JP2009196825A - Method for manufacturing chlorine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing chlorine where the exchange of an oxidation catalyst can be performed without stopping the whole manufacturing plant for chlorine and where chlorine can be manufactured continuously even in a period to exchange the oxidation catalyst. <P>SOLUTION: The method for manufacturing chlorine includes a reaction step to obtain chlorine by oxidizing a gas containing hydrogen chloride with oxygen using a fixed bed reactor packed with the oxidation catalyst. The reaction step is performed by being divided into two or more series in the method. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to a method for producing chlorine, and more particularly to a method for producing chlorine by oxidizing hydrogen chloride with oxygen by catalytic gas phase reaction using a fixed bed reactor filled with an oxidation catalyst.

  Hydrochloric acid oxidation process in which hydrogen chloride is oxidized with oxygen in the presence of a catalyst to obtain chlorine includes, for example, chlorine from hydrogen chloride gas by-produced in the process of obtaining isocyanates by the reaction of amine and phosgene and vinyl chloride monomer synthesis process. This is a useful technology that can be applied to a recycling system that manufactures and reuses the same, and has already been industrialized (for example, see Patent Document 1 regarding the hydrochloric acid oxidation process).

Hydrochloric acid oxidation reaction methods include a fixed bed gas-phase circulation method and a fluidized bed gas-phase circulation method, but the former reaction method using a fixed bed is more volatile than the fluidized bed method. It is a reaction system that has advantages such as low occurrence of scattering and scattering, possible reaction at a lower temperature, and high conversion rate, and is suitably applied in industrial processes.
JP 2000-272906 A

  However, the reactor (fixed bed reactor) used in the fixed bed gas phase circulation system is usually composed of several thousand to several tens of thousands of reaction tubes filled with an oxidation catalyst. Is very time consuming. Therefore, there was a problem that the production plant had to be stopped for a long time during the catalyst exchange.

  The present invention has been made in order to solve the above-described problems, and the object thereof is to replace the oxidation catalyst without stopping the entire chlorine production plant, and it is possible to continuously perform the oxidation catalyst replacement period. It is providing the manufacturing method of chlorine which can produce chlorine.

  That is, the present invention includes a reaction step of obtaining chlorine by oxidizing a gas containing hydrogen chloride with oxygen using a fixed bed reactor filled with an oxidation catalyst, and the reaction step is divided into two or more series. Provided is a method for producing chlorine.

  The chlorine production method of the present invention comprises an absorption step in which the gas obtained in the reaction step is brought into contact with water and / or hydrochloric acid water, and unreacted hydrogen chloride is absorbed into the water and / or hydrochloric acid water. A drying process for removing moisture in the gas obtained in the absorption process, and a gas obtained in the drying process is separated into a liquid or gas mainly containing chlorine and a gas mainly containing unreacted oxygen. It is preferable to further include a purification step.

  As said oxidation catalyst, the catalyst which has ruthenium oxide as a main component can be used suitably.

  According to the method for producing chlorine of the present invention, since the reaction system is divided into two or more, the operation of the other fixed bed reactors is performed while one fixed bed reactor is stopped and the catalyst is exchanged. By continuing the process, it is possible to continuously produce chlorine. That is, it is not necessary to completely stop the production plant during catalyst exchange, and continuous production is possible during catalyst exchange.

  Moreover, even if a failure occurs in any one of the fixed bed reactors, production using other fixed bed reactors is possible, and continuous supply of product chlorine is possible.

  FIG. 1 is a production process diagram showing a preferred embodiment of the production method of the present invention. The chlorine production method of the present embodiment includes a reaction step of obtaining chlorine from a gas containing hydrogen chloride as a raw material and oxygen by a catalytic gas phase oxidation reaction, and the gas obtained in the reaction step is mixed with water and / or hydrochloric acid water. An absorption step of bringing the unreacted hydrogen chloride into contact with the water and / or hydrochloric acid water by contacting, a drying step of removing moisture in the gas obtained in the absorption step, and a gas obtained in the drying step, And a purification step of separating the liquid or gas mainly containing chlorine into the gas mainly containing unreacted oxygen. Hereinafter, each step will be described in detail.

(1) Reaction Step The reaction step is a step of obtaining chlorine by oxidizing a gas containing hydrogen chloride with oxygen using a fixed bed reactor filled with an oxidation catalyst. By the oxidation reaction, a gas mainly composed of chlorine, water, unreacted hydrogen chloride and unreacted oxygen is obtained. In the present embodiment, the reaction process is divided into two series. By dividing the reaction process into two lines, the oxidation reaction can be continued using the other reactor even while the catalyst is exchanged in one reactor, and the chlorine production plant is completely shut down. There is no need. Moreover, even if a failure occurs in one reactor, the oxidation reaction can be performed using the other reactor, so that continuous production can be continued and 50% of the normal production amount can be secured. it can. In the present specification, “the reaction process is divided into two systems” means that a chlorine production facility includes two reactors connected in parallel with a raw material supply facility (for example, a raw material gas purification tower). This means that the two reactors are used so that the hydrochloric acid oxidation reaction can be performed in parallel.

  Examples of the gas containing hydrogen chloride as a raw material include pyrolysis reaction and combustion reaction of chlorine compound, phosgenation reaction of organic compound (for example, synthesis of isocyanates using amine and phosgene), chlorination reaction of organic compound ( For example, it may be anything including hydrogen chloride generated in the synthesis of vinyl chloride monomer. The concentration of hydrogen chloride in the gas is 10% by volume or more, preferably 50% by volume or more, and more preferably 80% by volume or more. When the concentration of hydrogen chloride is less than 10% by volume, the concentration of oxygen in the gas mainly composed of unreacted oxygen obtained in the purification process becomes low, and the gas supplied to the reaction process in the circulation process described later You may need to reduce the amount.

  The oxygen used as a raw material may be pure oxygen, for example, a gas containing oxygen such as air, but the concentration of oxygen in the gas containing oxygen is 80% by volume or more. Is preferable, and more preferably 90% by volume or more. 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.

  In the oxidation of hydrogen chloride, the theoretical molar amount of oxygen with respect to 1 mol of hydrogen chloride is 0.25 mol, but it is preferable to supply more than the theoretical amount, and about 0.25 to 2 mol of oxygen is supplied with respect to 1 mol of hydrogen chloride. It is more preferable. 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.

  A fixed bed gas phase flow system using a fixed bed reactor is applied to the oxidation reaction in the reaction step. By applying the fixed bed gas phase circulation method, volatilization and scattering of the catalyst component can be prevented, and a high conversion rate can be obtained even at a relatively low reaction temperature. A fixed bed reactor is usually composed of a bundle of a plurality of (for example, thousands to tens of thousands) reaction tubes filled with an oxidation catalyst. By supplying hydrogen chloride and oxygen as raw materials into such a fixed bed reactor, an oxidation reaction is carried out. As the fixed bed reactor preferably used, a reactor in which the temperature control of at least two reaction zones among the reaction zones is performed by a heat exchange system, for example, by the method described in JP-A No. 2000-272907 can be used. 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 these, Ni is preferable, and Ni having a carbon content of 0.02% by mass or less is particularly preferable.

  It is preferable to provide a jacket part outside the reaction tube of the fixed bed reactor. Thereby, the temperature in the reaction tube can be controlled by the heat medium of 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 mass of potassium nitrate and 50% by mass of sodium nitrite, and a mixture of 53% by mass of potassium nitrate, 40% by mass of sodium nitrite and 7% by mass of sodium nitrate.

  Conventionally known oxidation catalysts filled in the reaction tube include catalysts in which various compounds are added as a third component to copper chloride and potassium chloride, catalysts mainly composed of chromium oxide, and catalysts mainly composed of ruthenium oxide. Among them, it is preferable to use a catalyst in which ruthenium oxide is supported on a metal oxide support. By filling the reaction tube with a catalyst in which ruthenium oxide is supported on a metal oxide support, the influence of the catalyst poison can be reduced. In addition, by using ruthenium oxide, there is no trouble with clogging of piping due to volatilization or scattering of the catalyst component, and no treatment process for the volatilized or scattered catalyst component is required, and chlorine can be obtained at an equilibrium advantageous temperature. Since it can be manufactured, the absorption step, the purification step, and the step of supplying unreacted oxygen to the reaction step (circulation step to be described later) can be simplified, so that the equipment cost and the operating cost can be kept low.

  The content of ruthenium oxide in the oxidation catalyst is preferably 0.1 to 20% by mass. When the content of ruthenium oxide in the catalyst is less than 0.1% by mass, the catalytic activity is low and the conversion rate of hydrogen chloride tends to be low. Moreover, when the content of ruthenium oxide in the catalyst exceeds 20% by mass, the catalyst price tends to increase.

  The particle size of ruthenium oxide is not particularly limited, but is preferably in the range of 1 to 10 nm. The particle diameter of ruthenium oxide indicates a value measured by observation with an electron microscope, for example. Examples of the metal oxide support in the catalyst include a support formed of a metal oxide such as γ-alumina, α-alumina, rutile type titania, anatase type titania, silica, zirconia. Among them, it is preferable to use a metal oxide support formed of alumina or titania because the reaction activity is high and the reaction activity is difficult to decrease. As an oxidation catalyst particularly suitable for the reaction step, specifically, the ruthenium oxide content described in JP-A-10-338502 is 1 to 20% by mass, 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 shape of the oxidation catalyst may be a spherical shape, a cylindrical pellet shape, an extruded shape, a ring shape, a honeycomb shape, or a granular shape having a size that is pulverized and classified after molding. At this time, the catalyst diameter is preferably 5 mm or less. 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 reaction tube 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 a spherical shape, the diameter of a cross section in a cylindrical pellet shape, and the maximum diameter of a cross section in other shapes.

  The reaction temperature of the oxidation reaction in the reaction step is not particularly limited as long as it is within the temperature range usually selected in the oxidation reaction of hydrogen chloride, but is preferably within the range of 100 to 500 ° C, More preferably within the range of 400 ° C. When the reaction temperature is less than 100 ° C., the required reaction rate cannot be obtained and the reaction rate tends to be very low. On the other hand, when the reaction temperature exceeds 500 ° C., the activity tends to decrease due to sintering and volatilization of the catalyst. In addition, the reaction pressure of the oxidation reaction is preferably in the range of 0.1 to 1 MPaG, more preferably 0.1 to 0.7 MPaG so that the reaction rate is moderate and the equipment cost is not excessive. preferable.

  In this embodiment, two fixed bed reactors are used to carry out the reaction process in two series, but these two series of oxidation reaction conditions (for example, catalyst composition, reaction temperature, etc.) are different even if they are the same. Also good. However, considering the ease of process control and the uniformity of the quality of the product chlorine obtained, the same reaction conditions are preferable. The scales of the two reaction systems (for example, the capacities of the two fixed bed reactors) may be the same or different, but the process controllability in the absorption, drying, and purification steps is different due to the difference in scale. It is preferable to use the same scale because it may deteriorate and the quality fluctuation of the product chlorine obtained may occur. By using the same scale, even if one of the reactors cannot be used, 50% of the normal production can be secured. In addition, although a reaction process may be divided | segmented into 3 or more series, when the burden on manufacturing equipment etc. are considered, dividing into 2 series is preferable.

(2) Absorption process The absorption process recovers unreacted hydrogen chloride from the gas containing chlorine, water, unreacted hydrogen chloride and unreacted oxygen obtained in the above reaction process, and removes chlorine and unreacted oxygen. This is a step of obtaining a gas as a main component. The unreacted hydrogen chloride is recovered by bringing the gas obtained in the reaction step into contact with water or hydrochloric acid water, and optionally further cooling to absorb the unreacted hydrogen chloride in the water or hydrochloric acid water and hydrogen chloride. And a solution containing water as a main component. By the absorption step, a gas mainly containing chlorine and oxygen is obtained.

  In the present embodiment, the gases generated from the two series of reaction systems are integrated into one series and used for the absorption process. That is, the gas after the oxidation reaction sent out from two fixed bed reactors is introduced into the same absorption tower, and an absorption process is performed.

  In the absorption step, the temperature at which the gas obtained in the reaction step including unreacted hydrogen chloride is brought into contact with water or hydrochloric acid is not particularly limited, but does not impair the absorption of hydrogen chloride in water. And from a viewpoint which avoids dissolution of the gas component to hydrochloric acid water as much as possible, Preferably it is 0-100 degreeC. 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.

(3) Drying step 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. In this embodiment, the drying process is performed in one series. That is, the entire amount of gas obtained in the absorption process is supplied to one drying tower, and the drying process is performed. 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.

(4) Purification step The purification step is a step of obtaining 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. is there. In the present embodiment, the purification process is performed in one series. That is, the entire amount of gas obtained in the drying step is supplied to one purification tower, and the purification step is performed. 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 the gas introduced into the purification tower, and / or a known method ( JP-A-3-262514 and JP-A-11-500754). For example, by compressing and / or cooling the gas obtained in the drying step, the liquid mainly composed of chlorine is separated from the 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. 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 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 of the present embodiment is a known appropriate method that can be usually included in the chlorine production method, such as (5) diffusion step, (6) circulation step, and (7) detoxification step. These steps may optionally be included. Hereinafter, each of these steps will be described.

(5) Dissipation process A diffusion process is a process of obtaining the gas which has hydrogen chloride as a main component by dissipating the solution containing hydrogen chloride and water obtained by the absorption process. 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. The gas containing hydrogen chloride as a main component may be supplied to either of the two fixed bed reactors, or may be supplied to both. 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 partial operation for returning 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 step, a diffusion tower different from the diffusion tower used in the diffusion step is used, and the hydrochloric acid water obtained in the diffusion step is diffused under a pressure lower than that in the diffusion step. 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 absorption step and the diffusion step, the aqueous hydrogen chloride solution after the oxidation 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.

(6) Circulation step 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. The gas containing unreacted oxygen as a main component may be supplied to either of the two fixed bed reactors, or may be supplied to both, but is preferably supplied to both. 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.

(7) Detoxification process The detoxification process refers to a gas mainly composed of unreacted oxygen obtained in the purification process or a gas (purged gas) that has not been supplied to the reaction process in the above-described circulation process. In this process, chlorine contained in the gas is removed and then discharged out of the system. 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).

  In the present invention, the absorption process and thereafter may be divided into two series. By dividing not only the reaction step but also the absorption step and the subsequent steps into two lines, it is possible to sufficiently secure the processing capacity of the gas sent out by the two fixed bed reactors. For example, since the size (capacity) of an absorption tower that can be produced is limited, when only one series of absorption steps (one absorption tower) is provided for two series of reaction steps, There is a possibility that the gas sent from the reactor cannot be processed, but by providing two series of absorption steps (two absorption towers) corresponding to the two series of reaction steps, sufficient processing capacity is secured. Is possible. In addition, when only one series of absorption steps is provided, it is necessary to adjust the gas flow rate from the reactor or lengthen the treatment time in the absorption step so that the processing capacity of the absorption tower does not exceed the limit. In some cases, if the absorption process is performed in two lines, such a problem can be avoided, so that chlorine can be produced without lowering the production efficiency.

  The scales of the two absorption towers used and their processing capacities may be the same or different, but when the scales of the two reaction systems are the same, it is preferable that they are the same. Moreover, you may divide | segment into 2 series similarly after a drying process.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

It is a manufacturing-process figure which shows 1st Embodiment which concerns on the manufacturing method of this invention.

Claims (3)

Using a fixed bed reactor filled with an oxidation catalyst, and oxidizing a gas containing hydrogen chloride with oxygen to obtain chlorine,
The said reaction process is the manufacturing method of chlorine performed by dividing | segmenting into 2 or more series. An absorption step in which the gas obtained in the reaction step is brought into contact with water and / or hydrochloric acid water to absorb unreacted hydrogen chloride in the water and / or hydrochloric acid water;
A drying step for removing moisture in the gas obtained in the absorption step;
The method for producing chlorine according to claim 1, further comprising a purification step of separating the 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. .   The method for producing chlorine according to claim 1, wherein the oxidation catalyst is a catalyst mainly composed of ruthenium oxide.

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