EP0370910B1 - Process for cracking a heavy hydrocarbon feedstock into lower boiling hydrocarbons, and apparatus for carrying out this process - Google Patents

Abstract

The present invention relates to a process for cracking heavy hydrocarbons into lighter hydrocarbons, and to a device for carrying out this process. <??>This process consists in using a bed of particles, advantageously catalytic particles, in a reaction chamber, introducing a gas for the fluidisation of the bed in accordance with a predetermined flow rate so as to create a spurting fluidised bed and introducing a plasma jet, preferably containing argon, into the chamber, the jet being directed towards a defined zone of the bed so as to create a reaction space having at least two reaction zones at different temperatures, the zone at the higher temperature being that into which the plasma jet is directed, introducing the heavy hydrocarbons into the reaction zone at lower temperature and preferably introducing into the zone at higher temperature one or more light alkanes so as to bring about the cracking of the heavy hydrocarbons in the fluidised bed, the latter effecting a quenching of the reaction mixture and catalysing the cracking. The process furthermore consists in discharging the products obtained downstream from the zone at lower temperature. <??>The invention is particularly applicable in the chemical and energy-generating industries.

Description

The present invention relates to a process for cracking heavy hydrocarbons into lighter hydrocarbons and to a device for implementing this process.

The invention finds particular application in the chemical and energy industries.

There are currently several types of cracking processes such as thermal cracking, hydrocracking and catalytic cracking. However, these methods all have drawbacks linked to the difficulty of controlling the reaction, the excessive consumption of hydrogen and the need for frequent regeneration of the catalysts.

Also known from European patent application No. 0 120 625 is a process for cracking heavy hydrocarbons into lighter hydrocarbons corresponding to the preamble of claim 1. However, the process of this document has the drawback of requiring a temperature zone high for the formation of radical species which will participate in the cracking reaction and a zone mechanically separated from the first, of lower temperature for the cracking reaction proper.

Also, the object of the present invention is a process for cracking heavy hydrocarbons into lighter hydrocarbons which does not have the drawbacks of the prior techniques and which moreover makes it possible to obtain a selectivity in light hydrocarbons which is higher and with better yields.

To this end, the method of the present invention consists in fluidizing by a gaseous fluidizing current in said chamber a bed of advantageously catalytic particles and in introducing a jet of plasma preferably containing argon towards a location of said bed; to introduce the charge of heavy hydrocarbons in a place of said fluidized bed distant from the plasma jet in the zone of lower temperature, and to introduce the light alkane such as methane, or the mixture of light alkanes, in the zone of higher temperature located near the place of introduction of the aforementioned plasma jet to effect the cracking of said heavy hydrocarbons by means of quenching and catalysis by said fluidized bed, and to evacuate the products thus obtained downstream of the lower temperature zone.

According to other characteristics of the process of the invention:
The plasma is introduced at the periphery of the fluidized bed;
A determined residence time is imposed on the products obtained in an area downstream from that of lower temperature;
The flow rate of the fluidizing gas stream is determined to create a gushing fluidized bed;
The fluidizing gas stream comprises at least argon and / or hydrogen;
The plasma contains at least 80% by volume of argon and may additionally contain hydrogen;
The plasma and the heavy hydrocarbons are introduced on either side of the gushing fluidized bed;
The higher temperature reaction zone is at a temperature between about 5000 ° and 1000 ° C;
The lower temperature zone is at a temperature between about 900 ° C and 500 ° C;
Methane is introduced into the reaction zone, the temperature of which is between approximately 5000 ° C and 1000 ° C;
The charge of heavy hydrocarbons is introduced into the fluidized bed gushing into the reaction zone, the temperature of which is between approximately 900 ° C. and 500 ° C.

The fluidizing gas is preheated upstream of the fluidized bed to a temperature between 50 ° C and 500 ° C, preferably between 150 ° C and 350 ° C;
The charge of heavy hydrocarbons is preheated and vaporized in the reaction chamber;
The bed consists of particles of a refractory material chosen in particular from the group consisting of oxides, carbides, nitrides and borides;
The particles in the bed have a catalytic effect;
The bed also contains a catalyst;
The cracking reaction is continued downstream of the lower temperature zone of the fluidized bed in a area with a temperature between about 650 ° C and 550 ° C.

The present invention also relates to a device for implementing the above process, this device comprising a reaction chamber 1 comprising a bed of particles 2, means for injecting a gaseous stream of fluidization 3 of the bed located at the bottom of said chamber to produce a gushing fluidized bed, a plasma torch 6 preferably containing argon and adapted to inject the plasma into said reaction chamber towards said fluidized bed, means 4 for introducing the charge of heavy hydrocarbons located at a low temperature reaction zone, means for introducing a light alkane, such as methane, or a mixture of light alkanes into a reaction zone higher temperature and means 7 for continuing the cracking reaction and for removing the lighter hydrocarbons thus obtained.

According to other characteristics of the device of the invention;
The plasma torch 6 and the means for introducing heavy hydrocarbons 4 are arranged on either side of the gushing fluidized bed;
The means for introducing the charge of heavy hydrocarbons consist of an injection pipe or the like;
The means for introducing the light alkane, such as methane, or the mixture of light alkanes are constituted by an injection pipe or the like;
The means 7 for continuing the cracking reaction and for removing the hydrocarbons obtained consist for example of a tubular reactor;
The reaction chamber has a cylindrical, parallelepipedic, spherical or similar shape;
The plasma torch is preferably connected to a side wall of the chamber so that the plasma is injected laterally into the fluidized bed;
The walls of the reaction chamber are preferably made of a refractory material such as alumina;
The bottom 8 of the reaction chamber has an upwardly flared shape at the bottom of which open means 9 for injecting the fluidizing gas.

The invention will be better understood and other objects, characteristics, details and advantages thereof will appear more clearly during the explanatory description which follows, made with reference to FIGS. 1 and 2 appended, and in which FIG. 1 represents a preferred embodiment of the method and the device of the invention; and FIG. 2 represents a curve illustrating the influence of the methane flow rate on the cracking rate, d (l / min), signifying the CH₄ flow rate and% signifying the cracking rate.

The method of the invention is implemented using a device of the type shown in FIG. 1 and comprising a reaction chamber 1 having for example the general shape of a rectangular parallelepiped whose bottom 8 has an upward flared shape and connected at its lower part to means 3 for injecting a gaseous fluidization stream, and containing a mass of particles of a material intended to form a fluidized bed 2, and a plasma torch 6 of a gas preferably containing argon, suitable for introducing the plasma inside the reaction chamber and towards the fluidized particle bed. Preferably the plasma torch 6 is connected at a side wall of the reaction chamber, so that the plasma is introduced laterally into the fluidized bed.

A preferably tubular reactor 7 is connected to the upper part of the reaction chamber 1 so that the reactor 7 communicates with the interior of the reaction chamber.

Means 4 for introducing the charge of heavy hydrocarbons are provided and connected to a wall of the reaction chamber 1 in such a way that the heavy hydrocarbons are brought into contact with the fluidized bed in an area of the reaction chamber having a determined temperature between about 900 ° C and 500 ° C. The injection means 4 may in particular comprise an injection rod or the like.

Means 5 for injecting a light alkane, such as methane, or a mixture of light alkanes are provided and are connected at the bottom of the reaction chamber 1 so as to introduce the methane into the fluidized bed at a high temperature zone, between about 5000 ° C and 1000 ° C, of the reaction chamber 1. These introduction means 5 can be represented by an injection rod or the like.

The reaction chamber 1 has internal walls by example in refractory alumina 4mm thick, externally insulated by a layer of porous bricks 20mm thick bonded with refractory cement on the alumina. The layer of bricks is itself covered by a layer of glass wool about 14 mm thick wrapped in a layer of asbestos. Thermocouples (not shown) are installed in the reaction chamber to measure the fluidized bed temperatures.

The means 3 for injecting the gaseous fluidization stream comprise, for example, an opaque silica tube 9 with a length of approximately 300 mm and a diameter of approximately 40 mm opening at the bottom of the reaction chamber 1. The tube is surrounded by a 500 W heating tape (not shown) intended to preheat the fluidizing gas and it is lined with refractory balls with a diameter of approximately 2 to 6 mm favoring the heat exchanges between the gas and the wall of the tube. The lower part of the tube 9 is fitted with a brass injector 11.

The tubular reactor 7 is for example constituted by a silica tube of approximately 85 mm in diameter and approximately 500 mm in length. Thermocouples (not shown) are installed in this tube to measure the temperature of the gas stream flowing therein. The outlet of this tube can be connected to a water heat exchanger (not shown) in which the reaction mixture is cooled before being taken for analysis.

The plasma torch and the means for introducing heavy hydrocarbons are connected at the level of the reaction chamber so that the plasma and the heavy hydrocarbons are introduced on either side of the fluidized bed on the side opposite to the plasma torch. with respect to the jet of particles from the bed. We can vary the angle of insertion of the torch in the chamber from 0 ° to 90 °. Preferably the angle of introduction of the torch into the chamber is 20 ° relative to the horizontal section of the reaction chamber. Typically, this torch consists of two concentric tubes of silica, with an outside diameter of 30 mm, surrounded by five hollow inductive turns of water-cooled copper, traversed by an electric current at high frequency.

The bed consists of particles of a material chosen in particular from the group consisting of oxides, carbides, nitrides and borides. The following list can be used as an example:

Whatever the nature of the materials used, these must be refractory because the particles of beds must be able to withstand high temperatures and because they are in contact with the plasma jet. The particles of the bed can themselves act as a catalyst and it is also possible to add another catalyst to them. The particles of the fluidized bed have a diameter of between approximately 250 and 400 μ. The particle size chosen must allow a gushing fluidization without entraining the particles out of the reaction chamber 1.

It should be understood that the word "catalyst" is taken in its broad sense, that is to say that the particles can accelerate certain desired reactions or inhibit certain undesired reactions such as the formation of carbon black or coke.

In service, the operation of the device which has just been described is as follows. The mass of particles, of determined diameter, which may contain a catalyst, is made to fluidize into a gushing bed, having the shape of a fountain falling on the walls of the reaction chamber, by the constant flow of a fluidizing gas formed. argon or a mixture of argon and hydrogen. The fluidizing gas is preheated in the tube 9 which is lined with balls, for example of alumina.

The plasma torch 6 injects a plasma of a gas preferably containing argon towards the fluidized bed of particles where an efficient transfer of heat takes place between the plasma and the fluidized bed.

$${\text{CH₃ → CH₂}}^{\text{.}}{\text{+ H}}^{\text{.}}$$

etc...The injection rod 5 injects, for example, methane, inside the fluidized bed in an area close to that of the plasma injection and having a temperature between approximately 5000 ° C. and 1000 ° C. In this relatively high temperature zone, the methane will decompose as follows:
$${\text{CH₄ → CH₃}}^{\text{.}}{\text{+ H}}^{\text{.}}$$

$${\text{CH₃ → CH₂}}^{\text{.}}{\text{+ H}}^{\text{.}}$$

etc ...

Radicals favoring the cracking reaction of heavy hydrocarbons are therefore formed in this zone at relatively high temperature.

The heavy hydrocarbon injection pipe 4 makes it possible to introduce them into the fluidized bed in a determined region having a temperature between approximately 900 ° C. and 500 ° C. and lying approximately opposite the plasma injection zone. .

The nature of the bed, the flow rate of the gaseous fluidizing stream and the introduction of the plasma torch in a region opposite to that of the introduction of heavy hydrocarbons make it possible to create a reaction space having at least said two zones of different temperatures. mentioned above.

Thus, in the highest temperature zone, the methane will convert as described above inside the fluidized bed. The radicals thus formed will cross the fluidized bed in the direction of the zone of lower temperature at the level of which the charge of heavy hydrocarbons is introduced and will initiate the cracking reaction of the latter.

The primary advantage of this type of device is that it makes it possible to use methane directly to promote cracking and for this purpose the device has a reaction space at two zones of different temperatures by means of the jet of particles which allows to separate the reaction space into these two zones.

• ses propriétés de transfert de chaleur permettent une trempe efficace du plasma ;
• sa viscosité sensiblement égale à celle du plasma assure un très bon mélange entre celui-ci et le lit fluidisé ; et
• ses propriétés catalytiques éventuelles peuvent assurer la transformation directe des réactifs à convertir.

The use of a fluidized bed of this type in the process of the present invention has significant advantages for the following reasons:

• its heat transfer properties allow efficient quenching of the plasma;
• its viscosity substantially equal to that of plasma ensures a very good mixture between it and the fluidized bed; and
• its possible catalytic properties can ensure the direct transformation of the reactants to be converted.

Thus, the methane will be converted in the fluidized bed in a region close to the plasma injection and in which the quenching carried out by the fluidized bed makes it possible to have a temperature suitable for the transformation of methane into radicals. These radicals from the higher temperature zone will favor the cracking reaction of heavy hydrocarbons at a temperature lower than that of the higher temperature zone, while avoiding the formation of carbon black.

The reaction for converting heavy hydrocarbons into lighter hydrocarbons will continue in an area located downstream from the lower temperature area of the fluidized bed. In fact, a temperature gradient is created from the region downstream from the fluidized bed to the tubular reactor 7 varying from about 650 ° C to 550 ° C and thus allowing the completion of the cracking reaction.

The following examples illustrate the implementation of the process of the present invention.

In these examples, an aliphatic C₁₆ hydrocarbon was treated at a rate of about 14 to 25 g / minute to carry out the cracking reaction and the products were analyzed by chromatography using a flame ionization detector equipped with a 10% SE 30 column for the separation of liquid hydrocarbons and a 7% squalane column for the separation of gaseous and light hydrocarbons.

Example 1.

The plasma torch operates at a frequency of 5 MHz for an actual power of 2.38 kW. The injection angle is 20 °. The plasma gases introduced are argon at a flow rate of 27 l / min and hydrogen at a flow rate of 6 l / min. The bed is made up of alumina particles (650g) with a mean diameter of 300 µ. The particles of the bed are fluidized by a mixture of argon at a flow rate of 10 l / min and hydrogen at a flow rate of 14 l / min. The fluidizing gases are preheated to a temperature between 50 ° C and 500 ° C, preferably between 150 ° C and 350 ° C. The average cracking temperature is 727 ° C. Methane is introduced at a flow rate of 1 l / min.

Example 2.

The plasma torch operates at a frequency of 5 MHz for an actual power of 2.52 kW. The injection angle is 20 °. The plasma gases introduced are argon, at a flow rate of 27 l / min and hydrogen at a flow rate of 6 l / min. The bed is made up of alumina particles (650g) with a mean diameter of 300 µ. The particles of the bed are put in fluidization with a mixture of argon, at a flow rate of 10 l / min and of hydrogen at a flow rate of 14 l / min. The fluidizing gases are preheated to a temperature between 50 and 500 ° C, preferably between 150 ° C and 350 ° C. The average cracking temperature is 730 ° C. Methane is introduced at a flow rate of 0.46 l / min.

Example 3.

The plasma torch operates at a frequency of 5 MHz for an actual power of 2.45 kW. The injection angle is 20 °. The plasma gases introduced are argon, at a flow rate of 27 l / min and hydrogen at a flow rate of 6 l / min. The bed is made up of alumina particles (650g) with a mean diameter of 300 µ. The particles of the bed are fluidized by a mixture of argon at a flow rate of 10 l / min and hydrogen at a flow rate of 14 l / min. The fluidizing gases are preheated to a temperature between 50 and 100 ° C, preferably between 150 ° C and 350 ° C. The average cracking temperature is 725 ° C. Methane is introduced at a flow rate of 0.15 l / min.

Example 4.

The plasma torch operates at a frequency of 5 MHz for an actual power of 2.45 kW. The injection angle is 20 °. The plasma gases introduced are argon at a flow rate of 27 l / min and hydrogen at a flow rate of 6 l / min. The bed is made up of alumina particles (650g) with a mean diameter of 300 µ. The particles of the bed are fluidized by a mixture of argon at a flow rate of 10 l / min and hydrogen at a flow rate of 14 l / min. The fluidizing gases are preheated to a temperature between 50 and 500 ° C, preferably between 150 ° C and 300 ° C. The average cracking temperature is 720 ° C. We does not inject methane.

The results of Examples 1 to 4 are listed in the following table and FIG. 2 shows the evolution of the cracking rate as a function of the methane flow rate.

As can be seen from the table above and from FIG. 2, it can be seen that the introduction of methane promotes the cracking rate. As for the reaction products, essentially ethylene, propylene and butene are obtained.

In addition, the method and the device of the present invention allow rigorous control of the temperature in the cracking zone by the combined effects of the electric power supplied to the plasma, the angle of injection of the plasma, the flow rate of hydrocarbons. heavy and the fluidization gas flow.

Of course, the invention is in no way limited to the embodiments described and illustrated which are given only by way of example.

It is also understood that the plasma used can be produced in any way, in particular by blown, transferred electric arc or even by induction.

Claims (27)

1. Method of cracking a batch of heavy hydrocarbons into lighter hydrocarbons in a reaction chamber, consisting in feeding a light alkane or a mixture of light alkanes into a reaction zone of high temperature to produce free radicals, injecting the heavy hydrocarbons to be cracked into the reaction chamber and causing the free radicals to react with the said heavy hydrocarbons for the cracking of the latter within a zone of lower temperature, characterized in that it consists in fluidizing with a gaseous fluidizing stream in the said chamber an advantageously catalytic bed of particles and feeding a plasma jet preferably containing argon towards a place of the said bed; in that it consists in feeding the batch of heavy hydrocarbons into a place of the said fluidized bed remote from the plasma jet in the zone of lower temperature and feeding the light alkane such as methane or the mixture of light alkanes into the zone of higher temperature located near the place of introduction of the aforesaid plasma jet for carrying out the cracking of the said heavy hydrocarbons by means of a quenching and of a catalysis of the said fluidized bed and in that it consists in discharging the products thus obtained downstream of the zone of lower temperature.

2. Method according to claim 1, characterized in that the plasma is introduced at the periphery of the fluidized bed.

3. Method according to claims 1 and 2, characterized in that the heavy hydrocarbons and the plasma are introduced on either side of the fluidized bed.

4. Method according to claim 1, characterized in that one imposes a determined residence time upon the products obtained in a zone downstream of that of lower temperature.

5. Method according to claim 1, characterized in that the flow rate of the gaseous fluidizing stream is determined to create a springing fluidized bed.

6. Method according to one of claims 1 and 5, characterized in that the gaseous fluidizing stream comprises at least argon and/or hydrogen.

7. Method according to one of the foregoing claims, characterized in that the plasma contains at least 80% by volume of argon.

8. Method according to claim 7, characterized in that the plasma contains hydrogen.

9. Method according to claim 1, characterized in that the reaction zone of higher temperature is at a temperature lying between about 5,000° and 1,000°C.

10. Method according to claim 1, characterized in that the zone of lower temperature is at a temperature lying between about 900° and 500°C.

11. Method according to one of claims 1 or 9, characterized in that the methane is fed into the reaction zone the temperature of which is lying between about 5,000°C and 1,000°C.

12. Method according to one of claims 1 and 10, characterized in that the batch of heavy hydrocarbons is fed into the springing fluidized bed within the reaction zone the temperature of which is lying between about 900°C and 500°C.

13. Method according to any one of the foregoing claims, characterized in that the fluidizing gas is preheated upstream of the fluidized bed to a temperature lying between 50°C and 500°C, preferably between 150°C and 350°C.

14. Method according to any one of the foregoing claims, characterized in that it consists in preheating and vaporizing the batch of heavy hydrocarbons before feeding same into the reaction chamber.

15. Method according to any one of the foregoing claims, characterized in that the bed consists of particles of a refractory material selected in particular from the group consisting of oxides, carbides, nitrides and borides.

16. Method according to claim 15, characterized in that the particles have a catalytic effect.

17. Method according to one of claims 15 or 16, characterized in that the bed in addition contains a catalyst.

18. Method according to any one of the foregoing claims, characterized in that the cracking reaction is continued downstream of the zone of lower temperature of the fluidized bed within a zone exhibiting a temperature lying between about 650°C and 550°C.

19. Device for carrying out the method according to any one of the foregoing claims, characterized in that it comprises a reaction chamber (1) including a bed of particles (2), means (3) for injecting a gaseous stream for fluidizing the said bed, located at the level of the bottom of the said chamber to provide a springing fluidized bed, a plasma torch (6) with a plasma preferably containing argon and adapted to inject the plasma into the said reaction chamber towards the said fluidized bed, means (4) for introducing the batch of heavy hydrocarbons, located at the level of a reaction zone of low temperature, means (5) for introducing a light alkane such as methane or a mixture of light alkanes into a reaction zone of higher temperature and means (7) adapted to continue the cracking reaction and to discharge the lighter hydrocarbons thus obtained.

20. Device according to claim 19, characterized in that the plasma torch (6) and the means (4) for introducing heavy hydrocarbons are disposed on either side of the springing fluidized bed.

21. Device according to claim 19, characterized in that the means for introducing the batch of heavy hydrocarbons are constituted by an injection pipe or the like.

22. Device according to claim 19, characterized in that the means for introducing the light alkane such as methane or the mixture of light alkanes are constituted by an injection pipe or the like.

23. Device according to claim 19, characterized in that the means (7) for continuing the cracking reaction and for discharging the hydrocarbons obtained are constituted for example by a tubular reactor.

24. Device according to claim 19, characterized in that the reaction chamber exhibits a cylindrical, parallelepipedic, spherical or like shape.

25. Device according to one of the foregoing claims, characterized in that the plasma torch is connected preferably at the level of a side wall of the reaction chamber so that the plasma be laterally injected into the fluidized bed.

26. Device according to any one of the foregoing claims, characterized in that the walls of the reaction chamber are preferably of a refractory material suchs as alumina.

27. Device according to any one of the foregoing claims, characterized in that the bottom (8) of the reaction chamber exhibits an upwards flared shape at the upper portion of which are opening means (9) for injecting the fluidizing gas.

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