A continuous treatment method for TDI waste brine

Abstract

The present invention discloses a method for continuous treatment of TDI waste brine, which belongs to the technical field of wastewater treatment. The method of the present invention comprises the following steps: adjusting the pH value of the TDI waste brine to acidic, then subjecting the acidic waste brine to a peroxidation adsorption column and simultaneously subjecting it to ultraviolet irradiation to perform photocatalytic oxidation and adsorption reaction; after the reaction is completed, adjusting the pH value of the acidic waste brine to alkaline, then passing the alkaline waste brine through a stripping tower to remove small molecule organic matter, and obtaining waste brine after continuous treatment. The continuous treatment method of the present invention can completely remove organic matter from the TDI waste brine, and the treated waste brine has a TOC of less than 10 ppm and a TN of less than 3 ppm, and can be used as a raw material for the chlor-alkali ion membrane preparation process of caustic soda, so that the sodium chloride and water in the waste brine are recycled, achieving zero discharge of the waste brine and solving the problem of environmental pollution. In addition, the treatment method of the present invention is simple, easy to operate, and cost-effective.

Description

Technical Field

[0001] The invention belongs to the technical field of wastewater treatment, and in particular relates to a method for continuously treating TDI waste brine. Background Art

[0002] Toluene diisocyanate (TDI) is a polyisocyanate, a key building block for polyurethane (PU) materials. TDI is primarily used in the production of flexible polyurethane foam, polyurethane elastomers, coatings, and adhesives, and has significant applications in the chemical industry.

[0003] Currently, industrial TDI production primarily utilizes the phosgene process. During the phosgene production process, excess phosgene is destroyed by alkali, resulting in a large amount of alkaline waste brine. This waste brine contains approximately 6-8% sodium chloride, 6-8% sodium carbonate, and around 1% sodium hydroxide, along with small amounts of organic impurities such as ethyl chloride, toluene, and DEIP. The presence of these organic impurities causes the waste brine to exceed standards for total organic carbon (TOC) and total nitrogen (TN), failing to meet the requirements of the ion-exchange membrane caustic soda production process. Consequently, the waste brine must meet these standards and be discharged, resulting in significant waste of water and salt. Therefore, it is necessary to treat the TDI waste brine to meet the raw material requirements for chlor-alkali ion-exchange membrane caustic soda production, thereby enabling the regeneration and recycling of sodium chloride and water resources.

[0004] Patents CN 1030584247 B and CN 109293089 A describe a method for treating TDI wastewater using sodium hypochlorite as an oxidant in conjunction with activated carbon adsorption. However, since sodium hypochlorite cannot completely degrade organic matter into inorganic matter, the treated TOC content can reach as high as 30 ppm, failing to meet the electrolysis requirements of the ion-exchange membrane caustic soda production process and requiring significant sodium hypochlorite consumption. Patent CN 115925205 A discloses a biochemical method for treating TDI wastewater. However, this method is complex, with slow functional bacterial growth and reaction rates, making it difficult to reuse the treated water and achieving continuous production. Patent CN 112479460 A discloses a method for pre-treating TDI wastewater using chemical waste. This method utilizes a soluble catalyst and hydrogen peroxide, reacting at 130-180°C and 0.2-2 MPa. The reaction conditions are harsh and energy costs are high. Therefore, it is of practical significance to seek a continuous treatment method with simple process, convenient operation and low industrial investment cost. Summary of the Invention

[0005] The present invention provides a method for continuously treating TDI waste brine, comprising the following steps:

[0006] The pH value of the TDI waste brine is adjusted to acidic, and then the acidic waste brine is passed through an oxidation adsorption column and irradiated with ultraviolet light to perform photocatalytic oxidation and adsorption reactions. After the reaction is completed, the pH value of the acidic waste brine is adjusted to alkaline, and then the alkaline waste brine is passed through a stripping tower to remove small molecular organic matter to obtain waste brine after continuous treatment.

[0007] The waste brine obtained through the above continuous treatment meets the requirements of the ion membrane caustic soda process and can be mixed with the primary brine of the ion membrane caustic soda process and then subjected to secondary refinement using a chelating resin for subsequent application.

[0008] In the above-mentioned continuous treatment method, the TDI waste brine is waste brine generated during the TDI production process and contains organic impurities such as ethyl chloride, toluene, DEIP, and sodium carbonate. Typically, the waste brine contains approximately 0.1-2% ethyl chloride, approximately 100-500 ppm toluene, and approximately 50-100 ppm DEIP.

[0009] In the above continuous treatment method, the acidic pH value is selected from 1 to 7, preferably 2 to 4. The pH value of the waste brine can be adjusted with hydrochloric acid.

[0010] In the above continuous treatment method, the filler of the oxidation adsorption column is hydrotalcite loaded with zinc oxide. The jacket of the oxidation adsorption column is equipped with an ultraviolet lamp. The oxidation adsorption column can be a jacketed annular column, and its material can be selected from quartz.

[0011] In the above continuous treatment method, the irradiation power of the ultraviolet lamp is selected from 500~700W.

[0012] In the above continuous treatment method, the flow rate of the acidic waste brine in the oxidation adsorption column is selected from 1 / 3 to 1 BV / h; preferably from 1 / 3 to 1 / 2 BV / h.

[0013] In the above continuous treatment method, the alkaline pH value is selected from 7 to 14. Sodium hydroxide can be used to adjust the pH value of the waste brine.

[0014] In the above continuous treatment method, the temperature of the stripping tower kettle is selected from 85~100℃.

[0015] The present invention provides TDI waste brine treated by the above method.

[0016] The present invention provides the use of the treated TDI waste brine in an ion membrane caustic soda process.

[0017] The beneficial effects of the present invention are:

[0018] In the present invention, the oxidation adsorption column can perform photocatalytic oxidation degradation and macromolecular adsorption on acidic waste brine; using zinc oxide as a catalyst, under the irradiation of ultraviolet light, most macromolecular organic substances such as toluene and DEIP are degraded into small molecular organic substances through photocatalytic oxidation, and the remaining trace macromolecular organic substances are adsorbed and removed by hydrotalcite.

[0019] The continuous treatment method of the present invention can completely remove organic matter from TDI waste brine. The treated waste brine has a TOC of less than 10 ppm and a TN of less than 3 ppm. This waste brine can be used as raw material in a chlor-alkali ion membrane process to produce caustic soda, allowing the sodium chloride and water in the waste brine to be recycled, achieving zero waste brine discharge and addressing environmental pollution issues. Furthermore, the adsorption column of the present invention can simultaneously achieve oxidative degradation and adsorption of macromolecules, resulting in a simple treatment method, easy operation, and low industrial investment costs, thus saving costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is the process flow chart for the continuous treatment of TDI waste brine. DETAILED DESCRIPTION

[0021] In the present invention, the TDI waste brine is derived from waste brine produced by the production of TDI by Gansu Juyin Chemical Co., Ltd. Sampling and analysis of the TDI waste brine revealed a 0.3% ethyl chloride content, a 133 ppm toluene content, a 52 ppm DEIP content, a 6.7% sodium chloride content, a 6.1% sodium carbonate content, and a 0.8% sodium hydroxide content, with a pH of 14.

[0022] In the following embodiments, the continuous treatment method of TDI waste brine is as follows: Figure 1 shown.

[0023] The other materials used in the present invention, unless otherwise stated, can be obtained through commercial channels. Unless otherwise specified, other terms used in the present invention generally have the meanings commonly understood by those of ordinary skill in the art. The present invention will be further described in detail below with reference to specific examples and data. The following examples are merely for illustration of the present invention and are not intended to limit the scope of the present invention in any way. Example

[0024] The continuous treatment method of TDI waste brine has the following steps:

[0025] The TDI waste brine is introduced into an acid conditioning tank. Hydrochloric acid (30%) is then added and stirred to adjust the pH of the brine to 3. The feed pump is then activated to transfer the brine to an overhead tank. A 500W UV lamp in the adsorption column jacket is activated for continuous irradiation during the adsorption process. The brine then flows by gravity into the adsorption column (filled with zinc oxide-loaded hydrotalcite). A flowmeter controls the brine flow rate at 1 / 3 BV / h, resulting in an adsorption time of 3 hours. The adsorbed brine is then introduced into an alkali conditioning kettle, where sodium hydroxide solution is added to adjust the pH of the brine to 10. The brine is then introduced into a stripping tower, where the bottom temperature is maintained at 95°C. Small organic molecules are removed from the top of the tower, and brine is removed from the bottom of the tower, resulting in continuously treated brine.

[0026] After testing, the treated waste brine does not contain ethyl chloride and DEIP, with TOC of 2.6ppm and TN of 1.3ppm, which meets the requirements of the ion-membrane caustic soda process (TOC less than 10ppm, TN less than 3ppm). It can be mixed with the primary brine of the ion-membrane caustic soda process and then subjected to secondary refinement using chelating resin for subsequent applications. Example

[0027] The continuous treatment method of TDI waste brine has the following steps:

[0028] The TDI waste brine is introduced into an acid conditioning tank. Hydrochloric acid (30%) is then added and stirred to adjust the pH of the brine to 6. The feed pump is then activated to transfer the brine to an overhead tank. A 500W UV lamp is then activated within the jacket of the adsorption column to continuously irradiate the column during adsorption. The brine then flows by gravity into the adsorption column (filled with zinc oxide-loaded hydrotalcite). A flow meter controls the brine flow rate at 1 / 3 BV / h, resulting in an adsorption time of 3 hours. The adsorbed brine is then introduced into an alkali conditioning kettle, where sodium hydroxide solution is added to adjust the pH of the brine to 10. The brine is then introduced into a stripping tower, where the bottom temperature is maintained at 95°C. Small organic molecules are sampled from the top of the tower, while brine is sampled from the bottom of the tower, resulting in continuously treated brine.

[0029] After testing, the treated waste brine does not contain ethyl chloride and DEIP, the TOC is 6.3ppm, and the TN is 2.1ppm, which meets the requirements of the ion-membrane caustic soda process. It can be mixed with the primary brine of the ion-membrane caustic soda process and then subjected to secondary refinement using chelating resin for subsequent applications. Example

[0030] The continuous treatment method of TDI waste brine has the following steps:

[0031] The TDI waste brine is introduced into an acid conditioning tank. Hydrochloric acid (30%) is then added and stirred to adjust the pH of the brine to 1. The feed pump is then activated to transfer the brine to an overhead tank. A 500W UV lamp in the adsorption column jacket is activated for continuous irradiation during the adsorption process. The brine then flows by gravity into the adsorption column (filled with zinc oxide-loaded hydrotalcite). A flowmeter controls the brine flow rate at 1 / 3 BV / h, resulting in an adsorption time of 3 hours. The adsorbed brine is then introduced into an alkali conditioning kettle, where sodium hydroxide solution is added to adjust the pH of the brine to 10. The brine is then introduced into a stripping tower, where the bottom temperature is maintained at 95°C. Small organic molecules are removed from the top of the tower, and brine is removed from the bottom of the tower, resulting in continuously treated brine.

[0032] After testing, the treated waste brine does not contain ethyl chloride and DEIP, the TOC is 4.7ppm, and the TN is 1.9ppm, which meets the requirements of the ion membrane caustic soda process. It can be mixed with the primary brine of the ion membrane caustic soda process and then subjected to secondary refinement using chelating resin for subsequent applications. Example

[0033] The continuous treatment method of TDI waste brine has the following steps:

[0034] The TDI waste brine is introduced into an acid conditioning tank. Hydrochloric acid (30% concentration) is then added and stirred to adjust the pH of the brine to 3. The feed pump is then turned on to transfer the brine to an overhead tank. A 300W UV lamp is then activated within the jacket of the adsorption column to continuously irradiate the column during adsorption. The brine then flows by gravity into the adsorption column (filled with zinc oxide-loaded hydrotalcite). A flow meter controls the brine flow rate at 1 / 3 BV / h, resulting in an adsorption time of 3 hours. The adsorbed brine is then introduced into an alkali conditioning kettle, where sodium hydroxide solution is added to adjust the pH of the brine to 10. The brine is then introduced into a stripping tower, where the bottom temperature is maintained at 95°C. Small organic molecules are removed from the top of the tower, and brine is removed from the bottom of the tower to produce the continuously treated brine.

[0035] Testing revealed that the treated waste brine contained no ethyl chloride or DEIP, with a TOC of 10.7 ppm and a TN of 4.1 ppm. These TOC and TN levels fell short of the standards, failing to meet the requirements of the ion-exchange membrane caustic soda process and prohibiting its use in the brine treatment process. Example

[0036] The continuous treatment method of TDI waste brine has the following steps:

[0037] The TDI waste brine is introduced into an acid conditioning tank. Hydrochloric acid (30%) is then added and stirred to adjust the pH of the brine to 3. The feed pump is then activated to transfer the brine to an overhead tank. An 800W UV lamp is then activated within the jacket of the adsorption column to continuously irradiate the column during adsorption. The brine then flows by gravity into the adsorption column (filled with zinc oxide-loaded hydrotalcite). A flow meter controls the brine flow rate at 1 / 3 BV / h, resulting in an adsorption time of 3 hours. The adsorbed brine is then introduced into an alkali conditioning kettle, where sodium hydroxide solution is added to adjust the pH of the brine to 10. The brine is then introduced into a stripping tower, where the bottom temperature is maintained at 95°C. Small organic molecules are removed from the top of the tower, and brine is removed from the bottom of the tower, resulting in continuously treated brine.

[0038] After testing, the treated waste brine does not contain ethyl chloride and DEIP, the TOC is 2.3ppm, and the TN is 1.2ppm, which meets the requirements of the ion membrane caustic soda process. It can be mixed with the primary brine of the ion membrane caustic soda process and then refined twice with chelating resin for subsequent applications. Example

[0039] The continuous treatment method of TDI waste brine has the following steps:

[0040] The TDI waste brine is introduced into an acid conditioning tank. Hydrochloric acid (30%) is then added and stirred to adjust the pH of the brine to 3. The feed pump is then turned on to transfer the brine to an overhead tank. A 500W UV lamp in the adsorption column jacket is activated for continuous irradiation during the adsorption process. The brine then flows by gravity into the adsorption column (filled with zinc oxide-loaded hydrotalcite). A flowmeter controls the brine flow rate at 1 BV / h, resulting in an adsorption time of 1 hour. The adsorbed brine is then introduced into an alkali conditioning kettle, where sodium hydroxide solution is added to adjust the pH of the brine to 10. The brine is then introduced into a stripping tower, where the bottom temperature is maintained at 95°C. Small organic molecules are removed from the top of the tower, and brine is removed from the bottom of the tower, resulting in continuously treated brine.

[0041] After testing, the treated waste brine does not contain ethyl chloride and DEIP, the TOC is 9.6ppm, and the TN is 2.6ppm, which meets the requirements of the ion-membrane caustic soda process. It can be mixed with the primary brine of the ion-membrane caustic soda process and then subjected to secondary refinement using chelating resin for subsequent applications. Example

[0042] The continuous treatment method of TDI waste brine has the following steps:

[0043] The TDI waste brine is introduced into an acid conditioning tank. Hydrochloric acid (30%) is then added and stirred to adjust the pH of the brine to 3. The feed pump is then activated to transfer the brine to an overhead tank. A 500W UV lamp is then activated within the jacket of the adsorption column to continuously irradiate the column during adsorption. The brine then flows by gravity into the adsorption column (filled with zinc oxide-loaded hydrotalcite). A flow meter controls the brine flow rate at 1 / 4 BV / h, resulting in an adsorption time of 4 hours. The adsorbed brine is then introduced into an alkali conditioning kettle, where sodium hydroxide solution is added to adjust the pH of the brine to 10. The brine is then introduced into a stripping tower, where the bottom temperature is maintained at 95°C. Small organic molecules are removed from the top of the tower, and brine is removed from the bottom of the tower to produce the continuously treated brine.

[0044] After testing, the treated waste brine does not contain ethyl chloride and DEIP, the TOC is 2.4ppm, and the TN is 1.1ppm, which meets the requirements of the ion-membrane caustic soda process. It can be mixed with the primary brine of the ion-membrane caustic soda process and then subjected to secondary refinement using chelating resin for subsequent applications. Example

[0045] The continuous treatment method of TDI waste brine has the following steps:

[0046] The TDI waste brine is introduced into an acid conditioning tank. Hydrochloric acid (30%) is then added and stirred to adjust the pH of the brine to 3. The feed pump is then activated to transfer the brine to an overhead tank. A 500W UV lamp is then activated within the jacket of the adsorption column to continuously irradiate the column during adsorption. The brine then flows by gravity into the adsorption column (filled with zinc oxide-loaded hydrotalcite). A flow meter controls the brine flow rate at 1 / 3 BV / h, resulting in an adsorption time of 3 hours. The adsorbed brine is then introduced into an alkali conditioning kettle, where sodium hydroxide solution is added to adjust the pH of the brine to 10. The brine is then introduced into a stripping tower, where the bottom temperature is maintained at 85°C. Small organic molecules are sampled from the top of the tower, and brine is sampled from the bottom of the tower, resulting in continuously treated brine.

[0047] After testing, the ethyl chloride content in the treated waste brine was 12.1ppm, TOC was 13.4ppm, and TN was 1.7ppm. The TOC content did not meet the standards and did not meet the requirements of the ion-exchange membrane caustic soda process. It could not enter the brine process in the ion-exchange membrane caustic soda process. Example

[0048] The continuous treatment method of TDI waste brine has the following steps:

[0049] The TDI waste brine is introduced into an acid conditioning tank. Hydrochloric acid (30%) is then added and stirred to adjust the pH of the brine to 3. The feed pump is then activated to transfer the brine to an overhead tank. A 500W UV lamp is then activated within the jacket of the adsorption column to continuously irradiate the column during adsorption. The brine then flows by gravity into the adsorption column (filled with zinc oxide-loaded hydrotalcite). A flow meter controls the brine flow rate at 1 / 3 BV / h, resulting in an adsorption time of 3 hours. The adsorbed brine is then introduced into an alkali conditioning kettle, where sodium hydroxide solution is added to adjust the pH of the brine to 10. The brine is then introduced into a stripping tower, where the bottom temperature is maintained at 100°C. Small organic molecules are removed from the top of the tower, and brine is removed from the bottom of the tower, resulting in continuously treated brine.

[0050] After testing, the treated waste brine does not contain ethyl chloride and DEIP, the TOC is 2.3ppm, and the TN is 1.2ppm, which meets the requirements of the ion membrane caustic soda process. It can be mixed with the primary brine of the ion membrane caustic soda process and then refined twice with chelating resin for subsequent applications.

[0051] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other manner. Any person skilled in the art may utilize the above-disclosed technical content to modify or modify the present invention into equivalent embodiments. However, any simple modifications, equivalent variations, and modifications to the above embodiments that do not depart from the technical content of the present invention and are based on the technical essence of the present invention remain within the scope of protection of the present invention.

Claims

1. A method for continuous treatment of TDI waste brine, characterized in that: Here are the steps: The pH value of the TDI waste brine is adjusted to acidic, and then the acidic waste brine is subjected to a peroxidation adsorption column and simultaneously subjected to ultraviolet irradiation to perform photocatalytic oxidation and adsorption reactions. After the reaction is completed, the pH value of the acidic waste brine is adjusted to alkaline, and then the alkaline waste brine is passed through a stripping tower to remove small molecular organic matter to obtain continuously treated waste brine; The filler of the oxidation adsorption column is hydrotalcite loaded with zinc oxide; The irradiation power of the UV lamp is 500~700W; The flow rate of the acidic waste brine in the oxidation adsorption column is 1 / 3~1 BV / h; The temperature of the stripping tower kettle is 95-100°C; The waste brine obtained after continuous treatment is used in the ion membrane caustic soda process.

2. The method according to claim 1, characterized in that The acidic pH value is 2-4.

3. The method according to claim 1, characterized in that The flow rate of the acidic waste brine in the oxidation adsorption column is 1 / 3~1 / 2 BV / h.

4. The method according to claim 1, wherein The acidic pH value of the waste brine is adjusted by hydrochloric acid, and the alkaline pH value of the waste brine is adjusted by sodium hydroxide.

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