases the amount of precursors of TAME (ie 2-methylbutene-1 and 2-methylbutene-2) and to soften, at least partially, the essence of FCC. Table 1. FCC raw fuel cut Initial point 20 ° C Period 166 ° C S (total) 224 ppm S (mercaptan) 72 ppm Bromine index 67 MY V 20 Paraffins 29.9% weight Olefins, diolefins, cycloolefins 38.4% weight Naphthenes 9.1% weight Aromatics 22.6% weight section C₅, total 29.5% by weight C₅, unsaturated 15.5% weight C₅, etherifiable products 6.2% weight section C₆, total 22.3% weight C₆, unsaturated 9.8% weight C₆, etherifiable products 3.6% weight Example number 1 2 3 4 5 VVH liquid, h⁻¹ 1 5 10 10 10 H₂ / diolefins molar ratio 1.6 1.6 1.6 1.4 0.9 + 0.5 S (mercaptan), ppm 64 64 62 64 28 Bromine index 56 56 56 58 60 C₅, etherifiable products,% by weight 6.4 6.4 6.3 6.2 6.5 C₅, etherifiable yield 103% 103% 102% 100% 105% C₆, etherifiable products,% by weight 3.75 3.75 3.7 3.65 3.8 C₆, etherifiable yield 104% 104% 103% 101% 106% C6⁺, induction period (min) 470 470 440 435 480

Claims (14)

1 - Process for the treatment by selective hydrogenation of catalytic cracked gasoline having a diolefin content of less than 5%, a cyclopentadiene content of less than 1% and a mercaptan content of between 1 and 300 ppm, characterized in that the gasoline cut C °-210 ° C is brought into contact, under a pressure of 4-25 bar, at a temperature of 80-200 ° C, with an LHSV of 1-10 h¹, with a catalyst comprising 0.1 to 1% weight of palladium deposited on a support containing at least 50% of alumina. 2 - Process according to claim 1, characterized in that the catalyst contains 0.2-0.5% by weight of palladium. 3 - Method according to one of the preceding claims, characterized in that the support contains at least 90% alumina. 4 - Method according to one of the preceding claims, characterized in that the support is pure alumina. 5 - Method according to one of the preceding claims, characterized in that the catalyst also contains gold, in a weight ratio Au / Pd greater than or equal to 0.1 and less than 1. 6 - Method according to one of the preceding claims, characterized in that the temperature is between 130 and 200 ° C. 7 - Method according to one of the preceding claims, characterized in that the temperature is between 150 and 170 ° C. 8 - Method according to one of the preceding claims, characterized in that the pressure is between 10 and 20 bar. 9 - Method according to one of the preceding claims, characterized in that the pressure is between 12 and 16 bar. 10 - Method according to one of the preceding claims, characterized in that the LHSV is between 4 and 10 h⁻¹. 11 - Method according to one of the preceding claims, characterized in that the end point of the cut is 180 ° C. 12 - Method according to one of the preceding claims, characterized in that the end point of the cut is 160 ° C. 13 - Installation for the treatment by selective hydrogenation of a catalytic cracking gasoline comprising a catalytic cracking unit followed by a fractionation unit to separate a C₃-210 ° C cut, a debutanizer, then a separation unit chosen from one depentaniser and a dehexanizer, installation characterized in that a selective hydrogenation unit is placed between the debutanizer and the separation unit. 14 - Installation according to claim 13, characterized in that the selective hydrogenation unit consists of a reactor comprising two catalytic zones, the first being traversed by the liquid charge and an amount of hydrogen less than stoichiometry, the second receiving the liquid charge coming from the first zone as well as the rest of the hydrogen injected through a lateral tube.

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