DESCRIPTION

Field of the Invention

The present invention relates to a reactor for non-isothermal reactions and used for chemical synthesis.

Background art

As known from the state of the art, chemical synthesis takes place in various reactor configurations. In particular, in the presence of exothermic or endothermic reactions, it is essential to find devices which are able to efficiently transfer heat from one area of the reactor to another. A classic example is the synthesis of methanol, one of the most interesting and promising molecules of organic synthesis, but also one of the most complicated to obtain due to the exothermicity of the reaction, the risk of activating methanation reactions, even more exothermic and especially for the poor yield in the single passage. In this respect, countless technological solutions are known. In particular, the known reactor configurations can be classified into: gas phase technologies (adiabatic, isothermal, fluid bed), liquid phase technologies and membrane technologies. In detail, for the adiabatic gas-phase technologies, some examples are the Johnson Matthey Multi-stage Quench Converter, the Kellogg, Brown and Root fixed-bed spherical reactor (KBR), the Haldor-Topsoe/Udhe multi-stage reactor, the Haldor-Topsoe (Collect-Mix- Distribute reactor) and Halliburton reactors for revamping the quencher, the Casale ARC reactor and the MRF-Z® reactor of Toyo Engineering Corporation. Regarding the isothermal gas phase technologies, mention is made of the Linde helical tube reactor, the Lurgi combined reactor (among the most widespread in the world), the Mitsubishi Superconverter, the axial and axial-radial reactors developed by Casale and the Steam Raising Converter (SRC) reactors of Davy Process Technology. With regard to other types of reactors, it should be noted that they are also used in areas other than methanol, i.e., wherever it is necessary to exchange heat efficiently.

GB 553107 A discloses a tubular reactor in which tubes filled with catalyst extend between an upper chamber and a lower chamber. The reactor further comprises a first outer shell surrounding the tube bundle and a second outer shell surrounding the first outer shell so as to define an annular chamber. Inside the first shell and therefore in contact with the tube bundle, a cooling fluid is inserted. Thereby, an exothermic reaction takes place in the tube bundle thanks to the presence of the catalyst and the temperature of the liquid contained inside the first shell.

US 1834679 A describes a tubular reactor having an outer shell and a tube bundle into which the reaction gas passes. The shell is filled with a mercury alloy having a boiling point between that of mercury and the lowest boiling point of the metal forming the aforesaid alloy. In this case, the reaction gas entering from the head of the tube bundle is preheated by the gases produced by the liquid contained in the shell and maintained at a certain temperature. When the reaction is strongly exothermic it causes a slight increase in the temperature of the liquid contained in the shell, but at the same time a faster boiling with only a slight increase in the boiling point due to the fact that the vapours of the azeotropic mixture are richer in mercury than in the bath.

US 4921681 A Document D3 describes a tubular reactor designed for very exothermic reactions and in particular for the formation reaction of ethylene oxide from oxygen. Also in this case, it is a tube bundle surrounded by a cooling fluid (water). The tubes are divided into three zones, the first part where the preheating takes place, in which the gases are preheated by the water vapor present in the shell and formed by the heat developed in the reaction in the underlying part. This section is not empty but is packed with inert material to facilitate the exchange of heat between the shell and the reagents, before coming into contact with the catalyst in the underlying part, where the reaction takes place. In this zone the liquid (water in the shell) acts as a cooling fluid, controlling the temperature of the exothermic reaction. The gases from the reaction pass into the underlying section filled once more with inert material cooled by water in the so-called cooling zone. In this section there is a whole set of nozzles which allow the reaction mixture to be cooled in the tubes, but not evenly, especially if there are many tubes. To overcome this problem, there is an underlying defined zone of empty distribution. Due to the fact that it is empty, the effluent gases slow down the speed thereof, decreasing the heat exchange on the side of the tubes by about 10%, allowing a more uniform heat exchange between all the tubes, even the innermost ones.

US 2662911 A discloses a tubular reactor in which the tubes where the reaction takes place are completely filled with catalyst, while perforated plates or plates provided with bells are provided on the shell side to facilitate the liquid gas separation.

The need is therefore felt to find alternative solutions in order to improve the efficiency of heat exchange during the non-isothermal reactions with cooling/heating fluids, in order to maximize reactor efficiency, increasing reagent conversions and at the same time increasing the reaction yields in desired end products. The liquid pressure and temperature parameters are chosen such that the liquid is kept in a boiling state. Thereby, the vapor produced by the liquid is exported to the upper portion of the first shell and used to i) replenish the liquid inside the first shell following a condensation step, ii) fill the gap between the first and second shell, so as to exploit the latent evaporation heat to maintain the temperature of the liquid such as to favour the exothermic reaction.

Summary of the invention

In order to overcome the aforementioned problems, the reactor object of the present invention has been conceived. It is a reactor for gas-phase non-isothermal reactions comprising:

-a tubular reactor comprising at least one tube through which reaction fluids (A) pass, and in which tubular reactor a portion is defined where at least one non-isothermal reaction takes place;

- a shell external to said tubular reactor, in which a fluid which acts as a cooling /heating fluid of said reaction fluids passes. in which:

(i) the reaction fluids enter at the head of said tubular reactor and exit at the tail of said tubular reactor and said portion where at least an isothermal reaction takes place is filled with a specific catalyst for said reaction, while the remaining portion of the tubular reactor is empty

(ii) the cooling/heating fluid flowing in the shell can be introduced in the gas phase, in the liquid phase and/or a combination of both and acts both as a cooling fluid and as a heater of the reaction fluids in different portions of the same tubular reactor;

(iii) in said outer shell in which said cooling/heating fluid passes, at least one liquid-vapor separation zone is defined, in which at least one liquid vapor separation stage of the cooling fluid/heating fluid takes place.

LIST OF FIGURES

Figura 1: schematic depiction of a reactor for gas-phase non-isothermal reactions according to an embodiment of the present invention;

Figura 2: schematic depiction of the zones of the reactor for gas-phase non-isothermal reactions according to the embodiment of figure 1 ;

Figura 3: schematic representation of a reactor for gas-phase nonisothermal reactions according to an alternative embodiment of the present invention;

Figura 4: schematic depiction of the zones of the reactor for gas-phase non-isothermal reactions according to the embodiment of figure 3;

Figura 5: schematic depiction of a first detail of the reactor for gas-phase non-isothermal reactions according to the embodiment of figure 1 and figure 3;

Figura 6: schematic depiction of a second detail of the reactor for gasphase non-isothermal reactions according to the embodiment of figure 1 and figure 3;

Figura 7: schematic depiction of a third detail of the reactor for gas-phase non-isothermal reactions according to the embodiment of figure 1 and figure 3;

Figura 8: schematic representation of a reactor for gas-phase nonisothermal reactions according to an alternative embodiment of the present invention.

DETAILED DESCRIPTION

For the purposes of the present invention, the reaction fluids A may be of different types and characterized in that they reach the sufficient temperature and pressure conditions to carry out the non-isothermal reaction at the portion of the tubular reactor containing the catalyst. The reaction fluids A comprise the reagents necessary for the synthesis of the desired product and after passing through the catalyst-filled reactor portion, they also comprise the desired reaction product(s).

For the purposes of the present invention, the fluid B introduced into the shell 20 may be inserted in the gas phase, in the liquid phase and/or a combination of both. The fluid B is configured to act as both cooling fluid and heating fluid or vice versa for certain portions of the same tubular reactor according to the specific non-isothermal reaction.

The reactor is configured so that in the liquid vapor separation zone the fluid B, when in the vapor state, condenses, or if in the liquid state evaporates, thereby exploiting the latent evaporation heat twice to cool or heat the reaction fluids according to the specification of the non-isothermal reaction. In addition to this, the reactor object of the present invention, in addition to exploiting the latent evaporation heat twice, is also characterized in that, the vapor condensing on the tubes forms a thin film on the shell side for the entire external length of the tubes not occupied by the liquid fluid, further increasing the heat exchange.

Since the liquid fluid in the shell side covers at least the entire portion of the tubes filled by the catalyst, for the thin film to exert an appreciable heat exchange action it is essential that the volume of the catalyst-filled portion of the tubular reactor does not exceed 75%, preferably it is between 5 and 70%, more preferably between 10 and 60% and even more preferably between 15 and 50% by volume/total volume of each tube in the reactor.

Above 75%, given the high volume occupied by the catalyst-filled portion, any thin film formed is not able to carry out its activity since it would travel a very short distance before falling back into the liquid fluid.

Specifically, the reaction fluids A enter from the tubular reactor head and exit the tubular reactor tail. According to a preferred embodiment, the tubular reactor comprises a plurality of tubes which allow to maintain a uniform heat profile in the entire tubular reactor, ensuring heat exchange between the reaction fluids and the fluid B.

The reaction fluids entering from the head 10a of the tubular reactor 10 comprise one or more reagents configured to react with the catalyst therein at the reaction portion. The reaction fluids at least partially reacted inside the tubular reactor exit the tail of the tubular reactor and may contain, in addition to the reaction products, unconverted reagents, intermediate reaction products comprising a mixture of synthesis gases and reagents.

The reactor object of the invention may provide downstream at least one separation unit of the reaction products from the reagents, which are subsequently recycled to the head of the reactor.

The reactor shell comprises at least one liquid or vapor cooling/heating fluid inlet and at least one liquid or vapor phase outlet.

For the purposes of the present invention, the reaction portion of the tubular reactor generally containing the specific catalyst for the non-isothermal reaction is also defined as a first heat exchange zone between the reaction fluids, which flow into the tubular reactor and the cooling/heating fluid present in the outer shell. Likewise, liquidgas separation zone means a second heat exchange zone between the reaction fluids and the shell-side fluid. The reaction portion and the shell-side separation zone are contiguous along the reactor object of the invention.

According to a preferred embodiment the liquid-gas separation zone comprises a stage liquid-gas separator, arranged along said separation zone.

Preferably, the stage separator comprises a distillation column, a rectification column, a packed column or a structured packed column arranged along the reactor.

More preferably, the stage separator is a plate distillation or rectification column arranged along the tubular reactor, arranged in the shell near the remaining portion of the reactor not occupied by the catalyst.

Preferably, the plates are of the weir type. They are characterized in that the liquid descends from the upper plate, runs along the plate from one side to the other and then passes by falling through tubes or downcomers in the lower plate. The plates can be drilled, bell-shaped or valve-shaped. According to a particularly preferred solution as depicted in figures 5-7, the weir plates are perforated, each plate 42 comprises holes 42a for the passage of the cooling fluid/heating fluid in the form of vapor. Furthermore, each plate 42 comprises holes 42b for the passage of the tubes forming the tubular reactor. Preferably, the tubular reactor occupies about 80% of the total surface of each plate 42.

According to the above-described preferred embodiment shown in figures 5-7, each plate 42 also comprises a dam 42 c configured to keep at least one condensed liquid cooling/heating fluid head on the plate 42 and a downcomer 42d which directs the condensed liquid B to the lower plate facilitating the distribution of the condensed liquid.

As these are weir plates, the dams 42c and the downcomers 42d on overlapping plates are arranged alternately.

Each plate 42 may comprise guides 42e which facilitate the removal of the respective plate 42 during possible maintenance of the plant.

For the purposes of the present invention, non-isothermal reactions are endothermic reactions or exothermic reactions.

As a function of the type of reaction conducted inside the tubular reactor, the catalyst is positioned at the head or tail thereof as detailed below.

Specifically, as a function of the type of non-isothermal reaction and the number of stages used for the liquid-gas separation, three variants are identifiable in accordance with the present invention.

Reactor for single-stage exothermic reactions

In accordance with the present embodiment illustrated in figure 8, the nonisothermal reaction carried out inside the tubular reactor 10 is an exothermic reaction.

Preferably, in this embodiment the catalyst 31 inside the portion 30 is arranged in the tail 10b to the tubular reactor 10. Thereby, the portion 30 acts as a heating unit of the cooling/heating fluid B in place of a conventional -type external reboiler.

In this case the degree the catalyst-filled portion 30 occupies a volume between 30 and 60% and in accordance with the embodiment shown in this figure occupies about 40% of the total volume of the tubular reactor.

In accordance with the present variant, the fluid B is introduced into the shell in a liquid stage BL at the tail of the reactor. Thereby, the fluid B in the liquid state indicated with BL submerges the portion 30 of the tubular reactor 10. Preferably, in order to avoid overheating in the reaction zone and any breakage of the tubular reactor 10, the fluid B submerges not only the reaction portion 30 but also a contiguous part of the tubular reactor 10 in the direction of the head 10a.

In the present case, the reaction fluids A enter from the head 10a of the tubular reactor 10 at a lower temperature than the reaction temperature at the reaction portion 30. Preferably the tubular reactor is provided with a plenum 12 from which the reaction fluids A enter, reaching a uniform pressure and temperature and are pushed inside the one or more tubes 11 towards the tail 10b of the tubular reactor 10 and from which they exit.

The reaction fluids A exchanging heat with the fluid B in the vapor state BV at the separation portion 40 gradually increase the temperature during the passage from the head to the tail of the tubular reactor 10. In other words, the fluid B in the vapor state BV occupies the empty volume of the shell 20 at the liquid gas separation portion 40.

The reaction fluids A reach the reaction portion 30 where the catalyst 31 is arranged at a suitable temperature and react according to an exothermic reaction.

The heat produced by this reaction is removed by the fluid B which bathes the tubes 11 of the tubular reactor 10 externally. Thereby, the fluid B in the liquid state acting as a cooling fluid removes the heat produced by the exothermic reaction at least partially passing through the phase. Specifically, the fluid B in the liquid state passes to the vapor state BV, starting to migrate towards the head of the reactor 100.

The vapor-state fluid B condenses at least partially at the liquid-gas separation zone 40 defined by the shell 20. Specifically, the vapor-state fluid B migrating towards the head of the reactor 100 impacting on the plurality of tubes 11 condenses and exchanges heat with the reaction fluids A at a lower temperature than the fluid B in the vapor-state.

Advantageously, it is thereby possible to exploit the latent heat of the fluid B twice. In fact, by condensing, the fluid B in the vapor state releases the same latent heat, for evaporation, to the reagent fluids A.

Furthermore, it should be noted that the fluid B in the vapor state condensing on the plurality of tubes 11 at the liquid-gas separation zone 40 forms a thin film FS on the tubes themselves which improves the heat exchange between the fluid B and the fluids A with respect to a gas/gas exchange system (such as, for example, for the Lurgi or Davy Process Technology reactors).

In accordance with a preferred embodiment, any non-condensables deriving from the degradation of the fluid B in the liquid state and/or the dissolution of the fluid B in the gas state can be removed from the head of the shell 20 together with vapor portions which are not suitably recondensed.

It should be noted that the fluid B can be removed during the shutdown of the reactor at a discharge channel CS1 arranged in the tail 20b of the shell 20. It should also be noted that the reactor 100 comprises a further discharge channel CS2 for the fluid B in the liquid state BL arranged at the reaction zone 20 on the shell side 20, usable for the management of the liquid level on the shell side.

Furthermore, the reactor 100 on the shell side comprises a vent channel CS3 at the head 20a of the shell and configured to discharge the fluid B in the vapor state BV.

In accordance with the present variant, the catalyst 31 is loaded from the head 10a of the tubular reactor 10 by inserting it inside the tubes 11 and is discharged from the tail 10b of the tubular reactor 10 itself.

Advantageously, the present variant makes it possible to intensify the heat exchange in order to preheat the reagent fluids A in order to achieve an exothermic reaction.

In accordance with a preferred embodiment, the reactor 100 comprises a support grid 50 for the tubular reactor 10 at the tail thereof.

In maintenance operations the catalyst is discharged from the reactor tail. Reactor for multi-stage exothermic reactions

In accordance with the present embodiment illustrated in figures 1 and 2, the non-isothermal reaction achieved inside the tubular reactor is an exothermic reaction.

Preferably, in this embodiment the catalyst 31 is arranged in the tail 10b of the tubular reactor 10 defining the portion 30. Thereby, the reaction portion 30 acts as a heating unit in place of a reboiler known to those skilled in the art as illustrated in figure 2. Furthermore, it should be noted that such a reactor, differently from the single-stage variant, comprises a stage separator 41 of the type described above.

In this case, the catalyst-filled portion 30 occupies a volume between 10 and 30% and according to the specific embodiment achieved in figures 1 and 2 occupies a volume of about 15% of the total volume of the tubular reactor 10.

Also in this case, the fluid B is inserted inside the shell in the liquid state BL in order to keep the reaction zone 30 completely immersed.

As above, the reaction fluids A entering from the head of the tubular reactor 10 are preheated along the separation portion 40 and subsequently react at the reaction portion 30. The heat produced by the exothermic reaction is removed from the fluid B in the liquid state which passes at least partially to the vapor state BV. The vapor produced exchanges heat with the tubes 11 thus preheating the reaction fluids A. Also in this case, the heat exchange is optimized by the fact that the latent heat of the fluid B is exploited twice and by the formation of a thin film on tubes 11 on the shell side.

According to the present variant, the presence of the plate distillation column makes it possible to optimize the heat exchange at each plate 42 between the fluid B and the reaction fluids A. In fact, the liquid B in the vapor state migrating from the tail 20a to the head 20b of the shell 20 tends to condense at least partially on each plate 42.

The reactor 100 comprises an outlet channel CUI for the excess fluid B in the vapor state. Such excess vapor can be sent back to condensation.

Furthermore, according to a preferred embodiment, part of the fluid B following condensation outside the reactor is reintroduced into the reactor 100 on the shell side at an inlet channel CI1 preferably at the head 20a of the shell 20. The reactor 100 comprises a further inlet channel CI2 on the shell side to feed the fluid B in the liquid state BL.

It should be noted that the fluid B condensed at each plate 42 is directed by downcomers 42d to lower plates until the tail 20b of the shell 20.

Also in this case, during shutdown, the fluid B in the liquid state can be discharged from the tail of the reactor 100 by a further outlet channel CU2 in the tail 20b of the shell 20.

At the same time, the catalyst 31 is loaded at the head of the reactor and can be discharged when exhausted at the tail of the reactor.

In accordance with a preferred embodiment, the reactor 100 comprises a support grid 50 for the tubular reactor 10 at the tail thereof.

Reactor for multi-stage endothermic reactions

Figure 4 shows an embodiment of the reactor object of the invention for conducting endothermic reactions

Preferably in this embodiment the catalyst 31 is arranged in the head 10a of the tubular reactor 10 defining the portion 30 where the reaction takes place. Thereby, the reaction portion 30 acts as a cooling unit in place of a conventional type external condenser.

Also in this case, the catalyst-filled portion 30 of the tubular reactor 30 occupies a volume between 10 and 30% of the total volume of the tubular reactor 10. According to the specific preferred embodiment shown in figures 3 and 4, the volume of the catalyst-filled portion 30 constitutes about 15% by volume of the total volume of each tube.

In accordance with the present variant, after being rendered uniform in temperature and flow in a plenum 12 in the head 10a of the tubular reactor 10, the reaction fluids A enter the tubes 11 where they meet the catalyst 31 positioned in the head. Thereby, the reaction fluids A react according to an endothermic reaction thus acting as condensers of the fluid (B) passing through the shell side.

The fluid B is introduced inside the shell 10 in the gas state BV from the tail 20b of the shell 20. Specifically, the fluid B in the gas state BV is introduced by means of an inlet duct CI3 arranged at the tail 20b of the shell 20. According to a preferred embodiment, the fluid B is introduced inside the shell in the liquid state by means of an inlet channel CI4 arranged between the head 20a and the tail 20b.

Thereby, during the ascent from the tail 20b to the head 20a, the fluid B in the vapor state exchanges heat with the one or more tubes 11 of the tubular reactor 10 condensing on the shell side. Also in this case, the fluid B forms a thin film on the outer surface of each tube 11 of the tubular reactor 10, optimizing the heat exchange.

The fluid B arriving at the head condenses further, exchanging heat at the reaction zone 30.

The excess vapor exits from the shell at the head 20a by means of an outlet channel CU3 while a part of the condensate BL in the reaction zone 30 exits from the shell 20 in the form of a distillate by means of a further outlet channel CU4. The latter is preferably arranged below the reaction zone 30.

In accordance with the present variant, the reactor 100 comprises a plate distillation, 41 which in this case collects the condensed fluid B in the various stages along the reactor 100 and discharges it from the tail 20b of the shell by means of an outlet channel CU5.

In accordance with the present invention, the catalyst 31 is loaded and discharged from the head of the tubular reactor 10. In fact, a basket 60 containing the catalyst is arranged at each tube 11 during the operation of the reactor, which therefore holds it at the top of the tubular reactor in order to carry out the endothermic reaction.