Process of Producing Chlorine Gas

Abstract

A process of producing chlorine gas by catalytic oxidation of hydrogen chloride including: incorporating an oxidizing agent such as ozone, hydrogen peroxide solution etc. into a gas stream of hydrogen chloride containing impurities, conducting oxidation pretreatment of the gas stream under the action of ultrasonic wave, such that the impurities contained in the gas stream are oxidized; where the gas stream obtained after the oxidation pretreatment is allowed to pass through a separating device, the oxidized impurities in the form of liquid and/or the oxidized impurities in the form of solid are removed from the gas stream so as to obtain a purified gas stream of hydrogen chloride, and thereafter the purified gas stream of hydrogen chloride is well mixed with a gas stream containing molecular oxygen, the resultant gas mixture is preheated to a reaction temperature, and then catalytically oxidized to produce chlorine gas.

Claims

1. A process of producing chlorine gas by catalytic oxidation of hydrogen chloride, comprising: A) incorporating an oxidizing agent into a gas stream of hydrogen chloride containing impurities, conducting oxidation pretreatment of said gas stream under the action of ultrasonic wave, such that said impurities in the gas stream are oxidized; B) the gas stream obtained after the oxidation pretreatment in step A) is allowed to pass through a separator device wherein the oxidized impurities in the form of liquid and/or the oxidized impurities in the form of solid are removed from said gas stream so as to obtain a purified gas stream of hydrogen chloride; and C) the purified gas stream of hydrogen chloride from step B) is well mixed with a gas stream containing molecular oxygen, the resultant gas mixture is preheated to a reaction temperature, and then introduced into an oxidation reactor and catalytically oxidized in the presence of a catalyst to produce chlorine gas; wherein the oxidizing agent used in step A) does not generate additional or new impurities in the whole reaction system; the impurities contained in the gas stream of hydrogen chloride are inorganic or organic compounds containing sulfur, organic compounds containing halogen, or hydrocarbons not containing halogen; said oxidizing agent is selected from the group consisting of hydrogen peroxide solution, ozone, hypochlorous acid, chlorine, chlorine dioxide, chlorine trioxide, and combinations thereof.

2. The process according to claim 1, wherein the oxidizing agent is added in an amount of <10% (mol/mol), based on the amount of hydrogen chloride.

3. The process according to claim 2, wherein the oxidizing agent is added in an amount of <6% (mol/mol), based on the amount of hydrogen chloride.

4. The process according to claim 1, wherein the inorganic or organic compounds containing sulfur include H.sub.2S, COS, mercaptans, thioethers, cyclothioethers, disulfides, thiophenes and also homologues thereof; and the organic compounds containing halogen include monohalo- or polyhalo-aromatics, monohalo- or polyhalo-alkynes, monohalo- or polyhalo-olefins, monohalo- or polyhalo-cycloalkanes, saturated monohalo- or polyhalo-alkanes, and also monohalo- or polyhalo-organic acids.

5. The process according to claim 1, wherein the content of the inorganic or organic compounds containing sulfur, the organic compounds containing chlorine, or the hydrocarbons not containing chlorine is <4% (mol/mol), based on the amount of hydrogen chloride.

6. The process according to claim 1, wherein the content of the inorganic or organic compounds containing sulfur, the organic compounds containing chlorine, or the hydrocarbons not containing chlorine is <3% (mol/mol), based on the amount of hydrogen chloride.

7. The process according to claim 1, wherein the oxidizing agent is dispersed as gas phase or in the form of liquid drops by a disperser and introduced into the gas stream of hydrogen chloride, and conduct oxidation pretreatment, in order to oxidizing the impurities contained in the gas stream.

8. The process according to claim 7, wherein said disperser can be any type of static dispersers, dynamic dispersers or jet dispersers.

9. The process according to claim 1, wherein the frequency of the ultrasonic wave used is 20 kHz120 kHz.

10. The process according to claim 9, wherein the frequency of the ultrasonic wave used is 22 kHz80 kHz.

11. The process according to claim 1, wherein the power of the ultrasonic device used for generating ultrasonic wave is 100 W200 kW.

12. The process according to claim 11, wherein the power of the ultrasonic device used for generating ultrasonic wave is 130 W150 kW.

13. The process according to claim 1, wherein said separator is one which may separate gas components from liquid components, and/or may separate gas components from solid components, and/or may separate gas components from liquid components and solid components.

14. The process according to claim 1, wherein said separator is a screen separator, a cyclone separator or a separator comprising a filler layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0043] FIG. 1 shows a process flow diagram for carrying out the oxidation pretreatment and catalytic oxidation of hydrogen chloride of the present invention continuously, wherein:

[0044] Before the oxidation reaction of hydrogen chloride, the gas stream s1 containing impurities is firstly mixed with the stream s2 of an oxidizing agent by a disperser M1, and conducting oxidation pretreatment in the disperser M1, wherein the oxidation pretreatment is performed in an ultrasonic environment generated by an ultrasonic device U1. The gas stream obtained after the oxidation pretreatment firstly passes through a separator S1 to remove the liquid or solid oxidation products (i.e., oxidized impurities) which might be produced in the oxidation pretreatment, then is mixed with a gas stream s3 containing oxygen in a disperser M2, then enters into a pre-heater E1 to be heated to the temperature required by the reaction, and finally is introduced to a reactor R1 to conduct the catalytic oxidation reaction, thereby obtaining a reaction gas s4 containing chlorine.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

[0045] The embodiments of the present invention are further described with reference to the Drawing and Examples. The present invention should not be interpreted to be limited to these examples, rather comprise all variations and modifications within the scope of the claims.

[0046] The main raw materials used in the Examples are obtained as follows.

[0047] Purified/crude hydrogen chloride gas: manufactured by NINGBO WANHUA POLYURETHANES CO., LTD., industrial products; based on hydrogen chloride, the crude hydrogen chloride gas contains 501200 ppm(mol/mol), usually 1001000 ppm (mol/mol), in particular 20800 ppm(mol/mol) of chlorinated aromatics such as chlorobenzene etc. and a small amount of other compounds containing sulfur and compounds containing halogen. Based on hydrogen chloride, the purified hydrogen chloride gas has the impurities content of <10 ppm(mol/mol).

[0048] Oxygen gas: manufactured by Ningbo Wanhua Industry Park-Linde Air Separation Plants, industrial products; Purity >99.2%

[0049] The impurities in hydrogen chloride gas are analyzed by gas chromatography. A sample of hydrogen chloride gas is collected by using a gas cylinder, and the gas sample is injected to a gas chromatograph by a sampler. Gas chromatograph: Agilent GC6820; Chromatographic column: Capillary column 19095P-k25 HPAl.sub.2O.sub.3/KCl, specification: 50 m15 m0.53 mm (internal diameter); Injection port temperature: 150 C.; Split ratio: 20:1; Manual FID detector, detector temperature: 250; Carrier gas: Hz; Detector makeup gas: N.sub.2.

[0050] The contents of Chlorine and hydrogen chloride gas are determined as follows.

[0051] (1) The Detection Principle is Based on the Following Reaction Formula:

Cl.sub.2+2KI=2KCl+I.sub.2

I.sub.2+2Na.sub.2S.sub.2O.sub.3=2NaI+Na.sub.2S.sub.4O.sub.6

HCl+NaOH=NaCl+H.sub.2O

[0052] (2) Formulating and Titrating 0.1 Mol/L of Na.sub.2S.sub.2O.sub.3 Solution

[0053] Weigh about 6.2 g of Na.sub.2S.sub.2O.sub.3.5H.sub.2O, dissolve it in an appropriate amount of distilled water (which is just boiled and cooled to remove O.sub.2 and CO.sub.2 solved in water), and thereto add 0.050.1 g Na.sub.2CO.sub.3 (which is used to inhibit microorganism) to formulate 250 ml of a solution. The resulting solution is stored in a brown vial in the dark. After storing 12 week(s), titrate the solution.

[0054] Precisely weigh 0.15 g K.sub.2Cr.sub.2O.sub.7 (baked for 2 hours at 110 C.) into an iodine flask, add 1020 ml water into the flask to dissolve the K.sub.2Cr.sub.2O.sub.7, and add thereto 2 g KI and 10 ml H.sub.2SO.sub.4. Shake it well, allow it to stand for 5 minutes, and then dilute the contents with 50 ml water. Titrate it with the above-described Na.sub.2S.sub.2O.sub.3 solution until the color of the solution changes to light yellowish green, at this moment, add 2 ml starch indicator, further titrate with the Na.sub.2S.sub.2O.sub.3 solution until the color of the solution changes from blue to light green (the titration end presents the very light green of Cr.sup.3+). Perform parallel titrations three times and average the results.

[0055] (3) Analysis and Detection

[0056] The atmosphere of a 250 ml sampling bottle is displaced with the exhaust gas of reaction (i.e., hydrogen chloride exhaust gas) for three minutes (bottom: inlet, top: outlet), to ensure that the air in the sampling bottle is displaced completely. Allow the gas in the sampling bottle react with KI sufficiently to produce 12 solution, and then perform the titration.

[0057] Add 25.00 ml of the I.sub.2 solution into a 250 ml Erlenmeyer flask, dilute it with 50 ml distilled water, and titrate with the formulated Na.sub.2S.sub.2O.sub.3 solution until a light yellow color is produced. Add 2 ml a starch solution, further titrate until blue color just disappears (i.e. the endpoint). Calculate the concentration of 12 solution.

[0058] HCl Titration:

[0059] To the sample subjected to the I.sub.2 titration add 23 drops or more of Phenolphthalein agent dropwise, until the colorless solution change into red color and the red color does not change over 0.5 min. Using Phenolphthalein as an indicator, titrate the unreacted HCl in the catalytic oxidation reaction with a standard solution of NaOH.

[0060] (4) The Calculation Formula of the Conversion Rate (or Referred to as Yield) of Hydrogen Chloride in the Sample

[00001]$\frac{a.Math.b.Math.{10}^{-3}}{a.Math.b.Math.{10}^{-3}+c.Math.d.Math.{10}^{-3}}100.Math.\%$

Wherein:

[0061] a denotes the concentration of the Na.sub.2S.sub.2O.sub.3 solution, mol/L;
b denotes the milliliter number of Na.sub.2S.sub.2O.sub.3 solution consumed by the titration, ml;
c denotes the concentration of the NaOH standard solution, mol/L;
d denotes the milliliter number of NaOH solution consumed by the titration, ml;

EXAMPLES

[0062] The invention is illustrated by the following examples using the gas stream of hydrogen chloride from the process of producing isocyanates, but the present invention is in no way limited by these examples.

Comparative Example 1

[0063] Conduct the catalytic oxidation reaction of hydrogen chloride using the copper-based catalyst, and the catalyst is prepared as described in the example 1 of Chinese patent application No. 201010567038.9.

[0064] Fill 5 kg of the above-described catalyst to a fixed bed reactor, and as hydrogen chloride feed gas of the oxidation reaction, gas streams of hydrogen chloride and of oxygen are introduced respectively at flow rates of 5 m3/hr to the reactor. The reaction is conducted at the temperature of 400 C. and the pressure of 0.2 MPa. The hydrogen chloride used is a purified hydrogen chloride gas from an industrial production, which has impurities content of <10 ppm (mol/mol, based on hydrogen chloride). The oxidation reaction is conducted for 100 hr, and the chlorine yield of 87.2%89.4% is obtained, without any obvious change of the catalyst activity.

[0065] Refill 5 kg of the catalyst to the reactor and conduct the oxidation reaction at the same reaction conditions as above. But, as hydrogen chloride feed gas of the oxidation reaction, use the unpurified crude hydrogen chloride gas obtained after phosgenation, i.e. the industrial crude hydrogen chloride gas produced in the process of preparing MDI (4,4-diphenylmethane diisocyanate) from MDA (4,4-diphenylmethane diamine) by phosgenation, which contains 425 ppm of chlorobenzene (mol/mol, based on hydrogen chloride) and a small amount of other organic compounds containing chlorine and compounds containing sulfur (the total content of these impurities is 0.05% (mol/mol, based on hydrogen chloride)). After about 40 hrs of reaction, the yield of chlorine is notably decreased. After 100 hrs of reaction, the yield of chlorine is reduced from initial 88.1% to 42.7%, and the catalyst is notably deactivated.

Comparative Example 2

[0066] Conduct the catalytic oxidation reaction at the same reaction condition as those of Comparative example 1, except that use the above-mentioned industrial purified hydrogen chloride as the hydrogen chloride feed gas, and introduce 240 ppm of H.sub.2S (mol/mol, based on hydrogen chloride) to the hydrogen chloride feed gas by a mini-type gas flow meter. After about 50 hrs of reaction, the yield of chlorine is notably decreased. After 100 hrs of reaction, the yield of chlorine is reduced from initial 87.0% to 56.4%, and the catalyst is notably deactivated.

Comparative Example 3

[0067] Conduct the catalytic oxidation reaction at the same reaction conditions as those of Comparative example 1, except that use the above-mentioned industrial purified hydrogen chloride as the hydrogen chloride feed gas, and introduce an impurity mixture to the hydrogen chloride feed gas by a micro syringe pump, such that the gas stream of hydrogen chloride contains 2% of ortho-dichlorobenzene and 0.5% of carbon disulfide, and the total content of both amounts to 2.5% (all the above-described impurity contents are the mole percent based on hydrogen chloride). After about 20 hrs of oxidation reaction, the yield of chlorine is notably decreased. After 100 hrs of reaction, the yield of chlorine is reduced from initial 88.1% to 35.2%, and the catalyst is notably deactivated.

Comparative Example 4

[0068] Conduct the catalytic oxidation reaction at the same reaction conditions as those of Comparative example 1, except that use the above-mentioned industrial purified hydrogen chloride as the hydrogen chloride feed gas, and introduce 1% of chlorobenzene, 1% of chloropropylene, and 1.9% of thiophene to the hydrogen chloride feed gas by a micro-metering pump, such that the total content of the above-described impurities amounts to 3.9% (all the above-described impurity contents are the mole percent based on hydrogen chloride). The yield of chlorine is 66.4% in the beginning, and after about 20 hrs of reaction, is reduced to 31.2%. When opening the reactor, find a lot of viscous material present in the reactor. The catalyst is obviously agglomerated.

Example 1

[0069] Conduct the catalytic oxidation reaction using the same catalyst and the same reaction conditions as those of Comparative example 1, wherein the hydrogen chloride feed gas used is the unpurified crude hydrogen chloride gas obtained after phosgenation, i.e. the industrial crude hydrogen chloride produced in the process of preparing MDI (4,4-diphenylmethane diisocyanate) from MDA (4,4-diphenylmethane diamine) by phosgenation, which is determined to contain 425 ppm of chlorobenzene (mol/mol, based on hydrogen chloride) and a small amount of other organic compounds containing chlorine and compounds containing sulfur (the total content of these impurities is 0.05% (mol/mol, based on hydrogen chloride)). Before the hydrogen chloride gas enters into the reactor, introduce ozone at the rate of 10 L/hr of ozone (based on gaseous ozone) into the gas stream of hydrogen chloride by a jet disperser, the jet disperser comprises a jet (nozzle) section and a disperser section, wherein the disperser section is tubular in shape, and has an internal diameter of 40 mm and a length of 540 mm. Furthermore, apply (or emit) ultrasound wave around the disperser via water medium by using an ultrasonic device, wherein the ultrasonic power is set to 120 W, and the ultrasonic frequency is set to 25 kHz. The catalytic oxidation reaction is conducted continuously for 100 hr, and the chlorine yield of 86.7%88.2% is obtained, without any obvious change of the catalyst activity. After 200 hrs of oxidation reaction, the liquid oxidized impurities that deposited in the above-mentioned screen separator are discharged from the bottom of the screen separator.

Example 2

[0070] Conduct the catalytic oxidation reaction using the same catalyst and the same reaction conditions as those of Comparative example 1, wherein the hydrogen chloride feed gas used is the unpurified crude hydrogen chloride gas obtained after phosgenation, i.e. the industrial crude hydrogen chloride produced in the process of preparing MDI (4,4-diphenylmethane diisocyanate) from MDA (4,4-diphenylmethane diamine) by phosgenation, which is determined to contain 425 ppm of chlorobenzene (mol/mol, based on hydrogen chloride) and a small amount of other organic compounds containing chlorine and compounds containing sulfur (the total content of these impurities is 0.05% (mol/mol, based on hydrogen chloride)). Before the hydrogen chloride gas enters into the reactor, inject a hydrogen peroxide solution into the gas stream of hydrogen chloride by a micro-metering pump, and mix them in a pipe-line disperser having an internal diameter of 35 mm and a length of 700 mm, wherein the hydrogen peroxide solution is introduced at the rate of 15 g/hr based on hydrogen peroxide. Furthermore, apply (or emit) ultrasound wave around the disperser via water medium by using an ultrasonic device, wherein the ultrasonic power is set to 120 W, and the ultrasonic frequency is set to 75 kHz. The catalytic oxidation reaction is conducted continuously for 100 hr, and the chlorine yield of 87.7%89.0% is obtained, without any obvious change of the catalyst activity. After 200 hrs of oxidation reaction, the liquid oxidized impurities are discharged from the bottom of the screen separator.

Example 3

[0071] Conduct the catalytic oxidation reaction using the same catalyst and the same reaction conditions as those of Comparative example 2, wherein the hydrogen chloride feed gas used is the industrial purified hydrogen chloride as above, and 240 ppm of H.sub.2S (mol/mol, based on hydrogen chloride) is introduced to the hydrogen chloride by a mini-type gas flow meter. Before hydrogen chloride gas enters into the reactor, inject a hydrogen peroxide solution into the gas stream of hydrogen chloride in the same way as that of Example 2, and the pretreatment conditions and the conditions of subsequent catalytic oxidation reaction are also the same as that of Example 2. The oxidation reaction is conducted continuously for 100 hr, and the chlorine yield of 86.9%88.1% is obtained, without any obvious change of the catalyst activity. After 200 hrs of catalytic oxidation reaction, the solid particles of the oxidized impurities are discharged from the bottom of the cyclone separator. The present example shows that a H.sub.2S impurity can be removed.

Example 4

[0072] Conduct the catalytic oxidation reaction using the same catalyst and the same reaction conditions as those of Comparative example 3, wherein the hydrogen chloride feed gas used is the industrial purified hydrogen chloride as above, and an impurity mixture is introduced to the hydrogen chloride feed gas by a micro syringe pump, such that the gas stream of hydrogen chloride contains 2% of ortho-dichlorobenzene and 0.5% of carbon disulfide, and the total content of both amounts to 2.5% (the content of each impurity is the mole percent based on hydrogen chloride). Before hydrogen chloride gas enters into the reactor, introduce ozone into the gas stream of hydrogen chloride in the same way as that of Example 1 at the ozone flow rate of 250 L/hr. Furthermore, apply (or emit) ultrasound wave around the disperser via water medium by using an ultrasonic device, wherein the ultrasonic power is set to 2 KW, and the ultrasonic frequency is set to 100 kHz. The oxidation reaction is conducted continuously for 100 hr, and the chlorine yield of 87.4%88.5% is obtained, without any obvious change of the catalyst activity. After 200 hrs of reaction, the liquid and solid oxidized impurities are discharged from the bottom of the cyclone separator.

Example 5

[0073] Conduct the catalytic oxidation reaction using the same catalyst and the same reaction conditions as those of Comparative example 4, wherein the hydrogen chloride feed gas used is the industrial purified hydrogen chloride as above, and 1% of chlorobenzene, 1% of chloropropylene, and 1.9% of thiophene is introduced to the gas stream of hydrogen chloride by a micro-metering pump, such that the total content of the above-described impurities amounts to 3.9% (the content of each impurity is the mole percent based on hydrogen chloride). Before hydrogen chloride gas enters into the reactor, inject a hypochlorous acid solution into the gas stream of hydrogen chloride by a micro-metering pump, wherein additionally the hypochlorous acid solution is obtained by dissolving chlorine gas in water, and based on hypochlorous acid, the introduction rate of the hypochlorous acid solution is 1.1 kg/hr. Furthermore, apply (or emit) ultrasound wave around the disperser via water medium by using an ultrasonic device, wherein the ultrasonic power is set to 5 KW, and the ultrasonic frequency is set to 120 kHz. The oxidation reaction is conducted continuously for 100 hr, and the chlorine yield of 85.4%86.1% is obtained, without any obvious change of the catalyst activity. After 200 hrs of reaction, the liquid and solid oxidized impurities are discharged from the bottom of the cyclone separator. When opening the reactor, the reactor is found to be relatively clean, the catalyst used therein is still in the same form of dispersed particles as that of new catalyst, with a very small amount of coking in the reactor.

[0074] As seen from the above-described Examples and Comparative Examples, by employing the pretreatment method of hydrogen chloride feed gas of the present invention, the impurities can be removed from hydrogen chloride effectively, and the stability of the catalyst can be maintained. The process of the present invention can be used continuously and used conveniently for a large-scale industrial production of chlorine from hydrogen chloride gas.