Apparatus for the production of nitriles and use thereof

Abstract

It is an object of the invention to specify an electrically heatable reactor for hydrogen cyanide production and the production of other nitriles, which enables a differentiated temperature profile and works with inexpensive standard components. The core of the inventive apparatus (0) is a chamber (1) made from gas-permeable, thermally insulating material that constitutes the actual reaction space. Electrical heating elements (5) project into the chamber (1), such that the chamber (1) can be heated from the inside by heating elements (5). The electrical terminals of the heating elements are outside the reaction space but within the surrounding shell. Unlike in the case of the industrially implemented BMA process, the heat is thus not transported into the reaction space from the outside but generated in the reaction space. Heat is generated by conversion of electrical energy by means of the heating elements (5) by the principle of resistance heating. In order to ensure gastightness of the apparatus (0), a shell (9) is provided, which surrounds the chamber (1) in a gastight manner.

Description

[0001] Apparatus for the production of nitriles and its use

[0002] The invention relates to an apparatus for producing at least one product gas from at least one reactant gas. In particular, the apparatus is intended for the production of nitriles. Furthermore, the invention relates to the use of the apparatus in the production of nitriles, in particular hydrogen cyanide, and in the provision of negative control power.

[0003] Hydrogen cyanide (HCN), the simplest nitrile, is an important synthetic building block in organic chemistry. Hydrogen cyanide is usually produced on an industrial scale using the Andrussow process or the BMA process.

[0004] An introduction to the technology of hydrogen cyanide production is provided by:

[0005] Gail, E., Gos, S., Külzer, R., Lorösch, J., Rubo, A., Sauer, M„ Kellens, R., Reddy, J., Steier, N. and Hasenpusch, W. (201 1). Cyano Compounds, Inorganic. In Ullmann's Encyclopedia of Industrial Chemistry, (Ed.). DOI 10.1002 / 14356007.a08_159.pub3

[0006] In the BMA process (BMA = hydrogen cyanide from methane and ammonia), hydrogen cyanide is produced from methane (CH4) and ammonia (NH3) in a highly endothermic reaction that requires comparatively high reaction temperatures of 1000–1300°C. Unlike the Andrussow process, the BMA process is carried out in the absence of oxygen. The necessary use of fossil fuels to provide the reaction enthalpy, combined with the low energy yield for hydrogen cyanide, results in significant CO2 emissions.

[0007] The energy required for the BMA process is generated in a separate combustion chamber through the combustion of natural gas or recycled hydrogen (H2), which is produced as a byproduct of the BMA process. Due to the minimum temperatures required for the hydrogen cyanide reaction, only a portion of the heat energy is used for the reaction itself; the remaining portion is required to heat the combustion air and fuels.

[0008] As an alternative energy source, HCN can be produced using electricity instead of fossil fuels. When electricity from renewable sources is used, the process is largely CO2-neutral. Furthermore, an electrically heated BMA process offers further advantages over a fossil-fuel-fired BMA process, for example, in the area of ​​operating costs: • By avoiding the inevitable energy loss on the fuel gas side due to heating the combustion air to the high required minimum reaction temperature, a higher energy efficiency can be expected.

[0009] • Since no refractory materials need to be used to line the reactor, faster start-up and shut-down cycles are achieved.

[0010] • A more homogeneous temperature regime allows for higher yields, thereby reducing the specific amounts of methane and ammonia required for hydrogen cyanide production. It is known that significantly higher yields can be achieved with a homogeneous temperature distribution while simultaneously reducing by-product formation.

[0011] There are also advantages in terms of investment costs for an electrically heated BMA system compared to a thermally heated system:

[0012] • the absence of fuel gas and flue gas chambers allows a more compact design and higher space-time yields,

[0013] • Cost-effective, modular connections are also possible.

[0014] Finally, an electrically operated BMA process is more sustainable:

[0015] • the resulting hydrogen-containing residual gas can, if necessary, replace natural gas as heating gas in downstream processes and achieve an additional CO2 reduction.

[0016] • By eliminating the refractory materials and a process design that allows a higher degree of automation, flare times can be significantly minimized in the event of operational disruptions.

[0017] • The hydrogen in the resulting residual gas has a significantly lower CO2 footprint than hydrogen produced from fossil hydrocarbons in the steam reformer and can, after any necessary purification, be used as a raw material for further chemical reactions.

[0018] For all these reasons, there is interest in developing an electrically powered BMA process with which hydrogen cyanide can be produced on an industrial scale.

[0019] Various concepts are known for the production of HCN in electrically heated reactors: Firstly, the use of electrically heated fixed-bed reactors is described for hydrogen cyanide production, whereby the heating of the catalyst bed can be achieved by induction; cf. WO2017186437A1.

[0020] On the other hand, structured catalyst bodies, so-called monoliths, made of electrically conductive material are used, as described in WO2019228798A1 or WO2021 / 063799A1. In these publications, the reactants are passed through the catalyst-coated channels of an electrically heated structure (resistance heating).

[0021] DE10317197A1 discloses a reactor for producing hydrogen cyanide using the BMA process. It can be equipped with either induction heating or resistance heating. Heating is provided by a module arranged in the reaction chamber, through which the reaction mixture flows longitudinally. The reactor is surrounded by thermal insulation and provided with a gas-tight double jacket. The jacket is filled with an inert gas. The disadvantage of this reactor is its monolithic structure, which makes defect-free, homogeneous production from a green body very complex. It is prone to material stress and even cracks due to thermal stresses and is considered complex for industrial-scale installations.

[0022] In view of this state of the art, the present invention is based on the object of specifying an electrically heatable reactor for the production of gaseous products such as hydrogen cyanide and other nitriles, which is resistant to thermal (cyclic) stress and has a high availability of the heating elements, enables a differentiated temperature profile and requires cost-effective standard components.

[0023] This object is achieved by an apparatus according to claim 1. A first subject matter of the invention is therefore an apparatus for producing at least one product gas from at least one reactant gas, in particular for producing nitriles as a product, having the following features: a) the apparatus comprises a chamber with a gas-permeable and heat-insulating wall, with an inlet for the reactant gas, with an outlet for the product gas and with a main flow direction extending from the inlet to the outlet; b) the apparatus comprises a gas-tight jacket which encloses the chamber, with the inlet and the outlet being led through the jacket; c) an intermediate space is provided between the chamber and the jacket, which intermediate space encloses the chamber and is in turn enclosed by the jacket;d) the apparatus comprises at least one electrical heating element which extends through the chamber and pierces its wall at least once, and which has at least two electrical connections which are arranged inside the intermediate space and outside the chamber; e) the apparatus comprises an electrical voltage source arranged outside the casing, which is connected at least via a first electrical line to the first electrical connection of the heating element and via a second electrical line to the second electrical connection of the heating element, wherein the first and second electrical lines are passed through the casing; f) the apparatus comprises at least one connection element for a filling gas source arranged outside the casing, which can be fluidly connected to the intermediate space via a filling gas line in such a way that the intermediate space can be supplied with a filling gas obtained from the filling gas source;g) a catalyst is arranged in the chamber;

[0024] The core of the apparatus according to the invention is a chamber, which represents the actual reaction space. The electrical heating elements are located in the chamber, allowing the chamber to be electrically heated from the inside. Unlike in industrially practiced BMA processes, the heat is not transported into the reaction space from the outside, but is generated in the reaction space. Heat is generated in the heating elements by converting electrical energy according to the resistance heating principle. Unlike in industrially practiced BMA processes, the apparatus according to the invention does not experience energy loss due to flue gas generated at reaction temperature. This significantly increases energy efficiency.

[0025] A key aspect of the apparatus according to the invention is that the heating elements protrude through the wall of the chamber. This means that the heating elements are not only located inside the chamber, but also partially outside the chamber. The section of the heating elements located inside the chamber serves to heat the chamber. The sections of the heating elements located outside the chamber serve for the electrical connection. Each heating element has at least two sections located outside the chamber because each heating element requires at least two electrical connections. Each electrical connection is located on a section of the heating element that lies outside the chamber.

[0026] Since the wall of the chamber is lined with and / or made of a heat-insulating material, the temperature outside the chamber is lower than inside the chamber, making electrical contact easier to achieve there.

[0027] The inventive passage of the heating elements through the wall is also based on the realization that sealing the chamber in the area of ​​the heating elements is not possible anyway. Due to thermal expansion, sufficient play must be ensured in the passage of the heating elements to allow relative movement between the wall and the heating elements. According to the invention, the passage of the heating elements through the wall is intended to be gas-permeable. In order to prevent the transfer of reactant or product gases into the intermediate space, the added fill gas is used. This also means that the pressure in the intermediate space must always be at least the same or higher than that in the chamber in order to prevent reactant or product gases from escaping from the chamber.

[0028] To ensure the gas-tightness of the apparatus, the invention provides a jacket that encloses the chamber in a gas-tight manner. This creates an intermediate space between the jacket and the chamber wall. According to the invention, the intermediate space is filled with the filler gas, which cannot escape to the outside due to the gas-tight nature of the jacket. The filler gas is predominantly nitrogen, hydrogen, or a hydrocarbon, or a mixture of predominantly nitrogen, hydrogen, and hydrocarbon. The filler gas may contain traces of other gases. The filler gas can be recycled from the downstream process of the method, since the residual gas generated in the BMA process may contain the filler gases listed above.

[0029] During operation, the gas pressure in the gap is regulated so that it is continuously slightly higher than the reaction pressure in the chamber. This largely prevents gases from the interior of the chamber from entering the gap. If this does happen, it's not a problem because the jacket is gas-tight. Conversely, if some of the filling gas penetrates the gas-tight wall into the chamber, this is also uncritical.

[0030] The jacket is made of thermally conductive metal and also serves to dissipate heat. The jacket absorbs the heat radiation emanating from the wall and dissipates it into the environment. Since the space between the wall and the jacket is filled only with gas, the heat radiation from the wall to the jacket is unaffected.

[0031] To further improve heat dissipation, the gas-tight jacket can be equipped with an additional heat exchanger. The heat exchanger is located outside the jacket and connected to the jacket in a heat-conducting manner. The radiant heat absorbed by the jacket is thus dissipated via the heat exchanger. The heat exchanger is preferably supplied with a cooling fluid. For this purpose, the heat exchanger is fluidly connected to a cooling fluid source via a supply line and to a cooling fluid sink via a return line. In this way, the cooling fluid flows from its source through the supply line into the heat exchanger, absorbs the heat from the jacket, and flows via the return line to the sink. The temperature of the cooling fluid generally increases in the process, so that the temperature of the cooling fluid in the return line is higher than in the inlet. It is also conceivable to combine the source and sink of the cooling fluid in a second heat exchanger, thus creating a cooling fluid circuit.Suitable cooling fluids include air, gaseous or liquid nitrogen, gaseous argon, gaseous or liquid water, liquid oil, gaseous ammonia, gaseous hydrocarbons, or mixtures thereof. The cooling fluid can change its thermodynamic state in the heat exchanger, for example, by evaporating. It is also conceivable to use the reactant gas mixture as the cooling fluid and preheat it in the heat exchanger. The return flow then leads directly into the chamber or via the inlet into the chamber. The chamber thus serves as a coolant sink.

[0032] Various designs of the heat exchanger are possible. In a first embodiment, the gas-tight shell is double-walled (double shell). A cavity is created between the two walls of the shell, which is filled with the cooling fluid. Heat transfer then occurs directly from the inner wall of the double shell to the cooling fluid. The double shell filled with cooling fluid has the advantage of providing additional protection against gas escape should the inner shell fail.

[0033] Alternatively, it is conceivable for the heat exchanger to be designed as a cooling coil that is wrapped around the shell. The cooling coil connects the supply and return lines of the cooling fluid.

[0034] In its simplest form, the cooling coil is a tube filled with a cooling fluid, which is connected to the outside of the gas-tight casing via thermal bridges. The tube, like the casing, is made of steel. The thermal bridges are steel webs welded to the tube and casing. The steel webs thus serve to attach the cooling coil to the casing and also act as a thermal bridge between the casing and the cooling coil.

[0035] Alternatively, the cooling coil can be created by welding an open profile onto the outside of the gas-tight jacket. The cooling fluid is then located at least partially between the profile and the outside of the gas-tight jacket. This design has the advantage that heat transfer occurs directly from the jacket to the cooling fluid—without any detour via thermal bridges.

[0036] The chamber wall is preferably constructed of multiple layers. It preferably comprises an outer metal shell and an insulation layer made of a thermally insulating material arranged inside the shell. The metal shell stabilizes the chamber and radiates heat into the space. To minimize heat loss, insulation made of a thermally insulating material is used, the thermal conductivity of which is much lower than that of the metallic shell. The insulation is preferably made of a mineral or ceramic material with high temperature resistance and low specific thermal conductivity. Mineral microfiber panels are preferably used as insulation.

[0037] It is also conceivable to use multi-layer thermal insulation, with the individual layers of thermal insulation having different specific thermal conductivities.

[0038] Particularly preferably, the heat-insulating wall on the chamber side comprises an inner layer with a closed surface. A closed surface means that the surface is largely pore-free. This can be achieved, for example, by arranging individual structural elements with a suitable surface offset one above the other. In particular, the wall can be provided on its inner side with metallic or ceramic elements that are not made of fiber material. Metallic and ceramic elements can be manufactured largely pore-free using technologies commonly used for these materials.

[0039] A particularly preferred embodiment provides that the inner wall of the chamber is provided with a catalytically active or activatable coating containing the catalyst. This makes the chamber wall itself catalytically active, preventing deposits on the thermal insulation.

[0040] It can be advantageous if the chamber has a non-circular cross-section, viewed in the main flow direction. It is particularly useful if the chamber has a rectangular cross-section, viewed in the main flow direction. The heating elements can be distributed more evenly over a rectangular cross-section.

[0041] Regarding the arrangement of the heating elements, it should be noted that this is preferably done so that the heating elements are arranged one behind the other in the main flow direction or offset from each other. If the heating elements are arranged one behind the other in the main flow direction, a clear passage is created between the heating elements, which reduces flow resistance. If the heating elements are arranged offset from one another, the flow resistance is higher because there is no clear passage, but all flow paths come into contact with heating elements, resulting in more intensive heat transfer.

[0042] It is particularly preferred if the innermost layers of the heat-insulating wall with its closed surface possess a high resistance to thermal shock. This is achieved through material selection and processing. High thermal shock resistance has the advantage that the device can be heated and cooled quickly without damaging the wall's thermal insulation. This is particularly advantageous if the reactor can be used to provide negative control power as part of power grid stabilization. Conventional BMA reactors have a refractory lining that must be heated or cooled over several hours to avoid cracking. This is far too slow for the provision of control power; here, every minute counts.

[0043] The use of the apparatus according to the invention for providing negative control power for the purpose of stabilizing power grids is a further subject matter of the invention. The apparatus can preferably be used to provide a negative minute reserve. Negative control power means that the apparatus is only supplied with voltage drawn from the electrical voltage source when there is an excess of electrical power in the grid to which the electrical voltage source is connected. Conversely, the apparatus can also be disconnected from the electrical voltage source if there is a shortage of available electrical power. In both ways, the grid into which the electrical voltage source is integrated is stabilized. This is particularly interesting when the grid uses many natural power sources such as wind power or photovoltaics, whose power output fluctuates greatly.

[0044] One advantage of the device's design according to the invention is that conventional, commercially available heating elements, such as those used in conventional, electrically heated industrial furnaces, can be used as resistance heating. A special design for the electrical resistance heater or costly 3D printing is eliminated.

[0045] Electric heating elements are commercially available made of silicon carbide or molybdenum silicide or other materials and are resistant to the reaction conditions.

[0046] It is advantageous if the heating elements are aligned perpendicular to the flow. This results in the heating elements experiencing only minimal temperature differences. Since the apparatus according to the invention is designed for operation in a continuous process, regions of approximately uniform temperature are created during operation, extending through the chamber, essentially perpendicular to the main flow direction of the reactants through the chamber. If the heating elements are arranged along this direction, the stress on the heating elements due to temperature differences is very low.

[0047] In addition, the heating elements can be easily controlled separately. The use of separately controllable heating elements enables the setting of a temperature profile, if necessary, in order to specifically control the temperature progression of the reaction. This makes it possible to optimize the conversion and yield of the reaction and suppress the formation of undesirable by-products. The temperature profile is set by controlling the electrical power: Setting a power profile over the length of the reactor results in a temperature profile. The preferred design of the apparatus is based on the design of commercially available heating elements. These are either I-shaped, U-shaped, W-shaped, or M-shaped. All of these heating elements have an imaginary main resistance axis that is arranged perpendicular to the direction of flow.

[0048] The heating elements are essentially cylindrical in shape, but can also have other cross-sections, such as an elliptical cross-section. The I-shaped heating elements have exactly two electrical connections, one at each end. Once installed, the I-shaped heating elements extend linearly through the chamber, protruding from the wall with their end-face electrical connections. Their main resistance axis corresponds to their longitudinal axis.

[0049] The U-shaped heating elements also have two electrical connections, one at each open end of the legs. The connections are thus on the same side. When installed, the two legs extend parallel through the chamber. The legs penetrate the wall, so that the ends with the electrical connections protrude. The main resistance axis corresponds to the axis of symmetry.

[0050] The W-shaped heating elements resemble a double U and have three electrical connections. They are designed for use in three-phase systems. The main resistance axis corresponds to the axis of symmetry.

[0051] The heating elements are preferably installed so that the main resistance axis forms an angle ip with the main flow direction that is at least 0° and at most 90°. The angle ip is particularly preferably 90°. The main resistance axis of the heating elements is then perpendicular to the main flow direction. This is most favorable in terms of flow and thermodynamics.

[0052] Preferably, the device is positioned so that the main flow direction is vertical, i.e., parallel to the acceleration due to gravity. This prevents the main flow direction from being deflected by gravity, thus maintaining the alignment of the heating elements with the flow. Preferably, the main flow direction runs upwards, counter to the acceleration due to gravity. This prevents thermal buoyancy perpendicular to the flow direction.

[0053] Preferably, a plurality of heating elements are installed in the apparatus. These can be electrically connected to the first and second electrical lines, and optionally also to the third electrical line, via a series, parallel, or star connection, or a combination of these connections. Heating elements made of silicon carbide or molybdenum silicide coated with catalyst are preferably used. It may be useful to provide a protective coating on the surface of the heating elements, to which the catalyst is applied. This prevents a chemical or physical reaction between the catalyst and the core.

[0054] Alternatively, the catalyst can be applied to a conventional, unheated catalyst carrier and filled into the chamber.

[0055] Since short-circuit flows can develop in the wall area, this can lead to a suboptimal reaction process. To prevent the formation of undesirable flow regimes, unheated heating elements can be additionally introduced.

[0056] The inventive design of the apparatus thus opens up a multitude of advantages, which can be exploited in particular in the production of product gases such as hydrogen cyanide or other nitriles, for example aceto- or acrylonitrile.

[0057] A second subject matter of the invention is therefore a process for producing nitriles using the apparatus according to the invention. Such a process comprises the following steps: a) providing an apparatus according to the invention; b) applying a reactant gas mixture containing at least ammonia and gaseous hydrocarbon to the feed; c) applying electric current drawn from the electrical voltage source to the heating element; d) withdrawing a product gas mixture containing at least one formed nitrile from the effluent.

[0058] Hydrogen cyanide is preferably produced in this way. Hydrogen cyanide is a nitrile that is produced in the product gas mixture. The reactant gas mixture must contain the hydrocarbon methane. If hydrogen cyanide is to be produced, a material containing platinum is used as the catalyst.

[0059] If the reactant gas mixture also contains oxygen, a potentially flammable mixture is created. Ignitability exists when the oxygen concentration (KO) within the reactant gas mixture is above the oxygen limit concentration (SGK) of the mixture. The oxygen limit concentration (SGK) depends on the composition of the reactant gas mixture and can be found in the relevant tables. Preferably, the reactant gas mixture contains so little oxygen that the oxygen concentration (KO) is below the oxygen limit concentration (SGK). This means that the reactant gas mixture is not flammable. This allows for operational safety to be ensured with less effort.

[0060] A process for producing hydrogen cyanide that operates below the flammability limit is considered a BMA process. Since the heat energy required for the reaction is provided electrically, it is referred to below as the "E-BMA process."

[0061] Unlike the traditional, thermally heated BMA and Andrussow processes, the E-BMA process enables almost complete conversion of the reactants using electrical energy, potentially even CO2-neutral when using green electricity. (The methane used in the Andrussow process is always partially converted to CO2 due to the process characteristics.)

[0062] Thanks to the special design of the apparatus according to the invention, it is possible to optimize the E-BMA process operated with it in terms of yield and conversion so that it is competitive with classical BMA and Andrussow processes.

[0063] In addition to E-BMA processes, the apparatus according to the invention can also be used for similar reactions, for example for the production of aceto- and acrylonitrile.

[0064] The apparatus according to the invention is designed to operate at a reaction pressure PR of at least 1*10 5 Pa absolute and at most 5*10 5 Pa absolute. Preferably, a slightly higher gas pressure pc prevails in the intermediate space to create a small pressure gradient to the reaction chamber. This ensures that the reaction chamber walls are virtually pressure-free. The excess pressure relative to ambient pressure is absorbed by the shell walls. The shell walls must be designed to be pressure-resistant.

[0065] The gas pressure pc in the intermediate space is applied by the filling gas. The filling gas is predominantly nitrogen, hydrogen, or methane, or a mixture of predominantly nitrogen, hydrogen, and methane. The filling gas may contain traces of other gases.

[0066] Preferably, the process is operated in such a way that the heating elements in the reaction chamber are subjected to a uniform flow of heat, so that a nearly constant temperature profile is developed across each heating element at a constant surface area. This makes the heating elements more resistant to thermal stress, and extends their service life.

[0067] The temperature window for the reaction is between 800°C and less than 1500°C. The reaction temperature is not necessarily identical at all locations in the chamber, but can assume different values ​​within this temperature window. An intermediate temperature T c less than 400°C, preferably less than 150 D C.

[0068] To keep the temperature in the intermediate space below 400°C, heat is preferably removed from the jacket via a heat exchanger using a cooling fluid. For this purpose, the cooling fluid is continuously drawn from the cooling fluid source, the heat exchanger is continuously exposed to the cooling fluid, and cooling fluid is continuously withdrawn from the heat exchanger, with the temperature of the cooling fluid in the supply line being lower than in the return line.

[0069] In a special embodiment, the reactant gas mixture is used as the cooling fluid. The chamber of the apparatus then serves as the cooling fluid sink. In this way, the reactant gas mixture is preheated and the heat is recovered.

[0070] Examples of implementation

[0071] The invention will now be explained using exemplary embodiments. These are shown in the following:

[0072] Fig. 1 First embodiment of the apparatus (linear heating elements), schematic;

[0073] Fig. 2 Second embodiment of the apparatus (U-shaped heating elements), schematic.

[0074] Figure 1 schematically shows the apparatus 0 according to the invention. The apparatus 0 comprises a chamber 1 with a non-gas-tight wall 2. The wall 2 comprises a heat-insulating material and a surrounding shell made of a metallic material. A chemical reaction takes place within the chamber 1. The chamber 1 thus represents the reaction space.

[0075] The chemical reaction is, for example, the reaction of methane CH4 with ammonia NH3 in the absence of oxygen O2, which produces hydrogen cyanide HCN and hydrogen H2 (E-BMA process).

[0076] The reactant stream, which predominantly contains methane CH4 and ammonia NH3, is fed as a gas mixture through an inlet 3 via a distribution device (e.g., a perforated plate) into chamber 1. The products hydrogen cyanide HCN and hydrogen H2, as well as unused reactants and by-products, are also withdrawn from chamber 1 in gaseous form, namely through a designated outlet 4.

[0077] Thermal energy is required for the chemical reaction. According to the invention, this energy is generated by converting electrical energy within chamber 1. The heat is required at a temperature level in the range between 800°C and 1500°C (reaction temperature TR).

[0078] For this purpose, a plurality of heating elements 5 are provided in the chamber 1, which extend through the chamber 1. The heating elements 5 are, in the simplest case, cylindrical elements made of silicon carbide. Silicon carbide is very temperature-stable and, due to its physical properties, is frequently used in practice to convert electrical energy into heat. Each heating element 5 has at least two electrical connections + / -. Due to the high reaction temperature (7R = 800°C to 1500°C) that prevails within the chamber 1, it is important that the electrical connections (+ / -) of the heating elements 5 are located outside the chamber 1. For this reason, the heating elements 5 extend through the wall 2 of the chamber 1. In the area of ​​the feedthrough, a sleeve is arranged between the wall and the heating element (not shown).Since the wall 2 is made of heat-insulating material and the device 0 has an active cooling system described later, the temperature outside the chamber 1, in the area of ​​the electrical connections + / -, is much lower; it is approximately less than 400°C. This temperature is referred to here as the intermediate temperature T. c called.

[0079] In this lower temperature range, the electrical connections + / - are each connected to a first electrical line 71 and a second electrical line 72 by a first circuit 61 and a second circuit 62. The circuits 61, 62 can be a series circuit (not shown) or a parallel circuit (shown) or a mixture of both. In three-phase networks, a star connection is also possible (not shown). The first and second electrical lines 71, 72 lead to an electrical voltage source 8. In three-phase networks, a third electrical line to the voltage source 8 is required (not shown).

[0080] Voltage source 8 provides the energy required for the process in electrical form. Preferably, all the energy required for the chemical conversion of methane and ammonia into hydrogen cyanide and hydrogen is provided in electrical form.

[0081] During operation, the electrical heating elements are supplied with an electrical voltage U supplied from the electrical voltage source 8 via the electrical lines 71, 72 and the circuits 61, 62, so that an electrical current / flows through the electrical heating elements 5. The heating elements 5 convert the electrical energy into thermal energy, which heats the surface of the heating elements. This enables the reaction.

[0082] In contrast to the classic thermally heated BMA process, the heat required for the reaction is not introduced into the chamber 1 from the outside, but is generated in-situ in the reaction space with the heating elements 5.

[0083] To increase the reaction rate, a catalyst is used in chamber 1. The catalyst may contain platinum and is preferably applied to the surface of the heating elements 5. The hydrogen cyanide (HCN) produced in the process is highly toxic. To prevent a release of hydrogen cyanide, chamber 1 is surrounded by a gas-tight, double-walled jacket 9. The jacket 9 also serves as a heat exchanger 10, which is filled with a cooling fluid.

[0084] In order to ensure that the gaseous reactants CHU, NH3 pass through the gas-tight jacket 9 into the chamber 1 and that the products HCN, H2 and unreacted reactants as well as by-products pass out of the chamber 1 again, the inlet 3 and the outlet 4 are each led through the jacket 9 and sealed gas-tight against it.

[0085] A gap 12 extends between the jacket 9 and the chamber 1. The heating elements 5 extend through the wall 2 of the chamber 1 into the gap 12, where their electrical connections + / - are located.

[0086] The passage of the heating elements 5 through the wall 2 is not gas-tight because, due to thermal expansion, a certain degree of mobility of the heating elements 5 relative to the wall 2 is required. Unlike the jacket 9, the wall 2 of the chamber 1 is also not gas-tight, which is why reactants from the chamber 1 could enter the intermediate space 12. To prevent this, the intermediate space 12 can be statically pressurized with a filling gas, which may optionally contain small amounts of the reactants and which has a pressure gradient to the reaction space. The filling gas is drawn from a filling gas source 11 and fed into the intermediate space 12 via a filling gas line (not shown) and a connection element (not shown).

[0087] In a similar way, the double jacket 9 is supplied with a cooling fluid from the inside, which is drawn from a cooling fluid source 3. However, the cooling fluid is withdrawn from the jacket 9 again to a cooling fluid sink 4. The cooling fluid thus flows from its source 13 through the jacket 9 to its sink 14. In this way, heat is dissipated from the double jacket 9 via the cooling fluid. The double jacket 9 simultaneously acts as a heat exchanger 10. The apparatus 0 is thus actively cooled. For this purpose, a substance with a good specific heat capacity, such as liquid water or liquid oil, is used as the cooling fluid. The heat dissipated to the sink 14 via the cooling fluid is heat that has been transferred from the metallic shell of the wall 2 to the double jacket 9 by thermal radiation. Thanks to the insulation of the wall 2, this heat is comparatively low.

[0088] As an alternative to the double jacket 9, the heat exchanger 10 can also be implemented with a cooling coil that is wrapped around the jacket 9 (not shown). The jacket 9 can then be single-walled, because the cooling fluid flows through the cooling coil. If the gas pressure p c of the filling gas in the intermediate space 12 is only slightly greater than the reaction pressure PR in the chamber 1, the wall 2 of the chamber 1 is hardly subjected to any mechanical stress. In particular, it does not need to withstand any massive internal pressure. Consequently, the wall 2 can be optimized with regard to thermal insulation. However, the double jacket 9 is subjected to pressure. In contrast to the wall 2 of the chamber 1, this must withstand an internal pressure corresponding to the difference in gas pressure p cand the ambient pressure po. Since the jacket 9 is not subjected to such a high thermal load – the temperature 7j of the cooling fluid within the jacket 9 is usually less than 100°C – pressure safety is much easier to achieve here. Furthermore, the double jacket 9 can be made of steel, which, although not thermally insulating, is more mechanically resilient than an insulating material containing the wall 2 of the chamber 1. Thus, in the apparatus according to the invention, the wall 2 fulfills only the function of thermal insulation, while the functions of gas tightness and pressure maintenance are assumed by the jacket 9.

[0089] Another important aspect of the apparatus according to the invention is the orientation of its heating elements 5 in relation to the acceleration due to gravity g and the main flow direction V of the reactants:

[0090] The main flow direction V extends from the inlet to the outlet through chamber 1. Along this main flow direction V, the reactants CH4 and NH3 flow into chamber 1, and the products HON and H2, as well as unreacted reactants and by-products, flow out of chamber 1.

[0091] In the embodiment of an apparatus according to the invention shown in Figure 1, the heating elements 5 are arranged transversely to the main flow direction V, so that the longitudinal axis H of the heating elements 5 forms an angle of 90° with the main flow direction V.

[0092] This has the advantage that each heating element 5 experiences only slight temperature differences: The reaction temperature TR is not the same throughout the chamber 1, but varies along the main flow direction V. This is due, on the one hand, to the fact that the temperature changes along the main flow direction due to the progressive conversion. On the other hand, the heating elements 5 can also be set to different temperatures via the power supply in order to impose an optimal temperature profile on the reaction along the main flow direction. The power supply, and thus ultimately also the temperature, can be adjusted via the magnitude of the current drawn from the voltage source 8.

[0093] If the heating elements 5 are arranged transversely to the main flow direction V, the temperature profile at the position of an individual heating element is virtually constant. Consequently, the temperature expansion of the heating element is constant over its entire length, which in turn improves its stability. In the embodiment of an apparatus according to the invention shown in Figure 1, the main flow direction V is arranged vertically, specifically counter to the acceleration due to gravity g. Thus, the chamber 1 is preferably flowed through from bottom to top; other flow directions are also possible if the design requires it.

[0094] Provided that the main flow direction V extends vertically and the longitudinal axis of the heating elements 5 is at 90° transverse thereto, the longitudinal axis H of the heating elements 5 optimally runs horizontally.

[0095] In the embodiment shown in Figure 1, the apparatus 0 has cylindrical heating elements 5 in which the longitudinal axis H is arranged horizontally.

[0096] If heating elements of a different design are selected, the orientation within the chamber must be selected accordingly.

[0097] Figure 2 shows a second embodiment of an apparatus 0 according to the invention, in which the heating resistors 5 are U-shaped. In order to align U-shaped heating elements along an isotherm, the legs of the U should be aligned transversely to the main flow direction V and positioned at the same point along the main flow direction V in the chamber 1. With a vertical main flow direction V, the legs of the U can be at the same height level (not shown). In this respect, U-shaped heating elements, like cylindrical heating elements, extend along a main resistance axis H, which is arranged transversely to the main flow direction V. The legs of the U run parallel on both sides of the main resistance axis H, which corresponds to the axis of symmetry of the U. In the case of cylindrical heating elements (Figure 1), the longitudinal axis corresponds to the main resistance axis H.

[0098] Essential aspects of the invention should be summarized once again:

[0099] The invention is based on the object of specifying an electrically heatable reactor for the production of hydrogen cyanide and other nitriles, which enables a differentiated temperature profile and requires cost-effective standard components. The core of the apparatus 0 according to the invention is the chamber 1 made of gas-permeable, heat-insulating material, which represents the actual reaction space. The electrical heating elements 5 project into the chamber 1 so that the chamber 1 can be heated from the inside using the heating elements 5. The electrical connections of the heating elements are located outside the reaction space, but within the surrounding jacket. Unlike in the industrially practiced BMA process, the heat is therefore not transported into the reaction space from the outside, but is generated within the reaction space. Heat is generated by converting electrical energy by means of the heating elements 5 according to the principle of resistance heating.In order to ensure the gas-tightness of the apparatus 0, the jacket 9 is provided, which encloses the chamber 1 in a gas-tight manner.

[0100] Try

[0101] The following experiments illustrate the advantageous effect of the apparatus according to the invention.

[0102] The tests were simulations using computational fluid dynamics (CFD). The software used was Ansys Fluent (version Fluent 2021 R2).

[0103] The reaction chamber is rectangular and contains approximately 900 heating elements.

[0104] In all three experiments, the synthesis gas consists of ammonia and methane in a molar ratio of 1.1 : 1 at an absolute pressure of 2.8 bar (2.8*10 5 Pa). The gas is preheated to 200°C, and the reactant flow is 1440 kg / h. The simulations are conducted under adiabatic conditions with a heating power of 4.1 MW.

[0105] The results of the simulations are shown graphically in Figures 3 to 6:

[0106] Fig 3: Temperature along a heating element in the center of the reactor with horizontal and vertical orientation of the heating elements;

[0107] Fig 4: Temperature profile through the reactor;

[0108] Fig. 5: Yield curve;

[0109] Fig. 6: Performance profile in experiment 3.

[0110] Experiment 1 (vertical alignment of the heating elements - constant power)

[0111] The heating elements are arranged vertically, i.e. parallel to the acceleration due to gravity, and the reactor is flowed through horizontally. The power of the heating elements in the example described here is set to 38 kW / m 2 set.

[0112] Due to thermal buoyancy, temperature gradients of 500 to 700 K can occur along the heating element (see dashed line in Figure 3), which could negatively impact the lifetime of the heating element. The temperature profile through the reactor is shown in the dashed line in Figure 4. The yield of HCN based on NH3 is shown in the dashed line in Figure 5. The yield is 72%.

[0113] Experiment 2 (horizontal alignment of the heating elements - constant power)

[0114] The operating parameters of test 1 were retained, ie the power of the heating elements is also constant at 38 kW / m 2 However, the heating elements are arranged horizontally and the flow through the reactor is from bottom to top.

[0115] Due to the horizontal arrangement of the heating elements, a relatively homogeneous temperature is established above each heating element, which can positively influence the service life of the heating element (see solid line in Figure 3).

[0116] The temperature profile is shown in the dotted line in Figure 4. The HCN yield based on NH3 is shown in the dotted line in Figure 5. The maximum gas temperature is above 1400°C, which can negatively impact the service life of the heating element. The HCN yield based on NH3 is 80%.

[0117] Experiment 3 (horizontal alignment of the heating elements with variable power profile

[0118] The heating elements are arranged horizontally, and the reactor flows from bottom to top. The power of the heating elements is controlled via a profile, with the power being between 4 and 60 kW / m 2 varies. The performance profile is shown in Figure 6.

[0119] Due to the horizontal arrangement of the heating elements, a nearly uniform temperature is established across each heating element, which can positively influence the service life of the heating element. The temperature profile along the length of the rod is shown in the solid line in Figure 3.

[0120] The temperature profile throughout the reactor is shown in Figure 4 (solid line). The maximum gas temperature is in the range of 1300°C. Due to the decreasing power profile towards the end (Figure 6), the temperature also decreases again towards the end of experiment 3 (solid line in Figure 4).

[0121] The yield of HCN based on NH3 is shown in the solid line of Figure 5. The yield of HCN based on NH3 is 83%, which is higher than in Experiments 1 and 2. Conclusion

[0122] The highest yield is achieved when the heating elements are arranged horizontally and a variable power profile is provided. Furthermore, horizontal heating elements are less susceptible to thermal stress.

[0123] Reference symbol list

[0124] 0 device

[0125] 1 chamber

[0126] 2 wall

[0127] 3 Inlet

[0128] 4 Procedure

[0129] 5 Heating element

[0130] 61 first connection

[0131] 62 second interconnection

[0132] 71 first electrical line

[0133] 72 second electrical line

[0134] 8 electrical voltage source

[0135] 9 Jacket (designed as a double jacket)

[0136] 10 heat exchangers

[0137] 11 Filling gas source

[0138] 12 space

[0139] 13 Cooling fluid source

[0140] 14 Cooling fluid sink

[0141] + first electrical connection second electrical connection

[0142] Pt platinum catalyst

[0143] TR reaction temperature

[0144] T c Intermediate temperature

[0145] Ti temperature of the cooling fluid

[0146] P reaction pressure p c Back pressure po ambient pressure

[0147] CH4 methane

[0148] NH3 ammonia

[0149] HCN hydrogen cyanide

[0150] H2 hydrogen

[0151] O2 oxygen g acceleration due to gravity

[0152] V Main flow direction

[0153] H Main resistance axis

[0154] (|) angle

Claims

Patent claims 1 . Apparatus (0) for producing at least one product gas from at least one reactant gas, in particular for the production of nitriles, comprising the following features: a) a chamber (1) with a gas-permeable and heat-insulating wall (2), with an inlet (3) for reactant gas, with an outlet (4) for product gas and with a main flow direction (V) extending from the inlet (3) to the outlet (4); b) a gas-tight jacket (9) which encloses the chamber (1), wherein the inlet (3) and the outlet (4) are guided through the jacket (9); c) an intermediate space (12) arranged between the chamber (1) and the jacket (9), which encloses the chamber (1) and is in turn enclosed by the jacket (9);d) at least one electrical heating element (5) which extends through the chamber (1) and penetrates its wall (2) at least once, and which has at least two electrical connections (+,-) which are arranged inside the intermediate space (12) and outside the chamber (1); e) an electrical voltage source (8) arranged outside the casing (9), which is connected at least via a first electrical line (71) to the first electrical connection (+) of the heating element (5) and via a second electrical line (72) to the second electrical connection (-) of the heating element (5), wherein the first and second electrical lines (71, 72) are passed through the casing (9);f) at least one connection element for a filling gas source (11) arranged outside the casing (9), which can be fluidly connected to the intermediate space (12) via a filling gas line such that the intermediate space (12) can be supplied with a filling gas obtained from the filling gas source (11); g) a catalyst arranged in the chamber (1); 2. Apparatus (0) according to claim 1, characterized by at least one heat exchanger (10) arranged outside the gas-tight jacket (9) and connected to the jacket (9) in a heat-conducting manner.

3. Apparatus (0) according to claim 2, characterized in that the heat exchanger (10) comprises a cooling fluid, and that the heat exchanger (10) is fluidly connected via a flow line to a cooling fluid source (13) and via a return line to a cooling fluid sink (14).

4. Apparatus (0) according to claim 3, characterized in that the gas-tight jacket (9) is double-walled as a double jacket (9), and that the cooling fluid is at least partially conductible within the double jacket (9).

5. Apparatus (0) according to claim 3, characterized in that the heat exchanger (10) comprises a cooling coil which connects the flow with the return in a cooling fluid-conducting manner and is wound around the jacket (9).

6. Apparatus (0) according to claim 5, characterized in that the cooling coil is designed as a tube which is connected to the outside of the gas-tight jacket (9) via thermal bridges.

7. Apparatus (0) according to claim 5, wherein the cooling coil is obtained by welding an open profile onto the outside of the gas-tight jacket (9), and wherein the cooling fluid is at least partially conductible between the profile and the outside of the gas-tight jacket (9).

8. Apparatus (0) according to one of claims 3 to 7, characterized in that the Cooling fluid is selected from the group consisting of the following cooling fluids: air, gaseous nitrogen, gaseous argon, gaseous water, liquid water, liquid nitrogen, liquid oil, gaseous ammonia, gaseous Hydrocarbons or mixtures thereof.

9. Apparatus (0) according to one of claims 1 to 8, characterized in that the electrical heating element (5) has exactly two electrical connections (+, -) and extends linearly through the chamber (1).

10. Apparatus (0) according to one of claims 1 to 8, characterized in that the electrical heating element (5) has exactly two electrical connections (+, -) and extends in a U-shape or M-shape through the chamber (1) or that the electrical heating element (5) has exactly three electrical connections and extends in a W-shape through the chamber or combinations thereof.

11. Apparatus (0) according to claim 9 or 10, wherein the electrical heating element (5) extends along a main resistance axis (H) through the chamber (1), wherein the main resistance axis (H) and the main flow direction (V) enclose an angle (ip) which is at least 0° and at most 90°.

12. Apparatus (0) according to claim 11, characterized in that the angle (cp) is 90°.

13. Apparatus (0) according to claim 12, characterized in that the main flow direction (V) is vertical.

14. Apparatus (0) according to claim 13, characterized in that the main flow direction (V) runs counter to the acceleration due to gravity (g).

15. Apparatus (0) according to one of claims 1 to 14, characterized by a plurality of electrical heating elements (5) which are electrically connected to one another in series and / or parallel.

16. Apparatus (0) according to claim 15, characterized in that the catalyst is applied in the form of a catalytically active coating to the surface of at least one electrical heating element (5).

17. Apparatus (0) according to claim 16, characterized by at least one heating element (5) which is free of a catalytically active coating.

18. Apparatus (0) according to one of claims 1 to 14, characterized in that the heat-insulating wall (2) of the chamber (1) is constructed in multiple layers.

19. Apparatus (0) according to claim 18, characterized in that the heat-insulating wall (2) comprises at least two layers which differ in their specific thermal conductivity.

20. Apparatus (0) according to claim 18 or 19, characterized by an additional inner layer on the wall of the chamber with a closed surface.

21. Apparatus (0) according to one of claims 18 to 20, characterized in that the inner layer on the wall (2) of the chamber (1) is provided with a catalytically active or activatable coating which contains the catalyst.

22. Apparatus (0) according to one of claims 1 to 21, characterized in that the chamber (1) has a non-circular cross-section in the main flow direction (V).

23. Apparatus (0) according to one of claims 1 to 22, characterized in that the heating elements (5) are arranged one behind the other or offset from one another as seen in the main flow direction (V).

24. Apparatus (0) according to claim 22 or 23, characterized by at least one heating element (5) which runs in the immediate vicinity of the wall (2) parallel to the wall (2) and which is not connected to at least one of the two electrical lines (71, 72).

25. Apparatus (0) according to any one of claims 1 to 24, characterized in that the catalyst contains platinum (Pt).

26. Apparatus (0) according to one of claims 1 to 25, characterized in that the heating element (5) comprises a core made of silicon carbide or molybdenum silicide, a protective coating being applied to the core and a catalytically active coating being applied to the protective coating.

27. A process for the production of nitriles, in particular hydrogen cyanide (HCN), comprising the following steps: a) providing an apparatus (0) according to any one of claims 1 to 26; b) supplying the inlet (3) with a reactant gas mixture containing at least ammonia (NH3) and gaseous hydrocarbon, preferably methane (CH4); c) supplying the heating element (5) with electrical current obtained from the electrical voltage source (8); d) withdrawing a product gas mixture containing at least one formed nitrile, preferably hydrogen cyanide (HCN), from the outlet (4), and e) supplying the intermediate space (12) with a filling gas, so that a gas pressure (p c ) which is equal to or greater than the reaction pressure (PR) prevailing in the chamber (1 ).

28. Process according to claim 27, characterized in that the reactant gas mixture contains methane (CH3), so that hydrogen cyanide (HCN) is produced.

29. The method according to claim 27 or 28, wherein the reactant gas mixture additionally contains oxygen (O2), so that the reactant gas mixture is assigned a limiting oxygen concentration (LCO) above which the reactant gas mixture is ignitable, characterized in that the concentration of oxygen (KO2) within the reactant gas mixture is below the limiting oxygen concentration (LCO).

30. A process according to claim 27, 28 or 29, carried out at a reaction pressure (PR) prevailing in the chamber (1) of at least 1*10 5 Pa absolute and at most 5*10 5 Absolutely. 31 . Method according to one of claims 27 to 30, carried out continuously, in such a way that a flow along a main flow direction (V) through the chamber (1 ) is created, which extends from the inlet (3) to the outlet (4), wherein the heating element (5) extends along a main resistance axis (H) through the chamber (1 ), characterized in that the main flow direction (V) extends perpendicular to the main resistance axis (H) of the heating element (5).

32. A process according to any one of claims 27 to 31, carried out at least at one reaction temperature (7R) prevailing in the chamber (1) of greater than 800°C and less than 1500°C, wherein in the intermediate space (12) an intermediate temperature (T c ) of less than 400°C.

33. Method according to one of claims 30 to 33, characterized in that the filling gas is selected from the group consisting of the following filling gases: gaseous nitrogen, gaseous hydrogen, gaseous hydrocarbon, gaseous ammonia or mixtures thereof, 34. A method according to any one of claims 27 to 33, wherein an apparatus (0) according to any one of claims 3 to 26 is provided, characterized in that the cooling fluid is continuously drawn from the cooling fluid source (13), the heat exchanger (10) is continuously supplied with the cooling fluid, and that cooling fluid is continuously withdrawn from the heat exchanger (10), the temperature of the cooling fluid in the flow being lower than in the return.

35. Method according to claim 34, characterized in that the cooling fluid is a reactant gas mixture and that the cooling fluid sink is the chamber (1), so that the reactant gas mixture is preheated in the heat exchanger (10).

36. Use of an apparatus (0) according to one of claims 1 to 26 for providing negative control power for the purpose of stabilizing power grids.

Images