Method for producing methylamines in the gas phase with improved control of the reactor inlet temperature
Patent Information
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-04-15
- Publication Date
- 2026-03-04
AI Technical Summary
Current methods for preheating educts in methylamines production face challenges in precisely controlling reactor inlet temperature, leading to fluctuations and potential overheating, which can cause decomposition of methylamines and require complex and costly control valves, while existing pressure control methods are difficult to regulate and result in additional pressure loss.
Introducing a quench liquid with a boiling point between -40°C to 120°C into the hot product gas stream to cool it, allowing for precise adjustment of the educt stream temperature without energy loss or external energy input, using the evaporated liquid to heat the educts to the desired reactor inlet temperature range of 350°C to 410°C.
This method allows for quick, efficient, and precise control of reactor inlet temperature within a narrow range, reducing the risk of overheating, minimizing energy loss, and eliminating the need for external energy sources, thereby enhancing the stability and efficiency of methylamines production.
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Abstract
Description
[0001] Process for the production of methylamines in the gas phase with improved control of the reactor inlet temperature
[0002] Description
[0003] The present invention relates to a process for producing methylamines from methanol and ammonia in a continuous gas-phase reaction over a heterogeneous catalyst at an absolute pressure in the range of 15 to 35 bar. For this purpose, the reactant stream, comprising the reactants methanol and ammonia, is evaporated by means of a heat exchanger and heated to a reactor inlet temperature in the range of 350°C to 410°C. Since the reaction of methanol and ammonia to form methylamines is exothermic, the hot product gas stream, which contains the methylamines (monomethylamine, dimethylamine, and trimethylamine), water, unreacted ammonia, and unreacted methanol, is passed from the reactor through one or more heat exchangers to heat the reactants.The process according to the invention is characterized in that, to adjust the reactor inlet temperature, a quench liquid is introduced into the hot product gas stream before it is passed through the heat exchangers. The quench liquid has a boiling point in the range of -40°C to 120°C at atmospheric pressure and evaporates upon introduction into the product gas stream, thereby efficiently and specifically cooling it to the temperature required for the desired heating of the reactant stream. In a particular embodiment of the invention, condensate from the product gas stream is used as the quench liquid for cooling the product gas stream.The invention further relates to a corresponding device for continuously carrying out an overall exothermic reaction for which the reactants must be brought to a certain temperature at the reactor inlet. This device comprises (a) one or more reactors to which the reactants are fed and from which the product gas stream is withdrawn, (b) one or more heat exchangers upstream of the reactor or reactors, with which the reactants are brought to the required reactor inlet temperature and through which the product gas stream is passed for the heat input, and (c) a measuring device for measuring the reactor inlet temperature of the reactants.The device according to the invention is characterized in that it comprises a controlled introduction of evaporable liquid into the product gas stream before the latter is passed through one or more of the heat exchangers, by means of which the temperature of the product gas stream can be cooled by evaporation of the liquid and thus the desired reactor inlet temperature of the reactants can be adjusted.
[0004] Methylamines are monomethylamine, dimethylamine and trimethylamine, as well as mixtures thereof.
[0005] Methylamines can be produced from methanol and ammonia in the presence of a catalyst in a continuous gas-phase reaction. Although the reaction is exothermic overall, the reactants must be preheated for the reaction. The preheating of the reactants supplied is usually carried out in heat exchangers upstream of the reactor. As described in JP 60045550 A, the product gas stream resulting from the reaction can be used for preheating. For this purpose, the product gas stream is passed through the heat exchangers used for preheating. Due to the overall exothermic nature of the reactions, the temperature in the reactor between the reactor inlet and reactor outlet increases. Due to the higher temperature at the reactor outlet, when the product gas stream is used to heat the reactants in steady-state operation, no additional energy is required to preheat the reactants.
[0006] The required temperatures in the reactor are determined by technical limitations. The reactor inlet temperature must be sufficiently high so that the reaction on the catalyst starts immediately, the methanol is largely converted, and the reaction approaches thermal equilibrium. On the other hand, the temperature in the catalyst bed must not be too high, as this would otherwise lead to increased decomposition of the methylamines into gaseous and solid degradation products or exceed the maximum permissible reactor temperature. Precise adjustment of the reactor inlet temperature is therefore crucial for efficient methylamine production.
[0007] The reaction of methanol and ammonia to form methylamines typically produces more trimethylamine than required. Excess trimethylamine is typically recycled to the plant, added to the reactor feed, and converted to dimethylamine and monomethylamine in an endothermic reaction within the reactor. The recycling of trimethylamine to the reactor thus results in an overall less exothermic process. The same applies to the recycling of the other methylamines.
[0008] With the currently used processes for preheating the reactants, fluctuations in the reactor inlet temperature can occur due to ambient temperature fluctuations or varying amounts of recycled trimethylamine, as well as load changes. These fluctuations subsequently lead to fluctuations in the reactor temperatures. In the worst case, the reactor temperature becomes so high that the methylamines decompose or the maximum permissible reactor temperature is exceeded.
[0009] The theoretical possibility of limiting the reactor inlet temperature of the reactant stream by bypassing the product gas stream used for preheating when the upper temperature limit is reached is not feasible from a process engineering perspective. Rapidly and controlled diversion of the large volume of hot and pressurized product gas stream would require extremely complex and expensive control valves.
[0010] WO 2005 / 028416 A describes a process in which, by means of targeted pressure control of the reactant streams to be heated or the reactor effluent to be cooled, the evaporation or condensation temperature is adjusted so that exactly as much energy is transferred in the heat exchangers as is needed to reach the required reactor inlet temperature. The disadvantages of this process are that it is difficult to control, has a sluggish control characteristic, and causes additional pressure loss.
[0011] Furthermore, the process according to WO 2005 / 028416 A requires increased control interventions with increased heat recovery by preheating the reactant streams with other suitable energy sources that can be used within the process, resulting in a further increase in pressure loss. During partial load operation of the plant, the specific heat transfer may increase. To compensate for this increased specific heat transfer, control interventions are required in this process, which also generate additional pressure loss.
[0012] The present invention was therefore based on the object of providing a process for the production of methylamines from methanol and ammonia by gas-phase reaction, in which the reactor inlet temperature is adjusted quickly, efficiently, and precisely within a narrow range and without pressure loss. The aim was to minimize energy loss through heat dissipation, and to minimize the need for external energy input for preheating and superheating the reactants during steady-state operation.
[0013] Accordingly, the invention relates to a process for the production of methylamines by continuous gas phase reaction, in which a reactant stream comprising the reactants methanol and ammonia is evaporated in one or more heat exchangers and optionally further heating elements and heated to a reactor inlet temperature in the range from 350°C to 410°C, and then fed to one or more reactors, where it is converted in the presence of a heterogeneous catalyst at an absolute pressure in the range from 15 to 35 bar to the methylamines monomethylamine, dimethylamine and trimethylamine, which are withdrawn from the reactor as a product gas stream together with water and any unreacted reactants, as well as with any by-products, characterized in that the reactor inlet temperature of the reactant stream is adjusted by operating at least one of the heat exchangers with the product gas stream, which has previously been quenched by introducing a quench liquid,which has a boiling point in the range of -40°C to 120°C under normal pressure, is cooled to the required temperature in the product gas stream.
[0014] The process according to the invention for producing methylamine is therefore based on the concept of cooling the temperature of the product gas stream emerging from the reactor before it enters the heat exchanger to such an extent that the reactant stream is only heated to the desired reactor inlet temperature. The required cooling of the product gas stream is achieved by introducing and evaporating a suitable quench liquid, which then completely evaporates. Liquids that completely evaporate under the conditions of the product gas stream (i.e., at temperatures of at least 350°C and an absolute pressure of 15 to 35 bar) are generally suitable for this purpose. This is the case for liquids with a boiling point in the range of -40°C to 120°C at atmospheric pressure. The temperature of the product gas stream is lowered by the evaporation of the quench liquid without any energy being dissipated or lost.
[0015] To produce methylamine from methanol and ammonia, the reactants are first evaporated and superheated in one or more heat exchangers. The reactants, thus heated to a temperature in the range of 350°C to 410°C, preferably in the range of 350°C to 390°C, and particularly preferably in the range of 360°C to 380°C, are fed to the reactor at this temperature (reactor inlet temperature).
[0016] In addition to methanol and ammonia, the reactor is usually fed with methylamines, which are formed during the reaction in quantities that exceed the current demand. In particular, it may be necessary to recycle trimethylamine, which is usually formed in larger quantities than required, into the reaction and thus increase the proportion of monomethylamine and dimethylamine in the methylamines for the entire process. By recycling trimethylamine in this way and the associated endothermic transmethylation, the exothermicity of the overall reaction in the reactor is reduced. Due to the overall exothermic reaction, the temperature increases from reactor inlet to reactor outlet. To ensure that the temperature in the reactor does not rise above 450°C, the reactor inlet temperature of the reactant stream must be adjusted carefully.In this case, a relatively low reactor inlet temperature should be set if the reaction is run with low recirculation of methylamines, i.e., with high exothermicity (preferably a reactor inlet temperature of 350°C to 370°C), or a relatively high reactor inlet temperature should be set if the reaction is run with high recirculation of methylamines, i.e., with low exothermicity (preferably a reactor inlet temperature of 370°C to 410°C). Excess reaction heat can be removed by cooling the reactor if necessary. The reaction in the reactor is preferably run such that the product gas stream at the reactor outlet has a temperature in the range of 390°C to 450°C.
[0017] In the reactor, the reactants are converted into monomethylamine, dimethylamine, and trimethamine in the presence of a heterogeneous catalyst at an absolute pressure in the range of 15 to 35 bar. This pressure range typically applies not only to the reactor, but also to the entire feed of the reactant stream through the heat exchangers and the discharge of the product gas stream via the heat exchangers, including any liquid separators. Accordingly, an absolute pressure in the range of 15 to 35 bar is preferably also present at the point where the quench liquid is introduced into the product gas stream.
[0018] A product gas stream is withdrawn from the reactor, which contains the methylamines monomethylamine, dimethylamine, and trimethylamine, as well as water produced as a byproduct during the reaction. Typically, the product gas stream also contains unreacted methanol, unreacted ammonia, and other byproducts such as carbon monoxide and carbon dioxide.
[0019] The reaction can take place in one or more reactors. Preferably, the reaction takes place in one reactor. If multiple reactors are used, they can be connected in parallel or in series, or in combinations thereof.
[0020] The heterogeneous catalyst is typically a silicon dioxide-doped alumina, such as BASF's N7066 catalyst. The heterogeneous catalyst is typically used as a fixed bed.
[0021] The product gas stream can then be separated into the individual reaction products. Separation is typically carried out by distillation in several distillation columns. The formation of methylamines usually produces more trimethylamine than desired. The excess trimethylamine can then be recycled to the reaction in the reactant stream. The reaction of trimethylamine with ammonia to form monomethylamine and dimethylamine, or with monomethylamine to form dimethylamine, is endothermic. Similar endothermic reactions occur when the other methylamines are recycled. Part of the heat of reaction released during the exothermic reaction of ammonia and methanol to form methylamines is consumed for the endothermic reaction. For this reason, the reactor can also be operated adiabatically.
[0022] During the heat release to heat the reactant stream, the product gas stream is cooled and at least partially condensed in the heat exchangers. The condensate can preferably be separated from the gaseous components of the cooled product stream by means of a liquid separator. This can be a separate liquid separator downstream of the heat exchangers or, preferably, a liquid separator integrated into the heat exchangers. By means of such integrated liquid separators (condensate separators) or directly downstream of the individual heat exchangers, erosion caused by entrained condensate droplets can be avoided. The liquid product streams accruing in the condensate separators, like the product gas stream leaving the heat exchangers, are preferably subjected to further treatment for the separation and, if appropriate, fractionation of the methylamines.
[0023] The heat required to start the reaction can be supplied by additional heating of the reactants using externally heated heat exchangers or electric heating elements. If the product gas stream does not sufficiently heat the reactant stream during steady-state operation, the missing heat can also be supplied using externally heated heat exchangers or electric heating elements.
[0024] All heat exchanger designs known to those skilled in the art can be used as heat exchangers for preheating the reactant stream. Suitable heat exchangers include, for example, shell-and-tube heat exchangers, spiral heat exchangers, or plate heat exchangers. Preference is given to shell-and-tube heat exchangers. Modified floating-head heat exchangers are particularly preferred for this purpose. The heat exchangers used can be operated in cocurrent, countercurrent, or crosscurrent modes. Furthermore, any combination of crosscurrent, countercurrent, and cocurrent modes known to those skilled in the art is possible. For example, when using multiple heat exchangers, at least one heat exchanger can be operated in cocurrent, while the remaining heat exchangers operate in countercurrent. The preferred operating mode for heat exchangers for heating the reactants is countercurrent.The heat exchangers preferably have an integrated condensate separator for the separation of condensate that is produced when the product gas stream is cooled in the heat exchanger.
[0025] To regulate the reactor inlet temperature, measured values are typically recorded at various points in the methylamine production plant. For example, the flow rate of the ammonia-containing reactant stream and the flow rate of the methanol stream can be measured before the methanol is added to the ammonia-containing reactant stream. Furthermore, when methanol is added at various positions in the ammonia-containing reactant stream, the flow rate of the individual methanol substreams can be measured. If the product gas stream is split into several substreams, a flow rate measurement can be performed in each substream. A flow rate measurement can also be used to measure the amount of additional steam required to heat the reactants.
[0026] For targeted control of the reactor inlet temperature, it is necessary to measure the reactor inlet temperature of the reactant stream. In addition to the reactor inlet temperature, the temperature of the ammonia-containing reactant stream, the temperature of the methanol, temperatures within the reactor, and the temperature of the product gas stream at the reactor outlet can also be measured.
[0027] The process according to the invention preferably comprises an automatic control loop that controls the introduction of quench liquid into the product gas stream via a control valve depending on the measured reactor inlet temperature. In addition, other measured values, such as the flow rate of the various process streams, the reactor outlet temperature, and the temperature of the product stream after the introduction of the quench liquid, can be incorporated into the control loop to optimize the control of the reactor inlet temperature.
[0028] For an energy-efficient process for the production of methylamines, it is advisable to heat the reactant stream to reactor inlet temperature during steady-state operation, both at partial and full load, without the use of externally heated heat exchangers or electrical heating elements, i.e., only using heat exchangers heated by warm process streams, in particular the product gas stream. For example, it is fundamentally possible to heat and partially evaporate the liquid mixture of ammonia and any recycled methylamines with an external stream in the first heat exchanger (3) of the process shown in Fig. 1. However, this is preferably done using a warm process stream that is to be cooled, for example, a warm wastewater stream from the process.
[0029] Due to ambient temperature fluctuations, varying amounts of recycled methylamines, or other fluctuations in operational management, particularly at partial load, as well as fluctuations in the energy supplied to the preheaters (heat exchangers and electrical heating elements for heating, evaporation, and superheating of the reactant stream), a correspondingly energy-efficient process design can lead to undesirably high reactor inlet temperatures. Efficient and rapid control of the reactor inlet temperature is therefore essential for an energy-efficient process design.
[0030] In the process according to the invention for producing methylamines, the temperature of the product gas stream is cooled by introducing and evaporating a suitable liquid (quench liquid) to such an extent that the temperature of the reactants leaving the one or more heat exchangers heated by the product gas stream does not exceed the value required for proper operation of the reactor. A suitable quench liquid is a liquid having a boiling point in the range from -40 to 120°C under atmospheric pressure, preferably in the range from -35 to 105°C under atmospheric pressure. Such a quench liquid can be a pure substance or a mixture of several substances. Preferred quench liquids already present in the process are ammonia, methanol, water, mono-, di-, and trimethylamine, and mixtures thereof.Particularly preferred quench liquids are substances or mixtures thereof that do not result in significant additional expenditure during subsequent separation of the reactor effluent, such as water, condensate obtained during cooling of the product stream, or bottoms from distillation columns of this subsequent separation. The condensate obtained during heating of the reactant stream and the associated cooling of the product gas stream is very particularly preferred as the quench liquid.
[0031] The quench liquid is preferably introduced into the product gas stream by injection using a pump and control valve, by supply using a control valve and jet nozzle, or by hydrostatic supply via a control valve. Injection using a pump and control valve is particularly preferred. With injection using a pump and control valve, the pump builds up the required overpressure for the injection, and the control valve controls the inlet into the product gas stream. With hydrostatic supply, the system elements are arranged so that the quench liquid is supplied to the product gas stream via hydrostatic pressure. The control valve then controls the inlet into the product gas stream. When the quench liquid is introduced via a jet nozzle, the liquid is sucked in by the product gas stream itself and atomized in the nozzle.The inlet to the product gas stream is controlled by a control valve. This variant is applicable when the product gas stream has a sufficiently high pressure.
[0032] Rapid evaporation of the quench liquid introduced is desired. For this purpose, the quench liquid is preferably introduced into the product gas stream at a temperature that is only slightly below its boiling point at the operating pressure prevailing at the point of introduction, particularly preferably at a temperature of no more than 20°C below this boiling point and very particularly preferably at a temperature of no more than 10°C below this boiling point. In addition, for rapid evaporation, the quench liquid is preferably divided into small droplets with a high specific surface area by atomization in nozzles. Nozzle shapes known to the person skilled in the art, such as flat jet nozzles, hollow cone nozzles, full cone nozzles, spiral nozzles, mist nozzles or even propulsion jet nozzles, can be used for this purpose. The nozzles can be combined with a static mixer. Alternatively, the quench liquid can be dispersed on large surfaces, such asrandom beds or structured packings, as used in distillation technology. The flow through the random beds can be cocurrent, crosscurrent, or countercurrent to the flow direction of the quench liquid. In a preferred embodiment of the process in which the quench liquid is introduced by injection using a pump and control valve, the quench liquid to be introduced is distributed by means of a liquid distributor onto a random bed or structured packing or preferably by means of a nozzle in the product gas stream. In a preferred embodiment of the process in which the quench liquid is introduced by hydrostatic supply, the quench liquid to be introduced is distributed by means of a liquid distributor onto a random bed or structured packing in the product gas stream.Only small amounts of quench liquid are required to cool the product gas stream.
[0033] The invention also relates to a corresponding device for the continuous conversion of reactants to a product gas stream in an overall exothermic reaction, comprising a) one or more reactors to which the reactants are fed and from which the product gas stream is withdrawn, b) one or more heat exchangers upstream of the reactors, with which the reactants are brought to the required reactor inlet temperature and through which the product gas stream is passed for the heat input, and c) one or more measuring devices for measuring the reactor inlet temperature of the reactants, characterized in that the device comprises a controlled introduction of evaporable liquids into the product gas stream before it is passed through one or more of the heat exchangers.By means of this introduction, the temperature of the product gas stream can be cooled by evaporating the liquid, the heat exchange in the heat exchanger can be limited and thus the desired reactor inlet temperature of the reactants can be set.
[0034] In a preferred embodiment, the device according to the invention comprises one or more liquid separators, with which a condensate is separated from the product gas stream after or during passage through the heat exchangers, and a feed line which feeds the condensate to the controlled introduction, where it is introduced into the product gas stream as an evaporable liquid (quench liquid).
[0035] Accordingly, the invention relates to an apparatus for the continuous conversion of reactants to a product gas stream in an overall exothermic reaction, comprising a) one or more reactors to which the reactants are fed and from which the product gas stream is withdrawn, b) one or more heat exchangers upstream of the reactors, with which the reactants are brought to the required reactor inlet temperature and through which the product gas stream is passed for the heat input, c) one or more measuring devices for measuring the reactor inlet temperature of the reactants, and d) one or more liquid separators, with which a condensate is separated from the product gas stream after or during passage through the heat exchangers, characterized in that the apparatus comprises a controlled introduction of a portion of the condensate into the product gas stream before it is passed through one or more of the heat exchangers.By means of this introduction, the temperature of the product gas stream can be cooled by evaporating the condensate, the heat exchange in the heat exchanger can be limited and thus the desired reactor inlet temperature of the reactants can be set.
[0036] In a preferred embodiment of the device according to the invention, the controlled introduction of the evaporable liquid or condensate into the product gas stream comprises (a) a pump with a control valve or (b) a control valve with a jet nozzle or (c) a hydrostatic feed line via a control valve. In order to ensure faster evaporation of the evaporable liquid or condensate and thus faster cooling of the product gas stream, the device according to the invention can comprise a nozzle for introducing the evaporable liquid or condensate into the product gas stream. By means of the nozzle, the evaporable liquid or condensate can be introduced into the product gas stream in the form of small droplets, which evaporate quickly due to their relatively large surface area. A nozzle is particularly suitable for introducing condensate via a pump and control valve.In addition, a nozzle is an inherent element of introduction via a control valve and propulsion jet nozzle. Alternatively, the device according to the invention can also comprise a random bed or a structured packing at the point at which the evaporable liquid or condensate is introduced into the product gas stream, onto which the introduced evaporable liquid or condensate is distributed by means of a liquid distributor. Distributing the evaporable liquid or condensate over the large surface area of such a bed or packing also enables rapid evaporation. Such a bed or packing is particularly suitable for introducing evaporable liquid or condensate via a hydrostatic feed line via a control valve, but also for introducing evaporable liquid or condensate via a pump and control valve. Accordingly, this preferred embodiment is characterized in that:
[0037] • that when the evaporable liquid or the condensate is introduced by a pump with a control valve, the evaporable liquid or the condensate is distributed in the product gas stream via a liquid distributor and a random bed or structured packing or preferably via a nozzle, or
[0038] • that when the evaporable liquid or the condensate is introduced via a hydrostatic feed line via a control valve, the evaporable liquid or the condensate is distributed in the product gas stream via a liquid distributor and a random bed or a structured packing.
[0039] In a particular embodiment of the device according to the invention, the condensate passes through one or more purification devices before being returned to the product gas stream. These purification devices are preferably distillation columns in which methylamines are withdrawn overhead, and the bottom product is then returned to the product gas stream as condensate. Alternatively or additionally, condensate can also be introduced into the product gas stream, which forms in such purification devices from a gaseous product gas stream, for example, the liquid bottom product of a distillation column into which the gaseous product gas stream is fed and from which methylamines are withdrawn overhead. The invention is illustrated by the following figures:
[0040] Figures 1 to 3 show the flow diagrams of certain embodiments of the process according to the invention for producing methylamines from methanol and ammonia.
[0041] Figure 1 :
[0042] In the process for producing methylamines shown in Fig. 1, a first reactant stream ('ammonia and amines feed') forms the feed to a first preheater (3). In addition to ammonia, the feed may also contain recycled by-products and excess methylamines from the process. This reactant stream is heated in the first preheater (3). The supplied heat is provided by a warm process stream (1) to be cooled. In order to limit the heat transferred, if necessary, the warm process stream can be completely or partially bypassed around the preheater (3) via the control valve (2). This preheated first feed is then mixed with the methanol feed ('methanol feed') and fed to the second preheater (4). This stream is referred to below as the reactant stream. The second preheater (4) is heated with the product gas stream ('stream 4').The reactant stream, which has been further heated in this way, is passed through a third preheater (5), which is heated with steam. This is primarily used to heat the reactant stream during the start-up process. It is also used if insufficient heat is transferred in the two preceding preheaters (3 and 4). In the fourth preheater (6), the reactant stream is superheated to the reactor inlet temperature. This preheater (6) is heated with the product gas stream coming from the reactor (“Stream 4”). The reactant stream, heated to reactor inlet temperature, finally flows through a final electrically operated preheater (7) before being fed to the reactor (8) (“Stream 7”). This final preheater (7) is primarily used to heat the reactant stream during the start-up process. It is also used if the reactant stream does not reach the required reactor inlet temperature in the other preheaters.While the first preheaters (3, 4, 5 & 6) are heat exchangers heated by external (5 & possibly 3) or internal (4, 6 & possibly 3) streams, the last preheater (7) is an electric heating element. In the reactor (8), in addition to the exothermic conversion of methanol and ammonia to monomethylamine, dimethylamine and trimethylamine, the conversion of unused, recycled trimethylamine to dimethylamine and monomethylamine also takes place in an endothermic reaction. Overall, however, the reactions taking place in reactor (8) are exothermic. For this reason, the temperature across reactor (8) increases. The temperature of the reactor effluent ("Stream 2") is higher than that required at the reactor inlet ("Stream 7"). Therefore, the product gas stream from the reactor effluent in the preheaters (6 & 4) can be used to heat the reactor inlet.For this purpose, the product gas stream ("Stream 4") is passed in countercurrent through the fourth preheater (6) and the second preheater (4). After the second preheater (4), the cooled and now two-phase product stream is separated into a liquid and a gaseous phase in a liquid separator (10). The gas stream leaving the liquid separator (10) is fed to the processing stage. A portion of the condensate ("Stream 3") from the liquid separator (10) is injected into the reactor effluent ("Stream 2") via a pump (11) and a control valve (12) at a point (9.1) upstream of the fourth preheater (6). The injected liquid evaporates and extracts the necessary latent heat from the reactor effluent, thereby lowering the temperature of the product gas stream ("Stream 4") leading to the fourth preheater (6). Due to the reduced temperature, a smaller amount of heat is transferred to the reactor feed to be heated in the fourth preheater (6).Combined with a temperature measurement in the inlet to the reactor (8), a temperature control system can be established. This allows for rapid, direct control of the reactor inlet temperature. The condensate from the liquid separator (10), which is not required for temperature control, is also fed into the methylamine processing line.
[0043] In addition to the design variant shown here with a total of five preheaters (3, 4, 5, 6 and 7), a large number of variations regarding the number, arrangement and connection of heat exchangers for preheating the reactant stream are possible.
[0044] Instead of the countercurrent operation of the preheaters shown here, operation in cocurrent or crosscurrent is also possible, as well as any combination of countercurrent, cocurrent or crosscurrent.
[0045] Figure 2:
[0046] The process shown in Fig. 2 is a variant of the process shown in Fig. 1 for producing methylamines, in which the liquid is sucked in from the liquid separator (10) via a propulsion jet nozzle (9.2) and atomized in the nozzle. The product gas stream (“Stream 2”) itself is used as the propellant. This variant can be applied if the product gas stream has a sufficiently high pressure. Figure 3: The process shown in Fig. 3 is a variant of the process shown in Figure 1 for producing methylamines, in which the preheaters in the plant are arranged so that the liquid from the liquid separator (10) can be introduced hydrostatically into the product gas stream (“Stream 2”). In order to create the largest possible liquid surface, the liquid is distributed over a random bed or structured packing (9.3) distributed, as is also known from distillation technology.
[0047] Examples:
[0048] The following example illustrates the effect of the inventive introduction of quench liquid into the product gas stream of a process for producing methylamines, as described in more detail in Fig. 1 to Fig. 3. The reactor effluent (product gas stream) typically has a composition as summarized in Table 1. This composition can vary depending on the design and operating mode of the process. Table 1:
[0049] Typical composition of the product gas stream for the process according to the invention for
[0050] Production of methylamines
[0051] Typically, a reactor inlet temperature of, for example, 360°C is set. With an adiabatic temperature increase in the reactor of approximately 50°C to 80°C, as is usual for the process, a typical reactor outlet temperature of 410°C to 440°C results. Thus, a temperature reduction of the reactor output (product gas stream) of, for example, 10°C leads to a significant reduction in the temperature difference between the feed and output streams and thus to a likewise considerable reduction in the energy transferred in the preheater section. According to the invention, such a temperature reduction is achieved by introducing a suitable quench liquid into the product gas stream. Based on the process conditions (reactor output: 20.8 bar, 427.2°C, temperature of the quench liquid: seeUsing the temperature coefficient (Table 2) and the thermodynamic data of the product gas stream and the quench liquid introduced, the amount of quench liquid required to cool a given amount of product gas stream can be determined. These results are summarized in Table 2 for various possible quench liquids.
[0052] Table 2:
[0053] Determination of the amount of liquid to be introduced into the reactor effluent for various possible quench liquids required to reduce the temperature of the reactor effluent by 10°C.
[0054] Condensate here refers to the condensate that accrues when the reactor effluent is cooled in the heat exchangers of the preheater section by transferring heat to the reactor feed. In the process described in Figs. 1 to 3, condensate is used to reduce the temperature of the product gas stream. In principle, however, the other quench fluids listed in Table 2 can also be used to reduce the temperature. For a selected operating condition of the process according to Fig. 1, Table 3 shows the data (compositions, pressure, temperature, and state of aggregation) for cooling the reactor effluent from 427.2°C to 370°C with condensate as an example.
[0055] Table 3:
[0056] Compositions and physical parameters of the streams (streams 1 to 4) for carrying out the process for producing methylamines as shown in Fig. 1, in which the product gas stream is cooled by introducing condensate to such an extent that the required reactor inlet temperature of the reactant stream is maintained.
[0057] With the temperature reduction shown in this example, the temperature difference between the process stream leaving the last heat exchanger and the process stream entering the heat exchanger is reduced from 67.2°C to 10°C.
[0058] The amount of 85.92 kg of condensate per ton of reactor discharge required for cooling by 57.2°C corresponds to approximately 15 kg of condensate per ton of reactor discharge per 10°C cooling.
Claims
Patent claims 1. A process for the preparation of methylamines by continuous gas phase reaction, in which a reactant stream comprising the reactants methanol and ammonia is evaporated in one or more heat exchangers and optionally further heating elements and heated to a reactor inlet temperature in the range from 350°C to 410°C, and then fed to one or more reactors where it is converted in the presence of a heterogeneous catalyst at an absolute pressure in the range from 15 to 35 bar to the methylamines monomethylamine, dimethylamine and trimethylamine, which are withdrawn from the reactor as a product gas stream together with water and any unreacted reactants, as well as with any by-products, characterized in that the reactor inlet temperature of the reactant stream is adjusted by operating at least one of the heat exchangers with the product gas stream which has previously been quenched by introducing a quench liquid,which has a boiling point in the range of -40°C to 120°C under normal pressure, is cooled into the product gas stream to the required temperature.
2. The process according to claim 1, characterized in that the reactor inlet temperature is measured continuously.
3. The process according to claim 1 or 2, characterized in that the reaction in the reactor is carried out such that the product gas stream at the reactor outlet has a temperature in the range of 390°C to 450°C.
4. The process according to one of claims 1 to 3, characterized in that the evaporation and adjustment of the temperature of the reactants takes place by means of two or more heat exchangers and the introduction of the quench liquid into the product gas stream takes place upstream of the first heat exchanger for the product gas stream.
5. The process according to any one of claims 1 to 4, characterized in that the quench liquid comprises one or more components selected from the group consisting of monomethylamine, dimethylamine, trimethylamine, ammonia, methanol, water.
6. The process according to any one of claims 1 to 5, characterized in that the product gas stream is wholly or partially condensed and then the resulting methylamines are purified via one or more distillation columns and optionally separated into fractions of individual methylamines or methylamine compositions.
7. The process according to claim 6, characterized in that a trimethylamine-containing or trimethylamine-enriched fraction of the reaction is recycled to the reactor.
8. The process according to any one of claims 1 to 7, characterized in that a liquid stream occurring in the process is used as the quench liquid.
9. The process according to one of claims 1 or 7, characterized in that the product gas stream is cooled and thereby completely or partially condensed, and the resulting condensate is used as quench liquid.
10. The process according to claim 6 or 7, characterized in that a bottoms effluent from one or more of the distillation columns is used as the quench liquid.
11. The process according to any one of claims 1 to 10, characterized in that the quench liquid is introduced into the product gas stream by a) injection by means of a pump and control valve, b) supply by means of a control valve and jet nozzle, or c) hydrostatic supply via a control valve.
12. The process according to claim 11, characterized in that the injected quench liquid is distributed by means of a liquid distributor onto a random bed or structured packing or preferably by means of a nozzle in the product gas stream, or that the hydrostatically supplied quench liquid is distributed by means of a liquid distributor onto a random bed or structured packing in the product gas stream. 13 A device for the continuous conversion of reactants to a product gas stream in an overall exothermic reaction, comprising a) one or more reactors to which the reactants are fed and from which the product gas stream is withdrawn, b) one or more heat exchangers upstream of the reactors, with which the reactants are brought to the required reactor inlet temperature and through which the product gas stream is passed for the heat input, and c) one or more measuring devices for measuring the reactor inlet temperature of the reactants, characterized in that the device comprises a controlled introduction of evaporable liquids into the product gas stream before it is passed through one or more of the heat exchangers, by means of which the temperature of the product gas stream is cooled by evaporation of the liquid,the heat exchange in the heat exchanger is limited and thus the desired reactor inlet temperature of the reactants can be set.
14. The device according to claim 13, characterized in that the device according to the invention comprises one or more liquid separators, with which a condensate is separated from the product gas stream after or during passage through the heat exchangers, and a feed line which feeds the condensate to the controlled introduction, where it is introduced into the product gas stream as a vaporizable liquid.
15. The device according to claim 13 or 14, characterized in that the device for introducing the evaporable liquid into the product gas stream comprises a) a pump with a control valve, b) a control valve with a propulsion jet nozzle, or c) a hydrostatic supply line via a control valve.
16. The device according to claim 15, characterized in that when the evaporable liquid is introduced by means of a pump with a control valve, the evaporable liquid is distributed in the product gas stream via a liquid distributor and a random bed or structured packing or preferably via a nozzle, or that when the evaporable liquid is introduced by means of a hydrostatic feed line via a control valve, the evaporable liquid is distributed in the product gas stream via a liquid distributor and a random bed or structured packing.