A deodorization system and method for the production process of water-soluble fibers

Abstract

This invention relates to the field of organic solvent separation technology, specifically disclosing a deodorization system and method in the production process of water-soluble fibers. The treatment system includes a degassing tower and a purification tower connected by pipelines; a first condenser and a second condenser are sequentially connected to the top of the degassing tower, and a third condenser is located at the top of the purification tower. The treatment method using the above-mentioned system includes three treatment stages: stepwise feeding, extraction separation, and distillation purification. The technical solution provided by this invention can solve the technical problem in the production of water-soluble fibers where the volatilization of odorous substances such as thiols, sulfides, and dimethyl disulfide dissolved in the circulating methanol solvent causes foul odors at the work site, seriously affecting the physical and mental health of employees and the surrounding environment.

Description

Technical Field

[0001] This invention relates to the field of organic solvent separation technology, specifically to a deodorization system and method in the production process of water-soluble fibers. Background Technology

[0002] Water-soluble fibers are obtained from polyvinyl alcohol (PVA) through a dry-wet gel spinning process. PVA is dissolved in a mixed solvent of dimethyl sulfoxide (DMSO) and water, and the raw material is obtained by filtration and degassing. The desired water-soluble fibers are then obtained through subsequent processes.

[0003] In the production process, dimethyl sulfoxide (DMSO) is used as the main solvent for dissolving PVA. It easily diffuses into the methanol (MeOH) coagulation and extraction baths, resulting in a large amount of spinning wastewater containing DMSO, MeOH, and H₂O. This wastewater is currently recycled through separation. The current process for separating spinning wastewater is as follows: the wastewater from spinning enters a methanol distillation tower for atmospheric distillation. The methanol at the top of the tower is condensed by a cooler and then recycled into a storage tank. The bottom liquid of the methanol distillation tower is sent to a distillation kettle for vacuum deslagging, and the vapor phase enters a vacuum distillation tower to separate and purify dimethyl sulfoxide and methanol for recycling.

[0004] However, the recycled methanol separated by the current distillation process has a strong odor. This is because DMSO easily decomposes to produce odorous light components such as methanethiol, dimethyl sulfide, and dimethyl disulfide. These light components have boiling points close to methanol and are easily included in the recycled methanol solution during the distillation process. This results in the recycled methanol solution being odorous and impure. Furthermore, the odorous substances such as thiols, sulfides, and dimethyl disulfide dissolved in the recycled methanol solvent during use volatilize onto the site, causing a foul smell that seriously affects the physical and mental health of employees and the surrounding environment of the plant. Summary of the Invention

[0005] This invention provides a deodorization system and method for the production process of water-soluble fibers, which is used to separate odorous substances such as methanethiol, dimethyl sulfide, and dimethyl disulfide dissolved in circulating methanol during the production of water-soluble fibers, thereby achieving odorless and environmentally friendly operation of the equipment.

[0006] This invention provides the following technical solution:

[0007] A deodorization system for the production process of water-soluble fibers includes a degassing tower and a purification tower connected by pipelines; the degassing tower is provided with a methanol inlet and an extractant inlet; a first condenser and a second condenser are sequentially connected to the top of the degassing tower, and a third condenser is provided at the top of the purification tower.

[0008] Furthermore, the degassing tower is equipped with a methanol feed pump and an extractant feed pump in the middle.

[0009] Furthermore, the first condenser is provided with a reflux pipe H1, the inlet of which is connected to the first condenser pipeline, and the outlet of which is connected to the upper part of the degassing tower; the outlet of the second condenser is connected to an incinerator.

[0010] In this scheme, the first condenser is used to induce a phase change in the high-boiling-point substances in the mixed components, thereby separating them from low-boiling-point substances such as methanethiol and dimethyl sulfide. The high-boiling-point substances then flow back to the degassing tower. The second condenser is used to condense the low-boiling-point light components, facilitating their subsequent incineration in the incinerator.

[0011] Furthermore, a first reboiler is connected to the bottom of the degassing tower, and a reflux pipe H2 is provided between the first reboiler and the degassing tower. The inlet of the reflux pipe H2 is connected to the first reboiler, and the outlet is connected to the bottom of the degassing tower. The first reboiler is connected to the purification tower.

[0012] In this scheme, the extracted material is reboiled and vaporized in the first reboiler and then returned to the bottom of the degassing tower to provide energy for the distillation and separation of the degassing tower.

[0013] Furthermore, the third condenser is provided with a reflux pipe H3 and a distillation pipe G10. The inlet of the reflux pipe H3 is connected to the third condenser pipeline, and the outlet of the reflux pipe H3 is connected to the upper part of the purification tower.

[0014] In this scheme, the third condenser is used to condense and separate the purified methanol after distillation. Most of the methanol flows out through the distillation pipe after condensation, and a small portion of the methanol is returned to the purification tower through the reflux pipe H3 for further distillation and purification.

[0015] Furthermore, a second reboiler is connected to the bottom of the purification tower, and a reflux pipe H4 is provided between the second reboiler and the purification tower. The inlet of the reflux pipe H4 is connected to the second reboiler, and the outlet is connected to the bottom of the purification tower. The second reboiler is also provided with a distillation pipe.

[0016] In this scheme, the mixture after distillation and purification is heated and vaporized in the second reboiler and then returned to the purification tower to provide energy for the distillation and purification of the purification tower.

[0017] This solution also provides a deodorization method for the water-soluble fiber production process, employing the aforementioned deodorization system for the water-soluble fiber production process, including the following steps:

[0018] S1: In the pre-feeding stage, 30% of the extractant is first pumped into the degassing tower, and after the extractant is heated, it is pumped into the circulating methanol liquid.

[0019] S2: During the extraction and separation stage, when reflux appears at the top of the column, the remaining extractant is continuously pumped into the degassing column; the extractant extracts the methanol in the circulating methanol liquid to form aqueous methanol, and the odorous substances in the circulating methanol liquid form separation vapor.

[0020] S3: Reflux stage, the separated steam rises and flows into the top of the degassing tower, then passes through the first condenser to form odorous vapor and methanol reflux liquid. The odorous vapor then passes through the second condenser to form condensate liquid, which is then burned. The methanol reflux liquid flows back into the degassing tower through reflux pipe H1.

[0021] S4: In the distillation and purification stage, aqueous methanol is heated in the purification tower to form vapor, which is then condensed to form methanol distillate.

[0022] Furthermore, the ratio of the extractant to recycled methanol is 1 to 3:1.

[0023] In this scheme, the ratio of the extractant to the circulating methanol can increase the difference in volatility among the components in the circulating methanol solution, making it easier to distill off the azeotrope formed by water and malodorous impurities such as thiols and thioethers.

[0024] Furthermore, the reflux ratio at the top of the degassing tower is 10-30, and the temperature at the bottom of the tower is 80-90℃; the reflux ratio at the top of the purification tower is 1-3, and the temperature at the bottom of the tower is 110-120℃.

[0025] In this scheme, controlling the reflux ratio at the top of the degassing tower at 10-30 can ensure the separation effect of methanol and light components. The bottom temperature of the tower is 80-90℃, which can fully heat and vaporize the circulating methanol and light components for separation. This temperature is lower than the boiling point of high-boiling-point light components such as dimethyl disulfide and azo dyes, so the preliminary separation of high-boiling-point light components can also be achieved.

[0026] The purification column has a relatively low reflux ratio at the top, thus reducing costs. The high temperature at the bottom of the column allows for effective vaporization of the extractant and methanol, facilitating subsequent separation.

[0027] Furthermore, the temperature of the first condenser is 50-60°C, the temperature of the second condenser is 15-20°C, and the cooling medium is RW12 circulating water; the temperature of the third condenser is 50-60°C, and the cooling medium is 33°C circulating water.

[0028] In this scheme, the temperature of the first condenser is below the boiling point of methanol but above the boiling point of substances such as dimethyl sulfide, thus enabling the separation of methanol from light components such as dimethyl sulfide. The second condenser has a lower temperature and is used to cause substances such as dimethyl sulfide to undergo phase change, condense, and then incinerate. The temperature of the third condenser is above the boiling point of methanol but below the boiling point of the extractant, thus separating the extractant from methanol. The purified methanol after distillation can reach a purity of 99.9%.

[0029] The beneficial effects of this invention are:

[0030] 1. The principle of this application is simple, using desalinated water as the extractant. The raw material is inexpensive and readily available, making it suitable for large-scale industrial production. Furthermore, using desalinated water as the extractant does not introduce new impurities, ensuring that the purified methanol can still be used.

[0031] 2. In this application, the feed is added in stages during the pre-feeding stage. A portion of the extractant is first pumped into the degassing tower, creating a hot steam atmosphere within the tower. This allows the subsequently pumped circulating methanol to begin its heated vaporization and extraction distillation, reducing the loss of circulating methanol. Simultaneously, the extractant pumped in first, once vaporized, can directly react with the subsequently pumped circulating methanol, reducing reaction time.

[0032] 3. The effect of this application is significant. The odor removal rate of the circulating methanol treated by this application can reach 100%, and the purity of the circulating methanol after purification can reach 99.9%.

[0033] 4. This application further incinerates the separated odorous gases for further treatment, thereby reducing environmental pollution. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the deodorization system in the production process of water-soluble fiber according to the present invention. Detailed Implementation

[0035] The following detailed description illustrates the specific implementation method:

[0036] The markings in the accompanying drawings include: degassing tower 1, purification tower 2, first condenser 3, second condenser 4, incinerator 5, first reboiler 6, third condenser 7, second reboiler 8, extractant pump 9, and circulating methanol pump 10.

[0037] Extractant feed pipe G1, circulating methanol feed pipe G2, connecting pipe G3, connecting pipe G4, connecting pipe G5, connecting pipe G6, connecting pipe G7, connecting pipe G8, connecting pipe G9, distillation pipe G10, connecting pipe G11, distillation pipe G12, reflux pipe H1, reflux pipe H2, reflux pipe H3, reflux pipe H4.

[0038] Example

[0039] like Figure 1 As shown, a deodorization system in the production process of water-soluble fiber includes a degassing tower 1 and a purification tower 2. In this embodiment, both the degassing tower 1 and the purification tower 2 are packed towers.

[0040] The top of the degassing tower 1 is connected to a first condenser 3 and a second condenser 4 via connecting pipes G3 and G4. The first condenser 3 has a reflux pipe H1, which connects to the upper part of the degassing tower 1. The second condenser 4 is connected to the incinerator 5, and the condensate can be fed into the incinerator 5 for incineration. A methanol-water mixture condensate containing high concentrations of odorous components such as mercaptans, sulfides, and dimethyl disulfide is pumped to the incinerator 5 for treatment. The temperature inside the incinerator 5 is controlled at 750-850℃. The flue gas after combustion is transported to the desulfurization and denitrification unit via connecting pipe G6 for emission after meeting standards. The desulfurization and denitrification unit is located in... Figure 1 Not shown in the image.

[0041] The middle part of the degassing tower 1 is equipped with an extractant feed pipe G1 and a circulating methanol feed pipe G2. Both feed pipes G1 and G2 are equipped with corresponding extractant pumps 9 and circulating methanol pumps 10. The connection port between feed pipe G1 and degassing tower 1 is higher than that of feed pipe G2.

[0042] The bottom of the degassing tower 1 is provided with a connecting pipe G7, which is connected to a first reboiler 6. The first reboiler 6 is provided with a reflux pipe H2, which is connected to the lower part of the degassing tower 1.

[0043] The first reboiler 6 is connected to the purification tower 2 via connecting pipe G8. The top of the purification tower 2 is connected to the third condenser 7 via connecting pipe G9. The third condenser 7 is equipped with a reflux pipe H3 and a distillation pipe G10. The reflux pipe H3 is connected to the upper part of the purification tower 2.

[0044] The bottom of the purification tower 2 is provided with a connecting pipe G11, which is connected to a second reboiler 8. The second reboiler 8 is provided with a reflux pipe H4 and a distillation pipe G12. The reflux pipe H4 is connected to the lower part of the degassing tower 1.

[0045] This embodiment also describes a deodorization method in the production process of water-soluble fibers, which uses the above-mentioned deodorization system in the production process of water-soluble fibers and includes the following steps:

[0046] S1: In the pre-feeding stage, 30% of the extractant is first pumped into the degassing tower 1, and after the extractant is heated, circulating methanol liquid is pumped in.

[0047] Specifically, the device is started, and the extractant pump 9 pumps 30% extractant into the degassing tower 1, allowing the extractant to first form a steam circulation within the tower. In this embodiment, the extractant is demineralized water. When the temperature at the bottom of the tower rises to 84°C, the circulating methanol pump 10 is started, and the circulating methanol to be separated is pumped into the tower. The extractant pumped in first can extract the newly introduced circulating methanol, accelerating the reaction rate.

[0048] S2: During the extraction and separation stage, when reflux appears at the top of the tower, the remaining extractant is continuously pumped into degassing tower 1; the extractant extracts methanol from the circulating methanol liquid to form aqueous methanol, and the odorous substances in the circulating methanol liquid form separation vapor.

[0049] Specifically, when reflux liquid appears in the reflux pipe H1, the extractant pump 9 is turned on again to continuously and slowly introduce the extractant into the degassing tower 1, maintaining the ratio of extractant to methanol in the tower at 1.5. This ratio can increase the difference in volatility between the components in the circulating methanol solution, making it easier for water and malodorous impurities such as thiols and sulfides to form azeotropes and evaporate.

[0050] S3: Reflux stage, the separated steam rises and flows into the top of the degassing tower 1, and then passes through the first condenser 3 to form odorous vapor and methanol reflux liquid. The odorous vapor then passes through the second condenser 4 to form condensate liquid, which is then burned. The methanol reflux liquid flows back into the degassing tower 1 through the reflux pipe H1.

[0051] Specifically, under the action of the extractant, odorous substances (methanethiol, dimethyl sulfide, dimethyl disulfide, etc.) in the circulating methanol are separated from the circulating methanol after forming vapor. This vapor rises with the mixed vapor and enters the connecting pipe G3, where it encounters the first condenser 3. The condensation temperature of the first condenser 3 is 50°C. The extractant and methanol in the mixed vapor undergo a phase change and flow back to the degassing tower 1 through the reflux pipe H1, maintaining a reflux ratio of 10. The odorous substances then enter the second condenser 4 through the connecting pipe G4. The condensation temperature of the second condenser 4 is 15°C. Here, the odorous substances undergo a phase change, forming condensate that flows into the connecting pipe G5 and is incinerated in the incinerator 5 before being discharged.

[0052] S4: In the distillation and purification stage, aqueous methanol is heated in purification tower 2 to form vapor, which is then condensed to form methanol distillate.

[0053] Specifically, the extractive distillate after extractive distillation flows into connecting pipe G7, is heated and vaporized in the first reboiler 6, and then returns to the bottom of degassing tower 1 via reflux pipe H2. This further removes odorous substances and provides energy for the distillation separation in degassing tower 1. The reboiling temperature of the first reboiler 6 is 60℃. At this temperature, methanol and extractant will not be reboiled, so they flow into purification tower 2 via connecting pipe G8. At this time, the bottom temperature of purification tower 2 is 115℃, which allows methanol and extractant to quickly boil and vaporize into steam. The steam enters the third condenser 7 via connecting pipe G9. The condensation temperature of the third condenser 7 is 50℃. The pre-cooled extractant forms condensate, which flows back to purification tower 2 via reflux pipe H3, maintaining a reflux ratio of 1.5. Methanol is distilled out via distillation pipe G10.

[0054] The condensate and unvaporized methanol refluxed into purification tower 2 flow into connecting pipe G11 at the bottom of purification tower 2. After being heated and vaporized by the second reboiler 8, they flow back to the bottom of purification tower 2 through reflux pipe H4, improving the methanol recovery efficiency and providing energy for purification and separation in purification tower 2. The reboiling temperature of the second reboiler 8 is 90℃, which will not cause the extractant to vaporize. The extractant is discharged through distillation pipe 12.

[0055] The recycled methanol, after the above steps, was sampled and analyzed. The results are shown in Table 1 below:

[0056] Table 1. Experimental Data of Cyclic Methanol Extraction Distillation in Example 1

[0057] Methanol % DMSO% Methanethiol % Dimethyl sulfide % dimethyl disulfide azo % acetone% Acetaldehyde % Circulating methanol 96.268 0.2 0.031 0.18 0.63 0.43 0.017 0.043 1h tower pot 25.30 0.89 0 0 0 0 0 0.022 2h tower kettle 28.92 0.437 0 0 0 0 0 0 2h tower top 9.56 4.122 0.289 0.590 3.789 0.66 0.2 0.039

[0058] As shown in Table 1, demineralized water extraction and distillation can remove odorous substances such as dimethyl sulfide, methanethiol, dimethyl disulfide, acetone, and acetaldehyde from recycled methanol, achieving a 100% removal rate. The odorous substances accumulate at the top of the distillation column and are safely discharged after condensation and incineration, without polluting the environment. The methanol collected from the top of the purification column has a purity of up to 99.9%.

[0059] Example 2

[0060] The difference between this embodiment and Embodiment 1 is that the ratio of extractant to circulating methanol is 2, the reflux ratio at the top of Degassing Tower 1 is 20, the reflux ratio at the top of Purification Tower is 2, the temperature of the first condenser is 55°C, and the temperature of the third condenser is 55°C.

[0061] Example 3

[0062] The difference between this embodiment and Embodiment 1 is that the ratio of extractant to circulating methanol is 2.5, the reflux ratio at the top of Degassing Tower 1 is 30, the reflux ratio at the top of Purification Tower is 2.5, the temperature of the first condenser is 60°C, and the temperature of the third condenser is 60°C.

[0063] Comparative Example 1

[0064] The difference between this comparative example and Example 1 is that the S1 pre-feeding stage is not used. The specific steps are as follows: first, start the device, then start the extractant pump 9 to pump in the extractant, and finally start the circulating methanol pump 10 to pump in the circulating methanol.

[0065] Comparative Example 2

[0066] The difference between this comparative example and Example 2 is that the S1 pre-feeding stage is not used; the other steps are the same as described above.

[0067] Comparative Example 3

[0068] The difference between this comparative example and Example 3 is that the S1 pre-feeding stage is not used; the other steps are the same as described above.

[0069] The above comparative experiments showed that increasing the ratio of extractant to recycled methanol reduced the content of odorous substances such as thiols and sulfides in the bottom of the degassing tower. However, increasing the ratio of extractant to recycled methanol increased the distillation energy consumption of the methanol purification tower. The comparative experiments demonstrated that using S1 prefeeding was more effective in removing odorous substances from the recycled methanol. The comparison results are shown in Table 2.

[0070] Table 2

[0071] methanol content at the top of the degassing tower / % Methanol content in the bottom of the degassing tower / % Purity of extracted methanol / % Example 1 9.56 38.56 99.9 Example 2 6.32 28.92 99.95 Example 3 6.15 23.14 99.98 Comparative Example 1 10.75 36.78 99.89 Comparative Example 2 7.56 28.12 99.9 Comparative Example 3 6.28 28.92 99.9

[0072] The above are merely embodiments of the present invention, and the invention is not limited to the fields covered by these embodiments. Commonly known structures and characteristics in the solutions are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the structure of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A deodorization method in the production process of water-soluble fibers, characterized in that, A deodorization system for the production process of water-soluble fiber is adopted. The system includes a degassing tower (1) and a purification tower (2) connected by pipelines. The degassing tower (1) is provided with a methanol inlet and an extractant inlet. The top of the degassing tower (1) is connected to a first condenser (3) and a second condenser (4) in sequence, and the top of the purification tower (2) is provided with a third condenser (7). The middle part of the degassing tower (1) is provided with a methanol feed pump (9) and an extractant feed pump (10). The first condenser (3) is provided with a reflux pipe (H1). The inlet of the reflux pipe (H1) is connected to the pipeline of the first condenser (3), and the outlet of the reflux pipe (H1) is connected to the upper part of the degassing tower (1). The outlet of the second condenser (4) is connected to an incinerator (5). Includes the following steps: S1: In the pre-feeding stage, 30% of the extractant is first pumped into the degassing tower (1), and after the extractant is heated, it is pumped into the circulating methanol liquid; S2: During the extraction and separation stage, when reflux appears at the top of the tower, the remaining extractant is continuously pumped into the degassing tower (1); the extractant extracts the methanol in the circulating methanol liquid to form aqueous methanol, and the odorous substances in the circulating methanol liquid form separation vapor. S3: In the reflux stage, the separated steam rises and flows into the top of the degassing tower (1) and then passes through the first condenser (3) to form odorous vapor and methanol reflux liquid. The odorous vapor then passes through the second condenser (4) to form condensate and is then burned. The methanol reflux liquid flows back into the degassing tower (1) through the reflux pipe (H1). S4: In the distillation and purification stage, the aqueous methanol is heated in the purification tower (2) to form steam, which is then condensed to form methanol distillate.

2. The deodorization method in the production process of water-soluble fibers according to claim 1, characterized in that: The bottom of the degassing tower (1) is connected to a first reboiler (6), and a reflux pipe (H2) is provided between the first reboiler (6) and the degassing tower (1). The inlet of the reflux pipe (H2) is connected to the first reboiler (6), and the outlet is connected to the bottom of the degassing tower (1). The first reboiler (6) is connected to the purification tower (2).

3. The deodorization method in the production process of water-soluble fiber according to claim 2, characterized in that: The third condenser (7) is equipped with a reflux pipe (H3) and a distillation pipe (G10). The inlet of the reflux pipe (H3) is connected to the pipeline of the third condenser (7), and the outlet of the reflux pipe (H3) is connected to the upper part of the purification tower (2).

4. The deodorization method in the production process of water-soluble fiber according to claim 3, characterized in that: The bottom of the purification tower (2) is connected to a second reboiler (8), and a reflux pipe (H4) is provided between the second reboiler (8) and the purification tower (2). The inlet of the reflux pipe (H4) is connected to the second reboiler (8), and the outlet is connected to the bottom of the purification tower (2). The second reboiler (8) is also provided with a distillation pipe (G12).

5. The deodorization method in the production process of water-soluble fiber according to claim 4, characterized in that: In S1, the overall addition ratio of the extractant to the circulating methanol is 1 to 3:

1.

6. The deodorization method in the production process of water-soluble fiber according to claim 5, characterized in that: The degassing tower (1) has a top reflux ratio of 10 to 30 and a bottom temperature of 80 to 90°C; the purification tower (2) has a reflux ratio of 1 to 3 and a bottom temperature of 110 to 120°C.

7. The deodorization method in the production process of water-soluble fiber according to claim 6, characterized in that: The temperature of the first condenser is 50-60℃, the temperature of the second condenser is 15-20℃, and the cooling medium is 12℃ circulating water; the temperature of the third condenser is 50-60℃, and the cooling medium is 33℃ circulating water.

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