System for recovering sodium bicarbonate from purified terephthalic acid membrane concentrated water

Abstract

The utility model belongs to the field of chemical raw material recovery, and discloses a system for recovering sodium bicarbonate from purified terephthalic acid membrane concentrated water. The system comprises an acidification subsystem, a low-temperature evaporative crystallization subsystem and a salt leaching subsystem, the acidification subsystem comprises a concentrated water feeding pump and an acid feeding pump; the acidification tower comprises a tower body and a tower kettle which are connected up and down; an acid feeding hole is formed in the middle lower part of the tower body, and a concentrated water feeding hole is formed in the middle upper part of the tower body; the concentrated water feeding pump is connected with the concentrated water feeding hole; the acid feeding pump is connected with the acid feeding hole; the salt leaching subsystem comprises a salt leaching kettle; the salt leaching kettle is provided with a middle salt feeding hole, a middle solution feeding hole and a bottom material outlet; and a fresh saturated sodium bicarbonate solution feeding pipeline is connected with a middle solution feeding hole of the salt leaching kettle through a solution feeding pump. The utility model solves the technical problems of high energy consumption, low product purity and greenhouse effect during purified terephthalic acid membrane concentrated water treatment. And high-purity sodium bicarbonate is recovered from the purified terephthalic acid membrane concentrated water under low energy consumption.

Description

Technical Field

[0001] The utility model belongs to the field of chemical raw material recovery, and more specifically, relates to a system for recovering sodium bicarbonate from purified terephthalic acid membrane concentrated water. Background Technique

[0002] Purified terephthalic acid is the binary carboxylic acid with the largest output, mainly used for the production of polyester, especially for the production of polyethylene terephthalate. Currently, the annual domestic output of purified terephthalic acid exceeds 6 million tons, and a large amount of wastewater needs to be treated during the production process of purified terephthalic acid. The wastewater of purified terephthalic acid has a complex composition, mainly containing sodium carbonate and sodium bicarbonate. In addition, it also contains organic substances such as terephthalic acid, benzoic acid, and p-xylene, as well as various components such as calcium and magnesium ions, heavy metal ions, and bromide ions. The existing treatment methods mainly include three steps: the first step is to use resin adsorption, electrochemistry, biochemical treatment, extraction and other means for pretreatment to remove most of the organic substances, calcium and magnesium ions, and heavy metal ions; the second step is to use membrane separation means such as ultrafiltration, nanofiltration, and reverse osmosis to concentrate and reduce the amount of wastewater, obtaining most of the membrane-produced water and a small amount of membrane-concentrated water, among which the membrane-produced water can be returned to the system for reuse; the third step is to use evaporation crystallization, drying, or calcination and other means to treat the membrane-concentrated water, obtaining condensed water and miscellaneous salts, among which the condensed water can be returned to the system for reuse, while the miscellaneous salts become solid waste that needs to be outsourced for treatment, which will not only cause waste of resources but also generate a large amount of miscellaneous salt treatment costs. Therefore, how to classify and recover the miscellaneous salts in the purified terephthalic acid membrane concentrated water has become an urgent problem to be solved.

[0003] Patent Application No. 202310614689.6, Patent Application No. 202310701153.8, and Patent Application No. 202410015167.9 all propose a method for treating purified terephthalic acid (PTA) film concentrated wastewater, which first concentrates and incinerates the PTA film concentrated wastewater, and then dissolves the incineration residue. First of all, this process consumes a huge amount of energy. A large amount of energy has been consumed during the concentration and incineration of the PTA film concentrated wastewater. Subsequently, the incineration residue is dissolved in water. Since the solubility of sodium carbonate in water is very high when the temperature is above 35°C and it cannot crystallize at high temperatures, it is necessary to adopt the method of first heating and evaporating and then freezing and crystallizing to recover sodium carbonate, and a large amount of energy is generated again during the evaporation and freezing processes. Patent Application No. 202310614689.6 and Patent Application No. 202410015167.9 both adopt the above method of dissolving the incineration residue and then first evaporating and dehydrating and then freezing and crystallizing to separate sodium carbonate and sodium bromide. At the same time, the sodium carbonate obtained by crystallization in this scheme is a hydrate and needs to be further dried to obtain anhydrous sodium carbonate. Secondly, the sodium carbonate hydrate and sodium bromide obtained by crystallization need to be separated by solid-liquid separation through technical means such as filtration and centrifugation. After solid-liquid separation, the wet filter cake will inevitably contain 5-10% of the water introduced in the form of mother liquor, resulting in the introduction of impurities and a decrease in the purity of the two recovered products. Patent Application No. 202310701153.8 proposes a scheme of dissolving the incineration residue and then recovering sodium bicarbonate and bromine by electrolysis. A mixed solution of sodium bicarbonate solution with pH = 7-7.5 and bromine is obtained by carbon dioxide aeration. In fact, bromine can only exist in an acidic environment with pH < 5. Under neutral or slightly alkaline conditions, bromine will undergo self-oxidation-reduction reaction to generate bromide ions and hypobromite ions. Therefore, the above separation method has problems of low product purity and high energy consumption. At the same time, sodium bicarbonate decomposes during the incineration of the PTA film concentrated wastewater, and a large amount of carbon dioxide is discharged, resulting in the greenhouse effect. Utility Model Content

[0004] The purpose of the present utility model is to propose a system for recovering sodium bicarbonate from purified terephthalic acid (PTA) film concentrated wastewater in view of the deficiencies of the prior art. The present utility model solves the technical problems of high energy consumption, low product purity, and greenhouse effect during the treatment of PTA film concentrated wastewater, and recovers high-purity sodium bicarbonate from PTA film concentrated wastewater with low energy consumption.

[0005] To achieve the above purpose, the present utility model provides a system for recovering sodium bicarbonate from purified terephthalic acid (PTA) film concentrated wastewater, which includes an acidification subsystem, a low-temperature evaporation and crystallization subsystem, and a salt washing subsystem.

[0006] The acidification subsystem includes a concentrated water feed pump, an acid feed pump, a product extraction circulation pump, and an acidification tower; the acidification tower includes a tower body and a tower kettle connected up and down; a middle and lower part of the tower body is provided with an acid feed port, and a middle and upper part thereof is provided with a concentrated water feed port; the concentrated water feed pump is connected to the concentrated water feed port; the acid feed pump is connected to the acid feed port; a bottom of the tower kettle is provided with an acidification tower product outlet, and the acidification tower product outlet is connected to an inlet of the product extraction circulation pump; an outlet of the product extraction circulation pump is divided into two paths, one path is a first circulation pipeline, and the other path is a low-temperature evaporation and crystallization feed pipeline;

[0007] The salt washing subsystem includes a salt washing kettle; a stirring device is arranged inside the salt washing kettle, and the salt washing kettle is provided with a middle part salt feed port, a middle part solution feed port, and a bottom material outlet; a fresh saturated sodium bicarbonate solution feed pipeline is connected to the middle part solution feed port of the salt washing kettle through a solution feed pump; the bottom material outlet of the salt washing kettle is connected to an inlet of a first filtering device, and an outlet of the first filtering device is provided with a sodium bicarbonate product pipeline and a second circulation pipeline;

[0008] The low-temperature evaporation and crystallization subsystem includes a low-temperature evaporation kettle, a first-stage condenser, a second-stage condenser, a condensate receiving tank, and a second filtering device; the low-temperature evaporation kettle is provided with a middle part acidified concentrated water feed port, a top outlet of the kettle, and a bottom outlet of the kettle; the top outlet of the kettle is sequentially connected to a heat source inlet and outlet of the first-stage condenser, a heat source inlet and outlet of the second-stage condenser, and the condensate receiving tank; the low-temperature evaporation and crystallization feed pipeline and the second circulation pipeline converge and are connected to the middle part acidified concentrated water feed port through a cold source inlet and outlet of the first-stage condenser; the bottom outlet of the kettle is divided into two paths, and one path thereof is connected to an inlet of the second filtering device; an outlet of the second filtering device is provided with a mother liquor discharge pipeline and a salt feed pipeline; the salt feed pipeline is connected to the middle part salt feed port of the salt washing kettle.

[0009] Preferably, the first circulation pipeline is connected to the concentrated water feed port.

[0010] Preferably, a circulation feed port is further arranged on the tower body between the concentrated water feed port and the acid feed port, and the first circulation pipeline is connected to the circulation feed port;

[0011] Preferably, a top outlet of the acidification tower is arranged at the top of the tower body, and a back pressure valve is arranged at the top outlet of the acidification tower.

[0012] Preferably, the acidification tower is a plate tower and / or a packed tower.

[0013] Preferably, the number of theoretical plates of the acidification tower is 5 - 30.

[0014] Preferably, the salt washing subsystem includes a plurality of salt washing kettles connected in series.

[0015] Preferably, a stirring device is arranged inside each salt washing kettle, and each salt washing kettle is provided with a middle salt inlet, a middle solution inlet and a bottom material outlet; a corresponding-stage filtering device is arranged corresponding to each salt washing kettle;

[0016] The fresh saturated sodium bicarbonate solution feeding pipeline is connected to the middle solution inlet of the last salt washing kettle through a solution feeding pump; the bottom material outlet of each salt washing kettle is connected to the inlet of the corresponding-stage filtering device, and a filter cake outlet pipeline and a filtrate outlet pipeline are arranged at the outlet of each corresponding-stage filtering device;

[0017] Except for the filtrate outlet pipeline of the corresponding-stage filtering device of the first salt washing kettle, the filtrate outlet pipelines of the corresponding-stage filtering devices of other salt washing kettles are all connected to the middle solution inlet of the previous salt washing kettle; the filtrate outlet pipeline of the corresponding-stage filtering device of the first salt washing kettle is used as the second circulation pipeline;

[0018] Except for the filter cake outlet pipeline of the corresponding-stage filtering device of the last salt washing kettle, the filter cake outlet pipelines of the corresponding-stage filtering devices of other salt washing kettles are all connected to the middle salt inlet of the next salt washing kettle; the filter cake outlet pipeline of the corresponding-stage filtering device of the last salt washing kettle is used as the sodium bicarbonate product pipeline.

[0019] Preferably, the salt washing subsystem includes 2-3 serially-connected salt washing kettles.

[0020] Preferably, the low-temperature evaporation and crystallization subsystem further includes a forced circulation pump and a reboiler; the low-temperature evaporation kettle is further provided with a middle forced circulation material return port;

[0021] The other path of the bottom discharge port of the low-temperature evaporation kettle is sequentially connected to the middle forced circulation material return port through the forced circulation pump and the reboiler.

[0022] The beneficial effects of the technical solution of the present invention are as follows:

[0023] (1) The present invention solves the technical problems of high energy consumption, low product purity and greenhouse effect generation during the treatment of purified terephthalic acid film concentrated water. High-purity sodium bicarbonate is recovered from the purified terephthalic acid film concentrated water with low energy consumption.

[0024] (2) The present invention utilizes the property that the solubility of sodium bicarbonate is much smaller than that of sodium carbonate and it is easier to crystallize out from the mother liquor to directly evaporate and crystallize to recover sodium bicarbonate from the purified terephthalic acid film concentrated water, avoiding steps such as incineration, dissolution and freezing, and greatly reducing energy consumption. Through the acidification of the acidification tower, the present invention can ensure that the sodium carbonate in the purified terephthalic acid film concentrated water is converted into sodium bicarbonate to the greatest extent. Through the design of the feed port, it can effectively avoid the direct conversion of sodium carbonate into carbon dioxide due to excessive local acid concentration, resulting in the loss of carbonate radicals, and can increase the recovery rate of the recovered sodium bicarbonate by 20-30%.

[0025] (3) Through the salt washing step, the present utility model removes the impurity ions and organic matters introduced in the recovered sodium bicarbonate, making the purity of the recovered sodium bicarbonate ≥ 99.5%.

[0026] (4) The continuous flow process and equipment adopted by the present utility model are green and environment-friendly, without an incineration process and no emissions of pollutants or greenhouse effect gases such as carbon dioxide and ammonia nitrogen.

[0027] Other features and advantages of the present utility model will be described in detail in the subsequent specific implementation section. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] By describing the exemplary embodiments of the present utility model in more detail in conjunction with the drawings, the above-mentioned and other objects, features, and advantages of the present utility model will become more apparent. Among them, in the exemplary embodiments of the present utility model, the same reference numerals generally represent the same components.

[0029] Figure 1 The figure shows a schematic diagram of a system for recovering sodium bicarbonate from purified terephthalic acid (PTA) film concentrated water provided in Embodiment 1 of the present utility model.

[0030] Figure 2 The figure shows a schematic diagram of a system for recovering sodium bicarbonate from purified terephthalic acid (PTA) film concentrated water provided in Embodiment 3 of the present utility model.

[0031] The descriptions of the reference numerals in the drawings are as follows:

[0032] 1 - Acidification tower; 11 - Concentrated water feed pump; 12 - Acid feed pump; 13 - Product extraction circulation pump; 14 - Tower bottom; 15 - Tower body; 16 - Acid feed port; 17 - Concentrated water feed port; 18 - Acidification tower discharge port; 19 - Acidification tower top outlet; 110 - First circulation pipeline; 111 - Low-temperature evaporation crystallization feed pipeline; 112 - Back pressure valve;

[0033] 2 - Low-temperature evaporation kettle; 21 - Forced circulation pump; 22 - Reboiler; 23 - First-stage condenser; 24 - Second-stage condenser; 25 - Condensate receiving tank; 26 - Second filtration device; 27 - Middle forced circulation material return port; 28 - Middle acidified concentrated water feed port; 29 - Kettle bottom discharge port; 210 - Kettle top discharge port; 211 - Mother liquor discharge pipeline; 212 - Salt feed pipeline;

[0034] 3 - Salt washing kettle; 31 - Solution feed pump; 32 - Middle salt feed port; 33 - Middle solution feed port; 34 - Bottom material outlet; 35 - Stirring device; 36 - First filtration device; 37 - Sodium bicarbonate product pipeline; 38 - Second circulation pipeline;

[0035] 3-1 - First salt washing kettle; 32-1 - First-stage middle salt feed inlet; 33-1 - First-stage middle solution feed inlet; 34-1 - First-stage bottom material outlet; 35-1 - First-stage stirring device; 36-1 - First-stage first filtration device; 37-1 - First-stage filter cake outlet pipeline; 38-1 - First-stage filtrate outlet pipeline;

[0036] 3-2 - Second salt washing kettle; 32-2 - Second-stage middle salt feed inlet; 33-2 - Second-stage middle solution feed inlet; 34-2 - Second-stage bottom material outlet; 35-2 - Second-stage stirring device; 36-2 - Second-stage first filtration device; 37-2 - Second-stage filter cake outlet pipeline; 38-2 - Second-stage filtrate outlet pipeline. Detailed implementation mode

[0037] The preferred implementation mode of the present utility model will be described in more detail below. Although the preferred implementation mode of the present utility model is described below, it should be understood that the present utility model can be implemented in various forms and should not be limited by the implementation modes set forth herein. On the contrary, these implementation modes are provided to make the present utility model more thorough and complete, and to be able to convey the scope of the present utility model completely to those skilled in the art.

[0038] The present utility model provides a system for recovering sodium bicarbonate from purified terephthalic acid film concentrated water, and the system includes an acidification subsystem, a low-temperature evaporation crystallization subsystem, and a salt washing subsystem;

[0039] The acidification subsystem includes a concentrated water feed pump, an acid feed pump, a product extraction circulation pump, and an acidification tower; the acidification tower includes a tower body and a tower kettle connected up and down; a middle-lower part of the tower body is provided with an acid feed inlet, and a middle-upper part is provided with a concentrated water feed inlet; the concentrated water feed pump is connected to the concentrated water feed inlet; the acid feed pump is connected to the acid feed inlet; a bottom of the tower kettle is provided with an acidification tower discharge outlet, and the acidification tower discharge outlet is connected to an inlet of the product extraction circulation pump; an outlet of the product extraction circulation pump is divided into two paths, one path is a first circulation pipeline, and the other path is a low-temperature evaporation crystallization feed pipeline;

[0040] The salt washing subsystem includes a salt washing kettle; a stirring device is arranged inside the salt washing kettle, and the salt washing kettle is provided with a middle salt feed inlet, a middle solution feed inlet, and a bottom material outlet; a fresh saturated sodium bicarbonate solution feed pipeline is connected to the middle solution feed inlet of the salt washing kettle through a solution feed pump; the bottom material outlet of the salt washing kettle is connected to an inlet of a first filtration device, and an outlet of the first filtration device is provided with a sodium bicarbonate product pipeline and a second circulation pipeline;

[0041] The low-temperature evaporation and crystallization subsystem includes a low-temperature evaporation kettle, a first condenser, a second condenser, a condensate receiving tank, and a second filtration device; the low-temperature evaporation kettle is provided with a middle acidified thick water inlet, an outlet at the top of the kettle, and an outlet at the bottom of the kettle; the outlet at the top of the kettle is sequentially connected to the heat source inlet and outlet of the first condenser, the heat source inlet and outlet of the second condenser, and the condensate receiving tank; the low-temperature evaporation and crystallization feed pipeline and the second circulation pipeline merge and are connected to the middle acidified thick water inlet through the cold source inlet and outlet of the first condenser; the outlet at the bottom of the kettle is divided into two paths, one of which is connected to the inlet of the second filtration device; the outlet of the second filtration device is provided with a mother liquor discharge pipeline and a salt feed pipeline; the salt feed pipeline is connected to the middle salt inlet of the salt washing kettle.

[0042] In one example, the first circulation pipeline is connected to the thick water inlet.

[0043] In one example, a circulation inlet is further provided on the tower body between the thick water inlet and the acid inlet, and the first circulation pipeline is connected to the circulation inlet.

[0044] In one example, the top of the tower body is provided with an acidification tower top outlet, and a back pressure valve is provided at the acidification tower top outlet.

[0045] In one example, the acidification tower is a plate tower and / or a packed tower.

[0046] In one example, the number of theoretical plates of the acidification tower is 5 - 30.

[0047] In one example, the salt washing subsystem includes multiple salt washing kettles connected in series.

[0048] In one example, a stirring device is provided inside each salt washing kettle, and each salt washing kettle is provided with a middle salt inlet, a middle solution inlet, and a bottom material outlet; a corresponding filtration device is provided for each salt washing kettle;

[0049] The fresh saturated sodium bicarbonate solution feed pipeline is connected to the middle solution inlet of the last salt washing kettle through a solution feed pump; the bottom material outlet of each salt washing kettle is connected to the inlet of the corresponding filtration device, and the outlet of each corresponding filtration device is provided with a filter cake outlet pipeline and a filtrate outlet pipeline;

[0050] Except for the filtrate outlet pipeline of the corresponding filtration device of the first salt washing kettle, the filtrate outlet pipelines of the corresponding filtration devices of other salt washing kettles are all connected to the middle solution inlet of the previous salt washing kettle; the filtrate outlet pipeline of the corresponding filtration device of the first salt washing kettle serves as the second circulation pipeline;

[0051] Except for the filter cake outlet pipeline of the corresponding stage filtration device of the last salt washing kettle, the filter cake outlet pipelines of the corresponding stage filtration devices of other salt washing kettles are all connected to the middle salt feed inlet of the next salt washing kettle; the filter cake outlet pipeline of the corresponding stage filtration device of the last salt washing kettle serves as the sodium bicarbonate product pipeline.

[0052] In one example, the salt washing subsystem includes 2-3 serially connected salt washing kettles.

[0053] In one example, the low-temperature evaporation and crystallization subsystem further includes a forced circulation pump and a reboiler; the low-temperature evaporation kettle is further provided with a middle forced circulation material return port;

[0054] Another path of the bottom discharge port of the low-temperature evaporation kettle is sequentially connected to the middle forced circulation material return port through the forced circulation pump and the reboiler.

[0055] The present utility model also provides a method for recovering sodium bicarbonate from purified terephthalic acid membrane concentrated water. The method uses the above-mentioned system and includes the following steps:

[0056] S1: Acidification

[0057] Feed the purified terephthalic acid membrane concentrated water into the acidification tower from the middle upper part of the tower body, and feed the acid solution into the acidification tower from the middle lower part of the tower body to obtain acidified concentrated water;

[0058] S2: Low-temperature evaporation and crystallization

[0059] Send a part of the acidified concentrated water obtained in step S1 and the salt washing waste liquid from the salt washing subsystem to the low-temperature evaporation kettle for low-temperature evaporation treatment after heating to obtain the top discharge of the kettle and the bottom discharge of the kettle; filter a part of the bottom discharge of the kettle to obtain mother liquor and salt-rich materials;

[0060] S3: Salt washing

[0061] Feed the salt-rich materials into the salt washing kettle, and use saturated sodium bicarbonate aqueous solution as the salt washing liquid to wash away the impurity ions and organic matters in the salt-rich materials to obtain the bottom materials of the salt washing kettle and filter to obtain sodium bicarbonate products and the salt washing waste liquid.

[0062] In one example, the purified terephthalic acid membrane concentrated water is obtained by pretreating and membrane separating purified terephthalic acid wastewater; the pretreatment is at least one of resin adsorption, electrochemistry, biochemical treatment, and extraction; the membrane separation treatment is at least one of ultrafiltration, nanofiltration, and reverse osmosis.

[0063] In one example, the acid solution is at least one of hydrochloric acid, sulfuric acid, and nitric acid.

[0064] In one example, the pH of the acidified concentrated water is 7-8.5.

[0065] In one example, the operating pressure of the acidification tower is 0.1013 - 0.2 MPa, and the operating temperature is 0 - 40 °C, preferably 0 - 30 °C.

[0066] In one example, the method further includes returning the concentrated water with the remaining part acidified obtained in step S1 to the acidification tower from the concentrated water feed port or the circulating feed port.

[0067] In one example, the temperature of the low-temperature evaporation kettle is ≤60 °C, preferably ≤50 °C, and the operating pressure of the low-temperature evaporation kettle is controlled at an absolute pressure of 5 - 20 kPa.

[0068] In one example, the method further includes sending the discharge from the top of the kettle to a primary condenser to provide heat for heating and partial evaporation of the partially acidified concentrated water obtained in step S1 and the salt-washing waste liquid from the salt-washing subsystem, and obtaining the discharge from the top of the kettle with primary condensation; after sending the discharge from the top of the kettle with primary condensation to a secondary condenser to recover heat, sending it to a condensate receiving tank.

[0069] In one example, the method further includes circulating the remaining part of the discharge from the bottom of the kettle back to the low-temperature evaporation kettle through a forced circulation pump and a reboiler in sequence to achieve heating and circulation.

[0070] In one example, the method further includes discharging the mother liquor from the system. Optionally, bromine is extracted from the mother liquor in the discharge system.

[0071] In one example, the mass ratio of the saturated sodium bicarbonate aqueous solution to the salt-rich material is (0.5 - 5):1.

[0072] In one example, when the salt-washing subsystem includes multiple salt-washing kettles connected in series, the salt-rich material is sent to the first salt-washing kettle, and the fresh saturated sodium bicarbonate aqueous solution is sent to the last salt-washing kettle. The fresh saturated sodium bicarbonate aqueous solution is used as the salt-washing liquid to wash away the impurity ions and organic substances in the salt-rich material in the last salt-washing kettle, and the bottom material of the last salt-washing kettle is filtered to obtain a filtrate and a filter cake; the filtrate is sent to the salt-washing kettle before the last salt-washing kettle as the salt-washing liquid, so that the salt-washing liquid and the salt-rich material are in countercurrent contact step by step; the filtrate obtained by filtering the bottom material of the first salt-washing kettle is used as the salt-washing waste liquid; the filter cake obtained by filtering the bottom material of the last salt-washing kettle is used as the sodium bicarbonate product.

[0073] In the present utility model, as a preferred embodiment, when the salt washing subsystem includes two serially connected salt washing kettles, the rich salt material is fed into the first salt washing kettle, and fresh saturated sodium bicarbonate aqueous solution is fed into the second salt washing kettle. The fresh saturated sodium bicarbonate aqueous solution is used as the salt washing liquid to wash away the impurity ions and organic substances in the rich salt material in the second salt washing kettle. The bottom material of the second salt washing kettle is filtered to obtain a filtrate and a filter cake. The filtrate is fed into the first salt washing kettle as the salt washing liquid, so that the salt washing liquid and the rich salt material are in countercurrent contact step by step. The filtrate obtained by filtering the bottom material of the first salt washing kettle is used as the salt washing waste liquid. The filter cake obtained by filtering the bottom material of the second salt washing kettle is used as the sodium bicarbonate product.

[0074] In the following examples and comparative examples, the purified terephthalic acid wastewater generated by a purified terephthalic acid production device of an enterprise in Zhejiang is used. After pretreatment and reverse osmosis membrane concentration, the purified terephthalic acid membrane concentrate is obtained. The acid used for acidification is sulfuric acid. The ion detection in the membrane concentrate is carried out by titration method and ion chromatography method. The detection method for the recovered sodium bicarbonate is carried out according to the national standard of industrial sodium bicarbonate GB / T 1606-2008.

[0075] The composition of the purified terephthalic acid membrane concentrate before being treated by the systems and methods of the examples and comparative examples is shown in Table 1.

[0076] Table 1

[0077]

[0078] Example 1

[0079] This example provides a system for recovering sodium bicarbonate from purified terephthalic acid membrane concentrate, as Figure 1 shown. The system includes an acidification subsystem, a low-temperature evaporation crystallization subsystem and a salt washing subsystem.

[0080] The acidification subsystem includes a concentrated water feed pump 11, an acid feed pump 12, a product extraction circulation pump 13, and an acidification tower 1; the acidification tower 1 includes a tower body 15 and a tower bottom 14 connected up and down, the volume of the tower bottom 14 is 5L, the diameter of the tower body 15 is 50mm and the height is 2m, and glass spring packing with a diameter of 4mm is filled in the tower body 15; an acid feed port 16 is arranged at 0.2m from the tower bottom in the middle and lower part of the tower body 15, and a concentrated water feed port 17 is arranged at 1.8m from the tower bottom in the middle and upper part of the tower body 15; the concentrated water feed pump 11 is connected to the concentrated water feed port 17; the acid feed pump 12 is connected to the acid feed port 16; an acidification tower top outlet 19 is arranged at the top of the tower body 15, and a back pressure valve 112 is arranged at the acidification tower top outlet 19; an acidification tower discharge port 18 is arranged at the bottom of the tower bottom 14, and the acidification tower discharge port 18 is connected to the inlet of the product extraction circulation pump 13; the outlet of the product extraction circulation pump 13 is divided into two paths, one path is a first circulation pipeline 110, and the other path is a low-temperature evaporation crystallization feed pipeline 111; the first circulation pipeline 110 is connected to the concentrated water feed port 17. A pressure gauge is arranged in the acidification tower 1.

[0081] The salt washing subsystem includes a salt washing kettle 3; a stirring device 35 is arranged inside the salt washing kettle 3, and the salt washing kettle 3 is provided with a middle salt feed port 32, a middle solution feed port 33, and a bottom material outlet 34; the fresh saturated sodium bicarbonate solution feed pipeline is connected to the middle solution feed port 33 of the salt washing kettle 3 through a solution feed pump 31; the bottom material outlet 34 of the salt washing kettle 3 is connected to the inlet of a first filtering device 36, and a sodium bicarbonate product pipeline 37 and a second circulation pipeline 38 are arranged at the outlet of the first filtering device 36;

[0082] The low-temperature evaporation crystallization subsystem includes a low-temperature evaporation kettle 2, a first-stage condenser 23, and a second filtering device 26; the low-temperature evaporation kettle is provided with a middle acidified concentrated water feed port 28, a kettle top discharge port 210, and a kettle bottom discharge port 29; the low-temperature evaporation crystallization feed pipeline 111 and the second circulation pipeline 38 converge and are connected to the middle acidified concentrated water feed port 28 through the cold source inlet and outlet of the first-stage condenser 23; the kettle bottom discharge port 29 is divided into two paths, and one of the paths is connected to the inlet of the second filtering device 26; a mother liquor discharge pipeline 211 and a salt feed pipeline 212 are arranged at the outlet of the second filtering device 26; the salt feed pipeline 212 is connected to the middle salt feed port 32 of the salt washing kettle 3.

[0083] The low-temperature evaporation and crystallization subsystem further includes a secondary condenser 24, a condensate receiving tank 25, a forced circulation pump 21, and a reboiler 22; the top discharge port 210 of the kettle is sequentially connected to the heat source inlet and outlet of the primary condenser 23, the heat source inlet and outlet of the secondary condenser 24, and the condensate receiving tank 25. The low-temperature evaporation kettle 2 is further provided with a middle forced circulation material return port 27; another path of the bottom discharge port 29 of the kettle is sequentially connected to the middle forced circulation material return port 27 through the forced circulation pump 21 and the reboiler 22.

[0084] The secondary condenser 24 uses circulating water for condensation.

[0085] This embodiment further provides a method for recovering sodium bicarbonate from purified terephthalic acid membrane concentrated water. The method uses the above system and includes the following steps:

[0086] S1: Acidification

[0087] The purified terephthalic acid membrane concentrated water (feeding rate 1000 mL / h) is fed into the acidification tower 1 from the middle upper part of the tower body 15, 1.8 m away from the tower kettle, and 98% sulfuric acid (feeding rate 20 g / h) is fed into the acidification tower 1 from the middle lower part of the tower body 15, 0.2 m away from the tower kettle, to obtain acidified concentrated water. At the same time, 5000 ml / L of material is taken out from the tower kettle 14 and returned to the position 1.8 m away from the tower kettle through the first circulation pipeline 110 for circulation. The pH of the acidified concentrated water is reduced from 9.1 to 8.1, and the water quality after acidification is shown in Table 2:

[0088] S2: Low-temperature evaporation and crystallization

[0089] Part of the acidified concentrated water (feeding rate 1000 mL / h) obtained in step S1 is continuously heated together with the salt washing waste liquid from the salt washing subsystem and then sent to the low-temperature evaporation kettle 2 for low-temperature evaporation treatment (the temperature of the low-temperature evaporation kettle is 51 °C, the gas phase temperature is 48 °C, and the operating pressure of the low-temperature evaporation kettle 2 is controlled at an absolute pressure of 10 kPa), to obtain top discharge and bottom discharge of the kettle;

[0090] The top discharge of the kettle is sent to the primary condenser 23 to provide heat for the heating and partial evaporation of part of the acidified concentrated water obtained in step S1 and the salt washing waste liquid from the salt washing subsystem, to obtain the top discharge of the kettle after primary condensation; after the top discharge of the kettle after primary condensation is sent to the secondary condenser 24 to recover heat, 800 mL / h of condensed water is obtained and sent to the condensate receiving tank 25;

[0091] Part of the bottom discharge of the kettle is subjected to plate and frame filtration to obtain 135 mL / h of mother liquor and 88 g / h of wet cake of rich salt material; the remaining part of the bottom discharge of the kettle is sequentially circulated back to the low-temperature evaporation kettle 2 through the forced circulation pump 21 and the reboiler 22; the mother liquor is discharged from the system;

[0092] S3: Salt washing

[0093] Feed 100 g of the wet cake of the rich salt material obtained in step S2 into a 500 mL salt washing kettle 3. Use 200 g of saturated sodium bicarbonate aqueous solution as the salt washing liquid, stir to wash away the impurity ions and organic substances in the rich salt material. The stirring temperature is 25 °C and the time is 5 min. Obtain the bottom material of the salt washing kettle and carry out plate and frame pressure filtration to obtain 98 g of sodium bicarbonate product and 201 g of the salt washing waste liquid.

[0094] After drying, the purity of the recovered sodium bicarbonate is detected to be 99.6% and the recovery rate is 82%.

[0095] Table 2

[0096]

[0097] Example 2

[0098] This example provides a method for recovering sodium bicarbonate from purified terephthalic acid membrane concentrated water, and the method uses the system described in Example 1. The difference between this example and Example 1 is only that:

[0099] The temperature of the low-temperature evaporation kettle is 42 °C, the gas phase temperature is 37 °C, and the operating pressure of the low-temperature evaporation kettle is controlled at an absolute pressure of 5 kPa;

[0100] Obtain 135 mL / h of mother liquor and 89 g / h of wet cake of rich salt material;

[0101] After washing the salt once in step S3 in this example, the purity of the recovered sodium bicarbonate is detected to be 99.6% and the recovery rate is 82%.

[0102] Example 3

[0103] This example provides a system for recovering sodium bicarbonate from purified terephthalic acid membrane concentrated water. The difference between this example and Example 1 is only that:

[0104] The salt washing subsystem includes 2 salt washing kettles 3 connected in series;

[0105] Each salt washing kettle 3 is internally provided with a stirring device 35. Each salt washing kettle 3 is provided with a middle salt feed port, a middle solution feed port and a bottom material outlet; the fresh saturated sodium bicarbonate solution feed pipeline is connected to the secondary middle solution feed port 33-2 of the second salt washing kettle 3-2 through a solution feed pump 31; the bottom material outlet of each salt washing kettle is connected to the inlet of the corresponding stage filtration device, and the outlet of each corresponding stage filtration device is provided with a filter cake outlet pipeline and a filtrate outlet pipeline;

[0106] The filtrate outlet pipeline of the secondary first filtration device 36-2 is connected to the first-stage middle solution inlet 33-1 of the first salt-washing kettle 3-1; the filtrate outlet pipeline of the primary first filtration device 36-1 is used as the second circulation pipeline;

[0107] The filter cake outlet pipeline of the primary first filtration device 36-1 is connected to the secondary middle salt inlet 32-2 of the second salt-washing kettle 3-2; the filter cake outlet pipeline of the secondary first filtration device 36-2 is used as the sodium bicarbonate product pipeline.

[0108] This embodiment also provides a method for recovering sodium bicarbonate from purified terephthalic acid membrane concentrated water. The difference between this embodiment and Embodiment 1 is only that:

[0109] Feed 100 g of the salt-rich material obtained in step S2 into the first salt-washing kettle, and feed 200 g of fresh saturated sodium bicarbonate aqueous solution into the second salt-washing kettle. Use the fresh saturated sodium bicarbonate aqueous solution as the salt-washing liquid, stir to wash away the impurity ions and organic substances in the salt-rich material in the second salt-washing kettle. The stirring temperature is 25 °C and the time is 5 min. Plate and frame filter the bottom material of the second salt-washing kettle to obtain a filtrate and a filter cake; feed the filtrate into the first salt-washing kettle as the salt-washing liquid, so that the salt-washing liquid contacts the salt-rich material countercurrently (that is, the fresh saturated sodium bicarbonate aqueous solution contacts the salt-rich material in the second salt-washing kettle; the filtrate contacts the salt-rich material in the first salt-washing kettle); use the filtrate obtained by filtering the bottom material of the first salt-washing kettle as the salt-washing waste liquid; use the filter cake obtained by filtering the bottom material of the second salt-washing kettle as the sodium bicarbonate product.

[0110] After drying, the purity of the recovered sodium bicarbonate is detected to be 99.8% and the yield is 81%.

[0111] Comparative Example 1

[0112] This comparative example provides a method for recovering sodium bicarbonate from purified terephthalic acid membrane concentrated water, including the following steps:

[0113] S1: Acidification

[0114] Mix the purified terephthalic acid membrane concentrated water and 98% sulfuric acid evenly in an acidification tank and react to obtain acidified concentrated water. The water quality is shown in Table 3:

[0115] Table 3

[0116]

[0117] The difference between step S2 of this comparative example and step S2 of Embodiment 1 is only that: Continuously heat the acidified concentrated water (feed rate 1000 mL / h) obtained in step S1 of this comparative example together with the salt-washing waste liquid from the salt-washing subsystem and send it to the low-temperature evaporation kettle for low-temperature evaporation treatment; obtain 150 mL / h of mother liquor and 62 g / h of wet filter cake of the salt-rich material;

[0118] The difference between step S3 of this comparative example and step S3 of Example 1 is only that: 94 g of sodium bicarbonate product and 205 g of the salt-washing waste liquid are obtained.

[0119] After drying, the purity of the recovered sodium bicarbonate is detected to be 99.6%, and the yield is 52%. This is because the purified terephthalic acid film concentrated water is in direct contact with sulfuric acid, and the local acid concentration is too high, resulting in the direct conversion of sodium carbonate into carbon dioxide and causing the loss of carbonate radicals.

[0120] Comparative Example 2

[0121] This comparative example provides a method for recovering sodium bicarbonate from purified terephthalic acid film concentrated water. This comparative example uses the system described in Example 1. The difference between this comparative example and Example 1 is only that:

[0122] The temperature of the low-temperature evaporation kettle is 100 °C, the gas-phase temperature is 97 °C, and the operating pressure of the low-temperature evaporation kettle is normal pressure.

[0123] Mother liquor 165 mL / h and wet cake of rich salt material 44 g / h are obtained;

[0124] 88 g of sodium bicarbonate product and 210 g of the salt-washing waste liquid are obtained.

[0125] After drying, the purity of the recovered sodium bicarbonate is detected to be 99.5%, and the yield is 24%. This is because the evaporation crystallization temperature at normal pressure is too high, and sodium bicarbonate decomposes.

[0126] The embodiments of the present invention have been described above. The above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations are obvious to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A system for recovering sodium bicarbonate from purified terephthalic acid film concentrated water, characterized in that, The system includes an acidification subsystem, a low-temperature evaporation crystallization subsystem, and a salt washing subsystem; The acidification subsystem includes a concentrated water feed pump, an acid feed pump, a product extraction circulation pump, and an acidification tower; the acidification tower includes a tower body and a tower kettle connected up and down; a middle-lower part of the tower body is provided with an acid feed port, and a middle-upper part thereof is provided with a concentrated water feed port; the concentrated water feed pump is connected to the concentrated water feed port; the acid feed pump is connected to the acid feed port; a bottom of the tower kettle is provided with an acidification tower discharge port, and the acidification tower discharge port is connected to an inlet of the product extraction circulation pump; an outlet of the product extraction circulation pump is divided into two paths, one path is a first circulation pipeline, and the other path is a low-temperature evaporation crystallization feed pipeline; The salt washing subsystem includes a salt washing kettle; a stirring device is arranged inside the salt washing kettle, and the salt washing kettle is provided with a middle salt feed port, a middle solution feed port, and a bottom material outlet; a fresh saturated sodium bicarbonate solution feed pipeline is connected to the middle solution feed port of the salt washing kettle through a solution feed pump; the bottom material outlet of the salt washing kettle is connected to an inlet of a first filtering device, and an outlet of the first filtering device is provided with a sodium bicarbonate product pipeline and a second circulation pipeline; The low-temperature evaporation crystallization subsystem includes a low-temperature evaporation kettle, a first-stage condenser, a second-stage condenser, a condensate receiving tank, and a second filtering device; the low-temperature evaporation kettle is provided with a middle acidified concentrated water feed port, a top outlet of the kettle, and a bottom outlet of the kettle; the top outlet of the kettle is sequentially connected to a heat source inlet and outlet of the first-stage condenser, a heat source inlet and outlet of the second-stage condenser, and the condensate receiving tank; the low-temperature evaporation crystallization feed pipeline and the second circulation pipeline merge and are connected to the middle acidified concentrated water feed port through a cold source inlet and outlet of the first-stage condenser; the bottom outlet of the kettle is divided into two paths, and one path thereof is connected to an inlet of the second filtering device; an outlet of the second filtering device is provided with a mother liquor discharge pipeline and a salt feed pipeline; the salt feed pipeline is connected to the middle salt feed port of the salt washing kettle.

2. The system for recovering sodium bicarbonate from purified terephthalic acid film concentrated water according to claim 1, wherein, The first circulation pipeline is connected to the concentrated water feed port.

3. The system for recovering sodium bicarbonate from purified terephthalic acid film concentrated water according to claim 1, wherein A circulation feed port is further arranged on the tower body between the concentrated water feed port and the acid feed port, and the first circulation pipeline is connected to the circulation feed port.

4. The system for recovering sodium bicarbonate from purified terephthalic acid film concentrated water according to claim 1, characterized in that, A top of the tower body is provided with an acidification tower top outlet, and a back pressure valve is arranged at the acidification tower top outlet.

5. The system for recovering sodium bicarbonate from purified terephthalic acid film concentrated water according to claim 1, characterized in that, The acidification tower is a plate tower and / or a packed tower.

6. The system for recovering sodium bicarbonate from purified terephthalic acid film concentrated water according to claim 1, wherein, The number of theoretical plates of the acidification tower is 5 - 30.

7. The system for recovering sodium bicarbonate from purified terephthalic acid film concentrated water according to claim 1, wherein The salt washing subsystem includes multiple salt washing kettles connected in series.

8. The system for recovering sodium bicarbonate from purified terephthalic acid film concentrated water according to claim 7, wherein A stirring device is arranged inside each salt washing kettle, and each salt washing kettle is provided with a middle salt feed port, a middle solution feed port, and a bottom material outlet; a corresponding-stage filtering device is arranged corresponding to each salt washing kettle; The fresh saturated sodium bicarbonate solution feed pipeline is connected to the middle solution feed port of the last salt washing kettle through a solution feed pump; the bottom material outlet of each salt washing kettle is connected to an inlet of the corresponding-stage filtering device, and an outlet of each corresponding-stage filtering device is provided with a filter cake outlet pipeline and a filtrate outlet pipeline; Except for the filtrate outlet pipeline of the corresponding-stage filtration device of the first salt-washing kettle, the filtrate outlet pipelines of the corresponding-stage filtration devices of the remaining salt-washing kettles outside the first salt-washing kettle are all connected to the middle solution feed inlet of the previous salt-washing kettle; the filtrate outlet pipeline of the corresponding-stage filtration device of the first salt-washing kettle serves as the second circulation pipeline; Except for the filter cake outlet pipeline of the corresponding-stage filtration device of the last salt-washing kettle, the filter cake outlet pipelines of the corresponding-stage filtration devices of the remaining salt-washing kettles outside the last salt-washing kettle are all connected to the middle salt feed inlet of the next salt-washing kettle; the filter cake outlet pipeline of the corresponding-stage filtration device of the last salt-washing kettle serves as the sodium bicarbonate product pipeline.

9. The system for recovering sodium bicarbonate from purified terephthalic acid film concentrated water according to claim 7, wherein, The salt-washing subsystem includes 2 - 3 series-connected salt-washing kettles.

10. The system for recovering sodium bicarbonate from purified terephthalic acid film concentrated water according to claim 1, wherein, The low-temperature evaporation and crystallization subsystem further includes a forced circulation pump and a reboiler; the low-temperature evaporation kettle is further provided with a middle forced circulation material return port; Another path of the bottom discharge port of the kettle is sequentially connected to the middle forced circulation material return port through the forced circulation pump and the reboiler.

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