CN1269726C - Process for preparing chlorine gas - Google Patents

Abstract

The present invention provides a method for preparing chlorine gas, comprising oxidizing hydrogen chloride in a mixed gas containing hydrogen chloride and impurities as a raw material with oxygen, wherein said method includes an absorption step, an extraction step and an oxidation step.

Description

Method for producing chlorine gas

The invention relates to a method for preparing chlorine gas. More particularly, the present invention relates to a method for producing chlorine gas by oxidizing hydrogen chloride in a mixed gas containing hydrogen chloride and impurities as raw materials with oxygen, in which the raw material is divided into a solution containing hydrogen chloride and water as main components and The gas with impurities as the main component is carried out by absorbing hydrogen chloride in the raw material into water or unsaturated hydrochloric acid, the components released from the solution generate a gas containing hydrogen chloride as the main component, and oxidize hydrogen chloride with oxygen to generate chlorine gas , this method produces chlorine gas stably and in high yield by using a catalyst with stable activity, which simplifies or eliminates the complicated separation of produced chlorine gas, unreacted oxygen and various impurities contained in the original hydrogen chloride gas, therefore, from The cost of catalyst, the cost of equipment and the cost of treatment are all very beneficial.

As is well known, chlorine gas produced by oxidation of hydrogen chloride is often used as a raw material for vinyl chloride, phosgene and the like. For example, in this method of producing chlorine gas by catalytically oxidizing hydrogen chloride with molecular oxygen, a copper-containing catalyst called Deacon's catalyst is generally considered to have excellent activity. A number of catalysts containing copper chloride, potassium chloride and various additional compounds as a third component have been proposed. It is also proposed to use chromium oxide or its compound, or ruthenium oxide or its compound as a catalyst instead of the Deacon catalyst. When hydrogen chloride is used as a raw material, by-products of thermal decomposition reaction or combustion reaction of chlorine-containing compounds, phosgenation of organic compounds, etc., or chlorination are generally used, but they contain impurities due to the foregoing methods. For example, hydrogen chloride produced from isocyanate (amyl ester) in which amine and phosgene react contains carbon monoxide, carbon oxysulfide, organic compounds such as o-dichlorobenzene, monochlorobenzene, etc., and impurities such as nitrogen. However, the problem is that impurities in these hydrogen chlorides can lead to deactivation of the catalyst, foul smell of test tubes in the separation step of the gas formed in the reaction, accumulation in unreacted oxygen used for circulation, etc.

For example, JP-A-62-270404 discloses methods for reducing carbon monoxide content, one method is to generate carbon dioxide by burning carbon monoxide in the presence of a palladium catalyst supported on alumina, and one method is to liquefy and vaporize hydrogen chloride in exhaust gas It is separated to provide the gas in the raw material. One method is to scrub the exhaust gas with a copper chloride solution, because a large amount of carbon monoxide contained in hydrogen chloride as a raw material will deactivate the catalyst and increase the evaporation loss of the chromium component in the catalyst. .

Also, JP-A-63-45102 discloses a method for reducing the content of organic compounds, which includes liquefaction-distillation, washing with a solvent having a higher boiling degree, separation at low temperature or use of an adsorbent, since hydrogen chloride containing organic compounds is used as a raw material Used in oxidation reactions that lead to chlorination or partial chlorination of said organic compounds to form polychlorides, which precipitate on the surface of the catalyst, resulting in problems of catalyst deactivation and gas formation in the separation reaction step Pilot tubes smell foul.

Additionally, in all catalytic reactions, sulfides often accumulate on the surface of the catalyst and deactivate the catalyst. However, there is no known method for effectively removing sulfides from hydrogen chloride.

In addition to this, it is also known that the conversion rate of the oxidation reaction of hydrogen chloride is limited by chemical equilibrium and that the reaction is generally carried out under such conditions when an excess of oxygen based on the stoichiometric amount of hydrogen chloride is added. In this case, unreacted oxygen is separated from the chlorine and recycled back to the reaction. If inactive volatile impurities such as nitrogen are polluted, they are difficult to separate from oxygen and accumulate in the system at a higher concentration through circulation, resulting in the problem of reducing the concentration of hydrogen chloride and oxygen in the reaction vessel. Relative concentration and reduce the speed of the reaction. Therefore, after the separation of chlorine gas coming out of the system, part of the gas containing unreacted oxygen as a main component needs to be cleaned, but this leads to another problem: valuable oxygen and accompanying chlorine gas are discarded and lost.

Under such circumstances, the problem is solved by the present invention providing a method for producing chlorine gas by oxidizing hydrogen chloride in a mixed gas containing hydrogen chloride and impurities as a raw material with oxygen, which can be produced stably and in high yield through stable catalyst activity. Preparation of chlorine can simplify or eliminate the complex separation of prepared chlorine, unreacted oxygen and various impurities contained in the original hydrogen chloride gas. Therefore, from the perspective of catalyst cost, equipment cost and treatment cost is very helpful.

That is to say, the present invention relates to a kind of hydrogen chloride that contains hydrogen chloride and impurity mixed gas with oxygen oxidation as raw material to prepare chlorine method, wherein said method comprises the following steps:

Absorption step: This step is to absorb hydrogen chloride in the raw material into water or unsaturated hydrochloric acid to form a solution containing hydrogen chloride and water as main components, and a gas containing impurities as main components;

Extraction step: this step is to extract components from the solution obtained in the absorption step to generate a gas containing hydrogen chloride as a main component;

Oxidation step: This step oxidizes the hydrogen chloride in the gas obtained in the extraction step with oxygen to generate chlorine gas.

Figure 1 is a flow diagram representing an embodiment of the present invention; and

Figure 2 is a flow diagram representing an embodiment of the present invention;

The mixed gas containing hydrogen chloride and impurities may be any mixed gas containing hydrogen chloride and produced in thermal decomposition reaction or combustion reaction of chlorine-containing compounds, or phosgenation or chlorination of organic compounds, combustion in a combustion furnace, etc. The mixed gas containing hydrogen chloride and impurities may be a gas containing hydrogen chloride at a concentration of 10% by volume or higher, preferably 50% by volume or higher and more preferably 80% by volume or higher. When the concentration of hydrogen chloride is lower than 10% by volume, it is difficult to suppress the loss of hydrogen chloride while impurities are removed in the absorption step at a low level.

Impurities contained in hydrogen chloride include chlorinated aromatic hydrocarbons such as o-dichlorobenzene, monochlorobenzene, etc., aromatic hydrocarbons such as toluene, benzene, etc., such as vinyl chloride, 1,2-dichloroethane, methane chloride Chlorinated hydrocarbons such as , ethyl chloride, etc., hydrocarbons such as methane, acetylene, ethylene, propylene, etc., and inorganic gases such as nitrogen, argon, carbon dioxide, carbon monoxide, phosgene, hydrogen, carbon oxysulfide, etc.

In the present invention, impurities are selectively removed by absorbing hydrogen chloride into water or unsaturated hydrochloric acid. Among them, inorganic gases that can be effectively removed include carbon oxysulfide, carbon monoxide, carbon dioxide, phosgene, hydrogen, nitrogen, argon, etc., which are hardly soluble in hydrochloric acid. The concentration of unsaturated hydrochloric acid used in the absorption step may be any concentration lower than the saturation concentration at the temperature and pressure at which the absorption step is carried out, preferably 0 to 25% by weight. The absorption temperature is preferably 0°C-150°C, more preferably 35°C-100°C, and the absorption pressure is preferably 0.05MPa-2MPa, more preferably 0.1MPa-1MPa.

Because the absorption of hydrogen chloride can be carried out at lower temperature and pressure, low-cost acid-resistant materials can be used for this operation. In addition, this operation is characterized by more selective removal of compounds such as carbon oxysulfide, which are difficult to completely remove by liquefaction-distillation or absorption of hydrogen chloride because their boiling point is close to that of hydrogen chloride.

In the present invention, hydrogen chloride absorbed into water or unsaturated hydrochloric acid is released and the obtained hydrogen chloride is oxidized with oxygen to prepare chlorine gas. While the extracted hydrogen chloride is used to produce chlorine by oxygen oxidation, the moisture in the gas and hydrogen chloride are condensed by cooling the extracted gas to reduce the moisture in the gas, and then the uncondensed gas can be oxidized with oxygen to produce chlorine. Furthermore, extracted gas or uncondensed gas obtained by cooling the extracted gas may be contacted with concentrated sulfuric acid or the like to remove moisture, and then oxidized with oxygen to produce chlorine gas.

The extraction pressure is preferably 0.03MPa-1MPa, more preferably 0.1MPa-0.5MPa. There is no restriction on the concentration of hydrochloric acid in the bottom product, as long as it is higher than the concentration of hydrochloric acid of the highest azeotropic mixture of hydrogen chloride and water at the operating pressure, and lower than the concentration of hydrogen chloride in the raw solution used for extraction. In order to recover as much hydrogen chloride as possible into the extraction gas, it is preferably at a concentration close to that of the highest azeotropic mixture. The hydrogen chloride concentration (excluding water) in the gas obtained by extraction is preferably 95% by volume or more, more preferably 98% by volume or more, particularly preferably 99% by volume or more. The structure of the extraction device may include a separate heating device for providing the heat required for extraction. However, in order to recover greater amounts of hydrogen chloride in the feedstock for extraction, it is preferred that the concentration of hydrochloric acid in the bottom product be as low as possible in the range above the highest azeotropic mixture at the working pressure. Conversely, when the water content in the extracted gas obtained is low, the operating energy consumption can be reduced, and the amount of sulfuric acid can be reduced when the gas is dried before the reaction. Therefore, the preferred heating device (reboiler) is a column with one or more theoretical plates, preferably 3-9 theoretical plates, such that the concentration of hydrogen chloride in the extract gas and the concentration of hydrogen chloride in the bottom product are between The difference becomes larger.

Since hydrogen chloride and water form a maximum azeotropic mixture during the extraction step, hydrogen chloride remains in solution after extraction. However, since this unsaturated hydrochloric acid can be recycled as an adsorbent to the step for absorbing hydrogen chloride as the preceding step, the loss of hydrogen chloride in the absorption and extraction steps is very small.

When the theoretical stoichiometric molar ratio of oxygen to hydrogen chloride is 1/4, it is known that the reaction process is more efficient when the amount of added oxygen exceeds the stoichiometric amount (based on hydrogen chloride), because the oxidation reaction of hydrogen chloride is an equilibrium reaction. For this purpose, generally 1/4-1 mole of oxygen is used per mole of hydrogen chloride. Unreacted oxygen is separated from chlorine and is usually recycled to the reaction. In the present invention, since inert gases such as nitrogen, argon, hydrogen, carbon dioxide, etc. can be removed from hydrogen chloride used in the oxidation reaction, carbon monoxide and organic compounds can also be removed from the hydrogen chloride used in the oxidation reaction. In the process, no gases like carbon dioxide are produced by burning carbon monoxide and organic compounds. Therefore, when the stoichiometric amount of oxygen (based on hydrogen chloride) in the oxidation reaction is in excess, after the unreacted hydrogen chloride is separated from the reaction gas in the form of hydrochloric acid and water is produced, there is hardly any other gas in the gas other than oxygen and chlorine. Substances become impurities, so separation and recycling of unreacted oxygen can be performed very easily compared to conventional techniques.

In the present invention, the heat of the solution produced by absorbing hydrogen chloride can be effectively used as a heat source for the preheating of the raw material extraction before the hydrogen chloride is released from the solution, and heat can also be recovered from the bottom product after the extraction.

As the catalyst used in the oxidation reaction in the present invention, any of catalysts known in the process of producing chlorine gas by oxidizing hydrogen chloride can be used. Examples of such catalysts include catalysts containing copper chloride, potassium chloride and various additional compounds as a third component, catalysts containing chromium oxide as a main component, or catalysts containing ruthenium oxide as a main component, and the like. Among them, a catalyst containing ruthenium oxide as a main component is preferable.

Said oxidation reaction system includes flow control systems such as fixed bed and fluidized bed.

The reaction temperature is usually 100°C-500°C, more preferably 200°C-400°C, and the reaction pressure is usually 0.1MPa-5MPa.

A preferred embodiment of the method of the present invention will be described with reference to the accompanying flow chart.

Fig. 1 represents flow chart 1: the mixed gas containing hydrogen chloride and impurity (a) is absorbed and treated with water or unsaturated hydrochloric acid (b). Impurities that are poorly soluble in hydrochloric acid are removed from the top of the absorber and hydrochloric acid (c) is obtained from its bottom. Hydrogen chloride in the obtained hydrochloric acid (c) is released, and hydrogen chloride (d) is obtained from the top of the column. Chlorine gas is produced by oxidation of the hydrogen chloride obtained. Part or all of the unsaturated hydrochloric acid (e) obtained from the bottom of the column in the extraction step is used as unsaturated hydrochloric acid (b) in the hydrogen chloride absorption step.

FIG. 2 represents a flow diagram 2: production of chlorine gas by oxidation with oxygen of hydrogen chloride (f) obtained by removing moisture from hydrogen chloride (d) obtained in a manner similar to that of FIG. 1 .

The present invention provides a method for producing chlorine gas by oxidizing hydrogen chloride in a mixed gas containing hydrogen chloride and impurities as a raw material with oxygen, which can produce chlorine gas stably and in high yield through the stable activity of the catalyst, which can simplify or eliminate The complicated separation steps of produced chlorine, unreacted oxygen and various impurities contained in the raw hydrogen chloride gas are therefore very beneficial from the point of view of catalyst cost, equipment cost and disposal cost.

In the following, the absorption step and the extraction step are evaluated by calculation, and the oxidation step is the result of experiments.

Example 1

Absorption step: the mixed gas that contains 85% (volume) hydrogen chloride and 15% (volume) nitrogen is absorbed in the hydrochloric acid that the concentration of 3.75 times (weight) of gas gross weight is the situation of 20% (weight), simultaneously in absorption tower Cool under the condition that the top pressure of the tower is 0.15 MPa and the bottom temperature is 30° C. to obtain hydrochloric acid with a concentration of 35% by weight.

Extraction step: the concentration of 35% (weight) hydrochloric acid obtained in the absorption step is continuously passed from the top of the tower to an extraction tower with 5 theoretical plates, a condenser at the top and a reboiler at the bottom of the tower. The extraction column operation is that the pressure at the top of the tower is 0.101MPa, the temperature of the gas at the outlet of the condenser is 40°C and the temperature at the bottom of the tower is 109°C, and the hydrogen chloride containing 98.9% (volume) and 1.1% are obtained from the top of the tower % (volume) of moisture in the gas. This gas is contacted with 98% by weight sulfuric acid to remove moisture to obtain >99.5% by volume hydrogen chloride.

Oxidation step: The reaction was carried out using a catalyst prepared by the following method. 5% by weight of metallic ruthenium catalyst loaded on spherical titania with a diameter of 1-2 mm (manufactured by N.E. Chemcat) was impregnated with an aqueous potassium chloride solution until the surface of the catalyst was wetted, and then the catalyst was dried in air at 60°C . The calculated amount of potassium chloride was adjusted so that the molar ratio of ruthenium atoms was 1:1. The catalyst was then dried in air at 60°C for 4 hours, heated in air at room temperature to 350°C for 1 hour, and calcined at the same temperature for 3 hours to obtain a spherical solid. The obtained solid was treated with pure water and the catalyst was filtered. This step was repeated 5 times until the filtrate was added with 0.2 mol/l silver nitrate aqueous solution for a total of more than 5 hours without forming white turbidity. The obtained solid was then dried in air at 60° C. for 4 hours to obtain 6.6% by weight of ruthenium oxide catalyst supported on titania. The inner diameter is the ruthenium oxide catalyst loaded on the titania of the 6.6% (weight) that packs 12.2g obtained in the glass reaction tube of 12mm, uses salt bath (potassium nitrate: sodium nitrate=1: 1) to 330 ℃ from the outside ℃. >99.5% by volume of hydrogen chloride obtained in the absorption step was fed in at a rate of 200 NmL/min and oxygen gas was fed in at a rate of 100 NmL/min. Due to the heat of reaction, the temperature profile of the catalyst bed becomes 328°C-350°C.

The gas sample at the outlet was passed into a 30% by weight KI solution. The produced chlorine gas, unreacted hydrogen chloride and produced water were absorbed in the KI solution, and the amount of produced chlorine gas and unreacted hydrogen chloride were determined by titration iodine method and neutralization method, respectively.

According to the following formula, the obtained chlorine gas generation activity per unit weight of the catalyst is 2.65×10 ⁻⁴ mol/min·g catalyst. The gas remaining after separation of the produced chlorine, the unreacted hydrogen chloride and the produced water flowed at a flow rate of 64 NmL/min, and the oxygen content was >99% by volume. The flow velocity of residual gas is measured by a gas flow meter. This component was analyzed by gas chromatography.

Activity of chlorine gas produced per unit weight of catalyst (mol/min·g catalyst)

= the amount of chlorine produced per unit time at the outlet (mol/min)/weight (g) of the catalyst

Comparative Example 1

Except that the mixed gas containing 85% (volume) of hydrogen chloride and 15% (volume) of nitrogen is passed into the oxidation step at a speed of 200NmL/min, the absorption step and the extraction step are omitted and the operation of Example 1 is repeated. Due to the heat of reaction, the temperature profile of the catalyst bed becomes 327°C-348°C. The activity of chlorine gas produced per unit weight of catalyst is 2.52×10 ^-4 mol/min.g catalyst. Residual gas after separation of generated chlorine, unreacted hydrogen chloride and generated water had a flow rate of 99 NmL/min and a composition of 68% by volume of oxygen and 35% by volume of nitrogen.

Table 1 Example 1 Comparative Example 1 Reaction conditions Hydrogen chloride (volume %) (NmL/min) Oxygen (NmL/min) External salt bath (°C) Activity of chlorine gas produced as a result of the reaction ¹⁾ Residual gas (NmL/min) (volume %) >99.52001003302.6564 Oxygen >99 852001003302.5299 Oxygen/Nitrogen 68/35

¹⁾ Unit: mol/min.g catalyst (×10 ^-4 )

Example 2

Absorption step: the mixed gas containing 90.2% (volume) of hydrogen chloride, 9.5% (volume) of nitrogen and 0.3% of carbon oxysulfide is absorbed at a concentration of 3.96 times (weight) of the total weight of the gas and is 20% (weight) hydrochloric acid, and cooling under the condition that the tower top pressure of the absorption tower is 0.15MPa and the tower bottom temperature is 30 ℃ to obtain concentration is 35% (weight) of hydrochloric acid.

Extraction step: the concentration of 35% (weight) hydrochloric acid obtained in the absorption step is continuously fed from the top of the extraction tower with 5 theoretical plates, a condenser at the top and a reboiler at the bottom. The operation of extracting tower is that 0.101MPa is at tower top pressure, and the temperature of condenser outlet gas is that 40 ℃ and the temperature at the bottom of the tower are carried out under the condition of 109 ℃, to obtain the hydrogen chloride that contains 98.9% (volume) from the tower top and 1.1% (volume) moisture in gas. This gas is contacted with 98% by weight sulfuric acid to remove moisture to obtain >99.5% by volume hydrogen chloride.

Oxidation step: in the glass reaction tube that inner diameter is 12mm, load 3.8g with the 6.6% (weight) ruthenium oxide catalyst that is loaded on the titania that obtains in the same manner as embodiment 1, it is heated from the outside with salt bath to 310°C. >99.5% (volume) hydrogen chloride obtained in the absorption step is passed in at a rate of 302 NmL/min, and oxygen is passed in at a rate of 164 NmL/min. Due to the heat of reaction, the temperature profile of the catalyst bed becomes 319°C-328°C.

The gas sample at the outlet was passed into a 30% by weight KI solution. The produced chlorine gas, unreacted hydrogen chloride and produced water were absorbed in the KI solution, and the amount of produced chlorine gas and unreacted hydrogen chloride were determined by titration iodine method and neutralization method, respectively.

The activity of the chlorine gas produced/the weight of the catalyst is 4.32×10 ^-4 mol/min.g catalyst.

Comparative Example 2

Except that the mixed gas containing 90.2% (volume) of hydrogen chloride, 9.5% (volume) of nitrogen and 0.3% (volume) of carbon oxysulfide is passed through the oxidation step at a rate of 307NmL/min, the absorption step and the extraction step are omitted Repeat the operation of Example 2. Due to the heat of reaction, the temperature profile of the catalyst bed becomes 313°C-317°C. The activity of the chlorine gas produced/the weight of the catalyst is 1.07×10 ^-4 mol/min.g catalyst.

Table 2 Example 2 Comparative Example 2 Reaction conditions Hydrogen chloride (volume%) (NmL/min) Oxygen (NmL/min) External salt bath (°C) Activity of chlorine gas produced as a result of the reaction ¹⁾ >99.53021643104.32 90.23071643101.07

¹⁾ Unit: mol/min.g catalyst (×10 ^-4 )

Claims (7)

1. A method for preparing chlorine, comprising hydrogen chloride in the mixed gas containing hydrogen chloride and impurities as raw material with oxygen oxidation, wherein said method may further comprise the steps: Absorption step: this step absorbs hydrogen chloride in the raw material into water or unsaturated hydrochloric acid to form a solution containing hydrogen chloride and water as main components, and a gas containing impurities as main components; extraction step: this step is to extract components from the solution obtained in the absorption step to obtain a gas containing hydrogen chloride as a main component; and Oxidation step: This step is to oxidize hydrogen chloride in the gas obtained in the extraction step with oxygen to obtain chlorine gas. 2. The method according to claim 1, wherein the gas containing hydrogen chloride as a main component obtained in the extraction step is passed to the oxidation step after removing moisture in the gas. 3. The process according to claim 1, wherein the feedstock is a feedstock containing 10% by volume or more of hydrogen chloride. 4. The method according to claim 1, wherein the impurity in the raw material is at least one selected from chlorinated aromatic hydrocarbons, aromatic hydrocarbons, chlorinated hydrocarbons, hydrocarbons and inorganic gases. 5. The method according to claim 1, wherein the concentration of hydrogen chloride in the gas obtained in the extraction step is 95% by volume or more, excluding water. 6. The process according to claim 1, wherein the feedstock contains 50% by volume or more hydrogen chloride. 7. The process according to claim 1, wherein the hydrogen chloride in the feedstock is produced by an isocyanate process in which amines and phosgene are reacted.

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