Inner Loop Reactor

Abstract

The internal loop reactor comprises a vertically disposed cylindrical vessel with a sidewall and a reactor fluid outlet means, and at least one draft tube disposed vertically within the vessel. The draft tube has an inner surface and an outer surface, the draft tube provides a first conduit within the draft tube having a tube inlet end and a tube outlet end, and a second conduit outside the draft tube and within the sidewall, the first conduit being in fluid communication with the second conduit. The reactor comprises at least one nozzle disposed concentrically with the draft tube for injecting fluid into the first conduit from the tube inlet end. The inner surface of the draft tube is convexly curved such that the first conduit presents an annular constriction of cross section between the tube inlet end and the tube outlet end, the constriction being disposed near the tube inlet end. Additionally, the outer surface of the draft tube is convexly curved such that the draft tube presents a peripheral ridge between the tube inlet end and the tube outlet end. The present invention further relates to a process for conducting continuous high pressure reactions, in which fluids are introduced into an internal loop reactor and reacted fluids are removed through a fluid outlet of the loop reactor. The curved shape of the inner surface of the draft tube wall guides the fluids through the draft tube in an optimized manner.

Description

[Technical field]

[0001] The present invention relates to an internal loop reactor and a process for conducting continuous high pressure reactions in an internal loop reactor. [Background technology]

[0002] Internal loop reactors for continuous high pressure reactions are appropriately designed to provide a high degree of mixing to achieve sufficient conversion of reactants with high selectivity. One way of enhancing mixing is through the use of a draft tube. In a draft tube mixing system, a tube, usually cylindrical and open at both ends, is placed vertically inside the reactor to form a cylindrical space within the draft tube and a space outside the draft tube.

[0003] Typically, a loop reactor includes at least one draft tube disposed below a nozzle through which one or more reactants are injected into the reactor. The draft tube provides a first conduit within the draft tube and a second conduit in an opposite direction outside the draft tube. Reactants injected through the nozzle travel down the first conduit, and then a mixture containing reactants and reaction products is redirected in the opposite direction in the second conduit, where the mixture is backmixed with the injected reactants.

[0004] The flow pattern generated by the draft tube is a recirculation flow, which can be characterized by the circulation ratio (i.e., the total mass flow through the draft tube divided by the feed mass flow rate). The total mass flow includes the feed mass flow and the entrained fluid circulating through the reactor. In general, it is desirable to have a high circulation ratio. The circulation ratio depends on the pressure drop of the circulating fluid, which in turn depends on the fluid properties and the fluid flow pattern. Flow separation can occur, for example at the draft tube exit, resulting in increased pressure drop and leading to a reduced circulation ratio.

[0005] It has been shown that the circulation rate can be influenced by the choice of geometric length ratios, i.e. reactor diameter to reactor length and / or tube diameter to reactor length. Furthermore, the design of the deflection areas, e.g. the geometry of the draft tube edges, deflectors and interiors, as well as the surface properties of the reactor components, are considered. A summary is given in Blenke et al., Verfahrenstechnik 3 (1969), p. 444-452. Summary of the Invention [Problem to be solved by the invention]

[0006] There remains a great need to enhance the performance of loop reactors. [Means for solving the problem]

[0007] The present invention relates to - a vertically disposed cylindrical container having a side wall; at least one draft tube vertically disposed within the vessel, the draft tube having an inner surface and an outer surface, the draft tube providing a first conduit within the draft tube having a tube inlet end and a tube outlet end, and a second conduit within an exterior and sidewall of the draft tube, the first conduit being in fluid communication with the second conduit; at least one nozzle for injecting a fluid into the first conduit from a tube inlet end, the nozzle being disposed concentrically with the draft tube; - reactor fluid outlet means; An inner loop reactor comprising: an inner surface of the draft tube is convexly curved such that the first conduit presents an annular constriction of cross section between the tube inlet end and the tube outlet end, the constriction being located near the tube inlet end, the convex curvature of the inner surface of the draft tube extending over at least 70% of the length of the draft tube; Preferably, the outer surface of the draft tube is convexly curved such that the draft tube presents a peripheral ridge between the tube inlet end and the tube outlet end, the peripheral ridge being located near the tube outlet end, and the convex curvature of the outer surface of the draft tube extends over at least 70% of the length of the draft tube; For internal loop reactors, the edges of the draft tube are rounded.

[0008] The reactor is configured such that a fluid injected through a nozzle travels through a first conduit to obtain a reacted fluid, which is then redirected in the opposite direction to travel through a second conduit and then backmixed with the injected fluid. It has been found that the configuration of the draft tube according to the invention allows the boundary layer flowing over the edge of the draft tube to be controlled. When the angle of attack of the flow against the solid body reaches a certain limit, the adverse pressure gradient becomes too large for the flow to overcome. The flow then separates from the upper surface of the solid body, a condition commonly referred to as stall. The invention allows the flow separation to be reduced or delayed. The reduced flow separation reduces the pressure drop along the streamlines of the recirculating flow due to reduced liquid friction, which results in an improved circulation rate of the configuration. The curved shape of the inner surface of the draft tube wall guides the fluid through the draft tube in an optimized manner, comparable to the flow of the fluid over an airfoil.

[0009] The inner surface of the draft tube is curved in the longitudinal direction of the draft tube, or in other words has a convex shape, so that the first conduit presents a minimum cross-sectional area between the tube inlet end and the tube outlet end, i.e., the cross-section of the first conduit decreases from its cross-section at the tube inlet end to its minimum cross-sectional area and increases from its cross-sectional area at the tube outlet end.

[0010] The draft tube has a curved, generally conical section between the tube inlet end and the constriction, which is wider at the inlet end and narrower at the constriction. At least a portion of the fluid flowing downstream through the draft tube is deflected to flow along the inner surface of the draft tube until the draft tube ends. The flow through the tube remains primarily attached, so little pressure loss occurs. Near the constriction, the fluid flowing downstream through the draft tube is accelerated. Between the constriction and the tube outlet end, the cross-sectional area of ​​the draft tube widens again. As a result, the change in area, together with mass conservation, results in a slower velocity through a larger area than through a smaller area, with a conversion of dynamic pressure to static pressure. As the fluid flowing downstream through the draft tube is accelerated near the constriction, a radial velocity component is added to the flow, increasing mixing between the recirculation flow and the injection flow. By avoiding flow separation in this case, no significant pressure loss occurs.

[0011] In a first embodiment, the loop reactor comprises a draft tube and a nozzle. The inner surface of the draft tube defines a first conduit, and the outer surface of the draft tube and the sidewall of the vessel define a second conduit. In this case, the draft tube is preferably disposed essentially concentrically within the vessel. The nozzle is disposed concentrically with the draft tube.

[0012] In a second embodiment, the loop reactor comprises a plurality of draft tubes, one nozzle concentrically assigned to each draft tube, the draft tubes providing a first conduit defined by the inner surface of the draft tube and a second conduit on the outside of the draft tube and within a sidewall.

[0013] The discussion herein relates to both aspects unless otherwise stated, with embodiments of the first aspect being considered particularly preferred.

[0014] The ratio of the cross section of the first conduit at the constriction to the cross section of the first conduit at the tube outlet end is determined by the requirement to avoid flow separation. Thus, said ratio depends on the distance between the constriction and the tube outlet end. Preferably, the ratio of the cross section of the first conduit at the constriction to the cross section of the first conduit at the tube outlet end is selected so that the average opening angle α at the tube outlet end is 5°-8°. The "opening angle α" refers to the angle between the tangent of the curved inner surface of the draft tube and the tangent of the outer surface.

[0015] As used herein, the term "cross-section" should be understood to relate to the cross-sectional area defined by the perimeter of the region of interest, unless otherwise stated. Thus, the cross-section of the first conduit is defined by the inner surface of the draft tube. Due to the curved or convex shape of the inner surface of the draft tube, the cross-section of the first conduit varies along the length of the first conduit. The length of the first conduit should be understood to relate to the longitudinal extent of the draft tube.

[0016] The draft tube has a constriction between the tube inlet end and the tube outlet end such that the cross section at the constriction is smaller than both the cross sections at the tube inlet end and the cross sections at the tube outlet end. The cross sections of the first conduit at the tube inlet end and the cross sections of the first conduit at the tube outlet end may be essentially the same or different. In a preferred embodiment, the ratio of the cross section of the first conduit at the tube inlet end to the cross section of the first conduit at the tube outlet end is in the range of 0.5 to 3, preferably in the range of 1 to 3, more preferably in the range of 1 to 1.5, e.g. about 1.

[0017] In another preferred embodiment, the ratio of the cross section of the first conduit at the tube inlet end to the cross section of the second conduit at the tube outlet end is in the range of 0.5 to 3, preferably in the range of 1 to 3, more preferably in the range of 1 to 1.5, for example about 1. The cross section of the second conduit, minus the cross section of the tube inlet end, is defined by the side wall of a vertically disposed cylindrical vessel. The cross section of the tube inlet end is understood to include the draft tube wall.

[0018] The convex curvature of the inner surface of the draft tube extends over at least 70%, preferably at least 80%, and most preferably at least 90% of the length of the draft tube.

[0019] Preferably, the outer surface of the draft tube is curved such that the draft tube presents a peripheral ridge or bulge between the tube inlet end and the tube outlet end, the peripheral ridge being located near the tube outlet end. In this embodiment, the draft tube has a convex inner surface and a convex outer surface, or in other words, the draft tube has a biconvex longitudinal section.

[0020] Thus, in the first aspect, the second conduit presents a minimum cross-section between the tube outlet end and the tube inlet end, i.e. the cross-section of the second conduit decreases from the cross-section at the tube outlet end to the minimum cross-sectional area and increases from the minimum cross-sectional area to the cross-section at the tube inlet end. This embodiment is particularly preferred for the reactor of the first aspect.

[0021] The peripheral ridge is preferably located near the tube exit end. In a preferred embodiment, the peripheral ridge of the draft tube is located within 50% of the length of the draft tube from the tube exit end, preferably within 20 to 30% of the length of the draft tube from the tube exit end.

[0022] In a preferred embodiment, the ratio of the outer cross section of the draft tube at the tube outlet end to the maximum cross section of the ridge is in the range 0.3 to 1, preferably in the range 0.5 to 1.

[0023] The convex curvature of the exterior surface of the draft tube extends over at least 70%, preferably at least 80%, and most preferably at least 90% of the length of the draft tube.

[0024] The draft tube is secured to the reactor, for example, via one or more girders or cross beams. The means for securing the draft tube in the reactor advantageously stabilizes the draft tube while minimizing flow resistance. For example, it is preferred that the volume of the means for securing the draft tube to the reactor be as small as possible.

[0025] The spacing between the reactor sidewall and the draft tube can be adjusted to allow the fluid flow to be distributed evenly throughout the reactor. For example, if the space between the reactor sidewall and the draft tube is too large, most of the fluid may flow along the wall while the center of the reactor may have only a small amount of fluid. This can lead to uneven mixing in the second conduit. Thus, the placement of the nozzle, and therefore the draft tube(s), directly affects the mixing efficiency in the reactor.

[0026] The optimum spacing between the reactor sidewall and the draft tubes depends on various parameters, such as the reaction volume, the length and number of draft tubes, and the circulation rate of the reactor. Preferably, the spacing allows the circulating reaction mixture to be drawn into the inlet end of the tube from all sides at an essentially uniform flow rate.

[0027] In one embodiment, the draft tube is provided with openings in its walls (or side regions). The openings allow cross flow of fluid through the draft tube walls without migration through either end of the draft tube. Thus, the openings advantageously reduce pressure loss at the entry of the fluid flow into the draft tube and reduce flow separation. Additionally, the openings induce turbulence, thus improving the mixing efficiency of the reactor. The openings are typically located in the upper portion of the draft tube.

[0028] The openings may be perforations of many different shapes, including rectangular and circular, and are perforations of a size and location that allows a desired level of cross flow through the draft tube wall without significantly impairing the axial flow of the fluid through the draft tube. From the standpoint of ease of manufacture, it is preferred that the openings are slits. In broader embodiments of the invention, the specific shape and pattern of the openings is not particularly limited and will likely be selected depending on ease (or cost) of manufacture. Simple geometric shapes including rectangular, square, circular, and elliptical are some preferred examples. The openings may also be provided with geometric variations that promote turbulence, such as spikes.

[0029] The draft tube is designed to maintain the pressure in the reactor during operation of the reactor as well as during start-up and shutdown of the reactor. If the reaction carried out in the reactor requires high pressure, the draft tube typically comprises a solid or hollow wall with vents for pressure compensation. The manufacturing method of the draft tube must be selected such that the curvature of the profile can be reproduced with high accuracy, preferably by 3D printing and / or sintering.

[0030] The reactor comprises a nozzle for injecting fluid into the first conduit through the tube inlet end. In one embodiment, the nozzle is positioned to inject fluid into the first conduit in a generally downward direction, the draft tube is positioned essentially concentrically below the nozzle, the first conduit being a descending conduit and the second conduit being an ascending conduit. Preferably, the nozzle is positioned in the lid of the reactor. To allow for a high degree of mixing and to avoid stagnation areas, the nozzle should be flush with the lid.

[0031] In another embodiment, the nozzle is positioned to inject fluid into the first conduit in a generally upward direction, the draft tube is positioned essentially concentrically above the nozzle, the first conduit is an ascending conduit, and the second conduit is a descending conduit. Preferably, the nozzle is positioned at the bottom of the reactor. To allow for a high degree of mixing and to avoid stagnation areas, the nozzle should be flush with the bottom of the reactor.

[0032] The nozzle may be a one-component nozzle or a two-component nozzle. In a one-component nozzle, only one liquid is injected through the nozzle. A one-component nozzle presents the advantage of having a simple structure. In a two-component nozzle, two fluids are injected separately through the nozzle and only mix after leaving the nozzle.

[0033] In a preferred embodiment, the nozzle is a two-component nozzle. Such a two-component nozzle may be designed, for example, to provide an annular jet of a first reactant around a central jet of a second reactant. The injection velocities of these two jets may be the same or different. Preferably, the injection velocities are different to provide a high degree of turbulence and therefore a high degree of mixing.

[0034] It is particularly preferred that the two-component nozzle is designed to provide an annular jet of the first reactant around a central jet of the second reactant, with the injection velocities of these two jets being different. In this embodiment, the jet of the first reactant has a large shear plane towards both the central jet of the second reactant and the reaction mixture in the reactor, thereby allowing advantageous fast mixing of the reactants.

[0035] In a preferred embodiment, the ratio of the injection velocity of the second reactant to the injection velocity of the first reactant is in the range of 4:1 to 6:1, preferably in the range of 4.5:1 to 5.5:1, e.g., 5:1. For example, the injection velocity of the first reactant may be about 10 to 30 m / s, preferably 15 to 20 m / s. The injection velocity of the second reactant may be about 70 to 100 m / s, preferably 80 to 90 m / s.

[0036] In a second embodiment, the loop reactor comprises multiple draft tubes, with one nozzle concentrically arranged in each draft tube. In this embodiment, the nozzles are preferably operated in parallel. By arranging multiple nozzles in parallel, throughput can be increased while maintaining proper fluid mixing of the reaction mixture compared to a single nozzle. Preferably, multiple nozzles are arranged around a central nozzle. For example, three or more nozzles, such as four, five, or most preferably six nozzles, are arranged around the central nozzle. Preferably, three or more nozzles, such as four, five, or most preferably six nozzles, are arranged concentrically around the central nozzle.

[0037] The design of the deflection area, for example the shape of the draft tube edges and the presence and shape of the deflection means, may be modified to allow high circulation rates at low pressure drop.

[0038] In a preferred embodiment, the loop reactor comprises a deflection means arranged between the nozzle and the draft tube, the deflection means being suitable for deflecting the fluid traveling in the second conduit in an opposite direction.

[0039] The deflection means preferably comprises a surface that is concave with respect to the end of the draft tube that defines the tube inlet end. In a preferred embodiment, the deflection means has a partial toroidal surface. It is particularly preferred that the deflection means is provided in the shape of an upper part of a ring torus bisected by a plane parallel to the toroidal direction. This shape allows a particularly efficient deflection of the fluid moving in the second conduit. The deflection means may allow a stabilization of the injection fluid stream. This is particularly appropriate when the flow rate of the fluid moving in the second conduit is not uniform over the cross section of the reactor, which may lead to eccentricity of the injection fluid stream. Such eccentricity, if not addressed, may reduce the circulation rate.

[0040] In the case where the first conduit is a descending conduit and the second conduit is an ascending conduit, the shape of the deflection means preferably constitutes an upper part of a ring torus bisected by a plane parallel to the toroidal direction, the ring torus being bisected at least 50% of its height, for example at least 55% or 65% of its height. Thus, the upper part of the ring torus is the same size as or smaller than the lower part of the ring torus. In another preferred embodiment, the shape of the deflection means constitutes an upper part of a ring torus bisected by a plane parallel to the toroidal direction, the ring torus being bisected at most 85% of its height, for example at 80% of its height. In these ranges, the inlet of the deflection means is angled in a way that is particularly suitable for deflecting the fluid.

[0041] In the case where the first conduit is an ascending conduit and the second conduit is a descending conduit, the shape of the deflection means preferably constitutes the lower part of a ring torus bisected by a plane parallel to the toroidal direction, the ring torus being bisected at most 50% of its height, for example at most 45% or 35% of its height. Thus, the lower part of the ring torus is the same size as or smaller than the upper part of the ring torus. In another preferred embodiment, the shape of the deflection means constitutes the lower part of a ring torus bisected by a plane parallel to the toroidal direction, the ring torus being bisected at least 15% of its height, for example at most 20% of its height. In these ranges, the inlet of the deflection means is angled in a way that is particularly suitable for deflecting the fluid.

[0042] Preferably, the deflection means is not attached to the reactor lid or reactor bottom, but is arranged such that the gap between the reactor and the deflection means is large enough to avoid stagnation areas. For example, when the nozzle is arranged to inject fluid into the first conduit in a generally downward direction, the gap between the reactor lid and the deflection means is at least 15 mm, such as at least 20 mm. Similarly, when the nozzle is arranged to inject fluid into the first conduit in a generally upward direction, the gap between the reactor bottom and the deflection means is at least 15 mm, such as at least 20 mm. In a preferred embodiment, the deflection means is attached to a draft tube.

[0043] The loop reactor allows high circulation ratios, which should be understood as the total mass flow through the mixing draft divided by the feed mass flow rate. The total mass flow includes the feed mass flow and the entrained fluid circulating through the reactor. At circulation ratios above 10:1, the system advantageously approaches the behavior of a continuous stirred tank reactor (CSTR). Preferably, the circulation ratio is at least 15:1, preferably above 20:1.

[0044] As mentioned above, the first conduit is defined by the inner surface of the draft tube, and its length corresponds to the shortest distance between the tube inlet end and the tube outlet end. Similarly, the second conduit is defined by the outer surface of the draft tube, and its length corresponds to the shortest distance between the tube outlet end and the tube inlet end. Thus, the edges of the draft tube limit the spread of the first and second conduits. Although the edges of the draft tube are rounded, this should be understood to mean that the edges of the draft tube do not have sharp edges, but smoothly follow the curvature of the inner and outer surfaces of the draft tube, respectively. The rounded edges help the mixture of reactants and reaction products to adhere to the surfaces when deflected in the opposite direction. Such a draft tube design allows for low pressure drop and therefore high circulation rates.

[0045] The invention further relates to a process for carrying out a continuous high pressure reaction, wherein a fluid is introduced into the above-mentioned loop reactor and the reacted fluid is removed through the fluid outlet of the loop reactor.

[0046] The internal loop reactor of the present invention is useful in reaction processes requiring effective mixing between gas-liquid or liquid-liquid materials, uniform distribution of gas or liquid in the liquid phase, high flow rates of liquid along specific directions, and high mass transfer rates. The internal loop reactor of the present invention is particularly useful in reactions where mass transfer is the controlling step of the overall reaction process, or in high temperature and pressure reaction systems.

[0047] A specific example of a commercial process is a process for producing isoprenol (3-methyl-3-buten-1-ol) by reaction of a formaldehyde source, such as an aqueous formaldehyde solution, with isobutylene.

[0048] Although initial rapid and vigorous mixing of the reactants is desirable, it may be advantageous to continue and complete the reaction under conditions of limited backmixing. Thus, the reaction mixture may be passed to a post-reaction chamber located after the reactor of the present invention, where backmixing is limited.

[0049] The geometry of the draft tube can be controlled to improve the hydrodynamic dynamics throughout the reactor. By optimizing the draft tube geometry, higher circulation rates can be achieved to obtain maximum mixing efficiency. Among the parameters that can be controlled to achieve these results are maximum thickness, maximum length, location of the annular constriction, and / or optionally the location of the peripheral ridge.

[0050] To limit the computational demands of the optimization, the method may include selecting a predefined airfoil shape, which is then numerically optimized with respect to various design variables or parameters describing the airfoil shape.

[0051] Preferably, the predefined airfoil shape is selected from the NACA (National Advisory Committee for Aeronautics) airfoils, whose shape is described using a series of numbers. The digits of the numerical code can be entered into specific mathematical formulas to accurately generate the cross section of the airfoil and calculate its characteristics. Thus, a NACA four-digit airfoil section defines a profile by the first digit expressing the maximum camber as a percentage of the chord, the second digit expressing the distance of the maximum camber from the leading edge of the airfoil in tenths of the chord, and the last two digits expressing the maximum thickness of the airfoil as a percentage of the chord. For example, the NACA 2412 airfoil has a maximum camber of 2%, with the maximum camber located 40% from the leading edge (i.e. 0.4 times the chord) and a maximum thickness of 12% of the chord.

[0052] Suitable NACA airfoils include symmetrical or slightly asymmetrical airfoils, such as 4-digit airfoils of the types NACA 0XXX to NACA 2XXX, and airfoils having a thickness in the range of 10 to 20% of the airfoil length, such as 4-digit airfoils of the types NACA XX10 to NACA XX20. A particularly preferred type of airfoil is the NACA2412.

[0053] The maximum profile selection is determined by the length to thickness ratio of the reactor and draft tube design. Small variations in the leading and trailing edges of the profile can be made up to 20% of the length and may be necessary to "marry" the inner and outer profile shapes of the tube.

[0054] The design of the draft tube consists of the following steps: 1) selecting a standard profile description of an airfoil, in particular an airfoil selected from the group consisting of NACA 0XXX to NACA 2XXX or NACA XX10 to NACA XX20, preferably NACA 2412; 2) Scaling the profile according to the design dimensions of the reactor; and 3) Imagine the half-airfoil profile on the inside surface of the draft tube with the leading edge of the profile pointing towards the nozzle, and Assuming a half-airfoil profile on the outer surface of the draft tube with the trailing edge pointing towards the nozzle, where changes in the leading and trailing edges of the profile can be made within a maximum range of 20% of the length; 4) Optimizing the draft tube shape by computational fluid dynamics by varying the parameters describing the airfoil shape to reach the highest circulation rate; It can be optimized by:

[0055] Comparative computational fluid dynamics, taking into account the reactor kinetics, can be used to confirm the selectivity and conversion obtained by the optimized design. Kinetics calibration can be based on known selectivity and conversion obtained from existing reactor configurations.

[0056] The present invention will now be described in detail with reference to the accompanying drawings and examples. [Brief description of the drawings]

[0057] [Figure 1] FIG. 2 is a schematic side view of a comparative loop reactor. [Diagram 2]FIG. 1 is a schematic side view of a loop reactor according to the present invention. [Diagram 3] FIG. 2 is a schematic side view of a further loop reactor according to the invention; [Figure 4] FIG. 4 is a schematic top view of the deflection means shown in FIG. [Diagram 5] FIG. 1 is a schematic excerpt of the flow pattern in a known internal loop reactor with a cylindrical draft tube, obtained via CFD calculations. [Figure 6] FIG. 2 is a schematic excerpt of the flow pattern in an internal loop reactor according to the present invention obtained via CFD calculations. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0058] 1, the reactor 101 comprises a vertically disposed cylindrical vessel 102 with a sidewall, and a draft tube 103 disposed vertically and concentrically within the vessel. The draft tube has a tube inlet end 104, a tube outlet end 105, an inner surface, and an outer surface. The draft tube provides a first conduit 103 within the draft tube and a second conduit on the outside of the draft tube 103 and within the sidewall, the first conduit being in fluid communication with the second conduit.

[0059] The reactor 101 further comprises a nozzle 106 for injecting fluid into the first conduit from the tube inlet end 104. The nozzle is concentrically disposed above the draft tube 103. The reactor is designed such that when fluid is injected through the nozzle 106, the draft tube 103 provides a downflow conduit within the draft tube 103 and an upflow conduit outside the draft tube 103.

[0060] The reactor is provided with a reactor fluid outlet means (not shown in FIG. 1) through which the reaction products may be guided out of the reactor and subjected to further processing.

[0061] 2, reactor 201 comprises a vertically oriented cylindrical vessel 202 having a sidewall, and a draft tube 203 disposed vertically and concentrically within the vessel. The draft tube has a tube inlet end 204, a tube outlet end 205, an inner surface, and an outer surface.

[0062] The reactor 201 further comprises a nozzle 206 for injecting a fluid into the first conduit from the tube inlet end 204. The nozzle is concentrically disposed above the draft tube 203. The reactor is designed such that when a fluid is injected through the nozzle 206, the draft tube 203 provides a downflow conduit within the draft tube 203 and an upflow conduit outside the draft tube 203.

[0063] The inner surface of the draft tube 203 is curved such that the first conduit presents a cross-sectional constriction 207. The outer surface of the draft tube 203 is curved such that the draft tube 203 presents a peripheral ridge 208 located near the tube exit end 205. The draft tube provides a first conduit within the draft tube 203 and a second conduit on the outside and in a sidewall of the draft tube 203, the first conduit being in fluid communication with the second conduit.

[0064] The reactor may be provided with a reactor fluid outlet means (not shown in FIG. 2) through which the reaction products may be guided out of the reactor for further processing.

[0065] 3, reactor 301 comprises a vertically oriented cylindrical vessel 302 having a sidewall, and a draft tube 303 disposed vertically and concentrically within the vessel. The draft tube has a tube inlet end 304, a tube outlet end 305, an inner surface, and an outer surface.

[0066] The reactor 301 further comprises a nozzle 306 for injecting fluid into the first conduit from the tube inlet end 304. The nozzle is positioned concentrically above the draft tube 303. The reactor is designed such that when fluid is injected through the nozzle 306, the draft tube 303 provides a downflow conduit within the draft tube 303 and an upflow conduit outside the draft tube 303.

[0067] The inner surface of draft tube 303 is curved such that the first conduit presents a cross-sectional constriction 307. The outer surface of draft tube 303 is curved such that draft tube 303 presents a peripheral ridge 308 located near the tube exit end 305. The draft tube provides a first conduit within draft tube 303 and a second conduit on the outside and in a sidewall of draft tube 303, the first conduit being in fluid communication with the second conduit.

[0068] Furthermore, the reactor 301 comprises a deflection means 309 in the form of an upper part of a ring torus bisected by a plane parallel to the toroidal direction, the top view of which is shown in Figure 4. The deflection means 309 is designed to deflect the fluid moving upwards in the riser conduit in a downward direction, backmixing the fluid with the inlet fluid.

[0069] The reactor may be provided with a reactor fluid outlet means (not shown in FIG. 3) through which the reaction products may be guided out of the reactor for further processing. EXAMPLES

[0070] The internal loop reactor was evaluated by computational fluid dynamics simulations for the circulation rate (i.e. the total mass flow through the mixing draft divided by the feed mass flow rate) and the reaction selectivity. The total mass flow includes the feed mass flow and the entrained fluid circulating through the reactor. A commercial CFD code (ANSYS FLUENT) based on the finite volume method was used for the calculations. Numerical sub-models were used to consider turbulence, as well as temperature- and mixture-dependent material properties. The boundary conditions were obtained from the actual unit design conditions. As mentioned above, the draft tube geometry was optimized by varying the parameters describing the airfoil shape to reach the highest circulation rate.

[0071] Example 1 (Comparative) An internal loop reactor is assumed with a cylindrical draft tube located at the top of the reactor below nozzles for injecting isobutylene and formaldehyde. The top of the reactor, which forms a mixing chamber, is located above a post-reaction chamber located at the bottom of the reactor. The mixing and post-reaction chambers are separated by a perforated plate.

[0072] For the reactor, a mixing section height of about 5 m, a reactor diameter of about 1.4 m, and a draft tube length of about 3.5 m were assumed.

[0073] An aqueous formaldehyde solution (40 wt %) and supercritical isobutylene were assumed to be injected into a reactor having a pressure of 250 bara and a temperature of 270°C.

[0074] The reactor achieved a circulation rate (at 100% design load) of 20. The reaction selectivity in the mixing section of the reactor was calculated to be 70%.

[0075] At 50% design load, the reactor achieved a circulation rate of approximately 30%.

[0076] The flow pattern obtained from the CFD calculations of this reactor is shown in Figure 5. Figure 5 depicts a radial cross section from the central axis of the draft tube (far right in Figure 5). The upper portion of the draft tube wall, including the upper edge, is designated 501. The shaded area 502 indicates net upflow. The unshaded area 503 indicates net downflow.

[0077] The flow pattern shows a net upward flow outside the draft tube. Within the draft tube, there is a net downward flow 502. However, there is significant net upward flow along the inside wall of the draft tube. This indicates flow separation that leads to stagnation areas that increase pressure drop and reduce circulation rate.

[0078] Example 2 Consider an internal loop reactor according to the present invention, with a draft tube located at the top of the reactor below the nozzles injecting isobutylene and formaldehyde. The design of the draft tube was optimized according to the process discussed above, with NACA 2412 being selected as the standard profile description for the airfoil. The top of the reactor, which constitutes the mixing chamber, is located above a post-reaction chamber located at the bottom of the reactor. The mixing and post-reaction chambers are separated by a perforated plate.

[0079] For the reactor, a mixing section height of about 5 m, a reactor diameter of about 1.4 m and a draft tube length of about 3.2 m were assumed. The draft tube was shaped according to the present invention.

[0080] An aqueous formaldehyde solution (40 wt %) and supercritical isobutylene were assumed to be injected into a reactor having a pressure of 250 bara and a temperature of 270°C.

[0081] The reactor achieved a circulation ratio (at 100% design load) of 30. The reaction selectivity in the mixing section of the reactor was calculated to be 70 to 75%.

[0082] At 50% design load, the reactor achieved a circulation rate of approximately 50%.

[0083] It is clear that the reactor according to the present invention can improve the circulation rate and increase the selectivity.

[0084] The flow pattern obtained from the CFD calculations of this reactor is shown in Figure 6. Figure 6 depicts a radial cross section from the central axis of the draft tube (far right in Figure 6). The upper portion of the draft tube wall, including the upper edge, is designated 601. The shaded area 602 indicates net upflow. The unshaded area 603 indicates net downflow.

[0085] The flow pattern shows a net upflow outside the draft tube. Within the draft tube, there is a net downflow 602. There is a region of negligible net upflow along the inside wall of the draft tube, indicating essentially no flow separation. Thus, higher circulation rates and better mixing of the reactants are achieved, resulting in higher selectivity.

Claims

1. a vertically disposed cylindrical container (202) having a sidewall; at least one draft tube (203) vertically disposed within the vessel, the draft tube (203) having an inner surface and an outer surface, the draft tube (203) having a tube inlet end (204) and a tube outlet end (205), providing a first conduit within the draft tube (203) and a second conduit outside the draft tube (203) and within the sidewall, the first conduit being in fluid communication with the second conduit; at least one nozzle (206) for injecting a fluid into the first conduit from the tube inlet end (204), the nozzle (206) being concentrically disposed with the draft tube (203); reactor fluid outlet means; An inner loop reactor (201) comprising: the inner surface of the draft tube (203) is convexly curved such that the first conduit presents a cross-sectional annular narrowing (207) between the tube inlet end (204) and the tube outlet end (205), the narrowing being located near the tube inlet end (204), and the convex curvature of the inner surface of the draft tube (203) extends over at least 70%, preferably at least 80%, and most preferably at least 90% of the length of the draft tube; the outer surface of the draft tube (203) is convexly curved such that the draft tube (203) presents a peripheral ridge (208) between the tube inlet end (204) and the tube outlet end (205), the peripheral ridge (208) being preferably located near the tube outlet end (205), the convex curvature of the outer surface of the draft tube (203) extending over at least 70%, preferably at least 80%, and most preferably at least 90% of the length of the draft tube; An internal loop reactor (201) wherein the edges of said draft tube (203) are rounded.

2. 2. The reactor (201) of claim 1, wherein the ratio of the cross section of the first conduit at the constriction to the cross section of the first conduit at the tube outlet end (205) is selected so that the average opening angle α at the tube outlet end (205) is between 5° and 8°.

3. 2. The reactor (201) of claim 1, wherein a ratio of the cross section of the first conduit at the tube inlet end (204) to the cross section of the first conduit at the tube outlet end (205) is in the range of 0.5 to 3.

4. 2. The reactor (201) of claim 1, wherein a ratio of the cross section of the first conduit at the tube inlet end (204) to the cross section of the second conduit at the tube outlet end (205) is in the range of 0.5 to 3.

5. 2. The reactor (201) of claim 1, wherein the ratio of the outer cross section of the draft tube at the tube outlet end (205) to the maximum cross section of the ridge (208) is in the range of 0.3 to 1.

6. 10. The reactor (201) of claim 1, comprising a draft tube (203) concentrically disposed within the vessel and a nozzle (206) concentrically disposed within the draft tube (203).

7. 2. The reactor (201) of claim 1, comprising a plurality of draft tubes (203), one nozzle (206) concentrically assigned to each draft tube (203).

8. 2. The reactor (301) of claim 1, further comprising: a deflection means (309) disposed between the nozzle (306) and the draft tube (308), the deflection means (309) adapted to deflect fluid traveling in the second conduit in an opposite direction, the deflection means (309) having a partial toroidal surface.

9. 2. The reactor (201) of claim 1, wherein the nozzle (206) is positioned to inject the fluid into the first conduit in a generally downward direction, the draft tube (203) is positioned essentially concentrically below the nozzle (206), the first conduit is a downcomer conduit, and the second conduit is an upcomer conduit.

10. 2. The reactor (201) of claim 1, wherein the nozzle (203) is positioned to inject the fluid into the first conduit in a generally upward direction, the draft tube (203) is positioned essentially concentrically above the nozzle (206), the first conduit is an ascending conduit, and the second conduit is a descending conduit.

11. 10. A process for conducting a continuous high pressure reaction, wherein a fluid is introduced into the internal loop reactor (201) of claim 1 and a reacted fluid is removed through the fluid outlet of the loop reactor (201).

Images