JP2012180249A - Method for producing chlorine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing chlorine capable of preventing a reactor from being damaged, and initiating reaction without lowering catalyst activity.SOLUTION: The method of producing chlorine comprising oxidizing hydrogen chloride in a raw material gas containing hydrogen chloride, oxygen, and water with a fixed bed reactor in the presence of a catalyst initiates reaction by carrying out sequential steps of: streaming a heating gas to warm the reactor (first step); streaming an inert gas to convert the inside of the reactor to an inert gas atmosphere (second step); controlling the temperature of the reactor to a temperature within a range of 200-400°C (third step); and starting the gas feed in the sequence of oxygen, water vapor, and hydrogen chloride (fourth step).

Description

  The present invention relates to a method for producing chlorine by oxidizing hydrogen chloride in a raw material gas with oxygen using a gas containing hydrogen chloride, oxygen and moisture as raw materials in a fixed bed reactor in the presence of a catalyst.

  Chlorine is useful as a raw material for producing vinyl chloride, isocyanate compounds, polycarbonates, chlorinated hydrocarbons and the like, and is well known to be obtained by oxidation of hydrogen chloride. For example, in Japanese Patent Laid-Open No. 9-67103 (Patent Document 1), hydrogen chloride is oxidized with oxygen using a fixed bed reactor supporting, for example, a metal ruthenium catalyst, a ruthenium oxide catalyst, a ruthenium composite oxide catalyst or the like. A method for producing chlorine is disclosed.

  Japanese Patent Laid-Open No. 2005-219948 (Patent Document 2) describes a method for producing chlorine in which hydrogen chloride is oxidized with oxygen by catalytic reaction in a fixed bed, and the temperature of the catalyst bed in the fixed bed is maintained at 200 to 400 ° C. In addition to supplying oxygen to the catalyst layer, supplying oxygen to the catalyst layer, and supplying oxygen chloride to start the reaction, a method for starting the reaction is disclosed. According to such a method disclosed in Patent Document 2, there is an effect that the conversion rate of hydrogen chloride is increased.

JP-A-9-67103 JP 2005-219948 A

  However, in the oxidation reaction of hydrogen chloride, it is necessary to raise the temperature of the reactor to the reaction start temperature (usually 280 to 350 ° C.). However, if the temperature is rapidly changed from the atmospheric temperature before the start of the reaction, thermal expansion will occur. There was a problem of being damaged (thermal shock). Moreover, since the activity of the catalyst used for the oxidation reaction of hydrogen chloride is lowered when it is kept at a high temperature in the presence of oxygen, it is necessary to start the reaction so that such a decrease in the catalytic activity does not occur.

  The present invention has been made to solve the above-described problems, and the object of the present invention is to prevent the reactor from being damaged and to start the reaction without causing a decrease in the catalytic activity. It is to provide a method for producing chlorine.

  The method for producing chlorine of the present invention is a method for producing chlorine in which hydrogen chloride, oxygen, and water-containing gas are used as raw materials, and hydrogen chloride in the raw material gas is oxidized with oxygen in a fixed bed reactor in the presence of a catalyst. The reaction is started by sequentially performing the following steps.

1st process: The process of warming up a reactor by ventilation | gas_flowing of heating gas,
2nd process: The process which makes the inside of a reactor inert gas atmosphere by ventilation | gas_flowing of inert gas,
3rd process: The process which makes the temperature of a reactor into the temperature within the range of 200-400 degreeC,
4th process: The process which starts gas supply in order of oxygen, water vapor | steam, and hydrogen chloride.

  In the method for producing chlorine according to the present invention, the reactor is preferably a multitubular fixed bed reactor using a molten salt as a heating medium, and the warm-up temperature in the first step is preferably 150 to 200 ° C.

  The catalyst in the chlorine production method of the present invention is preferably ruthenium oxide.

  According to the present invention, since the temperature does not change abruptly from the atmospheric temperature before the start of the reaction, damage to the reactor (thermal shock) can be prevented, and the reaction start temperature is reached in the absence of oxygen. Since the temperature is raised, it is possible to prevent a decrease in catalyst activity.

It is a flowchart which shows typically a preferable example of the manufacturing method of the chlorine of this invention. It is a figure which shows typically the multitubular fixed bed reactor 1 used suitably in this invention.

  FIG. 1 is a flowchart schematically showing a preferred example of the method for producing chlorine according to the present invention. The present invention relates to a method for producing chlorine in which hydrogen chloride in a raw material gas is oxidized with oxygen in a fixed bed reactor using a gas containing hydrogen chloride, oxygen and moisture as a raw material in the presence of a catalyst. The step of warming up the reactor (first step), the step of bringing the inside of the reactor into an inert gas atmosphere by passing inert gas (second step), and the temperature of the reactor within the range of 200 to 400 ° C. The reaction is started by sequentially performing a step of temperature (third step) and a step of starting gas supply in the order of oxygen, water vapor, and hydrogen chloride (fourth step).

  Here, FIG. 2 is a diagram schematically showing a multitubular fixed bed reactor 1 suitably used in the present invention. In the present invention, it is preferable to use a multitubular fixed bed reactor 1 using a molten salt as a heating medium as shown in FIG. As such a multitubular fixed bed reactor 1, for example, as disclosed in Japanese Patent Application Laid-Open No. 2005-306734, the inside of the reactor shell is divided into a plurality of regions 3 by partition plates 2 in the tube axis direction A. What was divided | segmented and the heat medium was comprised so that it might circulate through each area | region 3 can be used conveniently. As a molten salt (HTS: Heat Transfer Salt) used as a heat medium, for example, a mixture of sodium nitrite 40% by mass, sodium nitrate 7% by mass and potassium nitrate 53% by mass, sodium nitrite 50% by mass and potassium nitrate 50% by mass A mixture etc. are mentioned, Usually, the melting | fusing point is 130-150 degreeC. Hereinafter, the steps of the chlorine production method of the present invention will be described in detail by taking as an example the case of using a multitubular fixed bed reactor 1 using a molten salt as a heating medium as shown in FIG.

[1] First Step In the first step, first, the fixed bed reactor is warmed up by aeration of heated gas. When the above-described molten salt is used as a heating medium, this first step is performed before the molten salt is introduced into the shell, but the reactor is in the vicinity of the atmospheric temperature. Although it is necessary to raise the temperature of the reactor near the atmospheric temperature to the reaction start temperature, if the molten salt is suddenly introduced into the reactor to raise the temperature, heat from salt consolidation and rapid temperature change of the reactor will occur. Due to the expansion, the reactor is damaged (thermal shock). Therefore, when molten salt is used as a heating medium, the temperature of the reactor must be raised to a temperature equal to or higher than the melting point (usually 130 to 150 ° C.) of the molten salt before filling the reactor with molten salt. Is preferred.

  The warming-up temperature may be a temperature equal to or higher than the melting point of the molten salt, preferably in the range of 150 to 200 ° C, and more preferably in the range of 150 to 180 ° C. When the warm-up temperature exceeds 200 ° C., the catalyst already filled in the reaction tube of the reactor does not contain hydrogen chloride and chlorine, and is active when kept at such a high temperature in a gas atmosphere containing oxygen. May decrease.

  Note that the temperature of the reactor is the same as the temperature from the inlet to the outlet of the reactor by installing a multipoint thermometer in the length direction of the tube inside some of the reaction tubes. It can be confirmed whether or not it is within the range.

  Moreover, it is preferable to warm up the reactor in the first step at a temperature increase rate that does not receive the above-described thermal shock. As such a temperature raising method, a method of introducing a temperature raising gas into the reactor and gradually raising the temperature of the introduced gas can be employed. Air, nitrogen, or the like is used as the temperature raising gas, and air is more preferable from the viewpoint of economy. The gas is preferably dehumidified. As a dehumidifying method, general methods such as deep cooling and adsorption can be applied. The temperature-raising gas is heated by a heat exchanger and supplied to the reactor via a raw material gas pipe. From the viewpoint of preventing thermal shock of the reactor, the rate of temperature rise in the heat exchanger of the temperature rising gas is preferably 30 to 50 ° C./h.

  As the gas aeration rate for raising the temperature, it is desirable that the gas be vented at 0.1 to 5 m / s at a standard superficial velocity in the reaction tube. When the gas velocity is low, the heat transfer to the reactor is deteriorated, and when it is too high, the differential pressure in the reactor is increased, and the capacity of the blower used for gas supply becomes excessive, which is economically disadvantageous.

  The aerated gas may be discharged from the vicinity of the outlet of the reactor to the atmosphere, or may be recycled as a temperature raising gas.

  When using a molten salt as a heating medium, after the warm-up of the first step, the molten salt is introduced into the shell of the reactor, and circulation of the heating medium is started. For example, as disclosed in Japanese Patent Application Laid-Open Nos. 2005-306734 and 2005-288441, the heat medium circulation system includes a heater and a cooling device for controlling the temperature. A configuration in which a heat medium cooled from the outside or from the outside can be suitably employed. The temperature of the circulating heat medium is maintained at 150 to 200 ° C.

[2] Second Step In the subsequent second step, the inside of the reactor is made an inert gas atmosphere by aeration of inert gas. When a gas containing oxygen such as air is used for warming up the reactor in the first step, the inside of the reactor does not contain hydrogen chloride or chlorine but has a gas atmosphere containing oxygen. From this state, when the temperature of the reactor is increased to 280 to 350 ° C. at which the reaction is started, the catalytic activity is lowered because it becomes 200 ° C. or higher in an oxygen atmosphere not containing hydrogen chloride or chlorine as described above. End up. In order to prevent this, it is necessary to replace the inside of the reactor with an inert gas containing no oxygen such as nitrogen, argon or helium before raising the temperature. From the viewpoint of versatility and cost, it is preferable to use nitrogen as the inert gas. When an inert gas such as nitrogen is used for warming up in the first step, the same inert gas may be used as it is in the second step, or a different inert gas may be used. Good.

  For example, when nitrogen is used as the inert gas, the amount is preferably 5 times or more the packed catalyst volume. It is preferable that the temperature of the reactor during the inert gas aeration be maintained at 150 to 200 ° C. as in the first step. In order to prevent the reverse flow of the gas containing moisture from the downstream process (quenching process) connected to the reactor, it is preferable to continue the aeration of the inert gas until the reaction is started.

  Moreover, when using nitrogen as an inert gas, it is preferable that a moisture content rate is 10 vol% or less, and it is more preferable that it is 5 vol% or less. This is because when the water content in nitrogen exceeds 10 vol%, the catalytic activity may be reduced and the apparatus material may be corroded.

[3] Third Step In the subsequent third step, the temperature of the reactor is set to a temperature within the range of 200 to 400 ° C. With the inside of the reactor in an inert gas atmosphere, the temperature of the heat medium circulated to the reactor shell side is raised to the target temperature set value before starting the reaction using a heater provided in the heat medium circulation system. . The temperature before the start of the reaction is determined according to the activity of the catalyst, but is usually 280 to 350 ° C.

  The rate of temperature increase in the third step is preferably 30 ° C./h or less, and more preferably in the range of 10 to 25 ° C./h.

[4] Fourth Step In the fourth step, gas supply is started in the order of oxygen, water vapor, and hydrogen chloride. By performing gas supply in this order, a high conversion rate of hydrogen chloride can be obtained.

  As oxygen to be supplied first, oxygen or air can be used. A gas containing unreacted oxygen separated from chlorine generated by oxidizing hydrogen chloride with oxygen may be used as a part of the oxygen.

  Next, water vapor is supplied. Thus, when the reaction is started by supplying hydrogen chloride, the temperature of the catalyst layer can be made uniform. The water vapor has a molar ratio to hydrogen chloride of preferably 0.001 to 1.0, more preferably 0.005 to 0.5, and particularly preferably 0.01 to 0.2. When the molar ratio of water vapor to hydrogen chloride is too small, the effect of uniformizing the temperature of the catalyst layer may be small, and when the molar ratio is excessive, the conversion rate of hydrogen chloride may be low.

  The temperature of the water vapor is preferably 50 to 400 ° C, more preferably 150 to 300 ° C. If the temperature of the water vapor is too low, corrosion of the reaction tubes and piping may occur. If the temperature of the water vapor is too high, excessive energy may be required, which may not be economical.

  Thereafter, hydrogen chloride is supplied. This hydrogen chloride is generated in the reaction of hydrogen and chlorine, pyrolysis reaction or combustion reaction of chlorine compounds, phosgenation reaction or chlorination reaction of organic compounds, chlorofluoroalkane production, hydrochloric acid heating, incinerator combustion, etc. Any containing hydrogen chloride can be used.

  The molar ratio of oxygen to hydrogen chloride is preferably 0.25 to 2, more preferably 0.25 to 1.5, and most preferably 0.25 to 1. If the molar ratio of oxygen to hydrogen chloride is too small, the conversion rate of hydrogen chloride may be low. On the other hand, if the molar ratio is excessive, separation of generated chlorine and unreacted oxygen may be difficult. .

  Hydrogen chloride is preferably supplied as soon as possible after supplying oxygen, and hydrogen chloride is preferably supplied within 60 minutes, more preferably within 30 minutes after the start of oxygen supply. This is because the activity of the catalyst is lowered when kept at a high temperature in an oxygen atmosphere not containing hydrogen chloride.

The flow rate of the raw material gas supplied to the reactor is 300 to 700 h ⁻¹ as the flow rate (GHSV) of hydrogen chloride gas per volume of the catalyst in the steady state after the start operation. It is desirable that the flow rate of each gas when starting the supply of the raw material gas is supplied at a flow rate of 30% or less, more preferably 20% or less of the gas amount in the steady state.

  When the reaction starts, the temperature of the catalyst packed bed becomes higher than the heat transfer medium temperature due to the heat of reaction, causing a temperature difference. This temperature difference (ΔT) is roughly proportional to the reaction rate, and thus is a measure of the reaction state. After confirming that the variation in ΔT is reduced and the reaction temperature is stabilized, each gas is gradually increased to the target gas amount in a steady state. The increase is 30% or less, preferably 20% or less, and more preferably 5% or less with respect to the steady-state gas amount. If the amount of gas is increased rapidly, the amount of reaction increases and the reaction temperature becomes difficult to control due to the reaction heat, leading to a runaway reaction.

  It is preferable to increase the order of gas when increasing the source gas in the order of hydrogen chloride, water, and oxygen. This is because if oxygen is increased first, the oxidation reaction rate increases and temperature control becomes difficult.

  By the above operation, the raw material gas flow rate is increased to a steady state amount, and the temperature of the catalyst packed bed is stabilized.

  A catalyst containing ruthenium oxide, preferably a catalyst containing ruthenium oxide and titanium oxide, is used as a catalyst for the reaction of oxidizing hydrogen chloride with oxygen to produce chlorine. Catalysts containing ruthenium oxide are described in, for example, Japanese Patent No. 3284879, Japanese Patent Application Laid-Open No. 10-338502, and Japanese Patent Application Laid-Open No. 2002-292279. Catalysts containing ruthenium oxide and titanium oxide are described in, for example, JP 2000-229239 A, JP 2000-281314 A, and JP 2002-79093 A.

  As described above, as the heating medium in the method for producing chlorine of the present invention, a molten salt can be suitably used as described above. However, conventionally known heating media other than the molten salt, such as alkyl biphenyls and biphenyls, can be used. And diphenyl oxides, biphenyls and diphenyl ethers, triphenyls, dibenzyltoluenes, alkylbenzenes, alkylnaphthalenes, arylalkyls and other organic heat transfer media, water, ionic liquids Of course, it may be used.

  After starting the reaction through the first step to the fourth step in the present invention, the absorption step in the absorption tower 11 and the drying step in the drying tower 21 as shown in FIG. Through the purification step in the chlorine purification tower 31, chlorine as a product is obtained.

  First, in the absorption step performed in the absorption tower 11, the gas mainly composed of chlorine, water, unreacted hydrogen chloride and unreacted oxygen obtained from the reactor 1 is brought into contact with water and / or hydrochloric acid water. And / or by cooling, a solution containing hydrogen chloride and water as main components is recovered, and a gas containing chlorine and unreacted oxygen as main components is obtained. The contact temperature is 0 to 100 ° C. and the pressure is 0.05 to 1 MPa. The concentration of hydrochloric acid to be contacted is preferably 25% by weight or less. In order to prevent precipitation of chlorine hydrate, it is preferable to employ the method described in JP-A-2003-261306.

  The obtained solution is used as it is or after removing chlorine contained in the solution by heating and / or bubbling with an inert gas such as nitrogen, and then adjusting the pH of the electrolytic cell, neutralizing boiler field water, and aniline. It can be used as a raw material for condensation transition reaction of formalin, hydrochloric acid water electrolysis, food addition and the like. Further, as described in FIG. 3.173 of Soda Handbook 1998, p315, all or part of hydrochloric acid is diffused to obtain HCl gas, and the chlorine yield as a reaction raw material can be increased. It is also possible to make the yield of chlorine almost 100% by removing water from the residual hydrochloric acid after the diffusion by the method described in JP-A-139305.

  Next, the drying process performed in the drying tower 21 is a process of obtaining a dried gas by removing moisture in the gas obtained in the absorption process. 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, etc. Among them, since it is easy to discharge after use, sulfuric acid is used as in the example shown in FIG. preferable. Examples of the method for removing moisture in the gas include a method in which chlorine obtained in the absorption step and a gas mainly composed of unreacted oxygen are brought into contact with sulfuric acid.

  The concentration of sulfuric acid added to the process is preferably 90% by weight or more. If the sulfuric acid concentration is less than 90% by weight, moisture in the gas may not be sufficiently removed. The contact temperature is 0 to 80 ° C. and the pressure is 0.05 to 1 MPa. 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.

  In the subsequent purification step, the chlorine purification tower 31 obtains chlorine by separating the dried gas obtained in the drying step into a liquid or gas mainly containing chlorine and a gas mainly containing unreacted oxygen. It is. As a method of separating the liquid or gas mainly containing chlorine and the gas mainly containing unreacted oxygen, a method of compressing and / or cooling and / or a known method (Japanese Patent Laid-Open No. 3-262514, JP-A-11-500954). For example, by compressing and / or cooling the gas obtained in the drying step, a liquid containing chlorine as a main component is separated from a gas containing unreacted oxygen as a main component. The liquefaction of chlorine is carried out to the extent that chlorine specified by pressure and temperature can exist in a liquid state. The lower the temperature, the lower the compression pressure, so the compression power can be reduced. However, industrially, due to problems with equipment, the compression pressure and cooling temperature take into account the optimal economic conditions within this range. Can be decided. In normal operation, the compression pressure for liquefaction of chlorine is 0.5 to 5 MPa, and the cooling temperature is −70 to 40 ° C.

  The obtained liquid containing chlorine as a main component can be used as a raw material for vinyl chloride, phosgene and the like as it is or after partially or completely vaporizing. When used after vaporizing part or all of the gas, heat exchange of the gas obtained in the drying step is performed to obtain part of the heat necessary for vaporization, and at the same time, the chlorine in the gas obtained in the drying step It is possible to reduce the cooling load due to the external refrigerant necessary for liquefaction. Similarly, it can be used for pre-cooling liquid chlorofluorocarbons or for cooling a reflux liquid such as a chlorine distillation column.

  In the method for producing chlorine, it is preferable to circulate part or all of the gas mainly composed of unreacted oxygen obtained in the purification step so as to be supplied to the reaction step. FIG. 1 shows an example in which the gas mainly composed of unreacted oxygen from the chlorine purification tower 31 is recycled after passing through the washing tower 41.

Claims (3)

A method for producing chlorine in which hydrogen chloride, oxygen, and moisture are used as raw materials in the presence of a catalyst in the presence of a catalyst to oxidize hydrogen chloride in the raw material gas with oxygen in a fixed bed reactor, and the following steps are performed in order. A method for producing chlorine, characterized in that the reaction is started by
1st process: The process of warming up a reactor by ventilation | gas_flowing of heating gas,
2nd process: The process which makes the inside of a reactor inert gas atmosphere by ventilation | gas_flowing of inert gas,
3rd process: The process which makes the temperature of a reactor into the temperature within the range of 200-400 degreeC,
4th process: The process which starts gas supply in order of oxygen, water vapor | steam, and hydrogen chloride.   The method according to claim 1, wherein the reactor is a multi-tubular fixed bed reactor using a molten salt as a heating medium, and the temperature of warm-up in the first step is 150 to 200 ° C.   The process according to claim 1 or 2, wherein the catalyst comprises ruthenium oxide.

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