Preparation system and preparation method of semi-aromatic polyamide

Abstract

The invention discloses a preparation system and a preparation method of semi-aromatic polyamide. The preparation system comprises a salt forming kettle, a concentration kettle and a polymerization kettle which are sequentially connected in series, the salifying kettle is connected with the concentrating kettle through a salifying pipeline, and the concentrating kettle is connected with the polymerizing kettle through a concentrating pipeline; the preparation system of the semi-aromatic polyamide further comprises a back flushing module. The semi-aromatic polyamide prepared by adopting the preparation system and the preparation method has high relative viscosity, low amino-terminated group content, stable relative viscosity and uniform molecular weight distribution.

Description

Technical Field

[0001] The present invention relates to a preparation system and a preparation method for semi-aromatic polyamide. Background Art

[0002] Semi-aromatic polyamide is a kind of polymer material with excellent comprehensive properties. Since its molecular main chain contains both aromatic rings and aliphatic chains, it combines the excellent properties of aromatic polyamide and the good molding processability of aliphatic polyamide, and generally has advantages such as high temperature resistance, corrosion resistance, and low water absorption rate. In recent years, it has been widely used in the fields of electronic appliances, automotive industry, equipment manufacturing, etc.

[0003] In industrial production, polyamide salts are usually used for the polymerization of polyamide. Polyamide salts are salts formed by the reaction of dibasic acids and diamines. By using different dibasic acids and diamines, various polyamide salt products can be prepared. Polyamide salts are the prerequisite for synthesizing polyamide. Therefore, the product quality of polyamide salts has a great impact on the quality of polyamide polymerization products. How to obtain polyamide salts with less impurities, high quality, and stable quality has become a key link in polyamide production.

[0004] In the industrial production of polyamide polymers, a single polymerization reactor is usually split into several reactors according to different stages of polyamide polymerization. For example, the salt formation and concentration stages in the polymerization process can be completed in different reactors, which can not only improve the dehydration efficiency and save the polymerization time of a single batch, but also increase the output of the polymer per batch. This greatly improves the production efficiency and reduces the production cost. However, there are still some problems with the aforementioned multi-reactor combined polymerization device. For example, the reactions of materials in different polymerization stages need to be carried out in different devices, so material transfer is required. Inevitably, some materials will remain in the previous device, transfer pipelines, or valves during the material transfer process, and these residues will affect the performance of the next batch of products. The existing systems and methods for preparing semi-aromatic polyamide in the prior art cannot achieve highly stable product quality. Summary of the Invention

[0005] In order to solve the above-mentioned defects existing in the prior art, the present invention provides a preparation system and a preparation method for semi-aromatic polyamide. The semi-aromatic polyamide prepared by using this preparation system and preparation method has high relative viscosity, low terminal amino group content, stable relative viscosity, and uniform molecular weight distribution.

[0006] The present invention provides a preparation system for semi-aromatic polyamide. The preparation system for semi-aromatic polyamide includes a salt formation kettle, a concentration kettle, and a polymerization kettle connected in series in sequence; the salt formation kettle and the concentration kettle are connected through a salt formation pipeline, and the concentration kettle and the polymerization kettle are connected through a concentration pipeline;

[0007] The preparation system of the semi-aromatic polyamide further includes a backwashing module. The upper end of the salification kettle is connected with a first drain pipe for discharging the salification waste liquid condensed from the gas phase; the upper end of the concentration kettle is connected with a second drain pipe for discharging the concentration waste liquid condensed from the gas phase; the upper end of the polymerization kettle is connected with a third drain pipe for discharging the polymerization waste liquid condensed from the gas phase.

[0008] The backwashing module includes a first backwashing branch, a second backwashing branch and a third backwashing branch connected in parallel. The first backwashing branch is connected to the downstream of the salification pipe for steam backwashing of the upstream of the salification pipe and the salification kettle. A first drain branch is provided upstream of the salification pipe for discharging the salification waste liquid. The second backwashing branch is connected to the downstream of the concentration pipe for steam backwashing of the upstream of the concentration pipe and the concentration kettle. A second drain branch is provided upstream of the concentration pipe for discharging the concentration waste liquid. The third backwashing branch is connected to the upstream of the third drain pipe for steam purging of the third drain pipe.

[0009] In the present invention, the preparation system of the semi-aromatic polyamide preferably further includes a collection tank. The collection tank is respectively connected to the outlet ends of the first drain pipe, the second drain pipe, the third drain pipe, the outlet end of the first drain branch and the outlet end of the second drain branch for collecting the salification waste liquid, the concentration waste liquid and the polymerization waste liquid.

[0010] Preferably, the collection tank is connected to the concentration kettle through a concentrated liquid recycling pipe for conveying the liquid collected in the collection tank to the concentration kettle for recycling.

[0011] Preferably, the first drain pipe and the first drain branch converge and are connected to the collection tank. More preferably, the first drain pipe, the first drain branch and the third drain pipe converge and are connected to the collection tank.

[0012] Preferably, the second drain pipe and the second drain branch converge and are connected to the collection tank. More preferably, the second drain pipe, the second drain branch and the third drain pipe converge and are connected to the collection tank.

[0013] In the present invention, a salification discharge valve is preferably provided on the first drain branch, and the position of the salification discharge valve is lower than the bottom of the salification kettle.

[0014] In the present invention, a concentration discharge valve is preferably provided on the second drain branch, and the position of the concentration discharge valve is lower than the bottom of the concentration kettle.

[0015] In the present invention, by providing a salt-forming discharge valve and a concentration discharge valve, the salt-forming waste liquid and the concentrated waste liquid can be discharged in a timely manner.

[0016] In the present invention, preferably, a concentration exhaust branch is provided on the second liquid discharge pipeline for discharging the gas generated in the concentration kettle.

[0017] In the present invention, preferably, a polymerization exhaust branch is provided on the third liquid discharge pipeline for discharging the gas generated in the polymerization kettle.

[0018] In some specific embodiments of the present invention, valves are provided on the salt-forming pipeline, the concentration pipeline, the first liquid discharge pipeline, the second liquid discharge pipeline, the third liquid discharge pipeline, the first backflush branch, the first liquid discharge branch, the second backflush branch, the second liquid discharge branch, and the third backflush branch to control the flow of materials.

[0019] By improving the preparation system of semi-aromatic polyamide, the present invention can effectively reduce the precipitation of semi-aromatic polyamide salt in the pipeline, and reduce the risk of blockage and production risk.

[0020] In a specific embodiment of the present invention, the concentration exhaust branch is connected to the backflush module for inputting the gas generated in the concentration kettle into the backflush module.

[0021] In a specific embodiment of the present invention, the polymerization exhaust branch is connected to the backflush module for inputting the gas generated in the polymerization kettle into the backflush module.

[0022] The present invention also provides a method for preparing semi-aromatic polyamide, which uses the above-mentioned preparation system of semi-aromatic polyamide, and includes the following steps:

[0023] S1: Add raw materials into the salt-forming kettle for salt-forming reaction to obtain a semi-aromatic polyamide salt solution; transfer the semi-aromatic polyamide salt solution to the concentration kettle through the salt-forming pipeline;

[0024] S2: Perform a concentration reaction on the semi-aromatic polyamide salt solution in the concentration kettle to obtain a concentrated semi-aromatic polyamide salt solution; transfer the concentrated semi-aromatic polyamide salt solution to the polymerization kettle through the concentration pipeline;

[0025] S3: Perform a polymerization reaction on the concentrated semi-aromatic polyamide salt solution in the polymerization kettle to obtain the product semi-aromatic polyamide;

[0026] The preparation method of the semi-aromatic polyamide further includes a first backwashing operation, a second backwashing operation, and a third backwashing operation, which are respectively implemented through the first backwashing branch, the second backwashing branch, and the third backwashing branch; the first backwashing operation is carried out after S1 ends, the second backwashing operation is carried out after S2 ends, and the third backwashing operation is carried out after S3 ends.

[0027] In the preparation method of the semi-aromatic polyamide of the present invention, purging is carried out after each stage is completed, which can efficiently and quickly clean the residual waste liquid in the reaction device.

[0028] Through the method of the present invention, the homogeneity and stability of each batch of semi-aromatic polyamide salt solution are greatly guaranteed, so that the relative viscosity difference of each batch of prepared semi-aromatic polyamide products is extremely small, that is, the stability between the relative viscosities of each batch of products is ensured, the quality of the final product is stable, and there is no quality fluctuation; at the same time, the problem of blockage caused by the precipitation of semi-aromatic polyamide salt is avoided, the production risk is reduced, the process stability is improved, the product yield is further increased, and the reaction cost is reduced. The prepared semi-aromatic polyamide salt has a high relative viscosity and a low PDI. In the present invention, PDI refers to the polydispersity index of the polymer, which is used to describe the molecular weight distribution of the polymer. The higher the PDI, the wider the molecular weight distribution, and the lower the PDI, the more uniform the molecular weight distribution.

[0029] Those skilled in the art generally understand that when performing step S3, the pressure in the polymerization kettle should be reduced to a safe value before performing the third backwashing operation.

[0030] Those skilled in the art generally understand that in the preparation method of semi-aromatic polyamide, an operation of replacing with nitrogen or other inert gases is carried out before feeding, and the main purpose is to replace the oxygen or other active gases in the device with nitrogen or other inert gases.

[0031] In the present invention, preferably, the purging medium used in the first backwashing operation, the second backwashing operation, and the third backwashing operation is steam, or a mixture of steam and inert gas.

[0032] In the present invention, preferably, the salt-forming waste liquid, the concentrated waste liquid, and the polymerization waste liquid are collected in a collection tank.

[0033] Among them, preferably, the liquid collected in the collection tank is transported to the concentration kettle for reuse. Among them, the transportation is preferably carried out by nitrogen pressure feeding. The waste liquid formed after purging is discharged into the collection tank, and these waste liquids can participate in the concentration-polymerization reaction of the next batch. Reusing the liquid collected in the collection tank can reduce the environmental protection pressure of steam condensate waste liquid treatment, improve the polymerization product yield, and reduce the polymerization cost.

[0034] In certain specific embodiments of the present invention, the gas generated after the concentration reaction is discharged through the concentrated exhaust branch.

[0035] In certain specific embodiments of the present invention, the gas generated after the polymerization reaction is discharged through the polymerization exhaust branch.

[0036] In the present invention, preferably, the raw materials include aliphatic dicarboxylic acids and aromatic diamines, or the raw materials include aliphatic diamines and aromatic dicarboxylic acids.

[0037] Among them, the aliphatic dicarboxylic acid is preferably one or more of succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid and dodecanedioic acid; more preferably one or more of adipic acid, sebacic acid and dodecanedioic acid.

[0038] Among them, the aromatic diamine is preferably one or more of p-phenylenediamine, p-xylylenediamine, m-phenylenediamine, m-xylylenediamine and 2-methyl-p-phenylenediamine, and more preferably m-xylylenediamine.

[0039] In certain specific embodiments of the present invention, the raw materials further include demineralized water.

[0040] In a specific embodiment of the present invention, the aliphatic dicarboxylic acid is adipic acid and the aromatic diamine is m-xylylenediamine.

[0041] In the present invention, the temperature of the salt-forming reaction is preferably 40 - 90 °C, and more preferably 50 - 70 °C.

[0042] In the present invention, the time of the salt-forming reaction is preferably 10 - 120 min, and more preferably 20 - 40 min.

[0043] In the present invention, the pH value of the semi-aromatic polyamide salt solution is preferably 6.5 - 8, and more preferably 6.9 - 7.5.

[0044] In the present invention, the mass concentration of the semi-aromatic polyamide salt solution is preferably 40 wt% - 70 wt%, and more preferably 50 wt% - 60 wt%.

[0045] In the present invention, the pressure of the concentration reaction is preferably 30 - 500 kPa, and more preferably 50 - 200 kPa.

[0046] In the present invention, the temperature of the concentration reaction is preferably 100 - 180 °C, and more preferably 110 - 160 °C.

[0047] In the present invention, the mass concentration of the semi-aromatic polyamide salt concentrate is preferably 60 wt% - 95 wt%, and more preferably 70 wt% - 85 wt%.

[0048] In the present invention, the temperature of the semi-aromatic polyamide salt concentrate is preferably 120 - 180 °C, more preferably 140 - 170 °C.

[0049] In the present invention, preferably, the polymerization reaction comprises the following steps: subjecting the semi-aromatic polyamide salt concentrate to a prepolymerization reaction first and then to a final polymerization reaction.

[0050] Among them, preferably, the third backflush operation is carried out after the prepolymerization reaction ends.

[0051] Among them, the pressure of the prepolymerization reaction is preferably 300 - 2000 kPa, more preferably 1500 - 1800 kPa.

[0052] Among them, the temperature of the prepolymerization reaction is preferably 160 - 260 °C.

[0053] Among them, the pressure of the final polymerization reaction can be atmospheric pressure or negative pressure.

[0054] Among them, the time of the final polymerization reaction is preferably 20 - 120 min, more preferably 40 - 80 min.

[0055] In some specific embodiments of the present invention, the vacuum degree of the final polymerization reaction is 20 - 90 kPa, more preferably 70 - 90 kPa.

[0056] In some specific embodiments of the present invention, the pressure of the final polymerization reaction is negative pressure, and the temperature of the final polymerization reaction is 250 - 280 °C, preferably 270 - 280 °C.

[0057] In the present invention, in steps S1 and S2, the transfer mode of the semi-aromatic polyamide salt solution and the semi-aromatic polyamide salt concentrate is preferably nitrogen pressure feeding or conveying by a transfer pump, and nitrogen pressure feeding is preferred.

[0058] In the present invention, the steam is preferably saturated steam or superheated steam prepared from soft water or demineralized water.

[0059] In the present invention, the steam is preferably low-pressure steam or medium-pressure steam. The meaning of low-pressure steam is steam with a pressure of 0.1 - 1 MPa, and the meaning of medium-pressure steam is steam with a pressure higher than 1 MPa and below 2 MPa.

[0060] In the present invention, preferably, the first backflush operation is carried out after S1 ends and before S2 starts.

[0061] In the present invention, preferably, the second backflush operation is carried out after S2 ends and before S3 starts.

[0062] In the present invention, the flow rates of the first backwashing operation, the second backwashing operation, and the third backwashing operation are preferably 100 - 1000 kg / h.

[0063] In the present invention, the times of the first backwashing operation, the second backwashing operation, and the third backwashing operation are preferably 1 - 30 min.

[0064] In the present invention, the numbers of times of the first backwashing operation, the second backwashing operation, and the third backwashing operation are preferably 1 - 3 times.

[0065] In a specific embodiment of the present invention, the gases used in the first backwashing operation, the second backwashing operation, and the third backwashing operation are the gases obtained from the concentration reaction and / or the gases obtained from the polymerization reaction.

[0066] The reagents and raw materials used in the present invention are all commercially available.

[0067] The positive and progressive effects of the present invention are as follows:

[0068] By using the preparation system and preparation method of the semi-aromatic polyamide of the present invention, it is possible to ensure the stable quality of the finally prepared semi-aromatic polyamide product without quality fluctuations; the prepared semi-aromatic polyamide has a high relative viscosity, a low terminal amino group content, a stable relative viscosity, and a uniform molecular weight distribution.

[0069] In some preferred embodiments, the yield can be further increased and the amount of waste water and waste steam can be reduced to zero. BRIEF DESCRIPTION OF THE DRAWINGS

[0070] Figure 1 It is a schematic diagram of the preparation system of the semi-aromatic polyamide in Example 1.

[0071] Description of the reference numerals:

[0072] 1 - salt-forming kettle; 2 - concentration kettle; 3 - polymerization kettle; 4 - collection tank; 5 - salt-forming discharge valve; 6 - concentration discharge valve; 7 - salt-forming kettle material transfer valve; 8 - salt-forming kettle exhaust valve; 9 - salt-forming kettle steam valve; 10 - concentration kettle cut-off valve; 11 - concentration kettle material transfer valve; 12 - concentration kettle exhaust valve; 13 - concentration kettle steam valve; 14 - polymerization kettle cut-off valve; 15 - third drain pipe cut-off valve; 16 - polymerization kettle exhaust valve; 17 - polymerization kettle steam valve; 18 - collection tank transfer valve;

[0073] 1001 - Salt formation pipeline; 1002 - Concentration pipeline; 1003 - First drain pipeline; 1004 - Second drain pipeline; 1005 - Third drain pipeline; 1006 - First backflush branch; 1007 - Second backflush branch; 1008 - Third backflush branch; 1009 - First drain branch; 1010 - Second drain branch; 1011 - Concentrate recycling pipeline; 1012 - Concentrate exhaust branch; 1013 - Polymerization exhaust branch. Detailed implementation manners

[0074] The present invention will be further described below by way of embodiments, but the present invention is not limited to the scope of the described embodiments. For the experimental methods without specific conditions in the following embodiments, they are carried out according to conventional methods and conditions, or selected according to the product specifications.

[0075] Embodiment 1

[0076] The schematic diagram of the preparation system of semi - aromatic polyamide adopted in Embodiment 1 is as Figure 1 shown.

[0077] It includes a salt formation kettle 1, a concentration kettle 2 and a polymerization kettle 3 connected in series in sequence; the salt formation kettle 1 and the concentration kettle 2 are connected through a salt formation pipeline 1001, and the concentration kettle 2 and the polymerization kettle 3 are connected through a concentration pipeline 1002;

[0078] The preparation system of semi - aromatic polyamide further includes a backflush module. The upper end of the salt formation kettle 1 is connected with a first drain pipeline 1003 for discharging the salt formation waste liquid obtained by gas - phase condensation; the upper end of the concentration kettle 2 is connected with a second drain pipeline 1004 for discharging the concentration waste liquid obtained by gas - phase condensation; the upper end of the polymerization kettle 3 is connected with a third drain pipeline 1005 for discharging the polymerization waste liquid obtained by gas - phase condensation;

[0079] The backflush module includes a first backflush branch 1006, a second backflush branch 1007 and a third backflush branch 1008 connected in parallel; the first backflush branch 1006 is connected to the downstream of the salt formation pipeline 1001 for steam backflushing the upstream of the salt formation pipeline 1001 and the salt formation kettle 1. A first drain branch 1009 is provided upstream of the salt formation pipeline 1001 for discharging the salt formation waste liquid; the second backflush branch 1007 is connected to the downstream of the concentration pipeline 1002 for steam backflushing the upstream of the concentration pipeline 1002 and the concentration kettle 2. A second drain branch 1010 is provided upstream of the concentration pipeline 1002 for discharging the concentration waste liquid; the third backflush branch 1008 is connected to the upstream of the third drain pipeline 1005 for steam purging the third drain pipeline 1005.

[0080] The preparation system of semi-aromatic polyamide further includes a collection tank 4, which is respectively connected to the outlet ends of the first liquid discharge pipeline 1003, the second liquid discharge pipeline 1004, the third liquid discharge pipeline 1005, the outlet end of the first liquid discharge branch 1009, and the outlet end of the second liquid discharge branch 1010, and is used for collecting salt-forming waste liquid, concentrated waste liquid, and polymerization waste liquid; the collection tank 4 is connected to the concentration kettle 2 through a concentrated liquid recycling pipeline 1011, and is used for conveying the liquid collected in the collection tank 4 to the concentration kettle 2 for recycling.

[0081] The first liquid discharge pipeline 1003, the first liquid discharge branch 1009, and the third liquid discharge pipeline 1005 converge and are connected to the collection tank 4; at the same time, the second liquid discharge pipeline 1004, the second liquid discharge branch 1010, and the third liquid discharge pipeline 1005 converge and are connected to the collection tank 4.

[0082] Among them, a salt-forming discharge valve 5 is provided on the first liquid discharge branch 1009, and the position of the salt-forming discharge valve 5 is lower than the bottom of the salt-forming kettle 1; a concentration discharge valve 6 is provided on the second liquid discharge branch 1010, and the position where the concentration discharge valve 6 is set is lower than the bottom of the concentration kettle 2;

[0083] Among them, a concentrated exhaust branch 1012 is provided on the second liquid discharge pipeline 1004, and is used for discharging the gas generated in the concentration kettle 2; a polymerization exhaust branch 1013 is provided on the third liquid discharge pipeline 1005, and is used for discharging the gas generated in the polymerization kettle 3;

[0084] Valves are provided on the salt-forming pipeline 1001, the concentration pipeline 1002, the first liquid discharge pipeline 1003, the second liquid discharge pipeline 1004, the third liquid discharge pipeline 1005, the first backflush branch 1006, the first liquid discharge branch 1009, the second backflush branch 1007, the second liquid discharge branch 1010, and the third backflush branch 1008 to control the flow of materials; such as the salt-forming kettle material transfer valve 7, the salt-forming kettle exhaust valve 8, the salt-forming kettle steam valve 9, the concentration kettle cut-off valve 10, the concentration kettle material transfer valve 11, the concentration kettle exhaust valve 12, the concentration kettle steam valve 13, the polymerization kettle cut-off valve 14, the third liquid discharge pipeline cut-off valve 15, the polymerization kettle exhaust valve 16, the polymerization kettle steam valve 17, the collection tank transfer valve 18, and the specific positions are shown in Figure 1 .

[0085] The preparation method of the semi-aromatic polyamide in Example 1 uses the above system, and includes the following steps:

[0086] The salt-forming reaction kettle is replaced 10 times with high-purity nitrogen;

[0087] Add 3215.1 g of adipic acid, 3005.2 g of m-xylenediamine, and 6220.3 g of deionized water into the salification kettle 1 for salification reaction to obtain a semi-aromatic polyamide salt solution; among them, the temperature of the salification reaction is 90 °C, and the time of the salification reaction is 40 min; test the pH of the salt solution to be 7.05, and transfer the semi-aromatic polyamide salt solution to the concentration kettle 2 through the salification pipeline 1001, and the transfer time is 30 s; after the salt solution transfer is completed, close the concentration kettle cut-off valve 10, open the salification kettle exhaust valve 8 and the salification kettle steam valve 9, and use low-pressure saturated steam at 0.8 Mpa and 120 kg / h to perform the first backwashing operation through the first backwashing branch 1006 to form salification waste liquid, and the time of the first backwashing operation is 1 min, and the number of times is 1 time; when the temperature of the salification kettle 1 drops to 90 °C, discharge the salification waste liquid into the collection tank 4.

[0088] Concentrate the semi-aromatic polyamide salt solution in the concentration kettle 2 to obtain a concentrated semi-aromatic polyamide salt solution; among them, the pressure of the concentration reaction is 200 kpa, the temperature of the concentration reaction is 155 °C, and the mass concentration of the concentrated semi-aromatic polyamide salt solution is 70 wt%; transfer the concentrated semi-aromatic polyamide salt solution to the polymerization kettle 3 through the concentration pipeline 1002, and the transfer time is 23 s; after the concentrated solution transfer is completed, close the polymerization kettle cut-off valve 14, open the concentration kettle exhaust valve 12 and the concentration kettle steam valve 13, and use low-pressure saturated steam at 0.8 Mpa and 120 kg / h to perform the second backwashing operation through the second backwashing branch 1007 to form concentrated waste liquid, and the time of the second backwashing operation is 2 min, and the number of times is 1 time; when the temperature of the concentration kettle 2 drops to 90 °C, discharge the concentrated waste liquid into the collection tank 4.

[0089] Carry out a polymerization reaction on the concentrated semi-aromatic polyamide salt solution in the polymerization kettle 3. The polymerization reaction includes the following steps: first carry out a prepolymerization reaction on the concentrated semi-aromatic polyamide salt solution and then carry out a final polymerization reaction; the pressure of the prepolymerization reaction is 1750 kpa. During the prepolymerization reaction, after the reaction temperature rises to 260 °C, depressurize; after the prepolymerization reaction depressurization is completed, close the third drain pipeline cut-off valve 15, open the polymerization kettle steam valve 17, and use low-pressure saturated steam at 0.8 Mpa and 120 kg / h to perform the third backwashing operation through the third backwashing branch 1008 to form polymerization waste liquid, and the time of the third backwashing operation is 2 min, and the number of times is 1 time; discharge the polymerization waste liquid into the collection tank 4; at the same time, carry out the final polymerization reaction. The vacuum degree of the final polymerization reaction is 80 kpa, the temperature of the final polymerization reaction is 270 °C, and the time of the final polymerization reaction is 60 min to obtain the product semi-aromatic polyamide, and the semi-aromatic polyamide is poly(m-phenylene adipamide) (MXD6). The mixed waste liquid formed by the salification waste liquid, concentrated waste liquid, and polymerization waste liquid in the collection tank 4 is transported to the concentration kettle 2 for reuse during the preparation of the next batch.

[0090] Example 2

[0091] Example 2 was carried out using the preparation system of semi-aromatic polyamide in Example 1, including the following steps:

[0092] The salt-forming reaction kettle was replaced 10 times with high-purity nitrogen.

[0093] 3215.1 g of adipic acid, 3005.2 g of m-xylenediamine and 4146.9 g of deionized water were added to the salt-forming kettle 1 for salt-forming reaction to obtain a semi-aromatic polyamide salt solution. Among them, the temperature of the salt-forming reaction was 90 °C, and the time of the salt-forming reaction was 40 min. The pH of the salt solution was measured to be 7.05. The semi-aromatic polyamide salt solution was transferred to the concentration kettle 2 through the salt-forming pipeline 1001, and the transfer time was 38 s. After the salt solution transfer was completed, the concentration kettle cut-off valve 10 was closed, the salt-forming kettle exhaust valve 8 and the salt-forming kettle steam valve 9 were opened. Low-pressure saturated steam with 0.8 Mpa and 120 kg / h was used to perform the first backwashing operation through the first backwashing branch 1006 to form salt-forming waste liquid. The time of the first backwashing operation was 1 min, and the number of times was 1 time. When the temperature of the salt-forming kettle 1 dropped to 90 °C, the salt-forming waste liquid was discharged into the collection tank 4.

[0094] The semi-aromatic polyamide salt solution was concentrated in the concentration kettle 2 to obtain a semi-aromatic polyamide salt concentrate. Among them, the pressure of the concentration reaction was 200 kpa, the temperature of the concentration reaction was 170 °C, and the mass concentration of the semi-aromatic polyamide salt concentrate was 80% wt. The semi-aromatic polyamide salt concentrate was transferred to the polymerization kettle 3 through the concentration pipeline 1002, and the transfer time was 32 s. After the concentrate transfer was completed, the polymerization kettle cut-off valve 14 was closed, the concentration kettle exhaust valve 12 and the concentration kettle steam valve 13 were opened. Low-pressure saturated steam with 0.8 Mpa and 120 kg / h was used to perform the second backwashing operation through the second backwashing branch 1007 to form concentration waste liquid. The time of the second backwashing operation was 2 min, and the number of times was 1 time. When the temperature of the concentration kettle 2 dropped to 90 °C, the concentration waste liquid was discharged into the collection tank 4.

[0095] The semi-aromatic polyamide salt concentrate is subjected to a polymerization reaction in the polymerization kettle 3. The polymerization reaction includes the following steps: first, the semi-aromatic polyamide salt concentrate is subjected to a prepolymerization reaction and then a final polymerization reaction; the pressure of the prepolymerization reaction is 1750 kPa. During the prepolymerization reaction, after the reaction temperature rises to 260 °C, the pressure is released; after the pressure release of the prepolymerization reaction ends, the cut-off valve 15 of the third drainage pipeline is closed, the steam valve 17 of the polymerization kettle is opened, and low-pressure saturated steam with a pressure of 0.8 Mpa and a flow rate of 120 kg / h is used to perform a third backwashing operation through the third backwashing branch 1008 to form polymerization waste liquid. The time of the third backwashing operation is 2 min and the number of times is 1; the polymerization waste liquid is discharged into the collection tank 4; at the same time, the final polymerization reaction is carried out. The vacuum degree of the final polymerization reaction is 80 kPa, the temperature of the final polymerization reaction is 270 °C, and the time of the final polymerization reaction is 60 min to obtain the product semi-aromatic polyamide, and the semi-aromatic polyamide is polyhexamethylene adipamide (MXD6). When preparing the next batch, the mixed waste liquid formed by the salt-forming waste liquid, concentrated waste liquid and polymerization waste liquid in the collection tank 4 is transported to the concentration kettle 2 for reuse.

[0096] Example 3

[0097] Based on Example 1, in Example 3, when preparing the next batch, the mixed waste liquid formed by the salt-forming waste liquid, concentrated waste liquid and polymerization waste liquid in the collection tank is not transported to the concentration kettle for reuse. The salt liquid transfer time is 28 s, and the rest are the same as in Example 1.

[0098] Comparative Example 1

[0099] Based on Example 1, in Comparative Example 1, the first backwashing operation, the second backwashing operation and the third backwashing operation are not carried out. The pH of the salt liquid is measured to be 7.09, the salt liquid transfer time is 41 s, and the concentrated liquid transfer time is 48 s. The rest are the same as in Example 1.

[0100] Comparative Example 2

[0101] Based on Example 1, in Comparative Example 2, the first backwashing operation is not carried out. The pH of the salt liquid is measured to be 7.03, the salt liquid transfer time is 37 s, and the concentrated liquid transfer time is 25 s. The rest are the same as in Example 1.

[0102] Effect Example 1

[0103] The following tests are carried out on the product semi-aromatic polyamide prepared in Examples 1 - 3 and Comparative Examples 1 - 2:

[0104] Test method for relative viscosity: Test the relative viscosity of the sample according to the method described in the standard GB 12006.1-2009. Place 0.5 g of the sample in 50 mL of 96% concentrated sulfuric acid, fully dissolve the sample to prepare a solution with a concentration of 0.01 g / mL. Under a constant temperature water bath environment at 25 °C, use an Ubbelohde viscometer with a capillary inner diameter of 1.03 mm to test the relative viscosity of the sample. Measure the time t0 for the blank sulfuric acid to flow through the Ubbelohde viscometer, and measure the time t for the sample to flow through the Ubbelohde viscometer. The relative viscosity η r = t / t0.

[0105] Test method for terminal amino groups: Use an automatic potentiometric titrator to test the content of terminal amino groups in the sample. Weigh 1.0 g of the sample and place it in 30 mL of hexafluoroisopropanol, fully dissolve the sample, and perform potentiometric titration with a 0.01 mol / L hydrochloric acid solution that has been calibrated. Calculate the content of terminal amino groups in the sample based on the volume of hydrochloric acid consumed.

[0106] Test method for PDI: Use gel permeation chromatography (GPC) to test PDI. Weigh approximately 10 mg of the sample to be tested, add 3 mL of hexafluoroisopropanol to dissolve it, and shake to dissolve. Filter the dissolved sample through a 0.45 μm PTFE filter membrane into the injection vial of GPC. Then, measure the sample and the standard product liquid according to the instrument test conditions, and calculate the weight-average molecular weight and number-average molecular weight by fitting the curves of the elution times of the sample and the standard product. PDI = weight-average molecular weight / number-average molecular weight.

[0107] List the above test results, the product yields, and the steam wastewater amounts in the preparation processes of Examples 1-3 and Comparative Examples 1-2 in Table 1 below:

[0108] Table 1

[0109]

[0110] As can be seen from the above table, compared with Comparative Examples 1-2, the semi-aromatic polyamide prepared in Examples 1-3 has a high relative viscosity, a low terminal amino group content, and a stable relative viscosity; the PDI of Examples 1-3 does not exceed 2.27, indicating a uniform molecular weight distribution.

[0111] Compared with Example 3, in Examples 1-2, the mixed waste liquid formed by the salt-forming waste liquid, concentrated waste liquid, and polymerization waste liquid in the collection tank is also transported to the concentration kettle for reuse in the next batch preparation, which can further improve the product yield and achieve 0 wastewater steam wastewater amount.

Claims

1. A preparation system for semi-aromatic polyamide, characterized in that, The preparation system of the semi-aromatic polyamide includes a salifying kettle, a concentration kettle and a polymerization kettle connected in series in sequence; the salifying kettle and the concentration kettle are connected by a salifying pipeline, and the concentration kettle and the polymerization kettle are connected by a concentration pipeline; The preparation system of the semi-aromatic polyamide further includes a back-blowing module. The upper end of the salifying kettle is connected with a first liquid discharge pipeline for discharging the salifying waste liquid obtained by gas-phase condensation; the upper end of the concentration kettle is connected with a second liquid discharge pipeline for discharging the concentration waste liquid obtained by gas-phase condensation; the upper end of the polymerization kettle is connected with a third liquid discharge pipeline for discharging the polymerization waste liquid obtained by gas-phase condensation; The back-blowing module includes a first back-blowing branch, a second back-blowing branch and a third back-blowing branch connected in parallel; the first back-blowing branch is connected to the downstream of the salifying pipeline for steam back-blowing of the upstream of the salifying pipeline and the salifying kettle. A first liquid discharge branch is provided at the upstream of the salifying pipeline for discharging the salifying waste liquid; the second back-blowing branch is connected to the downstream of the concentration pipeline for steam back-blowing of the upstream of the concentration pipeline and the concentration kettle. A second liquid discharge branch is provided at the upstream of the concentration pipeline for discharging the concentration waste liquid; the third back-blowing branch is connected to the upstream of the third liquid discharge pipeline for steam purging of the third liquid discharge pipeline.

2. The preparation system of the semi-aromatic polyamide according to claim 1, characterized in that, The preparation system of the semi-aromatic polyamide further includes a collection tank. The collection tank is respectively connected to the outlet ends of the first liquid discharge pipeline, the second liquid discharge pipeline, the third liquid discharge pipeline, the outlet end of the first liquid discharge branch and the outlet end of the second liquid discharge branch for collecting the salifying waste liquid, the concentration waste liquid and the polymerization waste liquid; the collection tank is connected to the concentration kettle through a concentrated liquid recycling pipeline for conveying the liquid collected in the collection tank to the concentration kettle for recycling.

3. The preparation system of the semi-aromatic polyamide according to claim 2, characterized in that, The first liquid discharge pipeline, the first liquid discharge branch and the third liquid discharge pipeline converge and are connected to the collection tank; Alternatively, the second liquid discharge pipeline, the second liquid discharge branch and the third liquid discharge pipeline converge and are connected to the collection tank.

4. The preparation system of the semi-aromatic polyamide according to claim 1, characterized in that, The preparation system of the semi-aromatic polyamide satisfies one or more of the following conditions: (a) A salifying discharge valve is provided on the first liquid discharge branch, and the position of the salifying discharge valve is lower than the bottom of the salifying kettle; (b) A concentration discharge valve is provided on the second liquid discharge branch, and the position of the concentration discharge valve is lower than the bottom of the concentration kettle; (c) A concentration exhaust branch is provided on the second liquid discharge pipeline for discharging the gas generated in the concentration kettle; preferably, the concentration exhaust branch is connected to the back-blowing module for inputting the gas generated in the concentration kettle into the back-blowing module; (d) A polymerization exhaust branch is provided on the third liquid discharge pipeline for discharging the gas generated in the polymerization kettle; preferably, the polymerization exhaust branch is connected to the back-blowing module for inputting the gas generated in the polymerization kettle into the back-blowing module; (e) Valves are provided on the salt formation pipeline, the concentration pipeline, the first liquid discharge pipeline, the second liquid discharge pipeline, the third liquid discharge pipeline, the first backflush branch, the first liquid discharge branch, the second backflush branch, the second liquid discharge branch and the third backflush branch to control the flow of materials.

5. A method for preparing a semi-aromatic polyamide, characterized in that, The method for preparing the semi-aromatic polyamide adopts the semi-aromatic polyamide preparation system as described in any one of claims 1-4, and comprises the following steps: S1: Add raw materials into the salt formation kettle for salt formation reaction to obtain a semi-aromatic polyamide salt solution; transfer the semi-aromatic polyamide salt solution to the concentration kettle through the salt formation pipeline; S2: Carry out a concentration reaction on the semi-aromatic polyamide salt solution in the concentration kettle to obtain a concentrated semi-aromatic polyamide salt solution; transfer the concentrated semi-aromatic polyamide salt solution to the polymerization kettle through the concentration pipeline; S3: Carry out a polymerization reaction on the concentrated semi-aromatic polyamide salt solution in the polymerization kettle to obtain the product semi-aromatic polyamide; The method for preparing the semi-aromatic polyamide further comprises a first backflush operation, a second backflush operation and a third backflush operation, which are respectively realized through the first backflush branch, the second backflush branch and the third backflush branch; the first backflush operation is carried out after S1 ends, the second backflush operation is carried out after S2 ends, and the third backflush operation is carried out after S3 ends.

6. The method for preparing the semi-aromatic polyamide according to claim 5, characterized in that, The purging medium used in the first backflush operation, the second backflush operation and the third backflush operation is steam, or a mixture of steam and an inert gas; And / or, the salt formation waste liquid, the concentration waste liquid and the polymerization waste liquid are collected in a collection tank; wherein, preferably, the liquid collected in the collection tank is transported to the concentration kettle for reuse; wherein, the transportation preferably adopts the method of nitrogen pressure feeding; And / or, the raw materials include aliphatic dicarboxylic acids and aromatic diamines, or the raw materials include aliphatic diamines and aromatic dicarboxylic acids; wherein, the aliphatic dicarboxylic acid is preferably one or more of succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid and dodecanedioic acid; more preferably one or more of adipic acid, sebacic acid and dodecanedioic acid; wherein, the aromatic diamine is preferably one or more of p-phenylenediamine, p-xylylenediamine, m-phenylenediamine, m-xylylenediamine and 2-methyl-p-phenylenediamine, and more preferably m-xylylenediamine; And / or, the raw materials further include demineralized water.

7. The method for preparing a semi-aromatic polyamide according to claim 5, characterized in that, The temperature of the salt formation reaction is 40-90 °C, preferably 50-70 °C; And / or, the time of the salt formation reaction is 10-120 min, preferably 20-40 min; And / or, the pH value of the semi-aromatic polyamide salt solution is 6.5-8, preferably 6.9-7.5; And / or, the mass concentration of the semi-aromatic polyamide salt solution is 40 wt%-70 wt%, preferably 50 wt%-60 wt%.

8. The method for preparing a semi-aromatic polyamide according to claim 5, characterized in that, The pressure of the concentration reaction is 30-500 kPa, preferably 50-200 kPa; And / or, the temperature of the concentration reaction is 100 - 180°C, preferably 110 - 160°C; And / or, the mass concentration of the semi-aromatic polyamide salt concentrate is 60wt% - 95wt%, preferably 70wt% - 85wt%; And / or, the temperature of the semi-aromatic polyamide salt concentrate is 120 - 180°C, preferably 140 - 170°C; And / or, the gas generated after the concentration reaction is discharged through the concentration exhaust branch; And / or, the gas generated after the polymerization reaction is discharged through the polymerization exhaust branch.

9. The preparation method of the semi-aromatic polyamide according to claim 5, characterized in that, The polymerization reaction includes the following steps: subjecting the semi-aromatic polyamide salt concentrate to a prepolymerization reaction first and then to a final polymerization reaction; Among them, preferably, the third backwashing operation is carried out after the prepolymerization reaction ends; Among them, the pressure of the prepolymerization reaction is preferably 300 - 2000 kPa, more preferably 1500 - 1800 kPa; Among them, the temperature of the prepolymerization reaction is preferably 160 - 260°C; Among them, the pressure of the final polymerization reaction is normal pressure or negative pressure; Among them, the time of the final polymerization reaction is preferably 20 - 120 min, more preferably 40 - 80 min; Among them, the vacuum degree of the final polymerization reaction is preferably 20 - 90 kPa, more preferably 70 - 90 kPa; Among them, when the pressure of the final polymerization reaction is negative pressure, the temperature of the final polymerization reaction is 250 - 280°C, preferably 270 - 280°C.

10. The method for preparing a semi-aromatic polyamide according to claim 5, characterized in that, In steps S1 and S2, the transfer method of the semi-aromatic polyamide salt solution and the semi-aromatic polyamide salt concentrate is nitrogen gas pressure feeding or transfer pump feeding, preferably nitrogen gas pressure feeding; And / or, the gas used in the first backwashing operation, the second backwashing operation and the third backwashing operation is the gas obtained from the concentration reaction and / or the gas obtained from the polymerization reaction; And / or, the steam is low-pressure steam or medium-pressure steam. The meaning of low-pressure steam is steam with a pressure of 0.1 - 1 MPa, and the meaning of medium-pressure steam is steam with a pressure higher than 1 MPa and below 2 MPa; And / or, the first backwashing operation is carried out after S1 ends and before S2 starts; And / or, the second backwashing operation is carried out after S2 ends and before S3 starts; And / or, the flow rate of the first backwashing operation, the second backwashing operation and the third backwashing operation is 100 - 1000 kg / h; And / or, the time of the first backwashing operation, the second backwashing operation and the third backwashing operation is 1 - 30 min; And / or, the number of times of the first backwashing operation, the second backwashing operation and the third backwashing operation is 1 - 3 times.

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