Butylene glycol recovery system for PBAT production device

Abstract

The utility model discloses a butanediol recovery system for a PBAT (poly (butylene adipate-co-terephthalate)) production device, which is characterized in that outlets of an esterification gas phase pipe and a polycondensation gas phase condensate pipe are connected to the lower part of an esterification separation tower, a tower bottom liquid phase space is provided with an esterification separation tower secondary heating medium coil pipe, and a bottom outlet of the esterification separation tower is connected with a butanediol recovery kettle through a liquid phase regulating valve; a top gas phase outlet of the butanediol recovery kettle is provided with a butanediol recovery tower, a top outlet of the butanediol recovery tower is connected with a shell pass gas inlet of a recovery tower top condenser, and a shell pass gas outlet of the recovery tower top condenser is connected with an inlet of a mechanical vacuum pump; a shell pass bottom liquid outlet of the recovery tower top condenser is connected with an inlet pipe of a tower top receiving tank and is provided with a liquid seal; and a bottom outlet of the tower top receiving tank is connected with a top spraying opening of the butanediol recovery tower and a slurry tank through a tower top circulating pump. According to the system, BDO with the purity being greater than or equal to 99.5% can be obtained, tetrahydrofuran is recycled, economic value is created, and the organic matter content and the sewage treatment load of the stripping tower are reduced.

Description

Technical Field

[0001] The utility model relates to a PBAT production device, in particular to a butanediol recovery system for a PBAT production device, belonging to the technical field of biodegradable material production devices. Background Technique

[0002] Poly(butylene adipate terephthalate) (PBAT), as a biodegradable material, its product waste can be quickly degraded in soil or water, and the degradation products are non-toxic. It has a wide range of applications and can be made into disposable shopping bags, agricultural films, biomedical polymer materials, packaging bottles, etc. It can effectively solve white pollution and is used more and more widely.

[0003] 1,4-Butanediol (BDO) is a raw material for producing PBAT. It participates in the reaction in the esterification stage to generate esterified products and water, and side reactions occur at high temperature to generate tetrahydrofuran and water. In the polycondensation stage, the esterified products condense to remove BDO.

[0004] The esterification gas phase contains excess BDO participating in the reaction in the esterification stage. The excess BDO, water, tetrahydrofuran generated by side reactions, and a small amount of dibasic acid and esterified products. The polycondensation gas phase contains the generated BDO, side reaction tetrahydrofuran and water, and the extracted oligomers. To reduce BDO consumption, the BDO in the esterification gas phase and the polycondensation gas phase needs to be purified and recycled.

[0005] The Chinese utility model patent with the publication number CN 206607181U relates to a 1,4-butanediol purification device, including a waste 1,4-butanediol storage tank and a waste 1,4-butanediol transfer pump. The bottom of the waste 1,4-butanediol storage tank is connected to the inlet of the waste 1,4-butanediol transfer pump. The outlet of the waste 1,4-butanediol transfer pump is connected to the material inlet of the preheater. The material outlet of the preheater is connected to the waste liquid inlet of the upper part of the stripping column. The top of the stripping column is provided with a stripping column gas outlet. The lower part of the stripping column is provided with a stripping column air inlet. The bottom of the stripping column is provided with a stripping column material outlet. The stripping column material outlet is connected with a pure liquid transfer pipe. The outlet of the pure liquid transfer pipe is connected to the inlet of the refined 1,4-butanediol transfer pump. The outlet of the refined 1,4-butanediol transfer pump is connected to the inlet of the refined 1,4-butanediol receiving tank. The stripping column gas outlet is connected to the incinerator through a pipeline. A standby pump is arranged between the waste 1,4-butanediol transfer pump and the refined 1,4-butanediol transfer pump. This purification device can greatly reduce the content of water and tetrahydrofuran, has a large processing capacity, good safety, and low energy consumption, but there are still the following problems:

[0006] 1. The stripping device used for wastewater treatment in the relying device cannot be used continuously, and both the treatment time and load are limited;

[0007] 2. The dibasic acid, esterified products in the esterification gas phase and the oligomers in the polycondensation gas phase cannot be treated cleanly, and when recycled and formulated into slurry, it affects the slurry components;

[0008] 3. The material contains a relatively large amount of tetrahydrofuran. There is a safety risk when using air for stripping, and using nitrogen results in a relatively high cost.

[0009] 4. The purity of the obtained butanediol is relatively low. Summary of the Utility Model

[0010] The purpose of the present utility model is to overcome the problems existing in the prior art and provide a butanediol recovery system for a PBAT production device, which can obtain 1,4 - butanediol with a purity ≥ 99.5%, recover tetrahydrofuran, create economic value, and reduce the organic matter content in the stripping tower and the sewage treatment load.

[0011] To solve the above - mentioned technical problems, a butanediol recovery system for a PBAT production device of the present utility model includes an esterification separation tower. The outlets of the esterification gas - phase pipe and the polycondensation gas - phase condensate pipe are respectively connected to the lower part of the esterification separation tower. A secondary heat - medium coil is provided in the bottom liquid - phase space of the esterification separation tower. The bottom outlet of the esterification separation tower is connected to the top inlet of a butanediol recovery kettle through a liquid - phase regulating valve. A butanediol recovery tower is installed at the top gas - phase outlet of the butanediol recovery kettle. The top outlet of the butanediol recovery tower is connected to the shell - side inlet of a recovery tower top condenser. The shell - side exhaust outlet of the recovery tower top condenser is connected to the inlet of a mechanical vacuum pump. The shell - side bottom drain outlet of the recovery tower top condenser is connected to the inlet pipe of a top receiving tank and is provided with a liquid seal. The bottom outlet of the top receiving tank is connected to the top spray port of the butanediol recovery tower and a slurry tank through a top circulation pump.

[0012] As an improvement of the present utility model, the tube side of the recovery tower top condenser is connected to a fresh butanediol supply pipe of the system.

[0013] As a further improvement of the present utility model, a falling - film reboiler is installed at the top of the butanediol recovery kettle. The bottom outlet of the butanediol recovery kettle is connected to the top falling - film liquid - distribution inlet of the falling - film reboiler through a high - boiling - point substance circulation pump. The shell side of the falling - film reboiler is connected to the butanediol recovery kettle through a secondary heat - medium pipe.

[0014] As a further improvement of the present utility model, the outlet of the high - boiling - point substance circulation pump is also connected to the fuel pipe of a natural - gas heat - transfer oil furnace through a high - boiling - point substance discharge regulating valve, and the opening of the high - boiling - point substance discharge regulating valve is controlled by the bottom liquid level of the butanediol recovery kettle.

[0015] As a further improvement of the present utility model, the top gas outlet of the esterification separation tower is connected to the inlet of the esterification top condenser, the liquid outlet of the esterification top condenser is connected to the top reflux tank, the bottom outlet of the top reflux tank is connected to the top reflux port of the esterification top condenser through a liquid storage elbow pipe, and the overflow port of the top reflux tank is connected to the tetrahydrofuran recovery system.

[0016] As a further improvement of the present utility model, the gas outlet of the esterification top condenser is connected to the esterification liquid ring vacuum pump group through a gas regulating valve, and the opening degree of the gas regulating valve is controlled by the top pressure of the esterification separation tower.

[0017] As a further improvement of the present utility model, the opening degree of the liquid regulating valve is controlled by the bottom liquid level of the esterification separation tower.

[0018] As a further improvement of the present utility model, the flow rate of the secondary heat transfer medium pipe for the recovery kettle is controlled by the bottom temperature of the butanediol recovery kettle.

[0019] Compared with the prior art, the present utility model has achieved the following beneficial effects: 1. An esterification separation tower is provided to pre-treat the esterification gas phase and the polycondensation gas phase condensate. Tetrahydrofuran and water are separated at the top of the tower and sent to the tetrahydrofuran recovery system for purification, creating economic benefits;

[0020] 2. The BDO, esterified product, dibasic acid, and oligomer at the bottom of the separation tower enter the recovery kettle for separation. To avoid the high-boiling substances formed by the esterified product, dibasic acid, and oligomer sticking to the coil, a falling film reboiling type is adopted;

[0021] 3. The esterification gas phase and the polycondensation gas phase are purified and separated to prevent the high-temperature cyclization of BDO. Vacuum distillation is adopted, and 1,4-butanediol with a purity of ≥99.5% is obtained at the top of the tower, and high-boiling substances are obtained at the bottom of the tower;

[0022] 4. The latent heat of vaporization of the BDO steam at the top of the tower is used to heat the fresh BDO, and the heat is fully utilized;

[0023] 5. The low-boiling substances are periodically taken out according to the liquid level and sent to the natural gas heat-conducting oil furnace for incineration, reducing the consumption of natural gas. Description of the Drawings

[0024] The following further describes the present utility model in detail in conjunction with the drawings and specific embodiments. The drawings are only for reference and illustration, and are not used to limit the present utility model.

[0025] Figure 1 It is a flow chart of the butanediol recovery system for the PBAT production device of the present utility model;

[0026] In the figure: 1. Esterification separation tower; 2. Butanediol recovery kettle; 2a. Falling film reboiler; 3. Butanediol recovery tower; 4. Condenser at the top of the recovery tower; 5. Mechanical vacuum pump; 6. Receiver tank at the top; 7. Circulation pump at the top; 8. Slurry tank; 9. High-boiling substance circulation pump; 10. Natural gas heat-conducting oil furnace; 11. Condenser at the top of the esterification tower; 12. Reflux tank at the top; 13. Esterification liquid ring vacuum pump group; 14. Tetrahydrofuran recovery system;

[0027] G1. Esterification gas pipe; G2. Condensate pipe for polycondensation gas phase; G3. Secondary heat medium coil in the esterification separation tower; G4. Secondary heat medium pipe for the recovery kettle; G5. Fresh butanediol pipe for system make-up. Specific implementation mode

[0028] In the following description of the present utility model, the orientation or positional relationship indicated by the terms "upper", "lower", "front", "rear", "left", "right", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present utility model and simplifying the description, rather than indicating that the device must have a specific orientation.

[0029] In order to make the technical means, creative features, achieved purposes and effects realized by the present utility model easy to understand, the present utility model will be further elaborated below with reference to specific drawings.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present utility model belongs. The terms used in the description of the present utility model in this specification are only for the purpose of describing specific embodiments, and are not intended to limit the present utility model.

[0031] As Figure 1 shown, in the butanediol recovery system for the PBAT production device of the present utility model, the outlets of the esterification gas pipe G1 and the condensate pipe G2 for the polycondensation gas phase are respectively connected to the lower part of the esterification separation tower 1. The gas phase outlet at the top of the esterification separation tower 1 is connected to the inlet of the condenser 11 at the top of the esterification tower. The liquid phase outlet of the condenser 11 at the top of the esterification tower is connected to the reflux tank 12 at the top. The bottom outlet of the reflux tank 12 at the top is connected to the top reflux port of the condenser 11 at the top of the esterification tower through a liquid storage elbow pipe. The overflow port of the reflux tank 12 at the top is connected to the tetrahydrofuran recovery system 14.

[0032] The gas phase outlet of the condenser 11 at the top of the esterification tower is connected to the esterification liquid ring vacuum pump group 13 through a gas phase regulating valve, and the opening degree of the gas phase regulating valve is controlled by the top pressure of the esterification separation tower 1.

[0033] The esterification separation tower 1 is provided with a secondary heat medium coil G3 in the bottom liquid phase space. The bottom outlet of the esterification separation tower 1 is connected to the top inlet of the butanediol recovery kettle 2 through a liquid phase regulating valve, and the opening degree of the liquid phase regulating valve is controlled by the liquid level at the bottom of the esterification separation tower 1.

[0034] At the top gas phase outlet of the butanediol recovery kettle 2, a butanediol recovery tower 3 is installed. The top outlet of the butanediol recovery tower 3 is connected to the shell side inlet of the recovery tower top condenser 4. The shell side exhaust port of the recovery tower top condenser 4 is connected to the inlet of the mechanical vacuum pump 5. The tube side of the recovery tower top condenser 4 is connected to the fresh butanediol pipe G5 for the system to preheat the fresh butanediol supplemented to the system.

[0035] The shell side bottom drain port of the recovery tower top condenser 4 is connected to the inlet pipe of the top receiving tank 6 and is provided with a liquid seal. The bottom outlet of the top receiving tank 6 is connected to the inlet of the top circulation pump 7. The outlet of the top circulation pump 7 is connected to the top spray port of the butanediol recovery tower 3. The outlet pipe section of the top circulation pump 7 is also connected to the slurry tank 8.

[0036] A falling film reboiler is also installed at the top of the butanediol recovery kettle 2. The bottom outlet of the butanediol recovery kettle 2 is connected to the inlet of the high-boiling substance circulation pump 9. The outlet of the high-boiling substance circulation pump 9 is connected to the top falling film liquid distribution inlet of the falling film reboiler and the natural gas heat transfer oil furnace 10. The shell side of the falling film reboiler is connected to the recovery kettle with the secondary heat transfer medium pipe G4.

[0037] The first stage

[0038] The water and 1,4-butanediol (i.e., BDO) produced by the esterification reaction, the by-product tetrahydrofuran (i.e., THF) of the cyclization reaction, the unreacted BDO, the entrained dibasic acid, and the esterified vapor composed of the esterified product enter the esterification separation tower 1 through the esterification gas phase pipe G1 at the top of the esterification kettle for separation.

[0039] The polycondensation gas phase condensate composed of the BDO removed by the polycondensation reaction, the by-product tetrahydrofuran and water of the BDO cyclization reaction at high temperature, and the oligomer is also pumped into the esterification separation tower 1 through the pump and the polycondensation gas phase condensate pipe G2 for separation.

[0040] The bottom of the esterification separation tower 1 uses a secondary heat transfer medium coil to heat the material to 180 - 190 °C. The steam flows upward through the separation tower packing and exchanges heat with the flowing-back liquid to form a new vapor-liquid equilibrium. From bottom to top, as the temperature of each layer of packing gradually decreases, the content of the heavy components in the gas phase gradually decreases.

[0041] The water and THF steam discharged from the top gas phase enter the esterification tower top condenser 11 and are directly condensed by the cooling water and then enter the top reflux tank 12 to become the esterification water. A part of the esterification water in the top reflux tank 12 is used as reflux to adjust the top temperature of the esterification separation tower 1, and the rest is sent to the tetrahydrofuran recovery system 14 for further treatment. The uncondensed process steam is pumped away by the esterification liquid ring vacuum pump group 13.

[0042] The BDO, dibasic acid, esterified product, and oligomer flowing out from the bottom of the esterification separation column 1 enter the butanediol recovery kettle 2 through the head difference for further treatment.

[0043] The second stage

[0044] The crude BDO (including BDO, dibasic acid, esterified product, and oligomer) discharged from the esterification separation column 1 is put into the material inlet of the butanediol recovery kettle 2 and controlled by the internal temperature regulating valve. The secondary heat medium for the recovery kettle is used to heat it up, and it is rectified by the butanediol recovery column 3. By controlling the top temperature of the column, the purity of BDO is controlled. The mechanical vacuum pump 5 is started, the steam flows from bottom to top, and the liquid flows from top to bottom for mass transfer and heat transfer. BDO with a purity of ≥99.5% is obtained at the top of the butanediol recovery column 3, enters the recovery top condenser 4 for condensation, and after condensation, enters the top receiving tank 6 for temporary storage, and is sent to the slurry tank 8 through the top circulation pump 7 for slurry preparation and then returns to the device to continue the reaction to produce PBAT products.

[0045] The high-boiling substances (including dibasic acid, esterified product, and oligomer) in the butanediol recovery kettle 2 are discharged through the liquid level cascade control regulating valve and then pumped to the natural gas heat-conducting oil furnace 10 by the high-boiling substance circulation pump 9 for combustion as fuel.

[0046] The pressure of the butanediol recovery column 3 is controlled at 8 - 9 KPa(A), and the temperature is controlled at 165 °C, which can avoid the cyclization reaction of BDO. In addition, to prevent the high-boiling substances from accumulating and carbonizing on the coil to affect heat transfer, the butanediol recovery column 3 uses a falling-film reboiler for heating. The material is forced to circulate to the top of the falling-film reboiler by the high-boiling substance circulation pump 9 and exchanges heat with the secondary heat medium for the recovery kettle.

[0047] The above is only the preferred and feasible embodiment of the present utility model, which shows and describes the basic principles, main features, and advantages of the present utility model. It is not intended to limit the patent protection scope of the present utility model. Those skilled in the art should understand that the present utility model is not limited by the above embodiments. Except for the above embodiments, without departing from the spirit and scope of the present utility model, the present utility model may have other implementation manners. The present utility model will also have various changes and improvements. All technical solutions formed by equivalent substitution or equivalent transformation fall within the protection scope required by the present utility model. The protection scope required by the present utility model is defined by the appended claims and their equivalents. The technical features not described in the present utility model can be realized by or adopted the existing technologies, and will not be elaborated here.

Claims

1. A butanediol recovery system for a PBAT production device, including an esterification separation tower, characterized in that, The outlets of the esterification gas-phase pipe and the polycondensation gas-phase condensate pipe are respectively connected to the lower part of the esterification separation tower. A secondary heat medium coil of the esterification separation tower is provided in the liquid-phase space at the bottom of the esterification separation tower. The bottom outlet of the esterification separation tower is connected to the top inlet of the butanediol recovery kettle through a liquid-phase regulating valve. A butanediol recovery tower is installed at the top gas-phase outlet of the butanediol recovery kettle. The top outlet of the butanediol recovery tower is connected to the shell-side inlet of the recovery tower top condenser. The shell-side exhaust outlet of the recovery tower top condenser is connected to the inlet of the mechanical vacuum pump; the shell-side bottom drain outlet of the recovery tower top condenser is connected to the inlet pipe of the top receiving tank and is provided with a liquid seal. The bottom outlet of the top receiving tank is connected to the top spray port of the butanediol recovery tower and the slurry tank through a top circulation pump.

2. The butanediol recovery system for the PBAT production device according to claim 1, wherein, The tube side of the recovery tower top condenser is connected to the system's fresh butanediol supply pipe.

3. The butanediol recovery system for the PBAT production device according to claim 1, characterized in that, A falling film reboiler is installed at the top of the butanediol recovery kettle. The bottom outlet of the butanediol recovery kettle is connected to the top falling film liquid distribution inlet of the falling film reboiler through a high-boiling substance circulation pump. The shell side of the falling film reboiler is connected to the secondary heat medium pipe for the recovery kettle.

4. The 1,4-butanediol recovery system for the PBAT production device according to claim 3, characterized in that, The outlet of the high-boiling substance circulation pump is also connected to the fuel pipe of the natural gas heat-conducting oil furnace through a high-boiling substance discharge regulating valve. The opening of the high-boiling substance discharge regulating valve is controlled by the bottom liquid level of the butanediol recovery kettle.

5. The butanediol recovery system for the PBAT production device according to claim 1, characterized in that, The top gas-phase outlet of the esterification separation tower is connected to the inlet of the esterification tower top condenser. The liquid-phase outlet of the esterification tower top condenser is connected to the top reflux tank. The bottom outlet of the top reflux tank is connected to the top reflux port of the esterification tower top condenser through a liquid storage elbow. The overflow port of the top reflux tank is connected to the tetrahydrofuran recovery system.

6. The butanediol recovery system for the PBAT production device according to claim 5, wherein, The gas-phase outlet of the esterification tower top condenser is connected to the esterification liquid ring vacuum pump set through a gas-phase regulating valve. The opening of the gas-phase regulating valve is controlled by the top pressure of the esterification separation tower.

7. The butanediol recovery system for the PBAT production device according to claim 5, characterized in that, The opening of the liquid-phase regulating valve is controlled by the bottom liquid level of the esterification separation tower.

8. The butanediol recovery system for the PBAT production device according to claim 3, characterized in that, The flow rate of the secondary heat medium pipe for the recovery kettle is controlled by the bottom temperature of the butanediol recovery kettle.

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