PROCESS 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 which comprises a plurality of parallel catalyst tubes which are filled with the catalyst and around which at least one fluid heat transfer medium flows, where a feed stream of a mixture of a chlorine input stream and a carbon monoxide input stream is fed into the catalyst tubes and is allowed to react to give a phosgene-comprising product gas mixture, wherein the reaction is carried out at an area load of more than 2.75 kg of phosgene/m2s. The invention also provides a reactor for carrying out the process.

Claims

1.-15. (canceled)

16. A process for producing phosgene by gas-phase reaction of carbon monoxide and chlorine in the presence of a catalyst in a reactor which comprises a plurality of parallel catalyst tubes which are filled with the catalyst and around which at least one fluid heat transfer medium flows, where a feed stream of a mixture of a chlorine input stream and a carbon monoxide input stream is fed into the catalyst tubes and is allowed to react to give a phosgene-comprising product gas mixture, wherein the reaction is carried out at an area load of more than 2.75 kg of phosgene/m.sup.2s.

17. The process according to claim 16, wherein the catalyst comprises an activated carbon catalyst.

18. The process according to claim 16, wherein the amount of carbon tetrachloride formed from the reaction of the activated carbon with chlorine is less than 125 g per metric ton of phosgene produced.

19. The process according to claim 16, wherein the reaction is carried out at an area load of from 3 to 9 kg of phosgene/m.sup.2s.

20. The process according to claim 19, wherein the reaction is carried out at an area load of from 4 to 6 kg of phosgene/m.sup.2s.

21. The process according to claim 20, wherein the reaction is carried out at an area load of from 4.1 to 6 kg of phosgene/m.sup.2s.

22. The process according to claim 16, wherein the feed stream has a stoichiometric excess of carbon monoxide over chlorine of from 0.1 to 50 mol %.

23. The process according to claim 16, wherein the feed stream is introduced with an absolute pressure in the range from 50 to 2000 kPa (from 0.5 to 20 bar).

24. The process according to claim 16, wherein the at least one fluid heat transfer medium flows around the catalyst tubes in separate cooling zones.

25. The process according to claim 16, wherein a liquid heat transfer medium is used as fluid heat transfer medium.

26. A reactor for producing phosgene by gas-phase reaction of carbon monoxide and chlorine in the presence of a catalyst, which comprises a plurality of parallel catalyst tubes which are filled with the catalyst and are at both ends thereof welded in each case into a tube plate, with introduction of the starting materials at the upper end of the catalyst tubes and discharge of the gaseous reaction mixture at the lower end of the catalyst tubes, in each case via a cap, and with input and discharge devices for a fluid heat transfer medium into the shell space between the catalyst tubes, wherein the plurality of the parallel catalyst tubes are designed for an area load of more than 2.75 kg of phosgene per square meter of internal cross-sectional area of the catalyst tubes per second.

27. The reactor according to claim 26, wherein the formation of carbon tetrachloride from the reaction of the activated carbon with chlorine is limited by the design of the reactor to less than 125 g per metric ton of phosgene produced.

28. The reactor according to claim 26, wherein the plurality of parallel catalyst tubes are designed for an area load of from 4.1 to 6 kg of phosgene per square meter of internal cross-sectional area of the catalyst tubes per second.

29. The reactor according to claim 26, wherein the reactor comprises from 1000 to 10000 catalyst tubes.

30. The reactor according to claim 26, wherein the shell space is divided into at least two cooling zones separated by intermediate plates.

Description

[0051] The drawings show

[0052] FIG. 1 a schematic depiction of a reactor of the prior art in longitudinal section;

[0053] FIG. 2 an inventive reactor modified for operation at an increased area load, proceeding from the reactor of FIG. 1; and

[0054] FIG. 3 a variant of the reactor of FIG. 2 with two cooling zones.

[0055] FIG. 1 shows a typical phosgene reactor 1 as is described in more detail, for example, in the international patent application WO 03/072273 by the applicant. The reactor 1 shown in longitudinal section in FIG. 1 has a bundle of catalyst tubes 2 which are fastened parallel to one another in the longitudinal direction of the reactor 1 into upper and lower tube plates 3 in a sealed manner. Caps 4 in which gas distributors 12 are arranged are provided at the two ends of the reactor. In the intermediate space 5 between the catalyst tubes 2, through which space a liquid heat transfer medium flows, there are deflection plates 6 which are arranged perpendicularly to the longitudinal direction and alternately leave through-openings 7 opposite one another free at the interior wall of the reactor. In the region of the through-openings 7, the reactor 1 is without tubes since only unsatisfactory cooling of the catalyst tubes would be possible in these regions due to the transition of the coolant flow from a transverse flow to a longitudinal flow. Ports or part-ring channels 11 are provided for the introduction and discharge of the heat transfer medium. In the example depicted, a compensator 10 is additionally provided on the reactor shell to equalize thermal stresses.

[0056] FIG. 2 schematically shows a longitudinal section of a reactor according to the invention which has been obtained by modification of the reactor of FIG. 1 in order to generate a greater area load (phosgene load) at an unchanged phosgene capacity and an unchanged GHSV. Elements which are identical to elements of the reactor of FIG. 1 have been provided with the same reference numerals increased by 100. The reactor 101 of the invention again has catalyst tubes 102 which are arranged parallel to one another in the longitudinal direction of the reactor and are fastened so as to form a seal in an upper tube plate 103a and a lower tube plate 103b. The feed gas mixture is introduced via an inlet port 113 into an upper cap 104a and is distributed over the catalyst tubes 102 with the aid of a gas distributor 112. In the example depicted, the catalyst tubes 102 consist of duplex steel 1.4462 and have a length L which corresponds essentially to the bed height of the catalyst present in the catalyst tubes. The catalyst tubes each have an internal 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 via the cap 104b located at the lower end and an outlet port 114. In countercurrent to the flow of the reaction gases, a fluid heat transfer medium is introduced at the lower end of the reactor 102 via a port 111a and is conducted through the reactor in a meandering flow by the deflection plates 106 which are arranged perpendicularly to the longitudinal direction of the reactor and alternately leave through-openings 107 free in the peripheral region of the reactor and exits again through an exit port 111b.

[0057] As can be seen by comparison of FIGS. 1 and 2, the number of catalyst tubes 102 in the embodiment according to the invention is decreased compared to the embodiment of the prior art, while the catalyst-filled length L of the catalyst tubes has been increased by the same factor, so that the total amount of catalyst in the reactors 1 and 101 is the same. In the example depicted, the area load (phosgene load) is, at an unchanged GHSV, increased by the same factor as the catalyst-filled length of the catalyst tubes in the comparison of the reactors of FIGS. 1 and 2.

[0058] FIG. 3 schematically shows a longitudinal section of a variant 201 of the reactor 101 of FIG. 2. Elements which are identical to elements of the reactor of FIG. 2 or perform a corresponding function have been denoted by the same reference numerals increased by 100 and are not explained in more detail in the following. In contrast to the reactor 101 of FIG. 2, the reactor 201 of FIG. 3 has two separate cooling zones 215, 216 which are separated from one another by an intermediate plate 217. At the lower end of the first cooling zone 215, a first fluid heat transfer medium is introduced in countercurrent to the flow of the reaction gases via a port 111a, is conducted in a meandering flow through the reactor by the deflection plates 206 which are arranged perpendicularly to the longitudinal direction of the reactor and each leave alternately through-openings 207 free in the peripheral region of the reactor and exits again from the first cooling zone 215 via an exit port 211b. A corresponding coolant flow is provided in the second cooling zone 216. Here, a second fluid heat transfer medium enters the second cooling zone via a port 218a, is again conveyed in countercurrent in a meandering fashion through the cooling zone and exits again from the second cooling zone 216 at a port 218b. The cooling zones 215 and 216 can be cooled using different heat transfer media. However, the same heat transfer medium is preferably used in neighboring cooling zones since the openings 219 in the intermediate plate 217 for passage of the catalyst tubes 202 can be sealed completely only with great difficulty. However, different cooling schemes can be used even when using the same heat transfer medium. For example, it is possible to use a liquid coolant which removes heat by means of evaporative cooling in the first cooling zone 215, while removal of heat occurs by means of pure liquid cooling in the second cooling zone 216.

Working Example

[0059] Activated carbon catalyst of the type Donaucarbon ED47 in the form of extrudates having a diameter of about 4 mm is introduced to a bed height of 2 m into a reaction tube having an internal diameter of 39.3 mm. Gaseous CO is fed in a stoichiometric excess of 10% together with gaseous chlorine into the reaction tube. Cooling is effected by a liquid coolant (chlorobenzene) having a temperature of 80° C.

[0060] The plant was operated at various area loads in the range from 1.7 to 3 kg of phosgene per m.sup.2 of tube area and second, with the fill height/bed height being increased proportionally to the load, so that space velocity/GHSV remain the same.

[0061] A 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 fitted to the operating data of the plant. From the model and gas-chromatographically determined CCl.sub.4 formation kinetics, data for the CCl.sub.4 concentration at the outlet were then determined for different area loads over a load range from 1.7 to 5.7 kg of phosgene per m.sup.2 of tube area and second.

[0062] The results are summarized in table 1 below.

[0063] It can be seen from the values that an increase in the area load leads to a decrease in the CCl.sub.4 concentration and a corresponding reduction in the specific CCl.sub.4 formation per metric ton of phosgene produced.

TABLE-US-00001 TABLE 1 Bed CCl.sub.4 Specific CCl.sub.4 Area load height GHSV concentration formation [kg/s/m.sup.2] [m] [Nm.sup.3/h/V.sub.Cat] [ppm] [g CCl.sub.4/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