Recycling method of acrylonitrile monomer in carbon fiber production

Abstract

The invention relates to a method for recycling acrylonitrile monomers in carbon fiber production, which solves the technical problem of high acrylonitrile unit consumption, uses an acrylonitrile monomer recycling device, and comprises the following steps: fresh acrylonitrile monomers enter a polymerization reaction kettle for reaction; unreacted acrylonitrile monomers are discharged from the polymerization reaction kettle and then enter a monomer removal tower, the unreacted monomers are removed from the polymerization liquid through the monomer removal tower and are absorbed by using dimethyl sulfoxide to obtain KM liquid, part of the KM liquid returns to the polymerization reaction kettle to participate in the polymerization reaction again, part of the KM liquid is conveyed to the monomer rectifying tower to be purified, and the purified KM liquid is obtained. And returning to the polymerization reaction kettle to participate in the polymerization reaction again so as to realize that all the non-polyacrylonitrile monomers are recycled. The method can be widely applied to carbon fiber production.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of high polymer chemical industry, and particularly relates to a recycling method of acrylonitrile monomer in carbon fiber production. BACKGROUND

[0002] In the production of carbon fiber precursor, polymerization reaction is an important part. In the production of polyacrylonitrile (PAN) based carbon fiber, acrylonitrile (AN) is used as the polymerization monomer, and dimethyl sulfoxide (DMSO) is used as the solvent. In the production process of carbon fiber polymerization stock solution, the monomer conversion rate is 87% to 90%, and the unreacted monomer is removed in the polymerization stock solution post-processing monomer removal process. The treatment after the removal of the unreacted monomer has a great impact on monomer consumption. Under normal circumstances, without recycling this part of the monomer, the acrylonitrile consumption reaches 1.12 t / t of polymerization dry basis.

[0003] In the current production process, about 10% of the unreacted monomer is removed from the polymerization solution by the monomer removal tower, is absorbed by dimethyl sulfoxide, and a material with a monomer concentration of 4% to 6% is obtained, which is referred to as KM liquid. By recycling the KM liquid, the acrylonitrile consumption can reach 1.06 t / t of polymerization dry basis. However, the RM liquid process control is unstable, the purity cannot reach more than 97%, and after use, it is easy to cause product quality fluctuations, so the recycling proportion is limited. Acrylonitrile consumption accounts for 50% of the energy and material consumption cost of the polymerization solution dry basis, and the acrylonitrile monomer consumption has not yet reached <1.0 t / t of polymerization solution dry basis.

[0004] The Chinese patent application with the publication number CN116063203A discloses a method for improving the recycling rate of acrylonitrile monomer in carbon fiber production, which improves the recovery rate of acrylonitrile monomer by washing tower absorption to achieve the purpose of reducing the loss of acrylonitrile monomer. However, the above method has the following problems: the acrylonitrile recovery rate is affected by the process conditions, the high proportion of KM input into the polymerization reaction will affect the product conversion rate and performance indicators, the method of absorbing acrylonitrile by washing tower improves the acrylonitrile recovery rate in waste gas, but the acrylonitrile in the KM liquid which is not recycled is still treated as hazardous waste, causing the increase of acrylonitrile consumption. SUMMARY

[0005] The present application provides a recycling method of acrylonitrile monomer in carbon fiber production to solve the technical problem of high acrylonitrile consumption.

[0006] Therefore, this invention provides a method for recycling acrylonitrile monomer in carbon fiber production. The method utilizes an acrylonitrile monomer recycling device, which includes a polymerization reactor, a monomer removal tower, and a pipeline connecting the polymerization reactor and the monomer removal tower. It also includes a monomer distillation tower, a monomer distillation tower condenser, and a monomer distillation tower separator. One end of the monomer distillation tower is connected to the monomer removal tower via a pipeline, and the other end is connected to the monomer distillation tower condenser and the monomer distillation tower separator via a pipeline. A feed loop is formed between the polymerization reactor and the monomer removal tower. Another feed loop is formed by the polymerization reactor, the monomer removal tower, and the monomer tower. The monomer distillation tower condenser condenses and liquefies the vapor at the top of the monomer distillation tower. The monomer distillation tower separator separates the condensed liquid from the monomer distillation tower condenser into distinct layers. The method includes the following steps: fresh acrylonitrile monomers are introduced into a polymerization reactor for reaction. Unreacted acrylonitrile monomers are discharged from the polymerization reactor and enter a monomer removal tower. In the monomer removal tower, unreacted monomers are removed from the polymerization liquid and absorbed by dimethyl sulfoxide to obtain KM liquid. 50% to 60% of the mass of KM liquid is returned to the polymerization reactor to participate in the polymerization reaction again. 40% to 50% of the mass of KM liquid is sent to a monomer distillation tower for purification treatment and then returned to the polymerization reactor to participate in the polymerization reaction again, thereby realizing the complete recovery and reuse of unreacted acrylonitrile monomers.

[0007] Preferably, the KM liquid is received through the monomer distillation column, purified by distillation, and stably separated into layers at a low temperature of 5-15℃ to obtain an RM liquid with an acrylonitrile monomer mass concentration ≥97%.

[0008] Preferably, in the polymerization reactor, the mass ratio of KM liquid is 22%–25%, the mass ratio of RM liquid is 1.0%–1.5%, the mass ratio of fresh acrylonitrile monomer is 16%–20%, the mass ratio of other auxiliaries is 1%–2%, and the remainder is dimethyl sulfoxide. Increasing the amount of KM and RM liquids tends to decrease the conversion rate and viscosity of the product. Increasing the amount of fresh acrylonitrile monomer can improve the polymer yield, but excessively high monomer concentration may lead to increased chain termination reactions during chain growth, resulting in a decrease in molecular weight and viscosity. Too low a concentration may result in a slow reaction rate. Other auxiliaries are mainly the molecular regulator thiol and the initiator azobisisobutyronitrile (AIBN). Appropriate amounts of auxiliaries can optimize the polymerization process, regulate molecular weight distribution, and stabilize product properties. However, both excessive and insufficient amounts may adversely affect viscosity. Excessive amounts may lead to excessive chain transfer reactions, a decrease in molecular weight, and a decrease in viscosity; insufficient amounts may fail to effectively regulate the reaction process, resulting in large viscosity fluctuations.

[0009] Preferably, the auxiliary agent includes the initiator azobisisobutyronitrile and the molecular weight regulator thiol, with a mass ratio of 1:(0.015-0.03).

[0010] Beneficial effects of this invention:

[0011] This invention can reduce acrylonitrile monomer consumption in carbon fiber production, with a recovery rate of up to 100%. It breaks through the previous limitation of acrylonitrile monomer consumption from 1.06 t / t dry basis of polymerization liquor to 1.0 t / t dry basis of polymerization liquor, thereby improving raw material utilization and reducing production costs. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the acrylonitrile monomer recycling device in this invention;

[0013] Explanation of symbols in the attached diagram: 1. Fresh monomer feed; 2. Fresh monomer feed filter; 3. Fresh monomer feed mass flow meter; 4. Fresh monomer feed control valve; 5. Polymerization reactor; 6. Demonomer feed pump; 7. Demonomer reboiler; 8. Demonomer tower; 9. Demonomer condenser; 10. Demonomer condensate tank; 11. KM pump; 12. KM feed filter; 13. KM feed mass flow meter; 14. KM feed control valve; 15. Monomer distillation column feed control valve; 16. Monomer distillation column; 17. Monomer distillation column condenser; 18. Monomer distillation column separator; 19. RM buffer tank; 20. RM pump; 21. RM feed filter; 22. RM feed mass flow meter; 23. RM feed control valve. Detailed Implementation

[0014] The present invention will be further described below with reference to the accompanying drawings and embodiments, so that those skilled in the art can easily implement the present invention.

[0015] like Figure 1 As shown, the acrylonitrile monomer recovery and utilization device of the present invention includes a fresh monomer feed filter 2, a fresh monomer feed mass flow meter 3, a fresh monomer feed control valve 4, a polymerization reactor 5, a monomer removal feed pump 6, a monomer removal reboiler 7, a monomer removal tower 8, a monomer removal condenser 9, a monomer removal condensate tank 10, a KM pump 11, a KM feed filter 12, a KM feed mass flow meter 13, a KM feed control valve 14, a monomer distillation tower feed control valve 15, a monomer distillation tower 16, a monomer distillation tower condenser 17, a monomer distillation tower separator 18, an RM buffer tank 19, an RM pump 20, an RM feed filter 21, an RM feed mass flow meter 22, and an RM feed control valve 23. The above components are connected by pipelines.

[0016] The fresh monomer feed filter 2, fresh monomer feed mass flow meter 3, and fresh monomer feed control valve 4 directly control the fresh monomer to enter the polymerization reactor 5; one end of the monomer distillation column 16 is connected to the monomer removal column 8 through a pipeline, and the other end is connected to the monomer distillation column condenser 17 and the monomer distillation column separator 18 through a pipeline; a feed loop is formed between the polymerization reactor 5 and the monomer removal column 8; the polymerization reactor 5, the monomer removal column 8, and the monomer distillation column 16 form another feed loop.

[0017] An RM buffer tank 19 is also provided between the monomer distillation column 16 and the polymerization reactor 5. Its function is to receive the monomer overflowing from the monomer distillation column separator 18 and store sufficient quantity for feeding. An RM feed filter 21 is also provided between the monomer distillation column 16 and the polymerization reactor 5. Its function is to filter out impurities contained in the monomer, ensuring the cleanliness of the recovered monomer. An RM feed mass flow meter 22 is also provided between the monomer distillation column 16 and the polymerization reactor. Its function is to measure the monomer feed rate and achieve precise control.

[0018] Example 1

[0019] Polymerization reactor 5 is selected as 35m 3 The volume is set at 6.3t acrylonitrile feed rate, monomer concentration 18%, and is efficiently controlled through fresh monomer feed filter 2, fresh monomer feed mass flow meter 3, and fresh monomer feed control valve 4, and fed into polymerization reactor 5. Through sequential control DCS program, according to the feed formula, the fixed proportions of comonomer and solvent are controlled, with azobisisobutyronitrile (azobisisobutyronitrile) set at 0.5t and the thiol (molecular weight adjuster) set at 0.0075t.

[0020] The polymerization reactor 5 produces a polymerization liquid with a conversion rate of 89.7% through a temperature-controlled reaction, which is then sent to the depolymerization tower 8 via the depolymerization feed pump 6.

[0021] Under the action of the monomer removal reboiler 7 and a vacuum of 1.2 kPa (A), all unreacted monomers are removed, and the residual monomer content is detected to be <100 ppm. The KM liquid is then condensed into the monomer removal condensate tank 10 through the monomer removal condenser 9 to obtain KM liquid with a monomer concentration of 4.5%, thus completing the recovery and storage of KM liquid.

[0022] KM liquid is fed into polymerization reactor 5 via KM pump 11 at a set feed rate of 7.7t. It is then efficiently controlled by KM feed filter 12, KM feed mass flow meter 13, and KM feed control valve 14 to participate in the polymerization reaction. This portion of KM liquid accounts for 22% of the total feed amount.

[0023] A portion of the KM liquid is sent to the single distillation column 16. Under a vacuum of 25 kPa (A), the single distillation column takes out light components acrylonitrile and water from the top of the column. After being cooled by the single distillation column condenser 17, acrylonitrile and water are separated at 10°C in the single distillation column separator 18, taking advantage of their immiscibility and large density difference.

[0024] The light component acrylonitrile at the top of the monomer distillation column overflows into the RM buffer tank 19, yielding an RM liquid with a monomer concentration of 97.5%.

[0025] The RM feed pump sets the feed rate to 0.377tRM liquid. The liquid is then efficiently controlled by the RM feed filter 21, RM feed mass flow meter 22, and RM feed control valve 23 before being sent to the polymerization reactor 5 to participate in the polymerization reaction. This portion of RM liquid accounts for 1.1% of the total feed amount.

[0026] The product specifications are shown in Table 1.

[0027] Example 2

[0028] Polymerization reactor 5 is selected as 35m 3 The volume is set at 6.3t acrylonitrile feed rate, monomer concentration 18%, and is efficiently controlled through fresh monomer feed filter 2, fresh monomer feed mass flow meter 3, and fresh monomer feed control valve 4, and fed into polymerization reactor 5. Through sequential control DCS program, according to the feed formula, the fixed proportions of comonomer and solvent are controlled, with azobisisobutyronitrile (azobisisobutyronitrile) set at 0.4t and the thiol (molecular weight adjuster) set at 0.0088t.

[0029] The polymerization reactor 5 produces a polymerization liquid with a conversion rate of 89.3% through a temperature-controlled reaction, which is then sent to the depolymerization tower 8 via the depolymerization feed pump 6.

[0030] Under the action of the monomer removal reboiler 7 and a vacuum of 1.3 kPa (A), all unreacted monomers are removed, and the residual monomer content is detected to be <100 ppm. The KM liquid is then condensed into the monomer removal condensate tank 10 through the monomer removal condenser 9 to obtain KM liquid with a monomer concentration of 5.0%, thus completing the recovery and storage of KM liquid.

[0031] KM liquid is fed into polymerization reactor 5 via KM pump 11 at a set feed rate of 7.7t. It is then efficiently controlled by KM feed filter 12, KM feed mass flow meter 13, and KM feed control valve 14 to participate in the polymerization reaction. This portion of KM liquid accounts for 22% of the total feed amount.

[0032] A portion of the KM liquid is sent to the single distillation column 16. Under a vacuum of 25 kPa (A), the single distillation column takes out light components acrylonitrile and water from the top of the column. After being cooled by the single distillation column condenser 17, acrylonitrile and water are separated at 10°C in the single distillation column separator 18, taking advantage of their immiscibility and large density difference.

[0033] The light component acrylonitrile at the top of the monomer distillation column overflows into the RM buffer tank 19, yielding an RM liquid with a monomer concentration of 97.5%.

[0034] The RM feed pump sets the feed rate to 0.370tRM liquid. The liquid is then efficiently controlled by the RM feed filter 21, RM feed mass flow meter 22, and RM feed control valve 23 before being sent to the polymerization reactor 5 to participate in the polymerization reaction. This portion of RM liquid accounts for 1.1% of the total feed amount.

[0035] The product specifications are shown in Table 1.

[0036] Example 3

[0037] Polymerization reactor 5 is selected as 35m 3 The volume is set at 7.0t acrylonitrile feed rate, monomer concentration 20%, and is efficiently controlled through fresh monomer feed filter 2, fresh monomer feed mass flow meter 3, and fresh monomer feed control valve 4, and fed into polymerization reactor 5. Through sequential control DCS program, according to the feed formula, the fixed proportions of comonomer and solvent are controlled, with azobisisobutyronitrile (azobisisobutyronitrile) set at 0.35t and the thiol (molecular weight adjuster) set at 0.0105t.

[0038] The polymerization reactor 5 produces a polymerization liquid with a conversion rate of 88.8% through a temperature-controlled reaction, which is then sent to the depolymerization tower 8 via the depolymerization feed pump 6.

[0039] Under the action of the monomer removal reboiler 7 and a vacuum of 1.3 kPa (A), all unreacted monomers are removed, and the residual monomer content is detected to be <100 ppm. The KM liquid is then condensed into the monomer removal condensate tank 10 through the monomer removal condenser 9 to obtain KM liquid with a monomer concentration of 5.5%, thus completing the recovery and storage of KM liquid.

[0040] KM liquid is fed into polymerization reactor 5 via KM pump 11 at a set feed rate of 8.1t. It is then efficiently controlled by KM feed filter 12, KM feed mass flow meter 13, and KM feed control valve 14 to participate in the polymerization reaction. This portion of KM liquid accounts for 23% of the total feed amount.

[0041] A portion of the KM liquid is sent to the single distillation column 16. Under a vacuum of 25 kPa (A), the single distillation column takes out light components acrylonitrile and water from the top of the column. After being cooled by the single distillation column condenser 17, acrylonitrile and water are separated at 10°C in the single distillation column separator 18, taking advantage of their immiscibility and large density difference.

[0042] The light component acrylonitrile at the top of the monomer distillation column overflows into the RM buffer tank 19, yielding an RM liquid with a monomer concentration of 97.5%.

[0043] The RM feed pump sets the feed rate to 0.455tRM liquid. The liquid is then efficiently controlled by the RM feed filter 21, RM feed mass flow meter 22, and RM feed control valve 23 before being sent to the polymerization reactor 5 to participate in the polymerization reaction. This portion of RM liquid accounts for 1.3% of the total feed amount.

[0044] Example 4

[0045] Polymerization reactor 5 is selected as 35m 3The acrylonitrile feed rate is set to 6.0t, with a monomer concentration of 17%. The feed is efficiently controlled via a fresh monomer feed filter 2, a fresh monomer feed mass flow meter 3, and a fresh monomer feed control valve 4, and delivered to the polymerization reactor 5. Through a sequential control DCS program, the fixed proportions of comonomers and solvents are controlled according to the feed formulation. The initiator azobisisobutyronitrile is set at 0.30t, and the molecular weight regulator thiol is set at 0.009t.

[0046] The polymerization reactor 5 produces a polymerization liquid with a conversion rate of 88.4% through a temperature-controlled reaction, which is then sent to the depolymerization tower 8 via the depolymerization feed pump 6.

[0047] Under the action of the monomer removal reboiler 7 and a vacuum of 1.2 kPa (A), all unreacted monomers are removed, and the residual monomer content is detected to be <100 ppm. The KM liquid is then condensed into the monomer removal condensate tank 10 through the monomer removal condenser 9 to obtain KM liquid with a monomer concentration of 4.0%, thus completing the recovery and storage of KM liquid.

[0048] KM liquid is fed into polymerization reactor 5 via KM pump 11 at a set feed rate of 8.7t. It is then efficiently controlled by KM feed filter 12, KM feed mass flow meter 13, and KM feed control valve 14 to participate in the polymerization reaction. This portion of KM liquid accounts for 25% of the total feed amount.

[0049] A portion of the KM liquid is sent to the single distillation column 16. Under a vacuum of 25 kPa (A), the single distillation column takes out light components acrylonitrile and water from the top of the column. After being cooled by the single distillation column condenser 17, acrylonitrile and water are separated at 10°C in the single distillation column separator 18, taking advantage of their immiscibility and large density difference.

[0050] The light component acrylonitrile at the top of the monomer distillation column overflows into the RM buffer tank 19, yielding an RM liquid with a monomer concentration of 97.5%.

[0051] The RM feed pump sets the feed rate to 0.500tRM liquid. The liquid is then efficiently controlled by the RM feed filter 21, RM feed mass flow meter 22, and RM feed control valve 23 before being sent to the polymerization reactor 5 to participate in the polymerization reaction. This portion of RM liquid accounts for 1.4% of the total feed amount.

[0052] Table 1: Key Indicators of Products in the Example Case

[0053]

[0054] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the scope of the claims of the present invention should be within the protection scope of the present invention.

Claims

1. A method for recycling acrylonitrile monomer in carbon fiber production, characterized in that, It utilizes an acrylonitrile monomer recovery and utilization device, which includes a polymerization reactor and a monomer stripping tower. A pipeline connects the polymerization reactor and the monomer stripping tower. The device also includes a monomer distillation tower, a monomer distillation tower condenser, and a monomer distillation tower separator. One end of the monomer distillation tower is connected to the monomer stripping tower via a pipeline, and the other end is connected to the monomer distillation tower condenser and the monomer distillation tower separator via a pipeline. A feed loop is formed between the polymerization reactor and the monomer stripping tower. The polymerization reactor, the monomer stripping tower, and the monomer distillation tower form another feed loop. The method includes the following steps: fresh acrylonitrile monomer is introduced into a polymerization reactor for reaction; unreacted acrylonitrile monomer is discharged from the polymerization reactor and enters a monomer removal tower to remove unreacted monomer from the polymerization liquid. The unreacted monomer is absorbed by dimethyl sulfoxide to obtain KM liquid. 50% to 60% of the mass of the KM liquid is returned to the polymerization reactor to participate in the polymerization reaction again; 40% to 50% of the mass of the KM liquid is sent to the monomer distillation tower for purification treatment and then returned to the polymerization reactor to participate in the polymerization reaction again, thereby realizing the complete recovery and reuse of unreacted acrylonitrile monomer.

2. The method for recycling acrylonitrile monomer in carbon fiber production according to claim 1, characterized in that, The KM liquid is received through the monomer distillation column, purified by distillation, and stably separated into layers at a low temperature of 5-15℃ to obtain an RM liquid with an acrylonitrile monomer mass concentration ≥97%.

3. The method for recycling acrylonitrile monomer in carbon fiber production according to claim 2, characterized in that, In the polymerization reactor, the mass ratio of KM liquid is 22% to 25%, the mass ratio of RM liquid is 1.0% to 1.5%, the mass ratio of fresh acrylonitrile monomer is 16% to 20%, the mass ratio of other additives is 1% to 2%, and the remainder is dimethyl sulfoxide.

4. The method for recycling acrylonitrile monomer in carbon fiber production according to claim 3, characterized in that, The auxiliary agent includes the initiator azobisisobutyronitrile and the molecular weight regulator thiol, with a mass ratio of 1:(0.015-0.03).

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