Coagulation bath regeneration method

Abstract

This invention relates to a method for regenerating a coagulation bath, wherein the coagulation bath contains XHCO3 and M2CO3, or XHSO3 and Y2SO3, wherein X, Y, and M are each selected from at least one of Li, Na, K, Rb, Cs, Fr, and NH4; the mass concentrations of XHCO3 and XHSO3 are each 0.1-25 wt%, and the mass concentrations of M2CO3 and Y2SO3 are each 3-35 wt%; the regeneration method includes: (1) contacting the coagulation bath with carbon dioxide or sulfur dioxide to obtain a first solution; (2) evaporating the water in the first solution so that the mass concentrations of XHCO3 and XHSO3 in the first solution are each 0.5-20 wt%, and the mass concentrations of M2CO3 and Y2SO3 are each 2-30 wt%. The regeneration method of this invention solves the problem of recycling high-concentration salts, reduces production difficulty and cost, and has broad application prospects.

Description

Technical Field

[0001] This invention relates to the field of coagulation bath technology for natural polymer materials, and specifically to a method for regenerating a coagulation bath. Background Technology

[0002] The composition of the coagulation bath in wet molding of natural polymer solutions not only directly affects and determines product performance, but also necessitates consideration of the separation and recovery of high-salt solutions and the treatment of waste generated after the reaction with solvents. In the wet molding process of viscose, cellulose regeneration mainly occurs through acid-base neutralization reactions, leading to a decrease in sulfuric acid content, an increase in sodium sulfate content, and the consumption of zinc sulfate in the acid bath. Currently, increasing the sulfuric acid content in the acid bath after spinning is primarily achieved through acid bath evaporation, which suffers from high steam consumption, inability to recover zinc sulfate, and the inability to precipitate sodium sulfate generated during spinning through high-temperature crystallization, resulting in high costs and energy consumption. To address this, CN102167293A, CN103388198B, and CN106868635A utilize bipolar membrane electrodialysis technology to produce sulfuric acid and sodium hydroxide solutions from the treated sodium sulfate wastewater. However, due to high costs and small processing volumes, large-scale application is difficult.

[0003] The alkali / urea system is a green, non-toxic, inexpensive, and highly efficient cellulose solvent. Currently, suitable coagulation baths for the alkali / urea system include sulfuric acid systems (patent application numbers 200510018799.8 and 200410013389.X), phosphoric acid systems (CN103757720A), citric acid systems (CN110042488A), and phytic acid systems (CN107653502A). These strong or weak acids react with alkali / urea to form mixed solutions of various salts, which are difficult to separate, leading to difficulties in salt recycling and directly increasing the difficulty and cost of salt separation and recovery as well as waste treatment. Physical coagulation and solvent recovery can be achieved using hot water and its salt solution (CN101921402A, CN102443869A) or organic solvent solution (CN 110129923A), but the coagulation speed is slow, the product performance is low, the residual alkali in the fiber is high, and the subsequent alkali removal process is added, which is not conducive to industrial production. Summary of the Invention

[0004] This application relates to the regeneration of a coagulation bath after solution spinning containing natural polymers. In this invention, the solution containing natural polymers contains a metal hydroxide and an auxiliary agent, the auxiliary agent being selected from at least one of urea, zinc oxide, and thiourea; the coagulation bath is a first coagulation bath containing XHCO3 and / or XHSO3; wherein X is selected from at least one of Li, Na, K, Rb, Cs, Fr, and NH4; the mass concentration of XHCO3 and / or XHSO3 in the coagulation bath is 0.5-30 wt%; or the coagulation bath is a second coagulation bath containing XHCO3 and M2CO3, or XHSO3 and Y2SO3; wherein M and Y are each selected from at least one of Li, Na, K, Rb, Cs, Fr, and NH4; the mass concentration of XHCO3 or XHSO3 is 0.5-30 wt%; the mass concentration of M2CO3 or Y2SO3 is 0.5-30 wt%.

[0005] In the aforementioned coagulation bath system provided by the present invention, after the solution containing natural polymers coagulates in the coagulation bath system, XHCO3 or XHSO3 generates corresponding carbonates or sulfites, and urea or thiourea accumulates in the coagulation bath. Therefore, the coagulation bath needs to be regenerated for reuse.

[0006] To achieve the above objectives, the present invention provides a coagulation bath regeneration method. Using the regeneration method described in the present invention, the coagulation bath can be recycled multiple times, solving the problem of recycling and processing high-concentration salts, reducing production difficulty and costs, and has broad application prospects.

[0007] This invention provides a method for regenerating a coagulation bath, wherein the coagulation bath contains XHCO3 and M2CO3, or XHSO3 and Y2SO3, wherein X, M, and Y are each selected from at least one of Li, Na, K, Rb, Cs, Fr, and NH4; the mass concentrations of XHCO3 and XHSO3 are each 0.1-25 wt%, and the mass concentrations of M2CO3 and Y2SO3 are each 3-35 wt%; the regeneration method includes:

[0008] (1) The coagulation bath is contacted with carbon dioxide or sulfur dioxide to obtain a first solution;

[0009] (2) Evaporate the water in the first solution so that the mass concentrations of XHCO3 and XHSO3 in the first solution are 0.5-30wt% and the mass concentrations of M2CO3 and Y2SO3 are 2-30wt% respectively, and obtain a regenerated coagulation bath.

[0010] Compared with existing technologies, this invention uses weak acid bicarbonate or bisulfite as the main components, contains no strong acids or organic solvents, and these salts are non-toxic, harmless, inexpensive, and readily available. The salt reacts with strong alkalis, and the accumulation of urea and / or thiourea in the coagulation bath with additives helps improve product performance. When the additive is a metal salt (e.g., zinc oxide), a corresponding precipitate is formed in the coagulation bath, which can be filtered out without affecting the regeneration of the weak acid bicarbonate or bisulfite. Using the regeneration method described in this invention, bicarbonate or bisulfite is regenerated through carbon dioxide or sulfur dioxide sulfation, then evaporated to reduce the water introduced into the coagulation bath. The resulting first solution can be recycled up to 100 times. When urea accumulates to a certain concentration in the coagulation bath, it is recrystallized and separated to obtain bicarbonate / sulfite products, which are then recycled along with the urea or thiourea products. Alternatively, quicklime is added to the coagulation bath to convert the coagulation bath solution into a solvent containing alkali, urea, and / or thiourea, which can be used to dissolve natural polymer materials. It solves the problem of recycling high-concentration salt, reduces production difficulty and cost, and has broad application prospects. Attached Figure Description

[0011] Figure 1 This is a schematic diagram of a coagulation bath regeneration system provided in a preferred embodiment of the present invention.

[0012] Explanation of reference numerals in the attached figures

[0013] 1—Coagulation bath 2—Acidification tower

[0014] 3—First Evaporator Tower; 4—Second Evaporator Tower

[0015] 5—Filtering device; 6—Drying device

[0016] 7—Sedimentation tank 8—Filter tank Detailed Implementation

[0017] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0018] This invention provides a method for regenerating a coagulation bath, wherein the coagulation bath contains XHCO3 and M2CO3, or XHSO3 and Y2SO3, wherein X, Y, and M are each selected from at least one of Li, Na, K, Rb, Cs, Fr, and NH4; the mass concentrations of XHCO3 and XHSO3 are each 0.1-25 wt%, and the mass concentrations of M2CO3 and Y2SO3 are each 3-35 wt%; the regeneration method includes:

[0019] (1) The coagulation bath is contacted with carbon dioxide or sulfur dioxide to obtain a first solution;

[0020] (2) Evaporate the water in the first solution so that the mass concentrations of XHCO3 and XHSO3 in the first solution are each 0.5-30wt%; and the mass concentrations of M2CO3 and Y2SO3 are each 2-30wt%, thus obtaining a regenerated coagulation bath. In this invention, weak acid bicarbonate or bisulfite is used as the main component, which does not contain strong acids or organic solvents. Moreover, these salts are non-toxic, harmless, inexpensive, and readily available. The salts react with strong alkalis but not with co-solvents, and the accumulation of urea in the coagulation bath is beneficial to improving the performance of the product. Therefore, by using the regeneration method described in this invention, the first solution obtained after regenerating bicarbonate or bisulfite by carbon dioxide or sulfur dioxide sulfation, followed by evaporation to reduce the water introduced into the coagulation bath, can be recycled up to 100 times.

[0021] According to a preferred embodiment of the present invention, in the coagulation bath, the mass concentrations of XHCO3 and XHSO3 are each 5-15 wt%, and the mass concentrations of M2CO3 and Y2SO3 are each 5-20 wt%.

[0022] In this invention, the solution containing natural polymers contains urea. When the solution containing natural polymers is coagulated and formed, and the additive in the natural polymer solution is zinc oxide, a corresponding precipitate is generated in the coagulation bath. When the additive in the natural polymer solution is urea and / or thiourea, it accumulates in the coagulation bath. The accumulation of urea and / or thiourea in the coagulation bath is beneficial to improving the performance of the product. According to a preferred embodiment of the present invention, the coagulation bath also contains urea and / or thiourea, and the mass concentration of urea and / or thiourea is 0.4wt%-60wt%.

[0023] According to a preferred embodiment of the present invention, in the first solution, the mass concentrations of XHCO3 and XHSO3 are each 10-20 wt%, the mass concentrations of M2CO3 and Y2SO3 are each 5-20 wt%, and the mass concentrations of urea and / or thiourea are 20-40 wt%.

[0024] In this invention, the range of selectable contact conditions in step (1) is relatively wide. According to a preferred embodiment of this invention, the contact conditions include: contact temperature 20-30℃.

[0025] According to a preferred embodiment of the present invention, the coagulation bath is filtered to remove impurities such as micelles or precipitates formed by zinc oxide before being contacted with carbon dioxide or sulfur dioxide.

[0026] In this invention, during the coagulation bath regeneration and recycling process, when the auxiliary agent is urea and / or thiourea, urea and / or thiourea accumulate in the coagulation bath. When the urea and / or thiourea accumulate to a certain concentration in the coagulation bath, they are recrystallized and separated to obtain bicarbonate and urea products for recycling. Alternatively, quicklime is added to the coagulation bath to convert the coagulation bath solution into a solution of alkali and urea or alkali and thiourea. After evaporation to remove water, urea or thiourea is added to adjust the ratio before being used to dissolve natural polymers. According to a preferred embodiment of the invention, when the concentration of urea and / or thiourea in the coagulation bath is greater than 40 wt%, carbonation is carried out, followed by low-temperature (40-50°C) evaporation and crystallization to obtain bicarbonate. When the urea and / or thiourea are close to saturation, they are further evaporated and crystallized at high temperature (55-80°C) to obtain urea and / or thiourea. The bicarbonate product is sold externally, while the urea and / or thiourea can be reused to prepare natural polymer solvents for repeated use.

[0027] The coagulation bath is brought into contact with quicklime to convert the mixed solution of bicarbonate, carbonate and urea or thiourea into a solution containing XOH, MOH and urea or thiourea. After adding urea or thiourea to adjust the ratio, it can be used to dissolve natural polymer materials.

[0028] According to a preferred embodiment of the present invention, when the urea concentration in the coagulation bath is greater than 55 wt%, the coagulation bath is brought into contact with quicklime to convert the mixed solution of bicarbonate, carbonate and urea or thiourea into a solution containing XOH, MOH and urea and / or thiourea. After adding urea or thiourea to adjust the ratio of the two, it can be used to dissolve natural polymer materials.

[0029] According to a preferred embodiment of the present invention, X, Y and M are the same element, preferably X, Y and M are both Na or K.

[0030] According to a preferred embodiment of the present invention, the regeneration method is performed in a regeneration system, the regeneration system comprising:

[0031] Coagulation bath, used for coagulating and molding strongly alkaline natural polymer solutions;

[0032] An acidification tower connected to a coagulation bath via a pipeline is used for contacting the coagulation bath with carbon dioxide or sulfur dioxide.

[0033] The first evaporation tower, connected to the acidification tower via a pipeline, is used to evaporate water generated from the solidification of natural polymer solutions and / or water introduced by strongly alkaline natural polymer solutions.

[0034] The regeneration method includes:

[0035] (i) The coagulation bath in the coagulation bath tank is introduced into the acidification tower, and the coagulation bath is contacted with carbon dioxide or sulfur dioxide in the acidification tower to obtain a first solution;

[0036] (ii) The first solution is passed into an evaporation tower to evaporate the water in the first solution, so that the mass concentrations of XHCO3 and XHSO3 in the first solution are 0.5-30wt% each; and the mass concentrations of M2CO3 and Y2SO3 are 2-30wt% each, thus obtaining a regenerated coagulation bath.

[0037] According to a preferred embodiment of the present invention, the regeneration system further includes:

[0038] The second evaporation tower, connected to the acidification tower via a pipeline, is used for evaporation and crystallization to obtain a solid-liquid mixture containing bicarbonate or a solid-liquid mixture containing urea and / or thiourea.

[0039] A sedimentation tank connected to a coagulation bath via a pipeline is used to react quicklime with the coagulation bath transferred from the coagulation bath to produce a suspension containing calcium carbonate or calcium sulfite.

[0040] According to a preferred embodiment of the present invention, the coagulation bath is in countercurrent contact with carbon dioxide or sulfur dioxide.

[0041] According to a preferred embodiment of the present invention, the regeneration system further includes: a second evaporation tower connected to the acidification tower via a pipeline, for evaporation and crystallization to obtain a solid-liquid mixture containing bicarbonate or a solid-liquid mixture containing urea and / or thiourea.

[0042] According to one embodiment of the present invention, the regeneration system further includes: a filtration device connected to a second evaporation tower via a pipeline, for separating a solid-liquid mixture containing bicarbonate or bisulfite or a solid-liquid mixture containing urea and / or thiourea, to obtain bicarbonate, bisulfite, urea and / or thiourea respectively.

[0043] According to one embodiment of the present invention, the filtration device is a centrifuge.

[0044] According to one embodiment of the present invention, the regeneration system further includes a drying device for drying the bicarbonate, bisulfite, urea and / or thiourea separated from the filtration device.

[0045] According to one embodiment of the present invention, the drying device is at least one of flash dryer, disc continuous dryer, fluidized bed dryer, vacuum rake dryer and rotary drum dryer.

[0046] According to one embodiment of the present invention, the drying device is a rotary drum dryer.

[0047] According to one embodiment of the present invention, the regeneration system further includes: a sedimentation tank connected to a coagulation bath via a pipeline, for reacting quicklime with XHCO3 or XHSO3 in the coagulation bath transferred from the coagulation bath to generate a suspension containing calcium carbonate or calcium sulfite.

[0048] According to one embodiment of the present invention, the regeneration system further includes: a filter tank connected in sequence to a sedimentation tank via a pipeline, for filtering the suspension in the sedimentation tank in sequence to obtain a solution containing XOH, MOH, urea and / or thiourea.

[0049] The present invention will be further illustrated by the following embodiments, but these embodiments in no way limit the scope of the present invention.

[0050] In the following embodiments, the coagulation bath to be regenerated is in such a state as Figure 1 Regeneration is performed in the regeneration system shown, which includes:

[0051] Coagulation bath 1 is used for the reaction of a strongly alkaline natural polymer solution with XHCO3 or XHSO3 to solidify and form a shape.

[0052] The acidification tower 2, which is connected to the coagulation bath 1 via a pipeline, is used to contact the coagulation bath after the reaction with carbon dioxide or sulfur dioxide.

[0053] The first evaporation tower 3, connected to the acidification tower 2 via a pipeline, is used to evaporate the water produced by the solidification reaction of natural polymer materials and the water brought in by the strongly alkaline natural polymer solution.

[0054] The second evaporation tower 4, connected to the acidification tower 2 via a pipeline, is used for evaporation and crystallization to obtain a solid-liquid mixture containing bicarbonate or a solid-liquid mixture containing urea and / or thiourea.

[0055] The filter device 5, connected to the second evaporator 4 via a pipeline, is used to separate solid-liquid mixtures containing bicarbonate or bisulfite, or solid-liquid mixtures containing urea, to obtain bicarbonate, bisulfite, urea, and / or thiourea, respectively.

[0056] Drying device 6 is used to dry the bicarbonate, bisulfite, urea and / or thiourea separated from the filtration device 5.

[0057] The filter tank 8, which is connected to the sedimentation tank 7 in sequence through pipes, is used to filter the suspension in the sedimentation tank in sequence to obtain a solution containing XOH, MOH, urea and / or thiourea.

[0058] In the following examples, the density, elongation, and average strength of the regenerated fibers were tested according to the bamboo pulp viscose filament standard (FZ-T 54012-2007).

[0059] Preparation Example 1

[0060] (i) Dissolve cellulose with a DP of 400 in a sodium hydroxide / urea / water system (mass ratio of 7:12:81) and degas to obtain a solution containing 7.5 wt% cellulose;

[0061] (ii) The solution in step (i) is wet-spun to obtain a fiber stream, which is then passed through a coagulation bath containing 14 wt% sodium bicarbonate and 2 wt% sodium carbonate (the temperature of the coagulation bath is 50°C) and subjected to 30% positive drawing to obtain nascent fibers and a coagulation bath to be regenerated (sodium bicarbonate content is 11 wt%, sodium carbonate content is 3.6 wt%, and urea content is 1.2 wt%).

[0062] (iii) The nascent fibers are sequentially washed with hot water at 65°C, oiled (with silicone oil), and dried at 110°C to obtain regenerated cellulose long fibers. The regenerated cellulose long fibers have a linear density of 133 dtex, a dry elongation of 12.1%, and an average strength of 1.7 cN / dtex.

[0063] Preparation Example 2

[0064] (i) Dissolve cellulose with a DP of 250 in a sodium hydroxide / urea / water system (mass ratio of 7:5:87) and degas to obtain a solution containing 8 wt% cellulose;

[0065] (ii) The solution in step (i) is wet-spun to obtain a fiber stream, which is then passed through a coagulation bath containing 15 wt% sodium bisulfite and 15 wt% sodium sulfite (the temperature of the coagulation bath is 20°C) and subjected to 30% positive drawing to obtain nascent fibers and a coagulation bath to be regenerated (sodium bisulfite content is 11 wt%, sodium sulfite content is 18 wt%, and urea content is 1.0 wt%).

[0066] (iii) The nascent fibers are sequentially washed with water at 65°C, oiled (with silicone oil), and dried at 130°C to obtain regenerated cellulose long fibers. The regenerated cellulose long fibers have a linear density of 133 dtex, a dry elongation of 15.6%, and an average strength of 1.9 cN / dtex.

[0067] Preparation Example 3

[0068] The method of Preparation Example 1 is the same, except that in step (ii), the composition of the coagulation bath is: 9 wt% sodium bicarbonate, 2 wt% sodium carbonate, and 20 wt% urea (the temperature of the coagulation bath is 20°C); the other conditions are the same as in Preparation Example 1.

[0069] The coagulation bath to be regenerated contains 7 wt% sodium bicarbonate, 3.6 wt% sodium carbonate, and 21.2 wt% urea.

[0070] The regenerated fiber has a linear density of 133 dtex, a dry elongation of 16%, and an average strength of 2.2 cN / dtex.

[0071] Preparation Example 4

[0072] (i) Chitin with a DP of 250 was dissolved in a potassium hydroxide / urea / water system (mass ratio of 12.7:5.7:81.6) and degassed to obtain a solution containing 7 wt% chitin;

[0073] (ii) The solution in step (i) is wet-spun to obtain a fiber stream. The fiber stream is passed through a coagulation bath (the temperature of the coagulation bath is 10°C) containing 20 wt% potassium bicarbonate, 15 wt% potassium carbonate and 20 wt% urea, and is subjected to 20% positive drawing to obtain nascent fibers and a coagulation bath to be regenerated (the content of potassium bicarbonate is 15.8 wt%, the content of potassium carbonate is 16.6 wt%, and the content of urea is 20.6 wt%).

[0074] (iii) The nascent fibers are sequentially washed with water at 65°C, oiled (with silicone oil), and dried at 130°C to obtain regenerated chitin fibers. The regenerated chitin fibers have a dry elongation of 12.3% and an average strength of 1.7 cN / dtex.

[0075] Example 1

[0076] (1) The coagulation bath to be regenerated in Preparation Example 1 was contacted countercurrently with carbon dioxide gas in an acidification tower at 25°C to obtain the first solution;

[0077] (2) The first solution is transferred to the first evaporation tower to evaporate water so that the sodium bicarbonate concentration is 14 wt%; in the first solution, the sodium bicarbonate concentration is 14 wt%, the sodium carbonate concentration is 2 wt%, and the urea concentration is 1.4 wt%.

[0078] (3) The first solution is circulated into the coagulation bath and spun according to the method of Preparation Example 1.

[0079] After repeating the above method 10 times, the prepared regenerated fiber was completely solidified, and its properties were basically the same as those of the regenerated fiber prepared in Preparation Example 1, with a linear density of 133 dtex, a dry elongation of 15.6%, and an average strength of 1.8 cN / dtex.

[0080] Example 2

[0081] (1) The coagulation bath to be regenerated in Preparation Example 2 was contacted countercurrently with sulfur dioxide gas in an acidification tower at 25°C to obtain the first solution;

[0082] (2) The first solution is transferred to the first evaporation tower to evaporate water so that the sodium bisulfite concentration is 15 wt%; in the first solution, the sodium bisulfite concentration is 15 wt%, the sodium sulfite concentration is 15 wt%, and the urea concentration is 1.2 wt%.

[0083] (3) The first solution is circulated into the coagulation bath and spun according to the method of Preparation Example 2.

[0084] After 20 cycles of the above method, the prepared regenerated fiber is completely solidified. The regenerated fiber has a linear density of 133 dtex, a dry elongation of 14%, and an average strength of 2.2 cN / dtex.

[0085] Example 3

[0086] (1) The coagulation bath to be regenerated in Preparation Example 3 was contacted countercurrently with carbon dioxide gas in an acidification tower at 25°C to obtain the first solution;

[0087] (2) The first solution is transferred to the first evaporation tower to evaporate water so that the sodium bicarbonate concentration is 9 wt%; in the first solution, the sodium bicarbonate concentration is 9 wt%, the sodium carbonate concentration is 2 wt%, and the urea concentration is 23.5 wt%.

[0088] (3) The first solution is circulated into the coagulation bath and spun according to the method of Preparation Example 1.

[0089] After repeating the above method 10 times, the prepared regenerated fiber is completely solidified. The regenerated fiber has a linear density of 133 dtex, a dry elongation of 15%, and an average strength of 2.5 cN / dtex.

[0090] Example 4

[0091] (1) The coagulation bath to be regenerated in Example 4 was contacted countercurrently with carbon dioxide gas in an acidification tower at 25°C to obtain the first solution;

[0092] (2) The first solution is transferred to the first evaporation tower to evaporate water so that the potassium bicarbonate concentration is 20 wt%; in the first solution, the potassium bicarbonate concentration is 20 wt%, the potassium carbonate concentration is 15 wt%, and the urea concentration is 23 wt%.

[0093] (3) The first solution is circulated into the coagulation bath and spun according to the method of Preparation Example 1.

[0094] After 50 cycles of the above method, the prepared regenerated fiber is completely solidified, and the dry elongation of the regenerated chitin fiber is 17%, with an average strength of 1.8 cN / dtex.

[0095] (4) After the coagulation bath (urea concentration of 50wt%) is recycled 50 times, the 80% mass fraction coagulation bath is contacted countercurrently with carbon dioxide gas in the acidification tower at 25°C to acidify potassium bicarbonate. After acidification, it is passed into the second evaporation tower and evaporated at 45°C to crystallize and precipitate potassium bicarbonate solid. After separating the mother liquor, it is evaporated and crystallized at 60°C to precipitate urea. After separating the mother liquor, urea is obtained.

[0096] Quicklime was added to the remaining 20% ​​coagulation bath to react with the solution, and the mixture was filtered to obtain a solution containing potassium hydroxide and urea.

[0097] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for regenerating a coagulation bath after spinning an aqueous solution containing natural polymers, characterized in that, The coagulation bath contains XHCO3 and M2CO3, where X and M are Na; the mass concentration of XHCO3 is 0.1-25 wt%, and the mass concentration of M2CO3 is 3-35 wt%. The coagulation bath also contains urea and / or thiourea, with a mass concentration of 0.4-40 wt%. The regeneration method includes: (1) The coagulation bath is brought into contact with carbon dioxide to obtain a first solution; (2) Evaporate the water in the first solution so that the mass concentration of XHCO3 in the first solution is 10-20wt%, the mass concentration of M2CO3 is 5-20wt%, and the mass concentration of urea and / or thiourea is 20-40wt%, to obtain a regenerated coagulation bath; When the concentration of urea and / or thiourea in the regeneration coagulation bath is greater than 40 wt%, evaporation and crystallization at 40-50 °C yields bicarbonate; further evaporation and crystallization at 55-80 °C yields urea and / or thiourea. The aqueous solution containing natural polymers contains metal hydroxides and additives, the additives being selected from urea and / or thiourea; the natural polymers are cellulose and / or chitosan.

2. The regeneration method according to claim 1, wherein, The regenerated coagulation bath has a XHCO3 mass concentration of 5-15 wt% and an M2CO3 mass concentration of 5-20 wt%.

3. The regeneration method according to claim 1, wherein, In step (1), the contact conditions include: contact temperature 20-30℃.

4. The regeneration method according to claim 1 or 2, wherein, The regeneration method is performed in a regeneration system, which includes: Coagulation bath, used for coagulating and molding strongly alkaline natural polymer solutions; An acidification tower connected to a coagulation bath via a pipeline is used for contacting the coagulation bath with carbon dioxide. The first evaporation tower, connected to the acidification tower via a pipeline, is used to evaporate water generated from the solidification of an aqueous solution containing natural polymers and / or water introduced by a strongly alkaline natural polymer solution. The regeneration method includes: (i) The coagulation bath in the coagulation bath tank is introduced into the acidification tower, and the coagulation bath is contacted with carbon dioxide in the acidification tower to obtain a first solution; (ii) The first solution is passed into an evaporation tower and the water in the first solution is evaporated to a mass concentration of 10-20 wt% for XHCO3, 5-20 wt% for M2CO3, and 20-40 wt% for urea and / or thiourea, to obtain a regenerated coagulation bath. When the concentration of urea and / or thiourea in the regeneration coagulation bath is greater than 40 wt%, evaporation and crystallization at 40-50 °C yields bicarbonate; further evaporation and crystallization at 55-80 °C yields urea and / or thiourea.

5. The regeneration method according to claim 4, wherein, The regeneration system also includes: The second evaporation tower, connected to the acidification tower via a pipeline, is used for evaporation and crystallization to obtain a solid-liquid mixture containing bicarbonate or a solid-liquid mixture containing urea and / or thiourea. A sedimentation tank connected to a coagulation bath via a pipeline is used to react quicklime with the coagulation bath transferred from the coagulation bath to produce a suspension containing calcium carbonate.

6. The regeneration method according to claim 5, wherein, The coagulation bath comes into countercurrent contact with carbon dioxide.

Images