JP4999406B2 - Chlorine production method - Google Patents

Description

  The present invention relates to a method for producing chlorine by oxidizing hydrogen chloride by catalytic gas phase reaction between hydrogen chloride and oxygen.

  It is well known that chlorine is useful as a raw material for vinyl chloride, phosgene, etc., and is obtained by oxidation of hydrogen chloride. For example, as a method for producing chlorine by catalytic oxidation of hydrogen chloride with molecular oxygen using a catalyst, a copper-based catalyst conventionally called Deacon catalyst is said to have excellent activity, and copper chloride and potassium chloride. Many catalysts have been proposed in which various compounds are added as a third component. In addition to the Deacon catalyst, a method using chromium oxide or this compound as a catalyst, or a method using ruthenium oxide or this compound as a catalyst has also been proposed.

  Here, as a source gas containing hydrogen chloride (hydrogen chloride source gas), a gas that is by-produced in a pyrolysis reaction or combustion reaction of a chlorine compound, a phosgenation reaction or a chlorination reaction of an organic compound is often used. Such hydrogen chloride source gas contains impurities derived from the source process in addition to hydrogen chloride. For example, when a gas containing hydrogen chloride generated from the step of reacting an isocyanate amine with phosgene is used as the hydrogen chloride source gas, impurities such as carbon monoxide, phosgene, and organic compounds are included in the hydrogen chloride source gas. It will be.

  As a method for removing these impurities from the hydrogen chloride source gas, conventionally, an adsorption method (for example, see JP-A-2003-112907 (Patent Document 1)) or an absorption / dissipation method (for example, JP-A-2000-34105 ( Patent Document 2)) is proposed. However, carbon monoxide in the raw material hydrogen chloride cannot be removed by the adsorption method, and the absorption / dissipation method has a problem that costs are high.

For example, International Publication No. 2005/090231 pamphlet (Patent Document 3) also proposes a method in which a part of impurities is introduced into a reactor for oxidizing hydrogen chloride as it is and burned and removed with a catalyst for oxidizing hydrochloric acid. ing. However, since carbon monoxide contained as an impurity in the hydrogen chloride source gas is a poisoning component of the hydrochloric acid oxidation catalyst, it is desirable not to bring it into the reaction system for oxidizing hydrogen chloride as much as possible. Further, the oxidation of carbon monoxide to carbon dioxide has a large calorific value (67 kcal / mol-CO), which is about 10 times the oxidation calorific value of hydrogen chloride to chlorine (7 kcal · mol-HCl). There is a possibility that the reaction temperature control in a fixed bed reactor usually used as a reaction for the oxidation of methane is hindered, and there is a limit in the allowable amount of acceptance.
JP 2003-112907 A JP 2000-34105 A International Publication No. 2005/090231 Pamphlet

  The present invention has been made in order to solve the above-mentioned problems, and the object of the present invention is to perform catalytic gas phase reaction with oxygen using hydrogen chloride after removing carbon monoxide as an impurity. It is to provide a method for producing chlorine by oxidation.

  The method for producing chlorine of the present invention includes a step of adding chlorine to a hydrogen chloride source gas containing carbon monoxide as an impurity, and further contacting with a phosgenation catalyst, and hydrogen chloride after contacting with the phosgenation catalyst. And a step of oxidizing the gas by catalytic gas phase reaction with oxygen.

Here, the phosgenation catalyst is preferably activated carbon.
Moreover, it is preferable that the density | concentration of the carbon monoxide contained in the said hydrogen chloride raw material gas in the manufacturing method of the chlorine of this invention is more than 1 volume%.

  The catalytic gas phase reaction in the chlorine production method of the present invention is preferably carried out using a fixed bed reactor.

  The catalyst for the catalytic gas phase reaction in the chlorine production method of the present invention is preferably a catalyst containing ruthenium oxide.

  According to the chlorine production method of the present invention, carbon monoxide contained as an impurity in a hydrogen chloride source gas is reacted with chlorine to produce phosgene, and the carbon monoxide contained in the hydrogen chloride source gas is removed. be able to. Thereby, the gas containing hydrogen chloride from which carbon monoxide has been removed can be subjected to oxidation by catalytic gas phase reaction with oxygen for the production of chlorine.

  According to the chlorine production method of the present invention, carbon monoxide, which is a catalyst poisoning component for the catalyst for the oxidation of hydrogen chloride, is removed by conversion to phosgene that does not cause catalyst poisoning. As a result, the influence on the catalyst can be reduced and the life of the catalyst can be extended compared with the case where the hydrogen chloride source gas containing carbon monoxide as an impurity is subjected to oxidation by catalytic gas phase reaction. .

  Further, when carbon monoxide or phosgene is supplied to the catalytic gas phase reactor, the oxidation heat generation amount of carbon monoxide to carbon dioxide is 67 kcal / mol, whereas the oxidation heat generation amount of phosgene is 41 kcal / mol. small. In the present invention, compared with the case where the gas containing hydrogen chloride that does not convert carbon monoxide into phosgene is subjected to oxidation by catalytic gas phase reaction, there is less risk of reaction temperature runaway, and temperature control of the catalytic gas phase reaction is possible. It becomes easy.

  FIG. 1 is a flowchart schematically showing a preferred example of the method for producing chlorine according to the present invention. The present invention presupposes a method for producing chlorine by oxidizing hydrogen chloride with oxygen by catalytic gas phase reaction in the presence of a catalyst. In the method for producing chlorine according to the present invention, a step of adding chlorine to a hydrogen chloride source gas containing carbon monoxide as an impurity and then bringing it into contact with a phosgenation catalyst (shown as a “pretreatment” step in FIG. 1). And hydrogen chloride obtained in this step is subjected to the catalytic gas phase reaction described above.

  As the hydrogen chloride source gas used in the present invention, any gas containing hydrogen chloride generated in pyrolysis reaction or combustion reaction of chlorine compound, phosgenation reaction or chlorination reaction of organic compound, combustion in incinerator, etc. is used. be able to.

  The concentration of hydrogen chloride in the hydrogen chloride source gas in the present invention is not particularly limited, but is preferably 10% by volume or more, more preferably 50% by volume or more, and particularly preferably 80% by volume or more. If the concentration of hydrogen chloride in the hydrogen chloride source gas is less than 10% by volume, the amount of hydrogen chloride removed together with the impurities tends to increase, making it difficult to reduce the loss of hydrogen chloride to a small amount. It is in. Further, when the concentration of hydrogen chloride in the hydrogen chloride raw material gas is smaller than 10% by volume, the concentration of oxygen in the gas mainly composed of unreacted oxygen obtained in the purification step described later is low, which will be described later. There is also a possibility that the amount of the gas supplied to the reaction process in the circulation process may have to be reduced.

  The hydrogen chloride source gas used in the present invention contains at least carbon monoxide as an impurity. The content of carbon monoxide contained in the hydrogen chloride source gas is not particularly limited, but is preferably more than 1% by volume in order to obtain an advantage in reaction control, and is 1.0 to 2. More preferably, it is in the range of 0% by volume. The content of carbon monoxide in the hydrogen chloride source gas can be analyzed using, for example, a gas chromatograph.

  Other impurities contained in the hydrogen chloride source gas include chlorinated aromatic hydrocarbons such as orthodichlorobenzene and monochlorobenzene, aromatic hydrocarbons such as toluene and benzene, and chlorinated hydrocarbons such as methyl chloride and ethyl chloride. And hydrocarbons such as methane, acetylene, ethylene and propylene, and inorganic gases such as nitrogen, argon, carbon dioxide, carbon monoxide, phosgene, hydrogen, carbonyl sulfide, hydrogen sulfide and sulfur dioxide. Hereinafter, Table 1 shows a composition in the case where isocyanate by-product hydrogen chloride gas is used as a hydrogen chloride source gas as a typical example. In Table 1, ODB represents o-dichlorobenzene and MCB represents monochlorobenzene.

  The amount of chlorine added to the hydrogen chloride source gas is not particularly limited, but the amount of carbon monoxide and chlorine contained in the hydrogen chloride source gas is 1: 0.5 to 10 (molar ratio). It is preferable to add the amount which becomes, and it is more preferable to add the amount which becomes 1: 1.05-8 (molar ratio). When carbon monoxide and chlorine are less than 1: 0.5 (molar ratio), the carbon monoxide removal rate may be insufficient, and carbon monoxide and chlorine may be 1:10 ( If the molar ratio is exceeded, the phosgenation catalyst may be deteriorated by residual chlorine.

  In addition, as chlorine added to this hydrogen chloride source gas, you may make it use a part of chlorine obtained by oxidizing hydrogen chloride with oxygen by catalytic gas phase reaction (example shown in FIG. 1), Separate chlorine not obtained in this way may be used.

In the present invention, as described above, chlorine is added to the hydrogen chloride source gas and then brought into contact with the phosgenation catalyst. Here, the phosgenation catalyst refers to a catalyst used in the following reaction for producing phosgene (COCl ₂ ) from carbon monoxide and chlorine.

CO + Cl ₂ → COCl ₂
As the phosgenation catalyst used in the present invention, conventionally known phosgenation catalysts can be used without particular limitation, generally activated carbon can be used, and examples thereof include wood, coconut husk, lignin, lignite, lignite, and coal. Can do. Specifically, when activated carbon is used as the phosgenation catalyst, coconut shell activated carbon is preferably used, and for example, a grade such as Shirasagi WH2C (manufactured by Nippon Enviro Chemical Co., Ltd.) is preferably used.

  In the chlorine production method of the present invention, as described above, chlorine is added to the hydrogen chloride source gas and brought into contact with the phosgenation catalyst, whereby carbon monoxide contained in the hydrogen chloride source gas is reacted with chlorine to react with phosgene. Thus, carbon monoxide is removed. In the present specification, the hydrogen chloride source gas after removing the carbon monoxide is simply referred to as “gas containing hydrogen chloride”. In the present invention, the gas containing hydrogen chloride thus obtained is used for the production of chlorine by oxidizing with oxygen by a catalytic gas phase reaction.

  Carbon monoxide is toxic to catalysts for catalytic gas phase reactions. In the method for producing chlorine of the present invention, as described above, the gas containing hydrogen chloride after the conversion of carbon monoxide contained in the hydrogen chloride source gas into phosgene that does not cause catalyst poisoning is oxidized by catalytic gas phase reaction. Therefore, compared with the case where a hydrogen chloride source gas containing carbon monoxide as an impurity is subjected to oxidation by catalytic gas phase reaction, the influence on the catalyst can be reduced and the life of the catalyst can be extended. it can.

  When carbon monoxide or phosgene is supplied to the catalytic gas phase reactor and oxidized, the calorific value of carbon monoxide to carbon dioxide is 67 kcal / mol, whereas the oxidative calorific value of phosgene is 41 kcal / mol. As small as mol. In the present invention, compared with the case where the gas containing hydrogen chloride that does not convert carbon monoxide into phosgene is subjected to oxidation by catalytic gas phase reaction, there is less risk of reaction temperature runaway, and temperature control of the catalytic gas phase reaction is easy. It also has the advantage of becoming.

  As shown in the flow chart of FIG. 1, the oxidation of hydrogen chloride by catalytic gas phase reaction in the present invention is usually performed by [1] reaction step (performed in the reactor in FIG. 1), [2] absorption step ( 1 is performed in the absorption tower), [3] drying step (performed in the drying tower in FIG. 1), and [4] purification step (performed in the purification tower in FIG. 1). Basically includes one process.

[1] Reaction step In this step, a gas containing hydrogen chloride is oxidized with oxygen under a catalyst to obtain a gas mainly composed of chlorine, water, unreacted hydrogen chloride and unreacted oxygen. As the gas containing oxygen for reacting with the gas containing hydrogen chloride, oxygen or air is used. Preferably, the oxygen concentration is 80% by volume or more, more preferably 90% by volume or more. 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 process is low, and the amount of the gas supplied to the reaction process in the circulation process is reduced. There are things you have to do. 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. Examples of components other than hydrogen chloride in a gas containing oxygen include nitrogen (N ₂ ) and argon (Ar).

  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 excessive, it may be difficult to separate generated chlorine and unreacted oxygen.

  When oxidizing hydrogen chloride with oxygen, it is preferable to use a catalyst in which ruthenium oxide is supported on a metal oxide support.

  The content of ruthenium oxide in the catalyst is preferably 0.1 to 20% by weight. This is because if the ruthenium oxide content in the catalyst is less than 0.1% by weight, the catalytic activity tends to be low and the conversion rate of hydrogen chloride tends to be low, and the ruthenium oxide content in the catalyst is 20%. This is because the catalyst price tends to increase when the amount exceeds wt%.

  The particle size of ruthenium oxide is not particularly limited, but is preferably in the range of 1 to 10 nm. In addition, the particle size of the ruthenium oxide refers to a value measured by observation with an electron microscope, for example.

  Examples of the metal oxide support in the catalyst of the present invention include a support formed of a metal oxide such as γ-alumina, α-alumina, rutile titania, anatase titania, silica, zirconia. Among them, it is preferable to use a metal oxide support formed of alumina, titania, or silica because the reaction activity is high and it is difficult to decrease.

  As a particularly suitable catalyst in the present invention, specifically, the ruthenium oxide content described in JP-A-10-338502 is 1 to 20% by weight, and the center diameter of ruthenium oxide is 1.0. A supported ruthenium oxide catalyst or ruthenium oxide composite oxide type catalyst having a diameter of ˜10.0 nm can be mentioned, but is not limited thereto.

  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 if the catalyst diameter exceeds 5 mm, the activity may decrease. 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.

  As the reaction method, it is preferable to apply a fixed bed gas phase flow method using a fixed bed reactor. As the fixed bed reactor in the present invention, a reactor in which the temperature control of at least two reaction zones among the reaction zones is performed by a heat exchange method, for example, by the method described in JP-A No. 2000-272907 may be used. In such a reactor with two or more reaction zones, two first-stage reaction zones are prepared. Before the second and subsequent stages are poisoned, the first stage is switched alternately. If used, problems can be substantially avoided. However, preparing two expensive reactors is also disadvantageous from the viewpoint of cost.

  Examples of the fixed bed reactor include a single fixed bed or a plurality of fixed bed reaction tubes connected in series and having a jacket portion outside the reaction tube. The temperature in the reaction tube is controlled by the heat medium in the jacket portion. The reaction heat generated by the reaction can be recovered by generating steam through the heat medium. Examples of the heat medium include a molten salt, an organic heat medium, and a molten metal, but a molten salt is preferable in terms of heat stability and ease of handling. Examples of the composition of the molten salt include a mixture of 50% by weight of potassium nitrate and 50% by weight of sodium nitrite, and a mixture of 53% by weight of potassium nitrate, 40% by weight of sodium nitrite and 7% by weight of sodium nitrate. Examples of the material used for the reaction tube include metal, glass, and ceramic. Examples of the metal material include Ni, SUS316L, SUS310, SUS304, Hastelloy B, Hastelloy C, and Inconel. Among them, Ni is preferable, and Ni having a carbon content of 0.02% by weight or less is particularly preferable.

  In the chlorine production method of the present invention, the reaction temperature during the oxidation of hydrogen chloride is usually 100 to 500 ° C, preferably 200 to 400 ° C, and the reaction pressure is usually about 0.1 to 5 MPa.

[2] Absorption process By bringing the gas mainly composed of chlorine, water, unreacted hydrogen chloride and unreacted oxygen obtained in the reaction process into contact with water and / or hydrochloric acid and / or by cooling. In this step, a solution containing hydrogen chloride and water as main components is collected to obtain a gas containing chlorine and unreacted oxygen as main components. 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.

[3] Drying step In this step, a dried gas is obtained by removing moisture in the gas 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 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.

[4] Purification step In this step, chlorine is obtained 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, 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 is within this range, the lower the compression pressure, and the smaller the compression power, but industrially, the compression pressure and the cooling temperature are determined in consideration of optimal economic conditions. 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 also be used for precooling liquid CFCs used as refrigerants for liquefaction of chlorine, and cooling and condensation of reflux liquids such as chlorine distillation towers.

  In the chlorine production method of the present invention, it is preferable to reuse unreacted oxygen during hydrogen chloride oxidation as a part of a reaction raw material for hydrogen chloride oxidation after washing with water. That is, in the example shown in FIG. 1, the liquid or gas mainly containing chlorine and the gas mainly containing unreacted oxygen after separation are washed with water in the purification step, and then the reaction step is performed. Supply. By doing in this way, there exists an advantage that an oxygen basic unit can be reduced. This washing of unreacted oxygen with water is not particularly limited and can be appropriately performed using a washing tower as conventionally known.

It is a flowchart which shows typically a preferable example of the manufacturing method of the chlorine of this invention.

Claims (5)

Adding chlorine to a hydrogen chloride source gas containing carbon monoxide as an impurity, and further contacting with a phosgenation catalyst;
And a step of oxidizing the gas containing hydrogen chloride after being brought into contact with the phosgenation catalyst by causing a gas phase reaction with oxygen to be oxidized.   The method according to claim 1, wherein the phosgenation catalyst is activated carbon.   The method according to claim 1 or 2, wherein the concentration of carbon monoxide contained in the hydrogen chloride source gas is more than 1% by volume.   The method according to claim 1, wherein the catalytic gas phase reaction is carried out using a fixed bed reactor.   The method according to claim 1, wherein the catalyst for the catalytic gas phase reaction is a catalyst containing ruthenium oxide.

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