A method for separating and recovering hydrogen chloride from tail gas in chlorocyanobenzene production

Abstract

A method for separating and recovering hydrogen chloride in tail gas from chlorocyanobenzene production comprises the following steps: S1, the tail gas is passed into a condenser for condensation, and chlorocyanobenzene-containing particles are separated to obtain tail gas I; S2, the tail gas I is heated and passed into a spray absorption tower, chlorine is absorbed in an absorbent, and a chlorine-containing absorbent and tail gas II are obtained; S3, the tail gas II is passed into a chlorine absorption tower, and the remaining chlorine is adsorbed by modified activated carbon loaded with iron metal oxide in the chlorine absorption tower, and nitrogen and hydrogen chloride mixed gas is extracted from the top of the tower; S4, the nitrogen and hydrogen chloride mixed gas is passed into a gas separation membrane separator, and hydrogen chloride passes through the gas separation membrane, thereby obtaining high-purity hydrogen chloride gas, and the recovery rate of hydrogen chloride gas is high; efficient recovery of chlorine and nitrogen is also achieved, and waste gas is thoroughly treated, resource recovery can be achieved, and resource waste is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of tail gas separation and recovery, and in particular to a method for separating and recovering hydrogen chloride in tail gas produced by chlorocyanobenzene. Background Art

[0002] At present, the industrial production method of chlorocyanobenzene compounds (tetrachloroterephthalonitrile, tetrachlorophthalonitrile, tetrachloroisophthalonitrile and pentachlorobenzonitrile) is mainly a high-temperature gas phase method, which uses terephthalonitrile, phthalonitrile, isophthalonitrile and benzonitrile as raw materials, and gasifies them by heating. The gasified raw materials are taken out of the gasifier by nitrogen and react with chlorine in the presence of a catalyst in a high-temperature gas phase. The obtained reaction gas is cooled and condensed to finally obtain the chlorocyanobenzene product. There is a large amount of hydrogen chloride in the tail gas of chlorocyanobenzene production. Hydrogen chloride is an extremely important chemical raw material and has a wide range of applications in many fields. For example, high-purity hydrogen chloride gas can be used for silicon before epitaxial growth, carbon fiber surface treatment, film production, etc. Hydrogen chloride can be used to prepare hydrochloric acid and is widely used in the pharmaceutical, fuel and food industries. Therefore, the separation and recovery of hydrogen chloride in the tail gas of chlorocyanobenzene production has important practical significance.

[0003] The traditional method mainly adopts the iron filings water chlorination method, that is, the iron filings are soaked in the water chlorination tower, and the tail gas is absorbed by the water chlorination tower to remove hydrogen chloride and chlorine. This method consumes a large amount of iron filings and has high investment costs. At present, the conventional method mostly adopts the "water-alkali segmented absorption method", that is, the tail gas passes through the falling film absorption tower, the hydrogen chloride is basically absorbed by water, and low-content hydrochloric acid is produced, and then the remaining chlorine and hydrogen chloride are absorbed by lime water. This method has low investment costs, but the tail gas contains not only hydrogen chloride generated by the reaction, but also unreacted chlorine, nitrogen, etc., which will affect the separation and recovery of hydrogen chloride.

[0004] Therefore, it is necessary to improve the existing method for separating and recovering hydrogen chloride in the tail gas of chlorocyanobenzene production. Summary of the invention

[0005] In view of the above situation, in order to overcome the defects of the prior art, the embodiment of the present invention provides a method for separating and recovering hydrogen chloride in the tail gas of chlorocyanobenzene production, which at least solves some of the problems in the prior art.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0007] A method for separating and recovering hydrogen chloride in tail gas from chlorocyanobenzene production comprises the following steps:

[0008] S1, the tail gas is passed into a condenser for condensation, and the particles containing chlorocyanobenzene are separated to obtain tail gas I;

[0009] S2, the tail gas I is heated and then passed into a spray absorption tower, where the chlorine is absorbed in the absorbent to obtain a chlorine-containing absorbent and tail gas II;

[0010] S3, tail gas II is passed into the chlorine absorption tower, the remaining chlorine is adsorbed by the modified activated carbon in the chlorine absorption tower, and the nitrogen and hydrogen chloride mixed gas is extracted from the top of the tower;

[0011] S4. The nitrogen and hydrogen chloride mixed gas is introduced into the gas separation membrane separator, and the hydrogen chloride passes through the gas separation membrane and is recycled.

[0012] In a further embodiment, in step S1, the tail gas contains nitrogen, chlorine, hydrogen chloride and hexachlorobenzene.

[0013] In a further embodiment, in step S1, the temperature of the condenser is -20 to -30° C. The tail gas passes through the condenser, and the hexachlorobenzene therein is condensed into liquid for recovery.

[0014] In a further embodiment, in step S2, the heating temperature is 70-80°C.

[0015] In a further embodiment, in step S2, the absorbent in the spray absorption tower is any one of trichloroethylene, n-hexane, butyltoluene, amyl acetate, and butanol.

[0016] In a further embodiment, in step S2, the temperature of the absorbent in the spray absorption tower is 20-30°C.

[0017] In a further embodiment, step S2 further includes: desorbing the chlorine-containing absorbent to obtain high-purity chlorine gas; the desorption temperature is 50 to 80°C.

[0018] In a further embodiment, in step S3, the chlorine absorption tower is filled with modified activated carbon, and the modified activated carbon is modified activated carbon loaded with iron metal oxides.

[0019] In a further preferred embodiment, in step S3, the loading amount of iron metal oxide in the modified activated carbon is 6.2-8.5%.

[0020] In a further embodiment, the modified activated carbon is prepared by the following method:

[0021] (1) Activate activated carbon at high temperature;

[0022] (2) The activated activated carbon is immersed in a metal salt solution and subjected to microwave treatment so that the metal salt forms metal oxides on the surface and in the pores of the activated carbon. After drying, the modified activated carbon is obtained.

[0023] In a further preferred embodiment, during the preparation of modified activated carbon, the temperature of the high temperature activation is 850 to 1000° C., and the time of the high temperature activation is 16 to 24 hours.

[0024] In a further preferred embodiment, during the preparation of modified activated carbon, the power of the microwave treatment is 200 to 300 W, and the time of the microwave treatment is 5 to 8 h.

[0025] In a further preferred embodiment, during the preparation of modified activated carbon, the metal salt solution is ferrous nitrate and / or ferric sulfate with a mass fraction of 5 to 10%.

[0026] In a further embodiment, the step S3 further comprises the following steps: desorbing the chlorine adsorbed by the modified activated carbon and recycling it; the desorption temperature is 140-175°C.

[0027] In a further scheme, in step S4, the gas separation membrane in the gas separation membrane separator is a polyimide / cellulose acetate composite membrane. In order to further improve the separation effect of nitrogen and hydrogen chloride, a composite membrane prepared by mixing polyimide and cellulose acetate in a mass ratio of 100:4.5-6 is selected. It is found that in actual production, not only the separation effect of hydrogen chloride and nitrogen can be improved, but also the polyimide / cellulose acetate composite membrane has good regeneration and long service life.

[0028] After the tail gas is treated by the first adsorption tower, the remaining tail gas components are a mixed gas of hydrogen chloride and nitrogen. The tail gas enters the gas separation membrane separator, where the hydrogen chloride gas passes through the gas separation membrane, while the nitrogen remains on the non-permeated side, thereby completely separating the hydrogen chloride from the nitrogen.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] The invention provides a method for separating and recovering hydrogen chloride in tail gas produced by chlorocyanobenzene. The method comprises the following steps: firstly, hexachlorobenzene in the tail gas is removed by condensation, and then chlorine in the tail gas is separated and recovered by a spray absorption tower and a chlorine absorption tower, and then nitrogen and hydrogen chloride are separated by a gas separation membrane, so as to obtain high-purity hydrogen chloride gas with a high recovery rate of hydrogen chloride gas. In addition, the method realizes efficient recovery of chlorine and nitrogen, and thoroughly treats waste gas, so as to realize resource recovery and reduce waste of resources. DETAILED DESCRIPTION

[0031] The following non-limiting examples can enable those skilled in the art to more fully understand the present invention, but do not limit the present invention in any way. The following content is only an exemplary description of the scope of the present invention, and those skilled in the art can make various changes and modifications to the invention of the present invention based on the disclosed content, and they should also fall within the scope of the present invention.

[0032] There are a lot of hydrogen chloride, chlorine, etc. in the tail gas of chlorocyanobenzene production. Hydrogen chloride is an extremely important chemical raw material. Therefore, the separation and recovery of hydrogen chloride in the tail gas of chlorocyanobenzene production has important practical significance. The traditional method mainly adopts the iron filings water chlorination method, which consumes a lot of iron filings and has high investment cost. At present, the "water-alkali segmented absorption method" is mostly used, but the tail gas contains not only hydrogen chloride generated by the reaction, but also unreacted chlorine, nitrogen, etc., which will affect the separation and recovery of hydrogen chloride; at the same time, there are by-products such as hexachlorobenzene in the tail gas, which are harmful. Therefore, the purity of the product separated and recovered by this method is limited, the recovery rate is low, and the harmful impurities are high.

[0033] The embodiment of the present invention first removes hexachlorobenzene in the tail gas by condensation, then separates and recovers chlorine in the tail gas by a spray absorption tower and a chlorine absorption tower, and then separates nitrogen and hydrogen chloride by a gas separation membrane, thereby obtaining high-purity hydrogen chloride gas with a high recovery rate of hydrogen chloride gas; in addition, efficient recovery of chlorine and nitrogen is achieved, the waste gas is thoroughly treated, resource recovery can be achieved, and waste of resources is reduced.

[0034] In order to solve the above problems, the present invention provides a method for separating and recovering hydrogen chloride in tail gas from chlorocyanobenzene production, comprising the following steps:

[0035] S1, the tail gas is passed into a condenser for condensation, and the particles containing chlorocyanobenzene are separated to obtain tail gas I;

[0036] S2, the tail gas I is heated by the heater and then passed into the spray absorption tower, and the chlorine is absorbed in the absorbent to obtain the chlorine-containing absorbent and tail gas II;

[0037] S3, tail gas II is passed into the chlorine absorption tower, the remaining chlorine is adsorbed by the modified activated carbon in the chlorine absorption tower, and the nitrogen and hydrogen chloride mixed gas is extracted from the top of the tower;

[0038] S4. The nitrogen and hydrogen chloride mixed gas is passed into the gas separation membrane separator, and the hydrogen chloride passes through the gas separation membrane into the hydrogen chloride recovery tank for recycling.

[0039] In a further embodiment, in step S1, the tail gas is a mixed gas comprising nitrogen, chlorine, hydrogen chloride, and hexachlorobenzene.

[0040] In a further embodiment, in step S1, the temperature of the condenser is -20 to -30° C. The tail gas passes through the condenser, and the hexachlorobenzene therein is condensed into liquid for recovery.

[0041] In a further embodiment, in step S2, the heating temperature is 70-80°C.

[0042] In a further embodiment, in step S2, the absorbent in the spray absorption tower is any one of trichloroethylene, n-hexane, butylated toluene, amyl acetate, and butanol.

[0043] In a further embodiment, in step S2, the temperature of the absorbent in the spray absorption tower is 20-30°C.

[0044] The tail gas from which hexachlorobenzene is removed, i.e., tail gas I, is introduced into a spray absorption tower from the top of the tower. The chlorine contained in the tail gas is removed by the redox reaction between ferrous chloride and chlorine in the absorbent without consuming hydrogen chloride and nitrogen. Most of the chlorine in the tail gas is absorbed by the absorbent, and the remaining tail gas is discharged from the bottom of the tower and enters the first packed tower for treatment.

[0045] In a further embodiment, in step S2, the chlorine-containing absorbent enters a distillation tower for desorption to obtain purified chlorine; the desorption temperature is 50-80°C.

[0046] In a further embodiment, in step S3, the chlorine absorption tower is filled with modified activated carbon, and the modified activated carbon is activated carbon loaded with iron metal oxides.

[0047] In a further embodiment, in step S3, the loading amount of iron metal oxide in the modified activated carbon is 6.2-8.5%.

[0048] In a further embodiment, the modified activated carbon is prepared by the following method:

[0049] (1) Activate activated carbon at high temperature;

[0050] (2) The activated activated carbon is immersed in a metal salt solution and subjected to microwave treatment so that the metal salt forms metal oxides on the surface and in the pores of the activated carbon. After drying, the modified activated carbon is obtained.

[0051] In a further embodiment, during the preparation of modified activated carbon, the temperature of the high temperature activation is 850-1000° C., and the time of the high temperature activation is 16-24 hours.

[0052] In a further embodiment, during the preparation of modified activated carbon, the microwave treatment condition is 200-300W, and the microwave treatment time is 3-5h.

[0053] In a further embodiment, during the preparation of modified activated carbon, the metal salt solution is ferrous nitrate and / or ferric sulfate with a mass fraction of 5 to 10%.

[0054] In a further embodiment, in step S3, after the tail gas is adsorbed by the modified activated carbon, the chlorine adsorbed by the modified activated carbon is sucked out by a vacuum pump, and the chlorine obtained by desorption in the distillation tower is sent to a chlorine recovery tank for recycling.

[0055] The tail gas discharged from the spray absorption tower mainly contains hydrogen chloride and nitrogen, and also contains a small amount of chlorine. The tail gas enters the first absorption tower, and the remaining chlorine in the tail gas is adsorbed by the special activated carbon in the chlorine absorption. Compared with conventional activated carbon, the present invention uses modified activated carbon to adsorb chlorine, and the activated carbon treated with microwaves and loaded with a small amount of iron metal oxides increases the adsorption of chlorine by the activated carbon, improves the adsorption efficiency, and can reduce the adsorption of hydrogen chloride, reduce the loss of hydrogen chloride, improve the recovery rate of hydrogen chloride, and recover the purity of chlorine as a whole. Through the spray tower and the chlorine absorption tower, the chlorine in the tail gas can be efficiently recovered, the recovery rate is more than 99%, and the recovery purity is high.

[0056] In a further embodiment, in step S4, the gas separation membrane in the gas separation membrane separator is a polyimide / cellulose acetate composite membrane. In order to further improve the separation effect of nitrogen and hydrogen chloride, a composite membrane prepared by mixing polyimide and cellulose acetate in a mass ratio of 100:4.5-6 is selected. It is found that in actual production, not only the separation effect of hydrogen chloride and nitrogen can be improved, but also the polyimide / cellulose acetate composite membrane has good regeneration and long service life.

[0057] After the tail gas is treated by the chlorine absorption tower, the remaining tail gas components are a mixture of hydrogen chloride and nitrogen. The tail gas enters the gas separation membrane separator, where the hydrogen chloride gas passes through the gas separation membrane, while the nitrogen remains on the non-permeated side, thereby completely separating the hydrogen chloride from the nitrogen.

[0058] The present invention is further described below by way of specific examples. Unless otherwise specified, the various chemical reagents used in the examples of the present invention are obtained through conventional commercial channels.

[0059] Embodiment 1: A method for separating and recovering hydrogen chloride in tail gas from chlorocyanobenzene production, comprising the following steps:

[0060] S1. The tail gas is passed into a condenser for condensation at a temperature of -20°C, and the particles containing chlorocyanobenzene are separated to obtain tail gas I.

[0061] S2. The tail gas I is heated to 70°C by a heater and then passed into a spray absorption tower, where the chlorine is absorbed in the absorbent to obtain tail gas II; the absorbent is n-hexane, and the absorbent temperature is 20°C; the saturated absorbent is desorbed at 50°C to obtain purified chlorine.

[0062] S3, tail gas II is introduced into the chlorine absorption tower, the remaining chlorine is adsorbed by the modified activated carbon in the chlorine absorption tower, and the nitrogen and hydrogen chloride mixed gas is extracted from the top of the tower; the chlorine adsorbed by the modified activated carbon is desorbed at 140°C and then recycled.

[0063] The modified activated carbon adsorption was prepared by the following method:

[0064] (1) High temperature activation of activated carbon at 850 °C for 24 h;

[0065] (2) The activated carbon was immersed in a 5% by mass ferric nitrate solution and subjected to microwave treatment at 100 W for 5 h to allow the metal salt to form metal oxides on the surface and in the pores of the activated carbon. After drying, the modified activated carbon (metal oxide loading 6.28%) was obtained.

[0066] S4, nitrogen and hydrogen chloride mixed gas is passed into the gas separation membrane separator, the gas separation membrane is a polyimide / cellulose acetate composite membrane (the mass ratio of polyimide and cellulose acetate is 100:4.5), and hydrogen chloride passes through the gas separation membrane into the hydrogen chloride recovery tank for recycling.

[0067] Embodiment 2: A method for separating and recovering hydrogen chloride in tail gas from chlorocyanobenzene production, comprising the following steps:

[0068] S1. The tail gas is passed into a condenser for condensation at a temperature of -30°C, and the particles containing chlorocyanobenzene are separated to obtain tail gas I.

[0069] S2. The tail gas I is heated to 80°C by a heater and then passed into a spray absorption tower, where the chlorine is absorbed in the absorbent to obtain tail gas II; the absorbent is amyl acetate, and the absorbent temperature is 30°C; the saturated absorbent is desorbed at 80°C to obtain purified chlorine.

[0070] S3, tail gas II is introduced into the chlorine absorption tower, the remaining chlorine is adsorbed by the modified activated carbon in the chlorine absorption tower, and the nitrogen and hydrogen chloride mixed gas is extracted from the top of the tower; the chlorine adsorbed by the modified activated carbon is desorbed at 175°C and then recycled.

[0071] The modified activated carbon adsorption was prepared by the following method:

[0072] (1) Activating the activated carbon at 1000°C for 16 h;

[0073] (2) The activated carbon was immersed in a 10% by mass ferric nitrate solution and subjected to microwave treatment at 100 W for 5 h to allow the metal salt to form metal oxides on the surface and in the pores of the activated carbon. After drying, the modified activated carbon (metal oxide loading 8.41%) was obtained.

[0074] S4, nitrogen and hydrogen chloride mixed gas is passed into the gas separation membrane separator, the gas separation membrane is a polyimide / cellulose acetate composite membrane (the mass ratio of polyimide and cellulose acetate is 100:6), and hydrogen chloride passes through the gas separation membrane into the hydrogen chloride recovery tank for recycling.

[0075] Example 3: The difference from Example 2 is that in step S3 of this example, the metal oxide loading in the modified activated carbon is 8.83%.

[0076] Example 4: The difference from Example 2 is that in step S3 of this example, the metal oxide loading in the modified activated carbon is 6.07%.

[0077] Example 5: The difference from Example 2 is that in step S3 of this example, microwave treatment is not performed on the modified activated carbon.

[0078] Example 6: The difference from Example 2 is that in step S3 of this example, the metal solution in the process of preparing modified activated carbon is copper nitrate.

[0079] Example 7: The difference from Example 2 is that in step S3 of this example, the modified activated carbon is replaced by unmodified activated carbon.

[0080] Example 8: The difference from Example 2 is that in step S4 of this example, the mass ratio of polyimide to cellulose acetate in the gas separation membrane is 100:3.5.

[0081] Example 9: The difference from Example 2 is that in step S4 of this example, the mass ratio of polyimide to cellulose acetate in the gas separation membrane is 100:7.

[0082] Embodiment 10: The difference from Embodiment 2 is that in step S4 of this embodiment, the gas separation membrane is a polyimide separation membrane.

[0083] Example 11: The difference from Example 2 is that in step S4 of this example, the gas separation membrane is a cellulose acetate separation membrane.

[0084] Example 12: The difference from Example 2 is that there is no step 3 in this example, that is, the tail gas II is directly introduced into the gas separation membrane separator for separation.

[0085] Example 13: The difference from Example 2 is that in step S3 of this example, the adsorbent in the chlorine absorption tower is 4A molecular sieve.

[0086] The contents of various components in the tail gas produced by chlorocyanobenzene are: 27.18% hydrogen chloride, 12.25% chlorine, and 42.36% nitrogen. The separation and recovery methods provided in the above embodiments and comparative examples are used for treatment, and the results are shown in Table 1 below.

[0087] Table 1

[0088]

[0089] As shown in the table, the concentration of hydrogen chloride in the tail gas treated by the separation and recovery method of hydrogen chloride in the tail gas of chlorocyanobenzene production provided by the present invention is reduced to below 0.01ppm, which meets the emission standards; the recovery rate of hydrogen chloride is more than 99.5%, and the purity of the recovered hydrogen chloride is more than 99.9%. In addition, the separation and recovery method provided by the present invention can also achieve efficient recovery of chlorine and nitrogen, with a recovery rate of more than 99%, reducing the waste of resources.

[0090] The adsorption performance of modified activated carbon for chlorine was tested using a PCT chlorine-specific adsorption device. The sample was placed in the adsorption tube of the test tube and filled with nitrogen to a certain pressure for chlorine adsorption. When the adsorption reached saturation, the pressure gauge reading no longer changed, and the data was recorded. Then the chlorine pressure was reduced and left for a period of time until the pressure gauge reading no longer changed. The amount of chlorine released was titrated to obtain the adsorption capacity; the modified activated carbon adsorbed saturated chlorine was placed in a muffle furnace for heating and desorption, and then retested. The measured results are shown in Table 2 below.

[0091] Table 2

[0092]

[0093] As shown in the table, compared with the unmodified activated carbon, the modified activated carbon has a significantly improved adsorption capacity for chlorine at 30°C and a pressure of 0.28 MPa, and the adsorption capacity of chlorine can still be maintained at more than 33% after repeated adsorption and desorption for 5 times, and the adsorption capacity has not decreased significantly, which means that the modified activated carbon provided by the present invention has good adsorption stability, multiple adsorption and desorption will not destroy its structure, good regeneration performance, and long service life.

[0094] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A method for separating and recovering hydrogen chloride from tail gas produced by chlorocyanobenzene, characterized in that: The following steps are involved: S1, the tail gas is passed into a condenser for condensation, and the particles containing chlorocyanobenzene are separated to obtain tail gas I; S2, the tail gas I is heated and then passed into a spray absorption tower, where the chlorine is absorbed in the absorbent to obtain a chlorine-containing absorbent and tail gas II; S3, tail gas II is introduced into a chlorine absorption tower, and the remaining chlorine is adsorbed by the modified activated carbon loaded with iron metal oxide in the chlorine absorption tower, and a mixed gas of nitrogen and hydrogen chloride is extracted from the top of the tower; S4, the nitrogen and hydrogen chloride mixed gas is passed into the gas separation membrane separator, and the hydrogen chloride passes through the gas separation membrane and is recycled; The modified activated carbon is prepared by the following method: (1) Activate activated carbon at high temperature; (2) immersing the activated activated carbon in a metal salt solution and subjecting it to microwave treatment to form metal oxides on the surface and in the pores of the activated carbon, and then drying to obtain the modified activated carbon; The power of the microwave treatment is 200-300W, and the time of the microwave treatment is 5-8h; The metal salt solution is ferrous nitrate and / or ferric sulfate with a mass fraction of 5 to 10%; The gas separation membrane in the gas separation membrane separator is a polyimide / cellulose acetate composite membrane; The mixing mass ratio of polyimide to cellulose acetate is 100:4.5-6.

2. The method for separating and recovering hydrogen chloride in tail gas from chlorocyanobenzene production according to claim 1, characterized in that: In step S1, the temperature of the condenser is -20 to -30°C.

3. The method for separating and recovering hydrogen chloride in tail gas from chlorocyanobenzene production according to claim 1, characterized in that: In step S2, the absorbent in the spray absorption tower is any one of trichloroethylene, n-hexane, butyltoluene, and amyl acetate.

4. The method for separating and recovering hydrogen chloride in tail gas from chlorocyanobenzene production according to claim 1, characterized in that: Step S2 also includes: desorbing the chlorine-containing absorbent to obtain high-purity chlorine gas.

5. The method for separating and recovering hydrogen chloride in tail gas from chlorocyanobenzene production according to claim 1, characterized in that: In step S3, the loading amount of iron metal oxide in the modified activated carbon is 6.2-8.5%.

6. The method for separating and recovering hydrogen chloride in tail gas from chlorocyanobenzene production according to claim 1, characterized in that: Step S3 also includes the following steps: recovering the chlorine adsorbed by the modified activated carbon after desorption.

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