EP0685552B2 - Process and use of an installation for the selective hydrogenation of catalytic cracking gasoline - Google Patents

Description

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

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

Etherification is thus an elegant way of reducing the content of olefins while transforming them into High octane research and engine ethers.

However, the presence of diolefins in catalytic cracking gasolines leads to deactivation of the etherification catalyst by the formation of gums, these also causing a degradation of the quality ether produced. Various methods have been proposed to solve this problem (EP-A-0 564 329, EP-A-0 554 151, FR-A-2 482 953, GB-A-1 346 778, GB-A-1 565 754).

We have therefore developed a process which makes it possible to selectively hydrogenate the diolefins to corresponding olefins, and to carry out, together with the hydrogenation of the diolefins, the isomerization at least in part of the olefins primary and / or secondary to tertiary olefins and for example the isomerization of 3-methylbutene-1 which cannot be etherified into etherifiable 2-methylbutene-2.

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

More specifically, the subject of the invention is a method as described in claim 1.

The catalyst must contain 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. We will generally operate under pressure in the presence of a quantity of hydrogen in small excess relative to the stoichiometric value required to hydrogenate diolefins. The hydrogen and the charge to be treated are injected in ascending or descending currents in a reactor preferably with a fixed bed of catalyst. The temperature is 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, more generally between 4 and 25 bar and preferably above 10 bar. 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 in the range of 100 to 500 ppm mole.

The invention relates exclusively to catalytic cracking gasolines.

Unlike pyrolysis essences which contain about 50% of diolefins, the essence cut of catalytic cracking generally contains from 15 to 40% of olefins (olefins, diolefins and cycloolefins) with a content of conjugated diolefins less than 5% and generally not more than 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 cracked gasoline is less than 1% by weight, and generally less than 0.5% by weight, whereas 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 special conditions make it possible to operate directly downstream of the cracker gas debutanizer catalytic without the need to add a preheater or a charge pump, and preferably with a single reactor.

The invention also relates to the use of an installation for a process for the treatment by selective hydrogenation of a catalytic cracking gasoline as described in claim 13 comprising a catalytic cracking unit followed by a fractionation unit for separating fraction C ₃ -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 process and the installation used 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. C ₃ at 210 ° C, preferably C ₃ at 180 ° C and advantageously C ₃ at 160 ° C and most preferably C ₃ at <160 ° C (i.e. end point of cutting 160 ° C).

In Figure 1, a section C ₃ -180 ° C is sent to the debutanizer 3 to separate the fraction C ₃ -C ₄ .

The C ₅ -180 ° C cut obtained (or the C ₅ -160 ° C or C ₅ -210 ° C cut depending on the fractionation carried out), called the C ₅₊ catalytic cracking gasoline cut, is introduced into a zone (or l '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 (separation C ₅ ) or a dehexanizer (separation C ₅ -C ₆ ). A C ₅ fraction or a C ₅ -C ₆ 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 reaction zone catalyst through which the entire charge and the quantity of hydrogen required to carry out the reactions desired.

According to a preferred embodiment of the invention, the catalytic hydrogenation reactor 10 is arranged so particular as shown in Figure 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 tube 5, less than the necessary stoichiometry to convert all the diolefins into mono olefins) entering via the pipe 15; in this first zone, the softening also takes place; the second 12 receiving the liquid charge coming from the first zone (as well as the rest hydrogen i.e. enough hydrogen to convert the remaining diolefins to mono olefins and to at least partially isomerize the primary and secondary olefins into tertiary olefins) for example injected by 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 15 to 30%.

Since the hydrogenation unit can operate at pressures lower than those required by the debutanizer and since the depentaniser (or dehexanizer) does not require a pressure of 13 to 15 bar, the circulation charge through the installation is obtained by 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 of C ₅₊ cut of catalytic cracking to operate without a charge preheating oven and to be very compact. . This leads to a unit with low investment and great flexibility which gives it unique advantages.

Compared to conventional hydrogenation units, the new process according to the invention of selective hydrogenation catalytic cracked gasoline does not require charge or recycling pumps or a preheating oven. Compared to a selective hydrogenation unit in a distillation column, the new process offers flexibility much larger by isolating the catalyst from the distillation column, allowing the catalyst to be replaced without stop downstream units. It also allows the catalyst to provide more 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 C ₅ , C ₆ and C ₇ -210 ° C. This therefore allows the pretreatment before etherification of cuts C ₅ and C ₆ by means of flexible and inexpensive selective hydrogenation. This process makes it possible to obtain the maximum of precursors of C ₅ and C ₆ ethers and moreover decreases the quantity of antioxidants to be used in the treated gasoline.

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

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

The example below illustrates the invention.

We have 100 cm ³ 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 cuts C ₃ and C ₄ 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 cm ³ / hour therefore a VVH of 1 h ^-1 ).

A quantity of hydrogen corresponding to an H ₂ / 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 the space velocity is determined by increasing the WH at 5 h ^-1 (example 2) then at 10 h ^-1 (example 3) while keeping the H ₂ / diolefin molar ratio at 1.6.

The effect of reducing the H ₂ / 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 cm ³ in the first zone and 75 cm ³ 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 makes it possible to add an additional quantity of hydrogen corresponding to a molar ratio of 0.5 relative to the quantity of diolefins initially present in the raw gasoline of FCC, example 5.

It is found that the staged addition of hydrogen under the conditions recommended in the present invention makes it possible not only to improve the conversion of the diolefins (show by increasing the induction period) but also to increase the amount of precursors of TAME (ie 2-methylbutene-1 and 2-methylbutene-2) and to soften, at least partially, the essence of FCC. 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 C ₅ , total 29.5% by weight C ₅ , unsaturated 15.5% weight K ₅ , etherifiable products 6.2% weight section C ₆ , total 22.3% weight C ₆ , unsaturated 9.8% weight K ₆ , etherifiable products 3.6% weight Examples according to the invention Example number 1 2 3 4 5 WH liquid, h ^-1 1 5 10 10 10 H ₂ / 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 K ₅ , etherifiable products,% by weight 6.4 6.4 6.3 6.2 6.5 K ₅ , etherifiable yield 103% 103% 102% 100% 105% K ₆ , etherifiable products,% by weight 3.75 3.75 3.7 3.65 3.8 K ₆ , etherifiable yield 104% 104% 103% 101% 106% C6 ⁺ , induction period (min) 470 470 440 435 480

Claims (14)

1. A process for treatment by selective hydrogenation of catalytic cracking gasoline having a diolefins content of less than 5%, a cyclopentadiene content of less than 1% and a mercaptan content of between 1 and 300 ppm, characterised in that the C₅-210°C gasoline cut is brought into contact, at a pressure of 4-25 bars, at a temperature of 80-200°C, and with a LHSV (liquid hourly space velocity) of 1-10h^-1, in the presence of a slight excess of hydrogen of up to 1.6 times the stoichiometry (1.0) required to hydrogenate the diolefins, with a catalyst comprising from 0.1 to 1% by weight of palladium deposited on a support containing at least 50% alumina, to reduce the mercaptan content in the gasoline.
2. A process according to claim 1, characterised in that the catalyst contains 0.2-0.5% by weight of palladium.
3. A process according to one of the preceding claims, characterised in that the support contains at least 90% of alumina.
4. A process according to one of the preceding claims, characterised in that the support is pure alumina.
5. A process according to one of the preceding claims, characterised in that the catalyst comprises mainly palladium.
6. A process according to one of the preceding claims, characterised in that the temperature is between 130 and 200°C.
7. A process according to one of the preceding claims, characterised in that the temperature is between 150 and 170°C.
8. A process according to one of the preceding claims, characterised in that the pressure is between 10 and 20 bars.
9. A process according to one of the preceding claims, characterised in that the pressure is between 12 and 16 bars.
10. A process according to one of the preceding claims, characterised in that the LHSV is between 4 and 10 h^-1.
11. A process according to one of the preceding claims, characterised in that the end point of the cut is 180°C.
12. A process according to one of the preceding claims, characterised in that the end point of the cut is 160°C.
13. Use of a facility for a process for treatment by selective hydrogenation of a catalytic cracking gasoline according to one of the preceding claims, the facility comprising a catalytic cracking unit followed by a fractionating unit for separating a C₃-210°C cut and a debutaniser for separating the C₃-C₄ cut to obtain the C₅-210°C cut, and a selective hydrogenation unit which is disposed between the debutaniser and a separation unit selected from a depentaniser and a dehexaniser.
14. Use according to claim 13, characterised in that the selective hydrogenation unit is formed by a reactor which comprises two catalytic zones, the first being traversed by the liquid feed and a quantity of hydrogen which is less than stoichiometry, and the second receiving the liquid feed deriving from the first zone and the remainder of the hydrogen which is injected by way of a lateral pipe.

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