LU86280A1 - FUEL PRODUCTION PROCESS - Google Patents

Description

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FUEL PRODUCTION PROCESS

The present invention relates to a process for producing gasoline having an improved octane number.

More and more countries impose the use of either unleaded petrol or petrol with a reduced lead content. It therefore became necessary to look for ways to improve the octane number of gasolines.

Essences are generally prepared by conventional oligomerization of olefinic hydrocarbons in the presence of catalysts based on phosphoric acid. These essences are mainly formed of dimers. Their octane number is improved by adding lead-free additives, among which methyl tert-butyl ether (MTBE) is most often used. Other additives, such as methyl tert-amyl ether (TAME), and other types of additives, such as alcohols, have also been tried.

More recently, essences have been prepared by oligomerization processes which consist in transforming normally gaseous olefins (alone or in mixture with paraffins) into olefinic essences by passing over various catalysts of the type "siliceous crystalline molecular sieve with medium-sized pores ", as described in US Patent 4,417,088. These catalysts include two classes: - crystalline aluminosilicates, commonly called "zeolites", which contain significant amounts of alumina in addition to silica; and - polymorphic crystalline silicas, practically 1 5 y i y * - 2 - free of alumina, for example silicalite.

One of the main advantages of these recent processes lies in the higher hourly liquid space velocities (LHSV), typically between 30 and 40, which can be used, while the conventional oligomerization processes on catalysts containing phosphoric acid Typically only allow LHSVs from 1 to 4. Another advantage is that the siliceous crystalline molecular sieves can be regenerated, unlike catalysts based on -phosphoric acid.

Many oligomerization processes have already been described on zeolites, for example: - on ZSM-5 having a controlled acidity and reduced aromatization properties (US Pat. 3,960,978); - on ZSM-4, _ ZSM-12, ZSM-18, Chabasite or Zeolite beta (US patent 4,021,502); - on ZSM-5 type catalysts in the presence of water (US patent 4,150,062); and on ZSM-12 (US Patent 4,254,295).

Polymorphic crystalline silicas have also been used in oligomerization processes - on silicalite (US patents 4,414,423 and US 4,417,088); and - on crystalline borosilicate (US patent 4,451,685).

However, the octane number of the olefinic gasolines obtained by the above processes is not sufficient, and it is therefore necessary to add to them lead-free additives such as MTBE or TAME.

There is therefore a need for a process for the production of gasoline having an improved octane number, which would require the addition of only a small amount of anti-detonant additive or which would not require it.

The subject of the invention is a process for the production of petrol with a better octane number.

It also relates to an integrated process in t - 3 -

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several steps to produce gasoline with a better octane number.

It also relates to a gasoline production process to which it is necessary to add less anti-detonating additive, or even no additive at all.

The process of the invention for producing petrol consists of the steps of (1) bringing into contact, under oligomerization conditions, a charge composed essentially of a mixture of butanes and butenes with a catalyst consisting of a medium pore siliceous crystalline molecular sieve, optionally in the presence of water; (2) removing the water from the effluent, if water was used in step (1); (3) optionally, removing all or part of the normally gaseous hydrocarbons from the effluent; (4) mixing the effluent with methanol; (5) contacting, under etherification conditions, the mixture resulting from step (4) with an acid cation exchange catalyst, · (6) distillation of the etherified effluent; and (7) recovery of a gasoline having a better octane number.

The Applicant has now unexpectedly found that by producing gasoline by the process of the invention, its octane number is greatly improved.

The process of the invention has the advantage of providing gasoline having an octane number which is much improved compared to that of gasoline produced by oligomerization on a siliceous crystalline molecular sieve with medium pores. Under the preferential conditions, the process of the invention even provided petrol with an octane number at least as good as that of petrol obtained by the conventional process of oligomerization on - 4 - ft 1 t catalyst containing phosphoric acid. This is all the more unexpected since the etherification of this latter gasoline does not improve its octane number.

As shown below, the advantages of the process of the invention result from the combination of steps as described.

The feedstock used for the process of the invention- · is a mixture of butanes and butenes, comprising j isobutane from 0 to 40% (by weight) n-butane from 5 to 30% 1- butene from 10 to 30% 2- butenes from 15 to 35% isobutene from 0 to 50% and which can contain up to 5% heavier and / or lighter hydrocarbons. The composition of the charge depends on its origin. As an example of typical fillers, mention may be made of C ^ fillers free of isobutene from an MTBE production unit, C ^ fillers from a catalytic cracking unit, and even C ^ cuts from '' a steam cracking unit (after removal of the butadiene). However, the latter two types of feed are increasingly used to produce MTBE by reacting isobutene with methanol, leaving mixtures composed mainly of butanes and r -butenes in approximately equal weight amounts. These mixtures are preferably used as filler for the process of the invention.

The oligomerization reaction is carried out in a known manner on a siliceous crystalline molecular sieve with medium pores.

These materials have the property of sorting molecules based on their size and / or shape. The medium-sized siliceous crystalline molecular sieves are capable of differentiating on the one hand large molecules and molecules containing carbons "" - 5 -

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quaternaries, and on the other hand small molecules. By medium-sized pores is meant here a pore size of approximately 0.5 to 0.65 nm when the molecular sieve is in H form, the preferred size being approximately 0.53 to 0.62 nm.

Although oligomerization can be carried out in the presence of silicalite, it is preferable to use halogenated stabilized silicalite; this catalyst and its preparation process are described in the patent application entitled "Stabilization process of silicalite type catalysts" and filed the same day in the name of the Applicant.

The oligomerization step can also be carried out on zeolite, as described in the prior art, preferably on zeolites having a low Al / Si ratio. However, the gasoline obtained by the process of the invention has an octane number which is less improved when a zeolite is used in the oligomerization step.

Water can be added for the oligomerization step, because it generally improves the stability of the catalyst. In addition, the octane number of the gasoline obtained by the process of the invention is generally improved by the use of water during the oligomerization.

The oligomerization reaction is carried out under well known conditions. Typically, the pressure can range from atmospheric pressure to approximately 60 bars (6 MPa), preferably from 3 to 20 bars (0.3 to 2 MPa) and more particularly approximately 15 bars (1.5 MPa). High pressures tend to improve the efficiency of the process gasoline, while low pressures tend to improve the octane number of the process gasoline. We have found that the highest pressures up to 60 bar (6 MPa) should only be used if the catalyst is a halogenated silicalite. Furthermore, it is economically advantageous for the pressure during the oligomerization step to be the same as in the etherification step.

The oligomerization step is generally carried out at a temperature of 200 to 500 ° C, but preferably between 250 and 450 ° C and in particular at around 350 ° C if silicalite is used (whether or not it is stabilized), and preferably between 200 and 350 ° C and in particular at about 280 ° C if a zeolite is used.

The liquid hourly space velocity (LHSV) of the charge is typically 2 to 20, but we have found that LH5V values as high as 50 can be reached.

When water is used during the oligomerization step, it is generally added in a water / charge molar ratio of 0.5 to 1.5, preferably 0.5 to 1.0 and more particularly about 0.7. However, the advantage of adding water is offset by the economic disadvantage, and it is therefore preferable to add as little water as possible.

The oligomerization step of the process of the invention is more effective with a fine particle screen than with large crystalline particles. Preferably, the molecular sieve crystals or crystallites are less than about 0.01 mm. The methods for preparing molecular sieve crystals of different sizes are known.

Molecular sieves can be mixed with inorganic supports, or can be used with an organic binder. It is preferable to use an inorganic support because the molecular sieves, because of the large internal volume of the pores, tend to be fragile and to be subject to collapse and wear during normal loading and unloading operations. unloading of the reactor as well as during oligomerization. When an inorganic support is used, it is far preferable that it has practically no hydrocarbon conversion activity.

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If a support having a hydrogen transfer activity is used, a significant part of the oligomers produced by the molecular sieve can be converted into paraffins, which largely destroys the advantages of the process of the invention.

If water was used in the oigomerization step, it must be removed from the effluent in the next step. Water removal is best done by decanting the water first and then drying the hydrocarbon mixture. No oil separation is normally carried out at this time. However, if desired, all or part of the normally gaseous hydrocarbons can be removed, for example to recover the isobutene which can, among other possibilities, be transformed into po 1 yis ob u tene, - however, the octane number of the gasoline obtained by the process of the invention is not as good if such separation has been carried out.

Normally gaseous hydrocarbons are understood to mean hydrocarbons up to C ^, which are gaseous at room temperature under atmospheric pressure.

Methanol is then added to the mixture of hydrocarbons, in an amount practically equimolar with respect to the iso-olefins contained in this mixture. By way of example, there may be mentioned a methanol / iso-olefin molar ratio of 0.9 to 1,], preferably of 0.95 to 1.05 and more particularly approximately equal to 1. For a given charge and igomerisation conditions given, the quantity of iso-olefins in the effluent can be determined experimentally by a quantitative measurement of the content of r-, -8- iso-olefins at to Cy in the mixture.

The etherification step is carried out in a known manner, on an acid cationic ion exchanger, for example on a styrene-divinylbenzene copolymer comprising sulfonic acid groups, in solid layer or in suspension, at a temperature of 30 to 120 °. C, preferably 40 to 90 ° C, under a pressure of 1 to 50 bar (0.1 to 5 MPa), preferably 3 to 20 bar (0.3 to 2 MPa) and more particularly about 15 bars (1.5 MPa), with an LHSV of 0.05 to 10 and preferably about 1. The etherification yield decreases at high LHSV values, while significant amounts of dimethyl ether are formed at LHSV weak. In this step, the pressure and the temperature are adjusted so that the reaction takes place in the liquid phase.

. After the etherification step, the etherified effluent is sent to a distillation column where the gasoline is separated from the residual C 1 and C 4 hydrocarbons and unreacted methanol. This column has for example 30 to 80 trays, preferably 40 to 70. It is possible to use a column with bubbling bells, a column with perforated trays, or any other distillation column comprising trays or a filling material which provide efficiency. sufficient separation. The distillation is carried out under a pressure of 1 to 10 bars (0.1 to 1 MPa), preferably from 3 to 7 bars (0.3 to 0.7 MPa) and more particularly from 4 to 6 bars (0.4 at 0.6 MPa).

The gasoline thus obtained has an improved octane number.

A preferred embodiment of the method of the invention is described below, by way of example only, with reference to the attached Figure which is a diagram of the operation of an installation making it possible to implement the method of the invention.

In the Figure, the load (1) and the water (2) are -9-, Γ-.

introduced into the oligomerization reactor (3). This reactor can be for example a fixed bed reactor or a tubular reactor, and it is preferably used in an ascending manner. The resulting mixture is sent through line (4) to a decanter (5), where most of the water (ô) is removed, then through line (7) to a drying unit (8).

The dried hydrocarbon mixture exiting through the line (9) is then mixed with methanol (10) and introduced into the etherification reactor (11). This reactor can be for example a fixed bed reactor or a tubular reactor, and it is preferably used in an ascending manner.

The etherified effluent leaving the reactor (11) is sent via the line (12) to a distillation column (13). The gasoline (14) is recovered at the bottom of the column, and the top product (15) consists essentially of a mixture of methanol and C ^ and e n C ^ hydrocarbons.

The following examples are given by way of illustration and should not be considered as limiting the scope of the invention.

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Example 1

Silicalite was charged to a reactor, and heated at 500 ° C for 3 hours under a stream of nitrogen with a gas hourly space velocity (GHSV) of 500. The temperature was then reduced to 280 ° C while maintaining the flow rate of nitrogen which was saturated for 4 hours with CCI. There was thus obtained stabilized silicalite 4 halogenated.

A hydrocarbon charge was mixed with water in a water / charge molar ratio of 0.7, and the mixture was passed over the halogenated stabilized silicalite at a temperature of 380 ° C, under a pressure of 15 bars (1.5 MPa) and with an LHSV of 30.

The hydrocarbon charge had the following composition- (% by weight): propane 1.71% p ropylene 0.09% isobutane 27.87% n-butane 12.16% butenes 58.09% heavier hydrocarbons 0.08 %

After decantation of the water and drying, the effluent was mixed with methanol in a methanol / effluent weight ratio of 0.3, then the whole was passed through an etherification reactor containing Duolite resin as catalyst. ES-276 (porous beads of strongly acid sulfonated benzene-diviny1 benzene copolymer, having a total exchange capacity of 1.8 mol H + per liter (Duolite is a registered trademark of Diamond Shamrock), at a temperature of 80 ° C, under a pressure of 15 bar (1.5 MPa) and with an LHSV of 1.

The etherified effluent was distilled, obtaining a gasoline having the following characteristics: - 11 - concentrations ΜΤΒΕ 16.7% by weight of ethers: TAME 19.7% by weight methyl tert-hexyl ether 6.0% by weight ether methyl .tert-heptyiique 3.1% by weight - octane indices: RON 97.2 MON 82.9 density :. 0.745

Comparative example Cl

The procedure of Example 1 was followed until the water was decanted and dried. The effluent was kept at atmospheric pressure until its analysis which gave the following results: octane numbers: RON 89.0 MON 78.2 density: 0.710

Comparative example C2

A hydrocarbon charge of composition identical to that of Example 1 was subjected to a polymerization on a catalyst based on phosphoric acid. The RON octane number of the gasoline obtained was 96.5.

This gasoline was then subjected to etherification under the conditions described in Example 1. The octane number RON was 96.0 after etherification.

This comparative example shows that the etherification of a gasoline obtained by the conventional process does not improve its octane number.

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Example 2

Silicalite was stabilized by halogenation as described in Example 1.

A charge of hydrocarbons of identical composition to that of Example 1 was mixed with water in a water / charge molar ratio of 0.72, and the whole was passed over the halogenated stabilized silicalite at a temperature 341 ° C, under a pressure of 14.9 bar (1.49 MPa) and with an LHSV of 30.7.

The process was continued under the conditions described in Example 1, and a gasoline was obtained having the following characteristics: MTBE concentrations 9.5% by weight of ethers: _ TAME 4.9% by weight of heavier ethers 11, 0% by weight octane numbers: RON 98.0 MON 82.7

Comparative example C3

The procedure of Example 2 was repeated until the water was decanted and dried after the oligomerization step. The effluent was kept at atmospheric pressure until its analysis which gave the following results: octane numbers: RON 93.4 MON 80.0

Example 3

Silicalite was charged to a reactor, and heated at 500 ° C for 3 hours under a stream of nitrogen with a GHSV of 500. The temperature was then reduced to -13- * 285 ° C while maintaining the nitrogen flow which has been saturated for 110 minutes with CCl ^. Halogenated silicalite was thus obtained.

A charge of hydrocarbons was mixed with water in a water / charge molar ratio of 0.7, and the mixture was passed over the halogenated stabilized silicalite at a temperature of 320 ° C, under a pressure of 15 - bars (1.5 MPa) and with an LHSV of 30.

The hydrocarbon charge had the following composition (% by weight): propane 0.77% propylene 0.17% isobutane 40.03% ri-butane 11.77% 'butenes 46.98% heavier hydrocarbons 0.28%

After decantation of the water, drying and separation of the normally gaseous hydrocarbons, the effluent was mixed with methanol in a methanol / effluent weight ratio of 0.1, then the whole was passed through a reactor. of etherification containing as catalyst Amberlyst 15 resin (styrene-divinylbenzene copolymer beads strongly acid sulfonated; Amberlyst is a registered trademark of Rohm & Haas), at a temperature of 75 ° C, under a pressure of 15 bars (1 , 5 MPa) and with an LHSV of 1.

The etherified effluent was distilled, obtaining a gasoline having the following characteristics: MTBE concentrations 0.4% by weight of ether: TAME 4.9% by weight higher ethers 11.0% by weight octane numbers: R0N 95, 8 MON 81.5, l t-

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Example 4

A charge of hydrocarbons is mixed with water in a moderate ratio * water / charge of 1, and the mixture is passed over the silicalite at a temperature of 310 ° C., under a pressure of 2 bars. (0.2 MPa) and with an LHSV of 40. '

The hydrocarbon charge had the following composition (% by weight): hydrocarbons in 0.9% isobutane 32.5% n-butane 11.8% J2 - butenes 53.8% isobutene 1.0%

After decantation of the water and drying, the effluent was mixed with methanol in a methanol / effluent weight ratio of 0.15, then the whole was passed through an etherification reactor containing Amberlyst resin as catalyst. 15 (described in Example 3), at a temperature of 75 ° C., under a pressure of 15 bars (1.5 MPa) and with an LH5V of 1.

The etherified effluent was distilled, obtaining a gasoline having the following characteristics: MTBE concentrations 14.4% by weight of ethers: TAME 4.4 * by weight higher ethers 6.5% by weight octane numbers: ROM 97.0 MY 82.3

Claims (17)

1. A process for the production of gasoline, comprising the steps of: (i) passing a charge, comprising a mixture of butanes and butenes, under conditions of oligomerization over a catalyst consisting of a siliceous crystalline molecular sieve with pores medium sized; (ii) mixing the effluent with methanol; (iii) passing the mixture resulting from step (ii) under etherification conditions over an acid cation exchange catalytic material; (iv) distilling the etherified effluent; and (v) recovery of a gasoline having an improved octane number. 2. Method according to claim 1, A characterized in that the oligomerization step is carried out in the presence of water, and in that, in an additional step, the water is removed from the o effluent 1igomerization and dried before mixing with methanol. 3. Method according to claim 2, characterized in that water is used in a water / charge molar ratio of 0.5 to 1.5, preferably 0.5 to 1.0, and more particularly of approximately 0.7. 4. Method according to claim 1, characterized in that it comprises the additional step of removing all or part of the normally gaseous hydrocarbons from the oligomerization effluent before mixing it with methanol. 5. Method according to any one of claims 1 to 4,, "" t t. * - 16 - characterized in that the charge comprises a mixture of butanes and n-butenes. 6. Method according to any one of claims 1 to 5, characterized in that the oligomerization step is carried out at a temperature of 200 to 500 ° C, under a pressure of 1 to 60 bars, and at an LHSV of 2 to 50. 7. Method according to any one of claims 1 to 6, characterized in that the step of 1igomerization is carried out under a pressure of 3 to 20 bars. 8. Method according to any one of claims 1 to 7, characterized in that the crystalline molecular sieve silic-them with medium pores is silicalite. £. 9. Method according to claim 8, characterized in that the silicalite has been stabilized by halogenation. 10. Method according to any one of claims 8 or 9, characterized in that the oigomerization step is carried out at a temperature of 250 to 450 ° C, and preferably at about 350 ° C. 11. Method according to any one of claims 1 to 7, characterized in that the siliceous crystalline molecular sieve with medium pore size is a zeolite. 12. The method of claim 11, characterized in that the oligomerization step is carried out at a temperature of 200 to 350 ° C, and preferably at about 280 ° C. 1 * t "" s. - 17 - 13. Method according to any one of claims 1 to 12, characterized in that the pressure during the step of igigomerization and the pressure during the step of etherification are practically equal to approximately 15 bars. 14. Process for improving the octane number of a gasoline produced by passing, under oigomerization conditions, a charge, comprising a mixture of butanes and butenes, over a catalyst consisting of a siliceous crystalline molecular sieve medium-sized pore, characterized in that it comprises the steps of: (i) mixing gasoline with methanol; (ii) passing the resulting mixture, under etherification conditions, over an acid cation exchange catalytic material; £ (iii) distillation of the etherified effluent; and (iv) recovering a gasoline having an improved octane number. 15. Method according to any one of claims 1 to 14, characterized in that methanol is added in an approximately equimolar amount with the isoolefins. 16. Method according to any one of claims 1 to 15, characterized in that the etherification step is carried out at a temperature of 30 to 120 ° C, under a pressure of 1 to 50 bars, and at an LHSV of 0.05 to 10. 17. Method according to any one of claims 1 to 16, characterized in that the etherification step is carried out at a temperature of 40 to 90 ° C, under a pressure of 3 to 20 bars, and at an LHSV d '' approximately 1. Brussels, the Par Pon of the Company known as LABOFINA SA