JP2012184133A - Method for stopping fixed bed reactor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a safe stopping method of a fixed bed reactor used for manufacture of chlorine by oxidizing hydrogen chloride with oxygen.SOLUTION: In the stopping method of a reaction step in the fixed bed reactor comprising a reaction tube packed with a catalyst layer containing a catalyst, and a reactor shell covering the circumference of the reactor and regulating the temperature of the reactor interior by circulating a heat medium, a raw material gas stopping operation (S10) of stopping the supply of a raw material gas to the reactor, a replacing operation (S20) of passing an inert gas in the reactor and replacing the reactor interior by the inert gas, and a cooling operation (S30) of cooling the reactor interior are carried out in order, wherein the raw material gas stopping operation (S10) and the replacing operation (S20) are carried out while the heat medium of a temperature of ≥270°C is circulated in the reactor shell.

Description

  The present invention relates to a method for operating a fixed bed reactor used for producing chlorine by oxidizing hydrogen chloride with oxygen.

  A method for producing chlorine by oxidizing hydrogen chloride with oxygen using a fixed bed reactor is conventionally known (see, for example, Patent Document 1). Chlorine is useful as a raw material for producing vinyl chloride, isocyanate compounds, polycarbonate, chlorinated hydrocarbons and the like. On the other hand, since chlorine is highly toxic, care must be taken in its production process. In the above production method using a fixed bed reactor, toxic hydrogen chloride is used in addition to chlorine.

JP-A-2005-306734

  An object of the present invention is to provide a method for safely stopping a fixed bed reactor used for producing chlorine by oxidizing hydrogen chloride with oxygen.

  The present invention is a method for stopping a reaction process in a fixed bed reactor used for producing chlorine, the fixed bed reactor comprising: a reaction tube filled with a catalyst layer containing a catalyst; And a reactor shell that is arranged so as to cover the surroundings and adjusts the temperature in the reaction tube by circulating a heat medium. The reaction step is a step in which source gas containing hydrogen chloride and oxygen is supplied into the reaction tube, and hydrogen chloride is oxidized with oxygen to generate chlorine. The stopping method of the present invention includes a raw material gas stopping operation for stopping the supply of the raw material gas into the reaction tube, and a replacement operation for ventilating the inert gas into the reaction tube and replacing the inside of the reaction tube with the inert gas. A cooling operation for cooling the inside of the reaction tube is sequentially performed, and the raw material gas stop operation and the replacement operation are performed by circulating the heat medium having a temperature of 270 ° C. or more through the reactor shell.

  In the replacement operation, the inert gas flow rate is preferably 100 times or more the volume of the catalyst.

  The fixed bed reactor is preferably a multitubular reactor having a plurality of reaction tubes, and the heating medium is preferably a molten salt.

The catalyst used in the fixed bed reactor preferably has a surface area of 10 m ² / g or more and 500 m ² / g or less.

  According to the method for stopping a fixed bed reactor of the present invention, the reaction step of producing chlorine by oxidizing hydrogen chloride with oxygen can be stopped by reducing the residual amount of harmful substances in the reaction tube to a safe level. .

It is a flowchart which shows the stop method of the fixed bed reactor of this invention. It is a cross-sectional schematic diagram which shows the multitubular fixed bed reactor which is an example of the fixed bed reactor used for this invention. It is a cross-sectional schematic diagram which shows the multitubular fixed bed reactor which is another example of the fixed bed reactor used for this invention. It is a graph which shows the relationship between the nitrogen ventilation time in an Example, the temperature of a heat medium, the density | concentration of hydrogen chloride in waste gas, or the density | concentration of chlorine in waste gas.

Hereinafter, the present invention will be described in detail with reference to the drawings.
The present invention is a method for stopping a reaction process in a fixed bed reactor used for producing chlorine by oxidizing hydrogen chloride with oxygen. The fixed bed reactor used in the present invention is arranged so as to cover a reaction tube filled with a catalyst layer containing a catalyst and the periphery of the reaction tube, and adjusts the temperature in the reaction tube by circulating a heat medium. And a reactor shell. The reaction step in the fixed bed reactor is a step in which a raw material gas containing hydrogen chloride and oxygen is supplied into a reaction tube, and hydrogen chloride is oxidized with oxygen to produce chlorine.

  FIG. 1 is a flowchart showing a method for stopping a reaction process in a fixed bed reactor of the present invention. As shown in FIG. 1, the method for stopping a fixed bed reactor according to the present invention is a reaction step in which a raw material gas containing hydrogen chloride and oxygen is supplied into a reaction tube, and hydrogen chloride is oxidized with oxygen to produce chlorine. For a certain fixed-bed reactor, a raw material gas stop operation (S10) for stopping the supply of the raw material gas into the reaction tube, and an inert gas is passed through the reaction tube to replace the reaction tube with the inert gas. A replacement operation (S20) and a cooling operation (S30) for ventilating a cooling gas in the reaction tube to cool the reaction tube are sequentially performed, and a raw material gas stop operation (S10) and a replacement operation (S20) are performed. ) Is performed by circulating a heat medium of 270 ° C. or higher in the reactor shell. Details of each operation will be described later.

[Fixed bed reactor]
First, the fixed bed reactor used in the present invention will be described. In the present invention, one or a plurality of reaction tubes filled with a catalyst layer containing a catalyst, and a reactor shell arranged so as to cover the periphery of the reaction tubes and adjusting the temperature in the reaction tubes by circulating a heat medium, A heat exchange type fixed bed reactor comprising at least By circulating the temperature-controlled heat medium in the reactor shell, the reaction heat generated by the oxidation reaction can be removed, or the temperature in the reactor can be adjusted to a desired temperature.

  FIG. 2 is a schematic cross-sectional view showing a multitubular fixed bed reactor which is an example of a fixed bed reactor used in the present invention.

  The multitubular fixed bed reactor 1 mainly comprises a plurality of reaction tubes 2 and a reactor shell 3. The reaction tube 2 is fixed to the reactor shell 3 by an upper tube plate 10 and a lower tube plate 12. Yes. The reactor shell 3 is divided into four stages 31 to 34 by a partition plate in the tube axis direction. The number of regions is not limited to four stages, and is usually 2 to 10 stages, preferably 3 to 8 stages, and more preferably 4 to 6 stages. When divided into three or more stages, and further four or more stages, the calorific value per area is relatively small, and the temperature of each area is easily controlled, and the multitubular fixed bed reactor used in the present invention Since the effect of 1 is easily exhibited, it is preferably applied. The reactor shell 3 may not be divided into a plurality of regions, but may be divided into a plurality of regions from the viewpoint of improving temperature controllability in each region as described above. preferable.

  In order to divide the reactor shell 3 into a plurality of regions 31 to 34, a partition plate 11 such as an intermediate tube plate or a blocking plate is usually used. The intermediate tube plate is a partition plate provided in the reactor shell 3 in close contact with the reaction tube 2 so that the heat mediums C1 and C2 do not move between the adjacent regions 31 and 32. The blocking plate is a partition plate 11 provided in the reactor shell 3 with a gap between the reaction tube 2 and allowing the heat mediums C1 and C2 to move slightly between the adjacent regions 31 and 32. is there.

  The heat mediums C1 to C4 circulating in each of the regions 31 to 34 are appropriately selected according to the target reaction temperature, ease of handling of the heat medium, and the like. For example, sodium nitrite 40% by mass, sodium nitrate 7% by mass And an inorganic heat medium composed of an inorganic substance such as a molten salt (HTS: Heat Transfer Salt) such as a mixture of 53% by mass of potassium nitrate, a mixture of 50% by mass of sodium nitrite and 50% by mass of potassium nitrate, alkylbiphenyls, biphenyls and diphenyl oxide A mixture of biphenyls and diphenyl ethers, triphenyls, dibenzyltoluenes, alkylbenzenes, alkylnaphthalenes, arylalkyls, organic heat transfer mediums, water, ionic liquids, etc. It is done.

  A baffle plate 13 may be provided in each of the regions 31 to 34 in the reactor shell 3 in order to adjust the flow direction of the heat mediums C1 to C4. Examples of the shape of the baffle plate include a disc shape, a perforated disc shape, and a missing circle shape. The baffle plate 13 is usually provided so that the flow direction of the heat medium C1 is substantially perpendicular to the reaction tube 2. The baffle plate 13 may be provided in all the regions 31 to 34, or may be provided only in a region where reaction heat is desired to be removed efficiently. Further, the number of baffle plates may be different for each region. The number of baffle plates provided in one region 31 is usually about 1 to 7. When installing a plurality of non-circular baffle plates, a method of staggering the baffle plate openings is generally used as described in US Pat. No. 3,807,963.

  The heat mediums C1 to C4 circulate in the respective regions 31 to 34, and temperature control means for controlling the temperatures of the heat mediums C1 to C4 are provided in the reactor. The temperature of the circulating heat medium is controlled by the temperature control means, and the temperature of the region is controlled. The temperature control means provided so as to correspond to the divided areas includes a cooler and / or a heater.

  In the multi-tubular fixed bed reactor 1 shown in FIG. 2, circulation pumps 61 to 64 and coolers 81 to 84 are provided for each region, and the coolers 81 to 84 are disposed for each region 31 to 34 by the circulation pumps 61 to 64. Cooling is performed by circulating the heat mediums C1 to C4 between the two. The temperature of the heat medium C1 to C4 in each region can be adjusted for each region 31 to 34 by a method of adjusting the cooling temperature of the heat medium C1 to C4 in each cooler 81 to 84.

  Furthermore, in the multitubular fixed bed reactor 1, a heater for heating the circulating heat mediums C1 to C4 in the middle of the piping between the flow control valves U1 to U4 and the divided regions 31 to 34. 41 to 44 are provided. Thereby, it can heat independently about the heat medium of other area | region about the heat medium C1-C4 of all the area | regions, respectively. The temperature of the heat mediums C1 to C4 in each region is adjusted by the coolers 81 to 84 and the heaters 41 to 44.

  FIG. 3 is a schematic cross-sectional view showing another example of a multitubular fixed bed reactor that can be used in the present invention. Similar to the multitubular fixed bed reactor shown in FIG. 2, the multitubular fixed bed reactor is divided into four stages 31 to 34. In the multitubular fixed bed reactor 1, the heat medium C <b> 1 to C <b> 4 in each region is cooled by adding a pre-cooled heat medium (C <b> 0) to each region 31 to 34. That is, in this multitubular fixed bed reactor 1, the circulation pumps 61 to 64 and the circulation tanks 51 to 54 are provided for each of the regions 31 to 34, and the regions 31 to 34 and the circulation tank 51 are provided by the circulation pumps 61 to 64. Heat mediums C1 to C4 are circulated between. At the same time, the heat medium (C0) cooled in advance from the heat medium tank 7 is distributed and added to each of the circulation tanks 51 to 54, thereby cooling the heat mediums C1 to C4 in the respective areas 31 to 34. is doing. The temperature of the heat medium C1 to C4 in each region can be measured by the circulation tanks 51 to 54 and / or thermometers installed in each region 31 to 34, and the heat medium is set so that the temperature becomes a predetermined value. Each region 31 to 34 can be adjusted by a method of adjusting the supply amount of the heat medium (C0) by the flow rate adjusting valves V1 to V4 provided between the tank 7 and the circulation tanks 51 to 54. .

  In this multi-tubular fixed bed reactor 1, the heat medium tank 7 is provided with a cooler 8, and the heat medium (C 0) whose temperature has been increased by reaction heat is cooled by the cooler 8. The As the refrigerant in the cooler 8, water is preferably used. In this case, steam is generated, and by utilizing this in the process, efficient reaction heat can be recovered. From each of the circulation tanks 51 to 54, the excess heat medium C 1 to C 4 overflows and is sent to the heat medium tank 7. Further, it is preferable that each of the circulation tanks 51 to 54 be provided as close as possible to each of the regions 31 to 34 because the piping between each region and the circulation tank can be shortened to prevent the molten salt from consolidating. . Moreover, in order to prevent caking in piping, it is preferable to heat from outside the piping with an electric heater or a high-temperature fluid trace. The heat medium tank 7 is provided with a preheater 9. When the operation is started, the preheater 9 preheats the heat medium (C 0) to a predetermined temperature, and each of the circulation tanks 51-1. 54 can also be supplied. As the preheater 9, an electric heater is preferably applied.

  In the multi-tubular fixed bed reactor 1, when the reactor shell 3 is divided by the blocking plate, each circulation tank can be reduced in that the movement of the heat mediums C 1 to C 4 between the regions 31 to 34 can be reduced. It is preferable to match the height of the liquid level of the heat medium in 51 to 54, and to further minimize the movement of the heat medium C1 to C4 between the regions 31 to 34, the circulation flow rate control valves U1 to U4 It is also preferable to adjust the circulation flow rate between each region 31 to 34 and the circulation tanks 51 to 54. The liquid level of the heat medium in each of the circulation tanks 51 to 54 can be measured by a normal liquid level gauge (not shown).

  The multitubular fixed-bed reactor 1 includes heaters 41 to 44 that heat the heating media C1 to C4 independently. Examples of the heaters 41 to 44 include an electric heater and a heat exchange type heater, and an electric heater is preferably used.

  As the circulation pumps 61 to 64 used in FIGS. 2 and 3, an axial flow pump, a centrifugal vortex pump, or the like is used, and among them, a vertical centrifugal vortex pump is preferably used. Further, the reactor 1 is preferably made of nickel or a nickel lining at a portion in contact with the process gas such as the reaction tube 2 from the viewpoint of preventing corrosion.

  According to the multitubular fixed bed reactor 1 shown in FIG. 2 and FIG. 3, it becomes easy to finely adjust the temperature of each region if necessary. For example, the supply amount of the raw material gas is small and the exothermic reaction is performed. Even when the calorific value is small, the region can be easily maintained at a predetermined reaction temperature.

  The catalyst packed near the inlet of the reaction tube 2 tends to deteriorate relatively quickly, whereas the catalyst near the outlet tends to deteriorate relatively slowly. Therefore, the catalyst in the region 31 corresponding to the vicinity of the inlet deteriorates. When the yield in this region 31 decreases, the reaction temperature can be raised by heating the heat medium C4 in the region 34 corresponding to the vicinity of the outlet, and the conversion rate of hydrogen chloride in this region 34 can be increased.

  The temperature control method is not limited to one having a circulation pump for each of the regions shown in FIGS. 2 and 3 and circulating the heat medium, and the heat medium from the heat medium tank as shown in FIG. In addition, a method of supplying the heat medium via a flow rate adjusting valve, a cooler, or a heater without providing a circulation tank and returning the heat medium directly from the respective regions to the heat medium tank may be used.

  In the reaction tube 2, catalysts having different catalytic activities are usually packed in layers in the direction from the inlet to the outlet, preferably so that the catalytic activity is increased. Specifically, a catalyst having a different catalytic activity due to a difference in composition, production method and / or particle size is used, or the catalyst is diluted with a packing formed only of an inert substance and / or a carrier and then packed. . An inert substance may be filled in the inlet and outlet portions of the catalyst layer and further between the catalyst layers. The inert substance is a solid inert to the process gas, and a molded body made of alumina, silica, silicon carbide, nickel or the like can be applied. In particular, a spherical body made of α-alumina is preferably used.

  The catalyst can be filled so that the catalytic activity is different for each portion of the reaction tube 2 corresponding to the divided region of the reactor shell 3, but this is not necessarily limited, and it corresponds to one region. The reaction tube 2 portion may be filled with a plurality of catalysts having different catalytic activities, or the reaction tube 2 portions corresponding to a plurality of continuous regions may be filled with the same catalyst activity catalyst. That is, the areas of the catalyst different from the divided reactor shell 3 do not have to coincide.

  As a catalyst used for producing chlorine by oxidizing hydrogen chloride with oxygen, a ruthenium oxide catalyst is preferable, and a catalyst in which ruthenium oxide is supported on a titanium oxide-containing support is particularly preferable. As these ruthenium oxide catalysts, those prepared by the methods described in JP-A-9-67103 and JP-A-2000-281314 are preferably used. As a particularly suitable catalyst in the present invention, specifically, a supported ruthenium oxide catalyst or an oxide having a ruthenium oxide content of 1 to 20% by mass and a ruthenium oxide central diameter of 1.0 to 10.0 nm. Although a ruthenium complex oxide type catalyst can be mentioned, it is not limited to this.

The catalyst may be used in the form of a spherical particle, a cylindrical pellet, an extruded shape, a ring shape, a honeycomb shape, or an appropriately sized granule that has been pulverized and classified after molding. At this time, the catalyst diameter is preferably 5 mm or less. This is because the activity may decrease when the catalyst diameter exceeds 5 mm. The lower limit of the catalyst diameter is not particularly limited, but if it is excessively small, the pressure loss in the catalyst packed bed increases, so that a catalyst having a diameter of 0.5 mm or more is usually used. The catalyst diameter here means the diameter of a sphere in the case of spherical particles, the diameter of a cross section in the case of a cylindrical pellet, and the maximum diameter of a cross section in other shapes. The surface area of the catalyst is preferably 10 m ² / g or more and 500 m ² / g or less. When the surface area is less than 10 m ² / g, it is difficult to obtain sufficient reaction activity, and when it exceeds 500 m ² / g, the thermal stability of the catalyst becomes poor.

  When producing chlorine by oxidizing hydrogen chloride with oxygen, the above-described multitubular fixed bed reactor is divided into a plurality of regions by partition plates in the tube axis direction in the shell of the reactor, and at least Using a reactor equipped with a temperature control means for circulating heat medium in one divided region, the above ruthenium oxide catalyst is preferably charged by the above method.

  In the fixed bed reactor 1, in the reaction step, a raw material gas containing hydrogen chloride and oxygen is supplied from the inlet according to arrow A, and a product gas containing unreacted hydrogen chloride and oxygen from the outlet according to arrow B along with chlorine. Is taken out. The reaction step in the fixed bed reactor 1 is, for example, one step of the chlorine production method described in detail below.

[Chlorine production method]
The method for producing chlorine exemplified here includes at least a reaction step in a fixed bed reactor and an absorption step, a drying step, and a purification step in equipment other than the fixed bed reactor.

<Reaction process>
In the reaction step, a raw material gas containing hydrogen chloride and oxygen is supplied from the inlet of the reaction tube of the fixed bed reactor. In the reaction step, the pressure in the reaction tube is preferably about 0.1 to 1 MPaG, more preferably about 0.1 to 0.8 MPaG, and particularly preferably about 0.1 to 0.6 MPaG. The temperature in the reaction tube is about 200 to 500 ° C, preferably about 200 to 380 ° C. If the reaction temperature is too low, the conversion rate of hydrogen chloride may be low. On the other hand, if the reaction temperature is too high, the catalyst component may volatilize or the metal reaction tube may corrode.

  The source gas is a mixture of a gas containing hydrogen chloride and a gas containing oxygen. As the gas containing hydrogen chloride, a gas containing hydrogen chloride generated in a pyrolysis reaction or combustion reaction of a chlorine compound, a phosgenation reaction or chlorination reaction of an organic compound, combustion in an incinerator, or the like can be used. As gas containing hydrogen chloride, hydrogen chloride supplied in gaseous form from the source of hydrogen chloride is used as it is, or hydrogen chloride is absorbed in water and hydrochloric acid supplied is heated to generate hydrogen chloride gas. May be. As the gas containing oxygen, oxygen or air can be used. In addition, a gas containing unreacted oxygen separated from chlorine generated by oxidizing hydrogen chloride with oxygen can be used as part of a gas containing oxygen.

  If hydrogen chloride contains impurities or impurities such as organic substances or sulfur compounds, the purity of the resulting chlorine may be reduced, polychlorinated products may be generated, and the activity of the catalyst may be reduced. Therefore, it is removed and supplied by adsorption with an adsorbent, washing with water or the like. As a method for removing impurities, for example, when hydrogen chloride gas contains something that is difficult to dissolve in water, such as carbonyl sulfide, it is absorbed in water to remove impurities as hydrochloric acid, and the resulting hydrochloric acid is heated to produce hydrogen chloride gas. Is generated and supplied. Organic compounds are adsorbed and removed by activated carbon. When hydrogen chloride is a gas, it may be directly adsorbed on activated carbon or the like, but it may be adsorbed and removed on activated carbon or the like after condensing and removing organic substances by pressurization and cooling. Impurities may include aromatic compounds such as benzene, toluene, chlorobenzene, dichlorobenzene, nitrobenzene, etc., but these aromatic compounds are easily adsorbed on activated carbon in the gas phase and in the liquid phase, and easily on activated carbon. Can be removed. The activated carbon on which the organic matter is adsorbed can be regenerated and reused by a known method such as passing a gas such as heated nitrogen or air to desorb the organic matter. In addition, low boiling point organic compounds such as ethane, propane, dichloroethane, chloroform and the like have a small adsorption capacity to activated carbon, and when these organic compounds are contained, a large amount of the organic compound is absorbed by absorbing the generated hydrogen chloride gas in water. The portion may be removed, and the resulting hydrochloric acid may be heated to generate hydrogen chloride gas for use.

  In order to generate hydrogen chloride from hydrochloric acid, it is usually supplied to a stripping tower and heated with a reboiler using steam. When hydrogen chloride gas is generated, hydrochloric acid having an azeotropic composition is usually obtained from the bottom of the column. This hydrochloric acid is preferably used for absorption of hydrogen chloride if it is used at that concentration, or recycled to a hydrogen chloride generation plant. Hydrochloric acid with higher hydrogen chloride concentration requires less steam to generate hydrogen chloride. However, heat steam is reduced by exchanging heat with hydrochloric acid with a high temperature extracted from the bottom of the tower and the supplied hydrochloric acid. preferable. Tantalum, carbon, fluororesin lining, etc. can be applied as the material for the stripping tower.

  The reaction is carried out at a pressure of about 0.1 to 1 MPaG, so that a gas containing hydrogen chloride may be pressurized using a known compressor. Examples of the compressor include a turbo type axial flow compressor, a centrifugal compressor, a positive displacement reciprocating compressor, a screw type (screw) compressor, and the like, and are appropriately selected in consideration of the required pressure and air volume. Is done. From the viewpoint of the corrosion of the compressor, it is preferable to pressurize a gas containing dry hydrogen chloride.

As the gas containing oxygen, oxygen or air is used. Preferably, the oxygen concentration is 80% by volume or more, more preferably 90% by volume or more. Examples of components other than oxygen include nitrogen (N ₂ ), argon (Ar), carbon dioxide (CO ₂ ), and the like. When the oxygen concentration is less than 80% by volume, the oxygen concentration in the gas mainly composed of unreacted oxygen obtained in the purification step described later is low, and the gas supplied to the reaction step in the circulation step described later You may need to reduce the amount of. A gas containing oxygen having an oxygen concentration of 80% by volume or more can be obtained by an ordinary industrial method such as an air pressure swing method or a cryogenic separation.

  Although the theoretical molar amount of oxygen with respect to 1 mol of hydrogen chloride is 0.25 mol, it is preferable to supply more than the theoretical amount, and more preferably 0.25 to 2 mol of oxygen with respect to 1 mol of hydrogen chloride. If the amount of oxygen is too small, the conversion rate of hydrogen chloride may be low. On the other hand, if the amount of oxygen is too large, separation of generated chlorine and unreacted oxygen may be difficult.

  Normally, a gas containing hydrogen chloride and oxygen is mixed and supplied to the reactor. By smoothing the temperature distribution in the catalyst layer, the catalyst layer is effectively used and the stable activity of the catalyst is maintained. Therefore, the reaction is preferably performed in the presence of moisture. The molar ratio of water to hydrogen chloride is preferably 0.001 to 1.0, more preferably 0.005 to 1.0, and most preferably 0.01 to 1.0. If the molar ratio of water to hydrogen chloride is too small, it may be difficult to smooth the temperature distribution in the catalyst layer. If the molar ratio is excessive, the conversion rate of hydrogen chloride is low. May be.

  As a method of adding moisture, a method of simply adding it into a gas containing hydrogen chloride, a method of generating hydrogen chloride from hydrochloric acid, and adding moisture accompanying hydrogen chloride to the raw material hydrogen chloride gas, chlorine generated after the reaction, and There is a method in which after unreacted hydrogen chloride is recovered, it is humidified when unreacted oxygen gas is recovered and added to the raw material hydrogen chloride gas.

The feed rate of hydrogen chloride, GHSV is represented by (0 ° C., hydrogen chloride in 0.1 MPa (volume) / catalyst (volume)), usually 10～2000H ^-1, preferably 200～1000H ^-1, more preferably 300 Done at ~ 700h- ¹ .

  Along with the supply of the raw material gas into the reaction tube, a heated heat medium is circulated in the reactor shell. Thereby, the source gas in the reactor is heated and the reaction proceeds. Usually, a heating medium of about 260 to 280 ° C. is first circulated to each region. And the temperature in a catalyst layer changes with the activity of the catalyst currently filled. The temperature of the heat medium is adjusted so that the difference (ΔTmax) between the maximum temperature of the catalyst layer (reaction zone) in the reaction tube in the divided region and the heat medium temperature is within a predetermined range.

  The ΔTmax of each reaction zone is, for example, in the case of a multi-tube fixed bed reactor in which the shell is divided into five and has five reaction zones, the first zone from the reactor inlet side is 15 to 40 ° C., preferably 20 to 35 ° C, the second zone is 10-30 ° C, preferably 15-25 ° C, the third zone is 10-25 ° C, preferably 10-20 ° C, the fourth and fifth zones are 0-15 ° C, preferably 5 -10 ° C. If ΔTmax exceeds 40 ° C., temperature runaway may occur and temperature control may become impossible. ΔTmax can be measured by a temperature sensor attached to the center of the reaction tube in the tube axis direction. Usually, using a plurality of reaction tubes and temperature sensors, one temperature sensor is arranged for each reaction tube so that the positions of the temperature detectors in the tube axis direction are different in the plurality of reaction tubes, and ΔTmax of each reaction zone. Are measured simultaneously. However, when a catalyst poison component is mixed in the raw material gas, the activity of the catalyst may decrease from the inlet side, and ΔTmax may move downstream. In order to accurately measure ΔTmax, the detection position of the temperature sensor Need to be moved. Therefore, it is preferable to use a multipoint thermometer in which a plurality of temperature measuring units are attached to one temperature sensor because ΔTmax can be easily detected.

  By performing such temperature control, the conversion rate of hydrogen chloride at the outlet of each zone is about 15-25%, about 35-45%, about 50-60%, about 65-75%, about 80-90, respectively. %become. Except for the conversion rate at the final outlet, the experiment is performed for each zone, and specifically, the final conversion rate is set to about 80 to 90%.

  As the reaction continues, the activity of the catalyst gradually decreases and the conversion rate of hydrogen chloride decreases, so the temperature of the first zone heat medium is increased while maintaining the above range of ΔTmax, and the final conversion rate is set to the above value. Adjust so that it is within the range. Next to the first zone, the temperature of the second zone and the third zone is sequentially increased. In general, the temperature of the final zone filled with the most active catalyst should be kept as low as possible. Eventually, renewal of the catalyst is considered when the maximum temperature of the reaction zone exceeds 500 ° C, preferably 400 ° C.

  The product gas taken out from the outlet of the reaction tube contains unreacted hydrogen chloride and oxygen together with chlorine.

<Absorption process>
The absorption step recovers unreacted hydrogen chloride from the product gas containing chlorine, water, unreacted hydrogen chloride and unreacted oxygen obtained in the reaction step, and contains chlorine and unreacted oxygen as main components. It is the process of obtaining the gas to perform. The unreacted hydrogen chloride is recovered by bringing the product gas obtained in the reaction step into contact with water or hydrochloric acid water, and further cooling it to absorb the unreacted hydrogen chloride in the water or hydrochloric acid water. It is carried out by preparing a solution mainly composed of hydrogen chloride and water. By the absorption step, a gas mainly containing chlorine and oxygen is obtained.

  In the absorption process, the temperature at which the product gas obtained in the reaction process including unreacted hydrogen chloride is brought into contact with water or hydrochloric acid is not particularly limited, but the absorption of hydrogen chloride into water is not limited. It is preferably 0 to 100 ° C. from the viewpoint of not damaging and avoiding the dissolution of the gas component in hydrochloric acid water as much as possible. Moreover, the pressure at the time of making it contact is 0.05-1.0 MPaG from a viewpoint which does not impair the absorptivity to the water of hydrogen chloride, and avoids dissolution of the gas component to hydrochloric acid water as much as possible. In the absorption step, it is preferable to employ the method described in JP-A-2003-261306 in order to prevent precipitation of chlorine hydrate. The solution mainly composed of hydrogen chloride and water obtained in the absorption step can be subjected to a diffusion step described later.

<Drying process>
The drying step is a step of obtaining a dried gas by removing moisture in the gas mainly composed of chlorine and unreacted oxygen obtained in the absorption step. The moisture in the gas after the drying step is 0.5 mg / l or less, preferably 0.1 mg / l or less. Examples of the compound that removes moisture in the gas include sulfuric acid, calcium chloride, magnesium perchlorate, zeolite, and the like. Among them, sulfuric acid is preferable because it can be easily discharged after use. Examples of the method for removing moisture in the gas include a method in which a gas mainly composed of chlorine and unreacted oxygen obtained in the absorption step is brought into contact with sulfuric acid.

  The concentration of sulfuric acid used in the drying step is preferably 90% by mass or more. If the sulfuric acid concentration is lower than 90% by mass, moisture in the gas may not be sufficiently removed. The contact temperature is preferably 0 to 80 ° C., and the pressure is preferably about 0.05 to 1 MPaG. When sulfuric acid is used as the desiccant, it is preferable to remove the sulfuric acid mist immediately after the drying step. For example, a blink eliminator or a method described in JP-A No. 2003-181235 can be applied.

<Purification process>
The purification step is a step of obtaining chlorine by separating the dried gas obtained in the drying step into a liquid or gas containing chlorine as a main component and a gas containing unreacted oxygen as a main component. As a method of separating the liquid or gas mainly containing chlorine and the gas mainly containing unreacted oxygen, for example, by compressing and / or cooling the gas obtained in the drying step, Is separated from a gas mainly composed of unreacted oxygen. The liquefaction of chlorine is carried out to the extent that chlorine specified by pressure and temperature can exist in a liquid state. Industrially, the compression pressure and the cooling temperature are determined in consideration of the optimal economic conditions within this range due to problems such as equipment. In normal operation, the compression pressure for liquefaction of chlorine is 0.5 to 5 MPaG, and the cooling temperature is in the range of −70 to 40 ° C.

  The obtained liquid containing chlorine as a main component can be used as product chlorine as it is or after part or all of the liquid is vaporized. Product chlorine can be used as a raw material for vinyl chloride, phosgene, and the like. When vaporizing a part or all of the liquid mainly composed of chlorine, the gas obtained in the drying process is obtained at the same time as obtaining a part of the heat necessary for vaporization by performing heat exchange of the gas obtained in the drying process. It is possible to reduce the cooling load due to the external refrigerant necessary for liquefying the chlorine in the inside. Similarly, it can be used for pre-cooling liquid chlorofluorocarbons or for cooling a reflux liquid such as a chlorine distillation column.

  In addition to the above steps, the chlorine production method may optionally include known appropriate steps that can be normally included in the chlorine production method, such as a diffusion step, a circulation step, and a detoxification step. Hereinafter, each of these steps will be described.

<Dissipation process>
The stripping step is a step of obtaining a gas containing hydrogen chloride as a main component by stripping the solution containing hydrogen chloride and water obtained in the absorption step. The solution containing hydrogen chloride and water that is diffused in the stripping step usually contains more hydrogen chloride than the azeotropic composition of hydrogen chloride and water under pressure during the stripping step. The composition of such a solution containing hydrogen chloride and water is usually 25 to 40% by mass of hydrogen chloride and 60 to 75% by mass of water.

  The pressure during the stripping step (pressure at the top of the stripping tower used in the stripping step) is selected to be higher than the pressure during the dehydration step when the dehydration step described later is performed following the stripping step. It is preferably 0.05 to 1.0 MPaG. The temperature in the stripping process (the temperature at the bottom of the stripping tower) is determined by the composition of the solution containing hydrogen chloride and water used for stripping in the stripping process and the above pressure, but is usually 100 to 180 ° C. .

  In the stripping step, a gas mainly composed of high concentration hydrogen chloride is obtained from the top of the stripping tower. The gas containing hydrogen chloride as a main component thus obtained can be suitably used as a raw material for the hydrochloric acid oxidation reaction. In addition, although the gas mainly composed of hydrogen chloride obtained in the stripping step contains some water, it is cooled, and by adding a contraction operation to return the condensed hydrogen chloride aqueous solution to the stripping tower, Water contained in the gas can be reduced. It is preferable that the hydrochloric acid water after separating the gas containing hydrogen chloride as a main component is subjected to a dehydration step, separated into hydrochloric acid and waste water, and the recovered hydrochloric acid is recycled to the absorption step.

  In the dehydration process, a distillation tower different from the stripping tower used in the stripping process is used, and the hydrochloric acid water obtained in the stripping process is stripped under a pressure lower than that in the stripping process. The hydrochloric acid water contains more water than the azeotropic composition of hydrogen chloride and water at the pressure in the dehydration process. In this dehydration step, the hydrochloric acid water is diffused, water is recovered from the top of the stripping tower, and hydrochloric acid separated from the water is recovered from the bottom of the stripping tower.

  What is necessary is just to set the pressure in the case of a spin-drying | dehydration process lower than the pressure in the case of the diffusion process mentioned above, Although it does not restrict | limit in particular, It is preferable that it is -0.090-0.05MPaG. Moreover, the temperature in the dehydration step is appropriately determined depending on the pressure and the composition of hydrochloric acid water used for diffusion, but is usually 50 to 90 ° C. Since this temperature is lower than the temperature of the dehydration step when a strong electrolyte such as sulfuric acid is added as the third component, the heating source to be used can be selected from a wider range, and the equipment material of the equipment is also selected. However, relatively inexpensive materials such as glass lining and glass fiber-containing resins can be used.

  By including the diffusion step and the dehydration step, the hydrogen chloride aqueous solution after the absorption step, which is difficult to separate and recover, can be efficiently separated and recovered into hydrogen chloride and water without adding a third component, By using the gas containing hydrogen chloride as a main component thus obtained again for the reaction step, chlorine can be produced more efficiently.

<Circulation process>
The circulation step is a step of supplying a part or all of the gas mainly composed of unreacted oxygen obtained in the purification step to the reaction step. Preferably, the gas containing unreacted oxygen as a main component is partially purged and the entire remaining amount is subjected to the reaction step in order to avoid accumulation of impurities. When the gas containing unreacted oxygen as a main component is circulated in the reaction step, it is preferable to remove the sulfuric acid mist by washing the gas with water.

<Detoxification process>
The detoxification step refers to a gas containing unreacted oxygen obtained in the purification step as a main component, or a gas (purged gas) not supplied to the reaction step in the circulation step described above. This is a step of discharging to the outside of the system after removing. As a method for detoxifying chlorine, the gas may be an aqueous solution of an alkali metal hydroxide, an aqueous solution of an alkali metal thiosulfate, an aqueous solution in which an alkali metal sulfite and an alkali metal carbonate are dissolved, or an alkali metal sulfite. A method of detoxification by contacting with an aqueous solution in which an alkali metal carbonate is dissolved or an aqueous solution in which an alkali metal hydroxide and an alkali metal sulfite are dissolved, and a known method for separating and recovering chlorine in a gas -262514, JP-A-10-25102, JP-A-11-500754).

[How to stop the fixed bed reactor]
Next, the details of each operation in the method for stopping the fixed bed reactor according to the present invention shown in the flowchart of FIG. 1 will be described.

<Raw material gas stop operation (S10)>
In the fixed bed reactor in the reaction step, first, a raw material gas stop operation (S10) is performed. In the source gas stop operation (S10), the supply of the source gas into the reaction tube 2 is stopped. Even if the source gas stop operation (S10) is performed, the circulation of the heat medium in the reactor shell 3 continues. At this time, the heater for heating the heat medium is controlled so that the temperature of the heat medium to be circulated is maintained at 270 ° C. or higher. The supply of the raw material gas can be stopped by closing a valve installed between the raw material gas pipe and the reaction tube.

<Replacement operation (S20)>
The source gas stop operation (S10) is performed, and after the pressure in the reaction tube 2 is reduced to near atmospheric pressure, the replacement operation (S20) is performed. In the replacement operation (S20), an inert gas is supplied from the inlet of the reaction tube 2, and the reaction tube 2 is vented and exhausted from the outlet. Nitrogen, argon, etc. can be used as the inert gas. Also in the replacement operation (S20), the circulation of the heat medium in the reactor shell 3 is continued. At this time, the temperature of the circulating heat medium is maintained at 270 ° C. or higher. By circulating an inert gas through the reaction tube 2 while circulating a heat medium of 270 ° C. or higher, the desorption of hydrogen chloride and chlorine, which are harmful substances adsorbed on the catalyst, is promoted and harmful to the reaction tube 2 The substance can be prevented from remaining. When the temperature of the heat medium is less than 270 ° C., desorption of harmful substances may not be sufficient.

As a flow rate of the inert gas, the flow rate GHSV with respect to the catalyst volume is preferably in the range of 3 to 10 hr ⁻¹ . When the aeration rate GHSV is larger than 10 hr ⁻¹ , the diffusion rate is limited within the pores of the catalyst, and the desorption effect of harmful substances may be insufficient. If the ventilation rate GHSV is less than 3 hr ⁻¹ , it may take time to desorb the harmful substances.

  The total aeration amount of the inert gas in the reaction tube in the replacement operation (S20) is preferably 100 times or more the catalyst volume. When the total aeration amount is less than 100 times the catalyst volume, desorption of harmful substances in the catalyst may be insufficient. In addition, if the total aeration amount is 100 times or more of the catalyst volume, it is difficult to desire a remarkable improvement in desorption even if it is increased more than this, and it may lead to waste of inert gas. Double or less is preferable.

By performing the above operation, water in the reaction tube is also sufficiently removed. The portion of the reaction tube that contacts the source gas is preferably made of nickel or nickel lining. When water remains in the reaction tube 2, the water is condensed in the cooling operation (S30) performed after the replacement operation (S20), and HCl and Cl ₂ are dissolved therein, thereby causing nickel chloride. Things will deliquesce and a strong corrosive environment will be formed. By performing the replacement operation (S20), the water in the reaction tube 2 is sufficiently removed, so that the formation of such a corrosive environment can be suppressed.

  In addition, the inert gas used by substitution operation (S20) and exhausted from the exit of the reaction tube 2 is sent to the equipment used in each process after the reaction process of the above-mentioned chlorine manufacturing method, and vents these. Therefore, the replacement operation (S20) facilitates desorption of harmful substances not only in the reaction tube 2 of the reactor 1 but also in each facility connected thereto.

<Cooling operation (S30)>
In the cooling operation (S30), first, the temperature of the heat medium circulated in the reactor shell is preferably lowered to 200 ° C. or lower to cool the inside of the reaction tube. At this time, as in the replacement operation (S20), it is preferable to continue the flow of the inert gas into the reaction tube. When the temperature of the heat medium is lowered to 200 ° C. or lower, circulation of the heat medium is stopped and the heat medium is extracted from the reactor shell. The melting point of the molten salt used as the heat medium is 130 to 150 ° C. in the case of a mixture of two or more of sodium nitrite (NaNO ₂ ), potassium nitrate (KNO ₃ ), and sodium nitrate (NaNO ₃ ). The molten salt is preferably extracted before solidification.

  In order to further lower the temperature of the reaction tube 2 toward the opening of the reactor 1, a cooling gas is preferably passed through the reaction tube 2. Nitrogen, argon, air, etc. can be used as the cooling gas, and these are preferably dehumidified. Economically, it is preferable to use air. Air is also preferably used from the viewpoint of preventing suffocation of workers when the reactor 1 is opened. As the ventilation speed of the cooling gas, it is preferable that the gas is vented at 0.05 to 5 m / s at a standard superficial velocity in the reaction tube 2. When the gas velocity is less than 0.05 m / s, the heat transfer to the reaction tube 2 is poor, and when it exceeds 5 m / s, the differential pressure in the reaction tube 2 increases, and the capacity of the compressor used for gas pressure increase. Becomes excessively disadvantageous economically.

  The reaction process of the fixed bed reactor 1 is stopped by the above operation. After performing the method for stopping the fixed bed reactor of the present invention, the reactor 1 may be opened for maintenance or the like, or may be stored for a long time. When opening, there is no residual of harmful substances that affect the safety of workers, and the work safety at the time of opening can be ensured. Further, since the catalyst is not maintained in a state in which harmful substances are attached for a long period of time, damage to the catalyst can be prevented.

  When the fixed bed reactor is stored for a long period of time, an inert gas (for example, a cooling gas in the cooling operation) is vented into the reactor 1 in order to prevent inflow of moisture from the outlet side of the reaction tube 2. It is preferable to continue.

  EXAMPLES Hereinafter, although an Example is shown and this invention is demonstrated in detail, this invention is not limited to this Example.

  Using the following multi-tube fixed bed reactor, chlorine was produced under the following reaction conditions using a gas containing hydrogen chloride and oxygen as a raw material gas.

(1) Multitubular fixed bed reactor A multitubular fixed bed reactor similar to that shown in Fig. 2 was used except that the inside of the reactor shell 3 was not divided into a plurality of regions. As a reaction tube, an Ni straight tube having an inner diameter of 25 mm was used, a sheath tube having an outer diameter of 6 mm was inserted into the center of the straight tube, and a temperature sensor was installed in the sheath tube. As the heat medium, a molten salt composed of NaNO ₂ (50 mass%) and KNO ₃ (50 mass%) was used.

  The reaction tube was filled with cylindrical pellets of a supported ruthenium oxide catalyst prepared by the following method with a catalyst filling amount of 1.25 m. The filling amount in each reaction tube was 779 g. A region of the reaction tube not filled with the supported ruthenium oxide catalyst pellets was filled with α-alumina spheres as an inert substance.

The method for preparing the supported ruthenium oxide catalyst pellets is as follows. 50 parts by mass of titanium oxide (“STR-60R” manufactured by Sakai Chemical Co., Ltd., 100% rutile type), 100 parts by mass of α-alumina (“AES-12” manufactured by Sumitomo Chemical Co., Ltd.), titania sol [Sakai Chemical “CSB” manufactured by Co., Ltd., titania content: 38% by mass] 13.2 parts by mass, and 2 parts by mass of methyl cellulose [“Metroze 65SH-4000” manufactured by Shin-Etsu Chemical Co., Ltd.] were mixed and then finely mixed. 33 parts by mass of pure water for adjusting the pore volume was added and kneaded. The kneaded product was extruded into a cylindrical shape having a diameter of 3.0 mmφ, dried, and then crushed to a length of about 4 to 6 mm. The obtained molded body was fired in air at 800 ° C. for 3 hours to obtain a carrier made of a mixture of titanium oxide and α-alumina. This carrier is impregnated with an aqueous solution of ruthenium chloride, dried, and then fired in air at 250 ° C. for 2 hours, whereby ruthenium oxide is supported on the carrier at a loading ratio of 2% by mass. Ruthenium oxide catalyst pellets were obtained. The catalyst surface area of this supported ruthenium oxide catalyst pellet was 14 m ² / g.

(2) Reaction step Hydrogen chloride gas (purity 99 vol% or more) 924 cc / min, oxygen gas (purity 99 vol% or more) 463 cc / min while controlling the temperature of the heat medium circulated in the reactor shell to 300 ° C Was fed to the reaction tube of the multi-tube fixed bed reactor. The molar ratio of hydrogen chloride / oxygen was calculated as 2/1, the GHSV of hydrogen chloride was calculated as 146 h ⁻¹ , and the gas linear velocity based on the empty space of the raw material gas was calculated as 0.05 m / s. The pressure in the reaction tube was controlled to atmospheric pressure.

(3) Conversion rate of hydrogen chloride to chlorine In the above reaction step, the conversion rate of hydrogen chloride to chlorine was 88.6%. The conversion rate of hydrogen chloride to chlorine is determined by sampling the product gas discharged from the outlet of the reaction tube into an aqueous potassium iodide solution to absorb the generated chlorine, unreacted hydrogen chloride, and generated water. The amount of chlorine produced was determined by measuring the amount of unreacted hydrogen chloride by neutralization titration.

(4) Stopping the reaction process After carrying out the reaction process for 2 hours, the supply of the raw material gases (hydrogen chloride gas and oxygen gas) was stopped (raw material gas stop operation). Subsequently, nitrogen was supplied from the inlet of the reaction tube while maintaining the temperature of the heat medium circulated in the reactor shell at 300 ° C. (substitution operation). The flow rate of nitrogen gas was 4.1 L / hr, and GHSV was 7.1 h ⁻¹ . Nitrogen gas aeration was continued for 21 hours under these conditions. The total amount of nitrogen aerated was 149 times the volume of the catalyst. Thereafter, the temperature of the heat medium circulated in the reactor shell was lowered to 200 ° C. or lower (cooling operation).

(5) Evaluation of residual amount of harmful substances During the operations of (4) above, the concentrations of hydrogen chloride and chlorine in the exhaust gas (gas discharged from the outlet of the reaction tube) were detected. FIG. 4 shows the relationship between the nitrogen aeration time and the temperature of the heat medium, the concentration of hydrogen chloride in the exhaust gas, or the concentration of chlorine in the exhaust gas, with the time point when the supply of nitrogen is started as 0 hour in the above (4) Indicates. The concentrations of hydrogen chloride and chlorine in the exhaust gas were measured with a hydrogen chloride detector tube and a chlorine detector tube manufactured by GASTEC. The working environment allowable concentrations of hydrogen chloride and chlorine determined by the Japanese industrial hygiene academia are 5 ppm by volume and 0.5 ppm by volume, respectively. In this example, the chlorine concentration after 21 hours of nitrogen aeration time is less than 0.5 ppm by volume, which is an allowable working environment concentration, and hydrogen chloride after 28 hours of nitrogen aeration time. The concentration of was lower than the working environment allowable concentration of 5 vol ppm.

  1 multi-tube fixed bed reactor, 2 reaction tubes, 3 reactor shells, 7 heat medium tank, 8 cooler, 9 preheater, 10 upper tube plate, 11 partition plate, 12 lower tube plate, 13 baffle plate, 31 -34 Divided area, 41-44 Heater, 51-54 Circulation tank, 61-64 Circulation pump, 81-84 Cooler, C0-C4 Heat medium, U1-U4 Flow control valve, V1-V4 Flow control valve .

Claims (4)

A method for stopping a reaction process in a fixed bed reactor used to produce chlorine, comprising:
The fixed bed reactor includes a reaction tube filled with a catalyst layer containing a catalyst, a reactor shell that is disposed so as to cover the periphery of the reaction tube, and adjusts the temperature in the reaction tube by circulating a heat medium. With
The reaction step is a step in which a raw material gas containing hydrogen chloride and oxygen is supplied into the reaction tube, and the hydrogen chloride is oxidized with the oxygen to generate chlorine.
The stopping method is:
A source gas stop operation for stopping the supply of the source gas into the reaction tube;
A replacement operation of passing an inert gas through the reaction tube and replacing the inside of the reaction tube with an inert gas;
A cooling operation for cooling the inside of the reaction tube, in order,
The method for stopping a fixed bed reactor, wherein the source gas stop operation and the replacement operation are performed by circulating the heat medium having a temperature of 270 ° C. or higher through the reactor shell.   2. The method for stopping a fixed bed reactor according to claim 1, wherein in the replacement operation, the flow rate of the inert gas is 100 times or more the volume of the catalyst.   The method for stopping a fixed bed reactor according to claim 1 or 2, wherein the fixed bed reactor is a multitubular reactor having a plurality of the reaction tubes, and the heat medium is a molten salt. The surface area of the catalyst is not more than ^{10 m} 2 / g or more 500m ² / g, the method of stopping the fixed bed reactor according to claim 1.

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