Shell and tube type heat exchange reactor for performing catalytic gas phase partial oxidation reaction and process for performing catalytic gas phase partial oxidation

Abstract

A shell-and-tube type heat exchange reactor for performing a catalytic gas-phase partial oxidation reaction, comprising a shell-side heat exchange passage for circulating a heat transfer medium and a reaction passage including a plurality of reaction tubes, an inlet for introducing a reaction stream into the reaction passage, and an outlet from the reaction passage for recovering the discharge stream from the reaction tubes. The reaction tubes include a reactant preheating zone adjacent to the inlet and a reaction zone downstream of the reactant preheating zone, the reaction zone having a catalytically active wire matrix insert having a catalytically active noble metal on at least a part of its surface. This reactor reduces the need for frequent maintenance in the form of catalyst regeneration and / or replacement. The catalyst can be easily arranged in the reaction tubes and can be easily removed from the reaction tubes. Only the portion of the entire reaction stream that flows near the wall of the hot reaction tubes is heated. As a result, the portion of the reaction stream flowing through the center of the reaction tubes is not heated to the reaction temperature, and thus blind reactions of unstable starting materials are reduced or even avoided.

Description

Technical Field

[0001] The present invention relates to a shell-and-tube type heat exchange reactor for performing a catalytic gas-phase partial oxidation reaction, including a shell-side heat exchange passage for circulating a heat transfer medium and a reaction passage including a plurality of reaction tubes, an injection port for introducing a reaction material flow into the reaction passage, and an outlet from the reaction passage for collecting the discharge flow from the reaction tubes. The present invention further relates to a process for performing a catalytic gas-phase partial oxidation reaction in a shell-and-tube type heat exchange reactor. The present invention further relates to a process for preparing prenol, 3,7-dimethyl-octa-2,6-dienal (citral), menthol, and linalool.

Background Art

[0002] Catalytic gas-phase reactions in the chemical industry, such as oxidation, hydrogenation, dehydrogenation, nitration, alkylation, etc., are usually carried out using a shell-and-tube type reactor with a solid catalyst disposed in a fixed bed. Such reactions carried out in a shell-and-tube type reactor can be either endothermic or exothermic reactions. The fixed bed is located within the reaction tubes of the shell-and-tube type reactor. Currently, commonly used shell-and-tube type reactors can have at least 5,000 to a maximum of 45,000 reaction tubes. This plurality of reaction tubes is called a reaction tube bundle and is generally arranged annularly and vertically and surrounded by a reactor shell. Both ends of the aforementioned reaction tube bundle are sealed with tube sheets. The feed gas flow is usually introduced into the upper part of the shell-and-tube type reactor through a hood and supplied to the reaction tubes through the tube sheet. The resulting product gas mixture is discharged to the lower part of the shell-and-tube type reactor through the opposite tube sheet and hood. Alternatively, the feed gas flow is introduced into the lower part of the shell-and-tube type reactor and discharged from the shell-and-tube type reactor through the upper tube sheet and hood.

[0003] Catalysts containing a catalytically active noble metal such as copper or silver on a suitable support are known to be useful for catalyzing specific chemical oxidation reactions. Catalysts commonly used in the fixed beds of state-of-the-art processes include, for example, a porous solid catalyst impregnated with silver for oxidizing ethylene to ethylene oxide, or, for example, a shell catalyst coated with silver for oxidizing isoprenol to prenal, or for oxidizing a primary alcohol to an aldehyde, etc.

[0004] Introducing such a catalyst composed of individual catalyst bodies into a reaction tube and settling the catalyst in a fixed bed is a complex and time-consuming process. For example, it is necessary to measure the filling level to confirm that there is a sufficient amount of catalyst in the reaction tube.

[0005] Gas-phase fixed-bed tubular catalytic reactors often exhibit an undesirable temperature profile along the length of the reaction tube. Typically, the temperature profile of an exothermic catalytic reaction is low at the inlet, rises to a maximum, and then decreases as the reactants in the reaction stream are depleted.

[0006] When the temperature of the reactor is outside the optimal temperature range for a specific reaction, undesirable products are formed, resulting in a decrease in selectivity. Thus, at temperatures below the ignition temperature of the reaction, organic components of the feed gas stream deposit on the surface of the active catalyst material in the reaction tube in the form of carbonaceous deposits, for example, in the form of coke. As a result of this deposition, a part of the active catalyst material is deactivated, and the pressure drop also increases as the deposition increases. Therefore, regular maintenance in the form of catalyst regeneration and / or even replacement is necessary. For example, when using the above-mentioned shell catalyst coated with silver to oxidize isoprenol to prenal, it is necessary to perform a maintenance process in the form of regeneration once a week. As a result, the annual operating hours are significantly shortened, and the existing production capacity cannot be fully utilized.

[0007] Furthermore, in a catalyst material with high thermal conductivity such as copper or silver, there may be generated a "moving hot spot", i.e., a hot spot moving in the direction of the inlet of the reaction tube. As a result, the residence time of the formed target product becomes longer, which in turn leads to subsequent reactions of the target product and a decrease in the selectivity to the target product.

[0008] The occurrence of a significant and undesirable temperature "bump" or "hot spot" is caused by insufficient heat transfer between the catalyst and the heat transfer medium in the reaction tube. To mitigate this problem, attempts have been made to provide a non-catalytic heat exchange region in front of the reaction region filled with the catalyst in the reaction tube so that the reaction stream is heated to the reaction start temperature before contacting the catalyst. Also, to avoid further undesirable reactions of the product as much as possible and to recover the product in an unchanged form as much as possible, it has been proposed to provide a heat exchange region downstream of the reaction region where the effluent stream is heat-exchanged with the heat transfer medium and thereby cooled.

[0009] To optimize the function of the heat exchange region for industrial-scale use, various packing materials existing as individual elements such as balls or rings are recommended as flow obstacles in the heat exchange region. However, these packing materials have the drawbacks of causing a significant pressure loss on the one hand and rapid deposition of combustion residues due to their large specific surface area on the other hand. In addition, heat exchange through the wall of the reaction tube is not efficient because the reaction stream is forced to pass through the voids in the packing of the individual elements.

[0010] U.S. Patent Application Publication No. 2007 / 274882 relates to a reactor comprising at least (a) a reaction region containing at least one solid catalyst and (b) a coolable heat exchanger region containing at least one housing that at least partially houses an insert, where the reaction region and the coolable heat exchanger region are in fluid communication.

[0011] U.S. Patent Application Publication No. 2012 / 0277473 describes a process for producing C1-C 10 aldehydes by oxidative dehydrogenation of C1-C 10 alcohols on a shaped catalyst support that can be obtained by three-dimensional shaping and / or spatial arrangement of silver-containing fibers and / or threads. The average diameter or average diagonal length of the substantially rectangular or square cross-section of these silver-containing fibers and / or threads is in the range of 30 μm to 200 μm. SUMMARY OF THE INVENTION PROBLEM TO BE SOLVED BY THE INVENTION

[0012] Accordingly, an object of the present invention is to provide a reactor for performing a catalytic gas-phase partial oxidation reaction that requires reducing the frequency of maintenance in the form of catalyst regeneration and / or replacement. A further object of the present invention is to facilitate the placement of the catalyst in the reaction tube and its removal therefrom. MEANS FOR SOLVING THE PROBLEM

[0013] Accordingly, the present invention provides - a reaction passage including a shell-side heat exchange passage for circulating a heat transfer medium and a plurality of reaction tubes, - an inlet for introducing a reaction stream into the reaction passage, - an outlet from the reaction passage for recovering the discharge stream from the reaction tubes, and relates to a shell-and-tube type heat exchange reactor for performing a catalytic gas-phase partial oxidation reaction, The reaction tubes include a reactant preheating zone adjacent to the inlet, a reaction zone downstream of the reactant preheating zone, which has a catalytically active wire matrix insert having a catalytically active noble metal on at least a part of its surface, and.

[0014] As used herein, "downstream" or "upstream" refers to the flow direction of the reaction stream.

[0015] The term "reactant preheating zone" refers to a section of the reaction tube, i.e., a section within the reaction tube where essentially no catalytic gas-phase partial oxidation reaction occurs and the gas flow through the reaction tube is heat-exchanged via the circulating heat transfer medium and the wall of the tube. The preheating zone upstream of the reaction zone is accompanied by a net heat flow into the reaction tube, ensuring that when the reactant stream reaches the reaction zone, the reactant stream is sufficiently heated to a temperature close to or at the reaction temperature.

[0016] When contacting the catalyst surface, the oxidation reaction starts immediately. Otherwise, if a "cold" reactant stream that does not reach the reaction start temperature of the reaction reaches the catalyst surface, coke formation may occur. With less coke formation, advantageously, the operation of the reactor can be prolonged without the need to burn off coke from the catalyst surface.

[0017] Preferably, the reactant preheating zone is adapted to enable laminar flow of the reactants within the reactant preheating zone. That is, there are no obstacles to the reactant stream that would cause a transition from laminar flow to turbulent flow in the reactant preheating zone. Thus, the reactant preheating zone preferably has an essentially free cross-section, i.e., the preheating zone is empty.

[0018] In the case of an "essentially free cross-section", the reactant preheating zone can be empty. Alternatively, the reactant preheating zone can accommodate fixtures made of a material with zero or limited catalytic activity, and these fixtures have a negligible cross-section in a plane perpendicular to the longitudinal axis of the reaction tube. The aforementioned fixtures can be attached to the catalytically active wire matrix present in the reaction zone, and the aforementioned wire matrix inserts can be easily placed in or removed from the reaction zone. For example, what may not need to be attached can be stainless steel wires or rods.

[0019] With this setup, only the portion of the entire reaction stream that flows near the wall of the hot reaction tube can be heated. As a result, the portion of the reaction stream flowing through the center of the reaction tube is not heated to the reaction temperature, and thus, the blind reaction of the unstable starting material is reduced or even avoided. A "blind reaction" is a non-selective oxidation reaction that occurs in the absence of a catalyst. When the reaction stream reaches the reaction zone, the oxidation reaction is initiated. Since this reaction is exothermic, energy is released, and the rest of the reaction stream is rapidly heated to the reaction start temperature, and the reaction proceeds. This rapid heating of most of the reaction mixture reduces unwanted side reactions and thus improves selectivity.

[0020] Alternatively, the reactant preheating zone may have a wire matrix insert with zero or limited catalytic activity. The wire matrix insert can reduce or eliminate the temperature gradient without causing any flow obstacles that promote turbulent flow characteristics. The wire matrix insert does not significantly catalyze the gas-phase partial oxidation reaction in question and is considered to have zero (or in other words, "inactive") catalytic activity when the chemical composition of the flow passing through the wire matrix insert does not change significantly. Similarly, when the catalytic activity of the matrix insert is lower than that of the reaction zone, the matrix insert is considered to have limited catalytic activity. In one embodiment, the wire matrix insert with zero or limited catalytic activity is made of an inert material, preferably stainless steel.

[0021] As used herein, the term "reaction zone" refers to the region of the reaction tube where the catalytic gas-phase partial oxidation reaction occurs. According to the present invention, the reaction zone includes a catalytically active wire matrix insert having catalytically active noble metal on at least a part of its surface. Since the wire matrix included in the reaction zone has a more open structure compared to the packing of individual elements, most of the reaction heat is released to the wall of the reaction tube by radiation and does not need to be dissipated by the reaction fluid stream. The specific flow characteristics of the reaction fluid stream passing through the reaction tube with the wire matrix insert attached improve heat transfer through the wall of the tube. The formation of significant hot spots can be avoided. As a result, the organic components of the reaction fluid stream are prevented from depositing on the surface of the active catalyst material and the accompanying pressure drop from occurring. Overall, the need for regular maintenance in the form of catalyst regeneration and / or replacement is reduced. Since the annual operating hours can be increased and the existing production capacity can be utilized to the maximum, the operating costs are reduced and the profits are increased.

[0022] In contrast to individually existing catalyst bodies, the wire matrix insert can be formed continuously or integrally. Therefore, it becomes very easy to place the wire matrix insert in the catalyst confinement region of the reaction tube and remove it therefrom.

[0023] The "reaction zone" can be composed of a single continuous reaction zone. Alternatively, the reaction zone can include regions having catalytically active wire matrix inserts alternating with regions having essentially free cross-sections or wire matrix inserts having zero or limited catalytic activity.

[0024] The "wire matrix insert" is understood to be a self-supporting skeletal structure made of coiled, curved, or crimped metal wires adapted to be inserted into the reaction tube of a shell-and-tube reactor. The wire matrix insert has a structure with a larger volume than the longitudinal wires.

[0025] Fasteners such as stainless steel wires or rods can be attached to the wire matrix insert, thereby allowing the wire matrix insert to be easily placed in the reaction zone or easily removed from the reaction zone.

[0026] In one embodiment, the catalytically active wire matrix insert includes an elongated core having a plurality of wire loops extending from the elongated core, where the wire loops are arranged longitudinally and are helically shifted, i.e., adjacent wire loops have an angular offset. The loops can be formed by helically bending the wire over the length of the wire matrix insert. Considering ease of manufacture, the elongated core preferably includes at least two longitudinal core wire members, and these core wire members are twisted together to form a winding of the core wire, and the wire loops are accommodated in the winding of the core wire.

[0027] The wire loops can be formed from a single wire, or one or more intertwined wires, preferably four intertwined wires.

[0028] The wire matrix insert included in the reaction zone has a catalytically active noble metal on at least a portion of its surface. The wire forming the wire loop can be a bulk noble metal wire or a wire coated with a noble metal. The core wire can be made of brass alloy or high-grade steel. The thickness of the noble metal coating layer deposited on the surface of the core is, for example, 10 μm. However, generally, a bulk noble metal wire has a longer service life and is preferred. When the wire loops are formed from a plurality of intertwined wires, at least one of the intertwined wires is made of a bulk noble metal wire or a wire coated with a noble metal, while the other intertwined wires can be made of an inert material.

[0029] Generally, the catalytically active noble metal is selected from copper, silver, palladium, platinum, ruthenium, and rhodium, preferably silver. A silver wire having the same composition throughout its cross-section and containing at least 92.5 wt% Ag can be suitably used. The silver wire is bent in a helical shape to form a wire loop and is combined with at least two longitudinal core wire members, which are twisted together to form a winding of the core wire, and the wire loop is accommodated in the winding of the core wire. The longitudinal core wire members can also be silver wires or inert metal wires.

[0030] Generally, the catalytically active wire matrix insert has a cylindrical envelope surface with a diameter that matches the inner diameter of the reaction tube. This includes the state where the diameter of the cylindrical envelope surface of the undeployed wire matrix insert is slightly larger than the inner diameter of the reaction tube. Due to the elasticity or resilience of the wire matrix insert, the wire loop can be inserted into the reaction tube with a slight backpressure so that it fits tightly against the inner wall of the reaction tube.

[0031] A suitable structure of the wire matrix insert is known as described in British Patent Application Publication No. 2097910. A part of this type of insert is disclosed in British Patent Application Publication No. 1570530. Other inserts, and their manufacturing processes, are disclosed in British Patent Application Publication No. 2097910A. The matrix insert is commercially available from Cal Gavin Ltd., England and is sold under the trade name HiTRAN®.

[0032] In one embodiment, the porosity of the reaction zone of the reaction tube is 0.60 to 0.99, preferably 0.80 to 0.97, more preferably 0.89 to 0.94. The "porosity" is defined as the ratio of the void volume (i.e., the total volume of the void space within the cylinder enclosing the wire matrix insert) to the total volume occupied by the wire matrix insert (i.e., the volume of the cylinder enclosing the wire matrix insert). In other words, the porosity is defined as the ratio of the void volume to the sum of the void volume and the volume occupied by the wire loops and the elongated cores constituting the wire matrix insert.

[0033] Since the porosity of the wire matrix contained in the reaction zone is high compared to the packing of individual elements such as the fixed bed of individual catalyst particles, most of the reaction heat is released to the wall of the reaction tube by radiation and does not need to be dissipated by the reaction fluid flow.

[0034] In one embodiment, the catalytically active wire matrix insert is adapted to radially mix the laminar boundary layer of the reaction fluid flow through the reaction tube into the bulk reaction fluid flow. Convective heat transfer generally involves the exchange of thermal energy between a surface and a moving fluid. The arranged wire matrix insert disrupts the flow boundary layer close to the wall, and the reaction fluid flow forms relatively weak vortices near the wall, thereby reducing the thermal resistance of the fluid at the wall. Due to the spiral offset of the wire matrix insert causing the fluid to rotate, the fluid flows from the center of the tube towards the wall and collides and mixes again with the vortices generated by the wire loops near the wall, thereby enhancing heat transfer.

[0035] Preferably, the catalytically active wire matrix insert is adapted to allow a flow of the reaction stream characterized by a Reynolds number of 12,000 or less, preferably 8,000 or less, more preferably 2,300 or less. In such a low Reynolds flow regime, the flow velocity is low and the level of flow turbulence is relatively low, so the pressure drop across the tube due to the wire matrix insert is not a major concern. Due to these low Reynolds numbers, the heat transfer between the catalytically active wire matrix insert and the inner wall of the reaction tube is 3 to 5 times better compared to the normal fixed bed packing of individual elements such as balls or rings. At such low Reynolds numbers, heat transport by conduction and radiation in the direction of the reaction tube wall is preferred over convection. Both conduction and radiation are improved by the open wire matrix insert. Suitably, regions having an essentially free cross-section, or regions having a wire matrix insert with zero or limited catalytic activity, such as a reactant preheating zone, are adapted to allow a flow of the reaction stream characterized by a Reynolds number of 12,000 or less, preferably 8,000 or less.

[0036] For example, it is possible to manipulate both the active catalyst surface and the mass of catalyst per unit volume by the thickness of the incorporated wire. In one embodiment, the ratio of the inner diameter of the reaction tube to the diameter of the wire is in the range of about 10 to 100, preferably about 10 to 50, more preferably about 20 to 40. The wire diameter of the wire is preferably in the range of 50 μm to 5,000 μm, more preferably 200 μm to 2,000 μm.

[0037] Furthermore, it is possible to increase the mass transfer in the boundary layer around the catalytically active wire. The mass transfer rate in the boundary layer of such thin wires is typically higher compared to the rings or spheres typically used, due to the low characteristic diameter of the wire used in the wire matrix insert.

[0038] In one embodiment, the ratio of the length of the reaction zone to the length of the reactant preheating zone is in the range of 0.01 to 100, preferably 0.05 to 5, more preferably 0.1 to 1. The aforementioned ratio enables an appropriate length of the reactant preheating zone within the reaction tube.

[0039] In one embodiment, the reaction tube includes an effluent cooling zone downstream of the reaction zone. The term "effluent cooling zone" refers to the section of the reaction tube where essentially no catalytic gas-phase partial oxidation reaction occurs and the gas flow through the reaction tube is heat-exchanged with a heat transfer medium circulating through the wall of the tube. This is accompanied by a net heat flow from the reaction tube. The hot effluent stream is cooled and the heat transfer medium outside the reaction tube absorbs the heat dissipated by the effluent stream.

[0040] The effluent cooling zone preferably has an essentially free cross-section or has a wire matrix insert with zero or limited catalytic activity. Preferably, the effluent cooling zone includes a wire matrix insert. The cooling zone downstream of the reaction zone has the advantage of avoiding consecutive reactions such as peroxidation to carbon oxides.

[0041] The characteristic design of a shell and tube type heat exchange reactor is known per se to those skilled in the art. A shell and tube type heat exchange reactor is appropriately limited by a "reactor shell" which is a generally cylindrical main body, and the upper and lower ends of the aforementioned reactor shell are limited by an "upper hood" and a "lower hood", in which case the upper hood and the lower hood are airtightly connected to the reactor shell. Inside the shell and tube type heat exchange reactor, there are a plurality of "reaction tubes" vertically arranged such that the reactor shell surrounds the plurality of reaction tubes. Generally, the term "a plurality of" reaction tubes refers to a vast number of reaction tubes present in the shell and tube type heat exchange reactor, for example, at least 5,000 and up to 45,000 reaction tubes. In a preferred embodiment, the inner diameter of the reaction tube is preferably in the range of 0.10 cm to 5.0 cm, more preferably in the range of 0.50 cm to 3.0 cm. Preferably, the length of the reaction tube is at least 5 cm, preferably in the range of 10 to 100 cm, particularly in the range of 25 to 60 cm. The upper end of the reaction tube is airtightly connected to an "upper tube sheet", and the lower end of the reaction tube is airtightly connected to a "lower tube sheet". In other words, both ends of the reaction tube are sealed within the tube sheet. Accordingly, an airtight region is formed by the space between the upper hood and the upper tube sheet and the space between the lower tube sheet and the lower hood within the reaction tube. In the aforementioned region, a feed gas mixture is introduced into the shell and tube type heat exchange reactor and subjected to a chemical reaction assumed in the shell and tube type heat exchange reactor within the reaction tube, for example, a catalytic gas phase partial oxidation reaction, and then removed from the shell and tube type heat exchange reactor.

[0042] During the "operation mode" of the shell and tube type heat exchange reactor, a reaction assumed in the shell and tube type heat exchange reactor, for example, a catalytic gas phase partial oxidation reaction, is carried out. The reaction is generally carried out at a reaction temperature which is high.

[0043] Generally, in order to control the temperature of a shell and tube type heat exchange reactor and / or to provide a high temperature, a heat exchange medium is circulated in a liquid-tight region between an upper tube sheet, a lower tube sheet, the inside of the reactor shell, and the outside of the reaction tubes. The heat exchange medium is selected from, for example, low melting point metals such as sodium or mercury, or alloys of different metals, or a molten salt melt of a eutectic mixture containing nitrate sites, for example, a mixture of at least two salts selected from alkali nitrates, alkali nitrites, and alkali carbonates, preferably a mixture of two or three salts out of potassium nitrate, sodium nitrate, and sodium nitrite.

[0044] Providing stable reaction conditions, i.e., conducting the reaction at a constant temperature, is very important. To provide such stable reaction conditions, the heat transfer medium is properly circulated vertically throughout the liquid-tight region at the intended temperature using a pump. By doing so, the reaction tubes can be cooled or heated, and subsequently, the heat transfer medium can be cooled or heated in a heat exchanger, for example, a heat exchanger arranged externally. Generally, for this purpose, the reaction tubes are arranged in a shell and tube type heat exchange reactor at equal distances from each other.

[0045] It is highly desirable to rapidly cool the discharge stream coming out of the outlet of the reaction passage. This can be done by quenching the discharge stream in an aqueous phase.

[0046] The shell and tube type heat exchange reactor of the present invention is suitable, although not exclusively, particularly for catalytic gas phase partial oxidation reactions, for example, the oxidation of alcohols to aldehydes. Accordingly, the present invention further relates to the use of the shell and tube type heat exchange reactor of the present invention for conducting catalytic gas phase partial oxidation reactions such as the production of aldehydes.

[0047] The present invention further relates to a process for conducting a catalytic gas phase partial oxidation reaction, which includes introducing a reaction stream into the inlet of a shell and tube type heat exchange reactor as described above. In this process, the reaction stream contains, for example, in the form of air, a partially oxidizable organic substrate and molecular oxygen.

[0048] In one embodiment, the noble metal is silver, and the partially oxidizable organic substrate is ethylene which is catalytically oxidized to ethylene oxide.

[0049] In one embodiment, the noble metal is silver, and the partially oxidizable organic substrate is methanol which is catalytically oxidized to formaldehyde.

[0050] In one embodiment, the noble metal is silver, and the partially oxidizable organic substrate is an alcohol which is oxidized to an aldehyde.

[0051] According to the present invention, various ethylenically unsaturated aldehydes can be produced. In one embodiment, the ethylenically unsaturated alcohol is 3-methylbut-2-en-1-ol (prenol), and the produced ethylenically unsaturated aldehyde is prenal (3-methyl-2-buten-1-al), or the ethylenically unsaturated alcohol is 3-methylbut-3-en-1-ol (isoprenol), and the produced ethylenically unsaturated aldehyde is 3-methyl-3-buten-1-al (isoprenal). The dehydration of isoprenol to isoprenal can proceed with partial isomerization to prenal.

[0052] Generally, the aforementioned process comprises a) a step of vaporizing (iso)prenol; b) a step of mixing the (iso)prenol vapor with an oxygen-containing gas; c) a step of introducing the reaction stream into the inlet of a shell-and-tube type heat exchange reactor as described above and reacting the gas mixture to form (iso)prenal.

[0053] For example, in the case of the catalytic gas-phase partial oxidation reaction of (iso)prenol to (iso)prenal, the reaction temperature ranges from 300 to 500 °C, preferably from 350 to 400 °C.

[0054] Prenol, which is useful as a starting material for the present invention, can generally be obtained by reacting a formaldehyde source with isobutylene under high temperature and high pressure in a reactor to obtain 3-methylbut-3-en-1-ol (isoprenol), and then isomerizing the obtained isoprenol.

[0055] In one embodiment, isoprenol is obtained by mixing a formaldehyde source and isobutylene and injecting them into a reactor through at least one nozzle, and reacting the formaldehyde source and isobutylene under supercritical conditions. To achieve supercritical conditions, formaldehyde and isobutylene are preferably reacted at a temperature in the range of at least 220 °C, for example, 220 - 290 °C, and an absolute pressure of at least 200 bar. The reaction of isobutene and formaldehyde can be carried out in the presence of a catalyst such as an amine base, for example, hexamethylenetetramine (urotropin).

[0056] In this specification, any reference to a "catalyst" is understood to include the possibility that the catalyst is a single catalyst species or a combination of two or more different catalyst species.

[0057] Formaldehyde can be provided as a liquid, for example, as a solution of paraformaldehyde. Preferably, the formaldehyde source is an aqueous formaldehyde solution. The formaldehyde source can be a single formaldehyde source or a combination of two or more different formaldehyde sources.

[0058] Rapid and strong initial mixing of the reactants is desirable, but it may be advantageous to continue and complete the reaction under conditions where backmixing is limited. Therefore, the reaction mixture can be sent to a post-reaction chamber located behind or at the bottom of the reactor. In the post-reaction chamber, backmixing is limited.

[0059] In one embodiment, the reactor includes an upper portion and a lower portion. The injection and mixing of reactants are carried out in a mixing chamber of the reactor disposed in the upper portion, and a fluid containing formaldehyde and / or isobutylene and / or isoprenol is sent from the mixing chamber to a post-reaction chamber disposed in the lower portion.

[0060] Further details regarding the reaction of a formaldehyde source with isobutylene to obtain isoprenol can be found in the pamphlet of International Publication No. WO 2020 / 049111 A1.

[0061] In one embodiment, reacting a formaldehyde source with isobutylene includes the steps of mixing the formaldehyde source and isobutylene and injecting them into an internal loop reactor through at least one nozzle and injecting them into a first conduit, and the internal loop reactor includes - a vertically disposed cylindrical container including side walls, - at least one draft tube vertically disposed in the container and having a tube inlet end and a tube outlet end, the draft tube being disposed concentrically with the nozzle and having an inner surface and an outer surface, the draft tube providing a first conduit inside the draft tube and a second conduit outside the draft tube and within the side walls, the first conduit being in fluid communication with the second conduit, at least one draft tube, - reactor fluid discharge means, and includes The inner surface of the draft tube is convexly curved such that the first conduit exhibits an annular constriction in cross-section between the tube inlet end and the tube outlet end, this constriction being located closer to the tube inlet end, and the convex curvature of the inner surface of the draft tube extends over at least 70%, preferably at least 80%, most preferably at least 90% of the length of the draft tube, The outer surface of the draft tube is convexly curved such that the draft tube exhibits a circumferential protrusion between the tube inlet end and the tube outlet end, this circumferential protrusion being preferably located closer to the tube outlet end, and the convex curvature of the outer surface of the draft tube extends over at least 70%, preferably at least 80%, most preferably at least 90% of the length of the draft tube, A fluid is obtained in which the formaldehyde source and isobutylene ejected from the nozzle move generally downward in the first conduit and react, and then the reacted fluid is diverted in the opposite direction so as to move in the second conduit, and then the end of the draft tube is rounded so as to be reversely mixed with the ejected fluid.

[0062] With this configuration of the draft tube, the boundary layer flowing through the end of the draft tube can be controlled. When the angle of attack of the flow with respect to the solid body reaches a certain limit, the adverse pressure gradient becomes too large for the flow to overcome. At this time, the flow separates from the upper surface of the solid body and enters a state generally called stall. With this configuration, it is possible to reduce or delay the separation of the flow, respectively. By reducing the separation of the flow, the friction of the liquid is reduced, so the pressure drop along the streamline of the recirculation flow becomes smaller, and as a result, the circulation rate of the configuration is improved. The curved shape of the inner surface of the draft tube guides the fluid passing through the draft tube in an optimized manner comparable to the fluid flow over an airfoil.

[0063] The inner surface of the draft tube is curved in the longitudinal direction of the draft tube, that is, in other words, has a convex shape, and as a result, the first conduit exhibits a minimum cross-sectional area between the tube inlet end and the tube outlet end. That is, the cross-section of the first conduit decreases from the cross-section at the tube inlet end to the minimum cross-sectional area and increases from the minimum cross-sectional area to the cross-section at the tube outlet end.

[0064] The draft tube has a curved, substantially conical section that is wide at the inlet end of the tube and narrow at the constriction, between the inlet end of the tube and 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. Since the flow through the tube remains mainly attached, the pressure loss generated is small. Near the constriction, the fluid flowing downstream through the draft tube is accelerated. Between the constriction and the outlet end of the tube, the cross-sectional area of the draft tube widens again. As a result, due to the change in area, combined with mass conservation, the velocity passing through the larger area is slower than the velocity passing through the smaller area, involving the conversion of dynamic pressure to static pressure. When the fluid flowing downstream through the draft tube is accelerated near the constriction, a radial velocity component is added to the flow, increasing the mixing between the circulating flow and the injection flow. By avoiding flow separation in this case, no large pressure loss occurs.

[0065] In a preferred embodiment, the nozzle is a two-component nozzle. In particular, the two-component nozzle is designed to provide an annular jet of isobutylene around the central jet of the formaldehyde source, and it is preferred that the injection velocities of these two jets are different. In this embodiment, the jet of isobutylene has a large shear plane towards both the central jet of the formaldehyde source and the reaction mixture in the reactor, enabling a preferred high-speed mixing of the reactants.

[0066] In a preferred embodiment, the loop reactor includes deflection means arranged between the nozzle and the draft tube, and the deflection means is suitable for deflecting the fluid moving through the second conduit in the opposite direction.

[0067] The biasing means preferably includes a surface that is concave with respect to the end of the draft tube that defines the pipe inlet end. In a preferred embodiment, the biasing means has a partial toroidal surface. It is particularly preferred that the biasing means is provided in the shape of the upper part of a ring torus bisected by a plane parallel to the toroidal direction. This shape enables the fluid moving in the second conduit to be deflected particularly efficiently. The biasing means can enable the stabilization of the injected fluid flow. This is particularly appropriate when the flow rate of the fluid moving in the second conduit is not uniform across the cross-section of the reactor and can lead to eccentricity of the injected fluid flow. Such eccentricity, if left unaddressed, can reduce the circulation rate.

[0068] When the first conduit is a downcomer and the second conduit is a riser, the shape of the biasing means constitutes the upper part of a ring torus bisected by a plane parallel to the toroidal direction, and the ring torus is preferably bisected at 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 the lower part of the ring torus or smaller than the lower part of the ring torus. In another preferred embodiment, the shape of the biasing means constitutes the upper part of a ring torus bisected by a plane parallel to the toroidal direction, and the ring torus is bisected at most 85% of its height, for example 80% of its height. Within these ranges, the inlet of the biasing means is angled particularly suitable for the deflection of the fluid.

[0069] High temperatures are required to obtain isoprenol in high yields from the reaction of formaldehyde and isobutylene. The effective removal of heat is important for the quality of the product and the safety of the process. The heat removed from isoprenol is used to raise the temperature of isobutylene before it enters the reactor. The flow of hot isoprenol contains sensible heat due to the chemical reaction. Sensible heat is potentially renewable energy and can be reused.

[0070] Advantageously, reacting the formaldehyde source with isobutylene preferably includes heat exchanging a hot isoprenol stream withdrawn from the reactor with an isobutylene stream directed to the reactor, where the heat exchange is carried out in at least two shell and tube heat exchangers, each of the heat exchangers including a plurality of tubes and shell-side heat exchange passages, the hot isoprenol being directed through the tubes of the heat exchanger and the isobutylene being directed through the shell-side passages, and at least two of the heat exchangers being connected in series with respect to both the shell-side flow and the tube-side flow.

[0071] Such a configuration can increase the operating interval during maintenance interruptions in such a process. The term "maintenance interruption" is intended to mean the shutdown of the process that is periodically required to clean the tubes of the heat exchanger clogged by fouling. An indicator indicating the need for a maintenance interruption is typically that the isobutylene discharged from the last heat exchanger is not sufficiently preheated and that even subsequent heaters can hardly add additional external heat to the isobutylene to bring the isobutylene to the required temperature before entering the reactor. One aspect of the present invention is that the preheating of the isobutylene stream can be maintained at a sufficiently high level for a longer time so that the desired temperature of the isobutylene can be easily reached before the isobutylene enters the reactor.

[0072] One particular area in a conventional shell and tube heat exchanger where fouling is likely to occur is the tube area near the tube sheet, near the inlets where the tube-side fluid exits the individual tubes. Excessive fouling in this area can cause clogging of the individual tubes and stagnation of the fluid along the entire length of these tubes. Stagnation of the fluid generally results in a decrease in heat transfer performance.

[0073] As a further result of the reduction in heat transfer performance caused by fouling, the energy required by the heater to adjust the temperature of the preheated isobutylene stream to the desired reaction temperature increases. As a result, more additional external heat is required, which is detrimental in terms of energy demand and process economics and, in many cases, negatively affects the carbon dioxide footprint of the product.

[0074] By using two or more heat exchangers, the impact of fouling in the individual tubes on the overall heat exchange capacity is reduced compared to a configuration where only a single heat exchanger is used. As a result, the heat transfer rate is maintained at a desirable level over a longer period, and thus the operating interval between maintenance interruptions is lengthened, and less additional external heat is required for preheating the isobutylene stream compared to a plant equipped with a single heat exchanger in a fouled state.

[0075] Separating isoprenol from unreacted formaldehyde is not an easy task. This difficulty arises from the fact that monomeric formaldehyde (and polymeric formaldehyde) forms both hydrates with water and hemiacetals with isoprenol. Hydrates and hemiacetals with different degrees of polymerization of formaldehyde have overlapping boiling points.

[0076] However, it has been found that by distilling at a temperature at which the hemiacetal decomposes into formaldehyde and isoprenol, formaldehyde can be separated from isoprenol substantially completely, and as a result, formaldehyde can be easily separated from isoprenol.

[0077] Therefore, crude isoprenol is purified by distilling a crude isoprenol stream containing isoprenol, water, and formaldehyde, or an isoprenol-containing fraction thereof, in a low-boiling-point separation column operated at a pressure of 2 bara or more, preferably 2.5 bara or more, to obtain a distillate stream containing aqueous formaldehyde and a bottoms stream containing isoprenol essentially free of formaldehyde.

[0078] In particular, formaldehyde can be substantially completely separated from isoprenol, and an aqueous formaldehyde solution concentrated to be suitable for recycling to isoprenol synthesis has an equilibrium shifted to the hemiacetal side of formaldehyde and isoprenol. As a result, essentially all of the formaldehyde remains at the bottom of the distillation column during the first distillation at a temperature where it remains, and the hemiacetal decomposes into formaldehyde and isoprenol. As a result, it has been found that formaldehyde can be obtained in a distillation train involving a second distillation at a temperature at which it can be easily separated from isoprenol.

[0079] Two low-boiling separation columns operated at different pressures are envisioned to enable a first distillation at a temperature below the dissociation temperature of isoprenol-formaldehyde and a second distillation at a temperature above the dissociation temperature of isoprenol-formaldehyde. Thus, at a relatively low pressure extending to the first low-boiling separation column, a first distillate containing water and low-boiling components essentially free of formaldehyde is obtained. At a relatively high pressure extending to the second low-boiling separation column, substantially all of the formaldehyde is separated from the isoprenol. By this process, isoprenol essentially free of formaldehyde can be obtained.

[0080] Thus, in a more preferred embodiment, the purification process comprises (i) feeding the aforementioned stream of crude isoprenol to a first low-boiling separation column operated at a pressure of 1.5 bara or less to obtain a first bottoms stream containing isoprenol and formaldehyde and a first distillate stream containing water and low-boiling components; (ii) feeding the first bottoms stream to a second low-boiling separation column operated at a pressure of 2 bara or more to obtain a second distillate stream containing aqueous formaldehyde and a second bottoms stream containing isoprenol; (iii) feeding the second bottoms stream to a finishing column to obtain pure isoprenol as a distillate stream and a bottoms stream containing high-boiling components; and includes.

[0081] The second distillation stream constitutes an aqueous formaldehyde solution concentrated and suitable for recycling to isoprenol synthesis.

[0082] The second low-boiling separation column is suitably operated at a pressure of 2.5 bara or more, preferably 2.8 bara or more, and most preferably 2.9 bara or more. The bottom temperature of the second low-boiling separation column is preferably in the range of 160 - 200 °C, more preferably 170 - 185 °C, and most preferably 175 - 180 °C. The top temperature of the second low-boiling separation column is preferably in the range of 115 - 160 °C, more preferably 125 - 145 °C.

[0083] In a particularly preferred embodiment, the second low-boiling separation column is operated at a pressure in the range of 2.9 - 3.5 bara, a bottom temperature in the range of 175 - 180 °C, and a top temperature in the range of 130 - 140 °C.

[0084] Further information regarding the process for recovering isoprenol essentially free of formaldehyde can be found in the pamphlet of International Publication No. WO 2022 / 189652 A1.

[0085] The obtained isoprenol can be subjected to catalytic isomerization to obtain prenol.

[0086] The isomerization of isoprenol to 3-methyl-2-buten-1-ol (prenol) can be carried out on a supported noble metal, preferably in the presence of hydrogen. A preferred catalyst is a fixed-bed catalyst containing palladium and selenium or tellurium or a mixture of selenium and tellurium supported on silicon dioxide. The isomerization is carried out at a temperature of 50 - 150 °C to produce a reaction mixture of prenol and isoprenol. Isoprenol can be recycled. Further details are described in the pamphlet of International Publication No. WO 2008 / 037693.

[0087] The (iso)prenol obtained as described above can be subjected to the catalytic gas-phase partial oxidation reaction of the present invention. Before contacting with the catalytically active wire matrix insert, it may be advantageous to treat the (iso)prenol by contacting it with a weakly acidic solid adsorbent to remove organically bound nitrogen from the (iso)prenol. In other words, by this process, organically bound nitrogen can be removed from the (iso)prenol.

[0088] The term "organically bound nitrogen" is taken to refer to any compound containing at least one nitrogen atom directly bonded to one or more carbon atoms. For example, such compounds containing at least one nitrogen atom can be selected from amines such as ethylamine, trimethylamine, aniline, pyridine, or piperidine. A particularly important amine in practice is hexamethylenetetramine (urotropine). (Iso)prenol can contain from about 5 to 30 ppm of organically bound nitrogen.

[0089] It has been found that the weakly acidic solid adsorbent can adsorb organically bound nitrogen in the presence of an abundant amount of (iso)prenol without interfering with the reactive carbon-carbon double bond.

[0090] The weakly acidic adsorbent can include an adsorbent material having an acidity sufficient to adsorb organically bound nitrogen from the (iso)prenol. In one embodiment, the solid adsorbent is a cross-linked resin having phosphonic acid functional groups. Preferably, the resin polymer is a vinyl aromatic copolymer, preferably cross-linked polystyrene, more preferably a polystyrene divinylbenzene copolymer. Other polymers having phosphonic acid functional groups can also be used. Preferably, the cross-linked resin having phosphonic acid functional groups is of the macroporous type. A preferred solid adsorbent is Purolite S956.

[0091] The resin is typically used in the form of beads and packed into a column. (Iso)prenol passes through the column while in contact with the resin beads. During contact, the organic-bonded nitrogen in (iso)prenol reacts with the functional groups, protons move to the nitrogen, and an exchange occurs where ionic bonds are formed with the anionic sites of the resin. The contact is maintained until a threshold level, i.e., the breakthrough concentration, is reached. At this breakthrough point, the process reaches equilibrium and additional organic-bonded nitrogen cannot be effectively removed. The flow is stopped and the column is backwashed with water, preferably deionized water or soft water. By countercurrent flow, the resin is fluidized and the solids trapped by the beads are loosened and removed.

[0092] In another embodiment, the solid adsorbent is a silica-alumina hydrate. Numerous silica-alumina catalyst compositions and their preparation processes are described in the patent literature. See, for example, U.S. Patent No. 4,499,197.

[0093] Preferably, the alumina content of the silica-alumina hydrate is from about 10 to about 90 wt% Al2O3. A preferred range of the alumina content is from about 30 to about 70 wt% Al2O3.

[0094] When silicon dioxide is introduced into aluminum oxide, acidic centers are introduced. The number of acidic centers can be controlled by the amount of silicon dioxide introduced. The number of acidic centers increases with the amount of silicon dioxide introduced up to the maximum number of acidic centers, and after reaching the maximum number of acidic centers, it decreases again when the amount of silicon dioxide is further increased.

[0095] Examples of commercially available silica-alumina hydrates are Siral® available from Sasol Germany Gmbh, Hamburg, Germany. Siral® is based on orthorhombic aluminum oxide hydroxide (boehmite, AlOOH) and doped with SiO2. Various grades of Siral® with different ratios of AI2O3 to SiO2 are available: Siral 1 (AI2O3 / SiO2 = 99 / 1), Siral 5 (AI2O3 / SiO2 = 95 / 5), Siral 10 (Al2O3 / SiO2 = 90 / 10), Siral 20 (AI2O3 / SiO2 = 80 / 20), Siral 28M (Al2O3 / SiO2 = 72 / 28), Siral 30 (AI2O3 / SiO2 = 70 / 30), Siral 40 (Al2O3 / SiO2 = 60 / 40). Siral40 is particularly preferred.

[0096] In one embodiment, (iso)prenol passes over a bed of a weakly acidic solid adsorbent. Suitably, the foregoing "passing over" step preferably means providing a layer ("bed") of the weakly acidic solid adsorbent in a typical reaction vessel known to those skilled in the art that can be equipped with a stirring device, for example, a stirred tank reactor. Then, (iso)prenol is introduced into the reaction vessel and guided through the reaction vessel to contact the weakly acidic solid adsorbent.

[0097] Alternatively, the weakly acidic solid adsorbent can be provided, for example, in the reaction tube of a tubular reactor, and then (iso)prenol continuously flows through the foregoing reaction tube while contacting the weakly acidic solid adsorbent.

[0098] In one embodiment, (iso)prenol contains less than 2 ppm of organically bound nitrogen after contacting an alcohol stream with a weakly acidic solid adsorbent. As used herein, "ppm" refers to the weight ppm of the compound incorporating organically bound nitrogen relative to the total weight of (iso)prenol.

[0099] Suitably, the content of organic bound nitrogen in (iso)prenol can be determined by Kjeldahl analysis. Alternatively, an oxidative combustion method with a chemiluminescence detector according to DIN 51444 can be used.

[0100] When isoprenol is subjected to the catalytic gas-phase partial oxidation reaction of the present invention, it may be preferable to maintain the weight ratio of formaldehyde to isoprenol in the reaction stream at less than 0.04, preferably less than 0.03, particularly less than 0.02, or less than 0.01. In an even more preferred embodiment, the weight ratio of formaldehyde to isoprenol is maintained at less than 0.002, or less than 0.001.

[0101] The weight ratio of formaldehyde to isoprenol in the reaction stream can be maintained below a certain level. However, when the weight ratio of formaldehyde to isoprenol in the reaction stream is decreased beyond a certain point, a point of rapid decrease is reached. The removal of formaldehyde requires additional equipment and operating costs. An economic balance must be struck between the improvement by lowering the ratio and the costs for maintaining such a ratio. Therefore, the weight ratio of formaldehyde to isoprenol is preferably 0.0005 or more, or in some cases 0.005 or more.

[0102] It has been found that reactor clogging and increased pressure drop are greatly affected by the presence of formaldehyde in the reaction stream. The fouling reaction of the catalyst by condensation and polymerization is considered to be the main reaction involved in the formation of carbon or coke on the catalyst. This carbon formation is thought to involve the thermal condensation of formaldehyde, or the thermal condensation of formaldehyde with isoprenol and (iso)prenal, which are olefinic hydrocarbons. In the presence of the catalyst, the primary condensation product tends to undergo dehydrogenation and polymerization-type reactions, adhere to the catalyst, and further undergo dehydrogenation and decomposition until a carbonaceous deposit is formed.

[0103] The presence of formaldehyde in the reaction stream is due to two main sources. Formaldehyde may be contained in the fresh feed stream sent to the reactor, i.e., as an impurity derived from the isoprenol production process. All formaldehyde that cannot be separated in the purification process after isoprenol synthesis will ultimately enter the reaction stream.

[0104] In addition, formaldehyde is also generated within the system. A portion of the isoprenol decomposes back to isobutene and formaldehyde. Since most continuous industrial processes operate with a recycle of unreacted isoprenol at a single-pass conversion level of 50 - 60%, formaldehyde may be present in the recycle stream of unreacted isoprenol if the process of purifying the stream containing unreacted isoprenol is not carried out. It has now been found that the recycle stream of unreacted isoprenol is the largest cause of formaldehyde contamination in the reaction stream. This process is generally carried out at a partial conversion, for example, 30 - 70%, preferably 50 - 60% conversion. The unreacted isoprenol stream is separated from the product stream. The unreacted isoprenol stream is recycled, i.e., mixed with the fresh feed stream containing isoprenol to supply the reaction stream. The unreacted isoprenol stream contains isoprenol as the main component, but may also contain prenal, isoprenal, isoamyl alcohol, isovaleraldehyde, isovaleric acid, prenol, formaldehyde. Also, it may contain trace amounts of other C3 and C2 aldehydes and acids.

[0105] According to the present invention, reducing the weight ratio of formaldehyde to isoprenol in the reaction stream can be achieved in several different ways. In one embodiment, formaldehyde is removed from the unreacted isoprenol stream before the unreacted isoprenol stream is mixed with the fresh feed stream.

[0106] In one embodiment, the unreacted isoprenol stream is mixed with the fresh feed stream and formaldehyde is removed from the mixed stream.

[0107] Alternatively, by mixing a sufficient amount of a freshly purified feed stream with the unreacted isoprenol stream, it is also possible to obtain the desired weight ratio of formaldehyde to isoprenol in the mixed stream.

[0108] In one embodiment, the fresh feed stream containing isoprenol is obtained from the process of reacting isobutene with formaldehyde and is purified until the weight ratio of formaldehyde to isoprenol is less than 0.04, preferably less than 0.03, particularly less than 0.02, or less than 0.01. In a more preferred embodiment, the fresh feed stream is purified until the weight ratio of formaldehyde to isoprenol is less than 0.002, or less than 0.001.

[0109] By conventional separation methods such as distillation, selective adsorption and / or selective reaction, in particular the purification process involving pressure swing distillation described above, formaldehyde can be removed from the isoprenol stream.

[0110] The prenal produced by the present invention is a useful intermediate in the preparation of citral. Citral is a mixture of the isomeric compounds neral and geranial.

[0111] 3,7-Dimethyl-octa-2,6-dienal (citral) can be prepared by obtaining prenal by the process described above, which further includes a step of condensing prenal with prenol to obtain diprenyl acetal of prenal, and a step of subjecting the diprenyl acetal of prenal to decomposition conditions to obtain citral via prenyl (3-methyl-butadienyl) ether and 2,4,4-trimethyl-3-formyl-1,5-hexadiene.

[0112] In particular, 3,7-dimethyl-octa-2,6-dienal (citral) is a) Condensing prenal with prenol in the presence of at least one catalyst in a reaction column, and simultaneously removing an acetal fraction containing the diprenyl acetal of prenal from the reaction column; b) Subjecting the acetal fraction in a decomposition column to decomposition conditions in the presence of at least one catalyst, and simultaneously removing a decomposition fraction containing at least one of prenyl (3-methyl-butadienyl) ether and 2,4,4-trimethyl-3-formyl-1,5-hexadiene, optionally containing citral, from the decomposition column; c) Reacting the decomposition fraction in a plug flow reactor to obtain citral; It can be prepared by a process comprising:

[0113] The overall reaction sequence is shown by the following reaction scheme. [Chemical formula]

[0114] In step a), an unsaturated acetal 3-methyl-2-butenal-diprenyl acetal (hereinafter referred to as "diprenyl acetal of prenal" or "diprenyl acetal") is formed from prenol and prenal using a catalyst. For this purpose, prenal reacts with prenol in the presence of a catalytic amount of an acid, and the water generated during the reaction is separated in the reaction column. In step b), the 3-methyl-2-butenal diprenyl acetal (diprenyl acetal) obtained in step a) is decomposed in a decomposition column in the presence of a catalyst to remove 3-methyl-2-buten-1-ol (prenol) to obtain prenyl (3-methylbutadienyl) ether. By the Claisen rearrangement of the obtained prenyl (3-methylbutadienyl) ether, 2,4,4-trimethyl-3-formyl-1,5-hexadiene is obtained, and subsequently, 3,7-dimethyl-2,6-octadienal (citral) is obtained by a Cope rearrangement.

[0115] Step a) is carried out in the presence of a catalyst, preferably an acid. In one embodiment, the catalyst for step a) is nitric acid.

[0116] Preferably, in step b), the acetal fraction is continuously subjected to decomposition conditions in a decomposition column. The "decomposition conditions" mean reaction conditions selected such that the diprenyl acetal contained in the acetal fraction is decomposed into prenyl (3-methylbutadienyl) ether and then can be rearranged into 2,4,4-trimethyl-3-formyl-1,5-hexadiene and citral.

[0117] The acetal fraction contains diprenyl acetal as a main component. The acetal fraction does not necessarily consist of pure diprenyl acetal, but may also contain prenol, prenal, and citral components.

[0118] Step b) is carried out in the presence of a catalyst, preferably an acid catalyst. Suitable acid catalysts are selected from non-volatile protonic acids such as sulfuric acid, p-toluenesulfonic acid, and phosphoric acid.

[0119] Suitably, the continuous decomposition in the decomposition column of step b) can be carried out at the bottom or a sump of a distillation column functioning as the decomposition column. Preferably, the acetal fraction and / or the catalyst are introduced into the bottom of the distillation column, the sump of the distillation column, or the evaporator of the distillation column.

[0120] If necessary, a high-boiling inert compound can be introduced into the sump of the decomposition column to ensure the minimum filling level of the sump and the evaporator. Suitable high-boiling inert compounds are selected from liquid compounds that are inert under the reaction conditions and have a higher boiling point than citral and diprenyl acetal. For example, the high-boiling inert compound can be selected from hydrocarbons such as tetradecane, pentadecane, hexadecane, octadecane, eicosane, or ethers such as diethylene glycol dibutyl ether, white oil, kerosene, or mixtures thereof.

[0121] Suitably, the distillation conditions are selected such that the diprenyl acetal is mainly retained at the bottom of the distillation column or in the sump. During the decomposition reaction, the decomposition fraction is continuously withdrawn from the decomposition column, and this decomposition fraction contains at least one of prenyl (3-methyl-butadienyl) ether and 2,4,4-trimethyl-3-formyl-1,5-hexadiene, and optionally citral. For ease of reference, prenyl (3-methyl-butadienyl) ether, 2,4,4-trimethyl-3-formyl-1,5-hexadiene and citral are collectively referred to as "citral components". This is because the former is an intermediate in the reaction pathway to citral and can be converted to citral in subsequent step c).

[0122] In addition, the prenol formed during the decomposition reaction in step b) is generally continuously removed from the reaction mixture at the top of the decomposition column.

[0123] The decomposition fraction can be withdrawn from the top of the distillation column together with the prenol formed.

[0124] Alternatively and preferably, it is also possible to withdraw the decomposition fraction in liquid or vapor form from the side outlet of the distillation column.

[0125] In step c), the decomposition fraction is reacted in a plug flow reactor to obtain citral. For this purpose, the decomposition fraction is led to a plug flow reactor at a temperature suitable for carrying out the rearrangement reaction to produce citral. By using a combination of a highly back-mixed decomposition column and a plug flow reactor, the selectivity and yield of the decomposition reaction can be increased. All the catalysts required for the decomposition reaction are preferably introduced into the decomposition column in step b), and preferably no catalyst is introduced into the plug flow reactor.

[0126] In one embodiment, the prenol removed in step b) is recycled to step a). Thereby, an improvement in yield is achieved in the process of the present invention.

[0127] Accordingly, in one aspect, the present invention relates to an improved process for preparing citral (3,7-dimethyl-octa-2,6-dienal), the process comprising: A) reacting a formaldehyde source with isobutylene to obtain 3-methylbut-3-en-1-ol (isoprenol), and subjecting at least a portion of the obtained isoprenol to isomerization to obtain prenol; B) preparing prenal (3-methylbut-2-en-1-al) from 3-methylbut-2-en-1-ol (prenol) using the above process, and / or preparing prenal via isoprenal (3-methylbut-3-en-1-al) generated from isoprenol using the above process; C) condensing prenal with prenol to obtain diprenyl acetal of prenal, and subjecting the diprenyl acetal of prenal to decomposition conditions to obtain citral via prenyl (3-methyl-butadienyl) ether and 2,4,4-trimethyl-3-formyl-1,5-hexadiene; and comprising.

[0128] Step A can be carried out as described above or by other methods known in the art, preferably by distillation at a temperature at which the hemiacetal decomposes into formaldehyde and isoprenol, so that the formaldehyde can be easily separated from the isoprenol. More preferably, a crude isoprenol stream containing isoprenol, water and formaldehyde, or an isoprenol-containing fraction thereof, is distilled in a low-boiling separation column operated at a pressure of 2 bara or more, preferably 2.5 bara or more, to obtain a distillate stream containing aqueous formaldehyde and a bottom stream containing isoprenol substantially free of formaldehyde.

[0129] Process B involves the oxidative dehydrogenation of prenol and / or isoprenol. The conversion of isoprenol by a catalytically active metal catalyst forms a reaction mixture of 3-methylbut-3-en-1-al and 3-methylbut-2-en-1-al. Subsequently, the former isomer can be isomerized under a base catalyst to obtain the desired 3-methylbut-2-en-1-al.

[0130] Process C can be carried out, for example, via steps a) to c) as described above.

[0131] The citral thus obtained is a useful intermediate for, for example, menthol or linalool.

[0132] Menthol can be prepared from citral via a process that includes - a step of catalytically hydrogenating citral to obtain citronellal, - a step of cyclizing citronellal in the presence of an acidic catalyst to obtain isopulegol, - a step of catalytically hydrogenating isopulegol to obtain menthol.

[0133] The overall reaction sequence is shown by the following reaction scheme.

Chemical formula

[0134] The hydrogenation of citral to obtain citronellal can be achieved by hydrogenation in the presence of a rhodium-phosphine catalyst.

[0135] The cyclization of citronellal to isopulegol can be achieved by cyclization in the presence of a Lewis acidic aluminum-containing catalyst such as a bis(diarylphenoxy)aluminum compound, which catalyst can be used in the presence of an auxiliary agent such as a carboxylic anhydride. Isopulegol can be recovered from the reaction product containing the catalyst by distillation separation, obtaining an upper product rich in isopulegol and a bottom product depleted in isopulegol. The catalyst can be regenerated from the bottom product. The isopulegol that can be obtained by cyclizing citronellal in this way can be further purified by suitable separation and / or purification methods, in particular by crystallization, to remove at least most of the undesirable impurities or by-products.

[0136] The hydrogenation of isopulegol can be achieved by hydrogenation in the presence of a heterogeneous nickel-containing catalyst, preferably a heterogeneous nickel and copper-containing catalyst.

[0137] Further details regarding the reaction sequence from citral to menthol can be found in U.S. Patent Application Publication No. 2013 / 46118A1, which is incorporated herein by reference.

[0138] Accordingly, in one aspect, the present invention relates to an improved process for the preparation of menthol by using the above process to produce citral and then producing menthol from citral. Menthol can be prepared as described herein or by other methods known in the art.

[0139] Linalool can be prepared from citral via a process that includes catalytically hydrogenating citral to obtain nerol and / or geraniol, and isomers thereof.

[0140] The hydrogenation of citral to obtain nerol and / or geraniol can be achieved by hydrogenation in the presence of a supported ruthenium, rhodium, osmium, iridium or platinum catalyst, preferably a ruthenium catalyst supported on carbon black.

[0141] The isomerization of nerol and / or geraniol to obtain linalool can be achieved by isomerization in the presence of a tungsten catalyst, particularly a dioxotungsten(VI) complex. Further details regarding the isomerization of nerol and / or geraniol can be found in U.S. Patent No. 7,126,033B2.

[0142] Accordingly, in one aspect, the present invention relates to an improved process for preparing linalool by using the above processes to produce citral and then producing linalool from citral. Linalool can be prepared as described herein or by other methods known in the art.

[0143] The present invention is further illustrated by the following examples and figures. However, it will be understood that the examples and figures are not intended to limit the scope of the present invention in any wax.

Brief Description of the Drawings

[0144]

Figure 1

Modes for Carrying Out the Invention

Examples

[0145] Prenol was continuously vaporized in a double-tube vaporizer. Prenol vapor was introduced into the reactor at the bottom of the reactor at a flow rate of 300 g / h, a temperature of 365° C., and a pressure of 1 atm. Together with the prenol vapor, air was introduced into the reactor at the bottom of the reactor at a flow rate of 100 Nl / h. The inner diameter of the reactor was 12 mm and the length was 500 mm. The exhaust stream was collected at the top of the reactor and analyzed by gas chromatography.

[0146] In the reactor, various catalytically active structures were tested: - a wire matrix insert (available from Calgavin) made of block silver wire with a porosity of 90.6% and a length of 300 mm (insert 1); - a wire matrix insert (available from Calgavin) made of block silver wire with a porosity of 90.6% and a length of 150 mm (insert 2); or - Packing of silver-coated steatite catalyst with a diameter of 2 mm.

[0147] The wire matrix insert was placed in the reactor tube such that one end of the wire matrix insert was located at the reactor tube outlet, i.e. the length of the reactant preheat zone was 200 mm (for insert 1) or 350 mm (insert 2). The silver coated steatite catalyst was placed at the reactor tube outlet, filling 300 mm of the reactor tube, i.e. obtaining a preheat zone of length 200 mm.

[0148] Three experiments were carried out for each of Insert 1 and Insert 2 (examples of the invention) and the silver-coated steatite catalyst (comparative example), and the results are shown in Tables 1 to 3 and FIG.

[0149] The normalized selectivities (selectivity of silver-coated steatite catalyst=100%) are shown in Table 1.

[0150] [Table 1]

[0151] The conversion rate of prenol and the selectivity of prenol are shown in Table 2.

[0152]

Table 2

[0153] The amount of gaseous product formed and the average selectivity of prenol are shown in Table 3.

[0154]

Table 3

[0155] The mass loss of the liquid is a measure of side reactions leading to gaseous products such as peroxidation to CO and / or CO2.

[0156] Figure 1 shows the pressure drop versus reaction time for three different catalytic active structures: Insert 1 and Insert 2 (examples of the present invention), and a silver-coated steatite catalyst (comparative example). For reference, the experiment at 350 °C using Insert 2 is also included in Figure 1. Since no reaction occurs at 350 °C, this experiment is an example of a pressure drop as low as possible with no deposit or coke formation.

[0157] It can be seen from Figure 1 that the pressure drop of the examples of the present invention is lower (reduced by almost half) than the pressure drop when using a silver-coated steatite catalyst (comparative example). This has the advantage of longer operating time and shorter annual shutdown time.

Claims

1. A shell-and-tube type heat exchange reactor for performing a catalytic gas-phase partial oxidation reaction, - A reaction passage including a shell-side heat exchange passage and multiple reaction tubes for circulating a heat transfer medium, - An inlet for introducing reaction logistics into the reaction passage, - An outlet from the reaction passage for recovering the discharge flow from the reaction tube, Includes, The reaction tube is A reactant preheating zone adjacent to the inlet, A reaction zone downstream of the reactant preheating zone, the reaction zone having a catalytically active wire matrix insert having a catalytically active noble metal on at least a portion of its surface, A shell-and-tube type heat exchange reactor, including one.

2. The shell-and-tube heat exchange reactor according to claim 1, wherein the reactant preheating zone has an essentially free cross-section or has a wire matrix insert with zero or limited catalytic activity.

3. The shell-and-tube heat exchange reactor according to claim 1, wherein the ratio of the length of the reaction zone to the length of the reactant preheating zone is in the range of 0.01 to 100, preferably 0.05 to 5, and more preferably 0.1 to 1.

4. The shell-and-tube heat exchange reactor according to claim 1, wherein the reaction zone includes alternating regions having catalytically active wire matrix inserts and regions having essentially free cross-sections or wire matrix inserts having zero or limited catalytic activity.

5. The shell-and-tube heat exchange reactor according to claim 1, wherein the reaction tube includes an exhaust cooling zone downstream of the reaction zone, and the exhaust cooling zone has a wire matrix insert having an essentially free cross-section or zero or limited catalytic activity.

6. The shell-and-tube heat exchange reactor according to claim 1, wherein the catalytically active precious metal is selected from copper, silver, palladium, platinum, ruthenium, and rhodium, preferably silver.

7. The shell-and-tube heat exchange reactor according to claim 2, wherein the wire matrix insert having zero or limited catalytic activity is made of an inert material, preferably stainless steel.

8. The shell-and-tube heat exchange reactor according to claim 1, wherein the catalytically active wire matrix insert includes an elongated core having a plurality of wire loops extending from the elongated core, the wire loops being arranged longitudinally and helically shifted, and the wire loops including a block of precious metal wire or a wire coated with precious metal.

9. The shell-and-tube heat exchange reactor according to claim 8, wherein the elongated core includes at least two longitudinal core wire members, the core wire members are twisted together to form a winding of core wire, and the wire loop is housed in the winding of core wire.

10. The shell-and-tube heat exchange reactor according to claim 8, wherein the ratio of the inner diameter of the reaction tube to the diameter of the block of precious metal wire or the wire coated with precious metal is in the range of about 10 to 100, preferably about 10 to 50, and more preferably about 20 to 40.

11. The shell-and-tube type heat exchange reactor according to claim 1, wherein the porosity of the reaction zone is 0.60 to 0.99, preferably 0.80 to 0.97, and more preferably 0.89 to 0.

94.

12. The shell-and-tube heat exchange reactor according to claim 1, wherein the catalyst-activated wire matrix insert is adapted to allow the laminar boundary layer of the reaction flow to be radially mixed into the bulk reaction flow through the reaction tube.

13. A method for carrying out a catalytic gas phase partial oxidation reaction, comprising introducing a reaction flow into the inlet of a shell-and-tube heat exchange reactor according to Claim 1, wherein the reaction flow comprises a partially oxidizable organic substrate and molecular oxygen.

14. The method according to claim 13, wherein the flow of the reaction logistics within the preheating zone is essentially laminar.

15. The method according to claim 13, characterized in that the flow of the reaction logistics within the reaction zone including the catalytically active wire matrix insert has a Reynolds number of 12,000 or less, preferably 8,000 or less, and more preferably 2,300 or less.

16. The noble metal is silver, and the partially oxidizable organic substrate is an alcohol, preferably 3-methylbuta-2-en-1-ol (prenol) or 3-methylbuta-3-en-1-ol (isoprenol). The method according to claim 13, wherein prenol is optionally obtained by isomerization of isoprenol.

17. The isoprenol mentioned above is obtained by reacting at least one formaldehyde source with isobutylene in a reactor to obtain isoprenol. The reaction of at least one formaldehyde source with isobutylene is preferably α and β: α) A step of mixing the at least one formaldehyde source with isobutylene and injecting it into an internal loop reactor through at least one nozzle and into a first conduit, wherein the internal loop reactor is - A cylindrical container arranged vertically, including its side walls, - At least one draft pipe, vertically arranged within the container, having a pipe inlet end and a pipe outlet end, wherein the draft pipe is concentric with the nozzle and has an inner and outer surface, and the draft pipe provides the first conduit within the draft pipe and the second conduit outside the draft pipe and within the side wall, and the first conduit is in fluid communication with the second conduit, - Includes reactor fluid outlet means, The inner surface of the draft pipe is curved convexly such that the first conduit shows an annular narrowing in the cross-section between the pipe inlet end and the pipe outlet end, the narrowing is located closer to the pipe inlet end, and the convex curve of the inner surface of the draft pipe extends over at least 70%, preferably at least 80%, and most preferably at least 90% of the length of the draft pipe. The outer surface of the draft pipe is curved convexly such that the draft pipe exhibits a circumferential projection between the pipe inlet end and the pipe outlet end, the circumferential projection is preferably located closer to the pipe outlet end, and the convex curvature of the outer surface of the draft pipe extends over at least 70%, preferably at least 80%, and most preferably at least 90% of the length of the draft pipe. The process involves the end of the draft pipe being rounded so that the at least one formaldehyde source and isobutylene, injected from the nozzle, move generally downward through the first conduit to react and obtain a fluid, and then the reacted fluid is diverted in the opposite direction to move through the second conduit and subsequently back-mixed with the injected fluid. β) A step of exchanging heat between a high-temperature isoprenol stream taken out of the reactor and an isobutylene stream sent to the reactor, Heat exchange is carried out in at least two shell-and-tube heat exchangers, each of which includes a plurality of tubes and shell-side heat exchange passages. The high-temperature isoprenol is introduced through the tube of the heat exchanger, the isobutylene is introduced through the shell-side passage, and at least two of the heat exchangers are connected in series with respect to both the shell-side flow and the tube-side flow. The method according to claim 16, comprising at least one of the following.

18. The method according to claim 16, wherein the partially oxidizable organic substrate is isoprenol, and the method is αα, ββ and γγ: αα) Isoprenol is purified by distilling a crude isoprenol stream containing isoprenol, water, and formaldehyde, or the isoprenol-containing fraction thereof, in a low-boiling-point separation column operated at a pressure of 2 bar or more, preferably 2.5 bar or more, to obtain a distillation stream containing aqueous formaldehyde and a bottom stream containing isoprenol that is essentially formaldehyde-free. ββ) A step of maintaining the weight ratio of formaldehyde to isoprenol at less than 0.04 in the reaction logistics described above. γγ) A step of treating the (iso)isoprenol by contacting it with a weakly acidic solid adsorbent before contacting it with the catalytically active wire matrix insert, thereby removing organically bound nitrogen from the (iso)prenol. A method further comprising at least one of the following.

19. A method for preparing 3,7-dimethyl-octa-2,6-dienal (citral), comprising the step of obtaining prenal by the method of Claim 16, further comprising the steps of: condensing the prenal with prenol to obtain a diprenyl acetal of prenal; and subjecting the diprenyl acetal of prenal to decomposition conditions to obtain citral via prenyl(3-methyl-butadienyl) ether and 2,4,4-trimethyl-3-formyl-1,5-hexadiene.

20. A method for preparing a citral-derived chemical substance, comprising the step of preparing citral by the method described in claim 19, and ααα, βββ or (βββ + γγγ): ααα) A step of converting the citral to obtain menthol, βββ) A step of converting the citral to geraniol and / or nerol, A method comprising at least one of the following steps: γγγ) converting the geraniol and / or nerol to obtain linalool.

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