Method and reactor for producing phosgene

Abstract

The invention relates to a process for producing phosgene by gas phase reaction of carbon monoxide and chlorine in the presence of a catalyst in a reactor comprising a plurality of catalyst tubes arranged parallel to one another, the catalyst tubes being filled with the catalyst and at least one fluid heat transfer medium flowing around the contact tubes, wherein a feed stream of a mixture of a chlorine inlet stream and a carbon monoxide inlet stream is fed to the catalyst tubes and reacted to form a phosgene-containing product gas mixture, characterised in that the reaction takes place at 2.75 kg phosgene / m 2 The present invention also relates to a reactor for carrying out the method.

Description

[0001] The present invention relates to a process and a reactor for producing phosgene by gas phase reaction of carbon monoxide and chlorine in the presence of a catalyst, in particular in the presence of an activated carbon catalyst.

[0002] Phosgene is an important auxiliary for the production of intermediates and end products in almost all branches of chemistry. In particular, phosgene is a widely used reagent for industrial carbonylations, for example in the production of isocyanates or organic acid chlorides. The largest area of ​​application is the production of diisocyanates for polyurethane chemistry, in particular toluene diisocyanate or diphenylmethane 4,4-diisocyanate.

[0003] Phosgene is produced industrially in the catalytic gas phase reaction of carbon monoxide and chlorine in the presence of a catalyst (e.g. an activated carbon catalyst) according to the following reaction equation:

[0004]

[0005] The reaction is highly exothermic, and the reaction enthalpy is ΔH is -107.6 kJ / mol. The reaction is usually carried out in a shell-and-tube reactor by the method described in the "Phosgene" chapter (5th edition, volume A19, page 413 and thereafter, VCH Verlagsgesellschaft mbH, Weinheim, 1991) of Ullmann's Encyclopedia of Industrial Chemistry. In this method, a particle catalyst having a particle size of 3 to 5 mm is loaded into a tube having a standard inner diameter of 35 to 70 mm, typically 39 to 45 mm. The reaction starts at a temperature of 40 to 50 ° C, but rises to a maximum of 400 ° C or even higher in the tube, and then rapidly decreases again. In the reaction, an excess of carbon monoxide is usually used to ensure that all chlorine reacts and produces phosgene that is substantially free of chlorine, because chlorine can cause undesirable side reactions in subsequent phosgene applications. The reaction can be carried out at atmospheric pressure, but is usually carried out at a gauge pressure of 200-600 kPa (2-6 bar). Within this pressure range, the phosgene formed can be condensed downstream of the reactor using cooling water or other media, for example organic heat transfer media, so that the condenser can be operated economically.

[0006] An important issue in phosgene reactor design is the removal of the generated heat of reaction.

[0007] The heat transfer medium flows around the catalyst tubes of the shell and tube reactor and carries the reaction heat generated from the reactor. It has been found that heat removal is improved when the heat transfer medium flows transversely to the catalyst tubes. For this reason, guide plates are usually installed in the reactor so that the heat transfer medium can flow transversely to the catalyst tubes by a circuitous flow of the heat transfer medium.

[0008] A typical industrial reactor for producing phosgene is described, for example, in the applicant's international patent application WO 03 / 072237 A1.

[0009] In industrial-scale reactors, the heat transfer coefficient at the interface between the catalyst tube and the heat transfer medium produces relatively large differences over the entire reactor cross section, for example due to the deflection of the heat transfer medium from transverse flow to longitudinal flow, and also due to the pressure drop experienced by the heat transfer medium in the shell space from the opening of one guide plate to the relative opening of the next guide plate, and due to the pressure drop through the gap between the outer wall of the catalyst tube and the guide plate (the gap is inevitable in manufacturing technology). The heat transfer coefficient of the area with good heat transfer and the area with poor heat transfer in the reactor cross section can definitely differ by a factor of 2. Therefore, the catalyst tube is not cooled enough in the area with poor heat transfer. However, since the catalyst tube is allowed to have a maximum temperature load (usually in the range of 160 to 200°C, depending on the material used, otherwise the corrosion of the material is greatly increased), the area with poor heat transfer therefore limits the processing capacity and production capacity of the reactor. For the duplex steel often used for catalyst tubes, the maximum temperature load is usually about 170 to 180°C.

[0010] The processing capacity of the reactor can be determined by the area load of the reactor. The phosgene load is defined as the amount of phosgene reacted per unit time (usually expressed in kg / s) based on the cross-sectional area of ​​the catalyst, i.e. the sum of the internal cross-sectional areas of the catalyst tubes filled with catalyst (usually expressed in m 2 Therefore, in order to control the reaction heat, 0.5 to 2 kg of phosgene / m 2 The phosgene area loading is therefore determined essentially on the assumption of complete conversion of the component being used in deficit, ie, in the case of an excess of carbon monoxide, for example, essentially by the chlorine feed.

[0011] In the present application, the term "reactor" includes all parts of the equipment in which the chemical reaction of carbon monoxide and chlorine to form phosgene occurs. In this sense, a reactor is normally a single component defined as a reactor vessel. However, for the purpose of the present application, a reactor may also include two or more components with separate reactor vessels, which are for example arranged one by one (in series). In this case, the area load is total conversion, i.e., the phosgene flow leaving the last reactor assembly (e.g., the last reactor vessel).

[0012] In the applicant's international patent application WO 2010 / 076208 A1, by optimizing the arrangement of the catalyst tubes and matching the flow paths of the heat transfer medium to each other in each reactor cross section, the heat transfer coefficient at the interface between the catalyst tubes and the heat transfer medium is balanced over the entire reactor cross section. Using an optimized heat transfer medium flow distribution in such a reactor, a maximum of 2.74 kg phosgene / m 2 s area load.

[0013] Another problem that arises in phosgene reactor design is the loss of catalyst material that occurs during operation.

[0014] For example, as described in the publication by Mitchell et al., "Selection of carbon catalyst for the industrial manufacture of phosgene", Catal. Sci. Technol., 2012, Vol. 2, pp. 2109-2115, there is also a loss of activated carbon during the phosgene synthesis. Firstly, this can be caused by the oxidation of carbon by trace amounts of oxygen in the chlorine supplied. Secondly, the reaction of chlorine with activated carbon to form volatile carbon tetrachloride (CCl4) can also occur at relatively high temperatures, usually above 300°C. This not only leads to a loss of the yield of the method used based on chlorine, but also in particular to a deactivation or disappearance of the catalyst, so that the equipment must be shut down after an appropriate operating time and the catalyst must be replaced. In addition, the carbon tetrachloride formed can lead to problems in terms of product quality, such as undesirable coloration in the subsequent processing of phosgene, such as in the production of acyl chlorides.

[0015] Also wish to reduce CCl4 formation as far as possible to prevent CCl4 accumulation, because CCl4 forms as intermediate boiling point substance (Zwischensieder) in this method and neither effectively discharges by low-boiling-point substance HCl nor by high-boiling-point substance isocyanate.The boiling point of phosgene is lower than CCl4 again, and the boiling point of commonly used solvent is higher.Therefore, CCl4 can accumulate in phosgene loop and solvent loop, and this can cause CCl4 removal cost is high.

[0016] The present invention therefore solves the technical problem of providing a process and a reactor for producing phosgene which greatly reduce the losses of activated carbon, in particular due to the formation of carbon tetrachloride, without increasing the thermal load on the catalyst tubes.

[0017] This technical problem is solved by the method of claim 1 of the present application and the reactor of claim 11 of the present application.

[0018] The present invention therefore provides a process for producing phosgene by gas phase reaction of carbon monoxide and chlorine in the presence of a catalyst in a reactor comprising a plurality of parallel catalyst tubes, the catalyst tubes being filled with the catalyst and at least one fluid heat transfer medium flowing around the catalyst tubes, wherein a feed stream of a mixture of a chlorine input stream and a carbon monoxide input stream is fed to the catalyst tubes and reacted to obtain a phosgene-containing product gas mixture, wherein the reaction is carried out at a temperature of more than 2.75 kg phosgene / m 2 s area load.

[0019] In the process of the invention, different catalysts can be used, for example SiC catalysts. Preferably, activated carbon catalysts are used.

[0020] Surprisingly, it was found that increasing the area load above the 0.5 to 2.74 kg / m 2 The range of s reduces the loss of activated carbon, and in particular reduces the concentration of carbon tetrachloride in the resulting product gas mixture. Carbon tetrachloride can be produced by the reaction of catalyst activated carbon with chlorine, and can also be produced by the reaction of chlorine with the methane contained in the feed gas. The increase in area load can increase the upstream time of the equipment (this improves the yield based on chlorine of the method used) and reduce the concentration of carbon tetrachloride in the phosgene produced. The amount of carbon tetrachloride formed by the reaction of activated carbon with chlorine is preferably less than 125g of phosgene produced per metric ton, preferably 0.1 to 125g of carbon tetrachloride formed by the reaction of activated carbon with chlorine per metric ton of phosgene produced, more preferably 10 to 115g of carbon tetrachloride formed by the reaction of activated carbon with chlorine per metric ton of phosgene produced, particularly preferably 10 to 105g of carbon tetrachloride formed by the reaction of activated carbon with chlorine per metric ton of phosgene produced, for example, less than 120g, less than 117g, less than 100g, less than 80g or less than 50g of carbon tetrachloride formed by the reaction of activated carbon with chlorine per metric ton of phosgene produced.

[0021] As is known from the publications such as Mitchell et al., due to the formation of carbon tetrachloride at a relatively high temperature, activated carbon is lost, and therefore initially it is opposed to increase the area load to solve the problem. However, surprisingly, it is found that, despite the increase in area load, the thermal stress on the catalyst tube does not increase. If the premise is that compared with the industrial method of the prior art, when implementing the method of the present invention, the phosgene production capacity (i.e. the amount of phosgene produced by the reactor per unit time) and the amount of the catalyst used for this purpose are constant, the volume flow of the reactants and the volume of the catalyst, i.e. the space velocity or GHSV (gas hourly space velocity), also remain unchanged. When the area load increases, the constant GHSV causes the flow velocity of the reactants used to increase, thereby improving the specific heat transfer, thereby reducing the thermal stress on the catalyst, especially at the center of the catalyst tube.

[0022] The area load in the method of the present invention is preferably 3 kg phosgene / m 2 s to 9kg phosgene / m 2 s, preferably 4 to 6 kg / m 2 s, more preferably 4.1 to 6 kg / m 2 s, more preferably 4.3 to 5.9 kg / m 2 s and particularly preferably 4.5 to 5.8 kg / m 2 s, for example 4.2 to 6 kg / m 2 s.

[0023] The feed stream in the process of the invention preferably has a stoichiometric excess of carbon monoxide to chlorine of 0.1 to 50 mol %, so that essentially complete conversion of the chlorine is ensured. If fluctuations in the chlorine concentration in the chlorine input stream are expected, a higher carbon monoxide excess tends to be selected, but for cost reasons, the excess is usually kept as small as possible as long as complete conversion of the chlorine is still ensured.

[0024] The feed stream is preferably fed at an absolute pressure of 50 to 2000 kPa (0.5 to 20 bar). The feed stream is particularly preferably fed at superatmospheric pressure, for example at an absolute pressure of 300 to 700 kPa (3 to 7 bar) (absolute pressure). The higher the pressure of the resulting reaction mixture at the reaction outlet, the higher the temperature at which the phosgene contained in the reaction mixture can be condensed. The pressure of the reaction mixture at the reactor outlet is preferably high enough to allow the phosgene to be at least partially condensed using cooling water.

[0025] In one embodiment of the invention, the reactor is divided into at least two cooling zones in the longitudinal direction of the catalyst tube, and the at least two cooling zones are separated from each other, for example, by an intermediate plate. Different heat transfer media can be used for different cooling zones, and the selection of these heat transfer media can match the thermal conditions of each cooling zone. However, due to the difficulty of completely sealing the catalyst tube through-holes in the intermediate plate, leakage must usually be expected in practice, so it is preferred to use the same heat transfer medium in different cooling zones. In this case, then, evaporative cooling can be performed, for example, in a cooling zone with particularly high heat release, and liquid cooling can be performed in another cooling zone. In the case of evaporative cooling, it is preferred not to provide any guide plate or a specially designed guide plate to prevent the accumulation of rising bubbles.

[0026] As fluid heat transfer medium, various materials and substance mixtures suitable for removing the heat of reaction can be used, for example due to their heat capacity or due to their enthalpy of vaporization. Liquid heat transfer media are often used, such as water, dibenzyltoluene (Marlotherm) or monochlorobenzene.

[0027] The increase in area load provided according to the invention can be achieved in existing reactors by appropriate adjustment of operating parameters, in particular by an increase in the volume flow of reactants. However, a newly designed reactor can be structurally designed to optimize operation under the area load provided according to the invention.

[0028] Therefore, the present invention also provides a reactor for producing phosgene by gas phase reaction of carbon monoxide and chlorine in the presence of a catalyst, in particular in the presence of an activated carbon catalyst, the reactor comprising a plurality of parallel catalyst tubes, the catalyst tubes being filled with catalyst and welded to tube sheets at both ends thereof, wherein the starting material is introduced via a cover at the upper end of the catalyst tubes and the gaseous reaction mixture is discharged at the lower end of the catalyst tubes, and having an input and discharge device for liquid heat transfer medium to / from the shell space between the catalyst tubes, wherein the plurality of parallel catalyst tubes in the reactor of the present invention are designed to have an area load of more than 2.75 kg of phosgene per square meter of the inner cross-sectional area of ​​the catalyst tubes per second.

[0029] The catalyst tube of the reactor is preferably designed to have an area load of 3 kg phosgene / m 2 s to 9kg phosgene / m 2 s, preferably 4 to 6 kg / m 2 s, more preferably 4.1 to 6 kg / m 2 s, more preferably 4.3 to 5.9 kg / m 2 s and particularly preferably 4.5 to 5.8 kg / m 2 s, for example 4.2 to 6 kg / m 2 s.

[0030] The reactor design according to the invention limits the amount of carbon tetrachloride formed by the reaction of activated carbon with chlorine in the reaction to form phosgene to less than 125 g per metric ton of phosgene produced. The formation of carbon tetrachloride is preferably limited to 0.1 to 125 g of carbon tetrachloride formed by the reaction of activated carbon with chlorine per metric ton of phosgene produced, more preferably limited to 10 to 115 g of carbon tetrachloride formed by the reaction of activated carbon with chlorine per metric ton of phosgene produced, particularly preferably limited to 10 to 105 g of carbon tetrachloride formed by the reaction of activated carbon with chlorine per metric ton of phosgene produced, for example limited to less than 120 g, less than 117 g, less than 100 g, less than 80 g or less than 50 g of carbon tetrachloride formed by the reaction of activated carbon with chlorine per metric ton of phosgene produced.

[0031] Starting from a typical industrial reactor of the prior art operating at a specific area load, the same phosgene capacity and the same GHSV as in the reactor of the prior art can be applied to design a reactor for carrying out the process of the invention. This application is also meaningful in practice, for example, when an existing reactor is replaced by a reactor of the invention, without affecting the overall process.

[0032] In a variant of the invention, the increase in the area load proposed according to the invention can be achieved by reducing the number of catalyst tubes in the reactor and correspondingly increasing the length of the catalyst tubes. For example, when the number of catalyst tubes is halved while maintaining the same tube diameter, both the area load and the tube length are doubled. Taking into account the teaching according to the invention, the corresponding reactors thus become more compact, i.e. they have a smaller diameter at a comparable GHSV, which is advantageous in terms of the manufacture and cooling of the catalyst tubes. Due to the higher gas velocity and the greater bed length, the pressure drop in the catalyst tubes becomes higher, but this at the same time allows a better distribution of the feed flow over all catalyst tubes.

[0033] In a further variant of the invention, the area loading can be achieved by reducing the diameter of the individual catalyst tubes and correspondingly extending the length of the catalyst tubes again compared to known reactors with the same phosgene capacity and catalyst quantity and unchanged number of tubes.

[0034] Of course, a combination of these two measures is also conceivable, namely reducing the number of tubes and also making the diameter of the individual tubes smaller.

[0035] In the working example of the above-mentioned international patent application WO 2010 / 076208 A1, a catalyst was prepared in a reactor having 5210 catalyst tubes at a temperature of 2.74 kg / m 2 Phosgene production was carried out at an area load of 100 s, the inner tube diameter D of the catalyst tubes being in each case 39.3 mm and the tube length L filled with catalyst (bed height) being in each case 3800 mm.

[0036] The length L of the catalyst tubes of the reactor according to the invention can be from 1.5 to 12 m, preferably from 2.5 to 8 m. Particularly preferred reactor tube lengths are from 6 to 6.5 m. Usually, there is no catalyst within about 25 cm of the beginning and end of each catalyst tube, because due to the installation of the tubes, the heat removal in this area is unsatisfactory.

[0037] On the other hand, the reactor according to the invention can achieve a desired increase in the area load while maintaining the same number of catalyst tubes, for example by reducing the inner tube diameter and increasing the tube length.

[0038] However, catalyst tubes with an internal diameter comparable to that of the prior art can also be used in the reactor according to the invention. The desired increase in area loading can then be achieved, for example, by reducing the number of catalyst tubes. Thus, in another embodiment, the reactor according to the invention is equipped with 1000 to 10000 catalyst tubes.

[0039] The reactor of the present invention may be cylindrical with an inner diameter of preferably 0.3 to 6 m, more preferably 2 to 5 m, especially 2.5 to 4 m.

[0040] In the reactor, there is a bundle (ie a plurality) of catalyst tubes which are arranged parallel to each other in the longitudinal direction of the reactor.

[0041] The catalyst tubes are made of corrosion-resistant materials, for example stainless steel, preferably duplex steel 1.4462, stainless steel 1.4571 or stainless steel 1.4541 or of nickel-based alloys or of nickel. The tube sheet or the entire reactor is also preferably made of the above materials, in particular duplex steel or stainless steel. However, the reactor housing and the reactor plates can also be made of cheaper metals and metal alloys, for example black steel. The components in contact with the reactants can then be coated with a protective layer consisting of a more valuable material.

[0042] The wall thickness of each catalyst tube is preferably from 2.0 to 4.0 mm, in particular from 2.5 to 3.0 mm, and the inner tube diameter is from 20 to 90 mm, preferably from 30 to 50 mm.

[0043] The contact tubes are fastened at both ends to the tube sheet in a liquid-tight manner, preferably welded to the tube sheet. The tube sheet also consists of a corrosion-resistant material, preferably stainless steel, in particular duplex steel, particularly preferably the same material as the catalyst tubes. The seal into the tube sheet is preferably achieved by welding. For example, each tube can be provided with at least two layers of weld seams offset at an angle, for example by 180°, so that the beginning and end of the individual layers do not overlap.

[0044] Both ends of the reactor are delimited on the outside by hoods. The reaction mixture is fed to the catalyst tubes via one hood and the product stream is removed via the hood at the other end of the reactor.

[0045] A gas distributor for equalizing the gas flows, preferably in the form of a plate, in particular a perforated plate, is preferably arranged in the housing into which the reaction mixture is fed.

[0046] The guide plate is arranged in the intermediate space between the catalyst tubes perpendicular to the longitudinal direction of the reactor. The guide plate may have a structure such as that the continuous guide plate has an opening that is arched and staggered relative to the inner wall of the reactor to ensure the circuitous route of the fluid heat transfer medium. In another embodiment, the bundle of tubes can also be divided into two bundles, wherein a guide plate has two arched openings that are staggered from each other, and the guide plate that follows it has a through hole in the central area of ​​the reactor. The guide plate causes the deflection of the heat transfer medium circulating in the reactor inside, in the intermediate space between the catalyst tubes, so that the heat transfer medium flows transversely to the catalyst tubes, which improves the removal of heat. The number of guide plates is preferably about 6 to 35. The guide plates are preferably arranged equidistantly from each other, but it is particularly preferred that the bottom guide plate and the top guide plate are preferably about 1.5 times farther from the tube sheet than the distance between the two continuous guide plates. In the through hole area, the reactor is not provided with a tube, that is, there is basically no catalyst tube. In one embodiment, individual catalyst tubes can be arranged in the through hole of the guide area. In another embodiment, the through-holes are completely free of catalyst tubes. Preferably, all guide plates have the same number of through-holes. The area of ​​each through-hole is preferably 5 to 20%, in particular 8 to 14%, of the reactor cross section.

[0047] The guide plates are preferably not arranged in a sealed manner around the catalyst tubes, but rather allow a leakage flow of up to 40% by volume of the total flow of the heat transfer medium. For this purpose, a gap of 0.1 to 0.6 mm, preferably 0.2 to 0.4 mm, is provided between the catalyst tubes and the guide plates. It is advantageous to configure the guide plates to be liquid-tight (except in the region of the through-holes to the inner wall of the reactor) so that no additional leakage flows occur therein.

[0048] The guide plate can be made of a corrosion-resistant material, preferably stainless steel, in particular duplex steel, preferably with a thickness of 8 to 30 mm, preferably 10 to 20 mm. However, since the guide plate is not in contact with the reactants and the catalyst tubes usually pass through the openings of the guide plate with a certain gap, the guide plate can also be made of a cheaper material (e.g. black steel).

[0049] In a preferred embodiment, the shell space of the reactor according to the invention is divided into at least two cooling zones separated by an intermediate plate. The intermediate plate is preferably made of a higher-quality material, since the openings in the intermediate plate through which the catalyst tubes pass should form a very tight seal to the catalyst tube shell by piercing.

[0050] The catalyst tubes are filled with a solid catalyst, preferably activated carbon. The interstitial volume of the catalyst bed in the catalyst tubes is preferably 0.33 to 0.6, in particular 0.33 to 0.45. The interstitial volume relates to the catalyst bed, wherein the solid catalyst is assumed to be solid. The porosity of the catalyst body itself (which can be 50%, for example) is not taken into account.

[0051] The present invention will be described in more detail below with the aid of schematic diagrams and working examples:

[0052] The accompanying drawings show

[0053] Figure 1 A schematic diagram of a longitudinal section of a reactor of the prior art;

[0054] Figure 2 from Figure 1 A reactor of the present invention modified to operate at an increased area load; and

[0055] Figure 3 Figure 2 Variant of the reactor with two cooling zones.

[0056] Figure 1 A typical phosgene reactor 1 is shown, such as described in more detail in the applicant's international patent application WO 03 / 072273. Figure 1 The reactor 1 shown in the longitudinal section of has a bundle of catalyst tubes 2, which are fastened in a sealed manner to the upper and lower tube sheets 3 in parallel with each other in the longitudinal direction of the reactor 1. A hood 4 is provided at both ends of the reactor, and a gas distributor 12 is arranged in the hood 4. In the intermediate space 5 between the catalyst tubes 2 (through which the liquid heat transfer medium flows), there are guide plates 6, which are arranged perpendicular to the longitudinal direction and alternately leave through holes 7 staggered from each other on the inner wall of the reactor. The reactor 1 is not provided with tubes in the region of the through holes 7, because due to the transition of the coolant flow from a transverse flow to a longitudinal flow, only unsatisfactory cooling of the catalyst tubes can be performed in these regions. Ports or component ring channels 11 are provided for the introduction and discharge of the heat transfer medium. In the depicted example, a compensator 10 is additionally arranged on the reactor shell to balance the thermal stresses.

[0057] Figure 2 Schematically shows a longitudinal cross-section of a reactor according to the invention, which has been modified Figure 1 The reactor is obtained to produce a larger area load (phosgene load) under the condition of constant phosgene production capacity and constant GHSV. Figure 1Elements of the reactor of the invention are provided with the same reference numerals increased by 100. The reactor 101 of the invention also has catalyst tubes 102, which are arranged parallel to each other in the longitudinal direction of the reactor and fastened to form a seal in the upper tube sheet 103a and the lower tube sheet 103b. The feed gas mixture is introduced into the upper cover 104a through the inlet port 113 and distributed throughout the catalyst tubes 102 by means of a gas distributor 112. In the depicted example, the catalyst tubes 102 are composed of duplex steel 1.4462 and their length L substantially corresponds to the bed height of the catalyst present in the catalyst tubes. The catalyst tubes each have an inner diameter D of 39.3 mm and are filled with cylindrical activated carbon catalyst particles having a diameter of 4 mm and a length of 5 mm. After flowing through the catalyst tubes, the reaction mixture is discharged through the cover 104b and the outlet port 114 located at the lower end. Countercurrent to the flow of the reaction gases, the fluid heat transfer medium is introduced at the lower end of the reactor 102 via the port 111a and is guided through the reactor in a circuitous flow by the guide plates 106, which are arranged perpendicularly to the longitudinal direction of the reactor and alternately leave through holes 107 in the peripheral area of ​​the reactor, and leaves again through the outlet 111b.

[0058] By comparison Figure 1 and Figure 2 It can be seen that the number of catalyst tubes 102 is reduced in the embodiment according to the invention compared to the prior art embodiment, while the catalyst filling length L of the catalyst tubes is increased by the same factor, so that the total amount of catalyst in the reactors 1 and 101 is the same. Figure 1 and Figure 2 In a comparison of the reactors of FIG. 1 , the area load (phosgene load) increases by the same factor as the catalyst filling length of the catalyst tube, while keeping the GHSV constant.

[0059] Figure 3 Schematically shows Figure 2 A longitudinal section of a variant 201 of the reactor 101. Figure 2 Elements that are identical to the elements of the reactor or that perform corresponding functions are denoted by the same reference numerals increased by 100 and are not explained in more detail below. Figure 2 The reactor 101 is different, Figure 3The reactor 201 has two separate cooling zones 215, 216, which are separated from each other by an intermediate plate 217. At the lower end of the first cooling zone 215, the first fluid heat transfer medium is introduced countercurrently to the reaction gas flow through the port 111a, guided through the reactor in a circuitous flow by the guide plate 206, and leaves the first cooling zone 215 again through the outlet port 211b, wherein the guide plates 206 are arranged perpendicular to the longitudinal direction of the reactor and each leaves an opening 207 alternately in the peripheral area of ​​the reactor. A corresponding coolant flow is provided in the second cooling zone 216. Here, the second fluid heat transfer medium enters the second cooling zone through the port 218a, is again conveyed through the cooling zone in a circuitous countercurrent, and leaves the second cooling zone 216 again at the port 218b. The cooling zones 215 and 216 can be cooled using different heat transfer media. However, it is preferred to use the same heat transfer medium in adjacent cooling zones because it is difficult to completely seal the openings 219 in the intermediate plate 217 for passing the catalyst tubes 202. However, even if the same heat transfer medium is used, different cooling schemes may be used. For example, a liquid coolant may be used that removes heat by evaporative cooling in the first cooling zone 215 and removes heat by pure liquid cooling in the second cooling zone 216.

[0060] Working Example:

[0061] An activated carbon catalyst of the Donaucarbon ED47 type with a diameter of about 4 mm in the form of extrudates was introduced into a reaction tube with an inner diameter of 39.3 mm at a bed height of 2 m. Gaseous CO was fed into the reaction tube with a 10% stoichiometric excess together with gaseous chlorine. Cooling was carried out by means of a liquid coolant (chlorobenzene) at a temperature of 80° C.

[0062] The device is per m 2 The tubes were operated at different area loadings ranging from 1.7 to 3 kg phosgene per second, with the filling height / bed height increasing in direct proportion to the loading, so that the space velocity / GHSV remained constant.

[0063] The reactor model (described in Mitchell et al., "Selection of carbon catalysts for the industrial manufacture of phosgene", Catal. Sci. Technol., 2012, 2, 2109-2115) was matched to the operating data of the device. Then, based on the model and the CCl4 formation kinetics determined by gas chromatography, the CCl4 formation kinetics for each m 2 CCl4 concentration data at the outlet for different area loadings of phosgene from 1.7 to 5.7 kg per second on the tube area.

[0064] The results are summarized in Table 1 below.

[0065] It can be seen from the values ​​that an increase in the area loading results in a decrease in the CCl4 concentration and a corresponding decrease in the specific CCl4 formation per metric ton of phosgene produced.

[0066] Table 1:

[0067] Area load Bed height GHSV <![CDATA[CCl4 concentration]]> <![CDATA[Specific CCl4 formation amount]]> <![CDATA[[kg / s / m 2 ]]]> [m] <![CDATA[[Nm 3 / H / V 催化剂 ]]]> [ppm] <![CDATA[[g CCl4 / t Phosgene]]]> 1.7 2 738 140.9 239.5 2.7 3.2 738 75.2 128.2 3.7 4.4 738 53.6 91.7 4.7 5.5 738 37.7 64.5 5.7 6.7 738 22.8 39

Claims

1. A process for producing phosgene, said process being carried out by gas phase reaction of carbon monoxide and chlorine in the presence of a catalyst in a reactor comprising a plurality of parallel catalyst tubes, said catalyst tubes being filled with catalyst and around which at least one fluid heat transfer medium flows, wherein a feed stream of a mixture of a chlorine input stream and a carbon monoxide input stream is fed to the catalyst tubes and reacted to obtain a phosgene-containing product gas mixture, wherein the reaction is carried out at a temperature of 3 to 9 kg phosgene / m 2 s under area load; The area loading is achieved by increasing the volume flow of the reactants.

2. The method according to claim 1, wherein an activated carbon catalyst is used as the catalyst.

3. The process according to claim 1 or 2, wherein the amount of carbon tetrachloride formed by the reaction of activated carbon with chlorine is less than 125 g of phosgene per metric ton of production.

4. The method according to claim 1 or 2, wherein the reaction is carried out at 4 to 6 kg phosgene / m 2 s area load.

5. The method according to claim 4, wherein the reaction is carried out at 4.1 to 6 kg phosgene / m 2 s area load.

6. The process of claim 1 or 2, wherein the feed stream has a stoichiometric excess of carbon monoxide to chlorine of 0.1 to 50 mole %.

7. The process of claim 1 or 2, wherein the feed stream is introduced at an absolute pressure of 50 to 2000 kPa (0.5 to 20 bar).

8. The process according to claim 1 or 2, wherein the at least one fluid heat transfer medium flows around the catalyst tubes in separate cooling zones.

9. The method according to claim 1 or 2, wherein a liquid heat transfer medium is used as the fluid heat transfer medium.

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