A method for depolymerization of caprolactam oligomers in APU oil to monomer

Abstract

The application discloses a method for depolymerizing caprolactam oligomers in APU oil into monomers and belongs to the technical field of chemistry and chemical industry. The method adds a catalyst and a solvent into the APU oil and carries out a depolymerization reaction under high temperature and high pressure, so that caprolactam monomers are obtained, the depolymerization rate can reach more than 28%, the operation is simple, intermittent production can be realized, the solvent and the catalyst can be recycled, the problems that the catalyst used in traditional caprolactam oligomer depolymerization is difficult to recover, the operation is complicated and cannot be adapted to oligomer recovery in APU oil can be effectively solved, the utilization rate of caprolactam resources can be improved, the production cost of enterprises is reduced, and the method has high practicability and industrial application value.

Description

Technical Field

[0001] This invention belongs to the field of chemical engineering technology, and specifically relates to a method for depolymerizing caprolactam oligomers in APU oil, a byproduct of caprolactam production, into monomers. Background Technology

[0002] Caprolactam is the core monomer for the production of nylon 6. In recent years, with the gradual increase in the market size and production capacity of nylon 6 in my country, the demand for caprolactam has risen in tandem with its production capacity. However, in the production, refining, polymerization, and recycling of nylon 6, a certain amount of caprolactam oligomers are inevitably generated. The accumulation of these oligomers in the process solution affects reaction efficiency and reduces product quality. Therefore, APU oil byproducts containing oligomeric caprolactam, caprolactam, aminocaproic acid, and inorganic substances are generated in the purification stage. Currently, most APU oil is treated by incineration to produce steam as a byproduct, but this method has low thermal efficiency and results in approximately 46 wt% of the organic components not being effectively utilized. This not only causes serious resource waste but also increases environmental protection pressure and raises production costs for enterprises.

[0003] Existing technologies for the efficient recovery of oligomers from APU oil are still immature. Existing methods for depolymerizing caprolactam oligomers suffer from the following drawbacks: First, low depolymerization efficiency and low monomer recovery rates result in a large amount of oligomers remaining unutilized, failing to meet the demand for efficient recovery from APU oil. Second, demanding depolymerization conditions often require high temperature and high pressure environments, leading to side reactions, impurities, and affecting the purity of caprolactam monomers. Third, the depolymerization process often uses traditional homogeneous catalysts such as phosphoric acid or highly corrosive reagents, increasing production costs and making subsequent separation and purification difficult, potentially causing equipment damage and environmental pollution. Some processes employ ionic liquid catalysis, which suffers from high costs and insufficient long-term stability. Fourth, the depolymerization process is complex, cumbersome, and impractical. Therefore, developing a method with high depolymerization efficiency, simple operation, adaptability to APU oil oligomer recovery, and the ability to depolymerize caprolactam oligomers into monomers has become a pressing technical problem in the chemical industry. Summary of the Invention

[0004] The purpose of this invention is to provide a method for depolymerizing caprolactam oligomers in APU oil into monomers, which solves the problem of difficult recovery of oligomers in existing APU oil and provides a new technical path for the resource recovery of APU oil.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A method for depolymerizing caprolactam oligomers in APU oil into monomers involves adding APU oil, solvent, and catalyst to a depolymerization reactor for reaction. After the reaction, the depolymerization mixture is taken out through a sampling port and extracted to obtain monomers. The remaining reaction mixture in the reactor is filtered to obtain liquid and solid materials. The liquid material is used as a raw material for recycling, and the obtained solid material is calcined and reused as a catalyst.

[0006] Furthermore, the APU oil contains 25% to 40% oligomers (mainly 2 to 4 polymers) and 6% to 9% caprolactam.

[0007] Furthermore, the solvent is water.

[0008] Furthermore, the catalyst is a solid acid particle.

[0009] Furthermore, the solid acid particles may be at least one of the following: metal oxides such as alumina and zirconium oxide; zeolites such as ZSM-5 and H-β; or trifluoromethanesulfonates such as lanthanum trifluoromethanesulfonate and scandium trifluoromethanesulfonate.

[0010] Furthermore, the mass ratio of APU oil to solvent used is 1:5 to 1:20.

[0011] Furthermore, the mass ratio of APU oil to catalyst used is 1:5 to 1:20.

[0012] Furthermore, the reaction temperature is 250~350 ℃, the initial pressure is 2~5 MPa, and the time is 0.5~3 h.

[0013] Furthermore, the extraction uses at least one of the following as the extractant: cyclohexanol, n-octanol, methylcyclohexanone, benzyl alcohol, n-butanol, n-heptanol, n-hexanol, isooctanol, and ethyl benzoate.

[0014] The technical advantages of this invention are: (1) Caprolactam oligomers have large molecules, while solid acid catalysts have limited pore sizes. Directly using solid acid catalysts for the reaction can easily lead to mass transfer limitations and prevent the reaction from proceeding. This invention uses water as a solvent and controls the reaction conditions to make it subcritical water to enhance mass transfer, thereby realizing the depolymerization of caprolactam oligomers using solid acid catalysts. Moreover, the solid acid catalysts used can be reused, which is chemically green.

[0015] (2) This invention treats the APU oil system, which can solve the problem of a large amount of related waste generated in industrial production and has industrial applicability.

[0016] (3) This invention targets the amide bond structure of polyamide oligomers and selects strong acid solid catalysts such as zirconium oxide to achieve effective depolymerization. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the process flow for depolymerizing caprolactam oligomers in APU oil into monomers according to the present invention. Detailed Implementation

[0018] A method for depolymerizing caprolactam oligomers in APU oil into monomers involves adding APU oil, solvent water, and a solid acid catalyst to a depolymerization reactor and reacting at 250–350 °C and an initial pressure of 2–5 MPa for 0.5–3 h. After the reaction, the depolymerized mixture is taken out through a sampling port, extracted with an extractant, and the organic phase is removed by rotary evaporation to remove the solvent, yielding the monomers. The remaining reaction liquid is filtered to obtain liquid and solid materials, with the liquid material being recycled as raw material and the resulting solid material being calcined and reused as a catalyst.

[0019] The mass ratio of APU oil to water used is 1:5 to 1:20. The mass ratio of APU oil to solid acid catalyst used is 1:5 to 1:20.

[0020] The APU oil contains 25% to 40% oligomers and 6% to 9% caprolactams by mass.

[0021] The solid acid catalyst may be at least one of the following: metal oxides such as alumina and zirconium oxide; zeolites such as ZSM-5 and H-β; or trifluoromethanesulfonates such as lanthanum trifluoromethanesulfonate and scandium trifluoromethanesulfonate.

[0022] The extractant is at least one of cyclohexanol, n-octanol, methylcyclohexanone, benzyl alcohol, n-butanol, n-heptol, n-hexanol, isooctanol, and ethyl benzoate.

[0023] To make the content of this invention easier to understand, the technical solution of this invention will be further described below with reference to specific embodiments, but this invention is not limited thereto.

[0024] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0025] The formula for calculating the depolymerization rate in the embodiment is: η = (X1 / X0-1) × C2 ÷ C1; Wherein, C1 is the mass fraction (%) of oligomers in the initial APU oil, C2 is the mass fraction (%) of caprolactam in the initial APU oil oligomers, X0 is the concentration (mg / L) of caprolactam in the reaction system, and X1 is the concentration (mg / L) of caprolactam in the depolymerized mixture after the reaction.

[0026] The formula for calculating monomer yield in the embodiment is: δ=(X1-X2)÷(X0÷C2×C1+X0). Where X2 is the concentration of caprolactam in the aqueous phase after extraction (mg / L).

[0027] The APU oil used in the examples has an oligomer mass fraction of 30% and a caprolactam mass fraction of 8%. Example 1

[0028] A method for depolymerizing caprolactam oligomers in APU oil into monomers, the specific steps of which are as follows: (1) Take 4.5 g of APU oil, 53 g of deionized water and 0.3 g of zirconium oxide (the concentration of caprolactam in the system is 7.36 mg / L). (2) The raw materials described in step (1) are added to the depolymerization reactor in sequence, and an inert gas (such as nitrogen) is introduced to make the initial pressure reach 4 MPa; (3) Set the heating program to 320 °C in 45 min, and then stir and depolymerize at 600 r / min for 2 h; (4) After the reaction is completed, the reaction vessel is cooled to room temperature. Then, the depolymerization mixture is taken from the sampling port. A small amount of sample is taken and measured by liquid chromatography-mass spectrometry (LC-MS) and the depolymerization rate at the end of the reaction is calculated. The remaining depolymerization mixture is added to cyclohexanol at a ratio of 3. After extraction by shaking on a shaker for 10 hours, the organic phase is taken and the solvent is removed by rotary evaporation to obtain the monomer. The aqueous phase is measured by LC-MS and the extraction rate is calculated. (5) The remaining reaction liquid in the reactor is filtered to recover zirconium oxide, and after washing and drying, it is recycled and reused; the remaining liquid material is returned to the feed for depolymerization.

[0029] The results showed that the concentration of caprolactam in the depolymerization mixture after the reaction was 17.53 mg / L, and the depolymerization rate was 36.8%; the concentration of caprolactam in the aqueous phase after extraction was 0.81 mg / L, and the extraction rate was 95.3%; the final yield of caprolactam was 47.8%. Example 2

[0030] A method for depolymerizing caprolactam oligomers in APU oil into monomers, the specific steps of which are as follows: (1) Take 4.5 g of APU oil, 53 g of deionized water and 0.3 g of alumina (the concentration of caprolactam in the system is 7.36 mg / L). (2) The raw materials described in step (1) are added to the depolymerization reactor in sequence, and an inert gas (such as nitrogen) is introduced to make the initial pressure reach 4 MPa; (3) Set the heating program to 300 °C in 45 min, and then stir and depolymerize at 600 r / min for 2 h; (4) After the reaction is completed, the reaction vessel is cooled to room temperature. Then, the depolymerization mixture is taken from the sampling port. A small amount of sample is taken and measured by liquid chromatography-mass spectrometry (LC-MS) and the depolymerization rate at the end of the reaction is calculated. The remaining depolymerization mixture is added to n-octanol at a ratio of 3. After shaking and extraction on a shaker for 10 h, the organic phase is taken and the solvent is removed by rotary evaporation to obtain the monomer. The aqueous phase is measured by LC-MS and the extraction rate is calculated. (5) The remaining reaction liquid in the reactor is filtered to recover alumina, and after washing and drying, it is recycled and reused; the remaining liquid material is returned to the feed for depolymerization.

[0031] The results showed that the concentration of caprolactam in the depolymerization mixture after the reaction was 15.73 mg / L, and the depolymerization rate was 30.3%; the concentration of caprolactam in the aqueous phase after extraction was 3.50 mg / L, and the extraction rate was 77.7%; the final yield of caprolactam was 35.0%. Example 3

[0032] A method for depolymerizing caprolactam oligomers in APU oil into monomers, the specific steps of which are as follows: (1) Take 4.5 g of APU oil, 53 g of deionized water, and 0.3 g of H-β (the concentration of caprolactam in the system is 7.36 mg / L). (2) The raw materials described in step (1) are added to the depolymerization reactor in sequence, and an inert gas (such as nitrogen) is introduced to make the initial pressure reach 4 MPa; (3) Set the heating program to 320 °C in 45 min, and then stir and depolymerize at 600 r / min for 2 h; (4) After the reaction is completed, the reaction vessel is cooled to room temperature. Then, the depolymerization mixture is taken from the sampling port. A small amount of sample is taken and measured by liquid chromatography-mass spectrometry (LC-MS) and the depolymerization rate at the end of the reaction is calculated. The remaining depolymerization mixture is added to n-octanol at a ratio of 3. After shaking and extraction on a shaker for 10 h, the organic phase is taken and the solvent is removed by rotary evaporation to obtain the monomer. The aqueous phase is measured by LC-MS and the extraction rate is calculated. (5) The remaining reaction liquid in the reactor is filtered to recover H-β, and after washing and drying, it is recycled and reused; the remaining liquid material is returned to the feed for depolymerization.

[0033] The results showed that the concentration of caprolactam in the depolymerization mixture after the reaction was 14.37 mg / L, and the depolymerization rate was 28.5%; the concentration of caprolactam in the aqueous phase after extraction was 3.65 mg / L, and the extraction rate was 74.5%; the final yield of caprolactam was 30.7%. Example 4

[0034] A method for depolymerizing caprolactam oligomers in APU oil into monomers, the specific steps of which are as follows: (1) Take 4.5 g of APU oil, 53 g of deionized water, and 0.3 g of ZSM-5 (the concentration of caprolactam in the system is 7.36 mg / L). (2) The raw materials described in step (1) are added to the depolymerization reactor in sequence, and an inert gas (such as nitrogen) is introduced to make the initial pressure reach 4 MPa; (3) Set the heating program to 320 °C in 45 min, and then stir and depolymerize at 600 r / min for 2 h; (4) After the reaction is completed, the reaction vessel is cooled to room temperature. Then, the depolymerization mixture is taken from the sampling port. A small amount of sample is taken and measured by liquid chromatography-mass spectrometry (LC-MS) and the depolymerization rate at the end of the reaction is calculated. The remaining depolymerization mixture is added to n-octanol at a ratio of 3. After shaking and extraction on a shaker for 10 h, the organic phase is taken and the solvent is removed by rotary evaporation to obtain the monomer. The aqueous phase is measured by LC-MS and the extraction rate is calculated. (5) The remaining reaction liquid in the reactor is filtered to recover ZSM-5, and after washing and drying, it is recycled and reused; the remaining liquid material is returned to the feed for depolymerization.

[0035] The results showed that the concentration of caprolactam in the depolymerization mixture after the reaction was 15.91 mg / L, and the depolymerization rate was 31.2%; the concentration of caprolactam in the aqueous phase after extraction was 3.11 mg / L, and the extraction rate was 80.5%; the final yield of caprolactam was 36.6%. Example 5

[0036] A method for depolymerizing caprolactam oligomers in APU oil into monomers, the specific steps of which are as follows: (1) Take 4.5 g of APU oil, 53 g of deionized water, 0.225 g of zirconium oxide, and 0.075 g of alumina (the concentration of caprolactam in the system is 7.36 mg / L). (2) The raw materials described in step (1) are added to the depolymerization reactor in sequence, and an inert gas (such as nitrogen) is introduced to make the initial pressure reach 4 MPa; (3) Set the heating program to 200 °C in 45 min, and then stir and depolymerize at 600 r / min for 2 h; (4) After the reaction is completed, the reaction vessel is cooled to room temperature. Then, the depolymerization mixture is taken from the sampling port. A small amount of sample is taken and measured by liquid chromatography-mass spectrometry (LC-MS) and the depolymerization rate at the end of the reaction is calculated. The remaining depolymerization mixture is added to n-octanol at a ratio of 3. After shaking and extraction on a shaker for 10 h, the organic phase is taken and the solvent is removed by rotary evaporation to obtain the monomer. The aqueous phase is measured by LC-MS and the extraction rate is calculated. (5) The remaining reaction liquid in the reactor is filtered to recover zirconium oxide and alumina, and then washed, dried and reused; the remaining liquid material is returned to the feed for depolymerization.

[0037] The results showed that the concentration of caprolactam in the depolymerization mixture after the reaction was 18.06 mg / L, and the depolymerization rate was 38.7%; the concentration of caprolactam in the aqueous phase after extraction was 4.19 mg / L, and the extraction rate was 76.8%; the final yield of caprolactam was 39.7%.

[0038] Comparative Example A method for depolymerizing caprolactam oligomers in APU oil into monomers, the specific steps of which are as follows: (1) Take 4.5 g of APU oil and 53 g of deionized water (the concentration of caprolactam in the system is 7.36 mg / L). (2) The raw materials described in step (1) are added to the depolymerization reactor in sequence, and an inert gas (such as nitrogen) is introduced to make the initial pressure reach 4 MPa; (3) Set the heating program to 300 °C in 45 min, and then stir and depolymerize at 600 r / min for 2 h; (4) After the reaction is completed, the reaction vessel is cooled to room temperature. Then, the depolymerization mixture is taken from the sampling port. A small amount of sample is taken and measured by liquid chromatography-mass spectrometry (LC-MS) and the depolymerization rate at the end of the reaction is calculated. The remaining depolymerization mixture is added to n-octanol at a ratio of 3. After shaking and extraction on a shaker for 10 h, the organic phase is taken and the solvent is removed by rotary evaporation to obtain the monomer. The aqueous phase is measured by LC-MS and the extraction rate is calculated. (5) The remaining reaction liquid in the reactor is returned to the feed for depolymerization.

[0039] The results showed that the concentration of caprolactam in the depolymerization mixture after the reaction was 13.22 mg / L, and the depolymerization rate was 21.5%; the concentration of caprolactam in the aqueous phase after extraction was 3.08 mg / L, and the extraction rate was 76.7%; the final yield of caprolactam was 29.0%.

[0040] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. A method for depolymerizing caprolactam oligomers in APU oil into monomers, characterized in that, APU oil, solvent, and catalyst are added to a depolymerization reactor for reaction, and the resulting depolymerization mixture is then extracted to obtain monomers.

2. The method for depolymerizing caprolactam oligomers in APU oil into monomers according to claim 1, characterized in that, The APU oil contains 25% to 40% oligomers and 6% to 9% caprolactams by mass.

3. The method for depolymerizing caprolactam oligomers in APU oil into monomers according to claim 1, characterized in that, The solvent is water.

4. The method for depolymerizing caprolactam oligomers in APU oil into monomers according to claim 1, characterized in that, The catalyst is a solid acid particle.

5. The method for depolymerizing caprolactam oligomers in APU oil into monomers according to claim 4, characterized in that, The solid acid particles are at least one of metal oxides, zeolites, or trifluoromethanesulfonates.

6. The method for depolymerizing caprolactam oligomers in APU oil into monomers according to claim 1, characterized in that, The mass ratio of APU oil to solvent used is 1:5 to 1:

20.

7. The method for depolymerizing caprolactam oligomers in APU oil into monomers according to claim 1, characterized in that, The mass ratio of APU oil to catalyst used is 1:5 to 1:

20.

8. The method for depolymerizing caprolactam oligomers in APU oil into monomers according to claim 1, characterized in that, The reaction was carried out at a temperature of 250-350 °C, an initial pressure of 2-5 MPa, and a time of 0.5-3 h.

9. The method for depolymerizing caprolactam oligomers in APU oil into monomers according to claim 1, characterized in that, The extraction process uses at least one of the following extractants: cyclohexanol, n-octanol, methylcyclohexanone, benzyl alcohol, n-butanol, n-heptanol, n-hexanol, isooctanol, and ethyl benzoate.

Images